an important question

Okay, you might think that I would know the answer to this question, but I don’t. Why is it that every map of Cordilleran accreted terranes depicts them, by and large, as highly elongate, often discontinuous, strips? Surely these terranes were plastered onto the western edge of North America by processes that involved subduction. It seems to be generally accepted that a subduction zone can swallow up normal oceanic crust, especially easily if it’s cold enough, but that thickened oceanic crust often sticks in its craw, so to speak. That is, it clogs the trench, possibly causing the trench to jump “outboard” thereby transferring the accreted block to the continent and forming an “exotic terrane” Right? So, in general thickened chunks of oceanic crust seem to be of two general sorts: volcanic arcs and oceanic plateaus. The first are elongate, the second roughly equidimensional. Cordilleran accreted terranes tend to be string beans. Does that mean that most, or all, of them were originally arcs? Or, as I have always assumed, were many – most?-of them roughly equant blobs that were attenuated post-accretion by dextral shear? Hawaii, or Iceland? Or, obviously, both?