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The Moldanubian zone of the Black Forest, Germany, part of the internal zone of the central European Variscan belt, exposes high-pressure metamorphic rocks as small eclogite lenses in host gneisses. We report zircon U-Pb and PbPb ages and garnet Sm-Nd and Pb-Pb ages for five eclogites. The less mobile trace element contents of these eclogites are similar to those of mid-ocean ridge basalts but have moderate to highly fractionated concentrations of the rare earth elements, enrichments in the incompatible elements, and negative anomalies in the high-field strength elements. Initial ∈[sub Nd] values range from -3 to +1.8, and initial[sup 87]Sr/[sup 86]Sr ratios range from 0.7040 to 0.7062. These characteristics of the eclogites suggest an origin from mantle-derived magmas contaminated either by evolved crustal material during intrusion or altered by fluid before or during eclogitization. A combination of zircon U-Pb and Pb-Pb evaporation dates of the eclogites constrains a magmatic episode between ∼486 and ∼445 Ma. This episode was contemporary with the early Paleozoic mafic to ultramafic magmatism in the eastern part of the Variscan belt and probably represents an early Paleozoic rift-stage product. Garnets subjected to the stepwise acid-leaching method from three eclogites yield Sm-Nd isochron ages of about 348-340 Ma, similar to the dates previously reported. The same garnets give less precise Devonian to Early Carboniferous Pb-Pb isochron ages of 406 ± 31 Ma, 386 ± 21 Ma, and 353 ± 89 Ma, which probably date to an earlier stage of the Variscan convergence. [ABSTRACT FROM AUTHOR]

The major Precambrian crustal growth in the North China Craton (NCC) has been thought to have occurred at ∼2.5 Ga. Here we present secondary ion mass spectroscopy (SIMS) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) zircon U-Pb ages and Hf isotope compositions from dioritic and tonalite-trondhjemite-granodiorite (TTG) gneisses of the Neoarchean-Paleoproterozoic metamorphic terrane in the central NCC. Zircons from the trondhjemitic samples yield emplacement ages at 2,702±7 and 2,722±9 Ma. Those from the dioritic gneiss yield an age of 2,704±14 Ma. The TTG gneisses are characterized by a Na-rich and K-poor (Na/K ratiosp2.7, 2.6) nature; strongly fractionated rare earth element patterns ([La/Yb] p35, 20); high Sr (418‰, 318‰) and Sr/Y (78, 49); low Y N (5.4‰, 6.4‰) and YbN (3.0, 3.6); and low MgO (0.89%, 1.10%), Mg# (47, 42), Cr (39‰, 20‰), and Ni (11‰, 8‰), Nb/ Ta (16, 12), which suggests that magmas were derived from the partial melting of a flatly subducted oceanic slab. The dioritic gneiss shows higher MgO (3.17%), Mg# (50), Cr (44‰), and Ni (40‰) and lower Sr/Y (22) and (La/Yb)N (8) ratios, which suggests contamination with mantle peridotite. All zircon grains from these Neoarchean gneisses yield high positive εHf (t) values that range from ε3.5 to ε7.7 and Hf model ages between 2.70 and 2.85 Ga. We propose that the widespread ∼2.5-Ga plutonic event found elsewhere in the NCC may represent a major reworking (melting) event, whereas the ∼2.7-Ga magmatism likely represents the main crustal growth of the NCC, comparable to those of other cratons worldwide [ABSTRACT FROM AUTHOR]

Numerous late Mesozoic (Late Jurassic to Early Cretaceous) granitic plutons are present along the southern margin of the North China Craton (s-NCC), which belongs to the northernmost tectonic unit of the eastern Qinling orogenic belt. This tectonic unit records multiple tectonothermal and metallogenic events that occurred after continental collision of the North and South China Cratons in the late Early to Middle Triassic. This study reports the zircon U-Pb ages and the whole-rock and apatite geochemical compositions of the Taishanmiao granite, one of the largest late Mesozoic plutons in eastern Qinling. Three phases of this granite, emplaced between ∼125 and ∼113 Ma, are characterized by uniformly high SiO2 and K2O but low CaO, TFe2O3, and MgO contents and enriched Nd isotopic composition with initial ε Nd values of −13.5 to −12.7. Geochemical features reveal that these are A-type granites derived from partial melting mainly of ancient crust. Temperatures obtained from Ti-in-zircon thermometry and oxygen fugacity (f O2) data indicate that the magma(s) formed at high crystallization temperatures (∼800°–840°C) and f O2 levels (fayalite–magnetite–quartz [FMQ] buffer −1.5 to +1.5). Comparison with neighboring granites, such as the ∼150–130 Ma adakitic Heyu granite and the ∼115 Ma Donggou ore-bearing granite porphyry, implies that the Heyu granite formed from thickened crust and that the Donggou granite porphyry and Taishanmiao granite likely originated from a consistent magma system during the crustal thinning that occurred ∼125–113 Ma, except the porphyry rock was more evolved. This finding implies that their uniform magma chamber could provide sufficient metals and associated materials and even energy for the Donggou Mo deposit. [ABSTRACT FROM AUTHOR]

The Qinling orogenic belt in central China resulted fromthe final collision of theNorth China and South China blocks in the Triassic. Early Mesozoic granitoids are widespread in the Qinling orogen. Their genesis can provide key constraints on the tectonic evolution of this orogenic belt. The Late Triassic Baoji pluton, located in the North Qinling unit, consists of granodiorites, monzogranites, quartz monzodiorites, and K-feldspar granites. U-Pb zircon dating via the laser ablation ICP-MS technique yields ages of 217.4 ± 1.4, 212.3 ± 1.8, 212.6 ± 1.6, and 195.1 ± 2.0 Ma for granodiorites, monzogranites, quartz monzodiorites, and K-feldspar granites, respectively. The granitoids have high-K calc-alkaline, metaluminous to weakly peraluminous composition(s). Silica contents increase andMg, Fe, Ti, Ca, and P contents decrease from quartz monzodiorites through granodiorites to monzogranites and K-feldspar granites. Combining our findings with evidence from whole-rock Sr-Nd and zircon Hf isotopes, we suggest that the granodiorites formed by magma-mixing processes involving metasomatized lithospheric mantle and Mesoproterozoic crustal material. Themonzogranites record the contribution of an asthenospheric mantle source. The quartzmonzodiorites were derived fromametasomatized lithosphericmantle source. Partialmelting of crustal lithologies generated the K-feldspar granites. It is argued that the Baoji pluton formed in a late-collision 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]

Post-Marinoan sedimentary rocks from the Yangtze block in South China were investigated to seek constraints on their provenance, genetic relationship with paleoclimate, depositional environment, and changes. Sedimentary rocks from the Doushantuo Formation in the Jiulongwan section of the Yangtze block were collected for whole-rock trace elements and Sr-Nd isotopic analyses. Flat-to-slightly middle rare earth element (REE)–enriched REE-plus-yttrium patterns, negative-to-positive Ce anomalies (Ce=Ce* of 0.86–1.40), positive La anomalies (La=La* of 1.02–1.42), and suprachondritic Y/Ho ratios (36.8–49.5) obtained for the Doushantuo cap carbonates indicate their deposition in a fluctuating inner-shelf setting where freshwater and seawater mixed together and the influence of hydrothermal fluid from the seafloor is absent. All Doushantuo carbonates and shales have variable Sr isotopic compositions, with initial Sr isotopic ratios (0.704030–0.712720) that support significant river-water contribution during the deposition of the Doushantuo Formation. Samples of the Doushantuo Formation collected across sedimentary profiles show distinct variations in Nd isotopic compositions and diagnostic trace elemental ratios (Th/Sc). The cap carbonates received significant input from a broad continental area undergoing extensive weathering immediately after the cease of the glaciation era. In contrast, the upper Doushantuo Formation sediments received more mature detritus from the nearby Archean Kongling complex, reflecting receding sea levels. In contrast to the negative Ce anomalies observed in lower Doushantuo rocks, negligible Ce anomalies in upper Doushantuo rocks suggest an anoxic setting, in agreement with the growth of phosphatic concretions and the presence of framboids of pyrite and a higher concentration of organic matter. [ABSTRACT FROM AUTHOR]

Zircon megacrysts found in basalts may provide a window into metasomatic processes and element transport in the upper mantle. However, little is known about the formation conditions of these zircons. Here we report U-Pb ages, Hf-O isotope compositions, trace element data, and mineral inclusion analyses for six large fragments of zircon megacrysts from the Gem village in northeastern Cambodia. The zircons have low contents of U, Th, Y, P, and rare earth elements (REEs; 130-288 ppm). The normalized REE pattern is characterized by a steeply rising slope from light REEs to heavy REEs and positive Ce anomalies. Secondary ion mass spectrometer isotopic analyses on the zircon megacrysts yield a mean U-Pb age of 0.98 ± 0.04 Ma (2σ) and homogeneous oxygen isotopic composition with a mean δ18 O value of 5.0‰ ± 0.18‰ (2σ), identical to the δ18 O mantle value. The 176 Hf/177 Hf values range from 0.282970 ± 0.000024 (2σ) to 0.283040 ± 0.000016 (2σ), with εHf (0.98 Ma) values of 6.6-9.0, obtained by the laser ablation-multicollector-inductively coupled plasma mass spectrometry technique, further points to the origin of the grains in the depleted mantle. The zircon megacrysts contain apatite inclusions and a reaction rim composed of baddeleyite and Al-Fe-Zr-silicate glass. This leads us to conclude that mantle zircon crystallized during a metasomatic event from phosphate-rich fluids and/or silicate melts enriched in zirconium. [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]

The Edong-Jiurui district is located more than 1000 km from the current Pacific subduction zone. It is part of the well-known middle and lower Yangtze River Cu-Fe-Au belt in central eastern China. Cu mineralization in this area is spatially and temporally associated with Late Mesozoic magmatic rocks. These rocks exhibit geochemical features of adakites, but their origin is not yet fully understood. To explore the relationship between Cu mineralization and Mesozoic magmatism, we report geochemical, Sr-Nd-Pb isotopic, and zircon U-Pb age data from adakitic rocks in the Edong-Jiurui area. Zircon U-Pb ages point to a protracted period of magmatic activity from 151 to 139 Ma. This time span coincides with the Cu mineralization (146-137 Ma) in the middle and lower Yangtze River belt. Adakitic features of the rocks are displayed by high contents of SiO2, Al2 O3, Na2O, and Sr; enrichment of light rare earth elements (REEs) and large-ion lithophile elements; depletion of heavy REEs; positive Sr and negative Nb, Ta, and Ti anomalies; and high Sr/Y and La/Yb ratios. We favor a model of melt segregation from a plagioclase-free and garnetbearing residue. Compared to non-Cu-bearing Mesozoic adakitic rocks in the Dabie terrane, adakitic rocks in the Edong-Jiurui area have higher initial εNd values (-3.4 to -6.3), Pb isotopic ratios, and Th contents and lower Pb/Ce values. Altogether, these features indicate that the melts were probably derived from subducted ocean mixed with marine sediment. [ABSTRACT FROM AUTHOR]