Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.550m&link_type=abstract
Meteoritics, vol. 30, no. 5, page 550
Computer Science
Calcite, Carbon, Craters, Ries, Metal, Shock Effect, Waves, Shock
Scientific paper
Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As calcite mineral shows high-pressure phase of aragonite it should have the "shocked phase" formed from high-pressure phase mixed with quenched materials of gas-melt reaction [2,3,4]. The main purposes of this paper are (1) to discuss new shocked materials of calcite found in the Noerdlingen Ries impact crater. Germany and artificial impact phases. and (2) to show new findings of fine Fe-grains and anomalous plagioclase in suevite. Single grains of anomalous calcite for X-ray analysis were selected from limestone with wormy or bubble-included texture in Buschelberg Ries impact crater (sample R8) [3 4]. Powdered and single grain samples of anomalous calcites show low X-ray intensity and high Bragg angle shift. compared with standard calcite of Akiyoshi limestone as listed in Table 1 [2.3.4]. The unit-cell dimensions of the single grain measured with the four-axes X-ray diffractometer in Yamaguchi University were determined by the least square calculation from the "highest X-ray intensity peak" of each crystal plane which is the same data of the powdered X-ray diffraction sample as an average structure . Both powdered and single grain data reveal high density of 2.76 g/cm^3 (between aragonite of density: rho=2.8g/cm^3, and normal calcite: rho=2.71g/cm^3) of the calcite cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous calcite contains minor amount of Si Fe Ti, though major cation is Ca of 99.4% in cation content. These foreign elements are mixed with during the formation in vapor plume [5]. Table 1, showing the x-ray density and unit-cell parameters of anomalous shocked calcite with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked calcites are found in artificial impact experiments of railgun of the ISAS. Japan. (a) Shocked calcite formed on oxidation condition (near the rim of vapor plume of impact [7]). (b)Shocked calcite formed on reduction condition (interior of vapor plume of impact [7]). The shocked calcites of the Buschelberg (R8) inside the crater are correspondent to shocked calcite with reduction state. which suggests recrystallization inside the crater. The detailed experiments of the R8 samples are checked on yellow (Fe-rich) colored sample of R8Yl and white colored sample (R8W). From the X-ray diffraction data of Bragg angle shift, the R8W1 is more close to reduction state during impact. The shocked calcites under oxidation state are formed as non-stoichiometric compound (and high density) after gas of C02 formation mainly near rim of vapor plume, which is the same data of artificial impact experiments of oxidation condition (i.e. sample No. LSRGl). The shocked calcite under reduction state are formed relatively as normal calcite (with normal or a little high density) and carbon after formation of gaseous materials of CO, 02 and Ca. Thus cabon source from target rock of limestone [2,3,4] can be explained as reduction formation of impact, as listed in Table 2. Table 2, showing, the formation process of shocked calcite materials by shock impact, appears here in the hard copy. References [1] Miura Y.(l991): Shock Waves, 1, 135-141. ?2] Miura Y. (1994): Proc. ISAS Lunar & Planet. Sci. (ISAS, Japan), 27, 204-207. [3] Miura Y. et al. (1995): Shock Waves, Japan, 613-624. [4] Miura Y. and Okanoto M. (19995): Antarctic Meteorites (NIP?), 20, 169-171. ?1989): Tma;l(-.t. r?r;lt.?rin? ?rhrfnr? llniv?r?i?v Pr? )A? 7?;
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