Holocene displacement field at an emerged oceanic transform-ridge junction: The Husavik-Flatey Fault – Gudfinnugja Fault system, North Iceland

Abstract

Our research focuses on Holocene tectonics in a broad area surrounding the junction between the active NW-SE trending Husavik-Flatey transform fault (HFF) and the N-S Gudfinnugja normal fault (GF), an exceptional example of onshore transform-ridge intersection. We mapped 637 minor and major faults, and measured the dip-slip and strike-slip offset components on the major faults. We also mapped 1016 individual fissures, as well as opening directions on the most reliable ones. The results indicate that this portion of the HFF comprises major right-stepping segments, with both normal and right-lateral strike-slip components, linked by local normal faults. The entire GF always shows pure dip-slip normal displacements, with a strong decrease in offset at the junction with the HFF. Fissure opening directions are in the range N45°-65°E along the HFF, N90°E along the GF, and N110°E within the area south of the HFF and west of the GF. Fault kinematics and fissure openings suggest a displacement field in good agreement with most of present-day GPS measurements, although our data indicate the possible long-term Holocene effects of the 2 superimposition of magma-related stresses on the regional tectonic stresses. The HFF and the GF work together as a structural system able to accommodate differential crustal block motion, and possibly past dyke intrusions.

Interaction between Transform Faults and Rift Systems: A Combined Field and Experimental Approach

“…of moving the plates very slowly (reaching high precision) and orthogonally to the sidewalls ( Figures 7A,B), simulating the E-W opening direction (extensional stresses) in the studied area, that has been acting for the last 14.5 ka (Pasquarè Mariotto et al, 2015); such opening direction is also supported by GPS data from Jouanne et al (2006).…”

“…Each of these systems consists of 5-20 km-wide and 60-100 kmlong swarms of normal faults, eruptive and tension fractures ( Figure 2C), and a main volcano (Saemundsson, 1974). Most research efforts focused on the Krafla system (e.g., Angelier et al, 1997;Acocella et al, 2000;Hjartardóttir et al, 2015), whereas the structures of the TFS were studied only recently in detail by Pasquarè Mariotto et al (2015), Tibaldi et al (2016), and regionally by Hjartardóttir et al (2015).…”

“…Near the junction area, along the HFF there are several transpressional and transtensional zones localized at NW-SE fault strands with left-stepping and right-stepping geometries, respectively (Gudmundsson et al, 1993;Pasquarè Mariotto et al, 2015). Approaching the junction with the GF, the HFF main fault plane rotates gradually and splays southwards into a set of minor faults that distribute the deformation.…”

“…Fault scarps face southward, suggesting transtensional kinematics with downthrow of the southern block. In two main zones, N125-135 • -striking fault strands with a rightstepping geometry are linked by fault swarms striking from N340 to N00 • , showing dip-slip normal kinematics (Pasquarè Mariotto et al, 2015). Several small, meter-sized pull-apart depressions are located at right-stepping overlap zones, whereas push ridges occur at left-stepping overlap zones.…”

“…In North Iceland (Figure 2A), the Theistareykir Fissure Swarm (TFS; Figure 2B), the westernmost section of the Northern Volcanic Zone, is affected by active surface tectonic activity as testified to by the presence of both Holocene faults and tension fractures (Gudmundsson et al, 1993;Magnúsdóttir and Brandsdóttir, 2011;Hjartardóttir et al, 2015;Pasquarè Mariotto et al, 2015; Figure 2C). Most of these structures strike N00 to N20 • .…”