Geochemical and Sr–Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco)

Abstract

In the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic–granitoid bimodal association and peraluminous granodiorites emplaced c. 330 Ma, intruded by younger leucogranites c. 300 Ma. The mafic–ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial εNd values and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic–granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial εNd values, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

“…The extensional/transtensional D 0 tectonics of the Jebilet massif from Late Devonian to Visean‐Namurian times is consistent with the opening of Devonian‐Carboniferous basins in the paleo Western Meseta (Figure a), controlled by pull‐apart tectonics (Aarab & Beauchamp, ; Bouabdelli & Piqué, ; Pique & Michard, ). By contrast, our results are opposed to the model proposed by Ben Abbou et al () and Roddaz et al () in the Nappe Zone, extended to the Jebilet massif by (Essaifi et al, , , ), who considered these basins as back‐arc foreland basins related to north‐westward propagation of a thrust‐and‐fold belt originating in the Eastern Meseta. Intracontinental rifting was associated with major bimodal and granodioritic magmatism dated in the Jebilet massif at 358–336 Ma.…”

Tectonic evolution of the Rehamna metamorphic dome (Morocco) in the context of the Alleghanian-Variscan orogeny

“…In this revised model, the SSW directed movement postdates sedimentation in the Visean to early Serpukhovian basins and is thus not connected to their formation as proposed by Essaifi et al . [] in the Jebilet. In the Central Massif, the folds and foliation trends form a V‐shape structure which is parallel to the Sehoul block boundary (Figure ).…”

Geochemical Evidence for Large‐Scale Drainage Reorganization in Northwest Africa During the Cretaceous

“…To characterize the sedimentary sources of the Cretaceous sediments deposited in the eastern Central Atlantic Ocean, we use a compilation of 794 published Sr and Nd isotope values measured on sedimentary and magmatic rocks of the WAC (supporting information Table S1, Ajaji et al, ; Ali et al, ; Allègre et al, ; Asiedu et al, ; Azzouni‐Sekkal et al, ; Bea et al, ; Blanc et al, ; Boher et al, ; Deckart et al, ; Dia et al, ; D'Lemos et al, ; Dupuy et al, ; El Baghdadi et al, ; Ennih & Liégeois, ; Errami et al, ; Essaifi et al, ; Fullgraf et al, ; Gasquet et al, ; Jakubowicz et al, ; Key et al, ; Kouamelan et al, ; Le Goff et al, ; Meyer et al, ; Montero et al, ; Othman et al, ; Pawlig et al, ; Peucat et al, ; Potrel et al, ; Roddaz et al, ; Samson et al, ; Schaltegger et al, ; Schoepfer et al, ; Soumaila et al, ; Mohammed et al, 2015; Tahiri et al, ; Taylor et al, ; Thomas et al, ; Toummite et al, ; Verati et al, ). This database allows a comprehensive picture of differences in the isotopic composition of the main geological units present in the WAC (Figure c).…”