The Alberta complex, a metamorphosed layered intrusion, north of Nauchas, South West Africa, the surrounding granites and repeated folding in the younger Damara system

Abstract

Abstract provided by author:

A study of the kata-, meso- and epinorms of the amphibolites of the Layered Sequence indicates that the Complex suffered intense mesozonal and subsequently mild epizonal metamorphism

The emplacement of the Weener quartz diorite, as large batholiths, probably initiated the intrusion of the Nauchas Granite Suite. The various members of this suite display a distinct serial relation both in modal and chemical composition. The granites were emplaced during post-, syn- and late-kinematic orogenetic phases and are tentatively correlated with the Cape granite

After a period of intense erosion the Sinclair Formation, in which volcanic rocks and clastic sediments alternate, was deposited. An angular unconformity separates the younger Tsumis Formation from the Sinclair Formation. The Tsumis formation comprises an alternation of psephitic, psammitic and pelitic rocks

The quartzite of the Kamtsas Formation follows unconformably on the Tsumis Formation and is in turn overlain by the Damara System in the northern part, and by the Nama System in the southern part of the area

The Hoornkranz Augen-gneiss originated as a result of the development of porphyroblasts of feldspar in the Gamsberg granite, a member of the Nauchas Granite Suite

The Damara and the Nama Systems are regarded as coeval and were deposited after severe peneplanation of the older rocks. The Damara System consists of a thick succession of metasediments which is subdivided into the Hakos and the Khomas Series. Intense deformation resulted in northeast-southwest-striking isoclinal folds e. g. the Djab Synclinorium and the Chaibis Anticlinorium. These major structures were refolded coaxially during a later deformation, which gave rise to the Hakos Anticline. Cross-folding played a minor role in the deformation of the Damara System

The metamorphic mineral assemblages in the Damara System indicate that conditions, of over-pressure rather than excessively high temperatures prevailed during the formation of the Djab Synclinorium. During the later deformation the grade of metamorphism never exceeded that of the biotite zone

The Karroo System in the area investigated is represented by Dwyka tillite and an eolian sandstone, probably the equivalent of the Cave Sandstone in the Republic of South Africa

Diabase and amphibolite were found as dykes and sills in all the rock formations except the Karoo System and the Tsumis and Kamtsas Formations

Eleven new chemical analyses of rocks are given - one of the Weener quartz diorite, five of the Nauchas Granite Suite and five of the amphibolite and serpentinite of the Alberta Complex