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ORBICULAR GABBRO AS AN INDICATOR OF MAGMA MIXING FROM STRANDJA MASSIF, NORTHWEST TURKEY: MINERAL CHEMISTRY AND CONFOCAL RAMAN SPECTROMETRY METHODS

Ezgi Ulusoy

Abstract

Strandja Massifs? units form the basement metamorphic units of north western edge parts of Turkey and intruded by the Late Cretaceous felsic and mafic intrusive rocks. The felsic and mafic rocks have a contact metasomatic effects at the border of sedimentary rocks resulting in the formation hornfels, metasandstone and calcsilicaticfels in the composition. Demirk?y is one of the youngest intrusive body which crops out at NE of the massif and mainly composed of granite, granodiorite, diorite and gabbro in composition. The intrusive body of the Demirk?y has a fresh out crop and mainly has fine to coarse crystalline texture and they have angular to elliptical shaped mafic microgranular enclaves (MME). The MEE are ranging in size from 1cm up to 30 cm in the composition of diorite and quartz diorite. The mafic intrusive rocks of Demirk?y body are in the composition of diorite at the contact with felsic intrusive and change to gabbro in composition at inner part of the body. The gabbroic rocks with the carbonate metamorphic rocks have orbicular textures. These scarce sections with special texture reveals specials conditions. Each orbicular rounded and elliptical shape with different size changing from 1 cm up to 30 cm in size. All orbicular consist of several concentric circles showing magmatic textures in hand specimen and under the microscope. The circle of orbicular is mainly composed of olivine, pyroxene, amphibole, plagioclases and Fe-Ti oxide minerals. The Orbicular rings of gabbroic rocks occupy repeating coarse grain minerals and fine grain crystals. Core of orbicular cycle have subophitic texture and composed of coarse grain crystals. Surrounded rings have subophitic texture with fine texture and rich in olivine with comparison to the core part of the circle. The Mineral chemistry studies with electron prob microanalysis (EPMA) reveal that the pyroxene are ranging in composition from augite to diopside, plagioclase are ranging in composition from bytownite to labrodorite and the olivine are generally in the composition of forsterite with high amount of Mg contents. The mineralogical, petrographical and geochemical features indicate that the orbicular body form a part of mafic magmatic enclaves within the mafic intrusive rocks and they are the products of the late injection of a basic magma in to the whole body of the main basic magma chamber and cause to acting with parent magma body resulting the crystallization of repeated circler body during the circular convection in the form of orbicular texture within the main intrusive body.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s01.047

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