Geochemical and petrological characteristics of the Kale (Gumushane) volcanic rocks: Implications for the eocene evolution of eastern pontide arc volcanism, northeast Turkey

The Kale (Gumushane) volcanic rocks crop out in the southern zone of the ea stern Pontide are, and consist mainly of agglomerate, andesite, minor basal t, and tuff associated with sediments (limestone, marl, siltstone, sandston e) deposited in a shallow basin environment. The volcanites show mainly por phyritic, hyalo-porphyritic, and rare fluidal and glomeroporphyritic textur es. These volcanic rocks consist predominantly of plagioclase, augite, homb lende, and lesser biotite, magnetite, and quartz, and secondary products of chloritization, carbonation, sericitization, and epidotization. In general , they show disequilibrium textures, possibly reflecting magma-mixing proce sses. The volcanic rocks are mainly calc-alkaline in composition, and show modera te potassium enrichment. Most of the major- and trace-element variations re flect the significant role of fractional crystallization during the evoluti on of the volcanic suite. The fractionating phases are dominantly homblende and augite, minor plagioclase, and magnetite. The rocks have high LILE and LREE enrichments, but are relatively depleted in HFSE relative to MORB. Mo reover, incompatible trace-element distributions show similarities to those of an E-type MORB source. The rocks have moderately fractionated REE patte rns with (La/Lu)(N) = 2-12. Geochemical data suggest that the volcanites ev olved by shallow-level fractional crystallization and magma-mixing contamin ation of a parental magma derived from metasomatized upper mantle by partia l melting after thickening of the Pontide are during the Paleocene-Eocene. Furthermore, differentiation took place in a magma chamber situated in the thickened are crust within an extensional tectonic regime.