Volcano Clustering Promoted by the Cessation of Back‐Arc Spreading and Ensuing Nascent Lithospheric Drips

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AbstractIn Northeast Japan and Izu‐Bonin, arc volcanoes form in clusters or as cross‐arc chains. Their occurrence emphasizes the non‐uniform distributions of sub‐arc temperature and fluids that control the spacing of arc volcanoes. Here, using 3‐D numerical models, we show that the cessation of back‐arc spreading promotes volcano clustering by triggering the formation of nascent lithospheric drips – downward protrusions of cold and dense lithosphere‐adjacent to the thinned back‐arc lithosphere. The nascent drips interfere with the flow of the hot asthenospheric mantle from the back‐arc toward the arc, leading to gradual development of alternating hot and cold regions beneath the arc. The results indicate that along‐arc variation in the sub‐arc mantle temperature is largest not during back‐arc spreading but after its cessation, explaining the time offset by several million years between back‐arc spreading and volcano clustering in Northeast Japan and Izu‐Bonin.