--> Role of Reactivation of Old Structures and Tectonic Inversion in Foreland Basement Uplifts: Some Comparisons Between the Rocky Mountain Foreland of Western U.S. and the Sierras Pampeanas of Argentina, by C. J. Schmidt; #90986 (1994).

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Abstract: Role of Reactivation of Old Structures and Tectonic Inversion in Foreland Basement Uplifts: Some Comparisons Between the Rocky Mountain Foreland of Western U.S. and the Sierras Pampeanas of Argentina

Christopher J. Schmidt

The Sierras Pampeanas of Argentina are considered to be a modern analogue of the Rocky Mountains. One of the best comparisons of the two regions can be described in terms of reactivation and inversion tectonics.

The basement fabric of the Rocky Mountain foreland and the Sierras Pampeanas is fundamentally anisotropic on a regional scale and commonly anisotropic on smaller scales. This fabric, both brittle and ductile, developed during Early Proterozoic collision and Middle Proterozoic rifting in the Rockies and during Ordovician collision in the Sierras Pampeanas, and it has been repeatedly reactivated since its creation.

In many cases the first reactivation occurred under extension, producing sediment filled rift basins that were later inverted during contraction, (e.g. Late Cretaceous inversion of the Upper Paleozoic Snowcrest trough to form the Snowcrest Range and inversion of the Upper Proterozoic Uinta trough to form the Uinta Range). In the Sierras Pampeanas both Triassic rift basins (Bolsones) and Cretaceous rift basins (west of Cordoba and west of San Luis) were inverted by Neogene contraction forming the Sierra de Valle Fertil, the Sierras Chicas, and the Serranias Occidentales of San Luis respectively.

Reactivation in both basement forelands also occurred without inversion of sedimentary basins, sometimes with significant strike slip displacement (northwest-trending faults in Montana and faults of the Sierra Pocho in the western Sierras de Cordoba).

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994