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

doi:10.1080/17445647.2019.1602854

Abstract

ABSTRACT Depending on its chemical and mineralogical composition, the serpentinite represents a peculiar rocky material, which plays a significant role in influencing pedogenetic weathering, vegetation ecology, geo-mechanical and tectonic processes, as well as gravitational slope failure. In serpentinite-bearing environments the response to gravitational stress is more effective than in other rock types. In the Monviso meta-ophiolite Complex (Western Alps), a close relation between landsliding and serpentinite rock occurrences is particularly evident. Our geological map (Main Map), at a scale 1:10,000, 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.

Highlights

The serpentinite represents a very unique rocky material in terms of pedogenic processes (Alexander & DuShey, 2011; Alexander, Coleman, Keeler-Wolf, & Harrison, 2007; Lee, Graham, Laurent, & Amrhein, 2004), plant ecology (D’Amico & Previtali, 2012; Kruckeberg, 1984), and tectonic processes (Hilairet et al, 2007)
In the Italian Alps, the IFFI project (Inventory of Landslide Phenomena in Italy; http://www. isprambiente.gov.it/en/projects/soil-and-territory/iffiproject) outlines a close relation between landsliding and serpentinite rock occurrences as evident in the Monviso meta-ophiolite Complex (MO hereafter; see Balestro et al, 2014; Balestro, Fioraso, & Lombardo, 2011, 2013) (Figure 1), which represents a remnant of the Jurassic Alpine Tethys stacked in the Western Alps (Balestro, Festa, Dilek, & Tartarotti, 2015; Festa, Balestro, Dilek, & Tartarotti, 2015; Lombardo, Rubatto, & Castelli, 2002)
Our findings provide a better understanding of the landslide evolution, which is useful for both the mitigation of potential future risks for local settlements, and the definition of useful criteria for study of similar serpentinite-related landslides around the world

Summary

Introduction

The serpentinite represents a very unique rocky material in terms of pedogenic processes (Alexander & DuShey, 2011; Alexander, Coleman, Keeler-Wolf, & Harrison, 2007; Lee, Graham, Laurent, & Amrhein, 2004), plant ecology (D’Amico & Previtali, 2012; Kruckeberg, 1984), and tectonic processes (Hilairet et al, 2007). In this paper and related geological map at 1:10,000 scale (Main Map), we illustrate the geology and geomorphological features of the Pui-Orgiera giant complex landslide, located on the left side of the Varaita Valley (southern slope of the Monviso Massif) between the hamlets of Confine and Villar (Figure 2). It represents one of the most impressive instability phenomena in ophiolite rock units of the Alps, in terms of size, kinematics and morphological evolution. Our findings provide a better understanding of the landslide evolution, which is useful for both the mitigation of potential future risks for local settlements, and the definition of useful criteria for study of similar serpentinite-related landslides around the world

Methods

Geological and morphological setting

The Pui-Orgiera landslide

Discussion and conclusions