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Reply to comments on “Intrusive rocks and tectono-metamorphic evolution of the Mako Paleoproterozoic belt (Eastern Senegal, West Africa)”
Journal of African Earth Sciences 55 (2009) 269–270
Contents lists available at ScienceDirect
Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
Discussion
Reply to comments on ‘‘Intrusive rocks and tectono-metamorphic evolution of the Mako Paleoproterozoic belt (Eastern Senegal, West Africa)” Mamadou Gueye a,*, Papa Malick Ngom b, Mouhamadane Diène a, Yaouba Thiam a, Siegfried Siegesmund c, Klaus Wemmer c, Sabine Pawlig d a
Institut des Sciences de la Terre, Université Cheikh Anta Diop BP, 16508 Dakar-Fann, Senegal Departement de Géologie, Université Cheikh Anta Diop Dakar, Senegal c Geoscience Center, Georg-August University, Goldschmidtstr. 3, 37077 Göttingen, Germany d Nu Instruments Limited, Unit 74, Clywedog Rd. South, Wrexham Industrial Estate, Wrexham LL13 9XS, United Kingdom b
We welcome the opportunity to address additional comments on our paper. The Eburnean thermotectonic event generally is of greenschist or amphibolite facies character. However, large bodies consisting of high-grade amphibolitic and gneissic xenoliths associated with trondjhemitic calcalkaline granitoids have been described within the Paleoproterozoic greenstone belts of parts of the West African Craton (WAC): Mako supergroup (Dia, 1988; Bertrand et al., 1989; Dia et al., 1997; Gueye et al., 2007), Liptako (Hirbec, 1992), Dabakala (Lemoine, 1988; Gasquet et al., 2003), Reguibat shield (Peucat et al., 2005). High-grade amphibolitic and gneissic rocks in the Mako Belt were first described by Dia (1988) and Dia et al. (1997). They describe gneissic facies that constitute a heterogeneous association of rocks with dioritic to more common tonalitic bulk composition. Field evidence and geochronological data recently obtained by zircon geochronology on high-grade metamorphic rocks suggest clearly the presence of an amphibolite–gneiss complex with ages of around 2200 Ma (Dia et al., 1997; Gueye et al., 2007). They have already been interpreted in the WAC as corresponding to an early Birimian magmatic event (Gasquet et al., 2003; Peucat et al., 2005). We agree with the comment of Dioh et al. that the major foliation occurring in the Layered Plutonic Complex is a magmatic foliation, as we described for the Tonkoutou unit. An age of 2158 ± 8 Ma was obtained by single-grain lead evaporation method on zircons from a sample of layered gabbros from the Sandikounda Layered Plutonic complex, and is interpreted as the crystallization age of this complex (Dia et al., 1997). This is coeval with belt-type plutons dated from 2180 to 2150 Ma elsewhere in West Africa (Hirdes et al., 1992; Davis et al., 1994; Kouamelan, 1996; Kouamelan et al., 1997a,b; Doumbia et al., 1998; Hirdes and Davis, 1998; Oberthür et al., 1998; Loh and Hirdes, 1999; Egal et al., 2002; Lahondière et al., 2002). We regret to find that Dioh et al. misinterpret our proposal. According to our work, we consider the tonalitic gneiss as a high-grade metamorphic xenolith in the Layered Plutonic Complex
DOI of original article: 10.1016/j.jafrearsci.2007.09.013; DOI of comment: 10.1016/j.jafrearsci.2009.05.011. * Corresponding author. E-mail address: [email protected] (M. Gueye). 1464-343X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2009.05.003
of Sandikounda, and the high-grade metamorphic assemblage is restricted to these gneisses. References Bertrand, J.M., Dia, A., Dioh, E., Bassot, J.P., 1989. Réflexion sur la structure interne du craton ouest africain au Sénégal Oriental et confins guinéo-maliens. Compte Rendu Académie Sciences Paris t309 (série II), 751–756. Davis, D.W., Hirdes, W., Schaltegger, U., Nunoo, E.A., 1994. U–Pb constraints on deposition and provenance of Birimian and gold-bearing Tarkwaian sediments in Ghana, West Africa. Precambrian Research 67, 89–107. Dia, A., 1988. Caractère et signification des complexes magmatiques et métamorphiques du secteur de Sandikounda-Laminia (Nord de la boutonnière de Kédougou, Est du Sénégal): un modèle géodynamique du Birimien de l’Afrique de l’Ouest. Thèse Université Dakar Sénégal 350pp. Dia, A., Van Schmus, W.R., Kröner, A., 1997. Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kédougou Inlier, eastern Senegal, West Africa. Journal African Earth Sciences 24, 197–213. Doumbia, S., Pouclet, A., Kouamelan, A., Peucat, J.J., Vidal, M., Delor, C., 1998. Petrogenesis of juvenile-type Birimian (Paleoproterozoic) granitoids in Central Côte d’Ivoire, West Africa: geochemistry and geochronology. Precambrian Research 87, 33–63. Egal, E., Thieblemont, D., Lahondière, D., Guerrot, C., Costea, C.A., Iliescu, D., Delor, C., Goujou, J.C., Lafon, J.M., Tegyey, M., Diaby, S., Kolié, P., 2002. Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kenema-Man domain (Guinea, West African Craton). Precambrian Research 117 (1–2), 57–84. Gasquet, D., Barbey, P., Adou, M., Paquette, J.L., 2003. Structure, Sr–Nd isotope geochemistry and zircon U–Pb geochronology of the granitoids of the Dabakala area (Côte d’Ivoire): evidence for a 2.3 Ga crustal growth event in the Palaeoproterozoic of West Africa? Precambrian Research 127, 329–354. Gueye, M., Siegesmund, S., Wemmer, K., Pawlig, S., Drobe, M., Nolte, N., 2007. New evidences for an early Birimian evolution in the West African Craton: an example from the Kédougou-Kénieba inlier, SE- Senegal. South African Journal of Geology 110, 511–534. Hirbec, Y., 1992. La structure birimienne du Liptako nigérien: un exemple d’interaction entre déformation régionale et mise en place de granitoides. Pangea 17/18, 48–55. Hirdes, W., Davis, D.W., 1998. First U–Pb zircon age of extrusive volcanism in the Birimian supergroup of Ghana/West Africa. Journal of African Earth Sciences 27, 291–294. Hirdes, W., Davis, D.W., Eisenlohr, B.N., 1992. Reassessment of Proterozoic granitoid ages in Ghana on the basis of U/Pb zircon and monazite dating. Precambrian Research 56, 89–96. Kouamélan, A.N., 1996. Géochronologie et géochimie des formations archéennes et protérozoique de la dorsale de Man en Côte d’Ivoire. Mémoir Géosciences Rennes 73, 289p. In : Implications pour la Transition Archéen–Protérozoique. Doctorat de l’Universté de Rennes I, 277pp. Kouamelan, A.N., Delor, C., Peucat, J.J., 1997a. Geochronological evidence for reworking of Archean terrains during the early Proterozoic (21 Ga) in the western Côte d´Ivoire (Man Rise-West African Craton). Precambrian Research 86, 177–199.
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M. Gueye et al. / Journal of African Earth Sciences 55 (2009) 269–270
Kouamelan, A.N., Peucat, J.J., Delor, C., 1997b. Reliques archéennes (3,15 Ga) au sein du magmatisme birimien (2,1 Ga) de Cote d’Ivoire, craton ouest-africain. Comptes Rendus de l’Académie des Sciences 324, 719–727. Lahondière, D., Thieblemont, D., Tegyey, M., Guerrot, C., Diabaté, B., 2002. First evidence of early Birimian (2.21 Ga) volcanic activity in Upper Guinea: the volcanics and associated rocks of the Niani suite. Journal of African Earth Sciences 35, 417–431. Lemoine, S. 1988. Evolution géologique de la région de Dabakala (Northeast Côte d´Ivoire) au Protérozoique inférieur. Unpublished PhD thesis, University of Clermont-Ferrand, France, 338pp.
Loh, G., Hirdes, W., 1999. Explanatory notes for the geological map of Southwest Ghana 1:100000: Sekondi (0402A) and Axim (0403B) sheets. Geologisches Jahrbuch B 93, 149. Oberthür, T., Vetter, U., Davies, W.D., Amanor, J.A., 1998. Age constraints on gold mineralization and Paleoproterozoic crustal evolution in the Ashanti belt of southern Ghana. Precambrian Research 89 (3–4), 129–143. Peucat, J.J., Capdevila, R., Drareni, A., Mahdjoub, Y., Kahoui, M., 2005. The Eglab massif in the West African Craton (Algerie), an original segment of the Eburnean orogeny belt: petrology, geochemistry and geochronology. Precambrian Research 136, 309–352.
Contents lists available at ScienceDirect
Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
Discussion
Reply to comments on ‘‘Intrusive rocks and tectono-metamorphic evolution of the Mako Paleoproterozoic belt (Eastern Senegal, West Africa)” Mamadou Gueye a,*, Papa Malick Ngom b, Mouhamadane Diène a, Yaouba Thiam a, Siegfried Siegesmund c, Klaus Wemmer c, Sabine Pawlig d a
Institut des Sciences de la Terre, Université Cheikh Anta Diop BP, 16508 Dakar-Fann, Senegal Departement de Géologie, Université Cheikh Anta Diop Dakar, Senegal c Geoscience Center, Georg-August University, Goldschmidtstr. 3, 37077 Göttingen, Germany d Nu Instruments Limited, Unit 74, Clywedog Rd. South, Wrexham Industrial Estate, Wrexham LL13 9XS, United Kingdom b
We welcome the opportunity to address additional comments on our paper. The Eburnean thermotectonic event generally is of greenschist or amphibolite facies character. However, large bodies consisting of high-grade amphibolitic and gneissic xenoliths associated with trondjhemitic calcalkaline granitoids have been described within the Paleoproterozoic greenstone belts of parts of the West African Craton (WAC): Mako supergroup (Dia, 1988; Bertrand et al., 1989; Dia et al., 1997; Gueye et al., 2007), Liptako (Hirbec, 1992), Dabakala (Lemoine, 1988; Gasquet et al., 2003), Reguibat shield (Peucat et al., 2005). High-grade amphibolitic and gneissic rocks in the Mako Belt were first described by Dia (1988) and Dia et al. (1997). They describe gneissic facies that constitute a heterogeneous association of rocks with dioritic to more common tonalitic bulk composition. Field evidence and geochronological data recently obtained by zircon geochronology on high-grade metamorphic rocks suggest clearly the presence of an amphibolite–gneiss complex with ages of around 2200 Ma (Dia et al., 1997; Gueye et al., 2007). They have already been interpreted in the WAC as corresponding to an early Birimian magmatic event (Gasquet et al., 2003; Peucat et al., 2005). We agree with the comment of Dioh et al. that the major foliation occurring in the Layered Plutonic Complex is a magmatic foliation, as we described for the Tonkoutou unit. An age of 2158 ± 8 Ma was obtained by single-grain lead evaporation method on zircons from a sample of layered gabbros from the Sandikounda Layered Plutonic complex, and is interpreted as the crystallization age of this complex (Dia et al., 1997). This is coeval with belt-type plutons dated from 2180 to 2150 Ma elsewhere in West Africa (Hirdes et al., 1992; Davis et al., 1994; Kouamelan, 1996; Kouamelan et al., 1997a,b; Doumbia et al., 1998; Hirdes and Davis, 1998; Oberthür et al., 1998; Loh and Hirdes, 1999; Egal et al., 2002; Lahondière et al., 2002). We regret to find that Dioh et al. misinterpret our proposal. According to our work, we consider the tonalitic gneiss as a high-grade metamorphic xenolith in the Layered Plutonic Complex
DOI of original article: 10.1016/j.jafrearsci.2007.09.013; DOI of comment: 10.1016/j.jafrearsci.2009.05.011. * Corresponding author. E-mail address: [email protected] (M. Gueye). 1464-343X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2009.05.003
of Sandikounda, and the high-grade metamorphic assemblage is restricted to these gneisses. References Bertrand, J.M., Dia, A., Dioh, E., Bassot, J.P., 1989. Réflexion sur la structure interne du craton ouest africain au Sénégal Oriental et confins guinéo-maliens. Compte Rendu Académie Sciences Paris t309 (série II), 751–756. Davis, D.W., Hirdes, W., Schaltegger, U., Nunoo, E.A., 1994. U–Pb constraints on deposition and provenance of Birimian and gold-bearing Tarkwaian sediments in Ghana, West Africa. Precambrian Research 67, 89–107. Dia, A., 1988. Caractère et signification des complexes magmatiques et métamorphiques du secteur de Sandikounda-Laminia (Nord de la boutonnière de Kédougou, Est du Sénégal): un modèle géodynamique du Birimien de l’Afrique de l’Ouest. Thèse Université Dakar Sénégal 350pp. Dia, A., Van Schmus, W.R., Kröner, A., 1997. Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kédougou Inlier, eastern Senegal, West Africa. Journal African Earth Sciences 24, 197–213. Doumbia, S., Pouclet, A., Kouamelan, A., Peucat, J.J., Vidal, M., Delor, C., 1998. Petrogenesis of juvenile-type Birimian (Paleoproterozoic) granitoids in Central Côte d’Ivoire, West Africa: geochemistry and geochronology. Precambrian Research 87, 33–63. Egal, E., Thieblemont, D., Lahondière, D., Guerrot, C., Costea, C.A., Iliescu, D., Delor, C., Goujou, J.C., Lafon, J.M., Tegyey, M., Diaby, S., Kolié, P., 2002. Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kenema-Man domain (Guinea, West African Craton). Precambrian Research 117 (1–2), 57–84. Gasquet, D., Barbey, P., Adou, M., Paquette, J.L., 2003. Structure, Sr–Nd isotope geochemistry and zircon U–Pb geochronology of the granitoids of the Dabakala area (Côte d’Ivoire): evidence for a 2.3 Ga crustal growth event in the Palaeoproterozoic of West Africa? Precambrian Research 127, 329–354. Gueye, M., Siegesmund, S., Wemmer, K., Pawlig, S., Drobe, M., Nolte, N., 2007. New evidences for an early Birimian evolution in the West African Craton: an example from the Kédougou-Kénieba inlier, SE- Senegal. South African Journal of Geology 110, 511–534. Hirbec, Y., 1992. La structure birimienne du Liptako nigérien: un exemple d’interaction entre déformation régionale et mise en place de granitoides. Pangea 17/18, 48–55. Hirdes, W., Davis, D.W., 1998. First U–Pb zircon age of extrusive volcanism in the Birimian supergroup of Ghana/West Africa. Journal of African Earth Sciences 27, 291–294. Hirdes, W., Davis, D.W., Eisenlohr, B.N., 1992. Reassessment of Proterozoic granitoid ages in Ghana on the basis of U/Pb zircon and monazite dating. Precambrian Research 56, 89–96. Kouamélan, A.N., 1996. Géochronologie et géochimie des formations archéennes et protérozoique de la dorsale de Man en Côte d’Ivoire. Mémoir Géosciences Rennes 73, 289p. In : Implications pour la Transition Archéen–Protérozoique. Doctorat de l’Universté de Rennes I, 277pp. Kouamelan, A.N., Delor, C., Peucat, J.J., 1997a. Geochronological evidence for reworking of Archean terrains during the early Proterozoic (21 Ga) in the western Côte d´Ivoire (Man Rise-West African Craton). Precambrian Research 86, 177–199.
270
M. Gueye et al. / Journal of African Earth Sciences 55 (2009) 269–270
Kouamelan, A.N., Peucat, J.J., Delor, C., 1997b. Reliques archéennes (3,15 Ga) au sein du magmatisme birimien (2,1 Ga) de Cote d’Ivoire, craton ouest-africain. Comptes Rendus de l’Académie des Sciences 324, 719–727. Lahondière, D., Thieblemont, D., Tegyey, M., Guerrot, C., Diabaté, B., 2002. First evidence of early Birimian (2.21 Ga) volcanic activity in Upper Guinea: the volcanics and associated rocks of the Niani suite. Journal of African Earth Sciences 35, 417–431. Lemoine, S. 1988. Evolution géologique de la région de Dabakala (Northeast Côte d´Ivoire) au Protérozoique inférieur. Unpublished PhD thesis, University of Clermont-Ferrand, France, 338pp.
Loh, G., Hirdes, W., 1999. Explanatory notes for the geological map of Southwest Ghana 1:100000: Sekondi (0402A) and Axim (0403B) sheets. Geologisches Jahrbuch B 93, 149. Oberthür, T., Vetter, U., Davies, W.D., Amanor, J.A., 1998. Age constraints on gold mineralization and Paleoproterozoic crustal evolution in the Ashanti belt of southern Ghana. Precambrian Research 89 (3–4), 129–143. Peucat, J.J., Capdevila, R., Drareni, A., Mahdjoub, Y., Kahoui, M., 2005. The Eglab massif in the West African Craton (Algerie), an original segment of the Eburnean orogeny belt: petrology, geochemistry and geochronology. Precambrian Research 136, 309–352.