Petrology and K-Ar chronology of the Neogene-Quaternary Middle Atlas basaltic province, Morocco

Abstract

The Middle Atlas basaltic province is the largest and youngest volcanic field in Morocco. A hundred well-preserved strombolian cones and maars emitted numerous mafic lava flows, which cover a surface of ca. 960 km2. The study of 103 samples from these volcanic units allows us to distinguish four lava types, to map their distribution, to provide new K-Ar ages and to discuss their petrogenesis on the basis of their petrologic and geochemical (major and trace element) features. Nephelinites represent only 1.2% of the total surface of volcanic units; they are scattered all over it as small monogenic volcanoes built during the Middle and Late Miocene (16.25-5.87 Ma) and the Plio-Quaternary (3.92-0.67 Ma). The three other types are exclusively Plio-Quaternary (3.77-0.60 Ma). Basanites cover 22.5% of the volcanic field area, and generally overlie the more widespread alkali basaltic flows (68.5% of the plateau surface). Finally, subalkaline basalts form the El Koudiate cone and associated flows (7.8% of the surface of the volcanic units) and their origin is ascribed to contamination of alkali basaltic magmas by the upper continental crust. We show that nephelinites, basanites and alkali basalts derive from temporally increasing but small degrees of partial melting of variably enriched spinel– and garnet-bearing peridotites from the base of the North-African lithospheric mantle, at depths of ca. 70 km. Partial melting was caused by an asthenospheric uprise, which induced dehydration melting of parga-site-bearing enriched peridotites, metasomatised during an earlier Cenozoic plume-related magmatic event.

Subduction and volcanism in the Iberia–North Africa collision zone from tomographic images of the upper mantle

“…960 km 2 (El Azzouzi et al, 2010). The volcanism in this region has been proposed as the result of a thin lithosphere (less than 90 km) leading to an asthenospheric uprising (El Azzouzi et al, 2010;Fullea et al, 2010). This coincides well with our model and other recent ones (Bezada et al, 2014;Palomeras et al, 2014) Fullea et al, 2010;Teixell et al, 2005) that indicate the presence of thin lithosphere (< 100 km) beneath these regions.…”

“…In this case the location of the maximum absolute value of the anomaly coincides with the location of the Middle Atlas basaltic province, which is the area of largest and youngest volcanism in Morocco, covering a surface of ca. 960 km 2 (El Azzouzi et al, 2010). The volcanism in this region has been proposed as the result of a thin lithosphere (less than 90 km) leading to an asthenospheric uprising (El Azzouzi et al, 2010;Fullea et al, 2010).…”

Short wavelength lateral variability of lithospheric mantle beneath the Middle Atlas (Morocco) as recorded by mantle xenoliths

“…11. Chondrite-normalized REE abundances in melts in equilibrium with group-1 clinopyroxenes (see text for definition) compared with Cenozoic alkali basalts from the Middle Atlas (shaded area, data from El Azzouzi et al, 2010). Equilibrium melts were calculated from Cpx LA-ICP-MS analyses and published Cpx/melt partition coefficients (Hart and Dunn, 1993;Kelemen et al, 1993).…”

“…The Middle Atlas volcanic province is the largest (~1000 km 2 ) and youngest (16 to 0.6 Ma) volcanic field in Morocco (El Azzouzi et al, 2010). About one hundred well-preserved strombolian cones and maars define a~120 km long, N160-170°E trending alignment (Fig.…”

Electrical signature of modern and ancient tectonic processes in the crust of the Atlas mountains of Morocco

“…These features coincide with a marked lithospheric thinning that has been modelled with potential fields Zeyen et al, 2005;Fullea et al, 2007), and has been associated either to Canary mantle plume flow beneath Africa (Duggen et al, 2009 or to the interplay between the Alpine contractional structures and the thermal erosion of the lithosphere (Berger et al, 2009). In either case, all authors agree that the velocity anomalies originate by low degree partial melting of sublithospheric mantle sources (Raffone et al, 2009;Duggen et al, 2009;Bouabdellah et al, 2010;El Azzouzi et al, 2010). The amount of partial melting necessary to explain the electrical resistivity observed in structure A (2-5 m) is between 2% and 8% according to the Modified Brick Layer Model (MBLM) suggested by (Partzsch et al (2000).…”