大别山造山带的糜棱岩

摘要

Mylonites in the Dabie orogen are fault and shear zone related rocks formed under metamorphic conditions. They can be divided into greenschist, amphibolite, granulite, and eclogite facies mylonites. The main criterion for identifying the mylonites in the Dabie Mountain is the ductile (plastic) deformation of index minerals of the constituent metamorphic facies. This is clearly different from the former definition and description of my-lonite. Formation epoch of the mylonites in the Dabie Mountain was approximately the same as (or a little later than) that of peak metamorphism of their host rocks. From older to younger, the series follows the order eclogite facies mylonite→granulite facies mylonite→amphibolite facies mylonite→greenschist facies mylonite. According to lithology and texture, the mylonites can be further divided into second and third subclasses if necessary. Former mylonites of eclogite and granulite facies are always superimposed by the later facies and show the appearance of amphibolite or even greenschist facies mylonites; the earlier formed mylonites are thus preserved as relics in their retrograded products. Mylonites in the low-grade metamorphic rocks in southern and northern Dabie Mountain only experienced the metamorphic history of greenschist and amphibolite facies mylonitization during the Paleozoic-Triassic period.%变质作用是糜棱岩的主要形成机制和鉴别标志.大别山糜棱岩是在变质作用条件下形成的与断层(或剪切带)有关的岩石,可分为绿片岩相、角闪岩相、麻粒岩相和榴辉岩相糜棱岩.大别山糜棱岩的主要鉴别标志是相应变质相标志矿物的韧(塑)性变形或晶内变形,这与以往关于糜棱岩的定义有明显不同.大别山高压(超高压带内的各类糜棱岩的形成时代与同相母岩峰期变质作用大致同期或略晚,从老到新的顺序是:榴辉岩相糜棱岩→麻粒岩相糜棱岩→角闪岩相糜棱岩→绿片岩相糜棱岩.根据需要,大别山的糜棱岩可按岩性和结构做次级和更次级的分类.早期形成的榴辉岩相和麻粒岩相糜棱岩常常受到晚期角闪岩相糜棱岩和/或绿片岩相糜棱岩的叠加而成残留体,并使大部分被改造成为晚期糜棱岩的外貌.大别山南部和北部低级变质岩内只有角闪岩相和绿片岩相糜棱岩,形成时代从古生代到三叠纪.