In this slide, we see the location of the eastern limit of the arc-related plutons. They trace across the entire western edge of the plate margin, suggesting that Andean-style subduction was active throughout most of the Mesozoic. An over-riding theme in this story of the Arc environment is HEAT. This is the driving factor for most of the structures that we observe. In the subduction zone environment, the isotherms are depressed where cold rocks of the subducting plate go down but to the east they are juxtaposed against the hot intrusive Arc environment. Moving further in-board from the arc, the rocks progressively cool to within the fold and thrust belt, finally returning to normal temperatures in the undeformed basement. This heat in the arc provides a possible mechanism for consuming the foot-wall of the antithetic fold and thrust belt, but it is hard to locate where this might be happening. Courtesy of Prof. Burchfiel.