A Systematic Regional Trend in Helium Isotopes Across the NorthernBasin and Range Province, Western North America
An extensive study of helium isotopes in fluids collectedfrom surface springs, fumaroles and wells across the northern Basin andRange Province reveals a systematic trend of decreasing 3He/4He ratiosfrom west to east. The western margin of the Basin and Range ischaracterized by mantle-like ratios (6-8 Ra) associated with active orrecently active crustal magma systems (e.g. Coso, Long Valley, Steamboat,and the Cascade volcanic complex). Moving towards the east, the ratiosdecline systematically to a background value of ~;0.1 Ra. The regionaltrend is consistent with extensive mantle melting concentrated along thewestern margin and is coincident with an east-to-west increase in themagnitude of northwest strain. The increase in shear strain enhancescrustal permeability resulting in high vertical fluid flow rates thatpreserve the high helium isotope ratios at the surface. Superimposed onthe regional trend are "helium spikes", local anomalies in the heliumisotope composition. These "spikes" reflect either local zones of mantlemelting or locally enhanced crustal permeability. In the case of theDixie Valley hydrothermal system, it appears to be a combination ofboth.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE. Assistant Secretary for Energy Efficiency andRenewable Energy. Solar and Renewable Resource Technologies
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 901239
- Report Number(s):
- LBNL-60930; GTMCAT; R&D Project: G32615; BnR: EB4005010; TRN: US200713%%211
- Journal Information:
- Geothermics, Vol. 35, Issue 1; Related Information: Journal Publication Date: Feb. 2006; ISSN 0375-6505
- Country of Publication:
- United States
- Language:
- English
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