“罗田穹隆”中的下地壳俯冲成因榴辉岩及其地质意义  

Eclogite from the Subducted Lower Crust of the Yangtze Plate within the Luotian Dome and its Geological Implication

作　　者：刘贻灿[1] 徐树桐[2] 李曙光[1] 陈冠宝[2] 彭练红 

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230026 [2]安徽省地质调查院,安徽合肥230001 [3]湖北省地质调查院,湖北武汉430022

出　　处：《地球科学（中国地质大学学报）》2005年第1期71-77,共7页Earth Science-Journal of China University of Geosciences

基　　金：国家"973"专项项目 (2 0 0 3CB71 6 5 0 0 ) ;国家重点基础研究发展规划项目 (G1 9990 75 5 0 3) ;国家自然科学基金项目 (No .40 1 72 0 79)

摘　　要：在“罗田穹隆”中发现了下地壳俯冲成因榴辉岩 .榴辉岩呈透镜状或板状产于含石榴子石条带状片麻岩中 .新鲜的榴辉岩主要由石榴子石、绿辉石、金红石等组成 ,含少量退变质的角闪石、斜长石、紫苏辉石、透辉石、(钛 )磁铁矿和石英等 .研究区榴辉岩以保留早期麻粒岩相变质矿物残留体以及经受晚期麻粒岩相和角闪岩相退变为特征 ,指示它们由扬子镁铁质下地壳麻粒岩相岩石俯冲到深部发生变质并形成榴辉岩 ,然后折返至下地壳发生麻粒岩相退变 ,由于麻粒岩相退变质阶段仅以后成合晶形式出现 ,因而它们可能在下地壳停留时间不长 ,就又进一步被构造抬升至中上地壳而发生角闪岩相退变 .大别山造山带乃至扬子板块北缘现今缺乏厚层镁铁质下地壳 ,它们也很少出露地表 ,推测这些俯冲的镁铁质下地壳可能已拆离再循环进入地幔 .从而为“罗田穹隆”的形成和演化以及大别山高压The eclogite produced from the subducted mafic lower crust of the Yangtze continental plate is a new finding within the Luotian dome in northern Dabie Mountains. The eclogites occur as lens in garnet-bearing banded gneisses. The mineral assemblage of the eclogite is garnet, omphacite, rutile and quartz; secondary minerals are hornblende, plagioclase, hypersthene, diopside and ilmenite. The eclogites from the Luotian dome have typical characteristics with relics of earlier hypersthene and plagioclase minerals of granulite-facies and latter overprinting of granulite-facies. No aqueous mineral formed during peak metamorphism may be related to their protoliths, which come from the lower crust. Petrologic evidence suggests that the eclogites studied were produced from the mafic lower crust of the Yangtze continent and suffered from granulite- and amphibohte-facies retrogressive metamorphism. At present, mafic rocks from the lower crust in the Dabie Mountains or even in the northern Yangtze plate have been scarce, which may be delaminated and recycled into underlying converting mantle. These provide key petrologic evidence for formation and evolution of the Luotian dome, and formation and exhumation processes and uplift of high-grade metamorphic rocks such as eclogite in the northern Dabie Mountains.

关 键 词：榴辉岩 麻粒岩相 下地壳 罗田穹隆 大别山 

分 类 号：P581[天文地球—岩石学]