Deep Structures and Mantle Processes

The main objective is to constrain the composition, structure and dynamic of the shallower asthenospheric mantle and lithosphere by combining complementary disciplines (seismology, petrophysics, volcanology, petrology, geochemistry and geochronology) and the observations at different temporal and spatial length-scales, in order to unravel the tectonomagmatic evolution and deep processes that are responsible for the current topography, high heat flow, and gravity and geoid anomalies in many areas of the NW Africa.

Beneficiary/Participant Organisations



Head of working group

 Deep structures and mantle processes

Abderrahmane Bendaoud (USTHB) & Jean Louise Bodinier (UM)

Task 3.1: Geophysical imaging of deep mantle and lithospheric structures

 Yelles-Chaouche Abdelkarim (GRAAG +UMV)Jesus Galindo Zaldivar (CSIC-UGR)

Task 3.2: Mantle rock as windows into mantle lithospheric thinning processes

Delphine Bosch (UM), Dalila Hammor (UBMA)Mohamed Talbi (USTHB)Kamal Targuisti (UAE)

Task 3.3: Investigating Volcanism to constrain the recent geodynamic evolution and deep mantle composition

Abla Azzouni (UABT)Houssa Ouali (OMI)Fleurice Parat (UM) 

Task 3.4: Metamorphic and magmatic evolution of the NW African margins and hinterlands

Abderrahmane Bendaoud (USTHB)Khadidja Ouzegane (USTHB)Bénédicte Cenki-Tok (UM)Antonio Acosta Vigil (CSIC-UGR), Youbi Massrredin (UCAM), Mohamed Belhassan (UMV)Jean-Marc Lardeaux (CRNS)


Description of work

Task 3.1 : Geophysical imaging of deep mantle and lithospheric structures: Asthenospheric upwelling and/or channelling have been suggested for the Atlas range on the basis of topography and geoid anomaly, but direct observations of the mantle seismic velocity structures and seismic anisotropy are still missing.It is ongoing international campaigns (e.g. PICASSO, Maroko-Münster) will partly fill this gap, but the central part of Morocco remains poorly instrumented and therefore the so-called “Moroccan Hot Line” will not be well documented. With an enlarged CNRST-ING seismic station network, we will; (i) determine the Moho, lithosphere-asthenosphere boundary and transition zone different thicknesses with P and S receiver functions; (ii) constrain the upper mantle flow with SKS splitting analysis;(iii) and investigate the rheological and thermal of the lithosphere with coherence and admittance analyses. We will compare the predicted thermal structure with geo-therms deduced from mantle xenoliths and seismic determinations of the LAB depth and compare it with the seismic velocity from seismic tomography models with the aim of discriminating between thermal and compositional anomalies.  In addition, in this task we will use, among others, gravity, magnetics and magnetotelluric prospecting at different length-scales to provide additional constrains on the structure of the lithosphere and shallowest asthenosphere that will be used to investigate mechanisms investigate mechanisms of different orogeny during time temporal scales.investigate mechanisms of different orogeny during time temporal scales of different orogenies at different temporal scales.

Task 3.2: Mantle rocks as windows into mantle lithospheric thinning processes: Tectonically emplaced peridotite massifs and mantle xenoliths brought up by basaltic volcanism convey valuable information on the mechanisms involved in lithospheric thinning. Exposures of subcontinental peridotite massifs in the Rif (e.g., Beni Bousera peridotite massif, N. Morocco) and Tell (e.g., Edough and Collo peridotite massif, N Algeria) preserve a unique record of the tectono-magmatic mantle processes associated with the Tertiary construction of these orogenic belts, and the tectonic processes responsible for their exhumation. On the other hand, mantle xenoliths brought up to the surface by volcanism provide a snapshot of the composition and structure of the mantle beneath volcanic centres at the time of eruption, providing complementary information and a unique temporal record of its evolution. Mantle xenoliths in alkali basalts furnish information on mantle deformation and fluid/melt processes responsible for lithospheric thinning along the “Hot Lines and Spots” in Morocco and Algerian belts around the West African Craton. We will perform an integrated, multi-disciplinary (petrophysics, petrology and geochemistry) study of these rocks to provide constraints on the composition, thermal structure and deformation history of the upper mantle. This study will provide new clues to understand how a combination of thermal, deformation and fluid-rock processes may change the composition and physical properties of the upper mantle and facilitate its convective erosion, in close connection with the aims of tasks in WP1.

Task 3.3: Investigating Volcanism  to constrain the recent geodynamic evolution and deep mantle composition: To constrain the nature and origin of the Neogene volcanism and its significance in terms of geodynamic reconstruction, from the study of samples collected from the northern Rif-Tell-Tunisia area to the southern, Anti-Atlas region and through the central, Middle Atlas in Morocco and similar hinterland in Algeria. An extensive multi-method, geochemical study (major, trace and volatile elements, and radiogenic isotopes) will be combined with detailed petrological investigations and absolute dating (40Ar/39Ar and K/Ar). This approach will enable us to determine the sources of the magmatic systems, their potential evolution through time, the pre-eruptive conditions of the magmas – with inference for the depth of the lithosphere-asthenosphere transition. The lavas will also complement the information retrieved from mantle xenoliths (Task 3.2) regarding melt/fluid-rock interactions at the base of the lithospheric mantle. This layer, the lower section of the “tectosphere”, is now widely considered to play a key role in the (de)coupling between tectonic plates and the convecting mantle. Combined with seismological and geophysical imaging, this data will provide constraints to evaluate the proposed geodynamic scenarios.

Task 3.4: Metamorphic and magmatic evolution of the NW African margins and hinterlands: This task will investigate the magmatic and metamorphic evolution of  Rift-Tell belt and the pericratonic terrains in Algeria and Morocco hinterlands to provide a better idea of the processes that have structured the lithosphere in these areas where sealed tectonic sutures have accreted different lithospheric sections and shaped the lithospheric structure, which might have influenced the current  magmatic activity in connection with other task in this WP and in WPs 1-2. This tasks will comprise structural, metamorphic geology and geochronological and geochemical studies of selected areas where MEDYNA researchers are currently working.