The mantle reflections have been interpreted as subduction scars formed during Siluro-Dcvonian, west-directed underthrusting
of Ganderia and Avalonia beneath Laurentia (van der Velden and Cook, 2002a).
The quake's size suggests that it was a plate boundary, or underthrusting
, quake, seismologists say.
The latter occurs along sedimentary and structural-tectonic conduits such as unconformities, faults, and the decollement (the prominent boundary between the overriding and underthrusting
plates shown in the figure on page 87) as well as through mud volcanoes.
These include complete continental underthrusting
, distributed shortening, indention tectonics and extrusion, delamination and lower crustal flow.
Precise U-Pb dating of Meguma basement xenoliths: new evidence for Avalonian underthrusting
. Canadian Journal of Earth Sciences, 36, pp.
(1982) reported southwards directed underthrusting
(See Oceanus Winter 1992/93 for a discussion of "Island Arcs, Deep-Sea Trenches, and Back-Arc Basins.) Ocean drilling has provided fundamental information about colliding-plate processes, including accretion of sediments and volcanic edifices from underthrusting
to overriding plates, emplacement of rocks that have been altered by the forces at work in colliding-plate zones, and the nature of continental collisions.
"I disagree with [the underthrusting
scenario] almost entirely.
The progressive northward underthrusting
of cold, Indian mantle lithosphere since collision shut off the source in the Lhasa block at ~10 Ma.
If the squeezing model were correct, he says, one would expect higher temperatures in the lower crust in order for it to be "squeezable." Chun thinks this cold layer is evidence of the underthrusting