ARCHITECTURE AND ANISOTROPY OF THE CRUST AND UPPERMOST MANTLE ACROSS GREENLAND AND THE NORTHWEST ATLANTIC: EVIDENCE FROM SURFACE WAVES (Invited Presentation)

Greenland and the Northwest Atlantic are characterised by a long history of tectonic and geodynamic processes, ranging from the formation of Archean and Proterozoic lithospheric keels through periods of Phanerozoic orogenesis to more recent seafloor spreading and hotspot tectonics. The tectonic structure of Greenland itself is difficult to study via surface geology due to the presence of the ice cap that covers over 80% of the continental interior. Inferences of tectonic boundaries and lithospheric architecture are largely based on geophysical data such as potential-field and seismic information.

Since 2010, data coverage from broadband seismic stations has greatly increased across Greenland, due largely to the establishment of the GLISN (Greenland Ice Sheet Monitoring Network) project, supplemented by data from shorter-term temporary networks and permanent stations. These data provide an excellent opportunity to study Greenland’s internal structure, using techniques such as receiver function analysis, ambient-noise and surface-wave tomography, and shear wave splitting, and recent years have seen a significant increase in new studies.

Our study takes advantage of the geometry of the mid-ocean ridges around Greenland, as well as a number of intra-plate earthquakes in northern Canada. We measured dispersion curves for these regional earthquakes at the GLISN network and combined the resulting data in a tomographic inversion that solved simultaneously for group velocities and azimuthal anisotropy. The isotropic part of the model was inverted to produce a 3D shear wave velocity model from 10 to 100 km depth, sampling the Greenland lithosphere and the northwest Atlantic crust and upper mantle. Moho depths beneath Greenland range from ~25 to >50 km, with significant intracrustal heterogeneity. In the mantle, the model highlights the distinction between the fast cratonic Greenland keel and the anomalously slow mantle in the vicinity of the Iceland hotspot. Seismic anisotropy is highly depth-dependent, and spatial variations at short periods may shed some light on the positions of crustal tectonic boundaries.