scholarly journals Mafic glass compositions: a record of magma storage conditions, mixing and ascent

2019 ◽  
Vol 377 (2139) ◽  
pp. 20180004 ◽  
Author(s):  
Katharine V. Cashman ◽  
Marie Edmonds
Keyword(s):  
Melt Inclusions ◽  
Storage Conditions ◽  
Magma Storage ◽  
Magma Evolution ◽  
Reservoir Architecture ◽  
Multiple Paths ◽  
Magma Compositions ◽  
Moho Depths ◽  
Crystallization Path ◽  
Magma System

The trans-crustal magma system paradigm is forcing us to re-think processes responsible for magma evolution and eruption. A key concept in petrology is the liquid line of descent (LLD), which relates a series of liquids derived from a single parent, and therefore tracks the inverse of the crystallization path. It is common practice to attribute multiple magma compositions, and/or multiple melt compositions (from melt inclusions and matrix glass), to a single LLD. However, growing evidence for rapid, and often syn-eruptive, assembly of multiple magma components (crystals and melts) from different parts of a magmatic system suggests that erupted magma and melt compositions will not necessarily represent a single LLD, but instead may reflect the multiple paths in pressure–temperature space. Here, we use examples from mafic magmatic systems in both ocean island and arc settings to illustrate the range of melt compositions present in erupted samples, and to explore how they are generated, and how they interact. We highlight processes that may be deduced from mafic melt compositions, including the mixing of heterogeneous primitive liquids from the mantle, pre-eruptive magma storage at a range of crustal and sub-Moho depths, and syn-eruptive mixing of melts generated from these storage regions. The relative dominance of these signatures in the glasses depends largely on the water content of the melts. We conclude that preserved melt compositions provide information that is complementary to that recorded by the volatile contents of crystal-hosted melt inclusions and coexisting mineral compositions, which together can be used to address questions about both the pre- and syn-eruptive state of volcanic systems. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

scholarly journals Dominica: transcrustal magmatic system and eruptive halogen budgets

2020 ◽  
Author(s):  
Thiebaut d'Augustin ◽  
Hélène Balcone-Boissard ◽  
Georges Boudon ◽  
Caroline Martel ◽  
Etienne Deloule ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Storage Conditions ◽  
Explosive Eruptions ◽  
Magma Storage ◽  
Equilibrium Data ◽  
Order Of Magnitude ◽  
First Time ◽  
Magma Storage Conditions ◽  
Degassing Budget

<p>Dominica island experienced the largest explosive eruptions (ignimbrites) of the Lesser Antilles arc. The recent revised chronostratigraphy of the Morne Trois Pitons – Micotrin eruptive activity evidenced a series of plinian eruptions that occurred between 18 ka and 9 ka BP. Here we focus on these recent eruptions in order to determine the magma storage conditions at depth and volatile degassing budget. Volatile concentrations (H<sub>2</sub>O, CO<sub>2</sub>) in melt inclusions indicate storage conditions of 200 MPa (~6-8 km deep) and 860-880°C in agreement with experimental constraints from phase-equilibrium data. The magmas were thus stored shallower than those involved during the ignimbritic eruptions (~16 km deep). Magma composition and halogen ratios suggest a common magma origin for all eruptions of Morne Trois Pitons Micotrin volcano in the last 60 kyrs. In addition, for the first time, a complete degassing budget including H<sub>2</sub>O, CO<sub>2</sub>, SO<sub>2</sub>, F, Cl, and Br has been established for all these explosive eruptions. The estimation of their eruptive fluxes towards the atmosphere supports the potential important role of halogen elements in the modification of atmosphere chemistry. Br degassing budget was the same order of magnitude as S whereas F and Cl budgets were 1 and 2 orders of magnitude higher than these two species.</p>

Feldspar crystallization under magma-mixing conditions shown by cathodoluminescence and geochemical modelling – a case study from the Karkonosze pluton (SW Poland)

2004 ◽  
Vol 68 (4) ◽  
pp. 561-577 ◽  
Author(s):  
E. Słaby ◽  
J. Götze
Keyword(s):  
Magma Mixing ◽  
Main Tool ◽  
Precise Determination ◽  
Geochemical Modelling ◽  
Magma Evolution ◽  
Sw Poland ◽  
Crystallization Path ◽  
Geochemical Mass Balance

AbstractFeldspars from the Karkonosze pluton (SW Poland) display many features compatible with magma mixing. The mixing hypothesis has been tested using a geochemical mass balance law resulting in two possible paths of magma hybridization. Based on the results of the geochemical calculation, feldspar samples have been chosen along both mixing lines for cathodoluminescence (CL) investigation which was used as the main tool for the reconstruction of their crystallization path. Changes in the conditions of nucleation and crystallization of the feldspars as well as their movement within the magma chamber have been recognized due to different luminescence characteristics. These changes in the conditions of crystallization obtained by CL allow a precise determination of the genetic affinity of the samples to more mafic or more felsic environments.The results of the present study proved CL to be a valuable tool for the study of crystal-growth morphologies in a dynamic, turbulent environment and also as a geochemical tool for the reconstruction of various petrogenetic mechanisms (e.g. magma hybridization). Accordingly, the combination of CL with geochemical modelling provides corresponding information about magma evolution in an open system.

scholarly journals Diffusion Timescales of Magmatic Processes in the Moinui Lava Eruption at Mauna Loa, Hawai`i, as Inferred from Bimodal Olivine Populations

2020 ◽  
Vol 61 (7) ◽  
Author(s):  
F K Couperthwaite ◽  
T Thordarson ◽  
D J Morgan ◽  
J Harvey ◽  
M Wilson
Keyword(s):  
Lava Flow ◽  
Storage Conditions ◽  
Magma Storage ◽  
Mauna Loa ◽  
Low Viscosity ◽  
Lava Flow Field ◽  
Magmatic Processes ◽  
Geochemical Variations ◽  
And Storage ◽  
Time Information

Abstract The 2·1 ka Moinui lava flow field, erupted from the southwest rift zone of Mauna Loa, Hawai`i, exhibits striking textural and geochemical variations, that can be used to interpret magma processes pre-, syn- and post-eruption. From this lava flow, the duration of magma storage and storage conditions, the timescales over which magma is transported to the surface, and flow emplacement mechanisms at Mauna Loa are determined. Electron microprobe analysis (EMPA) and diffusion chronometry of olivine crystals identify two distinct crystal populations: a primitive, polyhedral olivine population with core compositions of Fo90–88 and a more evolved, platy olivine population with core compositions of Fo83–82. Fe–Mg diffusion modelling of these olivine populations gives distinct timescales for each population; platy olivines yield timescales of days up to a few weeks, while polyhedral olivines yield timescales of months to years. Despite the nature of a well-insulated pāhoehoe flow, meaning that post-emplacement diffusion continues for some time, a wealth of time information can be retrieved concerning pre-eruptive magmatic processes as well as the processes associated with the lava extrusion. The short timescales obtained from the platy olivine crystals and the observed equilibrium between its cores and ambient melt suggest late-stage nucleation and crystal growth in the shallow conduit and during lava emplacement. Conversely, the longer timescales and olivine-melt disequilibrium of the polyhedral olivine crystals suggests accumulation from a deeper source and subsequent transportation to shallow magma storage beneath the summit of Mauna Loa months, or even years before eruption. The chemical and textural details of the Moinui lava reflect the mode of flow emplacement and may have implications for the interpretation of the distribution of spinifex and cumulate olivine within komatiites; high-temperature, low-viscosity lavas, common in the Archean.

scholarly journals Magmatic architecture below the Okataina Volcanic Centre, Taupō Volcanic Zone, Aotearoa New Zealand, inferred from basalt geochemistry

2021 ◽  
Author(s):  
Ery Hughes ◽  
Sally Law ◽  
Geoff Kilgour ◽  
Jon Blundy ◽  
Heidy Mader
Keyword(s):  
New Zealand ◽  
Melt Inclusions ◽  
Basaltic Magma ◽  
Taupo Volcanic Zone ◽  
Volcanic Centre ◽  
Volcanic Zone ◽  
Magma Evolution ◽  
Aotearoa New Zealand ◽  
Basalt Geochemistry ◽  
Rhyolitic Volcanism

The Okataina Volcanic Centre (OVC) is the most recently active rhyolitic volcanic centre in the Taupō Volcanic Zone, Aotearoa New Zealand. Although best known for its high rates of explosive rhyolitic volcanism, there are numerous examples of basaltic to basaltic-andesite contributions to OVC eruptions, ranging from minor involvement of basalt in rhyolitic eruptions to the exclusively basaltic 1886 C.E. Plinian eruption of Tarawera. To explore the basaltic component supplying this dominantly rhyolitic area, we analyse the textures and compositions (minerals and melt inclusions) of four basaltic eruptions within the OVC that have similar whole rock chemistry, namely: Terrace Rd, Rotomakariri, Rotokawau, and Tarawera. Data from these basaltic deposits provide constraints on the conditions of magma evolution and ascent in the crust prior to eruption, revealing that at least five different magma types (two basalts, two dacites, one rhyolite) are sampled during basaltic eruptions. The most abundant basaltic magma type is generated by cooling-induced crystallisation of a common, oxidised, basaltic melt at various depths throughout the crust. The volatile content of this melt was increased by protracted fluid-undersaturated crystallisation. All eruptions display abundant evidence for syn-eruptive mixing of the different magma types. Rotomakariri, consisting of a mafic crystal cargo mixed into a dacitic magma is the most extreme example of this process. Despite similar bulk compositions, comparable to other basaltic deposits in the region, these four OVC eruptions are texturally distinct as a consequence of their wide variation in eruption style.

Quartz crystals in Toba rhyolites show textures symptomatic of rapid crystallization

2020 ◽  
Vol 105 (2) ◽  
pp. 194-226
Author(s):  
Olivia Barbee ◽  
Craig Chesner ◽  
Chad Deering
Keyword(s):  
Melt Inclusions ◽  
Experimental Studies ◽  
Magma Evolution ◽  
Quartz Crystals ◽  
Rapid Crystallization ◽  
Morphological Transitions ◽  
Quantitative Analyses ◽  
Growth Transitions ◽  
Causal Sequence ◽  
Structural Instabilities

Abstract Textural and chemical heterogeneities in igneous quartz crystals preserve unique records of silicic magma evolution, yet their origins and applications are controversial. To improve our understanding of quartz textures and their formation, we examine those in crystal-laden rhyolites produced by the 74 ka Toba supereruption (>2800 km3) and its post-caldera extrusions. Quartz crystals in these deposits can reach unusually large sizes (10–20 mm) and are rife with imperfections and disequilibrium features, including embayments, melt inclusions, titanomagnetite and apatite inclusions, spongy morphologies, hollow faces, subgrain boundaries, multiple growth centers, and Ti-enriched arborescent zoning. Using a combination of qualitative and quantitative analyses (petrography, CL, EBSD, X-ray CT, LA-ICPMS), we determine that those textures commonly thought to signify crystal resorption, crystal deformation, synneusis, or fluctuating P–T conditions are here a consequence of rapid disequilibrium crystal growth. Most importantly, we discover that an overarching process of disequilibrium crystallization is manifested among these crystal features. We propose a model whereby early skeletal to dendritic quartz growth creates a causal sequence of textures derived from lattice mistakes that then proliferate during subsequent stages of slower polyhedral growth. In a reversed sequence, the same structural instabilities and defects form when slow polyhedral growth transitions late to fast skeletal-dendritic growth. Such morphological transitions result in texture interdependencies that become recorded in the textural-chemical stratigraphy of quartz, which may be unique to each crystal. Similar findings in petrologic experimental studies allow us to trace the textural network back to strong degrees of undercooling and supersaturation in the host melt, conditions likely introduced by dynamic magmatic processes acting on short geologic timescales. Because the textural network can manifest in single crystals, the overall morphology and chemistry of erupted quartz can reflect not only its last but its earliest growth behavior in the melt. Thus, our findings imply that thermodynamic disequilibrium crystallization can account for primary textural and chemical heterogeneities preserved in igneous quartz and may impact the application of quartz as a petrologic tool.

scholarly journals Crystal scavenging from mush piles recorded by melt inclusions

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Penny E. Wieser ◽  
Marie Edmonds ◽  
John Maclennan ◽  
Frances E. Jenner ◽  
Barbara E. Kunz
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Storage Conditions ◽  
Kilauea Volcano ◽  
Olivine Crystal ◽  
Kīlauea Volcano ◽  
Compositional Diversity ◽  
High Degree

AbstractOlivine-hosted melt inclusions are commonly used to determine pre-eruptive storage conditions. However, this approach relies on the assumption that co-erupted olivines have a simple association with their carrier melts. We show that primitive olivine crystal cargoes and their melt inclusions display a high degree of geochemical disequilibrium with their carrier melts at Kīlauea Volcano, Hawai’i. Within a given eruption, melt inclusions trapped in primitive olivine crystals exhibit compositional diversity exceeding that in erupted lava compositions since 1790 CE. This demonstrates that erupting liquids scavenge crystal cargoes from mush piles accumulating diverse melt inclusion populations over timescales of centuries or longer. Entrainment of hot primitive olivines into cooler, evolved carrier melts drives post-entrapment crystallization and sequestration of CO2 into vapour bubbles, producing spurious barometric estimates. While scavenged melt inclusion records may not be suitable for the investigation of eruption-specific processes, they record timescales of crystal storage and remobilization within magmatic mush piles.

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