Formation of subaqueous Felsic domes and accompanying pyroclastic depositson the Foca Peninsula (Izmi, Turkey)

In western Anatolia, a thick volcanic succession of andesitic to rhyolitic lavas and volcaniclastic rocks crops out extensively. On Foca Peninsula, th e westernmost part of the region, a dominantly rhyolitic sequence is expose d where massive rhyolites occur as dome or domelike stubby lava flows. Thes e rhyolite domes vertically and laterally pass into blanketing volcaniclast ic sequences. The gradational boundary relations and the facies characteris tics of the surrounding volcaniclastic sequences indicate that the silicic domes directly intruded a subaqueous environment and were shattered upon su dden contact with water to form hyaloclastic blankets. In and around these rhyolite domes, we have defined six different volcanic and volcaniclastic facies, consisting of. (1) massive rhyolite; (2) massive perlite; (3) hyaloclastic breccias; (4) rhyolite pumice and lithic fragmen t-bearing volcaniclastic rocks; (5) subaqueous welded ignimbrites; and (6) brecciated perlite. The massive rhyolite facies have distinct structures fr om the centers to the peripheries of the domes and stubby lava flows. Massi ve lava facies gradually pass into hyaloclastic breccias and massive perlit e facies, indicating water-magma interaction during the emplacement, Phreat omagmatic explosive activity and doming caused the subaqueous pyroclastic f lows on the flanks of the volcanic center. Welding in the upper parts of th ese pyroclastic flow deposits indicates the high-temperature emplacement of the pyroclastic material and relatively slow cooling caused by the cushion ing effect of the gas-vapor mixture and rapid deposition of younger pyrocla stic units.