Pub Date : 2024-05-29DOI: 10.5194/egusphere-2024-1507
Lonnie Justin Hufford, Leif Tokle, Whitney Maria Behr, Luiz Grafula Morales, Claudio Madonna
Abstract. Mafic oceanic crustal rocks at blueschist facies conditions are an important rheological component of subducting slabs and the interface at subduction plate boundaries. However, the mechanical properties and deformation mechanisms of glaucophane, a rheologically-controlling sodic amphibole in blueschists, are poorly constrained. To investigate its mechanical and microstructural properties, we conducted general shear constant rate and strain rate stepping experiments on glaucophane aggregates using a Griggs apparatus at temperatures of 700–750 °C, shear strain rates of ~3x10-6 to 9x10-5 s-1, varying grain sizes, and a confining pressure of ~1.0 GPa. The constant rate experiments show an initial stage of grain-size-dependent strain hardening followed by weakening associated with brittle slip along cleavage planes, kink-band development, cataclasis resulting in a fine-grained matrix, and dislocation glide. These experiments evolved to a steady-state stress that did not depend on starting grain size, showing evidence for subgrain development and dynamic recrystallization by bulge nucleation, interpreted to reflect dislocation creep with limited recovery by climb. The mechanical behavior and microstructures of glaucophane in our experiments are consistent with experiments on other low-symmetry minerals as well as microstructural observations from natural blueschists. The strain rate stepping experiments were used to develop a dislocation creep flow law for glaucophane with values of A = 2.23 x 105 MPa-n s-1, n = 3, and Q = 341 ± 37 kJ/mol. A deformation mechanism map comparing our dislocation creep flow law to an existing flow law for blueschist diffusion creep indicates dislocation creep should activate at lower temperatures, higher stresses and larger diffusion lengthscales. Viscosities predicted by our flow law for a typical subduction strain rate of 1 x 10-12 s-1 lie between quartz and eclogite dislocation creep for the blueschist stability field, implying that mafic oceanic crustal rocks remain strong relative to quartz-rich metasediments all along the subduction interface.
{"title":"Dislocation creep near the frictional-viscous transition in blueschist: experimental constraints","authors":"Lonnie Justin Hufford, Leif Tokle, Whitney Maria Behr, Luiz Grafula Morales, Claudio Madonna","doi":"10.5194/egusphere-2024-1507","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1507","url":null,"abstract":"<strong>Abstract.</strong> Mafic oceanic crustal rocks at blueschist facies conditions are an important rheological component of subducting slabs and the interface at subduction plate boundaries. However, the mechanical properties and deformation mechanisms of glaucophane, a rheologically-controlling sodic amphibole in blueschists, are poorly constrained. To investigate its mechanical and microstructural properties, we conducted general shear constant rate and strain rate stepping experiments on glaucophane aggregates using a Griggs apparatus at temperatures of 700–750 °C, shear strain rates of ~3x10<sup>-6</sup> to 9x10<sup>-5</sup> s<sup>-1</sup>, varying grain sizes, and a confining pressure of ~1.0 GPa. The constant rate experiments show an initial stage of grain-size-dependent strain hardening followed by weakening associated with brittle slip along cleavage planes, kink-band development, cataclasis resulting in a fine-grained matrix, and dislocation glide. These experiments evolved to a steady-state stress that did not depend on starting grain size, showing evidence for subgrain development and dynamic recrystallization by bulge nucleation, interpreted to reflect dislocation creep with limited recovery by climb. The mechanical behavior and microstructures of glaucophane in our experiments are consistent with experiments on other low-symmetry minerals as well as microstructural observations from natural blueschists. The strain rate stepping experiments were used to develop a dislocation creep flow law for glaucophane with values of <em>A</em> = 2.23 x 10<sup>5</sup> MPa<sup>-<em>n</em></sup> s<sup>-1</sup>, <em>n</em> = 3, and <em>Q</em> = 341 ± 37 kJ/mol. A deformation mechanism map comparing our dislocation creep flow law to an existing flow law for blueschist diffusion creep indicates dislocation creep should activate at lower temperatures, higher stresses and larger diffusion lengthscales. Viscosities predicted by our flow law for a typical subduction strain rate of 1 x 10<sup>-12</sup> s<sup>-1</sup> lie between quartz and eclogite dislocation creep for the blueschist stability field, implying that mafic oceanic crustal rocks remain strong relative to quartz-rich metasediments all along the subduction interface.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"13 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141167707","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}
Pub Date : 2024-05-27DOI: 10.5194/egusphere-2024-1338
Gonzalo Yanez, Jose Piquer, Orlando Rivera
Abstract. Plate coupling play a fundamental role in the way in which seismic energy is released during the seismic cycle. This process includes quasi-instantaneous release during megathrust earthquakes and long-term creep. Both mechanisms can coexist in a given subducting margin, defining a seismotectonic segmentation in which seismically active segments are separated by zones in which ruptures stop, classified for simplicity as asperities and barrier, respectively. The spatiotemporal stability of this segmentation has been a matter of debate in the seismological community for decades. At this regard, we explore in this paper the potential role of the interaction between geological heterogeneities in the overriding plate and fluids released from the subducting slab towards the subduction channel. As a case study, we take the convergence between the Nazca and South American plates between 18°–40° S, given its relatively simple convergence style and the availability of a high-quality instrumental and historical record. We postulate that trans-lithospheric faults striking at a high angle with respect to the trench behave as large fluid sinks that create the appropriate conditions for the development of barriers and promote the growth of highly coupled asperity domains in their periphery. We tested this hypothesis against key short- and long-term observations in the study area, obtaining consistent results. If the spatial distribution of asperities is controlled by the geology of the overriding plate, seismic risk assessment could be established with better confidence.
{"title":"On the role of trans-lithospheric faults in the long-term seismotectonic segmentation of active margins: a case study in the Andes","authors":"Gonzalo Yanez, Jose Piquer, Orlando Rivera","doi":"10.5194/egusphere-2024-1338","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1338","url":null,"abstract":"<strong>Abstract.</strong> Plate coupling play a fundamental role in the way in which seismic energy is released during the seismic cycle. This process includes quasi-instantaneous release during megathrust earthquakes and long-term creep. Both mechanisms can coexist in a given subducting margin, defining a seismotectonic segmentation in which seismically active segments are separated by zones in which ruptures stop, classified for simplicity as asperities and barrier, respectively. The spatiotemporal stability of this segmentation has been a matter of debate in the seismological community for decades. At this regard, we explore in this paper the potential role of the interaction between geological heterogeneities in the overriding plate and fluids released from the subducting slab towards the subduction channel. As a case study, we take the convergence between the Nazca and South American plates between 18°–40° S, given its relatively simple convergence style and the availability of a high-quality instrumental and historical record. We postulate that trans-lithospheric faults striking at a high angle with respect to the trench behave as large fluid sinks that create the appropriate conditions for the development of barriers and promote the growth of highly coupled asperity domains in their periphery. We tested this hypothesis against key short- and long-term observations in the study area, obtaining consistent results. If the spatial distribution of asperities is controlled by the geology of the overriding plate, seismic risk assessment could be established with better confidence.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"56 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141167705","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}
Pub Date : 2024-05-22DOI: 10.5194/egusphere-2024-1306
Luigi Marini, Claudia Principe, Matteo Lelli
Abstract. We revised the conceptual model of the Solfatara magmatic-hydrothermal system based on the results of new gas-geoindicators (Marini et al., 2022) and the available geological, volcanological, and geophysical information from surface surveys and deep geothermal wells. Using the new gas-geoindicators, we monitored the temperature and total fluid pressure over a time interval of ~40 years: (i) in the shallow reservoir (0.25–0.45 km depth), where CO equilibrates; (ii) in the intermediate reservoir (2.7–4.0 km depth), where CH4 attains equilibrium; (iii) in the deep reservoir (6.5–7.5 km depth), where H2S achieves equilibrium. From 1983 to 2022, the temperature and total fluid pressure of the shallow reservoir did not depart significantly from ~220 °C and ~25 bar, whereas remarkable, progressive increments in temperature and total fluid pressure occurred in the intermediate and deep reservoirs, with peak values of 590–620 °C and 1200–1400 bar in the intermediate reservoir and 1010–1040 °C and 3000–3200 bar in the deep reservoir, in 2020. The revised conceptual model allowed us to explain the evolution of: (a) pressurization-depressurization in the intermediate reservoir, acting as the “engine” of bradyseism, (b) time changes of total fluid pressure in the deep reservoir, working as the “on-off switch” of magmatic degassing. We also used the revised conceptual model to predict possible future scenarios in the lack of external factors.
{"title":"Revised conceptual model of the Solfatara magmatic-hydrothermal system (Campi Flegrei, Italy), time changes during the last 40 years, and prediction of future scenarios","authors":"Luigi Marini, Claudia Principe, Matteo Lelli","doi":"10.5194/egusphere-2024-1306","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1306","url":null,"abstract":"<strong>Abstract.</strong> We revised the conceptual model of the Solfatara magmatic-hydrothermal system based on the results of new gas-geoindicators (Marini et al., 2022) and the available geological, volcanological, and geophysical information from surface surveys and deep geothermal wells. Using the new gas-geoindicators, we monitored the temperature and total fluid pressure over a time interval of ~40 years: (i) in the shallow reservoir (0.25–0.45 km depth), where CO equilibrates; (ii) in the intermediate reservoir (2.7–4.0 km depth), where CH<sub>4</sub> attains equilibrium; (iii) in the deep reservoir (6.5–7.5 km depth), where H<sub>2</sub>S achieves equilibrium. From 1983 to 2022, the temperature and total fluid pressure of the shallow reservoir did not depart significantly from ~220 °C and ~25 bar, whereas remarkable, progressive increments in temperature and total fluid pressure occurred in the intermediate and deep reservoirs, with peak values of 590–620 °C and 1200–1400 bar in the intermediate reservoir and 1010–1040 °C and 3000–3200 bar in the deep reservoir, in 2020. The revised conceptual model allowed us to explain the evolution of: (a) pressurization-depressurization in the intermediate reservoir, acting as the “engine” of bradyseism, (b) time changes of total fluid pressure in the deep reservoir, working as the “on-off switch” of magmatic degassing. We also used the revised conceptual model to predict possible future scenarios in the lack of external factors.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"68 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141146234","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}
Pub Date : 2024-05-15DOI: 10.5194/egusphere-2024-721
Berkan Özkan, Tuna Eken, Peter Gaebler, Tuncay Taymaz
Abstract. Accurate estimates of the moment magnitude of earthquakes that physically measures the earthquake source energy are crucial for improving our understanding of seismic hazards in regions prone to tectonic activity. To address this need, a method involving coda wave modelling was employed to estimate the moment magnitudes of earthquakes in the Sea of Marmara. This approach enabled to model the source displacement spectrum of 303 local earthquakes recorded at 49 seismic stations between 2018 and 2020 in this region. The coda wave traces of individual events were inverted across twelve frequency ranges between 0.3 and 16 Hz. The resultant coda-derived moment magnitudes were found to be in good accordance with the standard local magnitude estimates. However, the notable move-out between local magnitude and coda-derived moment magnitude estimates for smaller earthquakes less than a magnitude of 3.5 likely occurs due to potential biases arising from incorrect assumptions for anelastic attenuation and the finite sampling intervals of seismic recordings. Scaling relations between the total radiated energy and seismic moment imply a nonself-similar behaviour for the earthquakes in the Sea of Marmara. Our findings suggest that larger earthquakes in the Sea of Marmara exhibit distinct rupture dynamics compared to smaller ones, resulting in a more efficient release of seismic energy. In conclusion, here we introduce an empirical relationship devised from the scatter between local magnitude and coda-derived moment magnitude estimates.
{"title":"Coda-derived source properties estimated using local earthquakes in the Sea of Marmara, Türkiye","authors":"Berkan Özkan, Tuna Eken, Peter Gaebler, Tuncay Taymaz","doi":"10.5194/egusphere-2024-721","DOIUrl":"https://doi.org/10.5194/egusphere-2024-721","url":null,"abstract":"<strong>Abstract.</strong> Accurate estimates of the moment magnitude of earthquakes that physically measures the earthquake source energy are crucial for improving our understanding of seismic hazards in regions prone to tectonic activity. To address this need, a method involving coda wave modelling was employed to estimate the moment magnitudes of earthquakes in the Sea of Marmara. This approach enabled to model the source displacement spectrum of 303 local earthquakes recorded at 49 seismic stations between 2018 and 2020 in this region. The coda wave traces of individual events were inverted across twelve frequency ranges between 0.3 and 16 Hz. The resultant coda-derived moment magnitudes were found to be in good accordance with the standard local magnitude estimates. However, the notable move-out between local magnitude and coda-derived moment magnitude estimates for smaller earthquakes less than a magnitude of 3.5 likely occurs due to potential biases arising from incorrect assumptions for anelastic attenuation and the finite sampling intervals of seismic recordings. Scaling relations between the total radiated energy and seismic moment imply a nonself-similar behaviour for the earthquakes in the Sea of Marmara. Our findings suggest that larger earthquakes in the Sea of Marmara exhibit distinct rupture dynamics compared to smaller ones, resulting in a more efficient release of seismic energy. In conclusion, here we introduce an empirical relationship devised from the scatter between local magnitude and coda-derived moment magnitude estimates.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"9 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141062034","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}
Pub Date : 2024-05-14DOI: 10.5194/egusphere-2024-1123
Fatemeh Gomar, Jonas Bruno Ruh, Mahdi Najafi, Farhad Sobouti
Abstract. Understanding the tectonic evolution and crustal-scale structure of fold-thrust belts is crucial for exploring geological resources and evaluating seismic hazards. We conducted a series of finite-difference two-dimensional thermo-mechanical numerical models with visco-elasto-plastic/brittle rheology to decipher how the interaction of inherited basement faults and salt décollement levels control the deformation process and structural style of the Fars Arc in the Zagros fold -thrust belt, during tectonic inversion. Results indicate that initial rifting is controlled by the geometry of inherited faults. During the convergence phase, fold-and-thrust belts display folding at two scales: large wavelength folds induced by basement deformation in the form of fault-propagation faults, and small wavelength folds and thrust systems emerge above the salt layer as detachment folds. Reactivated faults can serve as pathways for stress transfer, resulting in the emergence of new faults and thus seismic activity. The tectonic events in orogenic belts like the Zagros do not adhere to a fixed pattern; they are shaped by factors such as the properties of basement rocks and the orientation of faults. Shallow earthquakes predominantly occur along décollement anticlines, while deeper and larger ones are associated with basement faults. Additionally, we observe variations in resistance to deformation based on salt rheology and fault geometry, with listric faults minimizing resistance. The degree of basement involvement in deformation directly influences the model's resistance, with greater involvement facilitating easier deformation. Our results showing the temporal-spatial relationship between thin- and thick-skinned tectonics can work as an analogue for similar orogenic belts worldwide, such as Taiwan, the Pyrenees, the Alps, the Appalachians, and the Kopet Dagh.
{"title":"Importance of basement faulting and salt decoupling for the structural evolution of the Fars Arc, Zagros fold-and-thrust belt: A numerical modeling approach","authors":"Fatemeh Gomar, Jonas Bruno Ruh, Mahdi Najafi, Farhad Sobouti","doi":"10.5194/egusphere-2024-1123","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1123","url":null,"abstract":"<strong>Abstract.</strong> Understanding the tectonic evolution and crustal-scale structure of fold-thrust belts is crucial for exploring geological resources and evaluating seismic hazards. We conducted a series of finite-difference two-dimensional thermo-mechanical numerical models with visco-elasto-plastic/brittle rheology to decipher how the interaction of inherited basement faults and salt décollement levels control the deformation process and structural style of the Fars Arc in the Zagros fold -thrust belt, during tectonic inversion. Results indicate that initial rifting is controlled by the geometry of inherited faults. During the convergence phase, fold-and-thrust belts display folding at two scales: large wavelength folds induced by basement deformation in the form of fault-propagation faults, and small wavelength folds and thrust systems emerge above the salt layer as detachment folds. Reactivated faults can serve as pathways for stress transfer, resulting in the emergence of new faults and thus seismic activity. The tectonic events in orogenic belts like the Zagros do not adhere to a fixed pattern; they are shaped by factors such as the properties of basement rocks and the orientation of faults. Shallow earthquakes predominantly occur along décollement anticlines, while deeper and larger ones are associated with basement faults. Additionally, we observe variations in resistance to deformation based on salt rheology and fault geometry, with listric faults minimizing resistance. The degree of basement involvement in deformation directly influences the model's resistance, with greater involvement facilitating easier deformation. Our results showing the temporal-spatial relationship between thin- and thick-skinned tectonics can work as an analogue for similar orogenic belts worldwide, such as Taiwan, the Pyrenees, the Alps, the Appalachians, and the Kopet Dagh.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"35 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140925646","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}
Thomas Frasson, Stéphane Labrosse, Henri-Claude Nataf, Nicolas Coltice, Nicolas Flament
Abstract. The heat flux across the core–mantle boundary (CMB) is a fundamental variable for Earth evolution and internal dynamics. Seismic tomography provides access to seismic heterogeneities in the lower mantle, which can be related to present-day thermal heterogeneities. Alternatively, mantle convection models can be used to either infer past CMB heat flux or to produce statistically realistic CMB heat flux patterns in self-consistent models. Mantle dynamics modifies the inertia tensor of the Earth, which implies a rotation of the Earth with respect to its spin axis, a phenomenon called true polar wander (TPW). This rotation must be taken into account to link the dynamics of the mantle to the dynamics of the core. In this study, we explore the impact of TPW on the CMB heat flux over long timescales (∼1 Gyr) using two recently published mantle convection models: one model driven by a plate reconstruction and a second that self-consistently produces a plate-like behaviour. We compute the geoid in both models to correct for TPW. In the plate-driven model, we compute a total geoid and a geoid in which lateral variations of viscosity and density are suppressed above 350 km depth. An alternative to TPW correction is used for the plate-driven model by simply repositioning the model in the original paleomagnetic reference frame of the plate reconstruction. The average TPW rates range between 0.4 and 1.8° Myr−1, but peaks up to 10° Myr−1 are observed. We find that in the plate-driven mantle convection model used in this study, the maximum inertia axis produced by the model does not show a long-term consistency with the position of the magnetic dipole inferred from paleomagnetism. TPW plays an important role in redistributing the CMB heat flux, notably at short timescales (≤10 Myr). Those rapid variations modify the latitudinal distribution of the CMB heat flux, which is known to affect the stability of the magnetic dipole in geodynamo simulations. A principal component analysis (PCA) is computed to obtain the dominant CMB heat flux pattern in the different cases. These heat flux patterns are representative of the mantle convection cases studied here and can be used as boundary conditions for geodynamo models.
{"title":"On the impact of true polar wander on heat flux patterns at the core–mantle boundary","authors":"Thomas Frasson, Stéphane Labrosse, Henri-Claude Nataf, Nicolas Coltice, Nicolas Flament","doi":"10.5194/se-15-617-2024","DOIUrl":"https://doi.org/10.5194/se-15-617-2024","url":null,"abstract":"Abstract. The heat flux across the core–mantle boundary (CMB) is a fundamental variable for Earth evolution and internal dynamics. Seismic tomography provides access to seismic heterogeneities in the lower mantle, which can be related to present-day thermal heterogeneities. Alternatively, mantle convection models can be used to either infer past CMB heat flux or to produce statistically realistic CMB heat flux patterns in self-consistent models. Mantle dynamics modifies the inertia tensor of the Earth, which implies a rotation of the Earth with respect to its spin axis, a phenomenon called true polar wander (TPW). This rotation must be taken into account to link the dynamics of the mantle to the dynamics of the core. In this study, we explore the impact of TPW on the CMB heat flux over long timescales (∼1 Gyr) using two recently published mantle convection models: one model driven by a plate reconstruction and a second that self-consistently produces a plate-like behaviour. We compute the geoid in both models to correct for TPW. In the plate-driven model, we compute a total geoid and a geoid in which lateral variations of viscosity and density are suppressed above 350 km depth. An alternative to TPW correction is used for the plate-driven model by simply repositioning the model in the original paleomagnetic reference frame of the plate reconstruction. The average TPW rates range between 0.4 and 1.8° Myr−1, but peaks up to 10° Myr−1 are observed. We find that in the plate-driven mantle convection model used in this study, the maximum inertia axis produced by the model does not show a long-term consistency with the position of the magnetic dipole inferred from paleomagnetism. TPW plays an important role in redistributing the CMB heat flux, notably at short timescales (≤10 Myr). Those rapid variations modify the latitudinal distribution of the CMB heat flux, which is known to affect the stability of the magnetic dipole in geodynamo simulations. A principal component analysis (PCA) is computed to obtain the dominant CMB heat flux pattern in the different cases. These heat flux patterns are representative of the mantle convection cases studied here and can be used as boundary conditions for geodynamo models.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"64 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140925647","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}
Matthew S. Hodge, Guri Venvik, Jochen Knies, Roelant van der Lelij, Jasmin Schönenberger, Øystein Nordgulen, Marco Brönner, Aziz Nasuti, Giulio Viola
Abstract. Smøla island, situated within the mid-Norwegian passive margin, contains crystalline-basement-hosted intricate fracture and fault arrays formed during a polyphase brittle tectonic evolution. Its detailed study may strengthen correlation attempts between the well-exposed onshore domain and the inaccessible offshore domain, further the understanding of the passive margin evolution, and provide useful constraints on petrophysical properties of fractured basement blocks. A combination of geophysical and remote sensing lineament analysis, field mapping, high-resolution drill hole logging, 3D modelling, petrographic and microstructural studies, and fault gouge K–Ar geochronology made it possible to define five deformation episodes (D1 to D5). These episodes occurred between the post-Caledonian evolution of the regional-scale Møre–Trøndelag Fault Complex (MTFC) and the Late Cretaceous and younger crustal extension preceding the final stages of Greenland–Norway break-up. Each reconstructed deformation stage is associated with different structural features, fault and fracture geometries, and kinematic patterns. Synkinematic mineralisations evolved progressively from epidote–prehnite, sericite–chlorite–calcite, chlorite–hematite, hematite–zeolite–calcite, to quartz–calcite. K–Ar geochronology constrains brittle deformation to discrete localisation events spanning from the Carboniferous to the Late Cretaceous. Multiscalar geometrical modelling at scales of 100, 10, and 1 m helps constrain the extent and size of the deformation zones of each deformation episode, with D2 structures exhibiting the greatest strike continuity and D1 features the most localised. Overall, the approach highlighted here is of great utility for unravelling complex brittle tectonic histories within basement volumes. It is also a prerequisite to constrain the dynamic evolution of the petrophysical properties of basement blocks.
{"title":"Multiscalar 3D temporal structural characterisation of Smøla island, mid-Norwegian passive margin: an analogue for unravelling the tectonic history of offshore basement highs","authors":"Matthew S. Hodge, Guri Venvik, Jochen Knies, Roelant van der Lelij, Jasmin Schönenberger, Øystein Nordgulen, Marco Brönner, Aziz Nasuti, Giulio Viola","doi":"10.5194/se-15-589-2024","DOIUrl":"https://doi.org/10.5194/se-15-589-2024","url":null,"abstract":"Abstract. Smøla island, situated within the mid-Norwegian passive margin, contains crystalline-basement-hosted intricate fracture and fault arrays formed during a polyphase brittle tectonic evolution. Its detailed study may strengthen correlation attempts between the well-exposed onshore domain and the inaccessible offshore domain, further the understanding of the passive margin evolution, and provide useful constraints on petrophysical properties of fractured basement blocks. A combination of geophysical and remote sensing lineament analysis, field mapping, high-resolution drill hole logging, 3D modelling, petrographic and microstructural studies, and fault gouge K–Ar geochronology made it possible to define five deformation episodes (D1 to D5). These episodes occurred between the post-Caledonian evolution of the regional-scale Møre–Trøndelag Fault Complex (MTFC) and the Late Cretaceous and younger crustal extension preceding the final stages of Greenland–Norway break-up. Each reconstructed deformation stage is associated with different structural features, fault and fracture geometries, and kinematic patterns. Synkinematic mineralisations evolved progressively from epidote–prehnite, sericite–chlorite–calcite, chlorite–hematite, hematite–zeolite–calcite, to quartz–calcite. K–Ar geochronology constrains brittle deformation to discrete localisation events spanning from the Carboniferous to the Late Cretaceous. Multiscalar geometrical modelling at scales of 100, 10, and 1 m helps constrain the extent and size of the deformation zones of each deformation episode, with D2 structures exhibiting the greatest strike continuity and D1 features the most localised. Overall, the approach highlighted here is of great utility for unravelling complex brittle tectonic histories within basement volumes. It is also a prerequisite to constrain the dynamic evolution of the petrophysical properties of basement blocks.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"29 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140939594","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}
Pub Date : 2024-05-13DOI: 10.5194/egusphere-2024-1249
Paola Montone, Simona Pierdominici, Maria Teresa Mariucci, Francesco Mirabella, Marco Urbani, Assel Akimbekova, Lauro Chiaraluce, Wade Johnson, Massimiliano Rinaldo Barchi
Abstract. The ICDP STAR drilling project aims to study the seismic and aseismic fault slip behaviour of the active low-angle Alto Tiberina normal Fault (ATF) in the Northern Apennines, Central Italy, drilling and instrumenting six shallow boreholes with seismometers and strainmeters. During the STAR field work, a geophysical downhole logging campaign was carried on defining the optimal target depth for instrument deployment and formation rock characterization. In particular, the main objectives of this study were to define in situ physical properties of the rocks and the tectonic discontinuity geometry along the boreholes. The downhole logging data provide new findings and knowledge especially with regards to the physical properties such as resistivity, gamma ray and wave velocity. The collected parameters were compared to the results of literature data collected in similar lithologies, as well as with the results of logging performed in deeper wells drilled for commercial purposes. The physical properties of the Mesozoic-Early Tertiary calcareous formations show low Gamma Ray values and high compressional (Vp) and shear wave (Vs) velocities (up to 5.3 km/s and 2.9 km/s, respectively), whereas the overlying clay-rich Late Tertiary formations exhibit high Gamma Ray and low resistivity and relatively low Vp and Vs values (up to 3.5 km/s and 2.0 km/s, respectively). The results obtained from the analysis of the orientations of the tectonic structures, measured along the six boreholes, show a good agreement with the orientations of the present-day extensional stress field, NE-SW oriented. Our study allowed to bridge the gap between the physical properties obtained from literature data and those obtained from the deep wells measurements, representing a possible case history for future projects. These new data will contribute to the advancement of knowledge of the physical properties of the rocks at shallow depths, typically overlooked.
摘要ICDP STAR 钻探项目旨在研究意大利中部亚平宁半岛北部活跃的低角度 Alto Tiberina 正断层（ATF）的地震和非地震断层滑动行为，该项目使用地震仪和应变仪钻探了六个浅孔并安装了仪器。在 STAR 实地工作期间，进行了一次地球物理井下测井活动，以确定仪器部署和地层岩石特征描述的最佳目标深度。特别是，这项研究的主要目标是确定岩石的现场物理特性和沿钻孔的构造不连续几何形状。井下测井数据提供了新的发现和知识，特别是在电阻率、伽马射线和波速等物理特性方面。收集到的参数与在类似岩性中收集到的文献数据结果以及为商业目的钻探的深井测井结果进行了比较。中生代-早第三纪钙质地层的物理性质显示出较低的伽马射线值以及较高的压缩波（Vp）和剪切波（Vs）速度（分别高达 5.3 千米/秒和 2.9 千米/秒），而上覆富含粘土的晚第三纪地层则显示出较高的伽马射线值和较低的电阻率以及相对较低的 Vp 值和 Vs 值（分别高达 3.5 千米/秒和 2.0 千米/秒）。沿六个钻孔测量的构造结构方向分析结果显示，与当今东北-西南走向的伸展应力场方向十分吻合。我们的研究弥补了从文献数据中获得的物理性质与深井测量获得的物理性质之间的差距，为未来的项目提供了可能的案例。这些新数据将有助于增进人们对通常被忽视的浅层岩石物理性质的了解。
{"title":"Geophysical downhole logging analysis within the shallow depth ICDP STAR drilling project (Central Italy)","authors":"Paola Montone, Simona Pierdominici, Maria Teresa Mariucci, Francesco Mirabella, Marco Urbani, Assel Akimbekova, Lauro Chiaraluce, Wade Johnson, Massimiliano Rinaldo Barchi","doi":"10.5194/egusphere-2024-1249","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1249","url":null,"abstract":"<strong>Abstract.</strong> The ICDP STAR drilling project aims to study the seismic and aseismic fault slip behaviour of the active low-angle Alto Tiberina normal Fault (ATF) in the Northern Apennines, Central Italy, drilling and instrumenting six shallow boreholes with seismometers and strainmeters. During the STAR field work, a geophysical downhole logging campaign was carried on defining the optimal target depth for instrument deployment and formation rock characterization. In particular, the main objectives of this study were to define in situ physical properties of the rocks and the tectonic discontinuity geometry along the boreholes. The downhole logging data provide new findings and knowledge especially with regards to the physical properties such as resistivity, gamma ray and wave velocity. The collected parameters were compared to the results of literature data collected in similar lithologies, as well as with the results of logging performed in deeper wells drilled for commercial purposes. The physical properties of the Mesozoic-Early Tertiary calcareous formations show low Gamma Ray values and high compressional (Vp) and shear wave (Vs) velocities (up to 5.3 km/s and 2.9 km/s, respectively), whereas the overlying clay-rich Late Tertiary formations exhibit high Gamma Ray and low resistivity and relatively low Vp and Vs values (up to 3.5 km/s and 2.0 km/s, respectively). The results obtained from the analysis of the orientations of the tectonic structures, measured along the six boreholes, show a good agreement with the orientations of the present-day extensional stress field, NE-SW oriented. Our study allowed to bridge the gap between the physical properties obtained from literature data and those obtained from the deep wells measurements, representing a possible case history for future projects. These new data will contribute to the advancement of knowledge of the physical properties of the rocks at shallow depths, typically overlooked.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"121 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140939589","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}
Pub Date : 2024-05-13DOI: 10.5194/egusphere-2024-1264
Jinbao Su, Wenbin Zhu, Guangwei Li
Abstract. The late Mesozoic igneous rocks along the coastal South China Block (SCB) exhibit complex parental sources involving a depleted mantle, subducted sediment-derived melt, and melted crust. This period aligns with the magmatic flareup and lull in the SCB, debating with the compression or extension in coastal region. Our study employs numerical models to investigate the dynamics of the ascent of underplating magma along the Changle-Nan’ao Belt (CNB), simulating its intrusion and cooling processes while disregarding the formational background. The rheological structure of the lithospheric mantle significantly influences magma pathways, dictating the distribution of magmatism. This work reveals that the ascent of magma in the presence of faults is considerably faster than that in the absence of faults, and contemporaneous magmatic melts could produce different cooling and diagenetic processes. Additionally, the influence of pre-existing magma accelerates underplating magma emplacement. The ascending of magma forms a mush-like head, contributing to magmatic circulation beneath the crust and decreasing crustal thickness. Multiphase magmatism increases the geothermal gradient, reducing the lithospheric viscosity and promoting underplating magma ascent, leading to magmatic flare-ups and lulls. Our findings suggest that the Cretaceous magmatism at different times in the coastal SCB may be associated with the effects of lithospheric faults under similar subduction conditions. Boundary compression forces delay magma ascent, while rising magma induces a significant circulation, decreasing the crustal thickness of the coastal SCB. This study provides new insights into the complex interplay of magmatic processes during subduction, emphasizing the role of lithospheric structure in shaping the temporal and spatial evolution of coastal magmatism.
{"title":"Driven magmatism and crustal thinning of coastal South China in response to subduction","authors":"Jinbao Su, Wenbin Zhu, Guangwei Li","doi":"10.5194/egusphere-2024-1264","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1264","url":null,"abstract":"<strong>Abstract.</strong> The late Mesozoic igneous rocks along the coastal South China Block (SCB) exhibit complex parental sources involving a depleted mantle, subducted sediment-derived melt, and melted crust. This period aligns with the magmatic flareup and lull in the SCB, debating with the compression or extension in coastal region. Our study employs numerical models to investigate the dynamics of the ascent of underplating magma along the Changle-Nan’ao Belt (CNB), simulating its intrusion and cooling processes while disregarding the formational background. The rheological structure of the lithospheric mantle significantly influences magma pathways, dictating the distribution of magmatism. This work reveals that the ascent of magma in the presence of faults is considerably faster than that in the absence of faults, and contemporaneous magmatic melts could produce different cooling and diagenetic processes. Additionally, the influence of pre-existing magma accelerates underplating magma emplacement. The ascending of magma forms a mush-like head, contributing to magmatic circulation beneath the crust and decreasing crustal thickness. Multiphase magmatism increases the geothermal gradient, reducing the lithospheric viscosity and promoting underplating magma ascent, leading to magmatic flare-ups and lulls. Our findings suggest that the Cretaceous magmatism at different times in the coastal SCB may be associated with the effects of lithospheric faults under similar subduction conditions. Boundary compression forces delay magma ascent, while rising magma induces a significant circulation, decreasing the crustal thickness of the coastal SCB. This study provides new insights into the complex interplay of magmatic processes during subduction, emphasizing the role of lithospheric structure in shaping the temporal and spatial evolution of coastal magmatism.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"304 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140939587","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}
Abstract. Numerical models of subduction commonly use diffusion and dislocation creep laws from laboratory deformation experiments to determine the rheology of the lithosphere. The specific implementation of these laws varies from study to study, and the impacts of this variation on model behavior have not been thoroughly explored. We run simplified 2D numerical models of free subduction in SULEC, with viscoplastic slabs following (1) a diffusion creep law, (2) a dislocation creep law, and (3) both simultaneously, as well as several variations of model 3 with reduced resistance to bending. We compare the results of these models to a model with a constant-viscosity slab to determine the impact of the implementation of different lithospheric flow laws on subduction dynamics. In creep-governed models, higher subduction velocity causes a longer effective slab length, increasing slab pull and asthenospheric drag, which, in turn, affect subduction velocity. Numerical and analogue models implementing constant-viscosity slabs lack this feedback but still capture morphological patterns observed in more complex models. Dislocation creep is the primary deformation mechanism throughout the subducting lithosphere in our models. However, both diffusion creep and dislocation creep predict very high viscosities in the cold core of the slab. At the trench, the effective viscosity is lowered by plastic failure, rendering effective slab thickness the primary control on bending resistance and subduction velocity. However, at depth, plastic failure is not active, and the viscosity cap is reached in significant portions of the slab. The resulting high slab stiffness causes the subducting plate to curl under itself at the mantle transition zone, affecting patterns in subduction velocity, slab dip, and trench migration over time. Peierls creep and localized grain size reduction likely limit the stress and viscosity in the cores of real slabs. Numerical models implementing only power-law creep and neglecting Peierls creep are likely to overestimate the stiffness of subducting lithosphere, which may impact model results in a variety of respects.
{"title":"The influence of viscous slab rheology on numerical models of subduction","authors":"Natalie Hummel, Susanne Buiter, Zoltán Erdős","doi":"10.5194/se-15-567-2024","DOIUrl":"https://doi.org/10.5194/se-15-567-2024","url":null,"abstract":"Abstract. Numerical models of subduction commonly use diffusion and dislocation creep laws from laboratory deformation experiments to determine the rheology of the lithosphere. The specific implementation of these laws varies from study to study, and the impacts of this variation on model behavior have not been thoroughly explored. We run simplified 2D numerical models of free subduction in SULEC, with viscoplastic slabs following (1) a diffusion creep law, (2) a dislocation creep law, and (3) both simultaneously, as well as several variations of model 3 with reduced resistance to bending. We compare the results of these models to a model with a constant-viscosity slab to determine the impact of the implementation of different lithospheric flow laws on subduction dynamics. In creep-governed models, higher subduction velocity causes a longer effective slab length, increasing slab pull and asthenospheric drag, which, in turn, affect subduction velocity. Numerical and analogue models implementing constant-viscosity slabs lack this feedback but still capture morphological patterns observed in more complex models. Dislocation creep is the primary deformation mechanism throughout the subducting lithosphere in our models. However, both diffusion creep and dislocation creep predict very high viscosities in the cold core of the slab. At the trench, the effective viscosity is lowered by plastic failure, rendering effective slab thickness the primary control on bending resistance and subduction velocity. However, at depth, plastic failure is not active, and the viscosity cap is reached in significant portions of the slab. The resulting high slab stiffness causes the subducting plate to curl under itself at the mantle transition zone, affecting patterns in subduction velocity, slab dip, and trench migration over time. Peierls creep and localized grain size reduction likely limit the stress and viscosity in the cores of real slabs. Numerical models implementing only power-law creep and neglecting Peierls creep are likely to overestimate the stiffness of subducting lithosphere, which may impact model results in a variety of respects.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"23 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140887666","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}
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