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• Zircon grains from quartz monzonites and MMEs in the Mishuling pluton are all dated at ~215 Ma. • Three types of zircon are identified from the MMEs with distinct texture and ε Hf (t). • Type-1 and Type-2 zircon crystallized from compositionally different hybrid magmas. • Type-3 zircon is the xenocryst captured from less-evolved granitic magma. • Zircon grains from the MMEs record successive magma mixing processes in deep magma chambers. Extensive Mesozoic magmatism in the Qinling orogenic belt, Central China, has produced voluminous granitic plutons. In Western Qinling, the Triassic Mishuling pluton contains abundant mafic microgranular enclaves (MMEs), recording magma mixing processes in the generation of the pluton. The Mishuling pluton is composed of quartz monzonite, whereas the MMEs are mainly diorite and monzonite. In this study, zircons from the MMEs are all dated by LA-ICP-MS at ca. 215 Ma, clearly consistent with the crystallization age of the host pluton. Quartz monzonites have low Mg# (43–48), Cr (30–64 ppm), and Ni (11–39 ppm) and high Th/U relative to the MMEs. Quartz monzonites are considered to have been produced by melting of Neoproterozoic mafic rocks in the northwestern part of the Yangtze Block, whereas the MMEs were likely the products of mixed mafic and felsic magmas. The mafic magmas may have been derived from partial melting of the enriched lithospheric mantle. Both the MMEs and host quartz monzonites have nearly identical Sr-Nd isotopic compositions, indicating that the hybrid melts and felsic magmas may have reached Sr-Nd isotopic equilibrium due to magma mixing. Zircon grains from the MMEs can be further divided into three types on the basis of internal texture and ε Hf (t). Overall, all these types of zircon grains have Th/U ranging from 0.18 to 1.63, typical of magmatic origin. Type-1 zircon grains show well-developed {1 0 0} and {1 1 0} prisms as well as {1 0 1} and {2 1 1} pyramids, whereas Type-2 zircon grains show well-developed {1 0 1} pyramids and {1 1 0} prisms. Types-1 and 2 zircon grains have slightly higher ε Hf (t) (–0.2 to –4.4) than those of the zircon grains from quartz monzonites (ε Hf (t) = –2.7 to –5.4), indicating crystallization from different hybrid magmas. Type-3 zircon grains have morphology and ε Hf (t) similar to and Hf concentrations lower than those of the zircon grains from quartz monzonites. We interpret that the Type-3 zircon grains were likely captured from less evolved granitic magmas and are thus xenocrysts in the MMEs. Therefore, the three types of zircon grains from the MMEs record successive magma mixing processes in deep-seated magma chambers. Such a scenario may have broad implications for magma mixing in the generation of granitic plutons. [ABSTRACT FROM AUTHOR]

• Precambrian paragneisses from the Foping complex in South Qinling have a Neoproterozoic sedimentary protolith. • Neoproterozoic felsic igneous rocks in South Qinling and the Yangtze Block were the major sources of the sedimentary protolith. • Crustal growth in South Qinling occurred at ca. 1000–900 Ma, followed by reworking of ancient crust after ca. 900 Ma. • Tectonic shift from an island arc to a continental arc in the northern Yangtze Block occurred at ca. 900–860 Ma. Basement rocks within orogenic belts are useful for reconstructing crustal evolution. In the present study, we report the U-Pb ages and Hf isotopic compositions of detrital zircon and the geochemical of whole rock for Precambrian paragneiss from the Foping complex in South Qinling. The paragneiss samples had TiO 2 /Al 2 O 3 ratios of 1.84–5.70, Th/Sc ratios of 0.67–1.20, and Zr/Sc ratios of 11.0–18.1, suggesting felsic rocks as the major source. The immobile trace elements indicate that the source rocks were mostly derived from a continental arc environment. The U-Pb ages of detrital zircon are notably concentrated around two major peaks at ∼850 Ma and ∼700 Ma and two subordinate peaks at ∼2500 Ma and ∼2000 Ma with ε Hf (t) values varied widely from –26.0 to +12.4. The predominantly Neoproterozoic ages of the detrital zircon grains show a similar age distribution to those of Neoproterozoic igneous rocks in South Qinling and the Yangtze Block. Combining the results with the existing data for Neoproterozoic rocks in the study area, we propose that South Qinling was generally characterized by growth of the crust in the early Neoproterozoic (ca. 1000–900 Ma) that could have resulted from an intra-oceanic subduction along the northern margin of the Yangtze Block. Reworking of the ancient crust strengthened thereafter, which could be attributed to tectonic shift from an island–arc setting to a continental arc environment at ca. 900–860 Ma. Extensive formation of igneous rocks in the continental arc provided the main source for the Precambrian paragneisses in the Foping dome. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sediments of the late Ordovician Lancang Group in the Lancang Block, SW China, were sourced mainly from the northern margin of Gondwana. • Provenance change of the sediments might reflect initial subduction of the Proto-Tethys in the Ordovician. • The Lancang Block had affinity to Gondwana during the early Paleozoic. In the present study, we report zircon U-Pb ages, Hf isotopic compositions, and geochemistry for sedimentary rocks of the early Paleozoic Lancang Group in the Lancang Block of the western Yunnan Tethyan orogenic belt, SW China, to reveal the nature of sedimentary provenance with further implication on the orogenic evolution. Detrital zircon grains yield two major U-Pb age populations at 1300–900 Ma and 600–500 Ma, while their ε Hf (t) values range from –28.7 to + 13.0 with Hf model ages mostly cluster at ∼ 2200–2100 Ma. These features on zircon U-Pb age patterns and Hf isotopic compositions are extremely similar to those of exposed rocks in North India. It is noteworthy that the sedimentary provenance had changed dramatically from the lower to the upper sequences of the Lancang Group, as highlighted by the increase of Pan-African and younger Grenvillian (1100–900 Ma) materials accompanied by the decrease of older Grenvillian (>1100 Ma) sediments. Besides, whole rock Nd model ages also increase from the basal sequences upwards. Combining these findings with those of previous studies, we propose that the Lancang Block was adjacent to the northern margin of Gondwana during the early Paleozoic with sediments of the Lancang Group dominantly sourcing from North India. The provenance change recorded in the Lancang Group might have resulted from a transition from passive to convergent continental margin initialed by the subduction of Proto-Tethys in the late Ordovician along the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]