滇西双江县勐库地区（退变）榴辉岩的岩石学、矿物学特征

摘要

Retrograded eclogites are exposed in structural-sheet form in Naka River, Kongjiao and some other areas north of Mengku Town, Shuangjiang County of west Yunnan Province and occur in Ordovician Wanhe ophiolite mélange belt. According to different retrograde degrees, the exlogites can be divided into retrograded eclogites, garnet-amphibolite and garnet-bearing am⁃phibolite. The main minerals include garnet, clinopyroxene, amphibole, and plagioclase together with minor rutile, phengite, jade⁃ite,epidote, biotite, apatite, quartz etc. Omphacite, which is a typical HP-UHP metamorphic mineral, only exists as inclusions in a small amount of garnet and amphibole. Petrological and mineralogical characteristics show that the mineral assemblage at the meta⁃morphic peak is Omp+Gt+Ru+Q+Phen. Due to the growth of radial bulging cracks around some quartz inclusions in garnet, it is held that some quartz inclusions belong to retrograded coesite. The retrograded eclogite therefore must have undergone UHP meta⁃morphism.%滇西双江县勐库镇以北的那卡河、控角等地出露的(退变)榴辉岩以构造岩片的形式产于奥陶纪湾河蛇绿岩混杂岩带中。根据退变质程度差异依次划分为退变榴辉岩、榴闪岩、含石榴斜长角闪岩，主要矿物成分为角闪石、石榴子石、单斜辉石、斜长石，次要矿物成分为金红石、多硅白云母、硬玉、绿帘石、黑云母、磷灰石、石英等，特征的高压-超高压变质矿物绿辉石仅残余在少量的石榴子石、角闪石中，以包裹体形式产出。岩石学和矿物学研究显示，该榴辉岩峰期变质矿物组合为：绿辉石＋石榴子石＋金红石＋石英+多硅白云母。石榴子石中的部分石英包裹体周围发育放射状的胀裂纹，暗示其可能由柯石英转化而成。由此推断，该榴辉岩可能经历了超高压变质作用。