Evolution of migrating transform faults in anisotropic oceanic crust: examples from Iceland

Major transform fault zones link extensional segments of the North American – Eurasian plate boundary as it transects the Iceland Hotspot. Changes in plate boundary geometry, involving ridge jumps, rift propagation, and related transform fault zone migration, have occurred as the boundary has moved relative to the hotspot. Reconfiguration of transform fault zones occurred at about 6 Ma in northern Iceland and began about 3 Ma in southern Iceland. These systems show a range of different types of transform fault zones, ranging from diffuse, oblique rift zones to narrower, well-defined, transform faults oriented parallel to current plate motions. Crustal deformation structures correlate with the inferred duration and magnitude of strike-slip displacements. Collectively, the different expressions of transform zones may represent different stages of development in an evolutionary sequence that may be relevant for understanding the tectonic history of plate boundaries in Iceland as well as the structure of transform fault zones on more typical parts of the mid-ocean ridge system.

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Recent and active deformation in the North Evia domain, a diffuse plate boundary between Eurasia and Aegean plates in the Western termination of the North Anatolian Fault.

10.5194/egusphere-egu21-12153 ◽

2021 ◽

Author(s):

Fabien Caroir ◽

Frank Chanier ◽

Virginie Gaullier ◽

Julien Bailleul ◽

Agnès Maillard-Lenoir ◽

...

Keyword(s):

Fault Zone ◽

Plate Boundary ◽

Fault Zones ◽

North Anatolian Fault ◽

Fault System ◽

Eurasian Plate ◽

Slip Rates ◽

The North ◽

South West ◽

North Aegean

The Anatolia-Aegean microplate is currently extruding toward the South and the South-West. This extrusion is classically attributed to the southward retreat of the Aegean subduction zone together with the northward displacement of the Arabian plate. The displacement of Aegean-Anatolian block relative to Eurasia is accommodated by dextral motion along the North Anatolian Fault (NAF), with current slip rates of about 20 mm/yr. The NAF is propagating westward within the North Aegean domain where it gets separated into two main branches, one of them bordering the North Aegean Trough (NAT). This particular context is responsible for dextral and normal stress regimes between the Aegean plate and the Eurasian plate. South-West of the NAT, there is no identified major faults in the continuity of the NAF major branch and the plate boundary deformation is apparently distributed within a wide domain. This area is characterised by slip rates of 20 to 25 mm/yr relative to Eurasian plate but also by clockwise rotation of about 10&#176; since ca 4 Myr. It constitutes a major extensional area involving three large rift basins: the Corinth Gulf, the Almiros Basin and the Sperchios-North Evia Gulf. The latter develops in the axis of the western termination of the NAT, and is therefore a key area to understand the present-day dynamics and the evolution of deformation within this diffuse plate boundary area.Our study is mainly based on new structural data from field analysis and from very high resolution seismic reflexion profiles (Sparker 50-300 Joules) acquired during the WATER survey in July-August 2017 onboard the R/V &#8220;T&#233;thys II&#8221;, but also on existing data on recent to active tectonics (i.e. earthquakes distribution, focal mechanisms, GPS data, etc.). The results from our new marine data emphasize the structural organisation and the evolution of the deformation within the North Evia region, SW of the NAT.The combination of our structural analysis (offshore and onshore data) with available data on active/recent deformation led us to define several structural domains within the North Evia region, at the western termination of the North Anatolian Fault. The North Evia Gulf shows four main fault zones, among them the Central Basin Fault Zone (CBFZ) which is obliquely cross-cutting the rift basin and represents the continuity of the onshore Kamena Vourla - Arkitsa Fault System (KVAFS). Other major fault zones, such as the Aedipsos Politika Fault System (APFS) and the Melouna Fault Zone (MFZ) played an important role in the rift initiation but evolved recently with a left-lateral strike-slip motion. Moreover, our seismic dataset allowed to identify several faults in the Skopelos Basin including a large NW-dipping fault which affects the bathymetry and shows an important total vertical offset (>300m). Finally, we propose an update of the deformation pattern in the North Evia region including two lineaments with dextral motion that extend southwestward the North Anatolian Fault system into the Oreoi Channel and the Skopelos Basin. Moreover, the North Evia Gulf domain is dominated by active N-S extension and sinistral reactivation of former large normal faults.

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Petrology of a transform fault zone and adjacent ridge segments

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1971.0005 ◽

1971 ◽

Vol 268 (1192) ◽

pp. 423-441 ◽

Cited By ~ 122

Keyword(s):

Oceanic Crust ◽

Fault Zone ◽

Fracture Zone ◽

Volcanic Eruptions ◽

Spreading Ridge ◽

Transform Fault ◽

Transform Faults ◽

Near Surface ◽

The North ◽

Transform Fault Zone

The Verna Fracture Zone in the North Atlantic (9 to 11° N), which has been identified as a transform fault zone, contains exposures of serpentinized peridotites, while its adjacent ridge segments are floored mainly by typical abyssal ocean ridge basalts. This petrologic contrast correlates with the greater frequency of volcanic eruptions along the actively spreading ridge segments compared to the transform fault zone. Where rifting components occur across transform faults, exposures of the deeper zone of oceanic crust may result. The bathymetry of the Verna Fracture Zone suggests that some uplift parallel to the fracture zone as well as rifting led to exposures of deeper rocks. The basalts from the adjacent ridge axes contain ‘xenocrysts’ of plagioclase and olivine and more rarely of chromite. These appear to have a cognate origin, perhaps related to cooling and convection in near surface magma chambers. The basalts from the ridge axes, offset and on opposite sides of the transform fault, have similar features and compositions. The plagioclase peridotites have mineralogical features which indicate equilibration in the plagioclase pyrolite facies, suggesting maximum equilibration depths of around 30 km for a temperature of around 1200 °C. The chemical characteristics of the Vema F.Z. peridotites suggest that they may be undifferentiated mantle, emplaced as a subsolidus hot plastic intrusion or as a crystal mush. The abundance of peridotites and serpentinized peridotites is believed to reflect their abundance in seismic layer three of the oceanic crust.

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Structural mapping and analysis of rifting events using UAVs in the North Volcanic Zone (Iceland)

10.5194/egusphere-egu2020-19168 ◽

2020 ◽

Author(s):

Elisabetta Panza ◽

Joël Ruch ◽

François Martin

Keyword(s):

Structural Analysis ◽

Plate Boundary ◽

Plate Boundaries ◽

Volcanic Zone ◽

Structural Mapping ◽

Volcanic System ◽

North East ◽

The North ◽

Tectonic Events ◽

Fractured Medium

Volcano-tectonic events in extensional environments release over days or weeks tectonic strain deficit accumulated over several decades or hundreds of years.Thanks to its position, on top of both an extensional plate boundary and a mantle plume, several volcano-tectonic events occur in Iceland, and they have relatively accurately reported since the first settlements in ~ 870 AD. The eruptions and graben formation observed during these events are related to magma transport in the crust, which also causes the reactivation of pre-existing structures.However, the Earth&#8217;s upper crust is classically modelled as homogeneous and fully elastic and not as a pre-fractured medium. This study aims to analyse the role of pre-existing crustal structures on the propagation of magma in extensional environments.The 13 main Icelandic volcano-tectonic events, mostly concentrated in the North, East, and West Volcanic Zones, show a return period in the order of 200 years on average. The suggested cyclic nature of strain deficit loading and subsequent release is consistent with the stepwise nature of strain release at divergent plate boundaries: the crustal opening associated with dike emplacement during volcano-tectonic events is of the same order of magnitude of the strain deficit accumulated since the previous event in the same area.On this basis, we identified structurally relevant and logistically accessible fieldwork areas in the North Volcanic Zone to perform detailed structural mapping based on UAV-drone imagery. In August 2019 we carried out a UAV survey in Fjallagj&#225;, a graben ~15-20 m deep and ~1 km wide that extends parallel to Sveinagj&#225; graben for ~18 km, in the Askja volcanic system. During the volcano-tectonic event in 1875 in Askja volcanic system, Sveinagj&#225; graben was activated and it subsided 3 to 6 m.The UAV is a fixed-wing with a ground resolution down to 1 cm&#183;px-1 (flying at 100 m above ground), with an on-board PPK antenna. We installed a GNSS base, wich, in combination with the PPK correction, allows a centimetre-accuracy of the georeferencing of the drone images, with no need for aerial targets as GCPs. With this setup we managed to perform 21 flights, covering an area of ~15 km2.The processing of the drone images resulted in DEMs and orthorectified mosaics of the fieldwork area, allowing to perform a detailed morphological and structural analysis, looking at fracures, topography effects, and potential kinematic indicators. Specific attention is paid to obliquity between sets of structures. The aim is to reconstruct the paleostress history of this area of the plate boundary.The use of UAV high-resolution mapping paves the way to an efficient broadening of the fieldwork area and makes available a near-field structural analysis dataset much wider than previously possible.

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Propagation of a strike-slip plate boundary within an extensional environment: the westward propagation of the North Anatolian Fault

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2015-0129 ◽

2016 ◽

Vol 53 (11) ◽

pp. 1416-1439 ◽

Cited By ~ 32

Author(s):

Xavier Le Pichon ◽

A.M. Celâl Şengör ◽

Julia Kende ◽

Caner İmren ◽

Pierre Henry ◽

...

Keyword(s):

Plate Boundary ◽

Strike Slip ◽

Fault System ◽

Plate Boundaries ◽

Sea Of Marmara ◽

The North ◽

Gulf Of Corinth ◽

Northern Border ◽

North Aegean ◽

Narrow Plate

We document the establishment of the Aegea–Anatolia/Eurasia plate boundary in Pliocene–Pleistocene time. Before 2 Ma, no localized plate boundary existed north of the Aegean portion of the Anatolia plate and the shear produced by the motion of Anatolia–Aegea with respect to Eurasia was distributed over the whole width of the Aegean – West Anatolian western portion. In 4.5 Ma, a shear zone comparable to the Gulf of Corinth was formed in the present Sea of Marmara. The initial extensional basins were cut by the strike-slip Main Marmara Fault system after 2.5 Ma. Shortly after, the plate boundary migrated west of the Sea of Marmara along the northern border of Aegea from the North Aegean Trough, to the Gulf of Corinth area and to the Kefalonia Fault. There, it finally linked with the northern tip of the Aegean subduction zone, completing the system of plate boundaries delimiting the Anatolia–Aegea plate. We have related the change in the distribution of shear from Miocene to Pliocene to the formation of a relatively undeforming Aegea block in Pliocene that forced the shear to be distributed over a narrow plate boundary to the north of it. We attribute the formation of this block to the northeastward progression of the oceanic Ionian slab. We propose that the slab cuts the overlying lithosphere from asthenospheric sources and induces a shortening environment over it.

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Age and mantle sources of Quaternary basalts associated with “leaky” transform faults of the migrating Anatolia-Arabia-Africa triple junction

Geosphere ◽

10.1130/ges02266.1 ◽

2020 ◽

Author(s):

Michael A. Cosca ◽

Mary Reid ◽

Jonathan R. Delph ◽

Gençalioğlu Kuşcu Gonca ◽

Janne Blichert-Toft ◽

...

Keyword(s):

Partial Melting ◽

Fault Zone ◽

Triple Junction ◽

Lithospheric Mantle ◽

Seismic Imaging ◽

Plate Boundary ◽

Volcanic Field ◽

Plate Boundaries ◽

Transform Faults ◽

Volcanic Fields

The Anatolia (Eurasia), Arabia, and Africa tectonic plates intersect in southeast Turkey, near the Gulf of İskenderun, forming a tectonically active and unstable triple junction (the A3 triple junction). The plate boundaries are marked by broad zones of major, dominantly left-lateral transform faults including the East Anatolian fault zone (the Anatolia-Arabia boundary) and the Dead Sea fault zone (the Arabia-Africa boundary). Quaternary basalts occur locally within these “leaky” transform fault zones (similar to those observed within oceanic transform faults), providing evidence that mantle melting, basalt genesis, and eruption are linked to crustal deformation and faulting that extends into the upper mantle. We investigated samples of alkaline basalt (including basanite) from the Toprakkale and Karasu volcanic fields within a broad zone of transtension associated with these plate-boundary faults near the İskenderun and Amik Basins, respectively. Toprakkale basalts and basanites have 40Ar/39Ar plateau ages ranging from 810 ± 60 ka to 46 ± 13 ka, and Karasu volcanic field basalts have 40Ar/39Ar plateau ages ranging from 2.63 ± 0.17 Ma to 52 ± 16 ka. Two basanite samples within the Toprakkale volcanic field have isotopic characteristics of a depleted mantle source, with 87Sr/86Sr of 0.703070 and 0.703136, 143Nd/144Nd of 0.512931 and 0.512893, 176Hf/177Hf of 0.283019 and 0.282995, 206Pb/204Pb of 19.087 and 19.155, and 208Pb/204Pb of 38.861 and 38.915. The 176Hf/177Hf ratios of Toprakkale basalts (0.282966–0.283019) are more radiogenic than Karasu basalts (0.282837–0.282965), with some overlap in 143Nd/144Nd ratios (0.512781–0.512866 vs. 0.512648–0.512806). Toprakkale 206Pb/204Pb ratios (19.025 ± 0.001) exhibit less variation than that observed for Karasu basalts (18.800–19.324), and 208Pb/204Pb values for Toprakkale basalts (38.978– 39.103) are slightly lower than values for Karasu basalts (39.100–39.219). Melting depths estimated for the basalts from both volcanic fields generally cluster between 60 and 70 km, whereas the basanites record melting depths of ~90 km. Depth estimates for the basalts largely correspond to the base of a thin lithosphere (~60 km) observed by seismic imaging. We interpret the combined radiogenic isotope data (Sr, Nd, Hf, Pb) from all alkaline basalts to reflect partial melting at the base of the lithospheric mantle. In contrast, seismic imaging indicates a much thicker (>100 km) lithosphere beneath southern Anatolia, a substantial part of which is likely subducted African lithosphere. This thicker lithosphere is adjacent to the surface locations of the basanites. Thus, the greater melting depths inferred for the basanites may include partial melt contributions either from the lithospheric mantle of the attached and subducting African (Cyprean) slab, or from partial melting of detached blocks that foundered due to convective removal of the Anatolian lithosphere and that subsequently melted at ~90 km depth within the asthenosphere. The Quaternary basalts studied here are restricted to a broad zone of transtension formed in response to the development of the A3 triple junction, with an earliest erupted age of 2.63 Ma. This indicates that the triple junction was well established by this time. While the current position of the A3 triple junction is near the Amik Basin, faults and topographic expressions indicate that inception of the triple junction began as early as 5 Ma in a position farther to the northeast of the erupted basalts. Therefore, the position of the A3 triple junction appears to have migrated to the southwest since the beginning of the Pliocene as the Anatolia-Africa plate boundary has adjusted to extrusion (tectonic escape) of the Anatolia plate. Establishment of the triple junction over the past 5 m.y. was synchronous with rollback of the African slab beneath Anatolia and associated trench retreat, consistent with Pliocene uplift in Cyprus and with the current positions of plate boundaries. The A3 triple junction is considered to be unstable and likely to continue migrating to the southwest for the foreseeable geologic future.

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Imaging the past and present Owen transform fault: preliminary results from the VARUNA seismic cruise

10.5194/egusphere-egu2020-7974 ◽

2020 ◽

Author(s):

Alexandre Janin ◽

Mathieu Rodriguez ◽

Nicolas Chamot-Rooke ◽

Alain Rabaute ◽

Matthias Delescluse ◽

...

Keyword(s):

High Resolution ◽

Early Stage ◽

Plate Boundary ◽

Plate Boundaries ◽

Transform Fault ◽

African Plate ◽

Active Structure ◽

Carlsberg Ridge ◽

Regional Tectonic ◽

Seismic Lines

The Owen transform fault in the northwest Indian Ocean is a >300 km-long active structure that constitutes the active plate boundary between Somalia and India. The first-order fault geometry was reached in the Early Miocene when the Carlsberg Ridge propagated westward into the African plate to open the Gulf of Aden. Presently, it accommodates ~23 mm/yr of left-lateral strike-slip motion between the Sheba and Carlsberg spreading centers. &#160;The fault was recently surveyed in the Spring of 2019 during the VARUNA and CARLMAG cruises on BHO Beautemps-Beaupr&#233;, an oceanographic ship operated by the French Navy. Along with geophysical measurements (multibeam bathymetry, gravity and magnetic fields) a set of high-resolution seismic lines (> 5000 km) was acquired across both the active and fossil traces of the fault between 9&#176;N and 15&#176;N. The area is largely buried under the distal Indus turbiditic sediments and therefore offers a fairly unique continuous high-resolution stratigraphic record of past regional tectonic events. Here we present the first multibeam map of the Owen Transform system. A remarkable transpressive ridge borders the active trace of the fault along most of its length. At the intersection with the Carlsberg Ridge, the Owen Transform marks an 11&#176; bend characterized by ~1200 m of seafloor uplift. &#160;Our preliminary interpretation of the seismic lines brings to light the key unconformities related to Global Plate Reorganization Events. Off the main fault, new data reveal the magmatic nature of the Varuna Bank and similar partially buried highs. These have likely grown in the very early stage of formation of the oceanic crust carrying them, although tectonic emplacement cannot be completely ruled out. Some of the highs show internal structure, which can be interpreted either as carbonate caps or layered volcanic formations. This dataset, combined with previous cruises, offers unprecedented coverage of a 1500 km-long transform corridor along the Arabia-India and India-Somalia plate boundaries.

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MORGEN – The Mid Ocean Ridge GENerating algorithm

10.5194/egusphere-egu21-9494 ◽

2021 ◽

Author(s):

Thomas van der Linden ◽

Douwe van Hinsbergen

Keyword(s):

Conceptual Knowledge ◽

Smooth Curve ◽

Weddell Sea ◽

Plate Boundaries ◽

Plate Tectonic ◽

Transform Faults ◽

Ocean Ridges ◽

Euler Pole ◽

Mid Ocean Ridge ◽

Ocean Ridge

Paleo-digital elevation models (paleoDEM) based on plate tectonic and paleogeographic reconstructions use age grids of ocean floor to determine ocean bathymetry. In recent years, such age grids have also been developed for now-subducted oceans from the far geological past, as far back as the Neoproterozoic, using geology and paleomagnetism-based estimates of ocean opening. In such reconstructions, mid ocean ridges are drawn based on estimated Euler poles and rotations, and conceptual knowledge on the geometry consisting of spreading ridges and transform faults.Current procedures to draw mid ocean ridges in plate tectonic reconstructions are laborious, as new ridges are drawn every time the Euler pole location changes. Fortunately this is also a task that can be automated. We have written an algorithm using pyGPlates that takes as input a smooth curve at the approximate position of the reconstructed mid ocean ridge at the moment of its formation, and then calculates spreading and transform segments according to their typical geometries in modern oceans, assuming symmetric spreading. The algorithm allows gradual readjustment of ridge orientations upon Euler pole changes comparable to documented cases in the modern oceans (e.g., in the Weddell Sea). The algorithm also contains modules that can convert the calculated mid ocean ridges with other plate boundaries to boundary topologies &#8211; which can be used as input for the recently published TracerTectonics algorithm, produce isochrons which can be converted to age grids, check for subduction of isochrons and subsequently create bathymetry grids. We illustrate the use of the MORGEN algorithm with recently published reconstructions of subducted, as well as future oceans.

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Seismicity and tectonics of the North African-Eurasian plate boundary (Azores-Iberia-Tunisia)

Open-File Report ◽

10.3133/ofr86626 ◽

1986 ◽

Cited By ~ 4

Author(s):

A.F. Udias ◽

A.F. Espinosa ◽

J. Mezcua ◽

E. Buforn ◽

R. Vegas ◽

...

Keyword(s):

Plate Boundary ◽

Eurasian Plate ◽

North African ◽

The North ◽

Seismicity And Tectonics

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Earthquakes in Greenland

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-1982-31-02 ◽

1982 ◽

Vol 31 ◽

pp. 11-27

Keyword(s):

Plate Boundary ◽

Ice Age ◽

Plate Motion ◽

The Arctic ◽

Plate Boundaries ◽

Earthquake Activity ◽

Tectonic Plate ◽

Intraplate Earthquakes ◽

Ice Cap ◽

Ocean Ridge

Data on earthquakes in Greenland from the international and Canadian seismological bulletins have been checked against the seismograms of the seismological stations in Greenland. A few new earthquakes have also been located based on seismograms from Greenland and Canada. A total of 103 reliable earthquakes have been confirmed, located and relocated. The earthquakes occur mainly along the coasts of eastern, northern and western Greenland. The largest earthquakes in Greenland have magnitudes around 5. There is no tectonic plate boundary in Greenland. The intraplate earthquake zones in north-eastern and in northern Greenland are situated as linear continuations of the plate boundaries near the bend of the mid ocean ridge close to Station Nord, between Spitzbergen and Greenland. Under the ice cap only a few earthquakes have occurred. In eastern and in northern Greenland a few swarms of earthquakes have been found. In western Greenland a sequence of seismic signals is noticed at a distance of 17 5 km from Godhavn. Its origin may be small earthquakes. The time sequence of the earthquakes in Greenland shows two time intervals of increased earthquake activity after the two largest earthquakes. This indicates that stress adjustments in the largest earthquakes give rise to stress adjustments in the smaller earthquakes more than 1000 km away, in other parts of Greenland. There is only limited correlation between earthquake activity and surface geology. It can not be determined whether the main cause of the intraplate earthquakes in Greenland is isostatic uplift following the latest ice age or tectonic plate motion in connection with sea floor spreading in the Norwegian-Greenland Sea and in the Arctic Ocean.

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Serpentinized peridotite versus thick mafic crust at the Romanche oceanic transform fault

Geology ◽

10.1130/g49097.1 ◽

2021 ◽

Author(s):

Emma P.M. Gregory ◽

Satish C. Singh ◽

Milena Marjanović ◽

Zhikai Wang

Keyword(s):

Mantle Peridotite ◽

Transform Fault ◽

Equatorial Atlantic ◽

Low Velocity ◽

Transform Faults ◽

Velocity Anomaly ◽

The North ◽

Serpentinized Peridotite ◽

Equatorial Atlantic Ocean ◽

Alteration Processes

The crust beneath transform faults at slow-spreading ridges has been considered to be thin, comprising a thin mafic layer overlying serpentinized peridotite. Using wide-angle seismic data, we report the presence of a Moho at ~6 km depth and a low-velocity anomaly extending down to 9 km beneath the 20-km-wide Romanche transform valley floor in the equatorial Atlantic Ocean. The low crustal velocities above the Moho could be due to either highly serpentinized mantle peridotite or fractured mafic rocks. The existence of clear Moho reflections and the occurrence of a large crustal-depth rupture during the 2016 magnitude 7.1 earthquake suggest that the crust likely consists of fractured mafic material. Furthermore, the presence of low velocities below the Moho advocates for extensive serpentinization of the mantle, indicating that the Moho reflection is unlikely to be produced by a serpentinization front. The crust to the north of the transform fault likely consists of mafic material, but that in the south appears to be more amagmatic, possibly containing serpentinized peridotite. Our results imply that the transform fault structure is complex and highly heterogeneous, and thus would have significant influence on earthquake rupture and alteration processes.

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