HIGH-RESOLUTION AEROMAGNETIC SURVEY REVEALS DISTRIBUTION OF FAULTS IN DIXIE VALLEY, NEVADA

A high-resolution aeromagnetic survey (200m line spacing, 120m instrument height) acquired in Dixie Valley reveals, in a manner not possible by other techniques, the pattern of faulting in a basin with ~2km of sediment fill and over 3km of structural offset from the Stillwater Range to the west. The magnetic anomaly map shows the same gross features as earlier regional aeromagnetic surveys, and in addition shows many subtle, northeast-trending, short-wavelength anomalies that reflect abrupt juxtapositions of basin-fill layers with differing magnetic properties within 0.5km of the surface. These subtle magnetic contrasts are enhanced after application of a method that separates local from regional gradients. Many of the northeasterly-trending, curving and branching anomalies revealed by this method correspond closely with faults mapped on the basis of subtle surface evidence (small scarps and graben in surficial sediments, linear arrangements of artesian springs, straight stream channels, and inexplicable lineaments), and provide a much more complete picture of the fault pattern than can be discerned from surface mapping alone. A system of synthetic faults near the Stillwater range front, and a system of antithetic faults on the opposite side of the basin surround a relatively unfaulted block in the deepest part of the basin. The new aeromagnetic data near the range front also support the controversial hypothesis that the structural displacement between the range and the basin is accommodated by a steeply-dipping multiple fault system, much of which is buried by basin sediments.