Differentiating Induced vs. Spontaneous Subduction Initiation:From Thermal Expectations

Abstract:

Subduction is an essential process of Earth’s plate tectonics while the process of its initiation remains enigmatic. Two endmember modes of subduction initiation (SI) have been proposed: spontaneous and induced subduction initiation (SIS and ISI, respectively). However, the difference between their geological processes is poorly understood. One of the clues to the SI mode is the pressure-temperature (P-T) conditions that are recorded in metamorphic soles, which are interpreted as the slivers of the subducted oceanic crust that were metamorphosed during SI and subsequently exhumed. Here, we compute the temperature condition of the subduction interface during SSI and ISI, using 2-D numerical models. Subduction parameters that are varied among simulations include the ages of the overriding and subducting plates and the convergence rate. The model results show that in both modes, the highest temperature during SI is attained at the slab tip, making it the most favorable place to form low-pressure high-temperature metamorphic soles. However, the subduction interface is generally much hotter by up to a few hundred degrees during SSI than ISI. Based on the compiled P-T data of the global metamorphic soles, the results indicate that the metamorphic soles are more likely to from during SSI than ISI.