秦岭环斑结构花岗岩中暗色包体的岩浆混合成因及岩石学意义——元素和Nd、Sr同位素地球化学证据  

Genesis of mafic enclaves from rapakivi-textured granites in the Qinling and its petrological significance: evidence of elements and Nd, Sr isotopes.

作　　者：王晓霞[1,2] 王涛[3] Ilmari Happala 卢欣祥 

机构地区：[1]中国地质大学岩石圈构造,深部过程及探测技术教育部重点实验室,北京100083 [2]中国地质调查局发展研究中心,北京100037 [3]中国地质科学院地质研究所 [4]赫尔辛基大学,郑州450053 [5]河南省地质研究所

出　　处：《岩石学报》2005年第3期935-946,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(编号:40372043;40072064)中国地质大学"岩石圈构造;深部过程及探测技术"教育部重点实验室开放课题(编号:2003001)资助

摘　　要：秦岭环斑结构花岗岩中的暗色包体主要为闪长质岩浆包体,SiO2(50％-62％)低,K2O+Na2O(7．01％-9．4％) 高,里特曼指数(δ)为5-9,F、过渡性元素和稀土元素富集。包体和寄主岩石的主要氧化物之间具有良好的线性关系、稀土配分曲线和微量元素配分曲线相似,以及活动性组分、高场强元素、轻稀土和同位素特征等显示,寄主岩石和包体之间发生过明显的成分交换,这些成分在二者中大体上趋于平衡。这种特征表明,环斑结构花岗岩岩浆的形成至少与两种岩浆的混合有关。包体的(87Sr／86Sr)i较低(0．70514-0．70624)、εNd(t)值较高(-0．95--3．3)和富过渡性元素的特征揭示,形成包体的原始岩浆为起源于幔源的玄武质岩浆。包体和寄主岩石的关系显示岩浆的混合方式为基性岩浆注入到已经开始结晶的酸性岩浆。这些研究为环斑结构花岗岩是起源于地壳的酸性岩浆和起源于地幔的基性岩浆形成的混合岩浆结晶的产物提供了新证据;同时,也为环斑结构的混合成因研究提供了新思路和途径。The enclaves from rapakivi-textured granite plutons in the Qinling orogenic belt are mainly dioritic magmatic enclaves,having low content in SiO2（50% -62%）,high in K2O＋Na2O（7.01% -9.4%）, δ（5-9）, F, REE, Cr, Ni, V and Ga. The major oxide contents of the enclaves and their host rocks plots on the same linear trends. The pattern of REE, trace element and isotopic signatures of the enclaves are similar to those of the host granites. Exchanges of active elements, HLE and LREE occurredb etween the enclaves and the host rocks and almost reached equilibrium. Those characteristics were resulted from the nature of magma mingling/mixing, i. e. the formation of rapakivi-textured granite plutons at least involved two kinds of magmas hybrid. Low（ ^87 Sr/^86 Sr） i （ 0. 70514 - 0. 70624） , high εNd （t） （ - 0.95 -- 3. 3 ） , Cr, Ni and V of enclaves suggest that their magma of the enclave may have originated from mantle and may have been a basaltic magma in nature before its mixing with the silisic magma. The relationship between the enclaves and host rocks suggests that the way of the magma mingling/mixing is the basic magma injecting into the acidic magma. This study provides new evidence for the genesis of the rapakivi-textured granites. That is, the granites crystallized from a hybrid magma formed by mingling of the crust-derived acidic magma and the mantle- derived basic magma.

关 键 词：岩浆包体 岩浆混合 成分交换 同位素均一化 环斑结构 秦岭造山带 

分 类 号：P588.121[天文地球—岩石学] P597[天文地球—地质学]