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)


    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 (United States)

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


    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


    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)


    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


    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...

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

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


    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


    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. Petrogenesis and tectonic implications of the Neoproterozoic Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China (United States)

    Yang, Yi-Jin; Zhu, Wei-Guang; Bai, Zhong-Jie; Zhong, Hong; Ye, Xian-Tao; Fan, Hong-Peng


    Mafic-ultramafic dykes are important geological markers that can punctuate the onset of crustal extension during the breakup of a continent and provide valuable information on the mantle source. This study reports secondary ion mass spectroscopy zircon and baddeleyite U-Pb ages, elemental and Nd isotopic data for the Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China. Two kinds of rocks are confirmed: the picritic rock and the dolerite. Based on petrographic and geochemical features, the dolerite dykes are further subdivided into two groups: Group I mafic and Group II mafic dykes, which emplaced at ~760 Ma (zircon U-Pb) and ~800 Ma (zircon and baddeleyite U-Pb), respectively. All samples from the picritic rocks and the Group I mafic rocks show the features of high-Ti and alkaline basaltic magma in composition as well as "humped" trace element patterns, which are similar to those of typical alkaline basalts associated with continental rifts except for the slightly negative Nb-Ta anomalies. The Group II mafic rocks display the features of low-Ti and tholeiitic magma, moderately enriched in LILE and LREE, and characterized by distinctively negative Nb-Ta anomalies. The primary magmas of the picritic rocks and the Group I mafic rocks were generated from ca 25 % partial melting of an OIB-like, Nd isotopically depleted but incompatible elements relatively enriched mantle source within a garnet stable field. The Group II mafic rocks crystallized from crustal contaminated mafic magmas that were derived from a spinel-bearing sub-continental lithospheric mantle source, because of low ratios of La/Yb, Ti/Y and Sm/Yb. Geochemical features suggest that these groups of mafic-ultramafic dykes were formed in a continental rift setting, but derived from different mantle sources. In combination with other Neoproterozoic igneous rocks in the western margin of Yangtze Block, it is suggested that the Datian mafic-ultramafic dykes in the Panzhihua area

  9. Nature of mantle source contributions and the role of contamination and in situ crystallisation in the petrogenesis of Proterozoic mafic dykes and flood basalts Labrador (United States)

    Cadman, A. C.; Tarney, J.; Baragar, W. R. A.


    Proterozoic tholeiitic dyke swarms share many compositional features with, and pose similar petrogenetic problems to, Phanerozoic continental flood basalts, but there are few extrusive equivalents of such swarms. The Mesoproterozoic (1.27 Ga) Harp dyke swarm in Labrador is one where possible extrusive equivalents exist in the Seal Lake group, but are slightly displaced in space and time, and can probably be related by models of progressive crustal extension. Here we try to evaluate the roles of crystal differentiation, in situ crystallisation, crustal assimilation and the relative contributions of asthenosphere- and lithosphere-derived melts in the petrogenesis of the mafic magmas. Modelling of the major and trace element variations both within individual dykes and between dykes, and within the lava sequence, does not suggest an important role for continental crust involvement. While in situ crystallisation processes could account for some of the compositional variations, the most successful models invoke mixing or contamination of asthenospheric magmas with/by veined material in the lower lithosphere / upper asthenosphere which carries the ‘continental’ characteristics. The results imply an important role for hydrous phases such as phlogopite and hornblende in the sub-lithosphere mantle. Much of the low-MgO character of mafic dykes may result from significant removal of mafic phases during in situ crystallisation within the lithosphere.

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

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    Randive Kirtikumar


    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.

  11. 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 (United States)

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


    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.

  12. The mafic dyke swarm of Uaua (Brazil): geological and petrographical aspects

    International Nuclear Information System (INIS)

    The Uaua mafic dike swarm stands out as one of the most extensive swarms in the Sao Francisco craton. These dikes crop out around the town of Uaua (State of Bahia) and to the east near the Rio Capim greenstone belt. The dikes intrude the Archean basement which is composed of medium-to high-grade gneisses and migmatites. Table 1 shows the geochronological results for basement rocks, which have yielded ages between 2,730-3,016 m.y. (Tb-Sr,whole rock isochron) indicating a Late Archean evolution for these rocks. On the other hand, available 40 Ar-39 Ar (biotite) and K-Ar (amphibole) determinations for basement rocks yield Early Proterozoic ages, the result of overprinting of the Transamazonico orogenic cycle. (author)

  13. 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)


    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.

  14. Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey (United States)

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


    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

  15. K-Ar geochronology of mafic dyke swarms from the meridional part of Sao Francisco craton and implications on tectonic context

    International Nuclear Information System (INIS)

    The southern region of the Sao Francisco Craton is made up of gneissic-granitoid terranes (mainly of amphibolite facies) associated with supracrustals, which can be separed into two crustal provinces, the oldest formed during the Archean (3-2-2.6 Ga.), and the youngest in the Early Proterozoic (2.4-2.0 Ga.). Mafic dyke swarms inject the basement complexes in the area west of Belo Horizonte city, but not the Late proterozoic Bambui sedimentary cover. These dykes show NNW, NW, WNW, NNE and ENE trends and are of anorogenic character. Most dykes are tholeiitic in composition. Metamorphic recrystallization at greenschist to amphibolite facies as well as minor hidrothermal and/or deuteric transformations are characteristics in the majority of the these dykes. About sixty K/Ar determinations have been performed on plagioclases, amphiboles and whole rocks. They are interpretated combining the use of K/Ar diagrams and histogram, and according to the crustal evolution proposed for the craton. The available radiometric data suggest that the main period of mafic intrusions took place in the Early proterozoic as supported by the apparent ages on amphiboles. However, the beginning of the Middle Proterozoic (1.7-1.5 Ga.) probably corresponds to a period of tensional tectonics as well. On the other hand, most ages obtained on plagioclases and whole rocks, can be associated with Late Proterozoic processes of argon gain or loss. The results are tectonicaly associated with crustal rifting of the continental mass. This two radiometric groupings are characteristic for the evolution of the Early proterozoic crustal provine and of the Mid-Proterozoic intracratonic Espinhaco System respectively. The youngest Late Proterozoic apparent ages associated with the reflections of the contemporaneous evolution of the Braziliano marginal mobile belt which is also suggested by the partial resetting of the K/Ar ages of basement rocks within the eastern part of the Sao Francisco Craton. (author)

  16. 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 (United States)

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


    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.

  17. 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


    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

  18. Evidence for non-coaxiality of ferrimagnetic and paramagnetic fabrics, developed during magma flow and cooling in a thick mafic dyke

    Czech Academy of Sciences Publication Activity Database

    Silva, P. F.; Marques, F. O.; Machek, Matěj; Henry, B.; Hirt, A. M.; Roxerová, Zuzana; Madureira, P.; Vratislav, S.


    Roč. 629, August (2014), s. 155-164. ISSN 0040-1951 Institutional support: RVO:67985530 Keywords : paramagnetic * ferrimagnetic * fabrics * microstructures * dyke emplacement * stress field Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.872, year: 2014

  19. Country rock contamination of marginal mafic granulites bordering the Nain Plutonic Suite : implications for mobilization of Sr during high-grade contact metamorphism


    Royse, Katherine; Noble, Stephen; Tarney, John; Cadman, Andy


    The marginal mafic granulites that locally border the Nain Plutonic Suite (NPS) have a range of initial Nd-isotope ratios that overlap with that of the NPS anorthosites and associated Nain dykes. The similarity in Nd-isotope data suggests that gneissic Archaean country rocks have contaminated all the anorthosites, marginal mafic granulites, and dykes. Sr-isotope data for the mafic granulites and dykes support a country rock contamination scenario but preclude wholesale assimilation of rocks s...

  20. Betty Van Dyke: The Van Dyke Ranch


    Rabkin, Sarah


    Born in 1932 to Croatian American farmers in the Santa Clara Valley town of Cupertino, Betty Van Dyke saw her fertile home ground transformed, in a few decades, from seemingly endless orchards to unrelenting urban sprawl. As the energetic matriarch of a popular family-run fruit-growing business, she has since participated in the region’s organic agricultural renaissance, overseeing one of the first California operations to grow and dry fruit organically (becoming certified in 1986), and playi...

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

    Directory of Open Access Journals (Sweden)

    José Moacyr Vianna Coutinho


    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.

  2. Finding General Dyke. (United States)

    Dyke, Charles William; Dyke, Ann Bisconti


    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

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

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


    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

  4. The application aeromagnetic data for dyke swarm mapping (an example the Ladoga region, Russia) (United States)

    Vasilieva, T.; Frank-Kamenetsky, D.


    Vasilieva T.I., Frank-Kamenetsky D.A., Zayonchek A.V. The main factor of the Fennoscandian evolution in Late Proterozoic was inter- and intracratonic rifting. However, products of magmatic activity were removed by erosion. Thus, only plutonic bodies and dyke swarms allow us to reconstruct the Fennoscandian shield tectono-magmatic evolution in Late Proterozoic. The rifting processes in southeastern Fennoscandia took place in Riphean. The earlier are several massifs of rapakivi-granite accompanied by mafic dyke swarms with age about 1.64 to 1.51 Ga were formed. The Middle Riphean is characterized by rift structure forming. They are known in Russia (White Sea rift system, northern Kola, Ladoga Lake, probably, Onega Lake), Finland (Muhos, Satakunta) and central Sweden. The age of mafic magmatic complexes, corresponding with these rift systems, is 1.24 Ga (Suominen, 1991). There are at least two stages of Riphean evolution and magmatic complexes in Ladoga Lake region. They are the Salminski and Vyborg rapakivi-granites at first, Salminski volcano-sedimentary suite, Valaam sill, Hopunvaara intrusion and several dolerites dykes at second. Our detailed studies based on magnetic geophysical data. A combination of geophysical methods and GIS provided effective mapping of dyke swarms in NW Ladoga. It has shown that the Fe-enriched olivine dolerite dykes, it was described on the NW coast of Ladoga Lake, are very locally developed forming narrow zone, which runs through Sortavala town and several islands. The dykes were clearly observed, because of their extremely high magnetic susceptibility. The dykes strike toward NW corresponding to the longest axis of the graben. Chemical identity of the dykes and Salminski lavas allows considering the age of this rifting about 1.35 Ga. The other dyke complexes were being described in North-West Ladoga region. It is dykes of fresh clinopyroxene dolerites. Probably, the dykes are accompanying by rapakivi-granites. Unfortunately, very

  5. Tectonic setting of the Great Dyke, Chembadzi, Chewore and Atchiza layered complexes in Zimbabwe and Mozambique

    International Nuclear Information System (INIS)

    The Great Dyke of Zimbabwe is one of the largest ultramafic-mafic layered igneous complexexs in the world. Because of the economic importance of large layered intrusions like the Great Dyke, their tectonic setting is of great interest. The Chembadzi complex is a 14 km long, dyke-like layered intrusion up to 800m wide. The Chewore complex, which was thought to have the structure of an irregular lopolith, outcrops over an area of about 200 km in horst blocks in the lower Zambezi Valley in northern Zimbabwe. The Atchiza complex is situated just north of the Cahora Bassa lake and the Zambezi River valley in Mozambique. In considering the tectonic setting of the Great Dyke and its correlatives, most attention has been focussed on events in the Limpopo Mobile Belt, which were responsible for producing the fractures in the Zimbabwe craton that is occupied by the intrusives. 39 refs

  6. 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


    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.

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

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


    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.

  8. Dyke-Davidoff-Masson syndrome

    Directory of Open Access Journals (Sweden)

    Manas R Behera


    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.

  9. Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple Magma Types During Orogenic Collapse (United States)

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


    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

  10. Mafic magmatism in the Eastern Cordillera and Putumayo Basin, Colombia : causes and consequences


    Vásquez Parra, Mónica Fernanda


    The Eastern Cordillera of Colombia is mainly composed of sedimentary rocks deposited since early Mesozoic times. Magmatic rocks are scarce. They are represented only by a few locally restricted occurrences of dykes and sills of mafic composition presumably emplaced in the Cretaceous and of volcanic rocks of Neogene age. This work is focused on the study of the Cretaceous magmatism with the intention to understand the processes causing the genesis of these rocks and their significance in the r...

  11. Magma deformation and emplacement in rhyolitic dykes (United States)

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


    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

  12. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena


    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

  13. 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


    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.

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


    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. Flowage differentiation in an andesitic dyke of the Motru Dyke Swarm (Southern Carpathians, Romania) inferred from AMS, CSD and geochemistry (United States)

    Nkono, Collin; Féménias, Olivier; Diot, Hervé; Berza, Tudor; Demaiffe, Daniel


    Two dykes of different thickness (5.5 m for TJ31 and 23 m for TJ34) from the late Pan-African calc-alkaline Motru Dyke Swarm (S. Carpathians, Romania) have been studied by electron microprobe (mineral chemistry), crystal size distribution (CSD), anisotropy of magnetic susceptibility (AMS) and whole-rock geochemistry. All the physical and chemical variations observed across the dyke's width point to concordant results and show that the variations of both modal abundance and size of the amphibole and biotite microphenocrysts inside the dykes (deduced from the classical CSD measurements) are the result of a mechanical segregation of suspended crystals during magmatic transport. Despite a pene-contemporaneous regional tectonic, the flow-induced differentiation in the thicker dyke is characterized by the concentration of pre-existing Ti-rich pargasite-tschermakite, clinopyroxene and plagioclase crystals in the core of the dyke and of the extracted differentiated liquid near the walls. This mechanical differentiation induces a chemical differentiation with a basaltic andesite composition for the core of the dyke whereas the margins are andesitic. Thus the chilled margins appear as a slightly more evolved liquid with a Newtonian behaviour when compared to the average composition of the dyke. The localization of the liquid on both sides of the dyke has certainly facilitated the ascent of the central part of the dyke that behaved as a Binghamian mush.

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

    Directory of Open Access Journals (Sweden)

    Hannu Huhma


    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.

  17. Dyke-Davidoff-Masson Syndrome in Two Children


    MD, Mete ÖZDİKİCİ; MD, Volkan TANI; MD, Suat EREN; MD, Çetin ÇELENK


    A three year old boy and a 12 year old girl with uniateral cerebral atrophy were diagnosed as Dyke-Davidoff-Masson syndrome using cranial computed tomography. Magnetic resonance imaging was also done in the second case. The findings were compared with the relevant literature. Key words: Dyke-Davidoff-Masson syndrome, unilateral cerebral atrophy, radiology

  18. 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? (United States)

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


    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

  19. Mesozoic dyke swarms of the Falkland Islands (South Atlantic)


    Stone, P


    An aeromagnetic survey that allowed an improved discrimination of the principal dyke swarms of the Falkland Islands has been augmented by additional radiometric dates and geochemical analyses of representative specimens. Most of the dykes previously described as forming a “north-south” swarm of Jurassic age are associated with a set of NE-SW linear magnetic anomalies that are entirely separate from another set of N-S to NNW-SSE anomalies, The NE-SW Jurassic dyke swarm occurs mostly in West Fa...

  20. Paleomagnetism of Devonian dykes in the northern Kola Peninsula and its bearing on the apparent polar wander path of Baltica in the Precambrian (United States)

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


    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.

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


    Susanna Falsaperla; Marco Neri


    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...

  2. Mafic-silicic magma interaction in the layered 1.87 Ga Soukkio Complex in Mäntsälä, southern Finland

    Directory of Open Access Journals (Sweden)

    Toni T. Eerola


    Full Text Available The Svecofennian layered Soukkio Complex (1.87 Ga in Mäntsälä, southern Finland, consists of layered tholeiitic gabbro and porphyritic calc-alkaline monzonite, quartz monzonite and granite, mingled together. The gabbro belongs to a group of ten mafic-ultramafic intrusions of Mäntsälä, part of the 150 km long and 20 km wide, linear, E-W trending Hyvinkää–Mäntsälä Gabbroic Belt(HMGB, representing syn-collisional magmatism. Structures and textures related to magma mingling and mixing occur in a 1–2 km wide zone around Lake Kilpijärvi, located at the center of the Soukkio Complex. The complex is compositionally stratified and consists of four zones:its base, found at the Western Zone, is a dynamically layered gabbro. The followingtonalite is probably a result of magma mixing. Felsic amoeboid layers and pipes, alternating with or cutting the fine-grained gabbro in the Central-Western Zone, resemble those of mafic-silicic layered intrusions in general. Mafic magmatic enclaves (MMEs and pillows form the South-Central Zone and disrupted synplutonic mafic dykes or sheets intruded the granite in the Eastern Zone. The MMEs and disrupted synplutonic mafic dykes or sheets show cuspate and chilled margins against the felsic host, quartz ocelli, corroded K-feldspar xenocrysts with or without plagioclase mantles, and acicular apatite, all typical features of magma mingling and mixing. Mixing is suggested by intermediate composition of MMEs between granitoid and gabbro, as well as by their partly linear trends in some Harker diagrams. REE composition of the MMEs is similar to that of the Soukkio Gabbro, as expected for granite hosted MMEs. The model proposed for evolution of the Soukkio Complex involves intrusion of mafic magma into the crust, causing its partial melting. This generated granitic magma above the mafic chamber. Injections of mafic magma invaded the felsic chamber and those magmas interacted mainly by intermingling. Mingling and

  3. Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks (United States)

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


    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.

  4. Link between extension, dyking and subsidence as the reconstruction tool of intraplate rifting mechanism (backstripping data, modelling and geochronology) (United States)

    Polyansky, Oleg P.; Reverdatto, Vladimir V.; Babichev, Alexey V.


    predicted over a range of γ = 0.01-0.12 (average value 0.06, i.e., ~6%). This value seems acceptable if we consider cumulative sills and dykes thicknesses in the outcrops and borehole sections in the Upper Devonian-Lower Carboniferous sediments. For better rifting age resolution we sampled dolerites from the western, eastern and central dyke swarms, which were then analyzed by stepwise 40Ar/39Ar heating. The determined ages of the monomineral plagioclase and pyroxene fractions from the dyke samples (345-378 Ma) coincide well with fast subsidence and sedimentation phase in the Devonian defined by backstripping data. Dating of dyke intrusions shows following succession of rifting episodes: extension by dyking starts near the central axes (364-378 Ma), extending to the periphery areas on the opposite sides of the rift through (345-362 Ma). The established sequence of dyke intrusions is alternative to the oceanic crust spreading, at which the age of intrusions is increased from the spreading center in rift-perpendicular direction. Results of thermo-mechanical modelling of formation of the Vilyui rift basin are presented. The goal of 2D finite elements modelling is to demonstrate that the deep troughs can form in the continental crust under its limited extension. The 2D numerical simulation shows the possibility of considerable localized subsidence near the rift axis and explains why mafic dike swarms are concentrated on the basin periphery. Thus, the mechanism of the Vilyui basin formation by means of magmatic rifting is corroborated [Polyansky at al., 2013]. RFBR grant no. 14-05-00188.

  5. Geochemistry and geochronology of mafic rocks from the Luobusa ophiolite, South Tibet (United States)

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


    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

  6. U-Pb geochronology and paleomagnetism of the Neoproterozoic St Simeon dolerite dykes, Quebec: an eastern Laurentian perspective of Ediacaran Rodinia breakup (United States)

    Pisarevsky, Sergei; Murphy, Brendan; Hamilton, Mike; Söderlund, Ulf; Hodych, Joseph


    The St Simeon (SS) mafic dykes (150 km NE of Quebec City) are now dated at 548 ± 1 Ma (U-Pb; baddeleyite). This age is similar to a published LA-ICPMS zircon age of 550 ± 7 Ma for the Mt. St-Anselme (MS) basalts, which supports previous inferences of (i) a genetic relationship between them, (ii) the pene-contemporaneity of OIB-type mafic magmatism in East Laurentia and (iii) the existence of two late Ediacaran plumes that attended the final breakup of Rodinia and opening of the Iapetus Ocean and Tornquist Sea. Both the SS dykes and the MS basalts were sampled for paleomagnetic study. The paleomagnetic pole for SS is similar to the previously published pole for coeval basalts (Skinner Cove, SC) from Newfoundland. Unlike SC, the St Simeon pole represents rocks which are unambiguously coherent tectonically with the Laurentian Craton. This new pole is also coeval with high quality poles from the Winter Coast (Baltica) and provides paleomagnetic constraints on the history of the final breakup of Rodinia and opening of Eastern Iapetus and Tornquist Sea.

  7. 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


    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

  8. 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


    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.

  9. Local stresses, dyke arrest and surface deformation in volcanic edificesand rift zones

    Directory of Open Access Journals (Sweden)

    L. S. Brenner


    Full Text Available Field studies indicate that nearly all eruptions in volcanic edifices and rift zones are supplied with magma through fractures (dykes that are opened by magmatic overpressure. While (inferred dyke injections are frequent during unrest periods, volcanic eruptions are, in comparison, infrequent, suggesting that most dykes become arrested at certain depths in the crust, in agreement with field studies. The frequency of dyke arrest can be partly explained by the numerical models presented here which indicate that volcanic edifices and rift zones consisting of rocks of contrasting mechanical properties, such as soft pyroclastic layers and stiff lava flows, commonly develop local stress fields that encourage dyke arrest. During unrest, surface deformation studies are routinely used to infer the geometries of arrested dykes, and some models (using homogeneous, isotropic half-spaces infer large grabens to be induced by such dykes. Our results, however, show that the dyke-tip tensile stresses are normally much greater than the induced surface stresses, making it difficult to explain how a dyke can induce surface stresses in excess of the tensile (or shear strength while the same strength is not exceeded at the (arrested dyke tip. Also, arrested dyke tips in eroded or active rift zones are normally not associated with dyke-induced grabens or normal faults, and some dykes arrested within a few metres of the surface do not generate faults or grabens. The numerical models show that abrupt changes in Young's moduli(stiffnesses, layers with relatively high dyke-normal compressive stresses (stress barriers, and weak horizontal contacts may make the dyke-induced surface tensile stresses too small for significant fault or graben formation to occur in rift zones or volcanic edifices. Also, these small surface stresses may have no simple relation to the dyke geometry or the depth to its tip. Thus, for a layered crust with weak contacts, straightforward

  10. Explosive mafic volcanism on Earth and Mars (United States)

    Gregg, Tracy K. P.; Williams, Stanley N.


    Deposits within Amazonia Planitia, Mars, have been interpreted as ignimbrite plains on the basis of their erosional characteristics. The western flank of Hecates Tholus appears to be mantled by an airfall deposit, which was produced through magma-water interactions or exsolution of magmatic volatiles. Morphologic studies, along with numerical and analytical modeling of Martian plinian columns and pyroclastic flows, suggest that shield materials of Tyrrhena and Hadriaca paterae are composed of welded pyroclastic flows. Terrestrial pyroclastic flows, ignimbrites, and airfall deposits are typically associated with silicic volcanism. Because it is unlikely that large volumes of silicic lavas have been produced on Mars, we seek terrestrial analogs of explosives, mafic volcanism. Plinian basaltic airfall deposits have been well-documented at Masaya, Nicaragua, and basaltic ignimbrite and surge deposits also have been recognized there. Ambrym and Yasour, both in Vanuatu, are mafic stratovolcanioes with large central calderas, and are composed of interbedded basaltic pyrocalstic deposits and lava flows. Zavaritzki, a mafic stratovolcano in the Kurile Islands, may have also produced pyroclastic deposits, although the exact nature of these deposits in unknown. Masaya, Ambrym and Yasour are known to be located above tensional zones. Hadriaca and Tyrrhena Paterae may also be located above zones of tension, resulting from the formation and evolution of Hellas basin, and, thus, may be directly analogous to these terrestrial mafic, explosive volcanoes.

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

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Jia-fa


    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.

  12. 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


    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.

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

    Indian Academy of Sciences (India)

    Gautam Gupta; Vinit C Erram; Suyash Kumar


    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.

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

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


    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.

  15. Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania (United States)

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


    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.

  16. 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 (United States)

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


    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.

  17. Dyke emplacement and propagation: a new laboratory approach (United States)

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


    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

  18. Permanent groundwater storage in basaltic dyke fractures and termite mound viability (United States)

    Mège, Daniel; Rango, Tewodros


    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

  19. Rb-Sr ages of lamprophyre dykes from Schirmacher Oasis, Queen Maud Land, east Antarctica

    International Nuclear Information System (INIS)

    Lamprophyre dykes intrude the late proterozoic metamorphic terrain of Schirmacher Oasis, Queen Maud Land, east Antarctica. Rb-Sr whole-rock/mineral isochron ages of two lamprophyre dykes are 455± 12 Ma (Sri=0.70886 ± 5) and 458±6 Ma (Sri=0.71388 ± 98). This lamprophyre dyke activity of Schirmacher Oasis, may be interpreted as a manifestation of post orogenic alkaline magmatism related to the Ross orogeny of the Transantarctic mountains. (author)

  20. Rotation of the Falklands microplate reassessed after recognition of discrete Jurassic and Cretaceous dyke swarms


    Stone, P; G. S. Kimbell; Richards, P.C.


    Recently acquired aeromagnetic data for the Falkland Islands have shown that previous interpretations of the dolerite dyke swarms are inadequate. In particular, most of the dykes previously described from West Falkland as forming a ‘north–south’ swarm of Jurassic age are associated with a set of NE–SW linear magnetic anomalies that are entirely separate from another set of truly N–S anomalies. Very few dykes had been previously reported from East Falkland, but the aeromagnetic survey demonstr...

  1. Petrology and geochemistry of dolerite dykes of Dharmapuri and Salem districts of Tamil Nadu

    International Nuclear Information System (INIS)

    Dolerite dyke sets occur distributed in the Dharmapuri and Salem districts of northern Tamil nadu. These dykes have been emplaced in the older basement composed of granulite and gneissic rocks and cut across the later formed lineament controlled alkaline complexes. They are composed of medium to coarse calcic plagioclase and clinopyroxene with biotite, amphibole, uralite, olivine, orthopyroxene, and anhedral quartz as accessories. Based on geochemical characters, the olivine bearing dykes are classed as Type I and the quartz bearing dykes as Type II. The Type I dykes resemble basalt and the Type II dykes, basaltic andesite. They display LILE> HFSE in terms of abundance. The REE values indicate enrichment of LREE relative to MREE and HREE and an E-MORB or Plume MORB signature. The geochemistry of the sampled dykes suggests derivation from a mantle plume. This plume was emplaced into the garnet lherzolite layer and subsequently into the shallower spinel lherzolite layer in the mantle. Polybaric melting of lherzolite protoliths with varying proportions of garnet and spinel occurred with subsequent fractionation to produce a source melts with E-MORB characteristics. Emplacement of these dykes was aided by crustal extension and associated fracturing to develop a dyke swarm. (author)

  2. Cretaceous dykes discovered in the Falkland Islands : implications for regional tectonics in the South Atlantic


    Stone, P; Richards, P.C.; G. S. Kimbell; Esser, R. P.; Reeves, D.


    New aeromagnetic data resolve the dykes of the Falkland Islands into three swarms. A hitherto unrecognized suite of north–south dykes is established as early Cretaceous by an Ar–Ar date of about 121 Ma. Swarms of NE–SW and east–west dykes are both early Jurassic: the former gives an Ar–Ar age of about 178 Ma, whereas the latter has been previously dated to about 190 Ma. The intrusion of the Cretaceous dykes marks the onset of oceanic crust generation in the South Atlantic and so restricts to ...


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    Biswadev Basu


    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

  4. Paleomagnetism of diabase dykes, pegmatitic granites and TGG gneisses in the Olkiluoto area

    Energy Technology Data Exchange (ETDEWEB)

    Mertanen, S. (Geological Survey of Finland, Espoo (Finland))


    Paleomagnetic studies in the Olkiluoto area were carried out on two diabase dykes, on four sites of pegmatitic granites and on three sites of TGG gneisses. Remanent magnetizations in the diabase dykes are strong, and two remanence components were isolated. The other component is regarded as primary, formed during cooling of the dykes. Based on comparison to previously known Fennoscandian paleomagnetic data, the pole position of the primary component shows that the dykes are ca. 1560 Ma in age. The pole position of the poorly defined secondary component of the diabase dyke gives an age of ca. 250 Ma. Pegmatitic granites are weakly magnetized, but one pegmatitic granite site gave a rather consistent remanence direction which points to a remagnetization at ca. 1570 Ma, probably due to emplacement of the nearby rapakivi granites. The TGG gneisses do not carry any stable remanent magnetization. (orig.)

  5. Sr-Nd isotopic composition of lamprophyre dykes from Queen Maud Land, East Antarctica

    International Nuclear Information System (INIS)

    Alkali basaltic-lamprophyric dykes intrude precambrian gneisses in the Schirmacher oasis, Queen Maud land, East Antarctica. Rb-Sr and Sm-Nd isotopic data on two lamprophyre dykes are reported from the Schirmacher oasis. The lamprophyre dykes have given Rb-Sr biotite/whole rock isochron age of 439 ± 10 Ma (2σ). Large variations in εSr and εNd indicate higher degree of crustal assimilation. Higher εSr (+54 to +72) and lower εNd (-7 to -13) of these dykes also suggest that the source was contaminated by older crust. Biotite/whole rock Rb-Sr isotope data on lamprophyre dykes show that the terrain was affected by thermal event during early paleozoic which is correlated with the end of Pan-African orogeny. (author)

  6. Dyke Propagation Through a Partially Submerged Volcanic Edifice (United States)

    Tait, S.; Taisne, B.; Limare, A.; Manga, M.; Pasquet, E.


    We have studied using analogue experiments the ascent of magma through a volcanic edifice. The edifice is simulated using a cone of gelatine and the magma is an aqueous solution. The latter is injected at the base of the cone and propagates through the edifice in hydraulic fractures that represent dykes. The buoyancy of the magma with respect to the edifice is varied by adjusting salt concentration in the aqueous solution and/or sugar concentration in the gelatine. The system is axisymmetric. After the gelatin is released from its mold, it is partially submerged in a layer of water that represents the surrounding ocean. Because the gelatin is denser than water, its weight generates an axisymmetric stress field in the edifice whose amplitude depends, for a given edifice density, on the depth of the water which represents ''sea-level''. We derive the geometry and amplitude of this stress field by using birefringence in the gelatin that results from its photoelasticity. We document the geometry of the dykes as they propagate and the elevation of eruptive fissures on the edifice as a function of the dimensionless parameters governing the system. Positive buoyancy of the magma tends to favour summit eruptions and increasing weight of the edifice (lower sea-level with respect to edifice height) tends to favour flank eruptions. We compare the experimental results with a dataset from Piton de la Fournaise, Reunion Island and draw some general conclusions about expected changes in eruptive behaviour as a volcanic island grows to greater and greater altitude above sea-level.

  7. Palaeomagnetic and rock magnetic studies on the dykes of Goa, west coast of Indian Precambrian Shield (United States)

    Patil, S. K.; Rao, D. R. K.


    Detailed alternating field (AF) and thermal demagnetization techniques on 120 samples belonging to 10 dykes of the Goa region along the west coast of the Indian Precambrian Shield, have yielded characteristic remanent magnetization (ChRM) directions from 9 dykes of which 6 dykes exhibited a reverse magnetic polarity direction ( D=150°, I=44.30°, k=58, α95=5.8, N=6 dykes), while 3 dykes exhibited normal polarity D=351°, I=-50°, k=21, α95=14.9, N=3 dykes) direction. The remaining 1 dyke has shown stable direction, but with a strong overprint of the present earth field (PEF) direction, which could not be removed by either AF or thermal cleaning techniques. A Palaeomagnetic pole, computed by averaging the VGPs of 9 dykes is situated at 41.2°N 78.1°W ( N=9 dykes; A95=9.81°), which is close to that of the Deccan super pole (36.9°N, 78.8°W), suggesting that the dykes in the Goa region are related to the Deccan basaltic eruptions. Recently published 40Ar/ 39Ar dating on the normal polarity dykes of the studied area have assigned the ages as 62.8±0.2 Ma. These results demonstrate that the Deccan magnetism continued to affect western India for at least 1-2 Ma after the peak Deccan eruption during the K- T boundary. On the basis of published geological and geochemical information along with our Palaeomagnetic results, these intrusive bodies could be attributed as the feeders for the uppermost formations of Wai subgroup of the Western Ghat Deccan basalts, or to the major geodynamic events such as the opening of the Arabian Sea and the rifting of the Seychelles-Mascarene oceanic plateau, which occurred soon after the cessation of the Deccan volcanism. Rock magnetic experiments such as the Lowrie-Fuller test along with low-temperature magnetic susceptibility and isothermal remanent magnetization (IRM) measurements have identified single domain (SD) type titano-magnetite as the major characteristic remanent magnetization carrying magnetic mineral in the dyke samples.

  8. Continental rift and oceanic protoliths of mafic-ultramafic rocks from the Kechros Complex, NE Rhodope (Greece): implications from petrography, major and trace-element systematics, and MELTS modeling (United States)

    Baziotis, I.; Mposkos, E.; Asimow, P. D.


    The whole-rock chemistry of eclogites, partially amphibolitized eclogites, and dyke amphibolites from the metamorphic Kechros complex in the eastern Rhodope Mountains preserves evidence of the geodynamic framework for the origin of their protoliths. Major and trace-element concentrations define two distinct protolith groups for the eclogites. The low-Fe-Ti (LFT) eclogites have low-TiO2 content (HFT) eclogites have small to moderate LILE enrichment and lack Nb anomalies. The REE patterns of the HFT eclogites are characterized by LREE depletion and relatively flat MREE-HREE patterns. The rock compositions and petrographic features of the LFT eclogites resemble gabbros formed in a continental rift environment with minor to moderate contamination of a mantle-derived mafic magma by continental crust, whereas the HFT eclogites resemble mafic rocks formed in extensional oceanic environments. We interpret the HFT suite to represent a later stage in an evolution from continental rift to open ocean, following the origin of the LFT suite. Dyke amphibolite compositions, except for probable SiO2 loss associated with metamorphic dehydration reactions, appear to represent liquid compositions quenched in conduits through the lower crust. MELTS modeling shows that dyke amphibolite compositions can be related to each other by fractional crystallization under strongly oxidizing conditions at ~0.5 GPa pressure, and all can be derived from a low-degree melt of modified fertile peridotite from around 1.7 GPa. Cumulates crystallized from the parental liquids of the amphibolites under oxidizing conditions may have yielded the protoliths of the HFT suite.

  9. A Geochemical Investigation of the Early Cretaceous Ultrapotassic Dykes in the Raniganj Coalfields in Damodar Valley, India (United States)

    Jude, T. A.


    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.

  10. Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke (United States)

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


    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.

  11. Mangrove forest against dyke-break-induced tsunami on rapidly subsiding coasts (United States)

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


    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.

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

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    Yaşar Bükte


    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.

  13. Compositions of Normal and Anomalous Eucrite-Type Mafic Achondrites (United States)

    Mittlefehldt, D. W.; Peng, Z. X.; Mertzman, S. A.


    The most common asteroidal igneous meteorites are eucrite-type mafic achondrites - basalts and gabbros composed of ferroan pigeonite, ferroan 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. However, high precision O-isotopic analyses have shown that some mafic achondrites have small, well-resolved, non-mass-dependent differences that have been interpreted as indicating derivation from different asteroids. Some of these O-anomalous mafic achondrites also have anomalous petrologic characteristics, strengthening the case that they hail from distinct parent asteroids. We present the results of bulk compositional studies of a suite of normal and anomalous eucrite-type basalts and cumulate gabbros.

  14. Seepage investigation by using Isotope and Geophysical Techniques in Gumti Flood Embankment/Dyke, Comilla

    International Nuclear Information System (INIS)

    Gumti Flood Control Embankment/Dyke is vital for irrigation water supply and flood control. Water seepage/leakage and slope failures are the major issues in Gumti earthen dyke. The distinct seepage and slope failure zone were observed at three places (Farizpur, Kathalia and Ebdarpur) along the countryside of left dyke. The isotopic technique has been integrated in the conventional hydrologic investigations. The isotope methodology works essentially by developing a characteristics pattern of the isotopic composition to identify the sources and flow dynamics of seeping/leaking in the dykes. Two sampling campaigns were conducted; one was on October, 2002 and the other was on July, 2003; near the seepage/leakage site for chemical analysis and stable isotopic analysis (''2H and ''18O). Both samplings were done after recession of peak water level in the Gumti river. Interpretation of the hydrochemical data implies that the groundwater near the investigated seepage zones is Na-Ca-HCO3 type and the river water is Ca-Mg-HCO3 type. The chlorides content of both groundwater and river water are found mostly similar, indicating mixing between the two water system. The stable isotopes (''2H and ''18O) of groundwater fall on the Meteoric Water Line, ranging the oxygen-18 values from -4.98 to -5.46 per mil and deuterium values from -30.0 to -33.6 per mil. It indicates the recharge from the river water during peak water level in the river Gumti. On the other hand, the stable isotopes of the Gumti river show some evaporation effect, which might have occurred due to stagnation of flowing water in the river. The oxygen-18 and deuterium values for river water range from -3.61 to -4.43 per mil and from -22.30 to -28.48 per mil respectively. These isotope results reflect the hydraulic connectivity between the river water and groundwater through the base of dyke. The earth imaging resistivity survey was carried out in the dry period along the four above mentioned areas of the Gumti dyke

  15. 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

  16. 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


    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

  17. Apollo 16 Mafic Glass: Geochemistry, Provenance, and Implications (United States)

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


    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.

  18. Relamination of mafic subducting crust throughout Earth's history (United States)

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


    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

  19. Paleomagnetism, U-Pb geochronology, and geochemistry of Marathon dykes, Superior Province, and comparison with the Fort Frances swarm

    International Nuclear Information System (INIS)

    We report the first detailed study of the paleomagnetism, U - Pb geochronology and major element geochemistry of Paleoproterozoic north-trending Marathon dykes north of Lake Superior. The paleomagnetic and geochemical results demonstrate that Marathon dykes can be divided into two subsets, one of normal magnetic polarity, the other of reverse polarity. Normal and reverse Marathon paleomagnetic poles, at 43oN, 196oE (dm = 9o, dp = 7o, number of dykes N = 16) and 51oN, 175oE (dm = 9o, dp = 6o, N 12), respectively, are statistically distinct and may indicate different ages of normal and reverse dyke emplacement. A U-Pb baddeleyite age of 2121-7+14 Ma has been obtained at a normally magnetized Marathon paleomagnetic site. The reversely magnetized Marathon dykes are undated, but have a paleopole rather close to that of the reversely magnetized 2076-4+5 Ma Fort Frances dykes and major element geochemical signatures as portrayed on Jensen plots that are identical to those of the Fort Frances swarm. Therefore, reverse Marathon and Fort Frances dykes could define a giant radiating dyke swarm focused south of Lake Superior, supporting models that associate these dykes with Paleoproterozoic rifting along the southern margin of the Superior Province. The Marathon and Fort Frances paleopoles continue a northwesterly trend in southern Superior Province paleopoles, which has recently been defined by results for 2216-4+8 Ma Senneterre dykes and 2167 ± 2 Ma Biscotasing dykes. This trend contrasts with previous widely used polar wander paths for the same period that young in the opposite direction and illustrates the importance of collaborative studies of paleomagnetism and U - Pb geochronology. (author). 36 refs., 4 tabs., 10 figs

  20. 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


    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.

  1. Granitic pluton inner structural activities partition and its concomitant dykes mass activities of northern Guangdong province

    International Nuclear Information System (INIS)

    The granite mass inner structural activities distributed with agminate and the high frequency of directions and phases, in northern Guangdong province. The granite mass inner uranous mineralization are manipulatived with structure. Based on the geological characteristics of the Zhuguang and Guidong granite mass, interrelated information of numerous uranium field,and isotope ages, the text mark off ternary phases about the granite mass inner structural activities--the anterior, corresponding and posterior period of neutral-basic dykes activities. And go with these structural activities, it came into being activities about multi-phases dykess mass. The uranium ore brought at the volitant date of dykes and silicic dykesal mass, after the appearance of neutral-basic dykes. (authors)

  2. Rift magmatism on the Eurasia basin margin: U–Pb baddeleyite ages of alkaline dyke swarms in North Greenland

    DEFF Research Database (Denmark)

    Thórarinsson, Sigurjón B.; Söderlund, Ulf; Døssing, Arne; Holm, Paul M.; Ernst, Richard E.; Tegner, Christian


    The opening of the Arctic Ocean involved multiple stages of continental rifting and intrusion of extensive dyke swarms. To trace tectonomagmatic processes of the High Arctic, we present the first U–Pb ages for alkaline dyke swarms of North Greenland. Concordia ages of 80.8 ± 0.6 and 82.1 ± 1.5 Ma...

  3. Immiscible silicate-carbonate liquids as evidenced from ocellar diabase dykes, southeast Sinai (United States)

    Bogoch, R.; Magaritz, M.


    Diabase dykes containing spherical patches of carbonate intrude the Tarr albitite complex of SE Sinai. The morphology of these dykes indicates a highly gas-charged magma. Petrographic evidence points toward equilibrium during cooling of immiscible carbonate ocelli and silicate matrix. Dolomite is the main component of these ocelli, which are geochemically and isotopically similar to carbonatite. However, the low total REE content, and the presence of considerable marble in the country rock, suggest a process of stoping and melting of carbonate, followed by the “in situ” development of silicate-carbonate immiscibility.

  4. Traces of ancient mafic layers in the Tethys oceanic mantle (United States)

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


    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.

  5. Dyke-path formation in relation to the eruptions of Eyjafjallajökull 2010 and Bardarbunga-Holuhraun 2014 (United States)

    Gudmundsson, Agust


    Dykes are extension fractures and form when the magmatic overpressure is high enough to rupture (break) the host rock. Their formation is entirely analogous to that of many joints and human-made hydraulic fractures, such as are used to increase permeability in reservoirs. When generating their paths, dykes use existing weaknesses (e.g., cooling joints) in the host rock. The maximum depth of large tension fractures below the surface of a rift zone, however, is mostly less than a few hundred metres. If the fractures extend to greater depths, they must change into closed normal faults which are generally not used as magma paths. There are thus no large tension fractures or wide-open faults at great depths ready to be filled with magma to form a dyke. While magma flow in dykes, as in other fluid-driven fractures, is at any point in various directions dyke segmentation may indicate the overall large-scale flow direction. Thus, dykes composed of large-spaced disconnected segments in lateral sections are primarily formed in vertical magma flow at segmentation depth whereas those composed of large-spaced disconnected segments in vertical sections are primarily formed in lateral magma flow. The far-field displacement and stress fields of segmented dykes are similar to those generated by single, continuous dykes of similar dimensions, particularly when the distances between the nearby tips of the segments become small in comparison with segment lengths. Most dykes become arrested and never supply magma to eruptions. Feeder-dykes normally reach the surface only along parts of their lengths (strike-dimensions). The volumetric flow or effusion rate of magma through a feeder-dyke or volcanic fissure depends on the aperture (opening) of the dyke or fissure in the 3rd power. All these theoretical and observational results are here applied to the dyke emplacements associated with the eruptions of Eyjafjallajökull 2010 and Bardarbunga-Holuhraun 2014. The results make it possible to

  6. Formation conditions of leucogranite dykes and aplite-pegmatite dykes in the eastern Mt. Capanne plutonic complex (Elba, Italy): fluid inclusion studies in quartz, tourmaline, andalusite and plagioclase (United States)

    Bakker, Ronald J.; Schilli, Sebastian E.


    Leucogranite and aplite-pegmatite dykes are associated with the Mt. Capanne pluton (Elba) and partly occur in the thermally metamorphosed host rock (serpentinites). Crystallization conditions of these dykes in the late magmatic-hydrothermal stage are estimated from fluid inclusion studies and mineralogical characterisation, obtained from detailed microthermometry, Raman spectroscopy, and electron microprobe analyses. Fluid inclusion assemblages are analysed in andalusite, quartz, and plagioclase from the leucogranite dykes, and in tourmaline and quartz from the aplite-pegmatite dykes. The fluid inclusion assemblages record multiple pulses of low salinity H2O-rich magmatic and reduced metamorphic fluid stages. Magmatic fluids are characterized by the presence of minor amounts of CO2 and H3BO3, whereas the metamorphic fluids contain CH4 and H2. The highly reduced conditions are also inferred from the presence of native arsenic in some fluid inclusions. Several fluid inclusion assemblages reveal fluid compositions that must have resulted from mixing of both fluid sources. In leucogranite dykes, magmatic andalusite contains a low-density magmatic CO2-rich gas mixture with minor amounts of CH4 and H2. Accidentally trapped crystals (mica) and step-daughters (quartz and diaspore) are detected in some inclusions in andalusite. The first generation of inclusions in quartz that crystallized after andalusite contains a highly reduced H2O-H2 mixture and micas. The second type of inclusions in quartz from the leucogranite is similar to the primary inclusion assemblage in tourmaline from the aplite-pegmatite, and contains up to 4.2 mass% H3BO3, present as a sassolite daughter crystal or dissolved ions, in addition to a CO2-CH4 gas mixture, with traces of H2, N2, H2S, and C2H6. H2O is the main component of all these fluids ( x = 0.91 to 0.96) with maximally 7 mass% NaCl. Some accidentally trapped arsenolite and native arsenic are also detected. These fluids were trapped in the

  7. Rb-Sr age of a basic dyke, Schirmacher oasis, east Antarctica

    International Nuclear Information System (INIS)

    In order to understand the crustal evolution in east Antartica, detailed geological, geochemical and isotopic studies of the various rocks in the area are necessary. This paper reports the Rb-Sr isotopic data on a gabbroic dyke in the Schirmacher oasis

  8. Dyke Intrusion and Arrest in Harrat Lunayyir, western Saudi Arabia, in April-July 2009 (United States)

    Jónsson, Sigurjón; Pallister, John; McCausland, Wendy; El-Hadidy, Salah


    Dyke intrusion in Harrat Lunayyir (also known as Harrat Al-Shaqah), one of the volcanic provinces in Saudi Arabia, caused numerous small to moderate-sized earthquakes and extensive surface faulting in April-July 2009. The most intensive earthquake activity took place on 17-20 May when six magnitude 4.6-5.7 earthquakes occurred, resulting in some structural damage and prompting the Saudi civil protection authorities to evacuate more than 30000 people from the area. While the earthquake activity significantly decreased after 20 May, it continued throughout June and July with a few earthquakes as large as magnitude ~4, before quieting down in August. Much of what we have learned about the activity comes from interferometric satellite radar (InSAR) observations and from analysis of the seismic data collected by a broadband seismic network that was installed soon after the earthquake swarm started in April. The InSAR data show that large-scale (40 km × 40 km) east-west extension of over 1 m took place as well as broad uplift amounting to over 40 cm. The center of the uplifted area was transected by northwest-trending graben subsidence of over 50 cm, bounded by a single fault to the southwest showing up to ~1 m of faulting and by multiple smaller faults and cracks to the northeast. The observed deformation is well explained with a near-vertical dyke intrusion and graben-bounding normal faulting. The strike of the model dyke is NNW-SSE, parallel to the Red Sea rift, and its volume is about 0.13 km3. The modeling suggests that the shallowest part of the dyke reached within only 2 km of the surface, right below where the graben is the narrowest and under an area with a number of cinder cones from previous volcanic events. The main graben-bounding surface fault, to the southwest of the dyke, grew from ~3 km to ~8 km with the magnitude 5.7 earthquake on 19 May. Soon after this event the overall earthquake activity dramatically declined. The faulting appears to have

  9. Geophysical characteristics of Aswa shear, Nagasongola discontinuity and ring dyke complex in Uganda (United States)

    Ruotoistenmäki, Tapio


    During the years 2008-2012, the geology of most of Uganda was studied within the framework of the Sustainable Management of Mineral Resources Project (SMMRP). During the project, comprehensive airborne magnetic and radiometric surveys were flown over the entire country and geological, petrophysical, geochemical sampling, geological field studies and detailed geophysical field profiles were undertaken in selected sub-areas. This report concentrates on the geophysical properties of three major geophysical structures in the area considered during the project: the Pan-African (0.6-0.7 Ga) Aswa shear zone and Nagasongola discontinuity (suture), and the 1.36 Ga Uganda-Tanzania semi-circular ‘ring dyke' complex. The geophysical profiles across the Aswa shear indicate that the fault zone dips steeply, at about 60° to NE. The structure represents a magnetic, gravimetric (density), radiometric and topographic discontinuity, all diminishing from SW to NE across the zone. The zone is also characterized by complex radiometric anomalies. A schematic reconstruction of the evolution of the Aswa shear zone on the magnetic map suggests a nearly 60 km sinistral horizontal component of displacement along the zone. The Nakasongola zone is another distinct magnetic, gravimetric and radiometric discontinuity, interpreted to represent a collision (suture) zone, where the northern, low-magnetic block has been thrust over the southern, denser and more magnetic block. Modeling of gravity and magnetic data are consistent with a geometry in which the southern, magnetic and high-density block dips gently to great depth beneath the northern block. Bedrock exposures in both the Aswa shear zone and Nagasongola zone areas indicate a very protracted and complex history of tectonic processes commencing in the Archaean-Paleoproterozoic era and culminating in Pan-African orogenies. Both, the Aswa shear zone and Nagasongola discontinuity are cut by continuous younger dykes that show no signs of

  10. Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique (United States)

    Ibraimo, Daniel Luis; Larsen, Rune B.


    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

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

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


    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.

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

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


    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

  13. The fluid dynamics of xenocryst formation in mafic enclaves (United States)

    Jarvis, Paul; Blundy, Jon; Cashman, Katharine; Huppert, Herbert; Mader, Heidy


    Mafic enclaves produced by the mingling of felsic and mafic magmas commonly contain xenocrysts; crystals akin to those in the felsic host. These crystals are interpreted as having crossed the interface between the two magmas at some stage during the rock evolution. An understanding of the physical conditions that allow this exchange would give insight into the state of the system at the time of assimilation, providing information about the magmatic history of the rock. Using both numerical models and analogue experiments, the low Reynolds number gravitational settling of spheres on to fluid-fluid interfaces is studied as an analogue to this problem. Theoretical treatment suggests that whether or not a particle sinks or floats at an interface depends on four dimensionless parameters; Bond number, the viscosity ratio, a modified density ratio and the contact angle. Spheres are allowed to settle onto an interface for different values of the dimensionless groups and the behavioural regime boundaries are determined. Experimentally this consists of dropping spheres of varying radii and density onto an interface between two density stratified fluids (silicon oil and polyethylene glycol solution), both of which are lighter than the sphere. The spheres are sputter coated in gold to ensure a constant surface interaction. The numerical models are used to validate these results and apply them in geologic settings. Early results suggest that the presence of even a small interfacial tension between the two magmas is sufficient to inhibit the passage of crystals across interfaces in magmatic systems. An interesting feature of note in mafic enclaves is that the xenocrysts often occur in clusters. This can be compared with observations from the analogue experiments where 6mm nylon spheres were dropped onto the fluid interface. Although the spheres are light and small enough to individually be supported by the interface, the successive addition of spheres leads to the formation of

  14. Marquette Island: A Distinct Mafic Lithology Discovered by Opportunity (United States)

    Mittlefehldt, David W.; Gellert, R.; Herkenhoff, K. E.; Clark, B. C.; Cohen, B. A.; Fleischer, I.; Jolliff, B. L.; Klingelhoefer, G.; Ming, D. W.; Yingst, R. A.


    While rolling over the Meridiani Planum sedimentary terrane, the rover Opportunity has occasionally discovered large, > 10 cm erratics. Most of these have proven to be meteorites [1], but one - Bounce Rock - is a martian basaltic rock similar in composition to the meteorite EETA79001 lithology B [2]. Presently, Opportunity is intensively investigating an --30 cm tall rock named Marquette Island that may be a distinct type of martian mafic lithology. We report the results of its continuing investigation using the Microscopic Imager (MI); Mossbauer Spectrometer (MB) and Alpha Particle X-ray Spectrometer (APXS). A companion abstract discusses the results of Panoramic Camera (Pancam) imaging of the rock [3].

  15. 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)


    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.

  16. Geology and tectonic magmatic of emplacement of a longitudinal dyke swarm of Nico Perez(Minas) URUGUAY

    International Nuclear Information System (INIS)

    The Mina Verdun Group (Precambrian) was deposited prior to the subvolcanic emplacement of a longitudinal dyke swarm of basaltic to andesitic composition (Minas Subvolcanic Swarm of the Mina Verdun quarry - Nico Perez Terrane, Minas, Uruguay). The swarm and its country rocks predated a tectono-metamorphic event that produced fragileductile shear zones associated with very low- to low-grade dislocation metamorphism. We interpreted a K-Ar whole rock datum of 485,2 ± 12,5 Ma (andesitic dyke) as a minimum cooling age in relation with late- to post-swarm emplacement deuteric alteration stage. Another K-Ar whole rock datum of 108,5 ± 2,9 Ma on a basaltic dyke was assumed here as a degasification stage, while its geological meaning is still matter of debate. The Minas Subvolcanic Dyke Swarm was intruded at high crustal levels, suggesting that the Minas region was affected by a period of extensional tectonics

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

    Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin


    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

  18. Eocene slab breakoff of Neotethys as suggested by dioritic dykes in the Gangdese magmatic belt, southern Tibet (United States)

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


    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.

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

    Institute of Scientific and Technical Information of China (English)


    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.

  20. Dyke-Davidoff-Masson Syndrome Demonstrated by Current MR images. A Case Report. (United States)

    Hori, M; Mizuno, M; Katagiri, N; Takeshi, K; Tsujino, N; Araki, T; Shiraga, N


    Current magnetic resonance imaging techniques demonstrated MR findings of Dyke-Davidoff-Masson syndrome in a 44-year-old man. Statistical parametric mapping analysis of the T1-weighted images showed focal atrophy in the basal ganglia. Three-dimensional white matter fibers of corticospinal tracts, corpus callosum and cingulate bundle were demonstrated using diffusion tensor data correlated to the patient's clinical conditions. PMID:24209398

  1. The intensity of the geomagnetic field from 2.4 Ga old Indian dykes (United States)

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


    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. Dyke-Davidoff-Masson Syndrome: Cases of Two Brothers and Literature Review


    Park, Kyung-Il; Chung, Jae-Myun; Kim, Ji-Young


    Dyke-Davidoff-Masson syndrome (DDMS) has cerebral hemiatrophy and compensatory ipsilateral skull thickening, and is manifested by recurrent seizures and hemiparesis. We present one case with typical DDMS, who had a brother suffering from epilepsy with mild imaging abnormality relevant to DDMS and similar seizure semiology. A 26-year-old man had a history of developmental delay, mental retardation, hemiparesis and recurrent seizures. His brother, 23-year-old man had also experienced recurrent ...

  3. The geology and geochronology of the Belmont pluton and microgranite dykes from the Margate area

    International Nuclear Information System (INIS)

    Field, petrographic, geochemical and Rb-Sr isotope data are presented for two granitic units which are considered to represent amongst the youngest intrusive rocks in the Natal Metamorphic Province. These are the Belmont granite pluton and a suite of unfoliated biotite microgranite dykes from the Margate area. The data suggest that these rocks do not form part of a consanguineous suite as previously envisaged. It is concluded that the Belmont pluton (1055 ± 60Ma) should be assigned to the garnet leucogranite phase of the syntectonic Margate Suite, and that the dykes (∼965 Ma) represent the products of a discrete, late-stage magmatic event which took place towards the end of the Natal orogenesis. Furthermore, the high initial Sr isotopic ratio (∼0,715) of the dykes suggests that they were derived from the melting of pre-existing radiogenic crust. The termination of major tectono-magmatic events in the Late Proterozoic Namaqua-Natal Belt apparently youngs from west to east across South Africa. Reconstructions of Gondwanaland place the Falkland Plateau and the Maudheim Province of Antarctica off the southeast of Africa. Dates obtained from this region range from ∼1000Ma to ∼500Ma, suggesting a continued decrease in age of tectono-magmatic activity eastwards. The microgranite dykes described here are unequivocally amongst the youngest post-tectono-metamorphic intrusions of southern Natal, yet they do not preserve any whole-rock indication of Pan-African isotopic disturbances. Sparse Rb-Sr mineral isotopic data support this indication that there was no significant Pan-African activity in the Natal Metamorphic Province. 8 figs., 7 tabs., 38 refs

  4. 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)


    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.

  5. 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


    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.

  6. 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)


    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.

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

    Directory of Open Access Journals (Sweden)

    Tom Boyle


    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.

  8. Possible Mafic Patches at Mons Malapert and Scott Crater Highlight the Value of Site Selection studies (United States)

    Cooper, B. L.


    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".

  9. The nature and origin of Mafic Mound in the South Pole-Aitken Basin (United States)

    Moriarty, Daniel P.; Pieters, Carle M.


    "Mafic Mound" is a distinctive and enigmatic feature 75 km across and 1 km high near the center of the vast South Pole-Aitken Basin (SPA). Using several modern data sets, we characterize the composition, morphology, and gravity signature of the structure in order to assess its origin. Mafic Mound is found to exhibit a perched circular depression and a homogeneous high-Ca pyroxene-bearing composition. Several formation hypotheses based on known lunar processes are evaluated, including the possibilities that Mafic Mound represents (1) uplifted mantle, (2) SPA-derived impact melt, (3) a basalt-filled impact crater, or (4) a volcanic construct. Individually, these common processes cannot fully reproduce the properties of Mafic Mound. Instead, we propose a hybrid origin in which Mafic Mound is an edifice formed by magmatic processes induced by the formation and evolution of SPA. This form of nonmare volcanism has not previously been documented on the Moon.

  10. Laboratory tests of mafic, ultra-mafic, and sedimentary rock types for in-situ applications for carbon dioxide sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Rush, G.E.; O' Connor, William K.; Dahlin, David C.; Penner, Larry R.; Gerdemann, Stephen J.


    Recent tests conducted at the Albany Research Center have addressed the possibility of in-situ storage of carbon dioxide in geological formations, particularly in deep brackish to saline non-potable aquifers, and the formation of secondary carbonate minerals over time within these aquifers. Various rock types including Columbia River Basalt Group (CRBG) drill core samples, blocks of ultra-mafic rock and sandstone were used. A solution formulated from aquifer data, a bicarbonate salt solution, and distilled water were tested. Pressure and temperature regimens were used to mimic existing in-situ conditions, higher temperatures were used to simulate longer time frames, and higher pressures were used to simulate enhanced oil recovery (EOR) pressure. Results are encouraging, indicating mineral dissolution with an increase of desirable ions (Ca, Fe2+, Mg) in solution that can form the carbonate minerals, calcite (CaCO3), siderite (FeCO3), and magnesite (MgCO3).

  11. 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

  12. Fault and dyke detectability in high resolution seismic surveys for coal: a view from numerical modelling* (United States)

    Zhou, Binzhong 13Hatherly, Peter


    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.

  13. 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


    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.


    Directory of Open Access Journals (Sweden)

    Vipin Kumar


    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

  15. Granitoids and dykes of the Pine Island Bay region, West Antarctica


    Kipf, Andrea; Mortimer, Nicholas; Werner, Reinhard; Gohl, Karsten; van den Bogaard, Paul; Hauff, Folkmar; Hoernle, Kaj


    We present geochronological and geochemical data for eight plutonic rocks from five locations in the Pine Island Bay area of West Antarctica, collected during RV Polarstern expedition ANT-XXIII/4. Ar-Ar laser method dating yielded closure temperatures ages of c. 147–98 Ma for dioritic and granitic plutonic rocks and an age range of c. 97–95 Ma for granitoid and trachyandesitic dykes. Major and trace element compositions indicate that all rocks have an I-type subduction-related chemistry. Ther...

  16. Mafic Materials in Scott Crater? A Test for Lunar Reconnaissance Orbiter (United States)

    Cooper, Bonnie L.


    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.

  17. 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 (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.

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

    KAUST Repository

    Pallister, John S.


    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.

  19. The paleoproterozoic Monchetundra mafic massif (Kola Peninsula): New geological and geochronological data (United States)

    Borisenko, E. S.; Bayanova, T. B.; Nerovich, L. I.; Kunakkuzin, E. L.


    In view of the absence of an unambiguous intrusive contact between the main mafic rocks varieties in the Monchetundra massif, the latter was considered for a long time as a large complex of syngenetic mafic rocks. On the basis of data derived from study of the outcrops and drill core samples, researchers defined various numbers of zones characterized by certain rock types. The results of geological-petrographic investigations and data on the U-Pb system in zircon and baddeleyite provided grounds for revision of the views on the structure of the massif: at least four groups of different ages of mafic rocks are now definable in the Monchetundra massif. In this communication, we discuss the relations between two groups of mafic rocks and the results of their U-Pb isotopic dating, which imply a long multiphase formation of the massif.

  20. Sinkinematic ultramafic-mafic magmatism in the Red River shear zone

    International Nuclear Information System (INIS)

    To investigate into manifestations the mantle ultramafic-mafic magnetism synchronous with displacement motions in the Red River zone one carried out Ar-Ar-dating of the bulk samples of the amphibolic gabbros, pyroxenites and peridotites from various areas of the mentioned zone. One determined three phases of formation of the ultramafic-mafic association of the Red River zone that corresponded to the age equal to 49-42, 35 and 25 million years

  1. Petrology and geochemistray of Imam-Zadeh Hashem mafic and ultramafic bodies, southern Guilan province


    Mojgan Salavati; Reza Fahim Guilani


    Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic) are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setti...

  2. Palaeoproterozoic mafic and intermediate metavolcanic rocks in the Turku area, SW Finland


    Markku Väisänen; Gustav Westerlund


    Twenty two samples were analysed from mafic and intermediate volcanic rocks from the Turku area along ~60 km long north-south geotraverse. Geographically and lithologically the samples were divided into the Pargas, Turku and Vahto groups. The Pargas and Turku groups consist of mafic units and intercalations within migmatitic gneisses. Their geochemical compositions are very similar. In average, they show quite flat REE curves and the multielement diagrams show moderate LILE enrichments, minor...

  3. 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


    can be identified from crosscutting relations. The SN represents the fossil continent–ocean transition between the Baltic craton and the Iapetus Ocean, marking the initiation of seafloor spreading. Bubble-shaped pods and veinlets of diorite are present in the SDS sheeted dyke complexes. The pods are...... absent in the oldest dykes, but the younger a dyke, the more frequent the pods. The diorite pods are the equivalent of gabbro pegmatites, and both cogenetic and coeval with the dykes. The rapid successive emplacement of tholeiitic magma raised the ambient temperature in the dyke complex, so that...... discordant, indicating a crystallization age of 608±1 Ma (207Pb/206Pb=607.9±0.7 Ma, MSWD=0.33). This age is inferred to date the onset of seafloor spreading in the Iapetus Ocean along the Baltoscandian margin....

  4. Li isotope fractionation in peridotites and mafic melts (United States)

    Jeffcoate, A. B.; Elliott, T.; Kasemann, S. A.; Ionov, D.; Cooper, K.; Brooker, R.


    We have measured the Li isotope ratios of a range of co-existing phases from peridotites and mafic magmas to investigate high-temperature fractionations of 7Li/ 6Li. The Li isotopic compositions of seven mantle peridotites, reconstructed from analyses of mineral separates, show little variation (δ 7Li 3.2-4.9‰) despite a wide range in fertility and radiogenic isotopic compositions. The most fertile samples yield a best estimate of δ 7Li ˜ 3.5‰ for the upper mantle. Bulk analyses of olivine separates from the xenoliths are typically ˜1.5‰ isotopically lighter than co-existing orthopyroxenes, suggestive of a small, high-temperature equilibrium isotope fractionation. On the other hand, bulk analyses of olivine phenocrysts and their host melts are isotopically indistinguishable. Given these observations, equilibrium mantle melting should generate melts with δ 7Li little different from their sources (style of zoning is also observed in the phenocrysts of holocrystalline Hawaiian lavas. More dramatically, a single orthopyroxene crystal from a San Carlos xenolith shows a W-shaped Li isotope profile with a 40‰ range in δ 7Li, close to the isotope variability seen in all terrestrial whole rock analyses. We attribute Li isotope zonation in mineral phases to diffusive fractionation of Li isotopes, within mineral phases and along melt pathways that pervade xenoliths. Given the high diffusivity of Li, the Li isotope profiles we observe can persist, at most, only a few years at magmatic temperatures. Our results thus highlight the potential of Li isotopes as a high-resolution geospeedometer of the final phases of magmatic activity and cooling.

  5. Geochronological and geochemical constraints on the petrogenesis and tectonic significance of Paleozoic dolerite dykes in the southern margin of Alxa Block, North China Craton (United States)

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


    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.

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

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


    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

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


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


    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...

  8. Mafic Plinian volcanism and ignimbrite emplacement at Tofua volcano, Tonga (United States)

    Caulfield, J. T.; Cronin, S. J.; Turner, S. P.; Cooper, L. B.


    Tofua Island is the largest emergent mafic volcano within the Tofua arc, Tonga, southwest Pacific. The volcano is dominated by a distinctive caldera averaging 4 km in diameter, containing a freshwater lake in the south and east. The latest paroxysmal (VEI 5-6) explosive volcanism includes two phases of activity, each emplacing a high-grade ignimbrite. The products are basaltic andesites with between 52 wt.% and 57 wt.% SiO2. The first and largest eruption caused the inward collapse of a stratovolcano and produced the `Tofua' ignimbrite and a sub-circular caldera located slightly northwest of the island's centre. This ignimbrite was deposited in a radial fashion over the entire island, with associated Plinian fall deposits up to 0.5 m thick on islands >40 km away. Common sub-rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma-water interaction. The common intense welding of the coarse-grained eruptive products, however, suggests that the majority of the erupted magma was hot, water-undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water. We propose that the development of a water-saturated dacite body at shallow (roof to cause sudden evacuation of material, producing a Plinian eruption column. Following a brief period of quiescence, large-scale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements. This similar, but smaller eruption, emplaced the `Hokula' Ignimbrite sheet in the northeast of the island. A maximum total volume of 8 km3 of juvenile material was erupted by these events. The main eruption column is estimated to have reached a height of ˜12 km, and to have produced a major atmospheric injection of gas, and tephra recorded in the widespread series of fall deposits found on coral islands 40-80 km

  9. 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


    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.

  10. Age and intrusive relations of the Lamarck granodiorite and associated mafic plutons, Sierra Nevada, California

    Energy Technology Data Exchange (ETDEWEB)

    Joye, J.L.; Bachl, C.A.; Miller, J.S.; Glazner, A.F. (Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Geology); Frost, T.P. (Geological Survey, Spokane, WA (United States)); Coleman, D.S. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Earth, Atmospheric and Planetary Sciences)


    The compositionally zoned Late Cretaceous Lamarck granodiorite, west of Bishop, hosts numerous mafic intrusions ranging from hornblende gabbro to mafic granodiorite. Frost and Mahood (1987) suggested from field relations that the Lamarck and the associated mafic plutons were co-intrusive. Contact relations between the Lamarck host and the mafic intrusions are variable (sharp to diffuse) and in places suggest commingling. In order to constrain the intrusive relationships between the Lamarck and its associated mafic plutons, the authors have analyzed feldspars from the Mt. Gilbert pluton and the Lamarck granodiorite to see if feldspar compositions in the Mt. Gilbert overlap those in the Lamarck host and determined U-Pb zircon ages for the Mt. Gilbert and Lake Sabrina plutons to see if they have the same age as the Lamarck granodiorite. Feldspars from the Lamarck granodiorite are normally zoned and range compositionally from An[sub 38--32]; those in the Mt. Gilbert diorite are also normally zoned but range compositionally from An[sub 49--41] and do not overlap the Lamarck host. Four to five zircon fractions from each pluton were handpicked and dated using U-Pb methods. The Mt. Gilbert mafic diorite has a concordant age of 92.5 Ma and the Lake Sabrina diorite has a concordant age of 91.5 Ma. Ages for the two plutons overlap within error, but multiple fractions from each suggest that the Lake Sabrina pluton is slightly younger than the Mt. Gilbert pluton. These data and field relationships indicate: (1) plagioclase phenocrysts in the Mt. Gilbert pluton were not derived from the Lamarck granodiorite despite their textural similarity; but (2) the Lamarck granodiorite and its associated mafic plutons are co-intrusive as supported by the close agreement of the ages with the crystallization age obtained by Stern and others for the Lamarck granodiorite.

  11. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics. (United States)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio


    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

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

    Directory of Open Access Journals (Sweden)

    Ujjawal Roy


    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.

  13. Dyke-davidoff-masson syndrome: cases of two brothers and literature review. (United States)

    Park, Kyung-Il; Chung, Jae-Myun; Kim, Ji-Young


    Dyke-Davidoff-Masson syndrome (DDMS) has cerebral hemiatrophy and compensatory ipsilateral skull thickening, and is manifested by recurrent seizures and hemiparesis. We present one case with typical DDMS, who had a brother suffering from epilepsy with mild imaging abnormality relevant to DDMS and similar seizure semiology. A 26-year-old man had a history of developmental delay, mental retardation, hemiparesis and recurrent seizures. His brother, 23-year-old man had also experienced recurrent seizures, but he had no neurological deficits. Older brother experienced focal motor seizures with/without secondary generalization. Sometimes, he noted an auditory aura. MRI demonstrated the hemispheric atrophy with the adjacent bony hypertrophy. The seizures of younger brother were mainly of the auditory type and the MRI showed mild hemispheric atrophy with hippocampal sclerosis without any bony change. Our sibling cases might have a familial predisposition and support the idea that clinical courses and radiological findings of DDMS are varied even within one family. PMID:24977128

  14. Strain accommodation by slow slip and dyking in a youthful continental rift, East Africa. (United States)

    Calais, Eric; d'Oreye, Nicolas; Albaric, Julie; Deschamps, Anne; Delvaux, Damien; Déverchère, Jacques; Ebinger, Cynthia; Ferdinand, Richard W; Kervyn, François; Macheyeki, Athanas S; Oyen, Anneleen; Perrot, Julie; Saria, Elifuraha; Smets, Benoît; Stamps, D Sarah; Wauthier, Christelle


    Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions. These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July-August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning. PMID:19079058

  15. Single Silicate Crystal Paleointensity Analyses of the ca. 2.575 Ga Great Dyke of Zimbabwe (United States)

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


    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.

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

    Mandal, Aditi; Ray, Arijit


    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.

  17. Mafic magmatism and associated tectonism of the central High Cascade Range, Oregon (United States)

    Hughes, Scott S.


    Results are presented on chemical analyses of basaltic core samples obtained from holes drilled at three locations in the mafic platform within the central region of the High Cascade Range (Oregon), as well as of some surface samples to enhance the original data base. Analyses were obtained using a variety of procedures; the most appropriate data commensurate with the technique were selected. The data illustrate the development of the mafic platform in terms of geochemical variations and tectonic configurations required to satisfy petrochemical associations.

  18. Intrusion of lamprophyre dyke and related deformation effects in the host rock salt: A case study from the Loulé diapir, Portugal

    Czech Academy of Sciences Publication Activity Database

    Machek, Matěj; Roxerová, Zuzana; Závada, Prokop; Silva, P. F.; Henry, B.; Dědeček, Petr; Petrovský, Eduard; Marques, F. O.


    Roč. 629, August (2014), s. 165-178. ISSN 0040-1951 Institutional support: RVO:67985530 Keywords : AMS * lamprophyre dyke * rock salt * paleomagnetism * microstructure * CPO Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.872, year: 2014

  19. 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


    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.

  20. 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)


    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.

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


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


    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...

  2. Geological and Geochemical Study on Some Dykes And Hosting Stone-grey in Sheikh Salem Area, South Eastern Desert, Egypt

    International Nuclear Information System (INIS)

    Sheikh Salem area (45 km west of coastal Mersa Alam town .south Eastern Desert of Egypt) is occupied by Precambrian basement rocks including volcaniclastic metasediments, metagabbro-diorite complexes, metavolcanics and syenogranite. The studied area is dissected by numerous dyke swarms. The syenogranite is of I-type and characterized by peraluminous nature. Two sets of nearly vertical dykes cut the syenogranite. The younger one trends NNW-SSE, while the older trends ENE-WSW. The younger dykes are lamprophyres and mainly composed of plagioclase, hornblende, pyroxene and olivine. Calcite, epidote, antigorite and chlorite are secondary minerals, whereas opaques are accessories. The older dykes are andesites and mainly composed of plagioclase, hornblende. Saussurite, calcite, and epidote are secondary minerals, whereas opaques are accessories. The separated minerals from the lamprophyre samples include graphite, pyrite and zircon. A very important observation is the occurrence of graphite in most lamprophyre samples. The original magma of the lamprophyres is of high K.-calc alkaline to shoshonitic type with basaltic nature, while the original magma of the andesites is of high K-calc alkaline to calc alkaline type with andesitic nature. The lamprophyres have high content in Y, Ni, Cu, V and Zr, and low content in Rb, Pb, Zn, Ba and Ga compared with andesites. Both the lamprophyres and andesites show enrichment in Ba, Rb, Pb, Sr, Zr, Zn and Y and depletion in Cr and Ni compared with primitive mantle. The Syenogranite of Sheikh Salem area shows background radioactivity level giving eU contents of 7.4 ppm while eTh average content is 18.7 ppm and the mean value of eU/eTh ratio is 0.42

  3. 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


    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.

  4. Paleomagnetic and 40Ar/39Ar geochronologic data from late Proterozoic mafic dikes and sills, Montana and Wyoming (United States)

    Harlan, Stephen S.; Geissman, John William; Snee, Lawrence W.


    Paleomagnetic and 40Ar/39Ar results from mafic dikes and sills in northwestern Wyoming and western Montana yield similar virtual geomagnetic poles and isotopic dates. In combination with paleomagnetic and geochronologic data from elsewhere in the western Cordillera, these data provide evidence for a regional mafic magnetic event at 780 to 770 Ma that affected a large area of western North America.

  5. Early detection of eruptive dykes revealed by normalized difference vegetation index (NDVI) on Mt. Etna and Mt. Nyiragongo (United States)

    Houlié, N.; Komorowski, J. C.; de Michele, M.; Kasereka, M.; Ciraba, H.


    Flank-fissure eruptions involve lateral injection and propagation of magma in a volcanic edifice along pre-existing fractures in the direction of the rift zones where magma intrusion and lava flow production are concentrated over time. Thus, the identification and mapping of active fractures and faults is a fundamental aspect of studies of active volcanic systems. However, gradual dyke wedge emplacement at depth in well-fractured zones on volcano flanks and in volcanic rift zones does not necessarily trigger large amplitude deformation signals susceptible to be recorded months or even years before the actual eruption. Here we show that active and potentially eruptive areas can be detected up to 2 yrs before the arrival to the surface of the final eruptive dyke and venting of lava flows by processing satellite images applying a normalized difference vegetation index (NDVI) algorithm. A posteriori analysis of satellite images indeed reveals that the surficial effects of dyke wedge injection and ascent on plant growth were apparent for Mt. Etna from 2000 to 2002 and for Mt. Nyiragongo in 2001, thus months to years before they erupted.

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

    Directory of Open Access Journals (Sweden)

    S. Huang


    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.

  7. Geology, geochemistry and geodynamic implications of the mafic-ultramafic rocks from the Antalya Complex, SW Turkey (United States)

    Elitok, Ömer


    The Antalya Complex is bounded on the east and the west by the opposing carbonate platforms (the eastern Anamas-Akseki and the western Bey Daǧları) forming a north pointing cusp (so-called the Isparta Angle) in SW Turkey, and is made of an assemblage of allochthonous Mesozoic slope-basin deposits and ophiolitic thrust sheets. The allochthonous rock assemblages in the northern part of the Antalya Complex are mainly characterized by slope-basin deposits that are spatially associated with: Upper Triassic volcanic rocks varying in composition from alkali basalt to fractionated trachyandesite; Upper Jurassic-Lower Cretaceous tholeiitic volcanic rocks ranging in composition from basalt to rhyolite; and, MORB-type volcanic rocks, most likely in Cretaceous age, that are spatially associated with olistostromal and subophiolitic tectonic mélanges. Whole rock chemistry of the harzburgitic mantle peridotites (Eǧridir Kızıl Daǧ peridotites) within the apex region of the Isparta Angle and of the isolated dolerite dykes intruding the peridotites, and the mineral chemistry of the harzburgitic spinels collectively suggest a depleted residual mantle peridotite character that is characteristic of forearc tectonic settings. Also, the Upper Triassic volcanic rocks associated with different basin deposits can be traced to the south within the Isparta Angle area and within the Mamonia Complex (SW Cyprus) in the eastern Mediterranean region. Upper Triassic alkaline volcanic rocks are underlain by rift-related siliciclastic rocks, massive limestones, and are, in turn, locally overlain by small patchy carbonate deposits, indicative of an intra-continental rift basin, which may have evolved in the apex region of the Isparta Angle. In the southern part of the Isparta Angle (in the eastern and western side of the Gulf of Antalya), the Triassic lavas are interbedded with and/or overlain by Upper Triassic pelagic sedimentary rocks. The Upper Triassic lavas of the Mamonia Complex are also

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

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    Ahmet Faik Öner


    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.

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


    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

  10. 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


    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.

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

    Directory of Open Access Journals (Sweden)

    Zhen-kun MA


    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.

  12. Geochemical characteristics and genesis of niudai diabase dykes in northern Guangdong province

    International Nuclear Information System (INIS)

    The Niudai diabase dykes, located in the south of Zhuguang pluton of North Guangdong Province, are characterized with low SiO2(45.04%∼48.64%), high TiO2 (2.02%∼3.23%) and TFeO (17.00%∼19.80%), enrichment in LILE (Rb, Ba) and LREE, relatively high ΣREE(112.1 x 10-6∼132.7 x 10-6), slightly depletion in Nb and Ta, without negative Eu anomaly. All informations are similar to the basalt from asthenospheric mantle sources. Elements' ratios of incompatible elements,such as Zr/Ba, La/Nb, La/Ta, Ti/Y, Ba/Nb, Th/Nb and Th/La of Niudai diabase are close to the ratios of OIB. The tectonic discrimination diagrams show that the diabases all fall into the range of OIB. The Niudai diabases have Pb isotope (206Pb/204Pb=18.153∼18.594, 207Pb/204Pb=15.713∼15.730, 208Pb/204Pb=39.184∼39.206) and its εNd(t) ranges from 3.1 to 4.3, close to the scope of OIB. The geochemical characteristics indicate that the origin of Niudai Diabase had both ends of members of mixed characteristics of asthenospher mantle and lithosphere mantle, and the hybrid were related to the melts of overlying lithosphere mantle as asthenospher mantle upwelling. The Niudai diabases are formed while the fast invaded of magma in the tectonic environment that lithospher thinning leaded by asthenosphere mantle upwelling. (authors)

  13. Geochemistry and petrogenesis of mafic-ultramafic suites of the Irindina Province, Northern Territory, Australia: Implications for the Neoproterozoic to Devonian evolution of central Australia (United States)

    Wallace, Madeline L.; Jowitt, Simon M.; Saleem, Ahmad


    Petrological and geochemical data for magmatic mafic-ultramafic suites of the Irindina and Aileron provinces of the Eastern Arunta region, Northern Territory, Australia constrain the petrogenesis and tectonic setting of magmatic events covering ~ 500 million years. Six geochemically distinct magmatic suites, here named A-F, have been identified and provide evidence of the tectonic history of this region and also are linked to two mineralisation-related magmatic events: the Lloyd Gabbro (Ni-Cu-PGE mineralisation) and the Riddoch Amphibolite (Cyprus-style Cu-Co volcanogenic massive sulphide mineralisation). The whole-rock geochemistry of Suites A and F is indicative of melts derived from a range of mantle depths (garnet to spinel lherzolite) and source enrichment. Suite D is likely related to the ~ 1070 Ma Warakurna/Giles event of central Australia, including the Alcurra (Musgrave) and Stuart (Arunta) dyke swarms, and likely formed through either: a) melting of subduction modified, sub-continental lithospheric mantle (SCLM) by an upwelling mantle plume; or b) a combination of intra-plate tectonic processes involving a long-lived thermal anomaly, lithospheric-scale architecture that focussed magmatism, and large-scale tectonism. Suite F represents more alkaline magmas, derived from a deeper source, but most likely formed during the same Warakurna LIP event (possibly contemporaneously) as Suite D. Suite E (the Riddoch Amphibolite) was most likely emplaced in a back-arc basin (BAB) setting at ~ 600 Ma, coincident with Delamerian subduction and BAB formation along the eastern Proterozoic margin of Australia from Queensland to the eastern Arunta and possibly further south. Subsequent destabilisation of the SCLM underneath the North Australian Craton generated the ~ 510 Ma Kalkarindji LIP in the form of Suite B intrusions that assimilated some of the older Suite E (Riddoch) material. This event is locally known as the ~ 506 Ma Stanovos Igneous Suite and represents the most

  14. The Karoo triple junction questioned : Evidence from 40Ar/39Ar Jurassic and Proterozoïc ages and geochemistry of the Okavango dyke swarm (Botswana). (United States)

    Jourdan, F.; Féraud, G.; Bertrand, H.; Kampunzu, A. B.; Tshoso, G.; Le Gall, B.; Tiercelin, J. J.


    The lower Jurassic Karoo-Ferrar magmatism represents one of the most important Phanerozoic continental flood basalt (CFB) provinces. Karoo CFB is dominated by tholeiitic traps and apparently radiating giant dyke swarms covering altogether ca 3x106 km2. This study focuses on the giant N110° oriented Okavango dyke swarm (ODS) stretching over a distance of 1500 km through Botswana. This dyke swarm represents the main arm of the so-called Karoo triple junction which is generally considered as a key marker linking the Karoo magmatism to a starting mantle plume impact (Campbell and Griffiths, 1990). ODS dolerites yield twelve reliable plagioclase 40Ar/39Ar plateau (and mini-plateau) ages ranging from 178.3 +-1.1 (2 sigma) to 179.3 +-1.2 Ma (Le Gall et al, 2002 and unpublished data). The distribution of the ages along a narrow gaussian curve suggests a short period of magmatic activity centered around 178.9 Ma. In addition, small clusters of plagioclase separated from twenty-five other dykes and measured by total fusion, gave either Karoo or Proterozoïc ages. The Proterozoïc rocks range from 758.2 +-6.6 Ma and 1223.8 +-10.0 Ma (integrated ages) and, although petrographically indistinguishable in some cases, they display clear geochemical differences (e.g. TiO22%, Ti/Y>400). Geochemical data combined with available Ar/Ar dates allowed us to identify the two groups within a total set of seventy-eight dykes investigated: about 15 % of the bulk ODS dykes were emplaced during the Proterozoïc and, thus, the Jurassic Karoo dykes were emplaced along reactivated Proterozoïc structures. The validity of the Karoo triple junction-plume model, should therefore be revisited. Although available data on Proterozoïc dykes along the ODS are not precise enough to assess their exact emplacement age, they indicate that most of the Proterozoïc dykes were emplaced between 900 and 1100 Ma. This age range is the same as dating commonly reported for the Umkondo igneous province (UIP, about

  15. Paleomagnetic record of a geomagnetic field reversal from late miocene mafic intrusions, southern nevada. (United States)

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


    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

  16. The French Guyana doleritic dykes: geochemical evidence of three populations and new data for the Jurassic Central Atlantic Magmatic Province (United States)

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


    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.

  17. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of central Chile (United States)

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


    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.

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


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


    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...

  19. Geochronologic boundaries and geodynamic interpretation for alkaline-mafic magmatism of the Kuznetsky Alatau ridge

    International Nuclear Information System (INIS)

    The U-Pb isotope dating of zircon from nepheline syenite of the Dedovogorsky massif was performed for studying the stages of alkaline-mafic magmatism development in the northern part of the Kuznetsky Alatau ridge. Taking into account the morphological properties of the zircon studied, the isotope age value obtained, i. e. 400.9 ± 6.8 mln. years, was interpreted as the period of the above-mentioned syenites formation

  20. Physical abrasion of mafic minerals and basalt grains: application to Martian aeolian deposits (United States)

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


    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.

  1. Mesozoic mafic dikes from the Shandong Peninsula, North China Craton: Petrogenesis and tectonic implications

    International Nuclear Information System (INIS)

    Mesozoic mafic dikes are widely distributed in Luxi (Mengyin and Zichuan) and Jiaodong regions of the Shandong Peninsula, China, providing an opportunity of investigating the nature of the lost lithospheric mantle beneath the North China Craton (NCC). The mafic dikes are characterized by strong depletion in high field strength elements (HFSE), enrichment in light rare earth elements (LREE), highly variable Th/U ratios, high initial (87Sr/86Sr)i (0.7050-0.7099) and negative εNd(T) (-6.0 to -17.6). They were derived from melting of metasomatized portions of the subcontinental lithospheric mantle, followed by fractionation of clinopyroxenes. The similarity in Nd isotopic compositions between the Mengyin gabbro dikes and the Paleozoic peridotite xenoliths suggests that ancient lithospheric mantle was still retained at 120 Ma below Mengyin, although the ancient lithospheric mantle in many other places beneath NCC had been severely modified. There might be multiple enrichment events in the lithospheric mantle. An early-stage (before or during Paleozoic) rutile-rich metasomatism affected the lithospheric mantle below Mengyin, Jiaodong and Zichuan. Since then, the lithospheric mantle beneath Mengyin was isolated. A late-stage metasomatism by silicate melts modified the lithospheric mantle beneath Jiaodong and Zichuan but not Mengyin. The removal of the enriched lithospheric mantle and the generation of the mafic dikes may be mainly related to the convective overturn accompanying Jurassic-Cretaceous subduction of the paleo-Pacific plate. (author)

  2. Physical abrasion of mafic minerals and basalt grains: Application to martian aeolian deposits (United States)

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


    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.

  3. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction. (United States)

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


    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  4. Sentinel-1 TOPS interferometry for geophysical applications: Dyke intrusion imaged during 2014 Pico do Fogo eruption (United States)

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


    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.

  5. Pre-Elsonian mafic magmatism in the Nain Igneous Complex, Labrador: the bridges layered intrusion (United States)

    Ashwal, L.D.; Wiebe, R.A.; Wooden, J.L.; Whitehouse, M.J.; Snyder, Diane


    Decades of work on the pristine, unmetamorphosed, and well exposed anorthositic, mafic and granitic rocks of the Nain igneous complex, Labrador, have led to the conclusion that all plutonic rocks in that area were emplaced in a short time intercal at about 1300 ?? 10 Ma). We report here new isotopic data for mafic intrusive rocks that appear to have crystallized several hundred Ma earlier than the bulk of the plutonic activity in the Nain complex. The Bridges layered intrusion (BLI) is a small (15-20 km2) lens of layered mafic rocks about 1.5 km thick, surrounded and intruded by anorthositic, leuconoritic and leucotroctolitic plutons in the middle of the coastal section of the Nain igneous complex. BLI shows very well developed magmatic structures, including channel scours, slump structures, and ubiquitous modally graded layering. Most rocks, however, show granular textures indicative of recrystallization, presumably caused by emplacement of younger anorthositic rocks. BLI contains cumulate rocks with slightly more primitive mineral compositions (An60-83, Fo66-71) than those of other mafic intrusions in the Nain igneous complex, including Kiglapait. SmNd isotopic data for 7 BLI whole-rocks ranging in composition between olivine melagabbro and olivine leucogabbro yield an age of 1667 ?? 75 Ma, which we interpret as the time of primary crystallization. The internal isotopic systematics of the BLI have been reset, probably by intrusion of adjacent anorthositic plutons. A SmNd mineral isochron (plag, whole-rock, mafics) for a BLI olivine melagabbro gives an age of 1283 ?? 22 Ma, equivalent within error of a mineral array (plag, whole-rock, opx, cpx) for an adjacent, igneous-textured, leuconorite vein (1266 ?? 152 Ma). The initial Nd ratio for BLI corresponds to ??{lunate}Nd = -3.18 ?? 0.44. Other whole-rock samples, however, some with vein-like alteration (Chlorite, serpentine, amphiboles), show ??{lunate}Nd values as low as -9.1, suggesting variable contamination by

  6. Polarization of mafic and felsic rocks In the Skaergaard Layered Series (Invited) (United States)

    McBirney, A. R.; Johnston, A.; Webster, J. D.


    When it became apparent that plagioclase could never sink in a magma as iron rich and dense as that of the Skaergaard Intrusion, we were faced with the problem of explaining the formation of anorthositic layers, foundered blocks, and schlieren that consist almost entirely of plagioclase but were obviously stable on the floor of the intrusion. Sonnenthal (Jour. Pet., 1998, 39: 633-661) found that gabbroic blocks that fell from the roof series were originally more gabbroic and were altered metasomatically to anorthosites after they reached the floor were buried it the advancing front of crystallization. Their mafic components were expelled into the surrounding gabbro and replaced by plagioclase. Similar processes appear to have transformed parts of the Layered and Marginal Border Series into strongly polarized anorthosites and olivine pyroxenites. The studies of Filiberto and Treiman (Chem. Geol. 2009, 263: 50-68) of the effect of chlorine on the liquidus of basalts, together with our on-going experimental investigation of its effect on the system plagioclase-pyroxene, has opened new possibilities that may enable us to explain these enigmatic rocks. When Webster and his co-workers (Geoch Cosmoch. Acta, 2009, 73: 559-581) showed that, unlike water, chlorine is much more soluble in mafic silicate melts than felsic ones, these contrasting properties suggested that the effect of chlorine on the cotectic relations of plagioclase and pyroxene might be the opposite of that of water: it could depress the melting temperature of pyroxene just as water depressed that of plagioclase. Experiments currently underway at the American Museum of Natural History and University of Oregon are showing that this is indeed the case. Consider what might happen if a crystallizing gabbro were infiltrated by a chlorine-rich aqueous fluid of the kind that Larsen and Brooks (Jour. Pet., 1997, 35: 1651-79) have shown permeated the rocks while they were still at a high temperature. Flux melting

  7. 40Ar/39Ar phlogopite and U - Pb perovskite dating of lamprophyre dykes from the eastern Lake Superior region: evidence for a 1.14 Ga magmatic precursor to Midcontinent rift volcanism

    International Nuclear Information System (INIS)

    Thin lamprophyre dykes are abundant in the vicinity of the ca. 1.1 Ga Midcontinent Rift System and the late Archean - Early Proterozoic Kapuskasing Uplift in the Canadian Shield northeast of Lake Superior. However, the relationship between these dykes and spatially associated alkalic-carbonatite complexes has been unclear. To ascertain the temporal relationship between the two, we have determined, by 40Ar/39Ar and U-Pb dating, precise emplacement ages for six lamprophyre dykes from the region. The 1144-4+6 Ma U - Pb date for perovskite from the western Marathon and Wawa areas is indistinguishable from the 1144 ± 7 Ma 40Ar/39Ar date for phlogopite from the eastern Kapuskasing Uplift, and it is concluded that these dykes are part of a regional 1.14 Ga swarm that extends over 300 km. These dykes were therefore emplaced some 35 Ma prior to the 1109 Ma commencement of Midcontinent Rift volcanism and coeval alkaline-complex activity, but essentially simultaneously with emplacement of the 1141 ± 2 Ma Abitibi diabase dyke swarm. It is suggested that these widespread 1144 Ma lamprophyre dykes and the Abitibi diabase dykes represent the first magmatic response of initiation of the Midcontinent rifting event, and were precursors to the main rift magmatism at 1109 Ma. (author). 32 refs., 2 tabs., 5 figs

  8. Mineralogy and petrogenesis of a Ba-Ti-Zr-rich peralkaline dyke from Šebkovice (Czech Republic): Recognition of the most lamproitic Variscan intrusion (United States)

    Krmíček, Lukáš; Cempírek, Jan; Havlín, Aleš; Přichystal, Antonín; Houzar, Stanislav; Krmíčková, Michaela; Gadas, Petr


    A peralkaline, ultrapotassic dyke found at Šebkovice (Třebíč district, western Moravia) is a mineralogically extreme member of a dyke swarm occurring along the south-eastern border of the Moldanubian Region of the Bohemian Massif. The dyke shows a simple zoning, with a very fine-grained marginal zone grading into a medium-grained central zone. It has a primary mineral assemblage of microcline and potassic amphiboles, with accessory apatite and altered phlogopite. The microcline exhibits an unusual red luminescence colour and pronounced substitution of Fe3+ for Al, with measured contents of Fe2O3 up to 8.5 wt.% (0.31 apfu Fe3+). Amphiboles have very high K (up to 0.99 apfu) and Si contents; their compositions follow an alkaline fractionation trend from potassic-richterite to potassic-magnesio-arfvedsonite, characterized by an increase of Na/K and a decrease of Ca, Mg, Fe2+ and Ti via heterovalent substitutions [B]Ca + [C](Mg,Fe2+) → [B]Na + [C]Fe3+ and Ti + Mg → 2Fe3+. The most evolved apatite is significantly enriched in SrO (up to 9.7 wt.%; 0.49 apfu Sr). The core of the dyke and late veinlets contain unique late- to post-magmatic Ba-Ti-Zr-bearing mineral assemblages of baotite, henrymeyerite, titanite, rutile, benitoite and bazirite. Anhedral baotite fills interstices distributed inhomogeneously in the dyke centre; it is locally replaced by a Ba-bearing titanite + henrymeyerite + rutile + quartz assemblage. Henrymeyerite (the second record in a lamproite) shows variable Fe/Ti ratios and represents a solid solution of the hepta- and hexatitanate components. Euhedral crystals of benitoite and bazirite are enclosed in the late-stage quartz-titanite-apatite veinlets in the fine-grained margin of the intrusion. In terms of a mineralogical-genetic classification, the Šebkovice dyke can be considered as a new high-silica (~ 57 wt.% SiO2) variety of lamproite (variety Šebkovice), and represents a unique expression of post-collisional potassic magmatism on the

  9. 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


    -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.

  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


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


    Wes Hildreth; Brad Singer; Estanislao Godoy; Francisco Munizaga


    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...

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


    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

  13. Electromagnetic induction in a conductive strip in a medium of contrasting conductivity: application to VLF and MT above molten dykes (United States)

    Davis, Paul M.


    Very low frequency (VLF) electromagnetic waves that penetrate conductive magma-filled dykes generate secondary fields on the surface that can be used to invert for dyke properties. The model used for the interpretation calculates currents induced in a conductive strip by an inducing field that decays exponentially with depth due to the conductivity of the surrounding medium. The differential equations are integrated to give an inhomogeneous Fredholm equation of the second kind with a kernel consisting of a modified Bessel function of the second kind. Numerical methods are typically used to solve for the induced currents in the strip. In this paper, we apply a modified Galerkin-Chebyshev method, which involves separating the kernel into source and field spectra and integrating the source terms to obtain a matrix equation for the unknown coefficients. The incident wave is expressed as a Chebyshev series. The modified Bessel function is separated into a logarithmic singularity and a non-singular remainder, both of which are expanded in complex Chebyshev polynomials. The Chebyshev coefficients for the remainder are evaluated using a fast Fourier transform, while the logarithmic term and incident field have analytic series. The deconvolution then involves a matrix inversion. The results depend on the ratio of strip-size to skin-depth. For infinite skin-depth and a singular conductivity distribution given by τ_0 a/√{a^2 - z^2 } (where τ0 is the conductance, a is the half-length and z the distance from the centre), Parker gives an analytic solution. We present a similar analytic series solution for the finite skin-depth case, where the size to skin depth ratio is small. Results are presented for different ratios of size to skin depth that can be compared with numerical solutions. We compare full-space and half-space solutions. A fit of the model to VLF data taken above a magma filled dykes in Hawaii and Mt Etna demonstrates that while properties such as depth to top

  14. Uses of anisotropy of magnetic susceptibility in the study of emplacement processes of lava flows and dykes

    International Nuclear Information System (INIS)

    Complete text of publication follows. The anisotropy of magnetic susceptibility (AMS) is a powerful technique that can be used to explore in detail the mineral fabric of many types of rocks. In particular, it is well suited to determine mineral fabric of massive, otherwise featureless rocks, like for example the internal parts of many lava flows and dykes. Like most other mineral fabric indicators, the AMS is mainly acquired at a stage when flow-related deformation promotes a mineral array within the melted rock. Unlike is the case with other petrofabric methods, however, the effort required to obtain three-dimensional information of such mineral array using AMS is much reduced, although due to differences in the shape of various minerals involved in the process of fabric acquisition it is possible to find some differences between magnetic and optically determined mineral fabrics. When attention is given to the systematic variations of the AMS within a lava flow or dyke, however, the AMS method allows us to infer aspects of lava (magma) emplacement that are not easy to study through other traditional petrofabric techniques. Such detailed information can be used to obtain a detailed record of the internal deformation of one flow unit with relative ease and little effort. Despite of these advantages, the abundant information obtained from one single unit through AMS methods might not be interpreted in a simple form. The main complications arise from two contrasting premises. On the one hand it can be assumed that mineral fabric remains constant along one single unit, and therefore departures from an expected value are considered indicative of post-emplacement alteration. Alternatively, it can be considered that changes in the mineral fabric are to be expected due to changing conditions of emplacement. For this reason, a more thoroughly investigation that takes into consideration independent lines of information is always advisable. Nevertheless, AMS remains as the

  15. On the origin of pseudoleucite from Cenozoic phonolite dykes from Loučná/Böhmisch Wiesenthal, Krušné hory/Erzgebirge Mts., Bohemia

    Czech Academy of Sciences Publication Activity Database

    Pivec, Edvín; Ulrych, Jaromír; Langrová, Anna


    Roč. 179, č. 3 (2004), s. 221-238. ISSN 0028-3649 R&D Projects: GA AV ČR(CZ) IAA3048201 Keywords : pseudoleucite * phonolite * tinguaite * dyke * mineralogy * petrology * Cenozoic * Krušné hory/Erzgebirge Mts. * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.430, year: 2004

  16. Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust


    Bhattacharya, S.; Chaudhary, A.K.; Saw, A. K.; Das, P.; Chatterjee, D


    Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB). They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derive...

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


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


    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...

  18. Impacts of dyke development in flood prone areas in the Vietnamese Mekong Delta to downstream flood hazard (United States)

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


    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

  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. 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)


    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.).

  1. Petrology and geochemistray of Imam-Zadeh Hashem mafic and ultramafic bodies, southern Guilan province

    Directory of Open Access Journals (Sweden)

    Mojgan Salavati


    Full Text Available Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setting diagrams, display arc characteristic. The chondrite normalized REE patterns show low enrichment in LREEs relative to HREEs. The negative Nb and Ti anomalies in primitive mantle and MORB-normalized multi-element diagrams of the rocks are characteristic of island arc magmas. Also, enrichment in LILE and depletion of HFSE may indicate a subduction-related tectonic setting. According to geological and geochemical evidence, Imam-Zadeh Hashem ultramafic and sub-alkaline gabbro rocks can be as a part of the Southern Caspian Sea Ophiolite sequence (SCO that formed in a suprasubduction tectonic system.

  2. Palaeoproterozoic mafic and intermediate metavolcanic rocks in the Turku area, SW Finland

    Directory of Open Access Journals (Sweden)

    Markku Väisänen


    Full Text Available Twenty two samples were analysed from mafic and intermediate volcanic rocks from the Turku area along ~60 km long north-south geotraverse. Geographically and lithologically the samples were divided into the Pargas, Turku and Vahto groups. The Pargas and Turku groups consist of mafic units and intercalations within migmatitic gneisses. Their geochemical compositions are very similar. In average, they show quite flat REE curves and the multielement diagrams show moderate LILE enrichments, minor negative Ta-Nb anomalies and straight HFSE curves. We infer these as transitional between MORB and VAB. The Vahtogroup consists of thicker volcanic sequences in connection with synorogenic plutonic rocks. The data show enriched LREEs, LILEs, Th and P combined with negative Ta-Nb anomalies, i.e. the Vahto group shows subduction component. We interpret that the Vahto volcanicrocks belong to the Häme belt. The geochemical data indicate that the Pargas and Turku groups were formed in extensional, possibly back-arc or intra-arc setting while the Vahto group was formed at continental volcanic arc.

  3. Petrogenesis of Mesoproterozoic lamproite dykes from the Garledinne (Banganapalle) cluster, south-western Cuddapah Basin, southern India (United States)

    Rao, N. V. Chalapathi; Atiullah; Kumar, Alok; Sahoo, Samarendra; Nanda, Purnendu; Chahong, Ngazimpi; Lehmann, B.; Rao, K. V. S.


    We report mineral chemistry and whole-rock major and trace-element geochemistry for a recent find of Mesoproterozoic (~1.4 Ga) lamproites from the Garledinne (Banganapalle) cluster, south-western part of the Paleo-Mesoproterozoic Cuddapah Basin, southern India. The Garledinne lamproites occur as WNW-ESE-trending dykes that have undergone varying degree of pervasive silicification and carbonate alteration. Nevertheless, their overall texture and relict mineralogy remain intact and provide important insights into the nature of their magmas. The lamproite dykes have porphyritic to weakly porphyritic textures comprising pseudomorphed olivine macrocrysts and microphenocrysts, titanian phlogopite microphenocrysts, spinel having a compositional range from chromite to rarely magnesiochromite, Sr-rich apatite and niobian rutile. The Garledinne and other Cuddapah Basin lamproites (Chelima and Zangamarajupalle) collectively lack sanidine, clinopyroxene, potassic richterite, and titanite and are thus mineralogically distinct from the nearby Mesoproterozoic lamproites (Krishna and Ramadugu) in the Eastern Dharwar Craton, southern India. The strong correlation between various major and trace elements coupled with high abundances of incompatible and compatible trace elements imply that alteration and crustal contamination have had a limited effect on the whole-rock geochemistry (apart from K2O and CaO) of the Garledinne lamproites and that olivine fractionation played an important role in their evolution. The Garledinne lamproites represent small-degree partial melts derived from a refractory (previously melt extracted) peridotitic mantle source that was subsequently metasomatised (enriched) by carbonate-rich fluids/melts within the garnet stability field. The involvement of multiple reservoirs (sub-continental lithospheric mantle and asthenosphere) has been inferred in their genesis. The emplacement of the Garledinne lamproites is linked to extensional events, across the various

  4. Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion (United States)

    Whitney, D.L.; Tepper, J.H.; Hirschmann, M.M.; Hurlow, H.A.


    The Skymo Complex in the North Cascades, Washington, is a layered mafic intrusion within the Ross Lake fault zone, a major orogen-parallel structure at the eastern margin of the Cascades crystalline core. The complex is composed dominantly of troctolite and gabbro, both with inclusions of primitive olivine gabbro. Low-pressure minerals in the metasedimentary contact aureole and early crystallization of olivine + plagioclase in the mafic rocks indicate the intrusion was emplaced at shallow depths (magmatism. The Skymo mafic complex and the Golden Horn granite were emplaced during regional extension and collapse of the North Cascades orogen and represent the end of large-scale magmatism in the North Cascades continental arc. ?? 2008 Geological Society of America.

  5. Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review


    Seghedi, I.; Downes, Hilary; O. Vaselli; Szakács, A.; Balogh, K.; Z. Pécskay


    Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with deriv...

  6. Neoproterozoic ultramafic and mafic magmatism in the Eastern Cordillera of the central peruvian Andes: the Tapo Massif


    Tassinari, Colombo G.; Castroviejo Bolibar, Ricardo; Rodrigues, Jose F.; Acosta, Jorge; Pereira, Eurico


    A highly dismembered assemblage of ultramafic and mafic rocks is exposed in the Eastern Cordillera of the Central Peruvian Andes, extending along a discontinuous NW-SE belt over some 250 km between 12° and 9° S of latitude. One of the most important occurrences is the Tapo Mafic-Ultramafic Complex, which occurs at 3750 to 4200 m above sea level, 2 km to the west of Tapo locality, in the Tarma province, about 200 Km west of Lima. The Tapo complex is a lens-shaped body, 5 km long and 1-2...

  7. Postcollisional mafic igneous rocks record recycling of noble gases by deep subduction of the continental crust (United States)

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


    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.

  8. Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc (United States)

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


    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.

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

    Python, Marie; Abily, Bénédicte; France, Lydéric


    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

  10. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics. (United States)

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


    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

  11. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics (United States)

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


    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.

  12. Hydraulic fracturing as a possible mechanism of dyke-sill transitions and horizontal discordant intrusions in trachytic tabular bodies of Arraial do Cabo, State of Rio de Janeiro, Brazil

    Directory of Open Access Journals (Sweden)

    S.E. Sichel


    Full Text Available This paper presents some field descriptions and genetic considerations about dyke-sill transitions and horizontal-discordant intrusions of the early Tertiary felsic alkaline dyke swarm at Arraial do Cabo, State of Rio de Janeiro, Brazil. Two examples show the entire process of dyke-sill transition. Near sea level they are vertical-discordant; at middle height, oblique-concordant; at the top of the cliff, horizontal-discordant. The latter process cannot be explained by a traditional model of magma intrusion along weaknesses in the host body. It can be accounted for by hydraulic fracturing: magma pressure creates a new fracture normal to σ3, regardless of whether old fracture systems exist. The dyke-sill transition takes place at a depth such that σ3 changes direction from horizontal to vertical. In the specific case described here, the stress change could be caused by intrusion and volume expansion of the Cabo Frio Island syenitic body.

  13. 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


    @@ 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% ).

  14. Triassic mafic and intermediate magmatism associated with continental collision between the North and South China Cratons in the Korean Peninsula (United States)

    Yi, Sang-Bong; Oh, Chang Whan; Lee, Seung-Yeol; Choi, Seon-Gyu; Kim, Taesung; Yi, Keewook


    Triassic coeval mafic and intermediate magmatism occurred in the area suggested to be the southern margin of the North China Craton (NCC) in the Gyeonggi Massif (GM) of the Korean Peninsula. This study investigates aspects of the mafic and intermediate magmatism using SHRIMP zircon ages and whole-rock chemical and isotopic Sr-Nd data. The mafic and intermediate rocks intruded into a basement paragneiss in three areas (Yangpyeong, Odesan and Yangyang) within the GM at ca. 230 Ma. The paragneiss was metamorphosed in both the Paleoproterozoic and Triassic. Gabbros (hornblende gabbro and pyroxene-mica gabbro) from the study areas exhibit strong light REE (LREE) enrichment relative to chondrite (LaN/YbN = 11.1-30.6) and a high LILE/HFSE pattern, Ta-Nb-P-Ti troughs and positive Ba-K-Pb-Sr spikes on the N-MORB-normalized multi-element variation diagram. These features are typical characteristics of arc-related gabbros. The gabbros also show strongly enriched initial isotopic compositions (87Sr/86Sr(i) = 0.7100-0.7137; εNd(t) = - 13.1 to - 19.7). The coeval intermediate intrusive rocks also exhibit whole-rock chemical and isotopic features (87Sr/86Sr(i) = 0.7099-0.7143; εNd(t) = - 10.8 to - 18.6) similar to those of the gabbros. The mafic and intermediate intrusive rocks plot in the within-plate and/or post-collisional fields on tectonic discrimination diagrams. These data indicate that the mafic and intermediate magmatism in the study areas occurred during the Triassic post-collisional relaxation period via partial melting of sub-continental lithospheric mantle (SCLM) that was enriched in a subduction environment prior to (or during) the Permo-Triassic continental collision between the NCC and the South China Craton (SCC). The highly enriched mantle signatures revealed by the gabbros from the study areas are matched to the enriched features identified in Cretaceous mafic igneous rocks (ca. 130 Ma) on the southern margin of the NCC. Thus, this study suggests that the

  15. Interaction between magmatic and tectonic stresses during dyke intrusion Interacción entre esfuerzos magmáticos y tectónicos durante la intrusión de diques


    Jorge Skarmeta


    Cataclastic and mylonitic rocks exposed in the southwestern part of the Peninsula de Mejillones, northern Chile, are intruded at high angles of the foliation by younger, steeply inclined (±70°) basaltic dykes that resemble intrusive tension gashes with knife-edge contacts with the country rocks. These late dykes developed sigmoidaly-shaped, preferred orientation paths defined by oriented pyroxene phenocrysts that vary in size, aspect ratio, concentration and distribution across the width of a...

  16. The carbonatite-marble dykes of Abyan Province, Yemen Republic: the mixing of mantle and crustal carbonate materials revealed by isotope and trace element analysis (United States)

    Le Bas, M. J.; Ba-Bttat, M. A. O.; Taylor, R. N.; Milton, J. A.; Windley, B. F.; Evins, P. M.


    Dykes of carbonate rocks, that cut gneisses in the Lowder-Mudiah area of southern Yemen, consist of dolomite and/or calcite with or without apatite, barite and monazite. Petrographic observations, mineralogical, XRF and ICP-MS analyses reveal that some of the carbonate rocks are derived from sedimentary protoliths, whereas others are magmatic calcio- and magnesio-carbonatites some of which are mineralized with barite-monazite. The interbanded occurrence and apparent contemporary emplacement of these different rock types within individual dykes, backed by Sr Nd isotope evidence, are interpreted to show that intrusion of mantle-derived carbonatite magma was accompanied by mobilization of crustal marbles. That took place some 840 Ma ago but the REE-mineralization is dated at ca. 400 Ma.

  17. Sheeted and bulbous pluton intrusion mechanisms of a small granitoid from southeastern Australia: implications for dyke-to-pluton transformation during emplacement (United States)

    Fowler, T. J.


    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.

  18. 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)


    @@ 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.

  19. 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


    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.

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


    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

  1. Platinum-group element concentrations in pyrite from the Main Sulfide Zone of the Great Dyke of Zimbabwe (United States)

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


    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.

  2. 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


    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.

  3. The Importance of Sampling Strategies on AMS Determination of Dykes II. Further Examples from the Kapaa Quarry, Koolau Volcano, Oahu, Hawaii (United States)

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


    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.

  4. Mantle evolution in the Variscides of SW England: Geochemical and isotopic constraints from mafic rocks (United States)

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


    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.

  5. 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

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


    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

  7. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania (United States)

    Bonin, Bernard; Tatu, Mihai


    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).

  8. 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

  9. Petrogenesis of mafic magmatism in Arabia-Eurasia collision zone: valley filling flows in Armenia (United States)

    Meliksetian, Khachatur; Neill, Iain; Allen, Mark; Navasardyan, Gevorg


    The Turkish- Armenian-Iranian orogenic plateau grew after the Middle Miocene following the initial Paleogene Arabia- Eurasia collision. It is widely accepted, that uplift of the plateau is related to break-off of the southern Neo-Tethys slab beneath the Bitlis-Zagros Suture at ~15-10 Ma, coupled with continued plate convergence and regional crustal shortening. Since this time there has also been a widespread mantle-derived collision magmatism over large parts of NW Iran, Eastern Anatolia and the Lesser Caucasus, potentially hundreds of kilometres from the site of southern Neo-Tethys slab break-off, >10 Myr after the proposed break-off event. Detailed wholer rock geochemistry and Sr-Nd-Pb-Hf isotope data are presented for ~2.5 Ma trachy-basalt to trachy-basaltic andesite lavas erupted in Armenia in the South Caucasus. These thick (up to 400 m) mafic flows generated several plateaux within the Lesser Caucasus: the Javakheti Plateau (S Georgia and NW Armenia), and the Lori and Kotayk Plateaux (Armenia). These basalts sequences also extend to the NE Kars-Erzurum Plateau in eastern Turkey. It is demonstrated that studied series formed by Iranian Plateau, have Th/La ratios ≤ 0.2, much lower than the value of ~0.3 for continental crust, so infra-crustal recycling and/or lower crustal delamination are certainly required to produce andesitic high-Th/La bulk continental crust.

  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


    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. Petrogenesis and tectonic setting of the mafic-ultramafic rock association from NW Senja, West Troms Basement Complex


    Priyatkina, Nadezda


    The studied mafic-ultramafic rock association occurs within Archean tonalitic gneisses and metasupracrustal suites of the Astridal belt belonging to the West Troms Basement Complex in the northwestern part of the Senja Island. The rock association appears in lens-shaped bodies, up to 200 m long, which are oriented conformal to the major metamorphic fabric of the host rock. The rock association is made up by interlayered units of green spinel-bearing olivine orthopyroxene-hornblendite, hornble...

  12. Thermal, chemical and isotopic homogenization of syn-extensional I-type plutons and mafic microgranular enclaves (United States)

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


    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.

  13. Phase equilibrium constraints on the viscosity of silicic magmas with implications for mafic-silicic mixing processes


    Scaillet, Bruno; Whittington, Alan; Martel, Caroline; Pichavant, Michel; Holtz, François


    Isobaric crystallization paths obtained from phase equilibrium experiments show that, whereas in rhyolitic compositions melt fraction trends are distinctly eutectic-like, dacitic and more mafic compositions have their crystallinities linearly correlated with temperature. As a consequence, the viscosities of the latter continuously increase on cooling, whereas for the former they remain constant or even decrease during 80% of the crystallisation interval, which opens new perspectives for the f...

  14. 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.)

  15. 2480 Ma mafic magmatism in the northern Black Hills, South Dakota: A new link connecting the Wyoming and Superior cratons (United States)

    Dahl, P.S.; Hamilton, M.A.; Wooden, J.L.; Foland, K.A.; Frei, R.; McCombs, J.A.; Holm, D.K.


    The Laramide Black Hills uplift of southwest South Dakota exposes a Precambrian crystalline core of ???2560-2600 Ma basement granitoids nonconformably overlain by two Paleoproterozoic intracratonic rift successions. In the northern Black Hills, a 1 km thick, layered sill (the Blue Draw metagabbro) that intrudes the older rift succession provides a key constraint on the timing of mafic magmatism and of older rift-basin sedimentation. Ion microprobe spot analyses of megacrysts of magmatic titanite from a horizon of dioritic pegmatite in the uppermost sill portion yield a 207Pb/206Pb upper-intercept age of 2480 ?? 6 Ma (all age errors ??2??), comparable to two-point 207Pb/206Pb errorchron ages obtained by Pb stepwise leaching of the same titanites. Nearly concordant domains in coexisting magmatic zircon yield apparent spot ages ranging from 2458 ?? 16 to 2284 ?? 20 Ma (i.e., differentially reset along U-Pb concordia), and hornblende from an associated metadiorite yields a partially reset date with oldest apparent-age increments ranging between 2076 ?? 16 and 2010 ?? 8 Ma. We interpret these data as indicating that an episode of gabbroic magmatism occurred at 2480 Ma, in response to earlier rifting of the eastern edge of the Wyoming craton. Layered mafic intrusions of similar thickness and identical age occur along a rifted belt in the southern Superior craton (Sudbury region, Ontario). Moreover, these mafic intrusions are spatially aligned using previous supercontinent restorations of the Wyoming and Superior cratons (Kenorland-Superia configurations). This new "piercing point" augments one previously inferred by spatial-temporal correlation of the Paleoproterozoic Huronian (southern Ontario) and Snowy Pass (southeastern Wyoming) supergroups. We propose that layered mafic intrusions extending from Nemo, South Dakota, to Sudbury, Ontario, delineate an axial rift zone along which Wyoming began to separate from Superior during initial fragmentation of the Neoarchean

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

    Directory of Open Access Journals (Sweden)

    Gorazd Rajh


    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.

  17. Geochemistry and petrology of mafic enclaves of metasedimentary origin: case study from the Peninsular Ranges Batholith, California (United States)

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


    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

  18. Petrology of Mafic Bodies Associated with the Eocene "A-type" Golden Horn Batholith, North Cascades, WA (United States)

    Berkelhammer, S.; Tepper, J. H.; Petro, G. T.; Eckles, E. H.


    The 49 Ma Golden Horn batholith, the only "A-type" granite in the WA Cascades, is associated with coeval mafic bodies that represent samples of mantle-derived magmas that were present during melting and emplacement of the batholith. The most voluminous mafic rocks are dikes up to 10 m wide that occur in a NW-trending 48 Ma swarm roughly parallel to (but outside of) the SW margin of the batholith. Dike lithologies include hornblende lamprophyres, biotite-hornblende diorites, and hornblende-biotite tonalites. Mafic rocks also occur as plutons within the batholith, one studied example being the 48.4 Ma olivine-bearing pyroxene diorite at Cutthroat Peak. All of the Golden Horn mafic rocks have spidergrams with HFSE depletions that suggest an arc setting. They can be divided on the basis of chemistry into 5 types: low-silica adakites (LSA), high-silica adakites (HSA), Nb-enriched basalts (NEB), high-Nb basalts (HNB), and "typical" arc basalts (TAB). HSA traits (800-1400 ppm Sr, La/Ybn = 11-23, low HREE contents, SiO2 >60 wt. %) are consistent with an eclogite (slab) source. Conversely, the LSA (860-1100 ppm Sr, La/Ybn = 21-25, up to 650 ppm Cr, SiO2 peridotite sources. Traits of the TAB, represented by the Cutthroat Peak diorite (46-50 wt. % SiO2; La/Ybn = 3.5-6.1) suggest derivation from a mantle wedge without slab melt (eclogite) involvement. We suggest that the LSA, NEB, and HNB originated by melting of mantle wedge that had been enriched with (or assimilated by) slab melts, the latter possibly represented by the HSA. Elevated temperatures necessary for slab melting are associated with slab windows, and plate motion reconstructions (Engebretson et al., 1985) are compatible with migration of the Kula-Farallon slab window beneath the Golden Horn area during the mid-Eocene. Passage of this slab window provides an explanation for adakite formation and perhaps also enhanced lower crustal melting to produce the granitoid rocks. Pb, Sr, and Nd work is currently underway to

  19. Microchemistry of amphiboles near the roof of a mafic magma chamber: Insights into high level melt evolution (United States)

    Murphy, J. Brendan; Blais, Stephanie A.; Tubrett, Michael; McNeil, Daniel; Middleton, Matthew


    The Late Neoproterozoic Greendale Complex, located within the Avalon terrane of Nova Scotia, is a suite of appinitic rocks ranging from ultramafic to felsic in composition that were intruded during regional ensialic arc magmatism and crystallized at shallow crustal levels under conditions of high pH2O. Amphibole is the dominant mafic mineral in ultramafic to mafic rocks and displays the extraordinary variability in texture and modal abundance that is characteristic of appinite suites. These features allow sensitivity of amphibole composition (major, trace and REE) to the evolution of water-rich magma to be investigated. All amphiboles in mafic and ultramafic rocks are calcic, with (Ca + Na)B ≥ 1.34 and SiIV between 6.1 and 7.3. They predominantly range in composition from tschermakite to magnesiohornblende and display a dominance of edenite (Na,KA + AlIV = SiIV) substitution. Although each sample exhibits remarkably uniform Mg# over a wide range in Si of up to one formula unit, the mafic rock amphiboles are characterized by lower (0.5 to 0.7) Mg#, compared to the ultramafic rocks (0.7 and 0.9). REE profiles are bow-shaped, and are characterized by depletion in LREE (La/Sm ≈ 0.61), a slight depletion in HREE (Gd/Yb ≈ 1.55) as well as a negative Eu anomaly, which is attributed to co-precipitation of plagioclase. REE and trace element profiles of ultramafic amphiboles are divided into two groupings. Group A amphiboles occur in all specimens analyzed and their REE profiles are very similar to the whole-rock analyses of the mafic rocks and to those predicted from amphibole/melt partition coefficients. In contrast, Group B amphiboles display relative enrichment in light REEs (La/Sm ≈ 2.05), have lower ΣREE, and lack a negative Eu anomaly relative to Sm and Gd. Group B amphiboles are more enriched in Th and U and show a more pronounced depletion in Nb, Ti, Y and HREE. Group B amphiboles probably grew in a reaction relationship with olivine and pyroxene, and their

  20. Paleomagnetism of Proterozoic mafic dikes from the Tobacco Root Mountains, southwest Montana (United States)

    Harlan, S.S.; Geissman, J. Wm; Snee, L.W.


    Paleomagnetic data from Proterozoic mafic dikes in southwestern Montana provides evidence for two distinct episodes of subparallel dike emplacement at ca. 1450 and 780 Ma. Published geochemical data from dikes in the southern Tobacco Root Mountains has identified three distinct compositional groups, termed groups A, B, and C. Geochronological data from the group A dikes yielded a Sm-Nd age of 1448 ?? 49 Ma. Emplacement of these dikes is thought to reflect mafic magmatism associated with extension accompanying development of the adjacent Mesoproterozoic Belt Basin. Paleomagnetic results from these dikes and a group C dike yield antipodal magnetizations with a group-mean direction of D = 225.0??, I = 61.8?? (k = 27.9, ??95 = 7.7??, N = 14 independent means/24 sites). The average paleomagnetic pole (8.7??N, 216.1??E, A95 = 10.3??) is considered to be primary on the basis of positive baked contact tests and similarity to poles of ca. 1.45-1.4 Ga from intrusions elsewhere in North America, but is discordant with respect to poles from age equivalent sedimentary rocks of the Meosoproterozoic Belt Supergroup. 40Ar/39Ar dates from geochemical group B dikes are consistent with published U-Pb dates that demonstrate dike emplacement at 780 Ma as part of the regional Gunbarrel magmatic event. Hornblende concentrates from the group B dikes yield 40Ar/39Ar apparent ages of 778-772 Ma, whereas biotite from a baked contact zone yielded a plateau date of 788 Ma. Paleomagnetic results from the group B dikes yield a mean direction of D = 301.5??, I = -17.1?? (k = 65.7, ??95 = 4.0??, N = 12 independent means/23 sites) with a paleomagnetic pole at 14.6??N, 127.0??E (A95 = 3.2??). The combination of geochronologic data, results of a baked contact test, and spatial agreement of the paleomagnetic poles with poles of similar age elsewhere in North America indicates that this is also a primary magnetization associated with dike emplacement. Paleomagnetic data from some of the Tobacco Root

  1. 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


    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.

  2. Evolution of the East African rift: Drip magmatism, lithospheric thinning and mafic volcanism (United States)

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


    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.

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


    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.

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



    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 ...

  5. 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


    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)

  6. Pleistocene mafic volcanoes in the Puna Cordillera Oriental boundary, NW-Argentina (United States)

    Guzmán, S. R.; Petrinovic, I. A.; Brod, J. A.


    Los Gemelos and El Saladillo are both monogenetic, strombolian, basaltic-shoshonitic volcanoes that constitute the easternmost recognized examples of mafic Plio-Quaternary volcanism in the southern Central Andes. Two regional faults delimit the borders of the Calchaquí valley, as thrusts with opposite vergence: the eastern Calchaquí fault and the western Toro Muerto fault. While Los Gemelos are set in the hanging wall of Calchaquí back-thrust fault, El Saladillo are set in the footwall of Toro Muerto fault. As Los Gemelos volcanoes have well preserved morphological features, we highlight some relationship between them and their tectonic setting. Kinematic data and one new measurement, that indicate right strike-slip movement in the vicinity of Los Gemelos during the Pleistocene-Holocene. The emplacement of these volcanoes should be related to a transpression zone parallel to the valley, where the alignment of the cones is outlining the trend of conjugated faults. The magmas were derived from a small degree of partial melting of an enriched, garnet-bearing mantle source. The analysed rocks have primitive signature (high Ni, Cr, Co and MgO concentrations; presence of chromite and forsteritic olivine) and evidence for crustal contamination with felsic rocks (quartz ± plagioclase ± K-feldspar xenocrysts with coronas, reaction rims and/or embayments; high 87Sr/ 86Sr ratios, negative ɛNd values). The high Cr and Ni content, high Mg# and low crystal content suggest that no major fractional crystallization occurred, therefore precluding long residence periods. Rapid magma ascent across 60 km of continental crust was guided by magmatic overpressure favoured by important tectonic stresses also avoiding significant residence time at upper crust depth. Thus, we invoke a process of assimilation during turbulent ascent (ATA) to explain the contamination at crustal levels. Los Gemelos volcanoes were formed around 35,000 yr. as inferred from the age of lacustrine sediments

  7. Physical processes of shallow mafic dike emplacement near the San Rafael Swell, Utah (United States)

    Delaney, P.T.; Gartner, A.E.


    Some 200 shonkinite dikes, sills, and breccia bodies on the western Colorado Plateau of south-central Utah were intruded from approximately 3.7 to 4.6 Ma, contemporaneous with mafic volcanism along the nearby plateau margin. Thicknesses of dikes range to about 6 m; the log-normal mean thickness is 85 cm. Despite the excellent exposures of essentially all dikes in strata of the Jurassic San Rafael Group, their number is indeterminate from their outcrop and spacing because they are everywhere greatly segmented. By our grouping of almost 2000 dike segments, most dikes are less than 2 km in outcrop length; the longest is 9 km. Because the San Rafael magmas were primitive and probably ascended directly from the mantle, dike lengths in outcrop are much less than their heights. The present exposures probably lie along the irregular upper peripheries of dikes that lengthen and merge with depth. Orientations of steps on dike contacts record local directions of dike-fracture propagation; about half of the measurements plunge less than 30??, showing that lateral propagation at dike peripheries is as important as the vertical propagation ultimately responsible for ascent. The San Rafael dikes, now exposed after erosion of about 0.5-1.5 km, appear to thicken and shorten upward, probably because near-surface vesiculation enhanced magmatic driving pressures. Propagation likely ceased soon after the first dike segments began to feed nearby sills or vented to initiate small-volume eruptions. Most of the dikes are exposed in clastic strata of the Jurassic San Rafael Group. They probably acquired their strikes, however, while ascending along well-developed joints in massive sandstones of the underlying Glen Canyon Group. Rotation of far-field stresses during the emplacement interval cannot account for disparate strikes of the dikes, which vary through 110??, most lying between north and N25??W. Rather, the two regional horizontal principal stresses were probably nearly equal, and so

  8. Petrology and oxygen isotope geochemistry of the Pucon ignimbrite - Southern Andean volcanic zone, Chile: Implications for genesis of mafic ignimbrites

    International Nuclear Information System (INIS)

    Although mafic components of dominantly intermediate to silicic ignimbrites are rather common, voluminous, dominantly mafic ignimbrites are rare (e.g., Smith, 1979; cf. Freundt and Schmincke, 1995). Volcan Villarrica, the most active composite volcano in South America, located in the Southern Andean Volcanic Zone (SAVZ, Lopez-Escobar and Moreno, 1994a), has produced two such ignimbrites, respectively the Lican and Pucon Ignimbrites, in the last 14,000 years (Clavero, 1996). The two ignimbrites are low-Si andesite and basaltic-andesite to low-Si andesite, respectively, the former about twice as voluminous as the later (10 and 5 km3). Eruption of the ignimbrites produced calderas respectively 5 and 2 km in diameter (Moreno, 1995; Clavero, 1996). In addition to its mafic bulk composition, the Pucon Ignimbrite (PI) is also distinguished by numerous xenolithic fragments among and also within magmatic pyroclasts. Many of these are fragments of granitoid rocks. Volcan Villarrica has also produced numerous smaller mafic ignimbrites and pyroclastic surge deposits, as well as dominantly basaltic fallout and lava flows (Lopez-Escobar and Moreno, 1994; Moreno, 1995; Clavero, 1996; Hickey-Vargas et al., 1989; Tormey et al., 1991). Reasons for the unusual style of mafic explosive activity at Volcan Villarrica are unclear. Clavero (1996), based upon an exemplary thesis-study of the physical volcanology and petrology of the PI, suggests it formed in response to a sequence of events beginning with injection of a shallow basaltic andesite magma chamber by hotter basaltic magma. In his model mixing and heat transfer between the two magmas initiated a violent Strombolian eruption that destabilized the chamber causing infiltration of large amounts of meteoric-water saturated country rocks. The Pucon Ignimbrite formed in response to subsequent phreatomagmatic interactions. In contrast, Lopez-Escobar and Moreno (1994) infer on geochemical grounds that volatiles leading to the explosive

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


    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

  10. 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


    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...... mGal) 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...

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

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


    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

  12. Mantle derivation of Archean amphibole-bearing granitoid and associated mafic rocks: evidence from the southern Superior Province, Canada (United States)

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


    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

  13. Syntectonic emplacement of the Middle Jurassic Concon Mafic Dike Swarm, Coastal Range, central Chile (33 degrees S)


    C. Creixell; M.A. Parada; Roperch, Pierrick; D. Morata; Arriagada, C; Arce, C.P. de


    The Concon Mafic Dike Swarm (CMDS) consists of basaltic to andesitic dikes emplaced into deformed Late Palcozoic granitoids during the development of the Jurassic arc of central Chile. The dikes are divided into an early group of thick dikes (512 in) and a late group of thin dikes (0.5-3 m). Two new amphibole Ar-40/Ar-39 dates obtained from undeformed and deformed dikes, constrain the age of emplacement and deformation of the CMDS between 163 and 157 Ma. Based on radiometric ages, field obser...

  14. Opportunity to sample something different: The dark, unweathered, mafic sands of Cerberus and the Pathfinder 1997 Mars landing (United States)

    Edgett, Kenneth S.; Singer, Robert B.; Geissler, P. E.


    A very important surface component, typically described as 'dark gray material', was not seen at the Viking lander sites, but is common to all low-albedo regions on Mars. Dark material probably includes unaltered mafic volcanic and/or crustal rock and soil not coated by dust, weathering rinds, or varnish. A Pathfinder landing in Cerberus (9 deg N - 16 deg N, 194 deg W - 215 deg W) will guarantee examination of materials that are distinctly different from the two Viking lander sites. In situ study of dark material will provide vital ground truth for orbiter-based observations like those anticipated from Mars '94/'96 and Mars Global Surveyor.

  15. Study of the mining possibilities in the surroundings of Mahoma - Guaycuru phase I Feasibility of the mafic body of Mahoma-Guaycuru and of the complex mafic - Stratified ultramafic of the Cerros Negros and San Jose and Colonia provinces

    International Nuclear Information System (INIS)

    In Mahoma - Guaycuru area has been carried out regional cartography to place the geologic context, mainly the Mahoma bodies magmatic intrusive s, Guaycuru and Cerros Negros. The area has good mining possibilities due to their geologic environment. They exist also geochemical anomalies in the area that they should be taken as base for future works in the same one. In this environment studies were begun with the bodies magmatic mafic and ultramafic, due to its feasibility in Platino ides, Chromium, Nickel, Cobalt . It intent to adjust in a following stage (it Leaves II) a work methodology in an occurrence of minerals metallic. for future works,la occurrence of metallic minerals it lacks elements of economic interest in concentrations high, just as it demonstrates it the geochemical of rocks carried out, and the lack of anomalies in the geochemical of active silts and of floors. As element of interest single Gold appears in samples alluvial deposits but their source would not be the mafic rocks. Other occurrence of metallic minerals appears

  16. Trace elements in minerals from mafic and ultramafic cumulates of the central Sierra de Valle Fértil, Famatinian arc, Argentina (United States)

    Otamendi, Juan E.; Tiepolo, Massimo; Walker, Barry A.; Cristofolini, Eber A.; Tibaldi, Alina M.


    Trace element abundances in constituent minerals from mafic and ultramafic rocks of a deep arc crustal section are studied to observe their abundance and distribution. Five cumulate rocks were selected from a sequence that consists of pyroxene hornblende peridotite, olivine hornblende gabbronorite, pyroxene hornblende gabbronorite, hornblende gabbronorite, gabbro and anorthosite. Solid/liquid partition coefficients calculated with the equilibrium distribution model indicate that Cr, Ni, Co, Zn and V are highly compatible with an olivine-dominated mineral assemblage from the mafic and ultramafic cumulates. The compatibility of Ti and Sc would be dependent on the stability of clinopyroxene, amphibole and oxides in the magmatic system. With few exceptions, the other trace elements are incompatible with the minerals that form the cumulate. At most half the mass of Sr carried by a primitive arc magma could be stored in anorthite-rich plagioclase from the mafic cumulates. Magmatic amphibole fractionates Y, middle and heavy REE from other incompatible elements during crystal accumulation of mafic cumulates. In contrast, late magmatic to subsolidus amphibole has no effect on the differentiation of a primitive arc magma. In fact, the trace element variability of amphibole and clinopyroxene is easily related to different stages of magmatic evolution within the cumulate pile. The results presented here are helpful for modelling other cases of arc magma petrogenesis where the cumulate rocks with dominant mafic assemblages are not exposed.

  17. The Cerro Bitiche Andesitic Field: petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna (United States)

    Maro, Guadalupe; Caffe, Pablo J.


    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.

  18. 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)


    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.

  19. Chemical weathering on Mars - Thermodynamic stabilities of primary minerals /and their alteration products/ from mafic igneous rocks (United States)

    Gooding, J. L.


    Chemical weathering on Mars is examined theoretically from the standpoint of thermodynamic equilibrium between primary rock-forming minerals and the atmospheric gases O2, H2O, and CO2. The primary minerals considered are those common to mafic igneous rocks and include olivine, pyroxene, plagioclase, magnetite, troilite, pyrrhotite, and apatite. The importance of kinetics and reaction mechanisms in controlling possible weathering processes on Mars is discussed within the limits of currently available data, and the possible influence of liquid water on Martian weathering processes is evaluated where appropriate. For gas-solid weathering of mafic igneous rocks at the Martian surface, it is concluded that upon attainment of thermodynamic equilibrium: (1) oxides and carbonates should dominate the mineral assemblage of weathering products; (2) hematite rather than goethite should be the stable mineral form of Fe (III); (3) FeSO4 or FeSO4.H2O could be the stable weathering product of iron sulfides in the absence of liquid water; and (4) kaolinite is apparently the only clay mineral that should be thermodynamically stable over all ranges of temperature and water-vapor abundance at the Martian surface.

  20. K-Ar ages of allochthonous mafic and ultramafic complexes and their metamorphic aureoles, Western Brooks Range, Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Boak, J.L.; Turner, D.L.; Wallace, W.K.; Moore, T.E.


    New K-Ar ages from allochthonous mafic and ultramafic complexes of the western Brooks Range (Brooks Range ophiolite) show that igneous rocks yielded ages nearly identical to those of underlying metamorphic aureole rocks. Dated rocks of the Misheguk igneous sequence from Tumit Creek consist of (1) hornblende gabbro with minor greenschist and lower grade alteration, hornblende age 147.2 +/- 4.4 Ma; and (2) hornblende-bearing diorite, also slightly altered, age 155.8 +/- 4.7 Ma. Both samples come from presumed higher levels of the Misheguk sequence. Dated samples of metamorphic aureole rocks come from outcrops near Kismilot Creek and lie structurally beneath the Iyikrok Mountain peridotite body. The rocks consist of amphibolite and garnet-bearing biotite-hornblende gneiss considered to be metamorphosed Copter igneous sequence and related sedimentary rocks. Hornblende ages are 154.2 +/- 4.6 Ma and 153.2 +/- 4.6 Ma. metamorphism is clearly related to the structurally overlying perioditite, as the degree of alteration decreases downward. The authors suggest that the K-Ar ages of these rocks represent the effects of thermal metamorphism post-dating igneous crystallization, and are related to tectonic emplacement of the complex. Earlier K-Ar data on igneous rocks give similar ages and have been interpreted as reflecting tectonothermal events. The age of igneous crystallization of the mafic and ultramafic rocks of the Misheguk igneous sequence remains uncertain.

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

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


    -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.

  2. Geochronology, mantle source composition and geodynamic constraints on the origin of Neoarchean mafic dikes in the Zanhuang Complex, Central Orogenic Belt, North China Craton (United States)

    Deng, Hao; Kusky, Timothy; Polat, Ali; Wang, Junpeng; Wang, Lu; Fu, Jianmin; Wang, Zhensheng; Yuan, Ye


    Mafic granulitic and amphibolitic boudins dispersed in Archean felsic gneisses are widely distributed in the Central Orogenic Belt (COB) and the Eastern Block of the North China Craton (NCC) and are considered to constitute deformed mafic dike swarms. Previous studies have demonstrated that the mafic dikes in the Zanhuang Complex of the NCC intruded the fabrics of an Archean mélange belt and were boudinaged during younger deformation. Igneous zircons from an undeformed mafic dike yield a 207Pb/206Pb age of 2535 ± 30 Ma, which is interpreted as the crystallization age. In addition, pegmatites cutting across the mafic dikes in the field also yield an igneous zircon 207Pb/206Pb age of 2504 ± 16 Ma, providing strong evidence that the mafic dikes in the NCC intruded during the Neoarchean. Metamorphic zircons from one deformed mafic dike sample yield a metamorphic 207Pb/206Pb age of 2090 ± 83 Ma, and another four samples from deformed mafic dikes have a consistent metamorphic zircon age of ca. 1850 Ma, indicating that the mafic dikes underwent at least two generations of Paleoproterozoic metamorphism of ca. 2.1 Ga and ca. 1.85 Ga. Previously reported trace element systematics of the mafic dikes are consistent with an arc-related lithospheric mantle source region, rather than an ocean island basalt (OIB)-like source region. The new whole rock Nd isotopic composition (ɛNd(t) = + 0.71 to + 3.70) is relatively more evolved compared to that of the depleted mantle at 2.5 Ga, indicating an enriched lithospheric mantle source. Accordingly, the mafic dikes are proposed to have been formed in a subduction-related environment and their enriched mantle source was metasomatized by the melts and fluids derived from the subducted slab. Based on previous studies of the NCC and new geochronological and isotopic data in this contribution, a new comprehensive tectonic model is proposed for the evolution of the NCC between 2.7 Ga and 1.85 Ga: (1) from 2.7 to 2.5 Ga, an oceanic arc

  3. 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


    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.

  4. Estimated Flood-Inundation Mapping for the Upper Blue River, Indian Creek, and Dyke Branch in Kansas City, Missouri, 2006-08 (United States)

    Kelly, Brian P.; Huizinga, Richard J.


    In the interest of improved public safety during flooding, the U.S. Geological Survey, in cooperation with the city of Kansas City, Missouri, completed a flood-inundation study of the Blue River in Kansas City, Missouri, from the U.S. Geological Survey streamflow gage at Kenneth Road to 63rd Street, of Indian Creek from the Kansas-Missouri border to its mouth, and of Dyke Branch from the Kansas-Missouri border to its mouth, to determine the estimated extent of flood inundation at selected flood stages on the Blue River, Indian Creek, and Dyke Branch. The results of this study spatially interpolate information provided by U.S. Geological Survey gages, Kansas City Automated Local Evaluation in Real Time gages, and the National Weather Service flood-peak prediction service that comprise the Blue River flood-alert system and are a valuable tool for public officials and residents to minimize flood deaths and damage in Kansas City. To provide public access to the information presented in this report, a World Wide Web site ( was created that displays the results of two-dimensional modeling between Hickman Mills Drive and 63rd Street, estimated flood-inundation maps for 13 flood stages, the latest gage heights, and National Weather Service stage forecasts for each forecast location within the study area. The results of a previous study of flood inundation on the Blue River from 63rd Street to the mouth also are available. In addition the full text of this report, all tables and maps are available for download ( Thirteen flood-inundation maps were produced at 2-foot intervals for water-surface elevations from 763.8 to 787.8 feet referenced to the Blue River at the 63rd Street Automated Local Evaluation in Real Time stream gage operated by the city of Kansas City, Missouri. Each map is associated with gages at Kenneth Road, Blue Ridge Boulevard, Kansas City (at Bannister Road), U.S. Highway 71

  5. Formation of baotite - a Cl-rich silicate - together with fluorapatite and F-rich hydrous silicates in the Kvaløya lamproite dyke, North Norway (United States)

    Kullerud, Kåre; Zozulya, Dmitry; Ravna, Erling J. K.


    Baotite occurs as a late phase in the Kvaløya lamproite dyke and in the fenitized granite adjacent to the dyke, suggesting that baotite formed during reactions between rock and fluids derived from a volatile-rich lamproitic magma. Most of the analyzed grains of baotite from the Kvaløya lamproite show compositions close to the ideal Nb-free end-member Ba4Ti8Si4O28Cl. Compilation of all published baotite analyses suggests that the major compositional variations of baotite occur between the Nb-free end member Ba4Ti8Si4O28Cl, and a Nb-rich end member Ba4Ti2Fe²+ 2Nb4Si4O28Cl. However, a Pb-bearing baotite, showing significant concentrations of Ca, Sr, Pb and K, and approximately 3 Ba p.f.u., was also identified from the Kvaløya lamproite. Euhedral fluorapatite formed as an early phase during crystallization of the lamproite magma, while anhedral REE-rich fluorapatite overgrowths on the euhedral grains formed during reactions with the late magmatic fluid. Fluorapatite contains up to 1.2 F p.f.u., but only traces of Cl. Other F-rich, but Cl-poor minerals of the lamproite include fluoro-potassic-magnesio-arfvedsonite, fluoro-phlogopite, and yangzhumingite. The presence of baotite together with a range of high-F, but low-Cl mineral phases suggests that the minerals formed in equilibrium with a high-F, Cl-bearing hydrous fluid. The high Cl-content of baotite demonstrates that Cl is strongly partitioned into this mineral in the presence of a Cl-bearing F-rich hydrous fluid. We suggest that a combination of high aSi, aTi, aBa, and fO2, but low aCa of the fluid enabled baotite formation.

  6. 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)


    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.

  7. Chemical composition of spinel from Uralian-Alaskan-type Mafic-Ultramafic complexes and its petrogenetic significance (United States)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.


    Uralian-Alaskan-type mafic-ultramafic complexes are recognized as a distinct class of intrusions regarding lithologic assemblage, mineral chemistry and petrogenetic setting. In the present study, we discuss new data on the distribution of major elements in minerals of the spinel group in rocks from Uralian-Alaskan-type complexes in the Ural Mountains, Russia. Cr-rich spinel (Cr2O3 = 20-53 wt%) in dunite with interstitial clinopyroxene and in wehrlite cumulates indicate that it reacted with interstitial liquid resulting in the progressive substitution of Al2O2 and Cr2O3 by Fe2O3 and TiO2. A distinct change in the spinel chemistry in dunite (Cr2O3 = 47-53 wt%), towards Al2O3- and Cr2O3-poor but Fe2O3-rich compositions monitors the onset of clinopyroxene fractionation in wehrlite (Cr2O3 = 15-35 wt%, Al2O3 = 1-8 wt%, Fe2O3 = 25-55 wt%). In more fractionated mafic rocks, the calculated initial composition of exsolved spinel traces the sustained crystallization of clinopyroxene by decreasing Cr2O3 and increasing FeO, Fe2O3 and fO2. Finally, the initiation of feldspar crystallization buffers the Al2O3 content in most of the spinels in mafic rocks at very low Cr2O3 contents (<5 wt%). The fractionation path all along and the reaction with interstitial liquid are accompanied by increasing Fe2O3 contents in the spinel. This likely is caused by a significant increase in the oxygen fugacity, which suggests closed system fractionation processes. Spinel with Cr2O3 < 27 wt% is exsolved into a Fe2O3-rich and an Al2O3-rich phase forming a variety of textures. Remarkably, exsolved spinel in different lithologies from complexes 200 km apart follows one distinct solvus line defining a temperature of ca. 600°C. This indicates that the parental magmas were emplaced and eventually cooled at similar levels in the lithosphere, likely near the crust-mantle boundary. Eventually, these 600°C hot bodies were rapidly transported into colder regions of the upper crust during a regional tectonic

  8. 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


    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

  9. Geological evolution of the Coombs Allan Hills area, Ferrar large igneous province, Antarctica: Debris avalanches, mafic pyroclastic density currents, phreatocauldrons (United States)

    Ross, Pierre-Simon; White, James D. L.; McClintock, Murray


    The Jurassic Ferrar large igneous province of Antarctica comprises igneous intrusions, flood lavas, and mafic volcaniclastic deposits (now lithified). The latter rocks are particularly diverse and well-exposed in the Coombs-Allan Hills area of South Victoria Land, where they are assigned to the Mawson Formation. In this paper we use these rocks in conjunction with the pre-Ferrar sedimentary rocks (Beacon Supergroup) and the lavas themselves (Kirkpatrick Basalt) to reconstruct the geomorphological and geological evolution of the landscape. In the Early Jurassic, the surface of the region was an alluvial plain, with perhaps 1 km of mostly continental siliciclastic sediments underlying it. After the fall of silicic ash from an unknown but probably distal source, mafic magmatism of the Ferrar province began. The oldest record of this event at Allan Hills is a ≤ 180 m-thick debris-avalanche deposit (member m1 of the Mawson Formation) which contains globular domains of mafic igneous rock. These domains are inferred to represent dismembered Ferrar intrusions emplaced in the source area of the debris avalanche; shallow emplacement of Ferrar magmas caused a slope failure that mobilized the uppermost Beacon Supergroup, and the silicic ash deposits, into a pre-existing valley or basin. The period which followed ('Mawson time') was the main stage for explosive eruptions in the Ferrar province, and several cubic kilometres of both new magma and sedimentary rock were fragmented over many years. Phreatomagmatic explosions were the dominant fragmentation mechanism, with magma-water interaction taking place in both sedimentary aquifers and existing vents filled by volcaniclastic debris. At Coombs Hills, a vent complex or 'phreatocauldron' was formed by coalescence of diatreme-like structures; at Allan Hills, member m2 of the Mawson Formation consists mostly of thick, coarse-grained, poorly sorted layers inferred to represent the lithified deposits of pyroclastic density currents

  10. Silicate melt inclusions in clinopyroxene phenocrysts from mafic dikes in the eastern North China Craton: Constraints on melt evolution (United States)

    Cai, Ya-Chun; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Liu, Xuan; Liu, Yongsheng


    Silicate melt inclusions (SMIs) in magmatic minerals provide key information on the chemical and mineralogical evolution of source magmas. The widespread Cretaceous mafic dikes in the Jiaojia region of the eastern North China Craton contain abundant SMIs within clinopyroxene phenocrysts. The daughter minerals in these SMIs include amphibole, plagioclase, pyrite and ilmenite, together with CO2 + CH4 and CH4 as the major volatile phase. The total homogenization temperatures of the SMIs range between 1280 and 1300 °C. The host clinopyroxene phenocrysts in these dolerite dikes are dominantly augite with minor diopside. From LA-ICPMS analyses of the SMIs, we identify two compositional groups: (1) low-MgO (6.0-7.6 wt.%) SMIs and (2) high-MgO (11.2-13.9 wt.%) SMIs. The Low-MgO group exhibits higher concentrations of TiO2, Al2O3, Na2O, P2O5 and lower CaO and CaO/Al2O3 ratio as compared to the high-MgO SMIs. The trace element patterns of the two types of SMIs are similar to those of the host mafic dikes. However, the low-MgO SMIs and host mafic dikes are clearly more enriched in all the trace elements as compared to the high-MgO type, especially with regard to the highly incompatible elements. The estimated capture temperatures and pressures are 1351-1400 °C and 1.6-2.1 GPa for the high-MgO SMIs and 1177-1215 °C and 0.6-1.1GPa for the low-MgO type. The high-MgO and low-MgO SMIs were trapped at depths of ∼51-68 km and ∼20-35 km, respectively. Computations show that the parental melt is mafic with SiO2 content 49.6 wt% and Mg# 80.0 with relatively low total alkali contents (1.35 wt% Na2O + K2O) and high CaO (15.2 wt%). Exploratory runs with the program MELTS and pMELTS show that the low-MgO and high-MgO SMIs were derived from the same parental melt through different degrees of crystallization. Clinopyroxene and a small amount of olivine were the fractionating phases during the evolution from parental melts to high MgO melts, while the low MgO melts experienced

  11. 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

  12. Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials (United States)

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


    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.

  13. Geochemistry and zircon ages of mafic dikes in the South Qinling, central China: evidence for late Neoproterozoic continental rifting in the northern Yangtze block (United States)

    Zhu, Xiyan; Chen, Fukun; Liu, Bingxiang; Zhang, He; Zhai, Mingguo


    Neoproterozoic volcanic-sedimentary sequences of the southern Qinling belt, central China, were intruded by voluminous mafic dikes. secondary ion mass spectrometry zircon U-Pb dating indicates that these dikes were emplaced at 650.8 ± 5.2 Ma, coeval with mafic rocks occurring at the northern margin of the Yangtze block. The dikes are characterized by enrichment of large ion lithophile elements, high Ti contents (up to 3.73 wt%) and Nb/Ta ratios between 14.5 and 19.6, suggesting a mantle source of oceanic island basalt affinity. Initial 87Sr/86Sr ratios show positive correlation with SiO2 contents and negative correlation with Zr/Nb ratios, implying that these rocks were affected by crustal contamination during the magma ascend and emplacement process. The dikes have initial ɛ Nd values of +0.2 to +3.3, low 206Pb/204Pb ratios of 16.96-17.45, and moderate 87Sr/86Sr ratios of 0.7043-0.7076, likely pointing to the involvement of an enriched mantle source. The mafic dikes and coeval mafic volcanic equivalents in the South Qinling and the northern Yangtze are hypothesized to be related with the prolonged breakup of the supercontinent Rodinia, suggesting that continental rifting lasted until ca. 650 Ma.

  14. Geology, petrology, and tectonic setting of the Mafic rocks of the 1480 Ma old granite-rhyolite terrane of Missouri, USA (United States)

    Sylvester, P. J.

    Igneous and metamorphic mafic rocks form a volumetrically subordinate component of the 1480 Ma old granite rhyolite terrain of Missouri. The igneous rocks are present in the St. Francois Mountains and a drillcore from Shannon county and can be subdivided into two groups. The Silver Mines Mafic Group exhibits some calc-alkaline chemical affinities that may be the result of crustal contamination by a source with a bulk intermediate to felsic composition. The contaminant probably is not the exposed granites or rhyolites of the St. Francois Mountains. The 1500 to 1400 Ma old belt probably formed in an extensional tectonic setting. The Basin and Range province of the western United States may be the most similar modern analogue. Between 1400 to 1200 Ma ago, an incipient continental rift may have formed along the axis of the 1500 to 1400 Ma old magmatic belt. Mafic magma emplaced during the rifting event possibly included the Skrainka Mafic Group of Missouri, the Harp dikes and Seal Lake Group of Labrador, and some of the Gardar rocks of southwest Greenland.

  15. Petrogenesis of the Mesozoic Zijinguan mafic pluton from the Taihang Mountains, North China Craton: Petrological and Os-Nd-Sr isotopic constraints (United States)

    Liu, An-Kun; Chen, Bin; Suzuki, Katsuhiko; Liu, Ling


    Mantle peridotites show low Re/Os ratios and sub-chondritic 187Os/ 188Os ratios (hornblende pyroxenites, hornblende gabbros and gabbrodiorites. These rocks are enriched in LILE (e.g., Ba and Sr) and LREE, depleted in HFSE (e.g., Nb, Zr). They possess radiogenic Os isotopic compositions with 187Os/ 188Os = 0.187-0.603, and EM1-like Sr-Nd isotopic compositions (I Sr = 0.7058-0.7066, ɛNd( t) = -13.8 to -18.2). Petrography and elemental data suggest a significant fractionation and accumulation of olivine + pyroxene + hornblende in forming the mafic pluton. Clinopyroxene and plagioclase from the gabbrodiorites show complicated compositional zoning, suggesting a process of magma recharge in the late-stage of magma evolution. This is supported by their higher ɛNd( t) values (-14) than the other two rock types (-15 to -18). The parental magmas to the mafic pluton should be hydrous, which originated from an old, enriched lithospheric mantle, and were significantly contaminated by Precambrian mafic lower crust and TTG gneisses during magma evolution, as is suggested by the highly radiogenic Os- and unradiogenic Nd isotopic compositions of the mafic pluton.

  16. Petrogenesis of a Late Carboniferous mafic dike-granitoid association in the western Tianshan: Response to the geodynamics of oceanic subduction (United States)

    Tang, Gong-Jian; Chung, Sun-Lin; Wang, Qiang; Wyman, Derek A.; Dan, Wei; Chen, Hong-Yi; Zhao, Zhen-Hua


    Mafic dike-granitoid associations are common in extensional tectonic settings and provide important opportunities for understanding mantle and crust melting during the tectonic evolution of host orogenic belts. We report results of petrologic, whole rock geochemical, Sr-Nd isotopic data and in situ zircon U-Pb and Hf isotopes for a mafic dike-granitoid association from the Zhongyangchang pluton in the western Tianshan, in order to constrain their petrogenesis and tectonic significance. The intrusive rocks are mainly composed of granodiorite, monzogranite, and minor granitic dikes, with mafic dikes intruded into the pluton. Zircon LA-ICP-MS U-Pb ages indicate that the Zhongyangchang intrusive rocks were all emplaced during a short interval in the Late Carboniferous (317-310 Ma), establishing that the mafic and felsic magmas were coeval. The mafic rocks have low SiO2 and high MgO concentrations, with low 87Sr/86Sr ratios from 0.7048 to 0.7053 and positive εNd(t) and zircon εHf(t) values from + 2.9 to + 3.8 and + 12.2 to + 13.6, respectively. They are enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), which can be explained by an origin from melting of a depleted lithospheric mantle source and source fluxing by fluids derived from the down-going slab. Granitoids from the pluton have high SiO2 contents and low MgO concentrations, suggesting that they were mainly derived from crustal sources. They also have positive whole rock εNd(t) and zircon εHf(t) values ranging from + 0.2 to + 2.8 and + 6.6 to + 15.3, respectively, similar to those of the mafic dikes. They were generated by partial melting of juvenile basaltic lower crust as a result of magma underplating. The Late Carboniferous mafic dike-granitoid association was not related to a post-collisional setting, but rather formed in an arc environment related to oceanic subduction. The most likely tectonic model accounting for the genesis of these rocks involves

  17. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex (United States)

    Saikia, Ashima; Gogoi, Bibhuti; Ahmad, Mansoor; Ahmad, Talat


    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, cross-cutting 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.

  18. Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust

    Directory of Open Access Journals (Sweden)

    S. Bhattacharya


    Full Text Available Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB. They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / YbN ratios can be attributed to melting in the presence of residual garnet and hence at great depths (> 80 km. The variable enrichment in radiogenic 87Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143Nd between ε-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

  19. Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust (United States)

    Bhattacharya, S.; Chaudhary, A. K.; Saw, A. K.; Das, P.; Chatterjee, D.


    Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB). They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / Yb)N ratios can be attributed to melting in the presence of residual garnet and hence at great depths (> 80 km). The variable enrichment in radiogenic 87Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143Nd between ɛ-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga) that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths) could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

  20. 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


    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.

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


    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

  2. Accessory and rock forming minerals monitoring the evolution of zoned mafic ultramafic complexes in the Central Ural Mountains (United States)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.


    This study describes major and trace element compositions of accessory and rock forming minerals from three Uralian-Alaskan-type complexes in the Ural Mountains (Kytlym, Svetley Bor, Nizhnii Tagil) for the purpose of constraining the origin, evolution and composition of their parental melts. The mafic-ultramafic complexes in the Urals are aligned along a narrow, 900 km long belt. They consist of a central dunite body grading outward into clinopyroxenite and gabbro lithologies. Several of these dunite bodies have chromitites with platinum group element mineralization. High Fo contents in olivine (Fo 92-93) and high Cr/(Cr + Al) in spinel (0.67-0.84) suggest a MgO-rich (> 15 wt.%) and Al 2O 3-poor ultramafic parental magma. During its early stages the magma crystallized dominantly olivine, spinel and clinopyroxene forming cumulates of dunite, wehrlite and clinopyroxenite. This stage is monitored by a common decrease in the MgO content in olivine (Fo 93-86) and the Cr/(Cr + Al) value of coexisting accessory chromite (0.81-0.70). Subsequently, at subsolidus conditions, the chromite equilibrated with the surrounding silicates producing Fe-rich spinel while Al-rich spinel exsolved chromian picotite and chromian titanomagnetite. This generated the wide compositional ranges typical for spinel from Uralian-Alaskan-type complexes world wide. Laser ablation analyses (LA-ICPMS) reveal that clinopyroxene from dunites and clinopyroxenite from all three complexes have similar REE patterns with an enrichment of LREE (0.5-5.2 prim. mantle) and other highly incompatible elements (U, Th, Ba, Rb) relative to the HREE (0.25-2.0 prim. mantle). This large concentration range implies the extensive crystallization of olivine and clinopyroxene together with spinel from a continuously replenished, tapped and crystallizing magma chamber. Final crystallization of the melt in the pore spaces of the cooling cumulate pile explains the large variation in REE concentrations on the scale of a thin

  3. The significance of mafic microgranular enclaves in the petrogenesis of the Dehno Complex, Sanandaj-Sirjan belt, Iran (United States)

    Rajaieh, M.; Khalili, M.; Richards, I.


    Quartz-monzodioritic and granodioritic enclaves occur in the Upper Cretaceous-Paleocene Dehno Complex, NW of Isfahan, Iran. They are hosted by hornblende-granodiorite and granodiorite-monzogranite, respectively. The presence of xenocrystic plagioclase, biotite, quartz, magnesio-hornblende, occasionally with relics of clinopyroxene (in quartz-monzodiorites), minor K-feldspar and the lack of peraluminous minerals dominate the mineralogy of these rocks and suggest a metaluminous source. The plagioclase in the quartz-monzodioritic enclaves has higher An-content than that of the respective plagioclase of their host (hornblende-granodiorite) indicating crystallization from more mafic magma. The quartz-monzodioritic enclaves generally contain higher values of Fe 2O 3, MgO, CaO, MnO, Na 2O, transition elements (Ni, Cr, Co, V), REE and lower values of SiO 2, K 2O, P 2O 5 and Zr than their host which are in consistent with occurrence of abundant ferromagnesian minerals in these rocks. Compare to their host, the granodioritic enclaves have higher amount of Fe 2O 3, MgO, MnO, TiO 2, P 2O 5, Rb, Zr, Y, Ni, Cr, Co and lower concentration of SiO 2, K 2O and Ba. Aside from hornblende-granodiorite and granodiorite-monzogranite, the Dehno Complex comprises leucogranodiorite and tourmaline-leuco granites. Geochemically, the rocks of the Complex are metaluminous to strongly peraluminous and are enriched in LILE (e.g. Rb, K, Sr, Ba) and depleted in HFSE (e.g. Nb, Ta, P, Ti, Zr, Hf) with medium to high-K calc-alkaline nature. These geochemical features are proposed for the volcanic arc granites emplaced in an active continental margin. Whole-rock and quartz δ18O values for all rocks are high (9.7-14.4‰ and 10.1-14.9‰, respectively), suggesting the interaction of magma with crustal-derived components. The strongly peraluminous composition can be interpreted in terms of this hypothesis. All these mineralogical and geochemical features support the idea that the granitoid rocks of the

  4. Sr Nd Pb isotopic constraints on multiple mantle domains for Mesozoic mafic rocks beneath the South China Block hinterland (United States)

    Wang, Yuejun; Fan, Weiming; Cawood, Peter A.; Li, Sanzhong


    The Sr-Nd and Pb isotopic compositions of middle Jurassic to late Cretaceous mafic rocks across the Chenzhou-Linwu Fault within the South China Block are presented to constrain the characteristics and evolution of Mesozoic mantle source. These data, in combination with geochronological results, can be divided into four groups. Group 1 (~ 175-170 Ma) occurs on either side of the Chenzhou-Linwu Fault and has moderately depleted Sr-Nd and radiogenic Pb isotopes, akin to a FOZO-like source and is inferred to have originated from deep asthenospheric mantle with delaminated lower crustal signatures. Group 2 (~ 175-145 Ma) is restricted to the west of the fault and shows a significant Dupal anomaly and a binary mixing array between a component from an enriched mantle source (EM1) with low ɛNd( t) values and 206Pb/ 204Pb, and intermediate 87Sr/ 86Sr ratios and a FOZO-like component characterized by Group 1. Group 3 (~ 175-125 Ma) occurs to the east of the fault and exhibits low ɛNd( t) values and high Sr-Pb isotopic ratios, similar to EM2 component with minor DMM component. The Sr-Nd-Pb isotopic systematics for Group 4 (~ 93-80 Ma) resembles those of SE China Cenozoic basalts, suggestive of DMM-EM2 reservoir in response to the uppermost asthenospheric mantle source. These temporal and spatial variations, together with other geologic and paleomagnetic data, suggest that (1) the multiple mantle reservoirs include FOZO-, DMM-, EM1- and EM2-like components beneath the South China Block; (2) DMM-EM2 sources have dominated the mantle domains beneath SE Asia since late Cretaceous; (3) the Chenzhou-Linwu Fault corresponds with the early Mesozoic lithospheric boundary between the Yangtze and Cathaysia blocks within the South China Block. The Mesozoic mafic rocks within the South China Block developed in an active rift setting in response to the delamination of partially over-thickened lithospheric keel and upwelling of asthenosphere rather than a supra-subduction environment.

  5. Dating coeval mafic magmatism and ultrahigh temperature metamorphism in the Anápolis-Itauçu Complex, Central Brazil (United States)

    Giustina, Maria Emilia Schutesky Della; Pimentel, Márcio Martins; Ferreira Filho, Cesar Fonseca; de Hollanda, Maria Helena Bezerra Maia


    Dating granulites has always been of great interest because they represent one of the most extreme settings of an orogen. Owing to the resilience of zircon, even in such severe environments, the link between P-T conditions and geological time is possible. However, a challenge to geochronologists is to define whether the growth of new zircon is related to pre- or post-P-T peak conditions and which processes might affect the (re)crystallization. In this context, the Anápolis-Itauçu Complex, a high-grade complex in central Brazil with ultrahigh temperature (UHT) granulites, may provide valuable information within this topic. The Anápolis-Itauçu Complex (AIC) includes ortho- and paragranulites, locally presenting UHT mineral assemblages, with igneous zircon ages varying between 760 and 650 Ma and metamorphic overgrowths dated at around 650-640 Ma. Also common in the Anápolis-Itauçu Complex are layered mafic-ultramafic complexes metamorphosed under high-grade conditions. This article presents the first geological and geochronological constraints of three of these layered complexes within the AIC, the Damolândia, Taquaral and Goianira-Trindade complexes. U-Pb (LA-MC-ICPMS, SHRIMP and ID-TIMS) zircon analyses reveal a spread of concordant ages spanning within an age interval of ~ 80 Ma with an “upper” intercept age of ~ 670 Ma. Under cathodoluminescence imaging, these crystals show partially preserved primary sector zoning, as well as internal textures typical of alteration during high-grade metamorphism, such as inward-moving boundaries. Zircon grains reveal homogeneous initial 176Hf/177Hf values in distinct crystal-scale domains in all samples. Moreover, Hf isotopic ratios show correlation neither with U-Pb ages nor with Th/U ratios, suggesting that zircon grains crystallized during a single growth event. It is suggested, therefore, that the observed spread of concordant U-Pb ages may be related to a memory effect due to coupled dissolution

  6. Petrogenesis and tectonic significance of the late Triassic mafic dikes and felsic volcanic rocks in the East Kunlun Orogenic Belt, Northern Tibet Plateau (United States)

    Hu, Yan; Niu, Yaoling; Li, Jiyong; Ye, Lei; Kong, Juanjuan; Chen, Shuo; Zhang, Yu; Zhang, Guorui


    We present zircon U-Pb ages and geochemical data on the late Triassic mafic dikes (diabase) and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in the East Kunlun Orogenic Belt (EKOB). These rocks give a small age window of 228-218 Ma. The mafic dikes represent evolved alkaline basaltic melts intruding ~ 8-9 Myrs older and volumetrically more abundant A-type granite batholith. Their rare earth element (REE) and multi-element patterns are similar to those of the present-day ocean island basalts (OIBs) except for a weak continental crustal signature (i.e., enrichment of Rb and Pb and weak depletion of Nb, Ta and Ti). Their trace element characteristics together with the high 87Sr/86Sr (0.7076-0.7104), low εNd(t) (- 2.18 to - 3.46), low εHf(t) (- 2.85 to - 4.59) and variable Pb isotopic ratios are consistent with melts derived from metasomatized subcontinental lithospheric mantle with crustal contamination. The felsic volcanic rocks are characterized by high LREE/HREE (e.g., [La/Yb]N of 5.71-17.00) with a negative Eu anomaly and strong depletion in Sr and P, resembling the model upper continental crust (UCC). Given the high 87Sr/86Sr (0.7213-0.7550) and less negative εNd(t) (- 3.83 to - 5.09) and εHf(t) (- 3.06 to - 3.83) than the UCC plus the overlapping isotopes with the mafic dikes and high Nb-Ta rhyolites, the felsic volcanic rocks are best interpreted as resulting from melting-induced mixing with 45-50% crustal materials and 50-55% mantle-derived mafic melts probably parental to the mafic dikes. Such mantle-derived melts underplated and intruded the deep crust as juvenile crustal materials. Partial melting of such juvenile crust produced felsic melts parental to the felsic volcanic rocks in the EKOB. We hypothesize that the late Triassic mafic dikes and felsic volcanic rocks are associated with post-collisional extension and related orogenic collapse. Such processes are probably significant in causing asthenospheric upwelling, decompression melting

  7. 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


    Mário Sérgio Carvalho Dias; Luciana Costa Lima; Marcos Venícios de Castro; Pedro Martins Ribeiro Júnior; Enilson de Barros Silva


    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, físi...

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

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


    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 overlying ultramafic, mainly harzburgitic allochthon named the Ophiolitic Nappe, an intermediate mafic, mainly basaltic off-scraped melange, composed of kilometre-scale slices of oceanic upper crust, called the Poya Terrane, parts of which have been metamorphosed into an eclogite/blueschist facies complex, the Pouebo Terrane; and a lower, continental basement formed by the Norkolk Ridge terranes. Based upon exhaustive sampling of the mafic terranes and field surveys, our tectonic, micropaleontologic and geochemical data reveal that Poya and Pouebo terranes rocks originally formed within one single Campanian to late Paleocene oceanic basin, floored by tholeiitic basalt associated with some minor seamount-related intraplate alkali basalt. The tholeiitic basalt displays a continuous range of compositions spanning between "undepleted" and "depleted" end-members; the former being volumetrically predominant. The overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin, the South Loyalty Basin, which almost completely disappeared during Eocene convergence. The opening of this basin originally located to the east of the Norfolk Ridge was synchronous with that of Tasman Sea basin as a consequence of oceanward migration of the west-dipping Pacific subduction zone. Establishing the origin of the ultramafic Ophiolitic Nappe is beyond the scope of this paper; however, it appears to be genetically unrelated to

  9. Sequential emplacement of sheeted plutons and sill-dyke complexes: implication on crustal anatexis and lifespan of hydrothermal/geothermal systems (United States)

    Dini, A.


    Depending on initial melt composition, magma volumes, transfer rates, depth of emplacement and tectonic conditions, granite magmas can follow different crystallization paths leading to complex patterns of magmatic fluid/heat release and water-rock interaction in the host rocks at the emplacement level. In the case of multi-pulse magmatic complexes, several contact metamorphic and hydrothermal effects can overlap through time on a relatively small crustal portion. The net result of the described complex evolution is a magmatic system, where magmatic fluid exsolution, heat flow and triggering of meteoric fluid convection cells follow cyclically transient patterns with strong implication on ore forming processes and geothermal field lifespan. Detailed field mapping, coupled with petrographic-geochronologic-geochemical-isotopic data on Late Miocene-Pleistocene granite intrusions in Tuscany provided new insights on melting processes occurred in the roots as well as on paleo-hydrothermal circuits triggered at the roof of the intrusive complexes. Tuscan granite intrusions were constructed incrementally by amalgamation (sheeted plutons) and/or multilayer dispersion (sills and laccoliths) of different magma pulses, sequentially produced as the Apennine fold belt was progressively thinned, heated and intruded by mafic magmas. Partial melting was probably triggered by multiple, small-sized mafic intrusions, that allowed temporary overstepping of dehydration melting reactions into the already pre-heated crust. Dilution in time of the magmatic activity prevented melt homogenization at depth, allowing the formation at the emplacement level of multiple, isotopically distinct, intrusive sheets instead of a single, homogeneous, hybrid pluton. This could be also one of the major key factors explaining the prolonged hydrothermal activity recorded in this area by both fossil (Plio-Pleistocene ore deposits) and active (Larderello geothermal field) systems.

  10. PGE distribution in the Chromite bearing mafic-ultramafic Kondapalli Layered Complex, Krishna district, Andhra Pradesh, India

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    Meshram Tushar M.


    Full Text Available The Kondapalli Layered Complex (KLC is a dismembered mafic-ultramafic layered intrusion, mainly composed of gabbroic and anorthositic rocks with subordinate ultramafics and chromitite. Chromitite occurs as lenses, pods, bands and disseminations. Platinum group of minerals (PGMs occur as inclusions within chromite and silicates. The study indicates an inhomogeneous distribution of PGMs and distinct dominance of IPGEs over the PPGEs. The average ΣPGE content of chromite of KLC varies from 64 ppb to 576 ppb with Pt ranging from 5 to 495 ppb, Pd 5 to 191 ppb, Ir 3 to 106 ppb, Ru 3 to 376 ppb and Rh 3 to 135 ppb. The PGMs identified in the KLC indicate primary deposition of the IPGE, preceding chromite, indicating its orthomagmatic nature. Most of the PGM grains are usually below 10 μm. The identified PGMs are Laurite (RuS2, irarsite (Ir, As, S, iridosmine (Os, Ir, undetermined Os-Ir sulphide and Ru-Os-Ir-Zn alloys. Chromite also contains inclusions of pentlandite, millerite, chalcopyrite and pyrite. Study indicating that the KLC have orthomagmatic origin for PGE which are dominated by IPGE group and formed under surpa-subduction zone peridotite setting.

  11. Pyroxene zonation trends in mafic nepheline syenite and ijolite, Diamond Jo quarry, Magnet Cove igneous alkalic complex, Arkansas

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    Flohr, M.J.K.; Ross, M.


    Compositions of pyroxenes from mafic nepheline syenite and ijolite from Magnet Cove (NS and IJ) define zoning trends that reflect changing conditions in the crystallizing magmas and are used to contrast Magnet Cove with other alkalic complexes. The Na-Mg-Fe/sup 2 +/+Mn plot is used to compare NS and IJ pyroxenes with pyroxenes from nepheline syenites from S. Qoroq Centre, Greenland, and the Coldwell Complex intrusions, Ontario. Trends from the three areas are similar, but differences exists. Zoning in individual NS grains is greater than ranges for individual intrusions from S. Qoroq. Also, NS pyroxenes with compositions more magnesisan than Mg/sub 50/Nag are more Al-rich than S. Qoroq and Coldwell pyroxenes, indicating crystallization from a more undersaturated magma. These NS pyroxenes also contain 2-3 times more Ti and Fe/sup 3 +/. Despite different concentrations of Al, Ti, and Fe/sup 3 +/, the general crystallization trends shown by all elements considered are similar in NS and S. Qoroq pyroxenes. Sparse biotite and the absence of amphibole in NS indicate an H/sub 2/O-poor parent magma compared with those of the Coldwell and S. Qoroq nepheline syenites, which contain these phases. Mg-rich biotites and pyroxenes in IJ indicate that it formed from a less evolved liquid than NS.

  12. 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 (United States)

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


    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

  13. 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)

  14. Early stage evolution of the mafic-ultramafic belt at La Melada, Sierra de San Luis, Argentina: P-T constraints from metapyroxenite pseudosection modelling (United States)

    Cruciani, Gabriele; Franceschelli, Marcello; Brogioni, Norma


    At La Melada, Sierra de San Luis, Argentina, two lenses of mafic-ultramafic rocks, which underwent Famatinian metamorphism followed by shear deformation, form part of a NNE-SSW-trending belt along the eastern flank of the Sierra. Metapyroxenites from the lenses are granoblastic rocks made up of igneous and metamorphic minerals, with varying degrees of deformation and mylonitization. These rocks preserve evidence of post-magmatic re-equilibration that followed the emplacement of the mafic-ultramafic rocks. Microstructural investigation and P-T pseudosection modelling suggest that La Melada metapyroxenites experienced a temperature and pressure decrease from the M0 (800 °C talc + cummingtonite during the M2 stage and to the development of metamorphic plagioclase and dolomite in the post-M2 stage. The P-T segment reconstructed for La Melada metapyroxenites is consistent with a back-arc setting and with P-T paths previously reported in the literature.

  15. 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


    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.

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


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


    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) towh...

  17. Mixed pyroxenite-peridotite sources for mafic and ultramafic dikes from the Antarctic segment of the Karoo continental flood basalt province


    Heinonen, Jussi S.; Luttinen, Arto V.; Riley, Teal R.; Radoslaw M. Michallik


    Primitive rocks that are related to continental flood basalts are rare, but often reveal crucial information on the ultimate sources of these huge outpourings of mantle-derived magma. Here we present mineral chemical data for mafic and ultramafic dikes from the Antarctic extension of the Jurassic (~180 Ma) Karoo continental flood basalt province that was emplaced during the initial stages of the breakup of the Gondwana supercontinent. We concentrate on two previously recognized high-Ti dike r...

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

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


    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

  19. The mafic-ultramafic complex of Aniyapuram, Cauvery Suture Zone, southern India: Petrological and geochemical constraints for Neoarchean suprasubduction zone tectonics (United States)

    Yellappa, T.; Venkatasivappa, V.; Koizumi, T.; Chetty, T. R. K.; Santosh, M.; Tsunogae, T.


    Several Precambrian mafic-ultramafic complexes occur along the Cauvery Suture Zone (CSZ) in Southern Granulite Terrain, India. Their origin, magmatic evolution and relationship with the associated high-grade rocks have not been resolved. The Aniyapuram Mafic-Ultramafic Complex (AMUC), the focus of the present study in southern part of the CSZ, is dominantly composed of peridotites, pyroxenites, gabbros, metagabbros/mafic granulites, hornblendites, amphibolites, plagiogranites, felsic granulites and ferruginous cherts. The rock types in the AMUC are structurally emplaced within hornblende gneiss (TTG) basement rocks and are highly deformed. The geochemical signature of the amphibolites indicates tholeiitic affinity for the protolith with magma generation in island arc-setting. N-MORB normalized pattern of the amphibolites show depletion in HFS-elements (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Rb, Ba, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. Our new results when correlated with the available age data suggest that the lithological association of AMUC represent the remnants of the Neoarchean oceanic lithosphere.

  20. Caribbean affinities of mafic crust from northern Colombia: preliminary geochemical results from basaltic rocks of the Sinu-San Jacinto belt (United States)

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


    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.

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

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


    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.

  2. Cretaceous crust-mantle interaction and tectonic evolution of Cathaysia Block in South China: Evidence from pulsed mafic rocks and related magmatism (United States)

    Li, Bin; Jiang, Shao-Yong; Zhang, Qian; Zhao, Hai-Xiang; Zhao, Kui-Dong


    Cretaceous tectono-magmatic evolution of the Cathaysia Block in South China is important but their mechanism and geodynamics remain highly disputed. In this study we carried out a detailed geochemical study on the recently found Kuokeng mafic dikes in the western Fujian Province (the Interior Cathaysia Block) to reveal the petrogenesis and geodynamics of the Cretaceous magmatism. Kuokeng mafic dikes were emplaced in three principal episodes: ~ 129 Ma (monzogabbro), ~ 107 Ma (monzodiorite), and ~ 97 Ma (gabbro). Geochemical characteristics indicate that the monzogabbros were derived from the unmodified mantle source, while gabbros were likely derived from metasomatized mantle by subducted slab (fluids and sediments). Sr-Nd isotope compositions indicate that the parental magmas of the monzodiorites were generated by mixing of enriched, mantle-derived, mafic magmas and felsic melts produced by partial melting of crustal materials. Until the Early Cretaceous (~ 123 Ma), the dominant ancient Interior Cathaysia lithospheric mantle exhibited insignificant subduction signature, indicating the melting of asthenospheric mantle and the consequent back-arc extension, producing large-scale partial melting of the crustal materials under the forward subduction regime of the paleo-Pacific plate. The monzodiorites and gabbros appear to be associated with northwestward subduction of Pacific plate under an enhanced lithospheric extensional setting, accompanying with mantle modification, which triggered shallower subduction-related metasomatically enriched lithospheric mantle to melt partially. After ca. 110 Ma, the coastal magmatic belts formed due to a retreat and rollback of the subducting Pacific Plate underneath SE China in the continental margin arc system.

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

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


    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

  4. Regularities of spatial association of major endogenous uranium deposits and kimberlitic dykes in the uranium ore regions of the Ukrainian Shield (United States)

    Kalashnyk, Anna


    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

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

    Kocak, Kerim; Zedef, Veysel; Kansun, Gursel


    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.

  6. Petrogenesis and metallogenesis of the Xinjie layered mafic-ultramafic intrusion, China: Modeling of recharge, assimilation and fractional crystallization (United States)

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


    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.

  7. 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 (United States)

    Chen, Ming; Sun, Min


    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

  8. 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 (United States)

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


    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.

  9. 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)


    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.

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

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


    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

  11. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil (United States)

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


    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

  12. Metamorphic modifications of the Muremera mafic-ultramafic intrusions, eastern Burundi, and their effect on chromite compositions (United States)

    Evans, David M.


    The Muremera mafic-ultramafic intrusions were emplaced into metasedimentary rocks of the Karagwe-Ankole Belt in eastern Burundi, as part of the Mesoproterozoic Kibaran tectonomagmatic event. Igneous minerals of the Muremera intrusions have been partly altered to hydrous and carbonated metamorphic assemblages, although in most cases, the original igneous textures are well-preserved. Rounded, subhedral cumulus olivine has been partially and pseudomorphically replaced by lizardite-magnetite mesh-rim and lizardite-brucite mesh-centre assemblages, while anhedral interstitial plagioclase has been replaced by chlorite-tremolite. A later and localized event results in prograde alteration to antigorite-magnetite-chlorite-talc-carbonate and talc-carbonate-chlorite assemblages. The rocks are inferred to have undergone at least three separate metamorphic/alteration events resulting in: AS1 - an early alteration assemblage (mesh-rim lizardite-magnetite) characterized by very low fluid/rock ratios and widespread distribution; AS2 - a later, widespread low-temperature retrogressive (mesh-centre lizardite-brucite) assemblage associated with abundant close-spaced parallel veins; AS3 - later, prograde (antigorite-magnetite) and AT4 (talc-chlorite-carbonate) assemblages associated with more localized shearing and higher fluid/rock ratios. The AS1 assemblage most likely represents deuteric alteration that occurred soon after intrusion and cooling. The AS2 assemblage may relate to a continuation of this cooling, or may be correlated with the regional upright D2 folding event, while the AS3 and AT4 alteration assemblages are most likely correlated with the N-S oriented D3 faulting episode linked to the distal East African Orogeny. Euhedral to subhedral chromite grains are essentially unaltered where enclosed in primary unaltered olivine, pyroxene or plagioclase, as well as in AS1 lizardite-magnetite and AS2 lizardite-brucite altered olivine or pyroxene. In samples which show alteration

  13. 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.


    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.

  14. 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


    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

  15. Magmatic origin of low-T mafic blueschist and greenstone blocks from the Franciscan mélange, San Simeon, California (United States)

    Ukar, Estibalitz; Cloos, Mark


    The Franciscan mélange exposure near San Simeon contains abundant greenstone and minor blueschist blocks that were tectonically boudinaged while encased in the shale-matrix. Tectonic deformation of the blueschists is evident from variable amounts of cataclastic flow along their margins and in pinched tails. Major, trace, and rare earth elemental analyses indicate that blueschist and greenstone blocks in this area of the mélange were derived from sources with MORB-like composition along with some having trace element and REE patterns similar to OIB compositions. Most blocks are low LREE basalts that probably formed in an open ocean ridge setting, but some blocks have high LREE contents similar to off-axis seamounts. Linear trends of incompatible elements for both blueschist and greenstone blocks indicate that both lithologies were probably derived from a similar, variably fractionated, tholeiitic magma. Blueschist blocks with sodic amphibole + lawsonite ± epidote were pervasively recrystallized at 300-350 °C and foliated during ductile deformation that included folding. Their protolith can only be identified as mafic. A few blocks contain very small amounts of metasedimentary materials indicating some were probably seafloor basalts, but some may have been diabase or even gabbro. Where interlayered sediment was present, the mafic protolith was enriched in K, Rb, and Na. Greenstones, on the other hand, contain abundant pseudomorphic evidence of magmatic textures. Alteration to albite, chlorite and pumpellyite at temperatures of 100-200 °C is intense, especially in cataclastic margins and pinched tails. Some of the basaltic greenstones have attached radiolarian chert, and a few have relict diabasic textures. The mafic blueschists and greenstones in the mélange near San Simeon are probably fragments from the uppermost part of the Farallon plate. The blueschists may be mostly mafic slabs uprooted from the subducting crust, underplated to the base of the North

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


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


    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...

  17. Study of an aplite dyke from the Beira uraniferous province in Fornos de Algodres area (Central Portugal): Trace elements distribution and evaluation of natural radionuclides

    International Nuclear Information System (INIS)

    Highlights: • Distribution of natural radionuclides in an U-rich aplite from Central Portugal. • INAA, XRD and gamma spectrometry were applied to various types of samples. • Higher U values for clay/sand fractions, and core of spheroidal weathered aplite. • Large difference between pre-Rn and post-Rn values suggests high loss of radon. • Weathering of aplite is a potential source of radiological hazards. - Abstract: A uranium-rich aplite dyke with spheroidal alteration sited in the Beira uraniferous province, in Fornos de Algodres area (Northern Central Portugal) was studied, focusing on trace element distributions, especially U, in the aplite. A vertical profile, different size fractions, and various concentrically weathered layers of rock, were examined. The main goal of the work is to better understand the geochemical behavior and distribution of natural radionuclides in fine-grained granitic rocks, and changes that occur during weathering. The rock samples obtained from this site were examined using chemical and mineralogical methods: instrumental neutron activation analysis (INAA) and the X-ray diffraction (XRD). Field gamma spectrometry (FGS) and high resolution gamma spectrometry (HRGS) in the laboratory were also performed in order to determine concentrations of the natural radionuclides (K, Th and U) responsible for terrestrial gamma radiation, and for comparison of results with INAA measurements, enabling some information concerning radon losses. The U concentration in the studied samples vary between 4.5 and 83 ppm (always higher than upper continental crust value), with the higher values detected in the clay and sand fractions of weathered aplite (residual clay) and in the rounded boulders of aplite with spheroidal weathering, especially in the core. Strong variations in natural radionuclide contents, especially observed between residual clay and soil, relate to differences in source material. The large difference between pre-Rn and post

  18. 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) (United States)

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


    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

  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 (United States)

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


    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. Geochronology and Hf-Fe isotopic geochemistry of the Phanerozoic mafic-ultramafic intrusions in the Damiao area, Northern North China craton: implications for lithospheric destruction

    International Nuclear Information System (INIS)

    Timing and source of several Fe-mineralized mafic-ultramafic intrusions in the Damiao area are investigated here by coupling new geochronological and Hf-Fe isotopic data with previous results. Although regarded as a Late Paleoproterozoic assemblage previously, two ∼140 Ma intrusions are recognized by zircon U-Pb dating, indicating emplacement of these intrusions from Middle Devonian to Early Cretaceous times. Both Hf and Fe isotopic features lead to the conclusion that distinct mantle components contributed to their magma generation. As the first magmatic phase, the 395 Ma intrusions were mainly derived from the slightly-enriched SCLM that was prevalent during the Paleozoic. However, asthenospheric material was strongly involved in the formation of the ∼ 215 Ma Gaositai intrusion. Therefore, the initiation of lithospheric destruction in the northern NCC is inferred to have occurred in Late Triassic time, triggered by post-orogenic extension following the ∼ 250 Ma collision between the Siberian Craton and the NCC. The ∼140 Ma intrusions originated from a significantly-enriched mantle component probably resided in the predominant slightly-enriched SCLM. This mantle source would have melted in the Late Mesozoic, when the thin lithosphere enabled enhanced heat transfer from the asthenosphere. In summary, these distinct mantle sources of mafic-ultramafic magmatism provide a record of mantle heterogeneity and the gradual upward migration of the lithosphere-asthenosphere boundary during lithospheric destruction. (author)

  1. Petrology of the Motaghairat mafic-ultramafic complex, Eastern Desert, Egypt: A high-Mg post-collisional extension-related layered intrusion (United States)

    Abdel Halim, Ali H.; Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Shibata, Tomoyuki; El Mahallawi, Mahmoud M.; Yoshikawa, Masako; Arai, Shoji


    The geodynamic settings of the Precambrian mafic-ultramafic complexes in the Eastern Desert of Egypt have important bearing on understanding the geotectonic evolution of the Arabian Nubian Shield. We present a detailed petrological study on a layered mafic-ultramafic intrusion that is located at the contact between the Precambrian continental crust and the Miocene Red Sea oceanic crust. The Motaghairat layered intrusion consists of basal lherzolite, orthopyroxenite, troctolite, olivine gabbro and anorthosite on the top. Variations in modal mineralogy and mineral chemistry along with the chemical composition of these units suggest their derivation from a common high-Mg tholeiitic parent melt through fractional crystallization processes. The parental magma was derived from a metasomatised mantle source. The primitive mantle-normalized patterns of the calculated melts exhibit enrichment in U relative to Th and Ba relative LREE which indicate that the enriched lithospheric mantle source was metasomatised by fluids derived from a subducted oceanic crust rather than by a sediment melt. Geological and petrological evidences suggest that the layered Motaghairat intrusion was emplaced during post-orogenic extension following subduction break-off and lithospheric delamination after the collision between the amalgamated island arc terranes and the Saharan Metacraton. The heat source required to melt the metasomatised lithospheric mantle was derived from the upwelling of hot asthenosphere after the subduction-break-off.

  2. A major 2.1 Ga event of mafic magmatism in west Africa: An Early stage of crustal accretion (United States)

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


    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

  3. 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)


    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

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

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


    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

  5. Preliminary geochronological data of the Morro Agudo de Goias Dike Swarm

    International Nuclear Information System (INIS)

    The Morro Agudo Dyke Swarm consists of mafic and ultramafic dykes and ultramafic dykes and stocks that intrude Archean granite-gneiss terranes of the Goias Massif. The dyke swarm was subdivided into five rock groups: Group I-basaltic andesite in dykes; Group II-metadiabase, diabase, metagabbro and amphibolite in dykes: Group III-metadiabase associated with-meta ultramafic rocks in the same dyke; Group IV-meta ultramafic rocks in dykes; Group V-meta ultramafic rocks in stocks. Four basaltic andesite dyke samples were dated using the K-Ar whole-rock method, yielding 2,412 ± 30 Ma, 2,403 ± 48 Ma, 2,254 ± Ma and 2,006 ±45 Ma ages. A Sm-Nd isochronic diagram for Group III mafic-ultramafic dyke yielded a 2,331 ± 101 Ma age with 0.50976 initial ratio. It is believed that this age may be extensive to the other mafic-ultramafic dykes of the dyke swarm. (author)

  6. 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 (United States)

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


    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.

  7. Late Holocene hydrous mafic magmatism at the Paint Pot Crater and Callahan flows, Medicine Lake Volcano, N. California and the influence of H2O in the generation of silicic magmas (United States)

    Kinzler, R.J.; Donnelly-Nolan, J. M.; Grove, T.L.


    This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years B.P.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding episodes of mafic magmatism (from 10,600 to ~3000 14C years B.P.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence of H2O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in

  8. Geochemical and Sr-Nd isotopic constraints on the mantle source of Neoproterozoic mafic dikes of the rifted eastern Laurentian margin, north-central Appalachians, USA (United States)

    Volkert, Richard A.; Feigenson, Mark D.; Mana, Sara; Bolge, Louise


    Abundant and widely distributed unmetamorphosed mafic dikes intrude Mesoproterozoic rocks of the New Jersey Highlands. The age of the dikes is imprecisely known but interpreted to fall between 615 and 576 Ma, which is consistent with the range of ages of mafic dikes from Labrador and Nova Scotia south to Pennsylvania that were emplaced along the rifted eastern Laurentian margin. New Jersey Highlands dikes are a few cm to 18 m wide and have lengths of as much as several km. They have sharp, largely discordant contacts against enclosing Mesoproterozoic rocks and aphanitic chilled margins that grade into coarser grained interiors. Columnar joints are present locally and suggest emplacement at a shallow crustal level. Geochemical compositions of the dikes range from alkalic to less common tholeiitic basalt having generally high TiO2, P2O5, Zr, Nb, Y, and La/Yb, and low MgO, Cr, and Ni. TiO2 contents define high-Ti and low-Ti dikes that differ in high field strength elements (HFSE) and light rare earth elements (LREE) but overlap in abundances of most other elements. Dike magma evolved in an ascending mantle plume of OIB-like asthenosphere from enriched higher TiO2 compositions to more depleted lower TiO2 compositions. Subtle differences in the dike compositions are due to variations in the amount of partial melting within the plume and the depth of melt segregation. Sr-Nd isotope values of both dike compositions overlap and are characterized by εNd (T) of + 1.5 to + 3.8 and initial 87Sr/86Sr ranging from 0.7032 to 0.7077. Higher Sr isotope ratios are interpreted as resulting from local interaction of the dike magma with heterogeneous, high 87Sr/86Sr lithospheric mantle having EMI or EMII-like geochemical characteristics. Dikes form tabular structures that have long segments striking an average of N44°E and short segments striking about east-west. Their regional geometries form right-stepping, rhomb-shaped patterns due to emplacement into rift-related dilational

  9. Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys (United States)

    Sayit, Kaan; Marroni, Michele; Göncüoglu, M. Cemal; Pandolfi, Luca; Ellero, Alessandro; Ottria, Giuseppe; Frassi, Chiara


    A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Dağ Unit, the Saka Unit, the Daday Unit and the Arkot Dağ Mèlange) have been studied in detail along two selected transects. The Domuz Dağ Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Dağ Mèlange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis

  10. Plutonic ultramafic-mafic complexes of the Vel'may terrane, eastern Chukotka (Russia): first petrological results and preliminary geodynamic interpretations (United States)

    Ledneva, G. V.; Bazylev, B. A.; Kuzmin, D.; Ishiwatari, A.; Kononkova, N. N.; Sokolov, S. D.


    The Vel'may terrane (eastern Chukotka) is commonly considered as a continuity of the South Anyui Suture (SAS) zone (western Chukotka) and the Angaucham terrane (Brooks Range, Alaska), which marks the southern boundary of the Arctic Alaska - Chukotka displaced continental microplate (AACM). The correlation of terranes bounding the microplate is based on findings of similar upper Triassic (Norian) faunas (Tynankergav, Bychkov, 1987; Sokolov et al., 2009) and the ubiquitous occurrence of ultramafic-mafic plutonic complexes attributed to be ophiolite fragments. However, plutonic complexes of the Vel'may terrane haven't been petrologically investigated till now. In the study area they spatially associate with upper Jurassic-lower Cretaceous deposits of the Cross Bay zone and upper Triassic sequences of the Kolyuchinskaya Bay zone. In the Cross Bay zone ultramafic and mafic rocks compose small tectonic slices and are represented by non-spreading subduction-related restite spinel harzburgites and shallow-level plagioclase peridotite and gabbro cumulates (crystallization pressure is estimated at 3.5±1 and 1.5±1 kb ((Schmidt, 1992), respectively) closely resembling fragments of an ophiolitic assemblage. In the Kolyuchinskaya Bay zone tectonic slices of ultramafic and mafic rocks are dominated by clinopyroxene-bearing dunites, hornblende wehrlites/olivine clinopyroxenites and hornblende gabbros. This rocks are high-pressure cumulates (crystallization pressure is estimated at 8±1 kb (Schmidt, 1992)) of lower crustal magma-chambers originated in a mature island-arc or an Andean-type active continental margins. Remnants of subduction-related ophiolite and magma-chambers are typical of sutures indicative of an arc-continent collision; and they occur widely in the SAS zone (Lychagin, 1985; Ganelin, Sylantyev, 2008) and the Angayucham terrane (Loney, Himmelberg, 1989). Thus, the Vel'may terrane can be considered as a possible marker of the AACM boundary. This work was supported

  11. Strain localization and fluid infiltration during subduction initiation: the record from sheared mafic amphibolites at the base of the New Caledonian ophiolite (United States)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Vitale-Brovarone, Alberto; Monié, Patrick; Chauvet, Alain; Whitechurch, Hubert


    Most of our knowledge on subduction inception and obduction processes comes from metamorphic soles structurally associated with peridotite tectonites at the base of many ophiolites, and from early-obduction, rarely deformed, magmatic dikes emplaced at different level of the mantle sequence. These dikes record a partial refertilization of obducted ophiolites through subduction-derived fluids. However, these dikes are rarely deformed and/or metamorphosed. Here, we study the base of the New Caledonian ophiolite, using a combination of structural field studies and petrological-geochemical-geochronological analysis, with the aim of linking deformation and metasomatism through fluid infiltration and recrystallization. We report the existence of strongly sheared mafic amphibolites within the base of the New Caledonian obducted ophiolite, ~ 50-100 m above the basal thrust contact and peridotites), highly boudinaged and amphibolitized at high temperatures (750-800 °C), providing evidence that strain localized at the base of the ophiolite. Mafic protoliths of these amphibolites consisted of plagioclase and orthopyroxene (± olivine and calcic amphibole in places). We show that deformation is intimately associated to at least three major stages of fluid infiltration on mafic intrusions. The first stage of deformation and metasomatism coincides with amphibolitization and controlled the later channelization of fluids. The formation of calcic amphiboles records the percolation of Ca and Al-rich aqueous fluids. Amphibole-plagioclase geothermobarometry indicates high temperature and low pressure conditions (i.e. 750-800 °C; 3-5 kbar). Thermochronological data from hornblende (40Ar/39Ar) suggest that this deformation episode occurred at ~ 55 Ma, coinciding with E-dipping subduction initiation and incipient obduction. The main metasomatic stage is evidenced by a phlogopite-rich matrix wrapping peridotite and amphibolite boudins. The formation of phlogopite records the percolation

  12. 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 (United States)

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


    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

  13. Geology and age of mafic magmatism on Jeannette Island (De Long archipelago)—Implications for paleotectonic reconstructions for the Arctic (United States)

    Matushkin, N. Yu.; Metelkin, D. V.; Vernikovsky, V. A.; Travin, A. V.; Zhdanova, A. I.


    The paper presents the first data on the geology of a series of mafic dikes emplaced in the volcanogenic sedimentary sequence composing the structure of Jeannette Island. We show that the island hosts two generations of dikes consisting of fine-grained dolerites. Both magmatic stages were followed by fold deformations. The youngest and weakly deformed dikes are none the less chloritized and serpentinized. However, we were able to obtain the first ever precise geochronological 40Ar/39Ar data for them. According to this analysis, the emplacement age of the intrusive complex of Jeannette Island is close to the Ediacaran (553.6 ± 10.3 Ma). The ages of several superimposed tectonothermal events were determined: Middle Ordovician (463.3 ± 11.7 Ma), Late Silurian (425.3 ± 8.7 Ma), Late Devonian (360.7 ± 8.3 Ma) and Early Carboniferous (341.3 ± 6.8 Ma).

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

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


    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.

  15. Constraints on the evolutionary history of aluminous mafic rocks in the Ronda peridotite massif (Spain) from trace-element compositions of clinopyroxene and garnet

    International Nuclear Information System (INIS)

    Multiple trace-element compositions of clinopyroxene and garnet in aluminous mafic layers (±corundum and/or sapphirine) alternative with peridotites from the Ronda massif, Spain, were determined by an ArF 193 nm excimer laser system coupled with a quadrupole ICP-MS. The studied aluminous mafic rock is divided into several sublayers based on the modal mineral variations. Trace-element compositions of minerals vary between sublayers. Primitive mantle-normalized trace-element distribution patterns have more significant positive Eu anomaly for both garnet and clinopyroxene in the corundum-bearing sublayers than for those in the other sublayers whereas corundum-bearing sublayers contain more abundant secondary plagioclase than corundum-free sublayers. These geochemical signatures of the corundum-bearing sublayers intercalated with corundum-free sublayers were acquired as plagioclase-rich portions of gabbroic layered sequence originated at the lower crustal to the uppermost mantle sections rather than selective accumulation of metamorphic plagioclase due to deformation during the late stage of exhumation of the massif. Partition coefficients of trace elements between clinopyroxene and garnet show systematic variations with respect to major element composition, indicating local attainment of chemical equilibrium. The trace element compositions of clinopyroxene and garnet were equilibrated with secondary metamorphic plagioclase, i.e., a granulite-facies conditions, because plagioclase is required for the geochemical balance in Sr and Eu contents of the whole-rock trace element compositions. Positive Eu anomaly of clinopyroxene (±garnet) is also found in mantle-derived aluminous ecologitic xenoliths and ecologitic mineral inclusions in diamond captured in kimberlites, and is thus a useful indicator to explore recycled crustal components in the mantle. (author)

  16. Zircon U-Pb dating, geochemistry and Sr-Nd-Pb-Hf isotopes of the Wajilitag alkali mafic dikes, and associated diorite and syenitic rocks: Implications for magmatic evolution of the Tarim large igneous province (United States)

    Zou, Si-Yuan; Li, Zi-Long; Song, Biao; Ernst, Richard E.; Li, Yin-Qi; Ren, Zhong-Yuan; Yang, Shu-Feng; Chen, Han-Lin; Xu, Yi-Gang; Song, Xie-Yan


    The Early Permian Tarim large igneous province (Tarim LIP) consists mainly of basaltic lavas, mafic-ultramafic intrusions including dikes and, syenite bodies in the Tarim Basin, NW China. A major unit of the Tarim LIP, the Wajilitag intrusive complex, consists of olivine pyroxenite, clinopyroxenite and gabbro units (from bottom to top), diorite and syenite rocks occurred in the upper part of the complex and alkali mafic dikes intrude the clinopyroxenite phase. Here we report the zircon U-Pb age and Hf isotopes, geochemical characteristics and Sr-Nd-Pb isotopic data of the alkali mafic dikes, and diorite, aegirine-nepheline syenite and syenite porphyry units in the Wajilitag intrusive complex. Zircons from the diorite and alkali mafic rocks yield concordant crystallization ages of 275.2 ± 1.2 Ma and 281.4 ± 1.7 Ma, respectively. The diorite and syenitic rocks in Wajilitag area have a narrow range of SiO2 contents (51.9-57.3 wt.%), and are enriched in total alkalis (Na2O + K2O = 8.3-14.3 wt.%), among which the aegirine-nepheline syenite and syenite porphyry have the geochemical affinity of A-type granites. The alkali mafic rocks and syenitic rocks have high Al2O3 (19.4-21.1 wt.%), Zr, Hf, Ba contents, total rare earth element abundances and LREE/HREE ratios and low Mg# value, K, P and Ti contents. Diorites have lower Al2O3 contents, total REE abundances and LREE/HREE ratios and higher Mg# values than the alkali mafic rocks and syenitic rocks. The diorites and syenitic rocks have low initial 87Sr/86Sr ratios (0.7034-0.7046), and high εNd(t) values (0.1-4.1) and zircon εHf(t) values (- 0.9-4.4). All the diorites and syenitic rocks show the 206Pb/204Pb ratios ranging of 18.0-19.5, 207Pb/204Pb of 15.4-15.6 and 208Pb/204Pb of 38.0-39.9. Sr-Nd isotopic ratios indicate a FOZO-like mantle source for the diorite and syenitic rocks, similar to that of the mafic-ultramafic rocks in the Wajilitag complex. In contrast, zircon Hf isotopes of basalt and syenite elsewhere in the

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

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


    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

  18. Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination (United States)

    Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii


    The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the

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

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


    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

  20. 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 (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.


    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

  1. 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 (United States)

    Stern, C. R.


    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

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

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


    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.

  3. Plume-proximal mid-ocean ridge origin of Zhongba mafic rocks in the western Yarlung Zangbo Suture Zone, Southern Tibet (United States)

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


    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.

  4. 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


    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.

  5. 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)


    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.

  6. 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 (United States)

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


    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.

  7. 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

  8. Geology, geochemistry and geodynamic implications of the mafic-ultramafic rocks from the northern part of the Antalya Complex, SW Turkey (United States)

    Elitok, Ömer


    The Antalya Complex in the Isparta Angle area (SW Turkey) includes allochthonous Mesozoic rock assemblages occuring as nappe stacks or disrupted tectonic units formed in response to different mélange forming processes. The allochthonous rock assemblages in the northern part of the Antalya Complex are mainly characterized by slope basin deposits associated with the late Triassic volcanic rocks varying in composition from alkali basalt to fractionated trachyandesite, the late Jurassic-early Cretaceous tholeiitic volcanic rocks in composition from basaltic to rhyolitic, and MORB-type volcanic rocks most likely in Cretaceous age that spatially associated with olistostromal and subophiolitic tectonic mélange. Whole rock chemistry of the Eğridir Kızıl Dağ peridotites and the isolated diabasic dykes intruding the peridotites, the mineral chemistry of the harzburgitic spinels points to depleted residual mantle peridotite character and two tectonic settings: supra-subduction zone and ocean ridge environments, a characteristic feature of forearc setting. Extensive geological field investigations and previous studies from the Antalya Complex and the Mamonia Complex (SW Cyprus) have led to a conclusion that the late Triassic alkaline volcanic rocks are associated with continental rift-related deposits in the apex of the Isparta Angle, interbedded with thin pelagic limestone layers to the south, and overlain by the late Triassic reefal limestones and pelagic deposits in the Mamonia Complex, suggesting progressive deepening and widening in ocean basin towards the south during the late Triassic time. Moreover, the Triassic lavas of the southern part of the Isparta Angle and the Mamonia Complex range from WPB-type to transitional and MORB-type, suggesting rapid rifting and drifting in the southern part of the Antalya ocean giving rise to evolution of northward narrowing wedge-shaped ocean basin. Constrains on the geological and geochemical characteristics of the Mesozoic

  9. Sm/Nd isotopic data for the Santana do Ipanema high-K mega dykes as evidence for Brasiliano decompression melting at the Pernambuco-Alagoas (PE-AL) Massif, Borborema province

    International Nuclear Information System (INIS)

    This work deals with the Sm-Nd signatures of some mega dykes located close to the Northern limit of the batholith in the Santana do Ipanema plutonic complex (SIC), which comprises 6 intrusive suites. Their composition ranges from syenites to quartz syenites. They are mesocratic to leucocratic, usually equigranular but sometimes porphyritic. Their accessory mineralogy is comprised of sphene, opaque, amphibole, ± pyroxene, apatite, zircon, biotite, allanite and epidote. The main minerals are microcline, plagioclase and quartz. The SIC rocks are metaluminous and intermediate to acid, with Si O2 ranging from 55,6 wt% to 66.4 wt% and Ba ranging from 3889 ppm to 10253 pp,. The K2 O/Na2 O ratio ranges widely as well, from 0,59 to 2.07, making these rocks a quite heterogeneous suite. The diagram shows two patterns, one with troughs at Nb, Zr and Ti, while the other one shows troughs at Nb, Hf and Eu. The Zr data available show a wide range, from 133 ppm to 314 ppm, suggesting this suite was the result of different degrees of partial melting of a same enriched LIL protolith. Five isotope Sm-Nd data has been obtained for these rocks, yielding epsilon Nd (0.60 Ga) values which ranges from -9.3 to -3.6, and Tdm which ranges from 2.34 Ga to 1.26 Ga. The isotope data agree with the heterogeneous character showed by the trace elements

  10. 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 (United States)

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


    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

  11. 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 (United States)

    Kirchenbaur, M.; Münker, C.


    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

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

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


    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.

  13. 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 (United States)

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


    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 ( 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.

  14. Significance of mafic hornblende pegmatites intruding ultramafic rocks of the accreted oceanic plateau in Colombia: Ar-Ar and radiogenic isotope constraints (United States)

    Kerr, A. C.; Tarney, J.; Kempton, P. D.; Pringle, M.


    The accreted remnants of the Cretaceous basaltic oceanic plateau in Colombia are tectonically interleaved with flysch metasediment. At Bolivar, in the Western Cordillera, ultramafic/gabbro parts of the plateau are exposed are intruded by spectacular coarse hornblende pegmatites. Some pegmatites are deformed along with the enclosing mafic/ultramafic rocks but others are cross-cutting with magnesio-hornblendes growing out from the margins of the veins. The leucocratic veins vary from hypersthene leucogabbro, through dominant hornblende anorthosite to (rarer) tonalites with biotite and quartz. Clearly, the hydrous pegmatites were generated while the host rocks were still undergoing deformation, but continued to be emplaced when deformation of the hot mantle rock ceased. There are two potential explanations: that water from the intercalated metasediments migrated into the imbricated hot mantle sequence during tectonic accretion to the South American margin; or that these hydrous late-stage processes are part of the initial plume and plateau formation. New step-heating Ar-Ar plateau-ages indicate that the pegmatites are 90.5\\pm0.9 Ma, and so are indistinguishable in age from the basalts and high-MgO rocks of the Colombian-Caribbean oceanic plateau. Geochemically, the pegmatites are low in incompatible trace elements and have generally chondritic trace element ratios. They possess initial epsilon Hf and epsilon Nd values, which range from +12 to +15 and from +6.5 to +7.5 respectively. These values overlap the range of basaltic and picritic plateau rocks of the Caribbean-Colombian plateau. Critically, the pegmatites possess little trace element evidence of a subduction-related signature, and so it is difficult to argue for an arc-related setting, or for sedimentary involvement in their petrogenesis. Alternatively, it would seem that these hydrous pegmatites are part of the oceanic plateau itself, and are unrelated to later obduction. This bears upon whether mantle plumes

  15. Trace element partitioning in rock forming minerals of co-genetic, subduction-related alkaline and tholeiitic mafic rocks in the Ural Mountains, Russia (United States)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.


    The partitioning of trace elements between rock forming minerals in igneous rocks is largely controlled by physical and chemical parameters e.g. temperature, pressure and chemical composition of the minerals and the coexisting melt. In the present study partition coefficients for REE between hornblende, orthopyroxene, feldspars, apatite and clinopyroxene in a suite of co-genetic alkaline and tholeiitic mafic rocks from the Ural Mountains (Russia) were calculated. The results give insights to the influence of the chemical composition of the parental melt on the partitioning behaviour of the REE. Nepheline-bearing, alkaline melanogabbros (tilaites) are assumed to represent the most fractionated products of the melt that formed the ultramafic cumulates in zoned mafic-ultramafic complexes in the Ural Mountains. Co-genetic with the latter is a suite of olivine gabbros, gabbronorites and hornblende gabbros formed from a tholeiitic parental melt. Negative anomalies for the HFSE along with low Nb and Ta contents and a positive Sr anomaly indicate a subduction related origin of all parental melts. The nepheline gabbros consist predominantly of coarse-grained clinopyroxene phenocrysts in a matrix of fine grained clinopyroxene, olivine, plagioclase, K-feldspar and nepheline with accessory apatite. The tholeiitic gabbros have equigranular to porphyric textures with phenocrysts of olivine, pyroxene and hornblende in a plagioclase rich matrix with olivine hornblende, pyroxene and accessory apatite. Element concentrations of adjacent matrix grains and rims of phenochrysts were measured with LA-ICPMS. The distribution of REE between hornblende and clinopyroxene in the tholeiitic rocks is similar for most of the elements (DHbl•Cpx(La-Tm) = 2.7-2.8, decreasing to 2.6 and 2.4 for Yb and Lu, respectively). These values are about two times higher than published data (e.g. Ionov et al. 1997). Partition coefficients for orthopyroxene/clinopyroxene systematically decrease from the HREE

  16. Paleomagnetism of the Mesozoic Asik Mountain mafic complex in northern Alaska: implications for the tectonic history of the Arctic composite terrane (United States)

    Lewchuk, Michael T.; Foucher, Jamie; Elmore, R.D.


    At least three mutually exclusive hypotheses exist for the origin of the Arctic composite terrane and its Mesozoic location relative to the stable craton of North America. The most widely accepted hypothesis calls for counterclockwise rotation of the Arctic composite terrane as it rifted from the Arctic Archipelago. A second hypothesis calls for no relative movement, and a third places the Arctic composite terrane on the Kula plate as a part of a separate ribbon-shaped microcontinent. All three hypotheses predict unique positions for the Arctic composite terrane with respect to rotation and translation since the middle of the Mesozoic. Paleomagnetic and susceptibility studies were conducted on rocks from 15 sites in the ~160 Ma (K-Ar cooling age) Asik Mountain mafic to ultramafic complex in the western part of the Arctic composite terrane. Coherent data from 11 sites yielded a direction of dec = 255.1°, inc = 82.1° κ = 19.3, α95 = 9.6°, α63 = 5.6°. Contact and fold tests were not possible but the direction differs distinctly from the modern magnetic direction. The anisotropy of magnetic susceptibility revealed a well-developed oblate fabric of variable orientation. The orientation of the fabric was not related to the regional stress regime, so we conclude that the rocks were not deformed and metamorphosed during thrusting, and thus the magnetic remanence direction obtained is most likely primary. The direction yields a pole position at long = 166.8°E, lat = 59.8°N, A95 = 18.4°, A63 = 10.7° that is discordant to the expected 160 Ma reference direction for North America. Counterclockwise rotation of the Arctic composite terrane would yield a perfect fit to the 160 Ma reference pole with an allowance for up to 5° of northward translation. This result, combined with previous paleomagnetic data, makes a convincing argument that the Arctic composite terrane has not remained fixed in its current orientation with respect to North America. However, the data are

  17. 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


    [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

  18. 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 (United States)

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


    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

  19. The genetic relationship between mafic dike swarms and plutonic reservoirs in the mesozoic of central chile (30A degrees-33A degrees 45'S) : insights from AMS and geochemistry


    C. Creixell; M.A. Parada; D. Morata; Roperch, Pierrich; Arriagada, C


    Five mafic dike swarms between 30A degrees and 33A degrees 45'S were studied for their geochemical signature and kinematics of magma flow directions by means of AMS data. In the Coastal Range of central Chile (33A degrees-33A degrees 45'S), Middle Jurassic dike swarms (ConcA(3)n and Cartagena dike swarms, CMDS and CrMDS, respectively) and an Early Cretaceous dike swarm (El Tabo Dike Swarm, ETDS) display the presence of dikes of geochemically enriched (high-Ti) and depleted (low-Ti) basaltic c...

  20. 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 (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


    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 (parental magmas were most likely generated by the partial melting of a metasomatized lithospheric mantle wedge in the spinel stability field and emplaced in a continental arc setting. This consideration is consistent with the occurrence of Carboniferous ophiolitic and arc-related granitoids in the region, 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

  1. 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 (United States)

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


    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

  2. Petrology of mafic and ultramafic layered rocks from the Jaboncillo Valley, Sierra de Valle Fértil, Argentina: Implications for the evolution of magmas in the lower crust of the Famatinian arc (United States)

    Otamendi, J. E.; Cristofolini, E.; Tibaldi, A. M.; Quevedo, F. I.; Baliani, I.


    This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and peridotitic layered body that is lens-shaped and surrounded by gabbronorites, diorites, and metasedimentary migmatites. This body exposed at Jaboncillo Valley is one among several examples of mafic and ultramafic layered sequences in the Sierras Valle Fértil and La Huerta, which formed as part of the lower crust of the Ordovician Famatinian magmatic arc in central-western Argentina. The layered sequence grew at deep crustal levels (20-25 km) within a mafic lower crust. The base of the layered body was detached during the tectonic uplift of the Famatinian lower crust, whereas the roof of the layered body is exposed in the eastern zone. In the inferred roof, olivine-bearing rocks vanish, cumulate textures are less frequent, and the igneous sequence becomes dominated by massive or thinly banded gabbronorites. Mainly based on the petrographic relationships, the inferred order of crystallization in the gabbroic and peridotitic layered sequence is: (1) Cr-Al-spinel + olivine, (2) Cr-Al-spinel + olivine + clinopyroxene + magnetite, (3) Cr-Al-spinel + olivine + plagioclase + magnetite ± orthopyroxene, and (4) Al-spinel + orthopyroxene + amphibole. A strong linear negative correlation between olivine and plagioclase modal proportions combined with field, petrographic and geochemical observations are used to demonstrate that the physical separation of olivine and plagioclase results in rock diversity at scales of a few centimeters to tens of meters. However, the composition of olivine (Fo ˜ 0.81) and plagioclase (An > 94%) remains similar throughout the layered sequence. Spinels are restricted to olivine-bearing assemblages, and display chemical trends characteristic of spinels found in arc-related cumulates. Gabbroic and peridotitic layered rocks have trace element concentrations reflecting cumulates of early crystallizing minerals. The trace element patterns still retain the

  3. 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)



    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

  4. 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 (United States)

    Manya, Shukrani; Maboko, Makenya A. H.


    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

  5. 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)


    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.

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


    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

  7. 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 (United States)

    Saccani, Emilio; Allahyari, Khalil; Rahimzadeh, Bahman


    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.

  8. 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


    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

  9. Overlapping Sr-Nd-Hf-O isotopic compositions in Permian mafic enclaves and host granitoids in Alxa Block, NW China: Evidence for crust-mantle interaction and implications for the generation of silicic igneous provinces (United States)

    Dan, Wei; Wang, Qiang; Wang, Xuan-Ce; Liu, Yu; Wyman, Derek A.; Liu, Yong-Sheng


    In general, the mantle provides heat and/or material for the generation of the silicic igneous provinces (SIPs). The rarity of mafic microgranular enclaves (MMEs), however, hampers understanding of the mantle's role in generating SIPs and the process of crust-mantle interaction. The widespread distributed MMEs in the newly reported Alxa SIP provide an opportunity to study these processes. This study integrates in situ zircon U-Pb age and Hf-O isotope analyses, whole-rock geochemistry and Sr-Nd isotope results for the MMEs and host granitoids in the Alxa Block. SIMS zircon U-Pb dating reveals that there are two generations of MMEs and host granitoids. The MMEs in the Bayannuoergong batholith were formed at ca. 278 Ma, similar to the age (280 Ma) of host granitoids, and the MMEs and host granitoids in the Yamaitu pluton were formed at ca. 272-270 Ma. All MMEs have relatively low SiO2 (50.7-61.4 wt.%) and Th (0.8-2.8 ppm), but relatively high MgO (2.6-4.9 wt.%), Cr (23-146 ppm) and Ni (6-38 ppm) contents compared to the host granitoids, with SiO2 (63.6-77.5 wt.%), Th (5.2-41 ppm), MgO (0.23-2.1 wt.%), Cr (10-38 ppm) and Ni (5-14 ppm). All MMEs have whole rock Sr-Nd and zircon Hf-O isotope compositions similar to their corresponding host granitoids. The 280 Ma MMEs have lower whole rock εNd(t) (- 13.5) and higher initial 87Sr/86Sr values (0.7095) and zircon δ18O values (6.3‰) compared to the εNd(t) (- 11.5), initial 87Sr/86Sr values (0.7070) and zircon δ18O values (5.6‰) of the 270 Ma MMEs. The occurrences of quartz xenocrysts, K-feldspar megacrysts, corroded feldspars and acicular apatites indicate that the MMEs are the products of the mixing between mantle- and crust-derived magmas. The striking similarities in the zircon Hf-O isotopic compositions in both MME-host granitoid pairs indicate that the granitoids and MMEs have similar sources. The granitoids are proposed to be mainly sourced from magmas generated by remelting of newly formed mafic rocks, which

  10. 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 (United States)

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


    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.

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

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


    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

  12. U/Pb zircon ages and model ages (Sm/Nd) of ortho gneisses and meta mafic enclaves of the Barro Vermelho area (state of Pernambuco, Brazil), Alto Moxoto terrain, Borborema province, northeastern Brazil

    International Nuclear Information System (INIS)

    The Barro Vermelho area is located in the border between municipalities of Custodia and Sertania - PE, Pajeu-Paraiba Fold Belt, Borborema Province. Geological mapping at 1/25.000 scale allowed to distinguish two metamorphic domains respectively built up of orthoderivated rocks and paraderivated ones. The orthoderivated domain is formed mainly by augen gneisses more or less migmatized of granitic, monzogranitic, granodioritic, tonalitic and quartz-dioritic composition inside of which are found metamafic enclaves of leucogabbros, gabbronorites, gabbros/diorites, and anorthosites, apart from banded amphibolites, with a small occurrence of Fe-Ti ore enclosed by some of these enclaves. In addition, inserted in the orthogneisses are found also others enclaves and intrusions (some apparently concordant and others certainly discordant in relation to the prominent foliation of the area, Sn) of metric to hectometric dimensions, built up of amphibolites/metadiorites, metaplite, calcissilicate rocks of mafic ultramafic protholiths, weakly deformed granites and diorites, and two hectometric bodies of olivine diabase to troctolite. Field relations and similarities in terms of composition, texture and lithogeochemistry allowed to place the lithotypes of the orthoderivated domain in the following groups, considering them in a relative sequence of events from the older to the newest ones: anorthositic-gabbros xenoliths; tonalite (protolith of the orthogneisse of equal composition); enclaves/ dikes of amphibolites/metadiorites, synplutonic in relation to tonalite and comagmatic to the xenoliths; granitic orthogneisses formed from migmatization of tonalite; enclaves/dikes of amphibolites/metadiorite, synplutonic in relation to migmatization of tonalites; granites and diorites late to post migmatization; and olivine diabase to troctolite post the last tectonic-metamorphic event recorded in the area. Concordia diagrams U/Pb with colinear regression of three zircon fractions to

  13. Geological and tectonic description of the Klipperaas study site

    International Nuclear Information System (INIS)

    The Klipperaas study site is situated 45 km WNW of Kalmar in south-eastern Sweden. The site is situated between two regional NW-SE oriented lineaments. The site itself does not show any distinct lineaments. The site is flat, covered by till and with few outcrops. The precambrian rocks of this area are thought to be postorogenic in relation to the svecokarelien orogeny. The bedrock consists of 85 percent granites, 7 percent greenstones, 5.5 percent porphyries, 1.5 percent mafic dykes and 1 percent aplites. The granites are normally grey-red, medium grained and massive. They are, in a tectonically undisturbed condition, strongly magnetic. Closely associated with the granites are aplite dykes. The greenstones are schistos and present a number of originally different rocks. Some of them are xenolithes, others are dykes. The latter are often associated with dyke porphyries in composite dykes. The dyke porphyries have variable chemical compositions. Their width is usually 10 m and the directions group between W-WNW. The youngest rocks comprise a number of different, rather wellpreserved mafic dykes. Their width varies form ca 1 m to 10 m. The geophysical surface measurements display many discontinuities of variable intensity. They are oriented in two main directions,N-S and NE-SW. The dip of the fracture zones and the dykes vary from steep to 75 degrees. The horizontal fracture zone at the depth of 780 m is an exception. The widest investigated fracture zone has a width if 30 m. (authors)

  14. 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 (United States)

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


    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.

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

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


    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.

  16. 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:, e-mail:; Girardi, Vicente Antonio Vitorio [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail:; 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:


    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)

  17. 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 (United States)

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


    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

  18. 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.


    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.

  19. 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)


    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.

  20. The pyroclastic dyke and welded crystal tuff of the Morro dos Gatos alkaline intrusive complex, State of Rio de Janeiro, Brazil Dique piroclástico e tufo soldado com alto teor de cristais do complexo intrusivo de rochas alcalinas do Morro dos Gatos, RJ

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    Akihisa Motoki


    Full Text Available The present article reports the geologic, lithologic, and petrographic characteristics of the pyroclastic dyke and phenocryst-rich welded crystal tuff of the Morro dos Gatos alkaline intrusive body, State of Rio de Janeiro, Brazil. The intrusive complex has an extension of 1.2 x 0.8 km occupying an area of 0.5 km². It is constituted mainly by monzonite and trachyte. At the south flank of the massif, there exits a pyroclastic dyke and at the northwest flank, an intrusive welded crystal tuff. The pyroclastic dyke is 40 to 80 cm wide and intrudes into the basement porphyritic granite. This rock is constituted by welded tuff breccia with large amount of lapilli-size angular lithic fragments of trachyte. Along the contact plane of this dyke, there is an intercalation of the trachyte. The crystal tuff is characterised by abundant alkaline feldspar phenocrysts and mineral fragments of alkaline feldspar, quartz, biotite, and amphibole, showing a crystal matrix-supported texture. Large phenocrysts are aggregations of idiomorphic alkaline feldspar crystals with a general size of 2 mm and a maximum one of 6 mm. The matrix is composed mainly of mineral fragments of less than 1 mm in general size. The size-frequency diagram for the mineral fragments suggests that they have been originated from an explosive eruption. The matrix is strongly welded and completely devitrified showing a cryptocrystalline texture. The crystals were concentrated by sorting with the help of the volcanic gas ascending in the volcanic conduit during a continuous and effusive phase of the eruption. The limited special distribution of the pyroclastic rocks and small outcrop size indicate that they are not constituent of pyroclastic flow deposits, but of subvolcanic conduit and fissure.O presente artigo relata as características geológicas, litológicas e petrográficas do dique piroclástico e tufo soldado intrusivo com alto teor de fenocristais e fragmentos de minerais do complexo

  1. Trace element characteristics of mafic and ultramafic meta-igneous rocks from the 3.5 Ga. Warrawoona group: evidence for plume-lithosphere interaction beneath Archaean continental crust

    International Nuclear Information System (INIS)

    similar volcanic greenstones in the Superior Province (Canada). However, this concept is problematic for two reasons: (1) Modern oceanic crust is typically associated with overlying terrigenous/ pelagic sediments, both of which are introduced into the mantle via subduction. Mixing with mantle and subsequent partial melting invariably produces compositions with HFSE depletion and LREE enrichment at low to moderate degrees of melting. (2) Mixing of subduction-modified lithosphere into the mantle followed by melting should be detectable in volcanic rocks with strong depletions in elements such as Nb and Ti, but increased abundances in the LILE and LREE (La/Smpm >> 1). Compositionally, the Warrawoona meta-igneous rocks resemble compositions found in modern oceanic plateaus (e.g. Broken Ridge) which incorporated variable amounts of continental lithospheric mantle (CLM). Variability in trace element ratios (e.g. Nb/Ta, Ce/Pb, and Nb/U) may reflect source heterogeneity or the coexistence of tectonically accreted oceanic fragments with differing petrogenetic histories. However, well-defined co-variations in major and trace elements of samples from all three major stratigraphic units point to a common magmatic origin. In an attempt to link Archaean rocks to present day analogues, we conclude that the spatial association of ultramafic and mafic volcanics and crustally contaminated high-Mg, Fe rocks most resembles melting of a plume head with incorporation of CLM-components and volcanic outpouring within a (rifted?) continental environment. Support for the existence of pre-existing continental crust comes from published studies which report on xenocrystic zircons in basalts, underlying granitoids and sediments of pre-Warrawoona age and mafic inclusions within granitoid bodies. Temporal decreases in La/Smpm and Nb/Thpm ratios, along with unfractionated HREE may be interpreted as adiabatic upwelling of plume material and a decreasing influence of the lithospheric component ('CLM

  2. 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 (United States)

    Bulle, Florian; Layne, Graham D.


    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.

  3. 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


    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.

  4. 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

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    M. Florencia Gargiulo


    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

  5. Queerer than queer: reflections of a Kike dyke. (United States)

    Goldflam, A


    In this article the author, a Jewish lesbian academic, reflects on the positive and negative aspects of her dual identity and explores her feelings of exclusion from "in groups" in a range of settings. Annie Goldflam carries a legacy of fear from stories of medieval "witch" burnings and drownings and the twentieth century Jewish Holocaust, which she reflects on to compare the nature of anti-semitism and lesbophobia, considering the options of hiding from racist and homophobic forms of oppression or confronting them. She has chosen to confront, be "out" and politically active. PMID:10197550

  6. 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

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    A.M. Tibaldi


    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.

  7. Condiciones físicas de formación de gabros ymigmatitas derivadas de rocas máficas en el centro de la Sierra de ValleFértil, San Juan Physical conditions for the formation ofgabbros and migmatites derived from mafic rocks in the center of Sierra deValle Fértil, San Juan

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    AlinaM. Tibaldi


    resultadosexperimentales se demuestra que la transición desde rocas ígneas máficas amigmatitas máficas ocurrió por enfriamiento isobárico, y que el emplazamientocontinuo de magmas debió ser la fuente de calor que mantuvo la secuencia enfacies de granulitas sin dejar que el enfriamiento fuera rápido. Se interpretala geología del centro de la sierra de Valle Fértil como un ejemplo del núcleoplutónico-metamórfico del arco magmático Famatiniano donde el gradientemetamórfico anormalmente alto refleja que un volumen importante de magmasmáficos alcanzaban, y dominaban, en paleo-profundidades de entre 16 y 20kilómetros.A sequence of plutonicmafic rocks inter-stratified with both mafic- and metasedimentary-derivedmigmatites is found along the San Juan valley in the center of the Sierra deValle Fértil. This natural example shows the transition from igneous tometamorphic petrologic processes which occurred during the crystallization ofmafic magmas and the subsequent partial melting of crystallized gabbroic rocks.This work studies the mineralogical changes associate to this petrologictransition. Thermobarometric estimates based on amphibole-plagioclase indicatethat the mafic magmas crystallized at around 1100ºC and 5 ± 0.5 kbar. Theconditions under which gabbroic rocks were partially melted are estimated usingtwo pyroxenes thermometry and amphibole-plagioclase thermobarometry. Similarphysical conditions in the range between 740 and 840ºC and 5 to 6.5 kbar arerecovery from mineral assemblages in the mesosomes and leucosomes of maficmigmatites. The main mineral compositional changes that accompanied the partialprocess of the gabbroic rocks are: 1 depletion of aluminium content and Mg#ratio in pyroxenes; 2 depletion of anorthite mole fraction of theplagioclases; and 3 depletion of the Mg# ratio in amphiboles. These mineralcompositional variations are consistent with those found by experimentallymelting mafic protoliths. Experimental results showed that the temperature forpromoting

  8. 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

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    Florencia L Boedo


    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

  9. Constraints on the formation of geochemically variable plagiogranite intrusions in the Troodos Ophiolite, Cyprus (United States)

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


    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.

  10. 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

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    Baliani Ignacio


    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


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    Conti Bruno


    Full Text Available This work presents new results of a detailed geological and structural investigation focusing the easternmost Uruguayan Mesozoic magmatic occurrences related to the south Atlantic opening. Lithological descriptions, their stratigraphic relationships and complimentary lithochemical characterizations carried out in the San Miguel region (East Uruguay are presented. Three volcanic/sub-volcanic units have been recognized. The felsic volcanic association is composed by rhyolitic - dacitic flows, mainly with porphyritic textures and sub-alkalinenature and related pyroclastic rocks. The felsic sub-volcanic association is characterized by granophyres of about 25 km2 of exposed area, cross- cut by mafic and felsic dykes. Finally, a mafic association has been identified characterized by dykes and a small intrusion of gabbroic composition.All these units are Mesozoic in age (130 - 127 Ma and according to their chemical nature they correspond tosub-alkaline to weak peralkaline magmas.

  12. Significado de fábricas magnéticas en rocas volcánicas cuaternarias de la Isla Decepción (Shetland del Sur, Antártida)


    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


    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...

  13. 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

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


    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.

  15. 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


    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.

  16. Supra-subduction zone tectonic setting of the Muslim Bagh Ophiolite, northwestern Pakistan: Insights from geochemistry and petrology (United States)

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


    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., < 50-60 km, and to have risen through a slab window. The Bagh Complex is an assemblage of Triassic-Cretaceous igneous and sedimentary rocks, containing tholeiitic, N-MORB-like basalts and alkali basalts with OIB-type signatures. Nb-Ta depletion in both basalt types suggests possible contamination from continental fragments incorporated into the opening Tethyan

  17. 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


    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

  18. 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


    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

  19. Evolución tectonotermal ordovícica del borde occidental del arco magmático Famatiniano: metamorfismo de las rocas máficas y ultramáficas de la Sierra de la Huerta de Las Imanas (Sierras Pampeanas, Argentina Tectonothermal ordovician evolution of the western margin of the Famatinian magmatic arc: metamorphism of the mafic and ultramafic rocks of Sierra de la Huerta -Las Imanas (Pampean Ranges, Argentina

    Directory of Open Access Journals (Sweden)

    Juan A Murra


    énicosAn important magmatic and tectonometamorphic activity of Early and Middle Ordovician age is registered in the pre-Andean basement of the Sierras Pampeanas of Argentina. These were linked to the development of a continental magmatic arc during the Famatinian Orogeny, resulting from the approach and attachment of an alleged exotic terrane (the Precordillera Terrane, to the south western Gondwana's margin (present coordinates. A suit of meta-mafic and ultramafic rocks are exposed in the Sierras de La Huerta and Las Imanas, at the western limit of the famatinian orogen. Metaperidotites (Ol-Opx-Cpx-Am-Spl, coronitic metapyroxenites (Opx-Cpx-Spl-Am-Pl, metaquartz-norites (Opx-Pl-Am-Qtz-Bt±Grt and metadiorites (Pl-Am-Qtz-Bt-Ep are associated with metasedimentary rocks (marbles, gneisses and migmatites with Sil+Kfs+Grt that reached the peak and post-peak conditions of metamorphism at middle Ordovician time. The meta-mafic rocks record a first high-grade metamorphic event (M1-730ºC and 8.4±0.5 kbar and a second lower pressure event (M2, 720ºC and 4.5 kbar with Cum+Hbl+Mag in a coronitic assemblage. The meta-ultramafic rocks also record the two metamorphic events, but only for the second one it was possible to calculate the P-T conditions. At latitude 32º30'S, the Famatinian magmatic arc shows a systematic compositional variation normal to its trend, i.e. in an east-west direction, which could be related to present erosion levels. In this context, the mafic and ultramafic units of Sierras de La Huerta and Las Imanas, probably represent the deepest levels of the magmatic arc which is consistent with the position that they show marginal to the orogenic belt, i.e., where the uplift and erosion rates were larger

  20. Magma distribution and crustal extension in the Nigerian younger granite province: evidence from the wase area (United States)

    Turner, D. C.

    In the Wase area, situated E of the main belt of Jurassic (Younger Granite) ring complexes in Nigeria, the following sequence of events associated with Younger Granite magmatism took place: (1) Emplacement of minor syenite-granite central complexes and local felsite and microgranite dyke swarms; (2) dextral movement on the ENE-trending Dengi shear zone; (3) emplacement of an extensive swarm of mafic dykes. The S-shaped distribution pattern of ring complexes in the Nigerian Younger Granite province resembles a N-S spreading ridge truncated by ENE-trending transform faults. In the Wase area, the Dengi shear zone can be interpreted as an eastward continuation of the southern transform fault, developed in response to crustal extension in the N-S 'ridge' sector—the ring complex belt. The later mafic dyke swarm is correlated with a widespread Jurassic thermal event, known from basement rejuvenation ages W of the ring complex belt, and providing evidence for a much wider development of magma than is indicated by the closely grouped ring complexes.

  1. A love letter from NADIA (non-anglo dykes in Australia). (United States)

    Kizinska, R


    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. An isotope trace element study of the East Greenland Tertiary dyke swarm

    DEFF Research Database (Denmark)

    Hanghøj, Karen; Storey, Michael; Stecher, Ole


    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...

  3. Sissies, Faggots, Lezzies, and Dykes: Gender, Sexual Orientation, and a New Politics of Education? (United States)

    Lugg, Catherine A.


    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…

  4. The flood, the channels, and the dykes : managing legal information a globalized and digital world


    Breuker, Joost; Casanovas, Pompeu; Klein, Michel C. A.; Francesconi, Enrico


    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...

  5. Evaluation of erosion of soil used in dykes and earth embankments which are subjected to flood


    Reiffsteck, Philippe


    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...

  6. Petrology and geochemistry of Variscan dykes from the Jáchymov (Joachimsthal) ore district, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Štemprok, M.; Seifert, T.; Holub, F. V.; Chlupáčová, M.; Dolejš, D.; Novák, Jiří Karel; Pivec, E.; Lang, Miloš


    Roč. 53, č. 1 (2008), s. 65-104. ISSN 1802-6222 Institutional research plan: CEZ:AV0Z30130516 Keywords : lamprophyre * granite porphyry * uranium mineralization * magma mixing * Western Krušné hory/Erzgebirge Pluton Subject RIV: DB - Geology ; Mineralogy

  7. The use of Ground Penetrating Radar and alternative geophysical techniques for assessing embankments and dykes safety


    Mori, Guido


    The research is part of a survey for the detection of the hydraulic and geotechnical conditions of river embankments funded by the Reno River Basin Regional Technical Service of the Region Emilia-Romagna. The hydraulic safety of the Reno River, one of the main rivers in North-Eastern Italy, is indeed of primary importance to the Emilia-Romagna regional administration. The large longitudinal extent of the banks (several hundreds of kilometres) has placed great interest in non-destructive...

  8. 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.

    } and s(m) = {v 1 ,v 2 ,...,v m } be sets of orthogonal vectors ( i.e., column vectors of complete data space U and model space V) as detailed below: U={U p , U r-p , U 0 } is the complete data space where U p : optimised data space-set of p... eigenvectors corresponding to dominant eigenvalues such that λ’ 1 > λ ’ 2 > λ ’ 3 >…. >λ’ p ≠ 0. U r-p : set of (r-p) eigenvectors corresponding to remaining dominant eigenvalues such that λ’ p+1 > λ’ p+2 >..……> λ’ r ≠ 0 and U 0 : Null space...

  9. Homosexuals, dykes and queers: political positions in the lesbian and gay movement

    Directory of Open Access Journals (Sweden)

    Coll-Planas, Gerard


    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.

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


    Ma, Zhen-Kun; Zi-wu FAN; Zhang, Ming; Yi-lu SU


    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...

  11. Coeval Shoshonitic-ultrapotassic dyke emplacements within the Kestanbol Pluton, Ezine – Biga Peninsula (NW Anatolia)


    Akal, Cüneyt


    The Biga Peninsula, in the north-western part of Western Anatolia, is part of the Sakarya Zone of the Western Pontides and the tectonically overlying Ezine group. The basement rocks are intruded by the early Miocene Kestanbol Pluton and early to middle Miocene calc-alkaline to shoshonitic-ultrapotassic volcanic successions related to postcollisional continental extension. The Kestanbol Pluton mainly comprises monzonite and granodiorite and is cut by shoshonitic-ultrapotassic tephriphonolite d...

  12. Distribution of radioactivity in Um Dweila Dyke, south-eastern desert, Egypt

    International Nuclear Information System (INIS)

    Um Dweila area is characterized by the presence of an elongate dike extending about 10.5 km in a NE-SW direction. This dike is intruding metavolcanics and metasediments. Detailed field geologic and radiometric study was carried out in the whole area for the dike and the country rocks. It was found that the dike is composed of alkaline to subalkaline rocks. The country rocks are mainly metavolcanics and metasediments with small exposure of diorites. The main trends of dikes, faults and joints are represented in rose diagrams. Radioactivity measurements in the field showed that Dweila dike has promising potential because there are anomalous zones where the rocks are highly fractured and show alteration products. Moreover, the parts of the dike intruding metasediments show relative increase of radioactivity than those intruding metavolcanics. Two groups of samples were collected all over the dike. The first group was selected from the northern part of the dike while the second group represents samples chosen from the Central to Southern parts. The preliminary U and Th data show a significant variation in the two groups. In the first, U content ranges from 347 to 1600 ppm while Th content ranges from 1135 to 2817 ppm. The second group of samples have U content ranging from 229 to 1380, and Th content ranging from 8 to 97 ppm. The calculated Th/U ratios of the first group vary from 1.49 to 5.63 while in the second group from 0.010 to 0.120. In view of the obtained data, two phases of radioactive mineralization could be considered to occur in this area. A discussion has been given to explain our assumption

  13. 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


    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.

  14. The post-collisional volcanism of northern Tunisia: Petrology and evolution through time (United States)

    Halloul, Néji; Gourgaud, Alain


    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.

  15. Tectonic control of mesozoic mafic and alkaline bodies in the Amazon craton (Brazil)

    International Nuclear Information System (INIS)

    The main alkaline Mesozoic bodies in the Amazon Craton are the Maecuru (MEA), Maraconai (MRA), Camaipi (CA), Catrimani (CTA), and Seis Lagos (SLA) bodies. Of these, CTA is the only one which has been radiometrically dated (100 Ma), although all the others are also interpreted as Mesozoic. (author)

  16. Petrologic and Oxygen-Isotopic Investigations of Eucritic and Anomalous Mafic Achondrites (United States)

    Mittlefehldt, D. W.; Greenwood, R. C.; Peng, Z. X.; Ross, D. K.; Berger, E. L.; Barrett, T. J.


    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.

  17. 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


    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.

  18. Geochemistry of Precambrian mafic dikes, central Bighorn Mountains, Wyoming, U.S.A. (United States)

    Armbrustmacher, T.J.


    Precambrian quartz dolerites and metadolerites of the central Bighorn Mountains form dikes that intrude a Precambrian metamorphic and igneous terrane typical of the Laramide uplifts of the middle Rocky Mountains. They have a restricted range of major- and trace-element compositions and are typical of basalts in the middle stages of tholeiitic fractionation. Fractionation in the direction of iron enrichment occurred by removal of plagioclase. Average element concentrations of the two groups are nearly identical to one another, are comparable to those in Archean metabasalts from numerous shield areas, and are intermediate between those of modern oceanic tholeiites and continental tholeiites. These average concentrations suggest a depth of magma generation and thickness of crust intermediate between those for the oceanic and continental environments. ?? 1977.

  19. Paleo magnetism of the Para de Minas mafic dike swarm, west of Belo Horizonte, MG, Brazil

    International Nuclear Information System (INIS)

    Preliminary paleo magnetic results from 64 oriented hand samples belonging to 20 un metamorphosed dikes from west of Belo Horizonte, Minas Gerais are presented. The paleo magnetic analysis showed a complex magnetic behavior after AF (alternating field) and thermal treatments, when stable but incoherent directions were disclosed by samples of many dikes. 40 Ar/39 Ar age determinations on these granulite are in progress in order to constrain the age of this component of magnetization. (author)

  20. Separate zones of sulfate and sulfide release from subducted mafic oceanic crust (United States)

    Tomkins, Andrew G.; Evans, Katy A.


    Liberation of fluids during subduction of oceanic crust is thought to transfer sulfur into the overlying sub-arc mantle. However, despite the importance of sulfur cycling through magmatic arcs to climate change, magma oxidation and ore formation, there has been little investigation of the metamorphic reactions responsible for sulfur release from subducting slabs. Here, we investigate the relative stability of anhydrite (CaSO4) and pyrite (FeS2) in subducted basaltic oceanic crust, the largest contributor to the subducted sulfur budget, to place constraints on the processes controlling sulfur release. Our analysis of anhydrite stability at high pressures suggests that this mineral should dominantly dissolve into metamorphic fluids released across the transition from blueschist to eclogite facies (∼450-650 °C), disappearing at lower temperatures on colder geothermal trajectories. In contrast, we suggest that sulfur release via conversion of pyrite to pyrrhotite occurs at temperatures above 750 °C. This higher temperature stability is indicated by the preservation of pyrite-bornite inclusions in coesite-bearing eclogites from the Sulu Belt in China, which reached temperatures of at least 750 °C. Thus, sulfur may be released from subducting slabs in two separate pulses; (1) varying proportions of SO2, HSO4- and H2S are released via anhydrite breakdown at the blueschist-eclogite transition, promoting oxidation of remaining silicates in some domains, and (2) H2S is released via pyrite breakdown well into the eclogite facies, which may in some circumstances coincide with slab melting or supercritical liquid generation driven by influx of serpentinite-derived fluids. These results imply that the metallogenic potential in the sub-arc mantle above the subducting slab varies as a function of subduction depth, having the greatest potential above the blueschist-eclogite transition given the association between oxidised magmas and porphyry Cu(-Au-Mo) deposits. We speculate that this zoned sulfur liberation might be one of the factors that lead to the apparently redox-influenced zoned distribution of ore deposit types in the Andean arc. Furthermore, given the lack of sulfate-associated sea floor oxidation prior to the second great oxidation event, the pattern of sulfur transfer from the slab to the sub-arc mantle likely changed over time, becoming shallower and more oxidised from the Neoproterozoic onwards.

  1. Reactive Transport Modeling of Supercritical Carbon Dioxide Injection Into Mafic Rock Reservoirs (United States)

    Podgorney, R.; Hull, L.; Huang, H.; McLing, T.


    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.

  2. Structural control on basaltic dike and sill emplacement, Paiute Ridge mafic intrusion complex, southern Nevada

    International Nuclear Information System (INIS)

    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

  3. The Mont Collon mafic complex (Austroalpine Dent Blanche nappe) : permian evolution of the Western European mantle


    Monjoie P.


    Résumé: Le complexe du Mont Collon (nappe de la Dent Blanche, Austroalpin) est l'un des exemples les mieux préservés du magmatisme mafique permien des Alpes occidentales. Il est composé d'affleurements discontinus et d'une stratification magmatique en son centre (Dents de Bertol) et est composé à 95% de roches mafiques cumulatives (gabbros à olivine et/ou cpx, anorthositiques, troctolites, wehrlites et wehrlites à plagioclase) et localement de quelques gabbros pegmatitiques. Ces faciès sont r...

  4. The Mont Collon mafic complex (Austroalpine Dent Blanche nappe): permian evolution of the Western European mantle


    Monjoie, Philippe; Lapierre, Henriette; Pfeifer, Hans-Rudolf


    Le complexe du Mont Collon (nappe de la Dent Blanche, Austroalpin) est l’un des exemples les mieux préservés du magmatisme mafique permien des Alpes occidentales. Il est composé d’affleurements discontinus et d’une stratification magmatique en son centre (Dents de Bertol) et est composé à 95% de roches mafiques cumulatives (gabbros à olivine et/ou cpx, anorthositiques, troctolites, wehrlites et wehrlites à plagioclase) et localement de quelques gabbros pegmatitiques. Ces faciès sont recoupés ...

  5. Chernobyl exclusion zone protection dyke on the pripyat river: collective dose reduction and cost-benefit analysis

    International Nuclear Information System (INIS)

    The periodic floods at spring of the Pripyat river, near the Chernobyl plant, contribute to put back in suspension and to the dissolution of radioactive particles which settled during the accident of 1986 and remain present on the ground surface. These particles are then carried by the Pripyat river, then downstream by the Dnieper, to the black Sea. This secondary contamination is a significant radiological exposure source for the Ukraine population, living near the river. A project of a dam construction on the right side of the river, to supplement an existing similar dam on the left side, has been elaborated. A study of counter-evaluation relative to efficiency of the dam evaluation on a technical and a radiological domain, has been realized by the CEPN and the BG Consulting Engineers Ltd. In this framework, the CEPN realized the doses calculation and the cost benefit analysis. (A.L.B.)

  6. 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.

    .e., column vectors of complete data space U and model space V) as detailed below: U = {U p , U r-p , U 0 } is the complete data space where U p : optimised data space - set of p eigenvectors corresponding... and U 0 : Null space - having eigenvectors corresponding to r- min ( N OBS x m) zero eigenvalues. Similarly it follows in the case of complete model space (i.e. V={ V p , V r-p , V 0 }) and can also be explained...

  7. Characteristics of diamonds and xenoliths from the Star Kimberlite Dyke System, O.F.S., South Africa

    International Nuclear Information System (INIS)

    Surface features on diamonds indicate that they where subjected to a history of resorption and etching. The degree of resorption was noted to increase with decreasing diamond size. The kimberlite magma is proposed as the most likely resorbing agent. Xenolithic surface features on diamonds are evidence for late-stage disaggregation of xenoliths which released the respective sub-populations of diamonds into the kimberlite. Evidence from deformation features as well as xenolithic surface features observed on diamonds from Star complements the evidence from the inclusions that the diamonds are xenocrysts and formed in the mantle prior to incorporation in the kimberlite. The surface features on inclusion-free diamonds support the hypothesis that both inclusion-free and inclusion-bearing diamonds are xenocrystic. Since so few xenoliths were found in this study, it is not possible to model the detailed stratigraphy of the upper mantle below Star. However, our limited data suggests that garnet and chromite harzburgite with lenses of garnet lherzolite constitute the depth interval from 160-190 km. Eclogite xenoliths are also rare at Star and only fifteen samples were recovered for investigation. The eclogite xenoliths show a large range in chemical composition but because of the small size of the samples, no layering or inhomogeneities could be observed. A model is proposed whereby the eclogites are formed by the metamorphism of the basaltic component of an ophiolite suite during subduction. 13 refs

  8. Dykes of standards supporting polders of data: The practices used in the Netherlands for making archaeological data available and accessible


    Gilissen, V.


    In the Netherlands, the archiving and publication of archaeological research data has led to the establishment of EDNA, the e-Depot for Dutch Archaeology, accommodated at DANS (Data Archiving and Networked Services) 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 ...

  9. Influence of a metamorphosed gabbro in the control of uranium-bearing pegmatite dykes, Madawaska Mines, Bancroft, Ontario

    International Nuclear Information System (INIS)

    A study was undertaken to examine the structure in the vicinity of Madawaska Mines as a controlling factor for the uranium-bearing pegmatitic granites and syenites that constitute the orebodies. These relatively undeformed rocks are confined to the deformed anorthositic Faraday metagabbro complex. This paper examines firstly the strain distribution within the Faraday metagabbro complex in order to predict paths of least resistance along which the younger pegmatites were emplaced. Secondly, certain geochemical properties of the metagabbro host rock that may have had an influence on the formation of the ore deposits are described

  10. ESI-VI10 Jost Van Dyke, U.K. Virgin Islands 2000 (Environmental Sensitivity Index Map) (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...

  11. Does deformation saturate seismic anisotropy? (United States)

    Tatham, D. J.; Lloyd, G. E.; Butler, R. W.; Casey, M.


    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

  12. In situ determination of U-Pb ages and Sr-Nd-Hf isotopic constraints on the petrogenesis of the Phalaborwa carbonatite Complex, South Africa (United States)

    Wu, Fu-Yuan; Yang, Yue-Heng; Li, Qiu-Li; Mitchell, Roger H.; Dawson, J. Barry; Brandl, Günther; Yuhara, Masaki


    The Phalaborwa carbonatite Complex, situated in the northeastern part of South Africa, is characterized by copper and zirconium mineralization, and is composed principally of pyroxenites, phoscorite and carbonatite (banded and transgressive). The complex is transected by mafic dykes, and is geographically associated with a satellite syenite and minor granite intrusions. Zircon and baddeleyite U-Pb isotopic age determinations using CAMECA 1280 secondary ion mass spectrometry have shown that the outer pegmatitic pyroxenite at the Loolekop pipe was emplaced at 2060 ± 4 Ma, and the main phoscorite at 2062 ± 2 Ma. Both ages are identical to those of 2060 ± 2 and 2060 ± 1 Ma for the banded and transgressive carbonatites, respectively. The satellite syenite, which forms plug-like bodies outside of the border of the main complex, and the later mafic dyke have “similar” emplacement ages of 2068 ± 17 and 2062 ± 53 Ma, indicating that these intrusions were apparently near-synchronously emplaced. In contrast to other carbonatites, the Phalaborwa Complex is characterized by high initial Sr and low initial Nd and Hf isotopic compositions. In situ isotopic analyses of apatite, calcite, zircon and baddeleyite indicate that the primary magma was derived from an enriched mantle. As the complex was emplaced slightly earlier at ~ 2060 Ma than the nearby mafic phase of the Bushveld Complex (~ 2055 Ma), it is proposed that the Phalaborwa carbonatite magmatism was triggered by the same mantle plume activity, which partially melted the overlying lithospheric mantle. This contribution also highlights that isotopic studies used to constrain the genesis of ancient igneous complexes should concentrate on minerals with low parent/daughter elemental ratios, such as apatite and calcite for Sr isotopes, and zircon and baddeleyite for Hf isotopes.

  13. Sr-Nd-Hf isotopes of the intrusive rocks in the Cretaceous Xigaze ophiolite, southern Tibet: Constraints on its formation setting (United States)

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


    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

  14. Root zone of a continental rift: the Neoproterozoic Kebnekaise Intrusive Complex, northern Swedish Caledonides

    DEFF Research Database (Denmark)

    Kirsch, Moritz; Svenningsen, Olaf


    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...... represent a high-level magma plumbing system in a late-stage continental rift. The composition and volume of rift-related igneous rocks in the Seve Nappes are inconsistent with a mantle plume origin, but are thought to record progressive lithospheric thinning and increasing involvement of an asthenospheric...

  15. 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)

  16. Tectono-magmatic evolution of the younger Gardar southern rift, South Greenland

    Directory of Open Access Journals (Sweden)

    Brian G.J. Upton


    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

  17. The elusive Hadean enriched reservoir revealed by 142Nd deficits in Isua Archaean rocks. (United States)

    Rizo, Hanika; Boyet, Maud; Blichert-Toft, Janne; O'Neil, Jonathan; Rosing, Minik T; Paquette, Jean-Louis


    The first indisputable evidence for very early differentiation of the silicate Earth came from the extinct (146)Sm-(142)Nd chronometer. (142)Nd excesses measured in 3.7-billion-year (Gyr)-old rocks from Isua (southwest Greenland) relative to modern terrestrial samples imply their derivation from a depleted mantle formed in the Hadean eon (about 4,570-4,000 Gyr ago). As dictated by mass balance, the differentiation event responsible for the formation of the Isua early-depleted reservoir must also have formed a complementary enriched component. However, considerable efforts to find early-enriched mantle components in Isua have so far been unsuccessful. Here we show that the signature of the Hadean enriched reservoir, complementary to the depleted reservoir in Isua, is recorded in 3.4-Gyr-old mafic dykes intruding into the Early Archaean rocks. Five out of seven dykes carry (142)Nd deficits compared to the terrestrial Nd standard, with three samples yielding resolvable deficits down to -10.6 parts per million. The enriched component that we report here could have been a mantle reservoir that differentiated owing to the crystallization of a magma ocean, or could represent a mafic proto-crust that separated from the mantle more than 4.47 Gyr ago. Our results testify to the existence of an enriched component in the Hadean, and may suggest that the southwest Greenland mantle preserved early-formed heterogeneities until at least 3.4 Gyr ago. PMID:23128231

  18. Mineral and Whole-rock Geochemistry of the Kestanbol Granitoid (Ezine-Çanakkale) and its Mafic Microgranular Enclaves in Northwestern Anatolia: Evidence of Felsic and Mafic Magma Interaction




    The Miocene Kestanbol granitoid, in Ezine-Çanakkale, Turkey, is one of post-collision granitoids of western Anatolia, which have been related to the the late Cretaceous collision between the Anatolide-Tauride platform and the Pontides. Magmatism began during the early Miocene, with coeval alkaline to calc-alkaline plutonism and volcanism, controlled by the regional tectonic evolution. The Kestanbol pluton intruded regionally metamorphosed basement rocks. Volcanic and volcano-clastic sedimenta...

  19. 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


    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.

  20. Platinum-group elements in the Eastern Deccan volcanic province and a comparison with platinum metals of the western Deccan (United States)

    Crocket, James; Paul, Dalim; Lala, Trisha


    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. Sphene-centered ocellar texture as a petrological tool to unveil the mechanism facilitating magma mixing (United States)

    Gogoi, Bibhuti; Saikia, Ashima; Ahmad, Mansoor


    The sphene-centered ocellar texture is a unique magma mixing feature characterized by leucocratic ocelli of sphene enclosed in a biotite/hornblende-rich matrix (Hibbard, 1991). The ocelli usually consist of plagioclase, K-feldspar and quartz with sphene crystals at its centre. Although geochemical and isotopic data provide concrete evidence for the interaction between two compositionally distinct magmas, the exact processes by which mixing takes place is yet uncertain. So, textural analysis can be used to decipher the behaviour of two disparate magmas during mixing. Presented work is being carried out on the sphene ocelli, occurring in hybrid rocks of the Nimchak Granite Pluton (NGP), to understand its formation while two compositionally different magmas come in contact and try to equilibrate. The NGP is ca. 1 km2in extent which has been extensively intruded by number of mafic dykes exhibiting well preserved magma mixing and mingling structures and textures in the Bathani Volcano-Sedimentary Sequence (BVSS) located on the northern fringe of the Proterozoic Chotanagpur Granite Gneiss Complex (CGGC) of eastern Indian Shield. From petrographic and mineral chemical studies we infer that when basaltic magma intruded the crystallizing granite magma chamber, initially the two compositionally different magmas existed as separate entities. The first interaction that took place between the two phases is diffusion of heat from the relatively hotter mafic magma to the colder felsic one followed by diffusion of elemental components like K and incompatible elements from the felsic to the mafic domain. Once thermal equilibrium was attained between the mafic and felsic melts, the rheological contrasts between the two phases were greatly reduced. This allowed the felsic magma to back-vein into the mafic magma. The influx of back-veined felsic melt into the mafic system disrupted the equilibrium conditions in the mafic domain wherein minerals like amphibole, plagioclase and biotite

  2. Petrogenesis of Cretaceous adakite-like intrusions of the Gangdese Plutonic Belt, southern Tibet: Implications for mid-ocean ridge subduction and crustal growth (United States)

    Zheng, Yuan-chuan; Hou, Zeng-qian; Gong, Ying-li; Liang, Wei; Sun, Qing-Zhong; Zhang, Song; Fu, Qiang; Huang, Ke-Xian; Li, Qiu-Yun; Li, Wei


    We have conducted a whole-rock geochemical, U-Pb zircon geochronological, and in situ zircon Hf-O isotopic compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz-diorite). U-Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two-mica granite were emplaced at ca. 96 Ma and 80-76 Ma, respectively, and that the Nuri quartz-diorite was emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and mafic enclaves in the Langxian area, felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite-like rocks. The high Mg-numbers, high abundance of compatible elements, high ɛNd(t) (2.7 and 2.8) and δ18O (8.9 and 9.2‰) values, elevated zircon ɛHf(t) (11.0-17.0) values, and low 87Sr/86Sr(i) ratios (0.7040), collectively indicate that the Nuri adakite-like quartz-diorite was derived from partial melting of the low temperature altered Neo-Tethyan oceanic crust, and that these dioritic magmas subsequently interacted with peridotite as they rose upwards through the overlying mantle wedge. The observation of identical differentiation trends, similar whole-rock Sr-Nd and zircon Hf isotopic compositions, and consistently low (Dy/Yb)N ratios among the Langxian igneous suite rocks, indicates that the adakite-like granodiorite was produced by low-pressure fractional crystallization of precursor magmas now represented by the (relict) mafic enclaves. However, relatively high Al2O3 contents, low MgO, Cr and Ni contents, and low (La/Yb)N and (Dy/Yb)N values indicate that the two-mica granite was derived from partial melting of the southern Tibetan mafic lower crust in the absence of garnet, while isotopic data suggest that at

  3. Petrogenesis and timing of mafic magmatism, South Taimyr, Arctic Siberia: A northerly continuation of the Siberian Traps? (United States)

    Reichow, M. K.; Saunders, A. D.; Scott, R. A.; Millar, I. L.; Barfod, D.; Pringle, M. S.; Rogers, N. W.; Hammond, S.


    The Siberian large igneous province (LIP) forms the world's most extensive continental exposure of basalt and has several sub-provinces surrounding it, which may be genetically related. The Taimyr peninsula of north Siberia is one of these sub-provinces and is frequently assumed to be the northerly continuation of the basalts exposed at Noril'sk, the best-studied area of the Siberian LIP. However, the correlation is uncertain. We present new major and trace element data from 35 samples of extrusive and intrusive rocks from Taimyr, with Sr and Nd isotope data from a subset of ten. The Taimyr rocks fall into two groups with low (~ 7 wt.%) and elevated (~ 9 wt.%) MgO concentrations. The high-MgO rocks display a restricted range of initial 87Sr/86Sr (0.705 to 0.706) and 143Nd/144Nd (0.5122 to 0.5124) ratios, and share bulk silicate earth normalised rare earth element patterns strikingly similar to data observed in the ore-related Noril'sk intrusions. The remaining low-MgO group samples have a broader range with higher Sr and lower Nd isotope values and higher incompatible trace element ratios (e.g., Th/Ta > 5.3 and La/Smn > 1.7) similar to the crustally-contaminated Nadezhdinsky and Morongovsky suite basalts of the Noril'sk region. The major and trace element data for both groups are consistent with a process of fractional crystallisation coupled with small degrees of assimilation of incompatible-element-enriched lower crust involving different contaminants. Trace element model calculations indicate a process of magma formation at large degrees of partial melting and at pressures of less than 3 GPa, probably within the garnet-spinel transition zone or the spinel stability field of the asthenospheric mantle. We obtained an argon plateau age of ~ 252 (252.7 ± 1.5) Ma and a ~ 239 Ma total fusion age from a Taimyr lava and intrusive sample, respectively, confirming that volcanism is only partly contemporaneous with the activity of the Siberian LIP. Although this is in agreement with previous interpretations, we argue that the age difference between both events is only ~ 13 Ma and probably less (~ 5 Ma) although further investigation of the relationship is required. Our data allow correlation with distinct Noril'sk members and most importantly to the ore-bearing (Ni-Cu) intrusions implying that whole rock chemistry could have value as a prospecting tool in Taimyr.

  4. Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury (United States)

    Namur, Olivier; Charlier, Bernard; Holtz, Francois; Cartier, Camille; McCammon, Catherine


    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.

  5. The Sondalo gabbro contact aureole (Campo unit, Eastern Alps): implications for mid-crustal mafic magma emplacement (United States)

    Petri, B.; Mohn, G.; Štípská, P.; Schulmann, K.; Manatschal, G.


    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.

  6. Record of complex scoria cone eruptive activity at Red Mountain, Arizona, USA, and implications for monogenetic mafic volcanoes (United States)

    Riggs, N. R.; Duffield, W. A.


    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.

  7. 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


    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.

  8. Late Cretaceous remagnetization of Proterozoic mafic dikes, southern Highland Mountains, southwestern Montana: A paleomagnetic and 40Ar/39Ar study (United States)

    Harlan, S.S.; Geissman, J.W.; Snee, L.W.; Reynolds, R.L.


    Paleomagnetic results from Early Proterozoic metabasite sills and Middle Proterozoic diabase dikes from the southern Highland Mountains of southwestern Montana give well-defined, dual-polarity magnetizations that are statistically identical to those from a small Late Cretaceous pluton that cuts the dikes. The concordance of paleomagnetic directions from rocks of three widely separated ages indicates that the Proterozoic rocks were remagnetized, probably during Late Cretaceous time. Paleomagnetic, rock magnetic, and petrographic observations from the metabasite and diabase samples indicate that remanence is carried primarily by low-Ti magnetite. Combining virtual geomagnetic poles from metabasite sills, diabase dikes, and the Late Cretaceous pluton, we obtain a paleomagnetic pole at 85.5??N, 310.7??E (K = 19.9, A95 = 9.1??, N = 14 sites) that is similar to a reference pole from the 74 Ma Adel Mountain Volcanics of western Montana. Biotite and hornblende 40Ar/39Ar isotopic dates from host basement geneiss and a hornblende from a remagnetized metabasite sill yield ages of ca. 1800 Ma; these dates probably record cooling of the southern Highland Mountains following high-grade metamorphism at 1.9-1.8 Ga. The gneiss and metabasite age spectra show virtually no evidence of disturbance, indicating that the basement rocks were never heated to temperatures sufficient to cause even partial resetting of their argon systems. Thus, the overprint magnetization of the Highland Mountains rocks is not a thermoremanent magnetization acquired during conductive cooling of nearby Late Cretaceous plutons. Remagnetization of the metabasite sills and diabase dikes was probably caused by localized thermochemical and thermoviscous effects during circulation of Late Cretaceous hydrothermal fluids related to epithermal mineralization. The absence of significant disturbance to the 40Ar/39Ar age spectrum from the remagnetized metabasite hornblende indicates that some secondary magnetizations may go unrecognized and undated, even if 40Ar/39Ar dating is applied.

  9. Amphibolites and other metamorphic mafic rocks of the blastomylonitic graben in Western Galicia, NW Spain: field relations and petrography


    Arps, C.E.S.


    Within the strongly migmatized axial zone of the Hesperian massif in western Galicia a graben-like structure has been distinguished, characterized essentially by the presence of non-migmatic rocks that comprise orthogneisses with blastomylonitic textures, leucocratic gneisses, plagioclase-blastbearing paragneisses, pelitic schists, and numerous amphibolitic layers and lenses. In the southern and central part of the graben and at the borders in the north the majority of the amphibolites are me...

  10. The Formation of Carbonate Minerals and the Mobility of Heavy Metals during Water-CO2-Mafic Rock Interactions

    DEFF Research Database (Denmark)

    Olsson, Jonas

    basaltic host rock and liberates cations. Ideally, the cations react with the dissolved CO2 and form long time stable carbonate minerals. However, dissolution of the basaltic rock can lead to mobility of toxic metals, which is a potential threat to groundwater supplies and surface waters. Besides carbonate...... with the process of carbonation, and (2) they can form a passivating layer, which inhibit dissolution of the basaltic material and slow down the carbonation process. The purpose of this thesis was to identify formation products, relevant to CarbFix, and assess their ability to immobilize toxic metals...... analyzed 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...

  11. Sulfide minerals as new Sm-Nd geochronometers for ore genesis dating of mafic-ultramafic layered intrusions (United States)

    Serov, Pavel; Ekimova, Nadezhda; Bayanova, Tamara


    The main method of dating the ore process was the Re-Os method of sulfides (Luck, Allegre, 1983; Walker et. al., 1991). However, studies of Re-Os systematics of sulfide minerals do not always give the correct ages and showing the disturbances of the Re-Os systematics. At the same time, Sm-Nd age of sulfides in good agreement with the U-Pb dating on zircon and baddeleyite and suggests that the Sm-Nd system of sulfides is more resistant to secondary alteration processes. Our studies have shown that along with rock-forming, ore minerals (sulfides) can be used to determine the ore genesis time of industrially important geological sites, since exactly with the sulfides the industry Pt-Pd mineralization is closely connected. The Sm-Nd investigations steadily employ new minerals-geochronometers. Of these, sulfides of PGE-bearing layered intrusions are quite important in terms of dating the process of ore origin. Studying the REE distribution in the sulfides of MOR hydrothermal sources has shown possible REE presence in the sulfide lattice (Rimskaya-Korsakova et. al., 2003). These are difficult to carry out because the concentrations of Sm and Nd isotopes in sulfides are much lower than chondrites (Rimskaya-Korsakova et. al., 2003). For the first time in Russia with sulfide and rock-forming minerals and WR in Sm-Nd method have been dated impregnated and brecciform ores of the following objects: Pilguyarvi Cu-Ni deposits, Pechenga (1965±87 Ma); impregnated (2433±83 Ma) and redeposited (1903±24 Ma) ores of Ahmavaara intrusion (Finland); ore gabbronorites of Penikat PGE-bearing layered intrusion (2426±38 Ma (Ekimova, 2011); Pt-Pd gabbro-pegmatite ores (2476± 41 Ma, which agrees with the U-Pb zircon age - 2470±9 Ma (Bayanova, 2004) and gabbronorites (2483±86 Ma) of PGE Kievei deposit and Fedorova Tundra metagabbroids (2494±54 Ma); Monchetundra gabbronorites - 2489±49 Ma. In (Kong et. al., 2000) sulfides from two metamorphosed chondrites studied by instrumental neutron activation analysis (INAA) and ion probe. As shown, the level of REE in the sulfide phase determined by the ion probe is quite similar to that obtained by INAA. Although the concentrations of REE in the enstatite and the Fe, Si, Cr-rich inclusions are comparable to those in sulfide, estimates based on mass balance calculations show that the silicate inclusions would not noticeably contribute to the REE budget in sulfides (Kong et. al., 2000). These studies were supported by the RFBR 13-05-00493, OFI-M 13-05-12055, State Earth Division Program #4 and IGCP-599.

  12. Mechanisms of differentiation in shallow mafic alkaline intrusions, as illustrated in the Big Bend area, western Texas (United States)

    Carman, Max F.


    Syenitic bodies are a common feature in alkaline sills and laccoliths that range in composition from syenogabbroic to syenodioritic. The syenitic bodies are generally accepted to be the result of in-situ differentiation. Such bodies are usually called segregations, but relatively little discussion is given to the actual ways they may form. Subhorizontal sheets or layers are most common, although rounded ocelli and vertically elongated cylindroidal forms are also common. These are all systematically arranged in the intrusions. Such features are found in at least ten sills in the Big Bend area of Texas, and are reported as well in Montana, Utah, Australia, Sakhalin, Scotland and New Zealand. Detailed chemical and mineralogical analyses demonstrate crystal fractionation very convincingly for the generation of syenitic liquids that form the bodies. The analyses also allow the calculation of viscosities, cooling time and mineral settling rates in the sill studied most thoroughly. These factors indicate, or are compatible with, proposed mechanisms for the formation of syenite bodies. In many intrusions there is a bimodal distribution of syenite compositions; one type is relatively plagioclase rich and the other type is plagioclase poor. Mass balance calculations on several intrusions show that a residual liquid of plagioclase-rich composition will form after about 30% of the parent magma has crystallized, whereas a residual liquid of plagioclase-poor composition will form only after about 50% of the original magma has crystallized. The several mechanisms by which plagioclase-rich residual liquids are aggregated into the different forms of syenite bodies include localized crystal settling and sagging of a crystaline framework on a scale of tens of centimeters to a meter, within an upper solidification front; formation of cylindroidal columns of syenitic differentiate in a crystal mush within a lower solidification front, and diapiric rise of such masses. After the amount of magma crystallized reaches 50% or more, rupture of a rigid crystalline framework occurs through the processes of contraction upon cooling, shearing caused by deformation, and expansion of bubbles in the interstitial residual liquid, while plagioclase-poor differentiate flows into spaces created in these processes. Important for the effectiveness of these processes is the buildup of volatiles in the residual liquids, which results from crystallization of anhydrous minerals, that causes second boiling and lowering of the viscosity of the liquids.

  13. Clay mineralogy and geochemistry of the soils derived from metamorphic and mafic igneous parent rocks in Lahijan area

    International Nuclear Information System (INIS)

    The mineralogical and geochemical composition of the soils of three representative pedons formed on basaltic andesite, andesitic basalt and phyllite were investigated. Results by x-ray diffraction showed that progressive weathering of rocks have been marked by gradual accumulation of Al, Fe, Ti, Mg, H3O+ and depletion of Na, K, Ca and Si in the soil; although, predominant clay, loss and gain trend of elements was different on the various rocks. Based on x-ray diffraction analysis, minerals in basaltic andesite and andesitic basalt were similar but, the intensity of mica to smectite or vermiculite transformation for latter was relatively higher than the former. This process revealed the degradation mineral because of two reasons: (i) - smectite and vermiculite increased whereas mica decreased in surface horizons. (i i)-Irregular mixed layer of mica-smectite or vermiculite was present in deeper part (170 cm) of the soils from andesitic basalt but shallower depth (75 em) of the soils from basaltic andesite. Clay minerals in phyllite were mica and chlorite that stratified with vermiculite. However, the absence of smectite in phyllite might be attributed to more acidic condition or position of the Fe ion in the mineral lattice of chlorite (higher Fe in the interlayer hydroxide sheet)

  14. Extensional tectonics during the igneous emplacement of the mafic-ultramafic rocks of the Barberton greenstone belt (United States)

    Dewit, M. J.


    The simatic rocks (Onverwacht Group) of the Barberton greenstone belt are part of the Jamestown ophiolite complex. This ophiolite, together with its thick sedimentary cover occupies a complex thrust belt. Field studies have identified two types of early faults which are entirely confined to the simatic rocks and are deformed by the later thrusts and associated folds. The first type of fault (F1a) is regional and always occurs in the simatic rocks along and parallel to the lower contacts of the ophiolite-related cherts (Middle Marker and equivalent layers). These fault zones have previously been referred to both as flaser-banded gneisses and as weathering horizons. In general the zones range between 1-30m in thickness. Displacements along these zones are difficult to estimate, but may be in the order of 1-100 km. The structures indicate that the faults formed close to horizontal, during extensional shear and were therefore low angle normal faults. F1a zones overlap in age with the formation of the ophiolite complex. The second type of faults (F1b) are vertical brittle-ductile shear zones, which crosscut the complex at variable angles and cannot always be traced from plutonic to overlying extrusive (pillowed) simatic rocks. F1b zones are also apparently of penecontemporaneous origin with the intrusive-extrusive igneous processs. F1b zones may either represent transform fault-type activity or represent root zones (steepened extensions) of F1a zones. Both fault types indicate extensive deformation in the rocks of the greenstone belt prior to compressional overthrust tectonics.

  15. Metamorphic chlorite and "vermiculitic" phases in mafic dikes from the Maláguide Complex (Betic Cordillera, Spain)

    Czech Academy of Sciences Publication Activity Database

    Ruiz Cruz, M. D.; Novák, Jiří Karel


    Roč. 15, č. 1 (2003), s. 1-14. ISSN 0935-1221 Grant ostatní: Ministerio de Educación y Cultura (ES) BTE-2000-1150; Research Group(ES) RNM-199 Institutional research plan: CEZ:AV0Z3013912 Keywords : low-grade metamorphism * vermiculite * Betic Cordillera Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.185, year: 2003

  16. Tectonic Significance Of Structures On Ellef Ringnes Island, Queen Elizabeth Islands, Canada (United States)

    Evenchick, C.


    Ellef Ringnes Island lies near the centre of the Sverdrup Basin. Bedrock consists of Jurassic and Cretaceous clastic rocks of the Sverdrup Basin that are pierced by evaporite diapirs and intruded by mafic dykes and sills. Recent bedrock mapping on the island provides new detail of structures and newly recognized magmatism that provide insight into Cretaceous tectonism of the region. The distribution of map units on the island is controlled at the largest scale by gentle southeastward dip towards the centre of the Sverdrup Basin. Two suites of folds affect all strata. Folds interpreted to be associated with Eurekan deformation trend northwest and have wavelengths of several kilometres. Smaller scale folds appear to be associated with dip-slip faults and commonly trend northeast. Strata are offset by four suites of geographically and geometrically distinct faults. Faults spatially associated with evaporite diapirs occur in radial patterns around the diapirs and offset bounding Cretaceous strata. They are interpreted to have formed during active diapirism, and their history, revealed by differences in the thickness of stratigraphic units within and outside of grabens, elucidates the Cretaceous history of evaporite diapirism. The remaining three suites of faults each have consistent strike and are geographically restricted. The most widespread suite strikes north-northeast. These faults are interpreted to be extensional. They are parallel with the majority of dykes in the same area, as well as prominent aeromagnetic anomalies interpreted to be dykes in the subsurface that fed the widespread sills of the northern island. Possible explanations for this extension and mafic magmatism include association with the Alpha Ridge, as postulated previously, or a component of sinistral movement along the Amerasia Basin margin during the late Early and early Late Cretaceous. Other suites of folds include an east-trending suite of dip-slip faults at the northern limit of the island

  17. Polyphase deformation of a Paleozoic metamorphosed subduction-accretionary complex in Beishan Orogen, southern Altaids (United States)

    Song, Dongfang; Xiao, Wenjiao


    The Lebaquan Complex in central Beishan plays a significant role in understanding the subduction-accretion-collision processes of the Beishan orogenic collage, southern Altaids. This complex is a polyphase deformed upper greenschist to lower amphibolite facies metamorphic rock assemblages composed of metasedimentary sequence, gneissic plutons, metacherts, amphibolites and marbles, with multiple generations of syn-tectonic leucogranite-pegmatite and post-tectonic mafic dykes. Lithologic and geochemical characteristics show the Lebaquan Complex is a forearc-arc complex. Four stages of deformation can be recognized for the Lebaquan Complex. The D1 deformation is defined by pervasively developed foliations (S1) defined by alternative metamorphic layering and intrafolia isoclinal folds of quartz veins (F1). The D2 deformation is indicated by crenulation cleavage (S2) mainly developed in the schists, extensively-developed tight to open folds and asymmetric folds (F2) and pinch and swell structures. The D3 deformation is characterized by high-strain ductile shearing, which modified earlier structures. Small-scale asymmetric folds, σ-type porphyroclasts and S-C fabrics indicate dextral sense of shearing in east-west direction. The D4 deformation is represented by ductile to brittle structures including open/gentle folds, kink folds and small scale thrust faults which overprint earlier deformations. The overall deformation of this complex indicates a geodynamic setting change from initial north-south directed strong compression to later east-west directed transpression and finally extension. LA-ICP-MS zircon U-Pb dating was performed on key lithologies. Youngest age peak of detrital zircons from a garnet-mica-quartz schist is ~424 Ma, constraining the depositional age for the protolith of the metasedimentary sequence. A syn-deformation leucogranitic dyke that underwent D2 but did not experience D1 and a post-deformation mafic dyke that intrudes all the lithologies were

  18. Southward trench migration at ∼130-120 Ma caused accretion of the Neo-Tethyan forearc lithosphere in Tibetan ophiolites (United States)

    Xiong, Qing; Griffin, William L.; Zheng, Jian-Ping; O'Reilly, Suzanne Y.; Pearson, Norman J.; Xu, Bo; Belousova, Elena A.


    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

  19. Back-Arc Extension in the Southern Andes: A Review and Critical Reappraisal (United States)

    Dalziel, I. W. D.


    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.

  20. "Fruits", "fags", and "dykes": the portrayal of gay/lesbian identity in "nance" jokes of the 50s and 60s. (United States)

    Nardi, Peter M; Stoller, Nancy E


    What is humorous and how it is interpreted very much depends on the norms and values of a culture at a particular point in time, the characteristics of who is telling jokes, and the makeup of the audience. This article presents archival material and an analysis of an outsider's jokes about gays and lesbians. These were told to primarily heterosexual audiences by a heterosexual comic. They reveal the assumptions Americans held about gays and lesbians throughout the 1950s, 1960s, and a few years into the mid-1970s, when most of these jokes were compiled. Although generalizations about gay/lesbian humor in that period cannot be made from one person's private collection of nearly 1,000 jokes, they do reveal several clear patterns: Much of the humor about male homosexuality is used to debase men and their masculinity, by making them passive, feminine, or weak, except for their hypersexuality. The women are also depicted in the jokes as sexually eager, especially to give oral sex to possibly straight women or acting in the male insertor role. Rarely were the gay/lesbian jokes focused on political issues of discrimination, oppression, or romantic relationships. PMID:19042278

  1. 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)

  2. Geochemistry of sapphirine-apatite-calcite-bearing gabbroic dykes from the Finero Phlogopite Peridotite (Ivrea-Verbano Zone): evidence for multistage interaction with the ambient peridotite (United States)

    Tommaso, Giovanardi; Alberto, Zanetti; Maurizio, Mazzucchelli; Tomoaki, Morishita; Antonio, Langone


    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.

  3. The 2005 Ilan earthquake doublet and seismic crisis in northeastern Taiwan: evidence for dyke intrusion associated with on-land propagation of the Okinawa Trough


    Lai, Kuang-Yin; Chen, Yue-Gau; Wu, Yih-Min; Avouac, Jean-Philippe; Kuo, Yu-Ting; WANG Yu; Chang, Chien-Hsin; Lin , Kuan-Chuan


    Northern Taiwan underwent mountain building in the early stage of the Taiwan orogeny but is currently subjected to post-collisional crustal extension. It may be related to gravitational collapse or to the rifting of the Okinawa Trough, which lies offshore northeastern Taiwan. The Ilan Plain, northeastern Taiwan, which is bounded by the normal fault systems and filled up with thick Pliocene–Pleistocene sedimentary sequences, formed under such an extension environment. Over there on 2005 March ...

  4. Variations in magnetic anisotropy and opaque mineralogy along a kilometer deep profile within a vertical dyke of the syenogranite porphyry at Cínovec (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Hrouda, F.; Chlupáčová, M.; Novák, Jiří Karel


    Roč. 113, 1/2 (2002), s. 37-47. ISSN 0377-0273 R&D Projects: GA ČR GA205/95/0149; GA ČR GA205/96/0272; GA AV ČR IAA3013903 Keywords : magnetic anisotropy * syenogranite porphyry * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.974, year: 2002

  5. Rhyolites from the Roztoky Intrusive Centre, České středohoří Mts.: Xenoliths or Dyke Differentiates?

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Pivec, Edvín; Höhndorf, A.; Balogh, K.; Bendl, J.; Rutšek, J.


    Roč. 60, č. 4 (2000), s. 327-352. ISSN 0009-2819 R&D Projects: GA AV ČR IAA3111601 Grant ostatní: OTKA Foundation(HU) 014961; CZ-HU Hungarian-Czech Project(XC) "Comparative volcanostratigraphy of the Neodic volcanism of the Bohemian Massif and the Pannonian Basin"(Institute of Nuclear Research, Debrecen, and Institute of Geology of the Czech Academy of Sciences, Praha Subject RIV: DD - Geochemistry Impact factor: 0.147, year: 2000

  6. Roztoky intrusive centre in the České středohoří Mts.: Differentiation, emplacement, distribution, orientation and age of dyke series

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Balogh, K.


    Roč. 51, č. 6 (2000), s. 383-397. ISSN 1335-0552 R&D Projects: GA MK RK99P03OMG035 Grant ostatní: Hungarian Science Foundation(HU) T014961 Institutional research plan: CEZ:AV0Z3013912 Keywords : geochemistry * structural setting * volcanic center Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.156, year: 2000

  7. 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


    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

  8. Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia (United States)

    José Fernández, Francisco; Llana-Fúnez, Sergio; Valverde-Vaquero, Pablo; Marcos, Alberto; Castiñeiras, Pedro


    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

  9. Long hard road from Nuna to Rodinia (United States)

    Pisarevsky, Sergei


    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

  10. Origin of the Rubian carbonate-hosted magnesite deposit, Galicia, NW Spain: mineralogical, REE, fluid inclusion and isotope evidence (United States)

    Kilias, Stephanos P.; Pozo, Manuel; Bustillo, Manuel; Stamatakis, Michael G.; Calvo, José P.


    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

  11. The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar (United States)

    Cucciniello, C.; Tucker, R. D.; Jourdan, F.; Melluso, L.; Morra, V.


    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).

  12. 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


    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

  13. Geology of the Eoarchean, > 3.95 Ga, Nulliak supracrustal rocks in the Saglek Block, northern Labrador, Canada: The oldest geological evidence for plate tectonics (United States)

    Komiya, Tsuyoshi; Yamamoto, Shinji; Aoki, Shogo; Sawaki, Yusuke; Ishikawa, Akira; Tashiro, Takayuki; Koshida, Keiko; Shimojo, Masanori; Aoki, Kazumasa; Collerson, Kenneth D.


    The Earth is a unique planet, which has been highly evolved, diversified and complicated through geologic time, and underwent many key events, including giant impact, magma ocean, core formation, large-scale mantle differentiation and late heavy bombardment, especially in its dawn. But, our knowledge of early Earth is limited due to the lack of the Hadean supracrustal rocks. The supracrustal rocks with the Eoarchean ages provide key evidence for the Earth's early evolution, but few supracrustal rocks have been comprehensively investigated. Therefore, we mapped in seven areas of the Saglek Block, northern Labrador, where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses. Early studies suggested that some of them have the Mesoarchean ages because of the lack of the Mesoarchean Saglek dyke, but we found the Saglek dykes in the areas to recognize the Eoarchean Nulliak supracrustal rocks and Uivak Gneiss in all the areas. Recent reassessment of U-Pb dating and cathodoluminescence observation of zircons from the oldest suites of the Uivak Gneiss showed that the Uivak Gneiss has the Eoarchean age, > 3.95 Ga, and forms the Iqaluk-Uivak Gneiss series. Because our geological survey clearly showed that the Iqaluk-Uivak Gneisses were intruded into the Nulliak supracrustal belts, the Nulliak supracrustal rocks are the oldest supracrustal rock in the world. The supracrustal belts consist of piles of fault-bounded blocks, which are composed of the ultramafic rocks, mafic rocks and sedimentary rocks in ascending order, similar to modern ocean plate stratigraphy (OPS). In addition, small-scale duplex structures are found over the areas. The presence of duplex structure and OPS indicates that the > 3.95 Ga Nulliak supracrustal belts originate from an accretionary complex. The presence of the accretionary complex, ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early Earth.

  14. Geochronology and geochemistry of the Early Cretaceous Jigongshan and Qijianfeng batholiths in the Tongbai orogen, central China: implications for lower crustal delamination (United States)

    Zhang, Jinyang; Ma, Changqian; Li, Jianwei; She, Zhenbing; Zhang, Chao


    The Jigongshan and Qijianfeng batholiths in the Tongbai orogen consist mainly of porphyritic hornblende-biotite monzogranite, biotite monzogranite, and biotite syenogranite, which are variably intruded by lamprophyre, diorite, and syenogranite dykes. Mafic microgranular enclaves commonly occur in the hornblende-biotite monzogranite, whereas surmicaceous enclaves are found in the biotite monzogranite. Both batholiths have zircon U-Pb ages ranging from ca. 139 to 120 Ma, indicating their emplacement in the Early Cretaceous. The hornblende-biotite monzogranite has an adakitic affinity marked by relatively high Sr/Y and (La/Yb) N ratios, lack of Eu anomalies, low MgO and Ni contents, and Na2O > K2O. Its chemical compositions, combined with enriched Sr-Nd isotopic signatures, suggest formation by dehydration melting of mafic rocks in a thickened lower crust. This thickened crust resulted from the Permo-Triassic subduction-collision between the North China and South China blocks and persisted until the Early Cretaceous. The biotite monzogranite and biotite syenogranite have low Al2O3, CaO, and Sr contents, low Rb/Sr, FeOt/MgO, and (Na2O + K2O)/CaO ratios, and flat HREE patterns with moderate to weak Eu anomalies. They were produced by partial melting of crustal materials under relatively low pressure. Partial melting at different crustal levels could have significantly contributed to mechanical weakening of the crust. The diorite and lamprophyre dykes show linear trends between SiO2 and major or trace elements on Harker diagrams, with two lamprophyre samples containing normative nepheline and olivine. These rocks have high La/Yb and Dy/Yb ratios, both displaying co-variation with contents of Yb. They were originated from relatively deep lithospheric mantle followed by fractionation of olivine + clinopyroxene + apatite + Fe-Ti oxides. Extensive partial melting in the lithospheric mantle indicates relatively high temperatures at this level. We suggest that the presence of

  15. The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination? (United States)

    Harris, Chris; le Roux, Petrus; Cochrane, Ryan; Martin, Laure; Duncan, Andrew R.; Marsh, Julian S.; le Roex, Anton P.; Class, Cornelia


    Oxygen isotope compositions of Karoo and Etendeka large igneous province (LIP) picrites and picrite basalts are presented to constrain the effects of crustal contamination versus mantle source variation. Olivine and orthopyroxene phenocrysts from lavas and dykes (Mg# 64-80) from the Tuli and Mwenezi (Nuanetsi) regions of the ca 180 Ma Karoo LIP have δ18O values that range from 6.0 to 6.7 ‰. They appear to have crystallized from magmas having δ18O values about 1-1.5 ‰ higher than expected in an entirely mantle-derived magma. Olivines from picrite and picrite basalt dykes from the ca 135 Ma Etendeka LIP of Namibia and Karoo-age picrite dykes from Dronning Maud Land, Antarctica, do not have such elevated δ18O values. A range of δ18O values from 4.9 to 6.0 ‰, and good correlations between δ18O value and Sr, Nd and Pb isotope ratios for the Etendeka picrites are consistent with previously proposed models of crustal contamination. Explanations for the high δ18O values in Tuli/Mwenezi picrites are limited to (1) alteration, (2) crustal contamination, and (3) derivation from mantle with an abnormally high δ18O. Previously, a variety of models that range from crustal contamination to derivation from the `enriched' mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as K, and average ɛNd and ɛSr values of -8 and +16 in Mwenezi (Nuanetsi) picrites. However, the primitive character of the magmas (Mg# 73), combined with the lack of correlation between δ18O values and radiogenic isotopic compositions, MgO content, or Mg# is inconsistent with crustal contamination. Thus, an 18O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated. High δ18O values are accompanied by negative Nb and Ta anomalies, consistent with the involvement of the mantle lithosphere, whereas the high δ18O themselves are consistent with an eclogitic source. Magma δ18

  16. India's changing place in global Proterozoic reconstructions: A review of geochronologic constraints and paleomagnetic poles from the Dharwar, Bundelkhand and Marwar cratons (United States)

    Pradhan, Vimal R.; Meert, Joseph G.; Pandit, Manoj K.; Kamenov, George; Gregory, Laura C.; Malone, Shawn J.


    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.

  17. Aeromagnetic interpretation in the south-central Zimbabwe Craton: (reappraisal of) crustal structure and tectonic implications (United States)

    Ranganai, Rubeni T.; Whaler, Kathryn A.; Ebinger, Cynthia J.


    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

  18. 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


    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 alteratio