POST-RIFT TECTONIC HISTORY OF THE SONGLIAO BASIN, NE CHINA:COOLING EVENTS AND POST-RIFT UNCONFORMITIES DRIVEN BY OROGENIC PULSES FROM PLATE BOUNDARIES

The classic lithosphere-stretching model predicts that the post-rift evolution of extensional basin should be exclusively controlled by decaying thermal subsidence. However, the stratigraphy of the Songliao Basin in northeastern China shows that the post-rift evolution was punctuated by multiple episodes of uplift and exhumation events, commonly attributed to the response to regional tectonic events, including the far-field compression from plate margins. Three prominent tectonostratigraphic post-rift unconformities are recognized in the Late Cretaceous strata of the basin: T11, T03, and T02. The subsequent Cenozoic history is less constrained due to the incomplete record of younger deposits. In this paper, we utilize detrital apatite fission track (AFT) thermochronology to unravel the enigmatic timing and origin of post-rift unconformities. Relating the AFT results to the unconformities and other geological data, we conclude that in the post-rift stage, the basin experienced a multiepisodic tectonic evolution with four

distinct cooling and exhumation events. The thermal history and age pattern document the timing of the unconformities in the Cretaceous succession: the T11 unconformity at ~88–86 Ma, the T03 unconformity at ~79–75 Ma, and the T02 unconformity at ~65–50 Ma. A previously unrecognized Oligocene unconformity is also defined by a ~32–24 Ma cooling event. Tectonically, all the cooling episodes were regional, controlled by plate boundary stresses. We propose that Pacific dynamics influenced the wider part of eastern Asia during the Late Cretaceous until Cenozoic, whereas the far-field effects of the Neo-Tethys subduction and collision processes became another tectonic driver in the later Cenozoic.