Petrology and mineralogy of (retrograded) eclogites from Mengku area, Shuangjiang County, western Yunnan Provinc

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.