大别山东南部变质花岗岩中霓石的发现及其地质意义

THE DISCOVERY OF AEGIRINE IN METAMORPHOSED GRANITE OF SOUTHEASTERN DABIE MTS AND ITS GEOLOGICAL IMPLICATIONS

大别山超高压变质带是华北与扬子板块俯冲碰撞作用的产物。迄今为止，报导的超高压变质岩除镁铁、超镁铁质岩石外，主要为火山－沉积岩，然而除上述岩石外，大别山南部出露大量花岗质片麻岩。作者在近期对大别山东南部变质花岗岩岩石学研究中发现：变质花岗岩中含有Ｇｔ＋Ｒｕ＋Ｐｈｅ±Ａｃｇ＋Ａｕｇ±Ｄｉ＋Ｐｌ＋Ｎａ－Ａｍｐ＋Ｏｒ＋Ｑ组合，与钠长石共生的霓石或透辉石可能是早期矿物硬玉或富硬玉质绿辉石退变的，而岩石中石榴石分带特征，即内带以铁铝榴石（４３．０６％）和钙铝榴石（４６．２８％）为主，外带则以锰铝榴石（３０．４０％）和钙铝榴石（３５．６７％）为主，这些都表明它们是由高压向低压退化变质之产物。因此，变质花岗岩可能早期存在着这样的榴辉岩相峰期矿物组合Ｊｄ／ｏｍｐ＋Ｑ／ＣＳ＋Ｐｈｅ＋Ｒｕ＋Ｇｔ＋Ｏｒ，这个组合由于后期的压力降低而退变为中低压的矿物组合。

The Dabie ultrahigh pressure metamorphic belt is resulted from the collision of North China and Yangtze Plates.So far, the ultrahigh pressure metamorphosed rocks have been reported mainly as mafic and ultramafic rocks as well as volcanic-sedimentary rocks, in reality,a lot of granitic gneisses occur in southern Dabie Mt.s. Recently,the authors found an association of Gt+Ru+Phe±Aeg+Aug±Di+Pl+Na-Amp+Or+Q oc curring in metamorphosed granites of southeastern Dabic Mt. s. The aegirine or diopside coexisting with albite may be retrograded from the mineral jadeite of jadeite. The garnet compositon zoning in the rocks is characterized by an inner zone of almandine (43.06%) and grossular(46.28%) and an outer zone of spessartine (30.40%) and grossular(35.67%). All this indicates that the rocks are products of retrograde metamorphism from high pressure to low pressure. So. there might have been such a climax eclogite facies of mineral associatoin in metamorphosed granites as Jd/Omp+Q/Cs+Phe+Ru+Gt+Or.This association was retrograded into a mediumlow pressure one due to later pressure drop.