[IGPP Everyone] [EPSS Everyone] Geocheminar --- postponed until Friday, Oct. 13

[Kevin McKeegan]

Dear EPSS,
    Due to a conflict with a faculty meeting, the Geocheminar originally
scheduled for Monday, Oct. 9, will be postponed until Friday.  The speaker
is Dr. Paul Warren of UCLA.  The talk will be at noon in the Slichter
conference room.  A title and abstract follows below.  All are welcome.

*New forms of late fluid/redox alteration in basaltic meteorites (eucrites)*

          Paul Warren, UCLA


Until recently, all of the eucrites appeared to be simple products of
anhydrous basaltic magmas, mostly annealed by dry thermal metamorphism.
However, we now know that unannealed eucrites commonly feature secondary
veining, typically dominated by an anomalous combination of fayalitic
olivine and Na-poor plagioclase within pyroxene; from which secondary
volatile-rich fluids have been inferred. The unannealed NWA 11040 eucrite
shows new varieties of secondary alteration. Late, in-situ reduction is
suggested from: a high Fe-metal abundance; pyroxene Mg/Fe and Fe/Mn zoning
consistent with late diminution in [FeO]; and rims of many pyroxene grains,
especially near Fe-metal, show a distinctive corrosion texture, with
elongate silica-dominated inclusions oriented perpendicular to the rim,
suggesting FeO reduction caused decomposition of rim pyroxene. Also,
deposition from fluid at a far-subigneous T is implied by a peculiar
texture where compositionally anomalous pyroxene fills cracks within
cristobalite. But, you ask, then why pyroxene and not amphibole? Unearthly
low pressures make an asteroidal crust ill-disposed to engender igneous or
postigneous hydrous silicates.


FRIDAY, OCT. 13.   Noon.   Slichter conference room.




-------------------------------------------------------------
Kevin D. McKeegan
Professor of Cosmochemistry & Geochemistry
Dept. of Earth, Planetary, and Space Sciences
UCLA
Los Angeles, CA 90095-1567
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mckeegan at epss.ucla.edu
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