Polyphased Inversions of an Intracontinental Rift: Case Study of the Marrakech High Atlas, Morocco

Abstract

The High and Middle Atlas intraplate belts in Morocco correspond to Mesozoic rifted basins inverted during the Cenozoic during Africa/Eurasia convergence. The Marrakech High Atlas lies at a key location between Atlantic and Tethyan influences during the Mesozoic rifting phase but represents today high reliefs. Age and style of deformation and the mechanisms underlying the Cenozoic inversion are nevertheless still debated. To solve this issue, we produced new low‐temperature thermochronology data (fission track and [U‐Th]/He on apatite). Two cross sections were investigated in the western and eastern Marrakech High Atlas. Results of inverse modeling allow recognizing five cooling events attributed to erosion since Early Jurassic. Apart from a first erosional event from Middle/Late Jurassic to Early Cretaceous, four stages can be related to the convergence processes between Africa and Europe since the Late Cretaceous. Our data and thermal modeling results suggest that the inversion processes are guided at first order by the fault network inherited from the rifting episodes. The sedimentary cover and the Neogene lithospheric thinning produced a significant thermal weakening that facilitated the inversion of this ancient rift. Our data show that the Marrakech High Atlas has been behaving as a giant pop‐up since the beginning of Cenozoic inversion stages.

Exhumation and Surface Evolution of the Western High Atlas and Surrounding Regions as Constrained by Low‐Temperature Thermochronology

“…These data indicate cooling from temperatures <60 °C at ~10 Ma that is at the same time as the rapid cooling within the basement rocks of the hanging wall. Rapid cooling at 10 Ma is consistent also with the results of a previous thermochronologic study in the HA (Leprêtre et al, ). Along the geologic transect of Figure , within the basement rocks to the north of the drainage divide, a 5 Ma old AHe age is located deep in a gorge incised in the axial part of the belt (Mar44; Figures and ).…”

“…AHe ages become older toward the south up to 74.0 ± 4.0 Ma and toward the north up to 120.0 ± 9.7 Ma (Domènech, ; Ghorbal, ; Leprêtre et al, ). In the same region, AFT ages range from 33.0 ± 0.9 to 9.0 ± 0.5 Ma, and they become older southward up to 212.0 ± 15.0 Ma and northward up to 203.0 ± 5.0 Ma (Balestrieri et al, ; Ghorbal, ; Leprêtre et al, ; Missenard et al, ; Saddiqi et al, ). ZHe ages in the axial region of HA range from 309.0 ± 25.0 to 34.0 ± 2.7 Ma with only 8 out of 37 ages younger than 70 Ma located in the axial region of the western HA (Domènech et al, ).…”

“…The main erosion event across the HA occurred during the early‐middle Miocene (Balestrieri et al, ; Barbero et al, ; Missenard et al, ). However, multiple cooling events at 45, 20, and 10 Ma have been proposed based on modeling of AFT and AHe data (Leprêtre et al, ). In the AA, the AFT ages are all older…”

“…The amount of deformation is analyzed along a large‐scale geologic cross section, where thermochronologic data across major faults can be used to quantify vertical offsets. To these goals, we provide new thermochronologic data over a large area within the HA and partly also over the AA, and we integrate them into the existing extensive thermochronologic data set (Balestrieri et al, ; Barbero et al, ; Charton et al, ; Domènech, ; Domènech et al, ; Ghorbal, ; Ghorbal et al, ; Gouiza et al, ; Leprêtre et al, ; Malusà et al, ; Missenard et al, ; Oukassou et al, ; Ruiz et al, ; Saddiqi et al, ; Sebti et al, ; Sehrt, ; Sehrt et al, ). We quantify the amounts and rates of exhumation using a simple age‐to‐erosion inversion method (Willett & Brandon, ), and we investigate cooling histories through thermal modeling QTQt (Gallagher, ).…”

The Tell-Rif orogenic system (Morocco, Algeria, Tunisia) and the structural heritage of the southern Tethys margin

“…Laffitte (1939), who called it "Atlas Event", firstly identified this event in the Aurès Mountains (Algerian Atlas). Khomsi et al (2004Khomsi et al ( , 2016 and Leprêtre et al (2018).…”