Berteloot C

Folco L

Gattacceca J

Rochette P

Suavet C

English

Suavet C.

FOLCO, LUIGI

Archivio della Ricerca - Università di Pisa

MAGNETIC CLASSIFICATION, WEATHERING AND TERRESTRIAL AGES OF ANTARCTIC ORDINARY CHONDRITES.  P. Rochette1, L. Folco2 J. Gattacceca1, C. Berteloot1, and C. Suavet1. 1CEREGE University of Aix-Marseille 3, France. 2Museo Nazionale Antartide Siena Italy  Magnetic susceptibility (χprovides a means to dis-criminate rapidly between LL, L and H falls [1] . This method allows rapid scan of collections without sample preparation and with portable instruments [2]  However, the classification abili-ties are hampered by weathering: for example a weathered H chondrite can yield the same susceptibility as a fresh L chondrite. The three well separated Gaussian distributions for fresh LL, L and H [1]  are skewed and partially merged by the weathering effect. The use of density measurements [3] does not really help to solve the ambiguity. In order to delineate this effect, we pro-pose a simple mathematical model using the logχ versus terres-trial age function as input data. To constrain the model logχ ver-sus terrestrial age function, we can use meteorites with cos-mogenic isotopes derived ages. We will present data on Antarctic meteorites (from PNRA and ANSMET collections), showing a rather significant correlation for H and L, at odds with the litera-ture contention that terrestrial age is independent of weathering grade in Antarctic meteorites. This contradiction likely arises from the fact that the weathering grade adopted for Antarctic me-teorites (WG) is a sort of color color index, that does not repre-sent correctly the amount of metal oxidized in non-magnetic phase (akagaenite, goethite, paramagnetic Fe3+), which is actu-ally what logχ measures. We will discuss the dispersion observed in the correlation in terms of uncertainties in terrestrial age and log determination, as well as in terms of different weathering processes depending on the story of the meteorite on or in the ice. As a perspective the calibration curve can be used to predict the terrestrial age distribution of a given collection for which logχ measurements are available.  References: [1]  Rochette, P., et al.., 2003 Meteoritics & Plane-tary Science 38, 251-268. [2]  Folco, L. et al., 2006, Meteoritics and Planetary Sciences 41, 343–353. [3]  Consolmagno G. J. et al., 2006, Meteoritics and Planetary Sciences 41, 331-342.  69th Annual Meteoritical Society Meeting (2006) 5191.pdf

Magnetic classification, weathering, and terrestrial ages of Antarctic ordinary chondrites

https://arpi.unipi.it/bitstream/11568/102746/1/Rochette_5191_2006.pdf

Magnetic classification, weathering, and terrestrial ages of Antarctic ordinary chondrites

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