The crystal chemistry of detrital chromian spinel from the Southeastern Alps and Outer Dinarides: the discrimination of supplies from areas of similar tectonic setting?

Chromian spinel is a common heavy mineral in the fl ysch basins of the southeastern Alps and Outer Dinarides. Various tectonic settings have been found for the suites of chromian spinel studied herein, related to suprasubduction for both Internal and Outer Dinarides, and ocean-fl oor-spreading zones for the Outer Dinarides. Because the composition of the chromian spinel cannot discriminate between the two areas, we performed crystallochemical studies in order to fi nd some differences. These studies show that it is possible to discriminate between the suprasubduction zones of the Outer and Inner Dinarides by means of the positional parameter u of the oxygen atom, which is close to 0.2625 for spinel grains from Outer Dinarides and greater than 0.2626 for spinel grains from Inner Dinarides. Intracrystalline temperatures ranging from 790 to 1050°C have been calculated for spinels with u close to 0.2625, and 730 to 750°C for those with u higher than 0.2626. These temperatures are consistent with those calculated for Outer and Inner Dinarides, respectively.