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Analysis of 70 subduction initiation sites

Updated: Nov 24, 2021

Serge Lallemand and Diane Arcay provide an exhaustive, careful and insightful overview of the many Cenozoic subduction initiation sites (SIS) on our planet:

To address the question of the initiation and mechanisms involved in the process of subduction zone formation, we explored most of the available evidence. We targeted a total of 70 candidate sites that experience or experienced subduction initiation cumulating ~70,000 km of trench. Our strategy is to define four stages reached at each subduction initiation site (SIS) from the incipient-diffuse stage through incipient-localized stage and early arc magma production to self-sustained subduction. We have paid special attention to prematurely extinguished, i.e., aborted, subduction attempts in order to better understand the reasons for the termination of the process, and thus to clarify the conditions of success. The failure of SI results from a combination of hindering parameters (e.g., lithosphere cooling, frictional resistance, unfavorable age contrasts for intra-oceanic SISs) and insufficient external forcings (e.g., too low convergence velocity). From this comprehensive study, we find that new subduction regularly nucleates, and with a success rate of more than 70% to reach subduction maturity, generally in less than ~15 Myr, ~3-8 Myr for the shortest time between the very early stage and the self-sustained stage. Lithospheric forces are required to ensure the success of the process in the early (immature) stages, with the help of mantle forces in a third of the cases. Multiple triggers are common. Stress during the SI process is compressive in most, if not all, cases and oriented obliquely to the nascent plate boundary in more than half of the cases. The incipient plate boundary generally reactivates an old lithospheric fault, most often with a change in its kinematics, i.e., conversion of a transform plate boundary, a former normal or a detachment fault, or even a former spreading center. Sometimes, the new lithospheric fault reactivates a former subduction fault. There is no rule concerning the age of the subducting plate, which varies from 0 to 140 Ma in the examples studied. In the same vein, the subducting plate is not necessarily older than the overriding plate when it is oceanic. Both situations are equally observed.

Lallemand and Arcay (2021, Earth-Science Reviews)

Map of Cenozoic SISs in the NW Pacific region.

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