Seismic imaging of the lithosphere beneath Hudson Bay: Episodic growth of the Laurentian mantle keel

摘要: Abstract The Hudson Bay basin in northern Canada conceals one of the major collisional zones Canadian Shield, Trans-Hudson Orogen (THO), which marks Paleoproterozoic collision between Archean Superior and Western Churchill cratons at ∼ 1.9 – 1.8 Ga . Improved knowledge upper mantle structure beneath region is essential to establish nature THO, specifically whether Himalayan-style plate tectonics operated times. Detailed seismological constraints on lithospheric architecture are also required advance our understanding mechanism timing keel formation. We use surface wave tomography illuminate new details region, resolving both seismic wavespeed azimuthal anisotropy. Phase velocity maps calculated from fundamental-mode Rayleigh dispersion curves, then used construct a 3D model exploring depths 300 km Fast shear wavespeeds suggest thickness varying 180 almost 280 km region. study confirms previous inferences that there no correlation crustal ages thickness. Patterns anisotropy indicate layered lithosphere. In uppermost mantle, highest velocities anisotropic fast directions wrap around Bay. This likely related formation processes Paleozoic intracratonic basin. At greater depth ( 70 150 ) we resolve two high-wavespeed cores separated by relatively narrow near-vertical lower-velocity curtain. internal suggested result terminal phase modern-style plate-tectonic during orogeny, entrapping juvenile Proterozoic material. lower lithosphere ≥ 160 depth) has homogeneous across with distinct patterns closely resembling subsurface geometry THO. interpret this basal layer as or reworked material accreted base existing cratonic soon after orogeny. Laurentian thus occurred multiple phases, developing post-Archean times,