Characteristics of the amphibolites from Nigde metamorphics (Central Turkey), deduced from whole rock and mineral chemistry

Abstract

Whole rock and mineral chemistry of amphibolites are presented for the lower (Gumusler Formation) and higher parts (Kaleboynu Formation) of the Nigde Massif with the aim to constrain protolith genesis and metamorphic P-T-conditions. The amphibolites, associated with a series of supracrustal metasediments, as thin layers and discontinuous pod/small lenses, are of igneous origin with composition of subalkaline and tholeiitic basalts. Based on immobile elements content and ratios, amphibolites from both formations are thought to have formed mostly by fractional crystallisation of pyroxene ± spinel, amphibole, plagioclase as well as apatite and titanite; coupled with minor crustal contamination. Contamination is particularly clear for the Gumusler Formation formed in a back-arc basin (Paleothetys) during magmatic ascent through the thickened Central Anatolian crust. The basic rocks could have been metamorphosed later at 7.5-3 ± 0.6 kb and 850-420°C, with the temperature gradient ranging from 35 to 122°C/km at different depths in the Neo-Tethyan subduction zone, and exhumed from depths of approximately 20 km via regional extension. Copyright © 2007 by The Geochemical Society of Japan.