ORIGINAL PAPER Phase equilibria modeling of kyanite-bearing eclogitic metapelites in the NCKFMASHTO system from the Egere terrane (Central Hoggar, South Algeria) Amar Arab & Khadidja Ouzegane & Amar Drareni & Sidali Doukkari & Souad Zetoutou & Jean-Robert Kienast Received: 9 December 2013 /Accepted: 31 March 2014 # Saudi Society for Geosciences 2014 Abstract Kyanite-bearing metapelites from the Egere terrane (Central Hoggar, South Algeria) have a high-pressure eclogitic facies paragenesis; furthermore, they preserve evi- dence of partial melting with the development of metamorphic textures involving garnet–kyanite–biotite–white mica–plagio- clase – K-feldspar – quartz – rutile and ilmenite. Garnet porphyroblasts in these rocks display a calcium zonation formed during high-P metamorphism followed by decompres- sion. Moreover, the large garnet poikiloblasts reflect complex mineral–melt relationships, and their growth was strongly linked to melt production. In order to give an account of the various textures and explain the evolution of the different parageneses in relation with pressure and temperature, ther- modynamic modeling in the Na2O–CaO–K2O–FeO–MgO– Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) system is a powerful approach. The intersection of isopleths of gros- sular content and Fe/(Fe+Mg) of core of garnet provides constraints on the P–T conditions of the metamorphic peak. Kyanite-bearing metapelites experienced a clockwise P–T path culminating at about 850 °C and 17–19 kbar. Peak conditions were followed by decompression to about 9 kbar and 750 °C. Keywords Egere . Hoggar . High-P metapelites . Pseudosection . THERMOCALC Introduction The Egere terrane (north of Hoggar) exposes some of the highest grade metamorphic rocks in the Pan-African orogen. These rocks preserve a variety of textures related to partial melting. The studied metapelites are characterized by an older paragenesis of garnet–kyanite–phengite–quartz and rutile that characterize the metamorphic peak in eclogite facies. The retrograde P–T path is evidenced by the growth of a secondary paragenesis involving garnet–biotite–plagioclase–sillimanite– K-feldspar–ilmenite associated to melt crystallization. These features examined the framework of P–T pseudosections, provide constrains on the P–T conditions, and elucidate the trajectory followed by the studied samples which can place an essential constraint on the tectonothermal evolution of the Egere terrane. Detailed observations of the field relationship and textural features are essential for providing a framework to understand the P–T evolution and the exhumation history of migmatized high grade metapelites. Careful petrographic studies provide important information on the consumption or appearance of certain index minerals at different stages during the metamor- phic evolution. Observations and analysis of leucosomes and melanosomes commonly show that the leucosomes represent anhydrous early crystallized products formed during cooling, and being composed primarily of quartz and feldspars, where the melanosomes include mainly kyanite, biotite, and silli- manite; in addition, the greater part of H2O in the rock occurs inside the melanosome and is incorporated in hydrous phases such as micas (e.g., Ashworth 1976; Waters and Whales 1984; Waters 1988; Kriegsman and Hensen 1998; Kriegsman 2001; Brown 2002). Pseudosections approach can be used to constrain P–T conditions of the thermal peak by comparing the calculated isopleths of mineral compositions with the measured compo- sitions (Powell et al. 2005). For instance, the grossular A. Arab (*) : K. Ouzegane : A. Drareni : S. Doukkari : S. Zetoutou LGGIP, FSTGAT, USTHB, BP 32 El Alia, Dar el Beida, 16111 Algiers, Algeria e-mail: amarab@usthb.dz J.<R. Kienast IPGP, 1 rue Jussieu, 75238 Paris Cedex 05, France Arab J Geosci DOI 10.1007/s12517-014-1413-z