ORIENTAL MOROCCAN NEOGENE VOLCANISM AND STRIKE-SLIP FAULTING

The microtectonic analysis of faults and of volcano-plutonic associations in the Eastern Rif shows that the distribution of a large number of Miocene to Quaternary volcanic emission points is tectonically controlled. Their localisation, parallel to the strike-slip faults orientated N070-090, N040-050 and N-S suggests that the volcanic emissions could have occurred along tension gashes making an angle of 40-50-degrees to the initial strike-slip plane. The new orientation, of the principal compressional stress to N040-000 during upper Miocene, reactivates faults striking N 070, N 040-050 and N-S; the volcanic emissions with a NW-SE, NE-SW and N-S directions, occur along gashes developed in this system. During the Plio-Quaternary, the counterclockwise rotation of the main stress to NW-SE, initiate strike-slip movement along the N-S, N 090 and N 120-140 faults; the volcanic emissions take place on <<en echelon>> tension gashes developed in this system. In this area, subjected since 10 M.a. to a compressional regime, the crustal mega shear zones develop scattered fissures and tension gashes which initiate partial fusion at depth by pressure release. The gaps in volcanic activity may correspond to the changes in the stress field.