MIOGEOCLINAL STRATA IN HIGH SIERRA NEVADA PENDANTS: DETRITAL ZIRCON AGES REVEAL ADDITIONAL EVIDENCE FOR A CRETACEOUS “MOJAVE-SNOW LAKE FAULT” (MSLF)

A detrital zircon provenance study of metasedimentary pendants in the Sierra Nevada batholith resulted in new evidence for the MSLF (Lahren & Schweickert, 1989). This dextral intrabatholithic strike slip fault is proposed to have transported a belt of miogeoclinal strata 200-400 km north in the Early Cretaceous, where it is now sandwiched in between the western and eastern belts composed of metamorphosed basinal sediments.

We conducted LA-ICPMS U/Pb geochronology on detrital zircons from quartzites of the deformed metasedimentary pendants at Cinko Lake, Snow Lake, Benson Lake, May Lake and Quartzite Peak in and around Yosemite National Park. Except for the Cinko Lake pendant, which revealed mainly zircons of Jurassic age, all other pendants contain 1-3.3 Ga old zircons. Age distributions best fit data obtained from Late Proterozoic to Ordovician miogeoclinal strata. We interpret pendant strata from (1) Snow Lake as Wood Canyon through Carrara Formations, (2) Benson Lake strata as Zabriskie Quartzite, (3) May Lake strata as Eureka Quartzite, and (4) Quartzite Peak as Wood Canyon Formation. The oldest possible depositional age for the Cinko Lake sediments is Late Jurassic based on the youngest zircons at 148 Ma. Given the similar lithologies and proximity, its strata are comparable to L & S's (1989) “Triassic Fairview overlap sequence” at Snow Lake, suggesting a Jurassic age for this unit as well.

Our data require a fault or a series of faults that were active between 148-107 Ma based on ages of the Cinko Lake metasediments, and nearby plutons and metavolcanics that must have obliterated it/them. We note that the 400 km of offset disagree with proposed 200 km from isotope studies (Kistler, 1993), which move the pendants source farther to the north. Since the amount of offset along the MSLF is doubtful and miogeoclinal strata are widely distributed in Northwest America, we suggest that Kistler's term intrabatholithic fault be used until additional evidence for the source is acquired.

This study has implications for other Sierran metasedimentary pendants within the arc that have been grouped into the Kings Sequence (Bateman & Clark, 1974). It is reasonable that some are representing crustal slices composed of miogeoclinal strata, underlain by Precambrian basement and overlain by a Jurassic overlap sequence.