Snow Lake terrane
Snow Lake terrane
Early Jurassic and Cambrian to late pre-Cambrian
The terrane occurs in the Snow Lake, Benson Lake, May Lake, and Quartzite Peak roof pendants of the central Sierra Nevada. It consists of a lower sequence of quartzite, feldspathic quartzite, quartz-mica schist, marble, and calc-silicate schist, unconformably overlain by an Early Jurassic upper sequence of a basal conglomerate with clasts of marble and quartzite, overlain by calcareous siltstone and marble, siltstone, and limestone. Both units intruded by dikes. In the Snow Lake pendant, the lower sequence is intruded by Late Jurassic felsic and mafic dikes, probably related to the Independence Dike Swarm (unit Gid) that have yielded zircon U-Pb ages of ~147-153 Ma (Lahren and others, 1990). There the upper unit is also intruded by dikes but those have not been dated, and Memeti and others (2010) suggest they are related to the nearby younger plutons. Units in some pendants isoclinally folded. The lower sequence has yielded detrital zircon MDAs of ~600-1790 Ma (Grasse and others, 2001, Memeti and others, 2010; Attia and others, 2021). The upper sequence in the Snow Lake pendant has yielded Early Jurassic fossils (Memeti and others, 2010), and in the Snow Lake and Strawberry Mine pendants detrital zircon MDAs of ~183 and ~188 Ma (Memeti and others, 2010). Earlier detrital zircon analyses (Grasse and others, 2001) suggest the lower sequence is correlative with late Pre-Cambrian and Cambrian sedimentary units in Mojave Desert, but later detrital zircon analyses (Memeti and others, 2010) suggest the lower sequence derived from somewhere in Neoproterozoic to Ordovician passive craton-margin. On basis of lithology, Lahren and Schweickert (1989) initially correlated upper sequence with Triassic Fairview Valley Formation in Mojave Desert. However, with discovery of two Early Jurassic ammonites, Memeti and others (2010) correlate the upper sequence with similar marine miogeoclinal lithologies in various axial Sierra Nevada roof pendants, or with units in west-central Nevada. The early Jurassic upper member of this unit possibly correlates with the Kings terrane (unit KSM) on basis of lithology and age.