Saraçköy Volcanic Suite: implications for the subductional phase of arc evolution in the Galatean Arc Complex, Ankara, Turkey

Abstract

Abstract A sequence of upper Campanian volcanic rocks, hitherto considered as part of the Miocene calc‐alkaline Galatean volcanic sequence, crops out near Saraçköy, 40 km north of Ankara. These volcanic rocks, unconformably overlain by Eocene nummulitic limestones, comprise thin flows and volcaniclastic deposits. They can be divided compositionally into three distinct subunits: (i) basal massive trachyandesitic volcaniclastic rocks with a thin flow at the top, overlain by (ii) mixed volcaniclastic rocks and thin amygdaloidal flows of alkali basaltic composition, with (iii) trachyandesitic flows and subordinate volcaniclastic rocks at the top. This alkaline volcanic activity, associated with late Campanian forearc peripheral sedimentation, is indicative of late Campanian extension within a collisional regime, pre‐dating the compression accompanying Galatean arc development. Indeed, the composition of the Saraçköy Volcanic Suite and field evidence are consistent with a slab roll‐back process in an extensional supra‐subduction setting which resulted from the northward‐subducting, northern Neotethyan ocean floor during the late Campanian. They also imply that the present‐day Galatean volcanic plateau is a magmatic arc development in three stages: (i) late Campanian–Lutetian subductional phase, (ii) post‐Lutetian collisional phase, and (iii) Oligocene–Miocene post‐collisional phase. Copyright © 2003 John Wiley & Sons, Ltd.