scholarly journals Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 355-364 ◽  
Author(s):  
P. E. van Keken ◽  
S. Kita ◽  
J. Nakajima
Keyword(s):  
Subduction Zones ◽  
Thermal Structure ◽  
Finite Element Models ◽  
Local Conditions ◽  
Intermediate Depth ◽  
Upper Mantle Structure ◽  
Subduction System ◽  
Subducting Slab ◽  
Northern Japan

Abstract. The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

scholarly journals Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

2012 ◽  
Vol 4 (2) ◽  
pp. 1069-1093 ◽  
Author(s):  
P. E. van Keken ◽  
S. Kita ◽  
J. Nakajima
Keyword(s):  
Upper Mantle ◽  
Subduction Zones ◽  
Thermal Structure ◽  
Local Conditions ◽  
Intermediate Depth ◽  
Upper Mantle Structure ◽  
Subduction System ◽  
Subducting Slab ◽  
Northern Japan

Abstract. The cause of intermediate-depth (> 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instabilities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new high resolution finite elements models that predict the dynamics and thermal structure of the Japan subduction system with a high precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths > 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models, that take into account the seismically imaged modified upper mantle structure in this region, fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

The role of transform faults during back-arc spreading centre jumps

2020 ◽  
Author(s):  
Nicholas Schliffke ◽  
Jeroen van Hunen ◽  
Frederic Gueydan ◽  
Valentina Magni ◽  
Mark B. Allen
Keyword(s):  
Subduction Zones ◽  
3D Models ◽  
Parameter Study ◽  
Transform Faults ◽  
Strongly Coupled ◽  
Threshold Length ◽  
Scotia Arc ◽  
Back Arc ◽  
Subduction System

<p>Jumps in the location of back-arc spreading centres are a common feature of back-arc basins, but the controlling factors are not understood. In several narrow subduction zones with a long subduction history, such as the Scotia arc or Tyrhennian Sea, several spreading centres have been active in the course of history with regular, quasi-instantaneous jumps towards the retreating trench. A prominent feature of these regions are large bounding transform (‘STEP’) faults. However, whether STEP faults influence the (unknown) dynamics spreading centre jumps remains to be explored.</p><p> </p><p>We therefore run 3D-models to simulate a long narrow subducting slab, bound by continents, which retreats and creates necessary STEP-faults self-consistently. The results offer a new mechanism for back-arc spreading jumps: After the creation of a back-arc spreading centre in the retreating subduction system, transform faults between trench and back-arc basin form. Spreading jumps are thus a consequence of the fact that these constantly elongating transform faults, which decouple the overriding plate from neighbouring plates, fail to remain active once a threshold length (~1.3x plate width) is reached. Subsequently, the back-arc basin and neighbouring plates are strongly coupled, and ongoing trench retreat localizes stresses and rapidly ruptures the overriding plate closer to the trench while the old spreading centre is abandoned.  In a parameter study, the results further explain why the narrowest subduction zones, such as the Calabrian Arc, experience more frequent and closer spreading jumps than the long-period jumps of a wider subduction zone such as the Scotia Arc. The widest subduction zones should not undergo any back-arc spreading jumps with this mechanism, consistent with other natural examples.</p>

Numerical simulation of subduction zone pressure-temperature-time paths: constraints on fluid production and arc magmatism

1991 ◽  
Vol 335 (1638) ◽  
pp. 341-353 ◽  
Keyword(s):  
Heat Transfer ◽  
Partial Melting ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Transfer Model ◽  
Temperature Time ◽  
Subducting Slab

The location and sequence of metamorphic devolatilization and partial melting reactions in subduction zones may be constrained by integrating fluid and rock pressure-temperature-time ( P-T-t ) paths predicted by numerical heat-transfer models with phase diagrams constructed for metasedimentary, metabasaltic, and ultramafic bulk compositions. Numerical experiments conducted using a two-dimensional heat transfer model demonstrate that the primary controls on subduction zone P-T-t paths are: (1) the initial thermal structure; (2) the amount of previously subducted lithosphere; (3) the location of the rock in the subduction zone; and (4) the vigour of mantle wedge convection induced by the subducting slab. Typical vertical fluid fluxes out of the subducting slab range from less than 0.1 to 1 (kg fluid) m -2 a -1 for a convergence rate of 3 cm a -1 . Partial melting of the subducting, amphibole-bearing oceanic crust is predicted to only occur during the early stages of subduction initiated in young (less than 50 Ma) oceanic lithosphere. In contrast, partial melting of the overlying mantle wedge occurs in many subduction zone experiments as a result of the infiltration of fluids derived from slab devolatilization reactions. Partial melting in the mantle wedge may occur by a twostage process in which amphibole is first formed by H 2 O infiltration and subsequently destroyed as the rock is dragged downward across the fluid-absent ‘hornblende-out’ partial melting reaction.

scholarly journals Northern Chile intermediate-depth earthquakes controlled by plate hydration

2020 ◽  
Author(s):  
Leoncio Cabrera ◽  
Sergio Ruiz ◽  
Piero Poli ◽  
Eduardo Contreras-Reyes ◽  
Axel Osses ◽  
...  
Keyword(s):  
Template Matching ◽  
Thermal Structure ◽  
Seismic Source ◽  
Northern Chile ◽  
Large Magnitude ◽  
Aftershock Activity ◽  
Dramatic Decrease ◽  
Intermediate Depth ◽  
Subducting Plate

Summary We investigate the variations of the seismic source properties and aftershock activity using kinematic inversions and template-matching, for six large magnitude intermediate-depth earthquakes occurred in northern Chile. Results show similar rupture geometry and stress drop values between 7–30 MPa. Conversely, aftershocks productivity systematically decreases for the deeper events within the slab. Particularly there is a dramatic decrease in aftershock activity below the 400–450°C isotherm-depth, which separates high and low-hydrated zones. The events exhibit tensional focal mechanisms at unexpected depths within the slab, suggesting a deepening of the neutral plane, where the extensional regimen reaches the 700–800°C isotherm-depth. We interpret the reduction of aftershocks in the lower part of the extensional regime as the absence of a hydrated-slab at those depths. Our finding highlights the role of the thermal-structure and fluids in the subducting plate, in controlling the intermediated-depth seismic activity and shed new light in their causative mechanism.

Petrologic and geochemical role of serpentinite in subduction zones and plate interface domains

2015 ◽  
Vol 37 ◽  
pp. 61-64
Author(s):  
Marco Scambelluri ◽  
Enrico Cannaò ◽  
Mattia Gilio ◽  
Marguerite Godard
Keyword(s):  
Subduction Zones ◽  
Plate Interface

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

From converts to cooperation: Protestant internationalism, US missionaries and Indian Christians and ‘Professional’ social work between Boston and Bombay (c. 1920–1950)

2021 ◽  
pp. 1-20
Author(s):  
Michael Phillipp Brunner
Keyword(s):  
Social Work ◽  
North America ◽  
Social Gospel ◽  
Local Conditions ◽  
Historical Approach ◽  
The Social ◽  
Social Concerns ◽  
High Phase

Abstract The 1920s and 30s were a high phase of liberal missionary internationalism driven especially by American-led visions of the Social Gospel. As the missionary consensus shifted from proselytization to social concerns, the indigenization of missions and the role of the ‘younger churches’ outside of Europe and North America was brought into focus. This article shows how Protestant internationalism pursued a ‘Christian Sociology’ in dialogue with the field’s academic and professional form. Through the case study of settlement sociology and social work schemes by the American Marathi Mission (AMM) in Bombay, the article highlights the intricacies of applying internationalist visions in the field and asks how they were contested and shaped by local conditions and processes. Challenging a simplistic ‘secularization’ narrative, the article then argues that it was the liberal, anti-imperialist drive of the missionary discourse that eventually facilitated an American ‘professional imperialism’ in the development of secular social work in India. Adding local dynamics to the analysis of an internationalist discourse benefits the understanding of both Protestant internationalism and the genesis of Indian social work and shows the value of an integrated global micro-historical approach.

Nasal Dermoids in Children: Factors Influencing the Distant Result

2021 ◽  
Author(s):  
Michal Kotowski ◽  
Paulina Adamczyk ◽  
Jaroslaw Szydlowski
Keyword(s):  
Pediatric Patients ◽  
Surgical Techniques ◽  
Intracranial Extension ◽  
Recurrence Rates ◽  
Local Conditions ◽  
Aesthetic Result ◽  
Factors Influencing ◽  
Vertical Incision ◽  
External Rhinoplasty

AbstractThe aim of the study was to present a single institution’s treatment strategy for nasal dermoids and to identify factors influencing distant results. The study covered 24 surgically treated pediatric patients with nasal dermoids (NDs). The medical data concerning demographics, preoperative local inflammations and surgical procedures, form of the abnormality, imaging, surgical techniques, and a role of osteotomies and reconstructions were analyzed. The recurrence rates and distant aesthetic outcomes were assessed. The surgical approach included vertical incision in 21 patients, the external rhinoplasty approach in 2 cases, and bicoronal incision in 1 child. The intracranial extension was confirmed in 6 patients. Seven out of 8 cases with preoperative local inflammations and 3 out of 4 with secondary fistulization were < 4 years old. Nine patients required osteotomies. Three children required reconstruction of the nasal skeleton. None of the distant cosmetic results was described as hideous or unsatisfactory. The incidence of local inflammatory complications is unrelated to the age of the patients. The distant aesthetic result depends on both the initial extent of the disease and preoperative local conditions or interventions. Prompt surgical intervention is highly recommended.

The Role of Topology and Tissue Mechanics in Remora Attachment

2014 ◽  
Vol 1648 ◽  
Author(s):  
Michael Culler ◽  
Keri A. Ledford ◽  
Jason H. Nadler
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Tissue Mechanics ◽  
Unit Cell ◽  
Surface Topology ◽  
Finite Element Models ◽  
Cell Geometry ◽  
Critical Step ◽  
Tissue Material

ABSTRACTRemora fish are capable of fast, reversible and reliable adhesion to a wide variety of both natural and artificial marine hosts through a uniquely evolved dorsal pad. This adhesion is partially attributed to suction, which requires a robust seal between the pad interior and the ambient environment. Understanding the behavior of remora adhesion based on measurable surface parameters and material properties is a critical step when creating artificial, bio-inspired devices. In this work, structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry were developed to predict the behavior of the seal with respect to host/remora surface topology and tissue material properties.

Sign in / Sign up

Export Citation Format

Share Document