Early Indosinian Weiya Gabbro in Eastern Tianshan, China: Elemental and Sr-Nd-O Isotopic Geochemistry, and Its Tectonic Implications  

作　　者：ZHANG Zunzhong GU Lianxing WU Changzhi 

机构地区：[1]State Key Laboratory of Mineral Deposit Research （Nanjing University）, Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu 210093 [2]School of the Environment, Nanjing University, Nanjing, Jiangsu 210093

出　　处：《Acta Geologica Sinica(English Edition)》2007年第3期424-432,共9页地质学报（英文版）

基　　金：This study was jointly supported by National Natural Science Foundation of China （Nos. 40672040, 40472042 and 40603008）；National Basic Research Program of China （2001CB409802）；China Postdoctoral Science Foundation （No. 2005038237） ；Laboratory for Radiogenic Isotope Geochemistry, Institute of Geology and Geophysics, Chinese Academy of Sciences.

摘　　要：The Weiya gabbro in eastern Tianshan was formed during the early Indosinian. This rock, with low ratios of Ce/Pb （5.74-10.16）, is notably characterized by enrichment in large ion lithophile elements （LILE）, such as Rb, K, Ba and Pb, and in high field strength elements （HSFE）, such as U and Th, but depletion in Nb and Ta. All samples of the Weiya gabbro display similar chondrite-normalized patterns with moderate enrichment in LREE （72.58-135.61ppm）, moderate depletion in HREE （15.26-25.31ppm） and mild fractionation between LREE and HREE （L/ H=4.09-5.98）. The average initial Sr value of the rock is 0.7069, and δ18O values of the rock range from 5.67‰-8.04‰. In terms of Nd isotope ratios, the Weiya gabbro is characterized by positive eNd（t） values （0.52-0.76）. All these characteristics indicate that the source region of the Weiya gabbro was metasomatized by fluids released from subducted young continental crust, with limited crustal contamination during magma ascent and emplacement. Continental （A-type） subduction was induced by northward subduction of the Paleo-Tethyan oceanic plate during the latest Permian to Triassic. From this point of view, it is supposed that tectonic conversion from the Paleo-Asian to the Paleo-Tethys regime occurred during the latest Permian or earliest Triassic.The Weiya gabbro in eastern Tianshan was formed during the early Indosinian. This rock, with low ratios of Ce/Pb （5.74-10.16）, is notably characterized by enrichment in large ion lithophile elements （LILE）, such as Rb, K, Ba and Pb, and in high field strength elements （HSFE）, such as U and Th, but depletion in Nb and Ta. All samples of the Weiya gabbro display similar chondrite-normalized patterns with moderate enrichment in LREE （72.58-135.61ppm）, moderate depletion in HREE （15.26-25.31ppm） and mild fractionation between LREE and HREE （L/ H=4.09-5.98）. The average initial Sr value of the rock is 0.7069, and δ18O values of the rock range from 5.67‰-8.04‰. In terms of Nd isotope ratios, the Weiya gabbro is characterized by positive eNd（t） values （0.52-0.76）. All these characteristics indicate that the source region of the Weiya gabbro was metasomatized by fluids released from subducted young continental crust, with limited crustal contamination during magma ascent and emplacement. Continental （A-type） subduction was induced by northward subduction of the Paleo-Tethyan oceanic plate during the latest Permian to Triassic. From this point of view, it is supposed that tectonic conversion from the Paleo-Asian to the Paleo-Tethys regime occurred during the latest Permian or earliest Triassic.

关 键 词：Weiya gabbro mantle metasomatism intra-continental subduction easternTianshan XINJIANG 

分 类 号：P588[天文地球—岩石学]