Geochemistry and zircon U–Pb ages of the Neoproterozoic Shimian plutons on the western margin of the Yangtze Block, Sichuan Province

• Published in: Geological journal (Chichester, England) Vol. 56; no. 2; pp. 934 - 950
• Main Authors: Xie, Qi‐Feng, Cai, Yuan‐Feng, Zhai, Ming‐Guo
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.02.2021; Wiley Subscription Services, Inc
• Subjects: Aluminum oxide; Contamination; Geochemistry; Geochronology; Igneous rocks; Isotopes; Lead; monzogranite; Neoproterozoic; Orogeny; Plutons; Radiometric dating; Ratios; Silica; Silicon dioxide; South China; Subduction; Subduction (geology); syenogranite; Tectonics; Trace elements; Upper mantle; U–Pb dating; Yangtze Block; Yields; Zircon
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.3969

The Shimian Neoproterozoic plutons are located on the western margin of the Yangtze Block and are important for reconstructing the tectonic environment of this region. We present in situ zircon LA–ICP–MS U–Pb geochronological and Hf isotopic analyses for the plutons, as well as whole‐rock major‐ and trace‐element compositions. The monzogranite and syenogranite yield concordant ages of 773.6 ± 5.6 Ma and 812.2 ± 1.8 Ma, respectively, which indicates that they formed during the Tonian of the Neoproterozoic. The samples have very similar geochemistry, with high SiO2 (71.45–75.46 wt%) and Al2O3 (12.38–14.36 wt%) contents. The samples have a geochemical characteristics typical of peraluminous A‐type granites, including high Ga/Al and Rb/Sr ratios and elevated contents of high‐field‐strength elements. The samples also display high Rb/Sr (13.9–23.0) and Rb/Nb (12.5–19.2) ratios. The monzogranite and syenogranite yield positive εHf(t) values (+1.6 to +9.4 and + 5.2 to +9.8, respectively) and T2DM ages of 1.54–1.22 Ga and 1.51–1.21 Ga, respectively, which indicates that they were derived from partial melting of Mesoproterozoic crust or contamination with upper mantle. We propose that the syenogranite and monzogranite formed in a syn‐orogenic extensional setting during the Tonian period and that continuous subduction was responsible for the Neoproterozoic magmatic activities. The syenogranite and monzogranite distributed in Shimian County on the western margin of the Yangtze Block formed in 812.2 ± 1.8 Ma and 773.6 ± 5.6 Ma, respectively. They were derived from partial melting of Mesoproterozoic crust or contamination with upper mantle. The syenogranite and monzogranite formed in a syn‐orogenic extensional setting and that of continuous subduction was responsible for the magmatic activities.