Abstract Records of the Lomagundi–Jatuli Event (LJE) are well preserved globally, but high δ 13 C carb carbonates have not been identified in the North China Craton (NCC). Our results on ~ 3–4 km thick carbonates from the newly confirmed Palaeoproterozoic successions in Fanhe Basin in the northeastern NCC show that the ~2.20–2.06 Ga carbonates have positive carbon isotope excursion and those deposited after 2.06 Ga have normal carbon isotope. Specially, carbonates from the Daposhan Formation have δ 13 C carb values of 10.2‰–11.8‰, which is the largest positive carbon isotope excursion in the NCC. The ~2.20–2.06 Ga carbonates in Fanhe Basin have similar δ 13 C carb values as those contemporaneously deposited in other cratons and their δ 13 C carb values exhibit a decreasing trend from ~2.20 Ga to 2.06 Ga. Our identification of carbonates with high positive δ 13 C carb values in Fanhe Basin not only casts new lights on records of the LJE in the NCC, but also provides important constraints on global significance of the positive δ 13 C carb excursion of LJE.
Abstract A positive δ 13C excursion in Palaeoproterozoic carbonate sequences in Henan, China is reported in this paper. Carbon isotope analyses of samples from Wuzhiling and Huayu Formation of Songshan Group, a well-preserved Palaeoproterozoic-carbonate sequences in northern Henan, China present δ 13C values range from −1.0‰ to 4.2‰PDB, with a mean at 2.5‰PDB. Results of microscope observation, oxygen isotope, and Mn/Sr ratio indicate that Wuzhiling Formation suffered stronger alternation than Huayu, which suggested a higher initial δ 13C excursion of Wuzhiling Formation than present known value. The positive δ 13Ccarb excursions of Wuzhiling Formation support the Lamagundi Event as early oxygenation of the terrestrial environment, was also recorded in Palaeoproterozoic carbonate sequences in Henan, China. Keywords: positive δ13C excursionHenan/ChinaPaleoproterozoicatmospheric oxygenation Acknowledgments This work was supported by the National Basic Research Program of China (973 Program, No. 2007 CB815601). We are grateful to Prof. Guan Baode and Dr. Zhao Taiping for providing help to sample. We wish to thank Prof. Chen Yanjing and Dr. Liu Jun for their critical reading of an earlier version of this manuscript and providing the constructive opinions for the article.
Abstract The Proto-Tethys Ocean has played a significant role in the geological history of Earth. However, ongoing debates persist regarding the timing and polarity of its early subduction. Volcanic rocks associated with iron deposits in the Bulunkuole Complex, West Kunlun Orogen, offer insights into both the complex’s formation age and Proto-Tethys evolution. This study presents newly obtained zircon U–Pb age data (~536 Ma) along with comprehensive whole-rock major and trace element and Sr–Nd–Hf isotope analyses of these volcanic rocks. Our dataset implies that the Bulunkuole Complex partly formed in the early Paleozoic rather than entirely in the Paleoproterozoic, as previously suggested. Geochemically, the volcanic rocks exhibit enrichments in large ion lithophile elements and light rare earth elements, along with depletions in high-field strength elements. They also display elevated initial 87Sr/86Sr values (0.71093, 0.72025) and negative εNd(t) values (−5.13, −6.18), classifying them as continental arc volcanic rocks. These geochemical fingerprints, complemented by zircon εHf(t) values (−12.7 to −1.6), indicate that the parental magmas of the volcanic rocks were produced by partial melting of the lithospheric mantle wedge, which had been metasomatized by subducted sediment-derived melts. The available data, in conjunction with previously published findings, strongly suggest that the Proto-Tethys Ocean subducted southward prior to approximately 536 Ma due to the assembly of Gondwana. Subsequent slab rollback may have resulted in a crustal thinning of 9–25 km during 536–514 Ma. Further shifts in subduction dynamics led to the transition from high-angle subduction to either normal or low-angle subduction, facilitating the formation of a thicker crust ranging from 39 to 70 km between 514 and 448 Ma. This study, therefore, provides valuable insights into the early evolution of the Proto-Tethys Ocean and contributes significantly to our understanding of the tectonic history of the West Kunlun Orogen.
Abstract The bauxites in central Guizhou are hosted by the Lower Carboniferous Jiujialu Formation. Geochemistrial characteristics of the Lindai bauxite deposit indicate that the underlying Shilengshui Formation dolomite is the precursor rock of mineral resources. Weathering simulation experiments show that Si is most likely to migrate with groundwater, the migration rate of which is several magnitude higher than Al and Fe under nature conditions (pH=3–9). The neutral and acid non‐reducing condition is the most conducive to the Al rich and Si removal, while the acid reducing conditions is the most conducive to the Al rich and Fe removal. In the process of bauxite formation, coal beds overlying the Al‐bearing rock series or other rock formation rich in organic materials can produce acid reducing groundwater, which are important for the bauxite formation. Finally, propose the metallogenic model of the bauxite in central Guizhou Province and put forward three new words which are “original bauxite material”, “bauxite material” and “original bauxite”.
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