Download or read book Slab Behavior Overriding Plate Deformation and Topography at Subduction Zones and the India Eurasia Collision Zone written by and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: On earth, two types of convergent plate boundaries exist, namely subduction zones and collision zones. Subduction zones are the main driver of plate tectonics through sinking of negatively buoyant oceanic lithospheric slabs in the mantle and the subduction-induced large-scale mantle flow. Collision zones form when two positively buoyant continental plates meet and collide, following a phase of subduction. Both subduction zones and collision zones cause frequent and tremendous geological activities, which cause overriding plate deformation and form large-scale topography. However, the processes of subduction and collision and the mechanisms driving the associated overriding plate deformation and topography still remain unclear. Since subduction and collision operate at large spatial and temporal scales, a useful and effective way to investigate the processes of subduction and collision is by using analog or numerical modeling. Therefore, in this PhD project, I implement four-dimensional subduction and collision experiments to investigate different subduction/collision styles and mechanisms for deforming the overriding plate and forming topography during subduction/collision. This project comprises two equally weighted parts: (1) The first part investigates the two end-member styles of subduction, namely slab rollback and slab rollover, and their effect on overriding plate deformation and topography, because little research has been conducted on the rollover subduction style, and it remains unclear how and why these different subduction styles emerge. Therefore, Chapters 2 and 3 focus on subduction styles and how the two contrasting subduction styles affect mantle flow, overriding plate deformation and topography in subduction zones. This part of the thesis demonstrates how plate length can control the subduction style, and how the subduction style affects the overriding plate differently.

Download or read book Role of the Overriding Plate in the Subduction Process written by Zhihao Chen and published by . This book was released on 2015 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Subduction zones are thought to be the main driver of plate tectonics and mantle convection. Since the development of the theory of plate tectonics, subduction zones have been investigated and discussed, but in many ways they are still an enigma. Geodynamic modelling (analogue or numerical) can be an effective tool to gain insight into the temporal evolution of subduction zones as it provides quantitative and conceptual insights into the interactions between the plates, the slab and the mantle. Moreover, modelling results can then be compared to their natural prototypes providing crucial insight into regional processes.In my PhD project I use four-dimensional laboratory-based (analogue) geodynamic models to investigate the kinematics and dynamics of subduction, with a particular emphasis on the deformation in the overriding plate. I then compare and constrain my results with natural observations from subduction zones. My thesis has been divided into two parts. The first part focuses on the patterns of overriding plate deformation during progressive subduction when some parameters of the overriding plate are varied. In the first work (Chapter 4), the strength of the overriding plate (i.e., viscosity ratio between the overriding plate and the sub-lithospheric upper mantle, and the overriding plate thickness) is varied to quantify the energy dissipation of overriding plate deformation. The results show that only a small portion of the slab negative buoyancy force and its potential energy are used to deform the overriding plate, and the force required to deform the overriding plate is comparable in magnitude with the ridge push force. Furthermore, the results also show that the bending dissipation at the subduction zone hinge remains relatively low (during steady state subduction), irrespectively of including/excluding an overriding plate in the models. In the second work (Chapter 5), far-field boundary conditions of the overriding plate and subducting plate are varied. The results indicate that such a variation has an influence on the slab geometry and subduction kinematics. The models imply that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of a backarc basin (e.g., Tyrrhenian Sea, Aegean Sea, Scotia Sea) is generally expected to occur at a comparable location with respect to the trench, irrespective of the boundary condition. In addition, my models indicate that the style of forearc deformation (shortening or extension) is affected by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Finally, the results of the model with both plates fixed at their trailing edges are applied to the Calabria subduction zone. This model explains the latest Middle Miocene to present backarc and forearc extension at the Calabria subduction zone as a direct consequence of subduction of the narrow Calabrian slab and the immobility of both the subducting African plate and overriding Eurasian plate.The second part of this thesis focuses on the role of subduction-induced mantle flow in driving deformation of the overriding plate, including (horizontal) trench-normal backarc deformation (Chapter 6) and topography of the overriding plate (Chapter 7). In Chapter 6, a stereoscopic Particle Image Velocimetry (sPIV) technique was used to map simultaneously the horizontal overriding plate deformation and the 3D subduction-induced mantle flow underneath and around the overriding plate. The results show that the strain field of the overriding plate is characterized by localization of an area of maximum extension within its interior (at 300-500 km from the trench). The position of this maximum extension corresponds to that of the maximum trench-normal horizontal velocity gradient measured in the mantle at a scaled depth of 15-25 km below the base of the overriding plate. The results robustly support the hypothesis that in narrow subduction zones backarc extension in the overriding plate is mainly a consequence of the trench-normal horizontal gradients of basal drag force at the base of overriding plate. Such gradients result from a differential in the mantle flow velocity field induced by slab rollback. In Chapter 7, I also used the sPIV technique to investigate the vertical displacement of the overriding plate in a self-consistent subduction model with free boundary conditions. It is suggested that the trench suction force normal to the subduction zone interface, in combination with the shear force at the interface, has an overall influence on the topography of the overriding plate, through bending the overriding plate downward at the trench. Furthermore, the overriding plate is characterized by a transient topographic subsidence located in the forearc, at ~2-5 cm (scaling to 100-250 km) from the trench, with a magnitude of 0.65-1.35 mm (scaling to 3.25-6.75 km). These transient features are most pronounced during the early, transient, free slab sinking phase and predominantly results from the variation of the vertical component of the trench suction along the subduction zone interface, which is induced by the gradual slab steepening during this early phase. The downward mantle flow in the nose of the mantle wedge plays a minor role in the forearc subsidence.

Download or read book Interactions Between a Flat Slab and Overriding Plate written by Xiaowen Liu and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Subduction zones are active plate margins that have an important role in mantle and lithosphere processes. Subduction is driven by the negative buoyancy of the downgoing oceanic plate, resulting in a steep descent angle at most subduction zones. However, in approximately 10% of modern subduction zones, shallow to flat-slab subduction occurs. In these regions, the oceanic plate unbends to become subhorizontal, underplating the continental plate for several hundred kilometers inboard of the plate margin at depths of 45-150 km. Development of a flat slab is generally characterized by migration and termination of arc magmatism, reduced continental surface heat flow, and thick-skinned deformation in the continental interior. The mechanisms that lead to flat-slab subduction include anomalous buoyancy of the oceanic plate, high trenchward velocity of the continental plate, and increased suction force in the mantle wedge. Recent studies have made significant progress in mapping flat slabs and understanding how a flat slab develops. However, there are many fundamental problems that are still not well understood, such as why the depth of the flat slab varies between different regions, and how flat slabs affect the thermal structure and deformation of the continental upper plate. This thesis uses 2D thermal-mechanical models to investigate flat-slab dynamics and the interactions between a flat slab and the overlying continent. Models focus on regions of flat-slab subduction in western North and South America, where slab flattening is driven by a combination of trenchward continental motion and subduction of a buoyant aseismic oceanic ridge. The models show that flat-slab depth is primarily determined by the initial thickness of the overriding plate, such that the slab is deeper below an initially thick (cool) continent. The depth is also controlled by the strength of the continental mantle lithosphere, whereby a weak (hydrated) lithosphere is able to be displaced by the flat slab. Through reasonable variations in these parameters, the depth of the flat slab varies by more than 100 km, in good agreement with observed depths. The models also indicate that the observed low surface heat flow in flat-slab regions does not solely result from conductive cooling by the cold slab. The continental lithosphere cools over 10's of millions of years through conductive heat transfer after flat-slab emplacement. The timescale of cooling is mainly controlled by flat-slab depth, with an earlier onset of cooling and a greater amount of cooling for a shallower slab. The magnitude of cooling is also enhanced by longer slab emplacement times, faster convergence rate, and an older oceanic plate. The presence of a flat slab can also trigger thick-skinned deformation of the continent 100's of km from the plate margin. Deformation is the result of both high compressional stresses through end-loading at the distal plate margin and the presence of pre-existing weak structures in the continent. Deformation is modulated by dynamic topography associated with the flat slab, where dynamic uplift inhibits deformation. The model results are in good agreement with geological and geophysical observations from flat-slab regions. This thesis provides new insights into the flat-slab regions in both North and South America and deepens our understanding of flat-slab subduction dynamics and the origin of thermal anomalies and thick-skinned deformation of the Laramide Orogeny in North America and the Sierras Pampeanas in South America.

Download or read book The Impact of Surface Bending a Complete Mineralogical Model and Movement of the Overriding Plate on Subduction Zones written by Katrina Marie Arredondo and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Modern observations of subduction zones provide only snapshots of a complex geologic system that can last tens of millions of years. Surface velocity measurements and seismic tomography images provide information on the possible forces acting on the plate and influencing slab shape and behavior. Modern subduction zones exhibit a wide range of behavior, from the rapidly rolling back Tonga subduction zone (where the trench is moving toward the subducting plate) to stationary trenches to trench advance (where the trench is moving toward the overriding plate). Slabs may also stagnate at 660 km while others directly penetrate into the lower mantle. Numerical models can combine observations and laboratory data to test and study possible forces that may explain the wide variety of behavior observed in modern subduction zones. Past numerical model studies have not studied the impact on subduction zone behavior from: composition-dependent phase transitions, a complete mineralogical model and movement of the overriding plate. Here we show that: 1) weakening of the subducting plate can be observed from the forebulge to the trench using highly detailed bathymetry and gravity measurement tracks parallel to the trench, 2) using a complete mineralogy model is important for accurate numerical models because incomplete approximations may overestimate slab stagnation and slab rollback, 3) in free subduction models, the complete mineralogy model creates a strong feedback loop between broad slab folds and trench velocities, and 4) the movement of the overriding plate is very important for slab rollback. Results presented in Chapter 1 indicate that the rheology in the numerical models should produce weakening in the slab as it bends into the trench, which is observed in the models of Chapter 2 and 3. Past published models can be analyzed in relation to Chapter 2 and 3 to determine if their conclusions are skewed by an overestimation of slab stagnation or trench rollback. The presented results also indicate the importance of the additional phase transitions on slab dynamics, which hopefully encourages further research to better constrain Clapeyron slopes. Further field geology research may also help constrain trench behavior through time. The time-dependent slab folding, slab dip and trench velocity in Chapter 3 may help explain the wide variety of behavior observed with modern subduction zones. While the slab behavior regime of slab folding and cycles between trench retreat and advance had previously been discounted because it was only produced in simplistic numerical models, it is here reproduced in a realistic model with non-Newtonian viscosity, an overriding plate and complex mineralogy. The regime should be re-examined as a potential description of modern subduction zone behavior as it can explain incidences of trench advance, differences in slab dip and thick slab piles in the lower mantle.

Download or read book Collision and Collapse at the Africa Arabia Eurasia Subduction Zone written by Douwe J. J. van Hinsbergen and published by Geological Society of London. This book was released on 2009 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Mediterranean and northern Arabian regions provide a unique natural laboratory to constrain geodynamics associated with arc-continent and continent-continent collision and subsequent orogenic collapse by analysing regional and temporal distributions of the various elements in the geological archive. This book combines thirteen new contributions that highlight timing and distribution of the Cretaceous to Recent evolution of the Calabrian, Carpathian, Aegean and Anatolian segments of the Africa-Arabia-Eurasia subduction zone. These are subdivided into five papers documenting the timing and kinematics of Cretaceous arc-continent collision, and Eocene and Miocene continent-continent collision in Anatolia, with westward extrusion of Anatolia as a result. Eight papers provide an overview and new data from stratigraphy, structure, metamorphism and magmatism, covering the geological consequences of the largely Neogene collapse that characterizes the segments of interest, in response to late stage reorganization of the subduction zone, and the roll-back and break-off of (segments of) the subducting slab.

Download or read book Subduction and Collision Dynamics of Tectonic Plates written by Zhong-Hai Li and published by Frontiers Media SA. This book was released on 2022-11-07 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Surface Deformation Resulting from Subduction and Slab Detachment written by Susanne Janita Henriët Buiter and published by . This book was released on 2000 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Subduction Zones Part II written by Larry J. Ruff and published by Birkhäuser. This book was released on 2012-12-06 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Subduction zones consume oceanic lithosphere and are an indispensible part of plate tectonics. Unlike the oceanic lithosphere production system which can be linked as a nearly continuous, albeit sinuous, strand around the earth, subduction zones are a rather dissociated group and are found in several isolated corners of the world. While plate tectonics can predict that subduction zones are required along certain plate boundaries, it does not stipulate how subduction zones initiate and develop. The preservation of newly created oceanic lithosphere and the propensity for spreading centers to fragment continents leaves a wealth of geological informa tion on the initiation and evolution of spreading. On the other hand, the subject of subduction initiation has little observational basis. To find such observations, we need to look at some muddled tectonic regimes. The Macquarie Ridge complex presents a natural laboratory for studies of subduction initiation. 2. Tectonics of the Macquarie Ridge Complex The Macquarie Ridge complex is a complicated physiographic feature that trends approximately north-south between South Island, New Zealand and the Pacific-Antarctica spreading center. This feature consists of a sequence of troughs and ridges, with Macquarie Island as the only exposed expression. The seismically active Macquarie Ridge complex (hereafter: MRC) is crudely continuous with the Tonga-Kermadec-New Zealand seismic activity. The basic physiographic features and seismicity of the MRC are shown in Figure I. The earthquake epicenters generally cluster about the bathymetric expression of the MRC.

Download or read book Deformation Along the Subduction Plate Interface Above and Below the Seismogenic Zone written by Caroline Seyler and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Subduction zones host the world’s largest earthquakes, but seismic slip is only one style of deformation along the subduction interface. The deformation processes above and below the seismogenic zone are equally fundamental to understanding how relative motion is accommodated during subduction. The plate interface updip from the seismogenic zone is commonly localized within seafloor sediments overlying the subducting slab. Whether or not an earthquake propagates through those sediments to the surface controls the likelihood tsunami generation, making the mechanical behavior of seafloor sediments essential to our understanding of shallow earthquake rupture. On the downdip portion below, high temperatures allow continuous sliding that progressively loads the seismogenic zone. This thesis investigates the deformation behavior of the updip and downdip subduction interface through experimental, field, and microstructural studies on the active Cascadia subduction system and an exhumed analog, the Leech River Fault.To investigate the likelihood of earthquakes rupturing to the surface, high velocity rotary shear experiments were conducted over a range of normal stresses on three samples of Ocean Drilling Program core retrieved from Cascadia input sediments and a suite of individual clay species to measure their frictional properties and fracture energy. The Cascadia input sediment cores show little variation in fracture energy between samples. Clay species were tested under wet and dry conditions, and difference between extremely low fracture energy wet gouges and moderately low fracture energy dry gouges was more significant than the differences between species. Comparing these results with a global compilation of fracture energy estimates, wet clay-rich gouges have the lowest fracture energy of all lithologies, which may enhance earthquake rupture to the trench. Yet Cascadia sediments have a fracture energy that is nearly an order of magnitude higher than input sediments from other subduction zones, possibly inhibiting shallow earthquake rupture propagation and tsunamigenesis.Field, petrological, microstructural, and geochronological data rewrite the history of the Leech River Fault (LRF) as a subduction interface shear zone. The shear zone is defined by mylonites developed along the contact between the schist and metamorphosed basalt, whose strong, steeply dipping foliation, downdip lineation, and kinematic indicators indicate sinistral-reverse motion. Garnet and amphibole chemical zoning in the schist and metabasalt, respectively, indicate prograde, syn-kinematic growth. Syn-kinematic metamorphic conditions of ~575 °C and ~800 MPa were determined from the schist mylonite, which match the qualitative P-T conditions of amphibolite facies determined from amphibole rim compositions in the metabasalt mylonite. The structural and metamorphic history of the shear zone confirm that it was active as the downdip portion of the subduction interface.The strength of the subduction interface downdip is an important parameter for understanding subduction dynamics that cannot be determined geophysically. Integrating microstructural observations of the mylonites with experimentally derived flow laws, I determined the controls on shear zone rheology and estimated bulk rock strength under in situ conditions. Multiple deformation mechanisms operating in the schist and metabasalt mylonites were required to accommodate deformation, and the available flow laws indicate that the bulk strength of these rocks was significantly reduced by hydrous phases like phyllosilicates and amphibole. These observations suggest that hydration and metamorphic reactions play an essential role in weakening rocks and allowing the plate interface to creep aseismically at low stresses. Together, these new observations place important constraints on the dynamics of deformation above and below the seismogenic zone"--

Download or read book Subduction Zones written by Larry J. Ruff and published by . This book was released on 1989 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structural and Rheological Evolution of Subduction Interface Shear Zones Insights from Exhumed Rocks written by Alissa Jeanne Kotowski and published by . This book was released on 2019 with total page 788 pages. Available in PDF, EPUB and Kindle. Book excerpt: The subduction interface is an inherently heterogeneous distributed shear zone occupying the boundary between a down-going (i.e., subducting) plate and overriding crust and mantle. The sinking of cold, dense oceanic lithosphere creates a slab pull force, which is a driving force for Plate Tectonics. Interface rheology (i.e., deformation or flow) exerts a first-order control on plate boundary strength, seismic style, and the propensity for rocks to exhume, or return to the surface of the Earth from mantle depths. When subducted rocks are exhumed, they provide rare snapshots of the rheological behavior of these complex plate boundary shear zones, and how rocks are subsequently modified by brittle and semi-brittle processes in the upper crust. In this dissertation, I combine a variety of observational and analytical techniques to investigate exhumed subduction-type rocks from Syros Island (Cyclades, Greece) and the sub-ophiolite metamorphic sole in Oman. This work provides constraints on the rheological behavior of subduction plate boundary shear zones, to better inform geodynamic models and to contextualize geophysical observations of active subduction zones. Rheological heterogeneities (i.e., outcrop- to regional-scale features producing strain gradients and/or significant differences in deformation mode or mechanism) are thought to be directly related to the seismic style that occurs along the subduction interface. At relevant depth and temperature conditions for Syros (~50-60 km, 500°C), the important seismic style is an enigmatic, coupled seismic-aseismic phenomena deemed Episodic Tremor and Slow Slip (ETS). ETS involves accelerated - but aseismic - slip over ~10's-100's km2 of the interface, in conjunction with swarms of micro-seismicity, or tremor, and seems to occur nearly ubiquitously in subduction zones regardless of thermal structure, predicted depths of metamorphic dehydration reactions, or subducting rock type. In Chapter 2, I use exhumed blueschist- and greenschist-facies rocks on Syros to characterize the length scales, types, sources, and deformation mechanisms of rheological heterogeneities that occupy the deep subduction interface, and how they may contribute to enigmatic seismicity like ETS. Partial eclogitization of subducting rocks sets up stark rheological contrast across shear zones, which results in coupled brittle-viscous behavior assisted by near-lithostatic pore fluid pressures. Geologic observations are consistent with a mechanical model of ETS in which the deep interface comprises transiently brittle, potentially tremorgenic sub-patches, within a larger viscously creeping interface patch. These observations scale appropriately with geophysical constraints of tremor source areas and seismic moments. During a subduction-exhumation cycle, the length scales of mixing along the interface, maximum pressures (i.e., depths) that rocks reach, and mechanisms of rock exhumation depend in part on interface rheology. In Chapters 3 and 4, I combine structural and microstructural analysis, novel techniques in thermobarometry, and new interpretation of published metamorphic geochronology on Syros to understand bulk interface deformational style, progressive metamorphism, and rheology. The results are all consistent with a model of coherent subduction and underplating (i.e., transfer of subducting material to the overriding forearc), as opposed to large-scale, chaotic mixing in a mega-mélange. Exhumation of rocks on Syros occurred nearly entirely by buoyancy- and viscosity-driven subduction channel return flow, which accommodated vertical translations of ~40 km from peak depths (60 km) to the middle-lower crust. These inferences are consistent with calculated estimates of shear zone viscosity, and the balance between buoyancy forces and shear tractions at peak subduction depths. While exhumation mechanisms and mechanical behavior of thermally mature subduction zones are particularly important to an understanding of subduction tectonics, subduction initiation is even more enigmatic and poorly understood. The only geologic record of rocks deformed and metamorphosed in infant subduction zones are present as tectonic slivers beneath the world's ophiolite sequences, deemed metamorphic soles. In Chapter 5, I investigate the structural and petrologic signatures of subduction, return flow, and ophiolite emplacement in a 100 m section of "low-temperature" metamorphic sole acquired during Phase I of the Oman Drilling Project (Site BT-1B). The "low-temperature" sole rocks acted as a mechanically coherent slice preserving various evidence for subduction and return flow prior to obduction. Intraoceanic subduction initiation is characterized by rapid cooling of the plate interface, which exerts primary control on metamorphic grade and changes in deformation mechanisms. Exhumation in the subduction channel accommodated at least 15 km of vertical translation, and occurred concurrently with early stages of ophiolite emplacement.

Download or read book Structure and Fate of Subducting Slabs written by Thorne Lay and published by Academic Press. This book was released on 1997 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a paperback reprint of Advances in Geophysics, Volume 35 (1994, Academic Press). It provides an overview of the dramatic progress made in illuminating the properties of deep slabs and the surrounding mantle since the introduction of the plate tectonics model to the earth sciences more than 25 years ago. The thermal and chemical characteristics of the subducted lithosphere are determined through thermal and petrological modeling, with seismological observations providing critical constraints on model parameters. Down-wellings of the oceanic lithosphere play a critical role in plate tectonics by recycling to the mantle material that has risen at mid-ocean ridges and cooled at the earth's surface. To assist future efforts in developing detailed thermal and petrological models of oceanic lithosphere down-wellings, this volume includes a comprehensive review of seismological observations and models. A range of seismological procedures are considered, from travel time constraints on seismic velocity anomalies in the subducting lithospheric slabs, to wave conversions and reflections off internal and external slab boundaries. An extensive reference list will be useful to earth science researchers and seismological specialists as a directory to most of the critical literature on slab structure. Provides a comprehensive, chronological summary of seismological studies of slab structure Reviews 25-year history of progress in the field Distills the many contributions that provide a foundation for mastering the roots of the ideas and observations underlying todays paradigms Includes an extensive bibliography Effectively organized for course presentation

Download or read book Continental Deformation written by Paul L. Hancock and published by Pergamon. This book was released on 1994 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explains clearly and concisely the essential attributes of new concepts that have arisen during the last twenty years in structural geology and tectonics. Deformational and tectonic processes and relationships on all scales are discussed. Site or time specific assemblages are not emphasised with the exceptions of Archaean tectonics and neotectonics. The new nomenclature that has proliferated as a result of the need to express new ideas is highlighted.

Download or read book Lithospheric Structure of the Pampean Flat Slab Latitude 30 33S and Northern Costa Rica Latitude 9 11N Subduction Zones written by Lepolt Linkimer Abarca and published by . This book was released on 2011 with total page 482 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Pampean flat slab subduction in west-central Argentina (latitude 30-33S) and the steeply dipping Northern Costa Rica subduction zone (latitude 9-11N) show significant along-trench variations in both the subducting and overriding plates. This dissertation contains the results of three seismological studies using broadband instruments conducted in these subduction zones, with the aim of understanding the structure of the lithosphere and the correlation between the variability observed in the downgoing and the overriding plates. In the Costa Rica region, by analyzing teleseismic receiver functions we investigate the variability in the hydration state of the subducting Cocos Plate and the nature of three distinct crustal terranes within the overriding Caribbean Plate: the Nicoya and Chorotega terranes that display an oceanic character, and the Mesquito Terrane, which is more compatible with continental crust. In the Pampean region of Argentina, we apply a regional-scale double-difference tomography algorithm to earthquake data recorded by the SIEMBRA (2007-2009) and ESP (2008-2010) broadband seismic networks to obtain high-resolution images of the South America lithosphere. We find that most of the upper mantle has seismic properties consistent with a depleted lherzolite or harzburgite, with two anomalous regions above the flat slab: a higher Vp/Vs ratio anomaly consistent with up to 10% hydration of mantle peridotite and a localized lower Vp/Vs ratio anomaly consistent with orthopyroxene enrichment. In addition, we study the geometry and brittle deformation of the subducting Nazca Plate by determining high-quality earthquake locations, slab contours, and focal mechanisms. Our results suggest that the subduction of the incoming Juan Fernandez Ridge controls the slab geometry and that ridge buoyancy and slab pull are key factors in the deformation of the slab. The spatial distribution of the slab seismicity suggests variability in the hydration state of the subducting Nazca Plate and/or in strain due to slab bending. These observations support the hypothesis that the along-trench variability in bathymetric features and hydration state of the incoming plate has profound effects in the subducting slab geometry and the upper plate structure in both flat and steeply dipping subduction zones.

Download or read book Studies of Upper Plate Deformation at Subduction Zone Plate Boundaries written by Kirsty Mckenzie and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation I use observations of upper-plate deformation to constrain the kinematics and dynamics of tectonic processes that occur at subduction zones and within plate boundary transition zones. I combine observations that record deformation over weeks to decades (geodetic observations), tens to hundreds of thousands of years (field observations and geochronology), and millions of years (field observations and plate boundary reconstructions), with earthquake cycle modeling. This research is primarily focused on the Cascadia subduction zone, however the results are applicable across many subduction zones globally. Specific related cases that are highlighted include the Hikurangi margin (New Zealand) and the Nankai trough (SW Japan). The studies in my research range from using observations of slow slip earthquakes to constrain the plate motion direction and forces acting down-dip of the seismogenic zone, to observations of permanent upper-plate deformation to better understand the relationship between shallow mechanical locking on the plate interface and upper-plate deformation. Some key findings I present over several chapters are: (1) a model for the Cascadia subduction zone (and other obliquely-convergence subduction zones) that suggests that loading of the locked region at deep levels is down-dip and thus oblique to the loading direction at shallow levels; (2) a new coupling model for the Cascadia subduction zone that relates the variation in GPS velocities (and permanent deformation) from south to north across the margin to the locations of upper-plate strength (geologic terrane) boundaries; and (3) permanent coastal uplift is not being produced continuously, and instead observations from central Cascadia suggest uplift rates can change significantly over ~20 kyrs.

Download or read book Testing Spatial Correlation of Subduction Interplate Coupling and Forearc Morpho tectonics written by Grant David Kaye and published by . This book was released on 2003 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: The two largest earthquakes ever recorded, the 1964 M[subscript w] 9.2 Alaskan and 1960 M[subscript w] 9.5 Chilean, occurred on seismogenic plate interfaces at subduction zones. It has been theorized that the catastrophic failure of a locked zone along the contact between the downgoing slab and the upper plate causes these earthquakes, although determinations of the position, attitude and extent of this locked zone vary from model to model. Four methods used to constrain the positions of the locked zones are: (1) historical great earthquake rupture extents, (2) heat flow/thermal profiles along the seismogenic plate interface, (3) patterns of surface deformation across the subduction zone forearc, and (4) spatial patterns of upper plate seismicity. Secondary parameters, such as subducted sediment thickness, upper plate lithology, and dip angle of the subducting slab likely play a role in locked zone location as well. In addition to a locked zone, the upper plate of most subduction zones is marked by paired inner and outer forearc highs and basins between the deformation front (trench) and the volcanic arc. Although such surface morphological features are easy to recognize, their spatial and geometric relationships to the locked zone have not been investigated systematically. This thesis investigates correlation between the spatial position of these morpho-tectonic features and the underlying locked zone at the Aleutian, Alaskan, Cascadia, Costa Rican, Javanese, Sumatran, Nankai, and Southern Chilean subduction zones. For all subduction zones other than Cascadia, which has yet to experience a great earthquake in historical times, the applied means of determining the position of the locked zones place them on plate interface regions between the inner and outer forearc highs. A strong correlation exists between dip of the downgoing plate and the width of both the locked zone and the spacing of the forearc morphologic elements for each of the subduction zones examined. The concept of comparative subductology is updated and enhanced in this study by creating GIS databases incorporating geological, seismological, geodetic, and geophysical observations. Correlations between surface morphological features and geologic and geophysical observations provide insight into controls on the position of the locked zone responsible for great earthquakes within the eight subduction zones examined, indicating that forearc morphology and interplate coupling are related via basic subduction parameters and the structural-tectonic regime of the forearc region.

Download or read book Deep Carbon written by Beth N. Orcutt and published by Cambridge University Press. This book was released on 2019-10-17 with total page 687 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive guide to carbon inside Earth - its quantities, movements, forms, origins, changes over time and impact on planetary processes. This title is also available as Open Access on Cambridge Core.