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

The Koroglu caldera is a result of the eruption of 'Seydiler ignimbrites', which have been emplaced in two sequences known as Lower Seydiler (LS) and Upper Seydiler (US). The Koroglu caldera measures 13 km x 18 km, contains a resurgent dome in the center, and produced low aspect ratio ignimbrites, w hich have been transported up to 50 km away from the source. The ignimbrite s 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 cald era collapse. Two main trends of tectonic elements (NE-SW and NW-SE) have b een distinguished, the latter being; the younger. A NW-SE-striking fault wa s used by lamprophyric magmas which were extruded into the post-ignimbrite lacustrine deposits. The lava flows and dikes (trachybasalte, trachyandesit e) also occur along the ring fractures of the caldera. The dikes are compos ed of olivine + phlogopite + Cr-diopside + salite + K-feldspar + Ba-feldspa r (hyalophane). The lava flows contain scarce cognate inclusions. (C) 1998 Elsevier Science B.V. All rights reserved.