Lower Mantle Substructure Embedded in the Farallon Plate: The Hess Conjugate

Ko, Justin Yen-Ting; Helmberger, Donald V.; Wang, Huilin; Zhan, Zhao

doi:10.1002/2017gl075032

Cited by 8 publications

(6 citation statements)

References 43 publications

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“…Liu et al (2008Liu et al ( , 2010 developed a reverse convection model for the locations of the plateaus over time. The reconstructed present-day location of the Hess plateau conjugate places the top just below the transition zone in the central United States, in agreement with subsequent seismic tomography models (e.g., Ko et al, 2017;Schmandt & Lin, 2014). The plateau has probably been in the vicinity of our study region since mid-Miocene, allowing for metasomatic reactions due to rising silica-rich fluids.…”

Section: 1029/2020jb020625supporting

confidence: 85%

Joint Local and Teleseismic Tomography in the Central United States: Exploring the Mantle Below the Upper Mississippi Embayment and the Illinois Basin

2020

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Three-dimensional, high-resolution crustal and upper mantle P and S wave velocity (Vp and Vs) models are presented for the central United States using body wave tomography. The study utilizes local and teleseismic data recorded by the Northern Embayment Lithospheric Experiment stations, the CERI New Madrid Seismic Network, the Earthscope Transportable Array, and the Ozark Illinois INdiana Kentucky Flexible Array. Vp and Vs solutions are very similar and are well resolved in the depth range 40 to 400 km. Two anomalously slow regions are present below the Illinois Basin, forming a northwest dipping low-velocity zone (LVZ) extending from~200 to 400 km. Maximum anomaly magnitudes in the LVZ reach about −4% and −5% for Vp and Vs, respectively. The LVZ appears to connect to a well-documented LVZ located below the northern Mississippi Embayment. The Illinois Basin velocity anomalies cannot be explained by elevated temperature alone and require compositional heterogeneity involving elevated orthopyroxene content in addition to an increase in iron and water content. The need for additional orthopyroxene suggests that the LVZ is being produced by metasomatism of mantle rocks by hydrous, silica-rich fluids ascending from a slab fragment trapped in or near the transition zone. This supports previous interpretations for the existence of the LVZ below the Embayment. We suggest that the LVZs below the Mississippi Embayment and the Illinois Basin are linked to the presence of a large igneous province, which convection models suggest is currently located below the central United States. Plain Language Summary We present three-dimensional, high-resolution velocity models from the Earth's surface to 410 km depth under the central United States. Our study utilizes seismic tomographya technique that images the velocity structure of the Earth using seismic waves that traveled from earthquake sources to seismic stations. Travel-time data recorded by several seismic arrays (dense deployments of seismic stations) were acquired to increase the resolution of our model. In the resulting model, compressional wave and shear wave velocity anomalies are similar and are well-resolved in the depth range 40 to 400 km. An anomalously slow region is present below the Illinois Basin that dips to the northwest and extends to 400 km. The low velocity cannot be explained by elevated temperature alone and requires an increase in iron and water content as well as high amounts of orthopyroxene. Elevated orthopyroxene suggests that the mantle rocks have been chemically altered due to fluids coming from a trapped slab fragment. We suggest that the low-velocity zone below the Illinois Basin is associated with the presence of a slab fragment containing a thick oceanic plateau. According to several studies, the plateau was subducted millions of years ago and is presently located underneath the central United States.

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Section: 1029/2020jb020625supporting

confidence: 85%

Joint Local and Teleseismic Tomography in the Central United States: Exploring the Mantle Below the Upper Mississippi Embayment and the Illinois Basin

2020

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“…other regions, such as the Paleo-Tethys Ocean slab under India (e.g., Van der Voo et al, 1999;Zhao, 2015). In addition, a recent study of seismic waveform modeling has also confirmed the existence of the Hess Rise conjugate there (Ko et al, 2017).…”

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 89%

Tomography, Seismotectonics, and Mantle Dynamics of Central and Eastern United States

et al. 2019

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We study the 3‐D P wave velocity structure of the crust and mantle down to 1,000‐km depth beneath the central and eastern United States. A 3‐D velocity model is obtained by conducting a joint inversion of 236,670 arrival times of local earthquakes and 870,455 relative traveltime residuals of teleseismic events recorded by the EarthScope/USArray Transportable Array. Significant low‐velocity (low‐V) anomalies are revealed in the crust beneath the eastern arm of the Midcontinent Rift and the Triassic Basins along the East Coast, whereas a prominent high‐velocity (high‐V) anomaly is visible beneath the Llano Uplift in central Texas. The stable North American Craton exhibits high‐V anomalies at depths of 65–250 km. Low‐V anomalies exist along the eastern and southern margins of the craton, which may reflect relatively thin lithosphere there. A prominent low‐V anomaly is revealed at depths of 50–200 km beneath the New Madrid Seismic Zone, which is bounded by high‐V anomalies to its southeast and northwest. This feature reflects a weak lithosphere surrounded by relatively strong cratonic regions and stress concentration caused intraplate seismicity in the New Madrid region. Two high‐V bodies appear in the mantle transition zone (410‐ to 660‐km depths) beneath the Interior Low Plateaus, the central Great Plains, and the Central Lowland, which may reflect the subducted Farallon plate or delaminated lithosphere. At depths of 800–1,000 km, a high‐V anomaly is visible beneath the southeast United States, which may be the subducted Hess Rise conjugate.

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“…Seismic tomography shows three high‐velocity patches at ~871 km below the Great Lakes, the northern GOM, and the Caribbean (Simmons et al, ) (Figure ). The seismic anomaly below the northern GOM is characterized by sharp boundaries with a seismic shear‐wave velocity anomaly ( δV s ) elevated by 2.5% over a 50 km distance (Ko et al, ). This sharp seismic gradient cannot be explained by a cold Farallon slab, as thermal diffusion would reduce the gradient of δV s by ~7 times from that observed.…”

Section: Introductionmentioning

confidence: 99%

Rapid Cenozoic Subsidence in the Gulf of Mexico Resulting From Hess Rise Conjugate Subduction

Wang

Gurnis

Skogseid

2017

Geophysical Research Letters

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Enigmatic surface deflections occurred in North America starting from the Cretaceous, including the continental-scale drainage reorganization and the long-wavelength subsidence in the Western Interior Seaway. These surface undulations cannot be simply explained by sea level change or flexure loading. Coinciding with the large-scale surface deflection, the Gulf of Mexico (GOM) has an immense Paleocene sediment deposition probably caused by tectonic subsidence. Increasing evidence indicates a distinct seismic anomaly localized in the mantle below the GOM. With geodynamic models, we show that the Hess Rise conjugate coincides with the position of the seismic anomaly. The basalt-eclogite transition in the Hess conjugate can lead to a localized dynamic subsidence in the GOM, which is superimposed on the broad surface deflection caused by the Farallon slab. The Hess conjugate, transformed to eclogite, could tilt the surface southward in the U.S. and help frame the GOM as a main depocenter in the Cenozoic.

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Lower Mantle Substructure Embedded in the Farallon Plate: The Hess Conjugate

Cited by 8 publications

References 43 publications

Joint Local and Teleseismic Tomography in the Central United States: Exploring the Mantle Below the Upper Mississippi Embayment and the Illinois Basin

Joint Local and Teleseismic Tomography in the Central United States: Exploring the Mantle Below the Upper Mississippi Embayment and the Illinois Basin

Tomography, Seismotectonics, and Mantle Dynamics of Central and Eastern United States

Rapid Cenozoic Subsidence in the Gulf of Mexico Resulting From Hess Rise Conjugate Subduction

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