Three episodes of alkaline volcanism of Quaternary age have been recognized in the Kula Volcanic Province (KVP) in Western Turkey. The alkaline volcanic rocks of the KVP vary in composition from basanite to tephriphonolite and from trachybasalt to basaltic trachyandesite. Measured values for 87Sr/86Sr and 143Nd/144Nd in the rocks of the KVP range from 0.703029 to 0.703534 and 0.512773 to 0.512998, respectively, (Gulec, 1991; Alici, et al., 2002) suggesting that an isotopically depleted mantle component is involved in the genesis of the Kula lavas. This mantle component is also enriched in the most incompatible elements, as shown by OIB-like primitive mantle normalized multi-element patterns, this indicates that enrichment of the mantle source is probably a recent event.
The pMELTS algorithm of Ghiorso, et al., (2002) can be used to show that low degrees of partial melts, generated by fractional melting of a spinel peridotite mantle source (Maaloe and Aoki, 1977), can produce the alkaline magmas of the KVP. Assuming an underlying heat source, I used pMELTS to model the melting behavior of an average spinel peridotite mantle composition at melting at 23 kbar (~80 km) in the presence of 0.1% H2O at fO2 = QFM-1. The degree of partial melting is 8% for the KVP rocks and the primary magma composition is then subjected to polybaric fractional crystallization from 23 to 4 kbar. The compositional diversity displayed by the Kula volcanic rocks is reproduced successfully by the pMELTS polybaric fractionation calculations when the dP/dT gradient is set to 42 and 25 in the mantle and crust, respectively, and the oxygen fugacity is increased from one log unit below to one log unit above the QFM buffer at 13 kbar.
Generation and evolution of the Kula magmas were simulated successfully by using pMELTS. Eight per cent fractional melting of an average spinel lherzolite composition at 23 kbar generated the primary magma and polybaric fractional crystallization simulations with changing dP/dT and fO2 conditions generated diverse compositions that match the rocks of the KVP successfully.