Publications des scientifiques de l'IRD

Delalande M., Bergonzini L., Gherardi F., Guidi M., André L., Abdallah I., Williamson David. (2011). Fluid geochemistry of natural manifestations from the Southern Poroto-Rungwe hydrothermal system (Tanzania) : preliminary conceptual model. Journal of Volcanology and Geothermal Research, 199 (1-2), p. 127-141. ISSN 0377-0273.

Titre du document
Fluid geochemistry of natural manifestations from the Southern Poroto-Rungwe hydrothermal system (Tanzania) : preliminary conceptual model
Année de publication
2011
Type de document
Article référencé dans le Web of Science WOS:000286851100012
Auteurs
Delalande M., Bergonzini L., Gherardi F., Guidi M., André L., Abdallah I., Williamson David
Source
Journal of Volcanology and Geothermal Research, 2011, 199 (1-2), p. 127-141 ISSN 0377-0273
The South Poroto-Rungwe geothermal field, in the northern part of the Malawi rift, Tanzania divides in two main areas. The relatively high altitude northern area around the main Ngozi, Rungwe, Tukuyu and Kyejo volcanoes, is characterised by cold and gas-rich springs. In contrast, hot springs occur in the southern and low-altitude area between the Kyela and Livingstone faults. The isotopic signature of the almost stagnant, cold springs of the Northern district is clearly influenced by H2O-CO2(g) exchange as evidenced from negative oxygen-shifts in the order of few deltas permil. In contrast, the isotopic signature of waters discharged from the hot springs of the Southern district is markedly less affected by the H2O-CO2(g) interaction. This evidence is interpreted as an effect of the large, permanent outflow of these springs, which supports the hypothesis of a regional-scale recharge of the major thermal springs. Measurements of carbon isotope variations of the dissolved inorganic carbon of waters and CO2(g) from the Northern and Southern springs support a model of CO2(g)-driven reactivity all over the investigated area. Our combined chemical and isotopic results show that the composition of hot springs is consistent with a mixing between (i) cold surface fresh (SFW) and (ii) Deep Hot Mineralised (DHMW) Water, indicating that the deep-originated fluids also supply most of the aqueous species dissolved in the surface waters used as local potable water. Based on geothermometric approaches, the temperature of the deep hydrothermal system has been estimated to be higher than 110 degrees C up to 185 degrees C, in agreement with the geological and thermal setting of the Malawi rift basin. Geochemical data point to (i) a major upflow zone of geothermal fluids mixed with shallow meteoric waters in the Southern part of the province, and (ii) gas absorption phenomena in the small, perched aquifers of the Northern volcanic highlands.
Plan de classement
Géophysique interne [066]
Localisation
Fonds IRD [F B010053074]
Identifiant IRD
fdi:010053074
Contact