Abstract
We present a detailed field structural survey of the area of interaction between the active NW-striking transform Husavik-Flatey Fault (HFF) and the N-S Theystareykir Fissure Swarm (TFS), in North Iceland, integrated by analogue scaled models. Field data contribute to a better understanding of how transform faults work, at a much higher detail than classical marine geophysical studies. Analogue experiments are conducted to analyse the fracture patterns resulting from different possible cases where transform faulting accompanies or postpones the rift motions; different tectonic block configurations are also considered. West of the intersection between the transform fault (HFF) and the rift zone (TFS), the former splays with a gradual bending giving rise to a leading extensional imbricate fan. The westernmost structure of the rift, the N-S Gudfinnugja Fault (GF), is divided into two segments: the southern segment makes a junction with the HFF and is part of the imbricate fan; north of the junction instead, the northern GF appears right-laterally offset by about 20 m. Southeast of the junction, along the possible prolongation of the HFF across the TFS, the strike of the rift faults rotates in an anticlockwise direction, attaining a NNW-SSE orientation. Moreover, the TFS faults north of the HFF prolongation are fewer and have smaller offsets than those located to the south. Through the comparison between the structural data collected in the field at the HFF-TFS connection zone and a set of scaled experiments, we confirm a prolongation of the HFF through the rift, although here the transform fault has a much lower slip-rate than west of the junction. Our data suggest that transform fault terminations may be more complex than previously known, and propagate across a rift through a modification of the rift pattern.
Highlights
A transform fault is characterized by strike-slip motions that end abruptly and are turned into deformation at a companion structure
The examples reported below refer to the models that are more relevant to the discussion of the development of different structures around the Husavik-Flatey Fault (HFF)-rift junction
They are characterized by a normal component of movement that increases toward the east, and the overall geometry and kinematics resemble the model of Figure 1B in the form of a leading extensional imbricate fan
Summary
A transform fault is characterized by strike-slip motions that end abruptly and are turned into deformation at a companion structure. A classic example is given by a transform fault that merges into an expanding rift (Wilson, 1965). This type of intersection zone has been studied mainly by geophysical surveys in marine environments, using bathymetric maps and earthquake data. More detailed data on transform fault terminations have been collected and studied on-land, especially in regard to the transition to reverse fault/trench systems (e.g., Davis and Burchfiel, 1973; Bellier and Sebrier, 1995; Quebral et al, 1996; Tsutsumi and Okada, 1996; Freymueller et al, 1999; Norris and Cooper, 2000), while fewer are related to on-land rift zones (e.g., Joffe and Garfunkel, 1987; Mouslopoulou et al, 2007a)
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