Petrography, Mineralogyand Thermodynamic Modeling of Eclogitesfrom the Serkout Area, Central Hoggar,Algeria

Abstract

The Aleksod terrane Eclogites, sited in the Central Hoggar, preserve a selection of eclogite-facies assemblage (coarse garnet, omphacite, quartz, clinozoisite and amphibole). During retrogression, these minerals were partially substituted with coronas and symplectites of diopside-plagioclase and amphibole-plagioclase. The almandine-dominated garnet proves to enclose heterogeneous compositions (XAlm0.30–0.56). The omphacite displays a high XJd of 0.31. The eclogite-facies coarse amphibole is magnesio-hornblende with NaM4 = 0.31– 0.47. The plagioclase is usually secondary exhibiting a range of composition from oligoclase to anorthite (XAn = 0.20–0.99), where albite-rich and anorthite-rich compositions prove to correspond, respectively, to symplectite after omphacite and coronas around epidote. The relevant P-T pseudosections using THERMOCALC-340 are calculated to estimate peak conditions and trace the PT evolution. At H2O-saturated conditions, inclusions of amphibole in garnet core with garnet composition from core to inner rim are used to trace pre-peak P-T path from 14 kbar–610 °C to 18 kbar–700 °C. At H2O-undersaturated conditions, the retrograde path has been traced using secondary phases as plagioclase, diopside and amphibole at 10 kbar–720 °C