No description available.

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. Folded map in pocket. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 90-94).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 187-196).

In the hills and in the plain of the Khale area are exposed two sheets of quartz-dolerite, the upper sheet being locally mushroom-shaped. The rock corresponds loosely with the Downes mountain type of dolorite, and contains numerous horizons of coarse-grained dolorite-pegmatite. The plagioclase felspars are described with special reference to the variation of grain-size, the features of zoned crystals, and the possible causes of a peculiar brown clouding in the basic zones of the crystals. Phenocrysts of augite and pigeonite, as well as plagioclase are recorded in the chilled contact rock. The micrometric data indicate that the mineral composition of the specimens is largely governed by the oxidation state of the iron, and that the Soret effect has caused the marginal rock to be enriched in basic elements. Hydrothermal veinlets composed largely of chlorite occur in both the dolorite and the country rock, and evidence suggests that veins of both residual material and mobilised granite occur in the upper finer-grained dolorite.

No description available.

No description available.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

A plug-like intrusion of Karroo dolerite, near Dordrecht in the Eastern Cape of the Republic, is described. Field mapping with the, aid of aerial photographs has revealed that the contact of the intrusion, for the most part, dips very steeply outwards. In the south- eastern and eastern areas, however, sheet- or sill-like forms appear to be given off from the main intrusion. In plan view the intrusion is roughly oval shaped, its longer axis being aligned in a north-westerly direction. Its surface area measures approximately 60 square kilometres (24 square miles). A large number of xenoliths composed exclusively of Stormberg sediments, pyroclastic rocks and minor lavas, are to be found cropping out within the dolerite intrusion. These xenoliths, many of which occur in positions far above or below their normal stratigraphic elevation, are extremely variable in size - the largest having an area of approximately 15 square kilometres (6 square miles). The xenoliths represent fragments of the original "roof" of sediments and pyroclastics which have collapsed into and been engulfed by the dolerite magma. This type of dolerite intrusion is known as a "belljar" intrusion. A superficial classification of the dolerites, based chiefly on textural and certain mineralogical features, is presented. In the area surrounding the main intrusion are a number of dolerite dikes and sheets. The youngest phase of igneous activity is represented by the Dragon's Back dike, which cuts across the complex in a north-westerly direction. Several veining phenomena, as well as an interesting variety of metamorphic and metasomatic rocks, are associated with the main dolerite intrusion. Six diatremes are situated in the vicinity of the intrusion. Pyroclastic rocks are represented by a variety of types, and are to be found outside the area of the intrusion, and as xenoliths within it. A tentative interpretation of the mechanism of formation of the intrusion, which appears to be related to volcanic activity and cauldron subsidence, is presented.

No description available.