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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]

Abstract: The unified South China Block, comprising the Yangtze Block to the northwest and the Cathaysia Block to the southeast, has been central to recent studies on the Precambrian crustal evolution and position of South China in Proterozoic supercontinents. Here we present results from detailed U–Pb geochronology, Lu–Hf isotopes and rare earth geochemistry on zircons from three Ordovician and Devonian sandstone samples of southeastern Yangtze, together with those from a granodiorite sample and three Triassic sandstone samples in northeast and southeast Cathaysia. The southeastern Yangtze Block is characterized by extensive tectono-thermal events during 850–730Ma and 470–410Ma, which corresponded to the breakup of Rodinia and the Caledonian orogenic event, respectively. Major zircon populations with ages of 2800–2500Ma, 1990–1580Ma and 1260–920Ma are recorded from southeastern Yangtze, which are correlated, respectively, with the Neoarchean crustal growth, and histories of the Paleo-Mesoproterozoic Columbia and Neoproterozoic Rodinia supercontinents. In contrast, zircon U–Pb ages from southeast Cathaysia reveal prominent magmatic events during 2630–2300Ma, 2030–1770Ma and 280–190Ma, correlated with Neoarchean continental growth and the tectonothermal regimes associated with the history of the Columbia supercontinent as well as the Indosinian movement. The sector-zoned zircons from the granodiorite in northeast Cathaysia yielded weighted mean ages of 846.7±9.8Ma and 826.4±7.6Ma and positive ɛHf values, constraining the initial breakup of South China at ca. 848 Ma and extensive rift-related magmatism at ca. 826Ma. The Hf data suggest important episodes of juvenile magmatic addition at 3.1–2.8Ga and 2.4–1.5Ga for Yangtze, and at 3.3–2.3Ga for Cathaysia, indicating the existence of older crustal components in South China. The Hf data suggest that most zircons in both the blocks were derived from crustal magmas. Our results suggest distinct crustal evolution histories for the Yangtze and Cathaysia Blocks albeit with close affinities. [Copyright &y& Elsevier]

Abstract: This paper reports some new results from U–Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U–Pb age determinations define five major age populations: 2560–2380Ma (a peak of 2460Ma), 1930–1520Ma (a peak of 1700Ma), 1300–900Ma (a major peak at 970Ma and two subordinate peaks at 1250Ma and 1130Ma), 850–730Ma (a prominent peak of 780Ma) and 670–530Ma (a major peak at 540Ma and a subordinate peak at 650Ma). We also report zircon U–Pb concordia age of 3.96Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930–1520Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970Ma and two secondary peaks at 1250Ma and 1130Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850–730Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670–530Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6–2.8Ga and the second one at 3.5–3.9Ga. The zircons show a large range of εHf(t) values from +8.64 to −30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials. [Copyright &y& Elsevier]