P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

Trevor A. Bollmann, Suzan van der Lee, Andrew W. Frederiksen, Emily Wolin, Justin Revenaugh, Douglas A. Wiens, Fiona A. Darbyshire, Seth Stein, Michael E. Wysession, Donna Jurdy

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The remains of the 1.1-Ga Midcontinent Rift (MCR) lie in the middle of the tectonically stable portion of North America. Previous and ongoing studies have imaged strong heterogeneity associated with the MCR in the crust but have not imaged such within the mantle. It is unclear whether this is due to the absence of rift-related mantle structures or these studies had insufficient resolution to image them. To address this issue, we measured 46,374 teleseismic P wave delay times from seismograms recorded by the USArray Transportable Array, Superior Province Rifting EarthScope Experiment, and surrounding permanent stations. We included these and 54,866 delay times from prior studies in our tomographic inversion. We find that high-velocity anomalies are widespread in our study area, but there are also prominent low-velocity anomalies. Two of these are coincident with high-Bouguer gravity anomalies associated with the MCR in Iowa and the Minnesota/Wisconsin border at 50- to 150-km depth. Extensive resolution testing shows that these anomalies could be the result of downward vertical smearing of relatively low velocities from rift-related material that “underplated" the crust, although we cannot exclude that the subcrustal mantle lithosphere beneath the MCR is anomalously enriched, hydrated, or warm. Other anomalies occur at syntaxes of the Penokean Orogen. One with the Superior Province and Marshfield Terrane in southern Minnesota and another with the Yavapai and Mazatzal Terranes, both at 100- to 250-km depth. In the midmantle, we image two linear high-velocity anomalies, interpreted as subducted fragments of the Farallon and Kula plates.

Original languageEnglish (US)
Pages (from-to)1725-1742
Number of pages18
JournalJournal of Geophysical Research: Solid Earth
Volume124
Issue number2
DOIs
StatePublished - Feb 2019

Bibliographical note

Funding Information:
The relative P wave velocity model with respect to iasp91 and the traveltime pick files used to derive the model we present in this paper are available for download at http://geophysics.earth.northwestern.edu/seismology/SPREE18/. Data from the USArray Transportable Array and SPREE were obtained from the IRIS Data Management Center (http://www.iris.edu; last accessed April 2014). Network Codes and years of operation: SPREE-XI (2011?2013), USArray TA-TA (2003 to present), z-US (1990 to present), CNSN-CN (1980 to present), GSN-II (1980 to present), FedNor-WU (1991 to present), POLARIS-PO (2000 to present), FLED-XR (2001?2002), APT-89-91-003-APT (1989), and TW?ST-XK (1997). Maps were created with the Generic Mapping Tools (GMT; Wessel et al.,). All picking of traveltimes were completed using the AIMBAT traveltime picking tool (Lou et al.,). This research was supported by NSF grant EAR-0952345. The Superior Province Rifting Earthscope Experiment (SPREE) was supported by the Earthscope program through NSF grant EAR-0952154. This project would not have been possible without the support of the landowners that allowed for the installation of TA and SPREE seismic stations. Please see ttps://www.earth.northwestern.edu/spree/People.html for full acknowledgments. In addition, we thank Basil Tikoff for discussion about our velocity anomalies with respect to the structural and tectonic history of the midcontinent.

Funding Information:
The relative P wave velocity model with respect to iasp91 and the traveltime pick files used to derive the model we present in this paper are available for download at http://geophysics.earth. northwestern.edu/seismology/SPREE18/. Data from the USArray Transportable Array and SPREE were obtained from the IRIS Data Management Center (http://www.iris.edu; last accessed April 2014). Network Codes and years of operation: SPREE-XI (2011–2013), USArray TA-TA (2003 to present), z-US (1990 to present), CNSN-CN (1980 to present), GSN-II (1980 to present), FedNor-WU (1991 to present), POLARIS-PO (2000 to present), FLED-XR (2001–2002), APT-89-91-003-APT (1989), and TW ST-XK (1997). Maps were created with the Generic Mapping Tools (GMT; Wessel et al., 2013). All picking of traveltimes were completed using the AIMBAT traveltime picking tool (Lou et al., 2013). This research was supported by NSF grant EAR-0952345. The Superior Province Rifting Earthscope Experiment (SPREE) was supported by the Earthscope program through NSF grant EAR-0952154. This project would not have been possible without the support of the landowners that allowed for the installation of TA and SPREE seismic stations. Please see ttps://www.earth.northwestern.edu/ spree/People.html for full acknowledgments. In addition, we thank Basil Tikoff for discussion about our velocity anomalies with respect to the structural and tectonic history of the midcontinent.

Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.

Keywords

  • Midcontinent Rift
  • North America
  • VanDecar
  • body wave
  • tomography

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