Natural remanent magnetizations of chondrules, metallic grains and matrix of an Antarctic chondrite, ALH-769

概要

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For examining characteristics of NRM, 3 bulk specimens, 9 individual matrix materials, 12 large metallic grains and 12 individual chondrules were picked from the ALH-769 (L6) chondrite and their orientations were determined with respect to the bulk chondrite. NRM of the bulk chondrite is unstable against AF demagnetization. NRM of the matrix materials is stable up to 140 Oe peak, but its stability becomes worse for alternating fields larger than 140 Oe peak. NRM directions of the matrix materials are clustered within a hemisphere, suggesting that the presence of a magnetic field partially influenced the NRM acquisition. NRM of the metallic grains is unstable and its direction is widely scattered. NRM of the chondrules is fairly stable against AF demagnetization and thermal demagnetization. However, the direction of NRM is widely scattered within the bulk chondrite. The result of thermal demagnetization of the chondrules suggests that NRM of individual chondrules was acquired as TRM while they were making precessional motions during their cooling in the presence of a magnetic field before their assembling into the mother chondrite.
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