Mountain building processes at the orogenic front. A study of the unroofing Neogene foreland sequence (37ºS)

SAGRIPANTI, L., BOTTESI, G., KIETZMANN, D., FOLGUERA, A., RAMOS, V.A.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Año: 2012 p. 1 - 22

0718-7092

The orogenic front at 37ºS has been constructed through at least two constructional stages, as inferred from the exhumed major angular unconformities at the late Eocene and the late Miocene times. A Late Cretaceous event is restricted to the hinterland zones. A series of syntectonic sedimentary packages, that thin to the east is identified through a detailed description of the cannibalized westernmost Neogene foreland basin associated with the Sierra de Reyes. Their detrital microscopic and macroscopic descriptions reveal that the Neogene basin was fed from the west and particularly from the eastern Sierra de Reyes slope at the time of mountain incision. Detrital composition of the upper section reveals that a metamorphic component is present, implying that a domain further east has been exhumed, and therefore that the westernmost foreland basin has been cannibalized. This also implies that exhumation previous to Miocene times should have been minimum in the area, since the Neogene section represents a complete unroofing. The structural cross sections show Neogene shortening of about 20 %, leaving in comparison Eocene contraction as negligible.