Subduction initiation as recorded in the Izu-Bonin-Mariana forearc

Magmatic fingerprints of subduction initiation and mature subduction: numerical modelling and observations from the Izu-Bonin-Mariana system

“…In this manuscript we refer to the transform fault zone as the weak zone (WZ) (Figure 3). Similar setup has been used in previous numerical studies (e.g., Gerya et al, 2008;Zhou and Wada, 2022;Arcay et al, 2023) and it is in agreement with geochemical constraints (e.g., Li et al, 2019;Ishizuka et al, 2020;Reagan et al, 2023). The overall shape and dimension of the WZ in our model setup is supported by natural observations (e.g., Hensen et al, 2019;Gregory et al, 2021).…”

“…The timing of the spreading centre and the BAB emplacement can be compared with the Kyushu-Palau Ridge which was active between 25 Ma and 48 Ma (Ishizuka et al, 2011b). Geochemical interpretations of Ishizuka et al (2013) and Reagan et al (2023) point out that SI at IBM can be supported by a density gradient linked to a long transform fault zone (i.e., the WZ in our model setup), a mantle plume and by far field plate reorganisation (i.e., low convergence velocity in our model set up) (Wu et al, 2016;Wu et al, 2022). However, according to Reagan et al (2023) it is unclear whether the mantle plume was still active during SI of IBM due to the rapid timescale within the first 2 Myr after SI.…”

“…Geochemical interpretations of Ishizuka et al (2013) and Reagan et al (2023) point out that SI at IBM can be supported by a density gradient linked to a long transform fault zone (i.e., the WZ in our model setup), a mantle plume and by far field plate reorganisation (i.e., low convergence velocity in our model set up) (Wu et al, 2016;Wu et al, 2022). However, according to Reagan et al (2023) it is unclear whether the mantle plume was still active during SI of IBM due to the rapid timescale within the first 2 Myr after SI. The arrival of the mantle plume likely rejuvenated the Philippine Sea Plate leading to the initial set up of our models with a significant age gradient between the plates (Ishizuka et al, 2013;Reagan et al, 2023).…”

“…One ideal natural laboratory for studying intra-oceanic subduction initiation is the Izu-Bonin-Mariana (IBM) subduction zone. The rock record that has been emplaced during subduction inception has been preserved in the IBM fore-arc (e.g., Ishizuka et al, 2006;Reagan et al, 2010;Ishizuka et al, 2011a;Stern et al, 2012;Reagan et al, 2019;Ribeiro et al, 2020;Ribeiro et al, 2022;Reagan et al, 2023). This intra-oceanic plate boundary is located in the Western Pacific, where mid-Jurassic to Early Cretaceous oceanic floor from the Pacific plate gets subducted underneath the Philippine Plate (Figure 1) (Stern, 2004).…”

Inferring the Paleo‐Location of Proto‐Arc Magmas During Subduction Infancy in the Izu‐Bonin‐Mariana

“…A warmer slab P‐T path of the subducted Pacific plate in Eocene time is also supported by crustal melting of the incipient subducted Pacific plate in the amphibolite facies during boninitic magmatism (Li et al., 2019). Mantle upwellings triggered by the arrival of the Oki‐Daito mantle plume (Ishizuka et al., 2013) could have also warmed the nascent Pacific slab (Faccenna et al., 2010; Lallemand, 2016), while pre‐conditioning the mantle source of FABs and boninites (Ishizuka et al., 2022; Macpherson & Hall, 2001; Reagan et al., 2023; Shervais et al., 2019, 2021). A warmer incipient Pacific slab would result in the earlier breakdown of the intra‐slab mineral phases (Holt & Condit, 2021), which would efficiently release water and other volatiles much closer to the trench than predicted, as observed today in warm subduction zones such as Cascadia (van Keken et al., 2011) or Matthew‐Hunter (Patriat et al., 2019; Ribeiro, 2022).…”