北秦岭老君山、秦岭梁环斑结构花岗岩岩浆混合的岩相学证据及其意义  

Petrographic evidence of hybridization of magmas of the Laojunshan and Qinlingliang rapakivi-textured granites in the North Qinling and its significance

作　　者：王晓霞[1,2] 王涛[3] 卢欣祥 肖庆辉[5] 

机构地区：[1]中国地质大学地球科学与资源学院 [2]长安大学地球科学与国土资源学院陕西西安710054 [3]中国地质科学院地质研究所 [4]河南省地质科学研究所 [5]国土资源部信息研究院

出　　处：《地质通报》2002年第8期523-529,共7页Geological Bulletin of China

基　　金：国家自然科学基金(40072065);中国地质调查局"中国花岗岩重大地质问题研究"(200113900018);西北大学大陆动力学教育部重点实验和资助项目。

摘　　要：老君山和秦岭梁岩体具有明显的岩浆混合特征。岩体中暗色包体发育,主要类型为细粒闪长质和二长质的岩浆包体,有的岩浆包体具有细粒边,有的和寄主岩石呈过渡关系。包体的矿物组合明显不平衡:出现石英-角闪石眼斑;暗色矿物中有石英包裹体;磷灰石呈针状。在包体、寄主岩石及其边界上广泛出现卵球状的碱性长石斑晶。这些混合特征表明:老君山和秦岭梁环斑结构花岗岩、环斑结构与岩浆混合关系紧密;岩浆作用也具双峰式的特点,表现为基性岩浆和酸性岩浆的混合。这为探讨该类花岗岩和环斑结构的成因提供了直接的岩石学依据。同时,也为探讨北秦岭中生代壳幔混合作用和地壳增生提供了新的信息。Petrographic evidence suggests that mixing and mingling of magmas of contrasting compositions were important petrogenetic processes for the Laojunshan and Qinlingliang rapakivi-textured granite plutons.Melanocratic magmatic enclaves are well developed in the plutons.They are mainly fine-grained dioritic and monzonitic ones;some of them have fine-grained rims and others exhibit gradational contact relation-ships with the host rocks.The mineral assemblage of the enclaves shows markedly disequilibrium;therefore quartz phenocrysts mantled with mafic minerals,acicular apatite and spike zones in plagioclase can be ob-served in most of the enclaves and ovoid K-feldspar phenocrysts occur in the host rocks and enclaves and on their boundaries.These features suggest that the rapakivi texture of the plutons is closely related to mixing and mingling of magmas.The magmatism also shows bimodal features,which is manifested by the mixing of basic magma and acid magma.This offers the firsthand evidence for the study of the origin of the rapakivi texture and genesis of the rapakivi-textured granite in the North Qinling and also furnishes new information for the study of Mesozoic crust-mantle mixing and crustal accretion there.

关 键 词：老君山 秦岭 环斑结构 岩相学证据 环斑花岗岩 岩浆混合 秦岭造山带 中生代 

分 类 号：P588.121[天文地球—岩石学]