Depth of slab breakoff in Archean: the role of radiogenic heat production of continental crust and eclogitization of oceanic crust

Abstract

Abstract The slab breakoff has been applied to many collisional orogen around the world to explain postcollisional magmatism and metamorphism. For Phanerozoic orogens, multiple lines of evidence indicate that ultrahigh-pressure metamorphic rocks are exhumed from depths of 100–400 km, implying deeper slab breakoff depths. However, the slab breakoff depth in Archean orogens is less certain, and the factors governing the depth of slab breakoff remain poorly constrained. In this study, we use a 2D numerical model to identify the key parameters controlling slab breakoff and to quantitatively evaluate the depth of slab breakoff. The results indicate that a high degree of eclogization of oceanic crust, fast convergence rates, and low radiogenic heat production of continental crust generally promote slab breakoff at greater depths. Otherwise, the shallow slab breakoff mode is favored. For Archean collisional orogens, it is more likely for shallow breakoff to occur, due to the higher radiogenic heat production and mantle potential temperature, potentially explaining the rare occurrence of ultra-high pressure metamorphic rocks in the Archean. We also quantified the effects of other factors, including the density of subcontinental lithospheric mantle and age of oceanic lithosphere, which play secondary roles in determining slab breakoff depth.