Structural controls, alteration, permeability and thermal regime of Dixie Valley from new-generation MT/galvanic array profiling

Philip E. Wannamaker

关键词: AVAILABILITY;    BASEMENT ROCK;    COTTONWOODS;    FEEDING;    FUMAROLES;    GEOTHERMAL FLUIDS;    PERMEABILITY;    RESOLUTION;    STREAMS;    SUBSURFACE STRUCTURES;    VALLEYS;    WAVE PROPAGATION magnetotellurics;    dixie valley;    inversion;   

DOI  :  10.2172/920085
RP-ID  :  DOE/ID/14416-1
PID  :  OSTI ID: 920085
Others  :  TRN: US200825%%418

学科分类：再生能源与代替技术

美国|英语

来源: SciTech Connect

【 摘 要 】

State-of-the-art MT array measurements in contiguous bipole deployments across the Dixie Valley thermal area have been integrated with regional MT transect data and other evidence to address several basic geothermal goals. These include 1), resolve a fundamental structural ambiguity at the Dixie Valley thermal area (single rangefront fault versus shallower, stepped pediment; 2), delineate fault zones which have experienced fluid flux as indicated by low resistivity; 3), infer ultimate heat and fluid sources for the thermal area; and 4), from a generic technique standpoint, investigate the capability of well-sampled electrical data for resolving subsurface structure. Three dense lines cross the Senator Fumaroles area, the Cottonwood Creek and main producing area, and the low-permeability region through the section 10-15 area, and have stand-alone MT soundings appended at one or both ends for local background control. Regularized 2-D inversion implies that shallow pediment basement rocks extend for a considerable distance (1-2 km) southeastward from the topographic scarp of the Stillwater Range under all three dense profiles, but especially for the Senator Fumaroles line. This result is similar to gravity interpretations in the area, but with the intrinsic depth resolution possible from EM wave propagation. Low resistivity zones flank the interpreted main offsetting fault especially toward the north end of the field which may be due to alteration from geothermal fluid outflow and upflow. The appended MT soundings help to substantiate a deep, subvertical conductor intersecting the base of Dixie Valley from the middle crust, which appears to be a hydrothermal conduit feeding from deep crustal magmatic underplating. This may supply at least part of the high temperature fluids and explain enhanced He-3 levels in those fluids.