Post-rift anomalous thermal flux in the Songliao Basin, NE China, as revealed from fission track thermochronology and tectonic analysis

The Songliao Basin in northeastern China contains a nearly complete Cretaceous sedimentary record. It offers an unparalleled opportunity for studying the thermal behavior of a rifting basin adjacent to a subduction zone during various stages of its evolution. The post-rift thermal history of the Songliao Basin is here documented by systematic apatite and zircon fission track analyses on newly exhumed sandstone samples from the Upper Cretaceous Quantou and Qingshankou formations. The combination of thermochronology results and stratigraphic records indicates that there was an unambiguous post-rift thermal overprinting event in the Songliao Basin during the deposition of the Nenjiang Formation at ~85-80 Ma. This fossil thermal anomaly has not been previously recognized from organic maturity indicators and/or subsidence modeling. The zircon fission track results indicate an estimated maximum paleo-temperature as high as 170-220 °C near the Daqing Placanticline. Fission track analyses of sampled apatites further define a restricted thermal anomaly in the central part of the basin. Based on the context of local lithospheric structure and adjacent plate tectonic history, we conclude that the Late Cretaceous westward subduction of the Paleo-Pacific Plate not only produced vertical motions and directly controlled the topography of the Songliao Lake, but also dominated the mantle heat flow beneath East Asia. This finding has significant implications for the evolution of thermal flux in the basin.