Arc‐Type Magmatism Due to Continental‐Edge Plowing Through Ancient Subduction‐Enriched Mantle

• Published in: Geophysical research letters Vol. 47; no. 9
• Main Authors: Hinsbergen, Douwe J. J., Spakman, Wim, Boorder, Hugo, Dongen, Michiel, Jowitt, Simon M., Mason, Paul R. D.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.05.2020
• Subjects: absolute plate motion; Asthenosphere; Earth mantle; Electric arc melting; Enrichment; Geochemistry; Geological history; Lava; Lithosphere; Magma; magmatism; Melting; Melts; plate reconstruction; Plate tectonics; Plates (tectonics); Plowing; Rock; Rocks; Seismology; Signatures; Subduction; Subduction (geology); Subduction zones; tomography; Transform faults; Upper mantle; Volcanic activity; Volcanism; New Guinea
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL087484

The puzzling <7 Ma old “postsubduction” arc magmatism of New Guinea contains geochemical subduction‐type signatures yet did not occur above an active subduction zone. Here we show that these arc magmas formed at the North Australian continental lithospheric edge when it plowed northward through mantle above the detached Arafura slab remnant. This mantle preserved its subduction signature and the edge plowing process generated new melts that ascended via an active transform fault. Arafura slab subduction occurred at an intraoceanic subduction zone that ended ~30–25 Ma ago, when the Australian continental edge was still ~1,000 km to the south. Our absolute plate tectonic reconstruction of continental‐edge plowing suggests that ancient mantle wedges remain semistationary in the upper mantle and can preserve their geochemical signature for tens of Ma, explaining previously enigmatic “postsubduction” arc magmatism. Plain Language Summary During subduction, downgoing plate lithosphere (“slab”) releases water to the overlying mantle causing so‐called “arc volcanism.” A puzzling class of “postsubduction” arc magmatism bears geochemical signatures of subduction but occurs in a setting without subduction. Here we show that this magmatism is the result of remelting of mantle portions that were previously enriched by ancient subduction zones, slab relics of which are now found with seismological techniques below these enriched portions. From famous postarc magmatic rocks on New Guinea we identify that the “plowing” of the edge of a thick, continental lithosphere through a previously enriched mantle portion may provide a cause of melting, producing arc‐like magmatism. We also identify that pathways for the melts to rise to (close to) the surface, provided by major faults, are essential. The “New Guinea recipe” also explains magmatism on the Fiji Islands, California, and Colombia. A major implication of our work is that asthenospheric upper mantle rocks appear to move much slower than plates, such that lithosphere may have undergone a very different geological history than the currently underlying mantle. Key Points “Postsubduction” arc magmatism on New Guinea results from the Australian cratonic margin plowing through a previously enriched mantle wedge Mantle wedges may appear to remain semistationary in the mantle for tens of million years or even longer times and produce subduction signatures if remelted Absolute plate motions juxtapose mantle and crustal rocks with very different geological histories