New geochemical results indicate a non-alpine provenance for the Alpine Spectrum (epidote, garnet, hornblende) in quaternary Upper Rhine sediment

Our results show that the provenance of garnet, mostly pyrope-rich almandine is grain-size dependent. Particularly the pyrope content indicates that the 0.063-0.25 mm size fraction has an Alpine provenance whereas 0.25-0.5 mm grains derived from the Black Forest and the Vosges, which flank the Upper Rhine Graben. They mainly comprise of Paleozoic metamorphic and igneous rocks supplying a suite of heavy minerals similar to the Alpine Spectrum to the Rhine river. Amphibole, mostly Mg-hornblende, has an increasing TiO2 content from the south to the north of the graben, which also indicates an input from the graben shoulders. The new data indicate that the so-called Alpine Spectrum of heavy minerals in Rhine river sediment of the upper Rhine derived to significant degrees from non-Alpine sources. Furthermore, our results indicate a relatively uniform provenance for the Rhine River system during the past 1 Ma.