TOURMALINITE FORMATION IN THE YOZGAT BATHOLITH, CENTRAL ANATOLIAN CORE COMPLEX, TURKEY: A CASE STUDY FOR ITS STRUCTURAL SETTING

The Central Anatolian core complex (CACC) in Turkey consists of metamorphic rocks, granitoid intrusions and ophiolitic/ophiolitic mélange rocks. The Yozgat batholith, has mostly an E-W-trending and range from monzonite to granite/siyenite through diorite. Within the granitic rocks of the Yozgat batholith, numerous tourmalinite veins were formed with related to B-rich fluids of the magma. In outcrop, veins are filled with black tourmaline, lesser amount of milky quartz and pale green epidote. Quartz and tourmaline mineral aggregates in veins produce breccia, augean, lenticular and branching texture. They range from a few millimeters to 8 meters thick and can be traced laterally for tens meters. The wall rocks of the tourmalinite are granite, pegmatite and quartzite zone product of the same magma. Although tourmaline veins walls are sharp and generally strike ENE to NE less of them are irregular in shape and dimensions. Petrography and microstructures in tourmalinite veins and granitoids shows that tourmalinites occurred in three distinct stages with changes in fluid parameters in B-rich magma and structure in region. The first generation tourmaline is medium- to coarse-grained and generally brown and greenish brown in color indicating probably dravite. The second stage tourmaline is fine-grained and green and bluish green indicating schorl. Much of tourmaline formed in this stage. They surround the first stage tourmaline crystals and display overgrowths and embayment with them. After these two stage both granitoids and tourmalinites were affected by ductile and brittle deformations. Ductile deformation is commonly protomylonitic to mylonitic in character with a top to the north sense of shear indicators. Brittle deformation produced faults, brittle shear zones and fault rocks (breccia, cataclasite, pseudotachylyte). The third stage tourmaline result from the brittle deformation and this stage was accompanied by deposition of various combinations of epidote quartz, K-feldspar and tourmaline in extensional fractures. Based on some isotopic analysis in granitoids of CACC, these plutonic rocks range in age from Upper Cretaceous to Paleocene. The granitoid rocks in the study area are covered by unconformably Eocene conglomerates that contain tourmalinite grains with different size.