Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids:LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

The Dongnan Cu–Mo deposit,located in the southeast of the Zijinshan ore field(the largest porphyry–epithermal system in Southeast China),represents the complex magmatic and metallogenesis events in the region.The petrogenesis and metallogenesis of granitoids from the deposit are not determined,especially the interactions between ore-bearing(granodiorite porphyry)and barren samples(granodiorite and diorite).In the paper,the whole rock geochemical features shared a similar affinity to the middle-lower content and revealed that they derived from partial melting of the Cathaysian basement with the contribution of mantle materials,even represented that they generated in the plate subduction;LA-ICP-MS zircon U–Pb ages show that these granodiorites,granodioritic porphyry and diorite,were generated during 114–103 Ma.The ore-bearing samples mostly presented ε_(Hf)(t)of negative values(peak value is-4 to-3)with old two-stage Hf model ages(t_(DM)^(2))(peak value is 1.10–1.15 Ga),while the barren sample showed slightly negative ε_(Hf)(t)(peak value is-1 to 0)values with young t_(DM)^(2)(peak value is 1.00–1.05 Ga).The value of zircon Ce^(4+)/Ce^(3+)ratio mostly higher than 450 was first verified for the ore-bearing samples in the Dongnan Cu–Mo deposit,and the values of ore-bearing were found to be higher than those from the barren,which suggests that the ore-bearing formed in more oxidized parental magma with higher oxygen fugacity.Based on the geochemical characteristic of the element and isotope,we concluded that the Early Cretaceous multiphases magmatic activities,low melting temperature and low pressure of pluton,and high oxygen fugacity of zircon,were the favorable conditions for metallogenesis of Dongnan Cu–Mo deposit.

Multi-stage crustal growth and cratonization of the North China Craton

The North China Craton（NCC） has a complicated evolutionary history with multi-stage crustal growth,recording nearly all important geological events in the early geotectonic history of the Earth.Our studies propose that the NCC can be divided into six micro-blocks with ＆gt;～3.0-3.8 Ga old continental nuclei that are surrounded by Neoarchean greenstone belts（CRB）.The micro-blocks are also termed as highgrade regions（HGR） and are mainly composed of orthogneisses with minor gabbros and BIF-bearing supracrustal beds or lenses,all of which underwent strong deformation and metamorphism of granulite- to high-grade amphibolite-facies.The micro-blocks are,in turn,from east to west,the Jiaoliao（JL）,Qianhuai（QH）,Ordos（ODS）,Ji’ning（JN） and Alashan（ALS） blocks,and Xuchang（XCH） in the south.Recent studies led to a consensus that the basement of the NCC was composed of different blocks/terranes that were finally amalgamated to form a coherent craton at the end of Neoarchean.Zircon U-Pb data show that TTG gneisses in the HGRs have two prominent age peaks at ca.2.9-2.7 and2.6-2.5 Ga which may correspond to the earliest events of major crustal growth in the NCC.Hafnium isotopic model ages range from ca.3.8 to 2.5 Ga and mostly are in the range of 3.0-2.6 Ga with a peak at2.82 Ga.Recent studies revealed a much larger volume of TTG gneisses in the NCC than previously considered,with a dominant ca.2.7 Ga magmatic zircon ages.Most of the ca.2.7 Ga TTG gneisses underwent metamorphism in 2.6-2.5 Ga as indicated by ubiquitous metamorphic rims around the cores of magmatic zircon in these rocks.Abundant ca.2.6-2.5 Ga orthogneisses have Hf-in-zircon and Nd wholerock model ages mostly around 2.9-2.7 Ga and some around 2.6-2.5 Ga,indicating the timing of protolith formation or extraction of the protolith magma was from the mantle.Therefore,it is suggested that the 2.6-2.5 Ga TTGs probably represent a coherent event of continental accretion and major reworking（crustal melting）.As a distinct characteristic,nearly all GRBs in the NCC underwent amphibolite-facies metamorphism.Zircon U-Pb ages of metamorphosed GRB mafic rocks mainly show two peak ranges at ～2.6-2.5 and 2.8-2.7 Ga.The mafic rocks are commonly believed to be derived from metabasalts,it is therefore possible that the ages represent the time of metamorphism.The tectonic settings of the GRBs are still a problem.Their geochemical characteristics are,respectively,similar to back-arc basins,rifts,island arcs or suggest imprints of mantle plumes.BIFs occur in all GRBs but also in the HGRs.This metallogenic specificity is quite different from all Phanerozoic geotectonic settings.The-2.5 Ga metamorphic-magmatic event is stronger than in most other cratons in the world.How to understand the geological significance of the 2.5 Ga event？ The following points are emphasized：（1）nearly all old rocks ＆gt;2.5 Ga underwent metamorphism at ～2.52-2.5 Ga;（2） Archean basement rocks in the NCC experienced strong partial melting and migmatization;（3） granitoid rocks derived from partial melting include potassium granites,TTG granites and monzonites.These granitoids rocks intruded both the Archean greenstone belts and micro-blocks;（4） ～2.5 Ga mafic dikes（amphibolites）,granitic dikes（veins） and syenitic-ultramafic dykes are also developed.Therefore,we suggest an assembly model that all micro-blocks in the NCC were welded together by late Archean greenstone belts at the end of the late Neoarchean.We also propose that the various micro-blocks were surrounded by small ocean basins,and the old continental crust and the oceanic crust were hotter than today.Subduction and collision were on much smaller scales as compared to the Phanerozoic plate tectonic regime,although the tectonic style and mechanisms were more or less similar.The formation of crustal melt granites is one of the processes of cratonization,inducing generation of stable upper and lower crustal layers.This process also generated an upper crust of more felsic composition and a lower crust of more mafic composition,due to molten residual materials and some underplated gabbros.

Mineral Resource Science in China:Review and perspective

Mineral resources are essential to prosperity and security of modern societies.How mineral resources can guar-antee sustainable development of economy in countries,especially those developing countries,has long been a focus of attention of international communities.This paper provides a comprehensive summary for major ad-vance of the research on mineral resources in past decades,and proposes some key issues regarding ore-forming mechanism,exploration and utilization of major and critical mineral resources.On the basis of these aspects,we also identify four priority science issues to be addressed in the future,including(1)mechanism of both metal circulation and extremely high concentration,(2)theories and technologies of prospecting deep-earth resources,(3)investigation of mineral resources in seafloor and polar regions,and(4)efficient,clean and recycling utiliza-tion of mineral resources.It can be expected that new advances in these four issues would tremendously promote the innovation of mineral resource science,and provide scientific and technologic support to meet the demand of mineral resources for human activities and the harmonious development of both mineral-resource exploration and ecological restoration.

前板块构造与大陆起源研究进展及关键科学问题

本文总结了现阶段前板块构造与大陆起源研究的三大重要进展:(1)提出了地幔柱构造、重力凹沉构造和热管构造的前板块构造模式;(2)揭示了非板块构造与板块构造的标志;(3)发现了地球早期层圈演化地质记录.但是,现有的前板块构造并不能完美解释太古宙大陆的起源,板块构造在解释大陆起源与演化方面也遇到重大挑战.此外,阐述了我国开展前板块构造与大陆起源研究的必要性、研究优势及风险,并凝练了目前前板块构造与大陆起源研究的关键科学问题:(1)地球是先有陆还是先有板块构造;(2)海陆的形成是否同步;(3)冥古宙陆壳和英云闪长岩-奥长花岗岩-花岗闪长岩(tonalite-trondhjemite-granodiorite,TTG)的起源.基于学科发展,提出动力学热模拟和比较行星学在前板块构造与大陆起源研究中的重要性.在此基础上,认为未来5~10年前板块构造与大陆起源的研究重点领域为:(1)大陆的起源及其对早期地球环境和生命的影响;(2)前板块构造样式及其形成机制;(3)太古宙的构造热体制及热演化;(4)前板块构造与类地行星演化.

关注前寒武纪大陆形成演化研究

“前寒武纪地质学”研究的是寒武纪(5.4亿年)之前地质时代的地质问题,核心是大陆形成演化及相关环境资源效应.前寒武纪时间跨度约40亿年,占地球形成以来的90%,对理解地球的历史、现在以及未来具有重要意义.相关的重要科学问题包括圈层分异、大陆形成和演化,以及伴随的构造、物质(包括矿产)、环境和早期生命演化.地球是太阳系中唯一的具有花岗岩质陆壳以及出现板块构造的星球,前寒武纪地质的研究,对了解地球的形成演化、生命宜居环境,以至地球的未来命运都至关重要.地球早期历史中有3个重大的地质事件:大陆地壳的巨量生长和稳定化、构造体制的演化、地球环境的剧变,它们涵盖了地球的物质(资源)、构造和环境(灾害)科学的所有内容.

Sm-Nd age dating of high-pressure granulites and amphi-bolite from Sanggan area,North China craton

The high pressure (HP) metamorphic age has been dated to HP rocks from the Sanggan area, North China craton. We have got garnet+whole rock isochron ages of (1 842±38) Ma for HP granulite, and (1 856± 26) Ma for HP amphibolite. The Sm-Nd whole rock isochron of HP granulites give out an age of (1870±150) Ma with Nd depleted mantle model age of (2402-2 482) Ma. Considering the Nd isotope homogenization during the peak metamorphism of the HP granulite, Sm-Nd closure temperature and the retention of Nd isotopic memory in garnets partially broken down during decompression, all these isochron ages are thought to be HP metamorphic age. Furthermore, we proposed that the HP metamorphism took place at the end of Paleoproterozoic during the large-scale collision and assembly of the North China craton.

Late Mesoarchean crust growth event： evidence from the ca. 2.8 Ga granodioritic gneisses of the Xiaoqinling area, southern North China Craton

Recently, more attention has been paid to Precambrian magma events and crustal growth of the North China Craton(NCC), accompanying with controversy in activity stages and dynamic mechanism. In this study, we report the Archean(2802 ± 13 Ma) granodioritic gneisses in the Taihua Complex from the Xiaoqinling area, located in the southern margin of the NCC. The zircon Lu–Hf isotope analysis of the rocks showed ^(176)Hf/^(177)Hf ratios of0.280977–0.281228, corresponding to ε_(Hf)(t) values ranging from-3.5 to +6.6, and two–stage Hf model ages varying from 2836 to 3409 Ma. It was confirmed that late Mesoarchean(2.9–2.8 Ga) juvenile crust made contribution to the source material of these ca. 2.8 Ga granodioritic gneisses in the Xiaoqinling area. The whole rock geochemical data indicate that the granodioritic gneisses are high-K calc-alkaline series, probably generated at relatively high pressure and temperature, and formed under the continental arc setting. Statistically, we conclude that the magmatic activities during 2.9–2.7 Ga may represent the most intense crustal growth events in the NCC and these Archean rocks at different locations in southern NCC underwent a similar crustal evolution history.

Origin of early continents and beginning of plate tectonics

When and how plate tectonics began are two frontiers being hotly debated [1]. These two scientific questions directly concern the geodynamics of the early Earth and the processes and mechanism of Earth’s evolution. Earth has a long history up to 4.543 billion years with the oldest zircon from a terrestrial rock at ca.4.4 Ga, yet the formation history of continental crust is debating[2]. Being associated with the evolution of continental crust, the emergence of plate tectonics has been proposed to range from>4.0 Ga to ca. 0.7 Ga [1–6]. As for the question of ‘‘how", theories fall into two groups:uniformitarianism (rarely changed ever) or catastrophism (evolving all the time).

Crustal growth of the North China Craton at ca.2.5 Ga

长期以来2.7~2.8 Ga被普遍接受为华北克拉通太古宙地壳生长的主峰期,与全球地壳生长同步,其主要依据是华北克拉通多数锆石的亏损地幔Hf模式年龄的峰值分布在2.7~2.8 Ga.然而Hf模式年龄受源区成分和地幔模式的选择以及源区不均一性等多种因素影响,具体数值未必有确切地质含义.而全球公认的2.7 Ga地壳生长峰期并非依据模式年龄,而主要依据:以绿岩带为代表的巨量镁铁质岩浆活动峰期在2.7 Ga,由此引发的巨量长英质岩浆活动峰期在2.7 Ga,全球地幔亏损事件的峰期也在2.7 Ga.与此相对应,对于华北克拉通,以绿岩带为代表的巨量镁铁质岩浆活动峰期在2.5 Ga,由此引发的巨量长英质岩浆活动峰期也在2.5 Ga.因此,如不考虑不同构造背景保存偏差的影响,~2.5 Ga应被视作华北克拉通较为明确的地壳生长的主峰期.

Zircon U-Pb geochronology of tuffite beds in the Baishugou Formation:Constraints on the revision of Ectasian System at the southern margin of the North China Craton

The Xiamaling Formation of 1.4–1.35 Ga in Jixian Section and adjoining areas represents a unique Ectasian Period(Mesoproterozoic)sedimentary sequence in the North China Craton(NCC).Studies carried out during the last decade have contributed significantly in improving our understanding about the Ectasian sedimentation tectonics in the NCC during this transitional interval between the breakup of Supercontinent Columbia and the assembly of Rodinia.The present study reports,for the first time,tuffite beds interlayered with carbonaceous-siliceous slate-phyllite in the upper Baishugou Formation(western Henan Province),at the southern margin of NCC.The LA-MC-ICPMS U-Pb geochronology of zircons from two tuffite samples has yielded almost identical ages of 1330±10 Ma(MSWD=0.43,N=38)and 1332±10 Ma(MSWD=0.90,N=24),that constrain a 1.33 Ga depositional age(Ectasian Period)for the Baishugou Formation.A close similarity in lithological characteristics and their respective superimposed lithostratigraphic relationships of the Baishugou and Xiamaling formations,underline a comparable depositional environment for them.The high-precision geochronology data on the Baishugou Formation would stimulate a relook into the Meso-Neoproterozoic chronostratigraphic framework of the NCC,and further research would lead to a comprehensive understanding of the geological evolution of the NCC during Ectasian Period and its correlation with analogous global events.

Petrologic indicators of prograde metamorphism in Paleoproterozoic garnet mafic granulites from the Huai＇an complex, North China Craton

Reconstruction of pressure-temperature-time(P-T-t)paths and thermal regimes are essential for inferring tectono-metamorphic processes involved in the formation of metamorphic terranes.However,the P-T information,especially the prograde evolution is generally preserved incompletely due to the fast intra-or inter-grains diffusion under high-temperatures.It may result

Dating of monazite-apatite-allanite-epidote corona from the Bayan Obo Group in the northern margin of the North China Craton:implications for the time of regional Au and REE mineralization

The Mesoproterozoic Bayan Obo Group located along the northern margin of the North China Craton(NMNCC)hosts a world’s largest known rare-earth element(REE)deposit(Bayan Obo Fe-REE-Nb deposit)[1,2]and a number of large gold deposits(eg.,Haoyaoerhugong and Zhulazhaga gold deposits;Fig.1a)[3],and has a long and protracted thermal history spanning from1.3 Ga to 250 Ma[1].The tectonic history was associated with Proterozoic rifting with carbonatite magmatism at1.3 Ga[4]and subsequent subduction-accretion processes of the Paleo-Asian Ocean[5,6].The Paleo-Asian oceanic subduction beneath the North China Craton(NCC)initiated in the Middle Silurian[7,8]and the ocean was closed in the Permian to induce the accretion of arcs and terranes with the NCC[2].This long and protracted tectonic history increases the difficulties both in dating and understanding the genesis of the Bayan Obo REE deposit and black shale-hosted gold deposits(e.g.,Haoyaoerhudong deposit).Thus,it is important to understand the thermal history of the hosting strata in order to constrain the tectonic drive and timing of polymetallic mineraliza-tion.There have been few attempts to date the multistage thermal events which the Bayan Obo Group has witnessed,predominantly because of greenschist facies overprint of the host rocks and lack of reliable geochronometers[9,10].

Secondary Phosphatization of the Earliest Cambrian Small Shelly Fossil Anabarites from Southern Shaanxi

Biomineralization may have an extremely long evolutionary history since the Paleoarchean, while the widespread biomineralization among metazoan lineages started at the earliest Cambrian. However, the primary mineralogy of Anabarites shell remains controversial. Optical microscopic observations combined with the Back-Scattered Electron（BSE） and Energy-Dispersive X-ray Spectroscopy（EDS） analyses are used to study the shell of the fossil Anabarites from the Kuanchuanpu fauna in southern Shaanxi Province in China, which is correlated to the Cambrian Fortunian Stage. The EDS analysis shows that the phosphorus-rich layer closely adjacent to the calcified layer exhibits a Ca： P： C ratio compositionally similar to the mineral fluorapatite（Ca_5（PO_4,CO_3）_3（F,CO_3）. The result that the calcified layer and the phosphorus-rich layer have different chemical compositions is consistent with the optical observation that there is an obvious gap between these two layers and the phosphorus-rich layer can extend to the phosphatic material inside of the tube, suggesting the phosphorus-rich layer doesn＇t belong to the original shell. We suggest that the phosphorous-rich layer is diagenetic in origin, precipitated as a result of phosphorus release during the decay of organic matter by microbes. Considering the outermost shell layer（OMS, biologically controlled carbonate shell layer） should display different isotopic information from the carbonate matrix（i.e., OMS is ^（12）C concentrated due to the biogenic organic matter template is readily rich in ^（12）C）, Nano SIMS was used to map ion distributions of C and N in the shell of Anabarites and matrix. However, ion images show that the concentration differences of ^（12）C, ^（13）C and ^（26）CN among the OMS and the matrix are unclear, while ^（12）C and ^（26）CN are supposed to be enriched in the OMS. Therefore, the minor isotopic differences between the shell and the matrix is hard to be detected by Nano SIMS, at least in our sample, probably due to alteration of the ^（12）C-rich characteristic of the Anabarites OMS during the late diagenesis.

Radical change in tectonic regime and paleo-environment at the end of Neoarchean evidenced by a unique metal co-existing deposit

Banded iron formation and Cu-Zn sulfide deposits within volcanic-argillaceous sequences(as volcanogenic massive sulphide deposits(VMS)-like type) occur together in the Qingyuan greenstone belt of the North China Craton,recording the first appearance of oxidized ores and sulfide ores co-existing in the early Earth.The unique metal co-existing deposits should meet two requirements:tectonic setting and sedimentary environment.As regards to tectonic setting,plate-like tectonics might have started since the end of the Neoarchean because continents had grown large enough and there occurred volcanic arcs and backarc basins similar to modern ones in a way.Partial melting of subducted continental crust is conductive to providing ore-forming elements.As for sedimentary environment,late Neoarchean seawater was rich in Fe^(2+) and anoxic.Instantaneous oxidation of the seawater resulted possibly from frequent submarine volcanic eruptions and facilitated precipitation of the banded iron formation.At this point,it is also favorable for the enrichment of Cu and Zn ions in seawater.The VMS-like deposits tended to form when the seawater was reduced again.Studies of isotopic elements like sulfur,oxygen,iron and silicon support the above geological processes.It is shown that the geologic conditions only existed in the late Neoarchean and Paleoproterozoic for a short period of time.The banded iron formations disappeared around 1.85 Ga,and the associated sulfide metal deposits also became dominant sedimentary exhalative deposits in the meso-Neoproterozoic Boring Billion,as a result of increasing oxidation of the oceans and the increasing maturity of the continental crust.This study is significant not only for decoding metallogenic genesis but also helping understand rapid change in Precambrian tectonic regimes and Earth’s environments.

Origin of the Low δ^(18)O Signals in Zircons from the Early Cretaceous A-Type Granites in Eastern China:Evidence from the Kulongshan Pluton

The origin of lowδ^(18)O signals in zircons from the Early Cretaceous A-type granites in eastern China has long been disputed.It is uncertain whether the^(18)O-depleted features were inherited from high-temperature hydrothermal altered source rock or resulted from water-rock interaction after emplacement.In this paper,zircon oxygen isotopes in the~130 Ma Kulongshan A-type granites in the northern North China Craton are analyzed.The zircons could be subdivided into 5 types based on their luminescent intensity and internal structures in CL images.Theirδ^(18)O values also vary in different types and show negative correlation with U and Th contents and accompanying cumulativeα-decay doses,implying that theirδ^(18)O values may have been modified to various degrees by meteoric water-rock interaction after the accumulation of radiation damage.The idea is further confirmed by oxygen isotopic equilibrium calculation between co-existing mineral pairs.It is inferred that only the least-influenced zircons,with slightly elevatedδ^(18)O values than normal mantle,have preserved the magmatic oxygen isotopes.In combination with other evidences,it is proposed that the A-type granites are lower-crustal-derived,unnecessarily invoking a high-temperature hydrothermal altered source.The proposition is applicable to many other Cretaceous A-type granites that have similar zircon behaviors.