Middle Tertiary Contractile Deformation, Uplift, Extension, and Rotation in the San Emigdio Range, Southern California: ABSTRACT

Abstract

New data from the San Emigdio Range of southern California provide evidence of major tectonism during the middle Tertiary, including uplift of the adjacent Mojave region, disruption of marine basins, and rotation of the southern tail of the Sierra Nevada. The San Emigdio Range was the site of the southernmost marine deposition in the San Joaquin basin from the earliest through the middle Eocene, overlapping deeply eroded midcrustal granitic rocks. These marine rocks were associated with a northtrending, west-facing shoreline. To the north, the coast probably was embayed to the east as far as the Goler basin of southeastern California. This marine embayment was disrupted and the record of stratigraphic continuity between San Joaquin and Goler basins was destroyed as the result of uplift in the latest Eocene and Oligocene. Conglomerates of the uppermost Eocene and Oligocene nonmarine Tecuya Formation of the San Emigdios comprise an unroofing sequence whose provenance suggests marked uplift and erosion of the Mojave region. Geohistory analysis of the coeval marine Pleito Fm. suggests that the uplift and unroofing was related to contractile deformation. By about 22 Ma, extension replaced contractile deformation in the San Emigdios, as indicated by normal faulting and basaltic volcanism and synchronousmore » extension reported for the adjacent Mojave region. The authors paleomagnetic data from five sites from Tecuya Creek to Pleito Creek reveal that basalts are rotated 44{degree} (clockwise). This rotation occurred prior to 16 Ma and, perhaps between 18-20 Ma, if comparison with the Mojave region is valid. This episode of rotation accounts for most or all of the southwesterly trend of the southern tail of Sierra Nevada basement rocks.« less