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The mantle flow field beneath western North America
1Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA. silver@dtm.ciw.edu
Science (New York, N.Y.)
|February 9, 2002
Summary
Mantle flow beneath western North America moves east, opposing plate motion. This weak coupling suggests deep mantle density variations, possibly from the ancient Farallon plate, drive the flow.
Area of Science:
- Geophysics
- Tectonophysics
- Seismology
Background:
- Tectonic plate surface motions are well-understood.
- However, the corresponding horizontal mantle flow remains largely undetermined.
- Understanding mantle flow is crucial for plate tectonics.
Purpose of the Study:
- To estimate the horizontal mantle flow field beneath western North America.
- To investigate the coupling between mantle flow and tectonic plate motion.
Main Methods:
- Combined surface deformation observations with upper mantle seismic anisotropy data.
- Utilized a hot spot reference frame for velocity calculations.
Main Results:
- Estimated mantle velocity of 5.5 +/- 1.5 cm/year due east.
- Observed mantle flow is nearly opposite to North American plate motion (west-southwest).
- Mantle flow exhibits weak coupling with the surface plate, resulting in minimal drag force.
Conclusions:
- The estimated mantle flow field is likely influenced by mantle density heterogeneities.
- These heterogeneities may originate from the remnant of the ancient Farallon oceanic plate.
- This finding provides insights into deep Earth processes influencing surface tectonics.
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