Abstract

Two major rhyolitic tephra units (Lower and Upper Acigöl Tuffs) have been erupted from the Acigöl Complex. The Lower Acigöl Tuff (>13km3 uncompacted volume) was erupted more than c. 180 ka ago, forming an extensive Plinian pumice-fall deposit with associated ashfall and ignimbrite. Well-developed ignimbrite veneer facies are preserved where the pyroclastic flows passed over hilly topography. Following the eruption, a thick rhyolite coulée (Bogazköy obsidian) was extruded. The Upper Acigöl Tuff eruption (age 70 < t< 150 ka) generated a second major Plinian deposit, an ignimbrite preserved up to 24 km from the vent, and an 80 m thick proximal succession of surge and fallout deposits; it resulted in collapse of the 6×5 km Acigöl caldera. The two major tuffs are chemically similar but can be distinguished on the basis of lithic populations. Subsequent rhyolitic activity formed the c. 0.25 km3 dome of Kocadag Tepe (c.70ka) and five dome/maar clusters (c. 20 ka). Late Quaternary and/or Holocene basalts and andesites surround the Acigöl caldera, which developed in a zone of sinistral shear associated with approximate N-S compression. Vent distribution patterns, the eruption of young basalts, and the crystal-poor nature of the c. 20 ka rhyolites are consistent with basaltic stoking of a sizeable silicic magma chamber beneath the Acigöl Complex.

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