Postrift history of the eastern central Atlantic passive margin: Insights from the Saharan region of South Morocco

Abstract

The passive margin of South Morocco is a low-elevated passive margin. It constitutes one of the oldest margins of the Atlantic Ocean, with an Early Jurassic breakup, and little geological data are available concerning its postrift reactivation so far. We investigated the postrift thermal history of the onshore part of the margin with low-temperature thermochronology on apatite crystals. Fission track and (U-Th-Sm)/He ages we obtained are significantly younger than the breakup (~190 Ma). Fission track ages range from 107 ± 8 to 175 ± 16 Ma, with mean track lengths from 10.7 ± 0.3 to 12.5 ± 0.2 μm. (U-Th-Sm)/He ages range from 14 ± 1 to 185 ± 15 Ma. Using inverse modeling of low-temperature thermochronological data, we demonstrate that the South Moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases. The first exhumation event occurred during Late Jurassic/Early Cretaceous, and we attribute this to mantle dynamics rather than to intrinsic rifting-related processes such as flexural rebound. The second event, from Late Cretaceous to early Paleogene, might record the onset of Africa/Europe convergence. We show a remarkably common behavior of the whole Moroccan passive margin during its early postrift evolution. The present-day differences result from a segmentation of the margin domains due to the Africa/Europe convergence. Finally we propose that varying retained strengths during rifting and also the specific crustal/lithospheric geometry of stretching explain the difference between the topographical expressions on the continental African margin compared to its American counterpart.

Post-Variscan evolution of the Anti-Atlas belt of Morocco constrained from low-temperature geochronology

“…However, it is in agreement with recent studies that have revealed the existence of major tectonic vertical motions that affected large domains on the eastern margin of the Central Atlantic Ocean (Malusà et al 2007;Ghorbal et al 2008;Ghorbal 2009;Gouiza 2011;Ruiz et al 2011;Bertotti and Gouiza 2012;Oukassou et al 2013;Sehrt 2014;Leprêtre et al 2015). Thereby, our data and the subsequent interpretation imply that the Anti-Atlas domain experienced up to 10.5 km of crustal exhumation and denudation by the Middle Jurassic, in relation with continental rifting in the Central Atlantic and the Tethyan Atlas.…”

Paleogeographic and structural evolution of northwestern Africa and its Atlantic margins since the early Mesozoic

“…It is separated from the margins of the Central and future equatorial Atlantic margins by a wide erosional domain. Thermochrono logical data (Gunnell, 2003;Leprêtre, 2015;Leprêtre et al, 2015) as well as widespread kimberlitic magmatism are consistent with uplift in this domain. According to paleocurrent data, erosion of the upwarp fed the Saharan basin, which is, at the time, connected to the Tethys Ocean farther north .…”

“…A "trans-Saharan seaway" connected the Tethys Ocean, in the north, to the equatorial Atlantic Ocean, in the south (Reyment, 1980;Luger, 2003), and shallow-marine brackish shales and limestones were deposited (Dufaure et al, 1984;Zanguina et al, 1998). Thermochronological data suggest burial of the Hoggar and Reguibat shields (Rougier et al, 2013;Leprêtre et al, 2014Leprêtre et al, , 2015English et al, 2016), consistently with subsidence under the "trans-Saharan seaway" and the northwestern Sahara basin. A wide lagoonal domain formed between these two domains, which underwent alternating transgressions and regressions (Fabre et al, 1996).…”

“…Given its trend parallel to the Reguibat shield, segment II is likely an expression of the vertical movement history of this basement high. Leprêtre (2015) and Leprêtre et al (2015) suggested that the Reguibat shield underwent repeated upwarping during the Mesozoic in response to plate-boundary forces. Upwarp segment III is north trending (i.e., parallel to the coast) and narrow (400-450 km).…”

Contrasting Mesozoic evolution across the boundary between on and off craton regions of the South African plateau inferred from apatite fission track and (U‐Th‐Sm)/He thermochronology

“…A Bayesian approach to inverse thermal history modeling was performed by using the reversible jump Markov chain Monte Carlo (MCMC) method described by Gallagher [] and the software QTQt. The theoretical basis and application of this modeling technique has been well documented and discussed in previous studies [ Gallagher et al ., ; Gallagher , ; Cogné et al ., , ; Vermeesch and Tian , ; Guillaume et al ., ; Wildman et al ., , ; Leprêtre et al ., ]. The MCMC algorithm was run for a minimum of ~200,000 iterations after discarding an initial ~50,000 “burn in” runs [ Gallagher et al ., ; Gallagher , ].…”