Characteristics of Devonian extensional magmatic activity in the Jiefangyingzi area, northern margin of the North China Plate

• Published in: Geological journal (Chichester, England) England), 2020-02, Vol.55 (2), p.1262-1282
• Main Authors: Wang, Xing‐An, Liu, Zheng‐Hong, Li, Shi‐Chao, Jiang, Xiao‐Jun, Liu, Y.
• Format: Article
• Language: English
• Subjects: Aluminum; Anomalies; Arc deposition; A‐type granite; Calcium; Carboniferous; Devonian; extensional magmatic activity; Geochronology; Island arcs; Lava; Lead isotopes; Magma; Magnesium; Niobium; North China Plate; Palaeozoic; post‐collision; Radiometric dating; Ratios; Rocks; Schist; Schists; Silica; Silicon dioxide; Silurian; Subduction; Subduction (geology); Tectonics; Volcanic rocks; Zircon; Zirconium
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.3492

This paper presents geochronological, geochemical, and isotopic data relating to Devonian magmatic activity in the Jiefangyingzi area, northern margin of the North China Plate (NCP). LA‐ICP‐MS zircon U–Pb dating indicates that the Erfendi granites formed in the Middle Devonian and yield a concordant weighted mean age of 384.7 ± 2.5 Ma. The zircons have negative εHf(t) values ranging from −5.8 to −31.3 and two‐stage Hf‐model ages of TDM2 = 1,735–3,217 Ma. 206Pb/238U ages of zircon grains from a quartz–schist sample in the Shaiwusu Formation vary from 410 to 322 Ma, with a peak at 380 Ma, indicating that magmatic activity peaked during the Late Devonian. The Erfendi granites are silica‐ and alkali‐rich and calcium‐ and magnesium‐poor. The Erfendi granites belong to peraluminous rocks and have clear negative Eu anomalies (δEu = 0.49–0.84); P, Ti, and Nb depletions; Nd, Zr, and U enrichments; and high Ga/Al ratios, similar to aluminous A‐type granites. This suggests the Erfendi granites were generated by partial melting of lower crustal rocks. Geochemically, the Erfendi granites are A2‐type granites, reflecting a post‐collision tectonic setting. The southward subduction of the Palaeo‐Asian Oceanic Plate during the Early Palaeozoic formed Bainaimiao volcanic arc at the northern NCP and Deyanqimiao island arc. The collision between the Deyanqimiao island arc and the Bainaimiao volcanic arc was recorded by the Xibiehe molasse deposition and the Badangshan volcanic rocks at the northern margin of the NCP during the Late Silurian to Early Devonian. As a consequence, the Jiefangyingzi area experienced intense post‐collision extensional magmatism during the Middle Devonian, which generated massive A2‐type granites at the northern margin of the NCP. This collision was also recorded by the back‐arc deposition of the Late Carboniferous Shaiwusu Formation.