NERC Isotope Geosciences Laboratory

Keyworth, United Kingdom

NERC Isotope Geosciences Laboratory

Keyworth, United Kingdom
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News Article | May 12, 2017
Site: www.eurekalert.org

"This new research overturns our understanding of how the inside of the Earth convects and stirs, and how it is divided up, and for the first time explains observations that were first noted in the late 1980s" - Dr Tiffany Barry, University of Leicester, Department of Geology Images of the research and Dr Tiffany Barry available here: https:/ New insights into the convection patterns of the Earth's mantle and its chemical makeup have been revealed by a researcher from the University of Leicester. The new findings suggest that the mantle does not flow ubiquitously, as has been previously thought - and that it is instead divided into two very large domains that convect only within themselves, with little evidence of them mixing together. The research, led by Dr Tiffany Barry from the University of Leicester, Department of Geology and published in the journal Scientific Reports, Nature, suggests that one of these domains is found under the Pacific Ocean while the other exists outside of it. The research suggests that upper mantle material flows to lower parts of the mantle when it reaches a subduction zone, where one tectonic plate descends beneath another one. This descending slab of material acts as a sort of curtain, preventing upper mantle material mixing all the way around the globe and keeping the two domains separate. Dr Barry explained: "One of the ways our planet is unique is in the amazing way it has mobile plates at the surface that move and jostle about over time. This movement of the plates results in the process we call plate tectonics, and no other planet we know shows evidence of this process. Why or how plate tectonics started on this planet is not understood, but it has been utterly essential in the production of the crust and oceans that we recognise as Earth today. What is also not well constrained is what effect plate tectonics has on the internal workings of the Earth. "We have found that when mantle material reaches the bottom of the mantle, at the outer core, it does not spread out and go anywhere around the core, but instead returns to the same hemisphere of the globe from where it came. We have modelled this dominantly up-down motion of convection and found that it can persist for 100's millions of years. "On the basis of past plate motions and geochemical evidence, we speculate that this process of mantle convection could have been a dominant process since at least 550 million years ago, and potentially since the start of plate tectonics." The researchers combined spherical numerical computer models (3D finite element modelling) with the best available reconstructions of how Earth's plates have moved over the past 200 million years to track mathematical particles placed at different depths of the modelled mantle. With these models they examined where the mantle freely moves to during the history of plates moving around at the surface. Having tracked where particles flow in the models, the team then examined chemical isotope evidence from past ocean basins, which are a good analogy for the composition of the upper mantle in the past. With this data they were able to test whether former ocean basins, that are no longer present, had the same or different composition to subsequent basins that formed geographically in the same region of the globe. Dr Barry added: "I'm incredibly excited by this work; it has been a research question I've been pondering for nearly two decades. It feels like a real privilege to have been able to piece together a robust and convincing model that can explain the feature of the chemical differences in ocean floor crust. "This new research overturns our understanding of how the inside of the earth convects and stirs, and how it is divided up, and for the first time explains observations that were first noted in the late 1980s." The research was conducted with Professor Huw Davies of Cardiff University and Dr Martin Wolstencroft of JBA Risk Management, Skipton (formerly of Cardiff University) and Dr Ian Millar at the NERC Isotope Geosciences Laboratory at the British Geological Survey in Keyworth. The paper 'Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry' is available in Nature at the following link: http://www.


Slagstad T.,Geological Survey of Norway | Roberts N.M.W.,NERC Isotope Geosciences Laboratory | Kulakov E.,University of Oslo
Gondwana Research | Year: 2017

The Sveconorwegian orogeny in SW Baltica comprised a series of geographically and tectonically discrete events between 1140 and 920 Ma. Thrusting and high-grade metamorphism at 1140–1080 Ma in central parts of the orogen were followed by arc magmatism and ultra-high-temperature metamorphism at 1060–920 Ma in the westernmost part of the orogen. In the eastern part of the orogen, crustal thickening and high-pressure metamorphism took place at 1050 in one terrane and at 980 Ma in another. These discrete tectonothermal events are incompatible with an evolution resulting from collision with another major, continental landmass, and better explained as accretion and re-amalgamation of fragmented and attenuated crustal blocks of the SW Baltica margin behind an evolving continental-margin arc. In contrast, the coeval, along-strike Grenvillian orogeny is typically ascribed to long-lived collision with Amazonia. Here we argue that coeval, but tectonically different events in the Sveconorwegian and Grenville orogens may be linked through the behavior of the Amazonia plate. Subduction of Amazonian oceanic crust, and consequent slab pull, beneath the Sveconorwegian may have driven long-lived collision in the Grenville. Conversely, the development of a major orogenic plateau in the Grenville may have slowed convergence, thereby affecting the rate of oceanic subduction and thus orogenic evolution in the Sveconorwegian. Convergence ceased in the Grenville at ca. 980 Ma, in contrast to the Sveconorwegian where convergence continued until ca. 920 Ma, and must have been accommodated elsewhere along the Grenville–Amazonia segment of the margin, for example in the Goiás Magmatic Arc which had been established along the eastern Amazonian margin by 930 Ma. Our model shows how contrasting but coeval orogenic behavior can be linked through geodynamic coupling along and across tectonic plates. © 2017


Chambers J.,University of St. Andrews | Parrish R.,University of Leicester | Parrish R.,NERC Isotope Geosciences Laboratory | Argles T.,Open University Milton Keynes | And 2 more authors.
Tectonics | Year: 2011

In easternmost Bhutan the South Tibetan detachment (STD) is a ductile shear zone that juxtaposes the Radi (or Sakteng) klippe of the Tethyan Sedimentary Series from underlying high-grade Greater Himalayan rocks. In situ LA-ICPMS U-Th-Pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the STD within the shear zone at the base of the klippe, constrains north vergent normal shear to between 25 and 20 Ma. Coeval thrusting on the Main Central Thrust during this time supports a phase of channel flow-viscous wedge model activity, lasting only ∼3 Ma. Geochronologic data from the eastern Himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the Late Oligocene through to the Late Miocene, switching from channel flow-viscous wedge behavior to critical taper-frictional wedge behavior, each phase lasting approximately only 2 to 5 Ma. The tectonic evolution of the eastern Himalaya is comparable to central and western Himalayan tectonics during the Early Miocene, but during the Middle Miocene metamorphism and magmatism in the eastern Himalaya migrated toward the orogenic hinterland, a process not widely documented elsewhere in the Himalaya, thus highlighting the need for an orogenic model in three spatial dimensions. Copyright 2011 by the American Geophysical Union.


Blight J.H.S.,University of Leicester | Petterson M.G.,British Geological Survey | Crowley Q.G.,NERC Isotope Geosciences Laboratory | Crowley Q.G.,Trinity College Dublin | Cunningham D.,University of Leicester
Journal of the Geological Society | Year: 2010

The Palaeozoic-Mesozoic tectonic evolution of Central Asia, including the vast terrane collage that makes up Mongolia, has been a topic of considerable debate. The Oyut Ulaan Volcanic Group is a sequence of volcanic and sedimentary rocks in SE Mongolia that forms the southern part of the Devonian-Permian Saykhandulaan Inlier. Fieldwork traverses and mapping have established four distinct formations in the Oyut Ulaan Volcanic Group that record the nature of arc activity in part of the Central Asian Orogenic Belt during the Carboniferous. Physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles: (1) periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps; (2) highly effusive plateau andesite volcanism; (3) explosive rhyolitic effusion. Geochemical analyses of volcanic lithologies suggest that the group represents subduction-related, mature, continental arc volcanism. Geochemical results document an evolving magma system to which surface processes of the volcano-sedimentary model may be linked. Magma pulses and replenishments are identified from variations in chemostratigraphy. Newly obtained zircon ages from the volcanic succession fix its emplacement (eruption) at 323.0 0.7 Ma (mid-Carboniferous or late Mississippian). A granite cobble from the lower part of the Oyut Ulaan Volcanic Group gives a U-Pb zircon age of 338.9 0.4 Ma indicating that arc plutons were emplaced 10 Ma prior to the Oyut Ulaan volcanism and were eroded soon after. Our work provides timing constraints for final accretion and continental assembly in SE Mongolia, and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen.


Blight J.H.S.,University of Leicester | Crowley Q.G.,NERC Isotope Geosciences Laboratory | Crowley Q.G.,Trinity College Dublin | Petterson M.G.,University of Leicester | And 2 more authors.
Lithos | Year: 2010

The crust in southern Mongolia is part of the Central Asian Orogenic Belt, a vast accretionary orogen that records the opening and closure of the Palaeo-asian Ocean in the late Proterozoic to Palaeozoic. The crustal evolution of the region is revealed in basement inliers that also contain intrusion-related porphyry ore bodies that are important mineral exploration targets. The Saykhandulaan inlier in Southeast Mongolia is a Devonian-Carboniferous segment of island-arc crust, which is dominantly composed of extrusive and sedimentary lithologies, but which also contains the Oyut Ulaan I-type quartz-monzonite intrusion. A U-Pb zircon age for the Oyut Ulaan monzonite indicates emplacement at 330.0 ± 0.5 Ma. To the east of the Saykhandulaan inlier, intrusive complexes dominate the neighbouring Mandakh inlier. New ages are presented for four of these plutons; the Bronze Fox granodiorite (333.6 ± 0.6 Ma); the Narin Hudag monzonite (333.2 ± 0.6 Ma); the Shuteen quartz monzonite (325.5 ± 1.0 Ma); and the North Mandakh granite (292.3 ± 0.5). The intrusive bodies of the Saykhandulaan and Mandakh inliers have two distinct geochronological and geochemical associations: 1) mid-Carboniferous I-type monzonites that constitute the most easterly intrusive expression of the Southern Mongolia Carboniferous Arc and, 2) Early Permian A-type and peralkaline granites that represent a post-orogenic phase of voluminous granite emplacement. Both groups are significantly younger than the nearby Oyu Tolgoi and Tsagaan Suvarga Cu-porphyry ore bodies, which have previously been dated as early- and late-Devonian respectively. The new data presented here provide constraints on the timing of the transition from island-arc magmatism to post-collisional extension-related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to Cu-Au mineralisation. © 2010 Elsevier B.V. All rights reserved.


Curtis C.J.,University College London | Evans C.D.,Environment Center Wales | Goodale C.L.,Cornell University | Heaton T.H.E.,NERC Isotope Geosciences Laboratory
Ecosystems | Year: 2011

Various studies over the last 15 years have attempted to describe the processes of N retention, saturation and NO3 - leaching in semi-natural ecosystems based on stable isotope studies. Forest ecologists and terrestrial biogeochemists have used 15N labelled NO3 - and NH4 + tracers to determine the fate of atmospheric deposition inputs of N to terrestrial ecosystems, with NO3 - leaching to surface waters being a key output flux. Separate studies by aquatic ecologists have used similar isotope tracer methods to determine the fate and impacts of inorganic N species, leached from terrestrial ecosystems, on aquatic ecosystems, usually without reference to comparable terrestrial studies. A third group of isotopic studies has employed natural abundances of 15N and 18O in precipitation and surface water NO3 - to determine the relative contributions of atmospheric and microbial sources. These three sets of results often appear to conflict with one another. Here we attempt to synthesize and reconcile the results of these differing approaches to identifying both the source and the fate of inorganic N in natural or semi-natural ecosystems, and identify future research priorities. We conclude that the results of different studies conform to a consistent conceptual model comprising: (1) rapid microbial turnover of atmospherically deposited NO3 - at multiple biologically active locations within both terrestrial and aquatic ecosystems; (2) maximum retention and accumulation of N in carbon-rich ecosystems and (3) maximum leaching of NO3 -, most of which has been microbially cycled, from carbon-poor ecosystems exposed to elevated atmospheric N inputs. © 2011 Springer Science+Business Media, LLC.


Slagstad T.,Geological Survey of Norway | Roberts N.M.W.,University of Leicester | Roberts N.M.W.,NERC Isotope Geosciences Laboratory | Marker M.,Geological Survey of Norway | And 2 more authors.
Terra Nova | Year: 2013

The late Mesoproterozoic Sveconorwegian orogen in southwest Baltica is traditionally interpreted as the eastward continuation of the Grenville orogen in Canada, resulting from collision with Amazonia, forming a central part in the assembly of the Rodinia supercontinent. We challenge this conventional view based on results from recent work in southwest Norway demonstrating voluminous subduction-related magmatism in the period 1050-1020Ma, followed by geographically restricted high-T/medium-P metamorphism between 1035 and 970Ma, succeeded by ferroan magmatism over large parts of south Norway in the period 990-920Ma. This magmatic and metamorphic evolution may be better understood as reflecting a long-lived accretionary margin, undergoing periodic compression and extension, than continent-continent collision. This study has implications for Grenville-Sveconorwegian correlations, comparisons with modern continental margins, Rodinia reconstructions and how we recognize geodynamic settings in ancient orogens. © 2012 Blackwell Publishing Ltd.


Wilson G.P.,University of Portsmouth | Lamb A.L.,NERC Isotope Geosciences Laboratory
Journal of Quaternary Science | Year: 2012

In order to understand natural sea-level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom-based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom-based tidal-level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site-specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal-level transfer functions, may be more appropriate. © 2011 John Wiley & Sons, Ltd.


Abram N.J.,British Antarctic Survey | Abram N.J.,Australian National University | Mulvaney R.,British Antarctic Survey | Arrowsmith C.,NERC Isotope Geosciences Laboratory
Journal of Geophysical Research: Atmospheres | Year: 2011

The accumulation, isotopic and chemical signals of an ice core from James Ross Island, Antarctica, are investigated for the interval from 1967 to 2008. Over this interval, comparison with station, satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice. Accumulation at James Ross Island is enhanced during years when the circumpolar westerlies are weak, allowing more precipitation events to reach the northeastern Antarctic Peninsula. The stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope-temperature gradient across Antarctica, and preserves information about both summer and winter temperature variability in the region. Sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of James Ross Island and transported to the site by strengthened northerly and westerly winds in the winter. A strong covariance with temperature means that the sea salt record may be able to be utilized, in conjunction with the isotope signal, as an indicator of winter temperature. Marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of James Ross Island. This source region may have become significant only in recent decades, when the collapse of nearby ice shelves established new sites of open water with high summer productivity. These findings provide a foundation for interpreting the environmental signals in the James Ross Island ice core, which extends though the whole Holocene and represents the oldest ice core that has been recovered from the Antarctic Peninsula region. Copyright © 2011 by the American Geophysical Union.


Neill I.,Cardiffuniversity | Kerr A.C.,Cardiffuniversity | Hastie A.R.,University of Edinburgh | Pindell J.L.,Cardiffuniversity | And 2 more authors.
Journal of Petrology | Year: 2013

An elemental and radiogenic isotope study of Cretaceous island arc rocks onTobago, West Indies, reveals the magmatic processes taking place at the eastern edge of the Pacific-derived Caribbean Plate during development of the Greater Antilles Arc. The ̃110-103Ma Volcano-Plutonic Suite comprises the ultramafic-intermediate Tobago Pluton and genetically related Tobago Volcanic Group. The volcanic rocks (breccias, tuffs, and mafic-intermediate lavas) have undergone shallow-level fractional crystallization involving plagioclase, clinopyroxene, olivine, and Fe-Ti oxides, but also preserve trace element evidence for 'cryptic' amphibole fractionation. The suite is inferred to have formed from a spinel lherzolite mantle wedge source fluxed largely by slab- and recycled volcanogenic sediment- derived fluids. A tonalitic mega-dyke intruding the pluton resembles high-silica adakites, and geochemical constraints indicate a likely origin by partial melting of the arc crust. A mafic dyke swarm (̃103-91Ma) is partly coeval with the volcanic rocks, but some, perhaps the youngest dykes, are derived from isotopically distinct arc mantle sources compared with the volcanic rocks. Rare Nbenriched and high-Nb dykes may relate to melting of a high field strength element-enriched source. Current Caribbean tectonic models involve the continuation of east-dipping Farallon Plate subduction beneath the proto-Caribbean seaway either until an Early Cretaceous initiation of proto-Caribbean subduction, or collision of the Caribbean Oceanic Plateau with the Greater Antilles Arc at ̃90-80Ma. Both models may be compatible with the tectono-magmatic history ofTobago, whereinTobago is thought to have detached from the fore-arc of the Caribbean arc system during Eocene intraarc extension, the growth of the Grenada Basin, and inception of the Lesser Antilles Arc. Tobago- or La Deésirade-like Mesozoic arc crust underlies much of the present-day Lesser Antilles Arc and not, as has recently been proposed, portions of the plume-derived Caribbean Oceanic Plateau ©The Author 2013.

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