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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]

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]