The Mount Tallac roof pendant and its implications for the role of the Sailor Canyon Basin in Jurassic cordilleran tectonics.

摘要

The Mount Tallac pendant formed near the western edge of the Sailor Canyon basin (SCB), in the present-day northern Sierra Nevada Mountains, California. An unnamed Upper Triassic(?) limestone is overlain by the Sailor Canyon Formation (SCF), which contains late Pliensbachian(?) ammonites, and consists mainly of feldspathic, locally quartzose sandstone. The Middle Jurassic Tuttle Lake Formation truncates the SCF. It contains extensional trough-fill deposits overlain by marine volcanic rocks geochemically related to mafic hypabyssal intrusions. A thrust, two cleavages, and two fold sets cut the pendant. The structural chronology is consistent with Middle Jurassic (pre-Nevadan) deformation observed in the Sierra Nevada Foothills and west-central Nevada.;Examination of the SCB and other previously studied assemblages of west-central Nevada with regard to the Mojave-Snow Lake fault of Lahren and Schweickert (1988) resulted in the following conclusions:;The internal stratigraphy of the SCB implies it cannot contain the northern extension of the Mojave-Snow Lake fault. The SCB was not originally contiguous with the Sand Springs assemblage of Oldow (1984), and is not a part of the Luning-Fencemaker allochthon.;At the SCB's latitude, right-lateral translation occurred along several structures, including: (1) the Pine Nut fau (2) the structural boundary between the Sand Springs and Lovelock assemblages; (3) the structural boundary between the Lovelock and Humboldt assemblages; and (4) as-yet unidentified structures within these assemblages. Limited translation is also possible within the SCB. Translation of the SCB en masse is supported by: (1) the relation of a profound unconformity in the northern Sierra to the Colorado Plateau J-0 unconformity; (2) the distribution of cratonal Toarcian quartzose sand; (3) the occurrence of clasts in the northern Sierra Nevada probably derived from the Inyo Mountains; and (4) the distribution, style and intensity of Middle Jurassic deformation.;The SCB formed in a transitional intra-arc to back arc position. Middle Jurassic suturing in the Sierra Nevada Foothills had a minor effect on SCB rocks, whereas it imbricated the Luning-Fencemaker allochthon. Subsequent right-lateral translation has placed the less-deformed SCB between the intensely deformed Sierran Foothills and Luning-Fencemaker allochthon.