Magnetotelluric Evidence for the Paleo-Subduction Polarity and Recycled Carbonates within the Beishan Orogen, Southern Central Asian Orogenic Belt 

The Beishan Orogen, located in the southernmost part of the Central Asian Orogenic Belt, comprises ophiolitic complexes, passive-margin strata, arc assemblages, and Precambrian basement rocks, recording oceanic subduction, accretion of oceanic materials onto continental margins, and continental-arc collision. However, debates surrounding its origin and evolution persist, attributed in part to the absence of high-resolution geophysical data, leading to varying interpretations in tectonic evolution models regarding the involved terranes and paleo-subduction polarity (Li et al., 2023). In this study, we present an electrical resistivity model of the crust and uppermost mantle in the Beishan Orogen from magnetotelluric (MT) data. The resistivity model suggests an overall resistive upper crust, with conductive features indicating paleo-suture zones and tectonic boundaries. The high resistivity lithosphere beneath Niujuanzi indicates both north- and southward subduction of the Hongliuhe-Xichangjing Ocean, potentially unveiling remnants of a cold fossil oceanic lithosphere. Conductors in mantle wedges on both sides of the high resistivity body are inferred to result from recycled carbonates introduced deep into the Earth through oceanic subduction, which is substantiated by recent laboratory measurements (Jing et al., 2023). These measurements demonstrate that even unmelted carbonates can enhance electrical conductivity through cation exchange reactions with silicates in the lower crust and uppermost mantle. *This research is funded by the National Natural Science Foundation of China (42074089, 41774087, 41404060). Reference Jing, C., Hu, H., Dai, L., Sun, W., Wang, M., Hu, Z., 2023. Recycled carbonates elevate the electrical conductivity of deeply subducting eclogite in the Earth’s interior. Commun Earth Environ 4, 276. https://doi.org/10.1038/s43247-023-00936-w Li, J., Wu, C., Chen, X., Zuza, A.V., Haproff, P.J., Yin, A., Shao, Z., 2023. Tectonic evolution of the Beishan orogen in central Asia: Subduction, accretion, and continent-continent collision during the closure of the Paleo-Asian Ocean. GSA Bulletin 135, 819–851. https://doi.org/10.1130/B36451.