柴北缘鱼卡河榴辉岩的变质演化——石榴石成分环带及矿物反应结构的证据  

Metamorphic evolution of the Yuka eclogite in the North Qaidam,NW China:evidences from the compositional zonation of garnet and reaction texture in the rock.

作　　者：陈丹玲[1] 孙勇[1] 刘良[1] 张安达[1] 罗金海[1] 王焰[1] 

机构地区：[1]西北大学大陆动力学教育部重点实验室

出　　处：《岩石学报》2005年第4期1039-1048,共10页Acta Petrologica Sinica

基　　金：国家重点基础发展规划项目(G1999075508);国家自然科学基金(40472043)联合资助

摘　　要：柴北缘鱼卡河榴辉岩的典型矿物组合为石榴石-绿辉石-多硅白云母-金红石。其中粗粒石榴石变斑晶普遍保存进变质生长环带,从核部到边部石榴石的化学成分、包体矿物的种类和粒度皆呈现出规律的分带性。岩相学和矿物化学研究进一步表明,该榴辉岩经历了前榴辉岩相、榴辉岩相及后榴辉岩相三个主要变质演化阶段。前榴辉岩相以石榴石核部成分及核部包体矿物组合石榴石(GrtⅠ)+角闪石(AmpⅠ)+斜长石(PⅡ)+石英(Qtz)为特征,P-T 估算结果为450～500℃和0.6～0.7GPa。榴辉岩相变质阶段又可细分为早期、峰期榴辉岩和退变角闪榴辉岩三个亚相。早期榴辉岩亚相以石榴石幔部成分和幔部包体矿物组合石榴石(GrtⅡA)+绿辉石(OmpⅡA)+多硅白云母(PheⅡA)±黝帘石(Zoi)+金红石(Ru)为代表,估算的温压条件为580～640℃和2.4～2.5GPa;峰期榴辉岩相以石榴石的边部(GrtⅡB)及基质中绿辉石(OmpⅡB)和多硅白云母(PheⅡB)的核部为代表,矿物组合为 GrtⅡB+OmpⅡB+PheⅡB+Ru,估算的 P-T 条件为620～680℃和3.0～3.4GPa;退变角闪榴辉岩相以共生的石榴石的最边部(GrtⅡC)、基质绿辉石(OmpⅡC)和多硅白云母(PheⅡC)的边部及镁红闪石(AmpⅡ)组合为代表,矿物组合为 GrtⅡC+OmpⅡC+AmpⅡ+PheⅡC,估算的 P-T 条件为700～720℃和2.3～2.4GPa。后榴辉岩阶段主要为麻粒岩-高角闪岩相,以绿辉石分解形成透辉石+钠长石冠状体以及进一步分解形成韭闪石+斜长石,铁红闪石分解形成浅闪石+斜长石为代表,P-T 估算结果为550～600℃和0.6～1GPa。温压估算结果表明,鱼卡河榴辉岩经历了升温升压—升温降压—降温降压的一个顺时针 P-T 演化轨迹,它记录了从俯冲-超高压变质-抬升的连续的演化过程。峰期变质条件为630～680℃和3.0～3.4GPa,已达超高压变质范畴。榴辉岩中进变质矿物组合和生长环带的保存说明榴辉岩的形成经历了相�The typical mineral assemblage of the Yuka eclogite in North Qaidam is composed of garnet （ Grt）, omphacite （Omp） , phengite（Phe） and rutile（Ru）. Coarse-grained garnet porphyroblast with obvious zoning in both composition and mineral inclusions, can be divided, from core to rim, into four rings, i. e. , core （GrtⅠ） , mantle （GrtⅡA） , rim （GrtⅡB） and outermost rim （GrtⅡC）. Petrographic and mineral chemistry studies indicate that the Yuka eclogite has undergone three successive stages of pre-eclogite, eclogite and post-eclogite, recording a process evolved from subduction to exhumation of the rock. The pre-eclogite stage （ Ⅰ ） is represented by the assemblage in the core part of garnet porphyblast （ GrtⅠ ＋ AmpⅠ ＋ Zoi ＋ PlⅠ ＋ Q ） , P-T metamorphic conditions are estimated to be 450 to 500℃ and 0.6 to 0.7 GPa. Eclogite facies stage can be further divided into three sub-stages of early-, peak-and retrograde-eclogites. Early-eclogite stage （ⅡA） is characterized by the assemblage of GrtⅡA ＋ OmpⅡA ＋ PheⅡA ＋ Ru preserved in the mantle part of garnet porphyblast, which recorded the metamorphic conditions of 580 to 640℃ and 2.4 to 2.5 GPa. Peak-eclogite stage （ⅡB） is represented by the rim part of garnet porphyblast, and the core part of omphacites and phengites in the matrix （GrtⅡB ＋ OmpⅡB ＋ PheⅡB ＋ Ru） , P-T estimates give peak metamorphic conditions of 620 to 680℃and 3.0 to 3.4 GPa. Retrograde-eclogite stage （ⅡC） is characterized by the outermost rim part of garnet porphyblast, Mg- kataphaprite, the rim of omphacite and phengite in the matrix （ GrtⅡC ＋ OmpⅡC ＋ PheIIC ＋AmⅡ）, P-T estimates give the first retrograde conditions ofT00 to 720℃ and 2.3 to 2.4GPa. Post-eclogite stage is mainly of granulite-amphibolite facies, which is inferred from the breakdown of omphacite to produce diopside ＋ plagioclase amphibole symplectites. This was overprinted by abundant amphibole and plagioclase of am

关 键 词：石榴石环带 矿物反应结构 超高压榴辉岩 变质演化 柴北缘鱼卡河 

分 类 号：P588.348[天文地球—岩石学]