Origin of stable remanent magnetization in LL6 chondrite, St. Séverin Yongjae Yu a , Seong-Jae Doh b,⇑ , Wonnyon Kim c , Kyoungwon Min d a Department of Geology and Earth Environmental Sciences, Chungnam National University, Daejeon 305–764, Republic of Korea b Department of Earth and Environmental Sciences, Korea University, Seoul 136–713, Republic of Korea c Deep-sea and Marine Georesources Research Department, Korea Ocean Research and Development Institute, Ansan 426-744, Republic of Korea d Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA article info Article history: Received 9 December 2010 Received in revised form 8 June 2011 Accepted 8 June 2011 Available online 22 June 2011 Edited by: Keke Zhang Keywords: Chondrite Meteorite St. Séverin Tetrataenite Taenite Kamacite abstract Thermal demagnetization has been carried out on 20 mutually oriented chips to unravel the stable paleo- magnetic record of LL6 St. Séverin. Whereas the higher unblocking fractions (520–560 °C) of natural rem- anent magnetization (NRM) are directionally scattered, the lower unblocking fractions (<520 °C) are relatively well constrained along a great circle in a stereographic projection. Microscopic analysis revealed St. Séverin to contain paramagnetic troilite and a ferromagnetic Fe–Ni system. A sharp unblock- ing around 560 °C during thermal demagnetization strongly indicates that tetrataenite is the sole NRM carrier in St. Séverin. The absence of kamacite contribution on NRM and the presence of a scattered higher unblocking fraction (520–560 °C) of NRM imply a sequence of brecciation and a shock-induced metamor- phism rather than a thermal origin of NRM. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction To precisely decipher the early stage evolution of the solar sys- tem, mineral magnetic investigation is useful in constraining the cooling or metamorphic history of chondritic planetary bodies. Meteorites often contain stable natural remanent magnetization (NRM) of various origins (Stacey et al., 1961; Brecher et al., 1977; Collinson, 1987; Collinson and Morden, 1994; Weiss et al., 2008). Intensive cataloguing and systematic data compilation signifi- cantly have improved our understanding of the meteorite magne- tism (e.g., Rochette et al., 2003, 2008, 2009a,b; Weiss et al., 2010). Among various types of undifferentiated ordinary chondrites, the LL chondrites have drawn special attention because of their simi- larity to terrestrial igneous rocks such as relatively poor metal con- tents, high magnetic stability, and equilibrated mineralogy resulting from a slow cooling (e.g., Rochette et al., 2003). The LL6 St. Séverin meteorite fell to Earth on June 27, 1966. Five major pieces with a combined total weight of 221 kg were recov- ered in northern France (latitude: 45°18 0 N, longitude: 0°14 0 E). A shock stage S2 (Stöffler et al., 1991) and weathering grade W0 (Wlotzka, 1993) were assigned. Among many LL chondrites, LL6 St. Séverin was used in the present study for two reasons. First, it is one of the few meteorites whose crystallization age has been reliably determined by various radiometric dating techniques, including Pb-Pb (4543 ± 19 Ma, Manhes et al., 1978; 4559 ± 15 Ma, Chen and Wasserburg, 1981; 4553.6 ± 0.7 Ma, Göpel et al., 1994; 4554.9 ± 0.2 Ma, Bouvier et al., 2007), Sm–Nd (4550 ± 330 Ma, Jacobsen and Wasserburg, 1981), Rb–Sr (4510 ± 150 Ma, Dalrymple, 1991), Re–Os (4680 ± 150 Ma, Chen et al., 1998), and Ar–Ar (4430 ± 40 Ma, Dalrymple, 1991). Second, a few previous paleomagnetic investigations have yielded somewhat contradict- ing outcomes. For example, at an individual specimen level, alter- nating-field (AF) demagnetization of St. Séverin showed a stable component with a median destructive field (MDF) of 15 mT (Brecher and Ranganayaki, 1975). However, within-specimen com- parison failed to link the homogeneity of NRM with MDF > 50 mT in other chips (Brecher et al., 1977). Extremely AF-resistant NRM of St. Séverin was also reported in Sugiura (1977). On the basis of thermomagnetic analysis, it has been suggested that the coexis- tence of kamacite and tetrataenite is responsible for the extremely high-coercivity fraction of St. Séverin with MDF 100 mT (Nagata, 1982). Acquisition of thermoremanent magnetization (TRM) or thermochemical remanent magnetization was considered the ori- gin of the high-coercivity NRM of St. Séverin (Nagata and Funaki, 1982). On the contrary, at least some NRM fractions of St. Séverin were attributed to viscous remanent magnetization or shock- induced remanent magnetization (Morden and Collinson, 1992). In spite of diverse opinions on the origin of St. Séverin’s high- coercivity NRM, rock magnetic descriptions on the NRM carriers are rather similar. The Lowrie–Fuller test (Lowrie and Fuller, 1971) on St. Séverin revealed the presence of fine-grained 0031-9201/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.pepi.2011.06.004 ⇑ Corresponding author. Tel.: +82 2 3290 3173; fax: +82 2 3290 3189. E-mail address: sjdoh@korea.ac.kr (S.-J. Doh). Physics of the Earth and Planetary Interiors 187 (2011) 292–300 Contents lists available at ScienceDirect Physics of the Earth and Planetary Interiors journal homepage: www.elsevier.com/locate/pepi