Latitudinal and Longitudinal Patterns of Exhumation in the Andes of North-Central Chile

Abstract

New thermochronometric data provide evidence for an along-strike diachronous building of the Andes in north-central Chile (28.5–32°S). Geochronological (U-Pb zircon) and thermochronological (apatite fission track and (U-Th)/He) analyses of rock units were obtained in west-to-east transects across the western topographic front. Thermal models indicate that the area west of the topographic front was little exhumed since approximately 45 Ma. To the east of the western topographic front, the Main Cordillera shows both latitudinal and longitudinal differences in exhumation patterns. North of 31.5°S, Cenozoic exhumation began before approximately 40–30 Ma at the western and eastern limits of the Main Cordillera, building the Incaic Range. Later, accelerated exhumation focused on the core of the Main Cordillera and in the Frontal Cordillera at approximately 22–14 Ma and approximately 7 Ma, respectively. South of 31.5°S, accelerated exhumation in the Main Cordillera occurred mainly around 22–14 Ma, after an initial Eocene phase, and the locus of exhumation moved eastward by the late Miocene. Whereas accelerated exhumation in the early to mid-Miocene correlates with the breakup of the Farallon Plate, late Miocene accelerated exhumation correlates with the onset of flat subduction. Latitudinal differences on the exhumation timing along the western topographic front of the Main Cordillera may be due to the absence of the Paleozoic crystalline core south of 31.5°S, which seems to have acted as a buttress for shortening during the Eocene.