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

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, VI_NE-(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) HV_NW-, 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) HV_SW+, 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) HV_S- , 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 VI_NE- and the HV_SW+ components postdate adamallite intrusion dated by Rb-Sr and U-Pb at 1,73 Ga, although ⁴⁰Ar/³⁹Ar data suggest that the VI_NE- may be as old as 1,9 Ga.-from Authors