Three-Dimensional Mantle Flow and Temperature Structure Beneath the Shatsky Rise Ridge-Ridge-Ridge Triple Junction

The Shatsky Rise ridge-ridge-ridge triple junction is an ancient triple junction in the Western Pacific Ocean whose initial geodynamic process is poorly understood and can only be inferred based on indirect geological and geophysical constraints. In this paper, we present three-dimensional numerical models that simulate the Shatsky Rise triple junction and calculate its coupled mantle flow and temperature structure. The mantle flow velocity field shows several distinctive features: 1) stronger mantle upwelling closer to the ridge axis and triple junction; 2) greater upwelling velocity at the faster-spreading ridges; and 3) the most significant increase in upwelling velocity for the slowest-spreading ridge toward the triple junction. The calculated mantle temperature field also reveals distinctive characteristics: 1) sharp increases in the mantle temperature with depth and increases toward the spreading ridges and triple junction; 2) the faster-spreading ridges are associated with higher temperatures at depth and identical distances from the triple junction; and 3) the slowest-spreading ridge shows the greatest increase in the along-ridge-axis temperature toward the triple junction. Compared to many present-day triple junctions with slower spreading rates, the along-ridge-axis velocity and thermal fields of the Shatsky Rise are more altered due to the presence of the triple junction.