Mush Disaggregation in Basaltic Magma Chambers: Evidence from the ad 1783 Laki Eruption

Passmore, Emma; Maclennan, John; Fitton, Godfrey; Thordarson, T.

doi:10.1093/petrology/egs061

Cited by 72 publications

(36 citation statements)

References 71 publications

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“…A model where the ascending host liquid entrained crystals from different regions of a heterogeneous crystal mush is consistent with the wide compositional diversity within plagioclase, and with the textural observations indicating that some crystals were incorporated as coherent clusters that subsequently experienced resorption along the edges of the crystal clusters. This model is also consistent with previous observations of oxygen-isotope heterogeneity within crystals at Laki (Bindeman, et al 2006), and numerous studies documenting the importance of mush in producing compositional variation in Icelandic lavas (Carley, et al 2011;Gurenko and Sobolev 2006;Maclennan, et al 2003;Neave, et al 2013;Passmore, et al 2012;Thomson and Maclennan 2013).…”

Section: Nature Of the Source Of Plagioclase Crystalssupporting

confidence: 91%

“…These conclusions are consistent with recent work showing that variable amounts of previously-existing crystalline material has been incorporated into the magma system at Laki (Bindeman, et al 2012;Bindeman, et al 2006;Gurenko and Sobolev 2006;Neave, et al 2013;Passmore, et al 2012;Thomson and Maclennan 2013), with evidence for variable amounts of incorporation of a middle-to lower-crustal mush into the Laki lavas (Neave, et al 2013). …”

Section: Implications For Magmatic Processessupporting

confidence: 91%

“…Our data thus support previous models where most of the macroscopic crystals in Icelandic lavas were incorporated into the host liquid from a crystal mush during transport through the crust (Gurenko and Sobolev 2006;Hansen and Gronvold 2000;Neave, et al 2014;Passmore, et al 2012;Thomson and Maclennan 2013). A novel aspect of this study, however, is that we can 1.19, with higher activity ratios associated with basaltic compositions and lower activity ratios associated with dacites and rhyolites (Condomines, et al 1981;Hemond, et al 1988a;Kokfelt, et al 2003;Kokfelt, et al 2009;Koornneef, et al 2012a;Sigmarsson 1996;Sigmarsson, et al 1992a;Sigmarsson, et al 1992b;Sigmarsson, et al 1991;Zellmer, et al 2008 Th disequilibria will decay to secular equilibrium within ~8-10 kyr (depending on the magnitude of the initial disequilibrium), at least some part of the crystals in the measured bulk separates must have crystallized recently.…”

Section: Time Scale Estimatessupporting

confidence: 89%

“…Evidence for such complex interactions between crystals, magma mush, and melt is less obvious in oceanic island or midocean ridge settings, where there is often more limited compositional contrast between erupted magmas, but other studies have also suggested such recycling in midocean ridges (Costa, et al 2010;Feineman and DePaolo 2003;Saal and Van 3 Orman 2004;Van Orman, et al 2006;Zellmer, et al 2011), Hawaii (Clague 1987Helz 1987;Wright 1973) and Iceland. In the case of Iceland, recent work has documented abundant (albeit sometimes subtle) evidence for recycling of crystalline material within the magma reservoir, including diverse oxygen isotopic compositions of crystals (Bindeman, et al 2012;Bindeman, et al 2006), whole-rock major and trace-element compositional diversity within a given eruption (Passmore, et al 2012), plagioclase and melt inclusion compositions (Neave, et al 2013), olivine compositional diversity (Thomson and Maclennan 2013), textural evidence, such as crystal size distributions (CSDs) for multiple magmatic components (Higgins and Roberge 2007), and xenolith compositions related to crystal cargoes (Gurenko and Sobolev 2006).…”

Section: Introductionmentioning

confidence: 99%

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Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Cooper

Sims

Eiler

et al. 2016

Contrib Mineral Petrol

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Processes in upper-crustal magma reservoirs such as recharge, magma mixing, recycling of previously-crystallized material, and eruption, affect both the physical state and the chemical composition of magmas. A growing body of evidence shows that crystals in intermediate to silicic volcanic rocks preserve records of these processes that may be obscured due to mixing in the liquid fraction of magmas. Fewer studies have focused on crystals in basaltic lavas, but these show evidence for a more subtle, but still rich record of magmatic processes. We present new 238 U-230 Th-226 Ra data for plagioclase, combined with d 18 O and trace-element measurements of the same crystal populations, from basalts erupted at Krafla Volcanic Center, Iceland. These data document the presence of multiple crystal populations within each sample, with chemical and oxygen-isotope heterogeneity at a variety of scales: within individual crystals, between crystals in a given population, between crystal populations within the same sample, and between crystals in lavas erupted from different vents during the same eruption. Comparison to whole-rock or groundmass data shows that the majority of macroscopic crystals are not in trace-element or oxygen-isotope equilibrium with their host liquids. The most likely explanation for these data is that the macroscopic crystals originated within a highly heterogeneous crystal mush in the shallow magma reservoir system. U-series and diffusion data indicate that the crystals (and therefore the mush) formed recently (likely within a few thousand years of eruption, and with a maximum age of 8-9 ka), and that the crystals resided in their host magma prior to eruption for decades to a few centuries at most. These data, in conjunction with other recent studies, suggest a model where erupted Icelandic magmas are the result of interaction of diverse magmas entering the crust, followed by complex interactions between melts and previously-crystallized material at all crustal levels.

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Section: Nature Of the Source Of Plagioclase Crystalssupporting

confidence: 91%

Section: Implications For Magmatic Processessupporting

confidence: 91%

Section: Time Scale Estimatessupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Cooper

Sims

Eiler

et al. 2016

Contrib Mineral Petrol

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“…6(a)). The high H 2 O concentration and apparent hydration may reflect equilibration of this inclusion with an evolved mush liquid (Passmore et al, 2012) prior to entrainment of this olivine into the Laki carrier melt. Assuming an internal pressure of 2 kbar, then this inclusion has aH 2 O = 0.29.…”

Section: Hydration Of Enriched and Depleted Inclusionsmentioning

confidence: 96%

Diffusive over-hydration of olivine-hosted melt inclusions

Hartley

Neave

Maclennan

et al. 2015

Earth and Planetary Science Letters

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Editor: B. Marty Keywords: melt inclusion melt mixing diffusion water olivine IcelandThe pre-eruptive water content of magma is often estimated using crystal-hosted melt inclusions. However, olivine-hosted melt inclusions are prone to post-entrapment modification by H + diffusion as they re-equilibrate with their external environment. This effect is well established for the case of H + loss from olivine-hosted inclusions that have cooled slowly in degassed magma. Here we present evidence for the opposite effect: the addition of H + into inclusions that are held in melts that are enriched in H 2 O with respect to the trapped melts. The compositional variability in a suite of 211 olivine-hosted inclusions from the Laki and Skuggafjöll eruptions in Iceland's Eastern Volcanic Zone indicates that diffusive H + gain governs the H 2 O content of incompatible trace element depleted inclusions. Individual eruptive units contain olivine-hosted inclusions with widely varying incompatible element concentrations but near-constant H 2 O. Furthermore, over 40% of the inclusions have H 2 O/Ce > 380, significantly higher than the H 2 O/Ce expected in primary Icelandic melts or mid-ocean ridge basalts (150-280). The fact that the highest H 2 O/Ce ratios are found in the most incompatible element depleted inclusions indicates that hydration is a consequence of the concurrent mixing and crystallisation of compositionally diverse primary melts. Hydration occurs when olivines containing depleted inclusions with low H 2 O contents are juxtaposed against more hydrous melts during mixing. Melt inclusions from a single eruption may preserve evidence of both diffusive H + loss and H + gain. Trace element data are therefore vital for determining H 2 O contents of melt inclusions at the time of inclusion trapping and, ultimately, the H 2 O content of the mantle source regions. Crown

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Compositional variation and ²²⁶Ra‐²³⁰Th model ages of axial lavas from the southern Mid‐Atlantic Ridge, 8°48′S

Haase

Brandl

Devey

et al. 2016

Geochem Geophys Geosyst

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We present geological observations and geochemical data for the youngest volcanic features on the slow spreading Mid-Atlantic Ridge at 8848 0 S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km 2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226 Th disequilibria model ages of 1000 and 4000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 1008C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8848 0 S lava field support the model of low-frequency eruptions from single ascending magma batches that has been developed for slow spreading ridges.

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Mush Disaggregation in Basaltic Magma Chambers: Evidence from the ad 1783 Laki Eruption

Cited by 72 publications

References 71 publications

Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Diffusive over-hydration of olivine-hosted melt inclusions

Compositional variation and ²²⁶Ra‐²³⁰Th model ages of axial lavas from the southern Mid‐Atlantic Ridge, 8°48′S

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Mush Disaggregation in Basaltic Magma Chambers: Evidence from the ad 1783 Laki Eruption

Cited by 72 publications

References 71 publications

Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Timescales of storage and recycling of crystal mush at Krafla Volcano, Iceland

Diffusive over-hydration of olivine-hosted melt inclusions

Compositional variation and 226Ra‐230Th model ages of axial lavas from the southern Mid‐Atlantic Ridge, 8°48′S

Contact Info

Product

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Compositional variation and ²²⁶Ra‐²³⁰Th model ages of axial lavas from the southern Mid‐Atlantic Ridge, 8°48′S