Geologische Kartierung am Südrand des Damara Orogens, Farm Kromhoek Namibia

Abstract

Abstract provided by author:

The mapped area is located in the southwestern part of the Southern Margin Zone of the Upper Proterozoic Damara Orogen, Namibia, and contains five lithological units, which are believed to be rift sediments of the basal Damara Sequence: a unit of alternating chlorite-/biotite schists and quartzphyllites/micaceous quartzites, a ferruginous quartzite (magnetite quartzite), and diamictite containing mainly granite pebbles and boulders, a calcareous phyllite with inter- fingering carbonate beds and lenses

Two main deformation phases (Dl and D2 -D4) produced mainly isoclinal NE-vergent Fl -folds and overthrusts and SE-vergent folds and an extensive imbricate fan. Mineral assemblages of metapelites and -carbonates indicate metamorphic conditions of the upper greenschist facies with temperatures between 420 C and 560 C and a minimum pressure of 2 to 4 kb

The oligomict diamictites and conglomerates investigated occur at the base of the Damara Sequence. They are interpreted as gravity flows (mass flows), which were transported and deposited along the basin edges of an active rift zone

The granoblastic "Donkerhoek" boulders of the mapped area and the granoblastic, granophyric and porphyritic boulders of the "Kwakwas" conglomerate (Tweerivier Member) have granitic to alkali-granitic characteristics and are probably derived from the base south of the diamictite outcrops. The boulders show neither gneissic textures nor metamorphic mineral assemblages other than those produced by the Damara tectonometamorphic event