Late Cretaceous subduction initiation and Palaeocene–Eocene slab breakoff magmatism in South-Central Anatolia, Turkey

Abstract

The Late Cretaceous Alihoca ophiolite in the Inner Tauride suture zone (ITSZ) of South-Central Turkey represents part of a single ophiolitic thrust sheet that originated from the Inner Tauride ocean. The ophiolite contains upper mantle peridotites, cumulate wehrlites, layered-to-isotropic gabbros, and microgabbroic-to-doleritic dikes. An ophiolitic mélange beneath the Alihoca ophiolite includes blocks of limestone, peridotite, dolerite, basalt, and deep-sea sedimentary rocks (radiolarite, chert) in a matrix comprising sheared serpentinite and mudstone. Isotropic gabbro and dolerite dike rocks show enrichment in Sr, K, Rb, Ba, and Th (LILE) and depletion of Ta, Nb, Zr, Ti, and Y (HFSE), indicating an island arc tholeiite (IAT) affinity. Relatively younger dolerite rocks display low TiO₂ (<0.5 wt.%) contents, concave REE profiles with low HREE concentrations, and high LREE values, typical of boninitic affinities. The Alihoca ophiolite, hence, displays an IAT to boninitic geochemical progression in its magmatic evolution, reminiscent of many other Tethyan ophiolites in the region. It represents the remnant of a forearc oceanic crust, which developed during the early stages of subduction within the Inner Tauride ocean. Volcanic, volcano-sedimentary, and sedimentary rocks of the Ulukışla–Çamardı basin north of the ITSZ disconformably overlie the mafic-ultramafic rocks of the Alihoca ophiolite. Pillowed and massive lavas of the latest Cretaceous–Palaeocene Ulukışla Formation have alkaline basalt-to-basaltic andesite compositions, displaying relatively enriched LILE and LREE patterns with negative Nb and Ta anomalies. These geochemical features suggest that magmas of the Ulukışla–Çamardı volcanic rocks formed from partial melting of a metasomatized lithospheric mantle. This melting event was triggered by the influx of asthenospheric heat through a slab breakoff-induced window in the downgoing Tethyan oceanic lithosphere.

Keywords:

• Alihoca ophiolite (Tauride ophiolite belt)
• suprasubduction zone ophiolites
• forearc magmatism
• alkaline volcanics (Ulukışla–Çamardı basin)
• enriched lithospheric mantle source
• extensional tectonic setting
• slab breakoff

Acknowledgements

This study has been conducted as part of the projects of the General Directorate of the MTA – Turkey, ‘Geology of the Central Tauride Belt’ and ‘Ophiolite Inventory of Turkey’. E. Sarifakioglu thanks TUBITAK for a scholarship (2005-NATO-B2) granted for her geochemical studies at Keele University, UK. We also especially thank David Emley (Keele University) for his analytical assistance. Y. Dilek acknowledges National Science Foundation EAR-Tectonics Division and Miami University research grants for his work on the Tauride ophiolites. We are grateful to Osman Parlak, Erdin Bozkurt, and the anonymous referee for their constructive comments on an earlier version, which considerably improved this article.