Deep Electrical Structure of the Western Slope of the Songliao Basin and Its Geological Significances

ABSTRACT

The Tuquan–Baicheng segment, located on the western margin of the Songliao Basin, is recognised as a key tectonic belt associated with the closure of the eastern segment of the Paleo‐Asian Ocean and has undergone late‐stage tectonic reworking. However, inadequate geophysical investigations into deep subsurface structures in this area have impeded research on the regional tectonic framework and Late Palaeozoic evolutionary processes. In this study, a ~193 km long magnetotelluric (MT) profile was acquired across the eastern Greater Khingan Range and the western slope of the Songliao Basin. The electrical structure derived from elaborate MT data processing and inversion reveals three distinct high‐conductivity anomalies within the Tuquan Basin, flanked by massive high‐resistivity bodies. The distinct west‐dipping low‐resistivity strip (C1) that extends downward from beneath the Tuquan Basin into the upper mantle is interpreted as a remnant signature of Paleo Asian Ocean subduction. The low‐resistivity body (C3) within the upper mantle (60~100 km depth) beneath the Songliao Basin's slope zone extends upward into the Mesozoic strata and is likely to be associated with the migration of deep high‐temperature fluids. The shallow electrical structural model identifies four secondary fault depressions developed within the study area Upper Palaeozoic strata, whose depocenters are situated on the western slope of the Songliao Basin, to the east of the Nenjiang–Balihan Fault. The Upper Palaeozoic strata that filled these depressions experienced intense compression, uplift and denudation. During the Middle Jurassic to early Early Cretaceous, the regional depocenter migrated west to Tuquan, while extensional tectonics prevailed west of the Nenjiang–Balihan Fault, producing normal faults and fault depressions that controlled thick volcaniclastic deposition. From the early Early Cretaceous, extensional tectonism accompanied by eastward depocenter migration initiated sinistral strike‐slip motion along the Nenjiang–Balihan Fault, while extensional structures and fault depressions developed on the western Songliao slope with the Upper Cretaceous deposition. Distinct discrepancies in depocenter migration and tectono‐ sedimentary evolution between the Tuquan and Songliao basins are interpreted to reflect the spatiotemporal transition among three major tectonic domains: the Paleo‐Asian, Mongol–Okhotsk and Paleo Pacific Oceans. The electrical structural model and tectonic interpretations from this study provide key geophysical constraints for investigating deep lithospheric processes and superimposed reworking from multi‐domain tectonic interactions.