Insight into a rift volcanism with the petrogenesis of ultramafic enclaves and the host basalts: Kula Volcanic Field, Western Anatolia, Turkey

Abstract

The Quaternary Kula Volcanic Field (KVF), located on an E-W trending Plio-Quaternary horst, consists of at least 80 scoria cones, associated fissural lava flows and maars. Volcanic activity is divided into three main stages as BI (ca. 2-0.9 Ma), BII (ca. 300-50 ka) and BIII (ca. 10-0.7 ka). The volcanic products of BII and BIII contain ultramafic enclaves. They are generally spherical or elliptical varying in size from 1.7), and Nb/U (>31) ratios, reflecting that crustal contamination is insignificant. Petrogenetic modelling shows that Kula enclaves and host rocks are probably originating from 3-5% partial melting of garnet and spinel-peridotite mantle source mixtures. Rb/Sr (0.03-0.10) and slightly high Ba/Rb (9.5-23) ratios for host rocks demonstrate the presence of amphibole and phlogopite in their source, while low Rb/Sr (0.01-0.09) and high Ba/Rb (18-115) reveal that amphibole is present in the source. Estimated T/P conditions of early crystallizations are between 19.5–9.5 kbar, 63–31 km, and 1260–1130 °C for host rocks and 18.3–11.1 kbar, 59–36 km, and 1324–1208 °C for the enclaves, which suggests that the crystallization might have taken place in the lithospheric mantle.