This paper summarizes the main sedimentary sequences of major cratonic basins during the breakup of Rodinia and the assembly of Gondwana and extracts evolutionary stages of the Neoproterozoic basins around the Paleo‐Pacific Ocean and Iapetus Ocean tracts. During the breakup of Rodinia, sedimentary sequences and evolutionary stages of the main basins in major cratonic blocks, such as Yangtze, Australia, Eastern American, Western American, and Western Africa cratons, mostly experienced intracratonic rifting, drifting or passive continental margin, carbonate platform construction, and foreland basin stages. The time of rifting to drifting transition in Congo‐São‐Francisco precisely marked the closure of the Adamastor Ocean between Congo‐São‐Francisco and Rio de la Plata and presaged the opening of the Iapetus Ocean. The time of rifting to drifting transition of Eastern American of Laurentia and West Africa initiated at ~580 Ma also signified the opening of the Iapetus Ocean. The time of drifting stage of the main basins around the Paleo‐Pacific Ocean tracts is not only earlier than those of the Iapetus Ocean tracts but also is characterized by diachronism. The time of drifting onset of basins in the Yangtze Block is ~720 Ma, the time of drifting initiation of the Adelaide Fold Belt in South Australia is 680 Ma, and the time of drifting stage of the south‐western margin of Laurentia occurred at 550 Ma. The different times of rifting to drifting transition of the Adelaide Fold Belt in South Australia, the Yangtze Craton, and Western American of Laurentia signified the nonisochronous opening of the Neoproterozoic Paleo‐Pacific Ocean.
The Hongshan and Huobuxun sags are located in the eastern segment of the northern Qaidam Basin, and the provenances of Jurassic deposits in the two sags are unclear. Based on the tectonic setting of the northern Qaidam Basin before the Jurassic, this paper discusses provenances of the two sags by field geological survey, analysis of detritus, and heavy minerals of the Jurassic strata. The Jurassic sedimentation in the Hongshan Sag mainly came from the Zongwulong Orogen and the Oulongbuluke and Kuerleike mountains, and the Xitie Mountain was the secondary provenance. The Jurassic deposits of the Houbuxun Sag mainly came from the Xitie and Aimunike and Dadakenwula mountains. Because of the barrier of the Zongwulong Orogen, the sources of Jurassic deposits from the South Qilian Caledonian Orogen were much fewer. Four Jurassic provenance systems of the Hongshan and Huobuxun sags are recognized through heavy mineral assemblages: Kuerleike–Zongwulong, Zongwulong–Oulongbuluke, Xitie, and Aimunike–Dadakenwula mountains provenance systems. Based on the provenance analysis of the two sags, the paper further discusses the basin–mountain system in the eastern segment of the northern Qaidam Basin during the Jurassic. The two sags were not an open connected basin as considered by some geologists but two isolated sags. The Kuerleike, Oulongbuluke, and Zongwulong mountains together constituted the northern sedimentary boundary of the Hongshan Sag, and the southern sedimentary boundary was the Xitie Mountain. The northern boundary of the Huobuxun Sag was the Xitie, Aimunike, and Dadakenwula mountains, which separated the Hongshan Sag from the Huobuxun Sag, resulting in the two sags to evolve independently into the faulted basins during the Jurassic.
The prototypes and evolutionary history of the Mesozoic basins in the eastern segment of the northern Qaidam Block are controversial, and the stress field is unclear with temporal and spatial variation. First, we divide the tectonic units systematically according to orogenesis, orogen stratigraphy, radioisotope geochemistry, petrology, and tectonics in the study area. The tectonic framework of “two belts and two blocks” formed in the study area before the Jurassic. The intersection of the NW‐trending and NE‐trending basement‐involved faults influences the formation of the Mesozoic prototype basins in the northern Qaidam Block. Second, we use a balanced cross‐section restoration method to retrieve the Mesozoic evolutionary history and determine the prototypes of the Hongshan and Huobuxun sags. The two sags were pulled apart by transtension during the Early–Middle Jurassic, initiating the Mesozoic evolutionary stages. The Hongshan and Huobuxun sags were under different stress states at different tectonic evolutionary stages during the Mesozoic. The Hongshan Sag was controlled by transtension with the NE‐directed extension ratio larger than the NW‐directed one during the Early–Middle Jurassic. The relatively weak extension led to an initial depression during the Early Jurassic. With an intense extension, the subsequent faulted Hongshan Sag deepened during the Middle Jurassic. The tectonic reversal initiated at the beginning of the Late Jurassic, resulting in the formation of the compressive Hongshan Sag, with the NE‐directed shortening ratio larger than the NW‐directed one during the Late Jurassic. The Hongshan Sag was in a relatively weak compressive stress state during the Cretaceous. The initial depression of the Huobuxun Sag, also under transtension, began to develop into an extensional faulted basin at the beginning of the Middle Jurassic, with the NE‐directed extension ratio much larger than the NW‐directed one. The tectonic reversal led to the formation of the compressive Huobuxun Sag during the Late Jurassic, with the NE‐directed shortening ratio much larger than the NW‐directed one. The Hongshan Sag was under the stronger extension during the Early–Middle Jurassic and the stronger compression during the Late Jurassic than the Huobuxun Sag.
The analysis and interpretation of the Dachaidan area, Qaidam Basin, is difficult, owing to the co-location of two groups of thrust faults (N–E faults and N–W faults) there and the area’s complicated structural deformation history. To address this problem, field geological investigation, seismic study, well logging, and drilling data were used to identify the key fault systems and their distribution patterns through the area. By integrating surface and subsurface structural features and seismic and non-seismic data, we carried out studies using structural modeling and analysis of the Dachaidan area. Study results identified two systems of thrust faults (N–W faults and W–E faults). We found that these faults could be categorized into three systems: a basin-margin thrust system, an intro-basin thrust system, and an intro-basin compression and strike-slip fault system. These systems showed different features in different areas and zones. We also constructed interpretation models of different deformation mechanisms in the basin and on basin margins. Three tectonic systems (compression, extension, and strike-slip) were identified, which were further divided into eight structural domains. We also established structure coexistence and distribution patterns. The overall structural character of the area was summarized as the northern and southern parts belonging to different zones, with the western and eastern parts belonging to different systems. By analyzing the SW–NE tectonic evolution sections, we defined the back-propagation structural evolution sequences of thrust nappes (on the basin margin or in the basin) and back-thrust structures (in the basin) as well as their influence on the residual Mesozoic strata.
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