New constraints on the Polish moldavite finds: a separate sub-strewn field of the central European tektite field or re-deposited materials?
Abstrakt
Moldavites are known to occur in several geographically limited areas in Central Europe: South Bohemia, Western Bohemia (Cheb Basin), Western Moravia, the Horn area in Upper Austria, and Lusatia in Germany. In addition to these traditional finds, Central European tektites (CET) have recently been identified in Neogene sediments at three places in Lower Silesia in Poland.
Sandpits near Rusko and Mielęcin represent the most remote localities from the Ries impact structure with the distance of about 475 km. The previously published data were limited to electron-microprobe analyses of four specimens.
Here we provide additional compositional data for a single moldavite from the North Stanisław sandpit near Rusko. Combined data of electron microprobe (EPMA; major elements) and laser-ablation inductively-coupled- -plasma mass spectrometry (LA-ICP-MS; minor and trace elements) provide new insights into chemical variability of CET.
Electron-microprobe analyses supplemented with back-scattered electron images showed marked chemical heterogeneity of the Polish moldavite on the micrometre scale, confirmed also by LA-ICP-MS. The major-element composition of the volumetrically dominating glass of the specimen is indistinguishable from the majority of c. 5000 available EPMA analyses of moldavites from other regions and, consequently, it does not provide any unambiguous link to any of these sub-strewn fields.
Rare schlieren in the sample with unique Ca-Mg-rich composition have counterparts among several South Bohemian moldavites. In general, Polish moldavites are small (less than 0.5 g) irregular fagments or splinters of angular shape with multistage sculpturing.
Their morphological character and paleogeography of Central Europe in the last 15 Myr suggest that they were redeposited at time of the Gozdnica Fm. sedimentation from yet unknown sub--strewn field north of the Sudetic Mountains.