Implications for crustal rotation and tectonic evolution in the central Andes fore arc: New paleomagnetic results from the Copiapó region of northern Chile, 26°-28°S

Abstract

New paleomagnetic data from the Coastal Cordillera-Precordillera boundary area of northern Chile, east of Copiapó, between 26°600′S and 28°00′S are reported. Early Cretaceous to earliest Paleopene volcanics and sediments are nearly completely remagnetized, the remagnetization typically being carried by both magnetite and hematite. In a small minority of sites a pretilting remanence is retained, however, both pretilting and posttilting remanences yield similar directions. These remanences plus primary remanences from Paleocene intrusions indicate a significant >35° rotation of the whole area, in agreement with previous results from the region. The data suggest that the whole of this part of the Andean fore arc has undergone a substantial, regionally coherent, clockwise rotation. This rotation, it is argued, is in response to rapid and highly oblique Nazca-South American plate convergence in the period ∼60-45 Ma prior to later Incaic deformation in the east of the study area. In the east, heterogeneous rotations associated with the Domeyko Fault System are interpreted as being superimposed on this regional rotation resulting in a highly variable and localized pattern of rotations in the vicinity of the main structures comprising the fault system itself. Copyright 2007 by the American Geophysical Union.