216-2 Provenance of Detrital Monazite in Tertiary Coastal Plain and Modern Fluvial-Marine Sediments Based on Regional Monazite U-Pb Geochronology and Monazite Fertility of Blue Ridge-Inner Piedmont Crystalline Rocks (TN-SC-NC)

Session: Geochronology of Critical Mineral Deposits with Special Reference to U-Th-Pb Dating of Common-Pb-Rich Minerals

Presenting Author:

Riley Grove

Authors:

Grove, Riley¹, Ramsey, Abagle², Boege, Katelyn³, Moecher, David⁴, Thigpen, Ryan⁵, Mittwede, Steven⁶, Massey, Matthew⁷, Samson, Scott⁸, O'Brien, Timothy⁹

(1) Department of Earth & Environmental Sciences, University of Kentucky, Lexington, KY, USA, (2) Earth & Environmental Sciences, University of Kentucky, Lexington, KY, USA, (3) Earth & Environmental Sciences, University of Kentucky, Lexington, KY, USA, (4) University of Kentucky, Lexington, KY, USA, (5) University of Kentucky, Lexington, KY, USA, (6) Randolph School, Huntsville, AL, USA, (7) Kentucky Geological Survey, Lexington, KY, USA, (8) Syracuse University, Syracuse, NY, USA, (9) U.S. Geological Survey, Reston, VA, USA,

Abstract:

Decades of research by the USGS explored the occurrence of monazite as a Th and U resource in crystalline basement rocks and clastic systems of the southeastern U.S. Recent world economic developments bring these deposits into focus as potential REE critical mineral resources. Ce anomalies (a proxy for monazite abundance) based on the NURE database define two belts of monazite-enriched crystalline basement rocks (Eastern Blue Ridge and Inner Piedmont) paralleling a third Tertiary Upper Coastal Plain monazite belt. Monazite in potential Eastern Blue Ridge and Inner Piedmont belt crystalline source rocks and monazite from heavy mineral concentrates of first order streams in the region were systematically dated by U-Pb LASS-ICP-MS geochronology to (1) determine provenance of monazite in the Coastal Plain monazite belt and (2) assess fertility of potential ultimate crystalline source rocks. Monazite U-Pb ages in metamorphic rocks of the southern Appalachians delineate two distinct regions: exclusively Taconian (460-440 Ma) northwest of the Brevard Fault Zone (BFZ) or exclusively Neo-Acadian to Alleghanian (370-310 Ma) southeast of the BFZ (Thigpen et al. 2022, 2023 and this meeting). Monazite in thin sections of sillimanite-garnet-muscovite schist, biotite-plagioclase gneiss, and garnet metagranite of the Cowpens and Chesnee quadrangles (eastern Inner Piedmont) exhibits major Neo-Acadian/Alleghanian metamorphic with rare Acadian magmatic(?) age modes in metagranite. Heavy mineral concentrates (HMCs) panned from first order streams are dominantly ilmenite, sillimanite, and monazite, and monazite age distributions for HMCs are highly similar to bedrock samples. Ages are interpreted to correspond to the time of monazite growth during peak Neo-Acadian and retrograde Alleghanian tectonometamorphism. Metagranite and schists are the most monazite-fertile lithologies; biotite gneisses are the least fertile. Further research in progress will assess heavy mineral types/abundances in modern fluvial and coastal systems, expand the coverage of monazite dating in Piedmont basement rocks, and determine detrital monazite ages of sediment in (1) the modern Broad-Pacolet-Tyger-Enoree fluvial system; (2) Tertiary Upper Coastal Plain sediments paralleling the Fall Line; and (3) active coastal systems, in order to assess detrital monazite provenance in ancient and modern clastic systems of the southeastern US. Piedmont granites are also being dated by monazite and zircon U-Pb geochronology to determine crystallization ages of potential magmatic monazite source rocks and assess their monazite fertility.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8989

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