Geological record of fluid flow and seismogenesis along an erosive subducting plate boundary

Abstract

Tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the Earth's subduction zones. In situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone. Until now, a fossil erosive subduction channel-the shear zone marking the plate boundary-has not been recognized in the field, so that seismic observations have provided the only information on plate boundary processes at erosive margins. Here we show that a fossil erosive margin is preserved in the Northern Apennines of Italy. It formed during the Tertiary transition from oceanic subduction to continental collision, and was preserved by the late deactivation and fossilization of the plate boundary. The outcropping erosive subduction channel is approximately 500 m thick. It is representative of the first 5 km of depth, with its deeper portions reaching approximately 150 degrees C. The fossil zone records several surprises. Two décollements were simultaneously active at the top and base of the subduction channel. Both deeper basal erosion and near-surface frontal erosion occurred. At shallow depths extension was a key deformation component within this erosive convergent plate boundary, and slip occurred without an observable fluid pressure cycle. At depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast (co-seismic) and slow (inter-seismic) slip. In the deepest portions of the outcropping subduction channel, extension is finally overprinted by compressional structures. In modern subduction zones the onset of seismic activity is believed to occur at approximately 150 degrees C, but in the fossil channel the onset occurred at cooler palaeo-temperatures.

Crustal redistribution, crust–mantle recycling and Phanerozoic evolution of the continental crust

“…1). While there has been some debate about how tectonic erosion is actually accomplished (von Huene and Ranero, 2003;von Huene et al, 2004;Vannucchi et al, 2008) there is now a consensus that this process is even more important than subduction accretion in the evolution of active plate margins. Clift and Vannucchi (2004) produced the first volume budget for the global subduction system that attempted to quantify how much crustal material is being subducted.…”

Late Oligocene–early Miocene olistostromes (sedimentary mélanges) as tectono-stratigraphic constraints to the geodynamic evolution of the exhumed Ligurian accretionary complex (Northern Apennines, NW Italy)

“…This regional scale episode was recorded by positive tectonic inversion in the wedge-top basin succession, accompanied by thrusting (e.g., Pini 1999;Cerrina Feroni et al 2004;Marroni et al 2010;Remitti et al 2011;Codegone et al 2012b). Switching from tectonic accretion to tectonic erosion has been recently proposed (see Vannucchi et al 2008;Remitti et al 2011) to explain the instability of the leading slope and frontal part of the Ligurian accretionary complex, as a result of the underthrusting of external Subligurian Units.…”

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

“…between temperatures of 150 and 350-450 • C) and along the subduction interface is recognized as the site of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus site of episodic tremors and slow-slip events (Rogers and Dragert, 2003;Liu and Rice, 2007;Hacker et al, 2003;Vannucchi et al, 2008;Meneghini et al, 2010;Angiboust et al, 2014Angiboust et al, , 2015Andersen et al, 2014;Hayman and Lavier, 2014;Fagereng et al, 2014).…”