Paleoproterozoic crustal evolution of the Hengshan–Wutai–Fuping region, North China Craton

An arguable point regarding the Neoarchean and Paleoproterozoic crustal evolution of the North China Craton（NCC）is whether the tectonic setting in the central belt during the mid-Paleoproterozoic（2.35-2.0 Ga）was dominated by an extensional regime or an oceanic subduction-arc regime.A review of the midPaleoproterozoic magmatism and sedimentation for the Hengshan-Wutai-Fuping region suggests that a back-arc extension regime was dominant in this region.This conclusion is consistent with the observation that the 2.35-2.0 Ga magmatism shows a typical bimodal distribution where the mafic rocks mostly have arc affinities and the acidic rocks mainly comprise highly-fractioned calc-alkaline to alkaline（or A-type）granites,and that this magmatism was coeval with development of extensional basins characteristic of transgressive sequences with volcanic interlayers such as in the Hutuo Group.Although the final amalgamation of the NCC was believed to occur at ～1.85 Ga,recent zircon U-Pb age dating for mica schist in the Wutai Group suggests a collisional event may have occurred at ～1.95 Ga.The metamorphic ages of ～1.85 Ga,obtained mostly from the high-grade rocks using the zircon U-Pb approach,most probably indicate uplifting and cooling of these high-grade terranes.This is because（i）phase modeling suggests that newly-grown zircon grains in highgrade rocks with a melt phase cannot date the age of peak pressure and temperature stages,but the age of melt crystallization in cooling stages;（ii）the metamorphic P-T paths with isobaric cooling under 6-7 kb for the Hengshan and Fuping granulites suggest their prolonged stay in the middle-lower crust;and（iii）the obtained metamorphic age data show a continuous distribution from 1.95 to 1.80 Ga.Thus,an alternative tectonic scenario for the Hengshan-Wutai-Fuping region involves：（i）formation of a proto-NCC at ～2.5 Ga;（ii）back-arc extension during 2.35-2.0 Ga resulting in bimodal magmatism and sedimentation in rifting basins on an Archean basement;?     

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.     

Sm—Nd and Zircon U—Pb Isotopic Constraints on the Age of Formation of the Precambrian Crust in Southeast China

Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.     

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

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 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 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 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 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.     

Neoarchean (2.5-2.8 Ga) crustal growth of the North China Craton revealed by zircon Hf isotope: A synthesis

The crustal growth of the North China Craton(NCC) during the Neoarchean time(2.5—2.8 Ga) is a hotly controversial topic,with some proposing thai the main crustal growth occurred in the late Neoarchean (2.5—2.6 Ga),in agreement with the time of the magmatism,whereas others suggest that the main crustal accretion took place during early Neoarchean time(2.7—2.8 Ga),consistent with the time of crustalformation of other cratons in the world.Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC.In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC.The results suggest that both 2.7—2.8 Ga and 2.5—2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested.The Eastern block is characterized by the main 2.7—2.8 Ga crustal growth with local new crustal-formation at 2.5—2.6 Ga,and the Yinshan block is characterized by～2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group.Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some～2.6 Ga and minor Early- to Middle-Archean crustal components,and the crustal accretion in the Trans-North China Orogen(TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy.Zircon Hf isotope compositions,coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO,and the evolution and tectonic division of the NCC is more complex than previously proposed,probably involving multi-stage crustal growth and subduction processes.However, there is no doubt that 2.7—2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered,which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover,modern river sediments and Late Neoarchean syenogranites.     

Stratigraphy and Zircon Provenance of a Late Paleoproterozoic Terrestrial Sequence underlying the Xiong’er Volcanics in the Southern North China Craton

The late Paleoproterozoic Dagushi Formation comprises a fluvial-lacustrine succession and represents the initial fill of the Xiong’er Basin in the southern North China Craton. Employing integrated outcrop surveys and detrital zircon U-Pb-Hf dating, this study examines the provenance and depositional setting of the Dagushi Formation. Five major depositional facies, including braided channel, distributary channel, subaqueous stream/mouth bar, pro-delta and shallow lake, were identified, based on lithofacies and associations. They were interpreted as representing a braided river delta-lacustrine system. The ages of the last metamorphic event of the basement, covering volcanics and the youngest zircon together constrain a depositional age of ca. 1.79 Ga for the Dagushi Formation. Zircon age distributions reveal a provenance change from ca. 2.7–2.5 Ga rocks in the lower part, to ca. 2.3–1.9 Ga sources in the middle-upper part of the Dagushi Formation. Considering the vertical sedimentology, this provenance change could be induced by the rising water-level caused by a tectonic subsidence. The ca. 2.7–2.5 Ga zircons are suggested to be locally sourced from the late Neoarchean–Paleoproterozoic metamorphic basement. The northeast Zhongtiao Mts area (current co-ordinates) is supposed to have appeared as a paleo-uplift and served as a source area for the Paleoproterozoic grains. The Dagushi Formation records an early ‘underfilled’ stage of the Xiong’er Rift.     

Combined U-Pb SHRIMP and Hf isotope Complex, Rio Negro Province, Argentina： of the Patagonia composite terrane study of the Late Paleozoic Yaminué Implications for the origin and evolution

We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminue Complex,and re-evaluate this complex in the broader context of the tectonic evolution of the Patagonia composite terrane.In the metasedimentary unit （msuYC）,the youngest detrital zircon dated at 318±5 Ma（Mississippian/Pennsylvanian boundary） indicates a Pennsylvanian（or younger） depositional age.The three main age populations peak at 474,454 and 374 Ma.Preliminary Hf isotope data for two detrital zircons（447 and 655 Ma） yieldedε（Hf） values of -0.32 and 0.48,indicating that their primary sources contained small amounts of recycled crustal components(of Calymmian age;T_DM 1.56 Ga).Zircons from the orthogneiss（miuYC;intrusive into msuYC） show a crystallization age of 261.3±2.7 Ma（Capitanian;late middle Permian） which is broadly coeval with deformation,and Neoarchean-Paleoproterozoic inheritance.Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined,indicating the occurrence of Archean crust in this sector of Patagonia.Hf T_DM of Permian zircons is mainly Meso-Paleoarchean（2.97-3.35 Ga）,with highly negativeε（Hf） values（ca.-33）.Hf T_DM of inherited Neoarchean zircon cores is also Meso-Paleoarchean（3.14-3.45 Ga） but more juvenile（ε（Hf） = -0.3）.Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data,as well as geophysical models,we identify the Yaminue Complex within the La Esperanza-Yaminue crustal block flanked by two other,distinct crustal blocks:the Eastern block which forms part of the Patagonia terrane sensu stricto,located in the eastern Patagonian region,and the Western block forming part of the Southern Patagonia terrane.Their origins and timing of amalgamation to form the Patagonia composite terrane are also discussed.     

Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent: Insights from the shoshonitic high Ba–Sr Montezuma granitoids

New,integrated petrographic,mineral chemistry,whole rock geochemical,zircon and titanite UPb geochronology,and zircon Hf isotopic data from the Montezuma granitoids,as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex,provides new insights into the late-to post-collisional evolution of the northeastern Sao Francisco paleocontinent.U-Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca.2.2 Ga to 1.8 Ga and comprise distinct groups.Group I have crystallization ages between ca.2.15 Ga and 2.05 Ga and are interpreted as inherited grains.Group II zircon dates vary from 2.04 Ga to1.9 Ga and corresponds to the crystallization of the Montezuma granitoids,which were constrained at ca.2.03 Ga by the titanite U-Pb age.Inverse age zoning is common within the ca.1.8 Ga Group III zircon ages,being related to fluid isotopic re-setting during the Espinhaco rifiting event.Zircon ε_(Hf)(t) analysis show dominantly positive values for both Group I(-4 to+9) and Ⅱ(-3 to+8) zircons and T_(DM2) model ages of 2.7-2.1 Ga and 2.5-1.95 Ga,respectively.Geochemically,the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids,enriched in LILES and LREE,with high to moderate Mg#and depleted in some of the HFSE.Their lithochemical signature,added to the juvenile signature of both inherited and crystallized zircons,allowed its classification as a shoshonitic high Ba-Sr granitoid related to a late-to post-collisional lithosphere delamination followed by asthenospheric upwelling.In this scenario,the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc,being these hybrid magma interpreted as the source of the Montezuma granitoids.The Corrego Tingui Complex host rocks are akin to a syn-to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks.The results presented in this study have revealed the occurrence of juvenile rocks,probably related to an island arc environment,that are exotic in relation to the Paleo-to Neoarchean crust from the Sao Francisco paleocontinent's core.     

Recognition of Early Paleozoic Magmatisms in the Supposed Proterozoic Basements of Zhalantun, Great Xing’an Range, NE China

The Zhalantun terrane from the Xing'an massif, northeast China, was used to be considered as Proterozoic basements. However, amounts of detrital zircon ages from the meta-sedimentary rocks deny the existence of Precambrian basements recently. Notably, magmatic rocks were barely reported to limit the exact ages of the Zhalantun basements. In this study, we collected rhyolite, gabbro and quartz diorite for zircon in-situ U-Pb isotopic dating, which yield crystallization ages of ～505 Ma, ～447 Ma and ～125 Ma, respectively. Muscovite schist and siltstone define maximum depositional ages of ～499 Ma and ～489 Ma, respectively. Additionally, these dated supracrustal rocks and plutons also yield ancient detrital/xenocryst zircon ages of ～600–1000 Ma, ～1600–2220 Ma, ～2400 Ma, ～2600–2860 Ma. Based on the whole-rock major and trace element compositions, the ～505 Ma rhyolites display high SiO_2 and alkaline contents, low Fe_2O_3T, TiO_2 and Al_2O_3, and relatively high Mg O and Mg#, which exhibit calc-alkaline characteristics. These rhyolites yield fractionated REE patterns and negative Nb, Ta, Ti, Sr, P and Eu anomalies and positive Zr anomalies. The geochemistry, petrology and Lu-Hf isotopes imply that rhyolites were derived from the partial melting of continental basalt induced by upwelling of sub-arc mantle magmas, and then experienced fractional crystallization of plagioclase, which points to a continental arc regime. The ～447 Ma gabbros exhibit low Si O2 and alkaline contents, high Fe2 O3 T, Ti O2, Mg O and Mg#. They show minor depletions of La and Ce, flat MREE and HREE patterns, and negative Nb, Ta, Zr and Hf anomalies. Both sub-arc mantle and N-MORB-like mantle were involved in the formation of the gabbros, indicative of a probable back-arc basin tectonic setting. Given that, the previously believed Proterozoic supracrustal rocks and several plutons from the Zhalantun Precambrian basements were proved to be Paleozoic to Mesozoic rocks, among which these Paleozoic magmatic rocks were generally related to subduction regime. So far, none Proterozoic rocks have been identified from the Zhalantun Precambrian basement, though some ～600–3210 Ma ancient detrital/xenocryst zircons were reported. Combined with ancient zircon ages and newly reported ～2.5 Ga and ～1.8 Ga granites from the south of the Zhalantun, therefore, the Precambrian rocks probably once exposed in the Zhalantun while they were re-worked and consumed during later long tectonic evolutionary history, resulting in absence of Precambrian rocks in the Zhalantun.     

LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207Pb/206Pb age in the range of (2 493±54) -(2 500±180) Ma. The magmatic genesis-derived detrital zircon domain gives a 207Pb/206Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206Pb/238U age of (2 790±150) Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a dicsordia with an upper intercept age of (2 044.7±29.3) Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. ～2.8 Ga magmatism and ～2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at (2.04±0.03) Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT (ultrahigh temperature) metamorphosed slab.     

Genesis of the Ore-related Granite Porphyry and Molybdenite Re-Os Age of Laomiaogou Porphyry-skarn Mo Deposit,Western Henan Province: Implications for Regional MineralizationEI北大核心CSCD

The newly discovered Laomiaogou porphyry-skarn Mo deposit is located south of the Machaoying fault in western Henan province. The ore-body is hosted in the contact between the Laomiaogou granite porphyry dyke and the Duguan Formation. LA-ICP-MS U-Pb analyses for zircons from the granite porphyry yield a weighted mean 206Pb/238U age of 152.1±0.6 Ma, and seven molybdenite separates yield a weighted mean age of 151.9±0.9 Ma and isochron age of 151.6±5.1 Ma. Thus, the granite porphyry dyke and Mo mineralization are contemporaneous. The ore-related granite porphyry dyke is a peraluminous I-type granite with high contents of SiO2 and K2O. The rocks are strongly depleted in P, Nb, Ta and Ti, indicative of intensive fractionation of apatite and Fe-Ti oxides, and characterized by low whole-rock εNd(t) (-20.6 to -17.6) and zircon εHf(t) values (-26.9 to -22.6). The old tDM2(Nd) ages (2.37 to 2.61 Ga) and zircon tDM2(Hf) ages (2.62 to 2.88 Ga) suggest that the granite porphyry was likely derived from an ancient crustal source. Considering the tectonic evolution and geochemical characteristics of the granite as well as other Mesozoic granites in the southern margin of the North China Craton, we suggest that the Laomiaogou granite porphyry dyke and Mo were most likely derived from partial melting of the Taihua Group metamorphic rocks under extensional tectonic regime related to the subduction of the paleo-pacific plate. © 2018, Science Press. All right reserved.     

Petrogenesis of the Chaihulanzi Gneiss and its Tectonic Implications for the North China Craton

The Chaihulanzi area in eastern Inner Mongolia is tectonically situated on the northern margin of the North China Craton (NCC). The main Precambrian lithologies of the area have been referred to the Archean Jianping Group meta-supracrustal sequences. Based on field observations, petrographic, whole-rock geochemical, and zircon U-Pb geochronological results, a magmatic origin for the units is proposed. Our results show that the Chaihulanzi gneisses are mainly of granitic, dioritic and granodioritic compositions, and show typical magmatic rock textures and mineral assemblages. The dioritic and granodioritic gneisses show Na-rich tonalite–trondhjemite–granodiorite (TTG)-like affinity with zircon U-Pb dates of ca. 2.57–2.59 Ga, representing a juvenile continental growth for the northeastern NCC. The granitic gneiss is indeed potassic granite and yielded a zircon U-Pb date of ~2.50 Ga, which is contemporaneous with the Jining–Jiaoliao microblock collision (2.53–2.49 Ga), implying another crustal growth event. The well-developed gneissosity in 2.57–2.59 Ga dioritic and granodioritic gneisses together with the 2.5 Ga potassic granite, which crosscuts the gneissosity implies a 2.57–2.50 Ga (mainly 2.53–2.51 Ga) collisional orogeny, probably related to the Jining–Jiaoliao microblock collision. Our new geology and chronological results provide new evidence for the early Precambrian tectonic evolution of the NCC.     

The final collision of the CAOB: Constraint from the zircon U–Pb dating of the Linxi Formation, Inner Mongolia

The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt(CAOB).The Linxi Formation is composed of slate,siltstone,sandstone and plant,lamellibranch microfossils in the associated strata.Major and trace element data(including REE) for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity.LA-ICPMS U—Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation.425—585 Ma,together with the ~500 Ma age for the metamorphism event previously determined for Northeast China,indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China.A few older zircons with U-Pb ages at 1689-1801 Ma,1307-1414 Ma,593-978 Ma are also present,revealing the Neoproterozoic history of NE China.The youngest population shows a peak at ca.252 Ma,suggesting that the main deposition of the Linxi Formation was at late Permain.Moreover,the ca.250 Ma zircon grains of all four samples yield weighted mean ~(206)Pb/~(238)U ages of 250 ± 3 Ma,248 ± 3 Ma,249 ± 3 Ma,and 250 ± 2 Ma,respectively.These ages,together with the youngest zircon age in the sample ZJB-28(ca.238 Ma),suggest that the deposition of the Linxi Formation extended to the early Triassic.Combining with previous results,we suggest that the final collision of the Central Asian Orogenic Belt(CAOB) in the southern of Linxi Formation,which located in the Solonker-Xra Moron-Changchun suture,and the timing for final collision should be at early Triassic.     

Detrital Zircon U-Pb Geochronology and Provenance of the Hebukesaier Formation in the Shaerbuerti Mountains, Northern West Junggar: Implication for Devonian Subduction of the Junggar–Balkhash Ocean

Limited Devonian magmatic record in northern West Junggar leads to contrasting models on its tectonic evolution. In this study, we conducted LA-ICP-MS U-Pb dating on detrital zircons of two sandstones from the Hebukesaier Formation in the Shaerbuerti Mountains. Detrital zircons with oscillatory zoning are characterized by high Th/U (> 0.3) and low La/Yb (< 0.15), indicating their magmatic origin. The youngest zircon ages of two samples are 402 ± 2 Ma and 406 ± 2 Ma, respectively, suggesting that the Hebukesaier Formation was deposited at the Early Devonian. Detrital zircon age patterns show single peaks (at ca. 424 Ma, n =157), which indicates that these clastics were likely proximal accumulation after short distance transportation. Provenance of the Hebukesaier Formation was the Xiemisitai and Shaerbuerti Mountains. Detrital zircon ages range from 481 Ma to 395 Ma, which indicates that there was relatively continuous Early Paleozoic magmatism in the Xiemisitai and Shaerbuerti Mountains since the Early Ordovician. Age spectrums of sampled detrital zircons are distinct from those of Lower Devonian strata either in southern West Junggar or in East Junggar, which implies for individual tectonic evolution of northern West Junggar. We favor that Lower Devonian Hebukesaier Formation was developed in a fore–arc setting due to the northward subduction of the Junggar–Balkhash Ocean.     

Ages of the Laocheng Granitoids and Crustal Growth in the South Qinling Tectonic Domain, Central China: Zircon U-Pb and Lu-Hf Isotopic Constraints

The Laocheng granitoid pluton is located in the South Qinling tectonic domain of the Qinling orogenic belt,southern Shaanxi Province,and consists chiefly of quartz diorite,granodiorite and monzogranite.A LA-ICP-MS zircon U-Pb isotopic dating,in conjunction with cathodoluminescence images,reveals that the quartz diorite and granodiorite were emplaced from 220 Ma to 216 Ma,while the monzogranite was emplaced at～210 Ma.In-situ zircon Hf isotopic analyses show that theε_(Hf)(t) values of the quartz diorite a...     

Geochemistry and detrital zircon records of the Ruyang-Luoyu groups,southern North China Craton:Provenance,crustal evolution and Paleo-Mesoproterozoic tectonic implications

Paleo-to Mesoproterozoic sedimentary rocks in the southern margin of the North China Craton(NCC)are represented by the Ruyang and Luoyu groups.We studied the sedimentary rocks from the Yunmengshan and Beidajian formations of the Ruyang Group and the Cuizhuang and Sanjiaotang formations of the Luoyu Group.Detrital zircon grains from these formations have U–Pb age populations of 3.64–3.31 Ga,2.96–2.86 Ga,2.72–2.59 Ga,2.56–2.47 Ga,2.45–2.0 Ga,1.99–1.85 Ga and 1.84–1.65 Ga.The geochemical features of the sedimentary rocks suggest that some of the sediments were sourced from intermediate to felsic magmatic rocks.The age groups of the detrital zircon are roughly consistent with the tectono-thermal events in the southern margin of the NCC.The Hf isotopic compositions of detrital zircon from the sedimentary rocks in Ruyang and Luoyu groups suggest that significant crustal growth and reworking of the NCC took place during the Neoarchean and early-to mid-Paleoproterozoic,while crustal reworking at the Paleoarchean and late-Paleoproterozoic,and crustal growth at the Mesoarchean.We suggest the depositional times of the Ruyang Group and Luoyu Group are constrained to no older than 1.75–1.7 Ga and 1.7–1.65 Ga,respectively.Formation of late-Paleoproterozoic basins related to the strike slip and extrusion tectonics that cross-cut the NCC during the late Paleoproterozoic(<1.75 Ga),and the late Paleoproterozoic sedimentation once isochronous developed in the southern margin of the NCC through the Taihang region of the interior NCC and linked the Yanshan–Liaoxi regions of the northern NCC.     

Lower Cretaceous turbidites in the Shiquanhe–Namco Ophiolite Mélange Zone,Asa area,Tibet:Constraints on the evolution of the Meso-Tethys Ocean

Turbidites from the Shiquanhe–Namco Ophiolite Mélange Zone(SNMZ) record critical information about the tectonic affinity of the SNMZ and the evolutionary history of the Meso-Tethys Ocean in Tibet.This paper reports sedimentologic,sandstone petrographic,zircon U-Pb geochronologic,and clastic rocks geochemical data of newly identified turbidites(Asa Formation) in the Asa Ophiolite Mélange.The youngest ages of detrital zircon from the turbiditic sandstone samples,together with ～115 Ma U-Pb concordant age from the tuff intercalation within the Asa Formation indicate an Early Cretaceous age.The sandstone mineral modal composition data show that the main component is quartz grains and the minor components are sedimentary and volcanic fragments,suggesting that the turbidites were mainly derived from a recycled orogen provenance with a minor addition of volcanic arc materials.The detrital U-Pb zircon ages of turbiditic sandstones yield main age populations of170–120 Ma,300–220 Ma,600–500 Ma,1000–700 Ma,1900–1500 Ma,and ～2500 Ma,similar to the ages of the Qiangtang Terrane(age peak of 600–500 Ma,1000–900 Ma,～1850 Ma and ～2500 Ma) and the accretionary complex in the Bangong–Nujiang Ophiolite Zone(BNMZ) rather than the age of the Central Lhasa Terrane(age peak of ～300 Ma,～550 Ma and ～1150 Ma).The mineral modal compositions,detrital U-Pb zircon ages,and geochemical data of clastic rocks suggest that the Asa Formation is composed of sediments primarily recycled from the Jurassic accretionary complex within the BNMZ with the secondary addition of intermediate-felsic island arc materials from the South Qiangtang Terrane.Based on our new results and previous studies,we infer that the SNMZ represents a part of the Meso-Tethys Suture Zone,rather than a southward tectonic klippe of the BNMZ or an isolated ophiolitic mélange zone within the Lhasa Terrane.The Meso-Tethys Suture Zone records the continuous evolutionary history of the northward subduction,accretion,arc-Lhasa collision,and Lhasa-Qiangtang collision of the Meso-Tethys Ocean from the Early Jurassic to the Early Cretaceous.     

Early Neoproterozoic Granite-Gneisses of the Junggar Alataw (Southeastern Kazakhstan): Age, Petrogenesis and Tectonic Implications

The combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2-type granites. The whole-rock Nd isotopic characteristics (εNd(t) = ?4.9 to ?1.0 and TNd(DM-2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.     

Detrital Zircon of 4100 Ma in Quartzite in Burang, Tibet

A detrital zircon aged 4.1 Ga is discovered by the SHRIMP U-Pb method in a quartzite in Burang County, western Tibet. This is presently the oldest single-grain detrital zircon in China. The Th-U ratios of the two testing points of the 〉4.0 Ga zircon are between 0.76 and 0.86, indicating their magmatic origin. This discovery has offered an important age for investigating the geological evolution of the Qinghai-Tibet Plateau.     

Geochemistry, Geochronology, and Hf isotopic Composition of the Late Paleoproterozoic Lujiapuzi Formation, NE Yan-Liao Rift, Northern Liaoning

The metasedimentary Lujiapuzi Formation crops out along the northeastern margin of the North China Craton, close to the Yan-Liao Rift. The age and tectonic setting of the formation, and its relationship with the Yan-Liao Rift are currently unclear. Here we present detrital zircon U-Pb ages, and Hf isotopic and geochemical data for the Lujiapuzi Formation to constrain the timing of deposition, the provenance of the formation, and the regional stratigraphy relationship. Zircon U-Pb dating constrains the timing of deposition of the Lujiapuzi Formation to younger than 1780 Ma, and indicates that most grains were sourced from the Longgang Block and the Paleoproterozoic Liao-Ji Belt. Detailed field investigations and a correlation of the regional stratigraphy reveal that much of the Lujiapuzi Formation is equivalent to the Tuanshanzi Formation in the Yan-Liao Rift; the lower section may represent the earliest sediments deposited within the Fanhe Basin. Based on these results and the findings of previous studies, we suggest that the base of the Changcheng System has an age of 1.80 Ga. Zircon Hf isotopic data indicate that the main period of crustal growth along the northeastern margin of the North China Craton occurred at 3.2–2.5 Ga, with a peak at 2.9–2.7 Ga.