The Cenozoic alkaline volcanism of the Senegalo-Mauritania sedimentary basin presents an episodic long-lasting volcanic activity from the Eocene-Oligocene boundary up to the Quaternary. Two volcanic episodes are usual...The Cenozoic alkaline volcanism of the Senegalo-Mauritania sedimentary basin presents an episodic long-lasting volcanic activity from the Eocene-Oligocene boundary up to the Quaternary. Two volcanic episodes are usually distinguished on stratigraphical grounds: a Miocene one and a Quaternary one separated by a period of quiescence of several million years corresponding to the main phase of lateritic weathering. The Tertiary lavas are highly silica-undersaturated alkaline rocks ranging from nephelinites to basanites. They contain nepheline and fassaite-type clinopyroxene in their mineralogy. The Quaternary lavas are more evolved with Hy-normative in comparison to the Tertiary ones;they are composed of basanites and medium to coarser-grained dolerites. The distribution of the REE and other incompatible elements are typical of alkaline lavas with generally strong LREE enrichment without significant Eu anomaly. The Cenozoic Cap-Vert lavas have OIB (oceanic islands basalts)-affinities as shown by their relatively radiogenic Nd and unradiogenic Sr characters closed to the HIMU-OIB. This suggests a HIMU-type end member in the magma sources which is fairly comparable to those erupted in the Canaries and Cape Verde archipelagoes during the same period.展开更多
This work presents the results of geotechnical tests carried out in the laboratory on specimens of Quaternary olivine basanites from the Cap-Vert peninsula of Dakar. The samples were taken following geotechnical inves...This work presents the results of geotechnical tests carried out in the laboratory on specimens of Quaternary olivine basanites from the Cap-Vert peninsula of Dakar. The samples were taken following geotechnical investigations in the Fann-PE, Mermoz-Ouakam, Yoff and Ngor areas respectively. The results obtained show a dry density between 20.45 and 29.30 kN/m<sup>3</sup> which corresponds to medium to high density basanites. The porosity varies between 0.33% and 4.20%. For microlitic basanites, the porosity remains low, on the other hand, for micrograined basanites;a slight increase in porosity is noticed. As for the methylene blue adsorption test value measured, it is between 0.25 and 1.10. The uniaxial compression strength (Rc) and Young’s modulus (E) vary respectively from 12.19 MPa to 41.748 MPa and from 1477.6 MPa to 7699.1 MPa. The low strength values are recorded in altered and vesicular basanites. Also, a correlation was made between uniaxial compression strength and porosity and showed a gradual decrease in strength with increasing porosity.展开更多
文摘The Cenozoic alkaline volcanism of the Senegalo-Mauritania sedimentary basin presents an episodic long-lasting volcanic activity from the Eocene-Oligocene boundary up to the Quaternary. Two volcanic episodes are usually distinguished on stratigraphical grounds: a Miocene one and a Quaternary one separated by a period of quiescence of several million years corresponding to the main phase of lateritic weathering. The Tertiary lavas are highly silica-undersaturated alkaline rocks ranging from nephelinites to basanites. They contain nepheline and fassaite-type clinopyroxene in their mineralogy. The Quaternary lavas are more evolved with Hy-normative in comparison to the Tertiary ones;they are composed of basanites and medium to coarser-grained dolerites. The distribution of the REE and other incompatible elements are typical of alkaline lavas with generally strong LREE enrichment without significant Eu anomaly. The Cenozoic Cap-Vert lavas have OIB (oceanic islands basalts)-affinities as shown by their relatively radiogenic Nd and unradiogenic Sr characters closed to the HIMU-OIB. This suggests a HIMU-type end member in the magma sources which is fairly comparable to those erupted in the Canaries and Cape Verde archipelagoes during the same period.
文摘This work presents the results of geotechnical tests carried out in the laboratory on specimens of Quaternary olivine basanites from the Cap-Vert peninsula of Dakar. The samples were taken following geotechnical investigations in the Fann-PE, Mermoz-Ouakam, Yoff and Ngor areas respectively. The results obtained show a dry density between 20.45 and 29.30 kN/m<sup>3</sup> which corresponds to medium to high density basanites. The porosity varies between 0.33% and 4.20%. For microlitic basanites, the porosity remains low, on the other hand, for micrograined basanites;a slight increase in porosity is noticed. As for the methylene blue adsorption test value measured, it is between 0.25 and 1.10. The uniaxial compression strength (Rc) and Young’s modulus (E) vary respectively from 12.19 MPa to 41.748 MPa and from 1477.6 MPa to 7699.1 MPa. The low strength values are recorded in altered and vesicular basanites. Also, a correlation was made between uniaxial compression strength and porosity and showed a gradual decrease in strength with increasing porosity.
