What Happened in the Trans-North China Orogen in the Period 2560-1850 Ma?

The Trans-North China Orogen （TNCO） was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton （NCC）. Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greeustone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages. Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic （TTG） magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, -2250 Ma 2110-21760 Ma and -2050 Ma granites in the orogen. Contemporary volcano-sedimentary rocks developed in the back-arc or intra-are basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge, leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and the dosing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and transported some of the rocks into the lower crustal levels or upper mantle to form granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of asymmetric folds and symplectic textures in the rocks.

U-Pb Zircon Dating of the Granitic Conglomerates of the Hutuo Group:Affinities to the Wutai Granitoids and Significance to the Tectonic Evolution of the Trans-North China Orogen

The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and dassical cross-section in the middle segment of the Trans-North China Orogen, generally divided into Eastern and Western Blocks. Unconformably overlying the Wutai and Fuping Complexes is the Hutuo Group considered as the youngest lithostratigraphic unit in the region and important both for interpreting Precambrian history as well as the overall evolution of the Trans-North China Orogen. Lack of knowledge about provenance of the sedimentary rocks in this group has hindered understanding of the depositional environments and tectonic significance. LA-ICP-MS was applied to obtain U-Pb zircon ages for the granitic pebbles, the lowest lithostratigraphic rock of the Hutuo Group, which, combined with previous lithostratigraphic, geochronological, structural and metamorphic data, provides new constraints on the sedimentary provenance and tectonic evolution of the region. The sequence of the Hutuo Group ranges upward from lower basal conglomerates and volcaniclastic rocks （Doucun Subgroup）, through clastic sediments, slates, dolomites and marbles （Dongye Subgroup）, to sandstones and conglomerates at the top （Guojiazhai Subgroup）. Zircons from granitic pebbles preserved in the Doucun Subgroup basal conglomerates give weighted mean ^207pb/^206pb ages between 2517 Ma and 2566 Ma, which are the same as those for the late Archean Wutai Granitoids, indicating that the pebbles were derived from the Wutai granitic intrusions （2566-2515 Ma）. Based on the new data and previous studies, combined with an igneous zircon crystallization age of 2087±9 Ma obtained for volcanics in the Hutuo Group, the Hutuo Group was deposited in a subduction-related retro-arc foreland basin environment that developed behind the Wutai arc during the eastward-directed subduction of the Western Block beneath the western margin of the Eastern Block. This basin underwent long-lived sedimentation and finally closed during the -1850 Ma collisional event that resulted in the final amalgamation of the North China Craton.

U-Pb Age and Hf Isotope Study of Detrital Zircons from the Wanzi Supracrustals:Constraints on the Tectonic Setting and Evolution of the Fuping Complex,Trans-North China Orogen

Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton （NCC）. The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units： the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses （-2.5 Ga） and the Nanying granitic gneisses （2.0-2.1 Ga） and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from ＋1.4 to ＋10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to ＋6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.

LA-ICP-MS Zircon U-Pb Geochronology of the Fine-grained Granite and Molybdenite Re-Os Dating in the Wurinitu Molybdenum Deposit,Inner Mongolia,China

The Wurinitu molybdenum deposit,located in Honggor,Sonid Left Banner of Inner Mongolia,China,is recently discovered and is considered to be associated with a concealed fine-grained granite impregnated with molybdenite.The wall rocks are composed of Variscan porphyritic-like biotite granite and the Lower Ordovician Wubin'aobao Formation.LA-ICP-MS zircon U-Pb dating of the fine-grained granite reveals two stages of zircons,one were formed at 181.7±7.4 Ma and the other at 133.6±3.3 Ma.The latter age is believed to be the formation age of the fine-grained granite,while the former may reflect the age of inherited zircons,based on the morphological study of the zircon and regional geological setting.The Re-Os model age of molybdenite is 142.2±2.5 Ma,which is older than the diagenetic age of the fine-grained granite.Therefore the authors believe that the metallogenic age of the Wurinitu molybdenum deposit should be nearly 133.6±3.3 Ma or slightly later,i.e.,Early Cretaceous.Combined with regional geological background research,it is speculated that the molybdenum deposits were formed at the late Yanshanian orogenic cycle in the Hingganling-Mongolian orogenic belt,belonging to the relaxation epoch posterior to the compression and was associated with the closure of the Mongolia-Okhotsk Sea.

Ages and Hf isotopes of detrital zircons from the Permian strata in the engbatu area(Inner Mongolia) and tectonic implications

The Central Asian Orogenic Belt(CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoice Mesozoic time. To understand potential links among Paleozoic subduction and accretionary processes that were operative during the development of the southeastern CAOB, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from previously defined Devonian, Carboniferous and Early Permian strata in the Bengbatu area,Inner Mongolia. Detrital zircons from(meta-) sandstones in these strata commonly yield major Paleozoic age populations at ca. 300-261 Ma, 351-300 Ma and 517-419 Ma, and also give several Precambrian ages that range from 2687 Ma to 544 Ma. The youngest ages redefine the deposition of all these strata to be in the Middle Permian(Wordiane Capitanian) or later, much younger than previously considered.These ages, coupled with regional magmatic records, support an interpretation of most surrounding areas as possible detritus sources, including the Mongolian arcs to the north, the Northern Accretionary Orogen to the south, and the intervening Erenhote Hegenshan Ophiolite Belt. Zircons with magmatic ages of ca. 500-350 Ma and ca. 300-261 Ma display a large range of εHf(t) values(-13.97 to +15.31),whereas ca. 350-300 Ma zircons are dominated by positive εHf(t) values(+0.14 to +16.00). These results support the occurrence of two significant shifts of the zircon εHf(t) values, which has tectonic implications for the understanding of the Carboniferouse Permian evolution of the southeastern CAOB. A marked shift from mixed to positive zircon εHf(t) values at 350 -330 Ma likely manifests the incipient opening of the Hegenshan Ocean, due to the slab rollback of the subducting Paleo-Asian Oceanic lithosphere. Another shift from positive to mixed zircon εHf(t) values at ca. 300 Ma likely corresponds to a tectonic switch from syn-orogenic subduction-related to post-orogenic extensional setting, genetically related to the tectonic collapse of a formerly overthickened crust.

Biogeographic divergence in leaf traits of Sapindus mukorossi and Sapindus delavayi and its relation to climate

To explore differences in leaf morphology between Sapindus mukorossi and Sapindus delavayi,and how the environment might drive these differences,80 germplasm samples from the Sapindus germplasm nursery in Fujian Province were selected.The study revealed a wide variation and diversity in 16 germplasm traits,both within and between species grown under the same conditions.On average,the relative contribution of intraspecific variability to total variability was more important(83%) than the relative contribution of interspecific variability(17%).PERMANOVA analysis showed differences in leaflet thickness,length,perimeter,length to width ratio,and leaf hairs or trichome density.Correlation analyses between leaf morphological traits and environmental variables indicated that leaves tended to be larger,longer,and thicker in wetter,warmer,and low-altitude conditions.Our analysis of the relationship between climate and leaf morphology revealed that S.mukorossi had a greater sensitivity to climate variation,particularly in response to mean temperatures of the coldest and warmest seasons,which led to differences in leaf traits and the distribution of the two species.These findings contribute to the understanding of leaf morphology variations in S.mukorossi and S.delavayi,and provide a basis for the collection of Sapindus germplasm resources,their cultivation and use to help address climate change.

Geochemistry and Petrogenesis of Neoarchean Metamorphic Mafic Rocks in the Wutai Complex

Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns （Lan/Ybn=0.86-1.3）, the lowest total REEs （29-52 ppm）, and weak negative to positive Eu anomalies （Eun/Eun=0.84-1.02）, nearly flat primitive mantle normalized patterns and strong negative Zr（Hf） anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs （34-116 ppm）, LREE-enriched （Lan/Ybn=1.76-4.34） chondrite normalized REE patterns with weak Eu anomalies （Eun/Eun=0.76-1.16）, and negative Nb, Ta, Zr（Hf）, Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slab-derived fluids. Rocks in Group #3 are characterized by the highest total REEs （61-192 ppm）, the strongest LREEs enrichment （Lan/Ybn=7.12-16） with slightly negative Eu anomalies （Eun/Eun=0.81-0.95） in the chondrite normalized diagram. In the primitive mantle normalized diagram, these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies. They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts. The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.

Metamorphism of the northern Liaoning Complex:Implications for the tectonic evolution of Neoarchean basement of the Eastern Block,North China Craton

As one of the areas where typical late Archean crust is exposed in the Eastern Block of the North China Craton, the northern Laioning Complex consists principally of tonalitic-trondhjemitic-granodioritic （TTG） gneisses, massive granitoids and supracrustal rocks. The supracrustal rocks, named the Qingyuan Group, consist of interbedded amphibolite, hornblende granulite, biotite granulite and BIF. Petrological evidence indicates that the amphibolites experienced the early prograde （M1）, peak （M2） and post-peak （M3） metamorphism. The early prograde assemblage （M1） is preserved as mineral inclusions, represented by actinotite ＋ hornblende - plagioclase ＋ epidote ＋ quartz 4- sphene, within garnet porphyroblasts. The peak assemblage （M2） is indicated by garnet ＋ clinopyroxene ＋ hornblende ＋ plagioclase ＋ quartz ＋ ilmenite, which occur as major mineral phases in the rock. The post-peak assemblage （M3） is characterized by the garnet 4- quartz symplectite. The P-T pseudosections in the NCFMASHTO system constructed by using THERMOCALC define the P-T conditions of M1, M2 and M3 at 490-550 C＋（4.5 kbar, 780 810 C/7.65- 8.40 kbar and 630-670 ＋C]8.15-9.40 kbar, respectively. As a result, an anticlockwise P-T path involving isobaric cooling is inferred for the metamorphic evolution of the amphibolites. Such a P-T path suggests that the late Archean metamorphism of the northern Liaoning Complex was related to the intrusion and underplating of mantle-derived magmas. The underplating of voluminous mantle-derived magmas leading to metamorphism with an anticlockwise P-T path involving isobaric cooling may have occurred in continental magmatic arc regions, above hot spots driven by mantle plumes, or in continental rift envi- ronments. A mantle plume model is favored because this model can reasonably interpret many other geological features of late Archean basement rocks from the northern Liaoning Complex in the Eastern Block of the North China Craton as well as their anticlockwise P-T paths involving isobaric cooling.

Detrital zircon constraints on late Paleozoic tectonism of the Bogda region(NW China)in the southern Central Asian Orogenic Belt

The Chinese North Tianshan(CNTS)in the southern part of the Central Asian Orogenic Belt(CAOB)has undergone multistage accretion-collision processes during Paleozoic time,which remain controversial.This study addresses this issue by tracing the provenance of Late Paleozoic sedimentary successions from the Bogda Mountain in the eastern CNTS through U-Pb dating and Lu-Hf isotopic analyses of detrital zircons.New detrital zircon U-Pb ages(N=519)from seven samples range from 261±4 Ma to 2827±32 Ma.The most prominent age peak is at 313 Ma and subordinate ages vary from 441 Ma to 601 Ma,with some Precambrian detrital zircon ages(~7%)lasting from 694 Ma to 1024 Ma.The youngest age components in each sample yielded weighted mean ages ranging from 272±9 Ma to 288±5 Ma,representing the maximum depositional ages.These and literature data indicate that some previously-assumed"Carboniferous"strata in the Bogda area were deposited in the Early Permian,including the Qijiaojing,Julideneng,Shaleisaierke,Yangbulake,Shamaershayi,Liushugou,Qijiagou,and Aoertu formations.The low maturity of the sandstones,zircon morphology and provenance analyses indicate a proximal sedimentation probably sourced from the East Junggar Arc and the Harlik-Dananhu Arc in the CNTS.The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in the Harlik-Dananhu Arc.Zircon EHf(t)values have increased since^408 Ma,probably reflecting a tectonic transition from regional compression to extension.This event might correspond to the opening of the Bogda intraarc/back arc rift basin,possibly resulting from a slab rollback during the northward subduction of the North Tianshan Ocean.A decrease of zirconεHf(t)values at^300 Ma was likely caused by the cessation of oceanic subduction and subsequent collision,which implies that the North Tianshan Ocean closed at the end of the Late Carboniferous.

Screening of Sapindus germplasm resources in China based on agro-morphological traits

Sapindus L.species are widely cultivated for biodiesel,biomedical,and biochemical raw materials in southern China.However,yields fuctuate widely due to the lack of high-yielding,high-quality,stable cultivars.Therefore,the objectives of this study were to evaluate three species and one variety among 149 nationwide Sapindus species and screen for elite accessions which would serve as Sapindus breeding materials.Accessions were evaluated on 19 agro-morphological traits by correlation analysis and principal component analysis.These displayed substantial diversity and a broad range of economic traits.In particular,accessions of Sapindus mukorossi and Sapindus rarak had more variation in economic traits than Sapindus delavayi and Sapindus rarak var.velutinus.Increased saponin accumulation may be achieved at the cost of seed oil production.Thirty elite accessions for oil and saponin production,and for comprehensive utilization were screened and accessions no.80,110,and 112 had significant potential to produce high yields.These elite accessions will facilitate the identification of genetic determinants of valuable traits and the effective utilization of trait variability in Sapindus breeding.

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.

Pre-Cryogenian integrative stratigraphy,biotas,and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

The composition and geological evolution of pre-Cryogenian material in the Tibetan Plateau and its surrounding areas have played an important role in studying the formation and evolution of early supercontinents on Earth.This paper systematically summarizes the characteristics of pre-Cryogenian sedimentation,paleontology,magmatism,and metamorphism in the Tibetan Plateau and its surrounding areas.Based on existing data,the records of pre-Cryogenian sedimentation and paleontology are mainly concentrated in the Meso-Neoproterozoic,with relatively few records from the Paleoproterozoic or earlier.The oldest geological record is the Hadean detrital zircons in the metamorphosed sedimentary rocks of the Himalaya and Qamdo areas(ca.4.0 Ga).The Tibetan Plateau and surrounding areas preserve records related to the formation and evolution of the Kenor supercraton,and the Columbia,Rodinia,and Gondwana supercontinents.Pre-Cryogenian basements can be divided into three types:Tarim-,Yangtze-,and Lhasa-type.The Tarim-type basement has a paleogeographic affinity with the northern margins of the Australian and Indian continents and lacks detrital zircon age peaks and magmatic-metamorphic records related to the Rodinia assembly(ca.1.3-0.9 Ga).The Yangtze-type basement records volcanic activity related to global cooling in the latest pre-Cryogenian period and contains Meso-Neoproterozoic stromatolite and micropaleoflora fossils,as well as magmaticmetamorphic records related to Rodinia assembly(ca.1.1-1.0 Ga).The Lhasa-type basement is characterized by Neoproterozoic rift-related sediment records(ca.900 Ma)and high-pressure metamorphic events(ca.650 Ma),with a prominent peak of detrital zircon ages of ca.1.2-1.1 Ga.It is likely to have a paleogeographic affinity with the African continent.

前板块构造与大陆起源

建立于20世纪60年代并被誉为地球科学史上一场革命的板块构造理论能圆满地解释显生宙至元古宙几乎所有地质现象、过程和事件,但却无法解释太古宙大陆克拉通基本特征,包括绿岩带内高温(~1600°C)科马提岩的成因和缺乏岩浆弧安山岩的双峰式火山岩组合,占太古宙陆壳总面积70%以上、几乎同时侵位的英云闪长岩-奥长花岗岩-花岗闪长岩岩石成因,反映垂向运动的片麻岩穹窿构造样式,缺失典型的蛇绿岩、蓝片岩、榴辉岩和双变质带等板块构造特征标志.所有这些都说明,太古宙大陆可能不是起源于板块构造体制,而是起源于某种前板块构造体制,但目前已提出的前板块构造模式(如地幔柱构造、重力凹沉构造、热管构造、滞留盖构造等)同样皆不能圆满解释太古宙大陆的岩石组合、构造样式和变质作用演化等特征.正因如此,目前世界各国有若干研究团队正在攻克这一科学难题.我国学者虽无缘参与20世纪60年代板块构造理论的创立,但在过去40年里,在早期地球动力学体制和大陆起源与演化方面开展了大量工作,并取得令人瞩目的研究成果,积累了大量资料数据,有望在构建前板块构造理论方面率先取得突破.

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.

Early Cambrian high pressure/low temperature metamorphism in the southeastern Tarim craton in response to circum-Gondwana cold subduction

The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics.The metamorphic rocks with low thermobaric(T/P)ratios indicative of cold subduction in the present tectonic regime have not been well investigated.To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics,this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton.Mineral assemblage and chemistry,phase equilibrium modelling,and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane(Gln)-bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschistfacies at 520–545℃ and 16–19 kbar.It reflects high-pressure(HP)/low temperature(LT)metamorphism with low T/P ratios of<300℃/GPa and thermal gradients of<10℃/km.These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of<495℃ and<9.6 kbar during exhumation.Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520–506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522–516 Ma for the Gln-bearing quartz schist samples,suggesting that the peak HP/LT metamorphism occurred prior to ca.522 Ma.Based on new results and available data from the major Gondwana blocks,cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana.The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth’s history associated with the establishment of the modern plate tectonics,as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.

Newly discovered youngest UHT metamorphism on Earth,Western Sulawesi,Indonesia

Ultrahigh-temperature(UHT)metamorphism represents an extreme crustal thermal event with peak conditions exceeding 900C at 7–13 kbar.In the modern-style plate tectonic system,records of the UHT metamorphism are relatively rare due to the secular cooling of Earth.In the Palu region of Western Sulawesi,we newly discovered a series of HT-UHT metamorphic rocks including amphibolite,granulite,eclogites and gneiss.Of them,two granulite samples(18CS14-2,18CS14-4)with high garnet content(>50 mol%)are chosen for petrographic observation,phase equilibrium modelling,and zircon U-Pb dating.These rocks are characterized by a relic M1 assemblage of Grt+Ky+Bt+Rt and a M2 assemblage of Grt+Sil+Pl+Spl+Crd±Qtz+Ilm+melt.Phase equilibrium modelling based on effective bulk compositions yields UHT conditions of 7.2–8.5 kbar/940–1080C(18CS14-2)and 7.0–7.3 kbar/1000–1040C(18CS14-4).U-Pb analysis reveals two generations of metamorphic zircon with evolving REE content that is intimately related to garnet growth and decomposition.Zircon age of 36–5.3 Ma is ascribed to syn-to post-M1 metamorphism,whereas the young zircon age of 5.1–3.8 Ma is linked to syn-and post-M2 stage.The UHT metamorphism was probably the consequence of the upwelling of asthenospheric mantle triggered by post-collisional delamination of lithosphere in the MiocenePliocene(ca.5 Ma).It could represent the youngest known UHT metamorphism on Earth.

地质学科未来5~10年发展战略:趋势与对策

当代地球科学的内涵和外延已经拓展到涵盖整个固体地球内部及外部层圈形成演化及与资源能源富集、生态环境变迁、地球宜居性和社会可持续发展相关的地球系统科学问题.随着人类社会经济高速发展,与地球相关的资源能源、气候环境、地质灾害等问题日益突出.为了适应新时代地球科学发展形势,在地球系统科学理论框架下,准确分析我国地球科学未来5~10年的发展趋势、明确战略目标和优先发展领域,不仅能够大力促进和强化我国地球科学的发展、赶超世界领先水平、早日实现从地质大国到地质强国的转变,而且对于保障国家矿产能源安全、助推国家经济建设和人类社会可持续发展具有重大意义.

Two styles of plate tectonics in Earth’s history

When plate tectonics started to occur on Earth and how it has evolved through time are two of the most fundamental questions in earth sciences. While gravity-driven subducting has been accepted as a critical condition for the operation of plate tectonics on Earth, it is intriguing how the dynamic regime and thermal state of subduction zones have affected the style of plate tectonics in Earth’s history. The metamorphic rocks of regional distribution along convergent plate boundaries record reworking of crustal rocks through dehydration and melting at lithospheric depths. The property of regional metamorphism is determined by both dynamic regime and thermal state of plate margins. The two variables have secularly evolved in Earth’s history, which is recorded by changes in the global distribution of metamorphic facies series through time. This results in two styles of plate tectonics. Modern-style plate tectonics has developed since the Neoproterozoic when plate margins were rigid enough for cold subducting, whereas ancient-style plate tectonics has developed since the Archean when plate margins were ductile enough for warm subducting. Such a difference is primarily dictated by higher mantle temperatures in the Archean than in the Phanerozoic. The development of plate subduction in both cold and warm realms is primarily dictated by the rheology of plate margins. This leads to a holistic model for the style of plate tectonics during different periods in Earth’s history.

Genesis of the Xinfang Gold Deposit,Liaodong Peninsula:In-sights from Fluid Inclusions and S-Sr Isotopic Constraints

The North China Craton(NCC)has been continuously reactivated since the Mesozoic and this decratonization is responsible for its economically important gold mineralization in the Meso-zoic.The Early Cretaceous(110-130 Ma)gold mineralization in the NCC has been well-studied due to its significance,but little attention has been given to other episodes of gold mineralization related to polyphased reactivation of the NCC.The Xinfang mesozonal gold deposit(143 Ma)in the Liaodong Peninsula is related to the one of the episodes of the Yanshanian orogeny.The orebodies of the Xin-fang gold deposit were controlled by the low angle transpressive fault systems and hosted by the Neoarchean monzogranitic gneiss.Fluid inclusion microthermometry reveals that the mineralizing temperatures range from 220 to 280℃,with salinities from 6 wt.%NaCl eqv.to 15 wt.%NaCl eqv.,pressures from 199 to 321 Ma.The S isotopic characteristics of sulfides not only record a heterogene-ous source including magmatic or gneissic sulfur but also record inter-mineral isotope fractionation.The initial^(87)Sr/^(86)Sr values of pyrite(0.713480-0.729031)indicate a radiogenic crustal origin for the sources.The metamorphic dehydration of the underlying basement resulted in the genesis of the Xin-fang gold deposit.We summarize three episodes of gold mineralization in the Liaodong Peninsula re-lated to continuous reactivation of the NCC,which indicates a great exploration potential of this area.

Carboniferous slab-retreating subduction of backarc oceans:the final large-scale lateral accretion of the southern Central Asian Orogenic Belt

During Carboniferous time,tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt(CAOB),although its origin remains unclear.Herein,we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia.These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons,probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north,indicative of a continental arc nature.In addition,they have a main zircon U-Pb age of ca.370–330 Ma,positive Hf and Nd isotopes,and mafic-intermediate arc affinity,similar to the coeval arc magmatism.Moreover,the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time(ca.350–370 Ma;Visean and Bashkirian stages)earlier than that in the southern area(mainly ca.350–315 Ma;Serpukhovian and Bashkirian stages).Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean(PAO)during Carboniferous and Triassic times,we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback.Thus,the juvenile arc volcanism of Mongolia,together with other areas(e.g.,Junggar)in the southern CAOB,represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO.