Early Mars Sequence Stratigraphy and Lunar Picritic Glass Petrogenesis
Barker, Donald Carl 1966-
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This study in Martian and lunar planetary geology begins with the application of terrestrial sequence stratigraphy to hypothesize about the depositional conditions in an ancient Martian northern ocean. Progressive global cooling leading to the loss of surface and near-surface water from low-latitudes and eventual cold-trapping at higher latitudes, resulted in a unique, perpetual-forced regression within lowland-depositional environments. The Messinian Salinity Crisis (MSC) is proposed as an analogue for the progressive removal of large standing-water bodies. On Mars, diagnostic sequences of deposits, regional scale unconformities, intermittent resurfacing of the northern plains, and loss of an early ocean lasted through the end of the Hesperian era. The second and third chapters examine the crystallography, analyze major and trace elements, and conduct petrologic modeling using 60 picritic green, orange, and vitrophyric Apollo 15 glasses from aliquot 15421,67. Vitric glasses devoid of crystals and vitrophyric glasses, observed to contain only olivine crystals, were analyzed. Comparative analysis between crystal-free glass in both groups indicate that the uncrystallized regions are compositionally the same. Green glasses were compared to groups defined by Delano (1979). Sufficient analysis fell outside these historical groupings making reliable distinctions between groups difficult to discern and thus question original boundary validities. Glasses were best-fit categorized within these groups, only accounting for 3 of the 5 historical groups. This limited distribution points to sample collection bias for the co-bagged parent clods and regolith samples. Lastly, a series of petrologic models were run using MELTS/pMELTS software to examine potential origin of 15421,67 green glasses. These models examined the mixing processes between an adiabatic decompression melt from a primary undifferentiated lunar mantle magma with a remelted Lunar Magma Ocean (LMO) cumulate near the established 15A green glass multiple saturation point (1520 °C and 21 GPa). Three Bulk Silicate Earth (BSE) and two Bulk Silicate Moon (BSM) compositions were used as initial compositions of the primitive lunar mantle and four LMO compositions as cumulate remelts. Mixing lines between these end members were shown to be valid approximations of initial magma sources of the 15421,67 glasses and are generally consistent with previous modeling results.