May 16, 2014
(30 Sept. 2010) --- The Great Dyke of Zimbabwe, Africa is featured in this image photographed by an Expedition 25 crew member on the International Space Station. The Great Dyke of Zimbabwe is a prominent geological feature that extends for over 550 kilometers, varying from 3-12 kilometers in width across the center of the country northeast -- southwest; the southern end of the Dyke is illustrated in this view. The Dyke (or Dike in American English) is a layered mafic intrusion of igneous, metal-bearing rock that has been dated using uranium-lead isotopes to approximately 2.5 billion years in age, according to scientists. It intrudes even older rocks of the African craton, or core of oldest rocks forming the continent; in cross section, the Great Dyke looks somewhat triangular or keel-shaped suggesting to geologists that it rose along deep faults associated with extension of the African crust. Layered mafic intrusions are usually associated with economically important metals such as chromium, nickel, copper, platinum, titanium, iron, vanadium and tin. Chromium, in the form of the mineral chromite and platinum are particularly abundant in the Great Dyke and actively mined. Younger faults have offset sections of the Dyke along its length -- two of the most obvious faults in the image are indicated, with arrows showing the relative directions of offset relative to the main trend of the intrusion. While the Great Dyke and its metal ores are products of geologic processes operating in the deep past, more recent events have also left their mark on the landscape as illustrated by two large fire burn scars which are visible at top center.
Topics: Igneous petrology, Petrology, Geology, Great Dyke, Layered intrusion, Chromite, Dunite, Ultramafic rocks, Economic geology, Igneous rocks, Plate tectonics