Early Triassic roll-back of subducted Paleo-Tethys oceanic lithosphere: Insights from A2-type silicic igneous rocks in the Pingxiang area, southwest China

作者：Huang, Wen-Min; Liu, Xi-Jun^*; Liu, Lei; Li, Zheng-Lin; Liu, Xiao; Wu, Hao

来源：Geosphere, 2023.

DOI：10.1130/GES02617.1/5934112/ges02617

• A-TYPE GRANITES
• SOUTHERN LANCANGJIANG ZONE
• TRUONG SON BELT
• HF-O ISOTOPES
• VOLCANIC-ROCKS
• SW CHINA
• ZIRCON U
• GEOCHEMICAL CHARACTERISTICS
• INDOSINIAN-OROGENY
• NANPANJIANG BASIN

A suite of subduction- related early Triassic igneous rocks crops out in the Pingxiang area of the DianQiong suture (DQS) in southwest China; this suite represents an important geological record of subduction and closure of the Paleo- Tethys Ocean. In this study, we report geochronological, geochemical, and NdHf isotope data for newly discovered rhyolites and biotite granites in the Pingxiang area. We use these data to constrain their emplacement ages, origins, and geodynamic implications. Zircon U-Pb dating indicates that the rhyolites and biotite granites were emplaced at 251- 250 Ma and 249 Ma (early Triassic), respectively. The rhyolites and biotite granites have elevated FeOT/(FeOT + MgO) (0.78- 0.89) and 10,000 x Ga/Al (2.83- 4.11) ratios, with geochemical affinities to A2-type granites. These rocks are enriched in some large- ion lithophile elements (e.g., Rb, Th, and Ba) and depleted in high- ?eld- strength elements (e.g., Nb, Ta, and Ti), indicating their formation in a subduction- related arc. The rhyolites and biotite granites have negative whole- rock & epsilon;Nd(t) (-11.5 to -9.7) and zircon & epsilon;Hf(t) (-14.5 to -6.2) values, suggesting that these magmas were derived from an ancient crust- dominated source. Geochemical and Nd isotope data reveal that the peraluminous A2-type rhyolites and biotite granites were derived by partial melting of felsic crustal rocks under low- pressure and high- temperature conditions. By integrating all the available data with the regional tectonic evolution of the southwestern Youjiang Basin and adjacent regions, we attribute the generation of the peraluminous A2-type rhyolites and biotite granites to the extensional setting that existed during oceanic subduction, which was induced by roll- back of the Paleo- Tethys oceanic lithosphere at 251- 249 Ma. This study indicates that subduction- related magmatism related to Paleo- Tethys oceanic lithosphere was still active in the early Triassic.

• 单位
  桂林理工大学