Fig. 3
Deformation structures along the southeastern DBBT. a Sample FD21: Mylonite from the DBBT near the village Trois Villes showing ductile c’-type shear bands which indicate W-vergent shearing; Fol (229/20) Lin (268/16); crossed polarizers. b Sample FD21: Large quartz grains are flattened, show undulose extinction, deformation lamellae, and recrystallization by BLG indicating deformation at low-grade conditions between ca. 400 and 280 °C; grain sizes are strongly reduced within strained areas; crossed polarizers. c Sample FD21: Quartz recrystallized by BLG along top-W shear bands and between large grains leading to core-and-mantle structures; large quartz grains are strongly flattened; Fol (229/20) Lin (268/16); crossed polarizers. d Sheared quartz lense within metasediments at the base of the Becca d’Aver continental fragment in the western Valtournenche indicating top-NW shearing. e Sample FD356: Garnet-bearing metasediment from the base of the Becca d’Aver continental fragment showing top-ESE shear bands; chlorite is stable and albite is fractured along shear bands; Fol (187/22) Lin (118/07). f Sample 369: Becca d’Aver calcschist showing late top-NW shear bands cutting through the chlorite-bearing foliation; Fol (203/38) Lin (138/15); parallel polarizers. g Sample FD41: Gneiss from the DBBT at Lago di Cignana; quartz recrystallized by dominant SGR; a GSPO indicates top-NW shearing; intrafolial, isoclinal folds developed during progressive deformation; late discrete semi-ductile to brittle shear planes cut through the foliation; Fol (244/22) Lin (312/16); crossed polarizers. h Sample FD40: Quartzitic mylonite from the DBBT at Lago di Cignana; NW-vergent fold and GSPO of quartz indicate a top-NW shear sense; Fol (254/35) Lin (304/27); crossed polarizers and gypsum plate inserted. i Sample FD271: Polished hand-specimen of a mylonite from the DBBT southwest of Breuil-Cervinia showing network of slickenside-type semi-ductile to brittle top-NW shear planes; Fol (284/46) Lin (312/40). j Outcrop north of Breuil-Cervinia; semi-ductile to brittle top-NW shear planes cutting through the mylonitic foliation indicate top-NW deformation across the ductile–brittle transition. k Sample FD317: Mylonite from the DBBT north of Breuil-Cervinia showing ductile top-NW shear bands; quartz grains are flattened and recrystallized by BLG; Fol (36/13) Lin (306/01). l Sample FD317: Ductile top-NW shear bands are partly associated with top-SE shear bands suggesting a pure shear component during bulk top-NW shearing. m Folds within Combin calcschists in the footwall of the DBBT at Arbengandegge west of Zermatt deforming an earlier stretching lineation and foliation; fold and crenulation axes plunge to the northeast (48/02). n Folds within Combin calcschists in the footwall of the DBBT northwest of Zermatt deforming an earlier stretching lineation and foliation; fold axes plunge to the southwest (241/27). o Sample FD139: Gneiss from the DBBT northwest of Zermatt showing late semi-ductile top-NW shear band associated with growth of chlorite; Fol (199/40) Lin (135/21)