Seismic structure beneath the Lau Basin
According to the theory of plate tectonics, oceanic lithosphere, the rigid outermost shell of the Earth, is generated along mid-ocean ridges, and finally subducts into the interior of the Earth along oceanic trenches. The Pacific plate subducts beneath the Australian plate along the Tonga Trench, and induces the volcanic islands of Tonga. On the other hand, a series of back-arc spreading centers, i.e. new born mid-ocean ridges, exist west of the trench in the Lau basin, an oceanic basin between Tonga and Fiji. Therefore, the Tonga-Lau-Fiji region exhibits both the birthplace and the grave of oceanic lithosphere within an area of a few hundreds miles. By studying the mantle structure in this region, we can better understand how the lithosphere is born, how it dies, and how these two processes interact with each other.
52 broadband ocean bottom seismographs (OBSs) and 17 island-based seismic stations were deployed from 2009 to 2010. (Project ELSC supported by Ridge 2000 Program under National Science Foundation)
One of our studies uses Rayleigh wave tomography to infer the distribution of partial melt below the Lau Basin, revealing an unexpected relationship between the amount of in-situ melt and the water content of the magma. This indicates that the water carried by the down-going Pacific plate enhances melt extraction, and plays a crucial role in melting mantle and producing new seafloor at the nearby Lau basin.
- A more general introduction to this research can be found in WashU newsroom: https://news.wustl.edu/news/Pages/27872.aspx.
- A podcast about this research interviewed by Hold That Thought from Arts & Sciences at WashU: https://thought.artsci.wustl.edu/podcasts-earth/articles/383
Reference:
- Wei, S. S., et al. (2015), Seismic Evidence of Effects of Water on Melt Transport in the Lau Back-arc Mantle, Nature, 518(7539), 395-398, DOI: 10.1038/nature14113.