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Gülmez F, Prelević D, Förster MW, Buhre S, Günther J. Experimental production of K-rich metasomes through sediment recycling at the slab-mantle interface in the fore-arc. Sci Rep 2023; 13:19608. [PMID: 37949895 PMCID: PMC10638307 DOI: 10.1038/s41598-023-46367-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 10/31/2023] [Indexed: 11/12/2023] Open
Abstract
Sediment contribution to the mantle is the key step for the generation of orogenic magmatism to produce its isotopic and geochemical inventory. Even though they are exceptional for the post-collisional settings, there are worldwide examples of arc-related ultrapotassic mafic magmas which require complex multi-stage processes along with sediment melting e.g. in Italy or Pontides of Türkiye. To understand the metasomatism leading mantle to produce ultrapotassic mafic melts, we simulated the reactions of depleted (harzburgite) and fertile (lherzolite) mantle with subducted carbonate-rich sediment at relatively cold (800-850 °C) and shallow (2 GPa, 60-80 km) slab-mantle interfaces. The melting of sediments can trigger the formation of immiscible and conjugate carbonatitic and silicic melts which flux the mantle to develop hydrous minerals and dolomitic melt. The metasomatic growth product is a wehrlite composed of clinopyroxene, phlogopite, carbonate minerals and amphibole, representing a source of choice for Si-undersaturated ultrapotassic lavas. The occurrence of conjugate carbonatitic and silicic melts and their potential physical separation, offer a possibility for fractionation of several canonical trace element ratios such as Th/La, observed in Si-saturated ultrapotassic lavas. The synergy between peridotite-melt interaction and the physical separation of the carbonatitic and extremely K-enriched silicic melts are essential for the compositional evolution of ultrapotassic orogenic magmas and their mantle sources.
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Affiliation(s)
- Fatma Gülmez
- Department of Geological Engineering, Istanbul Technical University, 34469, Istanbul, Türkiye
| | - Dejan Prelević
- Faculty of Mining and Geology, University of Belgrade, Đušina 7, 11000, Belgrade, Serbia.
- Institut fur Geowissenschaften, Johannes-Gutenberg-Universität, 55099, Mainz, Germany.
| | - Michael W Förster
- School of Natural Sciences, Macquarie University, Sydney, NSW, 2109, Australia
| | - Stephan Buhre
- Institut fur Geowissenschaften, Johannes-Gutenberg-Universität, 55099, Mainz, Germany
| | - Jennifer Günther
- Institut fur Geowissenschaften, Johannes-Gutenberg-Universität, 55099, Mainz, Germany
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2
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Luffi P, Ducea MN. Chemical Mohometry: Assessing Crustal Thickness of Ancient Orogens Using Geochemical and Isotopic Data. REVIEWS OF GEOPHYSICS (WASHINGTON, D.C. : 1985) 2022; 60:e2021RG000753. [PMID: 36590030 PMCID: PMC9788079 DOI: 10.1029/2021rg000753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 05/04/2022] [Accepted: 05/11/2022] [Indexed: 05/26/2023]
Abstract
Convergent plate boundaries are key sites for continental crustal formation and recycling. Quantifying the evolution of crustal thickness and paleoelevation along ancient convergent margins represents a major goal in orogenic system analyses. Chemical and in some cases isotopic compositions of igneous rocks formed in modern supra-subduction arcs and collisional belts are sensitive to Moho depths at the location of magmatism, implying that igneous suites from fossil orogens carry information about crustal thickness from the time they formed. Several whole-rock chemical parameters correlate with crustal thickness, some of which were calibrated to serve as "mohometers," that is, quantitative proxies of paleo-Moho depths. Based on mineral-melt partition coefficients, this concept has been extended to detrital zircons, such that combined chemical and geochronological information extracted from these minerals allows us to reconstruct the crustal thickness evolution using the detrital archive. We discuss here the mohometric potential of a variety of chemical and isotopic parameters and show that their combined usage improves paleocrustal thickness estimates. Using a MATLAB® app developed for the underlying computations, we present examples from the modern and the deeper time geologic record to illustrate the promises and pitfalls of the technique. Since arcs are in isostatic equilibrium, mohometers are useful in reconstructing orogenic paleoelevation as well. Our analysis suggests that many global-scale correlations between magma composition and crustal thickness used in mohometry originate in the sub-arc mantle; additional effects resulting from intracrustal igneous differentiation depend on the compatible or incompatible behavior of the involved parameters.
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Affiliation(s)
- P. Luffi
- Sabba Stefanescu Institute of GeodynamicsBucharestRomania
- Geological Institute of RomaniaBucharestRomania
| | - M. N. Ducea
- Faculty of Geology and GeophysicsUniversity of BucharestBucharestRomania
- Department of GeosciencesUniversity of ArizonaTucsonAZUSA
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3
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Buntin S, Artemieva IM, Malehmir A, Thybo H, Malinowski M, Högdahl K, Janik T, Buske S. Long-lived Paleoproterozoic eclogitic lower crust. Nat Commun 2021; 12:6553. [PMID: 34772954 PMCID: PMC8589968 DOI: 10.1038/s41467-021-26878-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 10/25/2021] [Indexed: 11/23/2022] Open
Abstract
The nature of the lower crust and the crust-mantle transition is fundamental to Earth sciences. Transformation of lower crustal rocks into eclogite facies is usually expected to result in lower crustal delamination. Here we provide compelling evidence for long-lasting presence of lower crustal eclogite below the seismic Moho. Our new wide-angle seismic data from the Paleoproterozoic Fennoscandian Shield identify a 6–8 km thick body with extremely high velocity (Vp ~ 8.5–8.6 km/s) and high density (>3.4 g/cm3) immediately beneath equally thinned high-velocity (Vp ~ 7.3–7.4 km/s) lowermost crust, which extends over >350 km distance. We relate this observed structure to partial (50–70%) transformation of part of the mafic lowermost crustal layer into eclogite facies during Paleoproterozoic orogeny without later delamination. Our findings challenge conventional models for the role of lower crustal eclogitization and delamination in lithosphere evolution and for the long-term stability of cratonic crust. The nature of the lower crust and the crust-mantle transition is fundamental to Earth Sciences. Here, the authors provide evidence for long-lasting presence of lower crustal eclogite below the seismic Moho, challenging conventional models.
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Affiliation(s)
- Sebastian Buntin
- Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
| | - Irina M Artemieva
- Department of Geophysics, Stanford University, Stanford, CA, USA. .,Marine Geodynamics Section, GEOMAR Helmholtz Center for Ocean Research, Kiel, Germany. .,School of Earth Sciences, China University of Geosciences, Wuhan, China.
| | - Alireza Malehmir
- Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
| | - Hans Thybo
- School of Earth Sciences, China University of Geosciences, Wuhan, China. .,Eurasia Institute of Earth Sciences, Istanbul Technical University, Istanbul, Turkey.
| | | | - Karin Högdahl
- Department of Earth Sciences, Uppsala University, Uppsala, Sweden
| | - Tomasz Janik
- Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Stefan Buske
- Technical University Bergakademie Freiberg, Freiberg, Germany
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4
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Chen C, Förster MW, Foley SF, Liu Y. Massive carbon storage in convergent margins initiated by subduction of limestone. Nat Commun 2021; 12:4463. [PMID: 34294696 PMCID: PMC8298627 DOI: 10.1038/s41467-021-24750-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Accepted: 06/22/2021] [Indexed: 11/30/2022] Open
Abstract
Remobilization of sedimentary carbonate in subduction zones modulates arc volcanism emissions and thus Earth’s climate over geological timescales. Although limestones (or chalk) are thought to be the major carbon reservoir subducted to subarc depths, their fate is still unclear. Here we present high-pressure reaction experiments between impure limestone (7.4 wt.% clay) and dunite at 1.3–2.7 GPa to constrain the melting behaviour of subducted natural limestone in contact with peridotite. The results show that although clay impurities significantly depress the solidus of limestone, melting will not occur whilst limestones are still part of the subducting slab. Buoyancy calculations suggest that most of these limestones would form solid-state diapirs intruding into the mantle wedge, resulting in limited carbon flux to the deep mantle (< ~10 Mt C y−1). Less than 20% melting within the mantle wedge indicates that most limestones remain stable and are stored in subarc lithosphere, resulting in massive carbon storage in convergent margins considering their high carbon flux (~21.4 Mt C y−1). Assimilation and outgassing of these carbonates during arc magma ascent may dominate the carbon flux in volcanic arcs. Experiments and buoyancy calculations reveal that subduction of limestone results in massive carbon storage in arc lithosphere, forming an important carbon reservoir in convergent margins. Remobilization of this carbon reservoir during arc magma ascent may dominate carbon emissions at volcanic arcs.
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Affiliation(s)
- Chunfei Chen
- Department of Earth and Environmental Sciences and ARC Centre of Excellence for Core to Crust Fluid Systems, Macquarie University, North Ryde, NSW, Australia. .,State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan, China.
| | - Michael W Förster
- Department of Earth and Environmental Sciences and ARC Centre of Excellence for Core to Crust Fluid Systems, Macquarie University, North Ryde, NSW, Australia.,Research School of Earth Sciences, Australia National University, Canberra, ACT, Australia
| | - Stephen F Foley
- Department of Earth and Environmental Sciences and ARC Centre of Excellence for Core to Crust Fluid Systems, Macquarie University, North Ryde, NSW, Australia.,Research School of Earth Sciences, Australia National University, Canberra, ACT, Australia
| | - Yongsheng Liu
- State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan, China.
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Dong X, Yang D, Niu F, Liu S, Tong P. Adjoint traveltime tomography unravels a scenario of horizontal mantle flow beneath the North China craton. Sci Rep 2021; 11:12523. [PMID: 34131244 PMCID: PMC8206337 DOI: 10.1038/s41598-021-92048-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 06/04/2021] [Indexed: 02/05/2023] Open
Abstract
The North China craton (NCC) was dominated by tectonic extension from late Cretaceous to Cenozoic, yet seismic studies on the relationship between crust extension and lithospheric mantle deformation are scarce. Here we present a three dimensional radially anisotropic model of NCC derived from adjoint traveltime tomography to address this issue. We find a prominent low S-wave velocity anomaly at lithospheric mantle depths beneath the Taihang Mountains, which extends eastward with a gradually decreasing amplitude. The horizontally elongated low-velocity anomaly is also featured by a distinctive positive radial anisotropy (VSH > VSV). Combining geodetic and other seismic measurements, we speculate the presence of a horizontal mantle flow beneath central and eastern NCC, which led to the extension of the overlying crust. We suggest that the rollback of Western Pacific slab likely played a pivotal role in generating the horizontal mantle flow at lithospheric depth beneath the central and eastern NCC.
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Affiliation(s)
- Xingpeng Dong
- grid.12527.330000 0001 0662 3178Department of Mathematical Sciences, Tsinghua University, Beijing, 100084 China
| | - Dinghui Yang
- grid.12527.330000 0001 0662 3178Department of Mathematical Sciences, Tsinghua University, Beijing, 100084 China
| | - Fenglin Niu
- grid.21940.3e0000 0004 1936 8278Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX USA ,grid.411519.90000 0004 0644 5174State Key Laboratory of Petroleum Resources and Prospecting, and Unconventional Petroleum Research Institute, China University of Petroleum at Beijing, Beijing, China
| | - Shaolin Liu
- grid.12527.330000 0001 0662 3178Department of Mathematical Sciences, Tsinghua University, Beijing, 100084 China ,grid.59025.3b0000 0001 2224 0361Division of Mathematical Sciences, School of Physical and Mathematical Sciences and Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
| | - Ping Tong
- grid.59025.3b0000 0001 2224 0361Division of Mathematical Sciences, School of Physical and Mathematical Sciences and Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
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6
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Salimbeni S, Agostinetti NP, Pondrelli S. Insights Into the Origin and Deformation Style of the Continental Moho: A Case-Study From the Western Alps (Italy). JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2021; 126:e2020JB021319. [PMID: 34434686 PMCID: PMC8365725 DOI: 10.1029/2020jb021319] [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: 11/09/2020] [Revised: 05/22/2021] [Accepted: 06/03/2021] [Indexed: 06/13/2023]
Abstract
Several hypotheses on the origin of the continental Moho are still debated and multiple mechanisms may contribute to its formation. Here, we present quantitative estimation of the seismic properties and anisotropy of the crust-mantle transition in the Western Alps where an example of newly formed (proto)-continental Moho is unusually shallow. We make use of teleseismic P-to-S converted-waves recorded by stations deployed on top of the Ivrea Body (IB), a volume of possibly serpentinized mantle peridotite below exhumed (ultra-)high pressure crustal rocks. The IB has been mapped by gravity, magnetic, active and passive seismic surveys suggesting an extremely shallow Moho. We demonstrate that the P-to-S converted waves propagating through this region display coupled features: (a) they record expected presence of strong seismic velocity contrast at shallow depth as due to the lower crustal and upper mantle transition; (b) they are decomposed due to anisotropic properties of rocks involved. The proto-continental Moho is recognized as an increase in S-wave velocity (∼0.4-1 km/s) at shallow depths of 5-10 km. The presence of anisotropy within the IB and overlying crustal rocks is evidenced by back-azimuthal dependence of the amplitude of P-to-S phases. The strength of anisotropy is ∼-14% on average pointing out the presence of metamorphosed/hydrated material (e.g., serpentinite) below the Moho. Anisotropic directions are consistent across Moho in both crust and upper mantle. The similarity of the anisotropy parameters between crust and upper mantle suggests they have been shaped by the same deformation event.
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Affiliation(s)
| | - Nicola Piana Agostinetti
- Department of Earth and Environmental SciencesUniversity of Milano BicoccaMilanItaly
- Department of Geodynamics and SedimentologyUniversity of ViennaViennaAustria
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7
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Localized foundering of Indian lower crust in the India-Tibet collision zone. Proc Natl Acad Sci U S A 2020; 117:24742-24747. [PMID: 32958679 DOI: 10.1073/pnas.2000015117] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The deep structure of the continental collision between India and Asia and whether India's lower crust is underplated beneath Tibet or subducted into the mantle remain controversial. It is also unknown whether the active normal faults that facilitate orogen-parallel extension of Tibetan upper crust continue into the lower crust and upper mantle. Our receiver-function images collected parallel to the India-Tibet collision zone show the 20-km-thick Indian lower crust that underplates Tibet at 88.5-92°E beneath the Yarlung-Zangbo suture is essentially absent in the vicinity of the Cona-Sangri and Pumqu-Xainza grabens, demonstrating a clear link between upper-crustal and lower-crustal thinning. Satellite gravity data that covary with the thickness of Indian lower crust are consistent with the lower crust being only ∼30% eclogitized so gravitationally stable. Deep earthquakes coincide with Moho offsets and with lateral thinning of the Indian lower crust near the bottom of the partially eclogitized Indian lower crust, suggesting the Indian lower crust is locally foundering or stoping into the mantle. Loss of Indian lower crust by these means implies gravitational instability that can result from localized rapid eclogitization enabled by dehydration reactions in weakly hydrous mafic granulites or by volatile-rich asthenospheric upwelling directly beneath the two grabens. We propose that two competing processes, plateau formation by underplating and continental loss by foundering or stoping, are simultaneously operating beneath the collision zone.
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8
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Korenaga J. Crustal evolution and mantle dynamics through Earth history. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:rsta.2017.0408. [PMID: 30275159 PMCID: PMC6189559 DOI: 10.1098/rsta.2017.0408] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/31/2018] [Indexed: 05/13/2023]
Abstract
Resolving the modes of mantle convection through Earth history, i.e. when plate tectonics started and what kind of mantle dynamics reigned before, is essential to the understanding of the evolution of the whole Earth system, because plate tectonics influences almost all aspects of modern geological processes. This is a challenging problem because plate tectonics continuously rejuvenates Earth's surface on a time scale of about 100 Myr, destroying evidence for its past operation. It thus becomes essential to exploit indirect evidence preserved in the buoyant continental crust, part of which has survived over billions of years. This contribution starts with an in-depth review of existing models for continental growth. Growth models proposed so far can be categorized into three types: crust-based, mantle-based and other less direct inferences, and the first two types are particularly important as their difference reflects the extent of crustal recycling, which can be related to subduction. Then, a theoretical basis for a change in the mode of mantle convection in the Precambrian is reviewed, along with a critical appraisal of some popular notions for early Earth dynamics. By combining available geological and geochemical observations with geodynamical considerations, a tentative hypothesis is presented for the evolution of mantle dynamics and its relation to surface environment; the early onset of plate tectonics and gradual mantle hydration are responsible not only for the formation of continental crust but also for its preservation as well as its emergence above sea level. Our current understanding of various material properties and elementary processes is still too premature to build a testable, quantitative model for this hypothesis, but such modelling efforts could potentially transform the nature of the data-starved early Earth research by quantifying the extent of preservation bias.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.
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Affiliation(s)
- Jun Korenaga
- Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA
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9
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Chapman T, Clarke GL, Piazolo S, Daczko NR. Evaluating the importance of metamorphism in the foundering of continental crust. Sci Rep 2017; 7:13039. [PMID: 29026119 PMCID: PMC5638824 DOI: 10.1038/s41598-017-13221-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 09/20/2017] [Indexed: 11/17/2022] Open
Abstract
The metamorphic conditions and mechanisms required to induce foundering in deep arc crust are assessed using an example of representative lower crust in SW New Zealand. Composite plutons of Cretaceous monzodiorite and gabbro were emplaced at ~1.2 and 1.8 GPa are parts of the Western Fiordland Orthogneiss (WFO); examples of the plutons are tectonically juxtaposed along a structure that excised ~25 km of crust. The 1.8 GPa Breaksea Orthogneiss includes suitably dense minor components (e.g. eclogite) capable of foundering at peak conditions. As the eclogite facies boundary has a positive dP/dT, cooling from supra-solidus conditions (T > 950 ºC) at high-P should be accompanied by omphacite and garnet growth. However, a high monzodioritic proportion and inefficient metamorphism in the Breaksea Orthogneiss resulted in its positive buoyancy and preservation. Metamorphic inefficiency and compositional relationships in the 1.2 GPa Malaspina Pluton meant it was never likely to have developed densities sufficiently high to founder. These relationships suggest that the deep arc crust must have primarily involved significant igneous accumulation of garnet–clinopyroxene (in proportions >75%). Crustal dismemberment with or without the development of extensional shear zones is proposed to have induced foundering of excised cumulate material at P > 1.2 GPa.
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Affiliation(s)
- Timothy Chapman
- School of Geosciences, The University of Sydney, Sydney, NSW, 2006, Australia.
| | - Geoffrey L Clarke
- School of Geosciences, The University of Sydney, Sydney, NSW, 2006, Australia
| | - Sandra Piazolo
- ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia.,School of Earth and Environment, University of Leeds, Leeds, United Kingdom
| | - Nathan R Daczko
- ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia
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10
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Hamdy MM, Abd El-Wahed MA, Gamal El Dien H, Morishita T. Garnet hornblendite in the Meatiq Core Complex, Central Eastern Desert of Egypt: Implications for crustal thickening preceding the ∼600 Ma extensional regime in the Arabian-Nubian Shield. PRECAMBRIAN RESEARCH 2017; 298:593-614. [DOI: 10.1016/j.precamres.2017.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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11
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Cordillera Zealandia: A Mesozoic arc flare-up on the palaeo-Pacific Gondwana Margin. Sci Rep 2017; 7:261. [PMID: 28325934 PMCID: PMC5428235 DOI: 10.1038/s41598-017-00347-w] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 02/22/2017] [Indexed: 11/08/2022] Open
Abstract
Two geochemically and temporally distinct components of the Mesozoic Zealandia Cordilleran arc indicate a shift from low to high Sr/Y whole rock ratios at c. 130 Ma. Recent mapping and a reappraisal of published Sr-Nd data combined with new in-situ zircon Hf isotope analyses supports a genetic relationship between the two arc components. A reappraisal of geophysical, geochemical and P-T estimates demonstrates a doubling in thickness of the arc to at least 80 km at c. 130 Ma. Contemporaneously, magmatic addition rates shifted from ~14 km3/my per km of arc to a flare-up involving ~100 km3/my per km of arc. Excursions in Sr-Nd-Hf isotopic ratios of flare-up rocks highlight the importance of crust-dominated sources. This pattern mimics Cordilleran arcs of the Americas and highlights the importance of processes occurring in the upper continental plates of subduction systems that are incompletely reconciled with secular models for continental crustal growth.
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12
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Gonzalez-Ayala J, Calvo Hernández A, Roco JMM. From maximum power to a trade-off optimization of low-dissipation heat engines: Influence of control parameters and the role of entropy generation. Phys Rev E 2017; 95:022131. [PMID: 28297927 DOI: 10.1103/physreve.95.022131] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Indexed: 06/06/2023]
Abstract
For a low-dissipation heat engine model we present the role of the partial contact times and the total operational time as control parameters to switch from maximum power state to maximum Ω trade-off state. The symmetry of the dissipation coefficients may be used in the design of the heat engine to offer, in such switching, a suitable compromise between efficiency gain, power losses, and entropy change. Bounds for entropy production, efficiency, and power output are presented for transitions between both regimes. In the maximum power and maximum Ω trade-off cases the relevant space of parameters are analyzed together with the configuration of minimum entropy production. A detailed analysis of the parameter's space shows physically prohibited regions in which there is no longer a heat engine and another region that is physically well behaved but is not suitable for possible optimization criteria.
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Affiliation(s)
| | - A Calvo Hernández
- Departamento de Física Aplicada, Universidad de Salamanca, 37008 Salamanca, Spain
| | - J M M Roco
- Departamento de Física Aplicada and Instituto Universitario de Física Fundamental y Matemáticas (IUFFyM), Universidad de Salamanca, 37008 Salamanca, Spain
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13
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Abstract
Abstract
Subduction zones are tectonic expressions of convergent plate margins, where crustal rocks descend into and interact with the overlying mantle wedge. They are the geodynamic system that produces mafic arc volcanics above oceanic subduction zones but high- to ultrahigh-pressure metamorphic rocks in continental subduction zones. While the metamorphic rocks provide petrological records of orogenic processes when descending crustal rocks undergo dehydration and anataxis at forearc to subarc depths beneath the mantle wedge, the arc volcanics provide geochemical records of the mass transfer from the subducting slab to the mantle wedge in this period though the mantle wedge becomes partially melted at a later time. Whereas the mantle wedge overlying the subducting oceanic slab is of asthenospheric origin, that overlying the descending continental slab is of lithospheric origin, being ancient beneath cratons but juvenile beneath marginal arcs. In either case, the mantle wedge base is cooled down during the slab–wedge coupled subduction. Metamorphic dehydration is prominent during subduction of crustal rocks, giving rise to aqueous solutions that are enriched in fluid-mobile incompatible elements. Once the subducting slab is decoupled from the mantle wedge, the slab–mantle interface is heated by lateral incursion of the asthenospheric mantle to allow dehydration melting of rocks in the descending slab surface and the metasomatized mantle wedge base, respectively. Therefore, the tectonic regime of subduction zones changes in both time and space with respect to their structures, inputs, processes and products. Ophiolites record the tectonic conversion from seafloor spreading to oceanic subduction beneath continental margin, whereas ultrahigh-temperature metamorphic events mark the tectonic conversion from compression to extension in orogens.
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14
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15
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Continental crust formation at arcs, the arclogite “delamination” cycle, and one origin for fertile melting anomalies in the mantle. Sci Bull (Beijing) 2015. [DOI: 10.1007/s11434-015-0828-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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16
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Mougel B, Agranier A, Hemond C, Gente P. A highly unradiogenic lead isotopic signature revealed by volcanic rocks from the East Pacific Rise. Nat Commun 2014; 5:4474. [PMID: 25027032 DOI: 10.1038/ncomms5474] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Accepted: 06/20/2014] [Indexed: 11/09/2022] Open
Abstract
Radiogenic isotopes in oceanic basalts provide a window into the different geochemical components defining the composition of Earth's mantle. Here we report the discovery of a novel geochemical signature in volcanic glasses sampled at a sub-kilometre scale along the East Pacific Rise between 15°37'N and 15°47'N. The most striking aspect of this signature is its unradiogenic lead ((206)Pb/(204)Pb=17.49, (207)Pb/(204)Pb=15.46 and (208)Pb/(204)Pb=36.83). In conjunction with enriched Sr, Nd and Hf signatures, Pb isotopes depict mixing lines that trend away from any known mantle end-members. We suggest that this unradiogenic lead component sampled by magmatic melts corresponds to a novel upper mantle reservoir that should be considered in the Pb isotope budget of the bulk silicate Earth. Major, trace element and isotope compositions are suggestive of an ancient and lower continental origin for this unradiogenic lead component, possibly sulphide-bearing pyroxenites that were preserved even after prolonged stirring within the ambient upper mantle.
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Affiliation(s)
- Berengere Mougel
- Laboratoire Domaines Océaniques, UMR6538, IUEM, 29280 Plouzané, France
| | - Arnaud Agranier
- Laboratoire Domaines Océaniques, UMR6538, IUEM, 29280 Plouzané, France
| | - Christophe Hemond
- Laboratoire Domaines Océaniques, UMR6538, IUEM, 29280 Plouzané, France
| | - Pascal Gente
- Laboratoire Domaines Océaniques, UMR6538, IUEM, 29280 Plouzané, France
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Jagoutz O, Behn MD. Foundering of lower island-arc crust as an explanation for the origin of the continental Moho. Nature 2013; 504:131-4. [PMID: 24305163 DOI: 10.1038/nature12758] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Accepted: 10/03/2013] [Indexed: 11/09/2022]
Abstract
A long-standing theory for the genesis of continental crust is that it is formed in subduction zones. However, the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust. Accordingly, significant modifications of lower arc crust must occur, if continental crust is indeed formed from island arcs. Here we investigate how the seismic characteristics of arc crust are transformed into those of the continental crust by calculating the density and seismic structure of two exposed sections of island arc (Kohistan and Talkeetna). The Kohistan crustal section is negatively buoyant with respect to the underlying depleted upper mantle at depths exceeding 40 kilometres and is characterized by a steady increase in seismic velocity similar to that observed in active arcs. In contrast, the lower Talkeetna crust is density sorted, preserving only relicts (about ten to a hundred metres thick) of rock with density exceeding that of the underlying mantle. Specifically, the foundering of the lower Talkeetna crust resulted in the replacement of dense mafic and ultramafic cumulates by residual upper mantle, producing a sharp seismic discontinuity at depths of around 38 to 42 kilometres, characteristic of the continental Mohorovičić discontinuity (the Moho). Dynamic calculations indicate that foundering is an episodic process that occurs in most arcs with a periodicity of half a million to five million years. Moreover, because foundering will continue after arc magmatism ceases, this process ultimately results in the formation of the continental Moho.
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Affiliation(s)
- Oliver Jagoutz
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
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18
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CHENG S, ZHANG G, LI L. Lithospheric Electrical Structure of the Qinling Orogen and its Geodynamic Implication. ACTA ACUST UNITED AC 2013. [DOI: 10.1002/cjg2.3373] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Shunyou CHENG
- The Key Laboratory of Continental Dynamics, Ministry of Education, Department of Geology; Northwest University; Xi'an; 710069; China
| | - Guowei ZHANG
- The Key Laboratory of Continental Dynamics, Ministry of Education, Department of Geology; Northwest University; Xi'an; 710069; China
| | - Li LI
- Institute of Geophysical and Chemical Exploration; Ministry of National Land and Resources; Langfang; 065000; China
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19
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Lee CTA, Luffi P, Chin EJ, Bouchet R, Dasgupta R, Morton DM, Le Roux V, Yin QZ, Jin D. Copper systematics in arc magmas and implications for crust-mantle differentiation. Science 2012; 336:64-8. [PMID: 22491850 DOI: 10.1126/science.1217313] [Citation(s) in RCA: 381] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper's (Cu's) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust. Primary arc and mid-ocean ridge basalts have identical Cu contents, indicating that the redox states of primitive arc magmas are indistinguishable from that of mid-ocean ridge basalts. During magmatic differentiation, the Cu content of most arc magmas decreases markedly because of sulfide segregation. Because a similar depletion in Cu characterizes global continental crust, the formation of sulfide-bearing cumulates under reducing conditions may be a critical step in continent formation.
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Affiliation(s)
- Cin-Ty A Lee
- Department of Earth Science, Rice University, MS-126, 6100 Main Street, Houston, TX 77005, USA.
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20
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Constraints on continental crustal mass loss via chemical weathering using lithium and its isotopes. Proc Natl Acad Sci U S A 2011; 108:20873-80. [PMID: 22184221 DOI: 10.1073/pnas.1115671108] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chemical weathering, as well as physical erosion, changes the composition and shapes the surface of the continental crust. However, the amount of continental material that has been lost over Earth's history due to chemical weathering is poorly constrained. Using a mass balance model for lithium inputs and outputs from the continental crust, we find that the mass of continental crust that has been lost due to chemical weathering is at least 15% of the original mass of the juvenile continental crust, and may be as high as 60%, with a best estimate of approximately 45%. Our results suggest that chemical weathering and subsequent subduction of soluble elements have major impacts on both the mass and the compositional evolution of the continental crust.
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21
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Karlstrom L, Richards M. On the evolution of large ultramafic magma chambers and timescales for flood basalt eruptions. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jb008159] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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23
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Göğüş OH, Pysklywec RN. Near-surface diagnostics of dripping or delaminating lithosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005123] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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24
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Li ZXA, Lee CTA, Peslier AH, Lenardic A, Mackwell SJ. Water contents in mantle xenoliths from the Colorado Plateau and vicinity: Implications for the mantle rheology and hydration-induced thinning of continental lithosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005540] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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25
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Tatsumi Y, Shukuno H, Tani K, Takahashi N, Kodaira S, Kogiso T. Structure and growth of the Izu-Bonin-Mariana arc crust: 2. Role of crust-mantle transformation and the transparent Moho in arc crust evolution. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005121] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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Behn MD, Hirth G, Kelemen PB. Trench-Parallel Anisotropy Produced by Foundering of Arc Lower Crust. Science 2007; 317:108-11. [PMID: 17615354 DOI: 10.1126/science.1141269] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Many volcanic arcs display fast seismic shear-wave velocities parallel to the strike of the trench. This pattern of anisotropy is inconsistent with simple models of corner flow in the mantle wedge. Although several models, including slab rollback, oblique subduction, and deformation of water-rich olivine, have been proposed to explain trench-parallel anisotropy, none of these mechanisms are consistent with all observations. Instead, small-scale convection driven by the foundering of dense arc lower crust provides an explanation for the trench-parallel anisotropy, even in settings with orthogonal convergence and no slab rollback.
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Affiliation(s)
- Mark D Behn
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
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27
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Elkins-Tanton LT. Continental magmatism, volatile recycling, and a heterogeneous mantle caused by lithospheric gravitational instabilities. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2005jb004072] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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28
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Stern RJ. When and how did plate tectonics begin? Theoretical and empirical considerations. ACTA ACUST UNITED AC 2007. [DOI: 10.1007/s11434-007-0073-8] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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29
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Abstract
The continental crust covers nearly a third of the Earth's surface. It is buoyant--being less dense than the crust under the surrounding oceans--and is compositionally evolved, dominating the Earth's budget for those elements that preferentially partition into silicate liquid during mantle melting. Models for the differentiation of the continental crust can provide insights into how and when it was formed, and can be used to show that the composition of the basaltic protolith to the continental crust is similar to that of the average lower crust. From the late Archaean to late Proterozoic eras (some 3-1 billion years ago), much of the continental crust appears to have been generated in pulses of relatively rapid growth. Reconciling the sedimentary and igneous records for crustal evolution indicates that it may take up to one billion years for new crust to dominate the sedimentary record. Combining models for the differentiation of the crust and the residence time of elements in the upper crust indicates that the average rate of crust formation is some 2-3 times higher than most previous estimates.
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Affiliation(s)
- C J Hawkesworth
- Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.
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30
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Behn MD, Kelemen PB. Stability of arc lower crust: Insights from the Talkeetna arc section, south central Alaska, and the seismic structure of modern arcs. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006jb004327] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Mark D. Behn
- Department of Geology and Geophysics; Woods Hole Oceanographic Institution; Woods Hole Massachusetts USA
| | - Peter B. Kelemen
- Lamont Doherty Earth Observatory; Columbia University; Palisades New York USA
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Gao S, Rudnick RL, Yuan HL, Liu XM, Liu YS, Xu WL, Ling WL, Ayers J, Wang XC, Wang QH. Recycling lower continental crust in the North China craton. Nature 2005; 432:892-7. [PMID: 15602559 DOI: 10.1038/nature03162] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2004] [Accepted: 11/03/2004] [Indexed: 11/09/2022]
Abstract
Foundering of mafic lower continental crust into underlying convecting mantle has been proposed as one means to explain the unusually evolved chemical composition of Earth's continental crust, yet direct evidence of this process has been scarce. Here we report that Late Jurassic high-magnesium andesites, dacites and adakites (siliceous lavas with high strontium and low heavy-rare-earth element and yttrium contents) from the North China craton have chemical and petrographic features consistent with their origin as partial melts of eclogite that subsequently interacted with mantle peridotite. Similar features observed in adakites and some Archaean sodium-rich granitoids of the tonalite-trondhjemite-granodiorite series have been interpreted to result from interaction of slab melts with the mantle wedge. Unlike their arc-related counterparts, however, the Chinese magmas carry inherited Archaean zircons and have neodymium and strontium isotopic compositions overlapping those of eclogite xenoliths derived from the lower crust of the North China craton. Such features cannot be produced by crustal assimilation of slab melts, given the high Mg#, nickel and chromium contents of the lavas. We infer that the Chinese lavas derive from ancient mafic lower crust that foundered into the convecting mantle and subsequently melted and interacted with peridotite. We suggest that lower crustal foundering occurred within the North China craton during the Late Jurassic, and thus provides constraints on the timing of lithosphere removal beneath the North China craton.
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Affiliation(s)
- Shan Gao
- Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China.
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Zandt G, Gilbert H, Owens TJ, Ducea M, Saleeby J, Jones CH. Active foundering of a continental arc root beneath the southern Sierra Nevada in California. Nature 2004; 431:41-6. [PMID: 15343326 DOI: 10.1038/nature02847] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2004] [Accepted: 07/12/2004] [Indexed: 11/09/2022]
Abstract
Seismic data provide images of crust-mantle interactions during ongoing removal of the dense batholithic root beneath the southern Sierra Nevada mountains in California. The removal appears to have initiated between 10 and 3 Myr ago with a Rayleigh-Taylor-type instability, but with a pronounced asymmetric flow into a mantle downwelling (drip) beneath the adjacent Great Valley. A nearly horizontal shear zone accommodated the detachment of the ultramafic root from its granitoid batholith. With continuing flow into the mantle drip, viscous drag at the base of the remaining approximately 35-km-thick crust has thickened the crust by approximately 7 km in a narrow welt beneath the western flank of the range. Adjacent to the welt and at the top of the drip, a V-shaped cone of crust is being dragged down tens of kilometres into the core of the mantle drip, causing the disappearance of the Moho in the seismic images. Viscous coupling between the crust and mantle is therefore apparently driving present-day surface subsidence.
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Affiliation(s)
- George Zandt
- Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA.
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34
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Escrig S, Capmas F, Dupré B, Allègre CJ. Osmium isotopic constraints on the nature of the DUPAL anomaly from Indian mid-ocean-ridge basalts. Nature 2004; 431:59-63. [PMID: 15343331 DOI: 10.1038/nature02904] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Accepted: 07/30/2004] [Indexed: 11/09/2022]
Abstract
The isotopic compositions of mid-ocean-ridge basalts (MORB) from the Indian Ocean have led to the identification of a large-scale isotopic anomaly relative to Pacific and Atlantic ocean MORB. Constraining the origin of this so-called DUPAL anomaly may lead to a better understanding of the genesis of upper-mantle heterogeneity. Previous isotopic studies have proposed recycling of ancient subcontinental lithospheric mantle or sediments with oceanic crust to be responsible for the DUPAL signature. Here we report Os, Pb, Sr and Nd isotopic compositions of Indian MORB from the Central Indian ridge, the Rodriguez triple junction and the South West Indian ridge. All measured samples have higher (187)Os/(188)Os ratios than the depleted upper-mantle value and Pb, Sr and Nd isotopic compositions that imply the involvement of at least two distinct enriched components in the Indian upper-mantle. Using isotopic and geodynamical arguments, we reject both subcontinental lithospheric mantle and recycled sediments with oceanic crust as the cause of the DUPAL anomaly. Instead, we argue that delamination of lower continental crust may explain the DUPAL isotopic signature of Indian MORB.
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Affiliation(s)
- S Escrig
- Laboratoire de Géochimie et Cosmochimie, UMR 7579 CNRS, Institut de Physique du Globe de Paris, Université Denis Diderot (Paris 7), France.
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35
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Boyd OS, Jones CH, Sheehan AF. Foundering Lithosphere Imaged Beneath the Southern Sierra Nevada, California, USA. Science 2004; 305:660-2. [PMID: 15286370 DOI: 10.1126/science.1099181] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Seismic tomography reveals garnet-rich crust and mantle lithosphere descending into the upper mantle beneath the southeastern Sierra Nevada. The descending lithosphere consists of two layers: an iron-rich eclogite above a magnesium-rich garnet peridotite. These results place descending eclogite above and east of high P wave speed material previously imaged beneath the southern Great Valley, suggesting a previously unsuspected coherence in the lithospheric removal process.
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Affiliation(s)
- Oliver S Boyd
- Department of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Avenue, Boulder, CO 80309-0399, USA.
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36
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37
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Clift PD, Schouten H, Draut AE. A general model of arc-continent collision and subduction polarity reversal from Taiwan and the Irish Caledonides. ACTA ACUST UNITED AC 2003. [DOI: 10.1144/gsl.sp.2003.219.01.04] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractThe collision of the Luzon Arc with southern China represents the best example of arc-continent collision in the modern oceans, and compares closely with the Early Ordovician accretion of the Lough Nafooey arc of Connemara, Ireland, to the passive margin of Laurentia. We propose a general model for steady-state arc-continent collision in which arc crust is progressively added to a passive margin during a process of compression, metamorphism and magmatism lasting 3–10 Ma at any one location on the margin. Depending on the obliquity of the angle of collision, the timing of active collision may be diachronous and long-lived along the margin. Magmatism accompanying accretion can be more enriched in incompatible trace elements than average continental crust, contrasting with more depleted magmatism prior to collision. Accretion of a mixture of depleted and enriched arc lithologies to the continental margin allows the continental crust to grow through time by arc-passive margin collision events. During the collision the upper and middle arc crust are detached from the depleted ultramafic lower crust, which is subducted along with the mantle lithosphere on which the arc was founded. Rapid (2–3 Ma) exhumation and gravitational collapse of the collisional orogen forms the Okinawa and South Mayo Troughs in Taiwan and western Ireland, respectively. These basins are filled by detritus eroded from the adjacent collision zone. During subsequent subduction polarity reversal, continuous tearing and retreat of the oceanic lithosphere along the former continent-ocean transition provides space for the new subducting oceanic plate to descend without need for breaking of the original slab.
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Affiliation(s)
- Peter D. Clift
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA
| | - Hans Schouten
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA
| | - Amy E. Draut
- Woods Hole Oceanographic Institution-Massachusetts Institute of Technology Joint Program in Oceanography
Woods Hole, MA 02543, USA
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38
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Kelemen PB, Yogodzinski GM, Scholl DW. Along-strike variation in the Aleutian Island Arc: Genesis of high Mg# andesite and implications for continental crust. INSIDE THE SUBDUCTION FACTORY 2003. [DOI: 10.1029/138gm11] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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39
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Larter RD, Vanneste LE, Morris P, Smythe DK. Structure and tectonic evolution of the South Sandwich arc. ACTA ACUST UNITED AC 2003. [DOI: 10.1144/gsl.sp.2003.219.01.13] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractDetailed analysis of marine magnetic profiles from the western part of the East Scotia Sea confirms continuous, organized back-arc spreading since at least 15 Ma ago. In the eastern part of the East Scotia Sea, the South Sandwich arc lies on crust that formed at the back-arc spreading centre since 10 Ma ago, so older back-arc crust forms the basement of the present inner forearc. Interpretations of two multichannel seismic reflection profiles reveal the main structural components of the arc at shallow depth, including evidence of trench-normal extension in the mid-forearc, and other features consistent with ongoing subduction erosion. The seismic profile interpretations have been used to constrain simple two-dimensional gravity models. The models were designed to provide constraints on the maximum possible thickness of the arc crust, and it is concluded that this is 20 and 19.2 km on the northern and southern lines, respectively. On the northern line the models indicate that the forearc crust cannot be much thicker than normal oceanic crust. Even with such thin crust, however, the magmatic growth rate implied by the cross-section of the arc crust is within the range recently estimated for two other arcs that have been built over a much longer interval.
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Affiliation(s)
- Robert D. Larter
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Lieve E. Vanneste
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Peter Morris
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - David K. Smythe
- Department of Geology and Applied Geology, University of Glasgow
UK
- GeoLogica Ltd
191 Wilton Street, Glasgow G20 6DF, UK
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40
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Ducea MN. Constraints on the bulk composition and root foundering rates of continental arcs: A California arc perspective. ACTA ACUST UNITED AC 2002. [DOI: 10.1029/2001jb000643] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Mihai N. Ducea
- Department of Geosciences; University of Arizona; Tucson Arizona USA
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41
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Abstract
When mountains form through the collision of lithospheric plates, uplift of the Earth's surface is accompanied by thickening of the crust, and the buoyancy of these deep crustal roots (relative to the surrounding mantle) is thought to contribute to the support of mountain topography. Once active tectonism ceases, continuing erosion will progressively wear away surface relief. Here I provide new constraints on how crustal roots respond to erosional unloading over very long timescales. In old collisional mountain belts, ratios of surface relief to the thickness of the underlying crustal root are observed to be smaller than in young mountains. On the basis of gravity data, this trend is best explained by a decrease in the buoyancy of the crustal root with greater age since the most recent mountain-building episode which is consistent with metamorphic reactions produced by long-term cooling. An approximate balance between mountain and root mass anomalies suggests that the continental lithosphere remains weak enough to permit exhumation of crustal roots in response to surface erosion for hundreds of millions of years. The amount of such uplift, however, appears to be significantly reduced by progressive loss of root buoyancy.
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Affiliation(s)
- Karen M Fischer
- Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA.
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