Post-collision Extension in the Eastern Central Asian Orogenic Belt: Insight from the Late Triassic High-Mg Andesites
- 1State Key Laboratory of Geological Processes and Mineral Resources and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China
- 2Department of Geosciences, University of Padova, Padova 35151, Italy
- 3School of Earth Science and Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China
Central Asian Orogenic Belt (CAOB) with multiple blocks and suture zones is a key locality for understanding the process of plate tectonics. Extensive studies are mainly on the western CAOB, but less on the eastern side. Many questions remain unclear due to the lack of obvious structural records and ophiolite assemblages. In this study, we report the andesites sampled from Laolongtou Formation in the eastern CAOB with detailed geochronology and geochemistry analyses. The andesites are characterized by high Mg# values at their intermediate SiO2 contents, which are defined as typical high Mg# andesites. Zircon U-Pb ages show they erupted at the Late Triassic (~236 Ma) and the Ti-in-zircon thermometer indicates a potential high primary magma temperature. Geochemically, they show relatively high contents of Al2O3, Na2O, Cr, and Ni, with enrichment in light rare earth elements and depletion in high field strength elements. Besides, they are markedly depleted in Nb and Ta, enriched in Sr, Ba contents, and significantly differentiated in Th and U contents. They have homogeneous depleted Sr-Nd isotopic compositions that fall into the range of MORB and mantle-derived ranges. Together with the depleted zircon Hf isotopic compositions, showing the possible addition of a hot and depleted component. We propose that they were formed by interactions of components derived from a subducting slab and the overlying mantle wedge. The slab-derived components are most likely a low degree of partial melting of subducted oceanic crust that was able to stabilize garnet and rutile, without plagioclase in the melt residue. They subsequently interacted with the overlying mantle wedge, which resulted from an post-collisional setting related to the final closure of Paleo-Asian Ocean. The upwelling of the upper mantle triggered by the oceanic slab break-off may explain the genesis of the high Mg# andesites and the formation of the continental crust in northeast China.
How to cite: Zhang, L., Huang, F., Xu, J., and Liu, X.: Post-collision Extension in the Eastern Central Asian Orogenic Belt: Insight from the Late Triassic High-Mg Andesites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12573, https://doi.org/10.5194/egusphere-egu23-12573, 2023.
