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Vieira Duarte JF, Pettke T, Hermann J, Piccoli F. Oxide-silicate petrology and geochemistry of subducted hydrous ultramafic rocks beyond antigorite dehydration (Central Alps, Switzerland). CONTRIBUTIONS TO MINERALOGY AND PETROLOGY. BEITRAGE ZUR MINERALOGIE UND PETROLOGIE 2023; 178:60. [PMID: 38617192 PMCID: PMC11008075 DOI: 10.1007/s00410-023-02032-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 07/05/2023] [Indexed: 04/16/2024]
Abstract
Oxide minerals contained in ultramafic rocks are useful tools to assess the redox conditions of the rock and fluids liberated upon progressive serpentinite dehydration during subduction, as these minerals contain a relevant redox-sensitive element, iron. Previous studies have revealed that magnetite predominates across the antigorite-out reaction. However, the fate of magnetite and other oxides at higher pressure and temperature conditions has remained underexplored. We present a comprehensive petrological and geochemical study of oxide-sulfide-silicate mineral assemblages in metaperidotites beyond antigorite- and chlorite-out reactions (T = 650-850 °C and P = 1-3 GPa). Several ultramafic lenses, covering different bulk rock compositions and extents of oxidation upon oceanic serpentinization, were investigated from the Central Alps, Switzerland. Results point to two endmember scenarios: (i) Most frequently, metaperidotites have olivine with a Mg# of 89-91 (defined as molar Mg/(Mg + Fetot) × 100) and contain low oxide modes (0.06-1.41 vol.%), hematite is absent, and redox conditions are weakly oxidized and buffered by orthopyroxene-olivine-magnetite. (ii) Rare occurrence, high olivine Mg# > 94.5 metaperidotites display coexisting hematite and magnetite, high oxide modes (up to 4 vol.%), and redox conditions are hematite-magnetite (HM) buffered (Δlog10fO2,QFM of + 3 to + 4). Spinel displays evolving compositions from magnetite over chromite to Al-Cr-spinel, roughly correlating with increasing temperature. Most of the samples buffered by the olivine-orthopyroxene-magnetite assemblage contain coexisting pentlandite ± pyrrhotite, thus identifying stable sulfides beyond antigorite dehydration for these weakly oxidized samples (Δlog10fO2,QFM < 2.5). No sulfides were recognized in the highly oxidized sample. The transition of magnetite to chromite at around 700 °C goes along with a shift in fO2 to lower values. At the prevailing oxygen fugacity in the weakly oxidized metaperidotites sulfur in a coexisting fluid is always present in its reduced form. However, oxidized sulfur can be stable in the dehydration fluids released from highly oxidized serpentinites. Supplementary Information The online version contains supplementary material available at 10.1007/s00410-023-02032-w.
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Affiliation(s)
| | - Thomas Pettke
- Institute of Geological Sciences, Baltzerstrasse 1+3, 3012 Bern, Switzerland
| | - Jörg Hermann
- Institute of Geological Sciences, Baltzerstrasse 1+3, 3012 Bern, Switzerland
| | - Francesca Piccoli
- Institute of Geological Sciences, Baltzerstrasse 1+3, 3012 Bern, Switzerland
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Tulley CJ, Fagereng Å, Ujiie K, Piazolo S, Tarling MS, Mori Y. Rheology of Naturally Deformed Antigorite Serpentinite: Strain and Strain-Rate Dependence at Mantle-Wedge Conditions. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2022GL098945. [PMID: 36249466 PMCID: PMC9539589 DOI: 10.1029/2022gl098945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 08/02/2022] [Accepted: 08/17/2022] [Indexed: 06/16/2023]
Abstract
Antigorite serpentinite is expected to occur in parts of subduction plate boundaries, and may suppress earthquake slip, but the dominant deformation mechanisms and resultant rheology of antigorite are unclear. An exhumed plate boundary shear zone exposed near Nagasaki, Japan, contains antigorite deformed at 474°C ± 30°C. Observations indicate that a foliation defined by (001) crystal facets developed during plate-boundary shear. Microstructures indicating grain-scale dissolution at high-stress interfaces and precipitation in low-stress regions suggest that dissolution-precipitation creep contributed to foliation development. Analysis of crystal orientations indicate a small contribution from dislocation activity. We suggest a frictional-viscous rheology for antigorite, where dissolution-precipitation produces a foliation defined by (001) crystal facets and acts to resolve strain incompatibilities, allowing for efficient face-to-face sliding between facets. This rheology can not only explain aseismic behavior at ambient plate boundary conditions, but also some of the contrasting behaviors shown by previous field and laboratory studies.
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Affiliation(s)
- C. J. Tulley
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - Å. Fagereng
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - K. Ujiie
- Faculty of Life and Environmental SciencesUniversity of TsukubaTsukubaJapan
| | - S. Piazolo
- School of Earth and EnvironmentUniversity of LeedsLeedsUK
| | - M. S. Tarling
- Department of GeologyUniversity of OtagoDunedinNew Zealand
- Now at Department of Earth and Planetary SciencesMcGill UniversityMontrealQCCanada
| | - Y. Mori
- Kitakyushu Museum of Natural History and Human HistoryKitakyushuJapan
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Sources of dehydration fluids underneath the Kamchatka arc. Nat Commun 2022; 13:4467. [PMID: 35918359 PMCID: PMC9345910 DOI: 10.1038/s41467-022-32211-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2021] [Accepted: 07/21/2022] [Indexed: 12/04/2022] Open
Abstract
Fluids mediate the transport of subducted slab material and play a crucial role in the generation of arc magmas. However, the source of subduction-derived fluids remains debated. The Kamchatka arc is an ideal subduction zone to identify the source of fluids because the arc magmas are comparably mafic, their source appears to be essentially free of subducted sediment-derived components, and subducted Hawaii-Emperor Seamount Chain (HESC) is thought to contribute a substantial fluid flux to the Kamchatka magmas. Here we show that Tl isotope ratios are unique tracers of HESC contribution to Kamchatka arc magma sources. In conjunction with trace element ratios and literature data, we trace the progressive dehydration and melting of subducted HESC across the Kamchatka arc. In succession, serpentine (<100 km depth), lawsonite (100–250 km depth) and phengite (>250 km depth) break down and produce fluids that contribute to arc magmatism at the Eastern Volcanic Front (EVF), Central Kamchatka Depression (CKD), and Sredinny Ridge (SR), respectively. However, given the Tl-poor nature of serpentine and lawsonite fluids, simultaneous melting of subducted HESC is required to explain the HESC-like Tl isotope signatures observed in EVF and CKD lavas. In the absence of eclogitic crust melting processes in this region of the Kamchatka arc, we propose that progressive dehydration and melting of a HESC-dominated mélange offers the most compelling interpretation of the combined isotope and trace element data. Fluids released from progressive breakdown of minerals at increasing pressure within a mélange may explain the trace element systematics and stable thallium isotope data of the Kamchatka arc lavas from volcanic front to back arc.
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In Situ Study on Dehydration and Phase Transformation of Antigorite. MINERALS 2022. [DOI: 10.3390/min12050567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Antigorite is the main carrier of water in Earth’s subduction zones. The dehydration processes of antigorite were investigated by carrying out in situ phase transition experiments using a dynamic diamond anvil cell, with a time-resolved Raman scattering system, at 0.3–10 GPa and 396–1100 K. Three typical phase transformation reactions occurred within the P–T range of this study, corresponding to three reaction products. At low pressures (<0.7 GPa), antigorite transfers to talc and forsterite; as the temperature increases, the talc disappears and a combination of forsterite and clinoenstatite occurs. At moderate pressures (1.8–7.5 GPa), antigorite dehydrates into forsterite and clinoenstatite as temperatures increase; with the continuous increase in pressure, the dehydration products become clinoenstatite and phase A. At high pressures (>8.6 GPa), the products of the dehydration phase transition of antigorite are consistently clinoenstatite and phase A. Compared with the previous studies carried out by large-volume presses (such as a multi anvil press and a piston-cylinder press), the reaction to produce phase A occurs at higher P–T conditions, and the stable temperature region for talc as a dehydration product is narrower. Moreover, large quantities of pores with 5–10 μm in diameter formed in dehydration products, supporting the hypothesis that intermediate-depth earthquakes may result from dehydration embrittlement. The precise phase boundary determined by this in situ study provides a better understanding of the dehydration phase transition behavior and geological phenomena exhibited by antigorite under different pressure and temperature conditions.
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Zhang Y, Gazel E, Gaetani GA, Klein F. Serpentinite-derived slab fluids control the oxidation state of the subarc mantle. SCIENCE ADVANCES 2021; 7:eabj2515. [PMID: 34826248 PMCID: PMC8626075 DOI: 10.1126/sciadv.abj2515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 10/07/2021] [Indexed: 06/13/2023]
Abstract
Recent geochemical evidence confirms the oxidized nature of arc magmas, but the underlying processes that regulate the redox state of the subarc mantle remain yet to be determined. We established a link between deep subduction-related fluids derived from dehydration of serpentinite ± altered oceanic crust (AOC) using B isotopes and B/Nb as fluid proxies, and the oxidized nature of arc magmas as indicated by Cu enrichment during magma evolution and V/Yb. Our results suggest that arc magmas derived from source regions influenced by a greater serpentinite (±AOC) fluid component record higher oxygen fugacity. The incorporation of this component into the subarc mantle is controlled by the subduction system’s thermodynamic conditions and geometry. Our results suggest that the redox state of the subarc mantle is not homogeneous globally: Primitive arc magmas associated with flat, warm subduction are less oxidized overall than those generated in steep, cold subduction zones.
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Affiliation(s)
- Yuxiang Zhang
- Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong, China
- Laboratory for Marine Mineral Resources, Qingdao Pilot National Laboratory for Marine Science and Technology, Qingdao, Shandong, China
- Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, Shandong, China
| | - Esteban Gazel
- Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA
| | - Glenn A. Gaetani
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
| | - Frieder Klein
- Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
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Li HY, Zhao RP, Li J, Tamura Y, Spencer C, Stern RJ, Ryan JG, Xu YG. Molybdenum isotopes unmask slab dehydration and melting beneath the Mariana arc. Nat Commun 2021; 12:6015. [PMID: 34650082 PMCID: PMC8517010 DOI: 10.1038/s41467-021-26322-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 09/23/2021] [Indexed: 11/09/2022] Open
Abstract
How serpentinites in the forearc mantle and subducted lithosphere become involved in enriching the subarc mantle source of arc magmas is controversial. Here we report molybdenum isotopes for primitive submarine lavas and serpentinites from active volcanoes and serpentinite mud volcanoes in the Mariana arc. These data, in combination with radiogenic isotopes and elemental ratios, allow development of a model whereby shallow, partially serpentinized and subducted forearc mantle transfers fluid and melt from the subducted slab into the subarc mantle. These entrained forearc mantle fragments are further metasomatized by slab fluids/melts derived from the dehydration of serpentinites in the subducted lithospheric slab. Multistage breakdown of serpentinites in the subduction channel ultimately releases fluids/melts that trigger Mariana volcanic front volcanism. Serpentinites dragged down from the forearc mantle are likely exhausted at >200 km depth, after which slab-derived serpentinites are responsible for generating slab melts. How the subducted oceanic lithosphere provides fluids and melts to flux the subarc mantle source of arc magmas is controversial. Here the authors use Mo and other isotopes to show serpentinites formed in both the forearc mantle and the subducted lithosphere contribute to generating arc magmas.
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Affiliation(s)
- Hong-Yan Li
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China. .,CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China. .,Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China.
| | - Rui-Peng Zhao
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jie Li
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China.,CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
| | - Yoshihiko Tamura
- Research Institute for Marine Geodynamics (IMG), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, 237-0061, Japan
| | - Christopher Spencer
- Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON, K7L 3N6, Canada
| | - Robert J Stern
- Department of Geoscience, University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Jeffrey G Ryan
- School of Geosciences, University of South Florida, Tampa, FL, 33620, USA
| | - Yi-Gang Xu
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China.,CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China.,Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China
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Farsang S, Louvel M, Zhao C, Mezouar M, Rosa AD, Widmer RN, Feng X, Liu J, Redfern SAT. Deep carbon cycle constrained by carbonate solubility. Nat Commun 2021; 12:4311. [PMID: 34262043 PMCID: PMC8280166 DOI: 10.1038/s41467-021-24533-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 06/16/2021] [Indexed: 02/06/2023] Open
Abstract
Earth's deep carbon cycle affects atmospheric CO2, climate, and habitability. Owing to the extreme solubility of CaCO3, aqueous fluids released from the subducting slab could extract all carbon from the slab. However, recycling efficiency is estimated at only around 40%. Data from carbonate inclusions, petrology, and Mg isotope systematics indicate Ca2+ in carbonates is replaced by Mg2+ and other cations during subduction. Here we determined the solubility of dolomite [CaMg(CO3)2] and rhodochrosite (MnCO3), and put an upper limit on that of magnesite (MgCO3) under subduction zone conditions. Solubility decreases at least two orders of magnitude as carbonates become Mg-rich. This decreased solubility, coupled with heterogeneity of carbon and water subduction, may explain discrepancies in carbon recycling estimates. Over a range of slab settings, we find aqueous dissolution responsible for mobilizing 10 to 92% of slab carbon. Globally, aqueous fluids mobilise [Formula: see text]% ([Formula: see text] Mt/yr) of subducted carbon from subducting slabs.
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Affiliation(s)
- Stefan Farsang
- grid.5335.00000000121885934Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ UK
| | - Marion Louvel
- grid.5949.10000 0001 2172 9288Institut für Mineralogie, WWU Münster, Münster, 48149 Germany
| | - Chaoshuai Zhao
- grid.503238.f0000 0004 7423 8214Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing, 100094 China
| | - Mohamed Mezouar
- grid.5398.70000 0004 0641 6373European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble, 38000 France
| | - Angelika D. Rosa
- grid.5398.70000 0004 0641 6373European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble, 38000 France
| | - Remo N. Widmer
- grid.7354.50000 0001 2331 3059Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkerstrasse 39, Thun, 3602 Switzerland
| | - Xiaolei Feng
- grid.5335.00000000121885934Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ UK ,grid.503238.f0000 0004 7423 8214Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing, 100094 China
| | - Jin Liu
- grid.503238.f0000 0004 7423 8214Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing, 100094 China
| | - Simon A. T. Redfern
- grid.59025.3b0000 0001 2224 0361Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 Singapore
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Piccoli F, Ague JJ, Chu X, Tian M, Vitale Brovarone A. Field-Based Evidence for Intra-Slab High-Permeability Channel Formation at Eclogite-Facies Conditions During Subduction. GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS : G(3) 2021; 22:e2020GC009520. [PMID: 33867865 PMCID: PMC8047908 DOI: 10.1029/2020gc009520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/01/2021] [Accepted: 02/03/2021] [Indexed: 06/12/2023]
Abstract
Fluid release from subducting oceanic lithosphere is a key process for subduction zone geodynamics, from controlling arc volcanism to seismicity and tectonic exhumation. However, many fundamental details of fluid composition, flow pathways, and reactivity with slab-forming rocks remain to be thoroughly understood. In this study we investigate a multi-kilometer-long, high-pressure metasomatic system preserved in the lawsonite-eclogite metamorphic unit of Alpine Corsica, France. The fluid-mediated process was localized along a major intra-slab interface, which is the contact between basement and cover unit. Two distinct metasomatic stages are identified and discussed. We show that these two stages resulted from the infiltration of deep fluids that were derived from the same source and had the same slab-parallel, updip flow direction. By mass balance analysis, we quantify metasomatic mass changes along this fluid pathway and the time-integrated fluid fluxes responsible for them. In addition, we also assess carbon fluxes associated with these metasomatic events. The magnitude of the estimated fluid fluxes (104-105) indicates that major intra-slab interfaces such as lithological boundaries acted as fluid channels facilitating episodic pulses of fluid flow. We also show that when fluids are channelized, high time-integrated fluid fluxes lead to carbon fluxes several orders of magnitude higher than carbon fluxes generated by local dehydration reactions. Given the size and geologic features of the investigated metasomatic system, we propose that it represents the first reported natural analogue of the so-called high permeability channels predicted by numerical simulations.
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Affiliation(s)
- Francesca Piccoli
- Insitut de Minéralogie Physique des Matériaux et Cosmochimie (IMPMC) UMR7590 CNRS-UPMC-MNHN-IRD Paris France
- Institute of Geological Sciences University of Bern Baltzerstrasse Bern Switzerland Switzerland
| | - Jay J Ague
- Department of Geology and Geophysics Yale University New Haven CT USA
- Peabody Museum of Natural History Yale University New Haven CT USA
| | - Xu Chu
- Department of Earth Sciences University of Toronto Toronto Canada
| | - Meng Tian
- Center for Space and Habitability University of Bern Bern Switzerland
| | - Alberto Vitale Brovarone
- Insitut de Minéralogie Physique des Matériaux et Cosmochimie (IMPMC) UMR7590 CNRS-UPMC-MNHN-IRD Paris France
- Dipartimento di Scienze Biologiche Geologiche e Ambientali Alma Mater Studiorum Università di Bologna Bologna Italy
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Kempf ED, Hermann J, Reusser E, Baumgartner LP, Lanari P. The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland). SWISS JOURNAL OF GEOSCIENCES 2020; 113:16. [PMID: 33132816 PMCID: PMC7588401 DOI: 10.1186/s00015-020-00368-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 08/25/2020] [Indexed: 06/11/2023]
Abstract
Metamorphic olivine formed by the reaction of antigorite + brucite is widespread in serpentinites that crop out in glacier-polished outcrops at the Unterer Theodulglacier, Zermatt. Olivine overgrows a relic magnetite mesh texture formed during ocean floor serpentinization. Serpentinization is associated with rodingitisation of mafic dykes. Metamorphic olivine coexists with magnetite, shows high Mg# of 94-97 and low trace element contents. A notable exception is 4 µg/g Boron (> 10 times primitive mantle), introduced during seafloor alteration and retained in metamorphic olivine. Olivine incorporated 100-140 µg/g H2O in Si-vacancies, providing evidence for low SiO2-activity imposed by brucite during olivine growth. No signs for hydrogen loss or major and minor element diffusional equilibration are observed. The occurrence of olivine in patches within the serpentinite mimics the former heterogeneous distribution of brucite, whereas the network of olivine-bearing veins and shear zones document the pathways of the escaping fluid produced by the olivine forming reaction. Relic Cr-spinels have a high Cr# of 0.5 and the serpentinites display little or no clinopyroxene, indicating that they derive from hydrated harzburgitic mantle that underwent significant melt depletion. The enrichment of Mg and depletion of Si results in the formation of brucite during seafloor alteration, a pre-requisite for later subduction-related olivine formation and fluid liberation. The comparison of calculated bulk rock brucite contents in the Zermatt-Saas with average IODP serpentinites suggests a large variation in fluid release during olivine formation. Between 3.4 and 7.2 wt% H2O is released depending on the magnetite content in fully serpentinized harzburgites (average oceanic serpentinites). Thermodynamic modelling indicates that the fluid release in Zermatt occurred between 480 °C and 550 °C at 2-2.5 GPa with the Mg# of olivine varying from 68 to 95. However, the majority of the fluid released from this reaction was produced within a narrow temperature field of < 30 °C, at higher pressures 2.5 GPa and temperatures 550-600 °C than commonly thought. Fluids derived from the antigorite + brucite reaction might thus trigger eclogite facies equilibration in associated metabasalts, meta-gabbros, meta-rodingites and meta-sediments in the area. This focused fluid release has the potential to trigger intermediate depths earthquakes at 60-80 km in subducted oceanic lithosphere.
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Affiliation(s)
- Elias D. Kempf
- Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
| | - Jörg Hermann
- Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
| | - Eric Reusser
- Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
| | - Lukas P. Baumgartner
- Institute of Earth Sciences, University of Lausanne, Quartier UNIL-Mouline Batiment Géopolis 4885, 1015 Lausanne, Switzerland
| | - Pierre Lanari
- Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
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Subduction hides high-pressure sources of energy that may feed the deep subsurface biosphere. Nat Commun 2020; 11:3880. [PMID: 32759942 PMCID: PMC7406650 DOI: 10.1038/s41467-020-17342-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 06/25/2020] [Indexed: 11/10/2022] Open
Abstract
Geological sources of H2 and abiotic CH4 have had a critical role in the evolution of our planet and the development of life and sustainability of the deep subsurface biosphere. Yet the origins of these sources are largely unconstrained. Hydration of mantle rocks, or serpentinization, is widely recognized to produce H2 and favour the abiotic genesis of CH4 in shallow settings. However, deeper sources of H2 and abiotic CH4 are missing from current models, which mainly invoke more oxidized fluids at convergent margins. Here we combine data from exhumed subduction zone high-pressure rocks and thermodynamic modelling to show that deep serpentinization (40–80 km) generates significant amounts of H2 and abiotic CH4, as well as H2S and NH3. Our results suggest that subduction, worldwide, hosts large sources of deep H2 and abiotic CH4, potentially providing energy to the overlying subsurface biosphere in the forearc regions of convergent margins. Geological sources of H2 and abiotic CH4 have had a critical role in the evolution of life and sustainability of the deep subsurface biosphere, yet the origins of these sources remain largely unconstrained. Here the authors show that deep serpentinization (40–80 km) during subduction generates significant amounts of H2 and abiotic CH4, potentially providing energy to the overlying subsurface biosphere.
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11
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Idrissi H, Samaee V, Lumbeeck G, van der Werf T, Pardoen T, Schryvers D, Cordier P. In Situ Quantitative Tensile Testing of Antigorite in a Transmission Electron Microscope. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2020; 125:e2019JB018383. [PMID: 32714729 PMCID: PMC7375155 DOI: 10.1029/2019jb018383] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 02/18/2020] [Accepted: 02/19/2020] [Indexed: 06/11/2023]
Abstract
The determination of the mechanical properties of serpentinites is essential toward the understanding of the mechanics of faulting and subduction. Here we present the first in situ tensile tests on antigorite in a transmission electron microscope. A push-to-pull deformation device is used to perform quantitative tensile tests, during which force and displacement are measured, while the evolving microstructure is imaged with the microscope. The experiments have been performed at room temperature on 2 × 1 × 0.2 μm3 beams prepared by focused ion beam. The specimens are not single crystals despite their small sizes. Orientation mapping indicated that several grains were well oriented for plastic slip. However, no dislocation activity has been observed even though the engineering tensile stress went up to 700 MPa. We show also that antigorite does not exhibit a purely elastic-brittle behavior since, despite the presence of defects, the specimens accumulate permanent deformation and did not fail within the elastic regime. Instead, we observe that strain localizes at grain boundaries. All observations concur to show that under these experimental conditions, grain boundary sliding is the dominant deformation mechanism. This study sheds a new light on the mechanical properties of antigorite and calls for further studies on the structure and properties of grain boundaries in antigorite and more generally in phyllosilicates.
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Affiliation(s)
- Hosni Idrissi
- Institute of Mechanics, Materials and Civil EngineeringUCLouvainLouvain‐la‐NeuveBelgium
- Electron Microscopy for Materials ScienceUniversity of AntwerpAntwerpBelgium
| | - Vahid Samaee
- Electron Microscopy for Materials ScienceUniversity of AntwerpAntwerpBelgium
| | - Gunnar Lumbeeck
- Electron Microscopy for Materials ScienceUniversity of AntwerpAntwerpBelgium
| | - Thomas van der Werf
- Institute of Mechanics, Materials and Civil EngineeringUCLouvainLouvain‐la‐NeuveBelgium
- Electron Microscopy for Materials ScienceUniversity of AntwerpAntwerpBelgium
| | - Thomas Pardoen
- Institute of Mechanics, Materials and Civil EngineeringUCLouvainLouvain‐la‐NeuveBelgium
| | - Dominique Schryvers
- Electron Microscopy for Materials ScienceUniversity of AntwerpAntwerpBelgium
| | - Patrick Cordier
- Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207‐UMET‐Unité Matériaux et TransformationsLilleFrance
- Institut Universitaire de FranceParisFrance
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Lin Y, Hu Q, Meng Y, Walter M, Mao HK. Evidence for the stability of ultrahydrous stishovite in Earth's lower mantle. Proc Natl Acad Sci U S A 2020; 117:184-189. [PMID: 31843935 PMCID: PMC6955296 DOI: 10.1073/pnas.1914295117] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The distribution and transportation of water in Earth's interior depends on the stability of water-bearing phases. The transition zone in Earth's mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H2O in their structures at mantle temperatures. The extent to which water can be transported beyond the transition zone deeper into the mantle depends on the water carrying capacity of minerals stable in subducted lithosphere. Stishovite is one of the major mineral components in subducting oceanic crust, yet the capacity of stishovite to incorporate water beyond at lower mantle conditions remains speculative. In this study, we combine in situ laser heating with synchrotron X-ray diffraction to show that the unit cell volume of stishovite synthesized under hydrous conditions is ∼2.3 to 5.0% greater than that of anhydrous stishovite at pressures of ∼27 to 58 GPa and temperatures of 1,240 to 1,835 K. Our results indicate that stishovite, even at temperatures along a mantle geotherm, can potentially incorporate weight percent levels of H2O in its crystal structure and has the potential to be a key phase for transporting and storing water in the lower mantle.
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Affiliation(s)
- Yanhao Lin
- Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015;
| | - Qingyang Hu
- Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China;
| | - Yue Meng
- High-Pressure Collaborative Access Team (HPCAT), X-Ray Science Division, Argonne National Laboratory, Lemont, IL 60439
| | - Michael Walter
- Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015
| | - Ho-Kwang Mao
- Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China;
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13
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Piccoli F, Hermann J, Pettke T, Connolly JAD, Kempf ED, Vieira Duarte JF. Subducting serpentinites release reduced, not oxidized, aqueous fluids. Sci Rep 2019; 9:19573. [PMID: 31862932 PMCID: PMC6925189 DOI: 10.1038/s41598-019-55944-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 12/05/2019] [Indexed: 11/09/2022] Open
Abstract
The observation that primitive arc magmas are more oxidized than mid-ocean-ridge basalts has led to the paradigm that slab-derived fluids carry SO2 and CO2 that metasomatize and oxidize the sub-arc mantle wedge. We combine petrography and thermodynamic modelling to quantify the oxygen fugacity (fO2) and speciation of the fluids generated by serpentinite dehydration during subduction. Silicate-magnetite assemblages maintain fO2 conditions similar to the quartz-fayalite-magnetite (QFM) buffer at fore-arc conditions. Sulphides are stable under such conditions and aqueous fluids contain minor S. At sub-arc depth, dehydration occurs under more reducing conditions producing aqueous fluids carrying H2S. This finding brings into question current models in which serpentinite-derived fluids are the cause of oxidized arc magmatism and has major implications for the global volatile cycle, as well as for redox processes controlling subduction zone geodynamics.
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Affiliation(s)
- F Piccoli
- University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland.
| | - J Hermann
- University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland
| | - T Pettke
- University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland
| | - J A D Connolly
- Department of Earth Science, Swiss Federal Institute of Technology, Zurich, Switzerland
| | - E D Kempf
- University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland
| | - J F Vieira Duarte
- University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland
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14
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Influence of pH on Molecular Hydrogen (H2) Generation and Reaction Rates during Serpentinization of Peridotite and Olivine. MINERALS 2019. [DOI: 10.3390/min9110661] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Serpentinization produces molecular hydrogen (H2) that is capable of supporting communities of microorganisms in hydrothermal fields, which suggests that serpentinization may be closely related to the origin of life at the early history of the Earth and possibly other planets. In this study, serpentinization experiments were performed at 300 °C and 3.0 kbar with natural olivine and peridotite as starting reactants to quantify the influence of acidic and alkaline solutions on the processes of serpentinization. The results reveal that acidic and alkaline solutions greatly influence molecular hydrogen (H2) generation and the rates of serpentinization. Acidic (pH = 2.50) and alkaline solutions (pH = 13.5) increased H2 production and the rates of peridotite serpentinization. Highly acidic solutions (2 M HCl), however, decreased the production of H2 after peridotite serpentinization by around two orders of magnitude. The decrease in H2 production was associated with a sharp decline in the rates of reaction; e.g., when peridotite was reacted with neutral solutions (0.5 M NaCl), 88% of reaction progress was achieved after an experimental duration of 27 days, and the reaction extent decreased by ~50% for experiments with highly acidic solutions (2 M HCl) over the same period. In contrast, for experiments with solely olivine, highly acidic solutions (2 M HCl) promoted the rates of olivine serpentinization and H2 production. The contrasting effect of highly acidic solutions (2 M HCl) on the processes of olivine and peridotite serpentinization may reflect the influence of pyroxene minerals, which could release SiO2 during peridotite serpentinization and, consequently, hydrogen generation and reaction rates may decrease. The experimental results of this study suggest that H2 production and the rates of serpentinization can be greatly influenced by acidic and alkaline solutions and co-existing minerals (e.g., pyroxene).
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15
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Molybdenum systematics of subducted crust record reactive fluid flow from underlying slab serpentine dehydration. Nat Commun 2019; 10:4773. [PMID: 31636258 PMCID: PMC6803652 DOI: 10.1038/s41467-019-12696-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 09/19/2019] [Indexed: 11/13/2022] Open
Abstract
Fluids liberated from subducting slabs are critical in global geochemical cycles. We investigate the behaviour of Mo during slab dehydration using two suites of exhumed fragments of subducted, oceanic lithosphere. Our samples display a positive correlation of δ98/95MoNIST 3134 with Mo/Ce, from compositions close to typical mantle (−0.2‰ and 0.03, respectively) to very low values of both δ98/95MoNIST 3134 (−1‰) and Mo/Ce (0.002). Together with new, experimental data, we show that molybdenum isotopic fractionation is driven by preference of heavier Mo isotopes for a fluid phase over rutile, the dominant mineral host of Mo in eclogites. Moreover, the strongly perturbed δ98/95MoNIST 3134 and Mo/Ce of our samples requires that they experienced a large flux of oxidised fluid. This is consistent with channelised, reactive fluid flow through the subducted crust, following dehydration of the underlying, serpentinised slab mantle. The high δ98/95MoNIST 3134 of some arc lavas is the complement to this process. Fluid liberation and migration from subducted oceanic slabs play a critical role in arc magmatism but the volume and origin of the released fluids is unclear and difficult to trace. Here, the authors use Molybdenum isotope ratios to tackle these problems.
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16
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Origin of arc magmatic signature: A temperature-dependent process for trace element (re)-mobilization in subduction zones. Sci Rep 2019; 9:7098. [PMID: 31068627 PMCID: PMC6506526 DOI: 10.1038/s41598-019-43605-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 04/27/2019] [Indexed: 11/09/2022] Open
Abstract
Serpentinite is a major carrier of fluid-mobile elements in subduction zones, which influences the geochemical signature of arc magmatism (e.g. high abundances of Li, Ba, Sr, B, As, Mo and Pb). Based on results from Neoproterozoic serpentinites in the Arabian-Nubian Shield, we herein report the role of antigorite in the transportation of fluid-mobile elements (FME) and light rare earth elements (LREE) from the subducted slab to arc-related magma during subduction. The serpentinites contain two generations of antigorites: the older generation is coarse-grained, formed at a temperature range of 165-250 °C and is enriched in Li, Rb, Ba and Cs, whereas the younger generation is finer-grained, formed at higher temperature conditions (425-475 °C) and has high concentrations of B, As, Sb, Mo, Pb, Sr and LREE. Magnesite, on the other hand, remains stable at sub-arc depths beyond the stability field of both antigorites, and represents a potential reservoir of FME and LREE for deeper mantle melts. Magnesite has high FME and LREE absorbing capacity (over 50-60%) higher than serpentine phases. Temperature is the main controlling factor for stability of these minerals and therefore the release of these elements from subducted slabs into arc magmatism. As the liberation of these elements varies along the length of the slab, the resulting cross-arc geochemical variation trend can help to determine the subduction polarity of ancient arcs.
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17
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Water input into the Mariana subduction zone estimated from ocean-bottom seismic data. Nature 2018; 563:389-392. [PMID: 30429549 DOI: 10.1038/s41586-018-0655-4] [Citation(s) in RCA: 108] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 09/19/2018] [Indexed: 11/08/2022]
Abstract
The water cycle at subduction zones remains poorly understood, although subduction is the only mechanism for water transport deep into Earth. Previous estimates of water flux1-3 exhibit large variations in the amount of water that is subducted deeper than 100 kilometres. The main source of uncertainty in these calculations is the initial water content of the subducting uppermost mantle. Previous active-source seismic studies suggest that the subducting slab may be pervasively hydrated in the plate-bending region near the oceanic trench4-7. However, these studies do not constrain the depth extent of hydration and most investigate young incoming plates, leaving subduction-zone water budgets for old subducting plates uncertain. Here we present seismic images of the crust and uppermost mantle around the central Mariana trench derived from Rayleigh-wave analysis of broadband ocean-bottom seismic data. These images show that the low mantle velocities that result from mantle hydration extend roughly 24 kilometres beneath the Moho discontinuity. Combined with estimates of subducting crustal water, these results indicate that at least 4.3 times more water subducts than previously calculated for this region3. If other old, cold subducting slabs contain correspondingly thick layers of hydrous mantle, as suggested by the similarity of incoming plate faulting across old, cold subducting slabs, then estimates of the global water flux into the mantle at depths greater than 100 kilometres must be increased by a factor of about three compared to previous estimates3. Because a long-term net influx of water to the deep interior of Earth is inconsistent with the geological record8, estimates of water expelled at volcanic arcs and backarc basins probably also need to be revised upwards9.
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18
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Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic. Sci Rep 2017; 7:17776. [PMID: 29259321 PMCID: PMC5736666 DOI: 10.1038/s41598-017-18139-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 12/06/2017] [Indexed: 11/08/2022] Open
Abstract
Serpentinites are important reservoirs of fluid-mobile elements in subduction zones, contributing to volatiles in arc magmas and their transport into the Earth’s mantle. This paper reports halogen (F, Cl, Br, I) and B abundances of serpentinites from the Dominican Republic, including obducted and subducted abyssal serpentinites and forearc mantle serpentinites. Abyssal serpentinite compositions indicate the incorporation of these elements from seawater and sediments during serpentinization on the seafloor and at slab bending. During their subduction and subsequent lizardite-antigorite transition, F and B are retained in serpentinites, whilst Cl, Br and I are expelled. Forearc mantle serpentinite compositions suggest their hydration by fluids released from subducting altered oceanic crust and abyssal serpentinites, with only minor sediment contribution. This finding is consistent with the minimal subduction of sediments in the Dominican Republic. Forearc mantle serpentinites have F/Cl and B/Cl ratios similar to arc magmas, suggesting the importance of serpentinite dehydration in the generation of arc magmatism in the mantle wedge.
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19
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Wang D, Liu X, Liu T, Shen K, Welch DO, Li B. Constraints from the dehydration of antigorite on high-conductivity anomalies in subduction zones. Sci Rep 2017; 7:16893. [PMID: 29203777 PMCID: PMC5714963 DOI: 10.1038/s41598-017-16883-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 11/17/2017] [Indexed: 11/09/2022] Open
Abstract
Regions with high electrical conductivities in subduction zones have attracted a great deal of attention. Determining the exact origin of these anomalies could provide critical information about the water storage and cycling processes during subduction. Antigorite is the most important hydrous mineral within deep subduction zones. The dehydration of antigorite is believed to cause high-conductivity anomalies. To date, the effects of dehydration on the electrical conductivity of antigorite remain poorly understood. Here, we report new measurements of the electrical conductivity of both natural and hot-pressed antigorite at pressures of 4 and 3 GPa, respectively, and at temperatures reaching 1073 K. We observed significantly enhanced conductivities when the antigorite was heated to temperatures beyond its thermodynamic stability field. Sharp increases in the electrical conductivity occurred at approximately 848 and 898 K following the decomposition of antigorite to forsterite, enstatite and aqueous fluids. High electrical conductivities reaching 1 S/m can be explained by the presence of an interconnected network of conductive aqueous fluids. Based on these results for the electrical conductivity of antigorite, we conclude that high-conductivity regions associated with subduction zones can be attributed to dehydration-induced fluids and the formation of interconnected networks of aqueous fluids during the dehydration of antigorite.
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Affiliation(s)
- Duojun Wang
- College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. .,Mineral physics institute, State university of New York at Stony Brook, Stony Brook, 11794, NY, USA.
| | - Xiaowei Liu
- Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Lanzhou, 730000, China
| | - Tao Liu
- College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Kewei Shen
- College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - David O Welch
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, 11793, USA
| | - Baosheng Li
- Mineral physics institute, State university of New York at Stony Brook, Stony Brook, 11794, NY, USA
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20
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Mantle hydration along outer-rise faults inferred from serpentinite permeability. Sci Rep 2017; 7:13870. [PMID: 29066745 PMCID: PMC5654952 DOI: 10.1038/s41598-017-14309-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 10/09/2017] [Indexed: 11/25/2022] Open
Abstract
Recent geophysical surveys indicate that hydration (serpentinization) of oceanic mantle is related to outer-rise faulting prior to subduction. The serpentinization of oceanic mantle influences the generation of intermediate-depth earthquakes and subduction water flux, thereby promoting arc volcanism. Since the chemical reactions that produce serpentinite are geologically rapid at low temperatures, the flux of water delivery to the reaction front appears to control the lateral extent of serpentinization. In this study, we measured the permeability of low-temperature serpentinites composed of lizardite and chrysotile, and calculated the lateral extent of serpentinization along an outer-rise fault based on Darcy’s law. The experimental results indicate that serpentinization extends to a region several hundred meters wide in the direction normal to the outer-rise fault in the uppermost oceanic mantle. We calculated the global water flux carried by serpentinized oceanic mantle ranging from 1.7 × 1011 to 2.4 × 1012 kg/year, which is comparable or even higher than the water flux of hydrated oceanic crust.
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21
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Debret B, Sverjensky DA. Highly oxidising fluids generated during serpentinite breakdown in subduction zones. Sci Rep 2017; 7:10351. [PMID: 28871200 PMCID: PMC5583334 DOI: 10.1038/s41598-017-09626-y] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 07/27/2017] [Indexed: 11/17/2022] Open
Abstract
Subduction zones facilitate chemical exchanges between Earth’s deep interior and volcanism that affects habitability of the surface environment. Lavas erupted at subduction zones are oxidized and release volatile species. These features may reflect a modification of the oxidation state of the sub-arc mantle by hydrous, oxidizing sulfate and/or carbonate-bearing fluids derived from subducting slabs. But the reason that the fluids are oxidizing has been unclear. Here we use theoretical chemical mass transfer calculations to predict the redox state of fluids generated during serpentinite dehydration. Specifically, the breakdown of antigorite to olivine, enstatite, and chlorite generates fluids with high oxygen fugacities, close to the hematite-magnetite buffer, that can contain significant amounts of sulfate. The migration of these fluids from the slab to the mantle wedge could therefore provide the oxidized source for the genesis of primary arc magmas that release gases to the atmosphere during volcanism. Our results also show that the evolution of oxygen fugacity in serpentinite during subduction is sensitive to the amount of sulfides and potentially metal alloys in bulk rock, possibly producing redox heterogeneities in subducting slabs.
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Affiliation(s)
- B Debret
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK. .,Laboratoire G-Time, DGES, Université Libre de Bruxelles, ULB, CP 160/02, 1050, Brussels, Belgium.
| | - D A Sverjensky
- Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, 21218, USA
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22
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Paulatto M, Laigle M, Galve A, Charvis P, Sapin M, Bayrakci G, Evain M, Kopp H. Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles. Nat Commun 2017; 8:15980. [PMID: 28691714 PMCID: PMC5508134 DOI: 10.1038/ncomms15980] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 05/18/2017] [Indexed: 11/25/2022] Open
Abstract
Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60–100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120–160 km depth suggests that the slab’s mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics. During subduction water is transported into the mantle, but constraining its release remains challenging. Here, using seismic tomography of the Lesser Antilles arc, the authors track the multistage dehydration of the slab and its lateral variations associated with heterogeneous slab composition.
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Affiliation(s)
- Michele Paulatto
- Université Côte d'Azur, CNRS, IRD, Observatoire de la Côte d'Azur, Géoazur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France.,Imperial College London, Earth Science and Engineering, Prince Consort Road, London SW7 2BP, UK
| | - Mireille Laigle
- Université Côte d'Azur, CNRS, IRD, Observatoire de la Côte d'Azur, Géoazur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France
| | - Audrey Galve
- Université Côte d'Azur, CNRS, IRD, Observatoire de la Côte d'Azur, Géoazur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France
| | - Philippe Charvis
- Université Côte d'Azur, CNRS, IRD, Observatoire de la Côte d'Azur, Géoazur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France
| | - Martine Sapin
- Institut de Physique du Globe de Paris, PRES Sorbonne Paris-Cité, CNRS UMR 7154, 1 rue Jussieu, 75005 Paris, France
| | - Gaye Bayrakci
- University of Southampton, Ocean and Earth Science, European Way, Southampton SO14 3ZH, UK
| | - Mikael Evain
- IFREMER, Géosciences Marines, Centre Bretagne, ZI de la Pointe du Diable-CS 10070, 29280 Plouzané, France
| | - Heidrun Kopp
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany
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23
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Wang J, Zhao D, Yao Z. Seismic anisotropy evidence for dehydration embrittlement triggering intermediate-depth earthquakes. Sci Rep 2017; 7:2613. [PMID: 28572682 PMCID: PMC5453959 DOI: 10.1038/s41598-017-02563-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 04/13/2017] [Indexed: 12/01/2022] Open
Abstract
It has been proposed that dehydration embrittlement of hydrous materials can trigger intermediate-depth earthquakes and form a double seismic zone in a subducting slab. Seismic anisotropy may provide a possible insight into intermediate-depth intraslab seismicity, because anisotropic properties of minerals change with varying water distribution, temperature and pressure. Here we present a high-resolution model of P-wave radial anisotropy tomography of the Japan subduction zone down to ~400 km depth, which is obtained using a large number of arrival-time data of local earthquakes and teleseismic events. Our results reveal a close correlation between the pattern of intermediate-depth seismicity and anisotropic structures. The seismicity occurs in portions of the Pacific and Philippine Sea slabs where positive radial anisotropy (i.e., horizontal velocity being faster than vertical one) dominates due to dehydration, whereas the inferred anhydrous parts of the slabs are found to be aseismic where negative radial anisotropy (i.e., vertical velocity being faster than horizontal one) dominates. Our anisotropic results suggest that intermediate-depth earthquakes in Japan could be triggered by dehydration embrittlement of hydrous minerals in the subducting slabs.
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Affiliation(s)
- Jian Wang
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
| | - Dapeng Zhao
- Department of Geophysics, Tohoku University, Sendai, 980-8578, Japan
| | - Zhenxing Yao
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
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24
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Ferrand TP, Hilairet N, Incel S, Deldicque D, Labrousse L, Gasc J, Renner J, Wang Y, Green Ii HW, Schubnel A. Dehydration-driven stress transfer triggers intermediate-depth earthquakes. Nat Commun 2017; 8:15247. [PMID: 28504263 PMCID: PMC5440692 DOI: 10.1038/ncomms15247] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 03/13/2017] [Indexed: 11/29/2022] Open
Abstract
Intermediate-depth earthquakes (30–300 km) have been extensively documented within subducting oceanic slabs, but their mechanics remains enigmatic. Here we decipher the mechanism of these earthquakes by performing deformation experiments on dehydrating serpentinized peridotites (synthetic antigorite-olivine aggregates, minerals representative of subduction zones lithologies) at upper mantle conditions. At a pressure of 1.1 gigapascals, dehydration of deforming samples containing only 5 vol% of antigorite suffices to trigger acoustic emissions, a laboratory-scale analogue of earthquakes. At 3.5 gigapascals, acoustic emissions are recorded from samples with up to 50 vol% of antigorite. Experimentally produced faults, observed post-mortem, are sealed by fluid-bearing micro-pseudotachylytes. Microstructural observations demonstrate that antigorite dehydration triggered dynamic shear failure of the olivine load-bearing network. These laboratory analogues of intermediate-depth earthquakes demonstrate that little dehydration is required to trigger embrittlement. We propose an alternative model to dehydration-embrittlement in which dehydration-driven stress transfer, rather than fluid overpressure, causes embrittlement. Intermediate-depth earthquakes (30-300 km) occur in subducting oceanic slabs, but their generation mechanism remains enigmatic. Here, the authors show through high-pressure and dehydration experiments of antigorite that dehydration-driven stress transfer triggers intermediate-depth earthquakes.
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Affiliation(s)
- Thomas P Ferrand
- Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France
| | - Nadège Hilairet
- Unité Matériaux et Transformations - UMR 8207, CNRS, Univ. Lille, ENSCL, INRA, F-59000 Lille, France
| | - Sarah Incel
- Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France
| | - Damien Deldicque
- Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France
| | - Loïc Labrousse
- Institut des Sciences de la Terre de Paris, Université Pierre et Marie Curie, 75005 Paris, France
| | - Julien Gasc
- Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France
| | - Joerg Renner
- Institut für Geologie, Mineralogie und Geophysik, Ruhr Universität Bochum, Bochum D44780, Germany
| | - Yanbin Wang
- Center for Advanced Radiation Sources, University of Chicago, Argonne, Illinois 60439, USA
| | - Harry W Green Ii
- Department of Earth Science, University of California, Riverside, California 92521, USA
| | - Alexandre Schubnel
- Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France
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25
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Nielsen SG, Marschall HR. Geochemical evidence for mélange melting in global arcs. SCIENCE ADVANCES 2017; 3:e1602402. [PMID: 28435882 PMCID: PMC5384804 DOI: 10.1126/sciadv.1602402] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Accepted: 02/16/2017] [Indexed: 06/07/2023]
Abstract
In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated.
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Affiliation(s)
- Sune G. Nielsen
- NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Horst R. Marschall
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- Institut für Geowissenschaften, Goethe Universität Frankfurt, Altenhöferalle 1, 60438 Frankfurt am Main, Germany
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Lin A, Sano M, Wang M, Yan B, Bian D, Fueta R, Hosoya T. Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa-Shizuoka Tectonic Line, Japan. JOURNAL OF SEISMOLOGY 2016; 21:683-703. [PMID: 28729808 PMCID: PMC5496973 DOI: 10.1007/s10950-016-9629-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 11/14/2016] [Indexed: 06/07/2023]
Abstract
The Mw 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa-Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2-E8) prior to the 2014 Mw 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2-E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300-400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800-1400 and is associated with the 1791 Mw 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000-700, likely corresponding to the AD 841 Mw 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600-6000 years. The throw rate during the early Holocene is estimated to be 1.2-3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7-1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.
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Affiliation(s)
- Aiming Lin
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
| | - Mikako Sano
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
| | - Maomao Wang
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
| | - Bing Yan
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
- School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210046 China
| | - Di Bian
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
| | - Ryoji Fueta
- Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
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Seismic evidence for a cold serpentinized mantle wedge beneath Mount St Helens. Nat Commun 2016; 7:13242. [PMID: 27802263 PMCID: PMC5097125 DOI: 10.1038/ncomms13242] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 09/15/2016] [Indexed: 11/08/2022] Open
Abstract
Mount St Helens is the most active volcano within the Cascade arc; however, its location is unusual because it lies 50 km west of the main axis of arc volcanism. Subduction zone thermal models indicate that the down-going slab is decoupled from the overriding mantle wedge beneath the forearc, resulting in a cold mantle wedge that is unlikely to generate melt. Consequently, the forearc location of Mount St Helens raises questions regarding the extent of the cold mantle wedge and the source region of melts that are responsible for volcanism. Here using, high-resolution active-source seismic data, we show that Mount St Helens sits atop a sharp lateral boundary in Moho reflectivity. Weak-to-absent PmP reflections to the west are attributed to serpentinite in the mantle-wedge, which requires a cold hydrated mantle wedge beneath Mount St Helens (<∼700 °C). These results suggest that the melt source region lies east towards Mount Adams.
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The H 2/CH 4 ratio during serpentinization cannot reliably identify biological signatures. Sci Rep 2016; 6:33821. [PMID: 27666288 PMCID: PMC5036043 DOI: 10.1038/srep33821] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 09/02/2016] [Indexed: 12/02/2022] Open
Abstract
Serpentinization potentially contributes to the origin and evolution of life during early history of the Earth. Serpentinization produces molecular hydrogen (H2) that can be utilized by microorganisms to gain metabolic energy. Methane can be formed through reactions between molecular hydrogen and oxidized carbon (e.g., carbon dioxide) or through biotic processes. A simple criterion, the H2/CH4 ratio, has been proposed to differentiate abiotic from biotic methane, with values approximately larger than 40 for abiotic methane and values of <40 for biotic methane. The definition of the criterion was based on two serpentinization experiments at 200 °C and 0.3 kbar. However, it is not clear whether the criterion is applicable at a wider range of temperatures. In this study, we performed sixteen experiments at 311–500 °C and 3.0 kbar using natural ground peridotite. Our results demonstrate that the H2/CH4 ratios strongly depend on temperature. At 311 °C and 3.0 kbar, the H2/CH4 ratios ranged from 58 to 2,120, much greater than the critical value of 40. By contrast, at 400–500 °C, the H2/CH4 ratios were much lower, ranging from 0.1 to 8.2. The results of this study suggest that the H2/CH4 ratios cannot reliably discriminate abiotic from biotic methane.
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Dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust. Nature 2016; 530:81-4. [PMID: 26842057 DOI: 10.1038/nature16501] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/26/2015] [Indexed: 11/08/2022]
Abstract
Intermediate-depth earthquakes in cold subduction zones are observed within the subducting oceanic crust, as well as the mantle. In contrast, intermediate-depth earthquakes in hot subduction zones predominantly occur just below the Mohorovičić discontinuity. These observations have stimulated interest in relationships between blueschist-facies metamorphism and seismicity, particularly through dehydration reactions involving the mineral lawsonite. Here we conducted deformation experiments on lawsonite, while monitoring acoustic emissions, in a Griggs-type deformation apparatus. The temperature was increased above the thermal stability of lawsonite, while the sample was deforming, to test whether the lawsonite dehydration reaction induces unstable fault slip. In contrast to similar tests on antigorite, unstable fault slip (that is, stick-slip) occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed. Microstructural observations indicate that strain is highly localized along the fault (R1 and B shears), and that the fault surface develops slickensides (very smooth fault surfaces polished by frictional sliding). The unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions, regardless of the strain rate and temperature ramping rate. A thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones, indicating the potential for unstable frictional sliding within natural lawsonite layers.
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Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up. Proc Natl Acad Sci U S A 2015; 112:E3997-4006. [PMID: 26048906 DOI: 10.1073/pnas.1507889112] [Citation(s) in RCA: 384] [Impact Index Per Article: 42.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
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.
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Ko B, Jung H. Crystal preferred orientation of an amphibole experimentally deformed by simple shear. Nat Commun 2015; 6:6586. [PMID: 25858349 PMCID: PMC4403317 DOI: 10.1038/ncomms7586] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 02/09/2015] [Indexed: 11/09/2022] Open
Abstract
Seismic anisotropy has been widely observed in crust and mantle materials and plays a key role in the understanding of structure and flow patterns. Although seismic anisotropy can be explained by the crystal preferred orientation (CPO) of highly anisotropic minerals in the crust, that is, amphibole, experimental studies on the CPO of amphibole are limited. Here we present the results of novel experiments on simple shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480-700 °C). Depending on the temperature and stress, the deformed amphibole produced three types of CPOs and resulted in a strong seismic anisotropy. Our data provide a new understanding of the observed seismic anisotropy. The seismic data obtained from the amphibole CPOs revealed that anomalous seismic anisotropy observed in the deep crust, subducting slab and mantle wedge can be attributed to the CPO of amphibole.
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Affiliation(s)
- Byeongkwan Ko
- Tectonophysics Laboratory, School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea
| | - Haemyeong Jung
- Tectonophysics Laboratory, School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea
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Schaefer L, Sasselov D. THE PERSISTENCE OF OCEANS ON EARTH-LIKE PLANETS: INSIGHTS FROM THE DEEP-WATER CYCLE. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0004-637x/801/1/40] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Subduction of fracture zones controls mantle melting and geochemical signature above slabs. Nat Commun 2014; 5:5095. [PMID: 25342158 DOI: 10.1038/ncomms6095] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Accepted: 08/28/2014] [Indexed: 11/08/2022] Open
Abstract
For some volcanic arcs, the geochemistry of volcanic rocks erupting above subducted oceanic fracture zones is consistent with higher than normal fluid inputs to arc magma sources. Here we use enrichment of boron (B/Zr) in volcanic arc lavas as a proxy to evaluate relative along-strike inputs of slab-derived fluids in the Aleutian, Andean, Cascades and Trans-Mexican arcs. Significant B/Zr spikes coincide with subduction of prominent fracture zones in the relatively cool Aleutian and Andean subduction zones where fracture zone subduction locally enhances fluid introduction beneath volcanic arcs. Geodynamic models of subduction have not previously considered how fracture zones may influence the melt and fluid distribution above slabs. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that enhanced production of slab-derived fluids and mantle wedge melts concentrate in areas where fracture zones are subducted, resulting in significant along-arc variability in magma source compositions and processes.
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Cavallo A, Rimoldi B. Chrysotile asbestos in serpentinite quarries: a case study in Valmalenco, Central Alps, Northern Italy. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2013; 15:1341-1350. [PMID: 23770928 DOI: 10.1039/c3em00193h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The Valmalenco serpentinite (Central Alps, Northern Italy) is marketed worldwide as dimension and decorative stone. However, the same area was once subject to chrysotile asbestos mining, from the XIX century until 1975. Asbestos is a well-known carcinogen, and there is the possibility of releasing fibres during quarrying, subsequently exposing workers. From 2004 to 2011, extensive sampling and monitoring of quarry fronts, asbestos veins, commercial stones and airborne asbestos was carried out. Massive rock and vein samples were analyzed by a combined use of optical microscopy, X-ray powder diffraction (XRPD) and quantitative electron microscopy (SEM). Asbestos is concentrated almost exclusively in discrete horizons, that coincide with the main discontinuities of the rock mass. Commercial stones without fractures and veins are practically asbestos free, whereas there is a slight contamination (sometimes exceeding the 1000 ppm threshold) close to hydrothermal selvages. Quarry floors were always quite contaminated by chrysotile "beards" detached from the surface of the blocks. The airborne asbestos concentrations (PCM and SEM) were distributed over a wide range, mostly below the occupational exposure limit of 0.1 f ml(-1). Concentrations at the quarry property border or at the closest villages were always below the environmental exposure limit of 0.002 f ml(-1). The extreme thinness of chrysotile fibrils produced during quarrying activities, and the abundance of pseudo-fibrous antigorite cleavage fragments proved the SEM-EDS analytical procedure to be the most suitable. It is of crucial importance to avoid the interception of veins during quarrying and to remove all visible asbestos from the extracted blocks, before any further processing.
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Affiliation(s)
- Alessandro Cavallo
- University of Milan-Bicocca, Department of Earth and Environmental Sciences, Piazza della Scienza, 4, I-20126 Milano (MI), Italy.
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Ling MX, Liu YL, Williams IS, Teng FZ, Yang XY, Ding X, Wei GJ, Xie LH, Deng WF, Sun WD. Formation of the world's largest REE deposit through protracted fluxing of carbonatite by subduction-derived fluids. Sci Rep 2013. [PMCID: PMC3646268 DOI: 10.1038/srep01776] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Rare Earth Elements (REE) are essential to modern society but the origins of many large REE deposits remain unclear. The U-Th-Pb ages, chemical compositions and C, O and Mg isotopic compositions of Bayan Obo, the world's largest REE deposit, indicate a protracted mineralisation history with unusual chemical and isotopic features. Coexisting calcite and dolomite are in O isotope disequilibrium; some calcitic carbonatite samples show highly varied δ26Mg which increases with increasing Si and Mg; and ankerite crystals show decreases in Fe and REE from rim to centre, with highly varied REE patterns. These and many other observations are consistent with an unusual mineralisation process not previously considered; protracted fluxing of calcitic carbonatite by subduction-released high-Si fluids during the closure of the Palaeo-Asian Ocean. The fluids leached Fe and Mg from the mantle wedge and scavenged REE, Nb and Th from carbonatite, forming the deposit through metasomatism of overlying sedimentary carbonate.
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36
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Peacock SM. Thermal and Petrologic Structure of Subduction Zones. SUBDUCTION TOP TO BOTTOM 2013. [DOI: 10.1029/gm096p0119] [Citation(s) in RCA: 131] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Kirby S, Engdahl RE, Denlinger R. Intermediate-Depth Intraslab Earthquakes and Arc Volcanism as Physical Expressions of Crustal and Uppermost Mantle Metamorphism in Subducting Slabs. SUBDUCTION TOP TO BOTTOM 2013. [DOI: 10.1029/gm096p0195] [Citation(s) in RCA: 133] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Boron and Other Fluid-mobile Elements in Volcanic Arc Lavas: Implications for Subduction Processes. ACTA ACUST UNITED AC 2013. [DOI: 10.1029/gm096p0269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Seno T, Yamanaka Y. Double Seismic Zones, Compressional Deep Trench-Outer Rise Events, and Superplumes. SUBDUCTION TOP TO BOTTOM 2013. [DOI: 10.1029/gm096p0347] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Sandu C, Lenardic A, McGovern P. The effects of deep water cycling on planetary thermal evolution. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jb008405] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Contreras-Reyes E, Grevemeyer I, Watts AB, Flueh ER, Peirce C, Moeller S, Papenberg C. Deep seismic structure of the Tonga subduction zone: Implications for mantle hydration, tectonic erosion, and arc magmatism. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jb008434] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
The second critical endpoint in the basalt-H(2)O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770 °C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones.
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Melting above the anhydrous solidus controls the location of volcanic arcs. Nature 2010; 467:700-3. [DOI: 10.1038/nature09417] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2010] [Accepted: 07/23/2010] [Indexed: 11/08/2022]
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Green HW, Chen WP, Brudzinski MR. Seismic evidence of negligible water carried below 400-km depth in subducting lithosphere. Nature 2010; 467:828-31. [PMID: 20927105 DOI: 10.1038/nature09401] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Accepted: 08/04/2010] [Indexed: 11/09/2022]
Abstract
Strong evidence exists that water is carried from the surface into the upper mantle by hydrous minerals in the uppermost 10-12 km of subducting lithosphere, and more water may be added as the lithosphere bends and goes downwards. Significant amounts of that water are released as the lithosphere heats up, triggering earthquakes and fluxing arc volcanism. In addition, there is experimental evidence for high solubility of water in olivine, the most abundant mineral in the upper mantle, for even higher solubility in olivine's high-pressure polymorphs, wadsleyite and ringwoodite, and for the existence of dense hydrous magnesium silicates that potentially could carry water well into the lower mantle (deeper than 1,000 km). Here we compare experimental and seismic evidence to test whether patterns of seismicity and the stabilities of these potentially relevant hydrous phases are consistent with a wet lithosphere. We show that there is nearly a one-to-one correlation between dehydration of minerals and seismicity at depths less than about 250 km, and conclude that the dehydration of minerals is the trigger of instability that leads to seismicity. At greater depths, however, we find no correlation between occurrences of earthquakes and depths where breakdown of hydrous phases is expected. Lastly, we note that there is compelling evidence for the existence of metastable olivine (which, if present, can explain the distribution of deep-focus earthquakes) west of and within the subducting Tonga slab and also in three other subduction zones, despite metastable olivine being incompatible with even extremely small amounts of water (of the order of 100 p.p.m. by weight). We conclude that subducting slabs are essentially dry at depths below 400 km and thus do not provide a pathway for significant amounts of water to enter the mantle transition zone or the lower mantle.
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Affiliation(s)
- Harry W Green
- Institute of Geophysics and Planetary Physics and Department of Earth Sciences, University of California, Riverside, California 92521, USA.
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Cannat M, Fontaine F, Escartín J. Serpentinization and associated hydrogen and methane fluxes at slow spreading ridges. GEOPHYSICAL MONOGRAPH SERIES 2010. [DOI: 10.1029/2008gm000760] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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46
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Seno T. Determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones: Implications for strength of asperities and Andean-type mountain building. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008jb005889] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Guillot S, Hattori K, Agard P, Schwartz S, Vidal O. Exhumation Processes in Oceanic and Continental Subduction Contexts: A Review. SUBDUCTION ZONE GEODYNAMICS 2009. [DOI: 10.1007/978-3-540-87974-9_10] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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48
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Phase transition in the subducted oceanic lithosphere and generation of the subduction zone magma. CHINESE SCIENCE BULLETIN 2008. [DOI: 10.1007/s11434-008-0405-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Seno T. Conditions for a crustal block to be sheared off from the subducted continental lithosphere: What is an essential factor to cause features associated with collision? ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005038] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Hilairet N, Reynard B, Wang Y, Daniel I, Merkel S, Nishiyama N, Petitgirard S. High-Pressure Creep of Serpentine, Interseismic Deformation, and Initiation of Subduction. Science 2007; 318:1910-3. [DOI: 10.1126/science.1148494] [Citation(s) in RCA: 291] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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