| Johnson Granite Porphyry | |
| Period: | cretaceous |
| Age: | 85.4 Ma https://www.academia.edu/21350101/Build_up_of_the_Tuolumne_Batholith_California_the_Johnson_Granite_Porphyry?email_work_card=title |
| Type: | Geological formation |
| Area: | 1100km2 |
| Location: | Yosemite National Park |
| Country: | United States of America |
| Namedfor: | Johnson Peak |
| Location Ts: | Yosemite National Park |
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.[1]
Its area is estimated at 1100km2, the exposed area covering roughly 40km2.[2] Johnson Granite Porphyry is part of the Tuolumne Batholith.[3] Its boundaries are difficult to trace, and are irregular. It is both the youngest, and the most siliceous rock of Tuolumne Intrusive Suite.[4] [5]
The 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.
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] [8]
Johnson Granite Porphyry is composed of