TRACE ELEMENT FINGERPRINTING OF YELLOWSTONE HOTSPOT TRACK (YHT) MAJOR ERUPTIONS IN VOLCANIC ASHES FROM HIGH PLAINS STRATA IN KANSAS

Volcanic ash beds have been shown to be reliable stratigraphic marker beds because they can be reliably dated using magmatic minerals: e.g. zircon, sanidine etc. This is useful in any region containing ash beds, and can be especially helpful where beds are laterally discontinuous, such as in the Ogallala Formation in western Kansas. The formation contains abundant volcanic ashfall beds, but regional correlations of these have so far been limited, due to their non-continuous outcrops and complex stratigraphy. U-Pb dating of zircon by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at The University of Kansas from several ash outcrops shows that they correlate with Yellowstone hotspot track (YHT) eruptions. It has also been shown that volcanic glasses from individual eruptions exhibit unique geochemical signatures, therefore lending each eruption its own distinct geochemical fingerprint. This yields robust correlations between the ash beds in Kansas to their YHT source eruptions. We test the utility of trace element fingerprinting of glass shards by LA-ICP-MS from previously dated and undated ash beds in the Ogallala formation as a less labor-intensive alternative to zircon dating.

The YHT eruptions Lava Creek B (0.6 Ma), Huckleberry Ridge (2.1 Ma) of the Yellowstone Plateau and the Bruneau-Jarbidge (10.5-12.7 Ma) eruptive center of the Snake River Plain, have previously been correlated to ash beds in western and central Kansas using major and trace element concentrations. Ash samples were collected in Ellis, Smith, and Jewell Counties in Kansas. Trace element trends and Ti/Zr vs Ba data yields correlations of the Ellis and Smith county ashes to the Ibex Peak eruption (11.9 Ma) of the Bruneau-Jarbidge eruptive center when compared to published values. The same trace elements in glass from an ash bed in Jewell county correlate to Lava Creek B. The insight from this research into the provenance of volcanic glass will help further refine the understanding of dispersal of ash and other minerals from their associated eruptive centers, and the chronostratigraphy of the Ogallala Fm.