Charnockite genesis across the Archaean–Proterozoic terrane boundary in the South Indian Granulite Terrain: Constraints from major–trace element geochemistry and Sr–Nd isotopic systematics     

J.K. Tomson  Y.J. Bhaskar Rao  T. Vijaya Kumar  J. Mallikharjuna Rao 《Gondwana Research》2006,10(1-2):115

Major, trace element compositions and Sr–Nd isotopic characteristics of charnockitic gneisses from the Southern Granulite Terrain (SGT), South India are presented. The study region encompasses the central segment of the Cauvery Shear Zone system (CSZ) and regions within the Madurai Block (MB) immediately south of it (designated here as the CSZ/MB and MB domains). Differences in the compositions and source characteristics between charnockitic rocks of the CSZ vis-à-vis those of the CSZ/MB and MB regions are highlighted. Foremost, the charnockites and enderbites of the CSZ show highly fractionated REE patterns with positive Eu-anomalies, depleted HREE, Y and near chondritic εNd₀ and initial-⁸⁷Sr/⁸⁶Sr at ca. 2.5 Ga, consistent with hydrous partial melting of amphibolitic crust with residual garnet and hornblende for the parental melts. By contrast, modeled at ca. 1.8 Ga and 0.8 Ga, the CSZ/MB and MB charnockitic rocks, which show a wider range of Ti and P, relatively lower degree of HREE depletion, commonly negative Eu-anomalies and undepleted Y, present clear evidence for involvement of Archaean crustal components in sources of their magmatic protoliths. There is also evidence for significant intracrustal melting processes within a thickened crust at elevated temperatures between 800 and 1000 °C. Implications to the controversial Archaean–Neoproterozoic terrane boundary problem of the SGT are discussed.  相似文献   

Erratum to “Geochronology of the Khondalite Belt of Trivandrum Block, Southern India: Electron Probe Ages and Implications for Gondwana Tectonics” [Gondwana Research Volume 9 (2006) 261–278]     

M. Santosh  T. Morimoto  Y. Tsutsumi 《Gondwana Research》2006,10(1-2):203

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The timing of ultrahigh-temperature metamorphism in Southern India: U–Th–Pb electron microprobe ages from zircon and monazite in sapphirine-bearing granulites   总被引：1，自引：8，他引：1  

M. Santosh  A.S. Collins  I. Tamashiro  S. Koshimoto  Y. Tsutsumi  K. Yokoyama 《Gondwana Research》2006,10(1-2):128

We report here U–Pb electron microprobe ages from zircon and monazite associated with corundum- and sapphirine-bearing granulite facies rocks of Lachmanapatti, Sengal, Sakkarakkottai and Mettanganam in the Palghat–Cauvery shear zone system and Ganguvarpatti in the northern Madurai Block of southern India. Mineral assemblages and petrologic characteristics of granulite facies assemblages in all these localities indicate extreme crustal metamorphism under ultrahigh-temperature (UHT) conditions. Zircon cores from Lachmanapatti range from 3200 to 2300 Ma with a peak at 2420 Ma, while those from Mettanganam show 2300 Ma peak. Younger zircons with peak ages of 2100 and 830 Ma are displayed by the UHT granulites of Sengal and Ganguvarpatti, although detrital grains with 2000 Ma ages are also present. The Late Archaean-aged cores are mantled by variable rims of Palaeo- to Mesoproterozoic ages in most cases. Zircon cores from Ganguvarpatti range from 2279 to 749 Ma and are interpreted to reflect multiple age sources. The oldest cores are surrounded by Palaeoproterozoic and Mesoproterozoic rims, and finally mantled by Neoproterozoic overgrowths. In contrast, monazites from these localities define peak ages of between 550 and 520 Ma, with an exception of a peak at 590 Ma for the Lachmanapatti rocks. The outermost rims of monazite grains show spot ages in the range of 510–450 Ma.While the zircon populations in these rocks suggest multiple sources of Archaean and Palaeoproterozoic age, the monazite data are interpreted to date the timing of ultrahigh-temperature metamorphism in southern India as latest Neoproterozoic to Cambrian in both the Palghat–Cauvery shear zone system and the northern Madurai Block. The data illustrate the extent of Neoproterozoic/Cambrian metamorphism as India joined the Gondwana amalgam at the dawn of the Cambrian.  相似文献   

Early Paleozoic granitoids of the Aqtau-Dzungar microcontinent (Central Kazakhstan)     

K. E. Degtyarev  K. N. Shatagin  A. B. Kotov  E. B. Sal’nikova  M. V. Luchitskaya  S. Z. Yakovleva  Yu. V. Plotkina  A. M. Fedoseenko 《Doklady Earth Sciences》2006,411(1):1204-1208

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The seismic hazard assessment of the Dead Sea rift, Jordan   总被引：1，自引：0，他引：1  

Abdallah S. Al-Zoubi  Z.S.H. Abu-Hamatteh  Amrat Abdealkaderer 《Journal of African Earth Sciences》2006,45(4-5):489-501

The Dead Sea fault system and its branching faults represent one of the most tectonically active regions in the Middle East. The aim of this study is to highlight the degree of hazards related to the earthquake activities associated with the Dead Sea rift, in terms of speculating the possible future earthquakes. The present investigation mainly is based on available data and vertical crustal modeling of Jordan and the Dead Sea model for the Dead Sea basin with particular emphasis of the recent earthquake activities, which occurred on December 31st, 2003 (Mc = 3.7), February 11th, 2004 (strongest Mc = 4.9 R), and March 15th, 2004 (Mc = 4). The present research examines the location of the strong events and correlates them with the various tectonic elements in the area. The source mechanism of the main shock and the aftershock events is also examined. The analyses were based on the available short period seismogram data, which was recorded at the Natural Resources Authority of Jordan, Seismological Observatory. The seismic energy appears to have migrated from the south to the north during the period from December 31st up to March 12th, where the released seismic energy showed a migration character to the southern block of the eastern side of the Dead Sea, which led the seismic event to occur on March 15th.  相似文献   

Tin mineralization in the Dajing tin–polymetallic deposit, Inner Mongolia, China     

Y.W. Wang  J.B. Wang  L.J. Wang  Y.Z. Chen 《Journal of Asian Earth Sciences》2006,28(4-6):320-331

Dajing is a large-scale tin–polymetallic deposit that hosts the largest tin mine in North China. It is a hydrothermal vein-type deposit containing Sn, Cu, Pb, Zn, Ag, and minor components Co and In. The deposit consists of more than 690 veins hosted within Upper Permian sedimentary rocks.Three mineralization stages and six ore types are recognized with cassiterite constituting the dominant tin mineral. The SnO₂ content of cassiterite increases in the sequence of mineralization stages shear-deformation→cassiterite–quartz→cassiterite–sulfide (or chalcopyrite–pyrite) stage, while the content of FeO, TiO₂, Nb₂O₅, Ta₂O₅, and In₂O₅ tends to decrease with increases in NiO and Ga₂O₅. It is considered that the negative correlation between SnO₂ and FeO, Nb₂O₅, Ta₂O₅, and In₂O₅ results from elemental substitutions. The early stage cassiterite is much richer in Ta and the later stage cassiterite is much poorer in Ti and Fe than is usual in hydrothermal vein type tin deposits. This is interpreted to indicate that the component of early stage cassiterite reflects a granitic magma source while the composition of later stage cassiterite has a more obvious strata source. The compositional variation of cassiterite corresponds to decreasing crystallization temperatures within each stage and between sequential stages with time. The characteristics of REE in cassiterite from two stages are in accord with that of subvolcanic rocks and the Linxi formation. It suggests that tin transported during the cassiterite–quartz stage may have originated from subvolcanic dikes (e.g., dacite porphyry), while in the cassiterite–sulfide stage, tin may have been derived from wallrock (e.g. siltstone) of the Upper Permian-age Linxi Formation.  相似文献   

Contamination of Silurian volcanic rocks in the Tagil synform by Precambrian zircon     

V. N. Puchkov  O. M. Rosen  D. Z. Zhuravlev  E. V. Bibikova 《Doklady Earth Sciences》2006,411(2):1381-1384

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Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. I: Constraints on microcrystalline CaCO₃ precipitation     

JAMES W. BISHOP  DAWN Y. SUMNER 《Sedimentology》2006,53(5):1049-1068

Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO₃ precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO₃ evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.  相似文献   

Radiolaria – Siliceous plankton through time     

Peter O. Baumgartner 《Swiss Journal of Geoscience》2006,99(1):III-V

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Indium Enrichment in the Meng'entaolegai Ag-Pb-Zn Deposit, Inner Mongolia, China   总被引：3，自引：0，他引：3  

Qian Zhang    Xiaoqing Zhu    Yuliang He  Junjie Jiang  Dapeng Wang 《Resource Geology》2006,56(3):337-346

Abstract. The Meng'entaolegai In-rich Ag-Pb-Zn deposit is located in the eastern part of Inner Mongolia. It is one of the In-richest deposits in China. Large amounts of quartz and sulfide minerals constitute a hydrothermal quartz-sulfide vein deposit within a Hercynian acidic granite massif, which occupies an area of about 400 km². Thirty-six orebodies, controlled strictly by the E-W trend faults, are found in the orefield of 6 km in length from east to west and 200 to 1,000 m in width from south to north. The ore minerals are mainly galena, sphalerite and pyrite, and subordinate chalcopyrite, arsenopyrite, cassiterite and stannite with many Ag-minerals. The gangue minerals are mainly quartz, calcite, sericite and chlorite. Economic components of the deposit are dominated by Pb andZn (reserves of Pb and Zn are 0.17 Mt and 0.37 Mt, and their grades are 1 % and 2.3 %, respectively), with Ag, Sn, In and Cd (1,800 t Ag, >2,000 t Sn, >500 t In and 1,800 t Cd) as by-products. Indium is highly enriched in ores and its contents are 9 to 295 ppm in ores and 85 to 2,660 ppm in sphalerite. Analytical results show that the ore-forming fluid of this deposit contains 0.8–3.5 ppm In and 4–36 ppm Sn, and the two elements show a very good positive correlation with a correlation coefficient of 0.8672, while the correlation between In and Zn in the ore-forming fluids, with a correlation coefficient of 0.5723, is not as good as that between In and Sn. This indicates that indium has an affinity with tin in the ore-forming fluids. The authors think that this is probably the main reason why those In-rich deposits spread over the world are simultaneously enriched in tin.  相似文献