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La Garita Caldera

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Ages of early volcanic rocks in proximity to margins of La Garita caldera (Colorado, USA). Figure is modified from Lipman (2006); data are from Tables S1–S2 (see footnote 1). FCT—Fish Canyon Tuff; SJ—San Juan.

Ages of early volcanic rocks in proximity to margins of La Garita caldera (...

Published: 09 May 2022
Figure 3. Ages of early volcanic rocks in proximity to margins of La Garita caldera (Colorado, USA). Figure is modified from Lipman (2006) ; data are from Tables S1–S2 (see footnote 1 ). FCT—Fish Canyon Tuff; SJ—San Juan.
Image
Generalized map showing geometry of northern La Garita caldera, Colorado, USA. Green line is axis of moat paleovalley between northern wall and resurgent block. Red box shows location of Figure 2.

Generalized map showing geometry of northern La Garita caldera, Colorado, U...

Published: 07 December 2018
Figure 1. Generalized map showing geometry of northern La Garita caldera, Colorado, USA. Green line is axis of moat paleovalley between northern wall and resurgent block. Red box shows location of Figure 2 .
Journal Article

A supervolcano and its sidekicks: A 100 ka eruptive chronology of the Fish Canyon Tuff and associated units of the La Garita magmatic system, Colorado, USA

Leah E. Morgan, Samuel A. Johnstone, Amy K. Gilmer, Michael A. Cosca, Ren A. Thompson
Journal: Geology
Published: 21 March 2019
Geology (2019) 47 (5): 453–456.
DOI: https://doi.org/10.1130/G45898.1
...Leah E. Morgan; Samuel A. Johnstone; Amy K. Gilmer; Michael A. Cosca; Ren A. Thompson Abstract Establishing temporal constraints on major volcanic eruptions is limited by the precision of existing geochronometers. Prior work on the La Garita caldera (Colorado, USA), created by the eruption...
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View PDF for article title, A supervolcano and its sidekicks: A 100 ka eruptive chronology of the Fish Canyon Tuff and associated units of the <span class="search-highlight">La</span> <span class="search-highlight">Garita</span> magmatic system, Colorado, USA
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Journal Article

Precursors to a continental-arc ignimbrite flare-up: Early central volcanoes of the San Juan Mountains, Colorado, USA

P.W. Lipman, M.J. Zimmerer, A.K. Gilmer
Journal: Geosphere
Published: 20 December 2023
Geosphere (2024) 20 (1): 23–73.
DOI: https://doi.org/10.1130/GES02691.1
... of focused eruptions and intrusions was prolonged, 5 m.y. or more, prior to the culminating ignimbrite at some centers in the San Juan Mountains. Some large-volume ignimbrites and related calderas, including the ~5000 km 3 Fish Canyon Tuff and associated La Garita caldera, formed as much as several million...
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Book Chapter

A geologic and anthropogenic journey from the Precambrian to the new energy economy through the San Juan volcanic field

Author(s)
Douglas B. Yager, Alison Burchell, Raymond H. Johnson
Book: Through the Generations: Geologic and Anthropogenic Field Excursions in the Rocky Mountains from Modern to Ancient
Series: GSA Field Guide
Publisher: Geological Society of America
Published: 01 January 2010
DOI: 10.1130/2010.0018(09)
EISBN: 9780813756189
... the San Juan-Uncompahgre and La Garita caldera-forming super-volcanoes. The region is famous for the geological, ecological, hydrological, archeological, and climatological diversity. These characteristics supported ancestral Puebloan populations. The area is also important for its mineral wealth...
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Abstract
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Abstract The San Juan volcanic field comprises 25,000 km 2 of intermediate composition mid-Tertiary volcanic rocks and dacitic to rhyolitic calderas including the San Juan-Uncompahgre and La Garita caldera-forming super-volcanoes. The region is famous for the geological, ecological, hydrological, archeological, and climatological diversity. These characteristics supported ancestral Puebloan populations. The area is also important for its mineral wealth that once fueled local economic vitality. Today, mitigating and/or investigating the impacts of mining and establishing the region as a climate base station are the focuses of ongoing research. Studies include advanced water treatment, the acid neutralizing capacity (ANC) of propylitic bedrock for use in mine-lands cleanup, and the use of soil amendments including biochar from beetle-kill pines. Biochar aids soil productivity and revegetation by incorporation into soils to improve moisture retention, reduce erosion, and support the natural terrestrial carbon sequestration (NTS) potential of volcanic soils to help offset atmospheric CO 2 emissions. This field trip will examine the volcano-tectonic and cultural history of the San Juan volcanic field as well as its geologic structures, economic mineral deposits and impacts, recent mitigation measures, and associated climate research. Field trip stops will include a visit to (1) the Summitville Superfund site to explore quartz alunite-Au mineralization, and associated alteration and new water-quality mitigation strategies; (2) the historic Creede epithermal-polymetallic-vein district with remarkably preserved resurgent calderas, keystone-graben, and moat sediments; (3) the historic mining town of Silverton located in the nested San Juan-Silverton caldera complex that exhibits base-metal Au-Ag mineralization; and (4) the site of ANC and NTS studies. En route back to Denver, we will traverse Grand Mesa, a high NTS area with Neogene basalt-derived soils and will enjoy a soak in the geothermal waters of the Aspen anomaly at Glenwood Springs.

Journal Article

Early incubation and prolonged maturation of large ignimbrite magma bodies: Evidence from the Southern Rocky Mountain volcanic field, Colorado, USA

Peter W. Lipman, Matthew J. Zimmerer, Amy K. Gilmer
Journal: Geology
Published: 09 May 2022
Geology (2022) 50 (8): 944–948.
DOI: https://doi.org/10.1130/G49964.1
...Figure 3. Ages of early volcanic rocks in proximity to margins of La Garita caldera (Colorado, USA). Figure is modified from Lipman (2006) ; data are from Tables S1–S2 (see footnote 1 ). FCT—Fish Canyon Tuff; SJ—San Juan. ...
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Image
Oblique view (Google Earth), looking north at Cochetopa and North Pass calderas. The topographic rim of Cochetopa Park caldera (~30 km across) is morphologically well preserved (dashed white lines): along its northwest and north sides, high points on the rim are marked by Sawtooth Mountain (STM) and Razor Creek Dome (RCD); the east rim is along the Continental Divide, which defines the boundary with the older North Pass caldera farther to the east; and the south boundary also follows the Continental Divide where the Cochetopa Park caldera merges with the northern segment of the La Garita caldera. The northeast-trending Los Pinos graben formed at the time of collapse at La Garita, and the parallel Cochetopa graben, which breaches the north wall of La Garita caldera and forms a low segment of Cochetopa rim, is filled by thick tongue of Nelson Mountain Tuff. This lobe of densely welded tuff was channeled northeast from its eruptive source within the San Luis caldera complex at lower left of image, and flowed into the Cochetopa Park caldera where it thins to only a few meters of nonwelded tuff in the southeastern parts of the caldera basin. Other geographic localities: CC—upper Cochetopa Creek; CCn—Cochetopa Canyon (outlet from Cochetopa Park caldera, carved in Precambrian granitic rocks); CD—Cochetopa Dome (sequence of crystal-poor lava flows of petrologically evolved rhyolite that accumulated within Cochetopa caldera shortly after its collapse); LBB—Long Branch Baldy (high point along Continental Divide, where 33-Ma Bonanza Tuff banks against high-standing erosional remnants of a large andesitic stratocone); NP—North Pass (followed by Colorado Hwy 114); LPC—Los Pinos Creek; SaC—Saguache Canyon (outlet from La Garita caldera, carved in &gt;32-Ma intermediate-composition lavas, and inherited from Oligocene topography); SM—Sargents Mesa (high flat along the Continental Divide, locally capped by Bonanza Tuff); SP—Saguache Park (Carpenter Ridge and Wason Park Tuffs, banked against the northern La Garita caldera wall); TM—Table Mountain (high-standing erosional remnant of Nelson Mountain Tuff that ponded within the La Garita caldera).

Oblique view ( Google Earth ), looking north at Cochetopa and North Pass ca...

Published: 01 July 2008
Garita caldera. The northeast-trending Los Pinos graben formed at the time of collapse at La Garita, and the parallel Cochetopa graben, which breaches the north wall of La Garita caldera and forms a low segment of Cochetopa rim, is filled by thick tongue of Nelson Mountain Tuff. This lobe of densely
Image
Figure 5. Geometry of the La Garita and Cochetopa Park calderas and associated rocks of the central San Juan caldera cluster. After eruption of the Fish Canyon Tuff at 27.8 Ma, seven additional large ignimbrite eruptions and associated calderas were localized within the La Garita caldera within 0.9 m.y. Map was modified from Lipman et al. (1997) and Lipman (2006), incorporating unpublished mapping in the Cochetopa Park area (2001–2005).

Figure 5. Geometry of the La Garita and Cochetopa Park calderas and associa...

Published: 01 February 2007
Figure 5. Geometry of the La Garita and Cochetopa Park calderas and associated rocks of the central San Juan caldera cluster. After eruption of the Fish Canyon Tuff at 27.8 Ma, seven additional large ignimbrite eruptions and associated calderas were localized within the La Garita caldera within 0.9
Image
Segmented knobs of welded Carpenter Ridge Tuff (locally called “The Five Sisters”) in moat of La Garita caldera, San Juan Mountains, Colorado, USA. View to west, from South Fork Saguache Creek. Overlying ignimbrites of Wason Park Tuff (Tw) and Nelson Mountain Tuff (Tn) also ponded with La Garita moat.

Segmented knobs of welded Carpenter Ridge Tuff (locally called “The Five Si...

Published: 07 December 2018
Figure 4. Segmented knobs of welded Carpenter Ridge Tuff (locally called “The Five Sisters”) in moat of La Garita caldera, San Juan Mountains, Colorado, USA. View to west, from South Fork Saguache Creek. Overlying ignimbrites of Wason Park Tuff (Tw) and Nelson Mountain Tuff (Tn) also ponded
Image

AGES OF YOUNGEST CONEJOS FORMATION AND REGIONAL IGNIMBRITES PROXIMAL TO LA ...

Published: 20 December 2023
TABLE 4. AGES OF YOUNGEST CONEJOS FORMATION AND REGIONAL IGNIMBRITES PROXIMAL TO LA GARITA CALDERA AND LIMITS ON REPOSE INTERVAL PRIOR TO ERUPTION OF FISH CANYON TUFF
Image
Reference map of the Colorado and New Mexico Oligocene calderas, with the five flora sites indicated (after Chapin, 2012). The floras studied are: (1) Florissant; (2) Antero; (3) Pitch-Pinnacle; (4) Platoro, and (5) Creede. The La Garita caldera is represented by the outline surrounding the group of San Juan volcanic field calderas clustered around Creede.

Reference map of the Colorado and New Mexico Oligocene calderas, with the f...

Published: 10 January 2019
Figure 1. Reference map of the Colorado and New Mexico Oligocene calderas, with the five flora sites indicated (after Chapin, 2012 ). The floras studied are: (1) Florissant; (2) Antero; (3) Pitch-Pinnacle; (4) Platoro, and (5) Creede. The La Garita caldera is represented by the outline
Image
A section of intracaldera Fish Canyon Tuff (in Canyon Diablo, CO), showing a lack of any kind of gradient from top to bottom. Up to 1 km thick section is exposed on the northern flank of the resurgent dome (La Garita mountains), with no base and top exposed, implying a thickness significantly greater than 1 km (estimated at an average of 2 km for the entire 80×30 km La Garita caldera collapse area; Lipman 2000).

A section of intracaldera Fish Canyon Tuff (in Canyon Diablo, CO), showing ...

Published: 01 January 2008
significantly greater than 1 km (estimated at an average of 2 km for the entire 80×30 km La Garita caldera collapse area; Lipman 2000 ).
Image
Simplified map showing caldera boundaries of central San Juan caldera cluster (southwestern Colorado, USA; modified from Lipman, 2006). Locations of analyzed samples are indicated, with northeastern and southwestern Pagosa Peak Dacite (PPD) samples separated. NCD—dacite of Nutras Creek; FCT—Fish Canyon Tuff; PPDN, PPDS—Pagosa Peak Dacite north and south, respectively; CO—Colorado; NM—New Mexico; LGC—La Garita caldera.

Simplified map showing caldera boundaries of central San Juan caldera clust...

Published: 21 March 2019
Creek; FCT—Fish Canyon Tuff; PPDN, PPDS—Pagosa Peak Dacite north and south, respectively; CO—Colorado; NM—New Mexico; LGC—La Garita caldera.
Image
Location map showing the preserved extent of the Oligocene San Juan volcanic field and the approximate distribution of the outflow facies of the Fish Canyon Tuff (modified from Steven and Lipman 1976). Ash-flow tuff volcanism in the San Juan volcanic field was concentrated in three caldera clusters. The source of the Fish Canyon eruptions is the La Garita caldera, the second (after buried source of Masonic Park Tuff) and largest of a series of eight calderas, which comprise the central San Juan caldera cluster (Lipman 2000). The distributions of younger deposits are not shown.

Location map showing the preserved extent of the Oligocene San Juan volcani...

Published: 01 August 2002
caldera clusters. The source of the Fish Canyon eruptions is the La Garita caldera, the second (after buried source of Masonic Park Tuff) and largest of a series of eight calderas, which comprise the central San Juan caldera cluster ( Lipman 2000 ). The distributions of younger deposits are not shown.
Image
Geologic map of northeast Sheep Mountain and slopes adjacent to South Fork Saguache Creek, within La Garita caldera, Colorado, USA. Segmented knobs of densely welded Carpenter Ridge Tuff on eastern ridge are wrapped by concentric zones (short-dashed contacts) of black vitrophyre and separated by intervening less-welded zones of this ignimbrite. Modified from Lipman (2006).

Geologic map of northeast Sheep Mountain and slopes adjacent to South Fork ...

Published: 07 December 2018
Figure 2. Geologic map of northeast Sheep Mountain and slopes adjacent to South Fork Saguache Creek, within La Garita caldera, Colorado, USA. Segmented knobs of densely welded Carpenter Ridge Tuff on eastern ridge are wrapped by concentric zones (short-dashed contacts) of black vitrophyre
Image
Comparison of single grain U–Pb zircon analyses from the Mount Givens Granodiorite (blue; Frazer et al. 2014) and the Fish Canyon Tuff (red; Wotzlaw et al. 2013). Horizontal axis sequences analyses from youngest to oldest for one Fish Canyon Tuff sample and twelve Mount Givens samples distributed throughout the intrusion. These two rock units are comparable compositionally and likely comparable volumetrically. The scale for both samples is the same, but note the difference in absolute age for the Mount Givens Granodiorite (left axis) and Fish Canyon Tuff (right axis). Maps show outlines for the Mount Givens pluton and the La Garita caldera (the source of the Fish Canyon Tuff) at the same scale. Inset: A typical zircon from the Mount Givens Granodiorite. The Mount Givens Granodiorite records an age range that is over an order of magnitude greater than that for the Fish Canyon Tuff.

Comparison of single grain U–Pb zircon analyses from the Mount Givens Grano...

Published: 01 April 2016
outlines for the Mount Givens pluton and the La Garita caldera (the source of the Fish Canyon Tuff) at the same scale. I nset : A typical zircon from the Mount Givens Granodiorite. The Mount Givens Granodiorite records an age range that is over an order of magnitude greater than that for the Fish Canyon
Journal Article

When ignimbrite meets water: Megascale gas-escape structures formed during welding

Peter W. Lipman
Journal: Geology
Published: 07 December 2018
Geology (2019) 47 (1): 63–66.
DOI: https://doi.org/10.1130/G45772.1
...Figure 1. Generalized map showing geometry of northern La Garita caldera, Colorado, USA. Green line is axis of moat paleovalley between northern wall and resurgent block. Red box shows location of Figure 2 . ...
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Journal Article

Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from?

Peter W. Lipman, William C. McIntosh
Journal: GSA Bulletin
Published: 01 July 2008
GSA Bulletin (2008) 120 (7-8): 771–795.
DOI: https://doi.org/10.1130/B26330.1
... Garita caldera. The northeast-trending Los Pinos graben formed at the time of collapse at La Garita, and the parallel Cochetopa graben, which breaches the north wall of La Garita caldera and forms a low segment of Cochetopa rim, is filled by thick tongue of Nelson Mountain Tuff. This lobe of densely...
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Results of Markov chain Monte Carlo (MCMC) characterization of argon geochronology of units from La Garita caldera (Colorado, USA). Bottom axes are derived from measured 40Ar/39Ar ratios (F-values [mean ratio of radiogenic to reactor-produced argon, 40Ar*/39ArK]), and top axes are calculated by asserting age of 28.201 for Fish Canyon Tuff (FCT) (Kuiper et al., 2008) for median of F-values from all sanidine from the Fish Canyon Tuff (FCs-EK) analyses. Distributions are histograms of 106 MCMC samples, divided into 100 evenly spaced bins and scaled so that the area under each curve integrates to 1. Credible intervals (CI) are shown as solid bars; preferred weighted mean ages (Table DR2 [see footnote 1]) are shown as dashed bars. A and B show F-values that best characterize units of FCT. C and D test the hypotheses that units pre- or post-date FCT (by time difference Δt) by assessing the probability of differences in ages of units from FCs-EK (e.g., Equation 5 in text). R is the ratio of unknown to standard ratios, Fu / Fm (Fu—measured F-value of the neutron fluence monitor; Fm—F-value of unknowns). NCD—dacite of Nutras Creek; PPDS, PPDN—Pagosa Peak Dacite south and north, respectively.

Results of Markov chain Monte Carlo (MCMC) characterization of argon geochr...

Published: 21 March 2019
Figure 3. Results of Markov chain Monte Carlo (MCMC) characterization of argon geochronology of units from La Garita caldera (Colorado, USA). Bottom axes are derived from measured 40 Ar/ 39 Ar ratios ( F -values [mean ratio of radiogenic to reactor-produced argon, 40 Ar*/ 39 Ar K ]), and top
Image
Generalized maps showing preserved remnants of composite Southern Rocky Mountain volcanic field, modified from McIntosh and Chapin (2004) and Lipman (2007); inferred original limit of volcanic rocks is from Steven (1975); intrusions are from Tweto (1979) and Lipman et al. (2013). (A) Ignimbrite calderas, associated granitic intrusions, inferred original extent of once nearly continuous mid-Tertiary volcanic cover, and later Tertiary sedimentary fill of the Rio Grande rift zone. Calderas and associated intrusions: B—Bachelor; Bz—Bonanza; Cr—Creede; C—Cochetopa Park; GP—Grizzly Peak; LG—La Garita; LGn—La Garita north; LGs—La Garita south; M—Marshall; MP—Mount Princeton–Aetna; NP—North Pass; Pl—Platoro; S—Silverton; SL—San Luis; SR—South River. Arrows indicate trend of Late Cretaceous–Early Tertiary (Laramide) intrusions of the Colorado mineral belt. (B) Ignimbrite calderas and eruption ages, documenting general southward progression and focusing of Oligocene ignimbrite eruptions in central San Juan region at 28–27 Ma. Ages are from Table 1; calderas are color-coded by regional location, as guide to Tables 1–2.

Generalized maps showing preserved remnants of composite Southern Rocky Mou...

Published: 01 June 2015
Garita; LGn—La Garita north; LGs—La Garita south; M—Marshall; MP—Mount Princeton–Aetna; NP—North Pass; Pl—Platoro; S—Silverton; SL—San Luis; SR—South River. Arrows indicate trend of Late Cretaceous–Early Tertiary (Laramide) intrusions of the Colorado mineral belt. (B) Ignimbrite calderas and eruption