Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..532l&link_type=abstract
Meteoritics, vol. 30, no. 5, page 532
Computer Science
1
Classification, Moldavites, Tektites
Scientific paper
Tektites of unusual chemical or textural composition can give us clues to a range of source materials involved in the formation of the whole population of ejected glasses. Inhomogeneities of moldavites are well known [e.g. 1, 2]. There have been several reports on Muong Nong or layered tektites in the moldavite strewn field [e.g. 3]. In a systematical study of 69 specimens of Lusatia and also from the Czech subfields (Moravia, Bohemia, Radomilice) new glasses were discovered with unusual composition. To the etablished groups of: Normal moldavites (SiO2 76-80 wt%, CaO/MgO about 1.3) including the Bohemian (MgO > 1.5 wt%, CaO > 2 wt%) and Moravian (MgO < 1.5 wt%, CaO < 2 wt%) types, HSi-moldavites (> 80 wt% SiO2) which is common in the Radomilice subfield, HCa/Mg-moldavites (CaO/MgO > 2) first described by [4], HFe-moldavites (Fe-rich moldavites FeO > 2 wt% and SiO2 typically < 76 wt% reported by [5] and layered moldavite (one specimen described by [3], with textural similiarities to Muong Nong-type tektites),we want to add new types found at Jankov (Bohemia) and Trebic (Moravia), "MB-JKV12", which is characterized by two optically distinct components of distinct chemical composition: 1. low SiO2 and high FeO (dark colored) areas and 2. areas of normal moldavite composition (pale areas). The halogen content and Cl/Br ratio are similiar to layered tektites from Indochina [6]. Figure 1 displays the inhomogeneity of this sample in the chemical composition of the two areas and "MM-TRB1" a LCa/Mg-moldavite with an low CaO/MgO-ratio of 0.5. In a diagram Eu versus CaO most of the groups above can be discriminated. New REE-analysis of MB-CLM1 (a HCa/Mg type) done with ID-MS display a less pronounced negative Eu anomaly compared to a normal moldavite from the same locality (MB-CLM2). The high Ca and higher Eu content could be indicative of a higher proportion of plagioclas in the source of this specimen. Whereas the Moravia specimens are very homogenous in their element ratios, the Bohemian subfield contains the tektites of unusual composition and covers a large range in element abundances and ratios. Moldavites from the Lusatian population contain glasses of mainly normal Bohemian and Moravian composition and also cover a large range in composition. So far no tektites of unusual composition have been discovered in the Lusatian subfield. References: [1] Bouska V. I. and Konta J. (1986) Acta Univ. Carolinae, Geol. 1, 1-126. [2] Delano J. W. and Lindsley D. H. (1982) GCA, 46, 2447-2452. [3] Rost R. (1966) Acta Univ. Carolinae, Geol. 4, 235-242. [4] Delano J. W. et al. (1988) Proc. 2nd Intl. Conf. Nat. Glasses, 221-230. [5] Bouska V. I. and Cilek V. (1992) Vestn. Cesk. Geol. Ust., 67, 225-234. [6] Meisel T. et al. (1993) Meteoritics, 28, 397-398.
Lange Michael J.
Meisel Th.
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