Neoproterozoic tectonic evolution of South Qinling, China: Evidence from zircon ages and geochemistry of the Yaolinghe volcanic rocks

作者：Zhu, Xiyan; Chen, Fukun^*; Nie, Hu; Siebel, Wolfgang; Yang, Yizeng; Xue, Yingyu; Zhai, Mingguo

来源：Precambrian Research, 2014, 245: 115-130.

DOI：10.1016/j.precamres.2014.02.005

• Neoproterozoic
• South Qinling
• Volcanic rock
• Zircon age
• Geochemistry

The South Qinling terrain is located at the northern margin of the Yangtze block. Neoproterozoic volcanic-sedimentary sequences of the Yaolinghe Group play the most significant role in studying the tectono-magmatic evolution of the South Qinling. Based on temporal and spatial geochemical variations the Yaolinghe Group can be divided into three volcanic cycles. Basaltic lavas of cycle 1 crystallized at 847 +/- 8 Ma and exhibit typical island arc basalt characteristics with enrichment of LILEs (Th, U) and LREEs, depletion of HFSEs (Nb, Ta, Zr, Hf, Ti) and homogeneous initial Nd-143/Nd-144 ratios ranging from 0.51162 to 0.51172 corresponding to initial Nd-epsilon values of +1.6 to +3.5. These features suggest that they were derived from a depleted mantle source during a subduction period. Volcanic rocks of cycle 2 show a complete lithological evolution from basalt through andesite to rhyolite without a significant gap of SiO2 content. They formed between 731 11 Ma and 768 7 Ma and display trace element signatures similar to arc-volcanics with positive LILE and negative HFSE anomalies. These basalts have lower initial Sr-87/Sr-86 ratios from 0.7030 to 0.7052 and higher initial Nd-143/Nd-144 ratios from 0.51172 to 0.51194 with positive initial Nd-epsilon values ranging from +0.9 to +5.3, whereas intercalated felsic rocks show lower initial 143Nd/144Nd ratios from 0.51150 to 0.51177 with initial Nd-epsilon values varying from -4.5 to +1.9, suggestive of metasomatic alteration of lithospheric mantle by slab-derived fluids/melts. Cycle 3 lavas show undepleted HFSEs (Nb, Ta, Zr, Hf) and slightly enriched LILEs (Th, U) and Ti concentrations. They were generated in a rift-related setting between similar to 680 Ma and 650 Ma. Geochronological and geochemical evidence from lavas of the Yaolinghe Group suggest that the Panxi-Hannan arc system extended to northern South Qinling and the magmatism in the northern margin of the Yangtze block evolved from arc to rift magmatism during the Neoproterozoic.

• 出版日期2014-5
• 单位中国科学技术大学; 中国科学院地质与地球物理研究所; 中国科学院地质与地球物理研究所兰州油气资源研究中心