Fission track thermochronology in South-Central Chile (37°S-42°S): implications for mass transfer and denudation along an active continental margin
Abstract
Seismicity, faulting and uplift point to active deformational processes along the South-Central Chilean continental margin and make this area a natural laboratory for investigations of long-term mass transfer patterns at convergent margins. Understanding the factors controlling the tectonic behaviour of the continental margin has some general implications for continental growth and the mass transfer processes in "subduction factories". In order to identify and quantify mass transfer processes we applied apatite and zircon fission track thermochronology along two N-S oriented, trench-parallel sections. The western profile is located within the Permo-Triassic accretionary complex of the Coastal Cordillera and provides information about the timing and magnitude of forearc uplift and/or subsidence. The eastern profile runs through the Main Cordillera and aims towards quantifying the denudation history and understanding the mechanisms of exhumation within the magmatic arc. Early Cretaceous to Early Tertiary fission track ages of the metamorphic and granitoid rocks of the Coastal Cordillera indicate that exhumation of less than 4 km occurred since about the Early Cretaceous. The exhumation rates were variable with time: while geomorphology and sedimentary cover on the basement rocks indicate uplift of several 100m during Pliocene and Quaternary, sedimentary basins suggest subsidence during Miocene times. Therefore, most of the recorded exhumation must be Early Cretaceous to Paleogene in age. The slow and discontinuous exhumation suggests that processes leading to vertical displacements, like basal underplating or tectonic erosion, were not active to any major extent here. In the Main Cordillera, apatite fission track ages at the southern end of the profile (40°S) range from Late Miocene to Late Pliocene, revealing that exhumation there is recent and rapid, with rates of nearly 1 km/Ma during the last 4 Ma. Fission track ages tend to get older along the profile until Eocene fission track ages at the northern end of the profile (38°S) indicate that exhumation there was more than an order of magnitude less efficient. Although variations of the geothermal gradient and tectonics may have influenced the age distribution pattern, climate seems to be an important factor. Younger ages towards the south correlate with drastic increases of precipitation rates and intensity of Pleistocene glaciation.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....9658G