Geology Reference
In-Depth Information
3
Bones in the Mountains
C
ONSIDER
M
OUNT
E
VEREST
. The world's highest mountain consists of three geological form-
ations separated by two faults, shattered zones across which rock formations slid into place.
Much as the layer-cake rock sequence exposed in the Grand Canyon captures the scope of
geologic time, the shuffled geology of Mount Everest reveals the power of unimaginably
slow deformation to transform the bottom of the sea into three different kinds of rocks and
stack them back up to crown the world. This would have been unimaginable to early Chris-
tians. Climb up the mountain and you can see it for yourself.
After leaving Katmandu and trekking more than a week through the glacier-carved valley
of the Dodh Kosi river, you'd arrive at Everest base camp, 17,590 feet above sea level. From
there it is another eleven and a half thousand feet up to the top. The bottom half of the moun-
tain, the part below about 23,000 feet, consists of the Rongbuk Formation, metamorphic
rock with a composition similar to granite. Like the Vishnu Schist at the bottom of the Grand
Canyon, the Rongbuk Formation formed when marine sediments were buried miles below
ground.
The suite of minerals in the Rongbuk indicates it formed at temperatures of 1000-1250°F
and at 8,000-10,000 times atmospheric pressure, more than fifteen miles down in Earth's
crust. Radiometric ages of unaltered mineral inclusions in the Rongbuk reveal that the ori-
ginal marine sediment was deposited some 490 million years ago. Once the rocks were
stacked up into enough of a pile to heat up, deform, and start melting its own base, numerous
granitic dikes rose like crystallized tendrils climbing their way up toward the surface.
