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Origin and significance of a quartz tourmaline breccia zone within the central anatolian crystalline complex, Turkey

Demirel, Serhat
The aim of this study is to investigate the petrography, geochemistry and evolution of quartz-tourmaline-rich rocks occurring in a wide breccia zone within the Late Cretaceous Kerkenez Granitoid (Central Anatolian Crystalline Complex (CACC), Turkey). The approximately 40-m wide main breccia zone has a NE-SW trend and is characterized by intense cataclastic deformation. The breccia zone can be traced several kilometers towards the west and generally occurs as tourmaline-filled faults and 1mm-30cm-thick veins within the granitoid. On the basis of mineralogical and textural features, rocks within this zone are defined as tourmaline veins, tourmaline-breccias and quartz-tourmaline rocks. These rocks are generally composed of quartz, tourmaline and granitic fragments. Petrographical investigations and electron-microprobe analyses indicate that, there are three optically and chemically different tourmaline generations. From oldest to youngest, the tourmalines are classified as blue pleochroic feruvites, blue-green pleochroic schorls and green-light green pleochroic schorls. The chemistry of the tourmalines suggests that these tourmalines crystallized from boron rich fluids derived from an evolving magma. Consequently, the quartz tourmaline-breccia zone is considered to have formed by the injection of overpressured boron rich fluids into faults and fractures present within the Kerkenez Granitoid. Fluid-filled faults and fractures were sealed by quartz-tourmaline crystallization. This led to further fractionation in the magma, new fluid pressure accumulations, reactivation of faults and crystallization of different tourmaline generations. Tourmaline-breccia zones are scarce in the literature and the presence of such rocks within the CACC is first reported in this study.