Résumé
A striking feature of the Imilchil alkaline province, in the Moroccan Central High Atlas, is the close association of magmatic intrusions with Triassic sediments exhumed by diapirism. This study reports field, petrographic, geochemical and Sr‐Nd isotopic data, as well as new U‐Pb zircon ages, which allow us to constrain the timing of the intrusions and to discuss their relationship to diapiric structures and the magmatic and hydrothermal processes. Our results indicate a restricted range of Late Jurassic ages (ca. 163 ± 1—ca. 149 ± 2 Ma) for the paroxysm of magmatic activity and confirm the diachronicity between diapirism and magmatism, albeit with a short interval of only a few My between the end of diapirism and the magmatic paroxysm. Deep‐seated faults associated with transtensional tectonics, accommodating the increasing spreading rate of the Central Atlantic during the Jurassic, played a key role in the close association of magmatic intrusions with diapirs. The faults first triggered active diapirism in the Early‐ Jurassic and then guided OIB‐type partial melts formed by local decompression melting of the mantle. At shallower depths, the diapiric structures acted as corridors for magma migration, probably using evaporites as preferential pathways. Magmas underwent fractional crystallization and interacted with evaporites to produce pervasive Na‐rich hydrothermal fluids.
This study focuses on the central Moroccan High Atlas of Imilchil, characterized by an association between alkaline igneous intrusions and Triassic sediments exhumed by salt diapirism. Our new field, petrographic, geochemical, and isotopic data and U‐Pb ages for five main intrusions indicate for the first time that these Imilchil intrusions are Late Jurassic in age (ranging from 163 Ma to 149 Ma) and provide a better understanding of the magmatic and hydrothermal processes involved in their formation. They also show that the regional major paleo‐faults reactivated by transtensional tectonics played a significant role in the association of these magmatic intrusions with the diapirs. These faults first generated active salt diapirism in the Early Jurassic, followed by passive diapirism associated with filling sedimentary mini basins in the Middle Jurassic. Subsequently, diapiric structures also facilitated the migration of mantle‐derived magma, which interacted with evaporites to generate Na‐rich hydrothermal fluids that locally modified differentiated igneous rocks during their crystallization.
First U‐Pb zircon ages constrained the precise timing and tectonic setting of the Moroccan Central High Atlas Jurassic alkaline intrusions An alkaline intrusive province closely associated with Triassic sediments exhumed by diapirism in the Central High Atlas of Morocco The relationship of the Central High Atlas Jurassic alkaline intrusions to diapiric structures and the magmatic and hydrothermal processes