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    SHRIMP U-Pb zircon geochronology of the Fuping Complex implications for formation and assembly of the North China Craton [查看] HongGuan、MinSun、SimonA.Wilde、XinhuaZhou、MingguoZhai
    The Fuping Complex, located within the central zone of the North China Craton, is composed of amphibolite to granulite facies orthogneisses, interleaved with minor supracrustal rocks at similar metamorphic grade. The oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a SHRIMP U–Pb zircon age of 27088 Ma. We consider these enclaves to represent fragments of ~2.7 Ga continental materials incorporated in the biotite gneiss. The biotite gneiss has a SHRIMP U-Pb zircon age of 2513±12 Ma, interpreted to be time of magmatic crystallisation of the igneous precursor, based on the igneous characteristics of the zircons. This indicates a major magmatic episode at 2.52 Ga in the Fuping Complex, identical to the age of felsic volcanism within the low-grade Wutai Complex which crops out immediately to the west. A gneissic granite that intrudes the biotite gneisses has a poorly-defined 207Pb/206Pb age of 2045±64 Ma. This is within error of the age of 2097±46 Ma obtained from a fine-grained gneiss interlayered with amphibolite of the Wanzi Supracrustal Suite (WSS), interpreted to be volcanic in origin. Zircons from both these samples have strong oscillatory zoning and provide the first indication of a Palaeoproterozoic magmatic event in the area, again similar in age to magmatic events recently recognised in the adjacent Wutai Complex. These data indicate a comparable history for the Fuping and Wutai Complexes and support geochemical evidence that they had a common origin and formed part of a Late Archaean arc, affected by later Palaeoproterozoic re-activation. Low-uranium zircons without oscillatory zoning, separated from a sample of biotite gneiss, yield data clustered at 181726 Ma, which is interpreted to reflect a period of new zircon growth during a major metamorphic event. These data support the recently-proposed tectonic model that amalgamation of the North China Craton occurred due to collision of the Eastern and Western Blocks along the central zone at 1.8 Ga ago.
    SHRIMP U-Pb zircon geochronology of granitoids fromDongping area, Hebei Province, China constraints on tectonicevolution and geodynamic setting for gold metallogeny [查看] LaichengMiao、YuminQiu、NealMcNaughton、ZhenkuanLuo、DavidGroves、YushengZhai、WeimingFan、MingguoZhai、KangGuan
    The Dongping area in the central part of the northern marginal zone of the North China Craton (NCC) is one of the most important gold-producing areas in China, and has been intruded by a number of alkaline and granitic batholiths or plutons spatially associated with gold deposits. Previous dates on these intrusions yield contradictory data, depending on the isotopic methodology used, and have led to ambiguity in understanding magmatic evolution and gold mineralization of the region.Detailed SHRIMP U–Pb zircon geochronology of the alkaline and granitic rocks in the study area now reveals details of its tectono-magmatic history. Zircons from a granitic gneiss hosting the Xiaoyingpan gold deposit yielded concordant ages of ca.2.5 Ga. This constrains regional metamorphism of the Archaean basement to late Archaean time. A second magmatic event at ca. 1.8 Ga is revealed by xenocrystic/inherited zircons with this age. These two Precambrian events are coeval with those in other parts of the NCC. The largest igneous intrusion in the region, the Shuiquangou syenite–monzonite complex, was emplaced at ca. 390 Ma, as indicated by the magmatic zircon populations of the two samples from the central and eastern parts of the complex. The accretion of a volcanic arc onto the northern margin of the NCC is considered as a plausible cause of this alkaline magmatism. The emplacement of the Guzuizi porphyritic granite pluton at 236F2 Ma represents another major magmatic event in the region, probably a response to postcollisional orogeny following amalgamation of the North China and Angara cratons. Latest magmatism is marked by the emplacement of the Shangshuiquan monzogranite at 142.2F1.3 Ma, which is most likely related to an underplating event that took place in the Dongping and its adjacent areas at ca. 140 Ma. More importantly, these results suggest that gold mineralization in the area, essentially a single event as indicated by similar deposit characteristics, is broadly coeval with this latest granite magmatism. Hence, this mineralization is about 250 Ma later than the emplacement of the Shuiquangou alkaline complex and, thus, is interpreted to preclude the widely accepted model that suggests gold deposits have genetic relationships with alkaline magmatism. The late timing of gold mineralization with respect to felsic magmatism in the area is similar to those observed in other major gold-producing provinces in the NCC. In all these major gold provinces, we suggest that gold mineralization is coeval with the latest granite magmatic event at about 140–120 Ma. This farther suggests that these mesothermal gold deposits were formed from similar tectono-magmatic environments
    Ca.2.5 billion year old coeval ultramafic-mafic and syenitic dykes in Eastern Hebei Implications for cratonization of the North China Craton [查看] TieshengLi、MingguoZhai、PengPeng、LiangChen、JinghuiGuo
    A group of extremely rare coeval ultramafic–mafic and syenitic dykes was discovered in the Eastern Hebei region of the North China Craton. These dykes intrude the 3.8–2.55 Ga old Caozhuang complex. An olivine gabbro dyke and syenite dyke yield, respectively, SHRIMP zircon U–Pb ages of 2516±26Ma and 2504±11 Ma, interpreted as the magmatic crystallization age. Their zircons have single-stage Hf model ages 2677Ma and 2705 Ma. The olivine gabbros have Mg# values of 59–63, similar to high-magnesian tholeiitic basalt. They show relatively LREE-enriched patterns without Eu anomalies (La/YbN = 9.28–9.78, Gd/YbN = 2.8, δEu = 0.96–1.00), with enrichment in LILEs and depletion in HFSEs. They also contain high Cr and Ni, and have Zr/Hf and Nb/Ta ratios similar to those of the primitive mantle. The syenites are alkaline in composition, with 8.67–8.88 wt.% Na2O+K2O, and show high total REE contents (543–854 ppm) and strong LREE-enriched patterns with minor Eu negative anomalies (La/YbN = 50–101, Gd/YbN = 5.2–5.3,δEu = 0.80–0.82). Trace element diagrams show strong LILE-enrichment relative to HFSE. Zr/Hf and Nb/Ta ratios are 47–49 and 26–76, respectively, which are much higher than those of primitive mantle and higher than the average Nb/Ta ratio of post-Archean continental crust. The petrological and geochemical features indicate that these dykes were derived from a deep subcontinental lithospheric mantle source, which implies that the NCC probably had continental crust of considerable thickness at this time. Combined with evidence for ∼2.5 Ga granite intrusion and metamorphism in the Eastern Hebei region and adjacent areas, we propose that the NCC has been a present scale craton at the end of Archean.
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