Tectonic evolution of the Corinth Rift

Abstract

The evolution of extensional processes at continental rift zones provides important constraints on the underlying lithospheric deformation mechanisms, level of seismic hazard and location of likely hydrocarbon traps. The Corinth rift in central Greece is one of the few examples that has experienced a short extensional history (< 5 Myr), has a relatively well–known pre–rift structure, is experiencing pure extension, and is located in a fluctuating marine–lacustrine setting producing characteristic cyclical stratigraphy. Traditionally, the rift has been described as an asymmetric half–graben controlled by N–dipping faults on the southern margin. This view has been challenged by increasing seismic data from the off-shore part of the rift which show it is more complex, analogous to more developed rifts like the East African rift and Red Sea. High resolution and deep penetration seismic reflection data across the entire offshore rift zone are combined with onshore geomorphological data to constrain: the architecture of major rift–bounding faults; basin structure; spatial and temporal evolution of depocentres; total extension across the rift; and slip rates of major faults from stratigraphic analysis and dislocation modelling of long term deformation. Stratigraphy within the offshore Corinth rift is composed of a non reflective older unit (oldest syn–rift sediments are ca. 1–2 Ma) and a well stratified younger unit separated by a ca. 0.4 Ma unconformity. Net basement depth is greatest in the present centre of the rift zone (2.7–3 km) and decreases to the east and west (1.5–1.6 km). The 0.4 Ma unconformity surface records an important change in rift geometry. Pre. 0.4 Ma, sediment deposition occurred in 20–50 km long isolated basins, controlled by both N and S–dipping faults. Post 0.4 Ma, sediment deposition and basement subsidence has been enhanced in areas between these originally isolated basins creating a single 80 km long central depocentre. Since 0.4 Ma activity has became focused on mostly N–dipping faults. However, in the west, N tilting stratigraphy and basement indicate S–dipping faults are locally structurally dominant. Late Quaternary averaged major fault slip rates are 3–6 mm/yr on the N-dipping south margin faults, >1.8 mm/yr on S–dipping offshore faults, and 1–3 mm/yr on faults in the eastern rift. Total extension over rift history (Late Pliocene to present) has been greatest in the west (8 km), with extension distributed over many faults (most now inactive) spaced at 5 km intervals. To the east total extension is reduced (5–6 km) and is distributed over fewer faults spaced at 15–35 km intervals. There are large differences in rift character along the rift axis and throughout rift history. The highest geodetic rates over the last 10–100 years are in the western part of the rift and do not correspond to the area of greatest offshore basement depth. This suggests a recent change in the locus of strain focusing, potentially analogous to the change that occurred in rift geometry ca. 0.4 Ma.

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