Magma-rich transform margins: example from the Limpopo transform fault zone between Mozambique and Antarctica

2020 ◽  
Author(s):  
Sylvie Leroy ◽  
Vincent Roche ◽  
François Guillocheau ◽  
Pierre Dietrich ◽  
Sidonie Revillon ◽  
...  
Keyword(s):  
Fault Zone ◽  
Magnetic Data ◽  
Transform Fault ◽  
Passive Margins ◽  
The North ◽  
Oceanic Spreading ◽  
Transform Margin ◽  
Seismic Reflection Profiles ◽  
Uplift And Erosion ◽  
Transform Fault Zone

<p>Transform continental margins known across the Earth represent 31% of passive margins. Resulting from first-order plate tectonic processes, transform margins record a diachronous evolution mainly defined by three successive stages, including intra-continental transform faulting, active and passive transform margin. Due to their high complexity and a lack of large hydrocarbon discoveries (i.e. not a target for oil industry), they have only been sparsely studied, especially when compared with other margin types (i.e. divergent or convergent).</p><p>                  We present the structure and evolution of the NS-trending Limpopo Transform Fault Zone (LTFZ), corresponding to the main fracture zone from western part of the Africa-Antarctica Corridor (AAC). Here, we combine published and unpublished dataset (seismic reflection profiles, wells, multibeam bathymetry, gravity, magnetic data) in order to propose an interpretation of the LTFZ structure and adjoining segments and their evolution through time, from rifting to spreading.</p><p>The LTFZ is composed of two main segments: the East Limpopo segment and the Astrid conjugate one and the North and South Natal segment including the Dana-Galathea Plateau (Mozambique side) and the Maud rise/east of Grunehogna craton (Antarctica margin). The LTFZ offsets the segments of divergent conjugate margins (Southern Natal-off Grunehogna craton in the west and Beira High Angoche-Riiser Larsen Sea in the east) since 155 Ma (chron M25). We focus on the evolution of the transform fault zone from its initiation at chron M25 up to chron M0 (~126 Ma, Barremian). Oceanic spreading onset at chron M25 in the south of Beira High segment and Dana-Galathea Plateau triggered the uplift and erosion of the proximal parts of the margin and the formation of several seaward dipping reflectors wedges. Plate kinematic implies an NNW-SSE opening of the LTFZ. The oblique component of opening promotes the setting up of several volcanic wedges. These wedges rejuvenate southward trough time, which is consistent with the sliding of Antarctica with respect to Africa and thus confirm the diachronous evolution of the transform fault zone.</p>

scholarly journals On the Segmentation of the Cephalonia–Lefkada Transform Fault Zone (Greece) from an InSAR Multi-Mode Dataset of the Lefkada 2015 Sequence

2019 ◽  
Vol 11 (16) ◽  
pp. 1848
Author(s):  
Nikos Svigkas ◽  
Simone Atzori ◽  
Anastasia Kiratzi ◽  
Cristiano Tolomei ◽  
Andrea Antonioli ◽  
...  
Keyword(s):  
Fault Zone ◽  
Surface Displacement ◽  
Interferometric Synthetic Aperture Radar ◽  
Transform Fault ◽  
Earthquake Relocation ◽  
The North ◽  
Available Information ◽  
Multi Mode ◽  
Additional Constraints ◽  
Transform Fault Zone

We use Interferometric Synthetic Aperture Radar (InSAR) to study the Cephalonia–Lefkada Transform Fault Zone (CTF) in the Ionian Sea. The CTF separates continental subduction to the north from oceanic subduction to the south, along the Hellenic Subduction Zone. We exploit a rich multi-modal radar dataset of the most recent major earthquake in the region, the 17 November 2015 Mw 6.4 event, and present new surface displacement results that offer additional constraints on the fault segmentation of the area. Based on this dataset, and by exploiting available information of earthquake relocation, we propose a new rupture process for the 2015 sequence, complementary to those published already. Our modelling includes an additional southern fault segment, oblique to the segment related with the mainshock, which indicates that the CTF structure is more complex than previously believed.

Petrology of a transform fault zone and adjacent ridge segments

1971 ◽  
Vol 268 (1192) ◽  
pp. 423-441 ◽  
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.

Slope failure and mass transport processes along the Queen Charlotte Fault Zone, western British Columbia

2018 ◽  
Vol 477 (1) ◽  
pp. 85-106 ◽  
Author(s):  
H. Gary Greene ◽  
J. Vaughn Barrie ◽  
Daniel S. Brothers ◽  
James E. Conrad ◽  
Kim Conway ◽  
...  
Keyword(s):  
Continental Slope ◽  
Fault Zone ◽  
Slope Failure ◽  
Transport Processes ◽  
North American Plate ◽  
Submarine Landslides ◽  
Mass Wasting ◽  
The North ◽  
Transform Margin ◽  
Seismic Reflection Profiles

AbstractMultibeam echosounder (MBES) images, 3.5 kHz seismic-reflection profiles and piston cores obtained along the southern Queen Charlotte Fault Zone are used to map and date mass-wasting events at this transform margin – a seismically active boundary that separates the Pacific Plate from the North American Plate. Whereas the upper continental slope adjacent to and east (upslope) of the fault zone offshore of the Haida Gwaii is heavily gullied, few large-sized submarine landslides in this area are observed in the MBES images. However, smaller submarine seafloor slides exist locally in areas where fluid flow appears to be occurring and large seafloor slides have recently been detected at the base of the steep continental slope just above its contact with the abyssal plain on the Queen Charlotte Terrace. In addition, along the subtle slope re-entrant area offshore of the Dixon Entrance shelf bathymetric data suggest that extensive mass wasting has occurred in the vicinity of an active mud volcano venting gas. We surmise that the relative lack of submarine slides along the upper slope in close proximity to the Queen Charlotte Fault Zone may be the result of seismic strengthening (compaction and cohesion) of a sediment-starved shelf and slope through multiple seismic events.

scholarly journals Seismic investigation of an active ocean–continent transform margin: the interaction between the Swan Islands Fault Zone and the ultraslow-spreading Mid-Cayman Spreading Centre

2019 ◽  
Vol 219 (1) ◽  
pp. 159-184 ◽  
Author(s):  
C Peirce ◽  
A H Robinson ◽  
A M Campbell ◽  
M J Funnell ◽  
I Grevemeyer ◽  
...  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Fault Zone ◽  
Lower Crust ◽  
P Wave ◽  
Fault System ◽  
Transform Fault ◽  
Apparent Lack ◽  
The North ◽  
Transform Margin

SUMMARY The Swan Islands Transform Fault (SITF) marks the southern boundary of the Cayman Trough and the ocean–continent transition of the North American–Caribbean Plate boundary offshore Honduras. The CAYSEIS experiment acquired a 180-km-long seismic refraction and gravity profile across this transform margin, ∼70 km to the west of the Mid-Cayman Spreading Centre (MCSC). This profile shows the crustal structure across a transform fault system that juxtaposes Mesozoic-age continental crust to the south against the ∼10-Myr-old ultraslow spread oceanic crust to the north. Ocean-bottom seismographs were deployed along-profile, and inverse and forward traveltime modelling, supported by gravity analysis, reveals ∼23-km-thick continental crust that has been thinned over a distance of ∼70 km to ∼10 km-thick at the SITF, juxtaposed against ∼4-km-thick oceanic crust. This thinning is primarily accommodated within the lower crust. Since Moho reflections are not widely observed, the 7.0 km s−1 velocity contour is used to define the Moho along-profile. The apparent lack of reflections to the north of the SITF suggests that the Moho is more likely a transition zone between crust and mantle. Where the profile traverses bathymetric highs in the off-axis oceanic crust, higher P-wave velocity is observed at shallow crustal depths. S-wave arrival modelling also reveals elevated velocities at shallow depths, except for crust adjacent to the SITF that would have occupied the inside corner high of the ridge-transform intersection when on axis. We use a Vp/Vs ratio of 1.9 to mark where lithologies of the lower crust and uppermost mantle may be exhumed, and also to locate the upper-to-lower crustal transition, identify relict oceanic core complexes and regions of magmatically formed crust. An elevated Vp/Vs ratio suggests not only that serpentinized peridotite may be exposed at the seafloor in places, but also that seawater has been able to flow deep into the crust and upper mantle over 20–30-km-wide regions which may explain the lack of a distinct Moho. The SITF has higher velocities at shallower depths than observed in the oceanic crust to the north and, at the seabed, it is a relatively wide feature. However, the velocity–depth model subseabed suggests a fault zone no wider than ∼5–10 km, that is mirrored by a narrow seabed depression ∼7500 m deep. Gravity modelling shows that the SITF is also underlain, at >2 km subseabed, by a ∼20-km-wide region of density >3000 kg m−3 that may reflect a broad region of metamorphism. The residual mantle Bouguer anomaly across the survey region, when compared with the bathymetry, suggests that the transform may also have a component of left-lateral trans-tensional displacement that accounts for its apparently broad seabed appearance, and that the focus of magma supply may currently be displaced to the north of the MCSC segment centre. Our results suggest that Swan Islands margin development caused thinning of the adjacent continental crust, and that the adjacent oceanic crust formed in a cool ridge setting, either as a result of reduced mantle upwelling and/or due to fracture enhanced fluid flow.

Early post-breakup kinematic adjustments of continental-oceanic transform fault zones; Cape Range, Coromandal and Romanche transform margin case study

2021 ◽  
pp. SP524-2021-110
Author(s):  
Michal Nemčok ◽  
Lucia Ledvényiova ◽  
Andreas Henk ◽  
Samuel Rybár ◽  
Sudipta T. Sinha ◽  
...  
Keyword(s):  
Fault Zone ◽  
Development Stage ◽  
Transform Fault ◽  
Content Type ◽  
Equatorial Africa ◽  
Crustal Thinning ◽  
Supplementary Material ◽  
Transform Margin ◽  
Tectonic Style ◽  
Transform Fault Zone

AbstractA comparison of transform margins that started their evolution as continental transforms shows differences in their tectonic style, which can be attributed to the variable kinematic adjustments they underwent during the post-breakup continental-oceanic stage of their development. Three end-member examples are presented in detail. The Cape Range transform fault zone (Western Australia) retained its strike-slip character during its entire continental-oceanic stage, as documented by the transform-perpendicular system of spreading-related magnetic stripe anomalies. The Coromandal transform fault zone (Eastern India) adjusted its kinematics to a transtensional one during its continental-oceanic stage, as indicated by the transform-oblique system of magnetic stripe anomalies and extensional component of movement indicated by a narrow zone of crustal thinning. The Romanche transform fault zone (Equatorial Africa) adjusted its kinematics to transpressional, as documented by the changing geometries of magnetic stripe anomalies and transpressional folding during its continental-oceanic development stage. Based on the recognition of the aforementioned adjustments, we suggest a new categorization of transforms into (1) those that experience transpressional adjustment, (2) those that experience transtensional adjustment and (3) those that do not experience any adjustment during their continental-oceanic development stage.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5762388

scholarly journals The 2014 Kefalonia Doublet (MW6.1 and MW6.0), Central Ionian Islands, Greece: Seismotectonic Implications along the Kefalonia Transform Fault Zone

2015 ◽  
Vol 63 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Vassilios Karakostas ◽  
Eleftheria Papadimitriou ◽  
Maria Mesimeri ◽  
Charikleia Gkarlaouni ◽  
Parthena Paradisopoulou
Keyword(s):  
Fault Zone ◽  
Transform Fault ◽  
Ionian Islands ◽  
Transform Fault Zone

Aeromagnetic Interpretations of the Crittenden County Fault Zone

2020 ◽  
Vol 92 (1) ◽  
pp. 494-507
Author(s):  
Christopher Marlow ◽  
Christine Powell ◽  
Randel Cox
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Reverse Fault ◽  
Maximum Magnitude ◽  
Fault Systems ◽  
Basement Faults ◽  
Seismic Reflection Profiles

Abstract The Crittenden County fault zone (CCFZ) is a potentially active fault zone located within 25 km of Memphis, Tennessee, and poses a significant seismic hazard to the region. Previous research has associated the fault zone with basement faults of the eastern Reelfoot rift margin (ERRM) and described it as a northeast-striking, northwest-dipping reverse fault. However, we suggest that there is an incomplete understanding of the fault geometry of the CCFZ and the ERRM in this region due to significant gaps in seismic reflection profiles used to interpret the fault systems. To improve our understanding of the structure of both fault systems in this region, we apply two processing techniques to gridded aeromagnetic data. We use the horizontal gradient method on reduction-to-pole magnetic data to detect magnetic contacts associated with faults as this technique produces shaper gradients at magnetic contacts than other edge detection methods. For depth to basement estimations, we use the analytic signal as the method does not require knowledge of the remnant magnetization of the source body. We suggest that the CCFZ extends approximately 16 km farther to the southwest than previously mapped and may be composed of three independent faults as opposed to a continuous structure. To the northeast, we interpreted two possible faults associated with the ERRM that intersect the CCFZ, one of which has been previously mapped as the Meeman–Shelby fault. If the CCFZ and the eastern rift margin are composed of isolated fault segments, the maximum magnitude earthquake that each fault segment may generate is reduced, thereby, lowering the existing seismic hazard both fault systems pose to Memphis, Tennessee.

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