9:00 AM - 9:15 AM
[SIT29-01] Stagnant slab tectonics of the Japan and northern Tonga slabs
Keywords:Stagnant slabs, seismic tomography, Japan slab, Tonga slab, Izanagi plate
In this study, we use new and recently published 3D slab mapping, slab unfolding and plate reconstruction constraints (Wu et al., 2016, JGR) from MITP08 and GAP_P4 global tomography (Li et al., 2008, G3; Fukao et al., 2013, JGR). We show that the Japan stagnant slabs are best reconstructed as Pacific slabs that subducted in the Cenozoic after Pacific-Izanagi ridge subduction between 60 to 50 Ma. Mantle flow forward models reproduce our Japan slab reconstruction results (Seton et al., 2015, GRL). Our reconstruction implies the Japan slabs moved laterally westwards within the upper mantle and transition zone after subduction at near-plate tectonic rates (~2 cm/yr over 50 Ma), indicating a greater lateral mobility of slabs within the upper mantle and transition zone than previously recognized.
Using our Japan slab subduction model, we re-examine the enigmatic Vityaz deep earthquakes under the Fiji Basin, which are widely thought to be a globally-unique case of seismicity within a foundered and detached slab. Our Tonga slab mapping shows the Vityaz earthquakes are actually part of a >2500 km-long mega-Wadati-Benioff zone of the northern Tonga stagnant slab. Our slab reconstruction suggests the northern Tonga slab moved laterally westward in a similar fashion to the Japan slabs, but at a faster rate of >5 cm/yr over 15 Ma within the upper ~660 km. Our results suggest that earthquakes can be produced thousands of kilometers away from a subduction zone from lateral movements of still-attached but mobile stagnant slabs within the uppermost ~660 km mantle.