Mineral chemistry of ophiolitic gabbros within central anatolia: Hirfanli dam gabbros

Abstract

The tectonic evolution of the magmatic rocks the Central Anatolia (CA) began at the late Mesozoic with closure of Neotethys in the region. The Central Anatolia has experienced several magmatic events including felsic and mafic intrusions originated from collisional and/or extensional tectonic events. The felsic magmatism of the CA are well reported and studied, whereas the origin and temporal distributions of the mafic magmatism are still controversial. This study includes the preliminary results of the TÜBİTAK project (116Y240) which aims to determine the mineralogical-petrographical, mineral chemistry and whole rock geochemistry of the Hirfanlı Dam gabbroic rocks in CA. The gabbroic rocks has dark to light green in color and fine-to-coarse grained crystal size. They are highly fractured, cracked and usually cut by fine crystalline gabbro and diabase dikes. According to the microscopic investigations, Hirfanlı Dam gabbroic rocks have holocrystalline granular and/or cumulate textures and mainly consist of plagioclase + pyroxene + amphibole + Fe-Ti oxides + chlorite + epidotite in composition. In addition, various alteration products such as uralitization, chloritization, epidotization, and carbonatization can be observed. These results are also supported by the Confocal Raman Spectrometry (CRS). Whole rock geochemistry of gabbroic rocks are characterized by relatively high Mg# (36.1±8.94) with remarkably low (Na2O+K2O) (1.56±0.92 wt.%), Zr (4.36±2.85 ppm), Th (0.64±0.64 ppm) contents. Moreover they have high TiO2 (1.13±0.75 wt.%), Fe2O3 (13.73±4.67 wt.%), CaO (12.27±0.74 wt.%) and V (867±801 ppm) contents. The gabbroic rocks are low-K tholeiite and show N-MORB in character. They display enrichment in LILE with relative to HFSE in MORB normalized multi-element diagrams. In this diagram, they exhibit depletions in Sr, Nb, Zr, TiO2 and Y as characteristics of subduction-related magmas. As a result, the petrographic and geochemical results suggest that gabbroic rocks of Hirfanlı Dam are the most probably products of supra-subduction ophiolite and may derived from N-MORB magma sources. © SGEM2019.