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• Spherical ministromatolite clumps in Mesoproterozoic dolostone. • Abundant microfossils within the organic matter surround the ministromatolite. • The unique silicification process favors the preservation of microfossils. • Biogenic and chemical process together contributes the formation of ministromatolite. Although the biogenicity of the very common millimeter-sized ministromatolites in the Proterozoic has been noted, direct biotic evidence is missing, leading to the discussion of a chemical origin that differs from that of the cyanobacteria-related stromatolites in the Phanerozoic. Distinctive ministromatolites were recently discovered in a microbial dolostone interval of the Mesoproterozoic Wumishan Formation, at Lingyuan, North China. Thin section examination of the ministromatolites reveals the presence of abundant coccoidal microfossils ranging 10–30 μm in diameter. Petrofabric analysis shows that the ministromatolites experienced three periods of diagenetic silicification, and that the microfossils are exclusively preserved within early diagenetic chert. This supports the view that silicification penecontemporaneous with mat growth is the key to unique preservation of microfossils. In contrast, the absence of microfossils in most Precambrian carbonate stromatolites may well be interpreted as the lack of hydrochemical conditions favorable for early silicification. Although chemically-formed fibrous carbonate minerals are the dominant components of these ministromatolites, the presence of abundant microfossils indicates that the role of microorganisms in the formation of ministromatolites has previously been underestimated. Therefore, this research suggests that Mesoproterozoic ministromatolites were not solely chemical products but consist of complex associations of both biotic and chemical fabrics. [ABSTRACT FROM AUTHOR]

• Major magmatic episodes in southwestern Yangtze at ca. 3.08, 2.85 and 2.36–2.32 Ga. • Northern and southwestern domains of the Yangtze show differences in crustal growth. • The two domains have independent evolutionary histories prior to mid-Paleoproterozoic. • The two domains share a common history during and after Nuna assembly. New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]

• Late Archean and late Paleoproterozoic magmatism occurs in the Phan Si Pan Complex, North Vietnam, of the Yangtze Block. • The 2.85–2.76 Ga potassic granites formed during collision-related crustal thickening. • The ca. 1.86 Ga A-type granite formed within an extensional tectonic setting. • The spatial changes in crustal compositions in the different Archean complexes of the Yangtze Block suggest they constitute separate terranes. • Final cratonization of the Yangtze Block likely relates to the assembly of the Nuna supercontinent. Precambrian igneous and metamorphic rocks of the Phan Si Pan Complex, North Vietnam, constitute the southern extension of the Yangtze Block, and provide a valuable record of the early evolution of the continental crust. We present results of U-Pb zircon geochronology and geochemistry for Precambrian granites in this complex to constrain their emplacement age and genesis. Granites from three plutonic bodies yielded ages of 2848 ± 15 Ma, 2768 ± 19 Ma and 1869 ± 30 Ma, which represent newly-recognized late Archean to Paleoproterozoic potassic granite plutonism in the southern Yangtze Block. The average ε Hf(t) values range from −6.2 to 0.1 for the 2.85 to 2.77 Ga granitic rocks and −13.1 to −9.2 for the ca. 1.86 Ga granitic rocks, with two-stage model ages of 3.64 to 3.20 Ga and 3.31 to 3.07 Ga, respectively, suggesting derivation from partial melting of Paleoarchean and Mesoarchean crust. The late Archean potassic granites exhibit high K 2 O, and high Sr/Y and (La/Yb) N ratios with negligible Eu anomalies, indicating derivation from melting of the thickened lower crust, which is inferred to have occurred in an active margin setting. The late Paleoproterozoic alkali feldspar granites are characterized by high FeO T /(FeO T + MgO)(0.96–0.99) and 10000 * Ga/Al (2.75–2.94) ratios, showing an affinity of A-type granite. These A-type granites exhibit flat chondrite-normalized HREE patterns and strong negative Eu anomalies, and low Sr/Y and (La/Yb) N ratios, corresponding to melting at a shallow depth, probably in a post-collisional extension setting. Comparison of the rock units and events recorded by the Phan Si Pan Complex with other Archean to Paleoproterozoic complexes (Houhe, Dongchuan, Yudongzi, Douling, Zhongxiang and Kongling complexes) in the Yangtze Block indicate spatially distinct histories of crustal growth, and thus may reflect independent terranes. The ca. 1.86 Ga post-collisional magmatism, which succeeds a 2.0–1.9 Ga metamorphic event, is distributed throughout the Yangtze Block, including the Phan Si Pan Complex, suggesting assembly of the disparate terranes and final cratonization of the Yangtze Block overlaps with, and may be related to, assembly of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]