The Archean Dongwanzi ophiolite complex, North China craton: 2.505-billion-year-old oceanic crust and mantle

We report a thick, Laterally extensive 2505 +/- 2.2-million-year-old (urani um-lead ratio in zircon) Archean ophiolite complex in the North China crato n. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumu lates, compositionally Layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a m ixed dike-pillow lava section, chert, and banded iron formation. The docume ntation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billio n years ago at divergent plate margins and that the temperature of the earl y mantle was not extremely elevated, as compared to the present-day tempera ture. Plate tectonic processes similar to those of the present must also ha ve emplaced the ophiolite in a convergent margin setting.