2012年6月，第18卷，第2期，291-306页 June 2012,Vol.18，No.2，p.291306
高校地质学报
Geological Journal of China Universities
秦岭早中生代壳慢岩浆混合作用
来自东江口花岗岩体闪长质包体的地球化学证据
李雷12，张成立"，周莹'，田会全，李小菲 1.西北大学大陆动力学国家重点实验室，西北大学地质学系，西安710069；
2.西北有色地质研究院，西安，710054
摘要：东江口花岗岩及闪长质包体分别获得了218Ma和224Ma的形成年龄，闪长质包体中存在岩浆不平衡结构并发育与寄主花岗岩相同的钾长石斑晶及淬冷形成的针状磷灰石，揭示了花岗岩形成过程中曾发生二元岩浆混合作用。这种混合作用已造成寄主花岗岩和闪长质包体化学组成的趋同，同时使得它们的Sr-Nd-Pb同位素组成发生强烈均一化。但暗色闪长质包体锆石具有较宽的er（t）值（-4.58~3.31），保留了二端元岩浆源区的特征。秦岭早中生代同期闪长质包体错石ear（t）> 10及寄主花岗岩错石（t）<-10的差异表明，它们分别来自相对亏损地慢源区和中元古代滞留于地壳的慢源基性物质，
而两个源区的岩浆，自224Ma以来发生强烈混合作用，形成大规模的壳慢混合花岗岩体。关键调：早中生代；闪长质包体；岩石地球化学；壳慢岩浆混合作用
中图分类号：P588.11；P595
文献标识码：A
文章编号：1006-7493（2012)02-0291-16
Early Mesozoic Crust-and Mantle-Derived Magmatic Mixing in the Qinling Orogeny:EvidenceFromGeochemistryofMaficMicrogranularEnclaves
intheDongjiangkouPluton
LI Lei,2, ZHANG Chengli', ZHOU Ying',TIAN Huiquan', LI Xiaofei
1. Key Laboratory of Continental Dynamies of Northwest University, Department of Geology, Northwest University, Xi'an 710069, China
2. Northwest Geological Institute of Norferrous Metals, Xian 710054, China
Abstract: The zircon U-Pb ages of 218 Ma and 224 Ma have been obtained from the Dongjiangkou granitoids and their mafic enclaves, respectively. The disequilibrium magmatic textures can be found in the mafic enclaves, which have some K-feldspars similar to those of host granitoids and needle-like apatite formed under a quenching condition, indicating a two-end member magmatic mixing in the early Mesozoic. The two-end member magmatic mixing resulted in similar geochemical compositions and strong homogenization of SrNdPb isotopes between host granitoids and their mafic enclaves, However, Hf isotopic composition of the mafic enclaves shows a wide range of μr(t) that varies from 4.58 to 3.31, registering the source features of two-end member magma, Thus, the positive μ(t) values (> 1O) of zircons from the contemporary mafic enclaves provide evidence that the mafic magma was derived from the depleted mantle. While, host granitoids with negative μdt) values (<1O) of zircons were products of partial melting of the Mid-Proterozoic mantle-derived basic rocks. Since then, the distinct crust- and mantle-derived magmas were mixed around 224 Ma, resulting in a large number of granitic intrusions with abundant mafic enclaves during the early Mesozoic in the Qinling orogeny.
Key words: Early Mesozoic; mafic enclave; petro-geochemistry; crust- and mantle-derived magmatic mixing
Corresponding author: Zhang Chengli, Professor; E-mail: elzhang@nwu.edu.cn 收稿日期：2012-0119；修回日期：2012-03-21
基金项目：国家自然科学基金重点项目（40830314）：西北大学大陆动力学国家重点实验室科技部专项基金联合资助作者简介：李雷，男，1985年生，硕土研究生，岩石地球化学专业；E-mail：lilei19850730@163.com；
通讯作者：张成立，教授；E-mail：clzhangnwu.edu.en