Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.524i&link_type=abstract
Meteoritics, vol. 30, no. 5, page 524
Mathematics
Logic
Central Mound Structures, Cratering, Modification Stage, Craters, Morphology, Impact Cratering, Puchezh-Katunky Impact Crater
Scientific paper
Previous investigations of the impact crater formation mechanics show that the late stage--a transient cavity collapse in a gravity field--may be modeled with traditional rock mechanics if one ascribes very specific mechanical properties of rock in the vicinity of a crater: An effective strength of rock needs is around 30 bar [1], an effective angle of internal friction is below 5 degrees [2]. The rock media with such properties may be named as "temporary fluidized" (see the review of hypotheses by [3]). Melosh [4,5] suggests an acoustic (vibration) nature of this fluidization. This model now seems to be the best approach to the problem. The specific of rock deformation is that the rock media deforms not as a plastic metal-like continuum, but as a system of discrete rock blocks. This approach allows to take into account an important phenomenon of localization of deformations at block boundaries. One of the main questions for modeling is the structure of a rock media under the crater. Is it a "rubble pile" or a solid uplifted "plug" of basement rocks? New data came from the study of the deep (5 km) drill hole in the center of a 40-km terrestrial crater in Russia [6]. The recovery core was investigated to estimate the size range of rock blocks constructed the central uplift. The set of petrographical and petrochemical evidences was used to recognize possible "blocks," fragments of rock that were shocked and moved with a crater-forming flow with minor internal relative displacement. This set includes gneiss foliation angle, the level of shock and postshock thermal metamorphism, and the level of mechanical damage. The preliminary analysis of the recovered core from the borehole at the central mound reveals the blocky structure of subsurface uplifted basement rocks. At depths from 1.8 to 3 km possible block sizes vary from 50 to 200 m with an average size about 100 m .Below 3 km we see larger blocks of 200 to 400 m. Below 4.2 km up to the final depth of 5.4 km the drill hole run inside one block or uniform basement. The average ratio of the total breccia sections length to the total block sections length is about 1:3. Numerical simulations [7] modeled shock waves passage and the transient cavity growth and collapse in the gravity field now is reconsidered in terms of a discrete block motion with observed dimensions of blocks. Acknowledgments: The work is partially supported by the International Science Foundation (grant # M9S00). References: [1] Melosh H. J. (1977) in Impact and Explosion Cratering, 1245-1260, Pergamon, New York. [2] McKinnon W. B. (1978) Proc. LPSC 9th, 3965-3973. [3] Melosh H. J. (1989) Impact Cratering: A Geologic Process, Oxford, New York, 245 pp. [4] Melosh H. J. (1979) JGR, 84, 7513-7520. [5] Melosh H. J. (1982) JGR, 87, 371-380. [6] Pevzner L. A. et al. (1992) LPS XXIII, 1063-1064. [7] Ivanov B. A. (1994) in GSA Spec. Pap. 293, 81-91.
Ivanov Boris A.
Kirjakov A. F.
Kocharyan G. G.
Kostuchenko V. N.
Pevzner Lev A.
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