Volcanologie physique et geochimie des komatiites de Spinifex Ridge, Formation de La Motte-Vassan, Abitibi (French text, Quebec).

摘要

The "La Motte-Vassan Formation" (FLV), dated at 2714 +/- 2 Ma, is found at the base of the Malartic Group, a volcano-sedimentary assemblage in the Southern Volcanic Zone of the Abitibi greenstone belt. The FLV, approximately 6km in thickness, is mainly composed of komatiitic lava flows (95%). Most of these flows were overprinted by regional green schist facies metamorphism that obliterated the original mineralogy. The emphasis of this study is aimed at the physical volcanology and geochemistry of the Spinifex Ridge komatiites, more precisely a 60 x 40m outcrop.; The flow morphologies are directly related to low viscosity and high emplacement temperature of the komatiitic lavas.; It is here proposed that the Spinifex Ridge subaqueous sheet-like and tube-shaped flows may be analogues to highly fluid, low to high volume, subaerial pahoehoe sheet flows and coalescent lobes. Once the komatiitic lava emplaced on the Achaean oceanic seafloor, it probably initially propagated laterally because of its low viscosity. Then a thin flexible crust was formed on the lava surface which gradually became a solid crust formed by water-magma interaction. (Abstract shortened by UMI.)