The mode of emplacement of the Honningsvåg Intrusive Suite, Magerøya, northern Norway

1998 ◽  
Vol 135 (2) ◽  
pp. 231-244 ◽  
Author(s):  
BRIAN ROBINS
Keyword(s):  
Magma Chamber ◽  
Basaltic Magma ◽  
Layered Intrusions ◽  
Magma Chambers ◽  
Neutral Buoyancy ◽  
Magma Body ◽  
Tectonic Rotation ◽  
Intrusive Suite ◽  
Structural Levels ◽  
Roof Rocks

The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the highest structural levels exposed. Cross-cutting relationships show that the Honningsvåg magma chambers were not active simultaneously but were emplaced sequentially, generally at successively higher structural levels. Olivine tholeiite magma initially pooled in a crustal zone where it had neutral buoyancy. Subsequent chambers are suggested to have been initiated by emplacement of magma along the density discontinuities that existed above and around crystallized intrusions and their associated hornfelses. Chambers evolved by fractional crystallization, assimilation of country rocks and periodic replenishment. The abandonment of magma chambers may have resulted from the expulsion of low-density residual melts.

Geophysical evidence for the locations, shapes and sizes, and internal structures of magma chambers beneath regions of Quaternary volcanism

1984 ◽  
Vol 310 (1514) ◽  
pp. 473-510 ◽  
Keyword(s):  
Magma Chamber ◽  
Upper Mantle ◽  
Yellowstone National Park ◽  
National Park ◽  
Three Dimensional ◽  
Upper Crust ◽  
Magma Chambers ◽  
Low Velocity ◽  
Magma Body ◽  
Kīlauea Volcano

This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and delineating magma chambers with minimum horizontal and vertical dimensions of about 6 km. This technique has been used successfully to detect low-velocity anomalies, interpreted as magma bodies in the volume range 10 3 -10 6 km 3 , in several volcanic centres in the U.S.A, and in Mt Etna, Sicily. Velocity models developed using teleseismic residuals of the Cascades volcanoes of Oregon and California, and Kilauea volcano, Hawaii, do not show appreciable storage of magma in the crust. However, regional models imply that large volumes of parental magma may be present in the upper mantle of these regions. In some volcanic centres, teleseismic delays are accompanied by P-wave attenuation, and linear inversion of spectral data have enabled computation of three-dimensional Q-models for these areas. The use of gravity data for magma chamber studies is illustrated by a study in the Geysers-Clear Lake volcanic field in California, where a strong gravity low has been modelled as a low-density body in the upper crust. This body is approximately in the same location as the low-velocity body delineated with teleseismic delays, and is interpreted as a magma body. In Yellowstone National Park, magnetic field data have been used to map the depth to the Curie isotherm, and the results show that high temperatures may be present at shallow depths beneath the Yellowstone caldera. The main application of electrical techniques in magma-related studies has been to understand the deep structure of continental rifts. Electromagnetic studies in several rift zones of the world provide constraints on the thermal structure and magma storage beneath these regions.

An ocean-ridge type magma chamber at a passive volcanic, continental margin: the Kap Edvard Holm layered gabbro complex, East Greenland

1992 ◽  
Vol 129 (4) ◽  
pp. 437-456 ◽  
Author(s):  
Stefan Bernstein ◽  
Minik T. Rosing ◽  
C. Kent Brooks ◽  
Dennis K. Bird
Keyword(s):  
Magma Chamber ◽  
Continental Margin ◽  
Basaltic Magma ◽  
Olivine Gabbro ◽  
Restricted Range ◽  
Layered Series ◽  
Field Evidence ◽  
Mineral Compositions ◽  
Intrusive Suite ◽  
Stratigraphic Height

AbstractThe gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more than 5000 m. Earlier work has shown that the range in cumulus mineral compositions is restricted (plagioclase An81—An51; olivine Fo85—Fo66; pyroxenes Ca43Mg46Fe11 to Ca43Mg37Fe20). Field evidence of magma injections is common, which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma. A detailed study of a 600 m section (900–1500 m) in the Lower Layered Series reveals a period of crystallization when the magma chamber behaved as a closed system (900–1300 m). The rocks formed during this periodare well-laminated olivine–gabbros (900–110 m), which evolved to well-laminated oxide-gabbros (1100–1300 m). Compositional trends in the cumulusminerals are towards more evolved compositions (plagioclase An64—An58, pyroxene Mg# from 80 to 76) with stratigraphic height. From 1300 m to 1500 m, granular olivine-gabbros dominate, with moreprimitive mineral compositions (plagioclase An67—An76, pyroxene Mg# from 78 to 82). The transition olivine–gabbro to oxide-gabbro at 1100m is a consequence of fractional crystallization, and it is shown how changes in activities of FeO and Fe203 in the magma are reflected in the total iron content of plagioclases.The transition from oxide-gabbro to olivine-gabbro at 1300 m results from replenishment by less evolved basaltic magma. On the basis of calcic pyroxene chemistry and the mineral crystallization sequence it is concluded that the Kap Edvard Holm Layered Series crystallized from a tholeiitic magma similar to MORB. Melanogabbroic units occur throughout the intrusion as discordant to subconcordant sill-like bodies 0.2–2.0 m thick. The melanogabbroic units consist of Cr-rich augite-olivine-plagioclase heteradcumulates and contain deformed mica crystals of pre-emplacement origin. These units crystallized from a wet, MgO-rich magma which was injected into the layered host gabbros after the formation of the cumulus pile, but before the magma was completely solidified.The Kap Edvard Holm Layered Series has several parallels with the plutonic part of ophiolite sequences. These include: cumulus mineral assemblage, compositions of the minerals and the restricted range in compositions with stratigraphic height; field evidence of repeated replenishment of basaltic magma; dyke swarms overlying the roof zone of the magma chamber; and the existence of a late intrusive suite of wet, MgO-rich magma. These parallels suggest that the processes involved in the formation of the Kap Edvard Holm Layered Series were similar to those involved in the formation of the crustalpart of many ophiolites and beneath present-day spreading ridges. The Kap Edvard Holm Layered Series is therefore believed to represent a shallow-level magma chamber which acted as a reservoir for basaltic flows at the continental margin during the opening of the North Atlantic Ocean.

Identification of Anorthite-enriched Plagioclase Antecrysts in the Bushveld Complex, South Africa

2019 ◽  
Vol 60 (6) ◽  
pp. 1109-1118 ◽  
Author(s):  
R Grant Cawthorn
Keyword(s):  
South Africa ◽  
Standard Deviation ◽  
Magma Chamber ◽  
Bushveld Complex ◽  
Alternative View ◽  
Layered Intrusions ◽  
Constant Composition ◽  
Magma Chambers ◽  
Anorthite Content ◽  
Deep Boreholes

Abstract The origin of cumulate grains in layered intrusions is actively debated. Earliest views assumed that all grains grew in the now-exposed magma chamber. An alternative view is that some grains were injected from deeper magma chambers (never to be exposed). Such grains have been called antecrysts. In this model upward reversals in the anorthite content of plagioclase grains in anorthosite-bearing sequences have been considered to indicate such processes, and are considered to represent the bases of cycles. Data from two deep boreholes in the upper half of the Bushveld Complex permit testing of such ideas. Careful inspection shows that anorthosites (over 45 in one core and 12 in another) do not show an increase in their anorthite contents relative to their immediate footwall samples. Further, all examples of cycles (where enough closely spaced samples are available) in one borehole show that there is a slow upward increase in the anorthite contents over tens of metres and several samples, and that anorthosite does not occur at the base of such reversals, inconsistent with injection and accumulation of a slurry of grains with constant composition. Multiple analyses of many grains in a single sample show a typical standard deviation of ±1·5% An. However, a very few samples from both boreholes show a much larger standard deviation. Examination of every single analysis from one core shows that there are rare, isolated grains with a much higher anorthite content (±5%) than the average, rarely more than one per sample (out of 10–20 analyses). It is perfectly possible that these grains are indeed antecrysts. They are not located specifically in anorthosite samples, but can occur in rocks with any proportion of plagioclase. Based on 3000 analyses they constitute of the order of 1% of the total analysed population. The injection of magma may have occurred, but its entrainment of slurries of plagioclase is not consistent with these data.

scholarly journals The Rustenburg Layered Suite formed as a stack of mush with transient magma chambers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zhuosen Yao ◽  
James E. Mungall ◽  
M. Christopher Jenkins
Keyword(s):  
Magma Chamber ◽  
Fractional Crystallization ◽  
Bushveld Complex ◽  
Mineral Deposits ◽  
Ultramafic Rocks ◽  
Layered Intrusions ◽  
Crustal Assimilation ◽  
Magma Chambers ◽  
Magma Chamber Processes ◽  
Lower Crustal

AbstractThe Rustenburg Layered Suite of the Bushveld Complex of South Africa is a vast layered accumulation of mafic and ultramafic rocks. It has long been regarded as a textbook result of fractional crystallization from a melt-dominated magma chamber. Here, we show that most units of the Rustenburg Layered Suite can be derived with thermodynamic models of crustal assimilation by komatiitic magma to form magmatic mushes without requiring the existence of a magma chamber. Ultramafic and mafic cumulate layers below the Upper and Upper Main Zone represent multiple crystal slurries produced by assimilation-batch crystallization in the upper and middle crust, whereas the chilled marginal rocks represent complementary supernatant liquids. Only the uppermost third formed via lower-crustal assimilation–fractional crystallization and evolved by fractional crystallization within a melt-rich pocket. Layered intrusions need not form in open magma chambers. Mineral deposits hitherto attributed to magma chamber processes might form in smaller intrusions of any geometric form, from mushy systems entirely lacking melt-dominated magma chambers.

scholarly journals Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 209
Author(s):  
Shoji Arai
Keyword(s):  
Partial Melting ◽  
Magma Chamber ◽  
Upper Mantle ◽  
Mantle Peridotite ◽  
Common Origin ◽  
Layered Intrusions ◽  
Magma Chambers ◽  
Genetic Link ◽  
Podiform Chromitites ◽  
Crustal Magma

No genetic link between the two main types of chromitite, stratiform and podiform chromitites, has ever been discussed. These two types of chromitite have very different geological contexts; the stratiform one is a member of layered intrusions, representing fossil magma chambers, in the crust, and the podiform one forms pod-like bodies, representing fossil magma conduits, in the upper mantle. Chromite grains contain peculiar polymineralic inclusions derived from Na-bearing hydrous melts, whose features are so similar between the two types that they may form in a similar fashion. The origin of the chromite-hosted inclusions in chromitites has been controversial but left unclear. The chromite-hosted inclusions also characterize the products of the peridotite–melt reaction or melt-assisted partial melting, such as dunites, troctolites and even mantle harzburgites. I propose a common origin for the inclusion-bearing chromites, i.e., a reaction between the mantle peridotite and magma. Some of the chromite grains in the stratiform chromitite originally formed in the mantle through the peridotite–magma reaction, possibly as loose-packed young podiform chromitites, and were subsequently disintegrated and transported to a crustal magma chamber as suspended grains. It is noted, however, that the podiform chromitites left in the mantle beneath the layered intrusions are different from most of the podiform chromitites now exposed in the ophiolites.

scholarly journals The emplacement and crystallization of the U–Th–REE-rich agpaitic and hyperagpaitic lujavrites at Kvanefjeld, Ilímaussaq alkaline complex, South Greenland

2011 ◽  
Vol 59 ◽  
pp. 69-92 ◽  
Author(s):  
Henning Sørensen ◽  
John C. Bailey ◽  
John Rose Hansen
Keyword(s):  
Magma Chamber ◽  
Alkaline Complex ◽  
Magma Body ◽  
North West ◽  
Fine Grained ◽  
Impervious Cover ◽  
The North ◽  
Residual Elements ◽  
Roof Rocks

The U–Th–REE deposit located at the Kvanefjeld plateau in the north-west corner of the Ilímaussaq alkaline complex, South Greenland, consists of lujavrites which are melanocratic agpaitic nepheline syenites. The fine-grained lujavrites of the Kvanefjeld plateau can be divided into a northern and a southern part with an intermediate zone between them. The northern part is situated along the north contact of the Ilímaussaq complex and continues east of the Kvanefjeld plateau as a lujavrite belt along the contact. This part has relatively ‘low’ contents of U, Th, and REE, and hyperagpaitic mineralogy is restricted to its highest-lying parts. The fine-grained lujavrites of the intermediate and southern part of the Kvanefjeld plateau occur between and below huge masses of country rocks which we show are practically in situ remnants of the roof of the lujavrite magma chamber. These lujavrites have high contents of U, Th, and REE, and hyperagpaitic varieties with naujakasite, steenstrupine and villiaumite are widespread. We present a model for the formation of the fine-grained lujavrites of the Kvanefjeld plateau. In this model, an off-shoot from the large lujavrite magma body in the central part of the complex intruded into a fracture zone along the north contact of the Ilímaussaq complex and was forcefully emplaced from north-west to south-east. The intruding lujavrite magma was bounded to the west, north, and at its roof by strong volcanic country rocks, and to the south by the weaker, earlier rocks of the complex. The magma stored in the fracture crystallized, squeezing volatile and residual ele-ments upwards. A subsequent violent explosion opened up fractures in the weaker southern rocks, and the residual volatile-enriched magma was squeezed into fractures in augite syenite, naujaite, and also in the overlying volcanic roof rocks. The removal of the volatile-rich lujavrite magma in the upper part of the fracture-bounded magma chamber made room for the rise of volatile-poor magma from the lower part of the magma chamber, and these lujavrites crystallized to form the northern continuous lujavrite belt. Transfer and accumulation of volatile and residual elements in a lujavrite magma crystallizing below an impervious cover played a key role in the formation of the Kvanefjeld U–Th–REE deposit, as it also did in the crystallization of the lujavrite magma body in the central part of the Ilímaussaq complex.

scholarly journals Temporal Evolution of Cooling by Natural Convection in an Enclosed Magma Chamber

Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 108
Author(s):  
Carlos Enrique Zambra ◽  
Luciano Gonzalez-Olivares ◽  
Johan González ◽  
Benjamin Clausen
Keyword(s):  
Natural Convection ◽  
Magma Chamber ◽  
Temporal Evolution ◽  
Basaltic Magma ◽  
Boussinesq Equations ◽  
Rhyolitic Magma ◽  
The Times ◽  
Volume Method ◽  
The Mathematical Model ◽  
Liquid Magma

This research numerically studies the transient cooling of partially liquid magma by natural convection in an enclosed magma chamber. The mathematical model is based on the conservation laws for momentum, energy and mass for a non-Newtonian and incompressible fluid that may be modeled by the power law and the Oberbeck–Boussinesq equations (for basaltic magma) and solved with the finite volume method (FVM). The results of the programmed algorithm are compared with those in the literature for a non-Newtonian fluid with high apparent viscosity (10–200 Pa s) and Prandtl (Pr = 4 × 104) and Rayleigh (Ra = 1 × 106) numbers yielding a low relative error of 0.11. The times for cooling the center of the chamber from 1498 to 1448 K are 40 ky (kilo years), 37 and 28 ky for rectangular, hybrid and quasi-elliptical shapes, respectively. Results show that for the cases studied, natural convection moved the magma but had no influence on the isotherms; therefore the main mechanism of cooling is conduction. When a basaltic magma intrudes a chamber with rhyolitic magma in our model, natural convection is not sufficient to effectively mix the two magmas to produce an intermediate SiO2 composition.

Igneous Layering in Basaltic Magma Chambers

2015 ◽  
pp. 75-152 ◽  
Author(s):  
O. Namur ◽  
Bénédicte Abily ◽  
Alan E. Boudreau ◽  
Francois Blanchette ◽  
John W. M. Bush ◽  
...  
Keyword(s):  
Basaltic Magma ◽  
Magma Chambers ◽  
Igneous Layering

An elastic 3D Finite-Element-Model for Grímsvötn, Iceland

2021 ◽  
Author(s):  
Sonja Heidi Maria Greiner ◽  
Halldór Geirsson
Keyword(s):  
Finite Element ◽  
Sea Level ◽  
Magma Chamber ◽  
Seismic Velocity ◽  
Source Parameters ◽  
Elastic Structure ◽  
Elastic Model ◽  
Magma Body ◽  
Dependent Relation ◽  
Deformation Models

<p>Deformation models are an important tool to study and monitor active volcanoes. However, in many cases models are strongly simplified either due to a lack of data or for the sake of speed and computational demands. The assumption of a magma body embedded in a homogeneous elastic half-space for example neglects the topography and heterogeneous crustal structures found at some volcanoes. This oversimplification can lead to a poor representation of individual systems and result in erroneous estimates of deformation source parameters like the location and geometry of a magma chamber.  The Finite Element Method (FEM) is a powerful tool to include complex heterogeneous structures and existing data sets into deformation models in order to create more realistic representations of individual volcanic systems. <br>In this study, the FEM-software COMSOL was used to build a three-dimensional elastic model of the subglacial volcano Grímsvötn, Iceland, accounting for the steep topography at the caldera rim, using a digital elevation model, as well as crustal heterogeneity. The elastic structure developed for this model is based on a density-structure, a seismic-velocity-structure and a pressure-dependent relation between the dynamic and static elastic moduli. The main feature of the elastic structure is a weak material (static shear modulus of G<sub>stat</sub>=0.6-9.8 GPa from 1 km above to 2 km below sea level) filing the caldera, which is surrounded by a stiffer, ring-like structure underneath the caldera rim (G<sub>stat</sub>=1.6-18 GPa from 1 km above to 2 km below sea level). The source parameters and geometry of forward models including the topography and elastic structure (individually and combined) were varied to fit the deformation observed at the nunatak GPS station GFUM, located at the caldera rim, during the last eruption (2011). While the topography has limited influence at the deformation at GFUM, the elastic structure requires the magma chamber to be significantly deeper than previous models suggested.</p>

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