The dynamics of large-scale silicic magmatic systems: case studies from Mangakino Volcanic Centre, Taupo Volcanic Zone, New Zealand

<p>This thesis research focuses on clast and crystal-specific studies to investigate the pre- and syn-eruptive magmatic processes of two supereruptions in the TVZ: the 1.21 Ma Ongatiti (>500 km3) and the 1.0 Ma Kidnappers (~1200 km3), together with the smaller (~200 km3) 1.0 Ma Rocky Hill eruption from the Mangakino Volcanic Centre (MVC). Crystallisation histories determined through SIMS U-Pb dating of zircons reveal that the paired Kidnappers and Rocky Hill eruptions were products of a common magmatic system, which built over ~200 kyr, in the time break after the Ongatiti eruption. U-Pb age spectra from the Ongatiti show a protracted crystallisation history (over ~250 kyr), in which the majority of zircon crystallised ~100 kyr prior to eruption in a crystal mush. Zircons then ascended with melt during accumulation of the final erupted magma body in the shallow crust. Zircons remained stable in the melt dominant body but underwent little further crystallisation. Zircons from all three systems record common geochemical processes governed by the fractionating assemblage (predominantly plagioclase and amphibole). In particular, the MREE/HREE ratios and Sr concentrations of zircons from the Ongatiti record imply two contrasting source regions governed by different proportions of crystallising amphibole. The in-situ major and trace element chemistry of glass shards and crystals from the Kidnappers fall deposit reveal that magma within the Kidnappers was stored in three discrete bodies, which were systematically tapped during the early stages of eruption. Temperature and pressure (T-P) estimates from amphibole and Fe-Ti oxide equilibria from each magma type are similar and therefore the three magma bodies were adjacent, not vertically stacked, in the crust. Amphibole model T-P estimates range from 770 to 840 °C and 90 to 170 MPa corresponding to pre-eruptive storage depths of ~4.0-6.5 km. The systematic evacuation of the three independent magma bodies implies that there was tectonic triggering and linkage of eruptions. The termination of fall deposition and onset of the overlying ignimbrite emplacement marks the point of widespread caldera collapse and the catastrophic evacuation of a wider variety of melt during the Kidnappers eruption. Pumice compositions from the Kidnappers ignimbrite fall into three groups, two of which (KI-1 and KI-2) can be matched to bodies tapped during the fall phase of the eruption, with the addition of a further discrete batch of lower SiO2 (KI-3) magma. Core-rim textural and chemical variations in major crystal phases (plagioclase, amphibole and orthopyroxene) suggest each compositional group was sourced from a common mush but underwent a unique magmatic history during the development of melt-dominant bodies in the final stages prior to eruption. The field relationships and distinctive appearance of the Rocky Hill ignimbrite (~200 km3 DRE) and the underlying Kidnappers ignimbrite suggests that the two deposits are from distinct eruption events. However, major and trace element chemistry of matrix glass, coupled with the textural and chemical signatures of crystals suggests the magma erupted during the Rocky Hill was generated from the same source or mush zone as the Kidnappers. The two largest melt-dominant bodies (KI-1 and KI-2) within the Kidnappers were renewed, underwent mixing and incorporation of marginal material to form two magma types (RH-1 and RH-2) in the time break prior to the Rocky Hill eruption. Fe-Mg interdiffusion timescales in orthopyroxenes from the Kidnappers and Rocky Hill deposits suggest the establishment of the final melt-dominant bodies, through extraction of melt and crystals from a common mush, occurred within 1000 years, and peaked within centuries of each eruption. In addition, one discrete batch of Kidnappers melt has evidence for interaction with a lesser evolved melt within 50 yrs prior to eruption. This rejuvenation event was not the eruption trigger but may have primed the magma for eruption. The difference in timescales from common zones from both the Kidnappers and Rocky Hill orthopyroxene, recording the same processes reveal the time break between the two eruptions was ~20-40 years. This work highlights the rapidity of rejuvenation and renewal of the melt-dominant bodies within the Kidnappers/Rocky Hill magmatic system. The textural and in-situ compositional signatures of crystals from the Ongatiti ignimbrite imply the final erupted magma body was assembled from a thermally and chemically zoned mush, which extended to the base of the quartzofeldspathic crust (~15km). The mush was close to water saturation and was dominated by amphibole crystallisation. Melt and crystals (including the majority of zircons) were extracted from the mush and ascended to 4-6 km depths during the development of a crystal-rich (20-30%), but melt-dominant body. Significant crystallisation of plagioclase (and lesser proportions of orthopyroxene and amphibole) occurred in an event involving the gradual heating and/or increase of water in the rhyolite, from a broadly andesitic underplated magma. Homogeneous crystal rim and matrix glass compositions imply the final erupted volume of magma was effectively mixed through convection. Eu/Eu* values of whole-rock and matrix glass suggest little crystal-melt separation occurred in the melt-dominant magma body prior to eruption. This work has implications for understanding the generation, storage and eruption of large-scale silicic magma systems. The Ongatiti ignimbrite does not represent either an erupted mush, or a stratified magma chamber, suggesting an alternative model for the development of eruptible magma within large-scale silicic systems. The Kidnappers/Rocky Hill sequence records a complex interplay of multiple melt-dominant bodies, which were established and renewed on rapid timescales. The rapid timescales for the development of melt-dominant bodies and the systematic tapping of magmas in the Kidnappers/Rocky Hill system imply that tectonics may have had a strong external control on the eruptions at Mangakino.</p>

The dynamics of large-scale silicic magmatic systems: case studies from Mangakino Volcanic Centre, Taupo Volcanic Zone, New Zealand

<p>This thesis research focuses on clast and crystal-specific studies to investigate the pre- and syn-eruptive magmatic processes of two supereruptions in the TVZ: the 1.21 Ma Ongatiti (>500 km3) and the 1.0 Ma Kidnappers (~1200 km3), together with the smaller (~200 km3) 1.0 Ma Rocky Hill eruption from the Mangakino Volcanic Centre (MVC). Crystallisation histories determined through SIMS U-Pb dating of zircons reveal that the paired Kidnappers and Rocky Hill eruptions were products of a common magmatic system, which built over ~200 kyr, in the time break after the Ongatiti eruption. U-Pb age spectra from the Ongatiti show a protracted crystallisation history (over ~250 kyr), in which the majority of zircon crystallised ~100 kyr prior to eruption in a crystal mush. Zircons then ascended with melt during accumulation of the final erupted magma body in the shallow crust. Zircons remained stable in the melt dominant body but underwent little further crystallisation. Zircons from all three systems record common geochemical processes governed by the fractionating assemblage (predominantly plagioclase and amphibole). In particular, the MREE/HREE ratios and Sr concentrations of zircons from the Ongatiti record imply two contrasting source regions governed by different proportions of crystallising amphibole. The in-situ major and trace element chemistry of glass shards and crystals from the Kidnappers fall deposit reveal that magma within the Kidnappers was stored in three discrete bodies, which were systematically tapped during the early stages of eruption. Temperature and pressure (T-P) estimates from amphibole and Fe-Ti oxide equilibria from each magma type are similar and therefore the three magma bodies were adjacent, not vertically stacked, in the crust. Amphibole model T-P estimates range from 770 to 840 °C and 90 to 170 MPa corresponding to pre-eruptive storage depths of ~4.0-6.5 km. The systematic evacuation of the three independent magma bodies implies that there was tectonic triggering and linkage of eruptions. The termination of fall deposition and onset of the overlying ignimbrite emplacement marks the point of widespread caldera collapse and the catastrophic evacuation of a wider variety of melt during the Kidnappers eruption. Pumice compositions from the Kidnappers ignimbrite fall into three groups, two of which (KI-1 and KI-2) can be matched to bodies tapped during the fall phase of the eruption, with the addition of a further discrete batch of lower SiO2 (KI-3) magma. Core-rim textural and chemical variations in major crystal phases (plagioclase, amphibole and orthopyroxene) suggest each compositional group was sourced from a common mush but underwent a unique magmatic history during the development of melt-dominant bodies in the final stages prior to eruption. The field relationships and distinctive appearance of the Rocky Hill ignimbrite (~200 km3 DRE) and the underlying Kidnappers ignimbrite suggests that the two deposits are from distinct eruption events. However, major and trace element chemistry of matrix glass, coupled with the textural and chemical signatures of crystals suggests the magma erupted during the Rocky Hill was generated from the same source or mush zone as the Kidnappers. The two largest melt-dominant bodies (KI-1 and KI-2) within the Kidnappers were renewed, underwent mixing and incorporation of marginal material to form two magma types (RH-1 and RH-2) in the time break prior to the Rocky Hill eruption. Fe-Mg interdiffusion timescales in orthopyroxenes from the Kidnappers and Rocky Hill deposits suggest the establishment of the final melt-dominant bodies, through extraction of melt and crystals from a common mush, occurred within 1000 years, and peaked within centuries of each eruption. In addition, one discrete batch of Kidnappers melt has evidence for interaction with a lesser evolved melt within 50 yrs prior to eruption. This rejuvenation event was not the eruption trigger but may have primed the magma for eruption. The difference in timescales from common zones from both the Kidnappers and Rocky Hill orthopyroxene, recording the same processes reveal the time break between the two eruptions was ~20-40 years. This work highlights the rapidity of rejuvenation and renewal of the melt-dominant bodies within the Kidnappers/Rocky Hill magmatic system. The textural and in-situ compositional signatures of crystals from the Ongatiti ignimbrite imply the final erupted magma body was assembled from a thermally and chemically zoned mush, which extended to the base of the quartzofeldspathic crust (~15km). The mush was close to water saturation and was dominated by amphibole crystallisation. Melt and crystals (including the majority of zircons) were extracted from the mush and ascended to 4-6 km depths during the development of a crystal-rich (20-30%), but melt-dominant body. Significant crystallisation of plagioclase (and lesser proportions of orthopyroxene and amphibole) occurred in an event involving the gradual heating and/or increase of water in the rhyolite, from a broadly andesitic underplated magma. Homogeneous crystal rim and matrix glass compositions imply the final erupted volume of magma was effectively mixed through convection. Eu/Eu* values of whole-rock and matrix glass suggest little crystal-melt separation occurred in the melt-dominant magma body prior to eruption. This work has implications for understanding the generation, storage and eruption of large-scale silicic magma systems. The Ongatiti ignimbrite does not represent either an erupted mush, or a stratified magma chamber, suggesting an alternative model for the development of eruptible magma within large-scale silicic systems. The Kidnappers/Rocky Hill sequence records a complex interplay of multiple melt-dominant bodies, which were established and renewed on rapid timescales. The rapid timescales for the development of melt-dominant bodies and the systematic tapping of magmas in the Kidnappers/Rocky Hill system imply that tectonics may have had a strong external control on the eruptions at Mangakino.</p>

INVESTIGATION OF THE EFFECT OF OXIDE ADDITIVES ON THE PROPERTIES OF HEAT-RESISTANT GLASS-CRYSTAL COATING

Experimental compositions of coatings based on SiO2–Al2O3–MgO matrix glass and modifying additives are considered. A number of refractory metal oxides were selected as modifying additives. The influence of these additives on the properties of the coating melt, such as the spreadability and the wetting edge angle, as well as the oxidability of the resulting compositions, is studied. It was found that the experimental coating modified with aluminum oxide has the best protective properties. The introduction of modifying additives in quantities of more than 5 % is considered inappropriate.

Design and Characteristic Analysis of Amalgamated Transparent Materials for Armor Structures Using Defeating Ballistic Experimentation

In armored platforms industry, the dominant material solution for ballistic transparency protection applications is relatively low-cost polycarbonate matrix glass. This research work aims to investigate the effects of geometrical designs of the amalgamated layers, engineering characteristics of the materials, and the interaction of both on the ballistic resistance of the transparent armor. The resulted models are used to analyze the strength feasibility of the material in the cost base. Ballistic measurements over a wide range of impact velocities including those well above the ballistic limits are deployed to the model. Under simple loading conditions, the polycarbonate matrix glass or ceramic can be regarded as elastic-brittle materials, however, when considering ballistic impacts the post-yield response of the ceramic becomes significant. A post-yield response model of ceramic materials is used for simulating the characteristics. The model incorporates the effect of damage on residual material strength and the resulting bulking during the compressive failure of the ceramic. A combination of relevant factors including the ability to dissipate ballistic energy and manufacturing processes was considered for the proper evaluation and selection of the armor. The model has been implemented into computer software to predict unsuccessful solutions and optimize the amalgamation with capabilities of defeating a wider range of ballistic impacts. The results will show more physical insight of the behavior and performance of the complex armor systems and provide guidelines/principles for the design and selection of the constituent materials.