Search

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]

• Ca. 2.30–2.27 Ga, 1.85–1.83 Ga, and 1.75 Ga granitoids in the Phan Si Pan Complex, north Vietnam. • The two older episodes of granitoids formed by partial melting of Archean basements. • The ca. 1.75 Ga trondhjemite formed by partial melting of juvenile crust. • The Yangtze Block was located between southern Siberia and northern Laurentia within Nuna. There is no consensus on the Precambrian paleogeographic reconstructions of Yangtze Block through the various supercontinent cycles and its linkage to other continental blocks. New data on the Paleoproterozoic tectonic history of the block enables linkage with other major Nuna-forming continents to be constrained. Zircon U-Pb-Hf isotopic and whole-rock elemental data highlight three episodes of Paleoproterozoic granitoids, dated at 2.30–2.27 Ga, 1.85–1.83 Ga, and 1.75 Ga from the Phan Si Pan Complex of the Phan Si Pan Zone, a southeast extension of the Yangtze Block in north Vietnam. The older two episodes of granitoid emplacement have negative ε Hf(t) values with similar T DM2 ages of 3.3–2.9 Ga, which suggest reworking of Archean basement rocks possibly at syn- to post-collisional settings. The 1.75 Ga A-type trondhjemite with positive ε Hf(t) values (0 to + 9) formed by partial melting of Paleoproterozoic juvenile crustal materials along with some mantle addition, most likely related to an intra-plate rift setting. Integrating the new results with compilations throughout the Yangtze Block, we suggest that the northern and southwestern Yangtze have different Archean and earliest Paleoproterozoic histories. Furthermore, correlations of Archean-Paleoproterozoic tectono-thermal and detrital zircon signatures between southwestern Yangtze and north Laurentia, and between northern Yangtze and southern Siberia, suggest they were close neighbors at these times. The collision between the northern and southwestern Yangtze in the late Paleoproterozoic is inferred to have led to the assembly of Laurentia and Siberia along a cryptic suture in central Yangtze and widespread crustal magmatism. Thus, we tentatively reconstruct the Yangtze Block as a key tie point between northern Laurentia and southern Siberia within 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]