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Tectonic framework on the western margin of the Yangtze Platform

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... The MD REE belt is located in the northern Kangdian axis (KDA) in WMYP (Figs. 1). The KDA underwent a complicated tectonic evolution from Proterozoic lithospheric accretion through the Paleozoic-Mesozoic continental margin, followed by a Cenozoic collision orogeny (Zhang Yunxiang et al., 1988;Yu Anguang et al., 1998). Specifically, it formed the Panxi rift under extensional tectonic activities in the Hercynian-Indosinian period (Miao Yikun et al., 1986) and the Jinpingshan mountain under intracontinental convergence in the Yanshan-Himalaya period, which is characterized by a double structure of earlier opening and later closing (Xu Zhiqin et al., 2007). ...
Article
The Mianning–Dechang (MD) rare earth element (REE) belt, located in the northern Kangdian axis (KDA) in the western margin of the Yangtze platform, is one of the most economically significant REE mineral belts in China. REE mineralization is associated with Himalayan carbonatite–alkaline complexes. The Lizhuang nordmarkite occurred in the northern part of the MD REE belt. The majority of zircons from the Lizhuang nordmarkite are characterized by pronounced positive Ce yet slightly negative Eu anomalies and high U/Yb. Moreover, all zircons have stable Hf isotopic compositions with initial ¹⁷⁶Hf/¹⁷⁷Hf ratios ranging from 0.282739 to 0.282808 and an average value of 0.282773. The negative Lu/Hf and positive εHf(t) range from −0.98 to −0.94 (average value of −0.96) and from −0.56 to 1.89 (the majority is positive, with an average of 0.66), respectively. These characteristics indicate that the rock is derived from an enriched mantle and subducted material. LA-ICP-MS analysis of the zircons from the intrusion yields a weighted mean ²⁰⁶Pb/²³⁸U age of 28.57±0.61Ma. During this period, the tectonic activity in the KDA is not plate subduction but an intraplate tectonic exhibiting fold–thrust and strike–slip behaviors in the western marginal zone of the Yangtze platform (WMYB). We suggest the possibility of an existing eastward old slab subduction under WMYB combined with a regional tectonic evolution. The Lizhuang nordmarkite may be derived from an enriched mantle beneath the western part of the Yangtze craton, which originated from the remelting of the Tethys subducting slab, because of the Himalayan strike–slip that formed a special type of REE deposit called strike–slip-type REE deposits.
... The YC is separated from the QQKO to the north by the Mianlue fault, from the WYO to the southeast by the Jiangshan-Shaoxing fault, and from the THO to the west by the Longmenshan fault. The YC consists of minor Archaean-Palaeoproterozoic crystalline basement that is surrounded by late Mesoproterozoic to early Neoproterozoic orogens (Yu and Guo 1998;Xu et al. 2002;Zheng et al. 2012). The magmatic rocks are unconformably overlain by weakly metamorphosed Neoproterozoic strata and unmetamorphosed Sinian cover (Zheng et al. 2012). ...
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Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous, increasing demand for Earth resources. China possesses the largest Mo reserves in the world (exceeding 19.6 Mt). The major ore deposits are of porphyry, porphyry–skarn, skarn, vein, and sedimentary types. Porphyry molybdenum deposits contain 77.5% of the Chinese Mo reserves, with lesser amounts in porphyry–skarns (13%), skarns (5.1%), and veins (4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical. The six Mo provinces are in the Northeast China, Yanliao, Qinling–Dabie, middle–lower Yangtze River Valley, South China, and Sanjiang areas. We recognize six ore-forming periods: (1) Precambrian (>541 Ma), (2) Palaeozoic (541–250 Ma), (3) Triassic (250–200 Ma), (4) Jurassic–Early Cretaceous (190–135 Ma), (5) Cretaceous (135–90 Ma), and (6) Cenozoic (55–12 Ma). The abundance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism, involving interactions between the Siberian, North China, Yangtze, India, and Palaeo-Pacific plates. Precambrian molybdenum deposits are related to Mesoproterozoic volcanism in an extensional setting. Palaeozoic Cu–Mo deposits are related to calc-alkaline granitic plutons in an island arc or a continental margin setting. Triassic Mo deposits formed in the syn-collision–postcollision tectonic setting between the Siberian and North China plates and between the North China and Yangzi plates. Jurassic–Early Cretaceous molybdenum deposits formed along the eastern margin of Asia and are associated with the palaeo-Pacific plate-subduction tectonic setting. Cretaceous Mo deposits are related to high-K calc-alkaline granitic rocks and formed in a lithospheric thinning setting. Cenozoic molybdenum deposits formed in a collision setting between the Indian and Eurasian continents and the subsequent extensional setting.
... K-Ar dating of hydrothermal sericite and Ar-Ar dating of sericite and quartz associated with auriferous quartz veins yielded ages of gold mineralization around 21 to 25 Ma (Chen et al., 1997;Luo and Yu, 1998;Yu and Guo, 1998;Luo and Yu, 2002;Yan et al., 2002). The lode gold deposits of Daduhe display many similarities with mesothermal/orogenic gold deposits (Groves, 1993;Groves et al., 1998). ...
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The Daduhe gold field comprises several shear-zone-controlled Tertiary lode gold deposits distributed at the eastern margin of the Tibetan Plateau. The deposits are hosted in a Precambrian granite–greenstone terrane within the Yangtze Craton. The gold mineralization occurs mainly as auriferous quartz veins with minor sulphide minerals. Fluid inclusions in pyrite have 3He/4He ratios of 0.16 to 0.86 Ra, whereas their 40Ar/36Ar ratios range from 298 to 3288, indicating a mixing of fluids of mantle and crust origins. The δ34S values of pyrite are of 0.7–4.2‰ (n = 12), suggesting a mantle source or leaching from the mafic country rocks. δ18O values calculated from hydrothermal quartz are between − 1.5‰ and + 6.0‰ and δD values of the fluids in the fluid inclusions in quartz are − 39‰ and − 108‰. These ranges demonstrate a mixing of magmatic/metamorphic and meteoric fluids. The noble gas isotopic data, along with the stable isotopic data suggest that the ore-forming fluids have a dominantly crustal source with a significant mantle component.
Article
Jinding superlarge deposit located in the northern part of Lanping Basin, western Yunnan Province. It has been studied for more than 20 years, and a lot of genetic models were proposed such as stratabound type, synsedimentation-late reformation and mantle-crust compound mineralization. But some elementary geological problems such as some of the wall-rock ages and the structures that constrained orebodies have been suspended till now. These embarrassed the explanation of the genesis about Jinding deposit and the tectonic or crustal evolution of Three-River (Nujiang, Lancangjiang and Jinshajiang rivers) orogenic belt. For these reasons, this paper selected some zircons from the wall-rocks to discuss the tectonic setting. Based on crystal features and shapes of the zircons, which were different from the normal weathered zircons in sandstones, the wall-rocks must be not far where their source rocks formed According to the process of zircon dating, 4 group of isotopic ages were obtained by SHRIMP II in Beijing Ion Microprobe Center. They are 240Ma, 415Ma, 820Ma and 1800 ∼ 2000Ma. These suggested that the Pb-Zn metallization age was younger than 240Ma. Further more, a number of Plaeoprotozoic ages (1910Ma, 1867Ma, 2021Ma, 2487Ma) were more significance in geological studies. First, it indicated that the source rocks of Lanping basin contained some Precambrian ages. These implied that the Precambrian basement of Yangtze Plate could spread to Lancanjiang river. Second, these isotopic ages suggested that the evolution of Lanping-Simao basin must be related to early Precambrian basement. Third, it implied that the Central Fault (or Zhongzou Fault) zone, which is nearly relevant to the genesis of Jinding deposit, should be a multi-phased fractured faults.
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