Abstract

Western Turkey's extension-related Cumaovası volcanic rocks (Lower Miocene, 17 Ma) are excellent examples of silicic eruptions. The sub-aerial silicic volcanism at Çubukludağ Graben between İzmir and Kuşadası in west–central Anatolia is mainly in the form of rhyolite domes, lava flows and pyroclastic deposits. The initial features of volcanism derived from phreatomagmatic explosive eruptions from silicic magma that came into contact with lake waters during Neogene times. Most of the volcanic succession represents pyroclastic density currents (PDCs), known as the Kuner ignimbrite. The deposits are fine grained and laminated at the base and pass laterally and vertically into deposits displaying well-developed traction structures, soft sediment deformation and/or erosion channels in the NE part of the region. Alternate deposits of massive, diffusely stratified lapilli and ash are the main products of the later explosive stage. Massive lithic breccias forming the top of the sequences are the proximal facies of the PDCs. The lava phase mainly consists of rhyolite extruded as dome and fissure eruptions of lavas, aligned along NE–SW-trending faults as well as from extensional cracks that are nearly perpendicular to the main graben faults. Considering the tectono-stratigraphical aspects and geochemical nature of the study area, we propose that the Cumaovası silicic volcanism was produced by extension-related crustal melting during the Late–Early Miocene period (17 Ma).

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