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Sample records for subducting pacific plate

  1. Investigating the Subduction History of the Southwest Pacific using Coupled Plate Tectonic-Mantle Convection Models

    Science.gov (United States)

    Matthews, K. J.; Flament, N. E.; Williams, S.; Müller, D.; Gurnis, M.

    2014-12-01

    The Late Cretaceous to mid Eocene (~85-45 Ma) evolution of the southwest Pacific has been the subject of starkly contrasting plate reconstruction models, reflecting sparse and ambiguous data. Disparate models of (1) west-dipping subduction and back-arc basin opening to the east of the Lord Howe Rise, (2) east-dipping subduction and back-arc basin closure to the east of the Lord Howe Rise, and (3) tectonic quiescence with no subduction have all been proposed for this time frame. To help resolve this long-standing problem we test a new southwest Pacific reconstruction using global mantle flow models with imposed plate motions. The kinematic model incorporates east to northeast directed rollback of a west-dipping subduction zone between 85 and 55 Ma, accommodating opening of the South Loyalty back-arc basin to the east of New Caledonia. At 55 Ma there is a plate boundary reorganization in the region. West-dipping subduction and back-arc basin spreading end, and there is initiation of northeast dipping subduction within the back-arc basin. Consumption of South Loyalty Basin seafloor continues until 45 Ma, when obduction onto New Caledonia begins. West-dipping Tonga-Kermadec subduction initiates at this time at the relict Late Cretaceous-earliest Eocene subduction boundary. We use the 3D spherical mantle convection code CitcomS coupled to the plate reconstruction software GPlates, with plate motions and evolving plate boundaries imposed since 230 Ma. The predicted present-day mantle structure is compared to S- and P-wave seismic tomography models, which can be used to infer the presence of slab material in the mantle at locations where fast velocity anomalies are imaged. This workflow enables us to assess the forward-modeled subduction history of the region.

  2. P-wave tomography of Northeast Asia: Constraints on the western Pacific plate subduction and mantle dynamics

    Science.gov (United States)

    Ma, Jincheng; Tian, You; Liu, Cai; Zhao, Dapeng; Feng, Xuan; Zhu, Hongxiang

    2018-01-01

    A high-resolution model of 3-D P-wave velocity structure beneath Northeast Asia and adjacent regions is determined by using 244,180 arrival times of 14,163 local and regional earthquakes and 319,857 relative travel-time residuals of 9988 teleseismic events recorded at ∼2100 seismic stations in the study region. Our tomographic results reveal the subducting Pacific slab clearly as a prominent high-velocity anomaly from the Japan Trench to the North-South Gravity lineament (NSGL) in East China. The NSGL is roughly coincident with the western edge of the stagnant Pacific slab in the mantle transition zone (MTZ). The subducting Pacific slab has partly sunk into the lower mantle beneath Northeast China, but under the Sino-Korean Craton the slab lies horizontally in the MTZ. The NSGL, as an important tectonic line in Mainland China, is marked by sharp differences in the surface topography, gravity anomaly, crustal and lithospheric thickness and mantle seismic velocity from the east to the west. These features of the NSGL and large-scale hot and wet upwelling in the big mantle wedge (BMW) in the east of the NSGL are all related to the subduction processes of the Western Pacific plate. The Changbai intraplate volcanic group is underlain by a striking low-velocity anomaly from the upper MTZ and the BMW up to the surface, and deep earthquakes (410-650 km depths) occur actively in the subducting Pacific slab to the east of the Changbai volcano. We propose that the Changbai volcanic group is caused by upwelling of hot and wet asthenospheric materials and active convection in the BMW. The formation of other volcanic groups in the east of the NSGL is also associated with the subduction-driven corner flow in the BMW.

  3. Geometry and Evolution of the Cangdong Sag in the Bohai Bay Basin, China: Implications for Subduction of the Pacific Plate.

    Science.gov (United States)

    Luo, Liang; Qi, Jiafu; Li, Hongxiang; Dong, Yueqi; Zhang, Shuai; Zhang, Xichen; Yu, Xiaoxia; Luo, Lingyan

    2017-11-13

    The Cangdong Sag is a complex Cenozoic rift basin at the center of the Bohai Bay Basin. Cenozoic structures in the Cangdong Sag can be subdivided into the Cangdong Fault System in the west and the Xuxi Fault System in the east. The geometry of the boundary faults varies along the axes of half-grabens. According to the cross-sectional strata geometry, unconformity and planar structural pattern, the Cenozoic structural evolution of the Cangdong Sag can be divided into four distinct stages: (1) major Paleocene initial rift, (2) latest Paleocene-early Eocene intensive rift, (3) late Eocene-Oligocene strike-slip superimposed rift, and (4) Neogene to present-day post-rift depression. The extensional deformation was mainly derived from horizontal stress induced by the upwelling of asthenosphere. The strike-slip structure of the Cangdong Sag provides important information related to the subduction of the Western Pacific Plate. It was found that the strike-slip movement of the southern Xuxi Fault Zone was activated during the deposition of the third member of Shahejie Formation to the Dongying Formation; therefore, ~43 Ma probably marks the time when the Western Pacific Plate initially changed its subduction direction from northwest to nearly west.

  4. Crustal structure and configuration of the subducting Philippine Sea plate beneath the Pacific coast industrial zone in Japan inferred from receiver function analysis

    Science.gov (United States)

    Igarashi, T.; Iidaka, T.; Sakai, S.; Hirata, N.

    2012-12-01

    We apply receiver function (RF) analyses to estimate the crustal structure and configuration of the subducting Philippine Sea (PHS) plate beneath the Pacific coast industrial zone stretching from Tokyo to Fukuoka in Japan. Destructive earthquakes often occurred at the plate interface of the PHS plate, and seismic activities increase after the 2011 Tohoku earthquake (Mw9.0) around the Tokyo metropolitan area. Investigation on the crustal structure is the key to understanding the stress concentration and strain accumulation process, and information on configuration of the subducting plate is important to mitigate future earthquake disasters. In this study, we searched for the best-correlated velocity structure model between an observed receiver function at each station and synthetic ones by using a grid search method. Synthetic RFs were calculated from many assumed one-dimensional velocity structures that consist of four layers with positive velocity steps. Observed receiver functions were stacked without considering back azimuth or epicentral distance. We further constructed the vertical cross-sections of depth-converted RF images transformed the lapse time of time series to depth by using the estimated structure models. Telemetric seismographic network data covered on the Japanese Islands including the Metropolitan Seismic Observation network, which constructed under the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area and maintained by Special Project for Reducing Vulnerability for Urban Mega Earthquake Disasters, are used. We selected events with magnitudes greater or equal to 5.0 and epicentral distance between 30 and 90 degrees based on USGS catalogues. As a result, we clarify spatial distributions of the crustal S-wave velocities. Estimated average one-dimensional S-wave velocity structure is approximately equal to the JMA2011 structural model although the velocity from the ground surface to 5 km in depth is slow. In particular

  5. Early Jurassic calc-alkaline magmatism in northeast China: Magmatic response to subduction of the Paleo-Pacific Plate beneath the Eurasian continent

    Science.gov (United States)

    Wang, Feng; Xu, Yi-Gang; Xu, Wen-Liang; Yang, Lei; Wu, Wei; Sun, Chen-Yang

    2017-08-01

    The subduction of the Paleo-Pacific Plate played an important role in the regional evolution of the eastern margin of the Eurasian continent, but the timing and extent of this event remain ambiguous. To address these issues, we examine the geochronology and geochemistry of Early Jurassic intrusive rocks in eastern Jilin Province, NE China. The Early Jurassic gabbro-diorites, diorites, granodiorites, and monzogranites are found to have been emplaced at 183-185 Ma and are characterized by enrichment in large ion lithophile elements and depletion in high field strength elements, similar to calc-alkaline arc-type igneous rocks. The Early Jurassic gabbroic and dioritic rocks have εHf(t) values of +2.1 to +10.1 and Hf single-stage (TDM1) model ages of 430-774 Ma, whereas the monzogranites have εHf(t) values of +6.7 to +8.9 and Hf single-stage (TDM1) ages of 597-718 Ma. The gabbro-diorites, diorites, and granodiorites described in this study are genetically linked and they represent the products of the fractional crystallization of a common mafic magma that was in turn derived from the partial melting of a mantle source that was metasomatized by subduction-related fluids. In contrast, the Early Jurassic monzogranites were generated by partial melting of a depleted lower crustal block that was probably accreted during the Neoproterozoic. More importantly, the Early Jurassic calc-alkaline igneous rocks in the east part of NE China form a NE-trending belt that is oriented perpendicular to the direction of Paleo-Pacific Plate movement at that time. West of this belt, contemporaneous bimodal igneous rocks occur in the Lesser Xing'an-Zhangguangcai Ranges. This magmatic configuration is best explained by continental arc magmatism along the continental margin and extensional magmatism in a back-arc setting, in each case triggered by the initial subduction of the Paleo-Pacific Plate beneath Eurasia in the Early Jurassic.

  6. Subducting characteristic of the Pacific slab beneath northeast China

    Science.gov (United States)

    Jiang, G.; Zhang, G.; Xu, Y.

    2012-12-01

    The volcanoes locating in northeast China are very active. Some researchers consider that the origin of volcanoes is closely related to the subducting western Pacific plate and the upwelling asthenosphere. The thickness and the existing range of the subducted plate are not clear as far although the seismic tomography results obviously show that the Pacific plate exists below the volcano region. Therefore, in this study, we adopted the method combining the teleseismic tomography with travel time forward modeling to further study the velocity structure beneath northeast China, especially the precise model of subducted Pacific plate. Our results show that (1) the average thickness and velocity perturbation of slab is 85 km and 1%, respectively, and the slab has not been thickened compared with the previous result of the Japan Sea; (2) the Pacific plate subducted into the mantle transition zone with a shallow dip angle, and changed horizontally when it touched the bottom of mantle transition zone, and extended westward to Longitude 127°E and then stops over there; (3) the horizontal slab locates right below the volcano region. These above features help people understand the origin of intraplate volcanoes and the geodynamical process better. (a) Tomographic result along 43°N. Red and blue colors represent the high and low velocity anomalies, respectively, and the scale is shown at the right-bottom; The profile line is shown in (b); The black triangles represent the volcanoes locating near the profile; The black solid and dashed lines show the depths of upper and lower boundaries of Pacific plate, respectively. The red dots represent the deep earthquakes around the profile. (b) Location of profile AA' along 43°N. Black triangles denote volcanoes; White squares represent the stations; Blue contours denote the depth of upper boundary of Pacific plate; Black and red dots represent the deep epicenters.

  7. Extending Alaska's plate boundary: tectonic tremor generated by Yakutat subduction

    Science.gov (United States)

    Wech, Aaron G.

    2016-01-01

    The tectonics of the eastern end of the Alaska-Aleutian subduction zone are complicated by the inclusion of the Yakutat microplate, which is colliding into and subducting beneath continental North America at near-Pacific-plate rates. The interaction among these plates at depth is not well understood, and further east, even less is known about the plate boundary or the source of Wrangell volcanism. The drop-off in Wadati-Benioff zone (WBZ) seismicity could signal the end of the plate boundary, the start of aseismic subduction, or a tear in the downgoing plate. Further compounding the issue is the possible presence of the Wrangell slab, which is faintly outlined by an anemic, eastward-dipping WBZ beneath the Wrangell volcanoes. In this study, I performed a search for tectonic tremor to map slow, plate-boundary slip in south-central Alaska. I identified ∼11,000 tremor epicenters, which continue 85 km east of the inferred Pacific plate edge marked by WBZ seismicity. The tremor zone coincides with the edges of the downgoing Yakutat terrane, and tremors transition from periodic to continuous behavior as they near the aseismic Wrangell slab. I interpret tremor to mark slow, semicontinuous slip occurring at the interface between the Yakutat and North America plates. The slow slip region lengthens the megathrust interface beyond the WBZ and may provide evidence for a connection between the Yakutat slab and the aseismic Wrangell slab.

  8. Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

    NARCIS (Netherlands)

    Schellart, W. P.; Spakman, W.

    The Tonga-Kermadec-Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with the

  9. Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

    NARCIS (Netherlands)

    Schellart, W.P.; Spakman, W.

    2012-01-01

    The Tonga–Kermadec–Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with

  10. Reaction-induced rheological weakening enables oceanic plate subduction

    OpenAIRE

    Hirauchi, Ken-ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-01-01

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite goug...

  11. Subducting Plate Breakup by Plume-Lithosphere Interaction

    Science.gov (United States)

    Koptev, A.; Gerya, T.; Jolivet, L.; Leroy, S. D.

    2016-12-01

    We use a 3D high-resolution thermo-mechanical modeling to investigate the impact of active mantle plume on a subducting lithospheric plate. Initial model setup consists of an overriding continental lithosphere and subducting lithospheric plate including oceanic and continental lithosphere. A mantle plume thermal anomaly has been initially seeded at the bottom of the model box underneath the continental segment of subducting plate. Mantle plume impingement on lithospheric bottom leads to thinning of continental lithosphere and decompressional melting of both lithospheric and sublithospheric mantle along stretched trench-parallel zone. Further continental breakup is followed by opening of an oceanic basin separating a newly formed microcontinent from the main subducting continent. Despite continuous push applied at the boundary of subducting plate, plume-induced oceanic basin opens during several Myrs reaching several hundred kilometers wide. Cooling of the mantle plume and beginning of collision between the separated microcontinent and the overriding continental plate lead to gradual closure of newly formed oceanic basin that gets further involved into subduction and collision. The final stage sees continental subduction of main body of subducting plate and simultaneous tectonic exhumation of the upper crust of the subducted microcontinent. This scenario involving a plume-induced rifting of a microcontinent away from main body of subducted plate can be compared to the Mesozoic-Cenozoic development of the African plate characterized by the consecutive separation of the Apulian microcontinent and Arabian plate (in the Jurassic and the Neogene, respectively) during subduction of Neo-Tethys oceanic lithosphere beneath the Eurasian margin.

  12. Geodynamical Analysis of Plate Reconstructions based on Subduction History Models

    Science.gov (United States)

    Quevedo, L. E.; Butterworth, N. P.; Matthews, K. J.; Morra, G.; Müller, R. D.

    2011-12-01

    We present a novel method to produce global subduction history models from plate reconstructions and use their predicted geodynamic behaviour as a quality metric for the physical consistency of absolute motions. We show that modelled slabs constructed by advecting material into the mantle according to absolute and relative plate motions given by a particular reconstruction are better correlated with the present day slab dips observed in mantle tomography than instantaneous kinematic quantities like present convergence rate. A complete simulation incorporating lithospheric thickness derived from oceanic age and a rheological model of the lithosphere was run using the Boundary Element Method-based software BEMEarth to infer the global pattern of mantle flow. The predicted plate motion orientations in the form of Euler pole location for the present day and mid-Cretaceous (125 Ma) were compared with the kinematic model for a set of rheologies and mantle structures, and found to be a robust and efficient indicator of the physical consistency of kinematic reconstructions based on their effect on the balance of plate driving forces. As an application example, during the Early Cretaceous, the predicted motion of the Farallon plate was found to be more consistent with the regional geology of the Western North American Cordillera system than the instantaneous motion suggested by a reconstruction at 125 Ma based on sparse hotspot track data on the Pacific Plate. This suggests that a methodology based on forward geodynamic modellling could be used to predict absolute plate motions in reconstructions for times that are ill-constrained by observations constraining absolute plate motions.

  13. Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

    Science.gov (United States)

    Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

    2018-01-01

    The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

  14. Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

    Science.gov (United States)

    Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

    2018-03-01

    The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

  15. Age of the subducting Pacific slab beneath East Asia and its geodynamic implications

    Science.gov (United States)

    Liu, Xin; Zhao, Dapeng; Li, Sanzhong; Wei, Wei

    2017-04-01

    We study the age of the subducting Pacific slab beneath East Asia using a high-resolution model of P-wave tomography and paleo-age data of ancient seafloor. Our results show that the lithosphere age of the subducting slab becomes younger from the Japan Trench (∼130 Ma) to the slab's western edge (∼90 Ma) beneath East China, and the flat (stagnant) slab in the mantle transition zone (MTZ) is the subducted Pacific plate rather than the proposed Izanagi plate which should have already collapsed into the lower mantle. The flat Pacific slab has been in the MTZ for no more than ∼10-20 million years, considerably less than the age of the big mantle wedge beneath East Asia (>110 million years). Hence, the present flat Pacific slab in the MTZ has contributed to the Cenozoic destruction of the East Asian continental lithosphere with extensive intraplate volcanism and back-arc spreading, whereas the destruction of the North China Craton during the Early Cretaceous (∼140-110 Ma) was caused by the subduction of the Izanagi (or the Paleo-Pacific) plate.

  16. Influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge

    NARCIS (Netherlands)

    Schellart, Wouter P.

    2005-01-01

    Geological observations indicate that along two active continental margins (East Asia and Mediterranean) major phases of overriding plate extension, resulting from subduction hinge-retreat, occurred synchronously with a reduction in subducting plate velocity. In this paper, results of fluid

  17. Slab detachment of subducted Indo-Australian plate beneath Sunda ...

    Indian Academy of Sciences (India)

    2007). We investigate the northward subduction of the. Indo-Australian plate along the eastern Sunda arc right from northwestern Sumatra, along Java to. Keywords. Slab detachment; subduction zone; Sunda arc; Indo-Australian slab; trench migration. J. Earth Syst. Sci. 120, No. 2, April 2011, pp. 193–204 c Indian Academy ...

  18. The subduction dichotomy of strong plates and weak slabs

    Science.gov (United States)

    Petersen, Robert I.; Stegman, Dave R.; Tackley, Paul J.

    2017-03-01

    A key element of plate tectonics on Earth is that the lithosphere is subducting into the mantle. Subduction results from forces that bend and pull the lithosphere into the interior of the Earth. Once subducted, lithospheric slabs are further modified by dynamic forces in the mantle, and their sinking is inhibited by the increase in viscosity of the lower mantle. These forces are resisted by the material strength of the lithosphere. Using geodynamic models, we investigate several subduction models, wherein we control material strength by setting a maximum viscosity for the surface plates and the subducted slabs independently. We find that models characterized by a dichotomy of lithosphere strengths produce a spectrum of results that are comparable to interpretations of observations of subduction on Earth. These models have strong lithospheric plates at the surface, which promotes Earth-like single-sided subduction. At the same time, these models have weakened lithospheric subducted slabs which can more easily bend to either lie flat or fold into a slab pile atop the lower mantle, reproducing the spectrum of slab morphologies that have been interpreted from images of seismic tomography.

  19. Electrical conductivity imaging in the western Pacific subduction zone

    Science.gov (United States)

    Utada, Hisashi; Baba, Kiyoshi; Shimizu, Hisayoshi

    2010-05-01

    Oceanic plate subduction is an important process for the dynamics and evolution of the Earth's interior, as it is regarded as a typical downward flow of the mantle convection that transports materials from the near surface to the deep mantle. Recent seismological study showed evidence suggesting the transportation of a certain amount of water by subduction of old oceanic plate such as the Pacific plate down to 150-200 km depth into the back arc mantle. However it is not well clarified how deep into the mantle the water can be transported. The electromagnetic induction method to image electrical conductivity distribution is a possible tool to answer this question as it is known to be sensitive to the presence of water. Here we show recent result of observational study from the western Pacific subduction zone to examine the electrical conductivity distribution in the upper mantle and in the mantle transition zone (MTZ), which will provide implications how water distributes in the mantle. We take two kinds of approach for imaging the mantle conductivity, (a) semi-global and (b) regional induction approaches. Result may be summarized as follows: (a) Long (5-30 years) time series records from 8 submarine cables and 13 geomagnetic observatories in the north Pacific region were analyzed and long period magnetotelluric (MT) and geomagnetic deep sounding (GDS) responses were estimated in the period range from 1.7 to 35 days. These frequency dependent response functions were inverted to 3-dimensional conductivity distribution in the depth range between 350 and 850 km. Three major features are suggested in the MTZ depth such as, (1) a high conductivity anomaly beneath the Philippine Sea, (2) a high conductivity anomaly beneath the Hawaiian Islands, and (3) a low conductivity anomaly beneath and in the vicinity of northern Japan. (b) A three-year long deployment of ocean bottom electro-magnetometers (OBEM's) was conducted in the Philippine Sea and west Pacific Ocean from 2005

  20. A subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration

    NARCIS (Netherlands)

    Schellart, W. P.

    2011-01-01

    The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (v S⊥) at the surface into its subducting plate motion component (vSP⊥) and trench migration component (vT⊥). Geodynamic models of progressive subduction

  1. Three-dimensional dynamic laboratory models of subduction with an overriding plate and variable interplate rheology

    NARCIS (Netherlands)

    Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.

    2013-01-01

    Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flowforce the

  2. Seismic Structure of the Subducted Cocos Plate

    Science.gov (United States)

    Clayton, R. W.; Davis, P. M.; Perez-Campos, X.

    2007-05-01

    The Meso-American Subduction Experiment (MASE) was designed to determine the critical parameters to necessary to simulate the subduction process in Central Mexico . A preliminary analysis of the data shows a 200km section of the slab that is subhorizontal and to within the resolution of the receiver functions it underplates the continental crust with no intervening asthenosphere. This is an interesting situation because the short-term (GPS) and long-term (geologic) strain measurements show almost no compressive strain in this region. This would imply that the crust is decoupled from the subducting slab. Near the coast, the receiver functions show that the slab cuts through the crust at an approximately a 15-degree angle, and under the Trans-Mexican Volcanic Belt the slab becomes detached from the crust, but its geometry at depth is not yet determined from the receiver functions, but a well-developed mantle wedge is apparent from the attenuation of regional earthquakes.

  3. Reaction-induced rheological weakening enables oceanic plate subduction.

    Science.gov (United States)

    Hirauchi, Ken-Ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-08-26

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the 'cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets.

  4. Finding the last 200Ma of subducted lithosphere in tomography and incorporating it into plate reconstructions

    Science.gov (United States)

    Suppe, J.; Wu, J.; Chen, Y. W.

    2016-12-01

    Precise plate-tectonic reconstruction of the Earth has been constrained largely by the seafloor magnetic-anomaly record of the present oceans formed during the dispersal of the last supercontinent since 200Ma. The corresponding world that was lost to subduction has been only sketchily known. We have developed methodologies to map in 3D these subducted slabs of lithosphere in seismic tomography and unfold them to the Earth surface, constraining their initial size, shapes and locations. Slab edges are commonly formed at times of plate reorganization (for example bottom edges typically record initiation of subduction) such that unfolded slabs fit together at times of reorganization, as we illustrate for the Nazca slab at 80Ma and the western Pacific slabs between Kamchatka and New Zealand at 50Ma. Mapping to date suggests that a relatively complete and decipherable record of lithosphere subducted over the last 200Ma may exist in the mantle today, providing a storehouse for new discoveries. We briefly illustrate our procedure for obtaining slab-constrained plate-tectonic models from tomography with our recent study of the Philippine Sea plate, whose motions and tectonic history have been the least known of the major plates because it has been isolated from the global plate and hotspot circuit by trenches. We mapped and unfolded 28 subducted slabs in the mantle under East Asia and Australia/Oceania to depths of 1200km, with a subducted area of 25% of present-day global oceanic lithosphere, and incorporated them as constraints into a new globally-consistent plate reconstruction of the Philippine Sea and surrounding East Asia, leading to a number of new insights, including: [1] discovery of a major (8000 km x 2500 km) set of vanished oceans that we call the East Asia Sea that existed between the Pacific and Indian Oceans, now represented by flat slabs in the lower mantle under present-day Philippine Sea, eastern Sundaland and northern Australia and [2] the Philippine Sea

  5. Subduction of oceanic plate irregularities and seismicity distribution along the Mexican Subduction Zone

    Science.gov (United States)

    Manea, Marina; Constantin Manea, Vlad; Gerya, Taras; Wong, Raul-Valenzuela; Radulian, Mircea

    2017-04-01

    It is known that oceanic plates morphology is not a simple one, but rather complicated by a series of irregularities as seamounts, fracture zones and mid-ocean ridges. These features present on the oceanic floor form part of the fabric of oceanic crust, and once formed they move together with the oceanic plates until eventually enter a subduction zone. Offshore Mexico the oceanic Cocos plate seafloor is littered with relatively small but numerous seamounts and seamount chains, and also large fracture zones. In this study we investigate the relationship between these oceanic irregularities located in the vicinity of the trench in Mexico and the distribution of subduction seismicity, including the rupture history of large subduction zone earthquakes. Since the interseismic locking degree is influenced by the rheological properties of crustal and mantle rocks, any variations along strike will result in significant changes in seismic behavior due to a change in frictional stability. Our preliminary study shows a direct relationship between the presence of seamounts chains on the incoming oceanic plate and the subduction seismicity distribution. We also found a clear relationship between the subduction of the Tehuantepec fracture zone (TFZ) and the low seismic activity in the region where this fracture zone intersects the trench. This region is also long term conspicuously quiet and considered a seismic gap where no significant large earthquake has occurred in more than 100 years. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations specifically tailored for the subduction of the Cocos plate in the region of TFZ we show that the weakened serpentinized fracture zone is partially scraped out in the forearc region because of its low strength and positive buoyancy. The presence of serpentinite in the fore arc apparently lowers the degree of interseismic locking, producing a seismic gap in southern Mexico.

  6. On the Enigmatic Birth of the Pacific Plate within the Panthalassa Ocean

    Science.gov (United States)

    Boschman, L.; Van Hinsbergen, D. J. J.

    2016-12-01

    The oceanic Pacific Plate started forming in Early Jurassic time within the vast Panthalassa Ocean that surrounded the supercontinent Pangea and contains the oldest lithosphere that can directly constrain the geodynamic history of the circum-Pangean Earth. Here, we show that the geometry of the oldest marine magnetic anomalies of the Pacific Plate attests of a unique plate kinematic event that sparked the plate's birth in virtually a point location, surrounded by the Izanagi, Farallon and Phoenix Plates. We reconstruct the unstable triple junction that caused the plate reorganization leading to the birth of the Pacific Plate and present a model of the plate tectonic configuration that preconditioned this event. We show that a stable, but migrating triple junction involving the gradual cessation of intra-oceanic Panthalassa subduction culminated in the formation of an unstable transform-transform-transform triple junction. The consequent plate boundary reorganization resulted in the formation of a stable triangular three-ridge system from which the nascent Pacific Plate expanded. We link the birth of the Pacific Plate to the regional termination of intra-Panthalassa subduction. Remnants thereof have been identified in the deep lower mantle of which the locations may provide paleolongitudinal control on the absolute location of the early Pacific Plate. Our results constitute an essential step in unraveling the plate tectonic evolution of `Thalassa Incognita' comprising the comprehensive Panthalassa Ocean surrounding Pangea.

  7. Constraining the hydration of the subducting Nazca plate beneath Northern Chile using subduction zone guided waves

    Science.gov (United States)

    Garth, Tom; Rietbrock, Andreas

    2017-09-01

    Guided wave dispersion is observed from earthquakes at 180-280 km depth recorded at stations in the fore-arc of Northern Chile, where the 44 Ma Nazca plate subducts beneath South America. Characteristic P-wave dispersion is observed at several stations in the Chilean fore-arc with high frequency energy (>5 Hz) arriving up to 3 s after low frequency (first motion dispersion observed at multiple stations, or the extended P-wave coda observed in arrivals from intermediate depth events within the Nazca plate. These signals can however be accurately accounted for if dipping low velocity fault zones are included within the subducting lithospheric mantle. A grid search over possible LVL and faults zone parameters (width, velocity contrast and separation distance) was carried out to constrain the best fitting model parameters. Our results imply that fault zone structures of 0.5-1.0 km thickness, and 5-10 km spacing, consistent with observations at the outer rise are present within the subducted slab at intermediate depths. We propose that these low velocity fault zone structures represent the hydrated structure within the lithospheric mantle. They may be formed initially by normal faults at the outer rise, which act as a pathway for fluids to penetrate the deeper slab due to the bending and unbending stresses within the subducting plate. Our observations suggest that the lithospheric mantle is 5-15% serpentinised, and therefore may transport approximately 13-42 Tg/Myr of water per meter of arc. The guided wave observations also suggest that a thin LVL (∼1 km thick) interpreted as un-eclogitised subducted oceanic crust persists to depths of at least 220 km. Comparison of the inferred seismic velocities with those predicted for various MORB assemblages suggest that this thin LVL may be accounted for by low velocity lawsonite-bearing assemblages, suggesting that some mineral-bound water within the oceanic crust may be transported well beyond the volcanic arc. While older

  8. Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods

    Science.gov (United States)

    Wu, Jonny; Suppe, John; Lu, Renqi; Kanda, Ravi

    2016-06-01

    We reconstructed Philippine Sea and East Asian plate tectonics since 52 Ma from 28 slabs mapped in 3-D from global tomography, with a subducted area of ~25% of present-day global oceanic lithosphere. Slab constraints include subducted parts of existing Pacific, Indian, and Philippine Sea oceans, plus wholly subducted proto-South China Sea and newly discovered "East Asian Sea." Mapped slabs were unfolded and restored to the Earth surface using three methodologies and input to globally consistent plate reconstructions. Important constraints include the following: (1) the Ryukyu slab is ~1000 km N-S, too short to account for ~20° Philippine Sea northward motion from paleolatitudes; (2) the Marianas-Pacific subduction zone was at its present location (±200 km) since 48 ± 10 Ma based on a >1000 km deep slab wall; (3) the 8000 × 2500 km East Asian Sea existed between the Pacific and Indian Oceans at 52 Ma based on lower mantle flat slabs; (4) the Caroline back-arc basin moved with the Pacific, based on the overlapping, coeval Caroline hot spot track. These new constraints allow two classes of Philippine Sea plate models, which we compared to paleomagnetic and geologic data. Our preferred model involves Philippine Sea nucleation above the Manus plume (0°/150°E) near the Pacific-East Asian Sea plate boundary. Large Philippine Sea westward motion and post-40 Ma maximum 80° clockwise rotation accompanied late Eocene-Oligocene collision with the Caroline/Pacific plate. The Philippine Sea moved northward post-25 Ma over the northern East Asian Sea, forming a northern Philippine Sea arc that collided with the SW Japan-Ryukyu margin in the Miocene (~20-14 Ma).

  9. Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

    Directory of Open Access Journals (Sweden)

    D. Arcay

    2012-12-01

    Full Text Available The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the brittle-ductile transition (BDT depth, zBDT, and, on the other hand, of the kinematic decoupling depth, zdec, simulated along the subduction interplate. The results show that both a high friction and a low ductile strength at the asthenospheric wedge tip shallow zBDT. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume if the BDT occurs at the interplate decoupling depth. Regarding the interplate decoupling depth, it is shallowed (1 significantly if mantle viscosity at asthenospheric wedge tip is low, (2 if the difference in mantle and interplate activation energy is weak, and (3 if the activation volume is increased. Very low friction coefficients and/or low asthenospheric viscosities promote zBDT = zdec. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close hinders the mechanical decoupling at the down-dip extent of the interplate

  10. Long distance transport of eclogite and blueschist during early Pacific Ocean subduction rollback

    Science.gov (United States)

    Tamblyn, Renee; Hand, Martin; Kelsey, David; Phillips, Glen; Anczkiewicz, Robert

    2017-04-01

    The Tasmanides in eastern Australia represent a period of continental crustal growth on the western margin of the Pacific Ocean associated with slab rollback from the Cambrian until the Triassic. During rollback numerical models predict that subduction products can become trapped in the forearc (Geyra et al., 2002), and can migrate with the trench as it retreats. In a long-lived subduction controlled regime such as the Tasmanides, this should result in an accumulation of subduction products with protracted geochronological and metamorphic histories. U-Pb, Lu-Hf, Sm-Nd and Ar-Ar geochronology and phase equilibria modelling of lawsonite-eclogite and garnet blueschist in the Southern New England Fold Belt in Australia demonstrate that high-P low-T rocks remained within a subduction setting for c. 40 Ma, from c. 500 to 460 Ma. High-P metamorphic rocks initially formed close to the Australian cratonic margin during the late Cambrian, and were subsequently transported over 1500 Ma oceanward, during which time subducted material continued to accumulate, resulting in the development of complex mélange which records eclogite and blueschist metamorphism and partial exhumation over 40 Ma. The duration of refrigerated metamorphism approximates the extensional evolution of the upper plate which culminated in the development of the Lachlan Fold Belt. The protracted record of eclogite and blueschist metamorphism indicates that rapid exhumation is not necessarily required for preservation of high-pressure metamorphic rocks from subduction systems. Reference: Gerya, T. V., Stockhert, B., & Perchuk, A. L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21(6), 6-1-6-19. doi:10.1029/2002tc001406

  11. Reevaluating plate driving forces from 3-D models of subduction

    Science.gov (United States)

    Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D.; Turnbull, R.

    2004-12-01

    Subducting lithospheric slabs mechanically attached to tectonic plates provide the main driving force for surface plate motion. Numerical models historically simulate slab dynamics as a 2-D process and further simplify the problem into either a density driven model (no heat transfer) or a corner-flow problem (thermal convection) [Christensen, 2001; Enns et al., (in revision); van Keken, 2003]. Recent 3-D global models of density driven flow incorporating a history of plate motion (Conrad and Lithgow-Bertelloni, 2002) have succussfully ruled out slab "suction" (basal shear traction induced by downward flow of the slabs) as a major driving force, but exact partitioning of the remaining forces acting on the slab remain unconstrained. A survey of trenches around the world reveals that over half of the slabs presently subducted in the upper mantle have a discontinuous edge (either a slab tip on a young slab, or the side edge of a slab with finite width) around which mantle can flow: prime examples being slabs in the Mediterranean and Carribean. However, even slabs with a wide lateral extent (and where a 2-D approximation may seem appropriate), show signs of having 3-D complexity. For example, on the surface Tonga appears relatively symmetric, but when the history of subduction is considered, the slab has a twisted, 3-D structure due to significant eastward retreat of just the northern part of an originally N-S oriented trench edge. Similarly the widest slabs, South American and Kamchatka, show seismic anisotropy attributed to trench parallel mantle flow (Russo and Silver, 1994; Peyton, et al., 2001, respectively), while the Aleutian trench has oblique subduction varying in magnitude from west to east, and medium width Central American slab likely has a slab window allowing 3-D flow (Johnston and Thorkelson, 1997). Recent laboratory experiments of subduction have demonstrated the full complexity of flow occuring in 3-D geometry (Kincaid and Griffiths, 2003; Schellart

  12. Plate tectonics on the Earth triggered by plume-induced subduction initiation.

    Science.gov (United States)

    Gerya, T V; Stern, R J; Baes, M; Sobolev, S V; Whattam, S A

    2015-11-12

    Scientific theories of how subduction and plate tectonics began on Earth--and what the tectonic structure of Earth was before this--remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics.

  13. A plate tectonics oddity: Caterpillar-walk exhumation of subducted continental crust

    NARCIS (Netherlands)

    Tirel, C.; Brun, J.-P.; Burov, E.; Wortel, M.J.R.; Lebedev, S.

    2013-01-01

    Since plate tectonics began on Earth, grandiose "subduction factories" have continually shaped the continents, accreting continental blocks and new crust at the convergent plate boundaries. An enigmatic product of subduction factories is the high-pressure to ultrahigh-pressure (HP-UHP) metamorphic

  14. A thermo-mechanical model of horizontal subduction below an overriding plate

    NARCIS (Netherlands)

    Hunen, Jeroen van; Berg, A.P. van den; Vlaar, N.J.

    2000-01-01

    Subduction of young oceanic lithosphere cannot be explained by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome by obduction of an actively overriding plate, which forces the young plate either to subduct or to collide. This

  15. Sr, Nd, water and carbon dioxide input of altered Pacific MORB into the Tonga subduction zone

    Science.gov (United States)

    Rosner, M.; Bach, W.; Erzinger, J.

    2003-04-01

    The hydrothermally altered and weathered uppermost section of subducting oceanic plates influences the budget of many fluid-mobile elements in supra-subduction zones. The characterisation of subducted upper basement is therefore an important parameter for the understanding of arc-magmatism. We present preliminary Sr and Nd isotope as well as H_2O^+ and CO_2 concentration data for altered basalts from ˜80 Ma Pacific crust drilled during DSDP Leg 91 (Site 595; 23^o49.3'S and 165^o31.6'W) 1000 km East of the Tonga trench. The sample set consists of 10 partially altered, aphyric microcrystalline basalts and subordinate breccia from the uppermost 55 m of basement. Smectite, celadonite, calcite, and Fe-oxides are the most abundant secondary phases, replacing igneous groundmass and filling fissures and void space. 87Sr/86Sr and 143Nd/144Nd isotope ratios vary between 0.70330 and 0.70445 and between 0.513059 and 0.513095, respectively. The H_2O^+ and CO_2 concentrations range from 2.2 to 4.3 wt.% and 0.21 to 3.13 wt.%, respectively. 87Sr/86Sr is positively correlated with H_2O^+ concentrations and alteration intensity (chiefly smectite abundance). Significant macroscopic authigenic carbonate is developed in only two samples, all others show slightly elevated concentrations between 0.21 and 0.82 wt.% related to trace calcite in veinlets. Interestingly, 143Nd/144Nd is negatively correlated with CO_2 abundance suggesting that the 143Nd/144Nd may by ascribed to seawater alteration rather than mantle source heterogeneity. Our preliminary data indicate that the intensity of alteration and the magnitude of chemical change may be greater at Site 595 than in the 6 Ma old eastern Pacific crust at Sites 504 and 896 (Alt et al., 1996) but somewhat smaller than at Sites 417/418 in 118 Ma Atlantic crust (Staudigel et al., 1995). In addition to Sites 801 and 1149 in old Pacific crust, Site 595 may provide insights into western Pacific subduction zone inputs with particular relevance for

  16. Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics

    DEFF Research Database (Denmark)

    Stotz, Ingo Leonardo; Iaffaldano, Giampiero; Davies, DR

    2017-01-01

    and the consequent subduction polarity reversal. The uncertainties associated with the timing of this event, however, make it difficult to quantitatively demonstrate a dynamical association. Here, we first reconstruct the Pacific plate's absolute motion since the mid-Miocene (15 Ma), at high-temporal resolution......, building on previous efforts to mitigate the impact of finite-rotation data noise. We find that the largest change in Pacific plate-motion direction occurred between 10 and 5 Ma, with the plate rotating clockwise. We subsequently develop and use coupled global numerical models of the mantle...

  17. Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics

    Science.gov (United States)

    Stotz, I. L.; Iaffaldano, G.; Davies, D. R.

    2017-07-01

    The timing and magnitude of a Pacific plate motion change within the past 10 Ma remains enigmatic, due to the noise associated with finite-rotation data. Nonetheless, it has been hypothesized that this change was driven by the arrival of the Ontong Java Plateau (OJP) at the Melanesian arc and the consequent subduction polarity reversal. The uncertainties associated with the timing of this event, however, make it difficult to quantitatively demonstrate a dynamical association. Here, we first reconstruct the Pacific plate's absolute motion since the mid-Miocene (15 Ma), at high-temporal resolution, building on previous efforts to mitigate the impact of finite-rotation data noise. We find that the largest change in Pacific plate-motion direction occurred between 10 and 5 Ma, with the plate rotating clockwise. We subsequently develop and use coupled global numerical models of the mantle/lithosphere system to test hypotheses on the dynamics driving this change. These indicate that the arrival of the OJP at the Melanesian arc, between 10 and 5 Ma, followed by a subduction polarity reversal that marked the initiation of subduction of the Australian plate underneath the Pacific realm, were the key drivers of this kinematic change.

  18. The Mesozoic accretionary complex in Northeast China: Evidence for the accretion history of Paleo-Pacific subduction

    Science.gov (United States)

    Zhou, Jian-Bo; Li, Long

    2017-09-01

    The Mesozoic accretionary complex in Northeast China, which mainly consists of the Jilin-Heilongjiang high-pressure (HP) metamorphic belt and the Nadanhada accretionary complex, are the key area to understand the Paleo-Pacific subduction-accretion. The Jilin-Heilongjiang HP belt is a HP metamorphic zone between the Jiamusi and Songliao blocks and consists of the Heilongjiang blueschist belt and the Zhangguangcai Complex. Previously published and our new geochronological data indicate that the collision between the Jiamusi and Songliao blocks along the Jilin-Heilongjiang HP belt occurred between 210 and 180 Ma, suggesting that the Jilin-Heilongjiang HP belt is an important unit for characterizing the geodynamic switch from the north-south closure of the Central Asian Orogenic Belt to the onset of westward accretion related to subduction of Paleo-Pacific plate in the Latest Triassic to Early Jurassic. Early Permian igneous rocks with arc affinity in the eastern margin of the Jiamusi Block are more likely related to the Mongol-Okhotsk subduction rather than the Paleo-Pacific subduction or the collision between the Jiamusi and Khanka blocks as previously considered. The Nadanhada accretionary complex lies to the east of the Jiamusi Block, and is composed of the Yuejinshan and Raohe complexes. Compilation of published geochronological data indicate that the Yuejinshan Complex was probably formed between 210 Ma and 180 Ma, similar to ages for the Jilin-Heilongjiang HP belt along the western margin of the Jiamusi-Khanka Block. The Raohe Complex was formed later in the Late Jurassic to Early Cretaceous (170-137 Ma), likely more related to the subduction-accretion of Paleo-Pacific plate. The final accretion in the target area took place in the Early Cretaceous (137-130 Ma).

  19. Kinematics of subduction and plate convergence under Taiwan and its geomorphic, geodetic and seismic expressions

    Science.gov (United States)

    Suppe, J.; Carena, S.; Kanda, R. V.; Wu, Y.; Huang, H.; Wu, J. E.

    2013-12-01

    Deciphering the kinematics of ongoing subduction and rapid plate convergence under Taiwan is neither trivial nor straightforward. A 3D synthesis of diverse constraints is required, for example tomography, geodesy, tectonic geomorphology, stress inversion, and Philippine Sea plate motions. Eurasian-Philippine Sea plate convergence is ~90mm/y in a mildly oblique 300° azimuth relative to the ~NS nearly vertically subducting Eurasian mantle lithosphere which extends to ~500km depth. If all the current plate convergence were consumed in subduction of Eurasian mantle, the subduction flexural hinge would migrate westward at ~80mm/y, which is fast relative to the ~30mm/y long-term slip rate on the Taiwan main detachment that represents the Eurasian subduction interface under the Taiwan Central Mountains. If this fast simple subduction were occurring, subduction would too quickly outrun the mountain belt in conflict with data. Instead we estimate that subduction of Eurasian lithosphere is proceeding at ~50mm/y with the remaining ~40mm/y convergence at a lithospheric level consumed by secondary subduction above and to the east of the main plate interface. This secondary subduction is largely transient deformation that is most obvious under the Coastal Range, which represents the deforming western margin of the Philippine Sea plate during the last ~1-1.5 Ma. The thrust faults of the Coastal Range function as subduction faults with the long-term net motion of their footwalls moving largely down relative to their only slowly uplifting hanging walls, with a net secondary subduction of ~40-50km in the last ~1-1.5Ma as estimated from seismic tomography and other data. In addition we find evidence for ongoing subduction of the eastern Central Mountains of Taiwan. The crest of the mountains coincides with the western edge of the migrating plate flexure, a band of extensional geodetic strain coincides with the flexure, and an extensional stress state in the upper 5-10km coincides

  20. Convective Removal of Continental Margin Lithosphere at the Edges of Subducting Oceanic Plates

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.

    2013-12-01

    Although oceanic lithosphere is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental lithospheric mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. Lithospheric mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle lithosphere from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. Lithospheric removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin lithospheric mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases lithospheric mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the lithosphere. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.

  1. Pacific plate slab pull and intraplate deformation in the early Cenozoic

    Directory of Open Access Journals (Sweden)

    N. P. Butterworth

    2014-08-01

    Full Text Available Large tectonic plates are known to be susceptible to internal deformation, leading to a~range of phenomena including intraplate volcanism. However, the space and time dependence of intraplate deformation and its relationship with changing plate boundary configurations, subducting slab geometries, and absolute plate motion is poorly understood. We utilise a buoyancy-driven Stokes flow solver, BEM-Earth, to investigate the contribution of subducting slabs through time on Pacific plate motion and plate-scale deformation, and how this is linked to intraplate volcanism. We produce a series of geodynamic models from 62 to 42 Ma in which the plates are driven by the attached subducting slabs and mantle drag/suction forces. We compare our modelled intraplate deformation history with those types of intraplate volcanism that lack a clear age progression. Our models suggest that changes in Cenozoic subduction zone topology caused intraplate deformation to trigger volcanism along several linear seafloor structures, mostly by reactivation of existing seamount chains, but occasionally creating new volcanic chains on crust weakened by fracture zones and extinct ridges. Around 55 Ma, subduction of the Pacific-Izanagi ridge reconfigured the major tectonic forces acting on the plate by replacing ridge push with slab pull along its northwestern perimeter, causing lithospheric extension along pre-existing weaknesses. Large-scale deformation observed in the models coincides with the seamount chains of Hawaii, Louisville, Tokelau and Gilbert during our modelled time period of 62 to 42 Ma. We suggest that extensional stresses between 72 and 52 Ma are the likely cause of large parts of the formation of the Gilbert chain and that localised extension between 62 and 42 Ma could cause late-stage volcanism along the Musicians volcanic ridges. Our models demonstrate that early Cenozoic changes in Pacific plate driving forces only cause relatively minor changes in Pacific

  2. Collapse risk of buildings in the Pacific Northwest region due to subduction earthquakes

    Science.gov (United States)

    Raghunandan, Meera; Liel, Abbie B.; Luco, Nicolas

    2015-01-01

    Subduction earthquakes similar to the 2011 Japan and 2010 Chile events will occur in the future in the Cascadia subduction zone in the Pacific Northwest. In this paper, nonlinear dynamic analyses are carried out on 24 buildings designed according to outdated and modern building codes for the cities of Seattle, Washington, and Portland, Oregon. The results indicate that the median collapse capacity of the ductile (post-1970) buildings is approximately 40% less when subjected to ground motions from subduction, as compared to crustal earthquakes. Buildings are more susceptible to earthquake-induced collapse when shaken by subduction records (as compared to crustal records of the same intensity) because the subduction motions tend to be longer in duration due to their larger magnitude and the greater source-to-site distance. As a result, subduction earthquakes are shown to contribute to the majority of the collapse risk of the buildings analyzed.

  3. Using global, quantitative models of the coupled plates/mantle system to understand Late Miocene dynamics of the Pacific plate

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Rhodri Davies, D.

    2017-04-01

    Knowledge of the evolution of continents, inferred from a variety of geological data, as well as observations of the ocean-floor magnetization pattern provide an increasingly-detailed picture of past and present-day plate motions. These are key to study the evolving balance of shallow- and deep-rooted forces acting upon plates and to unravel the dynamics of the coupled plates/mantle system. Here we focus on the clockwise rotation of the Pacific plate motion relative to the hotspots reference frame between 10 and 5 Ma, which is evidenced by a bend in the Hawaiian sea mount chain (Cox & Engebretson, 1985) as well as by marine magnetic and bathymetric data along the Pacific/Antarctica Ridge (Croon et al., 2008). It has been suggested that such a kinematic change owes to the arrival of the Ontong-Java plateau, the biggest oceanic plateau on the Pacific plate, at the Australia/Pacific subducting margin between 10 and 5 Ma, and to its collision with the Melanesian arc. This could have changed the local buoyancy forces and/or sparked a redistribution of the forces already acting within the Pacific realm, causing the Pacific plate to rotate clockwise. Such hypotheses have never been tested explicitly against the available kinematic reconstructions. We do so by using global numerical models of the coupled plates/mantle system. Our models build on the available codes Terra and Shells. Terra is a global, spherical finite-element code for mantle convection, developed by Baumgardner (1985) and Bunge et al. (1996), and further advanced by Yang (1997; 2000) and Davies et al. (2013), among others. Shells is a thin-sheet, finite-element code for lithosphere dynamics (e.g., Bird, 1998). By merging these two independent models we are able to simulate the rheological behavior of the brittle lithosphere and viscous mantle. We compare the plate velocities output by our models with the available kinematic reconstructions to test the above-mentioned hypotheses, and simulate the impact of

  4. Using Global, Quantitative Models of the Coupled Plates/Mantle System to Understand Late Neogene Dynamics of the Pacific Plate

    Science.gov (United States)

    Stotz, I.; Davies, R.; Iaffaldano, G.

    2016-12-01

    Knowledge of the evolution of continents, inferred from a variety of geological data, as well as observations of the ocean-floor magnetization pattern provide an increasingly-detailed picture of past and present-day plate motions. These are key to study the evolving balance of shallow- and deep-rooted forces acting upon plates and to unravel the dynamics of the coupled plates/mantle system. Here we focus on the clockwise rotation of the Pacific plate motion relative to the hotspots reference frame between 10 and 5 Ma, which is evidenced by a bend in the Hawaiian sea mount chain (Cox & Engebretson, 1985) as well as by marine magnetic and bathymetric data along the Pacific/Antarctica Ridge (Croon et al., 2008). It has been suggested that such a kinematic change owes to the arrival of the Ontong-Java plateau, the biggest oceanic plateau on the Pacific plate, at the Australia/Pacific subducting margin between 10 and 5 Ma, and to its collision with the Melanesian arc. This could have changed the local buoyancy forces and/or sparked a redistribution of the forces already acting within the Pacific realm, causing the Pacific plate to rotate clockwise. Such hypotheses have never been tested explicitly against the available kinematic reconstructions. We do so by using global numerical models of the coupled plates/mantle system. Our models build on the available codes Terra and Shells. Terra is a global, spherical finite-element code for mantle convection, developed by Baumgardner (1985) and Bunge et al. (1996), and further advanced by Yang (1997; 2000) and Davies et al. (2013), among others. Shells is a thin-sheet, finite-element code for lithosphere dynamics (e.g., Bird, 1998). By merging these two independent models we are able to simulate the rheological behavior of the brittle lithosphere and viscous mantle. We compare the plate velocities output by our models with the available kinematic reconstructions to test the above-mentioned hypotheses, and simulate the impact of

  5. Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California: insight into mélange origins and subduction-accretion processes

    Science.gov (United States)

    Wakabayashi, John

    2017-12-01

    the clastic OPS component. Such tectonic mélanges may include blocks and matrix derived from the olistostromes. Franciscan subduction and OPS accretion initiated in island arc crust at about 165-170 Ma, after which MORB and OIB were subducted and accreted following a long (tens of mega-ampere) gap with little or no accretion. Following subduction initiation, a ridge crest approached the trench but probably went dormant prior to its subduction (120-125 Ma), after which the subducted oceanic crust became progressively older until about 95 Ma. From 95 Ma, the age of subducted oceanic crust decreased progressively until arrival of the Pacific-Farallon spreading center led to termination of subduction and conversion to a transform plate boundary.

  6. Effect of a weak layer at the base of an oceanic plate on subduction dynamics

    Science.gov (United States)

    Carluccio, Roberta; Kaus, Boris

    2017-04-01

    The plate tectonics model relies on the concept of a relatively rigid lithospheric lid moving over a weaker asthenosphere. In this frame, the lithosphere asthenosphere boundary (LAB) is a first-order discontinuity that accommodates differential motions between tectonic plates and the underlying mantle. Recent seismic studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates. This thin layer has been interpreted as being weak and slightly buoyant and was suggested to affect the dynamics of subducting plates. However, geodynamically, the role of a weak layer at the base of the lithosphere remains poorly studied, especially at subduction zones. Therefore, we here use numerical models to investigate the first-order effects of a weak buoyant layer at the LAB on subduction dynamics. We employ both 2-D and 3-D models in which the slab and mantle are either linear viscous or have a more realistic temperature-dependent visco-elastic-plastic rheology. Results show that a weak layer affects the dynamics of the plates, foremost by increasing the subduction speed. The impact of this effect depends on the thickness of the layer and the viscosity contrast between the mantle and the weak layer. For moderate viscosity contrasts (1000), it can also change the morphology of the subduction itself, perhaps because this changes the overall effective viscosity contrast between the slab the and the mantle. For thinner layers, the overall effect is reduced. Yet, if seismological observations are correct that suggests that this layer is 10 km thick and partially molten, such that the viscosity is 1000 times lower than that of the mantle, our models suggest that this effect should be measurable. Some of our models also show a pile-up of weak material in the bending zone of the subducting plate, consistent with recent seismological observations.

  7. Reconstructing Farallon plate subduction beneath North America back to the Late Cretaceous.

    Science.gov (United States)

    Liu, Lijun; Spasojevic, Sonja; Gurnis, Michael

    2008-11-07

    Using an inverse mantle convection model that assimilates seismic structure and plate motions, we reconstruct Farallon plate subduction back to 100 million years ago. Models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy, requiring that the Farallon slab was flat lying in the Late Cretaceous, consistent with geological reconstructions. The simulation predicts that an extensive zone of shallow-dipping subduction extended beyond the flat-lying slab farther east and north by up to 1000 kilometers. The limited region of flat subduction is consistent with the notion that subduction of an oceanic plateau caused the slab to flatten. The results imply that seismic images of the current mantle provide more constraints on past tectonic events than previously recognized.

  8. Plate coupling across the northern Manila subduction zone deduced from mantle lithosphere buoyancy

    Science.gov (United States)

    Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun

    2017-12-01

    The Manila subduction zone is located at the plate boundary where the Philippine Sea plate (PSP) moves northwestward toward the Eurasian plate (EU) with a high convergence rate. However, historically, no large earthquakes greater than Mw7 have been observed across the northern Manila subduction zone. The poorly understood plate interaction between these two plates in this region creates significant issues for evaluating the seismic hazard. Therefore, the variation of mantle lithospheric buoyancy is calculated to evaluate the plate coupling status across the northern Manila subduction zone, based on recently published forward gravity modeling constrained by the results of the P-wave seismic crustal structure of the TAIGER (Taiwan Integrated Geodynamic Research) project. The results indicate weak plate coupling between the PSP and EU, which could be related to the release of the overriding PSP from the descending EU's dragging force, which was deduced from the higher elevation of the Luzon arc and the fore-arc basin northward toward the Taiwan orogen. Moreover, serpentinized peridotite is present above the plate boundary and is distributed more widely and thickly closer to offshore southern Taiwan orogen. We suggest that low plate coupling may facilitate the uplifting of serpentinized mantle material up to the plate boundary.

  9. The role of frictional strength on plate coupling at the subduction interface

    KAUST Repository

    Tan, Eh

    2012-10-01

    At a subduction zone the amount of friction between the incoming plate and the forearc is an important factor in controlling the dip angle of subduction and the structure of the forearc. In this paper, we investigate the role of the frictional strength of sediments and of the serpentinized peridotite on the evolution of convergent margins. In numerical models, we vary thickness of a serpentinized layer in the mantle wedge (15 to 25km) and the frictional strength of both the sediments and serpentinized mantle (friction angle 1 to 15, or static friction coefficient 0.017 to 0.27) to control the amount of frictional coupling between the plates. With plastic strain weakening in the lithosphere, our numerical models can attain stable subduction geometry over millions of years. We find that the frictional strength of the sediments and serpentinized peridotite exerts the largest control on the dip angle of the subduction interface at seismogenic depths. In the case of low sediment and serpentinite friction, the subduction interface has a shallow dip, while the subduction zone develops an accretionary prism, a broad forearc high, a deep forearc basin, and a shallow trench. In the high friction case, the subduction interface is steep, the trench is deeper, and the accretionary prism, forearc high and basin are all absent. The resultant free-air gravity and topographic signature of these subduction zone models are consistent with observations. We believe that the low-friction model produces a geometry and forearc structure similar to that of accretionary margins. Conversely, models with high friction angles in sediments and serpentinite develop characteristics of an erosional convergent margin. We find that the strength of the subduction interface is critical in controlling the amount of coupling at the seismogenic zone and perhaps ultimately the size of the largest earthquakes at subduction zones. © 2012. American Geophysical Union. All Rights Reserved.

  10. SubductionGenerator: A program to build three-dimensional plate configurations

    Science.gov (United States)

    Jadamec, M. A.; Kreylos, O.; Billen, M. I.; Turcotte, D. L.; Knepley, M.

    2016-12-01

    Geologic, geochemical, and geophysical data from subduction zones indicate that a two-dimensional paradigm for plate tectonic boundaries is no longer adequate to explain the observations. Many open source software packages exist to simulate the viscous flow of the Earth, such as the dynamics of subduction. However, there are few open source programs that generate the three-dimensional model input. We present an open source software program, SubductionGenerator, that constructs the three-dimensional initial thermal structure and plate boundary structure. A 3D model mesh and tectonic configuration are constructed based on a user specified model domain, slab surface, seafloor age grid file, and shear zone surface. The initial 3D thermal structure for the plates and mantle within the model domain is then constructed using a series of libraries within the code that use a half-space cooling model, plate cooling model, and smoothing functions. The code maps the initial 3D thermal structure and the 3D plate interface onto the mesh nodes using a series of libraries including a k-d tree to increase efficiency. In this way, complicated geometries and multiple plates with variable thickness can be built onto a multi-resolution finite element mesh with a 3D thermal structure and 3D isotropic shear zones oriented at any angle with respect to the grid. SubductionGenerator is aimed at model set-ups more representative of the earth, which can be particularly challenging to construct. Examples include subduction zones where the physical attributes vary in space, such as slab dip and temperature, and overriding plate temperature and thickness. Thus, the program can been used to construct initial tectonic configurations for triple junctions and plate boundary corners.

  11. Nitrogen recycling at the Costa Rican subduction zone: The role of incoming plate structure.

    Science.gov (United States)

    Lee, Hyunwoo; Fischer, Tobias P; de Moor, J Maarten; Sharp, Zachary D; Takahata, Naoto; Sano, Yuji

    2017-10-24

    Efficient recycling of subducted sedimentary nitrogen (N) back to the atmosphere through arc volcanism has been advocated for the Central America margin while at other locations mass balance considerations and N contents of high pressure metamorphic rocks imply massive addition of subducted N to the mantle and past the zones of arc magma generation. Here, we report new results of N isotope compositions with gas chemistry and noble gas compositions of forearc and arc front springs in Costa Rica to show that the structure of the incoming plate has a profound effect on the extent of N subduction into the mantle. N isotope compositions of emitted arc gases (9-11 N°) imply less subducted pelagic sediment contribution compared to farther north. The N isotope compositions (δ(15)N = -4.4 to 1.6‰) of forearc springs at 9-11 N° are consistent with previously reported values in volcanic centers (δ(15)N = -3.0 to 1.9‰). We advocate that subduction erosion enhanced by abundant seamount subduction at 9-11 N° introduces overlying forearc crustal materials into the Costa Rican subduction zone, releasing fluids with lighter N isotope signatures. This process supports the recycling of heavier N into the deep mantle in this section of the Central America margin.

  12. Numerical Modelling of Subduction Plate Interface, Technical Advances for Outstanding Questions

    Science.gov (United States)

    Le Pourhiet, L.; Ruh, J.; Pranger, C. C.; Zheng, L.; van Dinther, Y.; May, D.; Gerya, T.; Burov, E. B.

    2015-12-01

    The subduction zone interface is the place of the largest earthquakes on earth. Compared to the size of a subduction zone itself, it constitutes a very thin zone (few kilometers) with effective rheological behaviour that varies as a function of pressure, temperature, loading, nature of the material locally embedded within the interface as well as the amount of water, melts and CO2. Capturing the behaviour of this interface and its evolution in time is crucial, yet modelling it is not an easy task. In the last decade, thermo-mechanical models of subduction zone have flourished in the literature. They mostly focused on the long-term dynamics of the subduction; e.g. flat subduction, slab detachment or exhumation. The models were validated models against PTt path of exhumed material as well as topography. The models that could reproduce the data all included a mechanically weak subduction channel made of extremely weak and non cohesive material. While this subduction channel model is very convenient at large scale and might apply to some real subduction zones, it does not capture the many geological field evidences that point out the exhumation of very large slice of almost pristine oceanic crust along localised shear zone. Moreover, modelling of sismological and geodetic data using short term tectonic modelling approach also point out that large localised patches rupture within the subduction interface, which is in accordance with geological data but not with large-scale long-term tectonic models. I will present how high resolution models permit to produce slicing at the subduction interface and give clues on how the plate coupling and effective location of the plate interface vary over a few millions of year time scale. I will then discuss the implication of these new high-resolution long-term models of subduction zone on earthquake generation, report progress in the development of self-consistent thermomechanical codes which can handle large strain, high resolution

  13. Subduction of the Caribbean Plate and Basement Uplifts in the Overriding South American Plate

    Science.gov (United States)

    Kellogg, J. N.; Bonini, W. E.

    1982-06-01

    The new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs, seismic profiles, and radiometric and earthquake data. The present Caribbean-South American plate boundary is the South Caribbean marginal fault, where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30° to the southeast and terminates 200 km below the Maracaibo Basin. The Caribbean-South American convergence rate is estimated as 1.9 ± 0.3 cm/yr on the basis of the 390-km length of the seismic zone and a thermal equilibration time of 10 m.y. The Caribbean-South American convergence has produced a northwest-southeast maximum principal stress direction σ1 in the overriding South American plate. The mean σ1 direction for the Maracaibo-Santa Marta block is 310° ± 10° based on earthquake focal mechanism determinations, and structural and gravity data. On the overriding South American plate, basement blocks have been uplifted 7-12 km in the last 10 m.y. to form the Venezuelan Andes, Sierra de Perija, and the Colombian Santa Marta massif. Crystalline basement of the Venezuelan Andes has been thrust to the northwest over Tertiary sediments on a fault dipping about 25° and extending to the mantle. In the Sierra de Perija, Mesozoic sediments have been thrust 16-26 km to the northwest over Tertiary sandstones along the Cerrejon fault. A thrust fault dipping 15° ± 10° to the southeast is consistent with field mapping, and gravity and density data. The Santa Marta massif has been uplifted 12 km in the last 10 m.y. by northwest thrusting over sediments. The basement block overthrusts of the Perijas, Venezuelan Andes, and the Santa Marta massif are Pliocene-Pleistocene analogs for Laramide orogenic structures in the middle and southern Rocky Mountains of the United States. The nonmagmatic basement block uplifts along low-angle thrust faults reveal horizontal compression in the

  14. Geometry and seismic properties of the subducting Cocos plate in central Mexico

    Science.gov (United States)

    Kim, Y.; Clayton, R. W.; Jackson, J. M.

    2010-06-01

    The geometry and properties of the interface of the Cocos plate beneath central Mexico are determined from the receiver functions (RFs) utilizing data from the Meso America Subduction Experiment (MASE). The RF image shows that the subducting oceanic crust is shallowly dipping to the north at 15° for 80 km from Acapulco and then horizontally underplates the continental crust for approximately 200 km to the Trans-Mexican Volcanic Belt (TMVB). The crustal image also shows that there is no continental root associated with the TMVB. The migrated image of the RFs shows that the slab is steeply dipping into the mantle at about 75° beneath the TMVB. Both the continental and oceanic Moho are clearly seen in both images, and modeling of the RF conversion amplitudes and timings of the underplated features reveals a thin low-velocity zone between the plate and the continental crust that appears to absorb nearly all of the strain between the upper plate and the slab. By inverting RF amplitudes of the converted phases and their time separations, we produce detailed maps of the seismic properties of the upper and lower oceanic crust of the subducting Cocos plate and its thickness. High Poisson's and Vp/Vs ratios due to anomalously low S wave velocity at the upper oceanic crust in the flat slab region may indicate the presence of water and hydrous minerals or high pore pressure. The evidence of high water content within the oceanic crust explains the flat subduction geometry without strong coupling of two plates. This may also explain the nonvolcanic tremor activity and slow slip events occurring in the subducting plate and the overlying crust.

  15. Impact of Mantle Wind on Subducting Plate Geometry and Interplate Pressure: Insights From Physical Modelling.

    Science.gov (United States)

    Boutelier, D.; Cruden, A. R.

    2005-12-01

    New physical models of subduction investigate the impact of large-scale mantle flow on the structure of the subducted slab and deformation of the downgoing and overriding plates. The experiments comprise two lithospheric plates made of highly filled silicone polymer resting on a model asthenosphere of low viscosity transparent silicone polymer. Subduction is driven by a piston that pushes the subducting plate at constant rate, a slab-pull force due to the relative density of the slab, and a basal drag force exerted by flow in the model asthenosphere. Large-scale mantle flow is imposed by a second piston moving at constant rate in a tunnel at the bottom of the experiment tank. Passive markers in the mantle track the evolution of flow during the experiment. Slab structure is recorded by side pictures of the experiment while horizontal deformation is studied via passive marker grids on top of both plates. The initial mantle flow direction beneath the overriding plate can be sub-horizontal or sub-vertical. In both cases, as the slab penetrates the mantle, the mantle flow pattern changes to accommodate the subducting high viscosity lithosphere. As the slab continues to descend, the imposed flow produces either over- or under-pressure on the lower surface of the slab depending on the initial mantle flow pattern (sub-horizontal or sub-vertical respectively). Over-pressure imposed on the slab lower surface promotes shallow dip subduction while under-pressure tends to steepen the slab. These effects resemble those observed in previous experiments when the overriding plate moves horizontally with respect to a static asthenosphere. Our experiments also demonstrate that a strong vertical drag force (due to relatively fast downward mantle flow) exerted on the slab results in a decrease in strain rate in both the downgoing and overriding plates, suggesting a decrease in interplate pressure. Furthermore, with an increase in drag force deformation in the downgoing plate can switch

  16. Teleseismic P wave tomography of South Island, New Zealand upper mantle: Evidence of subduction of Pacific lithosphere since 45 Ma

    Science.gov (United States)

    Zietlow, Daniel W.; Molnar, Peter H.; Sheehan, Anne F.

    2016-06-01

    A P wave speed tomogram produced from teleseismic travel time measurements made on and offshore the South Island of New Zealand shows a nearly vertical zone with wave speeds that are 4.5% higher than the background average reaching to depths of approximately 450 km under the northwestern region of the island. This structure is consistent with oblique west-southwest subduction of Pacific lithosphere since about 45 Ma, when subduction beneath the region began. The high-speed zone reaches about 200-300 km below the depths of the deepest intermediate-depth earthquakes (subcrustal to ~200 km) and therefore suggests that ~200-300 km of slab below them is required to produce sufficient weight to induce the intermediate-depth seismicity. In the southwestern South Island, high P wave speeds indicate subduction of the Australian plate at the Puysegur Trench to approximately 200 km depth. A band with speeds ~2-3.5% lower than the background average is found along the east coast of the South Island to depths of ~150-200 km and underlies Miocene or younger volcanism; these low speeds are consistent with thinned lithosphere. A core of high speeds under the Southern Alps associated with a convergent margin and mountain building imaged in previous investigations is not well resolved in this study. This could suggest that such high speeds are limited in both width and depth and not resolvable by our data.

  17. Dynamics of subduction and continental collision: Influence of the nature of the plate contact. Geologica Ultraiectina (284)

    NARCIS (Netherlands)

    De Franco, R.

    2008-01-01

    At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction

  18. Subduction controls the distribution and fragmentation of Earth’s tectonic plates.

    Science.gov (United States)

    Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R Dietmar; Tackley, Paul J

    2016-07-07

    The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.

  19. Plate boundary deformation between the Pacific and North America in the Explorer region

    Science.gov (United States)

    Kreemer, Corné; Govers, Rob; Furlong, Kevin P.; Holt, William E.

    1998-08-01

    One of the consequences of plate tectonics is that a spreading ridge will eventually approach a subduction zone. The problem whether the possible break-up of the approaching ridge will lead to the development of independent micro-plates, or not, is still unresolved. Some 4 million years ago the interaction between the Juan de Fuca Ridge and the Cascadia subduction zone resulted in ridge fragmentation in the Explorer region. There are two proposed post-Miocene kinematic models: one that proposes the presence of a micro-plate and the other that treats the region as a transform deformation zone, or so-called pseudo-plate. We use earthquake strain rates derived from 74 events since 1948 to estimate a long-term velocity field for the region. By comparing this result with the predicted velocity fields for both models we try to discriminate between the two. The earthquake strain rates indicate the presence of a transform deformation zone between the North American (NAM) and Pacific (PAC) plates. The velocity field derived from the inversion of the earthquake strain rates indicates that seismic activity takes up 50±30% (1 σ) of the PAC-NAM relative motion (NUVEL-1A; DeMets et al., 1994. Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions. Geophys. Res. Lett. 21, 2191-2194.) within the seismogenic layer of this zone and is indistinguishable in direction from the NUVEL-1A PAC-NAM model. The presence of this Explorer transform zone is consistent with the strain rate and velocity field for the `pseudo-plate model' and indicates that seismicity defines a (new) plate boundary zone between the Pacific and North American plates. Earthquake-derived strain rates are low along the Nootka Transform, which accommodates relative motion between the Juan de Fuca and North American plates. The cause for the absence of significant seismic slip along this transform is unclear and may be closely linked to the fact that the adjacent

  20. The relationship between plate velocity and trench viscosity in Newtonian and power-law subduction calculations

    Science.gov (United States)

    King, Scott D.; Hager, Bradford H.

    1990-01-01

    The relationship between oceanic trench viscosity and oceanic plate velocity is studied using a Newtonian rheology by varying the viscosity at the trench. The plate velocity is a function of the trench viscosity for fixed Rayleigh number and plate/slab viscosity. Slab velocities for non-Newtonian rheology calculations are significantly different from slab velocities from Newtonian rheology calculations at the same effective Rayleigh number. Both models give reasonable strain rates for the slab when compared with estimates of seismic strain rate. Non-Newtonian rheology eliminates the need for imposed weak zones and provides a self-consistent fluid dynamical mechanism for subduction in numerical convection models.

  1. Structural discontinuities inside the Pacific plate offshore of the Tohoku and Kanto regions revealed by seismic reflection imaging

    Science.gov (United States)

    Panayotopoulos, Y.; Kasahara, K.; Hirata, N.; Abe, S.; Katou, M.; Kato, A.; Obara, K.

    2012-12-01

    We have investigated the material properties and the tectonic processes that govern the Pacific plate just before it is subducted in the Japan Trench Subduction zone. We reprocessed the 500 km long data retrieved by the summer 1991 seismic survey offshore of the Boso peninsula and Tohoku regions and produced a high resolution image of the Pacific plate crust and Mantle lithosphere beneath it. We have conducted a CMP gather analysis combining 18828 traces and applied a first arrival mute at almost every 4 shots. Consecutively we applied NMO corrections after determining stacking velocity values every 30 CMP gathers, which is equivalent to every 800 m along the profile. The corrected traces enabled us to retrieve a high resolution image of the sediments deposited on the Pacific plate. The upper part of the plate is characterized by a thick sequence of sediments offshore of the Boso peninsula that becomes progressively thinner towards the north in the region offshore the Tohoku region. This could be due to the geometry of the profile, since the southern part is further away from the trench than the north. Offshore Tohoku the sediments are possibly eroded and redeposit inside the trench by down going currents. Our profile intersects with a seamount range that is currently subducting under the Japan Trench. The sedimentary sequence on the Pacific plate around this range is disturbed by a thick sequence of possibly volcanic origin sediments derived from the seamount range. The sedimentary units offshore Boso peninsula display an uplift of several hundred meters. In the southernmost part of our profile we were able to observe several long scale discontinuities inside the plate, that stretch down to the Moho. This area greatly coincides with the Kashima fault zone, previously observed only by the shift of the magnetic anomalies on the plate. The Pacific sea plate crust immediately to the north of this fault zone is significantly thicker than the average crustal thickness

  2. Topography of the Overriding Plate During Progressive Subduction: A Dynamic Model to Explain Forearc Subsidence

    Science.gov (United States)

    Chen, Zhihao; Schellart, Wouter P.; Duarte, João. C.; Strak, Vincent

    2017-10-01

    Overriding plate topography provides constraints on subduction zone geodynamics. We investigate its evolution using fully dynamic laboratory models of subduction with techniques of stereoscopic photogrammetry and particle image velocimetry. Model results show that the topography is characterized by an area of forearc dynamic subsidence, with a magnitude scaling to 1.44-3.97 km in nature, and a local topographic high between the forearc subsided region and the trench. These topographic features rapidly develop during the slab free-sinking phase and gradually decrease during the steady state slab rollback phase. We propose that they result from the variation of the vertical component of the trench suction force along the subduction zone interface, which gradually increases with depth and results from the gradual slab steepening during the initial transient slab sinking phase. The downward mantle flow in the nose of the mantle wedge plays a minor role in driving forearc subsidence.

  3. The temporal evolution of a subducting plate in the lower mantle

    Science.gov (United States)

    Loiselet, C.; Grujic, D.; Braun, J.; Fullsack, P.; Thieulot, C.; Yamato, P.

    2009-04-01

    It is now widely accepted that some subducting slabs may cross the lower/upper mantle boundary to ground below the 660 km discontinuity. Indeed, geophysical data underline long and narrow traces of fast materials, associated with subducting slabs, from the upper mantle transition zone to mid-mantle depths that are visible beneath North and South America and southern Asia (Li et al, 2008). Furthermore, seismic tomography data (Van der Hilst et al., 1997; Karason and van der Hilst, 2000, 2001) show a large variety of slab geometries and of mantle flow patterns around subducting plate boundaries (e.g. the slab geometry in the lower mantle in the Tonga subduction zone). However, seismic tomography does not elucidate the temporal evolution of the slab behaviour and geometry during its descent through the upper and lower mantle. In this work, we therefore propose to study the deformation of a thin plate (slab) falling in a viscous fluid (mantle) by means of both analogue and numerical modelling. The combination of both analogue and numerical experiments provides important insights into the shape and attitude evolution of subducting slabs. Models bring information into the controls exerted by the rheology of the slab and the mantle and other physical parameters such as the density contrast between the slab and the surrounding mantle, on the rate at which this deformation takes place. We show that in function of a viscosity ratios between the plate and the surrounding fluid, the plate will acquire a characteristic shape. For the isoviscous case, the plate shape tends toward a bubble with long tails: a "jellyfish" form. The time necessary for the plate to acquire this shape is a function of the viscosity and density contrast between the slab and the mantle. To complete our approach, we have developed a semi-analytical model based on the solution of the Hadamar-Rybinski equations for the problem of a dense, yet isoviscous and thus deforming sphere. This model helps to better

  4. Tomography of the subducting Pacific slab and the 2015 Bonin deepest earthquake (Mw 7.9).

    Science.gov (United States)

    Zhao, Dapeng; Fujisawa, Moeto; Toyokuni, Genti

    2017-03-15

    On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab's fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.

  5. Dynamic Linkages Between the Transition Zone & Surface Plate Motion in 2D Models of Subduction

    Science.gov (United States)

    Arredondo, K.; Billen, M. I.

    2014-12-01

    Subduction zones exhibit a wide range of behavior, from slab stagnation at 660 km to direct penetration into the lower mantle. Due to uncertainties in the tectonic history of individual subduction zones, such as trench velocities, potential mechanisms for controlling slab behavior in the transition zone are explored using numerical models. Numerical simulations have utilized a range of assumptions to improve computational efficiency, such as ignoring latent heat, ignoring compositional effects or fixing the trench location: the net effect of these assumptions resulting modeled dynamics remains unclear. Additionally the eight major, composition-dependent, phase transitions for pyrolite, harzburgite and eclogite may be an important influence on subducting slab dynamics due to the additional forces that are dependent on depth and compositional layering within the slab (e.g., Ricard et al., 2005). With the goal of developing more complete, self-consistent, and less idealized simulations, we test the importance of various factors on slab behavior: the presence of shear, adiabatic and latent heating, compositional layering, composition-dependent phase transitions and explicit plate speeds versus dynamically evolving plate and trench velocities. Preliminary results indicate that individual components have a relatively minor effect, but produce large changes when combined together. The extent of slab folding and stagnation is overestimated by only modeling the 410 and 660 km phase transitions. Dynamic models with all seven composition-dependent phase transitions are very sensitive to the plate strength and weak zone viscosity, causing large changes in plate speed and slab detachment. Changes to the overriding plate buoyance and strength investigate the origin and influence of trench movement on slab deformation. These feedbacks and parameter-sensitive behavior indicate that the wide range of observed slab behavior may result from subtle differences in plate and plate

  6. Geodynamic models of continental subduction and obduction of overriding plate forearc oceanic lithosphere on top of continental crust

    NARCIS (Netherlands)

    Edwards, Sarah J.; Schellart, Wouter P.; Duarte, Joao C.

    2015-01-01

    Continental subduction takes place in the final stage of subduction when all oceanic lithosphere is consumed and continental passive margin is pulled into the mantle. When the overriding plate is oceanic, dense forearc oceanic lithosphere might be obducted onto light continental crust forming an

  7. Transformation from Paleo-Asian Ocean closure to Paleo-Pacific subduction: New constraints from granitoids in the eastern Jilin-Heilongjiang Belt, NE China

    Science.gov (United States)

    Ma, Xing-Hua; Zhu, Wen-Ping; Zhou, Zhen-Hua; Qiao, Shi-Lei

    2017-08-01

    The eastern Jilin-Heilongjiang Belt (EJHB) of NE China is a unique orogen that underwent two stages of evolution within the tectonic regimes of the Paleo-Asian and Paleo-Pacific oceans. 158 available zircon U-Pb ages, including 26 ages obtained during the present study and 132 ages from the literature, were compiled and analyzed for the Mesozoic and Cenozoic granitoids from the EJHB and the adjacent Russian Sikhote-Alin Orogenic Belt (SAOB), to examine the temporal-spatial distribution of the granitoids and to constrain the tectonic evolution of the East Asian continental margin. Five stages of granitic magmatism can be identified: Early Triassic (251-240 Ma), Late Triassic (228-215 Ma), latest Triassic to Middle Jurassic (213-158 Ma), Early Cretaceous (131-105 Ma), and Late Cretaceous to Paleocene (95-56 Ma). The Early Triassic granitoids are restricted to the Yanbian region along the Changchun-Yanji Suture, and show geochemical characteristics of magmas from a thickened lower crust source, probably due to the final collision of the combined NE China blocks with the North China Craton. The Late Triassic granitoids, with features of A-type granites, represent post-collisional magmatic activities that were related to post-orogenic extension, marking the end of the tectonic evolution of the Paleo-Asian Ocean. The latest Triassic to Paleocene granitoids with calc-alkaline characteristics were NE-trending emplaced along the EJHB and SAOB and young towards the coastal region, and represent continental marginal arc magmas that were associated with the northwestwards subduction of the Paleo-Pacific Plate. Two periods of magmatic quiescence (158-131 and 105-95 Ma) correspond to changes in the subduction direction of the Paleo-Pacific Plate from oblique relative to the continental margin to subparallel. Taking all this into account, we conclude that: (1) the final closure of the Paleo-Asian Ocean occurred along the Changchun-Yanji Suture during the Early Triassic; (2) the

  8. Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

    Science.gov (United States)

    Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

    2017-09-01

    Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge

  9. Pacific plate motion change caused the Hawaiian-Emperor Bend

    NARCIS (Netherlands)

    Torsvik, Trond H.; Doubrovine, Pavel V.; Steinberger, Bernhard; Gaina, Carmen; Spakman, Wim; Domeier, Mathew

    2017-01-01

    A conspicuous 60° bend of the Hawaiian-Emperor Chain in the north-western Pacific Ocean has variously been interpreted as the result of an abrupt Pacific plate motion change in the Eocene (∼47 Ma), a rapid southward drift of the Hawaiian hotspot before the formation of the bend, or a combination of

  10. Dynamic effects of plate-buoyancy subduction at Manila Trench, South China Sea

    Science.gov (United States)

    Jiang, L.; Zhan, W.; Sun, J.; Li, J.

    2015-12-01

    Bathymetric map of SCS plate shows two subducting buoyancies, the fossil ridge and the oceanic plateau, which are supposed to impact slab segmentation into the north from Taiwan to 18°N, and the south from 17°N to Mindoro. Hypocenter distribution show that slab dip angle turns lower southwards from 45° to 30° in the north segment, and relatively equals ~45° in the south segment at the depth of 100km. Moreover, volcano distribution can be segmented into Miocene WVC, Quaternary EVC in the north and combined SVC in the south (Fig. A). We found that WVC and SVC mostly locate in a parallel belt ~50km apart to Manila trench, however EVC turn father southwards from 50km to 100km (Fig. B). Above characters congruously indicate that SCS plate kept equal dip angle in Miocene; then the north segment shallowed at 18°N and developed northwards in Quaternary, resulting in lower dip angle than the invariant south segment. To check the transformation of slab dip angle from 45° to 30° between 17~18°N, focal mechanism solution nearby 17°N are found 90° in rake and dip angle, strike parallel to the fossil ridge, indicating a slab tear located coincident with the ridge, where is a weak zone of higher heat flow and lower plate coupling ratio than the adjacent zones and slab can be easily tore as an interface for SCS plate segmentation. Subduction of the two buoyancies within SCS plate is supposed as influential dynamic factor: It caused the trench retreat rate reduced, forming a cusp and a flat convex of Manila trench shape; Moreover, the buoyancies resisted subduction, resulting in shear stress heterogeneity of SCS plate, in consequence the fossil ridge as a fragile belt potentially became stress concentration zone that easily tore; Then the buoyant oceanic plateau might lead to shallowing of the northern SCS plate. To examine the hypothesis, dynamic effects of the two subducting buoyancies are being respectively investigated based on numerical models. (Grt. 41376063, 2013

  11. Evidences for recent plume-induced subduction, microplates and localized lateral plate motions on Venus

    Science.gov (United States)

    Davaille, Anne; Smrekar, Suzanne

    2017-04-01

    Using laboratory experiments and theoretical modeling, we recently showed that plumes could induce roll-back subduction around large coronae. When a hot plume rises under a brittle and visco-elasto-plastic skin/lithosphere, the latter undergoes a flexural deformation which puts it under tension. Radial cracks and rifting of the skin then develop, sometimes using pre-existing weaknesses. Plume material upwells through the cracks (because it is more buoyant) and spreads as a axisymmetric gravity current above the broken denser skin. The latter bends and sinks under the combined force of its own weight and that of the plume gravity current. However, due to the brittle character of the upper part of the experimental lithosphere, it cannot deform viscously to accomodate the sinking motions. Instead, the plate continues to tear, as a sheet of paper would do upon intrusion. Several slabs are therefore produced, associated with trenches localized along partial circles on the plume, and strong roll-back is always observed. Depending on the lithospheric strength, roll-back can continue and triggers a complete resurfacing, or it stops when the plume stops spreading. Two types of microplates are also observed. First, the upwelling plume material creates a set of new plates interior to the trench segments. These plates move rapidly and expand through time, but do not subduct.. In a few cases, we also observe additional microplates exterior to the trenches. This happens when the subducting plate contains preexisting heterogeneities (e.g. fractures) and the subducted slab is massive enough for slab pull to become efficient and induce horizontal plate motions. Scalings derived from the experiments suggest that Venus lithosphere is soft enough to undergo such a regime. And indeed, at least two candidates can be identified on Venus, where plume-induced subduction could have operated. (1) Artemis Coronae is the largest (2300 km across) coronae on Venus and is bounded over 270° of

  12. The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle

    NARCIS (Netherlands)

    Schellart, W. P.

    2007-01-01

    A geodynamic model exists, the westward lithospheric drift model, in which the variety of overriding plate deformation, trench migration and slab dip angles is explained by the polarity of subduction zones. The model predicts overriding plate extension, a fixed trench and a steep slab dip for

  13. Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction

    Science.gov (United States)

    Arredondo, K.; Billen, M. I.

    2013-12-01

    While slab pull is considered the dominant force controlling plate motion and speed, its magnitude is controlled by slab behavior in the mantle, where tomographic studies show a wide range of possibilities from direct penetration to folding, or stagnation directly above the lower mantle (e.g. Fukao et al., 2009). Geodynamic studies have investigated various parameters, such as plate age and two phase transitions, to recreate observed behavior (e.g. Běhounková and Cízková, 2008). However, past geodynamic models have left out known slab characteristics that may have a large impact on slab behavior and our understanding of subduction processes. Mineral experiments and seismic observations have indicated the existence of additional phase transitions in the mantle transition zone that may produce buoyancy forces large enough to affect the descent of a subducting slab (e.g. Ricard et al., 2005). The current study systematically tests different common assumptions used in geodynamic models: kinematic versus free-slip boundary conditions, the effects of adiabatic heating, viscous dissipation and latent heat, compositional layering and a more complete suite of phase transitions. Final models have a complete energy equation, with eclogite, harzburgite and pyrolite lithosphere compositional layers, and seven composition-dependent phase transitions within the olivine, pyroxene and garnet polymorph minerals. Results show important feedback loops between different assumptions and new behavior from the most complete models. Kinematic models show slab weakening or breaking above the 660 km boundary and between compositional layers. The behavior in dynamic models with a free-moving trench and overriding plate is compared to the more commonly found kinematic models. The new behavior may have important implications for the depth distribution of deep earthquakes within the slab. Though the thermodynamic parameters of certain phase transitions may be uncertain, their presence and

  14. Structure of the subducted Cocos Plate from locations of intermediate-depth earthquakes

    Science.gov (United States)

    Lomnitz, C.; Rodríguez-Padilla, L. D.; Castaños, H.

    2013-05-01

    Locations of 3,000 earthquakes of 40 to 300 km depth are used to define the 3-D structure of the subducted Cocos Plate under central and southern Mexico. Discrepancies between deep-seated lineaments and surface tectonics are described. Features of particular interest include: (1) a belt of moderate activity at 40 to 80 km depth that parallels the southern boundary of the Mexican Volcanic Plateau; (2) an offset of 150 km across the Isthmus of Tehuantepec where all seismic activity is displaced toward the northeast; (3) three nests of frequent, deep-seated events (80 to 300 km depth) under southern Veracruz, Chiapas and the coast of Mexico-Guatemala. The active subduction process is sharply delimited along a NW-SE lineament from the Yucatan Peninsula, of insignificant earthquake activity. The focal distribution of intermediate-depth earthquakes in south-central Mexico provides evidence of stepwise deepening of the subduction angle along the Trench, starting at 15 degrees under Michoacan-Guerrero to 45 degrees under NW Guatemala. Historical evidence suggests that the hazard to Mexico City from large intermediate-depth earthquakes may have been underestimated.

  15. Cascadia subducting plate fluids channelled to fore-arc mantle corner: ETS and silica deposition

    Science.gov (United States)

    Hyndman, Roy D; McCrory, Patricia A.; Wech, Aaron; Kao, Han; Ague, Jay j

    2015-01-01

    In this study we first summarize the constraints that on the Cascadia subduction thrust, there is a 70 km gap downdip between the megathrust seismogenic zone and the Episodic Tremor and Slip (ETS) that lies further landward; there is not a continuous transition from unstable to conditionally stable sliding. Seismic rupture occurs mainly offshore for this hot subduction zone. ETS lies onshore. We then suggest what does control the downdip position of ETS. We conclude that fluids from dehydration of the downgoing plate, focused to rise above the fore-arc mantle corner, are responsible for ETS. There is a remarkable correspondence between the position of ETS and this corner along the whole margin. Hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature, and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore-arc mantle. Laboratory data show that such fore-arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone. At the fore-arc mantle corner these fluids are released upward into the more permeable overlying fore-arc crust. An indication of this fluid flux comes from low Poisson's Ratios (and Vp/Vs) found above the corner that may be explained by a concentration of quartz which has exceptionally low Poisson's Ratio. The rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner.

  16. A satellite magnetic perspective of subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones

    Science.gov (United States)

    Purucker, M. E.; Whaler, K. A.

    2008-12-01

    Large and intermediate-scale tectonic features such as subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones are often seen to have a magnetic signature visible from the perspective of near-Earth magnetic field satellites such as CHAMP and Orsted. Why do these tectonic features have a magnetic signature, while others do not? A new model of the lithospheric field (MF-6, Maus et al., 2008) extending to spherical harmonic degree 120 (333 km wavelength) has been used to evaluate the magnetic state of the lithosphere under the assumption that the magnetization is either induced (with a seismic starting model), or remanent (with a minimum norm approach). Some of the features identified from these images include the Tethyan and NE Siberian diffuse plate boundary zones, the Red Sea rift, and Cretaceous rift basins developed on the West African shield. Almost without exception, subduction zones exhibit a magnetic signature, as do many large igneous provinces. In this talk we discuss some of the new insights this magnetic perspective provides, and speculate on the controls which determine whether tectonic features will be expressed magnetically.

  17. Tsunami Hazard Posed to New Zealand by the Kermadec and Southern New Hebrides Subduction Margins: An Assessment Based on Plate Boundary Kinematics, Interseismic Coupling, and Historical Seismicity

    Science.gov (United States)

    Power, William; Wallace, Laura; Wang, Xiaoming; Reyners, Martin

    2012-01-01

    We assess the tsunami hazard posed to New Zealand by the Kermadec and southern New Hebrides subduction margins. Neither of these subduction zones has produced tsunami large enough to cause significant damage in New Zealand over the past 150 years of well-recorded history. However, as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the Earth's subduction zones, it should not be assumed that what has been observed so far is representative of the long term. For each of these two subduction zones we present plate kinematic and fault-locking results from block modelling of earthquake slip vector data and GPS velocities. The results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur. We also review data on the larger historical earthquakes that have occurred on these margins, as well as the Global CMT catalogue of events since 1976. Using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the COMCOT tsunami code to estimate the subsequent tsunami propagation in the southwest Pacific, and from these the potential impact on New Zealand has been evaluated. Our results demonstrate that there is a significant threat posed to the Northland and Coromandel regions of New Zealand should a large earthquake ( M w ≳8.5) occur on the southern or middle regions of the Kermadec Trench, and that a similarly large earthquake on the southern New Hebrides Trench has the potential to strongly impact on the far northern parts of New Zealand close to the southern end of the submarine Three Kings Ridge. We propose logic trees for the magnitude-frequency parameters of large earthquakes originating on each trench, which are intended to form the basis for future probabilistic studies.

  18. Pacific Plate Deformation due to Plate Motion Relative to the Spin Axis on a Nonspherical Earth

    Science.gov (United States)

    Woodworth, D.; Gordon, R. G.

    2016-12-01

    The central tenet of plate tectonics is that the plates are rigid. In the 1970s, however, it was recognized that plate motion relative to the spin axis causes intraplate deformation as a plate conforms to Earth's radius of curvature, which varies with latitude [McKenzie 1972; Turcotte & Oxburgh 1974]. Here we quantify rates of intraplate strain produced by plate motion relative to the spin axis and compare them with strain rates due to other sources of intraplate strain, such as thermal contraction of the oceanic lithosphere [Collette 1974; Kumar & Gordon 2009]. We determine recent rates of plate motion relative to the spin axis using apparent polar wander (APW) paths [e.g. Torsvik et al. 2012] combined with known relative plate angular velocities [DeMets et al. 2010; Argus et al., 2011]. We estimate average strain rates for the fifty-six plates of MORVEL56 ranging from 10-11 to 10-3 Ma-1 (3 × 10-25 to 3 × 10-18 s-1). We estimate that the plate with the highest strain rates is the Australia plate, for which we find strain rates of 10-3 Ma-1 (3 × 10-17 s-1) due to plate motion over a nonspherical Earth. These indicated rates are consistent with Australia plate strain rates of 10-7 to 10-3 Ma-1 (3 × 10-21 to 3 × 10-17 s-1) previously inferred from seismic moment release [Burbridge 2004]. For the Pacific plate we predict much lower strain rates, with an average value, 10-6 Ma-1 (3 × 10-20 s-1), similar to the intraplate strain rate inferred from globally averaged intraplate seismic moment release. Our estimated strain rates only exceed those produced by thermal contraction in the oldest oceanic lithosphere [Mishra & Gordon 2016]. For this presentation, we will also determine past strain rates of the Pacific plate from movement over a nonspherical Earth through analysis of the Pacific plate APW path. We will compare the strain rate history to the chronology of the Hawaiian-Emperor chain and other Pacific plate tectonic events.

  19. Guadalupe Island, Mexico as a new constraint for Pacific plate motion

    Science.gov (United States)

    Gonzalez-Garcia, J. J.; Prawirodirdjo, L.; Bock, Y.; Agnew, D.

    2003-08-01

    We use GPS data collected on Isla de Guadalupe and in northern Baja California, Mexico, to estimate site velocities relative to Pacific plate motion. The velocities of all three geodetic monuments on Guadalupe fit a rigid Pacific plate model with residuals of 1 mm/yr. Using the Guadalupe data and data from five IGS stations on the Pacific plate (CHAT, KOKB, KWJ1, MKEA, and THTI) we estimate an angular velocity for this plate that is consistent with other recently-published estimates. Our results indicate that Isla de Guadalupe lies on the Pacific plate, and that GPS data collection on the island usefully constrains Pacific plate motion and rigidity.

  20. Intermittent plate tectonics?

    Science.gov (United States)

    Silver, Paul G; Behn, Mark D

    2008-01-04

    Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere. Given the evidence for Pacific-type closure in Earth's past, the absence of a direct mechanism for termination/initiation compensation, and recent data supporting a minimum in subduction flux in the Mesoproterozoic, we hypothesize that dramatic reductions or temporary cessations of subduction have occurred in Earth's history. Such deviations in the continuity of plate tectonics have important consequences for Earth's thermal and continental evolution.

  1. Upper Plate Response to Varying Subduction Styles in the Forearc Cook Inlet Basin in South Central Alaska

    Science.gov (United States)

    Sanchez-Lohff, S. K.; Enkelmann, E.; Finzel, E.; Reid, M. M.

    2016-12-01

    The Cook Inlet forearc basin strata record the upper plate response to changes in subduction since 170 Ma. Subduction of normal oceanic crust during the Jurassic and Cretaceous was followed by spreading ridge subduction in the Paleocene, which initiated near trench magmatism and a shallow subduction angle. This was followed by a period of normal subduction until the Oligocene when subduction of an oceanic plateau commenced causing flat-slab subduction. We study the sedimentary record of the Cook Inlet Basin and analyze the sediment provenance, magmatic sources, paleotopography, and rock exhumation of southern Alaska, and their changes through time. We use a double dating technique on single detrital zircon grains from 25 samples combining fission track and U-Pb dating. We collected Jurassic to Pliocene sandstone, and modern fluvial deposits. Eight Mesozoic samples were taken from the eastern inverted section of the Cook Inlet Basin. Seven Cenozoic samples were taken from outcrops on the northern and southern margin of the basin, and four from northern offshore cores. Six modern river sands were sampled from four rivers to analyze what is currently draining into the basin from the north, east, and south. Zircon fission track data reveal that the Jurassic samples have been fully reset, while Cretaceous and Eocene samples have been partially reset. Subduction of the spreading ridge probably increased the geothermal gradient in the upper plate and caused thermal resetting of the underlying strata. Oligocene to Pliocene sediments contain the youngest age populations with lag times ranging 13-25 Myr. Samples from the northern margin (arc side) yield generally shorter lag times than samples from the south side (prism side). This pattern is consistent with modern sediments that show the youngest ages are sourced from the Alaska Range, revealed by a 14 Ma age peak in the Susitna River. In contrast, the youngest age populations found in the sediments of rivers draining the

  2. Tomography of the subducting Cocos plate in central Mexico: Images of a truncated slab

    Science.gov (United States)

    Husker, A. L.; Davis, P. M.

    2007-12-01

    The location of the subducting slab beneath Mexico City and its relation to the Trans-Mexican Volcanic Belt (TMVB) has been unknown because of the absence of deep seismicity that could be used to define the Wadati-Benioff zone. We used data from a temporary seismic network to locate the slab using seismic tomography. A break is seen in the Cocos plate under the TMVB. The break is seen with both P-wave and S-wave tomography and in a constrained tomographic inversion that finds parameters for a simple slab temperature model. The data used are 172 teleseismic earthquakes recorded by the Middle American Subduction Experiment (MASE). MASE was made up of 100 broadband seismometers spaced every 5 km running from Acapulco north through Mexico City almost to the Gulf Coast. In order to determine arrival time differences, Dt, across the array, waveforms were cross correlated. When Dt is plotted with respect to the latitude of the seismometer at which it was recorded, a Dt minimum (early arrivals) is seen near the TMVB. This minimum is shifted northward for back azimuths from the south, and southward for back azimuths from the north. The shift in the Dt minimum is indicative of a fast structure at depth. If there were no break in the slab, the localized minimum would not be seen. Tomography reveals an approximately 50-80 km thick slab diving into the mantle at about 75° to approximately 550 km depth and 375 km inland from Acapulco. We speculate the absence of deep earthquakes is due to low stresses in a young plate that has been truncated at depth.

  3. Petrologic Aspects of Seamount and Guyot Volcanism on the Ancestral Mesozoic Pacific Plate: a Review

    Science.gov (United States)

    Natland, J. H.

    2007-12-01

    Hundreds of large seamounts and guyots are widely scattered almost in a "shotgun-blast" arrangement in an area about the size of the United States west of the Mississippi River on the Mesozoic Pacific plate between the Mariana Trench and the Gilbert Islands. Most of these formed between ~160-100 Ma while the Pacific plate was surrounded by spreading ridges and growing outward in all directions. There is little to no indication that the seamounts and guyots formed along linear seamount chains; existing radiometric-age data show no age progressions. The volcanoes appear to have formed in response to a uniform stress configuration across the plate, which was either not moving or moving very slowly at the time (1, 2), much like the modern Antarctic plate. When the growing plate started to encounter subduction systems in the western Pacific at ~90 Ma, consistent stress patterns began to develop, and the broad linear Gilbert and Line volcanic ridge systems began to form. Even then, however, considerable overlapping of volcanism occurred, and only the most general age progressions are evident in existing data. Petrologic data from samples obtained from dozens of volcanic summits by dredging and beneath several carbonate platforms by drilling reveal considerable diversity in development of differentiated alkalic magmatic lineages rooted in diverse parental basaltic rocks. These include transitional, alkalic and basanitic compositions, with differentiates of hawaiite, mugearite, trachyte and one phonolite. Many of the basaltic rocks are partly to significantly transformed by alteration under oxidative conditions (dredged rocks) and both oxidative and non-oxidative conditions (drilled rocks). This can make estimations of mantle geochemical provenance difficult. Nevertheless, the province has been linked by backtracking techniques to the modern SOPITA region of the South Pacific (3), and its rocks show enrichments in trace elements and isotopic characteristics similar to

  4. Topographic form of the Coast Ranges of the Cascadia Margin in relation ot coastal uplift rates and plate subduction

    Science.gov (United States)

    Kelsey, Harvey M.; Engebretson, David C.; Mitchell, Clifton E.; Ticknor, Robert L.

    1994-01-01

    The Coast Ranges of the Cascadia margin are overriding the subducted Juan de Fuca/Gorda plate. We investigate the extent to which the latitudinal change in attributes related to the subduction process. These attributes include the varibale age of the subducted slab that underlies the Coast Ranges and average vertical crustal velocities of the western margin of the Coast Rnages for two markedly different time periods, the last 45 years and the last 100 kyr. These vertical crustal velocities are computed from the resurveying of highway bech marks and from the present elevation of shore platforms that have been uplifted in the late Quaternary, respectively. Topogarphy of the Coast Ranges is in part a function of the age and bouyancy of the underlying subducted plate. This is evident in the fact that the two highest topographic elements of the Coast Rnages, the Klamath Mountains and the Olympic Mountains, are underlain by youngest subducted oceanic crust. The subducted Blanco Fracture Zone in southernmost Oregon is responsible for an age discontinuity of subducted crust under the Klamath Mountains. The norhtern terminus of hte topographically higher Klamaths is offset to the north relative to the position of the underlying Blanco Fracture Zone, teh offset being in the direction of migration of the farcture zone, as dictated by relative plate motions. Vertical crustal velocities at the coast, derived from becnh mark surveys, are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms. This uplift rate discrepancy indicates that strain is accumulating on the plate margin, to be released during the next interplate earthquake. In a latitudinal sense, average Coast Rnage topography is relatively high where bench mark-derived, short-term vertical crustal velocities are highest. Becuase the shore platform vertical crustal velocities reflect longer-term, premanent uplift, we infer that a small percentage of the

  5. First measurement of the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using GPS/acoustic technique

    Science.gov (United States)

    Tomita, Fumiaki; Kido, Motoyuki; Osada, Yukihito; Hino, Ryota; Ohta, Yusaku; Iinuma, Takeshi

    2015-10-01

    The subduction rate of an oceanic plate may accelerate after large earthquakes rupture the interplate coupling between the oceanic and overriding continental plates. To better understand postseismic deformation processes in an incoming oceanic plate, we directly measured the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using a GPS/acoustic technique over a period of 2 years (September 2012 to September 2014). The displacement rate was measured to be 18.0 ± 4.5 cm yr-1 (N302.0°E) relative to the North American Plate, which is almost twice as fast as the predicted interseismic plate motion. Because the sum of steady plate motion and viscoelastic response to the Tohoku-Oki earthquake roughly accounts for the observed displacement rate, we conclude that viscoelastic relaxation is the primary mechanism responsible for postseismic deformation of the Pacific Plate and that significant subduction acceleration did not occur at least not during the observation period.

  6. [Environmental response in the Pacific to aseismic Cocos Ridge subduction (Panama and Costa Rica)].

    Science.gov (United States)

    De Gracia, Carlos; O'Dea, Aaron; Rodríguez, Félix; D'Croz, Luis

    2012-06-01

    The evolution of the marine communities along the Pacific coast of Central America, may have changed in response to the formation of the Isthmus of Panama. To evaluate the effect of the Aseismic Cocos Ridge (DAC) subduction on the marine benthic communities, we reconstructed benthic assemblages from Neogene fossiliferous formations in Burica and Nicoya peninsulas of Panama and Costa Rica. Paleoecological and paleoenvironmental conditions were reconstructed by comparing community structure from bulk fossil samples with dredge collections from modern Tropical American seas, using principal component analysis. Our results indicate that during the early Pliocene, before the closing of the Isthmus, some oceanic islands existed with moderate upwelling in the Burica region. After the closure, during the late Pliocene and early Pleistocene the collision of the DAC caused an uplift of the seafloor, where water depth of 2 300m became shallow waters of less than 40m depth. Meanwhile, upwelling intensified in the open ocean the uplift that had formed small islands in coastal areas of Burica, creating protected areas and limiting the upwelling effect that was given in open ocean. The subduction of the DAC continued until the islands were joined to the mainland and gradually disappeared, allowing the return of the upwelling. During the middle Pleistocene a second process of accelerated uplift with speeds of 8m/1000 years provoked again the elevation of the seafloor and later the elevation of the Talamanca Range. The new range formed a barrier that blocked the passage of the Trade winds, created new ecological conditions and optimized and allowed the growth of the best coral reefs in the coasts of the tropical Eastern Pacific (POT) between Panama and Costa Rica.

  7. The Impact of Surface Bending, A Complete Mineralogical Model and Movement of the Overriding Plate on Subduction Zones

    Science.gov (United States)

    Arredondo, Katrina Marie

    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

  8. The effects of the overriding plate thermal state on the slab dip in an ocean-continent subduction system

    CERN Document Server

    Roda, Manuel; Spalla, Maria Iole; 10.1016/j.crte.2011.01.005

    2011-01-01

    To evaluate the effects of variations in the thermal state of the overriding plate on the slab dip in an ocean-continent subduction system, a 2-D finite element thermo-mechanical model was implemented. The lithosphere base was located at the depth of the 1600 K isotherm. Numerical simulations were performed while taking into account four different initial thicknesses for the oceanic lithosphere (60, 80, 95 and 110 km) and five different thicknesses of the overriding plate, as compared in terms of the continental-oceanic plate thickness ratio (100, 120, 140, 160 and 200% of the oceanic lithosphere thickness). The results of numerical modeling indicate that a high variability of the subducting plate geometry occurs for an oceanic lithosphere thickness ranging from 60 to 80 km, while the variability decreases where the oceanic plates are thicker (95 and 110 km). Furthermore, the slab dip strongly depends on the thermal state of the overriding plate, and, in particular, the slab dip decreases with the increase in...

  9. Relative motions of the Pacific, Rivera, North American, and Cocos plates since 0.78 Ma

    National Research Council Canada - National Science Library

    DeMets, Charles; Wilson, Douglas S

    1997-01-01

    We use magnetic anomaly and fracture zone crossings from 3°N–24°N along the East Pacific Rise to define the boundaries and relative velocities of the rigid Pacific, Rivera, North American, and Cocos plates...

  10. Plate Tectonic Consequences of competing models for the origin and history of the Banda Sea subducted oceanic lithosphere

    CERN Document Server

    Heine, Christian; McKay, Hamish; Müller, R Dietmar

    2012-01-01

    The Banda Arc, situated west of Irian Jaya and in the easternmost extension of the Sunda subduction zone system, reveals a characteristic bowl-shaped geometry in seismic tomographic images. This indicates that the oceanic lithosphere still remains attached to the surrounding continental margins of northern Australia and the Bird's Head microcontinent. Major controversies exist between authors proposing an allochthonous or autochthonous origin of the Bird's Head block. Either scenario has important implications for plate kinematic models aiming to reconstruct the tectonic evolution of the region and the late Jurassic seaoor spreading geometry of this now subducted Argo-Tanimbar-Seram (ATS) ocean basin. Wider implications affect the tectonic conguration of the Tethyan-Pacic realm, the distribution of plate boundaries as well as the shape and size of continental blocks which have been rifted off the northeastern Gondwana margin during the Late Jurassic and are now accreted to the SE Asia margin. We apply structu...

  11. Paleo-Pacific subduction-accretion: Evidence from Geochemical and U-Pb zircon dating of the Nadanhada accretionary complex, NE China

    Science.gov (United States)

    Zhou, Jian-Bo; Cao, Jia-Lin; Wilde, Simon A.; Zhao, Guo-Chun; Zhang, Jin-Jiang; Wang, Bin

    2014-12-01

    The Nadanhada Terrane, located along the eastern margin of Eurasia, contains a typical accretionary complex related to paleo-Pacific plate subduction-accretion. The Yuejinshan Complex is the first stage accretion complex that consists of meta-clastic rocks and metamafic-ultramafic rocks, whereas the Raohe Complex forms the main parts of the terrane and consists of limestone, bedded chert, and mafic-ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta-sedimentary rocks. Geochemical data indicate that the Yuejinshan metabasalts have normal mid-ocean ridge basalt (N-MORB) affinity, whereas the Raohe basaltic pillow lavas have an affinity to ocean island basalts (OIB). Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon analyses of gabbro in the Raohe Complex yield a weighted mean 206Pb/238U zircon age of 216 ± 5 Ma, whereas two samples of granite intruded into the complex yield weighted mean 206Pb/238U zircon ages of 128 ± 2 and 129 ± 2 Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb zircon analyses of basaltic pillow lava in the Raohe Complex define a weighted mean age of 167 ± 1 Ma. Two sandstone samples in the Raohe Complex record younger concordant zircon weighted mean ages of 167 ± 17 and 137 ± 3 Ma. These new data support the view that accretion of the Raohe Complex was between 170 and 137 Ma, and that final emplacement of the Raohe Complex took place at 137-130 Ma. The accretion of the Yuejinshan Complex probably occurred between the 210 and 180 Ma, suggesting that paleo-Pacific plate subduction was initiated in the Late Triassic to Early Jurassic.

  12. Segmentation of plate coupling, fate of subduction fluids, and modes of arc magmatism in Cascadia, inferred from magnetotelluric resistivity

    Science.gov (United States)

    Wannamaker, Philip E.; Evans, Rob L.; Bedrosian, Paul A.; Unsworth, Martyn J.; Maris, Virginie; McGary, R. Shane

    2014-01-01

    Five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km. Distinct changes in plate coupling, subduction fluid evolution, and modes of arc magmatism along the length of Cascadia are clearly expressed in the resistivity structure. Relatively high resistivities under the coasts of northern and southern Cascadia correlate with elevated degrees of inferred plate locking, and suggest fluid- and sediment-deficient conditions. In contrast, the north-central Oregon coastal structure is quite conductive from the plate interface to shallow depths offshore, correlating with poor plate locking and the possible presence of subducted sediments. Low-resistivity fluidized zones develop at slab depths of 35–40 km starting ∼100 km west of the arc on all profiles, and are interpreted to represent prograde metamorphic fluid release from the subducting slab. The fluids rise to forearc Moho levels, and sometimes shallower, as the arc is approached. The zones begin close to clusters of low-frequency earthquakes, suggesting fluid controls on the transition to steady sliding. Under the northern and southern Cascadia arc segments, low upper mantle resistivities are consistent with flux melting above the slab plus possible deep convective backarc upwelling toward the arc. In central Cascadia, extensional deformation is interpreted to segregate upper mantle melts leading to underplating and low resistivities at Moho to lower crustal levels below the arc and nearby backarc. The low- to high-temperature mantle wedge transition lies slightly trenchward of the arc.

  13. Evolving seismogenic plate boundary megathrust and mega-splay faults in subduction zone (Invited)

    Science.gov (United States)

    Kimura, G.; Hamahashi, M.; Fukuchi, R.; Yamaguchi, A.; Kameda, J.; Kitamura, Y.; Hashimoto, Y.; Hamada, Y.; Saito, S.; Kawasaki, R.

    2013-12-01

    Understanding the fault mechanism and its relationship to the sesimo-tsunamigenesis is a key of the scientific targets of subduction zone and therefore NantroSEIZE project of IODP and future new drilling project of International Ocean Discovery Program keeps focusing on that. Mega-splay fault branched from plate boundary megathrust in subduction zone is located around the border between outer and inner wedges and is considered to cause great earthquake and tsunami such as 1960 Alaska earthquake, 1944 and 1946 Nankai-Tonankai earthquakes, and 2004 Sumatra earthquakes. Seismic reflection studies for the mega-splay fault in 2D and 3D in the Nankai forearc present the reflector with negative or positive polarities with various amplitudes and suggest complicated petrophysical properties and condition of the fault and its surroundings. The Nankai mega-splay fault at a depth of ~5km is going to be drilled and cored by NantroSEIZE experiments and is expected for great progress of understanding of the fault mechanics. Before drilling the really targeted seismogenic fault, we are conducting many exercises of geophysical and geological observations. The core-log-seismic integrated exercise for the exhumed mega-splay fault by drilling was operated for the Nobeoka thrust in the Shimanto Belt, Kyushu, Japan. The Nobeoka thrust was once buried in the depth >~10km and suffered maximum temperature >~300 dgree C. As the core recovery is ~99%, perfect correlation between the core and logging data is possible. Thickness of the fault zone is >200 m with a ~50 cm thick central fault core dividing the phyllitic hanging wall and the footwall of broken-melange like cataclasite. A-few-meter-thick discrete damage zones with fault cores are recognized by difference in physical properties and visual deformation textures at several horizons in the fault zone. Host rocks for those damaged zones are completely lithified cataclasites with abundant mineral veins, which record the older and deeper

  14. Crustal and upper mantle structure of the Anatolian plate: Imaging the effects of subduction termination and continental collision with seismic techniques

    Science.gov (United States)

    Delph, Jonathan R.

    The neotectonic evolution of the eastern Mediterranean is intimately tied to interactions between the underthrusting/subducting slab along the southern margin of Anatolia and the overriding plate. The lateral variations in the subduction zone can be viewed as a temporal analogue of the transition between continuous subduction and subduction termination by continent-continent collision. By investigating the lateral variations along this subduction zone in the overriding plate, we can gain insight into the processes that precede continent collision. This dissertation summarizes the results of three studies that focus on different parts of the subduction margin: 1) In the west, where the development of a slab tear represents the transition between continuous and enigmatic subduction, 2) In the east, where continent-continent collision between the Arabian and Eurasian Plate is leading to the development of the third largest orogenic plateau on earth after complete slab detachment, and 3) In central Anatolia, where the subducting slab is thought to be in the processes of breaking up, which is affecting the flow of mantle material leading to volcanism and uplift along the margin. In the first study, we interpret that variations in the composition of material in the downgoing plate (i.e. a change from the subduction of oceanic material to continental material) may have led to the development of a slab tear in the eastern Aegean. This underthrusting, buoyant continental fragment is controlling overriding plate deformation, separating the highly extensional strains of western Anatolia from the much lower extensional strains of central Anatolia. Based on intermediate depth seismicity, it appears that the oceanic portion of the slab is still attached to this underthrusting continental fragment. In the second study, we interpret that the introduction of continental lithosphere into the north-dipping subduction zone at the Arabian-Eurasian margin led to the rollback and

  15. Small repeating earthquakes and inter-plate aseismic slip in and around the Kanto district after the 2011 off the Pacific coast of Tohoku earthquake

    Science.gov (United States)

    Igarashi, T.; Iidaka, T.; Sakai, S.; Obara, K.; Hirata, N.

    2013-12-01

    The 2011 off the Pacific coast of Tohoku earthquake (Mw9.0) was the largest earthquake in recorded history in Japan. For the stress changes by this earthquake, the seismic activities around the Kanto district including Tokyo metropolitan area have changed significantly. We detect many small repeating earthquakes beneath this area. They may suggest induced interplate aseismic slips at the subducting Philippine Sea (PHS) plate and the subducting Pacific (PAC) plate. The upper boundary of the PAC plate contacts the PHS plate beneath this area, but the northeastern limit of the PHS plate remains poorly understood. In this study, we first estimate the configuration of the subducting PHS plate and PAC plate and the limit of PHS plate beneath the Kanto district by applying receiver function (RF) analysis. Thereafter, we investigate the space-time characteristics of the inter-plate aseismic slips from sequences of small repeating earthquakes beneath the Kanto district after the 2011 Tohoku earthquake. We made many vertical cross-sections of depth-converted RF images to investigate plate configurations. Telemetric seismographic network data covered on the Kanto district including the Metropolitan Seismic Observation network, which constructed under the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area and maintained by Special Project for Reducing Vulnerability for Urban Mega Earthquake Disasters, are used. We selected events with a good S/N and epicentral distance between 30 and 90 degrees based on USGS catalogues. As a result, we elucidated the configuration of PHS plate and PAC plate beneath the Kanto district. The PHS plate subducts to the northwest and the direction coincides with plate motion. The northeastern limit of PHS plate is estimated from the change of plate thickness, which gradually decreases to the northeast after contact with the underlying PAC plate beneath the Tokyo metropolitan area. There is little seismic activity from

  16. Multichannel Seismic Imaging of the Rivera Plate Subduction at the Seismogenic Jalisco Block Area (Western Mexican Margin)

    Science.gov (United States)

    Bartolome, R.; Gorriz, E.; Danobeitia, J.; Barba, D. C., Sr.; Martí, D.; L Cameselle, A.; Nuñez-Cornu, F. J.; Bandy, W. L.; Mortera, C.; Nunez, D.; Alonso, J. L.; Castellon, A.; Prada, M.

    2016-12-01

    During the TSUJAL marine geophysical survey, conducted in February and March 2014 Spanish, Mexican and British scientists and technicians explored the western margin of Mexico, considered one of the most active seismic zones in America. This work aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in the offshore part of the Jalisco Block, to link the geodynamic and the recent tectonic deformation occurring there with the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out acquisition, processing and geological interpretation of a multichannel seismic reflection profile running perpendicular to the margin. Crustal images show an oceanic domain, dominated by subduction-accretion along the lower slope of the margin with a subparallel sediment thickness of up to 1.6 s two way travel time (approx. 2 km) in the Middle American Trench. Further, from these data the region appears to be prone to giant earthquake production. The top of the oceanic crust (intraplate reflector) is very well imaged. It is almost continuous along the profile with a gentle dip (<10°); however, it is disrupted by normal faulting resulting from the bending of the plate during subduction. The continental crust presents a well-developed accretionary prism consisting of highly deformed sediments with prominent slumping towards the trench that may be the result of past tsunamis. Also, a Bottom Simulating Reflector (BSR) is identified in the first half a second (twtt) of the section. High amplitude reflections at around 7-8 s twtt clearly image a discontinuous Moho, defining a very gentle dipping subduction plane.

  17. Earthquake Directivity, Orientation, and Stress Drop Within the Subducting Plate at the Hikurangi Margin, New Zealand

    Science.gov (United States)

    Abercrombie, Rachel E.; Poli, Piero; Bannister, Stephen

    2017-12-01

    We develop an approach to calculate earthquake source directivity and rupture velocity for small earthquakes, using the whole source time function rather than just an estimate of the duration. We apply the method to an aftershock sequence within the subducting plate beneath North Island, New Zealand, and investigate its resolution. We use closely located, highly correlated empirical Green's function (EGF) events to obtain source time functions (STFs) for this well-recorded sequence. We stack the STFs from multiple EGFs at each station, to improve the stability of the STFs. Eleven earthquakes (M 3.3-4.5) have sufficient azimuthal coverage, and both P and S STFs, to investigate directivity. The time axis of each STF in turn is stretched to find the maximum correlation between all pairs of stations. We then invert for the orientation and rupture velocity of both unilateral and bilateral line sources that best match the observations. We determine whether they are distinguishable and investigate the effects of limited frequency bandwidth. Rupture orientations are resolvable for eight earthquakes, seven of which are predominantly unilateral, and all are consistent with rupture on planes similar to the main shock fault plane. Purely unilateral rupture is rarely distinguishable from asymmetric bilateral rupture, despite a good station distribution. Synthetic testing shows that rupture velocity is the least well-resolved parameter; estimates decrease with loss of high-frequency energy, and measurements are best considered minimum values. We see no correlation between rupture velocity and stress drop, and spatial stress drop variation cannot be explained as an artifact of varying rupture velocity.

  18. Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

    Science.gov (United States)

    Kameda, Jun; Inoue, Sayako; Tanikawa, Wataru; Yamaguchi, Asuka; Hamada, Yohei; Hashimoto, Yoshitaka; Kimura, Gaku

    2017-04-01

    The alteration and dehydration of predominantly basaltic subducting oceanic crustal material are thought to be important controls on the mechanical and hydrological properties of the seismogenic plate interface below accretionary prisms. This study focuses on pillow basalts exposed in an ancient accretionary complex within the Shimanto Belt of southwest Japan and provides new quantitative data that provide insight into clay mineral reactions and the associated dehydration of underthrust basalts. Whole-rock and clay-fraction X-ray diffraction analyses indicate that the progressive conversion of saponite to chlorite proceeds under an almost constant bulk-rock mineral assemblage. These clay mineral reactions may persist to deep crustal levels ( 320 °C), possibly contributing to the bulk dehydration of the basalt and supplying fluid to plate-boundary fault systems. This dehydration can also cause fluid pressurization at certain horizons within hydrous basalt sequences, eventually leading to fracturing and subsequent underplating of upper basement rock into the overriding accretionary prism. This dehydration-induced breakage of the basalt can explain variations in the thickness of accreted basalt fragments within accretionary prisms as well as the reported geochemical compositions of mineralized veins associated with exposed basalts in onland locations. This fracturing of intact basalt can also nucleate seismic rupturing that would subsequently propagate along seismogenic plate interfaces.[Figure not available: see fulltext.

  19. South-American plate advance and forced Andean trench retreat as drivers for transient flat subduction episodes.

    Science.gov (United States)

    Schepers, Gerben; van Hinsbergen, Douwe J J; Spakman, Wim; Kosters, Martha E; Boschman, Lydian M; McQuarrie, Nadine

    2017-05-16

    At two trench segments below the Andes, the Nazca Plate is subducting sub-horizontally over ∼200-300 km, thought to result from a combination of buoyant oceanic-plateau subduction and hydrodynamic mantle-wedge suction. Whether the actual conditions for both processes to work in concert existed is uncertain. Here we infer from a tectonic reconstruction of the Andes constructed in a mantle reference frame that the Nazca slab has retreated at ∼2 cm per year since ∼50 Ma. In the flat slab portions, no rollback has occurred since their formation at ∼12 Ma, generating 'horse-shoe' slab geometries. We propose that, in concert with other drivers, an overpressured sub-slab mantle supporting the weight of the slab in an advancing upper plate-motion setting can locally impede rollback and maintain flat slabs until slab tearing releases the overpressure. Tear subduction re-establishes a continuous slab and allows the process to recur, providing a mechanism for the transient character of flat slabs.

  20. MASE: A seismological perspective of the sub-horizontal subduction of the Cocos Plate under North America

    Science.gov (United States)

    Pérez-Campos, X.; Clayton, R. W.; Davis, P.; Iglesias, A.; Husker, A.; Valdés-González, C. M.

    2006-12-01

    The main objective of the MesoAmerican Subduction Experiment (MASE) is the generation of a dynamic model of the subduction of Cocos plate underneath the North American plate. One component of this project is a seismic line consisting of 100 broadband seismometers, located every 5 km between Acapulco and Tampico, with its mid-point in Mexico City. The initial instrument was deployed at the end of 2004 and the full line will operate until January 2007. The purpose of this line is to derive a velocity and structure model along the transect, and to determine attenuation and viscosity in the mantle wedge. Various researchers from the three institutions involved (Caltech, UNAM, and UCLA) are using several techniques to achieve these goals, such as receiver functions, surface-wave dispersion, tomography and waveform modeling. Preliminary results from dispersion curves show clearly a Moho that correlates to one obtained with receiver functions, which show a flat subducting slab up to ~200 km from the trench. Also, tomography, together with the previous techniques and ray tracing, show a difference in behavior within the Trans Mexican Volvanic Belt. Furthermore, from microseism correlation, we can distinguish surface waves that give information about the crust structure.

  1. Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves

    Science.gov (United States)

    Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.

    2014-12-01

    A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

  2. Differential subsidence of the forearc wedge of the Ryukyu (Nansei-Shoto) Arc caused by subduction of ridges on the Philippine Sea Plate

    Science.gov (United States)

    Okamura, Yukinobu; Nishizawa, Azusa; Oikawa, Mitsuhiro; Horiuchi, Daishi

    2017-10-01

    The Philippine Sea Plate (PSP) carrying several ridges has been sudbucting under the Ryukyu (Nansei-Shoto) Arc since middle Miocene. Because no extensive accretionary prism has been growing along the Ryukyu Trench, the arc provides an opportunity to examine effects of ridge subduction on structure of the forearc wedge and a clue to reconstruct ancient plate motion of the PSP that is inferred to have changed between NW and NNW. To examine this perspective, we clarified structure of the Ryukyu forearc wedge based on seismic profiles and bathymetric data and related them to ridge subduction. An erosional unconformity between pre-Neogen and Neogene rocks is widely recognized through the Ryukyu Arc, and we divided the forearc wedges into Zones I to IV from southwest to northeast by difference of depth of the erosional unconformity. We correlated these four zones to the locations of ridge subduction that have been shifting NE or SW along the Ryukyu Trench. Zone I is underlain by the largely subsided unconformity and we attributed the structure to tearing of the Eurasia plate due to subduction of the western margin of the PSP including the Luzon Arc. Zone II consists of a wide terrace on the shallow erosional unconformity, and no ridge that was subducting in this zone is known. Zone III is characterized by the seaward descending unconformity covered with a thick sequence of Neogene sediments and is related to subduction of the NW-SE trending Daito Ridge and the E-W trending Amami Plateau. Zone IV has the deeper unconformity and slope geometry and corresponds to subduction of the NNW-SSE trending Kyushu-Palau Ridge. The structure of the Ryukyu forearc is consistently related to subduction of ridges on the PSP, suggesting that the change of the plate motion of the PSP can be precisely reconstructed by further detailed survey.

  3. Surface constraints on the temporal and spatial evolution of the Farallon-Pacific-North America plate boundary

    Science.gov (United States)

    McQuarrie, N.; Oskin, M.

    2009-05-01

    Extension and volcanism are two surface derived data sets used to infer mantle processes back in time. We integrate two new large GIS-based datasets to create palinspastic restorations of extension and volcanism allowing us to readdress the relationship between plate-boundary deformation, intra-plate extension and magmatism in western North America. Using ArcGIS and custom software, we retrodeformed the NAVDat (North American Volcanic Database, navdat.geongrid.org) using the western North America reconstruction of McQuarrie and Wernicke (2005). We compare this data to strain rates calculated over a 50 km-grid forward- deformed from 36 Ma to present. With the deformed grid and palinspastically restored volcanic dataset we quantitatively compare rates of magmatism and deformation and evaluate the age, location, and migration of Cenozoic volcanic arcs. A first order conclusion from this study is that magmatism, throughout the Basin and Range, is primarily driven by plate boundary effects. The plate boundary effects include subduction and rollback of the Farallon plate, creation and expansion of slab windows as the Pacific plate intercepts the North American plate and re-establishment of the ancestral Cascade arc along the eastern margin of the Sierra Nevada at ˜ 15 Ma. Notable exceptions include the Yellowstone hotspot system along the northern boarder of our study area and late-stage (<8 Ma) passive, extension related asthenospheric upwelling that accompanied a thinning lithosphere along the eastern and western margins of the Basin and Range. The palinspastic reconstructions presented here highlight that the classic, high-angle, Basin and Range faulting that comprises most of the physiographic Basin and Range province commenced during a remarkably amagmatic period. These observations largely contradicts the active rifting model where magmatism triggers Basin and Range extension

  4. Observing mesoscale eddy effects on mode-water subduction and transport in the North Pacific.

    Science.gov (United States)

    Xu, Lixiao; Li, Peiliang; Xie, Shang-Ping; Liu, Qinyu; Liu, Cong; Gao, Wendian

    2016-02-01

    While modelling studies suggest that mesoscale eddies strengthen the subduction of mode waters, this eddy effect has never been observed in the field. Here we report results from a field campaign from March 2014 that captured the eddy effects on mode-water subduction south of the Kuroshio Extension east of Japan. The experiment deployed 17 Argo floats in an anticyclonic eddy (AC) with enhanced daily sampling. Analysis of over 3,000 hydrographic profiles following the AC reveals that potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AC core, with enhanced subduction near the southeastern rim of the AC. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow--an effect that needs to be better represented in climate models.

  5. Subduction of the Tethys Oceans reconstructed from plate kinematics and mantle tomography

    NARCIS (Netherlands)

    Hafkenscheid, Edith

    2004-01-01

    This thesis is concerned with the large-scale history of subduction within the Tethyan region, the Alpine-Himalayan mountain chain that stretches from the Mediterranean to the Indonesian archipelago. We investigate whether we can contribute to a better understanding of the Tethyan evolution by

  6. Middle Miocene near trench volcanism in northern Colombia: A record of slab tearing due to the simultaneous subduction of the Caribbean Plate under South and Central America?

    Science.gov (United States)

    Lara, M.; Cardona, A.; Monsalve, G.; Yarce, J.; Montes, C.; Valencia, V.; Weber, M.; De La Parra, F.; Espitia, D.; López-Martínez, M.

    2013-08-01

    Field, geochemical, geochronological, biostratigraphical and sedimentary provenance results of basaltic and associated sediments northern Colombia reveal the existence of Middle Miocene (13-14 Ma) mafic volcanism within a continental margin setting usually considered as amagmatic. This basaltic volcanism is characterized by relatively high Al2O3 and Na2O values (>15%), a High-K calc-alkaline affinity, large ion lithophile enrichment and associated Nb, Ta and Ti negative anomalies which resemble High Al basalts formed by low degree of asthenospheric melting at shallow depths mixed with some additional slab input. The presence of pre-Cretaceous detrital zircons, tourmaline and rutile as well as biostratigraphic results suggest that the host sedimentary rocks were deposited in a platform setting within the South American margin. New results of P-wave residuals from northern Colombia reinforce the view of a Caribbean slab subducting under the South American margin. The absence of a mantle wedge, the upper plate setting, and proximity of this magmatism to the trench, together with geodynamic constraints suggest that the subducted Caribbean oceanic plate was fractured and a slab tear was formed within the oceanic plate. Oceanic plate fracturing is related to the splitting of the subducting Caribbean Plate due to simultaneous subduction under the Panama-Choco block and northwestern South America, and the fast overthrusting of the later onto the Caribbean oceanic plate.

  7. Fast intraslab fluid-flow events linked to pulses of high pore fluid pressure at the subducted plate interface

    Science.gov (United States)

    Taetz, Stephan; John, Timm; Bröcker, Michael; Spandler, Carl; Stracke, Andreas

    2018-01-01

    plate interface, which in turn, may trigger slip events reported from many subduction zones.

  8. Breaking the shell: Initiating plate tectonic-like subduction on Europa

    Science.gov (United States)

    Bland, Michael T.; McKinnon, William B.

    2017-10-01

    Europa’s prominent bands have been proposed to form by a seafloor-spreading-like mechanism involving complete separation of Europa’s lithosphere and the emplacement of fresh ice from below [Prockter et al. 2002]. This formation mechanism poses a challenge for Europa’s strain balance: extensional rifting at bands must be offset by lithospheric shortening elsewhere, yet few obvious contractional features have been observed. Kattenhorn and Prockter [2014] suggested that extension on Europa is accommodated by subduction of the lithosphere at linear, tabular zones termed subsumption bands. Subduction of Europa’s lithosphere implicitly requires that lithospheric-scale thrust faults can develop. This contrasts with previous numerical modeling, which found that lithospheric shortening is instead primarily accommodated by folding or passive thickening [Bland and McKinnon 2012, 2013]. Here we reevaluate the conditions required to form large-scale thrust faults using a numerical model of lithospheric shortening on Europa that includes realistic localization of brittle failure (non-associated plasticity). In the absence of strain weakening (wherein brittle failure decreases the subsequent yield strength) essentially all shortening results in folding or thickening, consistent with previous results. With moderate strain weakening, deformation becomes localized within fault-like zones for surface temperatures ≤100 K; however, the resulting surface deformation suggests a complex interplay between folding and faulting. Only if the ice shell weakens very easily does faulting dominate. Large-scale faults preferentially form at cold surface temperatures and high heat fluxes. Cold temperatures promote faulting (as opposed to folding), and high heat fluxes result in a thinner lithosphere, which is more easily subducted. The subsumption bands identified by Kattenhorn and Prockter [2014] are at a relatively high latitude (cold temperature), and are associated with putative

  9. Reducing risk where tectonic plates collide—U.S. Geological Survey subduction zone science plan

    Science.gov (United States)

    Gomberg, Joan S.; Ludwig, Kristin A.; Bekins, Barbara; Brocher, Thomas M.; Brock, John C.; Brothers, Daniel; Chaytor, Jason D.; Frankel, Arthur; Geist, Eric L.; Haney, Matt; Hickman, Stephen H.; Leith, William S.; Roeloffs, Evelyn A.; Schulz, William H.; Sisson, Thomas W.; Wallace, Kristi; Watt, Janet; Wein, Anne

    2017-06-19

    The U.S. Geological Survey (USGS) serves the Nation by providing reliable scientific information and tools to build resilience in communities exposed to subduction zone earthquakes, tsunamis, landslides, and volcanic eruptions. Improving the application of USGS science to successfully reduce risk from these events relies on whole community efforts, with continuing partnerships among scientists and stakeholders, including researchers from universities, other government labs and private industry, land-use planners, engineers, policy-makers, emergency managers and responders, business owners, insurance providers, the media, and the general public.Motivated by recent technological advances and increased awareness of our growing vulnerability to subduction-zone hazards, the USGS is uniquely positioned to take a major step forward in the science it conducts and products it provides, building on its tradition of using long-term monitoring and research to develop effective products for hazard mitigation. This science plan provides a blueprint both for prioritizing USGS science activities and for delineating USGS interests and potential participation in subduction zone science supported by its partners.The activities in this plan address many USGS stakeholder needs:High-fidelity tools and user-tailored information that facilitate increasingly more targeted, neighborhood-scale decisions to mitigate risks more cost-effectively and ensure post-event operability. Such tools may include maps, tables, and simulated earthquake ground-motion records conveying shaking intensity and frequency. These facilitate the prioritization of retrofitting of vulnerable infrastructure;Information to guide local land-use and response planning to minimize development in likely hazardous zones (for example, databases, maps, and scenario documents to guide evacuation route planning in communities near volcanoes, along coastlines vulnerable to tsunamis, and built on landslide-prone terrain);New tools

  10. The African Plate: A history of oceanic crust accretion and subduction since the Jurassic

    NARCIS (Netherlands)

    Gaina, C.; Torsvik, T.H.; van Hinsbergen, D.J.J.; Medvedev, S.; Werner, S.C.; Labails, C.

    2013-01-01

    We present a model for the Jurassic to Present evolution of plate boundaries and oceanic crust of the African plate based on updated interpretation of magnetic, gravity and other geological and geophysical data sets. Location of continent ocean boundaries and age and geometry of old oceanic crust

  11. Record of Permian-Early Triassic continental arc magmatism in the western margin of the Jiamusi Block, NE China: petrogenesis and implications for Paleo-Pacific subduction

    Science.gov (United States)

    Yang, Hao; Ge, Wenchun; Dong, Yu; Bi, Junhui; Wang, Zhihui; Ji, Zheng; Yang, H.; Ge, W. C.; Dong, Y.; Bi, J. H.; Wang, Z. H.; Ji, Z.

    2017-09-01

    In this paper, we report zircon U-Pb ages, Hf isotopes and whole-rock geochemical data for the Permian to Early Triassic granitoids from the western margin of the Jiamusi Block (WJB), NE China. The intermediate to felsic (SiO2 = 59.67-74.04 wt%) granitoids belong to calc-alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative Nb, Ta and Ti anomalies, revealing typical continental magmatic arc geochemical signatures. The zircon U-Pb determinations on the granodiorite, monzogranite, syenogranite and quartz diorite samples yielded ages between ca. 275-245 Ma, which, together with the published coeval intrusive rocks, indicates that Permian to Early Triassic continental arc magmatism occurred extensively in the WJB. The low and mainly negative zircon ɛ Hf( t) values between -7.6 and +1.6 and the zircon Hf model ages of 1.2-1.8 Ga, which are significantly older than their crystallization ages, suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components. The geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting, assimilation, storage, and homogenization, i.e., a MASHed zone at the base of Paleo- to Mesoproterozoic continental crust, where large portions of igneous rocks and minor clay-poor sediments involved in the source region. In combination with regional geological data, we argue that the Jiamusi Block was unlikely the rifted segment of the Songliao Block and two possible geodynamical models were proposed to interpret the formation of the ca. 275-245 Ma granitoids in the WJB. In the context of Permian global plate reconstruction, we suggest that Paleo-Pacific plate subduction was initiated in the Permian to Early Triassic beneath the Jiamusi Block, and even whole eastern NE China.

  12. Fluid release from the subducted Cocos plate and partial melting of the crust deduced from magnetotelluric studies in southern Mexico: Implications for the generation of volcanism and subduction dynamics

    OpenAIRE

    Jödicke, A; Jording, H.; Ferrari, L.; Arzate, J.; Mezger, K.; Rüpke, Lars

    2006-01-01

    In order to study electrical conductivity phenomena that are associated with subduction related fluid release and melt production, magnetotelluric (MT) measurements were carried out in southern Mexico along two coast to coast profiles. The conductivity-depth distribution was obtained by simultaneous two-dimensional inversion of the transverse magnetic and transverse electric modes of the magnetotelluric transfer functions. The MT models demonstrate that the plate southern profile shows enhanc...

  13. Sub-crustal earthquakes within the Australia-Pacific plate boundary zone beneath the Southern Alps, New Zealand

    Science.gov (United States)

    Boese, C. M.; Stern, T. A.; Townend, J.; Bourguignon, S.; Sheehan, A.; Smith, E. G. C.

    2013-08-01

    Sub-crustal earthquakes have been observed sporadically for ∼40 years in the central South Island of New Zealand. We report on 20 events recorded between December 2008 and February 2012 near the Alpine Fault in the continental collision zone between the Australian and Pacific plates. A subset of 18 events at depths of 47-74 km occurs south of Mt. Cook and together with recently reported tremor locations indicates along-strike variations in deformation behaviour along the plate boundary. The sub-crustal earthquakes south of Mt. Cook increase in depth, frequency and size southwards towards the Puysegur subduction zone. Focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike-slip and reverse faulting solutions. Stress inversion analysis of the focal mechanisms yields a stress field favouring oblique-reverse faulting. We interpret the geographic and vertical distributions of these sub-crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of New Zealand in the Eocene and was overridden when dextral strike-slip motion initiated on the Alpine Fault. We infer that sub-crustal earthquakes occur along the leading edge of this structure, which is attached to the continental Australian crust.

  14. The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate

    Science.gov (United States)

    Jones, T. D.; Davies, D. R.; Campbell, I. H.; Iaffaldano, G.; Yaxley, G.; Kramer, S. C.; Wilson, C. R.

    2017-05-01

    Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth’s core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea, and the systematic geochemical differences between them have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions; second, the recent azimuthal change in Pacific plate motion exposes high- and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific; and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite, dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa- and Kea-type lavas. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes.

  15. Plume-induced subduction

    Science.gov (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.

    2016-12-01

    Dominant present-day subduction initiation mechanisms require acting plate forces and/or pre-existing zones of lithospheric weakness, which are themselves consequences of plate tectonics. In contrast, recently discovered plume-induced subduction initiation could have started the first subduction zone without pre-existing plate tectonics. Here, we investigate this new mechanism with high-resolution 3D numerical thermomechanical modeling experiments. We show that typical plume-induced subduction dynamics is subdivided into five different stages: (1) oceanic plateau formation by arrival of a mantle plume head; (2) formation of an incipient trench and a descending nearly-circular slab at the plateau margins; (3) tearing of the circular slab; (4) formation of several self-sustained retreating subduction zones and (5) cooling and spreading of the new lithosphere formed between the retreating subduction zones. At the final stage of plume-induced subduction initiation, a mosaic of independently moving, growing and cooling small oceanic plates heading toward individual retreating subduction zones forms. The plates are separated by spreading centers, triple junctions and transform faults and thus the newly formed multi-slab subduction system operates as an embryonic plate tectonic cell. We demonstrate that three key physical factors combine to trigger self-sustained plume-induced subduction: (1) old negatively buoyant oceanic lithosphere; (2) intense weakening of the lithosphere by plume-derived magmas; and (3) lubrication of the forming subduction interface by hydrated oceanic crust. We furthermore discuss that plume-induced subduction, which is rare at present day conditions, may have been common in the Precambrian time and likely started global plate tectonics on Earth.

  16. Modeled temperatures and fluid source distributions for the Mexican subduction zone: Effects of hydrothermal circulation and implications for plate boundary seismic processes

    Science.gov (United States)

    Perry, Matthew; Spinelli, Glenn A.; Wada, Ikuko; He, Jiangheng

    2016-02-01

    In subduction zones, spatial variations in pore fluid pressure are hypothesized to control the sliding behavior of the plate boundary fault. The pressure-temperature paths for subducting material control the distributions of dehydration reactions, a primary control on the pore fluid pressure distribution. Thus, constraining subduction zone temperatures are required to understand the seismic processes along the plate interface. We present thermal models for three margin-perpendicular transects in the Mexican subduction zone. We examine the potential thermal effects of vigorous fluid circulation in a high-permeability aquifer within the basaltic basement of the oceanic crust and compare the results with models that invoke extremely high pore fluid pressures to reduce frictional heating along the megathrust. We combine thermal model results with petrological models to determine the spatial distribution of fluid release from the subducting slab and compare dewatering locations with the locations of seismicity, nonvolcanic tremor, slow-slip events, and low-frequency earthquakes. Simulations including hydrothermal circulation are most consistent with surface heat flux measurements. Hydrothermal circulation has a maximum cooling effect of 180°C. Hydrothermally cooled crust carries water deeper into the subduction zone; fluid release distributions in these models are most consistent with existing geophysical data. Our models predict focused fluid release, which could generate overpressures, coincident with an observed ultraslow layer (USL) and a region of nonvolcanic tremor. Landward of USLs, a downdip decrease in fluid source magnitude could result in the dissipation in overpressure in the oceanic crust without requiring a downdip increase in fault zone permeability, as posited in previous studies.

  17. Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico

    Science.gov (United States)

    Demets, Charles; Stein, Seth

    1990-01-01

    A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

  18. Origin of the Late Jurassic to Early Cretaceous peraluminous granitoids in the northeastern Hunan province (middle Yangtze region), South China: Geodynamic implications for the Paleo-Pacific subduction

    Science.gov (United States)

    Ji, Wenbin; Lin, Wei; Faure, Michel; Chen, Yan; Chu, Yang; Xue, Zhenhua

    2017-06-01

    The Late Mesozoic granitic belt in the northeastern Hunan province (situated in the south of the middle Yangtze region) represents the western front of the large magmatic province of SE China. In order to determine their ages and petrogenesis, we carried out zircon U-Pb dating, Hf isotope and whole-rock geochemical analyses for four granitic plutons, namely Taohuashan, Dayunshan-Mufushan, Wangxiang and Lianyunshan. Our SIMS zircon U-Pb ages, together with previously published data, reveal that the magmatic activities in this area can be roughly subdivided into three phases at 151-146 Ma, 132-127 Ma and ca. 117 Ma, and the Dayunshan-Mufushan batholith therein is a composite pluton. These four plutons are mainly composed of weakly to strongly peraluminous biotite or two-mica monzogranites, with a minor amount of biotite granodiorites. Their geochemical features are similar to S-type as well as fractionated S-type granites, with enrichment in LREEs and negative Ba, Sr, Nb, P and Ti anomalies. All samples show negative zircon εHf(t) values ranging from -12.5 to -3.6, corresponding to crustal Hf model (TDMC) ages of 1.4-2.0 Ga. It is inferred that these granitoids were derived from partial melting of metasedimentary rocks analogous to the Neoproterozoic Lengjiaxi Group, predominantly with psammitic component. Fractional crystallization probably played an important role in the magma evolution, while input of mantle-derived magma was insignificant. Combined with other geological evidence, our new data allow us to propose that the Cretaceous (132-127 Ma and ca. 117 Ma) magmatism might be response to episodic slab rollback of the Paleo-Pacific plate, while the early-stage (151-146 Ma) magmatism that overlapped the epilogue of Jurassic magmatic flare-up and subsequent magmatic quiescence probably foreshadowed the transformation from foundering of a subducted flat-slab to slab rollback. Alternatively, slab foundering after a SE-directed intracontinental subduction in the

  19. Absolute migration of Pacific basin mid-ocean ridges since 85 Ma ...

    African Journals Online (AJOL)

    ... northern Pacific. This may represent a period of tectonic instability for the Pacific plate during which the EPR was probably subducted beneath the North American continent. This period culminated by the appearance of the Galapagos propagator and a major reorganization of the East Pacific Rise south of the Galapagos.

  20. New constraints on relative motion between the Pacific Plate and Baja California microplate (Mexico) from GPS measurements

    Science.gov (United States)

    Plattner, C.; Malservisi, R.; Dixon, T. H.; LaFemina, P.; Sella, G. F.; Fletcher, J.; Suarez-Vidal, F.

    2007-09-01

    We present a new surface velocity field for Baja California using GPS data to test the rigidity of this microplate, calculate its motion in a global reference frame, determine its relative motion with respect to the North American and the Pacific plates, and compare those results to our estimate for Pacific-North America motion. Determination of Pacific Plate motion is improved by the inclusion of four sites from the South Pacific Sea Level and Climate Monitoring Project. These analyses reveal that Baja California moves as a quasi-rigid block but at a slower rate in the same direction, as the Pacific Plate relative to North America. This is consistent with seismic activity along the western edge of Baja California (the Baja California shear zone), and may reflect resistance to motion of the eastern edge of the Pacific Plate caused by the `big bend' of the San Andreas fault and the Transverse Ranges in southern California.

  1. The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate

    DEFF Research Database (Denmark)

    Jones, David T; Davies, D. R.; Campbell, I. H.

    2017-01-01

    Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub...... of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions; second, the recent...

  2. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc.

    Science.gov (United States)

    Timm, Christian; Bassett, Daniel; Graham, Ian J; Leybourne, Matthew I; de Ronde, Cornel E J; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B

    2013-01-01

    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  3. Fluid release from the subducted Cocos plate and partial melting of the crust deduced from magnetotelluric studies in southern Mexico: Implications for the generation of volcanism and subduction dynamics

    Science.gov (United States)

    JöDicke, H.; Jording, A.; Ferrari, L.; Arzate, J.; Mezger, K.; Rüpke, L.

    2006-08-01

    In order to study electrical conductivity phenomena that are associated with subduction related fluid release and melt production, magnetotelluric (MT) measurements were carried out in southern Mexico along two coast to coast profiles. The conductivity-depth distribution was obtained by simultaneous two-dimensional inversion of the transverse magnetic and transverse electric modes of the magnetotelluric transfer functions. The MT models demonstrate that the plate southern profile shows enhanced conductivity in the deep crust. The northern profile is dominated by an elongated conductive zone extending >250 km below the Trans-Mexican Volcanic Belt (TMVB). The isolated conductivity anomalies in the southern profile are interpreted as slab fluids stored in the overlying deep continental crust. These fluids were released by progressive metamorphic dehydration of the basaltic oceanic crust. The conductivity anomalies may be related to the main dehydration reactions at the zeolite → blueschist → eclogite facies transitions and the breakdown of chlorite. This relation allows the estimation of a geothermal gradient of ˜8.5°C/km for the top of the subducting plate. The same dehydration reactions may be recognized along the northern profile at the same position relative to the depth of the plate, but more inland due to a shallower dip, and merge near the volcanic front due to steep downbending of the plate. When the oceanic crust reaches a depth of 80-90 km, ascending fluids produce basaltic melts in the intervening hot subcontinental mantle wedge that give rise to the volcanic belt. Water-rich basalts may intrude into the lower continental crust leading to partial melting. The elongated highly conductive zone below the TMVB may therefore be caused by partial melts and fluids of various origins, ongoing migmatization, ascending basaltic and granitic melts, growing plutons as well as residual metamorphic fluids. Zones of extremely high conductance (>8000 S) in the

  4. The Role of Proto-Thrusts in Frontal Accretion and Accommodation of Plate Convergence, Hikurangi Subduction Margin, New Zealand

    Science.gov (United States)

    Barnes, P.; Ghisetti, F.; Ellis, S. M.; Morgan, J.

    2016-12-01

    Proto-thrusts are an enigmatic structural feature at the toe of many subduction accretionary wedges. They are commonly recognised in seismic reflection sections as relatively small-displacement (tens of metres) faults seaward of the primary deformation front. Although widely assumed to reflect incipient accretionary deformation and to mark the location of future thrusts, proto-thrusts have received relatively little attention. Few studies have attempted to characterise their displacement properties, evolution, and kinematic role in frontal accretion processes associated with propagation of the interface décollement. In this study, we make use of excellent quality geophysical and bathymetric imaging of the spectacular 25 km-wide Hikurangi margin proto-thrust zone (PTZ), the structure of which varies significantly along strike. From a detailed structural analysis, we provide the first substantial quantitative dataset on proto-thrust geometry, displacement profiles, fault scaling relationships, and fault population characteristics. These analyses provide new insights into the role of inferred stratigraphic inhomogeneity in proto-thrust development, and the role of proto-thrust arrays in frontal accretion. Our observations, combined with our own recently published reconstructions of the wedge, and ongoing numerical simulations, indicate a migrating wave of proto-thrust activity in association with forward-advancement of the décollement. Calculation of tectonic shortening accommodated by the active PTZ east of the present deformation front, from measurements of seismically-imaged fault displacements and estimates of sub-seismic faulting derived from power law relationships, reveal their surprisingly significant role in accommodating regional plate convergence. South of the colliding Bennett Knoll Seamount, the predominantly seaward-vergent PTZ has accommodated 3.3 km of tectonic shortening, of which 70% is at sub-seismic scale. In comparison, north of Bennett Knoll

  5. Tectonics and plate boundary processes along the Southeast Indian Ridge and the East Pacific Rise

    Science.gov (United States)

    Conder, James Andrew

    Classical plate tectonics describes crustal deformation in a simple kinematic way, with deformation occurring only at narrow boundaries of plates with rigid interiors. Many dynamic processes at these boundaries are not well understood. There are also apparent deviations from classical plate tectonics where significant intraplate deformation occurs. In this thesis, we analyze and model geophysical data from the Southeast Indian Ridge (SEIR) and the East Pacific Rise (EPR) to address some of these issues. Hotspots often affect the dynamics of nearby spreading centers. As shown by bathymetry, side-scan sonar, and magnetic anomaly data, the Amsterdam-St. Paul (ASP) hotspot has altered the spreading history and geometry of nearby SEIR spreading axes. The hotspot thickened the oceanic crust near the spreading center and reorganized the plate boundary through rift propagation and ridge jumps, creating the youngest known transform fault in the process. The region near the ASP plateau has been suggested as where a wide, diffuse, NW-SE trending oceanic plate boundary meets the SEIR. Using data from the SEIR, we perform a statistical analysis and examine predictions of the model to test its validity. The boundary is not confirmed on statistical grounds, but evidence suggests that it does exist. However, it does not extend south of the St. Paul Fracture Zone, narrowing the previously proposed boundary by 800 km where it meets the SEIR. We also test the hypothesis that deformation near the eastern end of the SEIR, including a large intraplate earthquake can be explained by an additional plate boundary. If the earthquake lies on a plate boundary, its sense of slip should be right-lateral rather than the observed left-lateral motion, ruling out the hypothesis. Asymmetric geophysical properties of the EPR near 17°S suggest more melt beneath the Pacific side than the Nazca side. Numerical modeling results indicate that the asymmetry may be produced by pressure-driven across

  6. Numerical simulations of temperature, dehydration, and flow fields associated with subduction of the Cocos plate, and its relation to the occurrence of interplate seismic events in southern Mexico

    Science.gov (United States)

    Suenaga, N.; Ji, Y.; Yoshioka, S.; Manea, M.; Manea, V. C.

    2016-12-01

    In southern Mexico, tectonic tremors mainly occur in the "flat slab region, and the last three SSEs in southern Mexico occurred in the shallower region. Besides, there are two seismic gaps of megathrust earthquakes in Guerrero and Oaxaca. To investigate generation mechanisms of megathrust earthquakes, tectonic tremors, and slow slip events (SSEs) in southern Mexico, we performed three-dimensional numerical simulations of temperature and mantle flow associated with subduction of the Cocos plate, and estimated dehydrated water content from the subducting plate. Here we considered retreat of the Middle American trench initiating about 16 Ma as one of the generation mechanisms of the slab flattening. In our model, we introduced the trench retreat effect during only a certain period between 16 Ma and present in order to best fit the observed heat flow data (from Global Heat Flow Database) as well as Curie point depths defined by the 580 ° isotherm. Our preliminary results show that trench rollback has a strong influence on temperature distribution. Models with trench rollback induce a weaker mantle wedge convection cell compared with models with stationary trench. Other parameter that is currently investigated in this study is the rate of trench retreat.

  7. Coupled Global Models of Mantle and Lithosphere Dynamics: Identifying the Forces Governing Pacific Plate Motions since the mid–Miocene

    DEFF Research Database (Denmark)

    Stotz Canales, Ingo Leonardo

    2017-01-01

    at the Melanesian arc. Furthermore, we demonstrate, for the first time, that the sub–Pacific asthenosphere features a significant component of pressure–driven flow (i.e., Poiseuille), and that this accounts for more than half of the Pacific plate motion over at least the past 15 Myr. Our results highlight the power......Almost all surface processes, including motions of the lithospheric plates, can be related to underlying mantle circulation. Geological expressions across Earth’s surface, such as the Andean mountain range in South America, the ancient cratons of Australia and the African continent’s unusual.......e. the direction and magnitude) of lithospheric plates. In this thesis, we have developed novel coupled global numerical models of mantle and lithosphere dynamics and, subsequently, used these to test hypotheses on the force–balance governing motion of the Pacific plate since the mid–Miocene. These coupled models...

  8. absolute migration of pacific basin mid-ocean ridges since 85 ma ...

    African Journals Online (AJOL)

    Mgina

    This may represent a period of tectonic instability for the Pacific plate during which the EPR was probably subducted beneath the North American continent. This period culminated by the appearance of the Galapagos propagator and a major reorganization of the East Pacific Rise south of the Galapagos. INTRODUCTION.

  9. Upper-plate splay fault earthquakes along the Arakan subduction belt recorded by uplifted coral microatolls on northern Ramree Island, western Myanmar (Burma)

    Science.gov (United States)

    Shyu, J. Bruce H.; Wang, Chung-Che; Wang, Yu; Shen, Chuan-Chou; Chiang, Hong-Wei; Liu, Sze-Chieh; Min, Soe; Aung, Lin Thu; Than, Oo; Tun, Soe Thura

    2018-02-01

    Upper-plate structures that splay out from the megathrusts are common features along major convergent plate boundaries. However, their earthquake and tsunami hazard potentials have not yet received significant attention. In this study, we identified at least one earthquake event that may have been produced by an upper-plate splay fault offshore western Myanmar, based on U-Th ages of uplifted coral microatolls. This event is likely an earthquake that was documented historically in C.E. 1848, with an estimated magnitude between 6.8 and 7.2 based on regional structural characteristics. Such magnitude is consistent with the observed co-seismic uplift amount of ∼0.5 m. Although these events are smaller in magnitude than events produced by megathrusts, they may produce higher earthquake and tsunami hazards for local coastal communities due to their proximity. Our results also indicate that earthquake events with co-seismic uplift along the coast may not necessarily produce a flight of marine terraces. Therefore, using only records of uplifted marine terraces as megathrust earthquake proxies may overlook the importance of upper-plate splay fault ruptures, and underestimate the overall earthquake frequency for future seismic and tsunami hazards along major subduction zones of the world.

  10. Mantle enrichment by volatiles as the Nazca plate subducts beneath the Payenia backarc of the Southern Volcanic Zone, Argentina

    DEFF Research Database (Denmark)

    Brandt, Frederik Ejvang

    , minerals, fluid and melt inclusions from the Payenia backarc province of the Andean Southern Volcanic Zone. Major emphasis has been on olivine hosted melt inclusions. The study gives evidence for the role of fluids in the metasomatism of the backarc mantle, and outlines the trend of the variation...... of the metasomatism in Payenia, which is also characterized by a variation in oxidation state and other geochemical parameters of the melt inclusions, and is moreover related to mantle lithological variations. The mantle metasomatism by melts of subducted crust and fluid-borne enrichment is quantitatively modelled......, the origin of Chlorine is explained via slab-derived fluids, and the contrast between backarc and frontal arc magmas is discussed. These results add to the understanding of the origin of the complexities in the mantle wedge under arc-backarc in a subduction zone which has transition to flat slab conditions...

  11. Postglacial (after 18 ka) deep-sea sedimentation along the Hikurangi subduction margin (New Zealand): Characterisation, timing and origin of turbidites

    OpenAIRE

    Pouderoux, Hugo; Proust, Jean-Noël; Lamarche, Geoffroy; Orpin, Alan; Neil, Helen

    2012-01-01

    International audience; Recent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific-Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidi...

  12. Seismicity and plate tectonics in south central Alaska

    Science.gov (United States)

    Van Wormer, J. D.; Davies, J.; Gedney, L.

    1974-01-01

    Hypocenter distribution shows that the Benioff zone associated with the Aleutian arc terminates in interior Alaska some 75 km north of the Denali fault. There appears to be a break in the subducting Pacific plate in the Yentna River-Prince William Sound area which separates two seismically independent blocks, similar to the segmented structure reported for the central Aleutian arc.

  13. On the initiation of subduction

    Science.gov (United States)

    Mueller, Steve; Phillips, Roger J.

    1991-01-01

    Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.

  14. A discussion of numerical subduction initiation

    Science.gov (United States)

    Buiter, Susanne; Ellis, Susan

    2016-04-01

    In nature, subduction can initiate in various ways: Shortening can localise at oceanic transform faults, extinct spreading centres, or inherited passive margin faults; or, alternatively, subduction can be triggered from existing subduction systems by along-strike trench propagation, polarity reversals, or trench jumps. Numerical studies that specifically address subduction initiation have highlighted the roles of sediment loading, rheological strength contrasts, strain softening, and continental topographic gradients, among others. Usually, however, numerical models that aim to investigate subduction dynamics prefer to bypass the subduction initiation phase and its complexities, and focus instead on the stages during which the slab is descending into the mantle. However, even in these models, subduction still needs to begin. It is disturbingly easy to define initial model geometries that do not result in subduction. The specific combination of initial model geometries and values for rheological parameters that successfully initiates subduction has even been referred to as 'the sweet spot' in model space. One cause of subduction initiation failure is when the subducting and overriding plates lock, resulting in either indentation or severe dragging downwards of the overriding plate. This may point to a difficulty in maintaining a weak subduction interface during model evolution. A second factor that may cause difficulties is that initial model geometry and stresses need to balance, as otherwise the first model stages may show spurious deformation associated with reaching equilibrium. A third requirement that may cause problems is that the surface needs to have sufficient displacement freedom to allow the overriding plate to overthrust the subducting plate. That also implies an exclusion of sharp corners in the subduction interface near the surface. It is the interplay of subduction interface geometry, interface strength and subducting plate rheology that determines

  15. Mantle Flow Beneath the Juan de Fuca and East Pacific Rise Spreading Centers and Adjacent Plates

    Science.gov (United States)

    Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.

    2010-12-01

    Observations of seismic anisotropy are a principal means of inferring the direction of mantle flow beneath tectonic plates. Azimuthal anisotropy of mantle head waves (Pn) observed in mid-plate settings, for example, has been used to infer that beneath oceanic crust the mantle flow that is frozen in is parallel to the paleospreading direction. While the agreement between historical measurements of azimuthal anisotropy and paleospreading direction is good, the combined uncertainties in experimental results (many of which date back 30 to 50 years) and in inferring the paleospreading direction are often 10-15°. In contrast to historical results from mid-plate settings, recent studies of Pn anisotropy beneath the East Pacific Rise (EPR) and the Mid-Atlantic Ridge reveal that the fast-direction of seismic anisotropy - and by inference the direction of mantle flow - is skewed with respect to the current spreading direction. This result indicates that sub-ridge mantle flow is not an entirely passive response to plate spreading. Here we use data from recent active-source seismic experiments to investigate azimuthal anisotropy of Pn arrivals in two near-ridge settings. These modern experiments, which use dense arrays of ocean-bottom seismometers (OBSs) and well-navigated seismic shooting lines, can constrain azimuthal anisotropy to within ±1°. One data set is from the multi-scale Endeavour seismic tomography experiment (ETOMO) that took place in September 2009. Seismic data were collected using 68 four-component OBSs at 64 sites and the 6600 in3 airgun array of the R/V Marcus G. Langseth. The study includes 5567 shots covering 90 km along-axis and 50 km across. The second data set is from the UNDERSHOOT experiment, which was conducted at the EPR between the Siqueiros and Clipperton transforms, a section of ridge that is sub-divided by the 9°03'N overlapping spreading center (OSC). Seismic data were collected using a combination of four-component OBSs and single

  16. Compression-extension transition of continental crust in a subduction zone: A parametric numerical modeling study with implications on Mesozoic-Cenozoic tectonic evolution of the Cathaysia Block.

    Science.gov (United States)

    Zuo, Xuran; Chan, Lung Sang; Gao, Jian-Feng

    2017-01-01

    The Cathaysia Block is located in southeastern part of South China, which situates in the west Pacific subduction zone. It is thought to have undergone a compression-extension transition of the continental crust during Mesozoic-Cenozoic during the subduction of Pacific Plate beneath Eurasia-Pacific Plate, resulting in extensive magmatism, extensional basins and reactivation of fault systems. Although some mechanisms such as the trench roll-back have been generally proposed for the compression-extension transition, the timing and progress of the transition under a convergence setting remain ambiguous due to lack of suitable geological records and overprinting by later tectonic events. In this study, a numerical thermo-dynamical program was employed to evaluate how variable slab angles, thermal gradients of the lithospheres and convergence velocities would give rise to the change of crustal stress in a convergent subduction zone. Model results show that higher slab dip angle, lower convergence velocity and higher lithospheric thermal gradient facilitate the subduction process. The modeling results reveal the continental crust stress is dominated by horizontal compression during the early stage of the subduction, which could revert to a horizontal extension in the back-arc region, combing with the roll-back of the subducting slab and development of mantle upwelling. The parameters facilitating the subduction process also favor the compression-extension transition in the upper plate of the subduction zone. Such results corroborate the geology of the Cathaysia Block: the initiation of the extensional regime in the Cathaysia Block occurring was probably triggered by roll-back of the slowly subducting slab.

  17. The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary

    Science.gov (United States)

    Fletcher, J. M.; Eakins, B. W.

    2001-12-01

    New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former east-dipping accretionary complex. Numerous lines of evidence indicate that Neogene faults are still active and accomplish a significant component ( ~1-5 mm/yr) of Pacific-North American shearing. Quaternary volcanoes are found offshore and along the Pacific coastal margin, Quaternary marine terraces are warped and uplifted as high as 200 masl. Many of the offshore faults have fresh escarpments and cut Holocene sediments. Extensive arrays of Quaternary fault scarps are found throughout the coastal region and in Bahia Magdalena they are clearly associated with major faults that bound recently uplifted islands. A prominent band of seismicity follows the coast and eight earthquakes (Ms>5.0) were teleseismically recorded between 1973 and 1998. This evidence for active shearing indicates that the Baja microplate has not yet been completely transferred to the Pacific plate. The best lithologic correlation that can be used to define the total Neogene slip across the borderland faults is the offset between the Magdalena submarine fan and its Baja source terrane. The distal facies of the fan drilled during DSDP leg 63 is dominated by mudstone and siltstone that contain reworked Paleogene cocoliths derived from strata correlative with the Tepetate formation found throughout the borderland and fine-grained sandstone derived from a source terrane of granitoid basement. The Middle Miocene La Calera formation of the Cabo trough is one of many granitoid-clast syn-rift alluvial deposits that could form the continental counterpart of the submarine fan near the mouth of the

  18. Linking the initial subduction of the South Tianshan Oceanic Plate and associated magmatism to Kazakhstan orocline: insights from petrogenesis of granites in the southern Yili Block

    Science.gov (United States)

    Bao, Zihe; Cai, Keda; Sun, Min; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping

    2017-04-01

    The Kazakhstan orocline is a striking collage system of the Central Asian Orogenic Belt. It has been documented to be a composite continent via assembly of several orogenic components by the Devonian and finally to attain its U-shaped structure through oroclinal bending in the Late Paleozoic. In order to reveal the relationship between the Kazakhstan orocline and regional magmatism, granitic rocks including monzogranites and K-feldspar granites in the south limb of the orocline have been conducted geochronological and geochemical studies. Zircon LA-ICP-MS U-Pb dating of the monzogranites gave crystallization ages of 360±1.8 Ma and 360.5±1.7 Ma, and the K-feldspar granites have a coeval age (361.3±1.8 Ma). Both of the granites are high-K granites, and show enrichment in light rare earth elements (LREE) and obvious negative Eu anomalies. They display negative anomalies in Ba, Nb, Sr, Eu, and Ti. The K-feldspar granites have higher SiO2, K2O contents and lower MgO, Fe2O3T, Zr contents than those of the monzogranites. Geochemical data support that the K-feldspar granites are highly fractionated I-type granites, and the monzogranites are unfractionated I-type granites. Distinguishable Nd and Hf isotope suggest that the K-feldspar granites and the monzogranites may share a common magma chamber. The negative Eu anomalies and depletions of Ba and Sr possibly imply plagioclase as residue in the magma source. The Sr-Nd isotopic data and the ɛHf(t) values (-3.6 - 2.9) indicate that the parental magma was probably derived from crustal rock with minor mantle-derived melt. The new geochemical data and regional geology evidences indicate that the granites may be generated in a continental back-arc environment, which was inferred to be a response to the initial subduction of the South Tianshan Oceanic Plate. Given that the Kazakhstan orocline was developed during this period, it is plausible to link the initial subduction of the South Tianshan Oceanic Plate and associated

  19. Formation and metasomatism of continental lithospheric mantle in intra-plate and subduction-related tectonic settings

    Science.gov (United States)

    Ionov, Dmitri

    2010-05-01

    , major and trace element and isotope compositions of fertile lherzolites and thus cannot provide viable alternatives to the concept of melt extraction from pristine mantle as the major mechanism of CLM formation. Published data on xenoliths from andesitic volcanoes and on supra-subduction oceanic peridotites [4] show that the most common rocks in mantle wedge lithosphere are highly refractory harzburgites characterized by a combination of variable but generally high modal opx (18-30%) with very low modal cpx (1.5-3%). At a given olivine (or MgO) content, they have higher opx and silica, and lower cpx, Al and Ca contents than normal refractory peridotite xenoliths in continental basalts; the Mg-Si and Al-Si trends in those rocks resemble those in cratonic peridotites. These features may indicate either fluid fluxing during melting in the mantle wedge or selective post-melting metasomatic enrichments in silica to transform some olivine to opx. High oxygen fugacities and radiogenic Os-isotope compositions in those rocks may be related to enrichments by slab-derived fluids, but these features are not always coupled with trace element enrichments or patterns commonly attributed to "subduction zone metasomatism" deduced from studies of arc volcanic rocks and experiments. The valuable insights provided by experimental work and xenolith case studies are difficult to apply to many natural peridotite series because late-stage processes commonly overlap the evidence for initial melting. References: [1] Herzberg C., J. Petrol. 45: 2507 (2004). [2] Ionov D. & Sobolev A., GCA 72 (S1): A410 (2008). [3] Ionov D., Contrib. Miner. Petrol. (2007) [4] Ionov D., J. Petrol. doi: 10.1093/petrology/egp090 (2010)

  20. Insights into a fossil plate interface of an erosional subduction zone: a tectono-metamorphic study of the Tianshan metamorphic belt.

    Science.gov (United States)

    Bayet, Lea; Moritz, Lowen; Li, Jilei; Zhou, Tan; Agard, Philippe; John, Timm; Gao, Jun

    2016-04-01

    Subduction zone seismicity and volcanism are triggered by processes occurring at the slab-wedge interface as a consequence of metamorphic reactions, mass-transfer and deformation. Although the shallow parts of subduction zones (60km). In order to better understand the plate interface dynamics at these greater depths, one has to rely on the rock record from fossil subduction zones. The Chinese Tianshan metamorphic belt (TMB) represents an ideal candidate for such studies, because structures are well exposed with exceptionally fresh high-pressure rocks. Since previous studies from this area focused on fluid-related processes and its metamorphic evolution was assessed on single outcrops, the geodynamic setting of this metamorphic belt is unfortunately heavily debated. Here, we present a new geodynamic concept for the TMB based on detailed structural and petrological investigations on a more regional scale. A ~11km x 13km area was extensively covered, together with E-W and N-S transects, in order to produce a detailed map of the TMB. Overall, the belt is composed of two greenschist-facies units that constitute the northern and southern border of a large high-pressure (HP) to ultra high-pressure (UHP) unit in the center. This HP-UHP unit is mainly composed of metasediments and volcanoclastic rocks, with blueschist, eclogite and carbonate lenses. Only the southern part of the HP-UHP unit is composed of the uppermost part of an oceanic crust (e.g., pillow basalts and deep-sea carbonates). From south to north, the relative abundance and size of blueschist massive boudins and layers (as well as eclogite boudins) decreases and the sequence is increasingly interlayered with metasedimentary and carbonate-rich horizons. This indicates that the subducted material was dominated by trench filling made of sediments and volcanoclastic rocks, with only subordinate pieces of oceanic crust/lithosphere. The whole sequence is cut by km-scale major shear planes orientated WNW-ESE showing

  1. Analysis of the Seismicity Associated to the Subduction of the Rivera Plate using OBS and Onland Stations.

    Science.gov (United States)

    Nuñez-Cornu, F. J.; Barba, D. C., Sr.; Danobeitia, J.; Bandy, W. L.; Zamora-Camacho, A.; Marquez-Ramirez, V. H.; Ambros, M.; Gomez, A.; Sandoval, J. M.; Mortera-Gutierrez, C. A.

    2016-12-01

    The second stage of TsuJal Project includes the study of passive seismic activity in the region of the plate Rivera and Jalisco block by anchoring OBS and densifying the network of seismic stations on land for at least four months. This stage began in April 2016 with the deployment of 25 Obsidian stations with sensor Le-3D MkIII from the northern part of Nayarit state to the south of Colima state, including the Marias Islands. This temporal seismic network complements the Jalisco Seismic Network (RESAJ) for a total of 50 stations. Offshore, ten OBS type LCHEAPO 2000 with 4 channel (3 seismic short period and 1 pressure) were deployed, in the period from 19 to 30 April 2016 using the BO El Puma from UNAM. The OBS were deployed in an array from the Marias Islands to offcoast of the border of Colima and Michoacan states. On May 4, an earthquake with Ml = 4.2 took place in the contact area of the Rivera Plate, Cocos Plate and the Middle America Trench, subsequently occurred a seismic swarm with over 200 earthquakes until May 16, including an earthquake with Ml = 5.0 on May 7. A second swarm took place between May 28 and Jun 4 including an earthquake with Ml = 4.8 on Jun 1. An analysis of the quality of different location methods is presented: automatic preliminary RESAJ location using Antelope; location with revised RESAJ phases in Antelope; relocation of RESAJ data with hypo and a regional velocity model; relocation of RESAJ data with hypo adding data from the temporal seismic network stations; and finally the relocation adding the data from the OBS network. Moreover, the tectonic implications of these earthquakes are discussed.

  2. A wave equation migration method for receiver function imaging: 2. Application to the Japan subduction zone

    Science.gov (United States)

    Chen, Ling; Wen, Lianxing; Zheng, Tianyu

    2005-11-01

    The newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the Japan subduction zone using the Fundamental Research on Earthquakes and Earth's Interior Anomalies (FREESIA) broadband data. Three profiles are chosen in the subsurface imaging, two in northeast (NE) Japan to study the subducting Pacific plate and one in southwest (SW) Japan to study the Philippine Sea plate. The descending Pacific plate in NE Japan is well imaged within a depth range of 50-150 km. The slab image exhibits a little more steeply dipping angle (˜32°) in the south than in the north (˜27°), although the general characteristics between the two profiles in NE Japan are similar. The imaged Philippine Sea plate in eastern SW Japan, in contrast, exhibits a much shallower subduction angle (˜19°) and is only identifiable at the uppermost depths of no more than 60 km. Synthetic tests indicate that the top 150 km of the migrated images of the Pacific plate is well resolved by our seismic data, but the resolution of deep part of the slab images becomes poor due to the limited data coverage. Synthetic tests also suggest that the breakdown of the Philippine Sea plate at shallow depths reflects the real structural features of the subduction zone, rather than caused by insufficient coverage of data. Comparative studies on both synthetics and real data images show the possibility of retrieval of fine-scale structures from high-frequency contributions if high-frequency noise can be effectively suppressed and a small bin size can be used in future studies. The derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure. The observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates. Moreover, the deep extent of the Pacific plate image and the shallow breakdown of the Philippine Sea plate image are

  3. Buoyant subduction on Venus: Implications for subduction around coronae

    Science.gov (United States)

    Burt, J. D.; Head, J. W.

    1993-01-01

    Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial subduction zones in planform and topographic cross-section were described, including trenches around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of subduction. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.

  4. Shear wave velocity structure in the lithosphere and asthenosphere across the Southern California continent and Pacific plate margin using inversion of Rayleigh wave data from the ALBACORE project.

    Science.gov (United States)

    Price, A. C.; Weeraratne, D. S.; Kohler, M. D.; Rathnayaka, S.; Escobar, L., Sr.

    2015-12-01

    The North American and Pacific plate boundary is a unique example of past subduction of an oceanic spreading center which has involved oceanic plate capture and inception of a continental transform boundary that juxtaposes continental and oceanic lithosphere on a single plate. The amphibious ALBACORE seismic project (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) deployed 34 ocean bottom seismometers (OBS) on 15-35 Ma seafloor and offers a unique opportunity to compare the LAB in continental and oceanic lithosphere in one seismic study. Rayleigh waves were recorded simultaneously by our offshore array and 82 CISN network land stations from 2010-2011. Here we predict phase velocities for a starting shear wave velocity model for each of 5 regions in our study area and compare to observed phase velocities from our array in a least-squares sense that produces the best fit 1-D shear wave velocity structure for each region. Preliminary results for the deep ocean (seafloor 25-32 Ma) indicates high velocities reaching 4.5 km/s at depths of 50 km associated with the lithosphere for seafloor 25-32 Ma. A negative velocity gradient is observed below this which reaches a minimum of 4.0 km/s at 160 km depth. The mid-ocean region (age 13-25 Ma) indicates a slightly lower magnitude and shallower LVZ. The Inner Borderland displays the highest lithospheric velocities offshore reaching 4.8 km/s at 40 km depth indicating underplating. The base of the LVZ in the Borderland increases sharply from 4.0 km/s to 4.5 km/s at 80-150 km depth indicating partial melt and compositional changes. The LVZ displays a very gradual positive velocity gradient in all other regions such as the deep seafloor and continent reaching 4.5 km/s at 300 km depth. The deep ocean, Borderlands, and continental region each have unique lithospheric velocities, LAB depths, and LVZ character that indicate stark differences in mantle structure that occur on a

  5. Geodynamic Modeling of the Subduction Zone around the Japanese Islands

    Science.gov (United States)

    Honda, S.

    2017-06-01

    In this review, which focuses on our research, we describe the development of the thermomechanical modeling of subduction zones, paying special attention to those around the Japanese Islands. Without a sufficient amount of data and observations, models tended to be conceptual and general. However, the increasing power of computational tools has resulted in simple analytical and numerical models becoming more realistic, by incorporating the mantle flow around the subducting slab. The accumulation of observations and data has made it possible to construct regional models to understand the detail of the subduction processes. Recent advancements in the study of the seismic tomography and geology around the Japanese Islands has enabled new aspects of modeling the mantle processes. A good correlation between the seismic velocity anomalies and the finger-like distribution of volcanoes in northeast Japan has been recognized and small-scale convection (SSC) in the mantle wedge has been proposed to explain such a feature. The spatial and temporal evolution of the distribution of past volcanoes may reflect the characteristics of the flow in the mantle wedge, and points to the possibility of the flip-flopping of the finger-like pattern of the volcano distribution and the migration of volcanic activity from the back-arc side to the trench side. These observations are found to be qualitatively consistent with the results of the SSC model. We have also investigated the expected seismic anisotropy in the presence of SSC. The fast direction of the P-wave anisotropy generally shows the trench-normal direction with a reduced magnitude compared to the case without SSC. An analysis of full 3D seismic anisotropy is necessary to confirm the existence and nature of SSC. The 3D mantle flow around the subduction zone of plate-size scale has been modeled. It was found that the trench-parallel flow in the sub-slab mantle around the northern edge of the Pacific plate at the junction between

  6. Mapping seismic azimuthal anisotropy of the Japan subduction zone

    Science.gov (United States)

    Zhao, D.; Liu, X.

    2016-12-01

    We present 3-D images of azimuthal anisotropy tomography of the crust and upper mantle of the Japan subduction zone, which are determined using a large number of high-quality P- and S-wave arrival-time data of local earthquakes and teleseismic events recorded by the dense seismic networks on the Japan Islands. A tomographic method for P-wave velocity azimuthal anisotropy is modified and extended to invert S-wave travel times for 3-D S-wave velocity azimuthal anisotropy. A joint inversion of the P and S wave data is conducted to constrain the 3-D azimuthal anisotropy of the Japan subduction zone. Main findings of this work are summarized as follows. (1) The high-velocity subducting Pacific and Philippine Sea (PHS) slabs exhibit trench-parallel fast-velocity directions (FVDs), which may reflect frozen-in lattice-preferred orientation of aligned anisotropic minerals formed at the mid-ocean ridge as well as shape-preferred orientation such as normal faults produced at the outer-rise area near the trench axis. (2) Significant trench-normal FVDs are revealed in the mantle wedge, which reflects corner flow in the mantle wedge due to the active subduction and dehydration of the oceanic plates. (3) Obvious toroidal FVDs and low-velocity anomalies exist in and around a window (hole) in the aseismic PHS slab beneath Southwest Japan, which may reflect a toroidal mantle flow pattern resulting from hot and wet mantle upwelling caused by the joint effects of deep dehydration of the Pacific slab and the convective circulation process in the mantle wedge above the Pacific slab. (4) Significant low-velocity anomalies with trench-normal FVDs exist in the mantle below the Pacific slab beneath Northeast Japan, which may reflect a subducting oceanic asthenosphere affected by hot mantle upwelling from the deeper mantle. ReferencesLiu, X., D. Zhao (2016) Seismic velocity azimuthal anisotropy of the Japan subduction zone: Constraints from P and S wave traveltimes. J. Geophys. Res. 121, doi

  7. Average slip rate at the transition zone on the plate interface in the Nankai subduction zone, Japan, estimated from short-term SSE catalog

    Science.gov (United States)

    Itaba, S.; Kimura, T.

    2013-12-01

    Short-term slow slip events (S-SSEs) in the Nankai subduction zone, Japan, have been monitored by borehole strainmeters and borehole accelerometers (tiltmeters) mainly. The scale of the S-SSE in this region is small (Mw5-6), and therefore there were two problems in S-SSE identification and estimation of the fault model. (1) There were few observatories that can detect crustal deformation associated with S-SSEs. Therefore, reliability of the estimated fault model was low. (2) The signal associated with the S-SSE is relatively small. Therefore, it was difficult to detect the S-SSE only from strainmeter and tiltmeter. The former problem has become resolvable to some extent by integrating the data of borehole strainmeter, tiltmeter and groundwater (pore pressure) of the National Institute of Advanced Industrial Science and Technology, tiltmeter of the National Research Institute for Earthquake Science and Disaster Prevention and borehole strainmeter of the Japan Meteorological Agency. For the latter, by using horizontal redundant component of a multi-component strainmeter, which consists generally of four horizontal extensometers, it has become possible to extract tectonic deformation efficiently and detect a S-SSE using only strainmeter data. Using the integrated data and newly developed technique, we started to make a catalog of S-SSE in the Nankai subduction zone. For example, in central Mie Prefecture, we detect and estimate fault model of eight S-SSEs from January 2010 to September 2012. According to our estimates, the average slip rate of S-SSE is 2.7 cm/yr. Ishida et al. [2013] estimated the slip rate as 2.6-3.0 cm/yr from deep low-frequency tremors, and this value is consistent with our estimation. Furthermore, the slip deficit rate in this region evaluated by the analysis of GPS data from 2001 to 2004 is 1.0 - 2.6 cm/yr [Kobayashi et al., 2006], and the convergence rate of the Philippine Sea plate in this region is estimated as 5.0 - 7.0 cm/yr. The difference

  8. Reconstructions of subducted ocean floor along the Andes: a framework for assessing Magmatic and Ore Deposit History

    Science.gov (United States)

    Sdrolias, M.; Müller, R.

    2006-05-01

    The South American-Antarctic margin has been characterised by numerous episodes of volcanic arc activity and ore deposit formation throughout much of the Mesozoic and Cenozoic. Although its Cenozoic subduction history is relatively well known, placing the Mesozoic arc-related volcanics and the emplacement of ore bodies in their plate tectonic context remains poorly constrained. We use a merged moving hotspot (Late Cretaceous- present) and palaeomagnetic /fixed hotspot (Early Cretaceous) reference frame, coupled with reconstructed spreading histories of the Pacific, Phoenix and Farallon plates to understand the convergence history of the South American and Antarctic margins. We compute the age-area distribution of oceanic lithosphere through time, including subducting oceanic lithosphere and estimate convergence rates along the margin. Additionally, we map the location and migration of spreading ridges along the margin and relate this to processes on the overriding plate. The South American-Antarctic margin in the late Jurassic-early Cretaceous was dominated by rapid convergence, the subduction of relatively young oceanic lithosphere (Verdes" in southern South America. The speed of subduction increased again along the South American-Antarctic margin at ~105 Ma after another change in tectonic regime. Newly created crust from the Farallon-Phoenix ridge continued to be subducted along southern South America until the cessation of the Farallon-Phoenix ridge in the latest Cretaceous / beginning of the Cenozoic. The age of the subducting oceanic lithosphere along the South American-Antarctic margin has increased steadily through time.

  9. The correlation between geomagnetic field reversals, Hawaiian volcanism, and the motion of the Pacific plate

    Directory of Open Access Journals (Sweden)

    W. Dong

    1996-06-01

    Full Text Available The correlation between geomagnetic field reversals and volcanism is investigated, according to the speculated consequence on volcanoes of the transient electric currents in the geodynamo, through Joule's heating, before and after every reversal event. We evaluate the temporal variation during the last ~ 70 Ma both of the magma emplacement rate Q(t from the Hawaii hot spot, and of the speed v(t of the Pacific plate, by means of the observed volumes of islands and seamounts along the Hawaii/Emperor Seamounts chain, and their respective radiometric datings. Results confirm expectations. A justification of the volcanic crises that lead to the generation of the large igneous provinces during the last ~ 250 Ma also emerged. We describe in detail the complex pattern of the timings of the different effects. Joule's power is generally responsible for ~ 75-80% of magmatism, and friction power only for ~ 20-25%; but, on some occasions almost ~ 100% is fuelled by friction alone. The visco-elastic coupling between lithosphere and asthenosphere results ~ 96% viscous, and ~ 4% elastic.

  10. A Comparative Analysis of Seismological and Gravimetric Crustal Thicknesses below the Andean Region with Flat Subduction of the Nazca Plate

    Directory of Open Access Journals (Sweden)

    Mario E. Gimenez

    2009-01-01

    Full Text Available A gravimetric study was carried out in a region of the Central Andean Range between 28∘ and 32∘ south latitudes and from 72∘ and 66∘ west longitudes. The seismological and gravimetrical Moho models were compared in a sector which coincides with the seismological stations of the CHARGE project. The comparison reveals discrepancies between the gravity Moho depths and those obtained from seismological investigations (CHARGE project, the latter giving deeper values than those resulting from the gravimetric inversion. These discrepancies are attenuated when the positive gravimetric effect of the Nazca plate is considered. Nonetheless, a small residuum of about 5 km remains beneath the Cuyania terrane region, to the east of the main Andean chain. This residuum could be gravimetrically justified if the existence of a high density or eclogitized portion of the lower crust is considered. This result differed from the interpretations from Project “CHARGE” which revealed that the entire inferior crust extending from the Precordillera to the occidental “Sierras Pampeanas” could be “eclogitized”. In this same sector, we calculated the effective elastic thickness (Te of the crust. These results indicated an anomalous value of Te = 30 km below the Cuyania terrane. This is further conclusive evidence of the fact that the Cuyania terrane is allochthonous, for which also geological evidences exist.

  11. Holocene faulting in the Bellingham forearc basin: upper-plate deformation at the northern end of the Cascadia subduction zone

    Science.gov (United States)

    Kelsey, Harvey M.; Sherrod, Brian L.; Blakely, Richard J.; Haugerud, Ralph A.

    2013-01-01

    The northern Cascadia forearc takes up most of the strain transmitted northward via the Oregon Coast block from the northward-migrating Sierra Nevada block. The north-south contractional strain in the forearc manifests in upper-plate faults active during the Holocene, the northern-most components of which are faults within the Bellingham Basin. The Bellingham Basin is the northern of four basins of the actively deforming northern Cascadia forearc. A set of Holocene faults, Drayton Harbor, Birch Bay, and Sandy Point faults, occur within the Bellingham Basin and can be traced from onshore to offshore using a combination of aeromagnetic lineaments, paleoseismic investigations and scarps identified using LiDAR imagery. With the recognition of such Holocene faults, the northernmost margin of the actively deforming Cascadia forearc extends 60 km north of the previously recognized limit of Holocene forearc deformation. Although to date no Holocene faults are recognized at the northern boundary of the Bellingham Basin, which is 15 km north of the international border, there is no compelling tectonic reason to expect that Holocene faults are limited to south of the international border.

  12. A revised estimate of Pacific-North America motion and implications for Western North America plate boundary zone tectonics

    Science.gov (United States)

    Demets, Charles; Gordon, Richard G.; Stein, Seth; Argus, Donald F.

    1987-01-01

    Marine magnetic profiles from the Gulf of Californa are studied in order to revise the estimate of Pacific-North America motion. It is found that since 3 Ma spreading has averaged 48 mm/yr, consistent with a new global plate motion model derived without any data. The present data suggest that strike-slip motion on faults west of the San Andreas is less than previously thought, reducing the San Andreas discrepancy with geodetic, seismological, and other geologic observations.

  13. Is subduction really in the plate tectonics driving seat, or do two other global mechanisms do the driving? A review in the 'deep-keeled cratons' frame for global dynamics

    Science.gov (United States)

    Osmaston, M. F.

    2012-04-01

    Introduction. The title poses a question very like that of my talk in 2003 [1], concluding then that, as a driver, subduction comes 'a doubtful third'. My purpose here is to show that subsequent developments now cause even that limited status to be denied it with great assurance, except in a rare situation, of which there is no current example. The key point is that studies of subduction have been importantly mistaken as to the nature of the plate arriving for subduction. Deep-keeled cratons? The 'deep-keeled cratons' frame for global dynamics [2 - 5] is the result of seeking Earth-behaviour guidance on the following outside-the-box proposition:- "If cratons have tectospheric keels that reach or approach the 660 km discontinuity, AND the 660 level is an effective barrier to mantle circulation, then obviously (i) when two cratons separate, the upper mantle to put under the nascent ocean must arrive by a circuitous route and, conversely, (ii) if they approach one another, the mantle volume that was in between them must get extruded sideways." Remarkably it has turned out [2 - 5] that Earth dynamical behaviour for at least the past 150 Ma provides persuasive affirmation of both these expectations and that the explanation for the otherwise-unexpected immobility of subcratonic material to such depths is a petrological one which is also applicable to the behaviour of LVZ mantle below MORs [6 - 8]. Straight away this result has major consequences for the character of the plate arriving for subduction. First, to construct them, we need a 'thick-plate' (>100km?) model of the MOR process which recognizes that this LVZ immobility renders invalid the existing concept of divergent mantle flow below MORs. I show that my now not-so-new model [1, 8 - 10], based on a deep, narrrow, wall-accreting sub-axis crack, possesses outstandingly relevant properties, even appropriately dependent on spreading rate. Second, the oceanic plate arriving for subduction is no longer just the cooled

  14. Horizontal mantle flow controls subduction dynamics.

    Science.gov (United States)

    Ficini, E; Dal Zilio, L; Doglioni, C; Gerya, T V

    2017-08-08

    It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age -the main control on buoyancy- exhibits little correlation with most of the present-day subduction velocities and slab dips. "West"-directed subduction zones are on average steeper (~65°) than "East"-directed (~27°). Also, a "westerly"-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an "easterly"-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

  15. Dynamics of intraoceanic subduction initiation: 2D thermomechanical modeling

    Science.gov (United States)

    Zhou, X.; Gerya, T.; LI, Z.; Stern, R. J.

    2016-12-01

    Intraoceanic subduction initiation occurs in previous weak zones which could be transform faults or old fracture zones, and concurrents with the change of plate motions. It is an important process to understand the beginning of plate tectonics. However, the dynamic process during (after) subduction initiation remain obscure. The process of suducting slabs move from down to downdip is also not revealed clearly. In order to obtain better understanding of the transitional process of subducting slab motion, we use finite difference and marker-in-cell methods to establish a series of self-sustainable subduction initiation models and explore many visco-plastic parameters to qualify the dynamical process of subduction initiation. The following parameters are systematic tested: (1) the age of the subducting slab; (2) friction coefficient of the mantle material; (3) the mantle potential temperature; (4) the age of the overriding slab. We find out the critical age of the oceanic lithosphere which can produce subduction initiation. And the age of subducting slab plays important roles during subduction initiation. The young subducting slab induces fast trench retreat and then trench begin to advance. For the old subducting slab, it induces relative slower trench retreat and then stop moving. The age of overriding slabs impacts coupling with the subducting slab. The friction coefficient of lithosphere also impacts the backarc spreading and subduction velocity. Stronger subducted plate gives lower subduction velocity and faster trench retreat velocity. The mantle potential temperature changes the critical age of subducted slabs.

  16. Intra-oceanic subduction shaped the assembly of Cordilleran North America.

    Science.gov (United States)

    Sigloch, Karin; Mihalynuk, Mitchell G

    2013-04-04

    The western quarter of North America consists of accreted terranes--crustal blocks added over the past 200 million years--but the reason for this is unclear. The widely accepted explanation posits that the oceanic Farallon plate acted as a conveyor belt, sweeping terranes into the continental margin while subducting under it. Here we show that this hypothesis, which fails to explain many terrane complexities, is also inconsistent with new tomographic images of lower-mantle slabs, and with their locations relative to plate reconstructions. We offer a reinterpretation of North American palaeogeography and test it quantitatively: collision events are clearly recorded by slab geometry, and can be time calibrated and reconciled with plate reconstructions and surface geology. The seas west of Cretaceous North America must have resembled today's western Pacific, strung with island arcs. All proto-Pacific plates initially subducted into almost stationary, intra-oceanic trenches, and accumulated below as massive vertical slab walls. Above the slabs, long-lived volcanic archipelagos and subduction complexes grew. Crustal accretion occurred when North America overrode the archipelagos, causing major episodes of Cordilleran mountain building.

  17. Modeling Crustal Thickness Variations Beneath the East Pacific Rise: Mantle Diapirs or Plate Kinematics?

    Science.gov (United States)

    George, S. A.; Toomey, D. R.

    2003-12-01

    Geophysical studies along the East Pacific Rise between the Siqueiros and Clipperton fracture zones reveal along- and cross-axis variations in crustal thickness whose origins are poorly understood. By one view, variations in crustal thickness are the result of three-dimensional upwelling of the mantle associated with a melt-rich diapir centered at 9° 50'N. Alternatively, it has been proposed that the migration of the 9° 03'N overlapping spreading center (OSC) alters the thickness of crust by increasing the amount of time that a crustal unit resides near the spreading axis. In this case, crustal thickness variations arise from plate kinematics, and not from three-dimensional variations in mantle upwelling. We report on a modeling study designed to explore how the evolution of OSCs may alter the thickness of newly-formed crust. OSC propagation is modeled using the kinematic algorithm developed by Wilson [1990], modified to track parcels of crust through time. Given an OSC's kinematic history and two-dimensional descriptions of the melt flux out of the mantle (i.e. invariant along the rise), we predict relative variations in crustal thickness. Our modeling assumes that underplating increases the thickness of the crust and/or Moho transition zone as long as a crustal unit resides over the source of mantle-derived melt. Results suggest two general kinematic mechanisms whereby variations in crustal thickness can occur: those due to an offset between the mantle-level magmatic system and the spreading axis, and those due to any relative reduction in the velocity of a crustal unit as it moves off axis. Offset-induced crustal thickness variations are manifest as long-wavelength ( ˜50 km), low-amplitude cross-axis asymmetries. Local slowing of crustal units as they move off axis -- in direct association with the OSC and its overlap basins -- results in relatively short-wavelength ( ˜10 km), high-amplitude variations in crustal thickness. Using a kinematic history

  18. HYBRID ACCRETIONARY/COLLISIONAL MECHANISM OF PALEOZOIC ASIAN CONTINENTAL GROWTH: NEW PLATE TECTONIC PERSPECTIVE

    Directory of Open Access Journals (Sweden)

    Karel Schulmann

    2017-01-01

    Full Text Available Continental crust is formed above subduction zones by well-known process of “juvenile crust growth”. This new crust is in modern Earth assembled into continents by two ways: (i short-lived collisions of continental blocks with the Laurussian or later Eurasian continent along the “Alpine Himalayan collisional/interior orogens” in the heart of the Pangean continental plates realm; and (ii long lived lateral accretion of ocean-floor fragments along “circum-Pacific accretionary/peripheral orogens” at the border of the PaleoPacific and modern Pacific oceanic plate.

  19. The Magellan seamount trail: implications for Cretaceous hotspot volcanism and absolute Pacific plate motion

    Science.gov (United States)

    Koppers, Anthony A. P.; Staudigel, Hubert; Wijbrans, Jan R.; Pringle, Malcolm S.

    1998-11-01

    The Magellan Seamount Trail (MST) delineates a northwest trending chain of four Cretaceous guyots in the West Pacific Seamount Province (WPSP). Seamount morphology, 40Ar/ 39Ar geochronology and Sr-Nd-Pb geochemistry of the MST provides evidence for a hotspot origin between the Samoa, Rarotonga and Society hotspots of the South Pacific Isotopic and Thermal Anomaly (SOPITA). The MST yields an excellent linear age progression of 47.6±1.6 mm/yr ( r2=1.000; MSWD = 0.23; 1 σ SE) including Vlinder guyot (95.1±0.5 Ma, n=5; 2 σ SD), Pako guyot (91.3±0.3 Ma, n=3) and Ioah guyot (87.1±0.3 Ma, n=2). The MST also exhibits a small range in Sr-Nd-Pb isotopic compositions indicating enriched mantle sources with an affinity of EMI. Nevertheless, three volcanic events are found out of sequence with linear MST hotspot volcanism: (1) an independent volcanic pedestal was formed 4-7 Myr before shield-volcanism started at Vlinder guyot, (2) a post-erosional volcanic cone was formed at least 20-30 Myr after drowning of Vlinder guyot, and (3) Ita Mai Tai guyot (118.1±0.5 Ma, n=3) was formed 34-36 Myr before the MST hotspot arrived at the predicted location of this guyot. By identifying and ruling out discordant volcanic events, we can use the age progression in MST to test the fixity of its hotspot. When presuming the fixed hotspot hypothesis, the local age progressions of the MST (47.6±1.6 mm/yr) and the copolar Musicians seamount trail (55.8±6.4 mm/yr) are not compatible with their 100-80 Ma Euler pole. We investigate two options: (1) acceptance of a `forced' Euler pole obeying the hotspot hypothesis by using both the age progressions and the azimuths of the studied seamount trails, or (2) acceptance of a `best-fit' Euler pole by using the azimuths of the studied seamount trail exclusively. In the first option, the angular speed of the Pacific plate during the 100-80 Ma stage pole is calculated at 0.502±0.017°/Myr. In the second option, the `best-fit' Euler pole is found

  20. A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc

    NARCIS (Netherlands)

    Arculus, Richard J.; Ishizuka, Osamu; Bogus, Kara A.; Gurnis, Michael; Hickey-Vargas, Rosemary; Aljahdali, Mohammed H.; Bandini-Maeder, Alexandre N.; Barth, Andrew P.; Brandl, Philipp A.; Drab, Laureen; Do Monte Guerra, Rodrigo; Hamada, Morihisa; Jiang, Fuqing; Kanayama, Kyoko; Kender, Sev; Kusano, Yuki; Li, He; Loudin, Lorne C.; Maffione, Marco; Marsaglia, Kathleen M.; McCarthy, Anders; Meffre, Sebastién; Morris, Antony; Neuhaus, Martin; Savov, Ivan P.; Sena, Clara; Tepley, Frank J.; Van Der Land, Cees; Yogodzinski, Gene M.; Zhang, Zhaohui

    2015-01-01

    The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence

  1. Isabella Anomaly: Lithospheric drip, delamination or fragment of the Farallon plate?

    Science.gov (United States)

    Forsyth, D. W.; Rau, C. J.

    2009-12-01

    The Isabella Anomaly or Central Valley Anomaly in California is perhaps the best known example of a high seismic velocity anomaly that has been interpreted as a lithospheric instability. High P and S velocities extend to a depth of at least 150 km and perhaps to several hundred km in a nearly cylindrical region 100-150 km across. The amplitude of the anomaly in the upper 200 km is similar to that of the subducted Gorda plate. This anomaly has been variously interpreted as a convective drip or as a remnant of the lithosphere delaminated from beneath the eastern Sierra Nevada. We suggest instead that the Isabella anomaly may represent a fragment of the subducted Farallon plate that is still attached to the Pacific lithosphere. Directly seaward of the anomaly is the fossil Monterrey microplate, which is a remnant of the Farallon plate that was left when subduction ceased before the spreading center itself subducted. The microplate was then incorporated into the Pacific plate, but it is not clear how much of the subducting slab remained attached to the surface microplate. New Rayleigh wave tomographic images of Baja California show that there are still fragments of the Farallon plate remaining attached to the unsubducted Guadelupe and Magdelena microplate remnants, with anomalies extending down to at least 150 km. The geometry of these anomalies in relationship to the microplates is very similar to that of the Isabella anomaly. A major question with this interpretation is whether a bit of oceanic lithosphere extending down into the asthenosphere could be dragged along with the surface microplate/Pacific plate for 20 Ma since subduction ceased. Another anomaly similar to the Isabella anomaly begins in the shallow mantle beneath the northern end of San Francisco bay and dips to the west - another candidate for a lithospheric drip or convective instability?

  2. Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback

    NARCIS (Netherlands)

    Stegman, D. R.; Freeman, J.A.; Schellart, W. P.; Moresi, L.; May, D.

    Subduction of tectonic plates limited in lateral extent and with a free-trailing tail, i.e., "free subduction,'' is modeled in a three-dimensional (3-D) geometry. The models use a nonlinear viscoplastic rheology for the subducting plate and exhibit a wide range of behaviors depending on such plate

  3. Seismicity and the subduction process

    Science.gov (United States)

    Ruff, L.; Kanamori, H.

    1980-01-01

    There is considerable variation between subduction zones in the largest characteristic earthquake within each zone. Assuming that coupling between downgoing and upper plates is directly related to characteristic earthquake size, tests for correlations between variation in coupling and other physical features of subduction zones are conducted: the lateral extent and penetration depth of Benioff zones, age of subducting lithosphere, convergence rate, and back-arc spreading. Using linear multivariate regression, coupling is correlated with two variables: convergence rate and lithosphere age. Secondary correlations within the data set are penetration depth versus lithosphere age, and lateral extent versus convergence rate. Taken together, the observed correlations suggest a simple qualitative model where convergence rate and lithosphere age determine the horizontal and sinking rates, respectively, of slabs: these parameters influence the seismic coupling in the subduction zone. In the limit of a fast sinking rate and slow convergence rate, back-arc spreading occurs and thereby appears to be a passive process.

  4. The earthquake cycle in subduction zones

    Science.gov (United States)

    Melosh, H. J.; Fleitout, L.

    1982-01-01

    A simplified model of a subduction zone is presented, which incorporates the mechanical asymmetry induced by the subducted slab to anchor the subducting plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the trench moves with respect to the deep mantle toward the subducting plate at a velocity equal to one-half of the convergence rate. A strong extensional pulse is propagated into the overthrust plate shortly after the earthquake, and although this extension changes into compression before the next earthquake in the cycle, the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back-arc region.

  5. Crustal strain phenomena in the Solomon Islands, constraints from field evidence, and relationship to the India-Pacific plates' boundary

    Science.gov (United States)

    Ramsay, W. R. H.

    1982-08-01

    The Solomon Islands lie along the India-Pacific plates' margin and have recorded a history of deformation resulting from the interaction of these two plates. Various kinematic models have been proposed for the Solomons and these have involved a variety of plate tectonic processes. It is pointed out that almost without exception these models have been based on a provincial geological classification of the island group in which it is assumed that two of these provinces—Pacific and Central provinces—commenced their geological development in regions distant from one another. Invariably such models require that Santa Isabel represents part of a collision zone between these two provinces, though field evidence from Santa Isabel for such a collision has in the past been largely lacking. These various kinematic models are examined in the light of more recent field evidence, and a premise on which they have been based—initial separate development for two of the provinces—is questioned. Rather it is here suggested that the Central and Pacific provinces developed in roughly similar positions, one with the other as they occur today, and that they were at least in part separated from Oligocene time onward by a linear peridotite-gabbro ridge, Korighole-Florida high, which acted as a sediment barrier to much of the coarser clastic and volcanogenic sedimentation. The initial development of the Solomon Islands began in an oceanic environment with the extrusion of extensive submarine tholeiitic 'flood basalts' and intrusion of associated gabbroic and ultramafic rocks at depth, during the Late Mesozoic to Early Tertiary. This igneous phase occurred with the whole of the island group representing the western margin of the Ontong Java Plateau. Subsequent asymmetric development of the Solomons during the Eocene and Oligocene resulted in uplift, shearing, and the initiation of arc volcanism, plutonism, and arc-related sedimentation in the Central province to the west. In contrast

  6. Indonesian Landforms and Plate Tectonics

    Directory of Open Access Journals (Sweden)

    Herman Th. Verstappen

    2014-06-01

    Full Text Available DOI: 10.17014/ijog.v5i3.103The horizontal configuration and vertical dimension of the landforms occurring in the tectonically unstable parts of Indonesia were resulted in the first place from plate tectonics. Most of them date from the Quaternary and endogenous forces are ongoing. Three major plates – the northward moving Indo-Australian Plate, the south-eastward moving SE-Asian Plate and the westward moving Pacific Plate - meet at a plate triple-junction situated in the south of New Guinea’s Bird’s Head. The narrow North-Moluccan plate is interposed between the Asia and Pacific. It tapers out northward in the Philippine Mobile Belt and is gradually disappearing. The greatest relief amplitudes occur near the plate boundaries: deep ocean trenches are associated with subduction zones and mountain ranges with collision belts. The landforms of the more stable areas of the plates date back to a more remote past and, where emerged, have a more subdued relief that is in the first place related to the resistance of the rocks to humid tropical weathering Rising mountain ranges and emerging island arcs are subjected to rapid humid-tropical river erosions and mass movements. The erosion products accumulate in adjacent sedimentary basins where their increasing weight causes subsidence by gravity and isostatic compensations. Living and raised coral reefs, volcanoes, and fault scarps are important geomorphic indicators of active plate tectonics. Compartmental faults may strongly affect island arcs stretching perpendicular to the plate movement. This is the case on Java. Transcurrent faults and related pull-apart basins are a leading factor where plates meet at an angle, such as on Sumatra. The most complicated situation exists near the triple-junction and in the Moluccas. Modern research methods, such as GPS measurements of plate movements and absolute dating of volcanic outbursts and raised coral reefs are important tools. The mega-landforms resulting

  7. Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

    NARCIS (Netherlands)

    Schellart, W. P.; Rawlinson, N.

    2013-01-01

    The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, Japan) and others producing relatively small earthquakes (e.g.

  8. Dynamics of intraoceanic subduction initiation : 1. Oceanic detachment fault inversion and the formation of supra-subduction zone ophiolites

    NARCIS (Netherlands)

    Maffione, Marco; Thieulot, Cedric|info:eu-repo/dai/nl/270177493; van Hinsbergen, Douwe J.J.|info:eu-repo/dai/nl/269263624; Morris, Antony; Plümper, Oliver|info:eu-repo/dai/nl/37155960X; Spakman, Wim|info:eu-repo/dai/nl/074103164

    Subduction initiation is a critical link in the plate tectonic cycle. Intraoceanic subduction zones can form along transform faults and fracture zones, but how subduction nucleates parallel to mid-ocean ridges, as in e.g., the Neotethys Ocean during the Jurassic, remains a matter of debate. In

  9. Tectonomagmatic controls on Gondwana break-up models: Evidence from the Proto-Pacific Margin of Antarctica

    Science.gov (United States)

    Storey, Bryan C.; Alabaster, Tony

    1991-12-01

    Geochemical and isotopic data are presented that suggest the existence of a large, Middle Jurassic subduction-related magmatic province common to both the Antarctic Peninsula and southern South America. We argue that during the initial stages of Gondwana breakup, Pacific margin magmas were derived from an enriched lithospheric mantle source similar to that for the contemporaneous within-plate Ferrar-Tasman suite. Enriched lithospheric initial-rifting magmas were succeeded, in at least part of the Rocas Verdes basin, by transitional early drift magmas and then by entirely asthenospheric mid-ocean ridge basalt (MORB) magmas representing lithospheric rupture and seafloor spreading. We propose a plate interaction model for the initial stages of Gondwana breakup relating the broad zone of lithospheric mantle melting to a reduction in plate boundary forces. The change from Gondwanide compression to lithospheric extension in the Jurassic is linked to a change from shallow to steeply dipping subduction and to a slowing of subduction rates caused possibly by a decreasing age of the subducting plate. Ridge-trench interaction may have followed subduction of young, hot oceanic lithosphere, possibly causing a temporary cessation of subduction and a further reduction in plate boundary forces, thus facilitating breakup.

  10. PLATE

    DEFF Research Database (Denmark)

    Kling, Joyce; Hjulmand, Lise-Lotte

    2008-01-01

    the Project in Language Assessment for Teaching in English (PLATE) language professionals from CBS’s Language Center observe teachers and provide feedback using evaluation criteria from the Common European Framework for Reference (CEFR) supplemented by some additional criteria which take the LSP nature......’s level of English is sufficient for the increasing number of courses offered in English each semester. This paper addresses these concerns and describes a pilot project initiated in 2003 at CBS to gauge the overall English language proficiency of those teaching content courses in English. Through...

  11. Kinematics of subduction and subduction-induced flow in the upper mantle

    NARCIS (Netherlands)

    Schellart, W. P.

    2004-01-01

    Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense highviscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not

  12. Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution.

    Science.gov (United States)

    Keith, S A; Baird, A H; Hughes, T P; Madin, J S; Connolly, S R

    2013-07-22

    Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions.

  13. Global patterns in Earth's dynamic topography since the Jurassic: the role of subducted slabs

    Science.gov (United States)

    Rubey, Michael; Brune, Sascha; Heine, Christian; Rhodri Davies, D.; Williams, Simon E.; Dietmar Müller, R.

    2017-09-01

    We evaluate the spatial and temporal evolution of Earth's long-wavelength surface dynamic topography since the Jurassic using a series of high-resolution global mantle convection models. These models are Earth-like in terms of convective vigour, thermal structure, surface heat-flux and the geographic distribution of heterogeneity. The models generate a degree-2-dominated spectrum of dynamic topography with negative amplitudes above subducted slabs (i.e. circum-Pacific regions and southern Eurasia) and positive amplitudes elsewhere (i.e. Africa, north-western Eurasia and the central Pacific). Model predictions are compared with published observations and subsidence patterns from well data, both globally and for the Australian and southern African regions. We find that our models reproduce the long-wavelength component of these observations, although observed smaller-scale variations are not reproduced. We subsequently define geodynamic rules for how different surface tectonic settings are affected by mantle processes: (i) locations in the vicinity of a subduction zone show large negative dynamic topography amplitudes; (ii) regions far away from convergent margins feature long-term positive dynamic topography; and (iii) rapid variations in dynamic support occur along the margins of overriding plates (e.g. the western US) and at points located on a plate that rapidly approaches a subduction zone (e.g. India and the Arabia Peninsula). Our models provide a predictive quantitative framework linking mantle convection with plate tectonics and sedimentary basin evolution, thus improving our understanding of how subduction and mantle convection affect the spatio-temporal evolution of basin architecture.

  14. Global patterns in Earth's dynamic topography since the Jurassic: the role of subducted slabs

    Directory of Open Access Journals (Sweden)

    M. Rubey

    2017-09-01

    Full Text Available We evaluate the spatial and temporal evolution of Earth's long-wavelength surface dynamic topography since the Jurassic using a series of high-resolution global mantle convection models. These models are Earth-like in terms of convective vigour, thermal structure, surface heat-flux and the geographic distribution of heterogeneity. The models generate a degree-2-dominated spectrum of dynamic topography with negative amplitudes above subducted slabs (i.e. circum-Pacific regions and southern Eurasia and positive amplitudes elsewhere (i.e. Africa, north-western Eurasia and the central Pacific. Model predictions are compared with published observations and subsidence patterns from well data, both globally and for the Australian and southern African regions. We find that our models reproduce the long-wavelength component of these observations, although observed smaller-scale variations are not reproduced. We subsequently define geodynamic rules for how different surface tectonic settings are affected by mantle processes: (i locations in the vicinity of a subduction zone show large negative dynamic topography amplitudes; (ii regions far away from convergent margins feature long-term positive dynamic topography; and (iii rapid variations in dynamic support occur along the margins of overriding plates (e.g. the western US and at points located on a plate that rapidly approaches a subduction zone (e.g. India and the Arabia Peninsula. Our models provide a predictive quantitative framework linking mantle convection with plate tectonics and sedimentary basin evolution, thus improving our understanding of how subduction and mantle convection affect the spatio-temporal evolution of basin architecture.

  15. Structural variation of the oceanic Moho in the Pacific plate revealed by active-source seismic data

    Science.gov (United States)

    Ohira, Akane; Kodaira, Shuichi; Nakamura, Yasuyuki; Fujie, Gou; Arai, Ryuta; Miura, Seiichi

    2017-10-01

    The characteristics of the oceanic Moho are known to depend on various factors, such as seafloor spreading rate, crustal age, and accretionary processes at a ridge. However, the effect of local magmatic activities on the seismic signature of the Moho is poorly understood. Here an active-source reflection and refraction survey is used to investigate crustal structure and Moho characteristics along a >1000-km-long profile southeast of the Shatsky Rise in a Pacific Ocean basin formed from the Late Jurassic to Early Cretaceous and spanning the onset of Shatsky Rise volcanism. Although the seismic velocity structure estimated from the refraction data showed typical characteristics of the oceanic crust of the old Pacific plate, the appearance of the Moho reflections was spatially variable. We observed clear Moho reflections such as those to be expected where the spreading rate is fast to intermediate only at the southwestern end of the profile, whereas Moho reflections were diffuse, weak, or absent along other parts of the profile. The poor Moho reflections can be explained by the presence of a thick crust-mantle transition layer, which is temporally coincident with the formation of the Shatsky Rise. We inferred that the crust-mantle transition layer was formed by changes in on-axis accretion process or modification of the primary Moho by off-axis magmatism, induced by magmatic activity of the Shatsky Rise.

  16. Coherent tilt signals observed in the Shumagin seismic gap Detection of time-dependent subduction at depth?

    Science.gov (United States)

    Beavan, J.; Bilham, R.; Hurst, K.

    1984-01-01

    Repeated surveys of short level lines in the Shumagin Islands, Alaska, reveal coherent tilt signals associated with subduction of the Pacific plate beneath the North American plate in the Shumagin seismic gap. Ten years of steady tilt down toward the trench is interrupted during 1978-1980 by a rapid episode of reverse tilt. The 'normal' tilt represents surface deformation as subduction occurs, with the plate boundary locked to at least 60 km depth. Using all available tilt, sea level, and seismic data, the tilt reversal is interpreted as due to an episodic reverse slip of about 80 cm magnitude on the plate boundary between about 70 km and 20 km depth, downdip from the main seismogenic zone, which remains locked. This event causes an increase of stress on the locked main thrust zone. It is speculated that such events may be a regular process at subduction zones, that great plate boundary earthquakes may be more common during their occurrence, and that their onset may be detectable early enough to give warning of an increase in probability for the occurrence of a great earthquake.

  17. Phanerozoic tectonic evolution of the Circum-North Pacific

    Science.gov (United States)

    Nokleberg, Warren J.; Parfenov, Leonid M.; Monger, James W.H.; Norton, Ian O.; Khanchuk, Alexander I.; Stone, David B.; Scotese, Christopher R.; Scholl, David W.; Fujita, Kazuya

    2000-01-01

    the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in the fragmentation of each continent and the formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. (2) From about the Late Triassic through the mid-Cretaceous, a succession of island arcs and tectonically paired subduction zones formed near the continental margins. (3) From about mainly the mid-Cretaceous through the present, a succession of igneous arcs and tectonically paired subduction zones formed along the continental margins. (4) From about the Jurassic to the present, oblique convergence and rotations caused orogenparallel sinistral and then dextral displacements within the upper-plate margins of cratons that have become Northeast Asia and North America. The oblique convergences and rotations resulted in the fragmentation, displacement, and duplication of formerly more nearly continuous arcs, subduction zones, and passive continental margins. These fragments were subsequently accreted along the expanding continental margins. (5) From the Early Jurassic through Tertiary, movement of the upper continental plates toward subduction zones resulted in strong plate coupling and accretion of the former island arcs and subduction zones to the continental margins. Accretions were accompanied and followed by crustal thickening, anatexis, metamorphism, and uplift. The accretions resulted in substantial growth of the North Asian and North American Continents. (6) During the middle and late Cenozoic, oblique to orthogonal convergence of the Pacifi c plate with present-day Alaska and Northeast Asia resulted in formation of the modern-day ring of volcanoes around the Circum-North Pacific. Oblique convergence between the Pacific plate and Alaska also resulted in major dextral-slip faulting in interior and southern Alaska and along the western p

  18. Trans Pacific Ocean in surface layer and subduction and re-circulation in the ocean interior of radiocaesium released from TEPCO FNPP1 accident through the end of 2015

    Science.gov (United States)

    Aoyama, Michio; Tsumune, Daisuke; Tsubono, Takaki; Hamajima, Yasunori; Inomata, Yayoi; Kumamoto, Yuichiro

    2016-04-01

    134Cs and 137Cs, hereafter radiocaesium, were released to the North Pacific Ocean by two major likely pathways, direct discharge from the Fukushima NPP1 accident site and atmospheric deposition off Honshu Islands of Japan, east and northeast of the site. Activities of radiocaesium released by the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident were measured by surface sampling at 408 stations in 2011-2013 and in vertical profiles at 24 stations in 2011 and 2012, at 13 station in 2015 in the North Pacific Ocean, and time-series samples were collected at two coastal stations. TEPCO and Japanese government also continue to monitor radiocaesium in seawaters close to the site. In this presentation, we present long term behavior of TEPCO FNPP1 released radiocaesium in the coastal region and the North Pacific Ocean based on the observations and model simulations during the period from just after the accident to 2016. After July 2012, 137Cs activity in the surface water near FNPP1 remained around 1000 Bq m-3 until the end of 2014, which corresponds to a discharge rate of about 10 GBq day-1. In 2015 137Cs activity in the surface water near FNPP1 tended to decrease around 100 Bq m-3. 137Cs activity at southern coastal stations at Tomioka became less than 100 Bq m-3 in 2014 and those at Hasaki became less than 10 Bq m-3 which are same level or less than those of 137Cs activity in surface water observed in 1960s in this region. FNPP1-derived radiocaesium spread eastward in surface water across the mid-latitude North Pacific with a speed of 7 km day-1 (8 cm s-1) until March 2012, and of 3 km day-1 (3.5 cm s-1) from March 2012 through August 2014. And Fukushima derived radiocaesium had detected trace amount at western coast of Canada in February 2015. Our model simulation results shows good agreement with the observed radiocaesium activities at western coast of Canada, while in the Mexican coast our model projection shows that it will reach in 2016 not in 2015. In June

  19. Earthquake nucleation in weak subducted carbonates

    NARCIS (Netherlands)

    Kurzawski, Robert M.; Stipp, Michael; Niemeijer, André R.; Spiers, Chirstopher J.; Behrmann, Jan H.

    Ocean-floor carbonate- and clay-rich sediments form major inputs to subduction zones, especially at low-latitude convergent plate margins. Therefore, knowledge of their frictional behaviour is fundamental for understanding plate-boundary earthquakes. Here we report results of mechanical tests

  20. Using paleomagnetism to expand the observation time window of plate locking along subduction zones: evidence from the Chilean fore-arc sliver (38°S - 42°S)

    Science.gov (United States)

    Hernandez-Moreno, Catalina; Speranza, Fabio; Di Chiara, Anita

    2017-04-01

    Fore-arc crustal motion has been usually addressed by the analysis of earthquake slip vectors and, since the last twenty years, by velocity fields derived from Global Positioning System (GPS) data. Yet this observation time window (few decades) can be significantly shorter than a complete seismic cycle or constrained to interseismic periods where the postseismic deformation release, the vicinity of other important faults, and the slip partitioning in oblique subduction may hinder the finite deformation pattern. Paleomagnetic data may yield finite rotations occurring since rock formation, thus provide a much longer observation time span in the order of millions or tens of millions of years. The cumulative permanent or nonreversing deformation in function of the considered geological formation age can represent the average over many seismic cycles, thus significantly complement "instantaneous" information derived from seismic and GPS data. With the aim of evaluate the strike-variation and evolution of the plate coupling along the Chilean subduction zone, here we report on the paleomagnetism of 43 Oligocene-Pleistocene volcanic sites from the fore-arc sliver between 38°S and 42°S. Sites were gathered west of the 1000 km long Liquiñe-Ofqui dextral fault zone (LOFZ) that represents the eastern fore-arc sliver boundary. Nineteen reliable sites reveal that the fore arc is characterized by counterclockwise (CCW) rotations of variable magnitude, except at 40°S - 41°S, where ultrafast (>50°/Myr) clockwise (CW) rotations occur within a 30 km wide zone adjacent to the LOFZ. CCW rotation variability (even at close sites) and rapidity (>10°/Myr) suggest that the observed block rotation pattern is related to NW-SE seismically active sinistral faults crosscutting the whole fore arc. According to previously published data, CW rotations up to 170° also occur east of the LOFZ and have been related to ongoing LOFZ shear. We suggest that the occurrence and width of the eastern

  1. Create Your Plate

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    Full Text Available ... Pacific Islanders American Indian/Alaska Native Programs Older Adults Family Link Diabetes EXPO Upcoming Diabetes EXPOs EXPO ... Plate! Click on the plate sections below to add your food choices. Reset Plate Share Create Your ...

  2. Subduction trench migration since the Cretaceous

    Science.gov (United States)

    Williams, S.; Flament, N. E.; Müller, D.; Butterworth, N. P.

    2015-12-01

    Much of our knowledge about subduction zone processes is derived from analyzing present-day Earth. Several studies of contemporary plate motions have investigated the balance between retreating and advancing trenches and shown that subduction zone kinematics are sensitive to the choice of Absolute Plate Motion (APM) model (or "reference frame"). For past times, the absolute motions of the lithospheric plates relative to the Earth's deep interior over tens of millions of years are commonly constrained using observations from paleomagnetism and age-progressive seamount trails. In contrast, a reference frame linking surface plate motions to subducted slab remnants mapped from seismic tomography has recently been proposed. APM models derived using different methodologies, different subsets of hotspots, or differing assumptions of hotspot motion, have contrasting implications for parameters that describe the long term state of the plate-mantle system, such as the balance between advance and retreat of subduction zones, plate velocities, and net lithospheric rotation. Here we quantitatively compare the subduction zone kinematics, net lithospheric rotation and fit to hotspot trails derived the last 130 Myr for a range of alternative reference frames and a single relative plate motion model. We find that hotspot and tomographic slab-remnant reference frames yield similar results for the last 70 Myr. For the period between 130 and 70 Ma, when hotspot trails become scarce, hotspot reference frames yield a much more dispersed distribution of slab advance and retreat velocities, which is considered geodynamically less plausible. By contrast, plate motions calculated using the slab-remnant reference frame, or using a reference frame designed to minimise net rotation, yield more consistent subduction zone kinematics for times older than 70 Ma. Introducing the global minimisation of trench migration rates as a key criterion in the construction of APM models forms the foundation

  3. Interactions between strike-slip earthquakes and the subduction interface near the Mendocino Triple Junction

    Science.gov (United States)

    Gong, Jianhua; McGuire, Jeffrey J.

    2018-01-01

    The interactions between the North American, Pacific, and Gorda plates at the Mendocino Triple Junction (MTJ) create one of the most seismically active regions in North America. The earthquakes rupture all three plate boundaries but also include considerable intraplate seismicity reflecting the strong internal deformation of the Gorda plate. Understanding the stress levels that drive these ruptures and estimating the locking state of the subduction interface are especially important topics for regional earthquake hazard assessment. However owing to the lack of offshore seismic and geodetic instruments, the rupture process of only a few large earthquakes near the MTJ have been studied in detail and the locking state of the subduction interface is not well constrained. In this paper, first, we use the second moments inversion method to study the rupture process of the January 28, 2015 Mw 5.7 earthquake on the Mendocino transform fault that was unusually well recorded by both onshore and offshore strong motion instruments. We estimate the rupture dimension to be approximately 6 km by 3 km corresponding to a stress drop of ∼4 MPa for a crack model. Next we investigate the frictional state of the subduction interface by simulating the afterslip that would be expected there as a result of the stress changes from the 2015 earthquake and a 2010 Mw 6.5 intraplate earthquake within the subducted Gorda plate. We simulate afterslip scenarios for a range of depths of the downdip end of the locked zone defined as the transition to velocity strengthening friction and calculate the corresponding surface deformation expected at onshore GPS monuments. We can rule out a very shallow downdip limit owing to the lack of a detectable signal at onshore GPS stations following the 2010 earthquake. Our simulations indicate that the locking depth on the slab surface is at least 14 km, which suggests that the next M8 earthquake rupture will likely reach the coastline and strong shaking

  4. Seismic coupling and uncoupling at subduction zones

    Science.gov (United States)

    Ruff, L.; Kanamori, H.

    1983-01-01

    Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

  5. Investigation on subduction erosion of the Central Costa Rica margin with seismic wide- angle data

    Science.gov (United States)

    Zhu, J.; Flueh, E. R.; Kopp, H.; Klaeschen, D.

    2007-12-01

    Seismic wide-angle investigations along the Pacific margin off Central Costa Rica were carried out using closely spaced ocean bottom hydrophones and seismometers along two parallel strike and two parallel dip lines, intersecting at the mid slope. The structure and the P-wave velocities of the subducted oceanic Cocos Plate and overriding Carribean Plate were determined by modeling the wide-angle seismic data combined with the analysis of coincident reflection seismic data and the use of synthetic seismograms. Detailed velocity-depth distributions of two dip-lines and two strike-lines on the continental slope will be presented. Below the slope sediment, a wedge-shaped body, the margin wedge is defined by high velocities (4.3-6.1 km/s). This wedge shows a high velocity gradient zone in the uppermost one to two km, underlain by a low velocity gradient to the plate boundary. Between the subducted plate and overriding plate the low velocity zone including a lense-type structure is seen. This Megalens (4.0-4.3 km/s) and the subducted sediment comprise a low velocity zone (LVZ) all along the plate boundary. This LVZ is constrained by joint analysis of reflection seismic data and wide-angle data. The thickness of the wedge varies along the strike, this is associated with the subduction of the extension of Quepos Plateau, which also resulted in uplift of the margin. The extensional forearc environment is manifested by the normal faults indicated on the the multi-channel seismic (MCS) data. The Megalens is most probably comprised of material transferred from upper margin wedge at the tip of the wedge. The velocity structure within the Megalense resembles the velocities at the tip of the wedge, and is clearly lower than the oceanic crust, but higher thn subducted sediment. If this interpretation is valid, this material has been transported 16 km landward, which implies it was detached from the upper plate 0.2 Ma ago.

  6. Linear volcanoes along the Pacific-Cocos plate boundary, 9°N to the Galapagos triple junction

    Science.gov (United States)

    Lonsdale, Peter

    1985-07-01

    A Seabeam-based reconnaissance of the 500 km of the East Pacific Rise crest between 7°N and 2°40'N shows that the axial ridge is segmented by four 4-13 km non-transform offsets into an en echelon string of distinctively different linear volcanoes. These axial volcanoes are oriented orthogonal to relative plate motion, except where their overlapping ends veer 15° toward each other and where small intra-volcano offsets of their crestal rift zones create abrupt kinks. Longitudinal gradients of the crestlines are less than 5 m/km, except where they plunge at rift-zones' overlapped ends and where they rise locally to small axial peaks. Transverse profiles vary from trapezoidal to triangular, with a steep shield-shaped cross-section being most common. Conventional sounding data indicate that this pattern continues to the 140 km-offset Siqueiros transform fault system at 8.2°N. Within this fault system is a short spreadingcenter volcano contained in a rift valley that links two strike-slip fault zones. Immediately to the north is the shallow 9.0°-8.3°N axial volcano, with unusual relief mapped by a deeply towed instrument package. At the southern end of the plate boundary, as the rise crest enters the region of the Pacific-Cocos-Nazca triple junction, the axial ridge narrows, deepens, and acquires a more irregular long profile. South of 2°30'N the rise crest has a 15 km-wide rift valley that contains multiple volcanic ridges with north-south strikes. Structural hypotheses suggested or supported by these morphologic observations include a point-source magma supply to the spreading center from mantle diapirs, the along-strike continuity of axial magma chambers on fast-spreading rises, even across small rift-zone offsets, and the importance of magma intrusion as well as eruption for building the axial ridge. Hypotheses inconsistent with the new data include magma supply and long-distance dispersal from a few widely spaced plumes, primary control of the topographic

  7. Animated tectonic reconstruction of the Southern Pacific and alkaline volcanism at its convergent margins since Eocene times

    Science.gov (United States)

    Eagles, Graeme; Gohl, Karsten; Larter, Robert D.

    2009-01-01

    An animated reconstruction shows South Pacific plate kinematics, in the reference frame of West Antarctica, between 55 Ma and the present-day. The ocean floor in the region formed due to seafloor spreading between the Antarctic, Pacific, Phoenix and Nazca plates (a plate formed by fragmentation of the Farallon plate early in Oligocene times). The Pacific-Antarctic Ridge remained fairly stable throughout this time, migrating relatively northwestwards, by various mechanisms, behind the rapidly-moving Pacific plate. The Nazca and Phoenix plates also moved quickly, but relatively towards the east or southeast, and were subducted in these directions beneath the South American and Antarctic plates. Segments of spreading centres forming at the trailing edges of the Nazca and Phoenix plates periodically collided with these subduction zones, resulting in the total destruction of the Nazca-Phoenix spreading centre and the partial destruction of the Nazca-Antarctica spreading centre (the Chile Ridge) and Antarctic-Phoenix Ridge, which ceased to operate shortly before its northeasternmost three segments could collide with the Antarctic margin. Following collision of segments of the Chile Ridge, parts of the Antarctic plate underwent subduction at the Chile Trench. After these collisions, slab windows should have formed beneath both the South American and Antarctic convergent margins, and the animation shows occurrences of alkaline volcanism that have been, or can newly be, related to them. Further occurrences of alkali basalts, at the margins of the Powell Basin and, more speculatively, James Ross Island, can be related to the formation of a slab window beneath them following the collision of segments of the South America-Antarctica spreading centre in the northwest Weddell Sea.

  8. Origin and dynamics of depositionary subduction margins

    Science.gov (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli; Kluesner, Jared W.

    2016-01-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a “depositionary forearc,” a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  9. Origin and dynamics of depositionary subduction margins

    Science.gov (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli A.; Kluesner, Jared W.

    2016-06-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a "depositionary forearc," a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  10. 3D geometry of a plate boundary fault related to the 2016 Off-Mie earthquake in the Nankai subduction zone, Japan

    Science.gov (United States)

    Tsuji, Takeshi; Minato, Shohei; Kamei, Rie; Tsuru, Tetsuro; Kimura, Gaku

    2017-11-01

    We used recent seismic data and advanced techniques to investigate 3D fault geometry over the transition from the partially coupled to the fully coupled plate interface inboard of the Nankai Trough off the Kii Peninsula, Japan. We found that a gently dipping plate boundary décollement with a thick underthrust layer extends beneath the entire Kumano forearc basin. The 1 April 2016 Off-Mie earthquake (Mw6.0) and its aftershocks occurred, where the plate boundary décollement steps down close to the oceanic crust surface. This location also lies beneath the trenchward edge of an older accretionary prism (∼14 Ma) developed along the coast of the Kii peninsula. The strike of the 2016 rupture plane was similar to that of a formerly active splay fault system in the accretionary prism. Thus, the fault planes of the 2016 earthquake and its aftershocks were influenced by the geometry of the plate interface as well as splay faulting. The 2016 earthquake occurred within the rupture area of large interplate earthquakes such as the 1944 Tonankai earthquake (Mw8.1), although the 2016 rupture area was much smaller than that of the 1944 event. Whereas the hypocenter of the 2016 earthquake was around the underplating sequence beneath the younger accretionary prism (∼6 Ma), the 1944 great earthquake hypocenter was close to oceanic crust surface beneath the older accretionary prism. The variation of fault geometry and lithology may influence the degree of coupling along the plate interface, and such coupling variation could hinder slip propagation toward the deeper plate interface in the 2016 event.

  11. Subduction zone and crustal dynamics of western Washington; a tectonic model for earthquake hazards evaluation

    Science.gov (United States)

    Stanley, Dal; Villaseñor, Antonio; Benz, Harley

    1999-01-01

    buttress occurs under the North Cascades region of Washington and under southern Vancouver Island. We find that regional faults zones such as the Devils Mt. and Darrington zones follow the margin of this buttress and the Olympic-Wallowa lineament forms its southern boundary east of the Puget Lowland. Thick, high-velocity, lower-crustal rocks are interpreted to be a mafic/ultramafic wedge occuring just above the subduction thrust. This mafic wedge appears to be jointly deformed with the arch, suggesting strong coupling between the subducting plate and upper plate crust in the Puget Sound region at depths >30 km. Such tectonic coupling is possible if brittle-ductile transition temperatures for mafic/ultramafic rocks on both sides of the thrust are assumed. The deformation models show that dominant north-south compression in the coast ranges of Washington and Oregon is controlled by a highly mafic crust and low heat flow, allowing efficient transmission of margin-parallel shear from Pacific plate interaction with North America. Complex stress patterns which curve around the Puget Sound region require a concentration of northwest-directed shear in the North Cascades of Washington. The preferred model shows that greatest horizontal shortening occurs across the Devils Mt. fault zone and the east end of the Seattle fault.

  12. 3-D imaging of two episodes of Hikurangi Plateau subduction in the southern South Island of New Zealand

    Science.gov (United States)

    Eberhart-Phillips, D. M.; Reyners, M.; Upton, P.; Gubbins, D.

    2016-12-01

    The Hikurangi Plateau (originally part of the Ontong Java large igneous province) has been subducted beneath New Zealand twice - firstly at ca. 108-105 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates. We have investigated the southern limit of this subducted plateau by supplementing the sparse GeoNet permanent seismograph network in the southeastern South Island with a forty-station broadband portable seismograph network. We have then used local earthquake tomography to determine detailed 3-D Vp and Vp/Vs structure in the southern South Island. We track a region of Vp 8.5 km/s (which has previously been associated with an eclogite layer at the base of the Hikurangi Plateau from studies in the North Island) across most of the southwestern South Island. Its southeastern edge runs diagonally from near Christchurch to northern Fiordland. It dips both to the northwest and the southwest, and impacts the subducted Australian plate in northern Fiordland, where it currently bends the subducted Australian slab to vertical. The plateau and its leading oceanic crust are distinguished by low Vp/Vs, consistent with extensive dehydration of the thick (ca. 35 km), buoyant plateau during ca. 500 km of flat subduction at the Gondwana margin. The plateau is also revealed by dipping zones of relocated earthquakes. The backstop of Gondwana subduction appears to be the ophiolitic Maitai terrane, which extends through the crust and forms the trenchward boundary of the ca. 60-65 km-thick Median Batholith. We image the low Vp crustal root associated with orogeny at the Gondwana margin in the southeastern South Island, as well as the crustal root resulting from the current convergent episode in the western South Island. The shapes of both crustal roots are controlled by the Hikurangi Plateau.

  13. Megathrust splay faults, forearc basins, and segment boundaries related to the Kodiak Islands segment of the Alaska subduction zone

    Science.gov (United States)

    Ramos, M. D.; Liberty, L. M.

    2016-12-01

    We have compiled and interpreted a comprehensive upper-crustal seismic reflection dataset revealing spatiotemporal Cenozoic deformation across the Kodiak forearc and accretionary prism. Pervasive splay faults and forearc basin growth and positioning with respect to the prism record both accreting and eroding margin episodes through time. Seafloor bathymetry, in conjunction with seismic reflection data, show that post-glacial splay fault motion can exceed 40 meters offshore Kodiak Island. We observe considerable differences in splay fault uplift rates and activation spanning the near-shore region to the continental shelf, with significant tsunamigenic fault motion from the 1964 Great Alaska Earthquake concentrated along the Kodiak Island shelf fault zone system. We utilize potential fields data to highlight the continuity of megathrust splay faults that span the southern Gulf of Alaska and to identify geophysical signatures of segment boundaries that represent subducting Pacific plate morphology which may define megathrust rupture limits. Constraints on interseismic deformation from compiled geodetic GPS, focal mechanism, and earthquake datasets reveal the seismotectonic character of the Kodiak segment and are consistent with the structural heterogeneity at both the plate interface and upper plate. Upper plate geometry of the Kodiak segment shows Holocene fault motion has been accommodated along distinct fault zone segments. This knowledge informs tsunami risk modelers to allow for different alternatives of coseismic splay fault uplift during megathrust rupture. Our results suggest growth of forearc structures is contemporaneous with the subduction of major Pacific plate morphologies and provide clear geophysical evidence that can explain the persistence of the Kodiak segment, which is a major step towards a composite Alaska subduction zone deformation model.

  14. Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations

    Science.gov (United States)

    Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

    2010-12-01

    We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian

  15. Metallogeny of subduction zones

    Directory of Open Access Journals (Sweden)

    Sorokhtin N. O.

    2017-03-01

    Full Text Available The paper deals with the multistage mechanism of the Earth's crust enrichment in ore elements in underthrust zones. The processes of metamorphism and the formation of hydrothermal solutions at pulling of the watered oceanic lithospheric plate into the subduction zone have been described. Some physical and chemical transformation regularities of structural-material complexes in these areas and mechanisms of the formation of ore deposits have been discussed. Spatio-temporal patterns of the localization of a number of endogenetic and exogenetic deposits have been described using metallogeny of the Ural and the Verkhoyansk-Kolyma Fold Belts as an example. It has been shown that in nature there are several effective mechanisms of the enrichment of the crust in ore minerals. One of them is the process of pulling into subduction zone of metalliferous sediments and ferromanganese crusts as well as seabed nodules, their metamorphic transformation, partial melting and transition of ore components into magmatic melts and mineralized fluids. In the future this leads to the release of ore material by magmas and hydrothermal solutions into the folded formations of island-arc and Andean types and the formation of igneous, metasomatic and hydrothermal deposits. Another, yet no less powerful natural mechanism of a conveyor enrichment of the crust in ore elements is the process of destruction and sedimentation of mineral deposits formed in the folded areas as well as the formation of placers and their transfer to the marginal parts of the continent. Later, during the collision of active and passive margins of two lithospheric plates, such as the collision of the Kolyma Massif with the eastern part of the Siberian craton in the middle of the Mesozoic there was a thrusting of a younger lithospheric plate over a more ancient one. As a result, the sedimentary sequences of the passive margin of the Siberian plate were submerged and partially melted by the basic magmas

  16. Plate Tectonics: A Paradigm under Threat.

    Science.gov (United States)

    Pratt, David

    2000-01-01

    Discusses the challenges confronting plate tectonics. Presents evidence that contradicts continental drift, seafloor spreading, and subduction. Reviews problems posed by vertical tectonic movements. (Contains 242 references.) (DDR)

  17. Deep vs. shallow expressions of continental cratons: Can cratonic roots be destroyed by subduction?

    Science.gov (United States)

    Perry-Houts, J.; Calo, M.; Eddy, C. L.; Guerri, M.; Holt, A.; Hopper, E.; Tesoniero, A.; Romanowicz, B. A.; Becker, T. W.; Wagner, L. S.

    2013-12-01

    Cratons are parts of continents that have remained tectonically quiescent over billion-year timescales. Although cratonic lithosphere has the stabilizing properties of chemical buoyancy and high viscosity, it can still be destroyed. The best known example of a missing cratonic root is beneath the eastern North China Craton (NCC). Despite strong evidence for the past existence of a craton in northern China, high heat flow, Mesozoic basin formation, extensive seismicity, and the lack of a fast seismic root imply that the deep cratonic lithosphere is missing. The mechanism for the lithospheric root loss is a source of much debate. Many mechanisms have been proposed, among them: shearing of the lithospheric root by asthenospheric flow induced by the Indo-Eurasian collision; ponding of the Pacific slab in the transition zone acting as a source of fluids that enable hydrous weakening; and thermal erosion due to the corner-flow upwelling of hot, deep material. It is generally agreed that the influence of subduction is key, both from the temporal coincidence of subduction with increased tectonomagmatic activity on the craton and from the spatial correlation of lithospheric loss adjacent to the Pacific trench. We investigate how cratons extend to depth through comparison between seismic signatures of the cratonic lithosphere in the upper mantle and surficial evidence of cratonic boundaries. We examine global and regional tomography, as well as receiver-function constraints on lithospheric thickness in the NCC. We define craton boundaries at the surface through analyses on crust and lithospheric mantle ages and kimberlite locations. We aim to identify regions where the fast cratonic root has been lost or altered beneath Archean and Proterozoic crust and in particular place constraints on the extent of the remaining cratonic root beneath North China. Given the common emphasis on the role of subduction as a driving force for the root loss beneath the eastern NCC, we focus on

  18. New insights into North America-Pacific Plate boundary deformation from Lake Tahoe, Salton Sea and southern Baja California

    Science.gov (United States)

    Brothers, Daniel Stephen

    Five studies along the Pacific-North America (PA-NA) plate boundary offer new insights into continental margin processes, the development of the PA-NA tectonic margin and regional earthquake hazards. This research is based on the collection and analysis of several new marine geophysical and geological datasets. Two studies used seismic CHIRP surveys and sediment coring in Fallen Leaf Lake (FLL) and Lake Tahoe to constrain tectonic and geomorphic processes in the lakes, but also the slip-rate and earthquake history along the West Tahoe-Dollar Point Fault. CHIRP profiles image vertically offset and folded strata that record deformation associated with the most recent event (MRE). Radiocarbon dating of organic material extracted from piston cores constrain the age of the MRE to be between 4.1--4.5 k.y. B.P. Offset of Tioga aged glacial deposits yield a slip rate of 0.4--0.8 mm/yr. An ancillary study in FLL determined that submerged, in situ pine trees that date to between 900-1250 AD are related to a medieval megadrought in the Lake Tahoe Basin. The timing and severity of this event match medieval megadroughts observed in the western United States and in Europe. CHIRP profiles acquired in the Salton Sea, California provide new insights into the processes that control pull-apart basin development and earthquake hazards along the southernmost San Andreas Fault. Differential subsidence (>10 mm/yr) in the southern sea suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline. In contrast to previous models, the rapid subsidence and fault architecture observed in the southern part of the sea are consistent with experimental models for pull-apart basins. Geophysical surveys imaged more than 15 ˜N15°E oriented faults, some of which have produced up to 10 events in the last 2-3 kyr. Potentially 2 of the last 5 events on the southern San Andreas Fault (SAF) were synchronous with rupture on offshore faults, but it appears that ruptures on

  19. Reorganization of convergent plate boundaries. Geologica Ultraiectina (340)

    NARCIS (Netherlands)

    Baes, M.|info:eu-repo/dai/nl/304824739

    2011-01-01

    It is still unclear where a subduction is initiated and what are the responsible mechanisms involved in subduction initiation process. Understanding of subduction initiation will advance our knowledge of how and when plate tectonics started on Earth. Another issue concerning the subduction process

  20. GPS Monitoring of Subduction Zone Deformation in Costa Rica

    Science.gov (United States)

    Lundgren, Paul

    1997-01-01

    The subduction of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high subduction rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America Trench (MAT) provide a unique opportunity to map variations in interseismic strain of the crust above the seismogenic zone in response to variations in seismic coupling.

  1. Surface deformation resulting from subduction and slab detachment

    NARCIS (Netherlands)

    Buiter, S.J.H.

    2000-01-01

    Convergence of lithospheric plates is accommodated at active margins by one plate moving beneath the other into the Earth's mantle. Changes in this subduction process may cause variations in the topography of the Earth's surface near a convergent plate margin. The focus of this thesis lies on

  2. Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan

    OpenAIRE

    TAKASHIMA, REISHI; NISHI, HIROSHI; YOSHIDA, TAKEYOSHI

    2006-01-01

    The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic–Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage ...

  3. Deciphering the 3-D distribution of fluid along the shallow Hikurangi subduction zone using P- and S-wave attenuation

    Science.gov (United States)

    Eberhart-Phillips, Donna; Bannister, Stephen; Reyners, Martin

    2017-11-01

    We use local earthquake velocity spectra to solve for the 3-D distribution of P- and S-wave attenuation in the shallow Hikurangi subduction zone in the North Island of New Zealand to gain insight into how fluids control both the distribution of slip rate deficit and slow-slip events at the shallow plate interface. Qs/Qp gives us information on the 3-D distribution of fluid saturation, which we can compare with the previously determined 3-D distribution of Vp/Vs, which gives information on pore fluid pressure. The Hikurangi margin is unusual, in that a large igneous province (the Hikurangi Plateau) is being subducted. This plateau has had two episodes of subduction—first at 105-100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates. We find that in the southern part of the subduction zone, where there is a large deficit in slip rate at the plate interface, the plate interface region is only moderately fluid-rich because the underlying plateau had already had an episode of dehydration during Gondwana subduction. But fluid pressure is relatively high, due to an impermeable terrane in the upper plate trapping fluids below the plate interface. The central part of the margin, where the slip rate deficit is very low, is the most fluid-rich part of the shallow subduction zone. We attribute this to an excess of fluid from the subducted plateau. Our results suggest this part of the plateau has unusually high fracture permeability, on account of it having had two episodes of bending—first at the Gondwana trench and now at the Hikurangi Trough. Qs/Qp is consistent with fluids migrating across the plate interface in this region, leaving it drained and producing high fluid pressure in the overlying plate. The northern part of the margin is a region of heterogeneous deficit in slip rate. Here the Hikurangi Plateau is subducting for the first time, so there is less fluid available from its

  4. Genesis of ultra-high-Ni olivine in high-Mg andesite lava triggered by seamount subduction.

    Science.gov (United States)

    Nishizawa, Tatsuji; Nakamura, Hitomi; Churikova, Tatiana; Gordeychik, Boris; Ishizuka, Osamu; Haraguchi, Satoru; Miyazaki, Takashi; Vaglarov, Bogdan Stefanov; Chang, Qing; Hamada, Morihisa; Kimura, Jun-Ichi; Ueki, Kenta; Toyama, Chiaki; Nakao, Atsushi; Iwamori, Hikaru

    2017-09-14

    The Kamchatka Peninsula is a prominent and wide volcanic arc located near the northern edge of the Pacific Plate. It has highly active volcanic chains and groups, and characteristic lavas that include adakitic rocks. In the north of the peninsula adjacent to the triple junction, some additional processes such as hot asthenospheric injection around the slab edge and seamount subduction operate, which might enhance local magmatism. In the forearc area of the northeastern part of the peninsula, monogenetic volcanic cones dated at subducted seamount triggered the ascent of Si-rich fluids to vein the wedge peridotite and formed a peridotite-pyroxenite source, causing the temporal evolution of local magmatism with wide compositional range.

  5. Flat-slab subduction, whole crustal faulting, and geohazards in Alaska: Targets for Earthscope

    Science.gov (United States)

    Gulick, S. P.; Pavlis, T. L.; Bruhn, R. L.; Christeson, G. L.; Freymueller, J. T.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Roeske, S.; Reece, R.; van Avendonk, H. J.; Worthington, L. L.

    2010-12-01

    Crustal structure and evolution illuminated by the Continental Dynamics ST. Elias Erosion and tectonics Project (STEEP) highlights some fundamental questions about active tectonics processes in Alaska including: 1) what are the controls on far field deformation and lithospheric stabilization, 2) do strike slip faults extend through the entire crust and upper mantle and how does this influence mantle flow, and 3) how does the transition from “normal” subduction of the Pacific along the Aleutians to flat slab subduction of the Yakutat Terrane beneath southeast and central Alaska to translation of the Yakutat Terrane past North American in eastern Alaska affect geohazard assessment for the north Pacific? Active and passive seismic studies and geologic fieldwork focusing on the Yakutat Terrane show that the Terrane ranges from 15-35 km thick and is underthrusting the North American plate from the St. Elias Mountains to the Alaska Range (~500 km). Deformation of the upper plate occurs within the offshore Pamplona Zone fold and thrust belt, and onshore throughout the Robinson Mountains. Deformation patterns, structural evolution, and the sedimentary products of orogenesis are fundamentally influenced by feedbacks with glacial erosion. The Yakutat megathrust extends beneath Prince William Sound such that the 1964 Mw 9.2 great earthquake epicenter was on this plate boundary and jumped to the adjacent Aleutian megathrust coseismically; this event illuminates the potential for transitional tectonic systems to enhance geohazards. The northern, southern, and eastern limits of the Yakutat microplate are strike-slip faults that, where imaged, appear to cut the entire crustal section and may allow for crustal extrusion towards the Bering Sea. Yakutat Terrane effects on mantle flow, however, have been suggested to cross these crustal features to allow for far-field deformation in the Yukon, Brooks Range, and Amerasia Basin. From the STEEP results it is clear that the Yakutat

  6. Intrinsic and Extrinsic Factors in Subduction Dynamics

    Science.gov (United States)

    Billen, Magali; Arredondo, Katrina

    2014-05-01

    Since the realization that tectonic plates sink into the mantle, in a process we now call subduction, our understanding of this process has improved dramatically through the combined application of observations, theory and modeling. During that time independent research groups focusing on different aspects of subduction have identified factors with a significant impact on subduction, such as three-dimensionality, slab rollback, rheology of the slab and mantle and magnitude of phase changes. However, as each group makes progress we often wonder how these different factors interact as we all strive to understand the real world subduction system. These factors can be divided in two groups: intrinsic factors, including the age of the slab, its thermal structure, composition, and rheology, and extrinsic factors including others forces on plates, overall mantle flow, structure of the overriding plate, rheology of the mantle and phase changes. In addition, while modeling has been a powerful tool for understanding subduction, all models make important (but often necessary) approximations, such as using two dimensions, imposed boundary conditions, and approximations of the conservation equations and material properties. Here we present results of a study in which the "training wheels" are systematically removed from 2D models of subduction to build a more realistic model of subduction and to better understand how combined effects of intrinsic and extrinsic factors contribute to the dynamics. We find that a change from the Boussinesq to the extended Boussinesq form of the conservation equations has a dramatic effect on slab evolution in particular when phase changes are included. Allowing for free (dynamically-driven) subduction and trench motion is numerically challenging, but also an important factor that allows for more direct comparison to observations of plate kinematics. Finally, compositional layering of the slab and compositionally-controlled phase changes also have

  7. Imaging of the subducted Kyushu-Palau Ridge in the Hyuga-nada region, western Nankai Trough subduction zone

    Science.gov (United States)

    Yamamoto, Yojiro; Obana, Koichiro; Takahashi, Tsutomu; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki

    2013-03-01

    We performed 3D seismic tomography of the Hyuga-nada region, western Nankai subduction zone, to investigate the relationship of the subducted part of Kyushu-Palau Ridge (KPR) to coseismic rupture propagation, seismicity, and shallow very low frequency earthquakes. Combining active-source and passive-source data recorded both onshore and offshore, we imaged the deep slab from near the trough axis to the coastal area. Our results show the subducted KPR as a low-velocity belt oriented NW-SE extending down the plate boundary to around 30 km depth. At this depth, we suggest that the subducted KPR detaches from the slab and becomes underplated on the overriding continental plate. As the coseismic slip areas of past large earthquakes do not extend into the subducted KPR, we suggest that it may inhibit rupture propagation. The interior of the subducted KPR shows active intraslab seismicity with a wide depth distribution. Shallow very low frequency earthquakes are continuously active above the location of the subducted KPR, whereas they are intermittent to the northeast of the subducted KPR. Thus, the subducted KPR appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region.

  8. How mantle slabs drive plate tectonics.

    Science.gov (United States)

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-04

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.

  9. Introduction to the structures and processes of subduction zones

    Science.gov (United States)

    Zheng, Yong-Fei; Zhao, Zi-Fu

    2017-09-01

    Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn-subduction

  10. Hafnium at subduction zones: isotopic budget of input and output fluxes; L'hafnium dans les zones de subduction: bilan isotopique des flux entrant et sortant

    Energy Technology Data Exchange (ETDEWEB)

    Marini, J.Ch

    2004-05-15

    Subduction zones are the primary regions of mass exchanges between continental crust and mantle of Earth through sediment subduction toward the earth's mantle and by supply of mantellic magmas to volcanic arcs. We analyze these mass exchanges using Hafnium and Neodymium isotopes. At the Izu-Mariana subduction zone, subducting sediments have Hf and Nd isotopes equivalent to Pacific seawater. Altered oceanic crust has Hf and Nd isotopic compositions equivalent to the isotopic budget of unaltered Pacific oceanic crust. At Luzon and Java subduction zones, arc lavas present Hf isotopic ratios highly radiogenic in comparison to their Nd isotopic ratios. Such compositions of the Luzon and Java arc lavas are controlled by a contamination of their sources by the subducted oceanic sediments. (author)

  11. Ablative subduction - A two-sided alternative to the conventional subduction model

    Science.gov (United States)

    Tao, Winston C.; O'Connell, Richard J.

    1992-01-01

    The plausibility of a two-sided fluid-based model of lithospheric subduction that is based upon current views of lithospheric structure is examined. In this model the viscous lower lithosphere flows downward, and the brittle upper lithosphere deforms in passive response. This process is potentially double-sided, since it is found that even a buoyant plate can be dragged downward by a dense descending neighbor. Thus an apparent overriding plate may be worn away by a process of viscous ablation, with the rate of ablation a function of plate buoyancy. This process, called 'ablative subduction,' makes it possible to simply interpret observations concerning slab profiles, interplate seismicity, back arc tectonics, and complex processes such as double subduction and subduction polarity reversal. When experiments modeling the evolution of simple fluid 'slabs' are performed, slab profile is found to be strongly influenced by ablation in the overriding plate. When ablation is weak, as when a buoyant continent borders the trench, deformable slabs adopt shallow Andean-style profiles.

  12. Volcanism and Subduction: The Kamchatka Region

    Science.gov (United States)

    Eichelberger, John; Gordeev, Evgenii; Izbekov, Pavel; Kasahara, Minoru; Lees, Jonathan

    The Kamchatka Peninsula and contiguous North Pacific Rim is among the most active regions in the world. Kamchatka itself contains 29 active volcanoes, 4 now in a state of semi-continuous eruption, and I has experienced 14 magnitude 7 or greater earthquakes since accurate recording began in 1962. At its heart is the uniquely acute subduction cusp where the Kamchatka and Aleutian Arcs and Emperor Seamount Chain meet. Volcanism and Subduction covers coupled magmatism and tectonics in this spectacular region, where the torn North Pacific slab dives into hot mantle. Senior Russian and American authors grapple with the dynamics of the cusp with perspectives from the west and east of it, respectively, while careful tephrostratigraphy yields a remarkably precise record of behavior of storied volcanoes such as Kliuchevskoi and Shiveluch. Towards the south, Japanese researchers elucidate subduction earthquake processes with unprecedented geodetic resolution. Looking eastward, new insights on caldera formation, monitoring, and magma ascent are presented for the Aleutians. This is one of the first books of its kind printed in the English language. Students and scientists beginning research in the region will find in this book a useful context and introduction to the region's scientific leaders. Others who wish to apply lessons learned in the North Pacific to their areas of interest will find the volume a valuable reference.

  13. Splay fault branching along the Nankai subduction zone.

    Science.gov (United States)

    Park, Jin-Oh; Tsuru, Tetsuro; Kodaira, Shuichi; Cummins, Phil R; Kaneda, Yoshiyuki

    2002-08-16

    Seismic reflection profiles reveal steeply landward-dipping splay faults in the rupture area of the magnitude (M) 8.1 Tonankai earthquake in the Nankai subduction zone. These splay faults branch upward from the plate-boundary interface (that is, the subduction zone) at a depth of approximately 10 kilometers, approximately 50 to 55 kilometers landward of the trough axis, breaking through the upper crustal plate. Slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion.

  14. Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

    Science.gov (United States)

    Butler, Jared P.; Beaumont, Christopher

    2017-04-01

    The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling

  15. Hidden Earthquake Potential in Plate Boundary Transition Zones

    Science.gov (United States)

    Furlong, Kevin P.; Herman, Matthew; Govers, Rob

    2017-04-01

    Plate boundaries can exhibit spatially abrupt changes in their long-term tectonic deformation (and associated kinematics) at triple junctions and other sites of changes in plate boundary structure. How earthquake behavior responds to these abrupt tectonic changes is unclear. The situation may be additionally obscured by the effects of superimposed deformational signals - juxtaposed short-term (earthquake cycle) kinematics may combine to produce a net deformational signal that does not reflect intuition about the actual strain accumulation in the region. Two examples of this effect are in the vicinity of the Mendocino triple junction (MTJ) along the west coast of North America, and at the southern end of the Hikurangi subduction zone, New Zealand. In the region immediately north of the MTJ, GPS-based observed crustal displacements (relative to North America (NAm)) are intermediate between Pacific and Juan de Fuca (JdF) motions. With distance north, these displacements rotate to become more aligned with JdF - NAm displacements, i.e. to motions expected along a coupled subduction interface. The deviation of GPS motions from the coupled subduction interface signal near the MTJ has been previously interpreted to reflect clock-wise rotation of a coastal, crustal block and/or reduced coupling at the southern Cascadia margin. The geologic record of crustal deformation near the MTJ reflects the combined effects of northward crustal shortening (on geologic time scales) associated with the MTJ Crustal Conveyor (Furlong and Govers, 1999) overprinted onto the subduction earthquake cycle signal. With this interpretation, the Cascadia subduction margin appears to be well-coupled along its entire length, consistent with paleo-seismic records of large earthquake ruptures extending to its southern limit. At the Hikurangi to Alpine Fault transition in New Zealand, plate interactions switch from subduction to oblique translation as a consequence of changes in lithospheric structure of

  16. Multiscale Architecture of a Subduction Complex and Insight into Large-scale Material Movement in Subduction Systems

    Science.gov (United States)

    Wakabayashi, J.

    2014-12-01

    The >1000 km by >100 km Franciscan complex of California records >100 Ma of subduction history that terminated with conversion to a transform margin. It affords an ideal natural laboratory to study the rock record of subduction-interface and related processes exhumed from 10-70 km. The Franciscan comprises coherent and block-in-matrix (mélange) units forming a nappe stack that youngs structurally downward in accretion age, indicating progressive subduction accretion. Gaps in accretion ages indicate periods of non-accretion or subduction erosion. The Franciscan comprises siliciclastic trench fill rocks, with lesser volcanic and pelagic rocks and serpentinite derived from the downgoing plate, as well as serpentinite and felsic-intermediate igneous blocks derived as detritus from the upper plate. The Franciscan records subduction, accretion, and metamorphism (including HP), spanning an extended period of subduction, rather than a single event superimposed on pre-formed stratigraphy. Melanges (serpentinite and siliciclastic matrix) with exotic blocks, that include high-grade metamorphic blocks, and felsic-intermediate igneous blocks from the upper plate, are mostly/entirely of sedimentary origin, whereas block-in-matrix rocks formed by tectonism lack exotic blocks and comprise disrupted ocean plate stratigraphy. Mélanges with exotic blocks are interbedded with coherent sandstones. Many blocks-in-melange record two HP burial events followed by surface exposure, and some record three. Paleomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow fault zones of structures, are accommodated by discrete faults or narrow shear zones, rather than by significant penetrative strain. Exhumation of Franciscan HP units, both coherent and mélange, was accommodated by significant extension of the overlying plate, and possibly extension within the subduction complex, with cross-sectional extrusion, and like subduction burial, took place at

  17. Plate tectonics, damage and inheritance.

    Science.gov (United States)

    Bercovici, David; Ricard, Yanick

    2014-04-24

    The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.

  18. Friction and stress coupling on the subduction interfaces

    Science.gov (United States)

    Tan, E.; Lavier, L.; van Avendonk, H.

    2011-12-01

    At a subduction zone, the down-going oceanic plate slides underneath the overriding plate. The frictional resistance to the relative motion between the plates generates great earthquakes along the subduction interface, which can cause tremendous damage in the civil life and property. There is a strong incentive to understand the frictional strength of the subduction interface. One fundamental question of mechanics of subuction is the degree of coupling between the plates, which is linked to the size of earthquakes. It has been noted that the trench-parallel (along-strike) gravity variation correlates positively with the trench-parallel topography anomaly and negatively with the activity of great earthquake (Song and Simons, 2003). Regions with a negative trench-parallel gravity anomaly are more likely to have great earthquakes. The interpretation of such correlation is that strong coupling along subduction interface will drag down the for-arc region of the overriding plate, which generates the gravity and topography anomalies, and could store more strain energy to be released during a great earthquake. We developed a 2D numerical thermo-mechanical code for modeling subduction. The numerical method is based on an explicit finite element method similar to the Fast Lagrangian Analysis of Continua (FLAC) technique. The constitutive law is visco-elasti-plastic with strain weakening. The cohesion and friction angle are reduced with increasing plastic strain after yielding. To track different petrologic phases, Lagrangian particles are distributed in the domain. Basalt-eclogite, sediment-schist and peridotite-serpentinite phase changes are included in the model. Our numerical models show that the degree of coupling negatively correlates with the coefficient of friction. In the low friction case, the subduction interface has very shallow dipping angle, which helps to elastically couple the downing plate with the overriding plate. The topography and gravity anomalies of the

  19. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    NARCIS (Netherlands)

    Hunen, Jeroen van

    2001-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling

  20. Flat-slab subduction, orogenesis, intraplate deformation, and glacial erosion in southern Alaska: A tectonic-glacial progression from STEEP

    Science.gov (United States)

    Pavlis, T. L.; Gulick, S. S.; Bruhn, R. L.; Christeson, G. L.; Enkelmann, E.; Freymueller, J. T.; Hallet, B.; Horton, B. K.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Ridgway, K. D.; Spotila, J. A.; Van Avendonk, H. J.

    2012-12-01

    The ST. Elias Erosion and tectonics Project (STEEP) is a Continental Dynamics multidisciplinary collaboration involving offshore and onshore studies of a modern example of an oceanic plateau collision with a continental margin in southern Alaska. These studies constrain erosion-tectonic interactions and clarify the timeline of northern Cordilleran orogenesis. At ~55 Ma an oceanic plateau formed on either the Kula-Farallon or Farallon-Resurrection spreading center. From 50-46 Ma, this plateau attempted to subduct beneath an accretionary complex, the Yakutat Group (YG), near offshore British Columbia. The YG was thrust onto the plateau to form what is now the Yakutat Terrane. From ~40 to as late as 33 Ma the Yakutat Terrane was part of North America and the proto-Transition Fault was active moving the remnant Kula Plate towards the Aleutian Trench, slicing off the southern edge of the Yakutat Terrane, and emplacing Pacific crust adjacent to the Terrane. From ~33 to 6 Ma the Yakutat Terrane moved northward with the Pacific Plate. There is some Oligocene paleogeographic uncertainly, but upper plate deformation and basin development starting ~ 20-25 Ma may be Yakutat related. At ~6 Ma the Pacific Plate underwent a clockwise shift in motion reactivating the Transition Fault, albeit at a slow rate, and this motion drove a component of oblique convergence along the Fairweather Fault and orogenesis in the St. Elias. Rejuvenation of the Transition Fault formed a stable triple junction with the Aleutian Trench and the Yakutat-North American subduction front. Uplift in the orogen seeded glacial systems that reached tidewater by ~5.5 Ma and the sediments produced were the glaciomarine, syn-orogenic Yakataga Formation. The eastern syntaxis of the St. Elias orogen began to focus exhumation as thickened crust generated along the transpressive Fairweather system was fed into the fully contractional core of the orogen. Between 4 and 3 Ma, the thicker portions of the Yakutat Terrane

  1. Depositionary Margins: The Destruction and Renovation of Subduction Forearcs

    Science.gov (United States)

    Vannucchi, P.; Morgan, J. P.; Silver, E. A.; Kluesner, J.

    2016-12-01

    A depositionary margin is a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  2. Subduction initiation and Obduction: insights from analog models

    Science.gov (United States)

    Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.

    2013-12-01

    Subduction initiation and obduction are two poorly constrained geodynamic processes which are interrelated in a number of natural settings. Subduction initiation can be viewed as the result of a regional-scale change in plate convergence partitioning between the set of existing subduction (and collision or obduction) zones worldwide. Intraoceanic subduction initiation may also ultimately lead to obduction of dense oceanic "ophiolites" atop light continental plates. A classic example is the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ~5-10 myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. We herein present analog models designed to study both processes and more specifically (1) subduction initiation through the partitioning of deformation between two convergent zones (a preexisting and a potential one) and, as a consequence, (2) the possible development of obduction, which has so far never been modeled. These models explore the mechanisms of subduction initiation and obduction and test various triggering hypotheses (i.e., plate acceleration, slab crossing the 660 km discontinuity, ridge subduction; Agard et al., 2007). The experimental setup comprises an upper mantle modelled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing on a piston at one end of the model with plate tectonics like velocities (1-10 cm/yr) onto (i) a continental margin, (ii) a weakness zone with variable resistance and dip (W), (iii) an oceanic plate - with or without a spreading ridge, (iv) a subduction zone (S) dipping away from the piston and (v) an upper active continental margin, below which the oceanic plate is being subducted at the start of the experiment (as for the Oman case). Several configurations were tested over thirty-five parametric experiments. Special emphasis was

  3. The initiation of subduction: criticality by addition of water?

    Science.gov (United States)

    Regenauer-Lieb, K; Yuen, D A; Branlund, J

    2001-10-19

    Subduction is a major process of plate tectonics; however, its initiation is not understood. We used high-resolution (less than 1 kilometer) finite-element models based on rheological data of the lithosphere to investigate the role played by water on initiating subduction. A solid-fluid thermomechanical instability is needed to drive a cold, stiff, and negatively buoyant lithosphere into the mantle. This instability can be triggered slowly by sedimentary loading over a time span of 100 million years. Our results indicate that subduction can proceed by a double feedback mechanism (thermoelastic and thermal-rheological) promoted by lubrication due to water.

  4. Subduction of a buoyant plateau at the Manila Trench: Tomographic evidence and geodynamic implications

    Science.gov (United States)

    Fan, Jianke; Zhao, Dapeng; Dong, Dongdong

    2016-02-01

    We determined P-wave tomographic images by inverting a large number of arrival-time data from 2749 local earthquakes and 1462 teleseismic events, which are used to depict the three-dimensional morphology of the subducted Eurasian Plate along the northern segment of the Manila Trench. Dramatic changes in the dip angle of the subducted Eurasian Plate are revealed from the north to the south, being consistent with the partial subduction of a buoyant plateau beneath the Luzon Arc. Slab tears may exist along the edges of the buoyant plateau within the subducted plate induced by the plateau subduction, and the subducted lithosphere may be absent at depths greater than 250 km at ˜19°N and ˜21°N. The subducted buoyant plateau is possibly oriented toward NW-SE, and the subducted plate at ˜21°N is slightly steeper than that at ˜19°N. These results may explain why the western and eastern volcanic chains in the Luzon Arc are separated by ˜50 km at ˜18°N, whereas they converge into a single volcanic chain northward, which may be related to the oblique subduction along the Manila Trench caused by the northwestern movement of the Philippine Sea Plate. A low-velocity zone is revealed at depths of 20-200 km beneath the Manila Accretionary Prism at ˜22°N, suggesting that the subduction along the Manila Trench may stop there and the collision develops northward. The Taiwan Orogeny may originate directly from the subduction of the buoyant plateau, because the initial time of the Taiwan Orogeny is coincident with that of the buoyant plateau subduction.

  5. Conjecture with water and rheological control for subducting slab in the mantle transition zone

    Directory of Open Access Journals (Sweden)

    Fumiko Tajima

    2015-01-01

    Full Text Available Seismic observations have shown structural variation near the base of the mantle transition zone (MTZ where subducted cold slabs, as visualized with high seismic speed anomalies (HSSAs, flatten to form stagnant slabs or sink further into the lower mantle. The different slab behaviors were also accompanied by variation of the “660 km” discontinuity depths and low viscosity layers (LVLs beneath the MTZ that are suggested by geoid inversion studies. We address that deep water transport by subducted slabs and dehydration from hydrous slabs could affect the physical properties of mantle minerals and govern slab dynamics. A systematic series of three-dimensional numerical simulation has been conducted to examine the effects of viscosity reduction or contrast between slab materials on slab behaviors near the base of the MTZ. We found that the viscosity reduction of subducted crustal material leads to a separation of crustal material from the slab main body and its transient stagnation in the MTZ. The once trapped crustal materials in the MTZ eventually sink into the lower mantle within 20–30 My from the start of the plate subduction. The results suggest crustal material recycle in the whole mantle that is consistent with evidence from mantle geochemistry as opposed to a two-layer mantle convection model. Because of the smaller capacity of water content in lower mantle minerals than in MTZ minerals, dehydration should occur at the phase transformation depth, ∼660 km. The variation of the discontinuity depths and highly localized low seismic speed anomaly (LSSA zones observed from seismic P waveforms in a relatively high frequency band (∼1 Hz support the hypothesis of dehydration from hydrous slabs at the phase boundary. The LSSAs which correspond to dehydration induced fluids are likely to be very local, given very small hydrogen (H+ diffusivity associated with subducted slabs. The image of such local LSSA zones embedded in HSSAs may not

  6. Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

    Science.gov (United States)

    Bowin, C. O.; Yi, W.; Rosson, R. D.; Bolmer, S. T.

    2015-09-01

    The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10-8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel-iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4-10 packet, and are an order of magnitude smaller than those from the core-mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and

  7. An updated digital model of plate boundaries

    Science.gov (United States)

    Bird, Peter

    2003-03-01

    A global set of present plate boundaries on the Earth is presented in digital form. Most come from sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions, and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL-1A poles (Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk, Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline, Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway Reef, Balmoral Reef, Futuna, Niuafo'ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez, Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total of 52 plates. No attempt is made to divide the Alps-Persia-Tibet mountain belt, the Philippine Islands, the Peruvian Andes, the Sierras Pampeanas, or the California-Nevada zone of dextral transtension into plates; instead, they are designated as "orogens" in which this plate model is not expected to be accurate. The cumulative-number/area distribution for this model follows a power law for plates with areas between 0.002 and 1 steradian. Departure from this scaling at the small-plate end suggests that future work is very likely to define more very small plates within the orogens. The model is presented in four digital files: a set of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of characteristics of each digitization step along plate boundaries, including estimated relative velocity vector and classification into one of 7 types (continental convergence zone, continental transform fault, continental rift, oceanic spreading ridge

  8. Crustal Recycling by Surface Processes Along the Pacific-North America Plate Boundary: From the Colorado Plateau to the Salton Trough and Gulf of California

    Science.gov (United States)

    Dorsey, R. J.

    2009-12-01

    uncertainties, the volume of sediment stored in sedimentary basins along the Gulf-Trough corridor is comparable to the volume of rock that likely was eroded from the Colorado Plateau in the past 5-6 m.y. Using the equivalent rock volume, age, and along-strike extent of these basins, the rate of crustal addition by sediment input is roughly 75-110 km3 per km strike length along the plate boundary per m.y. This is similar to rates of crustal growth by magmatic accretion at subduction-related island arcs and slow mid-ocean spreading centers. Miocene tectonic collapse of the Cordilleran orogen, followed by intensification of monsoonal flow to the Colorado Plateau at ca. 6 Ma, resulted in delayed re-routing of the Colorado River and subsequent rapid funneling of sediment into lowland basins along the plate boundary (Chapin, 2008). This catchment-to-basin conveyer belt operates at scales and volumetric rates comparable to igneous processes of crustal formation and recycling. Similar catchment systems may be expected to form in other settings where potential energy resulting from collapse of an orogenic highland combines with climate forcing related to induced changes in ocean circulation to erode and transfer crust from a stable continental interior to an active plate boundary.

  9. Transient thermal regimes in the Sierra Nevada and Baja California extinct outer arcs following the cessation of Farallon subduction

    Science.gov (United States)

    Erkan, Kamil; Blackwell, David

    2009-02-01

    We examine the thermal relaxation of the Sierra Nevada and Baja California extinct outer arc blocks following the progressive cessation of Farallon subduction under western North America beginning at ˜30 Ma. Being parts of the same outer arc until the inland jump of the San Andreas transform fault at ˜5 Ma, these two regions show many similarities in their geology, geomorphology, rigid body behavior, and their relatively low seismicity. In the thermal model, we combine results of different geophysical and geophysical studies to constrain the thermal state and geometry of the outer arcs before the cessation of subduction and then model the postsubduction temperature responses in these regions using the results of the tectonic reconstructions. A well-constrained regional thermal model of these blocks using the results of many earlier studies in these regions confirms that the present low heat flow values in these regions are the remnants of the very cold outer arc thermal regime of the subduction zone even as long as 30 Ma after cessation of subduction. Thus the entire Pacific boundary of the North American plate is still in a transient thermal state. The calculated low lithospheric temperatures in the Sierra Nevada and Peninsular blocks correlate very well with their rigid body behavior obtained from geodetic studies, and seismogenic layer thicknesses obtained from seismological studies. This is in contrast with the fact that both regions are surrounded by intense deformation associated with the western North America intraplate and extraplate motions. These low-temperature islands play important roles in the present interaction of the North American and Pacific plates and contribute to the broad deformation of the transform boundary. The thermal relaxation of the extinct outer arcs includes both vertical heating from the underlying asthenosphere and the lateral heating from the extinct back arc (Basin and Range), which has remained as a high heat flow region after

  10. Compilation of Surface Creep on California Faults and Comparison of WGCEP 2007 Deformation Model to Pacific-North American Plate Motion

    Science.gov (United States)

    Wisely, Beth A.; Schmidt, David A.; Weldon, Ray J.

    2008-01-01

    This Appendix contains 3 sections that 1) documents published observations of surface creep on California faults, 2) constructs line integrals across the WG-07 deformation model to compare to the Pacific ? North America plate motion, and 3) constructs strain tensors of volumes across the WG-07 deformation model to compare to the Pacific ? North America plate motion. Observation of creep on faults is a critical part of our earthquake rupture model because if a fault is observed to creep the moment released as earthquakes is reduced from what would be inferred directly from the fault?s slip rate. There is considerable debate about how representative creep measured at the surface during a short time period is of the whole fault surface through the entire seismic cycle (e.g. Hudnut and Clark, 1989). Observationally, it is clear that the amount of creep varies spatially and temporally on a fault. However, from a practical point of view a single creep rate is associated with a fault section and the reduction in seismic moment generated by the fault is accommodated in seismic hazard models by reducing the surface area that generates earthquakes or by reducing the slip rate that is converted into seismic energy. WG-07 decided to follow the practice of past Working Groups and the National Seismic Hazard Map and used creep rate (where it was judged to be interseismic, see Table P1) to reduce the area of the fault surface that generates seismic events. In addition to following past practice, this decision allowed the Working Group to use a reduction of slip rate as a separate factor to accommodate aftershocks, post seismic slip, possible aseismic permanent deformation along fault zones and other processes that are inferred to affect the entire surface area of a fault, and thus are better modeled as a reduction in slip rate. C-zones are also handled by a reduction in slip rate, because they are inferred to include regions of widely distributed shear that is not completely

  11. Reducing risk where tectonic plates collide

    Science.gov (United States)

    Gomberg, Joan S.; Ludwig, Kristin A.

    2017-06-19

    Most of the world’s earthquakes, tsunamis, landslides, and volcanic eruptions are caused by the continuous motions of the many tectonic plates that make up the Earth’s outer shell. The most powerful of these natural hazards occur in subduction zones, where two plates collide and one is thrust beneath another. The U.S. Geological Survey’s (USGS) “Reducing Risk Where Tectonic Plates Collide—A USGS Plan to Advance Subduction Zone Science” is a blueprint for building the crucial scientific foundation needed to inform the policies and practices that can make our Nation more resilient to subduction zone-related hazards.

  12. Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

    Science.gov (United States)

    Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

    2017-04-01

    The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

  13. Review of subduction and its association with geothermal system in Sumatera-Java

    Science.gov (United States)

    Ladiba, A. F.; Putriyana, L.; Sibarani, B. br.; Soekarno, H.

    2017-12-01

    Java and Sumatera have the largest geothermal resources in Indonesia, in which mostly are spatially associated with volcanoes of subduction zones. However, those volcanoes are not distributed in a regular pattern due to the difference of subduction position. Subduction position in java is relatively more perpendicular to the trench than in Sumatera. In addition, Java has a concentration of large productive geothermal field with vapour dominated system in the western part of Java, which may be caused by the various subduction dip along the island. In order to understand the relationship between the subduction process and geothermal system in the subduction zone volcanoes, we examined several kinematic parameters of subduction that potentially relevant to the formation of geothermal system in overriding plate such as slab dip, subduction rate, and direction of subduction. Data and information regarding tectonic setting of Sumatera and Java and productive geothermal field in Sumatera and Java have been collected and evaluated. In conclusion, there are three condition that caused the geothermal fluid to be more likely being in vapour phase, which are: the subduction is in an orthogonal position, the slab dip is high, and rate of subduction is high. Although there are plenty researches of subduction zone volcanoes, only a few of them present information about its formation and implication to the geothermal system. The result of this study may be used as reference in exploration of geothermal field in mutual geologic environment.

  14. Trench dynamics: Effects of dynamically migrating trench on subducting slab morphology and characteristics of subduction zones systems

    Science.gov (United States)

    Yoshida, Masaki

    2017-07-01

    Understanding the mechanisms of trench migration (retreat or advance) is crucial to characterizing the driving forces of Earth's tectonics plates, the origins of subducting slab morphologies in the deep mantle, and identifying the characteristics of subduction zones systems, which are among the fundamental issues of solid Earth science. A series of numerical simulations of mantle convection, focusing on plate subduction in a three-dimensional (3-D) regional spherical shell coordinate system, was performed to examine subduction zone characteristics, including geodynamic relationships among trench migration, back-arc stress, and slab morphology. The results show that a subducting slab tends to deflect around the base of the mantle transition zone and form a sub-horizontal slab because its front edge (its 'toe') is subject to resistance from the highly viscous lower mantle. As the sub-horizontal slab starts to penetrate into the lower mantle from its 'heel,' the toe of the slab is drawn into the lower mantle. The results for models with dynamically migrating trenches suggest that trench retreat is the dynamically self-consistent phenomenon in trench migration. The reason for this is that the strong lateral mantle flow that is generated as a sequence of events leading from corner flow at the subduction initiation to return flow of the formation of a sub-horizontal slab in the shallower part of mantle wedge produces the retreat of the subducting slab. In fact, a 'mantle suction force,' which is generated in the mantle wedge to fill space left by the retreating subducting plate, is enhanced by the subsequent trench retreat. Even when upwelling flow with significant positive buoyancy originates just above a mantle phase boundary at a depth of 410 km (as inferred from independent seismic tomographic, geodynamic, geochemical, and mineral physics), reaches the base of the overriding plate, and the overriding plate is slightly thinned, lithospheric stress tends to be

  15. Great earthquakes hazard in slow subduction zones

    Science.gov (United States)

    Marcaillou, B.; Gutscher, M.; Westbrook, G. K.

    2008-12-01

    Research on the Sumatra-Andaman earthquake of 2004 has challenged two popular paradigms; that the strongest subduction earthquakes strike in regions of rapid plate convergence and that rupture occurs primarily along the contact between the basement of the overriding plate and the downgoing plate. Subduction zones presenting similar structural and geodynamic characteristics (slow convergence and thick wedges of accreted sediment) may be capable of generating great megathrust earthquakes (M>8.5) despite an absence of thrust type earthquakes over the past 40 years. Existing deep seismic sounding data and hypocenters are used to constrain the geometry of several key slow subduction zones (Antilles, Hellenic, Sumatra). This geometry forms the basis for numerical modelling of fore-arc thermal structure, which is applied to calculate the estimated width of the seismogenic portion of the subduction fault plane. The margins with the thickest accretionary wedges are commonly found to have the widest (predicted) seismogenic zone. Furthermore, for these margins there exists a substantial (20-60 km wide) region above the up-dip limit for which the contribution to tsunami generation is poorly understood. As the rigidity (mu) of these high-porosity sediments is low, co-seismic slip here can be expected to be slow. Accordingly, the contribution to seismic moment will be low, but the contribution to tsunami generation may be very high. Indeed, recent seismological data from Nankai indicate very low frequency shallow-thrust earthquakes beneath this portion of the accretionary wedge, long-considered to be "aseismic". We propose that thick accumulations of sediment on the downgoing plate and the presence of a thick accretionary wedge can increase the maximum size of the potential rupture fault plane in two ways; 1) by thermally insulating the downgoing plate and thereby increasing the total downdip length of the fault which can rupture seismically and 2) by "smoothing out" the

  16. Asthenospheric outflow from the shrinking Philippine Sea Plate: Evidence from Hf-Nd isotopes of southern Mariana lavas

    Science.gov (United States)

    Ribeiro, Julia M.; Stern, Robert J.; Martinez, Fernando; Woodhead, Jon; Chen, Min; Ohara, Yasuhiko

    2017-11-01

    At subduction zones, sinking of the downgoing lithosphere is thought to enable a return flow of asthenospheric mantle around the slab edges, so that the asthenosphere from underneath the slab invades the ambient mantle flowing underneath the volcanic arc and the backarc basin. For instance at the northern end of the Lau Basin, trench retreat and slab rollback enable toroidal return flow of Samoan mantle beneath a transform margin to provide a supply of fresh, undepleted Indian mantle that feeds the backarc spreading center. Questions, however, arise about the sense of mantle flow when plate kinematics predict that the trench is advancing, as seen in the Mariana convergent margin. Does the mantle flow in or does it escape outward through slab tears or gaps? Here, we address the origin and sense of asthenospheric mantle flow supplying the southern Mariana convergent margin, a region of strong extension occurring above the subducting Pacific plate. Does the asthenosphere flow northward, from underneath the Pacific plate and Caroline hotspot through a slab tear or gap, or does it flow outward from the Mariana Trough, which possesses a characteristic Indian Ocean isotopic signature? To address these questions, we integrate geodetic data along with new Hf-Nd isotopic data for fresh basaltic lavas from three tectonic provinces in the southernmost Marianas: the Fina Nagu volcanic complex, the Malaguana-Gadao backarc spreading ridge and the SE Mariana forearc rift. Our results indicate that Indian mantle flows outward and likely escapes through slab tears or gaps to accommodate shrinking of the Philippine Sea plate. We thus predict that asthenospheric flow around the Pacific slab at the southern Mariana Trench is opposite to that predicted by most subduction-driven mantle flow models.

  17. A Cenozoic diffuse alkaline magmatic province (DAMP) in the southwest Pacific without rift or plume origin

    Science.gov (United States)

    Finn, Carol A.; Müller, R. Dietmar; Panter, Kurt S.

    2005-02-01

    Common geological, geochemical, and geophysical characteristics of continental fragments of East Gondwana and adjacent oceanic lithosphere define a long-lived, low-volume, diffuse alkaline magmatic province (DAMP) encompassing the easternmost part of the Indo-Australian Plate, West Antarctica, and the southwest portion of the Pacific Plate. A key to generating the Cenozoic magmatism is the combination of metasomatized lithosphere underlain by mantle at only slightly elevated temperatures, in contrast to large igneous provinces where mantle temperatures are presumed to be high. The SW Pacific DAMP magmatism has been conjecturally linked to rifting, strike-slip faulting, mantle plumes, or hundreds of hot spots, but all of these associations have flaws. We suggest instead that sudden detachment and sinking of subducted slabs in the late Cretaceous induced Rayleigh-Taylor instabilities along the former Gondwana margin that in turn triggered lateral and vertical flow of warm Pacific mantle. The interaction of the warm mantle with metasomatized subcontinental lithosphere that characterizes much of the SW Pacific DAMP concentrates magmatism along zones of weakness. The model may also provide a mechanism for warming south Pacific mantle and resulting Cenozoic alkaline magmatism, where the oceanic areas are characterized primarily, but not exclusively, by short-lived hot spot tracks not readily explained by conventional mantle plume theory. This proposed south Pacific DAMP is much larger and longer-lived than previously considered.

  18. Subduction-driven recycling of continental margin lithosphere.

    Science.gov (United States)

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.

  19. A model for the termination of the Ryukyu subduction zone against Taiwan: A junction of collision, subduction/separation, and subduction boundaries

    Science.gov (United States)

    Wu, F.T.; Liang, W.-T.; Lee, J.-C.; Benz, H.; Villasenor, A.

    2009-01-01

    The NW moving Philippine Sea plate (PSP) collides with the Eurasian plate (EUP) in the vicinity of Taiwan, and at the same time, it subducts toward the north along SW Ryukyu. The Ryukyu subduction zone terminates against eastern Taiwan. While the Ryukyu Trench is a linear bathym??trie low about 100 km east of Taiwan, closer to Taiwan, it cannot be clearly identified bathymetrically owing to the deformation related to the collision, making the location of the intersection of the Ryukyu with Taiwan difficult to decipher. We propose a model for this complex of boundaries on the basis of seismicity and 3-D velocity structures. In this model the intersection is placed at the latitude of about 23.7??N, placing the northern part of the Coastal Range on EUP. As PSP gets deeper along the subduction zone it collides with EUP on the Taiwan side only where they are in direct contact. Thus, the Eurasian plate on the Taiwan side is being pushed and compressed by the NW moving Philippine Sea plate, at increasing depth toward the north. Offshore of northeastern Taiwan the wedge-shaped EUP on top of the Ryukyu subducting plate is connected to the EUP on the Ryukyu side and coupled to the NW moving PSP by friction at the plate interface. The two sides of the EUP above the western end of the subduction zone are not subjected to the same forces, and a difference in motions can be expected. The deformation of Taiwan as revealed by continuous GPS measurements, geodetic movement along the east coast of Taiwan, and the formation of the Hoping Basin can be understood in terms of the proposed model. Copyright 2009 by the American Geophysical Union.

  20. Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone.

    Science.gov (United States)

    Calvert, Andrew J

    2004-03-11

    At convergent continental margins, the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single, thin interface known as a megathrust. Great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together. Earthquakes of lower magnitude occur within the underlying oceanic plate, and have been linked to geochemical dehydration reactions caused by the plate's descent. Here I present deep seismic reflection data from the northern Cascadia subduction zone that show that the inter-plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a >5-km-thick, approximately 110-km-wide region of imbricated crustal rocks. Earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter-plate boundary zone. This implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate. Slip on the shallower megathrust shear zone, which may occur by aseismic slow slip, will transport crustal rocks into the upper mantle above the subducting oceanic plate and may, in part, provide an explanation for the unusually low seismic wave speeds that are observed there.

  1. Variation of Seismic Velocity Structure around the Mantle Transition Zone and Conjecture of Deep Water Transport by Subducted Slabs

    Science.gov (United States)

    Tajima, F. C.; Stahler, S. C.; Ohtani, E.; Yoshida, M.; Sigloch, K.

    2011-12-01

    Seismic tomography models published in the past two decades determined common long-wavelength features of subducting plates as high velocity anomalies and upwelling plumes as low velocity anomalies, and have led to a new class of high-resolution three-dimensional (3D) modeling of global mantle convection with a link to tomography models [e.g., Becker and Boschi, 2002; Ritsema et al., 2007; Schuberth et al., 2009a,b]. However, even such high resolution numerical models do not account for the variation associated with different behaviors of subducting plates as they enter the mantle transition zone (MTZ), i.e., some flatten to form stagnant slabs with a large lateral extent and others descend further into the lower mantle. There are conventional interpretations applied for the cause of variation of the subducted slab behaviors, i.e., temperature difference due to different plate age, different geochemical compositions, different water content and subsequent possible reduction of viscosity etc., which could be taken as non-unique and somewhat equivocal. These parameters and conditions have been tested in two-dimensional numerical simulations, while the water content in the MTZ or the mechanisms of hydration and dehydration through subduction process are still in the realm of conjecture. Recent models of seismic P- and SH-wave velocities derived for the mantle structure beneath northeast China [Wang and Niu, 2010; Ye et al., 2011] using reflectivity synthetics with data from the dense Chinese networks of broadband seismic instruments, show a broader 660 km discontinuity (by about 30 to 70 km) and slower shear velocities above the MTZ than a global standard model iasp91 (Kennett and Engdahl, 1991). These features were interpreted with a mixture of different chemical properties which show delayed phase transformation, and effects of water above the flattened slab. Nonetheless, the SH-wave model has a structure similar to model TNA above the MTZ, which was derived for the

  2. Dynamics and Significance of Plume-Induced Subduction Initiation: Numerical Modeling

    Science.gov (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.

    2014-12-01

    How did the first subduction zone form? Most present-day subduction initiation mechanisms require acting plate forces and/or preexisting zones of lithospheric weakness, which are themselves the consequence of plate tectonics (Stern 2004). In contrast, spontaneous plume-induced subduction initiation - suggested on the basis of numerical thermo-mechanical experiments (Ueda et al., 2008) and supported by data re-interpretation of how subduction started in Late Cretaceous time around the Caribbean LIP (Whattam and Stern, 2014) - does not require pre-existing lithospheric fabric, such as are created by active plate tectonics and is viable for both stagnant lid and mobile/deformable lid conditions. Here, we present first results of high-resolution 3D numerical thermo-mechanical modeling of plume-induced subduction resulting from mechanical-magmatic interaction of an ascending thermal mantle plume with old, cold, dense oceanic lithosphere. We demonstrate that weakening of the strong lithosphere by plume-induced magmatism is the key factor enabling subduction initiation around the plume head. A large plume head is required to overcome ring confinement, and subduction initiation is further favored when plume activity and lithospheric weakening continues for several tens of Ma. We further discuss possible implications of this scenario for modern plate tectonics as well as for plate tectonics initiation in Precambrian time. ReferencesStern, R.J., 2004. Subduction initiation: spontaneous and induced. EPSL 226, 275-292.Ueda, K., Gerya, T., Sobolev, S.V., 2008. Subduction initiation by thermal-chemical plumes. PEPI 171, 296-312.Whattam, S.A., Stern, R. 2014. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of plate tectonics. Gondwana Research, (accepted).

  3. Influence of plate geometry, slabs, and viscosity structure on local and global surface motions

    Science.gov (United States)

    Gérault, M.; Becker, T. W.; Kaus, B. J.; Faccenna, C.

    2009-12-01

    Unraveling the dynamics of the Pacific domain is essential in order to understand the net rotation of the lithosphere and relative trench motions. The major processes responsible for plate motions in the Pacific region are still debated although they have been attributed recently to keels, mountains, and/or plate dimensions. In this study, we perform numerical experiments to test several combinations of ocean basin geometries and viscosity structures. Changes in global plate motions and trench behavior occur as a response to differential spreading rates, basin width, slab morphology, and plate asymmetry. The influence of strength of the plate boundaries on mantle flow is evaluated as well. The pressure, velocity, and stress fields in the lithosphere and the upper mantle are computed using the two-dimensional (2-D) finite element code MILAMIN. A comparison between Cartesian and cylindrical models provides a quantitative analysis of the interactions of flow related to each of these different configurations. Our results suggest that the dynamics of an oceanic domain surrounded by subducting slabs are significantly affected by the width and geometry of the basin. The asymmetry of plates in terms of length, thickness, and slab geometry leads to a net motion that is up to 15% of the maximum surface motion. We find that for each particular combination of asymmetry and viscosity structure, there exists a critical basin size that maximizes the net rotation of the lithosphere.

  4. Impact-driven subduction on the Hadean Earth

    Science.gov (United States)

    O'Neill, C.; Marchi, S.; Zhang, S.; Bottke, W.

    2017-10-01

    Impact cratering was a dominant geologic process in the early Solar System that probably played an active role in the crustal evolution of the young terrestrial planets. The Earth's interior during the Hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics. However, whether large impacts could have triggered tectonism on the early Earth remains unclear. Here we conduct global-scale tectonic simulations of the evolution of the Earth through the Hadean eon under variable impact fluxes. Our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events. Furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity. In contrast to contemporary subduction, the simulated localized subduction events are relatively short-lived (less than 10 Myr) with relatively thin, weak plates. We suggest that resurgence in subduction activity induced by an increased impact flux between 4.1 and 4.0 billion years ago may explain the coincident increase in palaeointensity of the magnetic field. We further suggest that transient impact-driven subduction reconciles evidence from Hadean zircons for tectonic activity with other lines of evidence consistent with an Earth that was largely tectonically stagnant from the Hadean into the Archaean.

  5. Create Your Plate

    Medline Plus

    Full Text Available ... and Pacific Islanders American Indian/Alaska Native Programs Older Adults Family Link Diabetes EXPO Upcoming Diabetes EXPOs ... Planning Meals Diabetes Meal Plans and a Healthy Diet Create Your Plate Meal Planning for Vegetarian Diets ...

  6. A two-way interaction between the Hainan plume and the Manila subduction zone

    NARCIS (Netherlands)

    Mériaux, Catherine A.; Duarte, João C.; Schellart, Wouter P.; Mériaux, Anne Sophie

    2015-01-01

    The interaction between mantle plumes and subducting slabs is well accepted, but the influence of slabs on plumes has more often been portrayed than the reverse. Here we present three-dimensional upper mantle laboratory models in which a compositional plume rises underneath a subducting plate.

  7. Izu-Bonin Arc: Intra-oceanic from the beginning? Unraveling the crustal structure of the Mesozoic proto-Philippine Sea Plate

    Science.gov (United States)

    Tani, K.; Ishizuka, O.; Ueda, H.; Shukuno, H.; Hirahara, Y.; Nichols, A. R.; Dunkley, D. J.; Horie, K.; Ishikawa, A.; Morishita, T.; Tatsumi, Y.

    2012-12-01

    The Izu-Bonin Arc is widely regarded as a typical intra-oceanic arc, where the oceanic Pacific Plate is subducting beneath the Philippine Sea Plate, an evolving complex of active and inactive arcs and back-arc basins. It is dominated by oceanic crust forming three large back-arc basins; Shikoku, Parece Vela, and West Philippine Basins, making the present Philippine Sea Plate look like an "oceanic" plate. However, all of these back-arc basins were formed after the inception of subduction at Izu-Bonin Arc, which began at ~52 Ma (Ishizuka et al. 2011, EPSL). Little is known about the proto-Philippine Sea Plate, which existed as a counterpart to the Pacific Plate during subduction initiation and before the formation of back-arc basins. To investigate the crustal structures of the proto-Philippine Sea Plate, we conducted manned-submersible SHINKAI6500 and Deep-Tow camera surveys during the April 2010 cruise of the R/V YOKOSUKA cruise (YK10-04) at the Amami Plateau, Daito Ridge, and Okidaito Ridge (ADO) region. The ADO region comprises the northwestern Philippine Sea Plate along with what are regarded as remnants of the proto-Philippine Sea Plate. Submersible observations and rock sampling revealed that ADO region exposes deep crustal sections of gabbroic, granitic, and metamorphic rocks, indicating that part of the proto-Philippine Sea Plate is composed of older, possibly continental, crust. Jurassic to Cretaceous magmatic zircon U-Pb ages have been obtained from the ADO plutonic rocks. These findings and tectonic reconstruction of the proto-Philippine Sea Plate (Deschamps and Lallemand 2002, JGR) suggests that subduction of the Izu-Bonin Arc initiated at the continental margin of the Southeast Asia, possibly correlating to the Mesozoic island-arc and ophiolite complexes exposed in the Philippine Islands and Borneo, and later acquired "intra-oceanic"-like setting through formation of the backarc basins. Furthermore, detrital zircon ages from volcaniclastic sandstones

  8. Transition Fault and the Yakutat-Pacific-North American Triple Junction

    Science.gov (United States)

    Gulick, S. P.; Christeson, G. L.; Norton, I. O.; Pavlis, T. L.; Reece, R.; van Avendonk, H.; Worthington, L. L.

    2011-12-01

    In the Gulf of Alaska the Pacific Plate, Yakutat Terrane, and North American Plate interact in a complexly deformed zone on the continental slope near Kayak Island. This zone can be viewed as a fault-trench-trench (FTT) triple junction that can only be stable if the two trench segments are aligned. In this case the trench segments are: the deformation front along which the Pacific Plate subducts beneath North America (the Aleutian Trench) and the deformation front along which the Yakutat Terrane subducts at a more westerly direction (when compared to the Pacific subduction) beneath North America (the Pamplona Zone). These two deformation fronts are, to a first order, locally aligned. The complex member of the system is the Transition Fault which is a long-lived strike-slip fault separating the 15-30 km thick Yakutat oceanic plateau crust from the 5-7 km thick Pacific Plate crust, which is itself deforming along the north-south trending Gulf of Alaska Shear Zone (GASZ). A series of seismic reflection profiles crossing the Transition Fault allow us to examine the evolution of deformation as a function of proximity to the triple junction. East of the triple junction and the GASZ, the Transition Fault is a single near vertical strike-slip zone. Moving west to the area where the GASZ interacts with the Transition Fault, three seismic profiles show that the Fault bifurcates into a southern transpressional strand with a few 100 meters of seafloor relief and a northern strike-slip dominated strand. West of the GASZ and within the region proximal to the triple junction, two seismic lines show that the Transition Fault is expressed as a southern transpressional structure with significant amounts shortening (seafloor expression increased to ~1.8 km) and a northern dominantly strike-slip fault with minor transpression. Mapping the top of basement shows that the southern arm lies within and deforms the Pacific oceanic crust with the top of ocean crust reflection to the north

  9. Paleomagnetism of the Paleocene Ghost Rocks, Kodiak Islands, Alaska: Implications for Paleocene Pacific-Basin/North America Plate Configurations

    Science.gov (United States)

    Housen, B. A.; Roeske, S. M.; Gallen, S.; O'Connell, K.

    2008-12-01

    Paleocene volcanic and sedimentary rocks of the Ghost Rocks, part of the Chugach accretionary complex, may provide important constraints for possible paleogeographic models of plate configurations along the NW margin of North America. The Ghost Rocks, along with other Late Cretaceous to E. Eocene units of southern Alaska, contain anomalous near-trench igneous rocks which decrease in age from NW to SE along this margin and record relative motion of a trench-ridge-trench triple junction with respect to the margin. Thick sections of similar-aged volcanic rocks also exist in coastal Washington and Oregon. Two models have been proposed to explain these anomalous volcanic rocks. Moore et al. (1983) ascribes the progression of ages of the TRT rocks to migration of the Chugach terrane past a Kula-Farallon-NA boundary located off of present- day Oregon. Haeussler et al. (2003) call for the existence of two TRT triple junctions, one located off the present-day Oregon margin, the other of which migrated from NW (Sanak) to SE (Baranof) between Paleocene and Eocene time, which requires an intervening oceanic plate (the Resurrection Plate). Our work has included extensive sampling of both volcanic and sedimentary units of the Ghost Rocks, and detailed structural studies. The geological work indicates that much of the Ghost Rocks, particularly the large section containing volcanics at Alitak Bay, is composed of intact blocks bordered by fault zones, with steep upright to locally overturned bedding. The paleomagnetic results have revealed that the majority of the sedimentary rocks have poorly-behaved magnetizations carried by authigenic sulphide minerals. The majority of the igneous rocks (primarily beautiful exposures of basaltic-andesite pillows) have well-defined magnetizations with unblocking temperatures ranging from 450 to 550 C. The sites from Alitak Bay were corrected for vertical-axis rotations by rotating site-specific bedding strikes to agree with an average regional

  10. Subduction, back-arc spreading and global mantle flow

    Science.gov (United States)

    Hager, B. H.; Oconnell, R. J.; Raefsky, A.

    1983-01-01

    It is pointed out that the subducted lithosphere associated with Benioff zones provides the only direct evidence about the flow in the earth's interior associated with plate motions. It is the primary objective of the present investigation to study the relation between the orientation of subducting lithosphere and the flow patterns (both local and global) near subduction zones. Most of the calculations conducted are based on simple flow models for radially symmetric, Newtonian viscous spheres. The investigation is concerned with the possibility that a simple model of global mantle flow could account for some features of subduction zones. It is found that such a model can account for the orientation of the seismic zones, and, in addition, also for features related to back-arc spreading and perhaps the maximum earthquake size.

  11. Seismicity, topography, and free-air gravity of the Aleutian-Alaska subduction zone

    Science.gov (United States)

    Wells, R. E.; Blakely, R. J.; Scholl, D. W.; Ryan, H. F.

    2011-12-01

    The Aleutian-Alaska subduction zone, extending 3400 km from the Queen Charlotte Fault to Kamchatka, has been the source of six great megathrust earthquakes in the 20th Century. Four earthquakes have ruptured the 2000-km-long Aleutian segment, where the Cenozoic Aleutian arc overlies the subducting Pacific plate. These include the 1946 M 8.6 earthquake off Unimak Is., the 1957 M 8.6 and 1986 M 8.0 earthquakes off the Andreanoff Is., and the 1965 M 8.7 Rat Is. earthquake. The source regions of these earthquakes inferred from waveform inversions underlie the well-defined Aleutian deep-sea terrace. The deep-sea terrace is about 4 km deep and is underlain by Eocene arc framework rocks, which extend nearly to the trench. It is bounded on its seaward and landward margins by strong topographic and fee-air gravity gradients. The main asperities (areas of largest slip) for the great earthquakes and nearly all of the Aleutian thrust CMT solutions lie beneath the Aleutian terrace, between the maximum gradients. Similar deep-sea terraces are characteristic of non-accretionary convergent margins globally (75% of subduction zones), and, where sampled by drilling (e.g., Japan, Peru, Tonga, Central America), are undergoing sustained subsidence. Sustained subsidence requires removal of arc crust beneath the terrace by basal subduction erosion (BSE). BSE is in part linked to the seismic cycle, as it occurs in the same location as the megathrust earthquakes. Along the eastern 1400 km of the Alaskan subduction zone, the Pacific plate subducts beneath the North American continent. The boundary between the Aleutian segment and the continent is well defined in free-air gravity, and the distinctive deep-sea terrace observed along the Aleutian segment is absent. Instead, the Alaskan margin consists of exhumed, underplated accretionary complexes forming outer arc gravity highs. Superimposed on them are broad topographic highs and lows forming forearc basins (Shumagin, Stevenson) and islands

  12. Where does subduction initiate and die? Insights from global convection models with continental drift

    Science.gov (United States)

    Ulvrova, Martina; Williams, Simon; Coltice, Nicolas; Tackley, Paul

    2017-04-01

    Plate tectonics is a prominent feature on Earth. Together with the underlying convecting mantle, plates form a self-organized system. In order to understand the dynamics of the coupled system, subduction of the lithospheric plates plays the key role since it links the exterior with the interior of the planet. In this work we study subduction initiation and death with respect to the position of the continental rafts. Using thermo-mechanical numerical calculations we investigate global convection models featuring self-consistent plate tectonics and continental drifting employing a pseudo-plastic rheology and testing the effect of a free surface. We consider uncompressible mantle convection in Boussinesq approximation that is basaly and internaly heated. Our calculations indicate that the presence of the continents alterns stress distribution within a certain distance from the margins. Intra-oceanic subudction initiation is favorable during super-continent cycles while the initiation at passive continental margin prevails when continents are dispersed. The location of subduction initiation is additionally controlled by the lithospheric strength. Very weak lithosphere results in domination of intra-oceanic subduction initiation. The subduction zones die more easily in the vicinity of the continent due to the strong rheological contrast between the oceanic and continental lithosphere. In order to compare our findings with subduction positions through time recorded on Earth, we analyse subduction birth in global plate reconstruction back to 410 My.

  13. Subduction Mode Selection During Slab and Mantle Transition Zone Interaction: Numerical Modeling

    Science.gov (United States)

    Shi, Yanan; Wei, Dongping; Li, Zhong-Hai; Liu, Ming-Qi; Liu, Mengxue

    2017-12-01

    Global seismic tomography of the subduction zones shows that the subducting slabs could either stagnate around the 660-km discontinuity, or penetrate into the lower mantle. The stagnating slabs also have various morphologies. These are directly related to the interaction between the subducting slabs and the mantle transition zone (MTZ), the dynamics of which are still debated. Using a 2-D thermo-mechanical model, we systematically investigated the modes of subduction in the mantle transition zone and explored the key constraints of various subduction styles. Four basic subduction modes are obtained in the numerical experiments, including one with slab penetrating through the 660-km discontinuity and three other modes with slab stagnating in the MTZ (i.e. folding, lying and rolling-back). The numerical models indicate that the age of subducting oceanic plate, the thickness of overriding continental lithosphere and the convergence velocity play crucial roles in the dynamics of subducting slab and MTZ interaction. In general, the young subducting slab favors the penetration or folding mode, whereas the old subducting slab tends to result in lying or rolling-back mode, although other parameters can also affect. Our models also show a strong correlation between the subduction mode selection and dip angle of the slab tip when reaching the 660-km phase boundary.

  14. Searching for the Lost Jurassic and Cretaceous Ocean Basins of the Circum-Arctic Linking Plate Models and Seismic Tomography

    Science.gov (United States)

    Shephard, G. E.; Müller, R.

    2012-12-01

    The tectonic evolution of the circum-Arctic since the breakup of Pangea involves the opening and closing of ocean basins including the Oimyakon, Angayucham, South Anuyi, Amerasia and Eurasia basins. The time-dependent configurations and kinematic history of the basins, adjacent continental terranes, and subduction zones involved are not well understood, and many published tectonic models for particular regions are inconsistent with models for adjacent areas. The age, location, geometry and convergence rates of the subduction zones associated with these ancient ocean basins since at least the Late Jurassic have implications for mantle structure, which can be used as an additional constraint for building plate and plate boundary models. Here we integrate an analysis of both surface and deep mantle observations back to 200 Ma. Based on a digitized set of tectonic features with time-dependent rotational histories we present a refined plate model with topologically closed plate polygons for the circum-Arctic with particular focus on the northern Pacific, Siberian and Alaskan margins (Fig 1). We correlate the location, geometry and timing of subduction zones with associated seismic velocities anomalies from global P and S wave tomography models across different depths. We design a plate model that best matches slabs imaged in seismic tomography in an iterative fashion. This match depends on a combination of relative and absolute plate motions. Therefore we test two end-member absolute plate motion models, evaluating a paleomagnetic model and a model based on hotspot tracks and large igneous provinces. This method provides a novel approach to deciphering the Arctic tectonic history in a global context. Fig 1:Plate reconstruction at 200Ma and 140Ma, visualized using GPlates software. Present-day topography raster (ETOPO2) segmented into major tectonic elements of the circum-Arctic. Plate boundaries delineated in black and selected subduction and arc features labeled in

  15. Cascadia subduction tremor muted by crustal faults

    Science.gov (United States)

    Wells, Ray; Blakely, Richard J.; Wech, Aaron G.; McCrory, Patricia A.; Michael, Andrew

    2017-01-01

    Deep, episodic slow slip on the Cascadia subduction megathrust of western North America is accompanied by low-frequency tremor in a zone of high fluid pressure between 30 and 40 km depth. Tremor density (tremor epicenters per square kilometer) varies along strike, and lower tremor density statistically correlates with upper plate faults that accommodate northward motion and rotation of forearc blocks. Upper plate earthquakes occur to 35 km depth beneath the faults. We suggest that the faults extend to the overpressured megathrust, where they provide fracture pathways for fluid escape into the upper plate. This locally reduces megathrust fluid pressure and tremor occurrence beneath the faults. Damping of tremor and related slow slip caused by fluid escape could affect fault properties of the megathrust, possibly influencing the behavior of great earthquakes.

  16. The Hainan Lone Plume Prompted By Encircling Subduction Zones around the South China Sea

    Science.gov (United States)

    Zhang, N.; Li, Z. X.

    2016-12-01

    The present of the late Mesozoic Hainan plume originated from the lower mantle of northern South China Sea has been documented by both seismic tomographic and geochemical-petrological work. The Hainan plume is one of the rare mantle plumes that are located away from the two large low shear velocity provinces (LLSVPs) in the lower mantle. Instead, it is within the broad global mantle downwelling zone, thus classified as a "lone plume". It had previously been proposed that this plume could have been triggered by subducting slabs into the lower mantle in the regions surrounding the South China Sea, a mechanism similar to what had been proposed for the formation of the LLSVPs. Here, we investigate the feasibility of such a plume-generation mechanism use a geodynamic modelling. Our geodynamic model has a high resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adoptive-mesh-refined, 3D mantle convection code ASPECT. The top mechanic boundary condition of the global domain uses the latest plate motion reconstruction. In a series of experiments, we explore the effects of various important mantle parameters on mantle plume generation. The results so far suggest that the Indo-Australian cold slab acted like a cold wall from the southwest side in the present-day South China Sea mantle domain since 80 Ma ago. Fossil slabs from much older Tethyan subduction systems plays a moderate role in blocking the deep mantle hot materials from escaping to the north. The Western Pacific subduction systems started to promote the initiation of Hainan plume some 50 Ma ago from near the core-mantle boundary (CMB). As the plume head rises, it first moved to the west, and finally to beneath the South China Sea. Our model results are not sensitive to whether there is a chemical layer (possible D" layer) near the CMB.

  17. Plate tectonics and crustal deformation around the Japanese Islands

    Science.gov (United States)

    Hashimoto, Manabu; Jackson, David D.

    1993-01-01

    We analyze over a century of geodetic data to study crustal deformation and plate motion around the Japanese Islands, using the block-fault model for crustal deformation developed by Matsu'ura et al. (1986). We model the area including the Japanese Islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity. Geodetic data are used to obtain block motions and average slip rates of faults. This geodetic model predicts that the Pacific plate moves N deg 69 +/- 2 deg W at about 80 +/- 3 mm/yr relative to the Eurasian plate which is much lower than that predicted in geologic models. Substantial aseismic slip occurs on the subduction boundaries. The block containing the Izu Peninsula may be separated from the rigid part of the Philippine Sea plate. The faults on the coast of Japan Sea and the western part of the Median Tectonic Line have slip rates exceeding 4 mm/yr, while the Fossa Magna does not play an important role in the tectonics of the central Japan. The geodetic model requires the division of northeastern Japan, contrary to the hypothesis that northeastern Japan is a part of the North American plate. Owing to rapid convergence, the seismic risk in the Nankai trough may be larger than that of the Tokai gap.

  18. Evolution of passive continental margins and initiation of subduction zones

    NARCIS (Netherlands)

    Cloetingh, Sierd

    1982-01-01

    The initiation of subduction is a key element in plate tectonic schemes for the evolution of the Earth's lithosphere. Nevertheless, up to present, the underlying mechanism has not been very well understood (e.g. Dickinson and Seely, 1979; Hager, 1980; Kanamori, 1980). The insight into the initiation

  19. Evolution of passive continental margins and initiation of subduction zones

    NARCIS (Netherlands)

    Cloetingh, S.A.P.L.

    1982-01-01

    The initiation of subduction is a key element in plate tectonic schemes for the evolution of the Earth's lithosphere. Nevertheless, up to present, the underlying mechanism has not been very well understood (e.g. Dickinson and Seely, 1979; Hager, 1980; Kanamori, 1980). The insight into the

  20. Some consequences of the subduction of young slabs

    NARCIS (Netherlands)

    England, P.; Wortel, R.

    The negative buoyancy force exerted by a subducting oceanic slab depends on its descent velocity, and strongly on its age. For lithosphere close to thermal equilibrium, this force dominates by a large margin the resisting forces arising from friction on the plate boundary and compositional buoyancy.

  1. Rapid change in drift of the Australian plate records collision with Ontong Java plateau.

    Science.gov (United States)

    Knesel, Kurt M; Cohen, Benjamin E; Vasconcelos, Paulo M; Thiede, David S

    2008-08-07

    The subduction of oceanic plateaux, which contain extraordinarily thick basaltic crust and are the marine counterparts of continental flood-basalt provinces, is an important factor in many current models of plate motion and provides a potential mechanism for triggering plate reorganization. To evaluate such models, it is essential to decipher the history of the collision between the largest and thickest of the world's oceanic plateaux, the Ontong Java plateau, and the Australian plate, but this has been hindered by poor constraints for the arrival of the plateau at the Melanesian trench. Here we present (40)Ar-(39)Ar geochronological data on hotspot volcanoes in eastern Australian that reveal a strong link between collision of the Greenland-sized Ontong Java plateau with the Melanesian arc and motion of the Australian plate. The new ages define a short-lived period of reduced northward plate motion between 26 and 23 Myr ago, coincident with an eastward offset in the contemporaneous tracks of seamount chains in the Tasman Sea east of Australia. These features record a brief westward deflection of the Australian plate as the plateau entered and choked the Melanesian trench 26 Myr ago. From 23 Myr ago, Australia returned to a rapid northerly trajectory at roughly the same time that southwest-directed subduction began along the Trobriand trough. The timing and brevity of this collisional event correlate well with offsets in hotspot seamount tracks on the Pacific plate, including the archetypal Hawaiian chain, and thus provide strong evidence that immense oceanic plateaux, like the Ontong Java, can contribute to initiating rapid change in plate boundaries and motions on a global scale.

  2. Laboratory models of the thermal evolution of the mantle during rollback subduction.

    Science.gov (United States)

    Kincaid, C; Griffiths, R W

    2003-09-04

    The subduction of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. Information on mantle flow, thermal conditions and chemical transport in subduction zones come from the geochemistry of arc volcanoes, seismic images and geodynamic models. The majority of this work considers subduction as a two-dimensional process, assuming limited variability in the direction parallel to the trench. In contrast, observationally based models increasingly appeal to three-dimensional flow associated with trench migration and the sinking of oceanic plates with a translational component of motion (rollback). Here we report results from laboratory experiments that reveal fundamental differences in three-dimensional mantle circulation and temperature structure in response to subduction with and without a rollback component. Without rollback motion, flow in the mantle wedge is sluggish, there is no mass flux around the plate and plate edges heat up faster than plate centres. In contrast, during rollback subduction flow is driven around and beneath the sinking plate, velocities increase within the mantle wedge and are focused towards the centre of the plate, and the surface of the plate heats more along the centreline.

  3. Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra.

    Science.gov (United States)

    Hüpers, Andre; Torres, Marta E; Owari, Satoko; McNeill, Lisa C; Dugan, Brandon; Henstock, Timothy J; Milliken, Kitty L; Petronotis, Katerina E; Backman, Jan; Bourlange, Sylvain; Chemale, Farid; Chen, Wenhuang; Colson, Tobias A; Frederik, Marina C G; Guèrin, Gilles; Hamahashi, Mari; House, Brian M; Jeppson, Tamara N; Kachovich, Sarah; Kenigsberg, Abby R; Kuranaga, Mebae; Kutterolf, Steffen; Mitchison, Freya L; Mukoyoshi, Hideki; Nair, Nisha; Pickering, Kevin T; Pouderoux, Hugo F A; Shan, Yehua; Song, Insun; Vannucchi, Paola; Vrolijk, Peter J; Yang, Tao; Zhao, Xixi

    2017-05-26

    Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records. Copyright © 2017, American Association for the Advancement of Science.

  4. Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up.

    Science.gov (United States)

    Kelemen, Peter B; Manning, Craig E

    2015-07-28

    Carbon fluxes in subduction zones can be better constrained by including new estimates of carbon concentration in subducting mantle peridotites, consideration of carbonate solubility in aqueous fluid along subduction geotherms, and diapirism of carbon-bearing metasediments. Whereas previous studies concluded that about half the subducting carbon is returned to the convecting mantle, we find that relatively little carbon may be recycled. If so, input from subduction zones into the overlying plate is larger than output from arc volcanoes plus diffuse venting, and substantial quantities of carbon are stored in the mantle lithosphere and crust. Also, if the subduction zone carbon cycle is nearly closed on time scales of 5-10 Ma, then the carbon content of the mantle lithosphere + crust + ocean + atmosphere must be increasing. Such an increase is consistent with inferences from noble gas data. Carbon in diamonds, which may have been recycled into the convecting mantle, is a small fraction of the global carbon inventory.

  5. The dynamical control of subduction parameters on surface topography

    Science.gov (United States)

    Crameri, F.; Lithgow-Bertelloni, C. R.; Tackley, P. J.

    2017-04-01

    The long-wavelength surface deflection of Earth's outermost rocky shell is mainly controlled by large-scale dynamic processes like isostasy or mantle flow. The largest topographic amplitudes are therefore observed at plate boundaries due to the presence of large thermal heterogeneities and strong tectonic forces. Distinct vertical surface deflections are particularly apparent at convergent plate boundaries mostly due to the convergence and asymmetric sinking of the plates. Having a mantle convection model with a free surface that is able to reproduce both realistic single-sided subduction and long-wavelength surface topography self-consistently, we are now able to better investigate this interaction. We separate the topographic signal into distinct features and quantify the individual topographic contribution of several controlling subduction parameters. Results are diagnosed by splitting the topographic signal into isostatic and residual components, and by considering various physical aspects like viscous dissipation during plate bending. Performing several systematic suites of experiments, we are then able to quantify the topographic impact of the buoyancy, rheology, and geometry of the subduction-zone system to each and every topographic feature at a subduction zone and to provide corresponding scaling laws. We identify slab dip and, slightly less importantly, slab buoyancy as the major agents controlling surface topography at subduction zones on Earth. Only the island-arc high and the back-arc depression extent are mainly controlled by plate strength. Overall, his modeling study sets the basis to better constrain deep-seated mantle structures and their physical properties via the observed surface topography on present-day Earth and back through time.

  6. Gondwana breakup via double-saloon-door rifting and seafloor spreading in a backarc basin during subduction rollback

    Science.gov (United States)

    Martin, A. K.

    2007-12-01

    A model has been developed where two arc-parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback. The resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double-saloon-doors about their hinges. As movement proceeds and the two terranes rotate, a gap begins to extend between them, where a third rift initiates and propagates in the opposite direction to subduction rollback. Observations from the Oligocene to Recent Western Mediterranean, the Miocene to Recent Carpathians, the Miocene to Recent Aegean and the Oligocene to Recent Caribbean point to a two-stage process. Initially, pairs of terranes comprising a pre-existing retro-arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents. Terrane docking reduces the width of the subduction zone, leading to a second phase during which subduction to strike-slip transitions initiate. The clockwise rotated terrane is caught up in a dextral strike-slip zone, whereas the counterclockwise rotated terrane is entrained in a sinistral strike-slip fault system. The likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline. By analogy with the above model, a revised five-stage Early Jurassic to Early Cretaceous Gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the Weddell Sea area. Seven features are considered diagnostic of double-saloon-door rifting and seafloor spreading: earliest movement involves clockwise and counterclockwise rotations of the Falkland Islands Block and the Ellsworth Whitmore Terrane respectively; terranes comprise areas of a pre-existing retro-arc fold thrust belt (the Permo-Triassic Gondwanide Orogeny) attached to an accretionary wedge/magmatic arc; the Falklands Islands Block is initially

  7. Structural and Tectonic Map Along the Pacific-North America Plate Boundary in Northern Gulf of California, Sonora Desert and Valle de Mexicali, Mexico, from Seismic Reflection Evidence

    Science.gov (United States)

    Gonzalez-Escobar, M.; Suarez-Vidal, F.; Mendoza-Borunda, R.; Martin Barajas, A.; Pacheco-Romero, M.; Arregui-Estrada, S.; Gallardo-Mata, C.; Sanchez-Garcia, C.; Chanes-Martinez, J.

    2012-12-01

    Between 1978 and 1983, Petróleos Mexicanos (PEMEX) carried on an intense exploration program in the northern Gulf of California, the Sonora Desert and the southern part of the Mexicali Valley. This program was supported by a seismic reflection field operation. The collected seismic data was 2D, with travel time of 6 s recording, in 48 channels, and the source energy was: dynamite, vibroseis and air guns. Since 2007 to present time, the existing seismic data has been re-processing and ire-interpreting as part of a collaboration project between the PEMEX's Subdirección de Exploración (PEMEX) and CICESE. The study area is located along a large portion of the Pacific-North America plate boundary in the northern Gulf of California and the Southern part of the Salton Trough tectonic province (Mexicali Valley). We present the result of the processes reflection seismic lines. Many of the previous reported known faults were identify along with the first time described located within the study region. We identified regions with different degree of tectonic activity. In structural map it can see the location of many of these known active faults and their associated seismic activity, as well as other structures with no associated seismicity. Where some faults are mist placed they were deleted or relocated based on new information. We included historical seismicity for the region. We present six reflection lines that cross the aftershocks zone of the El Mayor-Cucapah earthquake of April 4, 2010 (Mw7.2). The epicenter of this earthquake and most of the aftershocks are located in a region where pervious to this earthquake no major earthquakes are been reported. A major result of this study is to demonstrate that there are many buried faults that increase the seismic hazard.

  8. Deep electrical resistivity structure of Costa Rican Subduction Zone

    Science.gov (United States)

    Worzewski, T.; Jegen, M.; Brasse, H.; Taylor, W.

    2009-04-01

    The water content and its distribution play an important role in the subduction process. Water is released from the subducting slab in a series of metamorphic reactions and the hydration of the mantle wedge may trigger the onset of melting, weakening and changes in the dynamics and thermal structure of subduction zones. However, the amount of water carried into the subduction zone and its distribution are not well constrained by existing data and are subject of vigorous current research in SFB574 (Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters). We will show numerical modeling studies which are used to determine the resolution and sensitivity of the MT response to fluids in the crust and subducting slab under the special condition of a coastal setting. In 2007-2008 we conducted a long-period magnetotelluric investigations in northwestern Costa Rica on- and offshore, where the Cocos Plate subducts beneath the Carribean plate. Eleven marine magnetotelluric Stations newly developed and constructed by IFM-GEOMAR and University of Kiel were deployed on the 200 km long marine extension of the profile for several months. We will present the data and its processing, as well as our attempts to eliminate motion induced noise observed on some stations on the cliffy shelf due to tidal waves hitting the shelf and trench parallel- and perpendicular currents. The marine profile was extended landwards by the Free University of Berlin over length of 160 kilometers with further 18 stations. We present preliminary modeling results of land data, which revealed interesting features, inter alia a possible image of fluid release from the downgoing slab in the forearc, as well as ongoing modeling of the combined on- and offshore data sets.

  9. Plate Margin Deformation and Active Tectonics Along the Northern Edge of the Yakutat Terrane in the Saint Elias Orogen, Alaska and Yukon, Canada

    Science.gov (United States)

    Bruhn, Ronald L.; Sauber, Jeanne; Cotton, Michele M.; Pavlis, Terry L.; Burgess, Evan; Ruppert, Natalia; Forster, Richard R.

    2012-01-01

    The northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane into the cusp of southern Alaska. The nature and magnitude of accretion and translation on upper crustal faults and folds is poorly constrained, however, due to pervasive glaciation. In this study we used high-resolution topography, geodetic imaging, seismic, and geologic data to advance understanding of the transition from strike-slip motion on the Fairweather fault to plate margin deformation on the Bagley fault, which cuts through the upper plate of the collisional suture above the subduction megathrust. The Fairweather fault terminates by oblique-extensional splay faulting within a structural syntaxis, allowing rapid tectonic upwelling of rocks driven by thrust faulting and crustal contraction. Plate motion is partly transferred from the Fairweather to the Bagley fault, which extends 125 km farther west as a dextral shear zone that is partly reactivated by reverse faulting. The Bagley fault dips steeply through the upper plate to intersect the subduction megathrust at depth, forming a narrow fault-bounded crustal sliver in the obliquely convergent plate margin. Since . 20 Ma the Bagley fault has accommodated more than 50 km of dextral shearing and several kilometers of reverse motion along its southern flank during terrane accretion. The fault is considered capable of generating earthquakes because it is linked to faults that generated large historic earthquakes, suitably oriented for reactivation in the contemporary stress field, and locally marked by seismicity. The fault may generate earthquakes of Mw <= 7.5.

  10. 3D Numerical modelling of topography development associated with curved subduction zones

    Science.gov (United States)

    Munch, Jessica; Ueda, Kosuke; Burg, Jean-Pierre; May, Dave; Gerya, Taras

    2017-04-01

    retreat. Topography associated with slab retreat is curved. Coupling I3ELVIS with SPM yields more accurate topography of the curved subduction zone. This allows balancing the relative importance of surface and deep processes in the evolution of curved subduction zones and the development of their related topography. References: Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1), 83-105. Gerya, T. V., Stern, R. J., Baes, M., Sobolev, S. V., & Whattam, S. A. (2015). Plate tectonics on the Earth triggered by plume-induced subduction initiation. Nature, 527(7577), 221-225.

  11. Geologically current plate motions

    Science.gov (United States)

    DeMets, Charles; Gordon, Richard G.; Argus, Donald F.

    2010-04-01

    We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit-MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6-2.6mmyr-1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca-Antarctic and Nazca-Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also

  12. Geologic signature of early Tertiary ridge subduction in Alaska

    Science.gov (United States)

    Bradley, Dwight C.; Kusky, Timothy M.; Haeussler, Peter J.; Goldfarb, Richard J.; Miller, Marti L.; Dumoulin, Julie A.; Nelson, Steven W.; Karl, Susan M.

    2003-01-01

    A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach–Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfide deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief flare-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events - but most especially those in the accretionary prism - can be attributed with varying degrees of confidence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after

  13. Acoustic profiling and surface imaging of the coastal area near the subduction zone: the eastern coastal area of Boso Peninsula, Central Japan.

    Science.gov (United States)

    Furuyama, S.; Sato, T.

    2016-12-01

    The plate motion of the Philippine Sea plate and the Pacific plate influences geology of coastal area in the Pacific side in Japan and sometime causes extensive damage of human activity, such as the Great East Japan Earthquake. It is important to understand the geological structures in a coastal area for disaster prevention. Especially, rapid equipment of geoinformations is highly demanded in the Kanto region where covers capital Tokyo area. Geological Survey of Japan investigated the eastern coastal area in Boso Peninsula, eastern part of the Kanto region, Japan within two years from 2014 to 2015. We obtained seismic sections of ca. 1100 km in total length with a boomer and multi-channel streamer (24 channel with 3.125 m spacing) and report the geological significance of the subsurface structures. The survey area is divided into the northern part of Kujukuri area, the southern part of Kujukuri area, the coastal part of Kujukuri area based on topography and geological structures. In these Kujukuri areas, two strata that show distinct stratification bounded by distinct unconformity distribute and we define them as the Kujukuri A Unit and the Kujukuri B Unit, in ascending order. The lower sequence has some folds and normal faults. These folds that deformed the Kujukuri B Unit extend toward north-northeast in the northern part of Kujukuri area. They contributed to development of wide shelf distributed in this area. In the southern part of Kujukuri area, a lot of faults deformed the Kujukuri B Unit and some of them displaced the Kujukuri A Unit over 10 msec (two way travel). Normal faults developed in the Kujukuri B Unit over 10 msec made grabens and half grabens in the coastal part of Kujukuri area and these grabens and half grabens could make the lowland in the Kujukuri coastal area. The combination of these geological structures identified in the Kujukuri areas could reflect the transition of stress field associated with the subduction of the Philippine Sea plate

  14. Pervasive seismic low-velocity zones within stagnant plates in the mantle transition zone: Thermal or compositional origin?

    Science.gov (United States)

    Tauzin, B.; Kim, S.; Kennett, B. L. N.

    2017-11-01

    We exploit conversions between P and S waves for large-scale, high-resolution imaging of the mantle transition zone beneath Northwest Pacific and the margin of Eastern Asia. We find pervasive reflectivity concentrated in two bands with apparent wave-speed reduction of -2% to -4% about 50 km thick at the top of the transition zone and 100 km thick at the bottom. This negative reflectivity associated with the scattered-waves at depth is interpreted jointly with larger-scale mantle tomographic images, and is shown to delineate the stagnant portions of the subducted Pacific plate in the transition zone, with largely positive shear-wave velocity contrasts. The upper reflectivity zone connects to broad low-velocity regions below major intra-plate volcanoes, whereas the lower zone coincides locally with the occurrence of deep-focus earthquakes along the East Asia margin. Similar reflectivity is found in Pacific Northwest of the USA. We demonstrate that the thermal signature of plates alone is not sufficient to explain such features. Alternative explanations for these reflective zones include kinetic effects on olivine phase transitions (meta-stability), compositional heterogeneities within and above stagnant plates, complex wave-propagation effects in the heterogeneous slab structure, or a combination of such factors. We speculate that part of the negative reflectivity is the signature of compositional heterogeneities, as revealed by numerous other studies of seismic scattering throughout the mantle, and that such features could be widespread across the globe.

  15. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    OpenAIRE

    Maffione, Marco; van Hinsbergen, Douwe J.J.; de Gelder, Giovanni I.N.O.; van der Goes, Freek C.; Morris, Antony

    2017-01-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distribut...

  16. Episodic tremor and slip in Northern Sumatra subduction zone

    Science.gov (United States)

    Sianipar, Dimas; Subakti, Hendri

    2017-07-01

    The first reported observation of non-volcanic tremor in Sunda Arc in Sumbawa, Indonesia open a possibility of discovery of episodic tremor and slip (ETS) from out of Pacific Rim. Non-volcanic tremor gives some important information about dynamic of plate boundaries. The characteristics of these tremors are visually as non-impulsive, high frequency, long-duration and low-amplitude signals. Tectonic tremor occurred in a transition part of brittle-ductile of a fault and frequently associated with the shearing mechanism of slow slip. Tectonic tremor is a seismic case that also very interested, because it shows strong sensitivity to stress changes. Deep non-volcanic tremor is usually associated with episodic slow-slip events. Tectonic tremor is found in close association with geodetically observed slow-slip events (SSE) in subduction zones. One research found that there is possibility of SSE occurrence on Banyak Islands, North Sumatra revealed from coral observation. The SSE occurred on the Banyak Islands portion of the megathrust at 30-55 km depth, within the downdip transition zone. We do a systematic search of episodic tremor and its possible relationship with slow-slip phenomena in Northern Sumatra subduction zone. The spectrogram analysis is done to analyze the potential tremor signals. We use three component broadband seismic stations with 20, 25, and 50 sampling per second (BH* and SH* channels). We apply a butterworth 5 Hz highpass filter to separate the signal as local tremor and teleseismic/regional earthquakes. Before computing spectrogram to avoid high-frequency artifacts to remote triggering, we apply a 0.5 Hz filter. We also convert the binary seismic data into sound waves to make sure that these events meet the tectonic tremor criterion. We successfully examine 3 seismic stations with good recording i.e. GSI, SNSI and KCSI. We find there are many evidences of high frequency episodic tremor like signals. This include an analysis of potential triggered

  17. Experimental and observational evidence for plume-induced subduction on Venus

    Science.gov (United States)

    Davaille, A.; Smrekar, S. E.; Tomlinson, S.

    2017-04-01

    Why Venus lacks plate tectonics remains an unanswered question in terrestrial planet evolution. There is observational evidence for subduction--a requirement for plate tectonics--on Venus, but it is unclear why the features have characteristics of both mantle plumes and subduction zones. One explanation is that mantle plumes trigger subduction. Here we compare laboratory experiments of plume-induced subduction in a colloidal solution of nanoparticles to observations of proposed subduction sites on Venus. The experimental fluids are heated from below to produce upwelling plumes, which in turn produce tensile fractures in the lithosphere-like skin that forms on the upper surface. Plume material upwells through the fractures and spreads above the skin, analogous to volcanic flooding, and leads to bending and eventual subduction of the skin along arcuate segments. The segments are analogous to the semi-circular trenches seen at two proposed sites of plume-triggered subduction at Quetzalpetlatl and Artemis coronae. Other experimental deformation structures and subsurface density variations are also consistent with topography, radar and gravity data for Venus. Scaling analysis suggests that this regime with limited, plume-induced subduction is favoured by a hot lithosphere, such as that found on early Earth or present-day Venus.

  18. Dynamical effects of subducting ridges: Insights from 3-D laboratory models

    CERN Document Server

    Martinod, Joseph; Faccenna, Claudio; Labanieh, Shasa; Regard, Vincent; 10.1111/j.1365-246X.2005.02797.x

    2010-01-01

    We model the subduction of buoyant ridges and plateaus to study their effect on slab dynamics. Oceanic ridges parallel to the trench have a stronger effect on the process of subduction because they simultaneously affect a longer trench segment. Large buoyant slab segments sink more slowly into the asthenosphere, and their subduction result in a diminution of the velocity of subduction of the plate. We observe a steeping of the slab below those buoyant anomalies, resulting in smaller radius of curvature of the slab, that augments the energy dissipated in folding the plate and further diminishes the velocity of subduction. When the 3D geometry of a buoyant plateau is modelled, the dip of the slab above the plateau decreases, as a result of the larger velocity of subduction of the dense "normal" oceanic plate on both sides of the plateau. Such a perturbation of the dip of the slab maintains long time after the plateau has been entirely incorporated into the subduction zone. We compare experiments with the presen...

  19. Assessment of Optimum Value for Dip Angle and Locking Rate Parameters in Makran Subduction Zone

    Science.gov (United States)

    Safari, A.; Abolghasem, A. M.; Abedini, N.; Mousavi, Z.

    2017-09-01

    Makran subduction zone is one of the convergent areas that have been studied by spatial geodesy. Makran zone is located in the South Eastern of Iran and South of Pakistan forming the part of Eurasian-Arabian plate's border where oceanic crust in the Arabian plate (or in Oman Sea) subducts under the Eurasian plate ( Farhoudi and Karig, 1977). Due to lack of historical and modern tools in the area, a sampling of sparse measurements of the permanent GPS stations and temporary stations (campaign) has been conducted in the past decade. Makran subduction zone from different perspectives has unusual behaviour: For example, the Eastern and Western parts of the region have very different seismicity and also dip angle of subducted plate is in about 2 to 8 degrees that this value due to the dip angle in other subduction zone is very low. In this study, we want to find the best possible value for parameters that differs Makran subduction zone from other subduction zones. Rigid block modelling method was used to determine these parameters. From the velocity vectors calculated from GPS observations in this area, block model is formed. These observations are obtained from GPS stations that a number of them are located in South Eastern Iran and South Western Pakistan and a station located in North Eastern Oman. According to previous studies in which the locking depth of Makran subduction zone is 38km (Frohling, 2016), in the preparation of this model, parameter value of at least 38 km is considered. With this function, the amount of 2 degree value is the best value for dip angle but for the locking rate there is not any specified amount. Because the proposed model is not sensitive to this parameter. So we can not expect big earthquakes in West of Makran or a low seismicity activity in there but the proposed model definitely shows the Makran subduction layer is locked.

  20. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    NARCIS (Netherlands)

    Maffione, Marco; van Hinsbergen, Douwe J.J.; de Gelder, Giovanni I.N.O.; van der Goes, Freek C.; Morris, Antony

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia.

  1. Continuing evolution of the Pacific-Juan de Fuca-North America slab window system-A trench-ridge-transform example from the Pacific Rim

    Science.gov (United States)

    McCrory, P.A.; Wilson, D.S.; Stanley, R.G.

    2009-01-01

    Many subduction margins that rim the Pacific Ocean contain complex records of Cenozoic slab-window volcanism combined with tectonic disruption of the continental margin. The series of slab windows that opened beneath California and Mexico starting about 28.5 Ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime. The timing and areal extent of the resultant slab-window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin. The initial Pioneer slab window thermally weakened the overlying western Transverse Ranges and California Borderlands region starting about 28.5 Ma. A second thermal pulse occurred in the same region starting about 19 Ma during growth of the Monterey slab window. This additional heating, combined with the capture of a partially subducted Monterey plate fragment by the Cocos plate, initiated the pulling apart and rotation of the adjacent continental margin. Similarly, the capture of Guadalupe and Magdalena plate fragments by the Pacific plate and initiation of the Guadalupe-Magdalena slab window about 12.5 Ma are coeval with Baja California pulling away from the Mexico continental margin, with the break along the Comondú arc, in crust already thermally weakened by about 10 My of volcanism. In coastal California, distributed crustal extension and subsidence accompanied the new transform plate boundary, and continued until the slab windows cooled and plate motion coalesced along a through-going system of strike-slip faults. The transform boundary continues to evolve, and forward modeling predicts an instability with the current configuration as a result of convergence between the Sierra Nevada and Peninsular Ranges batholiths, starting about 2 My in the future. The instability may be resolved by a shift in the locus of transform motion from the San Andreas fault to the eastern California shear zone, or by

  2. Intra-Panthalassa Ocean subduction zones revealed by fossil arcs and mantle structure

    NARCIS (Netherlands)

    Meer, D.G. van der; Torsvik, T.H.; Spakman, W.; Hinsbergen, D.J.J. van; Amaru, M.L.

    2012-01-01

    The vast Panthalassa Ocean once surrounded the supercontinent Pangaea. Subduction has since consumed most of the oceanic plates that formed the ocean floor, so classic plate reconstructions based on magnetic anomalies can be used only to constrain the ocean’s history since the Cretaceous period, and

  3. Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone

    Science.gov (United States)

    Canales, J. P.; Carbotte, S. M.; Nedimović, M. R.; Carton, H.

    2017-11-01

    Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

  4. Post-Eocene Subduction Dynamics and Mantle Flow beneath Western U.S.

    Science.gov (United States)

    Liu, L.; Zhou, Q.; Leonard, T.

    2015-12-01

    Both surface geology and mantle seismic images suggest a complex late Cenozoic history of mantle dynamics over western U.S. We try to understand this history by simulating the Farallon subduction since 40 Ma. Forward subduction models assimilating time dependent seafloor ages, plate kinematics and evolving plate boundaries suggest that the present-day 3D distribution of fast seismic anomalies below western U.S. mostly represent late Cenozoic slabs, which experienced multiple phases of segmentation during subduction because of their young age and small mechanical strength (Liu & Stegman, 2011). A major slab segmentation event occurred around mid-Miocene, with the resulting slab tear and induced asthenosphere upwelling correlating with the Steens-Columbia River flood basalts (SCRB) eruption both in space and in time (Liu & Stegman, 2012). This suggests that a mantle plume is not required for the formation of the SCRB. Segmentation of the Farallon slab generates rapid toroidal flows around the newly formed slab edges beneath the Cascadia arc. These mantle flows may affect both the pattern and composition of arc volcanism through transportation of oceanic asthenosphere material into the mantle wedge. Based on the forward model, we further test the influence of slow seismic anomalies on mantle dynamics. On the one hand, we explicitly input a deep hot anomaly to represent the putative Yellowstone plume. On the other hand, we develop a hybrid scheme that combines the adjoint inverse method with the high-resolution forward simulation approach, so that the present-day mantle seismic structure is entirely consistent with the convection model. Our preliminary results suggest that a hot plume could actively rise up only when it is several hundreds of kilometers away from the slabs, as is the case prior to 20 Ma. Subsequently, the plume is dominated by the surrounding slabs, resulting in an overall downwelling mantle flow. This suggests that a plume might have contributed to

  5. Transient uplift after a 17th-century earthquake along the Kuril subduction zone.

    Science.gov (United States)

    Sawai, Yuki; Satake, Kenji; Kamataki, Takanobu; Nasu, Hiroo; Shishikura, Masanobu; Atwater, Brian F; Horton, Benjamin P; Kelsey, Harvey M; Nagumo, Tamotsu; Yamaguchi, Masaaki

    2004-12-10

    In eastern Hokkaido, 60 to 80 kilometers above a subducting oceanic plate, tidal mudflats changed into freshwater forests during the first decades after a 17th-century tsunami. The mudflats gradually rose by a meter, as judged from fossil diatom assemblages. Both the tsunami and the ensuing uplift exceeded any in the region's 200 years of written history, and both resulted from a shallow plate-boundary earthquake of unusually large size along the Kuril subduction zone. This earthquake probably induced more creep farther down the plate boundary than did any of the region's historical events.

  6. Tectonic block rotation, arc curvature, and back-arc rifting: Insights into these processes in the Mediterranean and the western Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Wallace, L M; Ellis, S [GNS Science, PO Box 30368, Lower Hutt (New Zealand); Mann, P [Institute for Geophysics, University of Texas at Austin, Austin, Texas (United States)], E-mail: l.wallace@gns.cri.nz

    2008-07-01

    The fastest modern-day tectonic block rotations on Earth (up to 9 degrees/Myr) occur in the forearcs of convergent plate margins where a transition from collision of a bathymetric high to subduction of normal oceanic crust occurs. GPS techniques have enabled accurate documentation of the kinematics of these rotations, leading us to develop a conceptual model where the change from collision to subduction exerts a torque on microplates within the plate boundary zone, causing them to spin rapidly about an axis at the collision point. We have investigated geophysical and geological data from several active plate boundaries (from the western Pacific and Mediterranean regions) to document a compelling spatial and temporal relationship between the transition from collision to subduction, plate boundary curvature, and rapid tectonic block rotations. In some cases, these microplate rotations can initiate back-arc rifting. We also present numerical modelling results supporting our conceptual model for block rotations at collision/subduction transition. Our results suggest that the rate of microplate rotation depends on the incoming indentor velocity, and can be greatly enhanced by: (1) extensional stresses acting at the subduction interface (possibly due to slab roll back), and (2) a low-viscosity back-arc. Where viscosity of the back-arc is low, forearc microplate rotation dominates. In contrast, tectonic escape of strike-slip fault-bounded microplates is predicted in areas where the back-arc viscosity is high. Previous workers have suggested that the kinematics of the Anatolian block and back-arc rifting in the Aegean are influenced by some combination of forces associated with Arabia/Eurasia collision, and/or subduction (including slab rollback) at the Hellenic trench. Based on previous work from active western Pacific arcs, we propose that the collision of two separate indentors (Arabian promontory in the east, Apulian platform in the west), is a fundamental tectonic

  7. A Late Cenozoic Kinematic Model for Deformation Within the Greater Cascadia Subduction System

    Science.gov (United States)

    Wilson, D. S.; McCrory, P. A.

    2016-12-01

    Relatively low fault slip rates have complicated efforts to characterize seismic hazards associated with the diffuse subduction boundary between North America and offshore oceanic plates in the Pacific Northwest region. A kinematic forward model that encompasses a broader region, and incorporates seismologic and geodetic as well as geologic and paleomagnetic constraints offers a tool for constraining fault rupture chronologies—all within a framework tracking relative motion of the Juan de Fuca, Pacific, and North American plates during late Cenozoic time. Our kinematic model tracks motions as a system of rigid microplates, bounded by the more important mapped faults of the region or zones of distributed deformation. Though our emphasis is on Washington and Oregon, the scope of the model extends eastward to the rigid craton in Montana and Wyoming, and southward to the Sierra Nevada block of California to provide important checks on its internal consistency. The model reproduces observed geodetic velocities [e.g., McCaffrey et al., 2013, JGR], for 6 Ma to present, with only minor reorganization for 12-6 Ma. Constraints for the older deformation history are based on paleomagnetic rotations within the Columbia River Basalt Group, and geologic details of fault offsets. Since 17 Ma, our model includes 50 km of N-S shortening across the central Yakima fold and thrust belt, substantial NW-SE right-lateral strike slip distributed among faults in the Washington Cascade Range, 90 km of shortening on thrusts of Puget Lowland, and substantial oroclinal bending of the Crescent Formation basement surrounding the Olympic Peninsula. This kinematic reconstruction provides an integrated, quantitative framework with which to investigate the motions of various PNW forearc and backarc blocks during late Cenozoic time, an essential tool for characterizing the seismic risk associated with the Puget Sound and Portland urban areas, hydroelectric dams, and other critical infrastructure.

  8. Using the Mesozoic History of the Canadian Cordillera as a Case Study in Teaching Plate Tectonics.

    Science.gov (United States)

    Chamberlain, Valerie Elaine

    1989-01-01

    Reviews a model used in the teaching of plate tectonics which includes processes and concepts related to: terranes and the amalgamation of terranes, relative plate motion and oblique subduction, the effects of continent-continent collision, changes in plate motion, plate configuration, and the type of plate boundary. Diagrams are included.…

  9. Three-dimensional Thermal Model of the Mexican Subduction Zone

    Science.gov (United States)

    Rosas, J. C.; Pimentel, F. D. C.; Currie, C. A.; He, J.; Harris, R. N.

    2015-12-01

    Along the Mexican section of the Middle America Trench (MAT), the Cocos plate subducts beneath the North American plate. The most important feature of this subduction zone is the flat-slab section below central Mexico, extending approximately 250 km landward from the trench at a depth of 50 km. Further west, the dip changes to 45-50º. This particular geometry has several unique consequences, such as a volcanic arc that is not aligned with the trench and very shallow slab seismicity. For the mantle wedge, the abrupt change in slab geometry could lead to a three-dimensional (3D) mantle wedge flow that departs from the classical 2D subduction-driven corner flow. Evidence of 3D flow in the region comes from seismic anisotropy studies, which show that olivine fast-direction axes have a component that is parallel to the MAT. In other subduction zones, such as Costa Rica-Nicaragua and Japan, 3D flow has been observed to increase temperatures by >50º C relative to corner flow models.For this study, we have created the first 3D finite-element model of the Mexican subduction zone in order to analyze its thermal structure. Our objective is to assess the effects of 3D mantle flow and hydrothermal circulation (HC) in the subducting slab. In this region, low surface heat flow values near the trench indicate that HC may remove heat from the oceanic plate. Our model incorporates the effect of HC through conductivity proxies in the subducting crust and a 2D oceanic geotherm that includes the age variations of the Cocos plate along the MAT. For an isoviscous mantle, our model shows that the slab dip variations induce a flow that departs from 2D corner flow near the transition between the flat-slab and normal-dipping sections. The mantle flows in eastward direction toward the flat slab, and its orientation is consistent with seismic anisotropy studies. The maximum along-margin flow rate is nearly 2 cm/yr, which is >30% of the convergence rate. Temperatures at the location of this

  10. Back-arc Extension: Critical Analisys of Subduction-related and Non Subduction-related Driving Mechanisms

    Science.gov (United States)

    Mantovani, E.; Viti, M.; Babbucci, D.; Tamburelli, C.; Albarello, D.

    It is argued that the opening of back arc basins can hardly be explained as an effect of subduction related forces, since this kind of interpretation has not yet provided plausible explanations for several major features of such processes in the world. In particular, it is not clear why back arc extension occurs in some subduction zones and not in others, why extension ceased in zones where subduction has remained active, why the arcs associated with back arc basins are often characterized by a strongly curved shape, why arc-trench-back arc systems do not develop along the entire length of consuming borders and why no significant correlation can be recognized between any parameter of subduction processes and the occurrence of back arc extension. In addition, modelling experiments indicate that the magnitude of the tensional stress induced in the overriding plate by subduction-related forces is significantly lower than the lithospheric strength. These problems are discussed, in particular, for three subduction-related interpretations, the "slab-pull", the "corner flow" and the "sea an- chor" models, which seem to be the most quoted in literature. It is then argued that possible solutions of the above problems may be provided by the extrusion model, which postulates that back arc basins are generated by the forced separation of the arc from the overriding plate, along a sector of the consuming border. This separa- tion is generally caused by the oblique indentation of strong and buoyant structures against the accretionary belt. In this view, subduction and back arc extension are not causally linked one to the other, but rather represent simultaneous effects of the lateral migration of the arc, driven by plate convergence. It is pointed out that the conditions required for the occurrence of this kind of mechanism may be recognized in the tec- tonic contexts where back arc basins developed in the wake of arc-trench migrating systems. On the other hand, in the zones

  11. The Geodynamics of Continental Lithosphere Entering a Subduction Zone

    Science.gov (United States)

    Steedman, C. E.; Kaus, B. J.; Becker, T. W.; Okaya, D.; Wu, F. T.

    2006-12-01

    As deformation patterns resulting from subduction of a passive continental margin are insufficiently understood, here we perform 2-D numerical simulations to explore the effects of continental lithosphere entering a subduction zone. The model setup consists of a subduction zone in which the oceanic part of a passive continental margin initially subducts beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the dynamics of the system. A novel new feature of the code is that the resolution of the model can be significantly increased in selected parts of the domain, which allows for self-consistent modelling of mantle-lithosphere interaction. In the present study this feature is employed to study how crustal scale deformation around the subduction zone is influenced by surface processes and by flow in the upper mantle. Using systematic 2-D numerical simulations, we explore the parameters that are dominant in controlling near- surface structures, both with regards to changes in topography over time, and subsurface features such as Moho undulations. The main parameters that have been varied are: the lithospheric density structure; the strength of the lower crust; the amounts of erosion; imposed pushing versus density-driven (slab-pull and ridge- push) convergence; the upper boundary condition (free surface versus free slip); rheology (non-Newtonian versus Newtonian, viscous, visco-elasto-plastic); and finally the effect of an imposed slab breakoff. In all cases we track surface uplift, subduction evolution and rock exhumation history. The results can be compared to evidence from areas such as Taiwan where continental subduction or convergence is thought to be happening. Preliminary results indicate that a low viscosity lower crust may contribute to crustal uplift.

  12. Subduction processes related to the Sea of Okhotsk

    Science.gov (United States)

    Zabarinskaya, Ludmila P.; Sergeyeva, Nataliya

    2017-04-01

    It is obviously important to study a role of subduction processes in tectonic activity within the continental margins. They are marked by earthquakes, volcanic eruptions, tsunami and other natural disasters hazardous to the people,plants and animals that inhabit such regions. The northwest part of the Sea of Okhotsk including the northern part of Sakhalin Island and the Deryugin Basin is the area of the recent intensive tectonic movements. The geological and geophysical data have made it possible to construct the geodynamic model of a deep structure of a lithosphere for this region. This geodynamic model has confirmed the existence of the ophiolite complex in the region under consideration. It located between the North Sakhalin sedimentary basin and the Deryugin basin. The Deryugin basin was formed on the side of an ancient deep trench after subducting the Okhotsk Sea Plate under Sakhalin in the Late Cretaceous-Paleogene. The North Sakhalin Basin with oil and gas resources was formed on the side of back-arc basin at that time. Approximately in the Miocene period the subduction process, apparently, has stopped. The remains of the subduction zone in the form of ophiolite complex have been identified according to geological and geophysical data. On a surface the subduction zone is shown as deep faults stretched along Sakhalin.

  13. Volcanism and vertical tectonics in the Pacific Basin related to global Cretaceous transgressions

    Science.gov (United States)

    Schlanger, Seymour O.; Jenkyns, Hugh C.; Premoli-Silva, Isabella

    1981-02-01

    The dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the Pacific Basin has been recognised since the time of Charles Darwin. Data gathered on several legs of the Deep Sea Drilling Project (DSDP) and numerous marine expeditions in the past decade have confirmed Menard's postulate that the Pacific Basin was the scene of volcanism on an enormous scale in Mesozoic time. Widespread mid-plate volcanism between ˜110 and 70 m.y. B.P. characterised the area bounded by the Line Islands, the Mid-Pacific Mountains and the Nauru Basin-Marshall Islands. Heating of the Pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a "normal" Parsons-Sclater subsidence curve. The Farallon plate, now almost entirely subducted, was also the scene of mid-plate volcanism that produced such features as the Nicoya Plateau now found as an allochthonous ophiolitic terrain landward of the middle America trench. Large, benthonic, reef-associated foraminifera comprising a pseudorbitoid fauna, hitherto considered to be largely restricted to Central America, have now been additionally recorded from DSDP Sites 165, 315 and 316 in the Line Islands, Site 462 in the Nauru Basin, and in New Guinea. The distribution of this fauna, of Campanian/Maastrichtian age, is interpreted as indicating "stepping stone" connections (aseismic ridges, plateaus and seamounts) between the Caribbean, Farallon, and Pacific plates 70-80 m.y. B.P. Similarities between the geology of the Nauru Basin and the Caribbean Ocean crust reinforce the interpretation of the latter as a former part of the Farallon plate. Estimates of the sea-level and continental freeboard change caused by the thermally induced uplift of the Pacific and Farallon plates, as well as substantial areas in the Atlantic and Indian Ocean Basins, indicate that such shallowing of the sea floor could have been

  14. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe; de Gelder, Giovanni; van der Goes, Freek; Morris, Antony

    2017-04-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Supra-subduction zone (SSZ) ophiolites (i.e., emerged fragments of ancient oceanic lithosphere accreted at supra-subduction spreading centers) were generated during this subduction event, and are today distributed in the eastern Mediterranean region along three E-W trending ophiolitic belts. Current models associate these ophiolite belts to simultaneous initiation of multiple, E-W trending subduction zones at 95 Ma. Here we report paleospreading direction data obtained from paleomagnetic analysis of sheeted dyke sections from seven Neo-Tethyan ophiolites of Turkey, Cyprus, and Syria, demonstrating that these ophiolites formed at NNE-SSW striking ridges parallel to the newly formed subduction zones. This subduction system was step-shaped and composed of NNE-SSW and ESE-WNW segments. The eastern subduction segment invaded the SW Mediterranean, leading to a radial obduction pattern similar to the Banda arc. Emplacement age constraints indicate that this subduction system formed close to the Triassic passive and paleo-transform margins of the Anatolide-Tauride continental block. Because the original Triassic-Jurassic Neo-Tethyan spreading ridge must have already subducted below the Pontides before the Late Cretaceous, we infer that the Late Cretaceous Neo-Tethyan subduction system started within ancient lithosphere, along NNE-SSW oriented fracture zones and faults parallel to the E-W trending passive margins. This challenges current concepts suggesting that subduction initiation occurs along active intra-oceanic plate boundaries.

  15. 3D geodynamic models for the development of opposing continental subduction zones: The Hindu Kush-Pamir example

    Science.gov (United States)

    Liao, Jie; Gerya, Taras; Thielmann, Marcel; Webb, A. Alexander G.; Kufner, Sofia-Katerina; Yin, An

    2017-12-01

    The development of opposing continental subduction zones remains scantly explored in three dimensions. The Hindu Kush-Pamir orogenic system at the western end of the Himalayan orogen provides a rare example of continental collision linked to two opposing intra-continental subduction zones. The subducted plates feature a peculiar 3D geometry consisting of two distinct lithospheric fragments with different polarities, subduction angles and slab-curvatures beneath the Hindu Kush and Pamir, respectively. Using 3D geodynamic modeling, we simulate possible development of two opposing continental subduction zones to understand the dynamic evolution of the Hindu Kush-Pamir orogenic system. Our geodynamic model reproduces the major tectonic elements observed: (1) the deeper subduction depth, the steeper dip angle and the southward offset of the Hindu Kush subduction zone relative to the Pamir naturally occur if convergence direction of the subducting Indian plate and dip-direction of the Hindu Kush subduction zone match. (2) The formation of the highly asymmetrically curved Pamir region and the south-dipping subduction is promoted by the initial geometry of the indenting Indian lithosphere together with the existence of a major strike-slip fault on the eastern margin of the Pamir region. (3) Subduction of only the lower continental crust during continental collision can occur if the coupling between upper and lower crusts is weak enough to allow a separation of these two components, and that (4) the subduction of mainly lower crust then facilitates that conditions for intermediate-depth seismicity can be reached. (5) The secondary tectonic features modeled here such as strike-slip-fault growth, north-northwest striking extension zone, and lateral flow of the thickened ductile upper crust are comparable to the current tectonics of the region. (6) Model results are further compared to the potentially similar orogenic system, i.e., the Alpine orogen, in terms of the curved

  16. Fore-arc deformation at the transition between collision and subduction: insights from 3D thermo-mechanical laboratory experiments.

    OpenAIRE

    D. Boutelier; Onno Oncken; A. Cruden

    2012-01-01

    Three-dimensional thermomechanical laboratory experiments of arc-continent collision investigate the deformation of the fore arc at the transition between collision and subduction. The deformation of the plates in the collision area propagates into the subduction-collision transition zone via along-strike coupling of the neighboring segments of the plate boundary. In our experiments, the largest along-strike gradient of trench-perpendicular compression does not produce sufficiently localized ...

  17. Seamount subduction at the North-Ecuadorian convergent margin : effects on structures, inter-seismic coupling and seismogenesis

    OpenAIRE

    Marcaillou, Boris; Collot, Jean-Yves; Ribodetti, Alessandra; d'Acremont, E.; Mahamat, A. A.; Alvarado, A.

    2016-01-01

    At the North-Ecuadorian convergent margin (1 degrees S-1.5 degrees N), the subduction of the rough Nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust. We used three selected pre-stack depth migrated, multi-channel seismic reflection lines collected during the SISTEUR cruise to investigate the margin structure and decipher the impact of the subducted Atacames seamounts on tectonic erosion, interseismic coupling, and seismogenesis...

  18. Oblique subduction modelling indicates along-trench tectonic transport of sediments.

    Science.gov (United States)

    Malatesta, Cristina; Gerya, Taras; Crispini, Laura; Federico, Laura; Capponi, Giovanni

    2013-01-01

    Convergent plate margins are currently distinguished as 'accretional' or 'erosional', depending on the tendency to accumulate sediments, or not, at the trench. Accretion and erosion can coexist along the same margin and we have noticed that this mostly occurs where subduction is oblique. Here we show that at oblique subduction zones, sediments that enter the trench are first buried, and later migrate laterally parallel to the trench and at various depths. Lateral migration of sediments continues until they reach a physical barrier where they begin to accumulate. The accretionary wedge size decreases along the trench moving away from the barrier. We therefore suggest that the gradual variation of the accretionary wedge size and sediment amount at the trench along one single subduction zone, as observed in many active plate margins worldwide, can be explained by the lateral tectonic migration of sediments driven by obliquity of subduction as well.

  19. Molybdenum mobility and isotopic fractionation during subduction at the Mariana arc

    Science.gov (United States)

    Freymuth, Heye; Vils, Flurin; Willbold, Matthias; Taylor, Rex N.; Elliott, Tim

    2015-12-01

    The fate of crustal material recycled into the convecting mantle by plate tectonics is important for understanding the chemical and physical evolution of the planet. Marked isotopic variability of Mo at the Earth's surface offers the promise of providing distinctive signatures of such recycled material. However, characterisation of the behaviour of Mo during subduction is needed to assess the potential of Mo isotope ratios as tracers for global geochemical cycles. Here we present Mo isotope data for input and output components of the archetypical Mariana arc: Mariana arc lavas, sediments from ODP Sites 800, 801 and 802 near the Mariana trench and the altered mafic, oceanic crust (AOC), from ODP Site 801, together with samples of the deeper oceanic crust from ODP Site 1256. We also report new high precision Pb isotope data for the Mariana arc lavas and a dataset of Pb isotope ratios from sediments from ODP Sites 800, 801 and 802. The Mariana arc lavas are enriched in Mo compared to elements of similar incompatibility during upper mantle melting, and have distinct, isotopically heavy Mo (high 98Mo/95Mo) relative to the upper mantle, by up to 0.3 parts per thousand. In contrast, the various subducting sediment lithologies dominantly host isotopically light Mo. Coupled Pb and Mo enrichment in the Mariana arc lavas suggests a common source for these elements and we further use Pb isotopes to identify the origin of the isotopically heavy Mo. We infer that an aqueous fluid component with elevated [Mo], [Pb], high 98Mo/95Mo and unradiogenic Pb is derived from the subducting, mafic oceanic crust. Although the top few hundred metres of the subducting, mafic crust have a high 98Mo/95Mo, as a result of seawater alteration, tightly defined Pb isotope arrays of the Mariana arc lavas extrapolate to a fluid component akin to fresh Pacific mid-ocean ridge basalts. This argues against a flux dominantly derived from the highly altered, uppermost mafic crust or indeed from an Indian

  20. The Two Subduction Zones of the Southern Caribbean: Lithosphere Tearing and Continental Margin Recycling in the East, Flat Slab Subduction and Laramide-Style Uplifts in the West

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Niu, F.; Schmitz, M.

    2015-12-01

    The southern Caribbean plate boundary is a complex strike-slip fault system bounded by oppositely vergent subduction zones, the Antilles subduction zone in the east, and a currently locked Caribbean-South American subduction zone in the west (Bilham and Mencin, 2013). Finite-frequency teleseismic P-wave tomography images both the Atlanic (ATL) and the Caribbean (CAR) plates subducting steeply in opposite directions to transition zone depths under northern South America. Ps receiver functions show a depressed 660 discontinuity and thickened transition zone associated with each subducting plate. In the east the oceanic (ATL) part of the South American (SA) plate subducts westward beneath the CAR, initiating the El Pilar-San Sebastian strike slip system, a subduction-transform edge propagator (STEP) fault (Govers and Wortel, 2005). The point at which the ATL tears away from SA as it descends into the mantle is evidenced by the Paria cluster seismicity at depths of 60-110 km (Russo et al, 1993). Body wave tomography and lithosphere-asthenosphere boundary (LAB) thickness determined from Sp and Ps receiver functions and Rayleigh waves suggest that the descending ATL also viscously removes the bottom third to half of the SA continental margin lithospheric mantle as it descends. This has left thinned continental lithosphere under northern SA in the wake of the eastward migrating Antilles subduction zone. The thinned lithosphere occupies ~70% of the length of the El Pilar-San Sebastian fault system, from ~64oW to ~69oW, and extends inland several hundred kilometers. In northwestern SA the CAR subducts east-southeast at low angle under northern Colombia and western Venezuela. The subducting CAR is at least 200 km wide, extending from northernmost Colombia as far south as the Bucaramanga nest seismicity. The CAR descends steeply under Lake Maracaibo and the Merida Andes. This flat slab is associated with three Neogene basement cored, Laramide-style uplifts: the Santa Marta

  1. Nonuniform subduction of the Indian crust beneath the Himalayas.

    Science.gov (United States)

    Guo, Xiaoyu; Li, Wenhui; Gao, Rui; Xu, Xiao; Li, Hongqiang; Huang, Xingfu; Ye, Zhuo; Lu, Zhanwu; Klemperer, Simon L

    2017-10-02

    Himalayan tectonic activity is triggered by downward penetration of the Indian plate beneath the Asian plate. The subsurface geometry of this interaction has not been fully investigated. This study presents novel constraints on this geometry provided by two newly obtained, deep seismic reflection profiles. The profiles cover 100- and 60-km transects across the Yarlung-Zangbo suture of the Himalaya-Tibet orogen at c. 88°E. Both profiles show a crustal-scale outline of the subducting Indian crust. This outline clearly shows Indian understhrusting southern Tibet, but only to a limited degree. When combined with a third seismic reflection profile of the western Himalayas, the new profiles reveal progressive, eastward steepening and shortening in the horizontal advance of the subducting Indian crust.

  2. Formation of mantle "lone plumes" in the global downwelling zone - A multiscale modelling of subduction-controlled plume generation beneath the South China Sea

    Science.gov (United States)

    Zhang, Nan; Li, Zheng-Xiang

    2018-01-01

    It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a "lone plume". Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top mechanical boundary condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

  3. Uplift in the Fiordland region, New Zealand: implications for incipient subduction.

    Science.gov (United States)

    House, M A; Gurnis, M; Kamp, P J J; Sutherland, R

    2002-09-20

    Low-temperature thermochronometry reveals regional Late Cenozoic denudation in Fiordland, New Zealand, consistent with geodynamic models showing uplift of the overriding plate during incipient subduction. The data show a northward progression of exhumation in response to northward migration of the initiation of subduction. The locus of most recent uplift coincides with a large positive Bouguer gravity anomaly within Fiordland. Thermochronometrically deduced crustal thinning, anomalous gravity, and estimates of surface uplift are all consistent with approximately 2 kilometers of dynamic support. This amount of dynamic support is in accord with geodynamic predictions, suggesting that we have dated the initiation of subduction adjacent to Fiordland.

  4. Boron cycling in subduction zones

    OpenAIRE

    Palmer, Martin R.

    2017-01-01

    Subduction zones are geologically dramatic features, with much of the drama being driven by the movement of water. The “light and lively” nature of boron, coupled with its wide variations in isotopic composition shown by the different geo-players in this drama, make it an ideal tracer for the role and movement of water during subduction. The utility of boron ranges from monitoring how the fluids that are expelled from the accretionary prism influence seawater chemistry, to the subduction of c...

  5. The dominant surface-topography contributions of individual subduction parameters

    Science.gov (United States)

    Crameri, Fabio; Lithgow-Bertelloni, Carolina; Tackley, Paul

    2017-04-01

    It is no secret, not any longer, that dynamic processes below the plate exert a significant contribution to the elevation of the plate at the surface (e.g., Flament et al., 2013). We have therefore studied* the individual impact each and every major subduction parameter has on surface topography. This allows us to qualitatively compare the different sources amongst each other, and to quantify their actual potential to vertically deflect the surface. The gained knowledge from this compilation is crucial: We might finally be able to link the directly-observable surface topography to the dynamics (buoyancy, rheology, and geometry) of the subduction system. *This study is made possible by the efficient convection code StagYY (Tackley 2008), the largely-automated post-processing and visualisation toolbox StagLab (www.fabiocrameri.ch/software), and crucial model developments (Crameri and Tackley, 2015; Crameri et al., G-cubed, submitted, Crameri and Lithgow-Bertelloni, Tectonophysics, submitted). REFERENCES 
Flament, N., M. Gurnis, and R. D. Müller (2013), A review of observations and models of dynamic topography, Lithosphere, 5(2), 189-210. Crameri, F., and P. J. Tackley (2015), Parameters controlling dynamically self-consistent plate tectonics and single-sided subduction in global models of mantle convection, J. Geophys. Res. Solid Earth, 120(5), 3680-3706. Crameri, F., C. R. Lithgow-Bertelloni, and P. J. Tackley (submitted), The dynamical control of subduction parameters on surface topography, Geochem. Geophys. Geosyst. Crameri, F., and C. R. Lithgow-Bertelloni (submitted), Dynamic Mantle-Transition-Zone Controls on Upper-Plate Tilt, Tectonophysics. Tackley, P.J (2008) Modelling compressible mantle convection with large viscosity contrasts in a three- dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors 171(1-4), 7-18.

  6. Complex Subduction Imaged by Diffractional Tomography of USArray Receiver Functions

    Science.gov (United States)

    Zhou, Y.

    2016-12-01

    Subduction of a large oceanic plate beneath a continental plate is a complex process. In the Western United States, fragmentation of the Farallon slab has been reported in recent tomographic models. In this study, we measure finite-frequency travel times of P410s and P660s receiver functions recorded at USArray Transportable Array (TA) stations for teleseismic events occurred between 2015 and 2011. We calculate the finite-frequency sensitivities of receiver functions to depth perturbations of the 410-km and 660-km discontinuities to obtain high resolution mantle transition zone models based on diffractional tomography. The high-resolution discontinuity models reveal several interesting anomalies associated with complex subduction of the Farallon plate. In particular, we observe a linear feature in both the 410-km and 660-km discontinuity models. This mantle transition zone anomaly is roughly located in the western Snake River Plain and aligns with a major slab gap imaged in an earlier finite-frequency S-wave velocity model. We show that non-stationary upwellings generated by eastward propagation of a slab tearing event, together with a westward motion of the North American plate at a rate of about 1 to 1.5 centimeters per year (comparable to the half spreading rate of the Mid-Atlantic Ridge) in the past 16 million years can explain the age-progressive Snake River Plain / Yellowstone volcanic track. The slab to the west of the anomaly shows a near vertical subduction, it is heavily fragmented and the 410-km and 660-km discontinuity topography indicates that the southern fragment north of the Mendocino triple junction has subducted down to the mantle transition zone.

  7. Crust and subduction zone structure of Southwestern Mexico

    Science.gov (United States)

    Suhardja, Sandy Kurniawan; Grand, Stephen P.; Wilson, David; Guzman-Speziale, Marco; Gomez-Gonzalez, Juan Martin; Dominguez-Reyes, Tonatiuh; Ni, James

    2015-02-01

    Southwestern Mexico is a region of complex active tectonics with subduction of the young Rivera and Cocos plates to the south and widespread magmatism and rifting in the continental interior. Here we use receiver function analysis on data recorded by a 50 station temporary deployment of seismometers known as the MARS (MApping the Rivera Subduction zone) array to investigate crustal structure as well as the nature of the subduction interface near the coast. The array was deployed in the Mexican states of Jalisco, Colima, and Michoacan. Crustal thickness varies from 20 km near the coast to 42 km in the continental interior. The Rivera plate has steeper dip than the Cocos plate and is also deeper along the coast than previous estimates have shown. Inland, there is not a correlation between the thickness of the crust and topography indicating that the high topography in northern Jalisco and Michoacan is likely supported by buoyant mantle. High crustal Vp/Vs ratios (greater than 1.82) are found beneath the trenchward edge of magmatism including below the Central Jalisco Volcanic Lineament and the Michoacan-Guanajuato Volcanic Field implying a new arc is forming closer to the trench than the Trans Mexican Volcanic Belt. Elsewhere in the region, crustal Vp/Vs ratios are normal. The subducting Rivera and Cocos plates are marked by a dipping shear wave low-velocity layer. We estimate the thickness of the low-velocity layer to be 3 to 4 km with an unusually high Vp/Vs ratio of 2.0 to 2.1 and a drop in S velocity of 25%. We postulate that the low-velocity zone is the upper oceanic crust with high pore pressures. The low-velocity zone ends from 45 to 50 km depth and likely marks the basalt to eclogite transition.

  8. Geographic information system (GIS) compilation of geophysical, geologic, and tectonic data for the Circum-North Pacific

    Science.gov (United States)

    Greninger, Mark L.; Klemperer, Simon L.; Nokleberg, Warren J.

    1999-01-01

    The accompanying directory structure contains a Geographic Information Systems (GIS) compilation of geophysical, geological, and tectonic data for the Circum-North Pacific. This area includes the Russian Far East, Alaska, the Canadian Cordillera, linking continental shelves, and adjacent oceans. This GIS compilation extends from 120?E to 115?W, and from 40?N to 80?N. This area encompasses: (1) to the south, the modern Pacific plate boundary of the Japan-Kuril and Aleutian subduction zones, the Queen Charlotte transform fault, and the Cascadia subduction zone; (2) to the north, the continent-ocean transition from the Eurasian and North American continents to the Arctic Ocean; (3) to the west, the diffuse Eurasian-North American plate boundary, including the probable Okhotsk plate; and (4) to the east, the Alaskan-Canadian Cordilleran fold belt. This compilation should be useful for: (1) studying the Mesozoic and Cenozoic collisional and accretionary tectonics that assembled this continental crust of this region; (2) studying the neotectonics of active and passive plate margins in this region; and (3) constructing and interpreting geophysical, geologic, and tectonic models of the region. Geographic Information Systems (GIS) programs provide powerful tools for managing and analyzing spatial databases. Geological applications include regional tectonics, geophysics, mineral and petroleum exploration, resource management, and land-use planning. This CD-ROM contains thematic layers of spatial data-sets for geology, gravity field, magnetic field, oceanic plates, overlap assemblages, seismology (earthquakes), tectonostratigraphic terranes, topography, and volcanoes. The GIS compilation can be viewed, manipulated, and plotted with commercial software (ArcView and ArcInfo) or through a freeware program (ArcExplorer) that can be downloaded from http://www.esri.com for both Unix and Windows computers using the button below.

  9. Topographic and sedimentary features in the Yap subduction zone and their implications for the Caroline Ridge subduction

    Science.gov (United States)

    Dong, Dongdong; Zhang, Zhengyi; Bai, Yongliang; Fan, Jianke; Zhang, Guangxu

    2018-01-01

    The Yap subduction zone in the western Pacific presents some unique features compared to normal intra-oceanic subduction zones such as the subduction of an oceanic plateau. However, due to the relative paucity of geophysical data, the detailed structure remains unknown in this area. In this study, we present the latest high-quality swath bathymetry and multi-channel seismic data acquired synchronously in 2015 across the Yap subduction zone. The topographic and sedimentary features are intensively investigated and a modified evolutionary model of the Yap subduction zone is proposed. The two-stage evolution of the Parece Vela Basin (PVB) produced fabrics that are N-S trending and NW-SE trending. Our seismic data clearly reveal landslide deposits at the upper slope break of the forearc, to the north of the Yap Island, which was identified as the fault notch denoting a lithological boundary in previous work. The swath bathymetry and seismic profile reveal detailed horst and graben structures, including a crescent-shaped fault zone near the contact between the Yap Trench and the Caroline Ridge. A simple geometric model is proposed to explain the structure formation, indicating that the higher topography of the Caroline Ridge resulted in enhanced bending-related extension. A seismic angular unconformity (named R1) is identified in the Sorol Trough, marking the onset of rifting in the trough. Based on the sequence thickness and deposition rate by Deep Sea Drilling Project (DSDP), it is deduced that the Sorol Trough formed at 10 Ma or even earlier. A modified model for the Yap subduction zone evolution is proposed, incorporating three major tectonic events: the proto-Yap Arc rupture in the Oligocene, the collision of the Caroline Ridge and the Yap Trench in the late Oligocene or middle Miocene, and the onset of the Sorol Trough rifting in the late Miocene.

  10. Chemical and isotopic diversity in basalts dredged from the East Pacific Rise at 10°S, the fossil Galapagos Rise and the Nazca plate

    Science.gov (United States)

    Batiza, Rodey; Oestrike, Richard; Futa, Kiyoto

    1982-01-01

    We present petrographic, chemical and isotopic data for fresh lava samples dredged from three regions: (1) the fossil Galapagos Rise; (2) an elongate volcano near this extinct spreading center; and (3) the East Pacific Rise at 10°S. The samples from the Galapagos Rise are among the first samples from any fossil spreading center to be analyzed. Alkalic picrites from the elongate seamount and transitional basalts from the East Pacific Rise are both somewhat unusual rock types considering their respective tectonic environments.

  11. Effect of the Earth's rotation on subduction processes

    Science.gov (United States)

    Levin, B. W.; Rodkin, M. V.; Sasorova, E. V.

    2017-09-01

    The role played by the Earth's rotation is very important in problems of physics of the atmosphere and ocean. The importance of inertia forces is traditionally estimated by the value of the Rossby number: if this parameter is small, the Coriolis force considerably affects the character of movements. In the case of convection in the Earth's mantle and movements of lithospheric plates, the Rossby number is quite small; therefore, the effect of the Coriolis force is reflected in the character of movements of the lithospheric plates. Analysis of statistical data on subduction zones verifies this suggestion.

  12. Subducting slab ultra-slow velocity layer coincident with silent earthquakes in southern Mexico.

    Science.gov (United States)

    Song, Teh-Ru Alex; Helmberger, Donald V; Brudzinski, Michael R; Clayton, Robert W; Davis, Paul; Pérez-Campos, Xyoli; Singh, Shri K

    2009-04-24

    Great earthquakes have repeatedly occurred on the plate interface in a few shallow-dipping subduction zones where the subducting and overriding plates are strongly locked. Silent earthquakes (or slow slip events) were recently discovered at the down-dip extension of the locked zone and interact with the earthquake cycle. Here, we show that locally observed converted SP arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern Mexico reveal that the ultra-slow velocity layer (USL) varies spatially (3 to 5 kilometers, with an S-wave velocity of approximately 2.0 to 2.7 kilometers per second). Most slow slip patches coincide with the presence of the USL, and they are bounded by the absence of the USL. The extent of the USL delineates the zone of transitional frictional behavior.

  13. Energy resources of Pacific Coast of Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Bueno Salazar, R.

    1986-07-01

    Despite failure of modest exploration efforts to yield commercial hydrocarbon production in the Choco-Pacific coastal basin of Colombia, recent geophysical, geochemical, and surface geologic investigations indicate a potential for petroleum accumulations, which could be related to fields located on the western basins of Ecuador that in fact constitute an extension of the Colombian Pacific geologic scheme. The Choco-Pacific coastal basin of Colombia covers an area of approximately 70,000 km/sup 2/, of which 14,000 km/sup 2/ lies offshore. The structural style of this area corresponds to a convergent plate basin created over folded oceanic sediments and adjacent to the subduction zone. Such a framework could be conducive to an attractive array of potential hydrocarbon-bearing traps. Geochemical knowledge of potential source rocks of Cretaceous and early Tertiary age confers an added attraction to the area. Most evaluations reveal kerogen-rich, gas-prone organic matter. Nevertheless, the existence of oil seeps from Cretaceous outcrops could indicate sufficient thermal maturity for oil generation. Adequate reservoirs could be found in sandy or calcareous rocks of late Eocene to Oligocene age, predominantly of marine origin with an estimated thickness exceeding 20,000 ft. Colombia has been one of the leading world producers of gold and platinum, mostly derived from the vast alluvial cover of the onshore area of the basin. In rocks cropping out in the Western Cordillera (eastern margin of the basin), deposits of potentially commercial value of porphyry copper and molybdenum, as well as massive sulfur, manganese, and bauxite, have been found.

  14. Petroleum geology of Pacific margin of Central America and northern South America, from Guatemala to Ecuador

    Energy Technology Data Exchange (ETDEWEB)

    Scrutton, M.E.; Escalante, G.F.

    1986-07-01

    Exploration for hydrocarbons along the Pacific margin of Central America and northern South America has been limited and spasmodic. Less than 100 exploration wells have been drilled, with nearly 50 of these being in the Santa Elena, Progreso, and Guayas basins in Ecuador. Shows have been reported in some wells, and a few oil seeps are known. The only commercial production established to date has been from the Santa Elena Peninsula in Ecuador in the extreme south of the study area. Understanding of the geology in this part of the continental margin is incomplete at best. This paper reviews present-day knowledge in an attempt to define the sedimentary basins better, to characterize their structure and stratigraphy, and to assess their petroleum prospects. The area of continental margin reviewed is to the north, located northwest of the trench system where oceanic crust of the Cocos plate subducts under the Caribbean plate, and to the south, where the northern part of the Nazca plate collides with the South American plate. This plate tectonic setting forms the framework on which local structural and sedimentary events have created a series of relatively small trench-slope and forearc basins in what is now the coastal plain and adjacent offshore area of Central and South America, south or west of a line of mountain ranges with active volcanism. Sedimentary fill is generally of Tertiary age. The basins and subbasins recognized and described include: in Ecuador - Guayas, Santa Elena, Progreso, Valdivia, Bajo Grande, Manta, Muisne-Esmeraldas, and Borbon; in Colombia - Choco-Pacific; in Panama - Gulf of Panama basin complex (Santiago, Tonosi, Sambu), and Burica-Chiriqui; in Costa Rica - Terraba and Coronado/Tempisque; in Nicaragua - San Juan del Sur; and in the Honduras, El Salvador, and Guatemala - the Pacific coastal basin.

  15. Earth's Decelerating Tectonic Plates

    Energy Technology Data Exchange (ETDEWEB)

    Forte, A M; Moucha, R; Rowley, D B; Quere, S; Mitrovica, J X; Simmons, N A; Grand, S P

    2008-08-22

    Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

  16. Necessity of the Ridge for the Flat Slab Subduction: Insights from the Peruvian Flat Slab

    Science.gov (United States)

    Knezevic Antonijevic, S.; Wagner, L. S.; Beck, S. L.; Long, M. D.; Zandt, G.; Tavera, H.

    2014-12-01

    Flattening of the subducting plate has been linked to the formation of various geological features, including basement-cored uplifts, the cessation of arc volcanism, ignimbrite flare-ups, and the formation of high plateaus and ore deposits [Humphreys et al., 2003; Gutscher et al., 2000; Rosenbaum et al., 2005]. However, the mechanism responsible for the slab flattening is still poorly understood. Here we focus on the Peruvian flat slab, where the Nazca plate starts to bend at ~80 km depth and travels horizontally for several hundred kilometers, at which point steep subduction resumes. Based on a 1500 km long volcanic gap and intermediate depth seismicity patterns, the Peruvian flat slab appears to have the greatest along-strike extent and, therefore, has been suggested as a modern analogue to the putative flat slab during the Laramide orogeny in the western United States (~80-55 Ma). Combining 3D shear wave velocity structure and Rayleigh wave phase anisotropy between ~10° and 18° S, we find that the subducting Nazca plate is not uniformly flat along the entire region, but fails to the north of the subducting Nazca Ridge. Our results show that, in combination with trench retreat, rapid overriding plate motion, and/or presence of a thick cratonic root, the subduction of buoyant overthickened oceanic crust, such as the Nazca Ridge, is necessary for the formation and sustainability of flat slabs. This finding has important implications for the formation of flat slabs both past and present.

  17. To what depth can continental crust be subducted: numerical predictions and critical observations

    Science.gov (United States)

    Gerya, T.; Faccenda, M.

    2006-12-01

    We performed systematic two-dimensional numerical modeling of continental collision associated with subduction of the lithospheric mantle. Results of our experiments suggest that two contrasting modes of lithospheric subduction below an orogen can exist: one-sided and double-sided. One-sided subduction brings continental crust subducting atop the slab to the contact with hot asthenosperic mantle wedge below the overriding plate. This can result in strong heating, partial melting and rheological weakening of the crust triggering its delamination from subducting mantle lithosphere in form of compositionally buoyant structures (cold plumes) propagating away from subducting plate, passing through the hot mantle wedge, underplating the overriding lithosphere and producing large amount of relatively felsic syn-orogenic magmas at sub-lithospheric depths. One-sided subduction of the buoyant continental crust can also result in a transient "hot channel effect" triggering formation and exhumation of coesite- and diamond- bearing rocks metamorphosed at 700 to 900oC. Anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper-crustal rocks. Low effective viscosity of the channel subsequent to increased temperature and partial melting permits profound mixing of mantle and crustal rocks. The hot channel exists during few million years only but rapidly produces and exhumes large amounts of ultrahigh-pressure, high-temperature rocks within the orogen. Double-sided subduction can follow the one-sided mode at later stages of orogeny when significant rheological coupling between two plates occurs during the collision. In this case the orogen is characterized by double- verging structure, the layer of subducting continental crust is embedded between two negatively buoyant lithospheric slabs and delamination of the crust does not occur. This mode of subduction can bring crustal rocks from the bottom of an

  18. Horizontal subduction zones, convergence velocity and the building of the Andes

    CERN Document Server

    Martinod, Joseph; Roperch, Pierrick; Guillaume, Benjamin; Espurt, Nicolas; 10.1016/j.epsl.2010.09.010

    2010-01-01

    We discuss the relationships between Andean shortening, plate velocities at the trench, and slab geometry beneath South America. Although some correlation exists between the convergence velocity and the westward motion of South America on the one hand, and the shortening of the continental plate on the other hand, plate kinematics neither gives a satisfactory explanation to the Andean segmentation in general, nor explains the development of the Bolivian orocline in Paleogene times. We discuss the Cenozoic history of horizontal slab segments below South America, arguing that they result from the subduction of oceanic plateaus whose effect is to switch the buoyancy of the young subducting plate to positive. We argue that the existence of horizontal slab segments, below the Central Andes during Eocene-Oligocene times, and below Peru and North-Central Chile since Pliocene, resulted (1) in the shortening of the continental plate interiors at a large distance from the trench, (2) in stronger interplate coupling and...

  19. Tectonic implications of tomographic images of subducted lithosphere beneath northwestern South America

    NARCIS (Netherlands)

    Hilst, R.D. van der; Mann, P.

    1994-01-01

    We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific lithosphere beneath the study area.

  20. Distribution of dehalogenation activity in subseafloor sediments of the Nankai Trough subduction zone.

    Science.gov (United States)

    Futagami, Taiki; Morono, Yuki; Terada, Takeshi; Kaksonen, Anna H; Inagaki, Fumio

    2013-04-19

    Halogenated organic matter buried in marine subsurface sediment may serve as a source of electron acceptors for anaerobic respiration of subseafloor microbes. Detection of a diverse array of reductive dehalogenase-homologous (rdhA) genes suggests that subseafloor organohalide-respiring microbial communities may play significant ecological roles in the biogeochemical carbon and halogen cycle in the subseafloor biosphere. We report here the spatial distribution of dehalogenation activity in the Nankai Trough plate-subduction zone of the northwest Pacific off the Kii Peninsula of Japan. Incubation experiments with slurries of sediment collected at various depths and locations showed that degradation of several organohalides tested only occurred in the shallow sedimentary basin, down to 4.7 metres below the seafloor, despite detection of rdhA in the deeper sediments. We studied the phylogenetic diversity of the metabolically active microbes in positive enrichment cultures by extracting RNA, and found that Desulfuromonadales bacteria predominate. In addition, for the isolation of genes involved in the dehalogenation reaction, we performed a substrate-induced gene expression screening on DNA extracted from the enrichment cultures. Diverse DNA fragments were obtained and some of them showed best BLAST hit to known organohalide respirers such as Dehalococcoides, whereas no functionally known dehalogenation-related genes such as rdhA were found, indicating the need to improve the molecular approach to assess functional genes for organohalide respiration.

  1. Geophysical detection of relict metasomatism from an Archean (approximately 3.5 Ga) subduction zone.

    Science.gov (United States)

    Chen, Chin-Wu; Rondenay, Stéphane; Evans, Rob L; Snyder, David B

    2009-11-20

    When plate tectonics started on Earth has been uncertain, and its role in the assembly of early continents is not well understood. By synthesizing coincident seismic and electrical profiles, we show that subduction processes formed the Archean Slave craton in Canada. The spatial overlap between a seismic discontinuity and a conductive anomaly at approximately 100 kilometers depth, in conjunction with the occurrence of mantle xenoliths rich in secondary minerals representative of a metasomatic front, supports cratonic assembly by subduction and accretion of lithospheric fragments. Although evidence of cratonic assembly is rarely preserved, these results suggest that plate tectonics was operating as early as Paleoarchean times, approximately 3.5 billion years ago (Ga).

  2. Seismic anisotropy and mantle flow below subducting slabs

    Science.gov (United States)

    Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

    2017-05-01

    Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth < 50 km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

  3. Fluid Release and the Deformation of Subducting Crust

    Science.gov (United States)

    Maunder, Benjamin; van Hunen, Jeroen; Magni, Valentina; Bouilhol, Pierre

    2014-05-01

    It is known that slab dehydration is crucial in subduction dynamics and for the formation of arc-magmatism. Previous studies of this process have constrained this intake and subsequent release of fluids into the mantle wedge by considering the stability hydrous phases within the slab. Other, more dynamical effects of this hydration state and partial melting have also been suggested, such as the possibility of "cold plumes", crustal delamination, and subduction channel return flow. These processes have been inferred to play a role in the generation of continental crust over time through accumulation and melting beneath the overriding plate. Water content and melt fraction have a strong control on the rheology of the system. Therefore we investigate the effect of these parameters on the dynamics of a subducting slab, with the aim to establish the physical bounds on the delamination process. To do this we use a coupled geodynamical-petrological model that tracks dehydration and melting reactions in order to factor in the rheological effect of metamorphism and magmatism on slab and mantle wedge dynamics. We focus primarily on the strength of the subducting crust and the possibility of delamination. We then extend this investigation by considering whether early earth crust formation could have been the result of such a processes by looking at a hypothetical Archean setting.

  4. Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology.

    Science.gov (United States)

    Keenan, Timothy E; Encarnación, John; Buchwaldt, Robert; Fernandez, Dan; Mattinson, James; Rasoazanamparany, Christine; Luetkemeyer, P Benjamin

    2016-11-22

    Where and how subduction zones initiate is a fundamental tectonic problem, yet there are few well-constrained geologic tests that address the tectonic settings and dynamics of the process. Numerical modeling has shown that oceanic spreading centers are some of the weakest parts of the plate tectonic system [Gurnis M, Hall C, Lavier L (2004) Geochem Geophys Geosys 5:Q07001], but previous studies have not favored them for subduction initiation because of the positive buoyancy of young lithosphere. Instead, other weak zones, such as fracture zones, have been invoked. Because these models differ in terms of the ages of crust that are juxtaposed at the site of subduction initiation, they can be tested by dating the protoliths of metamorphosed oceanic crust that is formed by underthrusting at the beginning of subduction and comparing that age with the age of the overlying lithosphere and the timing of subduction initiation itself. In the western Philippines, we find that oceanic crust was less than ∼1 My old when it was underthrust and metamorphosed at the onset of subduction in Palawan, Philippines, implying forced subduction initiation at a spreading center. This result shows that young and positively buoyant, but weak, lithosphere was the preferred site for subduction nucleation despite the proximity of other potential weak zones with older, denser lithosphere and that plate motion rapidly changed from divergence to convergence.

  5. Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

    Science.gov (United States)

    Baba, Kiyoshi; Tada, Noriko; Matsuno, Tetsuo; Liang, Pengfei; Li, Ruibai; Zhang, Luolei; Shimizu, Hisayoshi; Abe, Natsue; Hirano, Naoto; Ichiki, Masahiro; Utada, Hisashi

    2017-08-01

    Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of the old oceanic upper mantle. The areas are far from any tectonic activity, and "normal" mantle structure is therefore expected. The data were carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electrical conductivity and thus distort seafloor MT data. An isotropic, one-dimensional electrical conductivity profile was estimated for each area. The profiles were compared with those obtained from two previous study areas in the northwestern Pacific. Between the four profiles, significant differences were observed in the thickness of the resistive layer beyond expectations based on cooling of homogeneous oceanic lithosphere over time. This surprising feature is now further clarified from what was suggested in a previous study. To explain the observed spatial variation, dynamic processes must be introduced, such as influence of the plume associated with the formation of the Shatsky Rise, or spatially non-uniform, small-scale convection in the asthenosphere. There is significant room of further investigation to determine a reasonable and comprehensive interpretation of the lithosphere-asthenosphere system beneath the northwestern Pacific. The present results demonstrate that electrical conductivity provides key information for such investigation.[Figure not available: see fulltext.

  6. Multiple subduction imprints in the mantle below Italy detected in a single lava flow

    Science.gov (United States)

    Nikogosian, Igor; Ersoy, Özlem; Whitehouse, Martin; Mason, Paul R. D.; de Hoog, Jan C. M.; Wortel, Rinus; van Bergen, Manfred J.

    2016-09-01

    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western-Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  7. Shallow seismicity patterns in the northwestern section of the Mexico Subduction Zone

    Science.gov (United States)

    Abbott, Elizabeth R.; Brudzinski, Michael R.

    2015-11-01

    This study characterizes subduction related seismicity with local deployments along the northwestern section of the Mexico Subduction Zone where 4 portions of the plate interface have ruptured in 1973, 1985, 1995, and 2003. It has been proposed that the subducted boundary between the Cocos and Rivera plates occurs beneath this region, as indicated by inland volcanic activity, a gap in tectonic tremor, and the Manzanillo Trough and Colima Graben, which are depressions thought to be associated with the splitting of the two plates after subduction. Data from 50 broadband stations that comprised the MARS seismic array, deployed from January 2006 to June 2007, were processed with the software program Antelope and its generalized source location algorithm, genloc, to detect and locate earthquakes within the network. Slab surface depth contours from the resulting catalog indicate a change in subduction trajectory between the Rivera and Cocos plates. The earthquake locations are spatially anti-correlated with tectonic tremor, supporting the idea that they represent different types of fault slip. Hypocentral patterns also reveal areas of more intense seismic activity (clusters) that appear to be associated with the 2003 and 1973 megathrust rupture regions. Seismicity concentrated inland of the 2003 rupture is consistent with slip on a shallowly dipping trajectory for the Rivera plate interface as opposed to crustal faulting in the overriding North American plate. A prominent cluster of seismicity within the suspected 1973 rupture zone appears to be a commonly active portion of the megathrust as it has been active during three previous deployments. We support these interpretations by determining focal mechanisms and detailed relocations of the largest events within the 1973 and inland 2003 clusters, which indicate primarily thrust mechanisms near the plate interface.

  8. Kinematics and flow patterns in deep mantle and upper mantle subduction models : Influence of the mantle depth and slab to mantle viscosity ratio

    NARCIS (Netherlands)

    Schellart, W. P.

    Three-dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models, an upper mantle model and a deep mantle model, and for various subducting plate/mantle viscosity ratios (ηSP/ηM = 59-1375). The models investigate the mantle flow field,

  9. Water and the oxidation state of subduction zone magmas.

    Science.gov (United States)

    Kelley, Katherine A; Cottrell, Elizabeth

    2009-07-31

    Mantle oxygen fugacity exerts a primary control on mass exchange between Earth's surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/SigmaFe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/SigmaFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.

  10. Thermobarometric and fluid expulsion history of subduction zones

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, W.G. (Univ. of California, Los Angeles (United States))

    1990-06-10

    Phanerozoic, unmetamorphosed, weathered, and altered lithotectonic complexes subjected to subduction exhibit the prograde metamorphic facies sequence: zeolite {r arrow} prehnite-pumpellyite {r arrow} glaucophane schist {r arrow} eclogite. Parageneses reflect relatively high-P trajectories, accompanied by semicontinuous devolatilization. The thermal evolution of convergent plate junctions results in early production of high-rank blueschists, high-P amphibolites, and eclogites at depth. Inclusion studies suggest that two-phase immiscible volatiles are evolved in turn during progressive metamorphism of the subducted sections. Expulsion of pore fluids and transitions from weathered and altered supracrustal rocks to zeolite facies assemblages release far more fluid than the better understood higher-grade transformations. Many blueschist parageneses (e.g., Western Alps) have been partially overprinted by later greenschist and/or epidote-amphibolite facies assemblages. Less common blueschist terranes (e.g., Franciscan belt of western California) preserve metamorphic aragonite and other high-P minerals, and lack a low-pressure overprint; physical conditions during retrogression approximately retraced the prograde path or, for early formed high-grade blocks, reflect somewhat higher pressures and lower temperatures. The ease with which volatiles are expelled from a subduction complex and migrate upward along the plate junction zone is roughly proportional to the sandstone/shale ratio: low-permeability mudstones tend to maintain P{sub fluid} values approaching lithostatic, lose strength, and deform chaotically (forming melange belts), whereas permeable sandstone-rich sections retain structural/stratigraphic coherence and fail brittlely (forming coherent terranes).

  11. From the global scale to the Mediterranean plate kinematics

    OpenAIRE

    Riguzzi, F.

    2008-01-01

    Plate motions with respect to the mantle represent the most direct evidence to understand the origin of plate tectonic processes. The research here described has the aim to improve the knowledge on the global scale plate kinematics in “absolute” reference frames, or better, relative to the mantle, incorporating both geological–geophysical and space geodesy data. Geophysical and geological signatures of subduction and rift zones independently show a global polarity of current plate motions, su...

  12. Plate reconstructions and tomography reveal a fossil lower mantle slab below the Tasman Sea

    NARCIS (Netherlands)

    Schellart, W. P.; Kennett, B. L N; Spakman, W.; Amaru, M.

    2009-01-01

    The Southwest Pacific region is tectonically complex and is home to numerous fossil and active subduction zones. At the Earth's surface, there remains a geological controversy regarding the polarity and continuity of fossil subduction zones in New Zealand and New Caledonia, the origin of obducted

  13. Neotectonics of a subduction/strike-slip transition: the northeastern Dominican Republic

    Energy Technology Data Exchange (ETDEWEB)

    Winslow, M.A.; McCann, W.R.

    1985-01-01

    The Septentrional fault system in the northeastern Dominican Republic marks the zone where the North American-Carribean plate boundary is evolving from subduction to strike-slip motion, and where terranes appear to be forming and migrating laterally in a subduction complex/forearc region. On the Island of Hispaniola, slip vectors are oblique to the strike of the Puerto Rico trench, and oblique subduction thrusts the upper plate over normal seafloor. The offshore geology and seismicity of the northern Caribbean suggest that uplift, broad crustal warping, thrusting, and strike-slip faulting (ie. collisional tectonics) should be present in the northern part of the Dominican Republic. The high topography (>1000m), high levels of seismicity, and large earthquakes support the hypothesis of contemporary deformation in Hispaniola. In this region, the subduction regime dies out toward the west, and deformation is transferred to onshore, oblique-slip faults. As this change in tectonic style has occurred in Neogene to Recent times, we are investigating the modern evolution of a plate boundary. We have already documented: (1) the presence of a strike-slip faulting in the northeastern Dominican Republic; (2) an anomalous push-up structure; and (3) a region of numerous splay faults. In conclusion, recent seismicity suggest a wide zone of deformation and variations in interplate motions near Hispaniola. This island lies at the western limit of active underthrusting and at the eastern limit of onshore faulting, i.e., at an important transition from a subduction to strike-slip regime.

  14. Are diamond-bearing Cretaceous kimberlites related to shallow-angle subduction beneath western North America?

    Science.gov (United States)

    Currie, C. A.; Beaumont, C.

    2009-05-01

    The origin of deep-seated magmatism (in particular, kimberlites and lamproites) within continental plate interiors remains enigmatic in the context of plate tectonic theory. One hypothesis proposes a relationship between kimberlite occurrence and lithospheric subduction, such that a subducting plate releases fluids below a continental craton, triggering melting of the deep lithosphere and magmatism (Sharp, 1974; McCandless, 1999). This study provides a quantitative evaluation of this hypothesis, focusing on the Late Cretaceous- Eocene (105-50 Ma) kimberlites and lamproites of western North America. These magmas were emplaced along a corridor of Archean and Proterozoic lithosphere, 1000-1500 km inboard of the plate margin separating the subducting Farallon Plate and continental North America Plate. Kimberlite-lamproite magmatism coincides with tectonic events, including the Laramide orogeny, shut-down of the Sierra Nevada arc, and eastward migration of volcanism, that are commonly attributed to a change in Farallon Plate geometry to a shallow-angle trajectory (1999; Sharp, W.E., Earth Planet. Sci. Lett., v.21, pp.351-354, 1974.

  15. Deformation Patterns and Subduction Behavior of Continental Lithosphere Entering a Trench

    Science.gov (United States)

    Steedman, C. E.; Kaus, B. J.; Becker, T. W.; Okaya, D.

    2007-05-01

    We perform 2-D numerical simulations of continental lithosphere entering a subduction zone, to better understand deformation patterns resulting from subduction of a continental margin. The model consists of a subduction zone in which an attached slab drives subduction of a passive continental margin beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the dynamics of the system. A novel feature of the code is that the resolution of the model can be significantly increased in selected parts of the domain, which allows for self-consistent modelling of mantle-lithosphere interaction. In the present study we employ this feature to study how lithospheric-scale deformation around and within the subduction zone is influenced by surface processes such as erosion, and by flow in the upper mantle. Using systematic 2-D numerical simulations, we explore the parameters that are dominant in controlling near- surface structures, both with regards to changes in topography and trench location, and subsurface features such as Moho undulations. The main parameters that have been varied are: the lithospheric density structure; the lithospheric age and temperature structure; the strength of the lower crust; the presence of a weak zone at the plate interface; the amounts of erosion; the upper boundary condition (free surface versus free slip); rheology (non-Newtonian versus Newtonian, viscous, visco-elasto-plastic); and finally the effect of an imposed slab breakoff. In all cases we track surface uplift, subduction evolution and rock exhumation history. We find that the strength of the overriding plate influences surface uplift and the shape of subsurface deformation, and that the density and thermal structure of the subducting plate affects trench motion. Denser slab roll back, and younger, lighter slabs advance, while neither slab rheology nor the presence of erosion greatly affect trench location. For all cases

  16. Mantle hydration and Cl-rich fluids in the subduction forearc

    Science.gov (United States)

    Reynard, Bruno

    2016-12-01

    In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for

  17. Far-Field Deformation Resulting from Rheologic Differences Interacting with Tectonic Stresses: An Example from the Pacific/Australian Plate Boundary in Southern New Zealand

    Directory of Open Access Journals (Sweden)

    Phaedra Upton

    2014-07-01

    Full Text Available The Miocene in Southern New Zealand was dominated by strike-slip tectonics. Stratigraphic evidence from this time attests to two zones of subsidence in the south: (a a middle Cenozoic pull-apart basin and (b a regionally extensive subsiding lake complex, which developed east and distal to the developing plate boundary structure. The lake overlay a block of crust with a significantly weak mid-crustal section and we pose the question: can rheological transitions at an angle to a plate boundary produce distal subsidence and/or uplift? We use stratigraphic, structural and geophysical observations from Southern New Zealand to constrain three-dimensional numerical models for a variety of boundary conditions and rheological scenarios. We show that coincident subsidence and uplift can result from purely strike-slip boundary conditions interacting with a transition from strong to weak to strong mid-crustal rheology. The resulting pattern of vertical displacement is a function of the symmetry or asymmetry of the boundary conditions and the extent and orientation of the rheological transitions. For the Southern New Zealand case study, subsidence rates of ~0.1 mm/yr are predicted for a relative plate motion of 25 mm/yr, leading to ~500 m of subsidence over a 5 Ma time period, comparable to the thickness of preserved lacustrine sediments.

  18. Gravity and Magnetic Anomaly Interpretations and 2.5D Cross-Section Models over the Border Ranges Fault System and Aleutian Subduction Zone, Alaska

    Science.gov (United States)

    Mankhemthong, N.; Doser, D. I.; Baker, M. R.; Kaip, G.; Jones, S.; Eslick, B. E.; Budhathoki, P.

    2011-12-01

    Quaternary glacial covers and lack of dense geophysical data on the Kenai Peninsula cause a location and geometry of the Border Ranges fault system (BRFS) within a recent forearc-accretionary boundary of Aleutian subduction zone in southern Alaska are unclear. Using new ~1,300 gravity collections within the Anchorage and Kenai Peninsula regions complied with prior 1997 gravity and aeromagnetic data help us better imaging these fault and the subduction structures. Cook Inlet forearc basin is corresponded by deep gravity anomaly lows; basin boundaries are characterized by a strong gravity gradient, where are considered to be traces of Border Ranges fault system on the east and Castle Mountain and Bruin Bay fault system on the west and northwest of the forearc basin respectively. Gravity anomaly highs over accreted rocks generally increase southeastward to the Aleutian trench, but show a gravity depression over the Kenai Mountains region. The lineament between gravity high and low in the same terrenes over the Kenai Peninsula is may be another evidence to determine the Southern Edge of the Yakutat Microplate (SEY) as inferred by Eberhart-Phillips et al. (2006). Our 2.5-D models illustrate the main fault of the BRFS dips steeply toward the west with a downslip displacement. Gravity and Magnetic anomaly highs, on the east of the BRFS, probably present a slice of the ultramafic complex emplaced by faults along the boundary of the forearc basin and accretionary wedge terranes. Another magnetic high beneath the basin in the southern forearc basin support a serpentiznied body inferred by Saltus et al. (2001), with a decreasing size toward the north. Regional density-gravity models show the Pacific subducting slab beneath the foreacre-arc teranes with a gentle and flatted dip where the subducting plate is located in north of SEY and dips more steeply where it is located on the south of SEY. The gravity depression over the accreted terrene can be explained by a density low

  19. Processes and consequences of deep subduction

    NARCIS (Netherlands)

    Rubie, David C.; Hilst, R.D. van der

    2001-01-01

    Subduction of slabs of oceanic lithosphere into the deep mantle involves a wide range of geophysical and geochemical processes and is of major importance for the physical and chemical evolution of the Earth. For example, subduction and subduction-related volcanism are major processes through

  20. Tertiary plate tectonics and high-pressure metamorphism in New Caledonia

    Science.gov (United States)

    Brothers, R.N.; Blake, M.C.

    1973-01-01

    The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs. ?? 1973.

  1. Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry.

    Science.gov (United States)

    Barry, T L; Davies, J H; Wolstencroft, M; Millar, I L; Zhao, Z; Jian, P; Safonova, I; Price, M

    2017-05-12

    The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth's mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

  2. Building a Subduction Zone Observatory

    Science.gov (United States)

    Gomberg, Joan S.; Bodin, Paul; Bourgeois, Jody; Cashman, Susan; Cowan, Darrel; Creager, Kenneth C.; Crowell, Brendan; Duvall, Alison; Frankel, Arthur; Gonzalez, Frank; Houston, Heidi; Johnson, Paul; Kelsey, Harvey; Miller, Una; Roland, Emily C.; Schmidt, David; Staisch, Lydia; Vidale, John; Wilcock, William; Wirth, Erin

    2016-01-01

    Subduction zones contain many of Earth’s most remarkable geologic structures, from the deepest oceanic trenches to glacier-covered mountains and steaming volcanoes. These environments formed through spectacular events: Nature’s largest earthquakes, tsunamis, and volcanic eruptions are born here.

  3. Plate tectonics in the late Paleozoic

    OpenAIRE

    Domeier, Mathew; Torsvik, Trond H.

    2014-01-01

    As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lit...

  4. Implications for metal and volatile cycles from the pH of subduction zone fluids.

    Science.gov (United States)

    Galvez, Matthieu E; Connolly, James A D; Manning, Craig E

    2016-11-17

    The chemistry of aqueous fluids controls the transport and exchange-the cycles-of metals and volatile elements on Earth. Subduction zones, where oceanic plates sink into the Earth's interior, are the most important geodynamic setting for this fluid-mediated chemical exchange. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at subduction zone conditions has long been a major challenge in Earth science. Here we report thermodynamic predictions of fluid-rock equilibria that tie together models of the thermal structure, mineralogy and fluid speciation of subduction zones. We find that the pH of fluids in subducted crustal lithologies is confined to a mildly alkaline range, modulated by rock volatile and chlorine contents. Cold subduction typical of the Phanerozoic eon favours the preservation of oxidized carbon in subducting slabs. In contrast, the pH of mantle wedge fluids is very sensitive to minor variations in rock composition. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to soluble elements in low abundance in the host rocks, such as carbon, alkali metals and halogens, illustrates a feedback between the chemistry of the Earth's atmosphere-ocean system and the speciation of subduction zone fluids via the composition of the seawater-altered oceanic lithosphere. Our findings provide a perspective on the controlling reactions that have coupled metal and volatile cycles in subduction zones for more than 3 billion years(7).

  5. Spreading continents kick-started plate tectonics.

    Science.gov (United States)

    Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

    2014-09-18

    Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining.

  6. Defining Incipient Subduction by Detecting Serpentenised Mantle in the Regional Magnetic Field

    Science.gov (United States)

    Pires, Rui; Clark, Stuart; Reis, Rui

    2017-04-01

    Keywords: Subduction initiation, Incipient Subduction, Active Margins, Southeast Asia, Mantle wedge The mechanisms of subduction initiation are poorly understood. One idea is to look for incipient subduction zones in the present day and see what features are common in these zones. However, incipient subduction zones are very difficult to detect and debate surrounds particular cases as to whether they qualify as incipient or not. In the analysis conducted in this work, we use the signal of the presence of a mantle wedge in the magnetic anomaly field as an indicator of incipient subduction. Each subduction zone exhibits variations in the particular responses of the system, such as slab-dip angle, maximum earthquake depths and volcanism to various parameters. So far, attempts to reduce the system to a dominate controlling parameter have failed, probably as a result of the limited number of cases and the large variety of controlling parameters. Parameters such as down-going and overriding plate morphology and velocity, mantle flow, the presence of plumes or not, sediment transport into the trench are a few of the parameters that have been studied in the literature. However, one of the characteristics associated with a subduction zones is the presence of a mantelic wedge as a result of the partial melt of the subducting plate and the development of a mantle wedge between the subducting plate and the overriding plate. The wedge is characterised by the presence of water (coming from sediments in the down-going plate) as well as lower temperatures (because the wedge is between two relatively cold lithospheres). As a results a serpentinized mantle wedge is formed that contains hydrous minerals, of which magnetite is an example, that alter the composition and properties of this region. According to Blakely et.al. (2005), this region exhibits both higher magnetic susceptibility and lower densities than the surrounding medium. We analysed five active margin boundaries located

  7. Subduction and vertical coastal motions in the eastern Mediterranean

    Science.gov (United States)

    Howell, Andy; Jackson, James; Copley, Alex; McKenzie, Dan; Nissen, Ed

    2017-10-01

    Convergence in the eastern Mediterranean of oceanic Nubia with Anatolia and the Aegean is complex and poorly understood. Large volumes of sediment obscure the shallow structure of the subduction zone, and since much of the convergence is accommodated aseismically, there are limited earthquake data to constrain its kinematics. We present new source models for recent earthquakes, combining these with field observations, published GPS velocities and reflection-seismic data to investigate faulting in three areas: the Florence Rise, SW Turkey and the Pliny and Strabo Trenches. The depths and locations of earthquakes reveal the geometry of the subducting Nubian plate NE of the Florence Rise, a bathymetric high that is probably formed by deformation of sediment at the surface projection of the Anatolia-Nubia subduction interface. In SW Turkey, the presence of a strike-slip shear zone has often been inferred despite an absence of strike-slip earthquakes. We show that the GPS-derived strain-rate field is consistent with extension on the orthogonal systems of normal faults observed in the region and that strike-slip faulting is not required to explain observed GPS velocities. Further SW, the Pliny and Strabo Trenches are also often interpreted as strike-slip shear zones, but almost all nearby earthquakes have either reverse-faulting or normal-faulting focal mechanisms. Oblique convergence across the trenches may be accommodated either by a partitioned system of strike-slip and reverse faults or by oblique slip on the Aegean-Nubia subduction interface. The observed late-Quaternary vertical motions of coastlines close to the subduction zone are influenced by the interplay between: (1) thickening of the material overriding the subduction interface associated with convergence, which promotes coastal uplift; and (2) subsidence due to extension and associated crustal thinning. Long-wavelength gravity data suggest that some of the observed topographic contrasts in the eastern

  8. Are subduction zones invading the atlantic? Evidence from the southwest iberia margin

    NARCIS (Netherlands)

    Duarte, João C.; Rosas, Filipe M.; Terrinha, Pedro; Schellart, Wouter P.; Boutelier, David; Gutscher, Marc André; Ribeiro, António

    Subduction initiation at passive margins plays a central role in the plate tectonics theory. However, the process by which a passive margin becomes active is not well understood. In this paper we use the southwest Iberia margin (SIM) in the Atlantic Ocean to study the process of passive margin

  9. Structure and evolution of subducted lithosphere beneath the Sunda arc, Indonesia

    NARCIS (Netherlands)

    Widiyantoro, Sri; Hilst, R.D. van der

    1996-01-01

    Tomographic imaging reveals seismic anomalies beneath the Sunda island arc, Indonesia, that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers. The Sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the

  10. Thermal buoyancy on Venus - Underthrusting vs subduction

    Science.gov (United States)

    Burt, Jeffrey D.; Head, James W.

    1992-01-01

    The thermal and buoyancy consequences of the subduction endmember are modeled in an attempt to evaluate the conditions distinguishing underthrusting and subduction. Thermal changes in slabs subducting into the Venusian mantle with a range of initial geotherms are used to predict density changes and, thus, slab buoyancy. Based on a model for subduction-induced mantle flow, it is then argued that the angle of the slab dip helps differentiate between underthrusting and subduction. Mantle flow applies torques to the slab which, in combination with torques due to slab buoyancy, act to change the angle of slab dip.

  11. H2O and CO2 devolatilization in subduction zones: implications for the global water and carbon cycles (Invited)

    Science.gov (United States)

    van Keken, P. E.; Hacker, B. R.; Syracuse, E. M.; Abers, G. A.

    2010-12-01

    Subduction of sediments and altered oceanic crust functions as a major carbon sink. Upon subduction the carbon may be released by progressive metamorphic reactions, which can be strongly enhanced by free fluids. Quantification of the CO2 release from subducting slabs is important to determine the provenance of CO2 that is released by the volcanic arc and to constrain the flux of carbon to the deeper mantle. In recent work we used a global set of high resolution thermal models of subduction zones to predict the flux of H2O from the subducting slab (van Keken, Hacker, Syracuse, Abers, Subduction factory 4: Depth-dependent flux of H2O from subducting slabs worldwide, J. Geophys. Res., under review) which provides a new estimate of the dehydration efficiency of the global subducting system. It was found that mineralogically bound water can pass efficiently through old and fast subduction zones (such as in the western Pacific) but that warm subduction zones (such as Cascadia) see nearly complete dehydration of the subducting slab. The top of the slab is sufficiently hot in all subduction zones that the upper crust dehydrates significantly. The degree and depth of dehydration is highly diverse and strongly depends on (p,T) and bulk rock composition. On average about one third of subducted H2O reaches 240 km depth, carried principally and roughly equally in the gabbro and peridotite sections. The present-day global flux of H2O to the deep mantle translates to an addition of about one ocean mass over the age of the Earth. We extend the slab devolatilization work to carbon by providing an update to Gorman et al. (Geochem. Geophys. Geosyst, 2006), who quantified the effects of free fluids on CO2 release. The thermal conditions were based on three end-member subduction zones with linear interpolation to provide a global CO2 flux. We use the new high resolution and global set of models to provide higher resolution predictions for the provenance and pathways of CO2 release to

  12. Slab-mantle interactions in simulations of self-consistent mantle convection with single-sided subduction

    Science.gov (United States)

    Crameri, F.; Tackley, P. J.; Meilick, I.; Gerya, T. V.; Kaus, B. J. P.

    2012-04-01

    Subduction zones on present-day Earth are strongly asymmetric features (Zhao 2004) composed of an overriding plate above a subducting plate that sinks into the mantle. Our recent advances in numerical modelling allow global mantle convection models to produce single-sided subduction self-consistently by allowing for free surface topography on and lubrication between the converging plates (Crameri et al., 2012). Thereby, they are indicating important mantle-slab interactions. The increase of viscosity with depth is an important mantle property affecting the dynamics of subduction: a large viscosity increase on the one hand favours an immediate stagnant lid because the slab cannot sink fast enough, while a small increase on the other hand does not provide enough resistance for the sinking slab and therefore facilitates an immediate slab break-off. While in the mobile lid (plate tectonic like) regime, our model also shows that single-sided subduction in turn has strong implications on Earth's interior such as its rms. velocity or its stress distribution. The arcuate trench curvature is such a feature that is caused by single-sided subduction in 3-D geometry. The pressure difference between the mantle region below the inclined sinking slab and the region above it causes a toroidal mantle flow around the slab edges. This flow of mantle material is responsible for forming the slabs and subsequently also the subduction trenches above it towards an arcuate shape. For this study we perform experiments in 2-D and global spherical 3-D, fully dynamic mantle convection models with self-consistent plate tectonics. These are calculated using the finite volume multi-grid code StagYY (Tackley 2008) with strongly temperature and pressure-dependent viscosity, ductile and/or brittle plastic yielding, and non-diffusive tracers tracking compositional variations (the 'air' and the weak crustal layer in this case).

  13. Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

    Science.gov (United States)

    Maffione, Marco; van Hinsbergen, Douwe J. J.; de Gelder, Giovanni I. N. O.; van der Goes, Freek C.; Morris, Antony

    2017-05-01

    Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Suprasubduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers) were generated during this subduction event and are today distributed in the eastern Mediterranean region along three E-W trending ophiolitic belts. Several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra-Neo-Tethyan subduction zone. Here we present new paleospreading directions from six Upper Cretaceous ophiolites of Turkey, Cyprus, and Syria, calculated by using new and published paleomagnetic data from sheeted dyke complexes. Our results show that NNE-SSW subduction zones were formed within the Neo-Tethys during the Late Cretaceous, which we propose were part of a major step-shaped subduction system composed of NNE-SSW and WNW-ESE segments. We infer that this subduction system developed within old (Triassic?) lithosphere, along fracture zones and perpendicular weakness zones, since the Neo-Tethyan spreading ridge formed during Gondwana fragmentation would have already been subducted at the Pontides subduction zone by the Late Cretaceous. Our new results provide an alternative kinematic model of Cretaceous Neo-Tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old (and cold) lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges.

  14. Effect of Aseismic Ridge Subduction on Volcanism in the NE Lesser Antilles Arc

    Science.gov (United States)

    Stinton, A. J.; Hatfield, R. G.; McCanta, M. C.

    2014-12-01

    The interaction of aseismic ridges or buoyant crust in subduction zones can affect the volcanism occurring on the overriding plate. Here we describe the affect of the subduction of an aseismic ridge on volcanism in the NE Lesser Antilles. The Lesser Antilles island arc is a result of westward subduction of the North American plate beneath the Caribbean plate and stretches 800 km from Saba in the north to Grenada in the south. From Guadeloupe northwards, the arc bifurcates into an eastern, inactive arc (known as the Limestone Caribees) and a western, active arc (Volcanic Caribees). It has been suggested that this bifurcation is the result of the subduction of buoyant crust in the form of at least two aseismic ridges, in the North American plate. In 2012, IODP Expedition 340 recovered 130 m of core from site U1396, located 55 km SW of Montserrat, Lesser Antilles. The core contains a detailed record of volcanism, in the form of more than 180 tephra layers, that stretches back nearly 4.5 Ma. This is the longest and most complete record of volcanism for the NE Lesser Antilles and provides insight into the evolution and development of the island arc in this region. A variety of techniques are being applied to the tephra layers from U1396 to determine their age, chemistry, components and origin. Here we present preliminary results from paeleomagnetic age determinations for each tephra layer to show how the subduction of aseismic ridges on the North American plate has affected the rate of volcanism and development of the island arc in the NE Lesser Antilles over the last 4.5 Ma.

  15. Slow earthquakes linked along dip in the Nankai subduction zone.

    Science.gov (United States)

    Hirose, Hitoshi; Asano, Youichi; Obara, Kazushige; Kimura, Takeshi; Matsuzawa, Takanori; Tanaka, Sachiko; Maeda, Takuto

    2010-12-10

    We identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the Nankai megathrust rupture zone, southwest Japan. In 2003 and 2010, shallow very-low-frequency earthquakes near the Nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long-term slow slip event in between. This correlation suggests that the slow slip might extend along-dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone.

  16. Subduction dynamics and the origin of Andean orogeny and the Bolivian orocline.

    Science.gov (United States)

    Capitanio, F A; Faccenna, C; Zlotnik, S; Stegman, D R

    2011-11-23

    The building of the Andes results from the subduction of the oceanic Nazca plate underneath the South American continent. However, how and why the Andes and their curvature, the Bolivian orocline, formed in the Cenozoic era (65.5 million years (Myr) ago to present), despite subduction continuing since the Mesozoic era (251.0-65.5 Myr ago), is still unknown. Three-dimensional numerical subduction models demonstrate that variations in slab thickness, arising from the Nazca plate's age at the trench, produce a cordilleran morphology consistent with that observed. The age-dependent sinking of the slab in the mantle drives traction towards the trench at the base of the upper plate, causing it to thicken. Thus, subducting older Nazca plate below the Central Andes can explain the locally thickened crust and higher elevations. Here we demonstrate that resultant thickening of the South American plate modifies both shear force gradients and migration rates along the trench to produce a concave margin that matches the Bolivian orocline. Additionally, the varying forcing along the margin allows stress belts to form in the upper-plate interior, explaining the widening of the Central Andes and the different tectonic styles found on their margins, the Eastern and Western Cordilleras. The rise of the Central Andes and orocline formation are directly related to the local increase of Nazca plate age and an age distribution along the margin similar to that found today; the onset of these conditions only occurred in the Eocene epoch. This may explain the enigmatic delay of the Andean orogeny, that is, the formation of the modern Andes.

  17. Thermobarometric and fluid expulsion history of subduction zones

    Science.gov (United States)

    Ernst, W. G.

    1990-06-01

    Phanerozoic, unmetamorphosed, weathered, and altered lithotectonic complexes subjected to subduction exhibit the prograde metamorphic facies sequence: zeolite → prehnite-pumpellyite → glaucophane schist → eclogite. Parageneses reflect relatively high-P trajectories, accompanied by semicontinuous devolatilization. The thermal evolution of convergent plate junctions results in early production of high-rank blueschists, high-P amphibolites, and eclogues at depth within narrow subduction zones while the hanging wall lithosphere is still hot. Protracted underflow drains heat from the nonsubducted plate and, even at profound depths, generates very low-T/high-P parageneses. Inclusion studies suggest that two-phase immiscible volatiles (liquid H2O, and gaseous high-hydrocarbons, CH4 and CO2) are evolved in turn during progressive metamorphism of the subducted sections. Expulsion of pore fluids and transitions from weathered and altered supracrustal rocks to zeolite facies assemblages release far more fluid than the better understood higher-grade transformations. Many blueschist parageneses, such as those of the internal Western Alps, have been partially overprinted by later greenschist and/or epidote-amphibolite facies assemblages. Alpine-type postblueschist metamorphic paths involved fairly rapid, nearly adiabatic decompression; some terranes even underwent modest continued heating and fluid evolution during early stages of ascent. Uplift probably occurred as a consequence of the underthrusting of low-density island arc or microcontinental crust along the convergent plate junction, resulting in marked deceleration or cessation of lithospheric underflow, decoupling, and nearly isothermal rise of the recrystallized subduction complex. Other, less common blueschist terranes, such as the eastern Franciscan belt of western California, preserve metamorphic aragonite and other high-P minerals, and lack a low-pressure overprint; physical conditions during retrogression

  18. The Terminal Stage of Subduction: the Hindu Kush Slab Break-off

    Science.gov (United States)

    Kufner, S. K.; Schurr, B.; Sippl, C.; Yuan, X.; Ratschbacher, L.; Akbar, A. S. M.; Ischuk, A.; Murodkulov, S.; Schneider, F.; Mechie, J.; Tilmann, F. J.

    2016-12-01

    The terminal stage of subduction arrives when the ocean basin is closed and the continental margin arrives at the trench. The opposite forces of the sinking slab and buoyant continent ultimately leads to break-off of the subducted slab. This process, although common in geological history, is rarely observed, because it is short-lived. Here we report new precise earthquake hypocenters, detailed tomographic images and earthquake source mechanisms from the Hindu Kush region in Central Asia, which hint at continental subduction and plate necking. Our images provide a rare glimpse at the ephemeral process of slab break-off: the Hindu Kush slablet in its uppermost section is thinned or already severed and that intermediate depth earthquakes cluster at the neck connecting it to the deeper slab. From a strain rate analysis, we deduce that the deep portion of the slab is in the process of detaching from the shallower fragment at much higher rates than the current convergence rate at the surface. The increased strain rate might arise as the buoyant continental crust, which is dragged into the subduction system in its terminal stage, resists subduction, whereas the earlier subducted mantle lithosphere pulls from underneath.

  19. Modeling mantle circulation and density distributions in subduction zones: Implications for seismic studies

    Science.gov (United States)

    Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.; Long, M. D.; Behn, M. D.; Hirth, G.

    2009-12-01

    Subduction of ocean lithosphere drives plate tectonics, large-scale mantle circulation and thermal-chemical recycling processes through arcs. Seismologists have made important advances in our ability to map circulation patterns in subduction zones though anisotropy data/methods and in providing detailed images of mantle density fields. Increasingly, seismic and geodynamic disciplines are combining to extend our understanding of time varying subduction processes and associated vertical mass and energy fluxes. We use laboratory experiments to characterize three-dimensional flow fields in convergent margins for a range in plate forcing conditions and background, buoyancy-driven flow scenarios. Results reveal basic patterns in circulation, buoyant flow morphologies and density distributions that have implications for reconciling seismic data with mantle convection models. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000km of the mantle. Subducting lithosphere is modeled with a Phenolic plate and back-arc extension is produced using Mylar sheets. We recreate basic subduction styles observed in previous dynamic subduction models using simplified, kinematic forcing. Slab plate segments, driven by hydraulic pistons, move with various combinations of downdip, rollback and steepening motion. Neutral density finite strain markers are distributed throughout the fluid and used as proxies for tracking the evolution of olivine alignment through space and time in the evolving flow fields. Particle image velocimetry methods are also used to track time varying 3D velocity fields for use in directly calculating anisotropy patterns. Results show that complex plate motions (rollback, steepening, back-arc extension) in convergent margins produce relatively simple anisotropy patterns (e.g., trench-normal alignments) and underscore the importance of initial strain marker orientations on alignment patterns in the wedge. Results also

  20. New sedimentary-core records and a recent co-seismic turbidite help to unravel the paleoseismicity of the Hikurangi Subduction Zone, New Zealand

    Science.gov (United States)

    Barnes, Philip; Orpin, Alan; Howarth, Jamie; Patton, Jason; Lamarche, Geoffroy; Woelz, Susanne; Hopkins, Jenni; Gerring, Peter; Mitchell, John; Quinn, Will; McKeown, Monique; Ganguly, Aratrika; Banks, Simon; Davidson, Sam

    2017-04-01

    The Hikurangi margin straddles the convergent boundary between the Pacific and Australia tectonic plates and is New Zealand's potentially largest earthquake and tsunami hazard. The 3000 m-deep Hikurangi Trough, off eastern Marlborough, Wairarapa, Hawkes Bay, and East Cape, marks the location where the Pacific plate is subducting beneath the eastern continental margin of the North Island and northeastern South Island. To date the Hikurangi margin has a short historical record relative to the recurrence of great earthquakes and tsunami, and consequently the associated hazard remains poorly constrained. In October 2016 a new, international, 5-year project commenced to evaluate the pre-historic earthquake history of the margin. In November 2016 a RV Tangaroa voyage acquired 50 sediment cores up to 5.5 m long from sites on the continental margin between the Kaikoura coast and Poverty Bay. Core sites were selected using available 30 kHz multibeam bathymetry and backscatter data, sub-bottom acoustic profiles, archived sediment samples, and results from numerical modelling of turbidity currents. Sites fell into three general categories: turbidite distributary systems; small isolated slope-basins; and Hikurangi Channel, levees, and trough. Typical of the margin, the terrigenous-dominated sequence included layers of gravel, sand, mud, and volcanic ash. Many of these layers are turbidites, some of which may have been triggered by strong shaking associated with earthquakes (subduction megathrust and other coastal faults). Some cores contain up to 25 individual turbidites. This library of turbidites may provide the basis of new paleoseismic records that span several hundred kilometres of strike along the plate boundary. During the voyage the 14th November 2016 (NZDT) Mw 7.8 Kaikoura Earthquake occurred, causing strong ground shaking beneath the Kaikoura Canyon region. Sampling with a multicorer within five days of the earthquake, we recovered what appeared to be a very recently

  1. Kinematics of a former oceanic plate of the Neotethys revealed by deformation in the Ulukışla basin (Turkey)

    NARCIS (Netherlands)

    Gürer, Derya; van Hinsbergen, Douwe J J; Matenco, Liviu; Corfu, Fernando; Cascella, Antonio

    2016-01-01

    Kinematic reconstruction of modern ocean basins shows that since Pangea breakup a vast area in the Neotethyan realm was lost to subduction. Here we develop a first-order methodology to reconstruct the kinematic history of the lost plates of the Neotethys, using records of subducted plates accreted

  2. Convergent plate margin dynamics : New perspectives from structural geology, geophysics and geodynamic modelling

    NARCIS (Netherlands)

    Schellart, W. P.; Rawlinson, N.

    2010-01-01

    Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide.

  3. Tectonics of the Easter plate

    Science.gov (United States)

    Engeln, J. F.; Stein, S.

    1984-01-01

    A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.

  4. Influence of Initial Geometry and Boundary Conditions on Flat Subduction Models and Resulting Topography

    Science.gov (United States)

    Nelson, P.; Moucha, R.

    2014-12-01

    Numerical investigations of surface deformation in response to flat slab subduction began with seminal papers by Bird (1988) and Mitrovica et al. (1989). Recently, a number of numerical studies have begun to explore the complexity in the dynamics of flat-slab subduction initiation and continuation, but did not address the corresponding surface deformation (English et al., 2003; Pérez-Campos et al., 2008; Liu et al., 2010; Jones et al., 2011; Arrial and Billen, 2013; Vogt and Gerya, 2014). Herein, we explore the conditions that lead to flat-slab subduction and characterize the resulting surface deformation using a 2D finite-difference marker-in-cell method. We specifically explore how initial model geometry and boundary conditions affect the evolution of the angle at which a slab subducts in the presence/absence of a buoyant oceanic plateau and the resulting surface topography. In our simulations, the surface is tracked through time as an internal erosion/sedimentation surface. The top boundary of the crust is overlaid by a "sticky" (viscous 10^17 Pa.s) water/air layer with correspondingly stratified densities. We apply a coupled surface processes model that solves the sediment transport/diffusion erosion equation at each time step to account for the corresponding crustal mass flux and its effect on crustal deformation. Model results show the initial angle of subduction has a substantial impact on the subduction angle of the slab and hence the evolution of topography. The results also indicate plate velocity and the presence of an oceanic plateau in a forced subduction only have a moderate effect on the angle of subduction.

  5. Fault Trends and the Evolution of the Pacific-North America Transform in Southern California

    Science.gov (United States)

    Legg, M. R.; Kamerling, M. J.

    2004-12-01

    The Pacific-North America (PAC-NOAM) transform boundary evolved during the past 30 Ma, lengthening more than 1000 km and spanning a zone exceeding 200-km across southern California. The relative plate motion vector has been estimated using seafloor magnetic anomaly patterns. Orientations of major transform fault segments within this boundary provide direct evidence of the relative motion at the time these faults formed, where the faults preserve their original orientations. Avoiding areas of known vertical-axis block rotations, we find at least three major fault trends that document past and present tectonic kinematics. A northwest trend of 330 degrees is related to subduction trends in the forearc region that defined the late Mesozoic and early Tertiary coastline and has subsequently controlled the orientation of oblique rifting during the Neogene initiation and growth of the PAC-NOAM transform. This trend is manifest in the San Diego Trough and adjacent coastal rifts and associated fault zones including the Coronado Bank and Newport-Inglewood. The middle Miocene transform orientation appears to be 300-310 degrees, which imparted extensional character to faults reactivated with older subduction trends. Major faults inferred to represent Neogene transform fault segments with this trend include the Whittier, Palos Verdes Hills, Santa Cruz-Catalina Ridge, Catalina Escarpment, and possibly the Mojave segment of the San Andreas fault. In late Miocene time, the plate motion vector rotated clockwise eventually achieving its modern orientation of about 320 degrees. Active faulting showing pure strike-slip character on the San Clemente - San Isidro fault zone and the Imperial Fault show this trend, as do transform faults in the northern Gulf of California. An intermediate trend is apparent in some areas along the San Clemente fault zone in the Borderland, and along the Elsinore and San Jacinto fault zones, which transect the Peninsular Ranges. The intermediate trends may

  6. Geodetic Observations of Interseismic Strain Segmentation at the Sumatra Subduction Zone

    Science.gov (United States)

    Prawirodirdjo, L.; Bock, Y.; McCaffrey, R.; Genrich, J.; Calais, E.; Puntodewo, S. S. O.; Subarya, C.; Rais, J.; Zwick, P.; Fauzi

    1997-01-01

    Deformation above the Sumatra subduction zone, revealed by Global Positioning System (GPS) geodetic surveys, shows nearly complete coupling of the forearc to the subducting plate south of 0.5 deg S and half as much to north. The abrupt change in plate coupling coincides with the boundary between the rupture zones of the 1833 and 1861 (Mw greater than 8) thrust earthquakes. The rupture boundary appears as an abrupt change in strain accumulation well into the interseismic cycle, suggesting that seismic segmentation is controlled by properties of the plate interface that persist occupied through more than one earthquake cycle. Structural evidence indicates that differences in basal shear stress may be related to elevated pore pressure in the north.

  7. MACMA: a Virtual Lab for Plate Tectonics

    Science.gov (United States)

    Grigne, C.; Combes, M.; Tisseau, C.

    2013-12-01

    MACMA (Multi-Agent Convective MAntle) is a tool developed to simulate evolutive plate tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). The model relies mainly on a force balance to compute the velocity of each plate, and on empirical rules to determine how plate boundaries move and evolve. It includes first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. The MACMA interface was designed to be user-friendly and a simple use of the simulator can be achieved without any prerequisite knowledge in fluid dynamics, mantle rheology, nor in numerical methods. As a preliminary study, the simulator was used by a few students from bachelor's degree to master's degree levels. An initial configuration for plate tectonics has to be created before starting a simulation: the number and types of plate boundaries (ridge, subduction, passive margins) has to be defined and seafloor ages must be given. A simple but interesting exercise consists in letting students build such an initial configuration: they must analyze a map of tectonic plates, choose a 2-D section and examine carefully a map of seafloor ages. Students mentioned that the exercise made them realize that the 3-D spherical structure of plate tectonics does not translate directly in a simple 2-D section, as opposed to what is usually shown in books. Physical parameters: e.g. mantle viscosity, number of layers to consider in the mantle (upper and lower mantle, possible asthenosphere), initial time and mantle temperature, have to be chosen, and students can use this virtual lab to see how different scenarios emerge when parameters are varied. Very importantly, the direct visualization of the mobility of plate

  8. Lasting mantle scars lead to perennial plate tectonics.

    Science.gov (United States)

    Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell

    2016-06-10

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon.

  9. Lasting mantle scars lead to perennial plate tectonics

    Science.gov (United States)

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

  10. Controls on continental strain partitioning above an oblique subduction zone, Northern Andes

    Science.gov (United States)

    Schütt, Jorina M.; Whipp, David M., Jr.

    2016-04-01

    Strain partitioning is a common process at obliquely convergent plate margins dividing oblique convergence into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the subduction margin. In subduction zones, strain partitioning in the upper continental plate is mainly controlled by the shear forces acting on the plate interface and the strength of the continental crust. The plate interface forces are influenced by the subducting plate dip angle and the obliquity angle between the normal to the plate margin and the convergence velocity vector, and the crustal strength of the continent is strongly affected by the presence or absence of a volcanic arc, with the presence of the volcanic arcs being common at steep subduction zones. Along the ˜7000 km western margin of South America the convergence obliquity, subduction dip angles and presence of a volcanic arc all vary, but strain partitioning is only observed along parts of it. This raises the questions, to what extent do subduction zone characteristics control strain partitioning in the overriding continental plate, and which factors have the largest influence? We address these questions using lithospheric-scale 3D numerical geodynamic experiments to investigate the influence of subduction dip angle, convergence obliquity, and weaknesses in the crust owing to the volcanic arc on strain partitioning behavior. We base the model design on the Northern Volcanic Zone of the Andes (5° N - 2° S), characterized by steep subduction (˜ 35°), a convergence obliquity between 31° -45° and extensive arc volcanism, and where strain partitioning is observed. The numerical modelling software (DOUAR) solves the Stokes flow and heat transfer equations for a viscous-plastic creeping flow to calculate velocity fields, thermal evolution, rock uplift and strain rates in a 1600 km x 1600 km box with depth 160 km. Subduction geometry and material properties are based on a

  11. Analyzing One-Sided vs. Two-Sided Subduction Arising from Mantle Convection Simulations

    Science.gov (United States)

    Kaplan, M. S.; Becker, T. W.

    2013-12-01

    Purely thermal plate tectonic generation models struggle to consistently reproduce one-sided subduction as is observed on Earth (Tackley 2000; Van Heck and Tackley 2008; Foley and Becker 2009), and instead produce two-sided subduction where the subducting slab contains a significant flux of material from both plates. The models of Crameri et al. (2012) demonstrate that the implementation of a free upper surface boundary condition and the inclusion of a weak hydrated crust can facilitate one-sided subduction. We employ a similar model configuration to Crameri et al. (2012) to further investigate the dynamics and energetics which are associated with one-sided vs. two-sided subduction. We use a 2D finite difference code based off of the algorithms of I2ELVIS (Gerya and Yuen 2007) where material parameters are tracked on Lagrangian markers and the Stokes and Energy equations are solved on a Cartesian grid. A free surface is implemented by a low viscosity and density 'sticky air layer' (Schmeling et al., 2008; Crameri et al., 2012) with the stabilization routine of Duretz et al. (2011) to prevent the 'drunken seaman' instability (Kaus et al., 2010). The effects of a weak crust, shear heating, a free surface or free slip upper mechanical boundary condition, plasticity as a function of depth or pressure, and the sticky air layer thermal conductivity on one-sided vs. two-sided subduction are investigated. When we observe one-sided subduction it is transient and can smoothly evolve back to a two-sided configuration. In our models, 'sidedness' is a spectrum, rather than either discretely one or two sided, and the models move between the two regimes throughout the model runs. We observe that the thermal conductivity of the sticky air layer can influence the dynamics of the convective domain. Elevated values of thermal conductivity compared to those of rock must be implemented in the sticky air layer in order to maintain a constant temperature at the surface of the convective

  12. The Elephants' Graveyard: Constraints from Mantle Plumes on the Fate of Subducted Slabs and Implications for the Style of Mantle Convection

    Science.gov (United States)

    Lassiter, J. C.

    2007-12-01

    The style of mantle convection (e.g., layered- vs. whole-mantle convection) is one of the most hotly contested questions in the Geological Sciences. Geochemical arguments for and against mantle layering have largely focused on mass-balance evidence for the existence of "hidden" geochemical reservoirs. However, the size and location of such reservoirs are largely unconstrained, and most geochemical arguments for mantle layering are consistent with a depleted mantle comprising most of the mantle mass and a comparatively small volume of enriched, hidden material either within D" or within seismically anomalous "piles" beneath southern Africa and the South Pacific. The mass flux associated with subduction of oceanic lithosphere is large and plate subduction is an efficient driver of convective mixing in the mantle. Therefore, the depth to which oceanic lithosphere descends into the mantle is effectively the depth of the upper mantle in any layered mantle model. Numerous geochemical studies provide convincing evidence that many mantle plumes contain material which at one point resided close to the Earth's surface (e.g., recycled oceanic crust ± sediments, possibly subduction-modified mantle wedge material). Fluid dynamic models further reveal that only the central cores of mantle plumes are involved in melt generation. The presence of recycled material in the sources of many ocean island basalts therefore cannot be explained by entrainment of this material during plume ascent, but requires that recycled material resides within or immediately above the thermo-chemical boundary layer(s) that generates mantle plumes. More recent Os- isotope studies of mantle xenoliths from OIB settings reveal the presence not only of recycled crust in mantle plumes, but also ancient melt-depleted harzburgite interpreted to represent ancient recycled oceanic lithosphere [1]. Thus, there is increasing evidence that subducted slabs accumulate in the boundary layer(s) that provide the source

  13. Modeling Diverse Pathways to Age Progressive Volcanism in Subduction Zones.

    Science.gov (United States)

    Kincaid, C. R.; Szwaja, S.; Sylvia, R. T.; Druken, K. A.

    2015-12-01

    One of the best, and most challenging clues to unraveling mantle circulation patterns in subduction zones comes in the form of age progressive volcanic and geochemical trends. Hard fought geological data from many subduction zones, like Tonga-Lau, the Cascades and Costa-Rica/Nicaragua, reveal striking temporal patterns used in defining mantle flow directions and rates. We summarize results from laboratory subduction models showing a range in circulation and thermal-chemical transport processes. These interaction styles are capable of producing such trends, often reflecting apparent instead of actual mantle velocities. Lab experiments use a glucose working fluid to represent Earth's upper mantle and kinematically driven plates to produce a range in slab sinking and related wedge transport patterns. Kinematic forcing assumes most of the super-adiabatic temperature gradient available to drive major downwellings is in the tabular slabs. Moreover, sinking styles for fully dynamic subduction depend on many complicating factors that are only poorly understood and which can vary widely even for repeated parameter combinations. Kinematic models have the benefit of precise, repeatable control of slab motions and wedge flow responses. Results generated with these techniques show the evolution of near-surface thermal-chemical-rheological heterogeneities leads to age progressive surface expressions in a variety of ways. One set of experiments shows that rollback and back-arc extension combine to produce distinct modes of linear, age progressive melt delivery to the surface through a) erosion of the rheological boundary layer beneath the overriding plate, and deformation and redistribution of both b) mantle residuum produced from decompression melting and c) formerly active, buoyant plumes. Additional experiments consider buoyant diapirs rising in a wedge under the influence of rollback, back-arc spreading and slab-gaps. Strongly deflected diapirs, experiencing variable rise

  14. Three-dimensional structure and seismicity beneath the Central Vanuatu subduction zone

    Science.gov (United States)

    Foix, Oceane; Crawford, Wayne; Pelletier, Bernard; Regnier, Marc; Garaebiti, Esline; Koulakov, Ivan

    2017-04-01

    The 1400-km long Vanuatu subduction zone results from subduction of the oceanic Australian plate (OAP) beneath the North-Fijian microplate (NFM). Seismic and volcanic activity are both high, and several morphologic features enter into subduction, affecting seismicity and probably plate coupling. The Entrecasteaux Ridge, West-Torres plateau, and Bougainville seamount currently enter into subduction below the large forearc islands of Santo and Malekula. This collision coincides with a strongly decreased local convergence velocity rate - 35 mm/yr compared to 120-160 mm/yr to the north and south - and significant uplift on the overriding plate, indicating a high degree of deformation. The close proximity of large uplifted forearc islands to the trench provides excellent coverage of the megathrust seismogenic zone for a seismological study. We used 10 months of seismological data collected using the 30-instrument land and sea ARC-VANUATU seismology network to construct a 3D velocity model — using the LOTOS joint location/model inversion software — and locate 11655 earthquakes using the NonLinLoc software suite. The 3-D model reveals low P and S velocities in the first tens of kilometers beneath both islands, probably due to water infiltration in the heavily faulted upper plate. The model also suggests the presence of a subducted seamount beneath south Santo. The earthquake locations reveal a complex interaction of faults and stress zones related to high and highly variable deformation. Both brittle deformation and the seismogenic zone depth limits vary along-slab and earthquake clusters are identified beneath central and south Santo, at about 10-30 km of depth, and southwest of Malekula island between 10-20 km depth.

  15. Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model

    Science.gov (United States)

    Gripp, Alice E.; Gordon, Richard G.

    1990-01-01

    The NUVEL-1 model of current global relative plate velocities is presently incorporated into HS2-NUVEL1, a global model for plate velocities relative to hotspots; the results thus obtained are compared with those of the AM1-2 model of hotspot-relative plate velocities. While there are places in which plate velocities relative to the hotspots differ between HS2-NUVEL1 and AM1-2 by tens of degrees in direction and 15 mm/yr in speed, the hotspot Euler vectors differ with 95 percent confidence only for the Arabian and Indian plates. Plates attached to subducting slabs move faster relative to the hotspots than do plates without slabs.

  16. Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model

    Science.gov (United States)

    Gripp, Alice E.; Gordon, Richard G.

    1990-07-01

    The NUVEL-1 model of current global relative plate velocities is presently incorporated into HS2-NUVEL1, a global model for plate velocities relative to hotspots; the results thus obtained are compared with those of the AM1-2 model of hotspot-relative plate velocities. While there are places in which plate velocities relative to the hotspots differ between HS2-NUVEL1 and AM1-2 by tens of degrees in direction and 15 mm/yr in speed, the hotspot Euler vectors differ with 95 percent confidence only for the Arabian and Indian plates. Plates attached to subducting slabs move faster relative to the hotspots than do plates without slabs.

  17. Synthetic testing of the Pacific Northwest earthquake early warning system

    Science.gov (United States)

    Crowell, B. W.; Schmidt, D. A.; Bodin, P.; Vidale, J. E.; Gomberg, J. S.; Jamison, D.; Minson, S. E.; Hartog, J. R.; Kress, V. C.; Malone, S. D.; Usher, M.

    2014-12-01

    The Cascadia subduction zone poses one of the greatest risks for a megaquake in the continental United States and, because of this, the Pacific Northwest Seismic Network (PNSN) at the University of Washington is building a joint seismic and geodetic earthquake early warning system. Our two-stage approach to earthquake early warning includes: (1) detection and initial characterization using strong-motion and broadband data from the PNSN with the ElarmS package, and (2) geodetic modeling modules using GPS data from the Pacific Northwest Geodetic Array (PANGA) and combined seismogeodetic (GPS + strong-motion) data. Because of Cascadia's relatively low seismicity rate and the paucity of data from plate boundary earthquakes, we have prioritized the development of a test system and the creation of several large simulated events. The test system permits us to: (1) replay segments of actual seismic waveform data recorded from the PNSN and neighboring networks to represent both earthquakes and noise conditions, and (2) broadcast synthetic data into the system to simulate signals we anticipate from earthquakes for which we have no actual ground motion recordings. The test system lets us also simulate various error conditions (latent and/or out-of-sequence data, telemetry drop-outs, etc.) and to explore how best to mitigate them. Here, we report on the performance of the joint early warning system and the geodetic modeling modules in a simulated real-time mode using simulated 5-Hz displacements from plausible Cascadian earthquake scenarios. The simulations are created using the FK integration method for hypothetical source models for a wide array of possible faulting types and magnitudes. The results show that the geodetic modeling modules are able to properly characterize the simulated events, and we discuss the limitations with respect to latency, network architecture, and earthquake location throughout the Pacific Northwest.

  18. Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum: The Subduction Factory

    Science.gov (United States)

    Penniston-Dorland, S.; Stern, R. J.; Edwards, B. R.; Kincaid, C. R.

    2014-12-01

    The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate fundamental results from the MARGINS program into open-source college-level curriculum. Three Subduction Factory (SubFac) mini-lessons were developed as part of this project. These include hands-on examinations of data sets representing 3 key components of the subduction zone system: 1) Heat transfer in the subducted slab; 2) Metamorphic processes happening at the plate interface; and 3) Typical magmatic products of arc systems above subduction zones. Module 1: "Slab Temperatures Control Melting in Subduction Zones, What Controls Slab Temperature?" allows students to work in groups using beads rolling down slopes as an analog for the mathematics of heat flow. Using this hands-on, exploration-based approach, students develop an intuition for the mathematics of heatflow and learn about heat conduction and advection in the subduction zone environment. Module 2: "Subduction zone metamorphism" introduces students to the metamorphic rocks that form as the subducted slab descends and the mineral reactions that characterize subduction-related metamorphism. This module includes a suite of metamorphic rocks available for instructors to use in a lab, and exercises in which students compare pressure-temperature estimates obtained from metamorphic rocks to predictions from thermal models. Module 3: "Central American Arc Volcanoes, Petrology and Geochemistry" introduces students to basic concepts in igneous petrology using the Central American volcanic arc, a MARGINS Subduction Factory focus site, as an example. The module relates data from two different volcanoes - basaltic Cerro Negro (Nicaragua) and andesitic Ilopango (El Salvador) including hand sample observations and major element geochemistry - to explore processes of mantle and crustal melting and differentiation in arc volcanism.

  19. The relation between the rock record and changing plate motions at a convergent margin: The tertiary Shimanto belt of southwest Japan

    Science.gov (United States)

    Lewis, Jonathan Craig

    -central Pacific basin during the Paleogene. The kinematic data presented in Chapter two provide new constraints on relative motion between the Kula and Eurasia plates. The results of this reexamination have implications for the formation of the Philippine Sea plate, and help account for (1) thermal and age-lithology data from SW Japan that suggest the subduction of young crust and (2) evidence for a transition from sinistral to dextral obliquity along the Tertiary SW Japan margin.

  20. Two-dimensional Numerical Models of Accretionary Wedges Deformation in Response to Subduction and Obduction: Evidence from the Middle Part of the Manila Trench

    Science.gov (United States)

    Ma, L.; Ding, W.; Chen, L.; Gerya, T.

    2016-12-01

    The Manila Trench is located at the eastern boundary of the South China Sea (SCS). It was created by the subduction of the South China Sea Plate beneath the Philippine Sea Plate since the early Neogene, and also influenced by the northwestern movement of the Philippine Sea Plate. There is wide discussion whether the dual-subduction and widespread seamounts in the South China Sea would have play important roles in the 'S-shaped' geometry and the different diving angle along the Manila Trench. Multi-beam tectono-geomorphological studies on the accretionary wedges have suggested that: (1) the stress direction of the subduction along the middle part of the Manila Trench, between 17o and 18 o N, is NW55 o; (2) The Manila Trench is actually caused by obduction due to the northwestern movement of the Philippine Sea Plate. Although the NW 55 o stress direction has been supported by detailed analysis on the trend of the folds, thrust faults, extension fractures and large sea-floor canyon, its obduction-origin is purely based on regional structure. Here we use 2D numerical modeling experiments to investigate the deformation style of accretionary wedge in response to the seamounts subduction and obduction, and provide new insights into the mechanism responsible for the Luzon obduction along the Manila Trench. Our preliminary results show that: (1) the accretionary wedge is eroded faster in subduction model; (2) the velocity field direction of the slab differs in two models at the beginning of seamount subduction, which is vertical in obduction model, but oblique in subduction model; (3) both sides of the accretionary wedge deform strongly in subduction model, whereas in obduction model only the leading edge shows intensive deformation. Further modelling will focus on other parts of the Manila Trench with different slab age and subduction velocity to see their tectonic influences on the accretionary wedges.

  1. Cold plate

    Energy Technology Data Exchange (ETDEWEB)

    Marroquin, Christopher M.; O' Connell, Kevin M.; Schultz, Mark D.; Tian, Shurong

    2018-02-13

    A cold plate, an electronic assembly including a cold plate, and a method for forming a cold plate are provided. The cold plate includes an interface plate and an opposing plate that form a plenum. The cold plate includes a plurality of active areas arranged for alignment over respective heat generating portions of an electronic assembly, and non-active areas between the active areas. A cooling fluid flows through the plenum. The plenum, at the non-active areas, has a reduced width and/or reduced height relative to the plenum at the active areas. The reduced width and/or height of the plenum, and exterior dimensions of cold plate, at the non-active areas allow the non-active areas to flex to accommodate surface variations of the electronics assembly. The reduced width and/or height non-active areas can be specifically shaped to fit between physical features of the electronics assembly.

  2. Subduction of the oceanic Hikurangi Plateau and its impact on the Kermadec arc.

    Science.gov (United States)

    Timm, Christian; Davy, Bryan; Haase, Karsten; Hoernle, Kaj A; Graham, Ian J; de Ronde, Cornel E J; Woodhead, Jon; Bassett, Dan; Hauff, Folkmar; Mortimer, Nick; Seebeck, Hannu C; Wysoczanski, Richard J; Caratori-Tontini, Fabio; Gamble, John A

    2014-09-17

    Large igneous province subduction is a rare process on Earth. A modern example is the subduction of the oceanic Hikurangi Plateau beneath the southern Kermadec arc, offshore New Zealand. This segment of the arc has the largest total lava volume erupted and the highest volcano density of the entire Kermadec arc. Here we show that Kermadec arc lavas south of ~32°S have elevated Pb and Sr and low Nd isotope ratios, which argues, together with increasing seafloor depth, forearc retreat and crustal thinning, for initial Hikurangi Plateau-Kermadec arc collision ~250 km north of its present position. The combined data set indicates that a much larger portion of the Hikurangi Plateau (the missing Ontong Java Nui piece) than previously believed has already been subducted. Oblique plate convergence caused southward migration of the thickened and buoyant oceanic plateau crust, creating a buoyant 'Hikurangi' mélange beneath the Moho that interacts with ascending arc melts.

  3. Reconstruction of the Mesozoic subduction in the South China Sea and its implications on the opening of the South China Sea basins

    Science.gov (United States)

    Li, F.; Sun, Z.; Yang, H.

    2013-12-01

    was formed by the northwestward subduction of the Izanagi and Pacific plates beneath the Eurasia plate. The current locations of the Mesozoic arc indicate that it was separated by the opening of the SCS basins. In addition, the opening of the SCS basins may obliquely cut the proto-SCS oceanic crust in the northeast and the Eurasia continental crust in the southwest. Thus, the southwest segment of the Mesozoic arc is carried to the Nansha-Dangerous Ground, southeast to the ridge axis of the southwest sub-basin of the SCS. In comparison, the northeast portion of the Mesozoic subduction system is located northwest to the ridge axis of the SCS basins.

  4. Crustal Gravitational Potential Energy Change and Subduction Earthquakes

    Science.gov (United States)

    Zhu, P. P.

    2017-05-01

    Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called

  5. Seamount subduction underneath an accretionary wedge: modelling mass wasting and wedge collapse

    Science.gov (United States)

    Mannu, Utsav; Ueda, Kosuke; Willett, Sean; Gerya, Taras; Strasser, Michael

    2017-04-01

    Seamounts (h >1 km) and knolls (h = 500 m-1000 m) cover about one-fifth of the total ocean floor area. These topographical highs of the ocean floor eventually get subducted. Subduction of these topographical features leads to severe deformation of the overriding plate and can cause extensive tectonic erosion and mass wasting of the frontal prism, which can ultimately cause a forearc wedge collapse. Large submarine landslides and the corresponding wedge collapse have previously been reported, for instance, in the northern part of the Hikurangi margin where the landslide is known as the giant Ruatoria debris avalanche, and have also been frequently reported in several seismic sections along the Costa Rica margin. Size and frequency relation of landslides suggest that the average size of submarine landslides in margins with rough subducting plates tends to be larger. However, this observation has not yet been tested or explained by physical models. In numerical subduction models, landslides take place, if at all, on a much larger timescale (in the order of 104-105 years, depending on the time steps of the model) than in natural cases. On the other hand, numerical models simulating mass wasting events such as avalanches and submarine landslides, typically model single events at a much smaller spatio-temporal domain, and do not consider long-term occurrence patterns of freely forming landslides. In this contribution, we present a multi-scale nested numerical approach to emulate short-term landslides within long-term progressive subduction. The numerical approach dynamically produces instantaneous submarine landslides and the resulting debris flow in the spatially and temporally refined inner model. Then we apply these convoluted changes in topography (e.g. due to the submarine landslide etc.) back to an outer larger-scale model instance that addresses wedge evolution. We use this approach to study the evolution of the accretionary wedge during seamount subduction.

  6. Topography and subduction geometry in the central Andes: Clues to the mechanics of a noncollisional orogen

    Science.gov (United States)

    Gephart, John W.

    1994-01-01

    The central Andeean orogen between 12 deg and 32 deg S latitude exhibits a high degree of spatial order: principally an extraordinary bilateral symmetry that is common to the Earth's surface, the underlying Wadati-Benioff zone, and the Nazca/South America plate kinematics, which has been stable since the mid-Tertiary. This spatial order must reflect the physical mechanisms of mountain building in this noncollisional orogen. The shapes of the topography and subduction zone can be reduced to symmetric and antisummeric components relative to any verical symmetry plane; the particular plaen which minimizes the antisymmetry (and maximizes the symmetry) is well resolved and is essentially coincident with the stable Euler equator of Nacza/South America relative motion since the mid-Tertiary. That the topography, subduction geometry, and persistent mid-Tertiary plate kinematics share common spatial and geometric elements suggests that he distribution of topography in this orogen depends strongly on the dynamics of subduction. Other factors that might affect the topography and underlying tectonics, such as climate and inherited strutura fabric, which have different spatial characterisitcs, must be of less significance at a continental scale. Furthermore, the small components of asymmetry among the various elements of the orogen appear to be mutually relate in a simple way; it is possible that this coupled asymmetry is associated with a late Teriary change in plate kinematics. These observations suggest that there is a close connection between plate tectonics and the form of the Earth's surface in this noncollisional setting. It follows hta the distribution of topography near convergent plate boundaries may provide a powerful constraing for understanding the dynamics of subduction.

  7. Dynamics of double-polarity subduction: application to the Western Mediterranean

    Science.gov (United States)

    Peral, Mireia; Zlotnik, Sergio; Fernandez, Manel; Vergés, Jaume; Jiménez-Munt, Ivone; Torne, Montserrat

    2016-04-01

    The evolution of the Western Mediterranean is a highly debated question by geologists and geophysicists. Even though most scientists agree in considering slab roll-back to be the driving mechanism of the tectonic evolution of this area, there is still no consensus about the initial setup and its time evolution. A recent model suggests a lateral change in subduction polarity of the Ligurian-Thetys oceanic domain to explain the formation and evolution of the Betic-Rif orogenic system and the associated Alboran back-arc basin. Such geodynamic scenario is also proposed for different converging regions. The aim of this study is to analyze the dynamic evolution of a double-polarity subduction process and its consequences in order to test the physical feasibility of this interaction and provide geometries and evolutions comparable to those proposed for the Western Mediterranean. The 3D numerical model is carried out via the Underworld framework. Tectonic plate behavior is described by equations of fluid dynamics in the presence of several different phases. Underworld solves a non-linear Stokes flow problem using Finite Elements combined with particle-in-cell approach, thus the discretization combines a standard Eulerian Finite Element mesh with Lagrangian particles to track the location of the phases. The final model consists of two oceanic plates with viscoplastic rheology subducting into the upper mantle in opposite direction and the problem is driven by Rayleigh-Taylor instability. We study the influence of the boundary conditions in the model evolution, and the slab deformation produced by the proximity between both plates. Moreover the case of asymmetric friction on the lateral sides of slabs is also considered. Simulations of single subduction models are used as a reference, to compare results and understand the influence of the second plate. We observe slight differences in the trench retreat velocity and the slab morphology near the contact area when plates are

  8. What favors the occurrence of subduction mega-earthquakes?

    Science.gov (United States)

    Brizzi, Silvia; Funiciello, Francesca; Corbi, Fabio; Sandri, Laura; van Zelst, Iris; Heuret, Arnauld; Piromallo, Claudia; van Dinther, Ylona

    2017-04-01

    uncertainties related to the short observational timespan with respect to the seismic cycle duration, we are systematically testing the influence of Wtrench and Tsed with novel 3D analogue and numerical models, respectively. Analogue models consist of a gelatin wedge underthrusted by a planar, 10° dipping slab including a rectangular patch with velocity-weakening frictional behavior. The experimental setup, specifically designed for the purpose, has the advantage of varying Wtrench from 50 cm to 1.5 m (i.e., 300 to 1000 km in nature), thus offering the opportunity to investigate its influence on MMax. Numerical models are performed using the visco-elasto-plastic Seismo-Thermo-Mechanical code (STM; van Dinther et al., 2013). The 2D setup has been modified including a layer of sediments on top of the subducting plate to test the role of Tsed on MMax. Results coming from the different adopted methodologies will be coupled to develop an integrated conceptual model, pointing out the potential cause-effect relationships between subduction zone parameters and the MMax of STF earthquakes

  9. Subduction dynamics: Constraints from gravity field observations

    Science.gov (United States)

    Mcadoo, D. C.

    1985-01-01

    Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.

  10. Seismotectonics of the southern boundary of Anatolia, eastern Mediterranean region: Subduction, collision, and arc jumping

    Science.gov (United States)

    Rotstein, Yair; Kafka, Alan L.

    1982-09-01

    The pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of Anatolia in the eastern Mediterranean and southeastern Turkey. The results of this study show that this boundary is composed of two distinct parts. One, in southeastern Turkey and Syria, is a wide and complex zone of continental collision. The other, in the Levantine basin of the eastern Mediterranean, is a zone of oceanic subduction. In the region of continental collision three zones of seismicity are observed. Most of the seismic activity in this region follows the Bitlis zone and is associated with a zone of thrusting and mountain building. This appears to be the zone of most active deformation and plate consumption in the plate boundary region between Arabia and Turkey. A less active zone of seismicity to the north of the Bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south. In the subduction zone of the eastern Mediterranean the depth of the subducted slab and the rate of seismicity generally increase from east to west. The zone of present-day convergence between Africa and Turkey in the Levantine basin can be best outlined by the northern edge of the Mediterranean ridge. The subduction zone in this area sequentially jumps to the south as small continental fragments collide with existing zones of subduction. Deep seismic activity near the Gulf of Antalya is associated with a detached subducted slab north of the Anaximander Mountains that is distinctly different from the seismic trend which is associated with present-day active subduction. The plate boundary between Africa and Turkey at the center of the Levantine basin appears to have shifted to the south of the Anaximander Mountains and Florence rise. Most of the focal mechanisms of the

  11. Shear wave splitting and the dynamics of the hydrated mantle wedge in subduction regions constrained by the example of the Ryukyu subduction zone

    Science.gov (United States)

    Nagaya, T.; Walker, A.; Wookey, J. M.; Wallis, S.; Ishii, K.; Kendall, J. M.

    2016-12-01

    H2O-rich subduction fluids are a key component of convergent plate margin dynamics, essential to earthquake initiation and magma formation. These fluids in the wedge mantle are dominantly derived from antigorite dragged down by plate motion. However, the accurate distribution of antigorite-rich serpentinite related to the fluid transport in subduction zones has thus far been difficult to determine. Our approach is to model the S-wave splitting of the Ryukyu arc in order to constrain the distribution, amount and orientation of antigorite, while taking into account the geometry of seismic ray paths and the elastic anisotropy of deformed antigorite-bearing mantle. We have also carried out a full assessment of uncertainties associated with our analysis including time delay estimates from the seismic waves themselves, crustal anisotropy, averaging schemes for CPO, and the strength of antigorite CPO patterns. The results suggest the presence of a large-scale flow in the hydrous mantle with a low viscosity and more than 54% of this domain consists of antigorite. Other geophysical observations in the forearc mantle including the low seismic velocity and gravity anomaly are also compatible with our inference of the presence of induced flow in an antigorite-rich, hydrated mantle wedge in the Ryukyu arc. We have also constructed a geodynamic model to examine flow patterns in the hydrated shallow wedge mantle using the distribution and proportion of serpentinite derived from our seismic model and subduction parameters that are close to those of the arc. The results clearly show that convection occurs in the serpentinized mantle wedge and that this domain is associated with a low surface heat flow. S-wave splitting observations in other subduction zones implies this large-scale serpentinization and hydrous mantle flow is likely to be more widespread than generally recognized and the view that the forearc mantle of cold subduction zones lacks significant zones of hydration needs

  12. Long-term fore-arc basin evolution in response to changing subduction styles in southern Alaska

    Science.gov (United States)

    Finzel, Emily S.; Enkelmann, Eva; Falkowski, Sarah; Hedeen, Tyler

    2016-07-01

    Detrital zircon U-Pb and fission track double-dating and Hf isotopes from the Mesozoic and Cenozoic strata in the southern Alaska fore-arc basin system reveal the effects of two different modes of flat-slab subduction on the evolution of the overriding plate. The southern margin of Alaska has experienced subduction of a spreading-ridge ( 62-50 Ma) and an oceanic plateau ( 40-0 Ma). When a subducting spreading ridge drives slab flattening, our data suggest that after the ridge has moved along strike retro-arc sediment sources to the fore arc become more predominant over more proximal arc sources. Spreading-ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent, thin sedimentary strata in the fore-arc basin. When a subducting oceanic plateau drives slab flattening, our data suggest that basin catchments get smaller and local sediment sources become more predominant. Crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that, combined, create topography and increase rock exhumation rates. Consequently, the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation. The cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages. This study demonstrates the merit of double-dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large-scale tectonic processes in magmatic regions.

  13. Origin and consequences of western Mediterranean subduction, rollback, and slab segmentation

    Science.gov (United States)

    van Hinsbergen, Douwe J. J.; Vissers, Reinoud L. M.; Spakman, Wim

    2014-04-01

    The western Mediterranean recorded subduction rollback, slab segmentation and separation. Here we address the questions of what caused Oligocene rollback initiation, and how its subsequent evolution split up an originally coherent fore arc into circum-southwest Mediterranean segments. We kinematically reconstruct western Mediterranean geology from subduction initiation to present, using Atlantic plate reconstructions as boundary condition. We test possible reconstructions against remnants of subducted lithosphere imaged by seismic tomography. Transform motion between Africa and Iberia (including the Baleares) between 120 and 85 Ma was followed by up to 150 km convergence until 30 Ma. Subduction likely initiated along the transform fault that accommodated pre-85 Ma translation. By the 30 Ma inception of rollback, up to 150 km of convergence had formed a small slab below the Baleares. Iberia was disconnected from Sardinia/Calabria through the North Balearic Transform Zone (NBTZ). Subduction below Sardinia/Calabria was slightly faster than below the Baleares, the difference being accommodated in the Pyrenees. A moving triple junction at the trench-NBTZ intersection formed a subduction transform edge propagator fault between the Baleares and Calabria slab segments. Calabria rolled back eastward, whereas the Baleares slab underwent radial (SW-S-SE) rollback. After Kabylides-Africa collision, the western slab segment retreated toward Gibraltar, here reconstructed as the maximum rollback end-member model, and a Kabylides slab detached from Africa. Opening of a slab window below the NBTZ allowed asthenospheric rise to the base of the fore arc creating high-temperature metamorphism. Western Mediterranean rollback commenced only after sufficient slab-pull was created from 100 to 150 km of slow, forced subduction before 30 Ma.

  14. Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models

    Science.gov (United States)

    Yoshida, Masaki; Santosh, M.

    2011-03-01

    The periodic assembly and dispersal of supercontinents through the history of the Earth had considerable impact on mantle dynamics and surface processes. Here we synthesize some of the conceptual models on supercontinent amalgamation and disruption and combine it with recent information from numerical studies to provide a unified approach in understanding Wilson Cycle and supercontinent cycle. Plate tectonic models predict that superdownwelling along multiple subduction zones might provide an effective mechanism to pull together dispersed continental fragments into a closely packed assembly. The recycled subducted material that accumulates at the mantle transition zone and sinks down into the core-mantle boundary (CMB) provides the potential fuel for the generation of plumes and superplumes which ultimately fragment the supercontinent. Geological evidence related to the disruption of two major supercontinents (Columbia and Gondwana) attest to the involvement of plumes. The re-assembly of dispersed continental fragments after the breakup of a supercontinent occurs through complex processes involving 'introversion', 'extroversion' or a combination of both, with the closure of the intervening ocean occurring through Pacific-type or Atlantic-type processes. The timescales of the assembly and dispersion of supercontinents have varied through the Earth history, and appear to be closely linked with the processes and duration of superplume genesis. The widely held view that the volume of continental crust has increased over time has been challenged in recent works and current models propose that plate tectonics creates and destroys Earth's continental crust with more crust being destroyed than created. The creation-destruction balance changes over a supercontinent cycle, with a higher crustal growth through magmatic influx during supercontinent break-up as compared to the tectonic erosion and sediment-trapped subduction in convergent margins associated with supercontinent

  15. The characteristics of mantle lithosphere buoyancy revealed from the northern Manila subduction zone to the active collision in Taiwan region

    Science.gov (United States)

    Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun; Lin, Jing-Yi

    2017-04-01

    It has been widely studied on the complexity tectonic structure in the active Taiwan orogenesis, since the converging between the Philippine Sea plate (PSP) and the Eurasian plate (EU) along with the Manila subduction zone extended from the Philippine to offshore the southern Taiwan and the Ryukyu subduction zone in the east. Considering the separate contribution of the crust and the mantle lithosphere to the topography, we try to examine the mantle lithosphere buoyancy (Hm) behavior from the northern Manila subduction zone to the active collision in Taiwan region. In this study, we present several Hm profiles across the northern Manila subduction zone and the Taiwan island. In order to calculate the Hm, the crust structures are constrained by the forward gravity modeling, in which the density is provided from the multi-channel seismic data and on land seismic data (thanks to the Taiwan Integrated Geodynamic Research (TAIGER) project). The result shows that the Hm across the northern Manila subduction zone displays apparent undulations, and undulates more drastic approaching the north end of the subduction zone. It implies that the plate coupling between the PSP and the EU here is weak. The Hm across the southern Taiwan undulates still, but the amplitudes are smaller with relative gentle undulations. This reflects the contribution from the slab underneath while the initial collision occurs in south Taiwan. Into the central Taiwan, the Hm pattern behaves undulating mild comparing with that across the subduction zone because the slab structure effects not obvious. Besides, the Hm in the central Taiwan primarily is affects by both the thickening crust and high elevation caused by the strong lateral external compression stress.

  16. Seismotectonics of the southern boundary of Anatolia, Eastern Mediterranean region: subduction, collision, and arc jumping

    Energy Technology Data Exchange (ETDEWEB)

    Rotstein, Y.; Kafka, A.L.

    1982-09-10

    The pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of Anatolia in the eastern Mediterranean and southeastern Turkey. The results of this study show that this boundary is composed of two distinct parts. One, in southeastern Turkey and Syria, is a wide and complex zone of continental collision. The other, in the Levantine basin of the eastern Mediterranean, is a zone of oceanic subduction. In the region of continental collision three zones of seismicity are observed. Most of the seismic activity in this region follows the Bitlis zone and is associated with a zone of thrusting and mountain building. This appears to be the zone of most active deformation and plate consumption in the plate boundary region between Arabia and Turkey. A less active zone of seismicity to the north of the Bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south. In the subduction zone of the eastern Mediterranean the depth of the subducted slab and the rate of seismicity generally increease from east to west. The zone of present-day convergence between Africa and Turkey in the Levantine basin can be best outlined by the northern edge of the Mediterranean ridge. Deep seismic activity near the Gulf of Antalya is associated with a detached subducted slab north of the Anaximander Mountains that is distinctly different from the seismic trend which is associated with present-day active subduction. Most of the focal mechanisms of the earthquakes along the entire southern boundary of Anatolia indicate that N to NNW thrusting is the dominant mode of seismic deformation.

  17. Subduction zone forearc serpentinites as incubators for deep microbial life

    Science.gov (United States)

    Plümper, Oliver; King, Helen E.; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P.; Rost, Detlef; Zack, Thomas

    2017-04-01

    Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ˜10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth’s largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth’s history such as the late heavy bombardment and global mass extinctions.

  18. Subduction zone forearc serpentinites as incubators for deep microbial life.

    Science.gov (United States)

    Plümper, Oliver; King, Helen E; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P; Rost, Detlef; Zack, Thomas

    2017-04-25

    Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth's largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth's history such as the late heavy bombardment and global mass extinctions.

  19. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Science.gov (United States)

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-12-04

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

  20. Young Volcanism on 20 Million Year Old Seafloor: The DISCOL Area, Nazca Plate.

    Science.gov (United States)

    Devey, C. W.; Boetius, A.; Kwasnitschka, T.; Augustin, N.; Yeo, I. A.; Greinert, J.

    2016-12-01

    Volcanism in the ocean basins is traditionally assumed to occur only at the plate margins (mid-ocean ridges, subduction zones, possibly also transform boundaries) and areas of intraplate hotspot activity related to thermal plumes in the mantle. As a result, abyssal areas away from hotspots are seldom explored systematically for signs of volcanism and are generally regarded as volcanically "dead". Here we present serendipitous results from the Peru Basin, a site of Mn-nodule accumulation which was targetted in 1989 for a large-scale disturbance experiment (the DISCOL experiment) to simulate the effects of seabed nodule mining. The area is truly intraplate - it is 700 km from the south American subduction zone or the Galapagos Islands and 2000 km from the East Pacific Rise. A return trip to DISCOL in 2015 to assess the extent of environmental recovery also included a remotely-operated underwater vehicle (ROV) dive on a small (300m high) seamount adjacent to the Mn-nodule field. ROV video records show the seamount is generally heavily sedimented but has a small (100x150m) pillow mound and an area of indurated calcareous sediments apparently cut by basaltic dykes near its summit. The summit is also cut by N-S and E-W-trending faults, some with up to 20m of throw, whose scarps expose thick sedimentary sequences. The virtual absence of sediment covering the pillows or dyke outcrops suggest that they are very recent - the thick sediment pile exposed on the fault scarps suggests that they were erupted on top of an old seamount. Regionally, acoustic data (bathymetry and backscatter from the ship-mounted multibeam system) shows several other seamounts in the region which may have experienced recent volcanic activity, although no sign of a linear volcanic chain is seen. Taken together, these observations suggest that, even at age 20Ma, the Nazca Plate is volcanically active.

  1. Geoid anomalies in the vicinity of subduction zones

    Science.gov (United States)

    Mcadoo, D. C.

    1981-01-01

    In the considered investigation, attention is given to the line source model, a surface source model, an application of the model, and a model of the thermal lithosphere associated with marginal basins. It is found that undulations in the altimetrically observed geoid of the southwest Pacific are strongly controlled by positive density anomalies in the subducting slabs of the region and the effects of elevation of the geotherm in behind arc lithosphere (corresponding to young marginal basins). Finer details of slab geometry do not obviously manifest themselves in the observed geoid. Such gravitational effects are quite attenuated at sea level and are apparently mixed with crustal effects, oceanographic noise, etc. It appears that slabs in global composite may contribute substantially to intermediate and long wavelength portions (down to spherical harmonic degree 3 or 4) of the earth's gravity field.

  2. Oceanic-style Subduction Controls Late Cenozoic Deformation of the Northern Pamir and Alai

    Science.gov (United States)

    Sobel, E. R.; Chen, J.; Schoenbohm, L. M.; Thiede, R. C.; Stockli, D. F.; Sudo, M.; Strecker, M. R.

    2012-12-01

    The Pamir - Alai represents the preeminent example of an active intracontinental subduction zone in the early stages of continent-continent collision. Such zones are the least understood type of plate boundary because modern examples are few and of limited access, and ancient analogs have been extensively overprinted by subsequent continent-continent collision and erosion processes. In the Pamir, at least 300 km of convergence has apparently occurred between the North Pamir and the South Tien Shan. Published P-wave tomography and earthquake epicenters suggest subduction of a ~300 km-long slab. The MPT and Pamir Frontal Thrusts (PFT) correspond to the updip projection of this subduction zone. We have compiled ca. 260 published and 18 new apatite and zircon (U-Th)/He and fission track, and biotite and muscovite Argon cooling ages from basement samples as well as several detrital samples from key areas in the Pamir region. Our synopsis shows that the hanging wall of the MPT experienced relatively minor amounts of late Cenozoic exhumation. This is incompatible with a model of a huge overthrust such as the Himalayan Main Central Thrust. Rather, the bulk of the convergence is apparently accommodated by underthrusting. The Pamir orogen as a whole is an integral part of the overriding plate in a subduction system, while the remnant basin to the north constitutes the downgoing plate. Herein, we demonstrate that the observed deformation of the upper and lower plates within the Pamir-Alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback, subduction erosion, subduction accretion, and marginal slab-tear faults. We suggest that the curvature of the North Pamir is genetically linked to the short width and rollback of the south-dipping Alai slab; northward motion (indentation) of the Pamir is accommodated by crustal processes related to slab rollback and intracontinental subduction. Our model relates late Oligocene - early Miocene

  3. The interplay between subduction and lateral extrusion : A case study for the European Eastern Alps based on analogue models

    NARCIS (Netherlands)

    van Gelder, I. E.; Willingshofer, E.; Sokoutis, D.; Cloetingh, S. A.P.L.

    2017-01-01

    A series of analogue experiments simulating intra-continental subduction contemporaneous with lateral extrusion of the upper plate are performed to study the interference between these two processes at crustal levels and in the lithospheric mantle. The models demonstrate that intra-continental

  4. Mw 8.6 Sumatran earthquake of 11 April 2012: rare seaward expression of oblique subduction

    Science.gov (United States)

    Ishii, Miaki; Kiser, Eric; Geist, Eric L.

    2013-01-01

    The magnitude 8.6 and 8.2 earthquakes off northwestern Sumatra on 11 April 2012 generated small tsunami waves that were recorded by stations around the Indian Ocean. Combining differential travel-time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench-parallel component. The oblique plate convergence indicates that ~20-50 m of trench-parallel displacement could have accumulated since the last megathrust earthquake, only part of which has been taken up by the Great Sumatran fault. This suggests that the remaining trench-parallel motion was released during the magnitude 8.6 earthquake on 11 April 2012 within the subducting plate. The magnitude 8.6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the Sumatra-Andaman earthquake in 2004.

  5. Slow slip near the trench at the Hikurangi subduction zone, New Zealand.

    Science.gov (United States)

    Wallace, Laura M; Webb, Spahr C; Ito, Yoshihiro; Mochizuki, Kimihiro; Hino, Ryota; Henrys, Stuart; Schwartz, Susan Y; Sheehan, Anne F

    2016-05-06

    The range of fault slip behaviors near the trench at subduction plate boundaries is critical to know, as this is where the world's largest, most damaging tsunamis are generated. Our knowledge of these behaviors has remained largely incomplete, partially due to the challenging nature of crustal deformation measurements at offshore plate boundaries. Here we present detailed seafloor deformation observations made during an offshore slow-slip event (SSE) in September and October 2014, using a network of absolute pressure gauges deployed at the Hikurangi subduction margin offshore New Zealand. These data show the distribution of vertical seafloor deformation during the SSE and reveal direct evidence for SSEs occurring close to the trench (within 2 kilometers of the seafloor), where very low temperatures and pressures exist. Copyright © 2016, American Association for the Advancement of Science.

  6. Interplay between deformation, fluid release and migration across a nascent subduction interface: evidence from Oman-UAE and implications for warm subduction zones

    Science.gov (United States)

    Agard, Philippe; Prigent, Cécile; Soret, Mathieu; Guillot, Stéphane; Dubacq, Benoît

    2017-04-01

    Frozen-in subduction plate interfaces preserving the first 1-2 My of the subduction history are found beneath ophiolites. These contacts are a key target to study the inception of mantle wedge metasomatism and the mechanical coupling between the upper plate and the top part of the sinking slab shortly after subduction initiation. Combining structural field and EBSD data, detailed petrology, thermodynamic modelling and geochemistry on both sides, i.e. the base of the mantle wedge (Oman-UAE basal peridotites) and the underlying accreted crustal fragments from the subducting slab (metamorphic soles), this study documents the continuous evolution of the plate contact from 1 GPa 900-750°C to 0.6 GPa 750-600°C, with emphasis on strain localization and feedbacks between deformation and fluid migration. In the mantle wedge, the (de)formation of proto-ultramylonitic peridotites is coeval with mantle metasomatism by focused hydrous fluid migration. Peridotite metasomatism results in the precipitation of new minerals (clinopyroxene, amphibole and spinel ± olivine and orthopyroxene) and their enrichment in FMEs (particularly B, Li and Cs, with concentrations up to 40 times that of the PM). Boron concentrations and isotopes (δ11B of metasomatized peridotites up to +25‰) suggest that these fluids with a "subduction signature" are probably sourced from the dehydrating amphibolitic metamorphic sole. Concomitantly, deformation in the lower plate results in the stepwise formation, detachment and accretion to the mylonitic s.l. mantle of successive slices of HT metabasalts from the downgoing slab, equilibrated at amphibolite/granulite conditions (900-750°C). Two major stages may be outlined: - between 900 and 750°C, the garnet-clinopyroxene-amphibole bearing sinking crust (with melting < 6 vol%) gets juxtaposed and mechanically coupled to the mantle, leading to the transfer of subduction fluids and metasomatism (possibly into the arc zone ultimately). Deformation is

  7. Transfer of subduction fluids into the deforming mantle wedge during nascent subduction: Evidence from trace elements and boron isotopes (Semail ophiolite, Oman)

    Science.gov (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Lemarchand, D.; Soret, M.; Ulrich, M.

    2018-02-01

    The basal part of the Semail ophiolitic mantle was (de)formed at relatively low temperature (LT) directly above the plate interface during "nascent subduction" (the prelude to ophiolite obduction). This subduction-related LT deformation was associated with progressive strain localization and cooling, resulting in the formation of porphyroclastic to ultramylonitic shear zones prior to serpentinization. Using petrological and geochemical analyses (trace elements and B isotopes), we show that these basal peridotites interacted with hydrous fluids percolating by porous flow during mylonitic deformation (from ∼850 down to 650 °C). This process resulted in 1) high-T amphibole crystallization, 2) striking enrichments of minerals in fluid mobile elements (FME; particularly B, Li and Cs with concentrations up to 400 times those of the depleted mantle) and 3) peridotites with an elevated δ11B of up to +25‰. These features indicate that the metasomatic hydrous fluids are most likely derived from the dehydration of subducting crustal amphibolitic materials (i.e., the present-day high-T sole). The rapid decrease in metasomatized peridotite δ11B with increasing distance to the contact with the HT sole (to depleted mantle isotopic values in slab-derived elements to the locus of partial melting in subduction zones.

  8. Testing Spatial Correlation of Subduction Interplate Coupling and Forearc Morpho-Tectonics

    Science.gov (United States)

    Goldfinger, Chris; Meigs, Andrew; Meigs, Andrew; Kaye, Grant D.; VanLaningham, Sam

    2005-01-01

    Subduction zones that are capable of generating great (Mw greater than 8) earthquakes appear to have a common assemblage of forearc morphologic elements. Although details vary, each have (from the trench landward), an accretionary prism, outer arc high, outer forearc basin, an inner forean: basin, and volcanic arc. This pattern is common in spite of great variation in forearc architecture. Because interseismic strain is known to be associated with a locked seismogenic plate interface, we infer that this common forearc morphology is related, in an unknown way, to the process of interseismic Strain accumulation and release in great earthquakes. To date, however, no clear relationship between the subduction process and the common elements of upper plate form has emerged. Whereas certain elements of the system, i.e. the outer arc high, are reasonably well- understood in a structural context, there is little understanding of the structural or topographic evolution of the other key elements like the inner arc and inner forearc basin, particularly with respect to the coupled zone of earthquake generation. This project developed a model of the seismologic, topographic, and uplift/denudation linkages between forearc topography and the subduction system by: 1) comparing geophysical, geodetic, and topographic data from subduction margins that generate large earthquakes; 2) using existing GPS, seismicity, and other data to model the relationship between seismic cycles involving a locked interface and upper-plate topographic development; and 3) using new GPS data and a range-scale topographic, uplift, and denudation analysis of the presently aseismic Cascadia margin to constrain topographic/plate coupling relationships at this poorly understood margin.

  9. Seismotectonics in the Pamir: An oblique transpressional shear and south-directed deep-subduction model

    Directory of Open Access Journals (Sweden)

    Jiasheng Zhang

    2011-01-01

    Full Text Available The 3-D geometry of the seismicity in Hindu Kush–Pamir–western China region has been defined by seismic records for 1975–1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms ≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone (MSSZ. The MSSZ, which dips southwards in Pamir has a north-dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India–Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45–65 km, 95–120 km, and 180–220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW–SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80–120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduction, upper crustal zone of evolving antithetic (i.e. north-dipping back-thrusts that contribute to north-south crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between

  10. Quantitative Study of Seismogenic Potential Along Manila Trench: Effects of Scaborough Seamount Chain Subduction

    Science.gov (United States)

    Yu, H.; Liu, Y.; Li, D.; Ning, J.; Matsuzawa, T.; Shibazaki, B.; Hsu, Y. J.

    2014-12-01

    Modern seismicity record along the Manila Trench shows only infrequent Mw7 earthquakes, the lack of great earthquakes may indicate the subduction fault is either aseismically slipping or is accumulating strain energy toward rapid release in a megathrust earthquake. We conduct numerical simulations of the plate coupling, earthquake nucleation and dynamic rupture propagation processes along the Manila subduction fault (15-19.5ºN), taking into consideration the effects of plate geometry (including subducted seamounts), fault strength, rate-state frictional properties and pore pressure variations. Specifically, we use the bathymetry to depict the outline of Manila trench along its strike, 2681 background seismicity (1970/02/13 to 2013/09/06) from Chinese Earthquake Network Center and 540 focal mechanism solutions (1976/01/01 to 2013/01/27) from Global CMT project to constrain the geometry of the subducting Sunda/Eurasian slab. The compilation of seismicity and focal mechanism indicates the plate dipping angle gradually changes from 28º (south of the Scaborough Seamount Chain) to 12º (north of it). This geometric anomaly may due to the subducted part of the seamount chain. Preliminary modeling results using gabbro gouge friction data show that the Scaborough Seamount Chain could be a barrier to earthquake rupture propagation. Only earthquakes larger than Mw7 can overcome the barrier to rupture the entire Manila trench. Smaller earthquakes would cease rupturing when it encounters the seamount chain. Moreover, we propose that Manila trench subduction zone has the potential of rupturing in a Mw8 megathrust earthquake, if the simulation period is long enough for an Mw8 earthquake cycle and dynamic rupture overcomes the subducted Scaborough Seamount Chain. Our model parameters will be further constrained by laboratory rock mechanics experiments conducted on IODP Expedition 349, South China Sea (SCS), drilling samples (work in progress at China Earthquake Administration

  11. Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California

    Science.gov (United States)

    Calmus, Thierry; Pallares, Carlos; Maury, René C.; Aguillón-Robles, Alfredo; Bellon, Hervé; Benoit, Mathieu; Michaud, François

    2011-08-01

    The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: "regular" calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific-Farallon plate formed the Comondú and central coast of the Sonora volcanic arc. In the extensional domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the Basin and Range province. The end of the Farallon subduction was marked by the emplacement of much more complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline activity became sporadic and was replaced by unusual post-subduction magma types including adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The spatial and temporal distribution of these lavas is consistent with the development of a slab tear, evolving into a 200-km-wide slab window sub-parallel to the trench, and extending from the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts of subslab origin ascended through this window, and adakites derived from the partial

  12. Isotopic Characteristics of Thermal Fluids from Mexican Subduction Zone

    Science.gov (United States)

    Taran, Y.; Inguaggiato, S.

    2007-05-01

    Chemical (major and trace elements) and isotopic (H,O,N,C,He) composition of waters and gases from thermal springs and geothermal wells of Mexican subduction zone have been measured. Three main geochemical profiles have been realized: (1) along the frontal Trans-Mexican Volcanic Belt (TMVB) zone through high- temperature Acoculco, Los Humeros, Los Azufres and La Primavera hydrothermal systems, Colima and Ceboruco volcanoes; (2) along the for-arc region of Pacific coast (12 groups of hot springs); (3) across the zone, from Pacific coast to TMVB, through the Jalisco Block. Fluids from El Chichon volcano in Chiapanecan arc system and Tacana volcano from the Central America Volcanic Arc have also been sampled. The frontal zone of TMVB is characterized by high 3He/4He ratios, from 7.2Ra in Ceboruco fumaroles to 7.6Ra in gases from Acoculco and Los Humeros calderas (Ra is atmospheric value of 1.4x10-6). These values are significantly higher than those published earlier in 80-s (up to 6.8Ra). Gases from coastal springs are low in 3He, usually < 1Ra with a minimum value of 0.2Ra in the northernmost submarine Punta Mita hot springs and a maximum value of 2.4Ra in La Tuna springs at the southern board of the Colima graben. An important feature of the TMVB thermal fluids is the absence of excess nitrogen in gases and, as a consequence, close to zero d15N values. In contrast, some coastal for-arc gases and gases from the Jalisco Block have high N2/Ar ratios and d15N up to +5 permil. Isotopic composition of carbon of CO2 along TMVB is close to typical "magmatic" values from -3 permil to -5 permil, but d13C of methane varies significantly indicating multiple sources of CH4 in geothermal fluids and a partial temperature control. High 3He/4He ratios and pure atmospheric nitrogen may indicate a low contribution of subducted sediments into the TMVB magmas and magmatic fluids. In contrast, El Chichon and Tacana fluids show some excess nitrogen (N2/Ar up to 500) and variable d15N, but

  13. From transpressional to transtensional tectonics in Northern Central America controlled by Cocos - Caribbean subduction coupling change

    Science.gov (United States)

    Alonso-Henar, Jorge; Alvarez-Gomez, José Antonio; Jesús Martinez-Diaz, José

    2017-04-01

    The Central American Volcanic Arc (CAVA) is located at the western margin of the Caribbean plate, over the Chortís Block, spanning from Guatemala to Costa Rica. The CAVA is associated to the subduction of the Cocos plate under the Caribbean plate at the Middle America Trench. Our study is focused in the Salvadorian CAVA segment, which is tectonically characterized by the presence of the El Salvador Fault Zone (ESFZ), part of the western boundary of a major block forming the Caribbean plate (the Chortis Block). The structural evolution of the western boundary of the Chortis Block, particularly in the CAVA crossing El Salvador remains unknown. We have done a kinematic analysis from seismic and fault slip data and combined our results with a review of regional previous studies. This approach allowed us to constrain the tectonic evolution and the forces that control the deformation in northern Central America. Along the active volcanic arc we identified active transtensional deformation. On the other hand, we have identified two deformation phases in the back arc region: A first one of transpressional wrenching close to simple shearing (Miocene); and a second one characterized by almost E-W extension. Our results reveal a change from transpressional to transtensional shearing coeval with a migration of the volcanism towards the trench in Late Miocene times. This strain change could be related with a coupled to decoupled transition on the Cocos - Caribbean subduction interface, which could be related to a slab roll-back of the Cocos Plate beneath the Chortis Block. The combination of different degrees of coupling on the subduction interface, together with a constant relative eastward drift of the Caribbean Plate, control the deformation style along the western boundary of the Chortis Block.

  14. Tectonic history of subduction zones inferred from retrograde blueschist P-T paths

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, W.G. (Univ. of California, Los Angeles (USA))

    1988-12-01

    Many Phanerozoic convergent plate junctions are marked by discontinuous blueschist belts, reflecting relatively high-pressure (P) prograde trajectories. Common blueschist paragneisses, such as those of the western Alps, exhibit widespread overprinting by greenschist and/or epidote-amphibolite facies assemblages. For this type of high-P belt, retrograde metamorphism involved fairly rapid, nearly isothermal decompression; some terranes underwent continued heating during early stages of pressure release. Uplift probably occurred as a consequence of the entrance of an island arc, oceanic plateau, or segment of continental crust into the subduction zone (collision), resulting in marked deceleration or cessation of underflow and buoyant, approximately adiabatic rise of the stranded, recrystallized subduction complex. Other high-P belts, such as the Franciscan of western California, preserve metamorphic aragonite and lack a low-P overprint; retrogression approximately retraced the prograde P-T (temperature) path, or for early formed high-grade blocks, occurred at even higher P/T ratios. Parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration. Upward motion took place as tectonically imbricated slices, as laminar return flow in melange zones, and perhaps partly a lateral spreading/extension of the underplated accretionary prism. Retrograde P-T trajectories of high-P belts therefore provide important constraints on the tectonic evolution of convergent plate junctions.

  15. Receiver function imaging of upper mantle complexity beneath the Pacific Northwest, United States

    Science.gov (United States)

    Eagar, Kevin C.; Fouch, Matthew J.; James, David E.

    2010-08-01

    Small-scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions. Subduction of the Juan de Fuca plate and other tectonic processes dominating the Pacific Northwest, United States in the Cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3-D temperature variations. We address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km. We utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations, primarily those of the Earthscope/USArray Transportable Array. We find the average depths of the discontinuities to be 412 km and 658 km, respectively, with no obvious 520 km discontinuity detected. The peak-to-peak range is greater on the '410' than the '660', suggesting the possibility of more significant regional dynamic processes at upper mantle depths. Our results are not consistent with a mantle plume below central Oregon in the High Lava Plains region. Our observation of a thinner transition zone beneath the western Snake River Plain region, however, is consistent with a regional increase in mantle temperatures, perhaps due to either asthenospheric flow from beneath and around the southern edge of the Juan de Fuca plate, or to vertical flow in the form of regional mantle upwelling related to the Snake River Plain / Yellowstone hotspot track. Further, our results are not consistent with a simple subducting Juan de Fuca slab morphology, but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies. We find evidence for a thickened and therefore cooler mantle transition zone beneath the Wallowa / Idaho Batholith region, consistent with tomographic models which suggest

  16. Does slab-window opening cause uplift of the overriding plate? A case study from the Gulf of California

    Science.gov (United States)

    Mark, Chris; Chew, David; Gupta, Sanjeev

    2017-11-01

    Complete subduction of an oceanic plate results in slab-window opening. A key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab-window opening generate a detectable topographic signature in the overriding plate. We focus on the Baja California Peninsula, which incorporates the western margin of the Gulf of California rift. The topography and tectonics of the rift flank along the peninsula are strongly bimodal. North of the Puertecitos accommodation zone, the primary drainage divide attains a mean elevation of ca. 1600 m above sea level (asl), above an asthenospheric slab-window opened by Pacific-Farallon spreading ridge subduction along this section of the trench at ca. 17-15 Ma. To the south, mean topography decreases abruptly to ca. 800 m asl (excluding the structurally distinct Los Cabos block at the southern tip of the peninsula), above fragments of the oceanic Farallon slab which stalled following slab tear-off at ca. 15-14 Ma. Along the peninsula, a low-relief surface established atop Miocene subduction-related volcaniclastic units has been incised by a west-draining canyon network in response to uplift. These canyons exhibit cut-and-fill relationships with widespread post-subduction lavas. Here, we utilise LANDSAT and digital elevation model (DEM) data, integrated with previously published K-Ar and 40Ar/39Ar lava crystallisation ages, to constrain the onset of rift flank uplift to ca. 9-5 Ma later than slab-window formation in the north and ca. 11-10 Ma later in the south. These greatly exceed response time estimates of ca. 2 Ma or less for uplift triggered by slab-window opening. Instead, uplift timing of the high-elevation northern region is consistent with lower-lithospheric erosion driven by rift-related convective upwelling. To the south, stalled slab fragments likely inhibited convective return flow, preventing lithospheric erosion and limiting uplift to the isostatic response

  17. Geophysical surveys of the Queen Charlotte Fault plate boundary off SE Alaska: Preliminary results

    Science.gov (United States)

    Ten Brink, U. S.; Brothers, D. S.; Andrews, B. D.; Kluesner, J.; Haeussler, P. J.; Miller, N. C.; Watt, J. T.; Dartnell, P.; East, A. E.

    2016-12-01

    Recent multibeam sonar and high-resolution seismic surveys covering the northern 400-km-long segment of Queen Charlotte Fault off SE Alaska, indicate that the entire 50 mm/yr right-lateral Pacific-North America plate motion is currently accommodated by a single fault trace. The trace is remarkably straight rarely interrupted by step-overs, and is often plate from continental forearc and arc terrains of a former subduction zone. This unusual setting for a transform plate boundary might have resulted from the northward passage of the thick crust of the Yakutat Terrane during the Late Cenozoic. A step-over at the mouth of Chatham Strait has formed a 20-km-long 1.6-km-wide pull-apart basin composed of 3 sub-basins. Internal basin stratigraphy indicates possible southward migration of the step-over with time. Slight outward curving of the southern strand may suggest the presence of a deeper barrier there, which could have terminated the northward super-shear rupture of the 2013 M7.5 Craig Earthquake. Whether this possible barrier is related to the intersection of the Aja Fracture Zone with the plate boundary is unclear. No other surficial impediments to rupture were observed along the 315 km trace between this fault step-over and a 20° bend near Icy Point, where the fault extends onshore and becomes highly transpressional. An enigmatic oval depression, 1.5-2 km wide and 500 m deep, south of the step-over and a possible mud volcano north of the step-over, may attest to possible vigorous gas and fluid upwelling along the fault zone.

  18. Insight into the subducted Indian slab and origin of the Tengchong volcano in SE Tibet from receiver function analysis

    Science.gov (United States)

    Xu, Mijian; Huang, Hui; Huang, Zhouchuan; Wang, Pan; Wang, Liangshu; Xu, Mingjie; Mi, Ning; Li, Hua; Yu, Dayong; Yuan, Xiaohui

    2018-01-01

    The subduction of the Indian Plate beneath SE Tibet and its related volcanism in Tengchong are important geologic processes that accompany the evolution of the Tibetan Plateau. However, it is still not clear whether the subduction and volcanism are confined to the upper mantle or if they extend deep into the mantle transition zone (MTZ). Here, we imaged MTZ structures by using receiver function methods with the waveforms recorded by more than 300 temporary stations in SE Tibet. The results show significant depressions of both the 410-km and 660-km discontinuities and a thickened MTZ (260-280 km) beneath SE Tibet. The depression of the 660-km discontinuity (by 10-30 km) and the thickened MTZ correlate well with high P-wave velocity anomalies in the MTZ, indicating the presence of a subducted Indian slab within the MTZ. Significant depression of the 410-km discontinuity (by 10-20 km) beneath the Tengchong volcano indicates that the volcano originates from the MTZ and is closely related to the subducted Indian slab. Our results confirm the deep subduction of the Indian plate and the deep origin of the Tengchong volcano. However, it remains unknown whether a slab gap exists and contributes to the Tengchong volcano.

  19. A numerical reference model for themomechanical subduction

    DEFF Research Database (Denmark)

    Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola

    2010-01-01

    response to systematic variations in input parameters, numerical studies often start from a 'reference' subduction model. However, the reference model often varies between different numerical studies, making it difficult to compare results directly. We aim therefore to define a numerical reference model......, and initial temperature distribution. We will show results of the evolution and dynamics of the subduction reference model using different numerical codes: a finite element code, SULEC, and two finite difference codes, YACC and FDcon....

  20. Regional ash fall hazard II: Asia-Pacific modelling results and implications

    Science.gov (United States)

    Jenkins, Susanna; McAneney, John; Magill, Christina; Blong, Russell

    2012-09-01

    In a companion paper (this volume), the authors propose a methodology for assessing ash fall hazard on a regional scale. In this study, the methodology is applied to the Asia-Pacific region, determining the hazard from 190 volcanoes to over one million square kilometre of urban area. Ash fall hazard is quantified for each square kilometre grid cell of urban area in terms of the annual exceedance probability (AEP), and its inverse, the average recurrence interval (ARI), for ash falls exceeding 1, 10 and 100 mm. A surrogate risk variable, the Population-Weighted Hazard Score: the product of AEP and population density, approximates the relative risk for each grid cell. Within the Asia-Pacific region, urban areas in Indonesia are found to have the highest levels of hazard and risk, while Australia has the lowest. A clear demarcation emerges between the hazard in countries close to and farther from major subduction plate boundaries, with the latter having ARIs at least 2 orders of magnitude longer for the same thickness thresholds. Countries with no volcanoes, such as North Korea and Malaysia, also face ash falls from volcanoes in neighbouring countries. Ash falls exceeding 1 mm are expected to affect more than one million people living in urban areas within the study region; in Indonesia, Japan and the Philippines, this situation could occur with ARIs less than 40 years.

  1. Investigating the Role of Dehydration Reactions in Subduction Zone Pore Pressures Using Newly-Developed Permeability-Porosity Relationships

    Science.gov (United States)

    Screaton, E.; Daigle, H.; James, S.; Meridth, L.; Jaeger, J. M.; Villaseñor, T. G.

    2014-12-01

    Dehydration reactions are linked to shallow subduction zone deformation through excess pore pressures and their effect on mechanical properties. Two reactions, the transformation of smectite to illite and of opal-A to opal-CT and then to quartz, can occur relatively early in the subduction process and may affect the propagation of the plate boundary fault, the updip limit of velocity-weakening frictional paper, and tsunamigenesis. Due to large variations between subduction zones in heat flow, sedimentation rates, and geometries, dehydration location may peak prior to subduction to as much as 100 km landward of the deformation front. The location of the dehydration reaction peak relative to when compaction occurs, causes significant differences in pore pressure generation. As a result, a key element to modeling excess pore pressures due to dehydration reactions is the assumed relationship between permeability and porosity. Data from Integrated Ocean Drilling Program (IODP) drilling of subduction zone reference sites were combined with previously collected results to develop relationships for porosity-permeability behavior for various sediment types. Comparison with measurements of deeper analog data show that porosity-permeability trends are maintained through burial and diagenesis to porosities <10%, suggesting that behavior observed in shallow samples is informative for predicting behavior at depth following subduction. We integrate these permeability-porosity relationships, compaction behavior, predictions of temperature distribution, kinetic expressions for smectite and opal-A dehydration, into fluid flow models to examine the role of dehydration reactions in pore pressure generation.

  2. Is plate tectonis withstanding the test of time?

    Directory of Open Access Journals (Sweden)

    O. Shields

    1997-06-01

    Full Text Available Since the theory of plate tectonics was first proposed thirty years ago, some problems have arisen in its practical application. These call into question its fundamental assumptions of horizontal plate motion, hotspot fixity, true polar wander, Panthalassa, and the Earth’s constant size while leaving seafloor spreading and subduction intact. A rapidity expanding earth solves these problems and privides an alternative viewpoint worth reconsidering.

  3. Record of mid-Archaean subduction from metamorphism in the Barberton terrain, South Africa.

    Science.gov (United States)

    Moyen, Jean-François; Stevens, Gary; Kisters, Alexander

    2006-08-03

    Although plate tectonics is the central geological process of the modern Earth, its form and existence during the Archaean era (4.0-2.5 Gyr ago) are disputed. The existence of subduction during this time is particularly controversial because characteristic subduction-related mineral assemblages, typically documenting apparent geothermal gradients of 15 degrees C km(-1) or less, have not yet been recorded from in situ Archaean rocks (the lowest recorded apparent geothermal gradients are greater than 25 degrees C km(-1)). Despite this absence from the rock record, low Archaean geothermal gradients are suggested by eclogitic nodules in kimberlites and circumstantial evidence for subduction processes, including possible accretion-related structures, has been reported in Archaean terrains. The lack of spatially and temporally well-constrained high-pressure, low-temperature metamorphism continues, however, to cast doubt on the relevance of subduction-driven tectonics during the first 1.5 Gyr of the Earth's history. Here we report garnet-albite-bearing mineral assemblages that record pressures of 1.2-1.5 GPa at temperatures of 600-650 degrees C from supracrustal amphibolites from the mid-Archaean Barberton granitoid-greenstone terrain. These conditions point to apparent geothermal gradients of 12-15 degrees C-similar to those found in recent subduction zones-that coincided with the main phase of terrane accretion in the structurally overlying Barberton greenstone belt. These high-pressure, low-temperature conditions represent metamorphic evidence for cold and strong lithosphere, as well as subduction-driven tectonic processes, during the evolution of the early Earth.

  4. Tectonics of the IndoBurma Oblique Subduction Zone

    Science.gov (United States)

    Steckler, M. S.; Seeber, L.; Akhter, S. H.; Betka, P. M.; Cai, Y.; Grall, C.; Mondal, D. R.; Gahalaut, V. K.; Gaherty, J. B.; Maung Maung, P.; Ni, J.; Persaud, P.; Sandvol, E. A.; Tun, S. T.

    2016-12-01

    The Ganges-Brahmaputra Delta (GBD) is obliquely colliding with the IndoBurma subduction zone. Most of the 42 mm/y of arc-parallel motion is absorbed in a set of dextral to dextral-convergent faults, the Sagaing, Kabaw and Churachandpur-Mao Faults. The 13-17 mm/y of convergence with the delta has built a 250-km wide active accretionary prism. The upper part of the 19-km sediment thickness consists of a shallowing-up stack of prograding strata that has shifted the shelf edge 3-400 km since the Himalayan orogeny at 50 Ma. The upper 3-5 km sandy shelf to fluvial strata are deformed into a broad fold and thrust belt above an overpressured décollement. It forms a flat shallow roof thrust in the frontal accretionary prism. The structure of the deeper part of the accretionary prism, which must transfer the incoming sediments to the upper plate, is unknown. GPS indicates the downdip end of the megathrust locked zone is 25 km at 92.5°E. The deformation front, marked by nascent detachment folds above the shallow décollement reaches the megacity of Dhaka in the middle of the GBD. The seismogenic potential of this portion of the prism is unknown. Arc volcanism in Myanmar, 500 km east of the deformation front, is sparse. Limited geochemical data on the arc volcanics are consistent with hot slab conditions. One possibility is that the deep GBD slab and basement are metamorphosed and dewatered early in the subduction process whereby most of the fluids are transferred to the growing prism by buoyancy driven migration or accretion of fluid-rich strata. Since it is entirely subaerial this little-studied region crossing Bangladesh, India and Myanmar provides an opportunity for a detailed multidisciplinary geophysical and geological investigation. It has the potential to highlight the role of fluids in subduction zones, the tectonics of extreme accretion and their seismic hazards, and the interplay between driving and resistance forces of a subduction zone during a soft collision.

  5. First results of high-resolution modeling of Cenozoic subduction orogeny in Andes

    Science.gov (United States)

    Liu, S.; Sobolev, S. V.; Babeyko, A. Y.; Krueger, F.; Quinteros, J.; Popov, A.

    2016-12-01

    The Andean Orogeny is the result of the upper-plate crustal shortening during the Cenozoic Nazca plate subduction beneath South America plate. With up to 300 km shortening, the Earth's second highest Altiplano-Puna Plateau was formed with a pronounced N-S oriented deformation diversity. Furthermore, the tectonic shortening in the Southern Andes was much less intensive and started much later. The mechanism of the shortening and the nature of N-S variation of its magnitude remain controversial. The previous studies of the Central Andes suggested that they might be related to the N-S variation in the strength of the lithosphere, friction coupling at slab interface, and are probably influenced by the interaction of the climate and tectonic systems. However, the exact nature of the strength variation was not explored due to the lack of high numerical resolution and 3D numerical models at that time. Here we will employ large-scale subduction models with a high resolution to reveal and quantify the factors controlling the strength of lithospheric structures and their effect on the magnitude of tectonic shortening in the South America plate between 18°-35°S. These high-resolution models are performed by using the highly scalable parallel 3D code LaMEM (Lithosphere and Mantle Evolution Model). This code is based on finite difference staggered grid approach and employs massive linear and non-linear solvers within the PETSc library to complete high-performance MPI-based parallelization in geodynamic modeling. Currently, in addition to benchmark-models we are developing high-resolution (Paleozoic-Cenozoic sediments above the uppermost crust in the Subandean Ranges. Future work will be focused on the origin of different styles of deformation and topography evolution in Altiplano-Puna Plateau and Central-Southern Andes through 3D modeling of large-scale interaction of subducting and overriding plates.

  6. No-net-rotation model of current plate velocities incorporating plate motion model NUVEL-1

    Science.gov (United States)

    Argus, Donald F.; Gordon, Richard G.

    1991-01-01

    NNR-NUVEL1 is presented which is a model of plate velocities relative to the unique reference frame defined by requiring no-net-rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model NUVEL-1 (DeMets et al., 1990). In NNR-NUVEL1, the Pacific plate rotates in a right-handed sense relative to the no-net-rotation reference frame at 0.67 deg/m.y. about 63 deg S, 107 deg E. At Hawaii the Pacific plate moves relative to the no-net-rotation reference frame at 70 mm/yr, which is 25 mm/yr slower than the Pacific plate moves relative to the hotspots. Differences between NNR-NUVEL1 and HS2-NUVEL1 are described. The no-net-rotation reference frame differs significantly from the hotspot reference frame. If the difference between reference frames is caused by motion of the hotspots relative to a mean-mantle reference frame, then hotspots beneath the Pacific plate move with coherent motion towards the east-southeast. Alternatively, the difference between reference frames can show that the uniform drag, no-net-torque reference frame, which is kinematically equivalent to the no-net-rotation reference frame, is based on a dynamically incorrect premise.

  7. No-net-rotation model of current plate velocities incorporating plate motion model NUVEL-1

    Science.gov (United States)

    Argus, Donald F.; Gordon, Richard G.

    1991-11-01

    NNR-NUVEL1 is presented which is a model of plate velocities relative to the unique reference frame defined by requiring no-net-rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model NUVEL-1 (DeMets et al., 1990). In NNR-NUVEL1, the Pacific plate rotates in a right-handed sense relative to the no-net-rotation reference frame at 0.67 deg/m.y. about 63 deg S, 107 deg E. At Hawaii the Pacific plate moves relative to the no-net-rotation reference frame at 70 mm/yr, which is 25 mm/yr slower than the Pacific plate moves relative to the hotspots. Differences between NNR-NUVEL1 and HS2-NUVEL1 are described. The no-net-rotation reference frame differs significantly from the hotspot reference frame. If the difference between reference frames is caused by motion of the hotspots relative to a mean-mantle reference frame, then hotspots beneath the Pacific plate move with coherent motion towards the east-southeast. Alternatively, the difference between reference frames can show that the uniform drag, no-net-torque reference frame, which is kinematically equivalent to the no-net-rotation reference frame, is based on a dynamically incorrect premise.

  8. Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

    Science.gov (United States)

    Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

    1997-01-01

    The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

  9. Organic matter cracking: A source of fluid overpressure in subducting sediments

    Science.gov (United States)

    Raimbourg, Hugues; Thiéry, Régis; Vacelet, Maxime; Famin, Vincent; Ramboz, Claire; Boussafir, Mohammed; Disnar, Jean-Robert; Yamaguchi, Asuka

    2017-11-01

    The pressure of deep fluids in subduction zones is a major control on plate boundary strength and earthquake genesis. The record, by methane-rich fluid inclusions, of large ( 50-100 MPa) and instantaneous pressure variations in the Shimanto Belt (Japan) points to the presence of large fluid overpressure at depth (300-500 MPa, 250 °C). To further analyze the connection between methane and fluid overpressure, we determined with Rock-Eval the potential for a worldwide selection of deep seafloor sediments to produce methane as a result of organic matter (OM) cracking due to temperature increase during subduction. The principal factor controlling the methanogenesis potential of sediments is OM proportion, while OM nature is only a subordinate factor. In turn, OM proportion is mainly controlled by the organic terrigenous input. Considering a typical sediment from ocean-continent subduction zones, containing 0.5 wt% of type III OM, cracking of OM has two major consequences: (1) Methane is produced in sufficient concentration as to oversaturate the pore-filling water. The deep fluid in accretionary prisms is therefore a mechanical mixture of water-rich and methane-rich phases; (2) CH4 production can generate large fluid overpressure, of the order of several tens of MPa, The conditions for these large overpressure are a low permeability of the upper plate (z > 10 km) where OM thermal cracking occurs. At these depths, OM thermal cracking appears as a source of overpressure larger than the last increments of smectite-to-illite reaction. Such large overpressures play potentially a role in facilitating slip along the plate interface. Conversely, the scarcity of earthquakes in ocean-ocean subduction zones such as Marianna or Barbados may be related to the low influx of detrital OM and the limited methane/overpressure generation at depth.

  10. Fluid accumulation along the Costa Rica subduction thrust and development of the seismogenic zone

    Science.gov (United States)

    Bangs, Nathan L.; McIntosh, Kirk D.; Silver, Eli A.; Kluesner, Jared W.; Ranero, César R.

    2015-01-01

    In 2011 we acquired an 11 × 55 km, 3-D seismic reflection volume across the Costa Rica margin, NW of the Osa Peninsula, to accurately image the subduction thrust in 3-D, to examine fault zone properties, and to infer the hydrogeology that controls fluid accumulation along the thrust. Following processing to remove water column multiples, noise, and acquisition artifacts, we constructed a 3-D seismic velocity model for Kirchhoff prestack depth migration imaging. Images of the plate boundary thrust show high-reflection amplitudes underneath the middle to lower slope that we attribute to fluid-rich, poorly drained portions of the subduction thrust. At 5 km subseafloor, beneath the upper slope, the plate interface abruptly becomes weakly reflective, which we interpret as a transition to a well-drained subduction thrust. Mineral dehydration during diagenesis may also diminish at 5 km subseafloor to reduce fluid production and contribute to the downdip change from high to low amplitude. There is also a layered fabric and systems of both thrust and normal faults within the overriding plate that form a "plumbing system." Faults commonly have fault plane reflections and are presumably fluid charged. The faults and layered fabric form three compartmentalized hydrogeologic zones: (1) a shallow NE dipping zone beneath the slope, (2) a steeply SW dipping zone beneath the shelf slope break, and (3) a NE dipping zone beneath the shelf. The more direct pathway in the middle zone drains the subduction thrust more efficiently and contributes to reduced fluid pressure, elevates effective stress, and creates greater potential for unstable coseismic slip.

  11. Stress and Strength of Seismogenic and Creeping Subduction Faults (Invited)

    Science.gov (United States)

    Wang, K.; Bilek, S. L.; Wada, I.; Gao, X.; Brown, L.

    2013-12-01

    Force balance studies of subduction zone forearcs constrained by earthquake focal mechanisms, active faulting, and topography suggest very weak subduction megathrusts. If represented by an effective coefficient of frict