A Subduction Initiation Rule Origin for SW Pacific Ophiolites: Implications for Ophiolites, Forearcs and the Tectonic Evolution of the SW Pacific
Abstract
SW Pacific ophiolites in Papua-New Guinea (the Papuan Ultramafic Belt or PUB ophiolite), New Caledonia and Northland, New Zealand represent forearc basement fragments of an associated, NE-dipping intra-oceanic arc system that underwent cyclical episodes of subduction, consequent forearc-continent collision and ophiolite emplacement, as subduction propagated diachronously from north to south throughout the Paleogene. Existing chemotemporal constraints suggest a subduction initiation rule (SIR) origin for these ophiolites. The SIR, articulated on the basis of the chemostratigraphic progression of lavas comprising Tethyan ophiolites and the Izu-Bonin forearc, predicts that: (a) most ophiolites and forearc units form during SI; and, (b) the diagnostic magmatic chemostratigraphic progression of these forearc-derived units from less to more HFSE-depleted and LILE-enriched compositions is the result of mantle melting that received progressively greater slab-derived subduction enrichments over the course of SI. Production of 66 Ma ODP Leg 180 (Woodlark Basin) dolerites interpreted as a NE extension of the PUB ophiolite for example, was followed by eruption of 59-58 Ma boninites and in Northland, the production of 32-26 Ma subduction-modified tholeiites was followed by formation of 25-15 Ma boninitic-like intrusives and lavas. In both cases, extreme mantle source depletion as represented by boninites was probably facilitated by initial extraction of slightly older tholeiitic magmas. Recent studies demonstrate that the SIR explains the chemotemporal evolution of Late Cretaceous Middle American forearc units and Neoproterozoic boninite-tholeiite sequences in South China and this contribution marks the first attempt at determining the applicability of the SIR to Paleogene SW Pacific ophiolites. Confirmation of a SIR origin for these ophiolites has far reaching implications for not only the tectonic evolution of the SW Pacific but also for the formation of forearcs and ophiolites in general, and their relation to the process of SI.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T44A..03W
- Keywords:
-
- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICSDE: 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 8140 Ophiolites;
- TECTONOPHYSICS