Thermochemical Structure of the Hudson Bay Lithosphere, Northern Canada: Evidence from Multi-Observable Probabilistic Inversions

Fiona Ann Darbyshire, University of Quebec at Montreal UQAM, Centre de recherche GEOTOP, Montreal, QC, Canada and Juan Carlos Afonso, Macquarie University, ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Sydney, Australia

Contact First Author: Fiona Ann Darbyshire; darbyshire.fiona_ann@uqam.ca

Previously Published Material: About 30-40% of material was presented in an article: Darbyshire et al., 2013 (EPSL). About 80% was presented as an Invited talk at Fall AGU 2014.

Abstract ID#: 33810

 

English Abstract:
The Paleoproterozoic Trans-Hudson Orogeny (THO) was a Himalayan-style collision at ~1.8 Ga that brought together two of the largest North American cratonic blocks. The geometry of the collision is difficult to ascertain from surface geology, as much of the structure is concealed beneath the Paleozoic Hudson Bay intracratonic basin. However, seismographs placed around the periphery of the Bay have provided a wealth of data in recent years, allowing for regional-scale studies of lithospheric structure.

We use multi-observable probabilistic inversions to investigate the thermal and compositional structure of the Hudson Bay lithosphere. A joint inversion of Rayleigh wave phase velocities, geoid anomalies, elevation and surface heatflow is performed, giving a pseudo-3D model of the upper mantle.

Broadly, the Hudson Bay lithosphere is characterised by pervasive low temperatures and a high degree of chemical depletion. The thermal lithosphere is at least 250 km thick across the entire region, and may extend to 300 km depth in the centre of the Bay. The phase-velocity data are best explained by a stratified lithosphere, in which the upper layer is highly-depleted and the lower layer shows a slightly more fertile character (though still depleted compared to the average non-cratonic lithosphere). Within the upper layer, a relatively narrow zone of lower depletion is visible across the Bay and the Hudson Strait, coinciding with the inferred location of the THO collision zone. This zone likely preserves the signature of juvenile material trapped between the cratonic cores at the end of the THO collision.

Some outstanding issues remain; in some areas beneath the cratons, there is evidence from intermediate-period phase-velocities for anomalous mid-lithospheric structure. Variations in long-period phase velocities also suggest the presence of localised thermal heterogeneities in the sublithospheric mantle and transition zone beneath the region.

Back to: Multidisciplinary Perspectives on the Continental Mantle Lithosphere and Lithosphere-Asthenosphere Boundary I