GEODYNAMIC INFORMATION IN PERIDOTITE PETROLOGY

Abstract

Systematic differences are observed in the petrology and major element geochemistry of natural peridotite samples from the sea floor near oceanic ridges and subduction zones, the mantle section of ophiolites, massif peridotites, and xenoliths of cratonic mantle in kimberlite. Some of these differences reflect variable temperature and pressure conditions of melt extraction, and these have been calibrated by a parameterization of experimental data on fertile mantle peridotite. Abyssal peridotites are examples of cold residues produced at oceanic ridges. High-MgO peridotites from the Ronda massif are examples of hot residues produced in a plume. Most peridotites from subduction zones and ophiolites are too enriched in SiO 2 and too depleted in Al 2 O 3 to be residues, and were produced by melt–rock reaction of a precursor protolith. Peridotite xenoliths from the Japan, Cascades and Chile–Patagonian back-arcs are possible examples of arc precursors, and they have the characteristics of hot residues. Opx-rich cratonic mantle is similar to subduction zone peridotites, but there are important differences in FeO T . Opx-poor xenoliths of cratonic mantle were hot residues of primary magmas with 16–20% MgO, and they may have formed in either ancient plumes or hot ridges. Cratonic mantle was not produced as a residue of Archean komatiites.