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First timing constraints on the Ecuadorian Coastal Cordillera exhumation: Geodynamic implications

Abstract : In this study, we provide the first detrital apatite (U–Th-Sm)/He (AHe) and zircon U–Pb ages to establish a detailed short-term chronology of the burial and exhumation history, which occurred in the Coastal Cordillera along the forearc domain of Ecuador. First, our results allowed us to define a range of maximum deposition ages for the Angostura Formation from 9.6 ± 0.2 Ma to 11.5 ± 0.6 Ma, which records high enough temperatures to partially reset AHe ages. QTQt thermal inverse modeling of the AHe dataset reveals three main periods of exhumation along the Costal Cordillera at ∼2 Ma, ∼5–6 Ma and ∼8–10 Ma, independent of the sample geographic locations. We discuss the origin of these periods of exhumation in relation to the geodynamic frame. The oldest exhumation event, at ∼8–10 Ma, evidenced locally along fault systems, could be related to overriding plate kinematic changes or early arrival of Carnegie Ridge. The intermediate exhumation period, at ∼5–6 Ma, could be explained by a later arrival of the Carnegie Ridge or to the subduction of an along-strike positive relief of the ridge. Later, subduction of sea-floor asperities could be responsible for heterogeneous uplift of the Coastal Cordillera during the Pleistocene (∼2 Ma) that induced exhumation as supported by our models. These results are corroborated by previous studies and demonstrate that AHe data are sensitive enough to provide reliable constraints in sedimentary domains.
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https://hal-insu.archives-ouvertes.fr/insu-03022961
Contributor : Isabelle Dubigeon <>
Submitted on : Wednesday, November 25, 2020 - 9:35:32 AM
Last modification on : Thursday, November 26, 2020 - 10:18:23 AM

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S Brichau, P Reyes, C Gautheron, M Hernández, F Michaud, et al.. First timing constraints on the Ecuadorian Coastal Cordillera exhumation: Geodynamic implications. Journal of South American Earth Sciences, Elsevier, In press, ⟨10.1016/j.jsames.2020.103007⟩. ⟨insu-03022961⟩

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