Magnetic Classification of Ordinary Chondrites: Falls Versus Finds

Details Magnetic Classification of Ordinary Chondrites: Falls Versus Finds Magnetic Classification of Ordinary Chondrites: Falls Versus Finds

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmgp32a0195r&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #GP32A-0195

Other

1540 Rock And Mineral Magnetism, 3662 Meteorites, 3672 Planetary Mineralogy And Petrology (5410), 5440 Magnetic Fields And Magnetism, 5460 Physical Properties Of Materials

Scientific paper

We have undertaken a magnetic susceptibility (K) survey of various meteorite collections in Italy and Vatican, using a large coil (8 cm) Kappabridge instrument. This original database, merged with previous data from Finnish and Czech collections [1], allows us to analyze about 650 different ordinary chondrites, equally distributed in 3 categories: falls, Antarctic and non-Antarctic finds (half from Sahara). For a large number of meteorites, especially falls, we measured numerous samples from various collections, allowing testing the homogeneity of K values. It appears that in the majority of falls logK values are reproducible within 0.1, even at the 1 cc levels. Finds are less homogeneous, together with some brecciated or veined falls, where one expects locally variable metal concentrations. When falls are taken separately from finds a very narrow range of logK values appear to characterize H, L and LL classes, with no overlap (excluding 8 percent of petrographically anomalous samples). On the other hand finds show a variable decrease of logK, correlated to weathering grade. Antarctic finds (mostly from Frontier Mountain) appear on average less affected by weathering although logK histogram is clearly shifted toward low values compared to finds. Interestingly the FRO histograms exhibit quite narrow peaks, while other finds show a larger spread. This can be tentatively explained by a predominance of a few individual showers as suggested by cosmogenic isotope features [2] . From our analysis of a large number of samples, it appears clearly that finds, even from Antarctic, have to be excluded for the purpose of defining mean magnetic properties of asteroids related to ordinary chondrites. Simple in-situ probes could be designed for future asteroid missions to identify meteorite type using our database. References: [1] Terho M. et al. (1993) Studia Geoph. Geod.. 37, 65-82 [2] Welten K.C. et al. (2001) Mete-oritics & Planet. Sci., 36, 301-318.

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