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Dehydration, melting and related garnet growth in the deep root of the Amalaoulaou Neoproterozoic magmatic arc (Gourma, NE Mali)

Published online by Cambridge University Press:  17 September 2008

JULIEN BERGER ,
RENAUD CABY ,
JEAN-PAUL LIÉGEOIS ,
JEAN-CLAUDE C. MERCIER  and
DANIEL DEMAIFFE
JULIEN BERGER*
Affiliation:
Musée royal de l'Afrique centrale, Section de géologie isotopique, Leuvensteenweg 13, B-3080 Tervuren, Belgique Université libre de Bruxelles (U.L.B.), Géochimie isotopique et géodynamique chimique, CP 160/02, av. F. Roosevelt 50, B-1050 Bruxelles, Belgique Université de la Rochelle, UMR CNRS 6250 ‘LIENSs’, ILE, 2 rue Olympe de Gouges F-17042 La Rochelle-cedex 1, France
RENAUD CABY
Affiliation:
Université de Montpellier 2, Laboratoire de Tectonophysique, Place E. Bataillon, F-34095 Montpellier-cedex, France
JEAN-PAUL LIÉGEOIS
Affiliation:
Musée royal de l'Afrique centrale, Section de géologie isotopique, Leuvensteenweg 13, B-3080 Tervuren, Belgique
JEAN-CLAUDE C. MERCIER
Affiliation:
Université de la Rochelle, UMR CNRS 6250 ‘LIENSs’, ILE, 2 rue Olympe de Gouges F-17042 La Rochelle-cedex 1, France Université de Nantes, UMR CNRS 6112 ‘LPGN’, BP 92205, 2 rue de la Houssinière, F-44322 Nantes, France
DANIEL DEMAIFFE
Affiliation:
Université libre de Bruxelles (U.L.B.), Géochimie isotopique et géodynamique chimique, CP 160/02, av. F. Roosevelt 50, B-1050 Bruxelles, Belgique
*
§Author for correspondence: [email protected]
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Abstract

The Amalaoulaou Neoproterozoic island-arc massif belongs to the Gourma belt in Mali. The metagabbros and pyroxenites forming the main body of this arc root show the pervasive development of garnet. In the pyroxenites, the latter has grown by reaction between pyroxene and spinel during isobaric cooling. By contrast, in the metagabbros, garnet textures and relations to felsic veins exclude an origin through solid-state reactions only. It is proposed that garnet has grown following dehydration and localized melting of amphibole-bearing gabbros at the base of the arc. The plagioclase-saturated melts represented by anorthositic veins in the metagabbros and by trondhjemites in the upper part of the massif provide evidence for melting in the deep arc crust, which locally generated high-density garnet–clinopyroxene–rutile residues. Garnet growth and melting began around 850 °C at 10 kbar and the tonalitic melts were most probably generated around 1050 °C at P ≥ 10 kbar. This HT granulitic imprint can be related to arc maturation, leading to a P–T increase in the deep arc root and dehydration and/or dehydration-melting of amphibole-bearing gabbros. Observation of such features in the root of this Neoproterozoic island arc has important consequences, as it provides a link to models concerning the early generation of continental crust.

Keywords

Gourmadehydration-meltingisland arcNeoproterozoicgranulite
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 2 , March 2009 , pp. 173 - 186
Copyright
Copyright © Cambridge University Press 2008

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References

Bard, J. P., Maluski, H., Matte, P. & Proust, F. 1980. The Kohistan sequence; crust and mantle of an obducted island arc. Geological Bulletin, University of Peshawar 13, 87–93.Google Scholar
Bayer, R. & Lesquer, A. 1978. Les anomalies gravimétriques de la bordure orientale du craton ouest-africain: géométrie d'une suture panafricaine. Bulletin de la Société Géologique de France 20, 863–76.CrossRefGoogle Scholar
Beard, J. S. & Lofgren, G. E. 1991. Dehydration melting and water-saturated melting of basaltic and andesitic greenstones and amphibolites at 1, 3, and 6.9 kb. Journal of Petrology 32, 365–401.CrossRefGoogle Scholar
Behn, M. D. & Kelemen, P. B. 2006. Stability of arc lower crust: Insights from the Talkeetna arc section, south central Alaska, and the seismic structure of modern arcs. Journal of Geophysical Research – Solid Earth 111 (B11207), doi:10.1029/2006JB004327, 20 pp.CrossRefGoogle Scholar
Berger, J., Féménias, O., Coussaert, N. & Demaiffe, D. 2005. Magmatic garnet-bearing mafic xenoliths (Puy Beaunit, French Massif Central): P–T path from crystallization to exhumation. European Journal of Mineralogy 17, 687–701.CrossRefGoogle Scholar
Bertrand, P. & Mercier, J.-C. C. 1985. The mutual solubility of coexisting ortho- and clinopyroxene; toward an absolute geothermometer for the natural system? Earth and Planetary Science Letters 76, 109–22.CrossRefGoogle Scholar
Black, R., Latouche, L., Liégeois, J. P., Caby, R. & Bertrand, J. M. 1994. Pan-African displaced terranes in the Tuareg shield (central Sahara). Geology 22, 641–4.2.3.CO;2>CrossRefGoogle Scholar
Bradshaw, J. Y. 1989. Origin and metamorphic history of an Early Cretaceous polybaric granulite terrain, Fiordland, Southwest New Zealand. Contributions to Mineralogy and Petrology 103, 346–60.CrossRefGoogle Scholar
Burg, J. P., Bodinier, J. L., Chaudhry, S., Hussain, S. & Dawood, H. 1998. Infra-arc mantle–crust transition and intra-arc mantle diapirs in the Kohistan Complex (Pakistani Himalaya): petro-structural evidence. Terra Nova 10, 74–80.CrossRefGoogle Scholar
Caby, R. 1979. Les nappes précambriennes du Gourma dans la chaîne pan-africaine du Mali. Revue de Géologie Dynamique et de Géographie Physique 21, 367–76.Google Scholar
Caby, R. 1994. Precambrian coesite from Northern Mali – First record and implications for plate-tectonics in the Trans-Saharan segment of the Pan-African belt. European Journal of Mineralogy 6, 235–44.CrossRefGoogle Scholar
Caby, R., Andreopoulos-Renaud, U. & Pin, C. 1989. Late Proterozoic arc–continent and continent–continent collision in the Pan-African Trans-Saharan Belt of Mali. Canadian Journal of Earth Sciences 26, 1136–46.CrossRefGoogle Scholar
Caby, R., Buscail, F., Dembele, D., Diakite, S., Sacko, S. & Ball, M. 2008. Neoproterozoic garnet-glaucophanites and eclogites: new insights for subduction metamorphism of the Gourma fold-and-thrust belt (eastern Mali). In The boundaries of the West African Craton (eds Ennih, N. & Liégeois, J.-P.), pp. 203–16. Geological Society of London, Special Publication no. 297.Google Scholar
Daczko, N. R., Clarke, G. L. & Klepeis, K. A. 2001. Transformation of two-pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust, Fiordland, New Zealand. Journal of Metamorphic Geology 19, 547–60.CrossRefGoogle Scholar
DeBari, S. M. & Coleman, R. G. 1989. Examination of the deep levels of an island-arc – Evidence from the Tonsina ultramafic–mafic assemblage, Tonsina, Alaska. Journal of Geophysical Research – Solid Earth and Planets 94, 4373–91.Google Scholar
Desmurs, L., Müntener, O. & Manatschal, G. 2002. Onset of magmatic accretion within a magma-poor rifted margin: a case study from the Platta ocean–continent transition, eastern Switzerland. Contributions to Mineralogy and Petrology 144, 365–82.CrossRefGoogle Scholar
Dostal, J., Dupuy, C. & Caby, R. 1994. Geochemistry of the Neoproterozoic Tilemsi belt of Iforas (Mali, Sahara) – a crustal section of an oceanic island-arc. Precambrian Research 65, 55–69.CrossRefGoogle Scholar
Dostal, J., Caby, R., Dupuy, C., Mevel, C. & Owen, J. V. 1996. Inception and demise of a Neoproterozoic ocean basin: Evidence from the Ougda complex, western Hoggar (Algeria). Geologische Rundschau 85, 619–31.CrossRefGoogle Scholar
Duclaux, G., Menot, R. P., Guillot, S., Agbossoumondé, Y. & Hilairet, N. 2006. The mafic layered complex of the Kabye massif (north Togo and north Benin): Evidence of a Pan-African granulitic continental arc root. Precambrian Research 151, 101–18.CrossRefGoogle Scholar
Escuder-Viruete, J., De Neira, A. D., Huerta, P. P. H., Monthel, J., Senz, J. G., Joubert, M., Lopera, E., Ullrich, T., Friedman, R., Mortensen, J. & Perez-Estaun, A. 2006. Magmatic relationships and ages of Caribbean Island arc tholeiites, boninites and related felsic rocks, Dominican Republic. Lithos 90, 161–86.CrossRefGoogle Scholar
Féménias, O., Mercier, J. C. C., Nkono, C., Diot, H., Berza, T., Tatu, M. & Demaiffe, D. 2006. Calcic amphibole growth and compositions in calc-alkaline magmas: Evidence from the Motru Dike Swarm (Southern Carpathians, Romania). American Mineralogist 91, 73–81.CrossRefGoogle Scholar
Foden, J. D. & Green, D. H. 1992. Possible role of amphibole in the origin of andesite – some experimental and natural evidence. Contributions to Mineralogy and Petrology 109, 479–93.CrossRefGoogle Scholar
Ganguly, J. 1979. Garnet and clinopyroxene solid solutions, and geothermometry based on Fe–Mg distribution coefficient. Geochimica et Cosmochimica Acta 43, 1021–9.CrossRefGoogle Scholar
Garrido, C. J., Bodinier, J. L., Burg, J. P., Zeilinger, G., Hussain, S. S., Dawood, H., Chaudhry, M. N. & Gervilla, F. 2006. Petrogenesis of mafic garnet granulites in the lower crust of the Kohistan palaeo-arc complex (Northern Pakistan): Implications for intra-crustal differentiation of island arcs and generation of continental crust. Journal of Petrology 47, 1873–1914.Google Scholar
Green, D. H. & Ringwood, A. E. 1967. An experimental investigation of the gabbro to eclogite transformation and its petrological applications. Geochimica et Cosmochimica Acta 31, 767–833.CrossRefGoogle Scholar
Greene, A. R., Debari, S. M., Kelemen, P. B., Blusztajn, J. & Clift, P. D. 2006. A detailed geochemical study of island arc crust: the Talkeetna Arc section, south-central Alaska. Journal of Petrology 47, 1051–93.CrossRefGoogle Scholar
Harangi, S., Downes, H., Kosa, L., Szabo, C., Thirlwall, M. F., Mason, P. R. D. & Mattey, D. 2001. Almandine garnet in calc-alkaline volcanic rocks of the northern Pannonian Basin (eastern-central Europe): Geochemistry, petrogenesis and geodynamic implications. Journal of Petrology 42, 1813–43.CrossRefGoogle Scholar
Harley, S. L. 1984 a. The solubility of alumina in orthopyroxene coexisting with garnet in FeO–MgO–Al2O3–SiO2 and CaO–FeO–MgO–Al2O3–SiO2. Journal of Petrology 25, 665–96.CrossRefGoogle Scholar
Harley, S. L. 1984 b. An experimental study of the partitioning of Fe and Mg between garnet and orthopyroxene. Contributions to Mineralogy and Petrology 86, 359–73.CrossRefGoogle Scholar
Hermann, J., Müntener, O. & Gunther, D. 2001. Differentiation of mafic magma in a continental crust-to-mantle transition zone. Journal of Petrology 42, 189–206.CrossRefGoogle Scholar
Hofmann, A. W. 1988. Chemical differentiation of the Earth – the relationship between mantle, continental-crust, and oceanic-crust. Earth and Planetary Science Letters 90, 297–314.CrossRefGoogle Scholar
Hollis, J. A., Clarke, G. L., Klepeis, K. A., Daczko, N. R. & Ireland, T. R. 2003. Geochronology and geochemistry of high-pressure granulites of the Arthur River Complex, Fiordland, New Zealand: Cretaceous magmatism and metamorphism on the palaeo-Pacific Margin. Journal of Metamorphic Geology 21, 299–313.CrossRefGoogle Scholar
Jahn, B., Caby, R. & Monié, P. 2001. The oldest UHP eclogites of the World: age of UHP metamorphism, nature of protoliths and tectonic implications. Chemical Geology 178, 143–58.CrossRefGoogle Scholar
Jull, M. & Kelemen, P. B. 2001. On the conditions for lower crustal convective instability. Journal of Geophysical Research – Solid Earth 106, 6423–46.CrossRefGoogle Scholar
Kay, R. W. & Kay, S. M. 1988. Crustal recycling and the Aleutian arc. Geochimica et Cosmochimica Acta 52, 1351–9.CrossRefGoogle Scholar
Kelemen, P. B., Hanghoj, K. & Greene, A. R. 2003. One view of the geochemistry of subduction-related magmatic arcs, with emphasis on primitive andesite and lower crust. In Treatise on geochemistry vol. 3: The Crust (ed Rudnick, R. L.), pp. 593–659. Oxford: Elsevier-Pergamon.Google Scholar
Klein, E. M. 2003. Geochemistry of the igneous oceanic crust. In Treatise on geochemistry vol. 3: The Crust (ed. Rudnick, R. L.), pp. 433–63. Oxford: Elsevier-Pergamon.CrossRefGoogle Scholar
Kodaira, S., Sato, T., Takahashi, N., Miura, S., Tamura, Y., Tatsumi, Y. & Kaneda, Y. 2007. New seismological constraints on growth of continental crust in the Izu-Bonin intra-oceanic arc. Geology 35, 1031–4.CrossRefGoogle Scholar
Liégeois, J. P., Bertrand, J. M. & Black, R. 1987. The subduction- and collision-related Pan-African composite batholith of the Adrar des Iforas (Mali); a review. Geological Journal 22, 185–211.CrossRefGoogle Scholar
Lopez, S. & Castro, A. 2001. Determination of the fluid-absent solidus and supersolidus phase relationships of MORB-derived amphibolites in the range 4–14 kbar. American Mineralogist 86, 1396–1403.CrossRefGoogle Scholar
Ludwig, K. R. 2003. User's manual for Isoplot 3.00. A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication no. 4a.Google Scholar
Martin, H., Smithies, R. H., Rapp, R., Moyen, J. F. & Champion, D. 2005. An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution. Lithos 79, 1–24.CrossRefGoogle Scholar
Mattinson, J. M., Kimbrough, D. L. & Bradshaw, J. Y. 1986. Western Fiordland orthogneiss; Early Cretaceous arc magmatism and granulite facies metamorphism, New Zealand. Contributions to Mineralogy and Petrology 92, 383–92.CrossRefGoogle Scholar
McDonough, W. F. & Sun, S. S. 1995. The Composition of the Earth. Chemical Geology 120, 223–53.CrossRefGoogle Scholar
Mokri, M., Ouzegane, K., Kienast, J. R. & Caby, R. 2008. Evolution pression et température des métagabbros à grenat du complexe du camp Zora (terrane de l'Ahnet, Nord-Ouest du Hoggar). Bulletin du Service Géologique de l'Algérie 19, 17–31.Google Scholar
Müntener, O. & Ulmer, P. 2006. Experimentally derived high-pressure cumulates from hydrous arc magmas and consequences for the seismic velocity structure of lower arc crust. Geophysical Research Letters 33, L21308.CrossRefGoogle Scholar
Nimis, P. & Ulmer, P. 1998. Clinopyroxene geobarometry of magmatic rocks Part 1: An expanded structural geobarometer for anhydrous and hydrous, basic and ultrabasic systems. Contributions to Mineralogy and Petrology 133, 122–35.CrossRefGoogle Scholar
Pattinson, D. R. M. 2003. Petrogenetic significance of orthopyroxene-free garnet plus clinopyroxene plus plagioclase +/− quartz-bearing metabasites with respect to the amphibolite and granulite facies. Journal of Metamorphic Geology 21, 21–34.CrossRefGoogle Scholar
Rapp, R. P. & Watson, E. B. 1995. Dehydration melting of metabasalt at 8–32 kbar – Implications for continental growth and crust–mantle recycling. Journal of Petrology 36, 891–931.CrossRefGoogle Scholar
Ringuette, L., Martignole, J. & Windley, B. F. 1999. Magmatic crystallization, isobaric cooling, and decompression of the garnet-bearing assemblages of the Jijal Sequence (Kohistan Terrane, western Himalayas). Geology 27, 139–42.2.3.CO;2>CrossRefGoogle Scholar
Rudnick, R. L. 1995. Making continental crust. Nature 378, 571–8.CrossRefGoogle Scholar
Rushmer, T. 1993. Experimental high-pressure granulites – Some applications to natural mafic xenolith suites and Archaean granulite terranes. Geology 21, 411–14.2.3.CO;2>CrossRefGoogle Scholar
Schmidt, M. W. 1992. Amphibole composition in tonalite as a function of pressure – an experimental calibration of the Al-in-hornblende barometer. Contributions to Mineralogy and Petrology 110, 304–10.CrossRefGoogle Scholar
Selbekk, R. S. & Skjerlie, K. P. 2002. Petrogenesis of the anorthosite dyke swarm of Tromso, North Norway: Experimental evidence for hydrous anatexis of an alkaline mafic complex. Journal of Petrology 43, 943–62.CrossRefGoogle Scholar
Sen, C. & Dunn, T. 1994. Dehydration melting of a basaltic composition amphibolite at 1.5 and 2.0 GPa – Implications for the origin of adakites. Contributions to Mineralogy and Petrology 117, 394–409.CrossRefGoogle Scholar
Spear, F. S. 1993. Metamorphic phase equilibria and pressure–temperature–time paths. Washington: The Mineralogical Society of America, 799 pp.Google Scholar
Stevenson, J. A., Dackzo, N. R., Clarke, G. L., Pearson, N. & Klepeis, K. A. 2005. Direct observation of adakite melts generated in the lower continental crust, Fiordland, New Zealand. Terra Nova 17, 73–9.CrossRefGoogle Scholar
Taylor, S. R. & McLennan, S. M. 1985. The continental crust: Its composition and evolution. Oxford: Blackwell Scientific, 321 pp.Google Scholar
Vielzeuf, D. & Schmidt, M. W. 2001. Melting relations in hydrous systems revisited: application to metapelites, metagreywackes and metabasalts. Contributions to Mineralogy and Petrology 141, 251–67.CrossRefGoogle Scholar
Wolf, M. B. & Wyllie, P. J. 1991. Dehydration-melting of solid amphibolite at 10 kbar – textural development, liquid interconnectivity and applications to the segregation of magmas. Mineralogy and Petrology 44, 151–79.CrossRefGoogle Scholar
Wolf, M. B. & Wyllie, P. J. 1993. Garnet growth during amphibolite anatexis – Implications of a garnetiferous restite. Journal of Geology 101, 357–73.CrossRefGoogle Scholar
Yamamoto, H. & Yoshino, T. 1998. Superposition of replacements in the mafic granulites of the Jijal complex of the Kohistan arc, northern Pakistan: dehydration and rehydration within deep arc crust. Lithos 43, 219–34.CrossRefGoogle Scholar
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