No 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.

Connectivity of groundwater flow within crystalline-rock aquifers controls the sustainability of abstraction and baseflow to rivers, yet is often poorly constrained at a catchment scale. Here groundwater connectivity in a sheared gneiss aquifer is investigated by studying the intensively abstracted Berambadi catchment (84 km 2) in the Cauvery River Basin, southern India, with geological characterisation, aquifer properties testing, hydrograph analysis, hydrochemical tracers and a numerical groundwater flow model. The study indicates a well-connected system, both laterally and vertically, that has evolved with high abstraction from a laterally to a vertically dominated flow system. Likely as a result of shearing, a high degree of lateral connectivity remains at low groundwater levels. Because of their low storage and logarithmic reduction in hydraulic conductivity with depth, crystalline-rock aquifers in environments such as this, with high abstraction and variable seasonal recharge, constitute a highly variable water resource, meaning farmers must adapt to varying water availability. Importantly, this study indicates that abstraction is reducing baseflow to the river, which, if also occurring in other similar catchments, will have implications downstream in the Cauvery River Basin.

a b s t r a c tDeformation mechanisms and resultant fault architecture are primary controls on the permeability of faults in poorly lithified sediments. We characterise fault architecture using outcrop studies, hand samples, thin sections and grain-size data from a minor (1e10 m displacement) normal-fault array exposed within Gulf of Corinth rift sediments, Central Greece. These faults are dominated by mixed zones with poorly developed fault cores and damage zones. In poorly lithified sediment deformation is distributed across the mixed zone as beds are entrained and smeared. We find particulate flow aided by limited distributed cataclasis to be the primary deformation mechanism. Deformation may be localised in more competent sediments. Stratigraphic variations in sediment competency, and the subsequent alternating distributed and localised strain causes complexities within the mixed zone such as undeformed blocks or lenses of cohesive sediment, or asperities at the mixed zone/protolith boundary. Fault tip bifurcation and asperity removal are important processes in the evolution of these fault zones. Our results indicate that fault zone architecture and thus permeability is controlled by a range of factors including lithology, stratigraphy, cementation history and fault evolution, and that minor faults in poorly lithified sediment may significantly impact subsurface fluid flow.