Gasquet Et Al 2005

Precambrian Research 140 (2005) 157182

Contribution to a geodynamic reconstruction of the Anti-Atlas(Morocco) during Pan-African times with the emphasis on

a U

Abstract

New geodome (Oug531 5 Maand from th(>2100 Ma)and Eastern143Nd/144Ndfrom the lo

A recentland those frof the Eburthe Anti-Atshoshonitic

The accrextension, s

CorrespoE-mail ad

0301-9268/$doi:10.1016/inversion tectonics and metallogenic activity at thePrecambrianCambrian transition

Dominique Gasquet a,, Gilles Levresse b, Alain Cheilletz c,Moulay Rachid Azizi-Samir d, Abdellah Mouttaqi e

niversite de Savoie, CISM-EDYTEM, CNRS-UMR 5204, Campus Scientique, 73376 Le Bourget du Lac Cedex, Franceb UNAM, Centro de Geociencias, Campus Juriquilla, 76230 Santiago de Queretaro, Mexico

c CRPG-CNRS UPR A2300 and ENSG-INPL, BP 20, 54501 Vandoeuvre-le`s-Nancy Cedex, Franced Reminex, Groupe ONA, 26 Av. Allal El Fassi, Tissir 36-40, Marrakech, Morocco

e ONHYM, 5 Charia My Hassan, BP 99, Rabat, Morocco

Received 15 October 2004; received in revised form 22 April 2005; accepted 7 June 2005

chronological analyses (UPb SIMS zircon ages) have yielded ages of 552 5 Ma for the Bou Madine rhyoliticnat, eastern Anti-Atlas), 543 9 Ma for the Tachkakacht rhyolitic dyke (SaghroImiter, eastern Anti-Atlas), andfor the Aghbar trachytic sill (Bou Azzer, central Anti-Atlas). Inherited zircon cores from the Aghbar trachytic sille Bou Madine rhyolitic dome have been shown to be of Statherian age (ca. 16001800 Ma) and Paloproterozoicage, respectively, suggesting that a significantly older protolith underlies the Pan-African rocks in the CentralAnti-Atlas. Granodiorites and rhyolites from the SaghroImiter area have similar low 87Sr/86Sr (0.7020.706) and(0.51160.5119) initial ratios, suggesting a mixture of mantle and lower crust sources. This can also be inferred

w 187Os/188Os ratios obtained on pyrite crystals from the rhyolites.y published lithostratigraphic framework has been combined with these new geochemical and geochronological data,om the literature to produce a new reconstruction of the complex orogenic front that developed at the northern edgenian West African craton during Pan-African times. Three Neoproterozoic magmatic series can be distinguished inlas belt, i.e., high-K calc-alkaline granites, high-K calc-alkaline to shoshonitic rhyolites and andesites, and alkaline-trachytes and syenites, which have been dated at 595570, 570545 and 530 Ma, respectively.

etion of the Pan-African Anti-Atlas belt to the West African super continent (WAC) was a four-stage event, involvingubduction, moderate collision and extension. The calc-alkaline magmatism of the subduction stage was associated

nding author. Tel.: +33 3 79 75 86 45; fax: +33 3 79 75 87 77.dress:[email protected] (D. Gasquet).

see front matter 2005 Elsevier B.V. All rights reserved.j.precamres.2005.06.009

158 D. Gasquet et al. / Precambrian Research 140 (2005) 157182

with large-scale base metal and gold mineralisation. Metallogenic activity was greatest during the final extensional stage, atthe PrecambrianCambrian boundary. It is characterised by world-class precious metal deposits, basemetal porphyry andSEDEX-type occurrences. 2005 Else

Keywords: N rocco;

1. Introdu

The geois extremeopment ofwith metal-the lower cdevelop laral., 1999; Kstruct comunderstandlithospherimineral conical data foand geochelogical andNeoprotero(AA) of Mthat develoAfrican Craclass ore drecently being extensiof the ambifunded by tOne of thebeen to imactivity dutory of theproduced ddeposit (stoAg0) clearlelements fcrustal leveto draw uptions through the orogenic belt, taking into account newgeochronological data, in order to accurately definethe architenew U/Pbfrom the B

ne ints pubarerThe dynamias thisnorth

ity.

eologiocco

e Moern edn (Figesetia

. Thee Herg et aleseta

mleltffner,(Bao

), blocdefor

originbate atheticaornee

ih and(Piquent c

te Protaran t

mentary Palaeozoic rocks. The Precambrian basementoutcrops in several inliers within late Ediacaran andcture of the chain. This paper combinesgeochronological and geochemical data

ou Azzer, SaghroImiter and OugnatBou

younger units (Bas Draa, Ifni, Kerdous, Akka, Igherm,Sirwa, Zenaga, Bou Azzer, Saghro and Ougnat; Fig. 1)distributed along two major fault zones (South Atlasvier B.V. All rights reserved.

eoproterozoic; Zircon UPb dating; SrNd isotopes; Anti-Atlas; Mo

ction

dynamic reconstruction of ancient beltsly important for understanding the devel-ore deposits, particularly those associatedconcentration systems that involve parts ofrust and mantle and are therefore able to

ge-tonnage, high grade ore deposits (Ord etay and Mpodozis, 2001). In order to recon-

plex and long-lived orogenic fronts and tosome of the fundamental processes (on a

c scale) involved in the production of largecentrations, it is necessary to have geolog-r a whole region, particularly geophysicalmical data, supported by solid geochrono-structural data. This paper focuses on thezoic evolution of the Anti-Atlas Mountainsorocco, a segment of the Pan-African chainped along the northern edge of the Westton (WAC). The region houses large world-eposits (Fig. 1) and known reserves haveen increased by new discoveries made dur-ve exploration programs carried out as parttious National Geological Mapping Projecthe Moroccan Ministry of Energy and Mines.most important results of this project hasprove our understanding of metallogenicring the 300 Ma-long Neoproterozoic his-Anti-Atlas. For example, geochemical datauring a recent study of the Imiter AgHgck metal estimated at 8000 metric tonnes

y show a large-scale transfer of chalcophilerom the mantle to superficial (km-deep)ls (Levresse et al., 2004). It is also essentialprecise and reliable lithostratigraphic sec-

Madiresula clebelt.geodbelt,of theactiv

2. GMor

ThnorthCratothe MFaultby thCaritthe Mat TaHoepAtlas2002atelyTheto dehypoand C(Ennranes

basemto LaEdiacWest African Craton

liers (Eastern AA) with a discussion oflished by other workers in order to proposepicture of this Neoproterozoic orogeniciscussion focuses on the final stages of thec evolution of the Pan-African Anti-Atlasperiod is fundamental to the understandingern border of the WAC and its metallogenic

cal setting of the Anti-Atlas belt of

roccan Anti-Atlas belt is situated on thege of the Eburnian (ca. 2 Ga) West African. 1); it is separated from the High Atlas andn domains to the north by the South AtlasAnti-Atlas region was slightly reworked

cynian and Alpine orogenies (Pique, 1994;., 2004), which had a profound influence on-Atlas domains. In the High Atlas domain,in the East (Du Dresnay, 1976; Houari and2003) and in the western part of the Highuch, 1984; Ouazzani et al., 2001; Eddif,ks of Precambrian materials were moder-

med by the Variscan and Alpine tectonics.al position of these blocks is still subjectnd it is uncertain whether they belong to al North Moroccan continent (Villeneuve, 1994), to AvalonianCadomian terranesLiegeois, 2001), or to CarolinaIberia ter-

e, 2003). In the Anti-Atlas, the Precambrianomprises several units of Paloproterozoicerozoic age, unconformably overlain by lateo Cambrian rocks and then by mostly sedi-

D. Gasquet et al. / Precambrian Research 140 (2005) 157182 159

Fig. 1. (a) Th edrawnsketch map of eposits

Fault, andthe extent ostructure aAnti-Atlasconsensus

been reachmagmatichave beencorrespond(ii) a NeoPan-AfricaLancelot,Moussine-P1994; El AFekkak et aGasquet etof the Panthree-stagefollowed bsion stage.and break-uthe succesan island ablue-schist

; Heffassoc

or soe Anti-Atlas belt at the northern limit of the West African craton, rthe Anti-Atlas belt in southern Morocco and location of main ore d

Central Anti-Atlas Fault; Fig. 1). Due tof its sedimentary cover, for a long time thend tectonic evolution of the Pan-African

1974planenorthbelt was poorly understood, but now a basicon the major stages of its development hased. Two main periods of tectono-thermalactivity, associated with crustal accretion,recognised: (i) a Paloproterozoic period,ing to the Eburnean (Birimian) orogeny,proterozoic period, corresponding to then orogeny. Most authors (Leblanc and1980; Bassias et al., 1988; Leblanc and

ouchkine, 1994; Villeneuve and Cornee,ouli et al., 2001; Ennih and Liegeois, 2001;l., 2001; Thomas et al., 2002; Pique, 2003;al., 2004) consider that the development-African orogen can be explained by aprocess controlled by crustal extension,

y compression, and then by a second exten-(1) The first stage was related to the riftingp of the West African Craton and involved

sive development of an oceanic plateau,rc and a marginal basin, with associatedmetamorphism (ca. 800690 Ma; Clauer,

690605 Mward direcophiolite ocalc-alkalinwas associplane. (3)(605530 Mtation andforeland dethe south.(ca. 300 Mthe AA ex2004), whby polyhasedimentaronly subjec2004).

The newfor three sedescriptionthe Pan-Afafter Dallmeyer and Lecorche (1991). (b) Geological. SAF: South Atlas Fault.

eran et al., 2002). Whether the subductioniated with island arc development dipped

uth is still unclear. (2) The second stage (ca.

a) is characterised by basin closure, south-ted arccontinent collision (arc accretion),bduction, deformation, metamorphism ande magmatism. This convergence episode

ated with a southward dipping subductionThe final, post-collision extension stagea) is characterised by molasse sedimen-magmatism, which was followed by thevelopment of the Saharan cratonic basin toThe Statherian (ca. 1750 Ma) and Variscana) events did not have a major effect oncept in its western part (Gasquet et al.,

ere the Variscan shortening is expressedrmonic buckle folding in the Palozoicy cover. The Precambrian basement wast to faulting (Helg et al., 2004; Caritg et al.,

geochronological data we have obtainedlected inliers have allowed us to clarify theof the post-collision extensional stage of

rican orogeny.


3. Geological setting of the Ougnat, Saghro andBou Azzer inliers

3.1. Ougna

Cryogengreywackein the centFreton, 198facies andbearing grgeochronolThis basemvolcanic fomostly conwith basaltBou Madinby severalOne of thewith polymsations. Then-echelonscurrent tefault zoneet al., 199sequence urocks.

3.2. Saghr

In the Itary rocksof black shing formed(Marini androcks werefacies metevent. Theby an Edia(Ouarzazatfrom andetop. This swhich is n(Cheilletzsilver mineof felsic vdome), whtectonics (L

dated at 550 3 Ma by ion-probe U/Pb on zircons(Cheilletz et al., 2002). This epithermal event postdatesan earlier discrete base metal episode associated with

sive grat 5

alkalinlusite-e counet al.,tly trant aloe felsmilarambr

oic rough aoughuir et

Bou A

e Boulex p; Saqubasemts, is in formntinenii) a mlite (Lntinites, andtonesPan-A

are u

e mozazate00 m)ites, aaced d, 1998Tarou

sills oar). Tg theul et ar Ebuoped,tBou Madine

ian to early Ediacaran schistoses and black shales (Saghro Group) outcropre of the Bou Madine inlier (Fig. 2, after8). They are metamorphosed to greenschistintruded by quartz-diorites and garnet-

anites, the ages of which have not beenogically established (Abia et al., 2003).ent is unconformably overlain by Ediacaranrmations (Ouarzazate Supergroup), whichsist of ignimbrites and minor andesites,ic lava flows at the top. Moreover, in thee area, the ignimbrites have been intruded

rhyolitic domes and numerous felsic dykes.Ediacaran rhyolitic domes is associatedetallic ZnCuPbSnAgAu minerali-

ese mineral deposits occur in NNWSSEvein arrays related to Ediacaran tran-

ctonics represented by N30E strike-slips (Freton, 1988; At Saadi, 1992; Abia9, 2003). A Cambrian sedimentary covernconformably overlies the Neoproterozoic

oImiter

miter area (Fig. 3), the oldest sedimen-are represented by Cryogenian sequencesales (Saghro Group), interpreted as hav-in an extensional back-arc environmentOuguir, 1990; Ouguir et al., 1996). Thesefolded and subject to low greenschist

amorphism during the main Pan-Africanblack shales are unconformably overlain

caran volcanic and volcanoclastic sequencee Supergroup), with compositions that rangesitic at the bottom to ignimbritic at theequence hosts the Imiter AgHg deposit,ow considered to be of epithermal originet al., 2002; Levresse et al., 2004). Theralisation is genetically related to a seriesolcanics (Takhatert calc-alkaline rhyoliticich were coeval with regional extensionalevresse, 2001). These volcanics have been

intrudatedcalc-andain thWall(mosprese

Thare sidle Cterozalthoare th(Oug

3.3.

Thcomp1981zoicschisgeniaepicoand (ophioserpecanicsandsmainand(i) thOuar(10imbremplet al.zoicrare

AghbdurinBelfomajotelescanodiorites (Taouzzakt, Igoudrane; Fig. 3),72 5 Ma (Cheilletz et al., 2002). Thesee intrusive rocks produced a cordierite-

biotite contact-metamorphism assemblagetry rocks (Leistel and Qadrouci, 1991; De2001). Dykes of intermediate composition

chyandesite) and of various relative ages areng the Ediacaran Imiter normal fault zone.ic dykes, including the Tachkakacht dyke,in composition to the Takhatert dome. Mid-ian sedimentary rocks overly the Neopro-cks. The Variscan and Alpine orogenies,ctive in various sections of the AA belt,t to have had little effect in the Imiter areaal., 1994).

zzerAghbar

Azzer inlier (Fig. 4) is structurally the mostart of the whole Anti-Atlas (see Leblanc,aque et al., 1989, 1992). A Paloprotero-ent, including gneisses, amphibolites, andntruded by granites and overlain by Cryo-ations (Bou Azzer Group) comprising (i)

tal sedimentary and volcanoclastic rocksaficultramafic complex, interpreted as aneblanc, 1975; Brabers, 1988), comprisings, gabbros, quartz-diorites and mafic vol-associated with limestones, quartzites and

. These formations were deformed by thefrican shortening tectonic event (thrusts)

nconformably overlain by, successively:lassic Tiddiline Group, (ii) the Ediacaran

Supergroup, which consists of a thickvolcano-clastic pile (dacitic to rhyolitic ign-ndesites, conglomerates, sandstones, etc.)uring strong transtensive tectonics (Maacha), and (iii) the late Ediacaran to early Palo-dant Group (dolomites, sandstones andf syenite and trachyte at Jbel Boho andhe regional NS shortening that occurredVariscan orogeny (Soulamani et al., 1997;l., 2001; Caritg et al., 2004) reactivated the

rnean and Pan-African faults. A complex,polymetallic (CoNiAsFeCuAuAg)


Fig. 2. Main geological units of the OugnatBou Madine inlier (after Freton, 1988) and concordia diagram for zircons from the Bou Madinerhyolitic dome. Weighted mean ages, ellipses are 2 errors. Star represents the position of the dated rhyolite.


Fig. 3. Mainfrom the TachStars represen

mineral deand Variscathe mineraUPb datinat 218 8muscovitesgeological units of the SaghroImiter inlier (after Leistel and Qadrouci, 199kakacht rhyolitic dyke and (inset) the rhyolitic Takhatert dome (Cheilletz ett the position of the dated rhyolites.

posit was formed during these Pan-Africann events (Maacha et al., 1998). The age of

lisation is poorly constrained at 550 Ma byg on brannerite (En-Naciri et al., 1997) andMa by 40Ar/39Ar dating on hydrothermal(Levresse, 2001).

4. UPb gand Bou A

4.1. Analy

UPb dfrom Ouarz1; Levresse, 2001) and concordia diagram for zirconsal., 2002). Weighted mean ages, ellipses are 2 errors.

eochronology in the Ougnat, Saghrozzer inliers

tical procedures

ata were obtained for single zircon grainsazate and Taroudant Group volcanic rocks.


Fig. 4. Main geological units of the Bou Azzer inlier (simplified after Leblanc, 1981) and concordia diagram for zircons from the Aghbartrachyte. The 206Pb/238U age of the younger concordant point corresponds to the emplacement age of the trachyte sill (see text). Ellipses are2 errors. The age of the Jbel Boho syenite has been recalculated with Isoplot (Ludwig, 2003) from data of Ducrot and Lancelot (1977). Errorscorresponds to the error average given by the authors; the error correlation value is 0.98. Star represents the position of the dated trachyte andsyenite.

164D.G

asquetet

al./Preca

mbrian

Research140(2005)157182

Table 1UPb isotopic data (SIMS-CAMECA IMS 1270, Nancy, France) for zircon grains from the Ediacaran magmatism from the SaghroImiter, OugnatBou Madine and Bou AzzerinliersSample Measured data Concentration

(ppm)Tera-WasserburgConcordia data

Conventional concordiadata

Ages (Ma)

Is206Pb 207Pb/206Pb

204Pb/206Pb

206Pb/238U

UO/U Pb U Th 238U/206Pb

207 Pb/206Pb

207 Pb/235U

Error 206 Pb/238U

Error Correlationerror

206

Pb/238UError 207

Pb/235UError

BM7 (OugnatBou Madine, rhyolite, limpid grains)1218 4531 0.0644 0.00035 0.208 7.51 32 425 174 11.2938 0.1526 0.0644 0.0003 0.7356 0.0116 0.0885 0.0012 0.859 547 7 560 73814 3837 0.0648 0.00059 0.204 7.44 36 472 223 11.2687 0.2268 0.0648 0.0024 0.7020 0.0360 0.0887 0.393 548 11 540 21315 11314 0.1099 0.00361 0.127 7.77 80 1975 1099 21.3385 0.4168 0.1099 0.0006 0.3738 0.0117 0.0469 0.0009 0.623 295 6 322 940-3 5639 0.0603 0.00011 0.219 7.74 41 548 238 11.4911 0.1560 0.0603 0.0002 0.7131 0.0107 0.0870 0.0012 0.902 538 7 547 643-8 7893 0.0865 0.00187 0.175 7.55 62 1009 787 13.9941 0.2939 0.0865 0.0031 0.5909 0.0457 0.0715 0.0015 0.272 445 9 471 2943-9 2070 0.0734 0.00135 0.184 7.10 25 322 123 11.1924 0.3062 0.0734 0.0008 0.6858 0.0349 0.0893 0.0024 0.538 552 14 530 2144-4 5489 0.0591 0.00002 0.235 7.83 40 517 177 10.9875 0.1559 0.0591 0.0002 0.7475 0.0111 0.0910 0.0013 0.952 562 8 567 64-10 5948 0.0656 0.00041 0.214 7.64 50 662 266 11.4408 0.1538 0.0656 0.0003 0.7272 0.0132 0.0874 0.0012 0.743 540 7 555 84-7 6803 0.0754 0.00113 0.246 8.03 50 656 234 11.3496 0.1665 0.0754 0.0004 0.7244 0.0167 0.0881 0.0013 0.637 544 8 553 107-1 26581 0.0681 0.00063 0.380 9.41 62 850 356 11.8578 0.1007 0.0681 0.0003 0.6870 0.0088 0.0843 0.0007 0.665 522 4 531 57-12 11053 0.0660 0.00045 0.410 9.91 27 384 112 12.1114 0.0678 0.0660 0.0002 0.6793 0.0056 0.0826 0.0005 0.678 511 3 526 37-16 30385 0.0670 0.00038 0.400 9.48 63 834 320 11.3788 0.0846 0.0670 0.0008 0.7475 0.0413 0.0879 0.0007 0.389 543 4 567 87-19 19993 0.0599 0.00004 0.430 9.59 49 610 285 10.7606 0.0746 0.0599 0.0001 0.7629 0.0057 0.0929 0.0006 0.931 573 4 576 37-20 9929 0.0595 0.00004 0.450 9.98 24 315 174 11.0989 0.0705 0.0595 0.0003 0.7350 0.0057 0.0901 0.0006 0.814 556 3 559 37-21 12822 0.0604 0.00010 0.480 10.35 33 428 123 11.1435 0.0761 0.0604 0.0001 0.7328 0.0052 0.0897 0.0006 0.971 554 4 558 37-25 13215 0.0644 0.00038 0.450 9.84 32 399 166 10.8728 0.1277 0.0644 0.0004 0.7495 0.0109 0.0920 0.0011 0.809 567 6 568 67-3 17284 0.0595 0.00002 0.450 9.84 39 486 186 10.8019 0.0586 0.0595 0.0001 0.7587 0.0043 0.0926 0.0005 0.965 571 3 573 27-4 17866 0.0592 0.00001 0.420 9.59 43 551 239 11.0108 0.0622 0.0592 0.0001 0.7422 0.0043 0.0908 0.0005 0.981 560 3 564 2

BM7 (OugnatBou Madine, rhyolite, inherited core)7-2 9175 0.1800 0.00054 1.980 9.84 21 62 39 2.4780 0.0220 0.1800 0.0004 9.6636 0.0971 0.4035 0.0036 0.882 2185 16 2403 9

IM74 (SaghroImiter, Tachkakacht rhyolite, limpid grains)74-1 29146 0.1896 0.00920 0.566 10.08 59 797 196 11.5425 0.1204 0.1896 0.0018 0.6654 0.0450 0.0866 0.0009 0.154 536 5 518 2774-10 108462 0.2527 0.00108 0.552 11.01 245 3333 2540 11.6809 0.0965 0.2527 0.0034 2.8428 0.0485 0.0856 0.0007 0.484 530 4 1367 1374-11 23921 0.0786 0.00138 0.510 10.30 52 694 148 11.3672 0.0968 0.0786 0.0013 0.7132 0.0259 0.0880 0.0007 0.235 544 4 547 1574-12 79577 0.1716 0.00802 0.508 9.54 219 2887 1216 11.3506 0.0997 0.1716 0.0006 0.6647 0.0174 0.0881 0.0008 0.335 544 5 517 1174-13 15705 0.0873 0.00192 0.523 10.35 38 505 126 11.2928 0.0766 0.0873 0.0009 0.7296 0.0191 0.0886 0.0006 0.259 547 4 556 1174-14 33336 0.0604 0.00010 0.500 10.14 104 1332 341 11.0171 0.0626 0.0604 0.0001 0.7393 0.0044 0.0908 0.0005 0.957 560 3 562 374-15 71200 0.0766 0.00132 0.455 9.84 210 2876 1126 11.7491 0.0986 0.0766 0.0004 0.6744 0.0095 0.0851 0.0007 0.596 527 4 523 674-17 7509 0.1247 0.00452 0.736 11.76 41 492 88 10.4086 0.1085 0.1247 0.0015 0.7885 0.0402 0.0961 0.0010 0.205 591 6 590 2374-3 91970 0.1057 0.00327 0.481 10.16 202 2861 959 12.1917 0.1282 0.1057 0.0039 0.6598 0.0749 0.0820 0.0009 0.093 508 5 514 4574-5 39739 0.0604 0.00011 0.505 10.11 96 1217 362 10.8683 0.0656 0.0604 0.0002 0.7475 0.0063 0.0920 0.0006 0.714 567 3 567 4

BA06 (Bou Azzer, Aghbar trachyte, limpid grains)6-1 19113 0.0626 0.00018 0.490 10.51 61 779 195 10.9699 0.1355 0.0626 0.0002 0.7553 0.0103 0.0912 0.0011 0.904 562 7 571 66-11a 26251 0.0677 0.00061 0.460 10.17 79 972 451 10.5442 0.1338 0.0677 0.0009 0.7705 0.0212 0.0948 0.0012 0.460 584 7 580 126-11b 24248 0.0720 0.00089 0.460 10.19 74 924 406 10.6724 0.1324 0.0720 0.0018 0.7634 0.0368 0.0937 0.0012 0.257 577 7 576 216-15 12454 0.0620 0.00019 0.670 12.16 56 795 129 12.1024 0.1549 0.0620 0.0003 0.6761 0.0093 0.0826 0.0011 0.927 512 6 524 66-2 16074 0.0594 0.00003 0.400 10.3 49 720 149 12.5365 0.1219 0.0594 0.0001 0.6485 0.0064 0.0798 0.0008 0.979 495 5 508 46-4a 9940 0.0639 0.00021 0.550 10.64 30 351 120 10.1710 0.2004 0.0639 0.0007 0.8255 0.0227 0.0983 0.0019 0.715 605 11 611 136-4b 10041 0.0671 0.00040 0.550 10.61 30 351 119 10.1148 0.1602 0.0671 0.0014 0.8370 0.0303 0.0989 0.0016 0.437 608 9 618 176-9 1758 0.1400 0.00503 0.580 10.56 6 76 37 10.3185 0.2223 0.1400 0.0034 0.9071 0.0818 0.0969 0.0021 0.239 596 12 655 43

BA06 (Bou Azzer, Aghbar trachyte, inherited grains)6-12 1808 0.1100 0.00011 1.950 10.96 6 21 11 3.1350 0.0457 0.1100 0.0003 4.7745 0.0733 0.3190 0.0047 0.951 1785 23 1780 136-14 19449 0.1200 0.00033 2.030 12.18 104 488 12 4.0211 0.1036 0.1200 0.0010 3.9660 0.1091 0.2487 0.0064 0.937 1432 33 1627 22


A CAMECA IMS 1270 ion microprobe (CRPG-CNRS, Nancy, France) was used following the ana-lytical methods described in Deloule et al. (2002).Detailed options reveagrains. Thcussed belograms were2003).

4.2. Ougna

One samMadine meuhedral, b50150mcracks andmicas andtory zonincores.

Eleven sage of 552the crystallnat inlier.EdiacaranPaloprotecore may bolder under

4.3. Saghr

The Ta(2100 Ma) suggesting that thee an inherited xenocryst from a significantlylying basement.

oImiter

chkakacht rhyolitic dyke contains smallimpid zircons. They are euhedral and bipyra-

well-developed prisms. Primary cracksons (apatite, quartz, occasional micas) arelatory zoning of magmatic origin is seeny and none of the grains had inherited

b-concordant points gave a weighted mean 9 Ma (Fig. 3). This is in good agreement0 3 Ma age of the neighbouring Takhatertme and with the stratigraphic position ofolcanism, which belongs to the EdicaranSupergroup. Three other zircons yieldedages of between 560 and 600 Ma. They

epresent xenocrysts inherited from grani-Ediacaran volcanic rocks. Their ages arence with the inherited ages obtained by

4.4.

Olyzedverysionszonin

SiteredTheycoun

an agmentwas i1952the Jband L(ca. 1xeno

teroz

5. GCam

Th(OuaGrouusingAA,OugnTable

5.1.

(i)zzerAghbar

ple of the Aghbar trachytic sill was ana-zircons are limpid and sub-euhedral, with

prisms (5080m). They contain rare inclu-atite, quartz and micas and show oscillatory

agmatic origin and rare inherited cores.small (5060m) zircon grains are scat-the concordia between 560 and 615 Ma.

obably inherited zircons from the basementks. The youngest concordant zircon gives

531 5 Ma (Fig. 4). This age is in agree-the stratigraphic position of the sill, whichd into an early Cambrian series (Choubert,

anc, 1981), and with the 529 3 Ma age ofho syenite (Fig. 4) (recalculated from Ducrotot, 1977). Two zircons gave Statherian ages800 Ma; Table 1). They probably representinherited from the underlying Palopro-

sement.

mistry of the Ediacaran andmagmatism in the AA area

chemical characteristics of the Ediacarane Supergroup) and Cambrian (Taroudantst-orogenic magmatism were determinediously published UPb data for the wholeer with analyses from the SaghroImiter,u Madine and Bou Azzer inliers (Figs. 57;d 3).

and trace elements

95570 Ma magmatism is represented byeter-scale intrusive bodies of granites, gra-rites and tonalities, with minor dioritesabbros, and rare basalts and andesites.ock types show mostly metaluminous< SiO2 < 75%), high-K calc-alkaline affini-ig. 5a). Na2O/K2O ratios range from 0.287, REE patterns (Fig. 6a) are moderatelynated [6.43 < (La/Yb)N < 27.63] with rel-low YbN contents (10) and low nega-

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Research140(2005)157182

Table 2Representative major (wt.%) and trace (ppm) element analyses from SaghroImiter inlierSample type B. Madine Imiter B. Azzer

BM99-01 rhyolite SJ127 granite IM99-50 granite IM00-03 diorite IM99-72 rhyolite IM99-05 rhyolite IM99-74 rhyolite IM99-75 ignimbrite IM01-01 rhyolite BA99-6 trachyteSiO2 77.06 66.28 68.72 55.17 73.26 72.66 77.30 75.51 76.29 64.33Al2O3 12.33 15.45 14.53 17.14 13.53 13.56 11.99 12.98 12.51 13.87Fe2O3 0.83 4.00 3.10 8.36 2.31 1.80 1.13 1.36 1.26 7.63MnO 0.10 0.08 0.08 0.14 0.07


Table 3Available Sr and Nd isotopic compositions of (595570 Ma) granite-granodiorites and (570545 Ma) rhyolites from the Imiter InlierAge/sample Type Sr (ppm) Rb (ppm) 87Rb/86Sr 87Sr/86Sr (2) (87Sr/86Sr)tRb-Sr data

595570 MIM 99-50 2.6IM 00-03 0.6SJ 127 1.0

570545 MIM 99-72 3.1IM 99-74 5.3IM 99-75 4.0IM 01-01 3.2

Age/sample 4Nd (Sm-Nd data

595570 MIM 99-50 9 (11)IM 00-03 0 (21)SJ 127

570545 MIM 99-72IM 99-74IM 99-75IM 01-01

Analytical meSr, Sm and Nspectrometer.and 143Nd/144for Sr and JMare negligiblethe last two dito the deplete

tive Emostlyseriesmetalu

(ii) The 5thickignimintrustop ofbasaltet al.,atationof themon. U>2.04aGranodiorite 115.22 106.7Granodiorite 482.48 101.0Granite 349.57 125.5

aRhyolite 103.98 113.5Rhyolite 73.01 133.3Ignimb. rhyolite 87.05 120.3Rhyolite 101.96 112.8

Sm (ppm) Nd (ppm) 147Sm/144Nd 143Nd/14

a3.26 16.8 0.1172 0.512053.42 16.8 0.1228 0.51222

3.39 19.4 0.1059 0.512188 (11)

a4.55 27.4 0.1005 0.512267 (15)3.38 18.4 0.1110 0.512096 (9)2.75 18.0 0.0922 0.512158 (25)5.05 30.1 0.1015 0.512197 (18)

thod: Separation of RbSr and SmNd was made according to the methodd concentrations were determined by isotope dilution. Rb was analyzed bSr and Nd isotopic ratios and Sm concentration were measured using a FinnNd ratios were normalized to 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219,for Nd gave average ratios of 87Sr/86Sr = 0.710205 23 (2) and 143Nd/1(


Fig. 5. K2OScalc-alkaline tCambrian Agtered (LOI < 3Freton (1988)(1992), Cama(1997), Ouguet al. (2000),(2001), GasquOuazzani et a

5.2. Isotop

5.2.1. RbSrNd

tonic eventSaghroImFig. 7. The(0.7020.7

tial ratios, which attest to a mixing of mantle andlower crustal sources, based on the mean geochem-

haracteristics of these reservoirs as determinedaure (9557s (Tab1561

in thare thea youn

34ical cby Fthe 5canic1161foundageswithiO2 plots (Le Maitre et al., 1989) of selected Ediacarano alkaline plutonic (a) and volcanic (b) rocks and of thehbar trachytic sill (star) of the Anti-Atlas belt. Unal-%) rocks are from this study and from Lebrun (1982),, Ighid et al. (1989), Azizi Samir et al. (1990), At Saadira (1993), Mokhtari (1993), At Isha (1996), At Malekir (1997), Ikenne (1997), Eddif et al. (2000), ThomasBajja (2001), Barbey et al. (2001), Chalot-Prat et al.et et al. (2001), Karl et al. (2001), Levresse (2001),

l. (2001) and Thomas et al. (2002).

e geochemistry

Sr, SmNd, S and rare gasisotopic data for the 595570 Ma plu-and 570545 Ma volcanic episode in the

iter district are presented in Table 3 andtwo groups display the same low 87Sr/86Sr

06) and 143Nd/144Nd (0.51160.5119) ini-

The event indicing fluids, atopic reservet al., 2004gangue miratios rangiwith the absions, suggwith the ep

5.2.2. ReThe sulp

sured 187Ocating a dand, by inIn order todata basedals at ImitReOs geometal depodifferent g(Table 4).epithermalChinkuashShen andmal and poof measurethe degreetaminated bmantle: 0.1nental crusresults obtaconcur wit(see above)tial 187Os/1from the 5tive Sr sign2001). The calculated Nd model ages for0 Ma granites and 570545 Ma felsic vol-le 3) fall within the rather restricted range ofMa. No Mesoproterozoic rocks have beene AA, so it seems probable that these TDMresult of the mixing of an older 2 Ga sourceger Neoproterozoic one.

SCDT values for the silver mineralisationate preferential degassing of SO2 in ascend-s well as mixing between the magmatic iso-oir and the country rock reservoir (Levresse). Helium isotope analyses of sulphides andnerals yield similar results, with 3He/4Heng from 0.76 to 2.64Ra. These data, togethersence of 20Ne in the analyzed fluid inclu-est a mantle origin for the fluids associatedithermal silver event (Levresse et al., 2004).

Oshide phases and Ag0 minerals show mea-

s/188Os ratios of 0.1440.197, clearly indi-ominantly mantle source for the osmiumference, the silver (Levresse et al., 2004).

assess the validity of this ReOs isotopeinterpretation of the source of the met-

er, we have compared our data with thechemical signatures of a variety of precioussits from around the world, formed undereodynamic regimes and at different timesThe measured 187Os/188Os of the Imiterdeposit (0.1440.197) is similar to the

ih AuCu epithermal deposit (0.130.24;Yang, 2004). Other gold bearing epither-rphyry-type deposits show a larger range

d 187Os/188Os ratios (0.2190.2), indicatingto which the primitive magma was con-y crustal and/or host country rocks (mean20.13; Chen et al., 1998; mean conti-

t: 1.21.3; Esser and Turekian, 1993). Theined for the Imiter ReOs isotope system

h the data from other geochemical proxies. They are also consistent with the low ini-88Os ratios (0.280.62) obtained on pyrites45 Ma volcanics and their relatively primi-atures, reinforcing the probable genetic link

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Research140(2005)157182

169

Table 4ReOs isotopic compositions of the Epithermal AgHg Imiter deposit and a variety of precious metal deposits in the world formed in various geodynamic setting and differentepochs

Type of deposit Localization [Re] [Os] 187Re/188Os 187Os/188Os 187Os/188Os(i) Age ReferenceEpithermal-Ag Imiter, Morocco 00.06 ppb 0.0060.162 ppb 014.2 0.1440.197 0.0130.197 Late Proterozoic Levresse et al. (2004)Epithermal-Au Low-sulphidation,

Bucaramanga,Colombia

43153 ppb 2130 ppt 2441299 1.518.48 Paleocene Mathur et al. (2003)

High sulphidation,Bucaramanga,Colombia

0.833 ppb 1934 ppt 865156136 1.858.11 1.2 Paleocene Mathur et al. (2003)

AuCu, Chinkuashih,Taiwan

1.42.9 ppb 0.22.1 ppb 3.734.5 0.130.24 1.152.07 Pliocene Shen and Yang (2004)

Gold shear-zone Kimberley, Zimbabwe 3142378 ppt 28.488 ppt 50.4456.5 2.014.83 2 Late Archean Frei et al. (1998)Porphyry Base-metal PC, large,

Chile0.3320 ppb 4244 ppt 96-94730 0.2178.46 0.1551.23 Eocene Mathur et al. (2000a,b)

Base-metal PC, small,Chile

0.8464 ppb 632 ppt 1202120921 4.390.2 3.84.68 Eocene Mathur et al. (2000a,b)

CuMo PC,Bagdad-vein 1, USA

3.866.76 ppt 817 ppt 2.419.9 5.132.1 2.12 Maastrichtian Barra et al. (2003)

CuMo PC,Bagadad-vein 2, USA

1.684.1 ppt 612 ppt 1914 1.0610.8 0.130.83 Maastrichtian Barra et al. (2003)

CuAu PC stage 2,Grasberg, Irian Jaya

11140 ppb 321024 ppt 7515653 1.031.31 0.791.26 Pliocene Mathur et al. (2000a, 2000b)


Fig. 6. Chondarea (a, this stEvensen et al.

Fig. 7. 87Sr/8lites from the187Os/188Os sSaghroImite

between thmineralisat

The gedeposit app

Fig. 8. Structuand a propose(2002); CentrSamson et al.(2001), Cheillthree studiedrite-normalized REE patterns of the Ediacaran and Cambrian plutonic andudy) and from the Central and Eastern Anti-Atlas (b), after Bajja (2001) an(1978).

6Sr vs 143Nd/144Nd plot of late granites and rhyo-SaghroImiter area. The mantellic initial (550 Ma)

ignature of euhedral pyrite of rhyolitic intrusion fromr (Levresse et al., 2004) is also shown.is volcanic event and the epithermal silverion.ochemical characteristics of the Imiterear to be dominated by metals and fluids

ral map and reliable UPb radiometric ages (new and previous) of the Neoprd timetable. Western Anti-Atlas data are from Hassenforder (1987), At Mal Anti-Atlas from Ducrot and Lancelot (1977), Leblanc and Lancelot (19(2003), Inglis et al. (2004); Thomas et al. (2004); Eastern Anti-Atlas frometz et al. (2002). International stratigraphic ages (left, in red) are after Amthinliers.

of mostly mcentrationtonnes), isChilean basa direct relaconcentratihas been eldemonstrattectonic regevent (570a relativelymantle to ttion of othecurrently in

6. Discuss

6.1. Synthegeochronol

Three liup for threevolcanic rocks from the SaghroImiter and Bou Azzerd Chalot-Prat et al. (2001). Normalization values from

antle origin. This result, and the huge con-of silver at Imiter (more than 8000 metric

consistent with observations made onemetal porphyry deposits (Table 4), wheretionship between the volume of total metalon and the participation of a mantle sourceucidated (Mathur et al., 2000a,b). This alsoes the need to invoke a major extensionalime at the time of the Imiter mineralizing545 Ma) to account for the rapid transfer oflarge quantity of metals directly from the

he surface. The geochemical characterisa-r precious metal deposits in the AA belt isprogress.oterozoic plutonic and volcanic rocks in the Anti-Atlasalek et al. (1998), Gasquet et al. (2001), Walsh et al.

80), Mifdal and Peucat (1985), Thomas et al. (2002),Magaritz et al. (1991), Landing et al. (1998), Levresseor et al. (2003) and Gradstein et al. (2004). In bold the

ion

sis of the lithostratigraphic andogical data for the Pan-African AA

thostrathigraphic columns have been drawnsections of the Western, Central and East-


ern AA (Fig. 8). The lithostratigraphic subdivisions arebased on the latest results obtained by the MoroccanNational Geological Mapping Project and other recentcontributio2002; Bou2004). By chave been amore compbelt.

The matribution oproterozoicmentary plterozoic bawhich supption that thparts separcated by Cmarked hetsequencesand suggesranes (the Pan-Africaat 580 Ma,genic seriefinally to anous (up to(upper Oua(Fig. 8), thinliers andanomaly atsition betwsedimentartransgressicanic eventTata and Taunconformwith a lowpatible wit(Benssaoudynamic bOuarzazateTaroudantextensiona

Two Panthe three swas the larghas been in

ciated magmatism (Mifdal and Peucat, 1985) and at663 14 Ma from metamorphic rims on zircons fromthe Iriri migmatite (Thomas et al., 2002). The second,

ler evee the Oa).e AAationmbria, 1991analy

is no dthostraternatipston

, 2004

PrecisAtlas

tentaatic

ozoiceochr

8. Sevo majhe tec. Thes deves propoupedage 1:ified a; Admevidenhari e). Hoiitic mou Ae emed to

een dLancee of 7gneissp inthe e2 Mans (Thomas et al., 2002, 2004; Walsh et al.,ougri and Saquaque, 2004; Gasquet et al.,ombining all this geochronological data weble to produce a relatively homogenous andlete lithostrathigraphic synthesis of the AA

in points are: (i) Uniformity in the dis-f the four major units from the Palo-

basement to the Middle Cambrian sedi-atform series. (ii) A crystalline Palopro-sement underlying the entire AA region,orts Ennih and Liegeoiss (2001) proposi-e old division of the AA into two distinctated by the Central AA fault as advo-houbert (1963) be abandoned. (iii) A

erogeneity of Cryogenian to Ediacaran rockthat reflects their probable distinct originsts the presence of a collage of exotic ter-Anti-Atlas terranes, AAT) during the mainn tectonic events. (iv) A transition, datedfrom a Cryogenian/early Ediacaran oro-

s to an Ediacaran post-orogenic series andCambrian anorogenic series. (v) A volumi-

2 km thick) Ediacaran volcanic sequencerzazate Supergroup), deposited over 30 Maat covers most of the surface of the AAsuggests the existence of a huge thermaldeep lithospheric levels. (vi) A rapid tran-een a dominantly volcanic regime to a

y marine epicontinental carbonate platformon at ca. 550 Ma, based on the last dated vol-(Benssaou and Hamoumi, 1999, 2001). Theroudant Groups often unconformably/para-ably overly the edges of the different inliers,-angle angular discordance. This is com-h a progressive transgressive marine eventand Hamoumi, 1999, 2001). No major geo-reak exists between the upper part of the

Supergroup and the bottom of Tata andGroups; both of which are coeval with anl tectonic event.-African tectonic events are recognised in

ections of the AA. The first event, whicher of the two (Leblanc and Lancelot, 1980),

directly dated at 661 23 Ma from an asso-

smalbefor580 M

ThinternPrecaet al.threetherethe lito in(Comet al.

6.2.Anti-

AmagmPalThe gFig.ing tand ttifiedbelt istagebe gr

Stident1980lessBouk2002tholeAt Bto thassum

has bandan agorthoGroudated762 nt (Leblanc and Lancelot, 1980) took placeuarzazate Supergroup magmatic event (ca.

belt from Morocco has been used to testal stratigraphic correlations related to then/Cambrian boundary problem (Magaritz; Landing et al., 1998). However, for thezed sections (Fig. 8), it can be seen thatirect correlation between the major limits oftigraphic groups, as they do not correspond

onally recognised stratigraphic boundarieset al., 1992; Amthor et al., 2003; Gradstein).

e timing of Pan-African events in the(Figs. 9 and 10)

tive synthetic log of the tectonic andevents that characterise the Precambrianevolution of the AA is shown in Fig. 9.onological information is reproduced fromen major magmatic episodes correspond-or changes in geochemical characteristicstonic environment have been clearly iden-geodynamic evolution of the Pan-Africanloped in Fig. 10 according to the four majorosed in Fig. 9. These magmatic events caninto four stages.Ocean opening. This stage has been clearlyt Bou Azzer (Leblanc, 1975, 1981; Church,ou, 2000; Fekkak et al., 2003), but it ist in the Sirwa massif (Leblanc, 1975; Elt al., 1991; Chabane, 1991; Thomas et al.,wever, the precise age of the associatedagmatism has not been well-constrained.zzer, the thermal metamorphism linkedplacement of gabbroic dykes, which is

belong to the tholeiitic magmatic event,ated at 788 8 Ma (Clauer, 1976; Leblanclot, 1980). Thomas et al. (2002) obtained43 14 Ma for a tonalite protolith from an

of the ophiolitic sequence of the Bleidathe Sirwa inlier. Samson et al. (2003)mplacement of a tholeiitic plagiogranite at.


Fig. 9. Synthetic log of the Anti-Atlas series with the main tectonic events and UPb ages of magmatic episodes, obtained in this study orcompiled from the literature: Juery (1976), Charlot (1976), Ducrot and Lancelot (1977), Ducrot (1979), Leblanc and Lancelot (1980), Mifdaland Peucat (1985), Magaritz et al. (1991), Mrini (1993), At Malek et al. (1998), Landing et al. (1998), Gasquet et al. (2001), Walsh et al. (2002);Cheilletz et al. (2002), Thomas et al. (2002, 2004); Barbey et al. (2004); Inglis et al. (2004). Note that the number of geochronological data isroughly proportional at the volumetric importance of the magmatisms.


Fig. 10. Pan-African geodynamic evolution of the Anti-Atlas during Pan-African times. WAC: West African Craton, NAA: Northern Anti-Atlas(after Levresse, 2001 modified). See text.


Stage 2: Subduction. The calc-alkaline magmatismrelated to arc-subduction processes in Saghro and BouAzzer has not yet been precisely dated (Saquaque etal., 1989, 1whether thethe south (LHefferan eEnnih andIf viewed amargin (afProterozoicseveral micplanes within the AA bexplain thedifferent hythe high P-the Bou Amately 5 kb

Stage 3:

3a. This e(Leblaresponallochtrelated(6606low-grgneissetectoninot beeof this

3b. This eptectonifore-ar

Stage 4:

4a. This imat 595to felsrelatedLevresstitutesdistens

4b. The Edmajor hIt is intdeposi

and to base metal porphyry type mineralisations(Cheilletz and Gasquet, 2001; Abia et al., 2003).Although it has not been dated precisely, the Tiouit

esothlkalinelong997).n alk

he Cazzeroho (iselyelatedo whic

e Palarand bya (Hu330

tion irecen

7 Matotaln to Pthe

an tim

Inversambria

A magorogeg thenic an550 MThis enic toical anition, wd by eni et, 2001of no

l depor worl, 2002CuP992). There is currently no consensus onsubduction plane dipped to the north or toeblanc, 1975; Leblanc and Lancelot, 1980;

t al., 1992; Villeneuve and Cornee, 1994;Liegeois, 2001, 2003; Thomas et al., 2002).s an analogue to the modern western pacificter Lagabrielle, in Pomerol et al., 2005),

subduction zones in the AA might boundroplates, so there could have been severaldifferent dip directions. If this was the caseelt during early Pan-African times, it wouldconflicting interpretations and reconcile thepotheses. Stage 2 is also characterised by

low T metamorphism of the metabasites ofzzer inlier (T 350 C and P of approxi-ar; Hefferan et al., 2002).Arccontinent collision and ocean closure:

pisode was first recognised at Bou Azzernc, 1981; Hefferan et al., 1992). It cor-ds to the tectonic emplacement of thehonous oceanic ophiolitic slivers and isto the main Pan-African tectonic event

90 Ma). Accompanying features includeade metamorphism, partially anatectics and calc-alkaline intrusives. The mainc event in the western and eastern AA hasn precisely dated, which makes correlationevent over the whole AA difficult.isode, which is coeval with the later, minorc event, corresponds to the closure of thec and back-arc basin.

Extension and marine basin development:

portant magmatic episode has been dated570 Ma. It is represented by intermediateic (mainly high-K calc-alkaline) intrusives

to base metal ore deposits (CuPbZn;se, 2001; Cheilletz et al., 2002) and con-

a transition towards the main Ediacaranive tectonic event.iacaran (570545 Ma) is characterised by aigh-K calc-alkaline to alkaline magmatism.imately linked to the largest precious metalts (AuHg Imiter, Cheilletz et al., 2002)

m

a

b1

4c. AtABc

r

t

ThEdiacterise400 Mity atralisabeen301

AgeniaalongAfric

6.3.Prec

Afromdurinpluto605ism.orogetologtranstrolleChbaet al.tancemetaImiteet al.brianermal Au deposit is related to high-K calc-e magmatism and has been interpreted asing to the same event (Al Ansari and Sagon,

aline volcanic episode interbedded withinmbrian platform sedimentary series at BouAghbar (this work) and at Bou AzzerJbelDucrot and Lancelot, 1977) has been pre-dated at 530 Ma. This alkaline volcanism isto the general anorogenic tectonic regimeh the whole AA was subjected at this time.

ozoic geodynamic cycle started after theearly Cambrian evolution. It is charac-the injection of felsic dykes at 470 andch, 1988), followed by hydrothermal activ-

and 300 Ma. At least part of the Au mine-n the Iourirn deposit (Western AA) hastly attributed to a late Variscan event at(Gasquet et al., 2004).

thickness of approximately 13 km of Cryo-alozoic rocks were produced and accretednorthern border of the WAC during Pan-es.

ion tectonics at thenCambrian boundary

matic rocks present a progressive transitionnic magmatic suites, episodically emplacedperiod 690605 Ma, to high-K calc-alkalined volcanic rocks, formed during the perioda, and then, 20 Ma later, to alkaline volcan-volution clearly suggests a change from anan anorogenic tectonic regime. Sedimen-d structural evidence also indicates such aith the development of molasse basins con-

xtensional tectonics (Benziane et al., 1983;al., 1999; Fekkak et al., 1999; Soulamani; Soulaimani and Pique, 2004); the impor-rmal faulting in the localisation of precioussits, particularly in the epithermal AgHgd-class mine (Ouguir et al., 1994; Cheilletz); the formation of Sedex-type early Cam-bZn deposits (Viland, 1988; Benssaou and


Hamoumi, 1999). On the whole, the Ediacaran periodin the AA strongly reflects a tectonic inversion froma compressivetranstensive regime to an extensionalregime thaPan-Africaactive marggin of the Wtransition isuccessiveticularly trufaults in thSouth AtlaLiegeois, 2

6.4. Geodyactivity in t

It is notecesses of ththe large-scthis area atary. Stagesclearly corrduring theterised in theralisations690605 Mcollision, wening. Theobduction,ity, calc-alkand collageto the nortTerranes (Aduring thiscise geochrbe attributeinvolved thcoupled wment of mran cratonithere was ametallogenImiter gianLevresse eparte lowervolume ofcophile ele

The post-collisional features, related extensive high-Kcalc-alkaline magmatism and marine basin develop-ment, together indicate a high heat flow contribution

r due tllingmic elopmein thesits (e.l transextenseepes). Thir crus

nifical foras Imtel and

iter sanalo

onclu

e evoised bion-ex, the cever, w

e Pans (Avfor exhy, 20mainan maled bynd genn is mssionhism.rked

enic cisatioic act4 atcterissits (Imoccurrt is characteristic of the final stage of then orogeny, resulting in a change from anin to a passive margin at the northern mar-AC. The precise structural pattern of this

s not yet fully understood, mainly due toVariscan and Alpine overprints. This is par-e for the kinematic interpretation of majore AA, for example the Central AA or thes faults (Saquaque et al., 1992; Ennih and001; Oudra et al., 2003).

namic reconstruction and metallogeniche Pan-African AA (Fig. 10)

worthy that the geodynamic stages and pro-e AA Pan-African belt (Fig. 10) controlledale metallogenic activity that took place inthe PrecambrianLower Palozoic bound-1 and 2 are not developed here as they do notespond to a major metallogenic event exceptocean opening stage 1, which is charac-e Bleida inlier by base metal and gold min-(Mouttaqi, 1997; Belkabir et al., 2004). Thea stage 3 corresponds to an arccontinentith a moderate collision and crustal thick-main tectonic events were ocean floor

development of a regional NESW schistos-aline to high-K calc-alkaline magmatism,of meta-sedimentary and -magmatic rocks

hern border of the WAC to form the AAAT). A typical active margin developedstage 3. However, due to a lack of pre-

onological data no specific ore deposit cand to this event. The 605530 Ma stage 4e transition to a passive continental margin,ith extensional tectonics and the develop-arine basins to the North and the Saha-c basin to the South. During this period,long association between magmatism and

ic activity (e.g. felsic volcanism and thet AgHg deposit, Cheilletz et al., 2002;

t al., 2004). They have mantellic and procontinental crust signatures. Thus, a large

juvenile material, precious metals and chal-ments was added to the continental crust.

eitheupwedynadevetionsdepometa(e.g.the d2004loweis sigmodesuch(Leisthe Imbrian

7. C

ThactercollisHereHowof thchainetc.,MurpthreeAfricrevea

ing aorogesucce

morpis maallogorganlogenstagecharadepotypeo continental underplating and/or to mantle(Kearey and Vine, 1992). This type of geo-nvironment is particularly suitable for thent of superficial hydrothermal mineralisa-form of epithermal or base metal porphyryg. Cheilletz et al., 2002). Furthermore, hugefers suggest the existence of vertical drainsional fault zones) that were able to mobiliset parts of the lithosphere (Levresse et al.,s model, which involves a large part of thet and mantle (Kay and Mpodozis, 2001),ntly different to the earlier re-mobilisationthe origin of giant precious metal deposits,iter, from local superficial convective cellsQadrouci, 1991; Barodi et al., 1998). Thus,ilver deposit can be regarded as a Precam-gue to modern epithermal deposits.

sion: the northern margin of the WAC

lution of the Pan-African AA belt is char-y the successive development of extension-tension events, as in all modern orogens.

ollision event is subdivided into two stages.hen comparing the geodynamic evolution

-African AA belt with other Pan-Africanalonia, South-America, Carolina, Hoggar,ample: Murphy and Nance, 1989, 2002;02; Abdesalam et al., 2002; Neves, 2003),differences can be noted: (i) The AA Pan-in collisional stage (stage 3) is moderate, asthe absence of large-scale crustal thicken-

eralised thrusting. (ii) The AA Pan-Africanostly composed of a shallow-crust terranethat has been subject to low-grade meta-(iii) The end of the Pan-African evolutionby strong extensional tectonics. The met-onsequences of this specific orogenic beltn are highlighted. The most intense metal-ivity occurred during the late extensionalthe PrecambrianCambrian boundary. It ised by world-class precious metal epithermal

iter) and base metal porphyry- and Sedex-ences (Bou Madine; western AA early Cam-


brian mineralisations). It is noteworthy that orogenicgold mineralisations are lacking in the Pan-African AAbelt. This might be related to the moderate crustal thick-ening that tpermit the iand related

The tectined on thby Villeneutimes the wsubject toconsequenteastern mathe westernTherefore,(Rogers etson and Dis in a posifaults withdirection (L1994; Cabycan be conPan-AfricaEnnih andthis type othe Imiter fextensionaregime (Oumatic charaAA fault, Swithin thisattempt to rPan-Africaunderlie th

Acknowled

This stuation grantMinistry o0002). Weand M. Chties, C. Spaanalyses ana careful rethank the twtive criticis

numerous improvements in the quality and the clarityof the English text.

rence

alam, Metacrato

E.H.,neralisalOugn

ronologE.H., Ne polymgnat, eion of a, 2512u, H.,nafricaipublisha, M.,

rtementaghro orsity ofalek, HPb dalay (M(Maro

267.alek, Hochronnafricairdous ead. Sciaadi, 1leovolcne`se deBou M

hed Thesari, Ael Sagulfures

age pror, J.EmezaniCloudiundarySamir,lcanismntral (MlAfriq

A.,oprotergeodyntic evo

ogenic Irschunsook place during this orogeny, which did notnstallation of large-scale hydrothermal cellsgold re-mobilisations.onic evolution of the AA belt can be exam-e scale of the WAC. As clearly reportedve and Cornee (1994), during Pan-Africanestern and eastern margins of the WAC werecompletely different tectonic regimes andly exhibited very different behaviours Thergin was subject to a compressive regime;margin was subject to an extensive regime.within the West African super continent

al., 1995; Dalziel, 1997; Unrug, 1997; Sam-Lemos, 1999; Hefferan et al., 2000), the AAtion where the main faults acted as wrenchrespect to the main Pan-African shorteningapique et al., 1986; Liegeois et al., 1987,et al., 1989; Caby, 2003). Thus, the AA belt

sidered to have been a transfer zone duringn times (similar to the transpression belt ofLiegeois, 2001). The abundant evidence forf structural behaviour in this area includesault, which evolved from a pure NNWSSEl regime to a NWSE sinistral transtensionalguir et al., 1994; Levresse, 2001). The kine-cteristics of the other major faults (CentralAF, NAF) have not yet been well defined

late Pan-African framework. Therefore, anyeconstruct the plate tectonic geometry of then terranes, and the probable WAC limits thatem, would be highly hypothetical.

gements

dy was supported by two scientific cooper-s awarded to A.C. and D.G. by the Frenchf Industry (# 98 2 24 00 30 and # 00 224would like to thank E. Deloule, D. Manginampenois for the Cameca IMS1270 facili-tz and L. Reisberg for the SmNd and RbSrd J.M. Bertrand for fruitful discussions andview of early versions of the paper. We alsoo anonymous reviewers for their construc-

m. The comments of P. Henderson led to

Refe

AbdesM

Abia,midech

Abia,ThOulut36

AdmopaUn

At Ishfo(Sve

At MU-Vetalp.

At MGepaKeAc

At Spagedelis

Al An(Jba` s

dAmtho

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Azizivo

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Fos

.G., Liegeois, J-P., Stern, R.J., 2002. The Saharann. J. Afr. Earth Sci. 34, 119136.Nachit, H., Ibhi, H., Baroudi, Z., 1999. Lestions filoniennes a` Pb, Zn et Cu de la boutonnie`reat. relations avec les deformations et essai de calageique. Chron. Rech. min. 536/537, 137149.achit, H., Marignac, C., Ibhi, A., At Saadi, S., 2003.etallic AuAg-bearing veins of Bou Madine (Jbel

astern Anti-Atlas, Morocco): tectonic control and evo-Neoproterozoic epithermal deposit. J. Afr. Earth Sci.

71.2000. Structuration de la paleosuture ophiolitiquene de Bou Azzer-Siroua (Anti-Atlas central, Maroc).ed Thesis. University of Marrakech, p. 201.1996. Petrogene`se dun magmatisme moyennement a`potassique. Lexemple du massif panafricain dIkniounriental, Anti-Atlas Maroc). Unpublished Thesis. Uni-Marrakech, p. 243.., 1997. Petrologie geochimie et geochronologie

ssociations acide-basiques: exemples du massif duassif Central francais) et de lAnti-Atlas occiden-c). Unpublished Thesis. University of INPL, Nancy,

., Gasquet, D., Bertrand, J.M., Leterrier, J., 1998.ologie U/Pb sur zircon de granitodes eburneens etns dans les boutonnie`res proterozoques dIgherm, dut du Bas Draa (Anti-Atlas occidental, Maroc). C.R.

. Paris 327, 819826.992. Contribution a` letude de lenvironnement

anique du Proterozoque Superieur (PIII) et du mode des concentrations polymetalliques (Zn, Pb, Cu, Ag, Au)adine (Ougnat, Anti-Atlas oriental, Maroc). Unpub-sis. University of INPL, Nancy, p. 218.., Sagon, J.P., 1997. Le gisement dor de Tiouit

hro, Anti-Atlas) un syste`me mesothermal polyphase- or et hematite- or dans une granodiorite potassiqueterozoque superieur. Chron. Recher. Min. 527, 325.., Grotzinger, J.P., Schroder, S., Bowring, S.A.,, J., Martin Mark, W., Matter, A., 2003. Extinctionna and Namacalathus at the PrecambrianCambrianin Oman. Geology 31, 431434.M.R., Ferrandini, J., Tane, J.L., 1990. Tectonique ete tardi-Pan Africains (580560 Ma) dans lAnti-Atlasaroc): interpretation geodynamique a` lechelle du NW

ue. J. Afr. Earth Sci. 10, 549563.2001. Volcanisme syn a` post orogenique duozoque de lAnti-Atlas: implications petrogenetiquesamiques. In: De Wall, H., Greiling, R.P. (Eds.), Mag-lution of a Neoproterozoic Island-Arc Syn- to Post-gneous Activity in the Anti-Atlas (Morocco), vol. 45.zentrum Julich Gmbh, pp. 9228.


Baouch, S., 1984. Etude des ignimbrites et des roches associees dumassif de Tichrt (Haut-Atlas, Maroc). Contribution a` letude duvolcanisme-plutonisme du PIII. Unpublished Thesis, Univer-sity of Na

Barbey, P., Naing differgranitic pmagma em

Barbey, P., O2004. Thea clarifica

Barodi, E.B.,tife`res au531/532, 7

Barra, F., Ruistudy ofnorthern A

Bassias, Y., Wevolutionsouthern Mtem of MoNotes Ear

Belfoul, M.Adune tecdans la chAfr. Earth

Belkabir, A.,roots of Pfide depoColloquiu

Ben Othman,cesses in gstudied by290300.

Benssaou, Mmineralisaprecoce. C

Benssaou, Mtal du Mpaleogeog351372.

Benziane, F.PrecambrlAnti-AtlBull. Soc.

Boher, M., A1992. Cru97, 3453

Bouougri, E.Land correlton passivInliers, CeAfr. Earth

Brabers, P.MOrogeny iThe Atlaslution, Le

Caby, R., 2003. Terrane assembly and geodynamic evolution ofcentralwestern Hoggar: a synthesis. J. Afr. Earth Sci. 37,133159.

R., Anozoic an-Afric36114ra, L.SneralogImiter. U, S., Bur04. Foldlt of Mone, A.,Khzam

ecambrrmant. Ut-Prat,evremo

., Mortauille Sid5 bis, Mger, J.,evremo

t, R., 1ochronoi, B., Bregistrentinentalcaire-garoc). Cetz, A.,r the Anarrakecetz, A.adi, R.,orocco

l data. Imjor prec, 7727J.H., P

stematicoup elemta 62, 3ert, G.,nti-Atlaert, G.,aurore, pp. 35h, W.Rlegre, Clts, vol. 1051r, N., 19une schPrecam

nti-Atlancy I, p. 131.chit, H., Pons, J., 2001. Magmahost interactions dur-

entiation and emplacement of a shallow-level, zonedluton (Tarcouate pluton, Morocco): implications forplacement. Lithos 58, 125143.

berli, F., Burg, J.P., Nachit, H., Pons, J., Meier, M.,Palaeoproterozoic in western Anti-Atlas (Morocco):

tion. J. Afr. Earth Sci. 39, 239245.Maacha, L., Zinbi, Y., 1998. Les mineralisations argen-Maroc: cas du gisement dImiter. Chron. Rech. Min.792.

z, J., Mathur, R., Titley, S., 2003. A rheniumosmiumsulfides from the Bagdad porphyry CuMo deposit,

rizona, USA. Miner. Deposita 38, 585596.allbrecher, E., Willgallia, A., 1988. Tectono-thermal

of the late Panafrican Orogeny in the central Anti-Atlas;orocco. In: Jacobshagen, V.H. (Ed.), The Atlas Sys-

rocco, Studies on its Geodynamic Evolution. Lectureth Sci., vol. 15, pp. 4360.., Faik, F., Hassenforder, B., 2001. Mise en evidencetonique tangentielle anterieure au plissement majeurane hercynienne de lAnti-Atlas occidental. Maroc. J.Sci. 32, 723739.Maacha, L., Madi, A., Jebrak, M., 2004. Gold-rich

roterozoic ophiolite-hosted volcanogenic massive sul-sit, Bleida, Anti-Atlas, Morocco. In: Abstract, 20thm of African Geology, Orleans, p. 71.D., Fourcade, S., Alle`gre, C.J., 1984. Recycling pro-ranite-granodiorite complex genesis: the Querigut caseNdSr isotopic systematics. Earth Planet. Sci. Lett. 69,

., Hamoumi, N., 1999. Paleoenvironnements ettions de lAnti-Atlas occidental marocain au Cambrienhron. Rech. Min. 536/537, 113120.., Hamoumi, N., 2001. LAnti-Atlas occiden-aroc: etude sedimentologique et reconstitutions

raphiques du Cambrien inferieur. J. Afr. Earth Sci. 3,

, Prost, A.E., Yazidi, A., 1983. Le passage duien au Cambrien precoce volcanique et sedimentaire deas oriental; comparaisons avec lAnti-Atlas occidental.Geol. France 4, 549556.

bouchami, W., Michard, A., Albare`de, F., Arndt, N.,stal growth in West Africa at 2.1 Ga. J. Geophys. Res.69.., Saquaque, A., 2004. Lithostratigraphic framework

ation of the Neoproterozoic northern West African Cra-e margin sequence (SirouaZenagaBouazzer Elgraarantral Anti-Atlas, Morocco): an integrated approach. J.Sci. 39, 227238.

., 1988. A plate tectonic model for the Pan-Africann the Anti-Atlas, Morocco. In: Jacobshagen, V.H. (Ed.),System of Morocco, Studies on its geodynamic Evo-

cture Notes Earth Sci., vol. 15, pp. 6180.

Caby,terPa11

Camamid

Caritg20be

ChabadePrfo

ChaloChMFe41RoCh

Charloge

Chbanen

co

ca

MCheill

foM

CheillZy(Mca

ma

37Chen,

sygrAc

Choub(A

Chouba` l62

ChurcAlBepp

Clauedau

(Adreopoulous-Renaud, U., Pin, C., 1989. Late Pro-rccontinent and continentcontinent collision in thean Trans-Saharan belt of Mali. Can. J. Earth Sci. 26,6.., 1993. Etude cartographique, petrographique,ique et geochimique des granitodes du district miniernpublished Thesis. University of Marrakech, p. 143.

khard, M., Ducommun, R., Helg, U., Kopp, L., Sue, C.,interference patterns in the Late Palozoic Anti-Atlasrocco. Terra Nova 16 (1), 2737.1991. Les roches vertes du Proterozoique superieura (Siroua, Anti-Atlas central, Maroc), un exemple

ien dophiolite davant arc formee en contexte trans-npublished Thesis. University of Marrakech, p. 570.F., Gasquet, D., Roger, J., Hassenforder, B.,nt, P., Baudin, T., Razin, P., Benlakhdim, A., Benssaou,ji, A., Memoire explicatif, carte geol. Maroc (1/50000),i Bouaddi, Notes et Memoires Serv. Geol. Maroc, No.ICEM/BRGM. Geological map by Hassenforder, B.,

Baudin, T., Chalot-Prat, F., Gasquet, D., Berrhama, M.,nt, P., Marquer, D., Razin, P., Benlakhdim, A.976. The Precambrian of the Anti-Atlas (Morocco); alogical synthesis. Precamb. Res. 3, 273299.eauchamp, J., Algouti, A., Zouhair, A., 1999. Un

ment sedimentaire eocambrien dans un basin intra-l en distension: le cycle conglomerats de base-uniteres de Tikirt de Bou Azzer EL Graara (Anti-Atlas,.R. Acad. Sci. Paris 329, 317323.Gasquet, D., 2001. Specific plate tectonic environmentsti-Atlas ore deposits. In: Abstract, 3MA Colloquium,

h, Morocco, p. 84., Levresse, G., Gasquet, D., Azizi Samir, M.R.,Archibald, D.A., 2002. The Imiter epithermal deposit

): new petrographic, microtectonic and geochronologi-portance of the PrecambrianCambrian transition for

ious metals deposits in the Anti-Atlas. Miner. Deposita81.apanastassiou, D.A., Wasserburg, G.J., 1998. Re/Oss in chondrites and the fractionation of the platinuments in the early solar system. Geochim. Cosmochim.

379.1952. Le volcan georgien de la region dAlougoums). C.R. Acad. Sc., Paris 234 (3), 350352.1963. Histoire geologique de lAnti-Atlas de larcheendes temps primaries. Notes Mem. Serv. geol. Maroc0352.., 1980. Late Proterozoic ophiolites. In: Aubouin, J.,.J. (Eds.), BasicUltrabasic Associations in Orogenic

. 272. Centre National Recherche Scientifique, Paris,18.74. Utilisation de la methode Rb-Sr pour la datation

istosite de sediments peu metamorphises: applicationsbrien II de la boutonnie`re de Bou AzzerEl Graaras, Maroc). Earth Planet. Sci. Lett. 22, 404412.


Clauer, N., 1976. Geochimie isotopique du strontium des milieuxsedimentaires: application a` la geochronologie de la couverturedu craton Ouest-Africain. Sci. Geol. (Strasbourg) 45, 256.

Compston, W1992. ZircSoc. Lond

Dallmeyer, Rand circum

Dalziel, I.W.Dtectonics:Bull. Geo

De Wall, H., KAge and cof Imiter (rakech, M

Deloule, E., A2002. In-sin the eastJ. Earth S

Du Dresnay, RAnane (HMaroc, N

Ducrot, J., 19et conseqmetamorpmarocain.

Ducrot, J.,PrecambrUPb surEarth Sci.

Eddif, A., 200des intrusverture neUnpublish

Eddif, A., GintrusionsmagmatisSci. 31, 48

El Aouli, E.Hbasique dMaroc): udure nord309317.

El Boukhari, Aisme de latemoin demarge NE(Serie II),

En-Naciri, A.from the CMorocco.

Ennih, N., LieAfrican crimplicatio112, 289

Ennih, N., LieAfrican cr

Implications for the northern limit of the craton: reply to com-ments by E. H. Bouougri Precambr. Res. 120, 185189.

Esser, B., Turekian, K., 1993. The Osmium isotopic composi-n of th93310en, N.Mundancta 42, 1G., 200ringer,k, A.,, El Ams depotlaat Mg, 2953k, A., Pozoic Sion in arth Sci.k, A., Pet, D.,lcanitestal, Mar., NaglNd, Ushear-ze constrchim. A, R., 19Bou M

concentesis. UB.R., B

ost, C.DPetrol. 4et, D., Ccherie,lycycliciers (W7275.et, D.,Chevr

nssaou/50000)aroc, NoGasqu

arquer,zin, P.,tein, F.,04. A nmbriannforder,nti-Atl

-Sciencan, K.,nal bas

orocco.., Williams, I.S., Kirschvink, J.L., Zhang, Z., Ma, G.,on U/Pb ages for the early Cambrian timescale. J. Geol.on 149, 171184..D., Lecorche, J.P., 1991. The West African orogens

-Atlantic correlatives. Sringer Verlag, 405 p.., 1997. NeoproterozoicPalozoic geography andreview, hypothesis and environmental speculation.

l. Soc. Am. 109, 1642.ober, B., Errami, E., Greiling, R.O., Ennih, N., 2001.

rustal setting of the granitoid emplacement in the areaeastern Saghro). In: Abstract, 3MA Colloquium, Mar-orocco, p. 48.lexandrov, P., Cheilletz, A., Laumonier, B., Barbey, P.,itu UPb zircon ages for early Ordovician magmatismern Pyrenees, France: the Canigou orthogneisses. Int.ci. 91, 398405.., 1976. Carte geologique du haut Atlas dAnoualBouaut Atlas oriental) au 1/200 000. Edit. Serv. Geol

otes et Memoires 246.79. Datation a` 615 Ma de la granodiorite de Bleidauences sur la chronologie des phases tectoniques,hiques et magmatiques panafricaines dans lAnti-AtlasBull. Soc. Geol. France XXI (4), 495499.Lancelot, J.R., 1977. Proble`me de la limite

ienCambrien: etude radiochronologique par methodezircon du Jbel Bobo (Anti-Atlas marocain). Can. J.14, 27712777.2. Geochronologie, petrologie, geochimie et structureions tardi-panafricaines de Wirgane et de leur cou-oproterozoque a` paleozoque (Haut-Atlas occidental).ed Thesis. University of Rabat, p. 194.

asquet, D., Hoepffner, C., At Ayad, N., 2000. Lesde Wirgane (Haut Atlas occidental): temoins dun

me hercynien syn a` tardi-cinematique? J. Afr. Earth3498.., Gasquet, D., Ikenne, M., 2001. Le magmatisme

e la boutonnie`re dIgherm (Anti-Atlas occidental,n jalon des distensions neoproterozoques sur la bor-du craton ouest africain. Bull. Soc. Geol. France 3,

., Chabane, A., Rocci, G., Tane, J.L., 1991. Le volcan-region de NKob (SE du Siroua, Anti-Atlas Marocain)lexistence dun rift au Proterozoque superieur, a` ladu Craton ouest africain. C.R. Acad. Sci. Paris 312

735738., Barbanson, L., Touray, J.C., 1997. Brine inclusionsoAs(Au) Bou Azzer district, Anti-Atlas mountains,

Econ. Geol. 92, 360367.geois, J.P., 2001. The Moroccan Anti-Atlas: the Westaton passive margin with limited Pan-African activity.ns for the northern limit of the craton. Precamb. Res.302.geois, J.P., 2003. The Moroccan Anti-Atlas: the Westaton passive margin with limited Pan-African activity.

tio30

EvensabAc

Faure,Sp

FekkaA.deKe30

FekkatersitEa

Fekkaquvo

en

Frei, RSminagmo

FretondeetTh

Frost,FrJ.

GasquCoPoinl26

GasquT.,Be(1MJ.,MRa

Grads20ca

HasselAe`s

HeffersioMe continental crust. Geochim. Cosmochim. Acta 57,4.., Hamilton, P.J., ONions, R.K., 1978. Rare earth

es in chondritic meteorites. Geochim. Cosmochim.1991212.1. Origin of igneous rocks. In: The Isotopic Evidence.

Berlin, p. 494.Boualoul, M., Badra, L., Amenzou, M., Saquaque,

rani, I.E., 1999. Origine et contexte geotectoniques detritiques du Groupe neoproterozoique inferieur deouna (Anti-Atlas oriental, Maroc). J. Afr. Earth Sci.

11.ouclet, A., Benharref, M., 2003. The Middle Neopro-idi Flah Group (Anti-Atlas, Morocco): synrift depo-Pan-African continent/ocean transition zone. J. Afr.

37, 7387.ouclet, A., Ouguir, H., Ouazzani, H., Badra, L., Gas-2001. Geochimie et signification geotectonique desdu Cryogenien inferieur du Saghro (Anti-Atlas ori-

oc). Geodinam. Acta 14 (6), 373385.er, Th.F., Schonberg, R., Kramers, J.D., 1998. ReOs,Pb and stepwise Pb leaching isotope systematics

one hosted gold mineralization; genetic tracing andaints of crustal hydrothermal activity. Geochim. Cos-cta 62, 19251936.

88. Contribution a` letude metallogenique du districtadine (Anti-Atlas, Maroc): environnement tectoniquerations epithermales B.P.G.C. a` Ag et Au. Unpublishedniversity of INPL, Nancy, p. 246.arnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J.,., 2001. A geochemical classification for granitic rocks.2, 20332048.he`vremont, P., Baudin, T., Chalot-Prat, F., Guerrot, C.,A., Roger, J., Hassenforder, B., Cheilletz, A., 2004.magmatism in the Tagragra and Kerdous-Tafeltast

estern Anti-Atlas, Morocco). J. Afr. Earth Sci. 39,

Roger, J., Chalot-Prat, F., Hassenforder, B., Baudin,emont, P., Razin, P., Benlakhdim, A., Mortaji, A.,, M., 2001. Memoire explicatif, carte geol. Maroc, Feuille Tamazrar, Notes et Memoires Serv. Geol.. 415 bis, MICEM/BRGM. Geological map by Roger,

et, D., Baudin, T., Chalot-Prat, F., Hassenforder, B.,D., Chevremont, P., Berrhama, M., Destombes, J.,Benlakhdim, A.Ogg, J.G., Smith, A.G., Bleeker, W., Lourens, L.J.,

ew geologic time scale, with special reference to Pre-and Neogene. Episodes 27 (2), 83100.B., 1987. La tectonique panafricaine et varisque de

as dans le massif du Kerdous, Maroc. The`se Doctorates. Universite Louis Pasteur, Strasbourg, p. 249.Karson, J.A., Saquaque, A., 1992. Proterozoic colli-

ins in a Pan-African suture zone, Anti-Atlas Mountains,Precamb. Res. 54, 295319.


Hefferan, K.P., Admou, H., Hilal, R., Karson, J.A., Saquaque, A.,Juteau, T., Bohn, M., Samson, S.D., Kornprobst, J., 2002. Pro-terozoic blueschist-bearing melange in theAnti-Atlas Mountains,Morocco.

Hefferan, K.PAtlas (Mreconstruc

Helg, U., Burkand invers23, TC400

Houari, M.Rwrench-doton margin1124.

Huch, K.M.,tralen Antgie des STachoukadosten depp.

Ighid, L., Saqet la defo(BoutonniIIa 309, 6

Ikenne, M.,(Anti-Atlageochimiqrelations aAgadir, p.

Inglis, J.D., MH., Heffergranodiorof deformAfr. Earth

Juery, A., 197(Maroc). U

Karl, A., de WB., GreilinBou TegliSaghro (A(Eds.), MaTo Post-oForschuns

Kay, S.M., Mto evolvinGSA Toda

Kearey, P., ViPublicatio

Landing, E.,G., Heldmages of voSci. 35, 32

Lapique, F., Bcrustal decAlageria).

Le Maitre, R.Bas, M.J.,

A., Wooley, A.R., Zanettin, B., 1989. Classification of IgneousRocks and Glossary of Terms. Blackwell, Oxford.

Leblanc, M., 1975. Ophiolites precambriennes dans le PII de lAnti-las cent, p. 329c, M.,

balt (Bo306.c, M.,domai

nnees g, 1421c, M.,

nic evomb. Resn, J.,ion dI

prife`resd Orsayl, J.M.,roterozos minerxploratsse, G.,netiquebZnClas mar191.sse, L.,arty, B.,ults froposit, M7, 597is, J.P.,

llision-rs Iforasis, J.P.,

n-Africield, Niig, K.Rochronn), vol.a, L.,

baltife`rnditionsitz, M.zanov,: carb

n time0.i, F., Odistensutonnie`R. Acadr, R., Rr tonnatope raPrecamb. Res. 118, 179194.., Admou, H., Karson, J.A., Saquaque, A., 2000. Anti-orocco) role in Neoproterozoic Western Gondwanation. Precamb. Res. 103, 8996.hard, M., Caritg, S., Robert-Charrue, C., 2004. Foldingion tectonics in the Anti-Atlas of Morocco. Tectonics6, doi: 10.1029/2003T001576.

., Hoepffner, C., 2003. Late Carboniferous dextralminated transpression along the North African cra-(Esatern High-Atlas, Morocco). J. Afr. Earth Sci. 37,

1988. Die panafrikanische Khzama-Geosutur im zen-i-Atlas. Petrpographie, Geochemie und Geochronolo-ubduktionskomplexes der Tourtit-Ophiolithe und dercht-Gneise sowie einiger Kollisionsgesteine im Nor-s Sirwa-Kristallindoms. Verlag Schelzky & Jeep, 172

uaque, A., Reuber, I., 1989. Plutons syncinematiquesrmation panafricaine majeure dans le Saghro orientale`re dImiter, Anti-Atlas, Maroc). C.R. Acad. Sci., Paris15620.1997. La boutonnie`re precambrienne du bas Draas occidental, Maroc): caracterisation petrologique etue des roches magmatiques et metamorphiques et leursvec la deformation. Unpublished Thesis. University of259.acLean, J.S., Samson, S.D., DLemos, R.S., Admou,

an, K., 2004. A precise U-Pb zircon age for the Bleidaite, Anti-Atlas, Morocco: implications for the timingation and terrane assembly in the eastern Anti-Atlas. J.Sci. 39, 277283.6. Datation UPb du socle precambrien du Haut-Atlasnpublished Thesis. University of Paris, p. 85.all, H., Rieger, M., Schmitt, T., Errami, E., Kober,

g, R.O., 2001. Petrography and geochemistry of themt, Taouzzakt and Igoudrane intrusions in the Easternnti-Atlas, Morocco). In: De Wall, H., Greilling, R.P.gmatic evolution of a Neoproterozoic Island-Arc Syn-

rogenic Igneous Activity in the Anti-Atlas (Morocco)zentrum Julich Gmbh, vol. 45, pp. 243254.podozis, C., 2001. Central Andean ore deposits linkedg shallow subduction systems and thickening crust.y 11 (3), 49.ne, F.J., 1992. Global Tectonics. Blackwell Scientificns, Oxford, p. 302.Bowring, S.A., Davidek, K.L., Westrop, S.R., Geyer,aier, W., 1998. Duration of the Early Cambrian: UPblcanic ashes from Avalon and Gondwana. Can. J. Earth9338.ertrand, J.M., Meriem, D., 1986. A major Pan-Africanoupling zone in the Timgaouine area (Western Hoggar,J. Afr. Earth Sci. 5, 617625.

W., Bateman, P., Dudek, A., Keller, J., Lameyre, J., LeSabine, P.A., Schmid, R., Sorensen, H., Streckeisen,

AtVI

Leblanco

p.Leblan

dudo17

Leblanca

ca

Lebruregcu

SuLeiste

(pdele

Levrege(PAtp.

LevreMres

de20

Liegeoco

deLiegeo

PaSh

LudwGetio

Maachco

co

MagarRolemtia85

MarinlaboC.

Mathupeisoral (Maroc). Unpublished Thesis. University of Paris.1981. Ophiolites precambriennes et gtes arsenies deu-Azzer, Maroc). Notes Mem. Serv. Geol. Maroc 280,

Lancelot, J., 1980. Interpretation geodynamiquene panafricain de lAnti-Atlas (Maroc) a` partir deeologiques et geochronologiques. Can. J. Earth Sci.55.Moussine-Pouchkine, A., 1994. Sedimentary and vol-lution of a Neoproterozoic continental margin. Pre-. 70, 2544.1982. Etude du volcanisme precambrien de lassougrid (Ouarzazarte, Maroc) et des mineralisationsassociees. Unpublished Thesis. University of Paris-, p. 376.Qadrouci, A., 1991. Le gisement argentife`re dImiterque superieur de lAnti-Atlas, Maroc). Controlesalisations, hypothe`se genetique et perspectives pourion. Chron. Rech. Min. 502, 522.

2001. Contribution a` letablissement dun mode`ledes gisements dImiter (AgHg) Bou Madine

uAu) et Bou Azzer (CoNiAsAuAg) dans lAnti-ocain. Unpublished Thesis. University of INPL, Nancy,

Cheilletz, A., Gasquet, D., Reisberg, L., Deloule, E.,Kyser, K., 2004. Osmium, sulphur, and helium isotopicm the giant Neoproterozoic epithermal Imiter silverorocco: evidence for a mantle source. Chem. Geol.

9.Bertrand, J.M., Black, R., 1987. The subduction- andelated Pan-African composite batholith of the Adrar(Mali): a review. Geol. J. 22, 185211.Black, R., Navez, J., Latouche, L., 1994. Early and latean orogenies in the Air assembly of terranes (Tuaregger). Precamb. Res. 67, 5988.., 2003. Users Manual for Isoplot/Ex Version 3.00: aological Toolkit for Microsoft Excel (Special Publica-4. Geochronology Center, Berkeley, pp. 171.Azizi-Samir, M.R., Bouchta, R., 1998. Gisements

es du district de Bou Azzer (Anti-Atlas): structure etde gene`se. Chron. Rech. Min. 531/532, 6575.

, Kirschvink, J.L., Latham, A.J., Zhuravlev, A.Y.,A.Y., 1991. Precambrian/Cambrian boundary prob-on isotope correlations for Vendian and Tommo-between Siberia and Morocco. Geology 19, 847

uguir, H., 1990. Un nouveau jalon dans lhistoire deion pre-panafricaine au Maroc: le Precambrien II desres du Jbel Saghro nord-oriental (Anti-Atlas, Maroc).. Sci. Paris 310, 577582.

uiz, J., Munizaga, F., 2000a. Relationship between cop-ge of Chilean basemetal porphyry deposits and Ostios. Geology 28, 555.


Mathur, R., Ruiz, J., Herb, P., Hahn, L., Burgath, K.P., 2003. ReOsisotopes applied to the epithermal gold deposits near Bucara-manga, northeastern Colombia. J. South Am. Earth Sci. 15 (7),815821.

Mathur, R., RDifferentGrasberg714.

Michard, A., Gin Frenchcrustal evo

Mifdal, A., Pcanisme adans la rePrecambr

Mokhtari, A.,basique deavec les gNancy I, p

Mouttaqi, A.,avec le rifcuivre deversity of

Mrini, Z., 19(SrNdPpanafricaiUniversity

Murphy, J.B.,mentary Gevidencenian marg

Murphy, J.B.Avalonian

Murphy, J.B.tectonic trAppalach

Neves, S.P., 2(NE BrazAfrican bewana. Tec

Ord, A., Walsore deposito Process

Ouazzani, H.isme darc(Maroc), ude locean

Oudra, M.,Pan-AfricMorocco)NW bordMeeting op. 51.

Ouguir, H., 1dimiter (structuralAgHg. U

Ouguir, H., Macaudie`re, J., Dagallier, G., Qadrouci, A., Leistel,J.M., 1994. Cadre structural du gte AgHg dImiter (Anti-Atlas,Maroc): implications metallogeniques. Bull. Soc. Geol. France

5, 233r, H., MperieurodynamA., 199r evoluA., 200Latest

osci. 33ol, C.,ologie,s, J.J.Wndwann, R.Dic UP, Guern54.n, S.Dft, J., Htopic cosriwine: Abstracemberque, A.ecambrion. An

que, A.,1992.lt tectondsch.J.J., Yan-Cu detopic c83.mani, Arcynienaa (An1284.mani, Aestern Ame. J. Amani, AlAnti-

se de laperieur.as, R.J.,M., ArmS., MacSirwa

8, 157as, R.J.,

., 20001/50002, p. 84uiz, J., Titley, S., Gibbins, S., Margotomo, W., 2000b.crustal sources for Au-rich and Au-poor ores of theCuAu Porphyry Deposit. Earth Planet. Sci. Lett. 183,

urriet, P., Soudant, M., Albare`de, F., 1985. Nd isotopesPhanerozoic shales: external vs. internal aspects oflution. Geochim. Cosmochim. Acta 49, 601610.eucat, J.J., 1985. Datations U/Pb et Rb/Sr du vol-cide de lAnti-Atlas marocain et du socle sous-jacentgion de Ouarzazate. Apport au proble`me de la limiteienCambrien. Sci. Geol. Bull. 38, 185200.1993. Nouvelles donnees et interpretations du massifTagmout (Jbel Saghro, Anti-Atlas, Maroc): relations

ranitodes associes. Unpublished Thesis. University of. 251.1997. Hydrothermalisme et mineralisations en relationting proterozoque superieur: exemple du gisement deBleida (Anti-Atlas), Maroc. Unpublished Thesis. Uni-Marrakech, Maroc, p. 310.93. Chronologie (RbSr, UPb), tracage isotopiqueb) des sources des roches magmatiques eburneennes,nes et hercyniennes du Maroc. Unpublished Thesis.of Marrakech, Marocm p. 227.2002. Geochemistry of the Neoproterozoic metasedi-amble Brook Formation, Avalon Terrane, Nova Scotia:

for a rifted-arc environment along the West Gondwa-in of Rodinia. J. Geol. 110, 407419., Nance, R.D., 1989. Model for the evolution of theCadomian belt. Geology 17, 737738., Nance, R.D., 2002. SmNd isotopic systematics asacers: an example from West Avalonia in the Canadianians. Earth Sci. Rev. 59, 77100.003. Proterozoic history of the Borborema provinceil): correlations with neighboring cratons and Pan-lts and implications for the evolution of western Gond-tonics 22 (4), 1031.he, J.L., Hobbs, B.E., 1999. Geodynamics and giantts. In: Stanley, et al. (Ed.), Mineral Deposits: Processesing. Balkema, Rotterdam, pp. 13411344., Pouclet, A., Badra, L., Prost, A., 2001. Le volcan-

du massif ancien de lOuest du Haut-Atlas occidentaln temoin de la convergence de la branche occidentalepanafricain. Bull. Soc. Geol. France 172, 587602.

Gasquet, D., Hassenforder, B., Ikenne, M., 2003.an tectonics in the Igherm area (western Anti-Atlas,: consequences on the Neoproterozoic evolution of theer of the Wesrtern African craton. In: Abstract, Firstf IGCP 485-El Jadida, Morocco, December 12, 2003,

997. Contexte geologique du gisement argentife`reAnti-Atlas oriental, Maroc). Controle volcanique etde la mise en place des concentrations metalliques a`npublished Thesis. University of Mekne`s, p. 215.

16Ougui

su

gePique,

leuPique,

theGe

PomerGe

RogerGo

Samsozo

ite47

SamsoToisoTaInDe

SaquaPrreg

SaquaJ.,fauRu

Shen,Auiso71

SoulaheDr27

SoulaiWdo

Souladebasu

ThomB.G.the11

ThomP.Gau

39248.acaudie`re, J., Dagallier, G., 1996. Le proterozoquedImiter, Saghro oriental, Maroc: un contexte

ique darrie`re-arc. J. Afr. Earth Sci. 22, 173189.4. Geologie du Maroc. In: Les domaines regionaux ettion structurale. PUMAG, Rabat, p. 284.3. Evidence for an important extensional event duringProterozoic and Earliest Palaeozoic in Morocco. C.R.5, 865868.Lagabrielle, Y., Renard, M., 2005. Elements de

13th ed. Dunod, Paris, p. 629.., Unrug, R., Sultan, M., 1995. Tectonic assembly ofa. J. Geodyn. 19, 134.., DLemos, R.S., 1999. A precise Late Neoprotero-b zircon age for the syntectonic Perelle quartz dior-sey, Channel Islands, UK. J. Geol. Soc. London 156,

., Inglis, J.D., DLemos, R.S., Admou, H., Blichert-efferan, K., 2003. UPb age, geochemistry, and NdHfmposition of Neoproterozoic plagiogranites within theOphiolite, Siroua inlier, Anti-Atlas orogen, Morocco.ct, First Meeting of IGCP 485-El Jadida, Morocco,12, 2003, pp. 6468.

, Admou, H., Karson, J., Hefferan, K., Reuber, I., 1989.ian accretionary tectonics in the Bou AzzerEl Graarati-Atlas, Morocco. Geology 17, 11071110.Benharref, M., Abia, H., Mrini, Z., Reuber, I., Karson,

Evidence for a Pan-African volcanic arc and wrenchnics in the Jbel Saghro, Anti-Atlas, Morocco. Geol.81, 113.g, H.J., 2004. Sources and genesis of the Chinkuashih

posits in northern Taiwan: constrains from Os and Srompositions of sulfides. Earth Planet. Sci. Lett. 222,

., Le Corre, Cl., Farazdaq, R., 1997. Deformationne et relation socle/couverture dans le domaine du Bas-ti-Atlas occidental, Maroc). J. Afr. Earth Sci. 24 (3),

., Pique, A., 2004. The Tasrirt structure (Kerdous inlier,nti-Atlas, Morocco): a late Pan-African transtensivefr. Earth Sci. 39, 247255.., Pique, A., Bouabdelli, M., 2001. La serie du PIIIII

Atlas occidental (Sud marocain): un olistostrome a` lacouverture post-panafricaine (PIII) du ProterozoqueC.R. Acad. Sci. Paris 332, 121127.Chevallier, L.P., Gresse, P.G., Harmer, R.E., Eglington,strong, R.A., de Beer, C.H., Martini, J.E.J., de Kock,

ey, P.H., Ingram, B.A., 2002. Precambrian evolution ofWindow, Anti-Atlas Orogen, Morocco. Precamb. Res..De Beer, C.H., Chevallier, L.P., De Kock, G.S., Gresse,. Notice Explicative de la Carte Geologique du Maroc

0 feuille Assarag. Notes et Memoires Serv. Geol. Maroc.


Thomas, R.J., Fekkak, A., Ennih, N., Errami, E., Loughlin, E.S.,Gresse, P.G., Chevallier, L.P., Liegeois, J.P., 2004. A new lithos-tratigraphic framework for the Anti-Atlas orogen, Morocco. J.Afr. Earth Sci. 39, 217226.

Unrug, R., 1997. Rodinia to Gondwana: the geodynamic map ofGondwana supercontinent assembly. GSA Today 7, 15.

Viland, J.C., 1988. Le cuivre et les metaux associes de lAnti-Atlasmarocain. Notes Mem. Serv. Geol. Maroc 334, 127213.

Villeneuve, M., Cornee, J.J., 1994. Structure, evolution andpaleogeography of the West African craton and borderingbelts during the Neoproterozoic. Precamb. Res. 69, 307326.

Walsh, G.J., Aleinikoff, J., Benziane, F., Yazidi, A., Amstrong, T.R.,2002. U-Pb zircon geochronology of the Paloproterozoic Tagra-gra de Tata inlier and its Neoproterozoic cover, western Anti-Atlas, Morocco. Precamb. Res. 117, 120.

Contribution to a geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the emphasis on inversion tectonics and metallogenic activity at the Precambrian-Cambrian transitionIntroductionGeological setting of the Anti-Atlas belt of MoroccoGeological setting of the Ougnat, Saghro and Bou Azzer inliersOugnat-Bou MadineSaghro-ImiterBou Azzer-Aghbar

U-Pb geochronology in the Ougnat, Saghro and Bou Azzer inliersAnalytical proceduresOugnat-Bou MadineSaghro-ImiterBou Azzer-Aghbar

Geochemistry of the Ediacaran and Cambrian magmatism in the AA areaMajor and trace elementsIsotope geochemistryRb-Sr, Sm-Nd, S and rare gasRe-Os

DiscussionSynthesis of the lithostratigraphic and geochronological data for the Pan-African AAPrecise timing of Pan-African events in the Anti-Atlas (Figs. 9 and 10)Inversion tectonics at the Precambrian-Cambrian boundaryGeodynamic reconstruction and metallogenic activity in the Pan-African AA (Fig. 10)

Conclusion: the northern margin of the WACAcknowledgementsReferences

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Gasquet Et Al 2005