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The boring billion? - Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent

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Geoscience Frontiers 2013年第6期4卷 681-691页

作者： nick m.w.roberts NERC Isotope Geosciences Laboratory British Geological SurveyKeyworthNottingham NG12 5GGUK

The evolution of Earth＇s biosphere,atmosphere and hydrosphere is tied to the formation of continental crust and its subsequent movements on tectonic *** supercontinent cycle posits that the continental crust is periodically amalgamated into a single landmass,subsequently breaking up and dispersing into various continental *** is possibly the first true supercontinent,it amalgamated during the 2.0-1.7 Ga period,and collisional orogenesis resulting from its formation peaked at 1.95-1.85 *** and palaeomagnetic evidence indicate that Columbia remained as a quasi-integral continental lid until at least 1.3 *** break-up attempts are evidenced by dyke swarms with a large temporal and spatial range; however,palaeomagnetic and geologic evidence suggest these attempts remained *** than dispersing into continental fragments,the Columbia supercontinent underwent only minor modifications to form the next supercontinent （Rodinia） at 1.1 -0.9 Ga; these included the transformation of external accretionary belts into the internal Grenville and equivalent collisional *** Columbia provides evidence for a form of ‘lid tectonics’,modern style plate tectonics occurred on its periphery in the form of accretionary *** detrital zircon and preserved geological record are compatible with an increase in the volume of continental crust during Columbia＇s lifespan; this is a consequence of the continuous accretionary processes along its *** quiescence in plate tectonic movements during Columbia＇s lifespan is correlative with a long period of stability in Earth＇s atmospheric and oceanic *** variability starting at 1.3 Ga in the environmental record coincides with the transformation of Columbia to Rodinia; thus,the link between plate tectonics and environmental change is strengthened with this interpretation of supercontinent history.

关键词： Rodinia Columbia Supercontinents Continental growth Lid tectonics mesoproterozoic

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Zircon U-Pb-Hf constraints from Gongga Shan granites on young crustal melting in eastern Tibet

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Geoscience Frontiers 2019年第3期10卷 885-894页

作者： nick m.w.roberts michael P.Searle NERC Isotope Geosciences Laboratory British Geological Survey Environment Science Centre Department of Earth Sciences University of Oxford

The Gongga Shan batholith is a complex granitoid batholith on the eastern margin of the Tibetan Plateau with a long history of magmatism spanning from the Triassic to the Pliocene. Late miocene-Pliocene units are the youngest exposed crustal melts within the entire Asian plate of the Tibetan ***, we present in-situ zircon Hf isotope constraints on their magmatic source, to aid the understanding of how these young melts were formed and how they were exhumed to the surface. Hf isotope signatures of Eocene to Pliocene zircon rims(ε_(Hf)(t)=-4 to +4), interpreted to have grown during localised crustal melting, are indicative of melting of a Neoproterozoic source region, equivalent to the nearby exposed Kangding Complex. Therefore, we suggest that Neoproterozoic crust underlies this region of the Songpan-Ganze terrane, and sourced the intrusive granites that form the Gongga Shan batholith. Localised young melting of Neoproterozoic lower or middle crust requires localised melt-fertile lithologies. we suggest that such melts may be equivalent to seismic and magnetotelluric low-velocity and high-conductivity zones or "bright spots" imaged across much of the Tibetan Plateau. The lack of widespread exposed melts this age is due either to the lack of melt-fertile rocks in the middle crust, the very low erosion level of the Tibetan plateau, or to a lack of mechanism for exhuming such melts. For Gongga Shan, where some melting is younger than nearby thermochronological ages of low temperature cooling, the exact process and timing of exhumation remains enigmatic, but their location away from the Xianshuihe fault precludes the fault acting as a conduit for the young melts. we suggest that underthrusting of dry granulites of the lower Indian crust(Archaean shield) this far northeast is a plausible mechanism to explain the uplift and exhumation of the eastern Tibetan Plateau.

关键词： Tibet Himalaya Hf isotopes Zircon Crustal melting

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metamorphism at convergent plate margins:Preface

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Geoscience Frontiers 2022年第2期13卷 351-353页

作者： Richard m.Palin nick m.w.roberts Department of Earth Sciences University of OxfordOxford OX13ANUnited Kingdom Geochronology and Tracers Facility British Geological SurveyEnvironmental Science CentreNottinghamUnited Kingdom

*** The year 2020 will long be recognised as a period of sadness and frustration for academics worldwide,given the catastrophic impact that the spread of novel coronavirus“2019-nCoV”-or COVID-19-has had on research and teaching activities,as well as in their personal *** Special Issue was designed to represent an avenue for dissemination of many studies presented at the September2019 Geological Society of America session T23.

关键词： teaching America has

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Geochronological constraints on the metamorphic sole of the Semail ophiolite in the United Arab Emirates

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Geoscience Frontiers 2016年第4期7卷 609-619页

作者： nick m.w.roberts Robert J.Thomas Joachim Jacobs NERC Isotope Geosciences Laboratory British Geological SurveyKeyworthNG12 5GGUK Council for Geoscience P.O.Box 572Bellville 7535South Africa University of Bergen.Department of Earth Science PB 78035020 BergenNorway Norwegian Polar Institute Fram Centre9296 TromsoNorway

The Semail ophiolite of Oman and the United Arab Emirates （UAE） provides the best preserved large slice of oceanic lithosphere exposed on the continental crust, and offers unique opportunities to study processes of ocean crust formation, subduction initiation and obduction. metamorphic rocks exposed in the eastern UAE have traditionally been interpreted as a metamorphic sole to the Semail ophiolite. However, there has been some debate over the possibility that the exposures contain components of older Arabian continental crust. To help answer this question, presented here are new zircon and futile U-Pb geochronological data from various units of the metamorphic rocks. Zircon was absent in most samples. Those that yielded zircon and futile provide dominant single age populations that are 95-93 ma, partially overlapping with the known age of oceanic crust formation （96.5-94.5 ma）, and partially overlapping with cooling ages of the metamorphic rocks （95 90 ma）. The data are interpreted as dating high-grade metamorphism during subduction burial of the sediments into hot mantle lithosphere, and rapid cooling during their subsequent exhumation. A few discordant zircon ages, interpreted as late Neoproterozoic and younger, represent minor detrital input from the continent. No evidence is found in favour of the existence of older Arabian continental crust within the metamorphic rocks of the UAE.

关键词： Semail ophiolite United Arab Emirates metamorphic sole U-Pb geochronology Zircon Rutile

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Deep seated magmas and their mantle roots:Introduction

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Geoscience Frontiers 2017年第4期8卷 617-619页

作者： Igor V.Ashchepkov nick m.w.roberts V.S.Sobolev Institute of Geology and mineralogy SB RAS NERC Isotope Geosciences Laboratory British Geological Survey

In the last decade there has been a considerable effort to better understand the joint evolution of mafic and ultramafic magmatic systems and their deep mantle roots,through integrated petrological and thermo-barometric *** generation is regarded as the result of complex processes including melting,creation of channels for melt transfer,and interaction with the wall-rocks.

关键词： mantle magmatic creation branching melting garnet roots enriched geochemistry beneath

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Nomore blind dates with calcite: Fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin

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Geoscience Frontiers 2021年第4期12卷 163-174页

作者： nick m.w.roberts JiříŽák František Vacek JiříSláma Geochronology and Tracers Facility British Geological SurveyEnvironmental Science CentreNottingham NG125GGUK Institute of Geology and Paleontology Faculty of ScienceCharles UniversityAlbertov 6Prague 12843Czech Republic Department of mineralogy and Petrology National MuseumVáclavskénáměstí68Prague 11579Czech Republic Institute of Geology Czech Academy of Sciencesv.v.i.Rozvojová269Prague 16500Czech Republic

Dating of fracture-filling calcitewith U-Pb geochronology is becoming a rapidly adopted technique for determining the absolute timing of brittle deformation in the upper *** calcite is a desirable target,as it precipitates between individual fault slip displacement events,and provides additional kinematic *** we present a case study of slickenfibres formed on the Očkov thrust in the Lower Palaezoic Prague Basin,Bohemian massif,utilising a combination of petrographic and in situ *** demonstrate that slickenfibre external textures can be preserved,whilst internally primary textures are removed by fluid infiltration and recrystallization,leading to variable U and Pb *** slickenfibre yielded a date of ca.250 ma,which we interpret as recording fault slip along the Očkov *** cross-cutting slickenfibre yielded more scattered U-Pb data,with an imprecise apparent age around ca.95 *** slickenfibre is recrystallised,destroying the primary textures,and exhibits element *** meaning of this younger apparent age is therefore questionable;whereas it likely reflects Cretaceous U and Pb mobility assisted by fluid-flow along the fault plane,it may not reflect a period of fault *** results demonstrate that slickenfibre-based U-Pb dates do not unequivocally relate to fault motion,and that petrographic and elemental analyses are important requirements for interpreting calcite U-Pb data.

关键词： U-Pb geochronology Calcite Fault dating Fluid-flow Prague Basin LA-ICP-mS

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The dynamic Archean to Paleoproterozoic crustal evolution of Brazil:Preface

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Geoscience Frontiers 2022年第5期13卷 106-109页

作者： Hugo moreira mathias Schannor Kathryn Cutts nick m.w.roberts CNRS-UmR5243 Géosciences MontpellierUniversitéde MontpellierFrance Department of Earth Sciences University of CambridgeUK Department of Earth Sciences Freie Universität BerlinBerlinGermany Faculdade de Geologia Universidade do Estado do Rio de JaneiroBrazil Geological Survey of Finland P.O.Box 96FI-02151 EspooFinland Geochronology and Tracers Facility British Geological SurveyNottinghamUK

Brazil is the largest country in South America and contains the majority of the exposed Archean and Paleoproterozoic crust on the continent. As such, Brazil provides a natural laboratory for studies of the ancient Earth. In this Special Issue, contributions reflect the dynamic and protracted growth and reworking of former continents during a time frame of over a billion years, and depict how changes across the evolution of plate tectonics may have influenced the evolution of the interlinked crust-ocean-atmospheric Earth cycles over this period.

关键词： evolution Paleo Earth

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"miles wide and miles deep"-Exploring the depth and breadth of geoscience during the first ten years of Geoscience Frontiers

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Geoscience Frontiers 2019年第3期10卷 1219-1221页

作者： Christopher J. Spencer nick m.w.roberts Damian Nance The Institute of Geoscience Research (TIGeR) School of Earth and Planetary Sciences Curtin University NERC Isotope Geosciences Laboratory British Geological Survey Department of Geological Sciences Ohio University Department of Geology and Geophysics Yale University

when early explorers first crossed the Platte River in what is now Nebraska (USA), it was said the river was “a mile wide and an inch deep”(mokler, 1923;Smith, 1971). This phrase was used to describe not only the difficulty in crossing the river but also in navigating its length. The trouble with a river being too wide is the risk that it won’t provide the depth necessary to be useful. The same thing can be said of multidisciplinary scientific journals. while a journal can claim to be multidisciplinary, there is a risk of it being so broad that its articles can only engage the reader at a superficial level. Nothing could be further from the truth with Geoscience Frontiers. Over the past ten years, this journal has successfully navigated the wide breadth of geoscience while providing a level of depth and detail that rivals discipline-specific journals.

关键词： engage its was can past be is now

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Regional trends and petrologic factors inhibit global interpretations of zircon trace element compositions

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Geoscience Frontiers 2024年第5期15卷 300-307页

作者： nick m.w.roberts Christopher J.Spencer Stephen Puetz C.Brenhin Keller Simon Tapster Geochronology and Tracers Facility British Geological SurveyNottingham NG125GGUK Department of Geological Sciences and Geological Engineering Queen’s UniversityKingstonOntarioCanada 475 Atkinson Dr Suite 704HonoluluHI 96814USA Department of Earth Sciences Dartmouth CollegeHanoverNew HamphireUSA

The trace element composition of zircon reveals information about the melt that they are derived from,as such,detrital zircon trace element compositions can be used to interrogate melt compositions,and thus the evolution of the continental crust in time and ***,we present a global database of detrital zircon compositions and use it to test whether average global trends for five common petrogenetic proxies truly represent secular changes in continental *** demonstrate that the secular trend is broadly comparable across continental regions for Ti-in-zircon temperatures,but for other trace element ratios interrogated,secular trends are highly variable between continental *** trace element ratios result from multiple petrologic variables,we argue that these petrogenetic proxies can be overinterpreted if projected to global geologic *** particular,we caution against the interpretation of crustal thickness from trace elements in zircon,and we argue that our results negate current hypotheses concerning secular changes in crustal thickness.

关键词： Detrital zircon Trace elements Secular change Eu anomaly Crustal thickness

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Deconvolving the pre-Himalayan Indian margin-Tales of crustal growth and destruction

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Geoscience Frontiers 2019年第3期10卷 863-872页

作者： Christopher J.Spencer Brendan Dyck Catherine m.mottram nick m.w.roberts wei-Hua Yao Erin L.martin Earth Dynamics Research Group The Institute for Geoscience Research (TIGeR) Department of Applied Geology Curtin University NERC Isotope Geosciences Laboratory British Geological Survey Department of Earth Sciences Simon Fraser University University Drive Department of Environment Earth and Ecosystems The Open UniversityWalton Hall Milton Keynes MK7 6AA UK School of Earth and Environmental Sciences University of Portsmouth Schoolof Earth Sciences and Engineering SunYat-sen University

The metamorphic core of the Himalaya is composed of Indian cratonic rocks with two distinct crustal affinities that are defined by radiogenic isotopic geochemistry and detrital zircon age spectra. One is derived predominantly from the Paleoproterozoic and Archean rocks of the Indian cratonic interior and is either represented as metamorphosed sedimentary rocks of the Lesser Himalayan Sequence(LHS) or as slices of the distal cratonic margin. The other is the Greater Himalayan Sequence(GHS) whose provenance is less clear and has an enigmatic affinity. Here we present new detrital zircon Hf analyses from LHS and GHS samples spanning over 1000 km along the orogen that respectively show a striking similarity in age spectra and Hf isotope ratios. within the GHS, the zircon age populations at 2800-2500 ma,1800 ma, 1000 ma and 500 ma can be ascribed to various Gondwanan source regions; however, a pervasive and dominant Tonianage population(～860-800 ma) with a variably enriched radiogenic Hf isotope signature(eHf = 10 to-20) has not been identified from Gondwana or peripheral accreted terranes. we suggest this detrital zircon age population was derived from a crustal province that was subsequently removed by tectonic erosion. Substantial geologic evidence exists from previous studies across the Himalaya supporting the Cambro-Ordovician Kurgiakh Orogeny. we propose the tectonic removal of Tonian lithosphere occurred prior to or during this Cambro-Ordovician episode of orogenesis in a similar scenario as is seen in the modern Andean and Indonesian orogenies, wherein tectonic processes have removed significant portions of the continental lithosphere in a relatively short amount of time. This model described herein of the pre-Himalayan northern margin of Greater India highlights the paucity of the geologic record associated with the growth of continental crust. Although the continental crust is the archive of Earth history, it is vital to recognize the ways in which preservation

关键词： Himalaya Gondwana Zircon Subduction erosion

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