The control of pre-existing extensional structures on the evolution of the southern sector of the Aconcagua fold and thrust belt, southern Andes

Abstract

The Aconcagua fold and thrust belt, located in the Andean mountains at 32°30′ to 34°S, has been described as a classic model of a thin-skinned thrust belt. However, new structural data from its southern sector have shown that it has a complex structural framework reflected in multiple Mesozoic extensional phases, overprinted by structural inversion, as well as thin- and thick-skinned tectonics. Two major superimposed extensional structural styles have been identified for the Mesozoic characterized by distinctly oriented stress fields. A key role in the evolution of this part of the fold and thrust belt was played by a Late Triassic to Early Jurassic depocentre and by Late Jurassic block faulting. Shortening was accommodated by a combination of inversion of pre-existing normal faults, development of footwall short cuts and both thin and thick-skinned thrusting. Synrift and postrift sedimentary rocks were uplifted by reactivation of normal faults, with further shortening along newly formed thin-skinned thrust faults. The geometry of thin-skinned fault systems is controlled by the architecture of the rift basin, competent footwalls forming barriers to the lateral propagation of detachments.