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Based on studies of the geochemical elements of core sediments collected from the subaqueous Yangtze River delta front, combined with 210Pb and 137Cs nuclide dating, element recording profiles were set up and anthropogenic impacts on the sedimentary records were considered. The results suggest that (1) The core formed since 1945, of homogeneous clay and silt sediments. (2) The content of most elements underwent little change, but the content of S and Nb increased gradually. In particular concentrations of these elements and heavy metals increased rapidly and were maintained at high levels in the surface and sub-surface layers (i.e. since the 1990s). The elements S, As and Nb and principal factor 4 (F4), which were sensitive to anthropogenic impacts, could be used as indicators of human activities. (3) The value of each indicator has increased gradually since 1945, with a sharp increase over the last 20 years. When divided according to changing values of the indicators at 185 cm (1955), 97 cm (1978), 47 cm (1992), and 7 cm (2003), five periods of the geochemical elements records were obtained. These corresponded to the ages of from the Chinese Civil War to the early stages of planned economy, the implementation of planned economy, the reform and opening-up period, the market economy establishment phase and the environment control and protection stage after 2003, respectively. [ABSTRACT FROM AUTHOR]

The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. Based on field and petrographical observations, a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton. Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts. Alkali feldspars and quartz had two or more generations. Petrochemically, the Huashanguan rapakivi granites were characterized as having high values of Si, K, Fe, Th, U, La, Ga, Ce, Sm and LREE, low values of Ca, Mg, Sr, Nb, Y and HREE, and a negative Eu anomaly. These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites, and had an affinity to A-type granites. LA-ICP-MS U-Pb zircon dating also was conducted. The dating yielded a207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2), which represents the age of the pluton emplacement. The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton, and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation. The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block. These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Six pyrite samples from the giant Bayan Obo REE-Nb-Fe deposit are dated by Re-Os technique. Pyrite studied is associated with barite and separated from a vein cutting REE mineralization. Pyrites analyzed contain 16–30 ng Re and 0.10–0.16 ng Os, and yield a Caledonian isochron age of 439 ± 86 Ma. High Re/Os ratio, low Os concentration and highly radiogenic Os isotopic ratios of these samples suggest that they are of crustal origin. The northern margin of the North China Block was a passive continental margin, but not a subduction zone with enormous volcanic activities in the Early Paleozoic Era. Our Re-Os result provides new evidences, showing that Bayan Obo deposit experienced a thermal disturbance of crustal origin in the Caledonian time and some isotopic systems recorded only the time of the disturbance, not the mineralization age. [ABSTRACT FROM AUTHOR]

Alkali-feldspar syenites from the Maomaogou area of Huili County in Panxi of Sichuan Province, SW China are sodium alkaline rocks, the minerals of which are mainly composed of calcic ferroaugite, ferroamphibole and biotite. Most of the zircons (>80%) selected for SHRIMP U-Pb dating are magmatic compound zircons and they have relict inner cores and growing outer shells. The age of zircon SHRIMP U-Pb dating is 224±8 Ma, suggesting that the Maomaogou alkali-feldspar syenite was formed in the late Triassic period. At the same time, two old age periods of relict cores of zircon are determined, they are the Archean age (2692–2818 Ma) and Neoproterozoic age (622–691 Ma), respectively. These periods indicate that the cores derived from the crystal basement. Furthermore, the Archean age of zircon provides the first reliable SHRIMP U-Pb zircon dating evidence of >2.8 Ga basement in the Xikang-Yunnan Axis of southwest China. [ABSTRACT FROM AUTHOR]