We propose a model that involves breakoff of the east-dipping Eurasian slab beneath the Taiwan orogen to account for the flipping of subduction polarity in northern Taiwan. The breakoff was initiated in southern Ryukyu in the early Pliocene and then propagated southwestward into Taiwan, like an opening zipper. Detachment of the Eurasian slab has created a mantle window for the north-dipping Philippine Sea plate to move in laterally, causing a switch in the subduction polarity. Slab breakoff not only provides a testable model for the lithospheric structure of Taiwan, but also accounts for the high heat flow, rapid uplift, synorogenic extension, deep-focus earthquakes, and north-diminishing crustal contraction in the Taiwan mountain belt.

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