The University of Arizona

A weathering index for CK and R chondrites

A. E. Rubin, H. Huber

Abstract


We present a new weathering index (wi) for the metallic-Fe-Ni-poor chondrite groups (CK and R) based mainly on transmitted light observations of the modal abundance of crystalline material that is stained brown in thin sections: wi-0, <5 vol%; wi-1, 5–25 vol%; wi-2, 25–50 vol%; wi-3, 50–75 vol%; wi-4, 75–95 vol%; wi-5, >95 vol%; wi-6, significant replacement of mafic silicates by phyllosilicates. Brown staining reflects mobilization of oxidized iron derived mainly from terrestrial weathering of Ni-bearing sulfide. With increasing degrees of terrestrial weathering of CK and R chondrites, the sulfide modal abundance decreases, and S, Se, and Ni become increasingly depleted. In addition, bulk Cl increases in Antarctic CK chondrites, probably due to contamination from airborne sea mist.

Keywords


Composition of meteorites;CK carbonaceous chondrite meteorites;R chondrite Meteorites;Weathering

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