Emplacement history of mafic-ultramafic volcanic rocks in the northern Pontiac subprovince, Quebec, Canada

Detailed geological mapping of volcanic, sedimentary and intrusive rocks in the northern Pontiac subprovince of the Superior Province has identified multiple volcanic-sedimentary contacts at the margins of a 30 km long volcanic package of high-Fe tholeiites and Munro- to Barbertontype komatiitic flows and sills. Breccias displaying blocky, globular and tendril-like juvenile clasts in a massive sedimentary matrix were observed along the contacts of mafic-ultramafic intrusions with their host sedimentary rocks. These textures are consistent with peperite, a rock formed by the mixing and mingling of magma with wet, unconsolidated sediments. Geochemical data for one of the peperites indicates that the igneous component has a similar trace element composition to spinifex-bearing komatiite flows and the sedimentary component has a similar composition to the Pontiac Group wackes. Additionally, conformable unstrained contacts were observed between effusive volcanic rocks and turbiditic wackes. These relationships indicate a previously unrecognized ca. 2682 Ma mafic and ultramafic volcanic event synchronous with the deposition of the Pontiac subprovince sedimentary rocks. This suggests that the mafic-ultramafic volcanic package is synsedimentary and autochthonous, which is not consistent with previous interpretations of these rocks as structural thrust panels. We propose that the mafic-ultramafic volcanic package was emplaced during a previously unrecognized plume-related extensional event that facilitated the upward flow of mantle-derived magmas along major, mantle-penetrating structures during Pontiac sedimentation. Shortly after, tectonic compression folded and imbricated the Pontiac rocks and accreted them to the southern margin of the Abitibi subprovince.

Name thesis:degree_name

Master of Science (MSc) in Geology

Grantor dc:publisher

Laurentian University of Sudbury

Year dc:date.issued

2020

Author dc:creator

• Rehm, Adrian Gerhard Nutting

• Pontiac subprovince
• peperites
• synsedimentary volcanism
• komatites
• sedimentary basins,
• Archean tectonics

Language dc:language.iso

en

Repository record dc:identifier.uri

https://laurentian.scholaris.ca/handle/10219/3502

OAI record oai:identifier

https://laurentian.scholaris.ca/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Alaurentian.scholaris.ca%3A10219%2F3502