Zoned phenocrysts in volcanic rocks potentially provide an archive of magmatic processes. As a crystal grows and comes into contact with different melt batches, the chemical and textural signature of this journey is recorded within its crystal lattice. The timescale of some magmatic processes can be investigated through the relaxation of chemical gradients across crystal growth zones through the application of diffusion modeling techniques. One of the current limitations to diffusion modeling is the spatial and analytical resolution of the chemical profile that conventional techniques such as electron probe microanalyzer (EPMA), dynamic secondary ion mass spectrometry (SIMS), and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) can achieve. Here, for the first time, we present time-of-flight (TOF) SIMS (TOF-SIMS) data for zoning of orthopyroxene crystals from the May 1982 eruption of Mount St. Helens volcano, U.S.A., and cross-calibrate these data between backscattered electron images and EPMA. TOF-SIMS has the advantage of being able to achieve micrometer to nanoscale spatial resolution of major elements as well as analyses of light elements, such as Li, and trace and minor elements (Na, K, and Ni) at concentrations that cannot be achieved by EPMA, provided that convolution (overlap) effects and polyatomic mass inferences are carefully considered. With TOF-SIMS analyses we identified zoning of Li on a spatial scale (ca. 5-10 μm) that would be inaccessible to most other conventional analytical techniques. Preliminary results indicate that Li, a fast-diffusing element, may be introduced to the crystals in the minutes, hours, or days prior to eruption and may provide insights into pre-eruptive magmatic processes. Thus, TOF-SIMS has the potential to be a powerful tool for obtaining minor and trace element profiles across compositional interfaces within crystals at high-spatial resolution.
The Whakamaru eruption is the largest-volume eruption known to have originated from the hyper-productive Taupo Volcanic Zone, New Zealand. Major, minor and trace element concentrations of plagioclase crystals and cathodoluminescence images, used as a proxy for Ti concentrations in quartz crystals, have been used to explore their chemical zonation. Three plagioclase populations are identified. Group 1 crystals are characterized by inherited cores of composition An45–60, Ba 115–650 ppm and La 3–9 ppm, rims of c. An30, Ba 450–800 ppm and La 7–10 ppm and the presence of a thin overgrowth rim on several crystals cores. Group 2 crystals are oscillatory-zoned plagioclases of composition An30–40, Ba 450–730 ppm and La 8·5–9·5 ppm. Group 3 plagioclase crystals have cores of An25–35 and rims of An20–25 and low Sr contents (280–480 ppm). From the chemical composition of these plagioclase crystals, four physicochemically distinct rhyolitic melts are identified: (1) an andesitic progenitor melt in which the cores of Group 1 crystals crystallized; (2) a greywacke melt or greywacke protolith melt responsible for narrow overgrowth rims on Group 1 crystal cores; (3) melt derived from the rejuvenation of a mature crystal mush body from which Group 3 plagioclase crystals crystallized; (4) a final, rhyolitic melt created by the amalgamation of varying proportions of the andesitic, greywacke-derived and rejuvenated melts with subsequent, open-system fractional crystallization of a plagioclase-dominant crystal assemblage. Cathodoluminescence imaging of quartz crystals reveals complex zonation, the result of a dynamic crystallization history from potentially polygenetic sources. Diffusion modelling of the greyscale intensity of cathodoluminescence images (as a proxy for Ti content) for a selection of bright core–rim interfaces of quartz crystals suggests that renewed quartz growth at the rim zones occurred <300 years (peak likelihood 50–70 years) prior to and continued towards the climactic eruption. This is consistent with timescales of <280 years determined from core–rim interfaces of Group 1 plagioclase crystals, suggesting that the magma chamber was ephemeral, derived from mixing of magmas from multiple sources shortly prior to eruption. This study adds to a growing body of evidence for the ephemeral nature and geologically rapid mixing and mobilization of liquid silicic magma bodies leading to supereruptions, compared with the timescales of hundreds of thousands of years required to accumulate the precursor magma and crystals.
Whakaari/White Island is a partially submerged, offshore andesite island volcano, located at the northern end of the Taupō Volcanic Zone. Since the late 1960s, volcanic activity has alternated between quiescence, unrest, and eruption on short timescales. For this review we compiled extensive observational records, examined the rich scientific literature, and use newly acquired data, to understand the broad volcanic history and system dynamics. Based on recent bathymetry data, we propose a distinction exists between the Whakaari edifice and Te Paepae o Aotea/Volkner Rocks, which were previously considered to be part of the same edifice. Geochemical analyses of scoria samples from the island have been used to build a magma system model where dominantly andesitic-dacitic magma is periodically intruded by basalt. More dynamic processes are recorded in the hydrothermal system, where the location and activity of fumarolic features have been ephemeral and the crater lake has varied in scale over short time intervals. Eruptions of the dominantly andesitic magma have historically been small and range from phreatomagmatic through to magmatic, largely depositing ash and scoria to a restricted distance that is confined to the main crater floor. Phreatic eruptions are the most common eruption style, based on recently observed and monitored activity.
Variable mood is an important feature of psychiatric disorders. However, its measurement and relationship to objective measureas of physiology and behaviour have rarely been studied. Smart-phones facilitate continuous personalized prospective monitoring of subjective experience and behavioural and physiological signals can be measured through wearable devices. Such passive data streams allow novel estimates of diurnal variability. Phase and amplitude of diurnal rhythms were quantified using new techniques that fitted sinusoids to heart rate (HR) and acceleration signals. We investigated mood and diurnal variation for four days in 20 outpatients with bipolar disorder (BD), 14 with borderline personality disorder (BPD) and 20 healthy controls (HC) using a smart-phone app, portable electrocardiogram (ECG), and actigraphy. Variability in negative affect, positive affect, and irritability was elevated in patient groups compared with HC. The study demonstrated convincing associations between variability in subjective mood and objective variability in diurnal physiology. For BPD there was a pattern of positive correlations between mood variability and variation in activity, sleep and HR. The findings suggest BPD is linked more than currently believed with a disorder of diurnal rhythm; in both BPD and BD reducing the variability of sleep phase may be a way to reduce variability of subjective mood.
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