Magmas and magma chamber evolution, Troodos ophiolite, Cyprus

Abstract

The Troodos ophiolite traditionally has been considered to have formed by constructive processes at an oceanic spreading center. New information on the phase layering and cryptic variation in gabbros and ultramafic cumulates overlying tectonized harzburgites, however, does not support the existence of a large, steady-state, frequently replenished, axial magma chamber. Compositional evidence suggests that the Troodos ophiolite was formed by two distinct and chemically unrelated magmatic systems. A stratigraphically lower websteritic and gabbroic cumulate sequence exhibits only one major magma-chamber replenishment, suggesting a nonspreading environment. An upper gabbroic cumulate sequence suggests frequent magma-chamber replenishments, pointing to a relatively fast-spreading environment. This suggests that the alleged Troodos axial magma chamber formed in an off-axis, nonspreading tectonic environment, probably by magmatic underplating of a thin oceanic crust. Spreading-related magmatic activity in the Troodos ophiolite was confined to the upper gabbros and dike complex.