Magnetism of Shergottites

Introduction: New discoveries in cold (Antarctica) and hot desert areas have significantly increased the number of Martian meteorites (SNC) to more than 50 (unpaired) [1,2]. Martian meteorites are classified in four main groups in terms of their pe-trology and mineralogy, namely Orthopyroxenite (1 published member), Chassignites (dunite, 2), Nakhlites (clinopyroxenite, 7) and Shergottites (42) which are additionally subdivided in basal-tic, olivine-phyric, olivine-opx phyric, lherzolitic and one wehrlite [1]. Magnetism of shergottites: Recently, geochemical studies revealed that independently from the " old " scheme shergottites can be divided into 3 different subgroups based on their trace element and isotopic signature (enriched, depleted, and intermediate suite) [3]. This is interpreted as additionally reflecting the heterogeneity of the magma reservoirs [4]. The petrology and mineralogy of the lherzolitic shergottites is quite homogeneous (neglecting secondary processes) [5,6]. Their magnetic signature was found to follow specific trends, mainly depending on shock degree and terrestrial alteration effects, the latter in turn strongly depending on size/weight (TKW) of the individual Martian meteorites [7-9]. However, the magnetic signature of the members of the other shergottite groups appears quite scattered and was not found to follow distinct trends so far. In this study, we tried to (re-) compile published and original data, specifically addressing and incorporating new shergottite finds, concerning their magnetic signature in order to evaluate likely trends or groupings (such as for lherzolites). Additionally, the effects of secondary processes such as terrestrial alteration on the magnetic characteristics of the SNC were studied using the NWA 2975 (basaltic), SaU 005/008 and NWA 1068 (oliv.-phyric) and DaG 476 (oliv.-opx phyric) clans representing large sets of sample sizes and weights (TKW). The main result of our investigations is that only sufficiantly large sample sets and the respective databases allow to get insight and to eventually control these secondary processes in a satisfying manner.