Teleseismic studies of the lithosphere below the Abitibi-Grenville Lithoprobe transect

Abstract

Abstract:In the past decade, the Abitibi-Grenville Lithoprobe transect has been the site of numerous geological and geophysical surveys oriented towards understanding the lithospheric evolution of the southeastern Superior and adjoining Grenville provinces. Among the different geophysical methods that have been employed, earthquake seismology provides the widest range of information on the deep structures of the upper mantle. This paper presents a review of studies, both complete and ongoing, involving teleseismic datasets that were collected in 1994 and 1996 along the transect. A complete shear-wave splitting analysis has been performed on the 1994 dataset as part of a comparative study on electrical and seismic anisotropies. Results suggest a correlation between the two anisotropies (supported by xenolith data) and favour a lithospheric origin for the seismic anisotropy. The two anisotropies are believed to represent the fossilized remnants of Archean strain fields in the lithospheric roots of the Canadian Shield. Preliminary splitting results for the 1996 experiment suggest that the S-wave azimuthal anisotropy may be depth dependent and laterally varying. Ongoing receiver function analysis and traveltime inversion studies provide velocity models of the crust and upper mantle beneath the study area. Preliminary receiver function results reveal the presence of an S-velocity increase at -90-100 km depth which appears to be laterally continuous over 200 km. Traveltime inversion models indicate the presence of an elongate, low-velocity anomaly beneath the southern portion of the 1996 array which strikes obliquely to major geological structures at the surface (e.g., Grenville Front). Preliminary interpretation relates this anomaly to the same process (e.g., fixed mantle plume, continental rifting) responsible for the emplacement of the Monteregian Hills igneous province.Résumé : Au cours de la dernière décennie, de nombreuses campagnes géologiques et géophysiques ont été effectuées le long de la traverse Abitibi-Grenville du projet Lithoprobe, dans le but de comprendre l'évolution lithosphérique de la partie sud-est de la Province du Supérieur et de la Province de Grenville. Parmi les différentes méthodes géophysiques employées, la sismologie passive est sans doute celle qui procure le plus d'informations sur les structures profondes du manteau supérieur. Cet article passe en revue les études, complétées et en cours, s'appuyant sur les données télésismi-ques enregistrées en 1994 et en 1996, le long de la traverse. Une analyse complète de biréfringence des ondes S a été effectuée sur les données de 1994, dans le cadre d'une étude comparative entre l'anisotropie électrique et sismique. Les résultats obtenus suggèrent une corrélation entre les deux anisotropies (observation supportée par l'analyse de xénoli-thes), et favorisent une anisotropie sismique d'origine lithosphérique. Les deux anisotropies semblent associées à des champs de déformation archéens fossilisés dans les racines lithosphériques du Bouclier canadien...

Three billion years of crustal evolution in eastern Canada: Constraints from receiver functions

“…Sixty kilometers SE of the GF, Moho depth increases to 41-44 km ( Figure 5), consistent with wide-angle Lithoprobe surveys [e.g., White et al, 2000;Winardhi and Mereu, 1997;Martignole and Calvert, 1996]. Two receiver function profiles also image a sudden ∼10 km Moho depression ∼50 km SE of the Grenville Front [Rondenay et al, 2000;Eaton et al, 2006]. Increased thickness beneath the sections of the failed Iapetan Ottawa-Bonnechere Graben is also noted in a previous seismic survey that crosscuts the graben [Green et al, 1988].…”

Lithospheric variations across the Superior Province, Ontario, Canada: Evidence from tomography and shear wave splitting

“…[21] The four data sets (FedNor/CNSN, APT89, Abitibi, and TW$ST) do not overlap in time. Therefore their event [Silver and Kaneshima, 1993;Kay et al, 1999;Rondenay et al, 2000aRondenay et al, , 2000bEaton et al, 2004] are shown as gray arrows; black arrows are results for POLARIS, FedNor, and CNSN stations in this study. White triangles indicate stations with split times of 1 s or more.…”

Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

“…Additionally, a shallower lithosphere underlain by hydrated asthenospheric melts beneath the Appalachians may also be contributing to the observed decrease in seismic velocity [e.g., Rychert et al, 2005]. [Sénéchal et al, 1996;Rondenay et al, 2000b;Eaton et al, 2004;Frederiksen et al, 2006;Darbyshire et al, 2015;Gilligan et al, 2016]. Arrows are the APM vectors in the no-net-rotation frame [DeMets et al, 2010] (dark blue) and in the hot spot frame [Gripp and Gordon, 2002] (light blue).…”