scholarly journals Formation and dynamics of magma reservoirs

2019 ◽  
Vol 377 (2139) ◽  
pp. 20180019 ◽  
Author(s):  
R. S. J. Sparks ◽  
C. Annen ◽  
J. D. Blundy ◽  
K. V. Cashman ◽  
A. C. Rust ◽  
...  
Keyword(s):  
Rapid Development ◽  
High Viscosity ◽  
Magma Reservoir ◽  
Grand Challenge ◽  
Magma Chambers ◽  
Crustal Rocks ◽  
Reservoir Architecture ◽  
Magma Reservoirs ◽  
Magmatic Fluids ◽  
Host Rocks

The emerging concept of a magma reservoir is one in which regions containing melt extend from the source of magma generation to the surface. The reservoir may contain regions of very low fraction intergranular melt, partially molten rock (mush) and melt lenses (or magma chambers) containing high melt fraction eruptible magma, as well as pockets of exsolved magmatic fluids. The various parts of the system may be separated by a sub-solidus rock or be connected and continuous. Magma reservoirs and their wall rocks span a vast array of rheological properties, covering as much as 25 orders of magnitude from high viscosity, sub-solidus crustal rocks to magmatic fluids. Time scales of processes within magma reservoirs range from very slow melt and fluid segregation within mush and magma chambers and deformation of surrounding host rocks to very rapid development of magma and fluid instability, transport and eruption. Developing a comprehensive model of these systems is a grand challenge that will require close collaboration between modellers, geophysicists, geochemists, geologists, volcanologists and petrologists. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

scholarly journals How do volatiles escape their shallow magmatic hearth?

2019 ◽  
Vol 377 (2139) ◽  
pp. 20180017 ◽  
Author(s):  
Wim Degruyter ◽  
Andrea Parmigiani ◽  
Christian Huber ◽  
Olivier Bachmann
Keyword(s):  
Volcanic Activity ◽  
Physical Modelling ◽  
Volcanic Eruptions ◽  
Magma Reservoir ◽  
Volatile Elements ◽  
Reservoir Architecture ◽  
Magma Reservoirs ◽  
Crystal Fraction ◽  
Efficient Construction

Only a small fraction (approx. 1–20%) of magmas generated in the mantle erupt at the surface. While volcanic eruptions are typically considered as the main exhaust pipes for volatile elements to escape into the atmosphere, the contribution of magma reservoirs crystallizing in the crust is likely to dominate the volatile transfer from depth to the surface. Here, we use multiscale physical modelling to identify and quantify the main mechanisms of gas escape from crystallizing magma bodies. We show that most of the outgassing occurs at intermediate to high crystal fraction, when the system has reached a mature mush state. It is particularly true for shallow volatile-rich systems that tend to exsolve volatiles through second boiling, leading to efficient construction of gas channels as soon as the crystallinity reaches approximately 40–50 vol.%. We, therefore, argue that estimates of volatile budgets based on volcanic activity may be misleading because they tend to significantly underestimate the magmatic volatile flux and can provide biased volatile compositions. Recognition of the compositional signature and volumetric dominance of intrusive outgassing is, therefore, necessary to build robust models of volatile recycling between the mantle and the surface. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

scholarly journals Time scales and temperatures of crystal storage in magma reservoirs: implications for magma reservoir dynamics

2019 ◽  
Vol 377 (2139) ◽  
pp. 20180009 ◽  
Author(s):  
Kari M. Cooper
Keyword(s):  
Time Scales ◽  
Physical State ◽  
Large Range ◽  
Numerical Models ◽  
Magma Reservoir ◽  
Radiometric Dating ◽  
Reservoir Architecture ◽  
Magma Reservoirs ◽  
Magma System ◽  
Crustal Magma

The thermal and therefore physical state of magma bodies within the crust controls the processes and time scales required to mobilize magmas before eruptions, which in turn are critical to hazard assessment. Crystal records can be used to reconstruct magma reservoir histories, and the resulting time and length scales are converging with those accessible through numerical modelling of magma system dynamics. The goal of this contribution is to summarize constraints derived from crystal chronometry (radiometric dating and modelling intracrystalline diffusion durations), in order to facilitate use of these data by researchers in other fields. Crystallization ages of volcanic minerals typically span a large range (10 4 –10 5  years), recording protracted activity in a given magma reservoir. However, diffusion durations are orders of magnitude shorter, indicating that the final mixing and assembly of erupted magma bodies is rapid. Combining both types of data in the same samples indicates that crystals are dominantly stored at near- or sub-solidus conditions, and are remobilized rapidly prior to eruptions. These observations are difficult to reconcile with some older numerical models of magma reservoir dynamics. However, combining the crystal-scale observations with models which explicitly incorporate grain-scale physics holds great potential for understanding dynamics within crustal magma reservoirs. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

scholarly journals Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

1992 ◽  
Vol 154 ◽  
pp. 49-59
Author(s):  
T Winther
Keyword(s):  
Open Systems ◽  
Early Stage ◽  
Rift System ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Low Degree ◽  
Alkaline Magmas ◽  
Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

Deformation driven magma ascent in stratified magma reservoirs: an experimental study

2021 ◽  
Author(s):  
Amy Ryan ◽  
Mark Zimmerman ◽  
Lars Hansen
Keyword(s):  
Pore Pressure ◽  
Seismic Waves ◽  
Soda Lime ◽  
High Viscosity ◽  
Magma Ascent ◽  
Campi Flegrei ◽  
Soda Lime Glass ◽  
Borosilicate Glasses ◽  
Magma Intrusion ◽  
Magma Reservoirs

<p>Mature volcanic systems (e.g., Yellowstone, USA; Campi Flegrei, Italy) are fed by stratified magma reservoirs – small bodies of eruptible, crystal-poor silicic magma are suspended within a larger volume of non-eruptible, crystal-rich mush. Lavas erupted from these systems record geochemical evidence for long-term (10<sup>3</sup> to 10<sup>5</sup> years) deep storage followed by short (<1 to 10<sup>3</sup> years) residences in shallow chambers prior to eruption. Evidence for protracted magma ascent is frequently absent, suggesting deep-seated magmas rise quickly in reservoirs despite the high viscosity and low permeability of crystal-rich mushes. We hypothesize that deformation of a reservoir (by intrusion of new magma, passing seismic waves, tectonic stresses, etc.) allows low viscosity magmas to intrude high viscosity mush, creating mechanical instabilities that focus magma migration and facilitate rapid magma ascent through the reservoir.</p><p>To test this hypothesis, we are conducting high-temperature and high-pressure deformation experiments in a gas-medium, Paterson apparatus. Samples consist of a disk of soda lime glass (“magma”) stacked in series with a disk of a composite (“mush”) composed of borosilicate glass and fine quartz sand (44-106 μm). The mush has a crystal fraction of 80%. The stacked magma and mush disks are overlain by permeable ceramics. Sample assemblies are heated to 900°C (above the glass transition temperatures for soda lime and borosilicate glasses) and pressurized to 200 MPa confining pressure. At 900°C the magma viscosity is 10<sup>4</sup> Pa s and the mush viscosity is ~10<sup>12</sup>-10<sup>14</sup> Pa s. Following heating and pressurization, samples either dwell at high P-T conditions for extended time or are subjected to axial compression (strain rates of 10<sup>-5</sup>-10<sup>-3</sup> s<sup>-1</sup>; shortening up to 50% of the length of the mush disk) or pore pressure gradients (a pressure difference across the sample of 10-150 MPa, equivalent to 2-30 MPa/mm over the length of the mush disk). After dwelling or deformation, samples are rapidly quenched and decompressed, cut in longitudinal sections and polished. Polished samples are analyzed in an SEM to collect back-scatter electron images and compositional maps. BSE images can be used to look for melt structures (e.g., viscous channels, dikes) that form in the mush during deformation. The compositions of magma (soda lime) and mush (borosilicate) melts are different, therefore compositional maps can be used to look for their respective spatial distributions. In static experiments, no magma intrudes the mush. We expect deformation to facilitate magma intrusion and that the volume of intruding magma will increase with increasing strain rate, strain and pore pressure gradient. These experiments will shed light on the role deformation plays in instigating magma ascent in stratified magma reservoirs.</p>

Geology, petrology and tectonomagmatic evolution of the plutonic crustal rocks of the Sabzevar ophiolite, NE Iran

2013 ◽  
Vol 150 (5) ◽  
pp. 862-884 ◽  
Author(s):  
MORTEZA KHALATBARI JAFARI ◽  
HASSAN A. BABAIE ◽  
MOJTABA MIRZAIE
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Island Arc ◽  
Magma Chambers ◽  
Northern Margin ◽  
Crustal Rocks ◽  
Microscopic Studies ◽  
Element Enrichment ◽  
Spider Diagrams ◽  
Ocean Ridge

AbstractThe plutonic crustal sequence exposed northeast of Sabzevar is part of the ophiolitic belt of Sabzevar that occurs along the northern margin of the Central Iran micro-continent. The sequence includes olivine and pyroxene gabbro with cumulate characteristics, isotropic gabbro, foliated gabbro and a diabase sheeted dyke complex cut by wehrlite and olivine websterite intrusions, and pegmatite gabbro and plagiogranite as small intrusions and dykes. The sequence is comparable to gabbros in known ophiolite complexes. Microscopic studies show an abundance of the mesocumulate and heteradcumulate textures that represent open system magma chambers, which are common in supra-subduction zones. The olivine → plagioclase → clinopyroxene → ± orthopyroxene → amphibole trend of mineralization in the gabbros, similar to mid-ocean ridge basalt (MORB), and olivine → clinopyroxene → ± orthopyroxene → plagioclase → amphibole, similar to arc rocks, indicate the diversity in the formation of these rocks, and represent petrographic evidence of their formation in a supra-subduction zone. The rocks have calc-alkaline to tholeiitic affinities, and niobium depletion in the spider diagrams of diabase that matches the patterns of island arc magma. These patterns, and the light rare earth element enrichment of the diabase and plagiogranite, suggest the effect and introduction of the fluids, originating from the subducting slab, beneath the mantle wedge. The low titanium compositions, matching those of arc diabase and plagiogranite, plot in the island arc to MORB tectonomagmatic fields, and suggest formation of the Sabzevar ophiolitic plutonic crustal sequence in a supra-subduction zone during Late Cretaceous time.

scholarly journals Filling and plugging of a marine basin by volcanic rocks: the Tunoqqu Member of the Lower Tertiary Vaigat Formation on Nuussuaq, central West Greenland

1996 ◽  
Vol 171 ◽  
pp. 5-28
Author(s):  
A.K Pedersen ◽  
L.M Larsen ◽  
G.K Pedersen ◽  
K.S Dueholm
Keyword(s):  
Volcanic Rocks ◽  
Water Levels ◽  
North Coast ◽  
Magma Chambers ◽  
Tectonic Control ◽  
Crustal Rocks ◽  
The North ◽  
High Level ◽  
Marine Embayment ◽  
Volcanic Cycles

The volcanic Tunoqqu Member formed at the end of the second of three volcanic cycles in the Paleocene Vaigat Formation. The Tunoqqu Member consists of brown aphyric and feldspar-phyric basalts and forms a marker horizon within the grey picritic rocks of the Vaigat Formation. Most of the basalts are siliceous and were produced by contamination with crustal rocks of magmas ranging in composition from picrite to evolved basalt. Some of the basalts were erupted from local volcanic centres of which four have been identified, whereas other basalts form more regional flows. The four identified eruption centres are located along fault lines and zones of uplift and subsidence, indicating tectonic control. Tectonic control is also inferred to be important in terminating the volcanic cycle and causing the development of high-level magma chambers where the magmas stagnated, fractionated, and became contaminated. The basalts of the Tunoqqu Member form subaerial lava flows in western Nuussuaq. Central Nuussuaq constituted a marine embayment in which the volcanics were deposited as eastward prograding foreset-bedded hyaloclastite breccia fans which indicate water depths of up to 160 m. Eastern Nuussuaq was a gneiss highland with a more than 700 m high NW-SE-elongated gneiss promontory stretching into the sea. During Tunoqqu Member time the volcanic rocks reached the gneiss promontory and blocked the outlet from the south to the sea in the north. This resulted in increased water levels in the enclosed embayment and transformation of the outlet into a torrential river. This river eroded the concomitantly forming Tunoqqu Member volcanics and the gneiss promontory and deposited the material in up to more than 250 m thick foreset-bedded boulder conglomerates in the sea where the north coast of Nuussuaq is now situated.

TIME SCALES AND TEMPERATURES OF CRYSTAL STORAGE IN MAGMA RESERVOIRS: IMPLICATIONS FOR MAGMA RESERVOIR DYNAMICS

2018 ◽  
Author(s):  
Kari M. Cooper ◽  
◽  
Kevin L. Schrecengost ◽  
Tyler Schlieder ◽  
Richard W. Bradshaw ◽  
...  
Keyword(s):  
Time Scales ◽  
Magma Reservoir ◽  
Magma Reservoirs

Cognate xenoliths in the Tertiary uhrabasic dykes of south-west Skye

1969 ◽  
Vol 37 (288) ◽  
pp. 504-514 ◽  
Author(s):  
Fergus G. F. Gibb
Keyword(s):  
Upper Mantle ◽  
High Viscosity ◽  
Preferred Orientation ◽  
Mantle Material ◽  
South West ◽  
Host Rocks ◽  
Axial Concentration ◽  
Shape And Size

SummaryA group of ultrabasic dykes occurring in south-west Skye is typified by often abundant and diverse ultrabasic xenoliths composed of essentially the same minerals as the dykes. The xenoliths, which vary considerably in shape and size, are in sharp contact with the host rocks and exhibit no evidence of remelting by, or reaction with, the dykes. Although extensive axial concentration of olivine occurred in the dykes during intrusion, the xenoliths appear to be randomly distributed throughout all but the extreme margins of the dykes and often exhibit a preferred orientation. The orientation and distribution of the xenoliths are attributed to the suppression of rotation and axial migration of the xenoliths during the emplacement of the dykes because of the relatively high viscosity of the suspending medium.The ultrabasic xenoliths, unlike many of those occurring in basalts, kimberlites, etc., are considered unlikely to represent primary upper mantle material and it is suggested that they were probably derived by the disintegration of layered ultrabasic rocks genetically related to the dykes and hence are of cognate origin.

EOCENE MAGMA PLUMBING SYSTEM BENEATH CORTEZ HILLS CARLIN-TYPE GOLD DEPOSIT, NEVADA: IS THERE A DEEP-SEATED PLUTON?

2020 ◽  
Author(s):  
Celestine N. Mercer
Keyword(s):  
Gold Deposit ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Gold Mineralization ◽  
Magma Reservoir ◽  
Plumbing System ◽  
Isotopic Tracers ◽  
Geophysical Surveys ◽  
Magmatic Fluids ◽  
Gold Bearing

Abstract The magmatic-hydrothermal conceptual model for Carlin-type gold deposit genesis calls upon deep-seated Eocene plutons as the primary source of gold-bearing fluids. However, geophysical surveys, geologic mapping, drilling, geochronology, isotopic tracers, and fluid inclusion chemistry have returned ambiguous evidence for the existence of such plutons. The high-grade Cortez Hills gold deposit in northern Nevada hosts shallow, Eocene syn- and postmineralization intrusions, offering an ideal site to investigate the existence of a deep-seated pluton beneath the district. Here, major and trace element analyses of quartz-hosted melt inclusions from four Eocene rhyolite dikes cropping out within the Cortez Hills pit and results from independent thermobarometers provide a window into the subsurface Eocene magmatic plumbing system to test the existence of a deep-seated source pluton. Dissolved volatile contents, melt inclusion entrapment pressures, and thermodynamic phase equilibria indicate that dike magmas were sourced from ~4- to ≥9-km depth from a polybaric magma reservoir residing as a physically and geochemically interconnected crystal mush with extractable or eruptible magma pockets. Magmas ascended adiabatically (nearly isothermally), exsolving fluids, evolving modestly by fractional crystallization, while trapping quartz-hosted melt inclusions steadily from depth to subvolcanic levels where they were emplaced. These data represent the first unequivocal evidence for a deep-seated magma reservoir from which fluid-saturated magma emanated and released magmatic fluids beneath the Cortez district during gold mineralization. However, further investigation into the specific metallogenic potential and metal budget of parental magmas and the partitioning of gold between silicate melt and aqueous fluids will be necessary to provide evidence that exsolved magmatic fluids may have been gold bearing.

Sign in / Sign up

Export Citation Format

Share Document