|
Lavas and Sediments |
Grant Institute of Geology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, Scotland
An area of the eastern Troodos Massif has been mapped in detail to identify stages of volcanism, faulting and metallogenesis which could be related to the evolution of the late Cretaceous Troodos spreading axis. The field relations and comparisons with modern spreading ridges suggest the following succession of events. Pillowed and massive flows making up most of the lava volume were erupted on a relatively flat sea floor at the axis of a well-defined median valley. Volcaniclastic sediments accumulated during a hiatus in volcanism. The Mathiati massive sulphide formed in the vicinity of ridge-parallel fractures towards the margins of the rift valley, whilst ferromanganiferous oxide-sediments were deposited in the surrounding area. Normal faulting, at first parallel to the rift axis, then at 30–40° to it, accompanied formation of the rift-valley walls, together with renewed eruption of lavas, equivalent to the Upper Pillow Lavas. Small grabens and half-grabens, which formed during this stage, were fringed with lava talus, then gradually filled, first with ferromanganiferous umbers precipitated from local hydrothermal vents, then, as the spreading axis migrated away, by more hydrogenous metal-oxide sediments and later deep-sea deposits. In Cyprus, metallogenesis persisted from the median valley to the flanks of particular regions of crust. Also the inferred site of formation of the Mathiati sulphide towards the margin of the rift valley differs from that of the known ‘smokers’ which are active closer to the spreading axis.
