EVIDENCE FOR DEXTRAL SHEAR ALONG THE WESTERN MARGIN OF THE CARSON SINK: THE MISSING LINK BETWEEN THE CENTRAL AND NORTHERN WALKER LANE, WESTERN NEVADA

The Walker Lake and Pyramid Lake domains in the central and northern Walker Lane, respectively, contain systems of left-stepping, dextral faults that accommodate ~20% of the Pacific-North American plate motion. Between these two domains lies the Carson domain (CD) and large composite basin of the Carson Sink. Major NW-striking dextral faults have not been documented in the CD. Instead, ENE-striking sinistral faults are inferred to dominate the CD, with dextral shear presumably accommodated by modest clockwise rotation of fault blocks.

Recent detailed mapping and structural analysis in the NW part of the Carson Sink suggest, however, that major NW-striking dextral faults and ~90 deg clockwise rotations deform the eastern CD. Just SE of Fernley, NV, in the eastern Virginia Range (EVR), a thick sequence of 12-8 Ma volcanic and sedimentary strata are deformed into a broad WNW-trending anticline and subparallel subsidiary folds, which are cut by arrays of ~E-striking reverse and normal faults, ~N-striking normal faults, NW-striking dextral faults, and ENE-striking sinistral faults. The WNW-trending structural grain in the EVR gives way eastward in a relatively abrupt flexure to NNE-trending fault blocks, normal faults, and extensional folds typical of the northern Great Basin. This change in structural grain appears to represent a large, heretofore unrecognized oroclinal flexure induced by dextral shear in the Walker Lane. An earlier formed NNE-trending extensional anticline has probably been rotated ~90 deg clockwise into the WNW-trending anticline in the EVR and accentuated by ~N-S shortening in the Walker Lane, thereby accounting for the presence of both E-striking normal and reverse faults.

The oroclinal flexure may occupy a broad left step in the Walker Lane, with the Pyramid Lake fault dying out southward in the EVR and, to the east, a major dextral fault along the SW margin of the Carson Sink terminating northward. The latter appears to project southward into major NW-striking dextral faults in the central Walker Lane, including the Benton Spring and Agai Pah Hills faults. Thus, NW-striking dextral faults in the eastern CD may link the central and northern Walker Lane. Such faults are obscured, however, in the Carson Sink area by Pleistocene Lake Lahontan sediments and eolian reworking of such deposits in the Holocene.