# The geochronological evolution of the Paleoproterozoic Baoule-Mossi domain of the Southern West African Craton

Luis A. Parra-Avila, Anthony I. S. Kemp, Marco L. Fiorentini, Elena

Belousova, Lenka Baratoux, Sylvain Block, Mark Jessell, Olivier Bruguier, Graham C. Begg, John Miller, et al.

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## ► To cite this version:

Luis A. Parra-Avila, Anthony I. S. Kemp, Marco L. Fiorentini, Elena Belousova, Lenka Baratoux, et al.. The geochronological evolution of the Paleoproterozoic Baoule-Mossi domain of the Southern West African Craton. Precambrian Research, 2017, 300, pp.1-27. 10.1016/j.precamres.2017.07.036. hal-01623272

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https://hal.science/hal-01623272v1

Submitted on 4 Jul 2025

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# The geochronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton

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## Authors:

Luis A. Parra-Avila a,b, Anthony, I. S. Kemp a, Marco L. Fiorentini a,b, Elena Belousova b,

Lenka Baratoux c,d, Sylvain Block d, Mark Jessell a,d, Olivier Bruguier e, Graham C. Begg a, b, f,

John Miller a, James Davis a, T. Campbell McCuaig a.

## Affiliations:

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a Centre for Exploration Targeting, School of Earth Sciences, The University of Western

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Australia, Perth, WA 6009, Australia

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b Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS)

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and GEMOCARC Centre of Excellence for Core to Crust Fluid Systems, Department of Earth

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and Planetary Sciences Macquarie University, NSW 2109, Australia

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c IFAN, Université Cheikh Anta Diop, Dakar, Sénégal

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d Géosciences Environnement Toulouse, Observatoire Midi Pyrénées, 14 ave E. Belin, 31400,

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Toulouse, France

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e Géosciences Montpellier, Université de Montpellier, Place Eugene Bataillon, 34 095

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Montpellier cedex 5, France

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f Minerals Targeting International PL, West Perth, WA 6005, Australia

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Keywords

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West African Craton, Paleoproterozoic, Baoulé-Mossi domain, U-Pb zircon dating

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Abstract

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Generation and emplacement of felsic magmas in the Paleoproterozoic Baoulé-Mossi domain of the West African Craton does not match the apparent peaks of global crust generation identified between ca. 2900-2600, 1900-1600 and 1200-900 Ma. In contrast, across the Baoulé-Mossi domain, the emplacement of felsic intrusions ranges from ca. 2300 to 2000 Ma. It has proven difficult to place this magmatism within a robust geodynamic framework due to the lack of accurate geochronological data from across the West African Craton. The present study addresses this issue by presenting eighty-four new felsic intrusions zircon ion microprobe and LA-ICP-MS U-Pb ages from areas that up until now have not been targeted for geochronology.

The new dataset, when fully integrated with existing age data, reveals a craton-wide diachronous geochronological pattern characterized by a magmatic front that migrated westward. This migration proceeded at a rate of 35 km per million years, with an apparent offset of the initiation and cessation of felsic magmatic activity between the east and west of approximately 50 million years. The new data also show that although the entire Baoulé-Mossi domain was subject to continuous magmatic activity for approximately at least 150 million years, this magmatic activity displays a rather different record in the eastern and western portions of the domain. The differences are expressed as a westward migration of the magmatic activity, cessation of activity around ca. 2100 Ma (easternmost portion) and ca. 2050 Ma (westernmost portion) and a higher incidence of inherited ages in the westernmost portion when compared to the easternmost region. In addition, the new U-Pb data identify some of the oldest felsic intrusions in the region, including a granite from Burkina Faso (2265 ± 17 Ma) and a
diorite porphyry (2216 ± 5 Ma) in southern Mali. This study also reveals inherited Archean zircon cores from across southern Mali. The combination of the new data presented here, along with previously published data, suggests that the Baoulé-Mossi domain formed from the accretion of two major crustal blocks. The Archean inherited ages open a window for further investigation of the interaction between the Archean Kénéma-Man and the Paleoproterozoic Baoulé-Mossi domains.

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## 1 Introduction

Radiometric ages obtained from igneous and metamorphic rocks across the West African Craton are mainly concentrated between ca. 2300 and 2000 Ma. This period falls outside the main peaks of global magmatic activity preserved at ca. 2900-2600, 1900-1600 and 1200-900 Ma (Cawood et al., 2009 and references therein; Condie, 1998, 2009). It is possible that the complete magmatic record of the West African Craton is either under-represented or under-sampled in the current geochronological databases. The southern West African Craton, known as the Leo-Man Rise, comprises the Archean Kénéma-Man and the Paleoproterozoic Baoulé-Mossi domains (Figure 1). Despite the wealth of studies aimed at deciphering the large metallogenic endowment of the Leo-Man rise and in particular of the Baoulé-Mossi domain (e.g. Béziat et al., 2000; Feybesse et al., 2006a; Milési et al., 1991, 1992; Oberthür et al., 1998), the southern West African Craton remains one of the least understood and controversial lithospheric blocks on Earth. One of those controversies is directly related to the age of emplacement of the felsic igneous suites, and the apparent lack of involvement of older Archean crust in a region that is regarded to be the result of juvenile magmatic activity (Abouchami et al., 1990; Boher et al., 1992).

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Multiple studies on the geochronological evolution of the southern West African Craton have been carried out across the Baoulé-Mossi domain (e. g. Baratoux et al., 2011; Block et
al., 2016a; de Kock et al., 2011, 2012; Egal et al., 2002; Feybesse et al., 2006a, 2006b, 2006c; Gueye et al., 2007; Tshibubudze et al., 2013, 2015). Nonetheless, most of these studies are the result of mine-scale to belt-scale mapping projects, in many cases restricted to small regions or particular countries, thus failing to attempt large-scale correlations across the Baoulé-Mossi domain. According to these studies, the emplacement ages of felsic intrusions from across the domain are mainly associated with the Eburnean Orogeny (ca. 2200-1800 Ma, Liégeois et al., 1991) and represent approximately half of the total rock exposures across the domain (Boher et al., 1992; Roddaz et al., 2007).

Felsic intrusions from across the Baoulé-Mossi domain were described by Bessoles (1977) and originally divided into 3 main types: Belt or Dixcove, Sedimentary-Basin or Winneba and Basin or Cape Coast suites (e.g. Abouchami et al., 1990; Boher et al., 1992; Davis et al., 1994; Hirdes et al., 1992, 1996; Taylor et al., 1992). de Kock et al. (2011), (2012) further summarize the magmatic activity into 4 major age clusters or peaks at: ca. 2210-2190, 2185-2150, 2115-2100 and 2090-2070 Ma. Despite this apparent periodicity, published ages for these clusters tend to overlap within uncertainty, suggesting a continuous period of magmatic activity between ca. 2210 and 2050 Ma (de Kock et al., 2011, 2012).

The present study is a comprehensive evaluation of the chronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern portion of the West African Craton, aimed at establishing regional-scale correlations and shedding new light on the evolution of the region. The study area extends over Burkina Faso, southern Mali, eastern Guinea and parts of Ghana (Figure 1). A total of seventy-five new ion microprobe (SHRIMP II) and nine LA-ICP-MS U-Pb zircon ages are presented in this study and covers an area of over 250 000 km². The new data establish that the magmatic activity across the Baoulé-Mossi domain was continuous for approximately at least 150 million years (Myrs), and migrated westward at a rate of 35 km/Myrs.
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## 2 Geological Setting

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The West African Craton is composed of three major provinces: the Reguibat Rise to the north, the Kédougou-Kéniéba and Kayes Inliers to the west and the Leo-Man rise to the south (Abouchami et al., 1990; Bessoles, 1977; Boher et al., 1992) which circumscribe the younger Taoudenni Basin (Figure 1). The Leo-Man Rise, covering Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Liberia, Mali, Niger, Senegal, Sierra Leone and Togo is geologically divided into the Archean Kénéma-Man and the Paleoproterozoic Baoulé-Mossi domains (Figure 1). The Archean portion of the Leo-Man Rise is composed of highly metamorphosed, amphibolite to granulite facies, gneisses formed between ca. 3600 and 2600 Ma (Milési et al., 1992; Rollinson, 2016) and believed to be largely the result of the Leonian (ca. 3200-3000 Ma) and/or Liberian (ca. 2800-2700 Ma) orogenic cycles (Egal et al., 2002). Recently De Waele et al. (2015) refined the timing of crust formation to a pulse of magmatic activity at ca. 3400 Ma, which was followed by semi-continuous magmatic activity between ca. 3000 and 2600 Ma.

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The Paleoproterozoic counterpart which is divided into two main phases, the Eoeburnean or Tangaean (ca. 2266 and 2150 Ma) and the Eburnean (ca. 2130 and 1980 Ma) phases (Baratoux et al., 2011, 2015; Block et al., 2015; de Kock et al., 2012; Feybesse et al., 2006; Hein 2010; Perrouty et al., 2012; Vidal et al., 1996). The Paleoproterozoic crust comprises narrow sedimentary basins and linear to arcuate belts comprising volcanic and volcaniclastic rocks intruded by multiple generations of granitic rocks (Abouchami et al., 1990; Boher et al., 1992; Taylor et al., 1992). The Eoeburnean phase is dominated by mafic and felsic volcanism, granitic emplacement and folding as the result of a collisional event and crustal thickening (Baratoux et al., 2015; Lambert-Smith et al., 2016; Tshibubudze et al., 2015), while the Eburnean phase is characterized by plutonic activity. The Eoeburnean and Eburnean terminology and characteristics are not uniform across the entire Paleoproterozoic domain as
summarized by Lambert-Smith et al. (2016). The stratigraphic sequence of the Baoulé-Mossi
domain is defined in Vidal et al. (1996) and later refined by Béziat et al. (2000), de Kock et al.,
(2009, 2011), Baratoux et al. (2011), and Ganne et al. (2014) (Figure 2). Recent studies by
Pitra et al. (2010), Baratoux et al. (2011), Ganne et al. (2014) and Block et al. (2015) de Kock
et al., (2009, 2011), Baratoux et al. (2011), Béziat et al. (2000), and Ganne et al. (2014) (Figure
2). Recent studies by Baratoux et al. (2011), Block et al. (2015), Ganne et al. (2014) and Pitra
et al. (2010) have reiterated that the lithostratigraphic sequence has been generally affected by
greenschist facies metamorphism, but also highlight regional amphibolite facies and locally
granulite facies metamorphism.

## 2.1 The Birimian terranes

The term “Birimian terranes” after the type locality defined from the Birim River Valley
in Ghana (Kitson, 1918) is applied to the Paleoproterozoic domain of the southern West African
Craton. The Birimian stratigraphy (sensu lato) is defined, bottom to top, by the presence of: 1)
a thick sequence of locally pillowed basalts and gabbros of tholeiitic affinity (Hirdes et al.,
1996; Leube et al., 1990), interlayered with immature sedimentary rocks and carbonates; 2) a
volcano-sedimentary sequence mainly dominated by turbidites, mudstones and carbonates,
interbedded with calc-alkaline volcanic and volcaniclastic rocks (Kesse, 1985; Olson et al.,
1992); and 3) a coarse, clastic sedimentary sequence that was originally defined by Junner
(1940), (1954) and later by Trashliev (1974) as a series of turbidites (Attoh, 1982; Béziat et al.,
2000, 2008; Pouclet et al., 1996; Vidal et al., 1996).

Regionally, across Burkina Faso, the Birimian terranes comprise a series of basaltic to
basaltic andesitic belts, from east to west, the NNW-striking Bouroum Belt, the NW-striking
Goren Belt, and the N-S striking Boromo, Hounde and Banfora belts (Figure 1). All belts are
intruded by N-S trending granitic bodies (Hein, 2010; Metelka et al., 2011). Additionally,

Commented [JL1]: Should be in chronological order
Baratoux et al. (2011) and Castaing et al. (2003) summarized several NNW to NE-trending shear zones, defined as the Greenville-Ferkessedougou-Bobo Dioulasso, the Bossie, the West Batie and the Boromo-Poura shear zones (Figure 1).

Further to the west across southern Mali, the Birimian is composed of three N-S trending volcano-sedimentary belts and two regional shear zones. These belts from east to west are: 1) the Bagoe Belt, considered to be the NW extension of the Diaoulla-Boundiali Belt of Côte d'Ivoire (Traoré et al., 2016; Turner, 1995) near the Burkina Faso-Mali border; 2) the Morila Belt, just east of the large Bougouni granitic batholith (Hammond et al., 2011; Parra-Avila et al., 2016); and 3) the Yanfolila Belt, which sits between the town of Bougouni and the Mali-Guinea border. Major shear zones in the region are the Siekeroli and Bannifin shear zones (Figure 1) (Feybesse et al., 2006b, 2006c; Liégeois et al., 1991; McFarlane et al., 2011).

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## 2.2 Geochronology and geochemical overview of the Paleoproterozoic Baoulé-Mossi domain
### felsic intrusions

Felsic intrusions in Burkina Faso are divided according to their host volcanic belts. Across the NE-E portion of the country, authors such as Castaing et al. (2003), Hein et al. (2004), (2010), Naba et al. (2004), Tshibubudze et al. (2009), (2013), (2015) and Vegas et al. (2008) described the intrusions as NE-SW-trending, medium to coarse-grained equigranular granodiorites, tonalites, quartz-diorites, quartz-monzodiorites and granites. Zircon U-Pb ages indicate that the intrusions are as old as ca. 2260 Ma (Tshibubudze et al., 2015).

Metelka et al. (2011) subdivided the felsic intrusions across Burkina Faso into three types: 1) medium to coarse grained, amphibole and biotite rich, with minor occurrences of K-feldspar tonalites, trondhjemites and granodiorites, emplaced between ca. 2150 and 2130 Ma; 2) K-feldspar and biotite rich granodiorites and granites, rarely containing muscovite or
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amphibole, and granodiorites with ages between ca. 2110 and 2100 Ma; and 3) K-feldspar rich potassic granites, which occasionally bear muscovite (ca. 2110-2090 Ma, Eburnean).

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Baratoux et al. (2011) suggested that volcanic activity across western Burkina Faso occurred between ca. 2190 and 2160 Ma (Eoeburnean). Additionally, by combining field observations and airborne geophysical data Baratoux et al. (2011), Block et al. (2015), and Metelka et al. (2011) determined that the granitic intrusions in northern Ghana and western Burkina Faso can be grouped into four main magmatic episodes: granite, granodiorite and gabbroid emplaced between 2195 and 2160 Ma (Pre-ME1), ME1 composed mainly of tonalite, trondhjemite, granodiorite (TTG) emplaced at ca. 2160-2120 Ma; ME2, dominated by granodiorites and granites (ca. 2120-2110 Ma, Eburnean); and ME3 represented by granites (2110-2090 Ma, Eburnean).

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Farther to the west across southern Mali, felsic intrusions are far less studied, and no large-scale correlations have been made. Most studies across southern Mali are at the local/mine-scale. Liégeois et al. (1991) recognized three main types of N-S striking felsic intrusions around the Bannifin shear zone: 1) plagioclase, microcline, quartz, hornblende and biotite rich, equigranular, fine-grained (occasionally aplitic) quartz-diorites, quartz-monzodiorites and granodiorites (ca. 2075 Ma, Eburnean), locally known as the Sadiola type; 2) foliated homogenous potassic pink leucogranites known as the Massigui type; and 3) fine to medium grained granitic intrusions containing biotite and variable amounts of K-feldspar, locally known as the Doubalakoro type.

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In a study around the Morila gold mine, McFarlane et al. (2011) identified gold-bearing granodiorites as well as foliated porphyritic intrusive bodies and granites with pegmatitic textures. Granodiorite bodies are described as being biotite rich with plagioclase phenocrysts, similar to the Sadiola type. The porphyritic intrusions are composed of very fine grained plagioclase, quartz, actinolite and biotite. A second generation of intrusions is described as

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quartz diorites to biotite leucogranites similar to the Doubalakoro pluton of Liégeois et al. (1991). Finally, the third generation described by McFarlane et al. (2011) consists of leucogranites and two mica (muscovite/biotite) rich granites and pegmatites, with U-Pb zircon ages ranging between ca. 2130 and 2090 Ma (Eburnean). In addition to the types described by Liégeois et al. (1991) and McFarlane et al. (2011), an older generation has been documented by Feybesse et al. (2006b), (2006c) and references therein. This older intrusion is represented by a monzonitic orthogneiss that yielded a zircon U-Pb age of 2150 ± 15 Ma, with an inherited zircon population at 2174 ± 8 Ma (Eoeburnean) (Feybesse et al., 2006b, 2006c).

In general, intrusions across the Paleoproterozoic domain of the southern West African Craton have been mainly described as TTG-like (Doumbia et al., 1998; Vidal et al., 2009, and references therein), based on normative Anorthite-Albite-Orthoclase discrimination diagrams after Barker (1979) and O’connor (1965). The intrusions have historically been divided into three main groups: 1) amphibole bearing granitic rocks, with or without biotite, usually foliated; 2) biotite bearing granitic rocks without amphibole; and 3) potassic alkaline plutons (Castaing et al., 2003; Doumbia et al., 1998; Egal et al., 2002; Gasquet et al., 2003; Hirdes et al., 1992, 1996; Liégeois et al., 1991; Lompo, 2009; Naba et al., 2004; Oberthür et al., 1998; Tapsoba et al., 2013; Vegas et al., 2008). Supplementary Material A summarizes the emplacement ages reported for these intrusions.

The geochemistry of felsic intrusions across Burkina Faso, Mali and Ghana, are extensively documented and broadly summarized as calc-alkaline/magnesian with arc-like trace element signatures, including negative Nb, Ta, P, Ti as well as REE fractionation and Eu anomalies (e.g. Baratoux et al., 2011; Block et al., 2016a; Castaing et al., 2003; Egal et al., 2002; Eglinger et al., 2017; Feybesse et al., 2006a, 2006b, 2006c; Gasquet et al., 2003; Hein et al., 2004, 2010; Lambert-Smith et al., 2016; McFarlane et al., 2011; Metelka et al., 2011; Naba et al., 2004; Peterssen et al., 2016, Tapsoba et al., 2013 and Vegas et al., 2008).
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**3 Samples and Analytical Methods**

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To compare the magmatic activity of the Paleoproterozoic Baoulé-Mossi domain, where precise ages are scarce, with the age peaks recognized in the global magmatic record an integrated geochronological dataset on igneous rocks from southern Mali, was established. Additional samples from Burkina Faso and some from eastern Guinea and Ghana provide ages from the whole Paleoproterozoic domain. Samples were collected over 3 field seasons and were carefully selected to give the most representative and comprehensive overview of the characteristics of the different plutons across the region (Figure 3). Each sample was approximately 3-6 kg in weight.

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In Burkina Faso, granitic intrusions were sampled from east to west: 1) across the Po-Tenkodogo-Yamba region and the Goren Belt; 2) around the Inata-Belahouro gold district, Bouroum Belt; 3) in the surroundings of the Perkoa zinc mine, Boromo Belt; 4) in the Gaoua region, Hounde Belt; and 5) adjacent to the Banfora Belt. In Mali, sampling focused: 1) across the Syama Mine, Bagoe Belt; 2) on granitic intrusions around the Morila mine, Morila Belt; 3) on granitic outcrops of the Bougouni region; and 4) across the Kalana and Komana regions of the Yanfolila Belt. In Guinea, samples were obtained from granitic intrusions outcropping in the Siguiri Basin area. Finally, in Ghana samples were obtained from the Koudougou-Tumu granitic domain, northern Ghana, and across the Ashanti Belt-Kumasi Basin region of southern Ghana (Table 1, Figure 1 and larger insets with the sample points). In addition to surface samples, a series of felsic porphyries were collected from drill cores provided by exploration and mining operators, mainly across the Yanfolila Belt (Mali) and the Siguiri Basin (Guinea).

**3.1 Rock description and petrology**
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Rock classification was made based on 3 parameters: 1) hand specimen observations;
2) CIPW norm; and 3) modal composition determined from microscopic evaluation of thin
sections, characterized after Streckeisen (1976) (Tables 2 and 3).

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## 3.2 Zircon morphology and U-Pb dating

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# 4 Results

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## 4.1 Rock description and Petrology overview

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The petrological characteristics of the igneous rock samples are summarized in Table 2. Macroscopic and microscopic observations reveal that 48% of the samples are represented by granites while the rest is represented by granodiorites, monzodiorites, diorites, aplites and syenites. Additionally, two gabbros are identified. The drill core samples are classified as porphyries (Tables 1 and 2).

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Based on mineralogy, 3 main groups of intrusions were identified: 1) biotite bearing, characterized by plagioclase, alkali feldspar, quartz, with or without hornblende, titanite, apatite, zircon and variable amounts of sulfide and oxide phases (Figure 4-A, C and E); 2) two mica intrusions, rich in plagioclase, alkali feldspar, muscovite, biotite, quartz, and zircon as well as variable amounts of sulfides (Figure 4-B and G); and 3) porphyries, mainly from drill core samples, consisting of altered to very altered fine-grained and recrystallized matrix with
275 abundant calcite (Figure 4-H). Other minerals within the matrix include biotite, traces of
276 muscovite, epidote and chlorite. Overall, the biotite in the single mica intrusions is greenish to
277 (primarily) reddish-brown. Biotite in the two mica intrusions is mainly greenish and
278 occasionally reddish-brown. Hornblende appears to be only present in a limited number of
279 single mica samples. Titanite is mainly euhedral, bladed and light brown in color, but is also
280 present as wedge-shaped grains that are darker brown in color. Zircon forms euhedral,
281 elongated grains with visible oscillatory zoning, characteristic of an igneous origin.

282 In the case of the porphyry samples, original matrix textures are not easily identifiable.
283 Relict phenocrysts are for the most part plagioclase. Deformation and mineral alignment is
284 evident in some samples. Phenocryst grain boundaries appear sharp and unaltered in some
285 samples while in others they appear deformed, with signs of recrystallization.

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## 4.2 Zircon morphology

288 The majority of zircon grains are clear to slightly translucent and pale reddish-brown,
289 while a small percentage are more intense reddish-brown. Most crystals are elongated, with
290 either sharp or in some cases slightly rounded <ins>dipryramidal crystal form</ins><ins>prismatic terminations</ins>,
291 and between 25 to 80 µm wide and 120 to 300 µm in length. Fragmented or broken zircons are
292 probably the result of the mineral separation process. Most zircons show clear oscillatory
293 zoning of variable intricacy, whereas others have either faint or broad zoning. Additional
294 features evident in CL images include the recognition of high U concentration, which is
295 identified due to metamict features, and distinct central regions with very dark brown
296 coloration, possibly reflecting the presence of xenocrystic cores (Figure 5).

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## 4.3 Zircon U-Pb dating
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A total of 84 samples were dated by zircon U-Pb method, 27 samples from Burkina Faso, 50 from Mali, 5 from Guinea and 2 from Ghana (Figures 6 and 7, Table 3). Table 3 summarizes the ²⁰⁷Pb/²⁰⁶Pb age results (weighted mean ages are at 95% confidence limit). Figures 8 and 9 shows U-Pb Concordia plots and weighted mean ²⁰⁷Pb/²⁰⁶Pb ages for the 9 belts and 2 large batholiths studied. Supplementary Materials B (SHRIMP) C (LA-ICP-MS) contains the full set of (U-Th)-Pb isotope data.

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Zircons from 58 samples yielded a single age population, while the remaining 26 samples contain zircon with older cores, which are interpreted as inherited components. The number of inherited grains is variable between samples and ranges from 1 or 2 analyses to 10 (Table 3). Across Burkina Faso, the Goren Belt/Po-Tenkodogo-Yamba regions, yield ages between ca. 2270 and 2120 Ma. For the Belahouro region the ages are between ca. 2180 and 2120 Ma and in the Boromo-Hounde belts the range is between ca. 2180 and 2110 Ma, while the Banfora region have ages between ca. 2150 and 2110 Ma (Figures 6 and 7).

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In southern Mali, the felsic intrusion from the Syama mine (Bagoe Belt) is dated at ca. 2150 Ma. Farther to the west, the Morila Belt granites and granodiorites have inferred emplacement ages between 2140 to 2080 Ma. Across the Bougouni domain, the emplacement occurred between ca. 2100 and 2080 Ma while the Yanfolila Belt, was intruded between ca. 2220 and 2070 Ma (Table 3, Figures 6, 7 and 9).

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The rocks analyzed are mainly granites and granodiorites with the bulk dated between ca. 2140 and 2080 Ma. The other dated intrusions are mainly porphyries, diorites and tonalites (Figure 6). Three of the 9 diorites have inherited grains of up to ca. 3500 Ma. A total of 12 granites have inherited zircon cores up to ca. 2250 Ma. The porphyry intrusions shows significant inheritance of material up to ca. 2500 Ma old. The granitic intrusions with Archean inheritance are mainly biotite bearing, characterized by plagioclase, alkali feldspar, quartz, with or without hornblende and muscovite. Assimilation of older crust during the generation of the
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2 mica (biotite and muscovite) and 1 mica (mainly biotite) intrusions, as illustrated by inherited zircon, is also evident.

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## 5 Discussion

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The new data presented here constitute a comprehensive and spatially representative geochronological dataset from the Paleoproterozoic Baoulé-Mossi domain of the West African Craton. Together with previously reported ages, broad U-Pb age and inheritance patterns can be visualized across the craton. The implications of these new data for tectonic evolution are explored in the following sections.

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### 5.1 Magmatic activity from the Goren/Po-Tenkodogo-Yamba to the Banfora Belt

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A granodiorite from the Goren/Po-Tenkodogo-Yamba region (BF8) with an apparent age of 2265 ± 17 Ma is similar to that obtained by Tshibubudze et al. (2013), (2015) for granites across the Oudalan-Gorouol Belt (ca. 2265 Ma) expanding the known occurrences of older intrusives presented in compiled data, by e.g. Baratoux et al. (2011), de Kock et al. (2011), (2012), Feybesse et al. (2006b), (2006c), McFarlane et al. (2011), Tapsoba et al. (2013) and Tshibubudze et al. (2015).

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The youngest ages across the easternmost portion of the study area in Burkina Faso are ~2105 Ma (BF12-05), 2115 Ma (HO640C) and 2120 Ma (BF1), belonging to the Eburnean phase, which are mainly concentrated along the Banfora Belt region, with minor occurrences in the Boromo-Hounde and Belahouro belts. These young granite ages make it clear that felsic magmatic activity across the eastern portion of the Paleoproterozoic Baoulé-Mossi domain occurred over a period of about 150-160 Myrs. Within this period, magmatism was active between ca. 2275 and 2190 Ma, after which activity increased to peak between 2140-2130 Ma. Magmatic activity then waned, with the last
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bodies emplaced at ca. 2105 Ma (Figures 6, 7, and 9). After ca. 2105 Ma the magmatic activity appears to be concentrated in the western portion of the Baoulé-Mossi across southern Mali.

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## 5.2 Magmatic activity from the Banfora Belt to the Siguiri Basin

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West of the Banfora Belt and into southern Mali and eastern Guinea, this study clearly lengthens the magmatic evolution of the Baoulé-Mossi domain. Previous studies that evaluated the magmatic activity indicated a period of 30 Myrs between ca. 2100 and 2070 Ma, which was associated with the Eburnean orogenesis (Liégeois et al., 1991). Conversely, Doumbia et al. (1998), Hirdes and Davis (2002), and Hirdes et al. (1996) indicated that the granitic intruded between ca. 2150 and 2070, a period of 80 Myrs. The Porphyries from the Yanfolila Belt, however revealed intrusions at 2159 ± 11 Ma (MWAXI-135), 2174 ± 15 Ma (MWAXI-130) and 2216 ± 15 Ma (MWAXI-134) extending the range of magmatism across the region. The felsic magmatic activity progressively increased during the Eburnean phase between ca. 2100 Ma and 2070 Ma, peaking around ca. 2090 Ma and abruptly waning declining after ca. 2070 Ma (Figures 6, 7 and 9). Overall the range of magmatic activity lasted about 150 Myrs, mostly concentrated between ca. 2100 and 2070 Ma. These findings thus may suggest an accretionary evolution for the southern West African Craton (section 6).

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## 5.3 Broad age patterns across the Baoulé-Mossi domain

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The early and punctuated magmatic activity recorded in the Yanfolila Belt contrasts with the rest of southern Mali, where only a limited number of samples are older than ca. 2110 Ma. Volcanism in the belt has been recognized as early as ca. 2212 Ma by Lahondère et al. (2002) whom associated this early activity with felsic to intermediate volcanism resulting of from subduction or underplating. Early volcanism is present in the east of the Banfora Belt, as reported by Hein (2010) and Tshibubudze et al. (2013), (2015). Since these older ages (> ca.

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2250 Ma in Burkina Faso and > ca. 2200 Ma in southern Mali) are not more common, either
the overall volume of magmatism was relatively low during this period, or intrusions of this
age are buried or have been eroded away. Alternatively, a more mafic style of magmatism may
have resulted in less zircon crystallization.

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Integration of the new and published data shows that for the southern West African
Craton the emplacement ages fall into an “early” period at 2250-2260-2130 Ma, which is
dominated by pluton emplacement (Figure 11-A), followed diachronously by a “late” period
(2130-2050 Ma). The boundary between the early and late periods was chosen after considering
peak metamorphism in the region, deformation history, and spatial distribution of the ages
across the study area and identifiable age peaks (Figures 2, 6, 7 and 11). While the probability
of occurrence of ages shown in figure 10 suggests a boundary can be placed around ca. 2110
Ma, the spatial distribution is more in agreement with a boundary ca. 2140-2130 Ma.
Additionally, the peak metamorphism identified by Block et al. (2015) between ca. 2140-2130
Ma, roughly coincides with the peak of magmatism in the eastern portion of the study area.
The comparable to the Eoeburnean phase, The early period, which is comparable to the
Eoeburnean phase, is dominated by a major peak at ca. 2135 Ma and a secondary peak at ca.
2170 Ma. The late period coincides with the Eburnean phase of de Kock et al, (2011) and can
be further subdivided into two age brackets, between ca. 2130-2090 Ma (Figure 11-B)
dominated by craton wide magmatic activity, and 2090-2050 Ma (Figure 11-C) where
magmatic activity was predominantly concentrated in the western portion of the craton. As
observed in figures 2 and 11 emplacement and deformation events did not occurred
synchronously across the study area and it is clear that diachronism between east and west
presents difficulties in the definition of the Eoeburnean and Eburnean phases across the study
area as summarized in Lambert-Smith et al. (2016).

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Additionally, when all magmatic, metamorphic and detrital zircon ages are plotted as a function of longitude for the whole southern West African Craton (Figure 12-A), it is possible to define the onset and cessation of magmatic activity as a function of distance across the southern West African Craton. This reveals an apparent offset of 50 Myrs in the beginning and end of magmatism between the eastern and western part of the Baoulé-Mossi domain (Figure 12-B). Such patterns indicate that magmatic activity progressively retreated from east to west across the southern West African Craton at a rate of approximately 35 km/Myr (Section 6). This inference is strengthened by the fact that 95 % of the plotted ages lie above the dashed bottom arrow in Figure 12-B, which shows the diachronism in the onset and *offset cessation* of magmatism.

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## 5.4 Zircon inheritance

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The majority of the inherited zircons are within 50 Myrs or less of the crystallization ages of the individual intrusions, and mostly occur across southern Mali and to a lesser extent in the easternmost portion of Burkina Faso, across the Goren/Po-Tenkodogo-Yamba and Belahouro belts. Inheritance is mainly present in samples younger than ca. 2130 Ma. Only a limited number of samples have inherited cores/grains (30 out 90 samples), of which a half (15 samples) have inherited material older than 2200 Ma. The previous findings are in agreement with studies along the southern margin of the Bole-Nangodi Belt of northern Ghana, where de Kock et al (2011) identified Eoeburnean inheritance in intrusions up to 2130 Ma.

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Only 4 samples (KADD119-M, KL000274, ML12-078 in Mali, and BF9 in Burkina Faso) assimilated Archean crust, as indicated by inherited zircons with ages between ca. 3700 and 2500 Ma. Evaluation of rejected discordant analyses (criteria explained in Appendix A) does not reveal age groups different from the inferred crystallization ages, or from the reported inherited ages (Table 3).
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With the exception of de Kock, (2011) and Lambert-Smith et al. (2016) *that-who* identified inherited Archean zircons, in northern Ghana and in the Kédougou-Kéniéba *and Kayes*-Inliers of Mali, respectively early studies failed to identify Archean inheritance. The absence of Archean crust has been used to argue that the Baoulé-Mossi domain was mostly the result of juvenile magmatic activity (Abouchami et al., 1990; Boher et al., 1992; Tapsoba et al., 2013). The present study identified 2 zircon grains *with ages* between ca. 3600 and 3500 Ma, 1 grain at ca. 2880 Ma and 3 grains that yield ages between ca. 2600-2500 Ma; these are *from-across* the Goren/Po-Tenkodogo-Yamba region and Belahouro Belts in Burkina Faso and in the Yanfolila Belt in southwestern Mali (Table 3).

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### 5.4.1 Possible origin of the zircon inheritance

Two scenarios are envisaged to explain the zircon inheritance found in some samples: 1) assimilation of older crust by ascending magmas (contamination of ascending magmas by older basement rocks); and 2) assimilation from a sedimentary source where they were detrital grains. Both scenarios could potentially be the result of Eburnean orogenesis. According to Baratoux et al. (2011), Tshibubudze et al. (2013) and (2015) eastern Burkina Faso was subject to an early compressional event (2200-2160 Ma) that led to significant shortening and crustal thickening. *Across southern Mali*, Liégeois et al. (1991) also identified deformation events *across southern Mali* that resulted in intense folding and thickening and, plausibly, subsequent uplift. Recently, Block et al. (2015), (2016a), (2016b) described the implications of compressional deformation across northern Ghana and southwest Burkina Faso. These compressional events resulted in significant crustal thickening. Crustal thickening provides a way to underthrust and uplift sedimentary rocks, and allows greater interaction between the older basement rocks and ascending magmas, facilitating the entrainment of older zircons.
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The interleaving of Archean-Paleoproterozoic crust appears, to be limited and with the exception of western Côte d'Ivoire, surface expressions indicate a relatively sharp, well constrained Archean-Paleoproterozoic geological boundary (Eglinger et al., 2016), although this may not be the case at depth. In addition, within the study area, there is no geochronological or field evidence for the existence of large Archean exposures, arguing against the Paleoproterozoic Baoulé-Mossi domain having underthrust the Archean Kénéma-Man domain.

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If in contrast, the Archean block was overridden by, or resurfaced by, the Paleoproterozoic assemblage, it is likely that the juvenile magmas would have interacted with Archean crustal fragments during their ascent, potentially entraining the older zircons. This hypothesis is at odds with the majority of published isotope Nd and Hf isotope data that advocates a predominately juvenile origin with limited amount of reworked crust (e.g. Abati et al., 2012; Abouchami et al., 1990; Boher et al., 1992; Petersson et al., 2016; Tapsoba et al., 2013; Taylor et al., 1992).

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Alternatively, if the inherited ages are the result of reworking sedimentary rocks it is necessary to account for long distance transport of detritus now represented by the inherited components. The present geological configuration indicates that the distance between the Banfora and Yanfolila belts is over 300 km, whereas the distance from the known Archean Kénéma-Man domain and the Yanfolila Belt is over 80 km. It is expected that these distances were greater at the time of emplacement at ca. 2200-2000 Ma. The uplifted units following crustal thickening would have been eroded more easily, thus providing a source for the inherited zircon grains. This scenario provides a possible source for the Paleoproterozoic inheritance found across the western portion of the study area, as zircons from the early magmatic episode (ca. 2300-2130 Ma) are incorporated into magmatic intrusions emplaced after ca. 2130 Ma. Conversely, in the case of Archean inherited ages from across Burkina Faso a plausible source of transported grains would be the Archean basement identified within the

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Nigerian Shield, as reported by Bruguier et al. (1994) and Kröner et al. (2001) or previously unrecognized Archean slivers. The most likely source of inherited grains in the Mali samples is the Archean Kénéma-Man domain. We note that incorporation of older zircon cores from the reworking of sedimentary rocks is a testable hypothesis – in this case, the emplacement-aged zircons of the host granite should have high δ¹⁸O values -(e.g. Hawkesworth and Kemp, 2006; Kemp et al., 2007, 2009; Valley, 2003; Valley et al., 1994).

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# 6 Tectonic implications and accretionary model

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The crustal evolutionary patterns of the southern West African Craton, and in particular of the Baoulé-Mossi domain, reflect a complex assemblage (puzzle) that requires understanding of the spatial and temporal distribution of emplacement ages and the presence of inherited zircon grains. During the Phanerozoic, migrating magmatic fronts and abrupt cessations of magmatic activity, as inferred here, have been associated with arc type systems, such as the Andes in central Chile (Hildreth and Moorbath, 1988) and South China, where flat slab subduction has been proposed (Li and Li, 2007). It is possible that similar accretionary processes shaped the crustal evolution of the southern West African Craton

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> An If under such accretionary process may have involved at least two crustal blocks that join to formed the Baoulé-Mossi domain. During the Eoeburnean magmatic phase the magmatic activity was mainly concentrated in the easternmost block of the study area (minor peak at ca. 2170 Ma, figure 10). As the magmatic activity migrated westward a large pulse of magmatism is identified at around ca. 2135 Ma, potentially heralding preceding the docking of the two blocks at ca. 2130 Ma. After ca. 2130 Ma the magmatic activity appears concentrated in the westernmost region with peak magmatism at ca. 2090 Ma. The inherited age pattern is the result of the younger magmas sampling material derived from the easternmost portion suggest the westward migration of the magmatic front (Figure 13). Recently, Block et al.
(2016a) proposed a collision model between blocks in Ghana and Burkina Faso/Côte d'Ivoire. We suggest that the Paleoproterozoic Baoulé-Mossi domain was the result of the accretion of at least two crustal blocks that were subsequently amalgamated with the Archean Kénéma-Man domain (Figure 13).

The boundary between these inferred crustal blocks is based on the distribution of intrusion emplacement ages and inherited zircons. East of the Banfora-Bagoe belts, intrusion ages are predominantly older than ca. 2130 Ma, mostly free of inheritance, while to the west the ages are predominantly younger than ca. 2130 Ma and commonly contain an inherited component. Multiple crustal blocks explain the occurrences of inherited ages between ca. 2250 and 2150 Ma across Southern Mali, due to potential crustal thickening and subsequent underthrusting or uplift and erosion of older crust (section 5.4.1). Certainly, across southern Mali this study and previous studies (e.g. Feybesse et al. (2006b), (2006c)) have identified ages between ca. 2215 and 2150 Ma, but the geographical distribution and number of identified intrusions within that range does not account for the relatively widespread inheritance across southern Mali. Subsequently, the Paleoproterozoic crustal blocks of the Baoulé-Mossi domain, proposed here were accreted into the Archean Kénéma-Man domain.

## 7 Conclusions

The new data presented in this study support observations that the Paleoproterozoic portion of the southern West African Craton developed during an accretion process, as follows:

* Evaluation of all zircon ages (magmatic, metamorphic and detrital) plotted as a function of longitude supports the notion that the Paleoproterozoic Baoulé-Mossi domain underwent a diachronous evolution reflected by a westward migration of the magmatic front. It also highlights an abrupt cessation and retreat of activity across the southern West African Craton that started around ca. 2100 Ma at the eastern end of the craton

Commented [JL2]: I would say predominantly older than 2090 Ma – the 2090 to 2130 Ma map still has a large number of age data indicated in the eastern region....
and ended at ca. 2050 Ma at the westernmost portion. This retreat is represented by a westward migration of the magmatic front of approximately 35 km/Myr and is analogous to that shown by Phanerozoic subduction- accretion systems as described by e.g. Li and Li<sub>s</sub> (2007) and Hildreth and Moorbath<sub>s</sub> (1988).

* The offset of magmatism and distribution of inherited zircons indicates that the Paleoproterozoic domain part of this study was composed of at least two crustal blocks with the boundary probably located between the Banfora and Bagoe belts.

* An accretionary process might have started as early as ca. 2175 Ma. At this time a minor peak of magmatic activity is identified east of the Banfora Belt.

* Early peak metamorphism identified at ca. 2130 Ma (Block et al., 2015) is taken as an indication of the timing at which the two blocks were docked and it coincides with peak magmatism in the eastern portion of the study area. Intrusions younger than ca. 2130 Ma generally contain inherited grains with ages up to 2250 Ma. This suggests that the crust was thicker after that time, allowing for incorporation of older components, which is also consistent with an accretionary model. Additionally the distribution of inherited ages up to ca. 2250 Ma indicates that the ca. 2130 Ma magmas interacted with, or sampled sediments derived from, previously emplaced intrusions with ages between ca. 2250 and 2150 Ma.

These observations are consistent with an arc type environment, as suggested by e.g. Ama Salah et al. (1996), Béziat et al. (2000), Sylvester and Attoh (1992), Abati et al. (2012), Block et al. (2015) and (2016b), Lambert-Smith et al. (2016), Petersson et al. (2016) and Tapsoba et al. (2013). arc type environment, as suggested by e.g. Ama Salah et al. (1996), Béziat et al. (2000), Sylvester and Attoh (1992), Abati et al. (2012), Block et al. (2015), Lambert-Smith et al. (2016), Petersson et al. (2016) and Tapsoba et al. (2013), and Block et al. (2016).
This study identified Archean zircon inheritance, particularly in the <2130 Ma intrusions. These occurrences could imply a greater involvement of Archean crust in the Paleoproterozoic granitic magmas than previously proposed. Recent studies, Abati et al. (2012), Begg et al. (2009) and Petersson et al. (2016), have also advocated a greater role of Archean crust, and future isotope studies are required to evaluate this further. Ultimately, however, the distribution and scarcity of Archean inheritance points toward a predominately juvenile crustal growth during the Paleoproterozoic across the Baoulé-Mossi domain, as long argued by Nd and Hf isotope studies (e.g. Abati et al., 2012; Abouchami et al., 1990; Boher et al., 1992; Tapsoba et al., 2013; Taylor et al., 1992).

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## 8 Acknowledgements

We thank AMIRA International, industry sponsors, AusAid and the ARC Linkage Project LP110100667, for their support of the WAXI II project (P934A). We are also appreciative of the contribution of the various Geological Surveys and Departments of Mines in West Africa as sponsors in kind of WAXI. In addition we acknowledge the assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy, Characterization & Analysis (CMCA) of the University of Western Australia (UWA), of the John De Laeter Centre for Isotope Research, hosted at Curtin University, of the Key Centre for the Geochemical Evolution and Metallogeny of Continents (GEMOC), and the ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), Macquarie University. Parra-Avila acknowledges receipt of UWA Scholarships for International Research Fees (SIRF), University International Stipend (UIS) and Ad Hoc Safety-Net Top-Up Scholarship. Kemp acknowledges the ARC grant FT100100059 and Fiorentini acknowledges the ARC grant schemes FT110100241 and CE110001017. This is contribution 988 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1165 in the
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## 9 Tables, Figures and Supplementary Materials

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**Table 1** Sample information, location, rock type and basic field description as part of the present study.

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**Table 2** Summary of main mineralogical characteristics by volcanic belt or geologic region of interest.

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**Table 3** Summary of interpreted crystallization ages and identified inherited ages.

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**Figure 1** A) Simplified geological map of the West African craton after Boher et al. (1992). Sketch shows the extension of the Leo-Man rise in the southern portion of the craton, defined by the Archean Kénéma-Man and Paleoproterozoic Baoulé-Mossi domain. Boxed area shown in detail in insert B; B) Simplified geological map, after Lebrun et al. (2016) of the study areas delineated in insert A. Zone 1 covers Burkina Faso, Mali northern Ghana and eastern Guinea, while zone 2 covers a portion of the Ashanti belt in southern Ghana. Map includes major structures and samples collected for geochronological work.

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**Figure 2** Simplified lithostratigraphic, deformation, geochronological chart highlighting geologic areas of interest for the present study, showing the timing of emplacement of the studied felsic intrusions. Modified after Baratoux et al. (2011), Block et al. (2015), (2016b), Lebrun et al. (2016), Miller et al. (2013), Perrouty et al. (2012), (2015), Miller et al. (2013) and Tshibubudze et al. (2015).

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**Figure 3** A) Characteristic rock exposure found across southern Mali and Burkina Faso; B) Granitic intrusion mostly composed of a fine grained quartz matrix, mineral assemblage includes biotite, quartz, and plagioclase phenocrysts of 2 mm by 4 to 5 mm (ML12-080); C) Least deformed portion of the Diallo Granite, which is quartz-feldspar-biotite rich (SU-021); and D) A granite, of equigranular texture, fine to medium grained. K-feldspar dominated, quartz and some plagioclase, black minerals are mostly biotite (ML12-105). All images refer to exposures in southern Mali.

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**Figure 4** Thin section images in XPL of characteristic samples showing mineral composition of rock samples identified across the study area; A) Major minerals, K-feldspar, quartz, plagioclase, biotite, small amounts of hornblende. Chlorite, sericitic alteration and traces of sulphides, other minerals include zircons, titanite and some hematite (ML12-068); B) Quartz, plagioclase, small amounts of K-feldspar, traces of pyrite and chalcopyrite, biotite and hornblende (SU_002); C) Angular K-feldspar crystals, minor amounts of plagioclase, relatively large amounts of brownish red biotite and some hornblende, chlorite and quartz (SU_001); D) Sericitic alteration, primary structures relatively easy to identify, mainly composed of large plagioclase crystals within a quartz matrix

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and traces of biotite, titanite, zircon, epidote and chlorite (BE5); E) Plagioclase, K-feldspar, quartz. Biotite is common, small amounts of sericitic alteration, most feldspar crystals appear intact (ML12-104); F) Plagioclase rich, original textures hard to identify due to pervasive sericitic alteration from the center of the crystals outwards, amphibole (hornblende) in some cases visible alteration into chlorite, minor amounts of quartz and small amounts of biotite, visible apatite/zircons, and additionally extensive occurrence of opaque minerals, majority of which appear to be pyrite (BNF150559); G) Quartz, plagioclase, biotite and muscovite. Quartz matrix is fine grained when compared to the plagioclase crystals. Accessory minerals include titanite, zircon, chlorite, ilmenite, signs of alteration some sericite visible (SU_007); and H) Quartz content between 5 to 15%, sample is plagioclase dominated, k-feldspar is not visible as samples is strongly altered and it is difficult to identify minerals and textures. Biotite and hornblende are also present. Alteration products are chlorite, epidote, and maybe actinolite (ML12-086).

**Figure 5** Selected zircon images showing the different morphological characteristics of zircon. A and B) Granites from the Belahouro Belt; C) Granodiorite from the Boromo-Hounde belts; D and E) Represent zircons from a diorite and a granite from the Banfora Belt; F) Zircon obtain from a granite of the Morila Belt; G, H, I and J) Zircons representing a porphyry, two granites and a syenite representative of the Yanfolila Belt; and K, L and M) Zircons from a granite, a dacite and a diorite from the Siguiri Basin. Notice that the zircons from granites and granodiorites are mostly elongated and tabular, while the zircons from diorites are slightly more rounded and display a faint zoning instead of the well-defined oscillatory zoning of zircons from the granites. Scale bar in all images represents 100 µm.

**Figure 6** A) Histogram showing new interpreted U-Pb crystallization ages distributed by belts and regions of geologic interest as described in the regional geology section; and B) Histogram showing the age distribution of the studied samples base on identified rock types.

**Figure 7** Age distribution by longitude color coded by volcanic belts and regions of geologic interest. A) Shows all ages while B) focuses on the age range between 2400 and 2000 Ma. Solid symbols represent U-Pb ages interpreted as crystallization ages; open symbols represent individual U-Pb analyses interpreted to represent inherited ages.

**Figure 8** Left Weight mean average age; right Concordia age plots. Black symbols are accepted analyses while red symbols represent rejected analyses. From top to bottom samples: across Burkina Faso, BF1 (Goren/Po-Tenkodogo-Yamba), BE5 (Belahouro Belt), HO629 (Boromo-Hounde belts), BNF 150559 (Banfora Belt) and from Mali ML12-086 (Bagoe Belt).
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**Figure 9** Weight mean average age; right Concordia age plots. Black symbols are accepted analyses while red symbols represent rejected analyses. Samples from across Mali: ML12-105 (Morila Belt), ML12-107 Bougouni region, MWAXI-126 (Yanfolila Belt), and from Guinea, KL000565 (Siguiri Basin).

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**Figure 10** Relative probability density diagrams, top A) this study ages east of the Bagoe Belt dominated by ages older than 2130 Ma Main peak ca. 2135 Ma, secondary peak at 2175 Ma; Bottom B) ages west of the Bagoe Belt dominated by ages between ca. 2100 and 2070 with a major peak at ca. 2095 Ma. 2130 Ma boundary after peak metamorphism exhumation of high-grade rocks identified by Block et al. (2015).

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**Figure 11** Zircon and monazite U-Pb age distribution across the southern West African Craton for the period between 2250 and 2050 Ma. A) Ages between 2300 and 2130 Ma, showing a marked concentration of ages in the eastern craton, and no recorded ages within the Archaean host rocks; B) Ages between 2130 and 2090 Ma, showing a uniform coverage of ages across craton for this age bracket, and several ages recorded within the Archaean host rocks; and C) Ages for the period 2090-2050 Ma, clearly showing that most ages are concentrated west of the Banfora-Bagoe belts in the westernmost portion of the study area. (520 ages from bibliography, Supplementary Material A).

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**Figure 12** Longitudinal variations in magmatic activity. A) Zircon and monazite U-Pb age distribution as a function of longitude (520 ages from bibliography, Supplementary Material A, Table 1, WAXI II compilation and this work). Notice this compilation only includes interpreted crystallization ages and metamorphic ages. Other not specified refers to ages from which the reference does not clarify specify source rock type or if it is a crystallization or metamorphic age. The sharp cessation of magmatism across the craton is clearly defined, with subsequent reworking limited to the margins of the craton, dashed line; B) zircon and monazite U-Pb age distribution as a function of longitude for the age bracket 2300-2000 Ma (455 ages) (Table 1, WAXI II age compilation and this work). The progressive cessation of the magmatic activity from east to west during this period in the southern West African Craton equates to a migration of approximately 35 km/Myr. Over 95% of all ages plot above the offset of magmatism line "magmatic front" (dashed bottom arrow).

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**Figure 13** Schematic cartoon showing the proposed boundaries and crustal blocks. Top, shows the Archean Kénéma-Man and the Baoulé-Mossi domain. The Baoulé-Mossi domain, which is divided into two blocks during the period 2160-2130 Ma. During the mentioned period the assemblage blocks are affected by compressional forces, first N-S (D1) as mentioned described by Baratoux et al. (2011), Block et al. (2016a), and Perrouty et al. (2012) the followed by a E-W compression (D2) (Baratoux et al., 2011; Block et al., 2016a; Perrouty et al., 2012). Density of the dot pattern indicates distribution of magmatic activity. Greater density = greater magmatism, and

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less density = less magmatism; and Bottom shows the amalgamation of the Paleoproterozoic blocks under a D2
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compressions for the period 2130-2110 Ma. Notice the occurrence of inherited grains. Inheritance is mainly
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concentrated in the eastern portion of the Baoulé-Mossi and predominately represented by ages between ca. 2500
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and 2125 Ma which are common crystallization ages across the easternmost portion of the study area, indicating
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that the western block is contaminated by crustal material derived from the eastern block.

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**Supplementary Material A.** Summary of published ages. The ages include emplacement and metamorphic events
as well as multiple dating methods. Blank spaces indicate a lack of available information in the data source.

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**Supplementary Material B.** Raw SHRIMP U-Pb data.

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**Supplementary Material C.** Raw LA-ICP-MS data.

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**10 Appendix A – Sample Preparation and Analytical Methods.**

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**A.1 Zircon mount preparation**

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The epoxy mounts are discs of 5 mm thick by 25 mm diameter. Three to four samples
were placed in each mount. Chips of the primary zircon standards BR266 (559 Ma, 903 U ppm;
Stern (2001)) or M257 (561.3 Ma and 840 ppm; Nasdala et al. (2008)), were used for U/Pb
calibration. Accuracy and reproducibility was monitored by including the secondary zircon
standards OGC1 (3465 Ma; Stern et al. (2009)), and Temora2 (416.8 Ma; Black et al. (2004)).
In addition chips of the silicate glass NIST 610 were included in the mounts for instrument set-
up purposes. The mounts were polished with diamond film polishing mats as fine as 0.5 µm.
Subsequently, the epoxy discs were cleaned using ethanol and petroleum spirits, a soap
solution, and rinsed with deionized water in an ultrasonic bath. Mounts were oven dried (1 hour
at 60°C) and the analytical surface was coated with a 40 µm gold layer. Detailed mounting
procedures and preparation can be reviewed in Claoué-Long et al. (1995).

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Mounts were imaged using the backscattered electron and cathodoluminescence
detectors of a JEOL 6400 Scanning Electron Microscope (SEM) or a VEGA 3 Tescan SEM at
the Centre for Microscopy, Characterization and Analysis (CMCA), University of Western
Australia (UWA). The acquired images allowed the identification of internal structures. Grains
showing a large number of cracks or obvious radiation damage were not analyzed.

690

## A.2 Sensitive High Resolution Ion Micro Probe (SHRIMP) dating

Zircon mounts were analyzed by means of Sensitive High Resolution Ion Micro Probe (SHRIMP II) at the John de Laeter (JDL) Centre for Isotope Research of Curtin University, Perth, Australia. Details of instrument operating conditions are described in De Laeter and Kennedy (1998) and Kennedy and De Laeter (1994) while analytical conditions are described in detail in Claoué-Long et al. (1995), Compston et al. (1984), and Williams (1988). The analytical procedure usually includes the use of a 25-30 µm diameter elliptical spot due to a mass-filtered (O₂)⁻ primary beam between 2.0 and 2.5 nA. Each dataset included six scans through the mass range of ¹⁹⁶Zr₂O⁺ (2 seconds), ²⁰⁴Pb⁺ (10 seconds), background (204.1) (10 seconds), ²⁰⁶Pb⁺ (20 seconds), ²⁰⁷Pb⁺ (30 seconds), ²⁰⁸Pb⁺ (10 seconds), ²³⁸U⁺ (5 seconds), ²⁴⁸ThO⁺ (5 seconds), and ²⁵⁴UO⁺ (2 seconds) (Nasdala et al., 2008). The data from each sample were reduced using the excel-based add-in program SQUID version 2.2 (Ludwig, 2003). Data reduction procedures were after Wingate and Kirkland (2014).

Zircon is a very resilient, refractory mineral that can survive partial melting and high grade regional metamorphism without losing its isotopic information (Mezger and Krogstad, 1997 references therein; Scherer et al., 2007). However, low grade metamorphism, fluid circulation and in some instances weathering can affect the U-Pb systematics, which results in discordant U-Pb ages. These discordant ages are for the most part due to Pb-loss (Mezger and Krogstad, 1997 references therein). In order to minimize the difficulties associated with potentially disturbed U-Pb systematics, for the purpose of this study U-Pb ages were only calculated from concordant to near concordant grains (discordance between -5% and +10%). Additionally, analyses that comprise more than 1% of non-radiogenic ²⁰⁶Pb (i.e., from common lead) and yield U concentrations over a 1000 ppm were also rejected.
714

715

A.3 LA-ICP-MS Zircon dating

716

717

718

719

720

721

722

723

Laser ablation U-Pb zircon dating was carried out at the GEMOC/CCFS Centre. The method used an Agilent 7700 quadrupole Inducted Coupled Plasma Mass Spectrometer (ICP-MS) attached to a New Wave/Merchantek UP-213 laser ablation system (λ=213 nm). Beam diameter was set at 30 or 40µm, based on zircon size. Beam repetition was set at 5 Hz rate and energy around 0.06 µJ and 8 J/cm2. He was used as transport media, as it increases sample transport efficiency during the ablation process. Using He provides a more stable signal, and therefore a more reproducible Pb/U fractionation. Additional description and details are founded in Belousova et al. (2010) and Jackson et al. (2004).

724

725

726

727

728

729

730

731

732

733

734

735

736

737

738

U-Pb data was determined by analyzing twelve unknown samples for every two analyses of the GEMOC GJ-1 zircon standard (Elhlou et al., 2006). GJ-1, TIMS<sup>207</sup>Pb/<sup>206</sup>Pb age of 608.5 Ma (Jackson et al., 2004). Zircon standards 91500 (U-Pb age 1065 Ma, Wiedenbeck et al., 1995) and Mud Tank (U-Pb age 732 Ma, Black and Gulson, 1978) were analyzed as secondary control standards for reproducibility and instrument accuracy. U-Pb ages were calculated from the raw signal data using the GLITTER software program after Griffin et al. (2008). Further details on integrated ration, fractionation, time resolved intervals, and instrumental mass bias and calibrating procedures are provided in Griffin et al. (2008) and Jackson et al. (2004). Information on common-Pb correction procedures are provided in Andersen (2002). Analyses reported in this study were corrected assuming recent Pb-loss and a common-Pb composition similar to present day average orogenic Pb as given by the second-stage growth curve of Stacey and Kramers (1975) for <sup>238</sup>U/<sup>204</sup>Pb = 9.74. No correction has been applied to analyses that are concordant within 2σ analytical error in <sup>206</sup>Pb/<sup>238</sup>U and <sup>207</sup>Pb/<sup>235</sup>U, or which have less than 0.2% common-Pb. All described procedures are after Andersen et al. (2004), Belousova et al. (2010), Griffin et al. (2008) and Jackson et al. (2004).
Abati, J., Aghzer, A.M., Gerdes, A., Ennih, N., 2012. Insights on the crustal evolution of the
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zircon standards. Chemical Geology. 205, 115-140.
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model for late-orogenic Paleoproterozoic granitoids: the Tenkodogo–Yamba elongate

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pluton (Eastern Burkina Faso). Journal of African Earth Sciences 38, 41-57.

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mineralization and Paleoproterozoic crustal evolution in the Ashanti belt of southern

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Parra-Avila, L.A., Belousova, E., Fiorentini, M.L., Baratoux, L., Davis, J., Miller, J., McCuaig,

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Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of

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# The geochronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton

## Authors:

Luis A. Parra-Avila, Anthony, I. S. Kemp, Marco L. Fiorentini, Elena Belousova, Lenka Baratoux, Sylvain Block, Mark Jessell, Olivier Bruguier, Graham C. Begg, John Miller, James Davis, T. Campbell McCuaig.

## Highlights

* 84 new U-Pb zircon ages on rocks from across the Paleoproterozoic Baoulé-Mossi domain.

* Newly identified U-Pb age patterns and distribution across the southern West African Craton with a westward migration of the magmatic front.

* Recognition of U-Pb age inherited patterns as well as Archean inherited grains across the Paleoproterozoic Baoulé-Mossi domain of the West African Craton.
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# The geochronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern West African Craton

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## Authors:

Luis A. Parra-Avila a,b, Anthony, I. S. Kemp a, Marco L. Fiorentini a,b, Elena Belousova b,

Lenka Baratoux c,d, Sylvain Block d, Mark Jessell a,d, Olivier Bruguier e, Graham C. Begg a, b, f,

John Miller a, James Davis a, T. Campbell McCuaig a.

## Affiliations:

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a Centre for Exploration Targeting, School of Earth Sciences, The University of Western Australia, Perth, WA 6009, Australia

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b Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Macquarie University, NSW 2109, Australia

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c IFAN, Université Cheikh Anta Diop, Dakar, Sénégal

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d Géosciences Environnement Toulouse, Observatoire Midi Pyrénées, 14 ave E. Belin, 31400, Toulouse, France

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e Géosciences Montpellier, Université de Montpellier, Place Eugene Bataillon, 34 095 Montpellier cedex 5, France

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f Minerals Targeting International PL, West Perth, WA 6005, Australia

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26
27 **Keywords**

28 West African Craton, Paleoproterozoic, Baoulé-Mossi domain, U-Pb zircon dating

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30 **Abstract**

31 Generation and emplacement of felsic magmas in the Paleoproterozoic Baoulé-Mossi domain,
32 West African Craton does not match the apparent peaks of global crust generation identified
33 between ca. 2900-2600, 1900-1600 and 1200-900 Ma. In contrast, across the Baoulé-Mossi
34 domain, the emplacement of felsic intrusions ranges from ca. 2300 to 2000 Ma. It has proven
35 difficult to place this magmatism within a robust geodynamic framework due to the lack of
36 accurate geochronological data from across the West African Craton. The present study
37 addresses this issue by presenting eighty-four new felsic intrusions zircon ion microprobe and
38 LA-ICP-MS U-Pb ages from areas that up until now have not been targeted for geochronology.

39 The new dataset, when fully integrated with existing age data, reveals a craton-wide
40 diachronous geochronological pattern characterized by a magmatic front that migrated
41 westward. This migration proceeded at a rate of 35 km per million years, with an apparent
42 offset of the initiation and cessation of felsic magmatic activity between the east and west of
43 approximately 50 million years. The new data also show that although the entire Baoulé-Mossi
44 domain was subject to continuous magmatic activity for at least 150 million years, this
45 magmatic activity displays a rather different record in the eastern and western portions of the
46 domain. The differences are expressed as a westward migration of the magmatic activity,
47 cessation of activity around ca. 2100 Ma (easternmost portion) and ca. 2050 Ma (westernmost
48 portion) and a higher incidence of inherited ages in the westernmost portion when compared
49 to the easternmost region. In addition, the new U-Pb data identify some of the oldest felsic
50 intrusions in the region, including a granite from Burkina Faso (2265 ± 17 Ma) and a diorite
51 porphyry (2216 ± 5 Ma) in southern Mali. This study also reveals inherited Archean zircon
cores from across southern Mali. The combination of the new data presented here, along with
previously published data, suggests that the Baoulé-Mossi domain formed from the accretion
of two major crustal blocks. The Archean inherited ages open a window for further
investigation of the interaction between the Archean Kénéma-Man and the Paleoproterozoic
Baoulé-Mossi domains.

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## 1 Introduction

Radiometric ages obtained from igneous and metamorphic rocks across the West
African Craton are mainly concentrated between ca. 2300 and 2000 Ma. This period falls
outside the main peaks of global magmatic activity preserved at ca. 2900-2600, 1900-1600 and
1200-900 Ma (Cawood et al., 2009 and references therein; Condie, 1998, 2009). It is possible
that the complete magmatic record of the West African Craton is either under-represented or
under-sampled in the current geochronological databases. The southern West African Craton,
known as the Leo-Man Rise, comprises the Archean Kénéma-Man and the Paleoproterozoic
Baoulé-Mossi domains (Figure 1). Despite the wealth of studies aimed at deciphering the large
metallogenic endowment of the Leo-Man rise and in particular of the Baoulé-Mossi domain
(e.g. Béziat et al., 2000; Feybesse et al., 2006a; Milési et al., 1991, 1992; Oberthür et al., 1998),
the southern West African Craton remains one of the least understood and controversial
lithospheric blocks on Earth. One of those controversies is directly related to the age of
emplacement of the felsic igneous suites, and the apparent lack of involvement of older
Archean crust in a region that is regarded to be the result of juvenile magmatic activity
(Abouchami et al., 1990; Boher et al., 1992).

Multiple studies on the geochronological evolution of the southern West African Craton
have been carried out across the Baoulé-Mossi domain (e. g. Baratoux et al., 2011; Block et
al., 2016a; de Kock et al., 2011, 2012; Egal et al., 2002; Feybesse et al., 2006a, 2006b, 2006c;
Gueye et al., 2007; Tshibubudze et al., 2013, 2015). Nonetheless, most of these studies are the result of mine-scale to belt-scale mapping projects, in many cases restricted to small regions or particular countries, thus failing to attempt large-scale correlations across the Baoulé-Mossi domain. According to these studies, the emplacement ages of felsic intrusions from across the domain are mainly associated with the Eburnean Orogeny (ca. 2200-1800 Ma, Liégeois et al., 1991) and represent approximately half of the total rock exposures across the domain (Boher et al., 1992; Roddaz et al., 2007).

Felsic intrusions from across the Baoulé-Mossi domain were described by Bessoles (1977) and originally divided into 3 main types: Belt or Dixcove, Sedimentary-Basin or Winneba and Basin or Cape Coast suites (e.g. Abouchami et al., 1990; Boher et al., 1992; Davis et al., 1994; Hirdes et al., 1992, 1996; Taylor et al., 1992). de Kock et al. (2011), (2012) further summarize the magmatic activity into 4 major age clusters or peaks at: ca. 2210-2190, 2185-2150, 2115-2100 and 2090-2070 Ma. Despite this apparent periodicity, published ages for these clusters tend to overlap within uncertainty, suggesting a continuous period of magmatic activity between ca. 2210 and 2050 Ma (de Kock et al., 2011, 2012).

The present study is a comprehensive evaluation of the chronological evolution of the Paleoproterozoic Baoulé-Mossi domain of the southern portion of the West African Craton, aimed at establishing regional-scale correlations and shedding new light on the evolution of the region. The study area extends over Burkina Faso, southern Mali, eastern Guinea and parts of Ghana (Figure 1). A total of seventy-five new ion microprobe (SHRIMP II) and nine LA-ICP-MS U-Pb zircon ages are presented in this study and cover an area of over 250 000 km². The new data establish that the magmatic activity across the Baoulé-Mossi domain was continuous for at least 150 million years (Myrs), and migrated westward at a rate of 35 km/Myrs.
102 **2 Geological Setting**

103 The West African Craton is composed of three major provinces: the Reguibat Rise to
104 the north, the Kédougou-Kéniéba and Kayes Inliers to the west and the Leo-Man rise to the
105 south (Abouchami et al., 1990; Bessoles, 1977; Boher et al., 1992) which circumscribe the
106 younger Taoudenni Basin (Figure 1). The Leo-Man Rise, covering Burkina Faso, Côte
d'Ivoire, Ghana, Guinea, Liberia, Mali, Niger, Senegal, Sierra Leone and Togo is geologically
107 divided into the Archean Kénéma-Man and the Paleoproterozoic Baoulé-Mossi domains
108 (Figure 1). The Archean portion of the Leo-Man Rise is composed of highly metamorphosed,
109 amphibolite to granulite facies, gneisses formed between ca. 3600 and 2600 Ma (Milési et al.,
110 1992; Rollinson, 2016) and believed to be largely the result of the Leonian (ca. 3200-3000 Ma)
111 and/or Liberian (ca. 2800-2700 Ma) orogenic cycles (Egal et al., 2002). Recently De Waele et
112 al. (2015) refined the timing of crust formation to a pulse of magmatic activity at ca. 3400 Ma,
113 which was followed by semi-continuous magmatic activity between ca. 3000 and 2600 Ma.
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115 The Paleoproterozoic counterpart is divided into two main phases, the Eoeburnean or
116 Tangaean (ca. 2266 and 2150 Ma) and the Eburnean (ca. 2130 and 1980 Ma) phases (Baratoux
117 et al., 2011, 2015; Block et al., 2015; de Kock et al., 2012; Feybesse et al., 2006; Hein 2010;
118 Perrouty et al., 2012; Vidal et al., 1996). The Paleoproterozoic crust comprises narrow
119 sedimentary basins and linear to arcuate belts comprising volcanic and volcaniclastic rocks
120 intruded by multiple generations of granitic rocks (Abouchami et al., 1990; Boher et al., 1992;
121 Taylor et al., 1992). The Eoeburnean phase is dominated by mafic and felsic volcanism,
122 granitic emplacement and folding as the result of a collisional event and crustal thickening
123 (Baratoux et al., 2015; Lambert-Smith et al., 2016; Tshibubudze et al., 2015), while the
124 Eburnean phase is characterized by plutonic activity. The Eoeburnean and Eburnean
125 terminology and characteristics are not uniform across the entire Paleoproterozoic domain as
126 summarized by Lambert-Smith et al. (2016). The stratigraphic sequence of the Baoulé-Mossi
domain is defined in Vidal et al. (1996) and later refined by Béziat et al. (2000), de Kock et al., (2009, 2011), Baratoux et al. (2011), and Ganne et al. (2014) (Figure 2). Recent studies by Pitra et al. (2010), Baratoux et al. (2011), Ganne et al. (2014) and Block et al. (2015) have reiterated that the lithostratigraphic sequence has been generally affected by greenschist facies metamorphism, but also highlight regional amphibolite facies and locally granulite facies metamorphism.

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## 2.1 The Birimian terranes

The term “Birimian terranes” after the type locality defined from the Birim River Valley in Ghana (Kitson, 1918) is applied to the Paleoproterozoic domain of the southern West African Craton. The Birimian stratigraphy (sensu lato) is defined, bottom to top, by the presence of: 1) a thick sequence of locally pillowed basalts and gabbros of tholeiitic affinity (Hirdes et al., 1996; Leube et al., 1990), interlayered with immature sedimentary rocks and carbonates; 2) a volcano-sedimentary sequence mainly dominated by turbidites, mudstones and carbonates, interbedded with calc-alkaline volcanic and volcaniclastic rocks (Kesse, 1985; Olson et al., 1992); and 3) a coarse, clastic sedimentary sequence that was originally defined by Junner (1940), (1954) and later by Trashliev (1974) as a series of turbidites (Attoh, 1982; Béziat et al., 2000, 2008; Pouclet et al., 1996; Vidal et al., 1996).

Regionally, across Burkina Faso, the Birimian terranes comprise a series of basaltic to basaltic andesitic belts, from east to west, the NNW-striking Bouroum Belt, the NW-striking Goren Belt, and the N-S striking Boromo, Hounde and Banfora belts (Figure 1). All belts are intruded by N-S trending granitic bodies (Hein, 2010; Metelka et al., 2011). Additionally, Baratoux et al. (2011) and Castaing et al. (2003) summarized several NNW to NE-trending shear zones, defined as the Greenville-Ferkessedougou-Bobo Dioulasso, the Bossie, the West Batie and the Boromo-Poura shear zones (Figure 1).
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Further to the west across southern Mali, the Birimian is composed of three N-S trending volcano-sedimentary belts and two regional shear zones. These belts from east to west are: 1) the Bagoe Belt, considered to be the NW extension of the Diaoulla-Boundiali Belt of Côte d'Ivoire (Traoré et al., 2016; Turner, 1995) near the Burkina Faso-Mali border; 2) the Morila Belt, just east of the large Bougouni granitic batholith (Hammond et al., 2011; Parra-Avila et al., 2016); and 3) the Yanfolila Belt, which sits between the town of Bougouni and the Mali-Guinea border. Major shear zones in the region are the Siekeroli and Bannifin shear zones (Figure 1) (Feybesse et al., 2006b, 2006c; Liégeois et al., 1991; McFarlane et al., 2011).

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## 2.2 Geochronology and geochemical overview of the Paleoproterozoic Baoulé-Mossi domain
felsic intrusions

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Felsic intrusions in Burkina Faso are divided according to their host volcanic belts. Across the NE-E portion of the country, authors such as Castaing et al. (2003), Hein et al. (2004), (2010), Naba et al. (2004), Tshibubudze et al. (2009), (2013), (2015) and Vegas et al. (2008) described the intrusions as NE-SW-trending, medium to coarse-grained equigranular granodiorites, tonalites, quartz-diorites, quartz-monzodiorites and granites. Zircon U-Pb ages indicate that the intrusions are as old as ca. 2260 Ma (Tshibubudze et al., 2015).

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Metelka et al. (2011) subdivided the felsic intrusions across Burkina Faso into three types: 1) medium to coarse grained, amphibole and biotite rich, with minor occurrences of K-feldspar tonalites, trondhjemites and granodiorites, emplaced between ca. 2150 and 2130 Ma; 2) K-feldspar and biotite rich granodiorites and granites, rarely containing muscovite or amphibole, and granodiorites with ages between ca. 2110 and 2100 Ma; and 3) K-feldspar rich potassic granites, which occasionally bear muscovite (ca. 2110-2090 Ma, Eburnean).

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Baratoux et al. (2011) suggested that volcanic activity across western Burkina Faso occurred between ca. 2190 and 2160 Ma (Eoeburnean). Additionally, by combining field

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observations and airborne geophysical data Baratoux et al. (2011), Block et al. (2015), and Metelka et al. (2011) determined that the granitic intrusions in northern Ghana and western Burkina Faso can be grouped into four main magmatic episodes: granite, granodiorite and gabbroid emplaced between 2195 and 2160 Ma (Pre-ME1), ME1 composed mainly of tonalite, trondhjemite, granodiorite (TTG) emplaced at ca. 2160-2120 Ma; ME2, dominated by granodiorites and granites (ca. 2120-2110 Ma, Eburnean); and ME3 represented by granites (2110-2090 Ma, Eburnean).

Farther to the west across southern Mali, felsic intrusions are far less studied, and no large-scale correlations have been made. Most studies across southern Mali are at the local/mine-scale. Liégeois et al. (1991) recognized three main types of N-S striking felsic intrusions around the Bannifin shear zone: 1) plagioclase, microcline, quartz, hornblende and biotite rich, equigranular, fine-grained (occasionally aplitic) quartz-diorites, quartz-monzodiorites and granodiorites (ca. 2075 Ma, Eburnean), locally known as the Sadiola type; 2) foliated homogenous potassic pink leucogranites known as the Massigui type; and 3) fine to medium grained granitic intrusions containing biotite and variable amounts of K-feldspar, locally known as the Doubalakoro type.

In a study around the Morila gold mine, McFarlane et al. (2011) identified gold-bearing granodiorites as well as foliated porphyritic intrusive bodies and granites with pegmatitic textures. Granodiorite bodies are described as being biotite rich with plagioclase phenocrysts, similar to the Sadiola type. The porphyritic intrusions are composed of very fine grained plagioclase, quartz, actinolite and biotite. A second generation of intrusions is described as quartz diorites to biotite leucogranites similar to the Doubalakoro pluton of Liégeois et al. (1991). Finally, the third generation described by McFarlane et al. (2011) consists of leucogranites and two mica (muscovite/biotite) rich granites and pegmatites, with U-Pb zircon ages ranging between ca. 2130 and 2090 Ma (Eburnean). In addition to the types described by
Liégeois et al. (1991) and McFarlane et al. (2011), an older generation has been documented by Feybesse et al. (2006b), (2006c) and references therein. This older intrusion is represented by a monzonitic orthogneiss that yielded a zircon U-Pb age of 2150 ± 15 Ma, with an inherited zircon population at 2174 ± 8 Ma (Eoeburnean) (Feybesse et al., 2006b, 2006c).

In general, intrusions across the Paleoproterozoic domain of the southern West African Craton have been mainly described as TTG-like (Doumbia et al., 1998; Vidal et al., 2009, and references therein), based on normative Anorthite-Albite-Orthoclase discrimination diagrams after Barker (1979) and O’connor (1965). The intrusions have historically been divided into three main groups: 1) amphibole bearing granitic rocks, with or without biotite, usually foliated; 2) biotite bearing granitic rocks without amphibole; and 3) potassic alkaline plutons (Castaing et al., 2003; Doumbia et al., 1998; Egal et al., 2002; Gasquet et al., 2003; Hirdes et al., 1992, 1996; Liégeois et al., 1991; Lompo, 2009; Naba et al., 2004; Oberthür et al., 1998; Tapsoba et al., 2013; Vegas et al., 2008). Supplementary Material A summarizes the emplacement ages reported for these intrusions.

The geochemistry of felsic intrusions across Burkina Faso, Mali and Ghana, are extensively documented and broadly summarized as calc-alkaline/magnesian with arc-like trace element signatures, including negative Nb, Ta, P, Ti as well as REE fractionation and Eu anomalies (e.g. Baratoux et al., 2011; Block et al., 2016a; Castaing et al., 2003; Egal et al., 2002; Eglinger et al., 2017; Feybesse et al., 2006a, 2006b, 2006c; Gasquet et al., 2003; Hein et al., 2004, 2010; Lambert-Smith et al., 2016; McFarlane et al., 2011; Metelka et al., 2011; Naba et al., 2004; Peterssen et al., 2016, Tapsoba et al., 2013 and Vegas et al., 2008).

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## 3 Samples and Analytical Methods

To compare the magmatic activity of the Paleoproterozoic Baoulé-Mossi domain, where precise ages are scarce, with the age peaks recognized in the global magmatic record an
227 integrated geochronological dataset on igneous rocks from southern Mali, was established.
228 Additional samples from Burkina Faso and some from eastern Guinea and Ghana provide ages
229 from the whole Paleoproterozoic domain. Samples were collected over 3 field seasons and were
230 carefully selected to give the most representative and comprehensive overview of the
231 characteristics of the different plutons across the region (Figure 3). Each sample was
232 approximately 3-6 kg in weight.

233 In Burkina Faso, granitic intrusions were sampled from east to west: 1) across the Po-
234 Tenkodogo-Yamba region and the Goren Belt; 2) around the Inata-Belahouro gold district,
235 Bouroum Belt; 3) in the surroundings of the Perkoa zinc mine, Boromo Belt; 4) in the Gaoua
236 region, Hounde Belt; and 5) adjacent to the Banfora Belt. In Mali, sampling focused: 1) across
237 the Syama Mine, Bagoe Belt; 2) on granitic intrusions around the Morila mine, Morila Belt; 3)
238 on granitic outcrops of the Bougouni region; and 4) across the Kalana and Komana regions of
239 the Yanfolila Belt. In Guinea, samples were obtained from granitic intrusions outcropping in
240 the Siguiri Basin area. Finally, in Ghana samples were obtained from the Koudougou-Tumu
241 granitic domain, northern Ghana, and across the Ashanti Belt-Kumasi Basin region of southern
242 Ghana (Table 1, Figure 1 and larger insets with the sample points). In addition to surface
243 samples, a series of felsic porphyries were collected from drill cores provided by exploration
244 and mining operators, mainly across the Yanfolila Belt (Mali) and the Siguiri Basin (Guinea).

245

246 **3.1 Rock description and petrology**

247 Rock classification was made based on 3 parameters: 1) hand specimen observations;
248 2) CIPW norm; and 3) modal composition determined from microscopic evaluation of thin
249 sections, characterized after Streckeisen (1976) (Tables 2 and 3).

250

251 **3.2 Zircon morphology and U-Pb dating**
252

Zircon concentrates were obtained following the standard procedures described in Claoué-Long et al. (1995). Sample processing to obtain zircon concentrates, zircon mount procedures and zircon imaging, which include the use of backscattered electron (BSE) and cathodoluminescence (CL) detectors, are described in Appendix A1. Detailed information about U-Pb isotope analysis of zircon by SHRIMP (Appendix A2) and LA-ICP-MS (Appendix A3), the criteria for rejection of analyses and data reduction are explained in Appendix A2.

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# 4 Results

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## 4.1 Rock description and Petrology overview

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The petrological characteristics of the igneous rock samples are summarized in Table 2. Macroscopic and microscopic observations reveal that 48% of the samples are represented by granites while the rest are represented by monzodiorites, diorites, aplites and syenites. Additionally, two gabbros are identified. The drill core samples are classified as porphyries (Tables 1 and 2).

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Based on mineralogy, 3 main groups of intrusions were identified: 1) biotite bearing, characterized by plagioclase, alkali feldspar, quartz, with or without hornblende, titanite, apatite, zircon and variable amounts of sulfide and oxide phases (Figure 4-A, C and E); 2) two mica intrusions, rich in plagioclase, alkali feldspar, muscovite, biotite, quartz, and zircon as well as variable amounts of sulfides (Figure 4-B and G); and 3) porphyries, mainly from drill core samples, consisting of altered to very altered fine-grained and recrystallized matrix with abundant calcite (Figure 4-H). Other minerals within the matrix include biotite, traces of muscovite, epidote and chlorite. Overall, the biotite in the single mica intrusions is greenish to (primarily) reddish-brown. Biotite in the two mica intrusions is mainly greenish and occasionally reddish-brown. Hornblende appears to be only present in a limited number of single mica samples. Titanite is mainly euhedral, bladed and light brown in color, but is also

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present as wedge-shaped grains that are darker brown in color. Zircon forms euhedral,
elongated grains with visible oscillatory zoning, characteristic of an igneous origin.

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In the case of the porphyry samples, original matrix textures are not easily identifiable.
Relict phenocrysts are for the most part plagioclase. Deformation and mineral alignment is
evident in some samples. Phenocryst grain boundaries appear sharp and unaltered in some
samples while in others they appear deformed, with signs of recrystallization.

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## 4.2 Zircon morphology

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The majority of zircon grains are clear to slightly translucent and pale reddish-brown, while a small percentage are more intense reddish-brown. Most crystals are elongated, with either sharp or in some cases slightly rounded dipryramidal crystal form, and between 25 to 80 µm wide and 120 to 300 µm in length. Fragmented or broken zircons are probably the result of the mineral separation process. Most zircons show clear oscillatory zoning of variable intricacy, whereas others have either faint or broad zoning. Additional features evident in CL images include the recognition of high U concentration, which is identified due to metamict features, and distinct central regions with very dark brown coloration, possibly reflecting the presence of xenocrystic cores (Figure 5).

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## 4.3 Zircon U-Pb dating

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A total of 84 samples were dated by zircon U-Pb method, 27 samples from Burkina Faso, 50 from Mali, 5 from Guinea and 2 from Ghana (Figures 6 and 7, Table 3). Table 3 summarizes the ²⁰⁷Pb/²⁰⁶Pb age results (weighted mean ages are at 95% confidence limit). Figures 8 and 9 shows U-Pb Concordia plots and weighted mean ²⁰⁷Pb/²⁰⁶Pb ages for the 9 belts and 2 large batholiths studied. Supplementary Materials B (SHRIMP) C (LA-ICP-MS) contains the full set of (U-Th)-Pb isotope data.
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Zircons from 58 samples yielded a single age population, while the remaining 26 samples contain zircon with older cores, which are interpreted as inherited components. The number of inherited grains is variable between samples and ranges from 1 or 2 analyses to 10 (Table 3). Across Burkina Faso, the Goren Belt/Po-Tenkodogo-Yamba regions, yield ages between ca. 2270 and 2120 Ma. For the Belahouro region the ages are between ca. 2180 and 2120 Ma and in the Boromo-Hounde belts the range is between ca. 2180 and 2110 Ma, while the Banfora region have ages between ca. 2150 and 2110 Ma (Figures 6 and 7).

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In southern Mali, the felsic intrusion from the Syama mine (Bagoe Belt) is dated at ca. 2150 Ma. Farther to the west, the Morila Belt granites and granodiorites have inferred emplacement ages between 2140 to 2080 Ma. Across the Bougouni domain, the emplacement occurred between ca. 2100 and 2080 Ma while the Yanfolila Belt, was intruded between ca. 2220 and 2070 Ma (Table 3, Figures 6, 7 and 9).

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The rocks analyzed are mainly granites and granodiorites with the bulk dated between ca. 2140 and 2080 Ma. The other dated intrusions are mainly porphyries, diorites and tonalites (Figure 6). Three of the 9 diorites have inherited grains of up to ca. 3500 Ma. A total of 12 granites have inherited zircon cores up to ca. 2250 Ma. The porphyry intrusions shows significant inheritance of material up to ca. 2500 Ma old. The granitic intrusions with Archean inheritance are mainly biotite bearing, characterized by plagioclase, alkali feldspar, quartz, with or without hornblende and muscovite. Assimilation of older crust during the generation of the 2 mica (biotite and muscovite) and 1 mica (mainly biotite) intrusions, as illustrated by inherited zircon, is also evident.

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## 5 Discussion

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The new data presented here constitute a comprehensive and spatially representative geochronological dataset from the Paleoproterozoic Baoulé-Mossi domain of the West African
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Craton. Together with previously reported ages, broad U-Pb age and inheritance patterns can be visualized across the craton. The implications of these new data for tectonic evolution are explored in the following sections.

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## 5.1 Magmatic activity from the Goren/Po-Tenkodogo-Yamba to the Banfora Belt

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A granodiorite from the Goren/Po-Tenkodogo-Yamba region (BF8) with an apparent age of 2265 ± 17 Ma is similar to that obtained by Tshibubudze et al. (2013), (2015) for granites across the Oudalan-Gorouol Belt (ca. 2265 Ma) expanding the known occurrences of older intrusives presented in compiled data, by e.g. Baratoux et al. (2011), de Kock et al. (2011), (2012), Feybesse et al. (2006b), (2006c), McFarlane et al. (2011), Tapsoba et al. (2013) and Tshibubudze et al. (2015).

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The youngest ages across the easternmost portion of the study area in Burkina Faso are ~2105 Ma (BF12-05), 2115 Ma (HO640C) and 2120 Ma (BF1), belonging to the Eburnean phase, which are mainly concentrated along the Banfora Belt region, with minor occurrences in the Boromo-Hounde and Belahouro belts. These young granite ages make it clear that felsic magmatic activity across the eastern portion of the Paleoproterozoic Baoulé-Mossi domain occurred over a period of about 160 Myrs. During this period, magmatic activity was minor between ca. 2275 and 2190 Ma, after which it increased to peak between 2140-2130 Ma. Magmatic activity then waned, with the last bodies emplaced at ca. 2105 Ma (Figures 6, 7, and 9). After ca. 2105 Ma the magmatic activity appears to be concentrated in the western portion of the Baoulé-Mossi across southern Mali.

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## 5.2 Magmatic activity from the Banfora Belt to the Siguiri Basin

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West of the Banfora Belt and into southern Mali and eastern Guinea, this study clearly lengthens the magmatic evolution of the Baoulé-Mossi domain. Previous studies that evaluated

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the magmatic activity indicated a period of 30 Myrs between ca. 2100 and 2070 Ma, which was associated with the Eburnean orogenesis (Liégeois et al., 1991). Conversely, Doumbia et al. (1998), Hirdes and Davis (2002), and Hirdes et al. (1996) indicated that the granitic intruded between ca. 2150 and 2070, a period of 80 Myrs. The Porphyries from the Yanfolila Belt, however revealed intrusions at 2159 ± 11 Ma (MWAXI-135), 2174 ± 15 Ma (MWAXI-130) and 2216 ± 15 Ma (MWAXI-134) extending the range of magmatism across the region. The felsic magmatic activity progressively increased during the Eburnean phase between ca. 2100 Ma and 2070 Ma, peaking around ca. 2090 Ma and abruptly declining after ca. 2070 Ma (Figures 6, 7 and 9). Overall the range of magmatic activity lasted about 150 Myrs, mostly concentrated between ca. 2100 and 2070 Ma. These findings may suggest an accretionary evolution for the southern West African Craton (section 6).

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### 5.3 Broad age patterns across the Baoulé-Mossi domain

The early and punctuated magmatic activity recorded in the Yanfolila Belt contrasts with the rest of southern Mali, where only a limited number of samples are older than ca. 2110 Ma. Volcanism in the belt has been recognized as early as ca. 2212 Ma by Lahondère et al. (2002) whom associated this early activity with felsic to intermediate volcanism resulting from subduction or underplating. Early volcanism is present in the east of the Banfora Belt, as reported by Hein (2010) and Tshibubudze et al. (2013), (2015). Since these older ages (> ca. 2250 Ma in Burkina Faso and > ca. 2200 Ma in southern Mali) are not more common, either the overall volume of magmatism was relatively low during this period, or intrusions of this age are buried or have been eroded away. Alternatively, a more mafic style of magmatism may have resulted in less zircon crystallization.

Integration of the new and published data shows that for the southern West African Craton the emplacement ages fall into an “early” period at 2260-2130 Ma, which is dominated
by pluton emplacement (Figure 11-A), followed diachronously by a "late" period (2130-2050 Ma). The boundary between the early and late periods was chosen after considering peak metamorphism in the region, deformation history, and spatial distribution of the ages across the study area and identifiable age peaks (Figures 2, 6, 7 and 11). While the probability of occurrence of ages shown in figure 10 suggests a boundary can be placed around ca. 2110 Ma, the spatial distribution is more in agreement with a boundary ca. 2140-2130 Ma. Additionally, the peak metamorphism identified by Block et al. (2015) between ca. 2140-2130 Ma, roughly coincides with the peak of magmatism in the eastern portion of the study area. The early period, which is comparable to the Eoeburnean phase, is dominated by a major peak at ca. 2135 Ma and a secondary peak at ca. 2170 Ma. The late period coincides with the Eburnean phase of de Kock et al. (2011) and can be further subdivided into two age brackets, between ca. 2130-2090 Ma (Figure 11-B) dominated by craton wide magmatic activity, and 2090-2050 Ma (Figure 11-C) where magmatic activity was predominantly concentrated in the western portion of the craton. As observed in figures 2 and 11 emplacement and deformation events did not occur synchronously across the study area and it is clear that diachronism between east and west presents difficulties in the definition of the Eoeburnean and Eburnean phases across the study area as summarized in Lambert-Smith et al. (2016).

Additionally, when all magmatic, metamorphic and detrital zircon ages are plotted as a function of longitude for the whole southern West African Craton (Figure 12-A), it is possible to define the onset and cessation of magmatic activity as a function of distance across the southern West African Craton. This reveals an apparent offset of 50 Myrs in the beginning and end of magmatism between the eastern and western part of the Baoulé-Mossi domain (Figure 12-B). Such patterns indicate that magmatic activity progressively retreated from east to west across the southern West African Craton at a rate of approximately 35 km/Myr (Section 6). This inference is strengthened by the fact that 95 % of the plotted ages lie above the dashed
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bottom arrow in Figure 12-B, which shows the diachronism in the onset and cessation of magmatism.

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### 5. 4 Zircon inheritance

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The majority of the inherited zircons are within 50 Myrs or less of the crystallization ages of the individual intrusions, and mostly occur across southern Mali and to a lesser extent in the easternmost portion of Burkina Faso, across the Goren/Po-Tenkodogo-Yamba and Belahouro belts. Inheritance is mainly present in samples younger than ca. 2130 Ma. Only a limited number of samples have inherited cores/grains (30 out 90 samples), of which a half (15 samples) have inherited material older than 2200 Ma. The previous findings are in agreement with studies along the southern margin of the Bole-Nangodi Belt of northern Ghana, where de Kock et al (2011) identified Eoeburnean inheritance in intrusions up to 2130 Ma.

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Only 4 samples (KADD119-M, KL000274, ML12-078 in Mali, and BF9 in Burkina Faso) assimilated Archean crust, as indicated by inherited zircons with ages between ca. 3700 and 2500 Ma. Evaluation of rejected discordant analyses (criteria explained in Appendix A) does not reveal age groups different from the inferred crystallization ages, or from the reported inherited ages (Table 3).

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With the exception of de Kock, (2011) and Lambert-Smith et al. (2016) who identified inherited Archean zircons in northern Ghana and in the Kédougou-Kéniéba Inlier of Mali, respectively early studies failed to identify Archean inheritance. The absence of Archean crust has been used to argue that the Baoulé-Mossi domain was mostly the result of juvenile magmatic activity (Abouchami et al., 1990; Boher et al., 1992; Tapsoba et al., 2013). The present study identified 2 zircon grains with ages between ca. 3600 and 3500 Ma, 1 grain at ca. 2880 Ma and 3 grains that yield ages between ca. 2600-2500 Ma; these are from the Goren/Po-

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Tenkodogo-Yamba region and Belahouro Belts in Burkina Faso and in the Yanfolila Belt in
southern Mali (Table 3).

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5.4.1 *Possible origin of the zircon inheritance*

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Two scenarios are envisaged to explain the zircon inheritance found in some samples:
1) assimilation of older crust by ascending magmas (contamination of ascending magmas by
older basement rocks); and 2) assimilation from a sedimentary source where they were detrital
grains. Both scenarios could potentially be the result of Eburnean orogenesis. According to
Baratoux et al. (2011), Tshibubudze et al. (2013) and (2015) eastern Burkina Faso was subject
to an early compressional event (2200-2160 Ma) that led to significant shortening and crustal
thickening. Liégeois et al. (1991) also identified deformation events across southern Mali that
resulted in intense folding and thickening and, plausibly, subsequent uplift. Recently, Block et
al. (2015), (2016a), (2016b) described the implications of compressional deformation across
northern Ghana and southwest Burkina Faso. These compressional events resulted in
significant crustal thickening. Crustal thickening provides a way to underthrust and uplift
sedimentary rocks, and allows greater interaction between the older basement rocks and
ascending magmas, facilitating the entrainment of older zircons.

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The interleaving of Archean-Paleoproterozoic crust appears, to be limited and with the
exception of western Côte d'Ivoire, surface expressions indicate a relatively sharp, well
constrained Archean-Paleoproterozoic geological boundary (Eglinger et al., 2017), although
this may not be the case at depth. In addition, within the study area, there is no geochronological
or field evidence for the existence of large Archean exposures, arguing against the
Paleoproterozoic Baoulé-Mossi domain having underthrust the Archean Kénéma-Man domain.
If in contrast, the Archean block was overridden by, or resurfaced by, the Paleoproterozoic
assemblage, it is likely that the juvenile magmas would have interacted with Archean crustal

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fragments during their ascent, potentially entraining the older zircons. This hypothesis is at odds with the majority of published isotope Nd and Hf isotope data that advocates a predominately juvenile origin with limited amount of reworked crust (e.g. Abati et al., 2012; Abouchami et al., 1990; Boher et al., 1992; Petersson et al., 2016; Tapsoba et al., 2013; Taylor et al., 1992).

Alternatively, if the inherited ages are the result of reworking sedimentary rocks it is necessary to account for long distance transport of detritus now represented by the inherited components. The present geological configuration indicates that the distance between the Banfora and Yanfolila belts is over 300 km, whereas the distance from the known Archean Kénéma-Man domain and the Yanfolila Belt is over 80 km. It is expected that these distances were greater at the time of emplacement at ca. 2200-2000 Ma. The uplifted units following crustal thickening would have been eroded more easily, thus providing a source for the inherited zircon grains. This scenario provides a possible source for the Paleoproterozoic inheritance found across the western portion of the study area, as zircons from the early magmatic episode (ca. 2300-2130 Ma) are incorporated into magmatic intrusions emplaced after ca. 2130 Ma. Conversely, in the case of Archean inherited ages from across Burkina Faso a plausible source of transported grains would be the Archean basement identified within the Nigerian Shield, as reported by Bruguier et al. (1994) and Kröner et al. (2001) or previously unrecognized Archean slivers. The most likely source of inherited grains in the Mali samples is the Archean Kénéma-Man domain. We note that incorporation of older zircon cores from the reworking of sedimentary rocks is a testable hypothesis – in this case, the emplacement-aged zircons of the host granite should have high δ¹⁸O values (e.g. Hawkesworth and Kemp, 2006; Kemp et al., 2007, 2009; Valley, 2003; Valley et al., 1994).

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## 6 Tectonic implications and accretionary model
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The crustal evolutionary patterns of the southern West African Craton, and in particular of the Baoulé-Mossi domain, reflect a complex assemblage (puzzle) that requires understanding of the spatial and temporal distribution of emplacement ages and the presence of inherited zircon grains. During the Phanerozoic, migrating magmatic fronts and abrupt cessations of magmatic activity, as inferred here, have been associated with arc type systems, such as the Andes in central Chile (Hildreth and Moorbath, 1988) and South China, where flat slab subduction has been proposed (Li and Li, 2007). It is possible that similar accretionary processes shaped the crustal evolution of the southern West African Craton

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An accretionary process may have involved at least two crustal blocks that join to form the Baoulé-Mossi domain. During the Eoeburnean magmatic phase the magmatic activity was mainly concentrated in the easternmost block of the study area (minor peak at ca. 2170 Ma, figure 10). As the magmatic activity migrated westward a large pulse of magmatism is identified at around ca. 2135 Ma, potentially heralding the docking of the two blocks at ca. 2130 Ma. After ca. 2130 Ma the magmatic activity appears concentrated in the westernmost region with peak magmatism at ca. 2090 Ma. The inherited age pattern is the result of the younger magmas sampling material derived from the easternmost portion suggest the westward migration of the magmatic front (Figure 13). Recently, Block et al. (2016a) proposed a collision model between blocks in Ghana and Burkina Faso/Côte d'Ivoire. We suggest that the Paleoproterozoic Baoulé-Mossi domain was the result of the accretion of at least two crustal blocks that were subsequently amalgamated with the Archean Kénéma-Man domain (Figure 13).

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The boundary between these inferred crustal blocks is based on the distribution of intrusion emplacement ages and inherited zircons. East of the Banfora-Bagoe belts, intrusion ages are predominantly older than ca. 2130 Ma, mostly free of inheritance, while to the west the ages are predominantly younger than ca. 2130 Ma and commonly contain an inherited

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component. Multiple crustal blocks explain the occurrences of inherited ages between ca. 2250 and 2150 Ma across Southern Mali, due to potential crustal thickening and subsequent underthrusting or uplift and erosion of older crust (section 5.4.1). Certainly, across southern Mali this study and previous studies (e.g. Feybesse et al. (2006b), (2006c)) have identified ages between ca. 2215 and 2150 Ma, but the geographical distribution and number of identified intrusions within that range does not account for the relatively widespread inheritance across southern Mali. Subsequently, the Paleoproterozoic crustal blocks of the Baoulé-Mossi domain, proposed here were accreted into the Archean Kénéma-Man domain.

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## 7 Conclusions

The new data presented in this study support observations that the Paleoproterozoic portion of the southern West African Craton developed during an accretion process, as follows:

* Evaluation of all zircon ages (magmatic, metamorphic and detrital) plotted as a function of longitude supports the notion that the Paleoproterozoic Baoulé-Mossi domain underwent a diachronous evolution reflected by a westward migration of the magmatic front. It also highlights an abrupt cessation and retreat of activity across the southern West African Craton that started around ca. 2100 Ma at the eastern end of the craton and ended at ca. 2050 Ma at the westernmost portion. This retreat is represented by a westward migration of the magmatic front of approximately 35 km/Myr and is analogous to that shown by Phanerozoic subduction- accretion systems as described by e.g. Li and Li (2007) and Hildreth and Moorbath (1988).

* The offset of magmatism and distribution of inherited zircons indicates that the Paleoproterozoic domain part of this study was composed of at least two crustal blocks with the boundary probably located between the Banfora and Bagoe belts.

* An accretionary process might have started as early as ca. 2175 Ma. At this time a minor
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peak of magmatic activity is identified east of the Banfora Belt.

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Early peak metamorphism identified at ca. 2130 Ma (Block et al., 2015) is taken as an indication of the timing at which the two blocks were docked and it coincides with peak magmatism in the eastern portion of the study area. Intrusions younger than ca. 2130 Ma generally contain inherited grains with ages up to 2250 Ma. This suggests that the crust was thicker after that time, allowing for incorporation of older components, which is also consistent with an accretionary model. Additionally the distribution of inherited ages up to ca. 2250 Ma indicates that the ca. 2130 Ma magmas interacted with, or sampled sediments derived from, previously emplaced intrusions with ages between ca. 2250 and 2150 Ma.

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These observations are consistent with an arc type environment, as suggested by e.g.

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Ama Salah et al. (1996), Béziat et al. (2000), Sylvester and Attoh (1992), Abati et al. (2012), Block et al. (2015) and (2016b), Lambert-Smith et al. (2016), Petersson et al. (2016) and Tapsoba et al. (2013).

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This study identified Archean zircon inheritance, particularly in the <2130 Ma intrusions. These occurrences could imply a greater involvement of Archean crust in the Paleoproterozoic granitic magmas than previously proposed. Recent studies, Abati et al. (2012), Begg et al. (2009) and Petersson et al. (2016), have also advocated a greater role of Archean crust, and future isotope studies are required to evaluate this further. Ultimately, however, the distribution and scarcity of Archean inheritance points toward a predominately juvenile crustal growth during the Paleoproterozoic across the Baoulé-Mossi domain, as long argued by Nd and Hf isotope studies (e.g. Abati et al., 2012; Abouchami et al., 1990; Boher et al., 1992; Tapsoba et al., 2013; Taylor et al., 1992).

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**8 Acknowledgements**
We thank AMIRA International, industry sponsors, AusAid and the ARC Linkage Project LP110100667, for their support of the WAXI II project (P934A). We are also appreciative of the contribution of the various Geological Surveys and Departments of Mines in West Africa as sponsors in kind of WAXI. In addition we acknowledge the assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy, Characterization & Analysis (CMCA) of the University of Western Australia (UWA), of the John De Laeter Centre for Isotope Research, hosted at Curtin University, of the Key Centre for the Geochemical Evolution and Metallogeny of Continents (GEMOC), and the ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), Macquarie University. Parra-Avila acknowledges receipt of UWA Scholarships for International Research Fees (SIRF), University International Stipend (UIS) and Ad Hoc Safety-Net Top-Up Scholarship. Kemp acknowledges the ARC grant FT100100059 and Fiorentini acknowledges the ARC grant schemes FT110100241 and CE110001017. This is contribution 988 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1165 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).

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## 9 Tables, Figures and Supplementary Materials

Table 1 Sample information, location, rock type and basic field description as part of the present study.

Table 2 Summary of main mineralogical characteristics by volcanic belt or geologic region of interest.

Table 3 Summary of interpreted crystallization ages and identified inherited ages.

Figure 1 A) Simplified geological map of the West African craton after Boher et al. (1992) Sketch shows the extension of the Leo-Man rise in the southern portion of the craton, defined by the Archean Kénéma-Man and Paleoproterozoic Baoulé-Mossi domain. Boxed area shown in detail in insert B; B) Simplified geological map, after Lebrun et al. (2016) of the study areas delineated in insert A. Zone 1 covers Burkina Faso, Mali northern Ghana and eastern Guinea, while zone 2 covers a portion of the Ashanti belt in southern Ghana. Map includes major structures and samples collected for geochronological work.
Figure 2 Simplified lithostratigraphic, deformation, geochronological chart highlighting geologic areas of interest for the present study, showing the timing of emplacement of the studied felsic intrusions. Modified after Baratoux et al. (2011), Block et al. (2015), (2016b), Lebrun et al. (2016), Miller et al. (2013), Perrouty et al. (2012), (2015), Miller et al. (2013) and Tshibubudze et al. (2015).

Figure 3 A) Characteristic rock exposure found across southern Mali and Burkina Faso; B) Granitic intrusion mostly composed of a fine grained quartz matrix, mineral assemblage includes biotite, quartz, and plagioclase phenocrysts of 2 mm by 4 to 5 mm (ML12-080); C) Least deformed portion of the Diallo Granite, which is quartz-feldspar-biotite rich (SU-021); and D) A granite, of equigranular texture, fine to medium grained. K-feldspar dominated, quartz and some plagioclase, black minerals are mostly biotite (ML12-105). All images refer to exposures in southern Mali.

Figure 4 Thin section images in XPL of characteristic samples showing mineral composition of rock samples identified across the study area; A) Major minerals, K-feldspar, quartz, plagioclase, biotite, small amounts of hornblende. Chlorite, sericitic alteration and traces of sulphides, other minerals include zircons, titanite and some hematite (ML12-068); B) Quartz, plagioclase, small amounts of K-feldspar, traces of pyrite and chalcopyrite, biotite and hornblende (SU_002); C) Angular K-feldspar crystals, minor amounts of plagioclase, relatively large amounts of brownish red biotite and some hornblende, chlorite and quartz (SU_001); D) Sericitic alteration, primary structures relatively easy to identify, mainly composed of large plagioclase crystals within a quartz matrix and traces of biotite, titanite, zircon, epidote and chlorite (BE5); E) Plagioclase, K-feldspar, quartz. Biotite is common, small amounts of sericitic alteration, most feldspar crystals appear intact (ML12-104); F) Plagioclase rich, original textures hard to identify due to pervasive sericitic alteration from the center of the crystals outwards, amphibole (hornblende) in some cases visible alteration into chlorite, minor amounts of quartz and small amounts of biotite, visible apatite/zircons, and additionally extensive occurrence of opaque minerals, majority of which appear to be pyrite (BNF150559); G) Quartz, plagioclase, biotite and muscovite. Quartz matrix is fine grained when compared to the plagioclase crystals. Accessory minerals include titanite, zircon, chlorite, ilmenite, signs of alteration some sericite visible (SU_007); and H) Quartz content between 5 to 15%, sample is plagioclase dominated, k-feldspar is not visible as samples is strongly altered and it is difficult to identify minerals and textures. Biotite and hornblende are also present. Alteration products are chlorite, epidote, and maybe actinolite (ML12-086).

Figure 5 Selected zircon images showing the different morphological characteristics of zircon. A and B) Granites from the Belahouro Belt; C) Granodiorite from the Boromo-Hounde belts; D and E) Represent zircons from a
diorite and a granite from the Banfora Belt; F) Zircon obtain from a granite of the Morila Belt; G, H, I and J)
Zircons representing a porphyry, two granites and a syenite representative of the Yanfolila Belt; and K, L and M)
Zircons from a granite, a dacite and a diorite from the Siguiri Basin. Notice that the zircons from granites and
granodiorites are mostly elongated and tabular, while the zircons from diorites are slightly more rounded and
display a faint zoning instead of the well-defined oscillatory zoning of zircons from the granites. Scale bar in all
images represents 100 µm.

**Figure 6** A) Histogram showing new interpreted U-Pb crystallization ages distributed by belts and regions of geologic interest as described in the regional geology section; and B) Histogram showing the age distribution of the studied samples base on identified rock types.

**Figure 7** Age distribution by longitude color coded by volcanic belts and regions of geologic interest. A) Shows all ages while B) focuses on the age range between 2400 and 2000 Ma. Solid symbols represent U-Pb ages interpreted as crystallization ages; open symbols represent individual U-Pb analyses interpreted to represent inherited ages.

**Figure 8** Left Weight mean average age; right Concordia age plots. Black symbols are accepted analyses while red symbols represent rejected analyses. From top to bottom samples: across Burkina Faso, BF1 (Goren/Po-Tenkodogo-Yamba), BE5 (Belahouro Belt), HO629 (Boromo-Hounde belts). BNF 150559 (Banfora Belt) and from Mali ML12-086 (Bagoe Belt).

**Figure 9** Weight mean average age; right Concordia age plots. Black symbols are accepted analyses while red symbols represent rejected analyses. Samples from across Mali: ML12-105 (Morila Belt), ML12-107 Bougouni region, MWAXI-126 (Yanfolila Belt), and from Guinea, KL000565 (Siguiri Basin).

**Figure 10** Relative probability density diagrams, top A) this study ages east of the Bagoe Belt dominated by ages older than 2130 Ma Main peak ca. 2135 Ma, secondary peak at 2175 Ma; Bottom B) ages west of the Bagoe Belt dominated by ages between ca. 2100 and 2070 with a major peak at ca. 2095 Ma. 2130 Ma boundary after peak metamorphism exhumation of high-grade rocks identified by Block et al. (2015).

**Figure 11** Zircon and monazite U-Pb age distribution across the southern West African Craton for the period between 2250 and 2050 Ma. A) Ages between 2300 and 2130 Ma, showing a marked concentration of ages in the eastern craton, and no recorded ages within the Archaean host rocks; B) Ages between 2130 and 2090 Ma, showing a uniform coverage of ages across craton for this age bracket, and several ages recorded within the Archaean host rocks; and C) Ages for the period 2090-2050 Ma, clearly showing that most ages are concentrated
west of the Banfora-Bagoe belts in the westernmost portion of the study area. (520 ages from bibliography, Supplementary Material A).

**Figure 12** Longitudinal variations in magmatic activity. A) Zircon and monazite U-Pb age distribution as a function of longitude (520 ages from bibliography, Supplementary Material A, Table 1, WAXI II compilation and this work). Notice this compilation only includes interpreted crystallization ages and metamorphic ages. Other not specified refers to ages from which the reference does not clarify if it is a crystallization or metamorphic age. The sharp cessation of magmatism across the craton is clearly defined, with subsequent reworking limited to the margins of the craton, dashed line; B) zircon and monazite U-Pb age distribution as a function of longitude for the age bracket 2300-2000 Ma (455 ages) (Table 1, WAXI II age compilation and this work). The progressive cessation of the magmatic activity from east to west during this period in the southern West African Craton equates to a migration of approximately 35 km/Myr. Over 95% of all ages plot above the offset of magmatism line "magmatic front" (dashed bottom arrow).

**Figure 13** Schematic cartoon showing the proposed boundaries and crustal blocks. Top, shows the Archean Kénéma-Man and the Baoulé-Mossi domain. The Baoulé-Mossi domain, which is divided into two blocks during the period 2160-2130 Ma. During the mentioned period the assemblage blocks are affected by compressional forces, first N-S (D1) as mentioned described by Baratoux et al. (2011), Block et al. (2016a), and Perrouty et al. (2012) the followed by a E-W compression (D2) (Baratoux et al., 2011; Block et al., 2016a; Perrouty et al., 2012). Density of the dot pattern indicates distribution of magmatic activity. Greater density = greater magmatism, and less density = less magmatism; and Bottom shows the amalgamation of the Paleoproterozoic blocks under a D2 compressions for the period 2130-2110 Ma. Notice the occurrence of inherited grains. Inheritance is mainly concentrated in the eastern portion of the Baoulé-Mossi and predominately represented by ages between ca. 2500 and 2125 Ma which are common crystallization ages across the easternmost portion of the study area, indicating that the western block is contaminated by crustal material derived from the eastern block.

**Supplementary Material A.** Summary of published ages. The ages include emplacement and metamorphic events as well as multiple dating methods. Blank spaces indicate a lack of available information in the data source.

**Supplementary Material B.** Raw SHRIMP U-Pb data.

**Supplementary Material C.** Raw LA-ICP-MS data.

## **10 Appendix A – Sample Preparation and Analytical Methods.**

### **A.1 Zircon mount preparation**
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The epoxy mounts are discs of 5 mm thick by 25 mm diameter. Three to four samples were placed in each mount. Chips of the primary zircon standards BR266 (559 Ma, 903 U ppm; Stern (2001)) or M257 (561.3 Ma and 840 ppm; Nasdala et al. (2008)), were used for U/Pb calibration. Accuracy and reproducibility was monitored by including the secondary zircon standards OGC1 (3465 Ma; Stern et al. (2009)), and Temora2 (416.8 Ma; Black et al. (2004)). In addition chips of the silicate glass NIST 610 were included in the mounts for instrument set-up purposes. The mounts were polished with diamond film polishing mats as fine as 0.5 µm. Subsequently, the epoxy discs were cleaned using ethanol and petroleum spirits, a soap solution, and rinsed with deionized water in an ultrasonic bath. Mounts were oven dried (1 hour at 60°C) and the analytical surface was coated with a 40 µm gold layer. Detailed mounting procedures and preparation can be reviewed in Claoué-Long et al. (1995).

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Mounts were imaged using the backscattered electron and cathodoluminescence detectors of a JEOL 6400 Scanning Electron Microscope (SEM) or a VEGA 3 Tescan SEM at the Centre for Microscopy, Characterization and Analysis (CMCA), University of Western Australia (UWA). The acquired images allowed the identification of internal structures. Grains showing a large number of cracks or obvious radiation damage were not analyzed.

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## A.2 Sensitive High Resolution Ion Micro Probe (SHRIMP) dating

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Zircon mounts were analyzed by means of Sensitive High Resolution Ion Micro Probe (SHRIMP II) at the John de Laeter (JDL) Centre for Isotope Research of Curtin University, Perth, Australia. Details of instrument operating conditions are described in De Laeter and Kennedy (1998) and Kennedy and De Laeter (1994) while analytical conditions are described in detail in Claoué-Long et al. (1995), Compston et al. (1984), and Williams (1988). The analytical procedure usually includes the use of a 25-30 µm diameter elliptical spot due to a mass-filtered (O₂) - primary beam between 2.0 and 2.5 nA. Each dataset included six scans
through the mass range of ¹⁹⁶Zr₂O⁺ (2 seconds), ²⁰⁴Pb⁺ (10 seconds), background (204.1) (10 seconds), ²⁰⁶Pb⁺ (20 seconds), ²⁰⁷Pb⁺ (30 seconds), ²⁰⁸Pb⁺ (10 seconds), ²³⁸U⁺ (5 seconds), ²⁴⁸ThO⁺ (5 seconds), and ²⁵⁴UO⁺ (2 seconds) (Nasdala et al., 2008). The data from each sample were reduced using the excel-based add-in program SQUID version 2.2 (Ludwig, 2003). Data reduction procedures were after Wingate and Kirkland (2014).

Zircon is a very resilient, refractory mineral that can survive partial melting and high grade regional metamorphism without losing its isotopic information (Mezger and Krogstad, 1997 references therein; Scherer et al., 2007). However, low grade metamorphism, fluid circulation and in some instances weathering can affect the U-Pb systematics, which results in discordant U-Pb ages. These discordant ages are for the most part due to Pb-loss (Mezger and Krogstad, 1997 references therein). In order to minimize the difficulties associated with potentially disturbed U-Pb systematics, for the purpose of this study U-Pb ages were only calculated from concordant to near concordant grains (discordance between -5% and +10%). Additionally, analyses that comprise more than 1% of non-radiogenic ²⁰⁶Pb (i.e., from common lead) and yield U concentrations over a 1000 ppm were also rejected.

### A.3 LA-ICP-MS Zircon dating

Laser ablation U-Pb zircon dating was carried out at the GEMOC/CCFS Centre. The method used an Agilent 7700 quadrupole Inducted Coupled Plasma Mass Spectrometer (ICP-MS) attached to a New Wave/Merchantek UP-213 laser ablation system (λ=213 nm). Beam diameter was set at 30 or 40µm, based on zircon size. Beam repetition was set at 5 Hz rate and energy around 0.06 µJ and 8 J/cm². He was used as transport media, as it increases sample transport efficiency during the ablation process. Using He provides a more stable signal, and therefore a more reproducible Pb/U fractionation. Additional description and details are founded in Belousova et al. (2010) and Jackson et al. (2004).
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U-Pb data was determined by analyzing twelve unknown samples for every two analyses of the GEMOC GJ-1 zircon standard (Elhlou et al., 2006). GJ-1, TIMS$^{207}$Pb/$^{206}$Pb age of 608.5 Ma (Jackson et al., 2004). Zircon standards 91500 (U-Pb age 1065 Ma, Wiedenbeck et al., 1995) and Mud Tank (U-Pb age 732 Ma, Black and Gulson, 1978) were analyzed as secondary control standards for reproducibility and instrument accuracy. U-Pb ages were calculated from the raw signal data using the GLITTER software program after Griffin et al. (2008). Further details on integrated ration, fractionation, time resolved intervals, and instrumental mass bias and calibrating procedures are provided in Griffin et al. (2008) and Jackson et al. (2004). Information on common-Pb correction procedures are provided in Andersen (2002). Analyses reported in this study were corrected assuming recent Pb-loss and a common-Pb composition similar to present day average orogenic Pb as given by the second-stage growth curve of Stacey and Kramers (1975) for $^{238}$U/$^{204}$Pb = 9.74. No correction has been applied to analyses that are concordant within 2σ analytical error in $^{206}$Pb/$^{238}$U and $^{207}$Pb/$^{235}$U, or which have less than 0.2% common-Pb. All described procedures are after Andersen et al. (2004), Belousova et al. (2010), Griffin et al. (2008) and Jackson et al. (2004).

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944

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947

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949

950

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953

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956

957

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958

959

960

Nasdala, L., Hofmeister, W., Norberg, N., Martinson, J.M., Corfu, F., Dörr, W., Kamo, S.L.,
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962

963

964

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965

966

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978

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Key

<figure><img src="image_3.png" /></figure>

Archean

Paleoproterozoic

<figure><img src="image_4.png" /></figure>

Birimain Greenstone/volcanics

<figure><img src="image_5.png" /></figure>

Birimian Granites

<figure><img src="image_6.png" /></figure>

Birimian Sediments

<figure><img src="image_7.png" /></figure>

Late Basins (e.g. Tarkwa)

<figure><img src="image_8.png" /></figure>

Neoproterozoic/

Phanerozoic Sediments

<figure><img src="image_9.png" /></figure>

Samples
Geochronology

Study area

<figure><img src="image_10.png" /></figure>

Zone 1

<figure><img src="image_11.png" /></figure>

Zone 2

A

<figure><img src="image_12.png" /></figure>

Atlantic ocean

Archean

Paleoproterozoic

500 km

Neoproterozoic and Phanerozoic basin/cover

Pan-African orogenic belts

<figure><img src="image_13.png" /></figure>

Hercynian belts

B

<figure><img src="image_14.png" /></figure>

Zone 1

<figure><img src="image_15.png" /></figure>

Belahouro

Oudalan-Gorouol

Bouroum

Goren

Burkina Faso

Ougadougou

Boromo-Poura SZ

Bossie SZ

Boromo

Hounde

Koudougou-Tumu

Granitic domain

Po-Tenkodogo-

Yamba Structure

Yanfolila

Bamako

Bannifin SZ

Siekeroli SZ

Guinea

Kalana

Bougouni

Morila

Bagoe

Missigui

Komana

Sikasso

Siguiri Basin

Greenville-Ferkessedougou/

Bodo Dioulass SZ

West Batie SZ

Ghana
<figure><img src="image_16.png" /></figure>

## GUINEA

## MALI

## BURKINA FASO

## GHANA
A

<figure><img src="image_17.png" /></figure>

B

<figure><img src="image_18.png" /></figure>

C

<figure><img src="image_19.png" /></figure>

D

<figure><img src="image_20.png" /></figure>
<figure><img src="image_21.png" /></figure>

A

500 µm

<figure><img src="image_22.png" /></figure>

B

1000 µm

<figure><img src="image_23.png" /></figure>

C

500 µm

<figure><img src="image_24.png" /></figure>

D

500 µm

<figure><img src="image_25.png" /></figure>

E

500 µm

<figure><img src="image_26.png" /></figure>

F

500 µm

<figure><img src="image_27.png" /></figure>

G

500 µm

<figure><img src="image_28.png" /></figure>

H

500 µm
BE5

A

BE7

B

HO631A

C

BNF150559

D

100 µm

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

BNF150561

E

ML12-105

MWAXI-135

SU054

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

SU056

I

SU059

SI124

KL000274

KD000154

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

100 µm
<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>

<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /></figure>
<figure><img src="image_46.png" /></figure>

A

<figure><img src="image_47.png" /></figure>

<figure><img src="image_48.png" /></figure>

B

<figure><img src="image_49.png" /></figure>

West

<figure><img src="image_50.png" /></figure>

Siguiri

<figure><img src="image_51.png" /></figure>

Bougouni

<figure><img src="image_52.png" /></figure>

Bagoe

<figure><img src="image_53.png" /></figure>

Yanfolila

<figure><img src="image_54.png" /></figure>

Morila

<figure><img src="image_55.png" /></figure>

Banfora

<figure><img src="image_56.png" /></figure>

Boromo-Hounde

<figure><img src="image_57.png" /></figure>

Belahouro

<figure><img src="image_58.png" /></figure>

Goren/Po-Tenkodogo-Yamba

<figure><img src="image_59.png" /></figure>

Koudougou-Tumu

<figure><img src="image_60.png" /></figure>

Ashanti-Kumasi

Ghana
<figure><img src="image_61.png" /></figure>

<figure><img src="image_62.png" /></figure>

<figure><img src="image_63.png" /></figure>

<figure><img src="image_64.png" /></figure>

<figure><img src="image_65.png" /></figure>

<figure><img src="image_66.png" /></figure>

<figure><img src="image_67.png" /></figure>

<figure><img src="image_68.png" /></figure>
<figure><img src="image_69.png" /></figure>

<figure><img src="image_70.png" /></figure>

<figure><img src="image_71.png" /></figure>

<figure><img src="image_72.png" /></figure>

<figure><img src="image_73.png" /></figure>

<figure><img src="image_74.png" /></figure>

<figure><img src="image_75.png" /></figure>

<figure><img src="image_76.png" /></figure>

<figure><img src="image_77.png" /></figure>

<figure><img src="image_78.png" /></figure>
A

<figure><img src="image_79.png" /></figure>

B

<figure><img src="image_80.png" /></figure>
Zircon Ages Distribution

A

<figure><img src="image_81.png" /></figure>

B

<figure><img src="image_82.png" /></figure>

C

<figure><img src="image_83.png" /></figure>
A

<figure><img src="image_84.png" /></figure>

B

<figure><img src="image_85.png" /></figure>
## 2150-2130 Ma

### Age Migration E-W

<figure><img src="image_86.png" /></figure>

KEY

Archean Kenema-Man

Paleoproterozoic Baoule-Mossi

Block boundaries

Inheritance ca. 3600-2500 Ma

Inheritance ca. 2500-2125 Ma

*not to scale

<figure><img src="image_87.png" /></figure>

## 2130-2115 Ma

### (Wide spread magmatism)
<table><thead><tr><th>SAMPLE</th><th>Lat</th><th>Long</th><th>Rock type</th></tr></thead><tbody><tr><td>BE2</td><td>14.2875743</td><td>-0.951721163</td><td>Alkali Granite</td></tr><tr><td>BE3A</td><td>14.43560775</td><td>-1.006964971</td><td>Gabbro</td></tr><tr><td>BE5</td><td>14.33001685</td><td>-1.032425683</td><td>Granite</td></tr><tr><td>BE6</td><td>14.34137763</td><td>-1.044571053</td><td>Granite</td></tr><tr><td>BE7</td><td>14.43255296</td><td>-1.129127061</td><td>Granite</td></tr><tr><td>BE13</td><td>14.34197</td><td>-1.370551545</td><td>Granodiorite</td></tr><tr><td>H0253</td><td>10.31665</td><td>-3.21925255</td><td>Granite</td></tr><tr><td>H0254</td><td>10.31609019</td><td>-3.221127</td><td>Granite</td></tr><tr><td>H0257</td><td>10.30121734</td><td>-3.23070374</td><td>Granite</td></tr><tr><td>H0479A</td><td>12.35270146</td><td>-2.58412633</td><td>Gabbro</td></tr><tr><td>H0480</td><td>12.35803386</td><td>-2.58100659</td><td>Granodiorite</td></tr><tr><td>H0629</td><td>10.27159</td><td>-3.088572658</td><td>Tonalite</td></tr><tr><td>H0631A</td><td>10.26827034</td><td>-3.089174449</td><td>Granodiorite</td></tr><tr><td>H0631B</td><td>10.26827034</td><td>-3.089174449</td><td>Aplite</td></tr><tr><td>H0640A</td><td>12.37363901</td><td>-2.599927036</td><td>Diorite</td></tr><tr><td>H0640C</td><td>12.37363901</td><td>-2.599927036</td><td>Diorite</td></tr><tr><td>BF12-01</td><td>10.6494</td><td>-4.7971</td><td>Granite</td></tr><tr><td>BF12-04</td><td>10.7058</td><td>-4.3535</td><td>Syenogranite</td></tr><tr><td>BF12-05</td><td>10.53</td><td>-4.0682</td><td>Granite</td></tr><tr><td>BNF150559</td><td>10.44257378</td><td>-5.456932949</td><td>Diorite</td></tr><tr><td>BNF150561</td><td>10.47148353</td><td>-5.215988762</td><td>Granite</td></tr><tr><td>BNF150562</td><td>10.33388867</td><td>-5.275614224</td><td>Diorite</td></tr><tr><td>BNF150563</td><td>10.37617658</td><td>-5.404149353</td><td>Granite</td></tr><tr><td>BNF150564</td><td>10.36121027</td><td>-5.404318071</td><td>Monzogranite</td></tr><tr><td>BNF150565</td><td>10.33302388</td><td>-5.275215532</td><td>Monzogranite</td></tr><tr><td>ML12-086</td><td>10.57669277</td><td>-6.119712499</td><td>Diorite</td></tr><tr><td>SU_001</td><td>11.8375738</td><td>-6.76848865</td><td>Granite "Missigui"</td></tr><tr><td>SU_002</td><td>11.83296936</td><td>-6.76769245</td><td>Granite</td></tr><tr><td>SU_003</td><td>11.5957831</td><td>-6.83742302</td><td>Felsic intrusive</td></tr><tr><td>SU_004</td><td>11.68287648</td><td>-6.85295267</td><td>Granodiorite</td></tr><tr><td>SU_006</td><td>11.67487828</td><td>-6.852307165</td><td>Tonalite</td></tr><tr><td>SU_007</td><td>11.67930407</td><td>-6.849540564</td><td>Granodiorite</td></tr><tr><td>SU_012</td><td>11.41514981</td><td>-7.017465652</td><td>Granite</td></tr><tr><td>ML12-068</td><td>10.47100483</td><td>-7.047098</td><td>Granite</td></tr><tr><td>ML12-070</td><td>10.52080895</td><td>-7.09607438</td><td>Orthogranite</td></tr><tr><td>ML12-078</td><td>11.08404302</td><td>-7.43209708</td><td>Pegmatite</td></tr><tr><td>ML12-079A</td><td>11.12371556</td><td>-6.82612153</td><td>Gneiss</td></tr><tr><td>ML12-079B</td><td>11.12371556</td><td>-6.82612153</td><td>Granite</td></tr><tr><td>ML12-080</td><td>11.10897637</td><td>-6.81390868</td><td>Gneiss</td></tr><tr><td>ML12-082</td><td>11.22255518</td><td>-6.79942265</td><td>Granite</td></tr></tbody></table>
<table>
  <tr>
    <td>ML12-083B</td>
    <td>11.31124024</td>
    <td>-6.71976004 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-084</td>
    <td>11.32736923</td>
    <td>-6.73064603 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-083</td>
    <td>11.39186893</td>
    <td>-6.681166287 Granite</td>
  </tr>
  <tr>
    <td>ML12-105</td>
    <td>11.31350348</td>
    <td>-6.825446155 Granite</td>
  </tr>
  <tr>
    <td>ML12-107</td>
    <td>11.87412148</td>
    <td>-7.33345408 Granite</td>
  </tr>
  <tr>
    <td>ML12-125</td>
    <td>11.96698346</td>
    <td>-8.20531156 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-150</td>
    <td>11.85183162</td>
    <td>-8.06251897 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-187</td>
    <td>11.27952591</td>
    <td>-7.9443483 Granite</td>
  </tr>
  <tr>
    <td>SU_015</td>
    <td>11.37351992</td>
    <td>-7.412245005 Granite</td>
  </tr>
  <tr>
    <td>SU_016</td>
    <td>11.373538</td>
    <td>-7.412244905 Granite</td>
  </tr>
  <tr>
    <td>SU_034</td>
    <td>11.37379642</td>
    <td>-7.41177952 Aplite</td>
  </tr>
  <tr>
    <td>SU_037</td>
    <td>11.3482295</td>
    <td>-7.72442551 Granite "Bougouni"</td>
  </tr>
  <tr>
    <td>DS-014</td>
    <td>11.23657676</td>
    <td>-8.466991626 Porphyry</td>
  </tr>
  <tr>
    <td>KADD119A-M</td>
    <td>10.7921</td>
    <td>-8.19763 Diorite</td>
  </tr>
  <tr>
    <td>KADD119A</td>
    <td>10.7921</td>
    <td>-8.19763 Diorite</td>
  </tr>
  <tr>
    <td>ML12-066</td>
    <td>11.19229266</td>
    <td>-7.77283033 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-113</td>
    <td>12.007218</td>
    <td>-8.28057979 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-114</td>
    <td>11.9918252</td>
    <td>-8.24927883 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-116</td>
    <td>11.96591369</td>
    <td>-8.20923831 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-117</td>
    <td>11.9662435</td>
    <td>-8.20652098 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-118</td>
    <td>11.9662435</td>
    <td>-8.20652098 Granite</td>
  </tr>
  <tr>
    <td>ML12-153</td>
    <td>11.65719506</td>
    <td>-8.25081398 Diorite</td>
  </tr>
  <tr>
    <td>ML12-161</td>
    <td>11.42031503</td>
    <td>-8.41546666 Diorite</td>
  </tr>
  <tr>
    <td>ML12-165</td>
    <td>11.42234001</td>
    <td>-8.41488923 Diorite</td>
  </tr>
  <tr>
    <td>ML12-166</td>
    <td>11.41429296</td>
    <td>-8.42674208 Diorite?</td>
  </tr>
  <tr>
    <td>ML12-167</td>
    <td>11.41399633</td>
    <td>-8.4277692 Granite</td>
  </tr>
  <tr>
    <td>ML12-168</td>
    <td>11.41277014</td>
    <td>-8.42873638</td>
  </tr>
  <tr>
    <td>ML12-170</td>
    <td>11.50162468</td>
    <td>-8.41047247</td>
  </tr>
  <tr>
    <td>ML12-177</td>
    <td>11.54659871</td>
    <td>-8.26385253 Granodiorite</td>
  </tr>
  <tr>
    <td>ML12-178</td>
    <td>11.54894573</td>
    <td>-8.26451277 Diorite</td>
  </tr>
  <tr>
    <td>SU_019</td>
    <td>11.31540035</td>
    <td>-8.27508713 Granite</td>
  </tr>
  <tr>
    <td>SU_020</td>
    <td>11.31543798</td>
    <td>-8.27519953 Granite</td>
  </tr>
  <tr>
    <td>SU_021</td>
    <td>11.27172245</td>
    <td>-8.32079968 Granite "Diallo"</td>
  </tr>
  <tr>
    <td>SU_022</td>
    <td>11.27521033</td>
    <td>-8.31370968 Granite "Money"</td>
  </tr>
  <tr>
    <td>SU_023</td>
    <td>11.31563521</td>
    <td>-8.27516777 Granite "Siekerole"</td>
  </tr>
  <tr>
    <td>SU_029</td>
    <td>11.31551929</td>
    <td>-8.27492268 Granite "Siekerole"</td>
  </tr>
  <tr>
    <td>SU_051</td>
    <td>11.62984576</td>
    <td>-8.26297109 Granite</td>
  </tr>
  <tr>
    <td>SU_052</td>
    <td>11.62905493</td>
    <td>-8.261747 Granite</td>
  </tr>
  <tr>
    <td>SU_053</td>
    <td>11.6293177</td>
    <td>-8.26129119 Granite</td>
  </tr>
  <tr>
    <td>SU_054</td>
    <td>11.64054926</td>
    <td>-8.23177935 Granite</td>
  </tr>
  <tr>
    <td>SU_056</td>
    <td>11.62224063</td>
    <td>-8.18712585 Granite</td>
  </tr>
  <tr>
    <td>SU_057</td>
    <td>11.48782862</td>
    <td>-8.21077815 Granite</td>
  </tr>
</table>
<table>
  <tr>
    <td>SU_059</td>
    <td>11. 45287906</td>
    <td>-8. 25837747 Syenite</td>
  </tr>
  <tr>
    <td>MWAXI-126/DS-001</td>
    <td>11. 42209093</td>
    <td>-8. 347029861 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-127/DS-002</td>
    <td>11. 42655656</td>
    <td>-8. 34578184 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-128/DS-003</td>
    <td>11. 42655258</td>
    <td>-8. 345766655 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-129/DS-004</td>
    <td>11. 23765946</td>
    <td>-8. 466627555 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-130/DS-005</td>
    <td>11. 26638033</td>
    <td>-8. 393047578 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-131/DS-006</td>
    <td>11. 23053507</td>
    <td>-8. 466330319 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-132/DS-007</td>
    <td>11. 23053625</td>
    <td>-8. 466345622 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-133/DS-008</td>
    <td>11. 23053663</td>
    <td>-8. 466350257 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-134/DS009</td>
    <td>11. 20142263</td>
    <td>-8. 408768109 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-135/DS-010</td>
    <td>11. 26685152</td>
    <td>-8. 395215777 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-136/8DS-011</td>
    <td>11. 27042155</td>
    <td>-8. 395437157 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-137/DS-012</td>
    <td>11. 27039454</td>
    <td>-8. 39521619 Porphyry</td>
  </tr>
  <tr>
    <td>MWAXI-138/DS-013</td>
    <td>11. 24521424</td>
    <td>-8. 395821054 Porphyry</td>
  </tr>
  <tr>
    <td>SI-124</td>
    <td>11. 69892867</td>
    <td>-9. 366777442 Granite</td>
  </tr>
  <tr>
    <td>KD000154</td>
    <td>10. 57691572</td>
    <td>-8. 877497566 Diorite</td>
  </tr>
  <tr>
    <td>KL000274</td>
    <td>10. 77452268</td>
    <td>-8. 917751799 Dacite</td>
  </tr>
  <tr>
    <td>KL000565</td>
    <td>10. 78728611</td>
    <td>-8. 972577086 Granodiorite</td>
  </tr>
  <tr>
    <td>KL000630</td>
    <td>10. 77046183</td>
    <td>-8. 919851767 Granite</td>
  </tr>
  <tr>
    <td>BF1</td>
    <td>13. 75246</td>
    <td>-2. 53802 Granite</td>
  </tr>
  <tr>
    <td>BF2</td>
    <td>13. 38028</td>
    <td>-2. 38712 Tonalite</td>
  </tr>
  <tr>
    <td>BF3</td>
    <td>13. 01286</td>
    <td>-1. 83645 Granite</td>
  </tr>
  <tr>
    <td>BF4</td>
    <td>12. 4004</td>
    <td>-1. 70917 Granite</td>
  </tr>
  <tr>
    <td>BF5</td>
    <td>12. 39939</td>
    <td>-1. 11051 Tonalite</td>
  </tr>
  <tr>
    <td>BF6</td>
    <td>12. 01079</td>
    <td>-0. 31836 Tonalite</td>
  </tr>
  <tr>
    <td>BF7</td>
    <td>11. 89121</td>
    <td>-0. 29407 Granite</td>
  </tr>
  <tr>
    <td>BF8</td>
    <td>11. 54592</td>
    <td>0. 73965 Granodiorite</td>
  </tr>
  <tr>
    <td>BF9</td>
    <td>11. 47774</td>
    <td>1. 0282 Quatrz Diorite</td>
  </tr>
  <tr>
    <td>BF10</td>
    <td>14. 17631</td>
    <td>-0. 6011 Diorite</td>
  </tr>
  <tr>
    <td>BF11</td>
    <td>14. 66517</td>
    <td>-0. 43407 Granite</td>
  </tr>
  <tr>
    <td>BF12</td>
    <td>13. 35991</td>
    <td>-0. 52269 Granite</td>
  </tr>
  <tr>
    <td>NG1</td>
    <td>10. 75</td>
    <td>-2. 000001 Granite</td>
  </tr>
  <tr>
    <td>SG5</td>
    <td>6. 494627</td>
    <td>-1. 182057 Granite</td>
  </tr>
  <tr>
    <td>SG6</td>
    <td>5. 655136</td>
    <td>-0. 547377 Granite</td>
  </tr>
</table>
Field description

Post tectonic granite

Fine-grained gabbro/basalt

Magnetic-textured granite, coarse-grained and aplite phases

non-magnetic textured granite

Souma Diorite

Granodiorite

Sheared granite

Granite

Granite

Gabbro

Granodiorite, biotite-amphibole bearing

Foliated tonalite

Granodiorite

Aplite

Diorite, amphibole-bearing

Diorite, amphibole bearing, leucocratic

Granite with biotite ± amphibole

Syenogranite, medium-grained, quartz, K-fsp, plagioclase, biotite and amphibole

Banded granitoid: Lighter layers, quartzofeldspathic minerals and darker layers, ferromagnesian minerals

Mg equigranular diorite

Granitoid hanging wall Samavogo

Hbl diorite

Og lineated granitoid

Monzonite

Mg granitoid

Syenite/Syenogranite, highly magnetic, intrusive, no obvious foliation

Pink 'Massigui' Granite, magnetic, Morila area

Qtz-Fspar Dyke in Massigui granite, flattened sediment xenoliths (054 strike).

Qtz-Fspar-Bt, equigranular intrusive, little deformation

Granodiorite, Morila pit/West side

Tonalite, coarse-grained, Morila pit/south end

Granodiorite, Morila pit/centre

White/Grey 'Doubalakoro' Granite, Non-magnetic

Granite

Orthogranite, sediment and mafic xenoliths, 2-10mm plagioclase, ghost clasts, slightly banded

Pegmatite, massive feldspar, 040 fabric and 080 strike

Gneiss

Equigranular

Gneissic-granitoid

Gneissic-granitoid
Granodiorite

Diorite-granodiorite

Gneissic granitoid

K-feldspar rich granite

K-feldspar rich granite

Granodiorite

Granodiorite, stacked qtz vein array

Granite, Plag-qtz-bt, equigranular

3 Phase Granite, felsic phase

3 Phase Granite, more mafic phase.

Aplite dyke, aplite has fractionated into pegmatite on the margins

Granite, mafic phase, weak foliation 005-030, C-prime development (discrete shears) 040-055

Fine-grained porphyry intrusive

Diorite main body

Diorite east body

Granodiorite, mafic xenoliths, magmatic texture, sedimentary xenoliths

Granodiorite

Granodiorite

Granodiorite

Granodiorite

Feldspathic Intrusive

Qtz-Diorite Selingue Dam Quarry

Fine-grained intermediate intrusive

Porphyry intrusive within granodiorite-diorite

Felsic Intrusive? Feldspar rich, contains small bt rich xenoliths

Fine-grained intermediate intrusive

Dacite?

Felsic Intrusive? Feldspar rich, contains small bt rich xenoliths.

Granodiorite-diorite, magnetic and magmatic banding indicates 060 strike

Porphyry intrusive within granodiorite-diorite

Siekerole Granite, 64/048NW

Siekerole Granite, not oriented, Qtz-Fspar-Musc

Diallo granite, slightly deformed portion of the granite

Granite

Siekerole granite, not -oriented, sinistral shear, with qtz and offset.

Siekerole granite, sinistral shear, with qtz vein

Magnetic 2 feldspar granite, coarse-grained, variably deformed, xXenoliths of Qtz-bt schist common <10cm

Magnetic 2 feldspar granite, coarse-grained, variably deformed, C-Prime developed

Magnetic 2 feldspar granite, coarse-grained, variably deformed, sinistral movement sense

Granite, Qtz-Bt-Musc, strongly foliated

Granite, massive texture, cut by pegmatite dykes, xenoliths common, deformed and aligned

Granite, deformed
Syenite, occasional pegmatite dykes 70/343W

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

Diorite

monzogranite

Altered diorite

Altered dacite microporphyry

Granodiorite

Altered dacite porphyry

Megacrystic granite, megacrysts are K-feldspars

Coarse-grained tonalite locally affected by small scale (~ cm) shear bands

Leucocratic and fine-grained granite

Leucocratic and fine-grained granite

Tonalite slightly leucocratic and strongly foliated

Coarse-grained tonalite, dark minerals are biotite and hornblendes

Equigranular medium-grained granite with mesocratic color

Granodiorite roughly foliated and locally folded

Mesocratic to melanocratic quartz-diorite with phenocrysts of hornblendes

Quartz rich microdiorite

Pink-colored and medium to fine-grained granite

Leucocratic and fine-grained granite locally affected by small shear bands

quartz-plagioclase-hornblende -biotite granite

quartz -biotite -feldspar granite

quartz -biotite -plagioclase granitic rock with pegmatite veins
Region

The Belahouro Belt (BE)

The Boromo-Hounde Belts (HO)

Banfora

Syama

Morila

Bougouni

Yanfolila

Siguiri Basin