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Tertiary Volcanicity with quaternary recent

In the heart of Hoggar, several phases of volcanic activities intra-plates follow one another between 35 My (higher Eocene) and the subactuelle time. This volcanicity begin with the basalts recut from boxing ring-complex in the district from Anaef. These complexes vary in composition: gabbros, diorites, monzonites and syenites. One second volcanic phase (Miocene) very significant is in the district of Atakor and comprises two periods of emission dated between 20 My-12 My (equivalent of volcanicity miocene of the Gulf of Bejaa, on the northern coast of Algeria) and 7 My-4 My It comprises dominant basalts and less abundant trachytes and phonolites.The last phase of activity is after 3 My (Pliocene) and extends until paleolithic and even probably until the historical time. It includes especially alkaline basalts (95%). This volcanicity is interpreted (Inhabitant of Lige J.P. and Al, 1998) as the trace of a plume mantellic, located between 20 and 70 km of depth, and whose presence is suggested by a gravimetric anomaly, of regional extension, under Hoggar. However, measurements of heat flow show a thermic anomaly, more in north, under the basin of the Sahara, and the more specific anomalies under Hoggar what would tally better with a chain of small mantellic intrusions; the mechanism called upon for the genesis of these magmas being the crustal delamination along the shear major zones reactivated subsequently to Panafricain, following the convergence of the plates African and European. During the tertiary sector, a significant uplift of Hoggar (2000 to 3000 m) is marked by the presence of scraps cretaceous to more than 2000 m of altitude (Fabre J, 1976; Kidney P. and Al, 1983)

 
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