Depths and temperatures of <10.5 Ma mantle melting and the lithosphere-asthenosphere boundary below southern Oregon and northern California

Christy Till, Timothy L. Grove, Richard W. Carlson, Julie M. Donnelly-Nolan, Matthew J. Fouch, Lara S. Wagner, William K. Hart

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Plagioclase and spinel lherzolite thermometry and barometry are applied to an extensive geochemical dataset of young (<10.5 Ma) primitive basaltic lavas from across Oregon's High Lava Plains, California's Modoc Plateau, and the central-southern Cascades volcanic arc to calculate the depths and temperatures of mantle melting. This study focuses on basalts with low pre-eruptive H 2O contents that are little fractionated near-primary melts of mantle peridotite (i.e., basalts thought to be products of anhydrous decompression mantle melting). Calculated minimum depths of nominally anhydrous melt extraction are 40-58 km below Oregon's High Lava Plains, 41-51 km below the Modoc Plateau, and 37-60 km below the central and southern Cascades arc. The calculated depths are very close to Moho depths as determined from a number of regional geophysical studies and suggest that the geophysical Moho and lithosphere-asthenosphere boundary in this region are located in very close proximity to one another (within 5-10 km). The basalts originated at 1185-1383°C and point to a generally warm mantle beneath this area but not one hot enough to obviously require a plume contribution. Our results, combined with a range of other geologic, geophysical, and geochemical constraints, are consistent with a regional model whereby anhydrous mantle melting over the last 10.5 Ma in a modern convergent margin and back arc was driven by subduction-induced corner flow in the mantle wedge, and to a lesser extent, toroidal flow around the southern edge of the subducting Juan de Fuca and Gorda plates, and crustal extension-related upwelling of the shallow mantle.

Original languageEnglish (US)
Pages (from-to)864-879
Number of pages16
JournalGeochemistry, Geophysics, Geosystems
Volume14
Issue number4
DOIs
StatePublished - 2013
Externally publishedYes

Fingerprint

asthenosphere
lithosphere
Earth mantle
Melting
melting
mantle
basalt
temperature
arcs
Temperature
lava
Moho
plains
plateaus
cascades
corner flow
melt
plateau
barometry
convergent margin

Keywords

  • Cascades arc
  • depth of melting
  • high alumina olivine tholeiite
  • High Lava Plains
  • lithosphere-asthenosphere boundary
  • Modoc Plateau
  • thermometry

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Depths and temperatures of <10.5 Ma mantle melting and the lithosphere-asthenosphere boundary below southern Oregon and northern California. / Till, Christy; Grove, Timothy L.; Carlson, Richard W.; Donnelly-Nolan, Julie M.; Fouch, Matthew J.; Wagner, Lara S.; Hart, William K.

In: Geochemistry, Geophysics, Geosystems, Vol. 14, No. 4, 2013, p. 864-879.

Research output: Contribution to journalArticle

Till, Christy ; Grove, Timothy L. ; Carlson, Richard W. ; Donnelly-Nolan, Julie M. ; Fouch, Matthew J. ; Wagner, Lara S. ; Hart, William K. / Depths and temperatures of <10.5 Ma mantle melting and the lithosphere-asthenosphere boundary below southern Oregon and northern California. In: Geochemistry, Geophysics, Geosystems. 2013 ; Vol. 14, No. 4. pp. 864-879.
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AU - Fouch, Matthew J.

AU - Wagner, Lara S.

AU - Hart, William K.

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AB - Plagioclase and spinel lherzolite thermometry and barometry are applied to an extensive geochemical dataset of young (<10.5 Ma) primitive basaltic lavas from across Oregon's High Lava Plains, California's Modoc Plateau, and the central-southern Cascades volcanic arc to calculate the depths and temperatures of mantle melting. This study focuses on basalts with low pre-eruptive H 2O contents that are little fractionated near-primary melts of mantle peridotite (i.e., basalts thought to be products of anhydrous decompression mantle melting). Calculated minimum depths of nominally anhydrous melt extraction are 40-58 km below Oregon's High Lava Plains, 41-51 km below the Modoc Plateau, and 37-60 km below the central and southern Cascades arc. The calculated depths are very close to Moho depths as determined from a number of regional geophysical studies and suggest that the geophysical Moho and lithosphere-asthenosphere boundary in this region are located in very close proximity to one another (within 5-10 km). The basalts originated at 1185-1383°C and point to a generally warm mantle beneath this area but not one hot enough to obviously require a plume contribution. Our results, combined with a range of other geologic, geophysical, and geochemical constraints, are consistent with a regional model whereby anhydrous mantle melting over the last 10.5 Ma in a modern convergent margin and back arc was driven by subduction-induced corner flow in the mantle wedge, and to a lesser extent, toroidal flow around the southern edge of the subducting Juan de Fuca and Gorda plates, and crustal extension-related upwelling of the shallow mantle.

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