US EPA

6864389 

Journal Article 

METAMORPHIC OLIVINE IN PERIDOTITIC KOMATIITE FLOWS, LAC GUYER, QUEBEC 

Stamatelopoulou-Seymour, K; Francis, DM; , 

1980 

Yes 

Canadian Mineralogist
ISSN: 0008-4476
EISSN: 1499-1276 

MINERALOGICAL ASSOC CANADA 

QUEBEC 

265-270 

WOS:000208518700001 

Fresh olivine occurs throughout both massive and spinifex-textured peridotitic komatiite flows (now in the amphibolite facies) of the Lac Guyer Archean greenstone belt, James Bay. Quebec. This olivine encloses tremolite pseudomorphs of primary olivine and pyroxene skeletal crystals and contains secondary serpentine veinlets, two features that require it to be of metamorphic origin. It is also characterized by an unusually low forsterite content (Fo(60-65)), which reflects the low bulk Mg/(Mg+Sigma Fe) of the flows. This fresh olivine, unlike the metamorphic olivine reported in alpine peridotites, is in fact less Mg-rich than the expected primary olivine. Its distribution within individual flow units, however, reflects a chemical polarity developed by magmatic fractionation. Towards the base of the spinifex-textured flows, the metamorphic olivine becomes increasingly abundant and more idioblastic, but decreases in crystal size. The prominence of such olivine on weathered surfaces and its distribution pattern may constiute valuable field criteria for the recognition of komatiite flows in highly deformed and metamorphosed terrains.