nearest North Island volcanics. The seabed on the rise has a component from a large drowned Oligocene island of metamorphic rocks, mantle peridotite, and Gondwana derived continental rocks dating from 38 million years ago (the oldest basement is dated 37.5 Ma). These 39–36 million year old Eocene lavas are now known to be subordinate to later activity and are mainly confined to the western side of the ridge. However a 32 million year old andesitic centre has been characterised at the northeastern area of the ridge. There was a pulse of voluminous late Oligocene to early Miocene (25 to 22 million years ago) volcanic activity within the Cook Fracture Zone and the northern portions of the ridge that now dominate. The ridge surface is mainly trachybasalt and basaltic andesite, with some trachyandesite, and andesite, but no rhyolite volcanics. Its sides are basalt suggesting these are basement as they are also found in the nearly basins. Sporadic volcanic activity after this is evidenced by say samples of andesite from 20 million years ago. The ridge has been mainly below sealevel since 21 million years ago due to Australian and Pacific Plate extension but the present islands to the ridges south were still connected to each other, but not New Zealand, at the sea level minimum of 7000 years ago. Tectonic implications It has been postulated that the relatively rigid Three Kings Ridge had a role in the emplacement of the the Northland Allochthon and this may contain rocks inherited from a Three Kings arc collision. This collision as the continental crust of the ridge moved southeast about 25.5–22 million years ago would have been had to have been associated with a subduction flip in the postulated model. Islands, reefs and seamounts The ridge has to its south a group of 13 presently uninhabited islands where the South Pacific Ocean and Tasman Sea meet. These are separated from the New Zealand North Island by a wide submarine trough that is at least deep and may be associated with the Vening Meinesz Fault Zone. See also References Underwater ridges of the Pacific Ocean Zealandia Tasman Sea Volcanism of Zealandia Volcanoes of the New Zealand outlying islands Volcanoes of Zealandia Geology of Zealandia Geography of the New Zealand seabed Three Kings Islands Plateaus of Oceania