Remanent magnetic properties of unbrecciated eucrites

Abstract

The remanent magnetic properties of five unbrecciated eucrites, ranging from the coarse-grained cumulate Moore County, to the quenched melt rock ALH 81001, have been investigated in order to assess the strength of the magnetic field associated with their parent body during their formation. Two of the meteorites are judged as unlikely to have preserved their primary thermal remanence, because of large variations in subsample remanence intensity and direction (Ibitira), and lack of NRM resistance to AF and thermal demagnetization (PCA 82502). Furthermore, Moore County, because it is dominated magnetically by coarser-grained Fe, and because of its thermal instability, is considered as a poor candidate for paleointensity estimates. The low normalized NRM intensities for subsamples of ALH 81001 and Yamato 791195, may indicate the lack of a strong (> 0.01 mT) magnetizing field during their cooling on the eucrite parent body. This inference is supported by low paleofield values (0.001–0.005 mT) associated with blocking temperatures > 150°C, for a second subsample of Yamato 791195. These paleointensities were derived by a new version of the KTT experiment whereby remanence acquired and lost in discrete temperature intervals is measured at progressively higher temperatures. Although the magnetic data set for eucrites remains small, the lack of evidence for a strong thermal remanence in these and previously measured achondrites does not provide direct evidence for the existence of a strong T Tauri solar wind field which could be responsible for induction heating of the achondrite parent bodies.