A "Great Deepening": Chronology of rift climax, Corinth rift, Greece

Abstract

Continental rift deposits contain critical clues concerning the evolution of extensional tectonics, yet such evidence is often obscure due to poor geochronology, burial by younger deposits, or later tectonic overprinting. We revisit Corinth rift development, which began as distributed extension created synrift depocenters with rivers fl owing into shallow (<50 m) lakes. Subsequent focused deformation initiated a "Great Deepening" event, evidenced by fan deltas prograding into 300-600-m-deep water. A chronology is provided for the event from 40 Ar/ 39 Ar dating of the Xylocastro ash by singlecrystal CO 2 laser fusion, yielding a precise age of 2.550 ± 0.007 Ma (1σ, full error propagation). Sedimentological data indicate that the ash-bearing sediments were deposited as turbidites and hemipelagites on sublacustrine fans fed from the Mavro fan delta at the faulted south-central rift margin. The ash age and turbidite provenance data enable stratigraphic constraints for an estimate of central rift climax occurring between 3.2 and 3.0 Ma. This is some 0.8-1.0 m.y. earlier than radioisotopic-and magnetostratigraphicconstrained estimates for the eastern Corinth rift. Central rift climax was probably triggered by initial counterclockwise rotation of the Peloponnesus block with respect to central Greece. The rotation pole of this block subsequently migrated to its present position as rift climax moved eastward in an "unzipping" action, with the southern active margin also migrating northward. These events are unlikely to be due to local or regional fault kinematics, but rather to the consequences of deep-seated interactions between the rapidly southward-moving Aegean continental forearc and the slowly northward-subducting African oceanic plate. A possible scenario involves forearc "pushback" with décollement on a low-angle subducting lower plate. This causes acceleration and counterclockwise rotation of Peloponnesus with respect to central Greece and strain localization across the boundary; the Corinth rift.

Patterns of Quaternary uplift of the Corinth rift southern border (N Peloponnese, Greece) revealed by fluvial landscape morphometry

“…In the long term, it underlines a stable pattern of maximum activity in the central part of the rift and of its southern shoulder, confirming previous conclusions of absence of rift propagation during the Quaternary (Leeder et al, 2008). This is not necessarily contradictory with the eastward rift propagation more recently suggested by Leeder et al (2012) for an earlier, Late Pliocene stage of rift evolution, which cannot be inferred using our morphometric data. In the short term, it sheds new light on the possible E-W migration of the recently begun uplift phase, suggesting that fault activity and seismic hazard might concentrate in the immediate future in the Heliki-Aegion area at the western tip of this uplift wave.…”

“…1). These continental environments then progressively gave way to brackish environments interrupted by brief marine incursions, leading to a second evolution stage that would have started around 1.5 Ma (Rohais et al, 2007b;Leeder et al, 2012). This second stage was marked by an abrupt increase in extension (2-2.5 mm year -1 ) and subsidence rates (individual fault slip rates in the order of 1-2 mm year -1 ).…”

“…While Doutsos and Piper (1990) make the oldest rift fill Middle to Late Pliocene in age, Rohais et al (2007b) and put the initial stages of rifting in a time period encompassing the Upper Pliocene and the Lower Pleistocene and date the first rift deepening event from between 1.8 and 1.5 Ma. Recently, Leeder et al (2012) dated their so-called "Great Deepening event" from 3.2 to 3 Ma in the east-central rift sector. In their evolution scheme, it corresponds to focused extension on the Killini and Mavro faults and might therefore tentatively be correlated with the initial rifting stage of Rohais et al (2007b), although the latter authors envisage this phase as one of slow extension and subsidence.…”

Expedition 381 Scientific Prospectus: Corinth Active Rift Development

“…Offshore: Nixon et al (2016) building on Bell et al (2009);Taylor et al (2011). Onshore: Ford et al (2007Ford et al ( , 2013; Leeder et al (2012); Skourtsos and Kranis (2009) Figure F2. Onshore geology map including distribution of basement units (after Skourtsos and Kranis, 2009) and Pliocene-Quaternary synrift sequences.…”

“…Increased subsidence rates, depocenter deepening, and fault linkage followed, with large marginal fan deltas (locally >800 m thick) now uplifted and exposed onshore ("Middle Group"). The timing of the marked deepening ("rift climax") may have occurred at different times along the rift (e.g., ~2.2 Ma in the Alkyonides Gulf [eastern rift], ~3.0 Ma in the central rift [Leeder et al, 2008[Leeder et al, , 2012, and ~1.8 Ma in the west [Sackpazi et al, 2003]). This transition is thought to represent increased subsidence and sediment supply into the rift at the location of the modern Gulf of Corinth (Middle Group onshore; probable seismic Unit 1 offshore).…”