Table 1.
The main evidence of exploitation of “alternative” volcanic pozzolans other than pulvis puteolanus from the Gulf of Pozzuoli volcanic districts and harenae fossiciae from the Colli Albani volcanic district. *Legend: TPL-OM = Transmitted Polarized Light-Optical Microscopy; XRD = X-Ray Diffraction; SEM-EDS = Scanning Electron Microscopy coupled with Energy-Dispersive Spectroscopy; XRF = X-Ray Fluorescence; AES = Atomic Emission Spectrometry; AAS = Atomic Absorption Spectrometry.
Fig 1.
(a) Simplified geological map of the Euganean Hills Magmatic District, including the positioning of the geological samples constituting the reference database developed by the University of Padova; the figure was entirely produced by the authors.
In the red-dashed boxes the localization of the main quarries documented via UAV-LIDAR and on-site surveys is reported: (b) North-eastern area; (c) Central-eastern area, northern portion; (d) Central-eastern area, southern-eastern portion; (e) Central-eastern area, southern portion; (f) Central area. Black numbers refer to the sites from which rhyolitic/trachytic/latitic explosive diatreme breccia and submarine breccia samples were collected, discussed in the text: (b1) M. Sengiari outcrop; (c1) Villa Draghi outcrop; (c2) Via Scagliara di M. Castellone outcrop. Differently from geological map [46] reporting rhyolitic composition, our investigations demonstrated that the northern portion of M. Castellone outcrop (Via Scagliara) exhibits trachytic breccia composition; (d1) Turri north of M. Nuovo outcrop and (d2) Castel del Catajo zone; (e) M. Croce outcrop; (f1) M. Marco outcrop; (f2) M. Orsara outcrop; (f3) Outcrop of Galzignano A; (f4) Outcrop of Galzignano B; (f5) M. Venda outcrop.
Fig 2.
Mortar samples collected from the Via Scavi archaeological area in Montegrotto and their position in the plan.
(a) Positioning of Montegrotto in respect to the Euganean District (for geological color legend see Fig 1); (b) the archaeological area of Via Scavi with positioning of the analysed mortar samples (the labelling of the structures is reported according to [53,54]). The archaeological site basemap has been edited and reprinted from [https://www.aquaepatavinae.it/portale/?page_id=1690&recid=44] under a CC BY license, with permission from © Department of Cultural Heritage of the University of Padova, original copyright [2011]; (c – e) Representative images of the analysed structures with exact position of the sampled points.
Table 2.
The analysed samples from Via Scavi site, with indication of the structure of origin and the function of the mortar (the labelling of the structures is reported according to [53,54]).
Fig 3.
Mortar samples from Via Scavi archaeological area.
(a) fresh crosscut of two representative samples; (b-e) micrographs acquired in TPL-OM (XP and PP) of representative portions of the mortar samples. Legend: Vc = volcanic clasts, rVc = reacted volcanic clast; uVc = unreacted volcanic clast; rr = reaction rim; rD = reacted dolostone; Qz = quartz; Qtz = quartzite; Gt = granitoid, Mc = mica; Sn = sandstone; Bt = biotite; Pl = plagioclase; Op = opaque mineral.
Fig 4.
SEM Backscattered Electron (BE) images and EDS microanalyses of the analysed mortars.
(a) SEM-BE acquisition of an area of sample MG_02, between a reacted volcanic aggregate and the lime binder; (a1) EDS analysis of an unreacted zone of the volcanic groundmass within a volcanic aggregate; (a2) EDS analysis of an interface area, with enrichment in Ca from the lime binder and possible local development of C-A-S-H phases; (a3) EDS analysis of the matrix of the samples, indicating pronounced Si and Al peaks suggesting the diffusion of C-A-S-H products in the binders; (b) SEM-BE image of a Ca-enriched area (lime lump) in the binder matrix of sample MG_02; (c) magnification of the area indicated by the red square in Fig (b); (c1) EDS analyses of a Ca-rich core of the lime lump; (c2) EDS analysis of the binder matrix area surrounding the lump, with clear Si and Al peaks indicating the diffusion of C-A-S-H products in the binder.
Table 3.
Results of the QPA-XRPD analyses on binder-separated fractions of lime binder.
Fig 5.
XRPD spectra of the separated binder fraction of sample MG_01 and MG_05.
Mineral phases labelled according to [58] when mentioned: Ms = muscovite; AFm = AFm phases; Cal = calcite; Vtr = vaterite; Znc = zincite (internal standard).
Table 4.
Results of the QPA-XRPD analysis of selected clasts from mortar samples and quarry-correlated samples. b.d. = below detection limit; * = intrusive component from the mortar; ** = environmental alteration.
Fig 6.
TAS (Total Alkali Silica) diagram of selected clast samples removed from the mortars and analysed by XRF.
Legend: in blue = samples of the T-group; in green = samples of the T-TA group.
Fig 7.
Sr vs Ba, Sr vs Nb and Sr vs Nd scatterplots used for provenance discrimination of the archaeological volcanic rock clasts from mortars of Via Scavi in Montegrotto Terme (geological marker samples plotted from the UNIPD reference database).
The reference clusters with homogeneous samples from the same quarry sites are marked by dashed or dotted and dashed lines. Certain archaeological samples are labelled and described in detail in the main text.
Fig 8.
K2O vs Zr, K2O vs Na2O, K2O vs Al2O3 scatterplots used for provenance discrimination of the archaeological volcanic rock clasts from mortars of Via Scavi in Montegrotto Terme (geological marker samples plotted from the UNIPD reference database).
The reference clusters with homogeneous samples from the same quarry sites are marked by dashed or dotted and dashed lines. Certain archaeological samples are labelled and described in detail in the main text.
Fig 9.
Volcanic diatreme breccia samples from Villa Draghi and Via Scagliara quarries.
(a) fresh crosscut of a representative sample from Villa Draghi quarry; (b-d) micrographs acquired in TPL-OM (XP, PP) of representative portions of the Villa Draghi breccia samples; (e) fresh crosscut of a representative sample from Via Scagliara quarry; (f-h) micrographs acquired in TPL-OM (XP, PP) of representative portions of the Via Scagliara breccia samples. Legend: Bc = breccia clasts; Bt = biotite; Gm = groundmass; Ks = kaersutite (amphibole); Op = opaque minerals; Pl = plagioclase.
Table 5.
LDA classification matrix and model validation. The model correctly classified 100% of the training set (Full analysis and Stepwise Forward models). Classification was performed using equal prior probabilities (0.50) to avoid bias toward either source.
Table 6.
Results of the Linear Discriminant Analysis (LDA) of volcanic clast samples (Full analysis model), showing their probabilistic assignment to sources between the Villa Draghi and Via Scagliara di M. Castellone quarries. The discriminant function with a p-value < 0,05 is considered statistically significant at the 95% confidence level.
Table 7.
Results of the Linear Discriminant Analysis (LDA) of volcanic clast samples (Stepwise Forward model), showing their probabilistic assignment to sources between the Villa Draghi and Via Scagliara di M. Castellone quarries. The discriminant function with a p-value < 0,05 is considered statistically significant at the 95% confidence level.
Fig 10.
SEM-BSE images of magnetites from breccia clasts in selected mortar samples MG_01, MG_02, MG_05, MG_09.
Legend of minerals other than magnetites: Ap = apatite.
Fig 11.
SEM-BSE images of magnetites from breccia clasts in selected geological samples from Villa Draghi (VD_01, VD_22) and Via Scagliara of M. Castellone (MCA_09, MCA_16).
Legend of minerals other than magnetites: Ap = apatite; Bt = biotite.
Fig 12.
EDS chemical mapping of magnetite from Villa Draghi geological samples (VD_02).
Fig 13.
The Villa Draghi and Via Scagliara quarries.
(a-b) Manual extraction traces, consisting in 45° incisions let by picks at Villa Draghi and evidence of tunnel quarrying; (c) UAV-LiDAR based reconstruction of the Villa Draghi quarry front (from [48]); (d) Manual extraction traces, consisting in 45° incisions let by picks at Via Scagliara quarry; (e) UAV-LiDAR based reconstruction of the Via Scagliara quarry front (from [48]).