On the Temporal Evolution of Long-Wavelength Mantle Structure of the Earth Since the Early Paleozoic

Authors

Shijie Zhong, University of Colorado BoulderFollow
Maxwell L. Rudolph, Portland State UniversityFollow

Sponsor

This work was funded by the National Science Foundation through grant 1135382.

Published In

Geochemistry, Geophysics, Geosystems

Document Type

Article

Publication Date

5-2015

Subjects

Earth (Planet) -- Mantle -- Geomorphology, Paleogeophysics -- Paleozoic, Plate tectonics -- Mathematical models, Geodynamics

Abstract

The seismic structure of the Earth’s lower mantle is characterized by a dominantly degree-2 pattern with the African and Pacific large low shear velocity provinces (i.e., LLSVP) that are separated by circum-Pacific seismically fast anomalies. It is important to understand the origin of such a degree-2 mantle structure and its temporal evolution. In this study, we investigated the effects of plate motion history and mantle viscosity on the temporal evolution of the lower mantle structure since the early Paleozoic by formulating 3-D spherical shell models of thermochemical convection. For convection models with realistic mantle viscosity and no initial structure, it takes about ~50 Myr to develop dominantly degree-2 lower mantle structure using the published plate motion models for the last either 120 Ma or 250 Ma. However, it takes longer time to develop the mantle structure for more viscous mantle. While the circum-Pangea subduction in plate motion history models promotes the formation of degree-2 mantle structure, the published pre- Pangea plate motions before 330 Ma produce relatively cold lower mantle in the African hemisphere and significant degree-1 structure in the early Pangea (~300 Ma) or later times, even if the lower mantle has an initially degree-2 structure and a viscosity as high as 10²³ Pas. This suggests that the African LLSVP may not be stationary since the early Paleozoic. With the published plate motion models and lower mantle viscosity of 10²² Pas, our mantle convection models suggest that the present-day degree-2 mantle structure may have largely been formed by ~200 Ma.

Description

Copyright 2015. American Geophysical Union.

This is the publisher's final pdf. Originally published in G³ Geochemistry, Geophysics, Geosystems.

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DOI

10.1002/2015GC005782

Persistent Identifier

http://archives.pdx.edu/ds/psu/15630

Citation Details

Zhong, S., and M. L. Rudolph (2015), On the temporal evolution of longwavelength mantle structure of the Earth since the early Paleozoic, Geochem. Geophys. Geosyst., 16, 1599– 1615, doi:10.1002/2015GC005782.