Consequences of a crystal mush-dominated magma plumbing system: a mid-ocean ridge perspective

Lissenberg, C. Johan; Macleod, Christopher; Bennett, Emma N.

doi:10.1098/rsta.2018.0014

Cited by 60 publications

(54 citation statements)

References 120 publications

(184 reference statements)

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“…Beneath this magma reservoir, another LVB with Vp reduction of >5% occurs at depths of 20–50 km, suggesting a much larger basaltic lower crustal magma reservoir (~46,000 km 3 ) with a melt fraction of ~2% (Huang et al, ). Combined with the emerging evidence from geochemical, petrological, and geological observation, a magmatic reservoir is now suggested to be composed of a large transcrustal crystal mush with a few melt fractions and separated, small magma chambers (crystal content <50%) at the top (Cashman et al, ; Edmonds et al, ; Lissenberg et al, ; Sparks et al, ).…”

Section: Discussionmentioning

confidence: 99%

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

et al. 2019

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Understanding the deformation mechanisms of olivine has been considered as the crucial factor in tracing the dynamic processes from seismic anisotropy. Due to extensive overprinting of deformation and alteration, natural examples of original magmatic fabric of olivine are scarce. In this study we selected one wehrlite and three dunite samples from a deep borehole in the Poyi mafic-ultramafic intrusion in the Tarim Craton. The fresh samples show adcumulate texture and plastic deformation of dry olivine (≤10 ppm H 2 O). Thermobarometer calculations yield crystallization conditions at 200-400 MPa and >1,124-1,275°C. Olivine developed a B-type fabric characterized by a concentration of [001] axes parallel to the interpreted lineation and that of [010] axes normal to the interpreted foliation. Activation of [001] and [100] dislocations is confirmed by microstructural observations. Simulation of gravity-driven compaction process reveals extremely rapid compaction of kilometer-scale crystal mush in the Poyi magmatic system. During the early compaction with high porosity, crystallographic habit of olivine may produce shape-preferred orientation and the related B-type fabric. In the final stage of compaction and crystallization, the initial shape-preferred orientation was gradually overprinted, whereas the weak B-type fabric has remained with dislocation creep and dislocation-accommodated grain boundary sliding. Calculated seismic velocities of peridotite samples show low P and S wave anisotropies, with the fastest S wave polarization direction normal to the foliation. Hence, a mush-dominated ultramafic intrusion exhibits weak seismic anisotropy, which has potential to better understand seismic anisotropy in the transcrustal magmatic systems.

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Section: Discussionmentioning

confidence: 99%

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

et al. 2019

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“…The plagioclase BSE images and compositional data were supplemented by 34 host glass analyses, as well as modal analysis of phenocrysts in 94 lavas using EDS element maps. Both the glass data and modal proportions are reported in Lissenberg et al ( 2019 ).…”

Section: Methodsmentioning

confidence: 99%

The significance of plagioclase textures in mid-ocean ridge basalt (Gakkel Ridge, Arctic Ocean)

Bennett

Lissenberg

Cashman

2019

Contrib Mineral Petrol

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Textures and compositions of minerals can be used to infer the physiochemical conditions present within magmatic systems. Given that plagioclase is an abundant phase in many magmatic systems, understanding the link between texture and process is vital. Here, we present a database of textural and compositional data for > 1800 plagioclase crystals in mid-ocean ridge basalt from the Gakkel Ridge (Arctic Ocean) to investigate the physiochemical conditions and processes that govern the formation of plagioclase textures and compositions. The Gakkel basalts have high modal crystal contents (up to 50%). The crystal cargo is complex, with both individual plagioclase and glomerocrysts showing large variations in crystal habit, zoning and resorption. The most common types of zoning are reverse and patchy; we attribute patchy zoning to infilling following either skeletal growth or resorption. Resorption is abundant, with multiple resorption events commonly present in a single crystal, and results from both magmatic recharge and decompression. Periods of strong undercooling, distinct to quench crystallisation, are indicated by matured skeletal crystals and thin normally zoned melt inclusion-rich bands following resorption. Individual samples often contain diverse textural and compositional plagioclase groups. Furthermore, most plagioclase is not in equilibrium with its host melt. Finally, the porous open structures of some glomerocrysts suggest that they represent pieces of entrained disaggregated mush. We interpret this to indicate that the crystal cargo is not generally phenocrystic in origin. Instead, plagioclase crystals that formed in different parts of a mush-dominated plumbing system were entrained into ascending melts. The textures of individual crystals are a function of their respective histories of (under)cooling, magma mixing and decompression. The morphologies of melt inclusion trapped in the plagioclase crystals are associated with specific host crystal textures, suggesting a link between plagioclase crystallisation processes and melt inclusion entrapment. The database of plagioclase presented herein may serve as a template for the interpretation of plagioclase textures in magmatic systems elsewhere. Electronic supplementary material The online version of this article (10.1007/s00410-019-1587-1) contains supplementary material, which is available to authorized users.

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“…They have been interpreted as the result of RPF processes and partial assimilation of crystals during percolation of melt(s) through the permeability of a mush. Together with fractional crystallization (FC), RPF processes are increasingly considered as the predominant processes governing melt differentiation within the lower crust (Lissenberg et al, 2019). Here the implication of RPF is clear from the textures presented above, and in order to test if RPF had also an impact on the chemistry of minerals, we hereafter compare the measured compositions with FC and AFC models.…”

Section: Role Of Reactive Porous Flow In the Formation And Evolution mentioning

confidence: 99%

Magma Reservoir Formation and Evolution at a Slow-Spreading Center (Atlantis Bank, Southwest Indian Ridge)

et al. 2020

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Consequences of a crystal mush-dominated magma plumbing system: a mid-ocean ridge perspective

Abstract: One contribution of 15 to a Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

Cited by 60 publications

References 120 publications

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

The significance of plagioclase textures in mid-ocean ridge basalt (Gakkel Ridge, Arctic Ocean)

Magma Reservoir Formation and Evolution at a Slow-Spreading Center (Atlantis Bank, Southwest Indian Ridge)

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