华北东部中生代高镁埃达克质岩浆的起源：岩石学和Nd-Sr-Os同位素证据  

Origin of Mesozoic high-Mg adakitic rocks from northeastern China:Petrological and Nd-Sr-Os isotopic constraints

作　　者：陈斌[1] 陈长健[1] 贺敬博 刘安坤 

机构地区：[1]北京大学地球与空间科学学院、教育部造山带与地壳演化重点实验室,北京100871 [2]Department of the Geophysical Sciences, University of Chicago, Chicago IL 60637, USA

出　　处：《科学通报》2013年第20期1941-1953,共13页Chinese Science Bulletin

基　　金：国家自然科学基金重点项目(90914001);国家自然科学基金委员会创新研究群体基金(41121062);国家杰出青年科学基金(40625005)

摘　　要：华北东部中生代高镁闪长质岩石被许多研究者认为是属于高镁埃达克岩(中酸性、高镁、高Sr和Sr/Y),后者广泛发育在俯冲带和碰撞后等构造环境.大多数人认为这些高镁埃达克质岩石的形成与榴辉岩相部分熔融体与地幔橄榄岩的相互作用有关.本文报道的新的岩石学和同位素证据并不支持该模式,提出其成因与富集地幔起源的基性岩浆与壳源酸性岩浆的混合过程有关.该岩浆混合过程的主要证据包括:(1)自形高钙斜长石和高镁辉石分别包裹低钙斜长石和低镁辉石,(2)高镁闪长岩具有高放射性成因的Os同位素成分和近似线性反相关的Sr-Nd同位素成分.本文提出的壳幔岩浆混合模式可能对世界其他地区高镁埃达克岩的成因和构造环境研究具有重要意义.Mesozoic high-Mg dioritic rocks from northeastern China have been suggested to have an adakitic origin,attributed to the equilibration of partial melts from delaminated mafic crust(eclogite) with mantle peridotite.Here we present petrological and Nd-Sr-Os isotopic data that counter this delamination model for the formation of these rocks,and instead propose a process of magma mixing between siliceous crustal melts and basaltic magma from metasomatized mantle in a post-kinematic setting.The magma mixing process is supported by(1) euhedral overgrowths of high-Ca plagioclase and high-Mg pyroxene over low-Ca plagioclase and low-Mg pyroxene,respectively,and(2) highly radiogenic Os isotopic compositions,and negatively correlated Nd and Sr isotopic ratios.Our proposed model is probably generally applicable to the mode of origin and tectonic settings of high-Mg adakitic magmas.

关 键 词：华北东部 高镁闪长岩 埃达克岩 岩浆混合 Os同位素 

分 类 号：P597[天文地球—地球化学]