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The geological evolution of the Proto-Tethys Ocean remains vague. The Tianshuihai Terrane (TSHT), a subterrane of the West Kunlun, distributed to the south of the Proto-Tethys Ocean during the Early Palaeozoic, records abundant information on the geological evolution of the Proto-Tethys Ocean. In this study, we reported SHRIMP and LA-ICP-MS zircon U–Pb ages, whole-rock major and trace element composition data, and Sr-Nd-Hf isotopes of a suite of monzogranites and the monzonitic-syenitic enclaves in Zankan and syenogranites in Laobing regions of the TSHT, West Kunlun Orogenic Belt. The syenogranites in the Laobing region yielded SHRIMP zircon U-Pb ages of 550.4 ± 6.4 Ma to 547.5 ± 5.3 Ma, which were the earliest age records of subduction-related magmatism in the TSHT during the Late Neoproterozoic-Early Palaeozoic. The host monzogranites in the Zankan area yielded SHRIMP and LA-ICP-MS zircon U-Pb ages of 542.6 ± 8.4 Ma to 540.5 ± 2.8 Ma, which is coeval with the monzonitic-syenitic enclaves ages of 533.8 ± 3.4 Ma to 534.7 ± 3.0 Ma. We speculated that an active margin developed along the TSHT during the Cambrian and the initial subduction of the Proto-Tethys oceanic slab must have occurred prior to the Early Cambrian (>550 Ma). The TSHT and the Southern Kunlun Terrane were distributed between the northern margin of the East Gondwana continent and the Tarim Block. Additionally, the coexistence of two branches of the Proto-Tethys Ocean represented by the Kangxiwa Fault and Kudi Ophiolite Belt during the Early Palaeozoic. Based on the chronological statistics of micro-continental blocks in the northern margin of the East Gondwana continent, subduction of the Proto-Tethys Ocean could be diachronous, initially originating in the northwestern part of the East Gondwana continent, and gradually propagating to the east of the East Gondwana continent. [ABSTRACT FROM AUTHOR]

Early Cretaceous adakite or adakitic plutons are widely distributed in central eastern China, e.g. lower Yangtze river belt (LYRB), the south Tan-Lu fault (STLF), and the Dabie orogen. Their genesis, however, remains controversial. In this contribution, we present detailed geochemical and geochronological study on the Guandian pluton in central Anhui Province, eastern China, which has been formerly regarded as a part of the north belt in the LYRB and lately classified in the STLF. Namely, it is located near the boundary between ridge subduction related slab melting and partial melting of lower continental crust (LCC). The Guandian pluton consists of quartz monzonite and is metaluminous and high-K calc-alkaline according to the chemical composition. The samples show high SiO2 (59.15-62.32%), Al2O3 (14.51-15.39%), Sr (892-1184 ppm), Sr/Y (56.74-86.32), and low Y (12.65-18.05 ppm), similar to typical geochemical features of adakite. The Guandian adakitic rocks also exhibit high K2O (2.88-3.86%), MgO (3.89-5.24%), and Mg# (55-60), negative anomalies of high field strength elements (e.g. Nb, Ta, and Ti), and positive anomalies of Ba, Pb, and Sr. LA-ICP-MS zircon U-Pb dating yielded a weighted average age of 129.2 ± 0.7 Ma. Calculations of zircon Ce4+/Ce3+ (6.97-145) and (Eu/Eu*)N (0.23-0.42) on the basis of in situ zircon trace element analysis indicate that the magma had a lower oxygen fugacity relative to the ore-bearing adakites in the LYRB and Dexing, which is consistent with the fact of ore-barren in the research area. In combination with previous research, we propose that Guandian adakitic pluton was formed by partial melting of delaminated LCC triggered by Early Cretaceous ridge subduction of the Pacific and Izanagi plates. During ridge subduction, physical erosion destructed the thickened LCC and resulted in delamination, while thermal erosion facilitated partial melting of the delaminated LCC. [ABSTRACT FROM AUTHOR]

Large-scale Cu-Au mineralization is associated with Late Mesozoic intrusive rocks in the Tongling region of eastern China, which mainly comprise pyroxene monzodiorite, quartz monzodiorite, and granodiorite. To constrain the petrogenesis of the intrusive rocks and Cu-Au mineralization, detailed analyses of the geochronology, apatite in situ geochemistry, whole-rock geochemistry, and zircon Hf isotopic compositions were performed. Magmatic zircons from pyroxene monzodiorites, quartz monzodiorites, and granodiorites yield U-Pb ages of 136-149 Ma, 136-146 Ma, and 138-152 Ma, respectively, indicating that their formation ages are contemporaneous. Quartz monzodiorites and granodiorites (SiO2 = 57.9-69.5 wt.%) are highly potassic calc-alkaline rocks with adakitic affinity and have low MgO and Y contents, low zircon εHf(t) values (−11.7 to −39.0), high apatite Cl contents (>0.2 wt.%), and log fO2 values (−23.2 to −8.23), indicating that they may have formed when metasomatized mantle-derived magmas mixed with slab-derived magmas before undergoing crustal assimilation and fractional crystallization. Pyroxene monzodiorites (SiO2 = 48.4-53.0 wt.%) are shoshonitic and record high MgO, P2O5, and Y contents, high zircon εHf(t) values (1.55 to −7.87), high oxygen fugacity, low Nb and Ta contents, and low apatite Cl contents (mainly <0.2 wt.%), suggesting that they were primarily derived from a metasomatized lithospheric mantle-derived magma that experienced the assimilation of lower crustal materials. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization of the Tongling region resulted from the partial melting of the subducted oceanic slab in an oxidizing environment. [ABSTRACT FROM AUTHOR]

The Anqing region in Lower Yangtze River metallogenic belt is one of the important Cu polymetal producers in China. The origin of Cu polymetallic deposits in the region is closely related to Early Cretaceous adakitic intrusions. To constrain the petrogenetic and metallogenic significance of the adakitic rocks, a detailed geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic study was performed. The Anqing adakitic rocks (SiO2 = 57.4-64.2 wt.%) consist mainly of quartz monzodiorite, formed at 138.2 ± 1.7 Ma (Mean Standard Weighted Deviation (MSWD) = 0.61). They have high MgO, Al2O3, Sr, and low Rb, Y, Yb contents, together with high Sr/Y (50.5-222) and La/Yb (31.9-46.9) ratios. They also show negative whole-rock εNd(t) (−9.8 to −8.5) and zircon εHf(t) (−10.0 to −5.4), and high oxygen fugacity (mainly −17.0 to −8.01) values and radiogenic Pb isotopic compositions with (206Pb/204Pb)i = 17.692-17.884, (207Pb/204Pb)i = 15.413-15.511, and (208Pb/204Pb)i = 37.611-37.943. Coupled with negative Nb-Ta anomalies, low K2O/Na2O ratios (0.39-0.62), and high Mg# values (0.44-0.71), these data suggest the adakitic rocks and associated large-scale Cu-Au mineralization of the Anqing region resulted from partial melting of the high oxidized subducted oceanic crust. Addition of mantle-derived magmas and assimilation of crustal materials during emplacement are also possible. [ABSTRACT FROM AUTHOR]

The early tectonic evolution of the Lhasa Terrane remains poorly understood, although evidence for a substantial prehistory has been reported recently. We have carried out in situ zircon U-Pb dating and Hf-O isotopes of late Early Cretaceous monzogranites and get a surprising package of inherited zircons, not only because of their age profile, but also because the oldest Palaeoarchaean zircons are euhedral. The discovery of Palaeoarchaean euhedral zircons in the region suggests the presence of extremely old rocks in Tibet. Zircons from the Nagqu monzogranite yield five age peaks at ~3.45 Ga, ~2.56 Ga, ~1.76 Ga, ~900 Ma, and ~111 Ma. They have large variations in εHf(t) values (−45.1-9.2) and old Hf model ages (924-3935 Ma), with variable δ18O values of −5.80-9.64. Palaeoarchaean zircons (~3.20-3.45 Ga) are euhedral with magmatic zircon characteristics. One of the grains has negative εHf(t) value (−4.8), old Hf model age (3935 Ma), and high positive δ18O value (7.27), which suggests an ancient crustal origin. The source of Palaeoarchaean euhedral zircons should be proximal to prevent long-distance transport and abrasion, whereas the late Early Cretaceous monzogranites are I-type. Thus, Palaeoarchaean euhedral zircons are most likely captured from the country rocks by assimilation at depth or may be relics of previous magmatic zircons. Notwithstanding their exact history, Palaeoarchaean euhedral zircons indicate Palaeoarchaean materials near Nagqu in the Tibetan Plateau. The inherited zircons also experienced a Late Palaeoproterozoic event (~1.76 Ga) likely related to the evolution of the India block. The peak at ~900 Ma suggests affinity to the Qiangtang and Himalaya blocks. [ABSTRACT FROM AUTHOR]

Late Mesozoic granitoids are widely distributed in southern Anhui Province, southeastern China, which also contains significant W–Mo–Cu mineralization. This study presents new geochronological and geochemical data that reveal the petrogenesis and tectonic affinity of the granitoids in this region. These granitoids can be divided into a high-K calc-alkaline and peraluminous I-type granodiorites, and an alkaline and metaluminous A-type granites, with zircon U–Pb dating indicating that they formed at 150–138 and 133–124 Ma, respectively. The early stage I-type granodiorites are adakitic, enriched in the light rare earth elements, and depleted in Nb, Ta, P, and Ti. They have negative zircon εHf(t) values (–19.8 to –2.5) that correspond to Hf crustal model ages of 2.4–1.4 Ga. These early stage granodiorites were derived from partial melting of thickened Palaeoproterozoic–Mesoproterozoic lower crust. The late-stage A-type granites with strong depletion in Sr, P, and Ti, contain higher Zr, Y, and Yb contents, higher zircon εHf(t) values (–1.5 to +2.1), and younger zircon Hf model ages (1.1–1.3 Ga) than the early stage granodiorites. The geochemistry of these A-type granites indicates they were likely generated by the reworking of Mesoproterozoic to Neoproterozoic juvenile crustal material that experienced the fractional crystallization of plagioclase and accessory minerals. Combining these data with other geological data from the study area indicates that the early stage granodiorites formed in a continental arc setting, whereas the late-stage granites formed in an extensional setting associated with roll-back of the subducted Palaeo-Pacific slab. The results indicate that zircon Ce4+/Ce3+ value can provide useful insight into oxygen fugacity conditions during magmatism. [ABSTRACT FROM AUTHOR]

LA-ICPMS zircon U-Pb dating has been greatly advanced and widely applied in the past decade because it is a cheap and fast technique. The internal error of LA-ICPMS zircon U-Pb dating can be better than 1%, but reproducibility (accuracy) is relatively poor. In in order to quantitatively assess the accuracy of this technique, zircons from two dioritic rocks, a Mesozoic dioritic microgranular enclave (FS06) and a Neoproterozoic diorite (WC09-32), were dated independently in eight laboratories using SIMS and LA-ICPMS. Results of three SIMS analyses on FS06 and WC09-2 are indistinguishable within error and give a best estimate of the crystallization age of 132.2 and 760.5 Ma (reproducibility is ∼1%, 2RSD), respectively. Zircon U-Pb ages determined by LA-ICPMS in six laboratories vary from 128.3±1.0 to 135.0±0.9 Ma (2SE) for FS06 and from 742.9±3.1 to 777.8±4.7 Ma (2SE) for WC09-32, suggesting a reproducibility of ∼4% (2RSD). Uncertainty produced during LA-ICPMS zircon U-Pb analyses comes from multiple sources, including uncertainty in the isotopic ratio measurements, uncertainty in the fractionation factor calculation using an external standard, uncertainty in the age determination as a result of common lead correction, age uncertainty of the external standards and uncertainty in the data reduction. Result of our study suggests that the uncertainty of LA-ICPMS zircon U-Pb dating is approximately 4% (2RSD). The uncertainty in age determination must be considered in order to interpret LA-ICPMS zircon U-Pb data rationally. [ABSTRACT FROM AUTHOR]

The Dongping gold deposit is a large deposit with total gold reserves of >100tons. It is located at the northern margin of the North China Craton, northwestern Hebei province, China. The ore-bodies are hosted by the Devonian Shuiquangou syenite complex and consist mainly of auriferous quartz veins and disseminated ore in the altered and silicified syenite. U–Pb dating of zircon from hornblende syenite on the western margin of the complex yields a crystallization age of 400±3.5Ma (MSWD=0.018). Morphology, cathodoluminescence imaging and geochemical classifications of zircon from the first stage of disseminated ore and gray auriferous quartz veins, and from later stage, low grade quartz veins point to their newly crystallized hydrothermal origin. The hydrothermal zircon from the disseminated ore and auriferous gray quartz vein are dated at 389±1.0Ma and 385±5.7Ma, respectively, which are detectably younger than but close to the crystallization age of the syenite complex and might have been formed by post-magmatic hydrothermal processes. Both types of ore are dominant in the ore deposit, and we propose that the pervasive, post-magmatic hydrothermal alteration is the main ore forming stage. Hydrothermal zircon from a low grade auriferous quartz vein yields a U–Pb age of ~140Ma, interpreted as forming during a younger period of superimposed Yanshanian hydrothermal mineralization. Thus, the ore of the Dongping gold mine represents a post-magmatic Devonian hydrothermal ore deposit with Jurassic–Cretaceous hydrothermal overprinting. [ABSTRACT FROM AUTHOR]

Xihuashan tungsten deposit is one of the earliest explored tungsten deposits in southeastern China. It is a vein type deposit genetically associated with the Xihuashan granite pluton. Here we report new dating and zircon geochemistry results. Re-Os isotopic dating for molybdenite intergrowth with wolframite in the oldest generation of the Xihuashan pluton yielded an isochron age of 157.0 ± 2.5 Ma (2σ). Zircon U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating shows that the pluton crystallized at 155.7 ± 2.2 Ma (2σ). This age is similar to the molybdenite Re-Os age for the ore deposit within error. This, together with published data, suggests that the major W(Mo)-Sn mineralization occurred between 160-150 Ma in southeastern China. These deposits constitute a major part of the magmatic-metallogenic belt of eastern Nanlin. The lower Re content in molybdenite of the Xihuashan tungsten deposit shows crustal origin for the ore-forming material. The limited direct contributions from the subducting slab for the tungsten mineralization in the Nanling region suggest a change of the style of the paleo-Pacific plate beneath southeastern China. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Huangmeijian Pluton is an A-type granite located on the northern bank of the Lower Yangtze River in Anhui Province, east-central China. It intruded the SE edge of the Early Cretaceous Luzong volcanic basin. The moderate- to coarse-grained granite is mainly composed of alkali feldspar, plagioclase, and quartz and has a typical A-type geochemical signature. LA-ICP-MS zircon dating yielded a weighted mean 206Pb/238U age of 127.1 ± 1.4 Ma, similar to other A-type granites in the Lower Yangtze River belt, indicating an Early Cretaceous extensional environment. Temperatures calculated using the Ti-in-zircon thermometer suggest that the magma formed under high-temperature conditions (720-880°C). The low calculated Ce(IV)/Ce(III) ratio based on zircon rare earth element patterns indicates low oxygen fugacity for this A-type magma. Previous studies suggested that eastern China was an active plate margin related to the Early Cretaceous subduction of the Pacific and Izanagi plates. The ridge between these two plates probably passed under the Lower Yangtze River belt, forming A-type granites and adakites. The Huangmeijian Pluton is roughly the same age within error but is marginally older than the Baijuhuajian A-type granite in the eastern part of the Lower Yangtze River belt. A-type granite genesis in the Lower Yangtze River belt only lasted for 2-3 million years and slightly predates the transition from regional extension to compression. All these can be plausibly interpreted by the ridge subduction model, that is, A-type granites formed because of mantle upwelling through the slab window during subduction of the ridge separating the Pacific and Izanagi plates. [ABSTRACT FROM AUTHOR]

Mesozoic granitoids are widespread in the Qinling-Dabie-Sulu orogenic belt. Precise U-Pb dating on these granitoids can reveal the evolution of the continental collision orogen and thus provide information on the nature of magma sources. This study presents zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for two intrusions at Changba and Huangzhuguan in western Qinling. Zircon U-Pb ages for central and marginal phases of the Huangzhuguang intrusion are 214±1 Ma and 213±3 Ma, respectively. Zircons from the Changba intrusion yield a dominant cluster with an U-Pb age of 213±2 Ma. Collectively, these ages are younger than ages of 220 to 240 Ma for ultrahigh-pressure metamorphism due to the continental collision between the South China Block and the North China Block, corresponding to syn-exhumation magmatism. Some inherited zircons occur in the Changba intrusion, yielding a weighted mean of 206Pb/238U ages at 757±14 Ma. This indicates that the Changba intrusion has the crustal source of mid-Neoproterozoic ages and a tectonic affinity to the South China Block. Geochemically, the two intrusuons are both rich in LILE and LREE but depleted in HFSE and HREE, similar to arc-type igneous rocks. The Huangzhuguang intrusion exhibits linear correlations between SiO2 and the other major oxides, implying chemical evolution from a cognate magma source. It contains mafic enclaves, suggesting possible mixing of felsic-mafic magmas. The Changba granite is rich in Si and K but poor in Fe and Mg as well as has a high value of Fe*, suggesting strong differentiation of granitic magma. Therefore, the two intrusions were derived from the Late Triassic anatexis of the continental crust of different compositions in the northern margin of South China Block. This process may be coupled with exhumation of the subducted continental crust in the stage of late collision. [ABSTRACT FROM AUTHOR]

Abstract SHRIMP U–Pb dating and laser ablation ICP-MS trace element analyses of zircon from four eclogite samples from the north-western Dabie Mountains, central China, provide evidence for two eclogite facies metamorphic events. Three samples from the Huwan shear zone yield indistinguishable late Carboniferous metamorphic ages of 312 ± 5, 307 ± 4 and 311 ± 17 Ma, with a mean age of 309 ± 3 Ma. One sample from the Hong'an Group, 1 km south of the shear zone yields a late Triassic age of 232 ± 10 Ma, similar to the age of ultra-high pressure (UHP) metamorphism in the east Qinling–Dabie orogenic belt. REE and other trace element compositions of the zircon from two of the Huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase, namely in the eclogite facies, an interpretation supported by the presence of garnet, omphacite and phengite inclusions. Zircon also grew during later retrogression. Zircon cores from the Huwan shear zone have Ordovician to Devonian (440–350 Ma) ages, flat to steep heavy-REE patterns, negative Eu anomalies, and in some cases plagioclase inclusions, indicative of derivation from North China Block igneous and low pressure metamorphic source rocks. Cores from Hong'an Group zircon are Neoproterozoic (780–610 Ma), consistent with derivation from the South China Block. In the western Dabie Mountains, the first stage of the collision between the North and South China Blocks took place in the Carboniferous along a suture north of the Huwan shear zone. The major Triassic continent–continent collision occurred along a suture at the southern boundary of the shear zone. The first collision produced local eclogite facies metamorphism in the Huwan shear zone. The second produced widespread eclogite facies metamorphism throughout the Dabie Mountains–Sulu terrane and a lower grade overprint in the shear zone. [ABSTRACT FROM AUTHOR]

• Th-U mineralized dikes of Ra's Abdah have complex morphology. • Dikes and hosting granite LA-ICP-MS dating yield 597 ± 15 Ma and 663.2 ± 8.4 Ma. • Dikes and hosting granite have common parental magma sources. • Fractional crystallization produced dikes followed older granites by 66 Ma. • Maximum eU and eTh contents of syenogranitic dikes are 1782 and 7140.5 ppm. During the transition from compressional to extensional-related magmatism, at Ra's Abdah area of the northern Eastern Desert of Egypt, Ediacaran uraniferous syenogranite dikes with complex morphology sent offshoots into Cryogenian arc granitoids. This study defines new tectonic environment of these dikes and suggests their emplacement timing before the Egyptian late-collision granite intrusions. U–Pb zircon dating for Ra's Abdah dikes and arc granitoids yielded ages 597 ± 15 and 663.2 ± 8.4 Ma respectively; that extended the age of late Precambrian post-orogenic dikes in the Egyptian Nubian Shield to 597 ± 15 Ma. Zircons from dikes show significant enrichment of Th and U; while zircons from arc granitoids display typical igneous zircon patterns with Th and U enrichment but significant negative Nb, La, Pb and Sr anomalies. Average calculated zircon temperature crystallization of Ra's Abdah dikes is 698 °C whereas of the granitoids is 713 °C. Similar geochemical behavior of some individual trace elements and REE in zircons from dikes and host rocks intimates identical magma source (partial melting of subducted oceanic crust and its overlying magmatic wedge intercalated with older continental crust). High fractional crystallization of the parent magma after the first pulse managed the change from arc granitoids magma with high f O 2 values to syenogranite dikes phase with lower f O 2 following the transformation from a transpressional to an extensional tectonic. Volatile complexing in late-magmatic stage, mineral fractionation and concomitant zircon crystallization would increase all REE in the residual melt with special HREE enrichment and LREE elimination in zircon of dikes. The radioactive mineralization of dikes (Averaging eU = 124.7 ppm; eTh = 263.9 ppm) are syn -genetic followed by supergene enrichment. Suggested model explains the multistage propagation of complex morphology dikes by filling, opening and increasing expansibility of inclined or perpendicular pre-existing fracture framework. [ABSTRACT FROM AUTHOR]

• Ages of Cu-Mo polymetallic deposits and the granodiorites (porphyries) in the Chizhou region are simultaneous; • The granodiorite (porphyry) are a high-K calc-alkaline I-type granodiorite; • The granodiorites formed from a mixed magma; • The formation of Cu-Mo polymetallic deposits depends on slab-derived Cl-enriched fluids, an oxidizing mixed source. The Cu-Mo polymetallic deposits are widespread in the Chizhou region, the Middle and Lower Yangtze River metallogenic belt, eastern China, but the formation of Cu-Mo polymetallic deposits remains unclear. Geochronological, geochemical and Sr-Nd-Hf isotopic compositions of the Cu-Mo polymetallic deposits in the Chizhou region are systemically investigated to reveal the formation of Cu-Mo polymetallic deposits and petrogenesis of the granodiorite (porphyry). The geochronological dating results show the formation ages of Cu-Mo polymetallic deposits (molybdenite Re-Os age, 151–148 Ma) and the granodiorites (porphyries) (zircon U-Pb age, 150–146 Ma) in the Chizhou region are simultaneous (within error). The Chizhou granodiorites (porphyries) (SiO 2 = 62.9–65.7 wt%) are high-K calc-alkaline peraluminous I-type granodiorites. They have high Mg# (mainly >40) values and low Na 2 O (<4.3 wt%) contents, negative whole-rock ε Nd (t) (−5.83 to −5.71) and zircon ε Hf (t) (−12.7 to −3.03) values, high apatite Cl contents (>0.2 wt%), and high log fO 2 values (−28.3 to −6.22). The distinctly chemical and isotopic compositions indicate that the Chizhou granodiorites formed from metasomatized mantle-derived magmas mixing with Neoproterozoic crustal components. The results indicate that the formation of the Cu-Mo polymetallic deposits in the Chizhou region may depend on the slab-derived Cl-enriched fluids, an oxidizing environment and a mantle-crust mixed source. [ABSTRACT FROM AUTHOR]

The South China Block preserves important imprints of Neoproterozoic intraplate magmatism in a continental setting associated with the amalgamation of the Yangtze and Cathaysia sub-blocks. Here we investigate the Fuchashan Complex exposed to the east of the NE to NNE trending Tan-Lu Fault (TLF) that dissects the North China Craton (NCC) and South China Block (SCB) in East China. We performed an integrated geochemical and geochronologic study on the basaltic to granitic rocks from the complex. Most of the zircons from one amphibolite, two diorites and one granitoid are characterized by oscillatory zoning with homogeneous cores, high Th/U ratios, variable negative Eu anomalies, and extremely HREE-enriched patterns, attesting to magmatic origin. Zircons from the four samples yield consistent Neoproterozoic ages (ca. 794–812 Ma), correlating with the widespread bimodal rift magmatism along the northern margin of SCB, possibly related to the Mid-Neoproterozoic breakup of the supercontinent Rodinia. The zircons from amphibolites show negative ɛ Hf ( t ) values of −16.4 and −8.3 and Hf model ages of 1699 ± 14 Ma and 2023 ± 10 Ma, indicating origin from partial melting of Paleoproterozoic enriched mantle. Their low SiO 2 (48.28–51.75 wt%) contents also support mantle affinity. Furthermore, their high Mg numbers (54–60), and Cr (90–190 ppm) and Ni (31.6–51.1 ppm) content indicate primary and less evolved source magma. The markedly negative zircon ɛ Hf ( t ) values in the diorites and granitoids suggest partial melting of the Neoarchean to Paleoproterozoic lower crust. The extremely low zircon ɛ Hf ( t ) of −26.5 from a granitoid suggest reworking of Mesoarchean basement. A probable scenario for the generation of the extensive ca. 800 Ma bimodal suite in this region is the widespread Mid-Neoproterozoic intraplate magmatism triggered by asthenosphere upwelling, resulting in the partial melting of enriched subcontinental lithospheric mantle and underplating of mafic magma. Heat input from this magma led to further melting of lower continental crust at depths of 35–40 km, and the melt compositions controlled by fractionation of clinopyroxene and minor plagioclase under high fO 2 conditions. [ABSTRACT FROM AUTHOR]

The Fangshan intrusive suite is a composite pluton in the North China Craton that resulted from incremental assembly of small magma batches. The pluton consists of four intrusive units with abundant mafic enclaves. Here we clarify its crystallisation history through zircon U Pb dating, which indicates prolonged crystallisation of each intrusive unit at upper-crustal levels between 132.5 and 128.7 Ma. The magmas were episodically extracted from a deep storage area and ascended to the final intrusion level at a palaeo-depth of 10–16 km. Zircon trace element and Hf isotopic compositions and Ti-in-zircon temperature of the four intrusive units and mafic enclaves show significant differences and suggest that their crystallisation occurred in isotopically and chemically diverse magma batches. These magma batches formed in the lower crust from the mingling and mixing of various proportions of residual melts, derived from the fractional crystallisation of mafic magmas, with crustal partial melts at high temperatures. Four type of zircons were observed in mafic enclaves based on a simple textural classification, including antecrysts (type 1), xenocrysts (type 2 and type 3), and recrystallised zircon (type 4). Type 1 zircons were not formed at the emplacement level and are "antecrystic", having formed at a deeper, hotter level and been entrained into the ascending melts. Most type 2 zircons were captured from coarse-grained monzonite, and a very small number of grains were sourced from porphyritic granodiorite. Type 3 zircons display a core-rim texture, illustrating that xenocrysts may successively grow in mafic melts. Type 4 zircons display patchy zoning that represents a disequilibrium texture, manifested by the replacement of U–Th–REE-rich zircon by U–Th–REE-poor zircon, which occurred in response to magma mixing between mafic and felsic melts. This study shows that zircon chemistry coupled with detailed textural analyses can provide a powerful tool to elucidate the complex evolution of a magmatic system. • A model for the incremental growth by repeated magma injections is proposed. • The zircons may crystallize at different times and levels in the plumbing system. • Trace elements in zircons can be used to distinguish diverse magma batches. • The four type zircons from mafic enclaves recorded the entire evolutionary history. • The shallow plutons stands in strong causal interrelation with a deep source. [ABSTRACT FROM AUTHOR]

Abstract: Nanling is the largest W–Sn mineralization belt in the world, the formation of which remains obscure. In contrast to most other deposits in the Nanling region, Dabaoshan is a polymetallic deposit, located in north Guangdong province, southeastern China. Porphyry Mo deposit was found in 2008 in the north part of Dabaoshan ore district. Here we report zircon and molybdenite ages and geochemistry results of zircon and apatite. Zircon U–Pb LA–ICP-MS dating shows that the porphyry Mo deposit formed at 167.0±2.5Ma (2σ), which is identical to the molybdenite Re–Os age for the ore deposit (166±1Ma) within error. These ages are marginally older than the major W–Sn mineralization event in the Nanling region (160±5Ma). Zircon grains associated with the Dabaoshan porphyry Mo deposit have high Ce(IV)/Ce(III) values (356–1300), which indicate high oxygen fugacity, likely associated with plate subduction. Apatite from the Dabaoshan porphyry has high and varied F with low Cl concentrations, suggesting that it formed in a F-enriched environment with high F/Cl components in the magma source. This is consistent with abundant high-F granites in the Nanling region. Chlorine is highly mobile at the early stage of plate subduction. In contrast, F is mainly hosted by minerals that are fairly stable at shallow depths, e.g., apatite, phengite, such that is much less mobile than Cl before phengite decomposition. Therefore, the F/Cl ratio increases with increasing distance from the subduction zone. Compared to the Dexing porphyry deposit to the northeast, the Dabaoshan porphyry has lower Ce(IV)/Ce(III) and high F/Cl. It is also about 5Ma younger than the Dexing porphyry Cu deposits. All these phenomena can be plausibly interpreted by slab rollback of the obliquely subducted Pacific plate in the Jurassic. We propose that the subducting slab reached the Dabaoshan region before ~167Ma, through a “flat” subduction regime, resulted in high oxygen fugacity in the magmas, which is followed by abrupt slab rollback. The onset of slab rollback is the most favorable event that leads to decomposition of phengite in the subducting slab because of abruptly elevated temperatures, releases F and consequently increases F/Cl in magmas. The Ti-in-zircon temperatures of the mineralized porphyry range from 608 to 641°C, with an average of about 630±15°C, whereas average temperature of the barren granodiorite nearby is 700±9°C. Considering that the Mo porphyry deposit appears as an egg shell surrounding the granodiorite and the geochemical behavior of Mo, we propose that the mineralization was related to the assimilation of metamorphosed sedimentary rocks by the granodiorite. [Copyright &y& Elsevier]

Abstract: Zircon and apatite fission-track (FT) analyses were used to reveal the exhumation of Phanerozoic granitoid intrusions in the Dahinggan Mountains, northeastern China. Zircon FT ages ranging from 84±5 to 97±8Ma, and apatite FT ages from 47±3 to 67±4Ma with mean track lengths between 12.3±2.3 and 13.3±2.2μm, respectively, were obtained for the Phanerozoic granitoids sampled along a south–south-west to north–north-east transect across the Dahinggan Mountains. Three cooling stages from the Late Mesozoic to the Cenozoic have been identified in the studied region based on FT results and modeling. Stage one was a rapid cooling period from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110°C) during ∼90–57Ma. Stage two was a relatively slow cooling period (∼110–60°C) occurred between ∼57Ma and 20Ma, suggesting that the granitoids had been exhumed to depths of ∼1–2km. The final stage was a cooling period (60–20°C) occurred since the Miocene, which bring studied samples to the Earth’s surface at an accelerated exhumation rate. The estimated maximum exhumation is ∼5km assuming a steady-state geothermal gradient of 35°C/km. Our results indicate that this exhumation is possibly led by the Pacific plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. [Copyright &y& Elsevier]

Accretionary orogens are the primary sites for continental growth, but the rate and amount of crust generation throughout its evolution are poorly constrained. In this contribution, our new results about the genesis of two intermediate-felsic plutons are combined with a compiled granitoid dataset to evaluate the amount and rate of crustal growth throughout the evolution of the Western Kunlun orogen, which is a typical accretionary orogen associated with the consumption of the Proto-Tethys during the early Paleozoic. The ca.446 Ma Sanshili pluton was formed through interactions between metasomatized mantle wedge-derived oxidized magmas and the lower arc crust, as indicated by high whole-rock Mg#, high Ce4+/Ce3+ ratios (308–861) of ca.446 Ma zircons, and the existence of inherited zircons with ages of 546–472 Ma. The Yirba dioritic to granodioritic pluton was emplaced at 474 ± 3 Ma. Samples from the Yirba pluton are characterized by high K 2 O content, higher Mg# (40–49) than pure crustal melts, slightly higher Y + Nb concentrations, and high Th/Nb ratios, and slightly enriched to depleted Hf–Nd isotopes. Combined with the presence of the 502–531 Ma inherited zircons, the Yirba pluton is suggested to from through differentiation of the metasomatized lithospheric mantle derived-magmas beneath the juvenile intra-oceanic arc in combination with crustal reworking during regional extensions. The Yirba pluton, together with contemporary A 1 -type granites, thus marks an extension event at ca. 475 Ma in the Western Kunlun orogen. The compiled dataset reveals three magmatic flare-ups at 530–500 Ma, 480–470 Ma, and 445–430 Ma, corresponding to two slab rollback events and the slab break-off after the final closure of the Proto-Tethys. The three episodes of more intensive magmatism are associated with more radiogenic Hf–Nd isotopes and increased Nb/La and Nb/Y ratios, indicating more contributions from intraplate-like sources during lithospheric extensions. Meanwhile, element ratios (La/Yb, Sm/Yb, and Sr/Y) that are sensitive to crustal thickness are also elevated. These phenomena are consistent with rapid juvenile crust generation during extensional stages of accretionary orogens. Our study has also shown that the rate of new crust production is quite uniform for different extensional events. The crustal generation rate during slab break-off is much higher than that during slab rollback, although the proportions of juvenile inputs in granitoids formed during slab rollback are relatively higher. This may reflect extra inputs from partial melting of oceanic slabs and subducting sediments like those in continental collision zones and/or rapid asthenospheric upwelling coupled with enhanced crust reworking during slab break-off. • The Yirba pluton was formed at ca.475 Ma during regional extensions. • There are three magmatic flare-ups in the Western Kunlun orogen. • The crust generating rate is uniform for different extensional events. [ABSTRACT FROM AUTHOR]