Oxygen isotope composition and geothermometry of granulite to greenschist facies metamorphic rocks: a study from the Neoproterozoic collision-related nappe system, south of Sao Francisco Craton, SE Brazil

Garcia, M.D.G.M., Neto, M.C.C. and Fallick, A.E. (2003) Oxygen isotope composition and geothermometry of granulite to greenschist facies metamorphic rocks: a study from the Neoproterozoic collision-related nappe system, south of Sao Francisco Craton, SE Brazil. Journal of South American Earth Sciences, 15(8), pp. 871-883. (doi: 10.1016/S0895-9811(02)00143-8)

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Publisher's URL: http://dx.doi.org/10.1016/S0895-9811(02)00143-8

Abstract

Oxygen isotope studies were carried out across units of a Neoproterozoic nappe system, south of Sao Francisco Craton. A temperature decrease toward the base of the system is found, consistent with a previously recognized inverted metamorphic pattern. The tectonic contact of the basal unit and the reworked southern Sao Francisco craton show a steep temperature gradient, suggesting that low temperature thrusting acted as the dominant tectonic process. The contrasts between the delta(18)O values of the Tres Pontas-Varginha and Carmo da Cachoeira nappes and the differences among the samples and minerals are consistent with the preservation of sedimentary isotopic composition during metamorphism. The small differences in the delta(18)O values between the undeformed and the deformed calc-silicate samples (similar to1.6parts per thousand) suggest that the parts per thousand(18)O value of mylonitization fluids was close to that which equilibrated with the metamorphic assemblage. The distinct delta(18)O values of metapelitic and calc-silicate samples and the great temperature difference from one type to the other indicate that no large-scale fluid interaction processes occurred during metamorphism. Oxygen isotopic estimations of both Tres Pontas-Varginha undeformed rocks and Carmo da Cachoeira unaltered equivalents indicate delta(18)O values of up to 18parts per thousand. Comparison between these values and those from the 'basement' orthogneisses (8.3-8.5parts per thousand) indicates the latter are not sources for the metapelites.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fallick, Professor Anthony
Authors: Garcia, M.D.G.M., Neto, M.C.C., and Fallick, A.E.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of South American Earth Sciences
ISSN:0895-9811

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