•Granitoids from the Cuoke complex were mainly emplaced at ca. 2.36–2.22 Ga.•The Cuoke complex experienced a regional metamorphism at ca. 1.96 Ga.•The ca. 2.36–2.34 Ga I/S- and 2.22 Ga A2-type ...granitoids were formed in post-collisional and back-arc settings, respectively.•Paleoproterozoic tectonothermal history of the western and eastern Yangtze Block is significantly different.•The Yangtze Block was spatially linked with NW Laurentia in Columbia (Nuna).
The infrequent early Paleoproterozoic rocks are essential for investigating the early evolution of the Yangtze Block and its reconstruction in the global supercontinent. Here, we carried out an integrated study of petrology, whole-rock geochemistry, as well as zircon U-Pb-Hf isotope compositions for granitoids from the recently discovered Cuoke complex in the southwestern Yangtze Block. SHRIMP zircon U-Pb dating yields magmatic crystallization ages of ca. 2.22 and 2.35 Ga for two monzogranites, ca. 2.36 Ga for a granodiorite, and ca. 2.34 Ga for a granitic gneiss. The granitic gneiss also contains metamorphic zircons that give an age of ca. 1.96 Ga. These results, compiled with published geochronological data, suggest that the western part of the Yangtze Block (WYB) features extensive magmatism with ages of ca. 2.5–2.2 Ga and multiple regional metamorphism with peaks ca. 2.50, 2.36, 1.96 and 1.85 Ga. This characteristic is significantly different from the eastern part of the Yangtze Block (EYB), which is dominated by the ca. 2.15–1.95 Ga subduction- and collision-related metamorphism and magmatism with a peak ~2.0 Ga. Our studied granitoids show negative zircon εHf(t) values from −14.0 to −1.9, with corresponding two-stage model ages of ca. 3.50–2.93 Ga, indicative of their derivation by reworking of ancient crustal materials. Geochemically, the ca. 2.22 Ga monzogranites have high HFSEs (Zr + Nb + Ce + Y = 777–1136 ppm) and 10,000*Ga/Al ratios (3.73–4.56) with dramatically negative Eu, Ba, Sr and Ti anomalies. Together with high Y/Nb (2.75–3.15) and Yb/Ta (2.11–2.94) ratios, they are classified as A2-type granites. The ca. 2.36–2.35 Ga granitoids have high CIPW-normative corundum contents of 4.92–6.06 vol% and are strongly peraluminous with A/CNK values of 1.46–1.64, similar to S-type granites. They are enriched in LREEs ((La/Yb)N = 14.55–25.33) with moderately negative Eu anomalies (Eu/Eu* = 0.56–0.66), but depleted in Nb, Sr and Ti. The ca. 2.34 Ga granitic gneisses show intermediate geochemical signatures between S-type and I-type granites. They are featured by no discernible negative Eu and Sr anomalies and relatively steep HREE patterns with (Gd/Yb)N ratios between 1.94 and 2.50. In combination with available observations, our new geochronological and geochemical dataset indicates that these ca. 2.36–2.34 Ga granitoids represent the post-collisional magmatism immediately following a possible collision event in the WYB, while the 2.22 Ga A2-type monzogranites were likely formed in a back-arc extensional setting. In addition, we further suggest that the Yangtze Block and NW Laurentia share a common succession of major Paleoproterozoic tectonothermal events, favoring their tight spatial linkage in the global Columbia supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•This is the first to identify Mesoarchean (3.11–2.85 Ga) rocks in the southern Yangtze Block.•1.94 and 1.89 Ga granitic magmatism recorded in the Cuoke complex.•Multistage crustal growth and ...reworking occurred in the Cuoke complex.•The Yangtze Block experienced intense metamorphism and magmatism in the context of Nuna assembly.
The newly identified Cuoke Complex preserves voluminous early Precambrian granitoids, bearing key information for the early evolution of the Yangtze Block, South China. Here, we report new field observations, petrology, zircon U-Pb-Hf isotopes and trace elements for eight granitoids from this complex. The analyzed zircon domains are of magmatic origin, as evidenced by their oscillatory zoning, high Th/U ratios and magmatic rare earth element patterns. Three trondhjemitic gneisses yield crystallization ages of 3.11–3.06 Ga, documenting the oldest known rocks in the southern Yangtze Block. Their εHf(t) values vary from −3.2 to + 2.6 with depleted mantle two-stage (TDM2) model ages of 3.6–3.3 Ga, indicating reworking of Paleoarchean crustal materials. Three gneissic granitoids crystallized at 2.86–2.85 Ga and reveal a significant episode of granitoid magmatism in the late Mesoarchean. They possess positive εHf(t) values (+0.2 to +5.0) and slightly older TDM2 model ages (3.3–3.0 Ga), suggesting that these granitoids were most likely derived from remelting of juvenile continental crust. Two monzogranites with crystallization ages of 1.94 and 1.89 Ga display negative εHf(t) values (−13.0 to −8.1) and older TDM2 model ages (3.3–3.1 Ga), indicating substantial involvement of ancient crustal materials. Available zircon U-Pb-Hf isotopic data from the Cuoke Complex have revealed that the earliest crustal growth probably occurred in the early Paleoarchean, with significant crustal growth and reworking during the early Mesoarchean, followed by multistage crustal reworking during the late Mesoarchean to Paleoproterozoic. Integrating the results of this study with records from other Archean basement complexes in the Yangtze Block (i.e., Kongling, Zhongxiang, Douling, Yudongzi and Phan Si Pan), we propose that these complexes have diverse formation histories and generally experienced tectonothermal events at ca. 2.0–1.9 Ga, probably responding to the global-scale assembly of the Nuna supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•We present the rarely reported early Paleoproterozoic magmatic records in the Yangtze Block.•The ca. 2.36 Ga Cuoke monzogranites formed within post-collisional setting.•They were ...likely derived from a source comprising mainly Mesoarchean crustal materials.•The SW Yangtze Block likely underwent a collision event related to the Arrowsmith orogeny.•A spatial connection between Yangtze and Laurentia in the Columbia supercontinent is favored.
The early Paleoproterozoic is an essential period for understanding the early tectonic evolution of the Yangtze Block and its reconstruction in the Columbia supercontinent, whereas these issues are largely unknown due to the scarce preservation of early Paleoproterozoic geological records. This study presents rarely reported early Paleoproterozoic granitoids from the southwestern Yangtze Block, with integrated studies of zircon U-Pb ages, Lu-Hf isotopic compositions and whole-rock geochemistry. Magmatic zircon U-Pb dating for two monzogranite samples yields weighted mean 207Pb/206Pb ages of 2359 ± 16 Ma and 2363 ± 16 Ma, providing unambiguous evidence for the presence of early Paleoproterozoic magmatism in the Yangtze Block. All the samples have high A/CNK values of 1.30–1.61, typical of S-type granite. These rocks have low total REE contents of 72.5–139.0 ppm with marked enrichment in LREEs ((La/Yb)N = 10.73–23.83) and conspicuously negative Eu anomalies (Eu/Eu* = 0.46–0.55). The rocks exhibit uniform primitive mantle-normalized trace element patterns with enrichment in Rb, Th, U and Pb and depletion in Sr, Nb, Hf and Ti. These dated zircon grains have consistent negative εHf(t) values of −6.2 to −2.8 and TDM2 ages of ca. 2.97–3.16 Ga, indicative of Mesoarchean crustal materials as their magma source. Considering the existence of the ca. 2.36 Ga regional high-grade tectono-metamorphic event, we propose that the ca. 2.36 Ga monzogranites were most likely generated in the early stage of post-collisional extension. Therefore, the southwestern Yangtze Block likely experienced a collision event during ca. 2.40–2.36 Ga, indicative of the involvement of the Yangtze Block in the ca. 2.5–2.3 Ga Arrowsmith orogeny of Laurentia. In addition, a series of accretionary events might also have occurred in the western Yangtze Block before the final assembly of the Columbia supercontinent, implying a tight spatial connection between the Yangtze Block and northwestern Laurentia within this global-scale supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The mafic rocks in the Zhongxiang complex emplaced at ca. 2.03–2.02 Ga;•The 2.03 Ga and 2.02 Ga mafic rocks show MORB-like and arc-like geochemical features, respectively;•The ca. 2.03–2.02 Ga mafic ...rocks were formed in arc-back-arc settings.
To better understand Paleoproterozoic tectonic processes in the Yangtze Block during the assembly of the Columbia supercontinent, an integrated geochronological and geochemical study of amphibolite facies mafic rocks exposed in the Zhongxiang Complex in the northern Yangtze Block is presented. Based on trace element and rare earth element (REE) characteristics, these mafic rocks can be divided into two coeval groups. The MORB-like mafic rocks show flat REE patterns and are enriched in large-ion lithophile elements (e.g. Rb, Ba, K, Sr). Their zircon ɛHf(t) values range from + 3.43 to + 4.90. The other mafic rocks are arc-like and have elevated REE contents and display relatively light REE enriched patterns, as well as depletion in high field strength elements (e.g. Nb, Ta, Ti). The zircon ɛHf(t) values of the latter group range from + 0.17 to + 2.68. Zircon U-Pb dating yielded a weighted mean 207Pb/206Pb age of 2029 ± 15 Ma for the MORB-like mafic rocks, and 2023 ± 14 Ma for the arc-like mafic rocks, respectively. The elemental and isotopic characteristics indicate that the MORB-like mafic rocks may be derived from a depleted asthenospheric mantle source, whereas its counterpart with arc-like signatures originated from a lithospheric mantle source. The low (La/Yb)CN (1.10–2.84) and Sm/Yb (0.99–1.29) ratios indicate that the mafic rocks are formed by partial melting of spinel lherzolite mantle. Combined with other geological observations, these mafic rocks are inferred to constitute part of a mid-Paleoproterozoic continental arc–back-arc basin system. The 2.03–2.02 Ga mafic rocks from the northern Yangtze Block indicate that the continental margin experienced subduction in response to assembly of the Columbia supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•The sedimentation of the Huili Group lasted from ca. 1.1 Ga to 1.0 Ga.•A drastic provenance shift occurred within the Huili Group at 1.04 Ga.•The tectonic regime evolved from passive ...margin to convergence setting.•The Yangtze Block was not yet part of the Rodinia in the latest Mesoproterozoic.
The Huili Group, one of the most representative late Mesoproterozoic strata in the Yangtze Block, bears key information for the tectonic history of the South China Block in the context of the supercontinent cycle. We present an integrated dataset involving field observation, petrology, detrital zircon U-Pb dating, and Hf isotope analyses for the Huili Group. Our new detrital zircon U-Pb ages, in combination with available magmatic age data, confirm that the Huili Group was mainly deposited at ca. 1.1–1.0 Ga. The lower Huili Group is characterized by subrounded to rounded detrital zircon grains with age intervals of 2.80–2.40 Ga (~21%), 2.34–1.72 Ga (~64%), and 1.68–1.19 Ga (~14%). In contrast, zircon grains from the upper Huili Group have variable morphologies and yield two pronounced age populations of 2.00–1.25 Ga (~50%; subrounded to rounded grains) and 1.2–1.0 Ga (~46%; euhedral to subhedral grains). The majority of zircon grains have εHf(t) values and depleted mantle two-stage (TDM2) model ages comparable to those of magmatic rocks or older sediments in the Yangtze Block. Multiple sources are suggested to have contributed older detrital zircon grains to the lower Huili Group, whereas the upper part received greater proportions of zircon grains with ages close to or equal to the depositional age from proximal magmatic sources. This observation indicates a drastic provenance shift most likely occurred within the Huili Group at ~1.04 Ga. Through reappraising our detrital zircon results and available geological datasets, we suggest that the terrigenous clastic and carbonate rocks of the lower-middle Huili Group were deposited on a passive continental margin, but the upper volcano-sedimentary sequences were formed in a back-arc extensional setting. We further propose that the Yangtze Block was spatially separated from (i.e., not yet part of) the Rodinia supercontinent during the sedimentation of the Huili Group, supporting that a global supercontinent did not exist yet in the late Mesoproterozoic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The Xide diabase dykes formed in a continental rift setting at ca. 800–810 Ma.•Mid-Neoproterozoic continental rifting occurred in the western Yangtze Block.•The South China Block played a key role ...in the assembly and breakup of Rodinia.
The petrogenesis of widespread Mid-Neoproterozoic mafic dykes is crucial for the paleographic position of the South China Block (SCB) in Rodinia supercontinent and the mechanism of Rodinia breakup. Here, new detailed geochronological and geochemical data on the diabase dykes from Xide in the western Yangtze Block are presented. Zircon SHRIMP/LA-ICP-MS U-Pb dating shows that four diabase samples yield uniform crystallization age varying from 796±6Ma to 809±15Ma, while one sample gives a slight older age of 824±11Ma that is overlapped with ca. 810Ma within uncertainties. This suggests that the Xide diabase dykes emplaced at ca. 800–810Ma and were coeval with regional bimodal magmatism (e.g., the Suxiong bimodal volcanics). The Xide diabase dykes are characterized by low SiO2 contents, high Mg# values and Cr, Ni contents, relative enrichment of light rare-earth elements, and slight depletion of high field strength elements (e.g., Nb, Ta, Zr, and Hf) and nearly constant Zr/Hf, Nb/Ta and Nb/La ratios. Our analyses indicate that the diabase was mainly produced by interaction between lithospheric and asthenospheric mantle. Moreover, the diabase samples display geochemical characteristics affinity with typical intra-plate basalts. Together with the widespread coeval bimodal magmatic suite and sedimentary records in the Kangdian Rift, we proposed that the western Yangtze Block once experienced continental rifting during the Mid-Neoproterozoic, which also occurred in other Rodinia blocks, such as Tarim, Australia and North America. In addition, the Grenville-aged magmatism records throughout SCB with the widespread Mid-Neoproterozoic rift-related magmatism and sedimentation records imply that SCB probably played a key role in the assembly and breakup of Rodinia supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•The meta-basalts in the Caiziyuan-Tongan accretionary complexformed at 1.74–1.55 Ga.•The meta-basalts were derived from partial melting of the asthenospheric mantle.•There is a ...geodynamic transition from intra-continental rift to passive continental margin.•A long-term stretching of lithosphere responded to the breakup of Nuna supercontinent.
In order to better understand the role and position of the Yangtze Block in the assembly and breakup of the Nuna supercontinent, we present zircon U-Pb ages, Lu-Hf isotopes, and the bulk-rock geochemistry of meta-basalt samples from the recently identified Caiziyuan-Tongan accretionary complex (CTAC) in the southwestern Yangtze Block, South China. Three meta-volcanic samples yielded zircon U-Pb ages of 1722 ± 15 Ma, 1736 ± 17 Ma, and 1552 ± 33 Ma. These meta-basalt samples were subdivided into two groups according to their sampling positions, crystallization ages, and geochemical characteristics. Group 1 (∼1.7 Ga) meta-basalts are alkaline in composition and have consistently high TiO2 content (3.42–5.17 wt%). They are enriched in LREEs with (La/Yb)N ratios of 2.86–12.08 and show positive zircon εHf(t) values from + 1.4 to + 6.8. These features indicated that the Group 1 may form at depths in the asthenospheric mantle in an intra-continental rift setting. Group 2 meta-basalts (∼1.5 Ga) are tholeiitic in composition, and contain relatively low ΣREE (60.3–89.3 ppm) and slightly enriched LREEs, which were chemically similar to the features of MORB. These features indicated that they were derived from a moderately depleted asthenospheric mantle and formed in a mid-ocean ridge environment. Combined with the regional magmatic-sedimentary records, we propose that the southwestern Yangtze Block evolved from an intra-continental rift to a passive continental margin during the Paleo-Mesoproterozoic. This is the result of long-term lithospheric extension under the background of the global breakup of the Nuna supercontinent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report the oldest I-type granites in the Lengshui Complex of the Yangtze Craton, providing new insights for its tectonic evolution during the Neoarchean. An approach-combined study of zircon U-Pb ...dating and Lu-Hf isotopes, as well as whole-rock element geochemistry and Nd isotopes, were employed. LA-ICP-MS zircon U-Pb dating for the monzogranite sample LSG03 and LSG16 yielded ages of 2732 ± 13 Ma and 2738 ± 25 Ma, respectively. The more precise age of 2732 ± 13 Ma for the sample LSG03 was taken as the crystallization age of the monzogranite. These rocks have high SiO
2
(73.11-74.01 wt%), K
2
O (3.93-5.48 wt%), Na
2
O (3.93-4.86 wt%) and low CaO (0.30-0.69 wt%), MgO (0.17-0.30 wt%), TiO
2
(0.14-0.17 wt%), P
2
O
5
(0.01-0.06 wt%), Al
2
O
3
(14.11-14.37 wt%) content with weakly peraluminous affinity (A/CNK = 1.04-1.11). Geochemically, they belong to I-type granites, indicating partial melting of a thickened lower crust. Their relatively high Nb/Ta (15.2-34.8) ratios further suggest they formed under eclogite-facies conditions. The consistent whole-rock Nd and zircon Hf isotopic compositions indicate a homogeneous source. According to their ε
Hf
(t) values (−2.0 to 0.8), two-stage Hf model ages (3.1 to 3.2 Ga) and positive ε
Nd
(t) (1.4 to 2.1), we argue that they were probably generated by partial melting of a juvenile lower crust with little ancient materials. Monzogranites formed in a late-orogenic or collisional compressive tectonic regime, whereas subsequent ca. 2.73 Ga and 2.67-2.62 Ga A-type granites in the Zhongxiang Uplift (including the Lengshui Complex) may represent a prolonged extensional setting. Thus, Archean subduction (probably unlike modern subduction) likely occurred prior to ca. 2.73 Ga. Similar magmatism in the Kongling Complex implies that the Zhongxiang Uplift may have accrete to the Kongling Complex during the early Neoarchean. The transition from I-type to A-type magmatism may have resulted from a change in the geodynamic regime from the late-orogenic or collisional compressive environment to an extensional environment caused by the subsequent lithospheric collapse and mantle upwelling, suggesting an early Neoarchean orogenic event in the eastern Yangtze Craton.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
To better reveal the early Neoproterozoic tectonic process of South China with respect to the assembly of the Rodinia supercontinent, an integrated dataset of geochronology, whole-rock geochemistry, ...and Sr-Nd-Hf isotopic compositions for diabases that intruded the Kunyang Group in the southwestern Yangtze Block is herein presented. Zircon U-Pb dating gives four weighted mean 206Pb/238U ages of 946 ± 4 Ma, 948 ± 6 Ma, 939 ± 4 Ma, and 918 ± 7 Ma, suggesting mafic magmatism in the earliest Neoproterozoic. The diabases possess Nb = 12.3–30.5 ppm, Nb/U = 19.99–37.06, Nb/La = 0.78–1.05, (Nb/Th)PM = 0.44–0.80, and (Nb/La)PM = 0.75–1.02, geochemically resembling those of typical Nb-enriched basalts. They are tholeiitic in composition with low SiO2 (49.49–51.95 wt%), high TiO2 (2.03–4.65 wt%), MgO (2.50–6.14 wt%), and Fe2O3T (15.38–18.84 wt%) contents. They are enriched in light rare earth elements (LREEs) with weak negative Eu anomalies (Eu/Eu* = 0.75–0.96) and show E-MORB-like characteristics with slight to moderate Nb-Ta depletion. The samples show zircon εHf(t) values ranging from + 5.8 to + 10.3 and whole-rock εNd(t) values from + 0.5 to + 0.9. These elemental and isotopic characteristics suggest that the 0.95–0.92 Ga diabases may have derived from an E-MORB-like magma source with the injection of metasomatized slab melts. Integrating previous studies with our results, we propose that the southwestern Yangtze Block evolved from an intracontinental rift to a passive continental margin in the late Mesoproterozoic, followed by the development of an earliest Neoproterozoic continental arc-back-arc basin system analogous to the Northern Okinawa Trough. The distinct tectonic processes between the southern and northern parts of the Yangtze Block at ca. 1.0–0.9 Ga favour the hypothesis that the final cratonization of the present-day Yangtze Block occurred slightly later than ∼ 0.9 Ga in response to the Rodinia supercontinent assembly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
