Abstract
Breakdown of residual zircon in the Izu arc subducting slab during backarc rifting
Highlights
Depletion of high field strength elements (HFSEs: Nb, Ta, Zr, Hf, Ti) relative to largeion lithophile elements (LILEs: e.g., Rb, Ba, Sr) and rare earth elements (REEs) are commonly observed in lavas from subduction zones
In the Izu-Bonin-Mariana arc, slab-derived fluids that contributed to the source mantle are assumed to be saturated with rutile and zircon because basalts from the frontal and backarc volcanoes show distinctive Nb-Ta and Zr-Hf depletions (Tollstrup and Gill, 2005; Tollstrup et al, 2010)
Two types of basalts with different Zr contents were identified in the active rift zone of the Izu arc, which is the first stage of the backarc basin. We propose that their origin is related to the breakdown of residual zircon in the slab caused by high slab-surface temperatures related to the injection of asthenospheric material
Summary
Depletion of high field strength elements (HFSEs: Nb, Ta, Zr, Hf, Ti) relative to largeion lithophile elements (LILEs: e.g., Rb, Ba, Sr) and rare earth elements (REEs) are commonly observed in lavas from subduction zones. One of the possible explanations for HFSE depletion is that trace quantities of residual minerals in subducting slab, such as rutile and zircon, conserve HFSEs during the slab dehydration process (Elliott et al, 1997; Rubatto and Hermann, 2003). In the Izu-Bonin-Mariana arc (northwest Pacific Ocean), slab-derived fluids that contributed to the source mantle are assumed to be saturated with rutile and zircon because basalts from the frontal and backarc volcanoes show distinctive Nb-Ta and Zr-Hf depletions (Tollstrup and Gill, 2005; Tollstrup et al, 2010). In the Banda arc, partial melting of subducted material with breakdown of residual zircon caused by the high slab-surface temperature is anticipated (Nebel et al, 2011). It is suggested that injection of asthenospheric material in the Early Miocene, triggering backarc rifting of the northeast Japan arc, provided sufficient
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