Kelly Russell

Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.


Research Classification

Research Interests

magma rheology
geochemical thermodynamics

Relevant Degree Programs

Research Options

I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.

Research Methodology

field investigations

Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Glaciovolcanism in the Garibaldi volcanic belt (2020)

This thesis investigates glaciovolcanism in the Garibaldi volcanic belt (GVB) of southwestern British Columbia (SWBC), Canada. Field observations and modelling are used to investigate: i) the paleoenvironmental implications of glaciovolcanism in SWBC, ii) volcanic eruption processes in glaciovolcanic environments, and iii) causal linkages between the volcanic eruptions and the growth and decay of terrestrial ice masses. Throughout the Pleistocene, the GVB has experienced multiple alpine and continental glaciations. The GVB comprises >100 Quaternary volcanoes and much of the character of this volcanism is ascribed to the range of magma compositions (alkaline basalt to rhyolite), to the extreme relief of the landscape, and to interactions with ice. The three key findings are: i) The GVB volcanoes are established as a powerful proxy for the local paleoenvironment. The volcanic deposits are used in conjunction with a geometric model for mountain glacier growth and retreat to inform on the presence, thickness, and transient properties of the Cordilleran Ice Sheet over the last 1 Ma. ii) Studies of two effusive glaciovolcanoes (the Lillooet Glacier basalts, and the Table) show that eruption style and deposit morphology are strongly influenced by the nature of heat exchange between the erupted lava and the ice. Specifically, meltwater drainage attending eruptions exerts a critical control on eruptive behaviour (i.e., dictating the ephemeral presence of an englacial lake). Lava-dominated tuyas, may be constructed from eruptions involving within-ice dike injection, steep, well-drained bedrock topography and endogenous, englacial inflation of the massif. iii) Transient growth and decay of terrestrial ice masses can influence the timing, size and distribution of eruptions. Specifically, glacier-induced deformation of topography may impart local, shallow crustal stresses which influence eruption frequency, eruption size and vent distribution, depending on the rheology of the bedrock and the geometry of the topography. At the scale of the crust, transient loading and unloading of ice sheets may act as a glacial pump, bending the crust downwards during loading (causing a suppression in eruptions) and allowing the crust to rebound during unloading (causing an increase in eruptions). Supplementary materials available at:

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The timescales and consequences of solid-state sintering in volcanic systems (2020)

The permeability of rocks controls the movement of fluids and distribution of pore pressure in Earth’s crust. In volcanic systems the eruptive behavior of silicate magmas is governed by the volume and pressure state of magmatic gases. Reductions in permeability can promote explosivity. At the elevated pressure-temperature conditions endemic to volcanic systems, permeable pathways are ephemeral and can be destroyed by densification processes. The prediction of the intensity and timing of explosive eruptions depends on understanding the mechanisms that create and destroy permeable pathways, and their operational timescales. Solid-state sintering is a diffusion-driven process that converts unconsolidated, crystalline aggregates into dense, low-permeability composites. Elevated temperatures and pressures and substantial dwell times facilitate densification and lithification by solid-state sintering. However, solid-state sintering has largely been discounted in volcanic systems because densification timescales were assumed to be long. In this dissertation I show, for the first time, that solid-state sintering occurs in volcanic settings and on timescales short enough to influence volcanic activity. I use the chemistry, mineral contents, physical properties and microstructures of volcanic shear zones exhumed during two dome-building eruptions to show that they were densified and lithified within the volcanic conduit as a result of solid-state sintering. Reconstructions of each of the eruptions indicate sintering occurred on the timescale of magma ascent (months to years). I also use hot pressing experiments conducted at volcanic temperature-pressure conditions to further constrain the timescale of densification by solid-state sintering: the experiments produce dense, low-permeability rocks over periods of hours to days, and reproduce the dominant textures and properties of naturally-sintered volcanic rocks. The experimental dataset is the basis of a quantitative model that predicts the time-dependent evolution of material density as a result of solid-state sintering. Overall, I identify solid-state sintering as a viable, unrecognized mechanism driving rapid permeability loss and material strengthening in volcanic settings. Densification and lithification as a result of solid-state sintering hinder fluid flow and modulate eruptive behavior, including promoting cyclical explosivity. Finally, my work challenges the perception that crystal-rich aggregates in volcanic settings are persistently permeable and weak areas.

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Recovery of geochemical processes in komatiites using linear algebraic methods (2018)

The metasomatic reactions responsible for the mineralogical and chemical alteration of komatiites have not been fully identified. The geochemical effects of these reactions inhibit recovery of the nature and extent of magmatic processes recorded by komatiite rocks. Metasomatism is a challenge in lithogeochemical research because protolith variability and metasomatism together define high-dimensional geochemical spaces. Standard methods that require a conserved element are of limited use, as conserved elements may not be present. This work develops and applies linear algebraic techniques to test mass transfer hypotheses against whole rock compositions without assumptions of elemental behaviour. The methods enabled quantification of the stoichiometry and the relative effects of magmatic and metasomatic processes in komatiites. Such processes include magmatic differentiation, serpentinization, and breakdown of clinopyroxene to actinolite. Three main findings are: (1) geochemical and petrological evidence exists for within-flow differentiation and the possibility of lateral continuity between komatiite and komatiitic basalt flows; (2) serpentinization occurred neither by isochemical nor fully metasomatic processes in a lava flow from Pyke Hill in the Abitibi greenstone belt; and (3) small magnitudes of metasomatic reactions are sufficient to modify primary geochemical signals, such that their neglect in geochemical interpretation could lead to incorrect conclusions. Future studies could delve deeper into the possibility of lateral continuity between komatiites and komatiitic basalts, and expand determination of viable serpentinization reactions to a wider range of localities and lithologies.

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Volcanology of the A154N kimberlite at Diavik : implications for eruption dynamics (2009)

Eruptions of kimberlite volcanoes are a poorly-understood phenomena, as there been no historical eruptions of kimberlite, and primary deposits and edifices ofkimberlite volcanoes are rarely preserved. In particular, the styles of explosion, magmafragmentation, and primary deposition of kimberlite remain unclear. This thesiscomprises field and laboratory study of five kimberlite deposits within the A154Nkimberlite volcano at Diavik, NWT, Canada. These studies provide critical descriptiveand semi-quantitative data on the geometries, component variations, and relative agerelationshipsof deposits. These data are collected in order to link volcanic deposits witheruption processes in the following ways:A) Pyroclastic kimberlite hosted by the A154N pipe is shown to derive from adifferent kimberlite volcano. Thus, kimberlite volcanoes can act as receptacles forprimary volcanic products from the eruptions of adjacent kimberlite pipes, leading to a‘cross-fertilizing’ distribution of magma batches.B) Image analysis, based on manual and computer-assisted digitization, is used toestablish characteristic properties of olivine crystals in intrusive coherent kimberlite,including modal %, size range, shape variability, and population parameters. Theseproperties serve as a baseline in understanding kimberlite eruption style andfragmentation.C) Study of A154N deposits documents phase separation of kimberlite magmas intime and space during ascent and records an evolution in phase proportions (crystals:melt: gas) within and/or between emplacement events. Phase separation can determinethe surface expression of kimberlite volcanoes, the degree of melt separation from olivinecrystals during eruption and, thus, the amount of preserved crystallized kimberlite aroundolivine crystals in deposits.D) Measured and estimated physical properties of kimberlite magmas arecombined with 3-D models for conduit geometry to show eruption durations of minutesto hours for the A154N volcano.E) Observations of primary pyroclastic products in kimberlite deposits showeruptions can both modify the sizes, shapes and distributions of olivine crystals andseparate melt from olivine. Relative changes in the proportion of these two parameters aspreserved in deposits may serve as a proxy for kimberlite eruption intensity.Finally, these volcanic processes are shown to have direct implications for thedistribution of diamonds within kimberlite pipes.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Attrition of mantle cargo during kimberlite ascent: insights from analogue experiments (2020)

Kimberlite magmas transport mantle cargo in the form of xenoliths and xenocrysts to the surface of the Earth. Due to the lack of recent kimberlite eruptions and unanswered questions concerning melt composition and magma rheology, the mechanisms supporting efficient ascent of these cargo-rich magmas remains enigmatic. Although olivine is the dominant mineral phase in kimberlite, given the polymineralic nature of mantle xenoliths, xenocrysts are transported as a multi-mineral mixture. Within the ascending dyke, high particle concentrations and high velocities resulting in turbulent flow provides an environment for frequent particle-particle interaction. Xenocryst morphologies, textures and size distributions observed in kimberlite deposits are not reflective of how they occur in xenoliths and are therefore modified during ascent to the surface. The degree of modification of each mineral varies and is a function of its chemical and physical properties. Here I present a series of analogue attrition experiments on the mantle minerals: olivine, orthopyroxene, clinopyroxene, garnet and diamond designed to inform on the ascent of kimberlite magmas. Data is collected on particle size distributions, particle morphologies and particle velocities. Natural xenocrysts extracted from coherent kimberlite reveal remarkably similar surface features and morphologies to that of the experiments suggesting that attrition indeed operates during kimberlite ascent. Kimberlite ascent velocities are estimated by using a scaling analysis of the experiment conditions and by investigating impact pits observed on the surfaces of kimberlitic olivine and garnet xenocrysts. Both methods result in calculated ascent velocities of ~ 4 m s-1. In mineral mixtures, cleavage is shown to be a controlling factor in determining attrition rates whereby minerals with cleavage undergo accelerated breakdown. I suggest that the accelerated breakdown of orthopyroxene increases assimilation rates, contributing to the onset of turbulent ascent.

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Temperature-pressure-composition model for melt viscosity in the Di-An-Ab system (2020)

A model for the viscosity (η) of melts in the system CaMgSi₂O₆-CaAl₂Si₂O₈-NaAlSi₃O₈(Di-An-Ab) based on data compiled from the literature is presented. The model is calibrated on560 measurements of melt viscosity at 1 bar pressure on 40 individual melt compositions and 303measurements obtained at high pressures on 18 melt compositions. The model uses the Tammann-Vogel- Fulcher equation for temperature (T)- dependence and accounts for variations in melt composition (X) and pressure (P). At ambient pressures, the model spans 15 orders of magnitude of η, a T range of 933-2450 K, and reproduces the datasets well (RMSE = 0.26). The high-P model is calibrated over a T range of 970-2470 K and P range of 50 to 13100 MPa and reproduces the high-pressure data sets to within (larger) experimental uncertainties (RMSE = 0.35). The T-P-X model predicts the glass transition temperatures (Tg), melt fragilities (m) and activation energies (Ea) across the ternary with increasing P. Used in conjunction with chemical proxies for melt structural organization (i.e. SM and NBO/T), the model informs on changes in melt polymerization as functions of T, X, and P. Di-An-Ab melts with SM values > 25 have positive pressure coefficients and show a minimal to substantial increase in viscosity with increasing P. Melts with SM less than 25 show negative P-coefficients indicating a decrease in viscosity with increasing P. The P-effect might be correlated with the degree of polymerization and explained by the increasing coordination numbers of silicate and aluminum cations at elevated pressures. Model values of Tg for Di-An-Ab melts range between 930 K and 1130 K at ambient conditions; whilst at elevated pressures, Tg values are depressed for highly polymerized melts by as much as 150K at 5000 MPa but are higher for more depolymerized melts (i.e. SM > 25). A comparison of the liquidus surface topology for the ternary system to the corresponding isokoms of viscosity shows the relative effects of X and T on melt viscosity to be highly varied.

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The Cordilleran lithosphere beneath south-central British Columbia: insights from two xenolith suites (2019)

Mantle-derived peridotite xenoliths represent a valuable source of information about the structure, chemistry, origin, and evolution of the mantle lithosphere underlying various tectonic environments. Xenolith-bearing volcanic suites at Mt. Timothy and Summit Lake in south-central British Columbia are two particularly intriguing sites for evaluating the nature of the lithosphere beneath the southern Canadian Cordillera. The peridotite xenoliths at Mt. Timothy are texturally and mineralogically homogenous, while the xenoliths from Summit Lake contain a greater variety of textures and rock types, both mantle-derived and crustal. These peridotites are similar geochemically to other peridotite datasets from the Canadian Cordillera, indicating a geochemically homogenous mantle lithosphere and evolution from a fertile peridotite source. Enrichments of MREEs and LREEs in certain samples may indicate that these rocks were subject to a small degree of metasomatism. The geochemical signatures of the pyroxenes in these xenoliths are indicative of an orogenic lithospheric mantle. Temperatures and depths of equilibration for these peridotites have been determined by combining a two-pyroxene geothermometer with a geotherm constructed from several regional geophysical parameters. The Mt. Timothy peridotites sample an extensive window of mantle lithosphere ranging from the Moho (813 °C; 33 km) to relatively deep within the mantle lithosphere (1091 °C; 50.9 km), while the Summit Lake peridotites sample a very deep and narrow window of mantle lithosphere (1061 °C to 1119 °C; 49.0 km to 52.7 km). The window sampled by Mt. Timothy is most similar to a number of other xenolith suites scattered across the southern Cordillera, while the comparatively unique sampling range of the Summit Lake suite shares certain mineralogical characteristics with other xenolith suites straddling the boundary between the Cordillera and the North American craton.

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The glaciovolcanic origin of Kima'Kho mountain, northern British Columbia (2019)

Kima’Kho is one of several englacially erupted volcanoes located on the Tuya-Kawdy plateau in northwestern British Columbia. Evidence that Kima’Kho erupted into ice is recorded by lithofacies and stratigraphical features indicating deposition into a sustained but fluctuating englacial lake. Mapping of the edifice alongside analysis of an extensive sample suite, has elucidated the first in-depth model of physical growth for this glaciovolcano within the context of a reconstructed englacial lake. Four major stratigraphic units were mapped: lapilli tuffs (Lt₁/Lt₂), altered pillow bearing tuff breccias (Tb₁/Tb₂), basalt lavas (L₂/L₃/L₄), including pillow basalts (L₁), and basalt intrusions (IDS). This work also introduces new geochronological data and integrates stratigraphical relationships alongside geochemical data, to reconstruct volcanological evolution through time.⁴⁰Ar/³⁹Ar data indicate Kima’Kho formed ~1980 ka with an unexpected late phase of intrusive activity. This is demonstrated by cross-cutting relationships, variation in petrography and a chemical evolution describing an outlying group of evolved dykes, distinct and separate from other stratigraphical units. Mapping of Kima’Kho has defined six points in stratigraphic time where the englacial lake level can be established during the growth of the volcanic edifice. The first lake level recorded is associated with the initial explosive phase of eruption which formed a pyroclastic tephra cone that hosts a ‘passage zone’ – an inferred surface delineating the transition between sub-aqueous and sub-aerial deposition. Dynamic fluctuations in lake level are recorded by two later passage zones exposed at lower elevations on the flanks of the cone and also within effusive units. Effusive eruption is represented by basaltic pillow tuff breccias and subaerial lavas. The three lattermost passage zones are marked by the contact between these tuff breccias and lavas and record a second significant decline in lake level followed by relative stability, at which point the effusive lavas were able to cap the brecciated deposits. The decryption of the stratigraphy to this complex ancient glaciovolcano provides many insights that cannot be recovered from modern glaciovolcanoes, which are obscured by their present-day ice fields. This study demonstrates the feasibility of reconstructing glacial conditions through the proxy of englacial lake fluctuations recorded in the glaciovolcanic deposits.

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Water solubility and bubble growth dynamics in rhyolitic silicate melts at atmospheric pressure (2015)

This thesis is a high-temperature, low-pressure experimental study that quantifies the temperature-dependence of water (H₂O) solubility in a rhyolitic melt at atmospheric pressure, and assesses the sensitivity of the water exsolution and bubble growth processes to thermodynamic and kinetic parameters. In the investigation of H₂O solubility I defined the magnitude of retrograde solubility (-7.1x10-³ wt% H₂O per 100°C) and estimated the enthalpy and entropy of the H₂O exsolution reaction (ΔH⁰ = +17.8 kJ mol-¹, ΔS⁰ = 107 J K-¹ mol-¹). I also modelled the implications of retrograde solubility for the glass transition temperature (Tg) and outline the potential effect on cooling volcanic bodies at surface- and conduit-relevant pressures if cooling is slow enough to facilitate H2O resorption. In my investigation of bubble growth dynamics and the vesiculation process in my experimental products I recalibrated the estimates of H₂O exsolution enthalpy and entropy (ΔH⁰ = +18.5 kJ mol-¹, ΔS⁰ = 108 J K-¹ mol-¹). Additionally I identified the viscosity (η) dependence of average volumetric growth rate (dV/dt) (log dV/dt = -0.79 log η + 4.95) and have calculated the time to develop 60% porosity for melts of varying viscosities at conduit-relevant pressures that are up to 15% oversaturated with H₂O. By dismantling a complex system and individually investigating the behaviours of dissolved and exsolved H₂O I have developed models that can be used to study volcanic hazards past, present and future.

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Constraints on formation of columnar joints in basaltic lava (2013)

Columnar joints form as a brittle relaxation response to tensile stresses within cooling lava flows and magma bodies, and are found in lavas that vary greatly in chemistry and outcrop geometry. However, columnar joints do not form in all cooling igneous rocks, and the specific conditions under which columnar joints form are unknown. In this study, outcrops containing columns in the Cheakamus Valley basalt flows near Whistler, BC are studied, and the size, orientation, and distribution of columns is recorded. Forward numerical models using the finite element method are created with Matlab using the Partial Differential Equation Toolbox to model the outcrops in the Whistler field area, and determine the cooling rates (∂T/∂t) and thermal gradients (∂T/∂x) experienced by the lava flows during their formation. High temperature experimentation involving basalt rock samples is then used to determine the cooling rates and thermal gradients present during the cooling of these samples under a variety of naturally occurring conditions. This study finds that noticeable differences in the distribution of columns within an outcrop occur only when there are large differences in cooling rates between the upper and lower outcrop surfaces. Modeling shows that the cooling rates must differ by approximately an order of magnitude. High temperature experiments show that extremely high cooling rates (especially in the small sample sizes used in this study) between approximately 700 to 800 ˚C are necessary for the formation of columnar joints.

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Experimental investigation of subsurface fragmentation processes (2013)

Results of a rock deformation study designed to investigate the energy budgets of glass fragmentation under triaxial conditions are presented. This work comprises a series of room-temperature experiments designed to explore the fundamental mechanical behaviour of natural (obsidian) and synthetic glasses (Pyrex) under confining pressures of 0.1 - 100 MPa and at displacement rates of 40μm/s. The results quantify the amount of energy stored in the samples prior to failure, and establish a relationship between grain-size distributions of experimental-products (D-values) and the stress drop at failure. The relationship found for compressive fragmentation is significantly different from the relationship between D-values and energy densities established by previous authors for decompressive fragmentation. Furthermore, I show that natural glasses have less potential to store elastic energy after fragmentation than synthetic glasses. However, the stress storage capacity of natural glass can be enhanced (approaching synthetic glasses) through heat-treatment. The evolution of the physical properties (strain, porosity, permeability and ultrasonic wave velocities) of conduit breccia deposits during compaction is addressed. Compaction produces strongly anisotropic materials, and the measured physical properties are controlled by this anisotropy. Measurements of permeability are up to two orders of magnitude higher and seismic wave velocities up to twice as fast along the direction of elongation. Measurements of physical properties are combined with models describing the timescales of porosity loss and from that, the timescales of permeability reduction and re-pressurization of the edifice are discussed.

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Thermomechanical milling of lithics in volcanic conduits (2013)

Pyroclastic deposits resulting from explosive volcanic eruptions commonly contain clasts originating from the conduit wall rocks, which were entrained into the rapidly ascending stream of erupting material. These particles are termed accessory lithic clasts. Previous studies of the relative abundances and compositions of accessory lithic clasts have been used to identify the subsurface wall rocks of the volcanic conduit, to document variations in eruptive intensity, or to track changes in conduit or vent geometry over the course of the eruption. However, the morphological properties of accessory lithic clasts are largely ignored and offer an unused means of studying the processes operating in the conduit during explosive eruptions. During a volcanic eruption, wall rocks are violently fragmented to produce clasts that are incorporated into a hot, high velocity, particle-laden gas jet. There the clasts are subjected to elevated temperatures, blasting by volcanic ash, and occasional collisions with other large particles or with the conduit walls. The resultant morphologies of the accessory lithic clasts will be influenced by 1) the intrinsic physical properties of the clasts in question; 2) the specific physical and thermal processes to which the clasts were subjected within the conduit; and 3) the residence times of the clasts within the conduit. The 2360 B.P. Pebble Creek Formation of the Mount Meager Volcanic Complex in SW British Columbia is the product of the most recent explosive eruption in Canada. This formation includes a widespread pumice fallout deposit containing anomalously rounded and smoothed monzogranite accessory lithic clasts. In this study, I seek to explain the unusual shapes and surface textures of these clasts through detailed field work, analysis of sample morphology, and the computation of likely conditions within the conduit. My aim is to produce a comprehensive, mechanistic model of how these lithic clasts were reshaped within the volcanic conduit.

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The Eastgate-Whipsaw metamorphic belt as Paleozoic underpinnings to the Nicola Group (2012)

The enigmatic Eastgate-Whipsaw metamorphic belt (EWm belt) is located on the western margin of the Late Triassic to Early Jurassic Nicola Group’s southernmost exposure in the Princeton area of south-central B.C. (NTS 092H/SE). Previously affiliated to the Nicola Group, new Early Permian ages of 281.3 ± 3.3 Ma and 282.7 ± 3.7 Ma show the EWm belt to be significantly older and is likely a southern manifestation of the Late Paleozoic Harper Ranch Group. This suggests a previously unrecognized potential in the Harper Ranch for hosting VHMS-style mineralization.The belt comprises metamorphically deformed, upper greenschist to lower amphibolite facies volcanic and volcanic-derived sedimentary rocks as well as pre- to syn-deformational intrusive phases. These rock types are divided into: 1) mafic volcanic amphibole-rich schists defining the western margin of the belt; 2) a thick, south-central package of quartzofeldspathic volcanic-derived sedimentary schists that transition northward into 3) a series of intercalated volcanic-derived sedimentary schists; 4) mafic volcanic amphibole (chlorite)-epidote schists on the south-east margin of the EWm belt; 5) a north-eastern package of felsic volcanic and volcanically-derived sedimentary schists that contain relict quartz and plagioclase phenocrysts, and 6) consanguinous meta-gabbro and foliated plagioclase porphyry intrusions of unknown ages. The EWm belt originated within an intra-arc or back-arc marine setting, as two geochemically distinct volcanic types. The eastern type 1 volcanic rocks comprise calkalkaline and tholeiitic compositions from LREE-enriched island arc basalts. The western type 2 volcanic rocks comprise a suite of back (or intra)-arc basin basalts. A complex set of foliations, the result of strong metamorphic deformation, is preserved within minor rock types of the EWm belt. The foliation set includes: 1) a dominant N-S, steeply westward dipping S₂ foliation that is predominantly continuous but also develops into differentiated crenulation cleavages, 2) a shallow east-dipping S₁ that is crenulated and progressively dextrally rotated by S₂-associated deformation, 3) a poorly-developed S₃ fabric that shallows the dominant S₂ foliation on the eastern side of the EWm belt. Equal metamorphic temperatures, equivalent to the greenschist to amphibolite facies transition, were established across the width of the EWm belt.

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The Nature and Evolution of Conduit Faults in the 2004-2008 Mount St Helen's Lava Dome Eruption (2012)

Mount St. Helens reawakened 24 years after erupting in the 1980’s. This effusive eruption produced 95 million cubic meters of dacite in the form of 7 discrete, competent spines or domes of lava between September 2004- June 2008. The spines comprise low-porosity dacite that is inferred to have crystallized at a depth of about 1 km and are enveloped by a 1-3 meter carapace of fault gouge. The rate of linear extrusion of the spines peaked at 11 m/day in November 2004 and subsequently slowed to
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Carbonated Mantle Lithosphere in the Western Canadian Cordillera (2010)

Accessory minerals such as carbonates and sulfides are important indicators of metasomatic enrichment events in the mantle lithosphere and ultimately control mantle melting. However, these phases are rarely expressed modally in mantle-derived peridotitic xenoliths. Here we report on a unique occurrence of primary mantle-derived carbonate preserved in spinel peridotite xenoliths within a 19 Ma basanite dike. The dike, defined as part of the Cheslatta Lake suite, intrudes Jurassic volcaniclastic rocks near the Intermontane - Coast Belt boundary in western British Columbia, and contains primary magmatic calcite. The peridotite xenoliths are concentrated in a 4 metre interval where the dike is narrowest and are dominated by lherzolite, with less abundant harzburgite, dunite, and websterite. Thermometry (Taylor, 1998) produces paleoequilibration temperatures of 792 to 1044 °C, corresponding to approximately 32 to 49 km depth on an average geotherm for warm, thin Cordilleran-style lithosphere. Magnesian calcite occurs in all of the 51 xenoliths examined. The Mg-calcite appears as intergranular grains that appear to have been in textural equilibrium with neighbouring minerals, as inclusions, and as fracture-filling veins, commonly in association with pentlandite and chalcopyrite. Carbon-oxygen isotopic compositions of carbonates from the dike, wall rock, and xenoliths indicates that each have distinct compositions. Oxygen isotopic compositions of the xenoliths’ carbonate indicates that, consistent with textural observations, the carbonates have equilibrated with the host mantle, having δ¹⁸O compositions less than 3 ‰ greater than compositions interpreted for primary mantle-derived carbonatites. In addition, carbonates from the mantle xenoliths fall into two separate groups identified by different δ¹³C and ⁸⁷Sr/⁸⁶Sr isotopic compositions, indicating different sources for carbonate in the two xenolith groups, and thus multiple enrichment events. Strontium isotopic ratios also show that the dike scavenged carbonate from disaggregated mantle xenoliths, becoming enriched in CO₂. Timing of enrichment is unconstrained, and no relationships between the host magma and mantle-derived xenoliths is required, contrasting with other studies. A plausible metasomatic agent is a carbonate melt with associated monosulfide solution, derived from the subduction of oceanic crust beneath North America during Coast Plutonic Belt magmatism, when Mt. Preston was in an arc to back arc position.

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Volcanic facies architecture of the Chilcotin Group basalts at Chasm Provincial Park, British Columbia (2010)

The Chilcotin Group basalt (CGB) of south-central British Columbia, Canada defines a medium-sized igneous province (ca. 17, 000 km²), characterized by basaltic lavas, volcaniclastic deposits, and paleosols with minor ash deposits. The CGB has previously been mapped only at reconnasissance scale (1:250 000), and most studies concentrated on geochemical and petrological studies; no stratigraphic relationships or volcanological models were attempted. Chasm canyon exposes one of the thickest successions of the CGB. Here, I explicate the volcanic facies architecture at Chasm to reconstruct the emplacement history and volcanism in the Neogene using geological mapping, cross-sections, and graphic logs. Specifically, seven discrete facies are recognized. The coherent facies are: i) vesicular/amygdaloidal pahoehoe lobes; ii) columnar-jointed, sheet-like lava; and iii) intact basaltic pillow lava. The clastic facies are: iv) paleosols; v) pillow-fragment breccia; vi) hyaloclastite; and vii) lacustrine sandstone. Facies are grouped into broad facies associations including the subaerial facies and interstratified subaqueous and subaerial facies. The subaqueous facies are a minor component in the canyon stratigraphy. The geometry of the lavas is indicative of the eruptive style of volcanism at Chasm, which defines the volcanic facies architecture. Four architectural elements have been observed: i) tabular-classic (TC), which represents a steady continuous supply of subaerial effusive basaltic lavas; ii) compound-braided (CB), which is typical of a shield volcano where anastomosing, branching flow fields result; iii) transitional-mixed, a combination of TC- and CB-type suggestive of bimodal emplacement, perhaps sourced from coalesced shield volcanoes and flank fissures; and iv) foreset-bedded indicative of subaqueous lavas. The exposed rocks record the evolution of CGB volcanism through ten distinct eruptive episodes and intermittent lakes, with periods of quiescence characterized by the paleosol development. Whole-rock Ar-Ar dates were obtained; the duration of volcanism is calculated as 1.28 ± 0.61 m.y. Emplacement is suggestive of shield volcanoes and small fissure eruptions with a northerly flow direction. Laterally extensive paleosols, classified as Brunisolic soils, were examined closely and display a range of morphological features suggestive of the paleo-environment. Lateral variability amongst paleosols have been mapped over a distance of more than 8 km, including a subqueous to subaerial transition.

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