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Xie Y.-W.,Regional Geological Survey Party | Liu H.-F.,Tibet Institute of Geological Survey | Qiangba Z.-X.,Regional Geological Survey Party | Jiang G.-W.,Tibet Institute of Geological Survey
Geological Bulletin of China | Year: 2010

Original Chaqupu Formation of Early-Middle Triassic in the Quesang area of Lhasa is composed by the lower part carbonate rocks which contain abundant Early-Middle Triassic fossils and the upper part volcanic rocks with no information on paleontology or chronology. Based on their stratigraphic overlying relationship, the volcanic rocks were determined as the upper part of Chaqupu Formation, and its age was determined to be Early-Middle Triassic, which has become a classical formation sequence locally and been widely used. Recendy, SHRIMP U-Pb zircon dating was carried on the zircons of basaltic andesites of the volcanic rocks in the upper part of original Chaqupu Formation. The dating results show that these rocks were formed in Early Triassic (248 Ma±4 Ma), so the original Chaqupu Formation is a inversion tectonic, and the volcanic rocks used be under the carbonate rocks and contact conformably with Lielonggou Formation of Permian, which is a trustworthy evidence of the continuous deposition in this area from Permain to Triassic and further shows that this area existed magmatic activities in Early Triassic. The determination of the sequence of Chaqupu Formation has important significances in studying the evolution process of the Gangdise area.

Tang Y.,Chinese Academy of Geological Sciences | Zhai Q.,Chinese Academy of Geological Sciences | Liu T.,CAS Institute of Geology and Geophysics | Wang J.,Chinese Academy of Geological Sciences | And 3 more authors.
Geological Bulletin of China | Year: 2015

Located in the middle part of the Bangong Co-Nujiang River suture zone, the Daru Co granite porphyry was intruded into the ophiolite of this suture zone. In this study, the authors performed detailed field investigation, petrological and geochemical study, and zircon U-Pb and Hf isotopic analysis of the Daru Co granite porphyry. Using the LA-ICP-MS technique, the authors obtained the U-Pb age of 110±1 Ma for the Daru Co granite porphyry, and this age is interpreted as the formation age of granite porphyry. The Daru Co granite porphyry has pronounced negative zircon ε Hf(t) values in the range of -5.5~-2.6. Whole-rock geochemical data show that it is characterized by high K calc-alkaline series, A/CNK higher than 1.1, enrichment of LREE, Rb, Ba, Pb and Th, and depletion of Ta, Nb and Ti. All samples show negative Eu anomaly. These features indicate that the Daru Co granite porphyry belongs to the peraluminous S-type granite. It is considered that the Daru Co granite porphyry might have been formed by partial melting of the thickened continental crust in a syn-collision setting, and it was probably related to the hot asthenosphere upwelling under the Lhasa block. The ocean basin had been closed and continental collision started before 110Ma in the middle part of the Bangong Co-Nujiang River suture zone. Furthermore, the ophiolite in this area should be formed before 110Ma in terms of the relationship between the Daru Co granite porphyry and ophiolite. © 2015, Science Press. All right reserved.

Qiangba Z.,Regional Geological Survey Party | Wu H.,Jilin University | Gesang W.,Regional Geological Survey Party | Ciren O.,Regional Geological Survey Party | And 3 more authors.
Geological Bulletin of China | Year: 2016

The Dongqiao area is located across Bangong Co-Nujiang River suture zone (BNSZ) and the southern Qiangtang terrane. The study area has widely exposed diverse rock types such as diabases, rhyolites and granodiorites. In this paper, the authors report the LA-ICP-MS zircon U-Pb age and whole-rock major and trace element composition data of the diverse Early Cretaceous magmatic rocks from Dongqiao. The diabase sample yielded a zircon U-Pb age of 138. 7±1.0 Ma, and the zircons from rhyolite yielded an age of 110.4±0.4 Ma, indicating that the magmatic rocks in Dongqiao formed in two periods of magmatism. According to geochemical characteristics of the rocks, the diabases were produced by partial melting of the mantle, and the granodiorites by partial melting of ancient lithospheric mantle that had been modified by subduction-related components. In addition, the geochemical data indicate that rhyolites can be divided into two types of high Sr and low Sr rhyolites. Low Sr rhyolites were formed by partial melting of ancient lithospheric mantle, and the melt subsequently underwent intense fractional crystallization. High Sr rhyolites had an affinity with adakites, which were derived from partial melting of thickened lower crust. The new data obtained by the authors, together with recently published data, led the authors to develop a model of bidirectional subduction and subsequent slab break-off of the lith-osphere of the Bangong-Nujiang Ocean which can explain the two magmatic events in the region from BNSZ to the southern Qiangtang terrane. Research on high Sr rhyolites indicates that the extensive magmatism and continent-continent collision contributed significantly to the crustal growth after the closure of Bangong-Nujiang Ocean in Early Cretaceous. © 2016, Science Press. All right reserved.

Xie C.M.,Jilin University | Li C.,Jilin University | Su L.,China University of Geosciences | Wu Y.W.,Jilin University | Xie Y.W.,Regional Geological Survey Party
Science China Earth Sciences | Year: 2013

To better understand the Pan-African-early Paleozoic tectonothermal events of the Nyainrong microcontinent and the constraints on its tectonic evolution, here we report the results of zircon LA-ICP-MS U-Pb dating and geochemical features of Amdo gneiss in the Nyainrong microcontinent. The outcrops of Amdo gneiss is about 30 km south of Amdo County in northern Tibet. The field occurrence, mineral composition, textural characteristics, and whole-rock geochemical features of the four gneiss samples indicate the protolith of the gneisses is intermediate-acid intrusive rock. Gneiss zircon trace element tracing and genetic analysis shows that zircon has typical characteristics of magmatic zircon. The 206Pb/238U concordant age of zircon is 505-517 Ma, corresponding to the Middle-Late Cambrian, which is the formation age of the protolith. The samples have characteristics of high silicon, alkali-rich, alkalic rate AR =1.73-3.7, the differentiation index DI = 70.78-90.28; rock aluminum saturation index ranges from 1.02 to 1.05, FeO / MgO ranges from 2.63 to 4.50, 10000 × Ga/Al ranges from 2.12 to 2.41, and P2O5 and Al2O3 content decreased with SiO2 increasing. Th and Y contents have a good positive correlation with Rb content; the genetic type of protolith of the gneiss is the differentiation of subalkaline over aluminum I-type granite. Combined with regional data, the tectonic setting of the Amdo gneiss protolith is closely related to the collision orogenic process. The preliminary view is that the Middle-Late Cambrian magmatic events developed on the microcontinent could be the result of Andean-type orogeny along the Gondwana super-continental margin after the end of the Pan-African orogeny. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg.

Xie C.M.,Jilin University | Li C.,Jilin University | Su L.,China University of Geosciences | Dong Y.S.,Jilin University | And 2 more authors.
Acta Petrologica Sinica | Year: 2013

This paper reports the results of LA-ICP-MS U-Pb dating of the zircon in newly discovered high-pressure granulite, and the Ar-Ar isotopic dating of biotite in granitic gneiss of the surrounding rock of high-pressure granulite on Nyainrong microcontinent. There are two types of zircon in high-pressure granulites, the first type is a core-edge microstructure, the zircon residualed cores with typical features of magmatic zircon, zircon U-Pb age is 541 ± 8Ma ∼ 834 ± 11 Ma; the second zircon with typical structural characteristics of the causes metamorphic zircon, zircon U-Pb age is 179. 0 ± 1. 7Ma. In granite gneiss the biotite Ar-Ar plateau age of 166. 7 ± 1. 1 Ma. Age data show both granulite and its surrounding are with the Pan-African age information, granulite protolith experienced a Late Proterozoic-Early Paleozoic orogeny, and in the Early-Middle Jurassic occurred peak high-pressure metamorphic role in transformation, the metamorphic event may be related to a major role in collision which occurred in Bangong Co-Nujiang River suture zone in region it may represent the Nyainrong microcontinent and Qiangnan plate put together. With the Early-Middle Jurassic magmatism, granulite and its surrounding rapidly exhumation, exhumation of the time span is about 13Myr and at about 166. 7Ma uplift to shallow parts of the crust or near the surface.

Zhang X.Z.,Jilin University | Dong Y.S.,Jilin University | Xie C.M.,Jilin University | Xie Y.W.,Regional Geological Survey Party
Acta Petrologica Sinica | Year: 2010

The high-pressure gramdite (HP-gramdite) newly found is hosted in Nierong mieroeontinent which is located in Bangong Co-Nujiang plate suture zone. Through the intensive study on petrology, mineralogy and metamorphism, we attribute that the HP-granulite was made up by the early mineral assemblages of garnet (Grt) + clinopyroxene (Cpx) + plagioclase (PI) and the massive later retrograde mineral assemblages amphibole ( Hb) + plagioclase ( PI) . Garnets in high-presslire granulites are surrounded by plagioclase which forms the corona. Thermobarometric estimates based on equilibrium texture and mineral chemistry indicate that the early mineral assemblages formed at T = 790 ∼ 840°C, P = 11 ∼ I5kbar, and the later retrograde assemblages experienced near-isothermal decomposition to T = 700 ∼ 730°C, P = 4. 6kbar. It may be the product of the Yanshanian closure of Bangong Co-Nujiang plate suture zone or early collision event. Further study on the HP-granulite is of great significance to recognize the tectonic evolution of Bangong Co-Nujiang plate suture zone or re-recognize the tectonic framework of Tibetan Plateau, especially the Gangdese Terrane.

Zhai W.,Sun Yat Sen University | Zhai W.,Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering | Sun X.,Sun Yat Sen University | Sun X.,Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering | And 6 more authors.
Ore Geology Reviews | Year: 2014

The southern Tibet AuSb metallogenic belt in the Himalayan orogen consists of more than 50 gold, gold-antimony and antimony lode deposits, and associated placer gold deposit. The deposits are hosted in a Mesozoic metamorphosed turbidite sequence of the Indian passive continental margin. The Zhemulang Au deposit, Mazhala AuSb deposit, and Shalagang Sb deposit are three typical examples of such epizonal orogenic deposits. At Zhemulang, gold-bearing quartz veins occur in the Upper Triassic Songre Formation, consisting of carbonaceous phyllite and slate. Ore minerals are native gold, pyrite, galena, chalcopyrite, and limonite. At Mazhala, the gold- and stibnite-bearing quartz vein orebodies are hosted in Lower to Middle Jurassic slate, interlayered with metastandstone, metasiltstone, and limestone of the Lure Formation. Ore minerals are native gold, stibnite, pyrite, arsenopyrite, and trace amount of cinnabar. At Shalagang, the host rocks are Lower Cretaceous sandstone, siltstone, muddy limestone, and chert of the Duojiu Formation. Orebodies consist mainly of stibnite-bearing quartz veins and locally altered fault breccia. Ore minerals are stibnite, cinnabar, valentinite [Sb2O3], limonite, and trace amount of pyrite, arsenopyrite, and realgar. For the three deposits, the wallrock alteration has produced the minerals silica, carbonates, white mica, sulfide and chlorite. The three deposits have a similar element associations, but with a few slight variations. The Zhemulang, Mazhala, and Shalagang deposits, in order of element enrichments relative to crustal abundance, are anomalous in Au, Sb, Te, Bi, As, Pb, Ag, and W; Sb, Au, Te, As, Pb, Bi, Ag and W, to Sb, Te, As, Au, Hg, W, Pb, and Ag, respectively, and all depleted in Cu, Zn, Sn, and Mo.Various aqueous, carbonic, and hydrocarbon fluid inclusions were recognized in quartz and/or stibnite at the three deposits. These include type 1a one-phase aqueous inclusions, type 1b two-phase aqueous inclusions, type 2a carbonic inclusions, type 2b aqueous-carbonic inclusion, and rare type 3 hydrocarbon inclusions that include two-phase hydrocarbon inclusions (type 3a) and dark one-phase hydrocarbon inclusions (type 3b). The three deposits have the similar low-salinity H2OCO2CH4N2 ore fluids with trace amounts of hydrocarbons. For the Zhemulang, Mazhala, and Shalagang deposits, the salinities of aqueous inclusion range mainly between 3.3 and 6.4wt.% NaCl equiv., 2.5 and 4.9wt.% NaCl equiv. and 4.1 and 6.4wt.% NaCl equiv., respectively. The ore-forming temperatures vary mainly from 180 to 320°C, 160 to 300°C and 140 to 240°C, respectively. The estimated mineralization depths are 4 to 6km, 3 to 5km, and 1 to 4km of the epizonal environment, respectively. The different mineralization temperatures and pressures led to the different element enrichments at the three deposits.For the Zhemulang, Mazhala and Shalagang deposits, ore fluid isotopic compositions are δDH2O -107.5 to -36.7‰ and δ18Ofluid 2.8 to 8.2‰, δDH2O -119.0 to -72.7‰ and δ18Ofluid 7.5 to 16.2‰, and δDH2O -173.4 to -139.2‰ and δ18Ofluid 7.5 to 12.3‰, respectively; δ13Cfluid values are -11.7 to -9.6‰, -3.5 to -2.5‰, and -6.5 to -5.1‰, respectively; and δ34S values are -4.0 to -1.1‰, -0.8 to 2.3‰, and -3.9 to 2.1‰, respectively. The ore-forming fluids were partly derived from metamorphic devolatilization of immediate or deeper level country rocks, with a deposit's corresponding metamorphic degree controlling the fluid PTX. The ore-forming fluid for Zhemulang, Mazhala, and Shalagang consisted of predominantly metamorphic water with minor involvement of meteoric water, a mixture of metamorphic fluid and meteoric water, and predominantly meteoric water, respectively. Ore metals were derived from country rocks, including synsedimentary Sedex-like sulfide layers in the Jurassic strata observed at the Mazhala AuSb deposit. Among three deposits, the variation of δ13Cfluid and δ34S reflects the fact that the Zhemulang Au deposit formed from a relatively high content of organic carbon and low f{hook}O2 fluid, the Mazhala AuSb deposit from a relatively low content of organic carbon and high f{hook}O2 fluid, and the Shalagang Sb deposit from an intermediate content of organic carbon and f{hook}O2 fluid. Fluid immiscibility was the main mechanism for ore metal precipitation at all three deposits. The vertical zonation of Au, AuSb, and Sb mineralization suggests that additional gold resources may exist below the antimony or gold-antimony orebodies. Stream sediment and soil geochemical surveys and the occurrence of placer gold prospects are effective for identifying areas of orogenic gold and antimony deposits in the Himalayan and other orogens. © 2013 Elsevier B.V.

Xie L.,Chengdu University of Technology | Dun D.,Regional Geological Survey Party | Zhu L.-D.,Chengdu University of Technology | Ni M.-C.,Regional Geological Survey Party | And 5 more authors.
Geology in China | Year: 2015

Early Cretaceous granites are widely distributed in northern Gangdise, Tibet. The Zhaduding intrusive body, which belongs to monzogranite in lithology, is widely distributed and occurs in the form of batholith, being a typical case of the granites. Petrogeochemically it is characterized by high SiO2(70.05%-74.97%) and K2O (4.09%-5.35%), low CaO (0.93%-2.19%), TiO2 (0.22%-0.52%) and Al2O3 (12.81%-14.24%). Moreover, it belongs to metaluminous or weak peraluminous (A/CNK=0.99-1.06) high-K calc-alkaline series. The rocks are characterized by high REE content (Σ REE=199.36 × 10-6-247.91 × 10-6), rich LREE relative to HREE (LREE/HREE=5.82-6.88), and significant negative Eu anomalies (δEu=0.30-0.45). Chondrite-normalized REE patterns exhibit V-type with slight right-oblique feature. Trace elements show that the rocks are enriched in Rb, Th, K, Zr and Hf and depleted in Nb, Ta, Sr, Ba, P and Ti, with average (Zr+Nb+Ce+Y) 427.63. Bulk-rock zircon saturation temperature (828-838°C) shows that the temperature of magma formation was pretty high. The petrogeochemical characteristics show that the Zhaduding rock body is A-type granite. The LA-ICP-MS zircon U-Pb age of 103.8±1.0Ma indicates that Zhaduding rock body was formed in late Early Cretaceous, and is located in the post-collisional A2-type granite area in discrimination diagrams. It was formed by a certain degree of mixing of the lithosphere mantle and the crustal partial melts, resulting from asthenosphere material upwelling in the postcollision extensional setting.

Dai Z.-M.,Chengdu University of Technology | Sun C.-M.,Chengdu University of Technology | Zhang K.-Z.,Regional Geological Survey Party | Li Z.-J.,Regional Geological Survey Party
Geology in China | Year: 2011

The granitoid intrusions in the eastern part of the Songpan-Garzê terrane were mainly formed in Late Indo-Chinese-Early Yenshanian period, and the Four-Girl Mountain Granite(FGMG)is one of these intrusions. Zircons from FGMG commonly have characteristics of magma zircons. LA-ICP- MS zircon U-Pb dating of 23 zircon grains from biotite granodiorite of the FGMG yielded a weighted 206Pb/238U mean age of (191±l)Ma (Early Yenshanian), which is considered to be the magmtic crystallization age of FGMG. This age has great significance in understanding the initial formation time of the Longmenshan fault belt. The NW-trending Jingchuan-Lixian tectono-magmatic belt defined during the previous regional geological survey can't represent the product of the collision between he Yangtze massif and the Songpan -Garzê terrane, although the major axes and mineral directions of most single granitic masses assume parallel NW-trending arrangement in the Songpan-Garzê terrane. Therefore, the NE-trending Douhu-Jingchuan-Xiaojing-Heishui tectono-magmatic belt should be reasonably established. The Four-Girl Mountain Granite (FGMG)pluton is a representative granitic mass and represents the product of partial fusing in the low velocity layer existent in the middle-lower crust of the Songpan-Garzê terrane when the Yangtze massif was wedged into the Songpan-Garzê terrane along the Longmenshan structural belt. Deep geophysical exploration shows that the Four-Girl Mountain area has "roots of mountain", which are made up of many great granitic plutons. These roots of mountain did not cause the Wenchuan Earthquake, but might have weaken the damage influence during the northwestward seismic wave propagation towards the Tibetan Plateau, and probably prevented the southwestward expansion of the Longmenshan fault belt when the Wenchuan Earthequake occurred. In other words, the probability of aftershocks that occurred along the southwest section of the Longmenshan fault belt was reduced by the roots of mountain.

Zeng Q.-G.,CAS Guangzhou Institute of Geochemistry | Wang B.-D.,Regional Geological Survey Party | Wang B.-D.,Chengdu Institute of Geology and Mineral Resources Geological Survey | Qiangba Z.-X.,Regional Geological Survey Party | And 3 more authors.
Geological Bulletin of China | Year: 2010

The granitic gneiss was identified from the Jitang Group in the Leiwuqi area, eastern Tibet. All zircons from the granitic gneiss have shown regular oscillatory magmatic zoning and high Th/U ratios (≤ 0.49), being consistent with those of magmatic zircons. So we quoted 206Pb/238U ages to indicate crystallization age of the granitic magma. Analysis of Cameca zircon U-Pb isotope yielded a weighted mean 206Pb/238U age of 282.1 ± 0.9 Ma. The age of granitic gneiss implies that this magmatism event was triggered by the southwest subduction of the Lancangjiang suture in early Permian. In another word, magmatic growth in Lancangjiang suture had been taken place during early Permian.

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