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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.

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.

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 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.

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