The active southwest margin of the Colorado Plateau: Uplift of mantle origin: Discussion

Past studies of Colorado Plateau uplift have inferred a single primary upli ft mechanism across the entire plateau (e.g., Thompson and Zoback, 1979; Mo rgan and Swanberg, 1985) and in some cases have applied the same uplift mec hanism to much of western North America (Eaton, 1987; Spencer, 1996). In co ntrast, Parsons and McCarthy (1995) proposed that, within a small fraction of the Colorado Plateau in Arizona, uplift of different areas was due to di fferent mechanisms. This departure from past interpretations deserves serio us scrutiny, in part because if it is correct, it will complicate efforts t o understand Cenozoic uplift of the plateau and other areas in western Nort h America. Careful examination of Parsons and McCarthy's article (1995) reveals errors in data manipulation and a failure to address crustal thickness uncertaint ies that undermine their conclusion of laterally varying uplift mechanisms. The purpose of this comment is to provoke a reassessment of their conclusi ons based on correct data manipulation and more convincing analysis.