Micro‐PIXE determination of Zr in rutile: an application to geothermometry of high‐P rocks from the western Alps (Italy)

AbstractThe Western Alps of Northern Italy mostly consist of lithotectonic units which re‐crystallised and were metamorphosed at high depth in a subduction zone. During their exhumation to shallow crustal levels, however, the high‐pressure (high‐P) mineral assemblages were pervasively re‐equilibrated under low‐pressure (low‐P) conditions, making difficult to estimate the metamorphic thermal peak.Rutile [TiO2] is a typical high‐P mineral, occurring as relict phase in low‐P re‐equilibrated metamorphic rocks. Recent studies suggest that, in thermodynamic systems buffered by the occurrence of quartz and zircon in the rock, Zr content in rutile is a temperature–dependent function that can be modelled quantitatively.An application of rutile Zr‐geothermometer to continental and oceanic rocks of the Western Alps, pervasively re‐equilibrated under low‐P conditions, is presented.The selected rutile crystals were analysed by PIXE using a microbeam set‐up at the LABEC laboratory of INFN in Florence. The PIXE spectra and maps were processed by Geopixe software package. Micro‐PIXE analyses allowed determining the concentration and the distribution of Zr.Results obtained by applying the rutile Zr‐geothermometer gave a more precise indication about the temperatures of the metamorphic conditions suffered by Alpine metamorphic rocks with respect to phase relations and conventional geothermometry, showing that determination of Zr concentration by micro‐PIXE technique is a useful tool to reconstruct metamorphic events.The continental units, outcropping in separate zones of Western Alps, show two slightly different thermal peaks (Tmean = 530 ± 10 °C and Tmean = 555 ± 10 °C) for the same metamorphic event. The oceanic units provide Tmean estimates of 575 ± 10 °C slightly higher than the continental units. Copyright © 2008 John Wiley & Sons, Ltd

Sulfur isotope evolution in sulfide ores from Western Alps: Assessing the influence of subduction-related metamorphism

Sulfides entering subduction zones can play an important role in the release of sulfur and metals to the mantle wedge and contribute to the formation of volcanic arc-associated ores. Fractionation of stable sulfur isotopes recorded by sulfides during metamorphism can provide evidence of fluid-rock interactions during metamorphism and give insights on sulfur mobilization. A detailed microtextural and geochemical study was performed on mineralized samples from two ocean floor-related sulfide deposits (Servette and Beth-Ghinivert) in high-pressure units of the Italian Western Alps, which underwent different metamorphic evolutions. The combination of microtextural investigations with d34S values from in situ ion probe analyses within individual pyrite and chalcopyrite grains allowed evaluation of the effectiveness of metamorphism in modifying the isotopic record and mobilizing sulfur and metals and have insights on fluid circulation within the slab. Textures and isotopic compositions inherited from the protolith are recorded at Beth-Ghinivert, where limited metamorphic recrystallization is attributed to limited interaction with metamorphic fluids. Isotopic modification by metamorphic processes occurred only at the submillimeter scale at Servette, where local interactions with infiltrating hydrothermal fluid are recorded by metamorphic grains. Notwithstanding the differences recorded by the two deposits, neither underwent intensive isotopic reequilibration or records evidence of intense fluid-rock interaction and S mobilization during metamorphism. Therefore, subducted sulfide deposits dominated by pyrite and chalcopyrite are unlikely to release significant quantities of sulfur to the mantle wedge and to arc magmatism sources at metamorphic grades below the lower eclogite facies

Improvements to the analytical protocol of lapis lazuli provenance: First study on Myanmar rock samples

The study of lapis lazuli is important to find out information about the provenance of a materialused since the Neolithic Age for the manufacturing of precious carved artefacts. The Badakhshan depositsin Afghanistan are commonly considered as the main source of lapis lazuli in ancient times. However, otherquarries could have possibly been exploited since antiquity. A protocol to distinguish the provenance oflapis lazuli rocks among four known source areas (located in present-day Afghanistan, Tajikistan, Siberiaand Chile) by means of non-invasive techniques was set up in the last years. It is based on differences in thephysical-chemical properties measured in 45 lapis lazuli rocks that constitute our reference database. Theaim of the present paper is to extend the protocol analysing, by means of a multi-analytical approach, 10lapis lazuli rock samples, coming from the quarry district of Mandalay in Myanmar, to find out significantpetrographic and mineralogical markers. Optical microscopy and scanning electron microscopy were usedto perform a detailed petrographic and mineralogical characterisation allowing to distinguish the Myanmarlapis lazuli in three main groups. SEM-EDX analyses on selected mineral phases were performed

Arsenic-Bearing Calcite in Natural Travertines: Evidence from Sequential Extraction, μXAS, and μXRF

Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by μXRF elemental mapping and As K-edge μXAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability

Diverse Imaging Methods May Influence Long-Term Oncologic Outcomes in Oligorecurrent Prostate Cancer Patients Treated with Metastasis-Directed Therapy (the PRECISE-MDT Study)

: Metastasis-directed therapy (MDT) has been tested in clinical trials as a treatment option for oligorecurrent prostate cancer (PCa). However, there is an ongoing debate regarding the impact of using different imaging techniques interchangeably for defining lesions and guiding MDT within clinical trials. Methods: We retrospectively identified oligorecurrent PCa patients who had 5 or fewer nodal, bone, or visceral metastases detected by choline or prostate-specific membrane antigen (PSMA) PET/CT and who underwent MDT stereotactic body radiotherapy with or without systemic therapy in 8 tertiary-level cancer centers. Imaging-guided MDT was assessed as progression-free survival (PFS), time to systemic treatment change due to polymetastatic conversion (PFS2), and overall survival predictor. Propensity score matching was performed to account for clinical differences between groups. Results: Of 402 patients, 232 (57.7%) and 170 (42.3%) underwent MDT guided by [18F]fluorocholine and PSMA PET/CT, respectively. After propensity score matching, patients treated with PSMA PET/CT-guided MDT demonstrated longer PFS (hazard ratio [HR], 0.49 [95% CI, 0.36-0.67]; P < 0.0001), PFS2 (HR, 0.42 [95% CI, 0.28-0.63]; P < 0.0001), and overall survival (HR, 0.39 [95% CI, 0.15-0.99]; P < 0.05) than those treated with choline PET/CT-guided MDT. Additionally, we matched patients who underwent [68Ga]Ga-PSMA-11 versus [18F]F-PSMA-1007 PET/CT, observing longer PFS and PFS2 in the former subgroup (PFS: HR, 0.51 [95% CI, 0.26-1.00]; P < 0.05; PFS2: HR, 0.24 [95% CI, 0.09-0.60]; P < 0.05). Conclusion: Diverse imaging methods may influence outcomes in oligorecurrent PCa patients undergoing MDT. However, prospective, head-to-head studies, ideally incorporating a randomized design, are necessary to provide definitive evidence and facilitate the practical application of these findings