Petrogenetic mechanism and tectonic significance of Triassic Yushu volcanic rocks in the northern part of the North Qiangtang Terrane
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    Abstract:

    Triassic Yushu volcanic rocks are mainly composed of dacites and distributed in the northern part of the North Qiangtang (NQ) terrane. Zircon LA-ICP-MS U-Pb ages of 230±2 Ma (MSWD=0.5) could be interpreted as the formation time of these volcanic rocks. Most samples from the Yushu volcanic rocks are characterized by high SiO2 and Al2O3, obvious enrichment of large ion lithophile elements (LILEs: Rb, Ba, Th and U) and strong depletion of high field strength elements (HFSEs, such as Nb, Ta and Ti) relative to the primitive mantle. They exhibit high εNd(t) (-0.91~-0.53), low ISr (0.707) and positive εHf(t) (+3.81~+7.61), suggesting that they probably originated from partial melting of a juvenile crustal component. Compared with the other reported Triassic volcanic rocks of the (NQ), it could be found that most of the Middle to Late Triassic volcanic rocks (MLTV) are concentrated in the northern part or the southern part of the NQ. The Middle-Lower Triassic Yushu volcanic rocks from the south part of the NQ exhibit lower εNd(t) (-8.79~-1.77), higher ISr (0.706~0.714) and negative εHf(t) (-15.3~-10.1), implying these rocks might be derived from partial melting of the old crustal materials. Combined with the other new available observations, the authors hold that the Middle-Lower Triassic Yushu volcanic rocks in the southern part of the NQ were genetically related to the slab break-off during the collision between South Qiangtang terrane and NQ, whereas the southward subduction of the Ganzi-Litang Paleo-Tethyan ocean resulted in the generation of the Middle-Lower Triassic Yushu volcanic rocks from the northern part of the NQ.

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刘彬,马昌前,黄坚,熊富浩,张鑫,郭宇衡,2016,北羌塘北缘玉树三叠纪火山岩的成因机制及其构造意义[J].岩石矿物学杂志,35(1):1~15. LIU Bin, MA Chang-qian, HUANG Jian, XIONG Fu-hao, ZHANG Xin, GUO Yu-heng,2016,Petrogenetic mechanism and tectonic significance of Triassic Yushu volcanic rocks in the northern part of the North Qiangtang Terrane[J]. Acta Petrologica et Mineralogica,35(1):1~15.

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History
  • Received:September 21,2015
  • Revised:December 12,2015
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  • Online: January 22,2016
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