P wave tomography for 3-D radial and azimuthal anisotropy beneath
Greenland and surrounding regions
Abstract
We present the first 3-D images of P-wave radial anisotropy (RAN)
and azimuthal anisotropy (AAN) down to 750-km depth beneath Greenland
and surrounding regions. The results are obtained by applying a regional
tomographic method to simultaneously invert P wave arrival times
of 1,309 local events and P wave relative traveltime residuals of
7,202 teleseismic events, which were recorded mainly by the latest GLISN
network. A high-velocity body located beneath northeast Greenland (NEG)
to its offshore exhibits a strong negative RAN and a strong AAN with N-S
to NE-SW oriented fast-velocity directions (FVDs). The FVDs are
generally consistent with the direction of the fold axis of the
Caledonian fold belt, which is considered as an outcrop of the NEG body
on land. Beneath the Iceland, Jan Mayen, and Svalbard hotspots, a strong
positive RAN and a negligible or weak AAN are revealed, which may
reflect effects of upwelling mantle plumes. Among the three regions, a
weak AAN with a constant FVD is only revealed beneath Iceland, which may
reflect the existence of background mantle flow. The RAN and AAN
features beneath the Labrador Sea, Davis Strait, and Baffin Bay suggest
the following scenario on breakup between Greenland and Canada: the
breakup was initiated at the Labrador Sea due to local mantle upwelling,
but the northward propagation of the breakup was blocked by a strong
high-velocity anomaly beneath Davis Strait; the opening of Baffin Bay
might be caused passively by far-field plate forces.