DETRITAL PETROCHRONOLOGY FOR PROVENANCE ANALYSIS: U-PB AND RARE EARTH ELEMENT COMPOSITIONS IN ZIRCON FROM THE MODERN MISSISSIPPI/MISSOURI DRAINAGE BASIN

Petrochronology is an emerging field that combines geochronology and geochemical analysis. The application of this field is commonly used in igneous and metamorphic settings, however is not widely applied in sedimentary studies. To test the potential application of petrochronology, we present in-situ rare-earth element compositions and U-Pb ages of zircon from samples collected from modern channel and bank sediment from the major tributaries of the Missouri-Mississippi river system, including the: Upper Missouri, Yellowstone, Platte, Kansas, Red, and Lower Mississippi River. We present a data classification scheme that uses zircon Th/U values are used as a proxy for tectonic setting (i.e. compressional vs. extensional), zircon Ce/Ce* as a proxy for volatile content of source magmas, and U-Yb-Y to discriminate continental vs oceanic sourced zircon to compare the zircon record to known tectonic events throughout North America. Mountain building events correlate to highly variable Ce/Ce* values with lower Th/U (<0.75) values, while extensional events are only represented by sparse zircon. Zircon that are the age of Basin and Range extension (<45 Ma) contained lower Ce/Ce* (value) values and had an increasing Th/U trend (>0.75). The paucity of extensional zircon earlier in the North American detrital zircon record suggests that extensional magmatic events have lower preservation potential within the sedimentary record than orogenic mountain building events.