Constraints on the tectonic evolution of the Namaqua Province II: reconnaissance palaeomagnetic and 40 Ar/39Ar results from the Namaqua Province and Kheis Belt ( South Africa).

Tullis C. Onstott, R. B. Hargraves, P. Joubert

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Abstract

Palaeomagnetic samples were collected from sites along a 500 km traverse from the high-grade metamorphic rocks of the central area of the Bushmanland Subprovince near Okiep, to amphibolite facies rocks of the E area of the belt, along the W border of the Kaapvaal Craton. The Namaqua zone pole (Long. = 328oE, Lat. = 8oN, N = 6, K = 20, alpha 95 = 15), is consistent with previously published palaeomagnetic poles for the Okiep Norite and the Noncaip (Konkoonsie) Gabbro, although opposite in polarity to the Okiep remanence. Also reported is a new palaeomagnetic site pole from the Port Edward Charnockite (Long. = 149oE, Lat. = 5oN, n = 6, kappa = 57, alpha 95 = 9), which is also consistent with the Okiep results. Rocks from 4 sites distributed over 200 km along the E margin of the Gordonia Subprovince yield a completely different palaeomagnetic pole (Long. = 203oE, Lat. = 41oS, N = 4, K = 14 alpha 95 = 26). A 1,2 Ga40Ar/39Ar plateau date on cummingtonite from the Jannelsepan amphibolite, suggests that the metamorphic rocks of the E area may have cooled through their magnetic blocking temperatures at a significantly earlier time than the granulites of the central area.-from Authors

Original languageEnglish (US)
Pages (from-to)143-170
Number of pages28
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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