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The Tianshui area is located at the junction of the Qinling and Qilian Orogens, the evolution of which is crucial in understanding the Early Palaeozoic tectonic evolution of the Central China Orogenic System. We present here geochronological, geochemical, and Sr-Nd isotopic data for four representative Silurian magmatic rocks, termed the Dangchuan, Huamiao, Yanjiadian, and Hongtupu, along a cross section across the main rock units of the Tianhui area. The 432 Ma Dangchuan syenogranites are peraluminous with negative εNd(t) values, high initial 87Sr/86Sr ratios, and low Rb/Sr and high CaO/Na2O ratios. We interpret the syenogranites to be generated by partial melting of metagreywackes during a Silurian orogenic event. The 436 Ma Huamiao diorites are high-Mg diorites with high MgO contents and Mg# (63–65) and enriched Sr-Nd isotopic compositions. The 445 Ma Yanjiadian diorites are high-Mg adakitic rocks with high Sr and Mg# and low Y and Yb contents. They were both generated by the interaction between sediment/slab-derived fluids/melts and mantle peridotite in the subduction-related setting. The 445 Ma Hongtupu basalts include E-MORB and IAB with depleted Sr-Nd isotopic compositions. They were derived from enriched mantle and sediment-modified mantle, respectively, and formed in a back-arc basin setting. Synthesizing our new and published data, we propose a tectonic model involving generation of Baihua-Huluhe arc-back-arc system, subduction of the Huluhe back-arc oceanic basin, and collision between the North Qinling arc terrane and North China Block, which is closely associated with the closure of the Proto-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Zhangbaling Tectonic Belt (ZTB) is located in eastern Anhui province, adjacent to the Tan-Lu fault zone to the W and the Lower and Middle Yangtze River metallogenic zone to the E. Two types of gold deposits: (1) altered-tectonite gold and (2) quartz-vein gold are present in the ZTB. Three ranges of homogenization temperatures (Th) were obtained by fluid inclusion investigations of the altered-tectonite gold deposits: 115-165°C, 235-275°C, and 335-395°C; and of the quartz-vein gold deposits: 145-195°C, 205-255°C, and 255-335°C, respectively. δD values of the ore-forming fluids range from -52.2‰ to -75.3‰, and their isotopic compositions calculated from quartz analytical data show negative δ18O values (-6.3-0.1‰) for the quartz-vein gold deposits. The calculated δ18O values of water are evidently lower than magmatic water, and probably were derived from mixtures of magmatic and meteoric water. Although the total rare earth elements (REE) content of the quartz-vein gold ores are much lower than those of the spatially associated granites, their chondrite-normalized patterns are similar, indicating that ore-forming elements in the ZTB quartz-vein gold deposits probably were derived from the plutons. Ores from the altered-tectonite gold deposits show δEu values and chondrite-normalized REE patterns similar to those of the granites, indicating that ore-forming elements of the altered-tectonite gold deposits also were sourced in the Yanshanian plutons. The gold deposits in the ZTB are remarkably similar to those in the Jiaodong gold metallogenic province with regard to tectonic settings, mineralization-controlling factors, mineralization ages, and the ore-forming temperatures and the stable isotopic compositions. [ABSTRACT FROM AUTHOR]