Osmium Isotope Systematics of Pyroxenite Xenoliths from Hawaii: Implication on Age, and Origin of the Xenolith
I. Sen1, M. Bizimis2, and G. Sen1
1Florida International University
2Florida State University
Rhenium (Re) – Osmium (Os) isotopic studies provides an excellent method for age dating rock types, like peridotites black shales, organic rich mudrocks, as enrichment of Os in these rocks have been known for some time. This geochemical tool have been extensively used to constrain depositional age, source rock, metal - organic matter interaction and melt - rock reaction.
Here, we for the first time report Rhenium – Osmium isotopic composition of garnet pyroxenite xenoliths (broken rock fragments) from Hawaii and provide constraints on the age and origin of the rocks. These xenoliths are primarily composed of clinopyroxene with variable percentages of garnet, olivine and orthopyroxene. The xenoliths were digested with the carious tube inverse aqua regia method and measured by Multi Collector Inductively Coupled Plasma Mass Spectrometer at the National High Magnetic Field Laboratory, Florida State University. The samples have variable (187Os/188 Os ratio = 0.123-0.164) and radiogenic Osmium with a strong correlation with bulk rock Platinum Group and lithophile elements. The strong correlation indicates radiogenic Osmium is a primary mantle feature and not ingrowth, after crystallization. The Rhenium/Osmium ratios of the pyroxenite are high enough to evolve to a radiogenic composition in a very short time span (as low as 2 million year).We propose that the xenoliths shows near zero age and their origin lies within the Hawaiian mantle and contradict the xenoliths being 100 million year igneous veins trapped near Mid Ocean Ridge as proposed earlier.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas