CHEMICAL ALTERATIONS OF THE HOLBROOK CHONDRITE RESULTING FROM TERRESTRIAL WEATHERING

Abstract

The effects of chemical weathering on the Holbrook, Arizona chondrite were studied via major, minor, and trace element analysis along with noble gas measurements. Three samples of Holbrook were studied: a fresh specimen which fell in 1912, a specimen collected in 1931 and a specimen collected in 1968. The weathering of the meteorite produced changes in the Fe and Mg concentrations. The amount of metallic iron decreases with increasing degree of weathering. The MgO content decreases and the total iron content increases slightly with increasing weathering of the specimen, but these concentration differences are not necessarily due to weathering. Elemental concentrations for Ti, Ca, Al, P, Mn, Ni and Cr did not change significantly during weathering. Sodium may have been lost during weathering, whereas K showed a slight enrichment in abundance with terrestrial age. Trace elements C, Rb and Sr increased at least two‐fold during weathering of the meteorite. Abundances of the radiogenic and cosmogenic noble gases decreased with increasing terrestrial age. Concentration ratios of certain cosmogenic noble gas nuclides which are commonly used as indicators of gas loss and shielding in chondrites show unpredictable behavior in the weathered chondrite.