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1.
Ion-microprobe analysis of zircons from an andalusite-bearing orthogneiss within the major Alpujárride nappe complex in the central part of the Betic Cordilleras has yielded a Hercynian age of 285?±?5 (2σ) Ma for euhedral rims, interpreted as the magmatic age of the andalusite-bearing biotite granite parent rock for the gneisses. Zircon age zoning systematics suggest a Paleozoic sedimentation age for the parent material for the anatectic source rock. Zircon cores represent several groups of ages: (1) Archean, c. 2.7?Ga; (2) Early Proterozoic, 2.2–2.0?Ga; (3) Middle Proterozoic, 1.1–0.9?Ga; (4) Pan-African, 0.8–0.5?Ga; including a well-defined event at 612?±?13 (2σ) Ma. Paragenetic and textural relations indicate that gneissification took place during a high-P (12–13?kbar) low-T (450–500?°C) collisional event during which the primary Alpine nappe pile was produced. The second and final Alpine tectono-metamorphic event led to reorganization of the primary nappe pile by extensional tetonics with coeval very fast rock uplift and cooling (from c. 8? to c. 1?kbar and c. 600 to 100?°C within the period 19.5–18.5?Ma). The fast uplift/cooling stage was triggered by slab break-off which is thought to have induced diapiric underplating by high-T asthenospheric material. This may have heated the collisional wedge, causing thermal weakening which might have advanced the late stage fast uplift/cooling. The Alpine events did not leave a zircon crystallization record. The inherited, Archean–Pan-African zircon age pattern corresponds to that established for the Hercynian basement in central and southern Europe which is considered as reworked Gondwana crust. Deeper levels of core complexes within the Betic-Rif belt thus belong to the pre-Triassic basement of the Tethyan realm (Betic-Ligurian lithosphere) and represent reworked material ultimately derived from Archean and Proterozoic rock complexes from the Gondwana crustal domain. This study implies that thermobarometry of rock complexes which went through several phases of tectono-metamorphic reworking may render ambiguous results if based upon field observations and petrography alone. Zircon ion-microprobe dating may provide additional constraints required to arrive at a feasible tectono-metamorphic history, that is P-T-t trajectory, for such rock complexes.  相似文献   

2.
The Enshi area, Hubei Province in China, is a typical seleniferous environment, where seleniferous carbonaceous shale and carbonaceous siliceous rocks of Permian widely occur. In the 1960＇s, the first selenosis case in the human population in the world had even brought out at Yutangba Village, Shuanghe community, which resulted in move-off all local residenters The Enshi area possesses the advantageous natural conditions to develop Se-hyperaccnmulator. The selenosis case of human population may be related to having eaten the wild vegetable hyperaccumulating selenium. Mao Dajun （1997） found that the most seleniferous plant was cabbage in the Enshi area which contains Se 224.30 mg/kg. In order to find out Se-hyperaccnmulator in China as soon as possible, the present research made a lot of work on many numbers of wild plants which grow in Enshi, Hubei Province, China. Finally, we found Thlaspi arvenst L., the first Se-hyperaccumulator of China at Yutangba Village. In this plant, Thlaspi arvenst L., the contents of selenium （DW） are 802-870 mg/kg （the average 843 mg/kg） for the whole plant, 1121 mg/kg for root, 511 mg/kg for stem and 1427 mg/kg for leaf, respectively. The newly found Thlaspi arvenst L. by us is the most seleniferous plant which has been found in China up to now, whose Se in its leaf is higher than the international criterion of 1000 mg/kg for Se-hyperaccnmulator.  相似文献   

3.
Conodont Evidence for the Age of the Panxian Fauna,Guizhou, China   总被引：1，自引：0，他引：1  
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4.
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5.
Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite, which have subsolidus metamorphism-deformation textures such as triple-points, cataclastic boundaries and kink-bands. Mineral chemical characteristics show that the diposide, Ti-rich paragasite and phlogopite are derived from the mantle and are the products of mantle metasomatism. Compared with normal mantle-derived spinel-lherzolites, the xenoliths are enriched in TiO2, Fe2O3, CaO, Na2O and K2O, with apparent depletion in MgO. Chondrite-normalized REE patterns and primordial-mantle normalized trace elements data show that they are enriched in REE (especially LREE) and incompatible trace elements. The petrographic, mineralogical and petrochemical characteristics indicate that the xenoliths are metasomatized mantle xenoliths, which offers the evidence for mantle metasomatism and represents the anomalous mantle beneath the Early Paleozoic rift in northern Daba Mountains. The agents of mantle metasomatism are probably derived from the rising of mantle hot plumes. The processes of metasomatism varied from limited-range fluid metasomatism in deep mantle (>90 km) to pervasive metasomatism of silicate melt. This project was financially supported by the National Natural Science Foundation of China (No. 49402035).  相似文献   

6.
Please?refer?to?the?attachment(s)?for?more?details.  相似文献   

7.
1.IntroductionTheShan--Thai-MalayBlock(STMB)isadonorcontinentalfragmentintheSWborderregionofChinaandSoutheastAsia.IthaslongbeenrecognizedasablockdisplacedfromGondwanaintheLatePaleozoic(Mitchell,1981;Cao,1986).ThePaleozoicmarinesequenceandfossilassemblagesaremarkedlydifferentfromthoseofotherChineseblockssuchasYangtze,NorthChinaandTarim,aswellaseasternChineseblocks.Instead,specificsedimentaryfactessuchasEarlyPenmanglaciomarinedeposits,Carboniferouscool-coldwaterfaunaandPenmanGlossopt…  相似文献   

8.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

9.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

10.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

11.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

12.
The Bhimtal–Naukuchiatal Lake was created due to blocking of the valley by a huge debris flow along a narrow outlet at about 40 ka BP. The lake basin was filled intermittently due to fluvio-lacustrine and colluvial processes that deposited a thick sequence of interbedded mud and gravel. In the basin fill sequence five major lithofacies, most of them divisible into subfacies, have been identified and assigned to specific depositional environments. The coarsening upward (CU) mud-silt cycles represent sedimentation in a lake setting. The clasts-and mud-supported gravels consists of fining upward (FU) and CU sequences, respectively, indicating deposition by channel processes and debris flows. Having basin wide extent, the pedogenic mottled, clayey silt unit represents an important tectonic event when the lake was temporarily drained and sediments were sub-aerially exposed. Fluctuating arid–semiarid to humid climatic conditions and repeated tectonic activity may have governed the mode of sedimentation and ultimately the basin fill history.  相似文献   

13.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

14.
Abstract

This is a scanned image of the original Editorial Board page(s) for this issue  相似文献   

15.
The Toomba flow is the youngest flow of the Nulla volcanic province, located in north Queensland. This 120?km-long flow has yielded a published 40Ar/39Ar age of 21,000?±?3000 years. In contrast, seven published conventional radiocarbon (14C) analyses of carbon-bearing material beneath the flow yielded radiocarbon ages of 16,000 to <2500?BP. These radiocarbon ages are younger than the 40Ar/39Ar age, potentially due to contamination of the charcoal by younger carbon that was not removed by the acid–base pre-treatment. We have re-examined the radiocarbon age of Toomba flow using newly sampled charcoal buried beneath the Toomba flow in combination with hydrogen pyrolysis pre-treatment and accelerated mass spectrometer (AMS) measurements. We determined a calibrated radiocarbon age of 20,815–19,726?cal BP (2σ) for the material beneath the Toomba flow. Our radiocarbon age, therefore: (1) is older than previous radiocarbon ages for the Toomba flow, (2) provides the most precise age yet available for the Toomba flow, (3) is in agreement with the 40Ar/39Ar age, and (4) validates that hydrogen pyrolysis is a robust and effective pre-treatment method, for subtropical conditions where samples are susceptible to contamination by younger carbon. The Toomba flow erupted during the Last Glacial Maximum, but the preserved surface suggests that the rate of weathering and soil formation has been almost negligible in this region, despite being situated in a subtropical climate that experiences highly variable often intense rainfall.  相似文献   

16.
ZU Bo  XUE Chunji  ZHAO Yi 《地质学报》2014,88(Z2):957-958
Please refer to the attachment(s) for more details.  相似文献   

17.
Fethiye is an important region located in the eastern part of the Mediterranean Basin.This region which is the most active part of the south-western Anatolia ex...  相似文献   

18.
In this study, reservoir temperatures of Balıkesir geothermal waters in northwestern Turkey are estimated with various geochemical models. The geothermal fluids in the region are represented by Na–SO4, Na–HCO3 and Ca–HCO3 type waters with discharge temperatures up to 98°C. It was determined that the solubility of silica in most of the waters is controlled by the chalcedony phase. Equilibrium states of the Balıkesir thermal waters studied by means of Na–K–Mg–Ca diagram, mineral saturation calculations and activity diagrams in the system composed of Na2O–CaO–K2O–Al2O3–SiO2–H2O phases approximate a reservoir temperature of about 120°C. Most of the waters are found to be equilibrated with calcite, chalcedony ± quartz and muscovite at predicted temperature ranges, similar to those calculated from the chemical geothermometers.  相似文献   

19.
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20.
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