bulletin du Service G éologique de l Alg é rie Vol . 5 , n ° 1 , pp. 97 - 107 , 1 fig. , 1994 . Accrétion crustale et tectonique verticale à l Eburn éen dans les massifs des Eglab et du Yetti. ( Dorsale R é guibat , Alg é rie ) . Yamina MAHDJOUB * , Amar DRARENI * et Rachid GANI * * 1 ST , USTHB , BP. 32. El Alia Alger , ( Alg érie ) . * * Universit é de Tizi Ouzou , ( Alg é rie ) . R é sum é : La cro ûte é bum é enne des domaines Yetti - Eglab ( Dorsale r é guibat , Alg érie ) , montre des caract ères typiques de l' Arch é en . L ' essentiel de cette croûte birrimienne s ' est form é autour de 2 , 1 Ga à travers un important volume de mat ériel pr é sentant des caract ères juv é niles : les gneiss gris - granites syn à tardi - lectoniques dat é s à 2,2 - 2 ,1 Ga - et les granites post à anorogé niques - les granites aftouts datés à 2 , 0 Ga . Comme à l ' Arch é en, la tectonique verticale ( raccourcissement homog ène horizontal ) relay é e par une tectonique transcurrente , pr é domine sur l ' accr étion lat é rale . Mots cl é s : Craton Ouest Africain, Dorsale R é guibat , Yetti - Eglab, Alg é rie , Arché en , Ebumé en , accr é tion crustale , gé ochimie, gé ochronologie , d é formation, tectonique verticale , dé formation transcurrente . Eburnean crustal accretion and vertical displacement in Yetti - Eglag massifs . ( Ré guibat Rise , Algeria ) . English abriged version : Previous field studies showed that Lower Precambrian ofYetti - Eglab massifs ( East part of Ré guibat rise , Nord of West Africa craton ) consist of numerous and widespread bodies of granitoids which intruded Birrimian volcanosedimentary sequences weakly or not metamorphosed . Granitoids are emplaced during distinct magmatic episodes : ( 1 ) grey gneissses ( syn to late - orogenic granites ) and ( 2 ) red Aftout granites ( post to anorogenic granites ) . Aftout granites display calc - alkaline to alkaline association ( Kahoui, 1988 ) and 2.08 Ga zircon Pb - Pb age ( Kahoui et al . , submitted ) . Chemical compositions of grey gneisses are those of TTG ( trondhjemites , tonalit é s and granodiorites ) . New Sm - Nd , and Rb - Sr isopopic compositions of these grey gneisses ( granites and associated mafic intrusions ) and their zircon Pb - Pb data show their early proterozoi ' c age ( 2.2 - 2.1 Ga ) and suggest that most of them are generated from a protolith which mantellic origine and whitout significant participation of Archean continental material ( Drareni et Per % submitted ) . As in Guiana shield ( Gruau et al . , 1985) and other West African areas ( Abouchami et al . , 1990 and Boyer et ai , 1992 ) , Ebumean events in Yetti - Eglab are characterised by creation of juvenile crust which seems to occur far influence of Archean domains. However , contrary to other Birrimian area , major magnatic crustal growth seems generated by importante mass of 2.08 Ga post to anorogenic Aftout granites and during final Ebumean history.

Accrétion crustale et tectonique verticale à l Eburnéen

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Page 1: Accrétion crustale et tectonique verticale à l Eburnéen

bulletin du Service Géologique de l AlgérieVol. 5, n°1, pp. 97 - 107,1 fig., 1994.

Accrétion crustale et tectonique verticaleà l Eburnéen dans les massifs des Eglab et du Yetti.

(Dorsale Réguibat, Algérie).

Yamina MAHDJOUB*, Amar DRARENI* et Rachid GANI**

1ST, USTHB, BP. 32. El Alia Alger, (Algérie).** Université de Tizi Ouzou,( Algérie).

Résumé:La croûteébuméenne des domaines Yetti - Eglab (Dorsale réguibat,Algérie), montre des caractèrestypiques de l'Archéen. L'essentiel de cette croûte birrimienne s'est formé autour de 2,1 Ga à travers unimportant volume de matériel présentant des caractères juvéniles: les gneiss gris - granites syn à tardi-lectoniques datés à 2,2 - 2,1 Ga - et les granites post à anorogéniques - les granites aftouts datés à 2,0 Ga.Comme à l'Archéen, la tectonique verticale (raccourcissement homogène horizontal) relayée par unetectonique transcurrente, prédomine sur l'accrétion latérale.

Mots clés : Craton Ouest Africain, Dorsale Réguibat, Yetti-Eglab, Algérie, Archéen, Ebuméen,accrétion crustale, géochimie, géochronologie, déformation, tectonique verticale,déformation transcurrente.

Eburnean crustal accretion and vertical displacement in Yetti-Eglag massifs.(Réguibat Rise, Algeria).

English abriged version :Previous field studies showed that Lower Precambrian ofYetti-Eglab massifs (Eastpart of Réguibat rise, Nord of West Africa craton) consist of numerous and widespread bodies of granitoidswhich intruded Birrimian volcanosedimentary sequences weakly or not metamorphosed. Granitoids areemplaced during distinct magmatic episodes: (1) grey gneissses (syn to late-orogenic granites) and (2) redAftout granites (post to anorogenic granites).

Aftout granites display calc-alkaline to alkaline association (Kahoui, 1988) and 2.08 Ga zircon Pb-Pb age(Kahoui et al., submitted). Chemical compositions of grey gneisses are those of TTG (trondhjemites, tonalitésand granodiorites). New Sm-Nd, and Rb-Sr isopopic compositions of these grey gneisses (granites andassociated mafic intrusions) and their zircon Pb-Pb data show their early proterozoi'c age (2.2-2.1 Ga) andsuggest that most of them are generated from a protolith which mantellic origine and whitout significantparticipation of Archean continental material (Drareni et Per % submitted).

As in Guiana shield (Gruau et al.,1985) and other West African areas (Abouchami et al., 1990 and Boyeret ai , 1992), Ebumean events in Yetti-Eglab are characterised by creation of juvenile crust which seems tooccur far influence of Archean domains. However, contrary to other Birrimian area, major magnatic crustalgrowth seems generated by importante mass of 2.08 Ga post to anorogenic Aftout granites and during finalEbumean history.

Page 2: Accrétion crustale et tectonique verticale à l Eburnéen

ACCRETION CRUSTALE ET TECTONIQUE VERTICALE A L EBURNEEN DANS LES MASSIFS DES EGLAB ET DU YETTI.

Structural data show that Aftout granitic bodies intruded molassic Guelb El Hadid formations and in the otherhat the major deformation occured at 2.1Ga,during emplacement of Yetti and Chegga granitoides . Thisearly

formation resulted from Est-West shortening (N-S vertical foliation and strong vertical stretchingfcneation) and appeared to pre-date late transcurrent ductile deformation (foliation trajectories are perturbedfcy transcurrent shearing). These newdata suggered that early Ebumean tectonic in Yetti-Eglab massifs showiructural characteristics of Archean craton.

Key words : West African craton, Reguibat Rise, Yetti-Eglab, Algeria, Archean, Ebumean belt ,crustalgrowth,geochemistry,geochronology, verticaldisplacement,transcurrent deformation.