Formation conditions of igneous regions in ordinary chondrites: Chico, Rose City, and other heavily shocked H and L chondrites

Man Yolcubal*, Richard O. Sack, Ming Sheng Wang, Michael E. Lipschutz

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We report microprobe and radiochemical neutron activation analysis (RNAA) data for hosts and igneous inclusions in the heavily shocked ordinary chondrites Rose City (H5), Yanzhuang (H6), Farmington (L5), Malakal (L5), Chantonnay (L6), Chico (L6), and Tuan Tuc (L6). Based on these analytical results, equilibrium crystallization calculations [Ghiorso and Sack, 1995], phase equilibrium analysis [e.g., Sack and Ghiorso, 1994a,b; Sack et al., 1994], and experimental cooling rate studies [e.g., Walker et al., 1976], we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites. We infer that (1) unfractionated chondritic liquids were intruded to depth's >0.1 km in the parent asteroid of Rose City; (2) early chondritic liquids experiencing 5-10% olivine fractionation were erupted onto the surface of the parent asteroid(s) of Yanzhuang and Chantonnay; and (3) near-surface crystallization is also indicated for the liquids in Tuan Tue and Farmington, with Chico and Malakal crystallizing at slightly greater depths. In all but Chantonnay, liquids appear to have derived from melting of chondrite types corresponding to their hosts. In the L chondrite Chantonnay, the intrusive liquids derive from melting an H chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts. Heating effects are also reflected in the trace element contents of the chondrites. Our RNAA data for Rose City seem to reflect only the siderophile-lithophile fractionation evident in the metal distribution. The Yanzhuang RNAA data are generally similar to those of other H chondrites: severe shock not involving phase transport seems to leave H chondrites unaffected compositionally. Contents of the four most mobile elements (Cd, Bi, Tl, In) and Cs in Chico indicate loss, so that this assemblage experienced extended, low-temperature cooling after injection of dike material into the Chico host. RNAA data for the other four L chondrites examined indicate more rapid cooling.

Orijinal dilİngilizce
Makale numarası97JE01873
Sayfa (başlangıç-bitiş)21589-21611
Sayfa sayısı23
DergiJournal of Geophysical Research: Planets
Basın numarasıE9
Yayın durumuYayınlandı - 1997
Harici olarak yayınlandıEvet

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