A source-to-sink history of the supradetachment Gediz Graben (W Turkey): from exhumation of the Central Menderes Massif through the Gediz detachment fault to sedimentation in the basin

Abstract

The Menderes Massif is an outstanding example of Tertiary continental metamorphic core complex, exhumed in the upper Oligocene – Miocene time, during the deposition of a series of E-W trending basins. Several studies address to the exhumation history but the geometry of deposition and the depositional history is still poorly defined. The aim of this study is to reconstruct the source-to-sink evolution of the Gediz Graben, constraining the activation of the extensional detachment tectonics in the area, defining the exhumation/cooling pattern of the Central Menderes Massif at the footwall of the Gediz Detachment Fault and reconstructing the tectono-stratigraphic evolution of the supradetachment basin. We applied a multidisciplinary approach, mainly consisting in field observations and geological mapping, detrital apatite fission track analyses, in-situ U-Th-Pb titanite dating coupled with detailed textural and petrographic analyses, and micropaleontological analyses to constrain the age of sedimentation. Detrital apatite fission track revealed three exhumation events recorded in the area: (i) a Late Oligocene – Early Miocene event related to the regional exhumation of the menderes, (ii) a Late Miocene event involving only the southern margin of the basin and (iii) a Late Pliocene – Early Quaternary event extremely localized at the area of the Gediz Detachment; the reconstructed short-term exhumation pattern closely reflects this latter event. In-situ U-Th-Pb dating on two generation of titanite related to the magmatic intrusion of the Salihli Granodiorite and to the onset of ductile deformation on the Gediz Detachment revealed that the magmatic emplacement (at ~16-17 Ma) predates by ~2 Ma the onset of detachment extensional tectonics (at ~14 Ma) in the area. The integration of all the collected data allowed to propose a possible evolutionary model for the Gediz Graben that (i) started during Middle Miocene as a ramp-basin and during this phase recorded and upper Tortonian marine episode, (ii) evolved in to an half-graben in the Messinian with the activation of the southern margin and (iii) transformed in to a symmetric graben during the Quaternary.