A new study has identified evidence of a massive volcanic system beneath the South China Sea. The region may be in the early stages of what scientists call a large igneous province. This is a rare geological event that reshapes vast areas of the Earth’s crust over millions of years.
The study was published in Geochemistry, Geophysics, Geosystems and led by F. Yang of the Southern Marine Science and Engineering Guangdong Laboratory in Guangzhou, China. It centers on a volcanic rock sample collected by a deep-sea submersible from a small underwater mountain, or seamount, located about 700 kilometers (435 miles) from the island of Hainan.
Hainan plume debate finally gets rock-solid answer
Scientists have long debated whether a mantle plume exists beneath Hainan. A mantle plume is a column of superheated rock that rises from deep within the Earth toward the surface.
When it pushes against the underside of a tectonic plate, it can trigger enormous volcanic eruptions across a wide area. The challenge has been that Hainan showed geological signs of a plume but lacked the volcanic evidence needed to confirm one.
The basalt rock collected for this study changes that picture. Researchers found the sample formed about 2.55 million years ago, at the same time as the most active volcanic period recorded on Hainan. Chemical analysis showed the rock drew from two distinct sources: the Hainan mantle plume and the base of the local continental lithosphere, the rigid outer shell of the Earth.
This mixed origin is supported by seismic data showing a slow-moving zone of material beneath the lithosphere. Together, these findings suggest the plume head has been spreading sideways and interacting with the rock layer above it.
South China sea volcanic system may rival known provinces
Yang and colleagues also found that molten rock from this activity pooled in chambers deep within the crust, between roughly 8.5 kilometers (5.3 miles) and 16 kilometers (9.9 miles) below the surface. As this material cooled over time, it formed dense rock with unusually high seismic velocities.
These readings matched what geophysical surveys had already detected in the South China Sea region. Numerical modeling confirmed that intrusions older than two million years would have cooled enough to produce those high-velocity readings. The total volume of igneous rock linked to the Hainan plume across the northern region is estimated at at least 150,000 cubic kilometers (36,000 cubic miles). It includes seamounts and underground intrusions.
That figure rivals recognized large igneous provinces elsewhere on Earth. Researchers said this volcanic system may continue producing large amounts of magma over the next few million years. The plume head is expected to push farther into the continental margin above it.
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