#precammbrian

The Great Dyke is a 2.5 billion year old igneous intrusion in the middle of the Zimbabwe Craton, one of the ancient crustal slices that assembled to make the Gondwana supercontinent. A feature this long and this linear probably requires that the craton was being pulled apart by tectonic forces at the time, opening a huge fissure that molten rock could flow into. The igneous rock in the dyke is called a “layered mafic intrusion”. There is so much volume in this dyke that it required large amounts of molten rock supplied from below in multiple pulses. As the craton was being pulled apart, molten rock rose out of the mantle and filled a magma chamber. That magma chamber sent pulses of magma up in-between large faults to form the dyke. As the batches of magma entered the dyke, it lost heat and crystallized. The crystals then sank, forming layers that were each made of distinct mineral groups. Another batch of magma would then enter the dyke, causing the cycle to repeat and forming a sequence of repetitive layers. Basaltic magmas also carry elements that don’t easily go into the early-forming minerals. They will remain in the melt until a mineral begins forming that takes up those elements. Layers that are enriched in chromium and platinium in the Great Dyke are particularly valuable and are mined as major natural resources in Zimbabwe. -JBB Image credit: NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team https://asterweb.jpl.nasa.gov/gallery-detail.asp?name=Dyke Read more: https://earthobservatory.nasa.gov/images/46341/great-dyke-of-zimbabwe http://bit.ly/1f0pkBg https://africaincmag.com/2020/09/07/great-dyke-investments-set-to-raise-us500m-funding-for-first-phase-of-its-mining-project/ https://academic.oup.com/petrology/article-abstract/33/3/611/1422110 https://academic.oup.com/petrology/article-abstract/23/2/240/1469121