Petrography and Petrology of the Calc-Alkaline Sarıhan Granitoid (NE Turkey): An Example of Magma Mingling and Mixing

Authors: ZAFER ARSLAN

Abstract: There are many acidic intrusions of varying age in the northern and southern zones of the eastern Pontides, NE Turkey, and the Sarıhan Granitoid is one of these. The Maastrichtian Sarıhan Granitoid was emplaced into the pre-Permo-Carboniferous Pulur Massif, generally comprising medium-grade metamorphic rocks; the Liassic Hamurkesen Formation, that begins with the Dikmetaş conglomerate and continues upward into volcano-sedimentary rocks; and the Malm-Lower Cretaceous Hozbirikyayla Formation, comprising limestone and sandy limestones. The Sarıhan Granitoid crops out in an area of approximately 40 km2, has an ellipsoidal shape, and comprises mainly quartz monzodiorite, granodiorite and lesser quartz diorite. The pluton contains volcanic and silicified limestone xenoliths and dioritic mafic microgranular enclaves. The plutonic rocks show medium-grained, poikilitic, monzonitic, anti-rapakivi and sometimes myrmekitic textures, and contain 43-64% plagioclase, 6-18% orthoclase, 10-29% quartz, 5-20% hornblende, 1-85% biotite, 1-6% opaque oxides, accessory amounts of apatite, titanite and zircon, and secondary phases of calcite, chlorite and sericite. Some textures may suggest magma mixing, whereas the presence of mafic microgranular enclaves indicates that magma-mingling processes were operative in the evolution of the pluton. The pluton has 65-67% SiO2, 1.4-3.1% MgO, 4.1-5.5% Na2O and <1 K2O/Na2O. Generally, the pluton is I-type, metaluminous and has characteristics of cafemic-group granitoids, suggesting a hybrid source derived by mixing of sialic and mantle sources. The pluton has calc-alkaline composition and is characterised by a calc-alkaline granodiorite-series trend. TiO2, Al2O3, FeO, Fe2O3, MnO, MgO, CaO, P2O5, Ba and Ni decrease whereas Na2O, K2O, Rb and Nb increase with increasing SiO2 content. These geochemical variations indicate the importance of fractional crystallisation, which was mainly controlled by plagioclase and hornblende. However, some irregular variations in major and trace elements may be results of magma mixing. Zn, Rb, Sr, La, Pb, Th and Zr show enrichment whereas Ce, Cr and Ni exhibit depletion compared to continental crust values, resembling those of volcanic-arc granitoids. With regard to discrimination of tectonic setting, the pluton represents pre-plate collision volcanic-arc granitoids. The 87Sr/86Sr ratio (0.70504) of the pluton also indicates a hybrid magma which likely was derived by mixing of a mantle source with a crustal component. Field observations suggest a stoping type of ascent and emplacement style.

Keywords: eastern Pontides, Sarıhan Granitoid, mafic microgranular enclaves, magma mixing/mingling, Rb/Sr isotope, petrology, calc-alkaline volcanic-arc granite

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