Physical volcanology, stratigraphy, and lithogeochemistry of an Archean volcanic arc: Evolution from plume-related volcanism to arc rifting within the SE Abitibi Greenstone Belt, Val d'Or, Quebec, Canada

The 2714-2702 Ma eastern segment of the Southern Volcanic Zone (SVZ) of the Abitibi Greenstone Belt is a complex sequence of volcano-sedimentary rocks cut by syn- to post-Vocanic plutonic suites. This segment can be subdivided into two stratigraphic groups based on regional tectonics and volcano-sedimentary stratigraphy: the basal Malartic Group, composed of the La Motte-Vassan, Dubuisson, and Jacola formations, and the overlying Louvicourt Group, containing the Val d'Or and Heva formations. The Malartic Group represents an Archean oceanic floor controlled by extensional mantle plume tectonics and characterized by effusive komatiites and basalts and intrusive dykes and sills. The Louvicourt Group marked a change to subduction-related processes; whereby incipient arc construction, represented by the louver Val d'Or Formation, overlapped with the waning stages of plume-generated volcanism, represented by the Jacola Formation. This conternporaneous volcanic activity indicates a conformable relationship. Subsequent rifting, represented by the Heva Formation, formed voluminous lavas that flooded the arc-related lavas.; The Jacola Formation is characterized by komatiitec and Mg-rich basalt, which is related to a mantle-plume source, that formed an extensive tholeiitic submarine lava plain. The contact between the mafic-ultramafic Jacola Formation and the intermediate-felsic Val d'Or Formation is gradational and indicated by the first appearance of voluminous volcaniclastic (i.e., fragmental) deposits that are tholeiitic to transitional and have a geochemical arc-signature.; The 3-5 km-thick Val d'Or Formation is a complex subaqueous volcano-sedimentary arc composed of numerous sequences of discontinuous and laterally interstratified intermediate to felsic lavas and their associated volcaniclastic deposits that evolved from tholeiitic to calc-alkaline. These small volume sequences are composed of 1-100 m-thick massive, pillowed/lobate, and brecciated lavas flows that are variably vesicular (1-30-vol%) and interstratified with 1-50 m-thick amalgamated volcaniclastic deposits of normal- to reverse-graded beds composed of angular to subrounded tuff- to breccia-sized clasts and a vesicularity index between 15 to 35-vol%. In addition, numerous small felsic-dominated volcanic centers of limited areal extent, containing massive sulfide deposits, define the Val d'Or Arc. Contact between the Val d'Or and Heva formations is defined by the abrupt appearance of tholeiitic lavas, represented by a tholeiitic spherulitic felsic unit at the base of the Heva Formation. (Abstract shortened by UMI.)...