大别山北部榴辉岩的退变质特征及其地质意义  

Retrograde Characteristics of the Eclogites in Northern Dabie Mountains,Central China and their Geological Significance

作　　者：刘贻灿[1] 徐树桐[1] 李曙光[2] 陈冠宝[1] 

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

出　　处：《矿物岩石地球化学通报》2003年第4期299-304,共6页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金项目(40172079);科技部基础研究重大项目前期研究专项(2001CCB00900)资助

摘　　要：研究了大别山北部榴辉岩的变质岩岩石学。结果表明,该区榴辉岩相变质作用可分为早期(超高压)和晚期(高压)两个阶段,并在折返过程中形成了一系列特征性的退变质显微构造。其中,退变质结构主要包括:(1)由于压力降低而出溶形成的一些定向针状或叶片状矿物包裹体,如钠质单斜辉石中石英及石榴子石中的金红石、单斜辉石和磷灰石等;(2)冠状体或后成合晶,特别是石榴子石外围发育两期("双层")后成合晶;(3)反应边或退变边,如绿辉石的透辉石退变边、透辉石的角闪石退变边和金红石的钛铁矿退变边等。这些退变质结构为本区榴辉岩高级变质岩的快速折返过程和抬升历史提供了强有力的岩石学依据;石榴子石中针状矿物出溶体进一步证明研究区榴辉岩早期经历了超高压变质作用,峰期变质压力应大于4.0GPa,甚至可能达到5～7GPa或更高。The metamorphic petrology of eclogites from northern Dabie Mountains was performed. The results suggest that the metamorphism of eclogite-facies in northern Dabie Mountains could be subdivided into the earlier ultrahigh-pressure stage and the later high-pressure stage. The eclogites contain a series of characteristic retrograde textures, including: (1) oriented quartz needles in Na-clinopyroxene and rutile, clinopyroxene and apatite exsolution in garnet formed under the condition of decreasing pressure during exhumation; (2) corona or symplectite and, especially, two generations of symplectites developed at the rims of garnet grains; (3) reaction rim or retrograde rim, e.g., omphacite with diopside rim, diopside with amphibole rim, and ilmenite rim of rutile. These retrograde micro-textures provide petrological evidence for rapid exhumation process and uplift of the high-grade metamorphic rocks such as eclogite in northern Dabie Mountains. In addition, needle mineral exsolutions in garnet confirm that the studied eclogites experienced ultrahigh-pressure metamorphism with the pressure of over 4.0GPa or even over 5-7GPa, equivalent to a depth of over 200km below the surface.

关 键 词：榴辉岩 超高压 退变质作用 大别山 地质意义 

分 类 号：P588.3[天文地球—岩石学]