Tectonic escape from the Pangean megamonsoon via oceanic isolation modulated low-latitude hydroclimate

Abstract

The assembly of the Pangea supercontinent during the late Paleozoic ice age drove Earth’s most intense megamonsoon. Although climate models predict a humid low-latitude eastern Pangean margin, widespread red-bed records indicate extreme seasonal oxidation, creating a conspicuous “model-sediment” paradox. Located directly on this margin, the Xilinhot-Songliao block captures a “red-gray-red” sedimentary cycle that physically toggled between these conflicting arid and humid states. Here, we report ca. 315 Ma high-quality paleomagnetic data from the block to reconstruct its full drift trajectory (315−265 Ma). Integrated with geological proxies, the block is inferred to have maintained a close tectonic affinity with the Pangean margin initially (ca. 315 Ma), hosting megamonsoon-dominated red beds. Following the expansion of the Hegenshan Ocean to a N-S width of ∼2300 km by ca. 300 Ma, the block underwent “tectonic decoupling,” transitioning into a stable zonal climate depositing pure carbonates. Subsequent reattachment to the supercontinent (280−265 Ma) triggered a rapid reversion to arid megamonsoonal conditions. Occurring under a constant global icehouse, this “red-gray-red” oscillation demonstrates that tectonic distance to the supercontinent acted as the primary switch modulating land-sea thermal feedback. Our findings challenge paradigms relying solely on global climate cycles, highlighting how ocean basin evolution independently reshapes regional climatic landscapes.