Poster Number 13
See more from this Division: General Discipline Sessions
See more from this Session: Geochemistry; Geochemistry, Organic (Posters)
Sunday, 5 October 2008
George R. Brown Convention Center, Exhibit Hall E
Indra S. Sen1, Michael Bizimis2 and Gautam Sen1, (1)Earth Sciences, Florida International University, Miami, FL
(2)Dept. of Geological Sciences and NHMFL/ Isotope Geochemistry, Florida State University, Tallahassee, FL
Abstract:
Here we report the first in-situ sulfide and
bulk rock analyses of PGE in garnet pyroxenite xenoliths from Oahu, Hawaii. The
sulfides occur as globular inclusions (10-90 microns) mostly within
clinopyroxene and as interstitial phases (100 - 500 microns) in the xenoliths.
They were analyzed for major elements by electron microprobe. PGE analyses were
carried out in situ by LA-ICPMS, and bulk rock analyses were performed by the
carius tube digestion procedure and analyzed by solution ICP-MS. The sulfides
are monosulfide solid solutions (MSS, Fe = 54%, Ni =
7%, Cu = 1.3%, S = 37%, Zn = 0.18%) plotting in the 1000 1100°C MSS
field in the Fe-Ni-Cu-S system and two-pyroxene geothermometry of these
xenoliths suggests similar final mantle equilibration temperatures around 1100 -
1250°C. The PGE contents of the sulfides are highly variable (Os 0.009-1.42, Pt
0.006-0.669, Ir 0.003-1.43, Pd 0.026-1.044 and Ru 0.054-2.994 ppm) and are lower
by a factor of 10 to 100 than the typical peridotitic sulfides. A positive
correlation of (Pd/Ir)
N
vs. (Re/Os)
N and Ir
vs. Os indicates the PGE pattern in the sulfides to be a primary feature. The
(Pd/Ir)
N ratio of the bulk rock has a strong positive and
negative correlation with the Al
2O
3 and MgO content of the
clinopyroxene respectively.
Mass balance calculations between the sulfides and bulk rock PGE contents
indicate that sulfides are the major repository of PGEs in these pyroxenites.
From petrography and geochemical data we interpret these sulfides as immiscible
liquids, separated from a more voluminous silicate melt that crystallized the
garnet and clinopyroxene. Calculated PGE abundances for the parental melt are
very similar to that of erupted picritic and post erosional alkalic Hawaiian
lavas, suggesting a parental melt broadly similar to Hawaiian lavas.
See more from this Division: General Discipline Sessions
See more from this Session: Geochemistry; Geochemistry, Organic (Posters)