Tephrostratigraphy and Provenance From IODP Expedition 352, Izu‐Bonin Arc: Tracing Tephra Sources and Volumes From the Oligocene to Recent

S Kutterolf,A T Baxter,A H F Robertson,K.‐L Wang,A Avery,J C Schindlbeck,K Petronotis

doi:10.1002/2017gc007100

Abstract

AbstractProvenance studies of widely distributed tephras, integrated within a well‐defined temporal framework, are important to deduce systematic changes in the source, scale, distribution, and changes in regional explosive volcanism. Here, we establish a robust tephrochronostratigraphy for a total of 157 marine tephra layers collected during IODP Expedition 352. We infer at least three major phases of highly explosive volcanism during Oligocene to Pleistocene time. Provenance analysis based on glass composition assigns 56 of the tephras to a Japan source, including correlations with 12 major and widespread tephra layers resulting from individual eruptions in Kyushu, Central Japan, and North Japan between 115 ka and 3.5 Ma. The remaining 101 tephras are assigned to four source regions along the Izu‐Bonin arc. One, exclusively assigned to the Oligocene age, is proximal to the Bonin Ridge islands; two reflect eruptions within the volcanic front and back‐arc of the central Izu‐Bonin arc, and a fourth region corresponds to the Northern Izu‐Bonin arc source. First‐order volume estimates imply eruptive magnitudes ranging from 6.3 to 7.6 for Japan‐related eruptions and between 5.5 and 6.5 for IBM eruptions. Our results suggest tephras between 30 and 22 Ma reflect a subtly different Izu‐Bonin chemical signature compared to the recent arc. After a ∼9 Ma gap in eruption, tephra supply from the Izu‐Bonin arc predominated from 15 to 5 Ma, and finally a subequal mixture of tephra sources from the (palaeo)Honshu and Izu‐Bonin arcs occured within the last ∼5 Ma.

Highlights

Explosive eruptions and their related products in the deep sea are integral to arc volcanism, in ocean-ocean subduction zone settings where subaerial outcrops are sparse or absent
Our results provide a reference tephrochronostratigraphy for the wider IBM/Japan region, refine shipboard age models for the drill sites, allow insights into the evolution of explosive arc volcanism from Oligocene onwards and support palaeogeographic and palaeotectonic interpretations of the background hemipelagic sediments [Robertson et al in press]
The distal ash layers in the IBM forearc sediments help us to constrain the size of some IBM and Japan eruptions, increase the previous volume and magnitude estimates for known Japan eruptions (Table 1), and demonstrate how important distal deposits are for the characterization of large explosive eruptions

Summary

Introduction

Explosive eruptions and their related products in the deep sea are integral to arc volcanism, in ocean-ocean subduction zone settings where subaerial outcrops are sparse or absent. Our results provide a reference tephrochronostratigraphy for the wider IBM/Japan region, refine shipboard age models for the drill sites, allow insights into the evolution of explosive arc volcanism from Oligocene onwards and support palaeogeographic and palaeotectonic interpretations of the background hemipelagic sediments [Robertson et al in press]. The volcanoes of the Honshu arc, formed from subduction of the Pacific Plate and/or the Philippine Sea Plate beneath the Eurasian Plate (Fig. 1) are known for large-scale explosive eruptions [Machida, 1999]. Plio-Pleistocene Hokuriki Group [Tamura and Yamazaki, 2004] This dataset is complemented by geochemical characterization of 17 Late Pliocene tephras from caldera-forming eruptions of the (Paleo-) Honshu arc [Kimura et al, 2015, Satoguchi and Nagahashi, 2012]. During Early Pliocene to Recent time, sedimentation was characterized by weakly calcareous clay/claystone/mudstone, and nannofossil ooze with abundant air-fall tephras [Reagan et al, 2015; Robertson et al in press]

Methods

Findings

Conclusions