Metasedimentary rocks, metavolcanic rocks, and minor shallow metagranitic plutons
Metasedimentary rocks, metavolcanic rocks, and minor shallow metagranitic plutons
Early Cretaceous to Late Triassic
Occurs in central and southern Sierra Nevada in the Boyden Cave, Iron Mountain, and Mineral King roof pendants, and in adjacent roof pendants to the north and south. Metasedimentary rocks are chiefly marine quartzite, pelitic schist, metasandstone, calc-schist, and minor marble. Marine ammonites occur in metasedimentary rocks. Metavolcanic rocks are chiefly metamorphosed andesite, dacite, rhyolite flows and breccia, and dacite and rhyolite tuff. Minor metamorphosed basalt and basaltic andesite. Locally intruded by dikes of Independence Dike Swarm (unit Gid). Minor shallow metagranitic plutons are chiefly schistose dark granodiorite and lesser schistose diorite and gabbro occurring mainly in the Triple Divide Peak roof pendant. Samples with middle Cretaceous detrital zircon MDAs possibly from high-faulted and folded units of overlap (unit SHKOV).
Metavolcanic rocks from the Iron Mountain pendant have yielded zircon U-Pb ages of ~123-156 Ma (Attia and others, 2020; Bennett and others, 2024). Metavolcanic rocks from the western part of the Strawberry Mine pendant have yielded a detrital zircon MDA of ~103 Ma (Memeti and others, 2010). However, this age is within the span for the overlying Cretaceous overlap unit (SHKOV and SHKOG), so this age probably reflects a body of that unit too small to differentiate at map scale. From farther south in the western Boyden Cave pendant, Attia and others (2021) reported a detrital zircon MDA of ~114 Ma from this unit. From farther south, in the Big Baldy pendant, Sisson and Moore (1994) report a U-Pb age of ~110 Ma from metarhyolite tuff. From nearby in the southeast part of the Sequoia Park pendant, Attia and others (2021) reported a poorly constrained detrital zircon MDA of ~188 Ma. From still farther south in the Mineral King pendant, Sisson and Moore (2013, recalculated from Busby-Spera, 1983) report zircon U-Pb concordia ages of ~111 from metaandesite, ~131-140 Ma from metarhyolite tuff, ~171 and ~189 Ma from metadacite tuff, and ~214 and ~236 Ma from metaandesite. From the same pendant, Attia and others (2021) report detrital zircon MDAs of ~187 and ~265 Ma.