A complex pattern of mantle flow in the Lau backarc.

Prior research has established that mantle flow patterns are often linked to subduction zones and tectonic activity. However, the specific mantle flow dynamics beneath the Lau backarc remain poorly understood. It was already known that shear-wave splitting is a useful tool for inferring mantle anisotropy. No prior work had resolved the exact orientation of mantle flow in this region. This gap motivated the current study to examine anisotropy patterns in the Tonga arc and Lau backarc. The study aimed to determine whether mantle flow is coupled to the downgoing plate or follows a different mechanism. That uncertainty drove the use of local seismic events recorded on land and seafloor observatories. The results may provide new insights into mantle flow in complex tectonic settings.

The study aimed to investigate mantle flow patterns in the Tonga arc and Lau backarc using shear-wave splitting analysis. The specific problem addressed is the lack of clarity regarding mantle anisotropy in this region. Motivation arose from the need to understand whether mantle flow is coupled to subduction processes or follows an independent pattern. The researchers sought to determine the orientation of mantle flow beneath different geological features. This included the Fiji plateau, Lau basin, and Tonga arc. The study also aimed to correlate these findings with helium isotope data from the Samoan plume. The results may clarify how mantle flow interacts with tectonic structures in this region. The findings could contribute to broader understanding of mantle dynamics in subduction zones.

The study used shear-wave splitting analysis of local seismic events recorded on land and the ocean floor. These events were collected in the Tonga arc and Lau backarc regions. The data included both onshore and offshore seismic recordings. The analysis focused on azimuthal anisotropy patterns. The researchers compared anisotropy directions across different tectonic features. This included the Fiji plateau, Lau basin, and Tonga arc. The study also incorporated helium isotope data to map mantle flow. The results were interpreted in the context of mantle flow models.

The analysis revealed a complex pattern of azimuthal anisotropy in the study region. Mantle flow direction rotated from convergence-parallel in the Fiji plateau to north-south beneath the Lau basin. Anisotropy was arc-parallel beneath the Tonga arc. These findings suggest mantle flow is not coupled to the downgoing plate. The results correlate with helium isotope data from the Samoan plume. The data indicate mantle flow into the Lau basin through a tear in the Pacific plate. The observed anisotropy patterns could not be explained by subduction-related flow alone. These findings suggest an additional mantle flow component from the Samoan plume.

The authors propose that mantle flow in the Lau backarc is complex and not solely coupled to subduction processes. The observed anisotropy patterns suggest a rotation in mantle flow direction. This rotation occurs from convergence-parallel in the Fiji plateau to north-south beneath the Lau basin. The findings correlate with helium isotope data from the Samoan plume. The researchers suggest that mantle flow from the Samoan plume enters the Lau basin through a tear in the Pacific plate. The results may indicate that multiple mantle flow mechanisms are at play in this region. The study does not assign essentiality to any single mechanism. The findings may contribute to broader understanding of mantle dynamics in subduction zones.