Lithotectonic Units in the Golconda Allochthon, Nevada
TOMLINSON, ANDREW J., Stanford University, Stanford, CA, and BENITA L. MURCHEY, U.S. Geological Survey, Menlo Park, CA
The Golconda allochthon can be divided into several regional lithotectonic units. Each consists of an imbricate thrust stack of similar, but variably deformed, depositional sequences and represents a paleogeographic-depositional province of the basin(s) that existed prior to the Sonoma orogeny.
At least four lithotectonic units are recognized. (1) An eastern unit exposed in the Toiyabe, Monitor, and Shoshone Ranges, and Shoshone Mountains consists of Upper Mississippian(?) to Middle Pennsylvanian chert, Middle Pennsylvanian to Lower Permian argillite and calcarenite turbidites, and Permian phosphatic sandstones, calcarenites, and chert. (2) The second unit is exposed in the Shoshone Range and Mountains and Battle Mountain and consists of Middle Pennsylvanian greenstone, Middle Pennsylvanian to Lower Permian argillite and minor chert, middle Leonardian calcarenite, upper Leonardian chert and minor phosphatic, chert- and volcanic-lithic-rich sandstone, and Upper Permian sponge spicule chert turbidites. (3) The third unit is exposed in the Tobin Range, Edna Mountains, East Rang , Fish Creek Mountains, and above the Willow Creek Canyon thrust in Battle Mountain. This unit consists of Lower Mississippian basalts, Upper Mississippian to Middle Pennsylvanian clastic rocks and radiolarian chert, and Lower Permian calcarenites and calcareous sandstones. (4) The fourth unit consists of Mississippian to Permian volcaniclastic rock-bearing sections in the New Pass and Toiyabe Ranges, and includes the Mina Formation.
Units 1, 2, and 3 have rocks indicating they were deposited within or adjacent to the continental margin. Rocks in unit 4 have a volcanic terrane affinity. In each lithotectonic unit the youngest rocks of Leonardian or Guadalupian age are involved in the deformation and are conformable or paraconformable on older rocks indicating the shortening history in the allochthon is entirely post-deposition and represents a short-lived Permian-Triassic event.
AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)