Detachment faulting in a bivergent core complex constrained by fault gouge dating and low-temperature thermochronology

Heineke C, Hetzel R, Nilius N-P, Zwingmann H, Todd A, Mulch A, Wölfler A, Glotzbach C, Akal C, Dunkl I, Raven M, Hampel A.

Abstract

The central Menderes Massif in western Turkey is a bivergent metamorphic core complex characterised by two detachment faults that operated with opposite sense of shear. Here, we present K-Ar ages and hydrogen isotope data for fault gouge as well as fission track and (U-Th)/He ages for apatite and zircon from bedrock samples to constrain the timing of detachment faulting. Comparison of the K-Ar ages and low-temperature thermochronologic ages indicates brittle faulting at temperatures between ~240 and ~70°C. At the western termination of the Gediz detachment, K-Ar ages between ~12 and ~5Ma suggest rather continuous faulting since the mid-Miocene; a Pliocene phase of rapid slip is mainly recorded in the eastern part of this detachment. In contrast, K-Ar ages from the Büyük Menderes detachment cluster at 22–16 and 9–3Ma and provide evidence for two phases of faulting, which is in accordance with new and published low-temperature thermochronologic data. Hydrogen isotope ratios of –76 to –115‰ indicate infiltration of meteoric water during detachment faulting and gouge formation. The youngest K-Ar ages and cooling histories for hanging and footwall rocks imply that the activity of both detachments ended ~3Ma ago when the currently active grabens were established.