Mantle contamination and the Izu-Bonin-Mariana (IBM) 'high-tide mark': evidence for mantle extrusion caused by Tethyan closure

Western Pacific basins are characterized by three remarkable attributes: (1 ) complex kinematic histories linked to global-scale plate interactions; (2 ) DUPAL-like contaminated mantle; and (3) rapid post-Mesozoic rollback of t he confining are-trench systems. The coincidence of slab steepening, extrem e are curvature, and vigorous basin opening associated with the Mariana con vergent margin suggests that rollback continues in response to an east-dire cted mantle 'wind'. Against a backdrop of conflicting kinematic and genetic interpretations we explore the notion that eastward asthenospheric how dri ven by diachronous Tethyan closure caused stretching of eastern Eurasia and concomitant opening of western Pacific basins. Marking the eastern boundar y of the latter, the Izu-Bonin-Mariana forearc may be regarded as a litho-t ectonic 'high-tide mark' comprising igneous and metamorphic products from s uccessive episodes (since ca, 45 Ma.) of are sundering and backarc basin op ening. The foreare also forms an isotopic boundary separating contaminated western Pacific mantle from the N-MORB Pacific Ocean reservoir. While the i sotopic composition of western Pacific mantle resembles that feeding Indian Ocean hotspot and spreading systems, its spatial-temporal variation and th e presence of subduction barriers to the south appear to preclude northward flow of Indian Ocean mantle and require an endogenous origin for sub-Euras ian contaminated mantle. It is concluded that the extrusion of Tethyan asth enosphere, contaminated by sub-Asian cratonic lithosphere, was a major caus e of western Pacific are rollback and basin opening. The model is consisten t with paleomagnetic acid geologic evidence supporting independent kinemati c histories for constituent parts of the Philippine Sea and Sunda plates al though interpretation of these is speculative. Compounded by effects of the Australia-Indonesia collision, late-Tethyan mantle extrusion appears to ha ve produced the largest DUPAL domain in the northern hemisphere. (C) 2001 E lsevier Science B.V. All rights reserved.