The Hawaiian PLUME Project Successfully Completes its First Deployment

Geology and Geophysics Department, Yale University, P.O. Box 208109, New Haven, CT 06520-8109 United States
AGU Fall Meeting Abstracts 11/2006; -1:0657.


The Hawaiian PLUME (Plume-Lithosphere Undersea Melt Experiment) project
is a multi-disciplinary program to study the deep mantle roots of the
Hawaiian hotspot. The nearly linear alignment of the Hawaiian Islands
has heretofore prevented high-resolution, three-dimensional imaging of
mantle structure in the region from land seismic observations, a
situation that has permitted debates to persist over whether or not the
Hawaiian hotspot is underlain by a classical plume from the deep mantle
and how mantle upwelling interacts with the overlying lithosphere
beneath the Hawaiian Swell. The centerpiece of the PLUME project is a
large broadband seismic network that includes ocean-bottom seismometers
(OBSs) as well as portable land stations. Occupying a total of more than
80 sites and having a two-dimensional aperture of more than 1000~km,
this network includes one of the first large-scale, long-term
deployments of broadband OBSs. The seismic experiment has been conducted
in two stages to record teleseismic body and surface waves over a total
duration of two years. A first deployment of 35 OBSs extended from
January 2005 through January 2006 and was centered on the island of
Hawaii, the locus of the hotspot. A second OBS deployment, with a larger
aperture and larger station spacing was carried out in May 2006 to
collect data for another year. The first deployment was a technical
success, with 32 of 35 OBSs recovered and many large events at suitable
distances and azimuths well recorded. We recorded 225 events with scalar
seismic moments greater than 5× 1017Nm. Our database includes the
great 28 March 2005, M_S=8.2 aftershock of the 26 December 2004
Sumatra-Andaman earthquake and two large earthquakes on the Juan de Fuca
plate on 15 and 17 June 2005. Our surface wave analysis will be based on
102 large, shallow (h_0<200 km) earthquakes with scalar seismic
moments M_0≥ 20/times 1017Nm. This number of events is about 20% more
than what was gathered during the year--long SWELL pilot deployment in
the same region in 1997-98 using solely differential pressure gauges.
The database also includes excellent long-period body wave waveforms
suitable for tomographic imaging as well as horizontal- component data
suitable for a shear-wave splitting analysis and for identifying
converted phases from the upper-mantle transition zone with receiver
function techniques. In addition to the seismic experiment, nine of
eleven dredges on the first deployment cruise yielded coral and basalt
samples that will help to constrain subsidence rates of the Hawaiian
Islands and the origin of rift volcanism. On the two deployment cruises
we also obtained high-resolution multi-beam bathymetry along previously
unmapped transects covering areas of the eastern parts of the Maui and
the Molokai Fracture Zones as well as portions of the Bach Ridge at the
southern end of the Musician Seamounts.

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    ABSTRACT: The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding N. America plate producing a ~600-km wide ~300-m high topographic swell centered on the Yellowstone Plateau. Plume-plate interaction has produced the 800 km long, 17 Ma Yellowstone-Snake River Plain-Newberry (YSRPN) volcanic field. Large-scale geophysical experiments of the YSRP provided seismic and GPS images of the hotspot and data on its kinematic and dynamic properties. Seismic tomography reveals a Yellowstone crustal magma body, 6 to 15 km deep, that is fed by an upper-mantle plume-shaped low velocity body made up of melt blobs, 80 km to 650 km, tilting 60° NW. The plume originates in the mantle transition zone. Mantle tomography using USArray information further delineates that the plume may be underlain by a more widespread low velocity layer that may be its melt source. Contemporary deformation of Yellowstone is dominated by SW-extension at up to ~0.3 cm/yr, a fourth of the total Basin-Range opening rate, but with superimposed volcanic uplift and subsidence at decade scales, averaging ~2 cm/yr. An unprecedented episode of caldera uplift, up to 7 cm/yr from 2004-2008, was modeled as recharge of the crustal magma body at 10-km depth. Mantle convection models are characterized by eastward upper-mantle flow beneath Yellowstone at 5 cm/yr and opposite in direction to the overriding plate motion. This suggests that the strong eastward flow deflects the ascending melt into a tilted configuration, i.e. "a plume caught in the mantle wind". Dynamic modeling reveals relatively low excess plume temperatures, up to 120° K, consistent with a weak buoyancy flux of ~0.25 Mg/s but strong enough to produce the notable topographic swell. Kinematic and dynamic modeling of GPS, fault slip, and seismic data reveal excess gravitational potential of the Yellowstone swell that drives the SW motion of the YSRP lithosphere "downhill" as part of a pattern of clockwise rotation of western U.S. intraplate block motions. The hotspot swell has re-oriented the regional stress field, causing a rotation of tensional stresses from E-W in the Basin-Range to NE-SW at the Yellowstone Plateau. High lithospheric temperatures reduce the average effective lithospheric viscosity of the YSRP. Magmatic reworking of the lithosphere and thermal subsidence reduce the gravitational potential of the Snake River Plain, reducing stresses along the hotspot track. We extrapolated the location of the Yellowstone mantle-source southwestward 800 km to an initial position at 17 million years ago beneath eastern Oregon and the southern LIP Columbia Plateau basalt field, suggesting a common origin for the YSRP and LIP volcanism. We propose that the original plume head ascended vertically behind the subducting Juan de Fuca plate, but at ~12 Ma was entrained in faster mantle flow beneath continental lithosphere and tilted into its present configuration. In this integrated model, Yellowstone plume-plate processes have "continentalized" oceanic lithosphere, enhanced intraplate extension, and modified the topography of over much of the northwest U.S. interior.
    No preview · Conference Paper · Nov 2008
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    ABSTRACT: Integration of geophysical and geological data show that the Yellowstone hotspot resulted from a mantle plume interacting with the overriding North America plate, a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16-17Ma, 700-km-long Yellowstone-Snake River Plain (YSRP) silicic volcanic system. Accessibility of the YSRP allowed large-scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements. Seismic tomography reveals a crustal magma reservoir of 8% to 15% melt, 6km to 16km deep, beneath the Yellowstone caldera. An upper-mantle low-P-wave-velocity body extends vertically from 80km to 250km beneath Yellowstone, but the anomalous body tilts 60°WNW and extends to 660km depth into the mantle transition zone. We interpret this conduit-shaped low-velocity body as a plume of up to -3.5% Vp and -5.5% Vs perturbation that corresponds to a 1-2% partial melt. Models of whole mantle convection reveal eastward upper-mantle flow beneath Yellowstone at relatively high rates of 5cm/yr that deflects the ascending plume into its west-tilted geometry. A geodynamic model of the Yellowstone plume constrained by Vp and Vs velocities and attenuation parameters suggests low excess temperatures of up to 120K, corresponding to a maximum 2.5% melt, and a small buoyancy flux of 0.25Mg/s, i.e., properties of a cool, weak plume. The buoyancy flux is many times smaller than for oceanic plumes, nonetheless, plume buoyancy has produced a ~400-km-wide, ~500-m-high topographic swell centered on the Yellowstone Plateau. Contemporary deformation derived from GPS measurements reveals SW extension of 2-3mm/yr across the Yellowstone Plateau, one-fourth of the total Basin-Range opening rate, which we consider to be part of Basin-Range intraplate extension. Locally, decadal episodes of subsidence and uplift, averaging ~2cm/yr, characterize the 80-year Yellowstone caldera monitored history and are modeled as hydrothermal-magmatic sources. Moreover a recent episode, 2004-2009, of accelerated uplift of the Yellowstone caldera at rates up to 7cm/yr has been modeled as resulting from magmatic recharge of a 10-km-deep sill at the top of the crustal magma reservoir. Regionally, gravitational potential energy of the Yellowstone swell drives the lithosphere southwest and “downhill” from the Yellowstone Plateau 400km where it coalesces with Basin-Range province-wide westward extension. Based on the geometry and its assumed 660km depth, we extrapolate the plume source southwest to its original location at 17Ma and 600km southwest and 200km north of the YSRP. Importantly, this location is beneath the southern part of the Columbia Plateau flood basalt field of the same age and implies that the Yellowstone mantle plume may be the common source for both of these large volcanic fields. Our time-progression model suggests that the original plume head rose vertically behind the Juan de Fuca plate, but at ~12Ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler, thicker continental lithosphere, becoming entrained in eastward upper-mantle flow. These results reveal that Yellowstone plume-plate processes have had a profound effect on Late Cenozoic geologic evolution and topography of a large part of the western U.S.
    Full-text · Article · Nov 2009 · Journal of Volcanology and Geothermal Research