› › Modeling The Magmatic Plumbing System Beneath An Off Rift Volcanic Deposit On Iceland Using Textural Analyses And Geothermobarometry

Modeling the Magmatic Plumbing System Beneath an Off-rift Volcanic Deposit on Iceland, Using Textural Analyses and Geothermobarometry

Author : David Burney

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Page : 64 pages

File Size : 44,3 MB

Release : 2015

Category : Magmas

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The emplacement of tholeiitic magmas along two NE-SW trending rift zones is the dominant mechanism of crustal accretion on Iceland. Small volumes of transitional to alkaline magmas are also erupted through older crust in several off-rift settings, including the Snæfellsnes Peninsula in western Iceland where the basement is formed by 6-8 Ma flood basalts. In this study, we are investigating how these off-rift magmatic plumbing systems compare to those in the main rift zones, given the significant differences in crystal structure and degree of crustal extension, through application of quantitative textural analysis and mineral geothermobarometry. Our focus is Vatnafell, a sub-glacial eruptive unit (414 ±11 ka) at the western end of the off-rift Ljósufjöll volcanic system in the Snæfellsnes volcanic zone. Samples are highly phyric (~14% phenocrysts), with large phenocrysts (1-12 mm) of clinopyroxene, olivine, and plagioclase. Crystal size distributions for olivine and clinopyroxene both show kinked profiles, indicating two distinct populations. Glomerocrysts in which large clinopyroxene oikocrysts enclose smaller rounded olivine chadacrysts are common, and a small horizon strongly enriched in large (> 5 mm) olivine and clinopyroxene crystals was found near the base of the unit. These observations suggest incorporation of olivine gabbroic/wehrlitic cumulates by the host magma. Analyses show a bimodal composition for clinopyroxene (cores: mg# 83-88; rims/groundmass mg# 72-77), and calculations suggest crystallization of cores at or near the moho in the deep crust (~ 25 km). More extensive analyses of mineral compositions have been used to calculate residence times and ascent rates of the crystalline cargo, and indicate rapid ascent soon after the incorporation of the wehrlitic cumulate. These data have been used to develop a more complete picture of an extension-limited off-rift magmatic plumbing system and allow a more detailed comparison with plumbing systems beneath the extension-dominated main rift zones on Iceland.



Studies of the Mechanics and Structure of Shallow Magmatic Plumbing Systems

Author : Mikel Díez

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Page : pages

File Size : 38,39 MB

Release : 2008

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ABSTRACT: Volcanic activity, and the resultant deposits and structures at the Earth's surface, are the outcome of the inner workings of underground magmatic plumbing systems. These systems, essentially, consist of magma reservoirs which supply magma to the surface through volcanic conduits feeding volcanic eruptions. The mechanics and structure of plumbing systems remain largely unknown due to the obvious challenges involved in inferring volcanic processes occurring underground from observations at the surface. Nevertheless, volcanologists are beginning to gain a deeper understanding of the workings and architecture of magmatic plumbing systems from geophysical observations on active volcanoes, as well as from geological studies of the erosional remnants of ancient volcanic systems. In this work, I explore the relationship between the structure and mechanics of shallow plumbing systems and the volcanic eruptions these systems produce. I attempt to contribute to the understanding of this complex relationship by linking geological and geophysical observations of an eroded basaltic subvolcanic system, and the eruptive and tectonic activity of an active volcano, with mathematical models of magma ascent and stress transfer. The remarkable exposures of the Carmel outcrop intrusions, near the San Rafael swell, southeast Utah, U.S.A., allow detailed geological and geophysical observations of the roots of volcanic conduits that emerge from a subhorizontal magma feeder reservoir. These observations reveal a new mechanism for magma ascent and eruption triggering through gravitational instabilities created from an underlying feeding sill, and shed light on the mechanics of sill emplacement. Geophysical and geological observations of the 1999 and xii 1992 eruptions of the Cerro Negro volcano, Nicaragua, are used to explore the coupling between changes in the stress field and the triggering of volcanic eruptions, and magma ascent through the shallow crust. Modeling results of stress transfer and conduit flow highlight the importance of the surrounding stress field and geometry of the volcanic conduits that comprise shallow plumbing systems.



Grimsvötn

Author : Kyle Rawson

Publisher :

Page : 40 pages

File Size : 25,28 MB

Release : 2012

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Abstract: Volcanoes in Iceland pose an enormous threat to not only the environment but a large portion of the population due to the sheer number and potential destruction that lies under each one. Grimsvötn, being the most frequently erupting volcano in Iceland, is a great locality to develop more of an understanding into how these volcanoes actually work and what we can do to better prepare ourselves for future events. Basaltic glass samples were taken and analyzed using various methods in order to determine partial pressures of crystallization. From this we can deduce magma chamber depth and interpret through various petrological methods, a possible system which lies beneath the volcanoes. As a result of completing this procedure we have concluded that the data are best explained by the presence of a complex plumbing system, consisting of both a shallow and deep chamber, and plexus of small chambers at various depths, or a deep chamber linked to the surface by dikes. Similar models have been proposed for the plumbing systems beneath other volcanoes in Iceland.



Volcanoes

Author : John P. Lockwood

Publisher : John Wiley & Sons

Page : 677 pages

File Size : 41,97 MB

Release : 2013-04-26

Category : Science

ISBN : 1118687949

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Book Description

Volcanoes are essential elements in the delicate global balance of elemental forces that govern both the dynamic evolution of the Earth and the nature of Life itself. Without volcanic activity, life as we know it would not exist on our planet. Although beautiful to behold, volcanoes are also potentially destructive, and understanding their nature is critical to prevent major loss of life in the future. Richly illustrated with over 300 original color photographs and diagrams the book is written in an informal manner, with minimum use of jargon, and relies heavily on first-person, eye-witness accounts of eruptive activity at both "red" (effusive) and "grey" (explosive) volcanoes to illustrate the full spectrum of volcanic processes and their products. Decades of teaching in university classrooms and fieldwork on active volcanoes throughout the world have provided the authors with unique experiences that they have distilled into a highly readable textbook of lasting value. Questions for Thought, Study, and Discussion, Suggestions for Further Reading, and a comprehensive list of source references make this work a major resource for further study of volcanology. Volcanoes maintains three core foci: Global perspectives explain volcanoes in terms of their tectonic positions on Earth and their roles in earth history Environmental perspectives describe the essential role of volcanism in the moderation of terrestrial climate and atmosphere Humanitarian perspectives discuss the major influences of volcanoes on human societies. This latter is especially important as resource scarcities and environmental issues loom over our world, and as increasing numbers of people are threatened by volcanic hazards Readership Volcanologists, advanced undergraduate, and graduate students in earth science and related degree courses, and volcano enthusiasts worldwide. A companion website is also available for this title at www.wiley.com/go/lockwood/volcanoes





Numerical Modeling of Magma Ascent Through the Lithosphere

Author : Nicolas Berlie

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Page : 0 pages

File Size : 30,15 MB

Release : 2023

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Magmatic systems and volcanoes are found throughout the entire world, yet the processes responsible for the ascent of magmatic melt, as well as the structure of these systems, are still poorly constrained due to a lack of direct observations. All hypotheses in this field are derived from indirect observations (geophysical surveys, fieldwork and petrological studies on fossil exhumed systems or at the surface of currently active volcanic systems) and robust physical and geochemical models need to be developed to validate, quantify or refine these ideas. We address these challenges in this thesis in two parts. First, we study the melt depletion of a magmatic reservoir connected to the surface by a weak conduit. Using a 2D model, we simplify the rheology and structure of the system to a few parameters and determine how sensitive the velocities within the conduit are to variations in these parameters. Several modes of transport are identified and translated into analytical scaling laws. We then apply these scaling laws to the 2021 eruption of the Cumbre Vieja volcano to constrain the structure of the magmatic system located beneath La Palma in the Canary Islands. Second, we develop tools to model magmatic systems in more detail and in a self-consistent manner across the lithosphere. One of these tools is an extension of the numerical continuum approach commonly used in geodynamics to model both shear and tensile plastic failure. This enables us to include dykes, the main form of melt transport in the elasto-plastic upper crust, in our models. The constitutive equations presented include compressible visco-elasto-plasticity with viscoplastic regularization and non-linear rheologies. A new yield function, adapted to work reliably in tensile conditions without introducing unphysical stress states into the model, is also presented. Another tool described in this thesis is MAGEMin, a Gibbs energy minimizer applied to igneous systems. MAGEMin is an efficient and highly scalable minimization package that opens up new possibilities for petrological applications as well as for use in conjunction with thermomechanical models. It uses a combination of linear programming, extended Partitioning Gibbs Energy and gradient-based minimization. The implementation of the thermodynamic dataset (Holland et al., 2018) was benchmarked against THERMOCALC.



Magma Plumbing Systems Along the Juan de Fuca Ridge

Author : Lindsey Danielle Hernandez

Publisher :

Page : pages

File Size : 15,63 MB

Release : 2020

Category : Magmas

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The depth of magma storage beneath volcanoes has been a primary focus of recent geophysical and petrological research. Investigation of magma plumbing systems has important implications for volcanic hazard mitigation and eruption forecasting, and also for our understanding of the origin and evolution of magmas. This work is particularly important at mid-ocean ridges, as they are responsible for the formation of the majority of Earth’s crust. Previous petrologic studies of mid-ocean ridges have suggested that olivine-plagioclase-clinopyroxene-liquid cotectic crystallization begins at mantle depths, which has far-reaching implications for our understanding of the mechanisms for crustal accretion. We demonstrate a procedure for processing pressure results using the Kelley & Barton (2008) geobarometer, which significantly changes the interpretation of these results. This process allows for high-resolution interpretation of the pressures, and thus depths, of partial crystallization in mafic systems. Application of this approach to data from the Juan de Fuca Ridge suggests that olivine-plagioclase-clinopyroxene-liquid cotectic crystallization occurs within the crust, and not in the mantle as suggested previously. The results suggest that partial crystallization along the ridge is polybaric. In the southern portion of the ridge, seismically imaged melt lenses are within range of the calculated pressures, however, the average pressures suggest that the majority of olivine-plagioclase-clinopyroxene-liquid cotectic crystallization occurs at greater depths than the imaged melt lenses. This suggests multi-depth magma storage along much of the Juan de Fuca Ridge, with only the shallowest magma reservoirs being imaged by seismic studies.





Petrological Constraints on Magma Plumbing Systems Along Mid-ocean Ridges

Author : Jameson Lee Scott

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Page : pages

File Size : 33,49 MB

Release : 2011

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Abstract: Plate spreading at the mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the flows and dikes is related to the heat flux - the higher the heat flux the shallower the magma chamber. To examine this hypothesis, I determined the depths of magma chambers beneath the intermediate spreading Juan de Fuca Ridge (JdF) in the northeast Pacific and the slow spreading Reykjanes Ridge (RR) south of Iceland. Pressures of partial crystallization were determined by comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and clinopyroxene at different pressures and temperatures using the method described by Kelley and Barton (2008). Chemical analyses mid-ocean ridge basalts glasses sampled from along the RR and JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 519 for the RR and 479 samples for the JdF were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. The RR results indicate that the pressure of partial crystallization decreases from 102 ± 33 MPa at the Charlie Gibbs Fracture Zone to 21 ± 12 MPa at 56°N, then increases to 367 ± 68 MPa as Iceland is approached. Four magma lenses were identified at depths of 2.5±.8km, 5.2±.8km, 5.9±1km, and 6.7±1. The magma lens at 2.46±.83 km agrees very well with seismically imaged sill at 2.5 km (Peirce et al 2007). The JDF results indicate that the pressure of partial crystallization decreases from 200 to100±50 MPa from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 87±.53MPa along ridge segments to the north of the Cleft. Two magma lenses were identified at depths of 4.47±.89km and 4.08±1.5km. Pressures calculated for samples from single lava flows along the Cleft segment described by Stakes et al (2006) allow identification of two magma chambers at depths of 4.91±.77km and 4.33±1.07km which agree well with the depth of 5 to 6 km for a seismically imaged sill (Canales et al 2009). The average depth of partial crystallization of both ridges increase with increasing heat flux. While calculated pressures provide evidence for some crystallization in axial melt lenses, results obtained for some samples from virtually every locality also suggest partial crystallization in the crust beneath these lenses, and therefore the results support the many sill or crystal mush models for accretion of oceanic crust for both ridges. The average difference between pressures calculated with both methods within the uncertainty in the calculation. The Herzberg method returns slightly lower pressures for most samples.