Troodos Ophiolite Mantle Section Exposed Along Atalante Geo-Trail, Troodos Geopark, Cyprus

GEOSCIENCE RECORDS Field trip to … • DOI: 10.1515/georec-2016-0005 • Geosci. Rec. • 3–1 • 2016 • 01–6

Troodos ophiolite mantle section exposed along Atalante Geo-Trail, Troodos Geopark, Cyprus

Michał Bukała1, Katarzyna Zboińska2, Mateusz Szadkowski2

1AGH – University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Al. Mickiewicza 30, 30-059 Kraków 2 University of Wrocław, Institute of Geological Sciences, ul. Cybulskiego 32, 50-205 Wrocław, Poland

Record

Peridotites from ophiolite sequence in the Troodos Geopark, Cyprus, record processes of mantle magmatic evolution and serpentinisation.

Abstract Keywords

The following paper presents the field trip through the unique mantle sequence com- ophiolite, peridotite, serpentinite, Troodos Massif posed of peridotites and exposed along Atalante Geo-Trail in Troodos Geopark, Cyprus. This manuscript briefly summarises data from many papers and presents authors’ own field observations, in order to provide information on evolution of enigmatic Troodos Received: 21 November 2016 mantle peridotites. Accepted: 5 December 2016

1. Introduction The definition of an ophiolite has undergone a revolution since the first Penrose conference. Currently, the best known authori- The Troodos Massif is located in the centre of the western part ties studying ophiolites distinguish several types of ophiolites de- of Cyprus, and its highest peak – Mt. Olympos – is 1,952 m asl. pending on the tectonic setting – for example, Dilek (2003) lists Amongst the numerous tourists visiting Cyprus throughout the seven types. year, a major group, not surprisingly, is represented by geologists. On the geological map, the Troodos Massif streched latitudi- In the second half of the twentieth century, the theory of plate nally in the shape of an oval. Part of the massif, with an area of tectonics was born, and since then, the genesis of the Troodos 1,147 km2, comprises the Troodos Geopark, belonging to the Massif was better understood and it has become a pilgrimage UNESCO Global Geoparks Network. The Troodos Geopark occu- place for countless Earth scientists from all over the world. The pies 36% of the massif and 12% of Cyprus. The Park was estab- uniqueness of Troodos is represented by the fact that it is one of lished to preserve the natural values of the area. the world’s first completely recognised and described ophiolite. The geological fame of Cyprus, and especially the Troodos ophio- The structure of an ophiolite sequence has been a subject of dis- lite, became an impulse to organise the field trip to this region of cussion for years. The term ‘ophiolite’ is derived from Greek and the world by the Student Science Association of Geologists of the means ‘snake stone’ – inspiration for this name was green, ‘snake- University of Wrocław (SKNG UWr). The expedition was held from like’ colour of rocks preserved in ophiolite complexes. The history April 24 to May 1, 2016, and was attended by eight SKNG UWr of the ophiolite concept began in 1813, when Alexandre Brong- members and two students from the AGH University of Science niart, the famous French mineralogist, used this term in reference and Technology. In this paper, we summarise our observations to the complex of rock in the Northern Apennines, composed of and present them in the context of the scientific literature on the serpentinite, gabbro and diabase (Bortolotti, 2012). The defini- subject. Our aim was to present as wide literature information as tion of an ophiolite changed over the years until 1972, when the possible, but the paper is still our personal view and our personal first Penrose conference on ophiolites was held, during which the interpretation of what we saw and read. knowledge about these sequences was summarised. Using the term ‘ophiolite’, scientists describe the fragment of an oceanic lithosphere that was incorporated into the continental 2. Geological background of Troodos ophiolite lithosphere as a result of geological processes. A typical, simplified ophiolite sequence consists of (from bottom to top) mantle The Troodos ophiolitic sequence was classified as one of the peridotites, ultramafic and mafic cumulates, layered and isotropic Cretaceous Mediterranean ophiolites, and it was recognised as gabbros, sheeted dykes and pillow lavas on which lie deep-sea a remnant of the southern part of the Tethys, the closure which deposits. This sequence may be incomplete, tectonically dis- is associated with the Alpine orogenesis. The Troodos ophiolite, membered or even metamorphosed (Dilek & Furnes, 2011). similar to other ophiolites from the Mediterranean area – for

1 GEOSCIENCE RECORDS Field trip to … • DOI: 10.1515/georec-2016-0005 • Geosci. Rec. • 3–1 • 2016 • 01–6

Figure 1. (a) Simplified geological map of mantle section of Troodos ophiolite (modified after Büchl et al. 2004). (b) Simplified map showing location of Troodos ophiolite (red rectangle).

example, Kizildag in Turkey or Oman ophiolites – is thought to sive sequence consists of island arc tholeiite lavas or depleted be the suprasubduction zone (SSZ) ophiolite (the classification of boninitic rocks (Dilek & Furnes, 2009). Dilek & Furnes, 2009). It is believed that the mentioned Tethyan In the terms of lithology within the Troodos Massif, the cross ophiolites were created because of the forearc extension (Sher- section of the entire ophiolitic sequence can be observed from vais, 2001) and the SSZ ophiolites have more in common with is- serpentinised peridotites by gabbros, sheeted dikes to extrusive land arcs than with mid-ocean ridges. However, the geodynamic rock, on which lie sedimentary rocks (Figure 2). environment, in which the Troodos ophiolite was formed, prob- The mantle part of the ophiolite consists of tectonized harzbur- ably changed through the history of ophiolite formation, and gites, cut by pyroxenite dykes and containing dunite – chromite now the ophiolite is composed of several types, for example, part pods. Above them, there are ultramafic cumulates on which lie of the mantle section has MORB-like source, whereas the extru- sets of layered to isotropic gabbros. Within the plutonic complex,

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Figure 2. Cross section of Troodos ophiolite (modified after Dilek & Furnes, 2009) sill intrusions, diorites and plagiogranites are located. Sheeted forms veins or blocks (both of various size) within the host rock dike complex comprises a diverse range of rocks – from basalts to (Figure 3b). Major serpentinite veins usually cut peridotite dis- rhyodacites, with a predominance of basalts and basaltic andes- cordantly, whereas systems of small veinlets are perpendicularly ites. Pillow lavas lying on it can be divided into two groups: Lower oriented to the main vein and penetrate the host rock (Figure 3c). Pillow Lavas and Upper Pillow Lavas. Pillow lavas composition Serpentinite blocks (up to tens of metres) are not homogeneous range from basalts, through andesites to dacites. Volcanogenic and are cut by dense system of veinlets containing platy lizardite Massive Sulphide ore and umber deposits occur within the Pillow and fibrous chrysotile (Figure 3d). Spinel, if not forming dissemi- Lavas. Extrusive section is covered with chalk deposits, dated as nated specks, concentrates as pods or layers within the dunite. the upper Cretaceous. On them lie pelagic limestones of Maas- Chromite ore displays various textures from massive, nodular, trichtian-lower Eocene age and upper Eocene-Oligocene carbon- disseminated (Figure 4b,c,d) to occluded silicate to chromite-net ates. The youngest marine sediments that cover the sequence of texture. Recently, chromite hopper grains have been described the Troodos ophiolite are lower Miocene reefal limestones and (Prichard et al., 2015). Chromite grains are commonly lineated gypsum-evaporite deposits (Messinian) (Dilek & Furnes, 2009). (even the single nodules are elongated) and fractured, whilst cracks are filled with serpentine and chlorite. Both the chromite and the enclosing dunite are deformed together, concordant 3. Outrcrop description with the fabric of the surrounding harzburgite. Contacts between chromitite and the host rock are both sharp and gradational. The mantle member of the Troodos ophiolite outcrops around Gabbro pegmatites, as well as pyroxenites (Figure 1d), occur as the top of the Mt. Olympus (Figure 1). Variously serpentinised veins of various size cutting discordantly host rocks in many plac- harzburgite, lherzolite, dunite, pyroxenite, chromitite and gabbro es along a trail. pegmatites occurring within the upper mantle sequence pro- Western harzburgites contact on the eastern side with strongly vide the evidence of complex evolution, including percolation of serpentinised spinel lherzolites, whilst on the western side, they upwelling basalt melt through the host peridotite and later ser- contact with chromite-bearing dunite, wehrlite and pyroxenite pentinisation. All types of mantle rocks as well as relationships (Figure 1) with the last two representing paleo-Moho ultramafic between them can be observed along the Atalante Geo-Trail – cumulates. Harzburgites are less serpentinised compared to rocks the 14-km long footpath starting in the Troodos main square in the eastern part. They also record northwest trending tectonite (34.922020N/32.880014E) and circling around the mountain peak fabrics, which indicate high temperature deformation also affect- (Figure 1). ing underlying cumulates (Malpas, 1990). Harzburgites contain In general, Troodos mantle sequence could be divided into two, from 0.5 to 1.0 vol.% of clinopyroxene that is strongly depleted in eastern and western parts (e.g. Büchl et al., 2004). Western part heavy rare-earth elements and to a lesser degree in medium rare consists of refractory harzburgites and dunite pods, whereas earth elements (Batanova & Sobolev, 2000). On the basis of grains eastern, intensively serpenitised part is dominated by spinel- morphology, Batanova and Sobolev (2000) suggested that clino- lherzolites with subordinate clinopyroxene-bearing harzburgites pyroxene was formed by exsolution from orthopyroxene during and dunites (e.g. Merlini et al., 2011). coupled recrystalisation and deformation. Spinel displays narrow Within all the outcrops along the trail, harzburgite and dunite composition range with cr# (atomic ratio of Cr/(Cr+Al)) varying show brown weathering, typical for these rocks, owing to the oxi- from 0.51 to 0.70 (Sobolev & Batanova, 1995). These highly refrac- dation of Fe2+ in the primary minerals (Figure 3a). On weathered tory composition of mineral constituents in harzburgites were surfaces, spinel appears as disseminated black specks (Figure 3e), initially interpreted as records of partial melting that removed sometimes accompanied by platy bastite (up to 0.7 cm). Perido- primary clinopyroxene from the mantle (Sobolev & Batanova, tites are intermittently serpentinised, and usually serpentinite 1995). However, more recent interpretation is that because of the

3 GEOSCIENCE RECORDS Field trip to … • DOI: 10.1515/georec-2016-0005 • Geosci. Rec. • 3–1 • 2016 • 01–6

Figure 3. Photographs of various rocks exposed along trail: (a) slightly weathered harzburgite; (b) serpentinite block; (c) serpentinite vein within a host dunite; (d) serpentinite cut by chrysotile veins; (e) pyroxenite; (f) disseminated spinel within a dunite.

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Figure 4. Photographs of (a) entrance to closed Hadjipavlou chromite mine, (b) chromite pod within the host dunite, (c) disseminated chromite ore sample and (d) massive chromite ore sample. specific minerals composition, these harzburgites may be formed Malpas, 1990). Spinel-lherzolites have not been involved in the owing to open-system reaction between percolating melt and suprasubduction magma production, whereas they record per- initial lherzolite (Batatova and Sobolev, 2000). colation of suprasubduction melts (Batanova & Sobolev, 2000). In eastern part, composed mainly of lherzolites, harzburgites occur only in the contact zone between lherzolite and dunite. Spi- nel-lherzolite contains up to 7 vol.% of clinopyroxene, whereas 4. Former mining activity spinel cr# is low and varies from 0.22 to 0.28. Cpx-free dunite car- ries chromium-rich spinel (cr# from 0.70 to 0.84), whilst spinel in Cyprus has a long history of mining activity. The name ‘Cyprus’ harzburgite has slightly lower cr# (0.32–0.51). Harzburgite also itself was linked with copper since its production began at Bronze contains 1.5–4.5 vol.% clinopyroxene (Batanova & Sobolev, 2000). age (3900–2500 BC). Major copper ore bodies are VMS (volcano- Size of dunite pods, in places associated with clinopyroxenite and genic massive sulphide) type and, therefore, are associated with orthopyroxenite veins, varies over a broad range from 1 to 500 m the upper, volcanic part of ophiolite sequence, although dissemi- in length and 1 to 50 m in width. The formation of eastern lher- nated mineralisation is widespread in the other ophiolite mem- zolite unit, with characteristic circular shape, is still under debate. bers. The unit could be the part of a mantle wedge that was formed Within Troodos mantle rocks contain related chromite and asbes- above the melt-generation zone (Batanova & Sobolev, 2000) and tos deposits, both formerly exploited, but now all mining activi- was later juxtaposed with the western part unit during uplift of ties were abandoned. Asbestos was exploited in the biggest open the ophiolite. The uplift was probably linked to diapiric intrusion pit mine in Cyprus – the Amiandos mine – since 1904, and the related to increase in volume during hydration (e.g. Robinson & exploitation continued until 1988. It is estimated that more than

5 GEOSCIENCE RECORDS Field trip to … • DOI: 10.1515/georec-2016-0005 • Geosci. Rec. • 3–1 • 2016 • 01–6

150 million tons of chrisotile-rich rocks were extracted, providing, the top of Mt. Olympus. Despite of relatively high concentration after enrichment processes, about 940,000 tons of fibre concen- of Cr2O3, ranging from 45% to 60%, mines ceased exploitation in trate. Chrysotile mineralisation is limited to eastern, brecciated 1980s because of unfavourable changes in chromium prices on and serpentinised harzburgite and occurs as veins of various size global markets. Now, the only remnants of the former mines are (up to 1.5 cm thick) filled with fibres. ‘White’ asbestos was also shafts (only entrances are facilitated for tourists; Figure 4a) and exploited and composed mainly of chrysotile, although lizardite, old waste dumps where specimens of chromite ore can be found. brucite, magnetite, talc, tremolite and carbonates were also pres- It has been suggested that old mines still carry exploitable depos- ent. More than 80 years of asbestos mining caused environmen- its, although around 1,200,000 tons of ore have been extracted tal issues and people who live in nearby villages are struggling from mentioned deposits. with them until today. The largest environmental problems, be- side large mine pit, deforestation and slopes instability, are exten- sive asbestos waste dumps increasing air pollution with hazard- Acknowledgements ous component. Chromite mining started from 1920s of twentieth century when This work was supported by internal funds from the University of some small-scale excavations were carried out. Large-scale ex- Wrocław. The authors would like to thank the editorial board and ploitation began in 1930s and has been focused in Kokkinorotsos the reviewers for critical comments. They also thank K. Cieślawska, deposits, later (in 1940s) at the Kanoures and (in 1950s) at Hadji- K. Schab, M. Dajek, M. Bokła, P. Sobczak, K. Kosmińska and pavlou sites, all located at the uppermost part of massif, close to K. Faehnrich for participating in the field work.

References

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