The Pre-Cambrian era, spanning from the formation of the Earth approximately 4.
5 billion
years ago to 541 million years ago, is a vast and complex period in Earth's history. During
this time, the planet underwent significant transformations, including the formation of the
oceans, atmosphere, and continents. Zimbabwe, located in southern Africa, has an extensive
geological record of this era, with diverse rock associations that offer valuable insights into
the region's tectonic evolution. In Zimbabwe, Precambrian rocks are predominantly found in
the Zimbabwe Craton, a stable block of the Earth's crust that has remained relatively
unchanged for billions of years. These rocks provide valuable insights into the geological
processes that shaped the early Earth and are crucial for understanding the region's mineral
wealth.
The Zimbabwe Craton is one of the oldest geological formations on Earth, consisting mainly
of Archean rocks that date back to over 2.5 billion years. The craton is divided into several
greenstone belts, which are regions of metamorphosed volcanic and sedimentary rocks. These
belts are surrounded by granitic intrusions and are known for their rich mineral deposits,
including gold, nickel, and chromite.
These ancient volcanic and sedimentary sequences, such as the Sebakwian and Bulawayan
groups, are characterized by metamorphosed basalts, andesites, and sedimentary rocks. They
provide evidence of early crustal formation and oceanic crust subduction. The greenstone
belts are thought to have formed in an ancient oceanic environment, with volcanic activity
and sedimentation occurring in a shallow-water setting.
The Zimbabwe Craton, comprising granites, gneisses, and migmatites, represents a stable
continental core formed through multiple tectonic events. These rocks record a complex
history of magmatic and metamorphic processes, including partial melting, magma mixing,
and high-grade metamorphism. The granitoid terranes are thought to have formed through a
combination of mantle plume activity and continental collision.
The Lomagundi and Piriwiri groups, consisting of metamorphosed sedimentary and volcanic
rocks, contain valuable information on ancient depositional environments and tectonic
settings. These rocks provide insights into the region's paleogeography, including ancient
river systems, deltas, and coastal environments.
BIFs are another important rock type found within the greenstone belts. These formations
consist of alternating layers of iron-rich minerals and silica and are significant for their iron
ore deposits. The BIFs in Zimbabwe are primarily found in the Belingwe and Bulawayo
greenstone belts.
The Pre-Cambrian rock associations in Zimbabwe offer insights into the region's tectonic
evolution, including early oceanic crust formation and subduction, continental crust growth
through magmatic and metamorphic processes and ancient depositional environments and
paleogeography
These rock associations also host significant mineral deposits, such as gold, nickel, and
chromite, which have shaped Zimbabwe's economic history. The understanding of these
ancient rocks is crucial for unraveling the geological history of southern Africa, exploring
mineral resources and understanding the Earth's early history.
The study of BIFs provides valuable information about the early Earth's atmosphere and
ocean chemistry, as these formations are believed to have formed in an oxygen-poor
environment. The high-grade metamorphic rocks, on the other hand, offer insights into the
tectonic processes that have shaped the craton over billions of years.
The Pre-Cambrian rock associations in Zimbabwe provide a unique window into the Earth's
early history, showcasing the region's complex tectonic evolution. Understanding these rock
associations is crucial for both academic research and the continued exploration and
exploitation of mineral resources in the region.
References
Blenkinsop, T. G. (2008). Geology of Zimbabwe. Geological Society of Zimbabwe.
Dirks, P. H. G. M., & Jelsma, H. A. (2006). The Zimbabwe Craton. In M. R. Johnson et al.
(Eds.), The Geology of Africa (pp. 179-202). Geological Society of London.
Foster, R.P. (1988). Archaean gold mineralization in Zimbabwe: Implications for
metallogenesis and exploration. Bicentennial Gold 88, Melbourne, pp. 62–72.
Kisters, A.F.M., Kolb, J., & Meyer, F.M. (1998). Gold mineralization in high-grade
metamorphic shear zones of the Renco Mine, southern Zimbabwe. Economic Geology, 93(5),
pp. 587–601.
Jelsma, H. A., & Dirks, P. H. G. M. (2002). Geochemistry and petrogenesis of the Zimbabwe
Craton. Journal of African Earth Sciences, 35(2), 151-166.
Wilson, J. F., & Davies, R. D. (1984). The early history of the Zimbabwe Craton.
Precambrian Research, 25(2), 131-146.
Wilson, J.F. (1968). The Geology of the Country around Mashaba. Bulletin of the Rhodesian
Geological Survey, 68, pp. 239.
Wilson, J.F. (1964). The Geology of the country around Fort Victoria. Bulletin of the
Rhodesian Geological Survey, 58, pp. 147.
