Lithoprobe Abitibi-Grenville geologic transect

Abstract from Harvard Workshop on continental roots, Oct 10-13, 1997:

Thermomechanical erosion of the continental lithosphere beneath the
Precambrian Superior and Grenville provinces Canada relation to the
Monteregian hotspot track

S. Rondenay, MG Bostock Dept of Earth Ocean Sciences, University of
British Columbia, Vancouver, BC TM Hearn Department of Physics, New
Mexico State University, Las Cruces, NM, DJ White Department of
natrual Resources, Canada, Ottawa, ON

The Monteregian Hills, White Mountains and Kelvin Seamounts igneous
formations are widely considered to have a common origin. Their
mechanism of origin, however, has been explained by two conflicting
views tension induced rifting of the lithopshere versus motion of the
North American plate over a hotspot. Here, we present evidence in
support of the latter view using results of teleseismic body wave
travel time inversion. The data considered in this study were
collected along the LITHOPROBE Abitibi-Grenville transect in Quebec
and Ontario Canada. A N-S linear array of 28 IRIS/PASSCAL portable
broad band seismographs was deployed across the Superior
Abitibi-Pontiac and Grenville geological provinces, from May to
October 1996. A fairly small station spacing of 20 km was used to
facilitate later work on converted phases profiling and local
shear-wave splitting analysis. Two stations were deployed west of the
main line in order to provide additional spatial coverage of two
special geological features the Kirkland Lake kimberlites and the
Kapuskasing uplift. The seismic database used for the inversion was
augmented by recordings from two broad-band stations from the Canadian
National Seismic Network Geological Survey of Canada, and six short
period stations from the Southern Ontario Seismic Network University
of Western Ontario. Relative travel times of P and S waves from 123
and 40 teleseismic events, respectively, were inverted for velocity
perturbations in the upper mantle. Good resolution is obtained between
50 and 400 km depth for P phases and between 50 and 250 km depth for S
phases, as inferred from the respecteive ray coverages. The most
prominent feature of our model is a low velocity NW-SE corridor that
crosses the southern portion of the line at latitude 46N, and is well
constrained by both P and S travel time inversions. It is located
between 50 and 300 km depth, and has an average width of 125 km, which
appears to increase smoothly with depth. The low velocity corridor
coincides with the northwestward extrapolation of the trend defining
the Monteregian igneous formations and passes 100 km south of the
Kirkland Lake kimberlites. Our preliminary interpretation is that the
anomaly records the track of the Great Meteor hotspot through the
Superior and Grenville provinces of the Canadian Shield. The absence
of major igneous activity at the surface implies a thicker lithosphere
beneath the shield, which was more resistant to thermomechanical
erosion than that to the southeast. The temporal and spatial proximity
of the Kirkland Lake kimberlites suggests the ignition of small volume
kimberlite volcanism by plume activity.