CLAY MINERALOGY AND THERMAL HISTORY OF THE NEOGENE VINCHINA BASIN, CENTRAL ANDES OF ARGENTINA: ANALYSIS OF FACTORS CONTROLLING THE HEAT CONDITIONS

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

TECTONICS

AMER GEOPHYSICAL UNION

Año: 2011 vol. 30 p. 1 - 18

0278-7407

The Vinchina Foreland Basin, western Argentina, contains a chronologically-constrained 14 Neogene stratigraphy (ca. 19 to 3.4 Ma) with a thickness of ~7 km that shows a continuous illitization 15 progress (R0→R1→R3), consistent with an incipient burial history. The random clay mineral ordering 16 (R0) is persistent to ~7 km depth. This ordering is not stable at ~120ºC and its appearance even in the 17 deepest levels is consistent with previous thermochronologic studies on detrital apatites. The maximum 18 paleotemperature estimation and basin depth imply a low geothermal gradient of ~15°C/km and heat 19 flow values between 33 and 42 mWm-2. Therefore the Vinchina Basin can be classified as a cold basin. 20 The short “residence time” at maximum burial conditions, lateral migration of the depocenter and 21 sedimentation rate (thermal blanketing) were evaluated as alternative factors that might have affected 22 the analyzed succession. Only the thermal blanketing might have contributed up to ~20% in reducing the 23 steady state thermal conditions, which would raise the heat flow between ~40 and 51 mWm-2. 24 Nevertheless, these are records of refrigerated lithospheres and consequently an additional mechanism is 25 required to explain such a low-heat flow values. Our thermal approaches suggest the central Andes was 26 dominated since the Miocene by heat flow transfer derived mostly from crustal contributions with a 27 minimum input from the asthenosphere. This refrigerated lithosphere is typical of segments affected by 28 flat subduction, where thin asthenospheric wedges exert a poor thermal influence on the overall heat 29 flow balance. A preliminary thermal model based on previous geodynamic approaches supports our 30 conclusions.