Abstract Trachyte of the Euganean Hills is a subvolcanic porphyritic rock historically used as carving and building stone in northern and central Italy–primarily from Roman times onward–with the first evidence of its use dating back to prehistory. The numerous quarries and very similar trachyte varieties, as well as the widespread use of this stone, create several problems in defining its provenance for archaeological and historical materials. New petrographic and geochemical tracers for recognizing the provenance quarry of Euganean trachyte are presented here, providing a comprehensive reference database for archaeometric studies. The petrographic markers principally include quantitative data on mineralogical composition and textural features of phenocrysts and groundmass, determined by image analysis of chemical maps acquired by micro X‐ray fluorescence and scanning electron microscope‐energy‐dispersive X‐ray spectroscopy; particular use has been made of data on the abundance and grain‐size distribution of feldspar phenocrysts, phenocrysts‐groundmass ratio, content of SiO 2 phases in the groundmass, and the arrangement and grain‐size of microlites in the matrix. The geochemical tracers involve composition of bulk rock and phenocrysts, determined by X‐ray fluorescence and laser ablation inductively coupled plasma mass spectrometry, respectively; quarry recognition can be achieved using plots built from concentrations of major and trace elements, with mineral‐scale chemistry being the most effective and precise discriminant property, especially in the case of biotite and, secondarily, augite, kaersutite, and magnetite.
Two types of metamorphic phengites are known: one is linked to high pressure and is 3T; the other is 2M1, and its composition is linked to rock-compositional constraints. This work investigates the octahedral sheet crystal-chemical differences between the two phengite types. Seven dioctahedral micas were studied: (1) one 3T phengite from an ultrahigh-pressure metagranitoid in the Dora Maira massif, Italy (P ~ 4.3 GPa, T ~ 730 °C); (2) five 2M1 phengites from medium-P orthogneisses in the Eastern Alps metamorphic basement, Italy (P ≤ 0.7 GPa, T ~ 500-600 °C); and (3) one 2M1 ferroan muscovite from pegmatite in Antarctica (P ≤ 0.2 GPa, T ~500 °C). All micas display significant extents of celadonite substitution. In particular, the 2M1-phengite formulae (calculated on the basis of 11 O) have 0.68 < IVAl < 0.82 atoms per formula unit (apfu); octahedral atoms are dominated by Al (1.6-1.8 apfu), with minor and variable Fe (0.20-0.35 apfu) and Mg (0.05-0.17 apfu), and very minor Ti, Mn, and Cr. Total octahedral occupancies are slightly above 2.00 apfu, i.e., there seems to be partial occupancy of the third M site. For all micas, we recorded XAFS spectra on mosaics of carefully separated flakes oriented flat on a plastic support that could be rotated so as to account for the polarization of the synchrotron radiation beam, and we processed them on the basis of the AXANES theory. Spectra show angle-dependent absorption variations for Al and Fe, which can be deconvoluted and fitted by dichroic effects. Pre-edges consistently show most Fe to be Fe3+ and little angle-dependent intensity variations. The 2M1-ferroan muscovite from Antarctica displays the same AXANES behavior as 2M1-phengites. By contrast, the ultrahigh-pressure 3T-phengite from Dora Maira (having IVAl = 0.42 apfu, and Al and Mg as the dominant octahedral constituents) has XAFS spectra that differ significantly. Not only is the IVAl feature strongly reduced, in agreement with the increased Si content, but also Fe XAFS spectra show one broad feature only, indicating that all Fe is Fe2+ in a fully disordered distribution with no angle-dependent variations. We conclude that this 3T-phengite is actually contaminated by exsolved Fe-bearing pyrope platelets, which cannot be resolved under SEM examination; by contrast, the 2M1-phengites, unrelated to high-pressure, suggest Al/Fe3+ order over the M1 and (M2, M3) sites, as also does the 2M1 pegmatitic muscovite.
Aims of CSPThe overall objectives of the Commission on Systematics in Petrology (CSP) are the classification of igneous, metamorphic and sedimentary rocks; the elaboration of principles and recommendations; and establishing data bases, leading to a comprehensive nomenclature of magmatic, metamorphic and sedimentary rock-types.These objectives aim at co-ordinating international efforts and international communication in the field of systematics.Achieving classificatory schemes for rocks which are internationally accepted will result in strengthening international co-operation and scientific communication in the broadest frame of geological research.
Abstract RamanCrystalHunter (RCH) is a new software program designed to pre-process, analyse and identify Raman spectra by comparison with spectra in the RamanCrystalHunter Database (RCHDB). The software is free and can be downloaded from the website; https://www.fabrizionestola.com/rch. RCH is characterized by a simple graphical user interface, making it suitable for both specialist and non-specialist users and it has been developed mainly for applications in Earth Sciences (processing the spectra of minerals), but can be used to process the Raman spectra of any synthetic or natural inorganic or organic material. RCH allows users to visualize, pre-process (e.g., using smoothing, noise reduction, and baseline correction operations), and analyse (e.g., using fitting or various calculation tools) Raman spectra. Moreover, it is equipped with the RCHDB, a new database of high-quality mineral spectra that can be downloaded for free along with the RCH program. The RCHDB contains the Raman spectra of minerals (including single- and multi-phase inclusions within mineral hosts, for example diamonds) and related synthetic compounds allowing for rapid and accurate identification of unknown spectra. The RCH software includes highly customizable yet efficient and user-friendly methods for processing and analysis of Raman spectra and represents a valuable contribution to the field of Raman spectroscopy whose applications have expanded greatly in recent years, especially in Earth Sciences. Two practical examples of novel ways in which this software can be used for geoscience applications are presented.
Ultramylonites and margarite-bearing quartz-feldspar S-C mylonites, containing amphibolite lenses with symplectitic texture, were encountered in a borehole (Bajánsenye-B-M-I) close to the west of the Transdanubian Central Range Unit. These rocks demonstrate a ductile, horizontal extensional shear zone attaining a thickness of 300 m. Microstructural data, mineral parageneses and mineral chemistry of these rocks indicate a multistage metamorphic evolution, which is consistent with that of the Koralm-Pohorje basement. The youngest mylonitic event (Early Tertiary) took place in the Bajánsenye mylonites at 430-450oC (greenschist-facies); it rejuvenated coarse-grained muscovite crystals of eo-Alpine age (Early-Middle Cretaceous). The radiometric data presented in this paper demonstrate for the first time an important Early Tertiary tectonic zone in this area.
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