Insights from combined detrital monazite geochronology and Nd isotopic composition on recording tectonic events and quantifying sedimentary recycling
Abstract
Minerals chosen for provenance studies are typically those that are resistant to resetting during low-moderate temperature metamorphic events and thus preserve information about their source region. However, minerals that are extremely resistant to weathering (e.g. quartz, zircon) can be recycled, often multiple times, and thus can cause confusion about the amount of material derived from immediate sources versus those from the original source region. Resistant minerals, such as zircon, that generally only form under very high temperature events (i.e. magmatic events) often miss recording orogenic events that are dominated by moderate temperature, magma-poor, metamorphic events. To overcome some of these difficulties we have analyzed detrital monazite from Modern alluvium and Pennsylvanian-Permian sandstones from the southern Appalachian Mountains for texture, U-Th-Pb age, and Nd isotopic composition. Previous studies have investigated these units, and related ones, using U-Pb dating of detrital zircon. Because monazite can form at temperatures much lower than that of zircon crystallization it is able to record lower grade metamorphic events in addition to original source signals, thus a more complete provenance analysis can be completed. The results from our detrital monazite U-Th-Pb analysis show a distinctly bimodal signature of both Grenville ages and Paleozoic ages. The significant amount of 300-500 Ma grains provides much more detailed information about the distinct stages of the Appalachian orogeny than any of the previous detrital zircon studies; U-Pb zircon dates in those studies were dominated by an overpowering Grenville (1 -1.2 Ga) signal. The Nd isotopic composition information allows for further distinction of sources within some of the more common age clusters. Where grains of the same age are typically assigned to one particular source, assuming no other information, dramatically different Nd values would indicate crystallization in a different source material. These dual detrital monazite characterization methods provide a high throughput work flow for detailed provenance as well providing additional information about sediment recycling. Such information is critical to a more comprehensive understanding of sedimentary systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP52A..02K
- Keywords:
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- 1051 Sedimentary geochemistry;
- GEOCHEMISTRYDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGYDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICS