扬子克拉通北缘神农架群火山岩锆石Hf同位素特征  

Zircon Hf isotope of Shennongjia volcanic rocks on the northern margin of the Yangtze craton

作　　者：邱啸飞[1,2] 凌文黎[2] 柳小明[3] 杨红梅[1] 段瑞春[1] 卢山松[1] 

机构地区：[1]中国地质调查局武汉地质调查中心/同位素地球化学研究室,湖北武汉430205 [2]中国地质大学(武汉)地球科学学院,湖北武汉430074 [3]西北大学/大陆动力学国家重点实验室,陕西西安710069

出　　处：《地质通报》2013年第9期1394-1401,共8页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41173048);中国地质调查局项目(编号:1212011121102;1212011220515)

摘　　要：报道神农架群安山质熔结凝灰岩中锆石的Hf同位素数据，以此对其岩浆来源与岩石成因进行约束。结果显示，Nd—Hf同位素之间存在脱耦现象，虽然各样品之间显示出较为一致的元素地球化学和Nd同位素组成，但同一样品中具有高度变化的锆石￡酏）值，对应锆石Hf同位素模式年龄为2587-1608Ma，表明岩浆在形成和上升过程中可能受到了陆源碎屑物质组分的混染。该组分改变了岩浆结晶时部分锆石中的Hf同位素组成，然而未改变全岩地球化学及Nd同住素组成，可能表明锆石原位Hf同位素在反映岩浆形成和演化过程中对于碎屑沉积岩混染的识别比全岩Nd同位素具有更为灵敏的指示意义。结合该岩石的全岩地球化学特征，认为神农架安山质熔结凝灰岩来自深部幔源岩浆上涌引起的元古宙基性下地壳岩石部分熔融，且在上升过程中受到了俯冲碎屑沉积岩的混染。Based on documented geochronological and whole-rock geochemical data, this paper reports for the first time the zircon Hf isotopic composition of the Shennongjia andesitic ignimbrite, with the purpose of constraining the magmatic source and petro- genesis. The results obtained by the authors reveal that the Nd-Hf decoupling occurs in the rocks. Although the samples have rel- atively constant elemental geochemical characteristics and Nd isotopic composition, highly variable zircon 8,c（t） values （-24.0-＋0.3） are existent in a single sample, corresponding to zircon Hf isotope model age （Try, a） of 2587-1608 Ma and suggesting that terrestrial clastic components contamination occurred during the generation and upwelling of magma. Such a component evidently modified part of the zircon Hf isotopic composition during magma crystallization but did not affect the whole geochemical and Nd isotopic composition, revealing that the zircon in-situ Hf isotope was more sensitive to the clastic contamination than whole-rock Nd iso- tope during the formation and evolution processes of magma. Combined with whole-rock geochemical features, this paper points out that the Shennongjia andesitic ignimbrite might have been derived from Proterozoic mafic lower crustal anatexis caused by up- welling of mantle-derived magma, and experienced the contamination of subducted clastic rocks during its upwelling.

关 键 词：扬子克拉通北缘 神农架群 安山质熔结凝灰岩 锆石HF同位素 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]