Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.262m&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 262
Mathematics
Logic
Scientific paper
Shocked quartz minerals from the Cretaceous-Tertiary (K/T) boundary and impact craters have been mainly discussed from distribution of optical directions, mean optical refractive index, and X-ray data (1). The purpose of the present study is presentation of the detailed mineralogical data of shocked quartz found in the K/T boundaries and terrestrial impact craters (2,3,4,5). X-ray powder diffraction pattern of shocked quartz aggregate reveals that all Xray peaks are split into major three peaks composed of low-density quartz (LQ), normal quartz (Q), and shocked quartz with high density (SQ). X-ray peaks of (110), (200), (201), (202), and (211) in the hexagonal cell are also split into many peaks. The X-ray intensity among LQ, Q, and SQ phases indicates that the SQ phase shows 36% to 53% in six K/T boundary samples (5). The relative X-ray intensity ratio of shocked quartz to standard rock crystal decreases into 13% to 37%, which suggests that shocked quartz materials contain major parts of diaplectic amorphous phases (G1) in the K/T boundary and impact crater. Although the LQ and Q type quartz phases, which can be also obtained at artificial impact processes (2,3,4,5), could not be distinguished from magmatic terrestrial origins, the SQ type quartz with high density has been selected for X-ray structure analysis to obtain the atomic arrangement of shocked quartz crystal. The detailed X-ray structural analyses of the SQ type shocked quartz indicate that atomic distance between oxygen and oxygen is shrunk largely (-0.8% than standard quartz Q), but that between silicon and oxygen is shrunk relatively small (-0.3%). The structural shrinkage is considered to be major causes of high density value of the SQ parts (up to +0.8% of the density deviation) (4,5). The chemical composition of shocked quartz phase (SQ) from electron and ion microprobe analyzers shows almost pure silica without Al element, though amorphous silica glassy phases (G2) contain Al contamination (ca. 0.5 wt% Al2O3). Thus, four major parts of shocked quartz silica aggregates from the K/T boundary and impact crater are divided into amorphous silica glasses (G1), low-density quartz (LQ), normal standard quartz (Q), and high-density shocked quartz (SQ) that have been formed by artificial impact experiments (2,3,4,5) in the powder state, as follows: Shocked quartz aggregate (SQA) = SQ + Q + LQ + G1. Single grain of SQ type shocked quartz phases consists of crystalline phase (SQ) and diaplectic amorphous regions (G2), as follows: Shocked quartz grain (SQG) = SQ + G2. Diaplectic amorphous phases (G2) reveal from coarse-grained silica (as multiple sets of lamellae) to submicroscopic fine-grained silica phases throughout SQG grains. Anomalous experimental data of shocked quartz with high density and shrinkages of atomic arrangements (2,3,4,5) are observed only the SQ crystalline phase. Shocked quartz as crystalline mineral means only crystalline SQ phase, whereas mixed shocked silica materials are considered to be "shocked quartz grain (SQG)" or "shocked quartz aggregate (SQA)." The experimental values of mean refractive index and bulk density of shocked quartz materials (i.e., SQA powder of LQ+Q+SQ+G1 phases, and SQG single grain of SQ+G phases), therefore, show bulk data with lower values. The similar relic phases with high-density crystal and amorphous phases formed by impact processes can be found in shocked graphite, diamond, and coesite. References: (1) Bohor B.F., Foord E.E., Modreski P.J. and Triplehorn D.W. (1987) Science, 224, 867-869. (2) Miura Y. (1991) Shock Waves (Springer-Verlag), 1, 35-41. (3) Miura Y. (1991) Lunar Planet. Sci. (abstract), 22, 905-908. (4) Miura Y. and T. Kato (1992) Celestial Mechanics (July issue), 5 pp. (in press). (5) Imai M. (1992) Master Sci. Thesis, Yamaguchi University, 89 pp.
Imai Motoharu
Kato Taichi
Miura Yas.
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