Bihai Zheng

Neoproterozoic ages of the Kuluketage diabase dyke swarm in Tarim, NW China, and its relationship to the breakup of Rodinia

The widely exposed Kuluketage diabase dyke swarm, Tarim Block, NW China, has been considered to have been emplaced in Permian times. New precise zircon U–Pb SHRIMP ages for two samples from the dyke swarm yield Neoproterozoic ages of 823.8 ± 8.7 Ma and 776.8 ± 8.9 Ma. Correlated with peaks of magmatism in South China and Australia at c. 825 Ma and c. 780 Ma, these two new ages provide significant information for palaeocontinental reconstructions. The prolonged duration of the magmatic events, combined with regional stratigraphic relationships, imply that the Tarim Block may have been affected by a mantle plume during the breakup of Rodinia.

Subducted Precambrian oceanic crust: geochemical and Sr–Nd isotopic evidence from metabasalts of the Aksu blueschist, NW China

Abstract: The Aksu Proterozoic blueschist terrane in northwestern China is regarded as one of the oldest well-substantiated Precambrian blueschist terranes in the world. Previous work has focused on the high-pressure metamorphism: both the age and P–T conditions of the metamorphic event have been well discussed. However, little attention has been paid to protolith identification of the blueschist terrane. In this paper, we present geochemical and Sr–Nd analyses of metabasalt samples from the blueschist terrane. The results show that the protoliths of these mafic schists were enriched mid-ocean ridge basalt (E-MORB). Crystal fractionation has led to differentiation of trace element concentrations. This provides the opportunity to obtain a protolith Sm–Nd isochron age of 890 ± 23 Ma (MSWD = 0.68). We conclude that the Aksu blueschist terrane represents part of an ocean crust at the NW edge of Rodinia around Tarim at c. 890 Ma. It experienced subduction and exhumation followed by accretion to the Tarim craton. If the north margin of present Tarim faced outboard of Rodinia during subduction, it might form one section of the arcuate subduction zone around the supercontinent. Alternatively, the subduction zone may have been located between Tarim and Australia and would later be closed.

Cenozoic inversion of the East China Sea Shelf Basin: implications for reconstructing Cenozoic tectonics of eastern China

The structural styles of the East China Sea Shelf Basin are described based on the interpretation of seismic profiles. The basin is divided into West and East Rift regions. It has undergone four phases of compressive structural inversions during the late Palaeocene Oujiang Event, the late Eocene Yuquan Event, the early Miocene Huagang Event, and the latest Miocene Longjing Event. Structural inversions have superimposed on the Cenozoic extensional rift basin during these compression events, forming regional unconformity reflectors (T4°, T3°, T2°, and T1°). The Changjiang Depression located in the north of the West Rift Region is characterized by a number of NW-, EW-, to NE-trending faults. However, the other depressions in the East China Sea Shelf Basin are dominated by NNE- to NEE-trending faults. During the Palaeocene, the Taibei Depression was in a marine environment, whereas the Changjiang Depression was terrestrial, although both depressions are located in the West Rift Region. The Hongzhouwan–Okinawa Fault separates the East China Sea Shelf Basin into south and north. The structural styles and the sedimentary environment change longitudinally and transversely, which are controlled by basement structures. The depocentre of the East China Sea Shelf Basin has gradually migrated and became younger from west to east. The structural inversion also becomes younger from west to east, but the intensity of inversion increases from south to north. These structural inversion events reveal a periodic compression and imply that the compressive uplift of eastern China resulted from subduction of the Pacific Plate as well as collision of the Luzon arc and the Asian continent rather than the remote effect of India–Asian collision.

Wide rift model in Bohai Bay Basin: insight into the destruction of the North China Craton

The Bohai Bay Basin is a Cenozoic extensional basin along the eastern aspect of Asia. Whether the Bohai Bay Basin is a pull-apart or rift basin is controversial. The Bohai Bay Basin exhibits a high density of extensional faults and records destruction of the North China Craton. Many structural analyses have been performed on the Bohai Bay Basin, especially the Tan-L and Taihang Mountain fault systems which control its boundary. The initial deposition of Kongdian Formation was mainly distributed along the boundary of Bohai Bay Basin during the Palaeocene–early Eocene. Subsequently, tectonic activity migrated toward the interior of the basin during deposition of Shahejie Formation in the middle Eocene–early Oligocene. Bohai Bay Basin crust was thickened in early Mesozoic time and has thinned since late Mesozoic time. The crustal strength profile of Bohai Bay Basin is characterized by very weak lower crust, which differs from that of adjacent crust. In regard to the crustal structure, lithospheric thickness, and extensional style, an alternative rift model is proposed. Initial Bohai Bay Basin rifts were characterized by metamorphic core complexes affecting the North China Craton, which reflects collapse of parts of the early Mesozoic intra-plate orogen. Furthermore, westward subduction of the Palaeo-Pacific Plate led to upwelling of asthenosphere mantle. Persistent upwelling of mantle decreased the strength of lower crust and led to the warm heat-flow regime and generation of a lower crustal fluid layer and wide rifting. Outward flow of ductile lower crust following late Cretaceous extension thinned the lower crust and generated the overall sag appearance of the basin in early Cenozoic time. The model supports a model whereby a wide rift narrows with time. For the Bohai Bay Basin, extension and strike-slip faulting were two independent deformation systems superimposed on each other.