摘要
研究I型花岗岩中再循环晶的成分和结构特征,对揭示岩浆系统的形成和演化历史以及壳源和幔源岩浆的相互作用具有重要的意义。本文以西秦岭北西段三叠纪过马营复式岩体内的不同造岩矿物为主要研究对象,通过对具有不同结构特征的斜长石“粗晶”和黑云母展开电子探针(EMPA)、LA-ICP-MS微量元素面扫描、原位Sr同位素分析,来探讨含高An斜长石的成因,示踪不同岩浆房端员的属性,约束岩浆演化过程并建立多级岩浆房模型。过马营复式岩体的岩性分为偏铝质花岗岩类和过铝质花岗闪长岩类,两类岩性中均存在An值呈突变的筛状结构斜长石,即高An(72~85)区与低An(20~55)区在同一颗粒中并存,其对应主、微量元素也存在截然变化。与低An区相比,高An区具有高Fe、Mg,高Ba的特征。高钙区斜长石可进一步分为两类,第1类高钙区斜长石(An_(80-85)),和第2类高钙区斜长石(An_(72-78))。第1类高钙区比第2类高钙斜长石区具有更高的Ca、Al、Fe、Mg、Ba含量。本研究中斜长石晶体存在核_(高An)-边_(低An)与核_(低An)-幔_(高An)-边_(低An)两种不同类型的环带结构,表明其各自的生长过程有所不同。高An区与低An区之间An值跳跃式的变化与对应主、微量元素Fe、Mg、Sr、Ba含量特征均指示斜长石成分差异并非晶内扩散、动力学作用以及物理条件的变化造成的,更可能形成于开放的岩浆系统。本文认为斜长石粗晶为再循环晶,其内部的高An区形成于深部富H 2O玄武质岩浆,低An区形成于浅部酸性岩浆房(偏铝质与过铝质)。两种不同高钙区斜长石及其对应的主、微量元素差异指示它们很可能结晶于两批次不同的玄武质岩浆,其中第1类高钙区斜长石的母岩浆相对更富Fe、Mg、Ba。两种玄武质岩浆携带高An斜长石沿岩浆通道向上运移,上升过程熔蚀先前结晶的高An斜长石,将其带入浅部酸性岩浆房后与内部花
The study of the compositional and textural characteristics of the antecrysts in I-type granite is essential to reveal the formation and evolution history of the trans-crustal magmatic system and the interaction between crustal-and mantle-derived magmas.Here we investigate the rock-forming minerals in the Triassic Guomaying composite pluton(GCP)in West Qinling.We carried out the electron probe microanalysis(EPMA),LA-ICP-MS mapping,and in-situ Sr isotope analysis on the plagioclase macrocrysts with various textures to explore the origin of high-anorthosite(An)plagioclase,to reveal the nature of the different endmembers in magma chambers,to constrain the evolution of magma,and to establish the model of trans-crustal magma system.The lithology in the GCP can be divided into two groups,i.e.,the metaluminous granitoids and the peraluminous granodiorites.The plagioclase macrocrysts with spongy textures and heterogeneous compositions occur in both lithologies.Some parts in the plagioclase macrocrysts have higher-An contents(72~85)in comparison with other parts with lower An contents(20~55),together with marked compositional differences in terms of both major and trace elements.Compared with the low-An parts,the high-An parts in plagioclase have higher Fe,Mg and Ba contents.The high-An parts in plagioclase macrocrysts can also be divided two types:Type-1 zones with higher An contents(80~85)have higher Ca,Al,Fe,Mg,Ba contents than those of Type-2 zones(An contents:72~78).The plagioclase macrocrysts show various zoning patterns(core-rim/core-mantle-rim),implying significant changes in terms of external magmatic compositions during crystal growth.The marked compositional variations between high-An parts and low-An parts in plagioclase indicate that these differences are not caused by the intracrystalline diffusion,kinetic effects or the changes in physical conditions,but more likely formed in an open magmatic system.These data lead to the conclusion that the plagioclase macrocrysts are antecrysts,the high-An parts crystalli
作者
宁亚格
李小伟
胡俊强
莫宣学
孙雨沁
张国坤
谢元惠
汪方跃
NING YaGe;LI XiaoWei;HU JunQiang;MO XuanXue;SUN YuQin;ZHANG GuoKun;XIE YuanHui;WANG FangYue(State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Science and Mineral Resources,China University of Geosciences,Beijing 100083,China;Research Center of Genetic Mineralogy,Resources Exploration Experiment and Training Center,China University of Geosciences(Beijing),Beijing 100083,China;MNR Key Laboratory of Gold Mineralization Processes and Resources Utilization,Shandong Key Laboratory of Mineralization Geological Processes and Resources Utilization in Metallic Minerals,Shandong Institute of Geological Science,Jinan 250013,China;School of Resources and Environmental Engineering,Ore Deposit and Exploration Centre,Hefei University of Technology,Hefei 230009,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第11期3527-3547,共21页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41872066、41730426)
中央高校基本科研业务费(2652018121)联合资助.
关键词
再循环晶
筛状结构
高An斜长石
过马营岩体
Antecryst
Spongy texture
High-An plagioclase
Guomaying composite pluton
