- Source: Johnson Granite Porphyry
Johnson Granite Porphyry is found in Tuolumne Meadows, Yosemite National Park.
Johnson Granite Porphyry was named for Johnson Peak, the highest mountain in Tuolumne Meadows, Yosemite National Park.
Its area is estimated at 1,100 square kilometres (420 sq mi), the exposed area covering roughly 40 square kilometres (15 sq mi). Johnson Granite Porphyry is part of the Tuolumne Batholith. Its boundaries are difficult to trace, and are irregular. It is both the youngest, and the most siliceous rock of Tuolumne Intrusive Suite.
Geology
The innermost, most felsic part of the Tuolumne Batholith is the Johnson Granite Porphyry. It is a highly irregular, elongated body. Completely surrounding it is the much larger body of Cathedral Peak granite.
Field observations and magnetic fabrics suggest an extrusive event, that is, Johnson Granite Porphyry may record possible volcanism. This may relate to deformation along active shear zones.
Johnson Granite Porphyry is composed of
quartz
K-feldspar
zoned plagioclase, and
locally contains coarse-grained feldspars
Biotite, the only mafic mineral, with accessory phases of;
sphene,
allanite,
apatite,
magnetite.
See also
Cathedral Peak Granodiorite
El Capitan Granite
Fine Gold Intrusive Suite
Geology of the Yosemite area
Intrusive Suite of Buena Vista Crest
Intrusive Suite of Merced Peak
Intrusive Suite of Sonora Pass
Kuna Crest Granodiorite
Porphyry
Sentinel granodiorite
Tuolumne Intrusive Suite
References
External links and references
Reference with a photo
Geologic and geophysical investigation of two fine-grained granites, Sierra Nevada Batholith, California: Evidence for structural controls on emplacement and volcanism
National Geologic Map Database site