Seminars & Meetings

Experimental petrology and diffusion chronometry can provide unique insights into the depths at which magmas originate and the rates at which they ascend to the surface. In this talk I will show how the concept of liquidus multiple saturation barometry can be used to determine mid-crustal magma source depths along the Cascades arc. Sr and Ba zoning profiles in plagioclase phenocrysts can then be used to show that magmas ascend from these depths on timescales of a year or less prior to eruption. Implications for crustal magmatic architecture and volcano monitoring will be discussed.

We investigate the rates of magmatic processes using clinopyroxene diffusion chronometry on volcanic products erupted in August 2017 at the end of the 9-month eruption of Bogoslof volcano. The eruptive products contain crystals which exhibit distinct chemical and/or textural boundaries and are occasionally observed in multi-phase crystal clots with shared zoning histories, indicating that the distinct rims of all mineral phases formed contemporaneously. We perform clinopyroxene diffusion chronometry to calculate plagioclase growth rates and determine timescales of magmatic processes.

We investigate the rates of magmatic processes using clinopyroxene diffusion chronometry on volcanic products erupted in August 2017 at the end of the 9-month eruption of Bogoslof volcano. The eruptive products contain crystals which exhibit distinct chemical and/or textural boundaries and are occasionally observed in multi-phase crystal clots with shared zoning histories, indicating that the distinct rims of all mineral phases formed contemporaneously. We perform clinopyroxene diffusion chronometry to calculate plagioclase growth rates and determine timescales of magmatic processes.

Diffusion chronometry modeling can provide insights into timelines of magma formation, potentially down to timescales of days. Current user-friendly programs, however, have limitations, including restrictions to certain minerals, processing platforms or potentially overly prescribed temperature conditions. To enhance wider-scale applicability of this the diffusion chronometry approach, we developed the MSURFED model, which allows users to input a range of parameters and provides a more realistic yet still quantitative approach to fitting diffusion chronometry timescales for studying magma assembly.

The talk will discuss the processes that form large bodies of silicic magma that lead to super-eruptions and will be partly based on the following Nature paper:

van Zalinge ME, Mark DF, Sparks RSJ, Tremblay MM, Keller CB, Cooper FJ, Rust A (2022) Timescales for pluton growth, magma-chamber formation and super-eruptions. Nature 608:87–92. https://doi.org/10.1038/s41586-022-04921-9

We use Sr diffusion in both plagioclase and hornblende to address the long term thermal evolution of the magma system that produced the 74 ka Youngest Toba Tuff (YTT). We find that YTT most plagioclase are recording decades to centuries above temperatures common for producing large volumes of eruptible melt at other large caldera systems, while hornblende may be recording significantly longer durations (up to 5000 years). Finally, we combine these results with pumice matrix glass compositions to show that although the YTT magmatic system was compositionally heterogeneous, it was thermally homogeneous.

Our view of magmatic systems has evolved from liquid-dominated magma chambers to complex crystal-dominated mush systems where eruptible pockets are typically localised and transient. In this new paradigm, erupted crystals and their carrier melts can be interrogated separately to reconstruct magmatic systems in space and time, and the tipping mechanisms that trigger them to erupt. This seminar will ‘deconstruct the mush’ to explore magmatic systems across the upper mantle and crust, across timescales of days to millions of years, and across contrasting tectonic settings.

Plagioclase microantecrysts from the southern Taupo Volcanic Zone were imaged for anorthite and Sr content to sub-micron resolution. We introduce a completely new method of assessing intra- Sr-disequilibria in complexly zoned crystals and show how Fourier Transform modelling of forward diffusion allows approximation of pre-eruptive Sr-contents through „back-diffusion“. Micro-antecryst residence times at magmatic temperatures range from <<2 to <<50 days, suggesting cold storage of these crystals during much of their complex growth and resorption history.

Kelud (Kelut) volcano is one of the most hazardous volcanoes in Indonesia because it produces frequent short-lived and highly explosive eruptions, and rare lava domes. Here I explain why Kelud is a ‘pressure cooker’ volcano, and present new insights into the mechanisms and timescales of recent explosive and effusive eruptions from Kelud.

One of the main potentials of the diffusion chronology is that it allows correlations between timescales of magmatic processes inferred from petrologic data and real-time monitoring signals. However, to do this, these techniques need of samples well constrained under the point of view of the time. One of the tasks of the petrological monitoring is to collect and to investigate samples among which the time relationships are known unequivocally.

In this talk, we present a brief description of the state of the art for petrological monitoring resulting from a recent survey conducted in the framework of the EUROVOLC project. The survey involved eighteen monitoring institutions that include volcano observatories, academia and research laboratories. These institutions monitor volcanoes with a large spectrum of magma composition and eruptive styles, and thus they can be considered representative of the multifaceted petrological monitoring performed worldwide.

After an initial historical perspective, that describes origins, development of these activities over time and some well-known case-histories, we will focus on how petrological monitoring is performed by the different institutions and what participants consider as the major problems. Then we scrutinize the survey results selecting analyses that are fast and easy to acquire (in terms of resources, equipment, and time availability) and provide relevant results in terms of knowledge on the magmatic system and on the eruptive behavior. On this basis we identify the best analytical practices for an efficient petrological monitoring and we propose possible future developments, among which the diffusive chronology plays a key-role.
Talk based on:

Re G, Corsaro RA, D’Oriano C, Pompilio M (2021) Petrological monitoring of active volcanoes: A review of existing procedures to achieve best practices and operative protocols during eruptions. Journal of Volcanology and Geothermal Research 419:107365. https://doi.org/10.1016/j.jvolgeores.2021.107365

Modelling diffusion of Mg in plagioclase is commonly used to estimate the timescales of magmatic processes that operate weeks to decades before eruption. This, however, requires knowledge of how the anorthite composition influences partitioning of Mg. We find that this partitioning relationship depends on the structural state of plagioclase, which in turn controls the shape of Mg diffusion profiles. The meaning of Mg compositional profiles may need to be reinterpreted, which may be important for using plagioclase zoning in order to understand thermal states and magmatic histories at a range of tectonic settings.

Magnesium-silicate post perovskite is thought to be present in and to control the dynamics of the D’’ region. Through a combination of Ab Initio simulation and experiment on isostructural analogues we find that there are up to 8 orders of magnitude of anisotropy in chemical diffusivity. This results in extremely anisotropic diffusion creep with attendant crystallographic preferred orientation development. In addition, coupling between grain shape development and shear rotation might cause grain size reduction during diffusion creep leading to a strong strain-weakening rheology. This could explain many anomalous features of the D’’ region.

The solar wind contains high-energy particles with nearly the solar composition that is a possible source of volatiles in terrestrial bodies in the solar system including H (and D). I will summarize the experimental results of high-energy H implantation to olivine, orthopyroxene and quartz and discuss their implications for hydrogen (and D/H) in Earth and other terrestrial bodies in the solar system. The interpretation of the experimental results and the applications to the solar nebula require the understanding of diffusion in the atomic scale as well as diffusion in the macroscopic scale (diffusion in the turbulent flow).

This will be a rather informal presentation of remembrances of studying kinetics 50 years ago. My career as a petrologist began as Plate Tectonics changed the way geologists looked at large scale processes. At the same time, instrumental developments and computers changed our ability to examine processes on a micro scale. Interest in kinetics grew as part of the resulting expansion of the geosciences. I will discuss these events from the perspective of a young petrologist trying to understand his rocks, as well as the practical and experimental challenges of the time.

Magma ascent rates and volatile budgets are two major factors that control volcanic eruption explosivity and styles. Our recent work has shown that both factors can be determined using volatile chemistry of apatite: a ubiquitous mineral in terrestrial and extra-terrestrial rocks. This talk will introduce a new diffusion chronometer and model (ApTimer) built on high-temperature experiments, instrumental analysis, and simulation of F-Cl-OH multicomponent diffusion in apatite. We applied this chronometer to Cl- and/or F-zoned apatite microphenocrysts from effusive and explosive eruptions at three volcanoes and obtained magma ascent time-rates consistent with those determined previously by different techniques. This apatite chronometer may provide new insights into the cause of effusive-explosive eruption transition at volcanoes and could be enhanced with future experimental and modelling efforts.

Intra-crystal temperature constraints and diffusion timescales from sanidine megacrysts of Taapaca volcano (Chile) put high resolution constraints on the thermal history of the magma reservoir and the associated timescales. This talk will illustrate how these results can be further “exploited” to constrain the dimensional parameters associated with the storage and mobilization of the mushy magma reservoir of Taapaca.

Chemical diffusion induces large isotope fractionations that can be predicted using laboratory diffusion experiments. This talk will illustrate the utility of stable isotopes in determining the contributions of crystal growth vs diffusion in generating mineral zoning. The ability to tease these two processes apart results in diffusion models that are more reliable compared to those that use chemical analyses alone.

The Mg-suite can provide unique constraints to the formation history of the Moon. Here, the pristine troctolite, 76535 is found to have striking heterogeneities. Diffusion chronometry reveals that maximum cooling timescales have to be much shorter than previously estimated.

Developing the ability to recognize how and when a magmatic system that is in a state of unrest evolves toward eruption is a major challenge in volcanology (Sparks & Cashman 2017). Most information about magma migration and accumulation within sub-volcanic plumbing systems is obtained by indirect geophysical observations, such as geodetic and seismic measurements, whilst any direct assessment of magmatic material can only be conducted after eruption commences. The role of the deeper parts of the magmatic system is key in the supply of magma, and is hence of critical interest during the transition from unrest to eruption1. Such regions are poorly-resolved by many geophysical techniques, where spatial resolution at depth may be too coarse to give insights into the spatial distribution of melt on a scale that is relevant to physical models of melt migration. For this reason, details of the transition towards eruption within the deepest parts of volcanic plumbing systems have a poor record of direct observation. By contrast, the magma that will subsequently erupt is a direct witness to those processes. Understanding the behaviour of the deeper part of the magmatic system may therefore require a temporal record of magmatic processes derived from the crystals carried by the magma itself, for combination with geophysical data.

The recent eruption at Fagradalsfjall on the Reykjanes Peninsula in SW Iceland presents an ideal opportunity to compare geophysical and petrological datasets to understand the link between magma mobilization manifested in the crystal record and geophysically observed eruption precursors in the lead-up towards a deep-sourced volcanic eruption.

Sparks RSJ, Cashman KV (2017) Dynamic Magma Systems: Implications for Forecasting Volcanic Activity. ELEMENTS 13:35–40. https://doi.org/10.2113/gselements.13.1.35

Ti-in-zircon diffusion experiments focusing on diffusion parallel to the c-axis reveal a large degree of anisotropy for this system. Between 600 – 950 °C, a typical range for zircon crystallisation, Ti diffusion parallel to the c-axis is ~7.5 – 11 orders of magnitude faster than diffusion perpendicular to the c-axis. Diffusion of Ti in natural zircons will predominantly occur parallel to the c-axis, and the Ti-in-zircon thermometer appears susceptible to diffusive modification under some crustal conditions.

Time-related information of pre-eruptive magmatic processes is locked in the chemical profile of compositionally zoned minerals and can be retrieved by means of elemental diffusion chronometry. However, only the timescale of the outermost rim is commonly resolved, limiting our knowledge of timescales to those directly preceding the eruption. Recent advances in geospeedometry allow to retrieve information from the entire core to rim compositional profile of single crystals providing a complete chronostratigraphy of the recorded pre-eruptive processes. Elemental diffusion chronostratigraphy can be fully resolved for crystals that have spent their lifetime in hot storage. Under this condition, crystals will be kept at the temperature(s) of the eruptible magma(s), and diffusion timescales approximate the storage of the crystal in question in different melt environments allowing an in-depth knowledge of the magmatic system far beyond late-stage pre-eruptive processes.

Fe-Mg interdiffusion in pyroxenes from active volcanoes are used to reconstruct the time-dependent elemental diffusion chronostratigraphies of single crystals and to discuss their implication on magma dynamics and the consequences on eruption style and magnitude. Combining elemental diffusion chronostratigraphy with monitoring data and other petrological, geological, and geophysical constraints at active volcanoes can greatly enhance our capability to inform volcanic hazard assessments.

There is a growing need for understanding the relationship between volcano monitoring – which seeks to mitigate this hazard – and the magmatic processes occurring at depth that initiate volcanic eruptions. Here we use a new literature data compilation and statistical analysis to show that there are significant differences in the composition, volume, style and timescales between eruptions initiated by different mechanisms. Knowledge of the processes that initiate eruptions at a given volcano may thus have significant predictive power.

Mineral zoning and the diffusion of elements across these zones has been widely used to determine the timescales of magmatic processes. Recent experimental work reveals that diffusion in feldspar, a ubiquitous phase in magmatic systems, is more complex than previously understood, reshaping the way we use chronometers to determine meaningful timescales. In this talk I will present a new experimentally derived diffusion chronometer, and apply it to the Lava Creek Tuff supereruption at Yellowstone in order to determine the timing of eruption initiation.

All diffusion in natural melts is complicated multicomponent diffusion. I will present our effort to obtain reliable 6 by 6 diffusion matrix in a 7-component haplobasalt, and 7 by 7 diffusion matrix in an 8-component basalt similar to MORB. It is possible now to roughly predict multicomponent diffusion in basalts. In addition, diffusion of potassium isotopes during multicomponent diffusion will also be discussed.