The volcanic stratigraphy and location of massive sulphide deposits in the Oman ophiolite
The volcanic stratigraphy of the Oman ophiolite complex is made up of three distinct mappable units termed (in order of eruption) the Geotimes, Lasail and Alley Units. The Geotimes Unit is dominantly basaltic pillow lavas whereas the Lasail and Alley Units comprise basalt-andesite-rhyolite fractionation series. Field observations and geochemistry indicate that each formation erupted in a different local tectonic environment: the Geotimes Unit at a fast-spreading ridge crest; the Lasail Unit as a series of discrete volcanic seamounts; and the Alley Unit in a submarine graben setting. Almost all significant massive sulphide deposits formed on the Geotimes pillow lavas just prior to eruption of the basalt pillow lavas of the Lasail Unit and all are locatyed in the seamount areas. The volcanicity and hydrothermal activity all took place within a geologically short period of time above a subduction zone, possibly as an incipient arc-basin complex.