Tektonika最新文献

{"title":"Exploring the Origin of Geoid Low and Topography High in West Antarctica: Insights from Density Anomalies and Mantle Convection Models","authors":"Bernard Steinberger, Maya-Laureen Grasnick, Ronja Ludwig","doi":"10.55575/tektonika2023.1.2.35","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.35","url":null,"abstract":"The deepest geoid low globally with respect to hydrostatic equilibrium is in the Ross Sea area. Nearby in West Antarctica is a residual topography high. Both are in a region with thin lithosphere, where a mantle plume has been suggested. Hence upper mantle viscosity could be regionally reduced, allowing for faster rebound than elsewhere upon melting of the West Antarctic Ice Sheet, one of the global climate system’s tipping elements. To study possible causes of the geoid low / topography high combination, we compute the effects of disk-shaped density anomalies. With -1% density anomaly and a global average radial viscosity structure, geoid low and topography high can be explained with disk radius about 10° and depth range ~150-650 km. Alternatively, there may be two separate disks somewhat laterally displaced, one just below the lithosphere and mainly causing a dynamic topography high and one below the transition zone causing the geoid low. If viscosity in the uppermost mantle is reduced by a factor 10 (from 50 to 350 km depth) to 100 (from 100 to 220 km), one shallow disk in the depth range 50-350 km would also be sufficient. In order to test the feasibility of such density models, we perform computations of a thermal plume that enters at the base of a cartesian box corresponding to a region in the upper mantle, as well as some whole-mantle thermal plume models, with ASPECT. These plume models have typically a narrow conduit and the plume tends to only become wider as it spreads beneath the lithosphere, typically shallower than ~300 km. These results are most consistent with the shallow disk model with reduced uppermost mantle viscosity, hence providing further support for such low viscosities beneath West Antarctica.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135612394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Holocene Earthquakes on the Tambomachay Fault near Cusco, Central Andes","authors":"Lorena Rosell","doi":"10.55575/tektonika2023.1.2.27","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.27","url":null,"abstract":"A system of active normal faults around the city of Cusco have severely damaged the city in major earthquakes in pre-hispanic times, 1650 and 1950 CE. Detailed studies of these faults adjacent to Cusco are therefore needed to build an understanding of seismic hazard in the region. We present new geomorphological and paleoseismological evidence for multiple Holocene earthquakes on the Tambomachay Fault, a 20 km-long normal fault that runs along the northern margin of the Cusco Basin. The western segment of the fault preserves fault scarps that cut moraine crests with a mean throw of 4.3 ± 0.4 m. We determine a 13.8 ± 0.6 ka depositional age of these moraines using 10Be cosmogenic surface-exposure dating of boulders embedded in the moraines, implying a Holocene-average fault slip rate of 0.3 ± 0.1 mm/yr. We also excavated a trench across the moraine crests. By reconstructing the trench stratigraphy with radiocarbon dating, we identified three surface-rupturing earthquakes over the last 8–9 ka. The oldest earthquake occurred between 8.5 and 8.3 ka, a second event between 6.8 and 5.5 kyrs, and the most recent earthquake between 1.2 and 0.9 ka. All of the ruptures predate Inca times (>1 ka). These surface-rupturing earthquakes are likely to have had moment magnitudes of Mw 6.4-6.9. Similar events have the capacity to severely damage modern-day Cusco due to their proximity to the city, which now has a population of 500,000.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135612395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shallow Composition and Structure of the Upper Part of the Exhumed San Gabriel Fault, California: Implications for Fault Processes","authors":"Kaitlyn Crouch, James Evans","doi":"10.55575/tektonika2023.1.2.30","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.30","url":null,"abstract":"Quantifying shallow fault zone structure and characteristics is critical for accurately modeling the complex mechanical behavior of earthquakes as energy moves within faults from depth. We examine macro- to microstructures, mineralogy, and properties from drill core analyses of fault-related rocks in the steeply plunging ALT-B2 geotechnical borehole (total depth of 493 m) across the San Gabriel Fault zone, California. We use macroscopic drill core and outcrop-sample analyses, core-based damage estimates, optical microscopy, and X-ray diffraction mineralogic analyses to determine the fault zone structure, deformation mechanisms, and alteration patterns of exhumed deformed rocks formed in a section of the fault that slipped 5-12 million years ago, with evidence for some Quaternary slip. The fault consists of two principal slip zones composed of cohesive cataclasite, ultracataclasite, and intact clay-rich, highly foliated gouge within upper and lower damage zones 60 m and 50 m thick. The upper 6.5 m thick principal slip zone separates Mendenhall Gneiss and Josephine Granodiorite, and a lower 11 m thick principal slip is enclosed within the Josephine Granodiorite. Microstructures record overprinted brittle fractures, cohesive cataclasites, veins, sheared clay-rich rocks, and folded foliated and carbonate-rich horizons in the damage zones. Carbonate veins are common in the lower fault zone, and alteration and mineralization assemblages consist of clays, epidote, calcite, zeolites, and chloritic minerals. These data show that shallow portions of the fault experienced fluid-rock interactions that led to alteration, mineralization, and brittle and semi-brittle deformation that led to the formation of damage zones and narrow principal slip zones that are continuous down-dip and along strike.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136304568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Upper-plate Shortening and Mountain-building in the Context of Mantle-driven Oceanic Subduction","authors":"Tania Habel","doi":"10.55575/tektonika2023.1.2.39","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.39","url":null,"abstract":"The mechanisms controlling mountain building at subduction zones remain debated. In particular the interaction between mantle flow and subduction has been poorly addressed while fundamental in controlling plate displacement and deformation. Here, we conduct three-dimensional analogue models at the scale of the upper mantle adding a horizontal mantle flow, so that plate displacement is not imposed as in most models, but is rather controlled by the balance of forces. We simulate three scenarios: no mantle flow (slab-pull driven subduction), mantle flow directed toward the subducting plate, and mantle flow directed toward the overriding plate. In that last scenario, we test the influence of pre-existing rheological contrasts in the upper plate to best reproduce natural cases where structural and rheological inheritance is common. Our experiments show that when plate convergence is also driven by a background mantle flow, the continental plate deforms with significant trench-orthogonal shortening (up to 30% after 60 Myr), generally associated with thickening. The upper plate shortening and thickening is best promoted when the mantle flow is directed toward the fixed overriding continental plate. The strength of the upper plate is also a key factor controlling the amount and rates of accommodated shortening. Deformation rates increase linearly with decreasing bulk strength of the upper plate, and deformation is mostly localized where viscosity is lower. Finally, we discuss the limits and strengths of our model results through a comparison to the Andes which are the best modern example of mountain building in a subduction context.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135612389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tektonika: The Community-Led Diamond Open-Access Journal for Tectonics and Structural Geology","authors":"David Fernandez -Blanco, Robin Lacassin, Mohamed Gouiza, Lucia Perez-Diaz, Craig Magee, Dave McCarthy, Tony Doré, Gwenn Péron-Pinvidic, Janine Kavanagh, Clare Bond, Renata Schmitt","doi":"10.55575/tektonika2023.1.1.56","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.1.56","url":null,"abstract":"Knowledge (b)locking impedes scientific breakthroughs and hinders societal development. Historically, the privileged and paid access to scholarly work has held captive the advancement of numerous brilliant minds and their ideas. The Tektonika initiative was born to remedy the unfairness of the current publishing scene by offering the community a platform where tectonics and structural geology research are freely and openly accessible to everyone. As part of a growing movement within academia, Tektonika provides an alternative to conventional publishing models that restrict access to scholarly work through costly paywalls and subscriptions. In this editorial, we explain why and how Tektonika exists, the structure of the journal, and how it is run a year after its launch. We also detail our peer-review process from manuscript submission to publication, and report on some of the challenges faced. We close by presenting our plan and ideas to sustain a community-led inclusive and equitable publishing landscape that secures a free-to-all access to Earth Science research over the long term.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135610872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural Observations of the Northern North Sea: Insights into Rift Failure Dynamics","authors":"Gwenn Peron-Pinvidic, Tor Åkermoen, Lars Leivestad","doi":"10.55575/tektonika2023.1.2.43","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.43","url":null,"abstract":"Lithospheric extension leads to rift formation and may continue to the point of breakup, with oceanic ridge initiation and the formation of two conjugate rifted margins. In some settings, extension can cease, and the rift may be abandoned. These so-called failed rifts archive snapshots of early phases of deformation, with geometries that may help better constrain the parameters that can prevent a rift from reaching breakup, such as lithospheric rheology, thermal state, rift opening direction and rate, inheritance. This contribution summarizes a study of the Norwegian Continental Shelf which includes the North Sea Rift and the Møre and Vøring rifted margins. We proceeded to the interpretation of a new dataset of deep penetrating seismic reflection profiles and worked at the regional scale, deliberately ignoring local particularities, to focus on the large-scale structural picture. The aim is to list architectural similarities and differences between the failed rift and the successful rifted margins. Our mapping shows that the North Sea structural geometries and basement seismic facies are very similar to the observations listed for the adjacent Møre and Vøring rifted margins. Various types of tectonic structures are observed, from thick anastomosing shear zones possibly evolving into core-complex geometries, to composite large-scale detachment faults and standard high-angle normal faults. These are categorized into five classes and interpreted as exemplifying the rift tectonic evolution through distinct generations of deformation structures that can activate, de-activate and re-activate. Based on these observations, rift failure dynamics are discussed, and it is proposed that the North Sea rift abandonment may not be related to pre-rift local conditions but rather to the ability to initiate specific tectonic structures such distal breakaway complexes.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136304846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Constraining the 3-D Geometry of Fold-Thrust Belts Using Section Balancing vs. 3-D Interpolative Structural and Probabilistic Modeling","authors":"Kevin Frings, Christoph von Hagke, Florian Wellman, Elisa Heim, Miguel de la Varga, Hugo Ortner, Elco Luijendik","doi":"10.55575/tektonika2023.1.2.21","DOIUrl":"https://doi.org/10.55575/tektonika2023.1.2.21","url":null,"abstract":"Quantitative uncertainty analysis, 2-D and 3-D modeling of the subsurface, as well as their visualization form the basis for decision making in exploration, nuclear waste storage and seismic hazard assessment. Methods such as cross-section balancing are well established and yield plausible kinematic scenarios. However, they are based on geological data with errors and subject to human biases. Additionally, kinematic models do not provide a quantitative measure of the uncertainty of structures at depth. New 3-D modeling approaches have emerged that use computational interpolation, which are less dependent on human biases. Probabilistic extensions enable the quantification of uncertainties for the modeled structures. However, these approaches do not provide information on the time evolution of structures. Here, we compare classical cross-section balancing (2-D, kinematic modeling) with 3-D computational modeling to pave the way towards a solution that can bridge between these approaches. We show the strengths and weaknesses of both approaches, highlighting areas where probabilistic modeling can possibly add quantitative structural uncertainty information to improve section balancing. On the other hand, we show where probabilistic modeling still falls short of being able to cover the observed geometric complexities. We ultimately discuss how a workflow that iteratively combines results of the approaches can improve structural and kinematic constraints. As an example, we use the fold-and-thrust belt of the northern Alpine Foreland, the so-called Subalpine Molasse, focusing on the Hausham Syncline (Bavaria) and adjacent areas. We take advantage of the fact that here the stratigraphy as well as the tectonic history are well constrained. We show that shortening within the syncline progressively increases from west to east, independent from structural uncertainties. Two equally viable models can explain this. First, strain in the west is accommodated underneath the syncline in a triangle zone that progressively tapers out, or second, the strain difference is accommodated in more internal units. This highlights the importance of introducing uncertainty modeling also in kinematic restorations, as it enables identifying key regions, where different hypotheses can be tested.","PeriodicalId":471092,"journal":{"name":"Tektonika","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136304847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}