Origin and evolution of the deep thermochemical structure beneath Eurasia

N Flament,R D Müller,S Williams,D J Bower,M Gurnis

doi:10.1038/ncomms14164

Abstract

A unique structure in the Earth’s lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia. It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. This challenges the current understanding of the evolution of the plate–mantle system in which plumes rise from the edges of the two LLSVPs, spatially fixed in time. New models of mantle flow over the last 230 million years reproduce the present-day structure of the lower mantle, and show a Perm-like anomaly. The anomaly formed in isolation within a closed subduction network ∼22,000 km in circumference prior to 150 million years ago before migrating ∼1,500 km westward at an average rate of 1 cm year−1, indicating a greater mobility of deep mantle structures than previously recognized. We hypothesize that the mobile Perm Anomaly could be linked to the Emeishan volcanics, in contrast to the previously proposed Siberian Traps.

Highlights

A unique structure in the Earth’s lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia
We address the questions raised by the discovery of the Perm Anomaly through comparison of the lowermost mantle thermal structure predicted by forward global mantle flow models constrained by tectonic reconstructions[25] (Methods) to tomography images
The spatial extent of the large hightemperature regions is in first-order agreement with the position and shape of the African and Pacific large low-shear velocity provinces (LLSVPs) in individual tomography models (for example, S40RTS, Fig. 1a) and in a vote map of tomography models[3] (Fig. 1), and the predicted smaller structure under eastern Europe and western Russia matches the location of the Perm Anomaly in tomography (Fig. 1)

Summary

Introduction

A unique structure in the Earth’s lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. The structure of the lower mantle is important for reconstructions of the plate–mantle system[4,5,6,7,8] in deep geological time because the reconstructed locations of most large igneous provinces (LIPs) and kimberlites over the past 320 million years (Myr) correlate with the edges of present-day LLSVPs, leading to the concept of a plume generation zone at LLSVP boundaries[6]. Because of its past mobility, the Perm Anomaly may not be linked to the Siberian Traps, but rather to the Emeishan volcanics

Methods

Results

Conclusion