藏南曲卓木地区酸性火山岩地球化学、Hf-Sr-Nd同位素特征及其成因
Geochemistry, Hf-Sr-Nd Isotopes and Petrogenesis of Acidic Volcanic Rocks in Quzhuomu Region of Southern Tibet

目前关于白垩纪酸性岩石的相关研究报道极少.近年来在曲卓木地区发现了较为广泛的酸性(英安岩)-基性(辉绿岩-玄武岩)火山岩浆活动，双峰式火山岩浆活动特征明显.对其进行了年代学、地球化学及Hf-Sr-Nd同位素研究.结果表明，英安岩成岩年龄为142.0±2.5 Ma，具有高的LREE及Nb、Zr、Hf、Y等高场强元素含量以及Ga/Al比值，显示A型花岗岩特征.锆石的εHf ( t )值为-13.1～-2.4，平均值为-7.1.岩石具有高的初始Sr同位素值(87Sr/ 86Sr)i值为0.722 024～0.722 698)以及低的初始Nd同位素值εNd ( t )为-12.2～-11.8).综合研究表明，曲卓木地区酸性火山岩是伸展背景下大陆地壳深熔作用的产物，其与区域上桑秀组酸性火山岩、Laguila酸性侵入岩、桑日则地区流纹岩具有相似的地球化学特征与相当的成岩年龄，可能同属于Comei-Bunbury大火成岩省的一部分，均是Kerguelen地幔柱早期岩浆活动产物，而Kerguelen地幔柱活动可能提前至140 Ma左右.
There are few related studies on the Cretaceous acid rocks currently, and this paper focuses on a wide range of acid (dyanite) basic (diabase-basalt) volcanic magmatism recently discovered in the Quzhuomu area where bimodal volcanic magmatic activity is obvious.Geochronology, geochemistry and Hf-Sr-Nd isotope analyses are carried out on these dacites.The results show that the diagenetic age of dacite is 142.0±2.5 Ma.The dacites show high contents of LREE and high fieldstrength elements (etc.Nb, Zr, Hf, Y) and high ratios of Ga/Al, indicating the characteristics of A-type granite.εHf ( t ) values of zircons range from -13.1 to -2.4, with an average of -7.1.The dacites also show high initial Sr isotope contents (87Sr/ 86Sr ratios of 0.722 024 to 0.722 698 ) and low initial Nd isotope contents with εNd ( t ) values from -12.2 to -11.8).The comprehensive research indicates that the acid volcanic rocks of Quzhuomu region are the products of the continental crust anataxis under extension setting.These dacites show the similar geochemical characteristics and diagenetic age with the Sangxiu formation acid volcanic rocks, Laguila acid intrusive rocks and rhyolites of Sangrize region.They are probably all the products of the ComeiBunbury large igneous province, which are the products of the early magmatic activity of Kerguelen mantle plume.The magma activities of Kerguelen mantle plume may be advanced to 140 Ma