A Revised Interpretation of 3D Seismic Data, Hawthorne Army Depot, Nevada: Faulted-Basin Reflections or Sill Intrusions?

Abstract

The Walker Lake Domain (WLD) of the Walker Lane contains the dextral strike-slip faults characteristic of the Walker Lane but also includes N-NNW striking normal range-front faults, the primary controls on geothermal systems in Nevada according to Surpless and Faulds. A 3D seismic reflection survey collected in 2001 by the Navy Geothermal Programs Office near Hawthorne, Nevada within the WLD reveals strong east-dipping reflectors intersected by strong synclinal reflection bands previously interpreted as migration artifacts. Similarities of these reflections to sill intrusions revealed in the North Sea by Thomson & Hutton have guided a reinterpretation of sill intrusions or lopoliths within the range-front faulted zone, as mapped in other WLD ranges by Valentine & Krogh. Stress models suggest that as magma intrudes, it becomes suspended at its level of neutral buoyancy but then can migrate up the normal fault forming structures similar to features within the 3D Navy data. Characteristics for sill intrusions present within these data include strong cohesive reflections that abruptly stop and uplifted sediments above bowl-like anticlines. However, no well data exist yet to correlate these features. Dip calculations based on a range of possible velocity models reveal a 22- to 40-degree dip range on the range-front normal fault. This 3D survey provides a rare opportunity to examine characteristics of possible sill intrusions within the Great Basin that have no surface exposure, as well as characteristics of Great Basin range-front faults.