Geochemistry and zircon U-Pb geochronology constrains late cretaceous plagiogranite intrusions in Mersin ophiolite complex (southern Turkey).


Nurlu N. , Türkmen S. , Şimşek G., Stepanov A. S.

ARABIAN JOURNAL OF GEOSCIENCES, cilt.11, 2018 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

In this study, LA-ICP-MS U-Pb zircon dating were used to determine the age of the newly discovered plagiogranite suite intruding gabbro and volcanic units of Mersin ophiolites from the Inner Tauride Belt. Obtained U-Pb zircon ages from the plagiogranite yielded crystallization ages of 93.0 +/- 1.5 to 94.2 +/- 2.4Ma (Turonian-Cenomanian) supporting the idea of Late Cretaceous active subduction factory in the Tauride Suture Zone. The plagiogranites are mainly granodioritic, and tonalitic in composition, and contain mafic microgranular enclaves (MME) ranging from 10 to 45cm in size. The plagiogranites are geochemically defined by low K2O (0.02-1.03wt%) and TiO2 (0.17-1.88wt%) and comparatively high Na2O (2.3-10.2wt%) and SiO2 (70-78wt%) compositions together with depletion in Ti, Ta, and Nb. The tectonomagmatic discrimination diagrams, trace, and REE-normalized multi-element patterns indicate that the plagiogranites are distinctive calc-alkaline, I-type volcanic arc granites. Plagiogranites are furthermore characterized by the diffuse presence of isotropic pseudomorphic growth of secondary calcic-amphibole (edenite and actinolite) over a pristine not preserved Ca-inosilicate. Inverse geothermobarometry models indicate a secondary amphibole genesis at ca. 600 degrees C and 1.5-1.7kbar, suggesting HT-metasomatism affecting the already intruded plagiogranites. While it is already accepted that Mersin ophiolite complex is generated in a supra-subduction zone, this study represents a new contribution on the evolution of the Mersin ophiolite during the Late Cretaceous Neotethys subduction and could shed light on the genesis of plagiogranites in arc-environments.