Multiple intrusion and deformation within the northwestern quadrant of the plutonic complex, Troodos Ophiolite, Cyprus

Dunsworth, Sherry Mary (1989) Multiple intrusion and deformation within the northwestern quadrant of the plutonic complex, Troodos Ophiolite, Cyprus. Masters thesis, Memorial University of Newfoundland.

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Abstract

Detailed geological mapping (1:5,000) of a 16 sq. km. area was completed within the northwestern quadrant of the Troodos plutonic complex, Cyprus. The plutonic complex incorporates an older, high-temperature deformed sequence of harzburgite, dunite, transition zone orthopyroxenite and layered olivine and hypersthene gabbro that is intruded and truncated/disrupted by a series of post-kinematic ultramafic-mafic (i.e.: wehrlite, feldspathic-wehrlite, lherzolite, feldspathic-lherzolite, clinopyroxenite, websterite and pyroxene-hornblende gabbro) plutons. Post-kinematic mafic dikes intrude both the older and younger magmatic suites, marking the final stage of magmatism within this section of the ophiolite. -- A penetrative, steep to subvertical regional S₁ foliation, traced intermittently from the harzburgite tectonite into portions of the layered olivine gabbro tectonite, is coaxial to large scale infolding of the dunite-harzburgite boundary. An equant granoblastic to porphyroclastic microfabric prevails in the harzburgite, dunite and transition zone lithologies whereas the layered gabbro exhibits both primary cumulate igneous and secondary ductile deformation textures. The structurally highest position of the high-temperature ductile deformation, termed the deformation front and marked by the transition from ductile to brittle deformation mechanisms, occurs within the layered olivine gabbro of the Troodos plutonic complex. -- The plutons of the younger suite represent variable sized, spatially and temporally distinct, fault-controlled magma chambers that are focused primarily along the transition zone of the older suite. Most of the older suite transition zone orthopyroxenite and part of both the dunite and layered gabbro have been removed through faulting and intrusion of the younger suite plutons. -- The fractional crystallization sequence of the older suite layered gabbro and the younger suite ultramafic-mafic lithologies is olivine -> clinopyroxene -> orthopyroxcne -> plagioclase -> +/- hornblende (+/- quartz). Textural features indicate simultaneous crystallization of the pyroxene phases within the gabbroic units. Electron microprobe studies indicate that the younger and older suites cannot be distinguished on the basis of their respective mineral chemistry, that fractionation trends occur within both the younger and older suites and that cryptic chemical layering cannot be detected over a 20 m section of the layered olivine gabbro. The mafic dikes exhibit a tholeiitic affinity (island-arc tholeiite) and an extremely depleted, Mg-rich and Ti-poor chemistry correlative with the depleted upper pillow lava suite and indicative of derivation from a residual mantle source that had undergone previous partial melting and melt extraction event(s). -- A dynamic crustal accretionary history consisting of multiple intrusion and ductile-brittle deformation is established for the Troodos plutonic complex. The geometrical relations between the penetrative regional foliation, infolding along the paleo-Moho and orientation of the enveloping surface of this folded dunite-harzburgite boundary at a high-angle to the regional foliation suggest that the Troodos ophiolite may represent a segment of diapirically flowing asthenosphere in an ancient ocean spreading region.

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