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Crustal and uppermost mantle structures of the North American Midcontinent Rift revealed by joint full-waveform inversion of ambient-noise data and teleseismic P waves.

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Title: Crustal and uppermost mantle structures of the North American Midcontinent Rift revealed by joint full-waveform inversion of ambient-noise data and teleseismic P waves.
Authors: He, Bin1,2 (AUTHOR) hebin14@mails.ucas.ac.cn, Wang, Kai3 (AUTHOR), Liu, Tianshi4 (AUTHOR), Lei, Ting4 (AUTHOR), Du, Nanqiao4 (AUTHOR), van der Lee, Suzan5 (AUTHOR), Darbyshire, Fiona Ann6 (AUTHOR), Frederiksen, Andrew7 (AUTHOR), Zhu, Hejun2,8 (AUTHOR), Lumley, David2,8 (AUTHOR), Halls, Henry9 (AUTHOR), Liu, Qinya1,4 (AUTHOR)
Source: Earth & Planetary Science Letters. Sep2024, Vol. 641, pN.PAG-N.PAG. 1p.
Subjects: Seismic anisotropy, Rifts (Geology), Gravity anomalies, Sills (Geology), Ore deposits, Volcanic ash, tuff, etc., Anorthosite
Geographic Terms: North America
Abstract: The Midcontinent Rift (MCR), hosting several world-class ore deposits, is the fossil remnant of a massive Mesoproterozoic rifting event (1.1 Ga) that did not lead to the formation of an ocean basin. To better understand the lithospheric processes associated with the rifting stage and its subsequent failure, we developed a novel full-waveform joint inversion method using ambient noise data and teleseismic P waves for this seismically inactive region. We apply this approach to three years (2011-2013) of seismic recordings from the Superior Province Rifting EarthScope Experiment (SPREE) (~12 km average station spacing) and the USArray Transportable Array (~70 km average station spacing), and obtain a new 3D high-resolution Vs model down to 100 km depth, as well as Vp and density models down to 60 km depth. The model shows major velocity anomalies in agreement with previous seismic studies for the western arm of the MCR. In particular, we observe high density (2.8-3.0 g/cm3), Vp (6.3-6.5 km/s), and Vs (3.6-3.7 km/s) structures in the shallow upper crust within the rift, likely associated with volcanic rocks. Similar to a previously identified underplated layer, we also observe extensive normal-to-high Vs (3.8-4.2 km/s) along the whole rift axis and Vp (6.8-7.5 km/s) beneath the northern segment of the rift within the lower crust. However, the Vs and Vp values are lower than average for typical underplated materials. We suggest that this underplated layer may represent a combination of different intrusive rock types (e.g., gabbro, anorthosite) developed during magma differentiation processes, or contamination of the mafic magma by surrounding crustal material, or intrusions of sills. • High-resolution crustal and uppermost mantle structure of the Midcontinent Rift in North America is imaged. • High Vp and density anomalies in the upper crust are consistent with high Bouguer anomalies within the rift. • Extensive and anomalous Vs and Vp structures indicate magmatic underplating within the lower crust. • Underplated materials may have variable compositions, such as gabbro and anorthosite. [ABSTRACT FROM AUTHOR]
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Abstract:The Midcontinent Rift (MCR), hosting several world-class ore deposits, is the fossil remnant of a massive Mesoproterozoic rifting event (1.1 Ga) that did not lead to the formation of an ocean basin. To better understand the lithospheric processes associated with the rifting stage and its subsequent failure, we developed a novel full-waveform joint inversion method using ambient noise data and teleseismic P waves for this seismically inactive region. We apply this approach to three years (2011-2013) of seismic recordings from the Superior Province Rifting EarthScope Experiment (SPREE) (~12 km average station spacing) and the USArray Transportable Array (~70 km average station spacing), and obtain a new 3D high-resolution Vs model down to 100 km depth, as well as Vp and density models down to 60 km depth. The model shows major velocity anomalies in agreement with previous seismic studies for the western arm of the MCR. In particular, we observe high density (2.8-3.0 g/cm3), Vp (6.3-6.5 km/s), and Vs (3.6-3.7 km/s) structures in the shallow upper crust within the rift, likely associated with volcanic rocks. Similar to a previously identified underplated layer, we also observe extensive normal-to-high Vs (3.8-4.2 km/s) along the whole rift axis and Vp (6.8-7.5 km/s) beneath the northern segment of the rift within the lower crust. However, the Vs and Vp values are lower than average for typical underplated materials. We suggest that this underplated layer may represent a combination of different intrusive rock types (e.g., gabbro, anorthosite) developed during magma differentiation processes, or contamination of the mafic magma by surrounding crustal material, or intrusions of sills. • High-resolution crustal and uppermost mantle structure of the Midcontinent Rift in North America is imaged. • High Vp and density anomalies in the upper crust are consistent with high Bouguer anomalies within the rift. • Extensive and anomalous Vs and Vp structures indicate magmatic underplating within the lower crust. • Underplated materials may have variable compositions, such as gabbro and anorthosite. [ABSTRACT FROM AUTHOR]
ISSN:0012821X
DOI:10.1016/j.epsl.2024.118797