Abstract

The Andean deformational pattern of the northern Chilean Precordillera between 26°30′ and 27°00′S suggests significant influence of an orogen-oblique (northwest-trending) pre-Andean basement structure. The left-lateral reactivation of this structure and the associated deformation can be explained by clockwise vertical-axis rotations of forearc-wide crustal blocks during the middle-late Eocene (ca. 39 ± 3 Ma) induced by the coupling stress due to oblique northeastward subduction of the oceanic Farallon plate beneath the South American continent. The compressive stress at the leading edges of the blocks may have been accommodated 200 km away from the Peru-Chile trench in what is now the Precordillera, where the magmatic arc was then located. The postulated large-scale domino mechanism explains the paleomagnetically observed in situ block rotations, as well as the orientation, segmentation, and shear sense of major structural elements within large parts of the present forearc in northern Chile.

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