Ancient plate tectonics deform Earth’s deep mantle on a global scale

Cientistas mapped deep regions of the Earth’s interior where the mantle undergoes deformation. The work analyzed seismic waves on a global scale and identified patterns of anisotropy. The results indicate that most of this distortion occurs where ancient tectonic plates would have sunk over millions of years.

The research examined around 75% of the lower mantle, a layer located just above the boundary with the core, approximately 2,900 kilometers deep. Ondas shear generated by earthquakes travels at different speeds depending on the direction and characteristics of the material. Essa directional variation, called seismic anisotropy, serves as an indicator of deformation in the mantle.

Análise from vast seismic dataset

The team gathered more than 16 million seismograms from 24 data centers around the world. The material includes multiple phases of waves that travel down the mantle, through the core, and back. Essa approach allowed mapping the distribution of strain over distances of hundreds of kilometers.

The set forms one of the largest collections of seismic data ever compiled. Pesquisadores of Universidade of Califórnia at Berkeley led the effort, with collaboration from other experts. The study was published in the journal The Seismic Record, linked to Seismological Society of America.

• Data covers nearly 75% of the lower mantle
• Anisotropia detected in about two-thirds of the regions analyzed
• Padrões more evident in areas associated with old subducted plates
• Ondas analyzed includes phases that interact with the core-mantle boundary
• Volume total seismograms exceeds 16 million records

Conexão with subducted tectonic plates

Deformation in the deep mantle is mainly concentrated in areas where ancient plates would have sunk. Modelos geodynamicists had already predicted this relationship, but the new mapping offers the first global view based on seismic observations.

Placas that descend carry with them structures formed when they were closer to the surface. Over time, extreme heat and pressure can alter minerals and create a new orientation in the material. Essa interaction also pushes and reshapes the mantle around the plates.

Jonathan Wolf, lead author and researcher of Universidade of Califórnia in Berkeley, commented on the finding. Ele noted that deformation in the upper mantle is well understood by the pull of moving plates. In the lower mantle, however, a similar large-scale understanding was lacking. The study moves in this direction.

Possíveis mechanisms behind anisotropy

One hypothesis considers that the plates preserve fossil anisotropy of their surface phase. Outra, considered more likely, points to intense deformation during sinking and contact with the core-mantle boundary. The process modifies the mineralogical fabric and generates a new anisotropic “structure”.

Nem all regions without clear anisotropic signal would be free of deformation. In some cases, the signal may simply be too weak for current methods to detect. The researchers highlight that the dataset continues to be a valuable source for future investigations.

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The work does not determine exact flow directions in the lower mantle, but it establishes a framework for studies that seek greater resolution. Wolf mentioned the desire to map global flows in more detail at different lateral scales.

Implicações for understanding the Earth’s interior

The Earth’s mantle slowly circulates through convection currents linked to the movement of tectonic plates. Essas currents not only move plates at the surface but also stretch and distort the mantle material itself. The study confirms long-held theories and offers observational evidence on a planetary scale.

Conhecer better understands these processes to understand the long-term dynamics of the planet. Deep deformation influences the thermal and chemical behavior of the Earth’s interior over millions of years. Additional Pesquisas with the same dataset may reveal more about flow patterns.

The full article provides methodological details and maps generated from the analysis. Ele reinforces the importance of global seismic databases for advances in geophysics.

Detalhes seismic survey technicians

The team analyzed seismic waves that travel large distances inside Terra. The variation in speed according to the propagation direction reveals preferential alignments in the mantle material. Essa property arises from accumulated deformation over geological time.

The core-mantle boundary, at around 2,900 km depth, represents a transition zone marked by extreme differences in temperature and pressure. Subducted Placas that reach these depths interact with the environment and contribute to the observed anisotropy.

• Profundidade approximate lower mantle studied: 2,900 km
• Cobertura of the lower mantle: almost 75%
• Número of seismograms analyzed: more than 16 million
• Centros of data involved: 24 on a global scale
• Fração with anisotropy detected: about two-thirds

Limitações and future prospects

The authors highlight that the absence of anisotropic signal in certain areas does not mean the absence of deformation. More sensitive Métodos or new data types may fill gaps in the future. The larger goal includes mapping lower mantle flow directions with greater precision.

The dataset represents an enduring resource for the scientific community. Pesquisadores will continue to explore it for insights into mantle convection and its relationship to plate tectonics.