THE PROVENANCE OF THE CRETACEOUS KAIPAROWITS FORMATION THROUGH ANALYSIS OF THE CORDILLERAN ARC ZIRCON GEOCHEMICAL SIGNATURE

The Cordilleran arc is currently exposed in eastern California, and was active between ~250 and 65 million years ago. Deposition of arc material within the Kaiparowits Formation in southern Utah occurred ~77-74 million years ago by means of river transport and volcanic ash fall. Zircons can provide a record of the chemical composition of the host magma through their accumulation of trace elements. These elements can be compared to other zircons throughout a magmatic arc to gain a broader, more comprehensive understanding of its geochemical changes through time. Significant geochemical variations in zircon throughout the Mesozoic Cordilleran arc divide it into the Sierran sector in the north and the Mojave sector in the south. Zircon geochemistry measured by RG-SHRIMP (Stanford-USGS) and LA-ICPMS (UCSB) was used to assess the provenance of the Kaiparowits Formation building on an earlier interpretation that sediments were dominantly derived from the southwest.

High U/Yb ratios indicate that Mesozoic zircons in the Kaiparowits Formation zircons are typical of continental crust. The trace element compositions are similar to compositions within the Cordilleran arc, but show a light rare earth element enrichment where Ce has a high concentration more similar to zircons from the Mojave arc sector. The zircons were also compared stratigraphically to look for changes in trace element trends, though no strong correlations were found. Similar trace element data between the Kaiparowits Formation and the Mojave sector of the Cordilleran arc support a southwest sediment origin and drainage from the Mojave region due to uplifts of the Sevier orogenic belt blocking drainage from the north and west.