Upper mantle structure Upper mantle structure beneath the eastern beneath the eastern Colorado Plateau and Rio Colorado Plateau and Rio Grande rift revealed by Grande rift revealed by Bouguer gravity, seismic Bouguer gravity, seismic velocities and xenolith velocities and xenolith data data Mousumi Roy, Jonathan K. Mousumi Roy, Jonathan K. MacCarthy, and Jane Selverstone MacCarthy, and Jane Selverstone G3, October 2005 G3, October 2005 Angela Magee ASU Earthscope Seminar April 16, 2007
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Upper mantle structure beneath the eastern Colorado Plateau and Rio Grande rift revealed by Bouguer gravity, seismic velocities and xenolith data Mousumi.
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Upper mantle structure Upper mantle structure beneath the eastern beneath the eastern
Colorado Plateau and Rio Colorado Plateau and Rio Grande rift revealed by Grande rift revealed by
Bouguer gravity, seismic Bouguer gravity, seismic velocities and xenolith datavelocities and xenolith data
Mousumi Roy, Jonathan K. MacCarthy, Mousumi Roy, Jonathan K. MacCarthy, and Jane Selverstoneand Jane Selverstone
G3, October 2005G3, October 2005
Angela Magee
ASU Earthscope Seminar
April 16, 2007
MotivationMotivation
Bouguer anomalies Bouguer anomalies under the Colorado under the Colorado Plateau and Rio Plateau and Rio Grande RiftGrande Rift
Most interested in the Most interested in the longer wavelength low longer wavelength low gravity anomaly under gravity anomaly under east edge of plateau east edge of plateau and the rift which and the rift which can’t be compeltely can’t be compeltely explained by upliftexplained by uplift
Data and MethodsData and Methods Use LA RISTRA Use LA RISTRA
teleseimic array, a teleseimic array, a compilation, and compilation, and CRUST 2.0 2X2 crustal CRUST 2.0 2X2 crustal model for the crustal model for the crustal thickness datathickness data
Crust thickness cannot Crust thickness cannot explain all the Bouguer explain all the Bouguer anomalyanomaly
Remove the Remove the contribution of crust contribution of crust thickness and thickness and background trend of background trend of density from the datadensity from the data
Data and Methods Data and Methods ContinuedContinued
Forward model Forward model density anomalies in density anomalies in upper crust and upper crust and upper mantleupper mantle
Upper crust: high Upper crust: high pass gravity data, pass gravity data, match up what can to match up what can to geological geological informationinformation
Also tried lower crust, Also tried lower crust, but upper mantle but upper mantle more reasonable more reasonable density contrasts density contrasts
ResultsResults Also compare Also compare
density model with density model with densities estimated densities estimated from xenolith data from xenolith data and with seismic and with seismic velocity datavelocity data
Low density Low density anomaly:anomaly: Broader at north, Broader at north,
narrower and narrower and stronger at southstronger at south
Oblique to and offset Oblique to and offset from Rio Grande Rift from Rio Grande Rift
ImplicationsImplications
Middle Tertiary ignimbrite flare-up Middle Tertiary ignimbrite flare-up and late tertiary magatismand late tertiary magatism Basalt extractionBasalt extraction Partial melt Partial melt High heat flowHigh heat flow
Broad upwarping of asthenosphere Broad upwarping of asthenosphere beneath thinned lithospherebeneath thinned lithosphere
Puzzle of relationship with Rio Puzzle of relationship with Rio Grande RiftGrande Rift
Additional ThoughtsAdditional Thoughts
Puzzle of relationship with Rio Puzzle of relationship with Rio Grande RiftGrande Rift