was particularly important as sheeted dyke complexes are diagnostic of oceanic crust in ophiolites on the modern Earth. However, this interpretation was strongly contested on the basis that the sheeted dykes proposed by Furnes et al. were in fact a much younger generation of dykes, the ~3.5 billion year old (Ga) Ameralik dykes, and therefore unrelated to pillow lavas and other volcanic rocks of the belt. Other objections related to the composition of the dykes, which are unlike those found in modern-day ophiolites. Despite the disagreement on the presence of a sheeted dyke complex at Isua, alternative lines of evidence have been proposed in support of an ophiolite origin for the belt. These are primarily based on the geochemistry of the volcanic rocks in the belt: tholeiitic amphibolites have been interpreted as metamorphosed island-arc tholeiites, and boninite-like amphibolites have been interpreted to represent metamorphosed boninites. However, subsequent studies have pointed out that the boninite-like amphibolites are in fact low-titanium basalts, with too little silica to classify as boninites, and recent geochemical modelling suggests that the entire volcanic compositional range at Isua can be explained without requiring a plate tectonic setting. A further line of evidence used to invoke an ophiolite origin for the Isua Greenstone Belt is the presence of peridotite lenses in the volcanic sequence, particularly two dunite lenses referred to as 'lens A' and 'lens B'. These were argued to represent mantle rocks on the basis of their geochemistry, textures, and the presence of apparently high-pressure minerals. If true, the presence of mantle rocks within the supracrustal sequence at Isua would require that these rocks had been thrust to the surface, supporting an ophiolite origin for the belt. However, more recent work disputes a mantle origin for these rocks, and suggests that all features of the dunite lenses can be explained by them representing ultramafic cumulates formed in magma chambers that fed the eruption of volcanic rocks in the Isua Greenstone Belt. If this is the case, then no thrusting is required to bring them into contact with the supracrustal rocks, and the dunite lenses do not provide evidence that the Isua Greenstone Belt is an ophiolite. Accretionary wedge models The northeastern part of the Isua Greenstone Belt has been interpreted as part of an accretionary wedge on the basis of numerous small faults and apparent repetitions of the supracrustal sequence, with similarities to modern accretionary wedges. This