Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.292s&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 292
Mathematics
Logic
4
Scientific paper
Introduction. The recently proposed classification system for shocked chondrites (1) is based on a microscopic survey of 76 non-Antarctic H, L, and LL chondrites. Obviously, a larger database is highly desirable in order to confirm earlier conclusions and to allow for a statistically relevant interpretation of the data. Here, we report the shock classification of an additional 54 ordinary chondrites and summarize implications based on a total of 130 samples. New observations on shock effects. Continued studies of those shock effects in olivine and plagioclase that are indicative of the shock stages S1 - S6 as defined in (1) revealed the following: Planar deformation features in olivine, considered typical of stage S5, occur occasionally in stage S3 and are common in stage S4. In some S4 chondrites plagioclase is not partially isotropic but still birefringent coexisting with a small fraction of S3 olivines. Opaque shock veins occur not only in shock stage S3 and above (1) but have now been found in a few chondrites of shock stage S2. Thermal annealing of shock effects. Planar fractures and planar deformation features in olivine persist up to the temperatures required for recrystallization of olivine (> ca. 900 degrees C). Shock history of breccias. In a number of petrologic types 3 and 4 chondrites without recognizable (polymict) breccia texture, we found chondrules and olivine fragments with different shock histories ranging from S1 to S3. Regolith and fragmental breccias are polymict with regard to lithology and shock. The intensity of the latest shock typically varies from S1 to S4 in the breccias studied so far. Frequency distribution of shock stages. A significant difference between H and L chondrites is emerging in contrast to our previous statistics (1), whereas the conspicuous lack of shock stages S5 and S6 in type 3 and 4 chondrites is clearly confirmed (Fig. 1). Correlation between shock and noble gas content. The concentration of radiogenic argon and of solar-wind implanted noble gases (2) decreases with increasing shock, as does the range of the measured concentrations, particularly above shock stage S3 (>10 GPa). Conclusions. From the present statistics of shock metamorphism of ordinary chondrites it appears that the H and L parent bodies experienced distinctly different collision histories, which also had different effects on the gas retention ages. Taking the distribution of exposure ages and 40Ar-39Ar ages (3) into account, the data may indicate that the unshocked, >4 b.y. old H chondrites result from a major catastrophic collision of one parent body some 6 m.y. ago, whereas the L chondrites and other H chondrites characterized by young Ar ages may be derived from repeated impact processing of their parent bodies over the past 90 m.y. References. (1) Stoffler, D., Keil, K. and Scott, E.R.D. (1991) Geochim. Cosmochim. Acta 55, 3845-3867. (2) Schultz, L. and Kruse, H. (1989) Meteoritics 24, 155-172. (3) Kerridge, J.F. and Matthews M.S., eds. (1988) Meteorites and the Early Solar System, Univ. of Arizona Press, Tucson, 1269 pp.
Keil Klaus
Scott Edward R. D.
Stäffler Dieter
No associations
LandOfFree
Shock Classication of Ordinary Chondrites: New Data and Interpretations 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 Shock Classication of Ordinary Chondrites: New Data and Interpretations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shock Classication of Ordinary Chondrites: New Data and Interpretations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209931