Geology topics

Antonio Lanzirotti

Publications and source records attributed to Antonio Lanzirotti.

3 recordsLinked to original sources

USGS2026

Widespread occurrence of Magnéli phases in wildland-urban interface fire ashes

The increasing activity of wildland–urban interface (WUI) fires has raised concerns regarding the potential environmental and human health impacts of residual ash remaining after burning. In this study, we investigated the concentration and speciation of titanium in WUI fire ash. Total titanium concentrations in WUI fire ash ranged from 0.53 to 80 g kg –1 . Synchrotron-based macro- and microscale X-ray absorption near-edge structure (XANES and μXANES, respectively) spectroscopy were used to quantify the relative abundance of major Ti phases in the fire ash, and the results were corroborated by high resolution-transmission electron microscopy (HR-TEM) measurements. Rutile (α-TiO 2 ), anatase (β-TiO 2 ), ilmenite (FeTiO 3 ), and titanium(III) oxide (Ti 2 O 3 ) were detected in all 20 ashes investigated by XANES and accounted for 0.26–0.83, 0.19–0.83, 0.33, and 0.17–0.72 of the spectral weight, respectively. Deeper analysis by μXANES of one sample demonstrated that Ti-bearing particles occurred as a mixture of rutile (α-TiO 2 ), anatase (β-TiO 2 ), ilmenite (FeTiO 3 ), and titanium(III) oxide Ti 2 O 3, with the absence of a pure Ti 2 O 3 phase. The presence of Ti 2 O 3 in the WUI fire ash is ascribed to the reduction of rutile and anatase to Magnéli titania (Ti n O 2 n– 1 , n = 4–9), which is estimated to be the dominant phase of titanium in the 20 WUI fire ashes investigated by XANES. The occurrence of Magnéli titania was corroborated by HR-TEM. Our findings demonstrate the impact of WUI fires on titanium speciation; fires convert titanium dioxides (e.g., rutile and anatase) to reduced titanium phases (e.g., Magnéli titania). Based on HR-TEM analyses, most of the titanium-bearing particles were less than 500 nm in size. Magnéli particles have been shown to be more toxic than rutile and anatase and have been linked to reduced lung function. Therefore, this study provides critical insights into the pollution characteristics and potential health risks of WUI fire ashes and associated particles, which are currently poorly understood.

California↗

USGS2019

Direct measurements of copper speciation in basaltic glasses: Understanding the relative roles of sulfur and oxygen in copper complexation in melts

Micro-analytical determination of copper (Cu) speciation in natural magmatic glasses, equilibrated below the nickel – nickel oxide (NNO) buffer, reveals that two copper species are commonly stabilized in such basaltic melts. X-ray absorption fine structure (XAFS) spectroscopic analysis of basaltic matrix glasses and melt inclusions (MI) from samples of mid-ocean ridge basalt (MORB), and from Nyamuragira, Etna and Kīlauea volcanoes show that both Cu(I)-sulfide and Cu(I)-oxide species are stabilized. The proportion of each species correlates with the measured sulfur (S) abundance of the glass. In glasses with S abundances greater than ~1000 ppm, Cu(I)-sulfide species are dominant, whereas in glasses with S abundances between 500 and 1000 ppm, both species are found to coexist. The Cu(I)-oxide species dominate at S concentrations below 500 ppm. In 1 atm S-free experimental glasses of basaltic composition that we analyzed, only Cu(I)-oxide species are detectable, regardless of the oxygen fugacity (fO2), even at relatively high fO2 values well above the NNO buffer. Our results demonstrate that XAFS techniques are highly sensitive in measuring Cu speciation in reduced (below NNO) basaltic glasses and that both oxide and sulfide complexes can be stabilized. The relative proportion of these two species is highly dependent on the concentration of S in the melt, and thus the Cu speciation in natural melts changes as S is lost from the melt by low pressure degassing.

Hawaii↗

USGS2018

Accurate predictions of microscale oxygen barometry in basaltic glasses using V K-edge X-ray absorption spectroscopy: A multivariate approach

Because magmatic oxygen fugacity ( f O2 ) exerts a primary control on the discrete vanadium (V) valence states that will exist in quenched melts, V valence proxies for f O2 , measured using X-ray absorption near-edge spectroscopy (XANES), can provide highly sensitive measurements of the redox conditions in basaltic melts. However, published calibrations for basaltic glasses primarily relate measured intensities of specific spectral features to V valence or oxygen fugacity. These models have not exploited information contained within the entire XANES spectrum, which also provide a measure of changes in V chemical state as a function of f O2 . Multivariate analysis (MVA) holds significant promise for the development of calibration models that employ the full XANES spectral range. In this study, new calibration models are developed using MVA partial least-squares (PLS) regression and least absolute shrinkage and selection operator (Lasso) regression to predict the f O2 of equilibration in glasses of basaltic composition directly. The models are then tested on a suite of natural glasses from mid-ocean ridge basalts and from Kilauea. The models relate the measured XANES spectral features directly to buffer-relative f O2 as the predicted variable, avoiding the need for an external measure of the V valence in the experimental glasses used to train the models. It is also shown that by predicting buffer-relative f O2 directly, these models also minimize temperature-relative uncertainties in the calibration. The calibration developed using the Lasso regression model, using a Lasso hyperparameter value of α = 0.0008, yields nickel-nickel oxide (NNO) relative f O2 predictions with a root-mean-square-error of ±0.33 log units. When applied to natural basaltic glasses, the V MVA calibration model generally yields predicted NNO-relative f O2 values that are within the analytical uncertainty of what is calculated using Fe XANES to predict Fe 3+ /ΣFe. When applied to samples of natural basaltic glass collected in 2014 from an active lava flow at Kilauea, a mean f O2 of NNO-1.15 ± 0.19 (1σ) is calculated, which is generally consistent with other published f O2 estimates for subaerial Kilauea lavas. When applied to a sample of pillow-rim basaltic glass dredged from the East Pacific Rise, calculated f O2 varies from NNO-2.67 (±0.33) to NNO-3.72 (±0.33) with distance from the quenched pillow rim. Fe oxybarometry in this sample provides an f O2 of NNO-2.54 ± 0.19 (1σ), which is in good agreement with that provided by the V oxybarometry within the uncertainties of the modeling. However, the data may indicate that V XANES oxybarometry has greater sensitivity to small changes in f O2 at these more reduced redox conditions than can be detected using Fe XANES.

Hawaii↗