Fracture systems of the Northern Volcanic Rift Zone, Iceland: an onshore part of the Mid-Atlantic plate boundary

Hjartardóttir, Ásta Rut; Einarsson, Páll; Magnúsdóttir, Sigríður; Björnsdóttir, Þ.; Brandsdóttír, Bryndís

doi:10.1144/sp420.1

Cited by 59 publications

(86 citation statements)

References 62 publications

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“…The North Iceland Rift coincides with the Northern Volcanic Zone (NVZ, Figure 2A) that comprises, in addition to the TFS, another four, about N-S-striking volcanic rift zones (Figure 2B), namely the Krafla (KFS), Fremrinámar (FFS), Askja (AFS), and Kverkfjöll volcanic systems (Hjartardóttir et al, 2015). 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).…”

Section: Geologic-tectonic Frameworkmentioning

confidence: 99%

“…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).…”

Section: Geologic-tectonic Frameworkmentioning

confidence: 99%

“…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 • .…”

Section: Introductionmentioning

confidence: 99%

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

2016

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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 analog scaled models. Field data contribute to a better understanding of how transform faults work, at a much higher detail than classical marine geophysical studies. Analog 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 and results are compared with field data in order to study as thoroughly as possible the interaction between the HFF and the TFS as well as the possible prolongation of the HFF into the TFS. 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.

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Section: Geologic-tectonic Frameworkmentioning

confidence: 99%

Section: Geologic-tectonic Frameworkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2016

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“…The lack of postglacial eruptive fissures within the Prestahnúkur fissure swarm, compared with fissure swarms in the faster spreading Northern Volcanic Zone, also suggests less activity within the Prestahnúkur fissure swarm. The highest number of eruptive fissures within fissure swarms is generally found within the centrally located fissure swarms of the Northern and Eastern Volcanic Zones in Iceland [ Hjartardóttir et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Fracturing and earthquake activity within the Prestahnúkur fissure swarm in the Western Volcanic Rift Zone of Iceland

et al. 2015

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The Prestahnúkur fissure swarm is located within the ultraslowly spreading Western Volcanic Zone in Iceland. The fissure swarm is characterized by normal faults, open fractures, and evidence of subglacial fissure eruptions (tindars). In this study, fractures and faults within the Prestahnúkur fissure swarm were mapped in detail from aerial photographs to determine the extent and activity of the fissure swarm. Earthquakes during the last ~23 years were relocated to map the subsurface fault planes that they delineate. The Prestahnúkur fissure swarm is 40–80 km long and up to ~20 km wide. Most of the areas of the fissure swarm have been glacially eroded, although a part of it is covered by postglacial lava flows. The fissure swarm includes numerous faults with tens of meters vertical offset within the older glacially eroded part, whereas open fractures are found within postglacial lava flows. Comparison of relocated earthquakes and surface fractures indicates that some of the surface fractures have been activated at depth during the last ~23 years, although no dike intrusions have been ongoing. The existence of tindars nevertheless indicates that dike intrusions and rifting events do occur within the Prestahnúkur fissure swarm. The low‐fracture density within postglacial lava flows and low density of postglacial eruptive fissures indicate that rifting episodes occur less often than in the faster spreading Northern Volcanic Zone.

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“…Some have relief of as much as 150 m. Collectively, these rift-parallel structures impart a strong anisotropy to the crust with closely spaced, roughly north-south, zones of weakness that may influence later tectonics. Unlike the simple linear arrangement of spreading segments on mid-ocean ridges, spreading segments that compose the post-glacial neovolcanic zone (NVZ) of Iceland have a complex, overlapping, en echelon arrangement 50-100 km wide (Hjartardóttir et al 2012(Hjartardóttir et al , 2015. Linkages between spreading segments are poorly exposed but include seismically defined accommodation zones (Green et al 2014).…”

Section: Upper Crust Of Icelandmentioning

confidence: 99%

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

Karson

2016

Can. J. Earth Sci.

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Rifting near hotspots results in mantle melting to create thick mafic igneous crust at volcanic rifted margins (VRMs). This mafic crust is transitional between rifted continental crust with mafic intrusions landward and oceanic crust into which it grades seaward. Seismic velocities, crustal drilling, and exhumed margins show that the upper crust in these areas is composed of basaltic lava erupted in subaerial to submarine conditions intruded by downward increasing proportions of dikes and sparse gabbroic intrusions. The lower crust of these regions is not exposed but is inferred from seismic velocities (Vp > 6.5 km/sec) and petrological constraints to be gabbroic to ultramafic in composition. Limited access to crustal sections generated along VRMs have raised questions regarding the composition and structure of this transitional crust and how it evolves during the early stages of rifting and subsequent seafloor spreading. Active processes in Iceland provide a glimpse of subaerial spreading with the creation of a thick (40-25 km) mafic igneous crust that may be analogous to the transitional crust of VRMs. Segmented rift zones that propagate away from the Iceland hotspot, migrating transform fault zones, and rift-parallel strike-slip faults create a complex plate boundary zone in the upper, brittle crust. These structures may be decoupled from underlying lower crustal gabbroic rocks that are capable of along-axis flow that smooths-out crustal thickness variations. Similar processes may be characteristic of the early history of VRMs and volcanic hotspot ridges related to rifting and seafloor spreading proximal to hotspots. Résumé :De la distension à proximité de points chauds génère une fusion du manteau créant une épaisse croûte ignée mafique aux marges de divergence des volcans (VRM). Cette croûte mafique constitue une transition entre la croûte continentale de divergence comportant des intrusions mafiques du côté continental et la croûte océanique dans laquelle elle s'intègre vers le large. Les vitesses sismiques, les forages dans la croûte et les bordures exhumées montrent que, dans ces secteurs, la croûte supérieure est composée de lave basaltique ayant fait éruption sous des conditions subaériennes à sous-marines et elle a été pénétrée par des intrusions gabbroïques éparses et des dykes dont les proportions augmentent vers le bas. La croûte inférieure de ces régions n'affleure pas mais selon les vitesses sismiques (Vp > 6,5 km/sec) et les contraintes pétrologiques elle serait de composition gabbroïque à ultramafique. L'accès limité aux sections de la croûte générées le long des VRM a soulevé des questions quant à la composition et la structure de cette croûte de transition et de son évolution durant les premiers stades de distension et d'étalement subséquent du plancher océanique. Des processus actifs en Islande fournissent un aperçu de l'étalement subaérien avec la création d'une épaisse (40-25 km) croûte ignée mafique qui pourrait être analogue à la croûte de transition des VRM. Des zones de rift ...

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Fracture systems of the Northern Volcanic Rift Zone, Iceland: an onshore part of the Mid-Atlantic plate boundary

Cited by 59 publications

References 62 publications

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

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

Fracturing and earthquake activity within the Prestahnúkur fissure swarm in the Western Volcanic Rift Zone of Iceland

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

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