Crustal thickness and Moho sharpness beneath the Midcontinent rift from receiver functions

Moidaki, Moikwathai; Gao, Stephen S.; Liu, Kelly H.; Atekwana, Estella A.

doi:10.4081/rg.2013.e1

Cited by 15 publications

(15 citation statements)

References 32 publications

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“…The receiver function analysis by Zhang et al () of all SPREE receiver functions revealed a complex crustal structure beneath the MCR that is remarkably consistent along the axial gravity high of the MCR. Together with the results and interpretation of Behrendt et al (), these SPREE findings on crustal structure provide a strong interpretation framework for inconclusive results from receiver function studies for a handful of individual stations on the MCR's gravity high (French et al, ; Moidaki et al, ; Shen et al, ). At first glance, receiver functions produce sharp peaks for Moho conversions away from the gravity high, but these peaks are weaker, broader, and less consistent for Moho conversions beneath the gravity high.…”

Section: Discussionsupporting

confidence: 63%

P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

et al. 2019

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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.

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Section: Discussionsupporting

confidence: 63%

P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

et al. 2019

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“…The Moho beneath the crustal MCR structures is a consistently elusive feature all along the MCR in our study region (Figures 6-8) and likely beyond [Tréhu et al, 1991;French et al, 2009;Moidaki et al, 2013; 10.1002/2016JB013244 Shen et al, 2013]. RFs of stations along the gravity high (the SM line) do not show a similar, clear P-to-S converted phase peak around 5 s as the other SPREE stations do (Figure 3).…”

Section: Discussionmentioning

confidence: 58%

Distinct crustal structure of the North American Midcontinent Rift from P wave receiver functions

et al. 2016

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Eighty‐two broadband seismic stations of the Superior Province Rifting Earthscope Experiment (SPREE) collected 2.5 years of continuous seismic data in the area of the high gravity anomaly associated with the Midcontinent Rift (MCR). Over 100 high‐quality teleseismic earthquakes were used for crustal P wave receiver function analysis. Our analysis reveals that the base of the sedimentary layer is shallow outside the MCR, thickens near the flanks where gravity anomalies are low, and shallows again in the MCR's center where the gravity anomalies peak. This pattern is similar to that found from local geophysical studies and is consistent with reverse faulting having accompanied the cessation of rifting at 1.1 Ga. Intermittent intracrustal boundaries imaged by our analysis might represent the bottom of the MCR's mostly buried dense volcanic layers. Outside the MCR, the Moho is strong, sharp, and relatively flat, both beneath the Archean Superior Province and the Proterozoic terranes to its south. Inside the MCR, two weaker candidate Mohos are found at depths up to 25 km apart in the rift's center. The intermediate layer between these discontinuities tapers toward the edges of the MCR. The presence of this transitional layer is remarkably consistent along the strike of the MCR, including beneath its jog in southern Minnesota, near the Belle Plaine Fault. We interpret these results as evidence for extensive underplating as a defining characteristic of the rift, which remains continuous along the Minnesota jog, where due to its orientation, it is minimally affected by the reverse faulting that characterizes the NNE striking parts of the rift.

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“…Analyzing older data, Moidaki et al . [] also measured crustal thickness using Ps information and inferred locally thick crust (~53 km thick) beneath a narrow section of the southern MCR near 41.5N, 94.5W, which is near the area with the thickest crust we find beneath the southern MCR (Figure a).…”

Section: Resultsmentioning

confidence: 99%

Crustal and uppermost mantle structure in the central U.S. encompassing the Midcontinent Rift

2013

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[1] Rayleigh wave phase velocities across the western arm of the Midcontinent Rift (MCR) and surrounding regions are mapped by ambient noise (8-40 s) and earthquake tomography (25-80 s) applied to data from more than 120 Earthscope/USArray stations across the central U.S. Receiver functions also are computed for those stations using harmonic stripping. Joint Bayesian Monte Carlo inversion is applied to generate 3-D posterior distributions of shear wave speeds (Vsv) in the crust and uppermost mantle to a depth of about 150 km, providing an overview of the seismic structure of the MCR and adjacent structures. Three major structural attributes are identified: (1) There is a high correlation between the long-wavelength gravity field and shallow Vs structure, but the MCR gravity high is obscured by clastic sediments in the shallow crust. This is consistent with an upper crustal origin to the MCR gravity anomaly as well as other anomalies in the region.(2) Thick crust (>47 km) underlies the MCR, but there is a gradient Moho in the northern part of the rift and a sharp Moho in the south. Thickened crust beneath the MCR is evidence for postrifting compression with pure-shear deformation along the entire rift; along-rift differences in lower crustal structure may signify magmatic underplating in the northern rift.

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Crustal thickness and Moho sharpness beneath the Midcontinent rift from receiver functions

Cited by 15 publications

References 32 publications

P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

Distinct crustal structure of the North American Midcontinent Rift from P wave receiver functions

Crustal and uppermost mantle structure in the central U.S. encompassing the Midcontinent Rift

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