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| 1 | The boring billion? - Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent显示文摘The evolution of Earth’s biosphere,atmosphere and hydrosphere is tied to the formation of continental crust and its subsequent movements on tectonic plates.The supercontinent cycle posits that the continental crust is periodically amalgamated into a single landmass,subsequently breaking up and dispersing into various continental fragments.Columbia is possibly the frst true supercontinent,it amalgamated during the 2.0e1.7 Ga period,and collisional orogenesis resulting from its formation peaked at 1.95-1.85 Ga.Geological and palaeomagnetic evidence indicate that Columbia remained as a quasi-integral continental lid until at least 1.3 Ga.Numerous break-up attempts are evidenced by dyke swarms with a large temporal and spatial range;however,palaeomagnetic and geologic evidence suggest these attempts remained unsuccessful.Rather than dispersing into continental fragments,the Columbia supercontinent underwent only minor modifcations 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 belts.Although Columbia provides evidence for a form of‘lid tectonics’,modern style plate tectonics occurred on its periphery in the form of accretionary orogens.The 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 margins.The quiescence in plate tectonic movements during Columbia’s lifespan is correlative with a long period of stability in Earth’s atmospheric and oceanic chemistry.Increased 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. | Nick M.W.Roberts | 2013 | Geoscience Frontiers2013，4，6： | 26 |
| 2 | In situ calcite U-Pb geochronology by high-sensitivity single-collector LA-SF-ICP-MS显示文摘U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method,with potential applications to a vast array of geological problems.Due to the low levels of U and Pb in calcite,measurement using higher-sensitivity instruments,such as sector field (SF) ICP-MS,have advantages over more commonly used quadrupole (Q) ICP-MS instruments.Using a Thermo Element XR ICP-MS,we demonstrate that the Jet+X cone combination with the N_(2) enhancement technique provides the best sensitivity for measuring U and Pb isotopes.This higher sensitivity improves the precision of calcite U-Pb isotope measurements,and permits dating at high spatial resolutions (<110μm) and for samples containing low contents of^(238)U (<1μg g^(–1)) and/or^(207)Pb (i.e.,young samples<10 Ma).Using a spot size of 85μm with a low fluence (~2.0 J cm^(–2)),the laser-induced elemental fractionation of^(206)Pb/^(238)U in the NIST SRM 614,ARM-3 and WC-1 reference materials are insignificant (<2.2%).Adopting the optimized instrument parameters,we analysed four commonly-used calcite U-Pb reference materials (WC-1,Duff Brown Tank,JT,and ASH-15).The results match well with published isotope dilution data,demonstrating the reliability of our technique.ARM-3,an andesitic glass,is shown to be an appropriate reference material for both^(207)Pb/^(206)Pb calibration and instrument optimization because of its moderate contents of U(~3.75μg g^(–1)) and Pb (~12.7μg g^(–1)).We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages. | Shitou WU Yueheng YANG Nick M.W.ROBERTS Ming YANG Hao WANG Zhongwu LAN Bohang XIE Tianyi LI Lei XU Chao HUANG Liewen XIE Jinhui YANG Fuyuan WU | 2022 | Science China Earth Sciences2022，65，6： | 6 |
| 3 | 高灵敏度-单接收杯LA-SF-ICP-MS原位方解石U-Pb定年显示文摘激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)方解石U-Pb定年是一种新兴的地质年代学方法,在解决一系列关键地质问题中具有广阔的应用前景.由于方解石中U和Pb含量低,采用高灵敏度扇形磁场电感耦合等离子体质谱仪(SF-ICP-MS)比四极杆电感耦合等离子体质谱仪(Q-ICP-MS)更有优势.研究发现对于Thermo Element XR型号的SF-ICP-MS仪器,当采用Jet+X锥组和N_(2)增敏技术时,U和Pb的灵敏度最佳.提高灵敏度不仅能明显改善方解石定年分析精度,而且可在高空间分辨率条件下(<110μm)实现低^(238)U(<1μg g^(−1))或^(207)Pb(如<10Ma)含量样品的定年测试.对于NIST SRM 614、ARM-3和WC-1这三个标准物质来说,在激光束斑85μm和能量密度~2.0J cm^(−2)的条件下,由激光剥蚀产生的^(206)Pb/^(238)U动态分馏不显著(<2.2%).在最佳仪器条件下,系统分析了四个常用的方解石U-Pb标准物质(WC-1、Duff Brown Tank、JT和ASH-15).结果与已发表的同位素稀释热电离质谱(ID-TIMS)数据相吻合,验证了方法的可靠性.研究进一步证明,基于LA-ICP-MS二维元素成像技术辅助选取样品定年区域可提高方解石U-Pb定年的成功率. | 吴石头 杨岳衡 Nick M.W.ROBERTS 杨明 王浩 兰中伍 谢博航 李天义 许蕾 黄超 谢烈文 杨进辉 吴福元 | 2022 | 中国科学:地球科学2022，52，7： | 3 |
| 4 | Deconvolving the pre-Himalayan Indian margin-Tales of crustal growth and destruction显示文摘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 bias and destruction of continental crust informs geologic models. | Christopher J.Spencer Brendan Dyck Catherine M.Mottram Nick M.W.Roberts Wei-Hua Yao Erin L.Martin | 2019 | Geoscience Frontiers2019，10，3： | 3 |
| 5 | Geochronological constraints on the metamorphic sole of the Semail ophiolite in the United Arab Emirates显示文摘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 rutile U-Pb geochronological data from various units of the metamorphic rocks.Zircon was absent in most samples.Those that yielded zircon and rutile 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. | Nick M.W.Roberts Robert J.Thomas Joachim Jacobs | 2016 | Geoscience Frontiers2016，7，4： | 2 |
| 6 | Generation and preservation of continental crust in the Grenville Orogeny显示文摘Detrital zircons from modern sediments display an episodic temporal distribution of U-Pb crystallization ages forming a series of 'peaks' and 'troughs'.The peaks are interpreted to represent either periods of enhanced generation of granitic magma perhaps associated with mantle overturn and superplume events,or preferential preservation of continental crust during global collisional orogenesis.The close association of those peaks with the assembly of supercontinents implies a causal relationship between collisional orogenesis and the presence of zircon age peaks.Here these two end-member models(episodic periodicity of increased magmatism versus selective preservation during collisional orogenesis) are assessed using U-Pb,Hf,and O analysis of detrital zircons from sedimentary successions deposited during the ~ 1.3-1.1Ca accretionary.~1.1-0.9 Ga collisional,and < 0.9 Ga extensional collapse phases of the Grenville orogenic cycle in Labrador and Scotland.The pre-collisional,accretionary stage provides a baseline of continental crust present prior to orogenesis and is dominated by Archean and Paleoproterozoic age peaks associated with pre-1300 Ma Laurentian geology.Strata deposited during the Grenville Orogeny display similar Archean and Paleoproterozoic detrital populations along with a series of broad muted peaks from~ 1500 to 1100 Ma.However,post-collisional sedimentary successions display a dominant age peak between 1085 and 985 Ma,similar to that observed in modern North American river sediments.Zircons within the post-orogenic sedimentary successions have progressively lower εHf and higherδ^(18)O values from ~ 1800 to ~ 1200 Ma whereupon they have higher εHf and δ^(18) within the dominant1085-985 Ma age peak.Furthermore,the Lu-Hf isotopic profile of the Grenville-related age peak is consistent with significant assimilation and contamination by older crustal material.The timing of this dominant age peak coincides with the peak of metamorphism and magmatism associated with the Crenville Orogeny,which is a typical collisional orogenic belt.The change from broad muted age peaks in the syn-orogenic strata to a single peak in the post-orogenic sedimentary successions and in the modern river sediments implies a significant shift in provenance following continental collision.This temporal change in provenance highlights that the source(s),from which detrital zircons within syn-orogenic strata were derived,was no longer available during the later stages of the accretionary and collisional stages of the orogenic cycle.This may reflect some combination of tectonic burial,erosion,or possibly recycling into the mantle by tectonic erosion of the source(s).During continental collision,the incorporated continental crust is isolated from crustal recycling processes operative at subduction margins.This tectonic isolation combined with sedimentaiy recycling likely controls the presence of the isotopic signature associated with the Grenville Orogeny in the modern Mississippi and Appalachian river sediments.These results imply that zircon age peaks,which developed in conjunction with supercontinents,are the product of selective crustal preservation resulting from collisional orogenesis. | Christopher J.Spencer Peter A.Cawood Chris J.Hawkesworth Anthony R.Prave Nick M.W.Roberts Matthew S.A.Horstwood Martin J.Whitehouse EIMF | 2015 | Geoscience Frontiers2015，6，3： | 1 |
| 7 | Nomore blind dates with calcite: Fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin显示文摘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 crust.Slickenfibre calcite is a desirable target,as it precipitates between individual fault slip displacement events,and provides additional kinematic information.Here 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 methods.We 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 mobilisation.One slickenfibre yielded a date of ca.250 Ma,which we interpret as recording fault slip along the Očkov thrust.Another cross-cutting slickenfibre yielded more scattered U-Pb data,with an imprecise apparent age around ca.95 Ma.This slickenfibre is recrystallised,destroying the primary textures,and exhibits element mobility.The 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 slip.Our 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. | Nick M.W.Roberts JiříŽák František Vacek JiříSláma | 2021 | Geoscience Frontiers2021，12，4： | 1 |
| 8 | Zircon U-Pb-Hf constraints from Gongga Shan granites on young crustal melting in eastern Tibet显示文摘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 Plateau.Here, 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. | Nick M.W.Roberts Michael P.Searle | 2019 | Geoscience Frontiers2019，10，3： | 1 |
| 9 | Deep seated magmas and their mantle roots:Introduction显示文摘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 studies.Magma generation is regarded as the result of complex processes including melting,creation of channels for melt transfer,and interaction with the wall-rocks.Complexities in magmatic systems involve metasomatism and the creation of metasomatic fronts,branching and splitting of magma volumes during their evolution,and vat- | Igor V.Ashchepkov Nick M.W.Roberts | 2017 | Geoscience Frontiers2017，8，4： | 0 |
| 10 | 'Miles wide and miles deep'-Exploring the depth and breadth of geoscience during the first ten years of Geoscience Frontiers显示文摘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. | Christopher J. Spencer Nick M.W.Roberts Damian Nance | 2019 | Geoscience Frontiers2019，10，3： | 0 |
| 11 | Metamorphism at convergent plate margins:Preface显示文摘1.Foreword 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 lives.This Special Issue was designed to represent an avenue for dissemination of many studies presented at the September2019 Geological Society of America session T23. | Richard M.Palin Nick M.W.Roberts | 2022 | Geoscience Frontiers2022，13，2： | 0 |
| 12 | The dynamic Archean to Paleoproterozoic crustal evolution of Brazil:Preface显示文摘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. | Hugo Moreira Mathias Schannor Kathryn Cutts Nick M.W.Roberts | 2022 | Geoscience Frontiers2022，13，5： | 0 |
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