Les complexes volcaniques Rhyolithiques quaternaires d'Anatolie centrale (Göllü Dag et Acigöl, Turquie) : Genèse, instabilité, contraintes environnementales

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During the Quaternary, important and rapid environmental changes occurred in central Anatolian in relation with calco-alcalme volcamsm. This volcanic activity generated two large rhyohtic complexes integrating calderas, several pyroclastic deposits and lavic extrusions interstratified with various detntic formations. Activity of the Gollu Dag and the Acigol complexes lasted respectively from the lower Pleistocene until the middle Pleistocene, and from the middle Pleistocene until the upper Pleistocene. Results presented here allow i) to evidence the Gollu Dag caldera for the first time, 11) to define the extension of the Acigol caldera according to new data, and ii) to reconstruct the successive phases in the evolution of both complexes. These complexes present three main types of activity : pre-, syn-, and post-caldera, each timing being responsible for various environmental changes related to different pyroclastite deposition characteristics (volume, types, dynamics, ...). Syn-caldera activity induced the most important environmental changes, which affected palaeogeography and palaeohydrology. During post-caldera activity, changes are less important and concern the extrusion of local rhyohtic domes, in the frame of an original model of extrusion presenting phreatomagmatism associated with annular obsidian dykes, pelean eruptions and rhyohtic extrusion. During Palaeolithic and Neolithic times, mining and chopping of obsidian caused the noticeable presence and activity of human societies. In companson with syn- caldera activities, the volumes of pyroclastites deposited dunng the post-caldera episodes were reduced, so that they are interbedded within alluvial and colluvial Pleistocene formations containing also some obsidian artefacts. This context offers interesting sequences where tephra layers, paleosol, reworked formations and archaeological (Palaeolithic) industries, give opportunities to set a quite precise chronology and to identify palaeogeographical changes. This study allows also to analyse factors controlling environmental changes in a volcanic region and to correlate these changes using a tephrostratigraphical framework detailed here for the first time.