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Studio dei materiali legati ad attività metallurgiche dall’isola di S. Andrea, Loppio (TN): risultati preliminari.
No full textMetallurgical activities leave several types of traces in the area in which they take place: remnants of structures of various nature such as plain burnt, furnaces or forges, holes/containers for the collection of the products deriving from pyrotechnologic activities (charcoal, mineral, fluxing, etc.), pits for placement or storing of tools functional to the metallurgic activity, such as hoods, anvil, benches or plain of support in wood; remains of discard materials such as cinders, mineral slag, charcoal, fragments of crucibles and tuyeres, more rarely real metallic cuttings, directly related to the raw material, the semi-worked or the final products of the metallurgic activity, or tools related to the specific metallurgic job. In this paper we present the results of investigations carried out to characterize some products of metallurgic activities identified on the site of Loppio. Our results indicate that the majority of the remnants of metallurgic processes found in Loppio are associable to iron working activities, and only a minor amount to the copper or copper alloy working process. In both the cases they are not related to reduction processes (primary working), but derive from secondary working process, such as smithing activities of iron. Based on morphological and physical parameters we classified and grouped the residues of metallurgical activity found in Loppio in 11 classes, 10 of which related to the ironworking. The results of petrographic, chemical and mineralogical investigations carried out on a few samples belonging to significant classes of materials provided the early specific information on the phases and the working processes. The chemistry and the mineralogy of two samples of plano-convex bottom (PCB) smithing slag, their morphology and the abundance of this specific class of slags in the site, all suggest that the iron smithing was related to ingots of metal and /or to recycled iron, but probably not to the bloom. Further bulk analyses on these class of slags are needed to confirm this observation. Moreover the two investigated PCB slags show different mineralogical composition, compatible with different oxi-reductive conditions of production, and in one case result similar to the SFR type and in the other to the SGD one described by Serneels and Perret (2003). The presence of various types of PCB indicate a variety of ironworking processes, at various temperature, oxidation condition and produced by the use of different amounts of flux. The flux used has a silica-lime rich composition. Mineralogical analysis indicate that the temperatures of formation of the slag in the forge range between 1100-1200°C, coherently with ‘optimum’ temperature reported in literature for iron smithing. Since the excavations have not shown holes of forge, the identification of numerous remnants of walls of forge allows to hypothesize the presence of raised forges that, based on iconographic evidences are known to be used since the Roman age. In similar way the use of tuyeres, not recovered in the site, can be proven by negative imprints observed a the edges of some slag. A preliminary statistic analysis of spatial and chronological distribution of the investigated materials, suggests that the metallurgic activity possibly begun in the III Period of the Loppio site, in an area corresponding or close to the building IIIc.; evidence of metallurgical activity are also observed in contexts related to the Periods V and VI, mainly in the Buildings IIIb and IIIc and in the corridor IIIb /c and, less abundant, in the area III and possibly in the building V. However, the phenomenon of the redistribution of metallurgical remains in a working site, and the stratigraphic disturbance due to the different life phases of the site do not allow to attribute with certainty such finding to the Longobard period. The same consideration holds for the slags found in building V in layers ascribed to the VII Period, as a reworking cannot be excluded. The workmanship of the copper and /or of its leagues, is testified finally only in Buildings IIIb and IIIc and in the corridor IIIb/c, relatively to the Period V. Finally, no trace of metallurgic activity has been observed around Building I of sector A, where two metal bars were recovered from (Maurina this vol. ), indicating that the presence of metal bars in this area is not related to working activities
Trace element analysis of archaeological glasses: comparison between LA-ICPMS and Electron Microprobe analysis.
No full textRiassunto presentato al Congresso congiunto SIMP-AIV-SoGeI-SGI "Il Pianeta Dinamico: sviluppi e prospettive a 100 anni da Wegener", Firenze, 2-4 Settembre 2015
Analisi archeometriche su manufatti vitrei
No full textObject of the present work is the archaeometric study of glass fragments found on the archaeological site of S. Andrea. The study
aims at investigating possible relationships between chemical composition and type and/or production techniques; at identifying
analogies with coeval glass from the Mediterranean area; at better contextualising the various phases of the site, and at extending
the database on Italian Medieval glass. Archaeometric study was carried out on a selection of glass fragments from Sectors
A and B for a total of 29 samples, composed of objects, glass-working residues and two glass ‘cakes’. Chemical composition
of glass fragments was obtained with CAMECA SX50 electron microprobe (EMPA) equipped with four wavelength-dispersive
spectrometers (WDS). Textural analyses were also performed by means of scanning electron microscopy (SEM), using CamScan
MX3000 instrument with LaB6 source. Results of chemical analysis show that all objects and glass-working residues are silicasoda-
lime in composition, with natron as flux in accordance with production technologies used in Early Medieval times. Various
compositional groups, named LP1a, LP1b and LP1c, were identified, consistent with some of the major ones identified in the
western Mediterranean during the first millennium AD. Group LP1a is chemically similar to unintentionally coloured Roman glass,
spanning the period between the 1st and the 4th centuries AD. The presence within LP1a group of both glass-working residues
and objects points to the existence of a Late Antique/Early Medieval secondary glass-workshop in the Loppio site. Traces of at
least one of the elements Cu, Sn, Sb, and Pb in quantities above 0.05 wt% in most of the LP1a objects, suggest possible recycling
of older glass. Further support to this hypothesis comes from the finding in the same site of one blue glass tessera, having high
contents of copper, tin, antimony and lead, and characterised by calcium antimonate as opacifier, mainly used in Roman period.
Group LP1b can be compared with ‘Group 2’ of Foy et al. 2003, a ‘weaker’ HIMT (High Iron, Manganese and Titanium) group,
which is datable to the 6th-8th centuries AD. Group LP1c shows chemical similarity with ‘Series 3.2’, a subgroup of ‘Group 3’ of
Foy et al. (2003). In particular, ‘Series 3.2’, characterised by lower Al2O3 and higher Na2O than other series of the same group,
with manganese as decolourant, comprises glass samples from the Western Mediterranean area dated from the late 5th to the early
6th century AD. Both groups LP1b and LP1c are entirely composed of objects. Whether groups LP1b and LP1c were obtained by
recycling earlier glass or whether they are the result of a new glass batch intentionally prepared in Late Antique/Early Medieval
period cannot be established with certainty. However, the bad match with previous Roman glass and the absence of glass-working
residues with comparable compositions seem to invalidate the hypothesis of recycling, as also confirmed by the generally low levels
of trace elements such as Cu, Co, Sb and Pb. Three outliers were also identified in the Loppio assemblage; they show similarities
with Roman glass decolourised with antimony or manganese, and with that intentionally coloured in black.
The two rough ellipsoidal glass ‘cakes’, with a concave-convex profile, show a chemical composition very different from other
samples from Loppio. The main mass of the Loppio ‘cakes’ is composed of a green, transparent glass containing frequent, submillimetric,
randomly distributed whitish inclusions. The main mass is completely surrounded by a 3-5 millimeters thick cortex of
a brownish colour characterised by frequent radial, and sometime open, fractures disposed orthogonal to the contact. The contact
between the main mass and the cortex is sharp. Both glass cakes show high potash and calcium contents and are chemically
comparable with Medieval wood ash glasses, likewise more than 80% of the finds analysed until now. The cortex appears to be
hydrated and highly depleted in K, Ca and Mg with respect to the main mass. It likely represents an alteration of the primary glass.
Although the function of these objects are still unclear, their finding may suggest contacts between the Loppio area and the North
European one.
In conclusion, the archaeometric research proves the presence of a local secondary glass workshop in Late Antique/Early Medieval
time. The identification of various natron compositional groups in Loppio glass assemblage, and of the two wood ash glass ‘cakes’,
indicates the coexistence of recycling practice of earlier glass and the supplying of ‘fresh’ glass in Late Antique/Early Medieval
period. This suggests, on the one hand, the extensive availability of older glass for re-use and, on the other, the good commercial
connections between Loppio and Mediterranean and/or European area
Perlina anulare di enstatite: caratterizzazione mineralogica e chimica e ipotesi su tecnica di produzione e zona di provenienza.
No full textThis bead represents a unicum in the Loppio collection. Its size is 4.22 mm in diameter, 1.76 mm in hole and 1.56 mm in height. A program of non-invasive analysis has been carried out to investigate its mineralogical and chemical composition. Optical, ESEM and SEM observations show that the bead has a white interior and a beige surface locally with a glossy appearance. The surface of the hole show no obvious drilling mark.
Micro-FTIR and micro-Raman analyses indicate that the bead was made of enstatite, the Mg-rich orthopyroxene. Results of XRD analysis also suggests that the enstatite is not a natural product, but is very likely synthetic. Qualitative EDS chemical analysis shows the presence of O, Mg, Si (with minor Fe), which is fully consistent with the composition of enstatite. The area with glossy appearance show a distinct composition with higher Si, Al, K and Ca contents. Since enstatite is very hard, in the range 5-6 of the Mohs scale, it is very unlikely that it was used as a raw material to carve such small beads. The production of enstatite beads and other artefacts by heating (burning) of steatite (or saponite) at temperatures above 900°C is well documented in the relevant literature. Enstatite (after steatite) beads are described from several sites in eastern and middle-eastern countries and dates to the 7th millennium. Very few information exists on the use of this pyro-technology in the Italian context during prehistory. Very few beads made of enstatite from Italy have been described (although ‘steatite’ beads are reported from several sites) and we suggest that this may be due to lack of archaeometric investigations. The present work not only provides a detailed chemical and mineralogical characterization of the small enstatite bead found in Loppio, but it also describes a non-invasive analytical protocol that can be easily and economically applied to the investigations of larger collections of similar beads. Our finds can also have important implications on assessing the trade and technological achievments in northern Italy area during the Copper Age
Glass from Loppio (Trento, Northern Italy): an archaeological and archaeometric study.
No full textObject of the present work is the archaeological and archaeometric study of glass fragments coming from the archaeological site of S. Andrea, in the Biotope “Loppio Lake” (Mori, Trento, Northern Italy), where the Museo Civico di Rovereto - Archaeological Department has been carrying out excavations since 1998. Aims are to investigate possible relationships between chemical composition and type and/or production techniques; to identify analogies with coeval glass from the Mediterranean area; to better contextualise the various phases of the site, and to extend the database on Italian Medieval glass. The research carried out so far unearthed the remains of a Medieval church (Sector C) surrounded by a late antique/early Medieval fortified settlement (Sectors A and B), characterized by a sequence of different building phases. Many finds belonging to weaponry and soldiers equipment suggest that this site, very strategically located along the ancient route going from the Adige Valley to the North Garda Lake, was settled for military reasons and lodged soldiers with their families. So far, it seems possible to identify an Osthrogoth/Byzantine phase, followed by a Lombard phase. A Carolingian presence is also documented in the site. Archaeometric study, carried out on a selection of glass fragments from Sectors A and C, shows that all samples are silica-soda-lime in composition. Natron was used as flux for the Early Medieval samples and soda ash for the Late Medieval ones. Compositional groups were identified, consistent with the major compositional groups identified in the western Mediterranean during the first millennium AD. In this context, two rough ellipsoidal glass “cakes”, about 8 cm large, with a concave-convex profile and with chemical compositions similar to Medieval wood ash glasses are unusual and puzzling. Although the function of these cakes are still unclear, their finding may suggest contacts between the Loppio area and the North European one
Episyenites within the Tauern Window metagranitoids: unpredictable?
Full text linkThe core of the Tauern tectonic window (Eastern Alps) consists of dominant pre-Alpine granitoids (∼ 295 Ma)\ud
that were metamorphosed and deformed during the Alpine orogenesis (at ∼ 30 Ma). Ductile deformation at peak conditions (550-600 ̊C and 0.5-0.7 GPa) was followed by cataclastic faulting (Pennacchioni and Mancktelow, 2007). Both deformation phases occurred in a fluid-rich environment with formation of veins filled with quartz-calcite-biotite-feldspar and quartz-chlorite-epidote-adularia-calcite, respectively. Faults are typically low displacement strike-slip structures (offset < 1m) organized in en-echelon arrays at different scales with a stepping geometry consistent with the sense of fault slip (e.g. left-stepping for dextral slip). Fault stepovers include pervasive fracturing dominated by a set of antithetic faults (Pennacchioni and Mancktelow, 2013). These faults were locally exploited by episyenitic alteration which represented the "last" event of fluid-rock interaction in the Tauern meta-granitoids. Episyenites within metagranodiorites have a macroscopic porosity in the range between 25 and 35% volume (determined by microtomography), mostly derived from dissolution of multi-mm-sized quartz. Recent glacier-polished outcrops provide a unique opportunity to investigate the relationships between episyenites and overprinted faults. Detailed field mapping of a selected outcrop indicates that episyenites: (i) are spatially linked to precursor faults and statically overprinted all previous structures; (ii) occur discontinuously along faults; (iii) have a thickness (of as much as a few meters) that does not correlate with either the amount of fault slip or the density of the fracture network; (iv) developed independently of rock type (passing "undisturbed" lithologic boundaries with conspicuous variations of quartz grain size of the protolith lithology). Although the faults in the studied outcrop are extensively decorated by relatively large volumes of episyenite, occurrences of episyenite in the Tauern granitoids are generally rare. This study indicates that there is not a simple way to predict the location and the extent of episyenite alteration from the geometry and fracturing patterns of the network of precursor cataclastic faults.\ud
The dominant quartz dissolution during episyenitization was accompanied and/or followed by: (i) pervasive substitution of oligoclase and chlorite/biotite of the metagranodiorite by albite and clay-minerals, respectively, and (ii) limited precipitation of new adularia, anatase, calcite, hematite and zeolite within pores. Isotopic data from calcite filling the episyenite porosity suggest a meteoric source of the fluids (δ18 O (SMOW) ≈ -2 per mil). In contrast, fluids synkinematic with previous episodes of fluid-rock interaction during faulting and ductile shearing had a deeper origin (δ18O (SMOW) ≈ 8-9 per mil).\ud
References\ud
Pennacchioni, G., Mancktelow, N.S., 2007. J. Struct. Geol. 29, 1757-1780.\ud
Pennacchioni, G., Mancktelow, N.S., 2013. Geol. Soc. Am. Bull. 125, 1468-1483
Episyenites within the Tauern Window metagranitoids: unpredictable?
No full textThe core of the Tauern tectonic window (Eastern Alps) consists of dominant pre-Alpine granitoids (∼ 295 Ma)
that were metamorphosed and deformed during the Alpine orogenesis (at ∼ 30 Ma). Ductile deformation at peak
conditions (550-600 ̊C and 0.5-0.7 GPa) was followed by cataclastic faulting (Pennacchioni and Mancktelow,
2007). Both deformation phases occurred in a fluid-rich environment with formation of veins filled with quartz-
calcite-biotite-feldspar and quartz-chlorite-epidote-adularia-calcite, respectively. Faults are typically low displace-
ment strike-slip structures (offset < 1m) organized in en-echelon arrays at different scales with a stepping geometry
consistent with the sense of fault slip (e.g. left-stepping for dextral slip). Fault stepovers include pervasive frac-
turing dominated by a set of antithetic faults (Pennacchioni and Mancktelow, 2013). These faults were locally
exploited by episyenitic alteration which represented the "last" event of fluid-rock interaction in the Tauern meta-
granitoids. Episyenites within metagranodiorites have a macroscopic porosity in the range between 25 and 35%
volume (determined by microtomography), mostly derived from dissolution of multi-mm-sized quartz. Recent
glacier-polished outcrops provide a unique opportunity to investigate the relationships between episyenites and
overprinted faults. Detailed field mapping of a selected outcrop indicates that episyenites: (i) are spatially linked to
precursor faults and statically overprinted all previous structures; (ii) occur discontinuously along faults; (iii) have
a thickness (of as much as a few meters) that does not correlate with either the amount of fault slip or the density of
the fracture network; (iv) developed independently of rock type (passing "undisturbed" lithologic boundaries with
conspicuous variations of quartz grain size of the protolith lithology). Although the faults in the studied outcrop
are extensively decorated by relatively large volumes of episyenite, occurrences of episyenite in the Tauern gran-
itoids are generally rare. This study indicates that there is not a simple way to predict the location and the extent
of episyenite alteration from the geometry and fracturing patterns of the network of precursor cataclastic faults.
The dominant quartz dissolution during episyenitization was accompanied and/or followed by: (i) pervasive sub-
stitution of oligoclase and chlorite/biotite of the metagranodiorite by albite and clay-minerals, respectively, and (ii)
limited precipitation of new adularia, anatase, calcite, hematite and zeolite within pores. Isotopic data from calcite
filling the episyenite porosity suggest a meteoric source of the fluids (δ18 O (SMOW) ≈ -2 per mil). In contrast, fluids
synkinematic with previous episodes of fluid-rock interaction during faulting and ductile shearing had a deeper
origin (δ18O (SMOW) ≈ 8-9 per mil).
References
Pennacchioni, G., Mancktelow, N.S., 2007. J. Struct. Geol. 29, 1757-1780.
Pennacchioni, G., Mancktelow, N.S., 2013. Geol. Soc. Am. Bull. 125, 1468-1483
Reclassification and thermal history of Trenzano chondrite
No full textWe present a new single-crystal X-ray diffraction (XRD) study performed on a suite of six orthopyroxene grains from the low-shocked H6 Trenzano meteorite. The quenched intracrystalline Fe2+-Mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature Tc, thus yielding useful constraints on the last thermal event undergone by the host rock. The orthopyroxene Tc of 522 ± 13 °C, calculated using a new calibration equation obtained by Stimpfl (2005b), is higher than in previously published H chondrite data. The orthopyroxene cooling rate at this Tc is about 100 °C/kyr. This fast rate is inconsistent with the much slower cooling rate expected for H6 in the onion shell structural and thermal model of chondrite parent bodies. A petrographic study carried out at the same time indicated that the Trenzano meteorite is an H5 chondrite and not an H6 chondrite, as it is officially classified. Furthermore, the two-pyroxene equilibrium temperature of Trenzano (824 ± 24 °C), calculated with QUILF95, is similar to the two-pyroxene temperature of 750-840 °C obtained for the Carcote (H5) chondrite (Kleinschrot and Okrusch 1999)
Constraints on the thermal history and oxidation state of MIL03346 martian meteorite: single-crystal XRD, electron microprobe ena Mossbauer analyses of clinipyroxene.
No full textEpisyenites in meta-granitoids of the Tauern Window (Eastern Alps): Unpredictable?
No full texttThe core of the Tauern tectonic window (Eastern Alps) consists of pre-Alpine granitoids (∼295 Ma) vari-ably deformed during Alpine (∼30 Ma) amphibolite-facies metamorphism. Episyenites occur as localalteration haloes (as wide as a few meters) surrounding steeply dipping, strike-slip faults, with offsets<1 m, overprinting the metamorphic deformation structures. Episyenites are well recognizable in the fieldby their macroscopic porosity, ranging between 25–35 vol% (meta-granodiorite) and 13% (meta-aplite),mainly derived from dissolution of quartz. Glacier-polished outcrops allow the detailed investigationof the relationships between the episyenites and the structure of the associated faults. Field mappingindicates that episyenites: (i) are spatially linked to pre-existing faults and statically overprinted thesestructures; (ii) are discontinuous along faults; (iii) have a thickness (of as much as a few meters) thatdoes not correlate with either the amount of slip along the pre-existing faults or the spatial density of thefracture network; (iv) developed with a similar extent in rocks with conspicuous variations of the origi-nal quartz grain size and structure. The studied outcrop includes a relatively large volume of episyeniteassociated with faults. However, despite the pervasiveness of faulting, episyenites are rare in the Tauernmeta-granitoids. This localized occurrence of episyenite is inferred to represent a section of a verticalpipe structure exploiting a portion of the fault network. Our study indicates that the location and theextent of episyenite alteration cannot be simply predicted from the geometry and the fracturing pat-terns of the pre-existing cataclastic faults. Quartz dissolution during episyenitization was accompaniedand/or followed by: (i) pervasive substitution of oligoclase and biotite/chlorite of the meta-granodioriteby albite and vermicular chlorite, respectively; and (ii) precipitation of adularia, albite, anatase, calcite,hematite and zeolites within pores. Isotopic data from the calcite filling of the pores suggest a surficialsource of fluids associated with this calcite precipitation (18O (SMOW) ≈−2‰ and −3‰). In contrast,fluids syn-kinematic with the older episodes of fluid-rock interaction, during faulting and ductile shear-ing, had a deeper origin (18O (SMOW) ≈8–9‰). In the structural history, episyenite marks the transitionfrom diffuse deformation to almost rigid-block behaviour of the Tauern tectonic unit, during progressiveexhumation and cooling (at T <300◦C). This transition reflects the transfer of deformation to localizedslip along the Brenner extensional detachment
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