Bushveld complex
The Bushveld Complex in South Africa is one of the largest intrusive complexes of basic melts on earth and is characterized by its magmatic layers ( English Layered Intrusions ). The concentration of platinum group elements - deposits is of geopolitical importance.
location and size
The complex is located in the border area of the four provinces of Northwest , Gauteng , Mpumalanga and Limpopo in South Africa . It originated around 2.06 billion years ago. With an exposed area of 460 × 245 km², the total thickness of the complex is up to 8 km.
Only parts of the complex are open ; a total of four bowl-shaped intrusion bodies (praise) are postulated on the basis of geophysical data. The praises consist of mafic and ultramafic rocks that dip on all sides at 10 ° to 20 ° towards the center. The result is a saucer-shaped body that is geologically referred to as a lopolith .
composition
The basic magmas from which the praises were created had an igneous stratification, so that a layer intrusion was created. The magma, with a lower density than the surrounding rock, rose from the earth's mantle into the area of the continental crust. During the crystallization, the magma was constantly chemically changed by the formation of relatively heavy crystals (e.g. olivine ), so that a fractional crystallization took place in the sense of Norman L. Bowen , the magmatic differentiation .
The base of the complex is formed by dunites and peridotites ; This is followed by Pyroxenite and Norite , from which the natural stone Impala is made.
The Merensky Reef within the complex base is an orthomagmatic deposit that is considered to be the world's most important platinum metal deposit . Also, chromium , copper and nickel are workable present.
The main part of the intrusion in the hanging wall consists of gabbroids .
Granophyres and granites form the upper end, presumably formed in the wake of the intrusion by melting the continental crust by the basic magma and by mixing the magmas.
Individual evidence
- ↑ Michiel Olivier de Kock, DAD Evans, JL Kirschvink, NJ Beukes, E. Rose, I. Hilburn: Paleomagnetism of a Neoarchean-Paleoproterozoic carbonate ramp and carbonate platform succession (Transvaal Supergroup) from surface outcrop and drill core, GriqualandWest region, South Africa. Precambrian Research, 169: 80-99, Amsterdam 2009 ISSN 0301-9268
