Distribution, Lithotypes and Mineralogical Study of Newly Formed Thermogenic Travertines in Northern Euboea and Eastern Central Greece

Cent. Eur. J. Geosci. • 4(4) • 2012 • 545-560 DOI: 10.2478/s13533-012-0105-z Central European Journal of Geosciences Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece Research Article Christos Kanellopoulos∗ National University of Athens, Department of Geology and GeoEnvironment, Panepistimiopolis, 15784 Athens Received 6 June 2012; accepted 20 September 2012 Abstract: In the northwestern part of Euboea Island and the neighbouring part of the mainland in eastern central Greece, many hot springs exist. We collected and analysed the newly formed material around the hot springs. The samples were studied at the lab with X-Ray Diffraction, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). In all cases the studied materials were thermogenic travertine presenting many different lithotypes. The studied travertine deposits consist mainly of aragonite and calcite, but in some cases, as the main mineral phase, an amorphous hydrous ferric oxyhydroxide, probably ferrihydrite (creating a laminated iron-rich travertine deposit), was identified. The lithotypes that were identified were of great variety (spicular, shrubs, etc). Some of them (pisoliths, rafts and foam rock types) are quite rare and one of them (framework type) is described for the first time. Morphological data and field observations suggest possible inorganic and organic controls on carbonate precipitation. Similar lithotypes have been recorded at Mammoth hot springs, Yellowstone National Park in USA and at Rapolano Terme, Italy. Keywords: hydrothermal system • lithotypes • Northern Euboea • Thermopylae • travertine deposits of hot springs © Versita sp. z o.o. 1. Introduction within a vadose or occasionally shallow phreatic environ- ment. Precipitation results primarily through the trans- fer (evasion or invasion) of carbon dioxide from or to a groundwater source leading to calcium carbonate super- Various researchers [1–6] have proposed many definitions saturation, with nucleation/crystal growth occurring upon for the term travertine. Perhaps the most comprehensive a submerged surface” and can take many forms. and clear definition was proposed by Pentecost [7], who defined travertine as “a chemically-precipitated continen- Travertine deposits exist in many places around the world. tal limestone formed around seepages, springs and along The most characteristic and studied travertine deposits streams and rivers, occasionally in lakes and consisting of are in Italy (Bagni San Filippo, Terme San Giovanni, calcite or aragonite, of low to moderate intercrystalline Tivoli, Guidonia Montecelio etc), USA (Yellowstone Na- porosity and often high mouldic or framework porosity tional Park), Turkey (Pamukkale), etc. [7–16] In Greece, there are hot springs in many areas. Magmatic ∗E-mail: [email protected] and volcanic processes and active fault systems favour the 545 Distribution, lithotypes and mineralogical study of newly formed thermogenic travertines in Northern Euboea and Eastern Central Greece Figure 1. Geological map showing the study area and the localities sampled. rise of deep waters that are discharged at the surface as 2. Geological setting hot springs. From 1985-1988, the Institute of Geological and Mineral The investigated area includes the northwestern part of Exploration in Greece (IGME) performed the first system- Euboea island and the neighbouring part of the mainland, atic study on all known Greek hot springs and, along with in eastern central Greece (Fig. 1). The studied area be- that, they recorded systematically for the first time all the longs geologically to the western part of the Geotectonic thermogenic travertines [17–19]. Units of the internal zones of Greece, more specifically, At the northwestern part of Euboea Island (e.g. Edipsos the Pelagonian and Sub-Pelagonian zones [20, 21]. and Ilia) and in the neighbouring part of the mainland Eastern central Greece and, more specifically, the Sper- in eastern central Greece (e.g. Thermopylae), many hot chios graben, were Thermopylae placed, belong to the springs exist (Fig. 1). On the island of Euboea and more so-called “Sub-Pelagonian Geotectonic Unit”. The rock specifically, in the Edipsos and Ilia, around the hot springs basement consists mainly of carbonate rocks (limestones is depositing thermogenic travertine. In Thermopylae a and dolomites) of Middle Triassic-Middle Jurassic age. An similar process take place. The Edipsos and Thermopy- ophiolitic thrust sheet that is a relic of the Thetysian lae are probably the largest active travertine systems in oceanic crust is overthrusted onto the carbonates [22]. Greece. Since the Neogene, fluvio-deltaic sediments fill the Thermogenic travertine deposit near to the hot springs graben with intercalation of marls, clays, sandstones and where the hot water cools, degasses and rapidly precip- conglomerates [23]. itates calcium carbonate, creating different depositional In the northern Euboea Island, Paleozoic and Mesozoic facies-lithotypes with different crystal forms. sequences were folded together or imbricated as the re- The aim of this paper is to describe the various lithotypes sult of two main tectonic events (Alpine and Eo-Alpine). of newly formed travertine deposits in Northern Euboea These sequences belong to the “Pelagonian Geotectonic and Eastern central Greece. Among the studied systems Unit”. The latter is represented by nappes which over- are those of Edipsos and Thermopylae, which are proba- thrusted the units of the External Hellenides domain dur- bly the largest active travertine systems of Greece. A fur- ing Late Eocene-Oligocene times. The Pelagonian se- ther aim of this paper is to study their main mineralogical quence is made of continental crust elements (basement), phases and their variety of crystal morphologies. Through syn-rift deposits, carbonate platform sediments as well as morphological and mineralogical study, indications of pos- that of volcano-sedimentary sequences. The syn-rift de- sible organic controls on carbonate precipitation can be posits are composed of continental detrital sediments and identified, in addition to the inorganic ones. Late Permian shallow water carbonate incursions. The 546 C. Kanellopoulos detrital formation is followed by dolomites of Middle Tri- 4. Location and Macroscopic de- assic age. The whole area is highly faulted due to ex- scription of travertine deposits tensional tectonics [24–26]. Vavassis’ study [27] has described a great number of linear tectonic features mostly NNE-SSW and NW-SE to E-W strike. In the studied area, newly formed thermogenic travertine deposits occur in three different areas: two in North- The volcanogenic islands of Lichades are located in the ern Euboea (Edipsos and Ilia) and one in Eastern Cen- center of the northern Euboea gulf [28]. They are made tral Greece (Thermopylae) (Fig. 1). In these areas the mainly of trachyandesite lava flows, dated at 0.5 Ma. The travertines are thermogenic, created by the local hot nearby Kamena Vourla outcrops (1.7 Ma) also comprise springs. In most cases along with the newly formed of lavas of trachyandesite composition. The total volume travertines, we also identified old travertine deposits. By of volcanic products is about 0.1 km3 [29]. The existence the term old travertines, we mean: all the travertines that of volcanic rocks is related to the tectonic processes of have been created in the past; and the precipitation pro- the area, because they are placed along one of the shear cess, which creates the specific form, has ended. zones [30]. This Plio-Pleistocene volcanic center is lo- In Thermopylae, extensive deposits of thermogenic traver- cated on the western continuation of the North Anatolian tine occur. Their color varies from white to grey. During Fault, in a back-arc position with respect to the active the field survey, we discovered newly formed travertine arc. Innocenti et al. [31], based on Sr–Nd–Pb isotopic deposits and some old ones, since the hot springs in the compositions, linked this volcanic center with the large area exist from historical times. Works for the construction volcanic belt that developed north of the Pelagonian– of a new National highway road as well as other support- Attic–Cycladic–Menderes massifs, encompassing a 35 Ma ing works were carried out in this area and many of these timespan which is widespread over a large area from NW works have destroyed the travertine lithotypes and mixed Greece–Macedonia to the Aegean–western Anatolia. the old and the new deposits (Fig. 2A). For these reasons it was not possible to identify, with certainty, which deposits are recent, with the only exception being that of 3. Materials and Methods the travertine deposits which are placed close to the hot- spring. Near the vent, newly formed thermogenic travertine deposits were identified which have a relatively high Over thirty samples were studied at the laboratories of the rate of deposition. Department of Geology and Geoenvironment, University of In the Edipsos area large deposits of thermogenic traver- Athens. tine occur, presenting great variety of morphological forms The samples were studied during the field survey and at and lithotypes. the lab with a stereoscope, for macroscopic structures. The most common active morphological forms in Edipsos are spring mounds, cascades and terraces. The spring The mineralogical composition was investigated mainly by mounds have fissure walls, which are usually between 10 X-Ray Diffraction.

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