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Ring Mountain (California): Difference between revisions

Coordinates: 37°54′35″N 122°29′09″W / 37.909691528°N 122.485779814°W / 37.909691528; -122.485779814
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==Geology==
==Geology==


Ring Mountain is a unique geological site, where rocks that formed in ancient [[subduction zone]]s can be observed.<ref>{{cite journal |last1=Tsujimori |last2=Matsumoto |last3=Wakabayashi |last4=Liou |title=Franciscan eclogite revisited: Reevaluation of the P-T evolution of tectonic blocks from Tiburon Peninsula, California, USA |journal=Mineralogy and Petrology |date=2006 |volume=88 |issue=1-2 |page=243 |url=https://link.springer.com/article/10.1007/s00710-006-0157-1 |accessdate=28 September 2019}}</ref>. Serpentinized [[peridotite]] crops out on the two summits of the mountain, and the steep upper slopes are underlain by serpentinite-matrix [[melange]] <ref>{{Cite web|url=https://ngmdb.usgs.gov/Prodesc/proddesc_101467.htm|title=Geology of Ring Mountain and Tiburon Peninsula, Marin County, California|last=Bero|first=David A.|date=2014|website=National Geologic Map Database|url-status=live|archive-url=|archive-date=|access-date=2019-09-28}}</ref>. The melange contains blocks of high-pressure, low-temperature metamorphic rocks associated with subduction zone metamorphism. Melanges of this general style are known from the [[Franciscan Complex]]<ref>{{cite journal |last1=Raymond |first1=Loren |title=Origin of Mélanges of the Franciscan Complex, Diablo Range and Northern California: An Analysis and Review |journal=geosciences |date=1 August 2019 |volume=9 |issue=8 |page=338 |url=https://www.mdpi.com/2076-3263/9/8/338 |accessdate=1 October 2019}}</ref>, but this melange is particularly notable for the size and variety of the metamorphic blocks. Dating of metamorphic minerals in the blocks indicates that they were produced over a protracted history of subduction which began ~175 million years ago<ref>{{Cite journal|last=Mulcahy|first=Sean R.|last2=Starnes|first2=Jesslyn K.|last3=Day|first3=Howard W.|last4=Coble|first4=Matthew A.|last5=Vervoort|first5=Jeffrey D.|date=2018|title=Early Onset of Franciscan Subduction|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017TC004753|journal=Tectonics|language=en|volume=37|issue=5|pages=1194–1209|doi=10.1029/2017TC004753|issn=1944-9194}}</ref>. The blocks preserve [[Metamorphic facies#Mineral Assemblages|mineral assemblages]] characteristic of greenschist facies, blueschist facies, amphibolite facies, and eclogite facies metamorphism<ref>{{Cite journal|last=Tsujimori|first=T.|last2=Matsumoto|first2=K.|last3=Wakabayashi|first3=J.|last4=Liou|first4=J. G.|date=2006-08-22|title=Franciscan eclogite revisited: Reevaluation of the P–T evolution of tectonic blocks from Tiburon Peninsula, California, U.S.A.|url=https://doi.org/10.1007/s00710-006-0157-1|journal=Mineralogy and Petrology|language=en|volume=88|issue=1|pages=243|doi=10.1007/s00710-006-0157-1|issn=1438-1168}}</ref>. The lower slopes are underlain by greywacke sandstones and shales of prehnite-pumpellyite metamorphic grade<ref>{{Cite journal|date=1984|title=Tectonostratigraphic Terranes of the San Francisco Bay Region|url=http://archives.datapages.com/data/pac_sepm/059/059001/pdfs/5.htm|language=en-US}}</ref>.
Ring Mountain is a unique geological site, where rocks that formed in ancient [[subduction zone]]s can be observed.<ref>{{cite journal |last1=Tsujimori |last2=Matsumoto |last3=Wakabayashi |last4=Liou |title=Franciscan eclogite revisited: Reevaluation of the P-T evolution of tectonic blocks from Tiburon Peninsula, California, USA |journal=Mineralogy and Petrology |date=2006 |volume=88 |issue=1-2 |page=243 |url=https://link.springer.com/article/10.1007/s00710-006-0157-1 |accessdate=28 September 2019}}</ref>. Serpentinized [[peridotite]] crops out on the two summits of the mountain, and the steep upper slopes are underlain by serpentinite-matrix [[melange]] <ref>{{Cite web|url=https://ngmdb.usgs.gov/Prodesc/proddesc_101467.htm|title=Geology of Ring Mountain and Tiburon Peninsula, Marin County, California|last=Bero|first=David A.|date=2014|website=National Geologic Map Database|url-status=live|archive-url=|archive-date=|access-date=2019-09-28}}</ref>. The melange contains blocks of high-pressure, low-temperature metamorphic rocks associated with subduction zone metamorphism. Melanges of this general style are known from the [[Franciscan Complex]]<ref>{{cite journal |last1=Raymond |first1=Loren |title=Origin of Mélanges of the Franciscan Complex, Diablo Range and Northern California: An Analysis and Review |journal=geosciences |date=1 August 2019 |volume=9 |issue=8 |page=338 |url=https://www.mdpi.com/2076-3263/9/8/338 |accessdate=1 October 2019}}</ref>, but this melange is particularly notable for the size and variety of the metamorphic blocks. Dating of metamorphic minerals in the blocks indicates that they were produced over a protracted history of subduction which began ~175 million years ago<ref>{{Cite journal|last=Mulcahy|first=Sean R.|last2=Starnes|first2=Jesslyn K.|last3=Day|first3=Howard W.|last4=Coble|first4=Matthew A.|last5=Vervoort|first5=Jeffrey D.|date=2018|title=Early Onset of Franciscan Subduction|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017TC004753|journal=Tectonics|language=en|volume=37|issue=5|pages=1194–1209|doi=10.1029/2017TC004753|issn=1944-9194}}</ref>. The blocks preserve [[Metamorphic facies#Mineral Assemblages|mineral assemblages]] characteristic of greenschist facies, blueschist facies, amphibolite facies, and eclogite facies metamorphism<ref>{{Cite journal|last=Tsujimori|first=T.|last2=Matsumoto|first2=K.|last3=Wakabayashi|first3=J.|last4=Liou|first4=J. G.|date=2006-08-22|title=Franciscan eclogite revisited: Reevaluation of the P–T evolution of tectonic blocks from Tiburon Peninsula, California, U.S.A.|url=https://doi.org/10.1007/s00710-006-0157-1|journal=Mineralogy and Petrology|language=en|volume=88|issue=1|pages=243|doi=10.1007/s00710-006-0157-1|issn=1438-1168}}</ref>. The lower slopes are underlain by greywacke sandstones and shales of prehnite-pumpellyite metamorphic grade, <ref>{{Cite journal|date=1984|title=Tectonostratigraphic Terranes of the San Francisco Bay Region|url=http://archives.datapages.com/data/pac_sepm/059/059001/pdfs/5.htm|language=en-US}}</ref>, but the contact between the sandstones and the serpentinite-matrix melange is not exposed.


The origins of the serpentinite-matrix melange, and the mechanism of mixing the metamorphic blocks of different ages and apparent thermal-burial histories, has been a matter of debate. Some authors argue that the metamorphic rocks were exposed at the surface, eroded and re-deposited into a subduction trench to form the melange as an [[olistostrome]]<ref>{{Cite journal|last=Wakabayashi|first=John|date=2012-09-28|title=Subducted sedimentary serpentinite mélanges: Record of multiple burial–exhumation cycles and subduction erosion|url=http://www.sciencedirect.com/science/article/pii/S0040195111004628|journal=Tectonophysics|series=Chaos and Geodynamics: Melanges, Melange Forming Processes and Their Significance in the Geological Record|volume=568-569|pages=230–247|doi=10.1016/j.tecto.2011.11.006|issn=0040-1951}}</ref>. Others interpret the melange as having formed in a subduction plate boundary where blocks of meta-basalt from the downgoing plate were mixed with serpentine from the upper plate mantle<ref>{{Cite journal|last=Ernst|first=W. G.|date=2016-04-03|title=Franciscan mélanges: coherent blocks in a low-density, ductile matrix|url=https://doi.org/10.1080/00206814.2015.1108879|journal=International Geology Review|volume=58|issue=5|pages=626–642|doi=10.1080/00206814.2015.1108879|issn=0020-6814}}</ref>
The origins of the serpentinite-matrix melange, and the mechanism of mixing the metamorphic blocks of different ages and apparent thermal-burial histories, has been a matter of debate. Some authors argue that the metamorphic rocks were exposed at the surface, eroded and re-deposited into a subduction trench to form the melange as an [[olistostrome]]<ref>{{Cite journal|last=Wakabayashi|first=John|date=2012-09-28|title=Subducted sedimentary serpentinite mélanges: Record of multiple burial–exhumation cycles and subduction erosion|url=http://www.sciencedirect.com/science/article/pii/S0040195111004628|journal=Tectonophysics|series=Chaos and Geodynamics: Melanges, Melange Forming Processes and Their Significance in the Geological Record|volume=568-569|pages=230–247|doi=10.1016/j.tecto.2011.11.006|issn=0040-1951}}</ref>. Others interpret the melange as having formed in a subduction plate boundary where blocks of meta-basalt from the downgoing plate were mixed with serpentine from the upper plate mantle<ref>{{Cite journal|last=Ernst|first=W. G.|date=2016-04-03|title=Franciscan mélanges: coherent blocks in a low-density, ductile matrix|url=https://doi.org/10.1080/00206814.2015.1108879|journal=International Geology Review|volume=58|issue=5|pages=626–642|doi=10.1080/00206814.2015.1108879|issn=0020-6814}}</ref>

Revision as of 14:37, 1 October 2019

Ring Mountain
Highest point
Elevation603 ft (184 m) NAVD 88[1]
Prominence402 ft (123 m)[2]
Coordinates37°54′35″N 122°29′09″W / 37.909691528°N 122.485779814°W / 37.909691528; -122.485779814[1]
Geography
Map
LocationMarin County, California, U.S.
Topo mapUSGS San Quentin
Pecked curvilinear nucleated petroglyphs on a rock on Ring Mountain

Ring Mountain is an elevated landform on the Tiburon Peninsula in Marin County, California. This mountain was named for George E. Ring, who served as a Marin County Supervisor from 1895 to 1903.[3]

A number of rare and endangered flora inhabit Ring Mountain.[4] The mountain's twin summits consist of serpentinite[5], a rock which is very high in magnesium, producing soils of unusual chemistry (serpentine soil). The landscape is strewn with many sizable boulders which exhibit a variety of lithologies including high-pressure metamorphic rocks of amphibolite, blueschist, greenschist, and eclogite grade.[6]

Native American pecked curvilinear nucleated petroglyphs created by the Coast Miwok people are also found here.[7]


Geology

Ring Mountain is a unique geological site, where rocks that formed in ancient subduction zones can be observed.[8]. Serpentinized peridotite crops out on the two summits of the mountain, and the steep upper slopes are underlain by serpentinite-matrix melange [9]. The melange contains blocks of high-pressure, low-temperature metamorphic rocks associated with subduction zone metamorphism. Melanges of this general style are known from the Franciscan Complex[10], but this melange is particularly notable for the size and variety of the metamorphic blocks. Dating of metamorphic minerals in the blocks indicates that they were produced over a protracted history of subduction which began ~175 million years ago[11]. The blocks preserve mineral assemblages characteristic of greenschist facies, blueschist facies, amphibolite facies, and eclogite facies metamorphism[12]. The lower slopes are underlain by greywacke sandstones and shales of prehnite-pumpellyite metamorphic grade, [13], but the contact between the sandstones and the serpentinite-matrix melange is not exposed.

The origins of the serpentinite-matrix melange, and the mechanism of mixing the metamorphic blocks of different ages and apparent thermal-burial histories, has been a matter of debate. Some authors argue that the metamorphic rocks were exposed at the surface, eroded and re-deposited into a subduction trench to form the melange as an olistostrome[14]. Others interpret the melange as having formed in a subduction plate boundary where blocks of meta-basalt from the downgoing plate were mixed with serpentine from the upper plate mantle[15]

Animal life

Though Ring Mountain is an island ecosystem surrounded by Highway 101 and suburbs, it hosts a variety of wildlife, including deer, skunks, and many birds and reptiles.

Recreation

Ring Mountain is a popular hiking area and provides spectacular 360 degree views of the northern Bay Area. [16]

See also

References

  1. ^ a b "Ring". NGS Data Sheet. National Geodetic Survey, National Oceanic and Atmospheric Administration, United States Department of Commerce. Retrieved 2014-02-12.
  2. ^ "Ring Mountain, California". Peakbagger.com. Retrieved 2014-02-13.
  3. ^ "Ring Mountain, Open Space Preserve". County of Marin. Archived from the original on 2008-06-21. Retrieved 2009-12-07.
  4. ^ Earth Metrics Inc. (1989) Marinero Estates Environmental Impact Report, Tiburon, California, prepared for the city of Tiburon, Ca.
  5. ^ Bero, David A. (2014). "Geology of Ring Mountain and Tiburon Peninsula, Marin County, California". National Geologic Map Database. Retrieved 2019-09-28.{{cite web}}: CS1 maint: url-status (link)
  6. ^ Anczkiewicz, Robert; Platt, John P.; Thirlwall, Matthew F.; Wakabayashi, John (2004-08-30). "Franciscan subduction off to a slow start: evidence from high-precision Lu–Hf garnet ages on high grade-blocks". Earth and Planetary Science Letters. 225 (1): 147–161. doi:10.1016/j.epsl.2004.06.003. ISSN 0012-821X.
  7. ^ Hogan, C. Michael (2008). Andy Burnham (ed.). "Ring Mountain, The Megalithic Portal,".
  8. ^ Tsujimori; Matsumoto; Wakabayashi; Liou (2006). "Franciscan eclogite revisited: Reevaluation of the P-T evolution of tectonic blocks from Tiburon Peninsula, California, USA". Mineralogy and Petrology. 88 (1–2): 243. Retrieved 28 September 2019.
  9. ^ Bero, David A. (2014). "Geology of Ring Mountain and Tiburon Peninsula, Marin County, California". National Geologic Map Database. Retrieved 2019-09-28.{{cite web}}: CS1 maint: url-status (link)
  10. ^ Raymond, Loren (1 August 2019). "Origin of Mélanges of the Franciscan Complex, Diablo Range and Northern California: An Analysis and Review". geosciences. 9 (8): 338. Retrieved 1 October 2019.
  11. ^ Mulcahy, Sean R.; Starnes, Jesslyn K.; Day, Howard W.; Coble, Matthew A.; Vervoort, Jeffrey D. (2018). "Early Onset of Franciscan Subduction". Tectonics. 37 (5): 1194–1209. doi:10.1029/2017TC004753. ISSN 1944-9194.
  12. ^ Tsujimori, T.; Matsumoto, K.; Wakabayashi, J.; Liou, J. G. (2006-08-22). "Franciscan eclogite revisited: Reevaluation of the P–T evolution of tectonic blocks from Tiburon Peninsula, California, U.S.A." Mineralogy and Petrology. 88 (1): 243. doi:10.1007/s00710-006-0157-1. ISSN 1438-1168.
  13. ^ "Tectonostratigraphic Terranes of the San Francisco Bay Region". 1984. {{cite journal}}: Cite journal requires |journal= (help)
  14. ^ Wakabayashi, John (2012-09-28). "Subducted sedimentary serpentinite mélanges: Record of multiple burial–exhumation cycles and subduction erosion". Tectonophysics. Chaos and Geodynamics: Melanges, Melange Forming Processes and Their Significance in the Geological Record. 568–569: 230–247. doi:10.1016/j.tecto.2011.11.006. ISSN 0040-1951.
  15. ^ Ernst, W. G. (2016-04-03). "Franciscan mélanges: coherent blocks in a low-density, ductile matrix". International Geology Review. 58 (5): 626–642. doi:10.1080/00206814.2015.1108879. ISSN 0020-6814.
  16. ^ http://www.marincounty.org/recreation Retrieved 2017-3-21
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