Crustal accretion and tectonic setting of the Troodos ophiolite, Cyprus

Abstract

The Troodos ophiolite is composed of two distinct magmatic suites. An early, relatively high-TiO 2 basaltic suite constitutes the upper gabbros, the sheeted dike complex, and the andesitic to rhyodacitic lower pillow lavas. A late, low-TiO 2 basaltic andesite suite constitutes the lower ultramafic to gabbroic cumulates and the upper pillow lavas. Parental magmas to the early suite originated as partial melts from hydrous, relatively undepleted, peridotite diapirs rising in a mantle wedge in response to dehydration of a subducting crust. The late basaltic andesite suite is highly depleted in incompatible elements and show similarities with “second-stage” or refractory basalts from oceanic spreading centers. The Troodos basaltic andesites and associated cumulates may thus have formed in response to continued adiabatic upwelling as second-stage melts from the hydrous, water-undersaturated peridotite diapirs from which the earlier spreading related magmas were extracted. The basaltic andesites formed in a relatively slow-spreading or non-spreading tectonic environment and dominantly crystallized in magma chambers underplating the Troodos ophiolite. The extrusion of the basaltic andesites of the upper pillow lavas occurred simultaneously with still active evolving volcanic centers belonging to the earlier magmatic suite. An alternative possibility would be that the basaltic andesites separated from renewed diapirs rising as a consequence of re-initiation of subduction and liberation of fluids from the subducting slab into the overlying depleted peridotite. The existence of LREE and LIL enriched lavas among the upper pillow lavas support this possibility. The apparent conflict between a spreading related geology and the arc petrology and geochemistry of the Troodos ophiolite may be an artifact of lack of detailed studies of the geology and chemistry of oceanic and back-arc rifting environments. However, it is proposed that the available data for the Troodos ophiolite are consistent with its formation in a short-lived spreading basin formed by splitting of an immature, submarine arc.