High Sierra terrane, volcanic and sedimentary rocks, and small, shallow-level granitic plutons
High Sierra terrane, volcanic and sedimentary rocks, and small, shallow-level granitic plutons
Cretaceous to Triassic (Pennsylvanian(?)
Occurs in the east-central Sierra Nevada in the Saddlebag Lake, Tioga Pass, eastern Ritter Range, western Mount Morrison, and adjacent roof pendants. Chiefly conglomerate, sandstone, rhyodacite ash-flow tuff, andesite, tuff breccia, volcanic conglomerate, and local basalt. Mostly subaerial deposition with local marine deposition. Named as Koip sequence (Kistler, 1966) and Virginia Lakes sequence (Chesterman, 1975), but further divided by Paterson and Memeti (2014), Schweickert and Lahren (2006), and Attia and others (2021) into the unconformably separated Cretaceous Cinko Lake, Jurassic Shadow Creek and Sawmill Canyon, and Triassic Koip sequences. Unit includes local shallow intrusive bodies ranging from quartz diorite, andesite porphyry, diorite, and dacite breccia. Unit includes Triassic-Jurassic silicic ash-flow tuff and andesite flow, sandstone, and local conglomerate on Mount Unit named the Dana sequence, which has yielded zircon U-Pb ages of ~195, ~213, and questionably ~222 Ma (Kistler, 1966; Ardill and others, 2020). Faulted against the Owens terrane to east. Faulted against the Goddard unit to the west along the Gem Lake fault (Gem Lake shear zone of Green and Schweickert (1995). Unconformably overlies unit HSS.
In the northwesternmost part of the unit, the Cinko Lake pendant is made up of thin-bedded quartzite and metasiltstone with lesser dolomite, amphibolite, and hornblende gneiss. The quartzite has yielded a detrital zircon MDA of ~145 Ma (Memeti and others, 2010). Just to the east, the Piute Meadow pendant is composed of felsic to mafic metatuff, with local flow rock, volcaniclastic, and metasedimentary interbeds. The metavolcanic rocks have yielded detrital zircon MDAs of ~103, ~104, and ~108 Ma (Memeti and others, 2010), and are probably part of unit SHKOV but too small to map separately. Stanback (2018) also maps coeval hypabyssal intrusives that are probably part of unit SHKOG but too small to show at scale as well. Metasediment about 3 km farther east in the same pendant has a detrital zircon MDA of ~136 Ma, which Attia and others (2021) assign to their sedimentary Cinko Lake sequence. Previous studies (Keith and Seitz, 1981; Wahrhaftig, 2000) mapped that area as metavolcanic, however, so the sample is either from a metasedimentary bed within the larger metavolcanic sequence (suggesting the sample better belongs to the younger volcanics) or is from a small unrecognized window of older metasediments beneath the metavolcanics. A few kilometers to the east, in the same pendant in the Matterhorn Peak 15’ Quadrangle, Chesterman (1975) mapped the Virginia Lakes sequence of interbedded rhyolite to basalt metavolcanics and mostly hornfels metasedimentary rocks including metaconglomerate and marble. Attia and others (2021) reports detrital zircon MDAs of ~154 and ~162 Ma from metasediments of this sequence, which they assign to their Shadow Creek sequence. They further report metasedimentary rocks from within an area mapped as metavolcanics with a detrital zircon MDA of ~230 Ma, which they assign to the volcanic lower part of their Koip sequence. Still farther east in the same pendant, Cao (2016) reports detrital zircon MDAs of ~320, ~335, ~340, and ~420 Ma from metavolcanic rocks, and ~430 Ma from metasedimentary rocks. If these MDAs reflect the depositional age of these rocks, then the rocks of the Virginia Lakes sequence spans from earliest Cretaceous to Silurian, though Attia and others (2018) suggest that a Late Devonian to Early Permian age is more likely representative of the actual depositional age. South of Twin Lakes in the Virginia Lakes sequence of Chesterman (1975) in the Saddlebag Lake pendant, Attia and others (2021) and Cao and others (2015) report volcanic zircon U-Pb ages of ~220 Ma, and detrital zircon MDAs of ~186, ~187, ~221, and ~225 Ma. Cao and others (2015) divide these rocks into a Triassic mostly volcanic Koip sequence on the east with a Jurassic mostly sedimentary Sawmill Canyon sequence in fault contact on the west. Farther south, around Saddlebag Lake, Schweickert and Lahren (2006) report volcanic zircon U-Pb ages of ~211 and ~222 Ma. They further report the presence of caldera deposits related to the ~222 Ma volcanics (tuff) marking a Late Triassic eruptive center near Tioga Pass. In the same area, Barth and others (2011) report volcanic zircon U-Pb ages of ~219, ~224, and ~232 Ma, and Attia and others (2021) report detrital zircon MDAs of ~163, ~171, ~191, ~212, and ~247 which they assign to their Shadow Creek and Koip sequences. From the Tioga Pass area just to the south, Ardill and others (2020) report volcanic zircon U-Pb ages of ~220 and ~230 Ma and detrital zircon MDAs of ~217 and two of ~220 Ma.
The Triassic and earliest Jurassic part of this unit, along with coeval parts of the Sierra Crest (unit SCGV) and Twin Lakes (unit TL) terranes and the Scheelite Intrusive Suite, make up the High Sierra arc.  The Early to Late Jurassic part of this unit, along with coeval parts of the Sierra Crest terrane (units SCGV and SCGG) and the Palisade Crest Intrusive Suite (unit Gpc) make up the Goddard arc.