New analyses of volcanic rock samples collected in the 1980s link the geologic histories of these South Pacific islands to explain their current locations and character.
New analyses of volcanic rock samples collected in the 1980s link the geologic histories of these South Pacific islands to explain their current locations and character.
The islands of Fiji and Vanuatu rise from the tropical waters of the South Pacific in one of the most tectonically active and geologically complex regions of the world. A new study of volcanism in this area sheds light on the ancient breakup of a long island arc, which swung apart like “double saloon doors.” Fiji and Vanuatu started out as close neighbors and ended up 800 miles apart on separate sections of what had once been a continuous arc.
Island arcs form where a plate of the oceanic crust sinks beneath an adjacent plate in a process known as subduction, giving rise to a belt of volcanoes parallel to the trench where the descending plate bends downward. The islands are the tallest peaks of vast underwater mountain ranges built up by volcanic activity in the subduction zone. One such range now goes from New Zealand up to Tonga, then bends westward to Fiji. Another extends from New Guinea down to Vanuatu.
“They all used to be connected to one another, and then they got split apart in the geologic past,” explained James Gill, professor emeritus of Earth and planetary sciences at UC Santa Cruz and first author of the new paper. “This paper attributes the breakup to the subduction of the Samoan Seamount Chain.”
Read more at University of California - Santa Cruz
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