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- Title
Joint Inversion of SPREE Receiver Functions and Surface Wave Dispersion Curves for 3‐D Crustal and Upper Mantle Structure Beneath the U.S. Midcontinent Rift.
- Authors
Aleqabi, G. I.; Wysession, M. E.; Wiens, D. A.; Shen, W.; Van der Lee, S.; Darbyshire, F. A.; Frederiksen, A. W.; Stein, S.; Jurdy, D.; Revenaugh, J.
- Abstract
Broadband seismograms from the EarthScope Transportable Array and Superior Province Rifting EarthScope Experiment (SPREE) deployments are used to map the crust and uppermost mantle structures beneath the failed Midcontinent Rift (MCR) of Minnesota/Wisconsin, USA. The results suggest the existence of a variable zone of mafic underplating that is up to 20 km thick (40–60 deep). We jointly invert receiver functions and Rayleigh wave dispersion curves to quantify the region's crustal and mantle shear‐wave velocity structure. Basin sediment thicknesses are mildly asymmetric about the rift axis, with thickest regions immediately beneath the rift. 3‐D modeling shows anomalous lower crust and crust‐mantle transitions beneath the MCR. Sub‐MCR crustal thicknesses are generally >50 km with lower crust Vs of 4.0–4.2 km/s. Away from the MCR, the crust is typically ∼40 km thick. Strong variations in apparent crustal thickness are found along the MCR, increasing significantly in places. An additional layer of shear velocities intermediate between typical lower crust and upper mantle velocities (4.1–4.6 km/s) exists beneath most of the MCR which is thickest beneath the rift axis and pinches out away from the rift. This structure corroborates previous proposals of the presence of an underplated layer near the Moho. Results cannot distinguish between different mechanisms of emplacement (e.g., mafic interfingering within a subsequently down‐dropped lower crust vs. development of a high‐density pyroxenitic residuum at the top of the mantle). Also observed are anomalously high (>4.7 km/s) sub‐rift shear‐wave velocities at ∼70–90‐km depths, suggesting the presence of cold, depleted upper mantle material. Plain Language Summary: The Mid‐Continent Rift (MCR) is a failed continental rift that nearly split North America into two continental fragments 1.1 billion years ago. Unlike typical continental rift zones, which are characterized by stretched, thinned, and normal‐faulted crust, the base of the crust beneath the MCR sits more than 10 km below the surrounding regions and has shown evidence of being infilled by a thick layer of erupted volcanic basalt that may be 15–20 km thick in places. In addition, the base of the crust beneath the rift appears to contain an underplated layer of mafic volcanic materials that is itself 15–20 km thick in places, extending to depths of up to 60 km. The unique nature of this tectonic event left significant alterations to the lithosphere of North America that retain a strong seismic signature, even 1.1 billion years after the event. Key Points: The crustal depth increases to at least 50 km beneath the Mid‐Continent Rift (MCR) of Wisconsin (WI) and Minnesota (MN)The Moho beneath the WI/MN MCR contains a thick layer 40–60 km deep (Vs = 4.1–4.6 km/s) that may be underplated mafic volcanic materialBeneath the WI/MN MCR, Vs is generally slower than average in the upper crust but faster than average in the lower crust/upper mantle
- Subjects
MINNESOTA; WAVE functions; RAYLEIGH waves; RIFTS (Geology); MOHOROVICIC discontinuity; DISPERSION (Chemistry); SEISMOGRAMS; EARTH'S mantle
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 12, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB026771