ARE MAFIC INTRUSIONS IN THE MAY LAKE AND SNOW LAKE PENDANTS RELATED TO THE INDEPENDENCE DIKES?

The Jurassic Independence Dike Swarm (IDS) is exposed ranging from the Mojave Desert, the Inyo mountains, and into the eastern central Sierra Nevada batholith. The dikes vary in their lithologies, ranging from lamprophyre to granite porphyry. They have been dated with U-Pb zircon geochronology at ca. 148 Ma (Chen and Moore, 1979). Isotopic ratios ranging in for the IDS suggest an isotopically evolved source (Glazner et al., 2008). Slightly older, up to 2-3 m wide rhyolitic and basaltic andesite IDS dikes of the Sierran King Creek pluton were dated with U-Pb zircon geochronology at ca. 153 Ma and yielded isotopic ratios Sr_i=0.70465-0.70470 and ɛNd=5.40 (rhyolite) and ɛNd=7.63 (andesite) that suggest a more primitive source than the eastern IDS.

IDS type of rocks are also found in metasedimentary pendants of the Snow Lake block on the west side of the Tuolumne intrusive complex in the central Sierra Nevada batholith (Lahren et al., 1990; Memeti et al., 2010), just north of the King Creek pluton. The gabbroic complex found at Snow Lake has a U-Pb zircon age of 148.4 +/-1.5 Ma and has been interpreted to represent the feeder for the IDS (Lahren et al., 1990). In the May Lake pendant, the amphibolite bodies appear to be elongate and discordant to the quartzite and metapelite structures, but they are also deformed due to the emplacement of the adjacent El Capitan and Tuolumne intrusions. Samples of an amphibolite dike from May Lake and the gabbroic complex from the Snow Lake pendant were collected to determine their relation to the IDS in the King Creek pluton and IDS in the eastern Inyo mountains and the Mojave desert. These samples will be analyzed with U-Pb zircon geochronology, with XRF and ICPMS to analyze for major and trace element geochemistry, and with ID-TIMS to determine Sr and Nd isotope values. A comparison of the new age and geochemistry data with published IDS data will help 1) determine whether the mafic outcrops in the Snow Lake block are part of the IDS as previously interpreted and used to suggest that the Snow Lake block was transported from the Mojave desert northwest-ward along the Mojave-Snow Lake fault, 2) and if they are IDS, whether the IDS in the Snow Lake block have a greater isotopic affinity to the more primitive isotope compositions of the IDS at King Creek, than the IDS to the east.