Mesozoic to Quaternary continental margin dynamics in South-Central Chile (36–42°S): the apatite and zircon fission track perspective

Abstract

Zircon and apatite fission track data provide constraints on the exhumation history, fault activity, and thermal evolution of the South-Central Chilean active continental margin (36°S–42°S), which we use to assess the tectonic and geomorphic response of the margin to the Andean subduction regime. Several domains with different exhumation histories are identified. The Coastal Cordillera is characterized by uniform and coherent exhumation between Late Triassic (∼200 Ma) and late Miocene times, with surprisingly slow average rates of 0.03–0.04 mm/a. Thermal anomalies, related to Late Cretaceous and early Miocene magmatism, have regionally modified fission track age patterns. The Upper Cretaceous thermal overprint is of previously unrecognized significance and extent in the Coastal Cordillera south of 39°S. With the exception of a local but distinct Pliocene to Recent exhumation period in the high-relief Cordillera Nahuelbuta segment between 37°S and 38°S, Cenozoic overall exhumation in the Coastal Cordillera was very slow. The sedimentary record shows that uplift and subsidence here was episodic, with low amplitudes and durations. This rules out large-scale, long-term, Cenozoic accretion, trench-parallel tilting, and tectonic erosion processes in the forearc. The Main Andean Cordillera shows markedly greater long-term exhumation rates than the Coastal Cordillera and, at ∼39°S, a steep exhumation gradient. To the south, long-term average Pliocene to Recent exhumation rates of ∼1 to ∼2 mm/a in the Liquine area (39°45′S) are almost an order of magnitude more rapid than average Paleogene to Recent exhumation near Lonquimay (38°30′S) and farther north. While no imprint of the intra-arc Liquine-Ofqui Fault Zone on the exhumation pattern is evident, long-term exhumation rates decrease from the crest of the Andes toward the western foothills. Exhumation gradients correlate with climatic gradients, suggesting a causal link to the variable intensity of late Miocene to Pleistocene glacial erosion.