Whipple Mountains - Geology

Geology

The present-day landform of the Whipple Mountains is a series of sub-parallel ridges trending northwest to southeast, cut at right angles by a large wash, (Whipple Wash), which bisects the entire range. These linear ridges mark the tops of tilted crustal blocks lying in the hanging wall of an extensive detachment fault, and the range as a whole comprises one of the best exposed and most studied metamorphic core complexes in the world.

In the western half of the range, the hanging wall has been eroded away completely, leaving antiformally upwarped lower-crustal mylonites exposed at the surface. To the east, unaltered tertiary volcanic and sedimenatary rocks along with non-mylonitic crystalline Pre-Cambrian rock in the hanging wall form the land surface, but the larger washes provide access to the detachment surface and the rocks surrounding it. Excellent examples of hydrothermal alteration, fluidized cataclasite injection, and other mid- and upper-crustal fault processes abound along the detachment surface. A number of high-angle normal faults accommodating tilting and extension within the hanging wall are easily visible as well.

The Whipple detachment fault is part of a larger complex of shallow, east dipping normal faults extending from the Whipples northward to the southern tip of Nevada, where a transition occurs to shallow, westward dipping normal faults. The entire region accommodated major crustal extension between the Sierra Nevada block and the Colorado Plateau during the early and middle Miocene. Upwards of 40 km of extension occurred in a region now 70 to 100 km across. The Whipples are part of the Maria fold and thrust belt.