Thesis (D.P.H.)--University of Hawaii at Manoa, 2000. / Heading on electronic reproduction: Morrow, James Walter. Includes bibliographical references (leaves 172-196). Also available on microfiche.

Dyke injection transports large volumes of magma over great distances, controlling the supply of magma to volcanoes and effectively releasing tensional stress at divergent plate margins. This thesis aims to improve understanding of dyke injection processes on different scales. Dyke shapes measured on the Isle of Rum have been analysed and show a mismatch between the currently accepted theory used to describe their shape, and the measured data. The measured dykes show wider edges than expected, consistent with wedging and cooling of magma in the dyke tips; wedged dykes can act as conduits for longer. Finite difference one- and two-dimensional models for the thermal evolution of the crust due to heat transfer from multiple dyke injection have been developed and applied to the geological setting of the actively spreading Main Ethiopian and Red Sea rifts, where the spreading rates are 5 and 16 mm yr-1 respectively. The model has shown that the spreading rate is the first order control on the temperature build up. Differences in crustal thickness exist between these two regions; the crust has thinned under the Red Sea Rift whilst under the Main Ethiopian Rift there has been no appreciable thinning. This difference has led to the conclusion that the spreading rate, and thus the temperature profile, is the principal cause for the differences in crustal thicknesses. Above the brittle-ductile transition temperature, the crust is likely to undergo pre- dominantly ductile deformation; for slow spreading rates (e.g. 5 mm yr-1), it takes up to 142 ka for the dyke injection site to reach this temperature. The position of the locus of strain at an actively rifting margin migrates with time. For slow spreading rates, the strain locus must remain fixed for at least 142 ka before appreciable crustal heating allows the onset of ductile stretching. Where the spreading rate is faster, the locus of strain must remain fixed for shorter lengths of time. Thus Ethiopia's evolving locus of strain and low spreading rate have likely caused much of the extension to be accommodated by magmatic intrusion rather than by stretching. Comparisons between the thermal model results and geophysical observations from a segment of the Red Sea rift have been made. The mag- netotelluric survey across the rift axis of the actively spreading Red Sea Rift segment has shown two bodies of hot material; one explanation is that the rift axis has jumped. Scaled experimental models have been used to study multiple dyke injection in an extensional tectonic setting. For a fixed overpressure, larger spacings between injections give smaller rotation angles between injections. This is consistent with the rotation angles and injection spacings observed between the recent dyke injections on the Red Sea Rift.

No description available.

Continental rifting, like other plate tectonic processes, plays a large role in shaping the Earth's crust. Active rift zones evolve from repeated tectonic and magmatic events including volcanic activity. Through investigations of currently and previously active rifts, scientists have discovered considerable interactions between these tectonic and magmatic processes during a rift's evolution; however questions remain about these interactions especially in youthful stages of rifts. We investigate an early phase magma-rich section of the East African Rift System (EARS), named the Eastern Branch to assess volcano-tectonic interactions. The Eastern Branch of the EARS consists of volcanically rich rifts that are actively spreading the Nubian Plate, Somalian plates, and Victoria block at different evolutionary stages making it an ideal study area for volcano-tectonic interactions. Our initial investigation of active volcano-tectonic interactions centered on a rifting event that occurred between 2007-2008 in the Natron Rift, a rift segment in the southern Eastern Branch located in Northern Tanzania. This rifting event contained multiple occurrences of tectonic, magmatic, and volcanic activity in close proximity. We examine the stress transferred from these events to the Natron Fault, which is the major border fault in the area, with analytical modeling using the USGS program Coulomb 3.4. We processed Global Positioning System (GPS) data that recorded slip on the major border fault in the region in early January 2008 and test which events could generate large enough stress changes to trigger the observed slip using a previously defined threshold of 0.1 MPa. These initial models were created using simplified model parameters, such as an elastic homogeneous half-space, and find that 1) magmatically induced stress perturbations have the potential to trigger fault slip on rift border faults, 2) magmatic events have the potential to trigger strike‐slip motions on a rift border fault, and 3) the proximity of magmatic activity may affect occurrences of slip on adjacent border faults. We then further investigate volcano-tectonic interactions in the Natron Rift by testing using numerical modeling with the CIG finite element code PyLith. We systematically test how adding topography, heterogeneous materials, and various reservoir volumes to a deflating 3 km deep magma reservoir system at the active volcano Ol Doinyo Lengai can affect stress transfer to the adjacent Natron Fault. We compare eight models with variations in topography, material properties, and reservoir volumes to calculate the percent differences between the models; to test their effects on the stress change results. We find that topography plays the largest role with the effect increasing with reservoir size. Finally, we seek to improve the capability of investigating volcano-tectonic interactions in the Natron Rift at faster time- scales by improving Global Navigation Satellite System (GNSS) positioning data (latitude, longitude, and height) collection and distribution capabilities. In the final part of this work, we describe a new Python-based data broker application, GNSS2CHORDS, that can stream real-time centimeter precision displacement data distributed by UNAVCO real-time GNSS data services to an online EarthCube cybertool called CHORDS. GNSS2CHORDS is applied to the TZVOLCANO GNSS network that monitors Ol Doinyo Lengai in the Natron Rift and its interactions with the adjacent rift border fault, the Natron Fault. This new tool provides a mechanism for assessing volcano-tectonic interactions in real-time. In summary, this work provides a new avenue for understanding volcano-tectonic interactions at unprecedented, 1-second time-scales, demonstrates slip can be triggered by small stress changes from magmatic events during early phase rifting, and provides insights into the key role of volcanic topography during volcano-tectonic interactions. / Doctor of Philosophy / Investigating interactions between active volcanoes and tectonics (fault zones) is important for understanding how continental rifts grow and evolve over time. Modern researchers use geodetic data, geologic models, and computer simulations of rift processes; like volcanic eruptions and fault movement; to understand how stress in transferred and material deforms due to rift activity. We are especially interested in understanding the stress interactions when volcanic eruptions and earthquakes happen together over a short time period. Our projects apply these tools to examine a segment of the largest active continental rift zone, the Natron Rift in the East African Rift System (EARS), to understand more about the details of these volcano-tectonic interactions when continents break apart (rifting). We first present results that stress transferred to the Natron Fault associated with magmatic activity from the volcano Ol Doinyo Lengai may trigger a major fault to move. Next, we continue our investigations into volcano-tectonic interactions by seeing how volcanic properties could affect stress transferred in the Natron Rift region. We choose to initially test stress variations associated with different 1) topography surfaces, 2) material properties, and 3) reservoir volumes associated with the volcano Ol Doinyo Lengai using a more advanced computer modeling approach. This deeper investigation provides information about the individual roles these parameters play in a younger rift region. We present results that topography has the most influence on the stress transferred to the Natron Fault in our models, and that the other parameters did not play a large role in influencing the stress transferred. Finally we work to increase the ability for researchers to perform geodetic studies in the Natron Rift by providing a new method to share surface displacement data at an unprecedented 1 position a second rate (near real-time). This new method is a data broker application called GNSS2CHORDS that can stream cm precision displacement data to an online cybertool called CHORDS. With our models and data provided through open source methods this work contributes significantly to our understanding of volcano-tectonic interactions.

The amount of volatile elements dissolved in silicate melts is a controlling factor in a range of geologic processes, which include hazardous volcanic eruptions, economically-significant ore-forming systems, and global-scale volatile fluxes, which contribute to planetary evolution. While melt volatile contents are important, estimating the origin and fate of volatiles distributed within magmas is challenging because volatiles exsolve from the melt during eruption and are transferred into the atmosphere. Therefore, the stratigraphic record of volcanic and intrusive deposits does not contain direct information regarding the pre-eruptive volatile content of the melt. However, melt inclusions trapped within growing phenocrysts present an opportunity to sample the melt before it has completely degassed. Analysis of melt inclusions is challenging owing to a range of processes which occur after the melt inclusion is trapped and which overprint the original texture and composition of the inclusion at the time of entrapment. Thus, efforts to accurately determine the current composition of the melt inclusion sample and then infer the original composition of the trapped melt which that inclusion represents require a combination of microanalytical, numerical, and/or experimental methods. In Chapter 1, we present a pedagogical approach for estimating the processes that affect the CO2 content of a magma from its origin during melting a C-bearing source material to its exsolution into a free fluid phase during crystallization and degassing. In Chapter 2, we explore different experimental, microanalytical, and numerical methods which may be used to estimate the CO2 contents of melt inclusions that contain fluid bubbles and describe the advantages and disadvantages of each approach. In Chapter 3, we apply some of the methods discussed in the previous chapters to estimate the pre-eruptive volatile content of Haleakala Volcano (Maui) and assess different melting mechanisms that may be active in the Hawaiian plume. / Doctor of Philosophy / Volcanoes are features which form on the Earth’s surface and are located above regions where material melts tens of kilometers (or more) below the surface. The process of melting is studied through laboratory experimentation, and therefore it is possible to estimate the composition of deep subsurface material based on the compositions of volcanic rocks which can be sampled on the Earth's surface. This sub-discipline of geologic research is called "igneous petrology." A fundamental problem in igneous petrology is estimating the volatile content of the Earth's deep interior. Volatile elements are those elements such as hydrogen and carbon, which are stable as gasses in the atmosphere rather than in the mineral components of a rock. It is thought that the gasses produced from volcanic vents, of which the compositions are well known, represent volatile elements which were originally present as dissolved components in the melt. Experiments performed on volcanic rocks have demonstrated that volatile elements can be dissolved in melts at high pressures corresponding to depths within the Earth's crust, and these elements exsolve from the melt when it approaches the surface -- similar to how CO2 can be dissolved in a carbonated beverage, which bubbles out when the beverage is opened. The only geologically-persistent features which preserves the pre-eruptive volatile content of a melt (i.e. how much gas was dissolved before eruption) are droplets of melt which are accidentally trapped within crystals that grow from the melt as it cools near the Earth's surface -- these are called "melt inclusions." While melt inclusions are useful in this regard, they are challenging to apply to geologic problems because they undergo a range of physical and chemical changes after they are trapped, which can alter their composition from the original composition of the melt that was trapped. This dissertation concerns the theory used to infer how volatile elements are distributed within the deep Earth, analytical and numerical methods used to gather relevant information from melt inclusion samples, and an application of these methods to investigate the volatile content of the mantle below Hawaii. Chapter 1 describes a framework for systematically determining the amount of CO2 distrubuted within a given volcanic setting. Chapter 2 compares different methods used to estimate the original volatile content of melt inclusions from Kamchatka, which have formed fluid bubbles -- a common feature present in melt inclusions. Chapter 3 applies the methods described in the first two chapters to estimate how volatile elements are distributed within the Earth's mantle below Hawaii, and how the process of melting transfers them to the Earth's atmosphere.

Thesis (Ph. D.)--California Institute of Technology, 1976. / Includes bibliographical references.

Hannover, University, Diss., 1999.

No description available.

No description available.

Understanding dykes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions. The 2014-15 Bárðarbunga-Holuhraun rifting event comprised the best-monitored dyke intrusion to date and the largest eruption in Iceland in 230 years. Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano, Iceland, along a 48 km path before erupting in the Holuhraun lava field on 29 August 2014. A huge variety of seismicity was produced, including over 30,000 volcano-tectonic earthquakes (VTs) associated with the dyke propagation at ∼ 6 km depth below sea level, and long-period seismicity - both long-period earthquakes (LPs) and tremor - associated with the eruption processes. The Cambridge University seismic network in central Iceland recorded the dyke seismicity in unprecedented detail, allowing high resolution analyses to be carried out. This dissertation comprises two parts: study of 1) the volcano-tectonic dyke-induced seismicity and 2) the long-period seismicity associated with eruption processes. Volcano-tectonic earthquakes induced by the lateral dyke intrusion were relocated, using cross-correlated, sub-sample relative travel times. The ∼ 100 m spatial resolution achieved reveals the complexity of the dyke propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dyke and seismicity. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dyke, and following this - after dyke opening - indicate a relationship with magma pressure changes (i.e. dyke inflation/deflation), followed by a general 'post-opening' decay. Seismicity occurs only at the base of the dyke, where dyke-imposed stresses - combined with the background tectonic stress (from regional extension over > 200 years since last rifting) - are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dyke section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. Long-period earthquakes and tremor were systematically detected and located during the dyke propagation phase and the first week of the eruption. Clusters of highly similar, repetitive LPs were identified, with a peak frequency of ∼ 1 Hz and clear P and S phases followed by a long-duration coda. The source mechanisms were remarkably consistent between clusters and also fundamentally different to those of the VTs. The clusters were accurately located near each of three ice cauldrons (depressions formed by basal melting) that were observed on the surface of Dyngjujökull glacier above the path of the dyke. Most events were in the vicinity of the northernmost cauldron, at shallower depth than the VTs associated with lateral dyke propagation. At the two northerly cauldrons, periods of shallow seismic tremor following the clusters of LPs were also observed. Given that the LPs occurred at ∼ 4 km depth and in swarms during times of dyke-stalling, it is inferred that they result from excitation of magmatic fluid-filled cavities and indicate magma ascent. The tremor may then represent the climax of the vertical melt movement, arising from either rapid, repeated excitation of the same LP cavities, or sub-glacial eruption processes. This long-period seismicity therefore highlights magma pathways between the depth of the dyke-VT earthquakes and the surface. Notably, no tremor is detected associated with each cauldron, despite melt reaching the base of the overlying ice cap, a concern for hazard forecasting.