Geochemical difference of basalts between polygenetic and monogenetic volcanoes in the central part of the Cameroon volcanic line

The 1600 km long Cameroon volcanic line is composed of large polygenetic volcanoes and small monogenetic volcanoes. The latter conform monogenetic volcano groups consisting of small lava flows, cinder cones and maars. Chemical analyses on basalts from the central part of the Cameroon volcanic line showed that CaO contents of the basalts of polygenetic volcanoes are higher than those of monogenetic volcanoes, while the reverse relation is found for SiO2 contents. Incompatible trace elements are high in both basalts, but HFS/LIL ratios and La/Ba ratio are higher for polygenetic volcanoes than monogenetic volcanoes. Rb-Ba-La relations, representing the most incompatible elements for uni-, di- and tri-valent cations, indicate that basalts of polygenetic volcanoes are similar to depleted mid-oceanic ridge basalts, whereas, the basalts of monogenetic volcanoes are akin to continental flood basalts or oceanic island basalts. It is suggested that the major sources of the polygenetic volcanoes are the upwelling asthenosphere underneath the African plate, while those of the monogenetic volcanoes are the lowest portion of the subcontinental lithosphere.

[1]  Y. Nojiri,et al.  Helium and carbon fluxes in Lake Nyos, Cameroon : Constraint on next gas burst , 1990 .

[2]  N. Rogers,et al.  Continental mantle lithosphere, and shallow level enrichment processes in the Earth's mantle , 1990 .

[3]  Takashi Ohsumi,et al.  The Lake Nyos gas disaster: chemical and isotopic evidence in waters and dissolved gases from three Cameroonian crater lakes, Nyos, Monoun and Wum , 1989 .

[4]  Y. Tatsumi.  Migration of fluid phases and genesis of basalt magmas in subduction zones , 1989 .

[5]  J. Fitton,et al.  Mantle Dynamics: A Nd, Sr, Pb and O Isotopic Study of the Cameroon Line Volcanic Chain , 1988 .

[6]  P. Hooper.  The Columbia River Basalt , 1988 .

[7]  R. Carlson,et al.  Flood Basalt Volcanism in the Northwestern United States , 1988 .

[8]  O. Ujike.  Mantle metasomatic enrichment in LILE of basalt magma sources beneath the Northeast Japan arc, as indicated by the LILE/Y-Zr/Y plots , 1987 .

[9]  M. J. Bas.  Nephelinites and carbonatites , 1987 .

[10]  J. Fitton,et al.  The Cameroon line, West Africa: a comparison between oceanic and continental alkaline volcanism , 1987, Geological Society, London, Special Publications.

[11]  M. McCulloch,et al.  The origins of ultrapotassic rocks as inferred from Sr, Nd and Pb isotopes , 1986 .

[12]  F. Frey,et al.  Trace element and isotopic geochemistry of lavas from Haleakala Volcano, east Maui, Hawaii: Implications for the origin of Hawaiian basalts , 1985 .

[13]  N. Takaoka,et al.  Noble-gas state in the earth's interior — Some constraints on the present state , 1985 .

[14]  J. Fitton,et al.  The Cameroon line, West Africa, and its bearing on the origin of oceanic and continental alkali basalt , 1985 .

[15]  W. White,et al.  HfNdSr isotopes and incompatible element abundances in island arcs: implications for magma origins and crust-mantle evolution , 1984 .

[16]  R. Evans,et al.  Petrologic and geochemical variations along the Mid-Atlantic Ridge from 29 degrees N to 73 degrees N , 1983 .

[17]  J. Fitton.  Active Versus Passive Continental Rifting: Evidence from the West African Rift System , 1983 .

[18]  C. Kilburn,et al.  1982 eruption of Mount Cameroon, West Africa , 1983, Nature.

[19]  B. Dupré,et al.  Subcontinental versus suboceanic mantle, II. NdSrPb isotopic comparison of continental tholeiites with mid-ocean ridge tholeiites, and the structure of the continental lithosphere , 1982 .

[20]  M. Perfit,et al.  143Nd/144Nd,87Sr/86Sr and trace element constraints on the petrogenesis of Aleutian island arc magmas , 1981 .

[21]  R. Kay.  Volcanic Arc Magmas: Implications of a Melting-Mixing Model for Element Recycling in the Crust-Upper Mantle System , 1980, The Journal of Geology.

[22]  B. Mysen,et al.  Melting phase relations of natural peridotite +CO 2 as a function of degree of partial melting at 15 and 30 kbar , 1980 .

[23]  J. Budahn,et al.  Origin of Hawaiian Tholeiites: Trace Element Constraints , 1980 .

[24]  S. R. Taylor,et al.  Spatial variations in the geochemistry of quaternary lavas across the Sunda arc in Java and Bali , 1979 .

[25]  The interpretation of igneous rocks , 1979 .

[26]  D. Eggler.  The effect of CO<2) upon partial melting of peridotite in the system Na<2) O-CaO-Al<2) O<3) -MgO-SiO<2) -CO<2) to 35 kb, with an analysis of melting in a peridotite-H<2) O-CO<2) system , 1978 .

[27]  G. Hanson.  Geochemical evolution of the suboceanic mantle , 1977, Journal of the Geological Society.

[28]  Kazuaki Nakamura,et al.  Volcanoes as possible indicators of tectonic stress orientation — principle and proposal , 1977 .

[29]  S. Banno,et al.  Crystal structure control in trace element partition between crystal and magma , 1977 .

[30]  B. Mysen,et al.  Melting of a Hydrous Mantle: II. Geochemistry of Crystals and Liquids Formed by Anatexis of Mantle Peridotite at High Pressures and High Temperatures as a Function of Controlled Activities of Water, Hydrogen, and Carbon Dioxide , 1975 .

[31]  G. A. Macdonald,et al.  Chemical Composition of Hawaiian Lavas1 , 1964 .