Koroglu caldera, mid-west Anatolia, Turkey: volcanological and magmatological evolution

The Koroglu caldera is a result of the eruption of `Seydiler ignimbritesʹ, which have been emplaced in two sequences known as Lower Seydiler (LS) and Upper Seydiler (US). The Koroglu caldera measures 13 km×18 km, contains a resurgent dome in the center, and produced low aspect ratio ignimbrites, which have been transported up to 50 km away from the source. The ignimbrites show argillaceous weathering which decreases from the bottom towards the top of the deposits. Such a transition (from ignimbrites to reworked tuffs) indicates the development of a lacustrine environment over the ignimbrites. SPOT image analysis shows that tectonic activity continued after the caldera collapse. Two main trends of tectonic elements (NE–SW and NW–SE) have been distinguished, the latter being the younger. A NW–SE-striking fault was used by lamprophyric magmas which were extruded into the post-ignimbrite lacustrine deposits. The lava flows and dikes (trachybasalte, trachyandesite) also occur along the ring fractures of the caldera. The dikes are composed of olivine+phlogopite+Cr-diopside+salite+K-feldspar+Ba-feldspar (hyalophane). The lava flows contain scarce cognate inclusions.