Phanerozoic Peridotitic and Pyroxenitic Komatiites from Newfoundland
H. D. UPADHYAY 1
1 Department of Earth Sciences, Northeastern Illinois University, Chicago 60625
Peridotitic and highly magnesian pyroxenitic komatiites, thus far known to occur almost exclusively in the Archean (before 2.5 x 109 years ago) terranes, are reported from an Ordovician (0.5 x 109 years) ophiolite suite in Newfoundland. Their occurrence as pillow lavas or as chilled dikes, their possession of quench textures and geochemical parameters such as high contents of magnesium oxide, nickel, and chromium and low contents of titanium dioxide and potassium monoxide, low ratios of iron to iron plus magnesium, and values of the ratio of calcium oxide to aluminum oxide of close to unity demonstrate that they were formed through the rapid cooling of a highly mobile komatiitic melt. These features resemble those of many Archean peridotitic-pyroxenitic komatiites and indicate that the Archean-type magmatism did prevail in the younger segments of the earth's history although perhaps in a more erratc manner.
Submitted on January 10, 1978
Revised on September 26, 1978
