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Impact of Permian to Early Jurassic Rifting in the Western Moroccan Meseta on Subsequent Orogenesis in the Moroccan Atlas Mountains

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part I

Presenting Author:

Dylan Vasey

Authors:

Vasey, Dylan A.¹, Gouiza, Mohamed², VanTongeren, Jill A.³

(1) Department of Earth and Climate Sciences, Tufts University, Medford, MA, USA, (2) School of Earth and Environment, University of Leeds, Leeds, USA, (3) Department of Earth and Climate Sciences, Tufts University, Medford, MA, USA,

Abstract:

The Atlas Mountains of Morocco are frequently considered the archetype of orogenesis by inversion of an intraplate continental rift. However, the width and lithospheric structure of the Permian to Early Jurassic Atlas rift system are largely unknown, limiting understanding of how weaknesses inherited from rifting have been exploited during subsequent orogenesis. Prior work focuses mostly on well-exposed Triassic to Jurassic rift strata in the present-day High Atlas, and it is often assumed that the topographic boundaries of the High Atlas contain the entirety of the rift that was inverted in the Late Cretaceous to Cenozoic. To test this assumption, we present field observations with detrital and igneous zircon U-Pb geochronology from the Western Moroccan Meseta region northwest of the High Atlas, as well as from the High Atlas itself.

Our field observations highlight the full extent of Permian to Triassic rocks associated with continental rifting in the Meseta, up to ~150 km northwest of the High Atlas. Detrital zircon geochronology indicates that Permian to Triassic sedimentary rocks in the Meseta and northwestern High Atlas contain Permian ages of 300 Ma to 260 Ma, whereas rocks in the southeastern High Atlas lack Permian ages but have Archean ages of 3.5 Ga to 2.5 Ga. These results suggest that the Atlas rift system was sufficiently wide and/or segmented to have distinct provenance domains. Our zircon U-Pb geochronology on igneous rocks in the Meseta, in conjunction with prior work, delineates distinct Carboniferous (~330 Ma) and Permian (~280 Ma) magmatic episodes in this region, which are largely absent in other parts of the Atlas Mountains.

We propose a model in which Permian magmatism during orogenic collapse and/or the earliest stages of continental rifting weakened the Western Moroccan Meseta and facilitated a subsequent episode of Middle Jurassic to Early Cretaceous shortening and thickening restricted to this region. The High Atlas by contrast remained thin throughout the Mesozoic, enabling strain localization and development of high topography during later Late Cretaceous to Cenozoic orogenic events.