Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53a1488h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53A-1488
Mathematics
Logic
[1028] Geochemistry / Composition Of Meteorites, [1039] Geochemistry / Alteration And Weathering Processes, [3662] Mineralogy And Petrology / Meteorite Mineralogy And Petrology, [5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering
Scientific paper
MIL 03346 was discovered in the Miller Range region of Antarctica in 2003, and subsequently classified as a member of the nakhlite group of Martian meteorites based on geochemical and petrological evidence. In common with other nakhlites, MIL 03346 contains aqueous-alteration assemblages. Using SEM-based X-ray imaging techniques, along with LA-ICP-MS trace element data, we compared the extent and composition of alteration between four thin sections from different regions of MIL 03346. The aim of our study is twofold: 1) to determine how pervasive the effects of terrestrial weathering are within the meteorite, and 2) to constrain the fluid composition(s) responsible for the pre-terrestrial alteration assemblages based upon our major and trace element datasets for these phases, in conjunction with previously published data. Our initial results indicate that MIL 03346 thin sections 173 and 174 contain higher modal abundances of alteration material compared to thin sections 126 and 128, with 128 containing the least alteration. Thin sections 173 and 174 have an “Antarctic varnish” layer on multiple edges, indicating they were cut from the outer regions of the stone. Varnish covers only one edge of thin section 126 and is not found on section 128, suggesting the latter was cut from an entirely internal part of the meteorite. It therefore appears that areas close to the surface of MIL 03346 were significantly affected by terrestrial weathering compared to the interior regions. A number of olivine grains contain incipient alteration, with Mg, Ca, Fe and Mn depletion, and Al, Si, P, S and K enrichment. This alteration is most intense in olivine grains towards the edge of thin sections 173 and 174, and is not present in thin section 128, indicating it may be purely of terrestrial origin. Alteration assemblages within olivine and pyroxene cracks mostly consist of Fe- and Si-rich clay materials, commonly containing 2.5-3.5 wt % MgO and < 1 wt % Al2O3, K2O, Na2O, SO3 and Cl. Cross-cutting relationships with fusion crust have been used to suggest a pre-terrestrial origin for the nakhlite clay material. The fact that these materials are limited to cracks within olivine and pyroxene grains suggests pre-terrestrial alteration was localised and in-situ. This interpretation is further supported by the presence of gypsum only in association with clinopyroxene cracks, as Ca cannot be extracted from olivine. Our dataset, along with those of previous studies, therefore indicates the Martian fluid which flowed through MIL 03346 had a composition largely controlled by basaltic weathering. Fluid heterogeneity was caused by a strong dependency upon the surrounding microenvironment. In-situ data from the Mars Exploration Rovers, mineral identifications from orbit, and element measurements by the Mars Odyssey Gamma-Ray Spectrometer are consistent with Martian aqueous alteration involving solutions containing SO3 and Cl.
Hallis L.
Stopar J.
Taylor Jacob
Velbel Michael Anthony
Vicenzi Edward P.
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