Abstract Title: Helium isotope "map" of the Basin and Range

Abstract Author(s): B. Mack Kennedy (LBNL) - M.C. van Soest (LBNL)  

Abstract: Noble gas isotopic compositions and abundances in crustal fluids 
uniquely identify fluid and heat source, fluid evolution, mixing, and flow 
paths. Noble gases provide a definitive distinction between crustal and 
magmatic fluid sources and in the case of crustal fluids, allow an evaluation 
of the presence, size, and involvement of a deep mantle-derived component; 
important factors for understanding tectono-magmatic processes. Since elevated 
3He fluxes, as measured by helium isotope compositions in crustal fluids, 
reflect mantle melting, helium isotopes provide constraints on models for 
regional high heat flux anomalies that call on large scale underplating of 
mantle derived melts. Helium isotopes may also distinguish zones of either 
local or regional high permeability through the crust. We are in the process of 
constructing a helium isotope ÒmapÓ of the greater Basin and Range. Preliminary 
data indicate an elevated 3He flux along the western margin that is associated 
with recent to active magmatism. Towards the east, ÒpeaksÓ in the 3He flux are 
superimposed on a general systematic decline in flux. We believe the ÒpeaksÓ 
reflect zones of high permeability related to active and deep range front fault 
structures, such as the Stillwater Fault in Dixie Valley.