San Juan volcanic field

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San Juan volcanic field
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San Juan volcanic field
Location in Colorado
Highest point
Coordinates 37°53′36″N106°46′28″W / 37.89333°N 106.77444°W / 37.89333; -106.77444
Geography
Location Colorado, United States
Geology
Mountain type Volcanic field

The San Juan volcanic field is part of the San Juan Mountains in southwestern Colorado. It consists mainly of volcanic rocks that form the largest remnant of a major composite volcanic field that covered most of the southern Rocky Mountains in the Middle Tertiary geologic time. [1] There are approximately fifteen calderas known in the San Juan Volcanic Fields; however, it is possible that there are two or even three more in the region. [1]

Contents

The region began with many composite volcanoes that became active between 35 and 40 million years ago, with peak activity in the time period around 35-30 million years ago. [1] Around this time the activity began to include explosive ash-flow eruptions. [2] Many of these volcanoes experienced caldera collapse, resulting in the fifteen to eighteen caldera volcanoes in the region today. [1]

Phases of Volcanism

The San Juan volcanic field experienced two phases of volcanism. [3]

The earlier volcanism took place during the Oligocene age of the Paleogene Period. It produced largely intermediate composition lavas and breccias, together with ash flow tuffs reflecting differentiation of the original magma. [3] The precaldera intermediate volcanic rocks include the Conejos Formation in the southeastern part of the field. [4] Intermediate volcanism did not cease with caldera eruptions, and included such voluminous intermediate volcanic rocks as the Huerto Andesite. [5]

The later volcanism took place from Miocene to Pliocene in ages of the Neogene Period. It was characterized by bimodal volcanism, producing both low-silica alkaline flows and high-silica rhyolites. It is usually interpreted as a partial melt of the lower crust that was erupted onto the surface. [3]

Cochetopa Dome (Cochetopa Caldera). Cochetopa Dome.JPG
Cochetopa Dome (Cochetopa Caldera).
Aerial of Colorado State Highway 114 near Cochetopa Dome and Cochetopa Hills. Colorado State Route 114, Near Cochetopa Dome, Colorado (14223891743).jpg
Aerial of Colorado State Highway 114 near Cochetopa Dome and Cochetopa Hills.

Notable calderas

NameAssociated tuff Coordinates Age
Lake CitySunshine Peak Tuff 38°02′N107°23′W / 38.03°N 107.38°W / 38.03; -107.38 [3] 22.93 ± 0.02 Ma [6]
Creede CalderaSnowshoe Mountain Tuff 37°46′N106°56′W / 37.76°N 106.94°W / 37.76; -106.94 [7] 26.5 ± 0.3 Ma [8]
Cochetopa Nelson Mountain Tuff 38°12′N106°45′W / 38.2°N 106.75°W / 38.2; -106.75 [7] 26.4 ± 0.5 Ma [8]
San LuisCebolla Creek Tuff
Rat Creek Tuff
38°01′N107°58′W / 38.01°N 107.97°W / 38.01; -107.97 [8] 26.9 Ma [8]
South RiverWatson Park Tuff 37°40′N106°56′W / 37.67°N 106.94°W / 37.67; -106.94 [8] 27.4? Ma [8]
BachelorCarpenter Ridge Tuff 37°49′N106°55′W / 37.82°N 106.91°W / 37.82; -106.91 [7] 27.45 ± 0.05 Ma [8]
La Garita Fish Canyon Tuff 37°46′N106°56′W / 37.76°N 106.94°W / 37.76; -106.94 [7] 27.45 ± 0.05 Ma [8]
Uncompahgre-San JuanSapinero Mesa Tuff 37°58′N107°32′W / 37.96°N 107.53°W / 37.96; -107.53 [8] 27.5 ± 0.5 Ma [8]
PlatoroTreasure Mountain Group [9] 37°21′N106°32′W / 37.35°N 106.53°W / 37.35; -106.53 [3] 28.4 Ma [9]
UnknownMasonic Park Tuff 37°42′N106°41′W / 37.70°N 106.69°W / 37.70; -106.69 [3] 28.7 Ma [10]
North PassSaguache Creek Tuff 38°12′N106°32′W / 38.20°N 106.54°W / 38.20; -106.54 [8] 32.2 Ma [8]
Bonanza [11] Bonanza Tuff 38°19′N106°05′W / 38.32°N 106.08°W / 38.32; -106.08 [12] 33.12 ± 0.03 Ma
MarshallThorn Ranch Tuff 38°20′N106°14′W / 38.34°N 106.23°W / 38.34; -106.23 [8] 33.6 ± 0.3 Ma [8]
Chalcopyrite-quartz rock specimen, from Idarado Mine in San Juan Volcanic Field. Chalcopyrite-quartz - Idarado Mine, San Juan Mountains, Colorado, USA (22487007594).jpg
Chalcopyritequartz rock specimen, from Idarado Mine in San Juan Volcanic Field.

Economic Impact

The San Juan volcanic field has been a historically important mining district, producing lead, zinc, copper, gold, and silver. The ores were mostly deposited in and near calderas that experienced significant postcaldera activity. Ore veins were concentrated in fractures associated with caldera activity and in postcaldera intrusive bodies. The greatest mineralization took place near the youngest and most silicic intrusions of each caldera cycle. [13]

See also

Related Research Articles

A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is gone. The ground surface then collapses into the emptied or partially emptied magma chamber, leaving a large depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur each century, the formation of a caldera is a rare event, occurring only a few times per century. Only seven caldera-forming collapses are known to have occurred between 1911 and 2016. More recently, a caldera collapse occurred at Kīlauea, Hawaii in 2018.

<span class="mw-page-title-main">Supervolcano</span> Volcano that has erupted 1000 cubic km of lava in a single eruption

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<span class="mw-page-title-main">Yellowstone Caldera</span> Volcanic caldera in Yellowstone National Park in the United states

The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corner of Wyoming. The caldera measures 43 by 28 miles, and postcaldera lavas spill out a significant distance beyond the caldera proper.

<span class="mw-page-title-main">Yellowstone hotspot</span> Volcanic hotspot in the United States

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<span class="mw-page-title-main">Mount Taylor (New Mexico)</span> Stratovolcano in the San Mateo Mountains, North America

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<span class="mw-page-title-main">La Garita Caldera</span> Large caldera in the state of Colorado, U.S.

La Garita Caldera is a large caldera in the San Juan volcanic field in the San Juan Mountains around the town of Creede in southwestern Colorado, United States. It is west of La Garita, Colorado. The eruption that created the La Garita Caldera is among the largest known volcanic eruptions in Earth's history, as well as being one of the most powerful known supervolcanic events.

<span class="mw-page-title-main">Timeline of volcanism on Earth</span>

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<span class="mw-page-title-main">Mogollon-Datil volcanic field</span> Volcanic field in western New Mexico, United States

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<span class="mw-page-title-main">Fish Canyon Tuff</span>

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<span class="mw-page-title-main">Keres Group</span> A group of geologic formations in New Mexico

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<span class="mw-page-title-main">Latir volcanic field</span> Volcanic field in New Mexico

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<span class="mw-page-title-main">Hinsdale Formation</span> A geologic formation in New Mexico

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The Bearwallow Mountain Andesite or Bearwallow Mountain Formation is a geologic formation exposed in and around the Mogollon Mountains of southwest New Mexico. It has a radiometric age of 27 to 23 million years, corresponding to the late Oligocene to early Miocene epochs.

<span class="mw-page-title-main">Hannegan caldera</span> Geologic caldera in Washington (state)

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References

  1. 1 2 3 4 Steven, Thomas A.; Lipman, Peter W. (1976). "Calderas of the San Juan Volcanic Field, Southwestern Colorado". U.S. Geological Survey Professional Papers. Washington, DC: U.S. Government Printing Office. 958: 1–35. Retrieved 2012-05-16.
  2. Lipman, Peter W.; Steven, Thomas A.; Mehnert, Harald H. (1970-08-01). "Volcanic History of the San Juan Mountains, Colorado, as Indicated by Potassium–Argon Dating". Geological Society of America Bulletin. 81 (8): 2329–2352. Bibcode:1970GSAB...81.2329L. doi:10.1130/0016-7606(1970)81[2329:VHOTSJ]2.0.CO;2. ISSN   0016-7606.
  3. 1 2 3 4 5 6 Lipman, P.W.; Doe, B.R.; Hedge, C.E.; Steven, T.A. (1978). "Petrologic evolution of the San Juan volcanic field, southwestern Colorado: Pb and Sr isotope evidence". Geological Society of America Bulletin. 89 (1): 59–82. Bibcode:1978GSAB...89...59L. doi:10.1130/0016-7606(1978)89<59:PEOTSJ>2.0.CO;2. ISSN   0016-7606.
  4. Colucci, M. T.; Dungan, M. A.; Ferguson, K. M.; Lipman, P. W.; Moorbath, S. (30 July 1991). "Precaldera lavas of the southeast San Juan Volcanic Field: Parent magmas and crustal interactions". Journal of Geophysical Research: Solid Earth. 96 (B8): 13413–13434. doi:10.1029/91JB00282.
  5. Parat, Fleurice; Dungan, Michael A.; Lipman, Peter W. (1 May 2005). "Contemporaneous Trachyandesitic and Calc-alkaline Volcanism of the Huerto Andesite, San Juan Volcanic Field, Colorado, USA" (PDF). Journal of Petrology. 46 (5): 859–891. doi: 10.1093/petrology/egi003 .
  6. Kennedy, Ben; Wilcock, Jack; Stix, John (October 2012). "Caldera resurgence during magma replenishment and rejuvenation at Valles and Lake City calderas". Bulletin of Volcanology. 74 (8): 1833–1847. doi:10.1007/s00445-012-0641-x.
  7. 1 2 3 4 Robinson, Joel E.; Dillon R. Dutton; David W. Ramsey; Peter W. Lipman; Tracey J. Felger (2006). Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado: Geologic Investigations Series. Vol. I-2799. U.S. Geological Survey. Retrieved 2010-05-03.
  8. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Lipman, Peter W.; McIntosh, William C.; Zimmerer, Matthew J. (2013). "From ignimbrite to batholith, northeastern San Juan Mountains, ColoradoBonanza, Cochetopa Park, and North Pass calderas". Classic Concepts and New DirectionsExploring 125 Years of GSA Discoveries in the Rocky Mountain Region. doi:10.1130/2013.0033(14).
  9. 1 2 Lipman, Peter W.; Dungan, Michael A.; Brown, Laurie L.; Deino, Alan (1 August 1996). "Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs". GSA Bulletin. 108 (8): 1039–1055. doi:10.1130/0016-7606(1996)108<1039:REASAT>2.3.CO;2.
  10. Sliwinski, J. T.; Bachmann, O.; Dungan, M. A.; Huber, C.; Deering, C. D.; Lipman, P. W.; Martin, L. H. J.; Liebske, C. (May 2017). "Rapid pre-eruptive thermal rejuvenation in a large silicic magma body: the case of the Masonic Park Tuff, Southern Rocky Mountain volcanic field, CO, USA". Contributions to Mineralogy and Petrology. 172 (5): 30. doi:10.1007/s00410-017-1351-3. hdl: 20.500.11850/216533 .
  11. Varga, Robert J.; Smith, Brian M. (1984). "Evolution of the Early Oligocene Bonanza Caldera, northeast San Juan Volcanic Field, Colorado". Journal of Geophysical Research. 89 (B10): 8679. doi:10.1029/JB089iB10p08679.
  12. Lipman, Peter W.; Zimmerer, Matthew J.; McIntosh, William J. (2015-12-01). "An ignimbrite caldera from the bottom up: Exhumed floor and fill of the resurgent Bonanza caldera, Southern Rocky Mountain volcanic field, Colorado". Geosphere. 11 (6): 1902–1947. Bibcode:2015Geosp..11.1902L. doi: 10.1130/GES01184.1 .
  13. Steven, Thomas A.; Luedke, Robert G.; Lipman, Peter W. (1974). "Relation of mineralization to calderas in the San Juan volcanic field, southwestern Colorado". J. Res. US Geol. Surv. 2: 405–409.