Abstract Title: Architecture, physical state and dynamics of the Great Basin as 
revealed through electrical conductivity structure under Earthscope 

Abstract Author(s): Philip E. Wannamaker, Univ. of Utah

Abstract: Electrical conductivity provides independent understanding of deep 
hydration, thermal regime, fluidization/melting, lithospheric-scale fabric and 
faulting, and economic resource controls. Long-period magnetotelluric (MT) 
instruments collocated with passive seismometers of the Bigfoot array in the 
Great Basin will offer a 3-D view of these states and processes, using 
constraints from seismology, heat flow, structure, and geodesy. The potential 
of the method is well exemplified by studies to date. Since the early 1970Õs, 
regional conductivity surveys have shown a first-order partitioning of current 
activity in the province, with the eastern and western margins being more 
anomalous w.r.t. a relatively quiescent Great Basin interior, in keeping with 
other indicators. The lower crust throughout the region is electrically 
conductive corresponding to a small fraction of hypersaline fluids, thus 
implying weak rheology. The thermal profile of the central province lies near 
the ACMA geotherm below ~75 km, and the upper mantle there appears horizontally 
isotropic and only weakly hydrated at most. In contrast, eastern Great Basin 
upper mantle appears substantially hotter, with significant probable melting 
and an abrupt, non-uniform vs depth transition eastward to the stable Colorado 
Plateau. Crustal-scale, steeply dipping conductive fault zones pervade the 
provinceÕs crust and may represent those where major deep earthquakes nucleate. 
Pre-Late Cenozoic heritage is revealed in detailed study of the Carlin Trend 
gold province, with a family of structures attributed to deep source rocks, 
Eocene intrusion, stratal deformation and alteration/graphitization. Lower 
crustal fabric inherited from the Proterozoic continental margin still appears 
to influence some deep electrical trends today.