Geochemistry of metalliferous sediments from the northern Oman ophiolite

Abstract

A range of siliceous, ferruginous and ferromanganiferous deposits are intercalated with, and overlie the lavas of the Late Cretaceous northern Oman ophiolite. Most of the deposits lie on the upper surface of the spreading event lavas; spreading event magmatism and later seamount-building events are coeval to relatively small metalliferous sediment deposits. The mineralogical and geochemical characteristics of these sediments are a function of the interaction between local hydrothermal systems, the marine depositional environment, and early diagenetic transformations. Various techniques are employed to objectively determine the actual end-member component compositions from which the metalliferous sediments formed. The sediments are a mixture of primary biosiliceous oozes and hydrothermal metallic components which were deposited at or near a marginal ocean-basin spreading axis during Cenomanian time. Factor analysis, selective acid leaching experiments and linear programming modelling identify six geologically reasonable end-members, which represent biosiliceous sediment, carbonate sediment, detrital sediment, hydrogenous sediment, and hydrothermal sediment. The techniques show that the sediments have a complicated hydrothermal history which is associated with the evolution of the Oman ophiolite. The hydrothermal component is sub-divided into high temperature and low temperature end-members which are characteristic of the proto-seamount and proto- rift event environments respectively. Vent proximal and vent-distal facies are described. The geochemistry of the deposits provides evidence for calcareous pelagic dissolution by hydrothermal fluids, which resulted in the relative concentration of a hyaloclastic component. The deposits which were not early-lithified are epidotized. Metamorphic transformation of the primary sediment occurred prior to eruption of the upper lava unit. The techniques which have been used to describe the range, composition and distribution of the end-member components provide a flexible framework for the characterisation of geological mixing in all marine metalliferous sediments.