MINERAL CHEMISTRY OF ULTRAMAFIC AND MAFIC CUMULATES AN INDICATOR OF THE ARC-RELATED ORIGIN OF MERSIN OPHIOLITE (SOUTHERN TURKEY)

The Mersin ophiolite, represented by approximately 6-km-thick oceanic lithospheric section on the southern flank of the Taurus calcareous ax is, formed in the Mesozoic Neo-Tethyan ocean some time during Late Cre taceous in southern Turkey. The ultramafic and mafic cumulates having over 3 km thickness consist of dunite+/-chromite, wehrlite, clinopyrox enite at the bottom and pass into gabbroic cumulates in which leucogab bro, olivine-gabbro and anorthosite are seen. Crystallization order is olivine (Fo(91-80)) +/-chromian spinel (Cr# 60-80), clinopyroxene (Mg # (95-77)), plagioclase (An(95.6-91.6)) and orthopyroxene (Mg# (68-77) ) Mineral chemistry of ultramafic and mafic cumulates suggest that hig hly magnesian olivines, clinopyroxenes and absence of plagioclase in t he basal ultramafic cumulates are in good agreement with products of h igh-pressure crystal fractionation of primary basaltic melts beneath a n island-are environment. Major, trace element geochemistry of the cum ulative rocks also indicate that Mersin ophiolite was formed in an are environment. Coexisting Ca-rich plagioclase and Fo-rich olivine in th e gabbroic cumulates show are cumulate gabbro characteristics. Field r elations as well as the geochemical data support that Mersin ophiolite formed in a supra-subduction zone tectonic setting in the southern br anch of the Neo-Tethys in southern Turkey.