Calcite strain analysis of the Central Andes: Northwest Argentina and southern Bolivia.

摘要

Deformation in the Central Andes has previously been interpreted by the use of kinematic studies, which predict that a generally NW direction of compression has been present over Andean history. This study conducted a kinematic strain analysis using calcite twins to examine deformation throughout the Eastern Cordillera, the Subandes, and the Santa Barbara System, 20°S to 25°S latitude. Samples were analyzed using the calcite strain gauge technique of Groshong (1974). Resultant shortening axes can be separated into two main groups, parallel to plate convergence and generally NW; the latter group is further divided into four distinct trends. Using the relationship between the maximum shortening axes and bedding, samples were classified as having pre- or post-folding twin formation, which was used to interpret timing of deformation. Changes in compression are found to occur at 10 Ma, with a north component of movement that is implied from derived velocity vectors, and at 2 Ma where shortening directions estimated by fault kinematic studies trend from NW-SE to NE-SW. The results from this study fit well with these multiple deformation events, supporting the use of calcite strain analysis in active mountain belts.