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The Cathaysia Block of the South China Craton includes a Proterozoic basement that experienced a prolonged Precambrian crustal evolution but to date lacks evidence of Proterozoic metamorphic ages. At Lichuan and Jianning, in the Wuyi Domain of the eastern Cathaysia Block, Proterozoic rock units include migmatized paragneiss of the Wanyuan Group and minor amphibolite of the Tianjingping Formation, which are enveloped by schist of Mayuan Group, and all are intruded by Paleozoic and Mesozoic igneous rocks. Detrital zircon grains from the Wanyuan paragneiss display metamorphic rims that yield concordant weighted average 206 Pb/ 238 U ages of 860 ± 6 Ma and 435 ± 5 Ma, along with variably disconcordant ages with lower intercept ages of 442 ± 41 Ma. The zircon core ages range from 3015 Ma to 851 Ma, with three major age populations at 930–865 Ma, 1850–1200 Ma and 2650–2400 Ma. Detrital zircon grains from Mayuan schist samples at Jianning generally lack core-rim structures and yield three main age populations at 860–736 Ma, 1835–1775 Ma and 2720–2500 Ma. Metamorphic ages of ca. 860 Ma and ca. 435 Ma for the Wanyuan paragneiss along with the youngest detrital zircon constrain the depositional age of the protolith to ca. 865–860 Ma, whereas the Mayuan Group is younger and probably deposited after ca. 736 Ma. Characteristics of detrital zircon age populations along with regional geological data suggest accumulation of the Wanyuan Group in a convergent and/or collisional setting. Metamorphism and a possible subduction-collision process within the Cathaysia Block at around 860 Ma suggest it was not a unified block in early Neoproterozoic. The growth of ca. 440 Ma metamorphic rims is likely related to granitic magmatism, such as that exposed in the Lichuan region. The sparse evidence for early Neoproterozoic metamorphism likely reflects widespread overprinting by the Paleozoic tectonothermal event at around 440 Ma. [ABSTRACT FROM AUTHOR]

The Jiangshan-Shaoxing fault zone lies along the SE margin of the Jiangnan belt, and delineates the northeastern margin of the Cathaysia Block of the South China Craton. At Shijiao in NE Zhejiang, the fault zone consists of hornblende schist intruded by migmatized quartz diorite. It constitutes a shear zone delineating the welded boundary between the Neoproterozoic Shuangxiwu Group of Jiangnan belt to the north and the Chencai Complex of Cathaysia Block to the south. The Shuangxiwu Group is composed mainly of basalt, andesite and flysch, whereas the Chencai Complex contains magmatic and sedimentary rocks that experienced amphibolite facies metamorphism. Zircons from quartz diorite and gabbro from the fault zone at Shijiao yield ages of 854 ± 6 Ma, 857 ± 5 Ma and 860 ± 5 Ma, with positive ɛHf( t ) values of 7.81–11.8 and 4.57–10.39. The quartz diorite and mafic-ultramafic rock samples display minor LREE enriched pattern with obvious depletion of Nb, Ta, Rb, Ba and Ti, compared to their neighboring elements and plot in the volcanic arc field on geochemical diagrams, similar to that of volcanic rocks from Shuangxiwu Group. Overall relationships within the Jiangshan-Shaoxing fault zone at Shijiao suggest the ca. 860–850 Ma rock suites were generated in a convergent plate margin and are part of the Jiangnan belt, and not the Cathaysia Block, thus constraining the location of the suture between the two lithotectonic units in NE Zhejiang area during Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Jiangnan orogenic belt in South China defines a subduction-collisional zone between the Yangtze and the Cathaysia blocks. The eastern part of this belt comprises the oceanic Huaiyu terrane, the northeast Jiangxi suture zone and the continental Jiuling terrane. We report zircon U–Pb and Hf isotope data and whole rock geochemistry on the arc magmatic rocks of andesite and basalt occurring as olistostromal blocks, as well as conglomerate in the Dengshan Group above the unconformity between cover sequence and the volcanic arc units. The andesites yield weighted mean ages of 864 Ma, 868 and 871 Ma, whereas the detrital zircons from the conglomerate yield a major age population of 863–810 Ma (peak of 833 Ma), with two minor ones of 1120–940 Ma (peak at 960 Ma) and 1780–1560 Ma (1670 Ma). A post-ca. 810 Ma depositional age is thus suggested for the Dengshan Group. The influx of olistostromal deposits into the Dengshan Group must post-date the youngest detrital zircon age of 810 Ma and is possibly related to the widespread Nanhua rifting associated with the breakup of Rodinia. Furthermore, the age distribution of detrital zircons from the phyllite associated with the arc units compared to its depositional age also suggest a convergent setting, and those from the conglomerate are plotted into a similar field. The andesite and basaltic trachyandesite have LREE enriched patterns, with minor negative Eu anomaly, and negative Nb, Ta, Cs and Ti anomalies. However, the basalt displays only minor LREE enrichment, with no Eu anomaly, and almost flat spidergram trace element patterns, except for a minor positive Sr, Ba and Ti anomaly and negative Rb anomaly. The andesite and basaltic trachyandesite are all plotted in the field of volcanic arc, suggesting an arc setting. The basalt is plotted between EMROB and volcanic arc domains, suggesting magma generation from metasomatised sub-arc sources with subducted oceanic components. The Hf isotopic data on zircons from the andesite yield positive ɛ Hf( t ) values of 2.79–15.51 and late Mesoproterozoic model ages, suggesting that the Neoproterozoic arc sources include reworking of subducted late Mesoproterozoic materials. Our results show that the amalgamation of the Yangtze and Cathaysia blocks in the eastern part occurred at some time between ca. 864 Ma and ca. 810 Ma. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan Orogen in South China records a succession of arc-trench-basin assemblages culminating in accretion of the bounding Yangtze and Cathaysia blocks to form the stabilized South China Craton. The orogen can be traced over some 1500 km and extends up to 100 km across strike. It is divisible into three domains: the northeast domain (also referred to as the Huaiyu or Shuangxiwu Terrane), the central domain (Jiuling Terrane), and an undifferentiated southwest domain. The northeast domain contains arc type volcanic suites and I-type granitoids dated at ca. 970–850 Ma. It is interpreted as an intra–oceanic terrane based on the juvenile radiogenic isotopic signature of the igneous rocks, the absence of older detritus and inherited xenocrysts, and the presence of ophiolites along its southwestern and western margins. The central and southwest domains contain trench-arc-basin assemblages of clastic sedimentary units, mappable magmatic arc suites and ophiolitic mélanges (Sibao and equivalent groups) that range in age from ca. 880 to 820–815 Ma. The presence of old zircon grains within these two domains, both as detritus within sedimentary units and as inherited zircon in arc basalt, suggest they formed at convergent continental margins. S-type granites dated at 845–815 Ma are a distinctive element of the central and southwest domains. The ages of these granites overlap with convergent plate magmatism in the two domains, arguing against previous models for plume-rift and post-collisional geodynamic settings. Instead, these bodies likely formed in an accretionary orogenic margin setting in which granitic magmatism occurred in an extensional regime triggered by slab rollback. The slab-rollback process triggered mantle-sourced thermal input and partial melting of the older and buried arc-bounding basin sediments. Early Paleozoic S-type granites in the Lachlan and New England belts in eastern Australia and Jurassic ones in the Cordillera belt of the western US provide analogous geodynamic environments. Isotopic data indicate that the central Jiangnan domain experienced significant crustal growth, whereas in the southwest domain there was a greater degree of crustal reworking. The character and distribution of the early Neoproterozoic sedimentary and igneous succession in the orogen suggests it represents a ca. 970–820 Ma accretionary orogen. Upper age limits on the Jiangnan Orogen are provided by a regional angular unconformity in the central and southwest domains at ca. 810–805 Ma, and in the northeast domain at ca. 825 Ma, along with the overlying bimodal volcanic and clastic sedimentary successions mostly dated at ca. 810–730 Ma. Thus, timing of final assembly of South China displays variations across the Jiangnan Orogen, from ca. 825 Ma in the northeast to ca. 820–805 Ma in the central and southwest of the orogen. Post-assembly successions are parts of the Nanhua Basin and are interpreted to have formed during regional lithospheric extension across the eastern and central South China Craton. The age patterns across the South China Craton are indicative of northwest directed accretion of fragments and suggest an external rather than an internal position of the craton within the assembled Rodinia supercontinent. Paleomagnetic data, regional correlations and sedimentary records are consistent with a position along the northern margin of Rodinia, adjacent to India and Australia. The Jiangnan Orogen recorded the accretion of trench-arc assemblages and ultimately the Yangtze Block to the Cathaysia Block that was already located on the margin of Rodinia. The Panxi-Hanan belt, which lies along the western and northwestern margin of the Yangtze Block, formed on the upper plate to a subduction system that both overlaps with, and is younger than, the Jiangnan Orogen. The belt provides a record of ongoing accretion on the Rodinia margin until the mid-Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Jiangnan Orogen and Cathaysia Block constitute integral components in the geological framework of the South China Craton. However, the tectonic attributes of these two regions remain controversial. In this study we present LA–ICP–MS zircon U–Pb ages, Lu–Hf isotopes, and major and trace elements data from a suite of clastic rocks. Two hundred and forty seven zircon U–Pb ages obtained from the Neoproterozoic meta-sandstones in western Jiangnan Orogen define three major age populations: 2564–2395 Ma, 2068–1849 Ma and 963–730 Ma, corresponding to the early Paleoproterozoic crustal growth, amalgamation of the supercontinent Columbia and tectonics associated with Rodinia. Two hundred and forty three zircon U–Pb age data from Cambrian and Ordovician sandstones in the western Cathaysia yield five age populations: 2626–2392 Ma, 2050–1518 Ma, 1173–904 Ma, 857–708 Ma and 630–502 Ma, which can be correlated to the Neoarchean–early Paleoproterozoic continental growth, the tectono-thermal events associated with the Columbia supercontinent, the assembly and breakup of Rodinia, as well as the Pan-African event. The 630–502 Ma population correlates with the assembly of Gondwana supercontinent during late Neoproterozoic to early Paleozoic, although direct geological evidence for this event has not yet been reported from this region. These results suggest that the western Jiangnan belt and western Cathaysia Block have distinct crustal evolution histories albeit with close affinities. The REE geochemisty and Lu–Hf isotope data also indicate that the provenances of the Neoproterozoic and early Paleozoic detritus in western Jiangnan belt and western Cathaysia are mostly composed of reworked crustal materials. The metamorphic rims of zircon grains with core–rim structures yield ages of 912–891 Ma and 853–835 Ma, suggesting two phases of metamorphic events during Neoproterozoic in the source areas. These two events are likely associated with the tectonics related to the collision of Yangtze and Cathaysia blocks in the western and eastern segments, respectively. [ABSTRACT FROM AUTHOR]