Constraints on the tectonic evolution of the Namaqua Province I: palaeomagnetic and 40 Ar/39Ar results from the Richtersveld subprovince ( South Africa).

Tullis C. Onstott, R. B. Hargraves, P. Joubert, D. L. Reid

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Abstract

Palaeomagnetic analysis of 80 samples from 13 sites in the Richtersveld Subprovince, together with 40Ar/39Ar measurements on selected samples give the following results: a) 3 sites in the Vioolsdrif quartz diorite revealed a single component of remanent magnetization, which is N-easterly with a negative inclination, VINE-(D = 46,I = 56, kappa = 258, alpha 95 = 8,N = 3); b) palaeomagnetic measurements of 19 samples from 3 sites in the Haib metavolcanics resolved the following 3 components: 1) HVNW-, a NW, negative inclination, post-deformation, direction (D = 341, I = 50, kappa = 62 alpha 95 = 16, N = 3) , which appears to be a Mesozoic overprint; 2) HVSW+, a SW, positive inclination, post-deformation direction (D = 264, I = 46, kappa = 38, alpha 95 = 20, N = 3), which may correlate with the Vioolsdrif direction of opposite polarity; 3) HVS- , a southerly, negative inclination direction (D = 199, I = 17, kappa = 10 alpha 95 = 88, n = 2), which is found in only a few samples and is of unknown age and origin. c) All 3 of these components are also detected at 2 sites (out of a total of 5 sites) in the Vioolsdrif adamellite and tonalite. The 40Ar/39Ar results and the above relationships suggest the the VINE- and the HVSW+ components postdate adamallite intrusion dated by Rb-Sr and U-Pb at 1,73 Ga, although 40Ar/39Ar data suggest that the VINE- may be as old as 1,9 Ga.-from Authors

Original languageEnglish (US)
Pages (from-to)117-142
Number of pages26
JournalTransactions - Geological Society of South Africa
Volume89
Issue number2
StatePublished - Jan 1 1986

All Science Journal Classification (ASJC) codes

  • Environmental Science(all)
  • Engineering(all)
  • Earth and Planetary Sciences(all)

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