Contemporaneous Late Cretaceous Calc-alkaline and Alkaline Magmatism in Central Anatolia, Turkey: O Isotope Constraints on Petrogenesis

Authors: NURDANE İLBEYLİ, JULIAN A. PEARCE, IAN G. MEIGHAN, ANTHONY E. FALLICK

Abstract: A wide variety of rock types were produced by the latest Cretaceous magmatism in the Central Anatolian Crystalline Complex. These rocks can be divided into three distinct units: (i) calc-alkaline, (ii) subalkaline/transitional, and (iii) alkaline. The calc-alkaline rocks are mainly metaluminous (I-type) ranging from monzodiorite to granite. The subalkaline/transitional rocks are also metaluminous (I-type) ranging from monzonite to granite. The alkaline rocks are mainly peralkaline (A-type), ranging from feldspathoid-bearing monzosyenite to granite. Whole-rock oxygen isotope data from the complex have a considerable range of \delta18O values between 6.5 per thousand and 14.8 per thousand. Initial 87Sr/86Sr versus 143Nd/144Nd ratios, and both ratios versus \delta18O values diagrams show that the intrusive rocks are derived from a subduction-modified mantle and also have experienced fractional crystallisation coupled with crustal assimilation. Delamination of a thermal boundary layer, and/or slab breakoff is the likely mechanisms for the initiation of the diverse magmatism in the complex.

Keywords: I-type granite, A-type granite, oxygen isotope, Kaman-Kırşehir region, central Anatolia, Turkey

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