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  See discussions, stats, and author profiles for this publication at: A multidisciplinary approach to understandingcarbonate deposition under tectonically controlled hydrothermal circulation...  Article   in  Sedimentology · October 2013 DOI: 10.1111/sed.12069 CITATIONS 14 READS 233 7 authors , including: Some of the authors of this publication are also working on these related projects: METODOLOGIE INTEGRATE PER LO STUDIO DI EDIFICI STORICI AFFRESCATI: IL CASO DELLA CAPPELLASCROVEGNI A PADOVA - (PRAT UNIPD 2014)   View projectRemediation of contaminated sites using non-invasive methods, Rare Earth Exploration andResource evaluation   View projectAnna GandinUniversità degli Studi di Siena 58   PUBLICATIONS   664   CITATIONS   SEE PROFILE Rita DeianaUniversity of Padova 81   PUBLICATIONS   536   CITATIONS   SEE PROFILE Paolo FabbriUniversity of Padova 50   PUBLICATIONS   203   CITATIONS   SEE PROFILE D. 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The user has requested enhancement of the downloaded file.  A multidisciplinary approach to understanding carbonatedeposition under tectonically controlled hydrothermalcirculation: A case study from a recent travertine mound in theEuganean hydrothermal system, northern Italy MARCO POLA*, ANNA GANDIN † , PAOLA TUCCIMEI ‡ , MICHELE SOLIGO ‡ ,RITA DEIANA § , PAOLO FABBRI* and DARIO ZAMPIERI** Dipartimento di Geoscienze, Universit   a degli Studi di Padova, Via Gradenigo, 6, 35131 Padova, Italy (E-mail: † Dipartimento di Scienze fisiche della Terra e Ambientali, Universita`  degli Studi di Siena, ViaLaterina, 8, 53100 Siena, Italy  ‡ Dipartimento di Scienze, Sezione di Scienze Geologiche, Universita`  degli Studi ‘Roma Tre’, LargoSan Leonardo Murialdo, 1, 00146, Roma, Italy  § Dipartimento dei Beni Culturali: Archeologia, Storia dell’arte, del cinema e della musica, Universita` degli Studi di Padova, Piazza Capitaniato, 7, 35139 Padova, Italy  ABSTRACT A multidisciplinary study was carried out on an Upper Pleistocene traver-tine mound (Montirone Hill; Abano Terme, south of Padova, Veneto, Italy)with the aim of developing a comprehensive understanding of the processesinteracting in structurally controlled thermal springs and the consequentdeposition of thermal limestones. The sedimentology, geochemistry, struc-tural characteristics and hydrogeology of the mound, which is associatedwith the Euganean geothermal field and the related complex structuralframework of the Schio-Vicenza fault system, were investigated. A palaeo-environmental model of the deposit has been reconstructed clarifying theconnection between the travertine deposition and the regional structuralsetting. Calcium-rich thermal waters rose from spring orifices (estimated tem-perature from 54 ° C to 61 ° C based on geochemical calculations) and produceda mound made of coalescent shield-like bodies. The dominant lime-mudstonefacies resulted from the accumulation of lime mud at the bottom of shallowcrater-like basins located on top of stacked cones. Soft sediment deformationsaffecting the lime mud sediment were most probably produced by the recur-rent uprising of gas bubbles. The overlying crystalline crusts were depositedon the flanks of the mound by waters overflowing from the vents with laminarflux. A deep hydrothermal circuit with a long period of water  –  rock interactionis supported by geochemical analyses. Furthermore, a local extensionalregime, enhancing the migration of thermal fluids to the surface, is inferred based on the results of the structural analysis carried out on the fault/fracturemesh that affects the mound. These results corroborate the well-establishedrelation among travertine deposits, hydrothermal systems and fault systems,and substantiate the structurally controlled conceptual model of the Euganeanhydrothermal system, suggesting that both the thermal and the fault systemswere active at least since 34 ka. Keywords  Dilational stepover, Euganean hydrothermal system, isotopegeochemistry, resistivity measurements, travertine depositional facies,travitonics.172  ©  2013 The Authors. Journal compilation  ©  2013 International Association of Sedimentologists Sedimentology   (2014)  61 , 172–199  doi: 10.1111/sed.12069  INTRODUCTION Studies of the relations between hydrothermalcirculation, travertine deposition and tectonicactivity have been valuable elements of neotec-tonic investigations in the last few decades (Alt-unel & Hancock, 1993; Hancock  et al. , 1999;Brogi, 2004; Uysal  et al. , 2007; Brogi & Capezzu-oli, 2009; Temiz  et al. , 2009; Brogi  et al. , 2010,2012). Faults and their related fractures are rec-ognized as the most efficient path for fluidmigration in the Earth’s crust (Caine  et al. , 1996;Curewitz & Karson, 1997; Gudmundsson, 2000;Faulkner  et al. , 2010), allowing the developmentof structurally controlled, hydrothermal systemsmanifest at the surface by hot water uprising( thermal springs ). If the hot waters are characte-rized by high calcium contents, then thermalcarbonate ( travertine ) may be deposited aroundthe thermal springs as well as in the fault/frac-ture meshes, sealing the path against fluid circu-lation. Because the thermal flow of fluids isstrictly related to the activity of faults, the distri- bution of active flow sites and/or preservedtravertine masses can provide a tool for studyingthe evolution of fault zones and their relatedhydrothermal systems (Altunel & Hancock, 1993;Curewitz & Karson, 1997; Hancock  et al. , 1999;Fouke  et al. , 2000; Brogi, 2004; Uysal  et al. , 2007;Faccenna  et al. , 2008; Brogi & Capezzuoli, 2009;Nelson  et al. , 2009; Temiz  et al. , 2009; Uysal et al. , 2009; Brogi  et al. , 2010; Guido & Campbell,2011; Kele  et al. , 2011; Brogi  et al. , 2012; DeFilippis  et al. , 2012; Guido & Campbell, 2012).The tectonic control of thermal fluid migration,hot springs and travertine deposits is well-demonstrated (Curewitz & Karson, 1997; and ref-erences therein) and generally is related to activeextensional structures, such as normal or trans-tensional faults (Altunel & Hancock, 1993;Hancock  et al. , 1999; Brogi, 2004; Brogi & Cape-zzuoli, 2009; Nelson  et al. , 2009). However, inaddition to the active regional tectonics, traver-tine deposition and lithofacies distribution could be influenced by other factors, such as climate(precipitation and temperature), hydrodynamics(fluid artesian pressure, pH and composition),topography, inherited fault/fracture meshes, highheat flow and CO 2  supply (Rihs  et al. , 2000;Pentecost, 2005; Faccenna  et al. , 2008; Uysal et al. , 2009; Guido & Campbell, 2011; De Filippis& Billi, 2012; De Filippis  et al. , 2012). Therefore,detailed (palaeo) geographical, (palaeo) environ-mental and (palaeo) hydrological reconstructionsare needed to achieve a broader view of the fac-tors that influence travertine depositional pro-cesses. Present knowledge of travertineenvironments results from sedimentological andstratigraphical investigations (Chafetz & Folk,1984; Folk  et al. , 1985; Pedley, 1990; Guo &Riding, 1992; Koban & Schweigert, 1993; Folk,1994; Guo & Riding, 1998; Chafetz & Guidry,1999; Guo & Riding, 1999; Riding, 2000; Pedley,2009) which are usually combined with: (i) mor-phological and structural analyses at the localand regional scales (Altunel & Hancock, 1993;Hancock  et al. , 1999; Brogi & Capezzuoli, 2009;Brogi  et al. , 2010; De Filippis & Billi, 2012; Guido& Campbell, 2011; Brogi  et al. , 2012); (ii) geo-chemical analyses of the stable isotope signature(Fouke  et al. , 2000; Rihs  et al. , 2000; Faccenna et al. , 2008; Gandin & Capezzuoli, 2008; Kele et al. , 2011; De Filippis  et al. , 2012; Rodr  ıguez-Berriguete  et al. , 2012); (iii) geochronologicalanalyses (Bargar, 1978; Uysal  et al. , 2007; Temiz et al. , 2009; Uysal  et al. , 2009; Brogi  et al. , 2010,2012); and (iv) geochemical investigations of thewaters in present-day thermal systems (Crossey et al. , 2006; Nelson  et al. , 2009; Banerjee  et al. ,2011). Integration of the results of these differentapproaches has the potential to provide a compre-hensive view of travertine depositional processesin terms of: (i) the sedimentological characteris-tics of the deposit; (ii) regional and local tectonicregimes, providing useful information regardingthe neotectonic history and palaeoseismology of the area; (iii) climatic control on travertine depo-sition; and (iv) features of the hydrothermal sys-tems controlling the chemical signature of thethermal fluids/travertines.This study reports a multidisciplinary studycarried out on a Late Pleistocene travertinedeposit (Montirone Hill) located within theEuganean geothermal field (EGF). The EGF is oneof the most important thermal fields of northernItaly and extends in a band of   ca  36 km 2 to thesouth-west of Padova (Veneto Region, Italy;Fig. 1A) comprising the well-known spa townsof Abano Terme, Montegrotto Terme and Batta-glia Terme. The temperature of the Euganeanthermal waters ranges from 60 ° C to 86 ° C, andtheir TDS (total dissolved solids) ranges from 3  5to 6 g l  1 with the principal constituents beingprimarily Cl  and Na + (70 wt.%) and secondarilySO 42  , Ca 2+ , Mg 2+ , HCO 3  and SiO 2  (Gherardi et al. , 2000; Fabbri, 2001; Fabbri & Trevisani,2005). At present,  ca  250 wells are active (with adepth from a few hundred up to 1000 m), andthe average total flow rate of exploited thermalfluids is 17 Mm 3 yr  1 . Although studies of the ©  2013 The Authors. Journal compilation  ©  2013 International Association of Sedimentologists,  Sedimentology  ,  61 , 172–199 A multidisciplinary approach to hydrothermal tectonically controlled carbonate deposition  173  chemistry and temperature of the Euganean ther-mal waters (Piccoli  et al. , 1973; Sartori  et al. ,1997; Gherardi  et al. , 2000; Boaretto  et al. , 2003),and attempts to reconstruct the subsurface geol-ogy based on the thermal well stratigraphy have been carried out (Antonelli  et al. , 1993), thestructural geology of the EGF remains poorlyunderstood. The multidisciplinary approach usedin this study comprises: (i) sedimentological(lithofacies description and interpretation) andgeochemical (U/Th dating, oxygen and carbonisotope ratio) analyses of the travertine deposit; AC DB Fig. 1.  (A) Location of the Euganean geothermal field (EGF) within the central part of the Veneto region (NE Italy)[the dashed white area corresponds to (B)]. (B) A structural sketch of the NW  –  SE trending Schio  –  Vicenza faultsystem (SVFS) bordering to the west the Veneto-Friuli foreland; the EGF is located in coincidence with a rhom- boid, left stepover that is bounded by two distinct, sub-parallel, NNW  –  SSE trending fault segments of the SVFS[the dashed white area corresponds to (C)]. (C) A schematic geological map of the subsurface of Montirone traver-tine mound in the Abano Terme area. (D) An aerial view of Montirone Hill (modified from Google Earth © ): the black contour lines represent the mound elevation (values given in metres). The red dots mark the sites of the twodrillings ( ca  1 m in depth) made to sample the travertine lithofacies. ©  2013 The Authors. Journal compilation  ©  2013 International Association of Sedimentologists,  Sedimentology  ,  61 , 172–199 174  M. Pola et al.  (ii) structural analysis of the fracture mesh affect-ing the carbonate body; and (iii) geophysical mea-surements of the area (electromagnetic frequencydomain mapping and electrical resistivity tomo-graphy). The results of this integrated approachhave provided a clearer understanding of: (i) thepalaeo-environmental model of deposition, suit-able for the interpretation of similar, worldwidetravertine deposits; (ii) the faults, kinematics andactivity that have enhanced thermal water flux;and (iii) the distinctive features of the relatedhydrothermal system (Piccoli  et al. , 1973; Sartori et al. , 1997; Gherardi  et al. , 2000; Boaretto  et al. ,2003; Zampieri  et al. , 2009; Pola  et al. , 2010,2013). GEOLOGICAL AND HYDROTHERMALSETTING The Euganean geothermal field (EGF) is locatedalong a regional fault, the Schio-Vicenza fault(main trend: NW  –  SE), which extends for  ca 100 km in the Veneto alluvial plain from theSchio area (foot of the pre-Alps) to the Conselvearea (south  –  east of the Euganei Hills) (De Pretto,1931; De Boer, 1963; Semenza, 1974; Pellegrini,1988; Massironi  et al. , 2006). This fault repre-sents the western border of the north-easternAdria plate indenter (Viti  et al. , 2006; Burrato et al. , 2008) and, together with the forelandstructural high of the Euganei Hills–Berici Hills-Lessini Mountains, separates the western fromthe eastern Southern Alps thrust belt fronts(Semenza, 1974; Zampieri  et al. , 2003; Massironi et al. , 2006). Recent investigations (Zampieri et al. , 2009) evidence a complex system of NW  –  SE and NNW  –  SSE trending, north-east dipping,high angle faults buried beneath the Veneto allu-vial plain and synthetic with the Schio-Vicenzafault ( Schio-Vicenza fault system  –   SVFS;Fig. 1B). The SVFS is most probably an inheritedextensional structure that srcinated during thePalaeogene, when the Veneto plain constitutedthe forebulge of the south-west-vergent Dinaricthrust belt (Doglioni & Bosellini, 1987; Zampieri,1995). Subsequently, during the Neogene, thefault system was reactivated with a sinistralstrike-slip or transtensional kinematics acting asa kinematic transfer of the Southern Alps short-ening between the ENE trending eastern SouthAlpine front and the north-east trending Giudica-rie front (Massironi  et al. , 2006). A closer inspec-tion of the SVFS shows a rhomboid structure bounded by two distinct, sub-parallel, NNW  –  SSEtrending fault segments in coincidence with theEGF (Fig. 1B). Given the present sinistral strike-slip/transtensional kinematics superimposed onthe faults, the structure accommodates along-strike local extension that enhances the bedrockfracturing and allows the development of perme-ability. Consequently, this structure is inter-preted as a left stepover zone (Cunningham &Mann, 2007) and, in more detail, as a releasingor dilational stepover (De Paola  et al. , 2005,2007). Because of the high bedrock fracturing/permeability, dilational stepovers are potentialsites of high fluid/heat flow such as the Coso geo-thermal area of California (Lees, 2002) and theCerro Prieto geothermal area of Mexico (Glowa-cka  et al. , 1999).Recently, a new conceptual model of theEuganean hydrothermal system has been pro-posed (Zampieri  et al. , 2009; Pola  et al. , 2010,2013) taking into account the well-established,structurally controlled, hydrothermal conceptualmodels (Curewitz & Karson, 1997; Faulkner  et al. ,2010) and the renewed SVFS architecture(Zampieri  et al. , 2009). The waters of meteoricsrcin [infiltration area up to 1500 m above sea-level (a.s.l.); Piccoli  et al. , 1973; Gherardi  et al. ,2000] infiltrate 80 km to the north of the EGF inthe Veneto pre-Alps. The waters then flow to thesouth within a Mesozoic carbonate reservoir,represented by the Dolomia Principale (UpperTriassic), Calcari Grigi (Lower Jurassic  –  Middle Jurassic) and Maiolica formations (Upper Jura-ssic  –  Upper Cretaceous), reach a depth close to3000 m and warm up to  ca  100 ° C by a normalgeothermal gradient (Gherardi  et al. , 2000). Theactive SVFS and the related highly permeabledamage zone (Caine  et al. , 1996; Gudmundsson,2000; Faulkner  et al. , 2010) enhance the migra-tion of the thermal waters in the middle part of the circuit. In the EGF area, the hot fluids inter-cept the dilational stepover and rise quickly tothe surface through the fault/fracture mesh devel-oped within the stepover. A water residence timegreater than 60 years (although probably on theorder of a few thousand years) is suggested bytritium and  14 C isotope analyses (Piccoli  et al. ,1973; Sartori  et al. , 1997; Gherardi  et al. , 2000;Boaretto  et al. , 2003). MONTIRONE HILL: MORPHOLOGICALAND GEOLOGICAL SETTING The Montirone Hill represents the only naturaloccurrence of the Euganean thermal waters in the ©  2013 The Authors. Journal compilation  ©  2013 International Association of Sedimentologists,  Sedimentology  ,  61 , 172–199 A multidisciplinary approach to hydrothermal tectonically controlled carbonate deposition  175
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