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

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• 作者：Xiyan Zhu^a ; ^b ; Fukun Chen^b ; ^{fkchen@ustc.edu.cn" class="auth_mail} ; ^{fukun-chen@mail.igcas.ac.cn" class="auth_mail} ; Hu Nie^b ; Wolfgang Siebel^c ; Yizeng Yang^b ; Yingyu Xue^b ; Mingguo Zhai^a
• 关键词：Neoproterozoic ; South Qinling ; Volcanic rock ; Zircon age ; Geochemistry
• 刊名：Precambrian Research
• 出版年：May, 2014
• 年：2014
• 卷：245
• 期：Complete
• 页码：115-130
• 全文大小：5219 K

文摘

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 卤 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 ¹⁴³Nd/¹⁴⁴Nd ratios ranging from 0.51162 to 0.51172 corresponding to initial 蓻_Nd 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 卤 11 Ma and 768 卤 7 Ma and display trace element signatures similar to arc-volcanics with positive LILE and negative HFSE anomalies. These basalts have lower initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7030 to 0.7052 and higher initial ¹⁴³Nd/¹⁴⁴Nd ratios from 0.51172 to 0.51194 with positive initial 蓻_Nd 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 蓻_Nd values varying from 鈭?.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 鈭?80 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.