The structures, stratigraphy and evolution of the Gulf of Corinth rift, Greece
Résumé
A multichannel seismic and bathymetry survey of the central and eastern Gulf of Corinth (GoC), Greece, reveals the offshore fault geometry, seismic stratigraphy and basin evolution of one of Earths most active continental rift systems. Active, right-stepping, en-echelon, north- dippingborder faults trendESEalongthesouthernGulf margin, significantlyoverlappingalong strike. The basement offsets of three (Akrata-Derveni, Sithas and Xylocastro) are linked. The faults are biplanar to listric: typically intermediate angle ( ∼35◦ in the centre and 45–48◦ inthe east) near the surface but decreasing in dip and/or intersecting a low- or shallow-angle(15–20◦ in the centre and 19–30◦ in the east) curvi-planar reflector in the basement. Major S-dipping border faults were active along the northern margin of the central Gulf early in the rift history, and remain active in the western Gulf and in the subsidiary Gulf of Lechaio, but unlike the southern border faults, are without major footwall uplift. Much of the eastern rift has a classic half-graben architecture whereas the central rift has a more symmetric w- or u-shape. The narrower and shallower western Gulf that transects the >40-km-thick crust of the Hellenides is associated with a wider distribution of overlapping high-angle normal faults that were formerly active on the Peloponnesus Peninsula. The easternmost sector includes the subsidiary Gulfs of Lechaio and Alkyonides, with major faults and basement structures trending NE, E–W and NW. The basement faults that control the rift architecture formed early in the rift history, with little evidence (other than the Vrachonisida fault along the northern
margin) in the marine data for plan view evolution by subsequent fault linkage. Several have maximum offsets near one end. Crestal collapse graben formed where the hanging wall has pulled off the steeper onto the shallower downdip segment of the Derveni Fault. The dominant strikes of the Corinth rift faults gradually rotate from 090–120◦ in the basement and early rift to 090–100◦ in the latest rift, reflecting a ∼10◦ rotation of the opening direction to the 005◦ presently measured by GPS. The sediments include a (locally > 1.5-km-) thick, early- rift section, and a late-rift section (also locally > 1.5-km-thick) that we subdivide into three sequences and correlate with seven 100-ka glacio-eustatic cycles. The Gulf depocentre has deepened through time (currently > 700 mbsl) as subsidence has outpaced sedimentation. We measure the minimum total horizontal extension across the central and eastern Gulf as varying along strike between 4 and 10 km, and estimate full values of 6–11 km. The rift evolution is strongly influenced by the inherited basement fabric. The regional NNW structural fabric of the Hellenic nappes changes orientation to ESE in the Parnassos terrane, facilitating the focused north-south extension observed offshore there. The basement-penetrating faults lose seismic reflectivity above the 4–14-km-deep seismogenic zone. Multiple generations and dips of normal faults, some cross-cutting, accommodate extension beneath the GoC, including low-angle (15–20◦) interfaces in the basement nappes. The thermally cool forearc setting and cross-orogen structures unaccompanied by magmatism make this rift a poor analogue and unlikely precursor for metamorphic core complex formation.
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