Reconstructing South China in Phanerozoic and Precambrian supercontinents

The South China Craton comprises the Yangtze Block in the northwest and Cathaysia Block in the southeast. Located in the southeastern Yangtze Block, the Jiangnan Orogen formed through the amalgamation between the Yangtze and Cathaysia Blocks. The Yangtze Block has sporadically exposed Archean rocks in the north, Paleoproterozoic to Mesoproterozoic volcano-sedimentary sequences in the southwest and widespread Neoproterozoic sedimentary sequences accompanied by syn-sedimentary igneous rocks on the western and southeastern margins.
\nThe late Paleoproterozoic to early Mesoproterozoic Dongchuan, Dahongshan and Hekou groups in the southwestern Yangtze Block formed in a series of fault-controlled, rift-related basins associated with the fragmentation of the supercontinent Columbia. These sedimentary sequences were deposited between 1742 and 1503 Ma, and recorded continuous deposition from alluvial fan and fluvial sedimentation during the initial rifting to deep marine sedimentation in a passive margin setting. Sedimentation during initial rifting received felsic detritus mainly from adjacent continents, whereas sedimentation in a passive margin basin received detritus from felsic to intermediate rocks of the Yangtze Block. Paleoproterozoic to Mesoproterozoic rift basins in the southwestern Yangtze Block are remarkably similar to those of north Australia and northwestern Laurentia in their lower part (1742-1600 Ma), but significantly different after ca. 1600 Ma. The southwestern Yangtze Block was likely connected with the north Australia and northwestern Laurentia in Columbia but drifted away from these continents after ca. 1600 Ma. 
\nTraditionally thought Mesoproterozoic sedimentary sequences in the southeastern Yangtze Block are now confirmed to be Neoproterozoic in age and include the 835-830 Ma Sibao, Fanjingshan and Lengjiaxi groups, and 831-815 Ma Shuangqiaoshan and Xikou groups. These sequences are unconformably overlain by the ~810-730 Ma Danzhou, Xiajiang, Banxi, Heshangzheng, Luokedong and Likou groups. The regional unconformity likely marked the amalgamation between the Yangtze and Cathaysia Blocks and thus occurred at ~815-810 Ma. The lower sequences (835-815 Ma) received dominant Neoproterozoic (~980-820) felsic to intermediate materials in an active tectonic setting related to continental arc and orogenic collision, whereas the upper sequences represent sedimentation in an extensional setting with input of dominant Neoproterozoic granitic to dioritic materials (~740-900 Ma). The upper 
\nparts of the Shuangqiaoshan and Xikou groups, uncomfortably underlain by lower units, are molasse-type assemblages with additional input of pre-Neoproterozoic detritus, representing accumulation of sediments in a retro-arc foreland basin associated with the formation of the Jiangnan Orogen. Stratigraphic correlation, similarly low-δ18O and tectonic affinity of igneous rocks from different continents suggest that the Yangtze Block should be placed in the periphery of Rodinia probably adjacent to northern India. Paleoproterozoic (~2480 Ma and ~2000 Ma) and Early Neoproterozoic (711-997 Ma) were the most important periods of crustal and magmatic events of the southeastern Yangtze Block, but there is a lack of significant Grenvillian magmatism. Early Neoproterozoic magmatism highlights the contribution from both juvenile materials and pre-existing old crust, whereas ~2480 Ma and ~2000 Ma events are marked by reworking of pre-existing continental crust. Magmatism at 1600-1900 Ma was dominated by reworking of pre-existing crust, whereas the 1400-1600 Ma magmatic event recorded some addition of juvenile materials.

South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover. Both the constituent Yangtze and Cathaysia blocks contain well‐preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature, but less is known about their earlier crustal history due to the incomplete rock record. Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre‐Neoproterozoic continental crustal evolution in South China. In this paper, we summarize the up‐to‐date pre‐Neoproterozoic records, including petrological, geochronological, geochemical and geophysical data, across South China, and discuss its spatiotemporal patterns of the pre‐Neoproterozoic crust and the relevant tectonic events. While the xenocrystic/inherited and detrital zircon records suggest widespread Archean (mainly ca. 2.5 Ga) crustal components within both the Yangtze and Cathaysia blocks, exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block. These Archean rocks are dominated by TTGs (tonalite‐trondhjemite‐granodiorite) with varied ages (3.3–2.5 Ga) and zircon Hf isotopes, indicating a compositionally heterogeneous nature of the Archean Yangtze Block and, by inference, the development of multiple ancient terranes. The early Paleoproterozoic (2.4–2.2 Ga) tectonomagmatic events characterize the western Yangtze Block and are supportive of an east‐west subdivision of the Yangtze basement, whereas the late Paleoproterozoic (2.1–1.7 Ga) orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block, and also the Cathaysia Block. The eastern Yangtze Block with generally northeastward‐younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05–1.75 Ga orogenic process welding the various Archean proto‐continents, consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part. The Cathaysia Block was probably involved in a short‐lived 1.9–1.8 Ga orogenic event. The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China, and are referred to be linked with the assembly of the Nuna Supercontinent. The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions (1.7–1.5 Ga) in the southwestern Yangtze Block, and the ca. 1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break‐up. Late Mesoproterozoic (1.2–1.0 Ga) magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent. Similar‐aged metamorphism (1.3–1.0 Ga) is recorded in Hainan Island, reflecting the Grenvillian continental collision during the Rodinia assembly, but further studies are necessary to better constrain the late Mesoproterozoic tectonic framework of South China.

K-bentonite, black-shale and flysch successions at the Ordovician–Silurian transition, South China: Possible sedimentary responses to the accretion of Cathaysia to the Yangtze Block and its implications for the evolution of Gondwana

Neoproterozoic amalgamation between Yangtze and Cathaysia blocks: The magmatism in various tectonic settings and continent-arc-continent collision

Unraveling the character and source of late Mesoproterozoic‐early Neoproterozoic sedimentary sequences is crucial in constraining Rodinia reconstructions. We carried out an integrated geochemical, zircon U‐Pb geochronological and Lu‐Hf isotopic study of the Shilu Group and the overlying Shihuiding Formation in Hainan, South China. These two successions are chemically mature and dominated by siliceous components. The Shilu Group was mainly derived from felsic arc lithologies whereas the Shihuiding Formation was from recycled sedimentary materials and records a transition from convergent to passive margin settings during the late Mesoproterozoic‐early Neoproterozoic in Hainan. Detrital zircons from the Shilu Group and Shihuiding Formation yield similar age populations, with maximum depositional ages of ~1,100–1,000 Ma and ~900 Ma, respectively. The Shilu Group matches well with the Kunyang Group outcropped in the Yangtze Block in depositional age, detrital zircon age populations and Lu‐Hf isotopic compositions, and geochemical characteristics, whereas the Shihuiding Formation exhibits significantly different detrital age populations from the Wanquan Group in the Cathaysia Block. This indicates that Hainan was linked to the Yangtze Block rather than the Cathaysia Block in the late Mesoproterozoic‐early Neoproterozoic. The Shilu and Kunyang groups have similar detrital age patterns to the late Mesoproterozoic to early Neoproterozoic strata in northwest India and are distinct from their equivalents in west Laurentia, suggesting an external location of Hainan‐Yangtze in Rodinia.

Spatiotemporal evolution and causes of marine euxinia in the early Cambrian Nanhua Basin (South China)

We use detrital provenance data from Cambrian sandstones to examine whether the Yangtze and Cathaysia blocks in South China were separated by an ocean during the Cambrian period. Zircons from the Cambrian sandstones exhibit a dominant ~ 800 Ma age peak in the central Yangtze Block, being sourced from the western Yangtze Block, whereas a ~ 980 Ma peak dominates in the northwestern Cathaysia Block, being sourced from an exotic continent once connected to Cathaysia. A mixed provenance with both age peaks is found in Cambrian sandstones from the southeastern Yangtze Block, indicating that detritus can travel from the Cathaysia Block to the Yangtze Block, and therefore arguing against the existence of a broad Cambrian ocean.

Fifteen sandstone samples taken from pre-Cretaceous strata of the Yangtze Block are analysed to constrain the evolution of the South China Block, especially the assembly between the Yangtze and Cathaysia blocks. The results show that the maximum depositional age of the Neoproterozoic Lengjiaxi Group adjacent to the Cathaysia Block isc. 830 Ma, differing from that of the Kunyang and Dahongshan groups (> 960 Ma) on the southwestern margin of the Yangtze Block. The detrital zircons from Palaeozoic samples from the Yangtze Block have similar age populations to those in the Cathaysia Block, and they may originate from the Cathaysia Block according to palaeogeographic, palaeocurrent and former research data. The detrital zircons of Middle–Upper Jurassic sandstones in the southwestern and central Yangtze Block yield dominant age populations at 2.0–1.7 Ga and subordinate groups of 2.6–2.4 Ga, 0.8–0.7 Ga and 0.6–0.4 Ga. The Upper Triassic strata may be derived from the southern Yangtze and North China blocks due to the collisions between the Indosina, South China and North China blocks, whereas the Jurassic sediments may be partly derived from uplift and erosion of the Jiangnan Orogen due to an intracontinental orogeny induced by Pacific subduction towards the Eurasia Plate. The detrital age spectra and provenance data for basement in the South China Block are analysed and compared with each other. The South China Block has affinity with Australia not only in the Columbia supercontinent but also in the Rodinia supercontinent. We infer the existence of an ancient orogen under the western Jiangnan Orogen, which may have occurred during the Columbia age, earlier than the Sibao orogeny. This is supported by seismic profile proof from the SinoProbe.

U–Pb and Hf isotopic study of detrital zircons from the meta-sedimentary rocks in central Jiangxi Province, South China: Implications for the Neoproterozoic tectonic evolution of South China Block

Detrital zircon U–Pb–Hf isotopes and whole‐rock geochemical compositions of exposed Neoproterozoic sedimentary rocks in the Xiangshan area are determined to discuss provenances and the boundary between the Yangtze and Cathaysia blocks. Zircon dating results reveal that the exposed Precambrian sedimentary rocks in the Xiangshan area were deposited in the Late Neoproterozoic era. The age spectra and whole‐rock geochemistry show that the detrital materials of the Shenshan Formation originated from the Yangtze Block and that the detritus of the Kuli and Shangshi formations came mainly from the Yangtze Block and partly from the Cathaysia Block. The source for the Neoproterozoic sedimentary rocks in the Xiangshan area may been intermediate rocks, mainly from a mixture of felsic and mafic rocks in the Yangtze Block. In combination with previous studies, we suggest that the Xiangshan area belonged to the Cathaysia Block before the amalgamation between the Cathaysia and Yangtze blocks and that the real boundary between the two blocks is located in the northern part of the Xiangshan area.

Evolution of the Indian Block can be traced through Earth9s Phanerozoic and Precambrian supercontinent cycles. The Paleoproterozoic tectonostratigraphic record of the North Indian Block and the Aravalli Delhi Fold Belt in the Nuna supercontinent assembly shows a close link with the events in the Cathaysia Block of South China. Accretion of the two terranes is documented by 1.97 to 1.92 Ga continental arc igneous rocks and 1.91 to 1.81 Ga syn- and post-collisional magmatism in the Lesser Himalaya, along with 1.88 to 1.86 Ga granulite metamorphism in both continental blocks. The connection between the North Indian Block and the Cathaysia Block continued through Nuna dispersal and was followed by the accretion of a series of terranes/microcontinents along the western margin of this united North India-Cathaysia Block during Rodinia assembly (ca. 1.0 Ga). This is recorded by accretion of the Marwar Block to the North Indian Block and Yangtze Block to the Cathaysia Block. Long-lived active continental margins continued along Marwar (NW India), Yangtze, Madagascar and the Seychelles until ca. 720 Ma that jointly occupied a peripheral or even independent paleoposition in the Rodinia reconstructions. The eastern margin of India sutured with the Western Australia-Mawson blocks along the Kunnga Orogen during the final assembly of Gondwana in the early Paleozoic, whereas microcontinental blocks including south Qiangtang and north Lhasa, were accreted to the northern margin of Gondwana in the vicinity of India. The collision of this ensemble of blocks with Africa (western Gondwana) is marked by the East African Orogen/Mozambique Belt, extending through central east Africa, Madagascar, South India and Antarctica. However, further north, India was separated from the Arabian-Nubian Shield by an embayment of the proto-Tethys that remained integral until the breakup of Gondwana. The accretion of Laurussia to Gondwana in the mid-Paleozoic during the assembly of Pangea corresponds with lithospheric extension along the northern margin of India (Gondwana) and separation of several continental blocks including South China, south Qiangtang, and north Lhasa, which then drifted northward across the Paleo-Tethys to collide with the Asian segment of Pangea in the Permo-Triassic.

To constrain the Mesozoic tectonic evolution and the lithospheric boundary between the Yangtze and Cathaysia blocks in South China, we present geochronological and geochemical data for Mesozoic basaltic lavas and related mafic dikes west (Group 1) and east (Group 2) of the Chenzhou-Linwu fault. Three episodes of mafic magmatism around the Chenzhou-Linwu fault were identified: ca.175 Ma, 125-150 Ma, and 80-95 Ma, respectively. Group 1 rocks (alkaline basanite and trachybasalt), with ages of >125 Ma, have a wide range of 87Sr/86Sr(t) values (0.7035-0.7069), and εNd(t) values (-3.75 to + 6.10). In contrast, Group 2 rocks (subalkaline basalt and basaltic andesite), with ages of > 125 Ma, exhibit 87Sr/86Sr(t) values of 0.7075-0.7087 and εNd(t) values of -2.04 to + 1.05. Both groups are strongly enriched in incompatible elements, with variable negative Nb-Ta anomalies. However, Group 1 rocks commonly have higher LREE and Ba/Nb, Rb/Nb, Ba/Th, and Ba/La ratios and lower Th/Nb, Th/La, and Zr/Nb ratios than Group 2 rocks. Rocks with ages of 80-95 Ma from both groups have very similar elemental and isotopic compositions (87Sr/86Sr(t) = 0.7033-0.7052, εNd(t) = +3.99 to + 8.00), consistent with those of OIB. Strong coupling between incompatible elemental ratios and isotopes suggests that Group 1 rocks might have been derived from an EMI-like continental lithospheric mantle with an OIB source. In contrast, Group 2 rocks come from an EMII-like mantle source contaminated by an OIB component. We conclude that Mesozoic mafic rocks with ages of >125 Ma originated chiefly from an enriched lithospheric mantle heated by ascending asthenosphere, whereas the mafic rocks with ages of ca. 80-95 Ma were derived from upwelling asthenospheric mantle in response to intra-continental lithospheric extension in the South China interior. The spatial variations of EMI-and EMII-like source signatures for Mesozoic mafic rocks around the Chenzhou-Linwu fault suggest that the fault represents the Mesozoic lithospheric boundary between the Yangtze and Cathaysia blocks. The Jinxian-Anhua fault was only a near-surface boundary between the sutured blocks. The crust of the Cathaysia block might have been thrust westward over the Yangtze block with a displacement of >400 km at a time no later than ca. 175 Ma. A model for crustal detachment collision (>ca. 175 Ma) and subsequent intra-continental lithospheric extension (175-80 Ma) is proposed for the Mesozoic tectonic evolution of South China.

<p>The Proto-Tethys Ocean is principally defined as an ancient ocean distributed to the northern margin of the Gondwana landmasses, which initiated during the breakup of the Rodinia supercontinent and closed in the Early Paleozoic during the final assembly of Gondwana. Major continental blocks of China, including Tarim, Qaidam, South China and North China, were distributed in this ocean. Locally in the Altyn-Tagh UHP belt in the southeastern margin of the Tarim Craton, the ocean is referred to as the Altyn Ocean. The Kulamulake ophiolitic mélange occur within the South Altyn Terrane and was extensively sheared and deformed, with its southern and northern margins of the ophiolitic mélange delineated by a top to the northwest thrusting fault zone and a ductile shearing zone, respectively. The mélange thrust on to the latest Mesoproterozoic-Neoproterozoic Altyn group and Neoproterozoic-Paleozoic Bashikuergan group on its northern and southern margins, respectively. Stratigraphically from bottom to top it is composed of sheared serpentinite on the basal thrust, layered dunite-harzburgite, pyroxene peridotite, layered olivine pyroxenite and fine-grained meta-gabbro, along with exotic blocks of marble. Pillow basalt and plagio-granite have also been reported from within the mélange, which might be upper components of the ophiolite stratigraphy. All the exposed lithostratigraphic sequences occur as structural blocks. Therefore, overall lithologies and structures resembles those of ophiolitic mélanges. Meta-gabbro components of the mélange yield concordia ages of 518 ± 2 Ma, along with juvenile zircon Hf and whole rock isotopic signatures. The analyzed mafic-ultramafic samples display chemical characters that are comparable to E-MORB, but with some island-arc signatures, resembling those of SSZ type ophiolite. In addition, correlations of major and trace element compositions of all analyzed samples are indicative of fractional crystallization from a depleted mantle source. The overall lithological assemblages, isotopes and chemical compositions are consistent with a disrupted ophiolitic mélange during initial oceanic subduction environment. Therefore, we concluded the Kulamulake ophiolite recorded the initiation of oceanic subduction within the Paleo-Tethys Ocean in northern Gondwana margin. This research was supported by NSFC Projects (41730213 and 41190075) and Hong Kong RGC GRF (17307918 and 17301915).</p>

Zircon U–Pb and Hf isotopic study of Mesozoic felsic rocks from eastern Zhejiang, South China: Geochemical contrast between the Yangtze and Cathaysia blocks

U–Pb age and Hf isotope composition of detrital zircons from Neoproterozoic sedimentary units in southern Anhui Province, South China: Implications for the provenance, tectonic evolution and glacial history of the eastern Jiangnan Orogen