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.

Ana Fonseca et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2113', Paul. Green, 23 Oct 2023
  • RC2: 'Comment on egusphere-2023-2113', Chiara Amadori, 30 Oct 2023

Ana Fonseca et al.


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Short summary
This study explores the erosion and exhumation processes and history of early continental crust hidden within the Amazonian rainforest. This crust forms part of the Amazon Craton, an ancient continental fragment. Our surprising findings reveal the area underwent rapid early Cretaceous exhumation, triggered by tectonic forces. This discovery challenges the traditional perception that cratons are stable and long-lived entities and shows they can deform readily under specific geological contexts.