Transcript Eighteenth lecture

Geology in the news:
They've recovered a fragment of the Russian Chelyabinsk meteorite from a local lake,
which weighed over 570 kg, one of the largest meteorite fragments ever found. (It
broke their scale!) See http://rt.com/news/largest-fragment-meteorite-lifted-258/ .
Plate Tectonics,
Part IV
(What might the FUTURE hold in store?)
Another possible scenario ...
The BASIN AND RANGE
Province of the western
U.S., including all of
Nevada and parts of
surrounding states, MAY be
an area where North
America is trying to split
apart!
You've already been introduced to the geology of this area .....
... the result of accreted terranes and ancient subduction zones, now
fractured into multiple slivers. How? Why?
The
mantle
upwelling
beneath the East Pacific
Rise doesn't just cease to
exist in between the Gulf
of California and the
Gorda Ridge.
Shallow subduction of the
Farallon Plate is believed
to also be a major factor.
(The Juan de Fuca Plate
and Gorda Plate are
small remnants of the
Farallon Plate.)
This region has been broadly UPLIFTED by tectonic
forces pushing up from beneath.
The plains of Wyoming are very
flat, but 7000-8000 feet (2100
to 2400 m) above sea level.
The Grand Canyon catches the
eye for its tremendous depth,
but the North Rim is also
over 8000 feet (2400 m)
above sea level! Note how
FLAT that upland surface is!
In most other areas, the rocks
have fractured in normal
faults, which are produced
only by stretching a brittle
material - pulling it apart.
On a larger scale, this then
shows up in repeated
patterns of block faulting
CRUST
A.
uplift
occurs
B.
Tensional stresses are set up
C.
Shallow, brittle rocks fracture - all go up, but some blocks
go up more than others.
D.
Erosion of horsts (high blocks) fills in grabens (low valleys).
This produces a series of downdropped
blocks called GRABENS in between the
uplifted HORSTS. (The grabens are the
valleys, the mountain ranges the horsts.)
The Humboldt Range of
Nevada, for example, is part
of this system.
Sierra Nevada
White Mtns. of California
Silver Peak Range of Nevada
Owens Valley
The Sierra Nevada marks
the western margin of the
Basin and Range. Owens
Valley, between the Sierra
(left) and White Mountains
(right) is a typical graben.
Direction of view
in previous slide
This is what has produced this pattern in the geologic maps.
Reno
Salt Lake
City
The distance from modern Reno, NV and Salt Lake City, Utah, has
increased by some 30 miles (50 km) in this process.
What COULD happen as an alternative scenario, as a result of
this process in the western U.S.?
It's thinking about
scenarios like this that
has led some geologists to
call geophysics
"The realm of conjecture,
speculation and dreams."
Coming NEXT: the origin of the Universe!