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21 June 2021 Aperto AperTO - Archivio Istituzionale Open Access dell'Università di Torino The Quaternary succession of the Bulè and Alpetto valleys (Monviso Massif, Piedmont) as a possible supply for prehistoric jade axes raw material This is the author's manuscript Original Citation: Availability: This version is available http://hdl.handle.net/2318/1525227 since 2015-09-22T08:19:50Z Published version: DOI:10.1007/s12210-015-0464-8 Terms of use: Open Access Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. (Article begins on next page) 06 October 2021 This is an author version of the contribution published on: Questa è la versione dell’autore dell’opera: The Quaternary succession of the Bulè and Alpetto valleys (Monviso Massif, Piedmont) as a possible supply for prehistoric jade axes raw material Rendiconti Lincei, 26, 2015, DOI: 10.1007/s12210-015-0464-8 The definitive version is available at: La versione definitiva è disponibile alla URL: http://link.springer.com/journal/12210 Title Page with all Author Contact Information Click here to download Title Page with all Author Contact Information: Forno et al ONCINO titolo e autori.docx The Quaternary succession of the Bulè and Alpetto valleys (Monviso Massif, Piedmont) as a possible supply for prehistoric jade axes raw material1 M. Gabriella Forno 2*, Silvia Avondetto2, Chiara Teresa Groppo2, Franco Rolfo2 2 Dipartimento di Scienze della Terra, Università degli studi di Torino, Via Valperga Caluso 35, 10125 Torino *Corresponding author: M.G. Forno [email protected] 1 This contribution is the extended, peer reviewed version of a paper presented at the conference THE FUTURE OF THE ITALIAN GEOSCIENCES, THE ITALIAN GEOSCIENCES OF THE FUTURE” held in Milano on September 10-12, 2014. Manuscript Click here to download Manuscript: Oncino definitivo.docx The Quaternary succession of the Bulè and Alpetto valleys (Monviso Massif, Piedmont) as a 1 possible supply for prehistoric jade axes raw material1 2 2* 2 2 2 3 M. Gabriella Forno , Silvia Avondetto , Chiara Teresa Groppo , Franco Rolfo 4 5 2 Dipartimento di Scienze della Terra, Università degli studi di Torino, Via Valperga Caluso 35, 10125 Torino 6 *Corresponding author: M.G. Forno [email protected] 7 8 9 Abstract 10 This contribution presents a geological mapping of the Quaternary succession of the Bulè and low 11 Alpetto tributary valleys (Po Valley, Piedmont), together with preliminary data on its petrography. 12 13 The investigated area, covering an altitude range between 3015 and 1485 meters a.s.l., is located in 14 the Monviso Massif Ophiolite Complex, at the contact with marble and calcschist of the Dora- 15 16 Maira Massif cover. 17 The Quaternary sequence mainly consists of glacial, outwash, debris and landslide deposits, with 18 local torrential/avalanche and colluvial bodies. The investigation on the petrographic composition 19 20 of these sediments has allowed to recognize the occasional occurrence of jadeitite boulders, likely 21 exploited during the Neolithic period for axe head production. Four possible jadeitite blocks have 22 3 23 been found, one of them is described here for the first time, sizing up to 1 m . In detail, one of the 24 finds is a Neolithic site of jade polishing in the high Bulè Valley, that was referred to the middle of 25 V millennium B.C. (Allisio, 2012). The jadeitite blocks have been found in the debris (site a), 26 27 landslide (site b), glacial (site c) and outwash (site d) sediments. The petrographic characterization 28 of the new jadeitite samples, might potentially shed light on the still controversial genesis of these 29 30 peculiar rocks. 31 32 Key words: Monviso Massif, prehistoric jade axes, Quaternary succession, jadeitite 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 1 This contribution is the extended, peer reviewed version of a paper presented at the session “Archaeometry 58 andCultural Heritage: the contribution of Geosciences” held during the conference “The future of the Italian 59 Geosciences, the Italian Geosciences of the future” organized by the Società Geologica Italiana and the Società Italiana 60 61 di Mineralogia e Petrologia, Milano, September 10-12, 2014. 62 63 64 65 1 2 3 1. Introduction 4 5 In the Antiquity Museum of Torino several ancient axes made of jadeitite and omphacitite are 6 7 exposed, related to the Neolithic period (Compagnoni et al. 1995). The petrographic composition of 8 9 the jadeitite axes, representing the most typical finds, suggests to previous authors a supply from the 10 western Alps, particularly from the Monviso Massif (Compagnoni et al. 2007). The petrographic 11 12 composition of the jadeitite axes was already studied in detail by previous research and will not be 13 14 further discussed in this paper. It is possible that the prehistoric man not directly scooped the 15 16 bedrock, the more difficult to sample because at high altitude and not easily accessible, but used 17 18 instead some ready boulders contained in the Quaternary sediments located at lower altitude than 19 the source outcrops (Allisio 2012). 20 21 What is actually missing is an exhaustive characterization of the nature of Quaternary sediments in 22 23 which these jadeitite blocks are found. The recognition of the nature of such deposits could 24 25 eventually led to the discovery of other jadeitite blocks still unknown and to the understanding of 26 27 the Quaternary glacial and post-glacial evolution of the area. 28 29 A detailed mapping of the Quaternary succession of the Monviso sector , however, is still missing. 30 The main goal of the present study is, therefore, to provide the geologic setting of these sediments 31 32 in the Bulè and Alpetto valleys, the most promising localities for the supply of jadeitite clasts. This 33 34 research is useful to clarify the location of some boulders and clasts used as raw material for the axe 35 36 production in the framework of the Quaternary succession of the Bulè and Alpetto Valleys. Another 37 38 purpose of this study is to make a petrographic analysis of the clasts within the different types of 39 40 Quaternary deposits, useful to infer possible different lithologies and source outcrops within the 41 different units in the Monviso Massif. 42 43 This study represents, therefore, an example of the combined use of both Quaternary geology and 44 45 petrography, providing a contribute useful to clarify an archeological issue. 46 47 48 49 2. Methods 50 51 A detailed geological and geomorphological survey on the field and a traditional and digital 52 analysis of aerial photos were carried out in order to map the Quaternary succession. The 53 54 distribution of the Quaternary sediments was reported on the Carta Tecnica Regionale (CTR) of the 55 56 Regional Agency for the Protection of the Environment (A.R.P.A. Piemonte), at the 1:10000 scale. 57 58 Different units have been distinguished within the Quaternary succession, basing on the sediments 59 60 facies. 61 62 63 64 65 A petrographic analysis of the Quaternary sediments was devoted to the study of representative 1 2 boulders outcropping on the surface of the studied Quaternary succession, because of lack of 3 outcrops. In order to achieve these results, the most promising boulders were selected in the field on 4 5 the basis of their mesoscopic petrographic features. Representative thin sections of the selected 6 7 boulders were studied by means of transmitted polarized light petrographic microscopy. Because a 8 9 detailed minero-chemical study of the jadeitite is beyond the aim of this paper, only the main 10 11 petrographic features of the jadeitite are discussed, with particular attention to the newly discovered 12 13 block (site d). 14 15 16 17 3. Finds of jadeitite axes in the Western Alps 18 19 The Monviso Massif in the Western Alps is regarded as one of the main production areas of 20 21 Neolithic axes made with “green stones” (Pétrequin et al. 2005). In particular, the Monviso Massif 22 23 was recently reported to be especially important for the supply of Neolithic axes made with jadeitite 24 (Compagnoni and Rolfo 2003). Jadeitite outcrops, mostly associated with ultramafic bodies, are 25 26 extremely rare and the Western Alps is one of the few areas in the world where jadeitite 27 28 occurrences have been reported so far (Fig. 1). The high specific weight, toughness and hardness of 29 30 the jadeitite, coupled with its peculiar green color, make this lithology particularly suitable for the 31 32 building of tools. The archaeological finds suggest that these “green stones” axes have got a wide 33 34 spread in the Neolithic period, reaching for example all of Western Europe (France, Germany, 35 Spain and England) (Harlow and Sorensen 2005; Fig. 2). 36 37 The Monviso jadeitite is macroscopically a generally homogeneous, fine-grained rock, pale green in 38 39 color and mainly consisting of jadeite (Na-Al-pyroxene). However, it may locally contain irregular 40 41 cm-sized coarse-grained pockets and veins or even pegmatoidal portions, rich in various minerals as 42 43 for instance phlogopite, chlorite, garnet (Compagnoni et al. 2007). Genetically, the Monviso 44 45 jadeitite is considered as the metamorphic equivalent of former trondhjemites, i.e. the final products 46 of the oceanic basalt magmatic differentiation process, originally occurring as dykes cutting across 47 48 upper-mantle peridotite, later hydrated to serpentinite and subsequently affected by regional 49 50 metamorphism (Compagnoni et al.
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