What Is The Most Plausible Explanation For The Anomalous Decrease In Pacific Plate Velocity At The Northern Boundary Of The Philippine Sea Plate, Considering The Competing Influences Of Slab Pull, Ridge Push, And Mantle Drag Forces On Plate Motion In This Region?
The anomalous decrease in the velocity of the Pacific Plate at the northern boundary of the Philippine Sea Plate can be attributed to a combination of factors involving mantle drag, slab pull, and the subduction zone's geometry. Here's a structured explanation:
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Mantle Drag: The primary factor is the increased mantle drag. The Pacific Plate is moving through a region of the mantle beneath the Philippine Sea Plate that is more viscous, providing greater resistance and slowing down the plate's movement.
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Slab Pull Dynamics: While the subducting slab exerts a pull, its effectiveness in propelling the Pacific Plate forward is reduced. This could be due to the slab's geometry or interaction with the surrounding mantle, leading to a less effective pull in the direction of plate motion.
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Subduction Zone Geometry: The specific angle and depth of subduction may alter the forces exerted by the slab. A shallower angle or increased interaction with the overriding plate could increase friction and resistance, further impeding the plate's movement.
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Combined Forces: The slowdown results from the interplay of increased mantle drag and the reduced effectiveness of slab pull. While slab pull typically accelerates the plate, in this region, the opposing forces dominate, leading to a net decrease in velocity.
In conclusion, the most plausible explanation is the increased mantle drag and less effective slab pull due to the subduction zone's geometry, which collectively cause the Pacific Plate to slow down at the northern boundary of the Philippine Sea Plate.