大别山榴辉岩一片麻岩杂岩的成因

ORIGIN OF ECLOGITE-GNEISS COMPLEXES FROM DABIE MOUNTAINS

大别山榴辉岩由辉长岩、大陆拉斑玄武岩和少量泥灰质经高压变质作用形成。大别地块可划分出四个形成条件不同的榴辉岩区，它们代表一种构造－岩石组合体。片麻岩杂岩中各种高压变质岩类的发现证明它们与榴辉岩一起经历了原地高压变质过程。二者变质作用Ｐ－Ｔ参数的差异归因于抬升过程中退变质反应速度的不同。不同地区榴辉岩退变质组合及Ｐ－Ｔ条件与围岩的一致性表明，大别杂岩现今所展示的“递增”变质带是由榴辉岩相退变质作用形成的。高压榴辉岩－片麻岩杂岩的产生是印支期扬子与华北两个大陆板块碰撞的结果。

The petrochemistry and geochemistry of eclogite from the Dabie Mountains indicate that the protolith is either gabbro formed in continental extension or the bedded continental tholeiites corresponding to Late Archean supercrustal rocks, with a minority derived from lime mudstone. The Dabie massif can be divided into four eclogite regions which formed at different metamorphic conditions. It is a tectonicpetrological assemblage. The recent discovery of high-pressure metamorphic rocks in the gneiss complexes suggests that eclogite together with its country rocks has experienced in-situ highpressure nietamorphism. Eclogite has a different velocity of retrograde metamorphic reactions, so a different P-T path from gneisses during uplift process. The consistency of retrograde metamorphic mineral assemblages and P-T conditions in eclogite and in its country rocks (gneiss complexes) indicates that the 'progressive' metamorphic zone occuring in the Dabie complexes is caused by the retrograde metamorphism of eclogite facies. Eclogite-gneiss complexes from the Dabie Mountains are the direct product of collision between two continental plates,the North China plate and the Yangtze plate.