Insights into the mechanics of En-Échelon sigmoidal vein formation using ultra-high resolution photogrammetry

Sigmoidal veins are a class of en-échelon vein characterised by their unusual S or Z shaped geometry (Beach 1975). There has been considerable uncertainty over the mechanisms controlling their formation (Nicholson & Pollard 1985; Rickard & Rixon 1983; Tanner 1992), and hence how best to interpret their significance in terms of far-field palaeostress orientations, principal strain axes and strain evolution over time (eg. Belayneh & Cosgrove 2010; Lisle 2013). This study (see also Thiele et al., in press) uses novel quantitative photogrammetric methods to examine the formation of a well-preserved sigmoidal vein array in a rock sample collected from Cape Liptrap, Victoria (Fig. 1a).