SW Cyprus Research Articles

Lateral extrusion in transpression zones: the importance of boundary conditions

The homogeneous transpression strain model formulated by Sanderson and Marchini ( Journal of Structural Geology 6, 449–458, 1984) has proved to be a useful tool in the analysis of complex three-dimensional deformation patterns. However, some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive. In this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically, but also horizontally in and out of the deforming zone parallel to its length—‘lateral extrusion’. Three end-member plane-strain components are defined: wrench simple shear; pure shear in XY (lateral stretch); and pure shear in YZ (vertical stretch). These biaxial strains can be viewed as the apices of a ‘strain triangle’ for unconfined transpression or transtension. The edges of the triangle correspond to: triaxial pure shear; non-coaxial, biaxial lateral extrusion; and the triaxial confined transpressional or transtensional strain of Sanderson and Marchini. During unconfined transpression, the orientation and, in particular, the geometry ( k-value) of the finite-strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike-slip parallel to the zone, but also upon the ratio of vertical to lateral stretch. This can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone-boundary displacements. Examples of transpression zones in which there is evidence of a component of lateral extrusion are described from SW Cyprus and central Scotland. These examples illustrate that antithetic strike-slip shearing is a kinematic requirement of laterally unconfined transpression, implying that synchronous shear-sense indicators may give opposite senses of movement in shear zones. Specific geometric and mechanical boundary conditions, together with internal fault-zone rheologies, may favour the lateral extrusion of material. Kinematic partitioning can occur to form fault-bounded domains in which end-member biaxial and/or non-coaxial strains are developed. Analysis of such domains can give a clearer understanding of regional-scale triaxial deformations. These findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones.

The development of a late Cretaceous microplate suture zone in SW Cyprus

Abstract Recent detailed mapping and volcanic geochemistry of rocks exposed in erosional windows through post-Cretaceous cover rocks in SW Cyprus have provided evidence for the development of a model for late Cretaceous microplate collision in the eastern Mediterranean. Two major juxtaposed terranes are recognized: the older Mamonia Complex consisting of Triassic ocean floor, accompanying seamounts and a series of continental rise prism sediments, and the younger Troodos Complex consisting of ophiolitic rocks formed in a supra-subduction zone environment, and modified in part by transform fault tectonics and magmatism. The two complexes were juxtaposed along an intricate suture zone, the evolution of which displays two main phases of contractional deformation of late Cretaceous age. These are a primary north- and northwest-directed thrusting, and a secondary backthrusting episode towards the west and southwest, that in places reorganized the initial structural stacking sequence. Extensional faulting of Troodos Complex rocks, that took place on the ocean floor prior to juxtaposition, clearly influenced the orientation of the later thin-skinned delamination. Although there is some evidence for strike-slip faulting, this process does not appear as extensive as proposed by previous workers.

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

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.

Canadian Palaipaphos (Cyprus) Survey Project: Second Prelilllinary Report, 1980–1982

During the second field season (1980) of the Canadian Palaipaphos Survey Project in the Paphos District of SW Cyprus, an archaeological survey was continued within the assumed boundaries of the Iron Age kingdom of Paphos. The survey, based on a stratified random sampling strategy, was confined to the Ezousas and Xeros river drainages, and resulted in the discovery of 102 sites ranging from Aceramic Neolithic to recent times. The Ezousas drainage shows a more extensive pattern of settlement both in terms of time and space than does the Xeros.Research conducted in 1980 and 1982 sought to identify the chert sources of the lithic artifacts from the region, and to locate evidence of copper: mining and smelting/refining. Analysis of the lithic material, macroscopic use-wear analysis of the tool edges, and ethnographic interviews with elderly knappers of dhoukani, or threshing-sledge, flints have enabled us to develop a functional classification system for lithic artifacts for the region. The ceramic and technological evidence relating to the copper exploitation indicates that it occurred during the 3rd through 7th centuries A.C.A preliminary geological reconnaissance identified and delimited the igneous and volcanic rocks of the Troodos Ophiolite zone, the Mamonia Complex, and the Mesozoic sedimentary formations. Rock specimens were collected from each lithologic unit examined and catalogued for further reference. A soil survey resulted in the description and classification of 12 major genetic soil units. The soils were characterized physically, chemically, and mineralogically, and a data base was established for the assessment of soil fertility.

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

The Kathikas mélange, SW Cyprus: late Cretaceous submarine debris flows

ABSTRACTThe Maastrichtian Kathikas mélange is shown to be of sedimentary origin, being a succession of undeformed, submarine, matrix‐supported debris‐flow deposits up to 270 m thick. Internal sedimentological features include beds emphasized by colour or clast size variation, pelagic chalk interbeds, planar clast fabrics and channels. A trend of upwards‐thinning beds in the mélange is interpreted as due to debris‐flow initiation on gradually increasing slopes. Debris was shed locally from the deformed and fragmented Mamonia Complex, a series of disrupted gravity‐slide sheets of Mesozoic sedimentary rocks and deformed igneous rocks. All Mamonia lithologies are represented in the mélange, and local facies variations permit identification of individual sources. The mélange probably pre‐dates emplacement of serpentinite into the Mamonia Complex. There was also local inter‐mixing of material from the adjacent and underlying Troodos sequences. The mélange rests unconformably on both Mamonia and Troodos sequences, and formed after the main deformation episode of the Mamonia Complex. The degree of resedimentation increases gradually away from the disrupted Mamonia source rocks. The thickness and volume of the Kathikas mélange are comparable with those of recent submarine debris flow deposits on unstable or seismically active continental margins.

The Kannaviou Formation, Cyprus: volcaniclastic sedimentation of a probable late Cretaceous volcanic arc

In SW Cyprus the upper pillow lavas of the Troodos Igneous Complex are directly overlain by up to 75° m of volcaniclastic sediments, ranging in age from Lower Campanian to Mid-Maastriehtian. The basal sediments are pre-dominantly non-calcareous bentonitic clays and radiolarian mudstones representative of relatively slow deposition, probably below the carbonate compensation depth. In contrast, stratigraphically higher calcareous bentonitic clays, volcaniclastic siltstones and volcaniclastic sandstones show evidence of much more rapid deposition by a combination of mass flow, traction and minor turbidity currents. The basal volcaniclastic sandstones were partly derived by submarine erosion of the subjacent Troodos lavas. In contrast, the overlying sequences contain abundant fine-grained pumice, basic to acid volcanics, and also terrigenous material derived predominantly from outside the present area of southern Cyprus. The hetero-geneous provenance of the Kannaviou sediments can be explained by postulating late Cretaceous subduction of Troodos-type oceanic-crust with genesis of a related volcanic arc and eventual tectonic juxtaposition of the Troodos Massif with a Mesozoic continental margin.

Le volcanisme alcalin du sud-ouest de chypre et le probleme de l'ouverture des regions tethysiennes au trias

An important volcanism of Late Triassic age is known from SW Cyprus. It occurs in the Mamonia nappe system emplaced during the Late Maastrichtian. Three main volcanic episodes interbedded with detrital and pelagic sediments can be seen from the base to the top: 1. (1) pyroclastic rocks (breccias, tuffs) associated with coarse-grained sandstone, suggesting explosive eruptions in grabens 2. (2) basaltic or andesitic pillowed flows, interbedded first with fine-grained sandstone and small Halobia limestone strata, then with pelagic limestones and radiolarian red cherts 3. (3) columnar trachyte flows. The whole volcanic series belongs to a very differenciated sodic suite with high titanium contents. The Mamonia lavas are very similar to the Afar volcanics and can be considered as belonging to an interplate volcanism in a rift system. This alkaline basaltic suite is found in many places of the East Mediterranean Alpine orogenic domain, especially in the Antalya nappes (South Turkey) and in the Baer-Bassit (Syria). In Greece, a similar volcanism has been noticed (Othrys—Pindos). In Italy there exists a Middle or Late Triassic volcanism with alkaline affinities. Therefore, this Late Triassic magmatism, which is widespread in the whole Mediterranean Alpine region and always in tectonic association with ophiolites, has a very great paleogeographic significance. We thus propose the existence of a rift system associated with an alkaline basaltic suite along the northern edge of the African plate during Norian—Carnian times. Afterwards a mid-oceanic ridge would have been formed during the Jurassic and Cretaceous. To explain this evolution two hypotheses can be proposed: 1. (1) A single mid-Tethysian ridge existed and all the ophiolites (Greece, Turkey, Cyprus, the ‘croissant ophiolitique peri-arabe’) have been thrust from the same area. 2. (2) A marginal sea existed along the mid-Tethysian ridge north of the African plate but separated from the Tethys by a carbonate shelf, where, after the Triassic events, oceanization began with slightly different ophiolites (a large sheeted complex, low-K tholeiites with some calc-alkaline affinities). Therefore, Troodos, Hatay, Zagros and Oman would not have come from the main ophiolite zone present further north, but from a marginal ocean, now obducted on the African plate. We think that the second hypothesis is more reasonable because the Upper Cretaceous sedimentary cover (Kannaviou Formation) of the Troodos is very similar to the detritic formation present in South Turkey (Kastel Formation) which is known to grade to shelf carbonates belonging to the Arabian plate towards the south.