Homogenization processes in silicic magma chambers by stirring and mushification (latent heat buffering)

Huber, Christian; Bachmann, Olivier; Manga, Michael

doi:10.1016/j.epsl.2009.03.029

Cited by 189 publications

(159 citation statements)

References 57 publications

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“…However, another idea holds that there are reactions between melts and residues [60][61][62][63], and neither MORB nor continental alkali basalts can represent primitive magmas. Subsequently more research was undertaken to investigate this mechanism, suggesting that the composition of MORB is homogenized by magma-chamber mixing, rather than derivation from a homogeneous mantle source [23,64,65]. Hence, it is still difficult to define the Os-isotope characteristics of the mantle source.…”

Section: Spinel Recording Mantle Sourcementioning

confidence: 99%

Os isotopic evidence for a carbonaceous chondritic mantle source for the Nagqu ophiolite from Tibet and its implications

et al. 2012

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Early-crystallizing chromian spinel (Cr-spinel) in the Nagqu ophiolite has high Os and low Re contents, and it is resistant to alteration during serpentinization, weathering and metamorphism. The chemical composition of primitive magma is preserved in Cr-spinel, which makes it suitable for determining the initial Os-isotope composition of the mantle source. This study presents Cr-spinel Os isotopes and zircon U-Pb ages for cumulate dunite and gabbro, respectively, in the same cumulate section of the ophiolite at Nagqu in Tibet. The results shed light on the formation and evolution of lithospheric mantle. The Nagqu ophiolite is located in the central part of the Bangong-Nujiang suture zone. It is a remnant of the Neotethyan oceanic crust, and contains cumulate dunite and gabbro. Zircon from the gabbro yielded a weighted mean 206 Pb/ 238 U age of 183.7±1 Ma. Cr-spinel exhibits  Os values of 0.2 to 0.3, suggesting that the mantle source for the dunite is similar to that of carbonaceous chondrites. Thus, the Tibetan lithosphere is primarily a relic of Tethyan oceanic lithosphere, which has formed by the transformation of the normal asthenospheric mantle in the Mesozoic. This is the first study to combine the spinel Os isotopes with accurate zircon U-Pb ages to constrain the geochemical characteristics of the mantle source for the ophiolite.Re-Os isotopes, spinel, ophiolite, Nagqu, Tibet Citation:Huang Q S, Shi R D, Liu D L, et al. Os isotopic evidence for a carbonaceous chondritic mantle source for the Nagqu ophiolite from Tibet and its implications. Chin Sci Bull, 2013, 58: 9298,

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Section: Spinel Recording Mantle Sourcementioning

confidence: 99%

Os isotopic evidence for a carbonaceous chondritic mantle source for the Nagqu ophiolite from Tibet and its implications

et al. 2012

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“…We conclude that eruptible magma reservoirs are generally long-lived (>100 ka), can continuously retain significant amounts of melt (<60% crystal fraction), and are stored broadly isothermally for timescales of tens to hundreds of thousands of years such that they can be rapidly mobilized and erupt. Volatiles liberated by hydrous magma recharge during decompression aid in rejuvenating the crystal mush by triggering the remelting process and facilitating eruption by decreasing melt viscosity (32).…”

Section: Significancementioning

confidence: 99%

Warm storage for arc magmas

Barboni

Boehnke

Schmitt

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

100

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Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the "cold storage" model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.volcano | eruption | arc magma | zircon D etermining the timescale of magma storage and remobilization in the upper crust is key to understanding the tempo and magnitude of volcanic eruptions (1-13). Whether a volcano can erupt is controlled by the recharge rate to the magma reservoir (13) (reservoir in this context refers to the portion of the igneous complex that is potentially eruptible), which in turn determines the duration of the "eruption window" [generally defined as the rheological state during which the subvolcanic reservoir is below ∼60% crystals and hence capable of eruption (4)]. However, estimates for how long this eruption window remains open vary over four orders of magnitude; this suggests either profound problems in assumptions underlying one or more of these estimates or a continuum of physical mechanisms that resist formulation of a unified model for the state of magma reservoirs before eruption (1-13). The preservation of sharp compositional gradients in plagioclase phenocrysts, assumed to have crystallized >10 ka before eruption, has recently been interpreted to indicate that arc volcanic reservoirs characteristically remain in "cold storage" at temperatures below the eruption window, possibly below the solidus, and thus only capable of erupting during brief recharge events (<10 ka) (1). In contrast, zircon dating and heat budget considerations are difficult to reconcile with this scenario; instead, they are consistent with continuously partially molten reservoirs capable of erupting (i.e., with melt portion ≥40%) ov...

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“…This assumption is valid as yield strength should begin when either plagioclase crystallinity exceeds 13 vol% or total crystallinity exceeds 20 vol% (Hoover et al 2001;Saar et al 2001). Many arc andesites, dacites, and rhyolites have crystallinities in excess of those values (e.g., Brophy 1991;Pallister et al 2008;Andrews et al 2008;Huber et al 2012); indeed, many magma bodies may be crystal mushes prior to eruption (e.g., Huber et al 2009;Gudmundsson 2012;Czuppon et al 2012). Our model predicts that mixing in low-crystallinity magmas should be dominated by ductile deformation and banding, enclaves should only form when small dikes are emplaced into the host magmas, T Ã log 10 l h0 of the mixing magmas is large, or enclaves are made from the chilled margins of larger dikes that primarily mix fluidly with their hosts.…”

Section: Discussionmentioning

confidence: 99%

Thermal and rheological controls on the formation of mafic enclaves or banded pumice

Andrews

Manga

2014

Contrib Mineral Petrol

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Magma mixing can occur in a fluid manner to produce banded pumice or in a brittle manner to form enclaves. We propose that the critical control on mixing style is a competition between developing networks of crystals in the intruding magma that impart a strength to the magma and melting and disrupting those networks in the host. X-ray computed tomography analysis demonstrates that banded pumice from the 1915 Mt. Lassen eruption lacks crystal networks. In contrast, rhyodacite hosts with mafic enclaves from Chaos Crags contain welldeveloped networks of large crystals. We present a onedimensional conductive cooling model that predicts mixing style, either ductile or brittle, as a function of magma compositions, temperatures, and the size of the intruding dike. Our model relies on three assumptions: (1) Mixing is initiated by the injection of a hot dike into a cooler magma body with a yield strength; (2) when magma crystallinity exceeds a critical value, 13 vol% plagioclase, the magma develops a yield strength; and (3) when total crystallinity exceeds 40 vol%, the magma has a penetrative crystal network and is effectively solid. Importantly, because the two magmas are of different compositions, their crystallinities and viscosities do not have the same variations with temperature. As the intruding magma cools, it crystallizes from the outside in, while simultaneously, host magma temperature near the intruder rises. Mixing of the two magmas begins when the host magma is heated sufficiently to (1) disrupt the crystal network and (2) initiate convection. If the shear stress exerted by the convecting host magma on the dike is greater than the yield strength of the dike margin (and dike crystallinity does not exceed 40 %), then fluid mixing occurs, otherwise enclaves form by brittle deformation of the dike. Application of the model to magma compositions representative of Lassen and Chaos Crags shows that emplacement of dikes \1 m thick should produce enclaves, whereas thicker dikes should generate fluid mixing and form banded pumice within days to weeks of emplacement. Similar relationships apply to other modeled magmatic systems, including Pinatubo, Unzen, and Ksudach/Shtuybel' volcanoes. For all studied systems, the absolute size of the intruding dike, not just its proportion relative to the host, influences mixing style.

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Homogenization processes in silicic magma chambers by stirring and mushification (latent heat buffering)

Cited by 189 publications

References 57 publications

Os isotopic evidence for a carbonaceous chondritic mantle source for the Nagqu ophiolite from Tibet and its implications

Os isotopic evidence for a carbonaceous chondritic mantle source for the Nagqu ophiolite from Tibet and its implications

Warm storage for arc magmas

Thermal and rheological controls on the formation of mafic enclaves or banded pumice

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