Abstract
Abstract Hudson Bay Lithospheric Experiment (HuBLE) was designed to understand the processes that formed Laurentia and the Hudson Bay basin within it. Receiver function analysis shows that Archaean terranes display structurally simple, uniform thickness, felsic crust. Beneath the Palaeoproterozoic Trans-Hudson Orogen (THO), thicker, more complex crust is interpreted as evidence for a secular evolution in crustal formation from non-plate-tectonic in the Palaeoarchaean to fully developed plate tectonics by the Palaeoproterozoic. Corroborating this hypothesis, anisotropy studies reveal 1.8 Ga plate-scale THO-age fabrics. Seismic tomography shows that the Proterozoic mantle has lower wavespeeds than surrounding Archaean blocks; the Laurentian keel thus formed partly in post-Archaean times. A mantle transition zone study indicates ‘normal’ temperatures beneath the Laurentian keel, so any cold mantle down-welling associated with the regional free-air gravity anomaly is probably confined to the upper mantle. Focal mechanisms from earthquakes indicate that present-day crustal stresses are influenced by glacial rebound and pre-existing faults. Ambient-noise tomography reveals a low-velocity anomaly, coincident with a previously inferred zone of crustal stretching, eliminating eclogitization of lower crustal rocks as a basin formation mechanism. Hudson Bay is an ephemeral feature, caused principally by incomplete glacial rebound. Plate stretching is the primary mechanism responsible for the formation of the basin itself.
Highlights
Cratonic regions are readily identified in global tomographic images where they are characterized by their deep-seated, fast wavespeed lithospheric keels
To address outstanding research questions exemplified by the Hudson Bay region, a broadband seismograph network in the Hudson Bay region was deployed by the Hudson Bay Lithospheric Experiment (HuBLE); stations have operated since 2003
The purpose of this contribution is to review the results of HuBLE, and to synthesize their implications for Precambrian processes, the formation of the Laurentian keel, and the reasons for the Phanerozoic development of the Hudson Bay basin
Summary
During multiple Wilson cycles over billions of years. Precisely how keels formed remains poorly understood, . In the heart of the Canadian Shield lies Hudson Bay, a vast inland sea, which masks a significant portion of the Trans-Hudson Orogen (THO), a Palaeoproterozoic collision between the Archaean Superior and Western Churchill cratons. The cratonic keel beneath the Hudson Bay region extends beneath both Archaean and Proterozoic terranes. Comprising several Archaean terranes brought together during a series of orogens during the Palaeoproterozoic, the region is one of the largest exposures of Precambrian rocks on Earth (Hoffman 1988). The Superior craton to the south is a collage of Meso- to Neoarchaean microcontinents and oceanic terranes amalgamated 2.72 –2.66 Ga. The Ungava Peninsula bounds eastern Hudson Bay and exposes 3.22 –2.65 Ga felsic orthogneiss and plutonic rocks that underlie c. The Ungava Peninsula bounds eastern Hudson Bay and exposes 3.22 –2.65 Ga felsic orthogneiss and plutonic rocks that underlie c. 2.0–1.87 Ga volcanic and sedimentary rocks of THE HUDSON BAY LITHOSPHERIC EXPERIMENT (a)
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