French Guiana Margin Evolution: From Gondwana Break-Up To Atlantic Opening

Knowledge of the Guiana Shield evolution during the Gondwana break-up is key to a better understanding of craton dynamics and margin response to transtensional opening. To improve this knowledge, we investigated the dynamics and thermal evolution of French Guiana, using several low-temperature thermochronology methods applied to basement rocks, including apatite and zircon (U-Th)/He and apatite fission tracks. Inverse modelling of results allows us to reconstruct the Phanerozoic thermal history of French Guiana margin and to give a preview of the Guiana Shield evolution. Three main events are inferred: firstly, a long-term period of relative stability since similar to 1.2 Ga, with no strong evidence for any erosional or burial event (>5-7 km); secondly, a heating phase between similar to 210 and similar to 140 Ma consistent with the Central Atlantic Magmatic Province-related event. Finally, an exhumation phase between similar to 140 and similar to 90 Ma, triggered by the Equatorial Atlantic opening, brought samples close to the surface (<40 degrees C).STATEMENT OF SIGNIFICANCEThis manuscript reports the first low-temperature thermochronological data obtained on the Guiana Shield (Northern South American continent), allowing to investigate its long--term geological history. This study combines apatite and zircon (U-Th)/He and apatite fission track data that have been inverted by using the latest diffusion and modelling improvement. Thermal modelling allows us to reconstruct, for the first time, the French Guiana thermal history from similar to 1.2 Ga to similar to 90 Ma and between 40 and 250 degrees C. We compare this thermal history to the Guiana Shield evolution, still poorly constrains, and bring for the first-time qualitative data about its evolution since Gondwana accretion to Atlantic opening. Based on those result, we demonstrate that the Guiana Shield was stable during the Gondwanan period, and we reconstruct the later impact of the Central and Equatorial Atlantic opening on the margin derived from the shield. We, therefore, believe that the topic of this study should interest many readers, especially those who are working on shields and margin evolution using low-temperature thermochronology approach and dealing with old (U-Th)/He ages and unconventional thermochronometers ages inversion. All authors have approved the manuscript and agree with its submission to TerraNova.