Isotopes track Tethyan seamount subduction beneath the Troodos spreading centre, Cyprus

Abstract

Supra-subduction zone volcanoes record the chemical transfer of sedimentary and igneous material from the subducting plate to the overlying mantle and lithosphere. This transfer is thought to preferentially involve fluid-mobile elements, which swamp the signature of similar trace elements in the supra-subduction mantle. Using high-resolution isotope measurements of fluid-mobile Pb, we have traced the evolution and inputs beneath the supra-subduction spreading ridge that is now the Troodos Ophiolite, Cyprus. It is apparent that variable but significant amounts of Pb are actually derived from the mantle wedge, and substantial amounts of the fluid-immobile elements like Nb are introduced from the slab. Our study identifies a chemical transformation of the spreading crust, which reflects a spatial change in the Neo-Tethyan slab. The west was influenced by the subduction of pelagic/carbonate sediments overlying MORB, whereas the east and south also include a high 206Pb/204Pb component, similar to high-μmantle plumes distributed around northern Africa. This chemo-tectonic switch is interpreted to represent the location of supra-subduction spreading relative to the path of a seamount chain colliding with and subducting beneath the Troodos trench. The Hecataeus Rise, located to the southeast of Cyprus, is a candidate to be a foundered relic of this seamount chain, locked in the subduction zone. We also demonstrate that the supra-subduction mantle wedge was of an Atlantic/Pacific-type composition, but the subducting Neo-Tethyan oceanic crust had an Indian Ocean signature. As such, this destructive plate boundary can be defined as the Cretaceous interface between the Atlantic and Indian mantle domains.

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Identifiers

ORCID for Rex N. Taylor: orcid.org/0000-0002-9367-0294

ORCID for Agnieszka Michalik: orcid.org/0000-0001-7715-6482

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