Tropical chemical weathering of a garnet rich micaschist in the rainforest zone of Cameroon

Abstract

Soils developed on garnet-rich micaschist in the Southern Cameroon plateau were investigated. Morphologically, two weathering materials constituted the study profile, fine earth and nodules. Each material has a singular evolution from the coarse saprolite to the upper set of clayey and loose horizons. There is Al2O3 enrichment in the fine earth concomitantly to Fe2O3, Na2O and K2O enrichment in nodules in major element–Al2O3 variation diagrams. A–CN–K and A–CNK–FM diagrams show a progressive depletion of Al in nodules concomitantly to an enrichment of this element in the fine earth. Three pedogenetic processes emerge from the evolution of weathering products. There is a ferruginization process whose importance increases from the coarse saprolite to the upper set of clayey and loose horizons, giving rise to the formation of dense nodules composed of hematite, goethite and gibbsite. This ferruginization occurs concomitantly with a desaluminization process, which causes Al2O3 depletion in nodules. These nodules are formed by the process of induration where the hydrated amorphous hydroxide and oxides are dehydrated to their crystalline oxide form, due to condensation. In addition, there is aluminization, which occurs in the fine earth, leading to the development of a red clayey material composed of kaolinite and gibbsite. 

Keywords

• Laterite,ferruginization,desaluminization,aluminization,Cameroon

References

1. Anderson, S.P., Dietrich, W.E., Brimhall, G.H., 2002. Weathering profiles, mass-balance analysis, and rates of solute loss: linkages between weathering and erosion in a small, steep catchment. GSA Bulletin 114(9): 1143–1158.
2. Aristizabal, E., Roser, B., Yokota, S., 2005. Tropical chemical weathering of hillslope deposits and bedrock source in the Aburra Valley, northern Colombian Andes. Engineering Geology 81(4): 389-406.
3. Beauvais, A., 1999. Geochemical balance of lateritization processes and climatic signatures in weathering profiles overlain by ferricretes in Central Africa. Geochimica et Cosmochimica Acta 63(23-24): 3939–3957.
4. Beauvais, A., 2009. Ferricrete biochemical degradation on the rainforest–savannas boundary of Central African Republic. Geoderma 150(3-4): 379–388.
5. Beauvais, A., Colin, F., 1993. Formation and transformation processes of iron duricrust systems in tropical humid environment. Chemical Geology 106(1-2): 77–151.
6. Beauvais, A., Tardy. Y., 1993. Degradation and dismantling of iron crusts under climatic changes in Central Africa. Chemical Geology 107(3-4): 277-280.
7. Bitom, D., Volkoff, B., Beauvais, A., Seyler, F., Ndjigui, P.D., 2004. Rôle des héritages latéritiques et du niveau des nappes dans l’évolution des modelés et des sols en zone intertropicale forestière humide. Comptes Rendus Geoscience 336(13): 1161-1170.
8. Brimhall, G.H., Alpers, C.N., Cunningham, A.B., 1985. Analysis of supergene ore-forming processes and ground-water solute transport using mass balance principles. Economic Geology 80(5): 1227-1256.

9. Brimhall, G.H., Dietrich, W.E., 1987. Constitutive mass balance relations between chemical composition, volume, density, porosity and strain in metasomatic hydrochemical systems: results on weathering and pedogenesis. Geochimica et Cosmochimica Acta 51(3): 567-587.
10. Brimhall, G.H., Lewis, C.J., Ague, J.J., Dietrich, W.E., Hampel, J., Teague, T., Rix, P., 1988. Metal enrichment in bauxites by deposition of chemically mature aeolian dust. Nature 333: 819-824.
11. Colin, F., Brimhall, G.H., Nahon, D., Lewis, C.J., Baronnet A., Danty, K., 1992. Equatorial rainforest lateritic mantles: a geomembrane filter. Geology 20(6): 523-526.
12. Colin, F., Viellard, P., Ambrosi, J.P., 1993. Quantitative approach to physical and chemical gold mobility in equatorial rain forest lateritic environment. Earth and Planetary Science Letters 114(2-3): 269-285.
13. Davy, R., El Ansary, M., 1986. Geochemical patterns in the laterite profile at the Boddington gold deposit, Western Australia. Journal of Geochemical Exploration 26(2): 119–124.
14. Deepthy, R., Balakrishnan, S., 2005. Climatic controle on clay mineral formation: Evidence from weathering profiles developed on either side of the Western Ghats. Journal of Earth System Science 114(5): 545-556.
15. Duzgoren-Aydin, N.S., Aydin, A., Malpas, J., 2002. Distribution of clay minerals along a weathered pyroclastic profile, Hong Kong. Catena 50(1): 17–41.
16. Embrechts, J., Stoops, G., 1982. Microscopical aspects of garnet weathering in humid tropical environment. European Journal of Soil Science 33: 535-545.
17. Fedo, C.M., Nesbitt, H.W., Young, G.M., 1995. Unraveling the effects of potassium metasomatism in sedimentary rocks and paleosols, with implications for paleoweathering conditions and provenance Geology 23(10): 921-924.
18. Gupta, A., Rao, K., 2001. Weathering indices and their applicability for crystalline rocks. Bulletin of Engineering Geology and the Environment 60(3): 201– 221.
19. Helgren, D.M., Butzer, K.W., 1977. Paleosols of the Southern Cape Coast, South Africa: Implications for laterite definition, genesis and age. Geographical Review 67(4): 430-445.
20. Irfan, T.Y., 1996. Mineralogy, fabric properties and classification of weathered granites in Hong Kong. Quaterly Journal of Engineering Geology and Hydrogeology 29(1): 5-35.
21. Irfan, T.Y., 1999. Characterization of weathered volcanic rocks in Hong Kong. Quaterly Journal of Engineering Geology and Hydrogeology 32: 317– 348.
22. Jayant K. Tripathi, V., Rajamani, 2007. Geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses, Mysore Plateau, Southern India. Geochimica et Cosmochimica Acta 71(7): 1674–1688.
23. Kamgang, K.B.V., Onana, V.L., Ndome, E.E.P., Parisot, J.C., Ekodeck, G.E., 2009. Behaviour of REE and mass balance calculations in a lateritic profile over chlorite schists in South Cameroun. Chemie der Erde - Geochemistry 69(1): 61-73.
24. Lambe, P., 1996. Residual soils. Landslides: investigation and mitigation. In: Turner, K., Schuster, R. (Eds.), Landslides Investigation and Mitigation, Special Report, Transportation Research Board, National Research Council, vol. 247, pp. 507– 524.
25. Letouzey, R., 1985. Notice explicative de la carte phytogéographique du Cameroun à l’échelle de 1/500 000. Institut de la Carte Internationale de la Végétation, Toulouse, France., 240p.
26. Marques, J.J., Schulze, D.G., Curi, N., Mertzman, S.A., 2004. Trace element geochemistry in Brazilian Cerrado soils. Geoderma 121(1-2): 31-43.
27. McFarlane, M.J., 1976. Laterite and Landscape. Academic Press, London, 151 p.
28. Nahon, D., 1991. Introduction to the Petrology of Soils and Chemical Weathering. John Wiley, New York, 313p.
29. Nahon, D., 2003. Weathering in tropical zone. Significance through ancient and still active mechanisms. Comptes Rendus Géoscience 335(16): 1109–1119.
30. Ndjigui, P.-D., Badinane, M.F.B., Nyeck, B., Nandjip, H.P.K., Bilong, P., 2013. Mineralogical and geochemical features of the coarse saprolite developed on orthogneiss in the SW of Yaoundé, South Cameroon. Journal of African Earth Sciences 79: 125–142.
31. Ndjigui, P.D., Bilong, P., Bitom, D., Dia, A., 2008. Mobilization and redistribution of major and trace elements in two weathering profiles developed on serpentinites in the Lomié ultramafic complex, South-East Cameroon. Journal of African Earth Sciences 50(5): 305-328.
32. Nesbitt, H.W., Young, G.M., 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 279: 715-717.
33. Nesbitt, H.W., Young, G.M., 1984. Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations. Geochimica et Cosmochimica Acta 48(7): 1523-1534.
34. Nesbitt, H.W., Young, G.M., 1989. Formation and diagenesis of weathering profiles. Journal of Geology 97(2): 129-147.
35. Nesbitt, H.W., Young, G.M., McLennan, S.M., Keays, R.R., 1996. Effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments, with implication for provenance studies. Journal of Geology 104(5): 525–542.
36. Ng, C.W.W., Guan, P., Shang, Y.J., 2001. Weathering mechanisms and indices of igneous rocks of Hong Kong. Quaterly Journal of Engineering Geology and Hydrogeology 34(2): 133-151.
37. Nguetnkam, J.P., Kamga, R., Villiéras, F., Ekodeck, G.E., Yvon, J., 2008. Variable weathering response of granite in tropical zones. Example of two sequences studied in Cameroon (Central Africa). Comptes Rendus Geoscience 340(7): 451-461.
38. Ozaytekin, H.H., and Uzum, C., 2012. Comparison of weathering rates of the soils classiefied in Alfisol and Entisol order developed on limestone in the Taurus Mountains at East Mediterranean region. Carpathian journal of Earth and Environmental Sciences 7(1): 109-120.
39. Parisot, J.C., Delvigne, J., Groke, M.C.T., 1983. Petrographical aspects of the supergene weathering of garmet in the "Serra dos Carajas" (Para, Brasil). Mémoires Sciences Géologiques 72 : 141-148.
40. Price, J.R., Velbel, M.A., 2003. Chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks. Chemical Geology 202(3-4): 397– 416.
41. Sherman, D.G., Ikawa, H., and Matsusaka, Y., 1969. Aluminous-ferruginous oxide mineral nodules in tropical soils. Pacific Science 23: 115-122.
42. Stoops, G., 2003. Guidelines for analysis and description of soil and regolith thin sections. Soil Society of America, INC., Madison, USA, 184p.
43. Suchel, J.-B., 1987. Les climats du Cameroun. Thesis. Université de Bordeaux III, France, 1186p.
44. Sueoka, T., Lee, I.K., Huramatsu, M., and Imamura, S., 1985. Geomechanical properties and engineering classification for decomposed granite soils in Kaduna district, Nigeria.. First International Conference of Geomechanics in tropical laterititc and saprolitc soils, Brasilia, 1: 175-186.
45. Tardy, Y., 1993. Pétrologie des latérites et des sols tropicaux. Masson, Paris, 459 p.
46. Tardy, Y., and Roquin, C., 1998. Dérive des continents, Paléoclimats et altérations tropicales. BRGM editions, Orléans, France, 431p.
47. Tardy, Y., Kobilsex, B., Paquet, H., 1991. Mineralogical composition and geographical distribution of African and Brazilian periatlantic laterites. The influence of continental drift and tropical paleoclimates during the past 150 million years and implications for India and Australia. Journal of African Earth Sciences (and the Middle East) 12(1/2): 283-295.
48. Tardy, Y., Nahon., D., 1985. Geochemistry of laterites, stability of Al-Goethite, Al-Hematite and F3+ Kaolinite in bauxites and ferricretes: an approach to the mechanism of concretion formation. American Journal of Science 285(10): 865-903.
49. Temgoua, E., 2001. Les accumulations ferrugineuses actuelles de bas versant en zone forestière humide du Sud- Cameroun. Evolutions pétrologiques des faciès et des éléments en traces en relation avec le cuirassement. Th. Doc., Université Lausanne, 165p.
50. Temgoua, E., Bitom, D., Bilong, P., Lucas, Y., Pfeifer, H. R., 2002. Démantèlement des paysages cuirassés anciens en zone forestière tropicale d’Afrique Centrale, formation d’accumulations ferrugineuses actuelles au bas des versants. Comptes Rendus Geoscience 334 (8) : 537-543.
51. Thiel, R., 1963. Zum system. FeOOH – AlOOH. Zeitschrift für anorganische und allgemeine Chemie 326(1-2) : 70-78.
52. Thomas, M.F., 1994. Geomorphology in the tropics. A Study of weathering and denudation in low latitudes. John Wiley & Sons., Chichester, 460p
53. Trolard, F.,Tardy, Y., 1987. The stabilities of gibbsite, boehmite, aluminous goethites and aluminous hematites in bauxites, ferricretes and laterites as a function of water activity, temperature and particle size. Geochimica et Cosmochimica Acta 51(4): 945–957.
54. Tsozué, D., Bitom D., Yongue-Fouateu, R., 2011. In Situ Genesis of Alumino-Ferruginous Nodules in a Soil Profile Developed on Garnet Rich Micaschist in the High Reliefs of South Cameroon Rainforest Zone (Central Africa). The Open Geology Journal 5: 56-66.
55. Tsozué, D., Bitom, D., Yongue-Fouateu, R., 2012. Morphology, mineralogy and geochemistry of a lateritic soil sequence developed on micaschist in the Abong-Mbang region, South-East Cameroon. South African journal of Geology 115(1): 103-116.
56. Voicu, G., Bardoux, M., 2002. Geochemical behavior under tropical weathering of the Barama-Mazaruni greenstone at Omai gold mine, Guiana Shield. Applied Geochemistry 17(3): 321-336.
57. Voicu, G., Bardoux, M., Jébrak, M., and Voicu, D., 1996. Normative mineralogical calculations for tropical weathering profiles. Geological Association of Canade and Mineral Association of Canadian Program with Abstract, 21: A-69.
58. Wouatong, A.S.L., Kitagawa, R., Tchoua, M.F., Talla V., Njopwouo, D., 2005. Kaolinization of saprolite developed on pana African granite of Batié district, west province of Cameroon. Clay Science 13(1): 7-18.
59. Wouatong, A.S.L., Yerima, B.P.K., Yongue Fouateu, R., Mvondo Ze, A., and Ekodeck G.E., 2013. The origin of etch pits recorded on residual grain surfaces from kaolinized granitic rocks west region Cameroon. Earth Science Research 2(2): 93-110.
60. Yongué-Fouateu, R., 1986. Contribution à l’étude pétrologique de l’altération et des faciès de cuirassement ferrugineux des gneiss migmatitiques de la région de Yaoundé. Th. Doc. 3e cycle, Univ. de Yaoundé, 214p.
61. Yongue-Fouateu, R., Ghogomu, R.T., Penaye, J., Ekodeck, G.E., Stendal, H., Colin, F., 2006. Nickel and cobalt distribution in the laterites of the Lomié region, south-east Cameroon. Journal of African Earth Sciences 45(1): 33–47.