Paleogeothermal Gradients Across an Inverted Hyperextended Rift System: Example of the Mauléon Fossil Rift (Western Pyrenees)

Abstract

The fossil rift in the North Pyrenean Zone, which underwent high temperature-low pressure metamorphism and alkaline magmatism during Early Cretaceous hyperextension, was studied to explore the geothermal regime at the time of rifting. In this work, we combined Raman lab analysis and thermal numerical modelling to shed light on the distribution of geothermal gradients across the inverted hyperextended Mauléon rift basin during Albian and Cenomanian time, its period of active extension. Data were acquired from a set of 155 samples from densely spaced outcrops and boreholes, analyzed using Raman spectroscopy of carbonaceous material. The estimated paleogeothermal gradient is strongly related to the structural position along the Albian-Cenomanian rift, increasing along a proximal-distal margin transect from~34°C/km in the European proximal margin to~37-47°C/km in the two necking zones and 57-60°C/km in the hyperextended domain. This pattern of the paleogeothermal gradient induced a complex interaction between brittle and ductile deformation during crustal extension. A numerical model reproducing the thermal evolution of the North Pyrenees since 120 Ma suggests that mantle heat flow values may have reached 100 mW/m 2 during the rifting event. This model reveals that above the thermal pulse, the temperature gradient varied within a small range of 55 to 62°C/km, as inferred from RSCM peak temperatures. We demonstrate that the style of reactivation during subsequent convergence influenced the thermal structure of the inverted rift system.

Recumbent folding in the Upper Cretaceous Eaux‐Chaudes massif: A Helvetic‐type nappe in the Pyrenees?

“…A 30°C/km gradient for the Iberian margin is near to the 34°C/km gradient estimated for the European conjugate margin by Saspiturry et al. (2020). However, a 30°C/km gradient would imply ~11 km of burial over the fold nappe, which is hard to reconcile with the tectonic pile that can be reconstructed above (Labaume & Teixell, 2020).…”

“…RSCM geothermometric results for the Jurassic–Lower Cretaceous rocks of the NPZ in the vicinity are in a range of 300–400°C (Clerc et al., 2015; Corre, 2017). However, this metamorphic peak is associated with the mid‐Cretaceous episode of crustal hyperextension in the Pyrenean rift (Clerc & Lagabrielle, 2014; Golberg & Leyreloup, 1990; Saspiturry et al., 2020), and not with the Alpine orogeny as in the Upper Cretaceous at Eaux‐Chaudes. The microstructural features observed at ECM are consistent with the RSCM estimates.…”

Review of Iberia–Eurasia plate‐boundary basins: Role of sedimentary burial and salt tectonics during rifting and continental breakup

“…Rifting and continental breakup in the Mauléon basin developed, from the Early Cretaceous to the mid‐Cenomanian (Figure 7e), under a high geothermal gradient, as indicated by (a) Raman spectroscopy of carbon materials (RSCM) showing peak temperatures consistent with a gradient of 60°C/km–75°C/km (Corre, 2017; Saspiturry, Lahfid, et al, 2020; Saspiturry, Razin, et al, 2019), (b) detrital zircon fission‐track data indicating a 80°C/km gradient (Vacherat et al., 2014) and (c) U–Th–Sm)/He thermochronology data indicating a 80°C/km–100°C/km gradient (Hart et al., 2017). Numerical thermal models suggest that the base of the hyperextended domain had a mantle heat flow of 100 mW/m 2 and a maximum temperature of 600°C during continental breakup (Saspiturry, Lahfid, et al, 2020; Saspiturry, Razin, et al, 2019). Vitrinite reflectance values from the Mauléon basin also weigh in favour of HT/LP syn‐rift metamorphism (Lescoutre, 2019; Lescoutre et al, 2019).…”

Large-scale vertical movements in Cenomanian to Santonian carbonate platform in Iberia: indicators of a Coniacian pre-orogenic compressive stress

“…It consists mainly of Paleozoic basement rocks with Mesozoic sediments on its flanks (Muñoz, 1992, and references therein). The North Pyrenean Zone represents the inverted Early Cretaceous Iberia-Eurasia plate boundary that was in the deepest part of a hyperextended rift (e.g., Mouthereau et al, 2014;Teixell et al, 2016;Espurt et al, 2019;Lagabrielle et al, 2020Saspiturry et al, 2020a, 2020b, 2021, and the Aquitaine Basin represents an inverted Early Cretaceous continental rift on the European proximal margin (e.g., Angrand et al, 2018;Issautier et al, 2020). The North Pyrenean Frontal Thrust separates the Aquitaine Basin and the North Pyrenean Zone (Biteau et al, 2006;Souquet et al, 1977).…”