February 12, 2015
JAMSTEC
1. Overview
Dr. Masaki Yoshida and Dr. Yozo Hamano, Department of Deep Earth Structure and Dynamics Research, Japan Agency for Marine–Earth Science and Technology (JAMSTEC: Asahiko Taira, President) carried out numerical simulations of 3-D spherical mantle conviction*1 using supercomputer facilities. As a result, they successfully reproduced the process of continental drift from breakup of the supercontinent Pangea*2 at 200 Ma to the present-day continental distribution and the Earth’s mantle interior that can’t be observed from the Earth’s surface. This is the world’s first achievement to reveal that mantle convection under Earth-like conditions is a major factor for breakup of the supercontinent Pangea and the subsequent continental drift, which have been a mystery for 100 years since the theory of continental drift was proposed first by Alfred Wegener*3.
These findings strongly support evidence based on JAMSTEC’s large-scaled researches on the oceanic plate structures (as reported on March 31, 2014). Unlike exiting models, this numerical simulation model developed for this study is revolutionary since it allows highly viscous continental materials to deform and drift independently under convective force of the ambient mantle.
In addition, these study results indicate that mantle flow pattern as driving force of continent drift depends on thermal insulation effect*4 in the supercontinent and cold plum*5 of mantles in the boundary of continents and oceans.
One of the most famous events in the history of continental drift after the Pangea breakup is formation of the Himalayas and Tibetan Plateau. During the breakup of Pangea, the Indian subcontinent*6 became isolated from the southern part of Pangea called Gondwanaland and moved northwards across the Tethys Ocean to collide with Eurasia, which resulted in the formation of Himalayans. These simulations approximately reproduced the high speed of northward drift of the Indian subcontinent. It was also revealed that a major factor of the northward drift of the Indian subcontinent was the large-scale cold mantle downwelling that developed spontaneously in the North Tethys Ocean.
The Himalayas and Tibetan Plateau brought not only a monsoon climate in Asia but also cooling of the Earth. Revealing the high speed of northward drift of the Indian subcontinent and driving force of Himalayans and Tibetan Plateau is likely to bring a significant progress in elucidating the origin of current climate system on the Earth.
This project was supported by a Grant-in-Aid for Scientific Research (B) from Japan Society for the Promotion of Science (JSPS KAKENHI Grant Number 23340132).
These study results have been posted on Scientific Reports, an online journal from the publishers of Nature on February 12 (JST: 19:00).
Title: Pangea breakup and northward drift of the Indian subcontinent reproduced by a numerical model of mantle convection
Authors: Masaki Yoshida1, Yozo Hamano1
Affiliation: 1. Department of Deep Earth Structure and Dynamics Research, Japan Agency for Marine–Earth Science and Technology (JAMSTEC)
*1 Numerical simulations of 3-D spherical mantle conviction
*2 Supercontinent Pangea
*3 Alfred Wegener (1880-1930)
*4 Thermal insulation effect of supercontinents
*5 Cold plume
*6 Indian subcontinent
*7 Tethys Ocean
Figure1:High-speed northward drift of the Indian subcontinent estimated based on precise geological and paleomagnetic data (Seton et al. 2012, Earth-Sci. Rev.). Time sequence of drifting continental blocks at each age from 200 Ma to the present. The Indian subcontinent that moved towards the north and collided with Eurasia is highlighted in thick contour lines.
Figure2:Examples from simulation results, showing time sequence of positions of drifting continents.
(a) 200 million years ago (b) 150 million years ago (C) 100 million years ago
(d) Present
Figure 3:Time sequence of 3-D views of mantle convection and drifting continents.
Each age corresponds to the figure 2. The temperature of the blue equivalent phases is 250 degrees lower than the average temperature at each depth, and the temperature of the yellow equivalent phases 100 degrees higher. The orange-colored areas on the surface show location of continents.
Figure 4:Diagram showing the mechanism of high speed of the northward drift of the Indian subcontinent.
Figure 5:High velocity anomalies under the present Indian subcontinent and the Mediterranean in seismic tomography data. Each cross-section diagram shows data at depth of 500 km, 800 km, 1200 km and 1600 km, respectively. These data are based on Ritsema et al. (2011, Geophys. J. Int.)
Figure 6:Two theories of driving force for continental drift
The top shows a theory that has been prevailed since 1975 (Forsyth & Uyeda, 1975, Geophysics. J. R. Astron. Soc.). Here, “mantle drag forces beneath plates” act as resistance to continental drift. As indicated in the bottom, however, the results of simulations suggest that “mantle driving forces beneath plates” act as a major factor of continental drift.
Supplementary
Figure 7:Mechanism of upwelling plumes beneath Pangea and high temperature anomaly due to the thermal insulation effect.
(Yoshida & Santosh, 2011, Earth-Sci. Rev.; Heron & Lowman, 2014, J. Geophys. Res.)