Lloyd wrote: How would the western volcanoes have linked to the Moho with the Pacific plate in between vertically? The Pacific plate would have had to fracture too. Wouldn't it? In order to get vulcanism started? Oh, wait. You said those basalt volcanoes are from melting of the Pacific plate, which is basalt. Would that have been a different kind of vulcanism that did not connect to the Moho? Or would electrical conduits to the Moho have been needed for those basalt flows too?
Yes, I believe that all lava flows originate as magma in the Moho, and that they follow conduits opened up by electric currents. So for there to be a basaltic flow at a continental margin, the overlying continental plate has to be fractured, and the underlying oceanic plate also has to get fractured, such that electric currents can get started. Under the circumstances, we'd expect both plates to be heavily fractured.
