Low-temperature deformation of sandstone, southern Appalachian fold-thrust belt

Abstract

Sandstone samples of Lower Pennsylvanian and Upper Mississippian units from a transect across the external southern Appalachian fold-thrust belt show variations in the relative abundances of the thin section-scale deformation mechanisms, including grain-boundary recrystallization, grain-boundary pressure solution, microfracturing, transgranular faulting, and cataclasis. The transect extends from the Sequatchie anticline in the northwest, crosses the Birmingham anticlinorium and the imbricate thrust belt, and ends in the Coosa deformed belt in the southeast. Thermal maturation data correlate to vitrinite reflectances of 1.0-2.0, the catagenic metamorphic regime. The deformation-mechanism abundances correlate with both position along the transect and proximity to thrust faults. Within a thrust sheet, 2%-11% of the grain boundaries are affected by recrystallization and 25%-29% by pressure solution in the samples from the external (northwestern) part of the transect, and 10%-14% by recrystallization and 47%-66% by pressure solution in the samples from the internal (southeastern) part of the transect. Regardless of location on the transect, fault-related damage zones are characterized by higher percentages (16%-48%) of grain-boundary recrystallization and 1%-19% transgranular deformation. The deformation-mechanism abundances thus prove to be sensitive indicators of regional structural position and deformation history.