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  • 2020-2023  (4)
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  • 1
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    Geological and geophysical characterization of transform offsets, TRANSFORMERS, Cruise No. M170, 11.01.2021 - 14.02.2021, Emden (Germany) - Emden (Germany) (2021)
    Gutachterpanel Forschungsschiffe
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    Publication Date: 2022-02-16
    Description: Fracture zones were recognized to be an integral part of the seabed long before plate tectonics was established. Later, plate tectonics linked fracture zones to oceanic transform faults (OTF), suggesting that they are the inactive and hence fossil trace of transforms. Yet, scientists spend little time surveying them in much detail. Recent evidence suggests that the traditional concept of transform faults as being conservative (non-accretionary) plate boundary faults might be wrong. Instead, numerical modelling results suggest that transform faults seem to suffer from extensional tectonics below their strike-slip surface fault zone, and a global compilation of legacy bathymetric data suggest that ridge-transform intersections seem to be settings of magmatic activity, modifying the lithosphere and burying the transform valley before it passes into the fracture zone region. During M170 we tested those hypotheses by collecting a suite of new data from the Oceanographer and Hayes transform faults offsetting the Mid-Atlantic Ridge to the south of the Azores near 35°N and hence conducted a pilot study revealing the state-of-stress derived from micro-earthquakes and bathymetry as well as geological sampling to evaluate magmatic and tectonic processes shaping transform faults. Preliminary analysis of 10-days of seismicity data recorded at hydrophone stations showed 10-15 local earthquakes per day and bathymetric data supports that ridge-transform intersections support indeed a second phase of magmatic accretion.
    Type: Report , NonPeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 2
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    Extensional tectonics at oceanic transform plate boundaries: evidence from seafloor morphology (2022)
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    Publication Date: 2022-06-01
    Description: Oceanic transform faults are among the most prominent morphologic features in ocean basins, offsetting mid-ocean ridges by tens to hundreds of kilometers. Since the inception of plate tectonics, transform faults have been assumed to be simple, two-dimensional strike-slip, conservative plate boundaries, where lithosphere is neither created nor destroyed. This concept nurtured an over-simplified understanding of oceanic transform faults for many decades. New advances in seafloor mapping revealed that the morphology of oceanic transform faults is difficult to explain exclusively by strike-slip faulting and differential thermal subsidence. We compiled ship-based bathymetric data of 94 oceanic transform faults, and parameterized their morphological characteristics (e.g., length, width, depth, etc.) using quantitative geomorphologic methods. A prominent feature of most oceanic transform plate boundaries is a deep valley extending along the active transform fault. Our statistical analysis indicates that these valleys are generally deeper and wider at slow- and ultraslow-slipping rates than at faster slipping rates. However, the key feature that governs structural variability, seems to be age-offset across a transform fault rather than spreading rate. While the correlation between transform morphology and spreading rate turns out to be rather weak, our statistical results consistently show that transform valleys get deeper and wider with increasing age-offset. The surface deformation pattern observed therefore supports the tectonic extension scaling with age-offset predicted by recent geodynamic simulations (Grevemeyer et al., 2021). Furthermore, at small age-offsets (〈 5 Myr), scatters especially in the depth of transform valley increase, indicating that small-age-offset transforms corresponding to weak lithospheric strength are easily affected by secondary tectonic processes, such as nearby hotspots and changes in plate motion. Now, five decades after Wilson (1965) published his seminal paper on transform faults, our quantitative submarine geomorphologic study emphasizes that oceanic transform faults are not simple conservative strike-slip plate boundaries, but that tectonic extension is an integral process affecting their morphology. The larger age-offset causes greater extension at OTFs and hence wider and deeper valleys as evidenced by our statistics on transform morphology.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 3
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    Impact of Spreading Rate and Age‐Offset on Oceanic Transform Fault Morphology (2022)
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    Publication Date: 2022-06-22
    Description: Oceanic transform faults (OTFs) are an inherent part of seafloor spreading and plate tectonics, whereas the process controlling their morphology remains enigmatic. Here, we systematically quantify variations in transform morphology and their dependence on spreading rate and age‐offset, based on a compilation of shipborne bathymetric data from 94 OTFs at ultraslow‐ to intermediate‐spreading ridges. In general, the length, width and depth of OTFs scale systematically better with age‐offset rather than spreading rate. This observation supports recent geodynamic models proposing that cross‐transform extension scaling with age‐offset, is a key process of transform dynamics. On the global scale, OTFs with larger age‐offsets tend to have longer, wider, and deeper valleys. However, at small age‐offsets (〈5 Myr), scatters in the depth and width of OTFs increase, indicating that small age‐offset OTFs with weak lithospheric strength are easily affected by secondary tectonic processes.
    Description: Plain Language Summary: In the past 5 decades, studies on oceanic transform faults (OTFs) have revealed significant complexity in their morphology, which calls for detailed quantitative analysis to study the processes controlling the morphology of OTFs. Using the most complete and advanced compilation of bathymetric data from ultraslow‐ to intermediate‐spreading ridges, we parameterized the morphological characteristics of OTFs and extracted length, width and depth for each transform fault from the compiled bathymetric data. Moreover, correlations between these morphological parameters and related tectonic factors (e.g., spreading rate, age‐offset) were investigated in this study. We find that correlations between morphological features and spreading rate are rather weak. Comparison of correlations suggests that age‐offset scales better with the morphological parameters, along with scatters mostly at small age‐offsets, indicating small‐age‐offset OTFs are unstable due to their weak lithospheric strength. Our observation evidences extensional tectonics at OTFs.
    Description: Key Points: We compiled multibeam bathymetric data of 94 oceanic transform faults (OTFs) to quantify their morphological characteristics. Morphology of OTFs is dominated by age‐offset rather than spreading rate. Transform valleys get systematically deeper and wider with increasing age‐offset, implying extensional tectonics at OTFs.
    Description: China Scholarship Council
    Description: http://doi.org/10.5281/zenodo.4774185
    Keywords: ddc:551
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 4
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    CAYMAN: Characterizing the crust using 2D & 3D seismic tomographic methods. (2021)
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    Publication Date: 2022-12-01
    Description: About 25% of the Earth’s mid-ocean ridges spread at ultraslow rates of less than 20 mm/yr. However, most of these ultraslow spreading ridges are located in geographically remote areas, which hamper investigation. Consequently, how the crust forms and ages at such spreading centres, which traditional models predict to be magma-starved and cold, remains poorly understood. One of the most accessible ultra-slow spreading centres is the Mid Cayman Spreading Centre (MCSC), in the Caribbean Sea, with spreading rates of ~15-17 mm/yr. CAYSEIS project was proposed to survey the Cayman Trough area in order to obtain new data that constraints the nature of the crust, tectonic structures, lithologies outcropping and hydrothermal processes taking place in this area. Understanding the sub-seabed geophysical structure of the MCSC is key to understanding not only the lithologies and structures exposed at the seabed, but more fundamentally, how they are related at depth and what role hydrothermal fluid flow plays in the geodynamics of ultraslow spreading. CAYSEIS was a joint and multidisciplinary programme of German, British and US American top tier scientists designed for the obtaining of a new high-quality dataset, including 3D Wide-Angle Seismic (WAS), magnetic, gravimetric and seismological data. During the CAYMAN project, we took leverage of the CAYSEIS dataset to invert a 3D tomographic model of the Cayman Trough lithosphere using the Tomo3D code (Meléndez et al., 2015; 2019). This is one of the first times that the Tomo3D code is used for 3D inversion of real datasets. Thus, we are checking our results comparing them with tomographic inversions of 2D lines and testing the different parameters to obtain the more accurate and higher resolution model as possible. The results of this experiment will show not only the lithospheric structure along and across the MSCS, including the exhumed Ocean Core Complexes in the surrounding areas, but the 3D lithospheric configuration of the region which is important to understand the crustal formation processes and the evolution of ultra-slow spreading settings.
    Description: Poster
    Description: poster
    Keywords: ddc:550 ; 3D tomography ; crustal characterization ; ultra-slow spreading ; Cayman Trough
    Language: English
    Type: doc-type:conferenceObject
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    CITATION GEO-LEO
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