Abstract
A submarine hydrothermal fluid discharge structure in Akureyri Bay, Eyjafjörður region, Iceland, was investigated by means of structural, geochemical, and mineralogical methods. Thermal and chemical gradients between the hydrothermal fluid and the subarctic seawater lead to an ongoing mineral precipitation. This process builds up hydrothermal chimneys of dozens of meters in height and they are still growing. The structural analysis reveals an internal stratification of the mineral precipitates at various scales from sub-micrometers to several decimeters. This stratification indicates random changes in the depositional system during the formation of the hydrothermal cones. Some mineral layers are characterized by a dominance of Si, Mg, and O. In contrast, others are dominated by Ca and O. However, the results of XRD analysis proved that the material consists mainly of a trioctahedral phyllosilicate of the smectite group, presumably saponite or stevensite. Additionally, aragonite and hisingerite could be present. The material is built up of numerous parallel tubes, which act as conductors in the hydrothermal chimneys. Consequently, a large amount of available pore space with pore volumes of up to 6 mm3 was detected in the sample by the porosity analysis.
Highlights
Due to its hot spot origin and position upon the Mid-Atlantic Ridge (MAR), Iceland is a predestined example for a volcanically determined depositional environment
In the north of Iceland, intensive hydrothermal activity is known in the Tjörnes fracture zone, which connects the neo-volcanic zone of Iceland to the Kolbeinsey Ridge, the northern extension of the MAR (Rögnvaldsson et al 1998; Riedel et al 2001)
The findings of geological investigations at the hydrothermal chimneys Strýtan in Northern Iceland presented in this publication contribute to the analysis of sedimentary processes in hydrothermal discharge structures
Summary
Due to its hot spot origin and position upon the Mid-Atlantic Ridge (MAR), Iceland is a predestined example for a volcanically determined depositional environment. Besides an exceptional amount of volcanic and volcaniclastic deposits, there exist many localities with intensive hydrothermal activity. In the north of Iceland, intensive hydrothermal activity is known in the Tjörnes fracture zone, which connects the neo-volcanic zone of Iceland to the Kolbeinsey Ridge, the northern extension of the MAR (Rögnvaldsson et al 1998; Riedel et al 2001). Stanulla et al Geotherm Energy (2017) 5:8 hydrothermal localities within the Tjörnes fracture zone are known: south of Kolbeinsey Island, east of Grimsey Island and in Akureyri Bay (Fig. 1a; Stoffers et al 1997, 2000; Hannington et al 2001); the former two comprise high-temperature geothermal fields (Hannington et al 2001; cf Ármannsson 2016). On the Kolbeinsey Ridge, hydrothermal discharge at a water depth of 100–110 m produces precipitates of orange-reddish mud or yellow-reddish iron hydroxide (Lackschewitz et al 2006)
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