Izanagi-Pacific ridge subduction revealed by a 56 to 46 Ma magmatic gap along the northeast Asian margin

Jeremy Tsung-Jui Wu,Jonny Wu

doi:10.1130/g46778.1

Abstract

Abstract Recent studies have debated the timing and spatial configuration of a possible intersection between the Pacific-Izanagi spreading ridge and the northeast Asian continental margin during Cretaceous or early Cenozoic times. Here we examine a newly compiled magmatic catalog of ∼900 published Cretaceous to Miocene igneous rock radioisotopic values and ages from the northeast Asian margin for ridge subduction evidence. Our synthesis reveals that a near-synchronous 56–46 Ma magmatic gap occurred across ∼1500 km of the Eurasian continental margin between Japan and Sikhote-Alin, Russian Far East. The magmatic gap separated two distinct phases of igneous activity: (1) an older, Cretaceous to Paleocene pre–56 Ma episode that had relatively lower εNd(t) (−15 to + 2), elevated (87Sr/86Sr)0 (initial ratio, 0.704–0.714), and relatively higher magmatic fluxes (∼1090 km2/m.y.); and (2) a younger, late Eocene to Miocene post–46 Ma phase that had relatively elevated εNd(t) (−2 to + 10), lower (87Sr/86Sr)0 (0.702–0.707), and a lower 390 km2/m.y. magmatic flux. The 56–46 Ma magmatic gap links other geological evidence across northeast Asia to constrain an early Cenozoic, low-angle ridge-trench intersection that had profound consequences for the Eurasian continental margin, and possibly led to the ca. 53–47 Ma Pacific plate reorganization.

Highlights

The Eurasian margin along East Asia has been a long-lived convergent margin since early Mesozoic times (e.g., Müller et al, 2016)
The high-angle ridgetrench intersection model proposed that a northwest-southeast–trending mid-ocean ridge that separated the Izanagi plate to the north and the Pacific plate to the south intersected the northeast Asian margin at a high angle; the resultant trench-trench-ridge triple junction swept from south to north in the late Cretaceous (Fig. 1B; Maruyama et al, 1997)
CHUR—chondritic unfractionated reservoir; (MORB) chemical characteristics extruded in BSE—bulk silica earth. (C) Early Cenozoic tectonic events 1–5 possibly the forearc region are considered the most disrelated to ridge subduction along the north- tinctive indicator of ridge-trench intersections east Asian margin

Summary

Introduction

The Eurasian margin along East Asia has been a long-lived convergent margin since early Mesozoic times (e.g., Müller et al, 2016). Three competing classes of plate tectonic reconstructions have been proposed for Pacific-Izanagi ridge-trench intersections along East Asia (Fig. 1) that imply alternative geological histories for the East Asian margin, for northwest Pacific Ocean plate reconstructions, and possibly for a 50 Ma Pacific hemisphere platemantle reorganization. The high-angle ridgetrench intersection model proposed that a northwest-southeast–trending mid-ocean ridge that separated the Izanagi plate to the north and the Pacific plate to the south intersected the northeast Asian margin at a high angle; the resultant trench-trench-ridge triple junction swept from south to north in the late Cretaceous (Fig. 1B; Maruyama et al, 1997). In the low-angle ridgetrench intersection model, a NNE-SSW–trending Izanagi-Pacific spreading ridge intersected subparallel to a large swath of the northeast Asian margin and was subducted beneath the margin in the early Cenozoic at 60–50 Ma (Fig. 1C; Whittaker et al, 2007; Seton et al, 2015). The marginal sea closure model involved the closure of now-vanished East Asian marginal seas in the early Cenozoic (Fig. 1D) (Domeier et al, 2017; Itoh et al, 2017)

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Discussion

Conclusion