Hi Jim. Not sure I understand what you mean by “collapse” of a plate. I don’t think they collapse as much as they are consumed. Take Care…Don in creepy town

For the past several hundred millions of years oceanic crust has been subducting along the western coast of North America. For the most part the subducting material has comprised the easterly moving Farallon and Kula Plates rather than the more northerly moving Pacific Plate. A spreading-ridge boundary existed between the Farallon/Kula Plates and the Pacific Plate. The boundary between the Farallon and Kula Plates may have been largely a transform boundary or some combination of transform and spreading boundaries. By around 40 m.y. ago all of the Kula Plate plus the Kula-Farallon and Kula-Pacific boundaries, as well as most of the Farallon Plate, had been consumed beneath North America.

• Farallon Plate