Growth, destruction and volcanic facies architecture of three volcanic centres in the Miocene Usak-Guere basin, western Turkey: Subaqueous-subaerial volcanism in a lacustrine setting

摘要

Early to Mid-Miocene extension in western Anatolia, related to plate tectonic motions, resulted in the development of a number of normal fault-bounded sedimentary basins as well as different styles and compositions of volcanic activity. The Usak and Guere basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadag, Itecektepe and Beydagi) and their deposits can overlap with each other and with the sediments produced by the background sedimentation. In addition, complete facies architectures of small-volume (monogenetic) volcanoes have been recognised in association with the three large complex (polygenetic) volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place. All three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits, with abundant evidences of magma-water interaction such as peperites for non-explosive magma-water interaction with the lacustrine water-saturated sediment and standing water body in a large alkaline lake. During the constructive phase, proximal successions of pyroclastic flows, pyroclastic falls, and rarely surge deposits are associated with distally-emplaced debris flow deposits, sometimes of mixed volcanogenic and terrestrial origins, and are interbedded with lacustrine sediments of the Inay Group. All three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15 Ma ago, most likely related to a combination of tectonic movements on NE-SW-trending basement faults, which triggered multiple flank collapses and volcanic debris avalanches (Elmadag), and voluminous ignimbrite eruptions that triggered caldera formation (Itecektepe and Beydagi volcanic centres). Lacustrine conditions persisted during the destruction and post-destruction stages of the volcano's evolution, as evidenced by indications of magma-water interactions within the central collapse structures, which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores.