FROM SOURCE TO SINK: A COMPARISON OF MUSCOVITE AGES FROM THE SOUTHERN APPALACHIAN BEDROCK AND CARBONIFEROUS BASIN

Orogenic sediment provides records of tectonic events that are otherwise obscured in hinterland exposures or removed by erosion or later stages of tectonism. In the case of tectonic studies of the active Himalayan orogen, laser single crystal ⁴⁰Ar/³⁹Ar ages of detrital muscovite have proven very useful for constraining the timing of multiple stages of tectonism and documenting nearly simultaneous exhumation, erosion and sedimentation of detritus from high-grade basement rocks. The ~ 1500 km-scale Alleghanian foreland basin (Pottsville Formation and associated units) is comparable to modern-day Himalayan basins, with the greater Black Warrior Basin (GBWB) situated in an orogenic syntaxis comparable to the modern Bengal fan. The now-deeply eroded basement core of the Appalachians comprises the Western Blue Ridge (WBR), Eastern Blue Ridge and Inner Piedmont (EBR/IP) and Carolina Superterrane, that formed through superimposed events that span the Paleozoic. Considering many samples, we find detrital muscovite from the GBWB yields prominent age modes of ca. 450 Ma, 380 Ma, and 320 Ma, that correspond well with Taconic, Acadian, and Alleghanian events outlined by chronometers with high closure temperature in the WBR and EBR/IP by bedrock studies. Vertical age variations in deep sections of the GBWB appear to reflect rapid changes in source drainage patterns and synorogenic Alleghanian tectonism. We commonly find the youngest detrital mineral ages are within a few million years of the stratigraphic age of the Pottsville Formation, comparable to the record of rapid, modern Himalayan denudation and sedimentation. About 800 km to the north, samples of the Early Pennsylvanian Bottom Creek Formation in Virginia yield three Paleozoic age modes, with Ordovician and Devonian ages similar to those determined in the GBWB. The youngest age mode, in contrast, is ca. 360 Ma. We find that laser ⁴⁰Ar/³⁹Ar ages of muscovite from foliated granite and phyllite near the basal thrust of the WBR in southwest Virginia also yields ages of ca. 360 Ma. The difference between the prominence of ca. 320 Ma ages in the GBWB and WBR or Georgia, and the ~ 360 Ma ages in similar sequences from Virginia, could reflect a decrease in Alleghanian and increase in Neoacadian metamorphism northward in the WBR.