Preprints
https://doi.org/10.5194/egusphere-2023-2113
https://doi.org/10.5194/egusphere-2023-2113
27 Sep 2023
 | 27 Sep 2023

Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro-Juruena belt (Amazonian Craton, Colombia)

Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, and Johan De Grave

Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro-Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modelling in South America has largely been restricted to the plate’s margins (e.g. Andean active margin, Brazilian passive margin and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data however show AFT central ages ranging from 79.1 ± 3.2 Ma to 177.1 ± 14.8 Ma with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo-Oriente-Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other West Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological time scales and highlights extensional settings as an important geological context for craton exhumation.

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Journal article(s) based on this preprint

01 Mar 2024
Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro–Juruena belt (Amazonian Craton, Colombia)
Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, and Johan De Grave
Solid Earth, 15, 329–352, https://doi.org/10.5194/se-15-329-2024,https://doi.org/10.5194/se-15-329-2024, 2024
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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This study explores the erosion and exhumation processes and history of early continental crust...
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