be modern analogues. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Archean; Mafic-felsic volcanism; Subaqueous; Volcanic facies; Composite arc volcano; Geochemistry
1. Introduction
The majority of volcanogenic massive sulphide deposits VMS in the geologic record are associ-
ated with rhyolitic rocks Rona, 1988; Barrie and Hannington, 1997, whereas modern VMS coun-
terparts are observed mainly in mid-ocean ridge spreading centers which are generally basaltic in
composition Rona, 1988. Only recently has there been a shift in research emphasis to VMS mineral-
ization in modern arc-backarc systems Rona and Scott, 1993; Ishibashi and Urabe, 1995. Studies
on active maficfelsic and felsic submerged arc- backarc settings are restricted to submersible
dives, such as the Sumisu Rift Smith et al., 1990, the Myojin knoll Iizasa et al., 1999, the Lau
Fouquet et al., 1993 or Mariana backarc basins Lonsdale and Hawkins, 1985 as well as the
Kermadec arc volcanoes Wright et al., 1998. In contrast, ancient arc sequences Sato and Amano,
1991; Kano et al., 1993; Martin-Barajas et al., 1995 are important windows for the study of
modern subaqueous arc-forming processes. The Abitibi Subprovince, a well documented Archean
greenstone belt, is composed of numerous felsic or maficfelsic volcanic edifices Chown et al., 1992,
which favors in-depth volcanological analyses of subaqueous felsic volcanic complexes related to
VMS deposits. Understanding the physical vol- canology of submerged volcanoes is important for
establishing eruptive mechanisms, mode of vol- canic emplacement and geometry of volcanic
edifices, as well as defining proximal and distal volcanic facies with respect to VMS deposits.
Characteristics of felsic and mafic Archean lava flows have been addressed in detail Dimroth,
1977; Dimroth et al., 1978; de Rosen-Spence et al., 1980; Cousineau and Dimroth, 1982, but
little emphasis has been placed on the evolution of entire subaqueous volcanic complexes Gibson
and Watkinson, 1990; Morton et al., 1991. The principal aim of this study is to document the
volcanic construction of the mafic to felsic Norme´tal volcanic complex NVC in the Abitibi
greenstone belt. A two-fold approach based on regional and detailed mapping, sampling and
structural analysis was conducted emphasizing: 1 physical volcanology; and 2 geochemistry. In
addition, the Norme´tal volcanic complex is com- pared to other volcanic centers in the Abitibi belt
and modern arc volcanoes in order to constrain Archean arc models.
2. Geological setting
