Sample records for amphibolitised mafic dykes

  1. Mafic dykes at the southwestern margin of Eastern Ghats belt ...

    Indian Academy of Sciences (India)

    the dykes indicate that they preserved time-integrated LREE enrichment. In view of the chemical signatures of OIB source, the mafic dykes could as well be related to continental rifting, around. 1.3 Ga, which may have been initiated by intra-plate volcanism. 1. Introduction. Mafic dyke swarms are common in most Archaean.

  2. Mafic dykes at the southwestern margin of Eastern Ghats belt ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 119; Issue 6. Mafic dykes at the southwestern margin of ... 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.

  3. Mineral Associations In The Boussouma Post Birimian Mafic Dyke ...

    African Journals Online (AJOL)

    Mineral Associations In The Boussouma Post Birimian Mafic Dyke And Their Petrogenetic Significance (Burkina Faso, West-African Craton) ... temperature hydrous phases. Keywords: Dolerite, micro-analysis, minerals, tholeiite, distension, geothermometry. Global Journal of Geological Sciences Vol. 6 (2) 2008: pp. 157-174 ...

  4. 1.99 Ga mafic dykes of the Lewisian Gneiss Complex of Scotland: An upper age limit for the Palaeoproterozoic Loch Maree Group (United States)

    Baker, Thomas; Prave, Tony; Spencer, Christopher


    Mafic dyke swarms are often used as geochronological markers, as they are widespread and emplaced over short timespans. The ca. 2.4 Ga Scourie dyke swarm is one such example that has played a key role in understanding the complex tectonic and metamorphic history of the Lewisian Gneiss Complex of Scotland (LGC), part of the North Atlantic Craton (NAC). The LGC consists of Archean and Palaeoproterozoic terranes that experienced polyphase deformation prior to their assembly at ca. 1.8 Ga. Zircons separated from a doleritic dyke from the Gairloch terrane have yielded a concordant U-Th-Pb age (1,989 +4.3 / -0.99 Ma) using the ID-TIMS method. The doleritic dyke is emplaced in Lewisian gneiss that experienced both granulite and amphibolite-facies metamorphism. Partial recrystallisation and amphibolitisation of the dyke demonstrate that it pre-dates the most recent (Laxfordian) amphibolite-facies metamorphic event. The age obtained from the dyke overlaps the U-Pb age of a previously dated olivine gabbro dyke from the Assynt terrane (1,992 Ma). These combined ages provide strong corroborating evidence for a ca. 2.0 Ga mafic dyke swarm event, distinct from the older ca. 2.4 Ga Scourie dyke event known from elsewhere in the LGC. The existence of a ca. 2.0 Ga mafic dyke swarm provides an upper age limit for the Loch Maree Group (LMG), a Palaeoproterozoic succession of metasediment and metavolcanic rocks that overlie the LGC and which are not cross-cut by the Scourie dykes. This study proposes that a period of crustal extension took place in the region at ca. 2.0 Ga. Later, subduction may have resulted in the accretion of the LMG and the adjacent Ard Gneiss, which has previously been regarded as a magmatic arc. The ca. 1.9 Ga age of the earliest stage of the Laxfordian metamorphic event, which affected the LMG, could therefore mark the onset of collision. This sequence of events can be correlated with other coeval areas of the NAC, including the Nagssugtoqidian mobile belt of

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


    Randive Kirtikumar; Hurai Vratislav


    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 xen...

  6. Paleomagnetic Results of the 925 Ma Mafic Dykes From the North China Craton: Implications for the Neoproterozoic Paleogeography of Rodinia (United States)

    Zhao, X.; Peng, P.


    Precambrian mafic dyke swarms are useful geologic records for Neoproterozoic paleogeographic reconstruction. We present a paleomagnetic study of the 925 Ma Dashigou dyke swarm from 3 widely separated locations in the central and northern parts of the North China Craton, which are previously unsampled regions. Stepwise thermal and alternating field demagnetizations were successful in isolating two magnetic components. The lower unblocking temperature component represents the recent Earth magnetic field. The higher unblocking temperature component is the characteristic remanent magnetization and yields positive baked contact test. Results from detailed rock magnetic measurements corroborate the demagnetization behavior and show that titanomagnetites are the main magnetic carrier in these rocks. There was no regional event that has reset the remanent magnetization of all the dyke sites, as indicated by the magnetization directions of both overlying and underlying strata. The similarity of the virtual paleomagnetic poles for the 3 sampled regions also argues that the characteristic remanent magnetizations are primary magnetization when the dykes were emplaced. The paleomagnetic poles from the Dashigou dyke swarm of the North China Craton are not similar to those of the identical aged Bahia dykes from the São Francisco Craton, Brazil, indicating that these mafic dykes may be not parts of a common regional magmatic event that affected North China Craton and NE Brazil at about 925 Ma.

  7. The structure of the Okavango giant mafic dyke swarm in the Karoo magmatic province of North Botswana (United States)

    Le Gall, B.; Tshoso, G.; Tiercelin, J. J.; Dyment, J.; Aubourg, C.; Feraud, G.; Jourdan, F.; Bertrand, H.


    Field structural measurements combined to magnetic dataset (including both aero- and ground magnetic records) allow a systematic investigation of the structure of the Okavango giant (2000 x 100 km) mafic dyke swarm in N Botswana. The results are discussed about a 55 km-long projected section lying perpendicular to the densest zone of the swarm and cutting through Proterozoic granito-gneissic host-rocks. A total dyke population of 423 (magnetic records) or 171 (field data) individual intrusions is identified and consists principally of basalts and dolerites. New high-precision dating (Jourdan et al., this congress) demonstrates the composite nature of the Okavango swarm that includes Karoo dykes (70%) and additional (30%) Proterozoic intrusions. The two dyke populations lie with a similar strike and show no discriminant petro-structural features in the field. These new results make it difficult 1) discriminating Karoo versus Proterozoic dyke groups within the total population derived from magnetics, and 2) defining their respective structural characteristics. About the Karoo dyke population (360 intrusions), field structural observations help to constrain the statistical analysis of some of its geometrical parameters, such as the strike (N110°E), dip (vertical), lenght (ca. 5 km), thickness (18-20 m), spacing, or direction of dyke opening. The dyke-induced crustal dilatation is estimated to 6-10% across the 55 km-long reference section. Structural observations also emphazise the control exerted by preexisting basement fabrics (brittle joints and dykes) on Karoo dyke emplacement. Synmagmatic deformation is restricted to wall-parallel tensile joint networks with no evidence for extensional faulting. The Karoo part of the Okavango giant dyke swam is inferred to have been emplaced under an unidirectional extensional stress field (N70°E). Furthermore, analyzing the anisotropy of magnetic susceptibility of a number of dykes (Tshoso et al., this congress) indicates an

  8. Plagioclase crystal size distribution in some tholeiitic mafic dykes in Cabo Frio-Buzios, Rio de Janeiro, Brazil (United States)

    Ngonge, E. Donald; Archanjo, C. J.; Hollanda, M. H. B. M.


    Crystal size distribution (CSD) has been constrained in plagioclase in two mafic dykes of the Conchas Beach and one at the Lagoinha Beach in the Cabo Frio-Buzios NE-trending dyke swarm. At contact with the metamorphic basement the texture is fine-grained and microporphyritic and intergranular at the center of the larger dykes. Samples were collected at the margins and at the center of the dykes. The plagioclase average characteristic size (C) varies from 0.07 to 0.13 mm at the margins of the narrow dykes and from 0.09 to 0.20 mm at the margins of the larger dyke. At the center of the Lagoinha and Conchas dykes C varies from 0.19 ± 0.02 mm and 0.60 ± 0.07 mm respectively. The CSDs at the dyke margins are concave-up. At the center of the larger Conchas dyke (8.2 m), the CSD is log-linear, consistent with simple steady-state crystallization pattern. From the mineralogy the plagioclase phenocrysts have a high An content (bytownite-labradorite) than the groundmass grains (labradorite-andesine). At the margins olivine is richer in Fo than at the center, and respectively, pyroxene is richer in Ca. These results indicate that the chilled margin is more mafic than the center suggesting a normal chemical evolution in a cooling magma that ascended upward from depths by Newtonian to pseudoplastic flow. The concave-up CSDs probably depict heterogeneous crystallization rates possibly induced by depressurization during the magma ascent followed by rapid cooling. The log-linear CSD pattern at the center of the Conchas dyke (8.2 m width) is attributed to a higher residence time of the magma which favors the processes of chemical diffusion and textural re-equilibration. From the calculated cooling rates the larger Conchas dyke (8.2 m in width) would be completely crystallized (at ~ 900 °C) in about 2 years.

  9. Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications (United States)

    Banerjee, Ayoti; Banerjee, Meenakshi; Dutta, Upama; Sengupta, Pulak; Bhui, Uttam K.; Rajagopal, Anand; Mukhopadhyay, Dhruba


    Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications Metamorphosed garnetiferous mafic dykes from Southern Granulite Terrain (SGT) are found intruding the high grade Archaean-Palaeoproterozoic felsic orthogneiss and their retrogressed equivalent. They contain phenocrysts of clinopyroxene (Cpx) and plagioclase (Pl) that preserve ophitic, subophitic and intergranular textures. The clinopyroxene contains closely spaced cleavage-parallel exsolution lamellae of orthopyroxene (Opx) and tiny rods of Fe-Ti oxides. Orthopyroxene is also found around clinopyroxene as granular exsolution. Large grains of Fe-Ti oxides occur within the interstitial space. Garnet (Grt) and quartz (Qtz) form at the contact of plagioclase and clinopyroxene. The product minerals are found as symplectite and/or corona rimming the reactants. In the corona, quartz always occurs near clinopyroxene whereas garnet forms close to the plagioclase. The proportions of garnet and quartz in symplectite are fairly constant and range from 75:25 to 70:30 (vol %). Similar coronitic texture is exhibited by amphibole (Amp) and quartz. Thin amphibole+quartz corona forms between plagioclase and clinopyroxene where amphibole occurs near plagioclase and quartz near clinopyroxene, though the rock is dominated by garnet over amphibole in the corona. Corona of garnet/amphibole is also found on Fe-Ti oxides at the contact of plagioclase and the products show TiO2 enrichement when they occur near Fe-Ti oxides. Formation of hydrous amphibole from anhydrous minerals necessitates the system to be open to H2O. Additionally, balanced chemical reactions for Pl+Cpx=Grt+Qtz and Pl+Cpx=Amp+Qtz require Fe+2 incorporation to explain the observed volume proportion of the product minerals. Formation of garnet/amphibole near plagioclase and quartz near clinopyroxene indicate restricted mobility of Al and Si within the reaction domain. Preferential enrichment of TiO2

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

    DEFF Research Database (Denmark)

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


    were derived at shallow depth from a fluid-enriched, relatively depleted, mantle source, but some have a component derived from mantle with residual garnet. They are suggested to have formed in a back-arc environment.The more than 200 narrow dykes are olivine tholeiites (some picritic), alkali basalts...

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

    Directory of Open Access Journals (Sweden)

    Randive Kirtikumar


    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.

  12. Upper Triassic mafic dykes of Lake Nyos, Cameroon (West Africa) I: K-Ar age evidence within the context of Cameroon Line magmatism, and the tectonic significance (United States)

    Aka, Festus Tongwa; Hasegawa, Takeshi; Nche, Linus Anye; Asaah, Asobo Nkengmatia Elvis; Mimba, Mumbfu Ernestine; Teitchou, Isidore; Ngwa, Caroline; Miyabuchi, Yasuo; Kobayashi, Tetsuo; Kankeu, Boniface; Yokoyama, Tetsuya; Tanyileke, Gregory; Ohba, Takeshi; Hell, Joseph Victor; Kusakabe, Minoru


    The hydrodynamic fragmentation that formed Lake Nyos in northwest Cameroon did not only make it the most unpopular lake in the world from a gas disaster perspective, it also opened a rare and formidable window through which much of the geology of Cameroon can be studied in a single locality. The Cambrian quartz monzonite cliff excavated by the maar-forming explosion and exposed in its northeastern shore is intruded by mafic dykes, two of which we dated. Even though close to one another, the dykes are different in composition. The alkaline dyke yields a slightly older (Carnian) K-Ar fedspar age of 231.1 ± 4.8 Ma, while the sub alkaline dyke yields an age of 224.8 ± 4.7 Ma (Norian). Based on radioisotopic age data available over the last 48 years (347 data) for the Cameroon Line magmatism comprising eruptives and volcano-plutonic complexes, the Nyos dykes are way older than the Cameroon Line, and even pre-date the Lower Cretaceous initiation of west Gondwana fragmentation in Equatorial Atlantic domain. They would therefore not have been directly linked to the formation of the Cameroon Line. Alternatively, they might be associated with the development of intra-continental rift systems in West Central Africa that pre-dated west Gondwana breakup to form the Atlantic Ocean.

  13. Major and trace element, and Sr isotope compositions of clinopyroxene phenocrysts in mafic dykes on Jiaodong Peninsula, southeastern North China Craton: Insights into magma mixing and source metasomatism (United States)

    Liang, Yayun; Deng, Jun; Liu, Xuefei; Wang, Qingfei; Qin, Cheng; Li, Yan; Yang, Yi; Zhou, Mian; Jiang, Jieyan


    Early Cretaceous mafic dyke swarms are widely developed on Jiaodong Peninsula in the southeastern part of the North China Craton (NCC), but their petrogenesis remains enigmatic. We have examined the in-situ major element, trace element and Sr isotope compositions of the clinopyroxene phenocrysts in these dykes in order to evaluate the extent of magma mixing and source metasomatism. Depending on the type of mineral zoning, the clinopyroxene phenocrysts in our samples can be classified into two groups: Group I (reverse zoning) and Group II (no zoning). Based on core compositions, the Group I phenocrysts with obvious reverse zoning can be divided into two subgroups: Groups IA and IB. The cores of Group IA clinopyroxenes have low values of Mg#, low Al2O3 contents, high Na2O contents, and high 87Sr/86Sr ratios, and they were probably derived from newly accreted lower crust that formed through the underplating of basaltic magma. In contrast, the cores of Group IB clinopyroxenes have lower Mg# values and lower contents of Al2O3, ΣREE (total rare earth elements), and incompatible elements, but they have similar 87Sr/86Sr ratios; these cores crystallised from crust-derived andesitic-dacitic magma. Group IA and IB clinopyroxene phenocryst rims (Group I rims) all have similar compositions with higher values of Mg# and higher Al2O3, Cr and Ni contents than the cores. The rims have high 87Sr/86Sr ratios, are enriched in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and are depleted in HFSEs (high field strength elements); these characteristics indicate that all the high-Mg rims were derived from a similar magma, possibly a relatively primitive magma derived from lithospheric mantle. We suggest, therefore, that the reversely-zoned clinopyroxene phenocrysts (Group I) in the Jiaodong mafic dykes provide evidence of magma mixing between a magma derived from lithospheric mantle and crust-derived andesitic-dacitic melt alongside with the newly accreted

  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)

    Teixeira, W.; Kawashita, K.; Pecchio, M.; Tame, N.R.


    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) [pt

  16. An AMS study of magma transport and emplacement mechanisms in mafic dykes from the Etendeka Province, Namibia (United States)

    Wiegand, Miriam; Trumbull, Robert B.; Kontny, Agnes; Greiling, Reinhard O.


    The Henties Bay Outjo dyke swarm (HOD) in NW Namibia is part of the early Cretaceous Paraná-Etendeka Large Igneous Province. The dykes are dominantly doleritic, compositionally equivalent to the erupted lava series and thus the HOD provides a look at the feeder systems of a flood basalt province. The subvertical dykes mostly strike NE-SW and minor NW-SE, parallel or perpendicular to the Damara Belt in which they intruded. We present a magnetic fabric study using the anisotropies of low-field magnetic susceptibility (AMS) and of anhysteretic remanent magnetization (AARM) with the aim to derive magma flow directions and better constrain emplacement mechanisms within the dyke swarm. Magnetic susceptibility and its anisotropy in the dykes is mainly controlled by distribution anisotropy of titanomagnetite that mimics the flow-oriented silicate fabric. The anisotropy is low in most samples, supporting a magmatic origin. In 66 of 110 investigated samples the AMS fabric is ;normal;, with the κmax axis (inferred flow orientation) within the dyke plane. Most samples yielded vertical to subvertical flow orientations regardless of location near or distant from the former rifted margin. The ;anomalous; magnetic fabrics, where κmax is inclined to the dyke plane, are attributed to two mechanisms. One is the single-domain effect of titanomagnetite, which was found by unequal orientations of AMS and AARM fabrics. The other case anomalous fabric is rotation of the AMS axes by shear within the magma, producing symmetric imbrication of AMS fabric on opposite dyke walls; or more commonly, asymmetric magnetic fabrics, which we relate to tectonic shear at the dyke walls during emplacement. Field support for syn-emplacement shear is given by dyke segmentation geometries including locally curved segment tips, en-echelon arrangements and left/right-stepping displacements. Regionally, syn-emplacement shear is consistent with the observed reactivation during Gondwana breakup of

  17. Integrated elemental and Sr-Nd-Pb-Hf isotopic studies of Mesozoic mafic dykes from the eastern North China Craton: implications for the dramatic transformation of lithospheric mantle (United States)

    Liu, Shen; Feng, Caixia; Santosh, M.; Feng, Guangying; Coulson, Ian M.; Xu, Mengjing; Guo, Zhuang; Guo, Xiaolei; Peng, Hao; Feng, Qiang


    Evolution of the lithospheric mantle beneath the North China Craton (NCC) from its Precambrian cratonic architecture until Paleozoic, and the transformation to an oceanic realm during Mesozoic, with implications on the destruction of cratonic root have attracted global attention. Here we present geochemical and isotopic data on a suite of newly identified Mesozoic mafic dyke swarms from the Longwangmiao, Weijiazhuang, Mengjiazhuang, Jiayou, Huangmi, and Xiahonghe areas (Qianhuai Block) along the eastern NCC with an attempt to gain further insights on the lithospheric evolution of the region. The Longwangmiao dykes are alkaline with LILE (Ba and K)- and LREE-enrichment ((La/Yb) N > 4.3) and EM1-like Sr-Nd-Pb-Hf isotopic signature ((87Sr/86Sr) i > 0.706; ε Nd (t) 16.6, (207Pb/204Pb) i > 15.4, (208Pb/204Pb) i > 36.8, ε Hf (t) 3.7), and display similar EM1-like isotopic features ((87Sr/86Sr) i > 0.706; ε Nd (t) 16.7, (207Pb/204Pb) i > 15.4, (208Pb/204Pb) i > 36.9, ε Hf (t) 2.4) and EM1-like isotopic features((87Sr/86Sr) i > 0.706; ε Nd (t) 16.7, (207Pb/204Pb) i > 15.4, (208Pb/204Pb) i > 36.9, ε Hf (t) 3.7) and EM1-like Sr-Nd-Pb-Hf isotopic features ((87Sr/86Sr) i > 0.706; ε Nd(t) 16.7, (207Pb/204Pb) i > 15.4, (208Pb/204Pb) i > 36.9, ε Hf (t) 9.3) and EM1-like isotopic composition ((87Sr/86Sr) i > 0.705; ε Nd (t) 16.9, (207Pb/204Pb) i > 15.5, (208Pb/204Pb) i > 36.9, ε Hf (t) 0.705; ε Nd (t) 16.9, (207Pb/204Pb) i > 15.5, (208Pb/204Pb) i > 36.9, ε Hf (t) < -8.6). Our data from the various mafic dyke suites suggest that the magmas were derived from EM1-like lithospheric mantle, corresponding to lithospheric mantle modified by the previously foundered lower crust beneath the eastern NCC. Our results suggest contrasting lithospheric evolution from Triassic (212 Ma) to Cretaceous (123 Ma) beneath the NCC. These mafic dykes mark an important phase of lithospheric thinning in the eastern North China Craton.

  18. 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.

  19. 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

  20. Geochemical characteristics of Mesoproterozoic metabasite dykes ...

    Indian Academy of Sciences (India)

    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, ...

  1. The Ediacaran volcanic rocks and associated mafic dykes of the Ouarzazate Group (Anti-Atlas, Morocco): Clinopyroxene composition, whole-rock geochemistry and Sr-Nd isotopes constraints from the Ouzellarh-Siroua salient (Tifnoute valley) (United States)

    Belkacim, Said; Gasquet, Dominique; Liégeois, Jean-Paul; Arai, Shoji; Gahlan, Hisham A.; Ahmed, Hassan; Ishida, Yoshito; Ikenne, Moha


    Belonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley volcanic rocks are located within a rigid salient of the Anti-Atlas that gives them special extreme characteristics. Due to the heavy greenschist alteration that affects this volcanic group, we focused the more immobile elements, but as REE can also be affected, we used the composition of unaltered clinopyroxene crystals to determine the nature of these volcanic rocks. The clinopyroxene is an augite diopside in the basalt, an augite in the andesite and an augite-salite in the dolerite. Petrography of the Tifnoute mafic volcanic rocks and clinopyroxene compositions indicate the presence of two magmatic series: (i) older high-K calc-alkaline (alkali-calcic) andesite and basalt characterized by the early crystallization of Fe-Ti oxides and of the late fractionation of plagioclase, the modal proportion of the latter increasing from the basalt to the andesite and (ii) younger alkalic dolerite dykes. With clinopyroxene trace element compositions obtained using laser ablation ICP-MS, we calculated the composition of the melts in equilibrium with the pyroxenes. The volcanic rocks of the Tifnoute Valley have positive εNd570 (+1.7 to +5.0), low Sri (volcanic rocks emplaced in a Pan-African transtensive post-collisional environment that evolved towards the major rifting event that will give rise to the Rheic ocean, in a similar way to what occurred just after the Variscan orogeny during the Triassic period that evolved to the Tethys ocean opening.

  2. ArcGIS studies and field relationships of Paleoproterozoic mafic ...

    Indian Academy of Sciences (India)

    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 ...

  3. ArcGIS studies and field relationships of Paleoproterozoic mafic ...

    Indian Academy of Sciences (India)

    lar trends (e.g., Srivastava 2006a, b; Srivastava and. Figure 1. Simplified geological map of the Dharwar Craton showing the principal distribution of Paleoproterozoic mafic dykes (modified after French and Heaman 2010; Srivastava et al. 2014c). Detailed mafic dyke map of the studied region, the red box marked on map, ...

  4. Interaction between felsic granitoids and basic dykes in ...

    Indian Academy of Sciences (India)


    Geothermal Reserh. 161 (3) 247–260. Jayananda M, Gireesh R, Sekhamo K-U and Miyazaki T 2014 Coeval felsic and mafic magmas in neoarchean calcalkaline magmatic arcs, Dharwar craton, southern India: Field and petrographic evidence from mafic to hybrid magmatic enclaves and synplutonic mafic dykes; J. Geol.

  5. Mineralogical and chemical characteristics of newer dolerite dyke ...

    Indian Academy of Sciences (India)

    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.

  6. Mineralogical and chemical characteristics of newer dolerite dyke ...

    Indian Academy of Sciences (India)

    The mafic dyke swarm, popularly known as the newer dolerite suite, traverses the Precambrian. Singbhum granitic complex in the districts of. Singbhum, Keonjhar and Mayurbhanj in eastern. India (Dunn 1929; Jones 1934; Krishnan 1936;. Dunn and Dey 1942; Saha 1948, 1952; Saha et al. 1972, 1973). The reticulate dyke ...

  7. Magnetic Investigations On The Okavango Giant Dyke Swarm (n Botswana) (United States)

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

    The Okavango Giant Dyke Swarm is one of the largest mafic dyke complex world- wide. It extends as a 1500 x 100 km intrusive system across the Karoo igneous province of E. Namibia, N. Botswana and W. Zimbabwe. It is marked by prominent magnetic anomalies on the many aeromagnetic surveys acquired by mining compa- nies. Beyond the analysis of these data, ground truth evidence has been collected along a 100 km continuous section nearly perpendicular to the dyke swarm on the Shashe River, which present excellent exposures of dykes and basement host-rocks. Samples have been cored on 15 dykes for paleomagnetic and rock magnetic analy- ses. The paleomagnetic poles determined from most of the dykes is consistent with a Karoo age on the Apparent Polar Wander path for Africa and confirm the radio- metric results obtained by Ar-Ar dating technique. A very different pole is obtained for one basement dyke dated at 880 Ma. Magnetic susceptibility and natural rema- nent magnetization have been compiled and used to constrain forward modeling of the aeromagnetic anomalies. The direction of magmatic flow within individual dykes is investigated through the analysis of magnetic susceptibility anisotropy.

  8. Palaeomagnetism of the Palaeoproterozoic Boonadgin Dyke Suite, Yilgarn Craton: Possible connection with India (United States)

    Liu, Y.; Li, Z. X.; Pisarevsky, S.; Kirscher, U.; Mitchell, R.; Stark, J. C.


    A palaeomagnetic study was carried out on the newly identified 1.9 Ga Boonadgin dyke swarm in the Yilgarn Craton, Western Australia. Ten dykes revealed a high-temperature characteristic remanent magnetisation (ChRM) with dual polarities, directing either SW shallow downward (4 sites) or NE shallow upward (6 sites). Our results reveal that the Yilgarn Craton was at an equatorial palaeolatitude at 1.9 Ga. Meanwhile, a paleopole from the ca. 1.9 Ga Dharwar dykes of South India, supported by a positive baked-contact test, puts India at a similar paleolatitude. The Boonadgin dyke swarm can be interpreted to represent an arm of a radiating dyke swarm that shared the same plume centre with coeval mafic dykes in the Dharwar and Bastar cratons of southern India. We therefore propose that the Western Australia Craton (WAC, consisting of the the Yilgarn and Pilbara cratons) and South India were connected at ca. 1.89 Ga.

  9. ArcGIS studies and field relationships of Paleoproterozoic mafic ...

    Indian Academy of Sciences (India)

    Google Earth Image and cross-cutting field relationships of distinct Paleoproterozoic mafic dykes from south of Devarakonda area in the Eastern .... range of applications (Legg 1994; Rajesh 2004). For the present study, an ArcGIS ... metric ages have been used as such studies could be the best elements to interpret their ...

  10. Mafic dykes at the southwestern margin of Eastern Ghats belt ...

    Indian Academy of Sciences (India)

    west of the Ongole domain of the Eastern Ghats granulite belt. Vijay Kumar and Leelanandam ... machine was 20/40 KV and nominal analysis time was 300 seconds for all major oxides. For the XRF analysis the overall .... can be seen, while P2O5 and TiO2 increase with decreasing MgO. Increasing CaO and decreasing.

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

    International Nuclear Information System (INIS)

    Master, S.


    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

  12. Tectonic significance of dykes in the Sarnu-Dandali alkaline complex, Rajasthan, northwestern Deccan Traps

    Directory of Open Access Journals (Sweden)

    Anjali Vijayan


    Full Text Available Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual case studies. The Sarnu-Dandali alkaline complex, near the northwestern limit of the Deccan Traps continental flood basalt province, contains mafic to felsic alkaline volcano-plutonic rocks and carbonatites. The complex is situated near the northern end of the 600 km long, NNW–SSE-trending Barmer-Cambay rift. Mafic enclave swarms in the syenites suggest synplutonic mafic dykes injected into a largely liquid felsic magma chamber. Later coherent dykes in the complex, of all compositions and sizes, dominantly strike NNW–SSE, parallel to the Barmer-Cambay rift. The rift formed during two distinct episodes of extension, NW–SE in the early Cretaceous and NE–SW in the late Cretaceous. Control of the southern Indian Dharwar structural fabric on the rift trend, as speculated previously, is untenable, whereas the regional Precambrian basement trends (Aravalli and Malani run NE–SW and NNE–SSW. We therefore suggest that the small-scale Sarnu-Dandali dykes and the much larger-scale Barmer-Cambay rift were not controlled by basement structure, but related to contemporaneous, late Cretaceous regional ENE–WSW extension, for which there is varied independent evidence.


    Directory of Open Access Journals (Sweden)

    G. A. Kallistov


    Full Text Available We present the results of geological, petro‐geochemical and mineralogical studies of synplutonic intrusive formations in the Chelyabinsk granitoid massif, South Urals. Numerous synplutonic intrusions in the study area are in early phases, composed of quartz diorites and granodiorites of the Late Devonian – Early Carboniferous. Such intru‐ sions are represented by a bimodal series of rocks from gabbro‐diorite to plagioleic granite. Both the mafic and salic members of the series form separate independent dykes and, jointly, compose the dyke bodies of complex structures. With respect to the relationships with host rocks, two types of the studied dykes are distinguished: (1 ‘classical’ synplutonic dykes with monolithic bodies that are split along strike by the enclosing granodiorite into separate frag‐ ments; and (2 ‘post‐granite’ dykes that clearly break through the host quartz diorites and granodiorites that are older that the dykes, but show similar isotope ages: the U‐Pb‐Shrimp ages of zircon in the samples taken from the dyke and the host quartz diorite are 362±4 и 358±5 Ma, respectively. The first group includes the dyke of melanocratic diorite, the second – granitoid dykes and dykes of gabbro‐diorites and diorites. The intrusion of acid rocks preceded the basites and was completed after their formation. As a result of the nearly simultaneous intrusion of both, the dykes of complex structures were formed. The material compositions of mafic rocks in these two groups are significantly dif‐ ferent. The ‘post‐granite’ dioritoids are moderately alkaline. Melanodiorite in the synplutonic dyke belongs to normal alkaline rocks. It has a very high content of MgO (12.5 mass % and is sharply enriched with chromium (~700 ppm vs. 100–350 ppm in the ‘post‐granite’ dykes. It is thus closer to sanukitoids. The acid ‘post‐granite’ dykes vary in compo‐ sition from plagoleic granite and adamellite to

  14. 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.

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

    Srivastava, Rajesh K.; Sinha, Anup K.; Kumar, Suresh


    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 calc-alkaline 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. Multi-element 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.

  16. Degassing of magma rising in a dyke (United States)

    Taisne, B.; Jaupart, C. P.


    Magma ascent and degassing proceed in markedly different ways in a volcanic conduit and in a dyke due to large differences in the vertical variations of magma pressure. In a propagating dyke, the width of the dyke and the distributions of magma velocity and pressure must be solved for simultaneously, in contrast to magma rising in a conduit, such that the conduit aperture and dimensions are fixed a priori. In these two cases, magma buoyancy is balanced in different ways depending on the magnitude of forces available to drive wall deformation. Numerical calculations of dyke ascent are used to investigate the different dynamics of magma ascent. The mixture of melt and gas is treated as a compressible viscous fluid below the fragmentation level and as a gas phase carrying melt droplets above it. The numerical code solves for elastic deformation of host rocks, the flow of the magmatic mixture and fracturing at the dyke tip. With volatile-free magma, a dyke fed at a constant rate in a uniform medium adopts a constant shape and width and rises at a constant velocity. With volatiles involved, magma expands and hence the volume flux of magma increases. With no fragmentation, the rheological properties of the magmatic mixture also change due to the presence of bubbles and to the increase of melt viscosity induced by degassing. There is still some uncertainty on a proper formulation for these complicated rheological effects. We use several parameterization schemes to show that, in all cases, the enhenced volume flux due to degassing leads to acceleration and thinning of the dyke. This is true even when one does not account for the effect of gas on the mixture viscosity. In this case, viscosity increases dramatically as magma loses its dissolved volatiles, but density variations more than compensate for such changes. Simple scaling laws allow accurate predictions of dyke width and ascent rate for a wide range of conditions. With fragmentation, dyke behaviour is markedly

  17. New paleomagnetic results on ˜ ˜2367 Ma Dharwar giant dyke swarm, Dharwar craton, southern India: implications for Paleoproterozoic continental reconstruction (United States)

    Babu, N. Ramesh; Venkateshwarlu, M.; Shankar, Ravi; Nagaraju, E.; Parashuramulu, V.


    Here we report new paleomagnetic results and precise paleopole position of the extensional study on ˜ 2367 Ma mafic giant radiating dyke swarm in the Dharwar craton, southern India. We have sampled 29 sites on 12 dykes from NE-SW Karimnagar-Hyderabad dykes and Dhone-Gooty sector dykes, eastern Dharwar craton to provide unambiguous paleomagnetism evidence on the spectacular radiating dyke swarm and thereby strengthening the presence of single magmatic event at ˜ 2367 Ma. A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four dykes show component (A) with mean declination of 94{{}°} and mean inclination of - 70{{}°} (k=87, α_{95}=10{{}°}) and corresponding paleopole at 16{{}°}N, 41{{}°}E (dp=15{{}°} and dm=17{{}°}) and 22 sites representing 8 dykes yielded a component (B) with mean declination of 41{{}°} and mean inclination of - 21{{}°} (k=41, α_{95}=9{{}°}) with a paleopole at 41{{}°}N, 200{{}°}E (dp=5{{}°} and dm=10{{}°}). Component (A) results are similar to the previously reported directions from the ˜ 2367 Ma dyke swarm, which have been confirmed fairly reliably to be of primary origin. The component (B) directions appear to be strongly overprinted by the 2080 Ma event. The grand mean for the primary component (A) combined with earlier reported studies gives mean declination of 97{{}°} and mean inclination of - 79{{}°} (k=55, α_{95}=3{{}°}) with a paleopole at 15{{}°}N, 57{{}°}E (dp=5{{}°}, dm=6{{}°}). Paleogeographical position for the Dharwar craton at ˜ 2367 Ma suggests that there may be a chance to possible spatial link between Dharwar dykes of Dharwar craton (India), Widgemooltha and Erayinia dykes of Yilgarn craton (Australia), Sebanga Poort Dykes of Zimbabwe craton (Africa) and Karelian

  18. 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

  19. Carbonatitic dykes during Pangaea transtension (Pelagonian Zone, Greece) (United States)

    Schenker, Filippo Luca; Burg, Jean-Pierre; Kostopoulos, Dimitrios; Baumgartner, Lukas P.; Bouvier, Anne-Sophie


    Carbonatitic dykes surrounded by K-Na-fenites were discovered in the Pelagonian Zone in Greece. Their carbonate portions have an isotopic mantle signature of δ13C and δ18O ranging from -5.18 to -5.56 (‰ vs. VPDB) and from 10.68 to 11.59 (‰ vs. VSMOW) respectively, whereas their mafic silicate portions have high Nb, Ta and ɛNd values, typical of alkaline basalts. Textural relationships hint at a cogenetic intrusion of silicate and carbonate liquids that according to antithetic REE profiles segregated at shallow depths (rims (δ18O = 6.78-7.02). From 300 to 175 Ma the ɛNd of the Pelagonian magmatism rose irregularly to more primitive values attesting to a higher increment of asthenosphere-derived melts. In this context, the carbonatite formed within a transtensional regime of an intra-Pangaea dextral transform fault that signalled the forthcoming penetrating breakoff of the supercontinent, manifested in the Permo-Triassic.

  20. Vegetation dynamics and erosion resistance of sea dyke grassland

    NARCIS (Netherlands)

    Sprangers, J.T.C.M.


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

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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


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

  3. Dyke belt in North Western margin of Siberian platform (United States)

    Ryabov, Victor


    The Early Triassic dyke swarm belt is strengthening at about 500 km (50-60 km width) along the northern margin of Siberian platform. Its locations is limited from the north by rift structure of the Yenisei-Khatanga trough, and from the south by Kystyktah-Ayan-Ambardah uprise. From west to east dyke belt is crossing Norilsk, Kamensky and Maimecha-Kotuiskaya province. In this direction the composition of dykes changing from basic rthrough alkali-basic to alkali-ultramafic varieties. The sickness of dykes varies from 0,5-10m up to 90 m and length - from 5-15 m to 140 km. The orientation of the bulk of dykes coincides with the direction of the major structural and tectonic lineaments of the region. Dykes are often refer to the fault planes. The composition of dykes may vary along the stretches. The density of hundreds of basaltic dykes and small intrusions in the dyke swarms is not permanent and sometimes essentially uneven. They form a compact dyke swarms of dykes, stocks and sub layering bodies veins. In dyke package on Huor-Uyallah river here are 20 subparallel dykes of different chemical composition at a distance of 2 km Lack of the evidence of the dykes crossing allows to assume their formation during the same magmatic cycle. Dykes cross cut through the entire incision of basaltic plateau. They did not created the flow effusions and refer to the final stage trap magmatism. Ar/Ar age of the youngest dykes in the province Kamenska 238-247 Ma. the age of lamproite dyke in Norilsk province is 235 Ma. Dykes are represented by dolerites trachydolerites, syenites, minettes, lamprophyres (camptonite, spessartite, vosgesite), avgitites, melanephelinite, alnoites, limburgites alkaline picrites, meimechites. Their content vary widely: SiO2 - 35,7-62,6; TiO2- 0,4-7,5; Al2O3- 4,4-17,5; Fe2O3- 4,6-20,6; MnO- 0,08-0,44; MgO- 0,8-31,5; CaO- 0,7-15,4; Na2O- 0,01-6,5; K2O 0,8-5,3 wt.%; P2O5 0,1-1,2 wt.%. The h Bolsheavamskaya volcanic basin in Kamensky province is most abundant in

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

    DEFF Research Database (Denmark)

    Hanghøj, Karen; Storey, Michael; Stecher, Ole


    Dykes of the East Greenland Tertiary dyke swarm can be divided into pre- and syn-break-up tholeiitic dykes, and post-break-up transitional dykes. Of the pre- and syn-break-up dykes, the most abundant group (Tholeiitic Series; TS) has major element compositions similar to the main part of the East...

  5. Petrogenesis and tectonic implications of Upper Triassic appinite dykes in the East Kunlun orogenic belt, northern Tibetan Plateau (United States)

    Liu, Bin; Ma, Chang-Qian; Huang, Jian; Wang, Lian-Xun; Zhao, Shao-Qing; Yan, Rong; Sun, Yang; Xiong, Fu-Hao


    This paper presents geochronological, mineralogical, geochemical, and Sr-Nd isotopic data for recently identified Upper Triassic appinite dyke swarms in the East Kunlun orogenic belt (EKOB), northern Tibetan Plateau. Zircon U-Pb isotopic analyses using SHRIMP and LA-ICP-MS techniques yield 206Pb/238U ages of 226.1 ± 1.9 Ma and 226.4 ± 3.5 Ma, which can be interpreted as the crystallization ages of the appinite dykes. All the samples are characterized by high Al2O3 contents, enrichments in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and strong depletions in Nb, Ta, Ti and P. These characteristics are comparable to those of subduction-related calc-alkaline high-Al basalts. Delayed plagioclase nucleation caused by relatively high-pressure conditions and high H2O contents is the most likely interpretation of the high Al contents. The geochemical and isotopic variations suggest that the appinite dykes were derived from partial melting of a mixed mantle source consisting of enriched lithospheric mantle and MORB-type asthenospheric mantle and had experienced some degree of crustal contamination during migration through continental crust. The appinite dykes are associated with previously documented, contemporaneous high-Ba-Sr and/or high-Sr/Y granites (225-223 Ma) derived from thickened mafic lower crust. These rocks provide important constraints on the compositional variations in the orogenic lithospheric mantle during the Late Triassic and provide evidence of a post-collisional environment associated with lithospheric delamination or slab break-off.

  6. Temporal geoelectric behaviour of dyke aquifers in northern Deccan ...

    Indian Academy of Sciences (India)

    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 ...

  7. Temporal correlation between dyke swarms and crustal extension in the middle Palaeozoic Vilyui rift basin, Siberian platform (United States)

    Polyansky, Oleg P.; Prokopiev, Andrei V.; Koroleva, Olga V.; Tomshin, Mikhail D.; Reverdatto, Vladimir V.; Selyatitsky, Alexander Yu.; Travin, Alexei V.; Vasiliev, Dmitry A.


    This paper presents results from new 40Ar/39Ar isotope dating of nine mafic dykes from three large dyke swarms (Vilyui-Markha, Kontai-Dzherba, and Chara-Sinsk) of the Yakutsk-Vilyui large igneous province (LIP), in addition to a reconstruction of the subsidence history of the middle Palaeozoic Vilyui paleorift basin (eastern Siberian platform). All previously published 40Ar/39Ar and U-Pb dates are summarized. Statistical analysis of the dyke ages reveals repeated magmatic events in the study area. Two major pulses of mafic magmatism are identified: one at the Frasnian-Famennian boundary, with a main peak at ca. 374.1 Ma, and another in the latest Devonian with a peak at ca. 363.4 Ma. The time of maximum intensity of dyke intrusion coincides (within uncertainty) with rapid subsidence in the Vilyui basin. The minimum total volume of middle Palaeozoic magmatism produced in the Yakutsk-Vilyui LIP is 100-215 K km3, which is much less than earlier estimates. Most of the mafic material within the Yakutsk-Vilyui LIP is related to the Vilyui basin and associated dyke swarms. Backstripping analysis of sedimentation in depressions of the Vilyui basin was carried out. Estimates were obtained for the spatial distribution of the stretching factor of the crust and mantle lithosphere, averaging 1.17 and 1.44, respectively. The amount of extension due to dyke intrusion is estimated to be 6%. Backstripping analysis of sedimentation in the Vilyui basin was used to assess the effect of both intraplate far-field forces and upwelling magma flows initiated by a mantle plume. A numerical thermomechanical model was developed to investigate the relations between two possible mechanisms by which the Vilyui rift was initiated: intraplate extension (passive rifting) and the ascent of a mantle magmatic diapir (active rifting). A model considering both of these mechanisms shows the contribution of the far-field extension forces and the effect of convective flows around the mantle plume, assuming

  8. Geochemistry and Petrogenesis of Biabanak–Bafq Mafic Mgmatism ...

    Indian Academy of Sciences (India)


    Precambrian magmatism in the Biabanak–Bafq district represents an extensive sequence of mafic magmatic rocks. Major, trace and rare earth elements reveal that the Low–Ti basement mafic rocks are magnesium tholeiite and Low–Ti cover a mafic rock belongs to Fe– tholeiite, whereas, the High–Ti alkaline mafic rocks, ...

  9. New insights on dyke width and upward velocity (United States)

    Taisne, B.; Jaupart, C.; Tait, S.


    Striking observations have been made that challenge our understanding of magma migration through the Earth's crust. How may a volatile rich magma stall at shallow depth as a growing crypto-dome such as during the 1980 Mount Saint Helens eruption? How can we explain the width of the 2005 mega-dyke intrusion in Afar, that attained more than 8 meters with a very small amount of magma emitted at the surface? We show that changes in the geometry and the dynamics of the propagation can be attributed to density variations in the host rocks, to solidification, to volatile exsolution and expansion or to changes in the input flux of magma at depth. We focus on the relationship between dyke width and ascent rate. Shallow levels are commonly made of low density rocks or volcanic deposits with strong impact on dyke ascent. The dynamics and width of the upper part of the dyke (the nose region) are determined by a local buoyancy balance, independently of the total buoyancy of the magma column between source and tip. In such conditions, the dyke swells and slows down and, in some cases, may not breach the surface. Using laboratory experiments we show that solidification of the magma may lead to a regime of intermittent propagation, even with constant physical conditions at the source. Interestingly the time between two steps can be related to the input flux at the source region. With volatile-bearing magmas, dyke propagation proceeds in two markedly different ways depending on whether or not fragmentation occurs. With no fragmentation, magma expansion leads to acceleration and thinning of the dyke. With fragmentation, the sharp drop of head loss that occurs in gas-rich fragmented material generates large internal overpressure and swelling of the nose region, leading to deceleration of the dyke. All the above effects lead to rapid and large changes of ascent rate. Large variations of magma flux at the source would be required to have similar impacts on dyke propagation. In an

  10. Peridotites and mafic igneous rocks at the foot of the Galicia Margin: an oceanic or continental lithosphere? A discussion

    Energy Technology Data Exchange (ETDEWEB)

    Korprobst, J.; Chazot, G.


    An ultramafic/mafic complex is exposed on the sea floor at the foot of the Galicia Margin (Spain and Portugal). It comprises various types of peridotites and pyroxenites, as well as amphibole-diorites, gabbros, dolerites and basalts. For chronological and structural reasons (gabbros were emplaced within peridotites before the continental break-up) this unit cannot be assigned to the Atlantic oceanic crust. The compilation of all available petrological and geochemical data suggests that peridotites are derived from the sub-continental lithospheric mantle, deeply transformed during Cretaceous rifting. Thus, websterite dykes extracted from the depleted MORB mantle reservoir (DMM), were emplaced early within the lithospheric harzburgites; subsequent boudinage and tectonic dispersion of these dykes in the peridotites, during deformation stages at the beginning of rifting, resulted in the formation of fertile but isotopically depleted lherzolites. Sterile but isotopically enriched websterites, would represent melting residues in the peridotites, after significant partial melting and melt extraction related to the thermal erosion of the lithosphere. The latter melts are probably the source of brown amphibole metasomatic crystallization in some peridotites, as well as of the emplacement of amphibole-diorite dykes. Melts directly extracted from the asthenosphere were emplaced as gabbro within the sub-continental mantle. Mixing these DMM melts together with the enriched melts extracted from the lithosphere, provided the intermediate isotopic melt-compositions - in between the DMM and Oceanic Islands Basalts reservoir - observed for the dolerites and basalts, none of which are characterized by a genuine N-MORB signature. An enriched lithospheric mantle, present prior to rifting of the Galicia margin, is in good agreement with data from the Messejana dyke (Portugal) and more generally, with those of all continental tholeiites of the Central Atlantic Magmatic Province (CAMP

  11. 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.

  12. The Daskop Granophyre Dyke: Inhomogeneous clast distribution and chemistry (United States)

    Kovaleva, Elizaveta; Huber, Matthew S.; Somers, Andrew; Bateman, Stuart


    The Vredefort Granophyre is present in the central basement of the Vredefort impact structure as a set of dykes up to 9 km long and up to 65 m wide and is considered to be the remnant of the impact melt sheet (e.g. French et al. 1989; French and Nielsen 1990). The dykes intruded into the floor of the structure's core during the crater modification and settling stages (e.g. Therriault et al. 1996). Granophyre is typically considered a well-homogenized and uniform melt (e.g., Nel 1927; Gibson and Reimold 2008). This study presents new insights into the chemical variety and inhomogeneous clast distribution of the Vredefort granophyre. The Granophyre dyke on the farm Daskop is located in the core of the impact structure and hosted by granitic gneiss of the Archean basement. The clast distribution was mapped in the eastern half of the dyke. Additionally, non-destructive geochemical methods (handheld µXRF and LIBS systems) were used to obtain chemical analysis of the dyke along strike. The map of clast distribution in the granophyre dyke reveals an inhomogeneous content of clasts, with a consistently higher concentration of clasts along the southern contact. This distribution suggests that either 1) the dyke orientation is non-vertical, allowing gravitational settling to affect the distribution of the clasts after the dyke intruded; or 2) that clasts were preferentially entrained along the southern margin of the dyke. Clast frequency also differs along strike. Many elongated clasts are oriented parallel to the dyke walls, indicating flow. We have also documented linear structures resembling flow channels. These structures are strictly parallel to the dyke walls and have a finer texture than the host granophyre. These may represent differentiation of the melt during crystallization. Chemical inhomogeneity of granophyre dyke has also been documented along strike. Such chemical variation may reflect local differences in the relative amounts of target rocks incorporated

  13. High Resolution Analysis of Dyke Tips and Segments, Using Drones (United States)

    Dering, G.; Micklethwaite, S.; Cruden, A. R.


    We analyse outstanding exposures of dykes from both coastal (Western Australia) and high altitude glacier-polished (Sierra Nevada, California) outcrops, representing intrusion at shallow upper-crustal and mid-crustal conditions respectively. We covered 10,000 m^2 of outcrop area sampling the ground at a scale of 3-5 mm per pixel. Using Structure-from-Motion photogrammetry from ground-based and UAV photographs lacking GPS camera positions (>500 images per study), we generated and calibrated a 3D geometry of dense point clouds by selectively using 25-30 ground control points measured by high precision GPS (40-90 mm error). Ground control points used in the photogrammetric model building process typically yielded a root mean square error (RMSE) of 5 cm. Half the ground control points were withheld from the model building process and when they were compared against the model they yielded RMSE values only 6-10% higher than the points used for georeferencing, suggesting good internal consistency of the dataset and accuracy relative to the reference frame, at least for the purposes of this study. The structural orientations of the dykes and associated fractures were then extracted digitally using the iterative Random Sample Consensus method (RANSAC) and least-squares plane fitting. Furthermore, fracture intensity relative to dykes was measured along a series of scanlines and the running average and variance calculated. All results were compared against field measurements. Results show fracture intensity increases toward the dykes in the shallow crustal examples (West Australia) but no such fractures exist around the mid-crustal (Californian) dykes. Despite this there is a remarkable uniformity of geometry, and by implication process, between the two dyke sets. In order to extract full value from the big visual data now available to us, the near-future requires dedicated research into software solutions for expert-driven, semi-automatic mapping of geology and structure.

  14. Asymmetrical to symmetrical magnetic fabric of dykes: Paleo-flow orientations and Paleo-stresses recorded on feeder-bodies from the Motru Dyke Swarm (Romania) (United States)

    Femenias, O.; Diot, H.; Berza, T.; Gauffriau, A.; Demaiffe, D.


    The fabric of crystals in a dyke is representative of the flow of magma, considered as a newtonian fluid. The AMS of the rocks (=magnetic mineralogy subfabric) gives a good representation of the shape preferred orientation related to the total fabric which, in turn is marker of the magmatic flow acquired during emplacement of the fluid within the dyke width. Generally, a symmetrical distribution of the fabric in terms of foliation and lineation across the dyke is in agreement with a model involving symmetrical differential displacements of the flow of the fluid within a channel. In this case, the flow direction is in relation with the imbrication of the symmetric foliations. In this study, we present the cases of both symmetrical and asymmetrical dyke fabric recording and involving different process of emplacement during a regional deformation. From a regional survey of a large Pan-African calc-alkaline dyke swarm (of basaltic-andesitic-dacitic-rhyolitic composition) of the Alpine Danubian window from South Carpathians of Romania, two populations of dykes have been described: thick (from 1 to 30 meters) N-S trending dykes and thin (less than 1 meter) E-W dykes. These two populations crosscut the country rocks without simple chronological relations between them. The thick dykes display asymmetrical fabric that involve a relatively long history of emplacement and important distance of flow. They record the regional sinistral movement of the walls. By contrast, the thin dykes are symmetrical and display frequently an arteritic morphology that limits the dyke length, with no cartographic extension. The mean orientations of the two types of dykes can be related to the same regional stress field and a continuum of emplacement is proposed for the two types of dykes during the regional deformation.

  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. Age and origin of fluorapatite-rich dyke from Baranec Mt. (Tatra Mts., Western Carpathians: a key to understanding of the post-orogenic processes and element mobility

    Directory of Open Access Journals (Sweden)

    Gawęda Aleksandra


    Full Text Available On the southeastern slope of the Baranec Mount in the Western Tatra Mountains (Slovakia an apatite-rich pegmatite-like segregation was found in the subvertical fault zone cutting metapelitic rocks. Two zones: felsic (F and mafic (M were found, differing in mineral assemblages and consequently in chemistry. Fluorapatite crystals yield a LA-ICP-MS U-Pb age of 328.6 ± 2.4 Ma. A temperature decrease from 634 °C to 454 °C at a pressure around 500 to 400 MPa with oxygen fugacity increasing during crystallization are the possible conditions for formation of the pegmatite-like segregation, while secondary alterations took place in the temperature range of 340 – 320 °C. The Sr-Nd isotope composition of both apatite and whole rock point toward a crustal origin of the dike in question, suggesting partial melting of (P, F, H2O-rich metasedimentary rocks during prolonged decompression of the Tatra Massif. The original partial melt (felsic component was mixed with an external (F, H2O-rich fluid, carrying Fe and Mg fluxed from more mafic metapelites and crystallizing as biotite and epidote in the mafic component of the dyke.

  17. 2367 Ma Dharwar giant dyke swarm, Dharwar craton, southern India

    Indian Academy of Sciences (India)


    Torsvik T H and Smethurst M A 1999 Plate Tectonic modeling: Virtual Reality with GMAP;. 406. Computer & Geosciences 25 395-402. 407. Valet J P, Besse J, Kumar A, Vadakke-Chanat S, and Philippe E 2014 The intensity of the. 408 geomagnetic field from 2.4 Ga old Indian dykes; Geochemis, Geophys, Geosys. 15 doi.

  18. Temporal geoelectric behaviour of dyke aquifers in northern Deccan ...

    Indian Academy of Sciences (India)

    Longitudinal geoelectrical sections along these dykes demonstrated carrier as well as barrier stretches which identified potential .... static water levels in all the wells vary from 6–12 m bgl during pre-monsoon, whereas the water lev- ..... Jarvis A, Reuter H I, Nelson A and Guevara E 2006. Hole-filled seamless SRTM data V3; ...

  19. New paleomagnetic results on 2367 Ma Dharwar giant dyke swarm ...

    Indian Academy of Sciences (India)

    N Ramesh Babu


    Feb 14, 2018 ... A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four ...

  20. Mafic and related complexes in Galicia: an excursion guide

    NARCIS (Netherlands)

    Arps, C.E.S.; Calsteren, van P.W.C.; Hilgen, J.D.; Kuijper, R.P.; Tex, den E.


    In Galicia occur several polymetamorphic complexes that contain mafic and ultramafic rocks. Mafic volcanics and gabbros are situated in or near the complexes. An episode of metamorphism and granitization encompassed the generation of the volcanics and gabbros. Gravity surveys revealed the existence

  1. Seismic footprints of shallow dyke propagation at Etna, Italy. (United States)

    Falsaperla, Susanna; Neri, Marco


    One of the key issues in forecasting volcanic eruptions is to detect signals that can track the propagation of dykes towards the surface. Continuous monitoring of active volcanoes helps significantly in achieving this goal. The seismic data presented here are unique, as they document surface faulting processes close (tens to a few hundred meters) to their source, namely the dyke tip. They originated nearby - and under - a seismic station that was subsequently destroyed by lava flows during eruptive activity at Etna volcano, Italy, in 2013. On February 20, a ~600 m-long and ~120 m wide NW-SE fracture field opened at an altitude between 2750 and 2900 m. The consequent rock dislocation caused the station to tilt and offset the seismic signal temporarily. Data acquisition continued until the arrival of the lava flow that led to the breakdown of the transmission system. Shallow ground fracturing and repeated low-frequency oscillations occurred during two stages in which the seismic signal underwent a maximum offset ~2.57 × 10(4) nm/s. Bridging instrumental recordings, fieldwork and conceptual modelling, these data are interpreted as the seismic footprints of a magmatic dyke intrusion that moved at speed ~0.02 m/s (first stage) and 0.46 m/s (second stage).

  2. Interaction between felsic granitoids and basic dykes in ...

    Indian Academy of Sciences (India)


    Element software from standard rock thin sections of coarse grained mafic rocks. All photomicrographs of a .... 5.b). This rock also contains higher amount of acicular apatite (Fig. 5.c). The needle shaped apatites are variable in size and haphazardly oriented. Most of the titanite grains show titanite- plagioclase ocelli and ...

  3. Trace metal contamination of Beaufort's Dyke, North Channel, Irish Sea: A legacy of ordnance disposal

    International Nuclear Information System (INIS)

    Callaway, Alexander; Quinn, Rory; Brown, Craig J.; Service, Matthew; Benetti, Sara


    Highlights: → Our samples are the first trace metal concentrations taken from the valley of Beaufort's Dyke. → There is no clear trend between concentrations of trace metals in Dyke and NMMP sediments. → Particle transport simulations show dispersal of trace metals from Beaufort's Dyke is possible. → Disposed ordnance may also contribute to contamination of surrounding areas. → These methods could help predict areas at risk of future trace metal contamination as a result of ordnance disposal. - Abstract: Beaufort's Dyke is a disused ordnance disposal ground within the North Channel of the Irish Sea. Over 1 million tonnes of ordnance were disposed of in the dyke over a 40 year period representing a substantial volume of trace metal pollutants introduced to the seabed. Utilising particle transport modelling software we simulated the potential transport of metal particles from Beaufort's Dyke over a 3 month period. This demonstrated that Beaufort's Dyke has the potential to act as a source for trace metal contamination to areas beyond the submarine valley. Trace metal analysis of sediments from the Dyke and surrounding National Marine Monitoring Programme areas demonstrate that the Dyke is not the most contaminated site in the region. Particle transport modelling enables the transport pathways of trace metal contaminants to be predicted. Implementation of the technique in other munitions disposal grounds will provide valuable information for the selection of monitoring stations.

  4. Dyke-Davidoff-Masson syndrome: A case report

    Directory of Open Access Journals (Sweden)

    Biswajyoti Rath


    Full Text Available Dyke-Davidoff-Masson Syndrome (DDMS, also called as cerebral hemiatrophy, is a rare clinical condition characterized by seizures, facial asymmetry, contralateral spastic hemiplegia or hemiparesis, with learning difficulties. It is commonly diagnosed in presence of associated radiologic findings, which include cerebral hemiatrophy with homolateral hypertrophy of the skull and sinuses. We present a 21-year female with increased frequency of convulsion and abnormal behavior for the last 2 months. She had a known seizure disorder for 15 years and had mental subnormality. On physical examination, she was disoriented with mild right hemiparesis. On CT scan the brain showed unilateral left cerebral atrophy.

  5. Petrology of the prehistoric lavas and dyke of the Barren Island ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    activity, whose deposits presently mantle inner and outer caldera walls, a new phase of intra- calderic 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 ...

  6. Fault-related carbonate breccia dykes in the La Chilca area, Eastern Precordillera, San Juan, Argentina (United States)

    Castro de Machuca, Brígida; Perucca, Laura P.


    Carbonate fault breccia dykes in the Cerro La Chilca area, Eastern Precordillera, west-central Argentina, provide clues on the probable mechanism of both fault movement and dyke injection. Breccia dykes intrude Upper Carboniferous sedimentary rocks and Triassic La Flecha Trachyte Formation. The timing of breccia dyke emplacement is constrained by cross cutting relationships with the uppermost Triassic unit and conformable contacts with the Early Miocene sedimentary rocks. This study supports a tectonic-hydrothermal origin for these breccia dykes; fragmentation and subsequent hydraulic injection of fluidized breccia are the more important processes in the breccia dyke development. Brecciation can be triggered by seismic activity which acts as a catalyst. The escape of fluidized material can be attributed to hydrostatic pressure and the direction of movement of the material establishes the direction of least pressure. Previous studies have shown that cross-strike structures have had an important role in the evolution of this Andean segment since at least Triassic times. These structures represent pre-existing crustal fabrics that could have controlled the emplacement of the dykes. The dykes, which are composed mostly of carbonate fault breccia, were injected upward along WNW fractures.

  7. Petrogenesis of Cretaceous (133-84 Ma) intermediate dykes and host granites in southeastern China: Implications for lithospheric extension, continental crustal growth, and geodynamics of Palaeo-Pacific subduction (United States)

    Yang, Jinbao; Zhao, Zhidan; Hou, Qingye; Niu, Yaoling; Mo, Xuanxue; Sheng, Dan; Wang, Lili


    This paper presents U-Pb zircon geochronology, petrology, and major and trace element, Sr-Nd and zircon Hf isotopic geochemistry of Cretaceous granites and intermediate dykes in the Quanzhou and Xiamen regions of southeastern China. These data are used to investigate igneous petrogenesis and Cretaceous tectonic evolution, and interpret the geodynamics of Palaeo-Pacific slab subduction. Granites in Quanzhou and Xiamen range in age from 133 Ma to 87 Ma, have high SiO2 and K2O contents, low abundances in P2O5, and an A/CNK index that ranges from 0.97 to 1.09, indicating that they are high-K calc-alkaline metaluminous I-type rocks. Slightly negative ɛ Nd (t) values (- 1.2 to - 4.4), young Nd model ages (0.87 Ga to 1.20 Ga) and positive ɛ Hf (t) values (- 0.5 to + 9.9) of zircon grains indicate that the granites were derived from magmas that melted amphibolite in the middle-lower crust, and which may have assimilated country rocks during emplacement in shallow chambers. The intermediate dykes have no genetic link to the granites and magma mixing was negligible. Eight dyke samples have low SiO2 and high MgO, Ni and Cr contents. Negative ε Nd (t) values (- 1.5 to - 2.7) and positive ε Hf (t) values (2.7 to 7.6) suggest that the dykes were derived from residual basic lower crust after mafic-crystal accumulation. Two samples of adakite-like dykes are characterised by high Sr/Y ratios (89 to 100) and high SiO2, low K2O, Ni, Cr contents. In combination with slightly negative ε Nd (t) values (- 1.7 to - 1.8) and positive ε Hf (t) values (2.9 to 4.3), the adakite-like dykes were derived from cumulate basic lower crust which had a mixed source between depleted mantle- and crust-derived melts. Based on our data, combined with previously published work, we suggest that extension-induced middle-lower crustal melting and underplating of mantle-derived basaltic melts were the principal driving mechanisms for Cretaceous granitic magmatism in coastal Fujian Province. Extension

  8. A c. 1710 Ma mafic sill emplaced into a quartzite and calcareous series from Ighrem, Anti-Atlas - Morocco: Evidence that the Taghdout passive margin sedimentary group is nearly 1 Ga older than previously thought (United States)

    Ikenne, Moha; Söderlund, Ulf; Ernst, Richard E.; Pin, Christian; Youbi, Nasrrddine; El Aouli, El Hassan; Hafid, Ahmid


    The Taghdout Group is a passive margin sequence deposited during rifting and break-up of the northern margin of the West African craton (WAC), culminating with the creation of an oceanic basin between the northern edge of the WAC and an unknown terrane. However, the age of this passive margin has been poorly constrained. It was previously thought to be c. 800-1000 Ma on the basis of age of the contact metamorphosed host rocks of the associated mafic dykes (Rb/Sr, 789 ± 10 Ma). However, with the U-Pb dating of numerous dyke swarms in the Anti-Atlas Inliers, at c. 870, 1416-1380, 1650, 1750, and 2040 Ma, it was suggested by Youbi et al. (2013) that the Taghdout Group could be Mesoproterozoic in age, with a preference for an age of 1750 Ma. In order to test this idea, a mafic sill within the Taghdout Group has been dated by the ID-TIMS U-Pb method on baddeleyite, yielding an approximate age of c. 1710 Ma. This preliminary age confirms that the Taghdout Group is much older than previously thought. Further geochronology work is required to determine whether this c. 1710 Ma age represents a new intraplate event in the WAC or whether more concordant data could yield an age closer to the known WAC LIP event of c. 1750 Ma. With this result we propose a new lithostratigraphic framework for the Proterorozoic in the Anti-Atlas.

  9. Hybridization in the subvolcanic Jaala-Iitti complex and its petrogenetic relation to rapakivi granites and associated mafic rocks of southeastern Finland

    Directory of Open Access Journals (Sweden)

    Salonsaari, P.T.


    Full Text Available The 1630 Ma Jaala-Iitti complex is an example of bimodal rapakivi granite magmatism in which the interaction of granite and diabase magmas have led locally to hybridization. The dyke-like complex is situated at the northwestern margin of the Wiborg rapakivi batholith in southeastern Finland, cutting both the Proterozoic Svecofennian metamorphic crust and the Wiborg batholith. The complex consists mainly of non-hybridized compositionally homogeneous granites, i.e., hornblende granite and hornblende-quartz-feldspar porphyry which represent the felsic end-member (ca. 68 wt% SiO2 of the complex. The mafic end-member (ca. 51 wt% SiO2 is present as globules of disaggregated Fe-rich tholeiitic magma forming magmatic mafic enclaves (MMEs and composite MMEs. Commonly MMEs and large (up to 2 metres in diameter pillow-like MMEs show magma mixing and mingling characteristics. Hybrid rocks in the complex are monzogranitic and are characterized by (a quartz grains and quartz aggregates (partially melted xenoliths mantled by amphibole rims (ocellar texture with occasional augite, (b alkali feldspar megacrysts mantled by a micrographic plagioclase-quartz intergrowth, and (c alkali feldspar megacrysts mantled by a plagioclase shell with occasional amphibole inclusions. These textures are also found in hybrid MMEs and especially in pillow-like MMEs. Alkali feldspar and quartz megacrysts in hybrid rocks are derived from partially crystallized felsic magma and from disaggregated rapakivi granite and granitoid xenoliths whereas in the MMEs the xenocrysts are solely derived from partially crystallized felsic magma. Disaggregation of the mafic magma to form MMEs and equilibration with the host have produced micro-enclaves and recrystallized borders of MMEs. Disaggregation of the mafic magma has also produced needle-like apatite crystals incorporated from the mafic magma into the hybrid magma; acicular apatite is typical in MMEs and pillow-like MMEs and is indicative

  10. 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


    indicate that north–south and east–west dykes are coeval. The north–south dykes reflect initial east–west rifting that led to break-up along the Gakkel Ridge and formation of the Eurasia Basin. The east–west dykes reflect local variations in the stress field associated with reactivated Palaeozoic faults...

  11. Pseudotachylitic breccia in mafic and felsic rocks (United States)

    Kovaleva, Elizaveta; Huber, Matthew S.


    Impact-produced pseudotachylitic breccia (PTB) is abundant in the core of the Vredefort impact structure and was found in many pre-impact lithologies (e.g., Reimold and Colliston, 1994; Gibson et al., 1997). The mechanisms involved in the process of forming this rock remain highly debated, and various authors have discussed many possible models. We investigate PTB from two different rock types: meta-granite and meta-gabbro and test how lithology controls the development of PTB. We also report on clast transport between different lithologies. In the core of the Vredefort impact structure, meta-granite and meta-gabbro are observed in contact with each other, with an extensive set of PTB veins cutting through both lithologies. Microstructural analyses of the PTB veins in thin sections reveals differences between PTBs in meta-granite and meta-gabbro. In granitic samples, PTB often develops along contacts of material with different physical properties, such as a contact with a migmatite or pegmatite vein. Nucleation sites of PTB have features consistent with ductile deformation and shearing, such as sigmoudal-shaped clasts and dragged edges of the veins. Preferential melting of mafic and hydrous minerals takes place (e.g., Reimold and Colliston, 1994; Gibson et al., 2002). Refractory phases remain in the melt as clasts and form reaction rims. In contrast, PTB in meta-gabbro develop in zones with brittle deformation, and do not exploit existing physical contacts. Cataclastic zones develop along the faults and progressively produce ultracataclasites and melt. Thus, PTB veins in meta-gabbro contain fewer clasts. Clasts usually represent multi-phase fragments of host rock and not specific phases. Such fragments often originate from the material trapped between two parallel or horse-tail faults. The lithological control on the development of PTB does not imply that PTB develops independently in different lithologies. We have observed granitic clasts within PTB veins in meta

  12. Dyke swarm emplacement in the Ethiopian Large Igneous Province: not only a matter of stress (United States)

    Mège, Daniel; Korme, Tesfaye


    In the Tana-Belaya area, western Ethiopia, field data and satellite imagery reveal the existence of two dyke swarms, the NE-SW Serpent-God dyke swarm, and the NW-SE Dinder dyke swarm. Both swarms are thought to have the same age, 30 Ma, and are likely to have contributed to feeding the traps. After a description of the swarms, this paper examines their relationships with the basement structures. The two dyke swarms follow major lithospheric weakness zones. The Serpent-God dyke swarm follows the Pan-African Tulu Dimtu ductile shear zone, and the Dinder dyke swarm follows a large NW-SE-trending Precambrian fracture zone already reactivated during the Mesozoic and Cenozoic as the northern boundary of the Blue Nile Rift. Because the dyke swarms are adjacent but their orientation differs, the stress trajectory patterns during their emplacement were spatially variable at local scale. Therefore, rather than plate-boundary processes, the origin of stress is thought to be primarily related to the Ethiopian plume. Postulating (in the absence of more data relating to the magma chambers that fed the traps) that dyke orientation is the result of an axisymmetric stress field, the location of the stress source can be placed close to Lake Tana, which is the centre of the Ethiopian broad negative regional Bouguer anomaly. The dykes in the Tana-Belaya area provide the first clues to the orientation of the stress field that prevailed in the early history of the Ethiopian mantle plume, and to some of the factors that guided the distribution of the trap feeders.

  13. Dyke thicknesses follow a Weibull distribution controlled by host-rock strength and magmatic overpressure (United States)

    Krumbholz, M.; Hieronymus, C.; Burchardt, S.; Troll, V. R.; Tanner, D. C.; Friese, N.


    Dykes are the primary transport channels of magma through the crust and form large parts of volcanic edifices and the oceanic crust. Their dimensions are primary parameters that control magma transport rates and therefore influence, e.g. the size of fissure eruptions and crustal growth. Since the mechanics of dyke emplacement are essentially similar and independent of the tectonic setting, dyke properties should generally follow the same statistical laws. The measurement of dyke thicknesses is, of all parameters, least affected by censoring and truncation effects and therefore most accurately accessible. Nevertheless, dyke thicknesses have been ascribed to follow many different statistical distributions, such as negative exponential and power law. We tested large datasets of dyke thicknesses from different tectonic settings (mid-ocean ridge, oceanic intra-plate) for different statistical distributions (log-normal, exponential, power law (with fixed or variable lower cut-off), Rayleigh, Chi-square, and Weibull). For this purpose, we first converted the probability density functions of each dataset to cumulative distribution functions, thus avoiding arbitrariness in bin size. A non-linear, least-squares fit was then used to compute the parameter(s) of the distribution function. The goodness-of-fit was evaluated using three methods: (1) the residual sum of squares, (2) the Kolmogorov-Smirnov statistics, and (3) p-values using 10,000 synthetic datasets. The results show that, in general, dyke thickness is best described by a Weibull distribution. This suggests material strength is a function of the dimensions of included weaknesses (e.g. fractures), following the "weakest link of a chain" principle. Our datasets may be further subdivided according to dyke lithology (magma type) and type (regional dyke vs. inclined sheet), which leads to an increasingly better fit of the Weibull distribution. Weibull is hence the statistical distribution that universally describes dyke

  14. 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


    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...

  15. Petrological and geochemical studies of ultramafic–mafic rocks from ...

    Indian Academy of Sciences (India)

    with patches of dark mafic minerals. Major min- erals of the rock are clinopyroxene, plagioclase, .... Reaction rim of hornblende (dark brown) around orthopyroxene (light brown with dusty inclusions) and olivine (white with .... Clinopyroxene of Irga web- sterite ranges in composition from Wo45En46Fs8 to. Wo47En45Fs8 and ...

  16. Mafic rocks from Erinpura gneiss terrane in the Sirohi region ...

    Indian Academy of Sciences (India)

    (2011). (b) Lithostratigraphic map (adapted from Roy and Sharma 1999) showing occurrence of the Daba mafic body within Erinpura granite terrane around Sirohi (SW Rajasthan). Sampled section along NW–SE traverse is also shown. sector of the Delhi Fold Belt (DFB) represents a. Grenvillian age (∼1 Ga) arc terrane ...

  17. Interaction of coeval felsic and mafic magmas from the Kanker ...

    Indian Academy of Sciences (India)

    R Elangovan


    Oct 5, 2017 ... Department of Geology and Water Resources Management, Pt. Ravishankar Shukla University,. Raipur 492 010, India. ... features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of ... occur during the magma mixing process (Barbarin and Didier ...

  18. Geochemistry and geochronology of the mafic dikes in the Taipusi ...

    Indian Academy of Sciences (India)

    Jing-Hua Wu


    Jul 6, 2017 ... The Taipusi area in the Bainaimiao Arc Belt is located in the northern margin of the North China. Craton, at the southern margin of the middle Central Asian Orogenic Belt. It is characterized by large exposures of mafic dikes. In this contribution, we present first-hand whole-rock major and trace elements ...

  19. Interaction of coeval felsic and mafic magmas from the Kanker ...

    Indian Academy of Sciences (India)


    20 crystallization of the latter, results in hybrid magmas under the influence of thermal and. 21 chemical exchange. The mechanical exchange occurs between the coexisting magmas due to. 22 viscosity contrast, if the mafic magma enters slightly later into the magma chamber, when the. 23 felsic magma started to crystallize.

  20. Challenging dyke ascent models using novel laboratory experiments: Implications for reinterpreting evidence of magma ascent and volcanism (United States)

    Kavanagh, Janine L.; Burns, Alec J.; Hilmi Hazim, Suraya; Wood, Elliot P.; Martin, Simon A.; Hignett, Sam; Dennis, David J. C.


    Volcanic eruptions are fed by plumbing systems that transport magma from its source to the surface, mostly fed by dykes. Here we present laboratory experiments that model dyke ascent to eruption using a tank filled with a crust analogue (gelatine, which is transparent and elastic) that is injected from below by a magma analogue (dyed water). This novel experimental setup allows, for the first time, the simultaneous measurement of fluid flow, sub-surface and surface deformation during dyke ascent. During injection, a penny-shaped fluid-filled crack is formed, intrudes, and traverses the gelatine slab vertically to then erupt at the surface. Polarised light shows the internal stress evolution as the dyke ascends, and an overhead laser scanner measures the surface elevation change in the lead-up to dyke eruption. Fluorescent passive-tracer particles that are illuminated by a laser sheet are monitored, and the intruding fluid's flow dynamics and gelatine's sub-surface strain evolution is measured using particle image velocimetry and digital image correlation, respectively. We identify 4 previously undescribed stages of dyke ascent. Stage 1, early dyke growth: the initial dyke grows from the source, and two fluid jets circulate as the penny-shaped crack is formed. Stage 2, pseudo-steady dyke growth: characterised by the development of a rapidly uprising, central, single pseudo-steady fluid jet, as the dyke grows equally in length and width, and the fluid down-wells at the dyke margin. Sub-surface host strain is localised at the head region and the tail of the dyke is largely static. Stage 3, pre-eruption unsteady dyke growth: an instability in the fluid flow appears as the central fluid jet meanders, the dyke tip accelerates towards the surface and the tail thins. Surface deformation is only detected in the immediate lead-up to eruption and is characterised by an overall topographic increase, with axis-symmetric topographic highs developed above the dyke tip. Stage 4 is



    Silva, Pedro; Henry, Bernard; Marques, Fernando; Madureira, Pedro; Mateus, António; Miranda, Miguel


    This work is focused on flow and propagation of magma along thick Jurassic dykes and the effects of such intrusive processes on the magnetic properties of host sedimentary rocks, which are still poorly understood. Therefore, an exhaustive study of rock magnetic and petrography analyses were performed on dolerite rocks collected along several sections across the Foum Zguid (FZD - Southern Morocco) and Messejana-Plasencia (MPD - Iberia) dykes, complemented with several sections across the sedim...

  2. Rock-forming minerals of lamprophyres and associated mafic dykes from the Krušné hory/Erzgebirge (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Pivec, Edvín; Holub, F. V.; Lang, Miloš; Novák, Jiří Karel; Štemprok, M.


    Roč. 47, 1-2 (2002), s. 23-32 ISSN 1210-8197 R&D Projects: GA ČR GA205/01/1127; GA AV ČR KSK1012601 Keywords : lamprophyres * greisenization * Krušné hory/Erzgebire Subject RIV: DB - Geology ; Mineralogy

  3. 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.

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

    Directory of Open Access Journals (Sweden)

    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.

  5. Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream? (United States)

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


    In the Vietnamese part of the Mekong Delta (VMD) the areas with three rice crops per year have been expanded rapidly during the last 15 years. Paddy-rice cultivation during the flood season has been made possible by implementing high-dyke flood defenses and flood control structures. However, there are widespread claims that the high-dyke system has increased water levels in downstream areas. Our study aims at resolving this issue by attributing observed changes in flood characteristics to high-dyke construction and other possible causes. Maximum water levels and duration above the flood alarm level are analysed for gradual trends and step changes at different discharge gauges. Strong and robust increasing trends of peak water levels and duration downstream of the high-dyke areas are found with a step change in 2000/2001, i.e. immediately after the disastrous flood which initiated the high-dyke development. These changes are in contrast to the negative trends detected at stations upstream of the high-dyke areas. This spatially different behaviour of changes in flood characteristics seems to support the public claims. To separate the impact of the high-dyke development from the impact of the other drivers - i.e. changes in the flood hydrograph entering the Mekong Delta, and changes in the tidal dynamics - hydraulic model simulations of the two recent large flood events in 2000 and 2011 are performed. The hydraulic model is run for a set of scenarios whereas the different drivers are interchanged. The simulations reveal that for the central VMD an increase of 9-13 cm in flood peak and 15 days in duration can be attributed to high-dyke development. However, for this area the tidal dynamics have an even larger effect in the range of 19-32 cm. However, the relative contributions of the three drivers of change vary in space across the delta. In summary, our study confirms the claims that the high-dyke development has raised the flood hazard downstream. However, it is not

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

    International Nuclear Information System (INIS)

    Ahmed, N.; Wallin, B. G.; Majumder, R. K.; Mikail, M.; Rahman, M. S.


    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 ''1 8 O). 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-HCO 3 type and the river water is Ca-Mg-HCO 3 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 ''1 8 O) 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

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

    International Nuclear Information System (INIS)

    Roeshoff, Kennert; Cosgrove, John


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

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

    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

  9. Geology, Petrography, Geochemistry and Radioactivity Studies on The Dyke Swarms of Gabal Al Aglab area, North Eastern Desert, Egypt

    International Nuclear Information System (INIS)

    Eldabe, M.M.M.


    Gabal Al Aglab area is located in the North Eastern Desert of Egypt bounded by lat. 27° 14'-27° 19' N and long. 33° 00'-33° 05' E. It is covered by pan African basement rocks. The present study concern with the geology, petrography, geochemistry and radioactivity of various types of the dyke swarms in Gabal Al Aglab area. The field studies revealed that the area comprises the following litho-tectonic units ; Dokhan volcanic (oldest) and Hamammat sedimentary rocks and younger granites are represented by both Gabal Um Twier and Gabal Al Aglab syenogranites (youngest). Many dykes of acidic, intermediate and basic composition have a large extension and dissect all the mentioned rock units. The dyke swarms intruding Gabal Al Aglab area include the acidic (felsite and granite porphyry) dykes, while the intermediate comprise andesite and andesite porphyry and the basic dykes show basalt and dolerites. The chronologic relations of these dykes indicate the following sequence of emplacement beginning with the oldest acidic, followed by intermediate and then basic ones. The geochemical studies indicate that the acidic dykes were derived from a highly differentiated calc- alkaline magma, while the basic and intermediate dykes were developed from magma of subalkaline nature. The dykes were derived from separate magmas and not by magmatic differentiation of single mother magma. The radioactivity of the studied dyke rocks revealed that the high levels of radioactivity mainly linked to the acidity, differentiation and alkalinity characters. Radioactive granitic spot was observed along the contact with some basic dykes due to their thermal effect during its emplacement on the granite, at the northern part of the studied area. This radioactive spot display anomalies with higher values in U and Th contents, than the normal background value of the younger granite.

  10. Rethinking monogamy's nature: From the truth of non/monogamy to a dyke ethics of "antimonogamy". (United States)

    Willey, Angela


    Following Lynne Huffer's work on queer feminism, this abridged essay centers the figure of the lesbian in order to develop a dyke ethics that engenders nuanced thinking about both monogamy and embodiment. The essay reads Alison Bechdel's comic strip, Dykes to Watch Out For, to elaborate a "dyke ethics of anti-monogamy." Grounded in notions of friendship, community, and social justice, this ethics decenters the sexual dyad in a way that polyamory does not. It also insists upon a theoretical and ethical disposition of respect for the simultaneously political and embodied nature of desire. In so doing, it offers first a way of re-thinking the story of monogamy's nature as a naturecultural tale about mononormative desire and further places that desire in a field of relationality that renders its significance as a feature of humanness and an object of scientific inquiry strange.

  11. Petrogenesis of low-δ18O quartz porphyry dykes, Koegel Fontein complex, South Africa (United States)

    Harris, Chris; Mulder, Kwenidyn; Sarkar, Saheli; Whitehead, Benjamin; Roopnarain, Sherissa


    This paper investigates the origin of low-δ18O quartz porphyry dykes associated with the 144-133 Ma Koegel Fontein Igneous Complex, which was intruded during the initial phase of breakup of Africa and South America. The 25-km diameter Rietpoort Granite is the largest and youngest phase of activity, and is roofed by a 10-km diameter pendant of gneiss. Quartz porphyry (QP) dykes, up to 15 m in width, strike NW-SE across the complex. The QP dykes that intruded outside the granite have similar quartz phenocryst δ18O values (average 8.0‰, ± 0.7, n = 33) to the granite (average 8.3 ± 1.0, n = 7). The QP dykes that intruded the roof pendant have quartz phenocrysts with more variable δ18O values (average 1.6‰, ± 2.1, n = 55). In some cases quartz phenocrysts have δ18O values as low as - 2.5‰. The variation in δ18O value within the quartz crystal population of individual dykes is small relative to the overall range, and core and rim material from individual quartz phenocrysts in three samples are identical within error. There is no evidence that quartz phenocryst δ18O values have been affected by fluid-rock interaction. Based on a Δquartz-magma value of 0.6‰, magma δ18O values must have been as low as - 3.1‰. Samples collected along the length of the two main QP dykes that traverse the roof pendant have quartz phenocryst δ18O values that range from + 1.1 to + 4.6‰, and - 2.3 to + 5.6‰, respectively. These δ18O values correlate negatively ( r = - 0.96) with initial 87Sr/86Sr, which can be explained by the event that lowered δ18O values of the source being older than the dykes. We suggest that the QP dykes were fed by magma produced by partial melting of gneiss, which had been variably altered at high temperature by 18O-depleted meteoric water during global glaciation at 550 Ma. The early melts had variable δ18O value but as melt pockets interconnected during melting, the δ18O values approached that of average gneiss. Variable quartz phenocryst

  12. Paleo magnetism of the Ceara-Mirim dyke swarm, Northeastern Brazil

    International Nuclear Information System (INIS)

    Ernesto, M.; Furtado, M.H.; Martins, G.; Macedo, J.W.P.


    The Mesozoic tholeiitic Ceara-Mirim dyke swarm has a general east-west trend cutting the Precambrian basement of northeastern Brazil. The dykes occur mainly in the State of Rio Grande do Norte (RN) but enter the neighbouring State of Ceara to the west where they trend SW-NE. Available K-Ar radiometric dates vary between 214 and 216 Ma. HORN et al. (1988) used a procedure which allowed the removal of argon-loss effects to conclude that the ages might be situated between Middle Jurassic and Early Cretaceous. Paleo magnetic data suggest that the emplacement of the sub-swarms was not simultaneous since they show distinct magnetization directions. New paleo magnetic results that confirm the above conclusion are presented here for the western part of the swarm, where the dykes show a SW-NE structural orientation. (author)

  13. 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

  14. Effect of volcanic dykes on coastal groundwater flow and saltwater intrusion: A field-scale multiphysics approach and parameter evaluation (United States)

    Comte, J.-C.; Wilson, C.; Ofterdinger, U.; González-Quirós, A.


    Volcanic dykes are common discrete heterogeneities in aquifers; however, there is a lack of field examples of, and methodologies for, comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport. We have applied an integrated multiphysics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer. The approach involved ground geophysical imaging (passive magnetics and electrical resistivity tomography), well hydraulic testing, and tidal propagation analysis, which provided constraints on the geometry of the dyke network, the subsurface saltwater distribution, and the sandstone hydrodynamic properties and connectivity. A three-dimensional variable-density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations. A good agreement of model simulations with tide-induced head fluctuations, geophysically derived pore water salinities, and measured apparent resistivities was obtained when dykes' hydraulic conductivity, storativity, and effective porosity are respectively about 3, 1, and 1 orders of magnitude lower than the host aquifer. The presence of the dykes results in barrier-like alterations of groundwater flow and saltwater intrusion. Preferential flow paths occur parallel to observed dyke orientations. Freshwater inflows from upland recharge areas concentrate on the land-facing side of the dykes and saltwater penetration is higher on their sea-facing side. This has major implications for managing groundwater resources in dyke-intruded aquifers, including in coastal and island regions and provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems.

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

    DEFF Research Database (Denmark)

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


    province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder...

  16. Petrogenesis of peralkaline granite dykes of the Straumsvola complex, western Dronning Maud Land, Antarctica (United States)

    Harris, Chris; Dreyer, Tanya; le Roux, Petrus


    Peralkaline syenite and granite dykes cut the Straumsvola nepheline syenite pluton in Western Dronning Maud Land, Antarctica. The average peralkalinity index (PI = molecular Al/[Na + K]) of the dykes is 1.20 ( n = 29) and manifests itself in the presence of the Zr silicates eudialyte, dalyite and vlasovite, and the Na-Ti silicate, narsarsukite. The dykes appear to have intruded during slow cooling of the nepheline syenite pluton, and the petrogenetic relationship of the dykes and the pluton cannot be related to closed-system processes at low pressure, given the thermal divide that exists between silica-undersaturated and oversaturated magmas. Major and trace element variations in the dykes are consistent with a combination of fractional crystallization of parental peralkaline magma of quartz trachyte composition, and internal mineral segregation prior to final solidification. The distribution of accessory minerals is consistent with late-stage crystallization of isolated melt pockets. The dykes give an Rb-Sr isochron age of 171 ± 4.4 Ma, with variable initial 87Sr/86Sr ratio (0.7075 ± 0.0032), and have an average ɛ Nd of - 12.0. Quartz phenocrysts have δ18O values of 8.4-9.2‰, which are generally in O-isotope equilibrium with bulk rock. Differences in the δ18O values of quartz and aegirine (average Δquartz-aegirine = 3.5‰) suggest aegirine formation temperatures around 500 °C, lower than expected for a felsic magma, but consistent with poikilitic aegirine that indicates subsolidus growth. The negative ɛ Nd (values averaging 8.6‰ (assuming Δquartz-magma = 0.6‰) are inconsistent with a magma produced by closed-system fractional crystallization of a mantle-derived magma. By contrast, the nepheline syenite magma had mantle-like δ18O values and much less negative ɛ Nd (average - 3.1, n = 3). The country rock has similar δ18O values to the granite dykes (average 8.0‰, n = 108); this means that models for the petrogenesis of the granites by

  17. 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

  18. 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

  19. Clastic dykes in over-consolidated tills: evidence for subglacial hydrofracturing at Killiney Bay, eastern Ireland (United States)

    Rijsdijk, Kenneth F.; Owen, Geraint; Warren, William P.; McCarroll, Danny; van der Meer, Jaap J. M.


    A swarm of vertical gravel-filled dykes up to 6 m high and several decimetres wide, cut through an over-consolidated till at Killiney Bay. The dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments — `burst-out structures'. Such features have not previously been described. These clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till. The burst-out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow. Evidence suggests that the hydrofractures formed subglacially, probably during a minor re-advance. Their presence in Late Devensian (26-13 ka BP) tills with an Irish Sea provenance (`Irish Sea till') may have important implications for the subglacial hydrology of the last Irish Sea ice sheet. These hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits. They greatly affect the geotechnical properties of Irish Sea tills, in particular providing very permeable routes through otherwise impermeable layers, with important consequences in situations elsewhere in the Irish Sea basin, where they have been used as aquicludes in landfill and low-level nuclear waste disposal sites.

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

    International Nuclear Information System (INIS)

    Dayal, A.M.; Hussain, S.M.


    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

  1. Petrology of the prehistoric lavas and dyke of the Barren Island ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    by the caldera wall, which forms a ridge all around the island. All the later eruptions were confined to the central part of this caldera depression. Bandy- opadhyay et al (1973) reported that the lava pile of the caldera wall was traversed by dykes, but no details about their location, disposition, petrogra- phy and chemistry were ...

  2. Thermal diffusivity of felsic to mafic granulites at elevated temperatures (United States)

    Ray, Labani; Förster, H.-J.; Schilling, F. R.; Förster, A.


    The thermal diffusivity of felsic and intermediate granulites (charnockites, enderbites), mafic granulites, and amphibolite-facies gneisses has been measured up to temperatures of 550 °C using a transient technique. The rock samples are from the Archean and Pan-African terranes of the Southern Indian Granulite Province. Thermal diffusivity at room temperature ( DRT) for different rock types ranges between 1.2 and 2.2 mm 2 s - 1 . For most of the rocks, the effect of radiative heat transfer is observed at temperatures above 450 °C. However, for few enderbites and mafic granulites, radiative heat transfer is negligible up to 550 °C. In the temperature range of conductive heat transfer, i.e., between 20 ° and 450 °C, thermal diffusivity decreases between 35% and 45% with increasing temperature. The temperature dependence of the thermal diffusivity is directly correlated with the thermal diffusivity at room temperature, i.e., the higher the thermal diffusivity at room temperature, DRT, the greater is its temperature dependence. In this temperature range i.e., between 20 and 450 °C, thermal diffusivity can be expressed as D = 0.7 mm 2 s -1 + 144 K ( DRT - 0.7 mm 2 s -1 ) / ( T - 150 K), where T is the absolute temperature in Kelvin. At higher temperatures, an additional radiative contribution is observed according to CT3, where C varies from 10 - 9 to 10 - 10 depending on intrinsic rock properties (opacity, absorption behavior, grain size, grain boundary, etc). An equation is presented that describes the temperature and pressure dependence thermal diffusivity of rocks based only on the room-temperature thermal diffusivity. Room-temperature thermal diffusivity and its temperature dependence are mainly dependent on the major mineralogy of the rock. Because granulites are important components of the middle and lower continental crust, the results of this study provide important constraints in quantifying more accurately the thermal state of the deeper continental

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

    International Nuclear Information System (INIS)

    Gonzalez, P.; Poire, D.; Canalicchio, J.; Garcia Repetto, F.


    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 [es

  4. Radial patterns of bitumen dykes around Quaternary volcanoes, provinces of northern Neuquén and southernmost Mendoza, Argentina (United States)

    Cobbold, Peter R.; Ruffet, Gilles; Leith, Leslie; Loseth, Helge; Rodrigues, Nuno; Leanza, Hector A.; Zanella, Alain


    Where the Neuquén Basin of Argentina abuts the Andes, hundreds of veins of solid hydrocarbon (bitumen) are visible at the surface. Many of these veins became mines, especially in the last century. By consensus, the bitumen has resulted from maturation of organic-rich shales, especially the Vaca Muerta Fm of Late Jurassic age, but also the Agrio Fm of Early Cretaceous age. To account for their maturation, recent authors have invoked regional subsidence, whereas early geologists invoked magmatic activity. During 12 field seasons (since 1998), we have tracked down the bitumen localities, mapped the veins and host rocks, sampled them, studied their compositions, and dated some of them. In the provinces of northern Neuquén and southernmost Mendoza, the bitumen veins are mostly sub-vertical dykes. They tend to be straight and continuous, crosscutting regional structures and strata of all ages, from Jurassic to Palaeocene. Most of the localities lie within 70 km of Tromen volcano, although four are along the Rio Colorado fault zone and another two are at the base of Auca Mahuida volcano. On both volcanic edifices, lavas are of late Pliocene to Pleistocene age. Although regionally many of the bitumen dykes tend to track the current direction of maximum horizontal tectonic stress (ENE), others do not. However, most of the dykes radiate outward from the volcanoes, especially Tromen. Thicknesses of dykes tend to be greatest close to Tromen and where the host rocks are the most resistant to fracturing. Many of the dykes occur in the exhumed hanging walls of deep thrusts, especially at the foot of Tromen. Here the bitumen is in places of high grade (impsonite), whereas further out it tends to be of medium grade (grahamite). A few bitumen dykes contain fragments of Vaca Muerta shale, so that we infer forceful expulsion of source rock. At Curacó Mine, some shale fragments contain bedding-parallel veins of fibrous calcite (beef) and these contain some bitumen, which is

  5. Controls on sill and dyke-sill hybrid geometry and propagation in the crust: The role of fracture toughness (United States)

    Kavanagh, J. L.; Rogers, B. D.; Boutelier, D.; Cruden, A. R.


    Analogue experiments using gelatine were carried out to investigate the role of the mechanical properties of rock layers and their bonded interfaces on the formation and propagation of magma-filled fractures in the crust. Water was injected at controlled flux through the base of a clear-Perspex tank into superposed and variably bonded layers of solidified gelatine. Experimental dykes and sills were formed, as well as dyke-sill hybrid structures where the ascending dyke crosses the interface between layers but also intrudes it to form a sill. Stress evolution in the gelatine was visualised using polarised light as the intrusions grew, and its evolving strain was measured using digital image correlation (DIC). During the formation of dyke-sill hybrids there are notable decreases in stress and strain near the dyke as sills form, which is attributed to a pressure decrease within the intrusive network. Additional fluid is extracted from the open dykes to help grow the sills, causing the dyke protrusion in the overlying layer to be almost completely drained. Scaling laws and the geometry of the propagating sill suggest sill growth into the interface was toughness-dominated rather than viscosity-dominated. We define KIc* as the fracture toughness of the interface between layers relative to the lower gelatine layer KIcInt / KIcG. Our results show that KIc* influences the type of intrusion formed (dyke, sill or hybrid), and the magnitude of KIcInt impacted the growth rate of the sills. KIcInt was determined during setup of the experiment by controlling the temperature of the upper layer Tm when it was poured into place, with Tm intermediate hybrid structures.

  6. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block (United States)

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang


    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of "hidden" large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

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

    International Nuclear Information System (INIS)

    Thomas, R.J.; Eglington, B.M.; Kerr, A.


    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

  8. Interagency partnership to assess and restore a degraded urban riverine wetland: Dyke Marsh Wildlife Preserve, Virginia (United States)

    Steury, Brent W.; Litwin, Ronald J.; Oberg, Erik T.; Smoot, Joseph P.; Pavich, Milan J.; Sanders, Geoffrey; Santucci, Vincent L.


    The narrow-leaved cattail wetland known as Dyke Marsh formally became a land holding of George Washington Memorial Parkway (GWMP, a unit of the national park system) in 1959, along with a congressional directive to honor a newly-let 30-year commercial sand and gravel dredge-mining lease at the site. Dredging continued until 1974 when Public Law 93-251 called for the National Park Service and the United States Army Corps of Engineers to “implement restoration of the historical and ecological values of Dyke Marsh.” By that time, about 83 acres of the marsh remained, and no congressional funding accompanied the passage of the law to effect any immediate conservation or restoration. Decades of dredge mining had severely altered the surface area of Dyke Marsh, the extent of its tidal creek system, and the shallow river bottom of the Potomac River abutting the marsh. Further, mining destabilized the marsh, causing persistent erosion, shoreline retreat, and tidal channel widening after mining ceased. Erosion has continued unchecked until the present; approximately 50 acres of the original marsh are now estimated to remain. The specific cause of persistent erosion had been unknown prior to this collaborative study but previously was assumed to be due to flooding by the Potomac River.

  9. Oxygen isotope composition of mafic magmas at Vesuvius (United States)

    Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.


    The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary magmas of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting

  10. Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius (United States)

    Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano


    Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic magmas, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still

  11. 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.

  12. Possible Mafic Patches in Scott Crater Highlight the Need for Resource Exploration on the Lunar South Polar Region (United States)

    Cooper, Bonnie L.


    Possible areas of mafic material on the rim and floor of Scott crater (82.1 deg S, 48.5 deg E) are suggested by analysis of shadow-masked Clementine false-color-ratio images. Mafic materials common in mare and pyroclastic 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 exist, even closer to the poles, which were originally mapped as purely anorthositic.

  13. Paleomagnetism and geochronological studies on a 450 km long 2216 Ma dyke from the Dharwar craton, southern India (United States)

    Nagaraju, E.; Parashuramulu, V.; Kumar, Anil; Srinivas Sarma, D.


    Paleomagnetic and geochronological studies were carried out on a ∼ 450 km long (from 17 sites) N-S striking Paleoproterozoic dyke swarm exposed along a natural crustal cross section of about 10 km (increasing from North to South) in the Dharwar Craton, to study the characteristics of paleomagnetism and geochronology in vertical dimension. U-Pb/Pb-Pb dating on baddeleyite gives a crystallisation age of 2216.0 ± 0.9 Ma for long dyke AKLD. Paleomagnetic data from this well dated ∼ 2216 Ma dyke swarm in Dharwar Craton are of excellent quality. High coercivity and high blocking temperature components are carried by single domain magnetite and show dual polarity remanence directions. Combined normal and reverse polarity remanences on AKLD and other N-S dykes define the most reliable paleomagnetic pole for ∼ 2216 Ma at latitude 36°S and longitude 312°E (A95 = 7°). Though paleomagnetic data is unavailable on other N-S dykes below the Cuddapah basin, high precision geochronology suggest that they are of similar age within errors. Though there is a variation in the crustal depth of Dharwar craton from north to south, consistent Pb-Pb/U-Pb baddeleyite geochronology and paleomagnetic studies along the AKLD established its continuity and preservation along its entire strike length. The virtual geomagnetic poles of these sites confirm a stable remanence and are almost identical to the previously reported paleomagnetic pole and also supported by positive reversal test. Positive paleomagnetic reversal test on these dykes signify that the remanent magnetization is primary and formed during initial cooling of the intrusions. Updated apparent polar wander path of Dharwar craton indicates relatively low drift rate during 2.21-2.08 Ga interval. Magnetogranulometry and SEM studies show that remanent magnetization in this dyke was carried by single domain magnetite residing within silicate minerals.

  14. Late Cretaceous dacitic dykes swarm from Central Iran, a trace for amphibolite melting in a subduction zone (United States)

    Nosouhian, N.; Torabi, G.; Arai, S.


    Late Cretaceous Bayazeh dyke swarm is situated in the western part of the Central-East Iranian Microcontinent (CEIM). These dykes with a dominant northeast-southwest trend occur in the Eastern margin of the Yazd block. They cross cut the Lower Cretaceous sedimentary rocks. The length of the Bayazeh dykes occasionally reaches up to the 2 km. Rock forming minerals of these dykes are plagioclase (andesine and oligoclase), amphibole (magnesio-hastingsitic hornblende, magnesio-hornblende and tschermakitic hornblende), quartz, K-feldspar (orthoclase), zircon and apatite. Secondary minerals are chlorite (pycnochlorite), albite, magnetite and calcite. The main textures are porphyritic, glomeroporphyritic and poikilitic. The felsic character of the Bayazeh dacitic dykes is shown by their high SiO2 (62.70 to 64.60 wt %) and low [Fe2O3* + MgO + MnO + TiO2] (average 4.64 wt %) contents. These dykes represent the peraluminous to metaluminous nature and their Na2O and K2O values are 5.20-7.14 and 1.51-2.59 wt %, respectively, which reveal their sodic chemistry. The trace element characteristics are the LREE enrichment relative to HREE, [La/Yb]CN = 13.27-22.99, and slightly negative or positive Eu anomaly. These geochemical characteristics associated with low Nb/La (0.16-0.25), Yb/Nd (0.04-0.05) and high Zr/Sm (37.60-58.25) ratios indicate that the melting of a metamorphosed subducted oceanic crust is occurred where the residual mineral assemblage is dominated by garnet amphibolite. The chemical compositions of the Bayazeh dykes resemble those of slab-derived tonalite-trondhjemite-granodiorite (TTG) series. They were formed by subduction of Mesozoic Neo-Tethys -related Nain and Ashin oceanic crusts.

  15. Silica-poor, mafic alkaline lavas from ocean islands and continents ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    rock major-element chemistry of silica-poor, mafic alkaline lavas with exper- ... Keywords. Silica-poor lavas; partial melting; mantle lherzolite; garnet clinopyroxenite. Proc. Indian Acad. Sci. (Earth Planet. Sci.), 113, No. 4, December 2004, pp.

  16. The influence of volatiles on the interaction of mafic and felsic magmas (United States)

    Pistone, M.; Jarvis, P.; Blundy, J. D.


    Mantle-derived mafic magmas provide heat, mass and volatiles to felsic plutons emplaced in the Earth's crust. Inputs of mafic magma lead to a wide range of physical and chemical interactions and have been frequently invoked as a means of sustaining shallow magmatic bodies and even triggering volcanic eruptions, like the case of the 2010 Eyjafjallajökull volcanic eruption where a mafic batch induced remobilization and explosion of a felsic reservoir. There is the general need to understand how hydrous mafic magmas interact with compositionally evolved plutons and how volatiles contribute to physical and chemical changes operating in mafic-felsic magma interaction. Thus, we experimentally constrained the effect of volatiles (mainly H2O) on the interaction of water-saturated mafic magmas and water-saturated felsic crystal mushes in the shallow crust (coronas around quartz crystals close to the interface of the two samples; v) lack of alkali (particularly, K) 'uphill diffusion' in the mafic end-member. The experimental and analytical results are against the existing state-of-the-art that does not consider the influence of volatiles in a realistic scenario where two magmas display different initial composition, water content and crystallinity prior to interaction. Moreover, the results demonstrate the striking chemical and microstructural similarity between the run products and what observed in the textures of natural enclaves within felsic host rocks. This research is fundamental for understanding numerous, well-documented physico-chemical processes such as: magma mixing/mingling, alkali migration, formation of mafic enclaves, magma defrosting or partial melting of crystal mushes and their rheological remobilization within the Earth's crust.

  17. Mafic inclusions in Yosemite granites and Lassen Pk lavas: records of complex crust-mantle interactions

    Energy Technology Data Exchange (ETDEWEB)

    Reid, J.B. Jr.; Flinn, J.E.


    This study compares three small-scale magmatic systems dominated by mafic/felsic interaction that appear to be analogs to the evolution of their larger host systems: mafic inclusions from modern Lassen Pk lavas along with inclusions and related synplutonic dike materials from granitoids in the Tuolumne Intrusive Series. Each system represents quickly chilled mafic melt previously contaminated by digestion of rewarmed, super-solidus felsic hosts. Contaminants occur in part as megacrysts of reworked oligoclase with lesser hb and biot. Within each group MgO-variation diagrams for Fe, Ca, Ti, Si are strikingly linear (r>.96); alkalis are decidedly less regular, and many hybrid rocks show a curious, pronounced Na enrichment. Field data, petrography, and best fit modeling suggests this may result from flow concentration of oligoclase xenocrysts within contaminated synplutonic dikes, and is preserved in the inclusions when dike cores chill as pillows in their felsic host. Dissolution of mafic inclusions erases these anomalies and creates a more regular series of two-component mafic-felsic mixtures in the large host system. The inclusions and dikes thus appear to record a variety of late-stage mafic-felsic interactive processes that earlier and on a larger scale created much of the compositional variety of their intermediate host rocks.

  18. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    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 ...

  19. Complicated and messy politics of inclusion: Michfest and the Boston Dyke March. (United States)

    Trigilio, Jo


    To illustrate the challenge of political organizing that grapples with identity politics and inclusion, I focus on two women-centered annual events with very different politics of inclusion: the Michigan Womyn's Music Festival and the Boston Dyke March. (1) arguments made by marginalized people for inclusion into established oppressed identity groups must be constructed with due care to avoid further marginalizing yet other liminal identities; (2) protesting/boycotting other oppressed groups for the purpose of achieving inclusion is often a problematic strategy; (3) the most effective strategy for honoring all people is to support organizations committed to the ideal of inclusion.

  20. Literature survey on the advance detection of dykes in underground coal mine workings.

    CSIR Research Space (South Africa)

    Fourie, GA


    Full Text Available Literature survey on the advance detection of dykes in underground coal mine workings Prof. G A Fourie Laboratory for Advanced Engineering University of Pretoria Project COL 503b October 1998 i Executive Summary To minimise risk, a more effective.... Average borehole lengths achieved with this method are now in ii the order of 1200 metres, however, development work is in progress to increase the effective reach to 2000 metres. Similar work is currently in progress at Sasol Coal. The use of ground...

  1. Magnetic fabric and flow direction in the Ediacaran Imider dyke swarms (Eastern Anti-Atlas, Morocco), inferred from the Anisotropy of Magnetic Susceptibility (AMS) (United States)

    Otmane, Khadija; Errami, Ezzoura; Olivier, Philippe; Berger, Julien; Triantafyllou, Antoine; Ennih, Nasser


    Located in the Imiter Inlier (Eastern Saghro, Anti-Atlas, Morocco), Ediacaran volcanic dykes have been studied for their petrofabric using Anisotropy of Magnetic Susceptibility (AMS) technique. Four dykes, namely TF, TD, FF and FE show andesitic compositions and are considered to belong to the same dyke swarm. They are oriented respectively N25E, N40E, N50E, and N10E and have been emplaced during a first tectonic event. The dyke FW, oriented N90E displays a composition of alkali basalt and its emplacement is attributed to a subsequent tectonic event. These rocks are propylitized under greenschist facies conditions forming a secondary paragenesis constituted by calcite, chlorite, epidote and sericite. The dykes TF, TD, FF and FE are sub-volcanic calc-alkaline, typical of post-collisional basalts/andesites, belonging to plate margin andesites. The FW dyke shows a within-plate basalt signature; alkaline affinity reflecting a different petrogenetic process. The thermomagnetic analyses show a dominantly ferromagnetic behaviour in the TF dyke core carried by single domain Ti-poor magnetite, maghemite and pyrrhotite. The dominantly paramagnetic susceptibilities in TF dyke rims and TD, FE, FF and FW dykes are controlled by ilmenite, amphibole, pyroxene and chlorite. The magnetic fabrics of the Imider dykes, determined by our AMS study, allows us to reconstitute the tectonic conditions which prevailed during the emplacement of these two generations of volcanic dykes. The first tectonic event was characterized by a roughly NE-SW compression and the second tectonic event is characterized by an E-W shortening followed by a relaxation recording the end of the Pan-African orogeny in the eastern Anti-Atlas.

  2. Late Neoproterozoic layered mafic intrusion of arc-affinity in the Arabian-Nubian Shield: A case study from the Shahira layered mafic intrusion, southern Sinai, Egypt

    Energy Technology Data Exchange (ETDEWEB)

    Azer, M.K.; Obeid, M.A.; Gahalan, H.A.


    The Shahira Layered Mafic Intrusion (SLMI), which belongs to the late Neoproterozoic plutonic rocks of the Arabian-Nubian Shield, is the largest layered mafic intrusion in southern Sinai. Field relations indicate that it is younger than the surrounding metamorphic rocks and older than the post-orogenic granites. Based on variation in mineral paragenesis and chemical composition, the SLMI is distinguished into pyroxene-hornblende gabbro, hornblende gabbro and diorite lithologies. The outer zone of the mafic intrusion is characterized by fine-grained rocks (chilled margin gabbroic facies), with typical subophitic and/or microgranular textures. Different rock units from the mafic intrusion show gradational boundaries in between. They show some indications of low grade metamorphism, where primary minerals are transformed into secondary ones. Geochemically, the Shahira layered mafic intrusion is characterized by enrichment in LILE relative to HFSE (e.g. Nb, P, Zr, Ti, Y), and LREE relative to HREE [(La/Lu)n= 4.75–8.58], with subalkaline characters. It has geochemical characteristics of pre-collisional arc-type environment. The geochemical signature of the investigated gabbros indicates partial melting of mantle wedge in a volcanic-arc setting, being followed by fractional crystallization and crustal contamination. Fractional crystallization processes played a vital role during emplacement of the Shahira intrusion and evolution of its mafic and intermediate rock units. The initial magma was evolved through crystallization of hornblende which was caused by slight increasing of H2O in the magma after crystallization of liquidus olivine, pyroxene and Ca-rich plagioclase. The gabbroic rocks crystallized at pressures between 4.5 and 6.9kbar (~15–20km depth). Whereas, the diorites yielded the lowest crystallization pressure between 1.0 to 4.4Kbar (<10km depth). Temperature was estimated by several geothermometers, which yielded crystallization temperatures ranging from 835

  3. 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.

  4. Intraplate mafic magmatism: New insights from Africa and N. America (United States)

    Ebinger, C. J.; van der Lee, S.; Tepp, G.; Pierre, S.


    Plate tectonic concepts consider that continental interiors are stable, with magmatism and strain localized to plate boundaries. We re-evaluate the role of pre-existing and evolving lithospheric heterogeneities in light of perspectives afforded by surface to mantle results from active and ancient rift zones in Africa and N. America. Our process-oriented approach addresses the localization of strain and magmatism and stability of continental plate interiors. In both Africa and N. America, geophysical imaging and xenolith studies reveal that thick, buoyant, and chemically distinct Archaean cratons with deep roots may deflect mantle flow, and localize magmatism and strain over many tectonic cycles. Studies of the Colorado Plateau and East African rift reveal widespread mantle metasomatism, and high levels of magma degassing along faults and at active volcanoes. The volcanoes and magmatic systems show a strong dependence on pre-existing heterogeneities in plate structure. Syntheses of the EarthScope program ishow that lateral density contrasts and migration of volatiles that accumulated during subduction can refertilize mantle lithosphere, and enable volatile-rich magmatism beneath relatively thick continental lithosphere. For example, the passive margin of eastern N. America shows uplift and magmatism long after the onset of seafloor spreading, demonstrating the dynamic nature of coupling between the lithosphere, asthenosphere, and deeper mantle. As demonstrated by the East African Rift, the Mid-Continent Rift, and other active and ancient rift zones, the interiors of continents, including thick, cold Archaean cratons are not immune to mafic magmatism and tectonism. Recent studies in N. America and Africa reveal ca. 1000 km-wide zones of dynamic uplift, low upper mantle velocities, and broadly distributed strain. The distribution of magmatism and volatile release, in combination with geophysical signals, indicates a potentially convective origin for widespread

  5. 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

  6. Lamprophyres from the Harohalli dyke swarm in the Halaguru and Mysore areas, Southern India: Implications for backarc basin magmatism (United States)

    Lanjewar, Shubhangi; Randive, Kirtikumar


    The Bangalore and Harohalli dyke swarms occur in the eastern part of the Dharwar craton. The older Bangalore dyke swarm is made up of dolerites, trending east-west, and the younger contains alkaline dykes that trend approximately north-south. The lamprophyres of the Harohalli dyke swarm occur in the Halaguru and Mysore industrial areas where they are exposed as fresh porphyritic - panidiomorphic dykes, containing crustal xenoliths, and showing chilled contacts with the country rock charnokites. They are chiefly composed of amphiboles which form well-developed phenocrysts. Clinopyroxenes are present in some of the dykes. Compositional zoning is observed in clinopyroxenes and amphiboles; their zoning patterns indicate that the magma experienced cryptic variations and that fractional crystallization was a dominant process in the evolution of the Harohalli Lamprophyres (HRL). The HRL are calc-alkaline with shoshonitic affinity and exhibit a K2O/Na2O ratio of ∼1. They show primitive (MORB-like) trace-element characters. LILE and LREE both show marginally enriched patterns; whereas HFSE and HREE show strongly depleted patterns. In the regional geologic sense, HRL dykes are characterised by two major influences; namely, (i) primary source region characteristics, which are geochemically more primitive, roughly falling within fields of primitive - MORB and enriched- MORB and (ii) the continental lithosphere. The data points for the HRL distinctly show their proximity to N-MORB and scatter towards the continental crust. Moreover, features like xenolith assimilation might influence the trace-element characteristics of the HRL dykes. Such magmas with mixed characters can be formed in a backarc basin environment. Geochemical proxies such as Ba/Nb vs Nb/Yb, Ba/Th vs Th/Nb, and the water content of magmas; which have been effectively used for discriminating backarc basin magmas worldwide, also indicate that the HRL magmas were generated in a backarc environment with inputs from

  7. Pesticides in soil and sediment of a dyke-protected area of the Red River Delta, Vietnam (United States)

    Braun, Gianna; Bläsing, Melanie; Kruse, Jens; Amelung, Wulf; Renaud, Fabrice; Sebesvari, Zita


    Coastal regions are densely populated but at the same time represent important agricultural areas for food production of the growing world population. To sustain high agricultural yields, in monocultures such as permanent rice systems, pesticides are used in high quantity and frequency. While earlier studies monitored the fate of pesticides in paddy rice systems, the overall fate of these compounds is altered nowadays due to the construction of dykes, which are needed in many delta regions to protect them from high tides, storm surges and salt water intrusion such as in the Red River Delta. The dyke system regulates the discharge and water exchange inside the diked area including irrigation channels for the paddy rice production. Local authorities observed increasing pollution towards the sea (highest pollution close to the dykes) and hypothesized that the dyke system would prevent water exchange and thus lead to an accumulation of pollutants within the diked area. Hence, the purpose of this study was to investigate the effect of dykes on pesticide pollution patterns in coastal delta regions of the Red River Delta. The study was conducted in the district Giao Thuy of the Red River Delta, Vietnam. This area is surrounded by a sea and river dyke; both have several inlet and outlet gates to control the water level in the irrigation channels. We determined the pesticide pollution pattern in a diked agricultural area, as well as along salinity gradients in and outside the diked areas. Samples were taken from rice fields and sediments from irrigation channels inside the diked area as well from saline aquaculture fields located outside the dyke. Pesticide analysis was conducted by accelerated solvent extraction (ASE), followed up by the clean-up process described by Laabs et al. (2007) and analyses using gas chromatography coupled with a mass selective detector (MSD). Preliminary results suggest that out of the 26 analysed compounds chlorpyrifos, propiconazole and

  8. Decontamination and/or revegetation of fly ash dykes through naturally growing plants. (United States)

    Gupta, Amit K; Sinha, Sarita


    Present study is focused on the decontamination and/or revegetation of fly ash dykes through naturally growing plants, namely Calotropis procera, Cassia tora, Chenopodium album, Sida cardifolia, Blumea lacera. The results of sequential extraction study showed that maximum amount of metals (Na, K, Fe, Mn, Cr, Pb, Ni, Cd) were associated with residual and Fe-Mn fractions. Diethylenetriamine penta acetic acid (DTPA)-triethanolamine (TEA) extraction assessed the bioavailability of the metals. The total metal accumulation in tested plants was found in the order; C. album>S. cardifolia>C. tora>C. procera>B. lacera. The maximum bioconcentration factor (BCF) was recorded in S. cardifolia for the metals (Na, Fe, Zn, Cd), in C. procera for the metals (Mn, Cu, Ni, Cr) and in C. album for the metals (Co, Pb). However, the translocation factor (TF) of most of the metals was found more in S. cardifolia followed by C. album than other plants. Among all the plants, C. album have shown high BCF and low TF values for toxic metals (Pb, Cd) and suitable for phytostabilization of these metals. Principal component analysis was used to predict translocation behavior of the metals in different parts of the plants which was found similar for the metals (Cu, Zn, Mn, Cr). All examined plants are suitable for revegetation (naturally grows on fly ash dykes) and S. cardifolia and C. album may be used for decontamination purposes.

  9. 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.

  10. 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


    Flooding in the Mekong Delta is an annual phenomenon causing inundation of large parts of the delta. This flooding is vital for the geomorphological stability of the delta, but is also the backbone of the highly productive agro-economy. However, extraordinary high floods are on the other hand a major hazard for the millions of people living in the delta. Therefore large scale developments of hydraulic structures took place in the Vietnamese part of the delta in the last decades. Particularly in the areas prone to deep and long lasting inundations many flood protection structures, mainly dykes, were built. These structures enable a blocking of inundation in large parts of these areas and by this the cropping of a third crop per year during the flood season. However, these structures are frequently blamed for increasing water levels in the areas downstream. Thus this study aimed at the investigation and attribution of changes in flood hazard in the Vietnamese Mekong Delta (VMD) due to high-dyke construction in deep flood prone areas, mainly in An Giang and Dong Thap provinces. This analysis started with the estimation of monotonic trends at key gauging stations in the delta: Kratie at the apex of the Mekong delta; Tan Chau and Chau Doc in the VMD just upstream of the areas with high-dyke construction; and Can Tho and My Thuan, located downstream of the high-dyke areas. The tests were undertaken assuming different magnitudes of errors in the data using historical records from 1978 - 2015, using the Mann-Kendall test and Sen's slope estimation. The obtained trends were thus tested for robustness against data errors. In order to obtain a better understanding of trends in the flood dynamics, the tests are performed on both flood peak and flood duration. In addition, the Pettitt test was applied to identify step changes in the water level data at 4 gauge stations located in the VMD. After the trend analysis, the impacts of high-dyke development were quantified with the

  11. Associations of the Van Dyke's salamander (Plethodon vandykei) with geomorphic conditions in headwall seeps of the Cascade Range, Washington State. (United States)

    A.P. McIntyre; R.A. Schmitz; C.M. Crisafulli


    We explored the association between Van Dyke's salamander (Plethodon vandykei) and hydrologic condition, geomorphology, and vegetation structure in headwall seeps in the Cascade Range of Washington State. We modeled occurrence of P. vandykei at three site scales: between seeps, within seeps, and between microhabitat sites...

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

    DEFF Research Database (Denmark)

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


    Abstract Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–...

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


    Piro, Ettore; Piccione, Maria; Marrone, Gianluca; Giuffr?, Mario; Corsello, Giovanni


    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...

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

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


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

  15. 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.

  16. Dyke-Davidoff-Masson Syndrome. An unusual cause of status epilepticus. (United States)

    Zawar, Ifrah; Khan, Ashfa A; Sultan, Tipu; Rathore, Ahsan W


    The Dyke-Davidoff-Masson Syndrome (DDMS) results from an insult to the growing brain in utero or early infancy, which lead to loss of neurons compromising the growth of the brain. Clinical presentation includes seizures, hemiparesis, facial asymmetry, and learning disability. Radiological findings include cerebral atrophy on one side. Here, we present a case with status epilepticus who had underlying DDMS. It is a rare syndrome and uncommon cause for status epilepticus. Infections of CNS, hypoxic ischemic encephalopathy, intracranial bleed, trauma, congenital vascular malformations are the common causes of this syndrome. Diagnosis is established after clinical history, examination, and MRI. Intractable seizures can be controlled with appropriate anticonvulsants. Subsequently, these children may require physiotherapy, speech therapy, and occupational therapy in addition to the anticonvulsant medication. Outcome is better if the seizures are controlled.

  17. Sr isotopic study of mafic inclusions from Uta-jima, Southwest Japan

    International Nuclear Information System (INIS)

    Ishizaka, Kyoichi; Yanagi, Takeru; Murakami, Nobuhide.


    K, Rb and Sr concentrations and Sr isotopic composition were determined for eight mafic inclusions found in Cenozoic alkali basalt of the Uta-jima (Uta Island) in the Japan Sea, Southwest Japan. The mafic inclusions are composed of gabbroic and granulitic rocks of presumably lower crustal origin. The mafic inclusions have 87 Sr/ 86 Sr ratios ranging from 0.70457 to 0.70612. Most of them are isotopically distinguishable from the host basalt (0.70360-0.70440), while one mafic inclusion is isotopically indistinguishable from the host, suggesting isotopic exchange. Data for separated minerals from one gabbroic inclusion define a crude isochron, yielding a young age of approximately 100 m.y. From the results of the present study and those reported for ultramafic inclusions from the Oki-Dogo Island, another island in the Japan Sea, Southwest Japan, it is inferred that the materials constituting the lowermost crust and the uppermost part of the mantle beneath the Southwest Japan arc have relatively high 87 Sr/ 86 Sr ratios from 0.705 to 0.706 and have relatively young ages. (author)

  18. Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong ...

    Indian Academy of Sciences (India)

    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.

  19. Thermal and Transport Properties of Mafic and Ultramafic Rocks of Oman Ophiolite

    Directory of Open Access Journals (Sweden)

    Sayyadul Arafin


    Full Text Available Thermal and other physical properties of rocks and minerals are of considerable significance for deriving mineralogical and compositional models of the Earth's mantle. We have determined these properties for the mafic rock such as gabbro and ultramafic rock like harzburgite of the Oman ophiolite suite by utilizing the Debye characteristic property ,Θ-

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

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


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

  1. 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

  2. Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion (United States)

    Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie


    The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid

  3. Variation of magnetic properties in sedimentary rocks hosting the Foum Zguid dyke (southern Morocco): Combined effects of re-crystallization and Fe-metasomatism


    Silva, Pedro; Henry, Bernard; Marques, Fernando; Mateus, António; Madureira, Pedro; Lourenço, Nuno; Miranda, Miguel


    The effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood. Therefore, we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the Foum Zguid dyke in southern Morocco. The study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments. The present study shows that: (1) close to Foum Zguid...

  4. Magnetic resonance imaging depiction of acquired Dyke-Davidoff-Masson syndrome with crossed cerebro-cerebellar diaschisis: Report of two cases. (United States)

    Gupta, Ranjana; Joshi, Sandeep; Mittal, Amit; Luthra, Ishita; Mittal, Puneet; Verma, Vibha


    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.

  5. Seismic constraints on a large dyking event in Western Gulf of Aden (United States)

    Ahmed, A.; Doubre, C.; Leroy, S.; Perrot, J.; Audin, L.; Rolandone, F.; Keir, D.; Al-Ganad, I.; Khanbari, K.; Mohamed, K.; Vergne, J.; Jacques, E.; Nercessian, A.


    In November 2010, a large number of events were recorded by the world seismic networks showing important activity occurring along the western part of the Aden Ridge. West of the Shulka El Sheik transform zone, events in this large seismic swarm (magnitudes above 5) occurred in a complex area, where the change of both the ridge direction and the bathymetry suggest the propagation of the ridge into a continental lithosphere and the influence of the thermal anomaly of the Afar Hot Spot. We combine several sets of data from permanent networks and temporary 3C broad stations installed after the beginning of the event along the southern and eastern coasts of Yemen and Djibouti respectively, we located more than 600 earthquakes with magnitudes ranging from 2.5 to 5.6 that occurred during the first months following the first event. The spatial distribution of the main seismicity reveals a very clear N115°-trending alignment, parallel to the mean direction of the en-echelon spreading segments that form the ridge at this longitude. Half of the events, which represent half of the total seismic energy released during the first months, are located in the central third section of the segment. Here several volcanic cones and recent lava flows observed from bathymetric and acoustic reflectivity data during the Tadjouraden cruise (Audin, 1999, Dauteuil et al., 2001) constitute the sea floor. In addition to this main activity, two small groups of events suggest the activiation of landslides into a large fan and the activity in a volcanic area 50 km due east from the main active zone. The time evolution of the seismicity shows several bursts of activity. Some of them are clearly related to sudden activities within the volcanic areas, when others exhibit horizontal migration of the events, with velocity around ~ 1 km/h. The time-space evolution of the seismicity clearly reveals the intrusion of dykes associated with magma propagation from the crustal magmatic centres into the rift

  6. Partitioning of Cu between mafic minerals, Fe-Ti oxides and intermediate to felsic melts (United States)

    Liu, Xingcheng; Xiong, Xiaolin; Audétat, Andreas; Li, Yuan


    This study used improved capsule technique i.e., Pt95Cu05 or Au95Cu05 alloy capsules as Cu sources to determine Cu partitioning between mafic minerals, Fe-Ti oxides and intermediate to felsic melts at 0.5-2.5 GPa, 950-1100 °C and various oxygen fugacities (fO2). In combination with the data from the mafic composition systems, the results demonstrate that Cu is generally highly incompatible in mafic minerals and moderately incompatible to compatible in Fe-Ti oxides. The general order of mineral/melt Cu partition coefficients (DCu) is garnet (0.01-0.06) ⩽ olivine (0.04-0.20) ≈ opx (0.04-0.24) ≈ amphibole (0.04-0.20) ⩽ cpx (0.04-0.45) ⩽ magnetite, titanomagnetite and Cr-spinel (0.18-1.83). The variations in DCu depend mainly on temperature, fO2 or mineral composition. In general, DCu for olivine (and perhaps opx) increases with decreasing temperature and increasing fO2. DCu increases for cpx with Na+ (pfu) in cpx, for magnetite and Cr-spinel with Fe3+ (pfu) in these phases and for titanomagnetite with Ti4+ (pfu) in this phase. The large number of DCu data (99 pairs) serves as a foundation for quantitatively understanding the behavior of Cu during magmatic processes. The generation of intermediate to felsic magmas via fractional crystallization or partial melting of mafic rocks (magmas) at deep levels of crust involves removal of or leaving assemblages of mafic minerals + Fe-Ti oxides ± sulfides. With our DCu data on mafic minerals and Fe-Ti oxides, DCubulk values around 0.2 were obtained for the sulfide-free assemblages. Cu will thus be concentrated efficiently in the derived melts during these two processes if sulfides are absent or negligible, explaining that high fO2 and sulfide-destabilization are favorable to formation of the porphyry Cu system.

  7. Basaltic dykes of the Eastern Belt of Peninsular Malaysia: The effects of the difference in crustal thickness of Sibumasu and Indochina (United States)

    Ghani, Azman A.; Lo, Ching-Hua; Chung, Sun-Lin


    Basaltic dykes of Peninsular Malaysia are confined to the Eastern Belt (Indochina/East Malaya block) as compared with the Western Belt (Sibumasu Block). The dyke intruded through a crustal fracture formed by stress developed from the evolution of two offshore basins (Malay and Penyu basins) east of Peninsular Malaysia. The Ar-Ar dating from the present study combined with the previous geochronological data indicate that the ages of dykes range from 79 ± 2 Ma to 179 ± 2 Ma. Thus it is difficult to correlate the dykes with the closure of Tethys during Permo-Triassic time because of the younger age of the dykes. The majority of the dykes exposed in the Eastern Belt may have been attributed to the difference of crustal thickness between the Eastern and Western belt of Peninsular Malaysia. A thicker Western Belt crust (13 km more than both Eastern and Central belts) is difficult to rupture with normal plate tectonic stress and therefore serves to contain the rise of a mantle derived melt. The chemistry indicates the basalts are olivine to quartz normative and are of the continental within-plate category.

  8. The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry (United States)

    Nkouandou, Oumarou Faarouk; Bardintzeff, Jacques-Marie; Mahamat, Oumar; Fagny Mefire, Aminatou; Ganwa, Alembert Alexandre


    Dolerite dykes are widespread in the Mongo area within the granitic Guéra Massif (Chad, Central Africa). Dykes are several hundred metres to several kilometres long, a metre to decametre thick, and vertical, crosscutting the Pan-African granitic basement rocks. They are controlled by major Pan-African NNE-SSW, NE-SW and ENE-WSW faults. Rocks constituting the dykes exhibit typical doleritic textures (i.e. intergranular, ophitic or subophitic). They are mainly composed of phenocrysts, microcrysts and microlites of clinopyroxene, amphibole, plagioclase, alkali feldspar and Fe-Ti oxides. Mongo dolerites are classified into two groups: Group 1 of basalt and trachybasalt and Group 2 of basaltic trachyandesite, which follow a trend with continental tholeiite affinities, and are differentiated through fractional crystallization. Trace element enrichment and REE contents show the high melting degree at shallow depths of enriched sub-continental lithospheric mantle, whose composition is intermediate between OIB and MORB, contaminated by small amounts of sediment during older subduction. Mongo dolerites are interpreted as imprints of either the final stage of stabilization of ancient continental crust, or the initiation of tectonic activity related to Pan-African mobile belts.

  9. Paleomagnetic study of 1765 Ma dyke swarm from the Singhbhum Craton: Implications to the paleogeography of India (United States)

    Shankar, Ravi; Srinivasa Sarma, D.; Ramesh Babu, N.; Parashuramulu, V.


    We report the first key paleopole as a result of paleomagnetic study on a precisely dated 1765.3 ± 1.0 Ma WNW-ESE trending dyke swarm from Singhbhum Craton. This pole has been used in this study to propose the paleogeographic reconstruction of India with Baltica Craton and North China Craton. Incremental alternating field (AF) and thermal demagnetization, isolated high coercivity components with north to north-westerly declination and shallow negative inclination from 9 sampling sites which are representing different individual dykes. The primary origin of the ChRM is supported by the positive baked contact test. The WNW-ESE trending dykes yield a mean paleomagnetic direction with a declination = 329.2° and an inclination = -22.8° (k = 31.6; α95 = 9.3°). The positive bake contact test proves the primary nature of remanence. The pole position of Singhbhum Craton at 1765 Ma is 45°N, 311°E (dp = 5.2 and dm = 9.9). Paleogeographic reconstruction at ca. 1770 Ma, supported by geological, tectonic and metallogenic evidences indicate that the Baltica Craton and India linkage can be stable for at least ∼370 Ma (∼1770-1400 Ma). There is also reasonable evidence in support of India-North China Craton spatial proximity at ∼1770 Ma.

  10. 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.

  11. Dyke-Davidoff-Masson syndrome: case report of fetal unilateral ventriculomegaly and hypoplastic left middle cerebral artery. (United States)

    Piro, Ettore; Piccione, Maria; Marrone, Gianluca; Giuffrè, Mario; Corsello, Giovanni


    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, adolescence and adult ages. We describe a female infant with prenatal diagnosis of unilateral left ventriculomegaly in which early brain MRI and contrast enhanced-MRI angiography, showed cerebral left hemiatrophy associated with reduced caliber of the left middle cerebral artery revealing the characteristic findings of the Dyke-Davidoff-Masson syndrome. Prenatal imaging, cerebral vascular anomaly responsible for the cerebral hemiatrophy and the early clinical evolution have never been described before in such a young child and complete the acquired clinical descriptions in older children. Differential diagnosis, genetic investigations, neurophysiologic assessments, short term clinical and developmental follow up are described. Dyke-Davidoff-Masson syndrome must be ruled out in differential diagnosis of fetal unilateral ventriculomegaly. Early clinical assessment, differential diagnosis and cerebral imaging including cerebral MRI angiography allow the clinicians to diagnose also in early infancy this rare condition.

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

    Directory of Open Access Journals (Sweden)

    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.

  13. 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.

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

    International Nuclear Information System (INIS)

    Liu Shen; Hu Ruizhong; Zhao Junhong; Feng Caixia; Zou, Haibo


    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 ( 87 Sr/ 86 Sr) i (0.7050-0.7099) and negative ε Nd (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)

  15. 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.

  16. Proterozoic Diabase Dyke Swarms of Northern Ontario: Paleomagnetic Indicators of Broad-Scale Crustal Deformation of the Archean Superior Province (United States)

    Halls, H. C.


    Several Proterozoic dyke swarms, all with precise U-Pb ages, (Matachewan, Senneterre, Biscotasing, Marathon and Fort Frances) occur over an area of the southern Superior Province covering more than 300,000 square kilometres. Cutting across this region is the Kapuskasing Zone, a 500 km-long fault zone along which dextral transpression at about 1.9 to 2.0 Ga has produced crustal uplift locally in excess of 20 km and lateral fault displacements of up to 70 km (Percival and West, 1994). The 2446-2473 Ma Matachewan swarm has been a subject for study throughout the last 40 years of Canadian paleomagnetism. However only in the last 20 years has the true size of the swarm been realised (Ernst and Halls, 1984; Halls et al., 1994), and the discovery made that regional variations in the direction of primary magnetization in the dykes are intimately related to the Kapuskasing Zone (KZ). The swarm is now known to span a single reversal of the Earth's magnetic field. The younger N polarity epoch, although barely recorded in the dying stages of the intrusive episode, is well preserved in dykes within uplifted crust inside the KZ. Here fine-grained magnetite, exsolved from dyke feldspars due to slow cooling of the swarm at depth, acquired a remanence of probable thermo-chemical origin prior to or during crustal uplift (Halls and Palmer, 1990; Halls et al., 1994; Halls and Zhang, 2003). The inference is that dykes intruded during the older R polarity epoch carry a near surface primary R magnetization but have been remagnetized to N at depth. Paleomagnetic data from that part of the swarm outside the KZ are therefore dominated by the older R polarity magnetization. They show that the western half of the shield has rotated counter-clockwise about 10 to 20 degrees relative to the eastern half across the KZ (Bates and Halls, 1991; Halls and Stott, 2003). This rotation is also seen in paleomagnetic data from the 2170 Ma Biscotasing swarm, which is now known to occur on both sides of the

  17. Petrology and Geochemistry of an Upper Crustal Mafic Complex- Hidden Lakes, Sierra Nevada Batholith, California (United States)

    Lewis, M.; Bucholz, C. E.; Jagoutz, O. E.; Eddy, M. P.


    Magmatic differentiation in arc settings is likely a polybaric process, with crystallization of primitive basalts occurring primarily in the lower crust and more evolved melts in the upper crust. The general lack of mafic-ultramafic cumulates in the silicic paleo-arc upper crust supports this model. However, the Sierra Nevada Batholith preserves numerous mafic intrusions up to 25 km2, suggesting that significant volumes of mafic magma may differentiate at shallow crustal levels. Previous studies on several such intrusions report ages contemporaneous with Cretaceous batholith emplacement (Coleman et al., 1995), but only a few have investigated their chemistry and relationship to arc magmatism (Frost, 1987; Frost & Mahood, 1987; Sisson et al., 1996). We present field observations, petrography, mineral chemistry, and bulk rock compositional data for the Hidden Lakes Mafic Complex (HLMC), located in the Central Sierra Nevada Batholith. Preliminary CA-ID-TIMS U-Pb zircon ages constrain crystallization between 90 and 95 Ma, slightly older than the surrounding Cretaceous felsic plutons (89-90 Ma) and younger than adjacent Jurassic granodiorites (172 Ma). This 2.2 km2 complex consists of biotite+amphibole gabbros through qtz-monzonites, in gradational contact, and contains local pods of biotite- and amphibole-bearing olivine-orthopyroxenites and gabbronorites. Mineral compositions and field relations suggest that these lithologies were derived from a common crystallization sequence. The most primitive olivine-pyroxenite contains olivine and orthopyroxene in equilibrium with a melt with Mg# 54. Subsequent crystallization over a temperature range of 1025 to 700°C produced more evolved lithologies up to qtz-monzonites. Al-in-hornblende calculations for HLMC qtz-monzonites indicate a crystallization depth of 9-10 km, well into the upper crust. The early crystallization of amphibole requires a parental basalt with >6 wt% H2O, which may have enabled it to ascend into the upper

  18. The Deccan tholeiite lavas and dykes of Ghatkopar-Powai area, Mumbai, Panvel flexure zone: Geochemistry, stratigraphic status, and tectonic significance (United States)

    Sheth, Hetu C.; Zellmer, Georg F.; Demonterova, Elena I.; Ivanov, Alexei V.; Kumar, Rohit; Patel, Rakesh Kumar


    Mumbai City, situated on the western Indian coast, is well known for exposures of late-stage Deccan pillow basalts and spilites, pyroclastic rocks, rhyolite lavas, and trachyte intrusions. These rock units, and a little-studied sequence of tholeiitic flows and dykes in the eastern part of Mumbai City, constitute the west-dipping limb of a regional tectonic structure called the Panvel flexure. Here we present field, petrographic, major and trace element and Sr-Nd isotopic data on these tholeiitic flows and dykes, best exposed in the Ghatkopar-Powai area. The flows closely resemble the Mahabaleshwar Formation of the thick Western Ghats sequence to the east, in Sr-Nd isotopic ratios and multielement patterns, but have other geochemical characteristics (e.g., incompatible trace element ratios) unlike the Mahabaleshwar or any other Formation. The flows may have originated from a nearby eruptive center, possibly offshore of Mumbai. Two dykes resemble the Ambenali Formation of the Western Ghats in all geochemical characteristics, though they may not represent feeders of the Ambenali Formation lavas. Most dykes are distinct from any of the Western Ghats stratigraphic units. Some show partial (e.g., Sr-Nd isotopic) similarities to the Mahabaleshwar Formation, and these include several dykes with unusual, concave-downward REE patterns suggesting residual amphibole and thus a lithospheric source. The flows and dykes are inferred to have undergone little or no contamination, by lower continental crust. Most dykes are almost vertical, suggesting emplacement after the formation of the Panvel flexure, and indicate considerable east-west lithospheric extension during this late but magmatically vigorous stage of Deccan volcanism.

  19. Mineral chemistry of monazite-(Nd, xenotime-(Y, apatite, fluorite and zircon hosting in lamprophyre dyke in Abu Rusheid area, South Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed A. Ali


    Full Text Available The studied mineralized lamprophyre dyke in Abu Rusheid area is trending NNW-SSE, and occurs withinAbu Rusheid mineralized shear zone, measuring 0.2 - 1.0 m in width and 0.5 - 1.0 km in length. It was emplacedparallel with the Abu Rusheid shear zone. The dyke is mainly composed of plagioclases, amphiboles, mica (musco-vite and biotite, relics of pyroxenes with K-feldspars and quartz derived from surrounding country rocks asphenocrysts embedded in fine-grained groundmass. The lamprophyre dyke hosts REE-minerals monazite-(Nd,xenotime-(Y, and REE-bearing minerals apatite, fluorite, zircon-(Hf, rutile with inclusions of xenotime and ironoxides. The emplacement of lamprophyre dyke caused heating in the mineralized shear zone of Abu Rusheid area.The lamprophyre dyke was subsequently affected by hydrothermal alterations (e.g. chlorite-carbonate, muscovitization,fluoritization.The REE were remobilized from the mineralized shear zones by hydrothermal solutionsand re-precipitatedas REE-minerals xenotime-(Y and monazite-(Nd around flourapatite, fluorite, zircon andrutile. The solid solutions between monazite-(Nd and xenotime-(Y were formed as a product precipitation fromhydrothermal solutions. Also, the apatite mineral in the lamprophyre dyke was subjected to the heating duringthe emplacement, which lead to its alteration and breakdown with concominant precipitation of xenotime-(Yand monazite-(Nd. The chemistry of monazite-(Nd and xenotime-(Y obtained by scanning electron microscopy(SEM, and electron probe microanalysis (EPMA, showed that these minerals are enriched in U and Th. Themonazite-(Nd associated with fluorapatite in the studied dyke is poor in Th (0.02 ≤ Th ≤ 0.81 wt%, but usuallyrich in U (0.92 ≤ U ≤ 2.91 wt%, which indicates that monazite formed as a result of flourapatite metasomatism.

  20. 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.

  1. Magnetic studies and U Pb geochronology of the Uruguayan dyke swarm, Rio de la Plata craton, Uruguay: paleomagnetic and economic implications (United States)

    Halls, Henry C.; Campal, Nestor; Davis, Don W.; Bossi, Jorge


    A U-Pb age on baddeleyite of 1790±5 Ma has been obtained from a single dyke of the Uruguayan tholeiitic dyke swarm from the Rio de la Plata craton. Palaeomagnetic results from this and 10 other dykes yield two components, one (A) has the following paleomagnetic parameters: declination=12°, inclination=-16°, α95=7°, latitude of paleopole=61°, longitude=-31°, dp=4°, dm=7°, paleolatitude=-8°, whereas another (B), about 20° steeper, has a direction closer to the present Earth's field direction in Uruguay. Neither magnetisation is considered primary, although the A component may represent a composite between B and a primary component. A field test for the primary nature of the remanences was inconclusive, and no primary pole positions of similar age from other South American cratons are available for comparison. The magnetic results demonstrate that darker-coloured andesite dykes that are sought for facing and monument stone (as 'black granite') can be easily differentiated from more andesi-basaltic, lighter coloured, less valuable dykes of the same swarm, using aeromagnetic data. The results suggest that a high resolution airborne magnetic survey could constitute an important exploration tool for the Uruguayan 'black granite' industry.

  2. Ultramafic lavas and pyroxene-spinifex high-Mg basaltic dykes from the Othris ophiolite complex, Greece (United States)

    Baziotis, Ioannis; Economou-Eliopoulos, Maria; Asimow, Paul


    This study aims to constrain the physico-chemical conditions and processes associated with the origin of ultramafic lavas of the Agrilia formation and high-Mg basaltic dykes in the Pournari area within the Othris ophiolite complex, a supra-subduction zone ophiolite of Mesozoic age (Paraskevopoulos & Economou, 1986; Barth et al., 2008). Hand-sample-scale spinifex texture is lacking from the ultramafic lavas and, despite whole-rock MgO contents greater than 31 wt.%, we infer an upper bound of 17 wt.% MgO for the erupted liquid, and thus identify these lavas as picrites containing accumulated olivine. We use textural and compositional criteria to divide the crystals within the Agrilia lavas between pre-eruptive and post-eruptive growth phases. The high-Mg basaltic dyke margins display a distinctive thin-section-scale micro-spinifex texture of skeletal and plumose Al- and Fe-rich clinopyroxene surrounded by large crystals of orthopyroxene. Normally zoned clinopyroxene in the Agrilia lavas and clinopyroxene of various textures (skeletal, needle- and dendritic-like) and sizes in the Pournari dykes display anomalous enrichment in Al2O3 and FeO* with decreasing MgO that require rapid, disequilibrium growth. Quantitative characteristics of the micro-spinifex pyroxene textures (Elements and related metals are Pd/Ir=11.5-13.0, Cu/Pd=6000-7210, Ti/Pd=22.78-31.97×103 for Agrilia lavas and Pd/Ir=4.5-14.0, Cu/Pd=3140-5550, Ti/Pd=4.66-17.32×103 for Pournari dykes; all are very close to those reported for typical komatiites (Barnes et al., 1988). Despite the absence of true komatiite lavas, a number of geochemical features of the Othris suite, including the PGE contents and ratios and the micro-spinifex, disequilibrium cpx growth, are similar to Mesozoic and Archaean komatiites. References Barnes et al., 1988. Journal of Petrology 29, 305-331. Barth et al., 2008. Lithos, 100(1), 234-254. Faure et al., 2006. Journal of Petrology 47, 1591- 1610. Paraskevopoulos, G., Economou, M

  3. A primitive mantle source for the Neoarchean mafic rocks from the Tanzania Craton

    Directory of Open Access Journals (Sweden)

    Y.A. Cook


    Full Text Available Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.% MgO. This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf = 32–35, Ti/Zr = 107–147, producing flat REE and HFSE profiles [(La/Ybpm = 0.9–1.3], with abundances of 3–10 times primitive mantle and with minor negative anomalies of Nb [(Nb/Lapm = 0.6–0.8] and Th [(Th/Lapm = 0.6–0.9]. Initial isotope compositions (ɛNd range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping ∼50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between ∼2830 and ∼2820 Ma; are compositionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

  4. Study on the formation process of composite MMEs (mafic magmatic enclaves) in Taejongdae, Busan Korea. (United States)

    Adam, Mohammed; Kim, Young-Seog; Kim, Taehyung


    Mafic Magmatic Enclave (MME) is a common feature in granitic rocks. However, the layered MMEs developed in the outcrop of Cretaceous granite in Taejongdae National Geopark, Busan show various patterns and interesting phenomena providing useful information on the formation of MMEs. We define here the layered MME as MME composed of several contrasting rock shells. Characteristics and origin of MMEs have been studied in several ways; descriptively, geochemically and through isotope studies due to their importance in the evolution of igneous rocks. This study aims to understand the formation mechanism of the composite MMEs, including the reasons for the diversity of the MME rock types. To achieve those tasks, the relationship between the MMEs and the host granite, and difference between the layers were investigated based on petrological, XRF and EPMA analyses. The important results include the followings: the MMEs can be categorized into two main types; Simple-type composed of a single rock type, and Layered-type composed of different surrounded rock shells. Most of the Simple-type have relatively angular shapes and small sizes, and their contacts with the host granite are commonly sharp but some show small dioritic mixing rims. The forming rocks of the simple MMEs are variable from mafic porphyritic, mafic fine to medium grains and felsic coarse-grained dioritic rocks. The layered MMEs have almost circular to elliptical shapes, and show gradual change in composition from mafic and porphyritic texture in the center to fine in the outer shells (like a chilled margin) and again surrounded by a dioritic layer. The dioritic layer shows another chilled margin with the host granite, indicating double cooling mechanism. Some MMEs are injected by granitic materials through cracks. The injection of the granitic materials into the layered MMEs may indicate fracturing during the cooling process. They may indicate two different phases of mingling and one phase of mixing event. The

  5. Does Deccan Volcanic Sequence contain more reversals than the three-Chron N-R-N flow magnetostratigraphy?- A paleomagnetic evidence from the dyke-swarm near Mumbai (United States)

    Basavaiah, N.; Satyanarayana, KVV; Deenadayalan, K.; Prasad, JN


    New paleomagnetic data from a series of Deccan-age dykes cutting across the basement of lava flows along east and south of Mumbai (18°-19° N and 72°-73.5° E) have uncovered both normal (N) and reverse (R) magnetizations. Out of 33 dykes investigated, 29 dykes have yielded stable characteristic remanent magnetizations (ChRM) amenable for statistical analysis. Twenty dykes exhibit N-polarity and nine dykes show R-polarity. The tilt-corrected dyke VGPs reveal two distinct groups of dykes. Each group consists of both N- and R- polarity dykes on the Indian Apparent Polar Wander Path (APWP). The mean of N-polarity dykes is antipodal to the mean of R-polarity dykes. Group I (GI) comprises nine N-polarity dykes with their mean at Dm = 337.8°, Im = -39.4° (k = 130.7, α95 = 4.5°), and three dykes of R-polarity whose mean is at Dm = 150.7°, Im = 44.1° (k = 147.1, α95 = 10.2°). The corresponding pole positions are at 43.5° S, 102.6° E (A95 = 4.6°) and 36.6° S, 107.6° E (A95 = 8.9°) respectively. These pole positions fall close to 65 Ma old Deccan Superpole (DSP) on the APWP, and may therefore be associated with magnetic Chron 29 N for the N-polarity and 29R for the R-polarity of the three-Chron (30N - 29R -29Ν) magnetostratigraphy of the Deccan Volcanic Province (DVP) used in the computation of DSP. In Group II (GII), eleven dykes display N-polarity with mean at Dm = 312.6°, Im = -45.2° (k = 93.3, α95 = 4.8°) and six dykes show R-polarity with mean at Dm = 130.1°, Im = 48.0° (k = 176.8, α95 = 5.1°). The corresponding pole positions at 25° S, 120.1° E (A95 = 5.3°) and 22.2° S, 119.1° E (A95 = 5.2°) respectively are significantly displaced (by more than 20°) from the DSP along the older segment (˜80 -90 Ma) of the Indian APWP. Hence, the dykes of GII appear to have been emplaced in an earlier episodic Deccan activity than that represented by the DSP. The paleolatituides corresponding to GI and GII are 23.2° S ± 4.0 and 27.6° S ± 4

  6. Metamorphic reactions and preliminary P-T estimates of ultrahigh-temperature mafic granulite from Tonagh Island in the Napier Complex, East Antarctica


    Tunogae,Toshiaki; Osanai,Yasuhito; Toyoshima,Tsuyoshi; Owada,Masaaki; Hokada,Tomokazu; Crowe,Warwick A.


    Metamorphic reactions and P-T conditions of mafic granulites from Tonagh Island in the Archean Napier Complex were examined to evaluate the nature of mafic granulite which has suffered ultrahigh-temperature (UHT) metamorphism. Although a peak mineral assemblage is preserved in plagioclase-orthopyroxene-clinopyroxene mafic granulites, initial mineral chemistry was completely reset by retrograde metamorphism. Evidence of UHT metamorphism was therefore inferred using lamella-bearing pyroxenes as...

  7. 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.

  8. The alkaline peralkaline granitic post-collisional Tin Zebane dyke swarm (Pan-African Tuareg shield, Algeria): prevalent mantle signature and late agpaitic differentiation (United States)

    Hadj-Kaddour, Zakia; Liégeois, Jean-Paul; Demaiffe, Daniel; Caby, Renaud


    The Tin Zebane dyke swarm was emplaced at the end of the Pan-African orogeny along a mega-shear zone separating two contrasting terranes of the Tuareg shield. It is located along the western boundary of the Archaean In Ouzzal rigid terrane, but inside the adjacent Tassendjanet terrane, strongly remobilized at the end of the Precambrian. The Tin Zebane swarm was emplaced during post-collisional sinistral movements along the shear zone at 592.2±5.8 Ma (19WR Rb-Sr isochron). It is a dyke-on-dyke system consisting of dykes and stocks of gabbros and dykes of metaluminous and peralkaline granites. All rock types have Sr and Nd isotopic initial ratios (Sr i=0.7028 and ɛNd=+6.2) typical of a depleted mantle source, similar to the prevalent mantle (PREMA) at that period. No crustal contamination occurred in the genesis of the Tin Zebane swarm. Even the samples showing evidence of fluid interaction (essentially alkali mobility) have the same isotopic signature. The peralkaline granites have peculiar geochemical characteristics that mimic subduction-related granites: this geochemical signature is interpreted in terms of extensive differentiation effects due to late cumulates comprising aegirine, zircon, titanite, allanite and possibly fergusonite, separated from the liquid in the swarm itself due to magmatic flow turbulence. The Tin Zebane dyke swarm is thus of paramount importance for constraining the differentiation of mantle products to generate highly evolved alkaline granites without continental crust participation, in a post-collisional setting.

  9. Clinopyroxenite dykes within a banded unit in the basal mantle section of the northern part of the Oman ophiolite: A record of the latest deep-seated magmatism (United States)

    Ishimaru, Satoko; Arai, Shoji; Tamura, Akihiro


    We found clinopyroxenite dykes in a banded harzburgite block within the Sumeini area in the uppermost part of the metamorphic sole of the northern part of the Oman ophiolite. The dykes clearly cut the deformational structure of the harzburgite and contain its fragments, indicating dyke formation during obduction of the ophiolite. The Mg# [= Mg / (Mg + total Fe)] of clinopyroxenes in the dykes ranges from 0.81 to 0.91, and increases up to 0.93 proximal to harzburgite fragments. Mantle minerals in the harzburgite fragments were modified chemically through interaction with the magma that formed the dyke, yielding lower clinopyroxene and spinel Mg#, and spinels with higher TiO2 contents than those in the unaltered harzburgite. These geochemical features indicate that the clinopyroxenite dykes are cumulates derived from a relatively deep-seated primitive magma enriched in light rare earth elements (LREE) with an ocean island basalt (OIB)-like affinity, geochemically similar to the V3 lavas of an off-ridge origin. Combining these data with geological observations suggests that the clinopyroxenite dykes represent root system of the V3 lavas. Our analyses of the clinopyroxenite dykes testify to the external nature of the V3 magmas, which was added to the sliced oceanic lithosphere from the outside. It is likely that the V3 magma underwent deep-seated crystallization of clinopyroxene and had limited interaction with mantle peridotite en route to the surface. The mode of occurrence of the Sumeini clinopyroxenites (i.e., emplaced into a banded harzburgite block surrounded by garnet amphibolite) is consistent with the generation of OIB-like magmas (V3 lava) beneath the Oman ophiolite resulting from the break-off of the "subducting slab" and subsequent infiltration of hot asthenospheric mantle. This view is consistent with the limited distribution of V3-related rocks in the Oman ophiolite. The production of such OIB-like magmas during ophiolite obduction is not a rare event

  10. 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

  11. Dykes and structures of the NE rift of Tenerife, Canary Islands: a record of stabilisation and destabilisation of ocean island rift zones (United States)

    Delcamp, A.; Troll, V. R.; van Wyk de Vries, B.; Carracedo, J. C.; Petronis, M. S.; Pérez-Torrado, F. J.; Deegan, F. M.


    Many oceanic island rift zones are associated with lateral sector collapses, and several models have been proposed to explain this link. The North-East Rift Zone (NERZ) of Tenerife Island, Spain offers an opportunity to explore this relationship, as three successive collapses are located on both sides of the rift. We have carried out a systematic and detailed mapping campaign on the rift zone, including analysis of about 400 dykes. We recorded dyke morphology, thickness, composition, internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes. Dykes were intruded along the rift, but also radiate from several nodes along the rift and form en échelon sets along the walls of collapse scars. A striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls. This dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events. The slump sides would create the necessary strike-slip movement to promote en échelon dyke patterns. The spreading flank would probably involve a basal decollement. Lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra-volcanic intrusive complexes. With continued magma supply, spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress. However, as magmatic intrusion persisted, a critical point was reached, beyond which further intrusion led to large-scale flank failure and sector collapse. During the early stages of growth, the rift could have been influenced by regional stress/strain fields and by pre-existing oceanic structures, but its later and mature development probably depended largely on the local volcanic and magmatic stress/strain fields that are effectively controlled by the rift zone growth

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

    International Nuclear Information System (INIS)

    Ruskeeniemi, T.; Blomqvist, R.; Lindberg, A.; Ahonen, L.; Frape, S.


    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.)

  13. A New Occurrence of Alkaline Magmatism on the Kola Peninsula: An Agpaitic Dyke in the Kandalaksha Region. (United States)

    Akimenko, Mariya; Kogarko, Lia; Sorokhtina, Natalia; Kononkova, Natalia; Mamontov, Vladimir


    A new occurrence of alkaline dyke magmatism was discovered in 2010 during the geological works performed by the Murmansk Geological Prospecting Expedition in the "Mokhnatye Roga" area located 55 km to the southeast of the Kovdor massif (67°15' N, 31°30' E). The "Mokhnatye Roga" area is located in the Ensk segment of the northwestern part of the Belomorian mobile belt. We performed a complete petrological and geochemical description of the sections in Holes 19 and 24, which reveal one of the largest dykes in the area. The dyke, with a length of ≈4 km and a width of ≈160 m, has an eastern orientation with steep dipping (60°-90°) to the north. The thickness of Quaternary deposits ranges from 0.8 to 4.0 m; alkaline rocks occur in the range of 4.0-93.9 m being followed by host amphibole-biotite gneiss with interbeds of plagioamphibolite (AR2 mt) along the section. Among the major minerals of the dyke are the minerals of the lamprophyllite group (20-25 vol %), aegirine-augite (10-15 vol %), enigmatite (10-15 vol %), nepheline (10-15 vol %), orthoclase (15-20 vol %), alkaline amphibole (5-10 vol %), and astrophyllite (up to 5 vol %). The minor minerals are represented by shcherbakovite, sodalite, natrolite, barite, Mn carbonate, ilmenite, rutile, sphalerite, and goethite. The texture of the rock is porphyric: the groundmass is composed of finegranular nepheline and orthoclase, which are observed as individual large euhedral crystals as well. In addition, large phenocrysts are represented by the minerals of the lamprophyllite, enigmatite, pyroxene, and alkaline amphibole groups. Based on the generally accepted classifications [1], the studied agpaitic rock may be related to nepheline syenite; according to the mineral and chemical compositions, it is close to syenite of the Niva massif [2] located 35 km to the northeast from the "Mokhnatye Roga" area. Agpaitic syenite of the "Mokhnatye Roga" area is extremely enriched in dispersed and rare lithophile elements. The

  14. Mineralization of atmospheric CO2 via fluid reaction with mafic/ultramafic rocks (United States)

    Westfield, I. T.; Kendall, T. A.; Ries, J. B.


    Atmospheric CO2 has increased nearly 50% since the Industrial Revolution, due primarily to increased fossil fuel combustion, cement production, and deforestation. Although subterranean reservoirs are presently considered the most viable sink for anthropogenically liberated CO2, concerns exist over the stability of these systems and their impacts on regional tectonics, aquifers, and subterranean microbial ecosystems. Direct mineralization of CO2 at the Earth's surface provides an alternative capable of generating useful carbon-negative mineral byproducts that may be used to supplement or replace conventional carbon-positive building materials, like cement. However, mineralization of anthropogenic CO2 requires large sources of alkalinity to convert CO2 to CO32-, and divalent cations (e.g., Mg2+, Ca2+, Fe2+, etc.) to bond with the aqueous CO32-. Ultramafic and mafic rocks, such as peridotites, serpentinites, and basalts, are globally abundant, naturally occurring sources of the divalent cations, and alkalinity required for CO2 mineralization. Here, we present the results of accelerated reactions between ultramafic/mafic rocks, water, and CO2/N2 gases, aimed at quantifying the carbonation potential of mafic/ultramafic rocks. Rock-fluid-gas batch reactions were carried out in vented 4 L borosilicate glass flasks filled with 3 L DI water and 200 g acetone-washed, 49-180μm-diameter grains of four ultramafic/mafic rock types: peridotite, dunite, websterite and basalt. Each of the four rock-water mixtures was reacted under pure CO2 and pure N2 and at 25 and 200 °C, for a total of 16 reactions. Mixtures were continuously heated and stirred for 14 days. Samples (330 mL) were obtained at 0, 1, 6, 24, 48, 96, 168, and 336 hrs and filtered at 0.4 μm. The pH of filtered samples was measured with a single-junction Ag/AgCl glass electrode, salinity was determined with a conductivity probe, total alkalinity (TA) was determined by closed-cell potentiometric Gran titration, and DIC

  15. The Mafic Lower Crust of Neoproterozoic age beneath Western Arabia: Implications for Understanding African Lower Crust (United States)

    Stern, R. J.; Mooney, W. D.


    We review evidence that the lower crust of Arabia - and by implication, that beneath much of Africa was formed at the same time as the upper crust, rather than being a product of Cenozoic magmatic underplating. Arabia is a recent orphan of Africa, separated by opening of the Red Sea ~20 Ma, so our understanding of its lower crust provides insights into that of Africa. Arabian Shield (exposed in W. Arabia) is mostly Neoproterozoic (880-540 Ma) reflecting a 300-million year process of continental crustal growth due to amalgamated juvenile magmatic arcs welded together by granitoid intrusions that make up as much as 50% of the Shield's surface. Seismic refraction studies of SW Arabia (Mooney et al., 1985) reveal two layers, each ~20 km thick, separated by a well-defined Conrad discontinuity. The upper crust has average Vp ~6.3 km/sec whereas the lower crust has average Vp ~7.0 km/sec, corresponding to a granitic upper crust and gabbroic lower crust. Neogene (Yemen to Syria. Many of these lavas contain xenoliths, providing a remarkable glimpse of the lower-crustal and upper-mantle lithosphere beneath W. Arabia. Lower crustal xenoliths brought up in 8 harrats in Saudi Arabia, Jordan, and Syria are mostly 2-pyroxene granulites of igneous (gabbroic, anorthositic, and dioritic) origin. They contain plagioclase, orthopyroxene, and clinopyroxene, and a few contain garnet and rare amphibole and yield mineral-equilibrium temperatures of 700-900°C. Pyroxene-rich and plagioclase-rich suites have mean Al2O3 contents of 13% and 19%, respectively: otherwise the two groups have similar elemental compositions, with ~50% SiO2 and ~1% TiO2, with low K2O (time. Lower crust of Arabia clearly formed during Neoproterozoic time, about the same time as its upper crust complement; a similar origin for the lower crust beneath the broad expanses of Neoproterozoic crust in N and E Africa is likely. There is no evidence that any of the mafic lower crust of Arabia formed due to underplating by

  16. Seismic constraints on a large dyking event and initiation of a transform fault zone in Western Gulf of Aden (United States)

    Ahmed, AbdulHakim; Doubre, Cecile; Leroy, Sylvie; Perrot, Julie; Audin, Laurence; Rolandone, Frederique; Keir, Derek; Al-Ganad, Ismael; Sholan, Jamal; Khanbari, Khaled; Mohamed, Kassim; Vergne, Jerome; Jacques, Eric; Nercessian, Alex


    In November 2010, a large number of events were recorded by the world seismic networks showing important activity occurring along the western part of the Aden Ridge. West of the Shulka El Sheik fracture zone, events in this large seismic swarm (magnitudes above 5) occurred in a complex area, where the change of both the ridge direction and the bathymetry suggest the propagation of the ridge into a continental lithosphere and the influence of the Afar plume. We combine several sets of data from permanent networks and temporary 3C broad stations installed after the beginning of the event along the southern and eastern coasts of Yemen and Djibouti respectively, we located more than 600 earthquakes with magnitudes ranging from 2.5 to 5.6 that occurred during the first months following the first event. The spatial distribution of the main seismicity reveals a very clear N115° -trending alignment, parallel to the mean direction of the en-echelon spreading segments that form the ridge at this longitude. Half of the events, which represent half of the total seismic energy released during the first months, are located in the central third section of the segment. Here several volcanic cones and recent lava flows observed from bathymetric and acoustic reflectivity data during the Tadjouraden cruise (Audin, 1999, Dauteuil et al., 2001) constitute the sea floor. In addition to this main activity, two small groups of events suggest the activiation of landslides into a large fan and the activity in a volcanic area 50 km due east from the main active zone. The time evolution of the seismicity shows several bursts of activity. Some of them are clearly related to sudden activities within the volcanic areas, when others exhibit horizontal migration of the events, with velocity around ˜ 1 km/h. The time-space evolution of the seismicity clearly reveals the intrusion of dykes associated with magma propagation from the crustal magmatic centres into the rift zone. Taking into account

  17. 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

  18. Dyke leakage localization and hydraulic permeability estimation through self-potential and hydro-acoustic measurements: Self-potential 'abacus' diagram for hydraulic permeability estimation and uncertainty computation (United States)

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


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

  19. Integration of geotechnical and geophysical techniques for the characterization of a small earth-filled canal dyke and the localization of water leakage (United States)

    Bièvre, Grégory; Lacroix, Pascal; Oxarango, Laurent; Goutaland, David; Monnot, Guy; Fargier, Yannick


    This paper investigates the combined use of extensive geotechnical, hydrogeological and geophysical techniques to assess a small earth dyke with a permanent hydraulic head, namely a canal embankment. The experimental site was chosen because of known issues regarding internal erosion and piping phenomena. Two leakages were visually located following the emptying of the canal prior to remediation works. The results showed a good agreement between the geophysical imaging techniques (Electrical Resistivity Tomography, P- and SH-waves Tomography) and the geotechnical data to detect the depth to the bedrock and its lateral variations. It appeared that surface waves might not be fully adapted for dyke investigation because of the particular geometry of the studied dyke, non-respectful of the 1D assumption, and which induced depth and velocity discrepancies retrieved from Rayleigh and Love waves inversion. The use of these classical prospecting techniques however did not allow to directly locate the two leakages within the studied earth dyke. The analysis of ambient vibration time series with a modified beam-forming algorithm allowed to localize the most energetic water flow prior to remediation works. It was not possible to detect the leakage after remediation works, suggesting that they efficiently contributed to significantly reduce the water flow. The second leakage was not detected probably because of a non-turbulent water flow, generating few energetic vibrations.

  20. The Ethiopian subcontinental mantle domains: geochemical evidence from Cenozoic mafic lavas (United States)

    Tommasini, S.; Manetti, P.; Innocenti, F.; Abebe, T.; Sintoni, M.; Conticelli, S.


    Since the Cenozoic, Ethiopia was affected by a widespread volcanic activity related to the geodynamic evolution of the Afar triple junction. The plateau building phase was followed by the formation of the Main Ethiopian Rift (MER) accompanied by a bimodal volcanic activity in both the inner parts of the rift and its shoulders. Outside the rift, a concurrent volcanic activity occurred mainly along transversal tectonic lineaments, the most important of which is the Yerer-Tullu Wellel Volcano-Tectonic Lineament (YTVL) developing for ˜500 km westward of Addis Abeba. Scattered Pliocene Quaternary volcanoes are reported also inside the plateau such as those out cropping nearby Lake Tana. Here we present the result of a study on carefully screened mafic lavas outcropping in two sectors located off-axis the MER, namely, the YTVL and the southern part of Lake Tana; and in one sector located in the southern tip of the MER close to Megado, in the Sidamo region. The screened samples are petrographically fresh and have SiO24 wt.%, to minimise crystal fractionation effects. Most of the samples belong to the Late Miocene Quaternary volcanic activity of the East African Rift System (EARS), although a number of samples along the YTVL are representative of the Late Eocene Early Miocene Ethiopian Volcanic Plateau flood basalts. The selected mafic lavas offer the opportunity to assess the geochemical diversity, if any, of the subcontinental mantle domains along the MER (Megado and the easternmost part of the YTVL) and in sectors far away from the MER (YTVL and Lake Tana). The samples have a wide compositional range: from basanite to alkali basalt, hy-normative basalt, qz-normative basalt, basaltic andesite, hawaiite, trachybasalt, and trachyandesite. The major and trace element characteristics of the mafic lavas demonstrate an origin from a relatively fertile and trace element enriched lithospheric mantle at pressure variable from ˜2.0 to 3.5 GPa. Moreover, systematic variations in


    Directory of Open Access Journals (Sweden)

    A. V. Ivanov


    Full Text Available The Siberian craton consists of Archean blocks, which were welded up into the same large unit by ca 1.9 Ga [Gladkochub et al., 2006; Rojas-Agramonte et al., 2011]. The history of the constituent Archean blocks is mosaic because of limited number of outcrops, insufficient sampling coverage because of their location in remote regions and deep forest and difficulties with analytical studies of ancient rocks, which commonly underwent metamorphic modifications and secondary alterations. In this short note, we report data on discovery of unusual for Archean mafic rocks of ultimate fresh appearance. These rocks were discovered within southwestern Siberian craton in a region near a boundary between Kitoy granulites of the Sharyzhalgai highgrade metamorphic complex and Onot green-schist belt (Fig. 1. Here we present preliminary data on geochronology of these rocks and provide their geochemical characterization.

  2. Rheological property of mafic schist and geological interpretation to the subduction dynamics (United States)

    Okazaki, K.; Hirth, G.


    To understand the spatial and temporal distribution of deformation (e.g., underplating and exhumation of metamorphic rocks) and earthquakes in subduction zones, it is important to constrain the rheological properties of metamorphic rocks (i.e., altered oceanic crust and sediments), and how they evolve during metamorphic reactions following hydration, carbonation and dehydration of the down-going slab. Metamorphism of oceanic crust has stimulated hypotheses on the relationship between intra-slab earthquakes and slab-wedge coupling along plate boundaries in subduction zone. While it is well known that metamorphisms have important effects on material circulation and arc volcanisms at subduction system, it remains unclear how the formation of metamorphic minerals followed by fluid release on the subduction dynamics influences rheology. Past experimental studies on mafic metamorphic rocks were mostly concentrated on phase equilibrium of mineral, thus there are very few reports on the mechanical data for these metamorphic rocks. We conducted triaxial deformation experiments on a mafic greenschist using Griggs-type solid pressure-medium apparatus installed in Brown University. Mafic schist (chlorite - amphibole - epidote - albite schist) containing calcite and quartz veins from Sambagawa metamorphic belt (Japan), which is metamorphosed at the condition of nearly the corner of mantle wedge in hot subduction (1 GPa of pressure and 520C of temperature), was used as experimental samples for typical metamorphic rocks composing oceanic crust in warm subduction zones. Constant strain rete experiments and strain rate step experiment were conducted at 1.0 GPa of confining pressure, 400 ~ 500C of temperature and 10-5 ~ 5×10-7 1/s of strain rate. At stable conditions of samples (1 GPa of confining pressure and 400 and 500C of temperature), differential stresses were higher than 1 GPa. Microstructure of recovered samples showed backing and several localized shear zones. Although

  3. Storage conditions of the mafic and silicic magmas at Cotopaxi, Ecuador (United States)

    Martel, Caroline; Andújar, Joan; Mothes, Patricia; Scaillet, Bruno; Pichavant, Michel; Molina, Indira


    The 2015 reactivation of the Cotopaxi volcano urges us to understand the complex eruptive dynamics of Cotopaxi for better management of a potential major crisis in the near future. Cotopaxi has commonly transitioned from andesitic eruptions of strombolian style (lava flows and scoria ballistics) or nuées ardentes (pyroclastic flows and ash falls) to highly explosive rhyolitic ignimbrites (pumiceous pyroclastic flows), which entail drastically different risks. To better interpret geophysical and geochemical signals, Cotopaxi magma storage conditions were determined via existing phase-equilibrium experiments that used starting materials chemically close to the Cotopaxi andesites and rhyolites. The results suggest that Cotopaxi's most mafic andesites (last erupted products) can be stored over a large range of depth from 7 km to ≥16 km below the summit (pressure from 200 to ≥400 MPa), 1000 °C, NNO +2, and contain 4.5-6.0±0.7 wt% H2O dissolved in the melt in equilibrium with 30-40% phenocrysts of plagioclase, two pyroxenes, and Fe-Ti oxides. These mafic andesites sometimes evolve towards more silicic andesites by cooling to 950 °C. Rhyolitic magmas are stored at 200-300 MPa (i.e. 7-11 km below the summit), 750 °C, NNO +2, and contain 6-8 wt% H2O dissolved in a nearly aphyric melt (<5% phenocrysts of plagioclase, biotite, and Fe-Ti oxides). Although the andesites produce the rhyolitic magmas by fractional crystallization, the Cotopaxi eruptive history suggests reactivation of either reservoirs at distinct times, likely reflecting flux or time fluctuations during deep magma recharge.

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

    Directory of Open Access Journals (Sweden)

    Adailde do Carmo Santos


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

  5. Study on Nd and Sr isotopes of Yianshanian mafic rocks in east Lanling area and their implication

    International Nuclear Information System (INIS)

    Zhang Shuming; Wu Jianhua; Zhou Weixun


    East Nanling's Yianshanian mafic magna activity can be divided into four phase. The four phase are the Middle Jurassic, the Late Jurassic, the Early Cretaceous and the Late Cretaceous. They are also four important episodes of extensional activities. The four phase mafic rock possess similar Nd-Sr isotope characteristics, high I Sr (commonly from 0.705 to 0.710) and ε Nd values change range wide (from -7.90 to 5.16). It shows crust-mantle mixed magma origin character. The mafic rock possess the character of within-plate basalts,indicated that they are formed within-plate, and showed there were post-orogenic phase at the early Yianshanian's Middle Jurassic in east Nanling area. The rocks formed pattern is mafic magma rise to the crust bottom, were contaminate by crustal materials, and formed in the setting of lithosphere extended and crust extension. East Nanling's Yianshanian magna activity is mainly magma event concern with mantle magma underplating. (authors)

  6. The influence of heterogeneity on coastal groundwater flow - physical and numerical modeling of fringing reefs, dykes and structured conductivity fields (United States)

    Houben, Georg J.; Stoeckl, Leonard; Mariner, Katrina E.; Choudhury, Anis S.


    Geological heterogeneity of the subsurface, caused by both discrete features and spatially distributed hydraulic conductivity fields, affects the flow of coastal groundwater. It influences the shape and the position of the interface between saltwater and freshwater, as well as the location and flux rate of freshwater discharge to the ocean. Fringing reefs lead to a bimodal regime of freshwater discharge, with discharge at the beach face and through deeper, submarine springs. Impermeable vertical flow barriers (dykes) lead to an impoundment of fresh groundwater and a compartmentalization of the aquifer but also to a delayed expulsion of saline water. Spatially distributed conductivity fields affect the shape of the interface and the geometry of the saltwater wedge. Higher effective conductivities lead to a further landward intrusion of the wedge toe. These flow characteristics can be important for groundwater extraction, the delineation of protection zones and the assessment of contaminant transport to coastal ecosystems.

  7. 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

  8. An example of post-collisional mafic magmatism: the gabbro-anorthosite layered complex from the Tin Zebane area (western Hoggar, Algeria) (United States)

    Aı̈t-Djafer, Saı̈da; Ouzegane, Khadidja; Paul-Liégeois, Jean; Kienast, Jean Robert


    The Tin Zebane gabbro-anorthosite layered mafic intrusion represented by plagioclase-rich cumulates forms a set of small lenticular to round-shaped mainly undeformed bodies intruding the Pan-African high-pressure metamorphic rocks from western Hoggar (Tuareg shield, southwest Algeria). The coarse-grained anorthosites are mainly made of slightly zoned bytownite (An 86-74) with the higher anorthite content at the cores. Anorthosites are interlayered with leucogabbros and gabbros that show preserved magmatic structures and with olivine gabbros characterised by coronitic textures. The primary assemblage in gabbros includes plagioclase (An 93-70), olivine (Fo 77-70), zoned clinopyroxene (En 43-48Fs 05-13Wo 41-49 with Al 2O 3 up to 4.3 wt.%) and rare orthopyroxene (En 73-78). Pyroxenes and olivine are commonly surrounded by Ca-amphibole. The olivine-plagioclase contact is usually marked by a fine orthopyroxene-Cr-spinel-amphibole symplectite. A magnesian pigeonite (En 70-75Fs 19-20Wo 6-10) is also involved in corona. The coronitic minerals have equilibrated with the primary mineral rims at P- T- aH2O conditions of 797 ± 42 °C for aH2O=0.5 and 808 ± 44 °C for aH2O=0.6 at 6.2 ± 1.4 kbar. The Tin Zebane gabbroic rocks are depleted in REE with a positive Eu anomaly, high Sr (>10 ∗ chondrite) and Al 2O 3 concentrations (17-33%) that support plagioclase accumulation with the extreme case represented by the anorthosites. The REE patterns can be modelised using plagioclase, clinopyroxene and orthopyroxene REE signature, without any role played by accessory minerals. High MgO content points to olivine as a major cumulate phase. Anorthositic gabbros Sr and Nd isotopic initial ratios are typical of a depleted mantle source (Sr i=0.70257-0.70278; ɛNd=+5.9 to +7.8). This isotopic signature is identical to that of the 10-km wide 592 Ma old dyke complex composed of alkaline to peralkaline granites and tholeiitic gabbros and one single bimodal complex can be inferred. The source

  9. Monogenetic Arc Volcanism in the Central Andes: The "Hidden" Mafic Component in the Land of Andesite and Ignimbrite (United States)

    van Alderwerelt, B. M.; Ukstins Peate, I.; Ramos, F. C.


    Faulting in the upper crust of the Central Andes has provided passage for small volumes of mafic magma to reach the surface, providing a window into petrogenetic processes in the region's deep crust and upper mantle. Mafic lavas are rare in the Central Andean region dominated by intermediate-composition arc volcanism and massive sheets of silicic ignimbrite, and provide key data on magmatic origin, evolution, and transport. This work characterizes fault-controlled, within-arc monogenetic eruptive centers representative of the most mafic volcanism in the Altiplano-Puna region of the Andes since (at least) the Mesozoic. Olivine-phyric basaltic andesite (54 wt% SiO2, 7.3 wt% MgO) at Cerro Overo maar and associated dome, La Albóndiga Grande, and an olivine-clinopyroxene flow (53 wt% SiO2, 6.7 wt% MgO) from Cordón de Puntas Negras have been erupted at the intersection of regional structural features and the modern volcanic arc. Bulk magma chemistry, radiogenic isotopes, and microanalyses of mineral and melt inclusion composition provide insight on the composition(s) of mafic magmas being delivered to the lowermost crust and the deep crustal processes which shape central Andean magma. Bulk major and trace elements follow regional arc differentiation trends and are clearly modified by crustal magmatic processes. In contrast, microanalyses reveal a much richer history with olivine-hosted melt inclusions recording multiple distinct magmas, including potential primary melts. Single crystal olivine 87Sr/86Sr from Cerro Overo (0.7041-0.7071) define a broader range than whole rock (0.7062-0.7065), indicating preservation of juvenile melt in olivine-hosted inclusions lost at the whole rock scale. Mineral chemistry (via EMPA) P-T calculations define a petrogenetic history for these endmember lavas. Field mapping, bulk chemistry, and microanalyses outline the generation, storage, transportation, and eventual eruption of the "hidden" mafic component of the Andean arc.

  10. Caractérisation géochimique des dykes basiques du massif de les Saras (Mayombe Congolais, Afrique Centrale): conséquences géodynamiquesGeochemical characterizations of basic dykes of the Saras massif (Congolese Mayombe Belt, Central Africa): geodynamic implications (United States)

    Boni, J. Mpemba; Vellutini, P. J.


    The Saras granodioritic massif is one of the Eburnean intrusive plutons of the Mayombe Belt. (South-West Congo, Central Africa) It is crosscut by a system of basic dykes, of diversified composition. Petrographic data and a comparative geochemical study, using incompatible trace elements, shows a tholeiitic transitional affinity, and allow us to suggest that these dykes are continental basaltic suites, from extensive areas. This basic magmatism, scattered in the whole Congo Craton, marks a widespread extensional episode in relation with the formation of subsidence basins or true aulacogens, at about 970 Ma (Pan African).

  11. Processes active in mafic magma chambers: The example of Kilauea Iki Lava Lake, Hawaii (United States)

    Helz, R.T.


    not show a decrease in density as temperature decreases, so neither process should have occurred in that lava lake. Because many mafic magmas crystallize significant olivine and/or pyroxene before they begin to crystallize plagioclase, the density relations observed for Kilauea Iki, and the processes that result from them, may be relevant to crystallization in other mafic magma chambers. The results for the 1965 Makaopuhi lava lake emphasize the role of bulk composition as a critical control on magmatic processes.

  12. 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

  13. 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.

  14. Late Paleozoic to Mesozoic extension in southwestern Fujian Province, South China: Geochemical, geochronological and Hf isotopic constraints from basic-intermediate dykes

    Directory of Open Access Journals (Sweden)

    Sen Wang


    Full Text Available The tectonic evolution of SE China block since late Paleozoic remains debated. Here we present a new set of zircon U-Pb geochronological, Lu-Hf isotopic data and whole-rock geochemistry for two stages of basic-intermediate dykes from the southwestern Fujian. The samples were collected from the NE-trending (mainly diabases and NW-trending (mainly diabasic diorites dykes and yielded zircon U-Pb ages of 315 and 141 Ma, with εHf (t values of −8.90 to 7.49 and −23.39 to −7.15 (corresponding to TDM2 values of 850 to 1890 Ma and 737 to 2670 Ma, respectively. Geochemically these rocks are characterized by low TiO2 (0.91–1.73 wt.% and MgO (3.04–7.96 wt.%, and high Al2O3 (12.5–16.60 wt.% and K2O (0.60–3.63 wt.%. Further they are enriched in LREEs and LILEs (Rb, Ba, Th and K, but depleted in HFSEs (Nb, Ta and Zr. The tectonic discrimination analysis revealed that the dykes were formed in an intraplate extensional environment. However, the NW trending dykes show crust-mantle mixed composition, which indicate an extensional tectonic setting with evidence for crustal contamination. The SE China block experienced two main stages of extensional tectonics from late Carboniferous to early Cretaceous. The tectonic evolution of the SE China block from late Devonian to Cretaceous is also evaluated.

  15. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: What Is the Message? (United States)

    El Atrassi, F.; Debaille, V.; Mattielli, N. D. C.; Berger, J.


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African Craton in Mauritania (Amsaga area). The Amsaga Archean Crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. Our main objectives aim to the identification of the mafic lithology origin and a better understanding of their role in the continental crust emplacement. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. The amphibolites are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. Two groups are distinct in their geochemical characteristics (major and trace elements), although both have tholeiitic basalt composition. The first group show LREE-enriched patterns and negative Nb-Ta anomalies. The second group is characterized by near-flat LREE patterns and flat HREE patterns. This second group clearly shows no Nb-Ta anomalies. The first group could be related to arc-like basalts, as it is many similarities with some Archean amphibolites probably formed in a supra-subduction zone, for instance the volcanic rocks from the southern edge of the Isua Supracrustal Belt. On the contrary, the second group has a MORB-like signature which is more unusual during the Archean. Different scenarios will be discussed regards to the Archean geodynamics.

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

    International Nuclear Information System (INIS)

    Ruskeeniemi, T.; Blomqvist, R.; Vuorela, P.; Frape, S.K.; Blyth, A.


    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.)

  17. Late Permian volcanic dykes in the crystalline basement of the Považský Inovec Mts. (Western Carpathians: U–Th–Pb zircon SHRIMP and monazite chemical dating

    Directory of Open Access Journals (Sweden)

    Pelech Ondrej


    Full Text Available This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U-Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th-U-Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps.

  18. Populations of Rice Grain Bug, Paraeuscosmetus pallicomis, (Hemiptera: Lygaeidae) in Weed-free Paddy Field, Weedy Paddy Field and Paddy Dykes. (United States)

    Abdullah, Tamrin; Nasruddin, Andi; Agus, Nurariaty


    Research on the populations of rice grain bug Paraeuscosmetus pallicomis Dallas (Hemiptera: Lygaeidae) in paddy field ecosystems was performed with the aim to determine the populations of rice grain bug in weed-free paddy field, weedy paddy field, and paddy dykes. Experiment was carried out in the village of Paccellekang in the district of Patallasang of Gowa Regency in South Sulawesi, Indonesia. Observations were performed during the milky grain stage (85 days after planting), the mature grain stage (105 days after planting), and one day after harvest (115 days after transplanting). Results showed that 85 days after the transplanting, the populations of rice grain bug was significantly higher in the weedy paddy field compared to weed-free field and paddy dykes with total numbers of 1.75, 3.53, and 0.31 insects per 2 hills, respectively. Similarly, 105 days after the transplanting, 2.53, 5.53, and 0.11 insects per hill, respectively. However, one day after the harvest (115 days after transplanting) the number of insects in weed-free field decreased, while in the dykes increased, and the weedy plot still had the highest number of insects per 2 hills. Our results suggested that weeds played an important role in regulating the bug population by providing alternative shelter and foods for the insect.

  19. Suture Dynamics of the Banda Arc Collision Zone: Geochemical and Age Analysis of Ultramafic and Mafic Bodies in Timor, Indonesia (United States)

    Valenza, J. M.; Harris, R. A.; Spencer, C. J.; Hoiland, C. W.; Flores, J. A.


    New age and geochemical data confirm that most ultramafic bodies on the north coast of Timor are derived from the distal reaches of the Australian continental margin lower plate that was exhumed by extension during Late Paleozoic to Mesozoic rifting. The ultramafic bodies were accreted to Timor during Late Miocene to present arc-continent collision. One of the lherzolitic ultramafic bodies near Caicua was previously unknown, but yields clear isotopic indicators that it is kin to the Hili Manu mafic and ultramafic complex further to the west. Zircon grains from metagabbro of the Hili Manu complex have cores with mostly Early Permian ages and rims of Latest Miocene ages. Isotopic analysis indicates abyssal plain, or passive margin affinity of the Caicua ultramafic body. One important exception to this pattern are mafic and ultramafic bodies associated with the Ocussi volcanics, which yield Miocene and Pliocene ages and supra-subduction zone chemical signatures. The Ocussi body is clearly part of the upper plate of the collision and formed after collision initiated further to the east. It is also structurally higher than the Hili Manu complex and has no affinities with the Australian plate. This study documents that both the upper and lower plates of the active arc-continent collision contribute mafic and ultramafic rocks to the evolving suture zone between the Indo-Australian and Asian plates in the Banda Arc region.

  20. The role of dyking and fault control in the rapid onset of eruption at Chaitén volcano, Chile. (United States)

    Wicks, Charles; de la Llera, Juan Carlos; Lara, Luis E; Lowenstern, Jacob


    Rhyolite is the most viscous of liquid magmas, so it was surprising that on 2 May 2008 at Chaitén Volcano, located in Chile's southern Andean volcanic zone, rhyolitic magma migrated from more than 5 km depth in less than 4 hours (ref. 1) and erupted explosively with only two days of detected precursory seismic activity. The last major rhyolite eruption before that at Chaitén was the largest volcanic eruption in the twentieth century, at Novarupta volcano, Alaska, in 1912. Because of the historically rare and explosive nature of rhyolite eruptions and because of the surprisingly short warning before the eruption of the Chaitén volcano, any information about the workings of the magmatic system at Chaitén, and rhyolitic systems in general, is important from both the scientific and hazard perspectives. Here we present surface deformation data related to the Chaitén eruption based on radar interferometry observations from the Japan Aerospace Exploration Agency (JAXA) DAICHI (ALOS) satellite. The data on this explosive rhyolite eruption indicate that the rapid ascent of rhyolite occurred through dyking and that melt segregation and magma storage were controlled by existing faults.

  1. The role of dyking and fault control in the rapid onset of eruption at Chaitén Volcano, Chile (United States)

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


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

  2. Geochemical characteristics of mafic and ultramafic rocks from the Naga Hills Ophiolite, India: Implications for petrogenesis

    Directory of Open Access Journals (Sweden)

    Ajoy Dey


    Full Text Available The Naga Hills Ophiolite (NHO represents one of the fragments of Tethyan oceanic crust in the Himalayan Orogenic system which is exposed in the Phek and Kiphire districts of Nagaland, India. The NHO is composed of partially serpentinized dunite, peridotite, gabbro, basalt, minor plagiogranite, diorite dyke and marine sediments. The basalts are mainly composed of fine grained plagioclase feldspar, clinopyroxene and orthopyroxene and show quenching and variolitic textures. The gabbros are characterized by medium to coarse grained plagioclase, orthopyroxene and clinopyroxene with ophitic to sub-ophitic textures. The ultramafic cumulates are represented by olivine, Cpx and Opx. Geochemically, the basalts and gabbros are sub-alkaline to alkaline and show tholeiitic features. The basalts are characterized by 44.1–45.6 wt.% of SiO2 with 28–38 of Mg#, and the gabbros by 38.7–43.7 wt.% of SiO2, and 26–79 of Mg#. The ultramafic rocks are characterized by 37.4–52.2 wt.% of SiO2, and 80–88 of Mg#. In multi-element diagrams (spidergrams both basalts and gabbros show fractionated trends with strong negative anomalies of Zr, Nb, Sr and a gentle negative anomaly of P. However, the rare earth element (REE plots of the basalts and gabbros show two distinct patterns. The first pattern, represented by light REE (LREE depletion, suggests N-MORB features and can be interpreted as a signature of Paleo-Tethyan oceanic crust. The second pattern, represented by LREE enrichment with negligible negative Eu anomaly, conforms to E-MORB, and may be related to an arc tectonic setting. In V vs. Ti/1000, Cr vs. Y and AFM diagrams, the basalts and gabbros plot within Island Arc Tholeiite (IAT and MORB fields suggesting both ridge and arc related settings. The ultramafic rocks exhibit two distinct patterns both in spidergrams and in REE plots. In the spidergram, one group displays highly enriched pattern, whereas the other group shows near flat pattern compared

  3. Mafic enclaves in dacitic domes and their relation with La Poruña scoria cone, Central Andes, northern Chile (United States)

    González-Maurel, O. P.; Gallmeyer, G.; Godoy, B.; Menzies, A.; le Roux, P. J.; Harris, C.


    Chao Dacite, Chillahuita, Cerro Pabellón, Chanka, Chac-Inca, and Cerro La Torta (or Tocorpuri) are dacitic domes of late Pleistocene age (30 to 140 ka; Renzulli et al., 2006; Tierney et al., 2016) located in Northern Chilean Central Andean province (NCCA; 17°20'S - 27°40'S). While, La Poruña is a 180 m high basaltic-andesite scoria cone erupted ca. 100 ka (Wörner et al., 2000). This scoria cone is also located at the NCCA, 26 km to the SW of Chanka and 45 km to the NW of Chao Dacite. The dacitic domes are generally porphyritic and highly crystalline lavas (30 - 50 vol % phenocrysts, plagioclase > biotite > amphibole > quartz ≥ accessory), with hyalopilitic or intersertal groundmass. These domes contain mafic enclaves, mostly andesite in composition, with plagioclase > amphibole > biotite ≥ clinopyroxene ≥ olivine ≥ accessory phenocryst (10 - 20 vol %) in a lightly oxidized groundmass with intersertal or intergranular textures. In contrast, La Poruña rocks are mostly aphanitic (75 - 85 vol % groundmass) and highly vesicular, with plagioclase > olivine ≥ clinopyroxene ≥ orthopyroxene phenocrysts in an intersertal or hyalopilitic groundmass. Although petrographically different, the composition (57 wt % SiO2; 580 ppm Sr, 87Sr/86Sr = 0.7066) of mafic enclaves from Cerro Pabellón dome are similar to the lava flows and pyroclastic blocks of La Poruña scoria cone (55 - 59 wt % SiO2; 560 - 610 ppm Sr; 0.7062 - 0.7066 87Sr/86Sr). Based on this data and the eruption ages of these volcanic structures, we suggest that the mafic enclaves and La Poruña magmas are co-genetic. Thus, we propose that the genesis of these mafic enclaves is associated with the origin of less evolved parental magmas erupted in the NCCA, such as those from La Poruña. In this case, the mafic enclaves would represent batches of less evolved magmas that ascended from deeper sources and probably contributed in the eruption of the dacitic domes. Renzulli et al., 2006. In XI Congreso Geol

  4. Mineralogy and geochemistry of alkaline basic dykes from the northern Indian plate: signs of more than one episode of rifting and associated magmatism (United States)

    Sajid, Muhammad; Andersen, Jens; Arif, Mohammad


    Rift related magmatism during Permian time in the northern margin of Indian plate, north-west Pakistan is shown by the occurrence of roughly linear array of alkaline rocks in the region. The constituent rocks include alkali granites, granodiorites, nepheline syenites, carbonatites and dykes of basic composition. The field relations, mineralogy and whole rock geochemistry of these basic dykes has been investigated. Significant textural and mineralogical distinctions have divided the basic dykes into a) dolerite and b) epidote amphibolites, cross cutting other alkaline rocks and pre-Permian rocks in the region. Clinopyroxene having augitic composition is a major mineral in dolerite, however, it is completely absent in epidote amphibolites. Amphiboles in dolerites are brown coloured having pargasitic composition while it is green to light green in colour having the composition of magnesio-hornblende in epidote amphibolites. Compositionally different types of olivine are present in dolerites while it is absent in epidote amphibolites. Intra-plate tectonic settings for both the rock types has been interpreted by Hf-Ta-Th and FeO-MgO-Al2O3 discrimination plots. Lower Zr/Nb ratio (<10) and K/Ba ratio (amid 20-40) for both the rock types further show their affinity to within-plate magmatism. Dolerites show depletion in REEs and other incompatible elements as compared to epidote amphibolites. The equilibrium partial melting models from primitive mantle using Dy/Yb, La/Yb, Sm/Yb, La/Sm and Nb/Y ratios show that both of these dykes originate form spinel lherzolite mantle. However, the degrees of partial melting from mantle is different i.e. epidote amphibolite show smaller degree (<5%) of partial melting of mantle than the dolerites (<10%). The contrasting geochemistry suggests that both of these dykes originated from heterogeneous mantle in two pulses with different degrees partial melting followed by fractional crystallization. Compositional zoning in plagioclase and

  5. Paleomagnetism of Early Cambrian Itabaiana mafic dikes (NE Brazil) and the final assembly of Gondwana (United States)

    Trindade, Ricardo I. F.; D'Agrella-Filho, Manoel S.; Epof, Igor; Brito Neves, Benjamim B.


    Paleomagnetic analysis on 15 early Cambrian mafic dikes from Itabaiana (Paraíba State) yielded a southern (northwestern) direction with steep upward (downward) inclination ( Dm = 167.5°, Im = - 63.7°, α95 = 7.3°). AF and Thermal demagnetization, thermomagnetic curves, and hysteresis results suggest that this component is dominantly carried by fine-grained SD magnetite. The high stability of this component and positive baked contact tests on three dikes indicate it represents a primary thermoremanent magnetization. Ar-Ar analysis on whole-rock samples from two sites provides a strong constraint on the age of the Itabaiana paleomagnetic pole (134.6° E, 34.9° S; A95 = 7.3, K = 28) defined by plateau ages of 525 ± 5 and 526 ± 4 Ma. This pole completely satisfies six out of the seven quality criteria proposed by Van der Voo [R. Van der Voo, The reliability of paleomagnetic data, Tectonophysics 184 (1990) 1-9.] and permits a tight constraint on the Early Cambrian sector of the Gondwana apparent polar wander path. Paleogeographic reconstructions consistent with the available paleomagnetic and geological record show that Gondwana was sutured along three major orogenies, the Mozambique (Brasilano/Pan-African) Orogeny (800-650 Ma), the Kuunga Orogeny (570-530 Ma) and the Pampean-Araguaia Orogeny (540-520 Ma). We suggest that after rifting away from Laurentia at the end of the Neoproterozoic, opening the Iapetus ocean, the Amazonian craton and minor adjoining blocks, such as Rio Apa and Pampia, collided with the proto-Gondwana by Cambrian times at ca. 530-520 Ma. Unless for small adjustments, Gondwana was completely formed by 525 Ma whose paleogeography is defined by the Itabaiana pole.

  6. Magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion (United States)

    Chen, Lie-Meng; Teng, Fang-Zhen; Song, Xie-Yan; Hu, Rui-Zhong; Yu, Song-Yue; Zhu, Dan; Kang, Jian


    Magnesium isotopic compositions of olivine, clinopyroxene, and ilmenite from the Baima intrusion, SW China, for the first time, are investigated to constrain the magnitude and mechanisms of Mg isotope fractionation among cumulus minerals in layered mafic intrusions and to evaluate their geological implications. Olivine and clinopyroxene have limited Mg isotope variations, with δ26Mg ranging from -0.33 to +0.05‰ and from -0.29 to -0.13‰, respectively, similar to those of mantle xenolithic peridotites. By contrast, ilmenites display extremely large Mg isotopic variation, with δ26Mg ranging from -0.50 to +1.90‰. The large inter-mineral fractionations of Mg isotopes between ilmenite and silicates may reflect both equilibrium and kinetic processes. A few ilmenites have lighter Mg isotopic compositions than coexisting silicates and contain high MgO contents without compositional zoning, indicating equilibrium fractionation. The implication is that the light Mg isotopic compositions of lunar high-Ti basalts may result from an isotopically light source enriched in cumulate ilmenites. On the other hand, most ilmenites have heavy Mg isotopic compositions, coupled with high MgO concentration and chemical zoning, which can be quantitatively modeled by kinetic Mg isotope fractionations induced by subsolidus Mg-Fe exchange between ilmenite and ferromagnesian silicates during the cooling of the Baima intrusion. The extensive occurrence of kinetic Mg isotope fractionation in ilmenites implies the possibility of widespread compositional disequilibrium among igneous minerals in magma chambers. Consequently, disequilibrium effects need to be considered in studies of basaltic magma evolution, magma chamber processes, and magmatic Fe-Ti oxide ore genesis.

  7. 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.

  8. Subglacial volcanic activity above a lateral dyke path during the 2014-2015 Bárdarbunga-Holuhraun rifting episode, Iceland (United States)

    Reynolds, Hannah I.; Gudmundsson, Magnús T.; Högnadóttir, Thórdís; Magnússon, Eyjólfur; Pálsson, Finnur


    The rifting episode associated with the Bárdarbunga-Holuhraun eruption in 2014-2015 included the first observations of major dyke propagation under ice. Three shallow ice depressions (ice cauldrons) with volumes ranging from 1 to 18 million m3 formed in Dyngjujökull glacier above the 48-km-long lateral path of the magma, at 4, 7 and 12 km from the northern glacier edge. Aircraft-based radar altimetry profiling was used to map the evolution of the cauldrons and construct a time series of the heat transfer rates. Out of the three scenarios explored: (1) onset or increase of hydrothermal activity, (2) convection within vertical fissures filled with water overlying intruded magma and (3) subglacial eruptions, the last option emerges as the only plausible mechanism to explain the rapid heat transfer observed in a location far from known geothermal areas. The thermal signals at two of the cauldrons are consistent with effusive subglacial eruptions. The formation of the northernmost cauldron was more rapid, indicating faster heat transfer rates. Radio-echo sounding data indicate that in contrast to the other two cauldrons, an intrusion of eruptive products occurred into the glacier, reaching 50-60 m above bedrock with the increased magma-ice contact explaining the more rapid heat transfer. We propose that the 2-m widening associated with graben formation increased the groundwater storage capacity of the bedrock, creating space for the meltwater to be stored, explaining the absence of meltwater pulses draining from Dyngjujökull.

  9. Mg isotope systematics during magmatic processes: Inter-mineral fractionation in mafic to ultramafic Hawaiian xenoliths (United States)

    Stracke, A.; Tipper, E. T.; Klemme, S.; Bizimis, M.


    , the clearly resolvable inter-mineral Mg isotope differences imply that crystallization or preferential melting of isotopically distinct minerals such garnet, spinel, and clinopyroxene should cause Mg isotope fractionation between bulk melt and residue. Calculated Mg isotope variations during partial mantle melting indeed predict differences between melt and residue, but these are analytically resolvable only for melting of mafic lithologies, that is, garnet pyroxenites. Contributions from garnet pyroxenite melts may thus account for some of the isotopically light δ26Mg observed in ocean island basalts and trace lithological mantle heterogeneity. Consequently, applications for high-temperature Mg isotope fractionations are promising and diverse, and recent advances in analytical precision may allow the full petrogenetic potential inherent in the sub per mill variations in δ26Mg in magmatic rocks to be exploited.

  10. Identification and quantification of gabbro cumulate partial melting in mafic igneous complexes (United States)

    Leuthold, J.


    In mafic magma chambers, olivine, plagioclase and clinopyroxene fractionate along the basaltic liquid line of descent. Ol-rich, troctolite and gabbro cumulates crystallize. Hot primitive magma sills are regularly injected into igneous complexes where they heat and partially melt surrounding hot rocks, percolate, hybridize and crystallize new and secondary phases (see Figure [1]). Here, I quantify the effect of gabbro cumulate partial melting and hybridization with invading primitive basalt using field observations, Cpx microtexture and core-rim geochemical profiles from the Rum sill complex (Scotland). I have run gabbro-basalt hybrid equilibrium and kinetic experiments to test the effect of gabbro assimilation on the basalt liquid and solid lines of descent. Rum poikilitic gabbro resorbed Cpx cores are overgrown by Cr-, Al-, Zr- and REE-depleted interstitial rim with high Mg#, Eu* and Sr* (see [2]). Plg is reversely zoned. Fractional crystallization fails to explain the combined dissolution texture and incoherent compatible and incompatible elements zoning. Gabbro cumulate partial melting produces a Cpx-depleted residue and a melt that is saturated in Cpx, depleted in Cr, Al, Zr and REE and with high SiO2 and Mg# contents [1]. REE-poor Cpx rim crystallized from a hybrid basalt-gabbro magma, despite a lower DREE. In picrite-gabbro kinetic experiments reacted at conditions where Ol, Plg and Cpx are stable in gabbro but only Ol is stable in primitive basalt (1210°C, NNO-2), gabbro Ol and Cpx are anhedral and reversely zoned and Plg is euhedral. In the reaction rim, Cpx is absent, Ol anhedral grains are small and Cr-Spl abundance strongly increased (to 1.8 vol%). Troctolite small-scale partial melting and hybridization with primitive basalt produces a hybrid Al-rich melt that is Spl over-saturated. Gabbro partial melting products can be very difficult to distinguish from cumulates crystallized along the basalt liquid line of descent, because of the limited

  11. Spectroscopic analysis (FTIR, Raman) of water in mafic and intermediate glasses and glass inclusions

    International Nuclear Information System (INIS)

    Mercier, Maxime; Di Muro, Andrea; Metrich, Nicole; Belhadj, Olfa; Giordano, Daniele; Mandeville, Charles W.


    Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H 2 O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH and molecular H 2 O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H 2 O content (H 2 O(T) = OH - + H 2 O m ) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterization) intensity of the 3550 cm -1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H 2 O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H 2 OT band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H 2 O by Raman spectroscopy irrespective of the procedure, whereas the parameterization mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H 2 O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm -1 . We provide new FTIR absorptivity coefficients ε 3550 ) for basalt (62.80 ± 0.8 L mol -1 cm -1 ) and basanite (43.96 ± 0.6 L mol -1 cm -1 ). These values, together with an exhaustive review of literature data, confirm the non

  12. Rb-Sr and Nd-Sr isotope geochemistry and petrogenesis of the Misho Mountains mafic dikes (NW Iran

    Directory of Open Access Journals (Sweden)

    Maryam Ahankoub


    Full Text Available Introduction There are some theories about the Paleotethys event during the Paleozoic that have been proposed by geologists (Metcalfe, 2006. Some scientist offered some pieces of evidence about the northern margin of Gondwana (Zhu et al., 2010. The Paleotethys Ocean and Hercynian orogenic report first in Iran, have been Offered from the Morrow and Misho Mountain (Eftekharnejad, 1981. Misho Mountains is located between the north and south Misho faults and cause the formation of a positive flower structure (Moayyed and Hossainzade, 2011. There is theory about Misho southern fault as the best candidate of the Paleotethys suture zone (Moayyed and Hossainzade, 2011. Geochemistry and Sr –Nd isotopic data of the A2 granitic and Synite rocks of the East Misho, indicate that the magmatism post collision has occurred in the active continental margin by extensional zones of the following the closure of the Paleotethys (Ahankoub, 2012. Granite and syenite rocks have been cut by mafic dikes. Mafic dikes are often formed in extensional tectonic settings related to mantle plume or continental break –up (Zhu et al., 2009. In this paper, we use the geochemistry and Nd-Sr isotope data to determined petrogenesis, tectono-magmatic setting and age of Misho mafic dikes. Materials and methods After petrography study of 30 thin sections of mafic dike rocks, 8 samples were selected for whole-rock chemical analyses using ICP-MS and ICP-AES instruments by ACME Company in Vancouver, Canada. We prepared 6 sample For Sm-Nd and Rb-Sr analysis. Sr and Nd isotope ratios were measured with a thermal ionization mass spectrometer, VG Sector 54–30 at the Nagoya University. The isotope abundances of Rb, Sr, Nd, and Sm were measured by the ID method with a Finnigan MAT Thermoquad THQ thermal ionization quadrupole mass spectrometer at the Nagoya University. NBS987 and JNdi-1 were measured as natural Sr and Nd isotope ratio standards (Tanaka et al., 2000. Averages and 2σ errors

  13. Mafic Volcanism Along the Sinaloa Coast, Mexico, and its Relation to the Opening of the Gulf of California (United States)

    Orozco Esquivel, T.; Ferrari, L.; Lopez Martinez, M.


    We report on new localities with mafic volcanism along the Sinaloa coast, which record changes in the magma generation processes along the eastern margin of the Gulf of California. South of Culiacán, Sinaloa, isolated outcrops of basaltic lavas built a ca. 60 km long belt aligned to the SE. The similarity in the mineralogy and composition of the lavas suggest that these outcrops could have been part of a single flow. Lavas contain abundant plagioclase (up to 3 mm), and olivine (up to 1.5 mm) phenocrysts, and scarce clinopyroxene, in a relatively coarse matrix. In multiement diagrams, the lavas show the negative Nb and Ta, and positive Pb and Sr anomalies characteristic of subduction related rocks. The age determination of these rocks is in process, nevertheless, rocks with similar compositions are known from ~11 Ma mafic dikes that outcrop in southern Sinaloa. The Pericos volcanic field, located about 25 km to the NW of Culiacán is composed by lava flows, shield volcanoes, and cinder cones of basaltic composition that cover an area of aprox. 20 x 32 km, and have a well preserved morphology suggestive of a Pliocene-Quaternary age. Lavas are porphyritic and contain olivine, plagioclase and clinopyroxene in a microcrystalline matrix. Some lava flows contain abundant megacrysts of green clinopyroxene (up to 8 cm), olivine (up to 1 cm), and/or plagioclase (up to 1 cm), or aggregates of olivine and clinopyroxene. Trace element abundances are remarkably uniform among all analyzed samples and are characteristic of intraplate magmas. Rocks with very similar composition, mineralogy, and also containing megacrysts, have been reported in the Pliocene Punta Piaxtla and Mesa Cacaxtla, located 200 km to the SSE at the Sinaloa coast. Those similarities indicate that mafic intraplate volcanism related to the opening of the Gulf of California is more broadly represented in the area than previously considered.

  14. Geochemical characteristics of granitoids and related mafic granulites from the Pan-African Dahomeyide belt, southeastern Ghana

    International Nuclear Information System (INIS)

    Aidoo, F.


    The Dahorneyide orogenic belt marks the southeastern limit of the West Africa craton (WAC). The belt consists of three structural units which include the deformed eastern edge of the WAC with its cover rocks made up of the Togo and the Buern Structural Units (external nappes), a suture zone assemblage of mafic and ultramafic rocks, and granitoid gneiss-rnigmatite assemblages (east of the suture zone). Geochemical and petrographic characteristics of the granitoids from the external nappes and mafic and ultramafic granulites roeks from the suture zone have been studied with the objective of inferring their petrogenesis and tectonic setting in which they were formed. Twenty five (25) representative samples were selected for petrographic studies and fifteen samples for major and trace elements composition using ICP-AES and ICP-MS respectively. The granitoids gneisses are mainly biotite muscovite gneisses, migmatites and granodiorites made up of quartz (25-68%), biotite (7-30%), plagioclase (8-40%), muscovite (4-20%) with some few pyroxene, sericite and calcite observed in some oF the samples. Within these rocks is an amphibole rich gneiss composed of about 45% amphiboles. The granitoid gneisses contain SiO 2 content of 40.60-68.90 wt. % with low Mg# of 36-46. Geochernically, they are classified as I-type, mctaluminous to peraluminous, magnessian to ferroan, calcic to calc alkali granitoids. They exhibit fractionated REE patterns with (La/Sm) N = 1.80-5.85 and (La/Yb) N = 3.76-76.30, and negative to positive Eu anomalies (Eu/Eu*'' = 0.68-2.10. The primitive mantle-normalised, trace element patterns show that the granitoid gneisses are characterised by enrichment in LILE relative to HFSE and in LREE relative HREE. They display subduction-related trace element characteristics of positive Ba and negative Ti, Ta, Nb and Hf anomalies. The mafic granulites are composed of quartz (16-43%), hornblende (12-45%), plagioclase (13-23%), pyroxene (13-17%), garnet (4

  15. Geochemical characteristics and tectonic setting of the Tuerkubantao mafic-ultramafic intrusion in West Junggar, Xinjiang, China

    Directory of Open Access Journals (Sweden)

    Yufeng Deng


    Full Text Available Mineral chemistry, whole-rock major oxide, and trace element compositions have been determined for the Tuerkubantao mafic-ultramafic intrusion, in order to understand the early Paleozoic tectonic evolution of the West Junggar orogenic belt at the southern margin of the Central Asian orogenic belt. The Tuerkubantao mafic-ultramafic intrusion is a well-differentiated complex comprising peridotite, olivine pyroxenite, gabbro, and diorite. The ultramafic rocks are mostly seen in the central part of the intrusion and surrounded by mafic rocks. The Tuerkubantao intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB. In addition, the Tuerkubantao intrusion displays relatively low Th/U and Nb/U (1.13–2.98 and 2.53–7.02, respectively and high La/Nb and Ba/Nb (1.15–4.19 and 37.7–79.82, respectively. These features indicate that the primary magma of the intrusion was derived from partial melting of a previously metasomatized mantle source in a subduction setting. The trace element patterns of peridotites, gabbros, and diorite in the Tuerkubantao intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The intrusive contact between peridotite and gabbro clearly suggest that the Tuerkubantao is not a fragment of an ophiolite. However, the Tuerkubantao intrusion displays many similarities with Alaskan-type mafic-ultramafic intrusions along major sutures of Phanerozoic orogenic belts. Common features include their geodynamic setting, internal lithological zoning, and geochemistry. The striking similarities indicate that the middle Devonian Tuerkubantao intrusion likely formed in a subduction-related setting similar to that of the Alaskan-type intrusions. In combination with the Devonian magmatism and porphyry mineralization, we propose that subduction of the oceanic slab has

  16. 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.

  17. 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)

    Coronel, N.; Techera, J.; Ramos, E.; Pineyro, G.


    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

  18. Retrograde corona texture in pre-Himalayan metamorphic mafic xenoliths, Sutlej valley, NW Himalaya: Implication on rare occurrence of high-grade rocks in the Himalaya (United States)

    Thakur, S. S.


    The present study documents extensive retrogression in mafic xenoliths embedded in the Kinnaur Kailash Granite (∼500 Ma), Sutlej valley, NW Himalaya. Most of the mafic xenoliths are hornblende-rich and are characterized by numerous retrograde corona textures such as garnet coronae around clinopyroxene and plagioclase, titanite coronae around ilmenite, and hornblende coronae around clinopyroxene. This implies that the mafic xenoliths had undergone granulite-facies metamorphism in the early stage of metamorphic evolution, and have been extensively retrograded at a later stage to the present day amphibole-rich mafic xenoliths. The retrogression path traced by these mafic xenoliths can be constrained through P-T estimates using hbl-grt and hbl-pl geothermometry, hbl-grt-pl geobarometry, and Thermocalc3.21 calculations. The estimated results suggest temperatures in the range of 536-662 °C and pressures in the range of 4.5-6.7 kbar for the formation of the corona textures. P-T calculation of garnet forming reaction rim around clinopyroxene further shows that retrogression had started at ∼650 °C and ∼7.3 kbar. These observations suggest that retrogression played a major role in the obliteration of most of the high-grade pre-Himalayan xenoliths from the Himalaya.

  19. 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.

  20. Role of mafic and ultramafic rocks in drinking water quality and its potential health risk assessment, Northern Pakistan. (United States)

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


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

  1. High pressure mafic granulites from the Mercara Suture Zone, southern India : Implications for deep subduction and subsequent exhumation (United States)

    Thenganodiyil, A.


    The Mercara Suture Zone in southern India, marked by steep gravity gradients along with electrical anomalies coincides the geologicaly marked transition zone in which the Coorg Block in Southern Granulite Terrain (SGT) is accreted to the Western Dharwar craton (WDC). The timing of high grade metamorphism as constrained from metamorphic overgrowths in zircons is ca. 3.0 Ga might marks the suturing event between the Western Dharwar Craton and the Coorg Block. Mafic granulites found as enclaves, bands or boudins within metaigneous and metasedimenatry rock suites along the Mercara suture and associated crustal blocks. These are medium to coarse grained rocks predominantly consisting of garnet, orthopyroxene, clinopyroxene, hornblende, plagioclase and quartz. Minor amounts of magnetite, rutile and ilmenite are also present as accessory phases. The available mineral assemblages and their reaction textues points towards the initial subduction, crustal thickening and subsequent exhumation, followed by cooling and retrogression of the terrain. The geothermobarometric computations based on phase equiliria modeling by pseudosections indicates high grade metamorphism at granulite facies conditions; substantiates the collisional mechanism invloved. Major and trace element chemistry of mafic granulites are suggestive that these rocks are essentially tholeiitic and are characterised by low silica, comparatively low alumina, high iron, high FeO/MgO ratio's. These signatures are also typical of subduction-related intraoceanic tholeiitic arc basalt. The high-density carbonic (1.15 g/cm3) fluids from these rocks is in conjunction with the mineral thermobarometry of the terrain and suggest deep subduction and subsequent exhumation.

  2. 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.

  3. 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)

  4. Mineralogy and geochemistry of picro-dolerite dykes from the central Deccan Traps flood basaltic province, India, and their geodynamic significance (United States)

    Dongre, Ashish; Viljoen, K. S.; Rathod, A.


    Constituent mineral compositions and whole rock major element geochemistry of picro-dolerite dykes from the central part of the Deccan flood basalt province are presented and discussed. The dykes are characterized by an MgO content of about 13 wt%, coupled with 13-16 modal percents of olivine. A high whole rock molar Mg# value of 71 and the presence of magnesian olivine phenocrysts ( Fo78) are consistent with a primitive (i.e. unevolved) geochemistry. The nature and composition of clinopyroxene (augite and pigeonite), plagioclase feldspar (labradorite) and Fe-Ti oxides (mostly ilmenite and magnetite) are also discussed, with implications drawn with respect to the geodynamics. High MgO magmas and rocks such as picrites are generally considered to be indicative of plume magmatism, formed by high degrees of partial melting in, e.g. the high-temperature region of a plume head. Recent age data is consistent with a model in which the Deccan LIP picritic magmatism is associated with the main phase of Deccan Trap activity at 66 Ma, as a result of a syn- to post rifting phase associated with the impact of the Rèunion mantle plume. It is speculated that the differentiation of primary olivine basaltic magma of picritic composition, may have been the mechanism for the generation of alkalic basalts which occurs in the Deccan Trap basaltic sequence.

  5. Geochronology, geochemistry, and petrogenesis of late Permian to early Triassic mafic rocks from Darongshan, South China: Implications for ultrahigh-temperature metamorphism and S-type granite generation (United States)

    Xu, Wang-Chun; Luo, Bi-Ji; Xu, Ya-Jun; Wang, Lei; Chen, Qi


    The role of the mantle in generating ultrahigh-temperature metamorphism and peraluminous S-type granites, and the extent of crust-mantle interaction are topics fundamental to our understanding of the Earth's evolution. In this study we present geochronological, geochemical, and Sr-Nd-Hf isotopic data for dolerites and mafic volcanic rocks from the Darongshan granite complex belt in western Cathaysia, South China. LA-ICP-MS U-Pb zircon analyses yielded magma crystallization ages of ca. 250-248 Ma for the dolerites, which are coeval with eruption of the mafic volcanic rocks, ultrahigh-temperature metamorphism, and emplacement of S-type granites in the Darongshan granite complex belt. The mafic volcanic rocks are high-K calc-alkaline or shoshonitic, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta and Ti. The dolerites are characterized by high Fe2O3tot (11.61-20.39 wt%) and TiO2 (1.62-3.17 wt%), and low MgO (1.73-4.38 wt%), Cr (2.8-10.8 ppm) and Ni (2.5-11.4 ppm). Isotopically, the mafic volcanic rocks have negative whole-rock εNd(t) values (-6.7 to -9.0) and high ISr values (0.71232 to 0.71767), which are slightly depleted compared with the dolerite samples (εNd(t) = -10.3 to -10.4 and ISr = 0.71796 to 0.71923). Zircons in the dolerites have εHf(t) values of -7.6 to -10.9. The mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent, whereas the dolerites formed by late-stage crystallization of enriched lithospheric mantle-derived magmas after fractionation of olivine and pyroxene. The formation of these mantle-derived mafic rocks may be attributed to transtension along a NE-trending strike-slip fault zone that was related to oblique subduction of the Paleo-Pacific plate beneath South China. Such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh-temperature metamorphism and S-type granites, and

  6. Hybridization in the subvolcanic Jaala-Iitti complex and its petrogenetic relation to rapakivi granites and associated mafic rocks of southeastern Finland


    Salonsaari, P.T.


    The 1630 Ma Jaala-Iitti complex is an example of bimodal rapakivi granite magmatism in which the interaction of granite and diabase magmas have led locally to hybridization. The dyke-like complex is situated at the northwestern margin of the Wiborg rapakivi batholith in southeastern Finland, cutting both the Proterozoic Svecofennian metamorphic crust and the Wiborg batholith. The complex consists mainly of non-hybridized compositionally homogeneous granites, i.e., hornblende granite and hornb...

  7. 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

  8. Evaluation of late Permian mafic magmatism in the central Tibetan Plateau as a response to plume-subduction interaction (United States)

    Liu, Bin; Ma, Chang-Qian; Guo, Pan; Sun, Yang; Gao, Ke; Guo, Yu-Heng


    An integrated study of the geochronology, mineralogy, geochemistry and Sr-Nd isotope compositions of the upper Permian Yushu mafic rocks in the central Tibetan Plateau (CTP) was conducted to evaluate the interaction between the Emeishan mantle plume and the Paleo-Tethyan subduction system. These mafic rocks can be geochemically subdivided into three groups. Group 1 rocks yielded a weighted mean 206Pb/238U age of 258 ± 2 Ma. They have relatively high TiO2, FeOt, Nb/Y and high εNd(t) values and display oceanic island basalts (OIB)-like rare earth and trace element patterns, with obvious enrichment of Nb and Ta. Group 2 and 3 rocks yield weighted mean 206Pb/238U ages of 258 ± 1 Ma and 257 ± 1 Ma, respectively. Both have relatively low TiO2, FeOt, Nb/Y and εNd(t) values and island arc tholeiites (IAT)-like rare earth and trace element patterns with obvious depletion of Nb and Ta. However, the Group 2 rocks have relatively low FeOt/MgO ratios, but high MgO, Mg#, Cr and Ni contents, resembling primitive magmas. They have lower light rare earth element (LREE), Nb, Ti and Zr contents and higher εNd(t) values than the Group 1 rocks. The geochemical and isotopic variations suggest that the Group 1 rocks might be derived from a plume-related mantle source, whereas Group 2 and Group 3 rocks originated from subduction-modified asthenospheric mantle and lithospheric mantle. Moderate degrees of olivine and clinopyroxene fractionation under low oxygen fugacities (fO2) appear to be responsible for the Fe-Ti enrichment in the Group 1 rocks. We propose a model involving plume-subduction interaction to explain the geodynamics and generation of the late Permian mafic magmatism in the CTP. The study region was rifted by the Emeishan mantle plume activity in association with rollback of Longmuco-Shuanghu oceanic lithosphere in late Permian times. Deep melting of the plume source led to the generation of the Group 1 plume-related magmas, whereas shallower melting of the subduction

  9. The timing of compositionally-zoned magma reservoirs and mafic 'priming' weeks before the 1912 Novarupta-Katmai rhyolite eruption (United States)

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


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

  10. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau (United States)

    El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a

  11. Typology of mafic-ultramafic complexes in Hoggar, Algeria: Implications for PGE, chromite and base-metal sulphide mineralisation (United States)

    Augé, Thierry; Joubert, Marc; Bailly, Laurent


    With the aims to bring new information about the typology and mineral potential of mafic-ultramafic complexes of the Hoggar, detailed petrological and chemical characterisation were performed on serpentinite bands and layered intrusions. The serpentinite bands locally contain pods, layers and disseminations of chromite showing all the characteristics (mode of occurrence, composition, nature and composition of silicate inclusions, etc.) of an "ophiolite" chromite. Some chromite concentrations in the serpentinite bands also contain inclusions of platinum-group minerals (described for the first time in the Hoggar) such as ruarsite (RuAsS), an Os, Ru, Ir alloy, and complex Os, Ir, Ru sulfarsenides and arsenides. The serpentinite probably corresponds to remnants of oceanic lithosphere—more specifically from the upper part of the mantle sequence, generally where chromitite pods are most abundant, and the basal part of the cumulate series with stratiform chromite concentrations—and marks suture zones; the rest of the oceanic crust has not been preserved. Considering the typology of the serpentinites bands, their potential for precious- and base-metals is suspected to be low. Of the two layered mafic-ultramafic intrusions that were studied, the In Tedeini intrusion has a wehrlite core intruded by olivine gabbronorite and surrounded by an olivine gabbro aureole; three orthocumulate units, containing disseminated magmatic base-metal sulphides and with a plagioclase composition varying around An 58.1 and An 63.3, that could have been derived from a single magma. The East Laouni intrusion has a basal unit of olivine gabbronorite with specific silicate oxide intergrowths, and an upper unit of more differentiated gabbro, both units containing disseminated magmatic Ni-Cu sulphides indicative of early sulphide immiscibility; the mineral composition of these two cumulate units indicates that they also could have been derived from a single magmatic episode. The characteristic of

  12. Mafic and ultramafic enclaves in Ustica Island lavas: Inferences on composition of lower crust and deep magmatic processes (United States)

    Alletti, M.; Pompilio, M.; Rotolo, S. G.


    Ustica Island, southern Tyrrhenian Sea, is constituted of Quaternary alkaline volcanics. A variety of enclaves representative of deep to supra-crustal settings were recently found in a hawaiitic lava flow. Enclaves consist of: (i) Ultramafic meta-cumulates, i.e. clinopyroxenites and wherlites characterized by variably deformed porphyroclastic to granoblastic textures. (ii) Mafic cumulates, i.e. gabbros (± amphibole) and troctolites, the first often characterized by frequent amphibole breakdown coronas (olivine + Ti-augite + plagioclase + magnetite + ilmenite + rhönite) in response to an H 2O decrease during the ascent, while the troctolites interpreted as meta-cumulates. (iii) Microsyenites, consist of anorthoclase and Fe-clinopyroxene organized in a granular sub-ipidiomorphic texture. Amphibole is absent in Ustica lavas and is found only in some old, now exposed, sub-intrusive volcanic bodies. This evidence suggests a late appearance of amphibole on the liquidus, at a high crystal content that inhibits further ascent of the magma. The importance of the amphibole as a medium pressure liquidus phase in Ustica mafic magmas is in the bearings on the geochemistry of lavas e.g. in buffering Na and Ti abundances, in trace elements partitioning, etc. Density measurements pointed out higher values for clinopyroxenites (3160 to 3300 kg/m 3) than for gabbros (ca. 2900 kg/m 3). Given the density contrast between enclaves and host lavas (2790 kg/m 3) and assuming appropriate rheological models, we calculated a minimum ascent rate of 0.01 m/s, corresponding to an ascent time in the range of 5-29 days for a depth of entrapment of 25 km.

  13. 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.

  14. The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia

    Directory of Open Access Journals (Sweden)

    A.Y. Barkov


    Full Text Available We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87. 5, which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. % are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96 formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts during a deuteric (autometasomatic alteration. In contrast, oikocrystic Opx (En 86.0 is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr are observed. We infer that (1 the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2 Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3 The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.

  15. A Thermodynamic Approach for Modeling H2O-CO2 Solubility in Alkali-rich Mafic Magmas at Mid-crustal Pressures (United States)

    Allison, C. M.; Roggensack, K.; Clarke, A. B.


    Volatile solubility in magmas is dependent on several factors, including composition and pressure. Mafic (basaltic) magmas with high concentrations of alkali elements (Na and K) are capable of dissolving larger quantities of H2O and CO2 than low-alkali basalt. The exsolution of abundant gases dissolved in alkali-rich mafic magmas can contribute to large explosive eruptions. Existing volatile solubility models for alkali-rich mafic magmas are well calibrated below 200 MPa, but at greater pressures the experimental data is sparse. To allow for accurate interpretation of mafic magmatic systems at higher pressures, we conducted a set of mixed H2O-CO2 volatile solubility experiments between 400 and 600 MPa at 1200 °C in six mafic compositions with variable alkali contents. Compositions include magmas from volcanoes in Italy, Antarctica, and Arizona. Results from our experiments indicate that existing volatile solubility models for alkali-rich mafic magmas, if extrapolated beyond their calibrated range, over-predict CO2 solubility at mid-crustal pressures. Physically, these results suggest that volatile exsolution can occur at deeper levels than what can be resolved from the lower-pressure experimental data. Existing thermodynamic models used to calculate volatile solubility at different pressures require two experimentally derived parameters. These parameters represent the partial molar volume of the condensed volatile species in the melt and its equilibrium constant, both calculated at a standard temperature and pressure. We derived these parameters for each studied composition and the corresponding thermodynamic model shows good agreement with the CO2 solubility data of the experiments. A general alkali basalt solubility model was also constructed by establishing a relationship between magma composition and the thermodynamic parameters. We utilize cation fractions from our six compositions along with four compositions from the experimental literature in a linear

  16. The propagation direction of mafic radial dikes inferred from flow-direction analysis of an exposed radial dike sequence, Summer Coon Volcano, Colorado, USA (United States)

    Harp, A.; Valentine, G.


    Mafic eruptions along the flanks of stratovolcanoes pose significant hazards to life and property due to the uncertainty linked to new vent locations and their potentially close proximity to inhabited areas. Flank eruptions are often fed by radial dikes with magma supplied either laterally from the central conduit or vertically from a deeper storage location. The highly eroded Oligocene age Summer Coon stratovolcano, Colorado reveals over 700 mafic dikes surrounding a series of intrusive stocks (inferred conduit). The exposure provides an opportunity to study radial dike propagation directions and their relationship with the conduit in the lower portions of a volcanic edifice. Detailed geologic mapping and a geophysical survey revealed that little or no direct connection exists between the mafic radial dikes and the inferred conduit at the current level of exposure. Oriented samples collected from the chilled margins of 29 mafic dikes were analyzed for flow fabrics and emplacement directions. Among them, 20 dikes show flow angles greater than 30 degrees from horizontal, and a single dike had flow fabrics oriented at approximately 20 degrees. Of the dikes with steeper fabrics nine dikes were emplaced up and toward the volcano's center between 30-75 degrees from horizontal, and 11 dikes emplaced up and away from the volcano's center between 35-60 degrees. The two groups of dikes likely responded to the stress field within the edifice, where steepest-emplaced had relatively high magma overpressure and were focused toward the volcano's summit, while dikes with lower overpressures propagated out toward the flanks. At Summer Coon, the lack of connection between mafic dikes and the inferred conduit and presence of only one sub-horizontally emplaced dike implies the stresses within lower edifice impeded lateral dike nucleation and propagation while promoting and influencing the emplacement direction of upward propagating dikes.

  17. Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey (United States)

    Deligne, Natalia I.; Mckay, Daniele; Conrey, Richard M.; Grant, Gordon E.; Johnson, Emily R.; O'Connor, Jim; Sweeney, Kristin


    The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disruption, and forest fires. Although the focus of this multidisciplinary field trip will be on mafic volcanism, we will also look at the hydrology, geomorphology, and ecology of the area, and we will examine how these elements both influence and are influenced by mafic volcanism. We will see mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. In addition, this field trip will occur during a total solar eclipse, the first one visible in the United States in more than 25 years (and the first seen in the conterminous United States in more than 37 years).The Cascade Range is the result of subduction of the Juan de Fuca plate underneath the North American plate. This north-south-trending volcanic mountain range is immediately downwind of the Pacific Ocean, a huge source of moisture. As moisture is blown eastward from the Pacific on prevailing winds, it encounters the Cascade Range in Oregon, and the resulting orographic lift and corresponding rain shadow is one of the strongest precipitation gradients in the conterminous United States. We will see how the products of the volcanoes in the central Oregon Cascades have had a profound influence on groundwater flow and, thus, on the distribution of Pacific moisture. We will also see the influence that mafic volcanism has had on landscape evolution, vegetation development, and general hydrology.

  18. 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

  19. 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.

  20. Catchment-wide weathering and erosion rates of mafic, ultramafic, and granitic rock from cosmogenic meteoric 10Be/9Be ratios (United States)

    Dannhaus, N.; Wittmann, H.; Krám, P.; Christl, M.; von Blanckenburg, F.


    Quantifying rates of weathering and erosion of mafic rocks is essential for estimating changes to the oceans alkalinity budget that plays a significant role in regulating atmospheric CO2 levels. In this study, we present catchment-wide rates of weathering, erosion, and denudation measured with cosmogenic nuclides in mafic and ultramafic rock. We use the ratio of the meteoric cosmogenic nuclide 10Be, deposited from the atmosphere onto the weathering zone, to stable 9Be, a trace metal released by silicate weathering. We tested this approach in stream sediment and water from three upland forested catchments in the north-west Czech Republic. The catchments are underlain by felsic (granite), mafic (amphibolite) and ultramafic (serpentinite) lithologies. Due to acid rain deposition in the 20th century, the waters in the granite catchment exhibit acidic pH, whereas waters in the mafic catchments exhibit neutral to alkaline pH values due to their acid buffering capability. The atmospheric depositional 10Be flux is estimated to be balanced with the streams' dissolved and particulate meteoric 10Be export flux to within a factor of two. We suggest a correlation method to derive bedrock Be concentrations, required as an input parameter, which are highly heterogeneous in these small catchments. Derived Earth surface metrics comprise (1) Denudation rates calculated from the 10Be/9Be ratio of the "reactive" Be (meaning sorbed to mineral surfaces) range between 110 and 185 t km-2 y-1 (40 and 70 mm ky-1). These rates are similar to denudation rates we obtained from in situ-cosmogenic 10Be in quartz minerals present in the bedrock or in quartz veins in the felsic and the mafic catchment. (2) The degree of weathering, calculated from the fraction of 9Be released from primary minerals as a new proxy, is about 40-50% in the mafic catchments, and 10% in the granitic catchment. Lastly, (3) erosion rates were calculated from 10Be concentrations in river sediment and corrected for sorting

  1. 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

  2. Metamorphic P-T path and zircon U-Pb dating of HP mafic granulites in the Yushugou granulite-peridotite complex, Chinese South Tianshan, NW China (United States)

    Zhang, Lu; Zhang, Lifei; Xia, Bin; Lü, Zeng


    Co-existing granulite and peridotite may represent relics of the paleo-suture zone and provides an optimal opportunity for better understanding of orogeny between two blocks. In this study, we carried out petrological and U-Pb zircon dating investigation on the HP mafic granulites associated with peridotite complex at Yushugou in Chinese South Tianshan. The studied samples include garnet-bearing high-pressure mafic granulites which can be subdivided into two types: Type I orthopyroxene-free and Type II orthopyroxene-bearing granulites and amphibolite. Type I granulite (Y21-2) has a mineral assemblage of garnet (33 vol.%), clinopyroxene (32 vol.%) and plagioclase (30 vol.%); and Type II granulite (Y18-8) has a mineral assemblage of garnet (22 vol.%), clinopyroxene (10 vol.%), orthopyroxene (14 vol.%), plagioclase (45 vol.%) and quartz. Garnet in both granulites exhibits core-rim structure characterized by increasing grossular and decreasing pyrope from core to rim. Petrographic observations and phase equilibrium modeling using THERMOCALC in the NCFMASHTO system for the mafic granulites (Y21-2 and Y18-8) show three stages of metamorphism: Stage I (granulite facies) was recognized by the large porphyroblastic garnet core, with P-T conditions of 9.8-10.4 Kbar and 860-900 °C (Y21-2) and 9.9-10.6 Kbar and 875-890 °C (Y18-8), respectively; Stage II (HP granulite facies) has peak P-T conditions of 12.1 Kbar at 755 °C (Y21-2) and 13.8 Kbar at 815 °C (Y18-8) using mineral assemblages combining with garnet rim compositions with maximum grossular and minimum pyrope contents; Stage III (amphibolite facies) was characterized by the development of calcic amphibole in granulites with temperature of 446-563 °C. Therefore, an anticlockwise P-T path characterized by simultaneous temperature-decreasing and pressure-increasing was inferred for the Yushugou HP mafic granulite. Studies of zircon morphology and inclusions, combined with zircon U-Pb dating and REE geochemistry

  3. The growth and contamination mechanism of the Cana Brava layered mafic-ultramafic complex: new field and geochemical evidences (United States)

    Giovanardi, Tommaso; Girardi, Vicente A. V.; Correia, Ciro T.; Sinigoi, Silvano; Tassinari, Colombo C. G.; Mazzucchelli, Maurizio


    The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest that Cana Brava underwent hyper- to subsolidus deformation during its growth, acquiring a high-temperature foliation that is generally interpreted as the result of a granulite-facies metamorphic event. The increase along the stratigraphy of the incompatible elements abundances (LREE, Rb, Ba) and of the Sr isotopic composition, coupled with a decrease in ɛNd(790), indicate that the complex was contaminated by the embedded xenoliths from the Palmeirópolis Sequence. The geochemical data suggest that the contamination occurred along the entire magma column during the crystallization of the Upper Mafic Zone, with in situ variations determined by the abundance and composition of the xenoliths. These features of the Cana Brava complex point to an extremely similarity with the Lower Sequence of the most known Niquelândia intrusion (the central of the three complexes). This, together with the evidences that the two complexes have the same age (c.a. 790 Ma) and their thickness and units decrease northwards suggests that Cana Brava and Niquelândia are part of a single giant Brasilia body grown through several melt impulses.

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

    Directory of Open Access Journals (Sweden)

    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.

  5. Aseismic creep of mafic fault rocks - an experimental study on the mechanical behaviour of deep-seated faults (United States)

    Marti, Sina; Heilbronner, Renée; Stünitz, Holger


    In order to gain more information about the mechanical behaviour of fault zones at deeper crustal levels, we performed experiments on gouge material with a mafic composition at different confining pressures (Pc), temperatures (T) and aseismic but 'fast' displacement rates. Shear-experiments are performed on a tri-axial Griggs-type deformation apparatus with solid confining medium, at Pc = 0.5 GPa and 1 GPa, T between 300° C and 700° C and at constant displacement rates of 10-8 ms-1 and 10-7 ms-1. To simulate the fault gouge we use a natural diabase (composed of ~ 57% Plagioclase, 41% Pyroxene, 2% accessories), crushed and sieved to a grain size of 500° C, abundant pore trails and the growth of fibres indicate that solution mass transfer processes are taking place. The deformation mechanism within the SLZs is not yet understood. Flow-structures within SLZs could indicate a viscous deformation mechanism, which would also explain the negative T dependence of the fault rock strength.

  6. 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

  7. The 1974 flank eruption of Mount Etna: an archetype for sub-volcano dyke (SVD) eruptions at basaltic strato-volcanoes and a benchmark in recent Etna’s history


    Corsaro, R. A.; Metrich, N.; Allard, P.; Andronico, D.; Miraglia, L.; Fourmentraux, C.


    Flank eruptions of Mt. Etna mostly result from drainage of plagioclase-rich magma from the central volcano conduits, but rarer ones emitting plagioclase-free aphyric magma, are driven by dyke propagation from beneath the volcano, bypassing the central conduits. An archetype of such events is the January-March 1974 eruption that developed in two explosive phases. New data for the mineralogy and geochemistry of the 1974 products and the coeval earthquake distribution, indicate that the eruption...

  8. 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

  9. Reconstruction of multiple P-T-t stages from retrogressed mafic rocks: Subduction versus collision in the Southern Brasília orogen (SE Brazil) (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Pedrosa-Soares, Antônio; Hermann, Jörg; Dussin, Ivo; Pinheiro, Marco Aurélio P.; Bouvier, Anne-Sophie; Baumgartner, Lukas


    The identification of markers of subduction zones in orogenic belts requires the estimation of paleo-geothermal gradients through pressure-temperature-time (P-T-t) estimates in mafic rocks that potentially derive from former oceanic units once. However, such markers are rare in supracrustal sequences specially in deeply eroded and weathered Precambrian orogens, and reconstructing their metamorphic history is challenging because they are commonly retrogressed and only preserve a few mineral relicts of high-pressure metamorphism. Metamorphosed mafic rocks from Pouso Alegre region of the Neoproterozoic Southern Brasília Orogen outcrop as rare lenses within continental gneisses. They have previously been classified as retrograde eclogites, based on the presence of garnet and the characteristic symplectitic texture replacing omphacite. These rocks were interpreted to mark the suture zone between the Paranapanema and São Francisco cratons. To test the possible record of eclogitic conditions in the Pouso Alegre mafic rocks, samples including the surrounding felsic rocks have been investigated using quantitative compositional mapping, forward thermodynamic modeling and in-situ dating of accessory minerals to refine their P-T-t history. In the metamorphosed mafic rocks, the peak pressure assemblage of garnet and omphacite (Jd20, reconstructed composition) formed at 690 ± 35 °C and 13.5 ± 3.0 kbar, whereas local retrogression into symplectite or corona occurred at 595 ± 25 °C and 4.8 ± 1.5 kbar. The two reactions were coupled and thus took place at the same time. A zircon U-Pb age of 603 ± 7 Ma was obtained for metamorphic rims and linked to the retrogression stage. Monazite and metamorphic zircon U-Th-Pb ages for the surrounding rocks are at ca. 630 Ma and linked to peak pressure conditions similar to the one recorded by the mafic rocks. The low maximal pressure of 14 kbar and the high geothermal gradient do not necessarily support subduction process

  10. The Magma Chamber Simulator: Modeling the Impact of Wall Rock Composition on Mafic Magmas during Assimilation-Fractional Crystallization (United States)

    Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.


    Although stoichiometric titration is often used to model the process of concurrent Assimilation and Fractional Crystallization (AFC) within a compositionally evolving magma body, a more complete treatment of the problem involves simultaneous and self-consistent determination of stable phase relationships and separately evolving temperatures of both Magma (M) and Wall Rock (WR) that interact as a composite M-WR system. Here we present results of M-WR systems undergoing AFC forward modeled with the Magma Chamber Simulator (MCS), which uses the phase modeling capabilities of MELTS (Ghiorso & Sack 1995) as the thermodynamic basis. Simulations begin with one of a variety of mafic magmas (e.g. HAB, MORB, AOB) intruding a set mass of Wall Rock (e.g. lherzolite, gabbro, diorite, granite, metapelite), and heat is exchanged as the M-WR system proceeds towards thermal equilibrium. Depending on initial conditions, the early part of the evolution can involve closed system FC while the WR heats up. The WR behaves as a closed system until it is heated beyond the solidus to critical limit for melt fraction extraction (fc), ranging between 0.08 and 0.12 depending on WR characteristics including composition and, rheology and stress field. Once fc is exceeded, a portion of the anatectic liquid is assimilated into the Magma. The MCS simultaneously calculates mass and composition of the mineral assemblage (Magma cumulates and WR residue) and melt (anatectic and Magma) at each T along the equilibration trajectory. Sensible and latent heat lost or gained plus mass gained by the Magma are accounted for by the MCS via governing Energy Constrained- Recharge Assimilation Fractional Crystallization (EC-RAFC) equations. In a comparison of two representative MCS results, consider a granitic WR intruded by HAB melt (51 wt. % SiO2) at liquidus T in shallow crust (0.1 GPa) with a WR/M ratio of 1.25, fc of 0.1 and a QFM oxygen buffer. In the first example, the WR begins at a temperature of 100o

  11. A 1400 km geochemical transect along the Central American Arc: Summary of mafic Holocene volcanism from Guatemala to Panama (United States)

    Geldmacher, J.; Hoernle, K.; Gill, J. B.; Hauff, F.; Heydolph, K.


    It is generally accepted that subducted oceanic crust and sediments contribute to the composition of arc magmas. Systematic variations of input parameters (including age, subduction angle, and chemical composition of the subducting material) make the Central American Volcanic Arc (CAVA), which extends from Guatemala in the northwest through El Salvador, Honduras, Nicaragua, Costa Rica and Panama to the southeast, a prime study object. We present a comprehensive (major and trace element and Sr-Nd-Pb-Hf isotope data) and consistent (all data generated in the same labs using the same methods and data reduction procedures) compilation of published and unpublished Holocene mafic volcanic rocks sampled along the entire arc. New data include Sr and, for the first time, Hf isotope data from the entire CAVA as well as major and trace element data for 43 samples from southern Nicaragua and central Costa Rica from which only isotopic compositions were previously published. The combined elemental and isotopic data confirm the influence of distinct subduction components on the composition of CAVA magmas. Along-arc geochemical variations (especially delta 208Pb/204Pb) of volcanic front magmas in Costa Rica and Panama have been explained by the different compositions of seamounts/ridges of the isotopically zoned Galápagos hotspot track that covers the subducting Cocos Plate in this sector of the arc (Hoernle et al. 2008, Nature 451). Our new data confirm this relationship with arc lavas from Costa Rica having higher 87Sr/86Sr ratios than those from western Panama reflecting a similar spatial-compositional distinction in the subducting hotspot track beneath them. In contrast, 176Hf/177Hf shows no comparable variations in this sector of the arc, indicating that the Hf is primarily derived from the mantle wedge rather than the subducting slab. Although small degree hydrous melts are believed to fertilize the mantle wedge beneath Costa Rica, residual zircon may hold back the Hf.

  12. 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.

  13. 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

  14. (ajst) euler deconvolution and spectral analysis

    African Journals Online (AJOL)


    Journal African Earth Sciences. 10, 483-501. Wilson, J. F., Jones, D. L. and Kramers, J. D., 1987. Mafic dyke swarms in Zimbabwe. In: Halls, H.C. and Fahrig,. W.F. (Eds.), Mafic Dyke Swarms. Geological. Association Canada, Special Paper 33, 433-444. Wilson, J.F., Nesbitt, R.W. and Fanning, C.M. 1995. Zircon.

  15. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil) (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas


    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  16. Young mafic back arc volcanic rocks as indicators of continental lithospheric delamination beneath the Argentine Puna plateau, central Andes (United States)

    Kay, Suzanne Mahlburg; Coira, Beatriz; Viramonte, Jose


    The spatial distribution of some major and trace element and isotopic characteristics of backarc Plio-Quaternary basaltic to high-Mg andesitic (51% to 58% SiO2) lavas in the southern Puna (25 S to 27 S) of the Central Andean Volcanic Zone (CVZ) reflect varying continental lithospheric thickness and the thermal state of the underlying mantle wedge and subducting plate. These lavas erupted from small cones and fissures associated with faults related to a change in the regional stress system in the southern Puna at approximately = 2 to 3 Ma. Three geochemical groups are recognized: (1) a relatively high volume intraplate group (high K; La/Ta ratio less than 25) that occurs over a thin continental lithosphere above a gap in the modern seismic zone and represents the highest percentage of mantle partial melt, (2) an intermediate volume, high-K calc-alkaline group (La/Ta ratio greater than 25) that occurs over intermediate thickness lithosphere on the margins of the seismic gap and behind the main CVZ and represents an intermediate percentage of mantle partial melt, and (3) a small-volume shoshonitic group (very high K) that occurs over relatively thick continental lithosphere in the northeast Puna and Altiplano and represents a very small percentage of mantle partial melt. Mantle-generated characteristics of these lavas are partially overprinted by mixing with melts of the overlying thickened crust as shown by the presence of quartz and feldspar xenocrysts, negative Eu anomalies (Eu/E(sup *) less than 0.90; most less than 0.80), and radiogenic Sr (greater than 0.7055) and Pb and nonradiogenic Nd (epsilon(sub Nd) less than -0.4) isotopic ratios. Mixing calculations show that the lavas generally contain more than 20% to 25% crustal melt. The eruption of the intraplate group mafic lavas, the change in regional stress orientation, and the high elevation of the southern Puna are suggested to be the result of the late Pliocene mechanical delamination of a block (or blocks) of

  17. SIMS zircon ages and Nd isotope systematics of the 2.2 Ga mafic intrusions in northern and eastern Finland

    Directory of Open Access Journals (Sweden)

    Eero Hanski


    Full Text Available Using the SIMS, ID-TIMS and Sm-Nd isotopic methods and the electron microprobe, we have studied several differentiated mafic intrusions of the c. 2.2 Ga gabbro-wehrlite association (GWA from four Paleoproterozoic schist belts and the Archean Kuhmo Greenstone Belt. Back-scattered electron images and electron microprobe analyses revealed that zircon crystals vary from well-preserved to turbid and highly altered with individual grains often displaying irregular, hydrated, CaO-bearing domains. In the most pristine domains, suitable for establishing the crystallization ages, SIMS 207Pb/206Pb ages fall in the range of 2210–2220 Ma, which is consistent with the most concordant ID-TIMS UPb ages. One of the studied intrusions that had previously yielded a conventional U-Pb date of less than 2.0 Ga, could be shown by spot analysis to belong to the 2.2 Ga family. In contrast to the well-preserved zircon domains, altered domains exhibit a variable and often strong U-Pb discordance up to 70 % and have distinctly lower 207Pb/206Pb ages. Some zircon grains record isotopic resetting at the time of the Svecofennian orogeny(ca. 1.8–1.9 Ga, while the most discordant ones project in the concordia diagram to late Paleozoic lower intercept ages indicating a relative recent Pb loss. The mineral chemistry of zircon suggests that the leakage of radiogenic Pb can be ascribed to an opensystembehavior related to hydrothermal alteration via action of CaCl2-bearing fluids.Common albitization of plagioclase in the GWA intrusions has caused this mineral to behave as an open system with regard to the Sm-Nd isotopic systematics. Despite this uncertainty, our Nd isotopic data indicate that the magma that produced the GWA intrusions in various parts of northern and eastern Finland was isotopically homogeneousand had an initial εNd(2220 Ma value of c. +0.6 precluding significant upper crustal contamination upon emplacement and subsequent fractional crystallization.

  18. Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China (United States)

    Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao


    The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by <10% partial melting of both phlogopite-lherzolite and garnet-lherzolite mantle sources. These sources are best interpreted to be in a subduction-related arc environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

  19. Late Archaean mantle metasomatism below eastern Indian craton ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    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 ...

  20. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    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 ...

  1. Petrogenesis of the Dalongkai ultramafic-mafic intrusion and its tectonic implication for the Paleotethyan evolution along the Ailaoshan tectonic zone (SW China) (United States)

    Liu, Huichuan; Wang, Yuejun; Zi, Jian-Wei


    Layered ultramafic-mafic intrusions are usually formed in an arc/back-arc or intra-plate tectonic environment, or genetically related to a mantle plume. In this paper, we report on an ultramafic-mafic intrusion, the Dalongkai intrusion in the Ailaoshan tectonic zone (SW China), whose occurrence is closely associated with arc/back-arc magmatic rocks. The Dalongkai intrusion is composed of plagioclase-lherzolite, hornblende-peridotite, lherzolite and wehrlite at the bottom, cumulate plagioclase-pyroxenite at the middle part, changing to fine-grained gabbro towards the upper part of the intrusion, forming layering structure. Zircons from the plagioclase-pyroxenites and gabbros yielded U-Pb ages of 272.1 ± 1.7 Ma and 266.4 ± 5.8 Ma, respectively. The plagioclase-pyroxenites show cumulate textures, and are characterized by high MgO (25.0-28.0 wt.%; mg# = 80.6-82.3), Cr (1606-2089 ppm) and Ni (893-1203 ppm) contents, interpreted as early cumulate phases. By contrast, the gabbros have relatively lower mg# values (56.3-62.7), and Cr (157-218 ppm) and Ni (73-114 ppm) concentrations, and may represent frozen liquids. The plagioclase-pyroxenites and gabbros share similar chondrite-normalized REE patterns and primitive mantle-normalized trace element profiles which are analogous to those of typical back-arc basin basalts. The εNd(t) values for both rock types range from +2.20 to +4.22. These geochemical and isotopic signatures suggest that the Dalongkai ultramafic-mafic rocks originated from a MORB-like mantle source metasomatized by subduction-related, sediment-derived fluids. Our data, together with other geological evidence, indicate that the emplacement of the Dalongkai ultramafic-mafic intrusion most likely occurred in a back-arc extensional setting associated with subduction of the Ailaoshan Paleotethyan branch ocean during the Middle Permian, thus ruling out the previously speculated linkage to the Emeishan mantle plume, or to an intra-continental rift.

  2. Geochemistry and geochronology of the mafic dikes in the Taipusi area, northern margin of North China Craton: Implications for Silurian tectonic evolution of the Central Asian Orogen (United States)

    Wu, Jing-Hua; Li, Huan; Xi, Xiao-Shuang; Kong, Hua; Wu, Qian-Hong; Peng, Neng-Li; Wu, Xi-Ming; Cao, Jing-Ya; Gabo-Ratio, Jillian Aira S.


    The Taipusi area in the Bainaimiao Arc Belt is located in the northern margin of the North China Craton, at the southern margin of the middle Central Asian Orogenic Belt. It is characterized by large exposures of mafic dikes. In this contribution, we present first-hand whole-rock major and trace elements, zircon U-Pb geochronology and in situ trace element geochemistry data for these mafic rocks, which reveal their petrogenesis and tectonic evolution. These mafic dikes display varied compositions of SiO2 (49.42-54.29%), TiO2 (0.63-1.08%), Al2O3 (13.94-17.60%), MgO (4.66-10.51%), Fe2O3 (1.59-3.07%), FeO (4.60-6.90%), CaO (4.57-8.91%), Na2O (1.61-4.26%), K2O (0.92-2.54%) and P2O5 (0.11-0.29%). They are mainly of high-K calc-alkaline series with indistinct Eu anomalies, enriched in large ion lithophile elements (e.g., Rb, Ba, K and Sr) but depleted in high field strength elements (e.g., Nb, P and Ti). These suggest that the crystallizing magma was derived from enriched mantle altered by metasomatic fluids in a subduction setting with imprints of active continental margin features. The high concentrations of Hf, U, Th, Pb and Y, pronounced positive Ce but slightly negative Eu anomalies in zircons indicating that the magma underwent a fractional crystallization and crustal contamination process, with medium to high fO2. Zircon LA-ICP-MS U-Pb dating yielded concordant ages of 437-442 Ma for these mafic dikes, which is consistent with the early Paleozoic volcanic arc magmatic activity in the Bainaimiao area. Hence, we conclude that the Bainaimiao Arc Belt is a continental arc formed by the southward subduction of the Paleo-Asian ocean during early Paleozoic.

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

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


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

  4. 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

  5. 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.; 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.

  6. 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

  7. Thermal Expansivity Between 150 and 800°C of Hydrothermally Altered Conduit Dyke Samples from USDP-4 Drill Core (Mt Unzen, Shimabara, Japan) (United States)

    Yilmaz, T. I.; Hess, K. U.; Vasseur, J.; Wadsworth, F. B.; Gilg, H. A.; Nakada, S.; Dingwell, D. B.


    When hot magma intrudes the crust, the surrounding rocks expand. Similarly, the cooling magma contracts. The expansion and contraction of these multiphase materials is not simple and often requires empirical constraint. Therefore, we constrained the thermal expansivity of Unzen dome and conduit samples using a NETZSCH® DIL 402C. Following experiments, those samples were scanned using a Phoenix v|tome|x m to observe the cracks that may have developed during the heating and cooling. The dome samples do not show petrological or chemical signs of alteration. However, the alteration of the conduit dykes is represented by the occurrence of the main secondary phases such as chlorite, sulfides, carbonates, R1 (Reichweite parameter) illite-smectite, and kaolinite. These alteration products indicate an (I) early weak to moderate argillic magmatic alteration, and a (II) second stage weak to moderate propylitic hydrothermal alteration. The linear thermal expansion coefficient aL of the dome material is K-1 between 150° and 800°C and shows a sharp peak of up to K-1 around the alpha-beta-quartz-transition ( 573°C). In contrast, aL of the hydrothermally altered conduit samples starts to increase around 180° and reaches K-1 at 400°C. We interpret this effect as being due to the water content of the kaolinite and the R1 illite-smectite, which induces larger expansions per degree temperature change. Furthermore, the altered conduit samples show a more pronounced increases of aL between 500 and 650°C of up to peaks at K-1, which is generated by the breakdown of chlorite, iron-rich dolomite solid solutions, calcite, and pyrite. We use a 1D conductive model of heat transfer to explore how the country rock around the Unzen conduit zone would heat up after intrusion. In turn, we convert these temperature profiles to thermal stress profiles, assuming the edifice is largely undeformable. We show that these high linear thermal expansion coefficients of the hydrothermally altered

  8. Lead isotope constraints on the mantle sources involved in the genesis of Mesozoic high-Ti tholeiite dykes (Urubici type from the São Francisco Craton (Southern Espinhaço, Brazil

    Directory of Open Access Journals (Sweden)

    Leila Soares Marques

    Full Text Available ABSTRACT: The first results of Pb isotope compositions of the high-Ti Mesozoic dykes of the Southern Espinhaço are presented. The results do not show large variations and are significantly more radiogenic than the Pb isotope compositions of the high-Ti tholeiites from the Paraná Continental Flood Basalts. The data combined with published geochemical and Sr-Nd isotope results rule out crustal contamination processes in the genesis of the dykes, requiring magma generation in metasomatized subcontinental lithospheric mantle with the involvement of HIMU-type and carbonatite components. The magmas may have been also derived from a mantle source containing ~4 - 5% of pyroxenite and ~1% of carbonatite melts, agreeing with published Os isotope compositions of high-Ti rocks from the Paraná Continental Flood Basalts. These metasomatizing agents could be responsible for mantle source refertilization, as was also proposed in the literature to explain the characteristics of xenoliths of the Goiás Alkaline Province, which also occurs in the border of the São Francisco Craton. Additionally, to evaluate the risks of Pb contamination during sample preparation for analysis, several experimental tests were accomplished, which indicate the need of sawed surface removal and a careful washing of small-sized rock fragments before powdering, especially for rocks with [Pb] < 7 µg/g.


    Directory of Open Access Journals (Sweden)

    A. G. Vladimirov


    Full Text Available In West Sangilen (South‐East Tuva, Russia, there are outcrops of metamorphic and magmatic complexes of early Caledonides, which are related to the period of long‐term collisional and post‐collisional events in the north‐ western edge of the Tuva‐Mongolian massif. The evolution of orogenic structures in West Sangilen is an example of the collapse of folded structures in case of changes in tectonic regimes from compression and transpression (collision period to intra‐ and marginal continental transform‐shear extension (post‐collision period. Numerous geologic fea‐ tures give evidence of changes in the kinematics and characteristics of deformations, as well as in the conditions of metamorphism and magmatism in the study region. However, thinning of the crust during the collapse of the colli‐ sional orogenic structure has not been supported by any direct data. Indicators of such events are the complexes of combined dykes, which are abundant in West Sangilen, especially in the area between the Erzin and Naryn rivers and on the right bank of the Erzin river. The most representative object is a combined basite‐granite dyke at the foot of the Tavit‐Dag mountain. Its position is controlled by the strike‐slip fault system. The thermochronological analysis of mingling rocks shows different ages of the closure of isotope systems: 494.8±5.4 Ma (U/Pb, zircon, basites, 489.7±7 Ma (U/Pb, zircon, granitoids, 471.2±1.9 Ma (Ar/Ar , amphibole, basites, and 462.5±1.0 Ma (Ar/Ar, biotite, basites. Taking into account the parameters of the closure of isotope systems (~800–900 °C, zircon, U/Pb; ~500 °C, amphi‐ bole, Ar/Ar; ~300 °C, biotite, Ar/Ar, the cooling curve of the mingling dyke is estimated. It corresponds to lowering of the temperature by 600 °C (900 °С  500 °С  300 °C in the period from 500 (494.8±5.4 Ma to 461 (462.5±1.0 Ma. It is shown that the recent thermal events did not affect the mingling dyke located

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

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


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

  11. Constraints from geochemistry and oxygen isotopes for the hydrothermal origin of orthoamphibole mafic gneiss in the New Jersey Highlands, north-central Appalachians, USA (United States)

    Volkert, Richard A.; Peck, William H.


    Rare exposures of orthoamphibole mafic (Oam) gneiss of Mesoproterozoic age in the north-central Appalachians are confined to the northwestern New Jersey Highlands where they form thin lens-shaped bodies composed of gedrite and sparse anthophyllite, oligoclase (An13-An20), biotite, magnetite, and local fluorapatite, rutile, and ilmenite. The gneiss is penetratively foliated and has sharp, conformable contacts against enclosing supracrustal paragneiss and marble. Orthoamphibole mafic gneiss is characterized by low SiO2 (48 ± 2.5 wt%), CaO (1.9 ± 1.3 wt%), and high Al2O3 (18 ± 1.2 wt%), Fe2O3 (10.5 ± 1.6 wt%), and MgO (12 ± 2.3 wt%). Trace element abundances overlap those of unaltered amphibolites in the study area and, coupled with δ18O values of 9.45 ± 0.6‰ (VSMOW) from gedrite separates, support an origin from a basalt protolith. The geochemical and isotopic data are consistent with the formation of Oam gneiss through sea floor hydrothermal alteration of basalt at low temperature of 150-200 °C. Mass-balance calculations indicate gains during alteration mainly in MgO and Al2O3 and losses in CaO, Sr, and light rare earth elements. Our results are compatible with the pre-metamorphic alteration of the basalt protoliths through chloritization and plagioclase dissolution that produced a Mg-rich and Ca-poor rock. Subsequent metamorphism of this chlorite-rich rock to the current mineral assemblage of Oam gneiss took place at ca. 1045 Ma, during the Ottawan phase of the Grenvillian Orogeny. The close spatial association in the study area of Oam gneiss bodies and sulfide occurrences suggests an affinity to the style of mineralization associated with volcanogenic massive sulfide (VMS)-type deposits.

  12. Occurrence and mineral chemistry of chromite and related silicates from the Hongshishan mafic-ultramafic complex, NW China with petrogenetic implications (United States)

    Ruan, Banxiao; Yu, Yingmin; Lv, Xinbiao; Feng, Jing; Wei, Wei; Wu, Chunming; Wang, Heng


    The Hongshishan mafic-ultramafic complex is located in the western Beishan Terrane, NW China, and hosts an economic Ni-Cu deposit. Chromite as accessory mineral from the complex is divided into three types based on its occurrence and morphology. Quantitative electron probe microanalysis (EPMA) have been conducted on the different types of chromites. Type 1 chromite occurs as inclusions within silicate minerals and has relatively homogeneous composition. Type 2 chromite occurs among serpentine, as interstitial phase. Type 3 chromite is zoned and exhibits a sudden change in compositions from core to rim. Type 1 chromite occurs in olivine gabbro and troctolite showing homogeneous composition. This chromite is more likely primary. Interstitial type 2 and zoned type 3 chromite has compositional variation from core to rim and is more likely modified. Abundant inclusions of orthopyroxene, phlogopite and hornblende occur within type 2 and type 3 chromites. The parental melt of type 1 chromite has an estimated composition of 14.5 wt% MgO, 12.3 wt% Al2O3 and 1.9 wt% TiO2 and is characterized by high temperature, picritic affinity, hydrous nature and high Mg and Ti contents. Compositions of chromite and clinopyroxene are distinct from those of Alaskan-type complexes and imply that the subduction-related environment is not reasonable. Post orogenic extension and the early Permian mantle plume are responsible for the emplacement of mafic-ultramafic complexes in the Beishan Terrane. The cores of zoned chromites are classified as ferrous chromite and the rims as ferrian chromite. The formation of ferrian rim involves reaction of ferrous chromite, forsterite and magnetite to produce ferrian chromite and chlorite, or alternaively, the rim can be simply envisioned as the result of external addition of magnetite in solution to the already formed ferrous chromite.

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

    International Nuclear Information System (INIS)

    Tomazzoli, Edison Ramos; Nilson, Ariplinio Antonio


    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)

  14. Geochemistry and origin of metamorphosed mafic rocks from the Lower Paleozoic Moretown and Cram Hill Formations of North-Central Vermont: Delamination magmatism in the western New England appalachians (United States)

    Coish, Raymond; Kim, Jonathan; Twelker, Evan; Zolkos, Scott P.; Walsh, Gregory J.


    The Moretown Formation, exposed as a north-trending unit that extends from northern Vermont to Connecticut, is located along a critical Appalachian litho-tectonic zone between the paleomargin of Laurentia and accreted oceanic terranes. Remnants of magmatic activity, in part preserved as metamorphosed mafic rocks in the Moretown Formation and the overlying Cram Hill Formation, are a key to further understanding the tectonic history of the northern Appalachians. Field relationships suggest that the metamorphosed mafic rocks might have formed during and after Taconian deformation, which occurred at ca. 470 to 460 Ma. Geochemistry indicates that the sampled metamorphosed mafic rocks were mostly basalts or basaltic andesites. The rocks have moderate TiO2 contents (1–2.5 wt %), are slightly enriched in the light-rare earth elements relative to the heavy rare earths, and have negative Nb-Ta anomalies in MORB-normalized extended rare earth element diagrams. Their chemistry is similar to compositions of basalts from western Pacific extensional basins near volcanic arcs. The metamorphosed mafic rocks of this study are similar in chemistry to both the pre-Silurian Mount Norris Intrusive Suite of northern Vermont, and also to some of Late Silurian rocks within the Lake Memphremagog Intrusive Suite, particularly the Comerford Intrusive Complex of Vermont and New Hampshire. Both suites may be represented among the samples of this study. The geochemistry of all samples indicates that parental magmas were generated in supra-subduction extensional environments during lithospheric delamination.

  15. Early Neoarchaean A-type granitic magmatism by crustal reworking ...

    Indian Academy of Sciences (India)

    Abhishek Topno


    Apr 11, 2018 ... crustal melting of tonalitic/granodioritic source similar to the ~3.3 Ga Singhbhum Granite. Intrusion of the Pala Lahara granites was coeval with prominent mafic magmatism in the Singhbhum craton (e.g., the Dhanjori mafic volcanic rocks and NNE–SSW trending mafic dyke swarm). It is suggested that the.

  16. Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic-ultramafic complex of Gaositai, North China Craton (United States)

    Yang, Fan; Santosh, M.; Tsunogae, T.; Tang, Li; Teng, Xueming


    The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and metasomatic rock suites. Here we investigate a composite mafic-ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro-serpentinite-dunite-pyroxenite-gabbro-diorite suite surrounded by hornblendites of this complex has long been considered to represent an "Alaskan-type" zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U-Pb and Lu-Hf data from the various rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt-peridotite interaction. Our new mineral chemical data from the mafic-ultramafic suite exclude an "Alaskan-type" affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U-Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433-2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to

  17. 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

  18. The Pan-African calc-alkaline granitoids and the associated mafic microgranular enclaves (MME around Wadi Abu Zawal area, North Eastern Desert, Egypt: geology, geochemistry and petrogenesis

    Directory of Open Access Journals (Sweden)

    Asran Mohamed Asran


    Full Text Available Introduction: The area around Wadi Abu Zawal is occupied by gneisses-migmatites, island arcs metavolcanics, Dokhan volcanics, Hammamat sediments, intrusive rocks of granitic and gabbroic composition and dyke swarms.Materials and Methods: The present work concerning on the geology, geochemistry and petrogenesis of the MME and the host granitoid rocks of that area. The analytical methods for major and trace elements of some representative samples were carried out by XRF technique at the Institute of BGR in Hannover, Germany.Results: Mineralogically, MME are composed mainly of plagioclase, hornblende, biotite and quartz with accessory of sphene, acicular apatite and opaque oxides, while chlorite and epidote are secondary ones. Whereas Abu Zawal granitoid rocks are subsolvus and consist of variable contents of plagioclase, K-feldspar, quartz, and biotite, with accessory sphene, zircon and opaque oxides, typical of I-type granites. The studied Abu Zawal area represents part of the northeastern Egypt which formed by regional crustal extension and magmatic-arc regimes during Pan-African orogenic event.The MME display major, trace element contents and tectonic setting comparable with the end members of (GDT and (IAG of the Eastern Desert which produced (by fractionation from a mantle-derived tholeiitic magma in an island-arc tectonic environment. Abu Zawal granitoid rocks exhibit trace element characteristics of volcanic-arc granites, and formed in an Andean-type setting.Conclusions: On the variation diagrams, major and trace element contents of the MME and granitoid rocks display conspicuous gap and two distinct trends one for the MME, (IAG and the other for the Abu Zawal granitoid rocks, which indicates that they are not genetically related and suggest the crustal source for the host granitoid rock.

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

    Directory of Open Access Journals (Sweden)

    Jorge Skarmeta


    Full Text Available 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 an individual dyke. This banding has z and s asymmetries that indicate the sense of displacement of the country rock. The relative involvement of the coeval, internal and external stresses that caused the finite strains is estimated by using a partition analysis. The phenocryst location and size distribution are related to the internal magma flow velocity (u m stress component, whereas the sigmoid banding is linked to the external tectonic wall displacement velocity (±u. Dyke wall sliding with or against the magma flow induced the asymmetric shear strain distribution. The measured strain and displacements are analyzed using the deformation model of viscous laminar flow confined between two parallel plates moving parallel to each other with opposed motion. The shear stresses related to magma intrusion and frictional dyke-wall shear are quantified on the basis of magma flow displacements, cooling times and the temperature dependent viscosity of basalts in the linear rheology range. At the estimated depth where the intrusion and deformation occurred, the state of stress was close to being hydrostatic. This conclusion is in agreement with established models of active-collapsing volcanic centres, where bulk permeability is accommodated by means of a mesh of interconnected dykes and active faults. This interactivity tends to re-equilibrate, locally and transiently, any excess differential stress and redistributes excess magmatic pressures to create a uniform

  20. A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units: Lunar Magma Ocean Viscosity

    Energy Technology Data Exchange (ETDEWEB)

    Dygert, Nick [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Knoxville TN USA; Lin, Jung-Fu [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Marshall, Edward W. [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Kono, Yoshio [HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne IL USA; Gardner, James E. [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA


    Much of the lunar crust is monomineralic, comprising >98% plagioclase. The prevailing model argues the crust accumulated as plagioclase floated to the surface of a solidifying lunar magma ocean (LMO). Whether >98% pure anorthosites can form in a flotation scenario is debated. An important determinant of the efficiency of plagioclase fractionation is the viscosity of the LMO liquid, which was unconstrained. Here we present results from new experiments conducted on a late LMO-relevant ferrobasaltic melt. The liquid has an exceptionally low viscosity of 0.22 $+0.11\\atop{-0.19}$to 1.45 $+0.46\\atop{-0.82}$ Pa s at experimental conditions (1,300–1,600°C; 0.1–4.4 GPa) and can be modeled by an Arrhenius relation. Extrapolating to LMO-relevant temperatures, our analysis suggests a low viscosity LMO would form a stratified flotation crust, with the oldest units containing a mafic component and with very pure younger units. Old, impure crust may have been buried by lower crustal diapirs of pure anorthosite in a serial magmatism scenario.

  1. Influencia de la temperatura y el tiempo de almacenamiento en la conservación del fruto de mango (Manifera indica L. variedad Van Dyke Influence of temperature and storage time on quality of mango fruit (Mangifera indica l. variety Van Dyke

    Directory of Open Access Journals (Sweden)

    Galvis Jesús A.


    Full Text Available Mangos (Mangifera índica L. Variedad Van Dyke en grado de madurez fisiológica, se almacenaron en tres temperaturas de refrigeración (12, 10 Y 7°C y H. R del 85 - 90%, por tiempos de 10, 20 y 30 días. Adicionalmente se almacenaron mangos a 18°C por 15 días, los cuales fueron tomados como testigo. Los mangos fueron cosechados de la finca Frutol, localizada
    en el municipio de El Espinal, departamento del Tolima.
    Temperatura media 29°C, altitud 431 m.s.n.m, humedad
    relativa del 70%, precipitación promedio anual 1368
    mm. Durante el almacenamiento se evaluaron características
    fisicas como porcentaje de pérdidas de peso, dureza del
    fruto y de la pulpa. Además se evaluaron algunos cambios
    químicos y bioquímicos como la variación de los °Brix, el pH, el porcentaje de acidez, el contenido de sacarosa, glucosa y fructosa y de ácidos (cítrico, málico, succínico y ascórbico. Finalmente se evaluaron los cambios de color de la corteza.
    Del estudio se concluyó que la mejor temperatura de
    almacenamiento fue 12°C, en la cual el fruto maduró
    hasta alcanzar la madurez organoléptica en el día 30, lo
    cual equivale al doble del tiempo de conservación respecto
    a los mangos almacenados a 18°C. El mango resultó ser sensible a las temperaturas de 10 y 7°C, la cual se caracterizó por la interrupción del proceso de maduración siendo más graves los daños por frío en la temperatura de 7°C. En la temperatura de 10°C, se presentó evolución de los cambios que caracterizan la maduración hasta el día 20, pero entre el día 21 y el día 30 los cambios fueron interrumpidos, lo que indica que los daños por frío se hicieron irreversibles a partir del día 21.Mangos variety Van Dyke harvested at physiologic maturity were stored at low temperatures (12, 10 and 7°C, 85% RH, for 10, 20 and 30 days. Control mangos were stored at 18°C by 15 days. The fruits were harvested in the Frutol

  2. 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.

  3. Impact on the deep biosphere of CO2 geological sequestration in (ultra)mafic rocks and retroactive consequences on its fate (United States)

    Ménez, Bénédicte; Gérard, Emmanuelle; Rommevaux-Jestin, Céline; Dupraz, Sébastien; Guyot, François; Arnar Alfreősson, Helgi; Reynir Gíslason, Sigurőur; Sigurőardóttir, Hólmfríiur


    Due to their reactivity and high potential of carbonation, mafic and ultramafic rocks constitute targets of great interest to safely and permanently sequestrate anthropogenic CO2 and thus, limit the potential major environmental consequences of its increasing atmospheric level. In addition, subsurface (ultra)mafic environments are recognized to harbor diverse and active microbial populations that may be stimulated or decimated following CO2 injection (± impurities) and subsequent acidification. However, the nature and amplitude of the involved biogeochemical pathways are still unknown. To avoid unforeseen consequences at all time scales (e.g. reservoir souring and clogging, bioproduction of H2S and CH4), the impact of CO2 injection on deep biota with unknown ecology, and their retroactive effects on the capacity and long-term stability of CO2 storage sites, have to be determined. We present here combined field and experimental investigations focused on the Icelandic pilot site, implemented in the Hengill area (SW Iceland) at the Hellisheidi geothermal power plant (thanks to the CarbFix program, a consortium between the University of Iceland, Reykjavik Energy, the French CNRS of Toulouse and Columbia University in N.Y., U.S.A. and to the companion French ANR-CO2FIX project). This field scale injection of CO2 charged water is here designed to study the feasibility of storing permanently CO2 in basaltic rocks and to optimize industrial methods. Prior to the injection, the microbiological initial state was characterized through regular sampling at various seasons (i.e., October '08, July '09, February '10). DNA was extracted and amplified from the deep and shallow observatory wells, after filtration of 20 to 30 liters of groundwater collected in the depth interval 400-980 m using a specifically developed sampling protocol aiming at reducing contamination risks. An inventory of living indigenous bacteria and archaea was then done using molecular methods based on the

  4. Origin of Mafic Microgranular Enclaves (MMEs and Their Host Rocks of the Cretaceous Xiaojiang-Liangnong Granitic Complexes in the Southeast Coast Magmatic Belt, S China

    Directory of Open Access Journals (Sweden)

    Pei-Shan Hsieh


    Full Text Available Cretaceous Late Yanshanian (LY magmatism produced large amounts of I-type granitoids in the Southeast Coast Mag matic Belt (SCMB. I-type granitoids from Xiaojiang-Liangnong complexes (N Zhejiang in the northern part of this belt are characterized by containing abundant mafic microgranular enclaves (MMEs. On the basis of petrography and mineralogy, two types of MMEs are recognized. One (Type 1, enclosed in the granodiorite, is composed of amphibole, high-Ti tabularbiotite, plagioclase, K-feld spar, and quartz. Us ing the Al-in-am phibole geobarometer, a shallow origin (4 - 8 km of am phiboles is suggested. The other (Type 2, enclosed in al kali feld spargranite, is amphibole-free and composed of low-Ti acicular biotite, plagioclase, K-feld spar, and quartz. Geo chemistry of major and traceel ements seems to re flect two different evolving trends for these host granitoids. The Sr-Nd isotopic features indicate that all the studied samples vary in a narrow range of Isr (0.7078 to 0.7082 and eNd(T (-5.6 to -8.3, except the Type 2 enclaves and hosts that show slightly morede pleted compositions (Isr = 0.7073 to 0.7075 and eNd(T = -5.0 to -6.0. U-Pb zir con ages obtained are 109.6 ¡_ 0.9 Ma for the granodiorite and 113.5 ¡_ 1.1 Ma for the alkalifeld spargran ite, with 103.2 ¡_ 0.9 Ma for the Type 2 MMEs. In her ited ages of 117.0 ¡_ 2.0 Ma and 119.8 ¡_ 1.1 Ma seem to presentin the former two samples. Similarities of mineral chemistry and isotopic composition among the MMEs-host pairs as well as the youn ger age of MMEs suggest that MMEs of Xiaojiang-Liangnong complexes most likely represent mixing/mingling products formed as a consequence of the in tru sion of ba saltic magma into the host granitoids un der dif fer ent cool ing con di tions. Judg ing from the pres ence of in her ited zir con ages, the com po si tion gap be tween high-Ti and low-Ti bi o tite in granodiorite and al kali feld spar gran ite, and lower zirconsaturation temperatures for

  5. Mafic microgranular enclaves (MMEs) in amphibole-bearing granites of the Bintang batholith, Main Range granite province: Evidence for a meta-igneous basement in Western Peninsular Malaysia (United States)

    Quek, Long Xiang; Ghani, Azman A.; Chung, Sun-Lin; Li, Shan; Lai, Yu-Ming; Saidin, Mokhtar; Amir Hassan, Meor H.; Muhammad Ali, Muhammad Afiq; Badruldin, Muhammad Hafifi; Abu Bakar, Ahmad Farid


    Mafic microgranular enclaves (MMEs) with varying sizes are a common occurrence in porphyritic amphibole-bearing granite of the Bintang batholith, which is part of the Main Range granite province. The MMEs of the amphibole-bearing granite are significant as they are related to the I-type granitoids within the Main Range granite province. Petrographic observations indicate the MMEs are mantled with coarse mafic crystals on the rim and contain similar minerals to the host (biotite + plagioclase + K-feldspar + pyroxene + amphibole), but in different proportions. Geochemical analyses indicate the MMEs are shoshonitic with mg# comparable to the granite host. Substantial similarities exist between the MMEs and granite with regards to the normalized rare earth element patterns and trace elements variation diagrams. The MMEs and granite are not completely coeval as the MME zircon U-Pb age (224.3 ± 1.2 Ma) is slightly older than its granite host zircon U-Pb age (216.2 ± 1.0 Ma). The age difference is also observed from the unusual 500 m-long Tiak MME and another amphibole-bearing granite sample from the south of the pluton, which yield 221.8 ± 1.1 Ma and 217.4 ± 1.0 Ma respectively. The oldest inherited zircons found in the MME and granite are 2.0 Ga and 1.3 Ga respectively, while the oldest xenocrystic zircons found in the MME and granite are 2.5 Ga and 1.5 Ga respectively. Identical negative εHf(t) values from zircon U-Pb and Lu-Hf analysis for a MME-granite pair indicates the rocks were generated from a similar, ancient source in the basement. Combining the results, we suggest that incongruent melting of an ancient protolith played an important part in the evolution of the MMEs and granite and the MMEs characteristics are best explained as restite. The zircon Hf model age (two-stage) and the I-type peritectic and restitic mineral assemblages in the MMEs further describe the protolith as Early Proterozoic-Late Archean (≈2.5 Ga) meta-igneous rock. This shows the

  6. Upper Paleozoic mafic and intermediate volcanic rocks of the Mount Pleasant caldera associated with the Sn-W deposit in southwestern New Brunswick (Canada): Petrogenesis and metallogenic implications (United States)

    Dostal, Jaroslav; Jutras, Pierre


    Upper Paleozoic ( 365 Ma) mafic and intermediate volcanic rocks of the Piskahegan Group constitute a subordinate part of the Mount Pleasant caldera, which is associated with a significant polymetallic deposit (tungsten-molybdenum-bismuth zones 33 Mt ore with 0.21% W, 0.1% Mo and 0.08% Bi and tin-indium zones 4.8 Mt with 0.82% Sn and 129 g/t In) in southwestern New Brunswick (Canada). The epicontinental caldera complex formed during the opening of the late Paleozoic Maritimes Basin in the northern Appalachians. The mafic and intermediate rocks make up two compositionally distinct associations. The first association includes evolved rift-related continental tholeiitic basalts, and the second association comprises calc-alkaline andesites, although both associations were emplaced penecontemporaneously. The basalts have low Mg# 0.34-0.40, smooth chondrite-normalized REE patterns with (La/Yb)n 5-6, primitive mantle-normalized trace element patterns without noticeable negative Nb-Ta anomalies, and their ɛNd(T) ranges from + 2.5 to + 2.2. The basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of 70-90 km. The calc-alkaline andesites of the second association have chondrite-normalized REE patterns that are more fractionated, with (La/Yb)n 7-8.5, but without significant negative Eu anomalies. Compared to the basaltic rocks, they have lower ɛNd(T) values, ranging from + 0.5 to + 1.9, and their mantle-normalized trace element plots show negative Nb-Ta anomalies. The ɛNd(T) values display negative correlations with indicators of crustal contamination, such as Th/La, Th/Nb and SiO2. The andesitic rocks are interpreted to have formed by assimilation-fractional crystallization processes, which resulted in the contamination of a precursor basaltic magma with crustal material. The parent basaltic magma for both suites underwent a different evolution. The tholeiitic basalts experienced shallow-seated fractional

  7. Zircon and baddeleyite from the economic ultramafic-mafic Noril'sk-1 intrusion (Russia): Hf-isotope constraints on source composition (United States)

    Malitch, K. N.; Belousova, E. A.; Badanina, I. Yu.; Griffin, W. L.


    The ultramafic-mafic Noril'sk-1 intrusion in the northwestern part of the Siberian Craton (Russia) represents one of three known Noril'sk-type, ore-bearing intrusions, which host one of the world's major economic sulphide platinum-group-element (PGE)-Cu-Ni deposits. Zircon and baddeleyite dated previously both by SHRIMP (i.e. 248.0 ± 3.7 Ma, Campbell et al. 1992) and ID-TIMS (251.1 ± 3.6 Ma, Kamo et al. 1996) have been restricted to one lithology (e.g. leucogabbro) of the Noril'sk-1 intrusion. To better constrain the age of igneous event and sources involved in its generation our multi-technique study utilized ten rock samples characteristic of unmineralized and mineralized lithologies. The rocks investigated comprise (from top to bottom) gabbro-diorite (sample N1-1), leucogabbro (N1-3), olivine-free gabbro (N1-2 and N1-4), olivine-bearing gabbro (N1-5), olivine gabbro (N1-6), plagiowehrlite and plagiodunite (N1-7), taxitic-textured rocks comprising melanotroctolite, olivine gabbro with relics of ultramafic rocks (N1-8, N1-9) and contact fine-grained gabbro (N1-10). Sulphide PGE-Cu-Ni ores occur in ultramafic (N1-7) and taxitic-textured rocks (N1-8 and N1-9), which have thickness of about 17 m, whereas the low-sulphide horizon of about 1 m thick occurs in the upper part of intrusion (N1-3). In situ U-Pb analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations (Malitch et al. 2012). The U-Pb ages of baddeleyite and the defined zircon populations cover a significant time span, from Late Paleozoic to Early Mesozoic (e.g., 290 ± 2.8; 261.3 ± 1.6; 245.7 ± 1.1; 236.5 ± 1.8 and 226.7 ± 0.9 Ma). The established distribution of U-Pb ages implies that crystallization of baddeleyite and zircon corresponds to several stages of protracted evolution of ultramafic-mafic magmas at deep-seated staging chambers and/or probably characterizes interaction of distinct magmas during formation

  8. San Andreas Fault dip, Peninsular Ranges mafic lower crust and partial melt in the Salton Trough, Southern California, from ambient-noise tomography (United States)

    Barak, Shahar; Klemperer, Simon L.; Lawrence, Jesse F.


    We use ambient-noise tomography to improve CVM-H11.9, a community velocity model of southern California. Our new 3-D shear-velocity model with 0.05° x 0.05° lateral and 1 km vertical blocks reveals new structure beneath the San Andreas Fault (SAF), Peninsular Ranges batholith (PRB), southern Sierra Nevada batholith (SNB), and the Salton Trough (ST). We use 4 years of data recorded on 849 broadband stations, vastly more than previous studies and including our own broadband Salton Seismic Imaging Project, a 40 station transect across the ST, as well as other campaign stations in both Mexico and the United States. Mean lower crust and upper mantle wave speeds (3.6 km/s at 20 km, 4.2 km/s at 40 km) are low by global standards. Across the SAF, southeast of San Gorgonio Pass, we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the Moho. Beneath the western PRB and westernmost southern SNB, we observe relatively high shear velocities (≥3.8 km/s) in the lower crust that we interpret as the mafic roots of the overlying arc. Relatively high-velocity upper mantle (up to ˜4.5 km/s) may be part of the intact arc, or possibly a remnant of the Farallon plate. Beneath the ST, we observe zones of low shear-velocity in the lower crust and upper mantle which permit up to ˜4.5% melt in the lower crust and up to ˜6% melt in the upper mantle, depending on the assumed composition and pore geometry. Our results preclude the existence of older continental crust beneath the ST and support the creation of new crust beneath the ST.

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

    Energy Technology Data Exchange (ETDEWEB)

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


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

  10. Efecto de Inhibidores de Pardeamiento y la Técnica de Atmósfera Modifcada en Mango (Mangifera Indica L Variedad Van Dyke Mínimamente Procesado

    Directory of Open Access Journals (Sweden)

    Jesús Antonio Galvis Vanegas


    Full Text Available El mango (Mangifera indica L variedad Van Dyke es un fruto apetecido a nivel nacional e internacional por su agradable aroma, intenso color amarillo y buen balance de ácidos/azúcares. La investigación se desarrolló en dos etapas. En la primera se determinó la respuesta de los trozos de fruto a la aplicación de tres inhibidores de pardeamiento en dos concentraciones: (ácido cítrico a 150 y 300 ppm; ácido ascórbico a 250 y 500 ppm y L-Cysteina a 100 y 200 ppm, con relación a la calidad y tiempo de almacenamiento; en la segunda, se estableció el tiempo de vida útil de modo que conserve sus características organolépticas, cuando se combina el mejor inhibidor de pardeamiento, con la técnica de atmósfera modificada en concentraciones de 5% de CO2, 5% de O2 y 90% de N2, empleando dos tipos de empaque: canastillas plásticas y bandejas de icopor, colocadas dentro de bolsas de polietileno de baja densidad (LDPE calibre 2 (0.035 mm de espesor.

  11. Lu-Hf isotopic memory of plume-lithosphere interaction in the source of layered mafic intrusions, Windimurra Igneous Complex, Yilgarn Craton, Australia (United States)

    Nebel, O.; Arculus, R. J.; Ivanic, T. J.; Nebel-Jacobsen, Y. J.


    Most layered mafic intrusions (LMI) are formed via multiple magma injections into crustal magma chambers. These magmas are originally sourced from the mantle, likely via plume activity, but may interact with the overriding lithosphere during ascent and emplacement in the crust. The magma injections lead to the establishment of different layers and zones with complex macroscopic, microscopic and cryptic compositional layering through magmatic differentiation and associated cumulate formation, sometimes accompanied by crustal assimilation. These complex mineralogical and petrological processes obscure the nature of the mantle sources of LMI, and typically have limited the degree to which parental liquids can be fully characterised. Here, we present Lu-Hf isotope data for samples from distinct layers of the Upper Zone of the Windimurra Igneous Complex (WIC), an immense late-Archean LMI in the West Australian Yilgarn Craton. Lu-Hf isotope systematics of whole rocks are well correlated (MSWD=5.6, n=17) with an age of ˜3.05±0.05 Ga and initial ɛHf˜+8. This age, however, is older than whole rock Sm-Nd and zircon U-Pb ages of the intrusion, both of which are ca. 2.8 Ga. Stratigraphically-controlled initial Hf isotope variations (associated with multiple episodes of emplacement at ca. 2.8 Ga) indicate isotope mixing between a near-chondritic and an ultra-radiogenic component, the latter with ɛHf[2.8 Ga]>+15. This Hf isotope mixing creates a pseudochron-relationship at the time of intrusion of ˜250 Myr that is superimposed on subsequent radiogenic ingrowth after crystallisation, generating an age that predates the actual emplacement event. Mixing between late-stage crystallisation products (melt + crystals) from the Middle Zone and replenishing, plume-derived liquids was followed by crystal accumulation in a chemically evolving magma chamber. The ultra-radiogenic Hf isotope endmember in the WIC mantle source requires parent-daughter ratios consistent with very early

  12. Magma Mixing and Mingling Processes in the Tiemann Shut-ins, St. Francois Mountains, Missouri: Constraints from Geochemical Variations Within Mafic Enclaves (United States)

    Brinkman, J.; Encarnacion, J. P.


    The formation of continental crust is still a topic of debate. Its average composition is similar to andesite, a rock type that is thought to be largely the product of magma mixing and mingling between basaltic and granitic magma. In the 1.5 billion-year old St. Francois Mountains of SE Missouri, an excellent exposure of magma mixing/mingling is preserved in the Tiemann Shutins area where a granitic pluton hosts decimeter- to meter-scale mafic enclaves. Previous studies (Lowell and Young, 1999) present enclave SiO2 values ranging from 59.1 to 70.0 weight %. With only one analysis per enclave, it is unclear whether the variability in the measurements is due to varying sampling location within each enclave from a population of heterogeneous enclaves or variable composition between more-or-less homogenous enclaves. Is each enclave homogeneous or are there variations within each enclave? Are these variations primary (magmatic) or secondary (subsolidus or hydrothermal)? How much variation exists within each enclave and do the enclaves all have similar variations? Constraining the magnitudes and spatial variations of enclave compositions may lead to a better understanding of the processes involved in magma mixing and mingling that may generate continental crust. We analyzed the variation of several elements (Si, Fe, Al, and Ti) within several enclaves with an Olympus Delta portable X-ray spectrometer (pXRF). The pXRF allows one to determine, non-destructively, the spatial variation of certain chemical elements within each enclave. Results show that the variation in SiO2 occurs within single enclaves (not just between enclaves) and occurs over a wider range of SiO2 (53-70%) than previously shown. Although more detailed analyses are forthcoming, present results do not show any obvious concentric chemical zoning, or other simple patterns in chemical variation, suggesting a possible more random, streaky compositional pattern in the enclaves. These results support a two

  13. Unusual Chemistry of the Miocene Central Basin and Range: zr and LREE Enriched Mafic Rocks of the Lucy Gray and Mccullough Mountains, Nevada (United States)

    Johnsen, R. L.; Smith, E. I.


    The dominantly intermediate mid-Miocene (ca. 16-12 Ma) volcanic section in the northern and central McCullough Range of the Basin and Range Province, Nevada, typifies igneous rocks in similar-aged, adjacent mountain ranges (e.g., the Highland Range and the Eldorado Mountains). Calc-alkaline andesite to dacite domes, flows, and related pyroclastic materials dominate while rhyolite and basalt are volumetrically minor constituents. These rocks have the typical "arc" chemical signature prevalent in subduction zones and in pre-extensional Basin and Range igneous rocks (Zr, Nb, Ti depletions, containing a typical mineral assemblage of iddingsitic olivine, clinopyroxene, and plagioclase are host to up to 700 ppm Zr, highly enriched Sr isotopes (0.709-0.714), over 200 ppm La, and up to 3000 ppm Sr and Ba. If the arc-signature "normal" rocks are produced in slab-fluid enriched LM, where, then, do the Zr- and LREE-enriched mafic rocks originate? One way to enrich a rock in LREEs is to partially melt a garnet-bearing source, such as garnet peridotite. Zr, Sr, Nb, and Ba enrichment cannot be explained through this method, however, and the extreme enrichment (1000x chondrite) of the LREEs is difficult to reproduce. Another option is to contaminate a garnet-bearing source with an upper crustal felsic rock such as granite or granitoid. Several types of upper crustal rocks are exposed in the Lucy Gray Mountains and the McCullough Range, all of them Precambrian in age: 1) 1.7 Ga granitoid, gneiss, and amphibolite; 2) 1.4 Ga Beer Bottle Pass Granite; and, perhaps most intriguing, 3) the ~1.4 Ga Sulphide Queen carbonatite and age-equivalent shonkinite, syenite, and granite of Mountain Pass. Shonkinites are well known for their extreme LREE enrichment and these in particular contain up to 1000 ppm Zr as well. Could a small amount of contamination of a highly enriched crustal rock such as shonkinite or syenite with a more normal OIB-like basaltic melt account for the odd character of

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

    Directory of Open Access Journals (Sweden)

    Torres-Roldán, R. L.


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

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

    Directory of Open Access Journals (Sweden)

    Galvis Jose Antonio


    ="font-size: 12pt; font-family: "> 

    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 de la corteza y de la pulpa y la Intensidad Respiratoria. El diseño experimental empleado fue completamente al azar.


    Se estableció que el tiempo que transcurre desde la antesis hasta alcanzar la madurez fisiológica es de 90 días. El crecimiento del fruto es de tipo Sigmoidal Simple. Se identificaron 3 etapas durante el crecimiento. El análisis de regresión permitió establecer modelos 1ineales para las características físicas.


    El fruto presentó alta intensidad respiratoria en los primeros días del crecimiento y fue disminuyendo hasta alcanzar valores mínimos al final de la etapa de crecimiento. Hubo una alta correlación inversa entre la I.R. y las variables físicas medidas.


  16. Lower Devonian paleomagnetic dating of a large mafic sill along the western border of the Murzuq cratonic basin (Saharan metacraton, SE Algeria). (United States)

    El-M. Derder, Mohamed; Maouche, Said; Liégeois, Jean-Paul; Henry, Bernard; Amenna, Mohamed; Ouabadi, Aziouz; Bellon, Hervé; Bruguier, Olivier; Bayou, Boualem; Bestandji, Rafik; Nouar, Omar; Bouabdallah, Hamza; Ayache, Mohamed; Beddiaf, Mohamed


    The Murzuq basin located in central North Africa, in Algeria, Libya and Niger is a key area, delineating a relictual cratonic area within the Saharan metacraton (Liégeois et al., 2013). On its western border, we discovered a very large sill ("Arrikine" sill), with a thickness up to 250m and a minimum length of 35 km. It is made of mafic rocks and is interbedded within the Silurian sediments of the Tassilis series. In the vicinity, the only known post-Pan-African magmatism is the Cenozoic volcanism in the In Ezzane area. Further south in Niger, also along the SW border of the Murzuq basin, large Paleozoic dolerite (Carte géologique du Sahara central, 1962) are probably related to the "Arrikine" sill magmatism, as they are in the same stratigraphical position. Several hundred kilometers westward and southwestward of Arrikine, Paleozoic magmatic products are known: Carboniferous basic intrusives (346 Ma; Djellit et al., 2006) are located in the Tin Serririne basin and Devonian ring complexes (407 Ma; Moreau et al, 1994) in the Aïr Mountains. For the Arrikine sill, K/Ar data gave a rejuvenation age (326 Ma) related to a K-rich aplitic phase and the LA-ICP-MS U-Pb method on zircon showed that only inherited zircons are present (0.6 to 0.7, 2.0 and 2.7 Ga ages), pointing to ages from the underlying basement corresponding to the Murzuq craton covered by Pan-African sediments (Derder et al., 2016). By contrast, a well-defined paleomagnetic pole yielded an age of 410-400 Ma by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age, similar to that reported for the Aïr complexes (Moreau et al., 1994), can be correlated with the deep phreatic eruption before Pragian time thought to be at the origin of sand injections, which gave circular structures observed on different borders of the Murzuq basin (Moreau et al,. 2012). This Lower Devonian magmatism had therefore a regional extension and can be related to a "Caledonian" transtensive reactivation of the

  17. Geochemistry and petrogenesis of early Cretaceous sub-alkaline ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    mafic dyke swarm. Besides Archaean gneisses, the Shillong plateau also comprises the Pro- terozoic Shillong group of rocks ('orthoquartzite' and phyllite), granite plutons (700–450 Ma; Ghose et al 1994), small bodies of metamorphosed mafic igneous rocks, and the Sylhet traps (a part of the Rajmahal-Sylhet flood basalt ...

  18. Geochemical characteristics of Mesoproterozoic metabasite dykes ...

    Indian Academy of Sciences (India)

    element spidergrams and rare-earth element patterns observed in these samples also corroborate their ... Trace element patterns observed for Nb–Ta, Hf–Zr, Sr and Y ...... Earth Planet. Sci. Lett. 19 290–300. Pearce J A and Gale G H 1977 Identification of ore- deposition environment from trace element geochemistry.

  19. Geochemical characteristics of Mesoproterozoic metabasite dykes ...

    Indian Academy of Sciences (India)

    Sarkar 1968;. Baksi 1995; Kent et al 2002; Ghose et al 2005;. Ghose and Chatterjee 2008). Ghose et al (2005) have studied metabasite rocks exposed south of the. Damodar valley and suggested their emplacement in an intracratonic setting.

  20. Origin of the mafic microgranular enclaves (MMEs) and their host granitoids from the Tagong pluton in Songpan-Ganze terrane: An igneous response to the closure of the Paleo-Tethys ocean (United States)

    Chen, Qiong; Sun, Min; Zhao, Guochun; Yang, Fengli; Long, Xiaoping; Li, Jianhua; Wang, Jun; Yu, Yang


    The Songpan-Ganze terrane is mainly composed of a Triassic sedimentary sequence and late Triassic-Jurassic igneous rocks. A large number of plutons were emplaced as a result of tectono-magmatic activity related to the late stages of Paleo-Tethys ocean closure and ensuing collision. Granitoids and their hosted mafic enclaves can provide important constraints on the crust-mantle interaction and continental crustal growth. Mesozoic magmatism of Songpan-Ganze remains enigmatic with regard to their magma generation and geodynamic evolution. The Tagong pluton (209 Ma), in the eastern part of the Songpan-Ganze terrane, consists mainly of monzogranite and granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (ca. 208-209 Ma). The pluton comprises I-type granitoid that possesses intermediate to acidic compositions (SiO2 = 61.6-65.8 wt.%), high potassium (K2O = 3.2-4.1 wt.%), and high Mg# (51-54). They are also characterized by arc-type enrichment of LREEs and LILEs, depletion of HFSEs (e.g. Nb, Ta, Ti) and moderate Eu depletions (Eu/Eu* = 0.46-0.63). Their evolved zircon Hf and whole-rock Nd isotopic compositions indicate that their precursor magmas were likely generated by melting of old lower continental crust. Comparatively, the MMEs have lower SiO2 (53.4-58.2 wt.%), higher Mg# (54-67) and show covariation of major and trace elements, coupled with field and petrographic observations, such as the disequilibrium textures of plagioclase and amphibole, indicating that the MMEs and host granitoids were originated from different magma sources but underwent mafic-felsic magma mixing process. Geochemical and isotopic data further suggest that the precursor magma of the MMEs was formed in the continental arc setting, mainly derived from an ancient metasomatized lithospheric mantle wedge. The Triassic granitoids from the Songpan-Ganze terrane show remarkable temporal-spatial-petrogenetic affinities to the counterparts of subduction zones in the Yidun and Kunlun arc

  1. 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.

  2. 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

  3. 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)

  4. Comment on ;Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications;. Tectonophysics, 662, 219-242 (2015) by Ishwar-Kumar et al. (United States)

    Goncalves, Philippe; Brandt, Sönke; Nicollet, Christian; Tucker, Robert


    Determining the possible tectonic regimes active during the Neoproterozoic is crucial for the knowledge of the evolution of the super-continent Gondwana. In Madagascar, that occupies a key position in Gondwana, there is an on-going debate regarding the location of possible suture zones and the implications in terms of paleo-geography. Recognizing high-pressure to ultra-high pressure conditions in mafic rocks is commonly viewed as a strong argument for paleo-subduction zones. Ishwar-Kumar et al. (2015) report unusual high pressure conditions (24 kbar) in Neoproterozoic to Cambrian rocks from North-Central Madagascar (Andriamena Complex). They propose a geodynamic model in which exhumation of the high pressure terranes from up to 80 km to 40 km occurred via vertical extrusion during the collision of various crustal blocks after subduction and closure of an oceanic domain during the formation of Gondwana in the late Neoproterozoic to Cambrian. We question this model and in particular the (ultra-)high pressure conditions reported, because their estimation is based on a misinterpretation of the petrography and inaccurate thermodynamic modeling for the crucial metabasite sample. The authors suggest that garnet-quartz coronas around orthopyroxene and ilmenite coexist with clinopyroxene. The postulated garnet-clinopyroxene-quartz assemblage is interpreted to document an eclogite facies overprint. However, the presence of abundant plagioclase in the sample and the lack of high jadeite content in clinopyroxene clearly refute the postulated eclogite facies conditions. According to the presented photographs clinopyroxene is part of the rock matrix. We therefore suggest that the sample represents a common two-pyroxene granulite, formed at mid- to low-pressure granulite facies conditions of > 700 °C and Madagascar, this interpretation is not justified by the data presented by Ishwar-Kumar et al. (2015).

  5. Natural factors and mining activity bearings on the water quality of the Choapa basin, North Central Chile: insights on the role of mafic volcanic rocks in the buffering of the acid drainage process. (United States)

    Parra, Amparo; Oyarzún, Jorge; Maturana, Hugo; Kretschmer, Nicole; Meza, Francisco; Oyarzún, Ricardo


    This contribution analyzes water chemical data for the Choapa basin, North Central Chile, for the period 1980-2004. The parameters considered are As, Cu Fe, pH, EC, SO₄⁻², Cl⁻¹, and HCO[Formula: see text], from samples taken in nine monitoring stations throughout the basin. Results show rather moderate contents of As, Cu, and Fe, with the exception of the Cuncumén River and the Aucó creek, explained by the influence of the huge porphyry copper deposit of Los Pelambres and by the presence of mining operations, respectively. When compared against results obtained in previous researches at the neighboring Elqui river basin, which host the El Indio Au-Cu-As district, a much reduced grade of pollution is recognized for the Choapa basin. Considering the effect of acid rock drainage (ARD)-related Cu contents on the fine fraction of the sediments of both river basins, the differences recorded are even more striking. Although the Los Pelambres porphyry copper deposit, on the headwaters of the Choapa river basin, is between one and two orders of magnitude bigger than El Indio, stream water and sediments of the former exhibit significantly lower copper contents than those of the latter. A main factor which may explain these results is the smaller degree of H( + )-metasomatism on the host rocks of the Los Pelambres deposit, where mafic andesitic volcanic rocks presenting propylitic hydrothermal alteration are dominant. This fact contrast with the highly altered host rocks of El Indio district, where most of them have lost their potential to neutralize ARD.

  6. Mafic magmatism in the Bakhuis Granulite Belt

    NARCIS (Netherlands)

    Klaver, M.; de Roever, E.W.F.; Thijssen, A.C.D.; Bleeker, W.; Söderlund, U.; Chamberlain, K.; Ernst, R.; Berndt, J.; Zeh, A.


    The Bakhuis Granulite Belt (BGB) is a metamorphic terrain within the Guiana Shield that experienced ultrahigh-temperature (UHT) metamorphism at 2.07–2.05Ga. In the southwest of the BGB, the Kabalebo charnockites were emplaced at ca. 1.99Ga and thus postdate UHT metamorphism by at least 60Myr. Two


    African Journals Online (AJOL)

    Si, and Ti/AL implied high pressure/temperature crystallization conditions under bimodal or tholeiitic-alkaline transition magmatism in an island arc environment. Key words: Pyroxenite Ultramafic amphibole Island arcs. [Global Jnl Geol. Sci.

  8. Matéria orgânica em solos desenvolvidos de rochas máficas no nordeste de Roraima Organic matter in soils developed from mafic rocks, in northeastern Roraima

    Directory of Open Access Journals (Sweden)

    Valdinar Ferreira Melo


    Full Text Available Solos desenvolvidos de rochas máficas no nordeste de Roraima são cultivados continuamente por populações indígenas em função da boa fertilidade natural. Este trabalho objetivou avaliar as alterações na matéria orgânica do solo por meio do fracionamento das substâncias húmicas, aplicação de análises de CHNS, estudos termogravimétricos e de Ressonância Paramagnética de Elétrons (EPR. Os maiores teores de C foram observados no Chernossolo sob cultivo contínuo. A fração humina foi predominante em todos os solos, tendo seus teores reduzidos em profundidade. No Nitossolo, houve menor relação ácido húmico/fúlvico. No Chernossolo cultivado, a posição no relevo e a incorporação dos restos culturais parece ter contribuído para manter a estabilidade do solo. Nos demais Chernossolos, a natureza química contribuiu para a ciclagem mais eficiente da matéria orgânica. No Chernossolo e nos Cambissolos não cultivados, a matéria orgânica se apresentou menos estável. No Chernossolo sob cultivo, houve aumento da polimerização do ácido húmico. Os solos com horizonte A chernozêmico, não cultivados, comportaram-se mais uniformes quanto à qualidade dos ácidos húmicos.Soils developed from mafic rocks in Northeastern Roraima are the preferred areas for indigenous shifting cultivation, in view of their high natural fertility. The study was focused on changes in the soil organic matter status, by means of humic substances fractionation, and application of CHNS analyses and termogravimetric studies and EPR. High C values were observed in Chernosol under continuous cultivation. The humin fraction was predominant in all soils, reducing with depth. The Nitosol showed smaller humic/fulvic acids ratio. The Chernosol under cultivation in a more conservative relief, with incorporation of crop residues, there was greater nutrient cycling. In the uncultivated Chernosol and Cambisol the soil organic matter was less stable. In the

  9. 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)

    Bolhar, R.; Hergt, J.; Woodhead, J.


    compositionally 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/Sm pm >> 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/Sm pm and Nb/Th pm ratios, along with unfractionated HREE may be interpreted as adiabatic upwelling of plume material and a decreasing influence of the lithospheric component

  10. Latest Cretaceous "A2-type" granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere (United States)

    Karsli, Orhan; Aydin, Faruk; Uysal, Ibrahim; Dokuz, Abdurrahman; Kumral, Mustafa; Kandemir, Raif; Budakoglu, Murat; Ketenci, Murat


    An integrated study of comprehensive geochronological, geochemical, and Sr-Nd-Hf isotopic data was undertaken for the A-type Topcam pluton that intruded within the Sakarya Zone (NE Turkey) with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous A-type granites. New LA-ICP-MS zircon U-Pb crystallization ages of 72 and 73 Ma indicate emplacement in the Late Cretaceous time, just after extensive metaluminous I-type magmatism in the area. The pluton consists mainly of alkali feldspar, quartz, plagioclase, amphibole, and biotite with accessory minerals such as magnetite, apatite, and zircon. The outcrop is composed of granite, syenite, monzonite, and quartz monzonite and possesses a wide range of SiO2 content (57-70 wt%) with elevated Ga/Al ratios and low Mg# (mostly earth elements (LREE) and significant negative Eu (Eu/Eu* = 0.31 to 0.86) anomalies on the chondrite-normalized REE diagram. The rocks are enriched in some large ion lithophile elements (e.g., Rb, Th and Ba), and spidergrams show a relative depletion in Nb, Ti, and Sr. The granitic rocks of the pluton have identical 87Sr/86Sr(i) ratios ranging from 0.70518 to 0.70716, relatively low εNd (t) values varying from - 5.5 to - 0.4, and TDM ages (0.82-1.19 Ga). In situ zircon analyses show that the rocks have variable negative and positive εHf (t) values (- 5.5 to 5.9) and Hf two-stage model ages (742 to 1468 Ma), which are indicative of minor addition of juvenile material. Sr-Nd isotope modelling suggests mixing of 70-90% of lower crustal-derived melt with 10-30% of mantle-derived melt at lower crust depths. The heat source for partial melting is provided by upwelling of hot asthenosphere triggered by slab roll-back events. Geochemical and isotopic data reveal that metaluminous A2-type granites were derived from partial melting of the Paleozoic lower continental crust dominated by mafic rocks in amphibolitic composition, with minor input of

  11. Early Neoarchaean A-type granitic magmatism by crustal reworking ...

    Indian Academy of Sciences (India)


    dyke swarm). It is suggested that the ~2.8 Ga A-type granites in the Singbhum craton mark a significant crustal reworking event attendant to mantle-derived mafic magmatism in an extensional tectonic setting. Key words: Granite; A-type; Geochemistry; Archaean; Crustal reworking; Singhbhum craton. Abstract. Click here to ...

  12. Islam and the Netherlands, what is happening behind the dykes

    NARCIS (Netherlands)

    Schnabel, P.


    In the European Union, besides the Netherlands, France is the only other country with a substantial Muslim population. In France, it is about 10% of the population, in the Netherlands about 5%. In both countries, but in France predominantly so, a major part of the Muslim population is of Moroccan

  13. Capture zone simulation for boreholes located in fractured dykes ...

    African Journals Online (AJOL)



    Apr 2, 2002 ... For more complex flow situations where boundaries are considered, borehole capture zones or catchments ... settings is investigated in an x, y plane. Theory of capture zone simulation using linesink ... Integration of Eq. (2c) would give the pathline distribution, which may be used to backtrack isochrones or ...

  14. The study of dykes has multi-faceted importance

    Indian Academy of Sciences (India)

    They can be geochemically fingerprinted such that swarms of different age can be distinguished and their chemistry reflects the composition of subcontinental lithosphere rather the effects of crustal contamination.

  15. Petrology and geochemistry of a boninite dyke from the western ...

    Indian Academy of Sciences (India)


    Pyroxenes are represented by subhedral to anhedral grains of both. 160 clinopyroxene (cpx) and orthopyroxene (opx). Clinopyroxene are dominant than. 161 ...... Ho. 0.62. 0.61. 1.39. 1.33. Er. 1.84. 1.87. 3.78. 3.83. Tm. 0.27. 0.28. 0.55. 0.53. Yb. 1.79. 1.74. 3.55. 3.39. Lu. 0.27. 0.26. 0.53. 0.5. # Expected. 678. † Analysed.

  16. Les filons basiques des boutonnières du Bas Drâa et de la Tagragra d'Akka: Témoins des distensions néoprotérozoïques de l'Anti-Atlas occidental (Maroc) (United States)

    Ikenne, Moha; Mortaji, Abdelaziz; Gasquet, Dominique; Stussi, Jean Marc


    The palaeoproterozoic basement of the Bas Drâa and Tagragra d'Akka inliers (western Anti-Atlas), is crosscut by three swarms of mafic dykes (N70°-110°E, N120°-150°E and N160°-20°E). The latter swarm is the most recently emplaced. The dykes consist of (i) gabbros, dolerites and basalts; and (ii) monzogabbros and trachybasalts. The primary mineral assemblage is modified by low to very low-grade metamorphism and/or hydrothermal alteration (phyllitisation, carbonatation, epidotisation, hematisation, pyritisation). According to the less mobile elements' geochemical signature, the magma affinities are defined as tholditic in the type (i) rocks, and alkaline in the type (ii) rocks. Whereas the trachybasalts are linked to the 120-150°E swarm, all the other types of mafic rocks occur in each of the three dyke swarms. The three swarms were emplaced in Neoproterozoic times, during and after the PII events and prior to the Audoudounian series deposition. They intruded, in late- to post-orogenic Pan-African times, a continental domain extending between the inner zones of the West Africa Craton and the orogenic domain of the central Anti-Atlas. The emplacement of the mafic dykes is related to the distensive events, which affects the orogenic hinterland to the Neoproterozoic subduction-obduction tectonics, which generates the main features of the central Anti-Atlas. The variability of composition of the mafic dykes occurring in each type of swarm is interpreted as resulting from partial melting, at different levels, of the sub-continental mantle.


    Directory of Open Access Journals (Sweden)

    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.

  18. Geochemistry and Petrogenesis of Biabanak–Bafq Mafic Mgmatism ...

    Indian Academy of Sciences (India)


    White and McKenzie 1989). ... to late Neoproterozoic–early. Paleozoic orogenic system that was active along the Proto–Tethyan margin of the .... perturbed (Figs. 4i to 4l). Major element ratio plots, MgO/TiO2 versus CaO/TiO2, Al2O3/TiO2 and. 1.

  19. Mafic rocks from Erinpura gneiss terrane in the Sirohi region ...

    Indian Academy of Sciences (India)

    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 ...

  20. Geochemistry and geochronology of the mafic dikes in the Taipusi ...

    Indian Academy of Sciences (India)

    ... South University, Changsha 410 083, People's Republic of China. Hunan Institute of Geological Survey, Changsha 410 016, People's Republic of China. Guangxi Land and Resources Planning Institute, Nanning 530 022, People's Republic of China. National Institute of Geological Sciences, University of the Philippines, ...

  1. Petrology, geochemistry and tectonic settings of the mafic dikes and ...

    Indian Academy of Sciences (India)

    In this article we summarize the petrological, geochemical and tectonic processes involved in the evolution of the Proterozoic intracratonic Cuddapah basin. We use new and available ages of Cuddapah igneous rocks, together with field, stratigraphic, geophysical and other criteria, to arrive at a plausible model for the ...

  2. Eruptive history of Mammoth Mountain and its mafic periphery, California (United States)

    Hildreth, Wes; Fierstein, Judy


    This report and accompanying geologic map portray the eruptive history of Mammoth Mountain and a surrounding array of contemporaneous volcanic units that erupted in its near periphery. The moderately alkaline Mammoth eruptive suite, basaltic to rhyodacitic, represents a discrete new magmatic system, less than 250,000 years old, that followed decline of the subalkaline rhyolitic system active beneath adjacent Long Valley Caldera since 2.2 Ma (Hildreth, 2004). The scattered vent array of the Mammoth system, 10 by 20 km wide, is unrelated to the rangefront fault zone, and its broad nonlinear footprint ignores both Long Valley Caldera and the younger Mono-Inyo rangefront vent alignment.

  3. Petrology, geochemistry and tectonic settings of the mafic dikes and ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Dikes and dike swarms provide evidence of the state of stress of the lithosphere, nature of crustal extension and rift- ing during basin evolution. Ages of dikes, sills and flows help in stratigraphic correlation as well as in providing timing constraints on processes involved in basin evolution. The igneous rocks in and around ...

  4. Petrology, geochemistry and tectonic settings of the mafic dikes and ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    evolution of the Proterozoic intracratonic Cuddapah basin. We use new and available ages of ... the basin in response to stresses, which may have been responsible for the evolution of the basin itself. Basaltic dike intrusion started on the ...... also provided the computer programs for phase equilibrium calculations, for which ...

  5. Petrological and geochemical studies of ultramafic–mafic rocks from ...

    Indian Academy of Sciences (India)

    Journal of Earth System Science. Current Issue : Vol. 126, Issue 8 · Current Issue Volume 126 | Issue 8. December 2017. Home · Volumes & Issues · Special Issues · Forthcoming Articles · Search · Editorial Board · Information for Authors · Subscription ...

  6. Petrological and geochemical studies of ultramafic–mafic rocks from ...

    Indian Academy of Sciences (India)

    The regional trend of the metamophites and granitoid gneiss is generally .... linear fashion. Allanite is associated with the opaques (≃1%). Ilmenite occurs as very fine to coarse grain associated with hornblende and pyrox- enes. Magnetite occurs as .... biotite and sheared or granulated appearance of the quartzofeldspathic ...

  7. Interaction of coeval felsic and mafic magmas from the Kanker ...

    Indian Academy of Sciences (India)

    R Elangovan


    Oct 5, 2017 ... Indian territory are very limited (Kumar et al. 2005; Kumar and Rino 2006; Jayananda et al. 2009, 2014; Prabhakar et al. 2009). Magma mix- ing process involves mixing and mingling of two compositionally different magmas to form a hybrid magma. The composition of the hybrid magma lies somewhere ...

  8. Geochemistry and geochronology of the mafic dikes in the Taipusi ...

    Indian Academy of Sciences (India)


    systems: evidence from Y/Ho, Zr/Hf, and lanthanide tetrad effect; Contrib. Mineral. Petrol. ..... 161(5) 773-781. Stampfli G M, Borel G D, 2002 A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrones; Earth. Planet. Sci. Lett. 196(1–2) 17–33.

  9. Mafic rocks from Erinpura gneiss terrane in the Sirohi region ...

    Indian Academy of Sciences (India)

    Melanie Hertel (both from GeoZentrum Nordbay- ern, Erlangen) for support in ICPMS and XRF analyses. Dr M Shamim Khan is thanked for pro- viding geochemical dataset on Phulad ophiolite samples. Constructive comments from three anony- mous reviewers have been helpful in improving the manuscript. Authors also ...

  10. Petrological and geochemical studies of ultramafic–mafic rocks from ...

    Indian Academy of Sciences (India)

    Journal of Earth System Science. Current Issue : Vol. 127, Issue 2 · Current Issue Volume 127 | Issue 2. March 2018. Home · Volumes & Issues · Special Issues · Forthcoming Articles · Search · Editorial Board · Information for Authors · Subscription ...

  11. Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber, Yelagiri Alkaline Complex, South India

    Directory of Open Access Journals (Sweden)

    M.L. Renjith


    Full Text Available Magma mixing process is unusual in the petrogenesis of felsic rocks associated with alkaline complex worldwide. Here we present a rare example of magma mixing in syenite from the Yelagiri Alkaline Complex, South India. Yelagiri syenite is a reversely zoned massif with shoshonitic (Na2O + K2O=5–10 wt.%, Na2O/K2O = 0.5–2, TiO2 <0.7 wt.% and metaluminous character. Systematic modal variation of plagioclase (An11–16 Ab82–88, K-feldspar (Or27–95 Ab5–61, diopside (En34–40Fs11–18Wo46–49, biotite, and Ca-amphibole (edenite build up three syenite facies within it and imply the role of in-situ fractional crystallization (FC. Evidences such as (1 disequilibrium micro-textures in feldspars, (2 microgranular mafic enclaves (MME and (3 synplutonic dykes signify mixing of shoshonitic mafic magma (MgO = 4–5 wt.%, SiO2 = 54–59 wt.%, K2O/Na2O = 0.4–0.9 with syenite. Molecular-scale mixing of mafic magma resulted disequilibrium growth of feldspars in syenite. Physical entity of mafic magma preserved as MME due to high thermal-rheological contrast with syenite magma show various hybridization through chemical exchange, mechanical dilution enhanced by chaotic advection and phenocryst migration. In synplutonic dykes, disaggregation and mixing of mafic magma was confined within the conduit of injection. Major-oxides mass balance test quantified that approximately 0.6 portions of mafic magma had interacted with most evolved syenite magma and generated most hybridized MME and dyke samples. It is unique that all the rock types (syenite, MME and synplutonic dykes share similar shoshonitic and metaluminous character; mineral chemistry, REE content, coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition. Outcrop-scale features of crystal accumulation and flow fabrics also significant along with MME and synplutonic dykes in syenite suggesting that Yelagiri syenite magma chamber had evolved

  12. Magnetic fabrics in characterization of magma emplacement and tectonic evolution of the Moyar Shear Zone, South India

    Directory of Open Access Journals (Sweden)

    P. Pratheesh


    Full Text Available The Moyar Shear Zone (MSZ of the South Indian granulite terrain hosts a prominent syenite pluton (∼560 Ma and associated NW-SE to NE-SW trending mafic dyke swarm (∼65 Ma and 95 Ma. Preliminary magnetic fabric studies in the mafic dykes, using Anisotropy of Magnetic Susceptibly (AMS studies at low-field, indicate successive emplacement and variable magma flow direction. Magnetic lineation and foliation in these dykes are identical to the mesoscopic fabrics in MSZ mylonites, indicating shear zone guided emplacement. Spatial distribution of magnetic lineation in the dykes suggests a common conduit from which the source magma has been migrated. The magnetic foliation trajectories have a sigmoidal shape to the north of the pluton and curve into the MSZ suggesting dextral sense of shear. Identical fabric conditions for magnetic fabrics in the syenite pluton and measured field fabrics in mylonite indicate syntectonic emplacement along the Proterozoic crustal scale dextral shear zone with repeated reactivation history.

  13. Petrogenesis and geodynamics of plagiogranites from Central Turkey (Ekecikdağ/Aksaray): new geochemical and isotopic data for generation in an arc basin system within the northern branch of Neotethys (United States)

    Köksal, Serhat; Toksoy-Köksal, Fatma; Göncüoglu, M. Cemal


    In the Late Cretaceous, throughout the closure of the Neotethys Ocean, ophiolitic rocks from the İzmir-Ankara-Erzincan ocean branch were overthrusted the northern margin of the Tauride-Anatolide Platform. The ophiolitic rocks in the Ekecikdağ (Aksaray/Central Turkey) region typify the oceanic crust of the İzmir-Ankara-Erzincan branch of Neotethys. The gabbros in the area are cut by copious plagiogranite dykes, and both rock units are intruded by mafic dykes. The plagiogranites are leucocratic, fine- to medium-grained calc-alkaline rocks characterized mainly by plagioclase and quartz, with minor amounts of biotite, hornblende and clinopyroxene, and accessory phases of zircon, titanite, apatite and opaque minerals. They are tonalite and trondhjemite in composition with high SiO2 (69.9-75.9 wt%) and exceptionally low K2O (<0.5 wt%) contents. The plagiogranites in common with gabbros and mafic dykes show high large-ion lithophile elements/high-field strength element ratios with depletion in Nb, Ti and light rare-earth elements with respect to N-MORB. The plagiogranites together with gabbros and mafic dykes show low initial 87Sr/86Sr ratios (0.70419-0.70647), high ƐNd( T) (6.0-7.5) values with 206Pb/204Pb (18.199-18.581), 207Pb/204Pb (15.571-15.639) and 208Pb/204Pb (38.292-38.605) ratios indicating a depleted mantle source modified with a subduction component. They show similar isotopic characteristics to the other supra-subduction zone (SSZ) ophiolites in the Eastern Mediterranean to East Anatolian-Lesser Caucasus and Iran regions. It is suggested that the Ekecikdağ plagiogranite was generated in a short time interval from a depleted mantle source in a SSZ/fore-arc basin setting, and its nature was further modified by a subduction component during intra-oceanic subduction.

  14. The Jeffers Brook diorite-granodiorite pluton: style of emplacement and role of volatiles at various crustal levels in Avalonian appinites, Canadian Appalachians (United States)

    Pe-Piper, Georgia; Piper, David J. W.


    Small appinite plutons ca. 610 Ma outcrop in the peri-Gondwanan Avalon terrane of northern Nova Scotia, with different structural levels exposed. Field mapping shows that the Jeffers Brook pluton is a laccolith emplaced along an upper crustal thrust zone, likely in a dilational jog in a regional dextral strike-slip system. The oldest rocks are probably mafic sills, which heated the area facilitating emplacement of intermediate magmas. Cross-cutting relationships show that both mafic and intermediate magmas were supplied throughout the history of pluton emplacement. The modal composition, mineral chemistry, and bulk chemistry of gabbro, diorite, tonalite, granodiorite, and granite have been studied in the main plutonic phases, dykes, and sills, and mafic microgranular enclaves. As with the type appinites in the Scottish Caledonides, the pluton shows evidence of high water content: the dominance of hornblende, locally within pegmatitic texture; vesicles and irregular felsic patches in enclaves; and late aplite dykes. Analyzed mafic microgranular enclaves are geochemically similar to larger diorite bodies in the pluton. Tonalite-granodiorite is distinct from the diorite in trace-element geochemistry and radiogenic isotopes. Elsewhere to the east, similar rocks of the same age form vertically sheeted complexes in major shear zones; hornblende chemistry shows that they were emplaced at a deeper upper crustal level. This implies that little of the observed geochemical variability in the Jeffers Brook pluton was developed within the pluton. The general requirements to form appinites are proposed to be small magma volumes of subduction-related magmas that reach the upper crust because of continual heating by mafic magmas moving through strike-slip fault pathways and trapping of aqueous fluids rather than venting through volcanic activity.

  15. Epidotisation and fluid flow in sheeted dyke complex : new field and experimental constraints (United States)

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


    Hydrothermal system in oceanic crust is usually studied via dredge samples and drilled holes but their equivalent are also found in ophiolitic complexes (Oman, Cyprus). In the deepest zone, the fluids react with the sheeted diabase dikes at 400°C and 400 bars to form epidosites by enrichment in epidote and quartz [1]. Mineralogy and chemistry of epidosites have been widely studied on fields [1] and hydrology is generally studied using numerical models [2]. However, the relations and the timing of the emplacement of diabase dikes, their alteration in epidosite and the regional deformation remain unclear. We performed experiments on diabase sampled in the Troodos complex (Cyprus), 1) to stress the P-T-fO2-fluid composition conditions of the reaction of epidotisation and, 2) to quantify interrelations between the permeability and the epidotisation during deformation. In Troodos, we observed two major types of epidosite: 1) a pervasive epidosite in the core of dikes and a banding which is parallel to chilled margins and, 2) assemblages of epidote and quartz as alteration fronts in cooling joints or in the form of veins cross-cutting non-epidotised dikes. This last type of epidotisation clearly appears to be a hydrothermal veining process. We synthesized epidote in a static autoclave with external heating at 500°C and 2500 bars. Epidote was formed by the following reaction: 6 albite + 2 hematite + anorthite + 7 Ca2+ + 6 H2O → 4 epidote + 8 quartz + 6 Na+ + 8 H+. The calculated variation of the molar volume is about -3% (creation of porosity). Two parameters are essential to synthesize epidote from diabase: the oxygen fugacity and the composition of the fluid (enriched in Ca and Fe). However, there is an obvious problem of nucleation at 400°C and 400 bars. In order to understand how fluid flows throughout sheeted dikes, in situ measurements of permeability during coaxial deformation have been performed in a Paterson apparatus by infiltration of Argon and water. The permeability of the diabase prior deformation is about 10-20 m2. After fracturation of the sample, the permeability increased rapidly up to 10-19 m2. After stress relaxation, the permeability decreased slowly to its initial permeability. Moreover, the permeability of epidosite is about 10-19 m2. So this suggests that epidotisation generates porosity. The main problem is the initiation of fluid flow because of the impermeability of diabase. From our results and field evidence, we suggest two hypotheses: 1) fluid flows via fractures and cracks and, 2) fluid flows into a rock in a subsolidus state (importance of degassing). To explore this last hypothesis, experiments will be performed at high temperature (T > 850°C) with an infiltration of water through a synthetic diabase placed under late magmatic conditions. So, in these conditions, nucleation of epidote could be facilitated from a glass. [1] Richardson C. J., Cann J. R., Richards H. G., Cowan J. G., 1987. Earth and Planetary Science Letters, 84, 243-253. [2] Coumou D., Driesner T., Geiger S., Heinrich C. A., Mattahai S., 2006. Earth and Planetary Science Letters, 245, 218-231.

  16. The Flood, the Channels and the Dykes: Managing Legal Information in a Globalized and Digital World

    NARCIS (Netherlands)

    Breuker, J.; Casanovas, P.; Klein, M.C.A.; Francesconi, E.; Breuker, J.; Casanovas, P.; Klein, M.C.A.; Francesconi, E.


    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

  17. 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…

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

    Directory of Open Access Journals (Sweden)

    Gerard Coll-Planas


    Full Text Available In this article I aim to explore conflicts among the variety of political projects in the lesbian and gay movement.I base the article on Alberto Mira’s (2004 proposed models for the expression of homosexuality: decadentist, homophile and camp. I discuss the main theoretical and political debates that arise from these models. Firstly, I ask whether life on the margins of mainstream social rules allows gays and lesbians to live a freer existence or merely means internalised homophobia (using Jean Genet’s and Michel Foucault’s approaches as examples. Secondly, I question whether the demand for “normality” entails the creation of new exclusions (following Judith Butler’s approach to normality: Finally, I consider whether camp culture reproduces and/or subverts gender rules (introducing a discussion between Sheila Jeffreys and Judith Butler’s positions. On the basis of this exploration of Mira's three cultural models, I develop a typology of political positions ('normalization of homosexuality', 'transformation' and 'queer', which I apply to the case study of the Catalan lesbian and gay movement.

  19. 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.

  20. 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.

  1. 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.

    ) in descending order. The noise in the data kernel prevailing in the form of small values increases the ranking of the matrix apart from amplifying the solution. This however does not provide any additional information on the model parameters. So, it can... (i.e. the dimension of activated space) besides amplifying the solution due to the presence of noise. Such a filtered data kernel has been utilized in 3-D form (Fig. 8), which almost represents the original data kernel to build GIO. In Fig. 6...

  2. Assimilation of carbonate country rock by the parent magma of the Panzhihua Fe-Ti-V deposit (SW China: Evidence from stable isotopes

    Directory of Open Access Journals (Sweden)

    Clément Ganino


    Full Text Available The Panzhihua intrusion in southwest China is part of the Emeishan Large Igneous Province and host of a large Fe-Ti-V ore deposit. During emplacement of the main intrusion, multiple generations of mafic dykes invaded carbonate wall rocks, producing a large contact aureole. We measured the oxygen-isotope composition of the intrusions, their constituent minerals, and samples of the country rock. Magnetite and plagioclase from Panzhihua intrusion have δ18O values that are consistent with magmatic equilibrium, and formed from magmas with δ18O values that were 1–2‰ higher than expected in a mantle-derived magma. The unmetamorphosed country rock has high δ18O values, ranging from 13.2‰ (sandstone to 24.6–28.6‰ (dolomite. The skarns and marbles from the aureole have lower δ18O and δ13C values than their protolith suggesting interaction with fluids that were in exchange equilibrium with the adjacent mafic magmas and especially the numerous mafic dykes that intruded the aureole. This would explain the alteration of δ18O of the dykes which have significantly higher values than expected for a mantle-derived magma. Depending on the exact δ18O values assumed for the magma and contaminant, the amount of assimilation required to produce the elevated δ18O value of the Panzhihua intrusion was between 8 and 13.7 wt.%, assuming simple mixing. The exact mechanism of contamination is unclear but may involve a combination of assimilation of bulk country rock, mixing with a melt of the country rock and exchange with CO2-rich fluid derived from decarbonation of the marls and dolomites. These mechanisms, particularly the latter, were probably involved in the formation of the Fe-Ti-V ores.

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

    DEFF Research Database (Denmark)

    Artemieva, Irina; Shulgin, Alexey


    , and geophysical characteristics typical of continental rifts in general and demonstrate that, except for magmatic and, perhaps, some gravity signature, the Lake Ladoga region lacks any other rift features. We also compare the geophysical data from the Lake Ladoga region with similar in age Midcontinent and Valday......) supercontinent, which led to magma intrusions as a series of mafic dykes along lithosphere weakness zones and ponding of small magma pockets within the cratonic lithosphere. Consequent magma cooling and its partial transition to eclogite facies could have led to the formation of a series of basement depressions...

  4. 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.

  5. Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong ...

    Indian Academy of Sciences (India)

    La and Cu/Pd vs. La/Sm plots strongly favours generation of the parent magma at ..... clase, a ctinolite, relict. Q uartz. 39. 6.35. 49.55. 4.30. HT p y roxene, b iotite, o paque n ormativ e. SH-29. F oliated m afic. A ctinolite, altered p lagio clase, o p x. ,. O livine. 4. 9. 8 ..... batch melting of cylindrical column has tradition- ally been ...

  6. Geochemical constraints on the evolution of mafic and felsic rocks in ...

    Indian Academy of Sciences (India)

    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 ...

  7. A Late Holocene explosive mafic eruption of Villarrica volcano, Southern Andes: The Chaimilla deposit (United States)

    Costantini, L.; Pioli, L.; Bonadonna, C.; Clavero, J.; Longchamp, C.


    Villarrica (Chile) is one of the most active volcanoes in South America having erupted about 60 times in the last 460 years. Although its historical eruptive activity has been mainly effusive and weakly explosive, it had strong explosive behaviour in postglacial times. Chaimilla (activity. The deposit is dispersed over an area of 250 km 2 and consists of 8 units (A-H) which were grouped into four sequences. Stratigraphic data suggest that the eruption had a relatively short duration and evolved from i) an Opening phase, dispersing ash, lapilli clasts, accretionary lapilli, blocks and bombs, to ii) a Pulsatory phase, originating a series of magmatic explosions, to iii) a Collapsing phase, characterised by unstable plumes which emplaced a series of pyroclastic density currents intercalated with thin fallout layers and finally to iv) a Climactic phase forming a more sustained plume which eventually collapsed generating the final pyroclastic density currents. The deposit (fall and flow) has a minimum cumulative volume of 0.6 km 3, with the main sustained phase being associated with a VEI 4 and the flow units having a minimum estimated total volume of 0.04 km 3. The erupted material has a homogenous chemical composition but displays a remarkable variability in both textural and physical properties. The density distribution of juvenile products shows a clear bimodality characterised by two main populations: P1 and P2. Population P1 consists of highly vesicular clasts (modal density around 1000 kg m - 3 ) with mostly sub-spherical bubbles and moderately crystallised groundmass with large-sized microlites. Clasts from population P2 are poorly vesicular (modal density around 1600 kg m - 3 ) with irregular to collapsed bubbles and numerous smaller microlites. The variability of both vesicularity and microlite characteristics suggests the involvement of two magma batches with distinct pre-eruptive degassing and rising histories. Our eruption conceptual model implies the arrival of new magma (represented in the deposit by P1 clasts) into a small, outgassed magma body which was accumulated at shallow level (mainly represented by P2 clasts). A new Chaimilla-type eruption could significantly affect the communities that have recently developed around Villarrica volcano and subsist mainly on tourism and forestry. As a result, a better understanding of the dynamics and evolution of the Chaimilla eruption is necessary for the identification of potential hazard scenarios at Villarrica volcano and, ultimately, for the risk mitigation of this populated area of Southern Chile.

  8. Emplacement of a Thick Mafic Extrusive Body: A CSD Solution to a Map-Generated Question (United States)

    Pollock, M.; Sloan, J. A.; Siler, D. L.; Karson, J.


    A petrological study of crystallization in thick extrusive bodies is motivated by the geologic mapping of glacially excavated volcanic crust exposed along the Vatnsdalsfjall mountain range in northwest Iceland. Vatnsdalsfjall reveals a regional flexure zone, in which ~7 Ma lava flows dip 5-10° westward toward the extinct Skagi-Hunafloi rift axis. The regional flexure is disrupted by a local bowl-shaped depression, where lava flows steepen to ~50° as they dip below a ~250 m thick, ~3 km long igneous unit known as the Hjallin lens (HL). Its lenticular shape and well-developed columnar jointing most likely led Annels (1968) to initially map the HL as a shallow-level intrusion. However, more recent field investigations by McClanahan and Wobus (2004) reveal that the HL is an extrusive body, as evidenced by a distinct basal contact that consists of a flow-banded rhyolitic ash flow tuff underlain by a sedimentary layer containing organic material. Based on preliminary petrologic and geochemical analyses, McClanahan and Wobus (2004) describe the HL as a fine-grained, aphyric basalt that is nearly uniform in mineralogy, texture, and composition. Further field work by Siler (2011) shows that the HL overlies basaltic lavas that thicken toward the center of the bowl-shaped depression, indicating that the lava flows were emplaced during subsidence. The mapped relationship of the HL to the underlying lava flows suggests that the lens is a syn- (or post-) subsidence extrusion emplaced into an existing paleotopographic low. When considered with the field relationships, the homogeneous and fine-grained character of the lens naturally presents a petrological question: Was the anomalously thick extrusive body emplaced in a single eruptive event or is the HL the product of multiple flows that erupted in rapid succession? To understand the formation the HL, we measured the crystal size distribution (CSD) of plagioclase in backscattered electron (BSE) images of 20 samples from three separate vertical transects. CSDs preserve the cooling history of igneous rocks and can be related to crystallization parameters, including cooling rate (e.g., Cashman, 1993; Resmini, 2007; Pupier et al., 2008). Variations in the lens CSDs are nonsystematic, revealing that the extrusive unit is not texturally uniform. Although the base of the lens generally contains fine plagioclase microlites (~3 μm long) set in a glassy matrix while plagioclase in the interior occurs as well-formed (~100 μm) laths, the irregular variations in CSDs suggest that cooling rate is not simply related to distance from the base. Furthermore, cooling rates interpreted from CSDs are at least 2 orders of magnitude larger than cooling rates expected by conductive cooling alone. Thus, CSDs are inconsistent with the formation of the HL as a simple, single body. CSDs will be combined with geochemical data to evaluate possible modes of emplacement for thick extrusive bodies (e.g., multiple flows; lava lake with catalyzed cooling). Understanding the mode of emplacement will yield insights into the relationship of the lens to the underlying lava flows and the timing of volcanic activity relative to subsidence.

  9. Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong ...

    Indian Academy of Sciences (India)

    For massive type, the plots fall mainly within horn- blende–gabbro field with a rare spill to pyroxene– ..... 1992). Modelling of PGE in magmas during mantle batch melting of cylindrical column has tradition- ally been based on batch melting of a columnar. (cylindrical) melting regime (Keyas 1995; Barnes and Maier 1999).

  10. An assessment of global correlations in major and trace element compositions of mafic arc lavas (United States)

    Turner, S. J.; Langmuir, C. H.; Dungan, M. A.


    A carefully filtered major and trace element dataset of work showing chemical correlations among compositions of arc front lavas, crustal thickness and slab thermal parameters. To minimize effects of crustal processes, the dataset for incompatible trace element ratios was restricted to lavas between 4 and 12 wt% MgO with Eu/Eu* near unity. For elemental concentrations, average "6-values" were calculated from a subset of this compilation using only samples with 6 × 0.5 wt% MgO. As demonstrated by Plank and Langmuir (1988), Na6 correlates well with Ca6 and depth to Moho. A newly observed correlation between Na6 and the thermal state of the slab beneath each arc is also notable. Na6 also correlates with Dy/Yb, La/Sm, Nb/Zr, Zr/Sm. Zr/Ti, Pb/Nb, Rb/Nb. and La/Nb, as well as with the majority of incompatible element 6-values, including La6, Zr6, P6, Nb6, Sr6, and Ba6. Arcs overlying thick crust are enriched in incompatible elements by a factor of 3 to 4 relative to arcs overlying the thinnest crust. A global increase of Dy/Yb with crustal thickness is accompanied by a depletion in Sc6, implicating garnet. In the very thickest crust (~70 km), high Dy/Yb is accompanied by massive enrichments in Sr and Nd isotopes, suggesting a garnet effect at crustal levels. In other continental arcs, however, experimental results suggest garnet fractionation is unlikely to take place in magmas with >6 wt% MgO (Muntener et. al, 2001), and massive excursions in isotopic data are not present. Aside from a possible crustal effect, two end-member models have been considered: "slab control", and "extent of mantle melting (F) control". To fit the data, both sets of models require a depleted mantle wedge composition in most oceanic arcs relative to continental arcs. In the slab control model, variations in slab surface temperature regulate the composition and volume of slab melts transferred to the mantle wedge, and thus the compositions of erupted magmas. In the mantle F control model, large variations in the average extent of mantle melting (F) exert primary control over the magma compositions. Large variations in F might be produced by changes in crustal thickness and convergence rate, which may lead to variations in the thermal state of the mantle wedge and the extent of potential upwelling. Alternatively, changes in F can be produced by variable water addition to the mantle wedge. Lower concentrations of mantle H2O might be present in subduction zones with hot slabs, as a hot slab may dehydrate prior to reaching the mantle. Near 1:1 correlations between, Sr6, P6, and Zr6 appear to be in conflict with the slab control model, as recent experimental data suggest Zr and P are buffered by accessory phases in the slab, while Sr is incompatible across a wide range of temperatures (e.g. Hermann & Rubatto, 2009). A model neglecting variation in slab temperature, however, is at odds with developing physical models of subduction zones, which indicate that the slab surface temperature below the arc might vary by >200° C. A hybrid of our end-member models may be necessary to resolve these discrepancies.

  11. Petrology of ultramafic and mafic xenoliths from Ruddon's Point, Fife, Scotland (United States)

    Matusiak-Malek, Magdalena; Sobczak, Paweł; Upton, Brian; Puziewicz, Jacek; Ntaflos, Theodoros


    The studied xenolith suite comprise of anhydrous spinel lherzolites, wehrlite, ol- clinopyroxenite, clinopyroxenite and websterite. Peridotites have porphyroclastic texture and consist of forsterite-rich olivine (Fo87-90), Al-rich pyroxenes (0.25-0.31 apfu in Cpx and 0.15-0.19 apfu in Opx) and Cr-poor spinel (Cr-number=0.15-0.20, Mg-number=0.70). Wehrlite has cumulative texture with cumulus olivine (Fo83-84) and intercumulus clinopyroxene (Mg-number=0.83-0.86, Al=0.23-0.29 apfu). Clinopyroxenites and websterites have adcumulative textures, and often contain pseudomorphs after mica (?). Olivine in clinopyroxenites and ol-clinopyroxenites is low magnesian- Fo78-82, clinopyroxenes have Mg-number from 0.75 to 0.85 with Al ranging from 0.17 to 0.30 apfu. Clinopyroxene-orthopyroxene equilibrium in most of peridotites was achieved in temperatures from 960 to 1010°C, in websterite it was 970-990°C (Brey and Köhler, 1991). Clinopyroxene forming peridotites is characterized by flat HREE and is slightly depleted to slightly enriched in LREE ((La/Lu)N=0.4-2.5). The only significant anomalies in clinopyroxene's multi-trace element patterns occur at Th-U (positive) and Nb-Ta (negative) contents. Orthopyroxene in peridotites contains elevated amounts of Th, U, Zr, Hf and Ti. Clinopyroxene in clinopyroxenites has concave downward REE pattern ((La/Lu)N=2.3-2.4 in clinopyroxenites and ((La/Lu)N=4.8 and 8.7 in ol-clinopyroxenite and websterite, respectively) and has slight negative Ti anomaly in olivine clinopyroxenite and websterite. The lherzolite xenoliths represent upper mantle rocks. Composition of clinopyroxene suggests the peridotites to suffer from 1 to 7% of melt extraction, composition of orthopyroxene points to higher degrees of depletion (10-15%; Upton et al., 2011). Peridotites have been metasomatised by subduction-related hydrous fluids enriching pyroxenes in Th and U. Clinopyroxene in wehrlite is texturally later than olivine, but strictly follows the general trace element characteristic of peridotites, thus may represent precipitate from the metasomatic melt. Subduction-related metasomatism seems to be widespread in Scottish lithosphere south from Moine Thrust Zone, but with numerous local variations (Bonadiman et al., 2008; Hughes et al., 2015; Upton et al., 2011). The ol- clinopyroxenites and clinopyroxenites are considered to have originated by crystal settling from an alkaline silicate melt. Their formation is possibly related with Carboniferous, rifting-controlled volcanism. This study was possible thanks to project NCN UMO-2014/15/B/ST10/00095 from the Polish National Centre for Science. Bonadiman et al. (2008). Geological Society, London, Special Publication 293, 303-333 Brey, Köhler (1991). Journal of Petrology 31, 1353-1378 Hughes et al. (2015). Mineralogical Magazine, 74, 877-908 Upton et al. (2011). Journal of the Geological Society 168, 873-886

  12. 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.

  13. A geochronological study of mafic and acidic lavas from Veneto Volcanic province (North-East Italy) (United States)

    Brombin, Valentina; Webb, Laura; Bonadiman, Costanza; Marzoli, Andrea; Coltorti, Massimo


    The Veneto Volcanic Province (VVP), in the North-East of Italy represents one of the most important magmatic province of the Adria Plate. VVP magmatism occurred in a period ranging from late Paleocene to late Oligocene (De Vecchi et al., 1976). Five main volcanic districts can be defined from north-west to south-east: Val d'Adige, Marosticano, Lessini Hills, Berici Hills and Euganean Hills. Most of the volcanic products are relatively undifferentiated lavas, ranging in compostion from mela-nephelinites to quartz-normative tholeiites (Beccaluva et al., 2007). By contrast in the Euganean Hills volcanic and subvolcanic rocks range from subordinate basalts to prevalently acidic types, mostly quartz-trachytes and rhyolites (Milani et al., 1999). Despite of the deep petrological knowledge about this province, the radioisotopic ages of the related volcanic activities for each district are still poorly defined or even totally missing. 40Ar/39Ar ages on 9 samples have been obtained to determine the age range for the VVP. 40Ar/39Ar whole rock step heating analyses yielded ages ranging from 40.7 ± 0.2 Ma to 23.3 ± 1.5 Ma for basanites of Val d'Adige and Marosticano area, respectively. For the Lessinean district, 40Ar/39Ar whole rock analyses for two basanites, one trachybasalt and one alkali basalt close to 40 Ma, while a tholeiite from the same area yielded the youngest age for this district (i.e. 32.9 ± 1.8 Ma). This young age is comparable to 40Ar/39Ar ages obtained for the Euganean Hills intermediate-acidic rocks (Jourdan, pers. comm., 2016), suggesting a time-related shift from more alkaline to Si-saturated magmatism in the whole province. References Barbieri G., Medizza F. (1969). Contributo alla conoscenza geologica della regione di Bolca (Monti Lessini). Memorie dell'Istituto di Geologia e Mineralogia dell'Università di Padova, 27, 1-36. Beccaluva L., Bianchini G., Bonadiman C., Coltorti M., Milani L., Salvini L., Siena F., Tassinari R. (2007). Intraplate lithospheric and sublithospheric components in the Adriatic domain: Nephelinite to tholeiite magma generation in the Paleogene Veneto Volcanic Province, Southern Alps. Geological Society of America, 418, 131-152. De Vecchi, G., Gregnanin, A., Piccirillo, E.M., 1976. Tertiary volcanism in the Veneto. Magmatology, petrogenesis and geodynamics implications. Geologische Rundschau, 65, 701-710. Milani, L., Beccaluva, L., Coltorti, M., 1999. Petrogenesis and evolution of the Euganean magmatic complex, north eastern Italy. European Journal of Mineralogy, 11, 379-399. Savelli, C., Lipparini, E., 1979. Età K/Ar di basalti del vicentino e la scala dei tempi del Paleogene. Bollettino Società Geologica Italiana, 98, 375-385.

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

    International Nuclear Information System (INIS)

    Carter Krogh, K.E.; Valentine, G.A.


    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

  15. Silica-poor, mafic alkaline lavas from ocean islands and continents ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Among ocean islands, lavas from Samoa and Hawaii are perhaps the products of very low degree of partial melting. Lavas from Gran Canaria and .... to be shifted toward lower SiO2 (wt%). Distinctly negative trends are seen in ..... lavas require melt contributions from mixed sources (i.e., garnet clinopyroxenite and carbon-.

  16. Geochemical constraints on the evolution of mafic and felsic rocks in ...

    Indian Academy of Sciences (India)

    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 ...... Basins (eds) Saunders A D and Norry M J, Geol. Soc. London Spec. Publ. 42 313–345. Sylvester P J 1998 Post-collisional strongly ...

  17. Silica-poor, mafic alkaline lavas from ocean islands and continents

    Indian Academy of Sciences (India)

    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 ...

  18. Petrogenesis of Post-collisional high Ba-Sr granitoids: the Solarya Pluton, NW Turkey (United States)

    Unal, Alp; Kamaci, Omer; Altunkaynak, Safak


    In NW Turkey, the Late Oligocene-Early Miocene phase of post-collisional magmatism is characterized by widespread granitic pluton emplacements straddling the continental collision zone marked by the Izmir-Ankara suture zone (IASZ). This granitic magmatism produced both low Ba-Sr- and high Ba-Sr granitoids with distinct geochemical properties. One of the major plutons emplaced to the north of İzmir-Ankara suture zone, the Solarya pluton is representative of high Ba-Sr granitoids. We present here whole-rock chemical and Sr-Nd-Pb-O isotopic compositions, as well as 40Ar/39Ar ages of the Solarya pluton to evaluate the timing, nature and genesis of potassic, high Ba-Sr granites. The Solarya pluton consists of three coeval granitic members (K-Feldspar megacrystalline granodiorite, fine grained granodiorite and haplogranite) and associated mafic magmatic enclaves/dykes of gabbroic diorite to dioritic in composition. K-feldspar megacrystalline granodiorite, fine grained granodiorite and haplogranite are high K calc-alkaline in character whereas low silica mafic magmatic enclaves and dykes are mildly alkaline and display shoshonitic affinity. Both granitic members and mafic enclaves/dykes are characterized by high Ba (710-2489 ppm), Sr (305-708ppm), low Y and HREE contents and lack of significant negative Eu anomalies. They are metaluminous and display enrichment in LILE and depletion in P, Ta, Nb and Ti. Sr-Nd-Pb and O isotope compositions of mafic enclaves and dykes are similar to their host granitoids. They have initial 87Sr/86Sr values of 0.70702- 0.70805 and 143Nd/144Nd values of 0.51235-0.51250 and their ɛNd values range between -4,9 and -2,05. 206Pb/204Pb and 207Pb/204 Pb isotopic values vary from 18,75 to 18,88 and 15,68 to 15,73, respectivelly. Whole rock and quartz 18O isotopic ratios range between 8 and 10,6. All these isotopic characteristics and major-trace element compositions of Solarya pluton and associated mafic enclaves/dykes suggest a subcontinental

  19. 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...

  20. A review of the timing of coalification in the light of coal seam erosion, clastic dykes and coal clasts

    Czech Academy of Sciences Publication Activity Database

    Pešek, J.; Sýkorová, Ivana


    Roč. 66, 1-2 (2006), s. 13-34 ISSN 0166-5162 R&D Projects: GA AV ČR IAA3111103 Institutional research plan: CEZ:AV0Z30460519 Keywords : timming of coalification * bituminous coal seam * erosion of coal seams Subject RIV: DD - Geochemistry Impact factor: 1.667, year: 2006

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

    NARCIS (Netherlands)

    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

  2. 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.

    --------------------------------------------------- .00 83.6 82.4 1.2 1.00 93.9 95.2 1.3 2.00 107.2 110.7 3.5 3.00 125.1 129.5 4.4 4.00 150.3 152.1 1.8 5.00 185.7 176.3 9.4 5.50 197.5 185.7 11.8 6.00 208.7 189.2 19.5 6.50 185.0 183.3 1.7 7.00 160.9 167.2 6.3 7.50 130.0 143.6 13.6 8.00 100.1 116.1 16.0 8....00 -185.7 -176.3 9.4 16.00 -150.3 -152.1 1.8 17.00 -125.1 -129.5 4.4 18.00 -107.2 -110.7 3.5 19.00 -93.9 -95.2 1.3 20.00 -83.6 -82.4 1.2 --------------------------------------------------- OBJECTIVE FUNCTION IS 2806. MODEL PARAMETERS ---------------- DEPTH...

  3. The Halti-Corrovarre enigma in the northern Scandes: new ID-TIMS U/Pb zircon data (United States)

    Andréasson, Per-Gunnar; Corfu, Fernando; Gee, David G.


    The Caledonides of northern Norway are dominated by the Kalak Nappe Complex (KNC), mainly composed of greenschist facies quartzo-feldspathic sandstones, variously intruded by dolerite dykes and minor granites. The highest components of the KNC, the Halti, Corrovarre, Seiland and Gjesvaer nappes (apparently the same structural level), are of higher metamorphic grade and include prominent igneous suites. The Halti and Corrovarre nappes comprise mafic dyke-swarms that intrude and partially melt the meta-sandstones and also include both ultramafites and gabbros. By contrast, the Seiland nappe is dominated by a major igneous province ranging in composition from alkaline gabbro to nepheline syenite and the Gjesvaer nappe is dominated by migmatites. The KNC overrides other thrust sheets, also dominated by siliciclastic successions, the Laksefjord and Gaissa nappes, and all these allochthons overlie a thin Cambrian-Ediacaran sedimentary veneer and the Precambrian crystalline basement of Baltica. Palinspastic reconstructions of the nappes indicate that the KNC has been emplaced at least two hundred kilometres southeastwards onto the Baltoscandian platform; attempts to balance cross-sections have suggested transport distance of the highest Kalak nappes to be in the order of three times this distance. Mapping of the Kalak nappes southwards into Sweden has established their correlation with the Särv and Seve nappes, together comprising the Middle Allochthon. Recent ID-TIMS, U/Pb dating by one of us (FC) of zircons extracted from granitic melts within the dyke-swarms of the Halti and Corrovarre nappes has confirmed the results of previous studies. In Halti, ages of 441-436 Ma compare well with previous zircon and baddeleyite studies; this dunite, troctolite, gabbro, sheeted-dyke suite is of early Llandovery age, overlapping in time with the early Scandian collision of Baltica and Laurentia. In Corrovarre, the granitic melts within the dyke-swarm yield 610 Ma ages, closely

  4. Subducted slab-plume interaction traced by magnesium isotopes in the northern margin of the Tarim Large Igneous Province (United States)

    Cheng, Zhiguo; Zhang, Zhaochong; Xie, Qiuhong; Hou, Tong; Ke, Shan


    Incorporation of subducted slabs may account for the geochemical and isotopic variations of large igneous provinces (LIPs). However, the mechanism and process by which subducted slabs are involved into magmas is still highly debated. Here, we report a set of high resolution Mg isotopes for a suite of alkaline and Fe-rich rocks (including basalts, mafic-ultramafic layered intrusions, diabase dykes and mantle xenoliths in the kimberlitic rocks) from Tarim Large Igneous Province (TLIP). We observed that δ26 Mg values of basalts range from -0.29 to - 0.45 ‰, -0.31 to - 0.42 ‰ for mafic-ultramafic layered intrusions, -0.28 to - 0.31 ‰ for diabase dykes and -0.29 to - 0.44 ‰ for pyroxenite xenoliths from the kimberlitic rocks, typically lighter than the normal mantle source (- 0.25 ‰ ± 0.04, 2 SD). After carefully precluding other possibilities, we propose that the light Mg isotopic compositions and high FeO contents should be ascribed to the involvement of recycled sedimentary carbonate rocks and pyroxenite/eclogite. Moreover, from basalts, through layered intrusions to diabase dykes, (87Sr/86Sr)i values and δ18OV-SMOW declined, whereas ε (Nd) t and δ26 Mg values increased with progressive partial melting of mantle, indicating that components of carbonate rock and pyroxenite/eclogite in the mantle sources were waning over time. In combination with the previous reported Mg isotopes for carbonatite, nephelinite and kimberlitic rocks in TLIP, two distinct mantle domains are recognized for this province: 1) a lithospheric mantle source for basalts and mafic-ultramafic layered intrusions which were modified by calcite/dolomite and eclogite-derived high-Si melts, as evidenced by enriched Sr-Nd-O and light Mg isotopic compositions; 2) a plume source for carbonatite, nephelinite and kimberlitic rocks which were related to magnesite or periclase/perovskite involvement as reflected by depleted Sr-Nd-O and extremely light Mg isotopes. Ultimately, our study suggests

  5. The Bero Volganic Group: New Lithological, Stratigraphic, and Geochemical Data of this Extension of the Parana-Etendeka Igneous Province into SW Angola with Implications (United States)

    Marsh, J.; Swart, R.


    The Bero Volcanic Group, an extension of the Etendeka-Paraná Igneous Province into SW Angola, forms the eroded basement to the on-shore Namibe Basin, an Early Cretaceous-Cenozoic terrestrial and marine sedimentary sequence. The igneous suite outcrops between latitudes 14.68o and 15.25o S and comprises quartz latite rheoignimbrites/lavas, tholeiitic basaltic lavas, pyroclastic/volcaniclastic deposits, minor aeolian sandstones, and mafic tholeiitic dykes and gabbroic sheets. Quartz latite lithologies dominate. In the Rio Bero area in the S quartz latites are underlain by several thin flows of basalt interbedded with, and underlain by, thin discontinuous lenses of aeolian sandstone. This sequence is consistent with the general stratigraphic sequence in the northern Etendeka of Namibia. To the N basalts and aeolian sandstones are absent and the quartz latites lie directly on Precambrian basement rocks in places. To date, data for a quartz latite correlated with a Chapecó rhyolites of the Paraná are available from only one locality in Angola. This study's wider sampling and major and trace element and radiogenic isotope analysis reveals the following: (1) all mafic rocks are high-Ti, the lavas being equivalent to the Khumiba/Urubici type; (2) mafic dykes cutting the quartz latites having affinities to the Paranapanema-Ribeira mafic lavas; (3) five quartz latite geochemical types are present, three of which are known from Etendeka/Paraná (Sarusas/Guarapuava, Khoraseb/Ourinhos and Ventura) and their stratigraphic relationships in Angola are consistent with those in the Etendeka and Paraná; (4) their Angolan occurrence significantly extends the area covered by, and potential eruptive volumes of, these silicic types; (5) two other quartz latite types are unknown in the Etendeka and Paraná and are probably products of low-volume, local eruptions. The Chinguau type is geochemically similar to the low-Ti quartz lalites of the southern Etendeka but has lower Epsilon Nd

  6. The geology, structure and mineralisation of the Oyu Tolgoi porphyry copper-gold-molybdenum deposits, Mongolia: A review

    Directory of Open Access Journals (Sweden)

    T.M. (Mike Porter


    Mineralisation is characterised by varying, telescoped stages of intrusion and alteration. Early A-type quartz veined dykes were followed by Cu-Au mineralisation associated with potassic alteration, mainly K-feldspar in quartz-monzodiorite and biotite-magnetite in basaltic hosts. Downward reflux of cooled, late-magmatic hydrothermal fluid resulted in intense quartz-sericite retrograde alteration in the upper parts of the main syn-mineral intrusions, and an equivalent chlorite-muscovite/illite-hematite assemblage in basaltic host rocks. Uplift, facilitated by syn-mineral longitudinal faulting, brought sections of the porphyry deposit to shallower depths, to be overprinted and upgraded by late stage, shallower, advanced argillic alteration and high sulphidation mineralisation. Key controls on the location, size and grade of the deposit cluster include (i a long-lived, narrow faulted corridor; (ii multiple pulses of overlapping intrusion within the same structure; and (iii enclosing reactive, mafic dominated wall rocks, focussing ore.

  7. Speleothem and biofilm formation in a granite/dolerite cave, Northern Sweden

    DEFF Research Database (Denmark)

    Sallstedt, T.; Ivarsson, M.; Lundberg, J.


    Tjuv-Antes grotta (Tjuv-Ante's Cave) located in northern Sweden is a round-abraded sea cave ('tunnel cave'), about 30 m in length, formed by rock-water abrasion in a dolerite dyke in granite gneiss. Abundant speleothems are restricted to the inner, mafic parts of the cave and absent on granite...... incorporated remains of microorganisms. Two types of microbial communities can be distinguished associated with the speleothems: an Actinobacteria-like biofilm and a fungal community. Actinobacteria seem to play an important role in the formation of speleothem while the fungal community acts as both...... a constructive and a destructive agent. A modern biofilm dominated by Actinobacteria is present in the speleothem-free parts of the dolerite and located in cave ceiling cracks. These biofilms may represent sites of early speleothem formation. Because of its unusual position in between two types of host rock...

  8. Implications of new ^{40}Ar/^{39}Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India (United States)

    Pillai, Shilpa Patil; Pande, Kanchan; Kale, Vivek S.


    The Kaladgi Basin on the northern edge of the Dharwar craton has characters diverse from the other epicratonic Purana basins of Peninsular India. Sedimentological studies in the basin have established the presence of three cycles of flooding separated by an event of intra-basinal deformation accompanied by low grade incipient metamorphism. The overall structural configuration of the basin indicates its development by supracrustal extension accompanied by shearing in a trans-tensional regime during the Mesoproterozoic. This was followed by sagging that yielded Neoproterozoic sedimentation in a successor nested basin. ^{40}Ar/^{39}Ar dating of an intrusive mafic dyke along the axial plane of a fold has yielded a plateau age of 1154{± }4 Ma. This helps constraint the age of the various events during the evolution of this basin.

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

    DEFF Research Database (Denmark)

    Olsson, Jonas

    CarbFix is a pilot project in Iceland created to lock away CO2 through in-situ mineralization in the subsurface. The goal is to dissolve CO2 from the geothermal power plant, Hellisheiði, in water and inject it into basaltic rock formation for permanent storage. The carbonated water dissolves...... the 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...... minerals, the reaction products are known to be manifold and reflect the complex composition of the basaltic material. Formation of secondary products, such aluminium and iron (hydr)oxides, are considered undesirable, because (1) they consume the cations that could be used to sequester CO2, thus compete...

  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


    Gal) positive gravity anomaly known as Silkeborg Gravity High. The intrusion has a minimum volume of 40,000 km3, which implies that the magma influx and the consequent cooling of the lithosphere from high temperature could have had profound effects on the subsidence of the Danish Basin, in particular because...

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

    DEFF Research Database (Denmark)

    Olsson, Jonas

    the 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 released from...... are consistent with values of controlled laboratory experiments from the literature for Ba, Cd, Co, Cu, Mg, Mn, Na, Ni, Sr and Zn. The calcium carbonates also scavenge other elements, including rare earth elements (REE) and the toxic metals As and Pb. This and the next study can be considered natural analogues...

  12. 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 - others: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

  13. Low Amplitude of Geomagnetic Secular Variations Recorded in Traps of the Southern Siberian Platform: Very Fast Emplacement or Regional Remagnetization? (United States)

    Veselovskiy, R. V.; Latyshev, A. V.; Pavlov, V. E.


    We have studied the lowest part of the Permo-Triassic Siberian trap sequence which is located in the middle course of the Angara river (Southern Siberia). This sequenced is composed by 200m thick volcanoclastic rocks (tuffs with bombs of different composition) and includes numerous mafic subvolcanic bodies (dykes and sills). Altogether more than 20 sites representing tuffs, bombs, dykes and sills stretched along the valley of the Angara river over the distance more than 30 km have been sampled and studied. Obtained site mean paleomagnetic directions are tightly grouped, showing very lower scatter. Taking into account that amplitude of geomagnetic secular variation at the P-T boundary was about of same order as in Late Cenozoic (Pavlov et al., 2011) this lower scatter can be either a sequence of very fast traps emplacement which could have disastrous environmental impact or a result of subsequent regional remagnetization. The only geological event in the region which seems to be capable to cause this remagnetization is emplacement of Early Triassic sills in nearby areas. In such the case we should expect that mean paleomagnetic directions from these sills will be very close to these ones obtained from site presented in this report. We present results of paleomagnetic studies of these sills and make a choice in favor of one of discussed options. This work was supported by grants NSF EAR 0807585 ("The Siberian Traps and end-Permian extinction") and RFBR 09-05-01180, 10-05-00557.

  14. Sinistral reactivation of the Transbrasiliano Lineament: Structural and geochronological evidences in the Cariré Granulite Zone, Borborema Province - NE Brazil (United States)

    Amaral, Wagner S.; Kraus, Rita K.; Dantas, Elton L.; Fuck, Reinhardt A.; Pitombeira, João Paulo A.


    The Precambrian basement in the region of Cariré, northeast Ceará Central Domain, NE Brazil, comprises essentially dioritic gneisses and granodiorites formed under high-grade metamorphism conditions. The granulites occur frequently as metric bodies or as boudins in mylonitic/cataclastic orthogneiss matrix, within shear zones related to Transbrasiliano Lineament. Geological mapping in this region confirmed a mylonitic foliation trending ∼ N20E and sub vertical dip (∼70°) towards NW or SE. Hornblende, biotite and orthopyroxene crystals define the lineation of the main extensional direction, with sub horizontal S-SW plunge (∼5-10°). Many outcrops show a large variety of structural elements linked to ductile deformation and typical structural elements representing the transition from ductile to brittle domains. Felsic and mafic dykes of various dimensions and both ductilely and brittlely deformed are found frequently. Analysis of kinematic indicators in the lineament shows both dextral and sinistral shear sense, although ductile dextral shear is more frequent. Structures developed in shallower crustal conditions, including micro-shear, tension gashes and faults trending N12E-N20E, show sinistral kinematics. Zircon crystals obtained from felsic dykes, dislocated by faults parallel to the regional trend of the Transbrasiliano Lineament, display four groups of concordant ages, the most recent of which is ca. 460 Ma. Our data suggest that throughout its complex history, the Transbrasiliano Lineament has been reactivated under brittle conditions from the Upper Ordovician onwards.

  15. Geological indicators for impact: The anomalous case of the Vredefort structure, South Africa (United States)

    Antoine, L. A. G.; Reimold, W. U.

    The Vredefort Dome is located within and almost central to the Witwatersrand basin in its presently known extent. It exposes a central Archean granite core which is surrounded by a collar of supracrustal rocks. These collar rocks outline a strong polygonal geometry. The Archean core is comprised of two concentric zones, the Outer Granite Gneiss (OGG), and the core central Inlandsee Leucogranofels (ILG). The rocks of the inner core display granulite facies metamorphism, while the OGG is in amphibolite facies. The inner core is believed from recent drill hole information to be underlain by mafic and ultramafic gneisses, the extent of which cannot be assessed at present. A fairly broad zone of charnockites separates the OGG and ILG domains. This zone is characterized by a high concentration of pseudotachylite and ductile shearing. Whereas a number of other domical structures are located within or surrounding the Witwatersrand basin, the Vredefort structure is anomalous, in that it has: a partly polygonal geometry; extensive alkali intrusives in the northwestern sector; granophyre dykes (ring-dykes peripheral to the contact collar-basement and NW-SE or NE-SW trending dykes within the Archean basement); contact metamorphism of the collar supracrustal rocks; the overturning of collar supracrustals in the northern sectors; deformation phenomena widely regarded as representing shock metamorphism (pseudotachylite, (sub)planar microdeformation features in quartz, shatter cones and occurrences of high-P quartz polymorphs); a positive 30 mgal gravity anomaly; and high amplitude magnetic anomalies. Recent geophysical, structural and petrological evidence pertinent for the identification of the processes that led to the formation of the Vredefort structure are summarized.

  16. First results from analysis of coordinated AVIRIS, TIMS, and ISM (French) data for the Ronda (Spain) and Beni Bousera (Morocco) peridotites (United States)

    Mustard, J. F.; Hurtrez, S.; Pinet, P.; Sotin, C.


    Ultramafic rocks are relatively rare at the Earth's surface but constitute the vast majority of the Earth by volume. Exposures of ultramafic bodies are therefore crucial for deducing many important processes that occur in the Earth's mantle. An important science question regarding the spatial distribution, abundance, and composition of mafic minerals in ultramafic bodies that can be examined with advanced sensor data is the melting process. When a lherzolite melts, clinopyroxene (cpx) melts first and therefore variations in the modal amount of cpx remaining in the mantle are a reflection of the amount of fractional melting that has occurred. Fe goes preferentially into the melt during melting but a 20 percent batch melting (i.e. closed system) acquires less Fe relative to 20 percent fractional melting (i.e. open system). Since the strength and wavelength of diagnostic absorptions is a strong function of Fe content, it is possible to make maps of the variation in Fe:Mg ratios which can be related to the general melting process. Accurate ground-truth information about local mineralogy provides internal calibration and consistency checks. Investigations using imaging spectrometer are very complementary to field studies because advanced sensor data can provide a synoptic view of modal mineralogy and chemical composition whereas field studies focus on detailed characterization of local areas. Two excellent exposures of ultramafic lithologies are being investigated with visible to mid-infrared imaging spectrometer data: the Ronda peridotite near Ronda, Spain and the Beni Bousera ophiolitic fragment in northern Morocco. Although separated by the Alboran Sea, these bodies are thought to be related and represent fertile sub-continental mantle. The Ronda peridotite is predominantly spinel lherzolite but grades into harzburgite and shows considerable variation in major and trace element compositions. Mafic layering and dykes (i.e. olivine gabbro) are also observed. This

  17. Voluminous and crystal-rich igneous rocks of the Permian Wurzen volcanic system, northern Saxony, Germany: physical volcanology and geochemical characterization (United States)

    Repstock, Alexander; Breitkreuz, Christoph; Lapp, Manuel; Schulz, Bernhard


    The North Saxon Volcanic Complex (NSVC) is a nested caldera edifice dominated by the c. 295 Ma Rochlitz Volcanic System and the c. 289 Ma Wurzen Volcanic System (WVS). The climactic activity of the WVS resembled a VEI ≥ 7 fissure `supereruption' resulting in voluminous and crystal-rich caldera-fill ignimbrites (minimum volume c. 199 km3); caldera outflow facies is not known sofar. Precursory to the WVS `monotonous intermediates', rhyolitic and rhyodacitic volcanic activity led to deposition of the low-volume Wermsdorf and Cannewitz ignimbrites. Modal analysis of the WVS pyroclastic units reveals an inhomogeneous crystal population (≤ 58 vol%) comprising k-feldspar, plagioclase, quartz, ortho- and clinopyroxene and minor amounts of biotite. The Wurzen caldera fill ignimbrites feature three types of fiamme: (1) felsic fiamme; (2) mafic fiamme; and (3) granite-porphyry fiamme. This, the modal variation, and the common presence of clinopyroxene and biotite indicate a strong magma mingling component in the WVS—characteristics which have not been observed in the precursory, Wermsdorf and Cannewitz ignimbrites. The caldera fill ignimbrites feature a large compositional variation from (basaltic) trachyandesite to rhyolite caused by basaltic injection and magma mingling. It is proposed that magmatic underplating led to reheating crystal mush and finally to convection processes within the WVS magma chamber. The predominance of either pyroxene or biotite as mafic mineral in the (trachy-) dacitic to rhyolitic ignimbrites indicates eruption of crystal mush from different magma batches. Prominent negative Nb and Ta anomalies of the Wurzen caldera fill ignimbrites, porphyries, and mafic dykes indicate enhanced melt-crust interaction or contamination of mantle melt. In the aftermath of the WVS caldera eruption, basaltic, trachyandesitic, andesitic and rhyolitic melts ascended puncturing the Wurzen-α and β ignimbrites leading to an array of NW-SE-trending dykes, subvolcanic

  18. Petrology and SHRIMP zircon geochronology of granulites from Vesleknausen, Lützow-Holm Complex, East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism

    Directory of Open Access Journals (Sweden)

    Toshiaki Tsunogae


    Full Text Available We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the Lützow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss (charnockite and minor biotite gneiss, mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750–850 °C, approximately 150 °C lower than those estimated for metasedimentary gneisses from Rundvågshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss, yielded a Concordia upper intercept ages of 2507.9 ± 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundvågshetta-Vesleknausen-Strandnibba region in southwestern Lützow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc magmatism. The Neoarchean magmatic terrane was tectonically mingled with other fragments (such as metasedimentary units in northern Lützow-Holm Bay by subduction/collision events during the assembly of Gondwana supercontinent, and subsequently underwent ∼850 °C granulite-facies metamorphosed during Neoproterozoic to Cambrian final collisional event.

  19. The land Piedra Alta : A geotectonic unit in the juvenile Paleoproterozoic craton del Rio de la Plata ( Uruguay )

    International Nuclear Information System (INIS)

    Preciozzi, F.; Sanchez Bettucci, L.; Oyhantcabal, P.; Pecoits, E.; Aubet, N.; Peel, E.; Basei, M.


    Brazilian Shield (Rio Grande do Sul) where Paleoproterozoic os land, located in the region Western, are covered by Paleozoic sediments of the Paraná Basin. The Neoproterozoic domains develop east of the Precambrian shield of Uruguay. The Exceptions to this comparative correlation are represented by the Campanero Unit and Field Suspect Punta del Este, only identified in Uruguayan territory. The Piedra Alta (Río de la Plata Craton, ss.) Is composed of a complex gneissic-migmatítico plant, essentially composed of porphyritic foliated granitoids interspersed with different types of mafic rocks Paleoproterozoicas Migmatites and, at least in the southern portion, where four metamorphic belts of different degree and extent are interleaved (Montevideo, San Jose, Cerros de San Juan and Arroyo Grande). Granites, granodiorites, and bodies mafic, of different composition, age and location environment are intruding the whole ground. The last magmatic activity is represented by a swarm of dykes aged mafic ca. 1750 - 1790 Ma (Bossi and Pitched, 1991, Halls et al., 2001) and meta tuffs acid intercalated in the Belt of Los Cerros de San Juan whose ages by the method U / Pb located in the vicinity of 1753 ± 5 Ma (Preciozzi et al, in prep.). The Piedra Alta Terrane no evidence of being affected by events tectonotérmicos Neoproterozoic and is separated from the Block Valentines by the shear zone Sarandi del Yi (Preciozzi et al., 1979). From geochronological studies U / Pb, Rb / Sr, K / Ar and Sm / Nd recent, carried out on the rocks Intrusive and Piedra Alta Land gneisses, it has been possible to observe a set of events that They affected the Land

  20. Petrogenetic and geodynamic origin of the Neoarchean Doré Lake Complex, Abitibi subprovince, Superior Province, Canada (United States)

    Polat, Ali; Frei, Robert; Longstaffe, Fred J.; Woods, Ryan


    The Neoarchean (ca. 2728 Ma) anorthosite-bearing Doré Lake Complex in the northeastern Abitibi subprovince, Quebec, was emplaced into an association of intra-oceanic tholeiitic basalts and gabbros known as the Obatogamau Formation. The Obatogamau Formation constitutes the lower part of the Roy Group, which is composed of two cycles of tholeiitic-to-calc-alkaline volcanic and volcaniclastic rocks, siliciclastic and chemical sedimentary rocks, and layered mafic-to-ultramafic sills. In this study, we report major and trace element results, and Nd, Sr, Pb and O isotope data for anorthosites, leucogabbros, gabbros and mafic dykes from the Doré Lake Complex and spatially associated basalts and gabbros of the Obatogamau Formation to assess their petrogenetic origin and geodynamic setting. Field and petrographic observations indicate that the Doré Lake Complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions, resulting in widespread epidotization (20-40%) and chloritization (10-40%) of many rock types. Plagioclase recrystallized mainly to anorthite and albite endmembers, erasing intermediate compositions. Metamorphic alteration also led to the mobilization of many elements (e.g., LILE and transition metals) and to significant disturbance of the Rb-Sr and U-Pb isotope systems, resulting in 1935 ± 150 and 3326 ± 270 Ma errorchron ages, respectively. The Sm-Nd isotope system was less disturbed, yielding an errorchron age of 2624 ± 160 Ma. On many binary major and trace element diagrams, the least altered anorthosites and leucogabbros, and the gabbros and mafic dykes of the Doré Lake Complex plot in separate fields, signifying the presence of two distinct magma types in the complex. The gabbros and mafic dykes in the Doré Lake Complex share the geochemical characteristics of tholeiitic basalts and gabbros in the Obatogamau Formation, suggesting a possible genetic link between the two rock associations. Initial

  1. Data report: The effect of dyke reinforcement on benthic species in the Oosterschelde: T0 Cluster 2 and T1 Cluster 1

    NARCIS (Netherlands)

    Brink, van den A.M.; Hartog, E.


    In dit rapport zijn de data van de bodembewonende levensgemeenschappen beschreven voor locaties in de Oosterschelde voorafgaand aan oeververdedigingsactiviteiten (T0 Cluster 2) en locaties in de Oosterschelde in de periode na oeverversterkingen (T1 Cluster 1). Op de Cluster 1 locaties zijn de oevers

  2. Mineralogical and geochemical characteristics of zircon from diorite porphyry dyke in Sergozerskoe gold occurrence (the Strel'ninsky greenstone belt, Kola region

    Directory of Open Access Journals (Sweden)

    Kudryashov N. M.


    Full Text Available Mineralogical and geochemical investigation of zircon from diorite porphyry from Sergozerskoe occurrence has been carried out. Study of morphology and inner structure of zircon crystals in back scattered electron rays as well as assaying for content and distribution of Rare Earth Elements in mineral grains have given important information about conditions of crystallization and following metasomatic alteration of zircon. Zircon characteristics show that it crystallized in a melt, enriched in fluid phase. Fluid influence lasted after zircon crystallization, this reflected in uneven composition of the mineral and in configuration of REE spectra, typical for metasomatic zircon. Similar zircon characteristics have been noted in zircons from other gold occurrences in greenstone belts in the Kola region

  3. Mineralogical and geochemical characteristics of zircon from diorite porphyry dyke in Sergozerskoe gold occurrence (the Strel'ninsky greenstone belt, Kola region)


    Kudryashov N. M.; Skublov S. G.; Kalinin A. A.; Lyalina L. M.


    Mineralogical and geochemical investigation of zircon from diorite porphyry from Sergozerskoe occurrence has been carried out. Study of morphology and inner structure of zircon crystals in back scattered electron rays as well as assaying for content and distribution of Rare Earth Elements in mineral grains have given important information about conditions of crystallization and following metasomatic alteration of zircon. Zircon characteristics show that it crystallized in a melt, enriched in ...

  4. Magmatic evolution of the Jbel Boho alkaline complex in the Bou Azzer inlier (Anti-Atlas/Morocco) and its relation to REE mineralization (United States)

    Benaouda, Rachid; Holzheid, Astrid; Schenk, Volker; Badra, Lakhlifi; Ennaciri, Aomar


    The Jbel Boho complex (Anti-Atlas/Morocco) is an alkaline magmatic complex that was formed during the Precambrian-Cambrian transition, contemporaneous with the lower early Cambrian dolomite sequence. The complex consists of a volcanic sequence comprising basanites, trachyandesites, trachytes and rhyolites that is intruded by a syenitic pluton. Both the volcanic suite and the pluton are cut by later microsyenitic and rhyolitic dykes. Although all Jbel Boho magmas were probably ultimately derived from the same, intraplate or plume-like source, new geochemical evidence supports the concept of a minimum three principal magma generations having formed the complex. Whereas all volcanic rocks (first generation) are LREE enriched and appear to be formed by fractional crystallization of a mantle-derived magma, resulting in strong negative Eu anomalies in the more evolved rocks associated with low Zr/Hf and Nb/Ta values, the younger syenitic pluton displays almost no negative Eu anomaly and very high Zr/Hf and Nb/Ta. The syenite is considered to be formed by a second generation of melt and likely formed through partial melting of underplated mafic rocks. The syenitic pluton consists of two types of syenitic rocks; olivine syenite and quartz syenite. The presence of quartz and a strong positive Pb anomaly in the quartz syenite contrasts strongly with the negative Pb anomaly in the olivine syenite and suggests the latter results from crustal contamination of the former. The late dyke swarm (third generation of melt) comprises microsyenitic and subalkaline rhyolitic compositions. The strong decrease of the alkali elements, Zr/Hf and Nb/Ta and the high SiO2 contents in the rhyolitic dykes might be the result of mineral fractionation and addition of mineralizing fluids, allowing inter-element fractionation of even highly incompatible HFSE due to the presence of fluorine. The occurrence of fluorite in some volcanic rocks and the Ca-REE-F carbonate mineral synchysite in the dykes

  5. The Proterozoic Ladoga rift (SE Baltic shield): Linking mantle dynamics to supercontinent cycle and regional tectonics (United States)

    Artemieva, Irina; Shulgin, Alexey


    Mesoproterozoic mafic magmatism at the southern part of the Baltic Shield (the Lake Ladoga region) is conventionally ascribed to epicratonic rifting. The region hosts a series of mafic dykes and sills of Mesoproterozoic ages, including a ca. 1.53-1.46 Ga sheet-like gabbro-dolerite sills and the Salmi plateau-basalts from the Lake Ladoga region. Based on chiefly geochemical data, the region is conventionally interpreted as an intracratonic Ladoga rift (graben). We question the validity of this geodynamic interpretation by analyzing regional geophysical data (crustal structure, heat flow, Bouguer gravity anomalies, magnetic anomalies, and mantle Vs velocities). Our analysis of characteristics of continental rifts demonstrates that: 1. the topography of the region lacks a linear horst-graben structure typical of modern rifts, however this feature might have been lost by surface erosion; 2. the crust has neither shallow Moho, nor magmatic high-velocity underplated material, and thus is not typical of continental rifts; 3. weakly negative Bouguer gravity anomalies, especially by comparison with adjacent "background" anomalies suggest the presence of high-density material at shallow, near-Moho depths; however, the shape of the anomaly is rounded rather than linear, and may not attest to the paleorifting event; 4. seismic velocities in the upper mantle show a possible weak low-Pn anomaly near Lake Ladoga, and strong positive (+5+7%) Vs anomaly at 75-125 km depth to the NE of the lake, but not in the region of Mesoproterozoic mafic magmatism; 5. no thermal anomaly or lithosphere thickness anomaly is currently present in the lithosphere of the region, which instead is marked by extremely low heat flow; however, given the age of magmatism any thermal anomaly may have long ceased and thus its absence does not disprove rifting origin of magmatism; 6. the absence of linear magnetic anomalies which are preserved in other paleorifts provides strong evidence that this region has

  6. Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites (United States)

    Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.


    The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths

  7. 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

  8. Petrogenesis and origin of the Upper Jurassic-Lower Cretaceous magmatism in Central High Atlas (Morocco): Major, trace element and isotopic (Sr-Nd) constraints (United States)

    Essaifi, Abderrahim; Zayane, Rachid


    During an uplift phase, which lasted ca. 40 Ma, from the Late Jurassic (165 Ma) to the Early Cretaceous (125 Ma), transitional to moderately alkaline magmatic series were emplaced in the Central High Atlas. The corresponding magmatic products include basaltic lava flows erupted within wide synclines and intrusive complexes composed of layered mafic intrusions and monzonitic to syenitic dykes emplaced along narrow anticlinal ridges. The igneous rock sequence within the intrusive complexes is composed of troctolites, olivine-gabbros, oxide-gabbros, monzonites and syenites. The chemical compositions of the various intrusive rocks can be accounted for by crystal accumulation, fractional crystallization and post-magmatic remobilization. The evolution from the troctolites to the syenites was mainly controlled by a fractional crystallization process marked by early fractionation of olivine, plagioclase and clinopyroxene, followed by separation of biotite, amphibole, apatite, and Ti-magnetite. Hydrothermal activity associated with emplacement of the intrusions within the Jurassic limestones modified the elemental and the Sr isotopic composition of the hydrothermally altered rocks In particular the monzonitic to syenitic dykes underwent an alkali metasomatism marked by depletion in K and Rb and enrichment in Na and Sr. As a result, their Sr isotopic composition was shifted towards higher initial Sr isotopic ratios (0.7067-0.7075) with respect to the associated gabbros (0.7036-0.7046). On the contrary, the Nd isotopic compositions were preserved from isotope exchange with the limestones and vary in a similar range to those of the gabbros (+1.6 High Atlas, the Middle Atlas and the eastern High Atlas domains during a period of relative tectonic quiescence.

  9. Petrogenesis of coexisting SiO 2-undersaturated to SiO 2-oversaturated felsic igneous rocks: The alkaline complex of Itatiaia, southeastern Brazil (United States)

    Brotzu, P.; Gomes, C. B.; Melluso, L.; Morbidelli, L.; Morra, V.; Ruberti, E.


    The Itatiaia alkaline complex is a Late Cretaceous intrusion (72 Myr) made up of felsic differentiates, with syenitic rocks dominant throughout and with presence of both nepheline- and quartz-rich varieties. Dykes with phonolitic or trachytic composition cross-cut the coarse-grained facies. The rocks are arranged concentrically, with the core of the complex being formed by SiO 2-oversaturated syenites (with a small outcrop of granites), and are radially displaced by faults related to regional tectonic lineaments. The minerals show gradual but significant changes in composition (salitic and augitic to aegirine-rich pyroxenes, hastingsite and actinolite to richterite and arfvedsonite amphiboles, sodic plagioclase to orthoclase feldspars and so on) and the whole-rock trends are broadly consistent with fractional crystallization processes dominated by alkali feldspar removal. Sr-isotopic data indicate more radiogenic ratios for the SiO 2-oversaturated rocks (0.7062-0.7067 against 0.7048-0.7054 for the SiO 2-undersaturated syenites), consistent with small amounts of crustal input. The favored hypothesis for the petrogenesis of the different syenitic groups is the prolonged differentiation starting from differently SiO 2-undersaturated mafic parental magmas (potassic alkali basalts to ankaratrites, present in the Late Cretaceous dyke swarms of the area), accompanied by variable crustal contamination prior to the final emplacement. The lack of carbonatite as a significant lithotype, the potassic affinity of the Itatiaia complex, and the relatively high Sr-isotopic ratios match the characteristics of the other complexes of the Rio de Janeiro-Sa˜o Paulo states coastline and confirm the ultimate derivation of these differentiated rocks from an enriched lithospheric mantle source.

  10. Continental origin of the Gubaoquan eclogite and implications for evolution of the Beishan Orogen, Central Asian Orogenic Belt, NW China (United States)

    Saktura, Wanchese M.; Buckman, Solomon; Nutman, Allen P.; Belousova, Elena A.; Yan, Zhen; Aitchison, Jonathan C.


    The Gubaoquan eclogite occurs in the Paleozoic Beishan Orogen of NW China. Previously it has been interpreted as a fragment of subducted oceanic crust that was emplaced as a mélange within continental rocks. Contrary to this, we demonstrate that the Gubaoquan eclogite protolith was a Neoproterozoic basic dyke/sill which intruded into Proterozoic continental rocks. The SHRIMP Usbnd Pb zircon dating of the metamorphic rims of the Gubaoquan eclogite yields an age 466 ± 27 Ma. Subdued heavy rare earth element abundances and lack of negative Eu anomalies of the metamorphic zircon domains confirm that this age represents eclogite facies metamorphism. The host augen orthogneiss has a Usbnd Pb zircon age of 920 ± 14 Ma, representing the timing of crystallization of the granitic protolith. A leucogranitic vein which intrudes the eclogite has a Usbnd Pb zircon age of 424 ± 8.6 Ma. This granitic vein marks the end of high-grade metamorphism in this area. The overcomplication of tectonic history of the Beishan Orogen is partially caused by inconsistent classifications and nomenclature of the same rock units and arbitrary subdivisions of Precambrian blocks as individual microcontinents. In an attempt to resolve this, we propose a simpler model that involves the partial subduction of the northern passive margin of the Dunhuang Block beneath the active continental margin developing on the Mazongshan-Hanshan Block to the north. Ocean closure and continental collision during the Late Ordovician resulted in continental thickening and eclogite facies metamorphism recorded by the mafic dykes/sills (now the Gubaoquan eclogite). In the light of the new data, the tectonothermal evolution of the Beishan Orogen is reviewed and integrated with the evolution of the Central Asian Orogenic Belt.

  11. Geochemistry and metamorphism of the Mouriscas Complex, Ossa-Morena/Central Iberian zone boundary, Iberian Massif, Central Portugal: Implications for the Cadomian and Variscan orogenies (United States)

    Henriques, S. B. A.; Neiva, A. M. R.; Tajčmanová, L.; Dunning, G. R.


    The Mouriscas Complex is a deformed and metamorphosed predominantly mafic igneous complex of Ediacaran and Ordovician age and crops out at the Ossa-Morena/Central Iberian zone boundary in the Iberian Massif, Central Portugal. It comprises amphibolite with Neoproterozoic protoliths (ca. 544 Ma), protomylonitic felsic dykes derived from younger trondhjemitic protoliths (ca. 483 Ma) and garnet amphibolite derived of even younger dioritic protoliths (ca. 477 Ma). The protoliths of the Neoproterozoic amphibolites are calc-alkaline magmas of basic to intermediate compositions with intraplate and active continental margin affinities and are considered to represent the final phase of the Cadomian arc magmatism. They are interpreted to have originated as coarse-grained intrusions, likely gabbro or diorite and generated from the partial melting of meta-igneous lower crust and mantle. Their emplacement occurred near the Cadomian metamorphic event dated at ca. 540 Ma (P = 7-8 kbar and T = 640-660 °C) which is interpreted to represent a continental collision. During the Late Cambrian-Early Ordovician an extensional episode occurred in the central-southern Iberian Massif and was also observed in other areas of the Variscan Orogen. It led to mantle upwelling and to the development of an aborted intracratonic rift located at the Ossa-Morena/Central Iberian zone boundary and to the opening of the Rheic Ocean to the south of the area studied in present coordinates (i.e., between the Ossa-Morena and South Portuguese Zones). This event has been dated at ca. 477 Ma and was responsible for the melting of deep ancient mafic crust and mantle with formation of bimodal magmatism in an intra-plate setting, as indicated by the protoliths of the protomylonitic felsic dykes with trondhjemitic composition and of the garnet amphibolite. Subsequent Variscan metamorphism took place under amphibolite facies conditions (P = 4-5.5 kbar; T = 600-625 °C) at lower P-T conditions than the Cadomian

  12. Portrait of a giant deep-seated magmatic conduit system: The Seiland Igneous Province (United States)

    Larsen, Rune B.; Grant, Thomas; Sørensen, Bjørn E.; Tegner, Christian; McEnroe, Suzanne; Pastore, Zeudia; Fichler, Christine; Nikolaisen, Even; Grannes, Kim R.; Church, Nathan; ter Maat, Geertje W.; Michels, Alexander


    The Seiland Igneous Province (SIP), Northern Norway, contains > 5000 km2 of mafic and ultramafic intrusions with minor alkaline, carbonatite and felsic rocks that were intruded into the lower continental crust at a depth of 25 to as much as 35 km. The SIP can be geochemically and temporally correlated to numerous dyke swarms throughout Scandinavia at 560-610 Ma, and is linked to magmatic provinces in W-Greenland and NE-America that are collectively known as the Central Iapetus Magmatic Province (CIMP). Revised mapping show that the SIP exposes 85-90% layered tholeiitic- alkaline- and syeno-gabbros, 8-10% peridotitic complexes, 2-5% carbonatite, syenite and diorite that formed within a narrow (roots of ultramafic rocks extending min 9 km into the crust. Together, the root structures represent the main volcanic conduits conveying thousands of km3 of mafic-ultramafic melts from the asthenosphere to the lithosphere. The ultramafic complexes were predominantly emplaced into the layered gabbros at four major igneous centres, respectively, Nordre Brumandsfjord, Melkvann, Kvalfjord and Reinfjord. All complexes are situated in a right-way-up position and are steep sided forming large plugs. A marginal hybrid zone forms at the contact with country-rock and transitions gradually from olivine-mela-gabbro over pyroxenites that grades in to an olivine-clinopyroxenite zone, which is followed by a wehrlite zone and, finally, the centre of the complexes comprises pure dunite. From pyroxenite to dunite, olivine changes from Fo72 to Fo85 and clinopyroxene from Di80 to Di92 i.e. the complexes observe a reverse fractional crystallisation sequence with time. Parental melt compositions modelled from early dykes indicate komatiitic to picritic melts with 16-22 wt% MgO, Cr of 1594 ppm and Ni of 611 ppm, which were emplaced at 1450-1500 °C. Melt compositions calculated from clinopyroxene compositions from Reinfjord are OIB-like with LREE enriched over HREE. The high abundance of

  13. Effect of pressure on Fe3+/ΣFe ratio in a mafic magma and consequences for magma ocean redox gradients (United States)

    Zhang, H. L.; Hirschmann, M. M.; Cottrell, E.; Withers, A. C.


    Experiments establishing the effect of pressure on the Fe3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO2 were performed from 100 kPa to 7 GPa and 1400-1750 °C. Fe3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O'Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe3+ ions of ∼5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe2+ ions, from ∼5 to ∼6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe2+ ions from ∼5.5 to ∼6, with negligible effects evident for Fe3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations indicate that oxygen fugacities at the surface of shallow magma oceans are more reduced than at depth. For magma oceans in which the pressure at the base is near 5 GPa, as may be appropriate for Mercury and the Moon, conditions at the surface are ∼1.5 log unit more reduced at the surface than at their base. If the results calibrated up to pressures of 7 GPa can be extrapolated to higher pressures appropriate for magma oceans on larger terrestrial planets such as Mars or Earth, then conditions at the surface are ∼2 or 2.5 log units more reduced at the surface than at the base, respectively. Thus, atmospheres overlying shallow magma oceans should be highly reduced and rich in H2 and CO.

  14. Effect of pressure on Fe3+/ΣFe ratio in a mafic magma and consequences for magma ocean redox gradients

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. L.; Hirschmann, M. M.; Cottrell, E.; Withers, A. C.


    Experiments establishing the effect of pressure on the Fe3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO2 were performed from 100 kPa to 7 GPa and 1400–1750 °C. Fe3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O’Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe3+ ions of ~5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe2+ ions, from ~5 to ~6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe2+ ions from ~5.5 to ~6, with negligible effects evident for Fe3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations indicate that oxygen fugacities at the surface of shallow magma oceans are more reduced than at depth. For magma oceans in which the pressure at the base is near 5 GPa, as may be appropriate for Mercury and the Moon, conditions at the surface are ~1.5 log unit more reduced at the surface than at their base. If the results calibrated up to pressures of 7 GPa can be extrapolated to higher pressures appropriate for magma oceans on larger terrestrial planets such as Mars or Earth, then conditions at the surface are ~2 or 2.5 log units more reduced at the surface than at the base, respectively. Thus, atmospheres overlying shallow magma oceans should be highly reduced and rich in H2 and CO.

  15. F, Cl, and S contents of olivine-hosted melt inclusions in mafic dikes and the environmental impact of flood volcanism in the Paraná-Etendeka LIP (United States)

    Marks, Linda; Trumbull, Robert; Keiding, Jakob; Veksler, Ilya; Wenzel, Thomas; Markl, Gregor; Wiedenbeck, Michael


    Large Igneous Provinces (LIPs) have been proposed to trigger mass-extinction events by the release of large quantities of volcanic gases which results in major climatic perturbations causing worldwide ecological stress and collapse. A prerequisite for understanding the proposed link between LIP volcanism and biological crisis is reliable information about the total gas emissions during these events. We present the first estimations of total F, Cl and S emissions from the Paraná-Etendeka LIP in the South Atlantic. Data from this province are of special interest because it is among the world's largest LIPs but is not associated to a mass extinction event. We have determined pre-eruption concentrations of F, Cl and S by in-situ analysis of melt inclusions preserved in olivine phenocrysts from basaltic dikes in the Etendeka province of NW Namibia. The melt inclusions have Mg-rich basaltic bulk compositions with about 8 to 18 wt.% MgO, overlapping the compositional range of the host rocks. A major feature of the melt inclusions is their wide variation in major and minor element concentrations, including F, Cl and S. This is attributed to trapping of variably-mixed melt fractions during crystallization of olivine in the roots of the dike system. Fluorine concentrations vary from about 190 to 450 ppm, Cl from destruction of the ozone layer.

  16. Mafic Spatter-Rich and Lava-Like Welded Ignimbrites Linked With Collapse of a Basaltic Caldera: The Halarauður Eruption, Krafla, Iceland (United States)

    Rooyakkers, S. M.; Stix, J.; Berlo, K.; Tuffen, H.


    Large, explosive basaltic or basalt-dominated eruptions linked with caldera collapse are uncommon and poorly understood, and collapse of basaltic calderas is more commonly driven by subsurface magma drainage and/or lava effusion. To better understand these rare events, we present field observations and interpretations of the Halarauður sequence, a complex series of pyroclastic deposits previously linked with formation of the Krafla caldera [1]. Basal units are locally dispersed and vary in both composition and mode of emplacement, reflecting tapping of discrete magma batches at widely-spaced vents. Very localised (t1/2 transition into two volumetrically dominant, regionally dispersed units. A remarkably heterogeneous, basaltic to hybrid intermediate spatter-rich welded tuff overlies the early-phase deposits, with a maximum thickness of 15 m. Welding intensity varies at the dm-scale both vertically and laterally, and is influenced by the local abundance of lithics. Lithic-rich horizons reflect periods of conduit instability, likely coincident with caldera collapse. This unit has previously been interpreted as a welded airfall [1], but features more consistent with lateral emplacement, including lithic concentration zones, dense welding > 7 km from probable vent sites, and rapid local thickness changes influenced by paleotopography suggest emplacement as a spatter-rich PDC. The unit grades up into a basaltic lava-like tuff with similar dispersal, interpreted as a lava-like ignimbrite deposited during the climactic phase. The Halarauður eruption is unusual for a basalt-dominated event in its complexity, explosivity, and the generation of welded ignimbrites. This event represents an endmember style of basaltic volcanism, and a worst-case scenario for eruptions at Icelandic calderas. [1] Calderone GM, Grunvold K, Oskarsson N (1990). J Volcanol Geotherm Res 44:303-314

  17. Directional change during a Miocene R-N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA (United States)

    Bogue, S. W.; Glen, J. M. G.; Jarboe, N. A.


    Recurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7°N, 243.2°E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30°N in NE Africa. After jumping to 83°N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core-mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.

  18. Origin of eclogite and garnet pyroxenite from the Moldanubian Zone of the Bohemian Massif, Czech Republic and its implication to other mafic layers embedded in orogenic peridotites

    Czech Academy of Sciences Publication Activity Database

    Obata, M.; Hirajima, T.; Svojtka, Martin


    Roč. 88, 1-2 (2006), s. 321-340 ISSN 0930-0708 R&D Projects: GA AV ČR IAA3013006 Institutional research plan: CEZ:AV0Z30130516 Keywords : eclogite * pyroxenite * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.038, year: 2006

  19. Continental Collision Structures and Post-Orogenic Geological History of the Kangerlussuaq Area in the Southern Part of the Nagssugtoqidian Orogen, Central West Greenland

    Directory of Open Access Journals (Sweden)

    Jon Engström


    Full Text Available Deep-seated continental collision sutures, formed at a depth of more than 20 km, are exposed near Kangerlussuaq, close to the Greenland ice cap, on the southern margin of the Nagssugtoqidian orogen in Central West Greenland, thus offering a rare opportunity to study the tectonic deformation style of such an orogen. This paper adds new information on the tectonic history of the southern flank of the Nagssugtoqidian orogen. It focuses on (1 the results of a detailed structural investigation of lineament zones revealed from remote sensing of geophysical and topographic data and aerial photo interpretation, (2 detailed geological mapping at key locations and (3 a tectonic structural model describing the geological development of the area. The area has undergone several episodes of deformation, which have been compiled into an event succession that recognizes eight tectonic events overprinting each other: Two stages of folding (F1 and F2 have been identified along with one major episode of intrusion of the Kangâmiut mafic dyke swarm (2.05 Ga into the Archaean continent. These dyke intrusions are very important, since by examining the style of deformation for these intrusions it is possible to define the transition from the North Atlantic Craton in the south to the mobile belts in the Nagssugtoqidian orogen in the north. Five different types of pronounced lineaments and one less pronounced lineament post-dating the Kangâmiut dykes extending from ductile deformation shearing events to brittle deformation with extensive faulting. These lineaments cover both the collisional and post-collisional tectonic history of the area. The study focused on two types of lineaments: one semi-ductile type trending E–W with a dextral sense of shear and a second, a pronounced lineament outlining the Kangerlussuaq–Russell thrust fault. These two features are interpreted to be related to the Nagssugtoqidian orogeny, while the latter lineaments have a more brittle

  20. Structure of the Crust Beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

    International Nuclear Information System (INIS)

    Tokam, Alain-Pierre K.; Tabod, Charles T.; Nyblade, Andrew A.; Jordi Julia; Wiens, Douglas A.; Pasyanos, Michael E.


    The joint inversion of Rayleigh wave group velocities and receiver functions was carried out to investigate the crustal and uppermost mantle structures beneath Cameroon. This was achieved using data from 32 broadband seismic stations installed for 2 years across Cameroon. The Moho depth estimates reveal that the Precambrian crust is variable across the country and shows some significant differences compared to other similar geologic units in East and South Africa. These differences suggest that the setting of the Cameroon Volcanic Line (CVL) and the eastward extension of the Benue Trough have modified the crust of the Panafrican mobile belt in Cameroon by thinning beneath the Rift area and CVL. The velocity models obtained from the joint inversion show at most stations, a layer with shear wave velocities ≥ 4.0 km/s, indicating the presence of a mafic component in the lower crust, predominant beneath the Congo Craton. The lack of this layer at stations within the Panafrican mobile belt may partly explain the crustal thinning observed beneath the CVL and rift area. The significant presence of this layer beneath the Craton, results from the 2100 Ma magmatic events at the origin of the emplacement of swarms of mafic dykes in the region. The CVL stations are underlain by a crust of 35 km on average except near Mt-Cameroon where it is about 25 km. The crustal thinning observed beneath Mt. Cameroon supported by the observed positive gravity anomalies here, suggests the presence of dense astenospheric material within the lithosphere. Shear wave velocities are found to be slower in the crust and uppermost mantle beneath the CVL than the nearby tectonic terrains, suggesting that the origin of the line may be an entirely mantle process through the edge-flow convection process. (author)

  1. The Cretaceous adakitic-basaltic-granitic magma sequence on south-eastern margin of the North China Craton: Implications for lithospheric thinning mechanism (United States)

    Liu, Sheng-Ao; Li, Shuguang; Guo, Sushu; Hou, Zhenhui; He, Yongsheng


    We present here a combined study of Early Cretaceous granodiorites, granites and mafic rocks from the Bengbu area on south-eastern margin of the North China Craton (NCC), in order to provide insights into the thinning mechanism of lithosphere on the cratonic margins. Zircon U-Pb and Ar-Ar dating reveals an adakitic-basaltic-granitic magma sequence with the adakitic intrusions (granodiorites; 123-115 Ma) formed prior to the granites and mafic dykes (both ca.112 Ma). The granodiorites are geochemically similar to low-Mg# adakitic rocks and isotopically have enriched Sr-Nd-Hf compositions, low radiogenic Pb (206Pb/204Pbi = 16.524-17.017), and mantle-like δ18Ozircon (5.8 ± 0.5‰). They were originated from the thickened lower continental crust (LCC) of the NCC. In contrast, the granites have low Sr/Y (generation of granitic and basaltic magmas. Anatexis of the pre-existing thickened LCC at 123-115 Ma that attenuated the LCC itself and left the residues denser as a result of felsic (adakitic) melt extraction is proposed to have resulted in gravitational instability and foundering of the lithosphere. Such a temporal sequence of magma generation and processes of lithospheric thinning also occurred on north margin of the NCC and are quite similar to the mountain-root removal beneath the Dabie Orogen in central China. This manifests that previous melting of the LCC is perhaps an important trigger responsible for lithospheric foundering in orogenic belts and cartonic margins, where the lithosphere underwent pre-thickening by continental collisions and had stabilized over a long time.

  2. Coronitic metagabbro and eclogite from the Grenville Province of western Quebec: interpretation of U-Pb geochronology and metamorphism

    International Nuclear Information System (INIS)

    Indares, A.; Dunning, G.


    We present new U-Pb and metamorphic data on high-pressure coronitic metagabbros from three distinct structural settings in the Parautochthonous belt of the Grenville Province in western Quebec. Intrusive ages are (i) 1217 -10 +15 Ma, for metagabbro close to the Grenville Front, correlative with the Sudbury dykes, defined in Ontario; (ii) 1403 -11 +14 Ma for an eclogitized lens at the base of the highest structural level (SL4), a new age for mafic magmatism in the western Grenville; and (iii) 1218 -34 +53 Ma for metagabbro from SL4, interpreted as correlative with metagabbros from the Algonquin and Shawanaga domains in Ontario. Metamorphism in all cases is Grenvillian, with the best constrained age of 1069 ± 3 Ma for the metagabbro of SL4. Metamorphic grade increases from the Grenville Front to the south. The mafic rocks preserve relict igneous textures overprinted by garnet + clinopyroxene that developed as coronas and (or) pseudomorphs after igneous phases. The highest grade metagabbros contain omphacite and some lack primary plagioclase, therefore being eclogites. However, interpretation of textures and mineral chemistry indicates that they were equilibrated during decompression (at 1350 MPa and 720 o C, sample 51: and at 1200 MPa and 740 o C, sample 29), so maximum depths of burial remain unconstrained. Their evolution is interpreted as follows: (i) high-pressure metamorphism by burial of the Laurentian margin under accreted terranes thrust toward the northwest between 1080 and 1060 Ma; (ii) residence at intermediate crustal levels, for a few tens of millions of years; and (iii) rapid exhumation by renewed thrusting that led to the emplacement of the high-pressure units over the northerly adjacent structural units of the Parautochthonous Belt. (author)

  3. The Juchatengo complex: an upper-level ophiolite assemblage of late Paleozoic age in Oaxaca, southern Mexico (United States)

    Grajales-Nishimura, José Manuel; Ramos-Arias, Mario Alfredo; Solari, Luigi; Murillo-Muñetón, Gustavo; Centeno-García, Elena; Schaaf, Peter; Torres-Vargas, Ricardo


    The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated by late Paleozoic magmatism. It consists of mafic and sedimentary rocks that have oceanic affinities, with internal pseudostratigraphic, structural and metamorphic characteristics, which resemble a typical upper-level ophiolite assemblage. New U-Pb zircon and previous hornblende K-Ar analyses yield ages of ca. 291-313 Ma (U-Pb) for plagiogranites and ca. 282-277 Ma for tonalites intruding the entire sequence, including pelagic sediments at the top, with a maximum deposition age of ca. 278 Ma and noteworthy local provenance. These data constrain the age of the JC to the Late Pennsylvanian-Early Permian period. Hf isotopic analyses obtained from zircons in the JC plagiogranite and tonalite show that they come from a similar primitive mantle source (176Hf/177Hf: 0.282539-0.283091; ƐHf(t): + 3.2 to + 15.0). ƐHf(t) values from near 0 to - 2.8 in the tonalites indicate a contribution from the continental crust. Trace elements and REE patterns in whole rock and zircons point to a primitive mantle source for differentiated mafic, plagiogranite dykes and tonalitic plutons. Geochronological and geochemical data address the generation of new oceanic crust above the subduction zone, probably in a backarc setting. In this tectonic scenario, the JC ophiolite originated due to the convergence of the paleo-Pacific plate below the already integrated Oaxacan and Acatlán complexes in western Pangea. The dextral displacement places the deformation in a transtensional regime during the late Paleozoic age.

  4. Multi-stage crustal growth and cratonization of the North China Craton

    Directory of Open Access Journals (Sweden)

    Mingguo Zhai


    The ∼2.5 Ga metamorphic-magmatic event is stronger than in most other cratons in the world. How to understand the geological significance of the 2.5 Ga event? The following points are emphasized: (1 nearly all old rocks >2.5 Ga underwent metamorphism at ∼2.52–2.5 Ga; (2 Archean basement rocks in the NCC experienced strong partial melting and migmatization; (3 granitoid rocks derived from partial melting include potassium granites, TTG granites and monzonites. These granitoids rocks intruded both the Archean greenstone belts and micro-blocks; (4 ∼2.5 Ga mafic dikes (amphibolites, granitic dikes (veins and syenitic-ultramafic dykes are also developed. Therefore, we suggest an assembly model that all micro-blocks in the NCC were welded together by late Archean greenstone belts at the end of the late Neoarchean. We also propose that the various micro-blocks were surrounded by small ocean basins, and the old continental crust and the oceanic crust were hotter than today. Subduction and collision were on much smaller scales as compared to the Phanerozoic plate tectonic regime, although the tectonic style and mechanisms were more or less similar. The formation of crustal melt granites is one of the processes of cratonization, inducing generation of stable upper and lower crustal layers. This process also generated an upper crust of more felsic composition and a lower crust of more mafic composition, due to molten residual materials and some underplated gabbros.

  5. The tectonic significance of the Cabo Frio Tectonic Domain in the SE Brazilian margin: a Paleoproterozoic through Cretaceous saga of a reworked continental margin

    Directory of Open Access Journals (Sweden)

    Renata da Silva Schmitt

    Full Text Available ABSTRACT: The Cabo Frio Tectonic Domain is composed of a Paleoproterozoic basement tectonically interleaved with Neoproterozoic supracrustal rocks (Buzios-Palmital successions. It is in contact with the Neoproterozoic-Cambrian Ribeira Orogen along the SE Brazilian coast. The basement was part of at least three continental margins: (a 1.97 Ga; (b 0.59 - 0.53 Ga; (c 0.14 Ga to today. It consists of continental magmatic arc rocks of 1.99 to 1.94 Ga. Zircon cores show a 2.5 - 2.6 Ga inheritance from the ancient margin of the Congo Craton. During the Ediacaran, this domain was thinned and intruded by tholeiitic mafic dykes during the development of an oceanic basin at ca. 0.59 Ma. After the tectonic inversion, these basin deposits reached high P-T metamorphic conditions, by subduction of the oceanic lithosphere, and were later exhumed as nappes over the basement. The Cabo Frio Tectonic Domain collided with the arc domain of the Ribeira Orogen at ca. 0.54 Ga. It is not an exotic block, but the eastern transition between this orogen and the Congo Craton. Almost 400 m.y. later, the South Atlantic rift zone followed roughly this suture, not coincidently. It shows how the Cabo Frio Tectonic Domain was reactivated as a continental margin in successive extensional and convergent events through geological time.

  6. Primordial crustal growth in northern Nigeria: preliminary Rb-Sr and Sm-Nd constraints from Kaduna migmatite-gneiss complex

    International Nuclear Information System (INIS)

    Dada, S. S.; Briqueu, L.; Birck, J. L.


    The Kaduna Migmatite-Gneiss Complex in the central area of the Northern shield includes variably migmatised granitotrondhjemitic gneisses and amphibolite of hitherto unknown age. The amphibolite enclaves and dykes are metatholeiites with comparatively unfractionated rare-earth patterns. The two main rock units (TTG and amphibolite) exhibit complementary geochemical signatures in the normalised abundance patterns of relatively incompatible elements and suggest possible derivation of the gneisses from subduction related mafic material. Sm-Nd and Rb-Sr isotopic data document early Archaean crustal formation of new crust and its subsequent late Archaean differentiation. These preliminary results form an evidence for a more extended crustal history in the heart of the Pan-African domain (ca. 600 Ma.). They suggest the differentiation of juvenile crustal protolith from a chondritic reservoir about 3.5 Ga. for the gneiss-amphibolite bimodal suite. A tectonothermal event about 3.1-3.0 Ga led to the emplacement of an early gneiss as indicated from Rb-Sr and U-Ph zircon analyses. Subsequent differentiation and/or reworking around 2.8-2.7 Ga is coherent with the Liberian orogeny within the West African- Latino American subregion

  7. The Paleoproterozoic Nattanen-type granites in northern Finland and vicinity – a postcollisional oxidized A-type suite

    Directory of Open Access Journals (Sweden)

    Esa Heilimo


    Full Text Available The ~1.8 Ga Nattanen-type granites in the Finnish Lapland and western Kola Peninsula are found as several relatively small, high-level, discordant plutons that are easily discernible as weak maxima on aeromagnetic maps. We present U–Pb mineral isotope data on the Finnishplutons. The concordia ages are in the 1.79−1.77 Ga range and there is little evidence for inheritance. Initial radiogenic isotope compositions (our common-Pb data combined with previously published whole-rock Nd and Hf data imply a major, yet varying, Archeansource component. Elemental geochemical data on five Finnish intrusions (the Nattanen stock, the Tepasto and Pomovaara complexes, the Riestovaara and Vainospää batholiths, as well as associated dyke rocks allow the Nattanen-type granites to be classified as oxidizedA-type granites. Their petrogenesis may be related to partial melting of the lower crust by mafic underplating (extensional setting or as a result of thermal relaxation in thickened crustal setting.

  8. Structure and geological evolution of the bedrock at southern Satakunta, SW Finland

    International Nuclear Information System (INIS)

    Paulamaeki, S.; Paananen, M.; Elo, S.


    , approaches to within 5 km of the Olkiluoto site. The results of gravimetric surveys have indicated that the margin of the Eurajoki stock slopes westward underneath the site, but to depths in excess of 3000 m. Plate tectonic reconstructions of the Precambrian of Finland, partly based on the results of major deep seismic sounding experiments, such as the international GGT/SVEKA project (along a NE-SW transect through the Satakunta area), indicate the pelitic and psammitic migmatite belts in Satakunta represent parts of the early Proterozoic Southern Finland and Central Finland continental arcs, respectively. Collision of these arc complexes took place 1890 - 1880 Ma ago, when the rocks were deformed and metamorphosed for the first time. The highT/lowP metamorphism was caused by mafic underplating, which led to a strong increase in temperature, and recrystallisation and partial remelting of the rocks in the upper crust. The collision of the arc complexes is characterised by an intense magmatic activity, which appears as synorogenic granitoids. In the next stage, 1860 - 1810 Ma ago, mafic underplating caused a second high-temperature metamorphic event and partial melting of the sedimentary rocks in southern Finland, producing the late-orogenic potassium. granites, dated at 1840 - 1830 Ma. The Subjotnian rapakivi granites associated with mafic rocks, the Jotnian Satakunta sandstone formation and the Postjotnian diabase dykes and sills represent the cratonisation stages of the Svecofennides. Rapakivi granites and related mafic rocks were generated in an anorogenic extensional regime by partial melting of the upper mantle and lower crust. The Jotnian Satakunta sandstone is a fluvial sediment formation deposited in a deltaic environment. The development of the graben or rift valley, where the sandstone was deposited, may have begun already during the Subjotnian, ca. 1650 Ma ago. The olivine diabase dykes represent the feeding channels of Postjotnian flood basalts. However, no such

  9. Structure and geological evolution of the bedrock at southern Satakunta, SW Finland

    Energy Technology Data Exchange (ETDEWEB)

    Paulamaeki, S.; Paananen, M.; Elo, S. [Geological Survey of Finland (Finland)


    , approaches to within 5 km of the Olkiluoto site. The results of gravimetric surveys have indicated that the margin of the Eurajoki stock slopes westward underneath the site, but to depths in excess of 3000 m. Plate tectonic reconstructions of the Precambrian of Finland, partly based on the results of major deep seismic sounding experiments, such as the international GGT/SVEKA project (along a NE-SW transect through the Satakunta area), indicate the pelitic and psammitic migmatite belts in Satakunta represent parts of the early Proterozoic Southern Finland and Central Finland continental arcs, respectively. Collision of these arc complexes took place 1890 - 1880 Ma ago, when the rocks were deformed and metamorphosed for the first time. The highT/lowP metamorphism was caused by mafic underplating, which led to a strong increase in temperature, and recrystallisation and partial remelting of the rocks in the upper crust. The collision of the arc complexes is characterised by an intense magmatic activity, which appears as synorogenic granitoids. In the next stage, 1860 - 1810 Ma ago, mafic underplating caused a second high-temperature metamorphic event and partial melting of the sedimentary rocks in southern Finland, producing the late-orogenic potassium. granites, dated at 1840 - 1830 Ma. The Subjotnian rapakivi granites associated with mafic rocks, the Jotnian Satakunta sandstone formation and the Postjotnian diabase dykes and sills represent the cratonisation stages of the Svecofennides. Rapakivi granites and related mafic rocks were generated in an anorogenic extensional regime by partial melting of the upper mantle and lower crust. The Jotnian Satakunta sandstone is a fluvial sediment formation deposited in a deltaic environment. The development of the graben or rift valley, where the sandstone was deposited, may have begun already during the Subjotnian, ca. 1650 Ma ago. The olivine diabase dykes represent the feeding channels of Postjotnian flood basalts. However, no such

  10. Progressive magmatism and evolution of the Variscan suture in southern Iberia (United States)

    Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; Gladney, Evan R.; Dupuis, Nicolle


    Magmatic activity is an integral component of orogenic processes, from arc magmatism during convergence to post-collisional crustal melting. Southern Iberia exposes a Late Paleozoic suture zone within Pangea and where a crustal fragment of Laurussia (South Portuguese Zone) is juxtaposed with parautochthonous Gondwana (Ossa Morena Zone). Fault-bounded oceanic metasedimentary rocks, mélanges and ophiolite complexes characterize the suture zone and are intruded by plutonic rocks and mafic dykes. The generation and emplacement of these intrusive rocks and their relationship to development of the suture zone and the orogen are undetermined. Field evidence combined with U/Pb (zircon) geochronology reveals three main phases of plutonism, a pre-collisional unfoliated gabbroic phase emplaced at ca 354 Ma, crosscut by a syn-tectonic ca 345 Ma foliated granodiorite phase followed by a ca 335 Ma granitic phase. Geochemical analyses (major, trace, rare earth elements) indicate that the gabbro exhibits a calc-alkaline arc signature whereas the granodiorite and granite are typical of post-collisional slab break-off. Taken together, these data demonstrate a protracted development of the orogen and support a complex late stage evolution broadly similar to the tectonics of the modern eastern Mediterranean. In this scenario, the highly oblique closure of a small tract of oceanic lithosphere postdates the main collision event resulting in escape of parautochthonous and allochthonous terranes toward the re-entrant.

  11. Geology and associated mineral occurrences of the Araxa Group, Mossamedes Region, Goias, Brazil

    International Nuclear Information System (INIS)

    Simoes, L.S.A.


    In the region of Mossamedes, State of Goias, Brazil, the Precambrian metamorphic rocks of the Araxa group were mapped at the scale of 1:25,000, with emphasis on stratigraphic, structural, petrographic and economic aspects. These metamorphites represent a continous stratigraphic sequence which, from bottom to top can be subdivided into five informal lithostratigraphic units: 1) psamitic unit (quartzite, metaconglomerate); 2) psamitic-pelitic unit (quartzite, quartz schist, muscovite schist); 3) lower pelitic - volcanic unit (chlorite - biotite schist, fine grained blastoporphyritic gneiss, amphibolite and calc-schist); 4) upper pelitic - volcanic unit (garnet muscovite schist, biotite schist and gneiss, amphibolite, magnetite muscovite schist); 5) gneissic unit (epidote biotite gneiss, amphibolite). Three types of meta-intrusive rocks were found, besides basic dykes related to Mesozoic magmatism. Four phases of deformation affected the volcano-sedimentary sequence;D 1 , D 2 , D 3 and D 4 , each of them developing distinct deformational features. Barrowian type metamorphism increases progressively from North to South from the biotite zone to the garnet zone (greenschist facies), reaching the staurolite-kyanite zone (amphibolite facies). The magmatism throughout the Group's evolution consists of mafic to felsic volcanic activity, mustly intermediary, as well as three intrusive events. Gold, copper and zinc minerals of economic interest occur within the studied area. The gold mineralizations are related to the pelitic-volcanic sequences. Copper occurs in several rocks from the pelitic-volcanic and gneissic sequences. (Author) [pt

  12. Structure, stability, and tsunami hazard associated with a rock slope in Knight Inlet, British Columbia (United States)

    van Zeyl, D. P.; Stead, D.; Sturzenegger, M.; Bornhold, B. D.; Clague, J. J.


    Rockfalls and rockslides during the past 12 000 years have deposited bouldery debris cones on the seafloor beneath massive rock slopes throughout the inner part of Knight Inlet. The 885 m high rock slope, located across from a former First Nations village destroyed in the late 1500s by a slide-induced wave, exposes the contact between a Late Cretaceous dioritic pluton and metamorphic rocks of the Upper Triassic Karmutsen Formation. The pluton margin is strongly foliated parallel to primary and secondary fabrics in the metamorphic rocks, resulting in highly persistent brittle structures. Other important structures include a set of sheeting joints and highly persistent mafic dykes and faults. Stability analysis indicates that planar and wedge rock slope failures up to about 500 000 m3 in volume could occur. We suspect that failures of this size in this setting would have the potential to generate locally hazardous waves. As several similar rock slopes fronted by large submarine debris cones exist in the inner part of Knight Inlet, it is clear that tsunami hazards should be considered in coastal infrastructure development and land-use planning in this area.

  13. A historical overview of Moroccan magmatic events along northwest edge of the West African Craton (United States)

    Ikenne, Moha; Souhassou, Mustapha; Arai, Shoji; Soulaimani, Abderrahmane


    Located along the northwestern edge of the West African Craton, Morocco exhibits a wide variety of magmatic events from Archean to Quaternary. The oldest magmatic rocks belong to the Archean Reguibat Shield outcrops in the Moroccan Sahara. Paleoproterozoic magmatism, known as the Anti-Atlas granitoids, is related to the Eburnean orogeny and initial cratonization of the WAC. Mesoproterozoic magmatism is represented by a small number of mafic dykes known henceforth as the Taghdout mafic volcanism. Massive Neoproterozoic magmatic activity, related to the Pan-African cycle, consists of rift-related Tonian magmatism associated with the Rodinia breakup, an Early Cryogenian convergent margin event (760-700 Ma), syn-collisional Bou-Azzer magmatism (680-640 Ma), followed by widespread Ediacaran magmatism (620-555 Ma). Each magmatic episode corresponded to a different geodynamic environment and produced different types of magma. Phanerozoic magmatism began with Early Cambrian basaltic (rift?) volcanism, which persisted during the Middle Cambrian, and into the Early Ordovician. This was succeeded by massive Late Devonian and Carboniferous, pre-Variscan tholeiitic and calc-alkaline (Central Morocco) volcanic flows in basins of the Moroccan Meseta. North of the Atlas Paleozoic Transform Zone, the Late Carboniferous Variscan event was accompanied by the emplacement of 330-300 Ma calc-alkaline granitoids in upper crustal shear zones. Post-Variscan alkaline magmatism was associated with the opening of the Permian basins. Mesozoic magmatism began with the huge volumes of magma emplaced around 200 Ma in the Central Atlantic Magmatic Province (CAMP) which was associated with the fragmentation of Pangea and the subsequent rifting of Central Atlantic. CAMP volcanism occurs in all structural domains of Morocco, from the Anti-Atlas to the External Rif domain with a peak activity around 199 Ma. A second Mesozoic magmatic event is represented by mafic lava flows and gabbroic intrusions in

  14. High-pressure granulite-facies metamorphism in central Dronning Maud Land (East Antarctica): Implications for Gondwana assembly (United States)

    Palmeri, Rosaria; Godard, Gaston; Di Vincenzo, Gianfranco; Sandroni, Sonia; Talarico, Franco M.


    Central Dronning Maud Land (DML; East Antarctica) is located in a key region of the Gondwana supercontinent. The Conradgebirge area (central DML) consists of orthogneisses, derived from both volcanic and plutonic protoliths, and minor metasedimentary rocks, intruded by Cambrian syn- to post-metamorphic plutons and dykes. Mafic-ultramafic boudins in the metavolcanic and metaplutonic gneisses from Conradgebirge consist of amphibolites and high-grade garnet-bearing pyroxene- and amphibole-rich granofels. They occur either as discontinuous levels or as pods boudinaged within highly-strained and strongly-migmatized gneisses. Bulk-rock major and trace-element compositions, together with geochemical discriminant diagrams (e.g., Th/Yb versus Ta/Yb and V versus Ti), suggest derivation from enriched mantle source for the mafic rocks boudinaged in metaplutonic gneisses, whereas a calc-alkaline signature is common for the mafic boudins in metavolcanic rocks. The microstructural study and P-T modelling of an ultramafic metagabbroic rock reveal a prograde metamorphic evolution from amphibolite-facies (ca. 0.5 GPa; 500 °C) up to high-P granulite-facies conditions (ca. 1.5-1.7 GPa; 960-970 °C). Partial melting is testified by "nanogranitoid" inclusions enclosed in garnet. An almost isothermal decompression down to ca. 0.4 GPa and 750-850 °C produced well-developed An + Opx-bearing symplectites around garnet. A final isobaric cooling at nearly 0.4 GPa is testified by Grt coronas around high-T symplectites. The above reconstruction traces a clockwise loading-heating P-T evolution with a peak metamorphism at high-P granulite-facies conditions suggesting crustal thickening at nearly 570 Ma, followed by a tectonically assisted rapid exhumation, and then, by an isobaric cooling. 40Ar-39Ar dating of amphibole and biotite at 505-480 Ma testify mineral re-equilibration at upper crustal level (T < 650 °C) during the isobaric cooling. This tectono-metamorphic scenario seems

  15. Coupling ground and airborne geophysical data with upscaling techniques for regional groundwater modeling of heterogeneous aquifers: Case study of a sedimentary aquifer intruded by volcanic dykes in Northern Ireland


    Dickson, Neil Edwin Matthew; Comte, Jean-Christophe; McKinley, Jennifer; Ofterdinger, Ulrich


    In highly heterogeneous aquifer systems, conceptualization of regional groundwater flow models frequently results in the generalization or negligence of aquifer heterogeneities, both of which may result in erroneous model outputs. The calculation of equivalence related to hydrogeological parameters and applied to upscaling provides a means of accounting for measurement scale information but at regional scale. In this study, the Permo-Triassic Lagan Valley strategic aquifer in Northern Ireland...

  16. Magnetic fabric and petrology of Miocene sub-volcanic sills and dykes emplaced into the SW Flysch Belt of the West Carpathians (S Moravia, Czech Republic) and their volcanological and tectonic implications

    Czech Academy of Sciences Publication Activity Database

    Hrouda, F.; Buriánek, D.; Krejčí, O.; Chadima, Martin


    Roč. 290, č. 1 (2015), s. 38 ISSN 0377-0273 Institutional support: RVO:67985831 Keywords : Miocene volcanics * Outer Western Carpathian Flysch belt * magnetic fabric Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 2.674, year: 2015

  17. Petrogenetic processes, crystallization conditions and nature of the Lower-Oligocene calc-alkaline spessartitic lamprophyres from Kal-e-kafi area (East of Anarak, Isfahan province

    Directory of Open Access Journals (Sweden)

    Gholam Hossain Nazari


    Full Text Available Introduction Lamprophyres are mesocratic to melanocratic igneous rocks, usually hypabyssal, with a panidiomorphic texture and abundant mafic phenocrysts of dark mica or amphibole (or both with or without pyroxene, with or without olivine, set in a matrix of the same minerals, and with alkali-feldspar restricted to the groundmass (Woolley et al., 1996. Lamprophyres are frequently associated with orogenic settings and a mantle modified by dehydration of subducted slab (Gibson et al., 1995. Small outcrops of lamprophyres with Paleozoic to Oligocene age are reported from the central parts of Iran (Torabi 2009 and 2010. The primary magmas of these lamprophyres were derived from decompression melting of the mantle induced by a tensional regime of continental crust (Torabi, 2010. Bayat and Torabi (2011 called the western part of the CEIM (Central-East Iranian Microcontinent (Anarak to Bayazeh a “Paleozoic lamprophyric province” and suggested that the lamprophyre magmas were formed by subduction of Paleo-Tethys oceanic crust from the Early to late Paleozoic which resulted in the mantle metasomatism and enrichment. Lamprophyric dykes and stocks of the Kal-e-kafi area (Central Iran, Northern part of Yazd Block cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. These lamprophyres are mainly composed of hornblende (magnesio-hastingsite, clinopyroxene (diopside and plagioclase (labradorite to bytownite as phenocryst, in a matrix of fine to medium grained of the same minerals and orthoclase, apatite, magnetite, chlorite and epidote. In this paper that is a report on the first study on the calc-alkaline lamprophyres of Central Iran, the petrography and mineral chemistry of calc-alkaline lamprophyric dykes of the Kal-e-kafi area are discussed. Materials and methods Chemical composition of minerals were conducted at Kanazawa University (Kanazawa, Japan using the wavelength-dispersive electron probe microanalyzer

  18. Zircon U-Pb ages and Hf isotope data from the Kukuluma Terrain of the Geita Greenstone Belt, Tanzania Craton: Implications for stratigraphy, crustal growth and timing of gold mineralization (United States)

    Kwelwa, S. D.; Sanislav, I. V.; Dirks, P. H. G. M.; Blenkinsop, T.; Kolling, S. L.


    The Geita Greenstone Belt is a late Archean greenstone belt located in the Tanzania Craton, trending approximately E-W and can be subdivided into three NW-SE trending terrains: the Kukuluma Terrain to the east, the Central Terrain in the middle and the Nyamullilima Terrain in the west. The Kukuluma Terrain, forms a NW-SE trending zone of complexly deformed sediments, intruded by the Kukuluma Intrusive Complex which, contains an early-syntectonic diorite-monzonite suite and a late-syntectonic granodiorite suite. Three gold deposits (Matandani, Kukuluma and Area 3W) are found along the contact between the Kukuluma Intrusive Complex and the sediments. A crystal tuff layer from the Kukuluma deposits returned an age of 2717 ± 12 Ma which can be used to constrain maximum sedimentation age in the area. Two granodiorite dykes from the same deposit and a small granodiorite intrusion found along a road cut yielded zircon ages of 2667 ± 17 Ma, 2661 ± 16 Ma and 2663 ± 11 Ma respectively. One mineralized granodiorite dyke from the Matandani deposit has an age of 2651 ± 14 Ma which can be used to constrain the maximum age of the gold mineralization in the area. The 2717 Ma crystal tuff has zircon grains with suprachondritic 176Hf/177Hf ratios (0.28108-0.28111 at 2717 Ma) and positive (+1.6 to +2.6) εHf values indicating derivation from juvenile mafic crust. Two of the granodiorite samples have suprachondritic 176Hf/177Hf ratios (avg. 0.28106 and 0.28107 at 2663 and 2651 Ma respectively) and nearly chondritic εHf values (avg. -0.5 and -0.3 respectively). The other two granodiorite samples have chondritic 176Hf/177Hf ratios (avg. 0.28104 and 0.28103 at 2667 and 2661 Ma respectively) and slightly negative εHf values (avg. -1.1 and -1.5 respectively). The new zircon age and isotope data suggest that the igneous activity in the Kukuluma Terrain involves a significant juvenile component and occurred within the 2720 to 2620 Ma period which, is the main period of crustal growth

  19. Emplacement and deformation of the A-type Madeira granite (Amazonian Craton, Brazil) (United States)

    Siachoque, Astrid; Salazar, Carlos Alejandro; Trindade, Ricardo


    The Madeira granite is one of the Paleoproterozoic (1.82 Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE-SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE-SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SFA-B-C), hydrothermal vein, normal fault (F1-2) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SFA-C and F1, are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SFB, F2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle

  20. Geological evolution of the Antongil Craton, NE Madagascar (United States)

    Schofield, D.I.; Thomas, Ronald J.; Goodenough, K.M.; De Waele, B.; Pitfield, P.E.J.; Key, R.M.; Bauer, W.; Walsh, G.J.; Lidke, D.J.; Ralison, A.V.; Rabarimanana, M.; Rafahatelo, J.-M.; Randriamananjara, T.


    The Antongil Craton, along with the Masora and Antananarivo cratons, make up the fundamental Archaean building blocks of the island of Madagascar. They were juxtaposed during the late-Neoproterozoic to early Palaeozoic assembly of Gondwana. In this paper we give a synthesis of the geology of the Antongil Craton and present previously published and new geochemical and U-Pb zircon analyses to provide an event history for its evolution.The oldest rocks in the Antongil Craton form a nucleus of tonalitic gneiss, characteristic of Palaeo-Mesoarchaean cratons globally, including phases dated between 3320 ?? 14. Ma to 3231 ?? 6. Ma and 3187 ?? 2. Ma to 3154 ?? 5. Ma. A series of mafic dykes was intruded into the Mesoarchaean tonalites and a sedimentary succession was deposited on the craton prior to pervasive deformation and migmatisation of the region. The age of deposition of the metasediments has been constrained from a volcanic horizon to around 3178 ?? 2. Ma and subject to migmatisation at around 2597 ?? 49. Ma. A subsequent magmatic episode generated voluminous, weakly foliated granitic rocks, that also included additions from both reworked older crustal material and younger source components. An earlier granodiorite-dominated assemblage, dated between 2570 ?? 18. Ma and 2542 ?? 5. Ma, is largely exposed in xenoliths and more continuously in the northern part of the craton, while a later monzogranite-dominated phase, dated between 2531 ?? 13. Ma and 2513 ?? 0.4. Ma is more widely developed. Together these record the stabilisation of the craton, attested to by the intrusion of a younger dyke swarm, the age of which is constrained by a sample of metagabbro dated at 2147 ?? 6. Ma, providing the first evidence for Palaeoproterozoic rocks from the Antongil Craton.The youngest events recorded in the isotopic record of the Antongil Craton are reflected in metamorphism, neocrystallisation and Pb-loss at 792 ?? 130. Ma to 763 ?? 13. Ma and 553 ?? 68. Ma. These events are

  1. Hydrothermal Ni Prospectivity Analysis of Tasmania, Australia (United States)

    Gonzalez-Alvarez, I.; Porwal, A.; McCuaig, T. C.; Maier, W.


    Tasmania contains the largest hydrothermal Ni deposit in Australia: Avebury (118,000 Ni metal tonnes). This Devonian deposit was discovered in 1998 in the Dundas geological region, and consists of a system of hydrothermal Ni ore bodies. They are hosted by an intensely altered and serpentinized Cambrian ultramafic suite in close proximity to major structural features. The mineralization is considered to be the result of hydrothermal scavenging and remobilization of the original nickel content of mafic/ultramafic rocks in the area, and subsequent re-deposition in favourable structural traps. This is based on the low sulphur, low Cu and Platinum element content of the mineralization. The mineralization is spatially (at the edge) and temporally related to a large granitic intrusion, the Heemskirk Granite, which is considered to be the source of the hydrothermal fluids as well as the necessary thermal gradients for the circulation of the fluids. Tasmania is largely covered by the Jurassic Ferrar continental flood basalt province in the East and constrains a number of early Cambrian ultramafic-mafic complexes in the West. The Ferrar large igneous province (LIP) extends over to Antarctica and is temporally and genetically related to the Karoo igneous province in southern Africa that comprises tholeiitic lava flows, sills, and dyke swarms. The Ferrar and Karoo igneous provinces were associated with the same thermal anomaly that was responsible for the break up of eastern Gondwana at ca 180 Ma. Despite of timeframe differences between the Avebury Ni deposits and the Ferrar LIP emplacement, similar geological settings to the Avebury could be duplicated along the Ferrar LIP. The presence of mafic/ultramafic rocks in favourable lithological packages and/or structural traps along the margins of the province indicate that this LIP could represent a possible exploration target for Ni hydrothermal deposits. Based on this background, a prospectivity analysis for hydrothermal Ni

  2. Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants? (United States)

    Benzaggagh, Mohamed; Mokhtari, Abdelkader; Rossi, Philippe; Michard, André; El Maz, Abdelkhader; Chalouan, Ahmed; Saddiqi, Omar; Rjimati, Ech-Cherki


    The aim of this paper is to describe the mafic rocks that crop out in the central-western Mesorif Zone (External Rif Belt), and discuss their geodynamic signification. Basalt flows, olistoliths and breccias occur in Oxfordian-Berriasian deposits of Mesorif units ascribed to the distal part of the African paleomargin. The climax of volcanic activity is observed at the northern border of a Kimmeridgian carbonate platform progressively dismembered during the Tithonian-Berriasian. In spite of the alteration of the basalts, their petrological and geochemical characters point to E-MORB affinities. The studied gabbro massifs (Bou Adel, Kef el Rhar west and north) occur as restricted slivers or klippes within the Senhadja nappe or mélange of the internal Mesorif, which overlies the basalt-bearing units and other, more external Mesorif units. The compositions range from troctolitic olivine gabbro to ferrogabbro with frequent ortho- to heteradcumulate textures; they display typical tholeiitic affinity. The gabbro massifs are crosscut by trondjhemite dykes and overlain by metabasalts, fault-scarp breccias, ophicalcites, marbles and radiolarites. Composition featuring initial near liquid composition, display multi elements patterns close to those of E-MORB, with a weak Eu negative anomaly and evidence of slight crustal contamination. These gabbro massifs were regarded as Jurassic-Cretaceous intrusions, locally dated (K-Ar) at 166 ± 3 Ma. Conversely, we assume they represent discrete samples of a Jurassic-Cretaceous oceanic basement (ophiolites), emplaced tectonically in the Senhadja nappe (mélange) of the central Mesorif. The correlation of both these types of mafic rock associations (paleomargin basalts and ophiolite klippes) with the serpentinites of the eastern Mesorif (Beni Malek) and Oran mountains (Algeria) is then briefly discussed. We conclude that the previous hypothesis of an intramargin “Mesorif suture zone” must be reconsidered, being challenged by that of a

  3. Mafic K- and Mg-Rich Magmatic Rocks from the Western Mühlviertel (Austria) Area and the Adjacent Part of the Šumava Mountains (Czech-Republic)

    Czech Academy of Sciences Publication Activity Database

    Breiter, Karel; Koller, F.


    Roč. 149, č. 4 (2009), s. 477-485 ISSN 0016-7800 Grant - others:Czech-Austrian agency for scientific cooperation ACTION(AT) 2005/2 Institutional research plan: CEZ:AV0Z30130516 Source of funding: V - iné verejné zdroje Keywords : granitoid * durbachite * glimerite * Bohemian Massif * Moldanubicum * Upper Austria * Czech Republic Subject RIV: DB - Geology ; Mineralogy

  4. F, Cl, and S concentrations in olivine-hosted melt inclusions from mafic dikes in NW Namibia and implications for the environmental impact of the Paraná-Etendeka Large Igneous Province (United States)

    Marks, Linda; Keiding, Jakob; Wenzel, Thomas; Trumbull, Robert B.; Veksler, Ilya; Wiedenbeck, Michael; Markl, Gregor


    Large Igneous Provinces (LIPs) have been proposed to trigger mass-extinction events by the release of large quantities of volcanic gases which results in major climatic perturbations causing worldwide ecological stress and collapse. A prerequisite for understanding the proposed link between LIP volcanism and biological crisis is reliable information about the total gas emissions during these events. In this paper we present the first estimations of total F, Cl and S emissions from the Paraná-Etendeka LIP in the South Atlantic. Data from this province are of special interest because it is among the world's largest LIPs but is not associated with a mass extinction event. We have determined pre-eruption concentrations of F, Cl and S by in situ analysis of melt inclusions preserved in olivine phenocrysts from basaltic dikes in the Etendeka province of NW Namibia. The melt inclusions have Mg-rich basaltic bulk compositions with about 8 to 18 wt.% MgO, overlapping the compositional range of the host rocks. A major feature of the melt inclusions is their wide variation in major and minor element concentrations, including F, Cl and S. This is attributed to trapping of variably-mixed melt fractions during crystallization of olivine in the roots of the dike system. Fluorine concentrations vary from about 190 to 450 μg/g, Cl from destruction of the ozone layer.

  5. Sm-Nd isotope and trace element evidence for heterogeneous igneous protoliths of Variscan mafic blueschists in the East Krkonoše Complex (West Sudetes, NE Bohemian Massif, Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Patočka, František; Pin, CH.


    Roč. 18, č. 5 (2005), s. 363-374 ISSN 0985-3111 R&D Projects: GA AV ČR(CZ) IAA3111102 Institutional research plan: CEZ:AV0Z3013912 Keywords : Blueschists * Bohemian Massif * Early Palaeozoic * Nd isotopes * Northern Gondwana * trace elements Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.842, year: 2005

  6. Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200 °C with implications for arsenic speciation and platinum sequestration in mafic igneous systems (United States)

    Canali, A. C.; Brenan, J. M.; Sullivan, N. A.


    To better understand the Pt-As association in natural magmas, experiments were done at 1200 °C and 0.1 MPa to measure the solubility of Pt and Pt-arsenide phases (melt and sperrylite, PtAs2), as well as to determine the oxidation state, and identify evidence for Pt-As complexing, in molten silicate. Samples consisting of synthetic basalt contained in chromite crucibles were subject to three experimental procedures. In the first, platinum solubility in the synthetic basalt was determined without added arsenic by equilibrating the sample with a platinum source (embedded wire or bead) in a gas-mixing furnace. In the second, the sample plus a Pt-arsenide source was equilibrated in a vacuum-sealed fused quartz tube containing a solid-oxide oxygen buffer. The third approach involved two steps: first equilibrating the sample in a gas-mixing furnace, then with added arsenide melt in a sealed quartz tube. Oxygen fugacity was estimated in the latter step using chromite/melt partitioning of vanadium. Method two experiments done at high initial arsenic activity (PtAs melt + PtAs2), showed significant loss of arsenic from the sample, the result of vapour transfer to newly-formed arsenide phases in the buffer. Method three experiments showed no loss of arsenic, yielding a uniform final distribution in the sample. Analyses of run-product glasses from experiments which did not show arsenic loss reveal significant increase in arsenic concentrations with fO2, varying from ∼10 ppm (FMQ-3.25) to >10,000 ppm (FMQ + 5.5). Despite very high arsenic loadings (>1000 ppm), the solubility of Pt is similar in arsenic-bearing and arsenic-free glasses. The variation in arsenic solubility with fO2 shows a linear relationship, that when corrected for the change in the activity of dissolved arsenic with the melt ferric/ferrous ratio, yields a solubility-fO2 relationship consistent with As3+ as the dissolved species. This result is confirmed by X-ray absorption near edge structure (XANES) determination on run-product glasses. Levels of arsenic required for Pt-arsenide saturation are 50-500 ppm over the fO2 range of most terrestrial basalts (FMQ to FMQ-2), >100× higher than the arsenic concentrations typical of such magmas, indicating significant enrichment of arsenic is required if Pt-arsenide saturation is to occur. In contrast, the level of dissolved Pt required to saturate in sperrylite is >8× lower than for pure Pt, suggesting that arsenic enrichment could lead to Pt removal at concentrations much less than required for pure metal saturation.

  7. Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia) (United States)

    Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo


    The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the

  8. Brittle/Ductile deformation at depth during continental crust eclogitization (Mont-Emilius klippe, Western Internal Alps). (United States)

    Hertgen, Solenn; Yamato, Philippe; Morales, Luiz; Angiboust, Samuel


    Eclogitic rocks are important for understanding tectonics at large scale as they provide key constraints on both the evolution (P-T-t-ɛ paths) and the deformation modes of the crust along the subduction interface. We herein focus our study on eclogitized mafic dykes remnants exposed within granulites from the continental basement silver of the Mt. Emilius klippe (Western Internal Alps, Italy). These eclogites exhibit highly deformed garnetite and clinopyroxenite levels. In some places, these rocks with a ± mylonitic aspect can be found as clasts within meter-thick brecciated fault rocks formed close to metamorphic peak conditions in eclogite facies. Especially, the garnet-rich levels tend to behave in a brittle fashion while deformation within clinopyroxene-rich levels is mostly accommodated by creep. This is evidenced by the presence of elongated grains, subgrain boundaries and intense grain size reduction close to rigid garnets. Crystallographic preferred orientation (CPO) measurements in garnets indicate a quasi-random distribution. In most of the clinopyroxenes levels nevertheless, the CPO is relatively strong, with multiples of uniform distribution varying from 4 to 5.5 (value of 1 is random texture). This CPO is characterized by a strong alignment of poles (001) parallel to the lineation and (100) and [010] distributed along girdles cross-cutting the foliation plane. Our study thus attests that the materials along the subduction interface at P~2.0-2.5 GPa and T~500-550°C can locally be brittle where deformation is classically envisioned as ductile. In addition to this deformation analysis, we present a petrological study of these eclogites, from the outcrop to the microscopic scale, tracking the chemical evolution associated to the observed deformation. Based on all these data, we finally propose a tectono-metamorphic history for these rocks allowing to explain the co-existence of ductile and brittle features developed in the same metamorphic facies, and

  9. Coexisting of ductile and brittle behaviors at depth during continental crust eclogitization (Mt. Emilius klippe, Western Alps) (United States)

    Morales, L. F. G.; Yamato, P.; Hertgen, S.; Angiboust, S.


    Eclogitic rocks provide key constraints on both the evolution (P-T-t-ɛ paths) and the deformation modes of the crust along the subduction interface and therefore are crucial for the understanding of tectonics at large scale. Here we present some preliminary results of a microstructural study on eclogitized mafic dykes exposed within granulites from the continental basement silver of the Mt. Emilius klippe (Western Internal Alps, Italy). In this region, highly deformed eclogites characterized by a strong layering between garnetite and clinopyroxenite bands is the most predominant feature. These different levels present very heterogeneous deformation patterns, and while the garnet-rich levels tend to have a brittle behavior, the deformation within clinopyroxene-rich levels is possibly accommodated by creep. This is evidenced by the presence of elongated grains, subgrain boundaries and intense grain size reduction close to rigid garnets. Crystallographic preferred orientation (CPO) measurements in garnets indicate a quasi-random distribution. In most of the clinopyroxenes levels nevertheless, the CPO is relatively strong, with multiples of uniform distribution varying from 4 to 5.5 (value of 1 is random texture). This CPO in the clinopyroxenes is characterized by a strong alignment of poles (001) parallel to the lineation and (100) and [010] distributed along girdles cross-cutting the foliation plane. These mylonitic rocks are sometimes found as clasts within meter-thick brecciated fault rocks formed at, or nearly close to, the metamorphic peak in eclogite facies. Therefore, the materials along the subduction interface at these P-T conditions (i.e., ~2.0-2.5 GPa; 500-550°C) can locally be brittle where deformation is classically envisioned as ductile. We propose a model that involves creep deformation, heterogeneous fluid circulation, and local brittle behavior to explain the co-existence of ductile and brittle features developed in the same depth region.

  10. Mantle source heterogeneity of the Early Jurassic basalt of eastern North America (United States)

    Gregory Shellnutt, J.; Dostal, Jaroslav; Yeh, Meng-Wan


    One of the defining characteristics of the basaltic rocks from the Early Jurassic Eastern North America (ENA) sub-province of the Central Atlantic Magmatic Province (CAMP) is the systematic compositional variation from South to North. Moreover, the tectono-thermal regime of the CAMP is debated as it demonstrates geological and structural characteristics (size, radial dyke pattern) that are commonly associated with mantle plume-derived mafic continental large igneous provinces but is considered to be unrelated to a plume. Mantle potential temperature ( T P) estimates of the northern-most CAMP flood basalts (North Mountain basalt, Fundy Basin) indicate that they were likely produced under a thermal regime ( T P ≈ 1450 °C) that is closer to ambient mantle ( T P ≈ 1400 °C) conditions and are indistinguishable from other regions of the ENA sub-province ( T Psouth = 1320-1490 °C, T Pnorth = 1390-1480 °C). The regional mantle potential temperatures are consistent along the 3000-km-long ENA sub-province suggesting that the CAMP was unlikely to be generated by a mantle plume. Furthermore, the mantle potential temperature calculation using the rocks from the Northern Appalachians favors an Fe-rich mantle (FeOt = 8.6 wt %) source, whereas the rocks from the South Appalachians favor a less Fe-rich (FeOt = 8.3 wt %) source. The results indicate that the spatial-compositional variation of the ENA basaltic rocks is likely related to differing amounts of melting of mantle sources that reflect the uniqueness of their regional accreted terranes (Carolinia and West Avalonia) and their post-accretion, pre-rift structural histories.

  11. Permo-Triassic anatexis, continental rifting and the disassembly of western Pangaea (United States)

    Cochrane, Ryan; Spikings, Richard; Gerdes, Axel; Ulianov, Alexey; Mora, Andres; Villagómez, Diego; Putlitz, Benita; Chiaradia, Massimo


    Crustal anatectites are frequently observed along ocean-continent active margins, although their origins are disputed with interpretations varying between rift-related and collisional. We report geochemical, isotopic and geochronological data that define an ~ 1500 km long belt of S-type meta-granites along the Andes of Colombia and Ecuador, which formed during 275-223 Ma. These are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon U-Pb dates ranging between 240 and 223 Ma. A model is presented which places these rocks within a compressive Permian arc setting that existed during the amalgamation of westernmost Pangaea. Anatexis and mafic intrusion during 240-223 Ma are interpreted to have occurred during continental rifting, which culminated in the formation of oceanic crust and initiated the break-up of western Pangaea. Compression during 275-240 Ma generated small volumes of crustal melting. Rifting during 240-225 Ma was characterized by basaltic underplating, the intrusion of tholeiitic basalts and a peak in crustal melting. Tholeiitic intrusions during 225-216 Ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust, and we assign this period to the onset of continental drift. Dissected ophiolitic sequences in northern Colombia yield zircon U-Pb dates of 216 Ma. The Permo-Triassic margin of Ecuador and Colombia exhibits close temporal, faunal and geochemical similarities with various crustal blocks that form the basement to parts of Mexico, and thus these may represent the relict conjugate margin to NW Gondwana. The magmatic record of the early disassembly of Pangaea spans ~ 20 Ma (240-216 Ma), and the duration of rifting and rift-drift transition is similar to that documented in Cretaceous-Tertiary rift settings such as the West Iberia-Newfoundland conjugate margins, and the Taupo-Lau-Havre System, where rifting and continental disassembly also occurred over periods lasting ~ 20 Ma.

  12. Magmatic emulsion texture formed by mixing during extrusion, Rauðafell composite complex, Breiðdalur volcano, eastern Iceland (United States)

    Charreteur, Gilles; Tegner, Christian


    The Rauðafell composite complex is part of the Neogene Breiðdalur volcano, eastern Iceland and is composed of a composite feeder dyke, a vent structure and a composite flow. The two end-members of the composite complex are rhyolite and basalt, and both are rich in plagioclase macrocrysts: bytownite in basalt and oligoclase in rhyolite. The rhyolite also includes ferroaugite macrocrysts. The mixed rocks are separated in three textural groups related to mixing proportions. When the basaltic end-member is dominant, a hybrid texture with a homogeneous matrix is observed and the only evidence of mixing is the presence of antecrysts of both end-members. When the basaltic end-member represents c. 65 to 30 % of the mixture, we observe emulsion textures composed of finely co-mingled basalt and rhyolite. The difference between these two textural expressions of mixing is due to effects of diffusion. The third texture shows mafic enclaves suspended in a rhyolitic matrix. In these rocks, the proportion of the basaltic end-member is inferior to 30 %, implying that the basalt froze solid in contact with the rhyolite. Zoning of plagioclase shows that the mixing processes are driven initially by highly efficient micro-mingling; the emulsification is possibly a result of compositional gradient stresses (Korteweg stress) between miscible basalt and rhyolite. This is followed by chemical diffusion (hybridisation) and tend to protect antecrysts from reaction with the primitive magmas. When antecrysts originated in the evolved magma, they undergo dissolution due to thermal disequilibrium during mingling and chemical disequilibrium during hybridisation. We argue that such mixing processes are important in producing intermediate rocks in Iceland and elsewhere that shows only the chemical attributes of an origin by mixing. The preservation of emulsion textures is rare and highly dependent on cooling history.

  13. Lesser Himalayan sequences in Eastern Himalaya and their deformation: Implications for Paleoproterozoic tectonic activity along the northern margin of India

    Directory of Open Access Journals (Sweden)

    Dilip Saha


    Full Text Available Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence (LHS of Eastern Himalaya, namely the Daling Group in Sikkim and the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite-slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. Multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic–Mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. Kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here: (1 the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; (2 the older deformation and metamorphism relate to a Pacific type

  14. Lithogeochemistry and geochronology of the subalkaline felsic plutonism that marks the end of the Paleoproterozoic orogeny in the Salvador-Esplanada belt, São Francisco craton (Salvador, state of Bahia, Brazil

    Directory of Open Access Journals (Sweden)

    Jailma Santos de Souza-Oliveira

    Full Text Available Studies conducted over the last decade concerning the rocks that underlie the municipality of Salvador have shown a complex geological history with a great diversity of medium- to high-grade metamorphic lithotypes, deformed in several phases and frequently cut by tabular mafic dykes and irregular granitic bodies. The latter, which were the subject of this study, frequently outcrop along the coastline of Salvador and are classified petrographically as monzo-syenogranites. They are classified as subalkaline and peraluminous according to their geochemical data, and stand out for being enriched in light rare earth elements and having a strong negative Europium (Eu anomaly. These rocks are produced from anatectic melts or through the interaction of mantle-derived magmas with crustal materials. The negative values of εNd(t (-6.08 corroborate with the crustal character and in the diagrams of tectonic ambience, they are plotted in the field of post-tectonic granites. The Sm-Nd model age (TDM around 2.9 Ga indicates a neoarchean source for these lithotypes, whereas their U-Pb zircon age (LA-ICPMS of 2,064 ± 36 Ma is similar to the U-Pb (SHRIMP and Pb-Pb (evaporation ages for late-tectonic granites of the Itabuna-Curaçá-Salvador belt. Considering the results of recent studies in the area of Salvador, the monzo-syenogranites can be interpreted as late-tectonic intrusions, since they are affected by dextral shear zones correlated with the last stage of deformation registered in the granulites of Salvador.

  15. Contrasted crustal sources as defined by whole-rock and Sr-Nd-Pb isotope geochemistry of neoproterozoic early post-collisional granitic magmatism within the Southern Brazilian Shear Belt, Camboriú, Brazil (United States)

    Florisbal, Luana Moreira; de Assis Janasi, Valdecir; de Fátima Bitencourt, Maria; Stoll Nardi, Lauro Valentim; Heaman, Larry M.


    The early phase of post-collisional granitic magmatism in the Camboriú region, south Brazil, is represented by the porphyritic biotite ± hornblende Rio Pequeno Granite (RPG; 630-620 Ma) and the younger (˜610 Ma), equigranular, biotite ± muscovite Serra dos Macacos Granite (SMG). The two granite types share some geochemical characteristics, but the more felsic SMG constitutes a distinctive group not related to RPG by simple fractionation processes, as indicated by its lower FeOt, TiO2, K2O/Na2O and higher Zr Al2O3, Na2O, Ba and Sr when compared to RPG of similar SiO2 range. Sr-Nd-Pb isotopes require different sources. The SMG derives from old crustal sources, possibly related to the Paleoproterozoic protoliths of the Camboriú Complex, as indicated by strongly negative ɛNdt (-23 to -24) and unradiogenic Pb (e.g., 206Pb/204Pb = 16.0-16.3; 207Pb/204Pb = 15.3-15.4) and confirmed by previous LA-MC-ICPMS data showing dominant zircon inheritance of Archean to Paleoproterozoic age. In contrast, the RPG shows less negative ɛNdt (-12 to -15) and a distinctive zircon inheritance pattern with no traces of post-1.6 Ga sources. This is indicative of younger sources whose significance in the regional context is still unclear; some contribution of mantle-derived magmas is indicated by coeval mafic dykes and may account for some of the geochemical and isotopic characteristics of the least differentiated varieties of the RPG. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas despite their emplacement within a low-strain zone. It may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of Paleoproterozoic orthogneisses from the Camboriú Complex.

  16. The association of tourmalinite with stratiform scheelite deposits (United States)

    Plimer, I. R.


    Three types of stratiform scheelite deposits are recognised. They all commonly have a close spatial association with tourmalinite. Regional prograde calc-silicate rocks in Precambrian rift settings commonly contain >100 ppm WO3 with enrichment to 0.5 1% WO3 in retrograde metamorphic assemblages at fold hinges, joints, faults, shears and granite and pegmatite dyke contacts. The calc-silicate progenitor was probably a impure dolomitic carbonate sediment. Amphibolite-hosted scheelite deposits occur in metamorphosed altered mafic volcanics formed in a narrow rift graben. Scheelite occurs both as stratiform and stratabound footwall stringer ore which has undergone minor remobilization during tectonism. Tourmalinites are rarely the host for stratabound quartz-scheelite±wolframite veins remobilized from the host tourmalinite and associated metavolcanics during tectonism. Tourmaline associated with stratiform scheelite deposits comprise zoned schorl-dravite and are no different from other tourmalines associated with submarine exhalative ores. Tourmalinites are characterized by high SiO2, Al2O3, B2O3 and Fe2O3 and, although they are commonly stratigraphically equivalent to submarine exhalative base metal deposits, they are depleted in P2O5, BaO and MnO. It is suggested that soft base-soft acid ligand complexes transported W from the mantle or leached crust for surficial submarine hot spring deposition. Enrichment during tectonism, especially in calc-silicate hosted deposits, took place at the sites of fluid focussing where P_{O_2 } , P_{H_2 O} and pH were high. This enrichment by up to 102 derives from dissolution of scheelite by chloride solutions resulting in redeposition of scheelite in retrograde metamorphic assemblages.

  17. Plagioclase-mantled K-feldspar in the Carboniferous porphyritic microgranite of Altenberg-Frauenstein, Eastern Erzgebirge/Krusné Hory

    Directory of Open Access Journals (Sweden)

    Axel Müller


    Full Text Available The Upper Carboniferous porphyritic microgranite of Altenberg-Frauenstein, formerly known as Granitporphyr (Dalmer 1896 and here abbreviated as GP, forms a 36 km long and up to 18 km wide complex of ring dykes related to the Teplice-Altenberg caldera in the German–Czech border region of the Eastern Erzgebirge/Krusné Hory. The microgranites are characterized by the occurrence of plagioclase-mantled K-feldspar phenocrysts. The microgranite varieties representtwo main stages of intrusion evolved from acid (GP I to intermediaterocks (GP II within the intrusion. The most acid rock (GP Icum occurs as enclaves in GP I and GP II and is interpreted as a cumulate of K-feldspar and quartz phenocrysts. The porphyritic microgranites show field, textural and geochemical evidence suggesting that some of them have formed as a result of interaction between felsic and mafic magmas. Mixing features are abundant in the porphyriticquartz-feldspar-hornblende microgranite (GP II interpreted as a hybrid rock. They are less discrete in the early phase (GP I and not obvious in the acid enclaves (GP Icum. This trend seems to reflect a continuous deflation of the magma chamber from the top to the bottom. According to the definition of rapakivi granites after Haapala and Rämö (1992, the porphyritic microgranite of Altenberg-Frauenstein may be considered as rapakivi granite although ovoid alkali feldspar megacrysts typical of classical rapakivi granites are not recorded.However, due to its Carboniferous age and being the only known granitewith rapakivi texture in the German–Czech part of the Variscan belt, the microgranite of Altenberg-Frauenstein is exceptional.

  18. Cambro-Ordovician post-collisional granites of the Ribeira belt, SE-Brazil: A case of terminal magmatism of a hot orogen (United States)

    Valeriano, Claudio de Morisson; Mendes, Julio Cezar; Tupinambá, Miguel; Bongiolo, Everton; Heilbron, Monica; Junho, Maria do Carmo Bustamante


    This work presents an overview of the geology and chemical composition of the Cambrian-Ordovician post-collisional (COPC) granites and associated rocks of Ribeira belt, SE-Brazil. These COPC granites make up some of the most picturesque and highest (>2000 m) rocky peaks and cliffs of Rio de Janeiro state, an accessible case of post-orogenic granitic magmatism associated with the terminal stages of a hot Ediacaran-Cambrian (Brasiliano-Panafrican) orogen. The COPC magmatism intruded tonalitic to granitic orthogneisses of the Rio Negro arc (∼790-600 Ma) and associated paragneisses of the São Fidelis Group. Post-collisional magmatism started ∼10 m.y. after the latest collisional event, the Buzios Orogeny, lasting discontinuously from ∼510 Ma until ∼470 Ma. The 15 largest intrusive bodies in Rio de Janeiro State are referred to in the literature as the Parati/Mangaratiba, Vila Dois Rios, Pedra Branca, Suruí, Silva Jardim, Favela, Andorinha, Teresópolis, Frade, Nova Friburgo, Conselheiro Paulino, São José do Ribeirão, Sana and Itaoca granites. They crop out as rounded/elliptical stocks or gently-dipping sheets, always with sharp contacts with the country rocks, along with pegmatite and aplitic veins and dykes. COPC granites are grey and pink undeformed medium-grained biotite monzogranites with (K-feldspar) porphyritic, mega-crystic, equigranular and serial textures. Magmatic flow foliation is frequently observed. Peripheric xenolith zones are common as well as isolated xenoliths from the country rocks. In a compilation of more than 100 chemical compositions, SiO2 contents display a major mode at 71wt%. The COPC magmatism generated high-K calc-alkaline granites and quartz monzonites with predominantly metaluminous granites. Meso to melanocratic gabbroic and dioritic enclaves also have calc-alkaline affinity and likely represent more resistant mafic xenoliths from the Rio Negro Arc.

  19. Nature of Beypazari Granitoid: Geology and geochemistry, Northwest Anatolia, Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Kadioglu, Y K; Zoroglu, O [Ankara University, Engineering Faculty, Geological Engineering Department, Ankara (Turkey)], E-mail:


    Beypazari Granitoid represents one of the widest exposure bodies within the Sakarya continent. It has several exposure bodies at Beypazari, Oymaagac, Tahir, Kirbasi and Yalnizcam of Eskisehir city. Although Beypazari Granitoid has several independence outcrops, the field geology and the aeromagnetic anomaly reveal that they are a unique body at the lower part of the crust. Field observations, mineralogical and petrographical investigations reveal that Beypazari Granitoid is composed of five different units these are monzonite, quartz monzonite, granodiorite, granite and alkali feldspar granite. Alkali feldspar granite cuts all the other subunits in the form of aplitic dyke. All the other subunits have gradual contact with the each other. Excluding alkali feldspar granite mafic enclaves are observed within the other 4 subunits as angular and elliptical in shape and changing from mm up to 20 cm in size. These enclaves can be divided genetically into three different types according to the field observation, textural features and mineralogical compositions. The first type has igneous texture, sharp contact with host rock, rimmed by fine crystalline mafic minerals and represents the abundant enclave type within the monzonite, quartz monzonite, granodiorite and granite as elliptical to sub-angular in shape. These enclaves mostly have subophitic texture in the composition of diorite, quartz diorite and monzodiorite. Ocellar quartz, acicular apatite, poiclitic feldspars and blade shaped biotite are the most characteristic features of the first type of these enclaves, which may represent the magma mixing/mingling enclaves in origin. The second type of these enclaves has a cumulate texture and is representing a segregation of early crystallization processes of mafic minerals. The second type of these enclaves is the product of the early crystallization of magmatic differentiation and is forming the magma segregation enclave types. The third type of the enclaves have

  20. Vesuvianite–wollastonite–grossular-bearing calc-silicate rock near ...

    Indian Academy of Sciences (India)

    metre to centimetre-scale felsic and mafic lay- ers (figure 2a). Felsic layers are white in colour, whereas mafic layers range from green, brown to grey colour depending on the modal abundance of different mafic minerals. Layers rich in diopside are green coloured and those rich in garnet are brown. Keywords. Vesuvianite ...

  1. Effects of geological structures on groundwater flow and quality in ...

    Indian Academy of Sciences (India)

    Analysis and field observations revealed that the north–south dykes act as a barrier of groundwater while the west–east oriented structures behave as a carrier of groundwater. Both quality and quantity of groundwater is different on the upstream and downstream sides of the dyke. Hence, it is conclusive that the west–east ...

  2. A 3D potential field model of the Pilanesberg Complex shape and structure

    CSIR Research Space (South Africa)

    Lee, SA


    Full Text Available system of alkaline intrusions that includes two dyke swarms that radiate to the north-west and south of the Complex, as well as smaller circular clinopyroxene intrusions throughout the Bushveld Complex. The Pilanesberg dyke swarms and the circular...

  3. Lithological and Structural Controls on the Development of Aquifer ...

    African Journals Online (AJOL)


    commonly arranged in an en-echelon fashion. Thickness estimation of the unit ... The unit is characterized by the presence of breccias-like appearance where angular limestone fragments/clasts of variable .... area is also characterized by the presence of dykes showing N50ºE and S50ºW trends. These dykes vary in texture ...

  4. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four dykes show ...

  5. Geochemical and Nd-isotopic systematics of the Permo-Traissic Gympie Group, southeast Queensland

    International Nuclear Information System (INIS)

    Sivell, W.J.; McCulloch, M.T.


    Nine subduction-related magma suites are recognised from drill core in the Upper Paleozoic - Mesozoic volcanic-intrusive sequence of the Gympie Group, part of the tectonically anomalous Gympie Province, southeast Queensland. Magmas of the Gympie Group include Lower Permian submarine (later subaerial) island-arc tholeiites, basaltic tuff-breccias and lavas comprising the Highbury Volcanics, as well as andesites and dacites in the unconformably overlying Rammutt Formation. Mantle-derived mafic-intermediate magmas also comprise several intrusive suites in the Gympie Group, some possessing alkaline and shoshonitic affinities. Most eruptives of the Highbury Volcanics and Rammutt Formation show uniformly high Nd-isotope ratios (εNd(270 Ma) = +7.4 to +8.1) and geochemical features (e.g. high Zr/Nb, Sr/Nd and La/Nb) that reflect depleted asthenospheric mantle sources metasomatised by hydrous fluids from subducted lithosphere. Predominant andesites from the Rammutt Formation have higher Zr/Y, Nb/Y, Ti/V, La/Y, P/Nd and K/P than isotopically similar basalts of the Highbury Volcanics, as well as high Al 2 O 3 , Zr and SiO 2 . The andesites may represent island-arc tholeiite magmas that assimilated as much as 40% isotopically primitive (young) terrigenous sediment, akin to turbiditic greywacke of Carboniferous accretionary complex origin in contiguous terranes of the New England Orogen. Rare dacites from the Rammutt Formation differentiated from island-arc tholeiite magmas similar to those of the Highbury Volcanics without incorporation of substantial metasedimentary components. Lower initial Nd-isotopic ratios characterise Gympie Group intrusive suites. In order of emplacement, these are: (i) the transitional-alkaline multiphase Langton Dolerite sill (εNd = +6.2 to +6.7); (ii) dolerite dykes intimately associated with gold mineralisation (εNd = + 4.3 to +5.7); and (iii) microdiorite dykes (εNd = +4.5 to +4.7) that include some near-primary magmas with features

  6. How 'cyclic' is the Supercontinental Cycle (United States)

    Pisarevsky, Sergei


    Precambrian paleogeography currently attracts a lot of attention from Earth scientists in various disciplines. This interest is particularly linked to the supercontinental cycle hypothesis and its relationship with global geodynamic processes. Most of the geoscience community accepts this hypothesis as plausible, but its details are still debated for several reasons. First of all, there is no consensus about the definition of a supercontinent. For example - is Gondwana a supercontinent? Depending on the answer, various estimations of the longevity of supercontinent cycle(s) arise. Another concern regards the methodological approach to paleogeographic reconstructions. For instance, some consider that the Precambrian supercontinent Nuna (aka Columbia) was assembled as a result of the widespread 2.0-1.8 Ga orogenies. However, careful consideration of geological, geochronological and paleomagnetic evidence instead suggests that supercontinent building blocks were assembled during this 2.0-1.8 Ga time interval, but that assembly of these building blocks into a supercontinent only occurred about 200 Myr later. There are only two quantitative tools for Precambrian paleogeographic reconstructions - paleomagnetic data and regional mafic dyke swarms geometries. Unfortunately, there are not yet enough high quality Precambrian paleomagnetic data to produce Apparent Polar Wander Paths (APWPs) for most Precambrian continents and to reconstruct their relative position with respect to each other, as was done for Phanerozoic paleogeography. Consequently all published reconstructions of Precambrian supercontinents are suggestive but not definitive. The only way to build a plausible Precambrian paleogeographic reconstruction is to combine paleomagnetic data with geological, geochemical and geochronological evidence. For example, the combination of paleomagnetic data with matching coeval Large Igneous Provinces (LIPs) and their regional dyke swarms, is helpful, but has limitations

  7. The ONKALO area model. Version 1

    International Nuclear Information System (INIS)

    Kemppainen, K.; Ahokas, T.; Ahokas, H.; Paulamaeki, S.; Paananen, M.; Gehoer, S.; Front, K.


    The geological model of the ONKALO area consists of three submodels: the lithological model, the brittle deformation model and the alteration model. The lithological model gives properties of definite rock units that can be defined on the basis the migmatite structures, textures and modal compositions. The brittle deformation model describes the results of brittle deformation, where geophysical and hydrogeological results are added. The alteration model describes occurrence of different alteration types and its possible effects. The rocks of Olkiluoto can be divided into two major classes: (1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and (2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subject to polyphased ductile deformation, including five stages. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result a polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. The bedrock in the Olkiluoto site has been subject to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300 deg C to less than 100 deg C. Two types of alteration can be observed: (1) pervasive (disseminated

  8. Mexican data indicating ca.700 Ma breakup of Rodinia and ca.550 Ma separation of Avalonia: analogous to events in western Laurentia (United States)

    Keppie, J. D.; Nance, R. D.; Miller, B. V.; Dostal, J.


    The supercontinent, Rodinia, appears to have been amalgamated by ca.1 Ga, however, its breakup in Laurentia appears to have occurred in two stages. Current hypotheses suggest that East Gondwana or Siberia separated from western Laurentia at ca.700 Ma followed by separation of (?) South China at ca.550 Ma producing two superposed passive margin sequences. Although prevailing wisdom suggests that the birth of Iapetus between North and South America occurred at ca.550 Ma, a similar 2-stage process is evident in both eastern Laurentia and Mexico. At ca.1 Ga, Mexico appears to have been located in or close to the North-South America suture and so provides crucial data. Geochronological data indicate that cooling following ca.1 Ga granulite facies orogenesis in Mexico followed two different paths. In southern Mexico the rocks initially cooled through ca.450° C at a rate of ca.8° C/my between 978 Ma and 945 Ma related to flat-slab subduction, followed by a cooling rate of ca.2° C/my through ca.150° C. In northern Mexico the rocks cooled at a steady rate of ca.1.8° C/my through ca.300° C and are cut by plume-related mafic dykes. Extrapolating these cooling paths to the surface indicates that southern Mexico reached the surface between 710 and 760 Ma, whereas northern Mexico reached the surface by 550 Ma. This may be partly explained by different depths of exhumation: 30 versus 37 km for southern and northern Mexico, respectively. On the other hand, the oldest rocks resting on the ca.1 Ga basement are Tremadocian (ca.490-480 Ma) in southern Mexico and Middle Silurian (ca.430-425 Ma) in northern Mexico. Thus it would appear that Mexico records two breakup stages: (1) at ca.700 Ma possibly related to the breakup of Rodinia; (2) at ca.550 Ma possibly related to the transcurrent separation of Avalonia followed by thermal equilibration at ca.500 Ma leading to subsidence and development of a passive margin. These data suggest that the breakup of Rodinia occurred at ca.700

  9. Strides in Preservation of Malawi's Natural Stone (United States)

    Kamanga, Tamara; Chisenga, Chikondi; Katonda, Vincent


    The geology of Malawi is broadly grouped into four main lithological units that is the Basement Complex, the Karoo Super group, Tertiary to Quaternary sedimentary deposits and the Chilwa Alkaline province. The basement complex rocks cover much of the country and range in age from late Precambrian to early Paleozoic. They have been affected by three major phases of deformation and metamorphism that is the Irumide, Ubendian and The Pan-African. These rocks comprise gneisses, granulites and schists with associated mafic, ultramafic, syenites and granite rocks. The Karoo System sedimentary rocks range in age from Permian to lower Jurassic and are mainly restricted to two areas in the extreme North and extreme Alkaline Province - late Jurassic to Cretaceous in age, preceded by upper Karoo Dolerite dyke swarms and basaltic lavas, have been intruded into the Basement Complex gneisses of southern Malawi. Malawi is endowed with different types of natural stone deposits most of which remain unexploited and explored. Over twenty quarry operators supply quarry stone for road and building construction in Malawi. Hundreds of artisanal workers continue to supply aggregate stones within and on the outskirts of urban areas. Ornamental stones and granitic dimension stones are also quarried, but in insignificant volumes. In Northern Malawi, there are several granite deposits including the Nyika, which is the largest single outcrop occupying approximately 260.5 km2 , Mtwalo Amazonite an opaque to translucent bluish -green variety of microcline feldspar that occurs in alkali granites and pegmatite, the Ilomba granite (sodalite) occurring in small areas within biotite; apatite, plagioclase and calcite. In the Center, there are the Dzalanyama granites, and the Sani granites. In the South, there are the Mangochi granites. Dolerite and gabbroic rocks spread across the country, treading as black granites. Malawi is also endowed with many deposits of marble. A variety of other igneous

  10. Rare Earth Element Fluorocarbonate Minerals from the Olympic Dam Cu-U-Au-Ag Deposit, South Australia

    Directory of Open Access Journals (Sweden)

    Danielle S. Schmandt


    Full Text Available Olympic Dam is a world-class breccia-hosted iron-oxide copper-gold-uranium ore deposit located in the Gawler Craton, South Australia. It contains elevated concentrations of rare earth elements (REE which occur as the REE minerals bastnäsite, synchysite, florencite, monazite, and xenotime. This is the first study to focus on the mineralogy and composition of the most abundant REE mineral at Olympic Dam, bastnäsite, and subordinate synchysite. The sample suite extends across the deposit and represents different sulfide mineralization styles (chalcopyrite-bornite and bornite-chalcocite and breccias of various types, ranging from those dominated by clasts of granite, dykes, and hematite. The REE-fluorocarbonates (bastnäsite and synchysite typically occur as fine-grained (<50 μm disseminations in Cu-Fe-sulfides and gangue minerals, and also within breccia matrix. They are also locally concentrated within macroscopic REE-mineral-rich pockets at various locations across the deposit. Such coarse-grained samples formed the primary target of this study. Three general textural groups of bastnäsite are recognized: matrix (further divided into disseminated, fine-grained, and stubby types, irregular (sulfide-associated, and clast replacement. Textures are largely driven by the specific location and prevailing mineral assemblage, with morphology and grain size often controlled by the associated minerals (hematite, sulfides. Major element concentration data reveal limited compositional variation among the REE-fluorocarbonates; all are Ce-dominant. Subtle compositional differences among REE-fluorocarbonates define a spectrum from relatively La-enriched to (Ce + Nd-enriched phases. Granite-derived hydrothermal fluids were the likely source of F in the REE-fluorocarbonates, as well as some of the CO2, which may also have been contributed by associated mafic-ultramafic magmatism. However, transport of REE by Cl-ligands is the most likely scenario. Stubby bastn

  11. Geological Model of the Olkiluoto Site. Version 2.0

    International Nuclear Information System (INIS)

    Aaltonen, I.


    The rocks of Olkiluoto can be divided into two major classes: 1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and 2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. In addition, the largest ductile deformation zones and tectonic units are described in 3D model. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300 deg C to less than 100 deg C. Two types of alteration can be observed: firstly, pervasive alteration and secondly fracturecontrolled alteration. Clay mineralisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the foliation and lithological trend. Kaolinite is also mainly located in the

  12. Geological model of the Olkiluoto site. Version 1.0

    International Nuclear Information System (INIS)

    Mattila, J.; Aaltonen, I.; Kemppainen, K.


    The rocks of Olkiluoto can be divided into two major classes: (1) supracrustal high-grade metamorphic rocks including various migmatitic gneisses, tonalitic-granodioriticgranitic gneisses, mica gneisses, quartz gneisses and mafic gneisses, and (2) igneous rocks including pegmatitic granites and diabase dykes. The migmatitic gneisses can further be divided into three subgroups in terms of the type of migmatite structure: veined gneisses, stromatic gneisses and diatexitic gneisses. On the basis of refolding and crosscutting relationships, the metamorphic supracrustal rocks have been subjected to polyphased ductile deformation, consisting of five stages, the D2 being locally the most intensive phase, producing thrust-related folding, strong migmatisation and pervasive foliation. In 3D modelling of the lithological units, an assumption has been made, on the basis of measurements in the outcrops, investigation trenches and drill cores, that the pervasive, composite foliation produced as a result of polyphase ductile deformation has a rather constant attitude in the ONKALO area. Consequently, the strike and dip of the foliation has been used as a tool, through which the lithologies have been correlated between the drillholes and from the surface to the drillholes. The bedrock at the Olkiluoto site has been subjected to extensive hydrothermal alteration, which has taken place at reasonably low temperature conditions, the estimated temperature interval being from slightly over 300 deg C to less than 100 deg C. Two types of alteration can be observed: (1) pervasive (disseminated) alteration and (2) fracture-controlled (veinlet) alteration. Kaolinisation and sulphidisation are the most prominent alteration events in the site area. Sulphides are located in the uppermost part of the model volume following roughly the lithological trend (slightly dipping to the SE). Kaolinite is also located in the uppermost part, but the orientation is opposite to the main lithological trend

  13. Mining hydrogeological data from existing AEM datasets for mineral Mining (United States)

    Menghini, Antonio; Viezzoli, Andrea; Teatini, Pietro; Cattarossi, Andrea


    resistivity model thus produced has allowed us to detect some alignments of conductive dykes, perforating the greenstone belt (made by volcanic Mafic and Ultramafic rocks or Metasedimentary formations), and correlated with the gold mineralization. Moreover, the conductive response of the basal serpentine-chloritized Ultramafic volcanic rocks, has allowed reconstructing the deeper structural features of the area. Therefore, the advantage in re-processing existing AEM data has been twofold, i.e. for both hydrogeological and geological-structural (hence mining) purposes. Concluding, we advocate for re-using of existing AEM datasets covering wide areas in underdeveloped and developing countries in to improve the hydrogeological characterizations of these nations where groundwater resources could cope with need of providing fresh / safe water to the population.

  14. Fold superimposition in the Permian groups in the central Beishan orogenic collage (northwestern China): highlights for the late evolution of the Altaids (United States)

    Zhonghua, Tian; Wenjiao, Xiao; Yehua, Shan


    inverted, when the Huaniushan arc collided presumably obliquely with the Tarim block in late Permian, to the west, and with the Duanhuang block in the Early to Middle Triassic. The latter collision eventually ended the evolution of the BOC. In interpretation, these collisions produced an earlier local E-W and later regional N-S compressions for the fold superimposition. Finally, the mafic dyke with the age of 219 Ma intruding the refolded Permian rocks post-dates the two stages of deformation.

  15. The First Paleomagnetic data from the Cambrian basalts of Henrietta Island (De Long Archipelago, Arctic Ocean) (United States)

    Metelkin, D. V.; Zhdanova, A.; Vernikovskiy, V. A.; Matushkin, N. Y.


    Henrietta Island in De Long archipelago (East-Siberian sea) still remains poorly studied geologically but last investigations show that its volcano-sedimentary sequences can help reconstruct tectonic evolution of East Russian Arctic in Early Paleozoic stage. The deposits lying on Precambrian basements are deformed to varying degrees and intruded by mafic dykes.The study was carried out on two basaltic lava flows whose 40Ar/39Ar age is 520.6±9.5 Ma. Previously the age of these basalts was assumed Cretaceous. According to available data the underlaying sediments contain zircons with Cambrian and Ordovician ages but all boundaries between these basalts and other strata are tectonic. So we suppose the age of basalts as Middle Cambrian but more precise geochronological data are required. All magnetic measurements were performed at the Laboratory of Geodynamics and Paleomagnetism of Institute of Petroleum Geology and Geophysics (Novosibirsk). Basalt samples has relatively high magnetic susceptibility values varying from 5x10-4 to 180x10-4SI units. NRM values range is from 3 to 170 mA/m. Petromagnetic parameters including also coercive characteristics point at the good potentially preserving primary magnetization. Stepwise thermal demagnetization permits to isolate characteristic components of magnetization and calculate mean directions in two lava flows: 1. Ds=294.3°, Is=29.1°, K=81.1, α95=5.1; 2. Ds=301.0°, Is=28.3°, K=34.4, α95=7.9). The mean paleomagnetic pole has coordinates: Plat=20.9°, Plong = 42.6°, dp/dm=14.3/7.9. Paleolatitude was defined as 15.3° but the question of the hemisphere for De Long Islands is open yet. In case of south hemisphere in Middle Cambrian according to available paleomagnetic data De Long islands could be placed close to Taimyr margin of Siberia and in case of northern hemisphere they may be located near south (in present-day coordinates) margin of Siberia. The work was supported by grant RFBR 14-05-31399 and Russian Research Fund

  16. The thickness of crystal mushy layers on magma chamber floors (United States)

    Holness, M. B.


    Heat loss through the margins of crustal magma bodies drives crystallization and the development of crystal mushy layers. In small intrusions the bulk composition of the mushy layers is the same as that of the intruded magma, but for larger bodies there is abundant evidence that residual mush liquid is expelled from the mushy layer on the chamber floor, driving fractionation of the bulk magma. There is debate about the precise mechanism(s) by which the residual liquid is expelled, with suggestions ranging from convection within the mushy layer driven by compositionally-controlled changes in density, compaction and collapse of the crystal framework, to diffusion and primary adcumulate growth at a hard-ground. The effective operation of these different mechanisms requires specific values of physical parameters. One of these parameters is the thickness of the mushy layer. Direct measurement of the crystal mushy layer on the floor of a magma chamber is not possible. Field observations of the effects of block settling and slumping, and downwards percolation of low viscosity dense liquids point to thicknesses of the order of metres, although numerical models of compaction and compositional convection require thicknesses of order 100 m. A new parameter that may be of use in constraining erstwhile mush thickness in fully solidified mafic intrusions is the median dihedral angle subtended at clinopyroxene-plagioclase-plagioclase junctions, Θcpp. Most gabbroic rocks are not in textural equilibrium, and Θcpp is controlled by the kinetics of crystal growth, resulting in values lower than the equilibrium value of 109˚. Θcpp in dolerites is a sensitive function of crystallization rate, rising from 78˚ in rapidly cooled small sills and dykes to > 100˚ in the centres of large sills. In fractionated bodies such as layered intrusions, Θcpp falls in the same range as that observed in dolerite sills population of cpx-plag-plag junctions is created entirely within the mush zone

  17. Unravelling the sulphur isotope systematics of an alkaline magmatic province: implications for REE mineralization and exploration (United States)

    Hutchison, W.; Finch, A.; Boyce, A.; Friis, H.; Borst, A. M.; Horsburgh, N. J.


    Some of the world's best alkaline rare earth element (REE) deposits are formed in magmatic systems that are sealed (i.e., those that are autometasomatised and maintain reducing conditions). Conversely, in open systems where oxidizing fluids infiltrate, it is commonly assumed that REE are redistributed over a wider (less concentrated) zone. Sulphur isotope fractionation is sensitive to variations in temperature and redox, and, although sulphide minerals are relatively abundant in alkaline systems, there have been few attempts to test these hypotheses and develop a sulphur isotope proxy for alkaline metasomatism and formation of associated REE deposits. The Gardar Rift Province in southern Greenland was volcanically active in two periods between 1300 and 1100 Ma and is an ideal natural laboratory to explore sulphur isotope systematics because a near-complete alkaline magmatic lineage is exposed. We present new δ34S from across the province with a particular focus on three alkaline systems (Ilímaussaq, Motzfeldt and Ivigtût) that also host major REE deposits. Primitive mafic rocks from regional Gardar dykes and lavas have a restricted range of δ34S between 0 and 3 ‰ and fractional crystallization imparts no observable change in δ34S. In a few cases high-δ34S rocks (>15 ‰) occur when intrusive units have assimilated local sedimentary crust (δ34S = 25 ‰). Most δ34S variation takes place in the roof zones of alkaline intrusions during late-magmatic and hydrothermal stages, and we identify clear differences between the complexes. At Ilímaussaq, where the magmatic series is exceptionally reduced (below QFM buffer), roof zone δ34S remains narrow (0-3 ‰). At Motzfeldt, a more open oxidizing roof zone (MH buffer), δ34S ranges from -12 ‰ in late-stage fluorite veins to +12 ‰ where local crust has been assimilated. Ivigtût is intermediate between these end-members varying between -5 to +5 ‰. The δ34S variations primarily relate to temperature and

  18. Late Paleoproterozoic-Neoproterozoic multi-rifting events in the North China Craton and their geological significance: A study advance and review (United States)

    Zhai, Mingguo; Hu, Bo; Zhao, Taiping; Peng, Peng; Meng, Qingren


    An important Paleoproterozoic mobile belt event took place in the North China Craton (NCC), termed the Hutuo Movement. This event has been interpreted to represent cratonic reworking characterized by rifting-subduction-collision processes. The NCC then evolved into a stable platform or para-platform tectonic setting in Earth's middle age period more than ~ 1.0 Ga. Thick Late Paleoproterozoic-Neoproterozoic sedimentary sequences were extensively deposited on the early metamorphic basement. The major sedimentary basins include the Xiong'er aulacogen system in the south-central NCC, the Yan-Liao aulacogen system in the north-central NCC, the Northern marginal rift system in the northwestern NCC and the Eastern marginal rift system in the eastern NCC. The following four stages of magmatic activity are recognized in the Late Paleoproterozoic to Neoproterozoic interval: (1) ~ 1800 to 1780 Ma Xiong'er igneous province (XIP), (2) ~ 1720 to 1620 Ma anorogenic magmatic association, (3) ~ 1350 to 1320 Ma diabase sill swarms, and (4) ~ 900 Ma mafic dyke swarms. These four magmatic events suggest that the NCC was situated in an intra-plate setting for a long time from ~ 1.8 Ga to ~ 0.7 Ga or even younger, and the magmatic events were associated with multi-stage rifting activities. We document that the NCC was in a long-term extensional tectonic setting during Late Paleoproterozoic-Neoproterozoic era. The main ore deposits in this period are magmatic type iron deposits related to anorthosite-gabbro bodies, REE-Nb-Fe and Pb-Zn-Cu-Fe deposits related to Mesoproterozoic-Neoproterozoic rifts. Orogenic metal deposits are absent. There is no evidence indicating that the Grenville or other orogenic events affected the NCC. The reason for the absence of Grenvillian aged events in the NCC is probably because it was far from the edge of the Nuna supercontinent, if such a supercontinent did exist. There is another possibility that the Earth's middle age represented a particular tectonic

  19. Two contrasting modes of continental break-up associated with the formation of the Paleo- and Neo-Tethys in Iran: Implications for petrological and geodynamic evolution at a regional scale (United States)

    Saccani, Emilio; Marroni, Michele; Pandolfi, Luca; Allahyari, Khalil; Azimzadeh, Zohreh


    In Iran, two partial ophiolitic sequences, which are broadly classifiable as "Continental Margin Ophiolite" (CMO), record the tectono-magmatic processes that occur during the continental break-up preceding oceanic basin formation. They are represented by: (1) the Early Carboniferous Misho Mafic Complex (NW Iran) and (2) the Triassic sequences in the Kermanshah ophiolite (Zagros Belt) that are associated with the formation of the Paleo- and Neo-Tethys, respectively. Both CMO sequences consist of gabbros, sheeted dykes and basaltic lavas. Moreover, the Kermanshah CMO also includes exhumed sub-continental mantle lherzolites. Both sequences include rocks showing variable incompatible element enrichments, ranging from N-MORB to E-MORB, P-MORB and alkaline basalt compositions and are interpreted to have formed from partial melting a depleted MORB-type mantle source (DMM) metasomatized by variable proportions of plume-type, enriched components. Nonetheless, geological evidence and petrogenetic modeling suggest that the continental break-up of the Paleo- and Neo-Tethys occurred in two quite different ways. The initial rift-drift tectonics of the Paleo-Tethys was triggered by a mantle plume activity and was strongly affected by plume-related magmatism and associated lithospheric weakening at a regional scale. This conclusion is consistent with the models proposed for the Paleo-Tethys margins in central-eastern Asia. In contrast, the initial rift-drift tectonics of the Neo-Tethys was characterized by a type of rifted margin, which is intermediate between the amagmatic type (Ligurian Tethys type) and the magmatic, plume-influenced type. Indeed, likewise the Ligurian Tethys, rifting occurred through passive (possibly, asymmetric) extension, which led to the exhumation of the sub-continental mantle. Meanwhile, high Sm/Yb rocks formed at the continent-ocean transition zone by partial melting of a DMM source locally bearing sub-continental garnet-pyroxenite relics. However, in

  20. Late Mesoproterozoic to Early Paleozoic history of metamorphic basement from the southeastern Chiapas Massif Complex, Mexico, and implications for the evolution of NW Gondwana (United States)

    Weber, Bodo; González-Guzmán, Reneé; Manjarrez-Juárez, Román; Cisneros de León, Alejandro; Martens, Uwe; Solari, Luigi; Hecht, Lutz; Valencia, Victor


    In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined "El Triunfo Complex" located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at 650 °C and 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian ( 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from 457 to 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of

  1. The Dovyren Intrusive Complex (Southern Siberia, Russia): Insights into dynamics of an open magma chamber with implications for parental magma origin, composition, and Cu-Ni-PGE fertility (United States)

    Ariskin, Alexey; Danyushevsky, Leonid; Nikolaev, Georgy; Kislov, Evgeny; Fiorentini, Marco; McNeill, Andrew; Kostitsyn, Yuri; Goemann, Karsten; Feig, Sandrin T.; Malyshev, Alexey


    The Dovyren Intrusive Complex (DIC, Northern Baikal region, 728 Ma) includes the layered dunite-troctolite-gabbronorite Yoko-Dovyren massif (YDM), associated mafic-ultramafic sills, and dykes of olivine-rich to olivine-free gabbronorite. Major rock types of the DIC are presented, including a diversity of olivine orthocumulates to olivine-plagioclase and gabbroic adcumulates, carbonate-contaminated ultramafics and Cu-Ni-PGE mineralisation. Detailed comparisons of complete cross-sections of the YDM in its centre and at the NE and SW margins demonstrate differences in the cumulate succession, mineral chemistry, and geochemical structure that likely reflect variations in parental magma compositions. Combining petrochemical reconstructions for most primitive rocks and calculations using the COMAGMAT-5 model, it is shown that the central and peripheral parts of the intrusion formed by olivine-laden parental magmas ranged in their temperatures by 100 °C, approximately from 1290 °C ( 11 wt% MgO, olivine Fo88) to 1190 °C ( 8 wt% MgO, olivine Fo86). Thermodynamic modelling suggests that the most primitive high-Mg magma was S-undersaturated, whereas its derivatives became S-saturated at T temperatures, producing Cu-rich sulphide precursors, which gave rise to the 'platinum group mineral' (PGM-containing) troctolite and low-mineralised PGE-rich anorthosite in the Main Reef. The geochemical structure of the YDM demonstrates C-shaped distributions of TiO2, K2O, P2O5, and incompatible trace elements, which are 3-5 fold depleted in the cumulate rocks from the inner horizons of the intrusion with respect to the relatively thin lower and upper contact zones. In addition, a marked misbalance between estimates of the average composition of the YDM and that of the proposed olivine-laden parental magmas is established. This misbalance reflects a significant deficit of the YDM in incompatible elements, which argues that 60-70% of basaltic melts had to have been expelled from the

  2. Origin of the Eastern Galicia Magnetic Anomaly (NW Spain). Implications for the Origin of Magnetic Anomalies in the Central Iberian Arc (United States)

    Ayarza, P.; Martinez-Catalan, J. R.; Villalain, J. J.; Alvarez Lobato, F.; Martin Paramio, M.; Rodriguez Gómez, S.; Sanz López, M.


    The aeromagnetic map of Iberia features outstanding anomalies that have been key to define the Central Iberian Arc, a late-orogenic orocline in the western part of the Variscan belt. The most studied of them is the EGMA (Eastern Galicia Magnetic Anomaly), which follows the Lugo-Sanabria extensional dome and is probably associated with it. Among the existing models of this anomaly, those relating it with magnetite-rich inhomogeneous granites and migmatites formed during late-Variscan extension seem to be more plausible ones. However, this and other interpretations involving deep-seated mafic/ultramafic bodies lack resolution as they are based on the aeromagnetic dataset. New ground magnetic data have been acquired in the northern part of the Xistral Tectonic Window, at the core of the Lugo dome where its deepest rocks crop out. The resulting maps show that the anomaly ranges ~1000 nT (vs. 190 nT on the aeromagnetic map) and that the most important maxima lie on top of extensional detachments located on high-grade metasediments or inhomogeneous granites. 2D forward modeling indicates that the magnetization is carried by upper Neoproterozoic and early Cambrian metasediments, partially melted during late-Variscan high-T and low-P metamorphic event linked to the extensional collapse. Furthermore, the anomaly maxima are spatially related with detachments, where the metasediments were strongly sheared. Therefore, the P-T, redox and fluid pressure conditions necessary for the formation of magnetite seem related with the extensional process and the dynamics of its structures. Many magnetic anomalies of the Central Iberian Arc lie on top of Variscan extensional domes and accordingly may have a similar origin. Special attention is paid to the Gredos Magnetic Anomaly, coincident with the batholith of the same name. Preliminary magnetic mapping and modeling indicate that the anomaly is previous to the intrusion of the Jurassic Alentejo-Plasencia dyke and to the tardi

  3. Subduction-related shoshonitic and ultrapotassic magmatism: a study of Siluro-Ordovician syenites from the Scottish Caledonides