Elemental and structural analysis of imapct melt-rocks and glass spherules

Elementni i mineralni sastav uzoraka stijena za koje se pretpostavljalo da su nastale iz impaktnih taljevina, analizirani su metodama TXRF, ICP-AES, PIXE i XRD, a staklene sferule i mikroskopske čestice analizirane su metodom :-PIXE. Za morfološku karakterizaciju površine i elementni sastav uzoraka u mikro-mjerilu korištena je metoda SEM-EDS. Analitičke metode TXRF, ICP-AES i PIXE primijenjene na istim uzorcima dale su usporedive rezultate. Elementne analize uzoraka stijena s otoka Krka, Raba i Cresa pokazale su da uzorci imaju heterogeni sastav i da nisu vulkanskog ni antropogenog porijekla. Elementni sastav analiziranih uzoraka ukazuje da su izvorišne stijene bile po sastavu slične lesu, te da bi mogli biti impaktno staklo iz predložene impaktne strukture na otoku Krku. Sferule permske starosti koje su po prvi put nađene, mogle su nastati uslijed impakta u današnjoj južnoj Kini. Sferule i mikrotektiti eocenske starosti vjerojatno su distalni izbačaj iz kratera Popigai (Rusija) i impaktne strukture Chesapeake Bay (SAD), dok su sferule miocenske starosti vjerojatno distalni izbačaj iz kratera Ries (Njemačka). Sferule pleistocenske starosti mogu potjecati iz predložene impaktne strukture na otoku Krku na što ukazuje njihov elementni sastav. Elemental and mineral compositions of suspected impact glass samples were analysed by TXRF, ICP-AES, PIXE and XRD methods. Glass spherules and microscopic particles were analysed by :-PIXE method. For morphological characterization of surface and elemental composition on micro-scale SEM-EDS method was used. Analytical methods TXRF, ICP-AES and PIXE applied on the same samples gave comparable results. The analyses of rock samples from Krk, Rab and Cres Islands documented their heterogeneous composition and denied their volcanic or anthropogenic origin. Elemental composition of analysed samples indicates their origin from rocks similar to loess by chemical composition and that they could represent impact glass from proposed impact structure on Krk Island. Spherules of Permian age, first reported herein, could originate from an unknown impact crater located somewhere in today's South China. Spherules and microtektites of Eocene age could be distal ejecta from Popigai crater (Russia) and Chesapeake Bay impact structure (USA), whereas spherules of Miocene age could originate from the Ries crater (Germany). Spherules of Pleistocene age probably originated from the proposed Krk impact structure as suggested by their elemental composition.