(U-Th)/He ages of Proterozoic-Paleozoic basement rocks from northern Chile (18-19° S) and implications on the Neogene uplift history of the Western Cordillera
ABSTRACT In the Western Cordillera of northern Chile, the Proterozoic-Paleozoic Belén Metamorphic Complex is covered by late Oligocene-early Miocene (25-18 Ma) rocks, and both units are involved in west-vergent contractional deformation, which results in exhumation. A Miocene age (18 to 6 Ma) for deformation has been previously constrained by stratigraphy and cross-cutting relationships. To understand the youngest exhumation event and reverse faulting, we obtained 21 (U-Th)/He ages from two samples of the metamorphic rocks and the associate inverse thermal modeling. Five zircon (U-Th)/He ages from one sample are 113 to 226 Ma, very scattered, while five zircon ages from the other, are 20 to 49 Ma. The high dispersion of zircon (U-Th)/He data prevents the geological interpretation of results. Apatite grains from both samples yielded 11 (U-Th)/He ages between 10.4 and 18.7 Ma, with 9 values from 12.0 to 15.5 Ma. A slight positive correlation between apatite single-grain dates and effective uranium for 4 crystals of one sample suggests relatively slow cooling. The T-t model including these 4 apatite ages shows continuous cooling from 15 to 0 Ma with a relatively more marked cooling period at 11-7 Ma. The middle-late Miocene thermal signal agrees with the geologic evolution of the region and would permit to date the last activity of the Chapiquiña-Belén reverse fault, which uplifted and exhumed the metamorphic rocks. This signal is relatively similar to that the eastern Altiplano, but differs considerably from that the forearc.
| Main Authors: | , , , |
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| Format: | Digital revista |
| Language: | English |
| Published: |
Servicio Nacional de Geología y Minería (SERNAGEOMIN)
2022
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| Online Access: | http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062022000300313 |
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