Geochemistry of the sheeted dyke complex, Troodos Ophiolite (Cyprus): Evidence for the magmatic evolution during subduction initiation

Abstract

Supra-subduction zone (SSZ) ophiolites, including the Troodos Ophiolite of Cyprus contain magmatic rocks with geochemical compositions indicating that they formed close to a subduction zone. However, the exact tectonic setting in which SSZ ophiolites were formed is debated, although it has been proposed that they represent fragments of fore-arc crust formed during subduction initiation. The sheeted dyke complex of an ophiolite provides information about the orientation and distance of the spreading axis relative to the slab. This study combines new and published geochemical data for the Troodos sheeted dyke complex with published data for volcanic glasses from the overlying lavas. We show that the sheeted dykes are generally tholeiitic compared to the tholeiitic to boninitic lavas, and most are less depleted (higher Zr/Yb) and contain less slab component (higher Ce/Pb) than the abundant boninitic Troodos lavas. This implies that the crust of the Troodos Ophiolite formed more distant from the trench than the off-axis boninites that mainly occur in the south of the ophiolite. Many of the Troodos dykes have compositions similar to fore-arc basalts from the Izu-Bonin-Mariana island arc, which were erupted during subduction initiation. Lavas equivalent to the sheeted dykes may exist in the lowermost lava pile of the Troodos Ophiolite. The observed geochemical evolution of Troodos from fore-arc basalt to boninite and tholeiite with a strong slab input resembles the stratigraphy of the Izu-Bonin-Mariana fore-arc. We suggest that the Troodos Ophiolite formed at a laterally propagating trench-ridge ‘double junction’ during subduction initiation.