14-10 Single crystal 40Ar/39Ar ages for muscovite from the southern Appalachian and Ouachita Orogens with implications for their Carboniferous foreland basins, drainage networks and tectonic histories of their source terranes

Session: New Research in the Appalachian-Ouachita Orogen: Integrated studies from the Foreland to the Hinterland

Presenting Author:

Authors:

Abstract:

Please note: authors are listed alphabetically, and references provided are for Auburn University M.S. theses.

Many studies have proven laser single-crystal ⁴⁰Ar/³⁹Ar dating of muscovite provides a relatively robust, reliable and useful tool in detrital geochronology. Muscovite from Mississippian sandstones of the Black Warrior Basin (BWB; Moore, 2012) and the Ouachita-Arkoma Basins (OAB; Thompson, 2019) yield age distributions with similar modes of ca. 445 and 365 Ma. However, they differ in that the Mississippian BWB contains a prominent 320 Ma mode that the OAB samples lack, and the Mississippian OAB samples have age distributions that are more complex with subordinate modes of 400, 465, 480, and 510 Ma. Stratigraphically lower Pennsylvanian arenitic sandstones of the BWB have clearly defined 445 and 365 age modes that come to include a 320 Ma mode in higher sections (Moore, 2012). In contrast, the Pennsylvanian OAB samples lack a 320 Ma mode (Thompson, 2019). For a given Mississippian to Pennsylvanian BWB sample from Moore (2012), the youngest muscovite single-crystal ages are approximately the same as the (high-resolution cyclostratigraphic) depositional age, indicating their combined time for exhumation and sediment residence to deposition was ~ 1 Ma or less.  Muscovite from metamorphic rock in outcrop exposures of the Western Blue Ridge is generally 335-290 Ma, with most ages clustering around 320 Ma, and muscovite sampled from sediment in modern rivers with WBR catchments (French Broad, Etowah, and Coosa rivers) have a similar, pronounced and single 320 Ma mode that skews to ages ranging up to ca. 400 Ma (Fan, 2016). Collectively, the 445, 365 and 320 Ma age modes are interpreted to correspond with culminating stages for metamorphism of the Laurentian margin during Taconic, Neoacadian and Alleghanian tectonic events. The lack of Alleghanian muscovite age signature in the OAB, and in the lower Pennsylvanian mature arenites of the BWB, are consistent with large-scale longitudinal transport of sediment to them from terranes within the northern Appalachians.  The presence of Alleghanian muscovite in other Pennsylvanian samples of the BWB (a stratigraphically lower immature litharenite and higher, more mature arenites) is evidence of local sources terranes, comparable to the modern outcrops and detritus of the WBR, and of transverse Carboniferous drainage networks with catchments in a steep and mountainous Alleghanian orogenic front.

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.