Receiver-function studies in the Trans-Hudson Orogen, Saskatchewan

Abstract

Teleseismic events were recorded on an array of three-component broadband and short-period seismographs in the Trans-Hudson Orogen over a period of almost 3 years. Receiver functions calculated from these data were used in a forward-modelling study to derive the local shear-wave velocity structure beneath 20 stations. Station FFC (Flin Flon), located within the Flin Flon belt, was one of two stations situated on bedrock and produced the highest quality receiver functions. The FFC velocity model correlates well with an interpretation of nearby reflection data and features a distinct lower crust interpreted as Archean basement which cores the entire Reindeer Zone. Both radial and tangential receiver functions at FFC show strong evidence for a northeasterly dipping shallow boundary within rocks of the Flin Flon belt with a dip angle of 20°. Total crustal thickness is 37 km. Eighteen stations are situated on Phanerozoic sedimentary cover ranging in thickness from 0.4 km to greater than 2 km. Receiver functions at these stations display prominent high-amplitude, low-frequency reverberations that obscure more subtle phases associated with deeper structure. Because of this, only the gross crustal velocity structure can be constrained by modelling. Depth to Moho, which is 40-43 km at most stations, is the most strongly constrained feature. Stations with relatively thick crust within the Glennie domain suggest a connection between two regions of thick crust previously inferred from reflection and refraction data. This crustal root, presumably associated with a structural culmination imaged by reflection data and cored by Archean basement, is confined to the southwestern Glennie domain. One-dimensional modelling results show that the reverberations can be explained by a thin layer (<0.7 km) at the top of the sediments with a very high Poisson's ratio (0.4-0.48). The degree to which later arrivals are affected by reverberations is directly related to the parameters of this uppermost layer. We present the results of synthetic studies that demonstrate the sensitivity of receiver functions to this type of feature.