『Abstract
In order to better interpret the Martian surface weathering-related
mineralogy, we focused on a relevant analogue of the Martian subsurface
i n terms of lithology and paleoclimate: the Jurassic-aged Ferrar
dolerite (Priestley Glacier, Transantarctic Mountains), weathered
in cold and dry climate. Together with chemical and mineralogical
studies, rock magnetic properties were investigated and completed
with Mossbauer（oの頭に¨） measurements. Weathering
of the decimetric block is evidenced by chemical profiles showing
an increase in Fe content (from 10.5 in the core to 13 wt.％ in
the surface) and a decrease in Si (from 57 to 53 wt.％, respectively).
According to mineralogical, thermomagnetic and hysteresis properties,
the main opaque mineral is inherited titanomaghemite, with a concentration
about 1％. Enhancement in low field magnetic susceptibility (from
4・10-6 to 10・10-6 m3/kg, respectively)
and saturation magnetization (from 0.44 to 0.96 Am2/kg,
respectively) indicates the neoformation of metastable maghemite.
Neoformed red ferric (oxy)hydroxides are abundant in the surface.
High field susceptibility normalized to iron concentration and
Mossbauer（oの頭に¨） spectra indicate a replacement
of Fe2+ from primary silicates (pyroxene) by poorly
crystalline antiferromagnetic Fe3+ (oxy)hydroxides.
Thus, highly magnetic titanomaghemite and maghemite coexist with
nanosized ferric (oxy)hydroxides and primary silicates, in accordance
with Martian in situ observations. Therefore, this study supports
the formation of the Martian regolith as resulting from a slow
weathering process in near present day conditions.
Keywords: Antarctica; Ferrar dolerite; Mars; regolith; rock magnetism;
weathering』
1. Introduction
2. Methods
2.1. Sample description and preparation
2.2. Rock magnetic properties
2.3. Petrologic, mineralogical study and chemical analyses
3. Experimental results
3.1. Chemical and mineralogical properties
3.1.1. Bulk chemical analyses
3.1.2. Observations with microscope and SEM
3.2. Magnetic properties
3.2.1. Low field magnetic susceptibility χLF
and thermomagnetic properties
3.2.2. High field magnetic susceptibility χHF
3.2.3. Hysteresis properties
3.2.4. Magnetic parameters normalized to iron content
3.3. Mossbauer（oの頭に¨） spectroscopy
4. Discussion
4.1. The magnetic phase in the Martian regolith
4.2. Iron (oxy)hydroxides on Mars
5. Conclusions
Appendix A. Supplementary figure
References