Metastable Olivine within Oceanic Lithosphere in the Uppermost Lower Mantle Beneath the Eastern United States


Approximately two-thirds of Earth's outermost shell is composed of oceanic plates that form at spreading ridges and recycle back to Earth's interior in subduction zones. A series of physical and chemical changes occur in the subducting lithospheric slab as the temperature and pressure increase with depth. In particular, olivine, the most abundant mineral in the upper mantle, progressively transforms to its high-pressure polymorphs near the mantle transition zone, which is bounded by the 410 km and 660 km discontinuities. However, whether olivine still exists in the core of slabs once they penetrate the 660 km discontinuity remains debated. Based on SKS and SKKS shear-wave differential splitting times, we report new evidence that reveals the presence of metastable olivine in the uppermost lower mantle within the ancient Farallon plate beneath the eastern United States. We estimate that the low-density olivine layer in the subducted Farallon slab may compensate the high density of the rest of the slab associated with the low temperature, leading to neutral buoyancy and preventing further sinking of the slab into the deeper part of the lower mantle.


Geosciences and Geological and Petroleum Engineering


This study was supported by the National Key R&D Program of China (grant 2017YFC1405502 to Y. Fang), the National Natural Science Foundation of China (grants 41890811 to J. Li, and 41976071 to F. Kong), and the U.S. National Science Foundation (grants 1919789 to S. Gao, 1830644 to K. Liu and S. Gao, and 2149587 to K. Liu).

International Standard Serial Number (ISSN)

1943-2682; 0091-7613

Document Type

Article - Journal

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Publication Date

01 Jul 2022