With uses ranging from jewelry to catalytic converters, platinum ranks
among the most prized and most expensive metals. About 70 percent of the
world’s platinum is mined in the Bushveld Igneous Complex in South Africa—a
geological formation roughly the same size as West Virginia. The Bushveld also
supplies significant quantities ofpalladium, rhodium, chromium, and vanadium.
The Advanced Spaceborne
Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite acquired this image of the Bushveld Igneous Complex on
October 24, 2006. It shows part of the Bushveld Complex, an area around the
Bospoort Dam.
ASTER combines infrared, red, and green wavelengths of light to
make false-color images. In this image, water appears in shades of blue, with
darker blue indicating greater water depths. The pale blue polygonal shapes
indicate reservoirs and tailings ponds associated with mining operations. Bare
rock and sparsely vegetated land appear in shades of red and red-brown.
Vegetation is green.
Bushveld is an example of a large igneous province, a massive
assemblage of rocks formed by volcanic activity. The Bushveld is not only big
in land area; its rock layers are several kilometers thick. The complex
consists of multiple “suites” of rocks, each of which in turn holds multiple
layers. Different layers are sources of different types of valuable metals;
some favor platinum, for example, while others are rich in chromium.
Bushveld is unusual in that, despite its great age—more than 2
billion years—it has not been significantly deformed by subsequent tectonic
activity. (It has undergone extensive erosion.) Despite years of extensive
study in the area, geologists have not reached a consensus about how this
igneous complex formed. One hypothesis is that the complex is a single, massive
feature shaped like a giant bowl. Others suggest that it consists of discrete,
disconnected structures. In either case, the complex might have received
multiple infusions of magma from different sources.
Although there is little agreement about precisely how it
formed, dating of the rocks from the Bushveld indicates that the igneous
complex formed over a relatively short time period, perhaps less than 10
million years. Before dating techniques constrained the ages of the rock layers
to a time around 2.06 billion years ago, many geologists suspected that the
complex formed over a period that might have exceeded 100 million years.
1. References
2.
ASTER. Bushveld Igneous Complex, South
Africa. NASA
Jet Propulsion Laboratory. Accessed February 21, 2013.
3.
Buck, J.S., Maas, R.,
Gibson, R. (2001) Precise
U-Pb titanite age constraints on the emplacement of the Bushveld Complex, South
Africa. Journal of the
Geological Society, 158(1), 3–6.
4.
Kinnaird, J.A. The Bushveld Large Igneous Province. School of Geosciences, University of the Witwatersrand. Accessed
February 21, 2013.
5.
Schouwstra, R.P.,
Kinloch, E.D., Lee, C.A. (2000). A short geological review of the Bushveld Complex. Platinum Metals Review, 44(1),
33–39.
6.
State of the Planet. Bushveld Igneous Complex. The Earth Institute. Columbia University. Accessed February 21,
2013.
NASA Earth Observatory image by Jesse Allen and Robert Simmon,
using data from NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption
by Michon Scott.
Instrument:
Terra -
ASTER
هیچ نظری موجود نیست:
ارسال یک نظر