COMPARISONS OF DETRITAL ZIRCON AGES AND CHARACTERISTICS OF METASEDIMENTARY PACKAGES IN THE SADDLEBAG LAKE PENDANT, SIERRA NEVADA: IMPLICATIONS FOR DEPOSITIONAL ENVIRONMENTS AND TECTONIC HISTORIES

In the Saddlebag Lake pendant, central Sierra Nevada, California, the implications for depositional environments and tectonic histories are being investigated by studying four distinct metasedimentary packages in the Virginia Canyon and Saddlebag Lake regions. The westernmost metasedimentary package exposed in Spiller Canyon contains clastic metasedimentary and metavolcaniclastic rocks, is intruded by a 232 Ma pluton, contains detrital zircons from 380 Ma to 2.8 Ga., and must be late Paleozoic. This package is juxtaposed along a pre-232 Ma thrust fault with a second, laterally extensive metasedimentary package, consisting of silty muds and siltstones, and less frequently, cross-bedded sandstones, local conglomerates, and limestones. All five samples from this marine package contain minimum zircon age peaks between 171-190 Ma and some PC zircons. This package of Jurassic metasediments is bordered on its eastern margin by a large, dextral strike-slip shear, which is interpreted to be part of the Eastern Sierra Crest Shear Zone. Late Triassic volcanics lie east of the shear zone, and conglomerate beds lie near their base. This unit, intruded by the 165 Ma Green Lakes pluton, contains in one nearby sample ~220-250 Ma zircons and rare PC zircon. Farther south near Saddlebag Lake the conglomerates, previously reported to contain clasts with Permian and Mississippian fossils, are bracketed by the late Triassic volcanics (Barth, personal comm., 2010). A fourth eastern package of metasediments, containing marine cherts and mudstones (previously mapped as Palmetto), is separated from the conglomerates by a dip-slip fault. Only 6 zircons from one sample were obtained from this unit and have ages ranging from 380 Ma-1.8 Ga. Compositions and zircon ages in the first package match volcanic and marine Golconda strata. Package two is interpreted to be part of a marine Jurassic overlap sequence now recognized in scattered pendants elsewhere in the Sierra. The Late Triassic conglomerates have Triassic arc derived(?) zircons and older clasts. The 4th package may also better match Golconda strata and ages but further zircon ages are needed. We conclude that all four packages represent distinct assemblages and are displaced by poorly constrained distances along Paleozoic thrusts and Cretaceous strike-slip faults.