Sultansazlığı (Kayseri) Havza Kenarı Miyo-Pliyosen Volkanizma Ürünlerinin Petrolojik Korelasyonu

Abstract

Upper Miocene - Pliocene sequence of the Sultansazlığı Basin consists of calc-alkaline magma series belonging to different systems in the east and west, and relatively young, nepheline normative, Na-alkaline effusive products with intercalated deposits of pyroclastic products. Sequence of the basin rim represents a unique area for tracking dynamic evolution, differentiation processes and temporal change in source characteristics since contains both earlier and contemporaneous products than the basin opening in different physicochemical characteristics. This thesis aims to the petrological evaluation of differentiation processes, thermo-dynamic evolutions, and dynamic processes of magmas at the Sultansazlığı Basin rim Mio-Pliocene volcanic sequence using numerical modeling techniques in the light of petrographic, mineralogical and geochemical data.

Common microlithic-porphyritic texture and the abundance of crystallized phases that usually deviate from the equilibrium condition with normal zoning trend from core to rim indicate closed system fractionation. Systematic enrichment of Rb, Th and K with increasing silica content and depletion of major element oxides with transition metals show effect of crystallization of plagioclase and ferromagnesian phases with a variable amount of crustal assimilation. According to the reservoir parameters, the majority of magmas are raised from MOHO – lower crustal depths and transported to medium-shallow levels throughout the broad ΔP/ΔT gradient (ΔP:10-0.2 kbar / ΔT:1306-700°C) under low-to-moderate oxidation conditions (QFM.: +1.09 ± 0.88 log fO2). Along this route, differentiation of magmas during both polybaric high pressure (10-5 kbar) fractionation and gradual fractionation (~%35) with crustal assimilation (20-45 %) has been simulated by pMELTS and various numerical models (FC, AFC). Based on the most primitive natural samples, the primitive melt composition for the approximate MOHO depth in equilibrium with the highest forsteritic olivine (XFo: 88.4 mole %) in natural samples was calculated for 1323 °C liquidus temperature using pMELTS reverse fractionation. From calculated primary melt compositions, high-pressure polybaric fractionation along lower-mid crust levels under high temperature (~1323 °C), low to medium water content (0,6 – 2,5 wt. % H2O), low to medium oxidation conditions (KFM 0 – +2 log fO2) explain the existence of composite pyroxenes (opx-cpx) and common disequilibrium textures in high An (≥ 75 mole %) plagioclase. High ΔP (~10 kbar) versus low ΔT (~300°C) values of the relatively less differentiated young magmas (≤ ~5.5 My) demonstrate that transtensional forces before the basin opening facilitate the formation of primitive magmas having with relatively high rising rate. In addition to the changes in the physicochemical properties of magmas under the influence of regional tectonics, the gradual transition from sub-continental (KAS) to the sub-lithospheric mantle (NAB) characteristics in basin margin magmas, from old to young, from north to south, present a petrological section that will contribute to the discussions of mantle heterogeneity and regional geodynamics.