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Modal and zircon typology analyses as provenance indicator of Late Miocene sands from Vrtlinska locality (Moslavačka Gora, SW Pannonian Basin, Croatia)

In the southwestern part of the Pannonian Basin huge quantities of sand detritus was deposited during the Late Miocene. There are two different opinions regarding the provenance of these sand deposits which associate the detritus either with a local source or with a universal regional source located outside of the study area. The first opinion is based on the modal composition of the sands and a correlation to the composition of nearby hills and mountains, build up mainly of granites and metamorphites (i.e. Blašković, 1982 ; Krkalo, 1998). However, Šimunić & Šimunić (1987) and Kovačić & Grizelj (2007) point out a uniformity in modal composition and textural maturity of sands from the wider area and connect their origin to the weathering processes of older sedimentary and metamorphic rocks in distant sources. Paleogeographic reconstructions of the Pannonian Basin evolution (i.e. Magyar et al., 1999) together with paleotransport measurements (Kovačić & Grizelj, 2007) suggest transport of material from the north. Moslavačka Gora is located in the SW part of Pannonian Basin and its crystalline core is composed of granite and metamorphic rocks (Korolija et al., 1986). That core is enveloped with Neogene and Quaternary sediments. Late Miocene white colored sand deposits up to 70 m thick can be found near the village Vrtlinska on the western slope of Moslavačka Gora (Krkalo, 1985). Modal composition of these sands shows predominance of quartz and feldspars as well as dominance of epidote, garnet, staurolite, kyanite, tourmaline and zircon in the heavy mineral association. A mineralogical peculiarity of the heavy mineral association from the Vrtlinska sands is the presence of andalusite. In comparison with other sands from the SW Pannonian Basin Vrtlinska sands contain non-weathered feldspars and increased quantities of zircons. Weathering of granitic rocks can produce a huge quantity of feldspars, which in circumstances of short transport may remain fresh, even in the warm and humid Late Miocene climate. Also, the peraluminous granites of Moslavačka Gora contain andalusite, tourmaline and zircon (Pamić et al., 1984 ; Pamić, 1990). So, it is a reasonable assumption that the Moslavačka Gora granites represented the source rocks for these sands. Comparison of zircon typology reveals a striking similarity and further strengthens the connection. However, occurrences of kyanite and staurolite in the Vrtlinska heavy mineral association can not be connected with a local source. These minerals are present in all Late Miocene sands in the SW Pannonian Basin and point to the uniform regional source (Kovačić & Grizelj, 2007). Modal and zircon typology analyses show that Late Miocene sands from the Vrtlinska locality on Moslavačka Gora contain combined detritus of local and regional source. Presence of local detritus implies that Moslavačka Gora was above Pannonian Lake water levels in the Late Miocene.

: modal analysis; sand; zircon typology; provenance; Late Miocene; Moslavačka Gora; Pannonian Basin; Croatia

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