LINKING TERRANES TO CRATONS: NEW PROVENANCE AND DEPOSITIONAL AGE DATA FOR THE EARLY–MIDDLE JURASSIC SAILOR CANYON FORMATION OVERLAP ASSEMBLAGE, NORTHERN SIERRA TERRANE, CA

The Sailor Canyon Fm. (SCFm) of the northern Sierra terrane (NST) is a clastic overlap assemblage that extends for ~100-km along strike northwest of the Tahoe basin. Lower–lower Middle Jurassic feldspathic marine turbidites of the SCFm unconformably overlie deformed early- to mid-Paleozoic rocks of the NST; however, sandstone from the basal SCFm near Cisco Grove, CA yielded only Mesozoic detrital zircon (n=31) of ca. 207–194 Ma (probability peak at ca. 198 Ma). These results indicate the NST was not a significant sediment source for the basal SCFm. Our sample requires a latest Triassic–earliest Jurassic arc (identification of which remains poorly constrained) that was being eroded during Pliensbachian time (i.e., maximum permissible depositional age [~188 Ma] for SCFm) to the south, based on sparse paleocurrent data.

Upsection in the SCFm, the appearance of quartz arenite represents a significant change in sediment provenance. To better constrain the age and source of this change, we sampled quartz arenite in Blackwood Canyon (Ellis Peak unit) west of Lake Tahoe. Our sample (n=135) yielded a multimodal zircon age distribution of 2.0–0.16 Ga with the youngest zircons suggesting a Toarcian depositional age (~177 Ma), consistent with that inferred for other Lower Jurassic quartz-rich clastic intervals in western NV and the Mojave Block of southeastern CA. While similar ages to those in the lower SCFm are still present in our quartz arenite sample, we suggest an addition of transcontinental sand shed from the greater Ouachita-Appalachian orogen enriched by more proximal southwestern Laurentian sources before entering the SCFm basin. Similar cratonic influence is also present in Lower–lower Middle Jurassic clastic rocks of the North Fork terrane, Klamath Mountains, CA and Izee terrane, Blue Mountains, OR, indicating a plate-scale link to west-draining fluvial systems which overcame the subdued topography of the Early Jurassic plate-margin arc. Although the NST lies outboard of several postulated zones of Mesozoic strike-slip displacement in the Sierra Nevada suggestive of transcurrent displacement since Jurassic time, the similarity of detrital zircon age distributions in ca. Lower Jurassic deposits along the plate margin reduces the potential utility of using detrital zircons for quantifying the scale of offset.