Geochemistry and Petrogenesis of Lower Jurassic Mafic Rock Suites in the External Rif Belt, and Chemical Geodynamics of the Central Atlantic Magmatic Province (CAMP) in Northwest Morocco

We present new field evidence, geochemical and isotopic data, and age constraints on Lower Jurassic mafic rock suites within a >200-km-long curvilinear belt in the Rif orogenic belt in northernMorocco and show that these rock assemblages formed as part of the Central Atlantic Magmatic Province (CAMP). The CAMP represents a large igneous province that straddles the edges of themodern peri-Atlantic continents. It developed similar to 200 Ma, following the initiation of the breakup of Pangea. Mainmagmatic rocks in the Rif External Zone include basaltic lavas, massive dolerite, and isotropic and cumulate gabbros, all intruded by dolerite and trondhjemite dikes and sills. Available U-Pb zircon ages from dolerite, gabbro, and trondhjemite dike rocks are 200 +/- 4, 196 +/- 4, and 192 +/- Ma, respectively. Based on their geochemical affinities and isotopic compositions, the analyzed rocks define basalt-dolerite and gabbro-cumulate gabbro-trondhjemite groups. The basalt-dolerite group samples are subalkaline in nature and have low TiO2 contents, whereas the gabbro-cumulate gabbrotrondhjemite group samples are alkaline and display high TiO2 values. Most samples are tholeiitic in character and show large-ion lithophile and light rare earth element enrichment and high field strength element depletion compared with normalmid-ocean ridge basalt (MORB). Samples of both groups display low Nd-143/Nd-144(201 Ma) (0.51182-0.51262) and high Sr-87/(86)Sri ratios with epsilon(Nd) values ranging from -1.51 to +4.85. The basalt-dolerite group rocks have enriched MORB compositions, compatible with the low-TiCAMP suites, whereas the gabbro-cumulate gabbro-trondhjemite group rocks have oceanic island basalt compositions reminiscent of high-TiCAMP suites in other continents. Magmas of the gabbrocumulate gabbro-trondhjemite group underwent differentiation through tholeiitic fractionation. Magmas of the rocks of both groups included melt components, originated from partial melting of a previously subduction-modified subcontinental lithospheric mantle. Our results indicate that the Early Jurassic CAMP magmatism in northern Morocco marked a major episode of continental magmatism before the opening of the Maghrebian Tethys between Africa and Iberia in the latest Jurassic.

Automated summary

The study revealed that the Lower Jurassic mafic rock suites in the Rif orogenic belt in northern Morocco are part of the Central Atlantic Magmatic Province and formed around 200 million years ago. These rocks exhibit alkaline characteristics and high TiO2 content, originating from partial melting of the subcontinental lithospheric mantle.