This indicates that transference subduction initiation does not generally occur because old oceanic lithosphere is too strong to rupture under compression.
We expect that a new subduction zone would have formed by transference INSZ in the Indian Ocean south of the India-Asia collision zone, but this has not happened in the 50 m.y. In contrast, there are no incontrovertible Cenozoic examples of transference INSZ. There are Cenozoic examples of polarity reversal INSZ (e.g., accompanying the Miocene collision of the Ontong Java Plateau with the Melanesian arc Holm et al., 2013) polarity reversal INSZ occurs readily because lithosphere around a hot arc is weak and easy to rupture. 1A) occurs when a new subduction zone (with unchanged polarity) forms within oceanic lithosphere outboard of the collision zone. 1B) occurs when a subduction zone dipping beneath an arc is clogged by buoyant crust, and a new subduction zone dipping in the reverse direction forms on the opposite side of the arc. There are two varieties of INSZ, polarity reversal and transference. Induced nucleation of a subduction zone (INSZ) is expected if plate convergence continues after a collision event arrests convergence in a preexisting subduction zone. There are two principal ways that a new subduction zone may form: it may be induced or it may form spontaneously ( Fig. This PISI hypothesis provides an integrated framework for understanding Siletzia, the Challis-Kamloops belt, Eocene core complexes from Idaho (U.S.) to British Columbia (Canada), underplated mafic rocks beneath Oregon and Washington (U.S.), post–17 Ma manifestations of the Yellowstone plume, and geophysical characteristics of the lithosphere beneath the Pacific Northwest. This destroyed the existing Cordilleran subduction zone and allowed the new Cascadia subduction zone to form by collapse of thermally weakened oceanic lithosphere over the hot western margin of the plume head. 55 Ma beneath western North America, generating Siletzia in situ on the North American margin, as well as generating the ∼1700-km-long Challis-Kamloops volcanic belt ∼600 km to the east of Siletzia. In this PISI hypothesis, a newly formed, ∼1200-km-diameter Yellowstone mantle plume head rose at ca.
This paper explores an alternative hypothesis for the reorganization, a plume-induced subduction initiation (PISI) mechanism, which has previously been applied to the initiation of Caribbean plate subduction zones in the Cretaceous. Oceanic lithosphere is strong and difficult to rupture, so this would represent a rare example of such a rupture initiating a new subduction zone. 56–48 Ma subduction zone reorganization in the Pacific Northwest of North America is that: (1) the Siletzia large igneous province erupted offshore to the west of North America, forming an oceanic plateau (2) Siletzia then collided with North America, clogging the Pacific Northwest segment of the Cordilleran subduction zone and (3) the oceanic lithosphere west of Siletzia then ruptured to initiate the new Cascadia subduction zone.
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