Deformation processes in the shallow levels of an accretionary prism: The Mesozoic Torlesse Terrane, South Island, New Zealand

Abstract

The deformation style of the Torlesse Terrane along the southern Kaikoura coast, South Island, New Zealand, records shallow level deformation processes within an accretionary prism during the Early Cretaceous. The beds exhibit complicated structural features resulting from multistage deformations in a lithological unit, that were intimately related with the dewatering and lithification of terrigenous sediments. The earliest phase of deformation throughout the transect studied was the development of pinch-and-swell structures and boudinage fabrics due to layer-parallel extension while the beds were poorly consolidated. This was followed locally by mesoscopic tight to close recumbent folding. The beds are cut locally by two phases of mudstone intrusions. The earlier phase was initiated by 'in situ' fluidization of mudstone layers, whereas the later phase represented intrusion of siliceous claystone probably derived from an overpressured decollement. Minor faults at high-angles to bedding by layer-normal shortening then disrupted the beds throughout the transect. The deformation was followed by formation of meso-and macroscopic scale open to gentle folds by layer-parallel shortening. Kilometer-scale differential stratal rotations were produced during the final main tectonic phase that occurred in association with postaccretion Neogene regional disturbance.

Progressive development of block‐in‐matrix fabric in a shale‐dominated shear zone: Insights from the Bobbio Tectonic Window (Northern Apennines, Italy)

“…Similar evidence reported from other exposed accretionary complexes have been related to early phases of prism advancement and footwall overloading (incipient tectonic compaction and layer parallel mineralized veins [ Meneghini et al , 2009]), mud diapirism, and/or gravity mass movement [ Barber et al , 1986; Byrne , 1985; Byrne and Fisher , 1990; Kano and Konishi , 2001; Alonso et al , 2006].…”

“…The potential similarity of these products, especially when partially lithified materials are involved, has produced long‐lasting debate in the international scientific community [e.g., Cowan , 1985; Osozawa et al , 2009; Festa et al , 2010a, 2010b]. The major interpretative problem concerns possible polyphase deformation and the mutual interaction of various processes like sedimentary mass transport events, diapirism of mud and loose sediments, in situ liquification (including both liquefaction and fluidization processes) [ Allen , 1982] and thrusting at shallow structural depths [ Elter and Trevisan , 1973; Vollmer and Bosworth , 1984; Barber et al , 1986; Kano and Konishi , 2001; Alonso et al , 2006; Yamamoto et al , 2009; Camerlenghi and Pini , 2009; Festa et al , 2010a, 2010b, and references therein]. Genetic processes and evolution of polygenetic BIM units developed through reworking of already disrupted and mixed rock masses are still poorly understood, although often suggested [ Aalto , 1981; Abbate et al , 1981; Osozawa et al , 2009].…”