Genesis of peridotites from the ophiolite complex of Macquarie Island, southwestern Pacific Ocean

Characteristic features of the mineral composition of peridotites from the ophiolite complex of Macquarie Island were studied for the first time. Four genetic rock types were distinguished on the basis of petrographic and petrologic investigations: (1) spinel harzburgites; (2) plagioclase-spinel harzburgites; (3) cumulative rocks of the dunite-wehrlite-troctolite series; and (4) cumulus olivine orthopyroxenites. The first three types are regarded as a complex formed in an oceanic spreading center with the plagioclase-spinel harzburgites being probably products of contact metasomatic alteration of spinel harzburgites under the influence of melt or related magmatic fluid. Rocks with similar mineralogical characteristics are widespread in mid-ocean ridges. The specific features of the mineral composition of the olivine orthopyroxenites preclude their formation in an oceanic spreading center and their provenance is related to the intraplate basaltic magmatism of oceanic plateaus, which is common in the western Pacific Ocean. The character of subsolidus metamorphism in the peridotites and the occurrence of high-temperature amphibolite metamorphism in some of the spinel harzburgites and olivine orthopyroxenites are comparable to the metamorphic parameters of oceanic peridotites in large transform faults. Copyright © 1998 by MAEe Cyrillic signK Hayκa/Interperiodica Publishing.