IRGHIZITES AND ZHAMANSHINITES: ZHAMANSHIN CRATER,USSR |
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| Authors: | VI Bouka P Povondra PV Florenskij Z &#x;anda |
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| Institution: | V.I. Bou?ka,P. Povondra,P.V. Florenskij,Z. ?anda |
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| Abstract: | Two irghizites, three zhamanshinites and one sample each of lechatelierite, vein-quartz, Palaeogene silty clay and Palaeogene quartzite were analyzed using neutron activation analysis. A silicate analysis of the Palaeogene silty clay has also been performed, as well as an incomplete analysis of the Palaeogene quartzite from the Zhamanshin impact crater. The REE abundances of irghizites resemble those of sedimentary rocks. On the Köhler and Raaz diagram all projection points of irghizites lie inside the field of tektites, and indicate that they were derived from terrestrial sedimentary rocks. The Zhamanshin impact glasses may be divided into three types: (a) silica-rich zhamanshinites (x?SiO2 = 73.89%), (b) zhamanshinites (x?SiO2 = 54.34%), and (c) silica-poor zhamanshinites (x?SiO2 = 39.64%). These are also characterized by varying proportions of alkalis and Al. Mn and Ca contents. Irghizites and silica-rich zhamanshinites display a depletion of Eu. Zhamanshinites do not show this Eu depletion. Partial melting is assumed to be an important process in the origin of zhamanshinites. |
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