Abstract
The diverging plate boundaries in North Iceland and its shelf display a complex tectonic at the Kolbeinsey Ridge (K-R), the Northern Rift Zone (NRZ), and the Tj?rnes Fracture Zone containing the Grímsey Oblique Rift (GOR), the Húsavík-Flatey Fault (HFF), and the Dalvík Lineament (DL). While active deformation is well-known, the structural pattern is sporadically mapped and a comprehensive account of the upper Tertiary-present deformation is not fully at hand. To address the gaps, this paper provides new regional tectonic maps with continuous coverage, and detailed analyses of the deformation. Faults, open fractures, prominent joints and volcanic edifices were identified on Multibeam/Single beam, Spot 5, and Digital Elevation Model, and subjected to multidisciplinary structural analysis and correlation with selected data. Some of the results are: 1) Six sets constitute the structural pattern. The N-S rift-parallel normal faults are 1/3, and the shear fractures of the transform zone and the oblique rift 2/3 of the fracture population. The en échelon arrangements above deep-seated shear zones indicate dextral slip on WNW to NW, and sinistral slip on NNE to ENE faults, conformable with earthquake data. 2) During the polyphase tectonic, the six sets led to basin and horst formation, block compartmentalisation, rotation, horsetail splay, rhomb-graben in relay zone of strike-slips, and volcanism. 3) Listric faults are absent and the steeply-dipping faults are antithetic, synthetic, or form extensional flower structures above 4 km depth. The Plio-pleistocene/present syn-sedimentary deformation caused a deep half graben in the Eyjafjarearáll Basin (Ey), fault growth, rollover, and sediment onlaps, with some of the faults still active. 4) The plate boundaries of K-R/Ey, GOR/?xarfjreur/NRZ, and DL delimit a major microplate labelled here as Grímsey-Tj?rnes-Dalvík. 5) The WNW earthquake cluster in GOR corresponds either to a blind horsetail splay fault or to initiation of a transform segment parallel to the HFF. The described tectonic-sedimentary-magmatic deformation is relevant to other diverging plate boundaries where similar sets control the hydrocarbon and geothermal resources.
Highlights
Diverging plate boundaries consist of both rift and transform segments [1] [2], regardless of whether they are above a hotspot or not
The diverging plate boundaries in North Iceland and its shelf display a complex tectonic at the Kolbeinsey Ridge (K-R), the Northern Rift Zone (NRZ), and the Tjörnes Fracture Zone containing the Grímsey Oblique Rift (GOR), the Húsavík-Flatey Fault (HFF), and the Dalvík Lineament (DL)
Geothermal manifestations are considered to be fracture-controlled [165] [166]. Their detailed tectonic settings, are overall poorly known, except in Theistareykir where a multidisciplinary tectonic investigation demonstrated that six sets of extensional and shear fractures belonging to the rift and transform zones control this resource [167] [168] [169]
Summary
Diverging plate boundaries consist of both rift and transform segments [1] [2], regardless of whether they are above a hotspot or not. The deformation becomes complex with time, and develops features such as diverse ridge geometry and failed rift segments [11], instability in rift and transform zones [12] [13] [14] [15] [16], anomalous magnetic chrons due to rift relocation, e.g., [17], or varied degree of rift obliquity [18] Due to their impacts on basin formation, petroleum system development, volcanism and hydrothermal fluid circulation, these boundaries have been studied in continental and ocean crusts of various ages, offshore as onshore. Are the results of this multidisciplinary structural analysis relevant to the geology of Iceland and other rift and transform zones, but they provide a knowledge base for exploration of geothermal or hydrocarbon resources in the context of diverging plate boundaries in general
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