| Tens of Mesozoic-Cenozoic sedimentary basins, widely distributed around NE China, not only provide abundant oil-gas and coal for China, but also offer important insights on complicated structural evolution and tectonic process in NE Asian continental margin. Eastern Heilongjiang is the most developed region for Mesozoic-Cenozoic sedimentary basins in NE China and developed multi-period superimposed basins, which produced quite complicated structural features. Despite some research on basinal strata, structural characteristics and evolution, chronostratigraphy, structural attribute and evolution history are still controversial. Making full use of the filed investigation and basinal seismic and well data and focusing on the Mesozoic-Cenozoic sedimentary basins in Eastern Heilongjiang, chronostratigraphy framework of Mesozoic-Cenozoic strata in Eastern Heilongjiang is improved by geochronological study on intercalated volcanics, and structural evolution histories of the basins are reconstructed by analyses on the structural deformation and structure balanced restoration, and research on two low temperature thermochronological sections with a strike of E-W going through the major basins and ranges in Eastern Heilongjiang are carred out based on that. The main conclusions are as follows:In Eastern Heilongjiang, the Didao formation formed in Hauterivian to early-mid Aptian (ca.133-117Ma), the Chengzihe formation formed in middle-late Aptian to early Albian (ca.116-110Ma), the Muling formation developed in Albian (ca.110-101 Ma) and the Dongshan formation formed in late Albian(ca.101Ma); the Houshigou formation formed in Cenomanian, and the Hailang deposited in Coniacian-Santonian, and the Qixinghe formation formed in late Santonian to early Campanian, and the Yanwo formation developed in Campanian to early Maastrichtian.Based on the structural dissection on the Sanjiang and Jixi basins, it is suggested that Eastern Heilongjiang underwent two rifting periods in late Middle Jurassic to early-mid Early Cretaceous, and post-rifting period in late Early Cretaceous, and two compressional deformation events in Late Cretaceous. The structural analyses on the Fangzheng and Tangyuan faulted basins indicate that the Eastern Heilongjiang suffered rifting in Paleocene to Eocene, strike-slip reformation in late Eocene, oblique rifting in Oligocene, and strike-slip reformation in late Miocene. The Paleocene to Eocene rifts give more extension than the rifts in Oligocene, and the strike-slip reformation in late Eocene and late Miocene play major roles in the basin evolution and source rocks-reservoir formation.The research on two regional low-temperature thermochronological sections indicates prominent spatial and temporal diversities of cooling and exhumation of the major ranges and uplifts in Eastern Heilongjiang. The Eastern Xiaoxingan range and the Zhanguangcai range underwent rapid cooling at an average rate of ca.2.3-3℃/Ma in Early Jurassic (ca.200-170Ma), but went into a slow cooling period with an average rate of ca.0.07-0.29℃/Ma in Middle Jurassic to Early Cretaceous (ca.165-101 Ma). The Nadanhada range, the Zhangguangcai range and the Jixi basin suffered rapid cooling at an average rate of ～1.0-8.5℃/Ma in Late Cretaceous (ca.95-70Ma), whereas the Eastern Xiaoxingan range entered into a slow cooling period (ca.100-65Ma) with an average rate of ca.0.08℃/Ma. In Paleogene, the Eastern Xiaoxingan range and the Huachuan-Fujin uplifts in the Sanjiang basin went into a rapid cooling stage (ca.50-30Ma) with an average rate of ca.3-8℃/Ma, while the Nadanhada range and the Zhangguangcai range underwent slow cooling (ca.65-23Ma) at an average rate of ～0.14℃/Ma. In Neogene-Quaternary (ca.23-0Ma), a majority of regions of Eastern Heilongjiang experienced relatively slow cooling at an average rate of ca. 0.14-0.3℃/Ma.Based on structural deformation and low temperature thermochronology analyses, and previous detrital zircon U-Pb geochronology, sedimentary Paleogeography, structural deformation and low temperature thermochronological study, it is inferred that the rapid exhumation of the Xiaoxingan and the Zhangguangcai range in Early Jurassic to early Middle Jurassic (ca.200-170Ma) is attributed to the coeval collision between the Jiamusi Block and the Songliao Block, spatially and temporally coupled with a peripheral foreland basin developed in Songliao Block; In Middle Jurassic to middle Early Cretaceous (ca.165-101Ma), the Xiaoxingan range and the Zhangguangcai range underwent slow exhumation, approximately corresponding to widespread multi-stage rifting and subsequent large scale post-rifting in NE China, produced the large post-rifting basins including the Songliao basin and the Large Sanjiang basin in Eastern Heilongjiang, and the regional intra-continental extension is related to the combined effect of the collapse of the Mongol-Okhotsk orogen and the roll-back of the Paleo-Pacific plate subduction; In Late Cretaceous(ca.100-66Ma), NE China experienced increasing compression stress, and the contractional deformation and uplifting migrated and propagated from the east to the west, led to the rapid uplifting of Eastern Heilongjiang during ca.95-70Ma and the large scale inversion and uplifting of the Songliao basin initiated until ca.70-65Ma, implying a tectonic switch from the Western Pacific-type to the Andean-type in the NE Asian active continental margin; Rapid exhumation of the Xiaoxingan range and the Huachuan uplift in the Sanjiang basin during ca.50-30Ma was initiated by the uplifting of hanging walls of normal faults developed in the Cenozoic extensional regime, indicating the widespread extension in Eastern Asian continental margin caused by the roll-back of the Pacific plate subduction in Cenozoic. |
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