St. Kevin Granite

What the map says

Medium- to coarse-grained, gray to light-pinkish-gray and pinkish-brown, euhedral equigranular to porphyritic, massive to locally weakly foliated biotite-muscovite monzogranite, with local gradational changes to granodiorite and other textural variations (Pearson and others, 1962; Tweto and Pearson, 1964; Tweto, 1974, 1987). The main batholith is characterized by a central region of coarse-grained monzogranite grading outward into medium- grained monzogranite and fine-grained foliated monzogranite and granodiorite with seriate-to-porphyritic texture commonly having Carlsbad twinning in aligned microcline phenocrysts. Within the map area, medium-grained, euhedral monzogranite is the common phase of the main plutonic body. Silicified, quartz-rich zones are mapped along the central-eastern portion of the map (Tweto, 1974) and indicated by dark blue, solid lines within unit Ygs. Rb-Sr isochron age is 1,390±60 Ma (Pearson and others, 1962), and a more recent U-Pb age from outside the quadrangle is 1,442±14 Ma (Moscati and others, 2017). Hydrothermally altered St. Kevin Granite, unit Ygs(a), bounds the north and south sides of the central region of Turquoise Lake along a generally north-trending fault zone. Farther north along the same north-trending fault zone, sheared and brecciated St. Kevin Granite, Ygs(s), is mapped between Porcupine and Longs Gulches and along the ridge between Homestake Reservoir and East Fork Homestake Creek

1:100,000 sheet: Ruleman and others, 2020, U.S. Geological Survey Scientific Investigations Map 3451 (2 crags). A contact line at that scale is about 100 m wide on the ground.

Fine-grained to medium-grained, gray to light pinkish gray, equigranular to porphyritic, massive to locally weakly foliated biotite-muscovite monzogranite or quartz monzonite. Displays a wide variety of textures, including a fine-grained facies, a “normal facies” (medium-grained, equigranular to porphyritic 2-mica monzogranite), a granodiorite facies, and a tracytoid hybrid facies containing close-packed aligned microcline crystals (Tweto, 1974a). Forms a batholith about 40 km long and 20 km wide with intricate boundaries, of which only the eastern part is within the map area. U-Pb zircon age is 1,425±12 Ma (Moscati and others, 2017)

1:100,000 sheet: Kellogg and others, 2017, U.S. Geological Survey Scientific Investigations Map 3382 (1 crag). A contact line at that scale is about 100 m wide on the ground.

Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.