Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.497m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 497
Computer Science
Geochronology, Glass, Hypervelocity Impact, Meteorite Craters, Strontium Isotopes, Chemical Composition, Geomorphology, Petrography, Textures, Weathering
Scientific paper
In 25 rock and glass samples from Zhamanshin impact crater, Kazakhstan, the Sr isotopic composition and Sr/Rb ratio were studied. All glasses irrespective of their chemical composition, texture, and morphology are plotted in the field restricted by the Rb-Sr characteristics of target rocks that confirms with confidence their impact origin. At the same time the identification of these glasses with certain types of target rocks is often difficult due to their variety. The Rb/Sr system of terrigenous target rocks series was subjected to alteration, probably caused by weathering in the Mesozoic. The comparison of this alteration with petrographic composition shows that it is most intensive in argillaceous and clayey-mica slates and is insignificant in quartzites. The correlation between Rb/Sr and Sr-87/Sr-86 ratios observed for terrigenous rocks does not correspond to any real age. A separate group of points corresponds to the age of approximately 600 m.y. and represents shocked quartz-chlorite shists regarded as greenstone series. Basic volcanic rocks, as well as impact glasses corresponded to composition and plotted in the compact swarm. This proves their origin by impact melting of these volcanics. Acid zhamanshinites form a compact separate group with similar Rb/Sr ratios and isotopic composition of Sr. This may indicate the significant participation of these acid volcanics in the origin of acid zhamanshinites. Strong dispersion of Rb/Sr characteristics of acid zhamanshinites and acid irghizites may be caused by broadly manifested mixing process of melts originated from different target rocks. Intermixture in different proportions of all types of target rocks may be responsible for all observed compositional differences of originated impact glasses. The results of this study coincide well with the data obtained from two irghizite samples in earlier investigation.
Karpinsky A. P.
Masaitis Victor L.
Shergina J. P.
Shkarbatova G. S.
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