CONSTRAINTS ON THE MAGNITUDE AND RATE OF PLIOCENE TO RECENT SLIP ALONG THE LEFT-LATERAL COALDALE FAULT, CENTRAL WALKER LANE BELT, NEVADA

Geodetic investigations have shown that ~25% of the Pacific-North American plate motion is currently accommodated to the east of the Sierra Nevada block within the ~N40°W striking right-lateral Walker Lane belt. The central portion of the Walker Lane belt, known as the Mina deflection, is characterized by several large pull-apart structures that are structurally controlled by active NE-trending normal faults and few EW-trending left-lateral faults, kinematically linking the right-lateral northern and southern segments of the Walker Lane belt. The most prominent E-W trending faults in the southern portion of the Mina deflection is the left-lateral Coaldale fault, which extends from the Queen Valley pull-apart structure at the northern termination of the Owens Valley fault system eastward to the southwestern corner of the Columbus Salt Marsh pull-apart basin. This study presents new data on the magnitude, timing, and rate of slip along the Coaldale fault, motivated by the need for the better spatial and temporal understanding of slip transfer across the central portion of the Walker Lane belt. The late Cenozoic stratigraphy adjacent to the trace of the fault primarily consists of Pliocene basalts and andesitic volcanic breccias that overlie rhyolitic tuff, tuffaceous sandstone, and lacustrine diatomite. These deposits unconformably overlie Oligo-Miocene conglomerate, sandstone, and ignimbrite in the Volcanic Hill and Miller Mountain areas. Detailed kinematic analyses and reconstructions of offset Pliocene volcanic units constrain the magnitude of left-lateral slip to ~1.5-2 km since ~3 Ma, suggesting a time-integrated Pliocene to recent left-lateral slip rate of ~0.5-0.7 mm/yr. Additional samples of faulted and offset basalt and rhyolite are in the process of being radiometrically dated and geochemically characterized to refine the magnitude and rates of fault slip along the Coaldale fault. Geomorphic features, such as offset stream drainages and shutter ridges indicate active left-lateral displacement along the Coaldale fault, despite the lack of evidence for Holocene surface ruptures. Our preliminary data implies that the Coaldale fault transfers a significant amount of strain from the northern Owens Valley eastward into the Columbus Salt Marsh region and the northern Walker Lane belt.