Geochemistry and petrogenesis of basaltic rocks from the Develidag volcanic complex, Central Anatolia, Turkey

摘要

The Develidag volcanic zone (DVZ) is a part of the Middle Miocene-Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia. The DVZ is located at the eastern side of the Plio-Quaternary Sultan-sazligi pull-apart basin, that opened along the Ecemis. left-lateral strike-slip fault. Towards the south, the volcanic rocks of the DVZ overlie the Paleozoic metamorphic rocks of the Taurus range. Regional strati-graphic studies indicate that volcanic rocks of the DVZ crop out in a ～N-S trending rectangular-shaped exposure in the middle of which Middle Miocene andesitic rocks are found surrounded by Upper Miocene basaltic rocks. The purpose of this paper is to present basic geochemical data for the DVZ rocks and discuss possible processes of magma generation.rnThe Develidag basalts are characterized by low LILE (Rb, K, Ba, Th) and high HFSE (Nb,Zr,Hf,Y) contents, whereas the andesites generally have high LILE and HFSE values except for Nb and Zr. Variable abundances of Pb (3.11-12.09 ppm) and U (0.36-2.64 ppm) are associated with high Ba content within the rock suites. Although low Nb/La (0.6-0.7) and relatively high Ba/Nb ratios indicate crustal involvement for the basalts, high Zr/Ba (0.5), Zr/Hf (42-47) and Th/U (3.13-4.69) values imply contributions from an asthenospheric source component. Furthermore, the high Zr/Hf values (>36) are the diagnostic feature of metasomatized mantle (Dupuy et al., 1992; Rudnick et al., 1993). Moreover, multi-element patterns show that Develidag basalts have similar trace element signatures to those of the US Cascades tholeuetes.rnThe ratios of Zr/Hf, Zr/Ba, Nb/Th and Sr/Ce indicate that basaltic rocks are derived from a MORB-like mantle, and calculated melting model reflects generation from a spinel peridotite source (3-4% melting), but the combined effects of melting and assimilation and fractional crystallization (AFC) processes seem to be partially responsible for the relatively evolved rocks. Typical tholeuetic-calk-alkaline associations are also observed among the volcanic rocks as a consequence of melting processes and crustal involvement, or due to the changes in the melting rate and degree. The lack of alkaline rocks that is conventionally observed during the final stage of many central Anatolian volcanic centers may be attributed either to the lack of extensional development or to a deficient amount of extension before the late Miocene.