Tectonic origin of supra-subduction zone ophiolites from the three-dimensional geochemical structure of the lava pile

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Ophiolites are fragments of oceanic crust preserved on land, and are often used to infer the internal structure of the oceanic crust and the processes by which it is formed. However, most ophiolites were not formed in typical mid-ocean ridge settings, and instead appear to have formed close to former subduction zones. The exact tectonic setting in which they were formed has been debated for over 40 years. If ophiolites represent fore-arc crust formed during subduction initiation events, then they provide insights into the initiation of subduction zones, an outstanding unresolved question in plate tectonics. If ophiolites were formed in back-arc or plate edge settings they may represent useful analogues for the internal structure of oceanic crust. If they were formed at a ridge-trench-trench or ridge-trench-transform triple junction then they could be used to investigate mantle wedge structure and processes. Different tectonic models predict different geochemical variations in ophiolite lavas with space and time. We will map out the 3D gechemical structure of the Troodos Ophiolite of Cyprus, one of the best preserved and exposed ophiolites. We will use major and trace element microanaysis of fresh volcanic glass in order to avoid the effects of alteration. Detailed high resolution sampling of sections through the Troodos volcanic section on both the northern and southern margins of the ophiolite will be used to determine the chemical evolution of magmatism. New 39Ar-40Ar ages for lavas from different stratigraphic levels in the Troodos lava sequence will be used to determine the age and duration of the volcanism, and rates of chemical evolution of magmatism with time. Our new geochemical and geochronological data will be used to test hypotheses for the tectonic origin of the Troodos ophiolite.