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Seismic imaging of the North American midcontinent rift using S-to-P receiver functions

Seismic imaging of the North American midcontinent rift using S-to-P receiver functions
Seismic imaging of the North American midcontinent rift using S-to-P receiver functions

North America's ~1.1-Ga failed Midcontinent Rift (MCR) is a striking feature of gravity and magnetic anomaly maps across the continent. However, how the rift affected the underlying lithosphere is not well understood. With data from the Superior Province Rifting Earthscope Experiment and the USArray Transportable Array, we constrain three-dimensional seismic velocity discontinuity structure in the lithosphere beneath the southwestward arm of the MCR using S-to-P receiver functions. We image a velocity increase with depth associated with the Moho at depths of 33–40 ± 4 km, generally deepening toward the east. The Moho amplitude decreases beneath the rift axis in Minnesota and Wisconsin, where the velocity gradient is more gradual, possibly due to crustal underplating. We see hints of a deeper velocity increase at 61 ± 4-km depth that may be the base of underplating. Beneath the rift axis further south in Iowa, we image two distinct positive phases at 34–39 ± 4 and 62–65 ± 4 km likely related to an altered Moho and an underplated layer. We image velocity decreases with depth at depths of 90–190 ± 7 km in some locations that do not geographically correlate with the rift. These include a discontinuity at depths of 90–120 ± 7 km with a northerly dip in the south that abruptly deepens to 150–190 ± 7 km across the Spirit Lake Tectonic Zone provincial suture. The negative phases may represent a patchy, frozen-in midlithosphere discontinuity feature that likely predates the MCR and/or be related to lithospheric thickness.

crustal underplating, Midcontinent Rift, MLD, receiver functions, rifting, SPREE
2169-9313
Chichester, Ben
dbeeac38-53e8-4e6c-b7ff-8c8e1e8a3f96
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
van der Lee, Suzan
931a2187-30f9-44ed-af47-67196efce294
Frederiksen, Andrew
517889d4-bbde-4b9b-81b6-70ade9415eb5
Zhang, Hao
6b809119-4403-4075-aedd-04dcc1c674ab
Chichester, Ben
dbeeac38-53e8-4e6c-b7ff-8c8e1e8a3f96
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
van der Lee, Suzan
931a2187-30f9-44ed-af47-67196efce294
Frederiksen, Andrew
517889d4-bbde-4b9b-81b6-70ade9415eb5
Zhang, Hao
6b809119-4403-4075-aedd-04dcc1c674ab

Chichester, Ben, Rychert, Catherine, Harmon, Nicholas, van der Lee, Suzan, Frederiksen, Andrew and Zhang, Hao (2018) Seismic imaging of the North American midcontinent rift using S-to-P receiver functions. Journal of Geophysical Research: Solid Earth. (doi:10.1029/2018JB015771).

Record type: Article

Abstract

North America's ~1.1-Ga failed Midcontinent Rift (MCR) is a striking feature of gravity and magnetic anomaly maps across the continent. However, how the rift affected the underlying lithosphere is not well understood. With data from the Superior Province Rifting Earthscope Experiment and the USArray Transportable Array, we constrain three-dimensional seismic velocity discontinuity structure in the lithosphere beneath the southwestward arm of the MCR using S-to-P receiver functions. We image a velocity increase with depth associated with the Moho at depths of 33–40 ± 4 km, generally deepening toward the east. The Moho amplitude decreases beneath the rift axis in Minnesota and Wisconsin, where the velocity gradient is more gradual, possibly due to crustal underplating. We see hints of a deeper velocity increase at 61 ± 4-km depth that may be the base of underplating. Beneath the rift axis further south in Iowa, we image two distinct positive phases at 34–39 ± 4 and 62–65 ± 4 km likely related to an altered Moho and an underplated layer. We image velocity decreases with depth at depths of 90–190 ± 7 km in some locations that do not geographically correlate with the rift. These include a discontinuity at depths of 90–120 ± 7 km with a northerly dip in the south that abruptly deepens to 150–190 ± 7 km across the Spirit Lake Tectonic Zone provincial suture. The negative phases may represent a patchy, frozen-in midlithosphere discontinuity feature that likely predates the MCR and/or be related to lithospheric thickness.

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Chichester_et_al-2018-Journal_of_Geophysical_Research__Solid_Earth - Version of Record
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Accepted/In Press date: 17 August 2018
e-pub ahead of print date: 27 August 2018
Keywords: crustal underplating, Midcontinent Rift, MLD, receiver functions, rifting, SPREE

Identifiers

Local EPrints ID: 423748
URI: http://eprints.soton.ac.uk/id/eprint/423748
ISSN: 2169-9313
PURE UUID: 3d306f70-6991-48d8-b46a-77c6746d20d5
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X

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Date deposited: 01 Oct 2018 16:30
Last modified: 20 Jul 2019 00:48

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