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Photomicrographs of the Neoproterozoic mafic-ultramafic rocks from the northern Guangxi Province, in the western JOB. (a) SBG cumulate peridotite; (b) SBG pyroxenite; (c) SBG gabbro; (d) SBG pillow lava; (e) DZG cumulate peridotite; (f) DZG pyroxenite; (g) DZG dolerite; (h) DZG pillow lava.
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The Jiangnan orogenic belt (JOB) has been interpreted as a suture zone between the Yangtze craton and Cathaysian terranes in South China. The Neoproterozoic mafic–ultramafic rocks are extensively exposed in the western JOB, providing an ideal opportunity to study the Neoproterozoic assembly and tectonic evolution of South China. We present integrat...
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... texture (Fig. 3b). Major primary minerals include olivine (45-65 vol.%) and clinopyroxene (25-40 vol.%), with minor brown hornblende (Table 1). The olivine is mostly replaced by serpentine and the clinopyroxene is mostly replaced by metamorphic amphibole, but relicts of primary olivine and clinopyroxene grains could be observed in sample D051-1 (Fig. 4a). Pyroxenite samples (JM02, JM05, JM06) have a dark-green color with fine-grained texture, and are mostly deformed and converted to actinolite-amphibole schist (Table 1; Fig. ...
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... serpentine and the clinopyroxene is mostly replaced by metamorphic amphibole, but relicts of primary olivine and clinopyroxene grains could be observed in sample D051-1 (Fig. 4a). Pyroxenite samples (JM02, JM05, JM06) have a dark-green color with fine-grained texture, and are mostly deformed and converted to actinolite-amphibole schist (Table 1; Fig. ...
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... SBG mafic rocks include gabbro and basaltic rocks. Gabbro samples (JM01, YJ03) are metamorphosed into plagioclase-amphibolite, and show gray-green colors with a palimpsest texture. The major minerals include hornblende (45-55 vol.%) and plagioclase (44-54 vol.%) ( Table 1; Fig. 4c). The rocks are strongly mylonitized along their boundaries with surrounding units (Fig. 3d), whereas the centers of the rock masses are characterized by weak deformation (Fig. 3c). Basaltic rocks (D009-1, D009-2, D009-4) occur as pillow lavas with a porphyritic texture, and the phenocrysts are dominated by fine-grained pyroxene ...
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... units (Fig. 3d), whereas the centers of the rock masses are characterized by weak deformation (Fig. 3c). Basaltic rocks (D009-1, D009-2, D009-4) occur as pillow lavas with a porphyritic texture, and the phenocrysts are dominated by fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite), and plagioclase (Table 1; Fig. ...
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... DZG ultramafic rocks include peridotite and pyroxenite. Peridotite samples (D011-1, SM09) are dark gray-green to dark-green in color with cumulate texture. The main primary minerals include oliv- ine and clinopyroxene (Table 1). The olivine is characterized by obvious serpentinization and the clinopyroxene entirely underwent tremolitization (Fig. 4e). Pyroxenite (D013-1), which is commonly metamorphosed into amphibolite, is gray-green in color with a fine-grained texture. The primary pyroxene grains are replaced by secondary amphibole (tremolite and actinolite) and chlorite (Table 1; Fig. ...
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... characterized by obvious serpentinization and the clinopyroxene entirely underwent tremolitization (Fig. 4e). Pyroxenite (D013-1), which is commonly metamorphosed into amphibolite, is gray-green in color with a fine-grained texture. The primary pyroxene grains are replaced by secondary amphibole (tremolite and actinolite) and chlorite (Table 1; Fig. ...
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... include dolerite and basaltic rocks. Dolerite (D012-1) is in thrust tectonic contact relationship with chert ( Fig. 3g), and is strongly deformed and metamorphosed into plagioclase- amphibolite. The dolerite is dark grayish-green, with a meta-diabasic texture. The major minerals include hornblende (40 vol.%) and plagioclase (55 vol.%) ( Table 1; Fig. 4f). Basaltic rocks (SM11, D013-2) are gray-green alternating with yellowish-brown color and preserve pillow structures ( Fig. 3f) with porphyritic texture (Fig. 4h), and the phenocrysts are composed chiefly of fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite) and plagioclase (Table ...
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... into plagioclase- amphibolite. The dolerite is dark grayish-green, with a meta-diabasic texture. The major minerals include hornblende (40 vol.%) and plagioclase (55 vol.%) ( Table 1; Fig. 4f). Basaltic rocks (SM11, D013-2) are gray-green alternating with yellowish-brown color and preserve pillow structures ( Fig. 3f) with porphyritic texture (Fig. 4h), and the phenocrysts are composed chiefly of fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite) and plagioclase (Table ...
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... of field and petrographic observations and immobile trace element characteristics can be used to constrain the tectonic environment in which the Neoproterozoic mafic-ultramafic rocks of the western JOB formed (see Pearce, 1975;Shervais, 1982;Beard, 1986;Pearce and Peate, 1995;Safonova and Santosh, 2014). On the Th/Yb versus Ta/Yb diagram (Fig. 14), all basalt samples plot in the active continental margin field. Shervais (1982) proposed a diagram using Ti/V ratios to discriminate different basalt types. Typical island arc tholeiites (IAT) have Ti/V ratios ranging between 10 and 20, MORB between 20 and 50, and oceanic island and alkaline basalts between 50 and 100. The SBG ...
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... DZG ultramafic rocks include peridotite and pyroxenite. Peridotite samples (D011-1, SM09) are dark gray-green to dark-green in color with cumulate texture. The main primary minerals include oliv- ine and clinopyroxene (Table 1). The olivine is characterized by obvious serpentinization and the clinopyroxene entirely underwent tremolitization (Fig. 4e). Pyroxenite (D013-1), which is commonly metamorphosed into amphibolite, is gray-green in color with a fine-grained texture. The primary pyroxene grains are replaced by secondary amphibole (tremolite and actinolite) and chlorite (Table 1; Fig. ...
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... DZG ultramafic rocks include peridotite and pyroxenite. Peridotite samples (D011-1, SM09) are dark gray-green to dark-green in color with cumulate texture. The main primary minerals include oliv- ine and clinopyroxene (Table 1). The olivine is characterized by obvious serpentinization and the clinopyroxene entirely underwent tremolitization (Fig. 4e). Pyroxenite (D013-1), which is commonly metamorphosed into amphibolite, is gray-green in color with a fine-grained texture. The primary pyroxene grains are replaced by secondary amphibole (tremolite and actinolite) and chlorite (Table 1; Fig. ...
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... SBG ultramafic rocks include peridotite and pyroxenite, in thrust tectonic contact relationships with the Sibao Group sedimentary rocks (Fig. 3a). Peridotite samples (D051-1, D051-2, JM03, JM04, YJ08) show dark gray-green to dark-green color with fine-grained cumulate texture (Fig. 3b). Major primary minerals include olivine (45-65 vol.%) and clinopyroxene (25-40 vol.%), with minor brown hornblende (Table 1). The olivine is mostly replaced by serpentine and the clinopyroxene is mostly replaced by metamorphic amphibole, but relicts of primary olivine and clinopyroxene grains could be observed in sample D051-1 (Fig. 4a). Pyroxenite samples (JM02, JM05, JM06) have a dark-green color with fine-grained texture, and are mostly deformed and converted to actinolite-amphibole schist (Table 1; Fig. ...
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... SBG ultramafic rocks include peridotite and pyroxenite, in thrust tectonic contact relationships with the Sibao Group sedimentary rocks (Fig. 3a). Peridotite samples (D051-1, D051-2, JM03, JM04, YJ08) show dark gray-green to dark-green color with fine-grained cumulate texture (Fig. 3b). Major primary minerals include olivine (45-65 vol.%) and clinopyroxene (25-40 vol.%), with minor brown hornblende (Table 1). The olivine is mostly replaced by serpentine and the clinopyroxene is mostly replaced by metamorphic amphibole, but relicts of primary olivine and clinopyroxene grains could be observed in sample D051-1 (Fig. 4a). Pyroxenite samples (JM02, JM05, JM06) have a dark-green color with fine-grained texture, and are mostly deformed and converted to actinolite-amphibole schist (Table 1; Fig. ...
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... SBG mafic rocks include gabbro and basaltic rocks. Gabbro samples (JM01, YJ03) are metamorphosed into plagioclase-amphibolite, and show gray-green colors with a palimpsest texture. The major minerals include hornblende (45-55 vol.%) and plagioclase (44-54 vol.%) ( Table 1; Fig. 4c). The rocks are strongly mylonitized along their boundaries with surrounding units (Fig. 3d), whereas the centers of the rock masses are characterized by weak deformation (Fig. 3c). Basaltic rocks (D009-1, D009-2, D009-4) occur as pillow lavas with a porphyritic texture, and the phenocrysts are dominated by fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite), and plagioclase (Table 1; Fig. ...
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... SBG mafic rocks include gabbro and basaltic rocks. Gabbro samples (JM01, YJ03) are metamorphosed into plagioclase-amphibolite, and show gray-green colors with a palimpsest texture. The major minerals include hornblende (45-55 vol.%) and plagioclase (44-54 vol.%) ( Table 1; Fig. 4c). The rocks are strongly mylonitized along their boundaries with surrounding units (Fig. 3d), whereas the centers of the rock masses are characterized by weak deformation (Fig. 3c). Basaltic rocks (D009-1, D009-2, D009-4) occur as pillow lavas with a porphyritic texture, and the phenocrysts are dominated by fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite), and plagioclase (Table 1; Fig. ...
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... DZG mafic rocks include dolerite and basaltic rocks. Dolerite (D012-1) is in thrust tectonic contact relationship with chert ( Fig. 3g), and is strongly deformed and metamorphosed into plagioclase- amphibolite. The dolerite is dark grayish-green, with a meta-diabasic texture. The major minerals include hornblende (40 vol.%) and plagioclase (55 vol.%) ( Table 1; Fig. 4f). Basaltic rocks (SM11, D013-2) are gray-green alternating with yellowish-brown color and preserve pillow structures ( Fig. 3f) with porphyritic texture (Fig. 4h), and the phenocrysts are composed chiefly of fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite) and plagioclase (Table ...
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... DZG mafic rocks include dolerite and basaltic rocks. Dolerite (D012-1) is in thrust tectonic contact relationship with chert ( Fig. 3g), and is strongly deformed and metamorphosed into plagioclase- amphibolite. The dolerite is dark grayish-green, with a meta-diabasic texture. The major minerals include hornblende (40 vol.%) and plagioclase (55 vol.%) ( Table 1; Fig. 4f). Basaltic rocks (SM11, D013-2) are gray-green alternating with yellowish-brown color and preserve pillow structures ( Fig. 3f) with porphyritic texture (Fig. 4h), and the phenocrysts are composed chiefly of fine-grained pyroxene (almost entirely replaced by metamorphic amphibole and chlorite) and plagioclase (Table ...
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... of field and petrographic observations and immobile trace element characteristics can be used to constrain the tectonic environment in which the Neoproterozoic mafic-ultramafic rocks of the western JOB formed (see Pearce, 1975;Shervais, 1982;Beard, 1986;Pearce and Peate, 1995;Safonova and Santosh, 2014). On the Th/Yb versus Ta/Yb diagram (Fig. 14), all basalt samples plot in the active continental margin field. Shervais (1982) proposed a diagram using Ti/V ratios to discriminate different basalt types. Typical island arc tholeiites (IAT) have Ti/V ratios ranging between 10 and 20, MORB between 20 and 50, and oceanic island and alkaline basalts between 50 and 100. The SBG basaltic rocks mostly plot in the IAT field with some samples overlapping with MORB and back-arc basin basalts (BABB), while the DZG basaltic rocks plot in the MORB-BABB field (Fig. 15). On the Zr versus TiO 2 diagram (Fig. 16), the SBG basaltic rocks plot into the volcanic arc basalt (VAB) field, whereas the DZG samples lie in the VAB and MORB overlapped field. Consequently, the SBG rocks are dominantly characterized by arc-like geochemical features, but DZG rocks show a mixture of MORB-and arc-like geochemical ...
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... Although the middle-late Mesozoic mafic rocks in eastern South China overall display a typical characteristic of continental-arc, there remains controversial about their eruption environment, i.e., fore-arc setting Yao et al., 2016;Zhao and Asimow, 2014) and back-arc basin setting (Li et al., 2013;Lin et al., 2016;Zhang et al., 2012). Volcanic rocks formed within a fore-arc setting commonly show a significant depletion in LREE, and the stratigraphic sequences of fore-arc volcanic associations consist mainly of low-silica boninite, high-Mg andesite and high-Si boninite from bottom to top (Brandl et al., 2017). ...
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... Some researchers suggested that these rocks were formed in an intraplate setting, associated with a mantle superplume that finally led to the break-up of the Rodinia supercontinent . On the contrary, other authors argued that these rocks are characterized by distinct geochemical signatures of an arc setting and thus formed in a subduction-related tectonic setting associated with the amalgamation of the YB and CB (Lin et al., 2016;Yao et al., 2016Yao et al., , 2019Shu et al., 2021). Moreover, the disrupted and pervasively sheared association of these mafic-ultramafic rocks, together with chert, siliceous marble, ophicalcite, and phyllite, have been recently interpreted as an imbricated ophiolitic mélange formed in a forearc arc and may represent the southwestern extension of the suture zone between the YB and CB (Shu et al., 2021;Yao et al., 2016Yao et al., , 2019. ...
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... Zr, Ti, Th, Hf, Nb, and Y) (Pearce 1975;Beard 1986;Pearce and Peate 1995). These elements are not sensitive to the processes of partial melting and fractional crystallization; thus, they can be used to deduce the characteristics of their mantle sources (Safonova and Santosh 2014;Lin et al. 2016). For example, within-plate basalts have higher Ti/Y, Nb/Y ratios and higher Zr contents than other types of basalts, indicating that their mantle source has experienced more mantle metasomatism processes relative to the MORB and volcanic arc basalts. ...
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... Central African Block and Columbia supercontinents) or comprised other parts now resting elsewhere in the world (e.g. North China craton) is still a theme of intense debate and a hot research topic (Rogers and Santosh, 2004;Peng et al., 2011;Cordani et al., 2013;Fu et al., 2015;Cederberg et al., 2016;Lin et al., 2016;e.g. Alkmim and Teixeira, 2017;D'Agrella-Filho and Cordani, 2017;e.g. ...
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... Ga 경에 충돌 후 환경에서 생성된 A-type 화성암과 차노카이트(Charnockite)가 변성작용과 함께 인지 된다 Li et al., 2008;Oh et al., 2009;Qiu et al., 2011). 일부 지역에 서는 820-780 Ma까지 섭입이 지속되었을 가능성이 있다 (Li et al., 2008;Lin et al., 2016;Kim, W.J. et al., 2021). 신원생대에 로디니아 초대륙이 형성되면서 양쯔판과 커테시아판이 충돌하였고 이로 인해 장난 (2015)). ...
... 이에 반해 남중국판에서는 북중국판보다 더 활발 한 신원생대 화성작용이 일어났다. 특히 남중국판의 북부에 해당하는 양쯔판의 북부와 남부 경계 지역에 서는 두 번의 신원생대 화성작용이 인지된다(표 2; Wang and Li, 2003;Li et al., 2008;Oh et al., 2009;Qui et al., 2011;Peng et al., 2012;Lin et al., 2016;Zhao et al., 2018;Kim, W.J. et al., 2021). 첫 번째 화 성작용은 섭입환경에서 일어났으며 로디니아 초대 륙 형성 이전인 1000-830 Ma에 일어났다 (그림 8: Li et al., 2008;Oh et al., 2009;Qiu et al., 2011;Zhao et al., 2018; 고원생대에서 트라이아스기까지의 한중 지질 대비 및 페름-트라이아스기 북동아시아 대륙충돌 모델 비교 평가 393 Cho et al., 2020). ...
... Kim, W.J. et al., 2021). 그 이후 열곡대 환경에서 일 어난 화성작용이 800-760 Ma에 주로 일어났으며 690 Ma까지 지속되었다 (Wang and Li, 2003;Li et al., 2008;Lin et al., 2016;Kim, W.J. et al., 2021). 이러한 두 화성작용이 일어난 시기 사 이에 양쯔판과 커테시아판이 충돌하면서 두 판들이 로디니아 초대륙의 일부가 되었을 것으로 해석하고 있다(그림 10; Li and Powell, 2001 (Wu et al., 2006;Zhang et al., 2013;Wang et al., 2014) Kim et al., 2013Kim et al., , 2020. ...
... Numerous studies have been done on the magmatism, deformation, stratigraphy, and ore mineralization on this orogen to reveal episodes of Proterozoic evolution and the processes that formed the orogen (Wang et al., 2017a;Wang et al., 2019b;Zhou et al., 2009;Zhang and Wang, 2016;Zhao et al., 2019). Correspondingly, many tectonic models, including the plume (Li et al., 2008c;Zhang et al., 2013a), plate-rift (Wang et al., 2010;Zheng, 2008a), slab-arc (Zhou et al., 2002) and intra-arc extension (Lin et al., 2016), have been proposed to interpret the geodynamic setting and magmatism, deformation, and metamorphism in the South China Block (SCB), especially regarding the tectonic transition of supercontinent assembly and break-up recorded in the Jiangnan orogen . These models, to some extent, could offer some perspectives on the Proterozoic tectonics of this orogen, or a contrasting view on each stage of the tectonic process (Li et al., 2016b;Qi et al., 2019;Zhao et al., 2011;Zhang et al., 2013c). ...
... Previous studies have focused on the Neoproterozoic volcanic rocks in the Jiangnan orogen due to the unique advantages of the widespread volcanic-sedimentary sequences Li et al., 2016a;Wang et al., 2012a;Wang et al., 2013a;Wan et al., 2019). In recent years, much attentions has been paid to the Neoproterozoic mafic rocks in the Jiangnan orogen (Lin et al., 2016;Wan et al., 2019;Wang et al., 2004;Wang et al., 2012a;Wang et al., 2013a;Zhou et al., 2009;Zhang et al., 2013a;Zhang et al., 2013b). Integrating detailed field investigation and geological mapping reports, we show that Neoproterozoic mafic-ultramafic rocks sporadically occur within the basement sedimentary sequences in the eastern Jiangnan orogen, whereas more have been identified in the western segment. ...
The Neoproterozoic NE-striking Jiangnan orogen in the South China Block (SCB) separates the Cathaysia microcontinent on the southeast from the Yangtze craton in the northwest. The origin and evolution of the Jiangnan orogen is unresolved, with individual models explaining part of the history, such as various magmatic, deformational, metamorphic, and sedimentary events including extensional, contractional, and transpressional modes. Here, we present detailed geochronological and Nd-Hf isotopic data for Neoproterozoic mafic and felsic intrusions in the Jiangnan orogen and identify three episodes of Neoproterozoic magmatism. The first stage ranging from ~1013–942 Ma is preserved predominantly in the eastern segment of the orogen, including a series of mafic rocks with ages of ~1010–952 Ma, contrasting with weak magmatic activity in the western segment with a peak at ~997 Ma. The second stage ranges from ~906 Ma to ~820 Ma, with intensive and extensive bimodal magmatism occurring in the eastern and western parts. The last stage mainly occurred in the western Jiangnan orogen in the period from ~800 to 780 Ma, associated with drastic mafic magmatism and weakly bimodal volcanic activities. The bimodal volcanism in the eastern segment exhibits a striking weak trend after ~823 Ma, distinctly different from the western segment where the magmatism lasted until ~785 Ma, indicating its syn- to post-collisional in nature. The pre-800 Ma magmatic rocks in western Jiangnan orogen have a dominant negative Nd isotopic signature but exhibit a significant positive trend after 800 Ma, different from those in east, which have a decreasing trend. Both parts display a roughly decoupled Nd-Hf isotopic character presented by a dominant positive pattern in Hf isotopes of the Neoproterozoic intrusive rocks, indicating a significant addition of previous slab-derived components or accretionary wedges in the pre-800 Ma magma evolution, and more depleted materials involved in the source in the later stages. Oceanic subduction under the northwestern Cathaysia Block occurred around ~1.0 Ga, slightly earlier than the subduction to the southeastern Yangtze. A gradual tectonic transition from post-orogenic extension to intracontinental rifting dominated the tectonics in Jiangnan orogen in the middle-late Neoproterozoic, followed by slab failure after ~790 Ma. Arc magmatism was the dominant source of crustal growth before 820 Ma in the SCB, but was exceeded in volume by later slab failure magmatism after ~790 Ma.
... Some researchers have suggested that the Jiangnan orogen belongs to part of the worldwide Grenvillian orogenic belts associated with the assembly of the Rodinia supercontinent Greentree et al., 2006;Ye et al., 2007;Li et al., 2008c), whereas others have considered that the amalgamation lasted until ca. 820 Ma or even younger Wang et al., 2007Wang et al., , 2008Yao et al., 2014;Zhao, 2015;Lin et al., 2016;Kou et al., 2018). ...
The crustal evolution of the Yangtze block and its tectonic affinity to other continents of Rodinia and subsequent Gondwana have not been well constrained. Here, we present new U-Pb ages and Hf isotopes of detrital zircons from the late Neoproterozoic to early Paleozoic sedimentary rocks in the northwestern margin of the Yangtze block to provide critical constraints on their provenance and tectonic settings. The detrital zircons of two late Neoproterozoic samples have a small range of ages (0.87−0.67 Ga) with a dominant age peak at 0.73 Ga, which were likely derived from the Hannan-Micangshan arc in the northwestern margin of the Yangtze block. In addition, the cumulative distribution curves from the difference between the depositional age and the crystalline age (CA−DA) together with the mostly positive εHf(t) values of these zircon crystals (−6.8 to +10.7, ∼90% zircon grains with εHf[t] > 0) suggest these samples were deposited in a convergent setting during the late Neoproterozoic. In contrast, the Cambrian−Silurian sediments share a similar detrital zircon age spectrum that is dominated by Grenvillian ages (1.11−0.72 Ga), with minor late Paleoproterozoic (ca. 2.31−1.71 Ga), Mesoarchean to Neoarchean (3.16−2.69 Ga), and latest Archean to early Paleoproterozoic (2.57−2.38 Ga) populations, suggesting a significant change in the sedimentary provenance and tectonic setting from a convergent setting after the breakup of Rodinia to an extensional setting during the assembly of Gondwana. However, the presence of abundant Grenvillian and Neoarchean ages, along with their moderately to highly rounded shapes, indicates a possible sedimentary provenance from exotic continental terrane(s). Considering the potential source areas around the Yangtze block when it was a part of Rodinia or Gondwana, we suggest that the source of these early Paleozoic sediments had typical Gondwana affinities, such as the Himalaya, north India, and Tarim, which is also supported by their stratigraphic similarity, newly published paleomagnetic data, and tectono-thermal events in the northern fragments of Gondwana. This implies that after prolonged subduction in the Neoproterozoic, the northwestern margin of the Yangtze block began to be incorporated into the assembly of Gondwana and then accept sediments from the northern margin of Gondwanaland in a passive continental margin setting.
... The third model suggests that oceanic arc activity between Yangtze and Cathaysia blocks continued until ca. 750 Ma, with final continental assembly not occurring until sometime later, possibly in the early Paleozoic (Gu et al., 2002;Lin et al., 2016;Qin et al., 2015). A key aspect of these contrasting models for the evolution of the South China concerns the setting of the mid-Neoproterozoic (820-720) volcanic and sedimentary rocks, and whether they are related to plume-induced rifting, part of a continental arc system, or formed through oceanic subduction. ...
... 800-760 Ma Shangshu, Daolinshan and Puling plutons, Li et al., 2018;Wang et al., 2010Wang et al., , 2012b, and basalt, basaltic andesite with minor intercalated rhyodacite in the western part (ca. 800-750 Ma Longsheng, Qianyang, Tongdao and Guzhang plutons, (Kou et al., 2018;Lin et al., 2016;Wang et al., 2007bWang et al., , 2004Zhou et al., 2007Zhou et al., , 2004b. Contemporaneous rock units overlying the Cathaysia Block have a limited distribution, and include the Dajiangbian Formation in the north Nanling range, and the Taoxi Group or equivalents in the south Wuyi range. ...
... This subduction zone lies along strike from contemporaneous magmatic activity extending from Madagascar, into the Seychelles and on through northwestern India, and indicates a long lived convergent plate margin setting on the periphery of Rodinia adjacent to India during mid-late Neoproterozoic (Archibald et al., 2017;Wang et al., 2017aWang et al., , 2017b. This region, together with the mafic-ultramafic rocks in South China of this age show typical arc elemental characteristics (Kou et al., 2018;Lin et al., 2016;Zhou et al., 2004b). These characteristics, together with the absence of significant plume-related magmatic rocks (Wang et al., 2012b;Zhou et al., 2004b), has led to a convergent plate margin setting for the period ca. ...
The tectonic affinity of mid - late Neoproterozoic magmatism in the South China Block provides a first order constraint on its role in the break-up of Rodinia and the subsequent amalgamation of Gondwana. The Yingyangguan area in the western margin of Cathaysia Block preserves a magmatic and sedimentary record of this period. U-Pb zircon age data indicate magmatism at around 750 Ma, followed by accumulation of a succession of tuff and carbonate rocks at ca. 670–660 Ma. All samples show evidence for ductile deformation and metamorphism. The geochemical characteristics of mid-Neoproterozoic mafic and intermediate rocks suggest crustal assimilation and fractional crystallization play an important role in magma evolution, and they were derived from a source dominated by modified lithospheric mantle sources previously metasomatized by slab-derived fluids. Analyzed samples, as well as contemporaneous mafic rocks in neighboring areas, have high Zr/Y ratios, and plot in the within-plate basalt field at ca. 750 Ma. In addition, zircons with ages between 1200 and 950 Ma and 850–770 Ma mostly fall within the arc-related field on discriminating diagrams based on zircon trace-element compositions, whereas, most ca. 750 Ma and 700–600 Ma zircons plot in the within-plate field. This evolving tectonic record of magmatic activity suggests a transformation from a convergent plate margin setting on the periphery of Rodinia to one involving within plate extension at ca. 750 Ma. Furthermore, the detrital zircons from samples of the Yingyangguan Group present abundant late Mesoproterozoic to early Neoproterozoic (1200–950 Ma) ages. These ages match the record of North India and Indo-Antarctica, and imply a peripheral setting for South China with respect to the supercontinent and most likely adjacent to India from at least 750 Ma. Thus, we suggest that the Yangtze Block accreted to Cathaysia on the northern margin of India in the early Neoproterozoic, and that the active plate boundaries located along the northern and western margins of South China continue to ca. 750 Ma. After this time, the tectonic setting within the South China Block transformed into a stable within-plate siliciclastic depositional environment that continued to receive detritus from East Gondwana until the early Devonian.
... However, no consensus has been made toward its emplacement mechanism, age, origin of magmas, and tectonic setting. Among the proposed models and interpretations for the Longsheng mafic-ultramafic suite, the major ones include the following: (1) it is an oceanic ophiolite suite (Xia 1984;Guo et al. 1984;Zhang et al. 1984;Yao et al. 2016); (2) it was a product of a prolonged subduction-collision between Yangtze and Cathysia blocks (Lin et al. 2016); (3) it was associated with a post-orogenic extension regime (Shu et al. 1994;Zhou et al. 2003;Wang et al. 2007Wang et al. , 2012bZheng et al. 2008;Yan et al. 2002); (4) it was related to an upwelling superplume that caused the Rodinia breakup (Ge et al. 2001a(Ge et al. , 2001bLi et al. 1994Li et al. , 2003Li 1999;Li et al. 2008). ...
The Longsheng mafic-ultramafic suite consists of more than 100 mafic and ultramafic intrusions and are extensively distributed within the Neoproterozoic Danzhou Group along the Jiangnan Orogenic Belt in northern Guangxi, China. The suite has been a hotly debated subject in the context of emplacement age, source of magmas, and tectonic setting for several decades. In this article, we present newly obtained LA-ICP-MS zircon U-Pb age data, whole-rock major and trace elemental data, and Sr-Nd and zircon Lu-Hf isotopic data. These data support a middle Neoproterozoic intrusive emplacement mechanism as a result of asthenospheric underplating and subsequent lithospheric thinning, extension, and rifting. This integrated process might well correspond to the early stage of the Rodinia breakup. For example, five mafic-ultramafic rock samples yielded an emplacement age of 774 ± 2 Ma. The samples contain a large number of inherited zircon xenocrysts dated at 821 ± 3 Ma, 1.4–2.1 Ga, and 2.3–2.8 Ga, indicative of crustal contamination. The mafic-ultramafic rocks are characterized by calc-alkaline to shoshonitic associations; their Zr/Nb, Th/Yb, La/Nb, Ba/La ratios, trace, and REE patterns show an OIB affinity. Their initial 87Sr/86Sr values range from 0.697721 to 0.708579 with an average of 0.702352. They have relatively low initial 143Nd/144Nd values of 0.511530–0.511859 with an average of 0.511661. Sixteen magmatic zircon grains from diabase samples show 176Hf/177Hf values of 0.281326–0.282638, εHf(t) values of − 34.48–11.89, and TDM2 of 925–3819 Ma. Their Nb/U and Th/Ta ratios support crustal contamination as well. It is concluded that the Longsheng mafic-ultramafic suite was originated from partial melting of the enriched upper mantle (EM-I type) due to asthenospheric underplating and lithospheric extension during the incipient Rodinia breakup, and that the magmas were contaminated with crustal material during ascent.
... In the southeastern Yangzte Block, these dykes and sills are represented as the Fanjingshan mafic dykes in northeastern Guizhou, and the Sanfang, Hejiawan, Baotan, Rongshui mafic-ultramafic dykes in northern Guangxi. The former intruded the Fanjingshan Group and the latter intruded the Sibao Group (Chen et al., 2018;Li et al., 1999;Lin et al., 2016;Zhou et al., 2009). Recently, Kou et al. (2018) reported the Jinche gabbro intruding Danzhou Group with U-Pb zircon age of B806 Ma (zircon U-Pb LA-ICP-MS method). ...
... They all intruded the Banxi Group. The B760-Ma mafic intrusions were also reported in northern Guangxi represented as Longsheng and Sanmen mafic-ultramafic dykes intruding the Danzhou Group, which were dated at 761 6 8 and 760 6 18 Ma by using zircon U-Pb ID-TIMS and LA-ICP-MS methods, respectively (Ge et al., 2001;Lin et al., 2016). In addition, the dykes are widely distributed in the western Sichuan Province. ...
China has three major Precambrian cratons, named the north China craton (NCC), the south China craton (SCC), and the Tarim craton. Each craton has some billion years of geological history. The authors of this chapter favor an NCC-N Australia connection for the interval between ~1.80 and ~1.32 Ga in the supercontinent Nuna/Columbia and an NCC-NW Laurentia connection between ~1.11 and 0.78 Ga in Rodinia, based on comprehensive analyses of geological and paleomagnetic data. High-quality paleomagnetic data indicate that the SCC had experienced a long journey from the north polar regions to the Equator between ~0.8 Ga and the early Cambrian and it was unlikely once located between Australian cratons and Laurentia in the center of Rodinia in that period. The SCC’s apparent polar wander path may contain a component of true polar wander that needs more precise age constraints. Two possible paleogeographic models, either by placing the Tarim craton against NW Australia or placing it in the center of Rodinia to be the link between Laurentia and the Australia-Mawson craton, were reviewed.
