Broken-formations of the Pulaski thrust sheet near Pulaski, Virginia

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Virginia Polytechnic Institute and State University


Broken-formations (Hsu, 1974; Harris and Milici, 1977) occur in the lower part of the Pulaski thrust sheet and contain some of the most strongly deformed sedimentary rocks in the Valley and Ridge province of the southern Appalachians. Deformation in this zone ranges from grain-scale cataclasis to regional-scale faulting. The broken-formations are distinguished from rocks structurally higher on the sheet and from rocks of the underlying Saltville sheet by (1) a sharp increase in the variability of fold and fault styles, (2) greater ranges in fold plunges and dips of axial surfaces, (3) a low degree of preferred orientation of folds and faults, (4) an increase in the frequency of mesoscopic structures, and (5) the presence of Max Meadows tectonic breccia. Structural analyses indicate that deformation in the broken-formations is Alleghanian in age and that the deformed zone formed under elastico-frictional conditions, possibly under elevated fluid pressures with temporally variant stresses and that lithology may have played an important role in localizing the broken-formations along the base of the Pulaski sheet.