4:45 PM - 5:00 PM
[SCG50-12] P-wave mantle tomography beneath South America and surrounding regions
South America is a region with strong tectonic complexities, where four lithospheric plates, i.e., the South American, Nazca, Caribbean, and Antarctic plates are interacting with each other. The Nazca Plate is moving toward the ENE at a rate of ~7 cm/yr and subducting beneath the South American Plate from the Peru-Chile Trench, inducing very active seismicity and arc magmatism. This region is also known as a long-lived subduction zone where the Farallon Plate subducted before its fission into the Cocos and Nazca plates.
Recent studies have suggested that the Mid-Atlantic Ridge (MAR) in the northern hemisphere was opened by hot mantle return-flow when the Farallon slab beneath North America sank into the lower mantle (e.g., Dal Zilio, 2018). A similar mechanism might work for the MAR in the southern hemisphere, but no study has shown it. Body-wave tomography is a powerful tool to investigate the 3-D mantle structure beneath a target region, which provides informative insights into mantle dynamics. However, the previous local and regional tomography models beneath South America are generally limited to the crust and upper mantle, and the existing global tomography models generally have low resolution (> 500 km) in this region.
In this study, we apply the updated technique of multi-scale global tomography (Zhao et al., 2017) to obtain high-resolution images of the whole-mantle 3-D P-wave velocity (Vp) structure beneath South America. The number of earthquakes and seismic stations used are 19,649 and 12,764, respectively. We analyze arrival times of not only direct P waves, but also surface-reflected pP and PP waves to improve the ray path coverage in the deep mantle. We used a total of 6,301,199 arrival times, including 5,996,872 P, 200,896 pP, and 103,431 PP arrivals.
Our results are summarized as follows: (1) a novel whole-mantle 3-D Vp model with a spatial resolution of ~160 km is obtained beneath South America; (2) the subducted Nazca-Fallaron slab seems split to several segments. Some segments have penetrated into the lower mantle, whereas others are stagnant in the mantle transition zone; (3) a prominent and continuous low-Vp anomaly is revealed from the surface to the core-mantle boundary beneath the MAR, suggesting that hot mantle upwelling driven by the Fallaron slab subduction also caused the MAR opening in the southern hemisphere.
References
Dal Zilio, L. (2018). Subduction-driven Earth machine. Nature Geoscience, 11, 229. https://doi.org/10.1038/s41561-018-0102-z
Zhao, D., Fujisawa, M., & Toyokuni, G. (2017). Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9). Scientific Reports, 7, 44487. https://doi.org/10.1038/srep44487
Recent studies have suggested that the Mid-Atlantic Ridge (MAR) in the northern hemisphere was opened by hot mantle return-flow when the Farallon slab beneath North America sank into the lower mantle (e.g., Dal Zilio, 2018). A similar mechanism might work for the MAR in the southern hemisphere, but no study has shown it. Body-wave tomography is a powerful tool to investigate the 3-D mantle structure beneath a target region, which provides informative insights into mantle dynamics. However, the previous local and regional tomography models beneath South America are generally limited to the crust and upper mantle, and the existing global tomography models generally have low resolution (> 500 km) in this region.
In this study, we apply the updated technique of multi-scale global tomography (Zhao et al., 2017) to obtain high-resolution images of the whole-mantle 3-D P-wave velocity (Vp) structure beneath South America. The number of earthquakes and seismic stations used are 19,649 and 12,764, respectively. We analyze arrival times of not only direct P waves, but also surface-reflected pP and PP waves to improve the ray path coverage in the deep mantle. We used a total of 6,301,199 arrival times, including 5,996,872 P, 200,896 pP, and 103,431 PP arrivals.
Our results are summarized as follows: (1) a novel whole-mantle 3-D Vp model with a spatial resolution of ~160 km is obtained beneath South America; (2) the subducted Nazca-Fallaron slab seems split to several segments. Some segments have penetrated into the lower mantle, whereas others are stagnant in the mantle transition zone; (3) a prominent and continuous low-Vp anomaly is revealed from the surface to the core-mantle boundary beneath the MAR, suggesting that hot mantle upwelling driven by the Fallaron slab subduction also caused the MAR opening in the southern hemisphere.
References
Dal Zilio, L. (2018). Subduction-driven Earth machine. Nature Geoscience, 11, 229. https://doi.org/10.1038/s41561-018-0102-z
Zhao, D., Fujisawa, M., & Toyokuni, G. (2017). Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9). Scientific Reports, 7, 44487. https://doi.org/10.1038/srep44487