Origin of stable remanent magnetization in LL6 chondrite, St. Severin

Abstract

Thermal demagnetization has been carried out on 20 mutually oriented chips to unravel the stable paleomagnetic record of LL6 St. Severin. Whereas the higher unblocking fractions (520-560 degrees C) of natural remanent magnetization (NRM) are directionally scattered, the lower unblocking fractions (<520 degrees C) are relatively well constrained along a great circle in a stereographic projection. Microscopic analysis revealed St. Severin to contain paramagnetic troilite and a ferromagnetic Fe-Ni system. A sharp unblocking around 560 degrees C during thermal demagnetization strongly indicates that tetrataenite is the sole NRM carrier in St. Severin. The absence of kamacite contribution on NRM and the presence of a scattered higher unblocking fraction (520-560 degrees C) of NRM imply a sequence of brecciation and a shock-induced metamorphism rather than a thermal origin of NRM. (C) 2011 Elsevier B.V. All rights reserved.