ALBERT

Description: Zircon from syenitic ejecta of Vesuvius (Campania, Italy) is unusually blue, a property shared with gem zircon from Ratanakiri province (Cambodia), which turns from natural reddish-brown to blue when heated under reducing conditions. Here, the origins of these unusual crystals were traced through geochronology, trace elements, and O-Hf isotopic compositions. The causes of its colour were investigated through optical and electron microscopy, optical absorption spectroscopy, and Raman microspectroscopy. Colour stability upon heating and ultraviolet light (UV) exposure was tested using Ratanakiri zircon as a control. Vesuvius zircon contains vesiculated zones with abundant inclusions ~2.5 μm to 〈100 nm in diameter (mostly U-rich thorianite and pyrochlore-group minerals), while homogeneous zircon domains are high in Th and U (up to 5.9 and 1.8 wt%, respectively). Its blue colouration is stable under UV radiation, as well as heat-treatment under reducing conditions (1000 °C; 〉15 h). Turbid domains rich in large inclusions change to yellow-brown after heating under oxidizing conditions, while transparent domains remain pale blue or colourless. Optical absorption spectra display sharp absorption lines attributed to U4+, and slightly elevated absorption towards shorter wavelengths. The ~1007 cm−1 ν3(SiO4) Raman band is broadened due to lattice distortion by non-stoichiometric elements in high-Th/-U zircon, whereas narrow bands in inclusion-rich domains indicate a decrease in lattice strain due to inclusion precipitation. Blue colouration in Vesuvius zircon is explained by the effect of light scattering (Rayleigh and/or Mie scattering) on highly refractive actinide-rich inclusions ranging in size from 〈1/10 to few multiples of the wavelengths of visible light. Inclusions likely formed during fluid-mediated coupled dissolution-reprecipitation that locally transformed lattice-strained actinide-rich zircon within several hundreds of years prior to eruption.

Description: Ruprecht-Karls-Universität Heidelberg (1026)

Description: Massif‐type anorthosite and comagmatic associations of rutile‐bearing ilmenitite (RBI) and oxide‐apatite‐rich amphibolite (OARA) from the Chiapas Massif Complex (CMC) in southeastern Mexico display a protracted billion‐year accessory mineral record encompassing magmatic crystallization at c. 1.0 Ga to recent ductile shear deformation at c. 3.0 Ma. Multiple discrete zircon populations between these age end‐members resulted from neoformation/recrystallization during local to regional metamorphism that affected the southeastern portion of the CMC. The ubiquitous presence of relict baddeleyite (ZrO2), along with various zircon generations spatially associated with pristine to partly retrogressed Zr‐bearing igneous and metamorphic minerals (e.g., ilmenite, rutile, högbomite and garnet), suggests significant Zr diffusive re‐equilibration (exsolution) during slow cooling and mineral breakdown followed by crystallization of baddeleyite. The subsequent transformation of baddeleyite into zircon was likely driven by reaction with Si‐bearing fluids in several geochronologically identified metamorphic stages. Strikingly contrasting compositional signatures in coeval zircon from anorthosite (silicate‐dominated) and comagmatic RBI (Ti‐Fe‐oxide‐dominated) indicate a major role of fluids locally equilibrating with the rock matrix, as indicated by distinct zircon trace element and oxygen isotopic compositions. A high‐grade metamorphic event at c. 950 Ma is likely responsible for the formation of coarse‐grained rutile (~0.1–10 mm in diameter), srilankite, zircon and garnet with rutile inclusions as well as metamorphic högbomite surrounding Fe‐Mg spinel. Zr‐in‐rutile minimum temperatures suggest 〉730°C for this event, which may correlate to rutile‐forming granulite facies metamorphism in other Grenvillian‐aged basement rocks in Mexico and northern South America. A younger generation of baddeleyite exsolution occurred during post‐peak cooling of coarse‐grained rutile, reflected in rimward Zr depletion and formation of discontinuous baddeleyite coronas. Baddeleyite around rutile was then transformed into zircon possibly during subsequent metamorphism at c. 920 or 620 Ma, resulting from syn‐kinematic and contact metamorphism, respectively. Regional metamorphism at c. 450 and 250 Ma extensively overprinted the existing zircon population, especially during the Triassic event, as suggested by a significant presence of zircon with this age. Nearly pristine baddeleyite occurring interstitial to ilmenite yielded an isochron age of c. 232 Ma according to in situ U–Pb secondary ion mass spectrometry (SIMS), suggesting either formation during metamorphic peak conditions or post‐peak cooling. Zircon with ages of c. 80–100 Ma in anorthosite is identified for the first time within the CMC and coincides with cooling ages of c. 100 Ma for coarse‐grained rutile. This age is similar to those of rocks occurring ~200 km further to the east in Guatemala, which are also bounded to the Polochic fault system but overprinted by eclogite facies metamorphism. A high‐pressure event in the southern CMC after 200 Ma, however, is presently unsupported. Although the abundance of rutile and ilmenite is unusually high in the CMC anorthosite assemblage compared with common igneous rocks, the reactions documented here nonetheless stress the importance of these phases for generating Zr‐bearing accessory minerals over a wide range of metamorphic conditions.

Description: Consejo Nacional de Ciencia y Tecnología (CONACYT) http://dx.doi.org/10.13039/501100003141

Description: Deutsche Forschungsgemeinschaft (DFG)

Description: Here we present zircon petrochronological data, tephra whole-rock/glass compositions, and amphibole thermobarometry comprising the last four explosive eruptions of Ilopango Caldera in El Salvador (Tierra Blanca eruptive suite, TB). Our datasets include 238U-230Th disequilibrium geochronology, trace-elements, and oxygen isotope compositions from polished and unpolished zircon crystals analyzed using a CAMECA IMS 1280-HR secondary ion mass spectrometer (SIMS) at Heidelberg University, Germany. Additionally, pumice clasts whole-rock chemical analyses from the TB suite were performed at the German Research Centre for Geosciences (GFZ) using a PANalytical AXIOS Advanced wavelength-dispersive spectrometer, whereas major and trace-elements, glass shard, and mineral compositions were collected using an electron microprobe analysis (EMPA) at GEOMAR - Helmholtz-Centre for Ocean Research Kiel and by Laser Ablation Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) at Institute of Earth Sciences, Academia Sinica in Taipei. Whole-rock Sr-Nd isotope determinations were carried out at Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE; Mexico) with a Nu-Instruments thermal ionization mass spectrometer (Nu-TIMS), whereas whole-rock U-series were determined using a ThermoFisher Neptune inductively-coupled mass-spectrometer multi-collector (ICP-MS-MC) at the University of Wyoming (UWYO, USA).

Description: This dataset includes results from oxygen isotope compositions from zircon crystal interiors (polished sections) of the Tierra Blanca Joven (TBJ) eruption from Ilopango caldera in El Salvador. Zircon crystals were analyzed employing Secondary Ion Mass Spectrometry at Heidelberg University.

Description: This dataset includes results from U-Pb dating from zircon crystal interiors (polished sections) of the Tierra Blanca Joven eruption (TBJ) from Ilopango caldera in El Salvador. Zircon crystals were analyzed employing Secondary Ion Mass Spectrometry at Heidelberg University.

Description: This dataset includes results from U-Th disequilibria dating from zircon rims (outermost crystal face) and crystal interiors (polished crystals) of the last four explosive silicic eruptions from Ilopango caldera in El Salvador (TBJ, TB2, TB3, and TB4). Zircon crystals were analyzed employing Secondary Ion Mass Spectrometry at Heidelberg University.

Description: This dataset includes results from trace element concentrations from zircon rims (outermost crystal face) and crystal interiors (polished sections) of the last four explosive silicic eruptions from Ilopango caldera (TBJ, TB2, TB3, and TB4) in El Salvador. Zircon crystals were analyzed employing Secondary Ion Mass Spectrometry at Heidelberg University.

Description: This dataset includes results from U-series and Sr-Nd whole-rock isotope compositions of the last four explosive silicic eruptions from Ilopango caldera in El Salvador (TBJ, TB2, TB3, and TB4). Sr and Nd isotope ratios were measured with a Nu Instruments thermal ionization mass spectrometer (Nu-TIMS) at Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) in the state of Baja California (Mexico), whereas U and Th concentrations and isotopes were measured at University of Wyoming (UWYO) were measured by isotope dilution using a ThermoFisher Neptune ICP-MS multicollector.

Description: This dataset includes results from amphibole geothermobarometry of explosive silicic eruptions from Ilopango caldera in El Salvador (TBJ, TB2, TB3, and TB4). Amphibole compositions were analyzed employing a JEOL JXA 8200 wavelength dispersive microprobe at the GEOMAR - Helmholtz-Centre for Ocean Research Kiel.

Description: This dataset includes results from X-ray fluorescence (XRF) analyses of the last four explosive silicic eruptions from Ilopango caldera in El Salvador (TBJ, TB2, TB3, and TB4). Samples were analyzed employing a PANalytical AXIOS Advanced wavelength-dispersive spectrometer.