Tertiary Tectonics of the White Pine–Grant Range Region, East-Central Nevada, and Some Regional Implications

The White Pine-Grant Range area is a 400 sq mile region located in east-central Nevada, east of the Antler erogenic front, and west of the Sevier-Laramide thrust belt. About 20,000 feet of Paleozoic rock are overlain by 3000 to 5000 feet of Eocene-Oligocene sedimentary and volcanic rocks, and 0 to 10,000 feet of Mio-Pliocene sedimentary rocks. The near concordance of Paleozoic and early Tertiary strata indicates that the major deformation of the area is post-Oligocene in age. Mesozoic tectonic movements were limited to the formation of gentle folds and high-angle faults of limited displacement.

The structure of the area is dominated by north-trending folds, some overturned, which involve both Tertiary volcanic and Paleozoic rocks. These folds are cut by a series of low-angle faults emplacing younger rocks over older; six faults are present in the White Pine Range and two in the northern Grant Range. A series of complex discrete slide masses 1 to 3 miles long characterizes the southwestern Horse Range; a relatively unfaulted overturned Paleozoic section characterizes the southeastern Horse Range. Displacement along these faults increases from the center toward the ends of the ranges; the faults are not continuous throughout the length of the range, and probably do not represent features of a regional d écollement. Relations suggest that deformation or movement on these faults was probably nearly surficial, partly a product of uplift of the ranges and partly the result of basement extension. Much observable movement took place during deposition of Mio-Pliocene sediments, accompanied by emplacement of gravity slide masses and monolithic breccia of Paleozoic and volcanic rock in the Mio-Pliocene sedimentary basin. Differences in intensity of folding and degree of low-angle faulting in the White Pine, Horse Range, and northern Grant Ranges suggest that these areas were deformed separately. The north-trending folds may be the result of gravity effects on the flanks of major uplifted blocks, but probably reflect a period of postvolcanic crustal shortening in this region.