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Acta Geologica Sinica(English Edition) 2013年第2期87卷 440-453页

作者： TAN Xiaohong ZHAO Bo LI Xikang XU Zhangbao ZHANG Zhen Institute of geological survey of Yunnan Province Institute of Mineral Resources Chinese Academy of Geological Sciences

The general classification of intermediate-acid intrusive rocks in the metamorphic zone of Gaoligong Mountains as one of the metamorphic terranes of Proterozoic Gaoligong Mountains is problematic regarding the intrusion stage and age, as well as the subsequent metamorphism and deformation. In this study, we investigated granitic gneiss in the metamorphic zone of Gaoligong Mountains based on the 1：50,000 regional geological survey of Qushi Street （2011-2013） and SHRIMP U-Pb zircon geochronology. Results showed that the SHRIMP U-Pb zircon dating of granitic gneiss ranged from 163.5±5.7 Ma to 74.0±2.0 Ma. Thus, the granitic gneiss was grouped into orthometamorphic rocks （metamorphic intrusions）. The dating data of granite rocks associated with intense metamorphism and deformation were divided into three groups, 163.5±5.7 to 162.3±3.1 Ma, 132.2-101.0 Ma and 99.4±3.5-74.0±2.0 Ma, which respectively represented three independent geologic events including an important magma intrusion with superimposed metamorphic effects in the late Middle Jurassic, regional dynamic metamorphism and superimposed reformation of fluid action in the early Cretaceous, and dynamic metamorphism dominated by ductile shear and metamorphism starting from the late Cretaceous.

关键词： Metamorphic zone granitic gneiss U-Pb zircon age Gaoligong Mountains Western Yunnan

SHRIMP Dating and Recrystallization of Metamorphic Zircons from a granitic gneiss in the Sulu UHP Terrane

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Acta Geologica Sinica(English Edition) 2004年第1期78卷 146-154页

作者： LI HongyanInstitute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037 Geosciences Rennes, Universite de Rennes 1, 35042 Rennes Cedex, France Chinese Acad Geol Sci Inst Mineral Resources Beijing 100037 Peoples R China Univ Rennes 1 Geosci Rennes F-35042 Rennes France

An unusual zircon SHRIMP dating result of a granitic gneiss from the Qinglongshan eclogite-gneiss roadcut section is presented in this paper. The very peculiar and complicated internal structures, as well as the very low Th/U ratios (0.01-0.08) of the zircons indicate that they were formed by metamorphic recrystallization. Strongly in contrast with previously published zircon U-Pb ages of the Dabie-Sulu UHP metamorphic rocks where protolith ages of 600-800 Ma are commonly recorded, only metamorphic age of 218±5 Ma, defined by 18 analytical spots either in rim or in core of zircons, are recorded in this granitic gneiss. This age represents the time of the complete metamorphic recrystallization overprint on primary magmatic zircons. The recrystallization was derived by the UHP metamorphism, and was strengthened by the early stage of retrograde metamorphic fluid activity.

关键词： recrystallization of zkcon metamorphic fluid SHRIMP dating granitic gneiss Qinglongshan Sulu China

Zircon SHRIMP U-Pb Dating, Geochemical Characteristics and Tectonic Significance of granitic gneisses in Amdo, Tibet

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Journal of Earth Science 2014年第3期25卷 473-485页

作者： Lu Lu Zhenhan Wu Zhen Zhao Daogong Hu Peisheng Ye Chinese Academy of Geological Sciences Institute of Geomechanics Chinese Academy of Geological Sciences

The Amdo microcontinent is located within the middle of Bangong-Nujiang suture（BNS） zone in the shape of lens. The basic geological research restricts geologists from understanding the histories of tectonic evolution of BNS and regional geology more deeply. This paper systematically studies the geochronology and geochemistry of granitic gneisses from Amdo basement. These data provide constraints on formation age, source characteristics and tectonic setting of their protolith. The SHRIMP zircon U-Pb dating is operated for granitic gneisses. Samples AGS-2 and AGS-3（granitic gneiss） yield average zircon U-Pb ages of 485±14 and 487±6 Ma, respectively. These ages should represent the formation age of protolith and indicate that they are formed in the Early Ordovician. granitic gneisses are characterized by high SiO2, Na2O, K2O and Al2O3, low Fe and Mg, enrichment in light rare earth elements（LREEs） and large ion lithophile elements（LILEs）, depletion in heavy rare earth elements（HREEs） and high field strength elements（HFSEs）, with negative Eu anomaly. The Rittmann index（σ） is 1.77 to 2.60, less than 3.3. The aluminum saturation index（A/CNK） values range from 0.88 to 1.26. These features suggest that protolith of granitic gneisses from Amdo basement show characteristics of calc-alkaline and S-type granite, and they could be derived from partial melting of metamorphic greywackes in the upper crust of low maturity. The tectonic setting is syn-collision. These all suggest that the formation of protolith of granitic gneisses from Amdo are caused by the Early Paleozoic orogeny, which could be related to proto-Tethyan oceanic subduction along Gondwana continental margins, and does not result from the production of Pan-African orogenesis.

关键词： granitic gneiss zircon U-Pb age geochemical Amdo Tibet.

Geochemical Characteristics and Genesis of the granitic gneisses from the Southeastern Dabie Mountains

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Acta Geologica Sinica(English Edition) 2001年第2期75卷 175-183页

作者：薛怀明董树文刘晓春 Chinese Academy of Geological Sciences Nanjing Institute of Geology and Mineral Resources Chinese Academy of Geological Sciences Institute of Geomechanics

The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characterized by rich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, particularly the alkali-feldspar granitic gneiss, have typical chemical characteristics of A-type granites. They resulted from partial melting of crustal materials existing in the rift zone along the northern margin of the South China block during the Neoproterozoic. These gneisses might not have undergone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of the UHP rocks from the middle and upper crust.

关键词： granitic gneiss A-type granite UHP complex Proterozoic Dabie Mountains