Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p51a..04b&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P51A-04
Mathematics
Logic
5410 Composition, 5415 Erosion And Weathering, 5455 Origin And Evolution, 5480 Volcanism (8450), 6225 Mars
Scientific paper
The Rb-Sr and Sm-Nd isotopic systems provide the basis for determining the crystallization ages of martian meteorites. However, determining an unambiguous age for the least weathered martian meteorites is often difficult because they are small, have low abundances of Sr and Nd, have experienced shock metamorphism, and have sometimes been weathered on Mars. The situation is complicated by the fact that most recent martian meteorite finds are from warm desert environments and have also undergone terrestrial weathering. Petrologic and isotopic analysis of the desert meteorite DaG476 reveals the extent to which terrestrial weathering can disturb the isotopic systematics of a meteorite. Significant weathering of this meteorite is indicated by high K/La ratios of the bulk rock and large amounts of secondary calcite. Despite several leaching steps in warm HCl, the Rb-Sr isotopic system provides no age constraints. This is a result of the fact that small amounts of terrestrial calcite survived the leaching procedure. The Sm-Nd isotopic system appears to be more robust and yields an age of 474 Ma. However, several fractions do not lie on this isochron. The leachates, for example, fall on a mixing line between terrestrial clays and igneous phosphates, suggesting desert soil has been added to the meteorite. Furthermore, SEM and SIMS analyses of representative grains from DaG476 mineral fractions reveal the presence of an amorphous high silica phase with REE abundances that are similar to the bulk rock. Thus, the isotopic systematics of DaG476 are potentially disturbed by the presence of calcite, clays, and amorphous silica. Generally, concordant ages from multiple isotopic systems are used as evidence that individual isochrons have not been disturbed. A second test is whether the trace element abundances of mineral fractions used to define the isochron are similar to elemental abundances predicted on the basis of igneous partitioning. In the case of DaG476, only one isotopic system yields an age and the Sm and Nd abundances of maskelynite (plagioclase) and olivine mineral fractions are not similar to those predicted on the basis igneous partitioning. However, mixing models demonstrate that the Sm-Nd isotopic systematics of DaG476 mineral fractions are not consistent with contamination by either clay or the amorphous silica phase. This probably reflects low abundances of these phases in the mineral fractions and the fairly low REE abundances in the amorphous silica. Instead, the isotopic systematics of maskelynite and olivine mineral fractions are consistent with mixing between pure minerals and magmatic glass inclusions. Therefore, despite abundant amounts of terrestrial contamination, careful application of the Sm-Nd isotopic system can yield the crystallization age of a meteorite weathered in a desert environment.
Borg Lars E.
Edmunson J.
No associations
LandOfFree
Rb-Sr and Sm-Nd Geochronology of Martian Meteorites: Disturbances Caused by Terrestrial Weathering does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Rb-Sr and Sm-Nd Geochronology of Martian Meteorites: Disturbances Caused by Terrestrial Weathering, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rb-Sr and Sm-Nd Geochronology of Martian Meteorites: Disturbances Caused by Terrestrial Weathering will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1239635