Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.551m&link_type=abstract
Meteoritics, vol. 30, no. 5, page 551
Other
Craters, Takamatsu, Gravity, Impact, Metal, Metamorphism, Shock, Waves
Scientific paper
Shocked quartz materials have been found in Japanese K.T boundary (Hokkaido) and mountains of middle main-islands of Japan, though there are few direct evidence of "natural circular structure" on the surface in Japan. However circular structure has been recently found as a buried crater(up to 150m deep) [1] which is ca. 4km in diameter with -10 mgal of Bouguer gravity anomaly from surrounding Rhyoke granitic region of the southern part of Takamatsu City, Kagawa Prefecture, northeast Shikoku, Japan [1,2,3]. Two boring cores of 300m deep near small mountains inside the crater could not reach the bottom of the crater so far. From model calculation of the negative gravity anomaly, the Takamatsu crater shows deep basin structure up to 1.4km. If the Takamatsu crater is considered to be only impact crater, it is difficult to discuss only surface materials on the crater. But anomalous minerals are found only around small volcanic intrusions inside the crater, which the mixed minerals are clearly different with those of other volcanic intrusions of the Yashima and Goshikidai outside the crater [1,2,3]. The small volcanic intrusions are not origin of large Takamatsu crater, because the small volcanic intrusions are found on whole areas of Kagawa Prefecture. Major different activity of the small intrusions inside the crater is to bring the brecciated materials of the interior (esp. crater sediments). The xenolith materials around only volcanic intrusion of andesite are divided into the following four major mineral materials:(a) round pebble fragments from the Rhyoke granitic basement (Sampling No.15), (b) rock fragments from intruded biotite andesites (Nos. 2,15), (c) impact-induced fragments of shocked Quartz grains (Nos. 2,3,6,15), diaplectic feldspars (Nos. 2,3,6,15), silica glasses (Nos. 2,15) and small Fe-Ni metallic grains (No.15), and (d) small sedimentary fragments of halite and mordenite, as listed in Table 1. Table I, showing the characterization of surface samples around small intrusions of the Takamatsu crater, appears here in the hard copy. The following anomalous mixed materials are considered to be impact-induced origin: 1) Fe-Ni grains: Black glassy rocks at Jissojiyama (No. 15) contain irregularly Fe-Ni grains of 10 to 100 micrometers in diameter. Chemical composition of the small Fe+Ni grains varies from ca. 18~90 atom. % mixed with the major granitic components. Atomic ratios of Fe/Ni are the same of kamacite as 3.4 to 68.7, but differ from those of awaruite (Fe/Ni<0.5) from the deep seated rock of the interior of the Earth [4]. The similar tiny Fe grains are found on the Wolf Creek and Ries impact craters. 2) Shocked quartz with high-density and shock lamellae: Anomalous quartz grains with undulatory anomalous extinction and shock lamellae are found at the Hiyama (Nos. 2,3,6 in whitish fine rocks) and Jissoiiyama (No. 15 in black glass) as brecciated xenolith from the interior of crater sediments. Typical shocked quartz grain shows with two sets of shock lamellae along pi (102) crystallographic planes [5]. The main X-ray diffraction peaks of each Miller plane show high Bragg angle and X-ray density (Delta rho=+0.9+/-0.3%) and lower values (ca.- 0.4%) of each plane-distance of all shock-generated Plane deformation features (PDFs). The structural data of high density are the same of shocked quartz grains in terrestrial impact craters [6,7]. 3) Diaplectic feldspars: Shock-generated diaplectic feldspars with compositions of albite plagioclases with undulatory extinction are observed with dark or partly dark (i.e. diaplectic) glassy materials under cross-polarized microscope (Nos. 2,3,6,15). Crushed plagioclases with circular or ellipsoidal shape are also found at Hiyama (No. 6) and Hiraike (No. ll). Diffuse and irregular textures of feldspar fragments are different with other localities outside the crater [2,3]. 4) G1asses of potassium feldspar compositions: Many glassy fragments with flow texture are observed from fine-grained sediments around Hiyama (Nos. 2,3,6), which have potassium feldspars compositions by the AEM of high-silica (SiO2=78~85wt.%) without MgO [2]. K-Ar dating of the glassy breccias is 14.2 +/-0.7(Ma). This suggests that fine-grained breccias are mixed with Hiyama andesitic intrusion, suggesting that formation of the Takamatsu crater is older than small and many volcanic intrusions [2,3]. Therefore, the Takamatsu crater is considered to be the similar type of crater as buried impact crater followed by small volcanic intrusions [2,3]. The Takamatsu crater seems to be the first impact crater in Japan. Referenocs: [1] Y. Kono et al. (1994): ISAS Lunar and Planetary Symp.(Japan), 27, 67-70. [2] Y. Miura et al. (1995): Lunar. Planet. Sci.(USA), XXVI, 987-988. [3] Y. Miura et al.(1995): Antarctic Metcorites (NIPR), 2?, 163-165. [4] Y. Miura et al. (1981): Contrib. Mineral. Petr?l., 76, 17-23. ?5] R.A.F.Grieve et al.(l988): LPI Technical RePorl (USA), No.88-03, 89 pp. [6] Y. Miura (1991): Shock ?aves (Springer-Verlag), 1, 35-41. [7] Y. Miura et al. (1992): Celestial ?echanic? ?4 ?4 ?
Fukuchi Tatsuro
Miura Yas.
Okamoto Makoto
No associations
LandOfFree
Impact Materials of Takamatsu Crater in Japan 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 Impact Materials of Takamatsu Crater in Japan, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Impact Materials of Takamatsu Crater in Japan will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-830203