Concentrating the Slab Fluid Input to Newberry Volcano, Oregon

Concentrating the Slab Fluid Input to Newberry
Volcano, Oregon
Richard W. Carlson
DTM, Carnegie Institution of Washington
Timothy L. Grove
EAPS, Massachusetts Institute of Technology
Julie M. Donnelly-Nolan
USGS, Menlo Park
Goldschmidt 2008
Newberry Volcano Sited at the Intersection of the Cascades
and the High Lava Plains Magmatic Province
Colored Regions Show Volcanic Deposits Younger than 17 Million Years
(Smith and Luedke, 1984)
South Sister, Oregon
Washington
< 5 5-10 10-17 Ma
Basalt
Andesite
Rhyolite Dacite
Montana
Idaho
Oregon
Wyoming
Cascades
California
Utah
Nevada
Diamond Craters
Arizona
Newberry
Calc-Alkaline vs. Fe-Enrichment, both Occur at Newberry
Hawaii, Juan de Fuca, Cascade and HLP data from EarthChem
A Subduction Signature in Both Newberry and HLP Basalts
(but only some!)
Hawaii, Juan de Fuca, Cascade and HLP data from EarthChem
The Subduction Contribution
87Sr/86Sr = 0.70317
187Os/188Os = 0.1518
87Sr/86Sr = 0.70382
187Os/188Os = 0.1922
What is the “Subduction Component”?
Hawaii, Juan de Fuca, Cascade and HLP data from EarthChem
What is the “Subduction Component”?
Hawaii, Juan de Fuca, Cascade and HLP data from EarthChem
What is the “Subduction Component”?
Hawaii, Juan de Fuca, Cascade and HLP data from EarthChem
How is the Subduction Signature Distributed Spatially?
Ba/Nb
0 - 25
25 - 50
50 - 75
75 - 150
150 - 300
Newberry
Primitive HAOT
HLP Basalt
Cascade Basalt
Cascade and HLP data from EarthChem
How is the Subduction Signature Distributed Spatially?
Ba/Nb
0 - 25
25 - 50
50 - 75
75 - 150
150 - 300
Newberry
Primitive HAOT
HLP Basalt
Cascade Basalt
Cascade and HLP data from EarthChem
Is Newberry a Cascade
or HLP volcano?
P-Wave Velocity
125 km Depth,
Roth et al. GRL, on line
Graphic by Lyn Topinka, 1996
Vulcan.wr.usgs.gov/Volcanoes/
Oregon/Grpahics/framework.html
Why is Activity Focused at Newberry and along the HLP?
A consequence of slab rollback and flow around the southern edge of the Juan-de-Fuca
Down-dip subduction,
Slab steepening
Plus edge flow
No behind arc activity
Trench parallel
rear arc volcanism
Trench perpendicular
rear arc volcanism
After Kincaid and Griffiths, G3, 2004
Conclusions:
1. Newberry primitive basalts include both calc-alkaline and
tholeitic-trend lavas. Slab components (high Ba/Nb)
strongly focused to center of Newberry shield.
2. Slab component has Pb isotopic characteristics similar to
Pacific Northwest offshore sediments. 1% or less by mass
of sediment plus mantle can explain isotope variation.
3. Newberry is underlain by a very local region of low
seismic velocity. Implies presence of melt and/or fluid.
4. Westward propagating HLP magmatic trace with current
point-source focus at Newberry consistent with wedge flow
induced by steepening dip and flow around southern edge
of the subducting Juan de Fuca plate.