Geology and geochronology of the Line Islands.

Abstract

Volcanic and fossiliferous sedimentary rocks were recovered in dredge hauls taken over the entire length of the Line Islands. The volcanic rocks are alkali basalts and hawaiites. In addition, a tholeiitic basalt and a phonolite have been recovered from the central part of the Line chain. Groundmass augite in the alkali basalts contains high TiO2 (1.0-4.0 wt.%) and Al2O3 (3.4-9.1 wt.%) and are of alkaline to peralkaline affinities. Major-element compositions of the Line Islands volcanic rocks are very comparable to Hawaiian analogues. Trace-element and REE data also indicate typical ocean island alkaline lavas. Radiometric and palaeontological dating at 20 localities along the chain from 18oN to 90oS define a mid-Cretaceous to late Eocene edifice or ridge building volcanic events. The single hot-spot model cannot account for all the volcanic edifices in this chain, although it does explain a general age progression of 9.6 + or - 0.4 cm/yr from N to S along the chain. The four hot-spot model accounts for more of the dated volcanic edifices but still does not explain all the available data. The petrological data argue against a mid-ocean ridge or transform fault origin.-W.H.B.