Recycling of depleted continental mantle by subduction and plumes at the Hikurangi Plateau large igneous province, southwestern Pacific Ocean

K Mochizuki,N Bangs,R Sutherland,S Kodaira,D Bassett,D Barker,Y Yamamoto,G Fujie,S Henrys,H Van Avendonk,R Arai

doi:10.1130/g46250.1

Abstract

Abstract Seismic reflection and refraction data from Hikurangi Plateau (southwestern Pacific Ocean) require a crustal thickness of 10 ± 1 km, seismic velocity of 7.25 ± 0.35 km/s at the base of the crust, and mantle velocity of 8.30 ± 0.25 km/s just beneath the Moho. Published models of gravity data that assume normal crust and mantle density predict 5–10-km-thicker crust than we observe, suggesting that the mantle beneath Hikurangi Plateau has anomalously low density, which is inconsistent with previous suggestions of eclogite to explain observations of high seismic velocity. The combination of high seismic velocity and low density requires the mantle to be highly depleted and not serpentinized. We propose that Hikurangi Plateau formed by decompression melting of buoyant mantle that was removed from a craton root by subduction, held beneath 660 km by viscous coupling to slabs, and then rose as a plume from the lower mantle. Ancient Re-Os ages from mantle xenoliths in nearby South Island, New Zealand, support this hypothesis. Erosion of buoyant depleted mantle from craton roots by subduction and then recycling in plumes to make new lithosphere may be an important global geochemical process.

Highlights

Hikurangi, Manihiki, and Ontong Java Plateaus were em placed coevally and possibly contiguously at ca. 120 Ma (Mahoney et al, 1993; Coffin and Eld holm, 1993)
The “Greater Ontong Java Event” included vol canism in the Nauru, East Mariana, Lyra, and possibly northwest Central Pacific Basins, and covered ~1% of Earth’s surface area (Coffin and Eldholm, 1994; Mahoney et al, 1993), but there is no consensus on what caused the event: mantle plumes (Mahoney et al, 1993), mid-ocean ridges, eclogite recycled by mantle circulation (Anderson, 2005), and bolide impacts (Ingle and Coffin, 2004) have all been invoked
Seismic reflection images (Fig. 2) and consideration of the stratigraphic and magmatic history of New Zealand reveal that it was pre viously subducted beneath the Chatham Rise, before 105–85 Ma, which is when Gondwana margin subduction ceased in this region (Bland et al, 2015; Bradshaw, 1989; Davy et al, 2008; Sutherland and Hollis, 2001)

Summary

Introduction

Manihiki, and Ontong Java Plateaus (southwestern Pacific Ocean) were em placed coevally and possibly contiguously at ca. 120 Ma (Mahoney et al, 1993; Coffin and Eld holm, 1993). Hikurangi Plateau is actively subducting be neath North Island, New Zealand, and can be recognized at depth as a geophysical anomaly on seismic tomography images (Reyners et al, 2011).

Results

Conclusion