CRAIER. Y. MIURA; Faculty of Science, Yapraguchi University

LPSC XYV 913

TRI TYPES [#; SHOCKFB MMR?Z AND GlWEllT AT BARRINGER WAn CRAIER. Y. MIURA; Faculty of Science, YaPraguchi University. Yoshida. Yamaguchi 753, Japan.

Material evidences of shocked silica and carbon have been considered to be difficult to obtain at impact craters and experiments. This is mainly because high- pressure type ainerals and impact materials are difficult to find at impact crater and speedy impact experiment, respectively. However, two types of shocked silica and carbon materials [l. 2.3.41 are considered to be formed at different stages of dwicimpact process. The purpose of this study is to describe the detailed coarpression stages of formation of shocked silica and carbon found at the Barringer mteorite crater.

I. Ner dmcked grapbitemd quartz aggregates from the Barringer csater Dimnd has been reported from the Barringer crater as cliftonite [5] and hexagonal diaslond (lonsdaleite [6]), though these data are based mainly on optical or powder (canera) data. Recently shocked quartz and shocked graphite (with fine size, high density, and mixture with fine amorphous glasses) are reported from the Barringer crater [7,8] as follows. 1-1. %mules: Graphite block sa~rpleof the Barringer crater used in this study was one of the evaporated impact sample including silica and carbon materials collected at 41011 west frm rim of the crater. Pure silica samples with various shock features were collected inside or on the rim of the crater. 1-2. Compositions and textures of two tm of two shocked materials : Optical, X-ray and analytical electron microscopic data reveal four major different shocked aggregates as follows [7,8] (Table 1) : a) Shocked graphite-1 in the matrix: Black fine-grained shocked graphites contain uniformly fine-grained Fe (frm kmcite) and trace of Ca (from Kaibab limestone) which were fodunder mixed gas state of impact. b) Shocked graphite-2 in vein metal: Crystallized shocked graphites and shocked hexagonal chaoite-like carbon are surrounded by kamacite-rich oletal under gas states of various comp~sitionsmixed frm iron meteorite, sandstones and limestone. c) Shocked quartz-1 in the rim: Karnacite-rich metal contains shocked quartz (mainly frola Coconino sandstone). Shocked quartz-1 grains with high density contain Fe and Ca. d) Shocked quartz-2: Clear shocked quartz -2 (and stishovite, and coesite) with pure silica formed frm the Coconino sandstone [I].

11. Dynaic foration procesr of shocked grapbites Two kinds of two different shocked carbon and quartz can be explained by the dynaoric impact process [9,101 as follows (Table 1). a) First explosion by super-heating: The first shocked graphite-1 aggregates were formed fran gas-state of Fe (from iron meteorite), C (from Kaibab limestone). and Ca (fran sandstofie) under ultra-high temperature condition from meteoritic kinetic energy to chemical heat energy. b) Secondary destruction by shock waves: The secondary shocked graphite-2 aggregates or shocked quartz-1 were formed frm huge destruction by shock waves which srakes gas- melt states of Fe. Ni. Ca. C and Si elements. After evaporating and ejecting iron, compression with jetting on the Coconino sandstone makes shocked quartz-2 aggregates. Origin of carbon of shocked graphites is considered to be frota Kaibab limestone. This is mainly because shocked graphites contain chaical inclusions from the target rocks of Kaibab limestone and Coconino sandstone, which cannot be obtained in fine graphite of original meteorite [2].

O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System 9 14 LPSC XXV

T#O TMOF SROCKED Q(JP;fm, AND GRr31TTF.: Miura Y.

Table 1. Fmtion stages with shocked carbon and silica in the Barringer crater [b].

Shock stage Impact condition Mineral assemblages

1)Coarpression High pressure and teapemture Fine mixture (disappeared to gas) 2) Cmpression-1 Vapor state (vapor plm) Fine &ed graphitel (+Fe.Ca) (with jetting) (in the major C matrix) 3) Cocppressian-2 Melt-solid state (mixed) Socked graphite2 (+Fe) and (with jetting) mite-like carbon in the vein 4) bmjression-1 Melt-solid state (mixed) Wed quartz-1 (tFe) in the rim (with jetting) 5) Coprpression-2 Solidmlt state (mixed) wedquartz-2 (tstishovite. (with jetting) coesite)

111. Forration procesz~esof Medagregab By applying two major impact formation-processes of two shocked graphite and quartz at the Barringer crater, two shocked features of the aggregates can be explained as two impact stages: (1) vapor plume stage, induced by initial cocepression and vaporization (found as dendritic or wormy texture), and (2) the second mupression stage [7.8] ( ohserved as planar feature), as listed in Table 2.

Table 2. Two major shocked materials of islpstct craters [7,8].

Stage of fomtian Type of shocked materials Emle

1)Initial cmpmsion Shcked quartz-1 (fine) Barringer crater (with wow glass) Shocked graphite-1 Artificial impact. 2) Second ccmpression Shocked graphite-2 Barringer crater (with lmellae) Shocked quartz-2 K/'I boundary Shocked stisbovite (mite) Artificial impact

IV. ConclIsion The present results are mizedas follows: a) Graphite block of the Barringer crater consists of two types of carbon materials. shocked graphite-1 and graphite-2 (chimitelike carbon), and a silica material, shocked quartz-1 with fine grained aggregates and high density. Shocked quartz-:! without iron contanination is found at the ria of the crater. b) The two types 1 and 2, shocked carbons and silica materials. are considered to be formed at compression-1 (by vapor-melt reaction) and compression-2 (by solid-melt reacticm) with jetting stages of impact. c) High pressure-type eaterials of silica and carbon are forpled by solid-atelt conditions at the final compression stage of islpact Ref ermces: [I] Miura Y. (1991) LPSC XXII (LPI. USA) ,22. 905-908. [2] Miura Y. (1991) Shock Waves. 1 35-41. [3] Miura Y. et al. (1992) Shock Waves (Springer-Verlag), 18, 403-408. [4] Miura Y. et al. (1992) Celestial Mechanics and Dymmiml Astronauy, 54, 249-253. [5] Foote A. E. (1891) Am. J. Sci., 42, 413-417. [61 Rannearann R.E. et al. (1967) Science. 155, 995- 997. [7] Miura Y. et al. (1993) Meteoritics, 28(3), 402. [81 Yiura Y. (1993) Roc. ISAS Lunar and Planet. Sm. (ISAS), 26, 98-101. [9] Gault D.E. et al. (1968) Shock Metamor- phi= of Natural Materials (ed. by French and Short), p.87-100. [lo] Melosh H. (1989) Impact. cratering (Oxford University Press), 245pp.

O Lunar and Planetary Institute Provided by the NASA Astrophysics Data System