Journal of Maps ISSN: (Print) 1744-5647 (Online) Journal homepage: https://www.tandfonline.com/loi/tjom20 Role of structural inheritance in the gravitational deformation of the Monviso meta-ophiolite Complex: the Pui-Orgiera serpentinite landslide (Varaita Valley, Western Alps) Gianfranco Fioraso, Gianni Balestro, Andrea Festa & Luca Lanteri To cite this article: Gianfranco Fioraso, Gianni Balestro, Andrea Festa & Luca Lanteri (2019) Role of structural inheritance in the gravitational deformation of the Monviso meta-ophiolite Complex: the Pui-Orgiera serpentinite landslide (Varaita Valley, Western Alps), Journal of Maps, 15:2, 372-381, DOI: 10.1080/17445647.2019.1602854 To link to this article: https://doi.org/10.1080/17445647.2019.1602854 © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps View supplementary material Published online: 02 May 2019. Submit your article to this journal Article views: 137 View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tjom20 JOURNAL OF MAPS 2019, VOL. 15, NO. 2, 372–381 https://doi.org/10.1080/17445647.2019.1602854 Science Role of structural inheritance in the gravitational deformation of the Monviso meta-ophiolite Complex: the Pui-Orgiera serpentinite landslide (Varaita Valley, Western Alps) Gianfranco Fiorasoa, Gianni Balestrob, Andrea Festab and Luca Lanteric aInstitute of Geoscience and Earth Resources - National Research Council, Turin, Italy; bDepartment of Earth Sciences, University of Torino, Turin, Italy; cARPA Piemonte - Regional Agency for the Protection of the Environment, Turin, Italy ABSTRACT ARTICLE HISTORY Depending on its chemical and mineralogical composition, the serpentinite represents a Received 23 May 2018 peculiar rocky material, which plays a significant role in influencing pedogenetic Revised 15 January 2019 weathering, vegetation ecology, geo-mechanical and tectonic processes, as well as Accepted 31 March 2019 gravitational slope failure. In serpentinite-bearing environments the response to ff KEYWORDS gravitational stress is more e ective than in other rock types. In the Monviso meta- Monviso meta-ophiolite ophiolite Complex (Western Alps), a close relation between landsliding and serpentinite Complex; serpentinite; rock occurrences is particularly evident. Our geological map (Main Map), at a scale 1:10,000, landslide; rock flow; talcschist illustrates the geology and geomorphological features of the Pui-Orgiera giant (2.98 km2) complex landslide, located on the southern slope of the Monviso Massif. This map clearly documents that the characteristics and kinematics of the landslide are closely associated to the anomalous thickening and widening increase of the Baracun Shear Zone, a remnants of an intra-oceanic detachment fault which separates serpentinite and meta-intrusives from metabasalt and metasediments of the Monviso meta-ophiolite Complex. 1. Introduction Stark, Newman, de la Peña, & Hillebrandt, 2011; The serpentinite represents a very unique rocky Yatabe, Bhandary, & Okamura, 2007). material in terms of pedogenic processes (Alexander In the Italian Alps, the IFFI project (Inventory of & DuShey, 2011; Alexander, Coleman, Keeler-Wolf, Landslide Phenomena in Italy; http://www. & Harrison, 2007; Lee, Graham, Laurent, & Amrhein, isprambiente.gov.it/en/projects/soil-and-territory/iffi- 2004), plant ecology (D’Amico & Previtali, 2012; project) outlines a close relation between landsliding Kruckeberg, 1984), and tectonic processes (Hilairet and serpentinite rock occurrences as particularly evi- et al., 2007). Depending on its chemical composition dent in the Monviso meta-ophiolite Complex (MO and the crystallographic specificity of serpentine min- hereafter; see Balestro et al., 2014; Balestro, Fioraso, erals (Guillot, Schwartz, Reynard, Agard, & Prigent, & Lombardo, 2011, 2013)(Figure 1), which represents 2015), the serpentinite favours the formation of loca- a remnant of the Jurassic Alpine Tethys stacked in the lized mechanical and rheological weakness horizons, Western Alps (Balestro, Festa, Dilek, & Tartarotti, which may act as lubricant surfaces (Amiguet, Van 2015; Festa, Balestro, Dilek, & Tartarotti, 2015; Lom- De Moortèle, Cordier, Hilairet, & Reynard, 2014), bardo, Rubatto, & Castelli, 2002). concentrating short to long-lived tectonic and gravita- In this paper and related geological map at 1:10,000 tional deformation. In subaerial serpentinite-bearing scale (Main Map), we illustrate the geology and geo- environments the response to gravitational stress is morphological features of the Pui-Orgiera giant com- more effective than in other rock types as well-docu- plex landslide, located on the left side of the Varaita mented by both large-scale mass wasting occurrences Valley (southern slope of the Monviso Massif) between in various ophiolitic complexes (Cowan & Mansfield, the hamlets of Confine and Villar (Figure 2). It rep- 1970; Yamagishi & Ito, 1994; Yatabe, Yagi, & Yokota, resents one of the most impressive instability phenom- 1997) and the close relationships between landslides ena in ophiolite rock units of the Alps, in terms of size, and pervasive deformed serpentinite (Brandolini, kinematics and morphological evolution. This land- Nosengo, Pittaluga, Ramella, & Razzore, 1999; Cole- slide, in turn, is located in a slope extensively affected man, 1996; Cowan & Mansfield, 1970; Dickinson, by an imposing deep-seated gravitational deformation. 1966; Fioraso, Tararbra, & Negro, 2010; Phipps, 1984; In addition to Quaternary deposits and morphological CONTACT Gianfranco Fioraso gianfranco.fi[email protected] Institute of Geoscience and Earth Resources - National Research Council, Via Valperga Caluso 35, Turin, Italy © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF MAPS 373 Figure 1. Structural sketch map of the Western Alps (modified from Bigi et al., 1990; and Piana et al., 2017). The red inset shows the investigated area represented in the Main Map. 2. Methods features, particular attention was paid to the mapping of both geological and structural settings of the bed- The Main Map, at a scale of 1:10,000, encompasses an rock, which are crucial to better constrain the collapse area of 23.74 km2 located on the southern slope of the mechanisms of the landslide, involving serpentinite Monviso Massif, in the central Cottian Alps (Figure 1). bedrock. Our findings provide a better understanding Detailed geological data and geomorphological features of the landslide evolution, which is useful for both were collected by original mapping performed at the mitigation of potential future risks for local settle- 1:5,000 scale. Field work was integrated with photoin- ments, and the definition of useful criteria for study terpretation of multi-temporal aerial images (2000 col- of similar serpentinite-related landslides around the our photographs 1:15,000/1:19,000 scale of the world. Piemonte Region; 2004 black and white photographs 374 G. FIORASO ET AL. Figure 2. Panoramic view of the left side of the Varaita Valley. Red dashed line: tectonic contact between the Monviso meta-ophio- lite Complex (MO) and the Dora-Maira Unit (DM). Yellow dashed lines: boundaries of the Pui-Orgiera landslide and related sectors (Ld1–Ld4). Blue lines: lateral moraine ridges related to the Last Glacial Maximum. Photo taken from Sampeyre Pass (2283 m a.s.l.), view looking N (Long. 7°07′09′′, Lat. 44°33′04′′). 1:27,000 scale of the Italian Military Geographic Insti- its hangingwall. Tight to isoclinal folds deformed this tute) and digital orthophotos (2009–2011 with 50 cm/ succession and developed a pervasive axial plane foli- pixel resolution) of the Piemonte Region. In addition ation (i.e. the main regional foliation). Both the litho- to bedrock geology, glacial, periglacial, alluvial and logical and the syn-metamorphic tectonic contacts slope deposits, different types of gravitational phenom- (i.e. the Granero-Casteldelfino Shear Zone of Balestro ena (deep-seated slope deformations, landslide et al., 2018) are parallel to the main foliation. Post- accumulations and related morphological features) metamorphic faults, E- to NE striking, crosscut the are shown in the Main Map. meta-ophiolite succession, fracturing rock masses and Field data are represented on a vector topographic filling them with vein networks (Figure 3(a)). map partially derived from the ‘Carta Tecnica Regio- The top of the massive antigorite- and magnetite- nale Numerica’ at a scale of 1:10,000 of the Piemonte bearing serpentinite is discontinuously characterized Region (Coordinate System WGS 1984 UTM, Zone by meta-ophicarbonate horizons (Figure 3(c)), up to 32N). Because part of the orography of the investigated ten of metres thick, which consists of ‘clasts’ of serpen- area has radically changed following the massive slope tinite, cm to dm in size, laced by calcite and dolomite collapse occurred in July 2009, new 10 m contour lines veins. The serpentinite hosts meta-intrusives, ranging were obtained using the LIDAR-derived DTM with in size from decimetres rodingite dykes to hectometres 5 m resolution of the Piemonte Region (DTM Lidar