Journal Article

A crustal model for Zealandia and Fiji

Amit Segev, Michael Rybakov and Nick Mortimer

in Geophysical Journal International

Volume 189, issue 3, pages 1277-1292
Published in print June 2012 | ISSN: 0956-540X
Published online June 2012 | e-ISSN: 1365-246X | DOI:
A crustal model for Zealandia and Fiji

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Existing maps of satellite (free-air) gravity and bathymetry, and the CRUST 2.0 global crustal structure model have been used to make new Bouguer gravity anomaly and crustal thickness maps of the SW Pacific region to analyse the region′s crustal structure. The new maps clearly outline the limits of the rifted, largely submerged continent of Zealandia. The Bouguer gravity anomalies of ocean crust, large igneous provinces and backarc basins vary simply and predictably with age. The bathymetric Fiji Platform lies in a water depth of <500 m and is some 400 × 200 km in size. This is significantly broader than the nearby volcanic Lau–Colville or Tonga–Kermadec ridges. Prominent low Bouguer anomalies (+20 to -’10 mGal) typify the Fiji Platform, New Caledonia and the northwest of Lord Howe Rise. Our analysis confirms a crustal thickness of >19 km for the entire Fiji Platform, comparable to stretched and submerged parts of Zealandia. The question whether the continental crustal thickness of Fiji is due to its actually being a rifted part of Gondwana–Zealandia or due to enhanced Eocene–Pliocene magmatism remains open, but testable, with the latter more likely. Using the new accurate 3-D crustal thickness and published radiometric dating of lavas, we estimate that the magmatic portions of Southwest Pacific Cenozoic subduction-related arcs (three Kings, Tonga and Vanuatu) have grown at net volumes which vary from 263 to ∼1400 km3 km–1 with net addition rates of 17–31 km3 km–1 Ma–1.

Keywords: Backarc basin processes; Oceanic plateaus and microcontinents; Dynamics: gravity and tectonics; Large igneous provinces; Crustal structure; Pacific Ocean

Journal Article.  10598 words.  Illustrated.

Subjects: Geophysics

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