Deriving Crustal Properties from the P Coda Without Deconvolution: the Southwestern Superior Province, North America

frederiksen, a. w. ; delaney, c.;

We present a new approach to measuring crustal thickness and bulk properties from teleseismic data. In contrast to the traditional H − k stacking approach, which involves receiver-function deconvolution followed by stacking along expected arrival-time curves, we eliminate the deconvolution step and generate synthetic transfer functions predicting the relationship between the vertical and radial components. Given a catalogue of precalculated transfer functions, we
convolve the vertical component with each assumed transfer function and then calculate a misfit between the real and predicted radial component. As a single-layer crust is no longer a necessary assumption, we use the transfer-function approach to extend H − k analysis to models containing sedimentary basins. Applied to a data set in Minnesota, North Dakota and South Dakota, where the Archean Superior Province, Paleoproterozoic Trans-Hudson Orogen and Meso/Neoproterozoic Mid-Continent Rift are largely overlain by sediments of the Williston Basin, we find that the transfer-function approach is able to recover approximate sedimentary thickness, as well as remove the contaminating effects of the sedimentary layers
from crustal thickness and basement P/S velocity ratio measurements. We find that the Superior Province has uniformly low P/S ratio, reflecting a highly felsic composition, but has substantial Moho topography, with substantial crustal thinning to the west possibly related to Trans-Hudson accretion. The Trans-Hudson has thick crust with higher (more mafic) P/S ratio; higher ratios in the Superior near the Trans-Hudson contact suggest that the Superior is over thrust on Trans-Hudson basement material. The vicinity of the Mid-Continent Rift shows thinned crust, elevated P/S ratio, and a localized zone of very high P/S ratio associated with a rift offset, possibly related to a former triple junction, that extends northwestward into the Superior following a recently detected linear mantle anomaly.