Solid EarthPub Date : 2024-05-07DOI: 10.5194/egusphere-2024-1263
Alan Chen, Xuanhua Chen
{"title":"Origin of the Bohai Sea, North China Craton and implication for bi-directional back-arc extension in East Asia continental margin","authors":"Alan Chen, Xuanhua Chen","doi":"10.5194/egusphere-2024-1263","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1263","url":null,"abstract":"<strong>Abstract.</strong> The Bohai Sea in eastern China is located in the back-arc extensional regime due to westward subduction of the Pacific Plate underneath the Eurasian Plate. It is one of the regions with frequent earthquakes. Previous recognition of the origin of the Bohai Sea was limited by the understanding of back-arc extensional mode perpendicular to the subduction zone in eastern Asian continental margin. In this paper, a new model for the genesis of the Bohai Sea is proposed, based on the construction of major fault system and investigation of several main boundaries enclosing the Bohai Sea. Through field investigation and analyses of tectonic landforms and boundary faults on the northwest coast of the Bohai Sea and eastern and western margins of the Liaodong Peninsula, and geological correlation of the Liaodong and Jiaodong Peninsulas and surrounding areas, we revealed a left-lateral strike-slip fault between the northwest coast of the Liaodong Bay and western margin of the Liaodong Peninsula, and proposed a right-lateral strike-slip fault between the eastern margin of the Liaodong Peninsula and northwestern margin of the Jiaodong Peninsula. This mode of movement may have been resulted from the NE stretching which is parallel to the subduction zone in northwestern Pacific margin. Therefore, we suggest that the formation of the Bohai Sea is resulted from the superimposition of the NE extension parallel to the subduction zone on the NW extension perpendicular to the subduction zone. We speculate that the two-direction extension perpendicular and parallel to the subduction zone should be the basic pattern of the back-arc extension with spherical-geometric effect.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"40 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140887717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-30DOI: 10.5194/se-15-555-2024
Joaquín Bastías-Silva, David Chew, Fernando Poblete, Paula Castillo, William Guenthner, Anne Grunow, Ian W. D. Dalziel, Airton N. C. Dias, Cristóbal Ramírez de Arellano, Rodrigo Fernandez
{"title":"Uplift and denudation history of the Ellsworth Mountains: insights from low-temperature thermochronology","authors":"Joaquín Bastías-Silva, David Chew, Fernando Poblete, Paula Castillo, William Guenthner, Anne Grunow, Ian W. D. Dalziel, Airton N. C. Dias, Cristóbal Ramírez de Arellano, Rodrigo Fernandez","doi":"10.5194/se-15-555-2024","DOIUrl":"https://doi.org/10.5194/se-15-555-2024","url":null,"abstract":"Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U–Th) / He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that while ZHe ages at the base of the sequence are fully reset, towards the top ZHe ages are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterized by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far southern Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. We suggest that the rift-related exhumation of the Ellsworth Mountains occurred throughout two events: (i) a Jurassic uplift associated with the disassembly of southwestern Gondwana and (ii) an Early Cretaceous uplift related with the separation between Antarctica and Australia, which is also recorded in the Transantarctic Mountains.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"69 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140839588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-29DOI: 10.5194/egusphere-2024-1135
Emanuele Scaramuzzo, Franz A. Livio, Maria Giuditta Fellin, Colin Maden
{"title":"Transpressional tectonics during the Variscan-Alpine cycle transition: supporting a multi-rifting model, evidence from the European western Southern Alps","authors":"Emanuele Scaramuzzo, Franz A. Livio, Maria Giuditta Fellin, Colin Maden","doi":"10.5194/egusphere-2024-1135","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1135","url":null,"abstract":"<strong>Abstract.</strong> We delve into the transition between the Paleozoic Variscan cycle and the Meso-Cenozoic Alpine supercontinent cycle, both of which have played a pivotal role in shaping the central European-Mediterranean plate’s architecture. Our focus is on the European western Southern Alps (Varese Area, N Italy), where we documented the tectonic events occurred during this transition. Two main scenarios have been proposed so far for this transition: i) a single, long-lasting, Permo-Triassic rifting event, culminating in the opening of the Alpine Tethys, or ii) multiple, distinct rifting events, preceding the onset of the Alpine cycle. By means of a tectono-stratigraphic and thermochronological approach, we recognized a first early Permian rifting stage associated with magmatic activity, followed during the early-middle Permian by transpressive tectonics and regional-scale erosion that signal the end of the first cycle of crustal rifting. During the Middle Triassic, a second event initiated, which, we propose, marks the onset of the Alpine Tethys opening. This event could represent the stretching phase, which predates the well documented Upper Triassic crustal-thinning phase. Based on our findings, we propose that the Middle Triassic stretching phase represents the first stage of the Alpine Tethys rifting, thereby rejecting the hypothesis of a continuous Permo-Triassic long-lasting phase of extension.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"42 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140808781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-26DOI: 10.5194/egusphere-2024-866
Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, Ales Bezdek
{"title":"Popigai and Chicxulub craters: multiple impacts and their associated grabens","authors":"Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, Ales Bezdek","doi":"10.5194/egusphere-2024-866","DOIUrl":"https://doi.org/10.5194/egusphere-2024-866","url":null,"abstract":"<strong>Abstract.</strong> More advanced data (gravity field model EIGEN 6C4 with GOCE gradiometry data instead of EGM2008) and more sophisticated method (using a set of the gravity aspects instead of the gravity anomalies and the radial second derivative of the disturbing potential only) enable a deeper study of various geological features, here the impact craters Chicxulub and Popigai. We confirm our results from 2010, extend them, and offer more complicated models, namely by means of the gravity strike angles. Both craters are double or multiple craters. The probable impactor direction is from NE for Chicxulub and SE-NW for Popigai. The both crater formations seem to be associated with impact induced tectonics that triggered development of impact grabens.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"41 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140804240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Seismic wave modeling of fluid-saturated fractured porous rock: including fluid pressure diffusion effects of discretely distributed large-scale fractures","authors":"Yingkai Qi, Xuehua Chen, Qingwei Zhao, Xin Luo, Chunqiang Feng","doi":"10.5194/se-15-535-2024","DOIUrl":"https://doi.org/10.5194/se-15-535-2024","url":null,"abstract":"Abstract. The scattered seismic waves of fractured porous rock are strongly affected by the wave-induced fluid pressure diffusion effects between the compliant fractures and the stiffer embedding background. To include these poroelastic effects in seismic modeling, we develop a numerical scheme for discretely distributed large-scale fractures embedded in fluid-saturated porous rock. Using Coates and Schoenberg's local-effective-medium theory and Barbosa's dynamic linear slip model characterized by complex-valued and frequency-dependent fracture compliances, we derive the effective viscoelastic compliances in each spatial discretized cell by superimposing the compliances of the background and the fractures. The effective governing equations for fractured porous rocks are viscoelastic anisotropic and numerically solved by the mixed-grid-stencil frequency-domain finite-difference method. The main advantage of our proposed modeling scheme over poroelastic modeling schemes is that the fractured domain can be modeled using a viscoelastic solid, while the rest of the domain can be modeled using an elastic solid. We have tested the modeling scheme in a single fracture model, a fractured model, and a modified Marmousi model. The good consistency between the scattered waves off a single horizontal fracture calculated using our proposed scheme and the poroelastic modeling validates that our modeling scheme can properly capture the fluid pressure diffusion (FPD) effects. In the case of a set of aligned fractures, the scattered waves from the top and bottom of the fractured reservoir are strongly influenced by the FPD effects, and the reflected waves from the underlying formation can retain the relevant attenuation and dispersion information. The proposed numerical modeling scheme can also be used to improve migration quality and the estimation of fracture mechanical characteristics in inversion.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140636961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-22DOI: 10.5194/egusphere-2024-1077
Pramit Chatterjee, Arnab Roy, Nibir Mandal
{"title":"Localized shear versus distributed strain accumulation as shear-accommodation mechanisms in ductile shear zones: Constraining their dictating factors","authors":"Pramit Chatterjee, Arnab Roy, Nibir Mandal","doi":"10.5194/egusphere-2024-1077","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1077","url":null,"abstract":"<strong>Abstract.</strong> Understanding the underlying mechanisms of strain localization in Earth’s lithosphere is crucial to explain the mechanics of tectonic plate boundaries and various failure-assisted geophysical phenomena, such as earthquakes. Geological observations suggest that ductile shear zones are the most important lithospheric structures of intense shear localization, sharing a major part of tectonic deformations. Despite extensive studies in the past several decades, the factors governing how they accommodate the bulk shear, whether by distributed homogeneous strain (i.e., development of S tectonic foliation normal to the principal shortening strain axis) or by localized shearing (formation of shear-parallel C bands) remain largely unexplored. This article aims to address this gap in knowledge, providing observational evidences of varying S and C development in ductile shear zones from two geological terrains of Eastern India. The field observations are complemented with 2D-viscoplastic numerical simulations within a strain-softening rheological framework to constrain the factors controlling the two competing shear-accommodation mechanisms: homogeneously distributed strain accumulation versus shear band formation. The model based analysis recognizes the bulk shear rate (<em>γ<sub>b</sub></em>), the bulk viscosity (<em>η<sub>v</sub></em>) and the initial cohesion (<em>C<sub>i</sub></em>) of a shear zone as the most critical factors to determine the dominance of one mechanism over the other. For a given <em>C<sub>i</sub></em>, low <em>γ<sub>b</sub></em> and <em>η<sub>v</sub></em> facilitate the formation of S foliation (uniformly distributed strain), which transforms to C-dominated shear-accommodation mechanism with increasing <em>η<sub>v</sub></em>. However, increasing <em>γ<sub>b</sub></em>, facilitates shear accommodation in a combination of the two mechanisms leading to CS- structures. The article finally discusses the conditions in which ductile shear zones can enormously intensify localized shear rates to produce rapid slip events, such as frictional melting and seismic activities.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140636977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-17DOI: 10.5194/egusphere-2024-1109
Moritz O. Ziegler, Robin Seithel, Thomas Niederhuber, Oliver Heidbach, Thomas Kohl, Birgit Müller, Mojtaba Rajabi, Karsten Reiter, Luisa Röckel
{"title":"The effect of stiffness contrasts at faults on stress orientation","authors":"Moritz O. Ziegler, Robin Seithel, Thomas Niederhuber, Oliver Heidbach, Thomas Kohl, Birgit Müller, Mojtaba Rajabi, Karsten Reiter, Luisa Röckel","doi":"10.5194/egusphere-2024-1109","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1109","url":null,"abstract":"<strong>Abstract.</strong> Even though the crustal stress state is primarily driven by gravitational volume forces and plate tectonics, interpretations of borehole breakout observations show occasionally abrupt rotations of horizontal stress orientation of up to 90° when faults are crossed. This indicates the influence of faults on the local stress state, which parameter control the degree of rotation. Herein, we investigate the phenomenon of principal stress rotation at a fault by means of a 2D generic numerical model. We parametrised the fault as a rock stiffness contrast and investigate systematically the full model parameter space in terms of the ratio of the applied principal stresses, the rock stiffness contrast, as well as the angle between fault strike and orientation of the principal stress axis. General findings are that the stress rotation is negatively correlated with the ratio of principal stresses. A small angle between the far field stress orientation and the fault facilitates stress rotation. A high contrast in rock stiffness further increases the stress rotation angle. Faults striking perpendicular to the maximum principal stress orientation experience no rotation at all. However, faults oriented parallel to the maximum principal stress orientation experience either no rotation or a 90° rotation, dependent on the ratio of principal stresses and the rock stiffness contrast. A comparison with observations from various boreholes worldwide shows that in general, the findings are well in agreement, even though the dip angle proves to have an influence on the stress rotation, in particular for shallow dipping faults.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"49 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140612579","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-09DOI: 10.5194/se-15-513-2024
Judith Freienstein, Wolfgang Szwillus, Agnes Wansing, Jörg Ebbing
{"title":"Statistical appraisal of geothermal heat flow observations in the Arctic","authors":"Judith Freienstein, Wolfgang Szwillus, Agnes Wansing, Jörg Ebbing","doi":"10.5194/se-15-513-2024","DOIUrl":"https://doi.org/10.5194/se-15-513-2024","url":null,"abstract":"Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"26 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-09DOI: 10.5194/se-15-493-2024
Roberto Emanuele Rizzo, Damien Freitas, James Gilgannon, Sohan Seth, Ian B. Butler, Gina Elizabeth McGill, Florian Fusseis
{"title":"Using internal standards in time-resolved X-ray micro-computed tomography to quantify grain-scale developments in solid-state mineral reactions","authors":"Roberto Emanuele Rizzo, Damien Freitas, James Gilgannon, Sohan Seth, Ian B. Butler, Gina Elizabeth McGill, Florian Fusseis","doi":"10.5194/se-15-493-2024","DOIUrl":"https://doi.org/10.5194/se-15-493-2024","url":null,"abstract":"Abstract. X-ray computed tomography has established itself as a crucial tool in the analysis of rock materials, providing the ability to visualise intricate 3D microstructures and capture quantitative information about internal phenomena such as structural damage, mineral reactions, and fluid–rock interactions. The efficacy of this tool, however, depends significantly on the precision of image segmentation, a process that has seen varied results across different methodologies, ranging from simple histogram thresholding to more complex machine learning and deep-learning strategies. The irregularity in these segmentation outcomes raises concerns about the reproducibility of the results, a challenge that we aim to address in this work. In our study, we employ the mass balance of a metamorphic reaction as an internal standard to verify segmentation accuracy and shed light on the advantages of deep-learning approaches, particularly their capacity to efficiently process expansive datasets. Our methodology utilises deep learning to achieve accurate segmentation of time-resolved volumetric images of the gypsum dehydration reaction, a process that traditional segmentation techniques have struggled with due to poor contrast between reactants and products. We utilise a 2D U-net architecture for segmentation and introduce machine-learning-obtained labelled data (specifically, from random forest classification) as an innovative solution to the limitations of training data obtained from imaging. The deep-learning algorithm we developed has demonstrated remarkable resilience, consistently segmenting volume phases across all experiments. Furthermore, our trained neural network exhibits impressively short run times on a standard workstation equipped with a graphic processing unit (GPU). To evaluate the precision of our workflow, we compared the theoretical and measured molar evolution of gypsum to bassanite during dehydration. The errors between the predicted and segmented volumes in all time series experiments fell within the 2 % confidence intervals of the theoretical curves, affirming the accuracy of our methodology. We also compared the results obtained by the proposed method with standard segmentation methods and found a significant improvement in precision and accuracy of segmented volumes. This makes the segmented computed tomography images suited for extracting quantitative data, such as variations in mineral growth rate and pore size during the reaction. In this work, we introduce a distinctive approach by using an internal standard to validate the accuracy of a segmentation model, demonstrating its potential as a robust and reliable method for image segmentation in this field. This ability to measure the volumetric evolution during a reaction with precision paves the way for advanced modelling and verification of the physical properties of rock materials, particularly those involved in tectono-metamorphic processes. Our work underscores the promise of d","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"54 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid EarthPub Date : 2024-04-05DOI: 10.5194/se-15-477-2024
Júlia Gómez-Romeu, Nick Kusznir
{"title":"Extensional fault geometry and evolution within rifted margin hyper-extended continental crust leading to mantle exhumation and allochthon formation","authors":"Júlia Gómez-Romeu, Nick Kusznir","doi":"10.5194/se-15-477-2024","DOIUrl":"https://doi.org/10.5194/se-15-477-2024","url":null,"abstract":"Abstract. Seismic reflection interpretation at magma-poor rifted margins shows that crustal thinning within the hyper-extended domain occurs by in-sequence oceanward extensional faulting which terminates in a sub-horizontal reflector in the topmost mantle immediately beneath tilted crustal fault blocks. This sub-horizontal reflector is interpreted to be a detachment surface that develops sequentially with oceanward in-sequence crustal faulting. We investigate the geometry and evolution of active and inactive extensional faulting due to flexural isostatic rotation during magma-poor margin hyper-extension using a recursive adaptation of the rolling-hinge model of Buck (1988) and compare modelling results with published seismic interpretation. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on published seismic reflection profiles can be generated by the flexural isostatic rotation of faults with initially high-angle geometry. Our modelling supports the hypothesis of Lymer et al. (2019) that the S reflector on the Galician margin is a sub-horizontal detachment generated by the in-sequence incremental addition of the isostatically rotated soles of block-bounding extensional faults. Flexural isostatic rotation produces shallowing of emergent fault angles, fault locking, and the development of new high-angle shortcut fault segments within the hanging wall. This results in the transfer and isostatic rotation of triangular pieces of hanging wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few kilometres in lateral extent and thickness. The initial geometry of basement extensional faults is a long-standing question. Our modelling results show that a sequence of extensional listric or planar faults with otherwise identical tectonic parameters produce very similar seabed bathymetric relief but distinct Moho and allochthon shapes. Our preferred interpretation of our modelling results and seismic observations is that faults are initially planar in geometry but are isostatically rotated and coalesce at depth to form the seismically observed sub-horizontal detachment in the topmost mantle. In-sequence extensional faulting of hyper-extended continental crust results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast, out-of-sequence faulting results in a transition to exhumed mantle with bathymetric relief.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"126 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140599933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}