The Beni Bousera orogenic lherzolite is a ~70 km² body of spinel- and garnet peridotites located in the Rif mountains of northern Morroco, along the Mediterranean shore. The massif is surrounded by an aureole of high-grade metamorphic rocks (felsic and mafic granulites) and is well known for showing a variety of mafic rocks interlayered with peridotites. These mafic layers notably include Al-rich, corundum-bearing granulites, garnet pyroxenites containing graphitized diamond pseudomorphs, but all transitions from garnet pyroxenites to Cr-rich pyroxenites through spinel pyroxenites are also present, as previously described in the neighbouring Ronda peridotite.

During the 2-days field trip, we shall :
(1)  visit key outcrops to discuss the structural relationships between peridotites and their metamorphic host ;
(2)  examine the gradation of peridotite textures across the massif, from garnet mylonites near the contact with granulites towards Seiland-facies, coarse granular peridotites in the inner parts of the ultramafic body ;
(3)  observe the different types of mafic layers, paying a special attention to the covariation between pyroxenites and peridotites facies.

The Neogene-Quaternary Middle Atlas basaltic province is the largest and youngest volcanic field in Morocco. It is situated atop a tabular Jurassic dolomitic limestone plateau, between Azrou and Timahdit, where a hundred strombolian cones and maars are well preserved. Lava flows cover a surface of about 960 km² and include minor nephelinites, some basanites and predominant alkali basalts. Some maar deposits contain abundant mantle xenoliths showing a variety of lithologies (from harzburgites to pyroxenites through spinel lherzolites and wehrlites), textures and metasomatic imprints. Several lava flows also contain peridotite xenoliths, with predominant coarse-granular textures.
During the 1-day excursion we shall observe typical, well-preserved volcanic structures and visit some of the xenolith localities.