Turkish Journal of Earth Sciences

Comperative Geochemistry of Four Plutons From the Cretaceous-Palaeogene Central Eastern Anatolian Alkaline Province (Divriği Region, Sivas, Turkey)




The Cretaceous-Palaeogene alkaline province, mainly located in the Kırşehir Block, extends E-W for some 300 km in Central Eastern Anatolia. The Dumluca, Murmana, Karakeban and Çaltı plutons constitute the easternmost part of the province. These plutons have introsive contacts with the Cretaceous Divriği ophiolitic melange and, except Karakeban, are associated with huge iron deposits. The Ypresian-Lutetian sediments unconformubly overly them. The four studied plutons belong to two completely different types of magmatic assocsiation, based on petrographic and geochemical (mainly major elements and REE) fetures. The dominant association comprises three plutons (Dumluca, Murmana, Karakeban) and is rather uniformly represented within each of them. These three plutons have a bimodal character evidenced by the coexistence of two groups of rocks, one mafic and the other felsic. The dominant felsic group, mainly composed of Na-rich and Ca-poor quartz monzonites and monzonites (Murmana, Dumluca), may also include syenites, quartz syenites, adamellites and granites (Karakeban). This group displays a cafemic alkaline over staurated trend, usually magnesian (Dumluca and Murmana) and common (Karakeban). The mafic group is mainly made up Na-rich and Ca-poor gabbros/diorites, monzogabbros/monzodiorites, rather often silica-undersaturated. This group represents a cafemic alkaline saturated to undersaturated trend either ferriferous (Karakeban) or magnesian (Dumluca) or or common (Murmana). Mafic dykes, cutting through the felsic rocks, belong to the same mafic group. These three plutons represent a composite alkaline association and the same type of association characterizes also each individual pluton. Field, petrographic and geochemical data suggest that the felsic group has not been derived from the mafic one by crystal fractionation, but that the two coevial groups may have interacted with each other. The subordinate association is represented by Çaltı pluton. This homogenous pluton, tonalitic and gronodioritic in composition, corresponds to a cafemic calc-alkaline association,with slight magnesian affinity. Such a coexistence of two quite different magmatic associations in the Divriği region has already been reported in the western part of Kırşehir Block. It shows that the alkaline character is restricted to only part of the plutons located in this block and may suggest that several successive magmatic events, related to quite different geodynamic conditions, occured in this domain. In this framework, the Dumluca, Murmana and Karakeban plutons are thougth to be derived from two different magma sources. One of them is mantle related mafic magma generated in a post-collisional lithospheric attenuation environment which accordingly caused to melt the lower parts of the continental crust forming the felsic magma source. This collisional event is attributed to the juxtaposition of the Pontide and Anatolide plates in the pre-Maastrictian time. The Çaltı pluton, representing different mineralogy and chemistry, should be solidified from the collision related and calcalkaline another hybrid magma source due especially to intruding the already obducted Divriği ophiolitic melange. Isotopic and geochronological data would be particularly helpful to better constrain this magmatic history.

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