@article{fdi:010042267,
  title = {{D}o decades of tropical rainfall affect the chemical compositions of basaltic lava flows in {M}ount {C}ameroon ?},
  author = {{C}hauvel, {C}. and {D}ia, {A}.{N}. and {B}ulourde, {M}. and {C}habaux, {F}. and {D}urand, {S}. and {I}ldefonse, {P}. and {G}{\'e}rard, {M}artine and {D}eruelle, {B}. and {N}gounouno, {I}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}o evaluate the effects of tropical rainfall on the compositions of basaltic lavas, we studied 20th century lava flows from {M}ount {C}ameroon in {A}frica. {W}eathering conditions are extreme because the climate is particularly warm and humid, and vegetation grows extremely quickly on the flows. {T}he high rainfalls and dense vegetation contribute to rapid and intense degradation of the volcanic rocks and should cause significant changes in chemical composition. {S}uch effects need to be quantified to constrain how young a lava flow must be so that its trace element and isotopic composition remains representative of the original magma. {F}resh inner parts and altered flowtops of four different lava flows were sampled and analysed for major and trace elements as well as {O}, {U}, {S}r, {N}d and {P}h isotopic compositions. {F}our samples of the 1999 eruption were also analysed to constrain the composition of fresh basalts. {A}lmost all major and trace elements display similar concentrations in inner and outer parts of the same flow. {T}his is notably the case for elements such as {K}, {R}b and {S}r, which are highly mobile during weathering. {T}he lack of variation suggests that the overall composition of the lava flows has not been significantly affected. {H}owever, some systematic chemical changes are observed: {L}oss-on-ignition ({LOI}) and delta(18){O} increase slightly from inner parts of flows to near surface samples; {N}a and, to a lesser extent, {U} display significant losses in the outer samples. {W}e interpret the {N}a loss in terms of hydration leading to exchange between {N}a+ and {H}+ ions. {T}his process, associated with oxidation of {F}e2+ to {F}e3+, accounts for the larger loss-on-ignition in the outer parts of flows. {A} change in {U} contents is only observed in the 1922 flow, which is covered by dense vegetation. {T}his emphasizes the role that complexation by organic ligands plays in {U} mobility. {W}hile {U} is not completely immobile, all volcanic rocks are in secular equilibrium (({U}-234/{U}-238) approximate to 1), indicating limited interaction between meteoric waters and basalts. {S}r and {N}d isotopic compositions remain constant and although {P}b-206/{P}b-204 ratios vary from inner to outer parts of the lavas, the changes are not systematic and cannot be attributed to weathering. {T}he absence of significant chemical mobility and substantial isotopic exchange suggests very limited interaction between water and lavas at the centimeter scale, due, most probably, to their relatively young age. {T}his work shows that over a period of about 100 years, no detectable geochemical changes are observed. {T}hese results are very promising for petrological and geochemical studies of ocean island basalts located in tropical areas since they provide direct evidence of very limited trace element mobility at the century time scale. (c) 2004 {E}lsevier {B}.{V}. {A}ll rights reserved.},
  keywords = {{M}ount {C}ameroon ; basalt ; major and trace element data ; isotopic compositions ; chemical weathering ; water/rock interaction},
  booktitle = {},
  journal = {{J}ournal of {V}olcanology and {G}eothermal {R}esearch},
  volume = {141},
  numero = {3-4},
  pages = {195--223},
  ISSN = {0377-0273},
  year = {2005},
  DOI = {10.1016/j.jvolgeores.2004.10.008},
  URL = {https://www.documentation.ird.fr/hor/fdi:010042267},
}