Late Miocene high-angle faulting in the Cyclades: offshore–onshore tectonic studies and U-Pb calcite dating

Aegean extension began during Eocene-Oligocene times and led to the thinning of the upper plate into a retreating slab system. The style of extension during the Miocene remains controversial, with a majority of studies arguing for extension accommodated by low-angle extensional brittle-ductile faults, called detachments. In other hands, the present-day active seismic faults in the Aegean Sea are only high-angle normal faults and dextral strike-slips. We aim to constrain and date the style of faulting in central Greece by combining analysis of 19 offshore seismic lines with onshore structural observations on Syros Island and LA-ICP-MS U-Pb dating of calcite sampled in two major fault zones of Syros (Palos and Fabrika faults). Three main sets of faults have been identified in the Central Cyclades: NW-SE trending normal faults, NNW-SSE oblique (sinistral)-normal faults, and NNE-SSW trending dextral strike-slip faults. High-angle normal faults define regularly spaced horsts and grabens, suggesting a wide rifting-type of extension. Dextral strike-slip faults occur at Syros, mainly offshore, and are kinematically compatible with normal faults. U-Pb dating of calcite crystallizing in normal fault planes at Syros yields ages at c.a. 10 Ma for high-angle normal faults activity. On these bases, we propose that wide rifting with high-angle normal faults accommodated Aegean extension when trench retreat accelerated in the middle to late Miocene. At this time, dextral strike-slip faults formed as a response of the onset of Anatolia lateral extrusion.