Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27s.261m&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 261
Computer Science
1
Scientific paper
It has been considered that quartz minerals can be formed by magmatic crystallization of the Earth or Earth-type planets under high-temperature condition of the magma. However, if similar high temperature can be obtained at impact processes, silica minerals will be formed even under impact condition (1,2,3,4). Impact experiments. The following various silica and feldspar minerals can be obtained in the artificial impact crater experiments of various type target rocks. a) Fine-grained shocked quartz aggregates crystallized from vaporization of feldspar compositions are shown by the increased abundance of shocked quartz (SQ) and feldspar(F) at the "fine ejecta"; that is, SQ/F=3.0 and 5.6 in the granite and gabbroic anorthosite, respectively (cf. Table 1). Chemical compositions of large fragments broken by impact processes reveal partly anomalous diaplectic feldspar grains with irregularly wavy extinction and nonstoichiometric composition. b) Impact effects of density change and shocked quartz formation (SQ/F) show larger in fine-grained gabbroic anorthosite than hard coarse-grained granite. c) Stishovite and coesite could not be observed in small laboratory experiments. d) The highest density of shocked quartz crystal (SQ) in fine-grained ejecta can be obtained in quartz-rich target-rock of sandstone, which is the same implication to the Barringer impact crater with sandstone (1,3). Shock metamorphism of lunar and planetary materials. By using the experimental impact results of shock metamorphism (4), major plagioclase minerals of anorthosite formed by magmatic ocean processes on the primordial planetary and lunar surfaces, can be changed to diaplectic plagioclases and shocked silica minerals by impact shock effects, resulting in the formation of shocked quartz (SQ) by rapid crystallization. The SU phases formed by impact can be changed to normal quartz (Q) by magmatic evolution process under high temperature. The present results of shock metamorphic evolution will be applied to lunar impact and recrystallized rocks (cf. KREEPy lunar rocks with feldspar and quartz aggregates), as follows. Feldspar (F) -->(shock waves) --> Diaplectic plagioclases --> (vaporization) --> (quenching) --> Silica minerals --> Shocked quartz (SQ type) --> (high temperature-type metamorphism) --> Quartz (normal Q type) References: (1) Miura Y. (1991) Shock Waves (Springer-Verlag), 1, 35-41. (2) Miura Y., Kato T., Kawashima N., Yamori A. and Imai M. (1991) Lunar and Planet Sci. (ISAS,Tokyo), 24, 46-52. (3) Miura Y., Takayama K. Kato T., Kawashima N. and Yamori A. (1992) Proc. 18th Intern. Sympo. Shock Wave (Springer-Verlag). 7 pp. (in press). (4) Miura Y. and Kato T. (1992): Celestial Mechanics (July issue), 4 pp.(in press). Table 1. Silica data and ratio of shocked quartz (SQ) to feldspar (F) of artificial impact craters of three target rocks (1,2,3.4). Target rock, Density....Density-dev..Ratio Remarks Sample No. rho(g/cm3).rho/rho0(%)..SQ/F 1) Granite Original(GP) 2.640(1)*.. -0.19(5)....1.6 Fine ejecta(GEF) 2.645(0)... +0.00.......3.0 High SQ/F 2) Gabbroic anorthosite Original (BP) 2.642(8)... -0.11(7)....0.02 Fine ejecta(BEF) 2.651(2)... +0.22(6)....5.60 High SQ/F 3) Sandstone Fine ejecta(SEF) 2.656(5)... +0.3(2).....- High ....................... density * Numbers in parentheses are standard deviation referring to the last decimal place.
Imai Motoharu
Kato Taichi
Miura Yas.
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