Phase Relationships and P-T path in NCFMASHTO System of the Eclogite from the Tighsi Area (Egere terrane, Central Hoggar, Algeria)

Abstract

The Tighsi area is situated in the northern part of the Egere-Aleksod terrane (Central Hoggar, South of Algeria). The eclogites and the garnet-amphibolites occur as lenses in marble, metapelite and quartzite. The petrological study shows that the high pressure paragenesis is characterized by the assemblage omphacite-garnet-rutile-quartz and epidote. Omphacite contains epidote, rutile and quartz inclusions. Due to the decompression, omphacite is the first mineral to destabilize into very thin symplectites of albite and clinopyroxene poorer of the jadeitic component. The paragenese of the lower pressure is represented by kelyphites and symplectites of amphibole-plagioclase separating garnet from omphacite and quartz. During this evolution, rutile transforms into ilmenite then, in the latest stage sphene replaces ilmenite. The thermodynamic modeling using THERMOCALC has confirmed these textural observations and suggests that the eclogites have experienced three stages of metamorphism...