scholarly journals A Geophysical Model for the Origin of Volcano Vent Clusters in a Colorado Plateau Volcanic Field

2017 ◽  
Vol 122 (11) ◽  
pp. 8910-8924 ◽  
Author(s):  
Fanghui Deng ◽  
Charles B. Connor ◽  
Rocco Malservisi ◽  
Laura J. Connor ◽  
Jeremy T. White ◽  
...  
Keyword(s):  
Colorado Plateau ◽  
Volcanic Field ◽  
Geophysical Model

Timing of the Cenozoic “Great Hydration” event beneath the Colorado Plateau: Th-Pb dating of monazite in Navajo volcanic field metamorphic eclogite xenoliths

Geology ◽  
2015 ◽  
Vol 43 (8) ◽  
pp. 727-730 ◽  
Author(s):  
Daniel J. Schulze ◽  
Donald W. Davis ◽  
Herwart Helmstaedt ◽  
Brian Joy
Keyword(s):  
Colorado Plateau ◽  
Volcanic Field ◽  
Navajo Volcanic Field

Massive Fluid Influx beneath the Colorado Plateau (USA) Related to Slab Removal and Diatreme Emplacement: Evidence from Oxygen Isotope Zoning in Eclogite Xenoliths

2020 ◽  
Author(s):  
William F Hoover ◽  
F Zeb Page ◽  
Daniel J Schulze ◽  
Kouki Kitajima ◽  
John W Valley
Keyword(s):  
Oxygen Isotope ◽  
Secondary Ion Mass Spectrometry ◽  
Colorado Plateau ◽  
Volcanic Field ◽  
Oxygen Isotope Ratios ◽  
Core Composition ◽  
Plateau Uplift ◽  
Flat Slab Subduction ◽  
Dehydration Processes ◽  
Navajo Volcanic Field

Abstract The Colorado Plateau has undergone as much as 1·8 km of uplift over the past 80 Myr, but never underwent the pervasive deformation common in the neighboring tectonic provinces of the western USA. To understand the source, timing and distribution of mantle hydration, and its role in plateau uplift, garnets from four eclogite xenoliths of the Moses Rock diatreme (Navajo Volcanic Field, Utah, USA) were analyzed in situ for δ18O by secondary ion mass spectrometry. These garnets have the largest reported intra-crystalline oxygen isotope zoning to date in mantle-derived xenoliths with core-to-rim variations of as much as 3 ‰. All samples have core δ18O values greater than that of the pristine mantle (∼5·3 ‰, mantle garnet as derived from mantle zircon in earlier work) consistent with an altered upper oceanic crust protolith. Oxygen isotope ratios decrease from core to rim, recording interaction with a low-δ18O fluid at high temperature, probably derived from serpentinite in the foundering Farallon slab. All zoned samples converge at a δ18O value of ∼6 ‰, regardless of core composition, suggesting that fluid infiltration was widely distributed. Constraints on the timing of this fluid influx, relative to diatreme emplacement, can be gained from diffusion modeling of major element zoning in garnet. Modeling using best estimates of peak metamorphic conditions (620 °C, 3·7 GPa) yields durations of <200 kyr, suggesting that fluid influx and diatreme emplacement were temporally linked. These eclogite xenoliths from the Colorado Plateau record extensive fluid influx, pointing to complex hydration–dehydration processes related to flat-slab subduction and foundering of the Farallon plate. Extensive hydration of the lithospheric mantle during this fluid influx may have contributed to buoyancy-driven uplift of the Colorado Plateau and melt-free emplacement of Navajo Volcanic Field diatremes.

scholarly journals Magmato-tectonic links: Ignimbrite calderas, regional dike swarms, and the transition from arc to rift in the Southern Rocky Mountains

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1893-1926 ◽  
Author(s):  
Peter W. Lipman ◽  
Matthew J. Zimmerer
Keyword(s):  
Inductively Coupled Plasma ◽  
Colorado Plateau ◽  
Gravity Data ◽  
Regional Scale ◽  
Rocky Mountain ◽  
Volcanic Field ◽  
San Juan ◽  
Inductively Coupled ◽  
Southern Rocky Mountains ◽  
Dike Swarms

Abstract Radial and linear dike swarms in the eroded roots of volcanoes and along rift zones are sensitive structural indicators of conduit and eruption geometry that can record regional paleostress orientations. Compositionally diverse dikes and larger intrusions that radiate westward from the polycyclic Platoro caldera complex in the Southern Rocky Mountain volcanic field (southwestern United States) merge in structural trend, composition, and age with the enormous but little-studied Dulce swarm of trachybasaltic dikes that continue southwest and south for ∼125 km along the eastern margin of the Colorado Plateau from southern Colorado into northern New Mexico. Some Dulce dikes, though only 1–2 m thick, are traceable for 20 km. More than 200 dikes of the Platoro-Dulce swarm are depicted on regional maps, but only a few compositions and ages have been published previously, and relations to Platoro caldera have not been evaluated. Despite complications from deuteric alteration, bulk compositions of Platoro-Dulce dikes (105 new X-ray fluorescence and inductively coupled plasma mass spectrometry analyses) become more mafic and alkalic with distance from the caldera. Fifty-eight (58) new 40Ar/39Ar ages provide insight into the timing of dike emplacement in relation to evolution of Platoro caldera (source of six regional ignimbrites between 30.3 and 28.8 Ma). The majority of Dulce dikes were emplaced during a brief period (26.5–25.0 Ma) of postcaldera magmatism. Some northeast-trending dikes yield ages as old as 27.5 Ma, and the northernmost north-trending dikes have younger ages (20.1–18.6 Ma). In contrast to high-K lamprophyres farther west on the Colorado Plateau, the Dulce dikes are trachybasalts that contain only anhydrous phenocrysts (clinopyroxene, olivine). Dikes radial to Platoro caldera range from pyroxene- and hornblende-bearing andesite to sanidine dacite, mostly more silicic than trachybasalts of the Dulce swarm. Some distal andesite dikes have ages (31.2–30.4 Ma) similar to those of late precaldera lavas; ages of other proximal dikes (29.2–27.5 Ma) are akin to those of caldera-filling lavas and the oldest Dulce dikes. The largest radial dikes are dacites that have yet younger sanidine 40Ar/39Ar ages (26.5–26.4 Ma), similar to those of the main Dulce swarm. The older andesitic dikes and precaldera lavas record the inception of a long-lived upper-crustal magmatic locus at Platoro. This system peaked in magmatic output during ignimbrite eruptions but remained intermittently active for at least an additional 9 m.y. Platoro magmatism began to decline at ca. 26 Ma, concurrent with initial basaltic volcanism and regional extension along the Rio Grande rift, but no basalt is known to have erupted proximal to Platoro caldera prior to ca. 20 Ma, just as silicic activity terminated at this magmatic locus. The large numbers and lengths of the radial andesitic-dacitic dikes, in comparison to the absence of similar features at other calderas of the San Juan volcanic locus, may reflect location of the Platoro system peripheral to the main upper-crustal San Juan batholith recorded by gravity data, as well as its proximity to the axis of early rifting. Spatial, temporal, and genetic links between Platoro radial dikes and the linear Dulce swarm suggest that they represent an interconnected regional-scale magmatic suite related to prolonged assembly and solidification of an arc-related subcaldera batholith concurrently with a transition to regional extension. Emplacement of such widespread dikes during the late evolution of a subcaldera batholith could generate earthquakes and trigger dispersed small eruptions. Such events would constitute little-appreciated magmato-tectonic hazards near dormant calderas such as Valles, Long Valley, or Yellowstone (western USA).

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