[meteorite-list] Volcano Bombs & Impact Breccia Identification

From: E.L. Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 10:09:59 2004
Message-ID: <3E894021.4030906_at_epix.net>

To releave the suspense, there are NO occurrences of volcanos/volcanic
geology in eastern North America since before the Triassic(200±mya).*
 The only volcanic stems left today in the Eastern North American plate
are a part of a plutonic and volcanic series in New England (Devonian
345 ±mya). All were along the margins of the eastern seaboard. There
are about 9 crypto-volcanic structures in the central US that have
been identified as astroblemes. After the Cretaceous(65 mya) volcanos
flourished in the western US.

As to the natural occurrence of "volcanic " material on the Wisconsin
and Michigan Peninsulas. Not unless it was imported for barbecues! I've
never seen a brecciated volcanic bomb and I don't think it exists by
definition. (Note Mark's post on magmas and xenoliths even if he did not
call them that) There is more smelting slag in the Great Lakes area than
another place I know of. It was used to pave roads, build railroad
ballast, even dumped into the lakes. ( Anyone remember the emerald
material left by aliens recovered on the lake floor some guy was selling
on the internet?)

Impact breccia could, in theory, have been transported from any of
several craters on the Canadian Shield.--by glaciers or as a part of
some smelting ore transport. NON impact related Breccia lenses can
occasionally be found along contact faces of faults and are occasionally
brought to surface in mining operations. Impact breccias look like
melts or rocks that have been roasted. Other breccias likely to be
found near you are more likely to have a limestone/calcium
content..which will effervesce in hydrochloric acid. They will most
likely contain clasts which look sedimentary.

I hope this helps to exclude volcanic bombs as a source...

Be it remembered that one or two lunar meteorites have been found with a
vessiculated fusion crust ( just to keep you on needles)

Regards,
Elton

* There may be a couple of islands in the arctic circle but those are
associated with the icelandic system and not the North American Plate.
Received on Tue 01 Apr 2003 02:30:41 AM PST