Burial history and estimation of ancient thermal gradients in deep synorogenic foreland sequences: the Neogene Vinchina basin, south-Central Andes.

COLLO, G., DÁVILA, F.M., NÓBILE, J., ASTINI, R.A.

Alemania

Simposio; LAK; 2009

The Vinchina Foreland Basin in western Argentina contains a chronologically-constrained exhumed Neogene stratigraphy with a thickness of ~10 km that shows a progressive illitization process (R0 → R1 → R3), consistent with a relatively incipient burial history. The random clay mineral ordering (R0) is persistent to a depth of ~7 km. This clay ordering is not stable at ~120ºC and its appearance, even in the deepest levels, is consistent with previous thermochronologic studies on detrital apatites. The maximum paleotemperature estimation and basin depth implies a very low geothermal gradient of ~17°C/km during the time between sedimentation (ca. 19 Ma) and tectonic exhumation after 3.4 Ma. Therefore the Vinchina Basin is interpreted as an immature and “cold basin”. Sedimentary basins recording low paleogeothermal gradients have been attributed to thermal blanketing effects or to brief burial residence time and/or deformation. However, the tectonic scenario of our Neogene case study combined with results from equivalent successions from exploration wells within the Bermejo Basin (Collo et al. this congress) indicates that this segment of the Central Andes has had a very low heat flow transfer, comparable with the heat contribution from the crust, with minimum input from the asthenosphere. This suggests a refrigerated lithosphere under segments with flat subduction and declining influence of the astenospheric wedge. Thus the geometry of subduction may exert a strong control on the temperature flux in this and perhaps other retroforeland sedimentary basins with similar characteristics that may by of importance to applied studies.