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Tectonic evolution of the Rehamna metamorphic dome (Morocco) in the context of the Alleghanian‐Variscan orogeny
Author(s) -
Chopin Francis,
Corsini Michel,
Schulmann Karel,
El Houicha Mohamed,
Ghienne JeanFrançois,
Edel JeanBernard
Publication year - 2014
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1002/2014tc003539
Subject(s) - geology , orogeny , metamorphism , greenschist , paleontology , massif , geochemistry , tectonic phase , metamorphic rock , supercontinent , basement , tectonics , craton , civil engineering , engineering
Structural and 40 Ar/ 39 Ar geochronological investigations of the Rehamna Massif (Meseta, Moroccan Variscan belt) provide new constraints on the tectonic evolution of the Alleghanian‐Variscan orogen during the Upper Paleozoic. Three main tectonic events have been recognized: (1) Southward thrusting of an Ordovician sequence over the Proterozoic basement, its Cambrian sedimentary cover, and the overlying Devono‐Carboniferous basin. This event caused subhorizontal shearing and prograde Barrovian metamorphism of the buried rocks. (2) Continuous shortening resulting in the development of a synconvergent extrusion of metamorphosed units to form a dome elongated E‐W. This was responsible for synconvergent detachment of the Ordovician upper crustal sequence. The timing of these two episodes is constrained to 310–295 Ma by cooling and metamorphic amphibole and mica ages (3) A NW‐WNW convergence in a direction orthogonal to the previous one and characterized by the accretion of the Rehamna dome to the continental basement in the east. Based on 40 Ar/ 39 Ar cooling ages from a syntectonic granitoid and its host rocks and metamorphic 40 Ar/ 39 Ar ages from greenschist facies mylonite, the timing of this event falls between 295 and 280 Ma. The end of the Variscan orogeny in the Moroccan Meseta is constrained by the 40 Ar/ 39 Ar cooling age of a posttectonic pluton dated at ~275 Ma. The tectonic events highlighted in Morocco coincide with the late Variscan‐Alleghanian tectonic evolution of southern Europe and North America and can be correlated with the global reorganization of plates that accompanied suturing of Pangaea at around 295 Ma.