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Source: AGU Advances
When plumes of magma well up through Earth’s lithosphere, they create volcanoes, islands, seamounts, and other features on the surface. Telltale hot spot tracks form as tectonic plates move over these plumes, marking plume locations and the movement of the crust above them through time. The most famous of these tracks in the Pacific include the islands of Hawaii. Another track includes the Samoan Islands, though that track is interrupted by a curious gap representing roughly 30 million years of Earth’s history.
Jackson et al. found an explanation for the missing portion of the Samoan hot spot track and identified older portions of it that stretch to the Mariana Trench and date back 100 million years. The authors suggest that around 60 million years ago, the motion of the Pacific tectonic plate carried the Ontong Java Plateau—a large volcanic province with extraordinarily thick lithosphere—over the Samoan plume. The plateau effectively capped the plume for 30 million years, suppressing mantle melting, halting the creation of new volcanic structures, and resulting in the 30-million-year gap in the Samoan chain.
Combining isotopic and geochronological data from lava samples with plate motion models allowed the researchers to link the older and younger segments of the hot spot track together. Key to their work was new evidence from the island of Malaita, part of the Solomon Islands about 3,000 kilometers east of the Samoan Islands. There, at the very edge of the Ontong Java Plateau, the researchers found 44-million-year-old volcanic rocks with geochemical fingerprints that match lavas from the Samoan hot spot. The findings suggested that the eruption that created the rocks originated from the same hot spot and provided the missing link between the sections.
The authors outline scenarios in which the Ontong Java Plateau either suppressed or diverted magma from the Samoan plume, arguing that mantle melting was likely largely suppressed, although the Malaita lavas could represent an exception. They say the new work, which identifies a previously unknown geological process, termed “plume-plateau” interactions, fleshes out previous theories about the history of the hot spot. The authors found evidence of this process elsewhere as well, suggesting the Ontong Java Plateau also moved over and suppressed the Rarotonga hot spot and, similarly, that the Manihiki Plateau suppressed the Pitcairn and Society hot spots. All three hot spots are linked to the creation of eponymous islands.
In an accompanying viewpoint, Huang suggests that plateaus may not always be thick enough to prevent plume melting entirely, which may lead to preferential melting of enriched material that melts at lower temperatures. Such preferential melting could mean hot spot lavas are not always representative of the plumes from which they emerged. In addition, Huang notes that the occurrence of plume-plateau interactions may mean that the global flux of material from mantle plumes is underestimated, as some plumes may be temporarily capped and unproductive. (AGU Advances, https://doi.org/10.1029/2023AV001079 and https://doi.org/10.1029/2024AV001464, 2024)
—Nathaniel Scharping (@nathanielscharp), Science Writer
Citation: Scharping, N. (2024), Tracking a disappearing mantle plume in ancient Samoa, Eos, 105, https://doi.org/10.1029/2024EO240482. Published on 25 October 2024.
Text © 2024. AGU. CC BY-NC-ND 3.0
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