青藏高原北部可可西里地区新生代钾质火山岩地球化学特征及成因  

Geochemistry and petrogenesis of Cenozoic potassic volcanic rocks in the Hoh Xil area, northern Tibet plateau.

作　　者：江东辉[1,2] 刘嘉麒[1] 丁林[3] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]中国科学院研究生院,北京100039 [3]中国科学院青藏高原研究所,北京100029

出　　处：《岩石学报》2008年第2期279-290,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金委项目(40772050、40773023);国家杰出青年科学基金项目(编号40625008);中国科学院知识创新工程重要方向项目(编号KZCX3-SW-143)资助成果

摘　　要：青藏高原北部可可西里地区分布的中新世钾质火山岩(7.77～17.82Ma)主要为粗面安山岩、粗面岩和少量次火山相的流纹斑岩。主量、微量元素及Sr-Nd-Pb同位素地球化学研究表明,该套钾质火山岩强烈富集大离子亲石元素和轻稀土元素,明显亏损Nb-Ta-Ti元素,具有较高的^(87)Sr/^(86)Sr:0.707346～0.714915,较低的ε_(Nd)值:-3.70～-6.97,和较高的放射性成因Pb同位素组成(^(207)Pb/^(204)Pb=15.65～15.76,^(208)Ph/^(204)Pb=38.98～39.35,^(206)Pb/^(204)Pb=18.67～18.78)。上述特征指示岩浆源区可能是与古俯冲消减物质有关的EMⅡ型富集地幔。三大岩类的地球化学成分变异表明:该钾质火山岩系列是富集地幔(金云母-尖晶石二辉橄榄岩和金云母-石榴石二辉橄榄岩)低度部分熔融产生的母岩浆经过较强结晶分异形成的,其中流纹斑岩在岩浆后期可能经历了更为复杂的地壳混染和结晶分异过程。Miocene potassic volcanic rocks （7.77 - 17.82Ma） in the Hoh Xil area of northern Tibet Plateau are mainly of three types： trachyandesite, trachyte and some subvolcanic rhyolitic porphyry. Major- and trace-elements as well as Sr-Nd-Pb isotope geochemistry researches show： these potassic rocks are strongly enriched in large-ion lithophile elements and LREE, and evidently depleted Nb-Ta-Ti. They have relatively high ^87Sr/^86 Sr： 0. 707346 - 0. 714915, low εNd ： - 3.70 - - 6.97, and relatively high radiogenic Pb （^207Pb/^204 Pb = 15. 65 - 15. 76, ^208Pb/^204 Pb = 38. 98 - 39. 35, ^206Pb/^204 Pb = 18.67 - 18. 78）. The above characteristics indicate that the source of the magmas is an enriched EMII mantle which possibly resulted from earlier episodes of oceanic slab subduetion. Geochemical variation of the three major rocks indicate this series of rocks are formed by fractional crystallization of parental magmas which is generated by low degree partial melting of enriched mantle （ phlogopite-spinel lherzolite and phlogopite-garnet lherzolite ）, and the rhyolitic porphyry may undergo much more complicated process of crustal assimilation and fractional crystallization.

关 键 词：青藏高原 可可西里 钾质火山岩 新生代 

分 类 号：P588.143[天文地球—岩石学]