Miocene forebulge development previous to broken foreland partitioning in the southern Central Andes, west-central Argentina

DÁVILA, F.M. ASTINI, R.A. JORDAN, T.E., GEHRELS, G. EZPELETA, M.

TECTONICS

Año: 2007 vol. 26 p. 1 - 17

0278-7407

In the distal region of the modern flat-slab segment in the southern Central Andes, an unusual stack of Middle Miocene paleosoils together with the regional upwarping and normal faulting indicates episodic aggradation and condensed sedimentation associated with foreland flexure. These features are consistent with development of a forebulge zone during the early stages of a proposed asymmetric foreland. Sedimentary thickness farther east and far from the Cordilleran tectonic loads suggests accommodation and preservation driven by “non-isostatic” dynamic subsidence. Regional overlapping relationships and basin modelling suggests that the Modern broken foreland (Present Sierras Pampeanas) can be interpreted as a reactivation of a formerly partitioned broad forebulge. The inherited extensional fabric clearly predated development of the contractional broken foreland from Late Miocene onwards and may have assisted in weakening the upper crust to initiate basement thrusting during regional shortening.