Mathematics – Logic
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24..947m&link_type=abstract
In Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M p 947-948 (SEE N94-16173 03-91)
Mathematics
Logic
3
Crystallization, Lithology, Mars Surface, Meteorites, Meteoritic Composition, Petrology, Planetary Geology, Shergottites, Basalt, Iron, Lava, Magma, Microanalysis, Olivine, Phosphates, Pyroxenes, Rock Intrusions, Spectroscopy
Scientific paper
The Zagami shergottite is a basaltic meteorite which formed when a phenocryst-bearing lava flow was emplaced at or near the surface of Mars. Recently, a cm-sized olivine-rich lithology has been identified in Zagami by Mossbauer spectroscopy. Olivine is extremely rare in shergottites, particularly in Zagami and Shergotty, where it occurs only as minute grains. We report petrologic and microprobe studies of this olivine-rich lithology. This material represents the last few percent of melt and is highly enriched in phosphates, opaques and mesostases, all of which are late-stage crystallization products. Phosphates replaced augite as a phenocryst phase when the magma became saturated in P. This late stage melt also includes a fayalite-bearing, multi-phase intergrowth which crystallized after the melt became too rich in iron to crystallize pigeonite. We can now reconstruct the entire crystallization history of the Zagami shergottite from a deep-seated magma chamber to crystallization of the final few percent of melt in a near-surface dike or thick flow. Small pockets (tens of microns) of late-stage melt pockets are ubiquitous but volumetrically minor in Zagami. We do not know the physical relationship between these areas and the cm-sized olivine-rich material described here. It is possible that these small pockets were mobile, forming larger areas. Perhaps inspection of the entire hand specimen of Zagami would clarify this relationship.
Jeffrey Taylor G.
Keil Klaus
McCoy Timothy James
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