Dynamics of subduction initiation with different evolutionary pathways

Abstract

[1] Changes of plate motion may have induced subduction initiation (SI), but the tectonic history of SI is different from one subduction zone to another. Izu-Bonin-Mariana (IBM) SI, accompanied by strong backarc spreading and voluminous eruption of Boninites, contrasts with the Aleutians which shows neither. Using finite element models, we explore visco-elasto-plastic parameters and driving boundary conditions for SI evolution. With an imposed velocity, we find three different evolutionary modes of SI: continuous without backarc spreading, continuous with backarc spreading and a segmented mode. With an increase in the coefficient of friction and a decrease in the rate of plastic weakening, the amount of convergence needed for SI increases from $20 to $220 km, while the mode changes from segmented to continuous with backarc spreading and eventually to continuous without backarc spreading. If the imposed velocity boundary condition is replaced with an imposed stress, the amount of convergence needed for SI is reduced and backarc spreading does not occur. These geodynamic models provide a basis for understanding the divergent geological pathways of SI. First, IBM evolution is consistent with subduction of an old strong plate with an imposed velocity which founders causing intense backarc spreading and Boninitic volcanism. Second, the New Hebrides SI is in the segmented mode due to its weak plate strength. Third, the Puysegur SI is in the continuous without backarc spreading mode with no associated volcanic activities. Fourth, the Aleutians SI has neither trench rollback nor backarc spreading because the slab is regulated by constant ridge-push forces.

Tectonic reconstructions for paleobathymetry in Drake Passage

“…Oceanic lithosphere on the South American side of the margin was thrust far enough beneath the Antarctic Peninsula and for long enough that subduction was forced to initiate (Leng and Gurnis, 2011). The loss of South American lithosphere in this way continued until segments of the South American-Antarctic mid-ocean ridge, approaching from southeast of the collision zone, started colliding with it in Miocene times.…”

Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction

“…(3) Spontaneous subduction involving the vertical sinking of older, denser lithosphere along a transform-fracture system, as proposed by many authors (e.g., Karig 1982;Stern and Bloomer 1992;Shervais and Choi 2011) can also be ruled out. First of all, reasonable numerical models indicate that compression across the boundary fault is required (e.g., Toth and Gurnis 1998;Gurnis et al 2004;Leng and Gurnis 2011;Leng et al 2012) and the classical mode of failure of lithosphere under compression is localization of the deformation along conjugated shear bands dipping at an angle of ∼50°, then failure along one of them and thrust development (e.g., Shemenda 1992). The theoretical conditions used in numerical models to initiate a "spontaneous" gravitational sinking lithosphere require an extremely young (newly formed) upper plate separated from an old, dense oceanic plate by a very weak boundary zone and sometimes even a no-slip condition on the down-going plate (Gerya et al 2008;Gerya 2012;Leng and Gurnis 2015).…”

“…Since the oldest lavas that include subduction components (near the KPRDaito Ridge intersection) are ∼48-49 Ma old (Ishizuka et al 2011a), we suppose that about 10 m.y. were necessary for the former transform boundary to turn into a subduction, as suggested by numerical models (Leng and Gurnis 2011;Leng et al 2012). At this stage, it is important to note that subduction did not initiate along a transform fault separating a younger and an older oceanic plate as has often been described (e.g., Shervais and Choi 2011;Stern et al 2012) but along a transform boundary between Mesozoic terranes characterized by a crust ∼20 km thick (Nishizawa et al 2014) and an oceanic plate characterized by a ∼6-7 km crust but with a lithosphere of highly variable thickness along the strike.…”

Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology

“…Subduction initiation has been addressed primarily through numerical modeling (2)(3)(4)(5)(6)(7)(8)(9). These studies have demonstrated the need for a weak zone in the lithosphere to facilitate subduction.…”