[meteorite-list] Mysterious Circular Structure Near Chemult, Oregon

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 12 Oct 2007 18:10:27 -0500
Message-ID: <028701c80d25$1488f490$b92ee146_at_ATARIENGINE>

Hi, All,

    The "hot spot" is technically a place where there is
more vulcanism that would be expected, usually a spot
that's not on a plate boundary but in the middle of a plate,
and produces way too much volcanic activity for that
location, or an unexplained elevation. One theory to account
for many hotspots is called the "mantle plume theory."

    They persist for geologically long times. Hawai'i is believed
to sit on a plume because of the chain of "Emperor Seamounts"
stretching on an arc to the NW. Active mantle plumes often
have caldera volcanoes atop them. Hawai'i is a low-silica
caldera, it's not as explosive and violent as the "usual" caldera
volcano. It considered a good case for the mantle plume
theory.

    The Yellowstone "Valley" is not a valley; it's an ancient
high-silica caldera volcano. When Yellowstone Caldera (last)
erupted 640,000 years ago, it released 1,000 cubic kilometers
of material (800 times as much as the Mt. St. Helens eruption)
that covered all of North America in up to two meters of debris.
That plume is moving too, and will reach Iowa someday. I
predict Trouble, right here in River City (as the song goes).

    Mantle plumes are believed to be produced by the interior
conditions at the core-mantle boundary and not by any exterior
event (like an impact). But at the same time, they are invoked to
explain flood basalt events (like the Deccan Traps or the Siberian
Traps), which out-do anything the worst volcano can do, and
only happen once every many tens of millions of years, and --
uh-oh! -- at the same time as really major impacts.

    Not all geologists like the mantle plume theory, and meteorite
impacts is one of a number of alternative theories. That area
(Oregon) is home to considerable traces of a relatively recent flood
basalt event, the Columbia River Flood Basalt Province of Idaho,
Washington and Oregon:
http://volcano.und.edu/vwdocs/volc_images/north_america/crb.html
although the round feature is just outside the Province of those
flood basalts.

    Check out:
http://en.wikipedia.org/wiki/Hotspot_%28geology%29
and
http://en.wikipedia.org/wiki/Mantle_plume

    One test of a "crater" is its relative depth. Others are
the lifted or up-turned rim, the presence of shatter-cones,
traces of an ejecta blanket, shocked rocks in the crater,
the presence of highly shocked minerals (coesite), signs
of a central uplift (if it's big enough to have one). And,
an impact that produced vulcanism would be obliterated
by the lavas it released, so proving that is kind of a problem.

    Good hunting!


Sterling K. Webb
-----------------------------------------------------------------------------
----- Original Message -----
From: "Jerry" <grf2 at verizon.net>
To: <pkmorgan at ctcweb.net>; "Stefan Brandes" <brandes at gmx.at>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Friday, October 12, 2007 4:50 PM
Subject: Re: [meteorite-list] Mysterious Circular Structure Near
Chemult,Oregon


Cool news ie. impact causing HOT SPOT. Sooooo Cool. If we generalize [which
I presume we must not without scientific data to support the supposition]
Yellowstone, Sunset Crater, etc. are all impact sites caused when the crust
was so deeply wounded the mantle material persists in melting whatever
crustal material attempts to scab the wound!
SUPER COOL!!
Jerry Flaherty
----- Original Message -----
From: <pkmorgan at ctcweb.net>
To: "Stefan Brandes" <brandes at gmx.at>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Friday, October 12, 2007 5:01 PM
Subject: Re: [meteorite-list] Mysterious Circular Structure Near Chemult,
Oregon


> Looks like something fun to check out either way. I've been meaning to
> get over and explore that general area. Of course it would have to be
> pretty obvious for me to notice anything :-)
>
> By the way, I have heard a theory that there was a large strike at some
> point in central Oregon causing a "hot spot" in the mantle (?) which has
> since migrated through the Snake River plain in southern Idaho and now
> lies beneath Yellowstone National Park resulting in all of the geothermal
> activity in that area.
>
> Thanks for sharing!
>
> Phil
>
>
>> Interesting formation :
>>
>> http://epod.usra.edu/archive/epodviewer.php3?oid=382976
>>
>> any ideas?
>>
>> Stefan
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>
>
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Received on Fri 12 Oct 2007 07:10:27 PM PDT