The Ayia Varvara Formation of SW Cyprus: A product of complex collisional tectonics

Abstract

The Ayia Varvara Formation is a wedge of amphibole schists and intercalated metasediments within the intensely deformed pre-upper Maastrichtian volcanosedimentary Mamonia Complex. All contacts are steep faults against Upper Triassic transitional to alkaline lavas with reefoidal limestones, subalkaline depleted Troodos-type lavas, and serpentinised harzburgite. Ophiolite-related metamorphics are believed to have been formed by dynamothermal processes, beneath young oceanic crust during emplacement. Characteristically, such rocks might be expected to show a decrease of metamorphic grade away from the contact. Mineral analyses from the Ayia Varvara metamorphics, however, show no systematic variations that would indicate a metamorphic gradient. Hornblende remains generally calcic and of tschermakitic hornblende composition with an almost complete substitution of Mg and Fe 2+, suggesting disequilibrium. Plagioclase is essentially albitic and remains so for a distance of some 800 m from the harzburgite contact. Trace element analyses of the amphibolites and surrounding extrusives define four lava types. Types 1-3 are transitional to alkaline intraplate lavas believed to be remnants of intraoceanic islands and atolls. Type 4-lavas are extremely depleted in the HFS elements and are very similar to the Arakapas transform-fault lavas. The amphibolites have, in part, a trace-element geochemistry that is close to mid-ocean ridge basalts (MORB), a type that has not previously been recorded from Cyprus. The small area around Ayia Varvara records a long and complicated tectonic history that provides an insight into the evolution and emplacement of the Troodos ophiolite. The Mamonia Complex is interpreted as a passive margin sequence with intra-oceanic islands that was accreted onto a Late Cretaceous north-dipping subduction zone. Suprasubduction spreading produced the Troodos ophiolite and associated fracture zones. Spreading and subduction ceased in the late Maastrichtian when the newly-formed Troodos crust underwent a 90° anticlockwise rotation which juxtaposed Mamonia and Troodos (Arakapas) fracture zone rocks along arcuate, steep, strike-slip faults. At least some of the Ayia Varvara metamorphic rocks most likely represent Triassic oceanic crust and sediments metamorphosed during subduction by the overriding young Troodos crust. © 1992.