Turkish Journal of Earth SciencesThe Coexistence of the Silica Oversaturated (ALKOS) and Undersaturated Alkaline (ALKUS) Rocks in the Kortundag and Baranadag Plutons from the Central Anatolian Alkaline Plutonism, E Kaman/NW Kırşehir, Turkey
Cumhuriyet Üniversitesi Jeoloji Mühendisliği Bölümü 58140, Sivas-TURKEY
Abstract: Baranadağ and Kortundağ plutons, outcropping in the Kaman-Kırşehir region, constitute the important members of the Central Anatolian post-collisional alkaline plutonism. The Baranadağ pluton comprises only one lithodem called Baranadağ quartz monzonite, whereas, the Kortundağ pluton consists of four mapable units such as Hamit quartz syenite, Durmuslu nepheline-nosean-melanite porphyritic syenite, Bayındır nepheline-cancrinite syenite, and Çamsarı quartz syenite. Among these units, the Baranadağ quartz monzonite and Hamit quartz syenite cut the metamorphics of the Kırşehir Block. On the other hand, Durmuslu, Bayindir and Çamsarı are emplaced in both the Hamit quartz syenite and the metamorphics. The Baranadağ quartz monzonite, Hamit quartz syenite and Çamsarı quartz syenite determine an association by means of geological setting, textural features, and mineralogical-chemical composition. These units contain feldspar megacrysts, an association of hornblende + augite + biotite, and have silica saturated alkaline (ALKOS) character. These units also show fractional crystallization from Baranadağ to Çamsarı by means of mineralogical and geochemical data. It has been proposed that these three units were formed by fractional crystallization from a single magma source. Durmuslu and Bayindir units, on the other hand, contain the same felsic and mafic mineral assemblages which consist of nepheline + sodalite, and melanite + arfvedsonite + aegirine/aegirine-augite, respectively. These two units show silica undersaturated alkaline (ALKUS) character. These mineralogical-chemical data also reveal that there has been a fractionation process occurred from the Durmuslu to Bayindir. In other words, alkaline rocks of Bayindir and Durmuslu formed by fractional crystallization from a magma source which is different than that of Baranadağ, Hamit and Çamsarı units. This different magma source of the Durmuslu and Bayindir units is also assumed to be generated subsequently from the enriched upper mantle material. It is proposed that ALKOS and ALKUS rocks were formed by fractional crystallization from two different magma sources which were probably formed by the partial melting of upper mantle material with different degrees of melting in different times.
Key Words: Central Anatolian post-COLG plutonism, Baranadağ and Kortundağ plutons, alkaline oversaturated magma, alkaline undersaturated magma, fractional crystallization, partial melting.
Turkish J. Earth Sci., 7, (1998), 241-258.
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