Ridge subduction sparked reorganization of the Pacific plate‐mantle system 60–50 million years ago

Abstract

A reorganization centered on the Pacific plate occurred ~53–47 million years ago. A “top‐down” plate tectonic mechanism, complete subduction of the Izanagi plate, as opposed to a “bottom‐up” mantle flow mechanism, has been proposed as the main driver. Verification based on marine geophysical observations is impossible as most ocean crust recording this event has been subducted. Using a forward modeling approach, which assimilates surface plate velocities and shallow thermal structure of slabs into mantle flow models, we show that complete Izanagi plate subduction and margin‐wide slab detachment induced a major change in sub‐Pacific mantle flow, from dominantly southward before 60 Ma to north‐northeastward after 50 Ma. Our results agree with onshore geology, mantle tomography, and the inferred motion of the Hawaiian hot spot and are consistent with a plate tectonic process driving the rapid plate‐mantle reorganization in the Pacific hemisphere between 60 and 50 Ma. This reorganization is reflected in tectonic changes in the Pacific and surrounding ocean basins.

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

“…Considering that the trench-transform distance likely depends on respective lithosphere thicknesses, it may vary along-strike depending on the plate's age. Since kinematic reconstructions, in Seton et al (2015), for example, indicate that the age of the Pacific plate increases southward from 0 to 80 Ma, we can reasonably assume that the Pacific fore-arc sliver will be wider in the south (Fig. 5).…”

“…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. Indeed, reconstructions by Zahirovic et al (2014) and Seton et al (2015) indicate that the age of the Pacific plate varies from ∼0 in the north to ∼80 Ma in the south of the proto-IBM arc. Sdrolias and Müller (2006) proposed a more restricted age range between 30 and 70 Ma.…”

“…Thirdly, transpression along a former transform boundary between two oceanic plates may allow the younger plate to subduct beneath the older as presently observed along the Hjort Trench (Meckel et al 2005). (4) The most reasonable trigger is the subduction of the Izanagi-Pacific (IP) Ridge beneath Asia at ∼ 60-55 Ma (Whittaker et al 2007;O'Connor et al 2013;Seton et al 2015). Rapid subduction of the still-spreading IP ridge, over a vast distance, likely triggered a chain reaction of tectonic plate reorganization (Fig.…”

“…Despite large uncertainties in rotational motions, they were able, using that model, to account for tectonic interactions with the Huatung Basin along the eastern margin during the Eocene. Seton et al (2015), assuming that the Izanagi slab detachment beneath East Asia was responsible for major plate reorganization, have examined the consequences on mantle flow in the Pacific region between ∼ 53 and 47 Ma. Their geodynamic calculations, compared with tomography data, let them argue that the flow changed from southward before 60 Ma to north-northeastward after 50 Ma, corroborating the paleolatitudes given by paleomagnetic data (Hall et al 1995c, Richter andAli 2015).…”

“…fossil arcs at that time) lay behind the active proto-Philippine Arc. These fossil arc terranes were separated from the Pacific oceanic plate by a transform fault that allowed the Izanagi and Pacific plates to subduct beneath East Asia (e.g., Seton et al 2015).…”