Tectono-stratigraphic evolution of a Mesozoic rift border system: the Chachil depocentre, southern Neuquén Basin, Argentina

FRANZESE, J., VEIGA, G.D., SCHWARZ, E. Y GÓMEZ-PÉREZ, I.

JOURNAL OF THE GEOLOGICAL SOCIETY

The Geological Society, Society

Lugar: London; Año: 2006 vol. 163 p. 707 - 721

0016-7649

The stratigraphic and tectonic evolution of a Mesozoic rift border system was studied in one of the early depocentres of southern Neuquén Basin (Argentina). The syn-rift volcanic fill is composed of andesites, rhyolites, primary and reworked volcaniclastic deposits. Non-marine coarse-grained deposits dominate the sedimentary fill, mainly as gravity flow and hyperconcentrated flow deposits. Stream flow deposits and minor non-marine carbonates are locally present. The evolution of the rift border system was characterised by important but uneven subsidence along the boundary fault, evidenced by drastic changes in the thickness of the syn-rift megasequence. Several episodes of tectonic reorganisation were identified throughout the succession. Each of these events is characterised by three litho-tectonic elements that record the interaction between tectonism, magmatism and sedimentation. Two major reorganisation events where identified in the succession leading to the definition of three evolutionary stages. The early-rift is defined by the interplay between bimodal volcanism and gravity-driven sedimentation. The mid-rift shows the transition to acidic magmatism – with andesitic volcanism being replaced by rhyolitic and pyroclastic flows – with coarse-grained non-marine deposits still important. The late-rift started after a reorganisation that led to the first marine sedimentation in the rift dominated by fine-grained turbidites and pyroclastic falls.