Geology & Geophysics Editors' Highlights

Previous Intra-oceanic Subduction Found Beneath South America?

Newly mapped fast velocity slabs in the lower mantle may be remnants of westward dipping intra-oceanic subduction, before flipping to the present eastward subduction beneath South America at 85 Ma.

Source: Journal of Geophysical Research: Solid Earth


High velocity slabs deeper than 1,000 kilometers have been imaged beneath the Amazon by various tomographic studies and have been interpreted as a continuation of the present Nazca slab. Mohammadzaheri et al. [2021] propose a new interpretation of these slab pieces deeper than about 900 kilometers. Geodynamic and plate reconstruction analyses of a new global P-wave tomography model (DETOX-P1, based on both travel time data and multi-frequency waveform picks) suggest that these 900-1800 kilometer deep high-velocity anomalies are actually remnants of a west-dipping intra-oceanic subduction zone during late Jurassic and Early Cretaceous times when South America’s paleo-position was near Africa, before the start of the present, east-dipping Andean subduction around 85 million years ago. This gives support to the hypothesis that slabs in the lower mantle sink vertically with implications on models of plate motion reconstructions.

Citation: Mohammadzaheri, A., Sigloch, K., Hosseini, K., & Mihalynuk, M. G. [2021]. Subducted lithosphere under South America from multifrequency P wave tomography. Journal of Geophysical Research: Solid Earth, 126, e2020JB020704.

—Marcelo Assumpção, Associate Editor, JGR: Solid Earth

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