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Highlights: [•] South Qinling consists of three magmatic cycles in Neoproterzoic. [•] The Panxi-Hannan arc system in NW Yangtze probably extends into South Qinling. [•] Young magmatic rocks of ∼680–650Ma are rift-related in northern Yangtze. [ABSTRACT FROM AUTHOR]

This study presents zircon ages and geochemical and Nd-isotopic data for metagranites and quartzites from the Susong high-pressure metamorphic zone in the Dabie–Sulu ultrahigh-pressure collisional belt. This belt belongs to the eastern part of the Qinling–Dabie orogenic belt that formed during Early Mesozoic collision of the North and South China Blocks. Two metagranites give zircon U–Pb model ages of 785±7 and 205±12 Ma, likely representing a Late Proterozoic magmatic event and an Early Mesozoic overprint. They have low initial ϵNd-values (−12.4 and −11.1 at 780 Ma), favouring a crustal origin. Flat heavy rare earth elements (REE) patterns (GdN/YbN∼1.2) probably reflect that melting took place at a shallow crustal section where heavy-REE-bearing mineral phases are unstable. All zircons of three quartzites yield young discordant U–Pb ages and define a discordia with U–Pb model ages of 784±6 and 213±3 Ma, identical to those of the metagranites. We assume that all detrital zircons had lost radiogenic Pb prior to the Early Mesozoic overprint, probably facilitated by fluid participation during a metamorphic event contemporaneous with the intrusion of the metagranites. This simultaneous metamorphic and magmatic event was probably related to a rift setting along the periphery of the Yangtze (South China) Block during Late Proterozoic. [Copyright &y& Elsevier]

• Sedimentary rocks in the Baoshan Block contain dominantly Precambrian zircon. • This block might not be involved into orogenic events along the Gondwana margin. • Sedimentary sources were akin to old crustal rocks of Northwest India. The Baoshan Block in western Yunnan is one of the major micro-continents in the eastern Tethyan orogenic belt, but its provenance and crustal evolution remain enigmatic. Sedimentary rocks prior to an amalgamation of continental blocks recorded key information about crustal evolution and the origin of terranes and can provide vital data for understanding orogenic processes. Here, we present U–Pb ages and Hf isotopic data on detrital zircon and Nd isotopic data on whole rock for Paleozoic sedimentary rocks from the Baoshan Block to constrain their provenance and tectonic history. Crystallization ages of detrital zircon grains illustrate that the magmatic activities of the source areas occurred at ~2.5 Ga, ~1.9 Ga, and ~1.0–0.5 Ga, with a major peak occurring around 0.95 Ga. Several old zircon grains from >3.0 Ga up to ~3.8–3.7 Ga were observed. Zircon Hf isotopic data from one sample suggest that the major crustal growth occurred at ~2.1 Ga. Cambrian to Carboniferous sedimentary rocks showed similar Nd isotopic features with two–stage Nd model ages of approximately 2.1 Ga. The age distribution patterns and isotopic data suggest that detritus material in the Paleozoic sedimentary rocks was mainly derived from continental terrane similar to the Indian craton, implying that the Baoshan Block was likely adjacent to Northwest India before the collision of the Baoshan and Simao blocks. No significant inputs of the juvenile crust were documented in the Nd–Hf isotopic data, appearing to be incompatible with a magmatic arc setting for the Baoshan Block during the Paleozoic. This block might have been situated at the interior of Gondwana before rifting and drifting northwards to the Eurasia continent. [ABSTRACT FROM AUTHOR]

South Qinling is a tectonic block in the Mesozoic Qinling orogenic belt, central China, which is generally believed to have had tight affinity with the Yangtze Block during Precambrian times. In recent years, it has been recognized that the South Qinling Block hosts several Precambrian basement complexes. Here we report U-Pb ages and Hf isotopic data for zircons and Sr-Nd isotopic data for whole-rocks of the Douling complex, the oldest rock unit exposed in South Qinling, to reveal the early evolution of this basement. The Douling complex mainly consists of paragneisses and granitic orthogneisses. Zircons of magmatic origin from three orthogneiss samples give U-Pb ages of c. 2.5 Ga, suggesting an early Paleoproterozoic magmatic activity. Zircon Hf isotopic compositions imply the growth of juvenile crust since c. 3.0 Ga. The magmatic activity at c. 2.5 Ga points to differences in the Precambrian history between South Qinling and the Archean Kongling terrene, the oldest basement of the Yangtze Block. Three paragneiss samples contain complex detrital zircons of different ages and origins. Their U-Pb ages mainly cluster around 2.5 Ga, 2.0 Ga, 1.5 Ga and 800 Ma. Zircon grains with ages of 2.0 Ga and 800 Ma have low Th/U ratios and no oscillatory zoning, implying two episodes of metamorphic overprint. Such Paleoproterozoic metamorphic event has also been traced in the Yangtze Block, confirming its close relationship with South Qinling. The record of Neoproterozoic amphibolite-facies metamorphism in detrital zircons suggest that the tectonic transition from convergent to extensional environments in the Yangtze Block must have occurred later than 800 Ma ago. [ABSTRACT FROM AUTHOR]

• Intrusive rocks of four types in South Qinling formed at ~750–730 Ma. • High-Ti gabbro originated from asthenosphere and low-Ti one from subcontinental mantle. • I-/S-type granites formed from source rocks in an extensional scenery. We report whole-rock Sr–Nd isotopic compositions and U–Pb ages and Hf isotopic compositions of zircon grains from Neoproterozoic intrusive rocks exposed in northern South Qinling, central China. The rocks have diverse compositions and were emplaced at ca 751–714 Ma. On the basis of their distinct geochemical signatures, four compositional groups are recognized. High-Ti gabbros are tholeiitic, with low SiO 2 and MgO, and high FeOT and TiO 2 contents, and exhibit enrichment in large-ion-lithophile elements and absence of Nb and Ta negative anomalies. These gabbros have high ε Nd (t) values of +1.9 to +5.3 that are similar to the compositions of E-MORB or OIB, implying an origin from asthenospheric mantle. Low-Ti gabbros are calc-alkaline and have high SiO 2 and MgO, and low FeOT and TiO 2 contents. These gabbros have typical arc-like trace-element signatures and ε Nd (t) values that vary from −3.2 to +6.0, consistent with derivation from the partial melting of heterogeneous lithospheric mantle that was modified by subduction. Elemental and Nd–Hf isotopic compositions of I-type granitoids imply significant contributions from both mantle and crustal rocks. S-type granites originated from the partial melting of metasedimentary rocks with isotopic compositions similar to paragneisses of the basement in South Qinling. The extensive melting of both mantle and crustal rocks under relatively low pressures and high temperatures suggests an extensional environment during the Neoproterozoic. Our data, in combination with existing data from basement rocks and Neoproterozoic igneous rocks, constrain the crustal evolution of the northern Yangtze Block and South Qinling, in which subduction along the northern margin of the Yangtze Block prior to ca 800 Ma led to arc–continent collision, inducing high-grade metamorphism of the basement rocks of the Douling Complex. Subsequent protracted continental rifting was related to breakup of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]