MIOCENE-PLIOCENE UPLIFT RATES OF THE SIERRA NEVADA, CALIFORNIA

Several studies along the central part of Sierra Nevada frontal fault including Huber (1981) and Gilbert and Reynolds (1973) indicate significant vertical displacement initiated around 8 to 10 Ma. Voluminous mafic outpouring around 8 to 10 Ma is also interpreted as indicating break-up of the Late Miocene landscape. About 1.4 degrees of Late Miocene (~10 Ma) and younger tilting followed deposition of the mafic flows that are widely distributed on the erosion surface (Lindgren Surface) of the Sierra Nevada block. This resulted in ~2100-2600 m uplift giving an average uplift rate of ~0.25 mm/yr. The stratigraphic record in the Great Valley and Sierra Nevada suggest the rotation and uplift rates increased significantly at about 4.0 to 3.5 Ma. The uplift estimated from rigid block rotation is about 850 m during the late Miocene and early Pliocene (~10 to 4 Ma), and about 1750 m during the late Pliocene and Pleistocene (~4 Ma to present), suggesting an initial uplift rate of ~0.14 mm/yr that increased to ~0.44 mm/yr in the Late Pliocene. Stratigraphic studies from the west side of the Sierra Nevada block indicate earlier tilting of ~0.3^o to 0.7^o around an axis trending ~310^o to 325^o between the middle Eocene and Oligocene. This early Cenozoic tilting occurred during ~25 m.y. span and resulted in ~1000 to 1300 m uplift with a negligible uplift rate of ~ 0.0004 mm/yr.

The early Tertiary stratigraphic record indicates that major river systems occupied many of the areas that are now in the crestal highlands as well as the entire west side of the block. Younger units that provide important constraints for the differential rotation rates during the last 10 Ma are: 1) the Friant pumice member of the Turlock Lake Formation, which contains the Bishop Tuff (~760 ka) (Sarna-Wojicki et al., 2000; Marchand and Allwardt, 1981); 2) part of the Laguna Formation which is correlated with gravels near the Yuba River containing the Nomlaki Tuff (~3.4 Ma) (Busacca et al., 1982, 1989), 3) gravels near the King River containing an ~3.76 Ma basalt clast, and Laguna Formation deposits in Merced county that contain a magnetic reversal interpreted as the Gilbert-Gauss reversal at ~ 3.4 Ma (Marchand and Allwardt, 1981); 4) mafic flows and clastic rocks of the Mehrten Formation (Eureka Valley Tuff member) at ~9.8 Ma (Dalrymple, 1963; Busby et al, 2009) and 5) trachyandesites of Kennedy Table at ~ 10.2 Ma (Huber, 1981).