International Journal of Geosciences, 2012, 3, 153-165
http://dx.doi.org/10.4236/ijg.2012.31017 Published Online February 2012 (http://www.SciRP.org/journal/ijg)
Structural Evolution of a Precambrian Segment: Example
of the Paleopro t erozoic Formations of the Mako Bel t
(Eastern Senegal, West Africa)
Mahamadane Diene1*, Mamadou Gueye1*, Dinna Pathé Diallo2, Abdoula ye Dia2
1Institut des Sciences de la Terre, Université Cheikh Anta Diop, Dakar, Senegal
2Departement de Géologie, Université Cheikh Anta Diop, Dakar, Senegal
Received November 15, 2011; revised December 26, 2011; accepted January 28, 2012
ABSTRACT
The western part of the Kedougou Kenieba Inlier is located in the West African Craton. It consists of paleoprotero zoic
NE-trending elongate belts (subprovinces) of metavolcanic and gran itic rocks that alternate with metasedimentary belts.
Major linear fault such as the MTZ which also approximate a north-easterly trend form the eastern boundaries. The field
observations and geophysics analyses were completed by a microscopic study. Based on these data we define across
this region four lithostruc tural do mains from east to west. Th e western domain is stru cturally complex. The rocks of this
domain have been subjected to a complex history of polyphase deformation and metamorphism. The structural analyse
allow us to distinguished three deformation events. The deformation results in the formation of D1 thrust tectonic and
D2 and D3 transcurrent tectonic. The structural evolution of the Mako Belt is characterized by deformation dominated
by the intrusion of large TTG batholiths (D1) followed by basins formation and transpression accommodating oblique
convergence an d collision (D2 and D3). The chang e from thrusting (D1 deformation to transcurrent motion (D2 and D3)
is recorded in the marginal basin of the central domain and in Tinkoto pull apart basin. The timing of these basins indi-
cates a diachronous evolution. Deformation styles within the basin are compatible with a dextral transpression which
terminated at ca 2090 Ma. Small extens ional basins formed over the rocks of the Mako Belt are filled with contin ental
detrital sedimentary rocks that show weak foliatio n and active felsic volcanism. We suggest that the sinistral transpres-
sive tectonic associated with oblique subduction may have generated the pull-apart basin and subaqueous volcanism. In
part these features are now related to terrain accretion, thrusting and strike slip movement during oblique convergence.
The inversion of the large scale structural evolution from thrusting to strike slip is common to modern orogenies.
Keywords: Kedougou Kenieba Inlier; Paleoproterozoic; Transpression; Mako Belt; Oblique Convergence; Collision;
Thrusting; Transcurrent
1. Introduction
Paleoproterozoic orogenic belts are the product of defor-
mation, metamorphism, and plutonism. Compilation of
structural data with petrologic and geochronological in-
formations is essential to unravel th eir evolution . Various
studies on these granite-greenstone terrains of the West
African Craton (WAC), using geochemical and isotopic
data have been carried out in the last decade (Bassot [1],
Dia [2], Abouchami et al., [3], Boher et al., [4], Ndiaye
et al., [5], Dia et al., [6], Pawlig et al., [7], Gueye et al.,
[8]). However the structural data and their role in the
evolution of the Paleoproterozoic orogenic belts are still
quite scarce in WAC, particularly in Senegal.
Knowledge of the timing of structural evolution of vol-
cano-plutonic belts is fundamental for the understanding
of the tectonic evolution of paleoproterozoic terrains of
the WAC.
The aim of this paper is to constrain the structural evo-
lution of the volcanic and plutonic belts of the Kedou-
gou Kenieba Inlier (KKI) particularly the Mako Belt
(MB) which lies at the western margin of the KKI.
We present a new interpretation of the paleoprotero-
zoic tectonic evolution of th e Mako Belt integrating geo-
physical data with detailed geological studies.
2. Geological Setting
2.1. The KedougouKenieba Inlier (KKI)
The lower Proterozoic KKI (Figure 1) lies between the
Taoudeni basin in the east and the senegalo-mauritanian
basin in the West. It is composed of NE-trending elon-
gate belts of metavolcanic and granitic rocks that alter-
nate with metasedimentary belts.
*Corresponding author.
C
opyright © 2012 SciRes. IJG

M. DIENE ET AL. 154
Figure 1. The Birimianterrane of the West African Craton (WAC) with the position of the Kedougou-Kenieba Inlier (KKI).
Geological map of Kedougou-Kenieba inlier. Modified after Peucat et al., 2005, Bassot, 1966; Ledru et al., 1989.
In the KKI two supergroups are represented (Bassot,
[1]):
 In the west the Makosupergroup of submarine volca-
nics, pyroclasti cs and pl utonic rocks
 In the east the Diale-Dalemasupergroup consisting of
metasediments with intermediate volcanics and hy-
byssal rocks.
The KKI features a series of NE-SW trending faults
with alternating high and low strain zones. Bertrand et al.,
[9] recognized the polycyclic character of the tectonic
evolution and place the Mako supergroup at the base
(lower Birimian). Milesi et al., [10] and Ledru et al., [11]
agree on the polycyclic character. The classical lithology
was revised by the application of geochemical data
(Bassot [1], Dia [2], Abouchami et al., [3], Pawlig et al,
[7]) which puts the volcanic series in a stratigraphically
lower position in reference to Archean greenstone belts
assemblage which are apparently very similar.
The tectonic evolution of the KKI isnot completely
documented, but three major tectonic events called D1
and D2 - D3 have been defined (Milési et al., [12]; Ledru
et al., [11]). The major D1 tectonic episode, which occur-
red around 2112 Ma to 2100 Ma (Feybesse et al., [13]
and [14]), is attributed to collisional tectonics between
archean and proterozoic domains. This phase was consi-
dered to be one of the principal criteria for distinguishing
B1 (Lover Birimian affected by thrusting D1) from B2
(Upper Birimian affected by only two later phases trans-
current deformations D2 and D3). It was associated to
deformation dominated by the intrusion of large batho-
liths.
The D2 and D3 phase interpreted as being between
2096 Ma and 2073 Ma, and consequently the duration of
the entire Eburnean deformation was thought to have

M. DIENE ET AL. 155
been 40 Ma (Feybesse et al., [13]). The D2 phase was
interpreted as transcurrent deformation along a network
of ductile shear zones (Milesi et al., [12], Ledru et al.,
[15]) and corresponds to transpression accommodating
the emplacement of the Laminia Kaourou Plutonic com-
plex (LKPC) (Gueye, [16]). It has been long postulated
that the elongated shape of most of the intrusions was
due to syntectonic emplacement in relation with the ac-
tivity of the shear zones (Pons [17], Gueye et al. [18]).
Two geodynamic env ironments for the Birimiantholeiitic
rocks have been proposed, either an intra-oceanic island-
arc setting (Zonou [19]; Dia [2]; Sylvester and Attoh [20],
Ama-Salah et al. [21], Pawlig et al. [7]) or an oceanic
plateau setting (Abouchami et al. [3]; Boher et al. [4];
Pouclet et al. [22]).
2.2. The Mako Belt (MB)
The paleoproterozoic Mako Belt lies at the western mar-
gin of the KKI. The belt consists of greenschist to lower
amphibolite facies sedimentary and volcanic successions
and associated granitic and mafic intrusions. The granite
plutons, including the Diombalou pluton in the north, the
Lay ered Plutonic Complex and the Laminia Kaourou Plu-
tonic Complex in the west, the Falombo and Bouroum-
bourou plutons in the centre and the Tinkoto pluton in
the south are composed mainly of deformed I-type gran-
ites and undeformed leucogranites. Mafic intrusions con-
sists of gabbros and dolerites most of which have been
metamorphosed to greenschist and amphibolite facies al-
though igneous texture (ophitic texture) are preserved.
Available geochronological data show that most of the
sediments and volcanic successions and granite in the
MB formed in the period 2200 - 2000 Ma and were me-
tamorphosed and deformed at 2100 Ma based on the bio-
tite 40 Ar/39 Ar age of 2100 Ma from the Badon granite,
interpreted as a metamorphic age (Gueye et al, [8]). A
post tectonic rhyolite that intrude the upper sequence of
the MB yields a Pb/Pb zircon age of 2056 Ma, which
provides a minimum age for the belt.
The Mako belt has a dominant NE-SW structural trend,
which deflects to an N-S direction in the north. The sha-
pe of the NE-trending greenstone belts is at least in part
controlled by a network of anatomising N to NE-trending
lineaments and shear zones. These form the boundaries
of the rock units and divide it into corridor or domains.
The major terrain boundary is d efined as fault zone. Two
main episodes of volcanism have been recognized in the
Belt:
 An older succession consisting of pillow basalts;
 A younger succession consisting of massive volcanic
rocks.
The older contain interlayered komatiite and tholeiitic
and high-Mg basalts. Pillowed and massive basalts are
interlayered with co-magmatic layered mafic sills. Green-
stone succession to the east of the belt contains interlay-
ered tholeiites with associated volcaniclastic rocks. The
calcalkaline volcanic sequences range from basalts to rh-
yolites, although predo minantly andesites and dacites.
Granitoids in Mako Belt fall into one of three catego-
ries: gneissic and intrusive complexes (Sandikounda and
Badon), diapiric (syntectonic) plutons of variable compo-
sition Diombalou, Bouroumbourou, Falombo), late gran-
itic plutons and rhyolite (Tinkoto, Mamakono).
Gneissic complexes and batholith which are dominan-
tly tonalitictrondhjemite and granodiorite so-called TTG
suite compose most of preserved paleoproterozoic crust.
Most granite and felsic volcanics are genetically related.
Detailed studies (Dia et al., [6]; Pawlig et al., [7]) of the
geochemistry of the Mako belt have demonstrated that
the plutons are calcalkaline and metaluminous. Pb-Pb
zircon age determination (Gueye et al., [8]) gives an age
range between 2200 and 2070 and indicates the absence
of older crustal material.
3. Structural and Kinematic Analysis within
the Mako Belt: New Results
Regional deformation in the KKI is diffusely accommo-
dated by ductile to ductile-brittle strike slip shear-zones,
lateral thrusts and isoclinal folds along the Mako Belt.
Deformation within the Mako Belt is fo und to be strong-
ly partitioned into shear zon es, which are unevenly distri-
buted across the area. Sinistral strike-slip fault systems in
the MB, with the NE-SW and N-S trending Main Trans-
current Zone (MTZ) and LeobaMoussala faults (LMFZ)
respectively, are the most noteworthy features dominate.
These fault zones acco mmodate strain localization and are
responsible for complex fold interference patterns and are
also associated with the emplacement of granitic plu tons.
They separate blocks with distinct structural-metamorphic
histories. Many authors have suggested a genetic relation-
ship between faults (or shear zones) and magmatism (Gue-
ye et al. [18], Pons [17]).
The Mako Belt displays a prominent N-S and NE-SW
structural trend resulting from regional NE to N-trending
folds with axial planar schistosity that is characteristic of
the belt. This schistosity (Figure 2) displays local varia-
tions in strike and dip which are attributed to either ob-
lique fault crosscutting the regional trend or deformation
aureole around resistant plutonic suites, although in gene-
ral steeply-dipping fabrics are p revalent in the Mako Belt.
Shallow dipping fabrics are recorded and are often rela-
ted to late thrusting. The belt-wide fold pattern that cor-
responds to a series of N-trending synclines, is occupied
by the sedimentary basins and anticlines which are gene-
rally cored by plutons. The first generations of structures
we recognize are a series of gently to steeply-plunging
mesoscopic folds, which are pervasive through the pillows
and are sometimes difficult to identify becaus e they have
been transposed, dismembered, or refolded (Figure 3).

M. DIENE ET AL. 156
Figure 2. Foliation trajectories within the Mako Belt. (MTZ: main transcurrent zone; SSZ: Sabodala shear zone; BNZS: Ba-
don-Niéniéko shear zone; YTZ: Yaaka transcurrent zone; LMSZ: Léoba-Moussala shear zone).
Figure 3. Photographs showing some example of superposed folds in the pillowed lavas. A: Superposed folds; B: Sheath fold;
C and D: Pillow transposed in the foliation plane.

M. DIENE ET AL. 157
3.1. The Main Tectonic Events
Three principal episodes of ductile to semi-ductile ebur-
nean deformation have been recognized in the studiedarea.
Macro-, meso- and microstructures within the belt can be
described in terms of D1, D2 and D3 deformational epi-
sodes.
3.1.1. The D1 Phase
The oldest deformation structures (D1) are preserved in
xenoliths within the undeformed parts of the Sandikoun-
da Layered Complex, the second oldest recognised intru-
sive component of the Mako Belt. In this area, thrusting
SE-verging deformation took place and is characterized
by a series of imbricate banded gneisses, volcaniclastics
and volcanic rocks dipping 40˚NW, with asymmetric
folds. Thrusting is post dated by the emplacement of the
Sandikounda Layered Plutonic complex (SLPC), placing
a tight constraint of 2160 - 2140 Ma (Dia et al., [6] ).
The preservation of flat lying thrusts in greenstone
belts is rare because thrusts are commonly refolded into
tight upright orientations due to subsequent shortening.
Features suggesting that the Sandikounda Fault is a
thrust, are well developed in the Tonkoutou area. Dip pa-
rallel stretching lineations are present. Schematic geolo-
gical cross-section NW-SE in this area (Figure 4), shows
a stacking of units to high grade metamorphism formed
by amphibolo-gneiss, on weakly metamorphic units formed
by the metabasalts, the volcaniclastic and layered pluto-
nic complex. The relationship between the foliation and
lineation, as well as recumbent folds, shows a th rust ch a-
racter with a SE-verging which would have affected the
lithological stack in this sector of Sandikounda.
This style characterizes a thrust deformation and is ob-
servable in this sector of Sandikounda.
However, some features of this thrusting, were affected
by subsequent phases of deformation but also by the phe-
nomena affecting migmatization amphibolites which are
due probably by the large heat flow accompanying the
introduction of the layered plutonic complex.
The reverse component of movement, deduced from
the juxtaposition of high er grade metamorphic rocks over
lower-grade metamorphic rocks changes the structural
interpretation of the area.
Figure 4. Schematic cross-section showing the tectonic contact between the Sandikounda amphibologneiss complex and the
metabasalts in Sandikounda area. Photograph in vertical se ction shows the superposed folds.

M. DIENE ET AL. 158
3.1.2. The D2 Phase
The NW-SE compression event, which we will name D2
in accordance with the classical terminology (Milési et
al., [12]; Ledru et al., [11]; Feybesse et al., [13]), is un-
doubtedly responsible for the map scale structures. N to
NE-trending structures developed in the shear zone dur-
ing D2 as the result of sinistral shear, are partially affec-
ted by late deformation. The D2 phase is characterized
by a NE-SW to N-S subvertical foliation associated with
assymmetric folds and astretching lineation parallel to
the axial planes of the fold. The stretching lineation plun-
ges gently (subhorizontal) or more steeply in the strike-
slip fault.
The D2 structures have been interpreted as the result of
eburnean NW-SE horizontal shortening in a transpressive
regime under amphibolite facies condition (Gueye [16]).
The predominantly transpressional regime represents a
major change in tectonic style in the Mako Belt. Steep
sinistral strike slip shear zones were produced during th is
D2 transpressional stage.
3.1.2. 1. Transcurren t Fau l t s
The north east trending faults: example of the Main Tran -
scurrent Zone (MTZ)
The 125 km wide MTZ (Figure 5) of SE Senegal and
Mali formed as a result of transcurrent motion between
two major crustal blocks namely Mako and Diale-Dale-
ma. Previously this shear zone was considered to be a
continuous lineament but our recent structural studies
show that it is divided into northern and southern bran-
ches. Ductile deformation is reflected in tight folding
with steeply dipping foliation.
Numerous structural signatures (shear sense indicators)
were identified along the strike of the MTZ, ranging
from dextral strike slip in the southern segment (Figures
6(b)-(c)) of the fault zone to sinistral strike slip in the
Malian part (Figure 6(a) ). The fault is composed of bands
of higher shear strain alternating with lower strain domains.
Figure 5. Structural map of the Mako Belt showing the position of the main faults zones MTZ and LMFZ. Stereoplots show-
ing the main NE and N-trending mylonitic foliation.

M. DIENE ET AL. 159
Figure 6. Photographs in vertical section and photomicrographs showing some example of shear sense indicators such as ob-
served along the MTZ and the LMFZ. (a) S-shaped fold which affects the mylonitic foliation of the MTZ; (b) and (c): Sedi-
mentary units of the MTZ displaying delta-shape structure that indicate sinistral sense of movement; (d) and (e) Mica fish
and delta-shaped clast indic a ting sinistr al se nse of movement along the LMFZ.
3.1.2.2. North-South-Trending Faults: Example of the
Leoba Moussala Fault Zone (LMFZ)
The LMFZ (Figure 5) represent a major N-trending shear
zone located in the central zone of the Belt. It is charac-
terized by the development of sinistraltranscurrent shear
sense indicators (Figures 6(d)-(e)) (e.g. Gueye [16]).
The fault features a wide deformation zone with a perva-
sive subvertical mylonitic fabric and a sub horizontal stre-
tching lineation. Shear sense indicators indicate sinistral
sense of movem ent .
The stretching lineation, which developed in coarsely
clastic rocks, has a pronounced oblate geometry, indicat-
ing significant flattening strains. The geometrical rela-
tionship between the shear sense indicators and stretch-
ing lineation is generally interpreted to be the product of
transpressional shear, a regime of shear zone boundary
parallel transcurrent movement accompanied by a large
amount of shear-zone-normal stretching. The timing of
the shear movement within the LMFZ is constrained by
the crystallization of the Kaourou monzogranite at 2130
Ma (Gueye [16]).
3.1.3. The Late Phase D3
The main structures of this phase are found in the Mako
Belt in the Sonkounkou and Kossanto area. They comprise
dextral transcurrent to slightly oblique well-developed

M. DIENE ET AL. 160
greenschist facies shears with consistently west-plunging
stretching lineations. Locally D3 produces minor asymme-
tric Z folds. D3 asymmetric fold axes ten d to be collin ear
with the D2 stretching lineation. Brittle-ductile to brittle
structures, including the dominantly 060˚ - 070˚-trending
crenulation cleavage, kink sets and dextral –070˚ - 080˚-
trending faults and asymmetric folds overprint the above
dextral greenschist facies shear but fit the same NW-SE
compressional framework. We interpret the structures to
have developed during one continuous phase of NW-SE
compression and oblique convergence. Absolute age con-
straints for this phase are not available, but it postdates
the intrusion of the Mamakono, Tinkoto and Saraya plu-
tons (age rang e between 2080 and 2070 Ma).
4. Tectonic Subdivisions of the Mako Belt
Recent works provide a significant amount of new struc-
tural metamorphic, geochemical and geochronological
data constraining the geodynamic evolution of the Mako
belt (Bassot [1], D ia [2], Abouchami et al., [3], Pawlig et
al., [7]). We propose a new definition of the lithotectonic
units and distinguish from west to east: many basaltic
segments are distinguished in the plutonic-volcanic com-
plex and correspond to the Sandikounda, the Sabodala
and the Mako segments; marginal basins and pull-apart
basins (Figure 7).
4.1. The Plutonic-Volcanic Complex
It forms a narrow band of magmatic and metamorphic
rocks. It is best exposed within the Badon-Sandikounda
area. The meta-lavas range in composition from basalt to
rhyolite but are dominated by dacite and andesite in the
southern domains. The volcanic, volcanoclastic sequence
is intruded by various dykes, sills of trondhjemites and
metagabbros. Metamorphic conditions grade from greens-
chistfacies in the southern part of the domain to amphi-
bolite and granulite facies and local anatexis in the San-
dikounda area (Gue ye et al., [18]).
Sandikounda Segment
The Sandikounda segment is considered to be an oceanic
arc island composed of tholeiitic basalts overlain by a ma-
fic-to-felsic volcanic calc alkaline sequence. Maficultra-
mafic massive, pillowed and volcanoclastic rocks are hi-
ghly strained.
The western margin is a fault contact against uplifted
basaltic basement, whereas the eastern margin is a fault.
The eastern margin is more structurally complex and linea-
tion and folds are indicative of t wo fold sets at high angles.
Clast elongation in the vo lcanoc lastic rock s of the San-
dikounda area in the footwall also have NW plunges, the-
reby suggesting that folds in the hanging wall have been
Figure 7. Major divisions in the Mako Belt.

M. DIENE ET AL. 161
rotated. Total X/Z strain states calculated from rounded
volcanic elements range from 4:2 in the hanging wall
volcanoclastics. These features are indicative of thrusting
of the gneiss over the volcanic succession.
4.2. The Marginal Basins
These basins occupy a marginal position with respect to
the plutonic-volcanic complexes and are filled by turbid-
ites derived from volcanic-volcanoclastic rocks. They are
composed of volcanic, volcanoclastic sequences intruded
by abundant plutonic rocks. The metavolcanics of these
basins are dominated by intermediate to felsic rocks.
They are characterized by breccia and coarse pyroclastics
sequence, which grade into finer grained tuff and epi-
clatites interlayered with cherts and carbonates. Closure
of the basins accommodates the emplacement of the cal-
calkaline plutons (Bouroumbourou and Diombalou). Me-
tamorphism is characterized by widespread greenschist
to amphibolite facies conditions with local anatexis near
the plutons. Crystallization of andalusite porphyroblasts
is limited to graphitic sequence in the vicinity of the
Bouroumbourou pluton. The low pressure and intermedi-
ate temperature metamorphism suggested by this assem-
blage are consistent with widespread contact metamor-
phism related to intrusion of plutonic rocks.
However, we have some sedimentary units dominated
by the flysch of the Sonkounkou formation. The schists
of the Soreto formation consist of flysch-like sediment-
tary sequences characterized by folded rhythmic alterna-
tions of graded greywackes-sandstone and tuff layers.
The basins were mainly filled with minor greywacke
and flysch-type sediments containing minor intercalations
of basic and acid volcanic rocks. The basins are thus in-
terpreted as flysch (foreland basins).
4.3. The Pull-Apart Basins
We found these basins to the north (Diombalou Basin) and
the south (Tinkoto basin)
4.3.1. Diombalou Basin
The Diombalou Basin is a lozenge shaped basin deline-
ated by faults. From the base to the top the sedimentary
pile is made of arkosic sandstones including larges lenses
of conglomerates, sandstone and shale, lava and pyroclas-
tic flow are interbeded in the lower part of the pile. Most
of the lavas are andesities. A few lavas are andesitic da-
cites. All the formations were affected by upright folding
and shearing along NE-SW transcurent shear zone corri-
dors. Some small pluton of biotite granite intruded the
deeper part of the basin, while a huge batholith of leu-
cogranite was emplaced on the western side.
Thermal metamorphism of the peliticshales produced
hornfels at the granite contact and staurolite and kyani-
teschists in the neigh bouring zone. Volcan ic and esitic ac-
tivity is coeval with basin formation (Fouldé).
4.3.2. Tinkoto Basin
Within the Tinkoto area (Figure 8), sedimentary rocks for-
med a lozenge shaped entity delineated by faults. Pull-
apart basin d ev elop ed within c alk -alk al in e ma g matis m an d
metamorphism localized within the fault zone. This was
followed by a phase of compression. The Tinkoto basin
was interpreted as a sinistral fault wedge basin, a type of
pull-apart structure formed along the western fault splay
of the MTZ. The Tinkoto basin was initiated after the
accretion of the volcanic rocks of the marginal basins. It
was initiated before 2070 Ma as indicated by the age of
the Tinkoto pluton.
The southern domain to the Mako belt, consists of bi-
modal mafic and felsic volcanic rocks erupted during ma-
jor cycles of volcanism. Intrusion of the younger grano-
diorite caused local amphibolite facies contact metamor-
phism that overprints nearby the volcanic complex. Ad-
ditional dikes and sills, ranging from gabbro to quartz
diorite, occur throughout the domain. The main structural
elements in the southern domain are dominantly N-S to
NNE-SSW and NW-SE oriented synvolcanic and later
reactivated faults.
Figure 8. Structural characteristics of the pull-apart basins:
diachronic evolution of the Tinkoto basin and the Makana
marginal basin.

M. DIENE ET AL. 162
5. Tectonic Signific a nce
The tectonic evolution of the Paleoproterozoic Mako Belt
in the West African Craton is explained by a various struc-
tural elements in the four domains. Concerning the previ-
ous tectonic structures, the D1 event should be compati-
ble with thickening processes. In this tectonic context,
high-temperature low pressure metamorphism conditions
and huge amounts of granite should be present. As in
other Paleoproterozoic regions, the geodynamic signifi-
cance of this horizontal tectonic structure can be attribu-
ted to lithospheric converg ence in a plate tectonic setting
(e.g. Feybesse et al., 2006).
The D2 bulk strain pattern is clearly related to a tran-
spressional regime during bulk horizontal shortening of
heated crust. This transpression, contemporaneous with
amphibolite facies conditions, resulted in a strain parti-
tioning between the anastomosing shear zone network in
the volcanic plutonic complex and the folded marginal
domain.
The dome-and-marginal basin domains are folded un-
der a pure shear-dominated strain regime, whereas the shear
zones show a component of the simple shear regime.
Inside the shear zones the strain also varies, from sim-
ple to pure shear, depending on their positions in space.
The vertical shear zone separate this two domains, record-
ing different pressure conditions . These regional pressure
differences, controlled by kilometric tectonic structures,
are compatible with exhumation during compression under
a transpressive regime (D2 strain pattern). The amount of
uplift that juxtaposes contrasted metamorphic domains
was controlled by the D2 strain gradient.
This hypothesis is confirmed by the strain gradient in-
creases in domains from west to east.
Towards the end of the Paleop roterozoic it is propo sed
that there was a change in the pattern of crustal growth
such that new crust was added as long narrow belts of
accretionary complexes along the margins of the older plu-
tonic volcanic complex.
6. Discussion and Conclusions
Makobasin-Volcanism and Tectonics:
Correlation between Oblique Convergence,
Basin Formation and Magmatism
An apparent correlation between plutonism, oblique con-
vergence and associated strike slip faulting observed in
the study area suggest that D2 faulting was responsible
for the basin formation. Basin subsidence, submarine vol-
canism and plutonic activity occurred in close spatial and
temporal relationship within the Mako volcano-plutonic
arc during the paleoproterozoic oblique convergence, in-
dicating that sinistral transpression was the trigger of pull-
apart basin formation and magmatism. Aligned syntec-
tonic granitic intrusions and small pull-apart basins indi-
cate local transtensional structures concurring with the
bulk transpressional regime.
The structural evolution of the Mako Belt (Figure 9) is
characterized by:
Figure 9. General model for the evolution of the Mako Belt in plan view explaining the formation of the marginal Makana
basin and the late oblique convergence.

M. DIENE ET AL. 163
 D1 thrust tectonism causing crustal thickening. This
deformation was accompagnied by the intrusion of
large TTG batholiths.
 Followed by transpression accommodating oblique
convergence and co llision (D2).
 Progressive burial of the sedimentary basins occurs in
the northern part of th e belt and is followed b y extru-
sion of the Bouroumbo urou area.
 An early phase of south-eastward thrusting followed
by a compressionnal NS phase, the whole being fol-
lowed by a late phase of extension. The broad zone in
the Sandikounda area records a progressive deforma-
tion sequence that includes early compressional struc-
tures modified by sinistral transpression. The rheologi-
cally rigid segments deflected deformation and was
domed, rotated and boudinaged because of its resis-
tance to compression. The partitioning of the struc-
tures in the domains is further dependent upon rheol-
ogy difference. The volcanic activity was in itiated im-
mediately after the rapid bloc uplift of the pillow lavas
and become widespread all over the belt providing
sub aerial lava flows and pyroclastics products.
Deformation styles within the basin are compatible
with a dextral transpression which terminated at ca 2090 .
Small extensional basin formed over the rocks of the
Mako Belt. The basins are filled with continental detrital
sedimentary rocks that show weak foliation and active
felsic volcanism.
The transpressive shear zone may result from oblique
convergence of the volcanic Mako domain and sediment-
tary Dalema domain following an early phase of thrust-
ing.
Some transcurrent shear zones of the KKI display dex-
tr al d isp lace men ts. Th ese ar e th e Mako K anoume r ing She ar
Zone. This opposite shear sense can be explained by ob-
lique convergence. These occur along releasing bends, and
are related to E-W, NE-SW and NW-SE-trending fault.
The thrust signature was either synchronous or late with
respect to the emplacement of these phases.
This interpretation is in agreement with mechanisms
related to oblique convergence, the later being typically
resolved into a str ongly orthogonal compressionnal co m-
ponent at the strike slip component.
The inversion of the large scale structural evolution from
thrusting to strike slip is common to modern orogenies.
The east-west shear zones either initiated as late thrust
faults that were reactivated as dextral strike-slip faults, or
are dextral transpression zones which accommodated the
oblique convergence of the volcanic domain. Strain par-
titioning into transcurrent deformation along the Leoba-
Moussala shear zone and NE–SW oriented shortening in
the marginal b asins, is cons iste nt with a sinis tral transp res-
sional regime during the second phase of deformation.
Transcurrent deformation continued during cooling of the
entire belt, giving rise to the localized low-temperature
mylonite.
The proposed structural evolution of the MB is con-
sistent with the models of Feybesse et al., [14] and Lom-
po [23], for the eburnean orogeny. These authors recog-
nize three phases of deformation D1, D2 and D3. Our in-
terpretation led us to define an early D1 tectonism, is in
agreement with Milési et al. [24]; Allibone et al. [25],
who also recognize the existence of an early event D1 in
Eburnean orogeny. In this, we differ from the interpreta-
tion of some authors (Eisenlohr and Hirdes, [26]; Blen-
kinsop et al., [27]) who propose that all Eburnean struc-
tures are related to single event may correspond to our
D2 and D3 phases.
The crustal shortening with Southeast directed is re-
lated to a NW-SE compression. This is in agreement with
Blenkinsop et al., [27]; Vidal and Alric [28]; Allibone et
al. [29], who note that all Eburnean structures are related
to a NW-SE compression.
Regionally significant sinistrallytranspressive deforma-
tion at ca 2140 Ma was accompanied by intracrustal me-
lting, migmatization and granitoid emplacement. We sug-
gest that the sin istral transpressive tectonic associa ted with
oblique subduction may have generated basins and suba-
queous v olcanism. Our interpretation follows that of Van-
derhaeghe et al., [30], who note that the Transamazo-
nian orogeny was marked by oblique convergence char-
acterized by the development of pull-apart basins and
marginal basins.
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