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Keywords:

  • Dilational stepover;
  • Euganean hydrothermal system;
  • isotope geochemistry;
  • resistivity measurements;
  • travertine depositional facies;
  • travitonics

Abstract

A multidisciplinary study was carried out on an Upper Pleistocene travertine mound (Montirone Hill; Abano Terme, south of Padova, Veneto, Italy) with the aim of developing a comprehensive understanding of the processes interacting in structurally controlled thermal springs and the consequent deposition of thermal limestones. The sedimentology, geochemistry, structural characteristics and hydrogeology of the mound, which is associated with the Euganean geothermal field and the related complex structural framework of the Schio-Vicenza fault system, were investigated. A palaeo-environmental model of the deposit has been reconstructed clarifying the connection between the travertine deposition and the regional structural setting. Calcium-rich thermal waters rose from spring orifices (estimated temperature from 54°C to 61°C based on geochemical calculations) and produced a mound made of coalescent shield-like bodies. The dominant lime-mudstone facies resulted from the accumulation of lime mud at the bottom of shallow crater-like basins located on top of stacked cones. Soft sediment deformations affecting the lime mud sediment were most probably produced by the recurrent uprising of gas bubbles. The overlying crystalline crusts were deposited on the flanks of the mound by waters overflowing from the vents with laminar flux. A deep hydrothermal circuit with a long period of water–rock interaction is supported by geochemical analyses. Furthermore, a local extensional regime, enhancing the migration of thermal fluids to the surface, is inferred based on the results of the structural analysis carried out on the fault/fracture mesh that affects the mound. These results corroborate the well-established relation among travertine deposits, hydrothermal systems and fault systems, and substantiate the structurally controlled conceptual model of the Euganean hydrothermal system, suggesting that both the thermal and the fault systems were active at least since 34 ka.