大别山碧溪岭榴辉岩相平衡模拟及温压计算  

Phase equilibrium modeling and P-T estimation of eclogites at Bixiling,Dabie Mountains

作　　者：吴倩怡 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [2]中国科学院研究生院,北京100049

出　　处：《南京大学学报（自然科学版）》2011年第6期718-730,共13页Journal of Nanjing University（Natural Science）

基　　金：国家自然科学基金(40873025;40673033)

摘　　要：大别山碧溪岭超高压榴辉岩主要由石榴石、绿辉石、柯石英/石英、蓝晶石、多硅白云母、金红石、黝帘石、滑石、角闪石组成.含滑石变斑晶的榴辉岩样品中石榴石变斑晶在背散射图像中可观察到深浅不一的两种色调.深色部分比浅色部分含有更高的XMg.矿物结构关系显示岩石可能曾经含有硬柱石.峰变质阶段后,随着温度和压力下降,硬柱石分解,形成硬柱石假象(蓝晶石+绿帘石+石英).但是,这些矿物所构成的结构也可以解释为帘石生长,包围属于峰变质阶段矿物组合的蓝晶石及石英(柯石英).相图计算结果指出这两种可能性对应于不同的P-T路径.浅色榴辉岩中滑石与早期形成的石榴石、绿辉石一同在榴辉岩变质演化初期已经存在.在经历峰变质阶段后,帘石开始生长.退变质过程进一步发生,滑石变斑晶生长.利用石榴石-绿辉石-多硅白云母-柯石英温压计计算得到浅色榴辉岩所经历的峰变质阶段的P-T条件为3.8GPa,640℃.The ultrahigh-pressure(UHP) eclogites at Bixiling mainly consist of garnet,omphacite,coesite/quartz,kyanite,phengite,rutile,zoisite,talc and amphibole.Backscattered electron imaging of the garnet porphyroblasts including talc shows two different grey shades.The dark parts have higher XMg values than the light parts.After peak metamorphic stage,on temperature and pressure decrease,lawsonite decomposes and forms lawsonite pseudomorphs(ky+ep+qtz clusters).However,such a texture can also be interpreted to be the growth of epidote surrounding kynite and coesite that formed at the peak metamorphic stage.The two different possibilities correspond to two different P-T paths.The talc,together with garnet and omphacite,existed at the beginning of the metamorphic progress in the light colored eclogite.Epidote began to grow after the peak metamorphic stage.In the retrograde process,the secondary talc grew as porphyroblasts.By using geothermobarometry,the peak P-T condition has been estimated to be 3.8 GPa and 640 ℃.

关 键 词：榴辉岩 相平衡 P-T路径 地质温压计 硬柱石 碧溪岭 

分 类 号：P58[天文地球—岩石学]