A comparative study of metamorphosed supracrustal rocks from the western Namaqualand metamorphic complex

A regional study of highly metamorphosed supracrustal rocks was undertaken in the western portions of the Namaqualand Metamorphic Complex. The study area was essentially restricted to a north-south section some 50 kilometres wide and 220 kilometres long. Eight east-west-trending belts of supracrustal rocks were examined, together with several smaller paragneiss remnants, in an area dominated by quartzo-feldspathic gneisses of granitic composition. The supracrustal rocks were classified into seven major lithological groups: quartzitic rocks, metapelitic and metapsammitic rocks, quartzo feldspathic rocks, metabasites, metacarbonate rocks, magnesium-rich cordierite rocks and iron formations. Further subdivision, based on variations in mineral constituents within each group, also occurred, as well as the presence of lithologies with compositions transitional between certain groups. The various supracrustal sequences were subdivided into formations containing minor distinctive members on an informal lithostratigraphic basis. Correlation between the major supracrustal belts was then undertaken. Four subgroups were identified across the study area, comprising a quartzo feldspathic gneiss subgroup and an overlying feldspathic quartzite/garnetcordierite gneiss subgroup that both predominate in the southern and central part of the area, a glassy quartzite/mica- sillimanite schist subgroup that predominates in the northern part, and a cordierite gneiss/metacarbonate subgroup that is restricted to the Geselskapbank synform. The supracrustal rocks appear to have been emplaced on a basement of augen gneisses. This relationship is, however, complicated by the intrusion of granit i c rocks within the contact zone.

Grantor dc:publisher.institution

Department of Geological Sciences

Year dc:date.issued

1986

Author dc:creator

• Moore, John Michael

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/22585

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/22585