Ar3. Ar geochronology, geochemistry and petrology of volcanic rocks from the Simav Graben, western Turkey. Major and trace element compositions with SrNd isotopic ratios, as well as ArAr radiometric ages of the Miocene volcanic rocks from the Neogene units around Simav region western Anatolia, are used to discuss the genetic relationship between 1 high voluminous LowerMiddle Miocene high potassic, calc alkaline HKCA and 2 Middle Miocene small voluminous high Mg. O shoshoniticultrapotassic SHOUK magmatic units in the region. All the HKCA rocks, including basaltic to rhyolitic and granitic samples, share similar trace element characteristics enrichments of LILE and LREE and depletions in HFSE as a common feature of orogenic magmatic rocks, with subtle differences in their 8. Sr8. 6Sri ratios basalts and rhyolites 0. Most of the samples of the high Mg. O SHOUK group are classified as shoshonite and latite, with some lamproites, sharing similar geochemical features with the other ultrapotassic rocks of the Mediterranean. All the rock groups have similar and high abundances of incompatible trace elements, and radiogenic Sr. Geochemical modeling of the trace element and isotopic ratios of the samples reveals that both the SHOUK and HKCA groups were derived from a common mantle source which had been highly metasomatized and enriched by continental materials during partial subduction of the crustal metamorphic slices in a continental collision setting. The geochemical variations of these rocks were mainly controlled by source characteristics such as heterogeneity and variable degrees of partial melting and subsequent effects of fractional crystallization, with low degrees of crustal contamination. The HKCA series were derived by higher degrees of partial melting of the lithospheric mantle source than the SHOUK rocks. The HKCA rocks then underwent two stage fractional crystallization clinopyroxene dominated followed by feldspar dominated fractionating mineral assemblages to form the high K calc alkaline basalt to rhyolite series, whereas the SHOUK rocks experienced comparatively little fractional crystallization. A tectonic scenario involving the rapidly extending and thinning of orogenic crust is compatible with the time dependent compositional variation of the magmatic rocks. Keywords. Geochemistry Geochronology Calc alkaline Lamproite Ultrapotassic Western Anatolia.