U–Pb zircon geochronology of silicic tuffs from the Timber Mountain/Oasis Valley caldera complex, Nevada: rapid generation of large volume magmas by shallow-level remelting

Bindeman, Ilya N.; Schmitt, Axel K.; Valley, John W.

doi:10.1007/s00410-006-0124-1

Cited by 63 publications

(27 citation statements)

References 85 publications

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“…In these models, we assumed zircon preferentially incorporates or retains U relative to Th. This assumption is consistent with the observation that most zircons have Th/U lower than whole rock values, and with estimated zircon‐melt D Th/U ~ 0.2 [e.g., Bindeman et al , ; Blundy and Wood , ; Schmitt et al , ; Wotzlaw et al , ]. We argue in section 4.2 that the inclusion‐rich zircons formed by dissolution‐reprecipitation of igneous zircons and Th is also typically expelled from zircon during these processes [ Tomaschek et al , ].…”

Section: Resultssupporting

confidence: 89%

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

et al. 2015

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New U/Pb analyses of zircon and xenotime constrain the timing of magmatism, magmatic assimilation, and hydrothermal metamorphism during formation of the lower crust at the Mid-Atlantic Ridge. The studied sample is an altered gabbro from the Vema lithospheric section (11°N). Primary gabbroic minerals have been almost completely replaced by multiple hydrothermal overprints: cummingtonitic amphibole and albite formed during high-temperature hydration reactions and are overgrown first by kerolite and then prehnite and chlorite. In a previous study, clear inclusion-free zircons from the sample yielded Th-corrected 206 Pb/ 238 U dates of 13.528 ± 0.101 to 13.353 ± 0.057 Ma. Ti concentrations, reported here, zoning patterns and calculated Th/U of the dated grains are consistent with these zircons having grown during igneous crystallization. To determine the timing of hydrothermal metamorphism, we dated a second population of zircons, with ubiquitous <1-20 μm chlorite inclusions, and xenotimes that postdate formation of metamorphic albite. The textures and inclusions of the inclusion-rich zircons suggest that they formed by coupled dissolution-reprecipitation of metastable igneous zircon during or following hydrothermal metamorphism. Th-corrected 206 Pb/ 238 U dates for the inclusion-rich zircons range from 13.598 ± 0.012 to 13.503 ± 0.018 Ma and predate crystallization of all but one of the inclusion-free zircons, suggesting that the inclusion-rich zircons were assimilated from older hydrothermally altered wall rocks. The xenotime dates are sensitive to the Th correction applied, but even using a maximum correction, 206 Pb/ 238 U dates range from 13.341 ± 0.162 to 12.993 ± 0.055 Ma and postdate crystallization of both the inclusion-rich zircons and inclusion-free igneous zircons, reflecting a second hydrothermal event. The data provide evidence for alternating magmatism and hydrothermal metamorphism at or near the ridge axis during accretion of the lower crust at a ridge-transform intersection and suggest that hydrothermally altered crust was assimilated into younger gabbroic magmas. The results of this study show that high-precision U-Pb dating is a powerful method for studying the timing of magmatic and hydrothermal processes at mid-ocean ridges.

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Section: Resultssupporting

confidence: 89%

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

et al. 2015

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“…Modern volcanic systems exhibit geochronologic characteristics analogous to those described herein, where some or all zircon ages are older than eruption age estimated by other means, including Geysers (Schmitt et al, 2003), Coso (Miller and Wooden, 2004), southwest Nevada (Bindeman et al, 2006), and modern convergent margin arc settings such as the Taupo Volcanic Zone (Charlier et al, 2005) and Aucanquilcha (Walker et al, 2010). Recycling of older, partially to completely solidifi ed parts of these magma systems is inferred from the persistence of these age differences, and from the on May 9, 2012 geosphere.gsapubs.org Downloaded from magnitude of the age differences in comparison to estimated solidifi cation rates.…”

Section: Discussionmentioning

confidence: 85%

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et al. 2012

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Trace-element analyses of zircons from ash-fl ow tuffs and granitic rocks in the eastcentral Sierran Nevada, combined with U-Pb zircon ages and trace-element abundances in whole rocks, allow us to interpret a shared magmatic heritage for widespread eruption of ash-fl ow tuffs and assembly of a typical Sierran granodioritic to granitic intrusive suite. The tuffs have 5%-15% phenocrysts of quartz, feldspar, biotite, and amphibole, silica contents ranging from 70% to 74%, and have variable alkali abundances but are consistently light rare-earth enriched with weak negative Eu anomalies, suggesting chemical classifi cation as hydrothermally altered, arctype, low-silica rhyolites. The tuffs yielded U-Pb zircon crystallization ages of 232, 224, and 219 Ma, indicating that explosive volcanism began before and continued throughout emplacement of granodioritic to granitic plutons in the underlying 226-218 Ma Scheelite Intrusive Suite, one of the oldest and largest intrusive suites in the Sierra Nevada batholith. Zircon crystals from ash-fl ow tuffs and contemporaneous felsic granodiorite and granite show distinct chemical zoning and extensive overlap in trace-element abundances, indicating crystallization of zircons from very similar melt compositions despite dissimilar late cooling histories. These data provide evidence for a unifi ed volcano-plutonic model for Sierran arc magmatism that describes a longlived, multi-stage magma system composed of an incrementally emplaced, granodioritic to granitic intrusive suite in the upper crust, overlain by widespread deposits of ignimbrite eruptions generated by thermal rejuvenation of felsic crystal mushes.

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“…(2) The presence of xenocrystic zircons is obvious in the three units that we have U‐Pb data for (ages up to 21 Ma). This is a common observation in silicic units [e.g., Lanphere and Baadsgaard , 2001; Schmitt et al , 2003; Simon and Reid , 2005; Bindeman et al , 2006, 2008], and is expected this area, where the pre‐existing crust hosts components that are at least 370 Ma old [ Smith et al , 2000].…”

Section: Discussionmentioning

confidence: 92%

The ⁴⁰Ar/³⁹Ar and U/Pb dating of young rhyolites in the Kos‐Nisyros volcanic complex, Eastern Aegean Arc, Greece: Age discordance due to excess ⁴⁰Ar in biotite

Bachmann

Schoene

Schnyder

et al. 2010

Geochem Geophys Geosyst

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[1] High-precision dating of Quaternary silicic magmas in the active Kos-Nisyros volcanic center (Aegean Arc, Greece) by both 40 Ar/ 39 Ar on biotite and U/Pb on zircon reveals a complex geochronological story. U/Pb ID-TIMS multi and single-grain zircon analyses from 3 different units (Agios Mammas and Zini domes, Kefalos Serie pyroclasts) range in age from 0.3 to 0.5 to 10-20 Ma. The youngest dates provide the maximum eruption age, while the oldest zircons indicate inheritance from local continental crust (Miocene and older).Step-heating 40 Ar/ 39 Ar experiments on 1-3 crystals of fresh biotite yielded highly disturbed Ar-release patterns with plateau ages typically older than most U/Pb ages. These old plateau ages are probably not a consequence of inheritance from xenocrystic biotites because Ar diffuses extremely fast at magmatic temperatures and ratios are reset within a few days. On the basis of (1) elevated and/or imprecise 40 Ar/ 36 Ar ratios, (2) shapes of the Ar release spectra, and (3) a high mantle 3 He flux in the Kos-Nisyros area, we suggest that biotite crystals retained some mantle 40 Ar that led to the observed, anomalously old ages. In contrast, sanidine crystals from the only sanidine-bearing unit in the Kos-Nisyros volcanic center (the caldera-forming Kos Plateau Tuff) do not appear to store any excess 40 Ar relative to atmospheric composition. The eastern edge of the Aegean Arc is tectonically complex, undergoing rapid extension and located close to a major structural boundary. In such regions, which are characterized by high fluxes of mantle volatiles, 40 Ar/ 39 Ar geochronology on biotite can lead to erroneous results due to the presence of excess 40 Ar and should be checked either against 40 Ar/ 39 Ar sanidine or U/Pb zircon ages.

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U–Pb zircon geochronology of silicic tuffs from the Timber Mountain/Oasis Valley caldera complex, Nevada: rapid generation of large volume magmas by shallow-level remelting

Cited by 63 publications

References 85 publications

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

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The ⁴⁰Ar/³⁹Ar and U/Pb dating of young rhyolites in the Kos‐Nisyros volcanic complex, Eastern Aegean Arc, Greece: Age discordance due to excess ⁴⁰Ar in biotite

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U–Pb zircon geochronology of silicic tuffs from the Timber Mountain/Oasis Valley caldera complex, Nevada: rapid generation of large volume magmas by shallow-level remelting

Cited by 63 publications

References 85 publications

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

U‐Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid‐Atlantic Ridge

Untitled

The 40Ar/39Ar and U/Pb dating of young rhyolites in the Kos‐Nisyros volcanic complex, Eastern Aegean Arc, Greece: Age discordance due to excess 40Ar in biotite

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The ⁴⁰Ar/³⁹Ar and U/Pb dating of young rhyolites in the Kos‐Nisyros volcanic complex, Eastern Aegean Arc, Greece: Age discordance due to excess ⁴⁰Ar in biotite