Paper No. 10
Presentation Time: 10:45 AM


ANFINSON, Owen A., Jackson School of Geoscience, University of Texas at Austin, 1 University Station Stop C1160, Austin, TX 78712, STOCKLI, Daniel F., Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712 and MILLER, Joseph C., Department of Geology, University of Kansas, Lawrence, KS 66045,

The sedimentary deposits of the Eocene to Miocene Northern Alpine Foreland Basin in Switzerland are well studied yet they lack thorough geochronologic analysis of detrital zircon and rutile. The tightly constrained depositional ages of the strata provide an excellent opportunity to use detrital zircon and rutile U-Pb ages and trace element data to elucidate the tectonic activity of the central Alpine Orogen from the late Eocene to middle Miocene.

The sedimentary strata of the central Northern Alpine Foreland Basin are characterized by two upward coarsening mega-sequences that are divided into five lithostratigraphic units: late Eocene North Helvetic Flysch (NHF), early Oligocene Lower Marine Molasse (LMM), late Oligocene to early Miocene Lower Freshwater Molasse (LFM), early Miocene Upper Marine Molasse (UMM), and middle Miocene Upper Freshwater Molasse (UFM). Over 2000 detrital zircon U-Pb ages from the Eocene to Miocene strata are primarily dominated by recycled basement ages of the Cadomian, Caledonian and Variscan Orogens. Although the external massifs containing these basement ages within the central Alps are spatially abundant, provenance changes are distinguished by the transition from a dominant source of Cadomian and Caledonian basement in the NHF, LMM, and lower LFM to dominantly Variscan in the upper LFM, UFM and UMM. The NHF is the only unit with an abundance of Tertiary ages clustering around 35-37 Ma. While analyzing for detrital zircon U-Pb ages with the LA-ICPMS, select samples were split-streamed to a second ICPMS to determine trace element concentrations of the detrital zircons. The trace element data provide a link between composition and genesis of the zircon.

Similar to zircon, rutile is one of the most stable detrital minerals within a sedimentary system and individual grains contain an informative geochronologic and trace element signature. Rutile U-Pb ages were analyzed to determine if mid-crustal detritus of Tertiary age was available to the sediment budget of the central Northern Alpine Foreland Basin during growth of the central Alps. The detrital rutile U-Pb results are dominated by Variscan ages and almost completely lack younger ages. Rutile trace element geochemistry is still ongoing.