ANIMATION OF SPACE-TIME TRENDS IN CENOZOIC MAGMATISM OF WESTERN NORTH AMERICA

Animation provides a powerful tool for discovering space-time patterns in magmatism, far more powerful than the static 2-dimensional time slices that can be portrayed on paper. Magmatic history has long been used to decipher the rich history of plate interaction along the west coast of North America, and animation of the NAVDAT dataset discloses several new and enigmatic patterns. NAVDAT (navdat.geo.ku.edu; see also earthchem.org) is a growing database of geochronologic and geochemical data on Cenozoic magmatism in western North America. This paper discusses western U.S. data in NAVDAT (currently about 6500 fully attributed analyses) and existing geochronologic databases from the USGS and the New Mexico, Arizona, and Nevada state surveys. Relevant animations are posted at the NAVDAT site.

Several first-order patterns are apparent in the animations, including: (1) A strong sweep starting in Montana ~55 Ma and moving rapidly southwestward into the Great Basin. This sweep enlarged to a wide band stretching from eastern California to western Utah ~27 Ma and then slowly moved southward to southern Nevada ~15 Ma. (2) A clockwise sweep around the Colorado Plateau, starting in southwestern New Mexico ~30 Ma and also ending in southern Nevada ~15 Ma. (3) A burst of magmatism in northern Nevada ~15 Ma that spread outward to Yellowstone, the central Sierra Nevada, and central Oregon. (4) Waves that converged in the Quaternary on the High Cascades from the west (slowly) and east (rapidly). (5) A Pliocene outburst in eastern California. (6) Several more local northward migrations, including late Cenozoic movements through the San Francisco Bay area and along the southern Wasatch Front, and Miocene-Recent movement through Phoenix to the San Francisco Peaks of Arizona.

The patterns displayed by these animations are clearly migratory at several scales, but it is difficult to tie them to simple models of plate interaction. Patterns that could be related to shallowing and steepening of the Farallon plate or to developing slab windows are not obvious. The “splash” of magmatism in the northern Great Basin is consistent with impingement of a Yellowstone plume head. The strongest pattern of all, the southwestward sweep of magmatism from Montana to Nevada, runs counter to plate motion.