The Sanbagawa belt is a “coherent” oceanic subduction-type metamorphic region representing a rock package predominantly derived from oceanic crust and accreted at depths of 20–80 km (300–700 °C). The thermal structure and lithological layers are complexly deformed but semi-continuous, in contrast to more commonly reported subduction-related domains dominated by mélange. The coeval Shimanto accretionary complex records accretion at depths <15 km and the rocks are primarily terrigenous sediments. The Sanbagawa belt has a greater proportion of mafic rocks than the Shimanto complex, implying progressive peeling-off of oceanic plate stratigraphy with more basaltic oceanic crust slices accreted at deeper levels. Tectonic exhumation can be explained by three separate phases dominated by buoyancy-driven upflow, ductile thinning, and normal faulting.
Abstract Eclogite‐bearing units in the Sambagawa Metamorphic Belt have long been considered tectonic blocks that have disparate tectonic and metamorphic histories that are distinct from each other and from the major non‐eclogitic Sambagawa schists. However, recent studies have shown that eclogite facies metamorphism of the Seba eclogite unit is related to the subduction event that caused the metamorphism of the non‐eclogitic Sambagawa schist. New structural data further show that the Seba eclogite unit, which appears to be isolated from the other eclogite units, is in fact in structural continuity with them, occupying the highest structural levels in the Sambagawa Belt. This suggests that eclogitic metamorphism of the other eclogite units is also related to the Sambagawa subduction event. It is, therefore, possible that all eclogite units in the Sambagawa Belt constitute a single coherent unit, the eclogite nappe, members of which underwent the same eclogitic metamorphism related to the Sambagawa subduction event.
