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Journal of the Geological Society; 2008; v. 165; issue.3; p. 739-753;
DOI: 10.1144/0016-76492007-079
© 2008 Geological Society of London

Original Article

Oxygen, carbon and strontium isotope constraints on the mechanisms of nappe emplacement and fluid–rock interaction along the subhorizontal Naukluft Thrust, central Namibia

JODIE A. MILLER1, GIULIO VIOLA2 & NEIL S. MANCKTELOW3

1 Department of Geology, University of Stellenbosch, Matieland, 7602, Stellenbosch, Republic of South Africa (e-mail: jmiller{at}sun.ac.za)
2 Geological Survey of Norway, N 7491, Trondheim, Norway
3 Geological Institute, ETH Zurich, CH-8092 Zurich, Switzerland

The Naukluft Thrust forms the floor thrust to the Naukluft Nappe Complex, a far-travelled, nappe stack of the Pan-African Damara belt in Namibia. The thrust tectonostratigraphy comprises three dolomitic components, a calc-mylonite horizon, and a discrete brittle fault. Stable isotope data indicate that the leading edge is characterized by positive {delta}13C values, whereas the trailing edge is characterized by negative {delta}13C values. There is a significant range in the {delta}18O values, over 15{per thousand} in different sections, with the leading edge showing a larger range than the trailing edge. {delta}18O values are characteristic of burial dolomites and secondary dolomitization is indicated by the presence of networks above and below the Naukluft Thrust zone. The large range in {delta}18O values and variations in {delta}13C vs. {delta}18O patterns are interpreted to be the result of interaction between the precursor to the Naukluft Thrust zone dolomites and fluids derived from different footwall lithologies. 87Sr/86Sr isotope ratios indicate that some fluids were derived from the basement. The data presented in this study suggest that an original carbonate-dominated horizon existed prior to thrusting and that the basal thrust of the nappe complex exploited this horizon.