A short, sharp pulse of potassium -rich volcanism during continental collision and subduction

Abstract

Potassic volcanic rocks are characteristic of collisional tectonic zones, with recyclingof continental crust playing an important role in their generation. Potassium-rich partial melts and/or fluids derived from subducted continental material initiate and/or mix with mantle-derived melts and then erupt at the surface with varying degrees of interaction with the overlying lithosphere. The details of how continental material incorporates into mantle melts are, however, uncertain. In particular, the depths from which the potassium-rich fluids/melts are released from the continental material and then reacts with the mantle-derived melts remain a subject of debate. We have measured the boron isotope composition of volcanic rocks from Western Anatolia that erupted between 52– 0.1 Ma, and span the lifetime of collisional events from initial arc-type eruptions to post collisional volcanism. These data and other geochemical indices show that ultra-potassicvolcanism was mainly confined to a narrow window between ~20–15Ma, consistent withrecycling of high-pressure phengite, with the timing of the potassic volcanism coincident with slab roll-back and break-off.

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ORCID for Matthew Cooper: orcid.org/0000-0002-2130-2759

ORCID for James Milton: orcid.org/0000-0003-4245-5532

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