Implications of Slab Mineralogy for Subduction Dynamics Craig R
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Density Difference Between Subducted Oceanic Crust and Ambient Mantle in the Mantle Transition Zone Density Difference Between S
Density Difference between Subducted Oceanic Crust and Ambient Mantle in the Mantle Transition Zone Since the beginning of plate tectonics, the were packed separately into NaCl or MgO sample oceanic lithosphere has been continually subducted chamber with a mixture of gold and MgO, and into the Earth’s deep mantle for 4.5 Gy. The compressed in the same high-pressure cell. The oceanic lithosphere consists of an upper basaltic pressure was determined by the cell volume for layer (oceanic crust) and a lower olivine-rich gold using an equation of state of gold [2], and the peridotitic layer. The total amount of subducted temperature was measured by a thermocouple. oceanic crust in this 4.5 Gy period is estimated to The cell volumes of garnet and ringwoodite were be at least ~3 × 1 0 23 kg, which is about 8% of the determined by least squares calculations using the weight of the present Earth’s mantle. Thus, the positions of X-ray diffraction peaks. The samples oceanic crust, which is rich in pyroxene and garnet, were compressed to the desired pressure at room may be the source of very important chemical temperature and heated to the maximum temperature heterogeneity in the olivine-rich Earth’s mantle. To to release non-hydrostatic stress. clarify behavior of the oceanic crust in the deep Pressure-volume-temperature data were collected mantle, accurate information about density under 47 different conditions. Figure 1 shows P -V - differences between the oceanic crust and the T data for garnet. The data collected by using an ambient mantle is very important. -
Mantle Transition Zone Structure Beneath Northeast Asia from 2-D
RESEARCH ARTICLE Mantle Transition Zone Structure Beneath Northeast 10.1029/2018JB016642 Asia From 2‐D Triplicated Waveform Modeling: Key Points: • The 2‐D triplicated waveform Implication for a Segmented Stagnant Slab fi ‐ modeling reveals ne scale velocity Yujing Lai1,2 , Ling Chen1,2,3 , Tao Wang4 , and Zhongwen Zhan5 structure of the Pacific stagnant slab • High V /V ratios imply a hydrous p s 1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, and/or carbonated MTZ beneath 2 3 Northeast Asia Beijing, China, College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, China, CAS Center for • A low‐velocity gap is detected within Excellence in Tibetan Plateau Earth Sciences, Beijing, China, 4Institute of Geophysics and Geodynamics, School of Earth the stagnant slab, probably Sciences and Engineering, Nanjing University, Nanjing, China, 5Seismological Laboratory, California Institute of suggesting a deep origin of the Technology, Pasadena, California, USA Changbaishan intraplate volcanism Supporting Information: Abstract The structure of the mantle transition zone (MTZ) in subduction zones is essential for • Supporting Information S1 understanding subduction dynamics in the deep mantle and its surface responses. We constructed the P (Vp) and SH velocity (Vs) structure images of the MTZ beneath Northeast Asia based on two‐dimensional ‐ Correspondence to: (2 D) triplicated waveform modeling. In the upper MTZ, a normal Vp but 2.5% low Vs layer compared with L. Chen and T. Wang, IASP91 are required by the triplication data. In the lower MTZ, our results show a relatively higher‐velocity [email protected]; layer (+2% V and −0.5% V compared to IASP91) with a thickness of ~140 km and length of ~1,200 km [email protected] p s atop the 660‐km discontinuity. -
Slab Pull? Density of Plate Slab
The plate tectonic story www.earthscienceeducation.com Geography Workshop GA Conference 2021 Duncan Hawley in association with the Earth Science Education Unit and EarthLearningIdea www.earthlearningidea.com Image: Free download https://www.kissclipart.com/visual-tectonic-plates-clipart-crust-earth-plate-t-nnw9dx/ The plate tectonic story www.earthscienceeducation.com Aims of this session The workshop and its activities aims to: • provide an integrated overview of the concepts involved in teaching the processes of plate tectonics at KS3, KS4 and A level • survey of some of the recent evidence and key ideas in understanding how plate tectonics works • offer improved explanations for the distribution and characteristics of volcanoes, earthquakes, and some surface landforms • suggest approaches to teaching the abstract concepts of plate tectonics • help teachers decide if and how they should adjust what they presently teach to reflect the current understanding about the way plate tectonics operates • help teachers develop students’ critical sense of ‘the plate tectonic story’ encountered in textbooks, on diagrams, on the news, via the internet and in other media. The plate tectonic story www.earthscienceeducation.com Where on Earth are earthquakes and volcanoes? - geobattleships www.earthlearningidea.com/PDF/79_Geobattleships.pdf Battleship grid for Geobattleships © Dave Turner Galunggung eruption by USGS, public domain ‘North All Trucks’ © USGS The plate tectonic story www.earthscienceeducation.com Where on Earth are earthquakes and volcanoes? -
Appendix 2. the Mystery of Guyot Formation and Sinking
Appendix 2 The Mystery of Guyot Formation and Sinking Origin of Guyots Unknown In 1946, geologist Harry Hess was the first geologist to describe guyots (flat-topped seamount).1 Since then, the number of guyots has become numerous. Resolution Guyot in the Mid-Pacific Mountains that was studied in the 1990s by the Deep Sea Drilling Project2 is a typical guyot. Figure A2.1 shows the silhouette. Ever since Hess’s time, the cause of the flat top has eluded explanation.3 Winterer and Met- Figure A2.1. Silhouette of Resolution Guyot zler maintain: “Since Hess first recognized them in the Mid-Pacific Mountains (drawn by Mrs. Melanie Richard). in 1946, the origin of flat-topped seamounts, or guyots, has remained one of the most persistent problems in marine geology.”4 Since guyots are believed to have been truncated near sea level, there are two suggested subsid- ence mechanisms used to explain why they are now found well below sea level. But some guyots must have become flat well below sea level. Not All Guyots Eroded At Sea Level Many scientists have simply assumed that the flat top of a guyot was eroded at or near sea level.5,6 ‘This has been challenged by a few marine geologists.’7,8 For instance, a number of guyots near the East Pacific Rise have been attributed to the infilling of calderas by small lava flows well below sea level.9,10,11,12 “But, these guyots are small 1 Hess, H.H., 1946. Drowned ancient islands of the Pacific Basin. American Journal of Science 244:772–791. -
Slab-Pull and Slab-Push Earthquakes in the Mexican, Chilean and Peruvian Subduction Zones A
Physics of the Earth and Planetary Interiors 132 (2002) 157–175 Slab-pull and slab-push earthquakes in the Mexican, Chilean and Peruvian subduction zones A. Lemoine a,∗, R. Madariaga a, J. Campos b a Laboratoire de Géologie, Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France b Departamento de Geof´ısica, Universidad de Chile, Santiago, Chile Abstract We studied intermediate depth earthquakes in the Chile, Peru and Mexican subduction zones, paying special attention to slab-push (down-dip compression) and slab-pull (down-dip extension) mechanisms. Although, slab-push events are relatively rare in comparison with slab-pull earthquakes, quite a few have occurred recently. In Peru, a couple slab-push events occurred in 1991 and one slab-pull together with several slab-push events occurred in 1970 near Chimbote. In Mexico, several slab-push and slab-pull events occurred near Zihuatanejo below the fault zone of the 1985 Michoacan event. In central Chile, a large M = 7.1 slab-push event occurred in October 1997 that followed a series of four shallow Mw > 6 thrust earthquakes on the plate interface. We used teleseismic body waveform inversion of a number of Mw > 5.9 slab-push and slab-pull earthquakes in order to obtain accurate mechanisms, depths and source time functions. We used a master event method in order to get relative locations. We discussed the occurrence of the relatively rare slab-push events in the three subduction zones. Were they due to the geometry of the subduction that produces flexure inside the downgoing slab, or were they produced by stress transfer during the earthquake cycle? Stress transfer can not explain the occurence of several compressional and extensional intraplate intermediate depth earthquakes in central Chile, central Mexico and central Peru. -
Continental Flood Basalts Derived from the Hydrous Mantle Transition Zone
ARTICLE Received 4 Sep 2014 | Accepted 1 Jun 2015 | Published 14 Jul 2015 DOI: 10.1038/ncomms8700 Continental flood basalts derived from the hydrous mantle transition zone Xuan-Ce Wang1, Simon A. Wilde1, Qiu-Li Li2 & Ya-Nan Yang2 It has previously been postulated that the Earth’s hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts. 1 ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. 2 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O.Box9825, Beijing 100029, China. Correspondence and requests for materials should be addressed to X.-C.W. -
Influence of Sediment Transport on Short-Term Recolonization by Seamount Infauna
MARINE ECO'R'OGY PROGRESS SERIES Vol. 123: 163-175,1995 Mu Published July 20 Ecol Prog Ser / Influence of sediment transport on short-term recolonization by seamount infauna Lisa A. Levin, Claudio DiBacco Marine Life Research Group, Scripps Instituliar of Oceanography, La Jolla, California 92093-0218, USA ABSTRACT: Rates and mechanisms of mEa'nnal recolonization in contrasting sediment transport regimes were examined by deploying hydrodynamically unbiased colonization trays at 2 sites -2 km apart on the flat summit plain of Fieberhg Cplyot in the eastern Pacific Ocean. Both study sites expe- rienced strong bottom currents and high shear velocity (U. exceeding 1.0 cm S-' daily). Macrofaunal recolonization of defaunated sediments on Werling Guyot was slow relative to observations in shal- low-water sediments, but rapid compared l&other unennched deep-sea treatments. Microbial colo- nization was slower but macrofaunal colon~isnwas faster at White Sand Swale (WSS, 585 m),where rippled foraminiferal sands migrate daily, than at Sea Pen Rim (SPR, 635 m), where the basaltic sands move infrequently. Total densities of macroiannal colonizers at WSS were 31 and 75% of ambient after 7 wk and 6.4 mo, respectively; at SPR they were 6 and 49% of ambient, respectively. Over % of the colonists were polychaetes (predominantly ksionids and dorvilleids) and aplacophoran molluscs. Species richness of colonizers was comparab.lle at SPR and WSS and did not differ substantially from ambient. Most of the species (91%) and indmduals (95%) recovered in colonization trays were taxa present in background cores. However, only 25% of the taxa colonizing tray sediments occurred in trays at both WSS and SPR. -
ASSESSMENT of the TSUNAMIGENIC POTENTIAL ALONG the NORTHERN CARIBBEAN MARGIN Case Study: Earthquake and Tsunamis of 12 January 2010 in Haiti
ISSN 87556839 SCIENCE OF TSUNAMI HAZARDS Journal of Tsunami Society International Volume 29 Number 3 2010 ASSESSMENT OF THE TSUNAMIGENIC POTENTIAL ALONG THE NORTHERN CARIBBEAN MARGIN Case Study: Earthquake and Tsunamis of 12 January 2010 in Haiti. George Pararas-Carayannis Tsunami Society International, Honolulu, Hawaii 96815, USA [email protected] ABSTRACT The potential tsunami risk for Hispaniola, as well as for the other Greater Antilles Islands is assessed by reviewing the complex geotectonic processes and regimes along the Northern Caribbean margin, including the convergent, compressional and collisional tectonic activity of subduction, transition, shearing, lateral movements, accretion and crustal deformation caused by the eastward movement of the Caribbean plate in relation to the North American plate. These complex tectonic interactions have created a broad, diffuse tectonic boundary that has resulted in an extensive, internal deformational sliver slab - the Gonâve microplate – as well as further segmentation into two other microplates with similarly diffused boundary characteristics where tsunamigenic earthquakes have and will again occur. The Gonâve microplate is the most prominent along the Northern Caribbean margin and extends from the Cayman Spreading Center to Mona Pass, between Puerto Rico and the island of Hispaniola, where the 1918 destructive tsunami was generated. The northern boundary of this sliver microplate is defined by the Oriente strike-slip fault south of Cuba, which appears to be an extension of the fault system traversing the northern part of Hispaniola, while the southern boundary is defined by another major strike-slip fault zone where the Haiti earthquake of 12 January 2010 occurred. Potentially tsunamigenic regions along the Northern Caribbean margin are located not only along the boundaries of the Gonâve microplate’s dominant western transform zone but particularly within the eastern tectonic regimes of the margin where subduction is dominant - particularly along the Puerto Rico trench. -
The Eyes Have It
news and views flow of heat and matter in the interior2. This Irifune and Isshiki1 have shown such transition to higher pressures (as can be seen flow, in turn, drives the tectonic evolution artificial separation to be misleading by in Irifune and Isshiki’s Fig. 3 on page 704), so of the surface, including the occurrence of experimentally demonstrating Mg–Fe ex- the onset of the transition in pyrolite is post- volcanism and seismicity. change between a, b, garnet and clino- poned to greater depths relative to that in Olivine, a solid solution of forsterite pyroxene. We have known5 for some time Fo89. On the other side of the phase change, b (Mg2SiO4) and fayalite (Fe2SiO4), has the that the proportions of these minerals vary does not partition Fe into garnet as strong- a b approximate composition (Mg0.89 Fe0.11)2SiO4 with depth, as shown by the bold white lines ly as does , so is not initially Mg-enriched, (called forsterite-89 or Fo89) in samples from in Fig. 1, but Irifune and Isshiki have now and the completion of the a–b transition the shallow mantle. It transforms from the measured the accompanying variations in is not postponed relative to Fo89. The net olivine (a) phase to wadsleyite (b), changing the compositions of coexisting minerals, effect of postponing onset but not co8m- again to ringwoodite (g) at greater depths shown by the colours. In isolated Fo89 pletion is to concentrate the transition into and eventually breaking down to a mixture of olivine, mineral compositions must remain a narrower range of depths, decreasing the silicate perovskite and magnesiowüstite. -
The Upper Mantle and Transition Zone
The Upper Mantle and Transition Zone Daniel J. Frost* DOI: 10.2113/GSELEMENTS.4.3.171 he upper mantle is the source of almost all magmas. It contains major body wave velocity structure, such as PREM (preliminary reference transitions in rheological and thermal behaviour that control the character Earth model) (e.g. Dziewonski and Tof plate tectonics and the style of mantle dynamics. Essential parameters Anderson 1981). in any model to describe these phenomena are the mantle’s compositional The transition zone, between 410 and thermal structure. Most samples of the mantle come from the lithosphere. and 660 km, is an excellent region Although the composition of the underlying asthenospheric mantle can be to perform such a comparison estimated, this is made difficult by the fact that this part of the mantle partially because it is free of the complex thermal and chemical structure melts and differentiates before samples ever reach the surface. The composition imparted on the shallow mantle by and conditions in the mantle at depths significantly below the lithosphere must the lithosphere and melting be interpreted from geophysical observations combined with experimental processes. It contains a number of seismic discontinuities—sharp jumps data on mineral and rock properties. Fortunately, the transition zone, which in seismic velocity, that are gener- extends from approximately 410 to 660 km, has a number of characteristic ally accepted to arise from mineral globally observed seismic properties that should ultimately place essential phase transformations (Agee 1998). These discontinuities have certain constraints on the compositional and thermal state of the mantle. features that correlate directly with characteristics of the mineral trans- KEYWORDS: seismic discontinuity, phase transformation, pyrolite, wadsleyite, ringwoodite formations, such as the proportions of the transforming minerals and the temperature at the discontinu- INTRODUCTION ity. -
Subduction-Transition Zone Interaction: a Review
Research Paper THEMED ISSUE: Subduction Top to Bottom 2 GEOSPHERE Subduction-transition zone interaction: A review Saskia Goes1, Roberto Agrusta1,2, Jeroen van Hunen2, and Fanny Garel3 1Department of Earth Science & Engineering, Royal School of Mines, Imperial College, London SW7 2AZ, UK GEOSPHERE; v. 13, no. 3 2Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK 3Géosciences Montpellier, Université de Montpellier, Centre national de la recherche scientifique (CNRS), 34095 Montpellier cedex 05, France doi:10.1130/GES01476.1 9 figures ABSTRACT do not; (2) on what time scales slabs are stagnant in the transition zone if they have flattened; (3) how slab-transition zone interaction is reflected in plate mo- CORRESPONDENCE: s .goes@ imperial .ac .uk As subducting plates reach the base of the upper mantle, some appear tions; and (4) how lower-mantle fast seismic anomalies can be correlated with to flatten and stagnate, while others seemingly go through unimpeded. This past subduction. CITATION: Goes, S., Agrusta, R., van Hunen, J., variable resistance to slab sinking has been proposed to affect long-term ther- Over the past 20 years since the last Subduction Top to Bottom volume and and Garel, F., 2017, Subduction-transition zone inter- action: A review: Geosphere, v. 13, no. 3, p. 1– mal and chemical mantle circulation. A review of observational constraints several reviews of subduction through the transition zone (Lay, 1994; Chris- 21, doi:10.1130/GES01476.1. and dynamic models highlights that neither the increase in viscosity between tensen, 2001; King, 2001; Billen, 2008; Fukao et al., 2009), information about upper and lower mantle (likely by a factor 20–50) nor the coincident endo- the nature of the transition zone and our understanding of how slabs dynami- Received 6 December 2016 thermic phase transition in the main mantle silicates (with a likely Clapeyron cally interact with it has increased substantially. -
On the Dynamics of the Juan De Fuca Plate
Earth and Planetary Science Letters 189 (2001) 115^131 www.elsevier.com/locate/epsl On the dynamics of the Juan de Fuca plate Rob Govers *, Paul Th. Meijer Faculty of Earth Sciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands Received 11 October 2000; received in revised form 17 April 2001; accepted 27 April 2001 Abstract The Juan de Fuca plate is currently fragmenting along the Nootka fault zone in the north, while the Gorda region in the south shows no evidence of fragmentation. This difference is surprising, as both the northern and southern regions are young relative to the central Juan de Fuca plate. We develop stress models for the Juan de Fuca plate to understand this pattern of breakup. Another objective of our study follows from our hypothesis that small plates are partially driven by larger neighbor plates. The transform push force has been proposed to be such a dynamic interaction between the small Juan de Fuca plate and the Pacific plate. We aim to establish the relative importance of transform push for Juan de Fuca dynamics. Balancing torques from plate tectonic forces like slab pull, ridge push and various resistive forces, we first derive two groups of force models: models which require transform push across the Mendocino Transform fault and models which do not. Intraplate stress orientations computed on the basis of the force models are all close to identical. Orientations of predicted stresses are in agreement with observations. Stress magnitudes are sensitive to the force model we use, but as we have no stress magnitude observations we have no means of discriminating between force models.