Geology of the Cook Islands

There are fifteen Cook Islands, all being related to extinct volcanoes that have erupted in the volcanic hotspot highway of the south-central Pacific Ocean.

Rock formations include late Pliocene to more recent volcanics, Oligocene and Miocene reefs and middle Tertiary limestone underlying atolls[1] More recent emergence of the coral reefs is characterised in several cases consistent with sealevel fall at Mangaia, of at least 1.7 m (5 ft 7 in) in the last 3400 years.

[2] While not all the islands have firm dates for technical reasons after modern composition and redating studies more is understood.

[1] The 18 million year old[4] basaltic volcanics have been subjected to extensive study as it is the type for a recycled basaltic magma reservoir believed to have elements over 500 million years old that is known as HIMU (high μ = 238U/204Pb) mantle reservoir.

[3] The Arago hotspot Cook Islands are: These are the islands of Manihiki, Nassau, Penrhyn atoll,Pukapuka, Rakahanga and Suwarrow and likely have limestone caps to their large, old volcanoes erupting from the early Tertiary that are now coral atolls.