Structural Development of Northernmost Snake Range, Kern Mountains, and Deep Creek Range, Nevada and Utah

Abstract

Regional metamorphism of the lower part of a sequence of Precambrian through upper Paleozoic rocks produced a rigid mass (autochthon) from which the overlying sediments (allochthon) were detached and thrust east-southeast (105°-110°). The principal plane of movement in the northern Snake Range and Kern Mountains is the Snake Range thrust of Misch and Hazzard. A foliated marble with thick schistose members and boudinage zones occurs as the highest part of the autochthonous sequence. In the southern Deep Creek Range a reverse fault, whose southward movement is believed to have occurred prior to eastward thrusting, separates parts of the regionally metamorphosed succession. Draped over the thrust (upthrown) block of this fault is a 12,000-18,000-foot-thick sequence that consists of previously metamorphosed rocks overlain by unmetamorphosed rocks. This apparent drape folding and the fault to which it is related are part of the structural pattern associated with a recumbent, transverse anticline whose axis strikes east-west (175°) and plunges west. Slaty cleavage parallels the axial plane. The orientation of this anticline is similar to that of pre-Snake Range thrust fold axes within the foliated marble of the autochthonous sequence south of Pleasant Valley. Both the transverse anticline and the fold axes are presumed to be contemporaneous. The fold is truncated by a decollement thrust that occurs beneath upper Paleozoic rocks. This thrust may be the same as Nolan's North Pass thrust of the Gold Hill district. Major metamorphic, stratigraphic, and structural differences distinguish the Deep Creek Range from the Kern Mountains. The zone between these ranges is called the Pleasant Valley lineament. These differences developed prior to the eastward thrusting, and the decollement thrust beneath the upper Paleozoic rocks appears to extend across the lineament and become the Snake Range thrust. The cause of divergence is believed to be transverse folding, but could include a later strike-slip movement along the same trend. The latest structural events along the Snake-Deep Creek Range mountain belt are discontinuous arching, intrusion, and high-angle, normal faulting (Basin-and-Range type). The arches, intrusions, and faults are roughly parallel. In the vicinity of Pleasant Valley the arch has a sharp eastward flexure. On the flank of the flexure is a fault trough that widens eastward and contains a thick sequence of Tertiary rocks. This trough lies along the same trend as the Pleasant Valley lineament.