A systematic relationship exists between seismically defined, master normal faults of the Albuquerque Basin and the structural style of rift shoulders on the basin margins. Rift shoulders occupying the footwalls of these master faults have at least three characteristics distinguishing them from the other shoulders of the basin: 1. They are the source areas for the basin’s major fanglomerates in the syn-rift Santa Fe Group. 2. They display distinctly Neogene apatite fission-track ages. 3. They have undergone the greatest amount of rift-related uplift in the Neogene. These relationships imply that uplift of these rift shoulders may be in part, the result of isostatic rebound of the lithosphere, accompanying tectonic unloading by the seismically defined master faults of the basin.

The central Panamint Mountains, Death Valley area, California, comprise three groups of rocks. The first consists of middle Proterozoic gneiss and upper Proterozoic sedimentary rocks that were regionally metamorphosed under low-pressure conditions during Middle Jurassic time, were intruded by the Late Cretaceous Hall Canyon granitic pluton, and were folded along NNW-trending axes during Late Cretaceous time. This group, called the Panamint metamorphic complex, makes up the core of the Panamint Mountains. The complex is cut by numerous west-dipping, low-angle normal faults that are locally intruded by the Miocene Little Chief stock. The second group consists of monolithologic breccias, called the Surprise breccia, derived from the local metamorphic rocks. The Surprise breccia forms the western slope of the Panamint Mountains north of Pleasant Canyon and forms the hanging wall of the west-dipping Surprise fault. Displacements along the fault, estimated from offset structures, are about 2,500 m down dip. The third group consists of the Nova Formation, which comprises fanglomerate, basalt, and minor breccia and which lies in the hanging wall of the west-dipping Emigrant fault. The fanglomerates contain abundant clasts of metamorphic and granitic rocks from the metamorphic complex. The three groups of rocks are separated from each other by intervening faults. The Panamint metamorphic complex is the structurally lowest group and is separated from the Surprise breccia by the Surprise fault. The breccia is separated from the structurally highest Nova Formation by the Emigrant fault. All these rocks lie above the regionally extensive Amargosa fault. The difference in rock character among fanglomerates, breccias, and relatively intact metamorphic core rocks is readily visible in Thematic Mapper (TM) and Shuttle Imaging Radar (SIR-B) images. The TM image, which is sensitive to differences in mineralogic compositions of the rock types, distinguishes the metamorphic complex from the Surprise breccia because the breccias are more highly weathered than the metamorphic complex. The SIR-B image, which is sensitive to differences in surface roughness and topography, readily distinguishes between the breccia and the fanglomerate. The breccia is characterized by closely spaced, parallel drainages, whereas the fanglomerate contains a dense dentate drainage pattern. The combination of the images is a significant mapping aid in the central Panamint Mountains. Most of the uplift of the Panamint metamorphic complex, from a Late Mesozoic depth of about 10 km to ~3 km, probably occurred during displacements along the Amargosa and related faults. Some of these faults were intruded by the late middle Miocene Little Chief stock. The maximum possible uplift rate at this time was 17 mm/yr; the actual rate could have been lower if some uplift occurred prior to faulting. The metamorphic complex was largely unroofed by the time of deposition of the Nova Formation. Uplift of the range prior to, and partly contemporaneous with, Nova deposition resulted in formation of the Surprise breccia. The Emigrant fault formed late. The fanglomerates dip ~25° eastward against the Emigrant fault, but this tilting appears to have resulted from aggregate rotation along several fault surfaces rather than from uniform eastward tilting of the entire Panamint Mountain block. Isolated remnants of Surprise breccia on ridge crests indicate that the unroofing of the metamorphic complex south of Wildrose Canyon probably was not completed until after the breccia-mass development.

Abstract 0.0 Prescottonian Motel, Prescott. Turn right onto Gurley Street and Arizona State Highway 69 to Phoenix. On the left is Yavapai College and, behind it, the U.S. Veterans Hospital at old Fort Whipple. The large construction project on top of the fanglomerate-capped hill to the northeast is a Sheraton Hotel under construction. 0.2 Intersection with U.S. Highway 89 north to Ash Fork. The left turn goes along Granite Creek and north through the Granite Dells, a picturesque area of granite spires underlain by the Dells Granite (fig, 43), a 1400±15 Ma (Silver and others, 1981) uranium-rich leucogranite (Anderson, in press). Stay to the right, on Arizona Highway 69 to Phoenix. Highway crosses the wash of Government Canyon. Roadcuts on the left beneath the Sheraton Hotel are Tertiary fanglomerate that locally overlies the 1740±15 Ma Government Canyon Granodiorite exposed in the beveled roadcuts. As the highway climbs the small hill past the Sheraton Hotel, we are crossing the Yavapai Indian Reservation, a 4 mi 2 tract of land on the northeast edge of Prescott. Roadcuts are in Government Canyon Granodiorite. View to the left at 9:00 down the small gully if of exposures of the Early Proterozoic Prescott Granodiorite across Granite Creek. 0.8 Chaparral-covered hillside to the right underlain by Government Canyon Granodiorite and Early Proterozoic gabbro. Large hill to the right is Badger Mountain, composed entirely of this gabbro. 1.0 Roadcuts on right in Government Canyon Granodiorite. Hills to the left at 9:00 to 12:00 are Tertiary fanglomerate. View behind and