Hydrothermal chert and associated siliceous rocks from the northern Pacific their geological significance as indication od ocean ridge activity

Analyses of 42 Cretaceous rock samples from Deep Sea Drilling Project (DSDP) L Leg 32, in the northern Pacific, show that chert and porcellanite are enriched in Fe, Mn, P, Cu, Ba, Mo, Ni and Pb relative to both Triassic biogenic cherts of central Japan and Cretaceous DSDP cherts of Leg 62. The iron enrichment (up to 6.68% Fe2O3, as total iron) is most prominent in chert immediately overlying basal basalt which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions. Chemical features characterized by a low ratio for AI/(Al +Fe+Mn) and Al2O3/TiO2 and a high ratio for total - Fe2O3/TiO2 - MnO/TiO2 and Mo/TiO2, as well as petrological evidence, indicate that the cherts formed in an intense submarine hydrothermal environment on or near the Cretaceous Japanese spreading center which separated the Kula plate from the Pacific plate. The spreading rate of the Cretaceous Japanese spreading center estimated from the chemical composition of the cherts was about 3.7 cm yr 1:the rate is comparable to that inferred from the geomagnetic data