New ages from the Hawaiian-Emperor chain and relations to other Pacific linear chains
Monterey Bay Aquarium Research Institute
The session focused on linear island chains on the Pacific Plate, because this eliminates the potentially large errors associated with reconstructions involving multiple plates. When only Pacific linear island chains are considered, there are a large number of chains that roughly parallel and are contemporaneous with the Hawaiian chain. These include Kodiak-Bowie, Marquesas, Society, Pitcairn-Gambier, Cook-Austral, Samoa, and the younger half of the Louisiville Ridge, Caroline Islands, and Fieberling-Jaspar.
With the exception of the Louisville Ridge, none are as long as the Hawaiian chain, and several lack an active volcano at the southeast end of the chain. Thus, most of these chains started at some time long after the Hawaiian chain, and many were completely constructed prior to the present. In addition, all the chains do not strictly lie on small circles around any inferred pole of rotation. In particular, the Marquesas chain is oblique to any small circle and indicates that the melting anomalies that produced these chains move at rates less than the rates of plate motion.
Of these many chains, the best dated is the Hawaiian-Emperor chain, with whole-rock ages published for many volcanoes. These ages are presently being supplanted by new Ar-Ar incremental heating ages on fresh mineral separates for many of the same samples dated previously. This work, by Warren Sharp and Dave Clague, has shown that several previous age determinations are in error by up to about 10%. In particular, the age of the dramatic bend between the Hawaiian and Emperor chains has been redetermined at about 47 Ma. Likewise, the age for ODP SITE 455 on Suiko Seamount has been redetermined at about 60 Ma, lower by several Ma than the previous determination. These ages refine the rates of volcanic migration along the two chains, but support the general idea that the volcanoes increase in age systematically to the northwest away from the active volcanoes in Hawaii.
It was remarked that the three primary parameters – volume of magma, orientation of chain and regularity of age-progression – vary greatly between chains, with volume varying from little to a great deal, orientation varying from parallel to the Hawaiian chain to significantly oblique, and regularity of age-progression varying from very regular to no progression at all. The Hawaiian-Emperor chain is an end-member feature in that the volume of magma is very high (particularly during the last 5 Myr) and the age progression very regular. No other parallel Pacific volcano chain is very similar to it.