Description

The Buckskin-Rawhide detachment fault separates a variety of Proterozoic through Cenozoic rock types from underlying mylonitic crystalline rocks. In the Swansea-Copper Penny area of the central Buckskin Mountains, the detachment fault defines a gently ENE-plunging synform. Upper-plate rocks are preserved in the synform, whereas lower-plate myloni tic crystalline rocks compose the flanking, topographically higher, ENE-trending antifonns. Mylonitization of lower-plate crystalline rocks was the result of ductile shearing along the down-dip projection of the Buckskin-Rawhide detachment fault early in its movement history. TWo assemblages of rocks are preserved in the upper plate of the Buckskin-Rawhide detachment fault in the Swansea-Cbpper Penny area: (l) Pre-Tertiary rocks, especially Paleozoic and Mesozoic metasedimentary rocks, are complexly deformed and have undergone greenschist-facies metamorphism. Metamorphism, folding, cleavage development, and tectonic interleaving of diverse rock types is interpreted to be the result of Merozoic thrust faulting. (2) A litholcgically diverse stratigraphic sequence of Miocene and upper Oligocene(?) volcanic and sedimentary rocks generally dips moderately to steeply to the southwest and is folded into two north-south trending, south-plunging anticlines.