Structural evolution of the Otish Basin: a Paleoproterozoic polymetallic-uranium rich meteorite impact structure, Québec, Canada

English Abstract:

The evolution of the Palaeoproterozoic sedimentary Otish Basin (OB), located in northern Québec, was mainly developed on the southeastern margin of the Superior craton. The OB lay unconformably on the Archean basement, covering an area of about 5200 km², averaging a thickness of 2,4 km and sitting north of the Mesoproterozoic Grenville province. The evolution of the OB has been disturbed by a major meteorite impact responsible for a widespread gabbro emplacement at around 2.1Ga. Shocked derived material (glass and PDFs) are observed in the sediments under the gabbro sheet and inside the large enclaves found in the gabbro itself that could be interpreted has a melt/breccia sheet. The gabbro has been emplaced in an extrusive manner according to their distribution and their physical relationship with the sediments.

A regional brittle-ductile deformation, possibly related to the Hudsonian orogeny (1.85 Ga), affected all the units of the OB. The main stress component was oriented NW-SE producing folding and overthrusting to the NW. The OB is an overturned syncline with a shallow plunge to the SW and later offset by NW and NNE conjugate faults. A correlation with the timing of the deformation of the Sudbury structure could possibly be proposed. The major deformation is pre-Grenvillian and post-Archean. Major faults and fractures were developed or reactivated along some ring or radial dykes formed during the meteorite impact. The morphological oval shape of the OB combine with the arc shape of the Mistassini Basin (MB), adjacent to the SW, with shatter cones of uncertain age, lead us to consider the MB as an element of our puzzling huge structure for which the postulated radius of the relevant structure is well over 250 km.

Mineralised hydrothermal fluid rich in uranium (1.7 Ga) and polymetallic (Cu, Au, Pb, Ag) deposits are filling early Proterozoic fractures and faults zones affecting both the OB and the Archean basement.