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The Geological history of the Kaapvaal Craton the Kaapvaal craton is an area in Southern Africa of ancient continental crust, being a part of the ancient continent of Gondwana, with rocks dating back to the early Neoarchean to the Paleoproterozoic Era, possibly as early as 2.7 to 2.0 billion years ago (Ga.).[1] The craton named Kaapvaal is centered on the Limpopo Province in South Africa. The rocks of the Zimbabwe Craton are separated from the rocks of the Kaapvaal Craton to the southeast by the 250 kilometres (160 mi) wide Limpopo Belt of granulite facies tectonites. The Limpopo belt formed contemporaneously with the Zimbabwe and Kaapvaal cratons, but remained geologically active until much later. It was only in the late Archean, ca. 2.8-2.5 Ga., that the two cratons were stabilized together and that high-grade metamorphism ceased in the Limpopo Belt. North of the Zimbabwe Craton is the Zambezi Belt.[2]
The Geological timeline
[edit]The Kaapvaal craton can be divided into several major phases. The oldest rocks, known as the Onverwacht Group, were formed during the Mesoarchaean Era (about 3.6 to 3.2 billion years ago) (Ga.). These rocks are mainly volcanic and sedimentary and were formed in an ancient oceanic environment, representing a time of significant volcanic activity and dynamic tectonic processes.
The Chronological Stratigraphy of the Kaapvaal craton
[edit]The Moodies Group and the Fig Tree Group, represent a change from a volcanic to a sedimentary environment of the Kaapvaal craton. These formations are rich in banded iron formations (BIFs), indicating a period when the Earth's atmosphere changed dramatically due to the emergence of photosynthetic cyanobacteria. This activity was crucial in oxidation of the atmosphere and oceans, marking the Great Oxidation Event.
Development of Greenstone belt terrances in the Kaapvaal craton
[edit]About 3 billion years ago(Ga.), the craton began to stabilize, leading to the development of granite-greenstone terranes. The greenstone belts, composed mainly of metamorphosed volcanic rocks, were intruded by granitic bodies, reflecting the complex tectonic history and evolution of the craton. This transition marked a shift towards a more stable environment.
Tectonic setting of the Kaapvaal craton
[edit]The geological history of the Kaapvaal Craton is also marked by major tectonic events, including the formation and break-up of supercontinents. From the Neoarchaean to the Paleoproterozoic Era (about 2.7 to 2.0 billion years ago), the craton underwent a series of tectonic changes, including the development of the Witwatersrand Basin, known for its gold deposits. This basin was formed during sedimentation in a stable cratonic environment influenced by uplift and erosion.
By the end of the Paleoproterozoic Era the Kaapvaal Craton had become an integral part of the Gondwana supercontinent. Its geological stability has allowed the preservation of ancient geological records, making it crucial for the study of early Earth processes. The extensive geological history of the Kaapvaal craton provides insights into the formation and evolution of the continental crust, highlighting the interactions between tectonics, sedimentation and biological evolution.
The geological history of the Kaapvaal Craton illustrates a complex interaction of volcanic activity, sedimentation, tectonic shifts and biological evolution over more than 3 billion years(Ga.). Its well-preserved formations and rich mineral resources make it a key area for understanding early Earth processes and the evolution of the planet's crust. The synchroneity and extent of the Tokwe Segment is considered strong evidence supporting a predominantly intra-cratonic origin for the Late Neoachaean cratons of Kaapvaal and refuting an arc accretion origin for the craton.<ref name="Blenkinsop-1997"
References
[edit]- ^ Coward, M. P. & Ries, A. C., eds. (1991), "geochronology of the Kaapvaal craton Neoarchaean felsic sequences in the Kaapvaal Craton: a review growth", Early Precambrian processes, Geological Society Special Publications, issue 95, London: Geological Society of London, pp. 109–126, ISBN 978-1-897799-36-9
- ^ Jelsma, H. A. and Dirks, P. H. G. M. (2002). "Neoarchean Tectonic Evolution of the Zimbabwe Craton". In Fowler, C. M. R.; Ebinger, C. L.; Hawkesworth, C. J. (eds.). The Early Earth: Physical, Chemical and Biological Development. Geological Society Special Publications, issue 199. London: Geological Society of London. pp. 183–211. ISBN 978-1-86239-109-3.
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