Tectonic control on travertine and silica sinter deposition in oceanic transform-fault setting: the case of the Lýsuskarð volcano-geothermal area, Snæfellsnes Peninsula, Iceland

ABSTRACT

Deposition of terrestrial carbonate (i.e. travertine) and silica sinter in geothermal areas is always closely linked to the presence of relevant crustal structures which enhance the permeability in the upper crust favouring the upflow of fluids to the surface. Most travertine deposits are originated by geothermal fluids stored within carbonate reservoirs in continental crust, and their morphology and areal distribution provide useful information on geometry, kinematics, and age of faults which control the fluid flow. In this paper, we focus on the tectonic control on a travertine depositional system, associated with silica sinter, developing in oceanic crust, in the Lýsuskarð volcano-geothermal area on the Snæfellsnes Peninsula, West Iceland. The presence of HCO₃ and Ca in the geothermal fluids is related to chemical-physical processes linked to fluid–rock interaction that occurs in the geothermal reservoir made up of tholeiitic basalt, by fluids enriched in CO₂ of deep origin (i.e. magmatic). Travertine deposits consist of mounds and slopes, which are still in formation and overlie the silica sinter deposits. Both sinter and travertine deposits derive from thermal springs aligned according to two trends: NNE-SSW and WNW-ESE. This evidence suggests the occurrence of buried, permeable, and thus active faults, which control the circulation of fluids containing HCO₃ and Ca. Faults are near parallel to those which define the rift systems and transform zones in Iceland, and probably comprise the still active sector of the abandoned transform zone that, starting with the Snæfellsnes Peninsula, interrupts eastward the northern continuation of the western and eastern rift-zones in the south-central Iceland. In this setting, we refer, for the first time, travertine and silica sinter deposition to an oceanic active crustal structure.

KEYWORDS:

• Travertine
• silica sinter
• geothermal system
• transform faults
• rifting
• Iceland

Aknowledgments

We are indebted with Jóhanna Ásgeirsdóttir, the owner of the Lýsuhóll farm, who allowed us to visit at length the main exposures, and geothermal manifestations within her propriety.

Brogi junior (Cesare) made his contribution to the geometrical and spatial analyses of the volcanic vents across the Snæfellsnes Peninsula on the satellite photographs.

We also thank Renè Groeben and Viggó Thor Marteinsson (Matís ohf. -Reykjavík) for the kind assistance and logistics offered during the fieldwork activity in Iceland.

This project was funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871,149.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2180779

Additional information

Funding

This project has received funding from the European Union's Horizon 2020 research and innovation programme undergrant agreement No 871149.