Petrography and petrology of the calc-alkaline Sarihan Granitoid (NE Turkey): An example of magma mingling and mixing


Aslan Z.

TURKISH JOURNAL OF EARTH SCIENCES, cilt.14, sa.2, ss.185-207, 2005 (SCI İndekslerine Giren Dergi) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 14 Konu: 2
  • Basım Tarihi: 2005
  • Dergi Adı: TURKISH JOURNAL OF EARTH SCIENCES
  • Sayfa Sayıları: ss.185-207

Özet

There are many acidic intrusions of varying age in the northern and southern zones of the eastern Pontides, NE Turkey, and the Sarihan Granitoid is one of these. The Maastrichtian Sarihan Granitoid was emplaced into the pre-Permo-Carboniferous Pulur Massif, generally comprising medium-grade metamorphic rocks; the Liassic Hamurkesen Formation, that begins with the Dikmeta conglomerate and continues upward into voicano-sedimentary rocks; and the Maim-Lower Cretaceous Hozbjrikyayla Formation, comprising limestone and sandy limestones. The Sarthan Granitoid crops out in an area of approximately 40 km(2), 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% plagiociase, 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 1-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 Sr-87/Sr-86 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.