Petrology of ultramafic rocks at DSDP Holes 82-556, 82-558, and 82-560

Spinels from Sites 556 and 560 have high Cr/(Cr+Al) (0.45-0.53). Those from Site 558 have Cr/(Cr+Al) values that are among the highest measured for any plagioclase-free oceanic peridotites (0.55-0.62). Whole-rock chemistry, although affected by serpentinization, suggests that the peridotites had relatively low CaO, TiO2, Al2O3, and Na2O.

Mineral and whole-rock chemistry and modal abundances suggest that Leg 82 peridotites are residua from partial melting, and that the extent of partial melting may have been greater in this region than farther south in the North Atlantic, or that the mantle was originally more depleted here.