Tectonic significance of bimodal volcanism in the Archean Michipicoten greenstone belt, Ontario

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6070229

Sylvester, P J

In the lower volcanic cycle (2750 Ma old) of the Michipicoten greenstone belt, Ontario, a basal mafic unit (MV1) consisting mainly of basalt-basaltic andesite (49.4-56.4 wt.% SiO/sub 2/, 8.77-12.36 wt.% FeO/sub t/) with enriched ((La/Sm)/sub n/=1.9-2.6, Th=2.0-4.1 ppm, Sr=310-570 ppm) and depleted ((La/Sm)/sub n/=0.55-1.07, Th=0.16-0.71 ppm, Sr<250 ppm) trace element characteristics is locally overlain by a felsic unit (FV1) dominated volumetrically by rhyolite (71.9-79.6 wt.% SiO/sub 2/) and subordinate dacite (62.2-68.8 wt.% SiO/sub 2/). The mafic rocks are pillowed, massive flows and hyaloclastites suggesting subaqueous emplacement, whereas the felsic rocks are dominantly subaerial to shallow subaqueous pyroclastic deposits. The basalts of MV1 are similar chemically to modern tholeiites formed in primitive island arc/marginal basin complexes. In contrast, the rhyolites and dacites of FV1 exhibit the calc-alkaline chemical characteristics and rock associations typical of some continental inner arc volcanics. The juxtaposition of primitive island arc/marginal basin and continental inner arc tectonic settings occurs at the present time in the Tonga-Kermadec-New Zealand island arc. According to this model, MV1 is analogous to the basalt/basaltic andesite-dominated volcanism of the Tonga-kermadec island arc/Lau back-arc basin, whereas FV1 is the equivalent of the voluminous rhyolitic ignimbrites of the Taupo inner arc basin. The model suggests that the lower volcanic cycle of the Michipicoten belt formed on a basement consisting of small blocks of continental crust surrounded by oceanic crust.

• Research Organization: Johnson Space Center, Houston, TX (USA)
• OSTI ID: 6070229
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ANDESITES
CHEMICAL COMPOSITION
PETROGENESIS
BASALT
ONTARIO
RHYOLITES
GEOCHEMISTRY
OCEANIC CRUST
PRECAMBRIAN ERA
SCHISTS
TECTONICS
VOLCANISM
CANADA
CHEMISTRY
EARTH CRUST
GEOLOGIC AGES
IGNEOUS ROCKS
METAMORPHIC ROCKS
NORTH AMERICA
ROCKS
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
&amp; Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)