The recognition of meteoric-hydrothermal and supergene processes in volcanic carbonatites, Nyanza Rift, western Kenya, using carbon and oxygen isotopes

Onuonga, I.O., Fallick, A.E. and Bowden, P. (1997) The recognition of meteoric-hydrothermal and supergene processes in volcanic carbonatites, Nyanza Rift, western Kenya, using carbon and oxygen isotopes. Journal of African Earth Sciences, 25(1), pp. 103-113. (doi: 10.1016/S0899-5362(97)00064-X)

Abstract

Carbon and O isotopic compositions were determined for calcite and siderite from the Buru and Kuge carbonatite centres. Wide ranges in the isotopic compositions of these minerals were observed with values of δ¹³C and δ¹⁸O for the Buru calcites ranging from +1.3 to −3.2% (PDB) and + 11.3 to +26.2% (SMOW), respectively. The δ¹³C and δ¹⁸O ranges for the Kuge calcites are −3.1 to −8.4% (PDB) and +18.1 to + 25.7% (SMOW). The Buru siderites plot in a narrow and restricted range at −3.1 to −4.4% (PDB) and +12.6 to + 16.1% (SMOW). Calcite and siderite from the Buru and Kuge volcanic carbonatite centres do not retain their isotope signatures expected for primary magmatic carbonatites. Most of the variations in C---O isotope composition can be attributed to secondary processes involving low-temperature hydrothermal alteration and isotope exchange between carbonatites and meteoric water. Higher δ¹⁸O values (+21.9 to +26.2%) with a significant increase in δ¹³C values (−1.5 to + 1.3%) shown by the most oxidised samples from the Buru carbonatite may indicate the involvement of supergene exchange with atmospheric CO₂ at surface temperatures.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Fallick, Professor Anthony
• Authors: Onuonga, I.O., Fallick, A.E., and Bowden, P.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of African Earth Sciences
• Journal Abbr.: J Afr Earth Sci
• ISSN: 1464-343X
• ISSN (Online): 1879-1956