1
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Gernon TM, Hincks TK, Brune S, Braun J, Jones SM, Keir D, Cunningham A, Glerum A. Coevolution of craton margins and interiors during continental break-up. Nature 2024; 632:327-335. [PMID: 39112622 PMCID: PMC11306106 DOI: 10.1038/s41586-024-07717-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Accepted: 06/13/2024] [Indexed: 08/10/2024]
Abstract
Many cratonic continental fragments dispersed during the rifting and break-up of Gondwana are bound by steep topographic landforms known as 'great escarpments'1-4, which rim elevated plateaus in the craton interior5,6. In terms of formation, escarpments and plateaus are traditionally considered distinct owing to their spatial separation, occasionally spanning more than a thousand kilometres. Here we integrate geological observations, statistical analysis, geodynamic simulations and landscape-evolution models to develop a physical model that mechanistically links both phenomena to continental rifting. Escarpments primarily initiate at rift-border faults and slowly retreat at about 1 km Myr-1 through headward erosion. Simultaneously, rifting generates convective instabilities in the mantle7-10 that migrate cratonward at a faster rate of about 15-20 km Myr-1 along the lithospheric root, progressively removing cratonic keels11, driving isostatic uplift of craton interiors and forming a stable, elevated plateau. This process forces a synchronized wave of denudation, documented in thermochronology studies, which persists for tens of millions of years and migrates across the craton at a comparable or slower pace. We interpret the observed sequence of rifting, escarpment formation and exhumation of craton interiors as an evolving record of geodynamic mantle processes tied to continental break-up, upending the prevailing notion of cratons as geologically stable terrains.
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Affiliation(s)
- Thomas M Gernon
- School of Ocean & Earth Science, University of Southampton, Southampton, UK.
| | - Thea K Hincks
- School of Ocean & Earth Science, University of Southampton, Southampton, UK
| | - Sascha Brune
- Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Potsdam, Germany
- University of Potsdam, Potsdam, Germany
| | - Jean Braun
- Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Potsdam, Germany
- University of Potsdam, Potsdam, Germany
| | - Stephen M Jones
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Derek Keir
- School of Ocean & Earth Science, University of Southampton, Southampton, UK
- Dipartimento di Scienze della Terra, Universita degli Studi di Firenze, Florence, Italy
| | - Alice Cunningham
- School of Ocean & Earth Science, University of Southampton, Southampton, UK
| | - Anne Glerum
- Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Potsdam, Germany
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2
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Zhang K, Liao J, Gerya T. Onset of double subduction controls plate motion reorganisation. Nat Commun 2024; 15:1513. [PMID: 38374036 PMCID: PMC10876953 DOI: 10.1038/s41467-024-44764-8] [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: 03/18/2023] [Accepted: 01/02/2024] [Indexed: 02/21/2024] Open
Abstract
Face-to-face double subduction systems, in which two oceanic plates subduct toward each other, are essential elements of plate tectonics. Two subduction zones in such systems are typically uneven in age and their spatially and temporally variable dynamics remain enigmatic. Here, with 2D numerical modelling, we demonstrate that the onset of the younger subduction zone strongly changes the dynamics of the older subduction zone. The waxing younger subduction may gradually absorb plate convergence from the older one, resulting in older subduction waning featured by the dramatic decrease in subduction rate and trench retreat. The dynamical transformation of subduction predominance alters the intraplate stress and mantle flow, regulating the relative motion among the three different plates. The process of waxing and waning of subduction zones controls plate motion reorganisation, providing a reference to interpret the past, present, and future evolution of several key double subduction regions found on the modern Earth.
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Affiliation(s)
- Kuidi Zhang
- School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou, China
| | - Jie Liao
- School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou, China.
- Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China.
- Guangdong Provincial Key Lab of Geodynamics and Geohazards, Guangzhou, China.
| | - Taras Gerya
- Department of Earth Sciences, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland
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3
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Timmerman S, Stachel T, Koornneef JM, Smit KV, Harlou R, Nowell GM, Thomson AR, Kohn SC, Davies JHFL, Davies GR, Krebs MY, Zhang Q, Milne SEM, Harris JW, Kaminsky F, Zedgenizov D, Bulanova G, Smith CB, Cabral Neto I, Silveira FV, Burnham AD, Nestola F, Shirey SB, Walter MJ, Steele A, Pearson DG. Sublithospheric diamond ages and the supercontinent cycle. Nature 2023; 623:752-756. [PMID: 37853128 PMCID: PMC10665200 DOI: 10.1038/s41586-023-06662-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Accepted: 09/20/2023] [Indexed: 10/20/2023]
Abstract
Subduction related to the ancient supercontinent cycle is poorly constrained by mantle samples. Sublithospheric diamond crystallization records the release of melts from subducting oceanic lithosphere at 300-700 km depths1,2 and is especially suited to tracking the timing and effects of deep mantle processes on supercontinents. Here we show that four isotope systems (Rb-Sr, Sm-Nd, U-Pb and Re-Os) applied to Fe-sulfide and CaSiO3 inclusions within 13 sublithospheric diamonds from Juína (Brazil) and Kankan (Guinea) give broadly overlapping crystallization ages from around 450 to 650 million years ago. The intracratonic location of the diamond deposits on Gondwana and the ages, initial isotopic ratios, and trace element content of the inclusions indicate formation from a peri-Gondwanan subduction system. Preservation of these Neoproterozoic-Palaeozoic sublithospheric diamonds beneath Gondwana until its Cretaceous breakup, coupled with majorite geobarometry3,4, suggests that they accreted to and were retained in the lithospheric keel for more than 300 Myr during supercontinent migration. We propose that this process of lithosphere growth-with diamonds attached to the supercontinent keel by the diapiric uprise of depleted buoyant material and pieces of slab crust-could have enhanced supercontinent stability.
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Affiliation(s)
- Suzette Timmerman
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
- Institute for Geological Sciences, University of Bern, Bern, Switzerland.
| | - Thomas Stachel
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
| | | | - Karen V Smit
- School of Geosciences, University of Witwatersrand, Johannesburg, South Africa
| | - Rikke Harlou
- Department of Earth Sciences, University of Durham, Durham, UK
| | - Geoff M Nowell
- Department of Earth Sciences, University of Durham, Durham, UK
| | - Andrew R Thomson
- Department of Earth Sciences, University College London, London, UK
| | - Simon C Kohn
- School of Earth Sciences, University of Bristol, Bristol, UK
| | - Joshua H F L Davies
- Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, Montreal, Quebec, Canada
| | - Gareth R Davies
- Faculty of Sciences, Vrije Universiteit, Amsterdam, The Netherlands
| | - Mandy Y Krebs
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Qiwei Zhang
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Sarah E M Milne
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Jeffrey W Harris
- School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
| | - Felix Kaminsky
- V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russian Federation
| | - Dmitry Zedgenizov
- A. N. Zavaritsky Institute of Geology and Geochemistry, Russian Academy of Sciences, Ekaterinburg, Russian Federation
| | - Galina Bulanova
- School of Earth Sciences, University of Bristol, Bristol, UK
| | - Chris B Smith
- School of Earth Sciences, University of Bristol, Bristol, UK
| | | | | | - Antony D Burnham
- Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory, Australia
| | | | - Steven B Shirey
- Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
| | - Michael J Walter
- Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
| | - Andrew Steele
- Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
| | - D Graham Pearson
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
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4
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Gernon TM, Jones SM, Brune S, Hincks TK, Palmer MR, Schumacher JC, Primiceri RM, Field M, Griffin WL, O'Reilly SY, Keir D, Spencer CJ, Merdith AS, Glerum A. Rift-induced disruption of cratonic keels drives kimberlite volcanism. Nature 2023; 620:344-350. [PMID: 37495695 PMCID: PMC10727985 DOI: 10.1038/s41586-023-06193-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Accepted: 05/10/2023] [Indexed: 07/28/2023]
Abstract
Kimberlites are volatile-rich, occasionally diamond-bearing magmas that have erupted explosively at Earth's surface in the geologic past1-3. These enigmatic magmas, originating from depths exceeding 150 km in Earth's mantle1, occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity4. Whether their mobilization is driven by mantle plumes5 or by mechanical weakening of cratonic lithosphere4,6 remains unclear. Here we show that most kimberlites spanning the past billion years erupted about 30 million years (Myr) after continental breakup, suggesting an association with rifting processes. Our dynamical and analytical models show that physically steep lithosphere-asthenosphere boundaries (LABs) formed during rifting generate convective instabilities in the asthenosphere that slowly migrate many hundreds to thousands of kilometres inboard of rift zones. These instabilities endure many tens of millions of years after continental breakup and destabilize the basal tens of kilometres of the cratonic lithosphere, or keel. Displaced keel is replaced by a hot, upwelling mixture of asthenosphere and recycled volatile-rich keel in the return flow, causing decompressional partial melting. Our calculations show that this process can generate small-volume, low-degree, volatile-rich melts, closely matching the characteristics expected of kimberlites1-3. Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles through progressive disruption of cratonic keels.
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Affiliation(s)
- Thomas M Gernon
- School of Ocean and Earth Science, University of Southampton, Southampton, UK.
| | - Stephen M Jones
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Sascha Brune
- Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Potsdam, Germany
- University of Potsdam, Potsdam-Golm, Germany
| | - Thea K Hincks
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
| | - Martin R Palmer
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
| | | | - Rebecca M Primiceri
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
| | | | - William L Griffin
- GEMOC ARC National Key Centre, Department of Earth and Environmental Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Suzanne Y O'Reilly
- GEMOC ARC National Key Centre, Department of Earth and Environmental Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Derek Keir
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
- Dipartimento di Scienze della Terra, Universita degli Studi di Firenze, Florence, Italy
| | - Christopher J Spencer
- Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario, Canada
| | | | - Anne Glerum
- Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, Potsdam, Germany
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5
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Westall F, Brack A, Fairén AG, Schulte MD. Setting the geological scene for the origin of life and continuing open questions about its emergence. FRONTIERS IN ASTRONOMY AND SPACE SCIENCES 2023; 9:1095701. [PMID: 38274407 PMCID: PMC7615569 DOI: 10.3389/fspas.2022.1095701] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/27/2024]
Abstract
The origin of life is one of the most fundamental questions of humanity. It has been and is still being addressed by a wide range of researchers from different fields, with different approaches and ideas as to how it came about. What is still incomplete is constrained information about the environment and the conditions reigning on the Hadean Earth, particularly on the inorganic ingredients available, and the stability and longevity of the various environments suggested as locations for the emergence of life, as well as on the kinetics and rates of the prebiotic steps leading to life. This contribution reviews our current understanding of the geological scene in which life originated on Earth, zooming in specifically on details regarding the environments and timescales available for prebiotic reactions, with the aim of providing experimenters with more specific constraints. Having set the scene, we evoke the still open questions about the origin of life: did life start organically or in mineralogical form? If organically, what was the origin of the organic constituents of life? What came first, metabolism or replication? What was the time-scale for the emergence of life? We conclude that the way forward for prebiotic chemistry is an approach merging geology and chemistry, i.e., far-from-equilibrium, wet-dry cycling (either subaerial exposure or dehydration through chelation to mineral surfaces) of organic reactions occurring repeatedly and iteratively at mineral surfaces under hydrothermal-like conditions.
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Affiliation(s)
| | - André Brack
- Centre de Biophysique Moléculaire, CNRS, Orléans, France
| | - Alberto G. Fairén
- Centro de Astrobiología (CAB, CSIC-INTA), Madrid, Spain
- Cornell University, Ithaca, NY, United States
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6
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Abstract
Continental, orogenic, and oceanic lithospheric mantle embeds sizeable parcels of exotic cratonic lithospheric mantle (CLM) derived from distant, unrelated sources. This hints that CLM recycling into the mantle and its eventual upwelling and relamination at the base of younger plates contribute to the complex structure of the growing lithosphere. Here, we use numerical modeling to investigate the fate and survival of recycled CLM in the ambient mantle and test the viability of CLM relamination under Hadean to present-day mantle temperature conditions and its role in early lithosphere evolution. We show that the foundered CLM is partially mixed and homogenized in the ambient mantle; then, as thermal negative buoyancy vanishes, its long-lasting compositional buoyancy drives upwelling, relaminating unrelated growing lithospheric plates and contributing to differentiation under cratonic, orogenic, and oceanic regions. Parts of the CLM remain in the mantle as diffused depleted heterogeneities at multiple scales, which can survive for billions of years. Relamination is maximized for high depletion degrees and mantle temperatures compatible with the early Earth, leading to the upwelling and underplating of large volumes of foundered CLM, a process we name massive regional relamination (MRR). MRR explains the complex source, age, and depletion heterogeneities found in ancient cratonic lithospheric mantle, suggesting this may have been a key component of the construction of continents in the early Earth.
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7
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Oxygen isotope (δ 18O, Δ' 17O) insights into continental mantle evolution since the Archean. Nat Commun 2022; 13:3779. [PMID: 35788136 PMCID: PMC9253152 DOI: 10.1038/s41467-022-31586-9] [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: 01/28/2022] [Accepted: 06/22/2022] [Indexed: 11/28/2022] Open
Abstract
Oxygen isotopic ratios are largely homogenous in the bulk of Earth’s mantle but are strongly fractionated near the Earth’s surface, thus these are robust indicators of recycling of surface materials to the mantle. Here we document a subtle but significant ~0.2‰ temporal decrease in δ18O in the shallowest continental lithospheric mantle since the Archean, no change in Δ′17O is observed. Younger samples document a decrease and greater heterogeneity of δ18O due to the development and progression of plate tectonics and subduction. We posit that δ18O in the oldest Archean samples provides the best δ18O estimate for the Earth of 5.37‰ for olivine and 5.57‰ for bulk peridotite, values that are comparable to lunar rocks as the moon did not have plate tectonics. Given the large volume of the continental lithospheric mantle, even small decreases in its δ18O may explain the increasing δ18O of the continental crust since oxygen is progressively redistributed by fluids between these reservoirs via high-δ18O sediment accretion and low-δ18O mantle in subduction zones. The 18 O/16 O ratio of the subcontinental mantle has decreased by 0.2‰, while crustal values increased by 4‰ via fluid transfer since the Archean due to the initiation of plate tectonics and subduction, in line with the crust-upper mantle mass balance
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8
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Perchuk AL, Gerya TV, Zakharov VS, Griffin WL. Depletion of the upper mantle by convergent tectonics in the Early Earth. Sci Rep 2021; 11:21489. [PMID: 34728677 PMCID: PMC8563749 DOI: 10.1038/s41598-021-00837-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2021] [Accepted: 10/12/2021] [Indexed: 11/09/2022] Open
Abstract
Partial melting of mantle peridotites at spreading ridges is a continuous global process that forms the oceanic crust and refractory, positively buoyant residues (melt-depleted mantle peridotites). In the modern Earth, these rocks enter subduction zones as part of the oceanic lithosphere. However, in the early Earth, the melt-depleted peridotites were 2-3 times more voluminous and their role in controlling subduction regimes and the composition of the upper mantle remains poorly constrained. Here, we investigate styles of lithospheric tectonics, and related dynamics of the depleted mantle, using 2-D geodynamic models of converging oceanic plates over the range of mantle potential temperatures (Tp = 1300-1550 °C, ∆T = T - Tmodern = 0-250 °C) from the Archean to the present. Numerical modeling using prescribed plate convergence rates reveals that oceanic subduction can operate over this whole range of temperatures but changes from a two-sided regime at ∆T = 250 °C to one-sided at lower mantle temperatures. Two-sided subduction creates V-shaped accretionary terrains up to 180 km thick, composed mainly of highly hydrated metabasic rocks of the subducted oceanic crust, decoupled from the mantle. Partial melting of the metabasic rocks and related formation of sodic granitoids (Tonalite-Trondhjemite-Granodiorite suites, TTGs) does not occur until subduction ceases. In contrast, one sided-subduction leads to volcanic arcs with or without back-arc basins. Both subduction regimes produce over-thickened depleted upper mantle that cannot subduct and thus delaminates from the slab and accumulates under the oceanic lithosphere. The higher the mantle temperature, the larger the volume of depleted peridotites stored in the upper mantle. Extrapolation of the modeling results reveals that oceanic plate convergence at ∆T = 200-250 °C might create depleted peridotites (melt extraction of > 20%) constituting more than half of the upper mantle over relatively short geological times (~ 100-200 million years). This contrasts with the modeling results at modern mantle temperatures, where the amount of depleted peridotites in the upper mantle does not increase significantly with time. We therefore suggest that the bulk chemical composition of upper mantle in the Archean was much more depleted than the present mantle, which is consistent with the composition of the most ancient lithospheric mantle preserved in cratonic keels.
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Affiliation(s)
- A L Perchuk
- Faculty of Geology, Lomonosov Moscow State University, Moscow, 119234, Russia.
- Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, 142432, Russia.
| | - T V Gerya
- Department of Earth Sciences, Swiss Federal Institute of Technology Zurich, Sonneggstrasse 5, 8092, Zurich, Switzerland
| | - V S Zakharov
- Faculty of Geology, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - W L Griffin
- Australian Research Council Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Macquarie University, Sydney, NSW, Australia
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9
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Abstract
The formation and preservation of cratons-the oldest parts of the continents, comprising over 60 per cent of the continental landmass-remains an enduring problem. Key to craton development is how and when the thick strong mantle roots that underlie these regions formed and evolved. Peridotite melting residues forming cratonic lithospheric roots mostly originated via relatively low-pressure melting and were subsequently transported to greater depth by thickening produced by lateral accretion and compression. The longest-lived cratons were assembled during Mesoarchean and Palaeoproterozoic times, creating the stable mantle roots 150 to 250 kilometres thick that are critical to preserving Earth's early continents and central to defining the cratons, although we extend the definition of cratons to include extensive regions of long-stable Mesoproterozoic crust also underpinned by thick lithospheric roots. The production of widespread thick and strong lithosphere via the process of orogenic thickening, possibly in several cycles, was fundamental to the eventual emergence of extensive continental landmasses-the cratons.
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10
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Liu J, Pearson DG, Wang LH, Mather KA, Kjarsgaard BA, Schaeffer AJ, Irvine GJ, Kopylova MG, Armstrong JP. Plume-driven recratonization of deep continental lithospheric mantle. Nature 2021; 592:732-736. [PMID: 33911271 DOI: 10.1038/s41586-021-03395-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 02/25/2021] [Indexed: 11/09/2022]
Abstract
Cratons are Earth's ancient continental land masses that remain stable for billions of years. The mantle roots of cratons are renowned as being long-lived, stable features of Earth's continents, but there is also evidence of their disruption in the recent1-6 and more distant7-9 past. Despite periods of lithospheric thinning during the Proterozoic and Phanerozoic eons, the lithosphere beneath many cratons seems to always 'heal', returning to a thickness of 150 to 200 kilometres10-12; similar lithospheric thicknesses are thought to have existed since Archaean times3,13-15. Although numerous studies have focused on the mechanism for lithospheric destruction2,5,13,16-19, the mechanisms that recratonize the lithosphere beneath cratons and thus sustain them are not well understood. Here we study kimberlite-borne mantle xenoliths and seismology across a transect of the cratonic lithosphere of Arctic Canada, which includes a region affected by the Mackenzie plume event 1.27 billion years ago20. We demonstrate the important role of plume upwelling in the destruction and recratonization of roughly 200-kilometre-thick cratonic lithospheric mantle in the northern portion of the Slave craton. Using numerical modelling, we show how new, buoyant melt residues produced by the Mackenzie plume event are captured in a region of thinned lithosphere between two thick cratonic blocks. Our results identify a process by which cratons heal and return to their original lithospheric thickness after substantial disruption of their roots. This process may be widespread in the history of cratons and may contribute to how cratonic mantle becomes a patchwork of mantle peridotites of different age and origin.
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Affiliation(s)
- Jingao Liu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing), Beijing, China. .,Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
| | - D Graham Pearson
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
| | | | - Kathy A Mather
- Department of Earth Sciences, Durham University, Durham, UK
| | | | | | | | - Maya G Kopylova
- Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada
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