Title: Neolithic polished greenstone industry from Castello di Annone (Italy): minero-petrographic
study and archaeometric implications
Running title: Neolithic greenstone industry of Castello di Annone (Italy)
Plan of the article:
Abstract
1. Introduction
2. Materials and methods
2.1 Archaeological case study and materials 2.2 Methods
3. Results
3.1 Stereo-microscopic observations and density measurements 3.2 X-ray powder diffraction
3.3 Optical polarizing-microscope and SEM-EDS 3.3.1 Na-pyroxene + Garnet rocks
3.3.1.1 Eclogites 3.3.1.2 Garnet-omphacitites 3.3.2 Na-pyroxene rocks 3.3.2.1 Mixed Na-pyroxenites 3.3.2.2 Omphacitites 3.3.2.3 Jadeitites 3.4 Geothermometry
3.5 Geologic survey and comparative petrographic study 4. Discussion 5. Conclusions Acknowledgements References Tables Figure captions
Corresponding author: Roberto Giustetto – Department of Earth Sciences, University of Turin, Via Valperga Caluso 35 – I-10125 Torino (Italy)
Tel: +39-011-6707122 – Fax: +39-011-6707128 e-mail: roberto.giustetto@unito.it
Computer/operating system: PC equipped with Windows 7 Enterprise Word Processor: Microsoft Word 2013
TITLE PAGE
Manuscript Title: Neolithic polished greenstone industry from Castello di Annone (Italy):
minero-petrographic study and archaeometric implications
Name of Authors:
Giustetto, Roberto: Department of Earth Sciences, University of Turin, via Valperga Caluso 35, 10125 Torino (Italy) and NIS (Nanostructured Interfaces and Surfaces) Centre, via Quarello 11, 10135 Torino (Italy)
e-mail: roberto.giustetto@unito.it
Perrone, Ursula
Compagnoni, Roberto: Department of Earth Sciences, University of Turin, via Valperga Caluso 35, 10125 Torino (Italy).
e-mail: roberto.compagnoni@unito.it
Corresponding author:
Giustetto, Roberto: Department of Earth Sciences, University of Turin, Via Valperga Caluso 35, 10125 Torino (Italy).
Tel. +39-011-6705122; Fax +39-011-6705128 e-mail: roberto.giustetto@unito.it
Neolithic polished greenstone industry from Castello di Annone (Italy): minero-petrographic study and archaeometric implications
Roberto Giustetto1,2, Ursula Perrone1, Roberto Compagnoni1
1Department of Earth Sciences, University of Turin, via Valperga Caluso 35, 10125 Torino (Italy)
2NIS (Nanostructured Interfaces and Surfaces) Centre, via Quarello 11, 10135 Torino (Italy)
*Corresponding author: roberto.giustetto @ unito.it – tel. +39-011-6705122 – fax +39-011-6705128
Abstract
High-pressure (HP) meta-ophiolites – usually termed ‘greenstones’ by archaeologists – were used in Neolithic to produce polished stone implements all over the Western Europe. Their accurate petrographic characterization may help to infer the provenance of the raw materials, thus
contributing to reconstruct the migratory routes of our ancestors. The lithic industry of Castello di Annone (Northwestern Italy) was investigated by means of a multi-analytical approach including density measurements, XRPD, optical microscopy, SEM-EDS and geothermometry. More than half of the studied tools (52%) are made of fine-grained eclogites subdivided in three different groups – each with a peculiar metamorphic history. Another 26% consists of Na-pyroxene-rich rocks, with mixed Na-pyroxenites (omphacite+jadeite-bearing rocks) more abundant than jadeitites. The remaining 22% is made up of serpentinites and a variety of minor lithologies. In most greenstone implements, both pyroxenes and garnets show a complex compositional zoning, almost unknown in geologic samples due to the lack of detailed petrologic data on these rocks. Therefore, though it has been ascertained that these HP meta-ophiolites derive from the Piemonte Zone, more systematic field and laboratory data are necessary to acquire more accurate information. A recent geologic survey in the Pellice Valley brought to uncover small boudins of fine-grained eclogites and omphacitites, similar to those found in the prehistoric tools. The Castello di Annone eclogites, poorly manufactured and probably collected among fluvial pebbles, must be considered low quality materials. This confirms the marginal role of this site in the production and distribution network of greenstone implements in Northern Italy during Neolithic.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Key-words: Neolithic stone implement; eclogite; Na-pyroxenite; jadeitite; omphacitite; Piemonte
Zone meta-ophiolites/calc-schists; Western Alps.
1. Introduction
A huge number of polished stone implements (mostly axes but also chisels, rings and pendants) have been found in various archaeological sites all over the Western Europe, dating from the Neolithic to the Copper/Bronze Age. Due to their typical colour and provenance, most of the rocks forming these implements were termed by archaeologists ‘Alpine greenstones’. The recurring lithotypes consist of meta-ophiolites, which include both serpentinites and high-pressure (HP) or ultrahigh high-pressure (UHP) metamorphic rocks such as eclogites and Na-pyroxenites. Other rocks, such amphibolites, glaucophanites and prasinites (formed by albite eyespots and the combined presence of chlorite, actinolite and epidote) may also be present. All these lithologies share an exceptional toughness, but the HP meta-ophiolites (especially eclogites and Na-pyroxenites) also possess high density and hardness, features very useful for the manufacture of high quality stone implements (Ricq-de-Bouard & Fedele, 1993; D’Amico
et al., 1995; D’Amico & Starnini, 2006).
Although commonly referred to as ‘Jades’, a significant part of these lithologies is characterized by an unusual mineralogical composition, mainly consisting of Na-clinopyroxenes plotting in the Jadeite (Jd) – Aegirine (Ae) – Wollastonite + Enstatite + Ferrosilite (WEF or Q) ternary diagram (Morimoto et al., 1988), eventually accompanied by garnets. A petrographic classification for these rocks, recently proposed by Giustetto & Compagnoni (2014), will be followed in this study.
The abundance of ‘Jades’ among the Neolithic implements of western Europe coupled to their apparent local geological scarcity, initially led to hypothesize an exotic origin. However, basing 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
on the pioneering studies of Gastaldi (1871), Damour (1881) and Franchi (1900), their prove-nance from the Alpine belt is nowadays unanimously accepted (D’Amico, 2005; Pétrequin et
al., 2005b; Compagnoni et al., 2006). About 90% of the HP metamorphic rocks forming the
prehistoric tools found on the southern side of the Western Alps near the Po Plain (eclogites and Na-pyroxenites) belong to the meta-ophiolites and calc-schists of the Piemonte Zone (Pig-gott & Powell, 1951; Ricq-de-Bouard, 1981; Compagnoni et al., 1995; D’Amico et al., 1991; 1995; 1997).
Several studies have been focused on the archaeometric characterization of the greenstone in-dustry from various sites of Northern Italy, aimed at identifying the possible supply sources of raw materials and eventually reconstruct the trade fluxes of ancient populations (Garibaldi et
al., 1996; Giustetto & Compagnoni, 2004; Chiarenza & Giustetto, 2010; D’Amico & De
Ange-lis, 2009; D’Amico et al., 1992; 1997; 2013). Recent geological surveys (D’Amico, 2005; Pétrequin et al., 2005a, 2005b, 2006; Compagnoni et al., 2012) proved that these lithotypes oc-cur as very small primary outcrops (few m3) in the Western Alps or secondary clastic deposits
derived from erosion of the previous ones. In these deposits, such lithotypes may be dressed be-cause more resistant than the associated rock types to physico-chemical alteration
(Com-pagnoni et al., 2006; D’Amico & Starnini, 2006; D’Amico & De Angelis, 2009).
The current study deals with the minero-petrographic characterization of the lithic industry of Castello di Annone – mostly represented by implements in greenstone and other subordinate HP-lithologies –and related archaeometric extrapolations.
2. Materials and methods
2.1 Archaeological case study and materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
The site of Castello di Annone, one of the most important in the Piedmont region, is located in Northwestern Italy near the town of Asti, on a hilly district following the course of the Tanaro River (Fig. 1; Venturino Gambari & Zamagni, 1996; Padovan & Salzani, 2014). (INSERT FIGURE 1)
Archaeological surveys identified several occupational phases from the middle Neolithic (half of V millennium BC) to middle Iron Age (VI - V century BC), with flourishing of pottery (Giustetto et al., 2013) and lithic industries open to trade exchanges with other areas of the Po Plane (Venturino Gambari et al., 1995; Venturino Gambari, 2014). The remains of the lithic industry consist of 301 implements (127 complete and/or fragmented tools and 174 splinters), mostly of Alpine greenstone, collected during an excavation performed while constructing a motorway (Barello et al., 2007). Basing on their functionality and remnants of manufacture/use, these instruments were aimed at cutting (axes, hatchels and chisels), striking (percussors) or abrading (grindstones and millstones).
(INSERT FIGURE 2)
Instruments for cutting (73 %, mostly axes and hatchels) show triangular to trapezoidal shapes typical of Neolithic (Fig. 2) and small to medium dimensions. Splinters were interpreted as either deriving from instruments broken during use or semi-manufactured fragments. Their chronological attribution is due to most tools being buried in levels associated to ceramics, datable from the Middle to Late Neolithic – a period in which the greenstone industry flourished in Northwestern Italy (Zamagni, 2014). However, possible attribution to later periods (Bronze and/or Iron Age) cannot be excluded.
Percussors (almost 18 %), showing distinct worn out edges, were directly obtained from almost spherical pebbles with no further manufacturing or, partly, after the recycling of broken axes. Abrading instruments, used actively and passively (Hamon, 2006), are even scarcer (about 9 %) and made of lithotypes other than greenstones (i.e., sandstones, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
quartzites or gabbros). The chronological attribution of tools for striking and abrading is troublesome, as their shapes do not vary in different periods (Starnini & Maggi, 1990; Panozzo, 1998).
Among the whole population, 212 implements (most for cutting) were selected for analysis.
2.2 Methods
A protocol suggested by Chiari et al. (1996) and Compagnoni et al. (2006) was used, which involves a global screening with non-destructive techniques (i.e., macroscopic and stereo-microscopic examination; density measures) and in-depth analyses on representative specimens with more invasive methods (X-ray powder diffraction, optical microscopy with plane-polarized light, SEM-EDS and geothermometry).
Specimens for in-depth analyses were extracted from broken tools and rough casts, by using a core barrel with a diamond corona. Drilled cores (6 mm diameter) were cut parallel to elongation in two: a 30 μm polished thin section was obtained with one half, whereas the other was partly crushed and partly stored for archival use.
X-ray powder diffraction (XRPD) data were collected on crushed samples in the 3-70° 2 range, using an automated Siemens D-5000 diffractometer with /2 setup in Bragg-Brentano geometry, Cu-K radiation and zero-background flat sample holder. Data were processed with the Diffrac Plus (2005) software (EVA 11,00,3).
Optical observations under plane-polarized light were performed by using a Zeiss WL Pol transmission polarizing microscope on standard thin sections (30 μm).
Scanning electron microscopy (SEM) was performed with a SEM Stereoscan 360, Cambridge Instrument, on polished and carbon-coated thin sections. Chemical
characterization was performed by an EDS Link Pentafet, Oxford instrument (operating 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
conditions: 50 s counting time, 15 kV accelerating voltage, 25 mm working distance, 300 pA beam current). The collected data were processed with the INCA 200 Microanalysis Suite Software, version 4.08, calibrated on natural mineral standards using the ZAF correction method.
Geothermometric data were obtained from garnet/omphacite pairs compositions in selected eclogits. This geothermometer is based on the Fe2+/Mg partitioning (K
D) between coexisting
garnet and omphacite, which is a function of the crystallization metamorphic temperature. The approach proposed by Spear (1993) was used for the determination of KD lines,
applying the Powell (1985) calibration.
3. Results
3.1 Stereo-microscopic observations and density measurements
All selected specimens (212) were observed under a stereomicroscope in reflected light to evaluate the average mineral grain-size, mineralogical heterogeneities and microstructural features. Density measurements were used to discriminate the lower (i.e., serpentinites and prasinites) from higher density lithotypes (i.e., Na-pyroxenites and Na-pyroxene+garnet rocks). Density values are reliable only if the HP rocks are not affected by greenschist-facies retrogression, which lowers these values due to growth of lighter minerals (e.g., albite). By combining these data, a preliminary lithotype determination was obtained. Despite few uncertainties, most implements consist of HP meta-ophiolites, namely ‘alpine greenstones’. The higher density rocks (dM 3.4 – 3.5; Fig. 3.b), consisting of Na-pyroxene+garnet,
(mainly eclogites) are more than half of the studied implements (about 52 %; Fig. 3.a). The rest, with slightly lower density (dM 3.3; Fig. 3.b), is mostly represented by Na-pyroxenites
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
(26 %: jadeitites, omphacitites and mixed Na-pyroxenites; Fig. 3.a). The lowest density rocks are serpentinites (12 %; dM 2.7), other HP lithotypes (e.g., metabasalts, metagabbros,
granulites and some low density prasinites; 5 %; dM 2.9, Fig. 3.b) and non-HP rocks (e.g.,
quartzites and sandstones; 5 %), forming the remaining fraction (Fig. 3.a). (INSERT FIGURE 3)
Basing on macroscopic features such as colour, density, mineralogy, grain-size and retrogression degree, 38 representative specimens of HP lithologies were selected and analyzed with a more invasive approach. Serpentinites and prasinites, as well as non-HP lithotypes, were disregarded being ubiquitously distributed in the Piemonte Zone and therefore unable to give further information (Giustetto et al., 2008).
The lithology of the 38 selected specimens is as follows:
22 Na-pyroxene+garnet rocks (17 eclogites and 5 garnet-omphacitites – 3 of which with jadeite);
14 Na-pyroxene rocks (7 mixed Na-pyroxenites, 4 omphacitites and 3 jadeitites); one doleritic metabasalt with zoisite;
one amphibolite with clinozoisite and garnet.
Table 1 provides the compositions of these samples, resulting from XRPD, optical polarizing-microscopy and SEM-EDS.
(INSERT TABLE 1)
3.2. X-ray powder diffraction
XRPD allowed a detailed study of the mineralogical composition of all 38 specimens. As already acknowledged in literature, the rocks used to manufacture prehistoric implements often contain more than one Na-pyroxene – usually both jadeite and omphacite (Giustetto & 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Compagnoni, 2014). Additional presence of further pyroxenes, such as aegirine-augite, is seldom observed (Schmidt & Stelcl, 1971; Woolley, 1983; D’Amico et al., 1995).
(INSERT FIGURE 4)
When more pyroxenes coexist in a specimen, the slight differences in their unit cells sometimes cause the main reflections in the diffraction pattern [i.e., (-221) and (310)] to split, thus allowing their discrimination (Fig. 4). By comparing the related peak intensities, a rough quantification of their mutual abundances might be inferred. Furthermore, if the dhkl
values of the three most representative reflections [(-221), (310) and (002)] are measured, a reliable estimate of pyroxene composition may be calculated (Giustetto et al., 2008). The obtained results (see section 4) are consistent with the average chemistry of pyroxenes inferred by SEM-EDS.
3.3. Optical polarizing-microscope and SEM-EDS
Optical microscope and SEM-EDS represent by far the most suitable techniques to study these HP meta-ophiolites (Giustetto & Compagnoni, 2014). Only these methods can grab the extreme chemical heterogeneity and complex zoning of clinopyroxenes and garnets. Optical microscopy, in particular, allows to roughly estimating the mutual amounts of the main phases, together with a thorough description of their textural relationships. Back-scattered electrons (BSE) SEM images, on the other hand, can show the heterogeneity and micro-structural relationships of pyroxenes (see, e.g., Fig. 6). Ultimately, EDS spot
analyses can sharply define the clinopyroxene and garnet composition and zoning
[Morimoto et al. (1988) for pyroxenes and almandine (Alm) + spessartite (Sps) – grossular (Grs) – pyrope (Prp) for garnets] and allow identification of minor and accessory phases. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
3.3.1 Na-pyroxene + Garnet rocks
3.3.1.1 Eclogites
The 17 analyzed specimens are heteroblastic rocks with weak mylonitic foliation, highlighted by the preferential orientation of tiny Na-pyroxene crystals and minor phases (rutile aggregates, titanite and opaque ores). Na-pyroxenes form a fine to very fine-grained matrix, with optical features typical of omphacite. Several specimens (i.e. PIEM 38, PIEM 46, PIEM 56, PIEM 64; Table 1) show two different pyroxene compositions: an older omphacite (I), grown as pseudomorph after a previous magmatic pyroxene, surrounded by fine-grained neoblastic Na-pyroxenes (II).
(INSERT FIGURE 5)
Sometimes subordinate and almost colourless domains of jadeite-rich pyroxenes can also be observed, which are surrounded by a prevailing, greener omphacite. When analyzed by SEM-EDS (8 samples), this omphacite matrix shows a marked compositional variability with Ae content increasing up to 30 wt.% and Jd ranging between 40-60 wt.% (PIEM 73, Fig. 5). The jadeite domains, marked by a darker contrast, are conversely quite homogeneous (Fig. 6). Often green-to-bluish, pleochroic omphacite crystals are observed, with an unusually high Ti content (up to 5 wt.%).
(INSERT FIGURE 6)
In the omphacite matrix, small to medium-sized sub-millimetric garnet
poikiloblasts occur, often with an atoll-like structure, which include elongated and randomly oriented pyroxene idioblasts. At SEM-EDS (Fig. 7) these garnets show 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
a marked compositional zoning from core (C) to rim (R), at times perceivable even at the optical microscope (reddish cores and palerrims; Fig. 8.a).
Minor mineral phases are also present (Table 1); among these, sometimes apatite, titanite, rutile and opaque ores occur as inclusions in garnets.
(INSERT FIGURE 7) (INSERT FIGURE 8)
3.3.1.2 Garnet-omphacitites
They are fine-grained rocks in which an omphacite matrix defines, together with garnets (5-25 vol. %), a marked mylonitic foliation and/or lineation. Garnets with a relict appearance are occasionally fractured and partially altered to chlorite. When analyzed with SEM-EDS (4 specimens), significant amounts of fine grained jadeite is observed associated to the omphacite matrix, (e.g., in PIEM 43, PIEM 55, PIEM 58; Fig. 5). The textural relationships between different
pyroxenes are somewhat structurally and chronologically complicated; usually the preferential dimensional orientation of jadeite crystals contributes to define, together with rutile and/or titanite aggregates, a weak foliation. Bluish, Ti-rich omphacites are also locally observed.
Medium-grained garnet poikiloblasts usually grow upon foliation and include tiny pyroxene crystals; garnets are zoned with a moderate (Alm+Sps)-increase from core to rim (e.g.,PIEM 37 and PIEM 55; Fig. 7). Minor and accessory phases, led by abundant rutile and titanite, are often observed (Table 1).
3.3.2 Na-pyroxene rocks 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
3.3.2.1 Mixed Na-pyroxenites
These rocks are marked by the coexistence of jadeite and omphacite in variable amounts. SEM observations, coupled with EDS analyses (i.e., PIEM 61 in Fig. 9), show that in most cases the two pyroxenes occur in equivalent amounts, though sometimes omphacite aggregates are included in a prevailing, fine-grained jadeite matrix. Locally a discontinuous mylonitic foliation is observed, defined by the preferred orientation of small pyroxene nematoblasts wrapping around pyroxene porphyroclasts, which are crowded with oriented needle-like rutile possibly exsolved from a primary Ti-bearing magmatic pyroxene. Apart from their grain-size, Na-pyroxenes show a marked compositional zoning. Omphacite is green and pleochroic, whereas a colourless jadeite often includes very small exsolution “droplets” of omphacite. Minor and accessory minerals also appear (Table1).
3.3.2.2 Omphacitites
They are fine to very fine-grained homeoblastic rocks containing up to 70 vol.% of omphacite, whose crystals are usually zoned with darker green cores and paler rims. Locally, bluish-cores of Ti/Fe-omphacite (TiO2 up to 5 wt.%) are observed,
surrounded by an almost colourless rim (Fig. 8.b). This peculiar zoning, detected also in some eclogites and garnet-omphacitites, shows complex trends when analyzed with SEM-EDS (see e.g., PIEM 52 in Fig. 9).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Small oriented rutile needles are included in omphacite, probably exsolutions from a former magmatic, Ti-rich pyroxene. Minor and accessory phases (forming the residual 30 vol. %) are reported in Table 1.
3.3.2.3 Jadeitites
They are homeoblastic rocks consisting of jadeite (≥ 80 vol. %) and variable glaucophane amounts, white mica, albite, rutile, titanite, zircon and opaque ores. Jadeite blasts, with variable dimensions sometimes in the same specimen, usually define a weak foliation. Occasionally rutile-needles aggregates occur in the core of the jadeite blasts, producing a dusty appearance.
In two analyzed specimens (PIEM 41 and PIEM 48; Fig. 9), jadeite is quite pure and contains small “droplets” of exsolved omphacite. A third one (PIEM 68) shows an extremely pure, very fine-grained jadeite aggregatein which phengite porphyroblasts grow.
(INSERT FIGURE 9)
3.4. Geothermometry
To get more information about the metamorphic conditions at which these HP rocks recrystallized, the garnet/omphacite geothermometer was tentatively applied on the 8 eclogites and one garnet-omphacitite (PIEM 55) analyzed by EDS. A significant problem is represented by both garnets and omphacites being highly zoned, thus making it difficult to choose the apt compositional pair to be used in calculations. Due to this, the obtained results (see Supplementary Material, Fig. S1) show a wide range of T values (between 400 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
and 650°C, at a nominal pressure of 15 kbar), reflecting the microstructural and
mineralogical heterogeneity of these rocks. However, the mean T values do not exceed 500°C, the lower ones being obtained for omphacites included in atoll-like garnets.
3.5 Geologic survey and comparative petrographic study
With the aim to perform a pilot comparative study between the HP rocks forming the Neolithic implements and geological specimens of analogous composition, a field survey was performed in the upper ‘Vallone dei Carbonieri’ (Pellice Valley; Fig. 1, upper left corner) on a small portion representative of the Monviso meta-ophiolite Massif (Blake et
al. 1995; Castelli et al., 2014). During this inspection, small fine-grained eclogite and
omphacitite boudins, apparently similar to those found in prehistoric implements, were sampled and studied with the same approach. Their petrographic features are exposed hereafter.
a. Eclogites (11 samples) show alternation of omphacite and garnet-rich domains. In the former, porphyroclastic omphacites (probably pseudomorphs after an original magmatic clinopyroxene) are observed surrounded by a second-generation of zoned, fine-grained omphacite nematoblasts defining, together with opaque ores and rutile aggregates, a foliation. These moderately zoned omphacites (Jd30-50 Q40-50 Ae10-25; Fig. 10.a) show an
EDS composition quite similar to that of some Neolithic tools (see, for example, PIEM 56 and 63 in Fig. 5). Medium to fine-grained almandine garnet poikiloblasts, poorly zoned with grossular decreasing from a reddish core to a paler rim (Fig. 10.b), often show an atoll-like structure including small omphacite crystals. A similar composition 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
and zoning is occasionally observed in the garnets of some eclogitic tools (e.g., PIEM 36; Fig. 7). Minor phases are amphibole, chlorite, apatite, quartz, rutile and titanite.
b. Garnet-omphacitites (2 samples) are heteroblastic rocks with a marked foliation, defined by the preferential orientation of omphacite and clinozoisite. Omphacite is always fine-grained while garnets appear as sub-millimetric relicts with reddish hue, usually replaced by green and slightly pleochroic chlorite. Other phases are clinozoisite, amphibole, white mica, apatite and rutile.
c. Omphacitites (6 samples) are composed mainly of omphacite heteroblasts (≈ 70%), defining a foliation together with small rutile aggregates and showing two different compositions: i) bigger crystals with pleochroic Cr-rich, yellow-to-deep green cores and clean rim; ii) medium-sized crystals, light-green to colourless, with murky cores
containing small rutile inclusions. Other phases include abundant epidote, white mica, chlorite, Na-amphibole, rutile, apatite and opaque ores.
(INSERT FIGURE 10)
4. Discussion
The performed study shows a marked predominance of HP metamorphic lithotypes in the Castello di Annone prehistoric lithic industry, deriving from the Piemonte zone of calc-schists with meta-ophiolites of the Western Alps. Na-pyroxene+garnet rocks prevail (52 %; Fig. 3), mostly represented by fine to ultrafine-grained eclogites with heterogeneous zoning of both pyroxenes and garnets. These rocks can be subdivided into three groups, characterized by different metamorphic histories.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
a. 1 st group eclogites show poorly zoned garnets and a strongly zoned omphacitic matrix,
whose heterogeneity consists of at least 3 different structural and compositional sites: i) relict omphacite porphyroclasts wrapped around by the foliation, with a diopside-richer core (Jd20) and a slightly Ae-richer rim (with Jd10) (i.e., groups A and B, respectively in PIEM 46;
group A in PIEM 49; Fig. 5); ii) a foliation defined by the preferred orientation of very fine-grained Na-pyroxene nematoblasts, which show two distinct and coexistent compositions, one with Jd55, Q40, Ae5 (i.e., group F in PIEM 46; group A in PIEM 70) and another with Ae
up to 15-30 wt.% (i.e., group G in PIEM 46; group B in PIEM 70; Fig. 5); iii) apatite-bearing veins where markedly zoned omphacite crystals, often retrogressed into epidote, albite and chlorite, show Jd-richer cores and slightly Ae-richer rims (i.e., groups C and D in PIEM 46 and 49, respectively; Fig. 5).
b. 2 nd group eclogites are characterized by a complex garnet zoning and a fairly homogeneous
omphacite composition. An omphacitic matrix with poor preferred orientation surrounds zoned poikiloblasts of garnets, sometimes atoll-like (with reddish cores and colourless rims), marked by a complex zoning in which pyrope and almandine slightly decrease from core to rim. Near the rim, the decrease in almandine is coupled to a sharp (5 to 25 wt.%) grossular increase (i.e., PIEM 56 and 63; Fig. 5). Omphacite forms a poorly foliated matrix in which mm-sized porphyroclasts are wrapped around by smaller nematoblasts, both with
homogeneous mean composition (Jd50 Q40 Ae10; e.g. in PIEM 56 and 63; Fig. 5).
c. 3 rd group eclogites show presence of two coexisting pyroxenes, a prevailing dark-green
omphacite and a subordinate pale-green-to-colourless jadeite. EDS analyses in ternary diagrams either plot as two separate clusters (e.g., PIEM 64 and 73) or an almost continuous 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
distribution between the compositional fields of omphacite and jadeite (e.g., in PIEM 36; Fig. 5).
Garnet-omphacitites show several analogies with eclogites. In particular, those lacking jadeite (e.g., PIEM 37) show a chemistry and zoning of both omphacite and garnets similar to those of 2nd group eclogites, suggesting a common origin. However, if small amounts of jadeite occur
(e.g. PIEM 43, 55 and 58; Figs. 5 and 7), their features resemble more to those of the 3rd group.
Predominance of Na-pyroxene+garnet rocks was also observed in the lithic industry of other coeval sites of Northern Italy (Fig. 1, upper left corner), such as Alba, Brignano Frascata, Gaione, Momperone, Ponte Ghiara, Rivanazzano, Rocca di Cavour, Sammardenchia and San Lazzaro di Savena (Andò, 1998; Bernabò Brea et al., 2000; Borgogno, 2000; D’Amico et al., 1995; 1997; 2000; 2013; D’Amico & Ghedini, 1996; D’Amico & Starnini, 2000; Giustetto & Compagnoni, 2004; Mannoni & Starnini, 1994). Besides, a similar compositional heterogeneity – namely the presence of small to subordinate amounts of jadeite in a dominant omphacite matrix (3rd group eclogites) – has already been reported (Giustetto et al., 2008; D’Amico et al.,
1995; 2003, Giustetto & Compagnoni, 2014).
For what concerns Na-pyroxenes rocks, the Castello di Annone mixed Na-pyroxenites are more abundant than jadeitites (15 vs. 8%), a trend observed also in other coeval, close sites. This tendency is reversed in discoveries from Southern France, where jadeitites prevail (Ricq-de-Bouard & Fedele, 1993). Alpine greenstones get scarcer by proceeding Westbound from the watershed between Italy and France (eclogites and Na-pyroxenites, but also glaucophanites), while hornfelses from Pyrenees become more common (Ricq-de-Bouard, 1996). Omphacitites are quite scarce (3%), with pyroxenes chemistry similar to that of some eclogites (namely the 1st group), with a rather high Ae content (5-40 wt.%; e.g., PIEM 52 in Fig. 9).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
The mean composition of Na-pyroxenes isomorphic mixtures can also be estimated by plotting the dhkl values of the main jadeite and omphacite reflections [(-221); (310); (002)] on the grid
proposed by Giustetto et al. (2008; see section 3.2). As observed in Figs. 5 and 9, despite their heterogeneity the estimated mean composition for clinopyroxenes (black spot) plot amidst the dispersion pattern of the spot EDS analyses for most samples, thus supporting reliability of the prospected method.
In addition to eclogites and Na-pyroxenites, presence of serpentinites is remarkable (12%) whereas other HP lithotypes (i.e., prasinites, metagabbros, metabasalts and granulites) are quite scarce (5%). Similar proportions among these minor lithotypes are also observed in
Rivanazzano (Mannoni & Starnini, 1994), Rocca di Cavour (Borgogno, 2000), Momperone (Giustetto & Compagnoni, 2004), Gaione (Bernabò Brea et al., 1996; Andò, 1998), Ponte Ghiara (Bernabò Brea et al., 2000) and San Lazzaro di Savena (Fabris, 1996).
The compositional variability of clinopyroxenes in the Castello di Annone lithic industry has also been found in other coeval sites: for example, most features observed in Jadeitites (i.e., presence of a felt of fine-grained, pure jadeite) were also reported from the implements of the Brignano Frascata atelier (D’amico et al., 2000). Unfortunately, the reported heterogeneity was seldom reported for clinopyroxenes in geological specimens of Na-pyroxenites and eclogites, due to lack of detailed petrologic data from the few known primary outcrops or secondary (conglomeratic) deposits (Compagnoni et al., 1995; Borgogno, 2000). Coexistence of
pyroxenes with different compositions has been reported not only from the Alps, but also from other ‘Jade’ occurrences (Harlow et al., 2012; Schertl et al., 2012). Usually different pyroxenes are not coeval, but formed at different times involving former phases partially replacing later ones in quite a complex sequence (Compagnoni et al., 2012). Moreover, the structural relationships among different pyroxenes are often not so evident. The current state-of-the-art suggests that these rocks, during the alpine HP evolution, may have undergone significant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
metasomatic processes as hinted by the occurrence of a complex chemical zoning in both pyroxenes and garnets, with evidence of corrosion and dissolution (e.g., in atoll-like garnets). This process were probably coupled with a localized shear deformation, as suggested by the systematic presence of a pervasive fine to very fine-grained mylonitic foliation.
The averaged peak eclogite-facies T values obtained by geothermometry (≤ 500 °C) are comparable to the recrystallization temperatures of eclogites from the Piemonte Zone of Western Alps (Benciolini et al., 1988). This evidence further confirms the local provenance of the raw materials, but provides no additional information about their more detailed location. Eclogites did experience a complex fluid infiltration during their formation, allowing rough estimates extrapolation of their metamorphic temperatures, but much promising information is expected from the detailed study of the composition and zoning of pyroxenes and garnets. Primary outcrops of eclogites and/or Na-pyroxenites with structural features comparable to those observed in the prehistoric implements are extremely scarce, small and located at high altitudes (Pétrequin et al., 2013). The performed geologic survey in the ‘Vallone dei
Carbonieri’ brought to locate samples of fine-grained eclogites and omphacitites, whose analyses proved to be quite similar to those existing in the Neolithic tools. These geologic specimens show relatively simple and similar compositions for garnet and omphacite, thus supporting the hypothesis that the same mineralogical signature should be preserved in each outcrop. Therefore, a careful determination of the composition and zoning of both omphacite and garnets may represent a potential tool to determine the supply sources of the raw materials exploited by our ancestors. Furthermore, in the surveyed geological context the intimate association between fine-grained eclogites and omphacitites, often described in the
archaeological specimens, was also observed. This comparative study confirmed therefore that fine-grained eclogites are not rare – but rather exposed as small volumes and intimately
associated with omphacitites, in the form of irregular metamorphic veins with a gradual 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
transition against the associated eclogite. Such an association explains why in several
prehistoric implements portions identified as eclogite coexist together with others classifiable as omphacitite. The petrographic classification of an archaeological artefact should therefore be made on the whole instrument – rather than on a restricted area. The similarities observed between geological specimens and Neolithic implements confirm that only reiterated field recognitions in the Piemonte Zone, followed by in-depth comparative studies, might help in achieving further information about a more accurate provenance of these materials.
5. Conclusions
Several archaeometric and archaeological implications lead to consider Castello di Annone as a marginal site in the production and distribution network of polished greenstone implements in Northern Italy during the Neolithic.
Due to the high number of broken and retrieved tools, the Castello di Annone eclogite should not be considered a first quality material (Delcaro, 2004). Possibly these rocks, often of small-to-moderate dimensions, were collected from alluvial and/or older conglomeratic deposits. The peripheral role of the investigated site can be inferred by keeping into account that: i) the global number of recovered lithic tools is scarce, if compared to the presumed duration of the anthropic colonization; ii) the number of broken implements is high and most of them show evidences of reuse, thus implying a non-particularly specialized manufacture technology; iii) lithotypes of excellent quality were seldom used, thus suggesting that trade purposes were neglected; iv) quite a few raw or splintered greenstone pebbles – raw materials potentially stockpiled for use and/or manufacture – were found. Lack of stock supplies, coupled to the scarceness of finished and/or valuable artifacts (destined to trade or symbolic purposes), reveal a prevailing contemporary and local use. However, these aspects might also suggest that the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
raw materials, instead of being collected from autochthon sources, were imported from other sites involved in a structural hierarchy of possible trades. Other close settlements (e.g., Alba and Brignano Frascata) certainly had a more important role.
Whatever their origin, these materials were probably selected directly on the supply site so not to bring unfit lithotypes in the populated areas – a trend observed also elsewhere (e.g.,
Rivanazzano; D’Amico & Starnini, 2012). Only after being shaped in the form of rough casts, these rocks were brought to the village and used without prior stocking. The only forms of in
situ manufacturing were possibly represented by bushhammering, polishing or functional
retrieval of broken tools (Giaretti et al., 2006).
Acknowledgements
Marica Venturino and Filippo Maria Gambari are thanked for precious help and support. Marina Giaretti, Stefania Padovan and Barbara Zamagni are acknowledged for cooperation in providing accurate archaeological characterization of the implements. Special thanks go to Giacomo Chiari and Giovanna Occhiena for help in collecting XRPD data. Most analytical data in this paper were taken from the Master thesis of Ursula Perrone (1999).
References
Andò M.C. (1998): La pietra levigata neolitica di Gaione (PR). Studio petroarcheometrico dei litotipi. Unpublished Master Thesis, Università di Bologna, 124 p.
Barello, F., Venturino-Gambari, M., Rubat-Borel, F., Arobba, D., Ottomano, C. (2007): Asti, autostrada A21 Torino-Piacenza, svincolo autostradale Asti Est. Materiali dell’antica Età del Bronzo e strada glareata di età romana. Quaderni
della Soprintendenza Archeologica del Piemonte, 22, 227-231.
Benciolini L., Lombardo B., Martini S. (1988): Mineral chemistry and Fe/Mg Exchange geothermometry of ferrogabbro-derived eclogites from the Northwestern Alps. Neues Jahrbuch Miner. Abh., 159, 199-222.
Bernabò Brea M., D'Amico C., Ghedini M., Ghiretti A., Occhi S. (1996): Gaione, loc. Case Catena. In: Venturino Gambari M.: Le vie della pietra verde. L’industria litica levigata nella preistoria dell'Italia settentrionale, Omega Ed., Torino, pp.122-136. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Bernabò Brea M., Battiston C., Mazzieri P., Ottomano C. (2000): Un gruppo di figurine fittili dal sito di Ponte Ghiara (Parma). In: La Neolitizzazione tra Oriente ed Occidente, 2000, 269-287.
Blake, M.C., Moore, D.E., Jayko, A.S. (1995): The role of serpentinite mélanges in the unroofing of UHPM rocks: an example from the Western Alps of Italy. In: Ultrahigh Pressure Metamorphism, G. Coleman & W. Xiaomin (Eds.), 182-203.
Borgogno, M. (2000): Petrografia delle asce neolitiche della Rocca di Cavour (TO) e di analoghi litotipi affioranti nel Massiccio Ofiolitico del Monviso (Alpi Cozie). Tesi inedita, Università degli Studi di Torino, 178 p.
Castelli D., Compagnoni R., Lombardo B., Angiboust S., Balestro G., Ferrando S., Groppo C., Rolfo F. (2014): Crust-mantle interactions during subduction of oceanic & continental crust. Day 1- The Monviso meta-ophiolite Complex: HP metamorphism of oceanic crust & interactions with ultramafics. 10th International Eclogite Conference,
Post-Conference Excursion, 9 September 2013, GFT – Geological Field Trips, 6 (1.3), 1-73. ISSN: 2038-4947 (DOI:
10.3301/GFT.2014.03). http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/geological-field-trips/crust-mantle-interactions-during-subduction-of-oceanic-continental-crust.
Chiarenza, N. & Giustetto, R. (2010): L’officina litica di Pertus (Paesana, CN): testimonianze di lavorazione ed analisi minero-petrografiche. Quaderni della Soprintendenza Archeologica del Piemonte, 25, 13-29.
Chiari G., Compagnoni R., Giustetto R., Ricq de Bouard M. (1996): Metodi archeometrici per lo studio dei manufatti in pietra levigata. In: Venturino Gambari M.: Le vie della pietra verde. L’industria litica levigata nella preistoria
dell'Italia settentrionale, Omega Ed., Torino, pp. 5-52.
Compagnoni, R., Ricq-de-Bouard, M., Giustetto, R., Colombo, F. (1995): Eclogite and Na-pyroxenite stone axes of Southwestern Europe: a preliminar petrologic survey. In: Studies on metamorphic rocks and minerals of the Western
Alps. A volume in memory of Ugo Pognante, B. Lombardo, ed., Bollettino del Museo Regionale di Scienze Naturali,
Torino, 13, suppl. 2, 329-359.
Compagnoni, R., Giustetto, R., Ricq-de-Bouard, M., Venturino Gambari, M. (2006): Studio archeometrico di reperti neolitici e dell’età del rame in pietra verde levigata: discussione sulle tecniche analitiche ed interpretazione dei risultati.
Atti XXXIX Riunione Scientifica dell’Istituto Italiano di Preistoria e Protostoria, Firenze, 25-27 Novembre 2004,
655-682.
Compagnoni, R., Rolfo, F., Castelli, D. (2012): Jadeitite from the Monviso meta-ophiolite, western Alps: occurrence and genesis from an oceanic plagiogranite. Eur. J. Mineral., 24, 333-343.
D’Amico, C. (2005): Neolithic ‘greenstone’ axe blades from North-western Italy across Europe: a first petrographic comparison. Archaeometry, 47(2), 235-252.
D’Amico, C. & De Angelis, M.C. (2009): Neolithic greenstone in Umbria, from the Bellucci Collection. Petrography, provenance, interpretation. Rendic. Lincei, 20, 61-76.
D’Amico C. & Ghedini M. (1996): La pietra levigata della Collezione Traverso di Alba nel Museo Etnografico “L. Pigorini” di Roma, Atti 10° Congresso A.N.M.S., Bologna 1994, Museologia Scientifica, 13, Supplemento, 292-312. D’Amico C. & Starnini E. (2000): Eclogites, jades and other HP metaophiolites of the neolithic polished stone tools from Northern Italy. Kristallinikum, 26, 11-20.
D’Amico, C. & Starnini, E. (2006): Prehistoric polished stone artefacts in Italy: a petrographic and archaeological assessment. In: Geomaterials in Cultural Heritage, M. Maggetti & B. Messiga, eds., Geological Society, London, Special Publications, 257, 257-272.
D’Amico, C. & Starnini, E. (2012): La production d’outils de pierre en Italie du nord vue depuis l’atelier de Rivanazzano (province de Pavie, Lombardie): matières premières et chaîne opératoire. In: Produire des Aches en Néolithique. De la matière première à l’abandon. Actes de la Table Ronde de Saint-Germain-en-Laye, march 16-17 2007, P.A. De Labriffe, E. Thirault, Paris.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
D’Amico, C., Bargossi, G.M., Felice, G., Mazzeo, M. (1991): Giade ed eclogiti in pietra levigata. Studio petroarcheometrico. Mineralogica et Petrografica Acta, 34, 257-283.
D’Amico, C., Felice, G., Ghedini, M. (1992): Lithic supplies in the early Neolithic to Sammardenchia (Friuli), Northern Italy. Science and Technology for Cultural Heritage, 1, 159-176.
D’Amico C., Campana R., Felice G., Ghedini M. (1995). Eclogites and jades as prehistoric implements in Europe. A case of petrology applied to Cultural Heritage. Eur. J. Mineral., 7, 29-41.
D’Amico C., Felice G., Gasparotto G., Ghedini M., Nannetti M.C., Trentini P. (1997): La pietra neolitica di Sammardenchia (Friuli). Catalogo petrografico. Mineralogica et Petrografica Acta, 40, 385-42.
D’Amico C., Starnini E., Voytek B.A. (2000): L’industria litica di Brignano Frascata (AL): dati paleoeconomici di un insediamento del Neolitico Antico attraverso l'analisi tipologica, funzionale e lo studio della provenienza delle materie prime. Preistoria Alpina, 31, 91-124.
D’Amico, C, Starnini, E., Gasparotto, G., Ghedini, M. (2003): Eclogites, jades and other HP-metaophiolites employed for prehistoric polished stone implements in Italy and Europe. Period. Mineral., 73, 17-42.
D’Amico, C., Nenzioni, G., Fabris, S., Ronchi, S., Lenzi, F. (2013): Neolithic tools in S. Lazzaro di Savena (Bologna). A petro-archaeometric study. Rendic. Lincei, 24(1), 23-38.
Damour, M.A. (1846): Analyse du jade oriental: réunion de cette substance à la tremolite. Ann.Chim. Phys., 3rd ser., 17, 469-474.
Delcaro, D. (2004): Analisi tecnologica dell’industria in pietra levigata. In : Alla Conquista dell’Appennino, le Prime
Comunità della valli Curone, Grue e Ossona. Omega Ed., Torino, pp. 61-68.
Diffrac Plus Evaluation Package (2005). Copyright © SOCABIM, 1996-2005.
Fabris S. (1996). Ricerche petrografiche e archeometriche sulla pietra levigata neolitica dell’area di S. Lazzaro di Savena (BO). Unpublished Master Thesis, Università di Bologna, 133 p.
Franchi, S. (1900): Sopra alcuni giacimenti di rocce giadeitiche nelle Alpi Occidentali e nell’Appennino Ligure. Boll.
R. Comit. Geol. It., 4, 119-158.
Garibaldi, P., Isetti, E., Rossi, G. (1996): Monte Savino (Sassello) e Appennino ligure-piemontese. In: Venturino Gambari M.: Le vie della pietra verde. L’industria litica levigata nella preistoria dell'Italia settentrionale, Omega Ed., Torino, pp. 113-119.
Gastaldi, B. (1871): Studi geologici sulle Alpi Occidentali. Mem. Descr. Carta Geol. Italia, 1, 1-36.
Giaretti M., Giustetto R., Perrone U. (2006): L’industria in pietra levigata da Castello d’Annone (AT). Atti della XXXIX
riunione scientifica dell’Istituto Italiano di Preistoria e Protostoria, Firenze, 25-27 Novembre 2004, 772-778.
Giustetto, R., Chiari, G., Compagnoni, R. (2008): An easy non-invasive X-ray diffraction method to determine the composition of Na-pyroxenes from high-density ‘greenstone’ implements. Acta Crystallographica, A64, 161–168. Giustetto, R. & Compagnoni, R. (2004): Studio archeometrico dei manufatti in pietra levigata del Piemonte sud-orientale: valli Curone, Grue ed Ossona. In M. Venturino Gambari: Alla conquista dell’Appennino. Le prime comunità
delle valli Curone, Grue e Ossona. Omega Ed., Torino, pp. 45-59.
Giustetto R. & Compagnoni R. (2014): Petrographic classification of unusual high-pressure metamorphic rocks of archaeometric interest. Eur. J. Mineral.,26(5), 635-642.
Giustetto R., Berruto G., Diana E., Costa E. (2013): Decorated prehistoric pottery from Castello di Annone (Piedmont, Italy): archaeometric study and pilot comparison with coeval analogous finds. Journal of Archaeological Science, 40, 4249-4263. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
Hamon, C. (2006): Broyage et abrasion au Néolithique Ancien. Caractérisation technique et fonctionelle de l’outillage en grès du bassin Parisien. Oxford, BAR, International Series, 1551.
Harlow, G.E., Tsujimori, T., Sorensen, S.S. (2012): Jadeitites: new occurrences, new data, and implications for subduction-zone fluids. Eur. J. Mineral., 24/2, 197-399.
Mannoni, T. & Starnini, E. (1994): Il contributo delle analisi petrografiche nello studio dell’officina litica di
Rivanazzano (PV). In: C. D’Amico e R. Campana, Le scienze della terra e l’archeometria. Università di Bologna, 21. Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., Seifert, S.A., Zussman, J., Aoki, K., Gottardi, G. (1988): Nomenclature of pyroxenes. American Mineralogist, 73, 1123-1133.
Padovan, S. & Salzani, P. (2014): La ceramica vascolare, il Neolitico. In : La memoria del Passato, Castello di Annone
tra Archeologia e Storia. LineLab. Ed., Alessandria, pp. 145-192.
Panozzo, N. (1998): Manufatti in pietra levigata : macinelli, macine e lisciatoi. In: Presso l’Adige ridente. Recenti
rinvenimenti archeologici da Este a Montagnana. Catalogo della Mostra, E. Bianchin Citton, G. Gambacurta, A Ruta
Serafini Eds., Padova, pp. 377-385.
Perrone U. (1999): Le asce neolitiche in “Pietra Verde” di Castello d’Annone (AT): caratterizzazione petrografica, aree di provenienza e realizzazione di una banca dati informatizzata. Unpublished Master Thesis, University of Torino, 161 p.
Pétrequin, P., Errera, M., Cassen, S., Billand, G., Colas, C., Maréchal, D., Prodéo, F., Vangele, F. (2005a): Des Alpes italiennes à l’Atlantique: les quatre grandes haches polies de Vendeuil et Maizy (Aisne), Brenouille (Oise). Hommage à Claudine Pommepuy. Revue archéologique de Picardie, numéro spécial 22, 75-104.
Pétrequin, P., Pétrequin, A.M., Errera, M., Cassen, S., Croutsch, C., Klassen, L., Rossy, M., Garibaldi, P., Isetti, E., Rossi, G., Delcaro, D. (2005b): Beigua, Monviso e Valais. All’origine delle grandi asce levigate di origine alpina in Europa occidentale durante il V millennio. Rivista di Scienze Preistoriche, 55, 265-322.
Pétrequin, P., Errera, M., Pétrequin, A.M., Allard, P. (2006): The neolithic quarries of Mont Viso (Piedmont, Italy). Initial radiocarbon dates. European Journal of Archaeology, 9/1, 7-30.
Pétrequin, P; Cassen, S.; Errera, M.; Klassen, L.; Pétrequin, A.M.; Sheridan, A. (2013): The value of things: the production and circulation of Alpine jade axes during the 5th – 4th millennia in a European perspective. Economic
Archaeology: from structure to performance in European archaeology. Habelt. Bonn., 65-82.
Piggot, S. & Powell, T.G.E. (1951): The excavation of three Neolithic chambered tombs in Galloway, 1949. Proc. Soc.
Antiq. Scot., 83,103-161.
Powell R. (1985): Regression diagnostics and robust regression in geothermometer/geobarometer calibration: the garnet-clinopyroxene geothermometer revisited. Journal of Metamorphic Geology, 3, 231-243.
Ricq-de-Bouard, M. (1981): Le diffusion de l’outillage de pierre polie en Provence oriental. In: Gallia Préhistoire, 24, 281-290.
Ricq-de-Bouard, M. (1996): Pétrographie et sociétés Néolitiques en France méditerranéenne. L’outillage en pierre polie.
Monographie du CRA, 16, CNRS Editions, Paris, 272 p.
Ricq-de-Bouard, M. & Fedele, F.G. (1993): Neolithic rock resources across the Western Alps: circulation data and models. Geoarchaeology, 8, 1–22.
Schertl, H.P., Maresch, W.V., Stanek, K.P., Hertwig, A., Krebs, M., Baese, R., Sergeev, S.S. (2012): New occurrences of jadeitite, jadeite quartzite and jadeite-lawsonite quartzite in the Dominican Republic, Hispaniola: petrological and geochronological overview. Eur. J. Mineral., 24, 199-216.
Schmidt, J. & Stelcl, J. (1971): Jadeites from Moravian Neolithic period. Acta Univ. Carolinae, Geol., 1-2, 141-152. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
Spear, F.S. (1993): The calculation of metamorphic phase equilibria I: geothermometry and geobarometry. In: Metamorphic phase equilibria and pressure-temperature-time paths. Mineralogical Society of America, Monograph, Washington, 15, pp. 511-545.
Starnini, E. & Maggi, R. (1990): L’industria litica levigata. In: Archeologia dell’Appennino ligure, R. Maggi Ed., Bordighera (Collezione di Monografie Preistoriche ed Archeologiche), pp. 89-126.
Venturino Gambari, M., Carraro, F., Perotto, A., Zamagni, B., Luzzi, M. (1995): Castello di Annone, loc. Castello. Indagine nell’area degli insediamenti pre-protostorici (tavv. CXXXI-CXXXII A). Quaderni della Soprintendenza
Archeologica del Piemonte, 13, 319-323.
Venturino Gambari, M. (2014): Lungo le vie di Annone. Preistoria e protostoria a castello di Annone. In: La Memoria
del Passato; Castello di Annone tra Archeologia e Storia. LineLab. Ed., Alessandria, pp. 39-68.
Venturino Gambari M. & Zamagni B. (1996): Castello di Annone. In: Venturino Gambari M.: Le vie della pietra verde.
L’industria litica levigata nella preistoria dell'Italia settentrionale, Omega Ed., Torino, pp. 98-105.
Woolley, A.R. (1983): Jade axes and other artefacts. In D.R.C. Kempe and A.P. Harvey (Eds.): The petrology of
Archaeological Artefacts. The Clarendon Press, Oxford, pp. 256-276.
Zamagni, B. (2014): L’industria litica in pietra non scheggiata. In: La Memoria del Passato; Castello di Annone tra
Archeologia e Storia. LineLab. Ed., Alessandria, pp. 347-362.
Tables
Inventory Thin Section Main minerals Minor and/or accessory minerals
Jd Omp Grt Rt Ttn Zrn All Lw
pseud. (Phe/Pg)WM (Zo/CZo)Ep Gln (Act/Hbl)AMPH Chl Ab Ilm Ap Na-pyroxene + garnet rocks (22 specimens)
Eclogites (17 specimens) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
1802/62/11 PIEM 36 X X X X X X X X X X X X 1554C 61 PIEM 38 X X X X X X X X X X X X 69326 PIEM 45 X X X X X CdA 2022/1 PIEM 46 X X X X X X X X 1802/62/1 PIEM 49 X X X X X X X X X X X X X CdA 95 C 25/2 PIEM 51 X X X X CdA 95 2057/4 PIEM 56 X X X X X X X 1802/6 PIEM 57 X X X X X AN1 40/1 PIEM 60 X X CdA 93 C505/114 PIEM 62 X X X X X X X CdA 95 D2045/10 PIEM 63 X X X X X 67176 PIEM 64 X X X X X X CdA 95D 2045/3 PIEM 66 X X X X X X X X AN1 74 PIEM 69 X X X X AN1 21 PIEM 70 X X X X X X X AN1 69 PIEM 73 X X X X X X X CdA 95 2057/1 PIEM 74 X X X X
Garnet-omphacitites (with jadeite) (3 specimens)
AN1 68/1 PIEM 43 X X X X X X X
CdA95D 2023/1 PIEM 55 X X X X X X X X X X
CdA 93 rim. C/1 PIEM 58 X X X X X X X X
Garnet-omphacitites (2 specimens)
1802/7 PIEM 37 X X X X X X X X X X X
AN1 031 PIEM 67 X X X X X X X X X X
Na-pyroxene rocks (Na-pyroxenites) (14 specimens) Mixed Na-pyroxenites (7 specimens)
1802/12 PIEM 39 X X X X CdA 95 2055/1 PIEM 44 X X X X X X X 1801/104/2 PIEM 47 X X X X X X X CdA 95 2057/3 PIEM 54 X X X X X X X CdA95D 2045/5 PIEM 59 X X X X X CdA 9 E 2039/1 PIEM 61 X X X X X X X X CdA 94 1428-1 PIEM 65 X X X X X X X Omphacitites (4 specimens) 1802/60 10 PIEM 50 X X 1801/103 69331 PIEM 52 X X X X X 1802/15 PIEM 53 X X X CdA 95 D 2051 PIEM 72 X X X X Jadeitites (3 specimens) CdA 93 411/14 PIEM 41 X X X X X X X CdA 95 2042/7 PIEM 48 X X X X X X X AN1 66 PIEM 68 X X X
Other lithotypes (2 specimens) Doleritic metabasalt with zoisite (1 specimen)
AN1 13 67221 PIEM 40 X X X X X X
Amphibolite with clinozoisite and garnet (1 specimen)
CdA 93 C 400/10 PIEM 42 X X X X X X X
Table 1. Qualitative mineralogical composition of the 38 representative specimens from Castello di Annone, obtained by combining XRPD, optical microscopy and SEM-EDS data [Jd: jadeite; Omp: omphacite; Grt: garnet; Rt: rutile; Ttn: titanite; Zrn: zircon; All: allanite; Lw pseudo: pseudomorphs after original lawsonite; WM (Phe/Pg): white mica (phengite/paragonite); Ep (Zo/Czo): epidote (zoisite/clinozoisite); Gln: glaucophane; AMPH (Act/Hbl): amphibole (actinolite/hornblende); Chl: chlorite; Ab: albite; Ilm: ilmenite; Ap: apatite].
Figure captions
Figure 1. Simplified tectonic map of the Western Alps, with location of the Castello di Annone
archaeological site. The external (Blueschists facies) and internal (Eclogite facies) Piemonte Zone have been distinguished. In the upper left corner, a simplified map of 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Northern Italy with indication of the tectonic map area (dotted line) and the location of analogous coeval sites and field survey is reported: 1) Castello di Annone; 2) Alba; 3) Brignano Frascata; 4) Gaione; 5) Momperone; 6) Ponte Ghiara; 7) Rivanazzano; 8) Rocca di Cavour; 9) Sammardenchia; 10) San Lazzaro di Savena; 11) Vallone dei Carbonieri.
Figure 2. Neolithic greenstone axes from the Castello di Annone site.
Figure 3. a) Lithotypes distribution and; b) specific weights of the 212 lithic implements from
Castello di Annone, obtained by combining stereo-microscopic observations and density measurements.
Figure 4. X-ray powder diffraction (XRD) pattern collected in the 5-60° 2 range on a mixed Na-pyroxenite specimen (PIEM 39). The magnification (in the upper right part) shows the 29-38° 2 interval, in which the 3 main reflections of clinopyroxenes [(-221; (310); (002)] appear; their splitting is due to the coexistence of two pyroxenes, jadeite (Jd) and omphacite (Omph).
Figure 5. Compositional variation of Na-pyroxenes analyzed by SEM-EDS in 8 eclogites [PIEM
46: A) core and B) rim of relict clasts; C)-D) core and E) rim of pyroxenes in veins; G)-F) fine-grained nematoblasts. PIEM 49: A) diopside-rich core and B) aegirin-augite-rich rim of porphyroclasts; C) fine-grained porphyroblasts. PIEM 70: A) Ae-poorer and B) richer omphacite nematoblasts] and 4 garnet-omphacitites [PIEM 37: A) core and B) rim of omphacite blasts. PIEM 43: core (C) → rim (R) zoning of omphacite porphyroclasts. PIEM 55: A) Jd poikiloblasts; B) bluish core and C) rim of Ti-Fe-omphacites; D) unzoned omphacite. PIEM 58: A) Jd poikiloblasts; B) bluish core and C) rim of Ti-Fe-omphacites], plotted in the ternary diagram of Morimoto et al. (1988).
Figure 6. Detail of a jadeite porphyroblast (darker grey) from an eclogite (PIEM 73), containing
tiny domains of exsolved omphacite (lighter grey). The omphacitic pyroxenes, located below jadeite, show quite a complex zoning (SEM image, BSE, 450 X).
Figure 7. Compositional variation of garnets analyzed by SEM-EDS from 8 eclogites and 4
garnet-omphacitites, plotted in the grossular (Grs) – pyrope (Prp) – almandine + spessartine (Alm+Sps) ternary diagram. Arrows indicate the compositional zoning from core (C) to rim (R).
Figure 8. a) Garnet poikiloblast from an eclogite (PIEM 63), showing a marked zoning with a
reddish core and a pink rim; the surrounding omphacitic matric is quite homogeneous (optical polarizing microscope: PPL=observations at plane-polarized light, detail of a 120 X image). b) zoned omphacite from omphacitite (PIEM 52), showing a bluish core rich in Ti/Fe (up to 5 wt.%, in the centre) and a colourless rim (PPL; detail of a 120 X image).
Figure 9. Compositional variation of Na-pyroxenes from a mixed Na-pyroxenite, an omphacitite [PIEM 52: compositional variation between A) bluish- and B) colourless pyroxenes] and 3 jadeitites, plotted in the ternary diagram of Morimoto et al. (1988).
Figure 10. Compositional variation of Na-pyroxenes a) and garnets b) from 2 eclogites collected in
the upper ‘Vallone dei Carbonieri’ (Val Pellice), plotted in the of Morimoto et al. (1988) and grossular (Grs) – pyrope (Prp) – almandine + spessartine (Alm+Sps) ternary
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
diagrams, respectively. For garnets, arrows indicate the compositional zoning from core (C) to rim (R).
1 2
