No abstract

Convergent plate margins are currently distinguished as 'accretional' or 'erosional', depending on the tendency to accumulate sediments, or not, at the trench. Accretion and erosion can coexist along the same margin and we have noticed that this mostly occurs where subduction is oblique. Here we show that at oblique subduction zones, sediments that enter the trench are first buried, and later migrate laterally parallel to the trench and at various depths. Lateral migration of sediments continues until they reach a physical barrier where they begin to accumulate. The accretionary wedge size decreases along the trench moving away from the barrier. We therefore suggest that the gradual variation of the accretionary wedge size and sediment amount at the trench along one single subduction zone, as observed in many active plate margins worldwide, can be explained by the lateral tectonic migration of sediments driven by obliquity of subduction as well.

No abstract

This geological map at the 1:10,000 scale shows the structural setting of two poly-deformed metaophiolite units, with different metamorphic peak conditions, i.e. the blueschist facies Montenotte Unit and the eclogite facies Voltri Unit, in a selected area of 8.2 km2 within the Ligurian Alps (northern Italy). This study focuses on the tectonic contact between the two tectono-metamorphic units and on their relationships with the Oligocene sediments of the Tertiary Piedmont Basin. The map is a composite report of our field and laboratory study of structures and metamorphism, that explains our interpretation of the tectonic history of the study area. It shows that the two units were coupled during their exhumation path, along a blueschist facies mylonitic contact. This contact has been later involved in thrust faults that caused the superposition of the metamorphic basement on top of the Oligocene sediments

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