DETRITAL TITANITE U-PB GEOCHRONOLOGY IN THE MISSISSIPPI AND THE OHIO RIVERS: A TECTONIC RECONSTRUCTION TOOL FOR PAST OROGENIC EVENTS?

In the past decades, the majority of provenance-related studies have relied on U­Pb dating of detrital zircon. However, because zircon is resistant to physical and chemical weathering, it can survive multiple sedimentary cycles, which can cause difficulties in distinguishing between proximal and ultimate sources. For instance, studies in the Mississippi river revealed that the detrital zircon age spectra are dominated by Grenvillian orogenic events, but other major events are not well recorded by the detrital zircons in this region. The limitations of using detrital zircon as a reliable sedimentary proxy to explain orogenic events have led to the exploration of other accessory minerals as provenance tools.

Recent studies have shown that detrital monazite may be a better alternative to zircon for recording past tectonic events. Because detrital monazite is rare compared to zircon, its utility could be limited in some cases. Other detrital minerals, more common than monazite, might also provide accurate reconstructions of tectonic events. Titanite could prove to be an additional useful mineral because of its relatively high initial U/Pb ratio, high U­Pb closure temperature, and its occurrence in a wide variety of lithologies. Unlike zircon, titanite crystallizes over a much broader temperature range, recording both metamorphic and magmatic episodes. To test the utility of detrital titanite U-Pb dating, samples of modern alluvium near the confluence of the Ohio and Mississippi rivers were collected. The Mississippi River drains much of North America as a result of its extensive tributary system. The Ohio River, a major tributary to the Mississippi River, drains the eastern portions of the USA, including part of the central Appalachians. U­Pb dates from 337 individual crystals from three samples were determined by LA-ICP­MS, and preliminary results reveal that, like zircon, Grenville orogenic events (1.2– 1.0 Ga) are well recorded. However, unlike zircon, detrital titanite ages also substantial peaks of Mesozoic to early Cenozoic ages (200-50 Ma). Additional samples collected further downstream have been processed and will be compared to the preliminary data. Initial results of this project suggest that detrital titanite could be an important additional accessory mineral for tectonic reconstruction studies.