High Lava Plains Project Matt Fouch Arizona State University School of Earth and Space Exploration 2007 EarthScope National Meeting, Monterey, CA MARGINS/GeoSwath Workshop

High Lava Plains Project: Understanding the Causes of Continental Intraplate Tectonomagmatism Arizona State University - Matt Fouch Carnegie Institution of Washington - Rick Carlson, David James Miami University - Bill Hart Massachusetts Institute of Technology - Tim Grove Oregon State University - Anita Grunder, Bob Duncan University of Oklahoma - Randy Keller University of Rhode Island - Chris Kincaid University of Texas, El Paso - Steve Harder Funded by NSF-ContinentalDynamics

Observations on Post-12 Ma Volcanism Two migrating volcanic tracesTwo migrating volcanic traces Migrating volcanism defined by rhyolitesMigrating volcanism defined by rhyolites Basaltic activity continuous along both tracesBasaltic activity continuous along both traces Volcanism in HLP associated with right-lateral S-S faulting as B&R extension dies out to NVolcanism in HLP associated with right-lateral S-S faulting as B&R extension dies out to N

Strong Temporal and Spatial Relationships with Basalt Composition HLP basalts become more primitive with timeHLP basalts become more primitive with time Composition shifts towards a high-Al tholeiite consistent with a very shallow mantle sourceComposition shifts towards a high-Al tholeiite consistent with a very shallow mantle source Primitive basalts across HLP show limited isotopic variationPrimitive basalts across HLP show limited isotopic variation Changes dramatically at border with Precambrian North AmericaChanges dramatically at border with Precambrian North America

Isostatic Gravity Eastern OR/WA show no gravity signal of underplated basalt, unlike SRPEastern OR/WA show no gravity signal of underplated basalt, unlike SRP Where are the fractionation products of 250,000 km 3 of flood basalts and underplating expected with HLP volcanism?Where are the fractionation products of 250,000 km 3 of flood basalts and underplating expected with HLP volcanism?

LOGISTICS: Local Contacts Essential 2-pager2-pager (Jenda Johnson) Town meetings / school visitsTown meetings / school visits “Kicking dirt”“Kicking dirt”

Local Contacts Essential

January, 2006 Installations

Timeline: Seismic Component October 2005Reconnaissance January 2006Install Phase Ia (4 instruments) June 2006Install Phase Ib (12 instruments) October 2006Recon (19 sites; vaults constructed) April 2007Recon (~60 sites) June 2007Complete Phase I (102 stations) September 2008Phase II (relocate ~70) Active source experiment Fall 2009Demobilization Summers: “Friends of HLP” meetings

Shear Wave Splitting Across the PNW Very simple across most of regionVery simple across most of region Local complexity near Cascades and accreted terranesLocal complexity near Cascades and accreted terranes N=439

Roth and Fouch, this meeting

Opportunities from Dense Seismic Coverage Across the Pacific Northwest Over 250 BB sites in addition to ~75 USArray and permanent stationsOver 250 BB sites in addition to ~75 USArray and permanent stations

Opportunities from Dense Seismic Coverage Across the Western U.S. Over 400 BB sites in addition to USArray and permanent stationsOver 400 BB sites in addition to USArray and permanent stations

Observations on Neogene Volcanism B&R and volcanism does not notice pC continental boundaryB&R and volcanism does not notice pC continental boundary Volcanism concentrated at B&R margins, particularly Northern boundaryVolcanism concentrated at B&R margins, particularly Northern boundary Volcanism does not obviously correlate with extension amountVolcanism does not obviously correlate with extension amount Largest volume of basalt erupted well N of SRP; no associated silicic volcanismLargest volume of basalt erupted well N of SRP; no associated silicic volcanism Bimodal volcanism characteristic of HLP, SRP and B&RBimodal volcanism characteristic of HLP, SRP and B&R ~4 Myr hiatus between flood basalts and beginning of rhyolite migrations~4 Myr hiatus between flood basalts and beginning of rhyolite migrations

January, 2006 Installations

Shear Wave Splitting Across the PNW Very simple across most of regionVery simple across most of region Larger splitting times in southern CascadiaLarger splitting times in southern Cascadia N=439