11:30 AM - 11:45 AM
[PPS10-16] The Difference Acidic Condition of Aqueous Alteration Event of Nakhla and Yamato 000593 Based on Chemical Speciation
Keywords:Nakhlite, Yamato 000593, Iron sulfate mineral, Laihunite, Acidic aqueous alteration on the Mars, FIB-assisted STXM/TEM
A polished chip sample of Y 000593 (subsample, 120) was prepared for this study. Iddingsite textures were observed using a FE-SEM/EDS first. A laser micro-Raman spectroscope was employed for phase identification. Ultra-thin sections of iddingsite textures were prepared by a FIB system for STXM and FE-TEM/STEM analyses.
Laihunite, Opal-A [SiO2・nH2O], jarosite, natrojarosite [NaFe3(SO4)2(OH)6], goethite [FeO(OH)], and ferrihydrite [5Fe2O3 9H2O] were identified from the iddingsite of Y 000593 based FIB-assited STXM-TEM/STEM analyses subsequent to FE-SEM/EDS and Raman analyses. The presence of natrojarosite, one of the quad phase of jarosite , suggests that Y 000593 experienced low pH (= 1-4), low temperature (80-240 °C), and SO4-rich aqueous alteration process. Iddingsite can form below 500 , and most of them were formed between 100 and 50 , which is consistent with the alteration temperature of Y 000593 deduced from the existence of natrojarosite. The alteration condition of Nakhala with siderite (FeCO3)-bearing iddingsite texture was estimated to be about mid pH (= 6-8), low temperature (150-200 ), and CO2-rich fluid . Because Mars rover Opportunity detected sulfate minerals such as jarosite and natrojarosite, Y 000593 is a better sample than the other near-surface nakhlaites to understand the late-stage acid-sulfate alteration event. Laihunite (was formed at temperatures between 400-800 in ) was only reported from Y 000593 and MIL 03346 in the near-surface nakhlaites, implying that these two nakhalite might have experience different alteration process compared to other near-surface nakhlaites . Our STXM-TEM/STEM analyses reveal the alteration process from original olivine to laihunite; Fe2+/Fe3+ ratio gradually decreases from olivine to laihunite, which probably corresponds to the difference of superlattices of laihunite (2M and 3M phase) . Short time oxidation related to formation of the 2M phase , suggests that Y 000593 experienced a temporary heating event. We found mismatch on the formation temperatures between natrojarosite and laihunite. The discrepancy may indicate that these minerals were formed different alteration events; i.e., laihunite was formed before the late-stage acid-sulfate alteration event.
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