Roughly
300 kilometers (200 miles) east-southeast of Tehran lies Iran’s Dasht-e Kavir,
or Great Salt Desert. To the untrained eye, Dasht-e Kavir looks like a place
that has been bone-dry since the dawn of time. But to the well-trained eyes of
a geologist, this desert tells a tale of wetter times. Tens of millions of
years ago, a salt-rich ocean likely occupied this region, surrounding a
microcontinent in what is now central Iran.
The
Thematic Mapper on the Landsat 5 satellite captured this natural-color image of
Dasht-e Kavir on October 15, 2011. The top image is a wide-area view, and the
area outlined in white is then shown in the close-up view below.
Dasht-e
Kavir is a complex landscape, but it can be mostly explained by the invasion
and subsequent evaporation of an ancient ocean. As the ocean dried up, it left
behind a layer of salt as much as 6 to 7 kilometers (4 miles) thick. Salt has a
fairly low density, so if a layer of new rock buries the salt layer—and if that
overlying rock is soft enough—the salt can slowly push up through it and form
domes.
As
its name implies, the Great Salt Desert is rich in salt domes, or diapirs.
Geologists have identified about 50 large salt diapirs in this region. Like any
other surface feature, a salt dome is subject to erosion. Wind and rain scrape
away particles of rock, gradually wearing away the top of the dome and exposing
it in cross-section.
But
erosion is not the only force at work in this region. In the close-up view, we
can see north-south-trending structures, some raised and some lowered. Callan
Bentley, a geologist at Northern Virginia Community College, identifies them as
folds or fault zones that run parallel to the trend of the region’s mountains.
Bentley attributes the deformation of the salt domes to plate tectonic activity
that has occurred since the salt domes formed. Bentley describes the landscape
as a “a palimpsest tale that helps constrain the age of the diapirism to
pre-folding.”
...
In
southern Iran, the collision between the Asian landmass and the Arabian
platform has folded rocks and pushed up the rugged Zagros Mountains. In places,
underlying deposits of salt have ascended in fluid-like plumes. Some of these
plumes have pushed through the rock above, like toothpaste from a tube, and
they are now visible as darkish irregular patches. This image shows a few of
over 200 similar features—called diapirs, or salt plugs—that are scattered
about this part of the Zagros Mountains.
Gravity
has caused the salt to flow like glaciers into adjacent valleys. The resulting
tongue-shaped bodies are more than 5 kilometers long, with repeating bow-shaped
ridges separated by crevasse-like gullies and with steep sides and fronts. The
darker tones are due to clays brought up with the salt, as well as the probable
accumulation of airborne dust. This ASTER perspective view was created by
draping a band 3-2-1 (RGB) image over an ASTER-derived Digital Elevation Model (2x
vertical exaggeration), and was acquired on August 10, 2001.
...
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