North American mantle processes during the Mesoproterozoic through Cenozoic Eras from seismic field experiments and visualizations

Bollmann, Trevor Alan

doi:https://doi.org/10.21985/n2-2rtx-j670

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North American mantle processes during the Mesoproterozoic through Cenozoic Eras from seismic field experiments and visualizations

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The structure of the North American crust and mantle was investigated using P wave teleseismic tomography and the links between seismic tomographic models, locations of volcanism, sediment isopachs, and continental scale crustal structures via plate reconstruction modeling. Nearly 50,000 teleseismic P wave delay times were measured from seismograms recorded by the USArray Transportable Array (TA), Superior Province Rifting EarthScope Experiment (SPREE), and permanent seismic stations; then combined with measurements from previous studies in a tomographic inversion for the mantle beneath the North American Midcontinent. High-velocity anomalies are prevalent in the study area but there are also prominent relatively low velocity anomalies. Two are coincident with rift-related Bouguer gravity anomaly highs and could be related to underplating of the Midcontinent Rift. Another two are located at the syntaxes of crustal terranes, amalgamated during the formation of Laurentia. In the mid-mantle we image high-velocity anomalies, interpreted as fragments of the subducted Farallon and Kula plates. Next, the anomalous morphology of the Western Interior Basin (WIB) was investigated through the use of sediment isopachs, surface expressions of volcanism, crustal structures, and subducted slab locations through time. By correlating these diverse datasets, two hypotheses for the formation of the WIB were tested. Although no hypothesis was conclusively proven or disproven, it was determined that a fragment of the subducted Farallon slab was in the correct location to interact with the overriding crust at the time of basin expansion. To facilitate the aforementioned studies, a seismic experiment was conducted. Best practices in seismic field work, a project overview, possible issues, and methods to overcome them were compiled. An assessment of the Canadian SPREE stations was completed to determine if noise sources identified during the siting phase of the project correlated with station quality. During this assessment, a number of noise characteristics were identified. Namely, a diurnal change in noise levels between day and night due to changes in cultural activity and prevailing wind changes throughout the day, summer/winter changes in long period noise attributed to atmospheric circulation, and the observation of microseisms that originated from Lake Superior.

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