Fracture Kinematics and Holocene Stress Field at the Krafla Rift, Northern Iceland

Noemi Corti,Sofia Bressan,Federico Pasquaré Mariotto,Ásta Rut Hjartardóttir,Alessandro Tibaldi,Páll Einarsson,Valentina Rigoni,Elena Russo,Fabio L Bonali

doi:10.3390/geosciences11020101

Abstract

In the Northern Volcanic Zone of Iceland, the geometry, kinematics and offset amount of the structures that form the active Krafla Rift were studied. This rift is composed of a central volcano and a swarm of extension fractures, normal faults and eruptive fissures, which were mapped and analysed through remote sensing and field techniques. In three areas, across the northern, central and southern part of the rift, detailed measurements were collected by extensive field surveys along the post-Late Glacial Maximum (LGM) extension fractures and normal faults, to reconstruct their strike, opening direction and dilation amount. The geometry and the distribution of all the studied structures suggest a northward propagation of the rift, and an interaction with the Húsavík–Flatey Fault. Although the opening direction at the extension fractures is mostly normal to the general N–S rift orientation (average value N99.5° E), a systematic occurrence of subordinate transcurrent components of motion is noticed. From the measured throw at each normal fault, the heave was calculated, and it was summed together with the net dilation measured at the extension fractures; this has allowed us to assess the stretch ratio of the rift, obtaining a value of 1.003 in the central sector, and 1.001 and 1.002 in the northern and southern part, respectively.

Highlights

The Northern Volcanic Zone (NVZ) of Iceland represents the emergence of the MidAtlantic Ridge and is composed of five parallel rift zones (Figure 1) that are, from west to east, the Theistareykir, Krafla, Fremrinámar, Askja and Kverkfjöll rifts [1]
Eruptive fissures are only found within a distance of 20 km north of the central volcano, and 30 km south of it, whereas they disappear further north or south (Figure 12b). This can be interpreted as a consequence of the lateral shallow propagation of dykes from the central volcano, which tend to deepen with distance [46], inducing surface deformation represented mainly by dry extension fractures
We have studied the geometry, kinematics and offset amount of the structures that form the active, N-S-trending Krafla Fissure Swarm (KFS), mapping and analysing all the extension fractures, normal faults and eruptive fissures of the rift by remote sensing and field survey

Summary

Introduction

The Northern Volcanic Zone (NVZ) of Iceland represents the emergence of the MidAtlantic Ridge and is composed of five parallel rift zones (Figure 1) that are, from west to east, the Theistareykir, Krafla, Fremrinámar, Askja and Kverkfjöll rifts [1]. Much research has been focused on the Krafla system [1,2,3,4], the most detailed studies on rift kinematics and geometry have been carried out at the Theistareykir rift [5,6,7,8,9,10] These works show a complex pattern of kinematics with the presence of transcurrent components of motions that, in particular, become systematic in the northern section of the Theistareykir rift, the Theistareykir Fissure Swarm (ThFS), where a right-lateral component is observed. This has been suggested to be generated by a heterogeneous simple shear with a smoothly increasing strain gradient produced by the WNW–ESE Grimsey Lineament right-lateral shear zone (GRL in Figure 1b) [7].

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Conclusion