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Sample records for amphibolitised mafic dykes

  1. Geochemistry of Late Mesozoic mafic dykes in western Fujian Province of China:Sr-Nd isotope and trace element constraints

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Bancun diabase dyke and the Bali hornblende gabbro dyke in western Fuiian Province were emplaced in the Early and Late Cretaceous periods,respectively;the former is designated to calc-alkaline series and the latter to K-high-calc-alkaline rock series.Both the dykes are characterized by such geochemical characteristics as high Al and Na2O>K2O.As for the Bancun dyke,A12O3=16.32%-17.54%and K2O/Na2O=0.65-0.77;as for the Bali dyke,A12O3=16.89%-17.81%and K2O,Na2O=O.93-O.99.Both the Bancun and Bali mafic dykes are relatively endched in LILE and LREE,but depleted in HSFE, displaying the geochemical characteristics of continental marginal arc,with high initial Sr isotopic ratios and low εNd values,The (87Sr/86Sr)i ratios of the Bancun diabase dyke are within the range of 0.708556-0.70903 and their εNd(t)values vary between-6.8 and-6.3;those of the Bali hornblende dyke are within the range of 0.708556-0.710746 and their εNd(t) values are -4.7--4.7,showing the characteristics of enriched mantle EM Ⅱ.The isotope and trace element data showed that the mafic dykes have not experienced obvious crustal contamination,and metasomatism caused by subduction fluids is the main factor leading to LILE and UREE enrichments.The enriched mantle is the source region for the mafic dykes,and mixing of subduction fluid metasomatized enriched mantle and EM Ⅱ-type mantle constituted the mantle source region of both the Bancun and Bali mafic dykes.Upwelling of the asthenosphere mantle provided sufficient heat energy for the generation of magmas.In accordance with the discrimination diagram of their tectonic settings as well as their trace element geochemical characteristics,it is considered that the dykes both at Bancun and Bali possess the characteristics of continental marginal arc,revealing the tectonic environment of formation of the mafic dykes,the continental dynamic background as an intraplate tensional belt in which the mafic dykes were emplaced.Meanwhile,it is also indicated

  2. Magnetic and plagioclase fabrics in Early Cretaceous mafic dykes from Namibia

    Science.gov (United States)

    Wiegand, M.; Greiling, R. O.; Kontny, A. M.; Trumbull, R. B.

    2011-12-01

    Mafic dyke swarms are major components of the South Atlantic Large Igneous Province, which originated during the Cretaceous break up of Africa and South America. We present data from the major Henties Bay-Outjo dyke swarm (HOD) in coastal and inland NW Namibia where dykes have been emplaced into the Neoproterozoic Damara mobile belt. Most of the dykes strike at a high angle to the coast (NE-SW), but minor proportions are coast-parallel (NNW-SSE), N-S or NNE-SSW. Depending on dyke thickness (ca. 0.1 m to >100 m), the rocks are variably fine- to medium grained with chilled margins. With few exceptions the dyke compositions are tholeiitic basalt to basaltic andesite. Main minerals are plagioclase, clinopyroxene, olivine, Fe-Ti oxides, and accessory apatite and sulphides. For the magnetic study, we investigated 1140 standard cylinders from 41 dykes. The samples were studied microscopically and the following magnetic properties were determined: bulk susceptibility, anisotropy of magnetic susceptibility (P'), field dependence, hysteresis, Natural Remanent Magnetization (NRM) and Anisotropy of Anhysteretic Remanent Magnetization (AARM). Magnetic susceptibilities vary between 0.16 and 151*10-3 SI units. Microscopic studies and measurements of the temperature-dependent susceptibility identify magnetite and titanomagnetite as the dominant magnetic minerals. Hysteresis loops show that the magnetic domain states of titanomagnetite are pseudo-single or a mixture of single and multi-domain. Anisotropy is mostly low, with P' values between 1.01 and 1.15. Rare values of up to 1.33 reflect a strong magmatic flow fabric. The shapes of the AMS ellipsoids range from prolate to neutral and oblate. Two main fabric types (normal and inverse) can be recognized. We used the normal fabric type samples to interpret magmatic flow fabrics and attribute steep magnetic lineations of normal fabrics to vertical magma flow and shallow magnetic lineations to horizontal flow along the dyke planes. In

  3. ArcGIS studies and field relationships of Paleoproterozoic mafic dyke swarms from the south of Devarakonda area, Eastern Dharwar Craton, southern India: Implications for their relative ages

    Indian Academy of Sciences (India)

    Amiya K Samal; Rajesh K Srivastava; Lokesh K Sinha

    2015-07-01

    Google Earth Image and cross-cutting field relationships of distinct Paleoproterozoic mafic dykes from south of Devarakonda area in the Eastern Dharwar Craton has been studied to establish relative emplacement ages. The Devarakonda, covering an area of ∼700 km2, shows spectacular cross-cutting field relationships between different generations of mafic dykes, and is therefore selected for the present study. Although some recent radiometric age data are available for distinct Paleoproterozoic mafic dykes from the Eastern Dharwar Craton, there is no analogous age data available for the study area. Therefore, relative age relationships of distinct mafic dykes have been established for the study area using cross-cutting field relationships and GIS techniques, which shows slightly different picture than other parts of the Eastern Dharwar Craton. It is suggested that NE–SW trending mafic dykes are youngest in age (probably belong to ∼1.89 Ga dyke swarm), whereas NNW–SSE trending mafic dykes have oldest emplacement age. Further, the NNW–SSE mafic dykes are older to the other two identified mafic dyke swarms, i.e., WNW–ESE (∼2.18 Ga) and N–S trending (∼2.21 Ga) mafic dyke swarms, as dykes of these two swarms cross-cut a NNW–SSE dyke. It provides an evidence for existence of a new set of mafic dykes that is older to the ∼2.21 Ga and probably younger to the ∼2.37 Ga swarm. Present study also supports existence of two mafic dyke swarms having similar trend (ENE–WSW to NE–SW) but emplaced in two different ages (one is ∼2.37 Ga and other ∼1.89 Ga).

  4. The discovery of the Neoarchean mafic dyke swarm in Hengshan and reinterpretation of the previous "Wutai greenstone belt"

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The structural mapping and section study indicate that the "greenstone belts" in the southern to central parts of Hengshan were intensively sheared and transposed mafic dyke swarm,which originally intruded into the Neoarchean grey gneiss and high-pressure granulite terrain(HPGT).The HPGT is characterized by flat-dipping structures,to the south it became steep and was cut by the Dianmen mafic dyke swarm.After high-pressure granulite-facies metamorphic event,the mafic dyke swarm occurred,and was associated with the extensional setting and reworked by the late strike-slip shearing.The zircon age dating proves that the Dianmen mafic dyke swarm was emplaced during the period between 2499±4 Ma and 2512±3 Ma,followed by late tectonothermal reworking.The Dianmen mafic dyke swarm further documents the extensional episode in the central to northern parts of North China Craton(NCC),providing the important constraint for the limit between Archean and Proterozoic and correlation between NCC and other cratonic blocks of the world.

  5. Geochemistry and petrology of mafic Proterozoic and Permian dykes on Bornholm, Denmark:

    DEFF Research Database (Denmark)

    Holm, Paul Martin; Pedersen, Lise E.; Højsteeen, Birte

    2010-01-01

    More than 250 dykes cut the mid Proterozoic basement gneisses and granites of Bornholm. Most trend between NNW and NNE, whereas a few trend NE and NW. Field, geochemical and petrological evidence suggest that the dyke intrusions occurred as four distinct events at around 1326 Ma (Kelseaa dyke), 1...

  6. Gridino melange zone of the Belomorian eclogite province: Succession of tectonic events and structural position of mafic dyke swarms

    Science.gov (United States)

    Babarina, I. I.; Sibelev, O. S.; Stepanova, A. V.

    2014-07-01

    Based on relationships between Paleoproterozoic mafic dykes, lithotectonic complexes, and tectonic structures of the Gridino Zone in the Belomorian eclogite province of the Fennoscandian Shield, deformations have been divided into groups differing in age and the succession of tectonic events has been reconstructed. The formation of Neoarchean eclogite-bearing melange was related to disintegration of large eclogite sheets in the course of near-horizontal ductile flow accompanied by syntectonic granitoid magmatism, multiple migmatization, and granulite-to amphibolite-facies metamorphism. The exotic blocks, including eclogites, were incorporated into TTG gneisses as sheets and lenses up to a few hundreds of meters in thickness and oriented conformably with gneissic banding. As a result of ductile flow, the lithotectonic complexes were transported at the level of discrete brittle-ductile deformations expressed as strike-slip faults and associated folds. Under conditions of a relatively rigid medium, individual structural elements underwent rotation approximately through 90° in plan view. Under the extension regime in the Early Paleoproterozoic, several swarms of mafic dykes were injected into the already cold framework rocks, as is evident from dyke morphology. The dykes crosscut all predated structures, included turned blocks, and are therefore important reference points for subdivision of Neoarchean and Paleoproterozoic processes. The Svecofennian postdyke tectonic activity was accompanied by local shearing and boudinage of metabasic rocks, development of quartz and pegmatite veins along tension cracks, disharmonic folding, and discrete retrograde metamorphism up to amphibolite-facies conditions. The postdyke deformations did not exert a substantial effect on the previously formed regional structure.

  7. Mafic dykes at the southwestern margin of Eastern Ghats belt: Evidence of rifting and collision

    Indian Academy of Sciences (India)

    S Bhattacharya; A K Chaudhary; W Teixeira

    2010-12-01

    The southwestern margin of the Eastern Ghats Belt characteristically exposes ma fic dykes intruding massif-type charnockites. Dykes of olivine basalt of alkaline composition have characteristic trace element signatures comparable with Ocean Island Basalt (OIB). Most importantly strong positive Nb anomaly and low values of Zr/Nb ratio are consistent with OIB source of the mafic dykes. K –Ar isotopic data indicate two cooling ages at 740 and 530 Ma. The Pan-African thermal event could be related to reactivation of major shear zones and represented by leuco-granite vein along minor shear bands. And 740 Ma cooling age may indicate the low grade metamorphic imprints, noted in some of the dykes. Although no intrusion age could be determined from the present dataset, it could be constrained by some age data of the host charnockite gneiss and Alkaline rocks of the adjacent Prakasam Province. Assuming an intrusion age of ∼1 .3 Ga, Sr –Nd isotopic composition of the dykes indicate that they preserved time-integrated LREE enrichment. In view of the chemical signatures of OIB source, the ma fic dykes could as well be related to continental rifting, around 1.3 Ga, which may have been initiated by intra-plate volcanism.

  8. Fluid Inclusion Study of Quartz Xenocrysts in Mafic Dykes from Kawant Area, Chhota Udaipur District, Gujarat, India

    Directory of Open Access Journals (Sweden)

    Randive Kirtikumar

    2015-09-01

    Full Text Available Unusual mafic dykes occur in the proximity of the Ambadongar Carbonatite Complex, Lower Narmada Valley, Gujarat, India. The dykes contain dense population of quartz xenocrysts within the basaltic matrix metasomatised by carbonate-rich fluids. Plagioclase feldspars, relict pyroxenes, chlorite, barite, rutile, magnetite, Fe-Ti oxides and glass were identified in the basaltic matrix. Quartz xenocrysts occur in various shapes and sizes and form an intricate growth pattern with carbonates. The xenocrysts are fractured and contain several types of primary and secondary, single phase and two-phase fluid inclusions. The two-phase inclusions are dominated by aqueous liquid, whereas the monophase inclusions are composed of carbonic gas and the aqueous inclusions homogenize to liquid between 226°C and 361°C. Majority of the inclusions are secondary in origin and are therefore unrelated to the crystallization of quartz. Moreover, the inclusions have mixed carbonic-aqueous compositions that inhibit their direct correlation with the crustal or mantle fluids. The composition of dilute CO2-rich fluids observed in the quartz xenocrysts appear similar to those exsolved during the final stages of evolution of the Amba Dongar carbonatites. However, the carbonates are devoid of fluid inclusions and therefore their genetic relation with the quartz xenocrysts cannot be established.

  9. 40Ar/39Ar geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: insights into magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps

    Science.gov (United States)

    Cucciniello, Ciro; Demonterova, Elena I.; Sheth, Hetu; Pande, Kanchan; Vijayan, Anjali

    2015-05-01

    The Central Saurashtra mafic dyke swarm in the northwestern Deccan Traps contains a few picrites, several subalkalic basalts and basaltic andesites, and an andesite. We have obtained precise 40Ar/39Ar ages of 65.6 ± 0.2 Ma, 66.6 ± 0.3, and 62.4 ± 0.3 Ma (2σ errors) for three of the dykes, indicating the emplacement of the swarm over several million years. Mineral chemical and whole-rock major and trace element and Sr-Nd isotopic data show that fractional crystallization and crystal accumulation were important processes. Except for two dykes (with ɛNd t values of -8.2 and -12.3), the magmas were only moderately contaminated by continental crust. The late-emplaced (62.4 Ma) basalt dyke has compositional characteristics (low La/Sm and Th/Nb, high ɛNd t of +4.3) suggesting little or no crustal contamination. Most dykes are low-Ti and a few high-Ti, and these contrasting Ti types cannot be produced by fractional crystallization processes but require distinct parental magmas. Some dykes are compositionally homogeneous over tens of kilometers, whereas others are heterogeneous, partly because they were formed by multiple magma injections. The combined field and geochemical data establish the Sardhar dyke as ≥62 km long and the longest in Saurashtra, but this and the other Central Saurasthra dykes cannot have fed any of the hitherto studied lava-flow sequences in Saurashtra, given their very distinct Sr-Nd isotopic compositions. As observed previously, high-Ti lavas and dykes only outcrop east-northeast of a line joining Rajkot and Palitana, probably because of underlying enriched mantle at ~65 Ma.

  10. SHRIMP U-Pb zircon age, geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan: Petrogenesis and tectonic significance

    Institute of Scientific and Technical Information of China (English)

    LIN GuangChun; LI XianHua; LI WuXian

    2007-01-01

    Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia supercontinent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780-760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplacement, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.

  11. SHRIMP U-Pb zircon age,geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan:Petrogenesis and tectonic significance

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super- continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780―760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplace- ment, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.

  12. Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey

    Science.gov (United States)

    Aydin, Faruk; Oguz, Simge; Baser, Rasim; Uysal, Ibrahim; Sen, Cüneyt; Karsli, Orhan; Kandemir, Raif

    2015-04-01

    Geological, petrographical and geochemical data of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc (EBMA), NE Turkey, provide new insights into the nature of the metasomatizing agents in subcontinental lithospheric mantle beneath the region during the late Mesozoic-early Tertiary. Mafic dykes from the Çaykara and Hayrat (Trabzon), and also Ikizdere (Rize) areas from the northern margin of the EBMA consist of basalts, dolerites, lamprophyres (basic member) and lesser basaltic andesites and trachyandesites (evolved member). All dykes have no deformation and metamorphism. The outcrops of these dykes vary, with thickness from 0.2 to 10 m. and visible length from 3 to 20 m. In general, the mafic dykes dip steeply and cut directly across the Kaçkar Pluton, and show NW- and NE-trending, roughly parallel to the orientations of the EBMA main faults. Most of the dyke samples display subaphyric to porphyritic texture with phenocrysts of plagioclase (up to 10%), clinopyroxene (5-20%), amphibole (5-15%), and some contain variable amount of biotite (5-20%), lesser quartz (1-2%), and minor euhedral zircon, apatite and Fe-Ti oxides. The basic members of the mafic dykes have SiO2 of 44.1-51.9%, MgO of 4.5-12.1%, and TiO2 >mostly 0.8% (up to 2.3%) with K2O+Na2O of 1.3-6.6% with mostly subalkaline character. They are relatively high in mg-number (0.45-0.73) and transition metals (V=171-376 ppm, Co=22-45 ppm, Ni=3-148 ppm, and Sc=21-49 ppm). The evolved members of the dykes exhibit relatively higher SiO2 (57.1-60.2%) and K2O+Na2O (5.6-9.0%), and lower MgO (2.2-5.9%) and TiO2 (0.5-0.8%) contents than those from the basic dykes. Also, these samples have slightly low mg-number (0.41-0.65) and transition metals (V=99-172 ppm, Co=9-22 ppm, Ni=1-43 ppm, and Sc=9-20 ppm). In the Harker diagrams, all samples of the mafic dykes form a continuous array, and exhibit similar geochemical characteristics. In general, SiO2 inversely correlates with MgO, Fe

  13. Composition of the ultramafic-mafic contact interval of the Great Dyke of Zimbabwe at Ngezi mine: Comparisons to the Bushveld Complex and implications for the origin of the PGE reefs

    Science.gov (United States)

    Maier, W. D.; Määttää, S.; Yang, S.; Oberthür, T.; Lahaye, Y.; Huhma, H.; Barnes, S.-J.

    2015-12-01

    The Great Dyke contains the world's second largest platinum resource after the Bushveld Complex. Isotopic and trace element data from the interval straddling the contact between the Ultramafic and Mafic Sequences of the Great Dyke indicate a less enriched composition than in the Bushveld Complex (Great Dyke: Sri 0.7024-0.7028, εNd mostly - 1 to + 1, Ce/Sm 2-6; Bushveld: Sri 705-0.709, εNd - 5 to - 7, Ce/Sm 5-15). These data are interpreted to reflect relatively moderate amounts of contamination of the Great Dyke parent magma. All analyzed isotopes show little variation across the Main Sulfide Zone and the ultramafic-mafic contact. This corroborates earlier work by other researchers that the Great Dyke crystallized from a single magma type. Mixing of compositionally distinct magmas, proposed to have caused sulfide melt saturation in the Bushveld Complex, seemingly played little or no role in the formation of the PGE mineralization in the Main Sulfide Zone, and neither did enhanced crustal contamination of specific magma batches. Instead, sulfide melt saturation of the magma was likely triggered by silicate fractionation. The mechanism of concentration of the sulfide melt remains uncertain, but theoretical considerations suggest that phase sorting in response to slumping of crystal mushes, possibly caused by chamber subsidence, played an important role. This model is consistent with the highly irregular, undulating nature of the contact between the mafic and ultramafic zones of the intrusion, in the hanging wall of the Main Sulfide Zone.

  14. 40Ar/ 39Ar ages of mafic dykes from the Mesoproterozoic Chhattisgarh basin, Bastar craton, Central India: Implication for the origin and spatial extent of the Deccan Large Igneous Province

    Science.gov (United States)

    Rao, N. V. Chalapathi; Burgess, R.; Lehmann, B.; Mainkar, D.; Pande, S. K.; Hari, K. R.; Bodhankar, N.

    2011-08-01

    We present 40Ar/ 39Ar whole-rock ages of 63.7 ± 2.7 Ma (2σ, 92% Ar release) and 66.6 ± 2.2 Ma (2σ, 96% Ar release) for two samples of sub-surface mafic dykes intrusive into the sedimentary rocks of the Mesoproterozoic Chhattisgarh basin, Bastar craton, Central India. The obtained ages are synchronous with those of the Deccan Traps whose nearest exposures are at a distance of ~ 200 km to the west, and the recently dated diamondiferous orangeites (Group-II kimberlites) of the Mainpur area (located ~ 100 km SE within the Bastar craton). The chemical composition of the Chhattisgarh mafic dykes is indistinguishable from the chemostratigraphic horizons of the upper Deccan lavas of the Wai Subgroup (Ambenali and Poladpur Formations) and confirms them to be a part of the Deccan Large Igneous Province (LIP). The geological setting of the Deccan-age mafic dykes in the Chhattisgarh basin is analogous to that observed in other LIPs of the world such as (i) Pasco Basin of NW U.S.A, (ii) Ellisras sub-basin of southern Africa, (iii) Rift basins of New England in the NE U.S.A and (iv) the West Siberian Basin of Russia where LIP-related basalts and sills have been emplaced in distant domains from the main province. The Deccan-age of the Chhattisgarh dykes and the Mainpur orangeites permits a substantial increase of at least 8.5 × 10 4 km 2 in the spatial extent of the Deccan LIP. The temporal link at ~ 65 Ma between the Deccan Traps and (i) sub-surface mafic dykes within the Chhattisgarh basin and orangeites in the Bastar craton, (ii) Ambadongar carbonatite in western India, (iii) Salma mafic dyke in the Eastern Indian craton, (iv) Rajahmundry Traps off the eastern coast of southern India and (v) tholeiitic dykes and basalts from the Seychelles, suggests a common tectonomagmatic control, via a vast mantle plume-head of the order of 2000-2500 km. Our study has relevance to the (i) origin (plume vs non-plume) of the Deccan LIP, (ii) plumbing system for Deccan dykes and lavas in

  15. Geochemistry and petrogenesis of early Cretaceous sub-alkaline mafic dykes from Swangkre-Rongmil, East Garo Hills, Shillong plateau, northeast India

    Indian Academy of Sciences (India)

    Rajesh K Srivastava; Anup K Sinha

    2004-12-01

    Numerous early Cretaceous mafic and alkaline dykes, mostly trending in N-S direction, are emplaced in the Archaean gneissic complex of the Shillong plateau, northeastern India. These dykes are spatially associated with the N-S trending deep-seated Nongchram fault and well exposed around the Swangkre-Rongmil region. The petrological and geochemical characteristics of mafic dykes from this area are presented. These mafic dykes show very sharp contact with the host rocks and do not show any signature of assimilation with them. Petrographically these mafic dykes vary from fine-grained basalt (samples from the dyke margin) to medium-grained dolerite (samples from the middle of the dyke) having very similar chemical compositions, which may be classified as basaltic-andesite/andesite. The geochemical characteristics of these mafic dykes suggest that these are genetically related to each other and probably derived from the same parental magma. Although, the high-field strength element (+rare-earth elements) compositions disallow the possibility of any crustal involvement in the genesis of these rocks, but Nb/La, La/Ta, and Ba/Ta ratios, and similarities of geochemical characteristics of present samples with the Elan Bank basalts and Rajmahal (Group II) mafic dyke samples, suggest minor contamination by assimilation with a small amount of upper crustal material. Chemistry, particularly REE, hints at an alkaline basaltic nature of melt. Trace element modelling suggests that the melt responsible for these mafic dykes had undergone extreme differentiation (∼50%) before its emplacement. The basaltic-andesite nature of these rocks may be attributed to this differentiation. Chemistry of these rocks also indicates ∼10–15% melting of the mantle source. The mafic dyke samples of the present investigation show very close geochemical similarities with the mafic rocks derived from the Kerguelen mantle plume. Perhaps the Swangkre-Rongmil mafic dykes are also derived

  16. Tectonic breccia of the Cabo Frio area, State of Rio de Janeiro, Brazil, intruded by Early Cretaceous mafic dyke: evidence of the Pan-African brittle tectonism? Brecha tectônica da área de Cabo Frio - RJ, intrudida por dique máfico do Eocretáceo: evidência do tectonismo rúptil do Pan-Africano?

    Directory of Open Access Journals (Sweden)

    Akihisa Motoki

    2011-03-01

    Full Text Available This paper presents the field descriptions and microscopic observations of a tectonic breccia in the basement gneiss of the Cabo Frio and Arraial do Cabo areas, State of Rio de Janeiro, Brazil, and its intrusive contact with the Early Cretaceous mafic dyke. At the sea cliff close to the Ilha do Japonês, there is an excellent contact outcrop between them. The tectonic breccia zone is 10 to 20m wide and has N30ºE direction. The breccia clasts are angular and characterized by auto-brecciation texture, and composed of breccia with similar aspect of the host tectonic breccia. The matrix is firmly consolidated by hydrothermalism and following silicification. The mafic dyke is 7 to 10m wide and of N45ºE direction. Along the contact, the dyke chilled margin featured by fine-grained basalt and prismatic joints can be observed. At the Conchas Beach and Arraial do Cabo city, there are four outcrops demonstrating the mafic dyke intrusion into the consolidated tectonic breccias. These outcrops prove that the tectonic breccias are older than the Early Cretaceous tholeiitic dykes. The fault breccias could have been formed during the brittle-phase tectonism of the last stage of the Pan-African Orogeny by hydrothermalism without magmatic activities, namely tectonic hydrothermalism. The existence of the clasts constituent of the breccia that are composed of breccia suggests that the fault movement and following hydrothermalism occurred repeatedly.Esse trabalho apresenta as descrições de campo e observações petrográficas de uma brecha tectônica no embasamento gnáissico das áreas de Cabo Frio e Arraial do Cabo, RJ, e seu contato intrusivo com um dique máfico do Eocretáceo. Na proximidade da ilha do Japonês, ocorre um excelente afloramento de contato entre esses litotipos. A zona da brecha tectônica tem 10 a 20 m de largura e tem direção de N30ºE. Os clastos da brecha são angulosos e caracterizados pela textura de auto-brechação, sendo similares

  17. U-Pb baddeleyite ages for the Scourie dyke swarm, Scotland: evidence for two distinct intrusion events

    Science.gov (United States)

    Heaman, L. M.; Tarney, J.

    1989-08-01

    PRECISE and accurate radiometric ages for continental mafic dyke swarms are a prerequisite for global correlation of mafic magmatic events, calibration of apparent polar-wander paths and deciphering mechanisms of dyke emplacement. Precambrian dyke swarms, such as the Scourie dyke swarm in north-west Scotland, are invaluable time-markers, so that a precise and accurate knowledge of their emplacement age is critical when unravelling the complex geological evolution of many terrains. Precise dating is often difficult, however, because magma interaction with country rock and subsequent metamorphic events can severely perturb some isotopic systems. Recent advances in U-Pb geochronology1-3 combined with the discovery that some mafic dykes contain trace amounts of uranium-bearing minerals such as baddeleyite (ZrO2) and/or zircon have made it possible to obtain U-Pb ages for these rocks with a precision typically on the order of 1-2 Myr4,5. Some of the first detailed U-Pb studies of Precambrian mafic dyke swarms5,6 have shown that large volumes of mafic magma, 100,000 km3, were emplaced into the continental crust in surprisingly short periods of time (<2 Myr). Here we report the results from a U-Pb study of three members of the Scourie dyke swarm, and find at least two periods of dyke emplacement at 2,418 and 1,992 Myr BP. We speculate on a potential global correlation of early Proterozoic mafic magmatism and hence on the origin of dyke swarms.

  18. The paleomagnetism and geological significance of Meso- proterozoic dyke swarms in the central North China Craton

    Institute of Scientific and Technical Information of China (English)

    HOU; Guiting

    2001-01-01

    [1]Ma Xinghua, Zhang Zhengkun, Paleomagnetism and its application to plate tectonics, in The Basic Problems of Plate Tectonics (in Chinese), Beijing: Seismology Press, 1985, 119-142.[2]Zhang Wenzhi, Li Pu, The paleomagnetic characteristics of Sub-Sinian Erathem in Jixian of China, Bulletin of the Chinese Academy of Geological Science, Branch Bulletin of Geological Institute of Tianjin, 1980, 1(1): 111[3]Halls, H. C., Paleomagnetism, structure and longitudinal correlation of middle Precambrian dykes from northwestern Ontario and Minnesota, Can. J. Earth Sci., 1985, 23: 142.[4]Qian Xianglin, Chen Yaping, Late Precambrian mafic swarms of the north China Craton, in Mafic Dyke Swarms, Geological Association of Canada (eds. Halls, H. C., Fahrig, W. F.), 1987, Special Paper, 34: 385.[5]Chen Yaping, Qian Xianglin, The paleomagnetism study of Late Precambrian mafic dyke swarms in Lüliang inlier of Shanxi, Acta Scientiarum Naturalium Universitatis Pekinensis (in Chinese), 1987, 2: 87.[6]Ernst, R. E., Head, J. W., Parfitt, E. et al, Giant radiating dyke swarms on Earth and Venus, Earth-Science Reviews, 1995, 4: 229[7]Radhakrishns, T., Joseph. M., Proterozoic palaeomagnetism of the mafic dyke swarms is the high-grade region of southern India, Precambrian Research, 1996, 76: 31.[8]Li Jianghai, Qian Xianglin, Zhai Mingguo, The tectonic classification of granulite facies of North China and its Early Precambrian tectonic evolution, Scientia Geologica Sinica (in Chinese), 1997, 32: 254.[9]Hou Guiting, Zhang Chen, Qian Xianglin, The formation mechanism and tectonic stress field of Mesoproterozoic mafic dyke swarms in the North China Craton, Geological Review (in Chinese), 1998, 44(3): 309.[10]Li Jianghai, He Wenyuan, Qian Xianglin, Genetic mechanism and tectonic setting of Proterozoic mafic dyke swarm: its implication for paleoplate reconstruction, Geological Journal of China University (in Chinese), 1997, 3(3): 272.[11]Hou Guiting, Mu

  19. Dyke Swarms of the Paraná Triple Junction, Southern Brazil

    Directory of Open Access Journals (Sweden)

    José Moacyr Vianna Coutinho

    2008-10-01

    Full Text Available This work intends primarily to survey the field, mineralogical and petrographic characters of the mafic dykes which occuron a stretch of 650 km along the Southeastern coast of Brazil, between the city of São Sebastião, and the island of SantaCatarina. New chemical and geochronological data are also presented. The coastal dyke swarms are envisaged as the northernand southern arms of a plume-generated triple junction system centered on the Paraná State coast, and related to the initialopening of the South Atlantic. Mafic magma intruded as dyke swarms along three directions: N-S (the southern arm, along theParaná-Santa Catarina coast, NW-SE (Ponta Grossa arch and NE-SW (the northern arm along the São Paulo coast. Fiftytwo dykes, almost all tholeiitic diabases, were mapped and sampled along the south arm coast. The Ponta Grossa arch dykes are chiefly composed of tholeiitic diabases and lesser intrusions of andesitic to rhyolitic composition. Over 240 dykes were sampled and identified along the north arm west of São Sebastião. Lamprophyres are here abundant, followed by diabases, microdiorite porphyries and lesser amounts of trachy-andesite, carbonatite and Precambrian dykes. Special attention was given to the study of lamprophyres, their field appearance relative abundance, mineral and chemical composition, enclaves and relations to neighboring alkaline intrusions.

  20. Finding General Dyke.

    Science.gov (United States)

    Dyke, Charles William; Dyke, Ann Bisconti

    2011-01-01

    A hemorrhagic stroke and aphasia suddenly changed the life of Charles William (Bill) Dyke, Army Lt. General (Retired), Ranger strong with 2 silver stars and 3 bronze stars among his many decorations and founder and CEO of a Washington, DC, consulting firm. Gen. Dyke and his wife Ann provide their personal perspectives on the path to his remarkable recovery and return to full-time work. They found that the most effective therapy linked to who he was and is. Standard therapy tools and impersonal approaches frequently created barriers. Instead, when health professionals related the therapy objectives to his interests and involved him in the process of setting objectives to meet the challenges, they gained his trust, cooperation, participation, and focus on learning. PMID:21447463

  1. Dyke emplacement at the incipient Namibian margin - structural and anisotropy of magnetic susceptibility (AMS) studies in the Henties Bay - Outjo Dyke Swarm

    Science.gov (United States)

    Wiegand, Miriam; Trumbull, Robert; Greiling, Reinhard O.

    2010-05-01

    During the Cretaceous breakup of western Gondwana, the conjugate Namibian and South American margins were the site of flood basalts, mafic dyke swarms and subvolcanic intrusive complexes which make up the South Atlantic Large Igneous Province and the volcanic margin of northwestern Namibia. This contribution presents data on internal fabrics in mafic dykes (mostly subalkaline tholeiitic dolerites) from the major Henties Bay-Outjo dyke swarm (HOD) in coastal and inland NW Namibia, which are discussed in terms of magma emplacement. The HOD is some 100 km wide and extends at least 500 km from the continental margin. The dykes were emplaced in Neoproterozoic (Panafrican) Damara mobile belt, which is bounded by the Angola/Congo craton on the north and the Kalahari craton on the south. Field relations and radiometric dates indicate Early Cretaceous emplacement ages for the dykes. In coastal exposures north of the HOD, dolerite dykes are mainly coast-parallel (NNW-SSE) and syn-tectonic with normal faults that offset Etendeka lavas. Coast-parallel dykes are also common within the HOD, but the great majority of dykes strike NE-SW. We observed the latter dykes to crosscut coast-parallel ones. But the opposite relationship is also found locally. The dominant NE-SW strike of HOD indicates the influence of the Damara Belt structural grain at a regional scale, but locally the dykes commonly crosscut basement foliations and lithologic contacts. Depending on dyke thickness, which varies in the HOD from a few cm to about 50 m), the dykes are variably fine grained with chilled margins. Vesiculation is seldom observed. Typical textures are intersertal to subophitic, with plagioclase, clinopyroxene and olivine being the main mineral phases. Common minor minerals include opaque oxides and acicular apatite. Linear dykes are composed of segments, 10 m to some km in length, which are connected by transfer zones. Often a minor horizontal displacement can be observed between these segments

  2. Geochemical characteristics of Mesoproterozoic metabasite dykes from the Chhotanagpur Gneissic Terrain, eastern India: Implications for their emplacement in a plate margin tectonic environment

    Indian Academy of Sciences (India)

    Rajesh K Srivastava; Anup K Sinha; Suresh Kumar

    2012-04-01

    A number of mafic intrusive bodies (mostly dykes) are exposed in the Chhotanagpur Gneissic Terrain (CGT). Most dykes trend in ENE–WSW to E–W following major structural trends of the region. These metabasite dykes show granoblastic to grano-nematoblastic textures and contain hornblende, plagioclase, chlorite, quartz and epidote which suggest their metamorphism under amphibolite grade P–T conditions. Although no radiometric age is available for the metabasite dykes, field relationships with host rock and available geochronology on granitoids suggest their emplacement during Mesoproterozoic. Geochemical characteristics of these dykes classify them as low-K tholeiite to medium-K calcalkaline type. At least two types of metabasite dykes are recognized on the basis of their HFSE contents; one group shows entirely calc-alkaline nature, whereas the other group has rocks of tholeiite-calc-alkaline series. High Mg#observed in a number of samples indicates their derivation from primary melt. Multielement spidergrams and rare-earth element patterns observed in these samples also corroborate their derivation from different magma batches. Trace element patterns observed for Nb–Ta, Hf–Zr, Sr and Y suggesting involvement of subduction related processes in the genesis of CGT metabasite dykes. Perceived geochemical characteristics suggest that metamorphism did not affect much on the chemistry of metabasites but source region, responsible for the generation of CGT metabasites, was possibly modified during subduction process. This study suggests that magma generated in a destructive plate setting fed the Mesoproterozoic mafic dykes of the CGT.

  3. Geochemistry of the Palitana flood basalt sequence and the Eastern Saurashtra dykes, Deccan Traps: clues to petrogenesis, dyke-flow relationships, and regional lava stratigraphy

    Science.gov (United States)

    Sheth, Hetu C.; Zellmer, Georg F.; Kshirsagar, Pooja V.; Cucciniello, Ciro

    2013-04-01

    Recent studies of large mafic dyke swarms in the Deccan Traps flood basalt province, India, indicate that some of the correlative lava flows reached several hundred kilometers in length. Here we present field, petrographic, mineral chemical, and whole-rock geochemical (including Sr-Nd isotopic) data on the Palitana lava sequence and nearby dykes in the Saurashtra region of the northwestern Deccan Traps. These rocks are moderately evolved, many with low-Ti-Nb characteristics. We infer that most dykes are notably (and systematically) less contaminated by ancient continental crust than the Palitana flows, but four dykes are equally or significantly more contaminated, with some of the most extreme Sr-Nd isotopic compositions seen in the entire Deccan Traps (initial ɛNd is as low as -18.0). A Bhimashankar-type and a Poladpur-type dyke are present several hundred kilometers from the type section of these magma types in the Western Ghats escarpment. We find no geochemical correlations between the Palitana sequence and three subsurface sequences in NE Saurashtra containing abundant picritic rocks, surface lavas previously studied from Saurashtra, or the Western Ghats sequence. Intriguingly, the Eastern Saurashtra dykes cannot have been feeders to any of these lava sequences. Feeder dykes of these sequences may be located in southwestern or central Saurashtra, or in the Dhule-Nandurbar-Dediapada areas across the Gulf of Cambay, 200-300 km east of Palitana. Our results indicate polycentric flood basalt eruptions not only on the scale of the Deccan Traps province, but also within the Saurashtra region itself.

  4. Dyke-Davidoff-Masson syndrome

    Directory of Open Access Journals (Sweden)

    Manas R Behera

    2012-01-01

    Full Text Available A 14-month-old male child presented with recurrent generalized seizures, spastic hemiplegia, microcephaly and had developmental delay in motor and speech domains. CT of the brain revealed characteristic features diagnostic of infantile type of cerebral hemiatrophy or Dyke-Davidoff-Masson syndrome.

  5. Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple Magma Types During Orogenic Collapse

    Science.gov (United States)

    Freeman, M.; Owen, J. P.; Hoskin, P. W.

    2009-05-01

    Eocene dyke swarms in southeastern British Columbia provide an important record of the tectonic and magmatic history of the Cordillera following orogenic collapse. New field mapping, petrographic, and geochemical data is presented for a swarm of more than thirty dykes located near the mining town of Trail, B.C. Detailed field mapping revealed that individual dykes are highly diverse, both in composition and morphology. As a group, the dykes trend northwest (average strike of 338 degrees) and dip steeply to the southwest. Their average thickness is approximately 1.5m, with a range from 4.5m to less than 1cm. Three sub-parallel dykes were mapped for a length of 2km, and exhibit irregularities in their form such as branching and offshoots that follow fractures in the country rock. Thin-section analysis shows a wide variety of rock types within the swarm, including: micro-quartz syenite, micro-syenite, micro-monzonite, latite, basalt, basaltic andesite, and lamprophyre. Texturally, these samples are consistently porphyritic and partially altered to chlorite and sericite. This alteration commonly occurs in concentric rims around phenocrysts. The samples are typically intergranular, although some display trachytic texture. Whole-rock geochemistry shows that the dykes have a wide range in composition, with SiO2 between 76.45 wt.% and 45.15 wt.% and MgO between 0.13 wt.% and 13.16 wt.%. The results also revealed that one dyke has very high values of Ni (430 ppm), Cr (1420 ppm), and Co (50 ppm), giving it a fairly primitive composition. Harker diagrams and trace element plots show three distinct groups: mafic calc-alkaline dykes, felsic calc- alkaline dykes, and minette lamprophyres. The felsic dykes are characterized by negative Eu and Sr anomalies suggesting fractionation of plagioclase feldspar, as well as pronounced negative P and Ti anomalies. The minettes are enriched in LILE and depleted in HSFE relative to the mafic dykes. The three groups do not appear to be

  6. Magma deformation and emplacement in rhyolitic dykes

    Science.gov (United States)

    McGowan, Ellen; Tuffen, Hugh; James, Mike; Wynn, Peter

    2016-04-01

    Silicic eruption mechanisms are determined by the rheological and degassing behaviour of highly-viscous magma ascending within shallow dykes and conduits. However, we have little knowledge of how magmatic behaviour shifts during eruptions as dykes and conduits evolve. To address this we have analysed the micro- to macro-scale textures in shallow, dissected rhyolitic dykes at the Tertiary Húsafell central volcano in west Iceland. Dyke intrusion at ~3 Ma was associated with the emplacement of subaerial rhyolitic pyroclastic deposits following caldera formation[1]. The dykes are dissected to ~500 m depth, 2-3 m wide, and crop out in two stream valleys with 5-30 m-long exposures. Dykes intrude diverse country rock types, including a welded ignimbrite, basaltic lavas, and glacial conglomerate. Each of the six studied dykes is broadly similar, exhibiting obsidian margins and microcrystalline cores. Dykes within pre-fractured lava are surrounded by external tuffisite vein networks, which are absent from dykes within conglomerate, whereas dykes failed to penetrate the ignimbrite. Obsidian at dyke margins comprises layers of discrete colour. These display dramatic thickness variations and collapsed bubble structures, and are locally separated by zones of welded, brecciated and flow-banded obsidian. We use textural associations to present a detailed model of dyke emplacement and evolution. Dykes initially propagated with the passage of fragmented, gas-charged magma and generation of external tuffisite veins, whose distribution was strongly influenced by pre-existing fractures in the country rock. External tuffisites retained permeability throughout dyke emplacement due to their high lithic content. The geochemically homogenous dykes then evolved via incremental magma emplacement, with shear deformation localised along emplacement boundary layers. Shear zones migrated between different boundary layers, and bubble deformation promoted magma mobility. Brittle

  7. Physical volcanology of the mafic segment of the subaqueous New Senator caldera, Abitibi greenstone belt, Quebec, Canada

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Lyndsay N; Mueller, Wulf U [Universite du Quebec a Chicoutimi, 555 boul. du l' Universite, Chicoutimi, Quebec, G7H2B1 (Canada)], E-mail: lyndsay.moore@uqac.ca

    2008-10-01

    Archean calderas provide valuable insight into internal geometries of subaqueous calderas. The New Senator caldera, Abitibi greenstone belt, Canada, is an Archean example of a subaqueous nested caldera with a basal stratigraphy dominated by gabbro-diorite dykes and sills, ponded magmas and basalt and andesite lava flows. The aim of our study is to focus on the use of physical volcanology to differentiate between the various mafic units found at the base of the New Senator caldera. Differentiation between these various mafic units is important from an exploration point of view because in modern subaqueous summit calders (e.g. Axial Seamount) margins of ponded magmas are often sites of VMS formation.

  8. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events

    Science.gov (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  9. Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting

    Science.gov (United States)

    Sengupta, Piyali; Ray, Arijit; Pramanik, Sayantani

    2014-06-01

    The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE-SW, NW-SE and NNE-SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite-actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.

  10. Mineralogical and chemical character- istics of newer Dolerite Dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting

    Indian Academy of Sciences (India)

    Piyali Sengupta; Arijit Ray; Sayantani Pramanik

    2014-06-01

    The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.

  11. Vegetation dynamics and erosion resistance of sea dyke grassland

    NARCIS (Netherlands)

    Sprangers, H.

    1999-01-01

    In the Netherlands, in addition to the width and height of the dyke body itself, renewed measures for reconstruction and maintenance of dykes have stressed the importance to the safeguarding of the dyke, of the grass cover's protection of the clay-layer against erosion.From an inventory of different

  12. Investigation of the Cascade Canal dyke assessing the risk of dyke performance problems

    Energy Technology Data Exchange (ETDEWEB)

    Cullum-Kenyon, Simon; Sobkowicz, John C.; Abraha, Dawit G.; Ramdharry, Bhamisha [Thurber Engineering Ltd., Alberta, (Canada); Taylor, Scott [TransAlta Generation Partnership, Alberta, (Canada)

    2010-07-01

    The Cascade Development is located on the Cascade River in the Banff National Park, Alberta. In 2005, two earth slumps occurred on the down slope face of the Cascade Canal dyke as a result of heavy rain. This paper presented the repair work and the investigation program carried out after the repair work. The program started with an initial phase which included six test holes along the crest of the dyke and twelve test pits along the toe of the dyke. Slotted standpipe piezometers were installed in the test holes. Moisture content, Atterberg limit and grain-size analysis tests were conducted on samples. The next phase used a combination of CPT testing and additional test holes drilled using a GeoProbe drill rig. A preliminary liquefaction analysis was conducted. Several areas along the dyke with loose or very loose soils within the downstream shoulder were found. The liquefaction analyses showed that these loose materials may be susceptible to earthquake liquefaction.

  13. Determining dyke-propagation paths at Santorini volcano, Greece

    Science.gov (United States)

    Drymoni, Kyriaki; Browning, John; Lecoeur, Nora; Gudmundsson, Agust

    2016-04-01

    The volcanic Island of Santorini constitutes a complex of collapse calderas which has experienced a range of explosive and effusive volcanic eruptions and is still active. Numerous stratigraphic horizons which constitute the upper part of the volcano have widely different mechanical properties, resulting in local stresses that may act as dyke-traps, preventing the dykes from reaching the surface to erupt. Several caldera collapses (arrested and some feeders) within a section of the northern caldera wall, allowing detailed examination. This ongoing study will (1) document the petrological and structural characteristics of feeder and non-feeder (arrested) dykes and estimate their frequency; (2) determine the physiochemical and mechanical conditions that control dyke arrest/dyke penetration at contacts between layers; (3) explore the fluid and mechanical conditions of the associated magma chamber(s) that must be satisfied for chamber rupture and dyke injection to occur; (4) make numerical and probabilistic models as to the likely dyke paths in heterogeneous and anisotropic crustal segments/volcanoes (such as Santorini), including the likelihood of injected dykes reaching the surface during an unrest period in a volcano of a given type; (5) compare the data collected from Santorini with existing data on dykes worldwide, particularly those on dykes in Tenerife and Iceland. The principal aim of the study is to provide models that, during an unrest period in Santorini and other similar volcanoes, allow us to forecast (a) the condition for magma-chamber rupture and dyke injection, and (b) the likely path of the resulting dyke. The latter includes assessment of the likelihood as to dyke arrest versus dyke propagation to the surface, the latter resulting in an eruption. For dyke-fed eruptions, the study will also provide methods for forecasting the likely volumetric flow rates and eruption magnitudes.

  14. Postmagmatic magnetite-apatite assemblage in mafic intrusions: a case study of dolerite at Olympic Dam, South Australia

    Science.gov (United States)

    Apukhtina, Olga B.; Kamenetsky, Vadim S.; Ehrig, Kathy; Kamenetsky, Maya B.; McPhie, Jocelyn; Maas, Roland; Meffre, Sebastien; Goemann, Karsten; Rodemann, Thomas; Cook, Nigel J.; Ciobanu, Cristiana L.

    2016-01-01

    An assemblage of magnetite and apatite is common worldwide in different ore deposit types, including disparate members of the iron-oxide copper-gold (IOCG) clan. The Kiruna-type iron oxide-apatite deposits, a subtype of the IOCG family, are recognized as economic targets as well. A wide range of competing genetic models exists for magnetite-apatite deposits, including magmatic, magmatic-hydrothermal, hydrothermal(-metasomatic), and sedimentary(-exhalative). The sources and mechanisms of transport and deposition of Fe and P remain highly debatable. This study reports petrographic and geochemical features of the magnetite-apatite-rich vein assemblages in the dolerite dykes of the Gairdner Dyke Swarm (~0.82 Ga) that intruded the Roxby Downs Granite (~0.59 Ga), the host of the supergiant Olympic Dam IOCG deposit. These symmetrical, only few mm narrow veins are prevalent in such dykes and comprise besides usually colloform magnetite and prismatic apatite also further minerals (e.g., calcite, quartz). The genetic relationships between the veins and host dolerite are implied based on alteration in the immediate vicinity (~4 mm) of the veins. In particular, Ti-magnetite-ilmenite is partially to completely transformed to titanite and magmatic apatite disappears. We conclude that the mafic dykes were a local source of Fe and P re-concentrated in the magnetite-apatite veins. Uranium-Pb ages for vein apatite and titanite associated with the vein in this case study suggest that alteration of the dolerite and healing of the fractures occurred shortly after dyke emplacement. We propose that in this particular case the origin of the magnetite-apatite assemblage is clearly related to hydrothermal alteration of the host mafic magmatic rocks.

  15. Three Paleoproterozoic A-type granite intrusions and associated dykes from Kainuu, East Finland

    Directory of Open Access Journals (Sweden)

    Hannu Huhma

    2010-12-01

    Full Text Available Mafic and felsic intrusive rocks aged 2.5–2.4 Ga have been observed over a large area in eastern and northern Finland, as well as in adjacent northwestern Russia. We describe three granite intrusions and associated dykes from Kainuu, Finland, that belong to this bimodal magmatic event. All these three granites show clear A2-type chemical affinities with high Y/Nb, HREE, Fe/Mg, Ga and Nb. Two of the intrusions, Rasinkylä and Pussisvaara, were dated at 2425±3 and 2427±3 Ma, respectively, using thermal ionisation mass spectrometry utilizing the chemical abrasion method (CA-TIMS. CA-TIMS ages are supported by single-grain age determinations obtained by using Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometer (LA-MC-ICPMS. New data on the previously described Rasimäki granite from southern Kainuu is presented, including an age of 2389±5 Ma obtained with LA-MC-ICPMS. The variable magnetite content of the granites is proposed to reflect the differences in the oxidation state of the source, which in our interpretation is the local Archean lower crust. Partial melting and the emplacement of the granites occurred in an extensional environment. Heat for the partial melting was provided by mafic magmas under and intraplating the extended crust.

  16. Petrological, geochemical and isotopic investigations on a carbonate-dyke and enclosed pyroxenite xenoliths from Val Mastallone (Ivrea-Verbano Zone): evidence of a cumulate carbonatite in the lower crust?

    Science.gov (United States)

    Galli, Andrea; Grassi, Daniele; Burg, Jean-Pierre; Schwab, Leo; Rickli, Jörg; Gianola, Omar

    2016-04-01

    The Ivrea-Verbano Zone (Italy/Switzerland) represents one of the best exposed mantle-crust sections worldwide. Its geological evolution has been governed by the Permian underplating of mantle-derived basic magmas („Mafic Complex") into the high-grade basement of the Southern Alps. In the Ivrea-Verbano Zone, marbles occur as concordant bodies or partly discordant carbonate-dykes. Generally, these dykes are constituted of calcite, diopside, scapolite, contain enclave of the host rocks and display sharp contacts to the host lithologies without evidences of alteration zones. In Val Mastallone, an up to 40 m thick carbonate-dyke with different characteristics occurs within mafic granulites. This dyke is composed of calcite, clinopyroxene and subordinate allanite and zircon. No scapolite is observed. The contacts to the host granulites are characterized by alteration zones composed of actinolite, chlorite, clinozoisite, plagioclase and calcite. The carbonate-dyke bears enclave of phlogopite-amphibole-apatite-rutile-ilmenite ± garnet or spinel clinopyroxenites. These rock type is not outcropping elsewhere in the proximity of the dyke, suggesting a significant transport. Host mafic granulite enclave are found exclusively at the margin of the dyke. Calcite dykelets rich in zircon, baddeleyite and other Ba, U, Th, REE-rich phases cut across the enclave. The carbonate-dyke shows an enrichment of LREE over HREE ((La/Yb)N = 14), with a Σ REE = 338 and Y/Ho = 27. On the chondrite-normalized REE abundances diagram, no Eu anomaly is observed. Mantle-normalized pattern shows strong negative anomalies at Cs, Rb, K, Pb, P, Zr, Hf, Ti and positive Ba, Th, Sr, Nd anomalies, similarly to the "world average carbonatites". Measured absolute trace element concentrations are lower than average carbonatites but significantly higher than typical limestones and similar to cumulate carbonatites found elsewhere in the world (e.g. India, China, Brazil). Grt-bearing clinopyroxenite enclave

  17. Engineering geotextile tubes to be used in dyke construction

    Institute of Scientific and Technical Information of China (English)

    ZHU Yuan-sheng

    2007-01-01

    Geotextile tube technology has been increasingly used in dykes. In this work reinforcement theory and circle method were employed to examine the allowable tensile limit of the geotextile tube and the stability factor of the slip surface of the dyke. The formulas to calculate the layer-to-layer spacing and size of geotextile tubes applied to double prism dykes were deduced. The application of these formulas was illustrated by several examples. The calculation results indicate that unequal spacing arrangement is more economical than equal spacing and the layer number of required geotextile tubes decreases with the increase of allowable tensile strength of the geotextile.

  18. Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks

    Science.gov (United States)

    Riley, T. R.; Curtis, M. L.; Flowerdew, M. J.; Whitehouse, M. J.

    2016-02-01

    New geochronology from a thick (> 800 m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178 ± 1 Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~ 170 Ma) of the Antarctic Peninsula. The geochemistry of other rare, but broadly contemporaneous, basaltic successions of the Antarctic Peninsula, along with Cretaceous-age mafic dykes, are used to interpret the influences of lithospheric and asthenospheric mantle sources during the Mesozoic. Two significant high magmatic addition rate events occurred along the Antarctic Peninsula continental margin at 170 and 110 Ma and can be correlated to events along the South American Cordillera. These 'flare-up' events are characterised by extensive silicic (mostly ignimbrite) volcanism of the Chon Aike Province (V2 event: 170 Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110 Ma). The 170 Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110 Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the 'flare-up' event at 170 Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170 Ma event indicates that extensive lithospheric thinning had occurred, which allowed the ascent of depleted mafic melts. The thinning was the direct result of widespread lower crustal/upper lithospheric melting associated with the silicic volcanism. In the southern Antarctic Peninsula, the lithosphere remained over thickened until the emplacement of the major batholiths of the Lassiter Coast intrusive suite at 110 Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.

  19. Paleomagnetism of Devonian dykes in the northern Kola Peninsula and its bearing on the apparent polar wander path of Baltica in the Precambrian

    Science.gov (United States)

    Veselovskiy, Roman V.; Bazhenov, Mikhail L.; Arzamastsev, Andrey A.

    2016-04-01

    Mafic dykes and large alkaline and carbonatite intrusions of Middle-Late Devonian age are widespread on the Kola Peninsula in NE Fennoscandia. These magmatic rocks are well characterized with petrographic, geochemical and geochronological data but no paleomagnetic results have been reported yet. We studied dolerite dykes from the northern part of the Peninsula and isolated three paleomagnetic components in these rocks. A low-temperature component is aligned along the present-day field, while a major constituent of natural remanent magnetization is an intermediate-temperature component (Decl. = 79.6°, Inc. = 78.5°, α95 = 5,9°, N = 17 sites) that is present in most Devonian dykes but is found in some baked metamorphic rocks and Proterozoic dykes too. Finally, a primary Devonian component could be reliably isolated from two dykes only. Rock-magnetic studies point to presumably primary low-Ti titanomagnetite and/or pure magnetite as the main remanence carriers but also reveal alteration of the primary minerals and the formation of new magnetic phases. The directions of a major component differ from the Middle Paleozoic reference data for Baltica but closely match those for the 190 ± 10 Ma interval recalculated from the apparent polar wander path of the craton. We assume that this Early Jurassic component is a low-temperature overprint of chemical origin. The main impact of the new results is not to mid-Paleozoic or Early Mesozoic times but to much older epochs. Analysis of paleomagnetic data shows that the directionally similar remanences are present in objects with the ages ranging from 500 Ma to ~ 2 Ga over entire Fennoscandia. Hence we argue that an Early Jurassic remagnetization is of regional extent but cannot link it to a certain process and a certain tectonic event. If true, this hypothesis necessitates a major revision of the APWP for Baltica over a wide time interval.

  20. Seismic footprints of shallow dyke propagation at Etna, Italy

    OpenAIRE

    Susanna Falsaperla; Marco Neri

    2015-01-01

    One of the key issues in forecasting volcanic eruptions is to detect signals that can track the propagation of dykes towards the surface. Continuous monitoring of active volcanoes helps significantly in achieving this goal. The seismic data presented here are unique, as they document surface faulting processes close (tens to a few hundred meters) to their source, namely the dyke tip. They originated nearby - and under - a seismic station that was subsequently destroyed by lava flows during er...

  1. Geochemistry and geochronology of mafic rocks from the Luobusa ophiolite, South Tibet

    Science.gov (United States)

    Zhang, Chang; Liu, Chuan-Zhou; Wu, Fu-Yuan; Zhang, Liang-Liang; Ji, Wei-Qiang

    2016-02-01

    This study presents geochemical compositions of mafic rocks outcropped in the Luobusa ophiolite that locates at the eastern part of the Yarlung Zangbo Suture Zone (YZSZ). The studied mafic rocks include gabbroic/diabase dykes cutting the peridotites and foliated amphibolites embedded within the subophiolitic mélange. The diabases have low K2O contents and display N-MORB-like geochemical characteristics, i.e., with flat REE patterns and weak enrichment in LILE (e.g., Rb, Ba, Th and U). The gabbros show LREE-depleted patterns and variable enrichment in Rb and Ba. Foliated amphibolites mainly consist of hornblendes and plagioclases, with minor titanites. They commonly show LREE-depleted patterns, with strong enrichment in LILE. Three diabases have depleted Sr-Nd-Hf isotope compositions, with initial 87Sr/86Sr ratios of 0.703009-0.703502, εNd(t) of + 5.0 to + 8.5 and εHf (t) of ca + 14. Two gabbros have similar Nd-Hf isotopes with the diabases, but slightly higher initial 87Sr/86Sr ratios (i.e., 0.704820 and 0.704550). Compared to both diabases and gabbros, the amphibolites have higher initial 87Sr/86Sr ratios (i.e., 0.705131-0.705825), but more depleted Nd-Hf isotope compositions, with εNd(t) of + 9.1 to + 11.6 and εHf(t) of + 18.2 to + 21.9. Geochemical compositions of the diabase dykes indicate that they were formed in a mid-ocean ridge setting. Zircon SIMS U-Pb dating of the gabbroic dyke cutting the serpentinites yields an age of 128.4 ± 0.9 Ma, which is identical within uncertainty to the zircon U-Pb age of the amphibolite (i.e., 131.0 ± 1.2 Ma). Low U and Th contents of zircons in the amphibolite support their metamorphic origin. Titanites in the amphibolites have been dated by LA-ICPMS and give U-Pb ages of ~ 131-134 Ma, which are similar to the zircon U-Pb ages of the dated gabbro and amphibolite. Therefore, we suggest that the Luobusa ophiolite was generated at the Early Cretaceous and underwent the intra-oceanic emplacement immediately after its

  2. Geochronological Significance of the Post-Orogenic Mafic-Ultramafic Rocks in the Hongqiling Area of Jilin Province, Northeast China

    Institute of Scientific and Technical Information of China (English)

    Zhang Guangliang; Wu Fuyuan

    2006-01-01

    Mafic-ultramafic complexes are widespread in Hongqiling in central Jinlin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-ultramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-ultramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-ultramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-ultramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-ultramafic complexes in the Xing'an-Mongolia Orogenic Belt

  3. Petrology, geochemistry of hornblende gabbro and associated dolerite dyke of Paharpur, Puruliya, West Bengal: Implication for petrogenetic process and tectonic setting

    Indian Academy of Sciences (India)

    Aditi Mandal; Arijit Ray; Mayukhee Debnath; Sankar Prasad Paul

    2012-06-01

    Paharpur gabbroic intrusive is an arcuate body running east–west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north–south. It is composed of clinopyroxene (Wo48En40Fs12–Wo51En40Fs09, mg no. 72–82), plagioclase (An52–An90), hornblende (magnesian hornblende to ferro-tschermackite), orthopyroxene (En76–En79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65–73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depletion suggest arc like geochemical signature for the gabbroic and doleritic rocks of Paharpur. Flat to slightly LREE fractionated pattern and variable degree of REE enrichment is observed. An early stage fractionation of clinopyroxene, plagioclase, orthopyroxene, ilmenite and late stage reaction of cumulate pile and evolved melt/hydrous fluid is suggested for magmatic evolution of gabbro. Associated dolerite dykes, which are geochemically similar to the gabbro, have tholeiitic with boninitic character. The mineralogical and chemical compositions of intrusive rocks also have some similarity with mafic rocks of ophiolite complex of subduction zone.

  4. Remobilization of granitoid rocks through mafic recharge: evidence from basalt-trachyte mingling and hybridization in the Manori-Gorai area, Mumbai, Deccan Traps

    Science.gov (United States)

    Zellmer, Georg F.; Sheth, Hetu C.; Iizuka, Yoshiyuki; Lai, Yi-Jen

    2012-01-01

    Products of contrasting mingled magmas are widespread in volcanoes and intrusions. Subvolcanic trachyte intrusions hosting mafic enclaves crop out in the Manori-Gorai area of Mumbai in the Deccan Traps. The petrogenetic processes that produced these rocks are investigated here with field data, petrography, mineral chemistry, and whole rock major, trace, and Pb isotope chemistry. Local hybridization has occurred and has produced intermediate rocks such as a trachyandesitic dyke. Feldspar crystals have complex textures and an unusually wide range in chemical composition. Crystals from the trachytes cover the alkali feldspar compositional range and include plagioclase crystals with anorthite contents up to An47. Crystals from the mafic enclaves are dominated by plagioclase An72-90, but contain inclusions of orthoclase and other feldspars covering the entire compositional range sampled in the trachytes. Feldspars from the hybridized trachyandesitic dyke yield mineral compositions of An80-86, An47-54, Ab94-99, Or45-60, and Or96-98, all sampled within individual phenocrysts. We show that these compositional features are consistent with partial melting of granitoid rocks by influx of mafic magmas, followed by magma mixing and hybridization of the partial melts with the mafic melts, which broadly explains the observed bulk rock major and trace element variations. However, heterogeneities in Pb isotopic compositions of trachytes are observed on the scale of individual outcrops, likely reflecting initial variations in the isotopic compositions of the involved source rocks. The combined data point to one or more shallow-level trachytic magma chambers disturbed by multiple injections of trachytic, porphyritic alkali basaltic, and variably hybridized magmas.

  5. Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements, REE geochemistry and Sr-Nd-O isotope systematics of ultramafic dykes

    Indian Academy of Sciences (India)

    Abhijit Roy; A Sarkar; S Jeyakumar; S K Aggrawal; M Ebihara; H Satoh

    2004-12-01

    Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sri ∼0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; ( HREE)N ∼ 2-3 times chondrite, (Gd/Yb)N∼1). The Nd(t) values vary from +1.23 to −3.27 whereas 18O values vary from +3.16‰ to +5.29‰ (average +3.97‰ ± 0.75‰) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (±silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable Nd, low Sri(0.702) and low 18O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.

  6. Dyke Foundation Classification%关于堤基的分段分类

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Jia-fa

    2001-01-01

    Main factors, which should be considered in the classification of dyke foundation, are discussed in this paper. Engineering conditions should be taken into accoun t when the levee safety is appraised based on engineering geologic appraisement and classificatio n. On the basis of safety appraisement, dyke foundation may be classified with regard of suitable r einforcement measures. Examples are presented to illustrate the instructive significance of dyke foundation cla ssification to dyke reinforcement design.

  7. Temporal geoelectric behaviour of dyke aquifers in northern Deccan Volcanic Province, India

    Indian Academy of Sciences (India)

    Gautam Gupta; Vinit C Erram; Suyash Kumar

    2012-06-01

    Vertical electrical resistivity soundings (VES) were carried out over four major dykes of Nandurbar district in the northern Deccan Volcanic Province (DVP) of Maharashtra to investigate the subsurface geological conditions, with an aim of identifying zones with groundwater resource potential. Dykes can act as pathways or barrier to the groundwater flow depending upon the intensity of fracturing in the dyke rock. Whether the dykes act as water conduits or as barriers depends on their structure, location and orientation with respect to the groundwater flow. The Nandurbar district is known for occurrence of dykes and dyke swarms. A total of 33 dykes were demarcated in the study region and four major dykes (D4, D5, D6, and D7) from these were chosen for detailed VES studies. Data were acquired over these four dykes during pre-monsoon and post-monsoon periods to observe the seasonal variation in groundwater movement. These studies revealed changes in field characters, their attitudes, thickness and structure of the dykes. Longitudinal geoelectrical sections along these dykes demonstrated carrier as well as barrier stretches which identified potential aquifers up to depths of 25–30m below which hard and compact rock exists. These studies also indicated that dykes with sufficient width, length and favourable hydrogeological structure form potential aquifers for the occurrence and movement of groundwater in the study area.

  8. Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

    Science.gov (United States)

    Pál-Molnár, Elemér; Batki, Anikó; Almási, Enikő; Kiss, Balázs; Upton, Brian G. J.; Markl, Gregor; Odling, Nicholas; Harangi, Szabolcs

    2015-12-01

    Mafic-ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75-73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~ 1000-1050 °C and ~ 0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting.

  9. New paleomagnetic data from 1.80-1.75 Ga mafic intrusions of Fennoscandia and Sarmatia: implications for the late Paleoproterozoic paleogeography of Baltica and Laurentia

    Science.gov (United States)

    Pisarevsky, Sergei; Lubnina, Natalia; Sokolov, Svetoslav; Bogdanova, Svetlana

    2016-04-01

    A series of recently dated 1.78-1.75 Ga lamprophyre and shoshonite intrusions are exposed north of Ladoga Lake in southern Karelia (Fennoscandia). We carried out a paleomagnetic study of these intrusions and an additional study of the coeval gabbro-dolerite Ropruchey sill near the Onega Lake. All studied rocks carry a stable primary remanence supported by positive contact tests. We also studied 14 mafic dykes and 1 mafic sill from Ukrainian shield (Sarmatia). Most of these intrusions have been dated or re-dated recently by U-Pb (baddeleyite) method at 1.80-1.75 Ga. Ukrainian dykes also carry a consistent stable bipolar remanence. Two positive contact tests suggest that this remanence is primary. A comparison of new and previously published paleomagnetic data shows a significant difference between Fennoscandian and Sarmatian 1.80-1.75 Ga paleopoles. This implies that the final assemble of Baltica by docking of Volgo-Sarmatia and Fennoscandia occurred after 1.75 Ga. Consequently these two parts of Baltica should be considered as independent blocks in pre-1.75 Ga paleogeographic reconstructions. Using late Paleoproterozoic paleomagnetic data from Laurentia together with geological constraints we have built a new kinematic paleogeographic model for Laurentia and Baltica in the Statherian.

  10. Dyke emplacement and propagation: a new laboratory approach

    Science.gov (United States)

    Bakker, R.; Benson, P.; Vinciguerra, S.

    2013-12-01

    It is well known that magma ascends trough the crust by the process of dyking. During dyke movement crustal rocks, specifically the volcano's basement rocks, fracture due to the stress imposed by the ascending magma, thus providing conduits for magma transport. Dykes are frequently seen in the field and have been reproduced via numerical and analogue studies. However, a number of assumptions regarding rock mechanical behavior frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. To bridge this gap, we have performed a suite of rock deformation experiments in both compressive and tensile regimes, using a Paterson-type triaxial apparatus on representative lithologies present in the basement of Mt. Etna. In the compressive regime, we find that sedimentary rocks present at a depth of aproximately 2 km show a B/D transition at around 300 degC and significant weakening with temperatures exceeding 400 degC. Volcanic rocks (basalt) shows a significant change in deformation behavior only at temperatures exceeding 800 degC. Such a large contrast in mechanical properties could be favorable for dyke deflection or dyke arrest. However, in the tensile regime, it remains a significant technical challenge to precisely reproduce the conditions of dyking in the lab. As a starting point, we are now testing an analogue material to replace the magma to avoid such high temperatures, relying of maintaining similar temperature/viscosity ratios between magma/country rock in the laboratory and the field. We chose PMMA (a.k.a. plexiglass) for this task as it displays a large range in viscosities (log(visc)range = 10 - 1) with temperatures between 100 and 300 degC, making it an excellent analogue material. In addition PMMA solidifies after the sample cools

  11. Geochemistry of eastern North American CAMP diabase dykes

    Science.gov (United States)

    Callegaro, S.; Marzoli, A.; Bertrand, H.; Reisberg, L. C.; Chiaradia, M.; Bellieni, G.

    2011-12-01

    The Piedmont area of the Appalachians and the coastal plains of eastern North America (ENA) were intruded between 202 and 195 Ma[1,2] by swarms of diabase (dolerite) dykes and a few sills of the Central Atlantic magmatic province (CAMP). Different trends are observed for the dykes, from NW (more frequent in the South), to N-S and NE, thus a radial pattern and a coeval emplacement driven by the bulging effect of a mantle plume were initially inferred[3]. Conversely, based on field data, an age progression can be defined from NW- to N- and NE-oriented dykes, supporting a diachronous northward rift-to-drift transition during Pangaea break-up. New geochemical data on 74 ENA dykes suggest a dominant lithospheric mantle source for these magmatic suite. A deep enriched mantle source is further discarded by the crystallization temperatures (ca.1350°C) calculated[4] for high-Fo (up to Fo89) olivines, which do not reflect very hot (i.e. mantle-plume) potential mantle temperatures. Incompatible trace element contents are fairly homogeneous and generally low, e.g. (La/Yb)Ch (0.54-2.39), typical of melts derived from a quite depleted shallow (spinel) mantle-source. However, isotopic compositions of ENA dykes display a considerable spread in initial isotopic signatures, do not show correlation with incompatible trace elements, and are independent of the orientation and age of the dykes, i.e. 87Sr/86Sr200Ma (0.7043-0.7088), ɛNd200Ma (-6.67-+2.42) and 206Pb/204Pb200Ma (17.46-18.61). Pb isotopic compositions plot above the NHRL, at positive Δ7/4 (10-17) and Δ8/4 (19-73), calling for an enriched ancient component in the mantle source. Unradiogenic 187Os/188Os200Ma ratios (0.127-0.144) argue for negligible amounts of crustal contamination and, coupled with the large range of Sr-Nd-Pb isotopic compositions, suggest generation from a strongly heterogeneous mantle source, probably metasomatized lithosphere. Lithospheric mantle underlying the Appalachian orogen may have undergone

  12. Permanent groundwater storage in basaltic dyke fractures and termite mound viability

    Science.gov (United States)

    Mège, Daniel; Rango, Tewodros

    2010-04-01

    Many basaltic dykes of the Ethiopian flood basalt province are observed in the northwestern Ethiopian lowlands. In this area, the termites preferentially build their epigeous mounds on the top of dolerite dykes. The relationship between termite mounds and dykes is investigated from the analysis of their distribution along one of these dykes, of thickness 2-5 m, that we could follow over 2000 m. Termite mounds are periodically spaced (mean distance 63 m, R2 = 0.995), and located exclusively where the topographic relief of the dyke is not more than 2 m above the surrounding area. From these observations and from the geological context, a hydrological circuit model is proposed in which (1) dykes are preferential conduits for groundwater drainage during the rainy season due to pervasive jointing, (2) during the dry season, the portion of the dyke forming a local topographic relief area dries up more quickly than the surroundings, the elevation difference between the dyke summit and the surroundings being a factor restricting termite mound development. For dyke topographic relief >2 m, drying is an obstacle for maintaining the appropriate humidity for the termite colony life. Periodic termite mound spacing is unlikely to be related to dyke or other geological properties. It is more likely related to termite population behaviour, perhaps to clay shortage, which restricts termite population growth by limiting the quantity of building material available for mound extension, and triggers exploration for a new colonization site that will be located along the dyke at a distance from the former colony that may be controlled by the extent of the zone covered by its trail pheromones. This work brings out the importance of dykes in channelling and storing groundwater in semiarid regions, and shows that dykes can store groundwater permanently in such settings even though the dry season is half the year long. It contributes also to shedding light on water supply conditions

  13. Seismic footprints of shallow dyke propagation at Etna, Italy

    Science.gov (United States)

    Falsaperla, Susanna; Neri, Marco

    2015-01-01

    One of the key issues in forecasting volcanic eruptions is to detect signals that can track the propagation of dykes towards the surface. Continuous monitoring of active volcanoes helps significantly in achieving this goal. The seismic data presented here are unique, as they document surface faulting processes close (tens to a few hundred meters) to their source, namely the dyke tip. They originated nearby - and under - a seismic station that was subsequently destroyed by lava flows during eruptive activity at Etna volcano, Italy, in 2013. On February 20, a ~600 m-long and ~120 m wide NW-SE fracture field opened at an altitude between 2750 and 2900 m. The consequent rock dislocation caused the station to tilt and offset the seismic signal temporarily. Data acquisition continued until the arrival of the lava flow that led to the breakdown of the transmission system. Shallow ground fracturing and repeated low-frequency oscillations occurred during two stages in which the seismic signal underwent a maximum offset ~2.57 × 104 nm/s. Bridging instrumental recordings, fieldwork and conceptual modelling, these data are interpreted as the seismic footprints of a magmatic dyke intrusion that moved at speed ~0.02 m/s (first stage) and 0.46 m/s (second stage). PMID:26173557

  14. A RARE CAUSE OF RESISTANT SEIZURES: DYKE DAVIDOFF MASSON SYNDROME

    Directory of Open Access Journals (Sweden)

    Biswadev Basu

    2013-11-01

    Full Text Available ABSTRACT : Dyke – Davidoff – Masson Syndrome (DDMS, is a rare clinical condition characterized by clinical triad of seizures, contralateral spastic hemiplegia or hemiparesis, with or without mental retardation. Diagnosis requires presence of cerebral hemiatrophy with homolateral hypertrophy of the skull and sinuses on brain imaging. Here we report a case of DDMS in a 16 year old girl who presented with seizures and hemiparesis.MRI of her brain showed hemiatrophy involving the left cerebral hemisphere with enlargement of ipsilateral sinuses and ventricles

  15. Dyke Monitorin by the Means of Persistent Scattering Interferometry at the Coast of Northern Germany

    Science.gov (United States)

    Seidel, M.; Marzahn, P.; Ludwig, R.

    2016-06-01

    40 percent of the world's population are presently living in coastal areas or along the main rivers. Taking into account that the vulnerability of these areas is increasing due to sea-level rise and coastal hazards such as storm surges or extreme rainfall events accompanied with floods, the importance of safety structures such as dykes is increasing as well. Hence, a spatial distributed dyke monitoring should be part of a sustainable adaptation strategy. Due to increasing amount of SAR-data from various satellites with high spatial and temporal coverage, the means of SAR-interferometry could be an essential tool to ensure this kind of required monitoring. Given this prospect, Persistent Scattering Interferometry (PSI) will be a very suitable monitoring technique for dyke structures to identify dyke movement with the accuracy of few millimetres. This procedure focuses on pixels that show a stable scattering behaviour in a sequence of multiple SAR-scenes. In opposition to ground-measurements, the spatial coverage of this technique provides comparable results for different parts of the dyke; furthermore weak segments with particular high movements could be identified in advance. This could prevent future dyke crevasses and help to reduce risks in high-populated areas. This paper attempts to describe the potential of the PSI technique for a spatial distributed dyke monitoring at the coast in northern Germany. 21 ERS-2 scenes and 16 Envisat ASAR scenes were analysed. Those Scenes cover an area of a sea shore dyke including a flood regulation barrage and results point out the potential for this technique to monitor dyke structures. Even though the observed dyke doesn't show any significant deformation rates, the two datasets show the same signal for the whole dyke.

  16. U-Pb (ID-TIMS) baddeleyite ages and paleomagnetism of 1.79 and 1.59 Ga tholeiitic dyke swarms, and position of the Rio de la Plata Craton within the Columbia supercontinent

    Science.gov (United States)

    Teixeira, Wilson; D'Agrella-Filho, Manoel S.; Hamilton, Mike A.; Ernst, Richard E.; Girardi, Vicente A. V.; Mazzucchelli, Maurizio; Bettencourt, Jorge S.

    2013-08-01

    Florida dykes allows three possible reconstruction scenarios for the position of Rio de la Plata Craton: i) in the southern hemisphere linked to the Pampia terrane, and the Amazonia + Rio Apa landmass as close as they are in present day; ii) in the northern hemisphere, as a nearest neighbor to the reconstructed NW Laurentia and Gawler blocks (proto-Australia); or iii) in the northern hemisphere near the boundary of Amazonia (proto-Amazonian Craton) and Baltica. Positions 2 and 3 are consistent with all three criteria: paleomagnetic poles and proximity to matching ca. 1790 Ma and 1590 Ma mafic magmatism. Our data are consistent with the idea that the Columbia supercontinent started major break up at 1.59 Ga.

  17. The Ni-Cu-PGE mineralized Brejo Seco mafic-ultramafic layered intrusion, Riacho do Pontal Orogen: Onset of Tonian (ca. 900 Ma) continental rifting in Northeast Brazil

    Science.gov (United States)

    Salgado, Silas Santos; Ferreira Filho, Cesar Fonseca; Caxito, Fabrício de Andrade; Uhlein, Alexandre; Dantas, Elton Luiz; Stevenson, Ross

    2016-10-01

    The Brejo Seco mafic-ultramafic Complex (BSC) occurs at the extreme northwest of the Riacho do Pontal Orogen Internal Zone, in the northern margin of the São Francisco Craton in Northeast Brazil. The stratigraphy of this medium size (3.5 km wide and 9 km long) layered intrusion consists of four main zones, from bottom to top: Lower Mafic Zone (LMZ; mainly troctolite), Ultramafic Zone (UZ; mainly dunite and minor troctolite); Transitional Mafic Zone (TMZ; mainly troctolite) and an Upper Mafic Zone (UMZ; gabbro and minor anorthosite, troctolite, and ilmenite magnetitite). Ni-Cu-PGE mineralization occurs at the contact of the UZ with the TMZ, consisting of an up to 50 m thick stratabound zone of disseminated magmatic sulfides. An Mg-tholeiitic affinity to the parental magma is indicated by the geochemical fractionation pattern, by the magmatic crystallization sequence and by the elevated Fo content in olivine. A Smsbnd Nd isochron yielded an age of 903 ± 20 Ma, interpreted as the age of crystallization, with initial εNd = 0.8. Evidence of interaction of the BSC parental magma with sialic crust is given by the Rare Earth and trace element patterns, and by slightly negative and overall low values of εNd(900 Ma) in between -0.2 and +3.3. Contrary to early interpretations that it might constitute an ophiolite complex, based mainly on the geochemistry of the host rocks (Morro Branco metavolcanosedimentary complex), here we interpret the BSC as a typical layered mafic-ultramafic intrusion in continental crust, related to an extensional regime. The BSC is chrono-correlated to mafic dyke swarms, anorogenic granites and thick bimodal volcanics of similar age and tectonic setting in the São Francisco Craton and surrounding areas. Intrusion of the BSC was followed by continued lithospheric thinning, which led to the development of the Paulistana Complex continental rift volcanics around 888 Ma and ultimately to plate separation and the generation of new oceanic crust (Monte

  18. Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland.

    Science.gov (United States)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S; Ófeigsson, Benedikt G; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A; Geirsson, Halldór; La Femina, Peter C; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J; Möllhoff, Martin; Braiden, Aoife K; Eibl, Eva P S

    2015-01-01

    Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries. PMID:25517098

  19. Looking for Asian butch-dykes: exploring filmic representations of East Asian butch-dykes in Donna Lee's Enter the Mullet.

    Science.gov (United States)

    Lin, Hui-Ling

    2009-01-01

    Asian butch-dykes have been overlooked in analyses of Chinese cinema, studies that often concentrate on "feminized" transgender roles. This article examines cinematic representations of Asian butch-dykes through film analysis of Enter the Mullet (2004), a five-minute short, and in-depth interviews with the filmmaker, Donna Lee, a Chinese-Canadian in Vancouver. Lee's film is inspired by Enter the Dragon (1973), starring Bruce Lee, the most recognized icon of Asian masculinity. Combining with the mullet hairstyle, which is often associated with White working-class, the filmmaker introduces viewers to the hybrid masculinity of Asian butch-dykes. The article argues that Asian female masculinity can be a strategic means of destabilizing the hegemony of White-male-middle-class masculinity.

  20. Utility of natural generalised inverse technique in the interpretation of dyke structures

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, M.M.M.; Murty, T.V.R.; Rao, P.R.; Lakshminarayana, S.; Subrahmanyam, A.S.; Murthy, K.S.R.

    Forward and Inverse methods of magnetic interpretation have been used to estimate the parameters of dyke like intrusion over the eastern continental shelf of India. In the forward problem, the tentative parameters of the causative source are assumed...

  1. A Geochemical Investigation of the Early Cretaceous Ultrapotassic Dykes in the Raniganj Coalfields in Damodar Valley, India

    Science.gov (United States)

    Jude, T. A.

    2015-12-01

    The early Cretaceous ultrapotassic dyke rocks intruding the Permocarboniferous coal bearing Gondwana sediments of the Eastern Damodar Valley, Singhbum craton, are known for their petrographic and geochemical diversity. They remain a 'Pandora's box of petrological confusion' with a variety of exotic, and potentially diamondiferous, rocks such as lamprophyre, lamproite, orangeite and kimberlite being continuously reported from them for over one century or more. Intra-plate volcanism of this type discloses hidden information about the interior of the Earth. Samples from two dykes intruding Raniganj coalfield is studied here. The samples from Dyke1 are characterized by fine grained texture and phlogopite+apatite+K-feldspar+rutile+ankerite+dolomite+ chromite+chlorite+quartz assemblage while the samples from Dyke2 are characterized by coarse grained texture and phlogopite+ pseudomorphosed-olivine+apatite+ clinopyroxene +dolomite+ankerite+calcite+norsethite+talc+rutile+quartz+Ca-Mg-Fe-Zr silicate+K-feldspar+monazite+ perovskite assemblage. Based on the TiO2-Al2O3-FeO trends observed in phlogopites, the dykes seem to be a lamproite-orangeite transitional variety. The phlogopites observed in Dyke2 show two stages of crystallization defined by Ti-poor overgrowths on Ti-rich cores indicating that Dyke2 consolidated from a melt that fractionated from a magma which was initially emplaced at a different depth while the Dyke 1 phlogopites do not show any such sudden drop in Ti concentration in their rims indicating single stage crystallization. Ti-in-Quartz Thermometry yields temperatures between 769°C to 1115°C for Dyke1 and 779°C to 1019°C for Dyke2 which must corresponds to the emplacement and crystallization of these dykes. Trace element and isotopic ratios can be used to constrain particular mantle source characteristics of the dykes. Rb-Sr method can be used to determine the emplacement ages of these dykes.

  2. Mangrove forest against dyke-break-induced tsunami on rapidly subsiding coasts

    Science.gov (United States)

    Takagi, Hiroshi; Mikami, Takahito; Fujii, Daisuke; Esteban, Miguel; Kurobe, Shota

    2016-07-01

    Thin coastal dykes typically found in developing countries may suddenly collapse due to rapid land subsidence, material ageing, sea-level rise, high wave attack, earthquakes, landslides, or a collision with vessels. Such a failure could trigger dam-break tsunami-type flooding, or "dyke-break-induced tsunami", a possibility which has so far been overlooked in the field of coastal disaster science and management. To analyse the potential consequences of one such flooding event caused by a dyke failure, a hydrodynamic model was constructed based on the authors' field surveys of a vulnerable coastal location in Jakarta, Indonesia. In a 2 m land subsidence scenario - which is expected to take place in the study area after only about 10-20 years - the model results show that the floodwaters rapidly rise to a height of nearly 3 m, resembling the flooding pattern of earthquake-induced tsunamis. The depth-velocity product criterion suggests that many of the narrow pedestrian paths behind the dyke could experience strong flows, which are far greater than the safe limits that would allow pedestrian evacuation. A couple of alternative scenarios were also considered to investigate how such flood impacts could be mitigated by creating a mangrove belt in front of the dyke as an additional safety measure. The dyke-break-induced tsunamis, which in many areas are far more likely than regular earthquake tsunamis, cannot be overlooked and thus should be considered in disaster management and urban planning along the coasts of many developing countries.

  3. Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke

    Science.gov (United States)

    Green, Robert G.; Greenfield, Tim; White, Robert S.

    2015-08-01

    Large earthquakes can generate small changes in static stress: increases that trigger aftershock swarms, or reductions that create a region of reduced seismicity--a stress shadow. However, seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity. This makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks. Dyke intrusions do not generate dynamic stresses, so provide an unambiguous test of the stress shadow hypothesis. Here we use GPS and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath Bárðarbunga Volcano, central Iceland, in August 2014. We find that during dyke emplacement, bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano. We calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke. Our results imply that static stress changes help control earthquake clustering. Similar small static stress changes may be important for triggering seismicity near geothermal areas, regions being hydrofractured and deflating oil and gas fields.

  4. Apollo 16 Mafic Glass: Geochemistry, Provenance, and Implications

    Science.gov (United States)

    Zeigler, R. A.; Korotev, R. L.; Jolliff, B. L.; Haskin, L. A.; Floss, C.

    2004-01-01

    Although the Apollo 16 mission landed in the feldspathic lunar highlands, mass-balance models suggest that there is a 5-6% mare component in the mature soils collected at the site. Only one mare basalt greater than 1 cm was found and two surveys of 2-4 mm particles found that less than 1% of this size fraction is mare basalt. Similar surveys of the less than 1 mm size fraction of A16 soils found very little lithic mare basalt, but several percent of basaltic green, yellow, and orange glass. The green glass beads were identified as VLT picritic glass and the orange/yellow glass shards were a mix of high and low Ti mare-like glass, high-Al basaltic glass, and KREEPy glasses. Most previous studies of glasses in the A16 regolith were surveys that identified a high proportion of feldspathic glass because most of the glass is produced by local impacts. Because the number of mafic glasses found was low, few compositional groupings were identified. As part of our ongoing study of the mafic components of the Apollo 16 site, we specifically targeted mafic glasses from Apollo 16, selecting against the more feldspathic glasses. In this way we were able to identify over 300 mafic glasses (greater than 10 wt % FeO). We present here the major- and trace-element chemistry of the main glass groups and discuss the likely provenance of each group.

  5. Dyke-Davidoff-Masson syndrome (cerebral hemiatrophy: Radiological findings

    Directory of Open Access Journals (Sweden)

    Yaşar Bükte

    2014-06-01

    Full Text Available Objective: The aim of this study was to present cross- sectional cranial imaging findings of cases with Dyke-Davidoff-Masson syndrome (DDMS. Methods: The findings of 16 cases in whom unilateral cerebral hemispheric atrophy was detected at computed tomography and/or magnetic resonance imaging were retrospectively evaluated. The cases consisted of 8 females and 8 males, the ages ranged between 5 and 53 (mean:24. Six of the cases were children and 10 were males. Five of the patients had CT and 13 had MRI scan. The images were retrospectively evaluated and cerebral parenchymal findings and compensatory cranial findings were noted. Results: All cases had unilateral cerebral hemispheric atrophy, ipsilateral cortical sulcal and lateral ventricular dilatation. Together with hemispheric atrophy ipsilateral atrophy of corpus callosum in 6 cases (37.5%, ipsilateral thalamic atrophy in 13 cases (81%, ipsilateral parahippocampal atrophy in 8 cases (50%, ipsilateral cerebral pedincular atrophy in 7 cases (44% and ipsilateral pontine atrophy in 3 cases (19% were detected. Gliotic signal changes were observed in 13 cases (81%. Of compensatory findings, unilateral calvarial thickening was focal in 4 cases (25%, and diffuse in 12 cases (75%. There was expansion in ipsilateral half of frontal sinus in 15 cases (94% and expansion in temporal bone aeration in 5 cases (31%. Conclusion: DDMS is a syndrome presenting with findings of cerebral hemiatrophy and calvarial hypertrophy. Cross-sectional radiological imaging findings may be variable among cases.

  6. Relamination of mafic subducting crust throughout Earth's history

    Science.gov (United States)

    Maunder, Ben; van Hunen, Jeroen; Magni, Valentina; Bouilhol, Pierre

    2016-09-01

    Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as "relamination") is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting. Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∼2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80-120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for

  7. Sedimentary dykes in the Oskarshamn-Vaestervik area. A study of the mechanism of formation

    Energy Technology Data Exchange (ETDEWEB)

    Roeshoff, Kennert [BBK AB, Solna (Sweden); Cosgrove, John [Imperial College, London (United Kingdom). Dept. of Earth Sciences and Engineering

    2002-07-01

    This study of the sedimentary dykes from the Oskarshamn-Vaestervik area, near Aespoe and surrounding region, is aimed at understanding the mechanism of their formation. In particular it is important to establish whether or not they formed by the injection of high pressure fluidized sediments and if so what the likely effect of any future over pressured sediments will be on the stability of the fracture network in the basement rocks at Aespoe. This report is made up of a review of the literature on sedimentary dykes, a discussion of the various mechanical models for hydraulic fracturing and a description of the field and laboratory study carried out on the sedimentary dykes. The literature review indicates a remarkable consensus on the mode of formation of these structures based on their fabric (particularly layering generated in part by variation in clast size) and the composition of the infilling material. Two modes of origin have been recognised. These are the passive infilling of dykes where the dyke material has entered an open fracture under the influence of gravity, and active, i.e. forceful injection of a fluidized sediment under high pressure into a pre-existing fracture or into a fracture generated by the high pressure fluid. The discussion of the theory of fluid induced fracturing leads to the recognition of three systems which are the two end members and an intermediate form of a complete spectrum of materials ranging from unconsolidated and incohesive sediments, through cemented but porous rocks to crystalline rocks with no intrinsic porosity and whose only porosity relates to that imparted by the fracture network that the rock contains. The theory best suited to analyses this latter system is one based on fracture mechanics and is known as the theory of external hydraulic fracturing. From the point of view of the sedimentary dykes in the study area around the Aespoe Hard Rock Laboratory, where the dykes occur in the fractured granitic basement, this is

  8. Sedimentary dykes in the Oskarshamn-Vaestervik area. A study of the mechanism of formation

    International Nuclear Information System (INIS)

    This study of the sedimentary dykes from the Oskarshamn-Vaestervik area, near Aespoe and surrounding region, is aimed at understanding the mechanism of their formation. In particular it is important to establish whether or not they formed by the injection of high pressure fluidized sediments and if so what the likely effect of any future over pressured sediments will be on the stability of the fracture network in the basement rocks at Aespoe. This report is made up of a review of the literature on sedimentary dykes, a discussion of the various mechanical models for hydraulic fracturing and a description of the field and laboratory study carried out on the sedimentary dykes. The literature review indicates a remarkable consensus on the mode of formation of these structures based on their fabric (particularly layering generated in part by variation in clast size) and the composition of the infilling material. Two modes of origin have been recognised. These are the passive infilling of dykes where the dyke material has entered an open fracture under the influence of gravity, and active, i.e. forceful injection of a fluidized sediment under high pressure into a pre-existing fracture or into a fracture generated by the high pressure fluid. The discussion of the theory of fluid induced fracturing leads to the recognition of three systems which are the two end members and an intermediate form of a complete spectrum of materials ranging from unconsolidated and incohesive sediments, through cemented but porous rocks to crystalline rocks with no intrinsic porosity and whose only porosity relates to that imparted by the fracture network that the rock contains. The theory best suited to analyses this latter system is one based on fracture mechanics and is known as the theory of external hydraulic fracturing. From the point of view of the sedimentary dykes in the study area around the Aespoe Hard Rock Laboratory, where the dykes occur in the fractured granitic basement, this is

  9. Traces of ancient mafic layers in the Tethys oceanic mantle

    Science.gov (United States)

    Sergeev, Dmitry S.; Dijkstra, Arjan H.; Meisel, Thomas; Brügmann, Gerhard; Sergeev, Sergey A.

    2014-03-01

    Oceanic basalts are formed by melting of a chemically and isotopically heterogeneous mantle source. The oceanic mantle probably resembles a marble cake containing layers of mafic rock - perhaps recycled ocean crust - stored in the mantle for >1 billion years. Many questions about the nature and distribution of these mantle heterogeneities remain. Here we show that lithological and isotopic traces of ancient mafic layers can still be seen in mantle rocks that have melted to form oceanic crust at a spreading centre in the Tethys Ocean. We have found centimetre-scale heterogeneity in initial osmium isotope ratios in mantle rocks from the Pindos Ophiolite. Deformed pyroxenite layers have high 187Os/188Os ratios (0.14-0.20) compared to adjacent host peridotites (187Os/188Os: 0.12-0.13). These layers were formed by a reaction between mantle rock and melt derived from ancient rocks with high Re/Os ratios. We interpret the pyroxenite layers as the wall rocks of billion-year old mafic layers that melted and transformed adjacent mantle peridotite into pyroxenite by melt-rock reaction. The pyroxenite layers are the relics of ancient metre-scale basaltic veins in a kilometre-sized marble cake domain in the oceanic mantle that has withstood homogenization on a billion-year time scale.

  10. Experiment and Simulation of Turbulent Flow in Local Scour around a Spur Dyke

    Institute of Scientific and Technical Information of China (English)

    Hao ZHANG; Hajime NAKAGAWA; Kenji KAWAIKE; Yasuyuki BABA

    2009-01-01

    The turbulent flow in the local scour hole around a single non-submerged spur dyke is investigated with both experimental and numerical methods.The experiments are conducted under clear-water scour regime with an impermeable spur dyke.The scour geometry and flow velocities are measured in details with a high-resolution laser displacement meter,electro-magnetic velocimetries and PIV (Particle image velocimetry).A 3D non-linear κ-ε model is developed to simulate the complex local flow field around the scour area.The numerical model is formulated using FVM (Finite volume method) on a collocated unstructured mesh,capable of resolving complex geometries and boundaries.It is found that the simulation results are reasonably consistent with those of the experimental measurements.Based on the study results,the nature of the flow structrue around a spur dyke with local scour hole is analyzed.

  11. 堤防加固设计中的若干技术问题%Problems about Design of Dyke Reinforcement

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Jia-fa

    2001-01-01

    The dyke experiences very high flood level more and more frequently. The timely issued " The Standard of Dyke Design" has played an important role in the design, measure fea sibility study and examination of dyke reinforcement. Safety appraisal is required before dyke rein forcement design. But, the conducted item is safety demonstration in the process of dyke reinforcement design at present. This paper suggests that at least 8 aspects should be considered in safety demo nstration. The effective water head is considered as the most important factor for dyke safety and reinfo rcement design. Seepage control measure design is an important part of dyke reinforcement design . Its correct train of thought is discussed in this paper. Some other factors for dyke reinforcement d esign are also pointed out.

  12. Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique

    Science.gov (United States)

    Ibraimo, Daniel Luis; Larsen, Rune B.

    2015-11-01

    The Atchiza mafic and ultramafic-layered suite (hereafter, "Atchiza Suite) crops out in an area 330 km2 west of the Mozambican Tete province. In an early account of the geology of this intrusion, it was considered the continuation of the Great Dyke of Zimbabwe, an idea that was aborted after detailed studies. Nevertheless, the Ni concentrations in the Atchiza outcrop rocks are considerable. Our investigation used field evidence, hand specimens and petrography descriptions, mineral chemistry studies using electron microprobe analysis and tectonic analysis to arrive at a plausible mineralogical composition and understanding of the tectonic setting for the igneous evolution. The mineral composition from the Atchiza Suite indicates that these are cumulates. The magmatic segregation from the petrographic and mineral composition reasoning indicates that dunite-lherzolitic peridotite-olivine gabbro-gabbronorite-gabbro-pegmatitic gabbro is the rock formation sequence. Olivine and chromite were the first phases formed, followed by pyroxene and plagioclase. In addition, it is shown that these minerals are near-liquidus crystallization products of basaltic magma with olivine Fo: 87.06 in dunite, mean values of clinopyroxene are (Wo: 36.4, En: 48.0, Fs: 15.2), orthopyroxene (Wo: 2.95, En: 73.0, Fs: 24.2) and plagioclase An: 71.3, respectively. Opaque minerals comprise Fe-Ti oxides and (Fe, Cr) spinel up to 4.8 vol.%, but chromitite layers are not present. Most of the opaque minerals are interstitial to pyroxene. Sulphides are common in gabbros, with pyrrhotite, pentlandite, chalcopyrite, pyrite and covellite together comprising 0.4-2.0 vol.%. The whole rock Rare Earth Element (REE) concentrations are mainly a result of differentiation, but slight crustal contamination/assimilation contributed to the REE contents. In addition, they also show Eu enrichment, suggesting that plagioclase fractionation was important in the rock. The Atchiza Suite preserves a deep-seated plumbing

  13. Mineral reactions and strain localization in a sheared mafic granulite infiltrated by melt (Seiland Igneous Province, Norway)

    Science.gov (United States)

    degli Alessandrini, Giulia; Menegon, Luca; Malaspina, Nadia; Dijkstra, Arjan; Anderson, Mark

    2016-04-01

    This study investigates the deformation mechanisms of a metagabbroic dyke experiencing syn-kinematic melt-rock interaction in a continental lower-crustal shear zone in the Seiland Igneous Province (northern Norway). Solid state shearing occurred at T ≈750-820 °C, P ≈0.75-0.95 GPa and was coeval with melt infiltration from dehydration melting of adjacent metasediments, as evident from thin leucosome veinlets within the dykes. The mylonite consists of cpx [Ca0.47,Mg0.35,Fe0.18]SiO3 + opx [Ca0.1,Mg0.5,Fe0.4]SiO3 + pl (An77Ab22Or1) porphyroclasts with localized grt and ilm coronas, embedded in a fine grained matrix of cpx + opx + pl + qtz + ilm ± kfs. Porphyroclasts range in size (diameter) between 25 to 650 μm, whereas the fine grain matrix is consistently below 10 μm (average 4-7 μm). Porphyroclasts show varying degrees of elongation, with the opx reaching aspect ratios of 1:16 and the cpx reaching rare maxima of 1:7. Cpx and pl porphyroclasts are micro-fractured and micro-boudinaged with fine-grained material infill. Texturally, opx porphyroclasts display a marked crystallographic preferred orientation (CPO) and activity of the {100} and minor {100} slip systems, whereas cpx and pl porphyroclasts are randomly oriented. All porphyroclasts have strong internal misorientations (undulatory and sweeping extinction) and lack recovery features (subgrains). The fine-grained polyphase matrix wrapping the porphyroclasts displays weak to absent CPO, with the exception of opx that shows a {100} poles-to-planes maxima perpendicular to the foliation. Based on the microstructure, we argue that a large part of the matrix is the product of metamorphic reactions in the presence of melt. To test this hypothesis, the interaction between the studied mafic dyke and an adjacent felsic leucosome was modelled using PerpleX for P-T conditions ranging between 7-9 kbar and 700-1000°C. Results show that the syn-kinematic mineral assemblage (opx + cpx + pl + qtz + ilm ± kfs) can be

  14. Evidences for multiple remagnetization of Proterozoic dykes from Iguerda inlier (Anti-Atlas Belt, Southern Morocco)

    Science.gov (United States)

    Neres, Marta; Silva, Pedro F.; Ikene, Moha; Martins, Sofia; Hafid, Ahmid; Mata, João; Almeida, Francisco; Youbi, Nasrrddine; Boumehdi, Ahmed

    2016-04-01

    Paleomagnetic data able to constrain the paleoposition of the West African Craton (WAC) during Paleo-Mesoproterozoic are absent, mainly due to gaps on the sedimentary record and intense remagnetizations. Dykes that intrude several Proterozoic inliers of WAC in the Anti-Atlas Belt (southern Morocco) have recently been subjected to geochronological studies, which revealed ages between Paleoproterozoic and early Neoproterozoic. Therefore, these dykes represent a window of opportunity for paleomagnetic studies aiming to infer about the paleoposition of WAC during Proterozoic. On this scope we conducted a paleomagnetic study on seven Proterozoic dykes of the Iguerda inlier. We determined the paleomagnetic directions and evaluated their meaning by rock magnetic and mineral analyses, complemented by petrographic observations. Results revealed that these rocks record the presence of a complex history of remagnetization events, mostly assigned to several Phanerozoic thermal/chemical events. In particular, we found components assigned to the late stages of Pan African orogeny (s.l.), to the Late Carboniferous Variscan orogeny, and to more recent events. The recognized remagnetization processes are related to widespread metamorphic events under greenschist facies followed by low-temperature oxidation, both responsible for the formation of new magnetic phases (magnetite and hematite). The primary (magmatic) thermo-remanent magnetization of the dykes was obliterated during these events through multiple thermal and chemical remagnetizations. For only one dyke the presence of primary magnetization is possible to infer, though not to confirm, and would place WAC at an equatorial position around 1750 Ma. The authors wish to acknowledge FCT (Portugal) - CNRST (Morocco) bilateral agreement for its major contribution without which this work wouldn't be possible. Publication supported by project FCT UID/GEO/50019/2013 - Instituto Dom Luiz.

  15. Cloning, expression, and characterization of β-mannanase from Bacillus subtilis MAFIC-S11 in Pichia pastoris.

    Science.gov (United States)

    Lv, Junnan; Chen, Yiqun; Pei, Honglei; Yang, Wenhan; Li, Zhimin; Dong, Bing; Cao, Yunhe

    2013-04-01

    The β-mannanase gene (1,029 nucleotide) from Bacillus subtilis MAFIC-S11, encoding a polypeptide of 342 amino acids, was cloned and expressed in Pichia pastoris. To increase its expression, the β-mannanase gene was optimized for codon usage (mannS) and fused downstream to a sequence-encoding modified α-factor signal peptide. The expression level was improved by 2-fold. This recombinant enzyme (mannS) showed its highest activity of 24,600 U/mL after 144-h fermentation. The optimal temperature and pH of mannS were 50 °C and 6.0, respectively, and its specific activity was 3,706 U/mg. The kinetic parameters V max and K m were determined as 20,000 U/mg and 8 mg/mL, respectively, representing the highest ever expression level of β-mannanase reported in P. pastoris. In addition, the enzyme exhibited much higher binding activity to chitin, chitosan, Avicel, and mannan. The superior catalytic properties of mannS suggested great potential as an effective additive in animal feed industry.

  16. Study on the carbonate ocelli-bearing lamprophyre dykes in the Ailaoshan gold deposit zone, Yunnan Province

    Institute of Scientific and Technical Information of China (English)

    HUANG; Zhilong(黄智龙); LIU; Congqiang(刘丛强); XIAO; Huayun(肖化云); HAN; Runsheng(韩润生); XU; Cheng(许成); LI; Wenbo(李文博); ZHONG; Kunming(钟昆明)

    2002-01-01

    Three carbonate ocelli-bearing lamprophyre dykes have been found in the Laowangzhai and Beiya gold orefields in the northern sector of the Ailaoshan gold deposit zone, Yunnan Province. Ocelli in the lamprophyre dykes are carbonates composed mainly of dolomite and calcite. Their trace elements, REE and C isotopic compositions are characteristic of carbonatite and the main mineral assemblages, major elements, trace elements and REE in the matrix are similar to those in the carbonate ocelli-barren lamprophyre dykes in the orefields, which are calc-alkaline lamprophyres that derived from the fertile mantle. The results indicate that the carbonate ocelli-bearing lamprophyre dykes in this area were produced at the time when the Himalayan lamprophyre magma evolved to a relatively late stage of silicate-carbonate liquid immiscibility. In the process of magmatic evolution there took place magmatic degassing with CO2 and H2O as the dominant released gases.

  17. Eocene slab breakoff of Neotethys as suggested by dioritic dykes in the Gangdese magmatic belt, southern Tibet

    Science.gov (United States)

    Ma, Xuxuan; Xu, Zhiqin; Meert, Joseph G.

    2016-04-01

    The Gangdese magmatic belt in southern Tibet demarcates an important boundary between the Indian and Eurasian plates. Due to its location and magmatic evolutionary history, it is key to understanding both the history of Neotethys closure and the Indo-Asian collisional process. This study presents new geochronological and geochemical data for dioritic dykes in the southern Gangdese magmatic belt in southern Tibet. U-Pb geochronological results reveal that the dykes were emplaced at ca. 41 Ma and thus broadly coeval with the 40-38 Ma Dazi volcanics and the 42-40 Ma Gaoligong-Tengliang basaltic dykes. Geochemically, these dykes are characterized by alkaline signature, high Mg# (57-63) and low TiO2 contents (~ 0.9-1.0), showing notable enrichment of light rare earth elements relative to the heavy rare earth elements, enrichment of incompatible elements (i.e. Cs, Rb, Ba, Th and U), and depletion of high field strength elements (i.e. Nb, Ta and Ti). In addition, a large variation of zircon εHf(t) values (- 10 to + 13) was shown, implying heterogeneity of magma sources. A heterogeneous source is also suggested by the occurrence of xenocrysts in the dykes. These observations suggest that the magma source of the dykes was dominated by partial melting of lithospheric mantle and then subsequently contaminated by crustal material during ascent. In combination with other geological data in the region, we suspect that the slab slicing of the Neotethys played a key role in the formation of the lithospheric mantle-derived dioritic dykes and adakitic granite, asthenosphere-derived volcanics, basaltic dykes, as well as the recently reported strongly fractionated granites.

  18. Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria)

    Science.gov (United States)

    Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin

    2016-06-01

    Dykes in the Strudengau area (SW Moldanubian Zone, Austria) can be mineralogically divided into lamprophyres (spessartites and kersantites) and felsic dykes (granite porphyries, granitic dykes and pegmatoid dykes). Geochemical analyses of 11 lamprophyres and 7 felsic dykes show evidence of fractional crystallization. The lamprophyres are characterized by metaluminous compositions, intermediate SiO2 contents and high amounts of MgO and K2O; these rocks have high Ba (800-3000 ppm) and Sr (250-1000 ppm) contents as well as an enrichment of large-ion lithophile elements over high field strength elements, typical for enriched mantle sources with variable modifications due to fractionation and crustal contamination. This geochemical signature has been reported from durbachites (biotite- and K feldspar-rich mela-syenites particularly characteristic of the Variscan orogen in Central Europe). For most major elements, calculated fractionation trends from crystallization experiments of durbachites give an excellent match with the data from the Strudengau dykes. This suggests that the lamprophyres and felsic dykes were both products of fractional crystallization and subsequent magma mixing of durbachitic and leucogranitic melts. Rb-Sr geochronological data on biotite from five undeformed kersantites and a locally deformed granite porphyry gave cooling ages of c. 334-318 Ma, indicating synchronous intrusion of the dykes with the nearby outcropping Weinsberger granite (part of the South Bohemian Batholith, c. 330-310 Ma). Oriented matrix biotite separated from the locally deformed granite porphyry gave an Rb-Sr age of c. 318 Ma, interpreted as a deformation age during extensional tectonics. We propose a large-scale extensional regime at c. 320 Ma in the Strudengau area, accompanied by plutonism of fractionated magmas of syncollisional mantle-derived sources, mixed with crustal components. This geodynamic setting is comparable to other areas in the Variscan belt documenting an

  19. Possible Mafic Patches at Mons Malapert and Scott Crater Highlight the Value of Site Selection studies

    Science.gov (United States)

    Cooper, B. L.

    2007-01-01

    Possible areas of mafic material on the rim and floor of Scott crater (82.1 S, 48.5 E) and on the northeast flank of Mons Malapert (85.5 S, 0 E) are suggested by analysis of shadow-masked Clementine false-colorration images. Mafic materials can produce more oxygen than can highlands materials, and mafic materials close to the south pole may be important for propellant production for a future lunar mission. If the dark patches are confirmed as mafic materials, this finding would suggest that other mafic patches may also exist, perhaps even closer to the poles. These preliminary findings illustrate the need for additional site selection studies in the lunar polar regions, to improve our capability to "live off the land".

  20. Geochemical Characteristics of a Carbonatite Dyke Rich in Rare Earths from Bayan Obo, China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The whole-rock geochemistry of a rare earths rich carbonatite dykes that locates at Dulahala and lies 3 km north-east to the East Ore body of the giant Bayan Obo RE-Nb-Fe deposit was analysed. The dyke cuts cross H1 coarse quartz sandstone and H2 fine quartzite of the Proterozoic Bayan Obo group. RE content in the dyke varies greatly up to 20%(mass fraction), which comprises rich RE ores. Light RE in carbonatites are extremely enriched and strongly fractionated relative to heavy RE, but no Eu anomaly. The carbonatite may be produced by mechanisms as follows: the carbonatite magma is directly formed by very low degree(F<1%) partial melting of enriched lithospheric mantle, leaving residual minerals characterized by abundant garnet;then the magma arises into a chamber within the crust where they will undergo fractional crystallization, which makes RE further concentrated in carbonatite. The RE patterns and spider diagrams of the carbonatite are identical to those fine-grained dolomite marble that is the ore-host rock for the Bayan Obo deposit. However, the carbonatite is calcic, which is different from the fine-grained dolomite marble in major element geochemistry. The difference is suggested to be resulted from that the carbonatite dyke is not affected by a large scale dolomitization, while the fine-grained dolomite marble might be the product of dolomitized carbonatite intrusive body that might set up a hydrothermal system in the region, which transported Mg from the Bayan Obo sediments, especially form the shales to the carbonatite intrusion.

  1. The intensity of the geomagnetic field from 2.4 Ga old Indian dykes

    Science.gov (United States)

    Valet, Jean-Pierre; Besse, Jean; Kumar, Anil; Vadakke-Chanat, Sayoob; Philippe, Edouard

    2014-06-01

    paleomagnetic records from dyke swarms provide a unique source of information regarding the Archean geomagnetic field and more specifically the average field strength produced by the early dynamo. We sampled 16 paleomagnetic sites from the Dharwar giant dyke swarm in southern India which was emplaced between 2.365 and 2.368 Ga. Despite taking great care in selecting locations exempt of any geological disturbance, only two of these sites provided primary directions with very steep inclinations and therefore were emplaced in close to a magnetic pole. Paleointensity experiments were conducted on a subset of samples from the dyke margins. The characteristic magnetization is carried by single domain magnetite grains with a very narrow range of unblocking temperatures inferred from the sharp decrease by at least 75% of their remanence above 520°C. The paleointensity results indicate an average low field of 9.2 ± 7 µT, consistent with reported values from Canadian dyke swarms for the same period. These results combined with the Thellier-Thellier determinations obtained so far for the Precambrian suggest that a low field period prevailed from circa 2.3 to 1.8 Ga, while the preceding and following time intervals are characterized by significantly stronger paleointensities. Although this suite of episodes is not fully incompatible with previous models for the long-term evolution of the geodynamo, it is tempting to make the link with the recent suggestion of an early dynamo sustained within a conductive magma layer at the base of the mantle from 3.5 to 2.5 Ga which progressively declined until convection became sufficiently efficient to reactivate a strong dynamo process within the Earth's liquid core.

  2. Excess pore water pressure induced in the foundation of a tailings dyke at Muskeg River Mine, Fort McMurray

    Energy Technology Data Exchange (ETDEWEB)

    Eshraghian, A.; Martens, S. [Klohn Crippen Berger Ltd., Calgary, AB (Canada)

    2010-07-01

    This paper discussed the effect of staged construction on the generation and dissipation of excess pore water pressure within the foundation clayey units of the External Tailings Facility dyke. Data were compiled from piezometers installed within the dyke foundation and used to estimate the dissipation parameters for the clayey units for a selected area of the foundation. Spatial and temporal variations in the pore water pressure generation parameters were explained. Understanding the process by which excess pore water pressure is generated and dissipates is critical to optimizing dyke design and performance. Piezometric data was shown to be useful in improving estimates of the construction-induced pore water pressure and dissipation rates within the clay layers in the foundation during dyke construction. In staged construction, a controlled rate of load application is used to increase foundation stability. Excess pore water pressure dissipates after each application, so the most critical stability condition happens after each load. Slow loading allows dissipation, whereas previous load pressure remains during fast loading. The dyke design must account for the rate of loading and the rate of pore pressure dissipation. Controlling the rate of loading and the rate of stress-induced excess pore water pressure generation is important to dyke stability during construction. Effective stress-strength parameters for the foundation require predictions of the pore water pressure induced during staged construction. It was found that both direct and indirect loading generates excess pore water pressure in the foundation clays. 2 refs., 2 tabs., 11 figs.

  3. Modelling the behaviour of the pervious foundation of a dyke and its treatment with relief wells

    Energy Technology Data Exchange (ETDEWEB)

    Zahra, M.; D' Astous, J.J.; Tremblay, H. [Centre d' expertise hydrique du Quebec, PQ (Canada); Chahde, J. [Hydro-Quebec, PQ (Canada)

    2009-07-01

    This paper presented the geotechnical conditions prevailing in the foundation of the Moncouche dyke. The 190 m long, 8.7 m high sand and gravel earth fill dyke is an important water retaining structure of the Kenogami lake reservoir. Following its first impoundment in 1924, heavy seepage forced the construction of a downstream pervious blanket and other remedial measures. During the 1996 July Saguenay flood, new seepage sources topped the blanket. This study analyzed the seepage in the foundation and simulated it through a 2D finite elements model in order to assess measures to reduce uplift seepage gradients. This paper described the modelling of the existing pore water pressures in the foundation. The pore pressures and seepage to be evacuated once the line of relief wells was in place were also estimated. They dyke's impervious core is a concrete wall connected at its lower end to a metal sheet piles driven to a variable depth. The existence of artesian conditions in the 30 m thick granular pervious fluvioglacial deposit combined with low to medium standard penetration tests and dynamic cone penetration test counts called for liquefaction hazard assessment relative to seismic loading. The construction of deep relief wells were shown to be an appropriate and cost effective measure to reduce seepage. 6 refs., 2 tabs., 13 figs.

  4. Petrology of the prehistoric lavas and dyke of the Barren Island, Andaman Sea, Indian Ocean

    Indian Academy of Sciences (India)

    M A Alam; D Chandrasekharam; O Vaselli; B Capaccioni; P Manetti; P B Santo

    2004-12-01

    Although Barren Island (Andaman Sea, Indian Ocean) witnessed several volcanic eruptions during historic times, the eruptions that led to the formation of this volcanic island occurred mainly during prehistoric times. It is still active and currently in the fumarolic stage. Its volcanic evolution appears to be characterized by a constructive phase with the piling up of lava flows and scoria deposits and Strombolian activities, followed by a sudden collapse of the main cone. Deposits of a possible caldera-forming eruption were not recognized earlier. After a period of peri-calderic hydromagmatic activity, whose deposits presently mantle inner and outer caldera walls, a new phase of intracalderic Vulcanian activities took place. A prominent dyke in the SE inner side of the caldera wall was recognized. Petrographically the lava flows and dyke are similar but they differ in their chemical composition (viz., SiO2, MgO, Ni, Cr) significantly. Similarity in major, minor and trace element composition (viz., K/La, K/Nb, K/Rb, K/Ti ratios) of these rocks together with Chondrite normalized trace element (Rb, Ba, Sr, P, Zr, Ti and Nb) and REE (La, Ce, Nd and Y) patterns of the Barren Island prehistoric lava flows and dyke and low-K lavas of Sunda Arc indicates that Barren Island must have evolved from a source similar to that of Sunda Arc lavas during the Quaternary Period.

  5. Understanding and using technological affordances: a commentary on Conole and Dyke

    Directory of Open Access Journals (Sweden)

    Tom Boyle

    2004-12-01

    Full Text Available The paper by Conole and Dyke sets the context by pointing to a number of problems that inhibit the widespread, effective use of Information and Communication Technologies (ICT to support learning. They argue that this situation highlights the need to explore a theoretical basis for the use of ICT to support learning. The central argument of the paper is that the notion of affordances can make a significant contribution to this endeavour. The paper aims to articulate the potential impact of these affordances primarily through the development of a taxonomy. It draws on social constructivist theory to help understand and articulate the impact of these affordances. The concept of affordances is potentially both rich and provocative. Conole and Dyke provide a refreshing and diverse look at the theoretical basis for the use of ICT to support learning. We have structured our commentary around six questions that are provided by Conole and Dyke in their Discussion section. Whilst examining these questions we highlight various issues raised by the paper, which we believe, need further consideration and clarification.

  6. Lithological Discrimination of the Mafic-Ultramafic Complex, Huitongshan, Beishan, China:Using ASTER Data

    Institute of Scientific and Technical Information of China (English)

    Lei Liu; Jun Zhou; Dong Jiang; Dafang Zhuang; Lamin R Mansaray

    2014-01-01

    The Beishan area has more than seventy mafic-ultramafic complexes sparsely distributed in the area and is of a big potential in mineral resources related to mafic-ultramafic intrusions. Many mafic-ultramafic intrusions which are mostly in small sizes have been omitted by previous works. This research takes Huitongshan as the study area, which is a major district for mafic-ultramafic occur-rences in Beishan. Advanced spaceborne thermal emission and reflection radiometer (ASTER) data have been processed and interpreted for mapping the mafic-ultramafic complex. ASTER data were processed by different techniques that were selected based on image reflectance and laboratory emis-sivity spectra. The visible near-infrared (VNIR) and short wave infrared (SWIR) data were trans-formed using band ratios and minimum noise fraction (MNF), while the thermal infrared (TIR) data were processed using mafic index (MI) and principal components analysis (PCA). ASTER band ratios (6/8, 5/4, 2/1) in RGB image and MNF (1, 2, 4) in RGB image were powerful in distinguishing the subtle differences between the various rock units. PCA applied to all five bands of ASTER TIR imagery high-lighted marked differences among the mafic rock units and was more effective than the MI in differen-tiating mafic-ultramafic rocks. Our results were consistent with information derived from local geolog-ical maps. Based on the remote sensing results and field inspection, eleven gabbroic intrusions and a pyroxenite occurrence were recognized for the first time. A new geologic map of the Huitongshan area was created by integrating the results of remote sensing, previous geological maps and field inspection. It is concluded that the workflow of ASTER image processing, interpretation and ground inspection has great potential for mafic-ultramafic rocks identifying and relevant mineral targeting in the sparsely vegetated arid region of northwestern China.

  7. Mafic Materials in Scott Crater? A Test for Lunar Reconnaissance Orbiter

    Science.gov (United States)

    Cooper, Bonnie L.

    2007-01-01

    Clementine 750 nm and multispectral ratio data, along with Lunar Orbiter and radar data, were used to study the crater Scott in the lunar south polar region. The multispectral data provide evidence for mafic materials, impact melts, anorthositic materials, and a small pyroclastic deposit. High-resolution radar data and Lunar Orbiter photography for this area show differences in color and surface texture that correspond with the locations of the hypothesized mafic and anorthositic areas on the crater floor. This region provides a test case for the upcoming Lunar Reconnaissance Orbiter. Verification of the existence of a mafic deposit at this location is relevant to future lunar resource utilization planning.

  8. Distribution and petrography of the mesozoic basic dykes of the San Gregorio de Polanco, Parana magmatic province, Uruguay

    International Nuclear Information System (INIS)

    The tectonomagmatic events developed in the lower Cretaceous, predating the South Atlantic Ocean opening, generated an intensive magmatic activity that covered an important surface of the South American platform (Parana-Etendeka Magmatic Province). Both the instability and rupture of the continental crust, as well as magma rising are registered by the presence of basic intrusions (dykes and sills), and lava flows located in the central-north portion of Uruguay. This paper deals with a detailed petrologic study focused on the San Gregorio de Polanco Dyke Swarm (Department of Tacuarembo). As result of semidetailed geological mapping, 17 dyke segments with 12km length and 20m width maximum have been identified. These dykes are concentrated in four main geographic zones named: Achar, San Gregorio de Polanco, La Paloma and San Jorge. The dykes define parallel to sub parallel trends, with a zig-zag pattern (N140°-170° and N080°-110°) controlled by basement lineaments. Their mineralogy includes calcic plagioclases (labradorite and andesine), calcic clinopyroxene (augite-pigeonite), opaques minerals (two populations), olivine; glass and apatite as accessories. In turn, the SEM-EDS analyses of the opaque minerals (modal 15%) of both populations allowed their classification as titanomagnetite correspondent to different crystallisation stages. The first population of titanomagnetite would correspond to the main crystallisation stage while the second one would be generated by partial dissolution of the former under low oxygen fugacity conditions and temperatures around 450°C

  9. Fault and dyke detectability in high resolution seismic surveys for coal: a view from numerical modelling*

    Science.gov (United States)

    Zhou, Binzhong 13Hatherly, Peter

    2014-10-01

    Modern underground coal mining requires certainty about geological faults, dykes and other structural features. Faults with throws of even just a few metres can create safety issues and lead to costly delays in mine production. In this paper, we use numerical modelling in an ideal, noise-free environment with homogeneous layering to investigate the detectability of small faults by seismic reflection surveying. If the layering is horizontal, faults with throws of 1/8 of the wavelength should be detectable in a 2D survey. In a coal mining setting where the seismic velocity of the overburden ranges from 3000 m/s to 4000 m/s and the dominant seismic frequency is ~100 Hz, this corresponds to a fault with a throw of 4-5 m. However, if the layers are dipping or folded, the faults may be more difficult to detect, especially when their throws oppose the trend of the background structure. In the case of 3D seismic surveying we suggest that faults with throws as small as 1/16 of wavelength (2-2.5 m) can be detectable because of the benefits offered by computer-aided horizon identification and the improved spatial coherence in 3D seismic surveys. With dykes, we find that Berkhout's definition of the Fresnel zone is more consistent with actual experience. At a depth of 500 m, which is typically encountered in coal mining, and a 100 Hz dominant seismic frequency, dykes less than 8 m in width are undetectable, even after migration.

  10. A RARE CAUSE OF SEIZURES WITH MENTAL RETARDATION AND HEMIPARESIS-DYKE-DAVIDOFF-MASSON SYNDROME

    Directory of Open Access Journals (Sweden)

    Vipin Kumar

    2014-09-01

    Full Text Available Cerebral hemi-atrophy with seizures, hemiplegia and mental retardation is uncommon clinical presentation in the early childhood and adolescence. The causes are various and usually grouped into congenital and acquired types. The Dyke-Davidoff-Masson Syndrome is one of the causes of these clinical manifestations, which is usually developed secondary to brain insult. Here we report two cases with similar symptoms- one case was an adult male of 35 years with long history of seizures and the second case was a young male of 22 years with cognitive impairment, difficulty in speech and walking

  11. Les dykes basiques du massif ancien de l'Ourika (Atlas de Marrakech, Maroc): géochimie et significationThe basic dykes of the Ourika old massif (High Atlas of Marrakech): Geochemistry and significance

    Science.gov (United States)

    Barakat, Ahmed; Marignac, Christian; Bouabdelli, Mohamed

    The Precambrian massif of Ourika is crosscut by two systems of basic dykes, striking N40°E and N90-120°E. Using incompatible trace elements, the two systems form two distinct chemical groups, displaying a continental tholeiitic affinity. The composition variations between the two defined groups can be due to heterogeneities of mantle sources and to contamination, during the magma ascent, by the continental crust. The emplacement of these basic dykes, before the late-PIII formations, can be related to the Neoproterozoic distension generalised to the Anti-Atlas chain. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 827-833.

  12. Onset of seafloor spreading in the Iapetus Ocean at 608 Ma: precise age of the Sarek Dyke Swarm, northern Swedish Caledonides

    DEFF Research Database (Denmark)

    Svenningsen, Olaf

    2001-01-01

    The Sarek Dyke Swarm (SDS) crops out in the Sarektjåkkå Nappe (SN) of the Seve-Kalak Superterrane in the northern Swedish Caledonides. The SN has two main components: (1) a 4–5 km thick succession of rift-related sedimentary rocks, which is intruded by (2) a suite of tholeiitic dykes (the SDS) co...

  13. Broad accommodation of rift-related extension recorded by dyke intrusion in Saudi Arabia

    KAUST Repository

    Pallister, John S.

    2010-09-26

    The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low- and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees. © 2010 Macmillan Publishers Limited. All rights reserved.

  14. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    Science.gov (United States)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia

    2016-04-01

    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18‑24Ab79‑82Or0.3‑0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  15. Palaeointensity and palaeodirection determinations of Paleoproterozoic dykes in the Kaapvaal Craton (South Africa)

    Science.gov (United States)

    Shcherbakova, V. V.; Lubnina, N. V.; Shcherbakov, V. P.; Zhidkov, G. V.

    2012-04-01

    A combined palaeodirectional and palaeointensity study of a representative collection from the Bushveld Igneous Complex from 27 dolerite dykes from the 2.9, 2.7, and 1.8 Ga age swarms radiating SE, E and NE, respectively [Olsson et al., 2010] was carried out. Conventional progressive thermal or AF demagnetization was applied to all specimens. The palaeomagnetic directions have been calculated after thermal demagnetization. The ChRMs were isolated over the temperature interval 440-590 C and their intensities amount to 95% of total NRMs. Paleopole calculate from the primary high-temperature component, separated in the 2.9 Ga SE-dykes, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78 Ga volcanics. The paleopole calculated for the 2.7 Ga age E-trending dykes of the eastern region does not correspond to any of the previously obtained Archean-Paleoproterozoic paleopoles for the Kaapvaal Craton. The paleopole calculated for some NE-trending dykes of the Black Ridge swarm in the NE region is close to the 1.87 Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Palaeointensity determinations were carried out on rocks from ten dykes of different ages using Thellier-Coe method with the "check-points" procedure on specimens of 1 cm in edge length cut from either drilled cores or hand samples. Rock magnetic measurements were made on sister specimens. Curie temperatures and the thermal stability of magnetic minerals were estimated from thermomagnetic heating-cooling cycles to incrementally higher temperatures Ti with a Curie balance in an external magnetic field H = 0.45 T. To assess the magnetic hardness and mineralogy of samples, measurements of magnetic susceptibility and hysteresis loop parameters were performed. The domain structure (DS) was estimated also from the thermomagnetic criterion by evaluating the tails of pTRMs. Wilson's method of palaeointensity determination based on comparison of thermodemagnetization curves

  16. Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong Plateau, NE India

    Indian Academy of Sciences (India)

    Sampa Hazra; Jyotisankar Ray; C Manikyamba; Abhishek Saha; S S Sawant

    2015-03-01

    The mafic rocks of east Khasi Hills of the Meghalaya Plateau, northeastern India, occur as an intrusive body which cut across the weakly metamorphosed Shillong Group of rocks. Other than Shillong Group of rocks, high grade Archaean gneissic rocks and younger porphyritic granites are also observed in the study area. The studied mafic rocks of east Khasi Hills cover an area of about 4 km2 and represent structurally controlled intrusion and varying grades of deformation. Structurally, these mafic rocks can be divided into massive type of mafic rocks, which are more or less deformation free and foliated type of mafic rocks that experienced deformation. Petrographically, this massive type can be classified as leuco-hornblende-gabbro whereas foliated type can be designated as amphibolite. On the basis of major oxide geochemistry, the investigated mafic rocks can be discriminated into high titanium (HT) (TiO2 > 2 wt%) and low titanium (LT) types (TiO2 < 2 wt%). Use of several geochemical variation diagrams, consideration of chondrite-normalized and mantle-normalized REE and PGE plots suggest role of magmatic differentiation (with almost no role of plagioclase fractionation) in a subduction controlled tectonic environment. The PGE trends of the studied rocks suggest relative enrichment of palladium group of PGE (PPGE) compared to iridium group PGE (IPGE). Critical consideration of Sm vs. La, Cu vs. La, Pd vs. La and Cu/Pd vs. La/Sm plots strongly favours generation of the parent magma at a columnar melting regime with batch melting of cylindrical column of the parent mantle to the tune of ∼25%. The characteristic PGE behaviours of the presently investigated mafic rocks of east Khasi Hills can be typically corroborated as `orogenic' (discordant) type. These rocks have an enriched mantle affinity with a co-magmatic lineage and they have been generated by slab-dehydration, wedge-melting and assimilation fractional crystallization process at a continental margin arc setting.

  17. Geochronological and geochemical constraints on the petrogenesis and tectonic significance of Paleozoic dolerite dykes in the southern margin of Alxa Block, North China Craton

    Science.gov (United States)

    Duan, Jun; Li, Chusi; Qian, Zhuangzhi; Jiao, Jiangang

    2015-11-01

    Dolerite dykes are common in the southern margin of Alxa Block which is the westernmost part of North China Craton. The ages and petrogenesis of the dolerite dykes, which are important for a better understanding of tectonic-magmatic evolution in the region, are uncertain. This paper reports the results of an integrated geochronological and geochemical study of the dolerite dykes in the Jinchuan area. Previously, these dolerite dykes were considered to be coeval with the ∼831 Ma Jinchuan ultramafic intrusion by some researchers, despite a cross-cutting relationship for the dykes. Our new zircon U-Pb dating indicates that the dolerite dykes were emplaced at ∼424 Ma, >400 Ma younger than the Jinchuan intrusion. The Jinchuan dolerite dykes contain 5-9 wt.% MgO and 47-51 wt.% SiO2, and are characterized by light REE (rare earth elements) enrichments relative to heavy REE, pronounced negative Nb anomaly, elevated initial 87Sr/86Sr from 0.7056 to 0.7068, negative εNd from -2 to -5, and zircon εHf from -2 to -20. The trace element and isotope data are consistent with an asthenosphere-derived parental magma that experienced 10-25% crustal contamination prior to final emplacement. Since the Jinchuan dolerite dykes are 20-40 Ma younger than the subduction-related basaltic volcanic rocks, blueschists and eclogites in the nearby North Qilian orogenic belt to the south, we propose that the Jinchuan dolerite dykes are the products of basaltic magmatism induced by delamination of previously subducted oceanic lithosphere and the associated asthenosphere upwelling in a post-subduction setting. The occurrence of ∼424 Ma post-subduction dolerite dykes in the Jinchuan area and the ∼450 Ma arc basalts to the south indicate that the southwestern margin of North China Craton was an active plate margin in Early Paleozoic.

  18. Petrological and geochemical studies of ultramafic-mafic rocks from the North Puruliya Shear Zone (eastern India)

    Science.gov (United States)

    Mandal, Aditi; Ray, Arijit

    2015-12-01

    Ultramafic and mafic rocks occur within a linear belt, trending nearly E-W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbro-norite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic-ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47-81) and Al 2 O 3 (5.5-17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic-ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic-ultramafic rocks of high grade terrain, Alaskan type ultramafic-mafic complex and ophiolites. It is observed that the ultramafic-mafic rocks of present study have similarity with Alaskan type complex.

  19. Dyke-Davidoff-Masson syndrome: case report of fetal unilateral ventriculomegaly and hypoplastic left middle cerebral artery

    OpenAIRE

    Piro, E.; Piccione, M; Marrone, G; Giuffrè, M; G. Corsello

    2013-01-01

    Prenatal ultrasonographic detection of unilateral cerebral ventriculomegaly arises suspicion of pathological condition related to cerebrospinal fluid flow obstruction or cerebral parenchimal pathology. Dyke-Davidoff-Masson syndrome is a rare condition characterized by cerebral hemiatrophy, calvarial thickening, skull and facial asymmetry, contralateral hemiparesis, cognitive impairment and seizures. Congenital and acquired types are recognized and have been described, mainly in late childhood...

  20. Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

    DEFF Research Database (Denmark)

    Jakobsen, J.K.; Tegner, Christian; Brooks, Kent;

    2010-01-01

    Abstract Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47...

  1. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics.

    Science.gov (United States)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

    2014-05-01

    It is well known that magma ascends trough the crust by the process of dyking. To enable dyke emplacement, basement rocks typically fail in a mode 1 fracture, which acts as conduits for magma transport. An overpressure of the ascending magma will further open/widen the fracture and permit the fracture to propagate. In order to further understand the emplacement and arrest of dykes in the subsurface, analogue and numerical studies have been conducted. However, a number of assumptions regarding rock mechanical behaviour frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. Here we present a new laboratory setup, which allows us to investigate the tensile fracturing properties under both temperature and confining pressure, and the emplacement of molten material within the newly formed fracture. We have modified a traditional tri-axial test assembly setup to be able to use a Paterson type High Pressure, High Temperature deformation apparatus. Sample setup consists of cylindrical rock samples with a 22 mm diameter and a 8 mm bore at their centre, filled with a material chosen as such that it's in a liquid state at the experimental temperature and solid at room temperature to enable post-experiment analysis. The top and lower parts of the rock sample are fitted with plugs, sealing in the melt. The assembly is then placed between ceramic pistons to ensure there are no thermal gradients across the sample. The assembly is jacketed to ensure the confining medium (Ar) cannot enter the assembly. A piston is driven into the sample such that the inner conduit materials pressure is slowly increased. At some point a sufficient pressure difference between the inner and outer surfaces causes the sample to deform and fail in the tensile regime

  2. Adult Presentation of Dyke-Davidoff-Masson Syndrome: A Case Report

    Directory of Open Access Journals (Sweden)

    Ujjawal Roy

    2016-01-01

    Full Text Available Dyke-Davidoff-Masson syndrome (DDMS is a rare disease which is clinically characterized by hemiparesis, seizures, facial asymmetry, and mental retardation. The classical radiological findings are cerebral hemiatrophy, calvarial thickening, and hyperpneumatization of the frontal sinuses. This disease is a rare entity, and it mainly presents in childhood. Adult presentation of DDMS is unusual and has been rarely reported in the medical literature. Key Messages: DDMS is a rare disease of childhood. However, it should be kept in mind as a diagnostic possibility in an adult who presents with a long duration of progressive hemiparesis with seizures and mental retardation. Cerebral hemiatrophy, calvarial thickening, and hyperpneumatization of the frontal sinuses are diagnostic for this illness on brain imaging.

  3. Single Silicate Crystal Paleointensity Analyses of the ca. 2.575 Ga Great Dyke of Zimbabwe

    Science.gov (United States)

    O'Brien, T.; Tarduno, J. A.; Hofmann, A.

    2014-12-01

    Recent considerations of core thermal conductivity suggest a relatively young (less than 1 billion-year-old) age for the inner core, excluding compositional convection associated with inner core growth as a driving mechanism for an Archean geodynamo. These reconsiderations provide further motivation for studying the nature of the field when core convection was predominantly related to core mantle boundary heat flow. Here we examine the ca. 2.575 Ga Great Dyke of Zimbabwe. We rely on deep drill core samples, eliminating the otherwise pervasive effects of lightning seen in surface samples. We apply single silicate crystal paleointensity (SCP) techniques (Tarduno et al., Rev. Geophys., 2006) on feldspars separated from orthopyroxene gabbros (norites). Scanning electron microscope (SEM) analyses indicate the presence of rare sub-micron equant to slightly elongate magnetic inclusions in the feldspars. The magnetite/titanomagnetite needles commonly observed in feldspars of slowly cooled igneous rocks are rarely observed in crystals from our Great Dyke gabbro samples. Selection criteria of crystals for analyses required feldspar crystals to be free of visible multi-domain inclusions. Natural remanent magnetic intensities of ca. 1 mm-sized feldspar crystal are relatively weak (approximately 1-2 x 10-8 emu), but well within the measurement range of the University of Rochester small bore ultra-high moment resolution 2G DC SQUID magnetometer. Preliminary total thermal demagnetization experiments suggest paleofield values within 50% of those of the present-day, similar to other results that imply a relatively strong magnetic field during the late Archean. Results from Thellier analyses will be used to test this interpretation.

  4. Orogenic potassic mafic magmatism, a product of alkaline-peraluminous mixing ? Variscan 'calc-alkaline' rocks from the Central Iberian and Ossa Morena Zones, Central Spain.

    Science.gov (United States)

    Scarrow, Jane H.; Cambeses, Aitor; Bea, Fernando; Montero, Pilar; Molina, José F.; Moreno, Juan Antonio

    2013-04-01

    Orogenic magmatic rocks provide information about mantle and crust melt-generation and -interaction processes. In this context, minor potassic mafic stocks which are formed of enriched mantle and crustal components and are common as late-orogenic intrusions in granitic plutons give insight into the timing of new crust formation and crustal recycling. Potassic mafic stocks are prevalent, albeit low volume, constituents of granite batholiths all through the European Variscan (350-280 Ma). In the Central Iberia Zone, Spanish Central System, crustal-melt, S-type, granitoid plutons are intruded by minor concomitant ultramafic-intermediate appinitic-vaugneritic stocks. Notwithstanding their whole-rock calc-alkaline composition, the stocks apparently did not have a subduction-related origin. Recent studies have attributed their genesis to mixing of alkaline mantle and peraluminous crustal melts. Their primary alkaline character, as indicated by amphibole and biotite mineral chemistry data, points, rather, towards an extension-related genesis. In the Ossa Morena Zone, south of the Central Iberian Zone, the igneous rocks also have a whole-rock calc-alkaline composition which has been considered to be the result of northward subduction of the South Portuguese Zone. Nevertheless, identification of a 'sill' of significant volume of mafic magma in the middle crust, the ´IBERSEIS reflective body', in a seismic profile across the Ossa Morena and South Portuguese Zones has cast doubt upon the calc-alkaline magmatism-subduction model; leading, instead, to the magmatism being attributed to intra-orogenic extension related to a mantle plume active from 340 Ma to 330 Ma. The aim here, then, is to reinvestigate the petrogenesis and age of the calc-alkaline rocks of the Ossa Morena Zone to determine their tectonomagmatic context be it subduction-, plume- or extension-related, and establish what they may reveal about mantle-crust interactions. Focussing, initially, on the Valencia del

  5. Magma Emplacement and Mafic-Felsic Magma Hybridisation: Structural, Microstructural and Geochemical Evidences From the Pan-African Negash Pluton, Northern Ethiopia

    Science.gov (United States)

    ASRAT, A.; BARBEY, P.; GLEIZES, G.; LUDDEN, J.

    2002-05-01

    The Negash pluton (50 sq. km) consists of late Pan-African, high-K, calc-alkaline granitoids intruded into low-grade metavolcanics and metasediments. This almost circular massif consists of monzogranites, granodiorites, monzodiorites, monzogabbros, and hybrid quartz monzodiorites. The rocks are enriched in LIL-elements, depleted in HFS-elements, have fractionated REE patterns, low 87Sr/86Sri (0.702344 - 0.703553) and 143Nd/144Ndi (0.512031 - 0.512133) ratios, positive ɛ Nd values (3.46 to 5.40), and Pan-African model Nd ages (0.83 to 1.08 Ga). These data, along with single zircon U-Pb dating, show that the pluton was emplaced at 608 Ma from primitive source (underplated material or juvenile island arc crust) with contamination by the country rocks. The pluton shows widespread mafic-felsic magma interactions of two types: (i) homogeneous and heterogeneous hybrid monzodiorites at the northwestern part; and (ii) mingled interfaces at the diorite-granodiorite contact zones in the Eastern and Southeastern parts. Detailed structural (using the method of the anisotropy of magnetic susceptibility) and microstructural studies have been applied to understand how these interactions occurred with respect to pluton construction. The monzodiorites constituting the northwestern part of the pluton, which are composed of complexly zoned plagioclases or unzoned plagioclase laths, euhedral hornblende with biotite cores and acicular apatites, are characterized by abundant net veining, synplutonic dikes, microgranitoid enclaves, and juxtaposed series of discrete mafic-felsic pulses of hybrid nature with vertical syn-emplacement structures. The mingled interfaces between the diorites and granodiorites, on the other hand, are characterized by lobate contacts with interfingering of diorites into granodiorites at the decametric scale, abundant inclined to horizontal granitic pipes, breccia dykes and veins, which are strongly enriched in megacrysts of K-feldspars, and numerous swarms of

  6. Nb/Ta variations of mafic volcanics on the Archean-Proterozoic boundary: Implications for the Nb/Ta imbalance

    Institute of Scientific and Technical Information of China (English)

    LIU; Yongsheng; GAO; Shan; WANG; Xuance; HU; Shenghong; WA

    2005-01-01

    The HFSE and REE of the Precambrian mafic volcanics from the North China craton demonstrate obvious A(Archean)-P(Proterozoic) boundary. The Neoarchean mafic vol-canics show weak correlation between HFSE and TiO2. Their superchondritic Nb/Ta ratio (18.8(1.2) could be attributed to partial melting of mantle peridotite in the presence of garnet. Compared with Neoarchean mafic volcanics, the Paleoproterozoic ones have higher HFSE contents and lower Nb/Ta ratio (15.6(2.9). The significantly elevated HFSE and REE contents of Paleoproterozoic mafic volcanics imply metasomatic enrichment of mantle source, in which Ti-rich silicates could be present as suggested by significant positive correlations between TiO2 and HFSE. The global database of Precambrian mafic volcanics shows a similar A-P boundary. 23 Archean mafic volcanic suites yield an average Nb/Ta ratio of 17.8(1.9 higher than or close to the PM value; Proterozoic mafic volcanics from 28 suites yield an average Nb/Ta ratio of 14.7(4.1 deficit could be mainly formed in post-Archean time. Archean mafic volcanics could be one of the geochemical reservoirs complementing the low Nb/Ta of the post-Archean continental crust and DM.

  7. Geochronology and Geochemistry of Mafic Dikes from Hainan Island and Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    CAO Jianjin; HU Ruizhong; LIU Shen; XIE Guiqing

    2009-01-01

    In the present study, the major and trace element compositions, as well as Sr, Nd isotopic compositions and K-Ar age data in mafic dikes from Hainan Island, China, have been analyzed. Whole-rock K-Ar dating yielded a magmatic duration of 61-98 Ma for mafic dikes. Mafic dikes have a very high concentration of incompatible elements, for example, Ba, Rb, Sr, K, rare earth elements, and especially light rare earth elements (LREE), and negative anomalies of Nb, Ta, and Ti in the normalized trace element patterns. The initial ~(87)Sr/~(86)Sr ratios and εSr(t) of the mafic dikes are 0.70634-0.71193 and +27.7 to +112.2, respectively. In the ~(87)Sr/~(86)Sr versus εNd(t) diagram, the Hainan Island mafic dikes plot between fields for depleted mantle and enriched mantle type 2. All these characteristics show that the mantle (source region) of mafic dikes in this area experienced metasomatism by fluids relatively enriched in LREE and large ion lithophile elements. The genesis of Hainan Island mafic dikes is explained as a result of the mixing of asthenospheric mantle with lithospheric mantle that experienced metasomatism by the subduction of the Pacific Plate. This is different from the Hainan Island Cenozoic basaits mainly derived from depleted asthenospheric mantle, and possibly, minor metasomatised lithospheric mantle. This study suggests that the Mesozoic and Cenozoic lithospheric revolutions in Hainan Island can be divided into three stages: (1) the compression orogenesis stage before 98 Ma. The dominant factor during this stage is the subduction of the ancient Pacific Plate beneath this area. The lithospheric mantle changed into enriched mantle type 2 by metasomatism; (2) the thinning and extension stage during 61-98 Ma. The dominant factor during this stage is that the asthenospheric mantle invaded and corroded the lithospheric mantle; and (3) the large-scale thinning and extension stage after 61 Ma. The large-scale asthenospheric upwelling results in the strong

  8. Retraction notice to "Ca. 2.5 billion year old mafic dykes in western Shandong Province: Implications for hybridization between subducted continental crust and the North China Craton, China"

    Science.gov (United States)

    Liu, Shen; Feng, Caixia; Zhai, Mingguo; Hu, Ruizhong; Gao, Shan; Lai, Shaocong; Zou, Haibo; Yan, Jun

    2015-02-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal. This article has been retracted at the request of the Editors-in-Chief. The article duplicates significant parts of a paper that had already appeared in, and was withdrawn from Precambrain Research (http://dx.doi.org/10.1016/j.precamres.2014.08.012") One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

  9. Magnetic resonance imaging depiction of acquired Dyke-Davidoff-Masson syndrome with crossed cerebro-cerebellar diaschisis: Report of two cases

    Directory of Open Access Journals (Sweden)

    Ranjana Gupta

    2015-01-01

    Full Text Available Acquired Dyke-Davidoff-Masson syndrome, also known as hemispheric atrophy, is characterized by loss of volume of one cerebral hemisphere from an insult in early life. Crossed cerebellar diaschisis refers to dysfunction/atrophy of cerebellar hemisphere which is secondary to contralateral supratentorial insult. We describe magnetic resonance imaging findings in two cases of acquired Dyke-Davidoff-Masson syndrome with crossed cerebro-cerebellar diaschisis.

  10. A Geochemical Study of an REE-rich Carbonatite Dyke at Bayan Obo, Inner Mongolia, Northern China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    An REE-rich carbonatite dyke was found in Dulahala, close to the Bayan Obo superlarge REE-Nb-Fe mineral deposit in Inner Mongolia, northern China. The REE content in the dyke varies greatly, from 1% up to 20% (wt), which might constitute rich REE ores. Light REEs in the carbonatite are enriched and highly fractionated relative to heavy REEs and there is no Eu anomaly. The REE and trace element distribution patterns of the carbonatite are identical to those of fine-grained dolomite marble which is the host rock of the Bayan Obo REE-Nb-Fe superlarge mineral deposit. This indicates a petrogenetic linkage between the REE-rich carbonatite and the mineralizations in this region.

  11. Ocellar lamprophyre dyke bearing mineralization, Wadi Nugrus, Eastern Desert, Egypt: Geology, mineralogy and geochemical implications

    Institute of Scientific and Technical Information of China (English)

    Ibrahim M.E.; Saleh G.M.; Dawood N.A.; Aly G.M.

    2010-01-01

    The ocellar lamprophyre dyke (ENE-WSW) is recorded at Wadi Nugrus, Eastern Desert, Egypt. It cuts porphyritic biotite granites and varies in thickness from 0.5 to 1.5 m and up to 3 km in length. The lamprophyre dyke has been altered, and it is characterized by porphyritic and panidiomorphic textures with plagioclase, olivine, and augite constituting the porphyritic phase in a fine groundmass of the same composition. Rutile, titanite, apatite, fluorite, graphite, calcite, allanite, autunite and Fe-Ti oxides are accessory minerals. Kaolinite, chlorite and epidote are secondary minerals. Carbonitization and hematitization are common. Rounded to sub-rounded porphyritic and zoned ocelli with radiate or brush-like shapes are generally common and represent physical traps for mineralization. The ocellar features are interpreted to represent the late stage of magmatic segregation or magmatic crystallization involving two immiscible magmatic liquids.Mineralogical studies of altered lamprophyre samples, based on X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), indicate the presence of secondary uranium minerals (autunite and uranophane), associated with gold, silver, nickel, atacamite, molybdenum, pyrite and zincite. The presence of kaolinite indicates a high temperature environment. The mixing of volatile fluids with meteoric water and fluid-wall rock interaction result in changes of pH and oxygen activity and deposition of base metals in reducing environs (graphite and pyrite). Precipitation of hematite probably decreased the pH of the solution and rose acidic fluids. The sudden change in pH and temperature of the fluids would lead to destabilization of base metal complexes favoring their deposition.The magma source of the Nugrus lamprophyre is determined to be between calc-alkaline and alkaline and it has HKCAB and shoshonitic nature and may be derived from decomposition melting of such a metasomatised lithospheric mantle. Olivine is a major

  12. Application of generalized inverse for analysis of magnetic anomalies due to a dyke model - Some numerical experiments

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, M.M.M.; Murty, T.V.R.; SuryaPrakash, S.; Chandramouli, P.; Murthy, K.S.R.

    light on data and model resolution and individual model parameter contribution. All these procedures and algorithms attempt to relate physical models to readily observable data and determine the "best-estimates" of model parameters... Software details - Annexure – I 26 Sample input/output & FORTRAN coding - Annexure – II 28 FIGURES Fig. 1 – Parameters of dyke model. Fig. 2 – Magnetic Profile off Visakhapatnam (at 40m depth) Fig. 3A- Synthetic anomaly and its...

  13. Permeability of sheeted dykes beneath oceanic ridges: Strain experiments coupled with 3D numerical modeling of the Troodos Ophiolite, Cyprus

    OpenAIRE

    Coelho, Gabriel; Branquet, Yannick; Sizaret, Stanislas; Arbaret, Laurent; Champallier, Rémi; Rozenbaum, Olivier

    2015-01-01

    Permeability laboratory measurements under in-situ pressures, temperature and strain have been performed on three different diabase alteration facies (metadiabase, chloritized diabase, epidosite) from the Troodos Ophiolite, Cyprus. This aims to study the relations between hydrodynamics, deformation and hydrothermal reaction in the sheeted dyke complex beneath oceanic ridges. The use of water as pore fluid in these experiments favors hydrothermal fluid-rock interactions. All experiments, perfo...

  14. Geochemistry of Metamafic Dykes from the Quanji Massif:Petrogenesis and Further Evidence for Oceanic Subduction, Late Paleoproterozoic, NW China

    Institute of Scientific and Technical Information of China (English)

    Hassan Abdelslam Mustafa; Qinyan Wang; Nengsong Chen; Fanxi Liao; Min Sun; Meshaal Abdelgadir Salih

    2016-01-01

    A suite of ~1.84–1.92 Ga metamafic dykes within the paragneiss suite (khondalite) of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evo-lution and possible links to the global Columbia supercontinent. Occurrence and field relations sug-gest that they were formed coevally with a previous studied ~1.83–1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geochemistry suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment where the metamafic dyke swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO2 (49.3 wt.%–52.5 wt.%) but low MgO (6.40 wt.%–7.76 wt.%) contents and Mg# (Mg#=[100×(MgO/40.3)]/[MgO/40.3+FeO/71.8]) values (45.7–52.1), suggesting evolved precursor magma. The high values of La/Ta (22.2–42.8) and La/Nb (1.71–2.47), mildly negativeεNd(t) values (-2.51–0.15), with depleted mantle model ages (TDM) of 2.45–2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides further evi-dence for oceanic plate subduction prevailing before or around ~1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly linked to the assembly of the Columbia supercontinent.

  15. Quasi 2D hydrodynamic modelling of the flooded hinterland due to dyke breaching on the Elbe River

    Directory of Open Access Journals (Sweden)

    S. Huang

    2007-01-01

    Full Text Available In flood modeling, many 1D and 2D combination and 2D models are used to simulate diversion of water from rivers through dyke breaches into the hinterland for extreme flood events. However, these models are too demanding in data requirements and computational resources which is an important consideration when uncertainty analysis using Monte Carlo techniques is used to complement the modeling exercise. The goal of this paper is to show the development of a quasi-2D modeling approach, which still calculates the dynamic wave in 1D but the discretisation of the computational units are in 2D, allowing a better spatial representation of the flow in the hinterland due to dyke breaching without a large additional expenditure on data pre-processing and computational time. A 2D representation of the flow and velocity fields is required to model sediment and micro-pollutant transport. The model DYNHYD (1D hydrodynamics from the WASP5 modeling package was used as a basis for the simulations. The model was extended to incorporate the quasi-2D approach and a Monte-Carlo Analysis was used to conduct a flood sensitivity analysis to determine the sensitivity of parameters and boundary conditions to the resulting water flow. An extreme flood event on the Elbe River, Germany, with a possible dyke breach area was used as a test case. The results show a good similarity with those obtained from another 1D/2D modeling study.

  16. Assessing the Stability of a Geologically Complex Slope Where Strong Dykes Locally Act as Reinforcement

    Science.gov (United States)

    Lee, S. G.; Hencher, S. R.

    2013-11-01

    This paper presents a case study of aspects of the design of large slope cuttings in complex geological conditions in South Korea. During the original cutting of the slopes to geometries prescribed by Korean standards for rock slopes, several translational slides occurred on daylighting bedding planes. From observation it was evident that away from the areas of distress, some parts of the slopes appeared to be relatively stable, apparently because of the strengthening influence of relatively strong and massive igneous dykes and sills through the sedimentary rock. This paper describes how the geological conditions were assessed and stability analysed, section-by-section, along the road. This was achieved using a form of the method of slices to account for those sections of potential failure surfaces where sliding could occur along bedding and others where failure would necessitate shear through the intrusive igneous rock. Results were checked using UDEC models of critical sections. Following these analyses, recommendations were made for localized additional preventive measures including anchors and drainage.

  17. Acute myeloblastic leukemia-associated Marfan syndrome and Davidoff-Dyke-Masson syndrome: a case report

    Directory of Open Access Journals (Sweden)

    Ahmet Faik Öner

    2008-12-01

    Full Text Available We present herein a 23-year-old man with acute myeloblastic leukemia (AML associated with Davidoff-Dyke-Masson syndrome (DDMS and Marfan syndrome (MS. The diagnosis of DDMS was based on findings including left facial asymmetry, left hemiparesis, mental retardation, right cerebral hemiatrophy, dilatation of the ipsilateral lateral ventricle and calvarial thickening. The diagnosis of MS was based on clinical findings including tall stature, myopia, retinitis pigmentosa, blue scleras, scoliosis, pectus excavatum, arachnodactyly and low ratio of upper/lower body segment. The patient developed hepatosplenomegaly, gingival hypertrophy and pancytopenia. Peripheral blood film and bone marrow examination showed that most of nucleated cells were blasts; immunophenotype of those cells showed CD11+, CD13+, CD14+, CD33+ and HLA-DR+. These findings confirmed the diagnosis of AML (FAB-M5. After induction chemotherapy, remission was obtained. To the best of our knowledge, our case is the third report of AML in MS syndrome, while AML associated with DDMS and MS has not been previously reported in the literature.

  18. Petrological and geochemical studies of ultramafic–mafic rocks from the North Puruliya Shear Zone (eastern India)

    Indian Academy of Sciences (India)

    Aditi Mandal; Arijit Ray

    2015-12-01

    Ultramafic and mafic rocks occur within a linear belt, trending nearly E–W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbronorite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic–ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47–81) and Al2O3 (5.5–17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic–ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic–ultramafic rocks of high grade terrain, Alaskan type ultramafic–mafic complex and ophiolites. It is observed that the ultramafic–mafic rocks of present study have similarity with Alaskan type complex.

  19. Can we see the distal dyke communicate with the caldera? Examples of temporal correlation analysis using seismicity from the Bárðarbunga volcano

    Science.gov (United States)

    Jónsdóttir, Kristín; Jónasson, Kristján; Tumi Guðmundsson, Magnús; Hensch, Martin; Hooper, Andrew; Holohan, Eoghan; Sigmundsson, Freysteinn; Halldórsson, Sæmundur Ari; Vogfjörð, Kristín; Roberts, Matthew; Barsotti, Sara; Ófeigsson, Benedikt; Hjörleifsdóttir, Vala; Magnússon, Eyjólfur; Pálsson, Finnur; Parks, Michelle; Dumont, Stephanie; Einarsson, Páll; Guðmundsson, Gunnar

    2016-04-01

    The Bárðarbunga volcano is composed of a large oval caldera (7x11 km) and fissures extending tens of kilometers away from the caldera along the rift zone, which marks the divergent plate boundary across Iceland. On August 16th, 2014 an intense seismic swarm started below the Bárðarbunga caldera and in the two weeks that followed a dyke migrated some 47 km laterally in the uppermost 6-10 km of the crust along the rift. The dyke propagation terminated in lava fields just north of Vatnajökull glacier, where a major (1.5 km3) six months long eruption took place. Intense earthquake activity in the caldera started in the period August 21-24 with over 70 M5 earthquakes accompanying slow caldera collapse, as verified by various geodetic measurements. The subsidence is likely due to magma withdrawal from a reservoir at depth beneath the caldera. During a five months period, October-February, the seismic activity was separated by over 30 km in two clusters; one along the caldera rims (due to piecewise caldera subsidence) and the other at the far end of the dyke (as a result of small shear movements). Here we present statistical analysis comparing the temporal behaviour of seismicity recorded in the two clusters. By comparing the earthquake rate in the dyke in temporal bins before and after caldera subsidence earthquakes to the rate away from these bins (background rate), we show posing a statistical p-value test, that the number of dyke earthquakes was significantly higher (p earthquake (>M4.6) in the caldera. Increased dyke seismicity was also observed 0-3 hours following a large caldera earthquake. Elevated seismicity in the dyke before a large caldera earthquake may occur when a constriction in the dyke was reduced, followed by pressure drop in the chamber. Assuming that the large caldera earthquakes occurred when chamber pressure was lowest, the subsiding caldera piston may have caused temporary higher pressure in the dyke and thereby increased the likelihood of an

  20. Can we see the distal dyke communicate with the caldera? Examples of temporal correlation analysis using seismicity from the Bárðarbunga volcano

    Science.gov (United States)

    Jónsdóttir, Kristín; Jónasson, Kristján; Tumi Guðmundsson, Magnús; Hensch, Martin; Hooper, Andrew; Holohan, Eoghan; Sigmundsson, Freysteinn; Halldórsson, Sæmundur Ari; Vogfjörð, Kristín; Roberts, Matthew; Barsotti, Sara; Ófeigsson, Benedikt; Hjörleifsdóttir, Vala; Magnússon, Eyjólfur; Pálsson, Finnur; Parks, Michelle; Dumont, Stephanie; Einarsson, Páll; Guðmundsson, Gunnar

    2016-04-01

    The Bárðarbunga volcano is composed of a large oval caldera (7x11 km) and fissures extending tens of kilometers away from the caldera along the rift zone, which marks the divergent plate boundary across Iceland. On August 16th, 2014 an intense seismic swarm started below the Bárðarbunga caldera and in the two weeks that followed a dyke migrated some 47 km laterally in the uppermost 6-10 km of the crust along the rift. The dyke propagation terminated in lava fields just north of Vatnajökull glacier, where a major (1.5 km3) six months long eruption took place. Intense earthquake activity in the caldera started in the period August 21-24 with over 70 M5 earthquakes accompanying slow caldera collapse, as verified by various geodetic measurements. The subsidence is likely due to magma withdrawal from a reservoir at depth beneath the caldera. During a five months period, October-February, the seismic activity was separated by over 30 km in two clusters; one along the caldera rims (due to piecewise caldera subsidence) and the other at the far end of the dyke (as a result of small shear movements). Here we present statistical analysis comparing the temporal behaviour of seismicity recorded in the two clusters. By comparing the earthquake rate in the dyke in temporal bins before and after caldera subsidence earthquakes to the rate away from these bins (background rate), we show posing a statistical p-value test, that the number of dyke earthquakes was significantly higher (p M4.6) in the caldera. Increased dyke seismicity was also observed 0-3 hours following a large caldera earthquake. Elevated seismicity in the dyke before a large caldera earthquake may occur when a constriction in the dyke was reduced, followed by pressure drop in the chamber. Assuming that the large caldera earthquakes occurred when chamber pressure was lowest, the subsiding caldera piston may have caused temporary higher pressure in the dyke and thereby increased the likelihood of an earthquake

  1. Paleomagnetic record of a geomagnetic field reversal from late miocene mafic intrusions, southern nevada.

    Science.gov (United States)

    Ratcliff, C D; Geissman, J W; Perry, F V; Crowe, B M; Zeitler, P K

    1994-10-21

    Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227 degrees to 310 degrees and inclinations of -7 degrees to 49 degrees , defining a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal. PMID:17816684

  2. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of central Chile

    Science.gov (United States)

    Hildreth, W.; Singer, B.; Godoy, E.; Munizaga, F.

    1998-01-01

    Cerro Campanario, a towering landmark on the continental divide near Paso Pehuenche, is a glacially eroded remnant of a mafic stratovolcano that is much younger than previously supposed. Consisting of fairly uniform basaltic andesite, rich in olivine and plagioclase, the 10-15 km3 edifice grew rapidly near the end of the middle Pleistocene, about 150-160 ka, as indicated by 40Ar/39Ar and unspiked K-Ar analyses of its lavas.

  3. The mafic dikes from the Panticosa pluton (Pyrenean Axial Zone): petrology and mineral chemistry

    OpenAIRE

    Tierz, Pablo; Lago San José, Marceliano; Galé, Carlos; Arranz, Enrique; Ubide, Teresa; Larrea, Patricia; Sanz, Tomás

    2012-01-01

    The Panticosa pluton is one of multiple granitic plutons cropping out in the Pyrenean Axial Zone, which corresponds to the Palaeozoic core of the Pyrenees. Mafic dikes cut both the Panticosa pluton and its Devonian metasedimentary country rocks. According to their mineralogy and mineral composition, these dikes can be classified into two different groups, with little textural variations: a calc-alkaline group and an alkaline group. The calcalkaline rocks (spessartites and ca...

  4. Physical abrasion of mafic minerals and basalt grains: application to Martian aeolian deposits

    Science.gov (United States)

    Cornwall, Carin; Bandfield, Joshua L.; Titus, Timothy N.; Schreiber, B. C.; Montgomery, D.R.

    2015-01-01

    Sediment maturity, or the mineralogical and physical characterization of sediment deposits, has been used to locate sediment source, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold, dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. Abrason tests have been conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical basalt grains. In addition, any volcanic glass present is likely to persist in a mechanical weathering environment while chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide details about erosional and sediment transport systems and preservation processes of layered deposits.

  5. Physical abrasion of mafic minerals and basalt grains: Application to martian aeolian deposits

    Science.gov (United States)

    Cornwall, C.; Bandfield, J. L.; Titus, T. N.; Schreiber, B. C.; Montgomery, D. R.

    2015-08-01

    Sediment maturity, or the mineralogical and physical characterization of sedimentary deposits, has been used to identify sediment sources, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold and dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. This paper reports the results of abrasion tests conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical polycrystalline materials, such as basalt. Volcanic glass is also likely to persist in a mechanical weathering environment while more fragile and chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide insights into erosional and sediment transport systems and preservation processes of layered deposits.

  6. Flood risk control of dams and dykes in middle reach of Huaihe River

    Directory of Open Access Journals (Sweden)

    Zhen-kun MA

    2014-01-01

    Full Text Available Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate with flood regulation of five key reservoirs, including the Meishan, Xianghongdian, Nianyushan, Mozitan, and Foziling reservoirs in the middle reach of the Huaihe River under different flood frequencies, the flood risk rate with river course flood release under design and check floods for the trunk of the Huaihe River in conjunction with relevant flood storage areas, and the flood risk rate with operation of the Linhuaigang Project under design and check floods. The calculated results show that (1 the five reservoirs can withstand design floods, but the Xianghongdian and Foziling reservoirs will suffer overtopping accidents under check floods; (2 considering the service of flood storage areas under the design flood conditions of the Huaihe River, the mean flood risk rate with flood regulation of dykes and dams from Xixian to the Bengbu floodgate is about 0.2, and the trunk of the Huaihe River can generally withstand design floods; and (3 under a check flood with the flood return period of 1 000 years, the risk rate of overtopping accidents of the Linhuaigang Project is not larger than 0.15, indicating that it has a high flood regulation capacity. Through regulation and application of the flood control system of the Linhuigang Project, the Huaihe River Basin can withstand large floods, and the safety of the protected area can be ensured.

  7. The French Guyana doleritic dykes: geochemical evidence of three populations and new data for the Jurassic Central Atlantic Magmatic Province

    Science.gov (United States)

    Nomade, S.; Pouclet, A.; Chen, Y.

    2002-12-01

    A petrographic and geochemical study of 15 Early Jurassic and 7 Proterozoic dolerites of French Guyana, and of one Jurassic dolerite from Ivory-Coast were carried out. The Early Jurassic SSW-NNE trending dykes have doleritic aphyric or gabbroic phyric texture. Their chemical compositions, slightly under-saturated to over-saturated, show moderate to low Mg-ratios (63-36), high TiO 2 contents (1.85-3.56 wt.%), weak rare earth element fractionation [1.8isotopic data of Bertrand et al. [Bertrand, H., Liegeois, J.P., Deckart, K., Féraud, G., 1999. High-Ti tholeiites in Guinea and Their Connection with the Central Atlantic CFB Province: Elemental and Nd-Sr-Pb Isotopic Evidence for Preferential Zone of Mantle Upwelling in Cause of Rifting. AGU spring meeting (Abst. p 317)] suggest that their magmatic source is different from that of the other basalts of the Central Atlantic Magmatic Province (CAMP). Such signatures are restricted to a central zone coinciding with the Panafrican Rokelides suture. We propose a model of sub-lithospheric preferential channelling of an asthenospheric ascent in this zone. Two other groups of dykes were identified in French Guyana. Compared to the Jurassic ones the Proterozoic dykes have NNW-SSE and E-W trending direction, more important LILE enrichment, low TiO 2 contents (<2 wt%) and Nb-Ta negative anomalies. Their calc-alkaline signature could be the result of a previous subduction and may be related to the 1800 Ma Venturi-Tapajós event, which contaminated the mantle source.

  8. Decoupling of whole-rock Nd-Hf and zircon Hf-O isotopic compositions of a 284 Ma mafic-ultramafic intrusion in the Beishan Terrane, NW China

    Science.gov (United States)

    Su, Ben-Xun; Qin, Ke-Zhang; Lu, Ying-Huai; Sun, He; Sakyi, Patrick Asamoah

    2015-10-01

    Abundant Permian mafic-ultramafic intrusions in the Beishan Terrane, NW China, are parts of the Tarim large igneous province. Among these intrusions, Luodong intrusion is composed of dunite, wehrlite and gabbro. These rocks have whole-rock Sr-Nd-Hf and zircon Hf-O isotope compositions that display significant decoupling. The decoupling of these generally well-correlated systems demonstrates contrasting evolving trends. Systematic compositional and mineralogical controls on decoupling have been investigated. Wehrlites and gabbros show MORB-like trace element patterns with negligible crustal contamination. They have high initial 143Nd/144Nd [ɛNd(t) = +6.6 to +11.2] and 176Hf/177Hf [ɛHf(t) = +12.2 to +16.9] and low initial 87Sr/86Sr [(87Sr/86Sr)i = 0.702949-0.704098] ratios and plot within the MORB field, indicating that their parental magmas were derived from a depleted mantle source. The enrichment features are present in the zircon crystals separated from the gabbro. These homogeneously unzoned zircon crystals have high U concentrations, low Th/U ratios and a U-Pb age of 284.0 ± 2.3 Ma. They are therefore interpreted as having formed rapidly in a highly fractionated/evolved magma. Their ɛHf(t) and δ18O values range from -9.3 to -6.7 and +10.25 ‰ to +11.42 ‰, respectively. The decoupling is linked with crustal contamination by ancient crust (probably Proterozoic schist in the Beishan Terrane) that occurred during zircon crystallization. However, the contamination signature in the whole-rock composition was soon overprinted by magma mixing process. The inference is evidenced by zoning textures preserved in plagioclase, clinopyroxene, spinel and particularly olivine, and the presence of coeval diabase dykes cutting through the intrusion. The isotope decoupling observed in this mantle-plume-related mafic-ultramafic intrusion supports the idea that Nd-Hf decoupling and Lu/Hf and Sm/Nd parent/daughter variations exist only on a small hand-size scale in a

  9. Sentinel-1 TOPS interferometry for geophysical applications: Dyke intrusion imaged during 2014 Pico do Fogo eruption

    Science.gov (United States)

    Gonzalez, Pablo J.; Marinkovic, Petar; Samsonov, Sergey; Hooper, Andrew; Larsen, Yngvar; Wright, Tim

    2015-04-01

    apply Sentinel-1 TOPS-InSAR to illuminate the deformation accompanying a recent volcanic eruption at Pico do Fogo volcano, Fogo (Cape Verde). The detected deformation is consistent with a shallow near-vertical dyke intrusion, which fed the fissure eruption. The modelling of the deformation interferograms do not seem affected largely by the variable LoS vector, in this case. The presented results prove the potential of Terrain observation by progressive scans (TOPS) interferometry for geophysical applications, in particular using ESA Sentinel-1 mission.

  10. P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications

    Institute of Scientific and Technical Information of China (English)

    HU Daogong; WU Zhenhan; JIANG Wan; YE Peisheng

    2004-01-01

    Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (Mi) is preserved only in the granulites and represented by plagioclase+homblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of gamet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of horublende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of homblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of gamet+clinopyroxene+plagioclase+homblende were estimated at 769-905°C and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800°C and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708°C and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.

  11. 北疆二叠纪镁铁-超镁铁岩铜、镍矿床的构造背景、岩体类型、基本特征、相对剥蚀程度、含矿性评价标志及成矿潜力分析%The Tectonic Setting, Style, Basic Feature, Relative Erosion Deee, ore-Bearing Evaluation Sign, Potential Analysis of Mineralization of Cu-Ni-Bearing Permian Mafic-ultramafic Complexes, Northern Xinjiang

    Institute of Scientific and Technical Information of China (English)

    秦克章; 邓刚; 唐冬梅; 苏本勋; 毛亚晶; 薛胜超; 田野; 孙赫; 三金柱; 肖庆华

    2012-01-01

    -ultramafic intrusions, can determine the relative erosion degree of the deposits synthetically. The relative erosion degree in combination with the regional element geochemical and geophysics anomalies, are the effective measures to evaluate the Cu-Ni mineralization potential in mafic-ultramafic complexes. Mafic dykes, small intrusion, ultramafic outcrop in large mafic-ultramafic complex, strongly altered mafic-ultramafic intrusive rocks, gravity and magnetic anomaly zone superimposed geochemical anomalies, are the important target for finding small intrusion with large scale magmatic Cu-Ni sulfide deposits.

  12. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of Central Chile

    OpenAIRE

    Wes Hildreth; Brad Singer; Estanislao Godoy; Francisco Munizaga

    1998-01-01

    ABSTRACT Cerro Campanario, a towering landmark on the continental divide near Paso Pehuenche, is a glacially eroded remnant of a mafic stratovolcano that is much younger than previously supposed. Consisting of fairly uniform basaltic andesite, rich in olivine and plagioclase, the 10-15 km³ edifice grew rapidly near the end of the middle Pleistocene, about 150-160 ka, as indicated by 40Ar/39Ar and unspiked K-Ar analyses of its lavas.La edad y formación del cerro Campanario, un estratovolcán má...

  13. The stable vanadium isotope composition of the mantle and mafic lavas

    Science.gov (United States)

    Prytulak, J.; Nielsen, S. G.; Ionov, D. A.; Halliday, A. N.; Harvey, J.; Kelley, K. A.; Niu, Y. L.; Peate, D. W.; Shimizu, K.; Sims, K. W. W.

    2013-03-01

    Vanadium exists in multiple valence states under terrestrial conditions (2+, 3+, 4+, 5+) and its isotopic composition in magmas potentially reflects the oxidation state of their mantle source. We present the first stable vanadium isotope measurements of 64 samples of well-characterized mantle-derived mafic and ultramafic rocks from diverse localities. The δ51V ranges from -0.27‰ to -1.29‰, reported relative to an Alfa Aesar (AA) vanadium solution standard defined as 0‰. This dataset is used to assess the effects of alteration, examine co-variation with other geochemical characteristics and define a value for the bulk silicate Earth (BSE). Variably serpentinised peridotites show no resolvable alteration-induced δ51V fractionation. Likewise, altered mafic oceanic crustal rocks have identical δ51V to fresh hand-picked MORB glass. Intense seafloor weathering can result in slightly (˜0.2-0.3‰) heavier isotope compositions, possibly related to late-stage addition of vanadium. The robustness of δ51V to common alteration processes bodes well for its potential application to ancient mafic material. The average δ51V of mafic lavas, including MORB, Icelandic tholeiites and lavas from the Shatsky Rise large igneous province is -0.88±0.27‰ 2sd. Peridotites show a large range in primary δ51V (-0.62‰ to -1.17‰), which co-varies positively with vanadium concentrations and indices of fertility such as Al2O3. Although these data suggest preferential extraction of heavier isotopes during partial melting, the isotope composition of basalts (δ51V=-0.88±0.27‰ 2sd) and MORB glass in particular (δ51V=-0.95±0.13‰ 2sd) is lighter than fertile peridotites and thus difficult to reconcile with a melt extraction scenario. Determination of fractionation factors between melt and mineral phases such as pyroxenes and garnet are necessary to fully understand the correlation. We arrive at an estimate of δ51VBSE=-0.7±0.2‰ (2sd) for the bulk silicate Earth by averaging

  14. A 100 Ma bimodal composite dyke complex in the Jiamusi Block, NE China: An indication for lithospheric extension driven by Paleo-Pacific roll-back

    Science.gov (United States)

    Sun, Ming-Dao; Chen, Han-Lin; Zhang, Feng-Qi; Wilde, Simon A.; Dong, Chuan-Wan; Yang, Shu-Feng

    2013-03-01

    A 125 m-wide bimodal composite dyke complex, consisting of rhyolite and dolerite dykes, was emplaced into Cretaceous volcanic strata of the Songmuhe Formation in the Jiamusi Block of NE China. The dolerite dykes are sub-vertical, strike north-south, and intruded into both the country rocks and rhyolite dykes soon after the latter solidified. SHRIMP zircon U-Pb dating shows that the rhyolite dykes were emplaced at 100 ± 2 Ma and the dolerite dykes were also most likely emplaced at 100 ± 2 Ma. The rhyolite is characterized by enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and depletion in high-field strength elements (HFSE). It shows a significant negative Eu anomaly, and has ɛNd(t) values ranging from 0.49 to 1.66 and two groups of initial 87Sr/86Sr ratios at 0.7045 and 0.7061. The rhyolite displays the compositional signature of Peraluminous Ferroan Granitoid, indicating it was derived by either differentiation of basalt and/or low pressure partial melting of crust. The dolerite is also characterized by enrichment in LILE and LREE, and depletion in HFSE. It has a weak negative Eu anomaly and has ɛNd(t) = - 1.22 to + 3.26, and (87Sr/86Sr)i = 0.7057-0.7074. The dolerite originated from partial melting of lithospheric mantle which was affected by subducted oceanic crust, and experienced different amounts of crustal contamination. Such bimodal dyke complexes are an important indicator of crustal extension under the influence of mantle processes. Thus the dyke complex in the Jiamusi Block indicates mid-Cretaceous intra-plate extension in NE China related to the subduction of the paleo-Pacific plate along the eastern Eurasian continental margin. When compared with Mesozoic bimodal magmatism further to the west, our new data support a temporal eastward migration of magmatism over a distance > 1000 km from ~ 160 Ma to ~ 100 Ma. This was most likely associated with roll-back of the paleo-Pacific Plate and consequent upwelling of

  15. Tectonic accretion and underplating of mafic terranes in the Late Eocene intraoceanic fore-arc of New Caledonia (Southwest Pacific): geodynamic implications

    OpenAIRE

    Cluzel, Dominique; Aitchison, Jonathan C.; Picard, Christian

    2001-01-01

    This paper deals with the tectonic events that result in the accretion of mafic terranes in the fore-arc region and a close juxtaposition of ultramafic rocks, low grade and high-grade mafic terranes in many collisional orogens. The example is taken from New Caledonia where tectonic accretion, subduction, underplating and obduction of mafic terranes took place during the late Eocene in an intra-oceanic forearc setting. The late Eocene tectonic complex comprised three major terranes: an overlyi...

  16. Study on Carbonate Limestone Dykes (Neptunian Dykes) of Upper Devonian in Nanbiancun, Guilin, Guangxi%广西桂林南边村上泥盆统沉积灰岩脉研究

    Institute of Scientific and Technical Information of China (English)

    彭阳; 陆刚; 胡贵昂

    2013-01-01

    、亮晶胶结物、铁泥质等,与孔隙水混合形成粘稠的液化颗粒灰岩流,灌入这些张裂隙.二者裂隙成因均与台缘同沉积断层的构造—地震活动密切相关.即:同沉积断层发生时,在南边村剖面层45中产生刚性张裂隙,而其上覆地层的沉积物还处在弱固结的塑性状态,发生混合、颗粒化形成塑性液化颗粒流灌入下伏裂隙中.因此,南边村剖面层45中的沉积灰岩脉是软硬岩层对同沉积断层活动诱发地震的不同响应.而南边村剖面晚泥盆世所处的台缘靠近斜坡的古地理位置是其沉积灰岩脉的内部结构构造与众不同的原因.%Carbonate neptunian dykes occurred commonly in Late Palaeozoic carbonate plateform margins in Guilin and Northwestern Youjiang basin, Guangxi Autonomous Region. In the Nanbiancun International Devonian- Carboniferous (bed 55 ~ 56) Boundary (DCB) Parastratotype Section of Guilin of Guangxi, carbonate neptunian dykes are identified in Bed 45 (a liquefied grainstone vein) and Bed 50 (some fine crystal fiber calcite veins, as signal of tension structure background) and is considered far different from those in the Miaotou section of Guilin and Youjiang Basin. In the Miaotou section of Guilin and the Youjiang Basin, the infillings of neptunian dyke are afterwards normal sea water sediments, while in the Nanbiancun section of Guilin are simultaneous overlain liquefied soft-sediment-flow, shown as skeletals and non-skeletal grains ( with dark Fe-bearing clays, fine calcites and fine skeletals) mixture. The non-skeletal grains deformed and impinged each other with very few cements among them That means they are not normal sea water deposits. The skeletal grains are mainly brachiopod and crinoid stems crowded floating in non-skeletal grains. A single Brachiopods shell are folded as "U" shape and then cut into several continuous parts in situ. That means a slowly soft press surrounding and wholly flowing. The upper part of the

  17. Hydrogeochemistry of deep groundwaters of mafic and ultramafic rocks in Finland

    Energy Technology Data Exchange (ETDEWEB)

    Ruskeeniemi, T.; Blomqvist, R.; Lindberg, A.; Ahonen, L. [Geological Survey of Finland, Espoo (Finland); Frape, S. [Waterloo Univ., ON (Canada)

    1996-12-01

    The present work reports and interprets the hydrogeochemical and hydrogeological data obtained from deep groundwaters in various mafic-ultramafic formations in Finland. The work is mainly based on the results of the research project `Geochemistry of deep groundwaters` financed by the Ministry of Trade and Industry and the Geological Survey of Finland. Five sites were selected for this study: (1) Juuka, (2) Keminmaa, (3) Maentsaelae, (4) Ranua, and (5) Ylivieska. Keminmaa and Ranua are located in Early Proterozoic layered intrusions dated at 2.44 Ga. The Juuka site lies within the massive Miihkali serpentinite, which is thought to represent the ultramafic part of a Proterozoic (1.97 Ga) ophiolite complex. The Maentsaelae gabbro represents the deep parts of the Svecofennian volcanic sequence, while the Ylivieska mafic-ultramafic intrusion is one of a group of Svecokarelian Ni-potential intrusions 1.9 Ga in age. For reference, groundwaters from four other sites are also briefly described. Three of these sites are located within the nickel mining regions of Enonkoski, Kotalahti and Vammala, while the fourth is a small Ni mineralization at Hyvelae, Noormarkku. The four reference sites are all of Svecokarelian age. (refs.).

  18. Oxygen isotopes of some trondhjemites, siliceous gneisses, and associated mafic rocks

    Science.gov (United States)

    Barker, F.; Friedman, I.; Hunter, D.R.; Gleason, J.D.

    1976-01-01

    Analyses of oxygen isotopes in whole-rock samples of 58 Precambrian and Phanerozoic trondhjemites and siliceous gneisses and of 28 cogenetic mafic to intermediate rocks from North America, Fennoscandia, and southern Africa give the following results: 1. (1) 47 trondhjemites, tonalites, and mostly Archean acidic gneisses that apparently are not isotopically disturbed show an overage ?? 15O of +7.3??? and a range of 5.2-8.9???; 11 other samples are slightly to moderately disturbed and show higher values; and 2. (2) the mafic rocks show a wide range of ??-values, from about 0-9??? but the undisturbed ones give an average ?? 18O of 5.2???. The ?? 18O values of the trondhjemitic intrusives and siliceous gneisses of similar composition are lower than those of most granitic rocks and support models for derivation of these rocks from basaltic parents. This approach, however, cannot be used to determine if individual bodies formed by differentiation or by partial melting. ?? 1976.

  19. Hydrogeochemistry of deep groundwaters of mafic and ultramafic rocks in Finland

    International Nuclear Information System (INIS)

    The present work reports and interprets the hydrogeochemical and hydrogeological data obtained from deep groundwaters in various mafic-ultramafic formations in Finland. The work is mainly based on the results of the research project 'Geochemistry of deep groundwaters' financed by the Ministry of Trade and Industry and the Geological Survey of Finland. Five sites were selected for this study: (1) Juuka, (2) Keminmaa, (3) Maentsaelae, (4) Ranua, and (5) Ylivieska. Keminmaa and Ranua are located in Early Proterozoic layered intrusions dated at 2.44 Ga. The Juuka site lies within the massive Miihkali serpentinite, which is thought to represent the ultramafic part of a Proterozoic (1.97 Ga) ophiolite complex. The Maentsaelae gabbro represents the deep parts of the Svecofennian volcanic sequence, while the Ylivieska mafic-ultramafic intrusion is one of a group of Svecokarelian Ni-potential intrusions 1.9 Ga in age. For reference, groundwaters from four other sites are also briefly described. Three of these sites are located within the nickel mining regions of Enonkoski, Kotalahti and Vammala, while the fourth is a small Ni mineralization at Hyvelae, Noormarkku. The four reference sites are all of Svecokarelian age. (refs.)

  20. K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China:Implications for Crustal Extension

    Institute of Scientific and Technical Information of China (English)

    LIU Shen; HU Ruizhong; ZHAO Junhong; FENG Caixia

    2004-01-01

    Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province.Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively.

  1. Dyke leakage localization and hydraulic permeability estimation through self-potential and hydro-acoustic measurements: Self-potential 'abacus' diagram for hydraulic permeability estimation and uncertainty computation

    Science.gov (United States)

    Bolève, A.; Vandemeulebrouck, J.; Grangeon, J.

    2012-11-01

    In the present study, we propose the combination of two geophysical techniques, which we have applied to a dyke located in southeastern France that has a visible downstream flood area: the self-potential (SP) and hydro-acoustic methods. These methods are sensitive to two different types of signals: electric signals and water-soil pressure disturbances, respectively. The advantages of the SP technique lie in the high rate of data acquisition, which allows assessment of long dykes, and direct diagnosis in terms of leakage area delimitation and quantification. Coupled with punctual hydro-acoustic cartography, a leakage position can be precisely located, therefore allowing specific remediation decisions with regard to the results of the geophysical investigation. Here, the precise localization of leakage from an earth dyke has been identified using SP and hydro-acoustic signals, with the permeability of the preferential fluid flow area estimated by forward SP modeling. Moreover, we propose a general 'abacus' diagram for the estimation of hydraulic permeability of dyke leakage according to the magnitude of over water SP anomalies and the associated uncertainty.

  2. Palaeomagnetism of Precambrian dyke swarms in the North China Shield: The ˜1.8 Ga LIP event and crustal consolidation in late Palaeoproterozoic times

    Science.gov (United States)

    Piper, John D. A.; Jiasheng, Zhang; Huang, Baochung; Roberts, Andrew P.

    2011-06-01

    The North China Shield (NCS) is cut by a laterally-extensive dyke swarm emplaced at 1.78-1.76 Ga when an extensional regime succeeded regional metamorphism and completion of cratonisation by ˜1.85 Ga. Palaeomagnetic study of these dykes and adjoining metamorphic country rocks identifies a dominant shallow axis comprising a contiguous population with NE to N declinations and rare opposite polarity. Dykes with NE shallow magnetic declination (A1, D/ I = 36/-1°) recognised from previous study and emplaced in granulite terranes in the north are displaced by more northerly declinations (A2, D/ I = 8/2°) in lower grade metamorphic terranes to the south. Contact tests indicate a primary cooling-related origin to these magnetisations although tests are in part ambiguous because magnetisations in the granulite basement are comparable. Petrologic and rock magnetic considerations imply that magnetisation of the dykes occurred during uplift from depths as deep as 20 km following the peak of metamorphism at ˜1.85 Ga. A temporal migration A2 → A1 is implied by the higher crustal level and earlier acquisition of the former, and the deeper source and later acquisition of the latter. A third population of dyke magnetisations (A3, D/ I = 18/43°) is distributed towards steeper inclinations and close to the Mesozoic-Recent palaeofield. These are either partial or complete overprints of A1-A2 magnetisations with greater degrees of alteration indicated by demagnetisation and thermomagenetic spectra, or are much younger dykes of Mesozoic-Tertiary age. A minority fourth (later Precambrian but presently undated) dual polarity population has a magnetisation (11 dykes, D/ I = 108/7°) with contact tests indicating a primary cooling-related origin. The ˜1.78-1.76 Ga time of emplacement of the dominant dyke swarms in this study is widely represented by contemporaneous igneous rocks in other major shields linked to major Large Igneous Province (LIP)-related events. The new definition of

  3. Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

    Science.gov (United States)

    Freymuth, Heye; Ivko, Ben; Gill, James B.; Tamura, Yoshihiko; Elliott, Tim

    2016-08-01

    We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series (238U/232Th, 230Th/232Th and 226Ra/230Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238U to 230Th, this results in elevated (230Th/232Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high (230Th/232Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from (230Th/232Th) = 1.2-2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments.

  4. Postcollisional mafic igneous rocks record recycling of noble gases by deep subduction of the continental crust

    Science.gov (United States)

    Dai, Li-Qun; Zheng, Yong-Fei; He, Huai-Yu; Zhao, Zi-Fu

    2016-05-01

    Recycling of noble gases from crustal rocks into the mantle is indicated not only by oceanic basalts and mantle xenoliths, but also by ultrahigh-pressure metamorphic rocks in collisional orogens. It is intriguing whether noble gases in continental crust were recycled into the mantle by deep subduction of the continental crust to mantle depths. Here we firstly report the He, Ne and Ar isotopic compositions of pyroxene from postcollisional mafic igneous rocks in the Dabie orogen, China. The results show that the pyroxene separates from the mafic rocks have low 3He/4He ratios of 0.002 to 1.8 Ra and air-like Ne isotope compositions. Furthermore, the pyroxene exhibits low 40Ar/36Ar ratios of 393.6 to 1599.8, close to those of the air. In combination with whole-rock geochemistry it is found that pyroxene 3He/4He ratios are correlated with whole-rock (La/Yb)N and Sr/Y ratios, εNd(t) values and MgO contents. These observations demonstrate the mass transfer from the deeply subducted continental crust to the overlying mantle wedge, recording the source mixing between the crust-derived melt and the mantle peridotite in the continental subduction zone. A direct addition of the crustal He via crust-derived melt to the mantle leads to the extremely low 3He/4He ratios in the orogenic lithospheric mantle, and the dissolved atmospheric Ar and Ne in the subducted supracrustal rocks results in the air-like Ar and Ne isotope ratios. Therefore, the noble gas isotopic signatures of supracrustal rocks were carried into the mantle by the continental deep subduction to subarc depths and then transferred to the postcollisional mafic igneous rocks via the melt-peridotite reaction at the slab-mantle interface in a continental subduction channel. Our finding firstly establishes the slab-mantle interaction model for recycling of supracrustal noble gases in the continental subduction zone.

  5. Metamorphic reactions, grain size reduction and deformation of mafic lower crustal rocks

    Science.gov (United States)

    Degli Alessandrini, Giulia; Menegon, Luca; Beltrando, Marco; Dijkstra, Arjan; Anderson, Mark

    2016-04-01

    This study investigates grain-scale deformation mechanisms associated with strain localization in the mafic continental lower crust, with particular focus on the role of syn-kinematic metamorphic reactions and their product - symplectites - in promoting grain size reduction and phase mixing. The investigated shear zone is hosted in the Finero mafic-ultramafic complex in the Italian Southern Alps. Shearing occurred at T ≥ 650° C and P ≥ 0.4-0.6 GPa. The shear zone reworks both mafic and ultramafic lithologies and displays anastomosing patterns of (ultra)mylonitic high strain zones wrapping less foliated, weakly deformed low strain domains. Field and microstructural observations indicate that different compositional layers of the shear zone responded differently to deformation, resulting in strain partitioning. Four distinct microstructural domains have been identified: (1) an ultramylonitic domain characterized by an amph + pl matrix (grain size size between 200μm and 5000μm) and rare garnets; (2) a domain rich in garnet porphyroclasts embedded in a matrix of monomineralic plagioclase displaying a core and mantle structure (average grain size 45μm) (3) a metagabbroic domain with porphyroclasts of clinopyroxene, orthopyroxene and garnets (200μm average grain size) wrapped by monomineralic ribbons of recrystallized plagioclase and (4) a garnet-free ultramylonitic domain composed of an intermixed amph + cpx + opx + pl matrix (6μm average grain size). In these domains, each porphyroclastic mineral responds differently to deformation: amphibole readily breaks down to symplectitic intergrowths of amph + pl or opx + pl. Garnet undergoes fracturing (in domain 2) or reacts to give symplectites of pl + opx (in domain 3). Plagioclase dynamically recrystallizes in mono-phase aggregates, whereas clinopyroxene undergoes fracturing and orthopyroxene undergoes plastic deformation. The behaviour of the different phases and their relative abundance in the layers are

  6. Impacts of dyke development in flood prone areas in the Vietnamese Mekong Delta to downstream flood hazard

    Science.gov (United States)

    Khanh Triet Nguyen, Van; Dung Nguyen, Viet; Fujii, Hideto; Kummu, Matti; Merz, Bruno; Apel, Heiko

    2016-04-01

    The Vietnamese Mekong Delta (VMD) plays an important role in food security and socio-economic development of the country. Being a low-lying coastal region, the VMD is particularly susceptible to both riverine and tidal floods, which provide, on (the) one hand, the basis for the rich agricultural production and the livelihood of the people, but on the other hand pose a considerable hazard depending on the severity of the floods. But despite of potentially hazardous flood, the area remain active as a rice granary due to its nutrient-rich soils and sediment input, and dense waterways, canals and the long standing experience of the population living with floods. In response to both farmers' requests and governmental plans, the construction of flood protection infrastructure in the delta progressed rapidly in the last twenty years, notably at areas prone to deep flooding, i.e. the Plain of Reeds (PoR) and Long Xuyen Quadrangle (LXQ). Triple rice cropping becomes possible in farmlands enclosed by "full-dykes", i.e. dykes strong and high enough to prevent flooding of the flood plains for most of the floods. In these protected flood plains rice can be grown even during the peak flood period (September to November). However, little is known about the possibly (and already alleged) negative impacts of this fully flood protection measure to downstream areas. This study aims at quantifying how the flood regime in the lower part of the VMD (e.g. Can Tho, My Thuan, …) has been changed in the last 2 recent "big flood" events of 2000 and 2011 due to the construction of the full-dyke system in the upper part. First, an evaluation of 35 years of daily water level data was performed in order to detect trends at key gauging stations: Kratie: upper boundary of the Delta, Tan Chau and Chau Doc: areas with full-dyke construction, Can Tho and My Thuan: downstream. Results from the Mann-Kendall (MK) test show a decreasing trend of the annual maximum water level at 3 stations Kratie, Tan

  7. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

    Science.gov (United States)

    Tang, Ming; Chen, Kang; Rudnick, Roberta L

    2016-01-22

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. PMID:26798012

  8. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

    Science.gov (United States)

    Tang, Ming; Chen, Kang; Rudnick, Roberta L

    2016-01-22

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago.

  9. Neogene to Recent Mafic Volcanism in Death Valley Reveals Architecture of Deep Mojavia Lithosphere

    Science.gov (United States)

    Rämö, O. T.; Calzia, J.

    2015-12-01

    At 10-0 m.y., the evolution of the Death Valley region, SE California, was characterized by repeated extrusion of mafic and intermediate lavas. The volume of these lavas appears to have diminished with time, from the relatively extensive (now faulted) Sheephead, Death Valley, Shoshone, and Funeral basalts to small monogenic volcanic centers (Split Cinder Cone, Ubehebe). A common denominator of these lavas is their transitional alkaline character (in general, trachybasalts to trachydacites with Na > K), relatively low MgO (1.5 to 6 wt.%), varying Fe2O3(tot) (4 to 12 wt.%) and Ni (10 to 80 ppm). They are all strongly enriched in the LREE: Chondrite-normalized La/Yb varies between 10 and 28, with the earlier, more voluminous lavas being less enriched (10 to 18) than the youngest volcanics (27 to 28). The initial Nd isotope composition of the lavas is outstandingly varying and does not correlate with fractionation stage. Their epsilon-Nd values vary from -10 to -2 and none of them thus registers a major asthenospheric component. Overall, these transitional mafic magmas probably represent relatively low-degree melts from the subcontinental lithosphere underneath the cratonic Mojavia crust. The 147Sm/144Nd ratios of the lavas show a restricted range (0.0930 to 0.1140) and, together with the measured 143Nd/144Nd ratios of the lavas, define Meso- to Neoproterozoic depleted mantle model ages between 800 and 1200 Ma. These have now spatial control across the Death Valley region and are clearly lower than those measured for the exposed craton. This suggest that the Mojavia cratonic mantle lithosphere may be a random amalgamation of ultramafic domains that vary in the degree of metasomatism and rejuvenation.

  10. Genesis of Soils Formed from Mafic Igneous Rock in the Atlantic Forest Environment

    Directory of Open Access Journals (Sweden)

    Adailde do Carmo Santos

    2016-01-01

    Full Text Available ABSTRACT Different parent materials participate in the formation of soils in the hilly landscape of “Mar de Morros” in the Atlantic Forest environment. Those derived from mafic igneous rock (gabbro frequently show erosion problems because of land use, which is aggravated by the mountainous relief and soil attributes. This study evaluated the main pedogenic processes of soils formed from mafic igneous rock (gabbro in a toposequence in Pinheiral (RJ by characterizing physical, chemical, mineralogical and micromorphological attributes. The profiles are located at different sections in the toposequence: summit (P1, shoulder (P2, backslope (P3 and footslope (P4.They were classified according to the Brazilian System of Soil Classification (SiBCS and correlated to Soil Taxonomy. The soil morphology of profiles P2, P3 and P4 is expressed by a brownish-red color, blocky structure with high to moderate development, clay films and clay loam to clay texture, with a textural B horizon. P1 shows less development, with a shallow profile and the sequence of horizons A-C-Cr. The soils have a slightly low degree of weathering, identified by the presence of pyroxenes and feldspars in the sand fraction and montorillonite in the clay fraction; the sum of bases is from 15 to 24 cmolc kg-1; and cation exchange capacity (CEC is from 12 to 22 cmolc kg-1. A significant presence of clay skins was observed in the field and was confirmed by thin section analysis, which showed features such as argillans, ferriargillans and iron nodules. The soil profile at the summit (P1 was classified as Neossolo Regolítico Órtico (Typic Udorthents, and the other profiles as Chernossolo Argilúvicos Órticos (Typic Argiudolls.

  11. Sinking mafic body in a reactivated lower crust: A mechanism for stress concentration at the New Madrid seismic zone

    Science.gov (United States)

    Pollitz, F.F.; Kellogg, L.; Burgmann, R.

    2001-01-01

    We propose a geodynamic model for stress concentration in the New Madrid seismic zone (NMSZ). The model postulates that a high-density (mafic) body situated in the deep crust directly beneath the most seismically active part of the NMSZ began sinking several thousands of years ago when the lower crust was suddenly weakened. Based on the fact that deformation rates in the NMSZ have accelerated over the past 9 k.y., we envision the source of this perturbation to be related to the last North American deglaciation. Excess mass of the mafic body exerts a downward pull on the elastic upper crust, leading to a cycle of primary thrust faulting with secondary strike-slip faulting, after which continued sinking of the mafic body reloads the upper crust and renews the process. This model is consistent with the youth of activity, the generation of a sequence of earthquakes, and the velocity evolution during interseismic periods, which depend upon the density contrast of the mafic body with respect to the surrounding crust, its volume, and the viscosity of the lower crust.

  12. Contrasting Peridotite Types in the Dabie UHP Belt, Eastern China: the Raobazhai and Bixiling Ultramafic-mafic Complex

    Institute of Scientific and Technical Information of China (English)

    Jianping Zheng; Min Sun; W. L. Griffin; Mei-Fu Zhou; Guochun Zhao

    2007-01-01

    @@ The Dabie UHP metamorphic belt, central China,contains two contrasting types of mafic-ultramafic complex. The Bixiling peridotite in the southern Dabie terrane contains abundant garnet (21.1-32.2 vol% )and thus has high CaO + Al2O3 (9.81-15.9 wt% ).

  13. Geological and Geochemical Characteristics of Early Cretaceous Mafic Dikes in Northern Jiangxi Province, SE China and Their Geodynamic Implications

    Institute of Scientific and Technical Information of China (English)

    XIE Guiqing; HU Ruizhong; MAO Jingwen; LI Ruiling; CAO Jinjian; JIANG Guohao; QI Liang

    2005-01-01

    The development of Early Cretaceous mafic dikes in northern and southern Jiangxi allows an understanding of the geodynamic setting and characteristics of the mantle in southeast China in the Cretaceous. Geological and geochemical characteristics for the mafic dikes from the Wushan copper deposit and No. 640 uranium deposit are given in order to constrain the nature of source mantle, genesis and tectonic implications. According to the mineral composition,the mafic dikes in northern Jiangxi can be divided into spessartite and olive odinite types, which belong to slightly potassium-rich calc-alkaline lamprophyre characterized by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), large depletion in high strength field elements (HSFE) and with negative Nb, Ta and Ti anomalies, as well as 87Sr/86Sr ratios varying from 0.7055 to 0.7095 and 143Nd/144Nd ratios varying from 0.5119 to 0.5122.All features indicate that the magma responsible for the mafic dikes was derived mainly from metasomatic lithosphere mantle related to dehydration and/or upper crust melting during subduction. Differences in geochemical characteristics between the mafic dikes in northern Jiangxi and the Dajishan area, southern Jiangxi were also studied and they are attributed to differences in regional lithosphefic mantle components and/or magma emplacement depth. Combining geological and geochemical characteristics with regional geological history, we argue that southeast China was dominated by an extensional tectonic setting in the Early Cretaceous, and the nature of the mantle source area was related to enrichment induced by asthenosphere upwelling and infiltration of upper crust-derived fluids responding to Pacific Plate subduction.

  14. P-T history and geochemical characteristics of mafic granulites and charnockites from west of Periya, North Kerala, southern India

    Science.gov (United States)

    Prakash, D.; Chandra Singh, P.; Arima, M.; Singh, Triveni

    2012-11-01

    The study region forms the northern part of Kerala (south India) and constitutes part of granulite-facies rocks of the exhumed Proterozoic south Indian Granulite Terrain (SGT). The SGT consists of a large variety of rock types with a wide range of mineral parageneses and chemical compositions, namely charnockite, mafic granulite, gneiss, schist, anorthosite, granite and minor meta-sedimentary rocks. Garnet-bearing mafic granulites occur as small enclaves within charnockites. We report for the first time P-T constraints on the prograde path preceding peak metamorphism in the northernmost part of Kerala. An increase of the Mg, Fe and decrease of Ca and Mn contents from the core towards the rim of garnet in the mafic granulites suggest prograde garnet growth. The prograde path was followed by peak metamorphism at a temperature of c. 800 °C and a pressure of c. 7.5 kbar as computed by isopleths of XMg garnet, XCa garnet and XAn plagioclase. The resorption of garnet in various reaction textures and the development of spectacular orthopyroxene-plagioclase, biotite-quartz and hornblende-plagioclase symplectites characterize the subsequent stages of metamorphism. The PT path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust. Diffusion modeling of Fe-Mg exchange between garnet and hornblende suggests a near-peak cooling rate of 10-70 °C/myr. Such cooling rates are too high to be accounted for by normal isostatic uplift and erosion and suggest that the terrain was tectonically exhumed. Charnockites are richer in SiO2 and lower in MgO and CaO when compared to mafic granulites. Their REE patterns are relatively flat and show prominent negative europium anomalies. The mafic granulites are metamorphosed tholeiitic basalts as revealed by major- and trace-element geochemistry.

  15. Magmatism and metamorphism at the sheeted dyke-gabbro transition zone: new insight from beerbachite from ODP/IODP Hole 1256D and Oman ophiolite

    Science.gov (United States)

    Python, Marie; Abily, Bénédicte; France, Lydéric

    2014-05-01

    During IODP Expedition 335, two-pyroxenes bearing granulites (beerbachites) were extensively recovered as drilling cuttings at the gabbro-sheeted dyke transition zone of ODP Hole 1256D (East Pacific Rise, 6°44.163'N, 91°56.061'W). This lithology results from high-temperature metamorphism of previously hydrothermally altered diabases, basalts and/or gabbros; the heat source likely stems from the melt lens located at the top of the magmatic chambers imaged along present-day fast-spreading ridges. This lithology, associated with gabbroic bodies, characterises the transition zone between the sheeted dyke complex and the uppermost gabbroic section and represents the interface between magmatic and hydrothermal convecting systems in an oceanic crust formed at fast-spreading ridges. Samples acquired during IODP Exp. 335 show a particularly high degree of recrystallisation and are characterised by the absence of hydrous phases like amphibole, suggesting very high-T metamorphism. The Beerbachites mineral chemical characteristics are rather homogeneous compared to gabbros or dolerite from the sheeted dyke but pyroxenes Mg#, Ti, Al and Cr contents as well as the anorthite content of plagioclase are closer to gabbro than dolerite. This similarity may be explained by two hypothesis: either beerbachites in Hole 1256D are metamorphosed gabbros, or they underwent a melt-rock reaction process with the gabbros parental magma and were re-equilibrated at high temperature until their mineral composition become similar to that of gabbros. The gabbro-sheeted dyke transition zone in the Oman ophiolite is also outlined by the presence of high grade metamorphic rocks. Fine grained granulites and amphibolites that may be derived from the transformation of altered sheeted dyke diabases are in direct contact with fresh gabbroic and troctolitic bodies which are themselves cross-cut by dolerite dykes. The observation of textures show that high-T recrystallisation occurred in the fine grained

  16. Mantle evolution in the Variscides of SW England: Geochemical and isotopic constraints from mafic rocks

    Science.gov (United States)

    Dupuis, Nicolle E.; Murphy, J. Brendan; Braid, James A.; Shail, Robin K.; Nance, R. Damian

    2016-06-01

    The geology of SW England has long been interpreted to reflect Variscan collisional processes associated with the closure of the Rhenohercynian Ocean and the formation of Pangea. The Cornish peninsula is composed largely of Early Devonian to Late Carboniferous volcanosedimentary successions that were deposited in pre- and syn-collisional basins and were subsequently metamorphosed and deformed during the Variscan orogeny. Voluminous Early Permian granitic magmatism (Cornubian Batholith) is broadly coeval with the emplacement of ca. 280-295 Ma lamprophyric dykes and flows. Although these lamprophyres are well mapped and documented, the processes responsible for their genesis and their relationship with regional Variscan tectonic events are less understood. Pre- to syn-collisional basalts have intra-continental alkalic affinities, and have REE profiles consistent with derivation from the spinel-garnet lherzolite boundary. εNd values for the basalts range from + 0.37 to + 5.2 and TDM ages from 595 Ma to 705 Ma. The lamprophyres are extremely enriched in light rare earth elements, large iron lithophile elements, and are depleted in heavy rare earth elements, suggesting a deep, garnet lherzolite source that was previously metasomatised. They display εNd values ranging from - 1.4 to + 1.4, initial Sr values of ca. 0.706, and TDM ages from 671 Ma to 1031 Ma, suggesting that metasomatism occurred in the Neoproterozoic. Lamprophyres and coeval granite batholiths of similar chemistry to those in Cornwall occur in other regions of the Variscan orogen, including Iberia and Bohemia. By using new geochemical and isotopic data to constrain the evolution of the mantle beneath SW England and the processes associated with the formation of these post-collisional rocks, we may be able to gain a more complete understanding of mantle processes during the waning stages of supercontinent formation.

  17. Petrogenesis of the Alaskan-type mafic-ultramafic complex in the Makkah quadrangle, western Arabian Shield, Saudi Arabia

    Science.gov (United States)

    Habtoor, Abdelmonem; Ahmed, Ahmed Hassan; Harbi, Hesham

    2016-10-01

    The Makkah quadrangle is a part of the Jeddah terrane in the Precambrian basement, Western Arabian Shield of Saudi Arabia. Gabal Taftafan mafic-ultramafic complex lies within the central part of the Makkah quadrangle. The Taftafan mafic-ultramafic complex is a well-differentiated rock association which comprises of dunite core, hornblende- and plagioclase-bearing peridotites, troctolite, clinopyroxenite and marginal gabbro, in a distinctive zonal structure. The bulk-rock geochemistry of the Taftafan mafic-ultramafic rocks is characterized by a tholeiitic/sub-alkaline affinity with high Mg in the ultramafic core (0.84) and is systematically decreased towards the marginal gabbro (0.60). The patterns of trace elements show enrichment in the fluid-mobile elements (Sr, Ba) and a pronounced negative Nb anomaly which reflect a hydrous parental magma generated in a subduction tectonic setting. The mafic-ultramafic rocks of the Taftafan complex have low total rare earth elements (REE) displaying sub-parallel patterns leading to the assumption that these rocks are comagmatic and are formed by fractional crystallization from a common magma type. The platinum-group elements (PGE) content of all rock types in the Taftafan complex is very low, with ∑ PPGE > ∑ IPGE; displaying slightly positive slopes of the PGE distribution patterns. The chemistry of ferromagnesian minerals is characterized by a high forsterite (Fo) olivine with wide range (Fo91-67), from ultramafic core to the marginal gabbro, Ca-rich diopsidic clinopyroxene, and calcic hornblende. Orthopyroxene is almost absent from all rock types, or very rare when present. Hornblende and Ca-plagioclase possess the longest crystallization history since they are present in almost all rock types of the complex. Spinels in the dunite and hornblende-bearing peridotite core show homogeneous composition with intermediate Cr# (0.53-0.67). Plagioclase-bearing peridotite and troctolite have two exsolved types of spinel; Al

  18. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    Science.gov (United States)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.

    2015-11-01

    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  19. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

    Science.gov (United States)

    Bonin, Bernard; Tatu, Mihai

    2016-01-01

    The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

  20. Charnockitic ortho gneisses and mafic granulite s of the Cerro Olivo complex, south-east Uruguay, Part 2: lithogeochemistry, mineral o chemistry and thermo barometry

    International Nuclear Information System (INIS)

    The Cerro Olivo complex in SE-Uruguay shows different kinds of orthogneisses containing biotite, amphibole and/or orthopyroxene-biotite (charnockitic gneisses). Minor occurrences of mafic granulites are associated. They include low and high pressure kinds. We present the lithogeochemistry and compared mineral chemistry analyses of both the charnockitic orthogneisses and the mafic rocks. Theres i a calc-alkaline geochemical affinity of the biotite-bearing and charnockitic gneisses, while the mafic rocks could derive from tholeitic gabbros. These results allow discrininatieg two kinds of mafic rocks: Low and hight MgO contents, both representing respectively garnet-bearing and garnet-free mafic granulites. The orthopyroxene in the Opx-Bt orthogneisses in FE-rich while MgO-rich mafic rocks show hypersthenes. The thermobarometric data of mafic granulites show temperatures higher than 850°C and two contrasting mineral assemblages, one formed by ∼ 1 Kbar and 770° - 800°C (pre-M). and the other by 5.5 Kbar and 680-700° (M). The mineral chemistry suggests the occurrence of contrasting protoliths to explain the stability of two different mineral associations

  1. 津巴布韦大岩墙铂族金属资源开发现状%Development Status of PGM Resources in Zimbabwe's Great Dyke

    Institute of Scientific and Technical Information of China (English)

    赵声贵; 陈元初

    2011-01-01

    介绍了津巴布韦大岩墙上铂族金属资源的特点、分布及开发情况,对津巴布韦在产铂金矿山的资源、矿石开采及选冶加工工艺、产能规模等基本情况进行总结,指出采矿是大规模开发津巴布韦大岩墙铂族金属资源的关键.%Characters and distribution of PGM resources in Zimbabwe's Great Dyke were introduced. The PGM resource, mining, processing and production capability of platinum mine in Zimbabwe were summarized in details. Indicate that mining is the key to develop the PGM resources in Zimbabwe's Great Dyke.

  2. Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ Recent re-valuation of the dating of the carbonatite dykes associated with the REE-Fe-Nb giant deposit at Bayan Obo has revealed an anomaly with one of the dates. Inspection of the post-1990 literature for the carbonatite dykes and H8 dolomite rocks and ores of Bayan Obo provides age data in the range 1223 +65 Ma to 1656 Ma, as Table 1 shows. Since Sm and Nd are relatively immobile elements, most of the Sm-Nd dates are considered to be little changed by the subsequent mineralization processes. That the dates occur in two clusters, 1656 ~ 1500 Ma and 1312 ~ 1223 Ma might refer to two related periods of carbonatitic magmatic activity, but that is not relevant at this moment.

  3. Sheeted and bulbous pluton intrusion mechanisms of a small granitoid from southeastern Australia: implications for dyke-to-pluton transformation during emplacement

    Science.gov (United States)

    Fowler, T. J.

    1994-06-01

    The small late syn-tectonic Carboniferous Davys Creek Granite (DCG) of southeastern Australia consists of microgranitic intrusive bodies of diverse geometry and structure. These bodies include: (1) subvertical concordant sheets; (2) bulbous peneconcordant plutons with apophyses and discordant lobes; and (3) subvertical dykes and stocks. The sequence of changing intrusive style is broadly 1-2-3. Transition from 1 to 2 was probably a response to rising magma pressures or declining tectonic stresses. The λ parameter of Emerman and Marrett (1990), which discriminates between stable sheet-like and potential stock/pluton/batholith emplacement modes, adequately predicts the transitions between sheet and pluton emplacements for the DCG. Ductile dyking along actively forming foliations appears to have been an important early intrusive mechanism. A transition from sheet to bulbous pluton intrusion style is suggested to have been in response to magma pressure increases.

  4. Contribution of the FUTUREVOLC project to the study of segmented lateral dyke growth in the 2014 rifting event at Bárðarbunga volcanic system, Iceland

    Science.gov (United States)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.

    2015-04-01

    The FUTUREVOLC project (a 26-partner project funded by FP7 Environment Programme of the European Commission, addressing topic "Long-term monitoring experiment in geologically active regions of Europe prone to natural hazards: the Supersite concept) set aims to (i) establish an innovative volcano monitoring system and strategy, (ii) develop new methods for near real-time integration of multi-parametric datasets, (iii) apply a seamless transdisciplinary approach to further scientific understanding of magmatic processes, and (iv) to improve delivery, quality and timeliness of transdisciplinary information from monitoring scientists to civil protection. The project duration is 1 October 2012 - 31 March 2016. Unrest and volcanic activity since August 2014 at one of the focus areas of the project in Iceland, at the Bárðarbunga volcanic system, near the middle of the project duration, has offered unique opportunities for this project. On 16 August 2014 an intense seismic swarm started in Bárðarbunga, the beginning of a major volcano-tectonic rifting event forming over 45 km long dyke extending from the caldera to Holuhraun lava field outside the northern margin of Vatnajökull. A large basaltic, effusive fissure eruption began in Holuhraun on 31 August which had by January formed a lava field with a volume in excess of one cubic kilometre. We document how the FUTUREVOLC project has contributed to the study and response to the subsurface dyke formation, through increased seismic and geodetic coverage and joint interpreation of the data. The dyke intrusion in the Bárðarbunga volcanic system, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground

  5. Platinum-group element concentrations in pyrite from the Main Sulfide Zone of the Great Dyke of Zimbabwe

    Science.gov (United States)

    Piña, R.; Gervilla, F.; Barnes, S.-J.; Oberthür, T.; Lunar, R.

    2016-02-01

    The Main Sulfide Zone (MSZ) of the Great Dyke of Zimbabwe hosts the world's second largest resource of platinum-group elements (PGE) after the Bushveld Complex in South Africa. The sulfide assemblage of the MSZ comprises pyrrhotite, pentlandite, chalcopyrite, and minor pyrite. Recently, several studies have observed in a number of Ni-Cu-PGE ore deposits that pyrite may host significant amounts of PGE, particularly Pt and Rh. In this study, we have determined PGE and other trace element contents in pyrite from the Hartley, Ngezi, Unki, and Mimosa mines of the Great Dyke by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Based on the textures and PGE contents, two types of pyrite can be differentiated. Py1 occurs as individual euhedral or subhedral grains or clusters of crystals mostly within chalcopyrite and pentlandite, in some cases in the form of symplectitic intergrowths, and is PGE rich (up to 99 ppm Pt and 61 ppm Rh; 1.7 to 47.1 ppm Ru, 0.1 to 7.8 ppm Os, and 1.2 to 20.2 ppm Ir). Py2 occurs as small individual euhedral or subhedral crystals within pyrrhotite, pentlandite, and less frequently within chalcopyrite and silicates and has low PGE contents (<0.11 ppm Pt, <0.34 ppm Rh, <2.5 ppm Ru, <0.37 ppm Ir, and <0.40 ppm Os). Py1 contains higher Os, Ir, Ru, Rh, and Pt contents than the associated pyrrhotite, pentlandite, and chalcopyrite, whereas Py2 has similar PGE contents as coexisting pyrrhotite and pentlandite. Based on the textural relationships, two different origins are attributed for each pyrite type. Py1 intergrowth with pentlandite and chalcopyrite is inferred to have formed by late, low temperature (<300 °C) decomposition of residual Ni-rich monosulfide solid solution, whereas Py2 is suggested to have formed by replacement of pyrrhotite and pentlandite caused by late magmatic/hydrothermal fluids.

  6. Platinum-group element concentrations in pyrite from the Main Sulfide Zone of the Great Dyke of Zimbabwe

    Science.gov (United States)

    Piña, R.; Gervilla, F.; Barnes, S.-J.; Oberthür, T.; Lunar, R.

    2016-10-01

    The Main Sulfide Zone (MSZ) of the Great Dyke of Zimbabwe hosts the world's second largest resource of platinum-group elements (PGE) after the Bushveld Complex in South Africa. The sulfide assemblage of the MSZ comprises pyrrhotite, pentlandite, chalcopyrite, and minor pyrite. Recently, several studies have observed in a number of Ni-Cu-PGE ore deposits that pyrite may host significant amounts of PGE, particularly Pt and Rh. In this study, we have determined PGE and other trace element contents in pyrite from the Hartley, Ngezi, Unki, and Mimosa mines of the Great Dyke by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Based on the textures and PGE contents, two types of pyrite can be differentiated. Py1 occurs as individual euhedral or subhedral grains or clusters of crystals mostly within chalcopyrite and pentlandite, in some cases in the form of symplectitic intergrowths, and is PGE rich (up to 99 ppm Pt and 61 ppm Rh; 1.7 to 47.1 ppm Ru, 0.1 to 7.8 ppm Os, and 1.2 to 20.2 ppm Ir). Py2 occurs as small individual euhedral or subhedral crystals within pyrrhotite, pentlandite, and less frequently within chalcopyrite and silicates and has low PGE contents (<0.11 ppm Pt, <0.34 ppm Rh, <2.5 ppm Ru, <0.37 ppm Ir, and <0.40 ppm Os). Py1 contains higher Os, Ir, Ru, Rh, and Pt contents than the associated pyrrhotite, pentlandite, and chalcopyrite, whereas Py2 has similar PGE contents as coexisting pyrrhotite and pentlandite. Based on the textural relationships, two different origins are attributed for each pyrite type. Py1 intergrowth with pentlandite and chalcopyrite is inferred to have formed by late, low temperature (<300 °C) decomposition of residual Ni-rich monosulfide solid solution, whereas Py2 is suggested to have formed by replacement of pyrrhotite and pentlandite caused by late magmatic/hydrothermal fluids.

  7. Design of sea dyke works in Zhuhai Hengqin port service area%珠海横琴新区口岸服务区段堤岸工程设计

    Institute of Scientific and Technical Information of China (English)

    柏宝忠; 吴雄远; 周志业

    2015-01-01

    介绍了珠海横琴新区口岸服务区段堤岸工程的概况,分析了堤岸工程设计的重点和难点。对堤岸断面设计、基础处理设计、涵洞结构设计以及工程耐久性设计等方面作了详细论述。说明了口岸服务区段堤岸工程设计不同于常规堤岸工程的特点和要求。目前,横琴新区基础设施工程的设计、施工正处于高峰阶段,该工程的一些设计经验对类似工程具有参考、借鉴作用。%The general conditions of sea dyke works in Zhuhai Hengqin port service area are introduced, the critical and diffi-cult points in the design of dyke works are analyzed, especially the dyke section design, foundation treatment, culvert structure and dyke durability. The characteristics and requirements of the dyke works in the port service area, which is different from the conventional dyke works, are explained. At present, the design and construction of infrastructure works in this area are in peak period, some experiences and measures can provide reference for the similar works.

  8. The Importance of Sampling Strategies on AMS Determination of Dykes II. Further Examples from the Kapaa Quarry, Koolau Volcano, Oahu, Hawaii

    Science.gov (United States)

    Mendoza-Borunda, R.; Herrero-Bervera, E.; Canon-Tapia, E.

    2012-12-01

    Recent work has suggested the convenience of dyke sampling along several profiles parallel and perpendicular to its walls to increase the probability of determining a geologically significant magma flow direction using anisotropy of magnetic susceptibility (AMS) measurements. For this work, we have resampled in great detail some dykes from the Kapaa Quarry, Koolau Volcano in Oahu Hawaii, comparing the results of a more detailed sampling scheme with those obtained previously with a traditional sampling scheme. In addition to the AMS results we will show magnetic properties, including magnetic grain sizes, Curie points and AMS measured at two different frequencies on a new MFK1-FA Spinner Kappabridge. Our results thus far provide further empirical evidence supporting the occurrence of a definite cyclic fabric acquisition during the emplacement of at least some of the dykes. This cyclic behavior can be captured using the new sampling scheme, but might be easily overlooked if the simple, more traditional sampling scheme is used. Consequently, previous claims concerning the advantages of adopting a more complex sampling scheme are justified since this approach can serve to reduce the uncertainty in the interpretation of AMS results.

  9. The geochemistry, age, and origin of groundwater in a mafic pluton, East Bull Lake, Ontario, Canada

    International Nuclear Information System (INIS)

    Atomic Energy of Canada Ltd. (AECL) is conducting geoscience investigations of several plutons in Canada's Precambrian Shield as part of the Canadian Nuclear Fuel Waste Management Program, to determine whether such rock masses are suitable for the safe disposal of nuclear fuel waste. The East Bull Lake (EBL) gabbro-anorthosite layered complex is unique in this program as it is the only mafic pluton in which hydrogeological and hydrogeochemical studies have been conducted. These results can be compared with those of similar studies of granitic rocks which have been investigated more extensively. During the period, 1983-85, hydrogeological testing and hydrochemical sampling were conducted by the National Hydrology Research Institute of Environment Canada and AECL in boreholes drilled to depths of up to 850 m into the EBL pluton (Raven et al., 1987). This paper discusses the hydrogeochemistry of the pluton and identifies the major rock-water interactions controlling the chemistry. The spatial variability in chemistry will be shown to be related to the nature of the groundwater flow systems present at this site. The ages and origins of the groundwaters and their solutes are inferred from isotopic analyses

  10. Melanite garnet-bearing nepheline syenite minor intrusion in Mawpyut ultramafic–mafic complex, Jaintia Hills, Meghalaya

    Indian Academy of Sciences (India)

    Monoj Maitra; J S David; S Bhaduri

    2011-12-01

    Mawpyut igneous suite in Jaintia Hills of Meghalaya plateau comprises differentiated suite of ultramafic–mafic rocks. The complex differs from other ultramafic–alkaline–carbonatite igneous emplacements of Shillong plateau and Mikir Hills like Jesra, Sung, Samchampi complexes, by the absence of alkaline–carbonatite rocks as major litho-units. Melanite garnet-bearing nepheline syenite, occurs as late phase minor intrusion in Mawpyut igneous complex, posseses alkaline character and shows inubiquitous relation with the host ultramafic–mafic rocks. On the other hand, this alkaline intrusive bodies of the Mawpyut igneous complex shows chemico-mineralogical resemblance with garnet-bearing nepheline syenite, ijolite litho-members of Jesra, Sung, Samchampi complexes of the region. It is interpreted that melanite garnet-bearing nepheline syenite intrusion in Mawpyut is contemporaneous with Jesra, Sung, Samchampi ultramafic–alkaline–carbonatite complexes and the host rocks of Mawpyut complex is an earlier magmatic activity possibly from a comparatively least enriched source.

  11. The role of dyking and fault control in the rapid onset of eruption at Chaitén Volcano, Chile

    Science.gov (United States)

    Wicks, C.; De La, Llera; Lara, L.E.; Lowenstern, J.

    2011-01-01

    Rhyolite is the most viscous of liquid magmas, so it was surprising that on 2 May 2008 at Chaitén Volcano, located in Chile’s southern Andean volcanic zone, rhyolitic magma migrated from more than 5 km depth in less than 4 hours and erupted explosively with only two days of detected precursory seismic activity. The last major rhyolite eruption before that at Chaitén was the largest volcanic eruption in the twentieth century, at Novarupta volcano, Alaska, in 1912. Because of the historically rare and explosive nature of rhyolite eruptions and because of the surprisingly short warning before the eruption of the Chaitén volcano, any information about the workings of the magmatic system at Chaitén, and rhyolitic systems in general, is important from both the scientific and hazard perspectives. Here we present surface deformation data related to the Chaitén eruption based on radar interferometry observations from the Japan Aerospace Exploration Agency (JAXA) DAICHI (ALOS) satellite. The data on this explosive rhyolite eruption indicate that the rapid ascent of rhyolite occurred through dyking and that melt segregation and magma storage were controlled by existing faults.

  12. Silicate geothermometry as an indicator of water-rock interaction processes in the serpentinized mafic-ultramafic intrusion of Ylivieska

    International Nuclear Information System (INIS)

    The aim of the study was to use oxygen and hydrogen isotopes to examine the origin of different generations of serpentine. Of special interest was the study of low-temperature generations that may be correlated with the present meteoric waters. The research was commenced with drill core logging in order to obtain insight into the fracture minerals and their distribution in a mafic-ultramafic intrusion. (39 refs., 17 figs., 5 tabs.)

  13. Thermal, chemical and isotopic homogenization of syn-extensional I-type plutons and mafic microgranular enclaves

    Science.gov (United States)

    Tatar Erkül, Sibel; Erkül, Fuat; Uysal, İbrahim

    2015-04-01

    Magma mixing and mingling processes are common phenomenon in the evolution of granitoid magmas. This study deals with examination of mineral chemical, geochemical and isotopic characteristics of enclaves and enclosing syn-extensional granite bodies in western Turkey to make an attempt to solve problems regarding their origin. Mafic microgranular enclaves have granodiorite, quartz monzonite, monzonite and monzodiorite compositions, are subalkaline/calc-alkaline and high-K in character and display typical mixing/mingling textures. Mafic enclaves have partially overlapping geochemical characteristics onto their host rocks in terms of mobile elements and their isotopes while distinct immobile element patterns occur within host rocks and enclaves. Contrasting geochemistry of enclaves is mainly defined by their low SiO2 and high MgO, Mg# and high Fe2O3 contents. Chondrite-normalized spidergrams of enclaves also reveal two contrasting patterns. One is relatively enriched in rare earth element content and the other is slightly enriched and displays relatively flat pattern. 87Sr/86Sr and 143Nd/144Nd contents of enclaves imply considerable amount of crustal input. Crustally derived felsic magma coeval with mafic magma have been chemically, thermally and mechanically exchanged with each other and resulting homogenization led to compositional and isotopic equilibration of mafic and felsic magmas. Fractional crystallization, mixing and the following crustal contamination were responsible for the final composition of syn-extensional granitoids. Such processes appear to have been widely occurred in continental extensional regime that caused melting and mixing of crustal and mantle sources at MOHO depth.

  14. Geochemistry and petrology of mafic enclaves of metasedimentary origin: case study from the Peninsular Ranges Batholith, California

    Science.gov (United States)

    Liao, K.; Morton, D.; Lee, C.

    2011-12-01

    Dark clasts rich in amphibole or biotite, commonly referred to as "mafic enclaves", are frequently found in felsic plutons and are traditionally interpreted to represent fragments of mafic magmas, such as basalt, entrained by or intruded into felsic magma bodies. However, during emplacement, magmas often assimilate pre-existing wallrock, begging the question of whether some dark enclaves might have non-igneous protoliths. To investigate this process of forming dark enclaves in more detail, we examined the Cretaceous Domenigoni Valley pluton in the Peninsular Ranges Batholith in southern California. This pluton was emplaced into pre-existing metamorphic country rock, composed of Paleozoic to early Mesozoic calc-silicates, phyllites, and calcareous quartzites. Dark enclaves, in the form of amphibole- or biotite-bearing angular fragments, are abundant in the pluton. However, evidence for wallrock stoping is also seen in the extensive presence of wallrock xenoliths in varying extents of thermal and chemical equilibration with the host tonalite pluton. Enclaves with a clear calc-silicate protolith are represented by quartz-diopside-wollastonite-plagioclase rocks, whereas enclaves with clear pelitic protoliths are represented by biotite-quartz-alkali feldspar rocks. Several lines of evidence, however, suggest that the dark amphibole-rich and biotite-rich enclaves, although mafic in composition (high Mg and Fe), represent the fully equilibrated state of these assimilated wallrocks rather than fragments of basaltic magmas. First, many of the dark, biotite- and amphibole-bearing enclaves have SiO2 contents greater than 60 %, too high to represent typical mafic magmas. Second, although some biotite-rich enclaves have SiO2 contents dark amphibole-bearing enclaves have bulk Al and K lower than the host tonalite but similar to the quartz-diopside-wollastonite-plagioclase rocks thought to have a calc-silicate protolith. Fourth, composite enclaves exist wherein hornblende

  15. Geochemistry and Petrogenesis of Neoarchean Metamorphic Mafic Rocks in the Wutai Complex

    Institute of Scientific and Technical Information of China (English)

    L(U) Yongjun; LIU Shuwen; Guochun ZHAO; LI Qiugen; Jian ZHANG; LIU Chaohui; K. H. PARK; Y. S. SONG

    2006-01-01

    Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns (Lan/Ybn=0.86-1.3), the lowest total REEs (29-52 ppm), and weak negative to positive Eu anomalies (Eun/Eun*=0.84-1.02), nearly flat primitive mantle normalized patterns and strong negative Zr(Hf) anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs (34-116 ppm), LREE-enriched (Lan/Ybn=1.76-4.34) chondrite normalized REE patterns with weak Eu anomalies (Eun/Eun*=0.76-1.16), and negative Nb, Ta, Zr(Hf), Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slabderived fluids. Rocks in Group #3 are characterized by the highest total REEs (61-192 ppm), the strongest LREEs enrichment (Lan/Ybn=7.12-16) with slightly negative Eu anomalies (Eun/Eun*=0.81-0.95) in the chondrite normalized diagram. In the primitive mantle normalized diagram,these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies.They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts.The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.

  16. Evolution of the East African rift: Drip magmatism, lithospheric thinning and mafic volcanism

    Science.gov (United States)

    Furman, Tanya; Nelson, Wendy R.; Elkins-Tanton, Linda T.

    2016-07-01

    The origin of the Ethiopian-Yemeni Oligocene flood basalt province is widely interpreted as representing mafic volcanism associated with the Afar mantle plume head, with minor contributions from the lithospheric mantle. We reinterpret the geochemical compositions of primitive Oligocene basalts and picrites as requiring a far more significant contribution from the metasomatized subcontinental lithospheric mantle than has been recognized previously. This region displays the fingerprints of mantle plume and lithospheric drip magmatism as predicted from numerical models. Metasomatized mantle lithosphere is not dynamically stable, and heating above the upwelling Afar plume caused metasomatized lithosphere with a significant pyroxenite component to drip into the asthenosphere and melt. This process generated the HT2 lavas observed today in restricted portions of Ethiopia and Yemen now separated by the Red Sea, suggesting a fundamental link between drip magmatism and the onset of rifting. Coeval HT1 and LT lavas, in contrast, were not generated by drip melting but instead originated from shallower, dominantly anhydrous peridotite. Looking more broadly across the East African Rift System in time and space, geochemical data support small volume volcanic events in Turkana (N. Kenya), Chyulu Hills (S. Kenya) and the Virunga province (Western Rift) to be derived ultimately from drip melting. The removal of the gravitationally unstable, metasomatized portion of the subcontinental lithospheric mantle via dripping is correlated in each case with periods of rapid uplift. The combined influence of thermo-mechanically thinned lithosphere and the Afar plume together thus controlled the locus of continental rift initiation between Africa and Arabia and provide dynamic support for the Ethiopian plateau.

  17. Electrical resistivity tomography investigations along the planned dykes of the HPP Brežice water accumulation basin

    Directory of Open Access Journals (Sweden)

    Gorazd Rajh

    2014-12-01

    Full Text Available Geophysical investigations were conducted using electrical resistivity tomography (ERT along planned dykes of the HPP Brežice water accumulation basin. The ERT profile is 7.3 km long and is located on the right riverbank of the Sava River on the Kr{ko-Brežice field (E Slovenia. A purpose of the investigations was to determine a boundary between semipermeable Miocene and permeable Plio-Quaternary (Pl-Q and Quaternary (Q sediments for the proper design of the jet grouting sealing curtain, which will prevent lateral outflow of water from the accumulation basin. In this paper we present processing of the section between 5100 and 6100 m of the profile line. In this section the measurement template was set to 25 depth levels, because a significant increase in a thickness of the Pl-Q sediments was expected. Modelling of the measured apparent electrical resistivity data was carried out with RES2DINV and RESIX 2DI inversion software. Different inversion parameters were used to create 15 geoelectrical models for each program, which were then compared and evaluated based on borehole data and on previous geological investigations of the area. With the final geoelectrical models it was possible to successfully determine areas of three expected stratigraphic members and limit an electrical resistivity range for each one of them. The boundary is well defined between Q and Pl-Q and also between Q and Miocene sediments with sharp contrast in electrical resistivity between them. A boundary between Pl-Q and Miocene sediments was not that obvious, but it was possible to determine its shape by the use of different inversion parameters. We propose a simplified geological cross section based on the interpreted geoelectrical models and borehole data.

  18. Integrated Approach (Geophysics and Remote Sensing) to identify Water-bearing Dyke Swarms and Fractured Basement in the Sinai Peninsula, Egypt

    Science.gov (United States)

    Mohamed, L.; Sultan, M.; Ahmed, M. E.; Sauck, W.; Abouelmagd, A. A.; Chouinard, K.

    2012-12-01

    An integrated approach utilizing Very Low Frequency (VLF) and magnetic field surveying and temporal remote sensing data including: (1) Advanced Space Borne Thermal Emission and Reflection (ASTER) data, (2) European Remote Sensing (ERS-1 and ERS-2) radar imagery, and (3) Tropical Rainfall Measuring Mission (TRMM) was used to delineate water-bearing sub-vertical shear zones within the basement complex of the Sinai Peninsula. The following steps were undertaken: (1) the shear zones and dyke swarms within the basement complex were delineated using false color ASTER band and band ratio images; (2) the spatial and temporal precipitation events over the basement complex were then identified from TRMM data, and (3) finally, observations extracted from temporal radar and thermal ASTER bands were used to identify the water-bearing shear zones and dyke swarms. A fracture or dyke was deemed to be water bearing if: (1) it witnessed a large increase in its reflectivity and emissivity compared to its surroundings following a precipitation event, and maintained such differences for periods ranging from days to months. Field observations and VLF investigations were then applied to test the validity of our satellite-based methodologies for locating targeted aquifer types and for refining the satellite-based selections. The VLF detects conductive water-saturated subvertical breccia zones in bedrock. Thirty two VLF transects were collected in September of 2011 and July of 2012 along with 10 magnetic profiles at the same VLF locations. Both VLF and magnetic transects were acquired along a traverse perpendicular to the dike orientations with station separations ranging from 10 to 25 m. The VLF receiver (T-VLF) measures the distortion of the normally horizontal electromagnetic flux lines by local electrical conductors. At each VLF station, and for each frequency used, the following were measured: the tilt of the electromagnetic field, from the horizontal (given in percentage), the

  19. Experimental and textural constraints on mafic enclave formation in volcanic rocks

    Science.gov (United States)

    Coombs, M.L.; Eichelberger, J.C.; Rutherford, M.J.

    2002-01-01

    We have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at Southwest Trident volcano, Alaska. Andesite enclaves are present throughout the four dacite lava flows produced by the eruption, and resemble mafic enclaves commonly found in other volcanic rocks. Our experiments replicate the pressure-temperature-time path taken by enclave-forming andesite magma as it is engulfed in dacite during magma mixing. Pressure and temperature information for the andesite and dacite are from [Coombs et al., Contrib. Mineral. Petrol. 140 (2000) 99-118]. The andesite was annealed at 1000??C, and then cooled to 890??C at rates of 110??C h1, 10??C h1 and 2??C h1. Once cooled to 890??C, andesite was held at this lower temperature from times ranging from 1 to 40 h. The andesite that was cooled at the slower rates of 2??C h1 and 10??C h1 most resembles enclave groundmass texturally and compositionally. Based on simple thermal calculations, these rates are more consistent with cooling of the andesite groundmass below an andesite-dacite interface than with cooling of enclave-sized spheres. If enclaves do crystallize as spheres, post-crystallization disaggregation must occur. Calculations using the MELTS algorithm [Ghiorso and Sack, Contrib. Mineral. Petrol. 119 (1995) 197-212] show that for incoming andesite to become less dense than the dacite to become less dense ???34 volume % of its groundmass must crystallize to undergo~18 volume % vesiculation; these values are similar to those determined for Southwest Trident enclaves. Thus such crystallization may lead to 'flotation' of enclaves and be a viable mechanism for enclave formation and dispersal. The residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments. Decompression experiments on Southwest Trident dacite suggest an average ascent rate for the eruption of ???2

  20. Integrated methodologies for the 3d survey and the structural monitoring of industrial archaeology: the case of the Casalecchio di Reno Dyke, Italy

    Science.gov (United States)

    Bitelli, Gabriele; Girelli, Valentina A.; Vittuari, Luca; Zanutta, Antonio

    2010-05-01

    The concept of "Industrial Archaeology" was introduced in the 1950s in England in order to consider the branch of Archaeology that, in integration with engineering, architecture and economics, studies the industrial past, with the purpose of document, protect and exploite the industrial-cultural heritage. The systematic study of this kind of structures and artefacts need a wide range approach, that starts from the investigation about the object historic fonts until its complete qualitative and quantitative description, also considering the characteristics of the surrounding territory. This task often needs the integration of different survey techniques for data capturing and processing, in order to perform the 3D modeling and to analize the structural deformations of manufactured articles. The paper presents the surveying and monitoring activities on the important structure of the Casalecchio di Reno dyke, near Bologna. The first historic notes on the dyke are very old; they are dated back to the I millenium A. D. and report the news of a wooden barrage of the Reno canal. The construction of the actual structure is in the period 1360-1367 and suffered during the centuries numerous interventions and restores. The surveying activities on the dyke were realized in 2005-2006 and 2009 and involved different techniques (classical topography, high precision geometric levelling, range-based method by terrestrial laser scanning, digital photogrammetry, thermal imagery) integrated together in a unique local reference system, in order to study the stability and the movements of the structure in a established period of time and to realize a 3D model. Together with detail surveys on the single parts of the structure, an analysis at a larger territorial scale was performed by aerial photogrammetry, either using current imagery and historical data. The topographic measurements with traditional differential techniques have achieved a very high level precision and the realized

  1. Analysis of the deconstruction of Dyke Marsh, George Washington Memorial Parkway, Virginia-Progression, geologic and manmade causes, and effective restoration scenarios

    Science.gov (United States)

    Litwin, Ronald J.; Smoot, Joseph P.; Pavich, Milan J.; Markewich, Helaine W.; Oberg, Erik; Helwig, Ben; Steury, Brent; Santucci, Vincent L.; Durika, Nancy J.; Rybicki, Nancy B.; Engelhardt, Katharina M.; Sanders, Geoffrey; Verardo, Stacey; Elmore, Andrew J.; Gilmer, Joseph

    2011-01-01

    This report is a synthesis of the latest findings from an ongoing study of Dyke Marsh, an eroding freshwater tidal wetland that is scheduled for federal restoration. Its purpose is to provide an accurate and up-to-date temporal and geological framework for the marsh, of which most is new information (plus a compilation of historical and recent information), that is directly relevant to the restoration effort and also is relevant to short-term and long-term land management decisions regarding this natural resource.

  2. Caracterizacion fisiológica del crecimiento y desarrollo del fruto de mango (mangifera indica l.) variedad van dyke en el municipio de el espinal

    OpenAIRE

    2011-01-01

    El estudio se realizó en la finca Frutol del Municipio de El Espinal, departamento del Tolima, situado a una altura de 431 m.s.n.m., con precipitación, temperatura y Humedad Relativa promedio anual de 1.368 mm / año, 29°C y 70%.   Se realizó el seguimiento de los cambios ocurridos durante el crecimiento y desarrollo del mango Variedad Van Dyke, desde la antesis hasta la madurez fisiológica: Diámetros longitudinal, transversal, el volumen, la gravedad específica, el peso fresco y seco, color ...

  3. Variable sediment flux in generation of Permian subduction-related mafic intrusions from the Yanbian region, NE China

    Science.gov (United States)

    Guo, Feng; Li, Hongxia; Fan, Weiming; Li, Jingyan; Zhao, Liang; Huang, Miwei

    2016-09-01

    This paper presents petrology, mineralogy, zircon U-Pb ages, and whole-rock major, trace element and Sr-Nd-Hf isotopic compositions of four Permian (273-253 Ma) subduction-related mafic intrusions (including the Qinggoushan and Qianshan gabbros, and the Wangqing and Shuguang diorites) from the Yanbian region, NE China, with aims to understand the role of subducted sediment flux in generation of arc mafic cumulates. These intrusions have mineral assemblages crystallized in water-saturated parental magmas and show variable degrees of crystal accumulation as observed in mafic cumulates in subduction zones. Mass-balance consideration indicates that their parental magmas were calc-alkaline with arc-type trace element features (enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) and depletions in Nb-Ta). They also have Sr-Nd-Hf isotopic compositions, i.e., 87Sr/86Sr(i) = 0.7029-0.7047, εNd(t) = + 0.9 ~ + 6.8, εHf(t) = + 5.6 ~ + 14.6, similar to modern arc basalts. The parental magmas were likely derived from a mantle wedge variably metasomatized by sediment melt and fluid from the subducting paleo-Asian Oceanic slab. Combined trace elemental and isotopic modeling results suggest that the parental magma of Qinggoushan gabbro was formed through 5-20% melting of the mantle wedge with 1% and 1.5% additions of sediment fluid and sediment melt, respectively; 5-10% melting of the mantle wedge through inputs of 1% sediment fluid and 2% sediment melt produced the Qianshan gabbro; 10-20% melting of the mantle wedge with additions of 1% sediment fluid and 3% sediment melt formed the Wangqing diorite; whereas 5-20% melting of the mantle wedge through an input of 1.5% sediment melt produced the Shuguang diorite. The Hf-Nd isotopic array of the Yanbian Permian mafic intrusions reflected the existence of an Indian Ocean-type mantle, which was isotopically distinct from the Pacific-type mantle during early Paleozoic in the Central Asian Orogenic

  4. Nature and Evolution of the Mafic Component(s) of the Early Cretaceous Sierra Nevada Batholith, CA

    Science.gov (United States)

    Clemens-Knott, D.; Seal, E.; Saleeby, J.

    2011-12-01

    Geochemical characterization of the mafic component(s) of the earliest phase of the voluminous Cretaceous Sierra Nevada batholith is facilitated by two rock assemblages exposed in the Stokes Mountain region of the western foothills near Visalia, CA: (1) km-scale blocks of modally layered olivine-plagioclase cumulates, and (2) two gabbroic-to-granitic ring dike complexes. Mineral compositions of a 100-m-thick section of a single layered cumulate block documents the presence of high-temperature mineral assemblages (e.g., Fo78 olivine; An93 plagioclase), approaching values that would be in equilibrium with mantle-derived primary magmas. Stratigraphic and core-to-rim variations in mineral chemistry (including nickel contents in olivine) demonstrate that the earliest stages of magma differentiation were dominated by down-temperature fractional crystallization, punctuated by repeated recharge of mantle-derived magmas. Fractional crystallization of troctolite cumulates is hypothesized to have produced buoyant, hornblende-rich gabbros-to-diorites that are represented by rare gabbroic intrusions (e.g., Stokes Mtn. region; Onion Valley) and possibly by the more abundant mafic enclaves that are found mingled with intermediate to silicic intrusions throughout the batholith. Geochemical systematics of the dominantly gabbroic to tonalitic ring dikes complexes encasing the mafic cumulate blocks document the temporal coexistence of at least two, spatially distinct source regions within the mantle wedge. REE and O-Sr-Nd isotopic data indicate that differentiation of ring dikes magmas occurred primarily by coupled assimilation-fractional crystallization. Some mixing with recharged mafic magmas is supported both by field observations and by geochemical data. Existence of a third, spatially distinct, mantle source may be documented by plutonic rocks found in a narrow zone of intense magma mingling and synmagmatic shear that separates the two ring complexes. These rocks have the

  5. Seismic constraints on a large mafic intrusion with implications for the subsidence mechanism of the Danish Basin

    DEFF Research Database (Denmark)

    Sandrin, Alessandro; Thybo, Hans

    2008-01-01

    Seismic refraction data from the ESTRID-1 profile are used for seismic velocity modeling along the strike of a large mafic intrusion in the Norwegian-Danish Basin, central Denmark. The P wave velocity structure identifies a ~8 km thick sedimentary succession with velocities between 1.8 and 5.7 km......Gal) positive gravity anomaly known as Silkeborg Gravity High. The intrusion has a minimum volume of 40,000 km3, which implies that the magma influx and the consequent cooling of the lithosphere from high temperature could have had profound effects on the subsidence of the Danish Basin, in particular because...

  6. Mantle derivation of Archean amphibole-bearing granitoid and associated mafic rocks: evidence from the southern Superior Province, Canada

    Science.gov (United States)

    Sutcliffe, Richard H.; Smith, Alan R.; Doherty, William; Barnett, Robert L.

    1990-08-01

    Amphibole-bearing, Late Archean (2.73 2.68 Ga) granitoids of the southern Superior Province are examined to constrain processes of crustal development. The investigated plutons, which range from tonalite and diorite to monzodiorite, monzonite, and syenite, share textural, mineralogical and geochemical attributes suggesting a common origin as juvenile magmas. Despite variation in modal mineralogy, the plutons are geochemically characterized by normative quartz, high Al2O3 (> 15 wt%), Na-rich fractionation trends (mol Na2O/K2O >2), low to moderate Rb (generallyenclaves and igneous layers and as intrusive units which exhibit textures indicative of contemporaneous mafic and felsic magmatism. Mafic mineral assemblages include: hornblende + biotite in tonalites; augite + biotite ± orthopyroxene ± pargasitic hornblende or hornblende+biotite in dioritic to monzodioritic rocks; and aegirine-augite ± silicic edenite ± biotite in syenite to alkali granite. Discrete plagioclase and microcline grains are present in most of the suites, however, some of the syenitic rocks are hypersolvus granitoids and contain only perthite. Mafic-ultramafic rocks have REE and Y contents indicative of their formation as amphibole-rich cumulates from the associated granitoids. Some cumulate rocks have skeletal amphibole with XMg(Mg/(Mg+ Fe2+)) indicative of crystallization from more primitive liquids than the host granitoids. Geochemical variation in the granitoid suites is compatible with fractionation of amphibole together with subordinate plagioclase and, in some cases, mixing of fractionated and primitive magmas. Mafic to ultramafic units with magnesium-rich cumulus phases and primitive granitoids (mol MgO/ (MgO+0.9 FeOTOTAL) from 0.60 to 0.70 and CT >150 ppm) are comagmatic with the evolved granitoids and indicate that the suites are mantle-derived. Isotopic studies of Archean monzodioritic rocks have shown LREE enrichment and initial 143Nd/144Nd ratios indicating derivation from mantle

  7. Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China)

    Science.gov (United States)

    Malaspina, Nadia; Hermann, Jörg; Scambelluri, Marco; Compagnoni, Roberto

    2006-08-01

    -800 °C. The petrological study, combined with bulk-rock and mineral trace element analyses, provides evidence of intense metasomatism affecting these eclogites. The bulk-rock major and trace element compositions indicate that the eclogites derive from basaltic protoliths with MORB and E-MORB affinity. Compared with such basalts, the studied rocks show strong depletion in SiO 2 and alkalis and enrichment in MgO and FeO. These features likely derive from element exchange with ultramafic rocks prior to subduction, possibly related with the influx of Si-depleted and Mg-enriched fluids produced during the serpentinisation of the associated lherzolitic rocks. On the other hand, the trace element bulk-rock compositions show strong enrichment in Cs, Ba and Pb. The same characteristic enrichment and fractionation is recorded by peak metamorphic clinopyroxene but not in retrograde amphibole. Therefore, influx of crustal fluids transporting LILE and light elements must have occurred during subduction at UHP conditions. This stage likely records the tectonic coupling of the mafic-ultramafic rocks with the associated crustal rock units and provides evidence of LILE mobility between different slab components.

  8. Why do mafic arc magmas contain ˜4wt% water on average?

    Science.gov (United States)

    Plank, Terry; Kelley, Katherine A.; Zimmer, Mindy M.; Hauri, Erik H.; Wallace, Paul J.

    2013-02-01

    The last 15 yr have seen an explosion of data on the volatile contents of magmas parental to arc volcanoes. This has occurred due to the intense study of melt inclusions trapped in volcanic phenocrysts, aliquots of magma that have presumably escaped degassing during eruption. The surprising first-order result is the narrow range in H2O concentrations in the least degassed melt inclusions from each volcano. Nearly all arc volcanoes are sourced with mafic magmas that contain 2-6 wt% H2O. The average for each arc varies even less, from 3.2 (for the Cascades) to 4.5 (for the Marianas), with a global average of 3.9±0.4 wt% H2O. Significant variations occur from volcano to volcano within each arc, but the means are indistinguishable within one s.d. The narrow range and common average value for H2O are in stark contrast to the concentrations of most other subduction tracers, such as Nb or Ba, which vary by orders of magnitude. A modulating process, either in the crust or mantle, is likely responsible for the restricted range in the H2O contents of arc melt inclusions. One possibility is that melt inclusion H2O values reflect vapor saturation at the last storage depth in the crust prior to eruption. In this scenario, magmas rise from the mantle with variable H2O contents (>4 wt%), become vapor-saturated and start degassing, and continue to degas up until the depth at which they stall. If the stalling depths are ∼6 km, which is common for storage depths beneath volcanoes, magmas would be saturated at ∼4 wt% H2O, and melt inclusions, most of which become closed during further ascent, would thus record ≤4 wt% H2O. Another possibility is that the mantle melting process modulates water content in the melt such that magmas rise out of the mantle with ∼4 wt% H2O. A strong relationship between the water content of the source, H2O(o) and the degree of melting (F) maintains nearly constant water contents in the melt for a restricted range in mantle temperature. Magmas with

  9. The Cerro Bitiche Andesitic Field: petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna

    Science.gov (United States)

    Maro, Guadalupe; Caffe, Pablo J.

    2016-07-01

    The Cerro Bitiche Andesitic Field (CBAF) is one of the two largest mafic volcanic fields in northern Puna (22-24° S) and is spatially and temporally associated with ignimbrites erupted from some central Andean Altiplano-Puna Volcanic Complex calderas. The CBAF comprises seven scoria cones and widespread high-K calcalkaline lava flows that cover an area of 200 km2. Although all erupted rocks have a relatively narrow chemical range (56-62 % SiO2, 3-6 % MgO), there is a broad diversity of mineral compositions and textures. The least evolved lavas (˜58-61 % SiO2) are high-Mg andesites with scarce (<10 %) microphenocrysts of either olivine or orthopyroxene. The small compositional range and low phenocryst content indicate evolution controlled by low percentages (<10 %) of fractional crystallization of olivine and clinopyroxene of magmas similar to the least evolved rocks from the field, accompanied by assimilation during rapid ascent through the crust. Evolved andesites (˜62 wt% SiO2), on the other hand, are porphyritic rocks with plagioclase + orthopyroxene + biotite and ubiquitous phenocryst disequilibrium textures. These magmas were likely stored in crustal reservoirs, where they experienced convection caused by mafic magma underplating, magma mixing, and/or assimilation. Trace element and mineral compositions of CBAF lavas provide evidence for complex evolution of distinct magma batches.

  10. Role of mafic and ultramafic rocks in drinking water quality and its potential health risk assessment, Northern Pakistan.

    Science.gov (United States)

    Begum, Shaheen; Shah, Mohammad Tahir; Muhammad, Said; Khan, Sardar

    2015-12-01

    This study investigates the drinking water (groundwater and surface water) quality and potential risk assessment along mafic and ultramafic rocks in the Swat district of Khyber Pakhtunkhwa Provence, Pakistan. For this purpose, 82 groundwater and 33 surface water samples were collected and analyzed for physico-chemical parameters. Results showed that the majority of the physico-chemical parameters were found to be within the drinking water guidelines set by the World Health Organization. However, major cationic metals such as magnesium (Mg), and trace metals (TM) including iron (Fe), manganese (Mn), nickel (Ni), chromium (Cr) and cobalt (Co) showed exceeded concentrations in 13%, 4%, 2%, 20%, 20% and 55% of water samples, respectively. Health risk assessment revealed that the non-carcinogenic effects or hazard quotient values through the oral ingestion pathway of water consumption for the TM (viz., Fe, Cr and Mn) were found to be greater than 1, could result in chronic risk to the exposed population. Results of statistical analyses revealed that mafic and ultramafic rocks are the main sources of metal contamination in drinking water, especially Ni and Cr. Both Ni and Cr have toxic health effects and therefore this study suggests that contaminated sites should be avoided or treated for drinking and domestic purposes. PMID:26608774

  11. Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Determining the global distribution of minerals on the Moon has been an important goal of lunar science. Hyperspectral remote sensing is an important approach to acquiring minerals on the Moon on the global scale. The wavelength of the absorption band center is the key parameter for identifying minerals with reflectance spectra as well as remote sensing data. The global absorption center map of the mafic minerals of the Moon was produced for the first time with the Chang’E-1 IIM data. This map shows the global distribution of mafic minerals such as orthopyroxenes, clinopyroxenes, and olivine and even plagioclase feldspar of the Moon. The validation for some representative areas indicates that the global map is reliable and even more detailed than the results derived from Clementine-data. Moreover, our method is insensitive to the topography and viewing and illumination geometries. The global absorption band center map not only contributes to the lunar science research, but also has other implications to be further studied. Moreover, the preprocessing methods such as calibration and correction introduced in this study can be useful in other research with IIM data.

  12. Determination of rare-earths and other trace elements in neo proterozoic-neo paleozoic dykes from Ceara state, Brazil, by neutron activation analysis

    Energy Technology Data Exchange (ETDEWEB)

    Anjos, Rafael Martins dos; Figueiredo, Ana M.G., E-mail: rafael.anjos@usp.b, E-mail: anamaria@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil). Centro do Reator Nuclear de Pesquisas. Lab. de Analise por Ativacao com Neutrons; Cardoso, Gustavo Luan; Marques, Leila S., E-mail: leila@iag.usp.b [Universidade de Sao Paulo (IAG/USP), SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas

    2011-07-01

    Trace elements such as rare earths, U, Th, Ta, Ba and Hf can be very useful in petrogenetic studies of igneous and metamorphic rocks, giving information about the origin and evolution of magmas. Instrumental Neutron Activation Analysis (INAA) is an accurate and precise for trace element analysis in geological samples, and provides the information required for this kind of studies. In this study, rare earths and incompatible trace elements were determined by INAA in the geological reference materials GS-N and BE-N, to quality control, and for the investigation of acid dykes of neo proterozoic-neo paleozoic ages, which outcrop in the Medio Coreau and Ceara Central domains from the Borborema Province (Ceara State). The powdered samples (particle sizes less than 100 mesh), crushed by using a mechanical agate mortar grinder, were irradiated at the IEA-R1 nuclear reactor at IPEN-CNEN/SP, and the induced activity was measured by high resolution gamma-ray spectrometry. The accuracy and precision of the method were evaluated and preliminary results of dyke samples are presented. (author)

  13. Variations in the chemical composition of lamprophyllite-group minerals and the crystal structure of fluorine-rich barytolamprophyllite from new peralkaline dyke

    Science.gov (United States)

    Akimenko, M. I.; Aksenov, S. M.; Sorokhtina, N. V.; Kogarko, L. N.; Kononkova, N. N.; Rastsvetaeva, R. K.; Rozenberg, K. A.

    2015-11-01

    The variations in the chemical composition of lamprophyllite-group minerals from a peralkaline dyke of the Mokhnatye Roga area (Kandalaksha region, Kola Peninsula), which are crystallized during the entire period of dyke formation and form several generations, have been investigated. The early generations differ in a steadily high fluorine content, while the later ones exhibit reduced amount of fluorine, impurity elements, and sodium, with a simultaneous increase in the potassium content. The crystal structure of fluorine- rich barytolamprophyllite (potentially a new representative of the lamprophyllite group, differing by the predominance of fluorine in the anion X site) has been analyzed by single crystal X-ray diffraction. This mineral is found to have a monoclinic unit cell with the following parameters: a = 19.5219(8) Å, b = 7.0915(2) Å, c = 5.3925(2) Å, β = 96.628(3)°, and sp. gr. C2/ m. The structure is refined to R = 5.73% in the anisotropic approximation of the atomic displacement parameters using 3668 I > 2σ( I). The idealized formula ( Z = 2) is (Ba,Sr)2[Na(Na,Fe)2(Ti,Mg)F2][Ti2(Si2O7)2O2].

  14. Deformation monitoring of the 2014 dyke intrusion and eruption within the Bárðarbunga volcanic system, and associated stress triggering at neighbouring volcanoes

    Science.gov (United States)

    Parks, Michelle; Árnadóttir, Thóra; Dumont, Stéphanie; Sigmundsson, Freysteinn; Hooper, Andrew; Drouin, Vincent; Ófeigsson, Benedikt; María Friðriksdóttir, Hildur; Hreinsdóttir, Sigrún; Rafn Heimisson, Elías; Vogfjörd, Kristín; Jónsdóttir, Kristín; Hensch, Martin; Guðmundsson, Gunnar; Magnússon, Eyjólfur; Einarsson, Páll; Rut Hjartardóttir, Ásta; Pedersen, Rikke

    2015-04-01

    The recent unrest and activity within the Bárðarbunga volcanic system, Iceland was initially identified by the onset of an intense earthquake swarm on the 16th August 2014 and concurrent movement registered at several nearby continuous GPS (cGPS) sites. Over the following weeks additional cGPS stations were installed, campaign sites were reoccupied and interferograms formed using X-band satellite images. Data were analysed in near real-time and used to map ground displacements associated with the initial dyke emplacement and propagation (NE of Bárðarbunga), responsible for the sudden unrest. On the 29th August 2014, a small fissure opened up just a few kilometers to the north of the Vatnajökull ice cap, at Holuhraun. The eruption lasted only a few hours, but was followed on 31st August by the onset of a fissure eruption, characterised by lava fountaining and the extrusion of extensive lava flows. The eruption continues at the time of writing (January 2015). We demonstrate how Interferometric Synthetic Aperture Radar (InSAR) analysis, in conjunction with GPS measurements and earthquake seismicity, has been instrumental in the continued monitoring of Bárðarbunga volcanic system since the onset of unrest. We also investigate how changes in the local stress field induced by the dyke intrusion and concurrent magma withdrawal may trigger seismicity and potentially renewed activity at neighbouring volcanoes. InSAR analysis has systematically been used throughout the eruption to monitor co-eruptive displacement in the vicinity of both the dyke and the eruption site, along with major co-eruptive subsidence occurring beneath the Bárðarbunga caldera - the latter is believed to have commenced shortly after the onset of the unrest and is associated with magma withdrawal beneath the central volcano, feeding the dyke and the ongoing eruption. We use Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) techniques to generate a time series of

  15. Mafic rocks from Erinpura gneiss terrane in the Sirohi region: Possible ocean-floor remnants in the foreland of the Delhi Fold Belt, NW India

    Indian Academy of Sciences (India)

    M K Pandit; H De Wall; H Daxberger; J Just; M Bestmann; K K Sharma

    2011-08-01

    A small isolated mafic body occurs to the south of Sirohi near village Daba within the Neoproterozoic Erinpura Granite in the southern sector of the Proterozoic Delhi Fold Belt in NW India. This mafic body occurs close to a 100 m wide NE–SW trending shear zone (Daba Shear Zone) which overprints the felsic rock fabrics. Further south, a small mafic body near village Kui was also sampled which forms the southern limit of the Phulad Ophiolite Suite which is a 300 km long major NE–SW trending lineament, described as Western Margin Fault. Some of the lithological components of the Daba mafic body show locally preserved magmatic fabric but completely transformed mineralogies under lower amphibolites facies metamorphic conditions where two-stage deformation has been inferred. Magnetic fabric analysis underlines a general correspondence of structural elements in both felsic and mafic lithologies. Binary correlations of Zr with other high field strength elements underline fractionation as the main process in the evolution of Daba and Kui rocks. Geochemical characteristics indicate subalkaline tholeiitic basalt affinity for these mafic rocks. The trace element characteristics, such as enriched LIL elements, high Th, absence of negative Nb anomalies and depletion in compatible elements in Daba samples suggest an enriched mantle source and lower degree of melting. The trace and rare earth element characteristics for Kui (Th anomaly, Nb–Ta trough and less spiked patterns, flat REE trends) indicate derivation from a refractory mantle source affected by fluids derived from subduction. Distinct differences in trace and REE characteristics between Daba and Kui can be interpreted in terms of different stages of ophiolite development.

  16. The timing of compositionally-zoned magma reservoirs and mafic 'priming' weeks before the 1912 Novarupta-Katmai rhyolite eruption

    Science.gov (United States)

    Singer, Brad S.; Costa, Fidel; Herrin, Jason S.; Hildreth, Wes; Fierstein, Judy

    2016-10-01

    The June, 6, 1912 eruption of more than 13 km3 of dense rock equivalent (DRE) magma at Novarupta vent, Alaska was the largest of the 20th century. It ejected >7 km3 of rhyolite, ∼1.3 km3 of andesite and ∼4.6 km3 of dacite. Early ideas about the origin of pyroclastic flows and magmatic differentiation (e.g., compositional zonation of reservoirs) were shaped by this eruption. Despite being well studied, the timing of events that led to the chemically and mineralogically zoned magma reservoir remain poorly known. Here we provide new insights using the textures and chemical compositions of plagioclase and orthopyroxene crystals and by reevaluating previous U-Th isotope data. Compositional zoning of the magma reservoir likely developed a few thousand years before the eruption by several additions of mafic magma below an extant silicic reservoir. Melt compositions calculated from Sr contents in plagioclase fill the compositional gap between 68 and 76% SiO2 in whole pumice clasts, consistent with uninterrupted crystal growth from a continuum of liquids. Thus, our findings support a general model in which large volumes of crystal-poor rhyolite are related to intermediate magmas through gradual separation of melt from crystal-rich mush. The rhyolite is incubated by, but not mixed with, episodic recharge pulses of mafic magma that interact thermochemically with the mush and intermediate magmas. Hot, Mg-, Ca-, and Al-rich mafic magma intruded into, and mixed with, deeper parts of the reservoir (andesite and dacite) multiple times. Modeling the relaxation of the Fe-Mg concentrations in orthopyroxene and Mg in plagioclase rims indicates that the final recharge event occurred just weeks prior to the eruption. Rapid addition of mass, volatiles, and heat from the recharge magma, perhaps aided by partial melting of cumulate mush below the andesite and dacite, pressurized the reservoir and likely propelled a ∼10 km lateral dike that allowed the overlying rhyolite to reach the

  17. Mineral chemistry, P-T-t paths and exhumation processes of mafic granulites in Dinggye, Southern Tibet

    Institute of Scientific and Technical Information of China (English)

    LIU; Shuwen; ZHANG; Jinjiang; SHU; Guiming; LI; Qiugen

    2005-01-01

    The mafic granulites in Dinggye, as various scale lense-shaped enclaves within the high Himalayan crystalline rock series, occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System (STDS) and the Xainza-Dinggye normal fault system. The main lithological assemblage comprises garnet plagioclase pyroxenite, garnet two-pyroxene granulite, pyroxene garnet amphibolite and so on. The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution. The first metamorphic stage, the garnet+clinopyroxene+quart mineral assemblage (M1) was probably formed under eclogite facies, the second stage, the plagioclase+clinopyroxene symplectite mineral assemblage (M2) was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage, the third stage, the plagioclase+clinopyroxene+ hypersthene symplectite mineral assemblage (M3) was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage, plagioclase+hornblende mineral assemblage (M4) was formed by hydrolysis of earlier mineral assemblages during late uplifting. The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites, whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite. These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyroblasts (M1) could be formed at the eclogite facies, the early decompressive breakdown (M2) occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃, the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃ and M4 plagioglase+hornblende retrograde mineral assemblage was produced under

  18. Petrogenesis of the Neoproterozoic Ngondo Plutonic complex (Cameroon, west central Africa): a case of late-collisional ferro-potassic magmatism

    Science.gov (United States)

    Tagne-Kamga, Gabriel

    2003-04-01

    The Ngondo complex is a late-collisional pluton, which was emplaced around 600 Ma along a N030° E strike-slip shear zone in the southwestern part of the Neoproterozoic Fold Belt of Cameroon. It comprises three successively emplaced plutonic groups of rocks: (i) mafic to felsic intrusive rocks (MFR), (ii) fine-grained granites (FGG) and (iii) coarse-grained granites (CGG). Late aplitic and pegmatite dykes were emplaced along brittle fractures in these plutons. The complex is metaluminous to weakly peraluminous, high-K, calc-alkaline to " trans-alkaline" ferro-potassic, with mineralogical and geochemical characteristic of I-type granites. The plutonic rocks are characterised by high Ba, Sr, Rb and ∑REE concentrations and low Ni and Cr contents in the mafic members. They also display chondrite-normalised REE patterns characterised by variable LREE enrichment, moderate to minor HREE fractionation with moderate to pronounced negative Eu anomalies (Eu/Eu∗: 0.6-0.9 (MFR), 0.2-0.5 (FGG), 0.3-0.7 (CGG)). Trace element distribution patterns for the three plutonic groups are similar with a distinctive depletion in Nb, Sr and Ti relative to other trace elements and a greater enrichment in LILE compared to HFSE. These plutonic groups present distinct evolutionary trends precluding their origin from differentiation of a single parental magma. The geochemical and isotopic data indicate that they derived from partial melting of heterogeneous (meta)-igneous mafic lower crustal materials, having possibly the composition of amphibolitised high-K calc-alkaline basaltic andesites and andesitic metagreywackes. Petrographic evidences such as the presence of quartz-ocelli, xenocrysts of feldspar, fragments of country rocks (migmatitic gneisses) strongly indicate that crustal contamination may have played an important role in the genesis of the plutonic rocks. This contamination process is further supported by the variation of major and trace elements together with Sr-Nd isotopic data

  19. Charnockitic ortho gneisses and mafic granulites of Cerro Olivo complex, proterozoic basement of SE Uruguay, Part 1: Geology

    International Nuclear Information System (INIS)

    Charnockitic ortho gneisses and mafic granulite s exposed in the Cerro Bori Block, in the center of Punta del Este terrain, were the first document occurrence of granulitic rocks from SE sector of the Uruguayan Shield. We present here their main geological features, with the purpose to suggest some petrologic and structural interesting problems for a future lithogeochemical, mineral chemistry, stable isotopes and fluid inclusion studies about these rocks. We propose some speculation form field-based studies considering a cognate magmatic origin of both kinds of rocks, previous to a homogeneous granulitic metamorphism. Some structural evidences indicate that after their uplift, these rocks were located on over thickened crust, at great to medium deepness. A cataclasis during anatexis and amphibolite-facies mineral association stabilization are common phenomena. Other evidences suggest a polycyclic character for the regional geologic evolution

  20. Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials

    Science.gov (United States)

    Fourny, Anaïs.; Weis, Dominique; Scoates, James S.

    2016-03-01

    Controlling the accuracy and precision of geochemical analyses requires the use of characterized reference materials with matrices similar to those of the unknown samples being analyzed. We report a comprehensive Pb-Sr-Nd-Hf isotopic and trace element concentration data set, combined with quantitative phase analysis by XRD Rietveld refinement, for a wide range of mafic to ultramafic rock reference materials analyzed at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. The samples include a pyroxenite (NIM-P), five basalts (BHVO-2, BIR-1a, JB-3, BE-N, GSR-3), a diabase (W-2), a dolerite (DNC-1), a norite (NIM-N), and an anorthosite (AN-G); results from a leucogabbro (Stillwater) are also reported. Individual isotopic ratios determined by MC-ICP-MS and TIMS, and multielement analyses by HR-ICP-MS are reported with 4-12 complete analytical duplicates for each sample. The basaltic reference materials have coherent Sr and Nd isotopic ratios with external precision below 50 ppm (2SD) and below 100 ppm for Hf isotopes (except BIR-1a). For Pb isotopic reproducibility, several of the basalts (JB-3, BHVO-2) require acid leaching prior to dissolution. The plutonic reference materials also have coherent Sr and Nd isotopic ratios (<50 ppm), however, obtaining good reproducibility for Pb and Hf isotopic ratios is more challenging for NIM-P, NIM-N, and AN-G due to a variety of factors, including postcrystallization Pb mobility and the presence of accessory zircon. Collectively, these results form a comprehensive new database that can be used by the geochemical community for evaluating the radiogenic isotope and trace element compositions of volcanic and plutonic mafic-ultramafic rocks.

  1. Lamprophyre or Lamproite Dyke in the SW Tarim Block?--Discussion on the Petrogenesis of These Rocks and Their Source Region

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The mineralogical, petrological and geochemical studies on Keliyang (克里阳) potassic dykes have been carried out to understand their rock types, the petrogenesis and the nature of their mantle sources. They are potassic lamprophyre, not lamproites as the previous researchers believed. In this study, the whole-rock major and trace element compositions of another 6 lamproite dykes recently discovered are reported. Major elements were determined by X-ray fluorescence spectrometry (XRF) techniques, while REE and trace elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). They can be classified into phlogopite-diopside lamprophyre, leucite-diopside lamprophyre and granular carbonatite-bearing diopside lamprophyre on the basis of their mineral components. They are all characterized by relatively low SiO2 (41.31% -44. 84%), TiO2 (0.75% -0.86%) and high MgO (7.30%-11.33%), K2O (4.01%-6.01%) concentrations with K2O/Na2O ratios of 2. 77-12.49. In addition, they display enrichment in large-ion iithophile elements (LILEs, e. g., Rb, Sr,Ba) and LREE, but a relative depletion in high-field-strength elements (HFSEs, e.g. , Nb, Ta, Zr, Hf and Ti). They display similar chondrite-normalized REE patterns with slight negative Eu anomalies (δEu=0.64-0. 82), and high initial 87Sr/86Sr ratios, which resemble those of high K/Ti and low-Ti potassic magmas formed in subduction-related settings. Consequently, we suggest that the parental magma was generated by partial melting of the phlogopite-amphibole- bearing garnet lherzolite within the lithospheric mantle that might have been metasomatized by a potassium-bearing fluid released from a subduction oceanic crust.

  2. Petrogenesis and tectonic implications of Triassic mafic complexes with MORB/OIB affinities from the western Garzê-Litang ophiolitic mélange, central Tibetan Plateau

    Science.gov (United States)

    Liu, Bin; Ma, Chang-Qian; Guo, Yu-Heng; Xiong, Fu-Hao; Guo, Pan; Zhang, Xin

    2016-09-01

    Although numerous Paleo-Tethyan ophiolites with mid-oceanic ridge basalts (MORB) and/or oceanic-island basalt (OIB) affinities have been reported in the central Tibetan Plateau (CTP), the origin and tectonic nature of these ophiolites are not well understood. The petrogenesis, mantle sources and geodynamic setting of the mafic rocks from these ophiolites are unclear, which is the main reason for this uncertainty. In this paper, we present new geochronological, mineralogical and Sr-Nd isotopic data for the Chayong and Xiewu mafic complexes in the western Garzê-Litang suture zone (GLS), a typical Paleo-Tethyan suture crossing the CTP. Zircon LA-ICP-MS U-Pb ages of 234 ± 3 Ma and 236 ± 2 Ma can be interpreted as formation times of the Chayong and Xiewu mafic complexes, respectively. The basalts and gabbros of the Chayong complex exhibit enriched MORB (E-MORB) compositional affinities except for a weak depletion of Nb, Ta and Ti relative to the primitive mantle, whereas the basalts and gabbros of the Xiewu complex display distinct E-MORB and OIB affinities. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The geochemical and Sr-Nd isotopic data reveal that the Chayong mafic rocks may have been derived from depleted MORB-type mantle metasomatized by crustal components and Xiewu mafic rocks from enriched lithospheric mantle metasomatized by OIB-like components. The ratios of Zn/Fet, La/Yb and Sm/Yb indicate that these mafic melts were produced by the partial melting of garnet + minor spinel-bearing peridotite or spinel ± minor garnet-bearing peridotite. We propose that back-arc basin spreading associated with OIB/seamount recycling had occurred in the western GLS at least since the Middle Triassic times, and the decompression melting of the depleted MORB-type asthenosphere mantle and partial melting of sub-continental lithosphere were metasomatized by plume

  3. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Indian Academy of Sciences (India)

    Ashima Saikia; Bibhuti Gogoi; Mansoor Ahmad; Talat Ahmad

    2014-07-01

    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, crosscutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

  4. Characteristics and origin of mafic and ultramafic xenoliths in trachyandesite lavas from Heikongshan volcano,Tengchong,Yunnan Province,China

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The trachyandesite lavas from Heikongshan volcano of the Tengchong volcanic cluster, Yunnan Province contain relatively abundant mafic and ultramafic small xenoliths comprising mainly gabbro, pyroxenite and rare lherzolites, all less than 2.5 cm in size. Gabbro xenoliths are characterized by "open" texture represented by relatively abundant vesicles and ground-mass fillings, while pyroxenite xenoliths are characterized by equigranular and poikilitic texture. Their mineral compositions (clinopyroxene ± orthopyroxene ± plagioclase) are similar to those of phenocrysts in lavas, and their equilibration temperature (1000-1125°C) is consistent with the crystallization temperature of the phenocrysts (998-1108°C). Thus, the textures and compositions of these xenoliths are different from those of lower crustal and mantle xenoliths, and were derived from the magma chamber. Among them, the gabbroic xenoliths come from the crystal-bubble-liquid zone at the top of the magma reservoir, while the pyroxenite xenoliths come from the cumulates in the bottom of magma reservoir. The studied single lherzolite xenolith with porphyroclastic texture has similar mineral compositions to the mantle xenoliths from eastern China, and is considered to be of upper mantle origin. It was brought into magma reservoir by replenishment magma, and might have experienced a cooling event before eruption. The formation of xenoliths in trachyandesite flows largely reflects the ascent, storage, evolution and eruption processes of magma.

  5. Rb-Sr geochronology and geochemical characteristics of mafic dikes in the Nova Lacerda and Conquista D'Oeste region, Mato Grosso, SW Amazonian Craton

    International Nuclear Information System (INIS)

    In the Nova Lacerda and Conquista D'Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafic dikes trending NNW intrude the Nova Lacerda Granite (1462±12 Ma), within the Jauru Domain, in the Rondonia-San Ignacio Province (1.55 - 1.3 Ga). The mafic swarm comprises diabases, metadiabases and amphibolites. Metadiabases originated from uralitization of diabases. These rocks have tholeiitic affinity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 ± 32 Ma and 1330 ± 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source. (author)

  6. Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: Constraints of geochemical and isotopic data

    Science.gov (United States)

    Ngonge, Emmanuel Donald; de Hollanda, Maria Helena Bezerra Maia; Archanjo, Carlos José; de Oliveira, Diógenes Custódio; Vasconcelos, Paulo Marcosde Paula; Muñoz, Patrício Rodrigo Montecinos

    2016-08-01

    The Ceará Mirim dyke swarm (northeastern Brazil) is composed of Cretaceous tholeiites with plagioclase, clinopyroxene (± olivine), Fe-Ti oxides and pigeonite in their groundmass. These tholeiites have been subdivided into three groups: high-Ti olivine tholeiites, evolved high-Ti tholeiites (TiO2 ≥ 1.5 wt.%; Ti/Y > 360), and low-Ti tholeiites (TiO2 ≤ 1.5 wt%; Ti/Y ≤ 360), with all exhibiting distinct degrees of enrichment in incompatible elements relative to Primitive Mantle. Negative Pb anomalies are found in all three groups, while Nb-Ta abundances similar to those of OIB-type magmas are found in the olivine tholeiites, with moderate to high depletions being observed, respectively, in the evolved high-Ti and low-Ti tholeiites. The low-Ti tholeiites exhibit some contamination with crustal (felsic) materials during ascent. The initial isotopic compositions of the olivine tholeiites show uniform and unradiogenic 87Sr/86Sr (~ 0.7035-0.7039) combined with (in part) radiogenic 143Nd/144Nd and 206Pb/204Pb (> 19.1) ratios, which together reveal a likely contribution of FOZO (FOcalZOne) component in their genesis. The other tholeiite groups show variable Sr-Nd ratios with relatively consistent 206Pb/204Pb ratios clustering towards an isotopically enriched mantle (EM1) component. Taken in conjunction with the Nb, this enriched signature reflects the involvement of a subduction-modified lithospheric mantle in the source of the evolved high-Ti and low-Ti tholeiites. Thus, we propose that FOZO and EMI components coexisted (including minor mixing with E-MORB magmas) and contributed in varying extents to the generation of the Ceará-Mirim dyke swarm primary melts, which segregated at 75 to 60 km in depth around the garnet-spinel facies transition zone. The mechanism that promoted melting was most likely non-plume related. We suggest that plate-boundary forces linked to the opening of the Atlantic Ocean promoted passive rifting and that the resulting asthenospheric

  7. Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry

    Institute of Scientific and Technical Information of China (English)

    HOU; Zhenhui; LI; Shuguang; CHEN; Nengsong; LI; Qiuli; LIU

    2005-01-01

    The mafic granulites from Huilanshan are outcropped on the center of the Luotian dome in the northern Dabie Mountains. The Sm-Nd isochron defined by granulite-facies metamorphic minerals (garnet + clinopyroxene + hypersthene) yields an age of 136(±)18 Ma indicating the early Cretaceous granulite-facies metamorphism. The cathodoluminescence (CL) images of zircons from the granulite show clearly core-mantle-rim structures. The zircon cores are characterized by typical oscillatory zoning and highly HREE enriched patterns, which suggests their magma origin. Some zircon cores among them with little Pb loss give SHRIMP U-Pb ages ranging from 753 to 780 Ma, which suggests that the protolith of Huilanshan granulite is Neoproterozoic mafic rocks. The zircon mantles usually cut across the oscillatory zone of the zircon cores have 3―10 times lower REE, Th, U, Y, Nb and Ta contents than the igneous zircon cores but have high common Pb contents. These characteristics suggest that they were formed by hydrothermal alteration of the igneous zircons. The part of zircon mantles with little Pb loss give a similar SHRIMP U-Pb age (716―780 Ma) to the igneous zircon cores, which implies that the hydrothermal events occurred closely to the magmatic emplacement. In view of the strong early Cretaceous magmatism in the Luotian dome, consequently, the Huilanshan mafic granulite was formed by heating of the Neoproterozoic mafic rocks in mid-low crust, which caused the granulite-facies metamorphism underneath the Dabie Mountains. The similarity between the granulite metamorphic age (136±18 Ma) defined by Sm-Nd isochron and K-Ar age of 123―127 Ma given by amphible from the gneiss in Luotian dome suggests a rapid uplifting of the Luotian dome, which may result in further exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains.

  8. Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Guba, Chukotka (NE Russia): Significance for interregional correlations

    Science.gov (United States)

    Ledneva, G. V.; Pease, V. L.; Sokolov, S. D.

    2008-12-01

    In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska-Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Guba, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U-Pb zircon age of 252+/-4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Guba region have major and trace element compositions identical the tholeiitic flood basalts of the main plateau stage of the Siberian LIP. They are strongly differentiated, the result of high-pressure equilibrium crystallization of a low-Ti/Y tholeiitic melt, and contaminated. The compositional variations in these rocks, however, neither proves nor disproves a correlation between the Permo-Triassic tholeiitic flood basalts of eastern Chukotka and the Siberian LIP. Thus, two alternative geodynamic interpretations are possible: 1) The hypabyssal mafic rocks and associated tholeiitic flows crystallized from a plume-derived melt; 2) The rocks are not related to plume activity, consequently eastern Chukotka was probably part of a passive rifted or extensional continental margin in the Permo-Triassic. Nonetheless, we prefer the first of these two possibilities. Funding for this work is gratefully acknowledged from the Swedish Polar Research Secretariat ("Beringia-2005"), the Swedish Research Council, the Russian Foundation for Basic Research (grant No 08-05-00547), Leading Scientific School (NSH-3172.2008.5) and ONZ RAS. Thanks are also extended to M.J. Whitehouse and the Nordsim facility - the Nordsim facility is funded by the research councils of Denmark, Norway, Sweden, the Geological Survey of Finland, and the Swedish Museum of

  9. Late Mesozoic crust-mantle interaction and lower crust components in South China: A geochemical study of mafic granulite xenoliths from Cenozoic basalts

    Institute of Scientific and Technical Information of China (English)

    于津海; 徐夕生; 周新民

    2003-01-01

    Mafic granulite xenoliths collected from Cenozoic basalts in SE China can be classified as magmatic granulite and cumulate granulite. Magmatic granulites are characterized by highly concentrated Al2O3, K2O, P2O5, Ba, Sr, Pb and REE, and low contents of Nb, Zr, Hf and Th, and have an incompatible element abundance pattern similar to that of continental arc basalts. Cumulate granulites aredepleted in K2O, P2O5, Rb, Cs and Ba. These granulite xenoliths were the products of crystallization and recrystallization of the basaltic magma underplating into crust-mantle boundary in Late Mesozoic. Sr and Nd isotopic compositions and variation trend of these mafic rocks are the result of crust-mantle mixing and controlled by assimilation and fractional crystallization process (AFC). However,trace element and major element variations were mainly controlled by fractionalcrystallization. The granulites are similar in geochemistry to surface Late Mesozoic gabbro and basalt in the study area, suggesting a close petrogenetic link between them. Late Mesozoic basaltic magma activities are the most important cause for the formation of extensive contemporaneous granite and rhyolite in the study area. This study and previous data indicate that the lower crust beneath South China is composed of a variety of Paleo- to Meso-proterozoic metamorphic rocks and Late Mesozoic mafic granulites.

  10. Caribbean affinities of mafic crust from northern Colombia: preliminary geochemical results from basaltic rocks of the Sinu-San Jacinto belt

    Science.gov (United States)

    Bustamante, C.; Cardona, A.; Valencia, V.; Weber, M.; Guzman, G.; Montes, C.; Ibañez, M.; Lara, M.; Toro, M.

    2009-12-01

    The petrotectonic characterization of accreted mafic remnants within the northern Andes and the Caribbean yield major insights on the growth and evolution of oceanic plates, as well as in the identification of the role of terrane accretion within the northern Andes orogeny. Within the northern termination of the Andes, in northern Colombia, several exposures of mafic and ultramafic rocks have been identified. However, extensive sedimentary cover and difficulties in field access have left the petogenetic analysis and tectonic implications of this rocks scarcely studied. Preliminary geochemical constrains from volcanic rocks obtained in outcrops and as clasts from a Paleocene-Eocene conglomerate indicate that the mafic rocks are mainly andesitic in composition, with well defined enrichment in Th and Ce and depletion in Nb and flat to weakly enriched LREE. These features suggest a relatively immature intra-oceanic volcanic arc setting for the formation of these rocks. Hornblende-dioritic dikes in peridotites also attest to the role of water in the magmatic evolution, and the affinity to a subduction related setting. The tectonic implications of this arc remnants and the relation between these rocks and other oceanic domains in the northern Andes suggest that the compositional and tectonic setting on the different accreted margins of the Caribbean plate are heterogeneous.

  11. Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

    Science.gov (United States)

    Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

    2005-01-01

    During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

  12. Note: Modified π-type Butterworth-Van Dyke model for dual-mode Lamb-wave resonator with precise two-port Y-parameter characterizations

    Science.gov (United States)

    Wang, Yong; Hong, Yan; Goh, Wang Ling; Mu, Xiaojing

    2016-10-01

    Dual-mode Lamb-wave resonator has become a powerful component for clock reference and sensing applications, enabling efficient compensations of temperature effects, concurrent measurements of multiple environmental parameters, etc. An equivalent circuit model for the dual-mode Lamb-wave resonator is indispensable as it provides a means as well as being an effective tool for evaluating device characteristics and to aid the designing of circuitry for the resonators. This could be the first time ever that an efficient equivalent-circuit model, i.e., modified π-type Butterworth-Van Dyke model for dual-mode Lamb-wave resonators is reported. Evaluated by experiments, this model attains noteworthy agreements on both the magnitudes and phases of Y11 and Y21 of the measurement results. Compared to literature, the proposed model is capable of modeling the dual resonances efficiently. Moreover, this work also proves more accurate when viewing the Y-parameters across a wide frequency range. The gained features of this model are most beneficial for the analysis of the dual-mode Lamb-wave resonator and also for the designing of circuits.

  13. Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)

    Science.gov (United States)

    Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh

    2016-09-01

    The Southern Oklahoma Aulocogen (SOA) stretches from southern Oklahoma through the Texas panhandle and into Colorado and New Mexico, and contains mafic through silicic magmatism related to the opening of the Iapetus Ocean during the early Cambrian. Cambrian magmatic products are best exposed in the Wichita Mountains (Oklahoma), where they have been extensively studied. However, their ultimate derivation is still somewhat contentious and centers on two very different models: SOA magmatism has been suggested to occur via [1] continental rifting (with or without mantle plume emplacement) or [2] transform-fault related magmatism (e.g., leaky strike-slip faults). Within the SOA, the subsurface in and adjacent to the Arbuckle Mountains in southern Oklahoma contains thick sequences of mafic to intermediate lavas, intrusive bodies, and phreatomagmatic deposits interlayered with thick, extensive rhyolite lavas, thin localized tuffs, and lesser silicic intrusive bodies. These materials were first described in the Arbuckle Mountains region by a 1982 drill test (Hamilton Brothers Turner Falls well) and the best available age constraints from SOA Arbuckle Mountains eruptive products are ~ 535 to 540 Ma. Well cuttings of the mafic through intermediate units were collected from that well and six others and samples from all but the Turner Falls and Morton wells are the focus of this study. Samples analyzed from the wells are dominantly subalkaline, tholeiitic, and range from basalt to andesite. Their overall bulk major and trace element chemistry, normative mineralogy, and Srsbnd Nd isotope ratios are similar to magmas erupted/emplaced in flood basalt provinces. When compared with intrusive mafic rocks that crop out in the Wichita Mountains, the SOA well cuttings are geochemically most similar to the Roosevelt Gabbros. New geochemical and isotope data presented in this study, when coupled with recent geophysical work in the SOA and the coeval relationship with rhyolites, indicates

  14. Evolution of the Bangong-Nujiang Tethyan ocean: Insights from the geochronology and geochemistry of mafic rocks within ophiolites

    Science.gov (United States)

    Wang, Bao-Di; Wang, Li-Quan; Chung, Sun-Lin; Chen, Jian-Lin; Yin, Fu-Guang; Liu, Han; Li, Xiao-Bo; Chen, Ling-Kang

    2016-02-01

    The Bangong-Nujiang suture zone (BNSZ) is located in the central Tibetan Plateau, and represents the relict of the Bangong-Nujiang Tethyan Ocean (BNTO). This paper presents zircon U-Pb ages and whole-rock geochemical and Sr-Nd isotope data for the ophiolitic rocks from the Rutog, Dongco, Dongqiao, Amdo, and Dengqen areas (from west to east) in the BNSZ. Zircon U-Pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 ± 2, 167 ± 2, 187 ± 2, 184 ± 2, 177 ± 3, and 164 ± 2 Ma, respectively. Mafic rocks (gabbros and basalts) in the BNSZ can be divided into MORB-like and OIB-type, based on geochemical data. The MORB-like rocks are tholeiitic and can be further divided into N- and E-MORB subtypes, marked by depleted and flat REE patterns, respectively. All MORB-like rocks show supra-subduction zone (SSZ) geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements, coupled with high and positive whole-rock εNd(t) values (+ 8.1 to + 5.4). The OIB-type rocks, which formed in the Early Cretaceous (~ 132-108 Ma), are exposed in the Dongco, Dongqiao, and Tarenben areas, and they consist mostly of alkali basalts with within-plate geochemical characteristics and positive εNd(t) values (+ 5.9 to + 4.5). On the basis of these new data, combined with information from the literature, we further support that the BNTO was an intra-oceanic arc-backarc basin that existed between the North Lhasa subterrane (NLT) and the South Qiangtang subterrane (SQT) during the Early-Middle Jurassic. This basin may have been active until the Early Cretaceous, when the OIB-type basalts erupted.

  15. Magma mixing/mingling in the Eocene Horoz (Nigde) granitoids, Central southern Turkey: evidence from mafic microgranular enclaves

    Science.gov (United States)

    Kocak, Kerim; Zedef, Veysel; Kansun, Gursel

    2011-11-01

    Mafic microgranular enclaves (MMEs) are widespread in the Horoz pluton with granodiorite and granite units. Rounded to elliptical MMEs have variable size (from a few centimetres up to metres) and are generally fine-grained with typical magmatic textures. The plagioclase compositions of the MMEs range from An18-An64 in the cores to An17-An29 in the rims, while that of the host rocks varies from An17 to An55 in the cores to An07 to An33 in the rims. The biotite is mostly eastonitic, and the calcic-amphibole is magnesio-hornblende and edenite. Oxygen fugacity estimates from both groups' biotites suggest that the Horoz magma possibly crystallised at fO2 conditions above the nickel-nickel oxide (NNO) buffer. The significance of magma mixing in their genesis is highlighted by various petrographic and mineralogical characteristics such as resorption surfaces in plagioclases and amphibole; quartz ocelli rimmed by biotite and amphibole; sieve and boxy cellular textures, and sharp zoning discontinuities in plagioclase. The importance of magma mixing is also evident in the amphiboles of the host rocks, which are slightly richer in Si, Fe3+ and Mg in comparison with the amphiboles of MMEs. However, the compositional similarity of the plagioclase and biotite phenocrysts from MMEs and their host rocks suggests that the MMEs were predominantly equilibrated with their hosts. Evidence from petrography and mineral chemistry suggests that the adakitic Horoz MMEs could be developed from a mantle-derived, water-rich magma (>3 mass%) affected by a mixing of felsic melt at P >2.3 kbar, T >730°C.

  16. Petrogenesis and metallogenesis of the Xinjie layered mafic-ultramafic intrusion, China: Modeling of recharge, assimilation and fractional crystallization

    Science.gov (United States)

    Li, Hongbo; Zhang, Zhaochong; Li, Yongsheng; Santosh, M.

    2015-12-01

    The Xinjie layered mafic-ultramafic intrusion in the central Emeishan large igneous province (ELIP), SW China, hosts Fe-Ti-V oxide ore in the upper part and Ni-Cu-platinum-group element (PGE) sulfide deposits in the lower part. In this study, we use published Sr-Nd isotopic data to simulate and evaluate the energy-constrained recharge, assimilation, and fractional crystallization (EC-RAFC) model with a view to track the petrogenesis and mineralization. In contrast to the energy-constrained assimilation fractional crystallization (EC-AFC) model, the EC-RAFC modeling shows that the Xinjie intrusion may represent a shallow crustal magma chamber system, where it experienced the RAFC processes. In the early stage of the magmatic process (Tm = 1460 °C), a pulse of magma was injected into an actively evolving magma chamber. Minor melting (Ma∗ = 0.257) and assimilation of the wallrock (underlying Emeishan basalts) occurred when the temperature of magma (Tm = 1245 °C) decreased close to the equilibration temperature (Teq = 1165 °C). The mass-temperature plots indicate that fractional crystallization was significantly affected by the recharge and assimilation processes, whereas the contaminated magma recharge favored the early crystallization of Fe-Ti oxides as well as the formation of the PGE-bearing immiscible melt in the lower part of the intrusion. In contrast, the formation of the Fe-Ti oxides ores in the upper part occurred probably through fractional crystallization and/or immiscibility of the evolved Fe-Ti-rich magma, resulting in the paragenesis of Fe-Ti-V oxides and Ni-Cu-PGE sulfides in the Xinjie layered intrusion.

  17. Petrology, 40Ar/39Ar age, Sr-Nd isotope systematics, and geodynamic significance of an ultrapotassic (lamproitic) dyke with affinities to kamafugite from the easternmost margin of the Bastar Craton, India

    Science.gov (United States)

    Rao, N. V. Chalapathi; Atiullah; Burgess, R.; Nanda, Purnendu; Choudhary, A. K.; Sahoo, Samarendra; Lehmann, B.; Chahong, Ngazipmi

    2016-04-01

    We report the mineralogy, bulk-rock geochemistry, 40Ar/39Ar (whole-rock) age and radiogenic (Sr and Nd) isotope composition of an ultrapotassic dyke from Sakri (Nuapada lamproite field) located at the tectonic contact between the easternmost margin of the Bastar craton and Eastern Ghats Mobile Belt, India. The Sakri dyke has a mineralogy which strongly resembles a lamproite sensu stricto (viz.,Ti-rich phlogopite, Na-poor diopside, Fe-rich sanidine, ulvospinel trend and Sr-rich apatite). However, its bulk-rock major element geochemical characteristics (viz., extreme silica-undersaturated nature) resemble sensu lato kamafugite from Toro Ankole, Uganda, East African Rift, and Alto Paranaiba Province, Brazil. The Sakri dyke also displays certain compositional peculiarities (viz., high degree of evolution of mica composition from phlogopite to biotite, elevated titanium and aluminum in clinopyroxene and significantly lower bulk Mg#) when compared to the ultrapotassic rocks from various Indian cratons. 40Ar/39Ar dating gave a plateau age of 1045 ± 9 Ma which is broadly similar to that of other Mesoproterozoic (i) lamproites from the Bastar and Bundelkhand cratons, and (ii) kimberlites from the Eastern Dharwar craton. Initial bulk-rock Sr (0.705865-0.709024) and Nd (0.511063-0.511154) isotopic ratios reveal involvement of an `enriched' source region with long-term incompatible element enrichment and a depleted mantle (TDM) Nd model age of 2.56 Ga straddling the Archaean-Proterozoic chronostratigraphic boundary. The bulk-rock incompatible trace element ratios (Ta/Yb, Th/Yb, Rb/Ba and Ce/Y) of the Sakri ultrapotassic dyke negate any significant influence of crustal contamination. Small-degree melting (1 to 1.5 %) of a mixed garnet-facies and spinel-facies phlogopite lherzolite can account for its observed REE concentrations. Whereas the emplacement of the Sakri ultrapotassic dyke is related to the amalgamation of the supercontinent of Rodinia, its overlapping geochemical

  18. Devonian granitoids and their hosted mafic enclaves in the Gorny Altai terrane, northwestern Central Asian Orogenic Belt: crust-mantle interaction in a continental arc setting

    Science.gov (United States)

    Chen, Ming; Sun, Min

    2016-04-01

    Granitoids are a major component in the upper continental crust and hold key information on how did the continental crust grow and differentiate. This study focuses on the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt (CAOB). The association of granitoids and mafic enclaves can provide important clues on the source nature, petrogenetic processes and geodynamic setting of the Yaloman intrusive complex, which in turn will shed light on the crustal evolution in the northwestern CAOB. Zircon U-Pb dating shows that the granitoids, including quartz diorites and granodiorites, were emplaced in ca. 389-387 Ma. The moderate Na2O + K2O contents and low A/CNK values indicate that these rocks belong to the sub-alkaline series with metaluminous to weakly peraluminous compositions. The granitoids yield two-stage zircon Hf model ages of ca. 0.79-1.07 Ga and whole-rock Nd model ages of ca. 0.90-0.99 Ga, respectively, implying that they were mainly sourced from Neoproterozoic juvenile crustal materials. The mafic enclaves show an almost identical crystallization age of ca. 389 Ma. The identification of coarse-grained xenocrysts and acicular apatites, together with the fine-grained texture, makes us infer that these enclaves are likely to represent magmatic globules commingled with the host magmas. The low SiO2 and high MgO contents of the mafic enclaves further suggest that substantial mantle-derived mafic melts were probably involved in their formation. Importantly, the SiO2 contents of the granitoids and mafic enclaves are well correlated with other major elements and most of the trace elements. Also a broadly negative correlation exists between the SiO2 contents and whole-rock epsilon Nd (390 Ma) values of the granitoids. Given the observation of reversely zoned plagioclases within the granitoids and the common occurrence of igneous mafic enclaves, we propose that magma mixing probably played an important role in the formation

  19. S saturation history of Nain Plutonic Suite mafic intrusions: origin of the Voisey's Bay Ni-Cu-Co sulfide deposit, Labrador, Canada

    Science.gov (United States)

    Lightfoot, Peter C.; Keays, Reid R.; Evans-Lamswood, Dawn; Wheeler, Robert

    2012-01-01

    The Voisey's Bay deposit is hosted in a 1.34-Ga intrusion composed of troctolite, olivine gabbro, and ferrogabbro. The sulfide mineralization is associated with magmatic breccias that are enveloped by weakly mineralized olivine gabbros and troctolites, and also occurs as veins along structures in adjacent paragneiss. A dyke is connected to the base of the north wall of the Eastern Deeps Intrusion, and the entry point of this dyke into the chamber is the locus of the Eastern Deeps nickel sulfide deposit. A detailed exploration in the area between the Eastern Deeps and the Ovoid has shown that these intrusions and ore deposits are connected by a splayed dyke. The Eastern Deeps Deposit is surrounded by a halo of moderately to weakly mineralized variable-textured troctolite (VTT) that reaches a maximum thickness above the axis of the Eastern Deeps Deposit along the northern wall of the Eastern Deeps Intrusion. The massive sulfides and breccia sulfides are petrologically and chemically different when compared to the disseminated sulfides in the VTT, and there is a marked break in Ni tenor of sulfide between the two. Sulfides hosted in the dyke tend to have low metal tenors ([Ni]100 = 2.5-3.5%), sulfides in Eastern Deeps massive and breccia ores have intermediate Ni tenors ([Ni]100 = 3.5-4%), and disseminated sulfides in overlying rocks have high Ni tenors ([Ni]100 = 4-8%). Four principal processes control the compositions of the Voisey's Bay sulfides. Coarse-grained loop-textured ores consisting of pyrrhotite crystals separated by chalcopyrite and pentlandite exhibit a two orders of magnitude variation in the Pd/Ir ratio which is due to mineralogical variations where pentlandite is enriched in Pd and Ir is dispersed throughout the mineral assemblage. A decrease in Ir and Rh from the margin of the Ovoid toward cubanite-rich parts at the central part of the Ovoid is consistent with fractionation of the sulfide from the margins toward the center of the Ovoid. The Ovoid

  20. Regularities of spatial association of major endogenous uranium deposits and kimberlitic dykes in the uranium ore regions of the Ukrainian Shield

    Science.gov (United States)

    Kalashnyk, Anna

    2015-04-01

    During exploration works we discovered the spatial association and proximity time formation of kimberlite dykes (ages are 1,815 and 1,900 Ga for phlogopite) and major industrial uranium deposits in carbonate-sodium metasomatites (age of the main uranium ore of an albititic formation is 1,85-1,70 Ga according to U-Pb method) in Kirovogradsky, Krivorozhsky and Alekseevsko-Lysogorskiy uranium ore regions of the Ukrainian Shield (UkrSh) [1]. In kimberlites of Kirovogradsky ore region uranium content reaches 18-20 g/t. Carbon dioxide is a major component in the formation of hydrothermal uranium deposits and the formation of the sodium in the process of generating the spectrum of alkaline ultrabasic magmas in the range from picritic to kimberlite and this is the connection between these disparate geochemical processes. For industrial uranium deposits in carbonate-sodium metasomatitics of the Kirovogradsky and Krivorozhsky uranium ore regions are characteristic of uranyl carbonate introduction of uranium, which causes correlation between CO2 content and U in range of "poor - ordinary - rich" uranium ore. In productive areas of uranium-ore fields of the Kirovogradsky ore region for phlogopite-carbonate veinlets of uranium ore albitites deep δ13C values (from -7.9 to -6.9o/oo) are characteristic. Isotope-geochemical investigation of albitites from Novokonstantynovskoe, Dokuchaevskoe, Partyzanskoe uranium deposits allowed obtaining direct evidence of the involvement of mantle material during formation of uranium albitites in Kirovogradsky ore region [2]. Petrological characteristics of kimberlites from uranium ore regions of the UkrSh (presence of nodules of dunite and harzburgite garnet in kimberlites, diamonds of peridotite paragenesis, chemical composition of indicator minerals of kimberlite, in particular Gruzskoy areas pyropes (Cr2O3 = 6,1-7,1%, MgO = 19,33-20,01%, CaO = 4,14-4,38 %, the content of knorringite component of most grains > 50mol%), chromites (Cr2O3 = 45

  1. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Science.gov (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

    2016-09-01

    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  2. Contamination in mafic mineral-rich calc-alkaline granites: a geochemical and Sr-Nd isotope study of the Neoproterozoic Piedade Granite, SE Brazil

    Directory of Open Access Journals (Sweden)

    Leite Renato J.

    2006-01-01

    Full Text Available The Piedade Granite (~600 Ma was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit and core (metaluminous titanite-bearing biotite monzogranite BmgT unit and felsic pink inequigranular granite (Bmg unit between them. Bmg has high LaN/YbN (up to 100, Th/U (>10 and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (~45, Ba and Sr, fractionated REE patterns (LaN/YbN= 45, 87Sr/86Sr(t~ 0.710, epsilonNd(t ~ -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta. The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t = 0.713-0.714; epsilonNd(t= -14 to -16, similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

  3. Early Jurassic subduction of the Paleo-Pacific Ocean in NE China: Petrologic and geochemical evidence from the Tumen mafic intrusive complex

    Science.gov (United States)

    Guo, Feng; Li, Hongxia; Fan, Weiming; Li, Jingyan; Zhao, Liang; Huang, Miwei; Xu, Wenliang

    2015-05-01

    Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear when this subduction began. Here we report an Early Jurassic (~ 187 Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb-Ta depletion). It also had Sr-Nd-Hf isotopic compositions (87Sr/86Sr(i) = 0.7042 to 0.7044, εNd(t) = + 2.5 to + 3.5 and εHf(t) = + 8.4 to + 10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3-4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N-S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean.

  4. A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

    Science.gov (United States)

    Dai, S.; Wang, X.; Chen, W.; Li, D.; Chou, C.-L.; Zhou, Y.; Zhu, Chen; Li, H.; Zhu, Xudong; Xing, Y.; Zhang, W.; Zou, J.

    2010-01-01

    The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5??g/g), V (121??g/g), Cr (33.6??g/g), Co (27.2??g/g), Ni (83.5??g/g), Cu (48.5??g/g), Ga (17.3??g/g), Y (68.3??g/g), Zr (444??g/g), Nb (23.8??g/g), and REE (392??g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that

  5. Temporal relationships between Mg-K mafic magmatism and catastrophic melting of the Variscan crust in the southern part of Velay Complex (Massif Central, France)

    OpenAIRE

    Couzini??, Simon; Moyen, Jean-Fran??ois; Villaros, Arnaud; Paquette, Jean-Louis; Scarrow, Jane H.; Marignac, Christian

    2014-01-01

    International audience Mg-K mafic intrusive rocks are commonly observed during the late stages of the evolution of orogenic belts. The Variscan French Massif Central has many outcrops of these rocks, locally called vaugnerites. Such magmas have a mantle-derived origin and therefore allow discussion of the role of mantle melting and crust-mantle interactions during late-orogenic processes. In the Southern Velay area of the French Massif Central, LA-ICPMS U-Pb dating on zircons and monazites...

  6. New Elemental and Isotopic Data From Mafic Lavas on the Puna Plateau and Re-Examining the Geochemical Signature of Convective Lithospheric Removal in the Central Andes

    Science.gov (United States)

    Murray, K. E.; Ducea, M. N.; Reiners, P. W.

    2009-12-01

    Foundering or delamination of the lower lithosphere into the convecting mantle is required by mass balance in convergent orogens such as the central Andes. In the central Andean volcanic zone (CVZ), late Miocene to Recent mafic lavas erupted on the Puna plateau are small volume fissure flows and cinder cones classically cited as evidence of convective lithospheric removal, in concert with a suite of observations including high surface elevation (>4000m) and anomalously thin lithosphere relative to other parts of the CVZ. Mafic lavas provide the best available geochemical window into the recent history of the upper mantle in this and other regions. However, an increasing number of elemental and isotopic data suggest that these melts are less distinct from the neighboring arc magmatism than originally predicted. This observation weakens the hypothesis that there is a distinct geochemical fingerprint for so-called delamination magmatism, while advancing our understanding of the size of delaminating bodies and the timescales over which they detach from the lithosphere and interact with the mantle wedge. In this contribution, we present elemental and radiogenic isotopic data from 20 newly sampled mafic lavas from the Puna plateau (24.5°S to 27°S). Preliminary major element analyses show that the Puna lavas are high-K to shoshonitic in composition, in broad agreement with other mafic lavas sampled though out the region. Several sampled flows contain xenotliths of granitoid composition, which likely represent the crustal end member that contributed to the more evolved lavas. Along with major, trace and rare earth element analyses, we will present 87Sr/86Sr and 143Nd/144Nd data to further characterize source regions of these melts. In sum, these data will allow us to (1) expand the spatial coverage of this dataset in the central Andes, (2) contribute to the effort to parse contributions from the subcontinental lithosphere, asthenosphere, subduction-related fluids, and

  7. Textural, mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke, Zimbabwe and the precious metals zone of the Sonju Lake Intrusion, Minnesota, USA

    Science.gov (United States)

    Li, C.; Ripley, E.M.; Oberthur, T.; Miller, J.D., Jr.; Joslin, G.D.

    2008-01-01

    Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type. ?? Springer-Verlag 2007.

  8. Design of the dam and south dyke at the Toulnustouc hydroelectric development project; Conception du barrage et de la digue sud de l'amenagement hydroelectrique de la Toulnustouc

    Energy Technology Data Exchange (ETDEWEB)

    Beausejour, N.; Bouzaiene, H. [RSW Inc., Montreal, PQ (Canada); Hammamji, Y.; Bigras, A.; Bergeron, A. [Hydro-Quebec Equipment, Montreal, PQ (Canada)

    2006-07-01

    The Toulnustouc hydroelectric dam is located approximately 120 km north of Baie-Comeau, Quebec and has been in operation since 2005. New development involved expanding the existing Lac-Sainte-Anne reservoir by 22 km{sup 2} through the construction of a new 77 m high and 535 m long dam and a 46 m high and 400 m long south dyke. This paper described the geology of the area and presented details of the main dam, instrumentation and stability analysis. The main concrete face rockfill dam (CFRD) lies on a foundation of bedrock. This paper presented the predictions of the upstream face displacements and the internal movements that develop in the rockfill embankment during the construction phase and the reservoir filling. The materials for the embankment dam were assumed to be non-linear, stress dependent and stress history dependent. The prediction displacements of the upstream face were compared to the displacement measured by monitors installed on the concrete face during the filling of the reservoir. The south dyke was constructed in an effort to control and reduce water infiltration under the foundation and to raise the crest of the reservoir. The principal criteria used for the design of the south dyke and the CFRD was presented. These included design wave and freeboard; ice loading on the upstream slab; geometry of the fill; material types with layer thickness and compaction criteria; stress and deformation of the fill; stability of the slope in both static and seismic conditions; extruded curb as stabilization method of the upstream slope, concrete slab, plinth, parapet, perimeter joint and waterstops; foundation treatment; and, instrumentation. During reservoir filling, the measured deformations and seepage were found to be lower than expected. 7 refs., 1 tab., 3 figs.

  9. Duration of a large Mafic intrusion and heat transfer in the lower crust: A SHRIMP U-Pb zircon Study in the Ivrea-Verbano Zone (Western Alps, Italy)

    Science.gov (United States)

    Peressini, G.; Quick, J.E.; Sinigoi, S.; Hofmann, A.W.; Fanning, M.

    2007-01-01

    The Ivrea-Verbano Zone in the western Italian Alps contains one of the world's classic examples of ponding of mantle-derived, mafic magma in the deep crust. Within it, a voluminous, composite mafic pluton, the Mafic Complex, intruded lower-crustal, high-grade paragneiss of the Kinzigite Formation during Permian-Carboniferous time, and is now exposed in cross-section as a result of Alpine uplift. The age of the intrusion is still debated because the results of geochronological studies in the last three decades on different rock types and with various dating techniques range from 250 to about 300 Ma. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age determinations on 12 samples from several locations within the Mafic Complex were performed to better constrain the age of the igneous event. The results indicate a long history of magma emplacement and cooling, which reconciles the spread in previously published ages. The main intrusive phase took place at 288 ?? 4 Ma, causing a perturbation of the deep-crustal geotherm, which relaxed to the Sm-Nd closure temperature in garnet-free mafic rocks after about 15-20 Myr of sub-solidus cooling at c. 270 Ma. These results suggest that large, deep crustal plutons, such as those identified geophysically at depths of 10-20 km within extended continental crust (e.g. Yellowstone, Rio Grande Rift, Basin and Range) may have formed rapidly but induced a prolonged thermal perturbation. In addition, the data indicate that a significant thermal event affected the country rock of the Mafic Complex at about 310 Ma. The occurrence of an upper amphibolite- to granulite-facies thermal event in the Kinzigite Formation prior to the main intrusive phase of the Mafic Complex has been postulated by several workers, and is corroborated by other geochronological investigations. However, it remains uncertain whether this event (1) was part of a prolonged perturbation of the deep-crustal geotherm, which started long before the onset of

  10. 黄河大堤加固工程饱和-非饱和土渗流分析%Analysis on seepage of saturated & unsaturated soil in reinforcement of the Yellow River dyke

    Institute of Scientific and Technical Information of China (English)

    李永乐; 舒笑天; 张红芬

    2012-01-01

    根据黄河大堤的岩土工程特性,利用饱和-非饱和土渗流理论,对洪水条件下未经加固和经过截渗墙、淤背、前戗三种不同工况加固的黄河大堤进行了饱和-非饱和土渗流分析,渗流分析表明:不同工况加固条件下,黄河大堤饱和-非饱和土渗流场均发生了明显的改变,工程加固后大堤内部浸润线明显低于未经加固堤防的浸润线,渗流溢出点较未经加固的堤防要低。文中对三种加固工况下渗流分析结果进行了比较,指出了不同工况条件下防渗加固的优点和缺点,为黄河大堤的加固和治理提供了科学依据。%According to the geotechnical engineering characteristics, and using saturated & unsaturated flow theory, for flood conditions, the Yellow River dyke is analyzed by saturated & unsaturated seepage through without reinforcement and reinforcement respectively, and the methods of consolidation are used for cut-off wall, back aggravation and the former banquette. The results show that under the condition of different reinforcement, saturated & unsaturated soil seepage field of the Yellow River dyke has obvious change, engineering strengthening internal line after dike reinforcement of the dyke, without significantly lower line, seepage spill point is to lower the dikes without reinforcement. In the article, under the three strengthening conditions, seepage analysis results are compared, and pointed out the different operating conditions of the advantages and disadvantages of the reinforcement of the Yellow River dyke, strengthening and provides the scientific basis.

  11. Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhengrong [Yale Univ., New Haven, CT (United States); Qiu, Lin [Yale Univ., New Haven, CT (United States); Zhang, Shuang [Yale Univ., New Haven, CT (United States); Bolton, Edward [Yale Univ., New Haven, CT (United States); Bercovici, David [Yale Univ., New Haven, CT (United States); Ague, Jay [Yale Univ., New Haven, CT (United States); Karato, Shun-Ichiro [Yale Univ., New Haven, CT (United States); Oristaglio, Michael [Yale Univ., New Haven, CT (United States); Zhu, Wen-Iu [Univ. of Maryland, College Park, MD (United States); Lisabeth, Harry [Univ. of Maryland, College Park, MD (United States); Johnson, Kevin [Univ. of Hawaii, Honolulu, HI (United States)

    2014-09-30

    A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trapping carbon dioxide (CO2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg2SiO4) reacting with CO2 brines in the form of sodium bicarbonate (NaHCO3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount

  12. A major 2.1 Ga event of mafic magmatism in west Africa: An Early stage of crustal accretion

    Science.gov (United States)

    Abouchami, Wafa; Boher, Muriel; Michard, Annie; Albarede, Francis

    1990-10-01

    Birimian terranes from West Africa (Mauritania, Senegal, Ivory Coast, Burkina Faso, Niger) comprise two major units: a dominantly mafic bimodal volcanic unit and a volcano-detrital unit with mostly felsic to intermediate protolith. Stratigraphic relationships of these units are still a matter of debate but current work suggest that they both formed in a short time interval around 2.1 Ga. Widespread basaltic magmas from the bimodal unit have been analyzed for REE distributions and Sr-Nd isotopes. Three Sm-Nd isochrons on tholeiitic lavas were obtained at 2.229±0.042 Ga and initial ɛNd = 3.6±1.0 for Mauritania, 2.126±0.024 Ga and initial ɛNd = 2.9±0.7 for Burkina Faso, 2.063±0.041 Ga and initial ɛNd = 3.1± .0 for Eastern Senegal, data which compare with the age of 2.11±0.09 Ga and initial ɛNd = 2.1±1.8 obtained in Guyana by Gruau et al. (1985). Samples from other localities (Ivory Coast, Niger) give generally similar results. Although the variations of Sm/Nd ratios and the scatter of ɛNd(T) values from +1.2 to +4.3 preclude a single origin for these magmas, initial isotopic heterogeneities are unlikely to bias significantly the ages given by the isochrons which are in good agreement with U-Pb zircon ages (Boher et al., 1989; unpublished data, 1990). Presence of lavas with frequent pillow structures and sediments virtually free of older recycled components suggests that Birimian terranes formed in ocean basins far from continental influence. The isotopic heterogeneities are not consistent with a MORB-like mantle source. Most lavas are slightly depleted in LREE and inversion of the data through a melting model suggests 5-15 percent melting of a slightly depleted Iherzolite. Strong depletion (Burkina Faso) and slight enrichment (Senegal) are occasionally observed. With a noticeable trend of Ti enrichment with differentiation intermediate between that of MORB and IAT, the geochemical signature of Birimian basalts does not fit the best known geodynamic

  13. Triggers on sulfide saturation in Fe-Ti oxide-bearing, mafic-ultramafic layered intrusions in the Tarim large igneous province, NW China

    Science.gov (United States)

    Cao, Jun; Wang, Christina Yan; Xu, Yi-Gang; Xing, Chang-Ming; Ren, Ming-Hao

    2016-08-01

    Three Fe-Ti oxide-bearing layered intrusions (Mazaertag, Wajilitag, and Piqiang) in the Tarim large igneous province (NW China) have been investigated for understanding the relationship of sulfide saturation, Platinum-group element (PGE) enrichment, and Fe-Ti oxide accumulation in layered intrusions. These mafic-ultramafic layered intrusions have low PGE concentrations (convecting mantle, without appreciable input of lithospheric mantle. The Mazaertag and Wajilitag intrusions have near-chondritic γOs(t) values (+13 to +60) against restricted ɛ Nd(t) values (-0.4 to +2.8), indicating insignificant crustal contamination. Rocks of the Piqiang intrusion have relatively low ɛ Nd(t) values of -3.1 to +1.0, consistent with ˜15 to 25 % assimilation of the upper crust. The rocks of the Mazaertag and Wajilitag intrusions have positive correlation of PGE and S, pointing to the control of PGE by sulfide. Poor correlation of PGE and S for the Piqiang intrusion is attributed to the involvement of multiple sulfide-stage liquids with different PGE compositions or sulfide-oxide reequilibration on cooling. These three layered intrusions have little potential of reef-type PGE mineralization. Four criteria are summarized in this study to help discriminate between PGE-mineralized and PGE-unmineralized mafic-ultramafic intrusions.

  14. Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhengrong [Yale Univ., New Haven, CT (United States); Qiu, Lin [Yale Univ., New Haven, CT (United States); Zhang, Shuang [Yale Univ., New Haven, CT (United States); Bolton, Edward [Yale Univ., New Haven, CT (United States); Bercovici, David [Yale Univ., New Haven, CT (United States); Ague, Jay [Yale Univ., New Haven, CT (United States); Karato, Shun-Ichiro [Yale Univ., New Haven, CT (United States); Oristaglio, Michael [Yale Univ., New Haven, CT (United States); Zhu, Wen-Iu [Univ. of Maryland, College Park, MD (United States); Lisabeth, Harry [Univ. of Maryland, College Park, MD (United States); Johnson, Kevin [Univ. of Hawaii, Honolulu, HI (United States)

    2014-09-30

    A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trapping carbon dioxide (CO2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg2SiO4) reacting with CO2 brines in the form of sodium bicarbonate (NaHCO3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount

  15. Variation of olivine composition in the volcanic rocks in the Songliao basin, NE China: lithosphere control on the origin of the K-rich intraplate mafic lavas

    Science.gov (United States)

    Zhang, L.-Y.; Prelević, D.; Li, N.; Mertz-Kraus, R.; Buhre, S.

    2016-10-01

    Lithospheric thickness and the heterogeneity of the mantle lithosphere are two major parameters that play a role in determining the final composition of the mafic melts and their minerals. The Songliao basin in northeast China represents an ideal natural laboratory to study the effect of these two parameters on early Pliocene to Holocene K-rich mafic lavas (K2O > 4 wt.%; K2O/Na2O > 1). A series of Cenozoic volcanic edifices (Erkeshan, Wudalianchi, Keluo and Xiaogulihe) are tentatively divided into three groups (Group 1 - thin, Group 2 - middle, and Group 3 - thick) according to the lithosphere thickness. They are located in the northern region of the Songliao basin extending in a near north-south direction along a broad zone where the lithosphere thickness increases gradually. We present a detailed petrographical and geochemical study on olivine macrocrysts in combination with new geochemical data on their host lavas, including major and trace element abundances as well as Sr, Nd, and Pb isotopic signatures. Our ultimate aim is to quantitatively and qualitatively determine the role of lithospheric mantle thickness (named as "lid effect") and composition in the variation of mafic lavas and olivine composition. When corrected to Mg# = 0.72, a number of major elements in the lavas correlate with increasing lithospheric thickness (L): Si72 and Al72 decrease, whereas Mg72, Fe72, Ti72 and P72 increase. Sm/Yb ratios in the lavas increase, implying that lithospheric thickness exerts an important control. Group 3 mafic lavas are ultrapotassic (showing lamproite affinity) with K2O/Na2O > 4: their La/Sm and Pb isotope ratios deviate from the above correlations, indicating that the lavas from the thickest part of the basin exhibit the highest extent of metasomatic enrichment of the mantle source. Several parameters (e.g. [Ni], Ni/Mg, Ni/(Mg/Fe), Mn/Fe and Ca/Fe) in melt-related olivine from Group 1 and Group 2 lavas are controlled by variable lithosphere thickness. Olivine

  16. Late Permian to Early Triassic mafic to felsic intrusive rocks from North Liaoning, North China: Petrogenesis and implications for Phanerozoic continental crustal growth

    Science.gov (United States)

    Zhang, Xiaohui; Zhang, Hongfu; Wilde, Simon A.; Yang, Yueheng; Chen, Haihong

    2010-06-01

    Zircon U-Pb dating, whole-rock major oxide, trace element and Sr-Nd-Hf isotopic data are presented for the Late Permian to Early Triassic Shijianfang batholith from Faku in North Liaoning Province, North China. Two main magmatic suites are documented: one, with an emplacement age of ca. 260 Ma, is mafic to intermediate in composition, forming small gabbroic to monzonitic intrusions; the other is felsic and quartz monzonitic to granitic in composition, with an emplacement age of ca. 250 Ma. Geochemically, the rocks from the mafic suite show strong enrichment of LILE and LREE and depletion in HFSE, and also have moderately depleted isotopic compositions, with ISr ranging from 0.7049 to 0.7054, ɛNd( t) from + 2.72 to - 1.82 and zircon ɛHf( t) values from + 3.4 to + 7.1. These features suggest derivation from high degree partial melting of a subduction-related metasomatized lithospheric mantle source. The rocks from the felsic suite range from 66.7 to 77.2 wt.% SiO 2, and define a continuous chemical evolutionary trend, from less-differentiated low-silica members displaying LREE enriched patterns, no Eu anomalies and high Ba, Sr, Zr and Hf, to more-differentiated, high-silica members with higher alkalis, strong depletion in Ba, Sr and Ti, enrichment in HFSE, fractionated REE patterns and strong negative Eu anomalies. However, they exhibit indistinguishable isotopic compositions from the mafic rocks, with ISr ranging from 0.7043 to 0.7062, ɛNd( t) from + 2.28 to - 0.55 and zircon ɛHf( t) values from + 3.6 to + 6.6. This suggests that the parental magma for the felsic suite originated from partial melting of mixed protoliths composed of juvenile basaltic underplate and ancient lower crustal materials. Subsequent fractional crystallization, with overprinting by magmatic hydrothermal fluids, can explain the geochemical variations of the felsic suite. The juvenile character of both lithospheric mantle and crustal rocks, as recorded by the Shijianfang batholith, suggests

  17. Controle da antracnose e qualidade de mangas (Mangifera indica L. cv. van dyke, após tratamento hidrotérmico e químico Anthracnose control and mango quality (Mangifera indica L. cv. van dyke after hydrothermal and chemical treatment

    Directory of Open Access Journals (Sweden)

    Mário Sérgio Carvalho Dias

    2005-04-01

    Full Text Available A antracnose causa severos danos à casca da manga. Por isso, há a necessidade de se fazer o tratamento fitossanitário pós-colheita dos frutos, utilizando a imersão em calda de fungicidas, a qual, associada ao tratamento hidrotérmico, tem resultado em melhores benefícios. Com o presente trabalho objetivou-se estudar o controle da antracnose e qualidade pós-colheita de mangas (Mangifera indica L., cv. Van Dyke, após tratamento hidrotérmico associado ao químico mediante as análises física, físico-químicas, químicas e fitopatológica. As mangas, provenientes de pomar comercial do município de Janaúba - MG, da safra 2000, foram colhidas em estádio de maturação comercial. Após seleção de acordo com a uniformidade de cor, tamanho e ausência de injúrias mecânicas e fisiológicas, as mesmas foram transportadas em caixas plásticas para a EPAMIG - CTNM - Nova Porteirinha - MG, Laboratório de Pós-colheita de frutos, onde as amostras foram submetidas ao tratamento hidrotérmico (55°C por 5minutos e banho frio em soluções contendo os fungicidas Thiabendazole (Tecto 400 mL/100 L, Prochloraz (Sportak 110 mL/100 L e Imazalil (Magnate 200 mL/100 L. Após secagem ao ar, os frutos foram acondicionados em bandejas plásticas e armazenados à temperatura ambiente (25±2°C e UR 70%, por um período de 12 dias e avaliados quanto às características intrínsecas de qualidade a cada 4 dias. O experimento foi conduzido em delineamento inteiramente casualizado, com 8 tratamentos, 4 repetições e unidade experimental composta de 4 frutos. As variações de pH, sólidos solúveis totais, acidez total titulável e açúcares solúveis totais não comprometeram as características organolépticas de mangas cv. Van Dyke armazenadas sob temperatura ambiente (25±2°C e UR 70% até os 8 dias de armazenamento. A associação do tratamento hidrotérmico com o químico foi eficiente no controle da antracnose dos frutos por até 12 dias de

  18. Mafic monogenetic vents at the Descabezado Grande volcanic field (35.5°S-70.8°W): the northernmost evidence of regional primitive volcanism in the Southern Volcanic Zone of Chile

    Science.gov (United States)

    Salas, Pablo A.; Rabbia, Osvaldo M.; Hernández, Laura B.; Ruprecht, Philipp

    2016-06-01

    In the Andean Southern Volcanic Zone (SVZ), the broad distribution of mafic compositions along the recent volcanic arc occurs mainly south of 37°S, above a comparatively thin continental crust (≤~35 km) and mostly associated with the dextral strike-slip regime of the Liquiñe-Ofqui Fault Zone (LOFZ). North of 36°S, mafic compositions are scarce. This would be in part related to the effect resulting from protracted periods of trapping of less evolved ascending magmas beneath a thick Meso-Cenozoic volcano-sedimentary cover that lead to more evolved compositions in volcanic rocks erupted at the surface. Here, we present whole-rock and olivine mineral chemistry data for mafic rocks from four monogenetic vents developed above a SVZ segment of thick crust (~45 km) in the Descabezado Grande volcanic field (~35.5°S). Whole-rock chemistry (MgO > 8 wt%) and compositional variations in olivine (92 ≥ Fo ≥ 88 and Ni up to ~3650 ppm) indicate that some of the basaltic products erupted through these vents (e.g., Los Hornitos monogenetic cones) represent primitive arc magmas reaching high crustal levels. The combined use of satellite images, regional data analysis and field observations allow to recognize at least 38 mafic monogenetic volcanoes dispersed over an area of about 5000 km2 between 35.5° and 36.5°S. A link between ancient structures inherited from pre-Andean tectonics and the emplacement and distribution of this mafic volcanism is suggested as a first-order structural control that may explain the widespread occurrence of mafic volcanism in this Andean arc segment with thick crust.

  19. Parasitic analysis and π-type Butterworth-Van Dyke model for complementary-metal-oxide-semiconductor Lamb wave resonator with accurate two-port Y-parameter characterizations

    Science.gov (United States)

    Wang, Yong; Goh, Wang Ling; Chai, Kevin T.-C.; Mu, Xiaojing; Hong, Yan; Kropelnicki, Piotr; Je, Minkyu

    2016-04-01

    The parasitic effects from electromechanical resonance, coupling, and substrate losses were collected to derive a new two-port equivalent-circuit model for Lamb wave resonators, especially for those fabricated on silicon technology. The proposed model is a hybrid π-type Butterworth-Van Dyke (PiBVD) model that accounts for the above mentioned parasitic effects which are commonly observed in Lamb-wave resonators. It is a combination of interdigital capacitor of both plate capacitance and fringe capacitance, interdigital resistance, Ohmic losses in substrate, and the acoustic motional behavior of typical Modified Butterworth-Van Dyke (MBVD) model. In the case studies presented in this paper using two-port Y-parameters, the PiBVD model fitted significantly better than the typical MBVD model, strengthening the capability on characterizing both magnitude and phase of either Y11 or Y21. The accurate modelling on two-port Y-parameters makes the PiBVD model beneficial in the characterization of Lamb-wave resonators, providing accurate simulation to Lamb-wave resonators and oscillators.

  20. Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: Chapter I in Mineral deposit models for resource assessment

    Science.gov (United States)

    Schulz, Klaus J.; Woodruff, Laurel G.; Nicholson, Suzanne W.; Seal, Robert R., II; Piatak, Nadine M.; Chandler, Val W.; Mars, John L.

    2014-01-01

    Magmatic sulfide deposits containing nickel (Ni) and copper (Cu), with or without (±) platinum-group elements (PGE), account for approximately 60 percent of the world’s nickel production. Most of the remainder of the Ni production is derived from lateritic deposits, which form by weathering of ultramafic rocks in humid tropical conditions. Magmatic Ni-Cu±PGE sulfide deposits are spatially and genetically related to bodies of mafic and/or ultramafic rocks. The sulfide deposits form when the mantle-derived mafic and/or ultramafic magmas become sulfide-saturated and segregate immiscible sulfide liquid, commonly following interaction with continental crustal rocks.

  1. Geochronology and geochemistry of mafic-intermediate intrusions in the Eastern Tianshan, NW China: Implications for a tectonic transition from subduction to post-collisional extension

    Science.gov (United States)

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.

    2016-04-01

    This study presents new whole-rock geochemical, Sr-Nd and zircon U-Pb-Hf isotopic data for mafic-intermediate rocks from the Eastern Tianshan (NW China) to constrain the final closure of the Junggar Ocean between the Central Tianshan and Junggar terranes, which is essential in understanding the final assembly processes of the southern Central Asian Orogenic Belt. LA-ICP-MS U-Pb dating on selected igneous zircons yields well-constrained weighted mean 206Pb/238U ages of ca. 310 Ma and ca. 290 Ma, interpreted as the best estimates of the crystallization ages of the intrusions. Petrographic and geochemical analyses reveal that the Late Carboniferous samples are characterized by typical subduction-related signatures, low Sm/Yb (<2.0) but high Lu/Hf (≥0.2) ratios and positive ɛNd(t) (+1.2 to +3.1) and zircon ɛHf(t) (+4.1 to +7.8) values, suggesting that their parental magmas were most likely emplaced in a continental arc setting, genetically related to the partial melting of a metasomatized mantle wedge in the spinel stability field. This consideration agrees well with the findings of Carboniferous ophiolitic and arc-related granitoids in the region, most probably resulted from the southward subduction of the Junggar oceanic plate. In contrast, the Early Permian samples show high TiO2 (2.7-3.2 wt.%) contents with elevated Ti/V (86.0-115.1) and Zr/Y (4.9-9.3) ratios, OIB-like trace element patterns and high ɛNd(t) (+1.1 to +4.5) and zircon ɛHf(t) (+3.0 to +9.8) values, exhibiting close affinities to typical within-plate basalts. Combined with previous investigations, we suggest that the Early Permian mafic magmatism was most likely generated by the partial melting of an asthenospheric mantle source in the garnet stability field, plausibly triggered by upwelling of asthenosphere during the slab break-off of the Junggar oceanic plate, which is supported by the linear distributions of Permian post-collisional mafic-ultramafic rocks in the Eastern Tianshan. Therefore

  2. Granite, gabbro and mafic microgranular enclaves in the Gejiu area, Yunnan Province, China: a case of two-stage mixing of crust- and mantle-derived magmas

    Science.gov (United States)

    Cheng, Yanbo; Spandler, Carl; Mao, Jingwen; Rusk, Brian G.

    2012-10-01

    Geochronological, geochemical, whole-rock Sr-Nd, and zircon Hf isotopic analyses were carried out on the Jiasha Gabbro, mafic microgranular enclaves (MME) and host Longchahe Granite samples from the Gejiu area in the southeast Yunnan province, SW China, with the aim of characterizing their petrogenesis. Compositional zoning is evident in the gabbro body as the cumulate textures and mineral proportions in the gabbro interior are distinct from the gabbro margin. The Longchahe Granite largely comprises metaluminous quartz monzonite with distinctive K-feldspar megacrysts, but also contains a minor component of peraluminous leucogranite. The MME have spheroidal to elongated/lenticular shapes with sharp, crenulated and occasionally diffuse contacts with the host granite, which we attribute to the undercooling and disaggregation of mafic magma globules within the cooler host felsic magma. Field observations, geochronology, geochemistry, Sr-Nd and zircon Hf isotopic compositions point to a complex petrogenesis for this granite-MME-gabbro association. Zircon 206Pb/238U ages determined by LA-ICP-MS for a mafic enclave, its host granite and the gabbro body are 83.1 ± 0.9 Ma, 83.1 ± 0.4 Ma and 83.2 ± 0.4 Ma, respectively, indicating coeval crystallization of these igneous rock units. Crystal fractionation processes can explain much of the compositional diversity of the Jiasha Gabbro. The geochemical features of the gabbro, such as high Mg# (up to 70) and Cr (up to 327 ppm), enrichment in LILEs (e.g., Rb, Ba, K2O) and LREEs, and depletion in HFSE (e.g., Nb, Ta, Ti), together with initial 87Sr/86Sr ratios of 0.708-0.709 and negative ɛNd(t) values (-5.23 to -6.45), indicate they were derived from a mantle source that had undergone previous enrichment, possibly by subduction components. The Longchahe Granite has a large range of SiO2 (59.87-74.94 wt%), is distinctly alkaline in composition, and has Sr-Nd-Hf isotopic compositions ((87Sr/86Sr)i > 0.712, ɛNd(t) = -6.93 to -7

  3. Evidence of heterogeneous crustal origin for the Pan-African Mbengwi granitoids and the associated mafic intrusions (northwestern Cameroon, central Africa)

    Science.gov (United States)

    Mbassa, Benoît Joseph; Kamgang, Pierre; Grégoire, Michel; Njonfang, Emmanuel; Benoit, Mathieu; Itiga, Zénon; Duchene, Stéphanie; Bessong, Moïse; Nguet, Pauline Wonkwenmendam; Nfomou, Ntepe

    2016-02-01

    The Mbengwi plutonics consist of intermediate to felsic granitoids forming a continuous magmatic series from monzonite to granite and mafic intrusions. Their mineralogical composition consists of quartz, plagioclases, K-feldspars, biotite, muscovite, and amphibole. The accessory phase includes opaque minerals + titanite ± apatite ± zircon, while secondary minerals are pyrite, phengite, chlorite, epidote, and rarely calcite. These plutonics are assigned high-K calc-alkaline to shoshonitic series, metaluminous to weakly peraluminous and mostly belong to an I-type suite (A/CNK = 0.63-1.2). They are typically post-collisional, with a subduction signature probably being inherited from their protoliths emplaced during the subduction phase. The Sr and Nd isotopic data evidence that these plutonics result from melting of the lower continental crust with variable contribution of the oceanic crust. Their geochemical features are similar to those of western Cameroon granitoids related to the Pan-African D1 event in Cameroon.

  4. Chemical and isotopic relationship of mafic and felsic magmas in a sub-volcanic reservoir: The Guadalupe Igneous Complex (GIC), Sierra Nevada, California

    Science.gov (United States)

    Ratschbacher, B. C.; Paterson, S. R.; Putirka, K. D.

    2013-12-01

    It is commonly believed that the interaction of mafic and felsic melts in the form of mixing/mingling as well as their genetic link in the form of fractionation play an important role in the formation of continental crust. The combination of whole rock major element content and isotopic signature, as presented in this study, is a powerful tool to identify the origin and genetic relation of mafic and felsic melts in magmatic arc settings where new material is added to the crust. The GIC is part of the Jurassic Sierran magmatic arc exposed in the Western Metamorphic Belt and contains two main units consisting of mafic (up to 9 wt. % MgO and 49 to 56 wt. % SiO2) and felsic (around 75 wt. % SiO2) rocks, which locally mingled and mixed to different proportions at a shallow emplacement level. In the lower parts of the GIC, fine-grained gabbros gradually evolve into the overlying diorite to meladiorite unit. A mingling zone separates these mafic rocks from granites, granophyres and overlying rhyolites in the upper part of the complex. Major element whole rock analyses show that the GIC is bimodal with gabbros and granitoids acting as endmembers in SiO2, MgO and CaO contents. For Al2O3, Na2O and other element oxides, the different units strongly overlap in compositions. Recent work using single grain zircon U-Pb dating found ages for both the gabbros and the felsic part of the complex of 151 Ma within uncertainty (Saleeby et al., 1989; Ernst et al., 2009, and unpublished data from this study). These ages are in agreement with Rb-Sr data from each unit, which fall on a 152×7 Ma isochron and therefore imply closed-system evolution. Major oxide data show that assimilation of the exposed surrounding host rocks is unlikely and cannot serve as an assimilant to reproduce the observed felsic compositions from the gabbroic rocks. Sri, Nd and Pb systematics show that all units except for capping granophyres and rhyolites plot close together implying a shared parental melt, which is

  5. Two tales of the continental lithospheric mantle prior to the destruction of the North China Craton: Insights from Early Cretaceous mafic intrusions in western Shandong, East China

    Science.gov (United States)

    Huang, Xiao-Long; Zhong, Jun-Wei; Xu, Yi-Gang

    2012-11-01

    Weakened lithospheric zones such as the Dabie-Sulu orogenic belt and Tan-Lu fault zone played important roles in the destruction of the North China Craton (NCC) during the late Mesozoic. Early Cretaceous mafic intrusions in western Shandong, contemporary with extensive magmatism during the destruction of the NCC, delineate two spatially distinct mantle domains (EM1- and EM2-like) beneath the craton’s interior and weakened lithospheric zones, respectively. The Jinan and Zouping gabbros from the craton interior (∼128 Ma) show fractionated LREE and nearly flat HREE patterns ([La/Yb]N = 2.94-8.95; [Dy/Yb]N = 1.23-1.69) with notable negative Ta, Nb and Ti anomalies. They have strong negative εNd(t) (-15.7 to -7.1), low initial 87Sr/86Sr (0.7039-0.7060) and negative zircon εHf(t) of -20.0 to -6.2. These “crustal fingerprints” cannot be explained by crustal contamination, but were likely derived from a hybrid mantle source. Crustal delamination or detachment during the Early Paleoproterozoic might be responsible for the involvement of Early Precambrian crustal materials in the Mesozoic mantle source beneath the southeastern NCC. In comparison, the Early Cretaceous mafic igneous rocks from regions (e.g., Yinan, Mengyin and Fangcheng) adjacent to the Dabie-Sulu orogenic belt and Tan-Lu fault zone have higher 87Sr/86Sr ratios (0.7059-0.7119), suggesting modification of the lithospheric mantle by melts/fluids derived from the Yangtze crust. The Mesozoic crustal delamination may have triggered the destruction of the lithospheric root beneath the Dabie-Sulu orogenic belt, whereas the lithospheric thinning beneath the interior of the southeastern NCC is attributed to the thermo-mechanical erosion by lateral convective asthenosphere.

  6. Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication

    Institute of Scientific and Technical Information of China (English)

    LING WenLi; REN BangFang; DUAN RuiChun; LIU XiaoMing; MAO XinWu; PENG LianHong; LIU ZaoXue; CHENG JianPing; YANG HongMei

    2008-01-01

    The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas-tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec-trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685:L±5) (2 samples, MSWD=0.36) and (679±J:3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forms-tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830-780 Ma igne-ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.

  7. Geochemistry of the Peramora Mélange and Pulo do Lobo schist: geochemical investigation and tectonic interpretation of mafic mélange in the Pangean suture zone, Southern Iberia

    Science.gov (United States)

    Dahn, Dustin R. L.; Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; Dupuis, Nicole; McFarlane, Christopher R. M.

    2014-07-01

    The Peramora Mélange is part of an accretionary complex between the South Portuguese Zone (a fragment of Laurussia) and the Ossa Morena Zone (para-autochthonous Gondwana) and is an expression of the Pangean suture zone in southwestern Iberia. The suture zone is characterized by fault-bounded units of metasedimentary rocks, mélanges, and mafic complexes. Detailed geologic mapping of the Peramora Mélange reveals a complex pattern of imbricated schists and mafic block-in-matrix mélanges. Geochemical signatures of the Pulo do Lobo schist (PDL) are consistent with derivation from both mafic and continental sources. The mafic block-in-matrix mélange displays normal mid-ocean ridge basalt (NMORB) geochemical signature, juvenile Sm-Nd isotopic compositions, and a range of zircon ages similar to those observed in the PDL, suggesting a sedimentary component. Taken together, these data suggest a complex tectonic history characterized by erosion of a NMORB source, mélange formation, and imbrication during underplating occurring during the final stages of continent-continent collision.

  8. Petrogenesis and geodynamic setting of Early Cretaceous mafic-ultramafic intrusions, South China: A case study from the Gan-Hang tectonic belt

    Science.gov (United States)

    Qi, Youqiang; Hu, Ruizhong; Liu, Shen; Coulson, Ian M.; Qi, Huawen; Tian, Jianji; Zhu, Jingjing

    2016-08-01

    A study using whole-rock major-trace elements and Sr-Nd isotopes as well as zircon U-Pb dating has been carried out on Early Cretaceous mafic-ultramafic intrusions from the Gan-Hang tectonic belt (GHTB), South China, to understand the origin of mantle sources and the sequential evolution of the underlying Late Mesozoic lithospheric mantle of this area. The study focused on two intrusions, one at Quzhou and the other at Longyou (see Fig. 1). They are primarily composed of mafic-ultramafic rocks with wide range of chemical compositions. The Quzhou mafic rocks have relatively narrow ranges of SiO2 (48.94-51.79 wt%), MgO (6.07-7.21 wt%), Fe2O3 (10.48-11.56 wt%), CaO (8.20-8.81 wt%), and Mg# (51.7-56.5) with relatively low K2O (0.56-0.67 wt%) and Na2O (3.09-3.42 wt%). By contrast, the ultramafic rocks from Longyou have distinct lower SiO2 (41.50-45.11 wt%) and higher MgO (9.05-9.90 wt%), Fe2O3 (12.14-12.62 wt%), CaO (8.64-10.67 wt%), and Mg# (59.5-61.1) with relatively higher K2O (1.32-1.75 wt%) and Na2O (4.53-5.08 wt%). They are characterized by Ocean Island Basalts (OIB)-type trace element distribution patterns, with a significant enrichment of light rare earth elements (LREE), large ion lithophile elements (LILE, i.e., Rb, Ba, K, and Sr) and high field strength elements (HFSE, i.e., Nb, Ta), and slight depletion of Th, U, Ti, and Y. The intrusions exhibit relatively depleted Sr-Nd isotope compositions, with (87Sr/86Sr)i range of 0.7035 to 0.7055 (143Nd/144Nd)i of 0.51264 to 0.51281 and εNd(t) values of + 3.0 to + 6.6. Zircon U-Pb dating of Longyou and Quzhou intrusions yields consistent magma emplacement ages of 129.0 ± 3.9 to 126.2 ± 2.4 Ma, respectively. The dating results are consistent with the peak of extension in Early Cretacerous throughout the Gan-Hang tectonic belt. Their magmas were principally derived from near-solidus partial melting of pyroxenites with different content of silica, and the pyroxenites were resulted from a juvenile SCLM peridotite

  9. Draped aeromagnetic survey in Transantarctic Mountains over the area of the Butcher Ridge igneous complex showing extent of underlying mafic intrusion

    Science.gov (United States)

    Behrendt, John C.; Damaske, D.; Finn, C.A.; Kyle, P.; Wilson, T.J.

    2002-01-01

    A draped aeromagnetic survey over the area surrounding the Butcher Ridge igneous complex (BRIC), Transantarctic Mountains, was acquired in 1997-1998 as part of a larger Transantarctic Mountains Aerogeophysical Research Activity survey. The BRIC is a sill-like hypoabyssal intrusion ranging in composition from tholeiitic basalt to rhyolite. An 40Ar/39 Ar age of 174 Ma and the chemical character of the basaltic rocks show the BRIC to be part of the widespread Jurassic Ferrar suite of continental tholeiitic rocks, that extends for 3500 km across Antarctica. The aeromagnetic survey shows a horseshoe-shaped pattern of anomalies reaching amplitudes as great as 1900 nT generally associated with the bedrock topography where it is exposed. It is apparent that the high-amplitude anomaly pattern is more extensive than the 10-km-long exposed outcrop, first crossed by a single 1990 aeromagnetic profile. The highest-amplitude anomalies appear south of the profile acquired in 1990 and extend out of the survey area. The new aeromagnetic data allow determination of the extent of the interpreted Butcher mafic(?) intrusion beneath exposures of Beacon sedimentary rock and ice in the area covered, as well as beneath the small BRIC exposure. The magnetic anomalies show a minimum area of 3000 km2, a much greater extent than previously inferred. Magnetic models indicate a minimum thickness of ???1-2 km for a horizontal intrusion. However, nonunique models with magnetic layers decreasing in apparent susceptibility with depth are consistent with of a 4- to 8-km-thick layered intrusion. These magnetic models indicate progressively deeper erosion of the interpreted mafic-layered body from the south to north. The erosion has removed more magnetic upper layers that mask the magnetic effects of the lower less magnetic layers. The probable minimum volume of the intrusion in the area of the survey is ???6000 km3. An alternate, but less likely, interpretation of a series of dikes can also fit the

  10. Mineralogy of Juventae Chasma: Sulfates in the light-toned mounds, mafic minerals in the bedrock, and hydrated silica and hydroxylated ferric sulfate on the plateau

    Science.gov (United States)

    Bishop, Janice L.; Parente, Mario; Weitz, Catherine M.; Noe Dobrea, Eldar Z.; Roach, Leah H.; Murchie, Scott L.; McGuire, Patrick C.; McKeown, Nancy K.; Rossi, Christopher M.; Brown, Adrian J.; Calvin, Wendy M.; Milliken, Ralph; Mustard, John F.

    2009-11-01

    Juventae Chasma contains four light-toned sulfate-bearing mounds (denoted here as A-D from west to east) inside the trough, mafic outcrops at the base of the mounds and in the wall rock, and light-toned layered deposits of opal and ferric sulfates on the plateau. Hyperspectral visible/near-infrared Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra were used to identify monohydrated and polyhydrated sulfate (PHS) outcrops of layered material on the bright mounds. Most of the monohydrated sulfate signatures closely resemble those of szomolnokite (FeSO4·H2O), characterized by a water band near 2.08 μm, while some areas exhibit spectral features more similar to those of kieserite (MgSO4·H2O), with a band centered closer to 2.13 μm. The largest PHS outcrops occur on the top of mound B, and their spectral features are most consistent with ferricopiapite, melanterite, and starkeyite, but a specific mineral cannot be uniquely identified at this time. Coordinated analyses of CRISM maps, Mars Orbiter Laser Altimeter elevations, and High Resolution Imaging Science Experiment images suggest that mounds A and B may have formed together and then eroded into separate mounds, while mounds C and D likely formed separately. Mafic minerals (low-Ca pyroxene, high-Ca pyroxene, and olivine) are observed in large ˜2-10 km wide outcrops in the wall rock and in smaller outcrops ˜50-500 m across at the floor of the canyon. Most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals. The plateau region northwest of Juventae Chasma is characterized by an abundance of light-toned layered deposits. One region contains two spectrally unique phases exhibiting a highly stratified, terraced pattern. CRISM spectra of one unit eroded into swirling patterns with arc-like ridges exhibit a narrow 2.23-μm band assigned to hydroxylated ferric sulfate. A thin layer of a fractured material bearing an

  11. Multiple sources for the origin of granites: Geochemical and Nd/Sr isotopic evidence from the Gudaoling granite and its mafic enclaves, northeast China

    Science.gov (United States)

    Yang, Jin-Hui; Wu, Fu-Yuan; Chung, Sun-Lin; Wilde, Simon A.; Chu, Mei-Fei

    2004-11-01

    Geochemical and Sr- and Nd-isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the Early Cretaceous Gudaoling batholith in the Liaodong Peninsula, NE China. The rocks include monzogranite, porphyric granodiorite and quartz diorite. Monzogranites have relatively high 87Rb/ 86Sr ratios (0.672-0.853), low initial 87Sr/ 86Sr ratios (0.7052-0.7086) and ɛ Nd(t) values (-18.5 to -20.9) indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time. Quartz diorites have high initial 87Sr/ 86Sr ratios (0.7118-0.7120) and negative ɛ Nd(t) values (-13.2 to -18.1) coupled with high Al 2O 3 and MgO contents, indicating they were derived from enriched lithospheric mantle with contributions of radiogenic Sr from plagioclase-rich metagreywackes or meta-igneous rocks, i.e., ancient lower crust. Two groups of enclaves with igneous textures and abundant acicular apatites are distinguished: dioritic enclaves and biotite monzonitic enclaves. Dioritic enclaves have low Al 2O 3 (13.5-16.4 wt%) and high MgO (Mg# = ˜72.3) concentrations, low initial 87Sr/ 86Sr ratios (0.7058-0.7073) and negative ɛ Nd(t) values (˜-7.2), and are enriched in LILEs and LREEs and depleted in HFSEs, suggesting they were derived from an enriched lithospheric mantle source. Biotite monzonitic enclaves have Sr and Nd isotopic compositions similar to the monzogranites, indicating they were crystal cumulates of the parental magmas of these monzogranites. Granodiorites have transitional geochemistry and Nd- and Sr-isotopic compositions, intermediate between the monzogranites, quartz diorites and the enclaves. Geochemical and Sr- and Nd-isotopic compositions rule-out simple crystal-liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, magma mixing of mafic mantle-derived and juvenile crustal-derived magmas, coupled with crystal fractionation and

  12. Petrogenesis and ore genesis of the Permian Huangshanxi sulfide ore-bearing mafic-ultramafic intrusion in the Central Asian Orogenic Belt, western China

    Science.gov (United States)

    Mao, Ya-Jing; Qin, Ke-Zhang; Li, Chusi; Xue, Sheng-Chao; Ripley, Edward M.

    2014-07-01

    The Permian Huangshanxi mafic-ultramafic intrusion hosts one of the two largest magmatic sulfide deposits in the Eastern Tianshan which is situated in the southern margin of the Central Asian Orogenic Belt. In this paper we use mineral compositions and whole-rock geochemical data to decipher the genetic relationship between magma evolution and sulfide mineralization. The Huangshanxi intrusion consists of three separate intrusive units. Important sulfide mineralization occurs in the base of the last intrusive unit, an elongated, layered ultramafic body composed of lherzolite at the bottom, olivine websterite in the middle and websterite at the top. Based on olivine-liquid equilibria and mass balance, the MgO and FeO contents in the parental magma for a lherzolite sample are estimated to be 8.71 and 8.36 wt.%, respectively. The Huangshanxi mafic-ultramafic intrusive rocks and the estimated "trapped liquids" for several olivine-orthopyroxene cumulate rocks all show light rare earth element enrichments relative to heavy rare earth elements and significant Nb depletions relative to Th and La, which are similar to the characteristics of coeval basalts in the region. The arc-like geochemical features are attributed to pre-Permian mantle metasomatism by slab-derived fluids. Partial melting of the previously-modified mantle is thought to have resulted from heating by upwelling asthenosphere associated with post-subduction lithosphere delamination or by mantle plume activity. The relationship between the Fo and Ni contents of olivine crystals from the Huangshanxi sulfide-poor ultramafic rocks (< 1 wt.% S) indicates cotectic sulfide segregation during olivine crystallization. Significant depletions in platinum group elements (PGE) relative to Ni and Cu in the bulk sulfide ores of the Huangshanxi deposit are likely due to sulfide retention in the source mantle. Stratigraphic reversals in olivine Fo contents and bulk sulfide PGE tenors suggest that multiple magma replenishments

  13. Rocas Verdes Ophiolite Complexes in the Southernmost Andes: Remnants of the Mafic Igneous Floor of a Back-arc Basin that Rifted the South American Continental Crust in the Late Jurrassic and Early Cretaceous

    Science.gov (United States)

    Stern, C. R.

    2001-12-01

    The Rocas Verdes are an en echelon group of late Jurassic and early Cretaceous igneous complexes in the southernmost Andes. They consist of mafic pillow lavas, dikes and gabbros interpreted as the upper portions of ophiolite complexes formed along mid-ocean-ridge-type spreading centers. When secondary metamorphic affects are accounted for, the geochemistry of mafic Rocas Verdes rocks are similar to ocean-ridge basalts (MORB). The spreading centers that generated the Rocas Verdes rifted the southwestern margin of the Gondwana continental crust, during the start of break-up in the southern Atlantic, to form the igneous floor of a back-arc basin behind a contemporaneous convergent plate boundary magmatic arc. Late Jurassic and early Cretaceous sediments from both the magmatic arc on the southwest and the continental platform on the northeast of the basin were deposited in the Rocas Verdes basin, and these sediments are interbedded with mafic pillow lavas along the margins of the Rocas Verdes mafic complexes. Also, mafic dikes and gabbros intrude older pre-Andean and Andean lithologies along both flanks of the Rocas Verdes, and leucocratic country rocks are engulfed in the Rocas Verdes mafic complexes. These relations indicate that the Rocas Verdes complexes formed in place and are autochthonous, having been uplifted but not obducted, which may explain the lack of exposure of the deeper ultramafic units. Zircon U/Pb ages of 150+/-1 Ma for the Larsen Harbour Formation, a southern extension of the Rocas Verdes belt on South Georgia Island, and 138+/-2 Ma for the Sarmiento complex, the northernmost in the Rocas Verdes belt, indicate that this basin may have formed by "unzipping" from the south to the north, with the southern portion beginning to form earlier and developing more extensively than the northern portion of the basin. Paleomagnetic data suggest that the Rocas Verdes basin developed in conjunction with the displacement of the Antarctic Peninsula and opening of

  14. A Special Issue (Part-II): Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization - dedication to Lia Nikolaevna Kogarko

    Science.gov (United States)

    Kogarko, Lia N.; Gwalani, Lalchand G.; Downes, Peter J.; Randive, Kirtikumar R.

    2015-10-01

    This is the second part of a two-volumespecial issue of Open Geoscience (formerly Central European Journal of Geosciences) that aims to be instrumental in providing an update of Mafic-Ultramafic Rocks and Alkaline- Carbonatitic Magmatism and Associated Hydrothermal Mineralization. Together, these two volumes provide a detailed and comprehensive coverage of the subjects that are relevant to the research work of P.Comin-Chiaramonti (Italy) and LiaN. Kogarko (Russia) towhomPart-I and Part- II have been respectively dedicated. To a significant extent, the development of advanced sampling technologies related to alkaline and carbonatitic magmatism by Lia N. Kogarko, has allowed geoscientists to measure and sample the deep crust of the planet not only for the exploration for the mineral deposits, but also to answer basic scientific questions about the origin and evolution of alkaline rocks (kimberlites, lamproites and related rocks associated with carbonatites). The papers presented in this Part-II of the special issue cover the petrology and geochemistry of the rocks collected from the surface and penetrated by drilling. Lia Kogarko proposed a new theory for the evolution of alkaline magmatism in the geological history of the Earth - that the appearance of alkaline magmatism at the Archaean-Proterozoic boundary (~2.5 - 2.7 Ga), and its growing intensity, was related to changes in the geodynamic regime of the Earth and oxidation of the mantle due to mantle-crust interaction.

  15. Structural, Petrographic and Geochemical Characteristics of Mafic Dikes Intrusive in Metasedimentary Rocks of the Crixás Greenstone Belt, Goiás

    Directory of Open Access Journals (Sweden)

    Hardy Jost

    2010-10-01

    Full Text Available Mafic dikes and stocks are a common feature in the Archean terrain of Goiás, Central Brazil, where they occur asswarms of 2.3 - 2.5 Ga within the granite-gneiss complexes (2.8 e 2.7 Ga, as well as intrusions related to the komatiite andbasalt flows of the greenstone belts lower stratigraphic units, but were unknown within the upper metasedimentary units.Detailed study of core sections from several drill-sites in the area of the Crixás greenstone belt gold deposits showed thatdike intrusion occurred after the main Paleoproterozoic deformation and metamorphism of the metasedimentary units,and literature data indicate that the magmatic zircons from the dikes yielded an age of 2,170 ± 17 Ma. Petrographic andgeochemical data show that they have the composition of epicratonic high-Ti diabases, which are similar to the largecontinental flood basalts of the Paraná Basin. The age of the intrusions may be correlated with the short time-interval of theRhyacian (2.20 to 2.17 Ga, during which successive localized episodes of mantle plume volcanism occurred on the Earth.

  16. Plume-proximal mid-ocean ridge origin of Zhongba mafic rocks in the western Yarlung Zangbo Suture Zone, Southern Tibet

    Science.gov (United States)

    He, Juan; Li, Yalin; Wang, Chengshan; Dilek, Yildirim; Wei, Yushuai; Chen, Xi; Hou, Yunling; Zhou, Aorigele

    2016-05-01

    The >2000 km-long Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet includes the remnants of the Mesozoic Neotethyan oceanic lithosphere, and is divided by the Zhada-Zhongba microcontinent into northern and southern branches in its western segment. Zircon U-Pb dating of a doleritic rock from the northern branch has revealed a concordant age of 160.5 ± 1.3 Ma. All of the doleritic samples from the northern branch and the pillow basalt and gabbro samples from the southern branch display consistent REE and trace element patterns similar to those of modern OIB-type rocks. The geochemical and Sr-Nd-Pb isotopic signatures of these OIB-type rocks from the western segment are identical with those of OIB-type and alkaline rocks from other ophiolite massifs along the central and eastern segments of the YZSZ, suggesting a common mantle plume source for their melt evolution. The enriched Sr-Nd-Pb isotopic character of the gabbroic dike rocks from the southern branch points to a mantle plume source, contaminated by subducted oceanic crust or pelagic sediments. We infer that the mafic rock associations exposed along the YZSZ represent the remnants of a Neotethyan oceanic lithosphere, which was developed as part of a plume-proximal seafloor-spreading system, reminiscent of the seamount chains along-across the modern mid-ocean ridges in the Pacific Ocean.

  17. 陕南凤凰岭南缘变质镁铁质-超镁铁质侵入岩矿物学特征--对Fe-Ti成矿作用的指示%Mineralogical characteristics of the meta-mafic-ultra- mafic intrusive rocks on the southern margin of Fenghuangling, southern Shaanxi:An indicator of Fe- Ti metallogenesis

    Institute of Scientific and Technical Information of China (English)

    黄杰; 覃小锋; 王宗起; 张英利; 杨文; 朱安汉; 宋炯

    2015-01-01

    陕南凤凰岭南缘变质镁铁质—超镁铁质侵入岩为富含Fe、Ti等有用元素的含矿岩体。利用岩石地球化学方法、偏光显微镜和电子探针技术对该区镁铁质—超镁铁质侵入岩的岩石学、地球化学和矿物学特征进行了研究,并对Fe-Ti氧化物的形成、富集进行了初步探讨,对成岩、成矿作用具有一定的参考意义。结果表明,成矿镁铁质—超镁铁质侵入岩与非成矿镁铁质—超镁铁质侵入岩为不同岩浆源区、同期岩浆作用的产物,镁铁质—超镁铁质侵入岩类的Fe-Ti矿化作用与初始岩浆的源岩之间具有密切关系。Fe-Ti氧化物主要以钛铁矿和榍石的形式存在,局部见少量金红石。化学成分上,钛铁矿具富锰贫镁特征,本区Fe-Ti氧化物的形成和富集过程经历了岩浆结晶分异阶段和热液蚀变阶段。%The meta-mafic-ultramafic intrusive rocks in southern Fenghuangling are ore-bearing rocks with abundant useful ele⁃ments such as Fe and Ti. In this study, geochemical method, polarizing light microscope and electron probe micro analysis (EPMA) were conducted to investigate the petrologic, geochemical and mineralogical characteristics of the meta-maficultramafic intrusive rocks. The Fe-Ti oxide formation and enrichment were also studied so as to probe into diagenesis and mineralization. The results show that, in this area, ore-bearing meta-mafic-ultramafic intrusive rocks and barren meta-mafic-ultramafic intrusive rocks resulted from simultaneous magmatism of different magma source areas, and the Fe-Ti mineralization of meta-mafic-ultramafic intrusive rocks had a close relationship with the initial magma source rocks. Fe-Ti oxides mostly exist in sphene and ilmenite but sometimes it also exists in a small amount of rutile. Ilmenite is rich in MnO but poor in MgO. The formation and enrichment process of Fe-Ti ox⁃ide experienced the stages of magma crystallization differentiation and

  18. A back-arc setting for mafic rocks of the Honeysuckle Beds, southeastern N.S.W.: the use of trace and rare earth element abundances determined by INAA

    Energy Technology Data Exchange (ETDEWEB)

    Dadd, K.A. [University of Technology, Sydney, NSW (Australia)

    1993-12-31

    Major, trace and rare earth elements abundance in mafic rocks of the Honeysuckle Beds was determined by x-ray fluorescence and neutron activation analysis . A comparison with typical mid-ocean ridge basalt compositions reveals an enrichment in light rare earths elements (Ba, Rb, and Th) and depletion in Nb, Ta and Ti, consistent with modifications of the source by subduction-related fluids. 9 refs., 6 figs.

  19. First evidence for expressive neoproterozoic intraplated mafic rocks and magma mixing in post-collisional A-PA type granites, Southern Brazil: Geochemistry and U-Pb (zircon), Nd-Sr-18O(zircon) isotope investigations

    International Nuclear Information System (INIS)

    New and recent geological investigations around Pien-Tijucas suture zone, between Luis Alves and Curitiba Microplates (Basei et al.2000) led to mapping of Palermo, Agudos do Sul and Rio Negro A-PA type Granites with expressive expositions of alkaline felsic ans mafic rocks and, associated mafic and felsic hybrid rocks. The suture zone is formed by subduction arc-related Pien-Mandirituba deformed calc-alkaline I-type granite belt and serpentinized supra subduction zone (SSZ) obducted mantle rocks with intrusive Neoproterozoic (650-630 Ma) very high Cr and Ni tholeitic gabbros. The Pien-Mandirituba calc-alkaline I-type Granite Belt is constituted by three main granite suites. The older emplaced pre-collisional suite is constituted by deformed to highly deformed amphibole and biotite-rich, magmatic epidote-absent quartz-monzodiorites and granodiorites formed between 620 and 610 Ma. The second sincollisional granite suite is constituted by deformed and slightly deformed low content amphibole-biotite-magmatic epidote-bearing, quartz-monzodiorites, granodiorites and leucogranodiorites emplaced between 605 and 595 Ma. The third, also sincollisional, granite suite is deformed to highly deformed biotite ± amphibole monzogranites. The deformation age of the three non-cogenetic granite suites of this granite belt is between 605-595 Ma. The granite rocks of the Pien-Mandirituba Granite Belt are meta-aluminous to slightly peraluminous, high K calc-alkaline, generally with high Ba, high Sr and low Rb contents. Palermo, Agudos do Sul and Rio Negro Granites are components of the expressive Neoproterozoic volcanic and plutonic alkaline-peralkaline Serra do Mar Suite (Kaul 1997), emplaced in extensional post-collisional and anorogenic settings along the central portion and northern border of the Luis Alves Microplate and southern border of the Curitiba Microplate. Magma mixing evidence is rare ou absent in the other components of the Serra do Mar volcanic and plutonic suite. The

  20. 武汉市龙王庙险段综合整治工程加固设计%Strengthening design of the dangerous Longwangmiao dyke section in Wuhan City

    Institute of Scientific and Technical Information of China (English)

    周琴; 张琳; 严浩

    2001-01-01

    龙王庙险段历来是汉江武汉市河段著名的险工段,是武汉市防汛的重中之重。1998年长江发生全流域性大洪水,党和国家领导人多次亲临视察,彻底根治龙王庙险段的工作也由此展开。整治工程遵循“扩展口门,改善河势,出险加固,综合整治”的原则。具体为:汉阳岸平均削坡后退60 m;汉口岸整治通过钻孔灌注桩和“L”型挡土墙解决岸坡整体稳定问题,并对老驳岸墙进行加固,对驳岸平台和码头采用复合土工膜防渗处理,采用水下抛石结合混凝土铰链沉排以稳固岸脚。工程完工后,经受了1999年汛期洪水(28.89 m,居历史第3位)的考验,各项检测资料表明,所采取的综合整治措施安全可靠,达到了设计预期效果。%The Longwangmiao dyke section was the well-known dangerous dyke section of the Hanjiang river in Wuhan City, also the focal point of the Wuhan urban flood control. Duing the 1998 Yangtze flood, Party and state leaders personally inspected the dangerous section many times, and then the works to thoroughly regulate the dangerous Longwangmiao dyke section started. The regulation project was constructed in accordance with the principle of “expanding the exit channel of the Hanjiang river, improving the river regime, strengthening dangerous locations and implementing comprehensive regulation”. The concrete contents of the project were that the river bank on Hanyang side retreated 60 m on an average with the original bank slope cutting; the river bank on Hankou side was regulated by building cast-in-situ-bored piles and an L-shaped retaining wall to improve integral stability, the old waterfront wall was strengthened, composite gemembrane was used for seepage prevention of the waterfront platforms and wharves, and the slope toe of the river bank was stabilized by dumpimg rubble stone and placing hinged concrete mattresses. The completed project experienced the 1999

  1. The behaviour of the extended HFSE group (Nb, Ta, Zr, Hf, W, Mo) during the petrogenesis of mafic K-rich lavas: The Eastern Mediterranean case

    Science.gov (United States)

    Kirchenbaur, M.; Münker, C.

    2015-09-01

    In arc lavas, elements of the extended high field strength element group (HFSE; Nb, Ta, Zr, Hf, W, and Mo) are valuable tracers to unravel magma source processes. These elements can also help to identify residual mineral assemblages in subducting slabs and in the mantle. Most high-precision studies on HFSE behaviour to date only focused on intra-oceanic arc suites and data for mafic lavas of the K-rich series (medium-K, high-K and shoshonitic) are scarce. Arguably, K-rich series are the most incompatible element-rich end-members of subduction zone magmatism, and they often record sediment recycling into the mantle. Understanding HFSE fractionation in K-rich lavas can therefore provide important insight into the global HFSE budget. Here we present a comprehensive extended HFSE dataset obtained by isotope dilution on well-characterised K-rich lavas from the Eastern Mediterranean, also including subducting sediment samples drilled during DSDP Leg 13 and ODP Leg 160 South and West of Crete. The volcanic samples include mafic calc-alkaline lavas from the active Aegean Island arc (Santorini) and post-collisional Tertiary lavas from SE Bulgaria. The Santorini lavas record a hydrous sediment melt-mediated source overprint of a depleted mantle source by components from the subducting African plate. The Bulgarian lavas tap lithospheric mantle sources that were overprinted by fluid- and melt-like subduction components during Eocene subduction of the African Plate. The sediments in this study comprise silts/sands, marl oozes, limestones and clay-rich debris flows and approximate the bulk sediment subducted beneath the Hellenic arc. The marked enrichment of all HFSE in the lavas is controlled by the composition of the subducted sediments as shown by low 176Lu/177Hf (0.008630-0.02433) and Zr/Nb (11.3-29.4), combined with variable εHf (-3 to +11) and elevated W contents (up to 2.45 ppm) in the lavas. Nevertheless, the lavas display unfractionated ratios of Nb/Ta and Zr/Hf of 12

  2. Minerals and melt inclusions as keys to understanding magma reservoir processes during formation of volcanic and plutonic mafic-ultramafic complexes in the Maimecha Kotui Province (Polar Siberia)

    Science.gov (United States)

    Simonov, Vladimir; Vasiliev, Yurii; Kotlyarov, Alexey; Stupakov, Sergey

    2016-04-01

    Magmatic complexes in the Maimecha Kotui Province (Polar Siberia) attract attention of researchers because they contain ultramafic volcanic rocks - meimechites, being products of crystallization of the ultrabasic deep mantle melts (Sobolev et al., 1991, 2009, 2011; Ryabchikov et al., 2002; Vasiliev, Gora, 2014). Effusive meimechites together with intrusive dunites of the Guli massif form ancient (253-246 Ma) volcanic and plutonic association, in which also pyroxenites and alkaline rocks are situated. Conditions of formation of this association were established with the help of minerals and melt inclusions study. The cumulative structure of the Guli massif dunites consists of rather large (2-4 mm) olivine crystals and dividing them zones (0.5-0.7 mm), filled with fine grains of clinopyroxenes and ore minerals (magnetite, ilmenite and chromite). The extended forms of well faceted pyroxene crystals testify to their fast growth from melt between cumulative olivines. Thus, crystallization of clinopyroxenes and ore minerals leads to formation between olivines ore pyroxenites, which are presented in the Guli massif by independent bodies. Analysis of olivine, Cr-spinel and clinopyroxene compositions testify to similarity of conditions of the Guli massif dunites crystallization on the one hand with formation of platinum-bearing Uralian-Alaskan-type mafic-ultramafic complexes and with another - show participation of meimechite magma. Major element composition of melt inclusions in Cr-spinel has shown that dunites of the Guli massif were crystallized with participation of subalkaline picrite magmatic systems, that are relative to melts, responsible of formation of platinum-bearing mafic-ultramafic complexes and meimechites. Peculiarities of trace and rare-earth elements distribution in melt inclusions in Cr-spinel of dunites are actually similar to inclusions in olivine of meimechites. Overall, data on composition of inclusions directly testify to formation of considered

  3. High-K andesite petrogenesis and crustal evolution: Evidence from mafic and ultramafic xenoliths, Egmont Volcano (Mt. Taranaki) and comparisons with Ruapehu Volcano, North Island, New Zealand

    Science.gov (United States)

    Price, Richard C.; Smith, Ian E. M.; Stewart, Robert B.; Gamble, John A.; Gruender, Kerstin; Maas, Roland

    2016-07-01

    This study uses the geochemistry and petrology of xenoliths to constrain the evolutionary pathways of host magmas at two adjacent andesitic volcanoes in New Zealand's North Island. Egmont (Mt. Taranaki) is located on the west coast of the North Island and Ruapehu lies 140 km to the east at the southern end of the Taupo Volcanic Zone, the principal locus of subduction-related magmatism in New Zealand. Xenoliths are common in the eruptives of both volcanoes but the xenoliths suites are petrographically and geochemically different. Ruapehu xenoliths are predominantly pyroxene-plagioclase granulites derived from Mesozoic meta-greywacke basement and the underlying oceanic crust. The xenolith population of Egmont Volcano is more complex. It includes sedimentary, metamorphic and plutonic rocks from the underlying basement but is dominated by coarse grained, mafic and ultramafic igneous rocks. Gabbroic xenoliths (Group 1) are composed of plagioclase, clinopyroxene and amphibole whereas ultramafic xenoliths are dominated by amphibole (Group 2) or pyroxene (Group 3) or, in very rare cases, olivine (Group 4). In Group 1 xenoliths plagioclase and clinopyroxene and in some cases amphibole show cumulate textures. Amphibole also occurs as intercumulate poikilitic crystals or as blebs or laminae replacing pyroxene. Some Group 2 xenoliths have cumulate textures but near monomineralic amphibole xenoliths are coarse grained with bladed or comb textures. Pyroxene in Group 3 xenoliths has a polygonal granoblastic texture that is commonly overprinted by veining and amphibole replacement. Group 1 and most Group 2 xenoliths have major, trace element and Sr, Nd and Pb isotope compositions indicating affinity with the host volcanic rocks. Geochemical variation can be modelled by assimilation fractional crystallisation (AFC) and fractional crystallisation (FC) of basaltic parents assuming an assimilant with the composition of average crystalline basement and Group 1 xenoliths have

  4. Subduction of fore-arc crust beneath an intra-oceanic arc: The high-P Cuaba mafic gneisess and amphibolites of the Rio San Juan Complex, Dominican Republic

    Science.gov (United States)

    Escuder-Viruete, Javier; Castillo-Carrión, Mercedes

    2016-10-01

    The Rio San Juan metamorphic complex (RSJC) exposes a segment of a high-P accretionary prism, built during Late Cretaceous subduction below the intra-oceanic Caribbean island-arc. In this paper we present new detailed maps, tectonostratigraphy, large-scale structure, mineral chemistry, in situ trace element composition of clinopyroxene (Cpx), and bulk rock geochemical data for representative garnet-free peridotites and mafic metaigneous rocks of the Cuaba and Helechal tectonometamorphic units of the southern RSJC. The Cuaba subcomplex is composed of upper foliated amphibolites and lower garnet amphibolites, retrograded (coronitic) eclogites, and heterogeneous metagabbros metamorphosed to upper amphibolite and eclogite-facies conditions. The lenticular bodies of associated peridotites are Cpx-poor harzburgites. The underlying Helechal subcomplex is composed of Cpx-poor harzburgites, Cpx-rich harzbugites, lherzolites and rare dunites. The presented data allow us to argue that the Cuaba subcomplex: (a) represents tectonically deformed and metamorphosed crust of the Caribbean island-arc, (b) contains fragments of its supra-subduction zone mantle, and (c) includes different geochemical groups of mafic protoliths generated by varying melting degrees of diverse mantle sources. These geochemical groups include mid-Ti tholeiites (N-MORB), normal IAT and calc-alkaline rocks, low-Ti IAT, metacumulates of boninitic affinity, and HREE-depleted IAT, that collectively record a multi-stage magmatic evolution for the Caribbean island-arc, prior to the Late Cretaceous high-P metamorphism. Further, these mafic protoliths present comparable geochemical features to mafic igneous rocks of the Puerca Gorda Schists, Cacheal and Puerto Plata complexes, all of them related to the Caribbean island-arc. These relations suggest that the southern RSJC complex represents part of the subducted fore-arc of the Caribbean island-arc, which experienced initial subduction, underplating below the arc

  5. 白云鄂博矿床碳酸岩墙/脉和赋矿白云岩中流体包裹体研究%Fluid inclusion study of carbonatite dykes/veins and ore-hosted dolostone at the Bayan Obo ore deposit

    Institute of Scientific and Technical Information of China (English)

    秦朝建; 裘愉卓; 周国富; 王中刚; 张台荣; 肖国望

    2007-01-01

    Fluid inclusion study has been carried out for the carbonatite dykes/veins and the ore-hosted dolostone of the Bayan Obo superlarge REE-Fe-Nb deposit in order to provide the evidence and constraint for their origin. Based on the detailed geological observation and mineralogical investigation, the heating and cooling stage and laser Raman spectroscopy were mainly used for the laboratory work of this study. Following results have been obtained: (1) The discovery of melt and melt-fluid inclusions from carbonatite dykes/veins in the Dulahara and Jianshan Mountains, combined with the fine-grained (aplitic) texture of rocks, as well as the types and features of fluid inclusions such as CO2 enrichment, higher homogenization temperature, provides a direct evidence for the magmatic origin of these dykes/veins. (2) The carbonatite dykes/veins distributed in two regions, nearby the axis of the Kuangou anticline and in the east to Bayan Obo town, mainly show coarse-grained texture. No melt inclusion was found, and the fluid inclusions possess features of less CO2, lower homogenization temperature and higher salinity. They are tentatively identified as veins formed by some carbonate-rich hydrothermal solution. (3) Bedding carbonate layers/lens within the hanging wall and foot wall of ore-hosted dolostone, previously recognized as of magmatic origin, mainly composed by dolomite. The existence of single phase pure aqueous inclusions with very low homogenization temperature indicates their sedimentary origin. (4) The ore-hosted dolostone possesses apparent bedding and laminated structures. No melt inclusion was found, but, both single phase pure aqueous inclusions and CO2bearing multi-phase fluid inclusions coexisted in dolostones. In the direction towards ore-bodies, the homogenization temperature and CO2 contents of fluid inclusion show an increasing tendency. It indicates the sedimentary origin of dolostone superimposed by late fluid metasomatism.

  6. Impingement of Deep Mantle-Derived Upwelling Beneath Northern, Subducted Extension of the East Pacific Rise and Palinspastically Restored Cenozoic Mafic Magmatism in Western North America

    Science.gov (United States)

    Rowley, D. B.; Moucha, R.; Forte, A. M.; Mitrovica, J. X.; Simmons, N. A.; Grand, S. P.

    2009-12-01

    Reconstruction of the retrodicted whole mantle flow, based on presently imaged distribution of variations in seismic velocity and its correlation to density (Simmons et al. 2009), over the past 30 Ma, in the North American fixed frame of reference, reveals that the northern, now subducted, extension of the East Pacific Rise is coincident with mantle buoyancy arising from near the core-mantle boundary and extending to the base of the lithosphere (Moucha et al. 2009 GRL, in press). Divergence of the reconstructed flow near the surface is independent of the surface plate(s) and results in predicted geological manifestations distinct from those predicted by traditional plate driven models of flow. Most particularly the retrodicted flow-related dynamic topography results in progressive west to east sweep of surface uplift, that is now centered on the Colorado Plateau (Moucha et al. 2008, 2009 GRL, in press). In addition, and the primary focus of the current study is the relationship between this retrodicted mantle-wide flow and the history of magmatism within the western U.S. and adjacent Mexico. There is a close spatial correlation between the impingement of upwelling with palinspastic restored western North America (McQuarrie and Wernicke, 2005) and onset and distribution of magmatism, particularly of mafic compositions as revealed in the Navdat (www.navdat.org) database. Although often attributed to effects of opening of a slab window (Snyder and Dickinson, 1979, McQuarrie and Oskins, 2008) associated with continued plate-driven separation, this model predicts active mantle flow induced upwelling and divergence resulting in mantle melting that sweeps across east-northeast across southern Basin and Range to the Rio Grande Rift with time and as seen in the distribution of magmatism in this region.

  7. High-Mg adakitic rocks and their complementary cumulates formed by crystal fractionation of hydrous mafic magmas in a continental crustal magma chamber

    Science.gov (United States)

    Ma, Qiang; Xu, Yi-Gang; Zheng, Jian-Ping; Sun, Min; Griffin, William L.; Wei, Ying; Ma, Liang; Yu, Xiaolu

    2016-09-01

    Understanding how adakitic magmas form is important for understanding the formation of the continental crust. Generating such high-Sr/Y rocks by crystal fractionation of basalts/basaltic andesites in magma chambers has been proposed in a wide range of tectonic settings. However, the complementary cumulates predicted by this scenario have rarely been observed. The late Triassic (~ 227 Ma) Ningcheng complex from the North China Craton is composed of a websterite - (Ol -/Hbl-) pyroxenite - gabbro unit and a quartz-diorite unit. They are interpreted as the products (cumulates and derivative melts, respectively) of fractionation from hydrous mafic magmas at mid- to lower-crustal pressures (4.9 ~ 8.3 kbar). The quartz diorites are high-Mg intermediate rocks with moderate SiO2 (57.0 ~ 62.9 wt%), high Mg# (> 49) and adakitic trace element signatures, such as high Sr (≥ 636 ppm) and light rare earth elements (REEs), low Y (≤ 17 ppm) and heavy REEs (Yb ≤ 1.8 ppm), lack of obvious Eu anomalies, and high Sr/Y (≥ 31) and La/Yb (≥ 24)). These adakitic signatures reflect differentiation of hydrous mantle-derived magmas in the deep crust, leaving behind a plagioclase-free residual solid assemblage in the early stages, which is represented by the coeval websterite-pyroxenite complex. This study therefore not only demonstrates that hydrous crystal fractionation is an important mechanism to form adakitic rocks, but also presents an example of a preserved fractionating system, i.e. high-Sr/Y rocks and their complementary cumulates. A geochemical comparison is made between representative adakitic rocks formed by fractionation of hydrous magmas and Archean TTGs. It is suggested that crystal fractionation is an efficient process for making Phanerozoic high Sr/Y rocks but was not responsible for the formation of Archean granitoids.

  8. Le magmatisme basique filonien néoprotérozoïque de la boutonnière de Zenaga, Anti-Atlas central, Maroc: pétrologie, géochimie et signification géodynamiqueNeoproterozoic basic dykes of the Zenaga Inlier, central Anti-Atlas, Morocco: petrology, geochemistry and geodynamic significance

    Science.gov (United States)

    Hafid, A.; Sagon, J. P.; Julivert, M.; Arboleya, M. L.; Saquaque, A.; El-Boukhari, A.; Saidi, A.; Soler, J. M. F.

    2001-05-01

    Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P 2O 5, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding.

  9. Determination of trace elements in Mesozoic dykes of the Serra do Mar by neutron activation; Determinacao de elementos tracos em diques mesozoicos da Serra do Mar por meio de ativacao com neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Vicentini, Caio M.; Marques, Leila S., E-mail: caio.vicentini@usp.br, E-mail: leila@iag.usp.br [Universidade de Sao Paulo (IAG/USP), Sao Paulo, SP (Brazil). Instituto de Astronomia, Geofisica e Ciencias Atmosfericas; Figueiredo, Ana Maria G., E-mail: anamaria@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2013-07-01

    The analysis of trace elements such as rare earths, Th, U, Ta, Hf, Ba, Rb and Ba, is a very important tool for petrogenetic studies. In order to study these processes in dykes of Enxame Serra do Mar (Coast of Sao Paulo and Rio de Janeiro), belonging to the Parana Magmatic Province (PMP), one of the most significant provinces of continental basalts in the world, were perform analyzes by neutron activation in these dikes. The technique, employed in Centro de Reator de Pesquisa of the Instituto de Pesquisas Energeticas e Nucleares, provided concentrations of trace elements with accuracy levels of 10% and 9%, which are suitable for petrogenetic studies. Due to the low concentrations of the elements analyzed, the experimental routine sample preparation processes covered very careful to avoid contamination. The samples investigated can be divided into four groups: basic rocks (SiO{sub 2} <55%) with Ti / Y> 500; basic rocks with Ti / Y <500; intermediate rocks (55% 63%). Dikes of intermediate and acid composition only occur at the Sao Sebastiao Island and adjacent coastal region. The concentrations of major and minor elements, as well as the abundance patterns of rare earths and other incompatible elements of these more differentiated rocks, show significant similarities with the type of the volcanic Chapeco, suggesting similar genesis, in other worlds, including also processes of crustal contamination.

  10. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating

    Institute of Scientific and Technical Information of China (English)

    WANG; Jianghai

    2002-01-01

    [1]Zhang, Q., Ma, B. L., Liu, R. X. et al., A remnant of continental lithospheric mantle above a subduction zone: Geochemical constraints on ultramafic rocks from Raobazhai area in Anhui Province, Sci. in China, Ser. B, 1995, 38(12): 1522- 1529.[2]Zhai, M. G., Cong, B. L., Petro-tectonics of the Sulu-Dabie Shan metamorphic belt, Central and East China, Sci. in China, Ser. D, 1996, 39(3): 319-328.[3]Li, S. G., Hart, S. R., Zheng, S. G. et al., Timing of collision between the North and South China Blocks-- the Sm-Nd isotopic age evidence, Sci. in China, Ser. B, 1989, 32(11): 1393-1400.[4]Ni, Y. H., Li, S. G., Sm-Nd ages of the syn-collisional mafic-ultramafic intrusions in the Dabie Mountains, Chinese Sci. Bull., 1998, 43(2): 160-163.[5]Chen, D. G., Wu, Y. B., Xia, Q. K. et al., Sm-Nd ages for the Jiaoziyan gabbro pluton and the characteristics of Nd isotopes, Acta Geosci. Sinica, 1997, 18(Suppl.): 9-11.[6]Jahn, B. M., Wu, F. Y., Lo, C. H. et al., Crust-mantle interaction induced by deep subduction of the continental crust: geochemical and Sr-Nd isotopic evidence from post-collisional mafic-ultramafic intrusions of the northern Dabie complex, central China, Chem. Geol., 1999, 157: 119-146.[7]Li, S. G., Jagoutz, E., Zhang, Z. Q. et al., Structure of high-metamorphic belt in the Dabie mountains and its tectonic implications, Chinese Sci. Bull., 1995, 40(Suppl.): 138-140.[8]Zhang, R. Y., Liou, J. G., Tsai, C. H., Petrogenesis of a high-temperature metamorphic terrain: a new interpretation for the north Dabie Shan, central China, J. Metamorphic Geol., 1996, 14: 319-333.[9]Wang, J. H., The Early Evolution of the Dabie Complex, with Special Reference to the Genetic Mechanism of Migmatites, Wuhan: China University of Geosciences Press, 1991, 1-140.[10]Suo, S. T., Zhong, Z. Q., You, Z. D., Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif

  11. Intensive hydration of the wedge mantle at the Kuril arc - NE Japan arc junction: implications from mafic lavas from Usu Volcano, northern Japan

    Science.gov (United States)

    Kuritani, T.; Tanaka, M.; Yokoyama, T.; Nakagawa, M.; Matsumoto, A.

    2015-12-01

    The southwestern part of Hokkaido, northern Japan, is located at the junction of the NE Japan arc and the Kuril arc. The subducting Pacific plate under this region shows a hinge-like shape due to the dip change of the subducting plate along the trench. Because of the interest in this unique tectonic setting, this arc-arc junction has been the focus of extensive geophysical studies (e.g. Kita et al., 2010, Morishige and van Keken, 2014; Wada et al., 2015). This region is also known as an area in which magmatism has been intense; there are many active volcanoes such as Usu, Tarumae, and Komagatake, and large calderas including Toya, Shikotsu, and Kuttara. In this region, the temporal and spatial evolution of the volcanism and the chemical compositions of the volcanic rocks are well characterized (e.g. Nakagawa, 1992). However, the generation conditions of magmas have not been estimated for these volcanoes, probably because of the scarcity of basaltic products. Therefore, a possible link between the tectonic setting and the intense magmatism is still unclear. In this study, we carried out a petrological and geochemical study on mafic lavas (49.6-51.3 wt.% SiO2) from Usu Volcano, and estimated the conditions under which the magmas were generated. By application of a plagioclase-melt hygrometer to the plagioclase and the host magma, the water content of ~6.5 wt.% was obtained for the basaltic magma. Using this information, as well as the olivine maximum fractionation model (Tatsumi et al., 1983), the composition of the primary magma is estimated to be 47.9 wt.% SiO2, 15.1 wt.% MgO, and 4.1 wt.% H2O. Analyses using the multi-component thermodynamics suggest that the primary magma was generated in the source mantle with 0.9 wt.% H2O at 1310ºC and at 1.6 GPa. The water content of 0.9 wt.% of the source mantle is significantly higher than the estimates for the source mantle in the main NE Japan arc (hinge-like shape, and many fractures might have been developed in the slab

  12. Paleomagnetic study on the Neoproterozoic mafic dikes and Early Permian volcanic-sedimentary rocks from NW Yili Block (NW China): Implications for post-orogenic kinematic evolution of the SW CAOB

    Science.gov (United States)

    Zhu, Xin; Wang, Bo; Chen, Yan; Liu, Hongsheng; Shu, Liangshu; Faure, Michel

    2016-04-01

    As one of the largest accretionary orogens of the world, the Central Asian Orogenic Belt (CAOB) has been the focus of geological studies in the last decades. However, several key points are still in hot debate, such as the formation process of the Paleo-Asian Ocean, the intracontinental movements among constituent blocks of the CAOB. In order to better understand these questions, we conducted a paleomagnetic study on the Neoproterozoic (ca. 780 Ma) mafic dikes and Early Permian (ca. 268 Ma) volcanic and sedimentary rocks from NW of the Yili Block (NW China). Ten sites have been sampled from three mafic dikes. The thickness of dikes varies from 10 to 40 meters. At about 15 km west of the mafic dikes, 4 sites were drilled in the Lower Permian basalts and limestones that unconformably overlay the Neoproterozoic mafic dikes. Mineralogical investigations show the titanium-poor magnetite as the major magnetic remanence carrier. Stepwise alternating field (AF) and thermal demagnetizations reveal two-component magnetizations. The low temperature (coercivity) component shows a viscous and unstable magnetic remanence, whereas the high temperature (coercivity) component stably decays toward to the origin and is considered as the characteristic remanent magnetization (ChRM). All ChRMs isolated from both the mafic dikes and volcanic-sedimentary samples exclusively show a reversed magnetic polarity. Based on the following 3 arguments, we suggest that the Neoprotozoic mafic dikes have been remagnetized in the Early Permian. 1. International reference of magnetostratigraphic polarity shows a dominance of the normal polarity for the Neoproterozoic period and a superchron of the reversed polarity for the late Carboniferous-Permian; 2. Two groups of sampling show coherent paleomagnetic poles with an undistinguishable angular difference; and 3. The widespread Early Permian magmatism in the sampling area could be the cause of the remagnetization. Consequently, an Early Permian

  13. Geochemistry and age relationships of metamorphosed mafic sills from Sierra de Enmedio and Sierra de Carrascoy (Eastern Betic zone, Southeastern Spain

    Directory of Open Access Journals (Sweden)

    Torres-Roldán, R. L.

    1989-12-01

    Full Text Available The presence of fairly abundant shallow-intrusive mafic bodies is a common feature of the almagride units, a recently defined group of tectonic elements of the Eastern Betic Zone whose paleogeographic and tectonic interpretation is particuIarly controversial. In this paper we focuse on the bulk geochemistry (including K/Ar data and possible age relationships of tbese rocks, and discuss them in view of their significance regarding possible tectonic framework of emplacement and subsequent crustal evolution. The analyses (49-55% SiO2 point to a derivation from tholeiitic magmas that interacted with continental crust, as indicated by enrichment in the less compatible elements, such as Ba, Rb, Th and K, whose amounts are similar to those of well known continental tholeiitic provinces. Thus, the magmatic event is inferred to have been generated in a tectonic environment comparable to that of continental rifts. Emplacement may have taken place in Upper Triassic to Middle Jurassic times, as bracketed by their intrusion within Triassic beds and one whole-rock KIAr date of 178±4 Ma from a less altered sample. Much younger analytical K/Ar ages, scattering between 41±5 and 57±2 Ma, are obtained from common samples, however, reflecting an Eocene or younger metamorphic event that caused partial recrystallisation under low-grade greenchist, to actinolite-pumpelIyite facies conditions. As compared to other mafic complexes in the Betics, the observed chemical evidence for crustal contamination makes the almagride metabasites more similar to those in the external zona (e.g. the so-calIed «opbites» than in tbe Nevado-Filábride Ensemble, thus being consistent with proposals that correlate these units with the Subbetic in the Murcia area.La frecuente presencia de cuerpos de metabasitas es una característica común de las unidades almágrides, un grupo de unidades tectónicas de la Zona Bética Oriental, de reciente definición, cuya interpretaci

  14. Tectonic transition from Late Carboniferous subduction to Early Permian post-collisional extension in the Eastern Tianshan, NW China: Insights from geochronology and geochemistry of mafic-intermediate intrusions

    Science.gov (United States)

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.; Sun, Min; Han, Yigui; Hou, Wenzhu; Liu, Dongxing; Wang, Bo; Liu, Qian; Xu, Bing; Zhu, Chloe Yanlin

    2016-07-01

    The closure of the Junggar Ocean between the Central Tianshan and Junggar terranes is essential in understanding the final assembly of the southern Central Asian Orogenic Belt. This study presents new whole-rock geochemical, Sr-Nd and zircon U-Pb-Hf isotopic data for mafic-intermediate intrusions from the Central Tianshan block to provide robust constraints on the final closure of the ocean. LA-ICP-MS U-Pb dating on magmatic-type zircons yields weighted mean 206Pb/238U ages of ca. 310 Ma and ca. 290 Ma, which are interpreted as the crystallization ages of the intrusions. Petrographic and geochemical analyses of the Late Carboniferous mafic-intermediate rocks, characterized by typical subduction-related signatures, low Sm/Yb (probably as a result of the southward subduction of the Junggar oceanic plate. In contrast, the Early Permian mafic magmatism exhibits typical within-plate basalt affinities, such as high TiO2 (2.7-3.2 wt.%) contents, elevated Ti/V (86.0-115.1) and Zr/Y (4.9-9.3) ratios, OIB-like trace element patterns and high εNd(t) (+ 1.1 to + 4.5) and zircon εHf(t) (+ 3.0 to + 9.8) values. In association with previous investigations, we suggest that their protoliths were most probably derived from the partial melting of an asthenospheric mantle source in the garnet stability field, plausibly induced by asthenosphere upwelling during the slab break-off of the Junggar oceanic plate, which agrees well with the linear distributions of Permian mafic-ultramafic rocks in the Eastern Tianshan. Collectively, our data pinpoint a tectonic transition from oceanic subduction to post-collisional extension during Late Carboniferous to Early Permian time, probably triggered by the closure of the Junggar Ocean and subsequent arc-continent collision between the Central Tianshan and Junggar terranes that gave rise to the final assembly of the Eastern Tianshan.

  15. Origin of mafic microgranular enclaves (MMEs) and their host quartz monzonites from the Muchen pluton in Zhejiang Province, Southeast China: Implications for magma mixing and crust-mantle interaction

    Science.gov (United States)

    Liu, Liang; Qiu, Jian-Sheng; Li, Zhen

    2013-02-01

    The origin of mafic enclaves in granitoid plutons has long been a matter of debate. In this paper, we present detailed petrographic, mineralogical, geochemical, and Srsbnd Ndsbnd Hf isotopic data, Usbnd Pb zircon dates, and field and petrological observations, for mafic microgranular enclaves (MMEs) and their host quartz monzonites from the Muchen pluton in Southeast China to evaluate their origins. LA-ICP-MS Usbnd Pb dating of zircon yields crystallisation ages of 112.4 ± 1.2 Ma and 112.1 ± 1.0 Ma for the MMEs and host quartz monzonites, respectively, indicating their coeval formation during the late Early Cretaceous. Field and petrological observations, such as spheroidal shapes, back-veining, double enclaves, xenocrysts, acicular apatites, and oscillatory zoning with repeated resorption surfaces in plagioclases, suggest that the MMEs are globules of a more mafic magma that was injected into and mingled with the host felsic magma. Geochemically, the host monzonites are intermediate-acidic, metaluminous, alkaline, and K-rich. In contrast, the MMEs are relatively poor in Si and K. The host monzonites are enriched in Rb, Th and U, and depleted in Sr, P, Nb, Ta and Ti, and show moderate to strong europium depletions (δEu = 0.12-0.60). These mineralogical and geochemical features classify the quartz monzonites as belonging to the I-type granitoids. The MMEs have broadly similar trace element signatures to those of the host monzonite, but are distinct in having relatively enriched Sr and P, more depleted Zr and Hf, and weak to moderate Eu depletions (δEu = 0.43-0.93). Major and trace element data plotted versus isotopic data for the MMEs and the host quartz monzonites yield covariant arrays that result from magma mixing during their petrogenesis. The MMEs and the host quartz monzonites have similar initial 87Sr/86Sr ratios (ISr) of 0.7058-0.7070 and 0.7062-0.7065, respectively, and both have high ɛNd(t) values (- 2.6 to + 0.6 for MMEs; - 3.2 to - 2.4 for quartz

  16. Generation of Palaeoproterozoic tonalites and associated high-K granites in southwestern Tanzania by partial melting of underplated mafic crust in an intracontinental setting: Constraints from geochemical and isotopic data

    Science.gov (United States)

    Manya, Shukrani; Maboko, Makenya A. H.

    2016-09-01

    The southwestern part of the 2.0-1.8 Ga Palaeoproterozoic Usagaran Belt in the Njombe area of SW Tanzania is intruded by two types of synchronous granitic rocks with different chemical and petrological characteristics. The first type consists of hornblende-rich tonalites that have major element compositions similar to those of Archaean TTG but differ significantly in their trace element composition. The tonalites are spatially and closely associated with felsic, high-K, I-type granites, some of which are gneissic and/or aplitic. U-Pb zircon geochronology shows that the emplacement of tonalites at 1887 ± 11 Ma was largely contemporaneous with emplacement of high-K granitic gneisses at 1877 ± 15 Ma and aplitic granites at 1857 ± 19 Ma. The data also reveal the presence of Archaean crust of 2648 ± 25 Ma in the zircon cores of some samples in the otherwise Palaeoproterozoic terrane. The tonalites are characterized by MgO contents of 1.60-4.11 wt.% at a SiO2 range of 58.1-67.9 wt.%, the Mg# of 34-55, lower Sr contents (220-462 ppm) and less fractionated REE patterns (La/YbCN = 3.55-12.9) compared to Archaean TTG (Sr > 500 ppm, La/YbCN > 20). These features, coupled with the εNd (1887 Ma) values of + 0.37 to - 0.66 as well as the associated mafic enclaves are suggestive of derivation of the tonalites by low pressure (below the garnet stability) partial melting of a mantle-derived mafic underplate that was subsequently contaminated with small amounts of pre-existing igneous crustal rocks. The evolved nature of the high-K granites (MgO = 0.20-1.30 wt.%, SiO2 = 65.5-73.9 wt.%, Mg# = 25-42, εNd = - 3.20 to - 4.75) coupled with old TDM ages which are 200-1000 Ma older than their emplacement age requires a higher degree of assimilation of older crustal material by the magma derived from partial melting of the underplated mafic crust which was subsequently followed by crystal fractionation involving plagioclase, pyroxene and amphibole. The close spatial and temporal

  17. Diques clásticos asociados a deformación transcurrente en depósitos sinorogénicos del Mioceno inferior de la Cuenca Austral Clastic dykes associated with strike-slip deformation, in synorogenic deposits from the Early Miocene of the Austral basin

    Directory of Open Access Journals (Sweden)

    M. C. GHIGLIONE

    2002-06-01

    Full Text Available RESUMEN Los diques clásticos caracterizan a los sedimentos del Mioceno inferior de la Cuenca Austral o de Magallanes, en la parte central de la Isla Grande de Tierra del Fuego, Argentina. Se analiza la orientación, espesor y espaciamiento de diques clásticos aflorantes en las localidades de Cabo San Pablo y Cabo Viamonte, sobre la costa atlántica de Tierra del Fuego. Las intrusiones laminares, en especial los diques intruidos en rocas homogéneas, se orientan perpendiculares al esfuerzo principal compresivo mínimo (sigma 3. Por lo tanto, la orientación preferencial de los diques clásticos se utilizó para calcular la disposición de sigma 3 al momento de la intrusión. Empleando la orientación calculada para sigma 3 y la alineación de las estructuras geológicas, se dedujo la distribución de los esfuerzos principales compresivos máximo e intermedio (sigma 1 y 2 respectivamente. En Cabo San Pablo el elipsoide de esfuerzos manifiesta un sistema transcurrente, con sigma 1 y 3 horizontales y sigma 2 vertical. Los diques clásticos se generaron durante la acumulación de los depósitos del Mioceno inferior. La presencia de rasgos sinorogénicos y la orientación de los diques clásticos y geometría de las estructuras que afectan a la secuencia, permiten reconocer dos pulsos tectónicos transpresivos diacrónicos que afectaron a la cuenca de antepaís Austral durante el Mioceno temprano. En conclusión, se propone sobre estas bases una evolución tectónica dominada por movimientos transcurrentes para el Mioceno inferior de la costa atlántica de la Isla Grande de Tierra del Fuego.Clastic dykes occur commonly within Early Miocene sediments of the Austral or Magallanes basin, in the central part of Tierra del Fuego, Argentina. The orientation, thickness and spacing of the clastic dykes along the Atlantic coast in the vacinity of Cabo San Pablo and Cabo Viamonte are examined. Sheet intrusions, especially dykes unaffected by previous

  18. Petrology and geochemistry of mafic magmatic rocks from the Sarve-Abad ophiolites (Kurdistan region, Iran): Evidence for interaction between MORB-type asthenosphere and OIB-type components in the southern Neo-Tethys Ocean

    Science.gov (United States)

    Saccani, Emilio; Allahyari, Khalil; Rahimzadeh, Bahman

    2014-05-01

    The Sarve-Abad (Sawlava) ophiolites crop out in the Main Zagros Thrust Zone and represent remnants of the Mesozoic southern Neo-Tethys Ocean that was located between the Arabian shield and Sanandaj-Sirjan continental block. They consist of several incomplete ophiolitic sequences including gabbroic bodies, a dyke complex, and pillow lava sequences. These rocks generally range from sub-alkaline to transitional character. Mineral chemistry and whole-rock geochemistry indicate that they have compositions akin to enriched-type mid-ocean ridge basalts (E-MORB) and plume-type MORB (P-MORB). Nonetheless, the different depletion degrees in heavy rare earth elements (HREE), which can be observed in both E-MORB like and P-MORB like rocks enable two main basic chemical types of rocks to be distinguished as Type-I and Type-II. Type-I rocks are strongly depleted in HREE (YbN 9.0). Petrogenetic modeling shows that Type-I rocks originated from 7 to 16% polybaric partial melting of a MORB-type mantle source, which was significantly enriched by plume-type components. These rocks resulted from the mixing of variable fractions of melts generated in garnet-facies and the spinel-facies mantle. In contrast, Type-II rocks originated from 5 to 8% partial melting in the spinel-facies of a MORB-type source, which was moderately enriched by plume-type components. A possible tectono-magmatic model for the generation of the southern Neo-Tethys oceanic crust implies that the continental rift and subsequent oceanic spreading were associated with uprising of MORB-type asthenospheric mantle featuring plume-type component influences decreasing from deep to shallow mantle levels. These deep plume-type components were most likely inherited from Carboniferous mantle plume activity that was associated with the opening of Paleo-Tethys in the same area.

  19. Rb-Sr isotopic composition of granites in the Western Krušné hory/Erzgebirge pluton, Central Europe: record of variations in source lithologies, mafic magma input and postmagmatic hydrothermal events

    Science.gov (United States)

    Dolejš, David; Bendl, Jiří; Štemprok, Miroslav

    2016-10-01

    The late Variscan (327-318 Ma) Western Krušné hory/Erzgebirge pluton (Czech Republic and Germany) represents a multiply emplaced intrusive sequence ranging from low-F biotite monzogranites (with rare minor bodies of gabbrodiorites and granodiorites) to high-F topaz-zinnwaldite alkali-feldspar granites. This granite suite is characterized by progressively increasing concentrations of incompatible elements (Li, Rb, F), monotonous decrease in mafic components and compatible elements (FeOtot, MgO, TiO2, CaO, Sr) with increasing silica. Consequently, this leads to extreme variations in the Rb/Sr ratios (0.52 to 59), which impose highly variable 87Rb/86Sr and 87Sr/86Sr signatures. The low-F biotite monzogranites represent isotopically heterogeneous mixture with (87Sr/86Sr)323 = 0.707-0.709 between partial melts from the Saxothuringian metasediments and mantle-derived mafic precursors. The medium-F two-mica microgranites show variable (87Sr/86Sr)323 = 0.708-0.714, indicating involvement of multiple precursors and more mature crustal protoliths. The evolved high-F topaz-zinnwaldite alkali-feldspar granites were derived from a precursor with (87Sr/86Sr)320 = 0.707-0.708 at 324-317 Ma by differentiation, which produced the extreme Rb/Sr enrichment and variations. The Li/Rb ratios remain nearly constant (~0.5), thus insensitive to the degree of geochemical differentiation. In comparison to terrestrial variations, the high Li/Rb values indicate derivation of granitic magmas from predominantly sedimentary precursors, in accord with 7Li-6Li and 143Nd-144Nd isotope composition reported previously. The Rb-Sr element variations in each granite unit are sligthly different and indicate ascent and emplacement of separate magma batches, which do not form a single liquid line of descent. We consider the enrichment of granites in incompatible elements (Li, Rb, F) and compatible depletion of ferromagnesian components, CaO and Sr as a combined effect of multiple precursors, changes in

  20. The role of magma mixing and mafic recharge in the evolution of a back-arc quaternary caldera: The case of Payún Matrú, Western Argentina

    Science.gov (United States)

    Hernando, Irene Raquel; Petrinovic, Ivan Alejandro; Llambías, Eduardo Jorge; D'Elia, Leandro; González, Pablo Diego; Aragón, Eugenio

    2016-02-01

    The Quaternary Payún Matrú volcano is a long-lived edifice that developed a summit caldera 8 km wide, with abundant pre- and post-caldera volcanic activity. It is the main volcano of the Payún Matrú Volcanic Field, which is located in the back-arc Payenia Basaltic Province, at mid-western Argentina. The composition of Payún Matrú is mainly trachytic, with lesser amounts of trachyandesitic and basaltic trachyandesitic lavas. The Payún Matrú Volcanic Field includes also the Payún Liso stratovolcano and more than 200 monogenetic basaltic cones and associated lava flows that are located east and west of the caldera. The aim of this work is to show the Payún Matrú evolution based on the mineralogical and textural characterization and to make inferences on the trigger mechanism for the explosive eruption which leads to the caldera formation. Some intermediate lavas and trachytes include phenocrysts with contrasting textures and composition, such as inverse zoning in plagioclase and clinopyroxenes, sieved plagioclases with a more calcic rim and calcic plagioclases with a more sodic rim, indicating that they could not have formed together and suggesting magma mixing processes. In addition, a few lavas show mafic enclaves or texturally different groundmasses with fluidal contacts, indicating mingling between two magmas. These lavas are found in the pre-caldera stage and the early post-caldera stage of Payún Matrú. The trachytic pyroclastic deposits related to the caldera collapse do not exhibit evidence of hybridization, although they present a minor proportion of dissolved feldspars and biotite replaced by anhydrous minerals, suggesting that a restricted zone of the chamber was reheated. This may be explained by a mafic recharge event where part of the host trachytic magma was heated, but without a complete homogenization between the host and recharging magmas. These features, in addition to the abundant basaltic volcanism east and west of the caldera, suggest

  1. The Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion, northeast of Beijing (North China): Implications for the mantle source of the giant Late Mesozoic magmatic event in the North China Craton

    Science.gov (United States)

    Liu, Ping-Ping; Zhou, Mei-Fu; Yan, Dan-Ping; Zhao, Guo-Chun; Su, Shang-Guo; Wang, Xiao-Lin

    2015-08-01

    The Early Cretaceous Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion in the Yanshan Belt northeast of Beijing is coeval with the giant Late Mesozoic igneous province in the eastern part of the North China Craton (NCC). This magmatic event was associated with lithospheric thinning and thus the igneous rocks have been used to characterize the nature of the Mesozoic mantle beneath the NCC. The Shangzhuang mafic pluton intruded a large granodioritic complex and crystallized at ~ 850-872°C at a depth of 13-14 km. It is composed, from the base upward, of troctolite, Fe-Ti oxide-bearing gabbronorite and gabbro. Rocks from this intrusion have low initial 87Sr/86Sr ratios (0.7053-0.7058), negative initial εNd values (- 9.4 to - 10.7), highly differentiated LREE and nearly flat HREE patterns indicative of an EMI-like mantle source unaffected by upper crustal contamination. The occurrence of Fe-Ti oxide ore layers, magnetite-ilmenite exsolution lamellae in hornblende and high TiO2 contents of the silicate rocks indicate that they formed from Fe- and Ti-rich ferrobasaltic magmas, which may have been generated by addition of magmas from a deeper mantle source. The presence of orthopyroxene, high-Mg ilmenite (up to 8.5 wt %), hornblende, biotite and high oxygen fugacities calculated from coexisting titanomagnetite-ilmenite pairs can be explained by derivation from an enriched EMI-type mantle modified by fluids from a subducted slab and mixed with asthenospheric or deeper-mantle materials in an extensional setting. Exposure of the complex occurred during large-scale uplift (at least 13 km) and exhumation of the Yanshan orogenic belt in the Early Cretaceous. Chemical metasomatism triggered by water and enhanced by heat from a deep magma source may have played an important role in removing the ancient cratonic root, generating partial melting of the lithospheric mantle and producing coeval magmatic activity in the Mesozoic eastern NCC.

  2. Two Cenozoic tectonic events of N-S and E-W extension in the Lhasa Terrane: Evidence from geology and geochronology

    Science.gov (United States)

    Huang, Feng; Xu, Ji-Feng; Chen, Jian-Lin; Wu, Jian-Bin; Zeng, Yun-Chuan; Xiong, Qiu-Wei; Chen, Xue-Feng; Yu, Hong-Xia

    2016-02-01

    Cenozoic active structures in the Tibetan Plateau are mainly regional N-S trending extensional faults and grabens, and E-W trending extensional tracks that are related to the transition from syn- to post-collision between India and Asia. E-W trending tracks are parallel to the direction of Neo-Tethyan oceanic convergence and consist of extensional volcanic-sedimentary basins and magmatic dykes in the southern Lhasa Terrane, Tibet. N-S trending tracks comprise faults and grabens, which are widely developed in Tibet. It remains unknown how and when the geodynamic transition from E-W to N-S trending tectonic tracks occurred. This study describes both E-W and N-S trending tectonic tracks identified at Dazi area of southern Lhasa Terrane, where E-W trending mafic dykes intruded a granitoid and late-stage N-S trending felsic dykes cut across E-W trending mafic dykes. Zircons from four granitoid samples yield consistent crystallization ages of ca. 60 Ma and positive εHf(t) values (~+ 9). An altered dioritic vein, which cuts the mafic dykes, yields an age of ca. 53 Ma. These new dating results indicate that E-W trending dykes, which formed due to regional N-S extension, were emplaced between 60 and 53 Ma. In addition, two N-S trending monzonitic porphyritic dykes, which cut the mafic dykes, yield U-Pb zircon ages of ca. 17 Ma with moderate positive εHf(t) values (+ 3 to + 9.6), as well as a NNE-SSW trending quartz monzonitic dyke, which cuts all other types of dykes, yields U-Pb ages of ca. 13 Ma. This suggests that E-W extension took place between 17 and 13 Ma. These results, in combination with existing age data for Gangdese granitoids and mafic magmatism, indicate the occurrence of two major extensional events at 60-53 Ma and 17-13 Ma. In turn, this implies that the transition from E-W to N-S trending tectonic and the onset of E-W extension occurred at ca. 17 Ma or slightly earlier. Paleocene granitoids have geochemical characteristics that are indicative of both

  3. Experience with fermentation of grass and grass silage from extensively used grassland. Feasibility study on monofermentation of grass silage from contaminated sites - biomass from grasslands of the Elbe dyke foreland; Betriebserfahrungen mit der Vergaerung von Gras und Grassilagen von extensiv genutztem Gruenland. Machbarkeitsuntersuchung zur Monovergaerung von Grassilagen schadstoffkontaminierter Standorte am Beispiel der eingesetzten Biomasse von Gruenlandflaechen aus dem Deichvorland der Elbe

    Energy Technology Data Exchange (ETDEWEB)

    Heuer, Hans-Juergen [Landwirtschaftskammer Niedersachsen, Bezirksstelle Uelzen (Germany)

    2011-07-01

    This feasibility study was concluded in 2011; monofermentation of grass silage from contaminated sites of the Elbe dyke foreland was investigated. It was found that a biogas operated in monofermentation of grass silage from extensively used grasslands is technically and economically feasible in batch operation. It was also shown that the fermentation residue can be used as agricultural fertilizer, provided that it is first turned in a compost turning unit and then worked into the soil. In view of the high pollutant concentration of the soils in the Elbe dyke foreland, the results of the project give the agricultural businesses in the Elbe valley grasslands an alternative use of the land. [German] Die Machbarkeitsuntersuchung zur Monovergaerung von Grassilagen schadstoffkontaminierter Standorte am Beispiel der eingesetzten Biomasse von Gruenlandflaechen aus dem Deichvorland der Elbe wurde Anfang Mai 2011 abgeschlossen. Im Ergebnis wurde herausgearbeitet, dass sich eine Biogaslage im Monovergaerungsverfahren mit ausschliesslich nur Grassilagen von extensiv gefuehrten Gruenlandflaechen technisch und wirtschaftlich in einer Batch-Anlage betreiben laesst. Auch wurde der Nachweis gefuehrt, dass die Biomasse aus dem Deichvorland der Elbe als Gaerrest auf das Gruenland im Deichvorland unter Beruecksichtigung von naturschutzfachlichen Vorgaben und nach den Vorgaben der guten fachlichen Praxis beim Duengen zurueckgefuehrt werden kann. Vor einer Aufbringung auf dem Gruenland sollte der feste Gaerrest jedoch mit einem Kompost-Umsetzer aufbereitet werden. Nach dem Ausstreuen auf dem Gruenland ist der Gaerrest mit einer Wiesenschleppe einzureiben. Vor dem Hintergrund der hohen Schadstoffbelastung der Boeden im Deichvorland der Elbe, tragen die im Projekt erarbeiteten Ergebnisse dazu bei, den landwirtschaftlichen Betriebsleitern in der Elbtalaue eine alternative Nutzung zur bisherigen Lebensmittelproduktion unterbreiten zu koennen.

  4. Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland – implications for crustal contamination at the Archaean/Proterozoic boundary

    Directory of Open Access Journals (Sweden)

    Hannu V. Makkonen

    2007-01-01

    Full Text Available Sm-Nd data were determined for eight mafic-ultramafic intrusions from the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland. The intrusions represent both mineralized and barren types and are located at varying distances from the Archaean/Proterozoic boundary.The samples for the 23 Sm-Nd isotope analyses were taken mostly from the ultramafic differentiates. Results show a range in initial εNd values at 1880 Ma from -2.4 to +2.0. No relationship can be found between the degree of Ni mineralization and initial εNd values, whilea correlation with the geological domain and country rocks is evident. The Majasaari and Törmälä intrusions, which have positive εNd values, were emplaced within the Svecofennian domain in proximity to 1.92 Ga tonalitic gneisses, which have previously yielded initialεNd values of ca. +3. In contrast, the Luusniemi intrusion, which has an εNd value of -2.4 is situated close to exposed Archaean crust. Excluding two analyses from the Rytky intrusion, all data from the Koirus N, Koirus S, Kotalahti, Rytky and Kylmälahti intrusions, withinerror limits, fall in the range -0.7 ± 0.3. The results support the concept of contamination by Archaean material in proximity to the currently exposed craton margin. The composition of the proposed parental magma for the intrusions is close to EMORB, with initialεNd values near +4.

  5. Syn-collisional adakitic granodiorites formed by fractional crystallization: Insights from their enclosed mafic magmatic enclaves (MMEs) in the Qumushan pluton, North Qilian Orogen at the northern margin of the Tibetan Plateau

    Science.gov (United States)

    Chen, Shuo; Niu, Yaoling; Li, Jiyong; Sun, Wenli; Zhang, Yu; Hu, Yan; Shao, Fengli

    2016-04-01

    The Qumushan (QMS) syn-collisional granodiorite, which is located in the eastern section of the North Qilian Orogen at the northern margin of the Greater Tibetan Plateau, has typical adakitic characteristics and also contains abundant mafic magmatic enclaves (MMEs). This recognition offers an unprecedented insight into the petrogenesis of both the adakitic host granodiorite and the enclosed MMEs. The MMEs and their host granodiorites share many characteristics in common, including identical crystallization age (~ 430 Ma), same mineralogy, similar mineral chemistry and whole-rock isotopic compositions, indicating their genetic link. The MMEs are most consistent with being of cumulate origin formed at earlier stages of the same magmatic system that produced the QMS adakitic granodiorite. Subsequent replenishment of adakitic magmas could have disturbed the cumulate piles as "MMEs" dispersed in the adakitic granodiorite host during emplacement. The geochemical data and petrogenetic modeling of trace elements suggest that the QMS adakitic host granodiorite is most consistent with fractional crystallization dominated by the mineral assemblage of the MMEs. The parental magma for the QMS granodiorite is best explained as resulting from partial melting of the ocean crust together with recycled terrigenous sediments during continental collision, which may have also experienced interaction with mantle peridotite during ascent.

  6. 白云鄂博碳酸岩墙碳氧同位素地球化学%Carbon and oxygen isotope geochemistry of carbonatite dykes from Bayan Obo, Nei Mongol

    Institute of Scientific and Technical Information of China (English)

    舒勇; 郑永飞; 魏春生; 周建波; 杨学明; 杨晓勇

    2001-01-01

    对内蒙古白云鄂博REE-Fe-Nb矿床周围碳酸岩墙中共存的方解石和白云石进行了C和O同位素分析。结果表明,方解石和白云石的δ13C值变化范围一致,均为-3.5‰~-7.3‰,落在正常地幔δ13C值范围(-5‰±2‰)内;而它们的δ18O值可分为两组,第Ⅰ组为9.5‰~18.0‰,第Ⅱ组为20.6‰~22.6‰,均远大于正常地幔δ18O值范围(5.7‰±1.0‰)。第Ⅰ组低δ18O值样品中共存白云石与方解石之间的C和O同位素分馏均为负值,因此处于热力学不平衡状态,指示它们自形成后受到过后期热液蚀变,与先前的岩石学观察一致。相反,第Ⅱ组高δ18O值样品中白云石与方解石之间的C和O同位素分馏均为正值,处于热力学平衡状态,指示它们自形成后未受到后期热液蚀变,因此可能沉淀于晚期低温高δ18O值流体。第Ⅰ组碳酸岩墙中白云石的C和O同位素组成不呈线性分布,指示碳酸岩浆并非由幔源碳酸盐与沉积碳酸盐混合形成。应用水-岩交换模型计算得到,第Ⅰ组碳酸岩在侵位后经历了碳酸岩浆期后热液的不均一蚀变,蚀变温度约在220~800℃之间,蚀变流体的CO2/H2O比值较小(1/500),但水/岩比值变化较大(10~400)。由于低温下方解石与热液之间的碳氧同位素交换速率大于白云石,导致这部分碳酸岩墙中共存白云石与方解石之间的C和O同位素分馏不平衡。%The carbon and oxygen isotope compositions of coexisting calcite and dolomite were measured for carbonatite dykes outside Bayan Obo REE-Fe-Nb deposit in Nei Mongol (Inner Mongolia). The results show that the δ13C values of the calcite and dolomite vary in the same range of-3.5‰ to-7.3‰, being within the normal mantle δ13C values of- 5‰±2‰; while their δ18O values can be classified into two groups, the first varies from 9.5%o to 18.0%o, and the second from 20.6‰ to 22.6‰, both being significantly

  7. Rb-Sr geochronology and geochemical characteristics of mafic dikes in the Nova Lacerda and Conquista D'Oeste region, Mato Grosso, SW Amazonian Craton; Geocronologia Rb-Sr e caracteristicas geoquimicas dos diques maficos da regiao de Nova Lacerda e Conquista D'Oeste (MT), porcao sudoeste do Craton Amazonico

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Paulo Cesar Correa da; Matos, Joao Batista de [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Recursos Minerais; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail: pccorrea@ufmt.br, e-mail: jmatos@cpd.ufmt.br; Girardi, Vicente Antonio Vitorio [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail: girardi@usp.br; Ruiz, Amarildo Salina [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Geologia Geral; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail: asruiz@rc.unesp.br

    2009-07-01

    In the Nova Lacerda and Conquista D'Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafic dikes trending NNW intrude the Nova Lacerda Granite (1462{+-}12 Ma), within the Jauru Domain, in the Rondonia-San Ignacio Province (1.55 - 1.3 Ga). The mafic swarm comprises diabases, metadiabases and amphibolites. Metadiabases originated from uralitization of diabases. These rocks have tholeiitic affinity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 {+-} 32 Ma and 1330 {+-} 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source. (author)

  8. A non-plume model for the Permian protracted (266-286 Ma) basaltic magmatism in the Beishan-Tianshan region, Xinjiang, Western China

    Science.gov (United States)

    Xue, Sheng-Chao; Li, Chusi; Qin, Ke-Zhang; Tang, Dong-Mei

    2016-07-01

    The convenient mantle plume model for the Permian protracted mafic-ultramafic intrusions and mafic dykes (266-286 Ma) in the Beishan-Tianshan region, northern Xinjiang, western China can be rejected, because their temporal-spatial distribution does not show a hotspot track predicted by such model. New zircon U-Pb ages reveal that two small mafic dyke clusters (Podong, 280.5 ± 2 Ma; Luodong, 266.2 ± 3.2 Ma) that are separated by only ~ 20 km in the Pobei area, the southernmost part of the Beishan-Tianshan region, have a large age difference of ~ 18 Ma. The older mafic dykes are characterized by nearly flat mantle-normalized rare-earth-element patterns, pronounced negative Nb-Ta anomalies and positive εNd(t) values from 5.5 to 7.5, similar to the majority of the Permian mafic-ultramafic intrusions in the region. The younger mafic dykes are characterized by significant light rare-earth-element enrichments as well as pronounced negative Nb-Ta anomalies, plus lower εNd(t) (- 1.2 to 2.6) values and higher initial 87Sr/86Sr ratios than the older mafic dykes. The observed compositional variations can be explained by source mantle heterogeneity plus different degrees of crustal contamination. Overall, the Permian mafic-ultramafic rocks in the Beishan-Tianshan region are geochemically consistent with the products of basaltic magmatism induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic zone.

  9. Sr-Nd constraints and trace-elements geochemistry of selected Paleo and Mesoproterozoic mafic dikes and related intrusions from the South American Platform: Insights into their mantle sources and geodynamic implications

    Science.gov (United States)

    Girardi, V. A. V.; Teixeira, W.; Mazzucchelli, M.; Corrêa da Costa, P. C.

    2013-01-01

    The study of selected mafic intrusions from cratonic areas of the South American Platform shows considerable differences among their mantle sources and geodynamic features, particularly regarding the dikes from the SW Amazonian and São Francisco Cratons. The tholeiites from the SW Amazonian Craton, which belong to the Serra da Providência Intrusive Suite (1.55 Ga), the Nova Lacerda swarm (1.44 Ga), the Colorado Complex (1.35 Ga), and the Nova Brasilândia Group (1.10 Ga), originated from a mantle source composed mainly of a N-MORB end-member, with a variable addition of slab fluids (up to 30%, according to the adopted model) from oceanic lithosphere due to episodic subductions during the Mesoproterozoic. Mafic intrusions from Nova Lacerda swarm and Colorado Complex are related to arc settings formed during the 1.47-1.35 Ga closure of the oceanic domain separating the Amazonian Craton and the Paraguá Terrane, whereas the tholeiites from the Serra da Providência Intrusive Suite and the Nova Brasilândia Group are considered intracratonic. The dike swarms of the São Francisco Craton are associated with intra-plate events. The inferred composition of the mantle source of the Lavras swarm (1.9 Ga) has a predominant E-MORB signature, and a modest contribution of up to 10% of an OIB component. The mantle composition underwent considerable changes during the Proterozoic, as indicated by the sources of the younger dikes, represented by the Diamantina (0.93 Ga) and the Salvador-Olivença swarms (0.92 Ga), to which considerable amount of slab derived fluids, probably from recycled crustal material, and OIB component were added. Changes in mantle composition and dikes intrusions could be related to the initial disruption of the Rodinia Supercontinent. The Florida (1.79 Ga) and Tandil (2.0 Ga) dikes are associated with extensional events of the Rio de La Plata Craton. In spite of the similarities between the tectonic framework of these swarms and that of Lavras (1.9 Ga

  10. Geochemical and isotopic studies of the Lady of the Lake Intrusion and associated tobacco root Batholith: Constraints on the genetic relation between Cretaceous mafic and silicic magmatism in Southwestern Montana

    Science.gov (United States)

    Sarkar, Arindam; Brophy, James G.; Ripley, Edward M.; Li, Chusi; Kamo, Sandra L.

    2009-12-01

    Small volumes of alkalic mafic intrusions are spatially associated with Cretaceous to Early Tertiary granodioritic to granitic intrusions in the batholithic province of southwestern Montana. The mafic rocks generally occur near the contacts of the Boulder, Pioneer, and Tobacco Root Batholiths with country rocks, but their genetic relation with the batholiths is uncertain. The Lady of the Lake Intrusion is a small layered body composed of melagabbro and gabbro that occurs along the south-central margin of the Tobacco Root Batholith near its contact with Archean country rocks. A diorite unit, spatially distinct from the granodiorite/quartz monzonite of the Batholith intrudes the gabbroic rocks of the Lady of the Lake Intrusion. Zircon crystals from the melagabbro and diorite units give U-Pb ages that are very similar to that of the Tobacco Root Batholith at 74.88 ± 0.17 Ma and 76.24 ± 0.08 Ma, respectively. Mineral chemistry, whole rock major and trace element compositions, and oxygen and sulfur isotope ratios have been utilized to evaluate the genetic relation between the Lady of the Lake Intrusion, the diorite, and the Tobacco Root Batholith. No significant variation in the composition of clinopyroxene is observed in different rock units of the Lady of the Lake Intrusion. Minor olivine with Fo 64 in the melagabbro unit is interpreted to represent early crystallization in the base of the intrusion. Whole rock major and trace element compositions, as well as results from modeling using the MELTS program, are consistent with the premise that the diorite was produced by fractional crystallization of the same magma that was parental to the gabbros of the Lady of the Lake Intrusion. Both whole rock chemistry and oxygen isotopes support the interpretation that the parental magma was an uncontaminated mantle-derived basaltic magma. In contrast, trace element and oxygen isotopes indicate that the quartz monzonitic and granodioritic rocks of the Tobacco Root Batholith and

  11. Implications for Early Proterozoic tectonics and the origin of continental flood basalts, based on combined trace element and neodymium/strontium isotopic studies of mafic igneous rocks of the Penokean Lake Superior Belt, Minnesota, Wisconsin and Michigan

    Energy Technology Data Exchange (ETDEWEB)

    Beck, J.W.

    1988-01-01

    Two major suits of mafic volcanics and intrusive rocks are juxtaposed across the Florence-Niagara Shear Zone within the central portion of the early Proterozoic Lake Superior Belt. To the north of this shear zone, the volcanics were erupted onto previously existing Archean crust during the rifting stages of a major Early Proterozoic rifting event circa 2.0 Ga ago. The volcanics and intrusives found just to the south of the shear zone however, are substantially different in character, and are part of a large magmatic terrane which resembles a modern volcanic arc. Neodymium isotopic systematics from tholeiites of the southern terrane yield an isochron age of 1.87 {plus minus} 0.05 Ga, and an {epsilon}{sub Nd} = +4.2. Such a large positive {epsilon}{sub Nd} is indicative of derivation from a mantle very depleted in light rare earth elements (LREE), and is similar to values predicted by some models for the source regions for mid-ocean ridge basalts (MORB) at 1.9 Ga. This characteristic, combined with the general geochemical characteristics and tectonic setting of these basalts, suggest that they may well have been erupted onto oceanic crust, and derived from an early Proterozoic depleted mantle type reservoir. The overall tectonic affinity of this southern terrane however, appears related to island arcs. In contrast, the Nd isotopic systematics of continental tholeiites from the northern terrane do not form an isochron, but rather indicate mixing with a continental crustal LREE enriched reservoir. Two component mixing models utilizing Nd isotopes, along with major and trace elements have been developed for the basalts of this northern terrane, and suggest that the source of the basaltic end-member of this mixing suite was the same as that which generated the LREE depleted basalts of the southern magmatic belt.

  12. Petrochemical composition characteristics of mafic microgranular enclaves in granites in SE China and their significance.%华南花岗岩暗色微粒包体的岩石化学组成特征及其意义

    Institute of Scientific and Technical Information of China (English)

    彭卓伦; Rodney Grapes; 庄文明; 张献河

    2011-01-01

    Inhomogeneous enclave is the most popular type in the marie microgranular enclave (MME) of gran ites in SE China, which is generally with a dark or more mafic tim. The lithologic units in the rim of MME range from monzonite to quartz monzonite and to monzodiorite, while those in the core from quartz monzodior ite to tonalite. A MME generally has decreasing Si and Ca contents and Na/K ratios, and increasing K, Al,Ti, P and Fe+Mg contents from its core to rim, indicating that the MMEs should have been mainly derived from restites of the partial melting rock. Further research revealed that the composition of restite in granites varies in the direction of increasing biotite as the melting degree of the rock increases and the biotite-rich en claves should be the final product of rock melting process.%对华南诸多花岗岩体暗色微粒包体的野外调查表明, 非均一包体是包体中最普遍的类型,常具有暗色基性边.岩石化学分析结果表明,包体边缘的岩性为二长岩-石英二长岩-二长闪长岩,中心则为石英二长闪长岩-英云闪长岩.从包体中心到边缘,具有Si、Ca含量和Na/K比值降低,K、Al、Ti、P和Fe+Mg含量升高的变化趋势,揭示包体应来自岩石部分熔融的残余熔渣.进一步研究还表明,花岗岩中残余熔渣(暗色包体)的组分随着岩石熔融程度升高而向黑云母增多的方向演化,暗示富云包体应是岩石熔融演化至末阶段的产物.

  13. Design and construction of a rockfill spur dyke on the Rupert River (PK 85) under the Eastmain1-A/LaSarcelle/Rupert diversion project; Conception et construction d'un epi en enrochement sur la riviere Rupert (PK 85) dans le cadre du projet Eastmain-1-A/LaSarcell/derivation Rupert

    Energy Technology Data Exchange (ETDEWEB)

    Pelletier, Pierre; Fecteau Sebastien, Thibodeau; Patrick [GENIVAR, Quebec, (Canada); Cote, Pierre; Grenon, Alain [Societe d' Energie de la Baie James, Montreal, (Canada)

    2010-07-01

    The Eastmain-1-A/Sarcelle plants and Rupert diversion project involved the partial diversion of the Rupert River in the direction of the La Grande complex. This diversion point on the Rupert River is located at the 314th kilometre, where a dam with a regulation works was constructed. A network of nine hydraulic works was designed and constructed to maintain the water levels in the slow flow section of the river to limit the environmental impact. A rockfill spur dyke was constructed at the 85th kilometre of the Rupert River, for control of the water levels over a distance of 10.8 kilometres. This paper presented the challenges facing the construction operation of this hydraulic work on the Rupert River. The design of this structure was first simulated by 2-D hydrodynamic models. A scale model built at the 1:40 scale was used to assess the stability of the temporary piers created for shelter during the construction process.

  14. 基于MlKE11水动力模型的大洋河丹东有堤段行洪能力分析%Analysis on Flood Discharge Capacity of Dayang River Dandong Section with Dyke Based on MIKE11 Hydrodynamic Model

    Institute of Scientific and Technical Information of China (English)

    冯金鹏

    2016-01-01

    河道现状行洪能力是河道所在地区防洪安全的核心,也是防汛主管管部门汛期指导防汛的重要依据。为分析大洋河丹东有堤段的行洪能力,采用水动力模型MIKE11计算、模拟河道及河网的一维洪水演进过程,准确判断其行洪能力,为保护沿岸居民防洪安全提供理论基础。%Flood discharge capacity of watercourse status is the core of flood control safety in the watercourse area, and is also as an important basis for flood prevention authorities directing the work of flood prevention during flood season. In order to analyze the flood discharge capacity of Dayang River Dandong section with dyke, we used hydrodynamic model MIKE11 to calculate and imitate one-di-mensional flood routing process of watercourse and river network, and estimated the flood discharge capacity correctly, providing the theoretical basis for preventing coastwise residents flood control safety.

  15. 安徽铜陵地区幔源镁铁质团块研究及其地质意义%Mantle Mafic Clots in Tongling Area, Anhui Province, and Their Geological Significance

    Institute of Scientific and Technical Information of China (English)

    李大鹏; 杜杨松; 于学峰; 秦新龙; Steve SCOTT; 王树星; Filipa MARQUES

    2014-01-01

    It is generally accepted that mantle input under crust-mantle interaction plays an important role in sustainable magma fractionation and eventually leads to release of magmatic fluids and formation of world class W, Sn and other types of ore deposits. Many models dealing with the evolution of mantle-derived magmas are derived from numerical simulations based on isotopic geochemistry, temperature and pressure or physical geography data. Few models use detailed chemical analysis of mantle-derived rock enclaves. The authors found direct evidence for crust-mantle interaction in Tongling area, East China, in the form of mafic clots (MFC), which are interpreted to represent fragments of altered alkaline basaltic magma in magma chambers at the base of the continental crust (BCC). These MFC are unevenly distributed within the microgranular dioritic enclaves (MME) which, in turn, are included in the host quartz monzodiorite. The authors have combined all available data with new element distribution maps of the MFC in order to present a general framework model for the evolution of mafic to siliceous magmas. Observations and researches indicate that the MFC were formed from the fractional crystallization and evolution alkaline basaltic magma in magma chambers at the BCC. The basaltic magma resulting from previous partial melting of the upper mantle was eventually brought to the magma chambers at the BCC by magmatic underplating and crust-mantle interaction at 140 Ma. And the MME were formed from the fractional crystallization and evolution dioritic magma by the assimilation of the derived magma from the base of the continental crust with the metamorphic rocks in a crust magma chamber at the depth of 12~16 km. The discovery of the MFC and MME effectively prove that the dioritic magma in the middle crust originated from the mixing basaltic magma of mantle-crust at the BCC.%幔源岩石包体研究,是认识上地幔岩石圈物质组成、幔源岩浆演化及壳幔动力学

  16. 新疆北山地区罗东镁铁质-超镁铁质层状岩体岩石成因%Petrogenesis of Luodong mafic-ultramafic layered intrusion, Beishan region, Xinjiang

    Institute of Scientific and Technical Information of China (English)

    凌锦兰; 夏明哲; 郭娜欣; 汪帮耀; 夏昭德; 姜常义

    2011-01-01

    罗东镁铁质-超镁铁质岩体位于塔里木板块东北部的新疆北山地区,岩体平面形态为眼球状,出露面积约2.1 km2.由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶韵律发育,属于层状岩体.岩浆演化过程中主要分离结晶/堆晶相是橄榄石和单斜辉石,此外还有斜长石、铬尖晶石和斜方辉石.岩石地球化学特征表明岩体与围岩之间的同化混染较弱.原生岩浆属于苦橄质岩浆(MgO=14.7%),并且具有高的岩浆结晶温度(1412℃).OIB型Nd、Sr同位素组成和高温苦橄质原生岩浆暗示,罗东岩体的形成可能与地幔柱活动有关,是地幔柱轴部部分熔融的产物.由此表明,塔里木板块东北部早二叠世幔源岩浆岩也应该隶属于塔里木大火成岩省.%Lens shaped Luodong mafic-ultramafic intrusion lies in Beishan region of Xinjiang in Northeastern Tarim Plate and covers an area of 2.1 km2. It consists of dunite, wehrlite, plagio-lherzolite, olivine websterite, peridotite pyroxenite, troctolite, olivine gabbro, gabbro, noritegabbro and leucogabbro. The Luodong intrusion is a layered intrusion with obvious cumulus textures and rhythmics. The mainly fractional crystallized or cumulated phases are olivine and clinopyroxene, together with minor plagioclase, orthopyroxene and Cr-spinel during magma evolution. The geochemical feature indicates weak crustal contamination. The primary magma is picritic with MgO contents up to 14.7% and high crystallization temperature of 1412 ℃. OIB-like Nd, Sr isotopic compositions and high temperature picritic primary magma indicate that Luodong intrusion may have an affinity with mantle plume and be formed by partial melting of axis plume. The Early Permain mantle-derived magmatic rocks in Northeastern Tarim Plate are thus a part of Tarim Large Igneous Province.

  17. Multi-element variations in olivine as geochemical signatures of Ni-Cu sulfide mineralization in mafic magma systems—examples from Voisey's Bay and Pants Lake intrusions, Labrador, Canada

    Science.gov (United States)

    Bulle, Florian; Layne, Graham D.

    2016-01-01

    gabbro (BG) and upper gabbro (UG) of the Pants Lake intrusion is fairly homogeneous (˜Fo60, ˜4300 ppm Mn, ˜460 ppm Zn, ˜340 ppm Ni, ˜50 ppm Cr), with a more evolved composition (˜2100 ppm Ca, ˜20 ppm Sc, ˜300 ppm Ti, ˜4 ppm Y) than the average olivine of the Voisey's Bay intrusion (˜570 ppm Ca, ˜6 ppm Sc, ˜65 ppm Ti, ˜0.3 ppm Y). Pants Lake olivine also commonly lacks the mutually Mn-Zn-rich signature of olivine from the basal breccia at Voisey's Bay that is characteristic of contamination of the parent magma by country rock gneiss, and there reflects a close proximity to massive sulfides. In conjunction with petrographic observation and the stratigraphic context, a multiple-element (V-Cr-Mn-Fe-Co-Ni-Zn) regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the Eastern Deeps part of the Voisey's Bay intrusion, over a distance exceeding 150 m. The compositional variations in olivine from the economic Voisey's Bay intrusion (bimodal and primitive) and the mainly barren Pants Lake intrusion (homogeneous and evolved) provide potential as a regional-scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization.

  18. 黄陵野马洞基性岩脉中锆石的U-Pb年龄和Hf同位素组成%Zircon U-Pb Age and Hf Isotope Composition from Yemadong Mafic Dikes in the Huangling Area

    Institute of Scientific and Technical Information of China (English)

    赵敏; 魏君奇; 王建雄

    2012-01-01

    By LA-ICP-MS methods,the U-Pb dating and Lu-Hf isotopic analysis were carried out for zircons from Yemadong mafic dikes in Huangling area,we can ascertain the forming and metamorphic age of TTG granites,and discuss whether there were some crustal remnants older than Kongling Group in the Huangling area.The Yemadong doleritic dikes intruded in the TTG gneisses,and captured many xenocrystic zircons from the country rocks.The xenocrystic zircons show the core-rim structure,the cores have magmatic oscillatory zoning,and the rims are not zoning,The thirty individual U-Pb spot analyses were done on magmatic cores of 30 xenocrystic zircon grains,and yielded three ages of 2949 Ma,2900 Ma and 2842 Ma,these indicate that the TTG granites is a complex intrusive which experiencing at least three stages of magmatism including 2949 Ma,2900 Ma and 2842 Ma.One U-Pb spot analysis was done on metamorphic rim of zircon grain,and yielded a concordant age of 2557 Ma,which is responsible for the timing of metamorphism.This provides the first demonstration for the occurrence of tectono-thermal event at about 2557 Ma,which has been connected to the Shuiyuesi movement.In the same time,the TTG granite has been metamorphism into the TTG gneisses during the tectono-thermal event resulted from the Shuiyuesi movement in the Huangling area.The xenocrystic zircons have the negative εHf(t) values of-9.85~0.89 with the average values of-4.07,and the Hf model age of 3.6~3.2 Ga,these reveals the existence of old crustal relicts with the age of 3.6~3.2 Ga rocks,which is older than the Kongling Group(3.2 Ga) in Huangling area.%采用激光剥蚀-等离子质谱(LA-ICP-MS)分析技术测定野马洞基性岩脉中锆石的U-Pb年龄和Hf同位素组成,以探讨黄陵地区TTG片麻岩原岩的形成及变质时间、是否存在比崆岭群更古老的地壳等问题。野马洞辉绿岩脉(1850 Ma)侵入TTG片麻岩,并从TTG片麻岩中捕获了大量捕掳晶锆石。捕掳

  19. 赣抚大堤防洪保护区洪水风险图编制洪水分析方案设置研究%Study on setting flood analysis scheme for flood risk mapping of flood protection area of Ganfu Grand Dyke

    Institute of Scientific and Technical Information of China (English)

    张秀平; 丁志雄

    2015-01-01

    编制洪水风险图是落实防汛工作从"控制洪水"向"洪水管理"转变和开展洪水风险管理的重要基础支撑,也是国内防洪减灾工作中重要的非工程类措施之一.洪水风险图编制是一个复杂的过程,涉及的基础资料较多,所需考虑的要素复杂,而洪水分析方案的设置是洪水风险图编制中至关重要的部分,关系到洪水风险图编制结果的实用性.本文以赣抚大堤防洪保护区为例,从洪水来源、洪水分析频率、洪水组合方式、可能溃口位置、溃口宽度、溃决时机等方面,并权衡实用性和易用性对设计方案优化组合,简述赣抚大堤洪水风险图编制过程中洪水分析方案的设置规则,为江西省及其他地区全面开展洪水风险图编制提供参考.%Flood risk mapping is an important foundation for the implementation of flood control work from flood control to flood management and provides an important foundation support for flood risk management.It is one of the improtant non-engineering measures for flood control and disaster relief in China.Flood risk mapping is a complicated process ,involving much basic informa-tion and the complex factors need to be considered.Flood analysis schemes are one of a vital part of the preparation of flood risk mapping,which is related to the practicality of flood risk mapping results.In this paper,we took flood protectition area of Ganfu Grand Dyke as an example,setting the rules for flood analysis schemes in the process of flood risk mapping of Ganfu Grand Dyke from these aspects ssuch as flood sources,flood analysis frequency,flood combinations,may breach position,breach wideth and out-burst opportunity and weighing the practicality and usability in order to optimize the analysis scheme are stated.It provides a refer-ence for this province and other areas to carry out a comprehensive flood risk mapping.

  20. Metasomatismo en ortoanfibolitas de la Faja máfica-ultramáfica del río de las tunas, Mendoza Metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt, Mendoza

    Directory of Open Access Journals (Sweden)

    M. Florencia Gargiulo

    2012-06-01

    áticos y la secuencia de reemplazo observada en ellos, sugieren que tales asociaciones se generaron a causa de un proceso metasomático, acontecido en condiciones de bajo grado a una presión menor a 4 kbar, durante los estadios finales del ciclo de metamorfismo regional evidenciado en el área.In this contribution, petro-mineralogical and chemical evidences of metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt in Frontal Cordillera of Mendoza province are provided. These orthoamphibolites integrate the metamorphic basement of the Frontal Cordillera and they belong to the Guarguaráz Metamorphic Complex. These rocks show mineral associations and textural relationships indicating disequilibrium conditions between some of the mineral phases. Hornblendic amphibole crystals show a reaction border with development of clinopyroxene (ferroan dioside; meanwhile the calcicplagioclase is mostly replaced by a fine-grained matrix integrated by the mineral association of garnet-epidotes.l -prehnite-pumpellyite- albite. The amphibole and clinopyroxene crystals are also partially replaced by pumpellyite and/or chlorite, meanwhile the matrix is slightly replaced by muscovite and calcite. Garnet compositions belong to the grossular-andradite series and their average composition is: Alm05Adr53Prp01Sps04Grs36Uv01. Some crystals with Cr2O3 content between 11.69-13.17 wt.% and with a subtle chemical zonation (uvarovitic core: Alm03Adr13Prp00Sps02Grs35Uv47 with more grossularic border: Alm03Adr12 Prp00Sps01Grs44Uv40 occur in relationship with magnetite crystals with up to 20% of the chromite component. Pressure estimations based on the compositional zoning of amphibole crystals gave values between 2.5-4.5 kbar. The observed mineral associations together with the textural and chemical characteristics of these rocks show that this kind of orthoamphibolites is completely different from the classical amphibolites of igneous protoliths outcropping in the study area

  1. Supra-subduction zone tectonic setting of the Muslim Bagh Ophiolite, northwestern Pakistan: Insights from geochemistry and petrology

    Science.gov (United States)

    Kakar, Mohammad Ishaq; Kerr, Andrew C.; Mahmood, Khalid; Collins, Alan S.; Khan, Mehrab; McDonald, Iain

    2014-08-01

    The geology of the Muslim Bagh area comprises the Indian passive continental margin and suture zone, which is overlain by the Muslim Bagh Ophiolite, Bagh Complex and a Flysch Zone of marine-fluvial successions. The Muslim Bagh Ophiolite has a nearly-complete ophiolite stratigraphy. The mantle sequence of foliated peridotite is mainly harzburgite with minor dunite and contains podiform chromite deposits that grade upwards into transition zone dunite. The mantle rocks (harzburgite/dunite) resulted from large degrees of partial melting of lherzolite and have also been affected by melt-peridotite reaction. The Muslim Bagh crustal section has a cyclic succession of ultramafic-mafic cumulate with dunite at the base, that grades into wehrlite/pyroxenite with gabbros (olivine gabbro, norite and hornblende gabbro) at the top. The sheeted dykes are immature in nature and are rooted in crustal gabbros. The dykes are mainly metamorphosed dolerites, with minor intrusions of plagiogranites. The configuration of the crustal section indicates that the crustal rocks were formed over variable time periods, in pulses, by a low magma supply rate. The whole rock geochemistry of the gabbros, sheeted dykes and the mafic dyke swarm suggests that they formed in a supra-subduction zone tectonic setting in Neo-Tethys during the Late Cretaceous. The dykes of the mafic swarm crosscut both the ophiolite and the metamorphic sole rocks and have a less-marked subduction signature than the other mafic rocks. These dykes were possibly emplaced off-axis and can be interpreted to have been generated in the spinel peridotite stability zone i.e., Muslim Bagh Ophiolite in the final stage of tectonic emplacement.

  2. Evolución metamórfica de granulitas piroxénicas asociadas a los complejos máficos Sol de Mayo y Suya Taco, norte de la Sierra de Comechingones, Córdoba Metamorphic evolution of the pyroxene granulites associated with the Sol De Mayo and Suya Taco mafic complexes, north of Sierra de Comechingones, Córdoba

    Directory of Open Access Journals (Sweden)

    A.M. Tibaldi

    2007-06-01

    sierra de Comechingones.This study reports the field relationships, petrology, mineral chemistry, and reaction history of garnet + orthopyroxene + cordierite- bearing granulites that occur as small lenses inside mafic igneous rocks. These high-temperature granulites were found in the Sol de Mayo and Suya Taco mafic complexes from the northern sierra de Comechingones. The most notable difference among the granulites of the two mafic complexes is one of the retrieved peak P-T conditions that are higher in Sol de Mayo (P ~ 8 kbar and T ~ 930 ºC area than in Suya Taco complex (P ~ 6 and T ~ 780 ºC. However, reaction textures document a prograde-retrograde path that is roughly similar for all the studied granulites. Garnet and orthopyroxene formed to a large extent as peritectic products of partial melting, and melt segregation led to a semipelitic granulite residue containing garnet and orthopyroxene. The retrograde evolution is recorded by coronas of orthopyroxene around garnet, being garnet and orthopyroxene separated by plagioclase + quartz. Continued decompression is evident from subsequently formed symplectites of cordierite + sillimanite and cordierite + spinel, both replacing garnet. This succession of reactions attests to a change from quasi-isobaric heating to decompression followed by final cooling. The deduced clockwise P-T history generally reflects rapid heating during entrapment of the granulite precursor by the mafic magmas, and subsequent decompression driven by either ascent of magmas carrying granulitic xenoliths or uplift of the mafic complexes as a whole lithologic package, or a combination of both processes. In any event, these granulites provide reliable evidence for assessing the level of emplacement of the mafic complexes within the supracrustal sequence of sierra de Comechingones.

  3. Is the Proterozoic Ladoga Rift (SE Baltic Shield) a rift?

    DEFF Research Database (Denmark)

    Artemieva, Irina; Shulgin, Alexey

    2015-01-01

    The southern part of the Baltic Shield hosts a series of mafic dykes and sills of Mesoproterozoic ages, including a ca. 1.53-1.46 Ga sheet-like gabbro-dolerite sills and the Salmi plateau-basalts from the Lake Ladoga region. Based on chiefly geochemical data, the region is conventionally interpre......The southern part of the Baltic Shield hosts a series of mafic dykes and sills of Mesoproterozoic ages, including a ca. 1.53-1.46 Ga sheet-like gabbro-dolerite sills and the Salmi plateau-basalts from the Lake Ladoga region. Based on chiefly geochemical data, the region is conventionally...... rifts, and provide alternative explanations for Mesoproterozoic geodynamic evolution of the southern Baltic Shield. We propose that Mesoproterozoic mafic intrusions in southern Fennoscandia may be associated with a complex deformation pattern during reconfiguration of (a part of) Nuna (Columbia...

  4. Screening the dykes of Oz: lesbian representation on Australian television.

    Science.gov (United States)

    Beirne, Rebecca

    2009-01-01

    This article provides a survey of lesbian representation in Australian-made television programming. Beginning with the 1970s, when Australia led the Anglophone world in terms of queer representation on television, the article discusses major instances of queer women appearing on Australian television including in such shows as Prisoner, Home & Away, Neighbours, All Saints, The Secret Life of Us, Last Man Standing, and Kick. PMID:19197661

  5. Caracterización de rocas ultramáficas, máficas y metasedimentarias del cordón del Peñasco, Precordillera Occidental, Mendoza Characterization of ultramafic, mafic and metasedimentary rocks of the Cordón del Peñasco, western Precordillera, Mendoza

    Directory of Open Access Journals (Sweden)

    Florencia L Boedo

    2012-06-01

    Full Text Available En el cordón del Peñasco, ubicado en el sector norte de la provincia de Mendoza, dentro del ámbito de la Precordillera Occidental, aforan metasedimentitas en contacto tectónico con una asociación máfica-ultramáfica. Dentro de las metasedimentitas en facies esquistos verdes se han reconocido dos asociaciones: metalimolitas carbonáticas y metaareniscas y metapelitas. Las rocas máficas-ultramáficas están representadas por serpentinitas derivadas de harzburgitas y dunitas, gabros bandeados metamorfizados en facies granulita; diabasas constituyendo diques o filones capa, metabasaltos amigdaloides y metahialoclastitas con bajo grado de metamorfismo. Se realizaron estimaciones termométricas en una granulita máfica (gabro bandeado utilizando el par granate-clinopiroxeno, obteniéndose temperaturas de 884°C. Las mismas permiten estimar que estos cuerpos experimentaron metamorfismo de alta temperatura, para posteriormente retrogradar a facies esquistos verdes, sobre la base de aspectos mineralógicos y texturales. Con respecto a las unidades metasedimentarias, el paleoambiente inferido para la unidad de metaareniscas y metapelitas corresponde a pie de talud continental con predominio de sedimentación gravitacional sobre la base de estructuras sedimentarias reconocidas. Mientras que la unidad de metalimolitas carbonáticas pertenecerían a un ambiente marino profundo. Estas unidades han sido asignadas al Eopaleozoico a partir de criterios estratigráficos y deformadas y metamorfizadas hacia fines del Devónico como consecuencia de la orogenia Chánica.In Cordón del Peñasco area, located in northern Mendoza province, western Precordillera, metasedimentites are in tectonic contact with a mafic-ultramafic association. The former have been under greenschist facies metamorphism and two associations have been recognized: carbonate metasiltstones and metasandstones and metapelites. The mafic-ultramafic association is represented by serpentinized

  6. Petrología y geoquímica de las rocas máficas-ultramáficas del área río Las Águilas - arroyo de Los Manantiales, Provincia de San Luis Petrology and geochemistry of mafic-ultramafic rocks in the Las Águilas River-of the Manantiales stream area, San Luis

    Directory of Open Access Journals (Sweden)

    G. Ferracutti

    2007-09-01

    Full Text Available Dada la carencia de información de campo detallada, se efectuó el mapeo y muestreo de los cuerpos máficos-ultramáficos aflorantes entre el río de Las Águilas y el arroyo de Los Manantiales en la provincia de San Luis. La escasa información de campo, petrográfica y geoquímica de las unidades de éste área dificultaba la vinculación entre las rocas aflorantes y aquellas reconocidas en los testigos de perforación. Los cuerpos ígneos de interés se hallan en contacto con el basamento metamórfico a través de fallas de alto ángulo de buzamiento y/o contactos intrusivos. En Las Higueras y Virorco, se identificaron afloramientos de rocas máficas-ultramáficas con textura magmática primaria de tipo estratificada no-uniforme de regularidad intermitente. El estudio de estos cuerpos generó un desafío particular debido a los procesos deformación, metamorfismo y alteración que los han afectado. Estos factores no solo modificaron la mineralogía de las rocas sino que ademas generaron bloques basculados reconocidos por la presencia de texturas de estratificación magmaticas cuya posición espacial no se corresponde con la magmática originaria. Los patrones de los elementos de tierras raras normalizados a condrita permiten identificar un proceso de diferenciación, con mayor enriquecimiento en los contenidos de tierras raras en las rocas más evolucionadas. En base a los contenidos de tierras raras de las rocas ultramáficas, se infiere que la cristalización magmática estuvo controlada por la presencia de olivino y ortopiroxeno.Geological mapping was completed in the area between Las Águilas River and the Manantiales stream in San Luis province due to the absence of a detailed geologic map of the mafic-ultramafic bodies which occur in this region. Also the lack of petrographic and geochemical information constituted a draw back when attempting to relate surface and subsurface rocks. In this contribution a geological map of the area and

  7. Constraints on the formation of geochemically variable plagiogranite intrusions in the Troodos Ophiolite, Cyprus

    Science.gov (United States)

    Freund, Sarah; Haase, Karsten M.; Keith, Manuel; Beier, Christoph; Garbe-Schönberg, Dieter

    2014-02-01

    The geochemistry and petrology of tonalitic to trondhjemitic samples ( n = 85) from eight different plagiogranite intrusions at the gabbro/sheeted dyke transition of the Troodos Ophiolite were studied in order to determine their petrogenetic relationship to the mafic plutonic section and the lava pile. The plagiogranitic rocks have higher SiO2 contents than the majority of the glasses of the Troodos lava pile, but lie on a continuation of the chemical trends defined by the extrusive rocks, indicating that the shallow intrusions generally represent crystallised magmas. We define three different groups of plagiogranites in the Troodos Ophiolite based on different incompatible element contents and ratios. The first and most common plagiogranite group has geochemical similarities to the tholeiitic lavas forming the lavas and sheeted dyke complex in the Troodos crust, implying that these magmas formed at a spreading axis. The second plagiogranite group occurs in one intrusion that is chemically related to late-stage and off-axis boninitic lavas and dykes. One intrusion next to the Arakapas fault zone consists of incompatible element-enriched plagiogranites which are unrelated to any known mafic crustal rocks. The similarities of incompatible element ratios between plagiogranites, lavas and mafic plutonic rocks, the continuous chemical trends defined by plagiogranites and mafic rocks, as well as incompatible element modelling results, all suggest that shallow fractional crystallisation is the dominant process responsible for formation of the felsic magmas.

  8. Geología y petrología del cuerpo Máfico-Ultramáfico Las Juntas, Sierra de Valle Fértil, Provincia de San Juan Geology and petrology of mafic-ultramafic body from Las Juntas, Valle Fértil, San Juan

    Directory of Open Access Journals (Sweden)

    Baliani Ignacio

    2012-03-01

    Full Text Available En el centro de la sierra de Valle Fértil aflora un cuerpo lenticular orientado en forma aproximada N-S que se encuentra encajado en un basamento ígneo de naturaleza máfica-ultramáfica. La morfología y posición actual de dicho cuerpo se debe a su emplazamiento tectónico, y la fábrica magmàtica interna presenta rumbo similar al del cuerpo y buzante al este. Las rocas que conforman el cuerpo de Las Juntas exponen una variedad litológica con las siguientes composiciones: norita olivínica, gabro anfibólico, dunita, gabronorita anfibólica y peridotita anfibólica piroxénica. Se caracterizan por presentar un encapado ígneo a escala de afloramiento y textura cumular a escala de muestra de mano, mientras que la microtextura predominante en estas rocas es de tipo coronítica. La relación cogenética entre las rocas máficas y ultramáficas de Las Juntas es determinada por la composición de silicatos de Mg y Fe presentes en ellas. El coeficiente de intercambio Fe-Mg entre olivino y clinopiroxeno con el líquido muestra un magma con una relación de #Mg (Mg/Mg + Fe-2 alrededor de 0,6; siendo inferior a la esperada para magmas generados en el manto peridotítico. Esto demuestra que el magma formador de estas rocas se habría originado en el manto litosférico, posteriormente ascendido y emplazado en niveles inferiores de la corteza (20 - 25 km. Este proceso petrológico es característico de magmatismo asociado a subducción, y relacionado al arco magmático Famatiniano.An elongate body of mafic and ultramafic plutonic rock crops out in central Sierra de Valle Fértil. The igneous body was tectonically emplaced and its internal magmatic fabrics strike roughly north-south and dip to the east. Rocks in the body are different from their hosting plutonic rocks in showing a layered igneous structure associated with pristine cumulate textural features at all observational scales. The layered body is composed of gabbronorite cumulates, ultramafic

  9. Vesta Evolution from Surface Mineralogy: Mafic and Ultramafic Mineral Distribution

    Science.gov (United States)

    DeSanctis, M. C.; Ammannito, E.; Palomba, E.; Longobardo, A.; Mittlefehldt, D. W.; McSween, H. Y; Marchi, S.; Capria, M. T.; Capaccioni, F.; Frigeri, A.; Pieters, C. M.; Ruesch, O.; Tosi, F.; Zambon, F.; Hiesinger, H.; Magni, G.; McFadden, L. A.; Raymond, C. A.; Russell, C. T.; Sunshine, J. M.

    2014-01-01

    Vesta is the only intact, differentiated, rocky protoplanet and it is the parent body of HED meterorites. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, a mineral that is a major component of the mantles of differentiated bodies, including Vesta. The HED parent body experienced complex igneous processes that are not yet fully understood and olivine and diogenite distribution is a key measurement to understand Vesta evolution. Here we report on the distribution of olivine and its constraints on vestan evolution models.

  10. Eruptive history of Mammoth Mountain and its mafic periphery, California

    Science.gov (United States)

    Hildreth, Wes; Fierstein, Judy

    2016-07-13

    This report and accompanying geologic map portray the eruptive history of Mammoth Mountain and a surrounding array of contemporaneous volcanic units that erupted in its near periphery. The moderately alkaline Mammoth eruptive suite, basaltic to rhyodacitic, represents a discrete new magmatic system, less than 250,000 years old, that followed decline of the subalkaline rhyolitic system active beneath adjacent Long Valley Caldera since 2.2 Ma (Hildreth, 2004). The scattered vent array of the Mammoth system, 10 by 20 km wide, is unrelated to the rangefront fault zone, and its broad nonlinear footprint ignores both Long Valley Caldera and the younger Mono-Inyo rangefront vent alignment.

  11. Significado de fábricas magnéticas en rocas volcánicas cuaternarias de la Isla Decepción (Shetland del Sur, Antártida)

    OpenAIRE

    Gil Imaz, Andrés; Gil Peña, Inmaculada; Galindo Zaldívar, Jesús; Rey Salgado, Jorge; Maestro González, Adolfo; Pueyo Anchuela, Óscar; Soto Marín, Ruth; Oliva Urcia, Belén; López Martínez, Jerónimo

    2010-01-01

    This work deals with the magnetic fabric (AMS technique) of different lithotypes related to quaternary volcanism of Deception Island (South Shetland Islands). The studied rocks include lava flows from basaltic to basaltic-andesitic composition, mafic dykes and several types of pyroclastic deposits. By combining the analysis of parametric aspects of the magnetic ellipsoids and their directional pattern, four types of magnetic fabrics have been recognized. Type I fabrics are related...

  12. Mantle influence on the character of I-type granitoids of the New England batholith: evidence from Sr and Nd isotopes

    International Nuclear Information System (INIS)

    Granitoid samples, together with an array of mafic to felsic dyke rocks, were collected from both the southern members of the high-K Moonbi Suite (Moonbi district) and the southern members of the low-K Clarence River Suite (Barrington Tops Granodiorite). These constitute the two most divergent compositions in the spectrum of I-type granitoids in the New England Batholith. Mafic plutonic rocks (quartz diorites) also coexist with granitoids at Barrington Tops (Eggins and Hensen 1987), and mafic dykes (high-K lamprophyres) have been observed in association with Moonbi Suite granitoids in the Hillgrove area (Kent 1994). Kent (1994) noted that lamprophyres in the Rockvale area extend the linear trends of the Moonbi granitoids on Harker plots, and the petrographic and chemical similarities between mafic and felsic intrusives at Barrington Tops have been described by Eggins and Hensen (1987). Shaw et al. (1992) also noted that lamprophyre dykes at Tulcumba Ridge (to the west of Tamworth) have similar ages and initial Sr isotopic compositions to Moonbi Suite granitoids (87Sr/86Sri 0.7042-0.7048). Lamprophyre dykes and felsic dykes of dacitic composition within the Moonbi Adamellite and the surrounding area were analysed for their Sr and Nd isotopic compositions, in an attempt to determine a link between mafic, mantle derived magmas and their granitoid hosts. Although isotopic and geochemical evidence provides a clear link between mantle-derived mafic magmas and granitoids within both the Moonbi and Clarence River suites, a clear explanation of the mechanisms and source rocks involved in magma generation remains elusive. Of critical importance is identification of the character of the lower crustal sources involved in each case, and clarification of the mechanism of interaction between the mantle and crustal sources. In particular, although the lamprophyres associated with the Moonbi Suite appear partly responsible for the isotopic and geochemical character (in particular

  13. Complete preservation of ophiolite suite from south Andaman, India: A mineralchemical perspective

    Indian Academy of Sciences (India)

    Abhishek Saha; Avik Dhang; Jyotisankar Ray; Suvankar Chakraborty; David Moecher

    2010-06-01

    Field studies supplemented by petrographic analyses clearly reveal complete preservation of ophiolite suite from Port Blair (11° 39′ N: 92° 45′E) to Chiriyatapu (11° 30′ 24′′N: 92° 42′ 30′′E) stretch of South Andaman. The ophiolite suite reveals serpentinite at the base which is overlain unconformably by cumulate ultramafic–mafic members with discernible cumulus texture and igneous layering. Basaltic dykes are found to cut across the cumulate ultramafic–mafic members. The succession is capped by well exposed pillow basalts interlayered with arkosic sediments. Olivine from the basal serpentinite unit are highly magnesian (Fo80.1–86.2). All clinopyroxene analyses from cumulate pyroxenite, cumulate gabbro and basaltic dyke are discriminated to be `Quad’ and are uniformly restricted to the diopside field. Composition of plagioclase in different lithomembers is systematically varying from calcic to sodic endmembers progressively from cumulate pyroxenite to pillow basalt through cumulate gabbro and basaltic dyke. Plagioclase phenocrysts from basaltic dyke are found to be distinctly zoned (An60.7–An35.5) whereas groundmass plagioclase are relatively sodic (An33–An23.5). Deduced thermobarometric data from different lithomembers clearly correspond to the observed preservation of complete ophiolite suite.

  14. Mineralogía y termo-barometría de los Complejos máficos Sol de Mayo y Suya Taco, Norte de las Sierras de Comechingones, Córdoba Mineralogy and thermo-barometry of the Sol de Mayo and Suya Taco mafic complexes from northern Sierra de Comechingones, Córdoba

    Directory of Open Access Journals (Sweden)

    Alina M. Tibaldi

    2008-03-01

    Full Text Available Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo-barometría de dos complejos máficos que afloran al norte de la sierra de Comechingones. Se aplicaron un conjunto de termómetros y barómetros empíricos con el propósito de determinar los rangos de P y T absolutas de cristalización de estas rocas. Las temperaturas de equilibrio en pares de piroxenos (cpx-opx se estimaron usando tres termómetros independientes. Dos calibraciones termométricas (Wells 1977, Kretz 1982 dan resultados consistentes y razonables indicando que los piroxenos registran condiciones de cristalización magmática (920-1150ºC, mientras que la tercera calibración (Lindsley 1983 estima temperaturas muy inferiores. Esta discrepancia puede estar relacionada con el hecho de que la última calibración no sería aplicable a rocas que cristalizaron a partir de magmas ricos en hierro. Por su parte, la termometría Amph-Pl sugiere temperaturas de equilibrio comprendidas entre 750-850ºC, para composiciones típicas de núcleos, mientras que para composiciones representativas de los bordes de grano las temperaturas estimadas son significativamente inferiores (This work presents a detailed study including petrography, mineral chemistry and thermo-barometry of igneous rock from two mafic complexes that outcrop in the north portion of the sierra de Comechingones. The range of absolute P and T under which these rocks crystallized is retrieved using a set of empiric barometers and thermometers. The estimations of equilibrium temperature determined in pairs of pyroxenes (cpx-opx were performed through three independent thermometers. Two of the thermometric formulations (Wells 1977, Kretz 1982 yield consistent and reasonable results indicating that these phases record magmatic crystallizations conditions (920-1150ºC, whereas the third calibration by Lindsley (1983 gives lower temperatures. This discrepancy is thought to reflect the fact that

  15. 东天山白石泉镁铁-超镁铁杂岩体的Nd-Sr-Os同位素成分及其对岩浆演化的意义%Nd-Sr-Os isotopic data of the Baishiquan mafic-ultramafic complex from East Tianshan, and implications for petrogenesis

    Institute of Scientific and Technical Information of China (English)

    陈斌; 贺敬博; 陈长健; 木合塔尔·扎日

    2013-01-01

    本文报道东天山有铜镍硫化物矿化的白石泉镁铁-超镁铁杂岩体(分布在中天山地块北部)的微量元素和Nd-Sr-Os同位素成分,以探讨其地幔源区性质和壳幔相互作用过程.白石泉杂岩体的地球化学特征是富集大离子亲石元素和轻稀土元素,但亏损高场强元素.全岩Sr和Nd同位素初始比值变化较大,分别是(87Sr/86Sr)i =0.7032~0.7066和εNd(t)=5.6~-0.9,两者呈反相关关系.全岩Os含量在80×10-12~29×10-12之间,富含放射性成因Os(187 Os/188 Os=0.295~ 1.18).据此,得出结论:(1)白石泉杂岩体的母岩浆在上升侵位过程中,受到地壳物质的强烈混染,导致各岩石类型的Nd-Sr同位素成分变化很大和Os同位素成分富集放射性成因Os的特征,这与前人认为的白石泉岩体侵位过程中没有地壳混染作用的模式明显不同;(2)白石泉杂岩体的母岩浆来自被古生代俯冲带熔/流体交代过的年轻岩石圈地幔,这要求我们重新认识中天山前寒武地块的性质和规模.%We report trace elements and Nd-Sr-Os isotopic data for the Baishiquan mafic-ultramafic complex that occurs in the East Tianshan Mountains (in the northern part of the Mid-Tianshan Precambrian block) and is accompanied by Cu-Ni deposits, to understand its mantle source characteristics and processes of mantle-crustal interaction. Geochemically, the complex is characterized by enrichment of LILEs and depletion of HFSEs. The whole-rock Sr-Nd isotopic compositions of the Baishiquan complex vary significantly, with (87Sr/ 86Sr)i =0. 7032 ~0. 7066 and εNd(t) =5. 6 ~ -0. 9, and the Nd-Sr isotopic ratios are negatively correlated. The complex shows very radiogenic Os isotopic compositions, with (187Os/188Os)i =0.295~1. 18 and Os=80 ×l0-12 ~29 ×l0-12. Based on these data, we conclude that (1) the parent magma of the Baishiquan complex experienced significant crustal contamination during magma emplacement, as is revealed by the negatively

  16. Petrogenesis and geodynamics of plagiogranites from Central Turkey (Ekecikdağ/Aksaray): new geochemical and isotopic data for generation in an arc basin system within the northern branch of Neotethys

    Science.gov (United States)

    Köksal, Serhat; Toksoy-Köksal, Fatma; Göncüoglu, M. Cemal

    2016-09-01

    In the Late Cretaceous, throughout the closure of the Neotethys Ocean, ophiolitic rocks from the İzmir-Ankara-Erzincan ocean branch were overthrusted the northern margin of the Tauride-Anatolide Platform. The ophiolitic rocks in the Ekecikdaǧ (Aksaray/Central Turkey) region typify the oceanic crust of the İzmir-Ankara-Erzincan branch of Neotethys. The gabbros in the area are cut by copious plagiogranite dykes, and both rock units are intruded by mafic dykes. The plagiogranites are leucocratic, fine- to medium-grained calc-alkaline rocks characterized mainly by plagioclase and quartz, with minor amounts of biotite, hornblende and clinopyroxene, and accessory phases of zircon, titanite, apatite and opaque minerals. They are tonalite and trondhjemite in composition with high SiO2 (69.9-75.9 wt%) and exceptionally low K2O (<0.5 wt%) contents. The plagiogranites in common with gabbros and mafic dykes show high large-ion lithophile elements/high-field strength element ratios with depletion in Nb, Ti and light rare-earth elements with respect to N-MORB. The plagiogranites together with gabbros and mafic dykes show low initial 87Sr/86Sr ratios (0.70419-0.70647), high ƐNd(T) (6.0-7.5) values with 206Pb/204Pb (18.199-18.581), 207Pb/204Pb (15.571-15.639) and 208Pb/204Pb (38.292-38.605) ratios indicating a depleted mantle source modified with a subduction component. They show similar isotopic characteristics to the other supra-subduction zone (SSZ) ophiolites in the Eastern Mediterranean to East Anatolian-Lesser Caucasus and Iran regions. It is suggested that the Ekecikdaǧ plagiogranite was generated in a short time interval from a depleted mantle source in a SSZ/fore-arc basin setting, and its nature was further modified by a subduction component during intra-oceanic subduction.

  17. Zircon U-Pb Age and Hf Isotopic Compositions of Quartz Monzonite and Enclosed Mafic Enclaves in Muchen Pluton, Zhejiang Province: Tracing Magma Mixing in Their Petrogenesis%浙江沐尘石英二长岩及其镁铁质包体的锆石U-Pb年龄和Hf同位素组成——对岩浆混合作用的示踪

    Institute of Scientific and Technical Information of China (English)

    刘亮; 邱检生; 李真

    2011-01-01

    Numerous mafic microgranular enclaves (MMEs) with different shapes are found in quartz monzonites of the Muchen pluton in Zhejiang Province. Precise LA-ICP-MS U-Ph dating was conducted on zircon grains extracted from the host quartz monzonites and the MMEs, yielding crystallization ages of 112.1±1. OMa and 112.4±1.2Ma, respectively. The consistent ages within analytical errors suggest that the host rocks and MMEs were coeval, providing crucial evidence for magma mixing during their petrogenesis. The MMEs commonly show plastic forms and contain similar K-feldspar megacrysts to the host rocks. Furthermore, plagioclases with core-rim zoning texture and apatites with euhedral acicular shape occur widely in the MMEs. These micrographic features are also consistent with the involvement of magma mixing in their petrogenesis. The MMEs and host quartz monzonites show similar zircon Hf isotopic signatures with εHf (t) values ranging from negative to positive. Integrated geological and geochemical characteristics suggest that the MMEs in Muchen pluton were most likely produced by magma mixing between mafic magmas derived from a depleted mantle source and induced felsic magmas generated from partial melting of crust materials.%浙江沐尘石英二长岩体中普遍发育形态各异的暗色镁铁质微粒包体.本文运用LA-ICP-MS锆石U-Pb定年技术,对该石英二长岩和其中的暗色镁铁质微粒包体进行了精确的年龄测定,获得的年龄分别为112.1土1.0Ma和112.4士1.2Ma,二者在误差范围内一致,说明它们同时形成,这为指示包体属岩浆混合作用成因提供了关键证据.包体野外多呈塑性形态,包体中可见与寄主岩中相似的钾长石斑晶,包体中的斜长石发育复杂的核边环带结构,并普遍出现针状磷灰石,这些特征也指示包体的形成经历了岩浆混合作用过程.包体与寄主岩样品具有相似的Hf同位素组成,其共同特点主要表现为εHf(t)值散布于正值与负

  18. Homosexuals, dykes and queers: political positions in the lesbian and gay movement

    Directory of Open Access Journals (Sweden)

    Gerard Coll-Planas

    2008-10-01

    Full Text Available In this article I aim to explore conflicts among the variety of political projects in the lesbian and gay movement.I base the article on Alberto Mira’s (2004 proposed models for the expression of homosexuality: decadentist, homophile and camp. I discuss the main theoretical and political debates that arise from these models. Firstly, I ask whether life on the margins of mainstream social rules allows gays and lesbians to live a freer existence or merely means internalised homophobia (using Jean Genet’s and Michel Foucault’s approaches as examples. Secondly, I question whether the demand for “normality” entails the creation of new exclusions (following Judith Butler’s approach to normality: Finally, I consider whether camp culture reproduces and/or subverts gender rules (introducing a discussion between Sheila Jeffreys and Judith Butler’s positions. On the basis of this exploration of Mira's three cultural models, I develop a typology of political positions ('normalization of homosexuality', 'transformation' and 'queer', which I apply to the case study of the Catalan lesbian and gay movement.

  19. The flood, the channels, and the dykes : managing legal information a globalized and digital world

    OpenAIRE

    Breuker, Joost; Casanovas, Pompeu; Klein, Michel C. A.; Francesconi, Enrico

    2009-01-01

    Information search and retrieval are part of daily routines of the legal profession. Lawyers, judges, prosecutors, and legal clerks usually access a number of electronic resources to browse, search, select, or update legal contents. Legal databases have currently become large digital libraries where the tasks related to information-seeking may sometimes be cumbersome. Adding semantics to support information search may provide significant results in terms of efficiency, efficacy, and user sati...

  20. Evaluation of erosion of soil used in dykes and earth embankments which are subjected to flood

    OpenAIRE

    Reiffsteck, Philippe

    2005-01-01

    Understanding the factors that control the transport of particles detached by water during storms and floods is essential to predict the likelihood of internal and surficial erosion of road or railway embankments. It would be extremely useful to be able at an early stage of project to foresee the sensitivity of the available soils to erosion, in order to choose another type of fill or to design appropriate erosion control measures. The study presented here which is based on laboratory tests w...

  1. A love letter from NADIA (non-anglo dykes in Australia).

    Science.gov (United States)

    Kizinska, R

    1999-01-01

    This article is a revised version of a paper I presented at the "Sappho Was A Wog Grrrl" conference in Melbourne, 22 October 1995, which was organized by "Interlesbian," a Melbourne-based political and support group for lesbians from Non-English Speaking Backgrounds (NESB). Utilizing a mixed genre format incorporating the first person fictional narrative form of letters to lovers, this parodic piece explores the identity terrains of sexuality, ethnicity and class in Melbourne's lesbian communities. It focuses on how the ethnocentric limits of sexual, cultural and racial identifications constrain the mythical beauty of coming out and staying in. The experiences reported and reflected upon here arose out of my participation as an activist member of Interlesbian. Contextualized in the form of a lover's discourse, this paper is an evocation of a passion towards the (re)visioning of a progressive local lesbian activist politics and community. PMID:10197552

  2. Homosexuals, dykes and queers: political positions in the lesbian and gay movement

    Directory of Open Access Journals (Sweden)

    Coll-Planas, Gerard

    2008-11-01

    Full Text Available (English In this article I aim to explore conflicts among the variety of political projects in the lesbian and gay movement.I base the article on Alberto Mira’s (2004 proposed models for the expression of homosexuality: decadentist, homophile and camp. I discuss the main theoretical and political debates that arise from these models. Firstly, I ask whether life on the margins of mainstream social rules allows gays and lesbians to live a freer existence or merely means internalised homophobia (using Jean Genet’s and Michel Foucault’s approaches as examples. Secondly, I question whether the demand for “normality” entails the creation of new exclusions (following Judith Butler’s approach to normality: Finally, I consider whether camp culture reproduces and/or subverts gender rules (introducing a discussion between Sheila Jeffreys and Judith Butler’s positions. On the basis of this exploration of Mira's three cultural models, I develop a typology of political positions ('normalization of homosexuality', 'transformation' and 'queer', which I apply to the case study of the Catalan lesbian and gay movement.

  3. Palaeointensity determinations on rocks from Palaeoproterozoic dykes from the Kaapvaal Craton (South Africa)

    Science.gov (United States)

    Shcherbakova, V. V.; Shcherbakov, V. P.; Zhidkov, G. V.; Lubnina, N. V.

    2014-06-01

    Palaeointensity study of the Proterozoic-Archean volcanic rocks from the Kaapvaal Craton South Africa) are reported. Palaeomagnetic study of this collection was performed earlier by Olsson et al. Electron microscope observations, thermomagnetic and hysteresis measurements indicate the presence of single-domain and pseudo-single-domain (SD-PSD) magnetite grains as the main magnetic mineral. The samples demonstrated a very good stability to heating, the electron micrograph observations revealed magnetite-ilmenite exsolution structure. Palaeointensity determinations were obtained by Coe-modified Thellier procedure. A total 58 samples from 14 sites were studied but only seven samples from one site NL28 of the Early Proterozoic age of 1.9 Ga passed palaeointensity selection criteria. Reliable palaeointensity determinations were obtained by both Thellier and Wilson methods on 18 cubes (subsamples) from site NL28 yielding rather low mean virtual dipole moment (VDM) = (2.82 ± 0.12) ×1022 Am2 which is in agreement with the suggestion of existence of the `Proterozoic dipole low period'.

  4. Flood risk control of dams and dykes in middle reach of Huaihe River

    OpenAIRE

    Ma, Zhen-Kun; Zi-wu FAN; Zhang, Ming; Yi-lu SU

    2014-01-01

    Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate...

  5. Sissies, Faggots, Lezzies, and Dykes: Gender, Sexual Orientation, and a New Politics of Education?

    Science.gov (United States)

    Lugg, Catherine A.

    2003-01-01

    Seeks to chart a course through the contested area of gender and sexual orientation in hopes of establishing a theoretical framework and an agenda for much needed future research. Draws from two research traditions, particularly in the areas of history and law: neo-Marxist theory generally and Queer Legal Theory specifically. (Contains 161…

  6. An isotope trace element study of the East Greenland Tertiary dyke swarm

    DEFF Research Database (Denmark)

    Hanghøj, Karen; Storey, Michael; Stecher, Ole

    2003-01-01

    of the East Greenland margin indicates that there is no systematic compositional change with distance from the presumed proto-Icelandic plume centre. This suggests that a northward-increasing crustal thickness observed offshore may be attributed to active upwelling rather than a systematic rise in...

  7. Effects of compaction method on the properties of asphalt concrete for dams and dykes

    Energy Technology Data Exchange (ETDEWEB)

    Grenier, Simon [Groupe Qualitas Inc., Montreal, (Canada); Konrad, Jean-Marie [University Laval, Quebec, (Canada); Perraton, Daniel [Ecole de technologie superieure, Montreal, (Canada); Peloquin, Eric [Hydro-Quebec, Montreal, (Canada); Longtin, Hugo [SNC-Lavalin, Montreal, (Canada)

    2010-07-01

    Asphalt concrete is used in embankment dams as an impervious lining on the upstream face or in the interior as a core wall. The mix needs to be compacted to a specific density to ensure low permeability, ductility and flexibility of the materiel. This paper investigated the influence of three compaction methods on the stress-strain curves and the strength of the asphalt concrete mixture. Comparisons between laboratory and field compaction methods of asphalt concrete mix with high bitumen content were carried out. Triaxial tests results on samples from the Nemiscau-1 Dam constructed in 2008 in Quebec, Canada and on laboratory-compacted asphalt concrete samples were compared. The results showed that the differences between materials can be explained by the specific aggregate structure obtained for each compaction method, which results in preferential grain orientation and in more or less interlocking between grains.

  8. The Patuki intrusive suite: closed-system fractionation beneath a slow-spreading ridge

    Science.gov (United States)

    Sivell, W. J.; Waterhouse, J. B.

    A wide range of mafic and ultramafic rock types, together with cogenetic silicic plagiogranites, form a structurally coherent intrusive sequence within the Patuki Volcanics at south D'Urville Island, New Zealand. In addition, gabbroic rocks comprise abundant tectonic inclusions in highly-sheared, concordant serpentinite bands which intrude the Patuki suite. Chemical evidence suggests many of the gabbros, including those in which recrystallization has obliterated original textures, represent magmatic cumulates and indicates extensive closed-system fractionation analogous to that known to occur beneath slow-spreading mid-oceanic ridges. Dyke intrusion occurred throughout the generation of the suite. An early stage of spreading is suggested by the anomalously low thickness of the sequence, the non-sheeted nature of the dyke suite and chemical characteristics of the lavas which comprise the extrusive component of the ophiolite.

  9. SHRIMP dating of the Bangong Lake SSZ-type ophiolite:Constraints on the closure time of ocean in the Bangong Lake-Nujiang River, northwestern Tibet

    Institute of Scientific and Technical Information of China (English)

    SHI RenDeng

    2007-01-01

    The Bangong Lake ophiolite is located in the westernmost part of the Bangong Lake-Nujiang River and massive lavas and mafic dykes with SSZ-type ophiolitic geochemical affinity formed at the end of a Wilson circle. The SHRIMP U-Pb ages of the co-magmatic zircon domains from one gabbroic dyke (Sample 01Y-155) range from 162.5±8.6 Ma to 177.1±1.4 Ma with an average of 167.0+1.4 Ma (n = 12,MSWD = 1.2), suggesting that the subduction of the Bangong Lake Neo-Tethyan Ocean started before the Middle Jurassic. It is inferred that the tectonic transform from spreading to subduction of the Neo-Tethyan Ocean began before the Middle Jurassic in the Bangong Lake area.

  10. The Continent-Ocean Transition in the Mid-Norwegian Margin: Insight From Seismic Data and the Onshore Caledonian Analogue in the Seve Nappe Complex

    Science.gov (United States)

    Abdelmalak, Mansour M.; Planke, Sverre; Andersen, Torgeir B.; Faleide, Jan Inge; Corfu, Fernando; Tegner, Christian; Myklebust, Reidun

    2015-04-01

    The continental breakup and initial seafloor spreading in the NE Atlantic was accompanied by widespread intrusive and extrusive magmatism and the formation of conjugate volcanic passive margins. These margins are characterized by the presence of seaward dipping reflectors (SDR), an intense network of mafic sheet intrusions of the continental crust and adjacent sedimentary basins and a high-velocity lower crustal body. Nevertheless many issues remain unclear regarding the structure of volcanic passive margins; in particular the transitional crust located beneath the SDR.New and reprocessed seismic reflection data on the Mid-Norwegian margin allow a better sub-basalt imaging of the transitional crust located beneath the SDR. Different high-amplitude reflections with abrupt termination and saucer shaped geometries are identified and interpreted as sill intrusions. Other near vertical and inclined reflections are interpreted as dykes or dyke swarms. We have mapped the extent of the dyke reflections along the volcanic margin. The mapping suggests that the dykes represent the main feeder system for the SDR. The identification of saucer shaped sills implies the presence of sediments in the transitional zone beneath the volcanic sequences. Onshore exposures of Precambrian basement of the eroded volcanic margin in East Greenland show that, locally, the transitional crust is highly intruded by dykes and intrusive complexes with an increasing intensity of the plumbing and dilatation of the continental crust ocean-ward. Another well exposed analogue for a continent-ocean transitional crust is located within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides. The best-preserved parts of SNC in the Pårte, Sarek, Kebnekaise, Abisko, and Indre Troms mountains are composed mainly of meta-sandstones and shales (now hornfelses) truncated typically by mafic dykes. At Sarek and Pårte, the dykes intrude the sedimentary rocks of the Favoritkammen Group, with a dyke density up

  11. Root zone of a continental rift: the Neoproterozoic Kebnekaise Intrusive Complex, northern Swedish Caledonides

    DEFF Research Database (Denmark)

    Kirsch, Moritz; Svenningsen, Olaf

    2016-01-01

    Mafic magmatic rocks formed between ca. 615 and 560 Ma along the Neoproterozoic margins of Baltica and Laurentia are classically attributed to continental rifting heralding the opening of the Iapetus Ocean. We report new data for the Kebnekaise Intrusive Complex (KIC) exposed in the Seve Nappes...... in northern Sweden. The KIC consists of sheeted dolerite dykes and gabbroic bodies with mutually intrusive relations. Major and trace element data exhibit a transitional- to normal-mid-ocean-ridge basalt-type geochemical signature. Differentiation processes and late-stage liquid immiscibility of a tholeiitic...... melt are considered to account for the compositional range exhibited by the KIC igneous rocks. U/Pb SIMS geochronological data from zircon rims yield an emplacement age of 578 ± 9 Ma. The KIC is thus younger and more depleted than coeval mafic rocks found in the Seve Nappe, and is interpreted...

  12. The post-collisional volcanism of northern Tunisia: Petrology and evolution through time

    Science.gov (United States)

    Halloul, Néji; Gourgaud, Alain

    2012-02-01

    The Neogene volcanism of Tunisia is bimodal, comprising both mafic lavas and rhyolites. The rhyolites occur as domes and related breccias, and as dykes in the Nefza area, associated with an albite granite. The rhyolites volcanics are 12.9-8.2 Ma. Mafic lavas occur in the Nefza and Mogods areas, as dykes and sills, and are younger than the felsic lavas at 8.4-5 Ma. The rhyolites exhibit phenocrysts of quartz, plagioclase (An 25-55), alkali feldspar (Or 63-91), biotite, Fe-Ti oxides and rare cordierite and tourmaline. A study of the cordierite shows it to be magmatic in character, in equilibrium with glass and other minerals, and with a large range of compositions (Fe * 34-64). Magmatic cordierite in rhyolites is exceptional and cordierite/liquid partition coefficients were determined for rare earth elements. According to mineralogical and geochemical data, including Sr isotopes, there are two groups of rhyolites. The first group is the cordierite bearing-rhyolites, which have Fe-rich biotite, and is related to localised crustal melting. The second group, which lack cordierite, but has Mg-rich biotite, is related to AFC processes. The mafic magma is represented by moderately Na-alkaline silica undersaturated hawaites and mugearites, with phenocrysts of olivine (Fo 69-85), plagioclase (An 49-67), clinopyroxene (augite) and ulvöspinel. Geochemical data suggest that they are transitional in nature, between calc-alkaline and alkaline magmas, as also found in Algeria and Morocco. These magmas evolved by fractional crystallization and crustal contamination. The magmatic change through time from calk-alkaline to transitional, as also found for Algeria and Morocco at the same point in time, is consistent with a slab breakoff process. The more recent mafic magmas are related to an extensional post-collisional environment.

  13. Structural control on basaltic dike and sill emplacement, Paiute Ridge mafic intrusion complex, southern Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Carter Krogh, K.E.; Valentine, G.A.

    1996-08-01

    Late Miocene basaltic sills and dikes in the Paiute Ridge area of southern nevada show evidence that their emplacement was structurally controlled. Basaltic dikes in this area formed by dilating pre-existing vertical to steeply E-dipping normal faults. Magma propagation along these faults must have required less energy than the creation of a self-propagated fracture at dike tips and the magma pressure must have been greater than the compressive stress perpendicular to the fault surface. N- to NE-trending en echelon dikes formed locally and are not obviously attached to the three main dikes in the area. The en echelon segments are probably pieces of deeper dikes, which are segmented perhaps as a result of a documented rotation of the regional stresses. Alternatively, changes in orientation of principal stresses in the vicinity of each en echelon dike could have resulted from local loads associated with paleotopographic highs or nearby structures. Sills locally branched off some dikes within 300 m of the paleosurface. These subhorizontal bodies occur consistently in the hanging wall block of the dike-injected faults, and intrude Tertiary tuffs near the Paleozoic-Tertiary contact. The authors suggest that the change in stresses near the earth`s surface, the material strength of the tuff and paleozoic rocks, and the Paleozoic bedding dip direction probably controlled the location of sill formation and direction of sill propagation. The two largest sills deflected the overlying tuffs to form lopoliths, indicating that the magma pressure exceeded vertical stresses at that location and that the shallow level and large size of the sills allowed interaction with the free (earth`s) surface. 32 refs., 4 figs., 1 tab.

  14. Silica-poor, mafic alkaline lavas from ocean islands and continents: Petrogenetic constraints from major elements

    Indian Academy of Sciences (India)

    Shantanu Keshav; Gudmundur H Gudfinnsson

    2004-12-01

    Strongly silica-poor (ne-normative), mafic alkaline lavas generally represented by olivine nephelinites, nephelinites, melilitites, and olivine melilitites have erupted at various locations during Earth’s history. On the basis of bulk-rock Mg#, high concentrations of Na2O, TiO2, and K2O, and trace element geochemistry, it has been suggested that these lavas represent low-degree melts that have undergone little crystal fractionation en route to the surface. Many of these lavas also carry highpressure mantle material in the form of harzburgite, spinel lherzolite, and variants of websterite xenoliths, and rare garnet-bearing xenoliths. However, phenocryst phases instead indicate that these magmas cooled to variable extents during their passage. We note subtle, yet important, differences in terms of CaO, Al2O3, CaO/Al2O3, and CaO/MgO. High-pressure experimental melting studies in CMAS-CO3 (3–8GPa) and natural lherzolitic systems (3GPa) demonstrate that at an isobar increasing leads to a moderate decrease in CaO + MgO, whereas CaO/MgO and CaO/Al2O3 sharply decrease. Relatively high CaO/Al2O3 indicates melting in the presence of garnet (≥ 85km). Studies also demonstrate that CO2-bearing lherzolitic systems, when compared with anhydrous ones, also have higher CaO content in the coexisting melt at a given and . Comparison of the bulk-rock major-element chemistry of silica-poor, mafic alkaline lavas with experimentally determined high-pressure melts indicates that melting of anhydrous mantle lherzolite or garnet pyroxenite is not able to explain many of the major element systematics of the lavas. However, high-pressure partial melts of carbonated lherzolite have the right major element trends. Among ocean islands, lavas from Samoa and Hawaii are perhaps the products of very low degree of partial melting. Lavas from Gran Canaria and Polynesia represent products of more advanced partial melting. On continents, lavas from South Africa and certain localities in Germany are the products of a very low degree of partial melting, and those from Texas and certain other localities in Germany are products of a slightly more advanced degree of partial melting of a carbonated lherzolite. Lavas from Deccan, Czech Republic, and Freemans Cove are the products of even more advanced degree of partial melting. The mere presence of mantle xenoliths in some of these lavas does not necessarily mean that the erupted lavas represent direct mantle melts.

  15. Experimental deformation of a mafic rock - interplay between fracturing, reaction and viscous deformation

    Science.gov (United States)

    Marti, Sina; Stünitz, Holger; Heilbronner, Renée; Plümper, Oliver; Drury, Martyn

    2016-04-01

    Deformation experiments were performed on natural Maryland Diabase (˜ 55% Plg, 42% Px, 3% accessories, 0.18 wt.-% H2O added) in a Griggs-type deformation apparatus in order to explore the brittle-viscous transition and the interplay between deformation and mineral reactions. Shear experiments at strain rates of ˜ 2e-5 /s are performed, at T=600, 700 and 800°C and confining pressures Pc=1.0 and 1.5 GPa. Deformation localizes in all experiments. Below 700°C, the microstructure is dominated by brittle deformation with a foliation formed by cataclastic flow and high strain accommodated along 3-5 major ultracataclasite shear bands. At 700°C, the bulk of the material still exhibits abundant microfractures, however, deformation localizes into an anastomosing network of shear bands (SB) formed from a fine-grained (structures such as fractures and SB. Experiments at 800°C show extensive mineral reactions, with the main reaction products Amph+Plg (+Zo). Deformation is localized in broad C' and C SB formed by a fine-grained (0.1 - 0.8 μm) mixture of Plg+Amph (+Zo). The onset of mineral reactions in the 700°C experiments shows that reaction kinetics and diffusional mass transport are fast enough to keep up with the short experimental timescales. While in the 700°C experiments brittle processes kinematically contribute to deformation, fracturing is largely absent at 800°C. Diffusive mass transfer dominates. The very small grain size within SB favours a grain size sensitive deformation mechanism. Due to the presence of water (and relatively high supported stresses), dissolution-precipitation creep is interpreted to be the dominant strain accommodating mechanism. From the change of Amph coronas around Px clasts with strain, we can determine that Amph is re-dissolved at high stress sites while growing in low stress sites, showing the ability of Amph to accommodate strain via dissolution precipitation creep. The transition from dominantly brittle, to dominantly viscous deformation is determined by the onset of diffusive mass transport. In the transitional regime, reaction kinetics are strongly dependent on strain energy and viscously deforming SB form most likely from an initial brittle stage in a dominantly brittle behaving rock. Viscous deformation in our experiments takes place at comparatively low experimental T, providing a realistic phase assemblage and likely deformation mechanism for the lower crust.

  16. Geochronology and geochemistry of the Heihe mafic pillow lavas in the Qinling Mountains, China

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Zongqing

    2001-01-01

    [1]Lee, C. Y., A preliminary study of plate tectonics of China, Bull. Chinese Acad. Geol. Sci. (in Chinese), 1980, 2(1): 11-19.[2]Lee, C. Y., Tectonic evolution of Asia, Bull. Chinese Acad. Geol. Sci. (in Chinese), 1984, 10: 3-11.[3]Ren Jishun, Jiang Chunfa, Zhang Zhengkun et al., The Geotectonic Evolution of China (in Chinese), Beijing: Science Press, 1980.[4]Ren Jishun, Chen Tingyu, Niu Baogui et al., Tectonic Evolution of the Continental Hithospheres and Metallogeny in Eastern China and Adjacent Areas (in Chinese), Beijing: Science Press, 1990.[5]Zhang Qiusheng, Zhu Yongzheng, The Paleozoic ophiolite in the east Qinling, J. Changchun College of Geology (in Chi-nese), 1984, 3: 1-13.[6]Xiao Siyun, Zhang Weiji, Song Ziji, The Metamorphic Strata of the Northern Qinling in China (in Chinese), Xi'an: Xi'an Jiaotong University Press, 1988.[7]Xu Zhiqin, Lu Yilun, Tang Yaoqing et al., Formation of the Composite Eastern Qinling Chains (in Chinese), Beijing: China Environmental Science Press, 1988.[8]Zhang Guowei, Formation and evolution of the Qinling orogenic belt (in Chinese), Xi'an: Northwest University Press, 1988.[9]Zhang Guowei, Meng Qingren, Yu Zaiping, Orogenesis and dynamics of the Qinling orogen, Science in China, Ser. D, 1996, 39(3):225-234.[10]Wu Liren, Xu Guizhong, Geological Evolution in the East Qinling-Dabieshan Collision Orogen (in Chinese), Beijing: Science Press, 1988.[11]Sun Yong, Yu Zaiping, A discussion of an ancient ocean and Caledonian in the east Qinling, in A Selection of Papers Pre-sented at the Conference on the Qinling Orogenic Belt (in Chinese), Xi'an: Northwest University Press, 1991, 167-173.[12]Zhang Zongqing, Liu Dunyi,Fu Guomin et al., Geochronology of Metamorphic Strata in the North Qinling Area (in Chi-nese), Beijing: Geological Publishing House, 1994.[13]Cui Zhilin, Sun Yong, Wang Xueren, Discovery of radiolarian fossils within the Danfeng ophiolite in the Qinling and its significance, Chinese Science Bull., 1995, 40(19):1686-1688.[14]Pei Xianzhi, Composition and Tectinic Evolution of the Shangdan Structural Zone in the East Qinling, China (in Chinese), Xi'an: Xi'an Maps Publishing House, 1997.[15]Jiang Changyi, Su Shengrui, Zhao Taiping et al., Intruded Rock Belt in the North Qinling Area and Jinning Movement (in Chinese), Beijing: Geological Publishing House, 1988.[16]Zhang Zongqing, Zhang Guowei, Fu Guomin et al., Geochronology of metamorpic strata in the Qinling Mountains and its tectonic implications, Science in China, Ser. D, 1996, 39(3): 283-292.[17]Zhang Qi, Zhang Zongqing, Sun Yong et al., Trace element and isotopic geochemistry of metebasalts from Danfeng Group in Shangxian-Danfeng area, Shaanxi Province, Acta Petrologica Sinica (in Chinese), 1995, 11(1): 43-54.[18]Zhang Benren, Luo Tingchuan, Ouyang Jianping et al., Geochemical Study of the Lithosphere, Tectonism and Metallo-genesis in the Qingling-Dabashan Region (in Chinese), Wuhan: China University of Geosciences Press, 1994.[19]Li, S., Hart, S. R., Zheng, S. et al., Timing of collision between the North and South China blocks: The Sm-Nd isotopic age evidence, Science in China, Ser. B, 1989, 32(3): 312-319.[20]Li, S., Chen, Y. Z., Zhang Guowei, A l Ga B. P. Alpine peridotite body emplaced into the Qingling group: Evidence for the existence of the late proterozoic plate tectonics in the North Qinling area, Geol. Review (in Chinese), 1991, 37(3): 235-242.[21]Zhang Guowei, Meng Qingren, Lai Shaocong, Tectonics and structure of Qinling orogenic belt, Science in China, Ser. B, 995, 38(10): 1379.[22]Liu Guohui, Zhang Shouguang, You Zhendong et al., The Major Metamorphic Rock Groups in the Qinling Orogenic Belt and Their Metamorphic Evolution (in Chinese), Beijing: Geological Publishing House, 1993.[23]You Zhendong, Suo Shutian, Han Yujing et al., The major characteristcs of the metamorphic complex of the Qinling oro-genic belt and their implication of the construction of the eastern Qinling continental crust, in A Selection of Papers Pre-sented at the Conference on the Qinling Orogenic Belt (in Chinese), Xi'an: Northwest University Press, 1991, 1-14.[24]Wang Tao, Li Wuping, Wang Xiaoxia, Zircon age of the Niujiaoshan granitoid gneisses in the Qinling complex of the Qinling orogenic belt, Regional Geology of China (in Chinese), 1998, 17(3): 262-265.[25]Lu Xinxiang, Dong You, Wei Xiangdong, Age of the Tuwushan A-type granite and its tectonic implications, Chinese Science Bulletin, 1999, 44(9): 975-978.

  17. Petrologic and Oxygen-Isotopic Investigations of Eucritic and Anomalous Mafic Achondrites

    Science.gov (United States)

    Mittlefehldt, D. W.; Greenwood, R. C.; Peng, Z. X.; Ross, D. K.; Berger, E. L.; Barrett, T. J.

    2016-01-01

    The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites (HEDs). However, Northwest Africa (NWA) 011 is mineralogically identical to eucrites, but has an O-isotopic composition distinct from them and was derived from a different asteroid. Modern analyses with higher precision have shown that some eucrites have smaller O-isotopic differences that are nevertheless well-resolved from the group mean.

  18. Reactive Transport Modeling of Supercritical Carbon Dioxide Injection Into Mafic Rock Reservoirs

    Science.gov (United States)

    Podgorney, R.; Hull, L.; Huang, H.; McLing, T.

    2007-12-01

    Technologies to reduce emissions of greenhouse gases and increase the sequestration of CO2 have received increasing attention since the development of the Kyoto protocol. One promising technology is the sequestration of CO2 in geologic formations. The suitability of a fractured basalt reservoir for CO2 sequestration is constrained by three broad categories of issues, which we refer to as physical, technical, and economic constraints. Physical constraints are beyond human control; thus, it is a requirement that a systematic method be developed by which a particular target reservoir may be evaluated to determine if it lies within the bounds required for safe and effective disposal. Technical constraints, on the other hand, are challenges to the ability to design, construct, and/or monitor a sequestration project as a result of limitations on our ability to determine the distribution of properties in the subsurface, our knowledge of the behavior of CO2 in the deep subsurface, and the current state of computational science and subsurface monitoring. Equally important are the heterogeneity of economic costs associated with sequestering CO2 at different sites and within different formations. The work presented here focuses on the technical aspects of CO2 injection, specifically examining reactive transport of CO2 in the subsurface in the vicinity of the injection well using the simulation code TOUGHREACT. Pressure distribution and propagation, kinetics of the geochemical reactions, and resultant changes in permeability/porosity are examined in order to evaluate injection scenarios that maximize the longevity of the injection well and sustainability of the reservoir.

  19. The Fazenda Gavião granodiorite and associated potassic plutons as evidence for Palaeoproterozoic arc-continent collision in the Rio Itapicuru greenstone belt, Brazil

    Science.gov (United States)

    Costa, Felipe G.; Oliveira, Elson P.; McNaughton, Neal J.

    2011-08-01

    Several granitic plutons have intruded the Palaeoproterozoic Rio Itapicuru greenstone belt, São Francisco craton, Brazil, in the time interval 2163-2080 Ma, but their tectonic significance is poorly understood. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with Archaean migmatite-gneiss basement. The pluton is mostly composed of hornblende granodiorite, occasionally crosscut by syn-plutonic mafic dykes. The FGG is metaluminous, medium- to high-K calc-alkaline with relatively constant silica abundances (SiO2 ˜ 63-66 wt%), high Sr (900-800 ppm) and high Ba (1000-1500 ppm). The associated mafic dykes are ultrapotassic, with high abundances of Ba, Sr, MgO, Ni, Cr, and light rare earth elements, suggesting derivation from partial melts of an enriched mantle source. The FGG originated probably by fractional crystallization from a primitive K-rich mafic magma that interacted with crustal melts. Its zircon U-Pb SHRIMP age of 2106 ± 6 Ma indicates that the FGG is younger than the early (2163-2127 Ma) tonalite-trondhjemite-granodiorite (TTG) and calc-alkaline arc plutons of the greenstone belt, and is closely related in time and space with potassic to ultrapotassic plutons (ca. 2110-2105 Ma). The negative ɛNd(t) of FGG and coeval K-rich plutons of the Rio Itapicuru greenstone belt contrasts markedly with the positive ɛNd(t) of the older arc plutons, indicating a major change of isotope signatures in granites of the Rio Itapicuru greenstone belt with time. This isotope shift may be related to magma contamination with older continental material and/or derivation of the parental potassic magma from enriched lithospheric mantle sources. We suggest that the K-rich plutons were emplaced during or shortly after Palaeoproterozoic arc-continent collision.

  20. Does deformation saturate seismic anisotropy?

    Science.gov (United States)

    Tatham, D. J.; Lloyd, G. E.; Butler, R. W.; Casey, M.

    2006-12-01

    The progressive simple shear deformation that characterizes ductile fault zones in the crust involves both rotation and intensification of the strain ellipsoid. These mathematic predictions have been confirmed repeatedly by finite strain determinations in outcrop studies of natural shear zones and used to test geodynamic models of mountain belts. Seismic anisotropy (SA) methods offer the opportunity to pursue these approaches in situ. First however, we must calibrate the magnitude and orientation of the SA ellipsoid against naturally deformed tectonites of known strain state and microstructure. Here we present data from a field analogue of mafic ductile crust in an amphibolite-facies shear zone developed in a deformed mafic dyke embedded within the Lewisian Gneiss (Badcall, NW Scotland). Deflection of pre-existing linear and planar elements and attenuation of the dyke into the shear zone are used to determine the strain gradient. Specimens collected along this gradient were used to establish the geometric fabric intensity defined by different minerals (hornblende grain alignment and ellipticity of plagioclase clots). Finally, petrophysical properties were calculated for the specimens using the SEM-EBSD measured populations of lattice preferred orientations (LPO) for all mineral phases. It is the hornblende-plagioclase LPO, combined in their modal proportions and modulated by the individual mineral single crystal elastic properties, which define the SA profile across the shear zone. Hornblende develops a strong preferred dimensional orientation and hence LPO at shear strains of about 2, whereas the plagioclase LPO remains close to random regardless of bulk strain. The modelled SA of the samples is dominated therefore by the amphibole LPO. Although the values of bulk shear strain vary across the shear zone (0 at the margins to greater than 12 in the centre), the calculated intensity of SA saturates at a shear strain of about 2. These results, if typical of large

  1. ESI-VI10 Jost Van Dyke, U.K. Virgin Islands 2000 (Environmental Sensitivity Index Map)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Environmental Sensitivity Index (ESI) maps are an integral component in oil-spill contingency planning and assessment. They serve as a source of information in the...

  2. Dykes of standards supporting polders of data: The practices used in the Netherlands for making archaeological data available and accessible

    OpenAIRE

    Gilissen, V.

    2014-01-01

    In the Netherlands, the archiving and publication of archaeological research data has led to the establishment of EDNA, the e-Depot for Dutch Archaeology http://www.edna.nl/, accommodated at DANS (Data Archiving and Networked Services) http://dans.knaw.nl/en. EDNA is a collaboration between DANS and the Cultural Heritage Agency (RCE). EDNA was set up as a project within the broader organisation of DANS. DANS is an institute of the Royal Netherlands Academy of Arts and Sciences (KNAW) and the ...

  3. Dykes of standards supporting polders of data : The practices used in the Netherlands for making archaeological data available and accessible

    NARCIS (Netherlands)

    Gilissen, V.

    2014-01-01

    In the Netherlands, the archiving and publication of archaeological research data has led to the establishment of EDNA, the e-Depot for Dutch Archaeology http://www.edna.nl/, accommodated at DANS (Data Archiving and Networked Services) http://dans.knaw.nl/en. EDNA is a collaboration between DANS and

  4. 护砂保堤固我"长城"%Protect the Sand Protect the Dyke Make the "Great Wall" Durable

    Institute of Scientific and Technical Information of China (English)

    陈汝军

    2004-01-01

    @@ 84km长的盐场海堤宛如一条巨龙横卧在黄海海岸线上,它不仅为金桥盐业有限公司挡潮抵浪,同时也保护着赣榆、灌云、新浦、连云两县两区2 000km2、150万人口的生命财产安全.

  5. Application of Ground Penetrating Radar Surveys and GPS Surveys for Monitoring the Condition of Levees and Dykes

    Science.gov (United States)

    Tanajewski, Dariusz; Bakuła, Mieczysław

    2016-08-01

    This paper analyses the possibility of using integrated GPS (Global Positioning System) surveys and ground penetrating radar surveys to precisely locate damages to levees, particularly due to the activity of small fossorial mammals. The technology of intercommunication between ground penetrating radar (GPR) and an RTK (Real-Time Kinematic) survey unit, and the method of data combination, are presented. The errors which may appear during the survey work are also characterized. The procedure for processing the data so that the final results have a spatial character and are ready to be implemented in digital maps and geographic information systems (GIS) is also described.

  6. Sr-Nd-Hf isotopes of the intrusive rocks in the Cretaceous Xigaze ophiolite, southern Tibet: Constraints on its formation setting

    Science.gov (United States)

    Zhang, Liang-Liang; Liu, Chuan-Zhou; Wu, Fu-Yuan; Zhang, Chang; Ji, Wei-Qiang; Wang, Jian-Gang

    2016-08-01

    The Cretaceous Xigaze ophiolite is best exposed at the central part of the Yarlung-Zangbo Suture Zone, Tibet Plateau. It consists of a thick section of mantle peridotites, but a relatively thin mafic sequence. This study presents geochronological and geochemical data for intrusive dykes (both mafic and felsic) and basalts to revisit the formation setting of the Xigaze ophiolite. The rodingites are characterized by high CaO and low Na2O contents relative to mafic dykes and show big variations in trace element compositions. Both gabbros and diabases have similar geochemical compositions, with MgO contents of 6.42-11.48 wt% and Mg# of 0.56-0.71. They display REE patterns similar to N-MORB and are variably enriched in large ion lithophile elements. Basalts have fractionated compositions and display LREE-depleted patterns very similar to N-MORB. They do not show obvious enrichment in LILE and depletion in high-field-strength elements, but a negative Nb anomaly is present. The studied plagiogranites have compositions of trondhjemite to tonalite, with high Na2O and low K2O contents. They have low TiO2 contents less than 1 wt%, consistent with melts formed by anatexis of gabbros rather than by differentiation of basalts. Zircons from seven samples, including three rodingites, three plagiogranites, and one gabbro, have been dated and yielded U-Pb ages of 124.6 ~ 130.5 Ma, indicating the Xigaze ophiolite was formed during the Early Cretaceous. They have mantle-like δ18O values of + 4.92 ~ + 5.26‰ and very positive εHf(t) values of + 16 ~ + 13.3. Ages of the rodingites and less altered gabbros indicate that serpentinization was occurred at ~ 125 Ma. Occurrence of both gabbroic and diabase dykes within the serpentinites suggests that the mantle lithosphere of the Xigaze ophiolite was rapidly exhumed. Both mafic and felsic dykes have slightly more radiogenic 87Sr/86Sr ratios relative to MORB, but depleted Hf-Nd isotpe compositions. They have a limited range of ε

  7. The giant Kalgoorlie Gold Field revisited

    Institute of Scientific and Technical Information of China (English)

    Noreen Mary Vielreicher; David Ian Groves; Neal Jesse McNaughton

    2016-01-01

    The Neoarchaean Kalgoorlie Gold Field contains the giant Golden Mile and world-class Mt Charlotte deposits, which have been the subject of much research for over 100 years. The Golden Mile deposit is a complex array of ductile to brittle vein and breccia lodes that are predominantly hosted in the highly-fractionated Golden Mile Dolerite sill. The Fimiston lodes comprise an array of narrow lodes that evolved broadly syn- to late-formation of the regional D2 NW-trending foliation. The lodes are charac-terized by pyrite veinlets and disseminations, quartz veinlets and breccias, and banded quartz-carbonate veins with sericite, carbonate, and pyrite-dominated alteration. Bonanza Green-Leader, or Oroya-style, lodes, with grades in excess of 1000 g/t Au, are similar to the Fimiston-style lodes, but are character-ized by abundant visible gold, native tellurium and more abundant telluride minerals within roscoelite-bearing alteration zones. The arguably structurally younger Mt Charlotte-style lodes are characterized by a pipe-shaped, coarse-grained quartz, carbonate and scheelite vein-stockwork with distinct vertically-zoned, carbonate-sericite-albite-pyrite ? pyrrhotite dominant alteration assemblages around veins within Unit 8 of the Golden Mile dolerite and porphyry dykes. The network of steep-and gently-dipping extension and shear fracture-fill veins are associated with NE-trending fault sets that cross cut the regional NW-trend. The deposit area is intruded by swarms of porphyry dykes, including syn-volcanic mafic dykes, early and volumetrically most significant c. 2.67 Ga feldspar-phyric porphyry dykes, as well as later c. 2.66‒2.65 Ga calc-alkaline hornblende-phyric dykes associated with younger c. 2.65‒2.64 Ga lamprophyre dykes. All post-volcanic dykes have similar orientations to the Fimiston lodes. The feldspar dykes are clearly overprinted by all styles of mineralization, although the relationship between hornblende-phyric and lamprophyre dykes and gold

  8. The Bero Volganic Group: New Lithological, Stratigraphic, and Geochemical Data of this Extension of the Parana-Etendeka Igneous Province into SW Angola with Implications

    Science.gov (United States)

    Marsh, J.; Swart, R.

    2015-12-01

    The Bero Volcanic Group, an extension of the Etendeka-Paraná Igneous Province into SW Angola, forms the eroded basement to the on-shore Namibe Basin, an Early Cretaceous-Cenozoic terrestrial and marine sedimentary sequence. The igneous suite outcrops between latitudes 14.68o and 15.25o S and comprises quartz latite rheoignimbrites/lavas, tholeiitic basaltic lavas, pyroclastic/volcaniclastic deposits, minor aeolian sandstones, and mafic tholeiitic dykes and gabbroic sheets. Quartz latite lithologies dominate. In the Rio Bero area in the S quartz latites are underlain by several thin flows of basalt interbedded with, and underlain by, thin discontinuous lenses of aeolian sandstone. This sequence is consistent with the general stratigraphic sequence in the northern Etendeka of Namibia. To the N basalts and aeolian sandstones are absent and the quartz latites lie directly on Precambrian basement rocks in places. To date, data for a quartz latite correlated with a Chapecó rhyolites of the Paraná are available from only one locality in Angola. This study's wider sampling and major and trace element and radiogenic isotope analysis reveals the following: (1) all mafic rocks are high-Ti, the lavas being equivalent to the Khumiba/Urubici type; (2) mafic dykes cutting the quartz latites having affinities to the Paranapanema-Ribeira mafic lavas; (3) five quartz latite geochemical types are present, three of which are known from Etendeka/Paraná (Sarusas/Guarapuava, Khoraseb/Ourinhos and Ventura) and their stratigraphic relationships in Angola are consistent with those in the Etendeka and Paraná; (4) their Angolan occurrence significantly extends the area covered by, and potential eruptive volumes of, these silicic types; (5) two other quartz latite types are unknown in the Etendeka and Paraná and are probably products of low-volume, local eruptions. The Chinguau type is geochemically similar to the low-Ti quartz lalites of the southern Etendeka but has lower Epsilon Nd

  9. Geochronology (U-Pb/Pb-Pb) and isotopic signatures (Rb-Sr/Sm-Nd) of the Paleoproterozoic Guanambi Batholith, southwest Bahia State (NE Brazil)

    International Nuclear Information System (INIS)

    The Guanambi batholith (GB) is located in south-western Bahia, Brazil, where it forms part of the Urandi-Paratinga mobile belt. The batholith extends over an area of almost 6,000 km2 and is mainly composed of syenites and monzonites, with subordinate granites, mafic syenites and lamprophyric dykes. Two main units can be recognized: the multiple intrusions, being divided into four regions (Paratinga, Laguna, Igapora and Guanambi) and the so-called late-intrusions forming the Cara Suja, Ceraima and Estreito massifs. U-Pb and Pb-Pb isotopic data demonstrate that the batholith was emplaced 2.05 Ga ago. GB has highly negative initial εNd (-7.4 to -10.6), pointing to an enriched source, and Sr initial ratios between 0.704 and 0.707. Both chemical and isotopic signatures suggest that GB formed by fractional crystallization of a lamprophiric magma derived from a Paleoproterozoic enriched mantle source. (author)

  10. SECONDARY MINERAL PARAGENESIS IN THE MAFIC EXTRUSIVE ROCKS FROM THE MT. MEDVEDNICA OPHIOLITE MÉLANGE (CROATIA

    Directory of Open Access Journals (Sweden)

    Damir Slovenec

    2012-12-01

    Full Text Available The samples of partly or completely altered basaltic extrusive rocks from Mt. Medvednica ophiolite mélange were analysed by the optical microscopy and by X-ray powder diffraction (XRD. The chemical composition of minerals from different paragenetic assembleges were determinated by electron probe microanalysis (EPMA and the measured microdomains were documented by back-scattered electrons (BSE imagery. The most widespread alteration processes that affected analysed rocks are albitization, chloritization, epidotization, prehnitization, pumpellyitization, zeolitization and titanitization. Subordinate processes that include formation of limonite, calcite, zoisite, siderite, hematite, Mn-oxydes, pyrite and SiO2-phases were not constrained in this paper. Albitization is fairly dominant alteration process in all rock and its progradation throughout a plagioclase grain is clearly documented by BSE microphotographs and microprobe chemical analysis. Prehnite and laumontite are sporadic alteration products of plagioclases. The chemical components released during the alterations of plagioclases and/or clinopyroxenes along with components from circulating and percolating heated see water and fluids enable formation of chlorites, epidote and pumpellyite. Chlorites and pumpellyite formed also by devitrification of volcanic glass in vitric rim of pillow lavas. Small patches of leucoxene, that is abundant in all samples, represent dense aggregates of titanite nanocrystals replacing ilmenite and/or Ti-magnetite. Epidote-bearing paragenesis in the analyzed rocks record comparatively the highest alterations grade that correspond to the middle grade of greenschist facies metamorphism typical of upper sequence of a see floor crust (the paper is published in Croatian.

  11. The Sondalo gabbro contact aureole (Campo unit, Eastern Alps): implications for mid-crustal mafic magma emplacement

    Science.gov (United States)

    Petri, B.; Mohn, G.; Štípská, P.; Schulmann, K.; Manatschal, G.

    2016-05-01

    Contact aureoles rimming plutonic rocks are the locus of metamorphism and deformations witnessing magma emplacement mechanisms in the crust. In this study, structural and petrological observations are combined to mineral equilibria modelling to unravel the polyphase tectono-metamorphic history of the Permian Sondalo gabbro and its host rock, the Campo unit (Eastern Alps). The Campo unit consists of Grt-St-Ms-Bt-Pl-Qtz ± Sil ± And ± Crd mica schists attesting of a Carboniferous prograde P- T path, reaching 6 kbar/600 °C and subsequently 5.6 kbar/650 °C. This metamorphism is coeval with the formation of a sub-vertical NE-SW trending foliation (S1) and its overprint by a sub-vertical NW-SE trending foliation (S2). The heat brought by the Permian intrusives subsequently caused heating of the Campo unit at around 3-4 kbar/540 °C reflected by regional static crystallization of cordierite and andalusite porphyroblasts. During the intrusion of the Sondalo gabbro, thermal peak conditions are recorded by Grt-Sil-Spl-Crd-Ilm granulitic xenoliths at ~5.5 kbar/930 °C, subsequently exhumed at ~4 kbar during the development of a new foliation (S3). This foliation is localized around the pluton and moderately dips away from the centre of the pluton. In the migmatitic contact aureole, Grt-Sil-Bt-Pl-Qtz-Ilm and Grt-Sil-Crd-Spl-Bt-Kfs-Ilm residual rocks bear the new foliation (S3) and document a decompression from 6 kbar/750 °C to 5 kbar/725 °C and from 5.2 kbar/800 °C to reach 4.8 kbar/770 °C, respectively. The P- T- d paths recorded by the host rock and the xenoliths point to a two-step magma emplacement. First the Sondalo gabbro intruded the Campo unit causing heating of the host rock without deformation at 3-4 kbar. Second, the ductile flow along the pluton margins developed a new foliation (S3) during exhumation of the pluton and its immediate contact aureole from 6 to 4 kbar. Altogether, it indicates a progressive increase in mechanical coupling between the pluton and the host rock during magma emplacement.

  12. Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

    Science.gov (United States)

    Namur, Olivier; Charlier, Bernard; Holtz, Francois; Cartier, Camille; McCammon, Catherine

    2016-08-01

    Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200-1750 °C), low- to high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S2- and forms complexes with Fe2+, Mg2+ and Ca2+. The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases with increasing reducing conditions (from 10 wt.% S at IW-8) and with increasing temperature. Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. We developed an empirical parameterization to predict SCSS in Mercurian magmas as a function of oxygen fugacity (fO2), temperature, pressure and silicate melt composition. SCSS being not strictly a redox reaction, our expression is fully valid for magmatic systems containing a metal phase. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. We make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and/or that the mantle contains a minor metal phase and combine our parameterization of SCSS with chemical data from MESSENGER to constrain the oxygen fugacity of Mercury's interior to IW- 5.4 ± 0.4. We also calculate that the mantle of Mercury contains 7-11 wt.% S and that the metallic core of the planet has little sulfur (<1.5 wt.% S). The external part of the Mercurian core is likely to be made up of a thin (<90 km) FeS layer.

  13. Record of complex scoria cone eruptive activity at Red Mountain, Arizona, USA, and implications for monogenetic mafic volcanoes

    Science.gov (United States)

    Riggs, N. R.; Duffield, W. A.

    2008-12-01

    Scoria cone eruptions are generally modeled as a simple succession from explosive eruption to form the cone to passive effusion of lava, generally from the base of the cone. Sector collapse of scoria cones, wherein parts of the cone are rafted on a lava flow, is increasingly recognized as common, but the reasons that a cone may not be rebuilt are poorly understood. Red Mountain volcano is a Pleistocene scoria cone in the San Francisco Volcanic Field of northern Arizona, USA. The cone lies along the trace of a major steeply dipping normal fault that originated during Proterozoic tectonism and was reactivated in Tertiary time. The earliest phase of eruption at Red Mountain was typical "Strombolian", forming a cone that was followed by or possibly synchronous with lava effusion, toward the west from the base of the cone. Rafting then ensued as the west side of the cone collapsed; approximately 15% of the cone is preserved in mounds as much as 30 m high. Rafting was extensive enough to remove most of the cone over the vent area, which effectively reduced the pressure cap on the magma conduit. Resultant low fountaining fed clastogenic lava flows and minor scoria fallback. Clastogenic flows traveled as far as 4 km and now form a cliff 30-40 m high at the edge of the lava platform. Although several possibilities explain the change in vent dynamics and eruptive style, we favor the interpretation that an increase in magma-rise rate caused collapse of the cone. The abrupt removal of 300 m of material over the vent removed a conduit "cork" and low fountaining began. Magma that had erupted effusively suddenly became explosive. This aspect of scoria cone rafting at Red Mountain is broadly similar to sector collapse followed by explosive eruption in larger systems. A steep-walled, 150-m-high amphitheatre on the northeast side of Red Mountain exposes weakly to strongly altered scoria cemented by calcite, iron, and zeolites. We suggest that vapor-phase alteration was responsible for sealing fine-grained ash beds in the cone, and a pressurized system developed. Residual heat from a dike that was emplaced as part of the magmatic activity provided heat that drove groundwater along the regional fault up into the cone. Eventually the overpressurized system exploded in a phreatic eruption that created the amphitheatre, which has subsequently been enlarged by water and wind erosion. The combined sequence of events at Red Mountain illustrates some of the complexities in monogenetic scoria cone eruptions that have received little attention to date.

  14. The Formation of Carbonate Minerals and the Mobility of Heavy Metals during Water-CO2-Mafic Rock Interactions

    DEFF Research Database (Denmark)

    Olsson, Jonas

    are consistent with values of controlled laboratory experiments from the literature for Ba, Cd, Co, Cu, Mg, Mn, Na, Ni, Sr and Zn. The calcium carbonates also scavenge other elements, including rare earth elements (REE) and the toxic metals As and Pb. This and the next study can be considered natural analogues...... for 74 elements. The effluent was alkaline and high release rates of mainly S, Na, Ca, Mg, F and Cl were observed during the first 10 minutes. After 12 hours, the most abundant element released was Si. Secondary phases of Al and Fe precipitated on the ash surfaces and these were suspected of scavenging...... to the carbonate precipitation in CarbFix project. In the third study, water and solid samples from two alkaline springs in Oman were examined. The elements detected in the spring waters in order of abundance were Na, Cl, Ca, Mg, SO4, K, Br, Si, F, B, Sr, Al, Fe, Mo, Zn, Ni, Cu, Mn, V, Ba, Cr, Co, Ti, Hg and Pb...

  15. Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury

    Science.gov (United States)

    Namur, Olivier; Charlier, Bernard; Holtz, Francois; Cartier, Camille; McCammon, Catherine

    2016-08-01

    Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200-1750 °C), low- to high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S2- and forms complexes with Fe2+, Mg2+ and Ca2+. The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases with increasing reducing conditions (from 10 wt.% S at IW-8) and with increasing temperature. Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. We developed an empirical parameterization to predict SCSS in Mercurian magmas as a function of oxygen fugacity (fO2), temperature, pressure and silicate melt composition. SCSS being not strictly a redox reaction, our expression is fully valid for magmatic systems containing a metal phase. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. We make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and/or that the mantle contains a minor metal phase and combine our parameterization of SCSS with chemical data from MESSENGER to constrain the oxygen fugacity of Mercury's interior to IW- 5.4 ± 0.4. We also calculate that the mantle of Mercury contains 7-11 wt.% S and that the metallic core of the planet has little sulfur (core is likely to be made up of a thin (<90 km) FeS layer.

  16. A model of sulphur solubility for hydrous mafic melts: application to the determination of magmatic fluid compositions of Italian volcanoes

    Directory of Open Access Journals (Sweden)

    M. Pichavant

    2005-06-01

    Full Text Available We present an empirical model of sulphur solubility that allows us to calculate f S2 if P, T, fO2 and the melt composition, including H2O and S, are known. The model is calibrated against three main experimental data bases consisting in both dry and hydrous silicate melts. Its prime goal is to calculate the f S2 of hydrous basalts that currently lack experimental constraints of their sulphur solubility behaviour. Application of the model to Stromboli, Vesuvius, Vulcano and Etna eruptive products shows that the primitive magmas found at these volcanoes record f S2 in the range 0.1-1 bar. In contrast, at all volcanoes the magmatic evolution is marked by dramatic variations in f S2 that spreads over up to 9 orders of magnitude. The f S2 can either increase during differentiation or decrease during decompression to shallow reservoirs, and seems to be related to closed versus open conduit conditions, respectively. The calculated f S2 shows that the Italian magmas are undersaturated in a FeS melt, except during closed conduit conditions, in which case differentiation may eventually reach conditions of sulphide melt saturation. The knowledge of f S2, fO2 and fH2O allows us to calculate the fluid phase composition coexisting with magmas at depth in the C-O-H-S system. Calculated fluids show a wide range in composition, with CO2 mole fractions of up to 0.97. Except at shallow levels, the fluid phase is generally dominated by CO2 and H2O species, the mole fractions of SO2 and H2S rarely exceeding 0.05 each. The comparison between calculated fluid compositions and volcanic gases shows that such an approach should provide constraints on both the depth and mode of degassing, as well as on the amount of free fluid in magma reservoirs. Under the assumption of a single step separation of the gas phase in a closed-system condition, the application to Stromboli and Etna suggests that the main reservoirs feeding the eruptions and persistent volcanic plumes at these volcanoes might contain as much as 5 wt% of a free fluid phase. Consideration of the magma budget needed to balance the amounts of volatiles emitted in the light of these results shows that the amount of nonerupted magma could be overestimated by as much as one order of magnitude.

  17. Tectono-magmatic evolution of the younger Gardar southern rift, South Greenland

    Directory of Open Access Journals (Sweden)

    Brian G.J. Upton

    2013-11-01

    Full Text Available The 1300–1140 Ma Gardar period in South Greenland involved continental rifting, sedimentation and alkaline magmatism. The latest magmatism was located along two parallel rift zones, Isortoq–Nunarsuit in the north and the Tuttutooq–Ilimmaasaq–Narsarsuaq zone in the south addressed here. The intrusive rocks crystallised at a depth of <4 km and are essentially undisturbed by later events. Magmatism in the southern zone began with the emplacement of two giant, ≤800 m wide dykes and involved intrusion of transitional olivine basaltic, high Al/Ca magmas crystallising to troctolitic gabbros. These relatively reduced magmas evolved through marked iron enrichment to alkaline salic differentiates. In the Older giant dyke complex, undersaturated augite syenites grade into sodalite foyaite. The larger, c. 1163 Ma Younger giant dyke complex (YGDC mainly consists of structureless troctolite with localised developments of layered cumulates. A layered pluton (Klokkenis considered to be coeval and presumably comagmatic with the YGDC. At the unconformitybetween the Ketilidian basement and Gardar rift deposits, the YGDC expanded into a gabbroic lopolith. Its magma may represent a sample from a great, underplated mafic magma reservoir, parental to all the salic alkaline rocks in the southern rift. The bulk of these are silica undersaturated; oversaturated differentiates are probably products of combined fractional crystallisation and crustalassimilation.A major dyke swarm 1–15 km broad was intruded during declining crustal extension, with decreasing dyke widths and increasing differentiation over time. Intersection of the dyke swarm and E–W-trending sinistral faults controlled the emplacement of at least three central complexes (Narssaq, South Qôroq and early Igdlerfigssalik. Three post-extensional complexes (Tugtutôq,Ilímaussaq and late Igdlerfigssalik along the former rift mark the end of magmatism at c. 1140 Ma. The latter two complexes have

  18. Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits

    Science.gov (United States)

    Patten, Clifford G. C.; Pitcairn, Iain K.; Teagle, Damon A. H.; Harris, Michelle

    2016-02-01

    Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by -46 ± 12, -27 ± 5, -2.5 ± 0.5, -27 ± 6, -8.4 ± 0.7, -9.6 ± 1.6, -7.9 ± 0.5 and -44 ± 6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.

  19. The Voisey's Bay Ni-Cu-Co Sulfide Deposit,Labrador,Canada:Emplacement of Silicate and Sulfide-Laden Magmas into Spaces Created within a Structural Corridor%The Voisey's Bay Ni-Cu-Co Sulfide Deposit,Labrador, Canada: Emplacement of Silicate and Sulfide-Laden Magmas into Spaces Created within a Structural Corridor

    Institute of Scientific and Technical Information of China (English)

    Peter C.Lightfoot; Dawn Evans-Lamswood; Robert Wheeler

    2012-01-01

    Abstract:The Voisey's Bay Ni-Cu-Co sulfide deposit is hosted in a 1.34 Ga mafic intrusion that is part of the Nain Plutonic Suite in Labrador,Canada.The Ni-Cu-Co sulfide mineralization is associated with magmatic breccias that are typically contained in weakly mineralized olivine gabbros,troctolites and ferrogabbros,but also occur as veins in adjacent paragneiss.The mineralization is associated with a dyke-like body which is termed the feeder dyke.This dyke connects the shallow differentiated Eastern Deeps chamber in the east to a deeper intrusion in the west termed the Western Deeps Intrusion.Where the conduit is connected to the Eastern Deeps Intrusion,the Eastern Deeps Deposit is developed at the entry line of the dyke along the steep north wall of the Eastern Deeps Intrusion.The Eastern Deeps Deposit is surrounded by a halo of moderately to weakly mineralized Variable-Textured Troctolite (VTT) that reaches a maximum thickness above the ENE-WSW axis of the Eastern Deeps Deposit.At depth to the west,the conduit is adjacent to the south side of the Western Deeps Intrusion,where the dyke and intrusion contain disseminated magmatic sulfide mineralization.The Reid Brook Zone plunges to the east within the dyke,and both the dyke and adjacent paragneiss are mineralized.The Ovoid Deposit comprises a bowl-shaped body of massive sulfide where the dyke widens near to the present-day surface.It is not clear whether this deposit was developed as a widened-zone within the conduit or at the entry point into a chamber that is now lost to erosion.The massive sulfides and breccia sulfides of the Eastern Deeps are petrologically and chemically different when compared to the disseminated sulfides in the VTT; there is a marked break in Ni tenor (Ni content in 100% sulfide,abbreviated to [Ni] 100) and Ni/Co of sulfide between the two.The boundary of the sulfide types is often marked by strong sub-horizontal alignment of heavily digested and metamorphosed paragneiss fragments

  20. Platinum-group elements in the Eastern Deccan volcanic province and a comparison with platinum metals of the western Deccan

    Indian Academy of Sciences (India)

    James Crocket; Dalim Paul; Trisha Lala

    2013-08-01

    This study is the first detailed investigation of the platinum-group elements (PGE) at the eastern margin of the Deccan volcanic province of India. One of the PGE, osmium, is not included largely because of analytical problems. The study is focused on mafic volcanics and dykes from four areas including Amarkantak, Umaria, Shahdol and Chirimiri. The first two localities represent two lava piles of about 170 and 400 m thickness respectively. In Umaria, 16 flows have been demarcated based on petrography and field studies. The Shahdol samples are basal lava formations overlying Gondwana sediments (Carboniferous) and the Chirimiri samples are dykes. In this study, the western Deccan province is defined as the Western Ghats plus Kutch. On average, the PGE are ∼20% higher in Amarkantak than Umaria and the flows are ∼13% higher in PGE than the dykes. A Zr vs. Pd scattergram found a strong positive correlation for these two elements except for one Umaria sample which indicated severe Pd loss. A comparison of west and east parts of the Deccan volcanic province using primitive mantle normalization showed that higher values prevailed in the western province suite in the Ni-Ir-Ru-Pt region. In contrast, eastern province values dominated in the Pd-Au-Cu region at the ‘Cu’ end of the profiles. A strong dominance of Pd in the eastern Deccan was also of interest. A number of factors, for example, percentage partial melting of the source rock and the temperature and pressure of partial melting strongly influence the character of these profiles. The observed PGE profile characteristics probably result in part from a long distance of subsurface transport of Deccan magma from the western to eastern regions.

  1. Crystallization and emplacement of the Lac St-Jean anorthosite massif (Quebec, Canada)

    Science.gov (United States)

    Woussen, G.; Dimroth, E.; Corriveau, L.; Archer, P.

    1981-05-01

    The Lac St-Jean anorthosite massif underlies an area of over 20,000 km2 and has been emplaced into migmatitic gneisses of the central granulite terrain of the Grenville Province of the Canadian shield. Field data and petrography in an area straddling the anorthosite-gneiss contact, close to Chicoutimi (Quebec) permits an outline of its tecto-magmatic evolution. Depositional magmatic textures in the massif reveals that it crystallized from a magma in a relatively calm tectonic environment. The absence of fusion in pelitic gneisses at the contact proves that the crystallization did not take place at the level presently exposed. The parallelism of subvertical foliation in the enveloping gneisses and the anorthosite indicates that both were deformed together. It is suggested that the deformation results from a diapiric ascent of the anorthosite massif after its consolidation at depth. The depth of consolidation of the anorthosite is estimated at ˜ 25 30 km from subsolidus reaction between plagioclase and olivine. The diapiric ascent is further substantiated by the fact that three sets of mafic dykes of different ages, intrusive into the anorthosite, have a mineralogy which indicates successively decreasing P, T conditions of emplacement from granulite fades to amphibolite facies. An evolution of the basement gneisses and the anorthosite is proposed as a working hypothesis; it relies on the fact that metabasite dyke swarms in the basement gneisses represent a period of major crustal extension and could be used as a stratigraphic subdivision of the Grenville Province.

  2. Southward trench migration at ∼130-120 Ma caused accretion of the Neo-Tethyan forearc lithosphere in Tibetan ophiolites

    Science.gov (United States)

    Xiong, Qing; Griffin, William L.; Zheng, Jian-Ping; O'Reilly, Suzanne Y.; Pearson, Norman J.; Xu, Bo; Belousova, Elena A.

    2016-03-01

    The preservation of ultrahigh-pressure and super-reduced phases (diamond, moissanite, etc.) in the harzburgites and chromitites of the Yarlung Zangbo ophiolites (South Tibet, China) has major implications for mantle recycling and lithosphere evolution in the tectonic system related to the closing of the Neo-Tethyan Ocean. However, important aspects of the genesis of these enigmatic ophiolites and the related geodynamic evolution are still unclear. In the Zedang ophiolite of the eastern Yarlung Zangbo Suture, detailed mineral chemical data reveal that the harzburgite domain in the east [spinel Cr# (mole Cr3+/(Cr3+ + Al3+) = 0.62-0.33] is more depleted than the lherzolite domain in the west (spinel Cr# = 0.30-0.17) and shows much lower equilibration temperatures (by ∼250-150 °C) than the lherzolites. Clinopyroxene trace-element compositions indicate that the harzburgites underwent pervasive metasomatism after melt extraction, while the lherzolites did not. New zircon U-Pb ages show that the harzburgites were intruded by dolerite dykes with chilled margins at ∼130-128 Ma, consistent with the widespread mafic magmatism at ∼130-120 Ma in the Yarlung Zangbo ophiolites. Nd-Hf isotopic data indicate that the Zedang lherzolites subcreted the pre-emplaced harzburgites concurrently with the intrusion of the dolerite dykes into the harzburgites, and that the lherzolites and dolerites both were derived from upwelling asthenosphere with minor slab input. Available zircon geochronology and Hf-isotope data show that juvenile magmatism in the adjacent Gangdese Arc was almost completely interrupted from ∼130-120 Ma. We suggest that the extension of the overlying harzburgitic lithosphere, subcretion of lherzolites, intrusion of mafic dykes, and the waning of Gangdese-Arc magmatism all reflect a southward trench migration in the Neo-Tethyan subduction system from the Gangdese Arc to the oceanic forearc lithosphere. This magmatic relocation and tectonic linkage are inferred to

  3. Back-Arc Extension in the Southern Andes: A Review and Critical Reappraisal

    Science.gov (United States)

    Dalziel, I. W. D.

    1981-03-01

    The interpretation that the mafic 'rocas verdes' (green rocks) complex of the southern Andes represents part of the uplifted floor of a Late Jurassic to Early Cretaceous back-arc basin has proved particularly useful in understanding the geological evolution of the southern Andes, the north Scotia Ridge and the Antarctic Peninsula. Clear field evidence of the back-arc setting of the 'rocas verdes' gabbro-sheeted dyke - pillow lava ophiolitic assemblages has encouraged fruitful petrological and geochemical comparison with mid-ocean ridge and marginal basin basalts, other onshore ophiolite complexes, and Archaean greenstone belts. Uncertainty still surrounds estimates of the original width and depth of the basin, as well as the proportion of new mafic crust, compared with relict sialic crust, in the basin floor. These questions are unresolved, owing mainly to the considerable Lower Cretaceous turbiditic basin infill and the effects of mid-Cretaceous compressional deformation. While the field relations clearly indicate that the 'rocas verdes' basin is not an older piece of ocean floor 'trapped' behind a volcanic arc, it is not yet clear whether the basin is directly subduction-related or falls in the category of back-arc 'leaky transforms' like the proto-Gulf of California or apparent 'rip-off' features like the Andaman Sea.

  4. Unusual evolution of silica-under- and -oversaturated alkaline rocks in the Cenozoic Ambohimirahavavy Complex (Madagascar): Mineralogical and geochemical evidence

    Science.gov (United States)

    Estrade, Guillaume; Béziat, Didier; Salvi, Stefano; Tiepolo, Massimo; Paquette, Jean-Louis; Rakotovao, Soatsitohaina

    2014-10-01

    The almost unknown Ambohimirahavavy ring complex in the Cenozoic alkaline province of northwestern Madagascar has recently attracted considerable interest because of the discovery of important rare-metal mineralization. The complex consists of arc-shaped bodies made up of silica-under- and -oversaturated syenites and extremely evolved peralkaline granitic dykes, as well as several mafic to felsic volcanic units, including basalt, phonolite and trachyte, all of which have an alkaline affinity. Uranium-lead zircon ages of 24.2 ± 0.6 Ma and 23.5 ± 6.8 Ma have been obtained for nepheline syenites and peralkaline granitic dykes, respectively, which, together with field data and ages of neighboring complexes, support emplacement controlled by regional lithospheric structures, rather than an evolving hot spot. Whole-rock major and trace-element and Sr-Nd isotopic data for the mafic suite suggest that the parental melt of this complex was generated by low degrees of melting of a metasomatized mantle source with residual amphibole. Fractional crystallization of this alkali basaltic melt likely produced the silica-undersaturated suite. We propose that the silica-oversaturated suite evolved from the undersaturated melt after contamination of the latter by crustal material. Further evolution to peralkaline compositions in both suites is attributed mainly to plagioclase and alkali feldspar segregation. Nepheline and feldspar compositions, as well as considerations of mineral equilibria among mafic silicates and Fe-Ti oxide minerals indicate crystallization temperatures of 1000 to 700 °C and an oxygen fugacity of 0.4 to 0.8 log units below the fayalite-magnetite-quartz (FMQ) buffer at 1 kbar for the silica-undersaturated melt, and temperatures of 860 to 570 °C and an oxygen fugacity of 1.5 to 3.8 log units below FMQ for the oversaturated syenitic melt. The undersaturated melt evolved towards a more peralkaline composition. Crystallization of arfvedsonite plus aegirine

  5. Mineralogical and geochemical characteristics of zircon from diorite porphyry dyke in Sergozerskoe gold occurrence (the Strel'ninsky greenstone belt, Kola region

    Directory of Open Access Journals (Sweden)

    Kudryashov N. M.

    2016-03-01

    Full Text Available Mineralogical and geochemical investigation of zircon from diorite porphyry from Sergozerskoe occurrence has been carried out. Study of morphology and inner structure of zircon crystals in back scattered electron rays as well as assaying for content and distribution of Rare Earth Elements in mineral grains have given important information about conditions of crystallization and following metasomatic alteration of zircon. Zircon characteristics show that it crystallized in a melt, enriched in fluid phase. Fluid influence lasted after zircon crystallization, this reflected in uneven composition of the mineral and in configuration of REE spectra, typical for metasomatic zircon. Similar zircon characteristics have been noted in zircons from other gold occurrences in greenstone belts in the Kola region

  6. Thermal history from Pocos de Caldas alkaline massif, SP/MG , Brazil and dyke rich margins using apatite fission track analysis

    International Nuclear Information System (INIS)

    The South American Platform in southeastern Brazil records a long history of tectonic magmatic and uplift events, which resulted from the opening of the South Atlantic Ocean, Cretaceous reactivation and epirogeneic processes. Specific manifestations include the basic magmatism of the Serra Geral Formation of the Parana Basin and alkaline magmatism of Pocos de Caldas - Cabo Frio Lineament, as well as the uplift of the Serra da Mantiqueira and Serra do Mar mountain ranges. Thermo tectonic and geochronological studies using the K-Ar method and apatite fission track analysis in samples of the Pocos de Caldas alkaline massif show an initial evolution beginning 89 Ma related to a tectonic uplift, interpreted as related to the intrusion's doming. This was followed by an important episode of rapid cooling related to the formation of the massif. At the same time, the mountains that surround the massif record heating events in response to the alkaline intrusion, between 70 and 50 Ma. Periods of slow uplift, probably related to the South American Erosion Cycle (between 50 and 30 Ma) and Velhas Erosion Cycle (from 25 Ma), indicate a strong manifestation of denudation in this area. (author)

  7. Combined Paleomagnetic And Petromagnetic Study Of Oligocene Dyke Swarms From Tecalitlan Area: Implications For Relative Motion Of Jalisco And Michoacan Blocks

    Science.gov (United States)

    Aguilar Reyes, B.; Rosas Elguera, J.; Gogichaishvili, A.; Alva Valdivia, L.

    2009-05-01

    Results of detailed paleomagnetic studies from Tecalitlan area are reported. Sexteen sites (about 150 oriented samples) were collected including one Ar-Ar dated ignimbrite. Rock-magnetic experiments permitted identification of the magnetic carriers and assessment of the paleomagnetic stability. Continuous susceptibility measurements vs temperature, in most cases yield reasonably reversible curves with Curie points close to that of magnetite. Judging from the ratios of hysteresis parameters, all samples appear to fall in the pseudo- single domain grain-size region, probably indicating a mixture of multi-domain and a significant amount of single-domain grains. Reliable paleomagnetic directions were obtained for 14 sites. The mean inclination is in reasonably good agreement with the expected value, as derived from reference poles for the stable North America. Declination is significantly different from that expected which may suggests a counterclockwise tectonic rotation of 19°.

  8. The preliminary unit price analysis of the vertical seepage control for the dyke%垂直防渗单价初析

    Institute of Scientific and Technical Information of China (English)

    杨国顺; 刘伟; 党爱琴

    2002-01-01

    垂直防渗作为一种近年来兴起的新方法、新工艺,它广泛应用于水利工程基础防渗中,其特点是防渗效果好、造价低.本文介绍了垂直防渗工程施工工艺,测算了垂直防渗中人工、材料、机械消耗,并作垂直防渗工程单价分析,与其他防渗方法作了对比分析,为合理控制防渗工程造价提供了科学依据.

  9. Geochemistry of sapphirine-apatite-calcite-bearing gabbroic dykes from the Finero Phlogopite Peridotite (Ivrea-Verbano Zone): evidence for multistage interaction with the ambient peridotite

    Science.gov (United States)

    Tommaso, Giovanardi; Alberto, Zanetti; Maurizio, Mazzucchelli; Tomoaki, Morishita; Antonio, Langone

    2016-04-01

    The Finero Phlogopite-Peridotite (FPP) is a mantle unit outcropping in the northernmost tip of the Ivrea-Verbano Zone (IVZ, Southern Alps). It shows a virtually complete recrystallization due to pervasive to channelled melt migration. The pervasive metasomatism formed a main lithologic association constituted by phlogopite harzburgites associated to phlogopite pyroxenites (mainly olivine-websterites, websterites and orthopyroxenites). These lithologies are also rich in amphibole and do not show significant chemical gradients among them (Zanetti et al., 1999). The channelled migration stages formed dunite bodies, which sometimes contain stratiform chromitites and, more rarely, pyroxenite layers similar to those associated to phlogopite harzburgite. The FPP also shows a discrete number of other, subordinate rock-types, which are characterised by the presence of apatite usually associated to carbonates (i.e. calcite or dolomite) and exhibit marked modal and chemical gradients with respect to the host phlogopite harzburgite. Examples of these lithologies are apatite-dolomite-bearing wehrlites and harzburgites (e.g. Zanetti et al. 1999; Morishita et al., 2008), apatite-calcite zircon-syenites and hornblendites. Ar-Ar amphibole analysis and U-Pb zircon and apatite data return Triassic ages for these rocks, which have been considered to document the time of melt/fluid injection. Notwithstanding the apparent mineralogical and chemical differences with the main lithologic sequences, apatite-carbonates-bearing rocks have been frequently interpreted as cogenetic to phlogopite harzburgites. To debate the petrogenesis of these rocks, a detailed field, petrological and geochemical investigation has been carried out on a swarm of apatite-calcite-bearing gabbroic veins that randomly cut the main lithologic association. Preliminary investigation evidenced as these veins show complex metasomatic haloes and a symmetric internal layering, characterised by crystallisation of magmatic sapphirine (Giovanardi et al., 2013). The mineral assemblage of the veins is dominated by titanian pargasite towards the host peridotite and by plagioclase at the vein centre. The veins also present phlogopite and spinel. Field and petrographic evidence, major and trace element data and the O isotopic composition of such gabbroic veins indicate that they formed at shallow mantle conditions by multistage fractional crystallisation of a migrating melt unrelated to those forming phlogopite harzburgites. Besides, local strong enrichments in LILE, LREE and 18O in vein minerals confirm that such melt was deeply modified by interaction with the host phlogopite peridotite. The genetic relationships with other intrusive events recorded by the FPP and the associated crustal sequence will be addressed with the aim of placing new constraints on the petrologic and geodynamic evolution of the IVZ. Giovanardi, T., Morishita, T., Zanetti, A., Mazzucchelli, M., Vannucci, R. (2013). Igneous sapphirine as a product of melt-peridotite interactions in the Finero Phlogopite-Peridotite Massif, Western Italian Alps. European Journal of Mineralogy 25, 17-31. Morishita, T., Hattori, K.H., Terada, K., Matsumoto, T., Yamamoto, K., Takebe, M., Ishida, Y., Tamura, A., Arai, S. (2008). Geochemistry of apatite-rich layers in the Finero phlogopite-peridotite massif (Italian Western Alps) and ion microprobe dating of apatite. Chemical Geology 251, 99-111. Zanetti, A., Mazzucchelli, M., Rivalenti, G., Vannucci, R. (1999). The Finero phlogopite-peridotite massif: an example of subduction-related metasomatism. Contributions to Mineralogy and Petrology 134, 107-122.

  10. An integrated approach (remote sensing, geophysics, field) to assess the structural control of groundwater flow in Wadi Feiran basement complex, Sinai, Egypt

    Science.gov (United States)

    Mohamed, L.; Sultan, M.; Ahmed, M.; Zaki, A.

    2013-12-01

    The groundwater flow and potentiality for groundwater accumulation in the fractured basement rocks and the overlaying alluvial deposits were examined in Wadi Feiran basin using remote sensing (Landsat ETM, Ikonos, and Envisat, TRMM, and SIR-C radar images), field (well location, depth to water table), and geophysical (Very Low Frequency [VLF], magnetic) datasets. Our approach encompassed the following steps: (1) head data from 52 wells was utilized to build an approximate potentiometric surface map for the basin; (2) Landsat ETM, 3D, hill shade, Ikonos and SIR-C radar images were used to delineate structures in the study area including faults and dikes; (3) major precipitation events were identified from three-hourly TRMM data; and (4) false color composite images were generated from pairs of multi-temporal Envisat images acquired before and after a precipitation event (17th and 18th of January 2010) to identify structures (faults and dykes) that show an increase in moisture content and radar reflectivity following precipitation events and persisting for periods of days to months. Examination of the radar images revealed: (1) a network of highly reflective interconnected structures and channels (wadis) that are here interpreted to indicate preferred groundwater flow direction in the study area; and (2) many of the identified highly persistent reflective structures were found to be sub-parallel (hereafter referred to as low angle) to groundwater flow directions indicating that they are exceptionally conducive to groundwater flow. We suspect that groundwater flow occurs along low angle faults and dykes within the fault damaged zones and the weathered borders of mafic dykes. These suggestions are further corroborated by: (1) VLF results that showed significant dip angles (up to 60%) indicative of presence of shallow sub-vertical, sheet-like conductors across the identified low angle faults and dykes, (2) the presence of groundwater accumulation down gradient, along

  11. What Happened in the Trans-North China Orogen in the Period 2560-1850 Ma?

    Institute of Scientific and Technical Information of China (English)

    Guochun ZHAO; LIU Shuwen; Min SUN; LI Sanzhong; Simon WILDE; Xiaoping XIA; Jian ZHANG; Yanhong HE

    2006-01-01

    The Trans-North China Orogen (TNCO) was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton (NCC). Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greenstone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages.Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic (TTG) magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, ~2250 Ma 2110-21760 Ma and ~2050 Ma granites in the orogen.Contemporary volcano-sedimentary rocks developed in the back-arc or intra-arc basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge,leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and

  12. An eastern Mediterranean analogue for the Late Palaeozoic evolution of the Pangaean suture zone in SW Iberia

    Science.gov (United States)

    Brendan Murphy, J.; Braid, James A.; Quesada, Cecilio; Dahn, Dustin; Gladney, Evan; Dupuis, Nicolle

    2014-05-01

    It has long been recognized that the Late Paleozoic evolution of SW Iberia preserves a record of collision and suturing between Laurussia (South Portuguese Zone) and Gondwana (Ossa Morena Zone), which is one of the key events in the development of the Variscan orogen and the amalgamation of Pangea. The suture zone (Pulo do Lobo Zone) is classically considered to be an accretionary complex and is characterized by an assemblage of greenschist facies, polydeformed and imbricated meta-sedimentary rocks, mélanges, and mafic complexes. However recent work has shown some of the metasedimentary rocks and mélange were likely derived from neither the upper or lower plates. Mafic complexes in the mélange have NMORB compositions, highly depleted Sm-Nd isotopic signatures and geochronological data imply that their protoliths probably formed between ca. 350 and 340 Ma. Geochronological data also imply that components of the mafic mélange contain a paucity of ancient continental detritus. The Pulo do Lobo Zone was also intruded by ca. 360-310 Ma composite plutons and related dykes ranging from gabbro to granite in composition. The oldest phases of these intrusions are syn- to late-tectonic with respect to the deformation. Taken together these recent observations suggest that much of the tectonic evolution of the Pulo do Lobo suture zone post-dates the onset of collisional tectonics elsewhere in the Variscan orogen, and is broadly analogous to the complex Cenozoic tectonic evolution of the eastern Mediterranean oceanic tracts relative to the ongoing collision between the African, Eurasian and Arabian plates.

  13. Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

    Science.gov (United States)

    José Fernández, Francisco; Llana-Fúnez, Sergio; Valverde-Vaquero, Pablo; Marcos, Alberto; Castiñeiras, Pedro

    2016-04-01

    High-grade, highly deformed gneisses crop out continuously along the Masanteo peninsula and constitute the upper part of the lower crustal section in the Cabo Ortegal nappe (NW Spain). The rock sequence formed by migmatitic quartzo-feldspathic (qz-fsp) gneisses and mafic rocks records the early Ordovician (ca. 480-488 Ma) injection of felsic dioritic/granodioritic dykes at the base of the qz-fsp gneisses, and Devonian eclogitization (ca. 390.4 ± 1.2 Ma), prior to its exhumation. A SE-vergent ductile thrust constitutes the base of quartzo-feldspathic gneissic unit, incorporating mafic eclogite blocks within migmatitic gneisses. A NW-vergent detachment displaced metasedimentary qz-fsp gneisses over the migmatites. A difference in metamorphic pressure of ca. 0.5 GPa is estimated between both gneissic units. The tectono-metamorphic relationships of the basal ductile thrust and the normal detachment bounding the top of the migmatites indicate that both discrete mechanical contacts were active before the recumbent folding affecting the sequence of gneisses during their final emplacement. The progressive tectonic exhumation from eclogite to greenschist facies conditions occurred over ca. 10 Ma and involved bulk thinning of the high-grade rock sequence in the high pressure and high temperature (HP-HT) Cabo Ortegal nappe. The necessary strain was accommodated by the development of a widespread main foliation, dominated by flattening, that subsequently localized to a network of anastomosing shear bands that evolved to planar shear zones. Qz-fsp gneisses and neighbouring mafic granulites were exhumed at > 3 mm yr-1, and the exhumation path involved a cooling of ˜ 20 °C/100 MPa, These figures are comparable to currently active subduction zones, although exhumation P-T trajectory and ascent rates are at the hotter and slower end in comparison with currently active similar settings, suggesting an extremely ductile deformation environment during the exhumation of qz

  14. New paleomagnetic data from Bornholm granitoids testing whether the East-European Craton rotated during the 1.50-1.45 Ga Danopolonian orogeny

    Science.gov (United States)

    Lubnina, N.; Bogdanova, S.; Cecys, A.

    2009-04-01

    According to the palaeogeographic reconstructions, the East-European Craton (EEC) was part of the Palaeo- to Mesoproterozoic supercontinent Nuna / Columbia (Hoffman, 1997; Rogers and Santosh, 2002). Particularly important was the period between 1.5 and 1.3 Ga, when incipient break-up of this supercontinent occurred (Condie, 2002) but the EEC ("Baltica") still remained in close connection with other continental blocks. During the entire Mesoproterozoic, however, the EEC featured different geodynamic regimes in its presently western and eastern parts. In the west, these were convergent, while rifting prevailed in the east (Bogdanova et al., 2008). Previously, paleomagnetic studies of the Mesoproterozoic Ladoga Lake mafic rocks in NE Russia and the Dalarna mafic dykes in Sweden have disclosed a regular trend from the older Dalarna dykes to the younger dolerites of Lake Ladoga, suggesting an anticlockwise rotation of about 20 degrees. That rotation could either have affected the entire EEC as a result of the Danopolonian orogeny at ca. 1.50-1.45 Ga or have been associated with local block-displacement events in the Pasha-Ladoga graben (Lubnina et al., 2005, 2007). In the present study, we have tested these alternative possibilities by carrying out new paleomagnetic studies of Mesoproterozoic granitoids from the Danish island of Bornholm in the South Baltic Sea, which is a key area of the Danopolonian orogeny. On SW Bornholm, the 1.46 Ga Ronne granodiorites, which are cut by NNW trending thin dolerite dykes have been sampled in the Klippelokke quarry. Remanence measurements were performed using a 2G cryogenic magnetometer at the Palaeomagnetic Laboratory of the Department of Geology, Lund University, Sweden. Conventional progressive thermal or alternating field (AF) demagnetizations were applied to all specimens. During the stepwise thermal and AF demagnetization experiments, two components of NRM were isolated in the majority of the granitoid specimens. The low

  15. Long hard road from Nuna to Rodinia

    Science.gov (United States)

    Pisarevsky, Sergei

    2014-05-01

    The popular concept of supercontinental cycles suggests the existence of at least two Precambrian supercontinents, referred to as Nuna (or Columbia) and Rodinia. The times of their assembly and breakup are debated, as are their constituents and configurations. The recent compilation of paleomagnetic data supported by the geological evidence suggests that Nuna have broken up at ca. 1450-1380 Ma by separation of the Australia-Mawson continent from western Laurentia. The recent robust paleomagnetic pole from 1210 Ma mafic dykes in Western Australia provides an additional evidence of wide separation of these continents by the time of the dykes' emplacement. On the other hand, there is the evidence that Laurentia and Baltica have been rigidly connected with present Scandinavia facing East Greenland until after 1270 Ma, when they broke up. Baltica then moved c.1000 km south and rotated clockwise 95° with respect to Laurentia by 1000 Ma and two continents recombined again with the Scandinavian margin of Baltica facing Scottish terranes of the Laurentian affinity, Rockall Bank and southeast Greenland. However, the published model of the simple fan-like opening of the Asgard Sea Between Laurentia and Baltica is somewhat hampered by the recent 1120 Ma paleomagnetic pole from Finland, which suggests a more complicated drift of Baltica with respect to Laurentia. There are also reasons to suggest that a large part of Nuna, which included Laurentia and Siberia has been incorporated into Rodinia after 1000 Ma. The c. 1300-1000 Ma Apparent Polar Wander Paths for Laurentia, Baltica, Australia, Amazonia and India are significantly different in their lengths and shapes suggesting relative movements of these continents with respect to each other. There is still not enough reliable published late Mesoproterozoic - early Neoproterozoic paleomagnetic data to make the unequivocal paleogeographic reconstructions for this time interval. However, it is unlikely that a large supercontinent

  16. The Tandilia System of Argentina as a southern extension of the Río de la Plata craton: an overview

    Science.gov (United States)

    Cingolani, Carlos A.

    2011-04-01

    The southernmost outcrops of the Río de la Plata cratonic region are exposed in the Tandilia System in eastern Argentina. The geological evolution comprises mainly an igneous-metamorphic Paleoproterozoic basement named Buenos Aires Complex, which is covered by Neoproterozoic to Early Paleozoic sedimentary units which display subhorizontal bedding. The basement of calc-alkaline signature consists mainly of granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks, and granitoid plutons. Subordinate rock-types include schists, marbles, and dykes of acid and mafic composition. Tandilia was recognized as an important shear belt district with mylonite rocks derived mainly from granitoids. The tectonic scenario seems related to juvenile accretion event (2.25-2.12 Ga) along an active continental margin, followed by continental collision (2.1-2.08 Ga) after U-Pb zircon data. The collisional tectonic setting caused thrusting and transcurrent faulting favouring the anatexis of the crustal rocks. The tholeiitic dykes constrain the time of crustal extension associated with the last stages of the belt evolution. The basement was preserved from younger orogenies such as those of the Brasiliano cycle. After a long paleoweathering process, the Sierras Bayas Group (c. 185 m thick) represents a record of the first Neoproterozoic sedimentary unit (siliciclastic, dolostones, shales, limestones), superposed by Cerro Negro Formation (c. 150-400 m thick, siliciclastics) assigned to Upper Neoproterozoic age. The final sedimentary transgression during Early Paleozoic was the Balcarce Formation (c. 90-450 m thick) deposited over all the mentioned Precambrian units. Based on all the geological background, a tectonic evolution is offered.

  17. The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar

    Science.gov (United States)

    Cucciniello, C.; Tucker, R. D.; Jourdan, F.; Melluso, L.; Morra, V.

    2016-04-01

    The Ampasindava alkaline province consists of a series of circular and elliptical intrusions, lava flows, dyke swarms and plugs of Cenozoic age emplaced into the Mesozoic-Cenozoic sedimentary rocks of the Antsiranana basin (NW Madagascar) and above the crystalline basement. The magmatism in the Ampasindava region is linked to a NW-SE trending extensional tectonic setting. New 40Ar/39Ar age determinations on feldspar separate of alkali granites and basaltic dykes yielded ages of 18.01 ± 0.36 Ma and 26 ± 7 Ma, respectively. Alkali basalts and basanites, nepheline syenites and phonolites, and silica saturated-to-oversaturated syenites, trachytes, granites and rhyolites are the main outcropping lithologies. These rocks have sodic affinity. The felsic rocks are dominant, and range from peraluminous to peralkaline. The mantle-normalized incompatible element patterns of the mafic lavas match those of Na-alkaline lavas in within-plate rift settings. The patterns are identical in shape and absolute concentrations to those of the Bobaomby (Cap d'Ambre) and Massif d'Ambre primitive volcanic rocks. These geochemical features are broadly compatible with variable degrees of partial melting of incompatible element-enriched mantle sources. The mineralogical and geochemical variations are consistent with fractional crystallization processes involving removal of olivine, feldspar, clinopyroxene, amphibole, Fe-Ti oxides and apatite. Removal of small amount of titanite explains the concave upward lanthanide pattern in the evolved nepheline syenites and phonolites, which are additionally rich in exotic silicates typical of agpaitic magmas (eudialyte, F-disilicates).

  18. Origin of the Rubian carbonate-hosted magnesite deposit, Galicia, NW Spain: mineralogical, REE, fluid inclusion and isotope evidence

    Science.gov (United States)

    Kilias, Stephanos P.; Pozo, Manuel; Bustillo, Manuel; Stamatakis, Michael G.; Calvo, José P.

    2006-10-01

    The Rubian magnesite deposit (West Asturian—Leonese Zone, Iberian Variscan belt) is hosted by a 100-m-thick folded and metamorphosed Lower Cambrian carbonate/siliciclastic metasedimentary sequence—the Cándana Limestone Formation. It comprises upper (20-m thickness) and lower (17-m thickness) lens-shaped ore bodies separated by 55 m of slates and micaceous schists. The main (lower) magnesite ore body comprises a package of magnesite beds with dolomite-rich intercalations, sandwiched between slates and micaceous schists. In the upper ore body, the magnesite beds are thinner (centimetre scale mainly) and occur between slate beds. Mafic dolerite dykes intrude the mineralisation. The mineralisation passes eastwards into sequence of bedded dolostone (Buxan) and laminated to banded calcitic marble (Mao). These show significant Variscan extensional shearing or fold-related deformation, whereas neither Rubian dolomite nor magnesite show evidence of tectonic disturbance. This suggests that the dolomitisation and magnesite formation postdate the main Variscan deformation. In addition, the morphology of magnesite crystals and primary fluid inclusions indicate that magnesite is a neoformed hydrothermal mineral. Magnesite contains irregularly distributed dolomite inclusions (modified basinal brines that have reacted and equilibrated with intercalated siliciclastic rocks. Magnesite formation is genetically linked to regional hydrothermal dolomitisation associated with lithospheric delamination, late-Variscan high heat flow and extensional tectonics in the NW Iberian Belt. A comparison with genetic models for the Puebla de Lillo talc deposits suggests that the formation of hydrothermal replacive magnesite at Rubian resulted from a metasomatic column with magnesite forming at higher fluid/rock ratios than dolomite. In this study, magnesite generation took place via the local reaction of hydrothermal dolostone with the same hydrothermal fluids in very high permeability zones at

  19. Petrological and geochemical characteristics of Paleoproterozoic ultramafic lamprophyres and carbonatites from the Chitrangi region, Mahakoshal supracrustal belt, central India

    Indian Academy of Sciences (India)

    Rajesh K Srivastava

    2013-06-01

    A number of ENE–WSW trending Paleoproterozoic dykes and plugs of mafic, ultramafic, alkaline and carbonatite rocks intrude Mahakoshal supracrustal belt (MSB), which is a part of the Central Indian Tectonic Zone (CITZ). Best exposures of these intrusions are found in the eastern parts of the MSB, particularly in and around Chitrangi area. Many of these intrusions have greenschist facies mineral composition and show sharp contact with supracrustal rocks. However, igneous textures, such as porphyritic/glomeroporphyritic, are still preserved in the form of partly pseudomorphed olivines, phlogopites and pyroxenes. Striking feature observed in some ultramafic samples is the presence of melanite garnet and rounded or elliptical carbonate ocelli. The petrographic characteristics suggest occurrence of carbonate-rich ultramafic lamprophyres; close to aillikite composition. Coarse-grained carbonatites show hypidiomorphic texture and mostly composed of calcite with appreciable amount of silicate minerals like clinopyroxene, phlogopite and olivine (often pseudomorphed by calcite, amphibole and chlorite). It is difficult to establish any direct genetic relationship between carbonatite and ultramafic lamprophyre samples on the basis of their chemistry; they were likely derived from distinct parental melts. High Mg#(up to ∼78), and high Ni and Cr contents (up to ∼1700 and ∼1100, respectively) and low HREE concentration in few ultramafic lamprophyre samples apparently suggest their derivation from a near-primary mantle-derived melts originated at great depths. Geochemistry and presence of carbonate ocellae in ultramafic lamprophyre samples suggest genesis of these silicate rocks and associated carbonatites through liquid immiscibility, however possibility of their derivation through vein-plus-wall-rock melting model cannot be ignored. A multi-stage veined mantle melting model is suitable in the latter case. It is suggested that early stages of rifting in the Mahakoshal

  20. Internal architecture and Fe-Ti-V oxide ore genesis in a Variscan synorogenic layered mafic intrusion, the Beja Layered Gabbroic Sequence (Portugal)

    Science.gov (United States)

    Jesus, Ana Patrícia; Mateus, António; Munhá, José Manuel; Tassinari, Colombo

    2014-03-01

    The Beja Layered Gabbroic Sequence (LGS) intruded the SW border of the Ossa Morena Zone at ca. 350 Ma during the early stages of the Variscan oblique continental collision in Iberia. It represents an exceptional case-study for the petrogenesis and metallogenesis of the rare class of synorogenic layered intrusions.

  1. Assessment of metallic mineral resources in the Humboldt River Basin, Northern Nevada, with a section on Platinum-Group-Element (PGE) Potential of the Humboldt Mafic Complex

    Science.gov (United States)

    Wallace, Alan R.; Ludington, Steve; Mihalasky, Mark J.; Peters, Stephen G.; Theodore, Ted G.; Ponce, David A.; John, David A.; and Berger, Byron R.; Zientek, Michael L.; Sidder, Gary B.; Zierenberg, Robert A.

    2004-01-01

    The Humboldt River Basin is an arid to semiarid, internally drained basin that covers approximately 43,000 km2 in northern Nevada. The basin contains a wide variety of metallic and nonmetallic mineral deposits and occurrences, and, at various times, the area has been one of the Nation's leading or important producers of gold, silver, copper, mercury, and tungsten. Nevada currently (2003) is the third largest producer of gold in the world and the largest producer of silver in the United States. Current exploration for additional mineral deposits focuses on many areas in northern Nevada, including the Humboldt River Basin.

  2. Magma dynamics at the base of an evolving mafic magma chamber: Incompatible element evidence from the Partridge River intrusion, Duluth Complex, Minnesota, USA

    Science.gov (United States)

    Chalokwu, Christopher I.; Ariskin, Alexei A.; Koptev-Dvornikov, Evgeny V.

    1996-12-01

    A characteristic feature of the Partridge River intrusion of the Keweenawan Duluth Complex is the approximately fivefold to ninefold increase in the concentrations of incompatible elements in the lower zone compared with cumulates stratigraphically higher. The concentrations of incompatible elements decrease from the lower zone upward to steady state values, which is ascribed to variations in the proportions of trapped liquid rather than variable degrees of fractional crystallization of a single parental magma. The calculated average composition of trapped liquid using our algorithm is similar to typical Keweenawan low-alumina, high Tisbnd P basalts associated with the Duluth Complex but is different from the leading edge ferrodioritic liquid quenched in the chilled margin of the intrusion. This difference suggests that the chilled margin does not represent the original (parental) magma composition from which the whole intrusion solidified, and that the enrichment of incompatible elements may be related to the local flotation of magmatic suspensions. To test the latter hypothesis numerically, we have used heat-mass transfer models, assuming a sheet-like magma chamber, to calculate the parameters of the model that best reproduce the observed distribution of incompatible elements in a mush zone at the base of the Partridge River intrusion. The results indicate that a mush zone enriched in the incompatible elements is produced if the velocity of movement of the lower solidification front into the magma body was less than the floating velocity of the bulk crystal mush. The dynamic parameters that best reproduce the observed distribution of incompatible elements include a magma emplacement pressure of 2 kbar, critical crystallinities of 50-68% in the mush zone from which the liquid is being expelled, and an emplacement temperature of ˜ 1160°C for the initial magma.

  3. Integrated Paleomagnetism and U-Pb Geochronology of Mafic Dikes of the Eastern Anabar Shield Region, Siberia: Implications for Mesoproterozoic Paleolatitude of Siberia and Comparison with Laurentia.

    Science.gov (United States)

    Ernst; Buchan; Hamilton; Okrugin; Tomshin

    2000-07-01

    This article reports the first joint paleomagnetic and U-Pb geochronologic study of Precambrian diabase dikes in the Anabar Shield and adjacent Riphean cover of Siberia. It was undertaken to allow comparison with similar published studies in Laurentia and to test Proterozoic reconstructions of Siberia and Laurentia. An east-trending Kuonamka dike yielded a provisional U-Pb baddeleyite emplacement age of 1503+/-5 Ma and a virtual geomagnetic pole at 16 degrees S, 221 degrees E (dm=17&j0;, dp=10&j0;). A paleomagnetic pole at 6 degrees N, 234 degrees E (dm=28&j0;, dp=14&j0;) was obtained from five Kuonamka dikes. An east-southeast-trending Chieress dike yielded a U-Pb baddeleyite emplacement age of 1384+/-2 Ma and a virtual geomagnetic pole at 4 degrees N, 258 degrees E (dm=9&j0;, dp=5&j0;). Kuonamka and Chieress poles are interpreted to be primary but do not average out secular variation. Assuming that the Siberian Plate has remained intact since the Mesoproterozoic, except for mid-Paleozoic opening of the Viljuy Rift, then the above results indicate that the Siberian Plate was in low latitudes at ca. 1503 and 1384 Ma, broadly similar to low latitudes determined for Laurentia from well-dated paleopoles at 1460-1420, 1320-1290, and 1267 Ma. This would allow Laurentia and Siberia to have been attached in the Mesoproterozoic, as suggested in several recent studies based on geological criteria. However, because paleomagnetic results from the Anabar Shield region do not average out secular variation and the ages of poles from Siberia and Laurentia are not well matched, it is not yet possible to distinguish between these reconstructions or to rule out other configurations that also maintain the two cratons at low paleolatitudes.

  4. Rb-Sr Geochronology and Geochemical Characteristics of Mafic Dikes in the Nova Lacerda and Conquista D´Oeste Region, Mato Grosso, SW Amazonian Craton

    Directory of Open Access Journals (Sweden)

    Amarildo Salina Ruiz

    2009-01-01

    Full Text Available In the Nova Lacerda and Conquista D’Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafi c dikestrending NNW intrude the Nova Lacerda Granite (1462 ± 12 Ma, within the Jauru Domain, in the Rondonia-San IgnacioProvince (1.55 - 1.3 Ga. The mafi c swarm comprises diabases, metadiabases and amphibolites. Metadiabases originatedfrom uralitization of diabases. These rocks have tholeiitic affi nity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 ± 32 Ma and 1330 ± 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source.

  5. Petrology, geochemistry and tectonic settings of the mafic dikes and sills associated with the evolution of the Proterozoic Cuddapah Basin of south India

    Indian Academy of Sciences (India)

    Nilanjan Chatterjee; Somdev Bhattacharji

    2001-12-01

    In this article we summarize the petrological, geochemical and tectonic processes involved in the evolution of the Proterozoic intracratonic Cuddapah basin. We use new and available ages of Cuddapah igneous rocks, together with field, stratigraphic, geophysical and other criteria, to arrive at a plausible model for the timing of these processes during basin evolution. We present petrological and geochronological evidence of dike emplacement along preferred lineament directions around the basin in response to stresses, which may have been responsible for the evolution of the basin itself. Basaltic dike intrusion started on the south Indian shield around 2400 Ma and continued throughout the Cuddapah basin evolution and sedimentation. A deep mantle perturbation, currently manifested by a lopolithic cupola-like intrusion under the southwestern part of the basin, may have occurred at the onset of basin evolution and played an important role in its development. Paleomagnetic, gravity and geochronological evidence indicates that it was a constant thermal source responsible for dike and sill emplacement between 1500 and 1200 Ma both inside and outside the basin. Lineament reactivation in the NW-SE and NE-SW directions, in response to the mantle perturbation, intensified between 1400 and 1200 Ma, leading to the emplacement of several cross cutting dikes. Fe-Mg partition coefficients of olivine and augite and Ca-Na partition coefficient of plagioclase, calculated from the composition of these minerals and bulk composition of their host rocks, indicate that the dikes outside the Cuddapah basin are cumulates. The contemporary dikes may be related by fractional crystallization as indicated by a positive correlation between their plagioclase Ca#(atomic Ca/[Ca+Na]) and augite Mg#(atomic Mg/[Mg+Fe]). A few NW-SE and NE-SW cross cutting dikes of the period between 1400 and 1200 Ma, preserve petrographic evidence of episodic magmatic intrusive activity along preferred directions. Petrological reasoning indicates that a magmatic liquid reacted with a set of cross cutting dikes, intruding into one that was already solidified and altering the composition of the magma that produced the other dike. The Cuddapah basin tholeiites may be related by fractional crystallization at 5 kb and 1019-1154°C, which occurred in the lopolithic cupola near the southwestern margin of the basin. Xenolith bearing picrites, which occur near the periphery of the cupola, originated by the accumulation of xenoliths in the tholeiites. This is indicated by the composition of the olivine in the xenoliths (Fo78.7−81.9), which are closely similar to calculated olivine compositions (Fo77.8−78.3) in equilibrium with the tholeiites under the same P-T conditions. It is inferred that fractionation in the cupola resulted in crystals settling on its walls. Hence, the xenolith-bearing sills occur at the periphery of the lopolithic body.

  6. Petrological insights into the 1976-2000 eruption episode of White Island, New Zealand: an eruption fuelled by repeated mafic recharge

    Science.gov (United States)

    Kilgour, Geoff; Moune, Severine; Della Pasqua, Fernando; Christenson, Bruce

    2016-04-01

    White Island is a partially submerged volcano located ~ 50 km to the NE of North Island, New Zealand. It is New Zealand's most active volcano and the island is a popular tourist destination. Surprisingly, little is known about the magmatic processes that led to historical eruptions given the potential vulnerability of tourists and its high level of historical activity. In addition, the volcano has been monitored with an array of methods since 1967; from geodetic surveying techniques to geochemical analyses of fluids and gases. Access to an excellent sample record has allowed us to examine a temporal record of magmatic processes, through the careful analysis of scoria clasts. We have then been able to compare apparent timescales of magmatic events to monitored signals. In this work we examine an extended eruptive episode (1976-2000) in order to determine the causes of signals produced throughout this sequence. Previous petrological and geophysical analysis of the 1976-2000 eruptive episode suggested that magma resided at a very shallow depth (i.e., ~ 500 m) for extended periods. This was primarily based on the focussed deformation signal and the low H2O ( 1 km depth prior to eruption. Significant magma degassing into the hydrothermal system was likely responsible for the deformation signal and is unrelated to very shallow magma residence. Taken together, these data provide an important link between petrology and geophysical monitoring at White Island.

  7. Geophysical and geochronological constraints on the extent and age of mafic intrusions in the basement of west Texas and eastern New Mexico

    Science.gov (United States)

    Keller, G. Randy; Hills, John M.; Baker, Mark R.; Wallin, E. Timothy

    1989-11-01

    A deep drill hole recently completed on the Central basin platform of west Texas provides a rare look at almost 5 km of basement rocks. Most of the crystalline rocks encountered were basic and ultrabasic in composition. A variety of geophysical data is available from the bore hole and vicinity. The petrographic and geophysical data suggest that a large, layered, basic intrusion was penetrated by the well. Geochronologic (U-Pb) data indicate an age of about 1.1 Ga for this intrusion. This date has significant tectonic implications because it indicates that commonly accepted analogies with the southern Oklahoma aulacogen (550 Ma rifting) are not valid. However, it is interesting to note that this feature formed during another widespread period of rifting (Keweenawan).

  8. Geophysical and geochronological constraints on the extent and age of mafic intrusions in the basement of west Texas and eastern New Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Keller, G.R.; Hills, J.M.; Baker, M.R. (Univ. of Texas, El Paso (USA)); Wallin, E.T. (Univ. of Kansas, Lawrence (USA))

    1989-11-01

    A deep drill hole recently completed on the Central basin platform of west Texas provides a rare look at almost 5km of basement rocks. Most of the cystalline rocks encountered were basic and ultrabasic in composition. A variety of geophysical data is available from the borehole and vicinity. The petrographic and geophysical data suggest that a large, layered, basic intrusion was penetrated by the well. Geochronologic (U-Pb) data indicate an age of about 1.1 Ga for this intrusion. This date has significant tectonic implications because it indicates that commonly accepted analogies with the southern Oklahoma aulacogen (550 Ma rifting) are not valid. However, it is interesting to note that this feature formed formed during another widespread period of rifting (Keweenawan).

  9. Petrography and Metamorphism of the Metasedimentary Country-Rocks of the Jacurici Valley Chromitite-Hosting Mafic-Ultramafic Complexes, Bahia, Northeastern Brazil

    Directory of Open Access Journals (Sweden)

    Eliane A. Del Lama

    2001-11-01

    Full Text Available This paper deal with on the metasedimentary country-rocks of the chromite-bearing ultramafic rocks that occur in the “Jacurici River Valley Chromium District” northeastern Bahia, Brazil. This region presents a complex geologic-petrologic framework of rocks that were intensely deformed, metamorphosed and transformed by metasomatic processes, making it difficult to interpret their volutionary/metamorphic record. Although the metasedimentary country rocks have also been affected by such processes, it is possible to distinguish evidence of a previous high-grade metamorphism that affected them. Thermobarometric data for the observed mineralogical associations indicate P-T conditions around 750-800ºC and 7-8 kb for the metamorphic peak, based mainly on the presence of olivine in marbles and the cordierite-garnet-sillimanitespinel association in aluminous gneisses.

  10. Origin of Miocene andesite and dacite in the Goldfield-Superstition volcanic province, central Arizona: Hybrids of mafic and silicic magma mixing

    Science.gov (United States)

    Fodor, R. V.; Johnson, Kelly G.

    2016-07-01

    The Miocene Goldfield-Superstition volcanic province (G-SVP), ∼8000 km2 in central Arizona, is composed largely of silicic pyroclastic rocks and lavas, and smaller volumes of alkalic basalt and intermediate-composition lavas. Volcanism began ∼20.5 Ma as sparse rhyolitic and mainly basaltic lavas followed by intermediate lavas, lasting until ∼19 Ma. At that time, ∼1 m.y. of silicic eruptions began, creating most of the G-SVP. Petrologic studies are available for basalts and some for silicic rocks, but petrologic/geochemical information is sparse for intermediate-composition lavas. These latter, andesites and dacites, are the focus of this study, in which we present the processes and sources responsible for their origins. Goldfield-Superstition andesites and dacites have SiO2 ∼56-70 wt.% and Na2O + K2O that qualifies some as trachy-andesite and -dacite. A prominent petrographic feature is plagioclase-phyric texture (∼11-30 vol% plagioclase), where oligoclase-andesine phenocrysts have cores surrounded by corroded, or reacted, zones, mantled by higher An% plagioclase. Where corroded zones are absent, margins are etched, curved, or embayed. Groundmass plagioclase is labradorite, also more calcic than the phenocrysts. Other minerals are quartz (subrounded; embayed), clinopyroxene, amphibole, biotite, and rare titanite and zircon. A salient compositional characteristic that provides insight to andesite-dacite origins with respect to other G-SVP rocks is revealed when using SiO2 as an index. Namely, abundances of many incompatible elements, mainly HFSE and REE, decrease over the low to high SiO2 range (i.e., abundances are lower in dacites than in co-eruptive andesites and underlying alkalic basalts). As examples: G-SVP basalts have ∼50-70 ppm La, and andesites-dacites have ∼59-22 ppm La; for Zr, basalts have ∼225-170 ppm, but most andesites-dacites have ∼180-50; for Y, basalts >20 ppm, andesites-dacites ∼18-9 ppm. To understand these trends of lower HFSE and REE with increasing SiO2, we modeled fractional crystallization of G-SVP alkalic basalt (∼50 wt.% SiO2; ∼9 wt.% MgO), dehydration melting (10-25%) of granodiorite and high-K amphibolite, and basalt-rhyolite magma mixing. Fractionation and melting each require specific modal percentages of titanite, zircon, and allanite (e.g., ⩽1%), the high ends of ranges for accessory-mineral/liquid partitioning coefficients, continual crystallization of accessory minerals from basalt to dacite (for fractionation), and specific source-melting percentages and low titanite, zircon, and allanite melting proportions (∼0.02; dehydration melting). These requirements are too stringent to be realistic. Moreover, accessory minerals are rare in these lavas, and neither fractionation nor melting accounts for the plagioclase textures observed. On the other hand, low-HFSE, -REE rhyolites (e.g., La 9-31 ppm; Zr 31-93; Nb 9-17; Y 4-10) containing Na-plagioclase are in the G-SVP and were temporally and spatially available to have mixed with G-SVP basalts. Mixing proportions of 20:80 to 90:10 for different rhyolite:basalt combinations yield hybrid compositions that overlap the G-SVP andesite-dacite compositional fields. Also, basalt invading rhyolite reservoirs containing mush zones can account for Na-plagioclase concentrations of ∼11-30 vol% formed after mush disruption and dispersal, plagioclase corroded-cores and higher-An% mantles and groundmass, and subrounded-embayed quartz. The straightforward explanation for G-SVP intermediate lavas, then, is repeated hybridization of basaltic and low-HFSE, -REE rhyolitic magmas during the early stages of G-SVP magmatism.

  11. Aeromagnetic interpretation in the south-central Zimbabwe Craton: (reappraisal of) crustal structure and tectonic implications

    Science.gov (United States)

    Ranganai, Rubeni T.; Whaler, Kathryn A.; Ebinger, Cynthia J.

    2015-12-01

    Regional aeromagnetic data from the south-central Zimbabwe Craton have been digitally processed and enhanced for geological and structural mapping and tectonic interpretation integrated with gravity data, to constrain previous interpretations based on tentative geologic maps and provide new information to link these structural features to known tectonic events. The derived maps show excellent correlation between magnetic anomalies and the known geology, and extend lithological and structural mapping to the shallow/near subsurface. In particular, they reveal the presence of discrete crustal domains and several previously unrecognised dykes, faults, and ultramafic intrusions, as well as extensions to others. Five regional structural directions (ENE, NNE, NNW, NW, and WNW) are identified and associated with trends of geological units and cross-cutting structures. The magnetic lineament patterns cut across the >2.7 Ga greenstone belts, which are shown by gravity data to be restricted to the uppermost 10 km of the crust. Therefore, the greenstone belts were an integral part of the lithosphere before much of the upper crustal (brittle) deformation occurred. Significantly, the observed magnetic trends have representatives craton-wide, implying that our interpretation and inferences can be applied to the rest of the craton with confidence. Geological-tectonic correlation suggests that the interpreted regional trends are mainly 2.5 Ga (Great Dyke age) and younger, and relate to tectonic events including the reactivation of the Limpopo Belt at 2.0 Ga and the major regional igneous/dyking events at 1.8-2.0 Ga (Mashonaland), 1.1 Ga (Umkondo), and 180 Ma (Karoo). Thus, their origin is here inferred to be inter- and intra-cratonic collisions and block movements involving the Zimbabwe and Kaapvaal Cratons and the Limpopo Belt, and later lithospheric heating and extension associated with the break-up of Gondwana. The movements produced structures, or reactivated older fractures

  12. The geology, structure and mineralisation of the Oyu Tolgoi porphyry copper-gold-molybdenum deposits, Mongolia:A review

    Institute of Scientific and Technical Information of China (English)

    T.M. Mike Porter

    2016-01-01

    The Oyu Tolgoi cluster of seven porphyry Cu-Au-Mo deposits in southern Mongolia, define a narrow, linear, 12 km long, almost continuously mineralised trend, which contains in excess of 42 Mt of Cu and 1850 t of Au, and is among the largest high grade porphyry Cu-Au deposits in the world. These deposits lie within the Gurvansayhan island-arc terrane, a fault bounded segment of the broader Silurian to Carboniferous Kazakh-Mongol arc, located towards the southern margin of the Central Asian Orogenic Belt, a collage of magmatic arcs that were periodically active from the late Neoproterozoic to Permo-Triassic, extending from the Urals Mountains to the Pacific Ocean. Mineralisation at Oyu Tolgoi is associated with multiple, overlapping, intrusions of late Devonian (w372 to 370 Ma) quartz-monzodiorite intruding Devonian (or older) juvenile, probably intra-oceanic arc-related, basaltic lavas and lesser volcaniclastic rocks, unconformably overlain by late Devonian (w370 Ma) basaltic to dacitic pyroclastic and volcano sedimentary rocks. These quartz-monzodiorite intrusions range from early-mineral porphyritic dykes, to larger, linear, syn-, late- and post-mineral dykes and stocks. Ore was deposited within syn-mineral quartz-monzodiorites, but is dominantly hosted by augite basalts and to a lesser degree by overlying dacitic pyroclastic rocks. Following ore deposition, an allochthonous plate of older Devonian (or pre-Devonian) rocks was overthrust and a post-ore biotite granodiorite intruded at w365 Ma. Mineralisation is characterised by varying, telescoped stages of intrusion and alteration. Early A-type quartz veined dykes were followed by Cu-Au mineralisation associated with potassic alteration, mainly K-feldspar in quartz-monzodiorite and biotite-magnetite in basaltic hosts. Downward reflux of cooled, late-magmatic hydrothermal fluid resulted in intense quartz-sericite retrograde alteration in the upper parts of the main syn-mineral intrusions, and an equivalent chlorite

  13. India's changing place in global Proterozoic reconstructions: A review of geochronologic constraints and paleomagnetic poles from the Dharwar, Bundelkhand and Marwar cratons

    Science.gov (United States)

    Pradhan, Vimal R.; Meert, Joseph G.; Pandit, Manoj K.; Kamenov, George; Gregory, Laura C.; Malone, Shawn J.

    2010-09-01

    The Precambrian history of the Earth is punctuated by a number of supercontinental assemblies and their disintegration. New paleomagnetic and geochronologic results from the Dharwar, Bundelkhand and Marwar cratons of the Indian subcontinent are presented here in an attempt to constrain the paleogeographic position of India within various proposed Precambrian supercontinents. Our paleomagnetic results from the Paleoproterozoic Gwalior traps of the Bundelkhand craton, all of a single polarity, yielded a combined tilt-corrected mean declination = 73.9° and an inclination of +4.4° ( k = 22, α95 = 11.2°). The paleomagnetic pole was calculated using a site location of 26°N, 78°E and is located at 15.4°N, 173.2°E. The U-Pb isotopic studies on the zircons obtained from the alkaline mafic dyke sample from Anantapur dyke swarm of the Dharwar craton, southern India, yielded a concordant age of 1027.2 ± 13 Ma (2 σ; MSWD = 5.0). An overall mean of our paleomagnetic studies combined with previously published results yielded a VGP at 10°N and 211°E with a mean declination = 65° and inclination = -57° ( k = 31, α95 = 10). In an effort to constrain the lower age limit of the Malani Igneous Suite (MIS) we report new U-Pb isotopic ages for the Harsani granodiorite. The granodiorite forms the basement for the Malani igneous province in NW India. The zircon U-Pb analyses from Harsani granodiorite yielded and age of 827.0 ± 8.8 Ma that we interpret as the age of intrusion and the 786.4 ± 5.6 Ma may relate to a disturbance marking onset of Malani volcanism. Along with these new data, we also review the paleomagnetic results from our previous studies on the Harohalli alkaline dykes, Upper Vindhyan sequence, Majhgawan kimberlite, and a widespread paleomagnetic overprint that we interpret to be of ˜580 Ma in an attempt to constrain the paleogeography of the Indian subcontinent from 1.8 Ga to 580 Ma.

  14. Continental Collision Structures and Post-Orogenic Geological History of the Kangerlussuaq Area in the Southern Part of the Nagssugtoqidian Orogen, Central West Greenland

    Directory of Open Access Journals (Sweden)

    Jon Engström

    2014-12-01

    Full Text Available Deep-seated continental collision sutures, formed at a depth of more than 20 km, are exposed near Kangerlussuaq, close to the Greenland ice cap, on the southern margin of the Nagssugtoqidian orogen in Central West Greenland, thus offering a rare opportunity to study the tectonic deformation style of such an orogen. This paper adds new information on the tectonic history of the southern flank of the Nagssugtoqidian orogen. It focuses on (1 the results of a detailed structural investigation of lineament zones revealed from remote sensing of geophysical and topographic data and aerial photo interpretation, (2 detailed geological mapping at key locations and (3 a tectonic structural model describing the geological development of the area. The area has undergone several episodes of deformation, which have been compiled into an event succession that recognizes eight tectonic events overprinting each other: Two stages of folding (F1 and F2 have been identified along with one major episode of intrusion of the Kangâmiut mafic dyke swarm (2.05 Ga into the Archaean continent. These dyke intrusions are very important, since by examining the style of deformation for these intrusions it is possible to define the transition from the North Atlantic Craton in the south to the mobile belts in the Nagssugtoqidian orogen in the north. Five different types of pronounced lineaments and one less pronounced lineament post-dating the Kangâmiut dykes extending from ductile deformation shearing events to brittle deformation with extensive faulting. These lineaments cover both the collisional and post-collisional tectonic history of the area. The study focused on two types of lineaments: one semi-ductile type trending E–W with a dextral sense of shear and a second, a pronounced lineament outlining the Kangerlussuaq–Russell thrust fault. These two features are interpreted to be related to the Nagssugtoqidian orogeny, while the latter lineaments have a more brittle

  15. New Understanding for Sanchahe Nephrite Deposit in East Kunlun%东昆仑三岔河软玉矿床成因的新认识

    Institute of Scientific and Technical Information of China (English)

    杨天翔; 杨明星; 刘虹靓; 吴钰; 李晶

    2013-01-01

    通过对三岔河软玉矿区野外地质现象以及所采样品的LA-ICP-MS测试数据、岩相学特征等的分析,从软玉形成的物源方面对矿床的形成模式提出了新的认识.根据野外地质现象,当仅有基性岩脉侵入到大理岩地层当中,或者仅有硅质流体侵入到大理岩地层中时,都不能形成软玉;而在基性岩脉侵入的大理岩地层中,后期有热液流体的参与时能形成软玉.样品中的岩相学特征说明了该地区大理岩中Mg含量不足,微量元素特征显示大离子亲石元素(LILE)K、U、Th、Rb、Ba、Sr的含量相对要高于高场强元素(HFSE) Ti、Ta、Nb、Zr、Hf、Y,说明在软玉形成的过程中有流体活动的参与.因此认为,该地区软玉的形成与大理岩、基性岩脉、后期的流体活动三者有关,后期的流体活动为软玉的形成提供了SiO2,基性岩脉为软玉提供了Mg,大理岩为软玉提供了Ca、Mg以及成矿场所.%Based on the analysis of the field geological phenomenon from Sanchahe Nephrite deposit,the sample test data of LA-ICP-MS and lithofacies character,this article advances a new understanding of the deposit forming model from the aspect of ore-forming source.From the field geological phenomenon,whether the mafic dikes intruded into the marble strata,or the silicic fluid intruded into the marble strata,the nephrite could not be fromed.But when the mafic dikes intruded into the marble strata,the later silicic fluid also intruded into the marble strata,the nephrite can be formed.The sample lithofacies character shows that the Mg in region marble is insufficient.The trace element characteristics show that the content of large ion lithophile elements (LILE) K,U,Th,Rb,Ba,Sr is relatively higher than that of high field strength elements (HFSE) Ti,Ta,Nb,Zr,Hf,Y,suggesting the process of nephrite formation has fluid activity.Therefore,the formation of nephrite relates to marble,mafic rock dyke and the later silicic fluid

  16. Geochemical, zircon U-Pb dating and Sr-Nd-Hf isotopic constraints on the age and petrogenesis of an Early Cretaceous volcanic-intrusive complex at Xiangshan, Southeast China

    Science.gov (United States)

    Yang, Shui-Yuan; Jiang, Shao-Yong; Jiang, Yao-Hui; Zhao, Kui-Dong; Fan, Hong-Hai

    2011-01-01

    The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U-Pb dating, and Sr-Nd-Hf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2 Myrs. The stratigraphically oldest rhyodacite yielded a zircon U-Pb age of 135 ± 1 Ma and the overlying rhyodacitic porphyry has an age of 135 ± 1 Ma. Three porphyritic lava samples yielded zircon U-Pb ages of 136 ± 1 Ma, 132 ± 1 Ma, and 135 ± 1 Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U-Pb ages of 137 ± 1 Ma and 137 ± 1 Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U-Pb age of 136 ± 1 Ma. All these newly obtained precise U-Pb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr-Nd-Hf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ɛNd(T) value higher than the other rocks

  17. Structure of the Crust Beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    International Nuclear Information System (INIS)

    The joint inversion of Rayleigh wave group velocities and receiver functions was carried out to investigate the crustal and uppermost mantle structures beneath Cameroon. This was achieved using data from 32 broadband seismic stations installed for 2 years across Cameroon. The Moho depth estimates reveal that the Precambrian crust is variable across the country and shows some significant differences compared to other similar geologic units in East and South Africa. These differences suggest that the setting of the Cameroon Volcanic Line (CVL) and the eastward extension of the Benue Trough have modified the crust of the Panafrican mobile belt in Cameroon by thinning beneath the Rift area and CVL. The velocity models obtained from the joint inversion show at most stations, a layer with shear wave velocities ≥ 4.0 km/s, indicating the presence of a mafic component in the lower crust, predominant beneath the Congo Craton. The lack of this layer at stations within the Panafrican mobile belt may partly explain the crustal thinning observed beneath the CVL and rift area. The significant presence of this layer beneath the Craton, results from the 2100 Ma magmatic events at the origin of the emplacement of swarms of mafic dykes in the region. The CVL stations are underlain by a crust of 35 km on average except near Mt-Cameroon where it is about 25 km. The crustal thinning observed beneath Mt. Cameroon supported by the observed positive gravity anomalies here, suggests the presence of dense astenospheric material within the lithosphere. Shear wave velocities are found to be slower in the crust and uppermost mantle beneath the CVL than the nearby tectonic terrains, suggesting that the origin of the line may be an entirely mantle process through the edge-flow convection process. (author)

  18. Evidence for multiple pulses of crystal-bearing magma during emplacement of the Doros layered intrusion, Namibia

    Science.gov (United States)

    Owen-Smith, T. M.; Ashwal, L. D.

    2015-12-01

    The Doros Complex is a relatively small (maximum 3.5 km × 7.5 km) shallow-level, lopolithic, layered mafic intrusion in the early Cretaceous Paraná-Etendeka Large Igneous Province. The stratigraphy broadly comprises a minor, fine-grained gabbroic sill and a sequence of primitive olivine-cumulate melagabbros, with a basal chilled margin, an intermediate plagioclase-cumulate olivine gabbro, and a sequence of mineralogically and texturally variable, intermediate, strongly foliated, plagioclase-, olivine- or magnetite-cumulate gabbros. An evolved syenitic (bostonite) phase occurs as cross-cutting dykes or as enclaves within the foliated gabbros. Major element modelling of the liquid line of descent shows that the spectrum of rock types, including the bostonite, is consistent with the fractionation of a basaltic parental magma that crystallised olivine, clinopyroxene, plagioclase, magnetite, K-feldspar and apatite. However, the stratigraphic succession does not correspond to a simple progressive differentiation trend but instead shows a series of punctuated trends, each defined by a compositional reversal or hiatus. Incompatible trace element concentrations do not increase upwards though the body of the intrusion. The major units show similar, mildly enriched rare earth element patterns, with minimal Eu anomalies. Back-calculation of the rare earth element concentrations of these cumulate rocks produces relatively evolved original liquid compositions, indicating fractionation of this liquid from a more primitive precursor. Based on combined field, petrographic, geochemical and geophysical evidence, we propose an origin for the Doros Complex by a minimum of seven closely spaced influxes of crystal-bearing magmas, each with phenocryst contents between 5% and 55%. These findings represent a departure from the traditional single-pulse liquid model for the formation of layered mafic intrusions and suggest the presence of an underlying magmatic mush column, i.e., a large

  19. U-Pb Dating, whole rock and Sr-Nd-Pb-O isotope geochemistry of collisional magmatism in the CACC: Çiçekdaǧ igneous complex (ÇIC)

    Science.gov (United States)

    Deniz, Kiymet; Kagan Kadioglu, Yusuf; Stuart, Finlay; Ellam, Rob; Boyce, Adrian; Condon, Daniel

    2015-04-01

    The closure of Neotethys induced from calcalkaline through alkaline magmatism within the Central Anatolia Crystalline Complex (CACC) during the late Cretaceous-early Paleogene. Timing of these magmatism is very important for understanding the magmato-tectonic evolution and the relation with the collision. Despite the genesis of felsic products are well understood, there is lack of petrogenetic explanation about especially alkaline mafic products. The relation between Neotethyan ophiolites and late alkaline dykes which haven't reported before is the most important undeclared gap. Çiçekdağ igneous complex (ÇIC) is one of the best area for explaining all of these problems within the CACC. In accordance with these purposes, we have carried out detailed petrographic, whole rock geochemical, Sr-Nd-Pb-O isotopic and geochronological (U/Pb and Ar/Ar) study of the rocks in the ÇIC in order to unravel the magmatic history of the CACC and thus constrain the tectonic history. The intrusive rocks of the ÇIC are differentiated into four main group as an ophiolites, calcalkaline series, alkaline series and late alkaline dykes. The felsic and mafic units intruded to the ophiolitic rocks. The calcalkaline series mostly composed of monzonites and monzodiorite porphyry whereas the alkaline series consist of syenites and feldspathoid-bearing gabbros. Variations in the major oxide compositions of both rock series can be attributed with fractionation of clinopyroxene, plagioclase, amphibole, apatite and iron titan oxide minerals. The high 87Sr/86Sr and low 143Nd/144Nd of both series are indicative of mantle sources with large continental crustal components. Feldspar and quartz oxygen isotope data from calcalkaline and alkaline series have a range of δ18O values 5.1-11.4o 8.3-9.2o and 7.7-14.1o 10.2-13.7o respectively and are compatible with the values for I-A-type granitoids. Both rock series represent the mixed (mantle-crustal) origin. The combination of all data suggest that

  20. Structure and geological evolution of the bedrock at southern Satakunta, SW Finland

    International Nuclear Information System (INIS)

    , approaches to within 5 km of the Olkiluoto site. The results of gravimetric surveys have indicated that the margin of the Eurajoki stock slopes westward underneath the site, but to depths in excess of 3000 m. Plate tectonic reconstructions of the Precambrian of Finland, partly based on the results of major deep seismic sounding experiments, such as the international GGT/SVEKA project (along a NE-SW transect through the Satakunta area), indicate the pelitic and psammitic migmatite belts in Satakunta represent parts of the early Proterozoic Southern Finland and Central Finland continental arcs, respectively. Collision of these arc complexes took place 1890 - 1880 Ma ago, when the rocks were deformed and metamorphosed for the first time. The highT/lowP metamorphism was caused by mafic underplating, which led to a strong increase in temperature, and recrystallisation and partial remelting of the rocks in the upper crust. The collision of the arc complexes is characterised by an intense magmatic activity, which appears as synorogenic granitoids. In the next stage, 1860 - 1810 Ma ago, mafic underplating caused a second high-temperature metamorphic event and partial melting of the sedimentary rocks in southern Finland, producing the late-orogenic potassium. granites, dated at 1840 - 1830 Ma. The Subjotnian rapakivi granites associated with mafic rocks, the Jotnian Satakunta sandstone formation and the Postjotnian diabase dykes and sills represent the cratonisation stages of the Svecofennides. Rapakivi granites and related mafic rocks were generated in an anorogenic extensional regime by partial melting of the upper mantle and lower crust. The Jotnian Satakunta sandstone is a fluvial sediment formation deposited in a deltaic environment. The development of the graben or rift valley, where the sandstone was deposited, may have begun already during the Subjotnian, ca. 1650 Ma ago. The olivine diabase dykes represent the feeding channels of Postjotnian flood basalts. However, no such

  1. Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (<25Ma) and hot.

  2. The Paleoproterozoic Nattanen-type granites in northern Finland and vicinity – a postcollisional oxidized A-type suite

    Directory of Open Access Journals (Sweden)

    Esa Heilimo

    2009-06-01

    Full Text Available The ~1.8 Ga Nattanen-type granites in the Finnish Lapland and western Kola Peninsula are found as several relatively small, high-level, discordant plutons that are easily discernible as weak maxima on aeromagnetic maps. We present U–Pb mineral isotope data on the Finnishplutons. The concordia ages are in the 1.79−1.77 Ga range and there is little evidence for inheritance. Initial radiogenic isotope compositions (our common-Pb data combined with previously published whole-rock Nd and Hf data imply a major, yet varying, Archeansource component. Elemental geochemical data on five Finnish intrusions (the Nattanen stock, the Tepasto and Pomovaara complexes, the Riestovaara and Vainospää batholiths, as well as associated dyke rocks allow the Nattanen-type granites to be classified as oxidizedA-type granites. Their petrogenesis may be related to partial melting of the lower crust by mafic underplating (extensional setting or as a result of thermal relaxation in thickened crustal setting.

  3. Structure, stability and tsunami hazard associated with a rock slope in Knight Inlet, British Columbia

    Directory of Open Access Journals (Sweden)

    D. P. van Zeyl

    2015-01-01

    Full Text Available Rockfalls and rockslides during the past 12 000 years have deposited bouldery debris cones on the seafloor beneath massive rock slopes throughout the inner part of Knight Inlet. The 885 m high rock slope situated across from the Kwalate site, a former First Nations village destroyed in the late 1500s by a slide-induced wave, exposes the contact between a Late Cretaceous dioritic pluton and metamorphic rocks of the Upper Triassic Karmutsen Formation. The pluton margin is strongly foliated in parallel with primary and secondary fabrics in the metamorphic rocks, resulting in highly persistent brittle structures. Other important structures include a set of sheeting joints and highly persistent mafic dykes and faults. Stability analysis identified the potential for planar and wedge failure. We made empirical estimates of impulse waves generated by potential slides ranging in size from 0.5 to 3.5 Mm3, with results suggesting mid-inlet wave heights in the order of 6 to 26 m. As several similar rock slopes fronted by large submarine debris cones exist in the inner part of Knight Inlet, it is clear that tsunami hazards should be considered in coastal infrastructure development and land-use planning in this area.

  4. Petrogenesis of late-Variscan high-K alkali-calcic granitoids and calc-alkalic lamprophyres: The Aber-Ildut/North-Ouessant complex, Armorican Massif, France

    Science.gov (United States)

    Caroff, Martial; Labry, Cyrill; Le Gall, Bernard; Authemayou, Christine; Grosjean, Denise Bussien; Guillong, Marcel

    2015-12-01

    The Aber-Ildut/North-Ouessant Variscan granitoid complex in the Armorican Massif is an example of high-K alkali-calcic zoned pluton, c. 304 Ma in age. A first magmatic batch intruded through a northern EW-trending sinistral transcurrent shear zone, before injecting southwards as a huge horizontal zoned sill, with moderately peraluminous muscovite-free granitoids in the north and strongly peraluminous muscovite-bearing leucogranites to the south. The second magmatic stage resulted in the intrusion of a large two-mica leucogranitic body from a root zone along the same shear zone, prior to the end of crystallization of the first injection. Finally, ultrapotassic dykes, including calc-alkalic lamprophyres (leucominettes), intrude the complex. The strongly peraluminous granites are interpreted as pure melting products of crustal clay-rich pelitic material. All the other petrographic types, including leucominettes, are thought to result from mixing of crustal melts and mantle-derived mafic liquids. Highly silicic tourmaline-bearing leucogranites are significantly affected by a tetrad effect, in relation with REE complexing behavior. Aber-Ildut/North-Ouessant granitoids probably formed during the Variscan late-orogenic stage associated with exhumation and lithospheric thinning, at low pressure and by advective heating of a ≤ 50 km-thick crust from hot metasomatized asthenosphere.

  5. Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

    Science.gov (United States)

    Oliveira, E. P.; Tarney, J.

    1995-08-01

    Caraiba, the largest Brazilian copper deposit under exploitation, consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early Proterozoic norite and hypersthenite. The mafic igneous complex comprises multiple intrusions of dykes, veins and breccias of norites and hypersthenites, with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere. The country rocks are high-grade gneisses, granulites and metasediments. Compositions of plagioclase(An60-40) and orthopyroxene(En70-60) fall in a narrow range similar to the Koperberg Suite from the Okiep copper district, South Africa, and to that in many massif-type anorthosites. Whole-rock major and trace element geochemistry indicate a parental magma enriched in Fe, LREE, P, K, and Cu. Negative Nb anomalies on multi-element plots and fractionated REE patterns, along with sulphide sulphur isotopes in the range δ34S = -1.495 to + 0.643‰, suggest a primary mantle lithosphere source, although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded. Geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent (partly transpressional) shearing event associated with the waning stage of evolution of the early Proterozoic Salvador-Curaçá orogen.

  6. Hydrogeochemical data as a tool for exploration and mapping: a case study from part of Afikpo Basin southeastern Nigeria.

    Science.gov (United States)

    Ibe, Kalu K; Akaolisa, Casmir C Z

    2010-01-01

    Fourteen (14) characters from six (6) water samples collected from springs, ponds, and streams located in Lower Cretaceous sedimentary area of Afikpo Basin have been analyzed. These include pH, turbidity, conductivity, total dissolved solid, hardness, Fe2+, Ca2+, Mg2+, K+, NO3-, Cl-, SO4(2-), and Na+. These sediments, which are Turonian and Coniacian in age, are subdivided into two by a basic rock dyke. Results of the analyses show clearly that the Turonian sediments, intruded by dolerite, have net Fe2+, HCO3-, Ca2+, Mg2+, Mn2+, Cl-, and SO4(2-) concentration while those from the younger Coniacian sediment have net higher amounts of K+, Na+, and Mn2+. The overriding mafic minerals in the basic intrusive rock possibly led to higher leaching into ground water system near it. On the other hand, the presence of feldsparthic to kaolinitic sands of the younger Coniacian units led to higher K+ and Na+ matter in the water from these zones. The formations dip away from the older sediments. Concentrations of these characters are within acceptable drinking water standards by World Health Organization but noticeable anomalous zones for Fe2+, Mg2+, and Ca2+ are zones of basic rock suites. Areas with greater Na+ and K+ are traceable to sandy units. It is thus concluded that more analysis of surface, subsurface, and pond water samples can be utilized for minerals search and geological mapping. At this stage, it forms a veritable reconnaissance tool. PMID:19105037

  7. Structure and geological evolution of the bedrock at southern Satakunta, SW Finland

    Energy Technology Data Exchange (ETDEWEB)

    Paulamaeki, S.; Paananen, M.; Elo, S. [Geological Survey of Finland (Finland)

    2002-02-01

    , approaches to within 5 km of the Olkiluoto site. The results of gravimetric surveys have indicated that the margin of the Eurajoki stock slopes westward underneath the site, but to depths in excess of 3000 m. Plate tectonic reconstructions of the Precambrian of Finland, partly based on the results of major deep seismic sounding experiments, such as the international GGT/SVEKA project (along a NE-SW transect through the Satakunta area), indicate the pelitic and psammitic migmatite belts in Satakunta represent parts of the early Proterozoic Southern Finland and Central Finland continental arcs, respectively. Collision of these arc complexes took place 1890 - 1880 Ma ago, when the rocks were deformed and metamorphosed for the first time. The highT/lowP metamorphism was caused by mafic underplating, which led to a strong increase in temperature, and recrystallisation and partial remelting of the rocks in the upper crust. The collision of the arc complexes is characterised by an intense magmatic activity, which appears as synorogenic granitoids. In the next stage, 1860 - 1810 Ma ago, mafic underplating caused a second high-temperature metamorphic event and partial melting of the sedimentary rocks in southern Finland, producing the late-orogenic potassium. granites, dated at 1840 - 1830 Ma. The Subjotnian rapakivi granites associated with mafic rocks, the Jotnian Satakunta sandstone formation and the Postjotnian diabase dykes and sills represent the cratonisation stages of the Svecofennides. Rapakivi granites and related mafic rocks were generated in an anorogenic extensional regime by partial melting of the upper mantle and lower crust. The Jotnian Satakunta sandstone is a fluvial sediment formation deposited in a deltaic environment. The development of the graben or rift valley, where the sandstone was deposited, may have begun already during the Subjotnian, ca. 1650 Ma ago. The olivine diabase dykes represent the feeding channels of Postjotnian flood basalts. However, no such

  8. Hydrogeochemical data as a tool for exploration and mapping: a case study from part of Afikpo Basin southeastern Nigeria.

    Science.gov (United States)

    Ibe, Kalu K; Akaolisa, Casmir C Z

    2010-01-01

    Fourteen (14) characters from six (6) water samples collected from springs, ponds, and streams located in Lower Cretaceous sedimentary area of Afikpo Basin have been analyzed. These include pH, turbidity, conductivity, total dissolved solid, hardness, Fe2+, Ca2+, Mg2+, K+, NO3-, Cl-, SO4(2-), and Na+. These sediments, which are Turonian and Coniacian in age, are subdivided into two by a basic rock dyke. Results of the analyses show clearly that the Turonian sediments, intruded by dolerite, have net Fe2+, HCO3-, Ca2+, Mg2+, Mn2+, Cl-, and SO4(2-) concentration while those from the younger Coniacian sediment have net higher amounts of K+, Na+, and Mn2+. The overriding mafic minerals in the basic intrusive rock possibly led to higher leaching into ground water system near it. On the other hand, the presence of feldsparthic to kaolinitic sands of the younger Coniacian units led to higher K+ and Na+ matter in the water from these zones. The formations dip away from the older sediments. Concentrations of these characters are within acceptable drinking water standards by World Health Organization but noticeable anomalous zones for Fe2+, Mg2+, and Ca2+ are zones of basic rock suites. Areas with greater Na+ and K+ are traceable to sandy units. It is thus concluded that more analysis of surface, subsurface, and pond water samples can be utilized for minerals search and geological mapping. At this stage, it forms a veritable reconnaissance tool.

  9. Precambrian crustal evolution of Peninsular India: A 3.0 billion year odyssey

    Science.gov (United States)

    Meert, Joseph G.; Pandit, Manoj K.; Pradhan, Vimal R.; Banks, Jonathan; Sirianni, Robert; Stroud, Misty; Newstead, Brittany; Gifford, Jennifer

    2010-11-01

    The Precambrian geologic history of Peninsular India covers nearly 3.0 billion years of time. India is presently attached to the Eurasian continent although it remains (for now) a separate plate. It comprises several cratonic nuclei namely, Aravalli-Bundelkhand, Eastern Dharwar, Western Dharwar, Bastar and Singhbhum Cratons along with the Southern Granulite Province. Cratonization of India was polyphase, but a stable configuration between the major elements was largely complete by 2.5 Ga. Each of the major cratons was intruded by various age granitoids, mafic dykes and ultramafic bodies throughout the Proterozoic. The Vindhyan, Chhattisgarh, Cuddapah, Pranhita-Godavari, Indravati, Bhima-Kaladgi, Kurnool and Marwar basins are the major Meso to Neoproterozoic sedimentary repositories. In this paper we review the major tectonic and igneous events that led to the formation of Peninsular India and provide an up to date geochronologic summary of the Precambrian. India is thought to have played a role in a number of supercontinental cycles including (from oldest to youngest) Ur, Columbia, Rodinia, Gondwana and Pangea. This paper gives an overview of the deep history of Peninsular India as an introduction to this special TOIS volume.

  10. Remote Sensing Exploration of Nb-Ta-LREE-Enriched Carbonatite (Epembe/Namibia

    Directory of Open Access Journals (Sweden)

    Robert Zimmermann

    2016-07-01

    Full Text Available On the example of the Epembe carbonatite-hosted Nb-Ta-LREE deposit, we demonstrate the use of hyperspectral reflectance data and geomorphic indicators for improving the accuracy of remote sensing exploration data of structurally-controlled critical raw material deposits. The results further show how exploration can benefit from a combination of expert knowledge and remotely-sensed relief, as well as imaging data. In the first stage, multi-source remote sensing data were used in lithological mapping based on Kohonen Self-Organizing Maps (SOM. We exemplify that morphological indices, such as Topographic Position Index (TPI, and spatial coordinates are crucial parameters to improve the accuracy of carbonate classification as much as 10%. The resulting lithological map shows the spatial distribution of the ridge forming carbonatite dyke, the fenitization zone, syenite plugs and mafic intrusions. In a second step, the internal zones of the carbonatite complex were identified using the Multi-Range Spectral Feature Fitting (MRSFF algorithm and a specific decision tree. This approach allowed detecting potential enrichment zones characterized by an abundance of fluorapatite and pyroxene, as well as dolomite-carbonatite (beforsite. Cross-validation of the mineral map with field observations and radiometric data confirms the accuracy of the proposed method.

  11. Gabbro-peridotite Interaction in the Northern Cache Creek Composite Terrane Ophiolite, British Columbia and Yukon

    Science.gov (United States)

    Zagorevski, A.

    2015-12-01

    The northern Cache Creek composite terrane comprises a thrust stack of chert, limestone, siltstone, basalt, gabbro and ultramafic complexes ranging in age from Mississippian to Triassic. Fields studies and geochemical investigations indicate that ophiolitic mafic-ultramafic complexes formed in a supra-subduction zone setting. Ophiolitic rocks in the southeast form a structurally disrupted Penrose-type ophiolite; however, northwestern ophiolitic rocks generally lack lower and middle crust in most sections, exhibit a direct contact between supracrustal and mantle sections and locally contain ophicalcites suggesting that supracrustal rocks were structurally emplaced over mantle along extensional detachment(s). Mantle peridotite in the footwall of the detachment is extensively intruded by vari-textured, fine-grained to pegmatitic gabbro sills, dykes and stocks. These gabbro intrusions are locally boudinaged within fresh peridotite suggesting that the host mantle was rapidly exhumed prior to emplacement of the gabbro. Intrusive relationships between gabbro and variably serpentinized mantle peridotite are observed throughout the northern Cache Creek terrane (>300 km) suggesting a presence of a regional-scale Middle Triassic ocean-core complex. Overall, these data indicate that parts of the northern Cache Creek terrane formed in a setting analogous to backarc ocean core complexes such as the Godzilla Megamullion in the Parece Vela backarc basin, western Pacific.

  12. Sm-Nd isotope geochemistry and U/Pb geochronological data of the Campina Grande complex, Paraiba State, NE Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, C.N. [Pernambuco Univ., Recife, PE (Brazil). Pos-Graduacao em Geociencias; Guimaraes, I.P.; Silva Filho, A.F. da [Pernambuco Univ., Recife, PE (Brazil). Dept. de Geologia; Beurlen, H. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Engenharia de Minas

    1997-12-31

    The Campina Grande Complex (CCG) constitutes a 250 Km{sup 2} intrusion within the high grade gneiss-migmatitic terrain, in the contact zone between the Mesoproterozoic Pajeu-Paraiba Fold Belt and the Archean Caldas Brandao Massif of the Borborema Province, NE Brazil. The contact of the complex is made by the Guarabira Shear Zone (west) and the Campina Grande Shear Zone in the south. The CCG is composed of coarse grained porphyritic quartz-monzonites, quartz-monzodiorites and medium grained porphyritic granodiorites. Mafic enclaves are common and show composition ranging from diorites to quartz diorites. Field and petrographic features point out to magma mixing and mingling processes involved in the CCG evolution. Basalts of probably Cretaceous age occur as dykes cutting in the CCG. This work presents and discusses the Sm-Nd isotope geochemistry of the CCG and a gabro which occur very close to the south contact of the CCG. This also presents the U/Pb in zircon geochronological data for the CCG. (author) 4 refs., 2 figs.

  13. Geology and associated mineral occurrences of the Araxa Group, Mossamedes Region, Goias, Brazil

    International Nuclear Information System (INIS)

    In the region of Mossamedes, State of Goias, Brazil, the Precambrian metamorphic rocks of the Araxa group were mapped at the scale of 1:25,000, with emphasis on stratigraphic, structural, petrographic and economic aspects. These metamorphites represent a continous stratigraphic sequence which, from bottom to top can be subdivided into five informal lithostratigraphic units: 1) psamitic unit (quartzite, metaconglomerate); 2) psamitic-pelitic unit (quartzite, quartz schist, muscovite schist); 3) lower pelitic - volcanic unit (chlorite - biotite schist, fine grained blastoporphyritic gneiss, amphibolite and calc-schist); 4) upper pelitic - volcanic unit (garnet muscovite schist, biotite schist and gneiss, amphibolite, magnetite muscovite schist); 5) gneissic unit (epidote biotite gneiss, amphibolite). Three types of meta-intrusive rocks were found, besides basic dykes related to Mesozoic magmatism. Four phases of deformation affected the volcano-sedimentary sequence;D1, D2, D3 and D4, each of them developing distinct deformational features. Barrowian type metamorphism increases progressively from North to South from the biotite zone to the garnet zone (greenschist facies), reaching the staurolite-kyanite zone (amphibolite facies). The magmatism throughout the Group's evolution consists of mafic to felsic volcanic activity, mustly intermediary, as well as three intrusive events. Gold, copper and zinc minerals of economic interest occur within the studied area. The gold mineralizations are related to the pelitic-volcanic sequences. Copper occurs in several rocks from the pelitic-volcanic and gneissic sequences. (Author)

  14. Seismic evidence of crustal heterogeneity beneath the northwestern Deccan volcanic province of India from joint inversion of Rayleigh wave dispersion measurements and P receiver functions

    Science.gov (United States)

    Deshpande, A. A.; Mohan, G.

    2016-10-01

    The northwestern Deccan volcanic province (NWDVP) of India, encompassing the Saurashtra peninsula and the adjoining Gulf of Cambay, is investigated through joint inversion of surface wave dispersion measurements and teleseismic P receiver functions, to estimate the crustal and shallow upper mantle shear wave velocity (Vs) structure. The Mw ∼ 7.7 Bhuj earthquake and the post Bhuj regional events, recorded during the period 2001-2010 at 7 stations along 37 source-receiver paths were used along with 35 teleseismic events. A joint curve fitting inversion technique is applied to obtain a best fit for the fundamental mode Rayleigh wave group velocity dispersion curves for time periods 5-50 s and high quality crustal P wave receiver functions obtained at each station. Significant crustal heterogeneity is observed within the study region with the average crustal Vs ranging from 3.5 km/s to 3.8 km/s with the paths cutting across the Gulf of Cambay exhibiting large reduction in shear wave velocities. Utilizing the average crustal Vs ≈ 3.66 km/s estimated for Saurashtra, together with the average crustal P wave velocity (Vp) ≈ 6.54 km/s derived independently through deep seismic sounding studies, yields a bulk Vp/Vs ratio of 1.786 or an equivalent crustal Poisson's ratio of 0.271. A major contribution to the high Poisson's ratio comes from the 12 to 16 km thick lower crustal layers with shear velocities ranging from 3.8 km/s to 4.19 km/s suggesting widespread magmatic underplating due to emplacement of mafic cumulates in the lower crust. The shallow uppermost mantle shear velocities are in the range 4.2-4.5 km/s averaging 4.36 km/s, which is less than that observed for the Indian shield, indicating the effects of residual thermal anomaly. The variation in the crustal Vs, high Poisson's ratios and low upper mantle shear velocities reflect the thermal and compositional effects of the Deccan volcanism which are manifested in terms of pervasive presence of mafic dykes

  15. Petrogenesis of the Late Cretaceous Demirköy Igneous Complex in the NW Turkey: Implications for magma genesis in the Strandja Zone

    Science.gov (United States)

    Karacık, Zekiye; Tüysüz, Okan

    2010-02-01

    The Srednogorie Zone in Bulgaria and its eastern continuation in NW Turkey, the Strandja Zone, consist of a Late Cretaceous magmatic belt comprised of plutonic, volcanic and associated volcano-sedimentary rocks. The Demirköy Igneous Complex is the biggest Cretaceous pluton within the Strandja Zone, and its age is between 71 and 84 Ma. The Demirköy pluton and additional smaller plutons are intruded into Triassic and older metamorphic basement rocks. A contact metamorphic aureole with hornblende-hornfels facies conditions was developed around the Demirköy pluton. The WNW-trending Demirköy pluton has an elliptical shape and a concentrically zoned internal structure. In this structure, gabbro/diorites and quartz diorites are only seen in the SW corner of the pluton, while granodiorites form the main body of the pluton surrounded by a zone of granite. The granodiorites contain dioritic mafic microgranular enclaves. Small quartz monzonite lenses and/or bodies and mafic dykes are also observed in the Demirköy Igneous Complex. Geochemically, the Demirköy Igneous Complex has calc-alkaline, metaluminous and medium-K characteristics. There is a significant correlation between the LREE/HREE ratios and SiO 2 values. Chondrite-normalized REE patterns are relatively flat (La N/Lu N = 2) in gabbros. This ratio ranges from 3 to 11 for the diorite/granodiorites, and from 14 to 35 for the granites. Dioritic enclaves have REE patterns similar to those of the main body and have La N/Lu N values between 3 and 6. Relatively enriched LILE (Sr, K, Rb, Ba and Th) and relatively depleted HFSE (Ta, Nb and Ti) values indicate the classic subduction-related origin of the complex. The initial isotopic signatures range from ɛNd( i) = - 0.45 to - 2.57 and 87Sr/ 86Sr( i) = 0.7042-0.7064 for gabbros and ɛNd( i) = - 0.43 to - 2.67 and 87Sr/ 86Sr( i) = 0.7048-0.7059 for granodiorites and granites. δ18O values range from + 6.18 to + 7.80‰ (VSMOW) for gabbros and from + 6.86 to + 8.89

  16. Tapiolite from the Koktokay No.3 Rare Metal Granitic Pegmatite Dyke, Altai, Xinjiang Autonomous Region%新疆阿尔泰可可托海3号伟晶岩脉重钽铁矿研究

    Institute of Scientific and Technical Information of China (English)

    张爱铖; 王汝成; 胡欢

    2003-01-01

    重钽铁矿是主要见于高度分馏花岗伟晶岩中的一种罕见的钽矿物.新疆阿尔泰可可托海3号伟晶岩脉中存在的重钽铁矿呈他形,与钽锰矿(因Ta含量的明显差异可分为钽锰矿I和钽锰矿II)和铀细晶石共生形成铌钽矿物集合体.钽锰矿I构成集合体的主体,而重钽铁矿与相对富Mn和Ta的钽锰矿II紧密共生并分布在集合体的边部.重钽铁矿的RTa[RTa=Ta/(Nb+Ta)]在0.96~0.99间变化,RMn[RMn=Mn/(Fe+Mn)]在0.10~0.21间变化.铌钽铁矿的共生组合和化学成分特征表明,重钽铁矿是钽锰矿I在非平衡条件下快速结晶后残余亚稳定相出溶的产物.

  17. A large scale investigation into changes in coal quality caused by dolerite dykes in Secunda, South Africa-implications for the use of proximate analysis on a working mine

    Science.gov (United States)

    Bussio, John P.; Roberts, James R.

    2016-05-01

    The coalfields of South Africa contain numerous dolerite intrusions, which affected the quality of the surrounding coal through thermal processes, commonly believed to be controlled by the size of the magmatic body. Data gathered from a working coalfield in Secunda, South Africa, suggest that the relationship between intrusive sills and coal is complex and factors other than intrusion width must be considered in relation to the contact metamorphic effect. The study area contains multiple dolerite intrusions of Karoo age, of which three intrusions occur as sills intruded close to the main coal seam of the. A large database (>8000 boreholes) of coal quality data was used to investigate the presence or absence of a change in coal quality relative to dolerite proximity. Reduction in coal quality was defined using three proximate analysis values, namely the ash, volatile content and dry ash free volatile (DAFV) as defined in the coal industry. The resultant investigation showed no correlation between the position and thickness of the dolerites, and changes in coal quality as measured by proximate analysis. In the absence of a linear relationship between coal quality and dolerite proximity, two processes are proposed to explain the absence of the contact metamorphic effects expected from previous studies. Firstly dolerite emplacement dynamics may influence the size of the metamorphic aureole produced by an intrusion, invalidating intrusion size as a measure of thermal output. Secondly, hydrothermal fluids mobilised by the dolerite intrusions, either from the country rock or the intrusion itself may percolate through the coal and act as the metamorphic agent responsible for changing coal quality, by dissolving the volatile and semi-volatile components of the coal and transporting them to other locations. These two processes are sufficient to explain the lack of a clear "metamorphic effect" related to the dolerite intrusions. However, the perceived lack of a clear correlation between the coal quality parameters and the metamorphic effects associated with dolerite intrusion may also reflect the inadequacies of proximate analysis techniques in quantifying geological processes within the coal.

  18. "SHRIMP geochronology for the 1450 Ma Lakhna dyke swarm: Its implication for the presence of Eoarchaean crust in the Bastar Craton and 1450-517 Ma depositional age for Purana basin (Khariar), Eastern Indian Peninsula": Comment

    Science.gov (United States)

    Basu, Abhijit; Bickford, M. E.

    2011-11-01

    As critical comments to the recent paper by Ratre et al. (2010, Journal of Asian Earth Sciences 39, 565-577) we cite U-Pb SHRIMP and CHIME ages of magmatic and detrital zircon and monazite from the Chhattisgarh and the Khariar basins in the Bastar craton to argue that these basins closed ca. 1000 Ma. We further argue that geochronologic data, geological evidence, and geological logic strongly indicate that sedimentation in the Khariar basin did not continue up to or beyond 517 Ma, as stated by Ratre et al. (op. cit).

  19. Test and Analysis on Soil Characteristics for the South Main Dyke of Jingjiang River%荆南长江干堤土性试验研究及分析

    Institute of Scientific and Technical Information of China (English)

    周小文; 何晓民; 龚壁卫

    2002-01-01

    In coordination of the construction of concealed work of levee project, the research on the soil quality of Jingnan levee in Hubei province was carried out through test. The results demonstrate: ① the Jingnan levee embankment is in bad quality, the compaction degree of most levee sections doesn't reach 92%; the average compressive coefficient of the levee backfilled soils is about 0.3 MPa; the seepage coefficients are 10\\+-5~10\\+-6 cm/s generally; the levee body was compacted unevenly; ② the soil layers of the levee foundation are distributed complicatedly and generally in low density; the void ratios of various soils are mostly in 0.7~1, indicating that the foundation soils are generally in loose state; ③ the pH value of levee body and foundation is 7.05~8.95, attributing to weak alkaline and not producing significant influence on liquid-plastic limit and shear strength of soils, the content of strongly soluble salt of levee foundation soils is 0.01%~0.52% and will not produce great influence on the mechanical behaviours of soils.

  20. Pre-caldera collapse of the Tastau volcanoplutonic ring complex (Eastern Kazakhstan)

    Science.gov (United States)

    Dokukina, K.

    2009-04-01

    Tastau volcanoplutonic ring complex belongs to the Zaisan Magmatic Province of Eastern Kazakhstan. ZMP consists of voluminous volcanic and plutonic rocks emplaced during regional extension affecting the Zaisan orogen. Extension affected crust previously thickened by the Late Carboniferous - Permian collision of the Kazakhstan with the Siberian craton (Buslov et al., 2004). Coeval mafic-felsic magmatism in the ZMP mostly consists of anatectic acidic magmas (Ermolov et al., 1983; Titov et al., 2001) with associated mantle-derived magmas having high-K calc-alkaline. Age of the Zaisan magmatism is Permian - Early Triassic (248 - 293 Ma) (Shcherba et al., 1998, Lyons et al., 2002). The hypabyssal Tastau volcanoplutonic ring complex 248 ± 34 Ma is the largest multiphase intrusive bodies which represent a volcanic root system. The complex intruded low-grade sedimentary rocks, which comprises sandstone and siltstone of a greywacke composition. The folded sedimentary complex was metamorphosed at a greenschist facies and up to hornblende hornfels facies during the intrusion of the complex. The volcanoplutonic complex has a form of an ellipse (13?18 km). Arc-shaped belts of composition dykes are intrude in the host rocks. A wide variety of magmatic rocks is represented within the Tastau volcanoplutonic complex: leucogranite, granite, granosyenite, gabbronorite and gabbro-diorite and calcium basite. Tastau magmatic rocks represent the continued calc-alkaline series and they are characterized by variations in chemical compositions (46 enclave are a subalcaline gabbro, a monzonite, a syenite and a quartz syenite (SiO2 = 46.2 - 62.8, Al2O3 = 15.8 - 19.6, TiO2 = 0.75 - 2.22, FeOtot = 4.7 - 11.5, MgO = 1.8 - 5.4, CaO = 2 - 7 wt.%) and high content of alkalines (Na2O+K2O = 5.2 - 9.3 wt.%). Mafic enclaves are depleted relatively the Maxut gabbro in Sr, Ca; and rich Rb, K. The felsic rocks are granite and felsite, which are depleted Ba, Sr, Tl, and rich U. All rocks have a similar

  1. Photograph of the month

    Science.gov (United States)

    2016-08-01

    Dykes in the Bidkhan strato-volcano located in the south eastern part of the Urumieh - Dokhtar magmatic arc, south west of Kerman, Iran. Repetitive dykes intrude through Oligo-Miocene Bidkhan pyroclastic sediments. A light dacitic dyke grew syntaxially within a gray andesitic dyke. The dykes trend NE and cross Oligo- Miocene lahar and pyroclastic sediments of the south west part of Bidkhan volcano caldera. Width of view appr. 10m. South of Bardsir city, SW Kerman, Iran. 29° 33.267≠ N, 056°, 27.25≠ E. Photograph © Reihaneh Keihanizadeh, Kerman, Iran. (http://keihanizadeh@gmail.com)

  2. Zircon and baddeleyite U-Pb geochronology and Hf isotopes from the Central Atlantic Magmatic Province (CAMP)

    Science.gov (United States)

    Davies, Joshua; Marzoli, Andrea; Bertrand, Herve; Youbi, Nasrrddine; Schaltegger, Urs

    2016-04-01

    Large Igneous Provinces (LIPs) are anomalously large volumes of dominantly mafic magma that erupted and intruded into the upper crust over short time scales. The origin of these volcanic provinces is very likely specific for each case, partly explained by plate tectonic processes or mantle plumes. Despite an ambivalent plate tectonic connection, there is a striking temporal correlation between the timing of LIPs and periods of mass extinction on Earth. However, establishing the relationship between these two is quite complicated since mass extinctions are typically recognised in the marine record, and LIPs are usually terrestrially emplaced. High precision geochronology of LIPs is essential to (i) establish the synchrony and infer the causal relationship with mass extinctions, and (ii) to understand how LIPs form. In this study, we apply high-precision zircon and baddeleyite U-Pb geochronology to rocks from the ~200 Ma Central Atlantic Magmatic Province (CAMP), in an attempt to reconstruct the overall timing of the event, its spatial distribution in time, and determine its relationship with the end-Triassic mass extinction. We also present Hf isotope data from the separated zircon and baddeleyite to both elucidate the origin of the LIP and also to determine if the magmas all originate from the same source. Our data suggest that the majority of the CAMP magmas were emplaced over a 0.5 Ma period from ~201.5 Ma to ~201.0 Ma with a possible small secondary event occurring much later at ~199 Ma. Spatially, it appears that CAMP magmatism occurred roughly simultaneously over the entire province (i.e. ~8000 Km North to South). However, the Hf isotopic composition varies over this length with the highest values (~5.5 ɛHf) occurring in a small area to the south of the province in Brazil and Sierra Leone. Towards the north, the ɛHf values become negative, indicating the presence of an older or more enriched component in the magmas. Our geochronology also indicates that CAMP

  3. The Archaean sanukitoid series of the Baltic Shield: geological setting, geochemical characteristics and implications for their origin

    Science.gov (United States)

    Lobach-Zhuchenko, S. B.; Rollinson, H. R.; Chekulaev, V. P.; Arestova, N. A.; Kovalenko, A. V.; Ivanikov, V. V.; Guseva, N. S.; Sergeev, S. A.; Matukov, D. I.; Jarvis, K. E.

    2005-01-01

    Archaean high-Mg granitoids (sanukitoids) occur in the Karelian granite-greenstone terrain in the Baltic Shield in two distinct zones. In the west of the Shield sanukitoid intrusions formed between 2700 and 2720 Ma and consist of a single igneous phase that varies in composition from diorite to granite. In the Eastern part of the Shield, sanukitoid intrusions formed between 2730 and 2745 Ma and are strongly differentiated, varying in composition from ultramafic to felsic. All the sanukitoids are enriched in light rare earth elements (LREE: La≤80 ppm, Ce≤150 ppm, La N/Yb N≤30-40), Sr≤2000 ppm, Ba≤2500 ppm, P 2O 5≤1.5%, alkalis (Na 2O+K 2O=5-10%), possess high mg# values (0.50-0.65), and show a negative Nb-Ta anomaly. They are spatially and temporally related to syenite intrusions and lamprophyre dykes. Sanukitoid intrusions in the Western and Eastern zones differ in composition. In the west, they have higher SiO 2 (mainly>60%) and lower alkalis, Sr, Ba, LREE than in the Eastern zone intrusions. The most differentiated intrusion, the Panozero intrusion in the Eastern zone, was formed in two magmatic cycles separated by ductile deformation. In the first cycle, ultramafic to monzonitic rocks formed, whereas, in the second cycle, the magmas were monzodioritic to quartz monzonite. Ultramafic and mafic rocks make up about 10% of the outcrop and occur as enclaves in monzonites and monzodiorites, and, as dykes, implies a number of discrete magmatic events. All rocks of the Panozero intrusion have high K 2O, and the composition of the initial melt, calculated from the weighted average of the first cycle magmas is monzodiorite (SiO 2=52%, mg#=0.55, Na 2O+K 2O˜6%). The presence of magmatic hornblende and biotite, a high carbonate content, widely distributed explosive breccias and evidence of liquid immiscibility are consistent with a high H 2O-CO 2 content in the sanukitoid melt. The geodynamic model which most satisfactorily explains our geological and

  4. Early Carboniferous (Viséan) emplacement of the collisional Kłodzko-Złoty Stok granitoids (Sudetes, SW Poland): constraints from geochemical data and zircon U-Pb ages

    Science.gov (United States)

    Mikulski, Stanisław Z.; Williams, Ian S.; Bagiński, Bogusław

    2013-06-01

    Sensitive high-resolution ion microprobe zircon U-Pb dating and geochemical data of igneous rocks from the composite Kłodzko-Złoty Stok (KZS) Granite Pluton, Sudetic Block, indicate that the granitoids represent an Early Carboniferous Viséan phase of Variscan metaluminous, high-K, I-type, syn-collisional granite magmatism within the Saxothuringian Zone of the Central European Variscides. Igneous zircon records hypabyssal magmatism that produced various granitoids and lamprophyre (spessartite) emplaced from ca. 340 to 331 Ma. The KZS granitoids have compositions ranging from granodiorite to monzonite, low A/CNK ratios (origin with high-K material from partly melted continental crust was probably a more important factor than fractional crystallization, in controlling the evolution of the magmas. The mean Pb-U ages of the main population of igneous zircon from a quartz monzodiorite (Żelazno) and hornblende monzonite (Droszków) are 340.2 ± 2.5 Ma and 339.5 ± 3.1 Ma, respectively. A slightly younger biotite-hornblende granodiorite from Chwalisław, 336.7 ± 2.5 Ma, was cut by a spessartite dyke at 333.1 ± 3.1 Ma. This indicates that mafic magmas were immediately intruded into fractured, probably incompletely solidified, granodiorites. The lamprophyric dyke also contains igneous zircon of Neoproterozoic age, 566.3 ± 6.4 Ma, typical of the crust in the Saxothuringian Zone. Tonalite from Ptasznik Hill near Droszków is of similar age to the spessartite, 331.5 ± 2.6 Ma. High REE contents in the tonalite and its igneous zircon indicate advanced differentiation of granitic magma, producing a more leucocratic melt associated with post-magmatic activity including abundant late crosscutting pegmatites and quartz veins, and contact metasomatic mineralization. The KZS granitoids have rather similar petrographic and geochemical characteristics to granitoids from other parts of the Central European Variscides, where a thickened orogenic root caused a substantial rise in

  5. Magmatic ore deposits in layered intrusions - Descriptive model for reef-type PGE and contact-type Cu-Ni-PGE deposits

    Science.gov (United States)

    Zientek, Michael L.

    2012-01-01

    Layered, ultramafic to mafic intrusions are uncommon in the geologic record, but host magmatic ore deposits containing most of the world's economic concentrations of platinum-group elements (PGE) (figs. 1 and 2). These deposits are mined primarily for their platinum, palladium, and rhodium contents (table 1). Magmatic ore deposits are derived from accumulations of crystals of metallic oxides, or immiscible sulfide, or oxide liquids that formed during the cooling and crystallization of magma, typically with mafic to ultramafic compositions. "PGE reefs" are stratabound PGE-enriched lode mineralization in mafic to ultramafic layered intrusions. The term "reef" is derived from Australian and South African literature for this style of mineralization and used to refer to (1) the rock layer that is mineralized and has distinctive texture or mineralogy (Naldrett, 2004), or (2) the PGE-enriched sulfide mineralization that occurs within the rock layer. For example, Viljoen (1999) broadly defined the Merensky Reef as "a mineralized zone within or closely associated with an unconformity surface in the ultramafic cumulate at the base of the Merensky Cyclic Unit." In this report, we will use the term PGE reef to refer to the PGE-enriched mineralization, not the host rock layer. Within a layered igneous intrusion, reef-type mineralization is laterally persistent along strike, extending for the length of the intrusion, typically tens to hundreds of kilometers. However, the mineralized interval is thin, generally centimeters to meters thick, relative to the stratigraphic thickness of layers in an intrusion that vary from hundreds to thousands of meters. PGE-enriched sulfide mineralization is also found near the contacts or margins of layered mafic to ultramafic intrusions (Iljina and Lee, 2005). This contact-type mineralization consists of disseminated to massive concentrations of iron-copper-nickel-PGE-enriched sulfide mineral concentrations in zones that can be tens to hundreds

  6. Juxtaposition of Neoproterozoic units along the Baruda - Tulu Dimtu shear-belt in the East African Orogen of western Ethiopia

    Science.gov (United States)

    Braathen, A.; Grenne, Tor; Selassie, M.G.; Worku, T.

    2001-01-01

    -K calc-alkaline volcanism characterised by pyroclastic deposits of andesitic composition, at an active continental margin at about 800 Ma. Subaerial arc volcanism was temporally and spatially overlapping with limited arc rifting, represented by submarine basalts compositionally transitional between enriched MORB and calc-alkaline magmas, and associated dyke swarms in the older carbonate-sandstone platform sequence. It is suggested that the large, mafic-ultramafic, bodies relate to this event and were originally formed as intrusions along one or more propagating rift axis within the arc complex. The regional Baruda shear-belt formed in response to contractional D1 deformation, and its location may have been largely controlled by competence contrasts between the array of rift-related intrusions and the marble-dominated lithologies. Associated shortening of the arc and back-arc region led to crustal thickening and emplacement of synkinematic, composite, batholiths at about 570-550 Ma. These are composed of moderately peraluminous granite and coeval, intermediate to mafic intrusions of shoshonitic affinity. D2 sinistral movements succeeded the contractional deformation. ?? 2001 Elsevier Science B.V.

  7. Petrogenetic evolution of the Early Miocene Alaçamdağ volcano-plutonic complex, northwestern Turkey: implications for the geodynamic framework of the Aegean region

    Science.gov (United States)

    Erkül, Sibel Tatar

    2012-01-01

    Extensional-tectonic processes have generated extensive magmatic activity that produced volcanic/plutonic rocks along an E-W-trending belt across north-western Turkey; this belt includes granites and coeval volcanic rocks of the Alaçamdağ volcano-plutonic complex. The petrogenesis of the Early Miocene Alaçamdağ granitic and volcanic rocks are here investigated by means of whole-rock Sr-Nd isotopic data along with field, petrographic and whole-rock geochemical studies. Geological and geochemical data indicate two distinct granite facies having similar mineral assemblages, their major distinguishing characteristic being the presence or absence of porphyritic texture as defined by K-feldspar megacrysts. I-type Alaçamdağ granitic stocks have monzogranitic-granodioritic compositions and contain a number of mafic microgranular enclaves of monzonitic, monzodioritic/monzogabbroic composition. Volcanic rocks occur as intrusions, domes, lava flows, dykes and volcanogenic sedimentary rocks having (first episode) andesitic and dacitic-trachyandesitic, and (second episode) dacitic, rhyolitic and trachytic-trachydacitic compositions. These granitic and volcanic rocks are metaluminous, high-K, and calc-alkaline in character. Chondrite-normalised rare earth element patterns vary only slightly such that all of the igneous rocks of the Alaçamdağ have similar REE patterns. Primitive-mantle-normalised multi-element diagrams show that these granitic and volcanic rocks are strongly enriched in LILE and LREE pattern, high (87Sr/86Sr)i and low ɛ Nd( t) ratios suggesting Alaçamdağ volcano-plutonic rocks to have been derived from hybrid magma that originated mixing of co-eval lower crustal-derived more felsic magma and enriched subcontinental lithospheric mantle-derived more mafic magmas during extensional processes, and the crustal material was more dominant than the mantle contribution. The Alaçamdağ volcano-plutonic complex rocks may form by retreat of the Hellenic

  8. Structure of the Gabon Margin from integrated seismic reflection and gravity data

    Science.gov (United States)

    Dupré, Stéphanie; Cloetingh, Sierd; Bertotti, Giovanni

    2011-06-01

    In the South Gabon Basin, deep multi-channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin. The thinned continental crust beneath the Gabon Margin appears to be composed of two distinct layers, separated by a clear, strong and more or less continuous reflector running in the 7-10 s TWT window. The lower crust is characterized by a higher density, intermediate between the lower values of the upper crust and the denser values of the mantle. The lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast. In the offshore thinned continental domain, the lower and upper crust form a 20-25 km thick body. Crustal thicknesses point to a relatively sharp and narrow transition, along a few tens of kilometers, between the unthinned and the thinned continental crust. The high density layer identified offshore Gabon presents similar characteristics in density, geometry and spatial distribution, as the underplated magmatic bodies observed along volcanic margins, e.g. along the South Atlantic Namibia Margin or the North Atlantic Vøring Margin. Although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks, we suggest that it could be composed of mafic rocks. Magmas resulting from partial melting during rifting may underplate the crust and/or be intruded in the lower crust through a system of dykes and sills. In this view, the present-day crustal thicknesses along rifted margins, characterized by magmatic underplating and/or intrusion, are not representative of the thinning that the crust experienced during rifting. Results of this study point to relatively shallow sedimentary basins along the South Gabon Margin. The deepest offshore depocenters located under the westernmost side of the continental platform appear to be associated with the deepest syn-rift basins These basins seem

  9. Age and Duration of the Paraná-Etendeka Flood Basalts and Related Plumbing System

    Science.gov (United States)

    Renne, P. R.

    2015-12-01

    The Paraná-Etendeka Igneous Province (PEIP) comprises a large volume sequence of continental flood basalts presently distributed assymetrically between South America (mainly southern Brazil but also parts of Uruguay, Paraguay and Argentina) and southwestern Africa (Namibia, Angola), following opening of the South Atlantic ocean. The PEIP is dominated by tholeiitic basalts to basaltic andesites, with subordinate silicic rocks spanning the dacite-trachyte-rhyolite fields, which occur as lava flows, sills and dike swarms as well as intrusive complexes closely related to the eruptive rocks. The PEIP has long been subject of 40Ar/39Ar geochronologic and paleomagnetic studies which led to conclude its rapid formation near the Hauterivian stage (~133 Ma) with onward progression to Barremian from the intrusive equivalents exposed northwards. Two decades after publication of the first 40Ar/39Ar ages for the Paraná flood basalts (Renne et al., 1992) we report here an updated study of the age and duration of this magmatic event. We calibrated a set of sixty published and new results to the calibration of Renne et al. (2011), which indicates an inception age of the volcanism now estimated at 135 ± 1 Ma, before the initiation of sea floor spreading. Lava extrusion progressed over ~2 Ma from south to north. A protracted duration of ~10 Ma inferred by Stewart et al. (1996) for PEIP volcanism is clearly incorrect, as also concluded by Thiede and Vasconcelos (2010). Low-Ti mafic magmas prevailed during the earlier stages followed over time by enhanced dominance of their silicic equivalents. Eruption of the high-Ti (mafic and silicic) magmas initiated simultaneously ~0.5 m.y. later, continuing up to ~133 Ma with injection of the Ponta Grossa dyke swarm. Despite several paleomagnetic polarity intervals recorded by the lava piles in the southern (> 27°S) and central (latitudes of ~24-27°S) domains of the Brazilian PEIP, the paleomagnetic data show small dispersion in agreement

  10. The Regularity of Gold Enrichment and Its Implications to Metallogenic Tectonics in Shuangwang Gold Deposit,Shaanxi Province%陕西双王金矿床矿化富集规律对成矿构造的指示意义

    Institute of Scientific and Technical Information of China (English)

    宫勇军; 姚书振; 谭满堂; 曹瑞荣; 程建军

    2016-01-01

    双王金矿床是秦岭地区大型的危机矿山之一,找矿工作是当务之急,但其成因类型特殊,人们对其成矿构造的演化过程和控矿机制尚存在争议.以该矿床KT5 矿体为例,研究了角砾岩体、断裂裂隙和金品位的空间分布关系,并结合趋势面分析,探讨了金矿化富集规律及其对成矿构造的指示意义.矿床地质特征及对矿区内基性岩墙的测年结果表明其成矿时代为印支期.在印支期秦岭造山过程中的 NS向主压应力背景下,成矿断裂早期右行斜向剪切作用奠定了角砾岩带的雏形;断裂中期活动引发的地震及伴生液压致裂作用,使矿区内形成了角砾岩主体和断裂裂隙系统,主成矿阶段角砾岩化作用减弱,断裂裂隙持续发育,并作为流体运移和成矿的主要通道和有利部位,使金的矿化富集呈面状展布,断裂裂隙带的产状变化是金沉淀的重要影响因素;晚期构造应力转换为近 EW向拉伸,近 NS向基性岩墙群侵位并受到成矿流体的改造.%Shuangwang gold deposit is one of the largest crisis mines in Qinling area with special genetic type,and it is urgent for us to undertake prospecting.But different scholars have some controversy over the evolution of the metallogenic tectonic as well as over the ore-controlling mechanism in this deposit.This paper studies the relationship of spatial distribution among the breccia bodies,fractures and fissures,and gold grade taking KT5 ore body in the deposit for an example.The regularity of gold enrichment and its implications to metallogenic tectonics are discussed,combined with trend surface analysis.According to mineralization characteristics and the age of the mafic dyke swarms in the mine area,it is suggested that the ore-forming process happened mainly in Indosinian.Under the compressive stress from north to south during Indosinian orogenesis in Qin-ling area,two sides of the metallogenic fault sheared obliquely with

  11. Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

    Science.gov (United States)

    Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

    2016-04-01

    The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the

  12. Permo-Triassic anatexis, continental rifting and the disassembly of western Pangaea

    Science.gov (United States)

    Cochrane, Ryan; Spikings, Richard; Gerdes, Axel; Ulianov, Alexey; Mora, Andres; Villagómez, Diego; Putlitz, Benita; Chiaradia, Massimo

    2014-03-01

    Crustal anatectites are frequently observed along ocean-continent active margins, although their origins are disputed with interpretations varying between rift-related and collisional. We report geochemical, isotopic and geochronological data that define an ~ 1500 km long belt of S-type meta-granites along the Andes of Colombia and Ecuador, which formed during 275-223 Ma. These are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon U-Pb dates ranging between 240 and 223 Ma. A model is presented which places these rocks within a compressive Permian arc setting that existed during the amalgamation of westernmost Pangaea. Anatexis and mafic intrusion during 240-223 Ma are interpreted to have occurred during continental rifting, which culminated in the formation of oceanic crust and initiated the break-up of western Pangaea. Compression during 275-240 Ma generated small volumes of crustal melting. Rifting during 240-225 Ma was characterized by basaltic underplating, the intrusion of tholeiitic basalts and a peak in crustal melting. Tholeiitic intrusions during 225-216 Ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust, and we assign this period to the onset of continental drift. Dissected ophiolitic sequences in northern Colombia yield zircon U-Pb dates of 216 Ma. The Permo-Triassic margin of Ecuador and Colombia exhibits close temporal, faunal and geochemical similarities with various crustal blocks that form the basement to parts of Mexico, and thus these may represent the relict conjugate margin to NW Gondwana. The magmatic record of the early disassembly of Pangaea spans ~ 20 Ma (240-216 Ma), and the duration of rifting and rift-drift transition is similar to that documented in Cretaceous-Tertiary rift settings such as the West Iberia-Newfoundland conjugate margins, and the Taupo-Lau-Havre System, where rifting and continental disassembly also occurred over periods lasting ~ 20 Ma.

  13. Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5.The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration).Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U-bearing minerals (astrocyanite, betafite and fergusonite).The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.

  14. Inorganic chemistry, petrography and palaeobotany of Permian coals in the Prince Charles Mountains, East Antarctica

    Science.gov (United States)

    Holdgate, G.R.; McLoughlin, S.; Drinnan, A.N.; Finkelman, R.B.; Willett, J.C.; Chiehowsky, L.A.

    2005-01-01

    Sampled outcrops of Permian coal seams of the Bainmedart Coal Measures in the Lambert Graben, eastern Antarctica, have been analysed for their proximates, ultimates, ash constituents and trace elements. A similar series of samples has been analysed for their principle maceral and microlithotype components and vitrinite reflectance. The coals are sub-bituminous to high volatile bituminous in rank; maturity increases markedly in southern exposures around Radok Lake where the oldest part of the succession is exposed and some strata have been intruded by mafic dykes and ultramafic sills. The coal ash is mostly silica and aluminium oxides, indicating that the mineral ash component is mostly quartz and various clay minerals. The ratio of silica to aluminium oxides appears to increase in an upward stratigraphic direction. The coal macerals include a relatively high liptinite content (mainly sporinite) that is significantly higher than for typical Gondwana coals. Greater degrees of weathering within the floodbasin/peat mire environments associated with climatic drying towards the end of the Permian might account for both preferential sporopollenin preservation and increased silica:aluminium oxide ratios up-section. Correlation of the coal maceral components to adjacent peninsula India coals indicates the closest comparative coals of similar age and rank occur within the Godavari Basin, rather then the Mahanadi Basin, which is traditionally interpreted to have been contiguous with the Lambert Graben before Gondwanan breakup. The petrological characteristics suggest that either previous interpretations of Palaeozoic basin alignments between Antarctica and India are incorrect, or that environmental settings and post-Permian burial histories of these basins were strongly independent of their tectonic juxtaposition. A permineralized peat bed within the succession reveals that the coals predominantly comprise wood- and leaf-rich debris derived from low-diversity forest

  15. Contrasted crustal sources as defined by whole-rock and Sr-Nd-Pb isotope geochemistry of neoproterozoic early post-collisional granitic magmatism within the Southern Brazilian Shear Belt, Camboriú, Brazil

    Science.gov (United States)

    Florisbal, Luana Moreira; de Assis Janasi, Valdecir; de Fátima Bitencourt, Maria; Stoll Nardi, Lauro Valentim; Heaman, Larry M.

    2012-11-01

    The early phase of post-collisional granitic magmatism in the Camboriú region, south Brazil, is represented by the porphyritic biotite ± hornblende Rio Pequeno Granite (RPG; 630-620 Ma) and the younger (˜610 Ma), equigranular, biotite ± muscovite Serra dos Macacos Granite (SMG). The two granite types share some geochemical characteristics, but the more felsic SMG constitutes a distinctive group not related to RPG by simple fractionation processes, as indicated by its lower FeOt, TiO2, K2O/Na2O and higher Zr Al2O3, Na2O, Ba and Sr when compared to RPG of similar SiO2 range. Sr-Nd-Pb isotopes require different sources. The SMG derives from old crustal sources, possibly related to the Paleoproterozoic protoliths of the Camboriú Complex, as indicated by strongly negative ɛNdt (-23 to -24) and unradiogenic Pb (e.g., 206Pb/204Pb = 16.0-16.3; 207Pb/204Pb = 15.3-15.4) and confirmed by previous LA-MC-ICPMS data showing dominant zircon inheritance of Archean to Paleoproterozoic age. In contrast, the RPG shows less negative ɛNdt (-12 to -15) and a distinctive zircon inheritance pattern with no traces of post-1.6 Ga sources. This is indicative of younger sources whose significance in the regional context is still unclear; some contribution of mantle-derived magmas is indicated by coeval mafic dykes and may account for some of the geochemical and isotopic characteristics of the least differentiated varieties of the RPG. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas despite their emplacement within a low-strain zone. It may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of Paleoproterozoic orthogneisses from the Camboriú Complex.

  16. Revealing the significance and polyphase tectonothermal evolution of a major metamorphic unit in an orogen: the central Sanandaj-Sirjan zone, Zagros Mts., Iran

    Science.gov (United States)

    Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Liu, Xiaoming; Dong, Yunpeng; Monfaredi, Behzad; Benroider, Manfred; Finger, Fritz; Waitzinger, Michael

    2016-04-01

    The Dorud-Azna region in the central Sanandaj-Sirjan metamorphic belt plays a key role in promoting the tectonic evolution of Zagros orogen, within the frame of the Arabia-Eurasia collision zone. From footwall to hangingwall, structural data combined with the U-Pb zircon and extensive 40Ar-39Ar mineral dating survey demonstrate three metamorphosed tectonic units, which include: (1) The Triassic June complex is metamorphosed within greenschist facies conditions, overlain by (2) the amphibolite-grade metamorphic Galeh-Doz orthogneiss, which is intruded by mafic dykes, and (3) the Amphibolite-Metagabbro unit. To the east, these units were intruded by the Jurassic Darijune gabbro. We present U-Pb detrital zircon ages of a garnet-micaschist from the Amphibolite-Metagabbro unit, which yield six distinctive age groups, including a previously unrecognized Late Grenvillian age population at ~0.93 to 0.99 Ga. We speculate that this unique Late Grenvillian group coupled with biogeographic evidence suggests either relationship with the South China craton or to the "Gondwana superfan". The laser ablation ICP-MS U-Pb zircon ages of 608 ± 18 Ma and 588 ± 41 Ma of the granitic Galeh-Doz orthogneiss reveals a Panafrican basement same as known from the Yazd block of Central Iran. Geochemistry and Sr-Nd isotopes of alka