The Troodos Ophiolite and the upper ocean crust; a reciprocal traffic in scientific concepts

Abstract

Current understanding of the processes that construct and modify the oceanic upper crust is the result of 40 years interplay between concepts derived from ophiolites and those derived from active mid-ocean ridges. In the oceans, rates of processes can be measured, and the spatial distribution of current activity determined. In ophiolites the resulting structure is exposed in three dimensions. The Troodos ophiolite in Cyprus has played a crucial role in this exchange, since there the upper ophiolitic crust is preserved for over 100 km across strike, and has scarcely been deformed or heated more than a few tens of degrees since it formed in a supra-subduction zone environment ∼90 million years ago. The presence of the sheeted dike complex in Troodos, demonstrating 70 km of 100% extension, was crucial in the early stages of the plate tectonic debate. Later, the recognition of the exhalative nature of the ore deposits within the volcanics prepared the way for the discovery of black smokers in the oceans. The oceanic observations in turn brought new insights into the hydrothermal systems that had fed the ophiolitic sulfide deposits. Research on these ophiolitic systems then illuminated the oceanic systems again. Demonstration of the narrowness of the zone of crustal construction in the oceans and determination of the structure of upper crust at oceanic spreading axes led to a reassessment of the structure of the upper crust in Troodos. This in turn generated, and is continuing to generate, new approaches to the construction of the upper crust in the oceans. Because of chemical differences between ophiolitic crust and that of major ocean basins, parallels must be drawn with care. Creative interplay between the ophiolitic and oceanic environments, so crucial early in the plate tectonic revolution, shows no sign of abating. This topic is not solely history; it is also science in progress.