Possible late Precambrian subduction zone in South West Africa

Abstract

CONTINENTAL margin plate tectonism during the late Precambrian in southern and central South West Africa and western Botswana is strongly suggested by the geographical distribution, stratigraphy, composition and evolutionary characteristics of the pre-Damara, pre-Nama formations (1,350–900 Myr old) occurring north of the Namaqua Tectonic Province¹. If the distribution of these units is considered it is apparent that a unique pattern exists (Fig. 1). The data for the generalised geological map of Fig. 1 are taken from various sources^2–9 and show : first, the distribution has the form of a prominent and extensive curvilinear feature or ‘arc’. Second, the arc separates the undeformed late Precambrian deposits (Nama Group¹⁰) of the stable platform area—the Kalahari Craton or Plate—from the highly deformed and metamorphosed deposits of the late Precambrian Damara orogenic belt, suggesting that the arc occupies a marginal cratonic position, and third, the trend of the arc and arc structures (such as major faulting) parallels that of the Damaran structural trends, suggesting a possible relationship between the geotectonic development of the arc and the Damaran Orogeny (see Fig. 1).