Johnson Granite Porphyry is found in Tuolumne Meadows, Yosemite National Park.
| Johnson Granite Porphyry | |
|---|---|
| Stratigraphic range: 85.4 Ma [1] | |
| Type | Geological formation |
| Area | 1,100 square kilometres (420 sq mi) |
| Location | |
| Location | Yosemite National Park |
| Country | United States of America |
| Type section | |
| Named for | Johnson Peak |
| Location | Yosemite National Park |
Johnson Granite Porphyry was named for Johnson Peak, the highest mountain in Tuolumne Meadows, Yosemite National Park.[1]
Its area is estimated at 1,100 square kilometres (420 sq mi), the exposed area covering roughly 40 square kilometres (15 sq mi).[2] Johnson Granite Porphyry is part of the Tuolumne Batholith.[3] Its boundaries are difficult to trace, and are irregular.[1] It is both the youngest, and the most siliceous rock of Tuolumne Intrusive Suite.[4][5]
Geology
editThe innermost, most felsic part of the Tuolumne Batholith is the Johnson Granite Porphyry.[6] It is a highly irregular, elongated body. Completely surrounding it is the much larger body of Cathedral Peak granite.[1]
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.[7][5][8]
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;
See also
editReferences
edit- ^ a b c Calkins, Frank C. "The Granitic Rocks of the Yosemite Region".
- ^ Glazner, Allen F, Stock, Greg M. (2010). Geology Underfoot in Yosemite. Mountain Press, p. 53. ISBN 978-0-87842-568-6.
- ^ Bracciali, Laura; Paterson, Scott R.; Memeti, Vali; Rocchi, Sergio; Matzel, J.; Mundil, Roland (2008). "Build-up of the Tuolumne Batholith, California: the Johnson Granite Porphyry" (published January 1, 2008).
- ^ Calkins, F.C. (1930). "National Geologic Map Database".
- ^ a b c Bracciali, Laura; Memeti, Vali; Paterson, Scott R.; Rocchi, Sergio (January 2008). "Build-up of the Tuolumne Batholith, California: the Johnson Granite Porphyry". ResearchGate.
- ^ Bracciali, Laura; Paterson, Scott; Memeti, Valbone; Rocchi, Sergio; Matzel, Jennifer; Mundil, Roland (2008). "Build-up of the Tuolumne Batholith, California: the Johnson Granite Porphyry".
- ^ Titus, Sarah J.; Clark, Ryan; Tikoff, Basil (September 2005). "Geologic and geophysical investigation of two fine-grained granites, Sierra Nevada Batholith, California: Evidence for structural controls on emplacement and volcanism". Geological Society of America Bulletin.
{{cite web}}: CS1 maint: date and year (link) - ^ Titus, S.; Clark, R.; Tikoff, S. (September 1, 2005). "Geologic and geophysical investigation of two fine-grained granites, Sierra Nevada Batholith, California: Evidence for structural controls on emplacement and volcanism". Geological Society of America Bulletin. 117 (9): 1256. doi:10.1130/B25689.1. S2CID 129298834.