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Evidence for crustal degassing of CF4 and SF6 in Mojave Desert groundwaters

Geochimica et Cosmochimica Acta

By:
, , , , , , , , and
DOI: 10.1016/j.gca.2007.11.027

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Abstract

Dissolved tetrafluoromethane (CF4) and sulfur hexafluoride (SF6) concentrations were measured in groundwater samples from the Eastern Morongo Basin (EMB) and Mojave River Basin (MRB) located in the southern Mojave Desert, California. Both CF4 and SF6 are supersaturated with respect to equilibrium with the preindustrial atmosphere at the recharge temperatures and elevations of the Mojave Desert. These observations provide the first in situ evidence for a flux of CF4 from the lithosphere. A gradual basin-wide enhancement in dissolved CF4 and SF6 concentrations with groundwater age is consistent with release of these gases during weathering of the surrounding granitic alluvium. Dissolved CF4 and SF6 concentrations in these groundwaters also contain a deeper crustal component associated with a lithospheric flux entering the EMB and MRB through the underlying basement. The crustal flux of CF4, but not of SF6, is enhanced in the vicinity of local active fault systems due to release of crustal fluids during episodic fracture events driven by local tectonic activity. When fluxes of CF4 and SF6 into Mojave Desert groundwaters are extrapolated to the global scale they are consistent, within large uncertainties, with the fluxes required to sustain the preindustrial atmospheric abundances of CF4 and SF6. ?? 2007 Elsevier Ltd. All rights reserved.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evidence for crustal degassing of CF4 and SF6 in Mojave Desert groundwaters
Series title:
Geochimica et Cosmochimica Acta
DOI:
10.1016/j.gca.2007.11.027
Volume
72
Issue:
4
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochimica et Cosmochimica Acta
First page:
999
Last page:
1013
Number of Pages:
15