Jianmin Hu

What drove continued continent-continent convergence after ocean closure? Insights from high-resolution seismic-reflection profiling across the Daba Shan in central China

We conducted deep seismic-reflection surveying across the Jurassic Daba Shan thrust belt of central China to investigate how and why the continued convergence between north and south China lasted ∼50 m.y. after the Triassic closure of their intervening oceans. Our study, together with surface geology, gravity surveying, and magnetic observations, indicates widespread occurrence of mafic plutons below the Daba Shan thrust belt. We propose that subduction of dominantly eclogitized mafic crust of northern south China provided the driving force for continued convergence between north and south China after ocean closure.

The c. 1000–900 Ma and c. 550–500 Ma tectonothermal events in the Prince Charles Mountains–Prydz Bay region, East Antarctica, and their relations to supercontinent evolution

Abstract The Prince Charles Mountains (PCM)–Prydz Bay region in East Antarctica experienced the late Mesoproterozoic/early Neoproterozoic (c. 1000–900 Ma) and late Neoproterozoic/Cambrian (c. 550–500 Ma) tectonothermal events. The late Mesoproterozoic/early Neoproterozoic tectonothermal event dominates the Rayner Complex and spreads over the main part of the Prydz Belt. This event includes two episodes (or stages) of metamorphism accompanying the intrusion of syn- to post-orogenic granitoids at c. 1000–960 Ma and c. 940–900 Ma. The c. 1000–960 Ma metamorphism in the northern PCM and Mawson Coast records medium- to low-pressure granulite facies conditions accompanied by a near-isobaric cooling path, whereas the c. 940–900 Ma metamorphism in Kemp Land reaches relatively higher P–T conditions followed by a near-isothermal decompression or decompressive cooling path. The late Mesoproterozoic/early Neoproterozoic orogeny (i.e. the Rayner orogeny) involved a long-lived (c. 1380–1020 Ma) magmatic accretion along continental/oceanic arcs and a protracted or two-stage collision of the Indian craton with a portion of East Antarctica, forming the Indian–Antarctic continental block independent of the Rodinia supercontinent. The late Neoproterozoic/Cambrian tectonothermal event pervasively overprinted on both Archaean–Proterozoic basements and cover sequences in the Prydz Belt. Except for high-pressure granulite boulders from the Grove Mountains, the metamorphism of most rocks records medium-pressure granulite facies conditions with a clockwise P–T path. In contrast, this event is lower grade (greenschist–amphibolite facies) and localized in the PCM. Regionally, the late Neoproterozoic/Cambrian tectonothermal event seems to have developed on the southeastern margin of the Indo-Antarctic continental block, suggesting that the major suture should be located southeastwards of the presently exposed Prydz Belt. The precise dating for different rock types reveals that the late Neoproterozoic/Cambrian orogeny (i.e. the Prydz orogeny) commenced at c. 570 Ma and lasted until c. 490 Ma, which is roughly contemporaneous with the late collisional stage of the Brasiliano/Pan-African orogenic systems in Gondwanaland. Therefore, the final assembly of the Gondwana supercontinent may have been completed by the collision of a number of cratonic blocks during the same time period.

Meso-Neoproterozoic Stratigraphic and Tectonic Framework of the North China Craton

The Meso-Neoproterozoic sedimentary strata of the North China Craton (NCC) occur mainly in the Xiong’er Rift in the southern marginal part of the craton, the Yanliao Rift in the central region, and the Zhaertai–Bayan Obo Rift on the northern margin. In recent years, high-precision zircon U-Pb dating ages from several crucial stratums in Yanliao rift system provided a strong foundation for reconstruction of Meso-Neoproterozoic stratigraphic framework in NCC. These revolutionary progresses require new recognitions for tectonic evolution of NCC in Meso-Neoproterozoic. Among these progresses, the most important breakthrough is that Neoproterozoic Xiamaling formation in former research is redivided into Mesoproterozoic stratums and redefined as building system. In the latest standard scheme of China stratigraphic chart, Changcheng system, Jixian system, building system, Qingbaikou system, Nanhua system, and Sinian system are, respectively, limited into 1.8–1.6 Ga, 1.6–1.4 Ga, 1.4–1.0 Ga, 1.0–0.78 Ga, 780–635 Ma, 635–541 Ma. Under the new stratigraphic framework, the Mesoproterozoic Changcheng System consists of clastic rocks of the tidal flat–littoral facies, and the Jixian System contains carbonate rocks of the neritic facies in the lower section and clastic rocks of the tidal flat–littoral facies in the upper section. Therefore, the sedimentary sequences of these systems record a complete sedimentary sequence from transgression to regression. The Neoproterozoic Qinbaikou and Nanhua systems are transgressive sequences consisting of clastic rocks of the tidal flat–littoral facies in lower sections and carbonate rocks of the neritic facies in upper sections. These changes in lithology indicate increasing water depth over time. The Sinian System is composed of tillite, which occurs along the western and southern margins of the NCC and in the Longshoushan area, on the southern margin of the Alxa Block. Based on the sedimentary characteristics of the Meso-Neoproterozoic strata, as well as multiple magmatic events, we identify five phases in the evolution of the NCC during this period: (1) continental rifting during the early Mesoproterozoic, (2) a passive continental margin during the middle Mesoproterozoic, (3) an active continental margin during the late Mesoproterozoic, (4) extrusion and uplift, and (5) continental rifting at the end of the Mesoproterozoic and beginning of the Neoproterozoic. The first two stages likely record the final break-up of the Columbia supercontinent, whereas stages three to five may have been linked to the assembly and break-up of the Rodinia supercontinent.

Provenance and tectonic significance of late Mesoproterozoic detrital zircons from the Tonian system, northern margin of the North China Craton

ABSTRACT The involvement of the North China Craton (NCC) in the assembly or breakup of Rodinia has long been debated. Studies of palaeomagnetism, mafic sills (dikes), igneous events, and sedimentary records have led to contrasting opinions on this topic. No igneous events related to the late Mesoproterozoic assembly of Rodinia have been reported in the NCC. However, the authors found numerous late Mesoproterozoic zircons in the Tonian system on the northern margin of the NCC. The Tonian Zhulazhagamaodao formation is composed of meta-sandstone, siltstone, slate, carbonate, and dolomine of the littoral to neritic facies and occurs mainly in the western part of the Bayan Obo–Zhaertai–Langshan rift. U–Pb dating of detrital zircons from the Tonian system reveals age peaks at 1079 ± 23 Ma, 1092 ± 22 Ma, 1175 ± 50 Ma, 1175 ± 18 Ma, 1260 ± 45 Ma, 1266 ± 16 Ma, and 1270 ± 26 Ma, which correspond to the timing of Rodinia assembly. Considering that coeval igneous rocks and orogenic belts developed mostly in the Laurentia–Baltica cratons, we propose that these cratons supplied clastic material to the northern margin of the NCC and that they had a close spatial relationship between each other during the Tonian.