Oligo-Miocene mafic intrusions of the San Juan Volcanic Field, southwestern Colorado, and their relationship to voluminous, caldera-forming magmas

Lake, Ethan T.; Farmer, G. Lang

doi:10.1016/j.gca.2015.02.020

Cited by 23 publications

(23 citation statements)

References 74 publications

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“…Basalt is nearly absent, despite repeated searches for primitive compositions. Mafic alkalic dikes (lamprophyres) with mantle isotopic signatures locally intrude pre-Tertiary rocks in the northern San Juan Basin (Gonzales et al, 2010;Lake and Farmer, 2015;Gonzales and Pecha, 2015), but such compositions have not been identified centrally within loci of large-volume San Juan volcanism. Volcanic centers tended to migrate from north to south in the SRMVF, both intermediate-composition lava eruptions and ignimbrites (Fig.…”

Section: Southern Rocky Mountain Volcanic Field and Its Batholithmentioning

confidence: 99%

“…without deep root of more-mafi c granitoid or any mantle input Lake and Farmer (2015) San Juan locus; mantle-magma input estimate from isotope data on May 30, 2015 geosphere.gsapubs.org Downloaded from Keller, 1994), the Marysvale volcanic field in Utah (Steven et al, 1984), Elkhorn Mountains volcanic field and underlying Boulder batholith in Montana (Robinson et al, 1968;Hamilton and Myers, 1974;Biehler and Bonini, 1969;Vejmelek and Smithson, 1995), and the Yellowstone caldera cluster (Eaton et al, 1975;Christiansen, 2001).…”

Section: Proposed For San Juan Locus (But Volcanic Volume Is Too Large)mentioning

confidence: 99%

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Ignimbrites to batholiths: Integrating perspectives from geological, geophysical, and geochronological data

2015

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Multistage histories of incremental accumulation, fractionation, and solidification during construction of large subvolcanic magma bodies that remained sufficiently liquid to erupt are recorded by Tertiary ignimbrites, source calderas, and granitoid intrusions associated with large gravity lows at the Southern Rocky Mountain volcanic field (SRMVF). Geophysical data combined with geological constraints and comparisons with tilted plutons and magmatic-arc sections elsewhere are consistent with the presence of vertically extensive (>20 km) intermediate to silicic batholiths (with intrusive:extrusive ratios of 10:1 or greater) beneath the major SRMVF volcanic loci (Sawatch, San Juan, Questa-Latir). Isotopic data require involvement of voluminous mantle-derived mafic magmas on a scale equal to or greater than that of the intermediate to silicic volcanic and plutonic rocks. Early waxing-stage intrusions (35-30 Ma) that fed intermediate-composition central volcanoes of the San Juan locus are more widespread than the geophysically defined batholith; these likely heated and processed the crust, preparatory for ignimbrite volcanism (32-27 Ma) and largescale upper-crustal batholith growth. Age and compositional similarities indicate that SRMVF ignimbrites and granitic intrusions are closely related, but the extent to which the plutons record remnants of former magma reservoirs that lost melt to volcanic eruptions has been controversial. Published Ar/Arfeldspar and U-Pb-zircon ages for plutons spatially associated with ignimbrite calderas document final crystallization of granitoid intrusions at times indistinguishable from the tuff to ages several million years younger. These ages also show that SRMVF caldera-related intrusions cooled and solidified soon after zircon crystallization, as magma supply waned. Some researchers interpret these results as recording pluton assembly in small increments that crystallized rapidly, leading to temporal disconnects between ignimbrite eruption and intrusion growth. Alternatively, crystallization ages of the granitic rocks are here inferred to record late solidification, after protracted open-system evolution involving voluminous mantle input, lengthy residence (10 5 -10 6 yr) as near-solidus crystal mush, and intermittent separation of liquid to supply volcanic eruptions. The compositions of the least-evolved ignimbrite magmas tend to merge with those of caldera-related plutons, suggesting that the plutons record nonerupted parts of long-lived cogenetic magmatic systems, variably modified prior to final solidification. Precambrian-source zircons are scarce in caldera plutons, in contrast to their abundance in some peripheral waning-stage intrusions of the SRMVF, implying dissolution of inherited crustal zircon during lengthy magma assembly for the ignimbrite eruptions and construction of a subvolcanic batholith. Broad age spans of zircons (to several million years) from individual samples of some ignimbrites and intrusions, commonly averaged and interpreted as "intrusion-emplacement age,...

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Section: Southern Rocky Mountain Volcanic Field and Its Batholithmentioning

confidence: 99%

Section: Proposed For San Juan Locus (But Volcanic Volume Is Too Large)mentioning

confidence: 99%

Ignimbrites to batholiths: Integrating perspectives from geological, geophysical, and geochronological data

2015

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“…10). Ignimbrites erupted from southeastern and western San Juan sources also differ from the central locus, mainly crystal-rich dacites in the southeast, crystal-poor rhyo lites from western calderas, all lacking large compositional zonations, and also characterized by subtle regional isotopic differences (Lipman et al, 1978;Lake and Farmer, 2015).…”

Section: Southern Rocky Mountain Volcanic Fieldmentioning

confidence: 99%

“…22 and 23). In the southern Great Basin and Altiplano-Puna, where the crust was thickest, the MASH zone appears to have been in the mid-to upper crust, based on geophysical data in the latter, whereas in the Southern Rocky Mountain field, it was probably in the lower crust, based on the isotopic compositions of the rocks (Lipman et al, 1978;Lake and Farmer, 2015).…”

Section: Elevated Temperatures In Thick Crustmentioning

confidence: 99%

“…However, the exact nature of the flat slab subduction and especially the thermal regime of the slab and its dehydration, or lack thereof, are subjects of current debate (e.g., English et al, 2003;Usui et al, 2003;Humphreys, 2009;Jones et al, 2011Jones et al, , 2015; this lends a degree of uncertainty to inferences regarding the dynamic interaction of the crust and mantle during the flareup. For the southern Great Basin, Christiansen and Best (2014) concluded that it might have been difficult to derive enough mantle magma to drive silicic magma production from the lithospheric mantle alone (contrast this with the conclusions of Farmer et al [2008] and Lake and Farmer [2015] for the Southern Rocky Mountain field). Thus, a major contribution from a sublithospheric source for the mafic magma may be required.…”

Section: Steepening Of the Subducting Platementioning

confidence: 99%

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Slab-rollback ignimbrite flareups in the southern Great Basin and other Cenozoic American arcs: A distinct style of arc volcanism

et al. 2016

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In continental-margin subduction zones, basalt magmas spawned in the mantle interact with the crust to produce a broad spectrum of volcanic arc associations. A distinct style of very voluminous arc volcanism develops far inland on thick crust over periods of 10-20 m.y. and involves relatively infrequent caldera-forming explosive eruptions of dominantly calc-alkaline rhyolite, dacite, and trachydacite with repose times of 10 4-10 6 yr. Volumes of individual eruptions are large (10 2-10 3 km 3), and nested super-eruptions of thousands of cubic kilometers are common. Calderas are as much as 60-75 km in diameter, and surrounding individual ignimbrite outflow sheets extend outward as much as 150 km, blanketing upwards of 10 5 km 2. Little or no basalt is extruded, whereas andesitic differentiates coeval with silicic ignimbrites range from minor to dominant in relative volume. A common feature in these flareups is essentially nonextending, thick, inland crust overlying a subducting oceanic plate with transverse tears that rolled back to a steeper dip from a previously flat configuration. Lithospheric delamination is locally possible. Large volumes of basalt that provide heat and mass for silicic magma generation in the crust form by fluid fluxing of the growing mantle wedge overlying the steepening dehydrating slab and from asthenospheric decompression. Variations in the mantle input, together with variations in crustal thickness, temperature, and composition, modulate the expression of the flareups. As a consequence of the high flux of mantle-derived magma into the thick crust, geotherms become elevated, and the brittle-ductile transition can rise to depths as shallow as 7 km. At this transition, diapirically rising magmas from a melting, assimilation, storage, and homogenization (MASH) zone are blocked and spread laterally into discoid chambers that grow until a thermomechanical threshold is attained, triggering climactic eruption and caldera collapse. This ignimbrite flareup style of continental arc volcanism is exemplified by the mid-Cenozoic southern Great Basin ignimbrite province; other examples include the contemporaneous Southern Rocky Mountain, Mogollon-Datil, vast Sierra Madre Occidental volcanic fields, and the late Cenozoic Altiplano-Puna volcanic complex in the Central Andes. Rhyolitic and trachydacitic ignimbrites typically have erupted, but where the crust was predominantly felsic, prewarmed, and orogenically thickened, well-developed MASH zones have spawned multiple super-eruptions of phenocryst-rich dacite, or monotonous intermediates, and smaller volumes of calc-alkaline rhyolite ignimbrite. In the Great Basin, eruptions of dry, hot trachydacite magma followed the monotonous intermediates. Partial melting in thinner crust with a major mafic component yielded more alkalic rhyolite and related trachydacite.

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Petrogenesis of episodic volcanic-intrusive rocks in SE China: Crystal-melt segregation and magma mixing

Xu,

Wang,

et al. 2024

Chemical Geology

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Oligo-Miocene mafic intrusions of the San Juan Volcanic Field, southwestern Colorado, and their relationship to voluminous, caldera-forming magmas

Cited by 23 publications

References 74 publications

Ignimbrites to batholiths: Integrating perspectives from geological, geophysical, and geochronological data

Ignimbrites to batholiths: Integrating perspectives from geological, geophysical, and geochronological data

Slab-rollback ignimbrite flareups in the southern Great Basin and other Cenozoic American arcs: A distinct style of arc volcanism

Petrogenesis of episodic volcanic-intrusive rocks in SE China: Crystal-melt segregation and magma mixing

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