Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites




The weathering products present in igneous terrestrial Antarctic samples were analyzed, and compared with those found in the four Miller Range nakhlite Martian meteorites. The aim of these comparisons was to determine which of the alteration phases in the Miller Range nakhlites are produced by terrestrial weathering, and what effect rock composition has on these phases. Antarctic terrestrial samples MIL 05031 and EET 96400, along with the Miller Range nakhlites MIL 03346 and 090032, were found to contain secondary alteration assemblages at their externally exposed surfaces. Despite the difference in primary mineralogy, the assemblages of these rocks consist mostly of sulfates (jarosite in MIL 05031, jarosite and gypsum in EET 96400) and iddingsite-like Fe-clay. As neither of the terrestrial samples contains sulfur-bearing primary minerals, and these minerals are rare in the Miller Range nakhlites, it appears that SO42−, possibly along with some of the Na+, K+, and Ca+ in these phases, was sourced from wind-blown sea spray and biogenic emissions from the southern ocean. Cl enrichment in the terrestrially derived “iddingsite” of MIL 05031 and MIL 03346, and the presence of halite at the exterior edge of MIL 090032, can also be explained by this process. However, jarosite within and around the olivine-bound melt inclusions of MIL 090136 is present in the interior of the meteorite and, therefore, is probably the product of preterrestrial weathering on Mars.