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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 South Yellow Sea basin in eastern China has experienced a multi-stage tectonic evolution history. The major structures were created when the basin was a foreland basin during the Mesozoic. However the geological evolution of the basin has not yet been corroborated by direct evidence from the underlying basement rocks. Qianliyan Island in the southern Yellow Sea provides an opportunity to study the formation and evolution of the basin by means of direct geochronological and geochemical evidence. On Qianliyan Island, basement rocks are exposed that consist of granitic gneiss, felsic gneiss and minor mylonite, and lenses of eclogite. Major and trace element characteristics of these four types of gneiss indicate that they originated from crustal material, varying in composition from pelite to greywacke. SHRIMP U-Pb zircon dating results of a felsic gneiss sample show that this rock crystallized between 659 and 796 Ma and underwent a metamorphic overprint at 229 ± 4 Ma. This age pattern resembles that of gneisses from the ultra-high-pressure terrain in the Dabie–Sulu belt. We conclude that the study area was part of the northern margin of the Yangtze Block during the Neoproterozoic. Neoproterozoic magmatic activity occurred along this margin and the basement sequence underwent Triassic metamorphic overprint during the northward subduction of the Yangtze Block beneath the North China Block. We further conclude that the deformation associated with this metamorphic event led to the formation of the southern Yellow Sea foreland basin. [ABSTRACT FROM PUBLISHER]

Abstract: The Hongqiyingzi Complex, located at the northern margin of the North China Craton, was previously defined as a Paleoproterozoic unit. It consists of volcanic and sedimentary rocks, which underwent greenschist- to amphibolite-facies metamorphism. This study presents zircon U–Pb ages and Hf isotopic composition and whole-rock Nd isotopic composition of metamorphosed igneous and sedimentary rocks from the Hongqiyingzi Complex. The age dating results show that different gneisses of this complex contain mainly late Paleoproterozoic (~1800Ma) and late Paleozoic (~275 to ~300Ma) zircons and minor late Archean zircons. Late Paleozoic zircons either occur as magmatic grains or as metamorphic overgrowth and both types of zircon can be distinguished by their Th/U ratios and internal structures. Most zircon grains of a Paleozoic magmatic rock (sample Hq14) have high εHf(t) values of 1.5 to 10.8, suggesting significant contribution of mantle or juvenile crustal material to the magma source(s). The results imply that the Hongqiyingzi Complex contains Precambrian supracrustal sequences and Paleozoic rocks of magmatic origin that underwent strong metamorphism and deformation during the late Paleozoic related to the closure of the Paleo-Asian Ocean between Siberia and the North China Craton. [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]

The lithospheric root underneath the Dabie orogen, which is the key part of the Central Orogen of China, experienced a cycle of thickening during Triassic continent-continent collision with subsequent post-collisional collapse during the Early Cretaceous. However, the process and mechanism of how thickened lithospheric roots are removed generally remain controversial. U–Pb ages and oxygen isotopes of zircons along with whole-rock geochemistry of post-collisional mafic–intermediate dykes in the region were used to track magmatic contributions from the lower crust, and constrain magma provenance from compositionally variable reservoirs in the upper mantle. Relict zircons show evidence of recycling of subducted continental crust of South China Block that not only has the Neoproterozoic ages and experienced the Triassic metamorphism, but also contains both 18O-depleted and enriched components. A first generation of hypersthene-normative tholeiitic dykes and nepheline-normative alkaline dykes were emplaced at ca. 130–120 Ma. They are overall characterized by arc-like geochemical patterns with εNd values from −21.6 to −4.6 and initial 87Sr/86Sr from 0.7056 to 0.7094. Coeval alkaline dykes are shifted towards more depleted-mantle like compositions, indicating simultaneous melt extraction from different mantle domains and depths. In contrast, second-generation hypersthene-normative mafic dykes (ca. 115–110 Ma) show OIB-like characteristics with εNd values from −1.5 to +4.8 and initial 87Sr/86Sr ratios from 0.7039 to 0.7049, indicating an increasing contribution from upwelling asthenospheric mantle during lithospheric thinning. The temporal evolution of the geochemical characteristics of mafic melts derived from the upper mantle in the Dabie orogen is consistent with foundering of thickened lithosphere and subsequent influx of asthenospheric mantle. The removal of thickened lithosphere root is suggested to be triggered by subduction of the Paleo-Pacific plate and lasted from ca. 130–115 Ma as constrained by the intrusive ages of two distinct types of tholeiitic dykes. • The Dabie orogen underwent post-collisional collapse during the Early Cretaceous. • First-generation of Hy- and Ne- normative dykes originated from hybrid mantle domains. • Second-generation tholeiitic dykes indicate removal of thickened lithospheric root. • Xenocrystic zircons show close affinities to crustal rocks of the South China Block. • The post-collisional collapse was triggered by subduction of Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

• 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]