A tectonic boundary should be defined by changes in tectonic elements. Tectonic elements would include such parameters as structural style, stress orientations, volcanism, heat flow, seismicity and changes in crustal thickness. Examination of these tectonic elements for the southern Colorado Plateau suggests that the southwestern part of the physiographic plateau appears to be tectonically part of the Basin and Range province. I therefore propose a boundary at 112° W longitude, the locus of seismicity and recent volcanism and also the site of crustal thickening and a change of structural style. The tectonic boundary of the southern Colorado Plateau is suggested to form part of the eastern boundary of the southern Basin and Range seismotectonic region. This seismotectonic region is bounded on the north by the Las Vegas shear zone/Nevada seismic zone and has a different stress orientation than the Northern Basin and Range from which it began to evolve separately 13 m.y. ago. The present principal stress orientation of the southern Basin and Range of Arizona appears to be the result of compound movements of the San Andreas transform and Garlock-Las Vegas shear zone resulting in a shear couple affecting the crust in Arizona and an associated NE-SW least principal stress orientation.
ASJC Scopus subject areas
- Earth-Surface Processes