Origin and evolution of the deep thermochemical structure beneath Eurasia.

Area of Science:

• Geophysics
• Earth Sciences
• Seismology

Background:

• A unique structure, the Perm Anomaly, has been identified in Earth's lowermost mantle beneath Eurasia.
• This anomaly seismologically resembles large low-shear velocity provinces (LLSVPs) but is significantly smaller.
• Its existence challenges the established understanding of mantle plume dynamics originating from fixed LLSVP edges.

Purpose of the Study:

• To model mantle flow over the past 230 million years.
• To understand the formation and evolution of the Perm Anomaly.
• To investigate the mobility of deep mantle structures and their potential links to surface volcanism.

Main Methods:

• Development of new mantle flow models covering the last 230 million years.
• Analysis of seismic data to characterize the Perm Anomaly's properties.
• Comparison of model results with present-day lower mantle structure.

Main Results:

• The models successfully reproduced the present-day lower mantle structure, including a Perm-like anomaly.
• The anomaly formed in isolation within a closed subduction network before 150 million years ago.
• The Perm Anomaly migrated approximately 1,500 km westward at an average rate of 1 cm/year, demonstrating significant mobility.

Conclusions:

• Deep mantle structures exhibit greater mobility than previously thought.
• The mobile Perm Anomaly is hypothesized to be linked to Emeishan volcanics, offering an alternative explanation to the Siberian Traps.