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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 Yangtze Block records Neoproterozoic magmatism and sedimentation related to the breakup of Rodinia and is an important piece in the reconstruction of the supercontinent. However, the tectonic setting and position of this block in Rodinia remain a subject of debate. In the present study, we report the zircon U-Pb ages and Hf isotopic composition of zircon and geochemical and Nd-Pb isotopic compositions for meta-volcanic rocks exposed in the Zhangbaling uplift of the NE Yangtze Block. The volcanic rocks, dominated by rhyolite and dacite, belong to the calc-alkaline series and show geochemical characteristics of arc rocks. Zircon U-Pb isotopic ages show that volcanic rocks in the Xileng Formation formed at ca. 790 Ma and ca. 760–700 Ma peaking at ~740 Ma. The late-stage volcanism was widely exposed in the uplift, characterized by a temporal-spatial trend becoming younger southwards. The old volcanic rocks have low initial εNd (−11.0) and εHf (−19.7 to −8.2) values and low Pb isotopic ratios, likely indicating an origin from ancient basement rocks underneath the Yangtze Block. The younger ones, being similar to continental arc andesite in trace element compositions, have relatively high initial εNd (mostly −4.6 to 0.5) and εHf (−0.4 to 8.8) values and high Pb isotopic ratios. These isotopic features point to an origin from the partial melting of juvenile crustal rocks. Sedimentary rocks of the Xileng Formation and the overlying strata also contain numerous zircon grains of ~700 Ma to ~630 Ma. The volcanic rocks in the Zhangbaling uplift might demonstrate long-lasting subduction along the northeastern margin of the Yangtze Block, probably active until ca. 700 Ma. [ABSTRACT FROM AUTHOR]

Yanshanian magmatisms are intensive in the eastern Jiangnan orogen and can be divided into early (150–136 Ma) and late (136–120 Ma) stages. About these granitic rocks, the petrogenesis and associated tectonic setting are still hotly debated. The Taiping–Huangshan complex, a representative granitic rock in this region, is selected to perform geochemical studies. Three lithologic units have been identified in the Taiping–Huangshan complex: granodiorite, monzogranite, and alkali‐feldspar granite with zircon U–Pb dating results of 149–144 Ma, 148 Ma, and 135–131 Ma, respectively, belonging to the early stage for the granodiorite and monzogranite, and late stage for the alkali‐feldspar granite. The granodiorite and monzogranite have similar major and trace element characteristics with intermediate‐acidic SiO2 contents ranging from 65.9 to 69.7 wt.%, low Mg# values of 35.8–38.4, enriched LREE, Pb, Th, and U contents, and weak Eu anomalies (δEu = 0.71–0.79). The alkali‐feldspar granite is characterized by high SiO2 contents (73.3–76.6 wt.%), low Mg# (2.6–10.0), enriched Th, U, Ta, Pb, and Nd, depleted high‐field‐strength elements, and pronounced negative Eu anomalies (δEu = 0.01–0.19). The granodiorite and monzogranite have consistent εHf(t) (−5.38 to −9.41) and δ18O (7.18‰ to 11.00‰) values, while the alkali‐feldspar granite has elevated εHf(t) values (−0.96 to −6.48) and δ18O values (6.27‰ to 8.34‰). Integrated geochemical characteristics and batch partial melting modelling constrain that the early stage granitic rocks derived from ca. 8% batch melting of the Neoproterozoic juvenile crust, and the late‐stage granites derived from a similar crust source with a little contribution from mantle. From early to late stage, the tectonic setting translated from post‐orogenic to anorogenic and the later corresponded to a back‐arc extensional setting as increasing of the slab subducted angle of the Palaeo‐Pacific Plate. [ABSTRACT FROM AUTHOR]

The Kashan plutons are situated in the central part of Urumieh-Dokhtar magmatic arc recording subduction-related magmatism within the Alpine-Himalayan orogeny in Iran. These rocks consist of different calc-alkaline plutonic rocks including gabbro, gabbroic diorite, microdiorite, monzodiorite, tonalite, granodiorite, and granite. The plutons were emplaced into the Jurassic sedimentary units (Shemshak Formation) and the Eocene calc-alkaline volcanic and pyroclastic rocks. New U-Pb zircon ages show that the Kashan plutons formed during two main periods at 35.20±0.71 Ma in the Late Eocene (Priabonian) and at 18.90±0.84, 19.26±0.83, 19.30±1.2, and 17.3±1.8 Ma in the Early Miocene (Burdigalian). The reported events in the Kashan plutons imply the final phases of subductionrelated magmatism before the collision which happened between the Arabian and Iranian plates in the Middle Miocene. The plutonic activity in the Kashan region occurred during the transition from Eocene subduction-related setting to Middle Miocene collisional setting. [ABSTRACT FROM AUTHOR]

The Jiaodong Peninsula of eastern Shandong Province comprises the Jiaobei terrain of North China affinity and the Sulu ultrahigh-pressure metamorphic terrain. In this study, we present zircon U-Pb ages, major- and trace-element data, and Sr-Nd-Pb isotopic compositions of intermediate to mafic dikes from the Linglong region of the Jiaobei terrain and the Rushan region of the Sulu terrain to discuss the nature of the mantle source(s) beneath eastern China during the Early Cretaceous. Zircon U-Pb dating yields Early Cretaceous dike emplacement ages ranging from ~124 to ~120 Ma for the Linglong region and from ~118 to ~108 Ma for the Rushan region. Dikes from both regions are all potassic, with "arc-like" trace-element distributions as well as high unradiogenic Pb isotopic composition, low initial εNd values (-19.64 to -10.80), and high radiogenic 87Sr/86Sr ratios (0.7075-0.7112), suggesting the involvement of an extensively enriched mantle component. Such isotopic characteristics are found in contemporaneous intermediate to mafic intrusive rocks in the whole Shandong Province and are explained in terms of a Triassic northwestwardsubduction model of the Yangtze Block beneath the North China Block. The dikes from the Linglong and Rushan regions have low Nb/U and Ce/Pb ratios, implying the involvement of upper-continental-crustal material. Combined with the southward younging of zircon U-Pb ages through Shandong Province, we suppose that the enriched mantle source beneath the Jiaodong Peninsula was formed by metasomatism of silicic melts or fluids derived from the subducted Yangtze continental crust during the Triassic, followed by decompression melting of this mantle during the Early Cretaceous due to rollback of the subducted Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

The Song Ma zone in NW Vietnam bears important tectonic implications as a potential subduction corridor between the Indochina and South China blocks. On the basis of U-Pb ages, the Hf isotopic characteristics of zircons and the geochemical composition of granitoids, a two-stage magmatic evolution process of the Song Ma zone at ~290-260 and ~245-230 Ma can be proposed. Isotopic analyses indicate magmatic contributions from Neoproterozoic oceanic island basalt, Proterozoic continental crust, and depleted mantle or juvenile lithosphere. By combining geochronological and geochemical data from the granitoid rocks, we suggest that the staged magmatic processes of Song Ma zone may be related to a long-lasting period of ocean subduction (ca. 290-260 Ma) and subsequent syn-/post-collisional evolution (ca. 245-230 Ma). [ABSTRACT FROM AUTHOR]

Late Mesozoic lithospheric extension in NE Asia resulted in the development of a large extensional province and widespread formation of volcanosedimentary basins. Songliao basin is the biggest in that region, situated between the Siberian and Sino-Korean (North China) cratons. The Songliao basin contains voluminous volcanic rocks as a major part of the basin fill. Volcanic successions form a significant but unexposed part of the late Mesozoic magmatic province in NE China. Here we report zircon U-Pb ages and geochemical data for felsic volcanic rocks from the Songliao basin. Zircon populations of two types of rhyolites with distinct I- and A-type affinities, analyzed by laser ablation inductively coupled plasma mass spectrometry, yielded similar U-Pb ages of 114 ± 2 and 113 ± 2 Ma, respectively. Whole-rock Nd and zircon Hf isotope data of the felsic rocks indicate an origin from newly formed crustal protoliths. The I-type dacites and rhyolites show geochemical signatures with subduction-related affinity, indicating generation by partial melting of juvenile crust that originated from melting of subduction-modified mantle sources, whereas the A-type rhyolites have higher heavy rare earth element and high field strength element concentrations and lower Ba/Nd ratios that are interpreted as evidence for melting of I-type felsic lower crustal sources in an intraplate tectonic environment. Typical geochemical compositions of A-type rhyolites indicate anorthite-rich plagioclase as a residual magmatic phase and imply melting at shallow crustal levels. The A-type felsic rocks were generated during a period of maximum lithospheric extension below eastern China around 110 Ma, and this thinning process was probably related to the retreat of the Paleo-Pacific trench. [ABSTRACT FROM AUTHOR]

Neoproterozoic volcanic-sedimentary sequences of the southern Qinling belt, central China, were intruded by voluminous mafic dikes. secondary ion mass spectrometry zircon U-Pb dating indicates that these dikes were emplaced at 650.8 ± 5.2 Ma, coeval with mafic rocks occurring at the northern margin of the Yangtze block. The dikes are characterized by enrichment of large ion lithophile elements, high Ti contents (up to 3.73 wt%) and Nb/Ta ratios between 14.5 and 19.6, suggesting a mantle source of oceanic island basalt affinity. Initial Sr/Sr ratios show positive correlation with SiO contents and negative correlation with Zr/Nb ratios, implying that these rocks were affected by crustal contamination during the magma ascend and emplacement process. The dikes have initial ε values of +0.2 to +3.3, low Pb/Pb ratios of 16.96-17.45, and moderate Sr/Sr ratios of 0.7043-0.7076, likely pointing to the involvement of an enriched mantle source. The mafic dikes and coeval mafic volcanic equivalents in the South Qinling and the northern Yangtze are hypothesized to be related with the prolonged breakup of the supercontinent Rodinia, suggesting that continental rifting lasted until ca. 650 Ma. [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]

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]

Abstract: Mesozoic granitoids are ubiquitous in China and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material, emplacement mechanisms and crustal architecture. Most of the plutons were created by multi-stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history. A multi-isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings. This study presents Rb–Sr isotope data for K-feldspar megacrysts and U–Pb ages and Hf isotopic composition for zircons from the composite Heyu pluton exposed in eastern Qinling orogen, central China. Zircon U–Pb concordia ages of 150 and 140Ma and single K-feldspar Rb–Sr isochron ages between 133 and 121Ma were obtained from early and late magmatic stages, respectively, consistent with slow cooling or isotopic re-equilibration of the Rb–Sr K-feldspar system. The distinct K-feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth, likely to be associated with a gravity-driven sinking model. Corresponding zircon εHf(t) values are −21.8 to −18.0 and −17.2 to −10.3 for early and late intrusive phases, respectively, indicating different magma sources. [Copyright &y& Elsevier]

Abstract: The Songliao basin, situated between the Siberian and Sino-Korean (North China) cratons, was tectonically shaped by convergence of the Mongol-Okhotsk and Paleo-Pacific oceans. The lack of isotopic and geochemical data from its sedimentary rocks has hindered a better understanding of the depositional–tectonic history of the basin so far. A continuous sedimentary sequence is preserved in the upper part of the Songliao basin (Denglouku and Quantou formations). These rocks provide clues to depositional processes operating in this region during the late Cretaceous. Dominant zircon populations of the underlying Denglouku Formation are largely Paleozoic (270–250Ma) and Mesozoic (190–170Ma) in age, whereas the overlying Quantou Formation contains mostly older zircon populations of ~1800Ma and ~2500–2900Ma. The youngest detrital zircons place the deposition ages of both rock formations at about ~117Ma and ~103Ma, respectively. The Denglouku Formation is characterized by less negative initial εNd values (−6.3 to −2.8), younger Nd model ages (1.05–1.39Ga) and lower initial 87Sr/86Sr ratios (0.7079 to 0.7088), compared to the Quantou Formation (−12.8, 1.75Ga and 0.7129), confirming that both formations were derived from different source areas. Our data suggest that Paleozoic and Mesozoic magmatic rocks were widespread in the northern periphery of the basin, and served as potential sources of the Denglouku Formation. In the south-east, old basement rocks of the North China craton provided sedimentary material for the Quantou Formation. The south-eastward migration of erosion center(s) in the Songliao basin in the late Mesozoic probably resulted from an abrupt change in basin uplift and subsidence. These processes were driven in response to regional tectonic changes toward an increasing dominance of the Pacific Ocean over the Mongol-Okhotsk Ocean subduction regime. [Copyright &y& Elsevier]

The location of the suture zone between the South China and Indochina blocks in northwest Vietnam has been under debate for decades. Generally, the boundary between these blocks has been placed along (1) the Ailaoshan–Red River zone or (2) the Song Ma zone. The Sin Quyen Formation, lying between these zones, was previously regarded as a Palaeo- and Mesoproterozoic sequence. It comprises its provenance and tectonic affinity. We analysed detrital zircons from two paragneisses and one migmatite of the Sin Quyen Formation employing laser ablation inductively coupled plasma mass spectrometry U–Pb dating techniques. U–Pb ages of these zircons show three main periods of zircon formation: ∼2.7–3.0, ∼2.2–2.5, and ∼1.8 Ga, suggesting that Sin Quyen rocks were mainly derived from Palaeoproterozoic and Archaean basement units. Inasmuch as the South China basement comprises rocks of similar ages, we conclude that the Sin Quyen Formation belongs to that block. Our new data strengthen the view that the suture between the South China and Indochina blocks is located within the Song Ma zone. In addition, zircons with U–Pb ages >3.0 thousand million years represent the oldest minerals reported in northwest Vietnam so far, indicating the existence of Mesoarchaean crustal remnants in this region. [ABSTRACT FROM AUTHOR]

Neoproterozoic sedimentary sequences in the South China Block provide great opportunity to examine the tectonic evolution and crustal accretion during this period. This study presents U-Pb ages and Hf isotope composition of detrital zircons and Nd isotope composition of whole rocks of the Neoproterozoic sequences from the Yangtze Block, part of the South China Block. Age patterns of detrital zircons imply that the source area experienced three major periods of magmatic activity at 2,300-2,560, 1,900-2,100 and 770-1,000 Ma and two major episodes of juvenile crust accretion at 2,600-3,400 and 770-1,000 Ma. The maximum age of the Gucheng glaciation can be restricted at ~768 Ma from the youngest detrital zircon ages, probably corresponding to the Kaigas glaciation rather than to the Sturtian glaciation. High La/Sc ratio and low Cr/Th, Sc/Th and Co/Th ratios of the sedimentary rocks point to a derivation from dominantly felsic upper continental crustal sources, whereas large variation of ε( t) and ε( t) values indicates that mantle-derived magmatic rocks also provided material to the sedimentary sequences in different degrees. The shift in ε( t) values of whole rocks and U-Pb age spectra of detrital zircons records the evolution from a back-arc to retro-arc foreland to a rift basin. Age distribution of detrital zircons from the Neoproterozoic sequences, compared with those of the major crustal blocks of Rodinia, implies that the position of the Yangtze Block was probably adjacent to northern India rather than between Australia and Laurentia before the breakup of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

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]

Abstract: The basement of the Romanian Carpathians is comprised of pre-Variscan metasedimentary and metaigneous units. Age patterns from corresponding detrital zircons show similarities to those from the eastern Mediterranean region. Consistently, these patterns suggest a northern Gondwanan origin for the Carpathian terranes with the most common detrital sources representing fragments of the Pan-African Orogen, Arabian-Nubian Shield, Kibaran Orogen, and West African Craton (Eburnean Orogen and Liberian-Leonian Orogens), as well as the Saharan metacraton. Some contributions from the Indian Craton are also possible. The youngest detrital zircon ages constrain the maximum age of the sedimentary rock protoliths to Middle Cambrian. On the other hand, the U/Pb zircon ages of the metaigneous protoliths indicate predominantly Early Ordovician ages and bracket most magmatism in the Carpathian pre-Variscan basement units between Middle Cambrian and Late Ordovician. An exception is the Neoproterozoic lower part of the Sebes–Lotru terrane, whose igneous ages are equivalent to the Danubian Domain in the South Carpathians. The Carpathian pre-Variscan terranes were originally located along the eastern extension of the Galatian superterrane, and thus within a Late Cambrian to Ordovician extensional tectonic setting. [Copyright &y& Elsevier]

Abstract: The Mesoproterozoic rifting and accompanying magmatism and sedimentation in the North China Craton are interpreted to be related to the breakup of the Paleoproterozoic supercontinent Columbia. This study presents zircon ages and Nd–Hf isotopic data of the low-grade Mesoproterozoic Zhaertai Group exposed along the northern margin of the North China Craton. Sandstones of the Zhaertai Group contain detrital zircon populations of about 2500Ma, which originated from the late Archean basement rocks underlying this group. A close match between the U–Pb ages and the TDM (Hf) ages with high initial ε Hf values (at 2500Ma) for the detrital zircon grains imply a juvenile origin for protoliths of the basement rocks. Sedimentation of the Zhaertai Group likely began around 1750Ma tentatively constrained by the formation time of an intercalated volcanic layer. The volcanic rocks have low initial ε Nd values of −8.0 to −8.5 (at 1750Ma), similar to those of contemporaneous mafic dyke swarms within the North China Craton, which have been interpreted to be related either to the breakup of the supercontinent Columbia or to the post-collisional collapse of the Trans-North China Orogen. A progressive increase of ε Nd values of whole-rock samples upwards in the stratigraphic sequence likely indicates an increase of juvenile material with time probably related to the contribution of Mesoproterozoic mantle-derived rocks. [Copyright &y& Elsevier]

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The Beihuaiyang zone of the Dabie ultrahigh-pressure collisional belt, which was formed by the Early Mesozoic collision of the North and South China (Yangtze) Blocks, is diversely interpreted as an active or a passive sedimentary sequence. It comprises the Luzhenguan and Foziling complexes. Six granitoid rocks of the Luzhenguan complex are dated at 770 Ma to 720 Ma and one schist sample also contains detrital zircons of 760 Ma to 720 Ma. These data indicate that this complex was of the South China affinity and probably originated from the northern Yangtze Block. Two quartzite samples of the Foziling complex contain abundant detrital zircons of Archean to Paleozoic ages, clustering around 2.5 Ga, 1.9–1.8 Ga, 1.0–0.7 Ga, and 0.5–0.4 Ga. This age spectrum demonstrates a mixed source of these two blocks. The youngest zircons suggest a Paleozoic deposition along an active continental margin south of the North China Block, while these Late Proterozoic zircons are characterized for the Yangtze Block. Subsequently, it is suggested that a terrain drifted from the northern Yangtze Block in Early Paleozoic must have been situated to the southern margin of the North China Block to provide material source prior to the final collision in Early Mesozoic. [Copyright &y& Elsevier]

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]

Two homogeneous zircons, zircon 91500 (Kuehl Lake, Ontario) and Phalaborwa zircon (South Africa), were analysed to study U and Pb behaviour during stepwise HF acid leaching. From the Phalaborwa zircon, ∼11% of radiogenic Pb and ∼7% of U were extracted into solution at the first leaching step and a reverse discordance was obtained. After extraction of ∼27.0% of the total radiogenic Pb budget and ∼24.5% of the U, the zircon residue gave concordant ages. It contained ∼75.8% of total radiogenic 206Pb budget, ∼76.4% of total radiogenic 207Pb budget, and ∼68.0% of total radiogenic 208Pb budget, indicating different mobility of Pb isotopes. The 208Pb*/206Pb* ratios of the solutions and the residue decrease systematically from ∼1.10 to ∼0.60. This pattern probably demonstrates that domains with different Th/U ratios were successively sampled during acid attack. In contrast to Phalaborwa zircon, only ∼1% of the total radiogenic Pb budget was extracted in leaching steps from each of three zircon 91500 fragments. Highly reverse discordant ages are observed in the first leaching step of the Phalaborwa zircon. This phenomenon is consistent with the recent studies of Mattinson [Partial dissolution analysis (PDF) of zircon: past, present, future. 11th Annual V. M. Goldschmidt Conference, Abstract volume, 3368.pdf. (2001)] and Davis and Krogh [Chem. Geol. 172 (2000) 41]. Due to the fractionations between U and Pb and between radiogenic Pb isotopes observed in the first leaching step, discordant domains or zonings of zircons have to be completely removed in the leaching steps to avoid any artificial high 207Pb*/206Pb* ratio in the residues. Evaluation of data from leaching studies shows that the extractability of Pb is positively correlated with the total radiogenic Pb budgets in zircons and subsequently with U contents and ages of zircons, indicating an important role of radiation damage. This correlation is consistent with the fact that old zircons with high U contents are much more susceptible to Pb loss than younger ones with low U contents. [Copyright &y& Elsevier]

Presents research on zircon and garnet ages of a mafic granulite from the Variscan belt in the Black Forest of Germany. The isotope closure temperature of garnet Sm-Nd and U-Pb systems; The age of zircon grains found by the U-Pb and evaporation methods; The Sm-Nd and Pb-Pb isochron ages of garnet; Suggestion that many zircons might have lost radiogenic Pb due to metamictization or recrystallisation during the granulite-facies metamorphism at ∼340 Ma; Evidence of pro-grade metamorphism in the garnet Sm-Nd and U-Pb systems; Possibility of a fluid-absence metamorphic environment; Assertion that garnet mineral could be a better candidate than zircon when dating high-grade metamorphism by the U-Pb and Sm-Nd methods.

Presents an approach for the correction of common lead contribution to [sup 207]lead/[sup 206]lead ages obtained by the zircon evaporation technique. Basis for the stepwise evaporation method for zircon dating; Outline of the evaporation technique.

• 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]

The geochemical compositions and zircon U-Pb ages of the Muhuguan and Mangling plutons of the North Qinling Terrane (NQT), China, provide insights into the basement rocks involved in magma genesis and the Mesozoic tectonic evolution of the NQT. Monzogranites from the two plutons are characterized by high SiO 2 contents (69.3–77.0 wt%), low Mg numbers (0.21–0.38), enriched light rare-earth elements, Th, U, and Pb, depleted high-field-strength elements, and negative Eu anomalies. The source of the Mangling monzogranite is interpreted to have been deeper than that of the Muhuguan monzogranite, on the basis of its higher Sr/Y, (Dy/Yb) N , and (La/Yb) N ratios and lower SiO 2 content. Sr-Nd isotopic compositions indicate similar but heterogeneous magma sources for the two granites: 87Sr/86Sr i = 0.7070–0.7103 and ε Nd (t) = −7.0 to −15.0 for the Muhuguan granite, and 87Sr/86Sr i = 0.7054–0.7083 and ε Nd (t) = −7.9 to −16.0 for the Mangling granite. The zircon U-Pb age results fall into two groups: (1) syn -magmatic zircons (153 to 140 Ma); and (2) inherited zircons that define five age clusters, namely Neoarchean-Paleoproterozoic (2633–2103 Ma), Paleoproterozoic to Mesoproterozoic (1988–1377 Ma), Neoproterozoic (975–605 Ma), Paleozoic (535–382 Ma), and Late Paleozoic – Early Mesozoic (329–187 Ma). These data are consistent with a derivation of the granites by mixing between melted underplated juvenile crust within the NQT and melts from basement rocks similar to those of the Xiong'er Group within the southern margin of the North China Craton (S-NCC). The involvement of S-NCC material is also supported by the unradiogenic whole-rock Pb isotopic composition of the Muhuguan and Mangling granites, which is similar to that of the S-NCC basement rocks. These results suggest that the widespread Late Jurassic to Early Cretaceous granitoid intrusions within the NQT were generated in an extensional geological setting associated with mantle upwelling. Melts were derived from underthrust S-NCC basement material and juvenile Neoproterozoic basaltic rocks. • Inherited zircons of Mesozoic granites indicate heterogeneous magma sources. • Basement rocks of North China were involved in the granitic magmas. • Low-silica diorite originated from enriched mantle source. [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]

Graphical abstract Highlights • Multi-stage magmatic activities of southern Anhui province, can be subdivided to three magmatics stages, i.e., ca. 152–136 Ma mainly of granodiorites, ca. 136–130 Ma mainly of mongranites, ca. 130–120 Ma mainly of K-feldspar granites. • Older granitoids of the Qingyang pluton originated from the mixing sources of mantle material and old crustal rocks, were related to the Paleo-Pacific subduction. • While younger A-type granite formed by the anatexis of more juvenile crustal rocks, were due to rollback of the Paleo-Pacific subduction. Abstract Late Mesozoic magmatic rocks are widely distributed in southern Anhui province, and are represented by the Qingyang-Jiuhuashan granitic complex, which consists dominantly of the Qingyang pluton of granodiorite and monzogranite, and the Jiuhuashan pluton of K-feldspar granite. These two plutons have zircon U-Pb ages of 138 Ma–128 Ma. Combining the new data with previously reported age data, the magmatism in southern Anhui province can be subdivided into three stages: early stage of ∼152–136 Ma, middle stage of ∼136–130 Ma, and latest stage of ∼130–120 Ma. Granodiorite (early stage) and monzogranite (middle stage) of the Qingyang pluton have SiO 2 contents of 66–68 wt%, total alkali contents of 7.5–8.6 wt%, K 2 O/Na 2 O ratios of 1.1–1.3, A/CNK ratios of 0.9–1.1, and low FeOT/(FeOT + MgO) values of 0.71–0.73. These rocks show depletion in Nb, Ta, and Zr and slightly negative Eu anomalies. K-feldspar granite (late stage) of the Jiuhuashan pluton is characterized by high SiO 2 contents (>75 wt%), K 2 O/Na 2 O ratios of 1.1–1.3, and A/CNK ratios of 0.9–1.2, and high FeOT/(FeOT + MgO) values of 0.88–0.93. They have high concentrations of Nb, Ta, and Zr, and strongly negative Eu anomalies. Initial ε Hf values of zircon grains from the granodiorite and monzogranite range from −8.01 to −6.71 and −11.40 to −9.43, with δ18O values varying from 7.16‰ to 8.04‰ and 7.26‰ to 8.06‰, respectively. Zircon grains from K-feldspar granites have relatively high initial ε Hf values of −7.62 to −4.78, but similar δ18O values of 7.03–8.84‰. Geochemical features of granodiorite and monzogranite point to an I-type signature, whereas those of K-feldspar granite show an A-type affinity. We propose that the granodiorite and monzogranite originated from mixing melts produced by partial melting of lithospheric mantle metasomatized by fluids and crustal rocks induced by underplating basaltic magmas, related to subduction of the Paleo-Pacific oceanic crust, whereas the K-feldspar granite formed from crustal anatexis in an extension setting caused by rollback of the subduction. [ABSTRACT FROM AUTHOR]

Migmatites provide a record of melt formation and crustal rheology. In this study we present zircon U-Pb ages and geochemical composition of migmatites from the Foping dome and granites from the Wulong pluton. U-Pb results from migmatite zircons indicate two episodes of partial melting. Rim domains from a leucosome in the Longcaoping area yield an age of ca. 209 Ma. Migmatites collected from the Foping dome yield U-Pb zircon ages of ~ 2910 to ~ 190 Ma, suggesting the involvement of meta-sedimentary source components. Rim domains of the zircons with low Th/U ratios (< 0.1) give ages of ~ 225–190 Ma and the youngest age domains (ca. 195 Ma) are characterized by low contents of heavy rare earth elements, which is related to crystallization of garnet. Magmatic rocks from the Wulong pluton can be subdivided into high Sr/Y and low Sr/Y granites. U-Pb zircon ages vary from 219 to 214 Ma for the high Sr/Y granites and from 214 to 192 Ma for the low Sr/Y granites. High Sr/Y granites have higher Na 2 O and Sr contents than the low Sr/Y granites. They also lack negative Eu anomalies and are depleted in HREE compared to the low Sr/Y granites. Initial 87 Sr/ 86 Sr ratios and ε Nd values of all the samples roughly overlap with those of Neoproterozoic basement rocks exposed in South Qinling. Including previous studies, we propose that the high and low Sr/Y granites formed by melting of thickened and normal crust, respectively. Close temporal-spatial relationship of the high and low Sr/Y granites with the two-stage migmatization events implies variation of crustal thickness and thermal overprints of the orogenic crust in post-collisional collapse. Following the collision of South Qinling and the Yangtze block prior to 219 Ma, partial melting of the deep crust occurred. The melts migrated upwards to form the high Sr/Y granites. This process occurred rapidly and caused collapse of the thickened crust and carried heat upwards, leading to further partial melting within the shallower crust and formation of the low Sr/Y granites. [ABSTRACT FROM AUTHOR]

The orogenic petrological processes associated with the amalgamation of Rodinia (ca. 1 Ga) and Gondwana (ca. 550 Ma) reflect distinct tectonic dynamics that might have contributed to the contrasting geochemical and biological evolution following the orogenies. In this study, we explore these differences using the time sequence analysis of geochemical proxies in the detrital zircons sourced from the margin of East Gondwana. The zircon Eu anomalies are stronger during the formation of Gondwana than Rodinia, indicating a thicker Gondwana crust than Rodinia; the hinterland of Rodinia (∼35 km) is significantly thinner than its core Grenville Province (55–60 km). The Ce to U and Ti ratio, U/Yb, and ε Hf (t) proxies suggest that the Rodinia assembly was dominated by non-arc intraplate magmatism, consistent with widespread high-temperature magmatism and protracted granulite-facies metamorphism. The thin crust and accordingly, low-elevation terrain, possibly overriding an anomalously hot mantle, limited continental weathering flux, and primary productivity in the Mesoproterozoic oceans. By contrast, the orogenies leading to the assembly of Gondwana may have proceeded in a modern-style plate tectonic manner, resulting in rapid uplift at the Gondwana margin, where voluminous clastic sediments were subsequently recycled and contributed to the post-orogenic magmatism from ca. 500 Ma. This massive crustal reworking is reflected by negative ε Hf (t) values of zircons that contrast ε Hf (t) ∼ 0 in the Mesoproterozoic. The emergence of extensive mountains accelerated erosion and delivered key nutrients that might have fueled the rapid diversification of life forms in the late Precambrian and early Paleozoic. • Zircons record Rodinian within-plate and Gondwanan arc-dominant magmatism. • Gondwanan magmas were more evolved and reflected active plate tectonics. • Distinct tectonic regimes result in a thicker Gondwana margin than that of Rodinia. [ABSTRACT FROM AUTHOR]

We report zircon ages and geochemical composition for mafic dykes that intruded Neoproterozoic volcanic–sedimentary sequences in the southern part of Wudang area, South Qinling. The results indicate that the dykes were emplaced during the Early Paleozoic ( c. 460 Ma) and Early Mesozoic ( c. 220 Ma). The dykes share similar major element composition, but have distinctive trace element pattern and Sr–Nd–Pb isotope distribution. Early Paleozoic mafic dykes are characterized by enrichment in LREEs, LILEs and HFSEs and EM II-type isotopic features. These geochemical features suggest derivation from an OIB-type mantle source that had undergone metasomatism during earlier subduction events. The Early Mesozoic mafic dykes can be subdivided into two distinct geochemical groups. Dykes of Group 1 are depleted in LREEs, LILEs and HFSEs and show depleted isotope compositions, indicating an origin by partial melting of asthenospheric mantle material. Dykes of Group 2 have high Rb-, Ba-, and K-contents and EM I-type isotopic features, suggesting input of lower crustal material to the magma source during Mesozoic subduction. We propose that the Early Paleozoic dykes are related to the opening of an oceanic basin separating South Qinling from the Yangtze Block, while the Early Mesozoic dykes were derived from partial melting of up-welling asthenosphere during the final amalgamation of these two blocks in the Early Mesozoic. A slab break-off model could explain not only the petrogenesis of the Mesozoic mafic dykes, but also the distinct geological features between the Dabie–Sulu and South Qinling orogens. We propose that slab break-off occurred at great depth in the Dabie–Sulu orogen and hence rare magmatism occurred. Whereas in South Qinling the break-off occurred at a shallow depth, the asthenospheric mantle material could rise further up into the overlying mantle where it experienced decompression and melting. As a consequence, crustal sections were heated up to produce extensive granitic magmatism. [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]

Abstract: Origin and genesis of post-collisional mafic–ultramafic rocks in the Dabie orogen of China are controversial issues with respect to Mesozoic transport of mass and energy between mantle and crust. Zircon U–Pb age, whole-rock major and trace elements, mineral and whole-rock oxygen isotopes, and carbon concentrations and isotope compositions of apatite and whole-rock were determined for these igneous rocks in order to find a resolution. The results show that the Dabie mafic–ultramafic rocks are characterized by strong LREE enrichment and negative HFSE (Nb, Zr, Ti and P) anomalies but positive anomalies of Pb and Ba. Zircon U–Pb dating yields consistent ages of 122–128 Ma for magma crystallization and 105–116 Ma for post-magmatic hydrothermal alteration. There is a large variation in oxygen isotope ratios of minerals and their host rocks, with whole-rock δ 18O values of 1.1–6.6‰, clinopyroxene 3.85–5.7‰, plagioclase 2.8–7.3‰, and zircon 3.85–6.04‰. Most of the zircons have δ 18O values different from the normal mantle values. Equilibrium oxygen isotope fractionations between minerals have been preserved for some of the samples, but the others show significant disequilibrium indicating post-magmatic subsolidus alteration. Carbon concentrations and isotope compositions vary widely from 0.03 to 0.18% and from −27.0 to −5.8‰, respectively. Most of the samples are characterized by the low δ 13C values typical of organic carbon. A comparison of the element and isotope data for the Cretaceous mafic–ultramafic rocks with the Triassic metamorphosed eclogites from the Dabie–Sulu orogenic belt shows that they share many geochemical and isotopic features in common, pointing to a genetic relationship in protolith origin between them. No signature of depleted mantle has been detected from Nd and Sr isotopes in the post-collisional igneous rocks. Protoliths of the Cretaceous mafic–ultramafic rocks and the Triassic eclogites are thus considered the mid-Neoproterozoic mafic–ultramafic rocks that were the products of rift magmatism along the northern margin of the Yangtze plate. Partial melting of the subducted lithosphere itself is proposed to produce the post-collisional igneous rocks. The Early Cretaceous superplume event is hypothesized to provide a heat source to trigger the melting of a large scale and a short period beneath the collisionally thickened orogen. [Copyright &y& Elsevier]

The Lantian-Xiaoqinling region, located at the southern margin of the North China Craton (S-NCC), exposes large-scale Late Mesozoic granitoids associated with molybdenum and hydrothermal gold deposits. This study presents zircon U-Pb-Hf isotope, whole-rock element and Sr-Nd-Pb isotope data of granitoids from two representative plutons (Laoniushan and Huashan) of the Lantian-Xiaoqinling region including previous data from the Lantian pluton. Zircon U Pb dating supports a prolonged magmatic history from c. 150 to 130 Ma. Different to the thick continental crust-derived high Sr/Y granitoids from the Dabie Mts., the granitoids of the Lantian-Xiaoqinling region are ordinary calc-alkaline granitoids which show evidence for fractional crystallization, implying no need for the existence of a thick continental crust during magmatism. The plutons share similar high whole-rock initial 87Sr/86Sr values ranging from 0.7070 to 0.7109, but variable ε Nd (t) (−23.4 to −9.0) and zircon ε Hf (t) values (−46.9 to −2.7) as well as continental crust-like initial Pb isotopes with 206Pb/204Pb(t) ratios of 17.1 to 17.9; 207Pb/204Pb(t) of 15.40 to 15.57 and 208Pb/204Pb(t) of 37.6 to 38.35. Nd-Hf-Pb isotopic compositions are more depleted compared to ancient lower NCC crust as represented by the Taihua and Xiong'er Groups and suggest involvement of some juvenile materials into the magma source. Positive correlation between SiO 2 and ε Nd (t) values suggests that the juvenile material was silica-rich with slightly negative ε Nd (t) values. Such material cannot be produced from a mantle source as previously stated. These compositional features make Neoproterozoic continental crust of Yangtze Block a likely source for the juvenile material. It is argued that the juvenile material originated from partial melting of subducted Neoproterozoic continental crust with abundant black shale. We propose that the Late Mesozoic granitoid plutons in the Lantian-Xiaoqinling region stem from a composite source, including rocks similar to the ancient lower NCC crust and a juvenile felsic melt derived from the subducted Yangtze plate. Heat input and melting was triggered by asthenosphere upwelling caused by subduction of the Paleo-Pacific oceanic plate. Unlabelled Image • Late Mesozoic granitoids of the Lantian-Xiaoqinling region are pseudo-adakites. • Subducted Yangtze crust was involved in the granitoid magmas. • Subduction of the Paleo-Pacific plate triggered the heat input and melting. [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]

• Jinan gabbro crystallized at ~900 °C in an emplacement depth of ~15–27 km. • The magma was derived from an enriched lithospheric mantle at ~130 Ma. • This pluton was rapidly uplifted with a cooling rate of ~50 °C/Ma before 120 Ma. • This uplift was related to the lithospheric delamination in eastern North China. The North China Craton underwent exceptional lithospheric thinning. A debate remains as to the mechanism and timing of this thinning partly as a result of the lack of information on the crustal uplift. Mantle-derived mafic rocks can carry key messages of lithospheric thinning and facilitate the determination of the time and mechanism. Gabbroic rocks from the Jinan area in eastern North China were emplaced in the peak period of the thinning and, for this reason, were chosen as the study object. Isotopic ages and P-T conditions of the Jinan gabbro pluton were measured to examine the uplifting and cooling history of the magma. Jinan gabbros were enriched in large ion lithophile elements and large rare earth elements but depleted in high field strength elements without a significant Eu anomaly. Their Sr-Nd-Pb isotopic features suggest that the magma was derived from the partial melting of an enriched lithospheric mantle (EMI). This pluton was emplaced at ~130 Ma, and crystallization temperatures of pyroxene and biotite were 909–1116 °C and 828–952 °C, respectively. The core and rim crystallization pressures of clinopyroxene and plagioclase are ~4.45 kbar and ~2.56–3.91 kbar, respectively. These might record the pressure changes during the uplift process from ~16.5 to 9.5 km. The Rb-Sr isotopic system of biotite was closed at ~121–117 Ma, constrained by the single–grain biotite Rb-Sr ages. This shows that the cooling depth of pluton is ~8.4 ± 2.4 km. Consequently, the pluton was rapidly uplifted from the ~16.5 km to ~8.4 km, at an uplift rate of 0.81 ± 0.24 km/Ma and/or a cooling rate of approximately 50 °C/Ma during 130–120 Ma. This fast uplift was related to the delamination and thinning of the lithosphere that caused activities associated with magmatism and mineralization in eastern North China during the late Mesozoic. [ABSTRACT FROM AUTHOR]