Tectonometamorphic evolution of the Rehamna dome (Morocco)

Volume: 42 Host publication title: The 2014 CETeG Conference "Lądek" Host publication sub-title: The Orlica-Śnieżnik Dome and the Upper Nysa Kłodzka Graben, the Sudetes 23-26 April 2014, Lądek Zdrój, Poland : Proceedings and Excursion GuideNon peer reviewe

Tectonometamorphic evolution of the Rehamna massif (Morocco, Variscan belt)

International audienceThe Morocco Variscan belt is considered to be the south-western continuation of the European Carboniferous orogen on the NW Gondwana margin. The Rehamna Massif, a paleozoic massif located on the Meseta domain which is part of this belt, is affected by three main deformation events (D1, D2 and D3) of variable intensity and geometry, associated with a Barrovian metamorphism. The first forms a flat-lying metamorphic foliation S1, which is deformed by WSW–ENE trending F2 folds with associated sub-vertical S2 cleavage, then heterogeneously reworked by NNE–SSW trending F3 folds with an S3 cleavage moderately to steeply dipping to ESE. Each deformation lead to the development of a new foliation and the crystallisation-deformation relationships show that biotite, chlorite, garnet, chloritoid and staurolite grew in the S1 fabric, and that chloritoid and staurolite continued their growth in the S2 and S3 fabrics. Two types of andalusite porpyroblasts located around granitic intrusions were identified: some are clearly post-tectonic whereas others are presumably coming from an early event. This study combines crystallisation-deformation relationships, in addition to the results of mineral chemistry and mineral zoning, with pseudosection modelling and geochronological datas. Based on the resulting P–T–d paths, 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 first in continuation of burial, then in the development of a syn-convergent extrusion of metamorphosed units to form a dome elongated E–W. This was responsible for syn-convergent detachment of the Ordovician upper crustal sequence. 3) The next episode of convergence took place in a ESE–WNW direction orthogonal to the previous one and is characterized by the accretion of the Rehamna dome to the continental basement in the west. Existing Ar/Ar dating shows that the first and the second deformations occurred during the Late Carboniferous to Early Permian (315–290 Ma) and that the third deformation took place during the Early Permian (290–275 Ma). Geochronology with in situ U/Pb dating on monazites is performed in order to date the individual phases of metamorphism and constrain the timing of the deformations events