Computer Science
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007gecoa..71.2383r&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 71, Issue 9, p. 2383-2401.
Computer Science
9
Scientific paper
Acapulcoites are modeled as having formed by shock melting CR-like carbonaceous chondrite precursors; the degree of melting of some acapulcoites was low enough to allow the preservation of 3 6 vol % relict chondrules. Shock effects in acapulcoites include veins of metallic Fe Ni and troilite, polycrystalline kamacite, fine-grained metal troilite assemblages, metallic Cu, and irregularly shaped troilite grains within metallic Fe Ni. While at elevated temperatures, acapulcoites experienced appreciable reduction. Because graphite is present in some acapulcoites and lodranites, it seems likely that carbon was the principal reducing agent. Reduction is responsible for the low contents of olivine Fa (4 14 mol %) and low-Ca pyroxene Fs (3 13 mol %) in the acapulcoites, the observation that, in more than two-thirds of the acapulcoites, the Fa value is lower than the Fs value (in contrast to the case for equilibrated ordinary chondrites), the low FeO/MnO ratios in acapulcoite olivine (16 18, compared to 32 38 in equilibrated H chondrites), the relatively high modal orthopyroxene/olivine ratios (e.g., 1.7 in Monument Draw compared to 0.74 in H chondrites), and reverse zoning in some mafic silicate grains. Lodranites formed in a similar manner to acapulcoites but suffered more extensive heating, loss of plagioclase, and loss of an Fe Ni S melt. Acapulcoites and lodranites experienced moderate post-shock annealing, presumably resulting from burial beneath material of low thermal diffusivity. The annealing process repaired damaged olivine crystal lattices, lending acapulcoites and lodranites the appearance of unshocked (i.e., shock-stage S1) rocks. Any high-pressure phases that may have formed during initial shock reverted to their low-pressure polymorphs during annealing. Some samples were subsequently shocked again; several acapulcoites reached shock-stage S2 levels, ALH 84190 reached S3, and the lodranite MAC 88177 reached S5.
No associations
LandOfFree
Petrogenesis of acapulcoites and lodranites: A shock-melting model does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Petrogenesis of acapulcoites and lodranites: A shock-melting model, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Petrogenesis of acapulcoites and lodranites: A shock-melting model will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-767431