| 青海南部三叠纪结扎群火山岩地球化学特征及其构造环境分析 |
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| 关键词:Triassic Gyeza Group volcanic rock geochemistry Qinghai |
| 基金项目:中国地质调查局1:25万直根尕卡幅、曲麻莱县区调项目(编号:20001300009121、200313000006) |
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| Geochemistry and Tectonic Settings of Volcanic Rocks in Late Triassic Gyeza Group of Southern Qinghai |
| Whole rock analyses comprising major,REE and trace elements and Sr-Nd isotopic geochemistry were conducted for samples of volcanic rocks from Late Triassic Gyeza Group of southern Qinghai to reveal the magma source signature of these volcanic rocks in Qiangtang Block and their tectonic setting.The results show that the volcanic rocks are composed of basaltic trachyandesite,trachyandesite and trachybasalt,characterized by poor Al and high Ti.In REE elements,they form a LREE-enriched distribution pattern with a strong contrast between LREE and HREE and the existence of weak negative Eu anomaly.In trace elements,the rocks have rich LILE and depleted HFSE with slight Nb and Ta negative anomalies.All the samples are plotted in the region of island arc basalt on Hf/3-Th-Nb/16 and 10TiO2-Al2O3-10K2O diagrams.ISr,INd isotope ratios range from 0.70728 to 0.70818 and from 0.512132 to 0.512249,respectively,whereas εNd(t) values are negative,ranging from-2.4 to-4.2,which indicate that the primary magma forming late Triassic volcanic rocks might have been of the crust-mantle mixing type.These characteristics suggest that the rocks were formed in an island arc setting.Spreading of Bangong Co-Nujiang ocean-floor during Late Triassic induced southwestward subduction of Garzê-Litang ocean and strong collision between Qiangtang and Yangtze Blocks,and then the mantle substance erupted with significant upper crust contamination during its upward movement.All this implies that volcanic rocks from Gyeza Group were derived from the continental margin arc under compressional orogenic mechanism. |
| MA Li-yan,BAI Yun-shan,NIU Zhi-jun,WANG Jian-xiang,DUAN Qi-fa.2007.Geochemistry and Tectonic Settings of Volcanic Rocks in Late Triassic Gyeza Group of Southern Qinghai[J].Acta Geoscientica Sinica,28(5):428-437. |
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