A dissertation submitted to the Faculty of Science of
the University of the Witwatersrand for the degree of
Master of Science / Detailed high precision geochronological studies have been performed on the 2054
Ma old Bushveld Complex, in an attempt to unravel its tectonic and thermal evolution
in the period immediately following intrusion and crystallisation. The geochronological
techniques used have been specifically chosen to sample specific temperature episodes
in the cooling of the Complex, rather than to necessarily provide an accurate
emplacement age, The Bushveld Complex is seen in this study as part of the Bushveld
Magmatic Province, rather than as an isolated intrusion, The geochronological data
are therefore interpreted in the context of the current understanding of the Proterozoic
tectonic and thermal history of the Kaapvaal Craton.
The development of clean chemical methods and accurate geochronological methods
are essential to this type of study. The reduction of laboratory blanks, especially for
lead and the development of laboratory techniques for the analysis of small samples
therefore played an important part in this study. It has been possible to lower
analytical blanks, especially lead blanks to levels where the analysis of small samples
is possible. In addition, the zircon evaporation technique was attempted.
Phlogopite micas from the Critical Zone of the Bushveld Complex give a wlde range
of Rb-Sr model ages, some almost 100Ma older than the preferred age. This indicates
a period of hydrothermal alteration of considerable duration at the same time as the
intrusion. The slightly young Rb-Sr age recorded for all the mica and whole rock data
collected for this study indicates the alteration of the micas which is evident from
petrographic and electron microprobe studies.
U-Pb and Pb-Pb zircon ages are also Significantly younger than the preferred age,
indicating a degree of alteration. This is also seen in the discordance of the zircons
seen in the U-Pb data. / AC2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/22842 |
| Date | January 1995 |
| Creators | Coetzee, Hendrik |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (110 leaves), application/pdf |
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