Petrological analysis of crustal xenoliths from Gourougou, Guelliz and Trois Fourches volcanoes, Northern Morocco. U-Pb zircon dating of magmatic dykes in Kariane, Western Meseta, Morocco.

Abstract

Part 1 Little is known about the petrology and P-T conditions beneath northeastern Morocco. To get a better understanding, crustal xenoliths from three volcanoes (Trois Fourches, Gourougou and Guilliz) were analysed. Only the eastern part of the Gourougou volcanic complex contained crustal xenoliths. These xenoliths were analysed using the optical microscope, the electron microprobe and thermodynamic software program Perplex (Connolly, 1990). The xenoliths indicate that during Tortonian and Pliocene there has been a magma chamber at a depth of 6 - 8 km in the metapelitic crust beneath the Gourougou volcanic complex. Part 2 In the Hercynian Meseta, at the base of the Middle Atlas, dykes are located. These dykes have, on structural grounds, been estimated to be Permian (Youbi et al., 1995; Bamoumen et al., 2008). Zircon dating of the dykes provided ages between 285 and 290 Ma, showing that these dykes formed during the final stage of the Hercynian orogeny. This confirms the ages based on structural grounds. The age of the youngest dyke is highly affected by common lead (204 P b) influences. No specific reason has been found why only this sample is so much affected by common lead and the others are not.