Collaborative Research: "Double-Double Dating" of Detrital Monazite and Detrital Zircon: Quantifying Sediment Recycling in Tectonic Studies

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Many geoscientists have suggested that it is likely that sedimentary rocks are "recycled", i.e. sediment is first eroded from pre-existing sedimentary rocks, gets placed back into the hydrologic cycle, and then is once again deposited into a basin to become a new sedimentary rock. Although this is an important suggestion, there are limited data that quantify to what degree this process occurs. This research will test a new approach, using a novel and relatively inexpensive method utilizing chemical analysis and dating of uranium and thorium isotopes in order to provide this needed quantitative data. If these new methods are successful, they can be used by a wide variety of scientists to develop a much better understanding of the history of a sedimentary basin - information critical not only to academic scientists but to those in both the petroleum and economic minerals industry as well. In addition to the scientific goals of the research, the project train undergraduate and graduate students in an important STEM (science, technology, engineering and mathematics) discipline, thus contributing to the education of the next generation of scientists. In addition, it will provide outreach to high schools for pathways for high school students to go into the earth sciences in both central New York and Kentucky, and will also facilitate the development of teaching modules for teachers and students based on the results of the research. Results of the research will be disseminated as peer-reviewed publications and as presentations at professional society meetings. Analytical data will be made available through publicly accessible online databases.Consideration of sediment recycling in tectonic studies is critical for accurate assessment of tectonic reconstructions such as terrane movement and collisional histories. Preliminary research indicates that some detrital monazite grains exhibit textural evidence of having formed diagenetically in an older clastic sequence (i.e. detrital diagenetic monazite) and therefore must be recycled. The principal investigators suggest that the detrital diagenetic grains are readily distinguishable, based on textures and ages, from detrital monazite derived from crystalline rocks in the source terranes. This project will test the effectiveness of this rapid approach for detecting recycling compared to the much more expensive and labor intensive method of "double dating" detrital zircon (i.e. Uranium-Lead geochronology combined with (Uranium-Thorium)/Helium thermochronology of the same crystal). The principal investigators will perform textural analysis, using backscatter electron imaging of monazite crystals, to characterize grains identified as diagenetic detrital monazite versus detrital metamorphic/igneous monazite. These grains will then be dated using Thorium-Lead geochronologic techniques followed by (Uranium-Thorium-Samarium)/Helium dating to quantitatively establish if our rapid, qualitative approach is valid. The researchers will also determine the Neodymium isotopic composition of the dated single monazite grains to determine if this is a new and useful approach to expand sedimentary provenance information. The isotopic methods will be applied to Neoproterozoic and Paleozoic sedimentary strata from the eastern United States.