West African Craton

ELSEVIER Precambrian Research 69 (1994) 307-326

Premmbriun Reseurth

Structure, evolution and palaeogeography of the West African craton and bordering belts during the Neoproterozoic

M. Vil leneuve a, J.J. Corn6e b

"Institut de G~odynamique, CNRS-UNSA, Sophia-Antipolis L 06560, Valbonne, France bCentre de SOdimentologie-Palkontologie, URA 1208 "Dynamique des platesformes carbonatbes", place Victor Hugo, 13331,

Marseille, Cedex 03, Case 67, France

Received October 28, 1992; revised version accepted January 27, 1994

Abstract

The West African craton consists of an Archaean or Palaeoproterozoic basement covered by sediments ranging from the Neoproterozoic to the present time. It is entirely surrounded by several Pan-African or Hercynian belts. The old basement is exposed in two shields, and the sedimentary units filled up three main basins: Tindouf, Taou- deni and Volta. The largest one, the Taoudeni basin, is located in the middle part of the West African craton. The Taoudeni basin is made of six different basins or troughs having a non-similar evolution. The structural and sedimentary evolution largely depends on the geodynamic evolution of the neighbouring belts. We have the intention to connect the sedimentary environments and the tectonics events that occurred around the craton. Five main tectonic events have been distinguished: the BI Anti-Atlas event on the northern margin (~ 685 Ma), the Pan- African I tectonic event on the western side ( ~ 660 Ma), the Eastern Pan-African tectonic event ( ~ 600 Ma) from Morocco to Brazil, the Pan-African II tectonic event which occurred on the southwestern pan at ~ 550 Ma and, finally, the Hercynian tectonic event (~ 300 ma) on the northwestern margin. Lithostratigraphic correlations between the differents basins take into account this tectonic diachronism. Thus, we distinguished several oceanic, rift, glacial or molassic stages. For example, three glacial events have been recognized from 980 Ma to 500 Ma. Finally, we are proposing here four palaeogeological schemes illustrating four key periods of the Neoproterozoic evolution. This emphasizes the Pan-African structural inheritance.

1. Introduction

The West African craton was located on the northwestern margin of the Gondwanaland. By late Precambrian time it was bounded (Fig. 1 ) by the Brazilian craton (southward), by the Benin-Nigeria shield (southeastward) and by the Hoggar shield (eastward). During the Car- boniferous it was linked (northwestward) to the North American craton. This West African craton which widely outcrops (2500 × 1000 km),shows a "guitar" shape. Its basement (Ar-

© 1994 Elsevier Science B.V. All rights reserved SSD10301-9268 (94) 00029-Q

chaean and Birrimian) is considered as tectoni- cally stable since 1700 Ma. This basement, built up during both the Archaean and Palaeoproter- ozoic orogens (Birrimian orogen, ~ 2000 Ma), outcrops in the Ivory Coast (or Leo) shield (south) and in the Reguibat shield (north). A small part of the Ivory Coast shield is now located in Brazil (Sflo Luis shield).This basement is covered by three main sedimentary basins: the Tindouf basin (in the northern part), the Taou- deni basin (in the central part) and the Volta basin located in the southeastern part. The

308 M. Villeneuve, J.J. Cornde /Precambrian Research 69 (1994) 307-326

Taoudeni basin is filled with both Proterozoic and Palaeozoic sediments, while the Tindouf basin is mainly made of Palaeozoic sediments and the Volta basin is mainly made of Protero- zoic sediments. The West African craton is surrounded by both Pan-African and Hercynian belts. Pan-African belts (800-530 Ma) are running all around the craton except for the northwestern part, while the Hercynian belt is located on the northwestern part, from Morocco to Senegal. Large parts of these Pan-African and Hercynian belts are covered by Mesozoic basins particularly in the northwestern Brasil. The West African craton and adjacent belts were studied by many geologists. However, works were fo- cused either on belts or on basins. Consequently, the linkage between sedimentary environment and tectonic events is not yet satisfactory. The aim of this work is to underline some close relationships between the sedimentary stages in the basins (from Neoproterozoic to the early Pa- laeozoic times) and the tectonic stages in the bordering Pan-African belts. During this period (800-500 Ma) four major Pan-African tectonic events have been distinguished around the West African craton. They probably had a strong influence on the sedimentation in the internal West African craton basins.

l:-.~_~L J 4 f 5

2. Geological setting of the West African craton

2.1. Pan-African tectonics at the boundary of the craton

2.1.1. The western margin The Pan-African belts extend over 1700 km,

from the Reguibat shield to the southern part of the Ivory Coast shield (Fig. 1 ). A large part of these belts is concealed underneath the Palaeo- zoic or Meso-Cenozoic basins. On this western side, Sougy (1962) recognized two different belts: the Mauritanides in the north and the Rokelides in the south. Later on Villeneuve (1984) distinguished three different belts: the Mauritanides, the Bassarides and the Rokelides, from the north to the south. The Bassarides arose at ~660 Ma and the Rokelides at ~ 550 Ma

Fig. 1. The main structural features of the West African craton and surroundings belts. Encircled numbers: /=Mauri tanide belt; 2=Bassaride belt; 3=Rokelide belt; 4=the Anti-Atlas belt; 5=the Ougarta belt; 6=the Pharu- side belt; 7=the Dahomeyide belt; 8= the Borborema belt; 9=the Paraguay belt; 10= the Araguay-Tocatins belt; / l = the Gurupi belt. TfB=Tindoufbasin; Td.B=Taoudeni basin; CWA = West African craton; GS= Guyana shield; SIC:= S~o Francisco craton; SLC=S~o Luis craton; ICS=Ivory Coast shield. Legend. 1 = crystalline basement; 2= main Hercynian belts; 3 = Pan-African and Braziliano belts; 4 = foreland basins; 5 = thrust directions; 6 = thrusts, 7= basin boundaries.

(Villeneuve and DaUmeyer, 1987). The Mauri- tanides appeared at the same time as the Bassar- ides belt but they were largely reworked by the Hercynian orogen. Many papers point out the thrusting of this belts onto the West African craton. In the northern part (Mauritanides), the external nappes are thrusted over the Palaeozoic formations of the Taoudeni basin, while in

M. Villeneuve, J.J. Cornde / Precambrian Research 69 (1994) 307--326 309

Guinea, on the contrary, the Cambro-Ordovi- cian Bov6 basin rests upon both the Bassarides and Rokelides (Sougy, 1962; Bassot, 1966; Vil- leneuve, 1984). In Sierra Leone and Liberia, the internal nappes of the Rokelide belt are thrusted over the Cambrian Rokelide formations (Thor- man, 1976; Culver and Williams, 1979 ).

Taking into account these observations, the western belts are considered as polyphased by various authors. According to new structural data, Villeneuve (1984) distinguished three different tectonics events, namely: (a) the Panafri- can I tectonic event occuring in the Bassaride belt (Bassaride orogen); this belt is covered uncon- formably by the Cambrian shales of the Mali Group; (b) the Panafrican H tectonic event which deformed the shales of the Mali Group along the Rokelide trough (Rokelide orogen); (c) the Hercynian tectonic event responsible for the internal nappes emplacement in the Mauri- tanide belt (Hercynian orogen).

Later on, these three different tectonic events were dated by the 4°/Ar39Ar radiometric method (Dallmeyer and Villeneuve, 1987; DaUmeyer and Lecorch6, 1989): 660-640 Ma for the Pan- African I tectonic event, 550-530 Ma for the Pan- African II tectonic event, and 320-270 Ma for the Hercynian tectonic event. Considering apart the Hercynian event which is linked to the Pa- laeozoic events, the main geodynamical stages occuring on this western margin during the late Precambrian can be summarized as follows (Fig. 2): (a) opening of a rift in the Bassaride area and probably of a small ocean (Villeneuve, 1984; Remy, 1987 ) in the Mauritanide area before 700 Ma; (b) westward-dipping subduction producing a calc-alkaline magmatism on the western margin (680-660 Ma); (c) collision between the West African craton (CWA) and the Senegalese block (SMB) at ~660 Ma (Pan-African I tectonic event) and deposition of molassic and glacial sediments between 660 and 640 Ma; the remnants of this sedimentation are now located in the Taban and Bakoye basins; (d) intracontinental rifting (Faleme and Rokelide troughs) and deposition of glacial and flysch type sediments before 550 Ma; (e) an intracontinental tectonic event producing a cryptic suture on the

southwestern margin of the West African craton at ~ 550 Ma (Pan-African II tectonic event), this event being followed by deposition of molasse- type sediments mainly in the Youkounkoun basin; (f) the whole area was then covered by Palaeozoic epicontinental sediments starting with the lower Cambrian transgression (Ville- neuve and Corn6e, 1991 ).

The Pan-African I orogen is located in the Mauritanides and Bassarides and the Pan-Afri- can H orogen, which was produced by the closure of an intracontinental graben (Allen, 1969; ViUeneuve et al., 1990; Culver et al., 1991 ) is located in the Rokelide belt.

2.1.2. The eastern margin The belts on this margin are more than 3000

km long between Morocco and Benin. Four seg- ments or belts can be distinguished from north to south: the Anti-Atlas belt, the Ougarta belt, the Western Pharusian belt (including the western Hoggar and the Adrar des Iforas) and the Da- homeyide belt. Except for the Anti-Atlas, these belts occurred at ~600 Ma (Caby et al., 1991; Affaton et al., 1991 ).

(a) The Anti-Atlas belt (685-615 Ma), located in southern Morocco, was mainly studied by Choubert (1963), Leblanc (1975, 1981), Clauer (1976), Chariot, (1976, 1982), Jean- nette and Tisserand (1977 ), Leblanc and Lan- celot (1980), Jeannette et al. ( 1981 ), Mifdal and Peucat ( 1985 ), Schemerhorn et al. (1986), Has- senforder (1987), Bassias et al. (1988), Saq- uaque et al. (1989a,b, 1992). The foreland corresponds to the northern edge of the Tindouf basin on which is obducted the Bou Azzer-E1 Graara ophiolitic complex (Fig. 3). Northward pieces of a Pan-African subduction complex are outcropping but the northern block (NMC) that collided with the West African craton is concealed underneath the Palaeozoic and Mesozoic sequences of the Moroccan Meseta.

The main geodynamic stages are deduced from radiometric data. Different geodynamic models have been proposed by Leblanc and Lancelot (1980), Schermerhorn et al. (1986) and Saq- uaque et al. (1992). Taking into account the different geodynamical interpretations and the geo-

W

MA

UR

ITA

NID

E

RO

CK

EL

1DF

,

W

BE

LT

+ +-

Xn

~-

+ +

~,1-

./-.

~ +

. .

vk

_ *

~ ..

..

~ -=

=_=_

= ~

=_=

--

~ :~

-~

Ik

- ,

+:,+

+++~

+++:

+

+-.+

:,+

• M

k

++

~.'

-r~

I|s

r:

:+~

:~:.

~;-

-++

++

~

@

, mm

~. + ~

N-.

-:PT

~ ,.+

' w+.

~.'

7m

+ +

~ +

+ ;

: +

+,

+

C)

E

WE

ST

A

FR

ICA

N

CR

A

TO

N

P

IIA

RU

SIA

N

E W

D

AII

OM

EY

AH

E

i}F

, L

T

®

@

- : .

..

.

~ ,/

.~:~

~.

.#:

s~,n

"'~x~

.':'':~

xy.

~ ~

aPp

:." .

':':'.

'~:

: --

~\~

*u

p,

~,

,,,

~.?..

0..~

.~

(~

.~,,

o.6

: I

nk~

~.;'

:.~.

-'~

1 ~-

.->-

-I~'

:._.

,~

- /

P~

Mk

:,',

-'.~

.'k6

" /

+:

..

"^

~ ~

--

,o

-+-

:- :-

:-~

" ~

/ K

~7

2..'-

g, ..

....

C

-

--

~.

~

9t

. :'

:-.

,'7,

\

....

..

+ +

~ +

t +

t- I

~c'-

-t*~

r'-+

+

b +

I +0

3()

(tin

1.

'r ;

+.~

+

+ +

+ +

+ +

®

,,,,

, +

©

Fig.

2.

Lit

host

rati

grap

hic

sequ

ence

s of

the

sou

ther

n T

aoud

eni

and

Vol

ta b

asin

s. D

iagr

amm

es i

llust

rati

ng t

he g

eody

nam

ical

evo

luti

on o

f th

e W

este

rn

(Mau

rita

nide

s, B

assa

ride

s an

d R

okel

ides

) an

d ea

ster

n (P

haru

side

s, D

ahom

eyid

es)

Pan

-Afr

ican

bel

ts.

(A)

Geo

dyl~

amic

int

erpr

etat

ion

of th

e w

este

rn

belts

: / =

intr

aexm

tine

~tal

bas

ins

fill

ed u

p w

ith

Supe

rgro

np 1

(P

rote

rozo

ic s

edim

ents

dep

osit

ed b

etw

een

the

Lat

e P

reca

mbr

ian

till

ites

); 2

=op

enin

g of

th

e B

assa

ride

rif

t an

d M

auri

tani

de s

ea;

3 =

clos

ure

of t

he M

anri

tani

de s

ea (

Pan

-Afr

ican

I t

ecto

nic

even

t);

4 =

open

ing

of t

he E

arly

Cam

bria

n tr

ough

s;

5 =

clos

ure

of t

he R

okel

ide

trou

ghs

(Pan

-Afr

ican

II

tect

onic

eve

nt);

6 =

dep

osit

ion

of t

he O

rdov

icia

n sa

ndst

ones

bla

nket

; W

AC

= W

est

Afr

ican

cra

ton;

SM

B=S

e~eg

ales

e bl

ock;

Bs=

Bas

sari

de r

ift;

Mk=

Mad

ina-

Kon

ta b

asin

; T

b=T

aban

bas

in;

Bk=

Bak

oye

basi

n; Y

k=Y

ouko

unko

un b

asin

; PI

=Pan

afri

can

I tec

toni

c ev

ent;

PII

= P

anaf

rica

n II

tect

onic

eve

nt.

(B)

Lit

host

rati

grap

hic

sect

ions

of t

he s

outh

ern

Tao

uden

i bas

in:

I= li

thos

trat

igra

phic

seq

uenc

e of

the

Mad

ina-

Kou

ta a

nd T

amba

oura

bas

ins;

IV

= li

thos

trat

igra

phic

seq

uenc

e of

the

Nar

a an

d B

amak

o ar

eas;

V

= lit

host

rati

grap

hie

sequ

ence

of

the

Mop

ti

trou

gh;

VI-

lith

ostr

atig

raph

ic s

eque

nce

of t

he "

s~ri

e po

urpr

~e"

(Tim

imou

n ar

ea);

VI/

=lit

host

rati

grap

hic

sequ

ence

of

the

Vol

ta b

asin

. P

an-A

fric

an I

an

d Ph

arus

man

pre

-tee

toni

c gr

oups

(m

ainl

y pl

atfo

rm d

epos

its

): S

G =

Seg

ou G

roup

; M

k =

Mad

ina-

Kou

ta G

roup

, K

l= K

olom

bine

Gro

up;

St =

Sot

uba

Gro

up;

Irm

=Ir

ma

Gro

up;

Ou/

Sn =

Oua

lo S

arny

ere

Gro

up;

Pdj

= P

endj

ari

Gro

up;

Bel

= B

ambo

uaka

Gro

up.

Pan-

Afr

ican

I m

olas

sie

grou

ps:

Bkg

= B

akoy

e G

roup

. Pan

-Afr

ican

I]

pre

tect

onic

gro

ups:

M/=

Mal

l G

roup

; T

r="t

riad

e';

Na=

Nio

ro a

nd N

ara

Gro

up.

Pha

rusi

an m

olas

sic

grou

ps:

Bdg

=Ban

diag

~ra

Gro

up;

Spp=

seri

e po

urpr

~e;

Tm

l=lo

wer

par

t of

the

Tam

ale

Gro

up;

Tm

l su

p. =

uppe

r pa

rt o

f th

e T

amal

e G

roup

. Pa

n-A

fric

an I

I m

olas

sic

grou

ps:

Yk =

You

koun

koun

Gro

up;

Pt =

Cam

bro-

Ord

ovic

ian

sand

ston

es (

Pit

a G

roup

); E

o =

Cam

bro-

Ord

ovic

ian

To, =

Ord

ovic

ian

tilli

te.

! = F

irst

hyp

othe

sis

for

corr

elat

ion

of t

he B

andi

agar

a G

roup

. 2

= Se

cond

hyp

othe

sis

for

corr

elat

ion

of t

he B

andi

agar

a gr

oup

(see

in

text

).

(C)

Geo

dyna

mic

int

erpr

etat

ion

of th

e P

haru

side

s/D

ahom

eyid

es b

elt:

1 =

dep

osit

ion

of th

e lo

wer

par

t of

Sup

ergr

oup

1; 2

= o

peni

ng o

f an

eas

tern

oce

an (

arou

nd 8

00 M

a )

and

buil

ding

of

the

Til

emsi

Isl

and

Arc

. 3

=int

erna

l de

form

atio

ns i

nto

the

Til

emsi

Isl

and

Arc

(co

llis

ion

wit

h th

e H

ogga

r sh

ield

); 4

= E

aste

rn P

an-A

fric

an t

ecto

nic

even

t an

d po

ssib

ly d

epos

itio

n of

the

Ban

diag

ara

Gro

up;

5 =

depo

siti

on o

f the

Tam

ale

Gro

up a

nd th

e "s

erie

pou

rpr6

e, g

':4C

= W

est

Afr

ican

cra

ton:

ES

C=

E

aste

rn S

ahar

ian

cont

inen

t: T

lc=

Til

emsi

Isl

and

Arc

: 7)

n/=

Tam

ale

Gro

up;

Slop

= s0

rie

pour

pr&

: B

de=

Ban

diag

ara

Gro

up.

Tm

l

....~

.'~

: ..~

...

~. d

- .e

.:..

:

Ph

aru

sian

~ .

..

.

m=

+

oro

go

n

¥'~

,~'-

'~:-

:

.-'~

//-~

l:

~ E

SC

63

5Ma

~-

+ r

+ +

' '

~

i ,_

:i

.v, I ~r

ND

ND

T ~

S W

ES

T

AF

RIC

AN

C

RA

TO

N

N

SC

3 T

o.

Co

/Ft.

SG2

¥k.

Oro

g.

PI1

Ml.

--

----

--

-~r.

-

Mk

.

SG1

Sg.

BI'

.

Ira.

i

J

I Bky

. I

_

~1

~0

•

At.

"L:

~,

-~

10

a0

Ch

II

440M

a

To.

a tl

A

~.

....

, ,.

....

..::

~..

...-..:.

..~_.

." 5-4

':: .~

,'.. : ;

,~

.~;::

.:-f~

".~,i.

!..

• .:.':

:. :. :

~ .'..

:f :..~

" '

'~W

:~

;

S.

....

. -T

o]

595

t 43

KN

.

~F

r

E~4L

....

..

77

51

52

M

r

/--

89

0.3

5

/ D

k.

991.

~I

I 21

00M

a

®

VII

I

111

;.ll'::'

.{.if."

l[;]:.

:

"::~

:-:i

~::;

:

/ E

.

/ ~

-I-

;

- ~

2- Q

- Q

- O

,~

~

Plll

;~2-

>,2

-~-~

= ~

: ~

~ai

~t

r~

--

t I

t t

i I

,t.

-- \

\ P

ill

\ \

\

PI

~":

i ':

::?)

/.

AN

TIA

TL

AS

S

BE

LT

N

P 534

il0

_ g-

jz

r (~

)

q" r

-i-

+

, ~

Z~

,_~

-.L

-

t i.

:tD

iWl

4-

t ol

a iv

la

595

*15

~

" S

Si

-.

i- I

-'

~'

q/

;¢

.~

/-

~'

~-

;'

l

- 4.

i

I CW

,,A, +

v ~.

2~. ~

,~L+I

~IIB

Ih'~

,~IN+

`C

M+.

I 68

5 M

a

SSi

..d_.

@

f~

,

~

~ .i

t- 72

0 70

5 ~

.~-_

_~

, ~

~F

_.!

~

'C~I~C

N M

' C

WA

+ m

.,.,

+Z

-v~

~ -,-

+.,_

~itm

.° ,

+7.0

u.

-~

" --

~ '

< "

+ M

®

afte

r Sch

enne

rhom

et al

. (1

986)

, m

odif

ied

Fig.

3. L

itho

stra

tigr

aphi

c se

quen

ces

of th

e no

rthe

rn T

aoud

eni

and

nort

hern

Tin

douf

bas

ins.

Dia

gram

ill

ustr

atin

g th

e ge

odyn

amic

evo

luti

on o

f th

e A

nti-

A

tlas

Pan

-Afr

ican

be

lt.

(A)

Lit

host

rati

grap

hic

sequ

ence

s in

: /=

the

Mad

ina-

Kou

ta

and

Tam

baou

ra

basi

ns;

H=

Ad

rar

basi

n; I

II=

Han

k ba

sin;

V

III=

nor

ther

n pa

rt o

f th

e T

indo

uf b

asin

; B

r= B

irri

mia

n ba

sem

ent.

Pre

-pha

se B

1 g

roup

s (A

nti-

Atl

as):

PI=

Pre

cam

bria

n I;

PIE

= l

ower

par

t of

Pre

cam

- br

ian

II. P

an-A

fric

an I

and

Pha

rusi

an p

re-t

ecto

nic

grou

ps (

mai

nly

plat

form

dep

osit

s; S

G =

Sup

ergr

oup

): S

g= S

egou

Gro

up;

Mk.

= M

adin

a-K

outa

Gro

up;

Ch.

=C

har

Gro

up;

At.

=A

tar

Gro

up;

Mr.

=E

l M

reit

i gr

oup;

Ah.

= A

ssab

et e

l Has

sian

e G

roup

. P

ost-

BI

tect

onic

dep

osit

s (A

nti-

Atl

as):

PlI

s=U

pper

par

t of

Pre

cam

bria

n II

(T

idil

ine,

Sir

oua

and

Ane

zi G

roup

s).

Pan

-Afr

ican

I m

olas

sic

grou

ps:

Bky

. =B

akoy

e G

roup

. P

an-A

fric

an I

I pr

e-te

cton

ic g

roup

s.

M/.

=M

ali

Gro

up;

Tr.

="tr

iade

";

Be.

=B

hta

t E

rgil

Gro

up;

KN

.=K

reb

en

N

aga

Gro

up;

Fa.

=F

al6m

6 G

roup

. P

ost-

phas

e B

2 (A

nti-

Atl

as):

P

III=

Pre

cam

bria

n II

I (O

uarz

azat

e G

roup

); A

d. =

Ado

udou

nian

Gro

up;

E. =

Mid

dle

and

Upp

er C

ambr

ian;

O. =

Ord

ovic

ian.

Pan

-Afr

ican

II

mol

assi

c an

d po

st m

olas

sic

grou

ps:

Yk.

= Y

ouko

unko

un G

roup

; O

uj. =

Ouj

eft

Gro

up;

Co/

Pt.

= C

ambr

o-O

rdov

icia

n sa

ndst

ones

; T

o. =

Ord

ovic

ian

tilli

te; S

. = S

iluri

an.

(B)

Geo

dyna

mic

evo

luti

on o

f th

e A

nti-

Atl

as b

elt:

/=

ocea

n

open

ing

in t

he n

orth

ern

part

of

the

Wes

t A

fric

an c

rato

n (7

88 M

a);

2=co

llis

ion

in

the

Siro

ua/S

ahro

Isl

and

Arc

(74

0-72

0 M

a);

3=op

hio

lite

s ob

duct

ion

onto

the

Wes

t A

fric

an c

rato

n (B

1 te

cton

ic e

vent

at

685

Ma)

; 4

=co

llis

ionn

al s

tage

in

the

Ant

i-A

tlas

(B

2 te

cton

ic e

vent

at

615

Ma)

; 5

= m

olas

sic

stag

e. C

WA

= W

est

Afr

ican

cra

ton;

CN

M=

Nor

th M

oroc

can

cont

inen

t; S

Si=

Sir

oua/

Sahr

o Is

land

Arc

; T

ZT

= T

izi'

n T

est

faul

t zo

ne.

? V

t~

312 M. Villeneuve, J.J. Cornbe / Precambrian Research 69 (1994) 307-326

chemical data from the Bou Azzer ophiolites (Bodinier et al., 1984) we propose here the fol- lowing stages (Fig. 3), modified from those of Schermerhorn et al. (1986 ).

( 1 ) According to Clauer (1976) there is an accretion of oceanic crust (MORB type) to the north of the West African craton at ~ 788_ + l0 Ma. An island arc is postulated by Schermerhorn et al. (1986) and a back-arc basin identified in the Bou Azzer ophiolites by Bodinier et al. (1984).

(2) According to Saquaque et al. (1989b), to the north ofBou Azzer (in the Sahro inlier), volcanics and volcaniclastics assumed to be the remnants of a talc-alkaline arc were strongly deformed (ductile in type) at 754 and 722 Ma. This might be produced by a local collision between an island arc and a supposed northern isolated block.

(3) According to Leblanc and Lancelot (1980), the Bou Azzer ophiolitic complex was obducted onto the West African craton at ~ 685 Ma. This ophiolitic complex was associated to an andesitic island arc and a northern fore-arc (Schermerhorn et al., 1986). The suturing zone of Bou Azzer is thought to have been created by an initial north subduction zone and should be the site of the collision between the West African craton and a northernmost island arc (Saquaque et al., 1989b). Obduction and local collision are thought to be a tectonic event associated to a greenschist syntectectonic metamorphism dated at 688 + 15 Ma by Clauer ( 1976 ). This first fold- ing episode is the B 1 Pan-African tectonic event of the Anti-Atlas belt (Leblanc, 1975). In this same episode, several ductile shear-zones were evidenced (Wallbrecher, 1988; Saquaque et al., 1989a).

(4) Deposition of clastic sediments including the Tidiline tillites (Siroua-Saghro series, Tid- diline series, Anezi series) was associated with calc-alkaline magmatism which underlines an active margin environment. On the western part, the Anezi series was deposited before a granitic intrusion dated at ~ 660 -+ 20 Ma (Clauer et al., 1982).

(5) The final collision stage associated to the B2 tectonic episode (Leblanc, 1975), occurred

between 615 Ma and 578 Ma (Ducrot, 1979; Jeannette et al., 1981 ). This collisional stage could be related to a collision with a northern Moroccan craton then incorporated in the Her- cynian Moroccan Meseta.

(6) Thick continental molasses with effusive acid volcanism and alkaline and calc-alkaline intrusions (between 615 and 563 Ma) were then deposited into graben or pull-apart basins (Ouarzazate and Tanalt series) during a post- collisional stage governed by a regional E-W- trending extension (Hassenforder, 1987; Azizi et al., 1990; Saquaque et al., 1992).

(7) During the latest Proterozoic and the Cambrian marine transgressions, sediments from shallow-marine environments progressively invaded the Tindouf and northern Moroccan basins (Destombes et al., 1985; Bernardin et al., 1988; Villeneuve and Cornre, 1991 ).

(b) The Ougarta belt, located in the Western part of the Algerian Sahara, was recently studied by Kurek and Priedl (1987). The most important part of the Ougarta belt is concealed underneath the Palaeozoic or the Meso-Cenozoic sedimentary formations. Despite a lack of information, and according to Kurek and Priedl (1987), a subduction stage is supposed to be more recent than 685 Ma, and the final collisional stage occurred at ~ 600 Ma. Conglomer- ates and volcanic intrusions including rhyolites, dacites and andesites were emplaced between 600 and 500 Ma.

(c) The Western Pharusian belt was mainly studied by Caby (1970), Bertrand et al. (1978) and Boullier (1991). The whole Hoggar shield emphasizes a polyphase history from the Palaeo- proterozoic to the early Palaeozoic. We will focus our attention on the western part of this belt which is thrusted onto the West African craton. This part shows a wide system of external nappes thrusted over the Gourma aulacogen or over the West African craton basement, from northeast to southwest (Fig. I). The Pan-African suture (Amalaoulaou suture) was apparently eastward dipping.

According to Caby (1989) and Caby et al. ( 1991 ), the geodynamic evolution of the eastern margin can be summarized as follows (Fig. 2):

M. Villeneuve, J.J. Corn~e / Precambrian Research 69 (1994) 307-326 313

( 1 ) deposition of clastic sediments and stroma- tolitic formations on the Tassendjanet platform between 1100 and 680 Ma; (2) building of an oceanic crust with ultramafic rocks and possible ophiolites ( ~ 800 Ma); (3) eastward-dipping subduction zone and building of an island arc (Tilemsi Island Arc) with calc-alkaline intrusions (mainly granodiorites) associated with greywackes and flysch facies rocks (green series)

~ 7 ~ 8

Fig. 4. Palaegeographical sketch map at ~ 700 Ma: 1 = marine domain; 2 = island arc domain; 3 = epicratonic and continental domain; 4 = basement; 5 = limit of basins; 6 = subduction zones; 7=oceanic ridges; 8=di rec t ion of transgressions. Rs=Reguibat uplift; IC.S= Ivory Coast craton; SNB = Sen- egalese block; GS= Guyana shield; SFC= S~o Francisco craton; SR/SH=Siroua/Sahro Island Arc; B a = B o u Azzer inlier; Ki= Kerdous inlier; li= Ifni inlier; Zb. = Zemmour basin; Am=Maur i t an i an Adrar; R t=Richa t trough; H b = H a n k basin; BS=Bassarides rift; M K = M a d i a n Kouta basin; Tb=Tambaoura basin; AfH= Affol6 high; GA = Gourma aulacogen; Vb.=Volta basin; Ach.H. =Achkaikar high; Tim = Tilemsi Island Arc.

between 730 and 620 Ma; (4) oblique collision between the Tilemsi Arc and the West African craton at ~ 620-600 Ma and deformation of the foreland sedimentary sequences; (5) deposition of molassic formations (serie pourprre) in several large intracontinental basins with a N-S trend, between 600 and 550 Ma; these molassic formations including glacial sediments (tillites) were associated with rhyolites and alkaline granitic intrusions.

(d) The Dahomeyide belt (or Beninian belt), studied successively by Bessoles and Trompette (1980), Affaton (1987), Caby (1989) and Af- faton et al. (1991), shows a very similar structural model as the Pharusian one (Fig. 1 ). The nappe complex is widely thrusted over the Volta basin which is folded beneath the foreland nappes. This foreland nappe complex is almost 100 km wide and moved from east to west.

According to Affaton et al. ( 1991 ), a similar geodynamic evolution can be considered regarding the Dahomeyide fold belt. The opening of an oceanic domain probably occurred between 1100 Ma and 700 Ma, followed by a convergent stage with eastward-dipping subduction. The collision with the West African craton is estimated at ~ 600 Ma. Molassic deposits are mainly deposited in the Tamale basin.

2.1.3. The southern margin (northeastern Brazil- ian shield)

According to several authors, the southern part of the West African craton can be observed in northeastern Brazil (S~o Luis craton) where it is surrounded by the Gurupi (west) and the Bor- borema (east) belts. This part of Gondwana was largely studied by Brazilian geologists (Almeida et al., 1981; Cordani et al., 1984) as well as by other geologists (Trompette, 1988; Caby, 1989; Caby et al., 1991 ). This area is largely covered by three Palaeozoic and Mesozoic basins (Ama- zonian basin, Parnaiba-Maranhao basin and Parana basin.). The old basement can be divided in two main units:

( 1 ) Archaean and Palaeo- to Mesoproterozoic shields, namely the Guyana shield, the Amazon- ian shield, the S~o Francisco craton and the S~o Luis craton. Some of them, like the Sao Fran-

314 M. Villeneu ve, J.J. CornOe / Precambrian Research 69 (1994) 307-326

cisco craton are blanketed by a Neoproterozoic sedimentary cover (Bambui Group).

(2) Neoproterozoic mobile belts made of Neoproterozoic sediments and Archaean and Proterozoic metamorphic rocks reworked during the later Brazilian ( = Pan-African) orogen (700-600 Ma).

Several belts can be linked to this Brazilian (=Pan-African) orogen, namely: the Borbor- ema belt of northeastern Brazil, the Gurupi belt (southwest of the Silo Luis craton), the Ara- guay-Tocatins belt and the Paraguay belt, both located on the eastern margin of the Amazonian craton and, finally, the Brazilian belt on the western side of the Silo Francisco craton. This paper only concerns the Brazilian belt which extends southwards the West African Pan-African belt. So we will give a short overview of the Bor- borema, Gurupi, and Araguay-Paraguay belts.

( a ) The Borborema belt is composed of Ar- chaean and Palaeoproterozoic rocks strongly reworked by the Braziliano/Pan-African tectono- metamorphic event (Caby et al., 1991). The nappes with a westward or a southwestward dis- placement are emplaced between 620 and 580 Ma. They are crosscut by WSW-ENE or SW-NE lineaments as the SW-NE Transbraziliano lineament (TBFZ) which corresponds to the southern extension of the African Kandi fault zone (Caby, 1989 ). These lineaments reflect a dextral strike-slip motion (Corsini et al., t 991 ). Molas- sic basins or troughs located along these fault zones, are dated by granitic intrusions at ~ 550 Ma (Nascimento et al., 1981 ).

(b) The Gurupi belt is composed of schists, biotite-schists and gneisses outcropping south of S~o Luis city. They display a biotite age of 504 and 520 Ma (Cordani et al., 1984).

(c) The Araguay-Tocatins belt, recently studied by Herz et al. (1989 ), is a Mesoproterozoic suture (Urua~uano tectonic event dated at 1100 Ma) reactivated at 550 Ma. However, Neopro- terozoic sediments like the conglomerates of the Rio das Barreiras formation were deposited along this suture.

(d) The Paraguay belt was well studied by AI- varenga (1990). It is considered as a continental trough filled with glacio-marine sediments, do-

lomites and arkosic sandstones. The fold verg- ence is rather to the east but not towards the Amazonian craton. According to Alvarenga (1990) the glaciogenic sediments were deposited before 600 or 630 Ma and suffered a ther- motectonic event at ~ 547 + 05 Ma (diagenesis of argilites). Post tectonic granites intruded these formations at ,,, 500 Ma.

Despite a large number of papers on the Bra- zilian geology, very few are published concern- ing the geodynamic model of the Braziliano ( = Pan-African) belts.

However, two main tectonic events can be distinguished in these belts. The first one (Borbor- ema belt) corresponds to the Brazilian orogen occurring at ~600 Ma (620-580 Ma) on the eastern side. The second one corresponds to an early Cambrian orogen (550-530 Ma) which occurs mainly on the western side (Paraguay, Araguay and Gurupi belts ).

2.1.4. The main Pan-African (Brazilian) orogens Around the West African craton, four separate

tectonic events corresponding to different orogens and belts are distinguishable, namely:

(1) The Anti-Atlas B1 tectonic event (685 Ma) which is related to an ophiolite obduction along the Bou Azzer fracture.

(2) The Pan-African I tectonic event (660- 640 Ma) which corresponds to a rift closure on the western side of the West African craton (Bassarides).

(3) The Eastern Pan-African tectonic event (620-600 Ma) which corresponds to the ocean closure on the eastern side of the West African craton (Pharusides, Dahomeyides and Borbor- ema). The final collision (Anti-Atlasides ?) between the northern part of the West African era- ton and an unknown northern Moroccan craton located north of the Anti-Atlas is contemporary (615-585 Ma).

(4) The Pan-African II tectonic event (550 Ma) which corresponds to an intracontinental trough deformation along the southwestern side of the West African craton. This tectonic event includes the Rokelide, the Gurupi and the Para- guay belts.

This list does not include other tectonic events

M. Villeneuve, J.J. Corn~e / Precambrian Research 69 (1994) 307-326 3l 5

occurring in the inner part of the surrounding belts like, for example, the different tectonic events of the Hoggar shield.

2.2. Location and stratigraphy of the main basins on the craton

2.2.1. General overview on the the West African craton structure

The West African craton (Fig. 5) includes three main basins (Tindouf, Taoudeni and Volta) separated by two old Precambrian shields (Reguibat and Ivory coast). According to gravi- metrical (Lesquer et al., 1984) and geological interpretations, the Taoudeni basin, located in the central part of the West African craton can be divided into several sub-basins or troughs. A synthetic view of the basement has already been done by Bessoles ( 1977 ) and Rocci et al. ( 1991 ). So, we will focus the present study on the sedimentary basins or troughs in Fig. 5.

2.2.2. The Tindoufbasin This is a deep (7 to 8000 m) and asymmetric

basin which extends over 150,000 km 2 as an open syncline. Deformations are increasing to the north and to the west (Sougy, 1962; Hassenfor- der, 1987). The Neoproterozoic and Cambrian formations outcrop essentially on the northern edge which is also the foreland of the Anti-Atlas Pan-African fold belt. Proterozoic carbonates occur also in the Zemmour area (Sougy, 1964) underneath the Hercynian thrusts. On the southern part of the Anti-Atlas, Leblanc ( 1975 ), Jean- nette et al. (1981) and Hassenforder (1987) distinguished three Proterozoic series (Fig. 3, log VIII) overlain by shallow-marine sediments (Adoudounian carbonates) which are mostly early Cambrian in age (Destombes et al., 1985 ). To the base they pointed out a schisto-quartzitic formation with interbedded ultrabasic rocks. This formation, interpreted as a passive margin deposit, is capped by tillites, argilites and calc- alkaline volcanic intrusions. These volcaniclas- tic sediments (Precambrian I1-III or Tidiline series) are interpreted as active-margin-derived materials. The last Proterozoic series corresponds to a molassic deposit with alkaline rhyo-

Fig. 5. Structural sketch map of the West African basins. NM=northern Meseta; TZT=Tizi'n Test fault zone; Ou = Ougarta belt; RS = Reguibat shield; HS= Hoggar shield; ICS= Ivory Coast shield; GS= Guyana shield; AS=Amazonian shield; SLC=S~o Luis craton; SFC=S~o Francisco craton; CAC=Central African craton; Bch b. = Bechar basin; MM b. = Mahon basin; Ah b. = Ahnet basin; Aj b. = Ajjer basin; Ul b. = Iullemeden basin; Ben b. = Benou6 basin; Ab = Accra basin; Mh b. = Parnaiba-Maranhao basin; Am b.=Amazonian basin; SMb=Senegalo-Mauritanian basin; Tf b.=Tindouf basin; Rg b.=Reggan basin; HK b.=Hank basin; A=Adrar basin; Rt=Richat trough; Hb.=Hodh basin; F t=Faleme trough; BTF=Bissau Tom- bouctou fault zone; Tbb. = Tambaoura basin (Bakoye basin); MAb.=Madina Kouta basin; Yb=Youkounkoun basin; Bb.=Bov6 basin; Rk. =Rokelide trough; Nt=Nara trough; Mt=Mopt i trough; GA=Gourma aulacogen; Vb.=Volta basin; Ma= Achkaikar high. 1 = sedimentary rocks; 2=Variscan orogen in North Africa and Faleme and Roke- lide troughs in West Africa; 3=Pan-African orogens; 4 = Precambrian shields; 5 = thrusts and location of logs shown in Figs. 3 and 4; 6=l imit of basins.

316 M. Villeneuve, J.J. Corn~e /Precambrian Research 69 (I 994) 307-326

lites and granites interpreted as post-orogenic deposits (Precambrian III or Ouarzazate series). Other Proterozoic rocks occur in the Zem- mour (western part of this Tindouf basin ) area (Sougy, 1964). To the east, the Tindouf basin extends through the Reggane basin where the Pa- laeozoic sediments are capped by Mesozoic sediments.

2.2.3. The Taoudeni basin Firstly, this name was assigned to a tiny basin

located in the northwestern part of the central syneclise around the village Taoudeni, in the Hank area (Villemur, 1967). The whole central depression, which extends over 2,000,000 km 2 was then called "Taoudeni basin". Now, we propose the name "Hank basin" for the small basin around Taoudeni, and to use the name "Taou- deni basin" for the whole central cratonic depression.

Nowadays, the Taoudeni basin can be divided into eight different sub-basins with different structures and sedimentological evolutions. From north to south we distinguish (Fig. 5 ) the Adrar basin (NW), the Hank basin (NE), the Gourma aulacogen and the Mopti trough (SE), the Nara trough (south-central), the Tambaoura and Ma- dina-Kouta basins (SW) and the Hodh basin (W). Each one can be well distinguished and is bounded by arches or highs like the Achkaikar high between the Hank and Gourma basins. The subsidence rates were not similar for all basins.

Many lithostratigraphic correlations were car- ded out by Deynoux ( 1971 ), Trompette ( 1973 ), Sougy et al. (1985) and Bertrand-Sarfaty et al. ( 1991 ). Most of them took into account the four main lithostratigraphic sequences identified in the Mauritanian Adrar by Deynoux ( 1971 ) and Trompette (1973). From the top to the bottom they distinguished (log II, Fig. 3): sequence 4 (Devono-Carboniferous), sequence 3 (Ordovi- cian and Silurian), sequence 2 (Cambro-Or- dovician ), sequence 1 (Neoproterozoic). These sequences are separated by regional unconform- ities (Fig. 2) and glaciogenic levels (late Pre- cambian tiUites separating sequences 1 and 2 and late Ordovician tillites separating sequences 2 and 3 ). Radiometric data by Clauer et al. (1982)

indicate the time of diagenesis of these different lithological units (see ages on log II, Fig. 3 ).

This lithostratigraphic sequence was then ex- tended to the whole Taoudeni syneclise. How- ever, new structural and sedimentological stud- ies (Moussine-Pouchkine and Bertrand-Sarfaty, 1978; Villeneuve, 1989; Deynoux et al.. 1989) pointed out many changes in the sedimentological environments of these basins: (a) The Adrar basin (log II, Fig. 3). According to Trompette (1973) the lithostratigraphic sequence is composed of the four main units previously described. Sequence 1 may be divided into two parts. The lower part (Char and Atar Groups) is made up by argilites, carbonates with Riphean stromatolites and sandstones from a marine epicontinental platform environment. The upper part (Assabet el Hassiane Group) is made up by marine siliclastic rocks which could be thicker than 3000 m in the Richat trough (Bronner et al., 1980). Ages of 998 ___ 32 for the base of the Char Group and 694 _+ 20 Ma for the base of the Hassabet el Hassiane Group are supported by Clauer et al. ( 1982 ).

Higher up, the tillites and argilites of the lower part of sequence 2 could represent a marine lower Cambrian transgression which followed a glacial period. (b) The Hank basin. To the east, this basin ex- hibits a sequence more or less similar to the Ad- rar one (log III, Fig. 3 ). However, the equivalent of the Ass,abet al Hassiane Group is strongly re- duced in thickness. (c) The Gourma basin. This basin includes the Gourma, the Mopti and the Nara troughs (logs IV and V, Fig. 2). The Gourrna trough itself is interpreted as an aulocogen connected to the East Pan-African sea (Moussine-Pouchkine and Ber- trand-Sarfaty, 1978).The sequence includes three groups: the Lower Group (Irma Group), deposited on a stable cratonic platform; the Middle Group (Hombori or Oualo-Sarnyere Group), which is very thick (more than 6000 m) in the aulacogen centre and is evidence of the detrital in filling of this aulacogen (Vendian to Cam- brian); the Upper Group (Bandiagara Group ), poorly deformed by the Pan-African tectonic event and considered by Bertrand-Sarfati et al.

M. Villeneuve, J.J. Cornbe/ Precambrian Research 69 (1994) 307-326 317

( 1991 ) as an erosive stage of the East Pan-Afri- can belt. However, fluviatile current directions indicate a transportation from the southwest to the north east, but not from the east to the west like molassic deposits should do. The two first groups were deformed during the Pan-African orogen. (d) The Tambaoura and Madina Kouta basins (Fig. 2). Both are located in the southwestern part of the Taoudeni basin. Five units have been distinguished (Deynoux et al., 1989; Villeneuve, 1989): unit I (Surokoto 1 and Segou Groups), which represents a platform deposit similar to the lower part of the Adrar basin sequence I; unit 2 (Surokoto 2 and Madina-Kouta Groups), which corresponds to a platform sequence; unit 3 (Bak- oye and Taban Groups) supposed to be of molassic origin (ViUeneuve, 1989); unit 4 (Nioro and Mali Groups), which corresponds to a marine transgression (Early Cambrian transgression ) over the West African craton, unit 5 (You- kounkoun Group), reputed from molassic origin. These molassic sediments mainly occur beneath the Palaeozoic Bov6 basin.

2.2.4. The Volta basin This foreland basin (log VII, Fig. 2 ) is located

in the eastern part of the Ivory Coast shield and it extends over 450,000 km 2. Affaton (1987) distinguished two superimposed basins:

( 1 ) A lower basin filled with clastic sediments deposited between ~ 1000 and 600 Ma. The lower part (Bombuaka Group), deposited before 660 Ma, mainly consists of sandstones and shales. The upper part (Pendjari Group), including glacial sediments (~ 660 Ma old), consists of tillites, shales, siltstones, limestones, greywackes and phosphatic siltstones. Affaton (1987) thought that this basin represented a passive-margin environment.

(2) An upper basin (Tamale Supergroup), filled with shales, sandstones and conglomerates including several levels of tillites. According to Affaton ( 1987 ) it could be a molassic basin. Its age is still not known precisely, but it could be younger than the lower part of the "srrie pourprre" (Affaton, 1987).

To summarize this section devoted to the in-

tracratonic basins we will point out some lithostratigraphic and environmental differences (rift sequence, aulacogen sequence, platform sequence, glacial and molassic environments, etc. ) between the basins which overlie the West Afri- can craton. That probably reflects the influence of local tectonosedimentary environments related to the closest Pan-African belts.

3. Palaeogeographical reconstructions of the West African craton and its borders during the Neoproterozoic

3.1. Lithostratigraphic correlations

Previously, the correlations were based upon lithologic reference levels like the Neoprotero- zoic tillite (620-600 Ma) or the late Ordovician tillites (440 Ma). Unfortunately, it is difficult to check the duration of a glacial event. However, other glacial events occurred like the Volta basin glacial event (660 Ma). Another solution is to correlate the sedimentary environments with the geodynamic stage of the adjacent belts. This has already been done on the eastern side (Bertrand- Sarfaty et al., 1977) as well as on the western side (Villeneuve, 1988) of the West African craton. An attempt has been made to correlate both sides of the West African craton (Bertrand-Sarfaty et al., 1991 ) but the geodynamic evolution of the western belts was not yet clear enough. Figs. 2 and 3 present new correlations based upon the geodynamical constraints as described above. The southwestern log (log I, Figs. 2 and 3 ) is used as a lithostratigraphical reference for the entire Taoudeni basin.

(a) The Madina-Kouta Group (log I) is correlated to the Oualo Sarnyere Group (log V), the Assabet el Hassianne Group (log II) and the Cheikia Bir Amrane Group (log III). These groups are linked to the opening of oceans and troughs which occurred before 660 Ma on both (east and west) sides of the West African craton. The Hassabet el Hassiane group, beginning at ~694 Ma (Clauer, 1976) is 3000 m deep in the Richat trough and it could be linked to the Pan- African I rift in the Mauritanides. According to

318 M. Villeneuve, J.J. Cornke / Precambrian Research 69 (1994) 307-326

Fig. 6. Palaeogcographical sketch map at ~650 Ma: 1 = marine domain; 2= island arc domain; 3 = marine epicontinental domain; 4= Bassarides molasses; 5=tfllites (Tl ) ; 6= Pan-African belts; 7=cratonic domains; 8= supposed block displacements; 9=subduction zone; lO--Pan-African thrusts; / / = b a s i n boundaries; 12=age of tectonic event , Bky= Bakoye Group; Tbn = Taban Group; Tb= Tambaoura basin; ESC=eastern Saharan continent. For further expla- nation see Fig. 4.

Bronner et al. (1980), the average subsidence rate in the Richat trough (Assabet el Hassiane group) was about 10 m/year, while it was less than 1 m/year during the previous periods (1000-800 Ma). This indicates the importance of the tectonic subsidence during this period.

(b) The Bakoye Group (log I, Fig. 2), including several levels of tillites, has been considered as the molassic stage of the Pan-African t orogen (Bassaride belt) by Villeneuve ( t 988). It has not been observed in the Adrar area (tog II). The

I

Fig. 7. Palaeogcographical sketch map, from 620 to 580 Ma: l = volcanic rocks; 2 = basement; 3 = Mali Group tillite ( T2 ); 4 = marine epicontinental domain; 5 = Pharusides, Dahome- yides and Borborema molasses; 6=marine domain; 7=Pan- African thrusts; 8 = main strike slip faults; 9= supposed mass displacements; 10=troughs boundaries. NMC=north Mo- roccan craton; Ft=Faleme trough; Rt=Rokelide trough; ARb=Araguay Tocatins trough; Gt=Gurupi trough; TBFZ=transbraziliano lineamant; KFZ=Kandi fault zone (Trans-saharan lineament); PpFZ=Pompeu lineament: PFZ= Patos lineament; PnbFZ= Pernambuco lineament: AF= Amadaoua lineament: ICS= Ivory Coast shield,

Bandiagara Group (log VI ) has not yet been correlated with another group. Either it is the eastern extension of the Bakoye Group but without glacial markers (solution 1 in Fig. 6), or it represents continental sediments deposited in the Mopti and Gourma troughs, after the deposition of the Bakoye Group and during the arising of the Pharuside belt (solution 2 in Fig. 6 ). North- westward sediment transportation is against a

M. Villeneuve, J.J. CornOe / Precambrian Research 69 (1994) 307-326 319

bonates, jaspers and sometimes phosphatic deposits. This reference level occurs at the base of the Mali group. But this "triade" has not yet been observed in the eastern basins. So, a correlation between this Mali Group and the base of the "se- de pourprre" (log VI) or the Tamale Group (log VII) is proposed, considering the geodynamic environment in the Pharuside belt. Fossils from the carbonates associated with the "triade" of eastern Senegal indicate an early Cambrian age (Culver et al., 1988).

(d) The Youkounkoun Group (log I) which represents the molassic stage of the Rokelide belt (ViUeneuve, 1988) is correlated with the lower part of the Oujeft Group (log II). To the east it can be correlated with the upper part of the "srrie pourprre" (Deynoux, 1980; Fabre, 1982). Correlations between the Taoudeni basin and the northern part of the Tindouf basin are still inac- curate, due to the specific evolution of the Anti- Atlas belt.

3.2. Sedimentary environments

Fig. 8. Palaeogeographical sketch map at ~520 Ma: 1 =marine domain; 2= marine epicontinental domain (scol- ithic sandstones); 3 = sandstones and siltstones; 4 = molassic deposits; 5 = Tamale Group tillites (T3); 6 = Rokelides, Gu- rupi and Araguay-Tocatins belt; 7=basement; 8--sediment transportation; 9= deltaic formations; 10 = major strike-slip faults; l l=Rokelide thrust; 12=grabens or oceanic hinge zone; 13=supposed continental mass displacements direc- tion. RS=Reguibat shield; ICS=lvory Coast craton; GC= Guyana craton; AA = Anti-Atlas area; Yb = Youkounkoun basin; Rk.b = Rokelide belt; Gb. = Gurupi belt; Pb. = Paraguay, Araguay, Tocatins belt; Tm= Tamale group; Al--Iforas Adrar; H=Hoggar shield; Ou=Ougarta trough; TBFZ=Transbraziliano lineament (=Sobral lineament); TSFZ=Kandi lineament (=Trans-saharan lineament); SPEZ= Borborema fault zone.

molassic interpretation (Pharuside molasses). (c) The Mali Group (log I) is correlated with

the Nara Group (log IV), the Bthat Ergil Group (log II) and the Kreb en Naga Group (log III). These correlations are based upon the "triade" which is a reference level including tillites, car-

Regarding the above-mentioned geodynamical evolution, several sedimentary environments can be distinguished.

3.2.1. Epicontinental platform sedimentation environment

Epicontinental and platform sedimentation have been emphasized all over the Taoudeni basin between 1000 and 800 Ma (Trompette, 1972; Bertrand-Sarfati et al., 1991). Bertrand- Sarfati et al. (1991) distinguished a siliclastic platform (Segou Group, Char Group, etc. ) and a carbonate platform with biostromes (stromatolites), including the Atar Group. The Mali and correlated groups deposited during the Neopro- terozoic or early Cambrian transgression indicate another silicastic epicontinental platform environment. Several troughs like the Faleme and Rokelide troughs were created in this platform.

3.2.2. Marine passive margin and rift environment Marine passive-margin sedimentation was

evidenced on the northern and eastern margins of the West African craton between 800 and 600

320 M. Villeneuve, J.J. Corn~e /Precambrian Research 69 (1994) 307-326

I ape tus ocean S aha r i an s ands tones HS ~ L ~ ~ J ~

I~-----"-~-----:----"~--~-----~-~-~:;';"~ +' ~~"; '~'*+ '~"* ; * " * '~ +"+ ~"+ '* ~ +'* +"~ ; ~'* * +": ~ ' ¢ ~ ' ~ - . ~ ; ~ ORDOVICIAN ~ _ ~ . ~ - ~ - - + + + + + + + + + + + + + + + + + ÷ + + + + + + + ~ + + + + + + + + + ~ + + ~ + ~ + + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

~ + + + + + + + + + + + + + + + + + + ÷ + + + + + + + + + + + + + + + ÷ + + + + + + + + + + + + + + + + + + + + ÷ + + + ~" + + ÷ + + + + + ++ ++ + + + + + + + + + + + + + ~ - + + + + + + + +

HS

yk. - - Gm. + Sp. Sp. ~ + + + t + • ~ t ÷ + + + +-% + + ÷ + t , .Y~ • ,,~-3E z '

+ + + + + + + ++ + + + + + + .++ + + + + ,o* . ++ * + + + + + + + + + + + + + + + + +

~ + +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + . . . . + ÷ + + +++++++++++++++++++.++÷++++.+++++++++++++++++++++++++++++ 550Ma

SBM.,,m__ Ft. j ~ Hd. ~ Sp. HS

. . . . . . . . ++++++,++++ + + , + ~ . . . . . . . . . . ~ , = ~ + + + y , ÷ , ~

Tb.n. ~¢__ ~ Bky. Gm.~j=~ IF. ..aL_.HS , Mp.

. . . . . +

Maur i . Tb.n:~m., ~ ~,L Bky. G m ~ ~ HS

Mp. Bg.

600Ma

660Ma

Maur i . Tim. SMB:.~. . ~ Tb. Mp. Gin. ~

Bs. Mk. To. Ba. ~ Gm, IF,

~ ~ 750Ma

® Mk, Tb. Ba. Gm. ~L ~')

.~= =--~ ~ . +~+ ~ ~ ~ - ~ - ~ . . . . ~ - ~ . . . . . . . ~ ~ ~ ~ i ~ I - - ~ " ~ ** ** ** + "~ "---:+ ÷+ . ~ ÷ ÷ , +÷, * 1000Ma

+++ + +++ + +÷ + + + + + + + ÷ + + + '+ + ++ + ÷ + + ÷

. . . . . . . . . . . . . . . . . . . . i+i+i . . . . . . . . .

M. Villeneuve, J.J. Corn?e /Precambrian Research 69 (1994) 307-326 321

Ma. The Pendjari Group of the Volta basin is the best example. Rift sedimentary series were ar- gued in the Bassaris ridge and parts of the Maur- itanide belt (Dupont et al., 1983; Villeneuve, 1984; Remy, 1987).

the tillites of the upper part of the "serie pourprre" (Moussine Pouchkine et al., 1988 ) and of the Tamale Group (Affaton, 1987 ) (T3), occurring between 520 and 480 Ma (comtemporary with the Youkounkoun Group).

3.2.3. Island-arc deposits Sedimentary rocks (andesites, greywackes,

cherts, etc.) were recorded from the Tilemsi (Pharusides) and Sahro (Anti-Atlasides) areas.

3.2.4. Aulacogen deposits A typical aulacogen sequence was studied in

the Gourma basin (Moussine-Pouchkine and Bertrand-Sarfaty, 1978 ). The Richat trough and the Madina-Kouta basin which are in a similar geodynamic context, do not present such a sequence.

3.2.5. Glacial-deposition records At least, three glacial periods can be distin-

guished during the Late Precambrian or Cam- brian times: (a) the Bakoye Group Tillites (TI) , deposited at ~ 660 Ma (680-640 Ma ?); this glacial episode was in a molassic context on the western part (Villeneuve, 1988; Deynoux et al., 1989 ), in a passive-margin context in the Volta basin (Affaton, 1987), and in an active-margin context in the Anti-Atlas area; (b) the Mali Group tillite (T2) which occurred between 620 and 570 Ma was in a marine epicontinental context on the western part (associated with jaspers and carbonates) and in an intramontanous context on the eastern part (Caby and Moussu, 1967; Fabre, 1982); according to Alvarenga (1990), the glacial sediments of the Paraguay belt (Bra- zil) are in a marine epicontinental context; (c)

3.2.6. Molassic deposits Different molassic stages have been evi-

denced. They are linked to the main tectonic events mentioned above: (a) the Tidiline and Anezi series representing the erosional stage of the B 1 tectonic event in the Anti-Atlas area (between 685 and 660 Ma); (b) the Taban and Bak- oye Groups representing the erosional stage of the Pan-African I tectonic event on the western margin (between 660 and 640 Ma); (c) the "serie pourprre", the Tamale Group (lower part) and the Precambrian III (Ouarzazate serie), respec- tively representing the molassic stages of the Pharusides, Dahomeyides and Anti-Atlas belts (between 600 and 550 Ma); (d) the Youkoun- koun Group, the Upper Tamale Group, the upper part of the "serie pourpr6e" (between 550 and 480 Ma).

3.3. Main geodynamical stages

According to these correlations we here propose five palaeogeographic sketch maps, show- ing some of the main important geodynamical steps of the West African craton evolution.

3.3.1. Palaeogeographical sketch map: ~ 700 Ma (Fig. 4)

The West African craton was surrounded by three main oceanic domains, on the eastern, northern and western parts. On the southwestern

Fig. 9. Cartoon reflecting the geodynamic evolution of the West African craton. From the bottom to the top we can see eight different stages: intracratonic stage, opening of the eastern oceanic domain, opening of the Bassaride rift, Pan-African I tectonic event (Bassarides and older Mauritanides belts), Eastern Pan-African belts, Lower Cambrian transgression, Pan-African II tectonic event (Rokelides), deposition of the Cambro-Ordovician sandstone blanket and connection with the lapetus Ocean. 1 = island arc domain; 2 = siliclastic marine deposits; 3 = molassic deposits; 4 = marine epicontinental sandstones with Scolithos; 5 = tillites or glacial deposits; 6 = calk-alcaline intrusions; 7= oceanic crust; 8 = continental crust. Mk. = Madina-Kouta basin; Tb. = Tarnbaoura basin; Ba. = Bamako area; Gm. = Gourma area; Bs. = Bassaris area; IF. = Iforas area; SMB. = Senegalese block; Mauri. =Mauritanian domain; Mp. =Mopt i trough; Tim. =Tilemsi Island Arc; Tb.n. =Taban basin; Bky. =Bakoye basin; Bg. = Bandiagara sandstones; HS= Hoggar shield; Ft. = Falrm6 trough; Hd. =Hodh basin; Sp. = srrie pourprre; Yk. = Youkounkoun basin.

322 M. Villeneuve, J.J. Corn~e / Precambrian Research 69 (1994,) 307-326

part it was connected to the Guyana shield. Or- ogenic island arcs were demonstrated on the northern and eastern margins. But the Anti-At- las presented a southward-dipping subduction zone, while the eastern margin presented an eastward-dipping subduction zone.

The West African craton itself was largely covered by sediments, particularly in its central part. Several types ofgeodynamic contexts can be distinguished: marine passive-margin platforms in the vicinity of the Anti-Atlas or Volta basin, aulacogen or continental trough in the Gourma, the Richat and the Mopti basins, rift in the Bassar- ide ridge, sag basins in the Hank, Tambaoura and Madina-Kouta basins.

Marine transgressions were running from the west in the Madina-Kouta basin (Villeneuve, 1984) and from the east in the Gourma aulacogen (Moussine-Pouehkine and Bertrand-Saffati, 1978).

The global tectonic regime was largely "extensive"; this being in contrast with a previous stable tectonic-period mainly represented by a thin carbonate platform (Bronner et al., 1980).

3.3.2. Palaeogeographical sketch map: ~ 650 Ma (Fig. 6)

Two separate orogens were demonstrated in this part of Africa: the southern Anti-Atlas orogen before 685 Ma and the Pan-African I orosen in the Bassaride (and Mauritanide belt) at ~ 650 Ma. In these two parts, some molassic-type sediments were deposited either in pull apart basins (Anti-Atlas or south Guinea) or in continental troughs (Senegal, north Guinea and Mali). We notice a large occurrence of volcanic rocks in the Anti-Atlas area. An oceanic domain still remains in the northern part of the Anti-Atlas area and it separated the Anti-Atlas Island Arc (Siroua- Sahro Island Arc) from a hypothetic northern continent (north Moroccan continent). The southward subduction produced the cale-alkaline rocks which fed the island arc.

On the eastern margin, sedimentation on the Iforas and Volta passive margin was still active. The Tilemsi Island Arc was still operating with deposition of tale-alkaline volcano-sedimentary rocks. Glacial deposits were identified in the

Volta basin, in the Anti-Atlas area, in southeast Mali and in north Guinea. The glacial formations of the Volta basin presenting the so-called "triade" association (tillites, silexites and carbonates rocks) were in a submarine environment, while those of the Anti-Atlas and Mauri- tania areas (without this typical association) were in a continental environment.

3.3.3. Palaeogeographical sketch map." 620-580 Ma (Fig. 7)

During this period, a Pan-African tectonic event occurred around 600 Ma (620-580 Ma) on the eastern margin. This event stopped the marine sedimentation (mainly in the Gourma aulacogen). Basins with molassic-type deposits occurred along this new belt particularly in the north of the Hoggar area and along the Transbra- ziliano lineament (TBFZ) in northeastern Bra- zil. TiUites were pointed out by Caby and Moussu (1967) in the northwestern Hoggar (srrie pourprre). At the same time a new tectonic event was recorded in the Anti-Atlas belt with a NE-SW compressional constraint on the eastern part and a N-S compressional constraint on the western part. This tectonic event seems to be related to the collision between the north Moroccan continent (CNM) and the Siroua-Sahro Island Arc. The talc-alkaline volcanic rocks related to the southward subduction turned into alkaline intrusions related to a crustal fusion process. Mo- lassic sediments were deposited in "pull-apart basins".

On the western margin, on the contrary, we observed the deposition of glaciogenic sediments then covered by argilites and sandstones ascribed to the Early Cambrian transgression. A N-S network of troughs occurred from the Mauritanide to Brazil. Glacial sediments from this period were also discovered in Liberia (Cul- ver and Williams, 1979).

So, the tectonic regime and consequently the behaviour of the western and eastern margins were completely different: compressive in the eastern and northern margins, extensive in the western margin.


3.3.4. Palaeogeographical sketch map: ~ 520 M a (Fig. 8)

A new belt occurred on the southwestern part, due to the northeastward moving of the Guyana and Amazonian shields. These belts are related to the closure of the Rokelide, Gurupi, Paraguay and Araguay intracontinental troughs. The thrusting of the Rokelide belt over the West Af- rican craton is well demonstrated in the Liberian Gibi Mountain klippen (Thorman, 1976 ) and in the central part of Guinea (Villeneuve, 1987). Geochronological investigations (Hurley et al., 1971; Cordani et al., 1984) pointed out an Early- Middle Cambrian orogen (550-520 Ma) along the Rokelide belt and along the Araguay belt and at about 520-504 Ma along the Gurupi belt. Mo- lassic formations from these belts were there deposited specially in the northern part (Youkoun- koun Group) where the Youkounkoun basin is filled up with 3000 m of red conglomeratic sandstones. South of the Reguibate shield, epicontinental scolitic sandstones were deposited. North of the Reguibat shield, the Adoudounian sea set- tled from the Zemmour area to the Ougarta area. A graben structure in the western part of the Anti- Atlas was reported by Villeneuve and Corn6e (1991 ). Many rhyolitic and granitic intrusions were pointed out in the Adoudounian formations. The Jbel Boho syenite, interbedded in the Adoudounian limestones, displays an age of 534_+ 10 Ma.

Molassic deposits with tillitic conglomerates were observed along the main N-S lineament in the Kandi fault zone (eastern side of the West African craton). These conglomeratic basins are linked to the Cambrian activity (565-535 Ma) of the main Pan-African lineaments. They fre- quently are associated with alkaline volcanics and granitic rocks (Nigerian and Cameroun young granites) emplaced at ~ 550 to 480 Ma. A foreland molassic basin exists on the top of the Volta basin (Tamale basin).

4. Conclusions

Comparisons between the evolution of basins and adjacent belts allow us to propose four pa-

laeogeographical schematic maps reflecting the evolution of the West African craton. Fig. 9 shows the diachronism between the Late Precambrian tectonic events occurring on both sides of the West African craton. These Pan-African events did not occur at the same time all around this craton. For example, the Bassarides and Roke- lides located on the western margin are respec- tively older and younger than the Pharusides and Dahomeyides located on the eastern margin. Consequently, the sedimentary environments (platform, aulacogen or molassic environments) of the foreland basins cannot be similar in the same period on both sides. So the correlation based upon lithologic similarities should be replaced by correlations supported by sedimentological investigations and geochronological data. In the same period (at ~ 650 Ma) molassic sediments were deposited on the western side, while a platform environment is still present on the eastern side of the West African craton. However, between 620 and 580 Ma, platform sediments were deposited on the western side, while some small molassic basins occurred along the eastern Pan-African belt. Later on (at ~ 520 Ma), a lot of molassic deposits covered both the eastern and western sides, while a marine epicontinental platform invaded the northern part of this West African craton.

The palaeogeographical sketch maps also underline the structural inheritance from the basement. )

References

Affaton, P., 1987. Le bassin des Volta (Afrique de l'Ouest): une marge passive d'~ge Proterozo'ique suprrieur, tecton- is6e au Panafricain (600_+ 50 Ma). Thrse Doc. Univ. Aix- Marseille III, Marseille, 462 pp.

Affaton, P., Rahaman, M.A., Trompette, R. and Sougy, J., 1991. The Dahomeyide Orogen: tectonothermal evolution and relationships with the Volta basin. In: R.D. Dall- meyer and J.P. Lecorche (Editors), The West African Or- ogens and Circum-Atlantic Correlatives. Springer-Verlag, Berlin, pp. 107-122.

Allen, P.M., 1969. Geology of part of an orogenic belt in western Sierra Leone, West Africa Geol. Rundsch., 58 (2): 588-620.

Almeida, F.F.M., Hasui, H., Brito Nieves, B.B. and Fuck, R.,

324 M. Villeneuve, J.J. Corn~e / Precambrian Research 69 (1994) 307-326

1981. Brazilian structural provinces. Earth. Sci. Rev., 17: 1-29.

Alvarenga, C.J.S., 1990. Phenom~nes sedimentaires, struc- turaux et circulation de fluides developprs ~ la transition chaine-craton. Exemple de la chaine Paraguay d'hge Pro- terozo'ique suprrieur, Mato Grosso, Brrsil. These Univ. Aix-Marseille III, Marseille, 250 pp.

Azizi Samir, M.R., Ferrandini, J. and Tane, J.L., 1990. Tec- tonique et volcanisme tardi-panafricains (580-560 Ma) dans l'Anti-Atlas central (Maroc): interprrtation grodynamique ¢t 1,rchelle du Nord-Ouest de l'Afrique. J. Afr. Earth Sci., 10: 549-563.

Bassias, Y., Wallbrecher, E. and WillgaUis, A., 1988. Tecton- othermal evolution of the late Panafrican orogeny in the Central Anti-Atlas (Southern-Morocco). In: J. Jacob- shagen (Editor), The Atlas System of Morocco---Contri- bution to its Geodynamic Evolution. Lect. Notes Earth Sci., 15: 43-59.

Bassot, J.P., 1966. Etude grologique du S~nrgal oriental et de ses confins guinro-maliens. Mem. Bur. Rech. Geol. Min., Paris, 40, 322 pp.

Bernardin, C., Cornre, J.J., Corsini, M., Mayol, S., Muller, J. and Tayebi, M., 1988. Variations d'rpaisseur du Cam- brien moyen en M~srta marocaine occidentale: signification grodynamique des donnres de surface et de subsur- face. Can. J. Earth Sci., 25 ( 12 ): 2104-2117.

Bertrand, J.M., Caby, R., Ducrot, J., Lancelot, J.R,, Mous- sine-Pouchkine, A. and Saadallah, A., 1978. The Late Panafrican intra-continental linear fold belt of eastern Hoggar (Central Sahara, Algeria), Precambrian Res., 7: 349-376.

Bertrand-Sarfaty,J., Moussine-Pouchkine, A., Affaton, P., Trompette, R. and Bellion, Y., 1991. Cover sequences of the West African Craton. In: R.D. Dallmeyer and J.P. Le- corche (Editors), The West African Orogens and Cir- cum-Atlantic Correlatives. Springer-Vedag, Berlin, pp. 65- 92.

Bessoles, B., 1977. Grologie de l'Afrique: le craton Ouest africain. Mem. BRGM, 88, 403 pp.

Bessoles, B. and Trompette, R., 1980. Geologic de l'Afrique. La chaine Panafricaine "mobile" de l'Afrique centrale et zone mobile soudanaise. Mem. Bur. Rech. Geol. Min., Paris, 92, 270 pp.

Bodinier, J.L., Dupuy, C. and Dostal, J., 1984. Geochemistry of Precambrian ophiolites from Bou Azzer, Morocco. Contrib. Mineral. Petrol., 87: 43-50.

Boullier, A.M., 1991. The Pan-African Trans Saharan Belt in the Hoggar shield (Algeria, Mali, Niger): a review. In: R.D. Dallmeyer and J.P. Lecorche (Editors), The West Afri- can Orogens and Circum-Atlantic Correlatives. Springer- Verlag, Berlin, pp. 85-105.

Bronner, G., Roussel, J., Trompette, R. and Clauer, N., 1980. Genesis and geodynamic evolution of the Taoudeni cratonic basin (Upper Precambrian and Paleozoic), West- ern Africa. In: A.W. Bally, A.L. Bender, T.R. McGetchin and R.I. Walcott (Editors), Dynamic of Plate Interior. Geodyn. Ser., Am. Geophys. Union, 1: 81-90.

Caby, R., 170. La chaine Pharusienne dans le NW de l'Ahag- gar. Thbse, Univ. Montpellier, Montpellier, 336 pp.

Caby, R., 1989. Precambrian terranes of Benin-Nigeria and Northeast Brazil and the Late Proterozoic South Atlantic fit. Geol. Soc. Am. Spec. Pap., 230: 145-158.

Caby, R. and Moussu, H., 1967. Une grande serie detritique du sahara. Bull. Soc. Geol. Fr., Paris, IX: 876-882~

Caby, R., Sial, A.N., Arthaud, M. and Vauchez, A,. 1991. Crustal evolution and the Brasiliano Orogeny in North- east Brazil. In: R.D. Dallmeyer and J.P. Lecorche (Edi- tors), The West African Orogens and Circum-Atlantic Correlatives. Springer-Verlag, Berlin, pp. 373-397~

Chariot, R., 1976. The Precambrian of the Anti-Atlas (Mo- rocco): a geochronological synthesis. Precambrian Res., 3: 273-299.

Chariot, R., 1982. Caractrrisation des 6vrnements 6bur- nrens et panafricains dans l'Anti-Atlas marocain, apport de la mrthode Rb/Sr. Th~se d'Etat, Univ. Rennes, 220 pp. (also: Notes Mrm. Serv. Grol. Maroc, 213:1-106 ).

Choubert, G., 1963. Histoire grologique du Prrcambrien de l'Anti-Atlas. Notes Mrm. Serv. Grol. Maroc, 162,352 pp.

Clauer, N., 1976. Grochimie isotopique du strontium des milieux srdimentaires. Application ~ la grochronologie de la couverture du craton ouest-africain. Sci. Grol, 45, 256 pp.

Clauer, N., Caby, R., Jeannette, D. and Trompette, R., 1982. Geochronology of sedimentary and meta-sedimentary rocks of the West-African craton. Precambrian Res., 18: 53-71.

Cordani, G.U., Brito Neves, B.B., Fuck, R.A., Porto, R. Thomaz Filho, A. and Bezzera da Cunha, F.M., 1984. Es- tudo Preliminar de Integragao do Pre Cambriano com os Eventos Tectonicos das Bacias Sedimentares Brasileiras. Petrobras, Rio de Janeiro, 70 pp.

Corsini, M., Vauchez, A., Archanjo, C. and De Sa, E.F.J., 199 t. Strain transfer at continental scale from a transcur- rent shear zone to transpressional fold belt: the Patos- Serido system, northeastern Brazil, Geology, 19: 586-589.

Culver, S.J. and Williams, H.R., 1979. The late Precambrian and Phanerozoic geology of Sierra-Leone. J. Geol. Soc. London, 136: 605-618.

Culver, S.J., Pojeta, J., Repetzki, J.E. and Robineau, B., 1988. Signification stratigraphique des fossiles du Cambrien in- frrieur dans le bassin de Taoudeni h la frontibre Guinre- Srnrgal. C.R. Acad. Sci., Paris, 307:651-656.

Culver, S.J., Williams, H.R. and Venkatakrishnan, R. 1991. The Rokelide orogen. In: R.D. Dallmeyer and J.P. Le- corche (Editors), The West African Orogens and Cir- cum-Atlantic Correlatives. Springer-Verlag, Berlin, pp. 123-150.

Dallmeyer, R.D. and Lecorchr, J.P., 1989.4°Ar/39Ar polyor- ogenic mineral age record within the central Mauritanide orogen, West Africa. Geol. Soc. Am. Bull., 101: 55-70.

Dallmeyer, R.D. and Villeneuve, M., 1987. 4°Ar/39Ar po- lyorogenic mineral age record of a polyphase tectonothermal evolution in the Southern Mauritanide orogen, southeastern Senegal. Geol. Soc. Am. Bull., 98:602-611.


Destombes, J., Hollard, H. and Willefert, S., 1985. Lower paleozoic rocks of Morocco. In: C.H. Holland (Editor), Lower Paleozoic Rocks of the World. Wiley, New York, N.Y., pp. 91-336.

Deynoux, M., 1971. Essai de synth6se stratigraphique du bassin de Taoudeni (Prrcambrien suprrieur et Palroz- oique d'Afrique occidentale), Trav. Lab. Sci. Terre, St- Jrr6me, Marseille, B, 3, 71 pp.

Deynoux, M., 1980. Les formations glaciaires du Prrcam- brien terminal et de la fin de l'Ordovicien en Afrique de l'Ouest. Trav. Lab. Sci. Terre, St. Jrr6me, Marseille, B, 17,554 pp.

Deynoux, M., Sougy, J. and Trompette, R., 1985. Lower Pa- leozoic rocks of West Africa and the western part of central Africa. In: C,H. Holland (Editor), Lower Paleozoic Rocks of the World. Wiley, New York, N.Y., pp. 337-495.

Deynoux, M., Kocurek, G. and Proust, J.N., 1989. Late Pro- terozoic periglacial aeolian deposits on the West African Platform, Taoudeni Basin, Western Mall, Sedimentology, 36: 531-549.

Ducrot, J., 1979. Datation h 615 Ma de la granodiorite de Bleida et consrquences sur la chronologie des phases tec- toniques, mrtamorphiques et magmatiques panafricaines dans l'Anti-Atlas marocain. Bull. Soc. Grol. Fr., 7, 21: 495-499.

Dupont, P.L., Villeneuve, M. and Lapierre H., 1984. Mise en 6vidence de religues ocraniques au sein de la chaine panafricaine des Mauritanides dans la rrgion des Bassaris (Guinre-Srnrgal). C.R. Acad Sci., Paris, 299, I1(2 ): 65- 70.

Fabre, J., 1982. Pan-African volcano-sedimentary formations in the Adrar des Iforas (Mali). Precambrian Res., 19: 201-214.

Hassenforder, B.. 1987, La tectonique panafricaine et var- isque de l'Anti-Atlas dans le massif du Kerdous (Maroc). Thbse Doctorat d'Etat, Universit6 Louis Pasteur, Stras- bourg, 198 pp.

Herz, N., Hasui, Y., Sena Costa, J.B. and Da Silva Matta, M.A., 1989. The Araguay fold belt, Brazil: a reactivated Brasiliano-Pan-African cycle (550 Ma) geosuture. Pre- cambrian Res., 42:371-386.

Hurley, P.M., Leo, G.W., White, R.W. and Fairbairn, H.W., 1971. Liberian age province (about 2700 Ma) and adjacent provinces in Liberia and Sierra-Leone. Geol. Soc. Am. Bull., 82: 3483-3490.

Jeannette, D. and Tisserant, D., 1977. Les 6pisodes tecto- niques et intrusifs du prrcambrien suprrieur de l'Anti-At- las occidental. Estud. Geol. Madrid, 33: 315-326.

Jeannette, D., Benziane, F. and Yazidi, A., 1981. Lithostra- tigraphie et datation du Protrrozo'ique de la boutonniere d'Ifni (Anti-Atlas, Maroc). Precambrian Res., 14: 363- 378.

Kurek, S. and Priedl, M., 1987. Le Precambrien des cha]nes d'Ougarta (Sahara Algrrien), sa place dans la structure de l'Afrique du Nord-Ouest. Curr. Res. In: J. Matheis and S.J. Schandelmeir (Editors), African Tectonics. Bal- kema, Rotterdam, pp. 61-68.

Leblanc, M., 1975, 1981. Ophiolites precambriennes et gites d'arsenics et de cobalt, Bou Azzer, Maroc. Thrse d'Etat, Paris 330 pp. (Also: Notes Mrm. Serv. Grol. Maroc, 280, 306 pp. )

Leblanc, M. and Lancelot, J.R., 1980. Interprrtation grodynamique du domaine Panafricain (Prrcambrien terminal ) de l'Anti-Atlas (Maroc) h partir des donnres grologiques et grochronologiques. Can. J. Earth Sci., 17:142-155.

Lesquer, A., Beltrao, J.F. and De Abreu, F.A.M., 1984. Pro- terozoic links between northeastern Brazil and West Af- rica; a plate tectonic model based on gravity data. Tecton- ophysics, 110 ( 1-2): 9-26.

Midfal, A. and Peucat, J., 1985. Datation U/Pb et Rb/Sr du volcanisme acide de l'Anti-Atlas marocain et du socle sous- jacent dans la rrgion de Ouarzazate. Apport au probl~me de la limite Prrcambrien/Cambrien. Sci. Grol. Bull., Strasbourg, 38 (2): 185-200.

Moussine-Pouehkine, A. and Bertrand-Sarfati, J., 1978. Le Gourma: un aulacogene du Prrcambrien superieur? Bull. Soc. Grol. Fr., 7, XX, 6: 851-857.

Nascimento, D.A., Gava, A., Pires, J.L. and Teixeira, W., 1981. Projeto RADAM, Brasil. 21 folha 24 (Fortaleza). Minist. Minas, Energ. Dep. Nac. Prod. Miner. Geol., Sao Paulo, 483 pp.

Remy, P., 1987. Le magmatisme basique des Mauritanides centrales: une ouverture ocranique limitre d'~ge Protrr- ozo'ique suprrieur en Afrique de l'Ouest. Th6se, Univ. Nancy I, Nancy, 281 pp.

Rocci, G., Bronner, G. and Deschamps, M., 1991. Crystal- line basement of the West African crazon. In: R.D. Dall- meyer and J.P. Lecorche (Editors), The West African Or- ogens and Circum-Atlantic Correlatives. Springer-Verlag, Berlin, pp. 31-61.

Saquaque, A., Admou, H., Karson, J.A., Hefferan, K. and Reuber, I., 1989a. Precambrian accretionary tectonics in the Bou Azzer-E1 Graara region, Anti-Atlas, Morocco. Geology, 17:1107-1110.

Saquaque, A., Admou, H., Cisse, A., Benyoucef, A.H. and Reuber, I., 1989b. Les intrusions calco-alcalines de la boutonnirre de Bou Azzer-El Graara (Anti-Atlas, Maroc): marqueurs de la drformation majeure panafricaine dans un contexte de collision d'arc. C. R. Acad. Sci., Paris, II, 308: 1279-1283.

Saquaque, A., Benhareff, M., Abia, H., Mrini, Z., Reuber I. and Karson, J.A., 1992. Evidence for a Panafrican volcanic arc and wrench fault tectonics in the Jbel Saghro, Anti-Atlas, Morocco. Geol. Rundsch., 81: 1: 1-13.

Schermerhorn, L.J.G., Wallbrecher, E. and Huch, K.M., 1986. Der Subduktionskomplex, Granitplutonismus und Scher- tektonik im Grundgebirge des Sirwa-Doms (Anti-Atlas, Marokko). Berl. Geowiss. Abh., 66: 301-332.

Sougy, J., 1962. West African fold belt. Geol. Soc. Am. Bull., 73(7): 871-876.

Sougy, J., 1964. Les formations palrozoiques du Zemmour noir (Mauritanie septentrionale). Etude stratigraphique, prtrographique et palrontologique. Ann. Fac. Sci. Univ. Dakar, 15, 679 pp.

326 M. Villeneuve, J.J. Cornde / Precambrian Research 69 (1994) 307-326

Thorman, C.H., 1976. Implications of klippen and a new sedimentary unit at Gibi Mountain, Liberia, West Africa, in the problem of Pan-african-Liberian age province boundary. Geol. Soc. Am. Bull., 87: 851-856.

Trompette, R., 1973. Le Prdcambrien supdrieur et le Pal6oz- clique inf6rieur de rAdrar de Mauritanie (bordure occidentale du bassin de Taoudeni, Afrique de l'Ouest). Un exemple de s6dimentation de craton. Etude stratigraphique et s6dimentologique. Tray. Lab. Sci. Terre, St-Jdr- 6me, Marseille, B, 7, 702 pp.

Trompette, R., 1988. Structural evolution and glacial events during Middle and Upper Proterozoic times in Brazil. Earth Glacial Record, 1988 Meeting, Cuiaba, Mato Grosso, pp. 19-23.

Villemur, J.R., 1967. Reconnaissance g6ologique et structur- ale du Nord du bassin de Taoudeni. Mdm. BRGM, 51, 151 pp.

Vfllcncuve, M., 1984. Etudc gdologiquc dc la bordure SW du Craton Oucst africain, Th~se Doctorat d'Etat, Universit6 Aix-Marscillc III, MarsciUe, 552 pp.

ViUcneuve, M., 1988. Evolution comparde du bassin de Taoudcni et de la chainc des Mauritanidcs cn Afrique de l'Oucst. C.R. Acad. Sci., Paris, II, 307: 663-668.

Villeneuve, M., 1989. The geology of the Madma-Kouta basin (Guinde-Sdndgal) and its outcomings on the geodynamic evolution of the western part of the West African craton during the upper Proterozoic period. Precambrian Res.. 44: 305-322.

Villeneuve, M. and Dallmeyer, R.D,, 1987. Geodynamic evolution of the Mauritanides, Bassarides and Rokelides orogens (West Africa). Precambrian Res., 37:19-28.

Villeneuve, M. and Corn6e, J.J., 1991. Evolution paleogeo- graphique de la marge nord ouest de rAfrique, du Cam- brien/t la fin du Carbonif'ere (du Maroc au Libdria). Can. J. Earth Sci., 28:1121-1130.

Villeneuve, M., Bonvalot, S. and Albouy, Y., 1990. L'agence- ment des chalnes (Panafricaines et Hercynienne) de la bordure occidentale du craton ouest africain. C.R. Acad. Sci., Paris, II, 310: 955-959.

Wallbrecher, E., 1988. A ductile shear zone in the Panafrican basement on the northwestern margin of the West-Afri- can craton (Siroua dome, Central Anti.Atlas). In: V. Ja- cobshagen (Editor), The Atlas System of Morocco-- Contribution to its Geodynamic Evolution. Lect. Notes Earth Sci., 15: 19-42.

Documents

West African Craton