Petrogenesis of Middle Miocene to Early Quaternary basalts from the Karayazı–Göksu plateau (Eastern Anatolia, Turkey): Implication for the role of pyroxenite and lithospheric thickness

Abstract

In Eastern Anatolia, the Karayazı–Göksu basaltic plateau is one of the basaltic eruption centers of post-collisional volcanism, located between the convergence zone of the Arabian and Anatolian plates. The geological and geochemical evolution of the plateau is documented using new 40Ar/39Ar age data, major-and trace element abundances, mineral geochemistry, and isotope compositions (Sr–Nd–Hf) for better understanding the petrogenesis and mantle source characteristics. Samples yield whole-rock 40Ar/39Ar ages of 12.53 ± 0.05 and 12.68 ± 0.05 Ma for transitional basalts (Middle Miocene), 5.88 ± 0.20 Ma for tholeiitic lavas (Late Miocene), and 2.28 ± 0.03 and 2.48 ± 0.12 Ma for alkali members (Early Quaternary). The results suggest that the fractional crystallization of olivine and clinopyroxene in transitional, tholeiitic and lower alkaline lavas, and clinopyroxene in upper alkaline lavas, played a crucial role in their magmatic evolution without significant crustal contamination. Clinopyroxene-liquid equilibria indicate that the crystallization of transitional basalts occurred at the Moho and lower crust (temperature range 1157–1215 °C), tholeiitic basalts at the lower crust (temperature range 1154–1195 °C), alkaline basalts at lower to mid-crustal depths (temperature range 1083–1195 °C). The subduction-related metasomatism is in the form of melts derived from subducted sediments and decrease from Middle Miocene transitional to alkaline Early Quaternary basalts, as indicated by the Sr–Nd–Hf isotopes and Ba/La and Th/Yb contents. The Early Quaternary alkaline basalts contain contributions from isotopically depleted but chemically enriched (enriched-MORB-like) asthenospheric mantle domain. Major elements–based parameters and olivine mineral chemistry yield that Karayazı–Göksu basalts could not be derived from a sole peridotite mantle source; the pyroxenite/eclogite-like mantle component would have contributed to the members of the plateau. Three-component mixing results using SrNd isotopes indicate that the altered oceanic crust contributes to 0.5%–1% of the melt (crust vs. sediment about 65:35) for tholeiitic and alkaline basalts and reach up to 4% for transitional basalts (crust vs. sediment about 55:45). Melt equilibration depths of the basalts indicate that the lithospheric thickness of the region has not been changed on a large scale since the Middle Miocene to the Early Quaternary.