Continental Flood Basalts Derived from the Hydrous Mantle Transition Zone
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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. -
STRUCTURE of EARTH S-Wave Shadow P-Wave Shadow P-Wave
STRUCTURE OF EARTH Earthquake Focus P-wave P-wave shadow shadow S-wave shadow P waves = Primary waves = Pressure waves S waves = Secondary waves = Shear waves (Don't penetrate liquids) CRUST < 50-70 km thick MANTLE = 2900 km thick OUTER CORE (Liquid) = 3200 km thick INNER CORE (Solid) = 1300 km radius. STRUCTURE OF EARTH Low Velocity Crust Zone Whole Mantle Convection Lithosphere Upper Mantle Transition Zone Layered Mantle Convection Lower Mantle S-wave P-wave CRUST : Conrad discontinuity = upper / lower crust boundary Mohorovicic discontinuity = base of Continental Crust (35-50 km continents; 6-8 km oceans) MANTLE: Lithosphere = Rigid Mantle < 100 km depth Asthenosphere = Plastic Mantle > 150 km depth Low Velocity Zone = Partially Melted, 100-150 km depth Upper Mantle < 410 km Transition Zone = 400-600 km --> Velocity increases rapidly Lower Mantle = 600 - 2900 km Outer Core (Liquid) 2900-5100 km Inner Core (Solid) 5100-6400 km Center = 6400 km UPPER MANTLE AND MAGMA GENERATION A. Composition of Earth Density of the Bulk Earth (Uncompressed) = 5.45 gm/cm3 Densities of Common Rocks: Granite = 2.55 gm/cm3 Peridotite, Eclogite = 3.2 to 3.4 gm/cm3 Basalt = 2.85 gm/cm3 Density of the CORE (estimated) = 7.2 gm/cm3 Fe-metal = 8.0 gm/cm3, Ni-metal = 8.5 gm/cm3 EARTH must contain a mix of Rock and Metal . Stony meteorites Remains of broken planets Planetary Interior Rock=Stony Meteorites ÒChondritesÓ = Olivine, Pyroxene, Metal (Fe-Ni) Metal = Fe-Ni Meteorites Core density = 7.2 gm/cm3 -- Too Light for Pure Fe-Ni Light elements = O2 (FeO) or S (FeS) B. -
Structure of the Earth
TheThe Earth’sEarth’s StructureStructure fromfrom TravelTravel TimesTimes SphericallySpherically symmetricsymmetric structure:structure: PREMPREM --CCrustalrustal StructuStructurree --UUpperpper MantleMantle structustructurree PhasePhase transitiotransitionnss AnisotropyAnisotropy --LLowerower MantleMantle StructureStructure D”D” --SStructuretructure ofof thethe OuterOuter andand InnerInner CoreCore 3-3-DD StStructureructure ofof thethe MantleMantle fromfrom SeismicSeismic TomoTomoggrraphyaphy --UUpperpper mantlemantle -M-Miidd mmaannttllee -L-Loowweerr MMaannttllee Seismology and the Earth’s Deep Interior The Earth’s Structure SphericallySpherically SymmetricSymmetric StructureStructure ParametersParameters wwhhichich cancan bebe determineddetermined forfor aa referencereferencemodelmodel -P-P--wwaavvee v veeloloccitityy -S-S--wwaavvee v veeloloccitityy -D-Deennssitityy -A-Atttteennuuaattioionn ( (QQ)) --AAnisonisotropictropic parame parametersters -Bulk modulus K -Bulk modulus Kss --rrigidityigidity µ µ −−prepresssuresure - -ggravityravity Seismology and the Earth’s Deep Interior The Earth’s Structure PREM:PREM: velocitiesvelocities andand densitydensity PREMPREM:: PPreliminaryreliminary RReferenceeference EEartharth MMooddelel (Dziewonski(Dziewonski andand Anderson,Anderson, 1981)1981) Seismology and the Earth’s Deep Interior The Earth’s Structure PREM:PREM: AttenuationAttenuation PREMPREM:: PPreliminaryreliminary RReferenceeference EEartharth MMooddelel (Dziewonski(Dziewonski andand Anderson,Anderson, 1981)1981) Seismology and the -
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. -
The Transition-Zone Water Filter Model for Global Material Circulation: Where Do We Stand?
The Transition-Zone Water Filter Model for Global Material Circulation: Where Do We Stand? Shun-ichiro Karato, David Bercovici, Garrett Leahy, Guillaume Richard and Zhicheng Jing Yale University, Department of Geology and Geophysics, New Haven, CT 06520 Materials circulation in Earth’s mantle will be modified if partial melting occurs in the transition zone. Melting in the transition zone is plausible if a significant amount of incompatible components is present in Earth’s mantle. We review the experimental data on melting and melt density and conclude that melting is likely under a broad range of conditions, although conditions for dense melt are more limited. Current geochemical models of Earth suggest the presence of relatively dense incompatible components such as K2O and we conclude that a dense melt is likely formed when the fraction of water is small. Models have been developed to understand the structure of a melt layer and the circulation of melt and vola- tiles. The model suggests a relatively thin melt-rich layer that can be entrained by downwelling current to maintain “steady-state” structure. If deep mantle melting occurs with a small melt fraction, highly incompatible elements including hydro- gen, helium and argon are sequestered without much effect on more compatible elements. This provides a natural explanation for many paradoxes including (i) the apparent discrepancy between whole mantle convection suggested from geophysical observations and the presence of long-lived large reservoirs suggested by geochemical observations, (ii) the helium/heat flow paradox and (iii) the argon paradox. Geophysical observations are reviewed including electrical conductivity and anomalies in seismic wave velocities to test the model and some future direc- tions to refine the model are discussed. -
Phase Transitions in Earth's Mantle and Mantle Mineralogy
Phase transitions in Earth’s Mantle and Mantle Mineralogy Upper Mantle Minerals: Olivine, Orthopyroxene, Clinopyroxene and Garnet ~13.5 GPa: Olivine Æ Wadsrlyite (DE) transition (ONSET TRANSITION ZONE) ~15.5 GPa: Pyroxene component gradually dissolve into garnet structure, resulting in the completion of pyroxene-majorite transformation >20 GPa: High CaO content in majorite is unfavorable at high pressure, leading to the formation of CaSiO3 perovskite ~24 GPa: Division of transition zone and lower mantle. Sharp transition silicate spinel to ferromagnesium silicate perovskite and magnesiowustite >24 GPa: Most of Al2O3 resides in majorite at transition zone pressures, a transformation from Majorite to Al-bearing orthorhombic perovskite completes at pressure higher than that of post-spinel transformation Lower Mantle Minerals: Orthorhobic perovskite, Magnesiowustite, CaSiO3 perovskite ~27 GPa: Transformation of Al and Si rich basalt to perovskite lithology with assemblage of Al-bearing perovskite, CaSiO3, stishovite and Al-phases Upper Mantle: olivine, garnet and pyroxene Transition zone: olivine (a-phase) transforms to wadsleyite (b-phase) then to spinel structure (g-phase) and finally to perovskite + magnesio-wüstite. Transformations occur at P and T conditions similar to 410, 520 and 660 km seismic discontinuities Xenoliths: (mantle fragments brought to surface in lavas) 60% Olivine + 40 % Pyroxene + some garnet Images removed due to copyright considerations. Garnet: A3B2(SiO4)3 Majorite FeSiO4, (Mg,Fe)2 SiO4 Germanates (Co-, Ni- and Fe- -
Label and Describe the Earth Diagram
Name_________________________class______ Label and Describe the Earth Diagram Read the definitions then use the information to color code, label and describe IN YOUR OWN WORDS each section of the diagram below. Definitions: crust – (green) the rigid, rocky outer surface of the Earth, composed mostly of basalt and granite. The crust is the thinnest of all layers. It is thicker on continents & thinner under the oceans. inner core – (gray) the solid iron-nickel center of the Earth that is very hot and under great pressure. mantle – (orange) a rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. Convection (heat) currents carry heat from the hot inner mantle to the cooler outer mantle. outer core – (red) the molten iron-nickel layer that surrounds the inner core. ______________________________________________ ______________________________________________ ______________________________________________ _______________________________________ _______________________________________ _______________________________________ ___________________________________ ___________________________________ ___________________________________ ___ __________________________________ __________________________________ __________________________________ __________________________ Name_________________________________cLass________ Label the OUTER LAYERS of the Earth This is a cross section of only the upper layers of the Earth’s surface. Read the definitions below and use the information to locate label and describe IN TWO WORDS the outer layers of the Earth. One has been done for you. continental crust – thick, top Continental Crust – (green) the thick parts of the Earth's crust, not located under the ocean; makes up the comtinents. Oceanic Crust – (brown) thinner more dense parts of the Earth's crust located under the oceans. Ocean – (blue) large bodies of water sitting atop oceanic crust. Lithosphere– (outline in black) made of BOTH the crust plus the rigid upper part of the upper mantle. -
Dehydration Melting Below the Undersaturated Transition Zone W Panero, C Thomas, R
Dehydration Melting Below the Undersaturated Transition Zone W Panero, C Thomas, R. Myhill, J Pigott, C. Raepsaet, H. Bureau To cite this version: W Panero, C Thomas, R. Myhill, J Pigott, C. Raepsaet, et al.. Dehydration Melting Below the Undersaturated Transition Zone. Geochemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2020, 10.1029/2019GC008712. hal-02870076 HAL Id: hal-02870076 https://hal.archives-ouvertes.fr/hal-02870076 Submitted on 16 Jun 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. RESEARCH ARTICLE Dehydration Melting Below the Undersaturated 10.1029/2019GC008712 Transition Zone Key Points: W. R. Panero1, C. Thomas2, R. Myhill3, J. S. Pigott4, C. Raepsaet5, and H. Bureau6 • Seismic reflections at ~750 km depth beneath Tibet are inconsistent with 1School of Earth Sciences, Ohio State University, Columbus, OH, USA, 2Institut für Geophysik, Westfälische Wilhelms‐ several previously proposed causes 3 4 for impedance contrast Universität Münster, Münster, Germany, School of Earth Sciences, University of Bristol, Bristol, -
Lithospheric Strength Profiles
21 LITHOSPHERIC STRENGTH PROFILES To study the mechanical response of the lithosphere to various types of forces, one has to take into account its rheology, which means knowing how it flows. As a scientific discipline, rheology describes the interactions between strain, stress and time. Strain and stress depend on the thermal structure, the fluid content, the thickness of compositional layers and various boundary conditions. The amount of time during which the load is applied is an important factor. - At the time scale of seismic waves, up to hundreds of seconds, the sub-crustal mantle behaves elastically down deep within the asthenosphere. - Over a few to thousands of years (e.g. load of ice cap), the mantle flows like a viscous fluid. - On long geological times (more than 1 million years), the upper crust and the upper mantle behave also as thin elastic and plastic plates that overlie an inviscid (i.e. with no viscosity) substratum. The dimensionless Deborah number D, summarized as natural response time/experimental observation time, is a measure of the influence of time on flow properties. Elasticity, plastic yielding, and viscous creep are therefore ingredients of the mechanical behavior of Earth materials. Each of these three modes will be considered in assessing flow processes in the lithosphere; these mechanical attributes are expressed in terms of lithospheric strength. This strength is estimated by integrating yield stress with depth. The current state of knowledge of rock rheology is sufficient to provide broad general outlines of mechanical behavior but also has important limitations. Two very thorny problems involve the scaling of rock properties with long periods and for very large length scales. -
The Lower Mantle and Core
Theory of the Earth Don L. Anderson Chapter 4. The Lower Mantle and Core Boston: Blackwell Scientific Publications, c1989 Copyright transferred to the author September 2, 1998. You are granted permission for individual, educational, research and noncommercial reproduction, distribution, display and performance of this work in any format. Recommended citation: Anderson, Don L. Theory of the Earth. Boston: Blackwell Scientific Publications, 1989. http://resolver.caltech.edu/CaltechBOOK:1989.001 A scanned image of the entire book may be found at the following persistent URL: http://resolver.caltech.edu/CaltechBook:1989.001 Abstract: The lower mantle starts just below the major mantle discontinuity near 650 km. The depth of this discontinuity varies, perhaps by as much as 100 km and is variously referred to as the "650-km discontinuity" or "670-km discontinuity." In recent Earth models there is a region of high velocity gradient for another 50 to 100 km below the discontinuity. This is probably due to phase changes, but it could represent a chemical gradient. The "lower mantle proper" therefore does not start until a depth of about 750 or 800 km. Below this depth the lower mantle is relatively homogeneous until about 300 km above the core-mantle boundary. If there is a chemical difference between the upper and lower mantle then, in a convecting dynamic mantle, the boundary will not be at a fixed depth. This clarification is needed because of the controversy about whether slabs penetrate into the lower mantle or whether they just push down the discontinuity. core. The Lower Mantle and Core I must be getting somewhere near the centre of the earth.