U-PB-DATING OF DETRITAL ZIRCONS APPLIED TO QUATERNARY SLOPE DEPOSITS: REGIONAL DIFFERENCES IN THE SOUTHWESTERN USA

We present a pilot study of the usability of U-Pb dating of detrital zircons (DZ), which is a well-established method in Geology for provenance analyses, on eolian components of colluvial slope deposits. We distinguish several layers of such deposits using a paleopedology-supported sequence-stratigraphic approach in several profiles and we attempt using the provenance of the zircons to reconstruct eolian transport directions. Therefore, we sampled several profiles within the Great Basin (GB) and Colorado Plateau (CP) and used U-Pb dating of the DZ. We found that the age variation of the GB zircons differs remarkably from the CP zircons, thus we can assign particular age peaks within the probability density estimates to a geographic area. We compared the GB and CP profiles against each other and can show that we miss signals from the southern orogens and the Uinta mountains (~ 1.2 and 1.7 Ga) in the GB samples, which we find in the CP profiles. However, we do have signals from the huge eruptions (~ 30 Ma) from the surrounding super volcano field only in GB profiles. Thus, we assume about the wind direction ~ 126 - 115 ka and ~ 50 ka in the CP. The main winds came either from the south or (less likely) from the north, but not from the west as modelled by various sources.