Hidden calderas evidenced by multisource geophysical data; example of Cappadocian Calderas, central Anatolia

The Cappadocian volcanic field in central Anatolia (Turkey) is characterise d by a sequence of 10 Neogene ignimbrites. The associated calderas have bee n partly dismantled and buried by subsequent tectonic and sedimentary proce sses and, therefore, cannot be readily recognized in the field. Recent prog ress in the understanding of the stratigraphic correlations and flow patter ns has identified two main probable source al eas for the ignimbrites. Deta iled study of these areas, based on gravity surveys, remote sensing data (S POT and ERS1 images) and digital elevation models (DEM), has provided evide nce for two major caldera complexes and their relationship to old stratovol canoes and Neogene tectonics. The older Nevsehir-Acigol caldera complex, lo cated between the towns of Acigol, Nevsehir and Cardak, is inferred to be t he source of the Kavak and Zelve ignimbrites. The Nevsehir-Acigol caldera c omplex is defined mainly by a -35 mGal circular gravimetry anomaly about 15 km in diameter. The boundaries of this, now buried, caldera complex are sh own by high gradients on the Bouguer gravity anomaly map. The younger Derin kuyu caldera complex, located between the Erdas stratovolcano and the Ciftl ik basin, is inferred to be the source of the Sarimaden, Cemilkoy, Gordeles and Kizilkaya ignimbrites. It is well-defined by a rectangular (35 x 23 km ) gravity low (-30 mGal) with a positive high (+ 20 mGal) in the center. Gr avity, remote sensing data and the DEM provide evidence that the Erdas stra tovolcano, on the northern margin of the Derinkuyu caldera complex, represe nts the remnants of a large stratovolcano partly cut by one or more caldera collapses. The positive anomaly within the Derinkuyu caldera complex is ce ntered on the 15-km-wide Sahin Kalesi volcanic massif. Field evidence and s tructural features inferred from the DEM and remote sensing data strongly s uggest that this massif is a resurgent doming associated with the Gordeles ignimbrite eruption. High-resolution ERS1, SPOT and DEM images reveal that the transtensive regime, active at least since the Miocene, influenced the location of eruptive centers and caldera complexes in Cappadocia. The two c aldera complexes are located in transtensive grabens. The subsidence of the se grabens, continuing after the caldera collapse events, most likely resul ted in the burying of the calderas and could explain the difficulties in id entifying them in the field. (C) 1998 Elsevier Science B.V. All rights rese rved.