1982, Journal of Geophysical Research, v. 87, p. 10,929 - 10,953.

Remagnetization and tectonic rotation of upper Precambrian and Lower Paleozoic strata from the Desert Range, southern Nevada

S. L. Gillett, Dept. of Earth and Space Sciences, State University of New York at Stony Brook
D. R. Van Alstine, Sierra Geophysics, Inc.

Abstract. In the Desert Range of southern Nevada, miogeoclinal sedimentary rocks, mostly shallow-water limestones of latest Precambrian through Early Ordovician age, yield three components of magnetization having different blocking temperature spectra: (1) a low blocking temperature component near the direction of the present axial-dipole field; (2) an intermediate blocking temperature component with northerly declination and inclination ~+60°; and (3) a characteristic component with southeasterly declination and inclination ~–20°. Combinations of alternating field and thermal demagnetization indicate that the intermediate and characteristic components reside in magnetite. The intermediate magnetization probably reflects a viscous partial thermoremanent magnetization (VPTRM) imposed between the Late Cretaceous and mid-Cenozoic; it was probably acquired when the strata were dipping slightly eastward. The characteristic magnetization is probably a VPTRM imposed during regional uplift in the Late Permian. The degree of heating required to have destroyed any primary magnetization is consistent with the conodont color alteration index observed in the Ordovician rocks; additionally, the characteristic magnetization in those rocks is younger than bedding disruption caused by major, late stylolitization. Red-purple mudstones from the middle member of the Wood Canyon Formation, in which a directionally similar characteristic magnetization resides in fine-grained hematite, also appear to have been remagnetized; in these rocks, the remagnetization probably reflects partial recrystallization, as the blocking temperatures are too high to have been reset by burial heating.

The sampled sections have undergone relative tectonic rotation about a vertical axis, consistent with late Tertiary oroflexural bending that had been proposed on independent geologic evidence. The characteristic magnetization probably provides a reliable estimate of the magnitudes of the vertical axis rotations, as the regional geology suggests the Desert Range strata were essentially horizontal throughout the Paleozoic. The total observed relative rotation is 44 ± 5°, representing absolute counterclockwise rotation (27 ± 14°) of the northern part of the Desert Range, and absolute clockwise rotation (17 ± 5°) of the southern part.

The only unit in the Desert Range sequence that may retain a primary magnetization is the late Precambrian Rainstorm Member of the Johnnie Formation. The characteristic magnetization of this unit exhibits two polarities and probably resides in specular hematite; after correction for 18° of counterclockwise rotation, the resulting pole (5°N, 151°E) is near other late Hadrynian poles from North America.