| Summary: | A wide variety of "geological evidence supports the contention that the Troodos massif, Cyprus is a fragment of Mesozoic sea-floor created at a constructive plate margin. Here, the metamorphism and geochemistry of the dyke/pillow lava sequence at the top of the igreous succession are shown to be compatible with this proposal. The greater part of the sequence is basaltic and is divided by a metamorphic discontinuity near the top which sometimes coincides with an unconformity. This boundary separates two groups of lavas and their related dykes. Each unit has a characteristic metamorphic petrology. Metabasalts from the lower division, here termed the Axis Sequence, are comparable to those dredged from oceanic spreading axes, whereas the overlying rocks, the Upper Pillow Lavas, differ, and represent material erupted after the earlier metamorphic event. This group was subsequently metamorphosed in an environment with a lower the thermal gradient and its effects are not displayed by the Axis Sequence. Oxygen and strontium isotope data strongly suggest that the basaltic rocks of the Troodos massif have interacted with large volumes of seawater during the metamorphic events. A model for sub-sea-floor metamorphism at or near the Troodos spreading axes is erected. Most of the major elements are labile during metamorphic processes. It is only certain trace elements, notably Ti, Zr, Y, Cz and the rare earths which are unaffected by hydrothermal alteration and, as such, provide a clue to the compositions of the Troodos magmas. Even so, geochemical studies alone are incapable of defining the tectonic environment in which the Trooclos massif was generated, but coupled with other geological evidence, a petrogenetic model has been formulated in which the whole massif is seen to have developed at a decelerating spreading axis, probably in a marginal sea, back-arc environment.
|
|---|
