Page 210 - Caldera Volcanism Analysis, Modelling and Response

Characterisation of Archean Subaqueous Calderas in Canada 185

intrusive synvolcanic to late tectonic activity occurred over a protracted period of
approximately 95 m.y. (2,735–2,640 Ma). The Abitibi supracrustal sequence
displays a modern plate tectonic succession of events from arc formation, to arc
evolution, to arc–arc collision and arc fragmentation (Chown et al., 1992; Mueller
et al., 1996). This evolutionary sequence is based on U–Pb zircon age
determinations (e.g. Ayer et al., 2002; Davis, 2002), the physical volcanology of
mafic (Cousineau and Dimroth, 1982; Dimroth et al., 1978, 1985) and felsic flows
(de Rosen-Spence et al., 1980), basin analyses (Mueller and Donaldson, 1992a),
structural studies (Daigneault et al., 2002, 2004) and plutonic emplacement history
(Chown et al., 1992, 2002). The usage of volcanic and sedimentary cycles is
retained in this study (Dimroth et al., 1982; Daigneault et al., 2002, 2004) as it best
expresses oceanic arc dynamics.

2.1. Abitibi greenstone belt divisions
The Southern (SVZ) and Northern Volcanic Zones (NVZ; Chown et al., 1992)
represent a collage of two arcs, separated by the crustal-scale Destor-Porcupine
Manneville Fault Zone (DPMFZ; Mueller et al., 1996). The E-trending Cadillac-
Larder Lake Fault Zone (CLLFZ) separates the SVZ from the Pontiac foreland
sedimentary rocks. These faults are considered arc terrane boundaries and are
characterised by remnant strike-slip basins (Mueller et al., 1996; Daigneault et al.,
2002, 2004). The divisions into a NVZ and a SVZ were based on the seminal work
of Dimroth et al. (1982, 1983) with internal and external zones. On a large-scale
geodynamic setting, the 2,735–2,705 Ma NVZ is an oceanic arc with numerous
central volcanic complexes that evolved from a diffuse and submerged arc (volcanic
cycle 1, ca. 2,735–2,720 Ma), to a mature and partially eroded arc, best
characterised by volcanic cycle 2 (2,720–2,705 Ma) in the Chibougamau region.
The subaqueous 2,734–2,728 Ma Hunter Mine and 2,728 Ma Normetal calderas
are integral components of NVZ volcanic cycle 1. Commensurate with volcanic
evolution are intra-arc flysch basins (sedimentary cycle 1) and clastic-dominated arc
aprons (sedimentary cycle 2; Mueller and Dimroth, 1987; Mueller and Donaldson,
1992a). The sedimentary basins were initiated during arc volcanism and continued
to evolve until 2,690 Ma.
The 2,714–2,696 Ma SVZ is separated from the Pontiac sedimentary
rocks (an accretionary prism) to the south by the CLLFZ and the DPMFZ to
the north, respectively. An extensive inter-arc sedimentary basin (sedimentary
cycle 3), over 200 km in length and represented by the Porcupine Group,
Kewagama Group and Caste Formation, connected the NVZ and SVZ prior to
shortening and transcurrent motion as indicated by layer-parallel faults (Mueller
et al., 1996; Daigneault et al., 2004). Sedimentary cycle 4 strike-slip basins
were formed in the fault zones of uplifted sedimentary cycle 3 basins that feature
local ultra-potassic volcanism and host abundant orogenic gold deposits (Robert,
2001).