Abstract:
The portion of Earth’s mantle lying below the hemispherical region occupied by the Pacific Ocean basin is characterized by a unique style of convection. The unique dynamics below the ‘Pacific Hemisphere’ are revealed by analyzing the mantle flow predicted on the basis of high-resolution seismic images of mantle structure. In the Pacific Hemisphere we find a dome-like upwelling, originating in the lower mantle, which actively transports material into the upper mantle. A unique aspect of this flow, found only in the Pacific Hemisphere, is a ‘demi-tour’ or U-turn of the circulation which occurs in the shallow mantle, west of the East Pacific Ridge. This ‘demi-tour’ connects the westward movement of the Pacific plate to the dome-like upwelling below the central Pacific Ocean and it also provides an explanation for the asymmetric distribution of seismic anisotropy on either side of the ridge axis. In a global analysis of the correlation between mantle flow and seismic anisotropy, we find the strongest agreement occurs in the Pacific Hemisphere mantle.
