江苏东海榴辉岩向斜长角闪岩转化的研究  

Transformation from the Donghai Eclogite to Amphibolite in the Southern Sulu UHPM Terrene

作　　者：杨天南[1] 许志琴[1] 陈方远[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2003年第4期510-521,共12页Acta Geologica Sinica

基　　金：国家重大科学工程"中国大陆科学钻探工程"项目;"中国大陆科学钻探工程"科学研究项目(编号 2001CCB00900);国土资源部科技项目(编号 2002207)资助的成果

摘　　要：东海榴辉岩曾被俯冲到上地幔,而后又折返回地表,经历了宽广的温度、压力、应力、流体条件等变化范围,形成了大量矿物反应结构,为研究岩石矿物反应提供了很好的素材。本文选取东海地区一个保留从初始榴辉岩到斜长角闪岩完整退变质序列的榴辉岩体作为研究对象,通过详细的显微结构观察、矿物成分分析、成分空间分析、成分迁移估算,揭示了东海榴辉岩向斜长角闪岩的转化过程。该过程可划分为两个阶段:早期为替代绿辉石的后成合晶形成阶段,通过绿辉石内部端元组分间的反应实现,反应产物之一的Fe^(2+)与金红石结合形成钛铁矿,Ca、Mg被排出到绿辉石体系之外。晚期退变为流体的渗滤交代作用,表现为石榴子石被角闪石部分取代、后成合晶的角闪石化,以及黝帘石、白云母的形成。退变质的最后阶段为石榴子石被绿帘石+角闪石+赤铁矿完全替代。榴辉岩转化成含帘石的斜长角闪岩。The Donghai eclogite in the Southern Sulu ultra-high pressure metamorphic (UHPM) terrene experienced wide-range variations of pressure, temperature, stress and fluid actions, resulting in a lot of microtextures, which provide indications for the study of mineral reactions. An eclogite sample retaining a complete retrograde process was analyzed in this study. Its transforming procedure from the eclogite phase to the amphibolite phase was revealed through detailed observations of microtexture, mineral chemistry, chemical space, and mass-balance. The procedure is divided into two stages: the earlier one is symplectitization. In this stage, diopside+ albite symplectite replaced omphacite only, which resulted from reactions among end-members within omphacite grains. The product Fe2+ was combined with rutile to form ilmenite; some products, such as Ca and Mg, were expelled out of the omphacite system. The latter stage is fluid infiltration caused by fluid action, which resulted in a hydrous mineral assemblage: hornblende + epidote (or ziosite) (+ phengite) + albite, replacing the earlier assemblage: garnet + diopside + albite. Finally, more and more fluids intruded the partially retrograded eclogite and then the remnant garnet was replaced by ziosite + hematite (+ hornblende). As a result, the eclogite was transformed to epidote-bearing amphibolite.

关 键 词：东海榴辉岩 渗滤交代 显微结构 成分迁移估算 后成合晶 

分 类 号：P588.3[天文地球—岩石学]