The marble that make up Fremont Peak are likely from the same ancient sea that formed the marbles in the roof pendants of the Sierra Nevada.
Fremont Peak is a California State Park and requires a use fee. There are a few parking lots, campgrounds, and trails. It likely gets very busy on beautiful weekends and popular stargazing nights as it has its own observatory.
Between 500 and 300 million years ago, limestone and mustone was deposited in a shallow sea off the coast of what would become North America.
Then between 104 and 90 million years ago, the Sierra Nevada Batholith intruded beneath the limestone as the Farallon plate subducted under the North American plate. This granitic magma migrated up toward the surface along fractures in the overlying rock. Near the surface there was a horizontal plane of weakness between an existing pluton and sedimentary rocks above it. The magma stopped its upward movement and instead began spreading out laterally along this horizontal contact.
Replace "Dinkey Creek Pluton" for the intruding magma.
The horizontal contact that the pluton spread across was not perfectly flat, and blocks of the sediment stuck down from the roof of the magma chamber fingers or necklace pendants, thus the term roof pendant. The sedimentary rocks above underwent metamorphosis from either contact with this hot magma or from the intrusion of the existing pluton.
Over time, uplift of the Sierra Nevada Mountains increased the erosion on the overlying meta-sedimentary rocks. At the same time, the San Andreas split off this block of rock and began transporting it northward to this spot. Erosion continued until most of the metamorphic rocks were eroded away, except where the pendants stuck down into the magma.
In addition to marble (limestone that has been metamorphosed), dolomite can also be found on the peak. Dolomite and limestone differ only in the amount of magnesium contained within the crystalline structure. Dolomite contains more magnesium than limestone.
The difference between the two can be seen in the weathering and structure. The marble still has light and dark bands in it that are related to the original sedimentary layers. The dolomite is generally a uniform dark gray. While rough, the limestone weathers relatively evenly and the dolomite has noticeable pock marks.
Logging requirements:
Send me a note with :
- The text "GC4TQP6 Fremont Peak Marble" on the first line.
- The number of people in your group (put in the log as well).
- In the outcrop at the coordinates, how much of it (rough percentage) is dolomite?
- Which way do the ancient layering go, parallel to the trail, parallel to the trail or perpendicular?
The following sources were used to generate this cache:
- Farallon Plate (http://en.wikipedia.org/wiki/Farallon_Plate
- Subduction Zones; Plate Tectonics, 1996 - 2005 platetectonics.com. http://www.platetectonics.com/book/page_12.asp
- Farallon Plate, USGS, http://pubs.usgs.gov/gip/dynamic/Farallon.html Last updated: 05.05.99
- The Farallon Plate NASA/Goddard Space Flight Center Scientific Visualization Studio; http://svs.gsfc.nasa.gov/vis/a000000/a001300/a001322/index.html
- Martin-Hernandez, F. et al Editors, Magnetic Fabric Methods and Applications, Geological Society, Special Publication 238, , Geological Society of London 2004
- Petford, N., Cruden, A., McCaffrey, K and Vigneresse, J-L., Granite magma formation, transport and emplacement in the Earth's crust, Nature, V. 408, p. 669-673, December 2000. limestone and Dolomite in the Northern Gabilan Range California. California Division of Mines Special Report 56. OLIVER E. BOWEN, JR. and CLIFFTON H. GRAY, JR. 1959
- The Fremont Peak Experience, Traveling Through Space and Time. Doris Sloan. April, 2008