Phase and cryptic variation through the ultramafic-mafic cumulates in the Mersin ophiolite (Southern Turkey)


OFIOLITI, vol.22, no.1, pp.81-92, 1997 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 22 Issue: 1
  • Publication Date: 1997
  • Title of Journal : OFIOLITI
  • Page Numbers: pp.81-92


Mersin ophiolite, one of the Cretaceous Neo-Tethyan realm in eastern Mediterranean, is situated in the southern part of the Taurus calcareous axis in Turkey. Cumulate rocks, occupying an area approximately 15 km2, crop out within the N-S oriented Sorgun valley (Mersin) in the western parr of the ophiolitic massif. Cumulates have over 3 km thickness. They start with 800 m of ultramafic rocks at the bottom and continue into 2500 m of gabbroic rocks. They show tectonic contacts with mantle harzburgites at their base and with basaltic rocks at the top. Polycyclic cumulate feature is observed in the mafic and ultramafic cumulate rocks. Ultramafic cumulates, showing adcumulate-heteradcumulate texture, consist mainly of dunite, wehrlite and pyroxenite. Igneous lamination, size grading and rhythmic layering are observed as accumulation features in the ultramafic cumulates. Mafic cumulates, mainly of gabbro, leucogabbro, olivine gabbro and anorthosite, constitute almost 2/3 of the whole cumulate section. Mafic cumulate rocks are fresh and present accumulate, mesocumulate and orthocumulate texture. Size grading and rhythmic layering are also seen in mafic cumulates. Cryptic variation is small throughout the entire thickness of the layered sequence. Olivine varies from Fo(91) to Fo(80) clinopyroxene from Mg# 93 to 77, and plagioclase from An(95) to An(91) through the 3 km vertical sequence. Adcumulate-mesocumulate growth in ultramafic and mafic cumulates indicates slow accumulation rate. Absence of zoning in the cumulus and intercumulus phase suggests a crystallization process bulk equilibrium condition at high temperature as confirmed by high Mg/Fe ratio and high Ca content of the plagioclase.