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Title: A systematic regional trend in helium isotopes across the northernbasin and range province, Western North America

Abstract

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 ratios decline systematically to a background value of ~;0.1 Ra. Theregional trend is consistent with extensive mantle melting concentratedalong the western margin and is coincident with an east-to-west increasein the magnitude of northwest strain. The increase in shear strainenhances crustal permeability resulting in high vertical fluid flow ratesthat preserve the high helium isotope ratios at the surface. Superimposedon the 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.

Authors:
;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE. Assistant Secretary for Energy Efficiency and Rene.Solar and Renewable Resource Technologies
OSTI Identifier:
919013
Report Number(s):
LBNL-61338
R&D Project: G32615; BnR: EB4005010; TRN: US200822%%97
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Conference
Resource Relation:
Conference: Annual Meeting of the Geothermal ResourcesCouncil, San Diego, California, 10-13 September2006
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; FLUID FLOW; FUMAROLES; GEOTHERMAL RESOURCES; HELIUM; HELIUM ISOTOPES; HYDROTHERMAL SYSTEMS; LONG VALLEY; MAGMA SYSTEMS; MELTING; PERMEABILITY; SHEAR; STRAINS; VALLEYS; Helium isotopes Basin and Range fault hosted permeabilityexploration Dixie Valley

Citation Formats

Kennedy, B. Mack, and van Soest, Matthijs C. A systematic regional trend in helium isotopes across the northernbasin and range province, Western North America. United States: N. p., 2006. Web.
Kennedy, B. Mack, & van Soest, Matthijs C. A systematic regional trend in helium isotopes across the northernbasin and range province, Western North America. United States.
Kennedy, B. Mack, and van Soest, Matthijs C. Mon . "A systematic regional trend in helium isotopes across the northernbasin and range province, Western North America". United States. doi:. https://www.osti.gov/servlets/purl/919013.
@article{osti_919013,
title = {A systematic regional trend in helium isotopes across the northernbasin and range province, Western North America},
author = {Kennedy, B. Mack and van Soest, Matthijs C.},
abstractNote = {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 ratios decline systematically to a background value of ~;0.1 Ra. Theregional trend is consistent with extensive mantle melting concentratedalong the western margin and is coincident with an east-to-west increasein the magnitude of northwest strain. The increase in shear strainenhances crustal permeability resulting in high vertical fluid flow ratesthat preserve the high helium isotope ratios at the surface. Superimposedon the 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.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2006},
month = {Mon May 01 00:00:00 EDT 2006}
}

Conference:
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  • 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.more » 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.« less
  • Fluids from the western margin of the Basin and Range have helium isotope ratios as high as {approx}6-7 Ra, indicating a strong mantle melt influence and consistent with recent and current volcanic activity. Moving away from these areas, helium isotope ratios decrease rapidly to ''background'' values of around 0.6 Ra, and then gradually decrease toward the east to low values of {approx}0.1 Ra at the eastern margin of the Basin and Range. Superimposed on this general regional trend are isolated features with elevated helium isotope ratios (0.8-2.1 Ra) compared to the local background. Spring geochemistry and local geology indicate thatmore » these ''He-spikes'' are not related to current or recent magmatic activity, suggesting that the spikes may reflect either localized zones deep mantle melting or deep permeable pathways (faults) with high vertical fluid flowrates. A detailed study of one of the He-spikes (Dixie Valley and the Stillwater Range Front Fault system), indicates that features with high 3He/4He ratios are confined to the range front normal faults characteristic of the extensional regime in the Basin and Range, suggesting that these faults are deep permeable pathways. However, not all range front fault systems transmit fluids with a mantle signature, implying that not all have deep permeable pathways.« less
  • The Cenomanian-Turonian boundary is noted by a global positive excursion in the carbon isotopic signature. Sediments deposited during this interval in Europe are rich in organic carbon this interval in Europe are rich in organic carbon. These data suggest unusually high productivity which should be expressed within the composition of the plankton. The authors have examined samples from three sections in the Western Interior Seaway from Manitoba, Colorado, Arizona, that represent nearshore and offshore calcareous litho facies. They analyzed the foraminifera and calcareous nannofossils to determine how biostratigraphic and paleoecologic events affected the makeup of faunal and floral assemblages. Themore » extinction of the calcareous nannofossil P. albianus occurs at the first appearance of the planktonic foraminifer W. archeocretacea, which marks the base of the boundary interval. Nearshore foraminiferal assemblages that include planktonic taxa, characteristically contain a benthic fauna composed of both arenaceous and calcareous species. During these blooms though, planktonics disappear as does the calcareous component of the benthic fauna, most notably the nodosariids. Co-occurring shifts in the relative abundance of the planktonic foraminifera and the calcareous nannofossils in the more offshore facies are also evident. Finally when the authors compare the faunal data with the record of carbon and oxygen isotopes, they find that the timing of the biostratigraphic events already described is coincident with the positive excursion of the carbon isotope.« less
  • Cretaceous rocks are widespread along the Pacific margin of North America and record the presence of various plutonic, metamorphic, and volcanic events, basin types, depositional systems, and tectonic regimes. More accurate time-stratigraphic divisions of Cretaceous rocks, based on improved biostratigraphic zonations and new radiometric dating, permit both improved paleogeographic and reconstructions and correlations with changes in global sea level, climate, and oceanic paleocirculation patterns. Better understanding of the mobility and interaction of tectono-stratigraphic terranes along the Pacific margin, supported by paleomagnetic studies of increased accuracy, have forced us to reevaluate all previous paleotectonic and paleogeographic reconstructions. Major accretionary events, markedmore » by regional structural deformation, metamorphism, and plutonism, characterized the Pacific margin in the Jurassic. The Cretaceous paleogeographic framework, in general, reflects the reconstruction of the margin into a more continuous and less complex magmatic arc, forearc basin, and subduction complex. The Paleogene was marked by renewed disruption, translation, dispersion, and accretion in most areas. Active Cretaceous magmatic belts were present, from south to north, in the Mojave Desert, Sierra Nevada, Idaho batholith, North Cascades, Coast plutonic complex, and Alaska Range. Cretaceous plutonic belts in the Salinian block, Transverse Ranges, and Peninsular Ranges of Alta and Baja California formed far south of their present locations and did not accrete until the Paleogene. Forearc basins west and south of the magmatic arcs were widespread and generally characterized by thick sequences of turbidites.« less
  • The Western Atlantic Ocean Experiment (WATOX) is designed to determine the advection, deposition and impact of selected sulfur, nitrogen, metal and organic compounds that are advected eastward from North America to the Western Atlantic. This paper presents a summary to date of WATOX accomplishments in defining these fluxes.