Geochemistry of post-collision Pliocene-Quaternary Karasar basalt (Di?vri??i?-Si?vas, Eastern Turkey): Evidence for partial melting processes

Abstract

The Pliocene-Quaternary Karasar basalt is located in the western part of the post-collisional volcanic field in Eastern Anatolia and occurs as lava flows on the continental sediments. According to normative mineralogy and geochemistry, Karasar basalt samples have hyperstene-normative tholeiites, nepheline-normative basalts, trachybasalts, and basaltic andesites with quartz-xenocrysts which occur at the base of the lava flows. Trace and rare element variations indicate that the trachybasalts are enriched in highly incompatible trace and light-rare earth elements relative to hyperstene- and nepheline-normative basalts. Hy-normative tholeiites have higher concentrations of medium-heavy rare earth elements relative to ne-normative basalts and trachybasalts. The trace element characteristics of the Karasar basalt imply that the quartz-bearing rocks indicate some crustal contributions, but the basaltic samples have a minimal or no crustal assimilation. Th/Yb-Nb/Yb and Hf/Sm N-Ta/LaN diagrams coupled with HFSE depletions display a subduction signature in the source region of these volcanics. REE modeling exhibits that the magmas forming the Karasar basalt originated from a spinel-peridotite source, although trachybasalts require mixing between melts from spinel- and garnet-peridotite source. Discrimination plots based on trace element data exhibit a within-plate character of the Karasar basalts. Correlations between trace element ratios (Ba/Nb-La/Nb and Ba/La-Ce/Pb) imply that the source of Karasar basalt is lithospheric rather than the asthenospheric mantle. These data reveal that the Karasar basalt is linked to a post-collisional extensional tectonic regime following the collision between the Eurasian and Arabian plates. Volcanism in this part of Anatolia is consistent with a model in which melting of lithospheric mantle occurred in response to lithospheric extension.