Vincent J. van Hinsberg

Intersector element partitioning in tourmaline: a potentially powerful single crystal thermometer

Hourglass sector zoning, and related polar overgrowths, are common features of metamorphic tourmaline, developing as a result of variations in element preference on the different growth surfaces. For sector-zoned crystals, three domains are present for each growth zone (c+, c− and a), with compositional differences most distinct for Ca and Ti, and among c+ and c− sectors. Intersector differences vary, commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade. Here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c+–c−and c+–a partitioning of Ca and Ti. These thermometers are applicable over a range of temperatures and bulk-rock compositions. Intersector partitioning is not affected by re-equilibration and records and preserves complete T-histories of individual tourmaline grains from prograde to peak and on to retrograde growth. Information on element mobility is preserved by tourmaline composition, because intersector partitioning is independent of element concentration. These factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline’s refractory nature preserves these signatures even into the sedimentary record.

Hourglass sector zoning in metamorphic tourmaline and resultant major and trace-element fractionation

Abstract A new type of sector zoning, with an hourglass shape, has been identified in metamorphic tourmalines that formed under a wide variety of physical and chemical conditions. The two sectors in the c-direction are not equivalent due to asymmetry in the crystal structure of tourmaline along the c-axis. The c+ sector is characterized by low concentrations of Ti, Ca, Mg, and Na, although Al is high, and has a pale (commonly blue or pale-green) color. Conversely, the c. sector is low in Mg and Al, and high in Ca, Fe, and Ti (the latter two causing the dark-brown color of this sector). The a-sector has intermediate characteristics and probably approximates a sector-free tourmaline. Thin sectioning of these sector-zoned tourmalines perpendicular to the c-axis can produce three types of apparent radial zoning patterns: blue-green cores, dark-brown cores, or no distinct cores. These apparent cores will further vary in relative diameter depending on the sectioning level. Furthermore, .core. boundaries can be straight or ragged depending on whether the relative growth speeds for the different faces was constant or variable. These textures have been used to argue for a prograde or detrital origin of tourmaline cores. However, sector zoning is a more appealing explanation for most of these textures, and can further explain the textural resemblance among metamorphic tourmalines from highly variable bulk-rock composition, metamorphic history, and mineral paragenesis. The sector zoning that is described here develops by preferential uptake of elements on the r growth plane, resulting from a combined effect of differences in surface charge and morphology of this plane in the c+ and c. directions. This leads to the preferential incorporation of more positively charged elements in the c. direction, and a preference for a vacant X-site in the c+ direction. Because the compositional differences among the sectors are pronounced in both major and trace elements and in the same order of magnitude as growth zoning variability, the presence of sector zoning must be established and taken into account when making inferences from tourmaline chemistry.

The geothermobarometric potential of tourmaline, based on experimental and natural data

Abstract The geothermobarometric potential of tourmaline has been assessed by investigating element exchange among tourmaline and coexisting minerals in metamorphosed pelites and graywackes, and in experimental exchange between tourmaline and biotite. In the natural samples, a temperature dependence of tourmaline Mg-Fe exchange with biotite, staurolite, garnet, chlorite, and muscovite, and Ca-Na exchange with plagioclase is observed. Equilibrium calculations for the complete mineral assemblage show that tourmaline is in compositional equilibrium with all coexisting phases, which would allow for an internally consistent set of thermometers among all these phases to be defined. However, a prohibitively large spread is present in the KD vs. T relations. This is not caused by analytical effects, compositional zoning, or disequilibrium among the minerals. The experimental results show that it is the result of inter-site partitioning of elements over the Y and Z octahedral sites of tourmaline. Variations in the element distribution over these sites, their relative participation in the exchange and differences in the temperature dependence of exchange with each site, strongly affects the KD vs. T relation observed, with the slope actually changing sign depending on the elements residing at each site. Non-ideal interactions among the elements at each site will also affect this, and furthermore link every exchange to the bulk tourmaline composition, and hence the element mobility in the rock. The promising potential of tourmaline geothermobarometry can therefore not be fulfilled until effects of inter-site partitioning and non-ideal interactions are known.

Kawah Ijen volcanic activity: a review

Kawah Ijen is a composite volcano located at the easternmost part of Java island in Indonesia and hosts the largest natural acidic lake in the world. We have gathered all available historical reports on Kawah Ijen’s activity since 1770 with the purpose of reviewing the temporal evolution of its activity. Most of these observations and studies have been conducted from a geochemical perspective and in punctuated scientific campaigns. Starting in 1991, the seismic activity and a set of volcanic lake parameters began to be weekly available. We present a database of those measurements that, combined with historical reports, allow us to review each eruption/unrest that occurred during the last two centuries. As of 2010, the volcanic activity is monitored by a new multi-disciplinary network, including digital seismic stations, and lake level and temperature measurements. This detailed monitoring provides an opportunity for better classifying seismic events and forecasting volcanic unrest at Kawah Ijen, but only with the understanding of the characteristics of this volcanic system gained from the historical review presented here.

Reading the mineral record of fluid composition from element partitioning

Earth is the “blue planet,” with more than 70% of its surface covered in water and the equivalent of up to four oceans of water in its interior. This abundance of water has a profound impact on the processes that shape our planet as well as the development of the organisms that inhabit it. To understand this impact, it is necessary to know the properties and compositions of this fluid. At present, this information is largely unavailable, because direct samples of fluid are rare, especially for early Earth and Earth9s interior, and other estimators are semiquantitative, at best. Here we propose a different approach in which the composition of the fluid is reconstructed from that of minerals, based on the characteristic trace element partitioning between minerals and aqueous fluids. We show experimentally that this partitioning is systematic and obeys lattice-strain theory. It depends strongly on element complexation in the fluid, but this dependence is predictable and can be accommodated. Unlike fluids, minerals with preserved compositions are readily available in the geological record, and this approach therefore provides a powerful and widely applicable tool to reconstruct a quantitative record of fluid composition for the full range of Earth environments and for its earliest history.

New insights into Kawah Ijen's volcanic system from the wet volcano workshop experiment

Abstract Volcanoes with crater lakes and/or extensive hydrothermal systems pose significant challenges with respect to monitoring and forecasting eruptions, but they also provide new opportunities to enhance our understanding of magmatic–hydrothermal processes. Their lakes and hydrothermal systems serve as reservoirs for magmatic heat and fluid emissions, filtering and delaying the surface expressions of magmatic unrest and eruption, yet they also enable sampling and monitoring of geochemical tracers. Here, we describe the outcomes of a highly focused international experimental campaign and workshop carried out at Kawah Ijen volcano, Indonesia, in September 2014, designed to answer fundamental questions about how to improve monitoring and eruption forecasting at wet volcanoes.

Element flux to the environment of the passively degassing crater lake-hosting Kawah Ijen volcano, Indonesia, and implications for estimates of the global volcanic flux

Abstract Volcanoes play an important role in the global cycling of elements by providing a pathway from the deep Earth to its surface. Here, we have constrained the flux to the environment for most elements of the periodic table for the passively degassing, crater lake-hosting Kawah Ijen volcano in the Indonesian arc. Our results indicate that emissions of Kawah Ijen are dominated by acid water outflow, especially for the ligands (Cl, F, Br), with active fumaroles contributing significant (semi)metals (e.g. Se, As, Sb, Hg), as well as C and S. The compositional signature of emissions from Kawah Ijen is similar to that of major volcanic emitters such as Etna, but element fluxes are smaller. This result provides the prerequisite foundation for extrapolating a small set of measured volcanic gas emissions to a global volcanic flux estimate. However, the aqueous flux (i.e. seepage of volcanic hydrothermal fluids and volcano-influenced groundwater) is at least as important in terms of element release, and the consideration of the gaseous flux alone thus represents a significant underestimate of the impact of volcanoes on their environment and the contribution of volcanic hydrothermal systems to global element cycling. Supplementary material: The full datasets of water and fumarole gas chemical analyses are available at https://doi.org/10.6084/m9.figshare.c.2134359

Thermo-chronology of the Barlet metamorphic basement unit: evidence for a Stephanian thermal event linked to Sb mineralization in the Haut Allier, France

A thermo-chronological analysis of the Barlet basement unit (French Massif Central) reveals a four-stage history. Peak metamorphism (650 °C and 7 kbar) was followed by retrograde growth of albite blasts and development of the main foliation at 600 °C, and chloritization of the ferromagnesian minerals. The third stage is a marked reversal of cooling, with recrossing of the biotite isograd and local reappearance of garnet at 450 °C. This thermal event, inferred to result from hot fluid infiltration, is also recognized in the adjacent basin of Langeac, where it gives rise to anomalous coal grades (recording 200 °C at 1 km). A Stephanian age for this event correlates with a regional thermal event recognized throughout the Variscan, where it has been linked to delamination of the continental crust. This work represents the first instance in the Massif Central that recognizes this event in the shallow basement itself. Final cooling is accompanied by extensive fluid-induced sericitization, starting immediately after the peak of the thermal event and continuing to temperatures inferred for Sb–As ore deposition. This continuum leads us to conclude that reheating-related silicate reactions and ore deposition are caused by the same fluid and related to the wider regional Variscan thermal event.

Metal contents of marine turtle eggs (Chelonia mydas; Lepidochelys olivacea) from the tropical eastern pacific and the implications for human health

ABSTRACT Concentrations of eight elements were measured in Chelonia mydas and Lepidochelys olivacea eggs collected along the Pacific coast of Panama. Manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and mercury (Hg) concentrations were similar to previous reports of these species from around the world, while lead (Pb) was lower than previous reports. Cd posed the highest health risk to people who regularly eat the eggs, with average consumption rates leading to target hazard quotients (THQ) of up to 0.35 ± 0.15. Our conclusions indicate that current turtle egg consumption in isolated, coastal Pacific communities may pose a health concern for young children, and that youth and young adults should limit their consumption of turtle eggs to reduce their total intake of nonessential metals.

A new method to deconvolute binary mixture in LA-ICP-MS analyses to quantify the composition of phases smaller than the laser spot size

Laser ablation ICP-MS is widely applied to geological materials for the in situ analysis of elemental and isotopic compositions at a tens of micrometers scale. Despite the advances in LA-ICP-MS technology made in the last few decades, analyzing features with a micron-sized diameter still faces technical challenges, in particular, contamination from the host material. Here, we provide a quantification strategy to deconvolute the data signal produced when ablating a mixture of the target material and the host, which enables quantification of features that are smaller than the effective size of the laser spot. Our strategy is to purposely ablate mixtures of the target and host material with varying proportions of the two. The resulting mechanical mixtures define a linear trend in compositional space of which the end points can be determined when at least one element is independently known for both phases (e.g., from microprobe analyses or stoichiometry). The theoretical basis of this approach is described. The methods are evaluated by application to experimental samples displaying liquid immiscibility, both at a >50 μm scale where we show that our methods produce equivalent data to traditional data processing, and to samples where the small liquid droplet size prevents traditional analysis. The methods outlined here allow for quantification of features as small as a few micrometers in size on a standard LA-ICP-MS system, and are ideal to analyse melt or fluid inclusions, crystal zonation as well as other small phases in natural or experimental systems.