What processes control the genesis of absarokite to shoshonite-banakite series in an intracontinental setting, as revealed by geochemical and Sr-Nd-Pb isotope data of Karadağ Stratovolcano in Central Anatolia, Turkey

Abstract

The Latest Cenozoic absarokite to shoshonite-banakite series (ASB) samples were discovered in the Karadağ stratovolcano (KS) which erupted in the Karaman basin in Central Anatolia, Turkey; and has a spatially close association with major strike-slip faults and pull-apart basins. The KS are made up of adakitic andesite and dacite, with minor ASB lava flows. Here, we present integrated data of mineral chemical, whole rock major and trace element, Sr-Nd-Pb isotope and conventional KAr age of the ASB series rocks in Central Anatolia. The rocks were dated by conventional KAr dating method in old of 393 ± 153 ka. The series are comprised of slightly differentiated absarokite and more fractionated shoshonite-banakite lava flows. The Ol-normative absarokites contain phenocrysts of olivine and diopside, whereas the Hyp-normative shoshonites-banakites are made up of olivine, diopside, phlogopite, K-feldspar and plagioclase. Both series have a potassic nature and near-primitive character with high MgO (5–11 wt%) and Mg# (62 to 74). The overall samples were characterized relatively by the enrichment in large ion lithophile elements (LILE) and the depletion in high field strength elements (HFSE), with insignificant negative Eu anomaly. They possess homogeneous and unradiogenic Sr and Nd isotopic compositions, marked by 87Sr/86Sr(t) = 0.70507 to 0.70540 and εNd(t) =0.6 to +1.2. TDM, and Pb isotopic ratios tending towards the EMII mantle end-member.These geochemical features favor the origin of a lithospheric mantle reservoir which was metasomatized by i) sediments of subducting oceanic slab and ii) asthenospheric agents associated with break-off of African slab. The existing geochemical fingerprints and trace element modeling indicate that the Ol-normative absarokites were derived from a parental magma by low degree partial melting (~ %5) of a chemically enriched lowermost subcontinental lithospheric mantle source, composing of a garnet- and phlogopite-bearing lherzolitic lithology. The shoshonites-banakites were formed by fractionation of the absarokitic magmas, with a minor crustal assimilation. We contend that the Quaternary volcanism was probably controlled by the extension of the pull-apart basin system, which was induced by the deep strike-slip faults. Then, the extension caused an upwelling of the hot asthenosphere, triggering partial melting of the mantle source. This data rule out the possibility of the Latest Cenozoic active and steady subducting setting in the region. Instead, our results reveal the period which is likely marked by a transtensional phase and this phase triggered the pull-apart basin formation where the ASB series erupted in an intracontinental setting in Central Anatolia.