The Great Dyke of Zimbabwe is a layered mafic intrusion
of igneous, metal-bearing rock that has been dated to approximately 2.5
billion years old. The dyke (or dike in American English) intrudes
through the even older rocks of African craton, the core of oldest rocks
forming the continent of Africa. 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.
This geological feature extends more than 550 kilometers (342 miles)
northeast to southwest across the center of Zimbabwe, varying from 3 to
12 kilometers (2-8 miles) in width. The southern end of the dyke is
captured in this astronaut photograph.
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.
While the Great Dyke and its metal ores are products of geologic
processes from the deep past, more recent events have also left their
mark on the landscape. Two large burn scars from fires are visible at
image top center.
An older, more detailed view of the Great Dyke can be found in an astronaut photograph available here.
Astronaut photograph ISS025-E-5538
was acquired on September 30, 2010, with a Nikon D2Xs digital camera
using a 180 mm lens, and is provided by the ISS Crew Earth Observations
experiment and Image Science & Analysis Laboratory, Johnson Space
Center. The image was taken by the Expedition 25 crew. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab
to help astronauts take pictures of Earth that will be of the greatest
value to scientists and the public, and to make those images freely
available on the Internet. Additional images taken by astronauts and
cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, NASA-JSC.