Abstract

Cordillera Darwin in the southernmost Chilean Andes is a tectonically denuded metamorphic core complex similar to those widely developed in the North American Cordillera. Detailed comparison can be drawn with the Shuswap metamorphic core complex in British Columbia and Washington. Analysis of the geotectonic history of the Darwin complex reinforces the view that the presence of tectonically thickened continental crust is critical for development of most, if not all, known core complexes and also suggests that inversion of a marginal basin during a compressional regime is one way of initiating such a crustal welt. The Cordillera Darwin complex is unique in the Andes and Antarctandes. This indicates that although low-angle normal faulting occurs at high levels in convergent plate settings such as the Central Andes and the Himalayas, extensional denudation of deep crustal levels in active Andean-type orogens may require special tectonic circumstances. Uplift of the Darwin complex began at about 70 Ma in a localized extensional setting within the developing transform zone between the South American and Antarctic plates. This strike-slip setting is analogous to some metamorphic core complexes in North America and possibly to a recently identified "core complex" in New Zealand. It is likely to be a common one for core complexes in convergent orogens.

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