TRANSITION BETWEEN BASIN AND RANGE EXTENSION AND WALKER LANE DEXTRAL MOVEMENT IN THE GILLIS RANGE, MINERAL COUNTY, NEVADA

The geology of the northwestern Gillis Range, Mineral County, NV is characterized by a structural regime with both normal dip slip and dextral strike slip shear zones. Lithologic dip directions in the range are either southwest or east depending on proximity to the Walker Lane dextral shear zone. Previous interpretations by Hardyman (1978 and 1980) relate rotation of Tertiary ash flow units on listric detachment faults related to dextal movement along the Walker Lane Shear Zone. This appears to be the case in the eastern portion of the range proximal to large dextral shear zones. Structural analysis of outcrops of both Tertiary ash flow units and presumably high-angle dikes and hydrothermal vein sets in the Mesozoic Gillis Pluton along the western edge of the range, distal to the major, high-angle shear zones indicate consistent dips, possibly caused by 30°-40° southwest rotation on east-dipping listric normal faults, similar those in the nearby Yerington district. The Gillis Range thus contains the transition zone between middle Tertiary extension and late Tertiary Walker Lane dextral shearing.