Abstract:

Garnet pyroxenite inclusions within marble, from Rongcheng, northern Sulu ultrahigh-pressure metamorphic (UHPM) terrane are studied in detail.The garnet pyroxenite samples are divided into three parts (core, mantle and rim) according to their petrographic characteristics.The core of the retrograded garnet pyroxenite is composed of garnet and clinopyroxene.In the mantle, fine grained symplectites of hornblende and epidote occur along the garnet and clinopyrocene grains.It is suggested that these symplectites are developed from  garnet and clinopyroxene reacted with fluids from the wall rock.The reaction was not completed which is evidenced by the  larger hornblende and clinopyroxene relics remained in the retrograded garnet pyroxenite mantle.The larger hornblende came from the clinopyroxene.The rim of the retrograded garnet pyroxenite is composed of hornblende and epidote.The results of Laser Raman experiments indicate no coesite existed in the retrograded garnet pyroxenite, whereas coesites are found in all other type of rocks near these sample sites.It is likely that the garnet pyroxenite also proceeded the ultrahigh pressure metamorphic condition.The reason of absence of coesite in the rock is merely that the primary rocks are ultramafic.

Key words: garnet pyroxenite, retrograde reaction, Sulu, UHP metamorphic belt