Fault interaction and stresses along broad oceanic transform zone: Tjörnes Fracture Zone, north Iceland

Homberg, Catherine; Bergerat, Françoise; Angelier, Jacques; Garcia, Sébastien

doi:10.1029/2008tc002415

Cited by 18 publications

(18 citation statements)

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“…Paleomagnetic sites are located in four main study localities (coherent blocks) with increasing distance away from the major offshore Húsavík‐Flatey Fault (HFF) Zone, and four subsidiary study localities adjacent to the fault zone to assess directional consistency and distinguish between different deformational models. These data may be relevant to the interpretation of deformation adjacent to major oceanic transforms and have implications on the tectonic evolution of northern Iceland, (Bergerat, Angelier, & Homberg, ; Bergerat, Angelier, & Villemin, ; Garcia et al, ; Homberg et al, ; Sæmundsson, ; Young et al, ). Collectively, the results and available structural data show that deformation in northern Iceland is considerably more complex than can be accounted for by typical deformation models from strike‐slip fault zones.…”

Section: Introductionmentioning

confidence: 99%

Large Rotations of Crustal Blocks in the Tjörnes Fracture Zone of Northern Iceland

Horst

Karson

2018

Tectonics

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The interpretation of uppermost crustal deformation near oceanic transform faults is based on bathymetric lineaments and earthquake focal mechanisms, and relatively little is known about the detailed kinematics within the transform tectonized zone. The Tjörnes Fracture Zone is a broad zone of deformation produced by right‐lateral transform shearing in north Iceland and is partly exposed on land providing the opportunity to study shallow‐level crustal structure of mid‐Miocene, thick, oceanic‐like crust formed by subaerial spreading. A pronounced structural curvature of lava and dike orientations near the Húsavík‐Flatey Fault within the transform zone is well documented, yet of controversial origin. In order to develop an assessment of deformation near the transform zone, samples of lavas and dikes were collected from 182 paleomagnetic sites within eight structural localities across the deformation zone on the Flateyjarskagi Peninsula. A progressive clockwise increase in locality mean remanence declinations over more than 10 km south of the fault broadly mimics the structural curvature of lava and dike orientations. Rotation estimates based on inclined rotation axes indicate significant clockwise rotation (74° ± 7° to 96° ± 9°) of multiple crustal blocks. When combined, all data from 108 sites within the deformed zone <12 km to the Húsavík‐Flatey Fault yield a best fit inclined axis rotation of 55° ± 7°. The paleomagnetic data and field relationships are consistent with a modified bookshelf faulting model, with relatively small (~1 km across) independently rotated crustal blocks with variable, and in some cases large‐magnitude rotations found within 10 km to the transform fault zone. Similar crustal deformation and comparable amounts of rotation may be present near other oceanic transforms, where accessibility and surficial deposits may limit documentation of more complex fault structures.

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Section: Introductionmentioning

confidence: 99%

Large Rotations of Crustal Blocks in the Tjörnes Fracture Zone of Northern Iceland

Horst

Karson

2018

Tectonics

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“…2) Geodetic monitoring of deformation [57] [58] and earthquakes [59] [60] [61], covering short-term tectonic activities. 3) Stress analysis [62] [63] [64], and a first comprehensive stress map [65]. 4) Topical features such as local fault geometry and fault termination [66].…”

Section: Introductionmentioning

confidence: 99%

Tectonic Control of the Theistareykir Geothermal Field by Rift and Transform Zones in North Iceland: A Multidisciplinary Approach

Khodayar¹,

Björnsson²,

Kristinsson³

et al. 2018

OJG

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This paper presents a multidisciplinary structural analysis of a 165 km 2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geothermal field and its surroundings. About 10729 fracture segments (faults, open fractures, joints) are identified in the upper Tertiary to Holocene igneous series. The segments were extracted from aerial images and hillshade, and then analyzed in terms of number of sets, geometry, motions, frequency, and relative age. The correlation with surface geothermal manifestations, resistivity, earthquakes, and occasional well data reveals the critical regional and local fractures at the surface, reservoir level and greater depth. The main conclusions of this study are: 1) The structural pattern consists of N-S rift-parallel extensional fractures and the Riedel shears of the transform zone striking NNE, ENE, E-W, WNW and NW, which compartmentalize together the blocks at any scale. 2) The en échelon segmentation shows strike and oblique slips on the Riedel shears, with a dextral component on the WNW and NW planes and a sinistral component on the NNE to ENE faults. 3) Fractures form under the influence of the transform mechanism and the effect of rifting becomes significant only with time. 4) The WNW dextral oblique-slip Stórihver Fault of the transform zone has a horsetail splay that extends eastwards into the geothermal field. There, this structure, along with few NW, ENE, NNE and N-S fractures, controls the alteration, alignment of fumaroles, emanating deep gases. These fractures also rupture during natural or induced earthquakes. 5) The resistivity anomalies present en échelon geometries controlled by the six fracture sets. These anomalies display clockwise and anticlockwise rotations within the upper 8 km crustal depth, but at 8 km depth, only three sets

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“…While the lineament is seismically defined (P. Einarsson, ; Rögnvaldsson et al, ), there is little field evidence for a through‐going transform fault other than a linear topographic depression. It is therefore unlikely that the Dalvík fault has accommodated large displacement (P. Einarsson, ; Gudmundsson et al, ; Homberg et al, ).…”

Section: Tectonic Settingmentioning

confidence: 99%

“…The ages of these three major lineaments within the Tjörnes Fracture Zone seem to decrease toward the northeast (Gudmundsson et al, ; Homberg et al, ). Models of GPS data support this hypothesis—two thirds of present‐day plate motion is accommodated on the northeastern‐most Grímsey fault with only a third on the central Húsavík‐Flatey fault (Metzger et al, ).…”

Section: Tectonic Settingmentioning

confidence: 99%

Distributed Deformation in an Oceanic Transform System: Applying Statistical Tools to Structural and Paleomagnetic Data Near the Húsavík‐Flatey Fault, Northern Iceland

et al. 2018

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The right-lateral Húsavík-Flatey fault is part of the Tjörnes Fracture Zone, which links the offshore and onshore rift axes in northern Iceland. There has been debate about whether rocks near this fault have accommodated distributed off-fault deformation, which is testable using paleomagnetic data. Recent studies from Flateyjarskagi show clockwise declination deflections that are largest near the fault. We augment these data with new structural and paleomagnetic measurements from 106 lava flows across three peninsulas-Flateyjarskagi, Tröllaskagi, and Tjörnes-also finding clockwise deflections that vary with distance from the fault. To test whether the deflections could be caused by off-fault deformation, we combine our measurements with other regional data sets, applying several statistical tools including regressions of structural or paleomagnetic directions versus fault-normal distance. To evaluate the significance and uncertainties of the regressions, we use permutation tests and bootstrapping. For Flateyjarskagi, our analysis suggests that lavas and dikes were deformed together; the regression results predict 4 ∘ -6 ∘ of rotation per kilometer about a steep, but not vertical, axis. Rocks on Tröllaskagi hint at similar spatial patterns with fault distance, but the data quality precludes a full analysis. Rocks on Tjörnes show no spatial patterns, but they preserve a temporal history, where rotation seems to have ceased after deposition of the Pliocene-age Tjörnes beds. Using constraints from our statistical analyses, geochronology, and comparisons with the transform system in southern Iceland, we propose several modifications to models for the evolution of axial rift zones in northern Iceland.

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Fault interaction and stresses along broad oceanic transform zone: Tjörnes Fracture Zone, north Iceland

Abstract: International audienc

Cited by 18 publications

References 59 publications

Large Rotations of Crustal Blocks in the Tjörnes Fracture Zone of Northern Iceland

Large Rotations of Crustal Blocks in the Tjörnes Fracture Zone of Northern Iceland

Tectonic Control of the Theistareykir Geothermal Field by Rift and Transform Zones in North Iceland: A Multidisciplinary Approach

Distributed Deformation in an Oceanic Transform System: Applying Statistical Tools to Structural and Paleomagnetic Data Near the Húsavík‐Flatey Fault, Northern Iceland

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