engleski

Changing heavy mineral associations along the Outer Dinaric Eocene flysch belt: evidence for different structures along the rising Dinarides

The Outer Dinaric coastal belt is dominated by thick Mesozoic to Paleogene platform carbonates, which are followed by Eocene flysch deposits and subsequently by various Eocene to Lower Oligocene clastics. Neogene lacustrine sediments are found only in small patches. The Eocene flysch trough streched all along present-day eastern Adriatic coastal belt. The flysch sediments are preserved in isolated areas as remnants of different sizes. The flysch is represented by gravity-flow deposits including debrites and turbidites, as well as hemipelagic marls. Sporadic carbonate gravity-flow intercalations stand out from the uniform successions of sandstones and marls. The age of the flysch ranges from the Middle Lutetian to the Priabonian. The largest flysch areas are located in Istria, Zadar environs (northern Dalmatia) and Split environs (Middle Dalmatia), which represent a 250 kn long portion of the former flysch trough. The flysch deposits in these three areas have been studied giving special attention to the heavy mineral associations in sandstone beds, as to identify differences in the composition of the source areas. The main results are shown below (ZTR = zircon+tourmaline+rutile): Istria - Main constitents: garnet, ZRT, chromspinel. Other constituents (<2%): mostly chloritoid. Zadar - Main constituents: garnet, ZRT, chromspinel. Other constituents (~15%): dominated by epidote group, titanite, staurolite. Split - Main constitents: hornblende, garnet, epidot group. Other constituents (~30%): mainly ZRT (7%) and augite (7%), less common diopside, tremolite, hyperstene, titanite, chromspinel, staurolite, disthene and some others. The three flysch areas have several heavy mineral species and groups in common: garnet, ZRT group and chromspinel. However, these areas differ from one another in (1) the proportion of these minerals, which decrease going SE, and (2) the proportion of other mineral species, including predominant "metamorphic" minerals, increases going in the same direction. The changes in the heavy mineral associations appear to occur gradualy going SE. The changes in heavy mineral associations from the NW to the SE reflect a difference in relevant source areas situated along the rising Dinarides of that time. The Dinaric hinterland of the Istrian part of the Eocene flysch trough differed in composition from the Split hinterland, which is envisaged to have additionally comprised important sources of particles of metamorphic origin, which did not exist to the NW. Hence, the structural evolution of the Dinarides was not uniform along the rising chain.

heavy minerals; flysch; Dinarides; Eocene

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