Evidence for a hot spot origin of the Caroline Islands

Abstract

The results of paleomagnetic, petrographic, and radiometric studies of the Eastern Caroline Islands in the western Pacific indicate that the islands were formed by a hot spot located near the paleoequator between 1 and 11 Ma. The islands show a linear progression of mean ages from 1 Ma in the east (Kusaie) to 11 Ma in the west (Truk). The results of volumetric measurements and geochemical studies suggest that the hot spot source is waning and perhaps was slowly dying during the time Truk, Ponape, and Kusaie were being formed. The dominant shield‐building magmas in the Caroline Islands are part of a differentiated alkalic series. The posterosional lavas are highly silica undersaturated and trace element enriched nephelinites. The latter were erupted subsequent to the cessation of the main shield phase of volcanism. The petrography and geochemical evolution of Truk are strongly reminiscent of that of the Hawaiian chain; however, the shield‐building lavas are compositionally similar to the alkalic lavas that typically form only thin, late‐stage caps on many Hawaiian volcanos. No tholeiitic rocks were found despite sampling deep within the eroded volcanic structure of the islands. This absence of tholeiitic lavas and dominance of alkalic lavas stand in contrast with Hawaii, where tholeiitic volcanism dominates and alkalic lavas form only a minor component of the exposed lavas. The absence of tholeiitic lavas in the main shield‐building phase of construction, however, is not unique to the Caroline Islands. Dominant alkalic volcanism appears characteristic of other seamounts in the Pacific, including the Samoan, Austral‐Cook, and Line Islands.

Cryptic diversity, molecular phylogeny and biogeography of the rock- and leaf litter-dwelling land snails of Belau (Republic of Palau, Oceania)

“…Rundell 2007, unpublished data). Despite the fact that the oldest part of Belau is nearly 30 Ma old (and Guam is greater than 20 Ma old), much older than Pohnpei and Kosrae (8.6-3.0 and 2.6-1.2 Ma, respectively; Keating et al 1984;Craig et al 2001), it is possible that other islands have acted as sources of colonists for these eastern Caroline Islands faunas.…”

“…Parts of Guam have been above sea level since at least 20 Ma; Guam rock exposures range in age from 43.8 to 2.3 Ma (Craig et al 2001;Hall 2002). By contrast, the Caroline Islands of Pohnpei and Kosrae originated on the Pacific plate and are young hot spot islands, 8.6-3.0 and 2.6-1.2 Ma old, respectively (Keating et al 1984;Craig et al 2001). The formation of Pohnpei and Kosrae was similar to that of the Hawaiian Islands (i.e.…”

Deformation from the convergence of oceanic lithosphere into Yap trench and its implications for early-stage subduction

“…The subducting plate has a rather unusual morphology in that a large region of volcanic seamounts and plateaus formed in the late Oligocene by the Caroline hotspot (Keating et al, 1984) lies on it. The slab is divided into two halves, north and south, by the Sorol Trough, a left-lateral strike-slip fault zone trending WNW-ESE (Figs.…”

Isostatic Compensation and Conduit Structures of Western Pacific Seamounts: Results of Three-Dimensional Gravity Modeling

“…Potassium-a.rgon ages for 16 rock samples from Kusaie and Pohnpei range from 1.2 ± 0.1 to 8.6 ± 0.6 m.y. (Keating et al, 1984 (1984). The results in Figure 14 have important implications for studies of the geological evolution of seamounts, oceanic islands, and the ocean basins.…”