DISTINGUISHING ARC AND NON-ARC MAGMATISM VIA HOTSPOTTING?

Two, if not three, hotspots/plumes are inferred to have contributed to the Cenozoic volcanic and tectonic evolution of the United States Cordillera. However, their hypothetical volcanic record is intermixed with other magmatism attributed to subduction and crustal extension. Models for plate motion relative to hotspots and crustal deformation of the Cordillera in the Cenozoic, together with available isotopic dates, provide a possible means of distinguishing among the potential sources of volcanism.

In oceanic regions, restoration of isotopic dates along hotspot traces produce clusters which represent inferred present hotspot locations (“Hotspotting”). Similarly, restoration of isotopic dates from the Cordillera in the hotspot frame should produce clusters for those dates which represent volcanism produced by hotspots. Two distinct hotspot reference frames, Tristan (Atlantic and Indian Ocean) and Hawaiian (Pacific), appear to exist over 130-140 Ma; their interface may well extend beneath the Cordillera. Reconstructions of isotopic dates of western US volcanism in each reference frame, also incorporating intra-Cordilleran palinspastic restoration, produce clustering “images” which reflect the sublithospheric locations of the inferred hotspots, from which loci can also be calculated for comparison with available isotopic dates. The resulting images and loci provide tantalizing hints of the origin of the Yellowstone and Raton hotspots when also compared with tomographic images.