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Reworking or growth of the Hadean (>4.0 Ga) continental crust provides important hints in understanding the early evolution history of Earth. In this study, a comprehensive program of zircon U-Pb dating and Hf isotope analyses, as well as whole-rock major and trace element analyses, has been carried out on the Muzidian granitic gneisses from the northern Dabie orogen. The Muzidian gneisses are tonalite or granodiorite in composition, and have geochemical features resembling those typical of the tonalite-trondhjemite-granodiorite (TTG) suites. Zircon U-Pb dates range from ~2.5–2.4 Ga in the magmatic cores and from ~2.1–2.0 Ga in the metamorphic rims. Both the zircon cores and the rims have highly negative ɛ Hf (t) values of −25.2 to −19.9 and −31.0 to −28.1, respectively, corresponding to T crust of 4.25 Ga to 3.98 Ga, thereby, indicating that the protoliths of the orthogneisses in the northern Dabie orogen were formed by reworking of Hadean continental crust. This provides strong evidence for the presence of Hadean continental crust in the northern Yangtze block. These remnants of Hadean rocks resided in the continental crust of the Yangtze block for more than about 1700 Ma before being reworked. Compared to the ancient crustal components in the Kongling area of the Yangtze block, the Muzidian area along the northern margin of the Yangtze block seems to be more prospective for further occurrences of the Hadean zircon and/or rocks. Unlabelled Image • The Muzidian TTG gneisses from the northern Dabie orogen are dated at 2.5-2.4 Ga, and underwent 2.1-2.0 Ga metamorphism. • The TTG gneisses were derived from reworking of potentially Hadean continental crust. • Hadean (>4.2 Ga) crustal components may potentially exist in the northern Dabie orogen. • There is more likelihood of finding Hadean crustal remnants in the northern Yangtze block than in the Kongling area. [ABSTRACT FROM AUTHOR]

Recent geological survey has identified the Early Paleoproterozoic meta-mafic intrusions in the southwestern Yangtze Block. We present geochronological, whole-rock geochemical and Nd isotopic data for these meta-mafic rocks to better address the tectonic evolution of the Yangtze Block during the Early Paleoproterozoic Period. Geochronological data show that the meta-mafic rocks have zircon ages of 2 395-2 316 Ma. They have high TiO2 contents of 1.40 wt.%3.66 wt.% and Nb concentrations of 13.7 ppm45.5 ppm, thus aregrouped as Nb-enriched mafic rocks. These mafic rocks are characterized by tholeiitic compositions with enrichment of LREEs and LILEs, and can be divided into two groups. Group 1 samples display E-MORB-like geochemical characteristics. Group 2 samples have positive εNd(t) values of 4.0–5.0. Geochemical data indicate that all meta-mafic rocks were likely derived from a depleted asthenospheric mantle. REE modeling indicates lower degree of partial melting for Group 2 samples (3%–10%) relative to Group 1 samples (15%–20%). Taking into account contemporaneous post-collisional granitoids in southwestern Yangtze Block, we propose that these meta-mafic rocks were formed in a post-collisional extension setting. These meta-mafic rocks can be compared with those in Africa, South America and Europe, and might be linked with the Arrowsmith orogenic belt. KEY WORDS: zircon dating, geochemistry, Early Paleoproterozoic, Nb-enriched rocks, Yangtze Block. [ABSTRACT FROM AUTHOR]

Highlights • Early Paleoproterozoic magmatism were reported in Phan Si Pan Complex in North Vietnam of the Yangtze Block. • The ca. 2.3 Ga quartz monzonite formed at a collision-related crustal thickening event. • The ca. 2.1 Ga A-type gneissic granite formed within an extensional tectonic setting. • The Phan Si Pan Complex was an independent terrane separated from other parts of the Yangtze Block during the early Paleoproterozoic. • The Yangtze Block was linked to northwestern Laurentia in the Pre-Nuna supercontinent. Abstract Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207Pb/206Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have ε Hf(t) values ranging from −4.1 to −2.1, corresponding to T DM2 model ages of 3002–2890 Ma, whereas zircons in the gneissic granite have ε Hf(t) values between −0.95 and +1.72 and corresponding T DM2 model ages of 2660–2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 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. Abstract 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 ε Hf (t) values of −6.2 to −2.8 and T DM2 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. [ABSTRACT FROM AUTHOR]

It is debated whether global-scale tectono-magmatic quiescence prevails on the Earth during the early Paleoproterozoic. The early Paleoproterozoic meta-mafic and intermediate rocks in the southwestern Yangtze Block of South China could provide an opportunity to constrain not only the tectonic evolution of the Yangtze Block itself but also augment our understanding of the global tectono-magmatic lull during the early Paleoproterozoic. Zircon U Pb geochronological study indicates that the meta-mafic rocks were emplaced at ca. 2.32 Ga, whereas the intermediate rocks were emplaced at ca. 2.35 Ga. These two lithologies are characterized by subduction-related whole-rock geochemical (such as depleted Nb, Ta and enriched Rb, K, Pb) and unradiogenic Nd Hf isotopic signatures (ε Hf (t) < 0, ε Nd (t) < 0), implying a derivation from a geochemically enriched lithospheric mantle modified by ancient subduction. Thermodynamic modeling further suggests that the intermediate rocks are products of the AFC process between mantle-derived basaltic magma and TTG-like basement rocks at shallow crustal levels. We interpret this as occurring within a post-orogenic extensional setting. Integrated with the published work, we further posit that the Yangtze Block experienced a tectonic regime transition from compressive orogenesis to post-orogenic extension during the early Paleoproterozoic, and the magmatic activities in several crustal blocks are still active until ~2.3 Ga and therefore places important constraints on the beginning of the tectono-magmatic lull. [Display omitted] • 2.35–2.32 Ga mafic-intermediate magmatism is identified in the SW Yangtze Block. • Mafic-intermediate rocks in this study were derived from the lithospheric mantle. • Tectonic transition from orogeny to post-orogenic extension at ~2.35 Ga in Yangtze. [ABSTRACT FROM AUTHOR]