HR: 0800h
AN: T41D-1342    [Abstracts]
TI: Oceanic Detachment Faults Observed in the Troodos Ophiolite, Cyprus
AU: * Cann, J
EM: j.cann@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: McCaig, A
EM: a.mccaig@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS2 9JT United Kingdom
AB: In the Limassol Forest area south of the Arakapas Transform Fault in the Troodos Ophiolite, structural relationships are much more complex than north of the transform fault. To the north, the ophiolite has a classic layer-cake structure of volcanics above sheeted dykes above gabbros above peridotites. To the south the same units are present, but are juxtaposed in a much more complex way. Two domal core complexes of serpentinised peridotites are capped by major low-angle extensional faults separating the core complexes from overlying slices of sheeted dykes, gabbros and volcanics. Stratigraphic arguments show that the extensional faulting can be shown to be contemporary with the construction of the ophiolitic crust. Fragments of serpentinite are found in clastic sediment that lies between lava flows a few kilometres south of the largest of the core complexes, and are also found in coarse clastic sediment overlain by a lava flow within the transform fault trough. In addition the core complexes are cut by small plutons and dyke swarms that were intruded after serpentinisation of the peridotite was complete. As is common with serpentinite, small-scale structures yield ambiguous indicators of movement direction, but larger-scale structures, such as a westerly structural deepening of individual units within the hangingwall blocks, suggest a generally top to the west sense of shear. East-west trending ridges in the outcrop of one of the fault zones on a scale of tens to hundreds of metres may be corrugations similar to those seen on oceanic detachment faults. One of the core complexes was not exposed at the ancient ocean floor, but remained covered by hangingwall blocks, raising the possibility of similar hidden core complexes within the ocean crust. Shear zones associated with the detachment faults contain tremolite-chlorite assemblages replacing peridotite that are texturally and mineralogically similar to detachment fault rocks from the Mid-Atlantic Ridge. Basaltic rocks from the hangingwall are altered to tremolite, chlorite, epidote, quartz and locally hydrogarnet, with plagioclase often completely chloritised. These observations are consistent with fluid flow along the detachment under greenschist facies conditions, with chemical exchange between mafic and ultramafic rocks.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3600 MINERALOGY AND PETROLOGY
DE: 8000 STRUCTURAL GEOLOGY
DE: 8400 VOLCANOLOGY
SC: Tectonophysics [T]
MN: Fall Meeting 2005