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Granitic rocks forming in the syn- to post-orogenic stages can trace the compositional and structural complexity of the crust beneath an orogenic belt. The Qinling orogenic belt undertook multiple stages of tectonics and magmatism, resulting in the multifaceted evolution and compositional diversity of the crust. In the present study, the Guangtoushan and Miba plutons in South Qinling were chosen to reveal the crustal heterogeneity in study area via isotopic geochemistry and zircon geochronology. The Guangtoushan pluton was emplaced between ~215 Ma and ~202 Ma and the Miba pluton formed at ~213 Ma, as constrained by zircon U-Pb isotopic dating. Granitic rocks of the Miba pluton are characterized by amphibole bearing and homogeneous composition, with relatively depleted Sr-Nd isotopic compositions (initial 87Sr/86Sr values of 0.7060 to 0.7084 and initial εNd values of −5.4 to −9.5) and high Pb isotopic values. The Guangtoushan pluton contains muscovite and complex inherited zircon grains and has variable Sr-Nd isotopic composition (initial 87Sr/86Sr values of 0.7050 to 0.7091 and initial εNd values of −4.5 to −12.9) and low Pb isotopic values. Felsic magmas of the Guangtoushan pluton should be derived mainly from meta-sedimentary rocks beneath South Qinling, while the Miba pluton originated primarily from partial melting of meta-igneous rocks. The compositional diversity recorded in the Early Mesozoic plutons was caused by the heterogeneous crust, and partial melting was induced by heating of the up-welling asthenosphere in a post-collision setting. [ABSTRACT FROM AUTHOR]

Sediments or clastic rocks can record the evolution history of basins, orogenic processes, crustal uplift and erosion, and even paleo-environments. Detrital minerals such as zircon, garnet, and apatite are useful media for studies of sedimentary sources and basin evolution. Detrital zircon has been widely taken as an indicator for provenances and tectonic evolution of geological terrenes via age distribution patterns. Apatite can remain stable during erosion and transportation and is also considered as an ideal object for source tracing. This mineral normally contains high Sr and negligible Rb. Its Sr isotopic composition can remain almost unchanged after crystallization. Unlike isotopic ages of detrital minerals, Apatite isotopic compositions have been less frequently used for tracing the provenance of sedimentary rocks in the last few decades. In the present study, we report on the Sr isotopic composition of individual apatite grains of Neogene and Jurassic conglomerates from the Hui-Cheng basin in the South Qinling orogenic belt, obtained via thermal ionization mass spectrometry. Detrital apatite grains of Jurassic rocks have narrow ranges of 87Sr/86Sr values from 0.7076 to 0.7100, but those of Neogene rocks gave variant 87Sr/86Sr values from 0.7055 to 0.7534, providing distinct evidence for complex sources of Neogene sedimentary rocks. Analytical results show that the distribution patterns of 87Sr/86Sr values of single-grain detrital apatite fit the distribution patterns of detrital zircon U-Pb from the isotopic ages very well. Detrital apatite Sr isotopic composition can provide essential information for tracing the origins and evolution of sedimentary sources. [ABSTRACT FROM AUTHOR]

The Qinling Orogen resulted from the collision between the North and South China blocks in the Triassic. Mesozoic granitoids, ranging from the Triassic to the Cretaceous, are widely distributed in this orogen, and they provide excellent clues for understanding the crustal evolution and geodynamic evolution of the orogenic belt. The Triassic belt is mostly located in the South Qinling, whereas the Cretaceous belt is located mostly in the North Qinling. The Taibai complex pluton is located at the conjunction of the two belts. Here we present a data set comprising zircon U-Pb dating and elemental and Sr-Nd isotopic geochemistry for Late Mesozoic granite and microgranular enclaves (MME) exposed in the Taibai complex pluton. The granite and MME yield concordant U-Pb zircon ages of 124 to 118 Ma, indicating that they were products of roughly simultaneous magmatism in the Late Mesozoic. The granite rocks are high-K, calc-alkaline, and weakly peraluminous in compositions, and they are characterized by enrichment in large ion lithophile elements (e. g., Rb, Ba), depletion in high field strength elements (e.g., Nb, Ta, Zr, Ti), and variable Sr/Y ratios of 7.64 to 63.6. Low MgO, Cr, and Ni contents imply that the magma(s) were essentially crust-derived. Both the granite and the MME show relative depletion in Sr-Nd isotopic composition (initial 87Sr/86Sr of 0.704 4 to 0.706 7, initial εNd values of −3.4 to −2.6), suggesting that the magma(s) originated from juvenile crustal rocks. These Sr-Nd isotopic characteristics are significantly different from those of other Late Mesozoic granitoids exposed elsewhere in the Qinling orogenic belt, which formed from much older and enriched sources and with negligible contributions from mantle or juvenile crust. We propose a reworking event of the juvenile crust during the Late Mesozoic that was triggered by the tectonic extension and subsequent asthenospheric upwelling that occurred in eastern China. [ABSTRACT FROM AUTHOR]

Magma mixing or mingling between mafic and felsic magmas is a common phenomenon in granitoid magmatism, and chemical and mechanical interactions between the magmas are frequently observed in granitic rocks. The Dongjiangkou pluton is an example of magma mixing among the numerous early Mesozoic granitoid plutons that are exposed in eastern South Qinling. This pluton is predominantly composed of granodiorite and contains abundant mafic/intermediate microgranular enclaves (MMEs) and is sporadically intruded by mafic dykes. Both the granodiorite and MMEs were crystallized at 224–214 Ma and have inherited zircons of similar age ranges. The granodioritic rocks had metaluminous to weak peraluminous features and adakitic signatures and belong to the high-K calc-alkaline series, whereas the MMEs and dioritic dykes had low SiO 2 contents and metaluminous features and belong to the high-K calc-alkaline to shoshonite series. All of the rocks had high Mg# values and similar geochemical characteristics regarding trace elements and Sr isotopes, but they had diverse whole-rock Nd-Pb and zircon Hf isotopic compositions. The Dongjiangkou granodiorite was produced by partial melting of old basement rocks and Paleozoic juvenile crust beneath South Qinling triggered by asthenospheric upwelling. Magma(s) of the Dongjiangkou MMEs may have been derived from deep mantle and injected into and mixed with the magma(s) of the granodiorite, but chemical and isotopic homogenization was not achieved during the magma mixing process. Clastic rocks may have played a major role in the formation of crust-derived magma(s), causing strong Nd-Hf isotopic decoupling of several granitoid plutons in South Qinling. • Dongjiangkou granite witnesses insufficient mixing of felsic and mafic magmas. • Nd and Hf isotopic equilibrium did not reach during the magma mixing. • Felsic magma originated from old basement and Paleozoic rocks in South Qinling. • Input of clastic rocks to granitic magma source caused Nd-Hf isotopic decoupling. [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]