High εNd Research Articles

Geochronology, geochemistry, Sr–Nd–Hf isotope composition of the late Permian adakite in West Ujimqin, Inner Mongolia: petrogenesis and tectonic implications

We report herein on new zircon U–Pb ages, the major and trace elements of whole-rock, and the Sr–Nd–Hf isotope composition for adakitic intrusives collected from the West Ujimqin district in the Southeast region of the Central Asian Orogenic Belt (CAOB). These data provide important constraints on the petrogenetic evolution and geodynamic setting of late Permian magmatism in the Southeast CAOB. The U–Pb dating of zircon shows that the ages of Seerbeng pluton and Nuhetingshala pluton in West Ujimqin are 255.3 ± 0.71 and 254.4 ± 1.2 Ma, respectively, which signifies that these are products of magmatic activity in the late Permian. The adakitic intrusives are characterized by high levels of Sr (Sr ≥ 741 ppm), low Y, low Yb, high Sr:Y ratios, and strongly fractionated rare earth elements (10.3 < LaN/YbN < 22.5), which is similar to the features of the adakite. The magmatic zircons exhibit positive Hf values (+8.1 to +13.3), and young two-stage model ages vary from 430 to 760 Ma. The high εNd(t) and low (87Sr:86Sr)i indicate that the adakitic granite derived from the partial melting of subducted oceanic slab. The high level of Mg# [100 × Mg/(Mg + Fe) in atomic number] and abundant Cr–Ni indicate that magmatic melts interacted with olivine rocks in the mantle. Considering these results and the regional rock assemblies, we conclude that the Paleo-Asian Ocean had not yet completely closed in the late Permian, and northward subduction continued, with the subducted slab possibly breaking off.

The Paleozoic-Mesozoic magmatic evolution of the Eastern Tianshan, NW China: Constraints from geochronology and geochemistry of the Sanchakou intrusive complex

The Sanchakou intrusive complex (containing quartz diorite, porphyritic granodiorite, granodiorite, fine-grained granodiorite, diorite porphyry and hornblende gabbro) is located at the eastern part of the Dananhu-Tousuquan island arc belt, Eastern Tianshan. Zircon U-Pb ages suggest that the above six units were emplaced at 446–238 Ma. The Sanchakou intrusive complex therefore provides a unique opportunity to gain a better understanding of the Paleozoic-Mesozoic magmatism and its evolution in the Eastern Tianshan.The granitoids form a subduction related calc-alkaline to low K (tholeiitic) magmatic series, characterized by enrichment in LILE and depletion in HFSE. They have low initial 87Sr/86Sr, high εNd(t) and εHf(t) values. As well as the above geochemical features, the quartz diorite, porphyritic granodiorite and fine-grained granodiorite have low Nb/U and Ta/U values, relatively high Mg#, Ti/Zr and Ti/Y values, indicating a potential role of the subducted slab in their petrogenesis. The granodiorite units have low Nb/U, Ta/U and Mg# values, and high (La/Yb)N values, suggesting an origin from the melting of juvenile lower crust. The Sanchakou diorite porphyry has positive εNd(t) and εHf(t), low SiO2 and (87Sr/86Sr)i, and high MgO, Mg#, Ti/Y and Ti/Zr values, indicating it was likely sourced from depleted mantle. The Mesozoic hornblende gabbro has low SiO2, relatively high TiO2, MgO, Al2O3 and (La/Yb)N, and minor depletion in Nb-Ta, implying an E-MORB-like mantle source.Integrating available tectonic, stratigraphic and geochemical data, we propose that the Sanchakou quartz diorite, porphyritic granodiorite, granodiorite and fine-grained granodiorite were formed in a double-side subduction system. The younger Permian diorite porphyry was produced in a post-collisional extensional setting and the Triassic hornblende gabbro was likely formed in an intraplate environment.

Genesis and mechanisms of metal enrichment in the Baimazhai Ni-Cu-(PGE) deposit, Ailaoshan Orogenic Belt, SW China

ABSTRACT The ∼259 Ma Baimazhai Ni-Cu-(platinum-group element) deposit is located in the Ailaoshan-Red River fault zone on the southwest margin of the Yangtze Plate in the Jinping area of southeastern Yunnan Province. The intrusion is lenticular (∼530 m long × 190 m wide × 24–64 m thick) and concentrically zoned (margin to core) from gabbro through pyroxenite to peridotite. It contains ∼50 kt of Ni-Cu-(platinum-group element) mineralization, concentrically zoned (margin to core) from disseminated through net-textured to massive sulfides with an average grade of 1.03 wt.% Ni, 0.81 wt.% Cu, and 0.02∼0.69 ppm Pd+Pt. The sulfide assemblage comprises pyrrhotite, chalcopyrite, and pentlandite, with lesser magnetite, violarite, galena, and cobaltite. The mineralization is enriched in Ni-Cu-Co relative to the platinum-group elements and the host rocks are enriched in highly incompatible lithophile elements relative to moderately incompatible lithophile elements with high Th/Yb and intermediate Nb/Yb ratios. These host rocks, and those at most other Ni-Cu-platinum-group element deposits in the Emeishan Large Igneous Province, have high γOs and intermediate εNd values, indicating that they crystallized from a magma derived from a subduction-modified pyroxenite mantle source and modified by crustal contamination. The initial concentrations of metals in the primary magma are estimated to have been on the order of 200 ppm Ni and 100 ppm Cu, but only 0.4 ppb Pd, 0.2 ppb Pt, 0.005 ppb Rh, 0.02 ppb Ru, and 0.01 ppb Ir. The δ34S values of ores and separated sulfides range from 5.8‰ to 8.6‰, between the ∼10‰ value of sulfides in the metasedimentary country rocks and the 0 ± 0.5‰ value expected for magmas derived from MORB-type mantle, or the –2.5 ± 0.3‰ value expected for subduction-modified mantle, consistent with equilibration at magma:sulfide mass ratios (R factors) of 100–1000. Variations in Ir100 and Pd100 (metals in 100% sulfide) are consistent with 40–60% fractional crystallization of monosulfide solid solution to form Ni-Co-intermediate platinum-group element (Ru, Os, Ir)-rich massive ores and Cu-palladium/platinum-group elements (Pt, Pd, Rh)-Au-rich residual sulfide liquids. This process is also recorded by magnetite: Type I (early magmatic), type II (late magmatic), and type III (secondary) magnetites exhibit progressively lower Cr-Ti-V concentrations. The platinum-group element contents in base-metal minerals are low, and only pentlandite, violarite, and cobaltite contain detectable concentrations of Pd, Rh, and Ru. There is abundant textural evidence for metamorphic-hydrothermal alteration of sulfides in the Baimazhai intrusion, with secondary violarite, chalcopyrite, and pentlandite being enriched (Ag, Sb, Au, Pb) or depleted (Sn) in more mobile chalcophile elements. The different tectonic and petrogenetic settings of the Baimazhai and other deposits in China highlight the potential of Ni-Cu-platinum-group element deposits to occur in subduction or post-subduction settings and demonstrate that the key controls are magma flux and access to crustal S. Exploration potential remains for the Ailaoshan orogenic belt to host additional magmatic Ni-Cu deposits.

Zircon U-Pb age, trace element, and Hf isotopic constrains on the origin and evolution of the Emeishan Large Igneous Province

The late Permian to Early Triassic volcano-sedimentary succession associated with the Emeishan Large Igneous Province (LIP) is well preserved in the Binchuan area, Southwest China. This paper presents coupled zircon U-Pb age, trace element, and Hf isotope analyses from the succession, together with whole-rock geochemical compositions, to reveal the origin and evolution of volcanic rocks of the LIP. Zircons from the matrix and a rhyolite clast in the Lower Triassic conglomerate bed yield identical U-Pb ages of ca. 260 Ma and have geochemical affinities to those crystallized from within-plate magmas. These features, combined with the dominance of rhyolite clasts from this horizon, imply a source related to Emeishan silicic volcanic rocks. Zircons from silicic ignimbrite and rhyolite in the upper volcanic succession of the LIP display high εHf(t) values (+4.2 to +12.9), low Th/Nb and U/Yb ratios, and similar εNd(t) values (−0.17 to +0.47) to high-Ti basalts. These chemical and isotopic characteristics are consistent with the eroded silicic volcanic rocks, indicating that the late-stage silicic volcanic rocks were generated by fractionation of high-Ti basaltic magmas without significant crustal contamination. Although the late Permian zircons from the lower and upper low-Ti basalt successions all show arc-like geochemical characteristics with high Th/Nb and U/Yb ratios, the former has much lower εHf(t) values (−11.7 to −3.6) than the latter (+4.4 to +11.6), and the zircons from the upper low-Ti basalt succession show positive εHf(t) values similar to the studied rhyolites. Samples from the lower low-Ti basalt succession have relatively higher εNd(t) values (−2.66 to +3.38) than those from the upper low-Ti basalt succession (−4.48 to −0.82). These geochemical features indicate the early-stage low-Ti basalts may be mainly derived from a previously enriched subcontinental mantle lithosphere, whereas the late-stage low-Ti basalts may be generated from the increasing involvement of asthenospheric mantle source with crustal contamination.

Petrogenesis of Early Cretaceous granitic rocks from the Haobugao area, southern Great Xing’an Range, northeast China: Geochronology, geochemistry and Sr-Nd-Hf-O isotope constraints

Early Cretaceous granitic rocks are widespread in the southern Great Xing’an Range (SGXR) in the eastern part of the Central Asia Orogenic Belt where they have been interpreted to have formed by remelting of juvenile materials derived from a depleted mantle source. We present new U-Pb ages, geochemistry and Sr-Nd-Hf-O isotopic data for ~140 Ma granitic rocks from the Haobugao area. The Xiaohanshan (XHS) quartz monzonite porphyry formed at 140 ± 2 Ma, the Wulanba (WLB) biotite granite formed at 142 ± 2 Ma, and the Wulanchulute (WLCLT) granite formed at 139 ± 2 Ma. They are A-type granites characterised by enrichment of light rare earth and high field strength elements. Based on the geochemistry and Sr-Nd-Hf-O isotope data, the quartz monzonite porphyry with elevated δ18O (6.6‰–7.4‰), high εNd(t) (5.8) and high εHf(t) (5.0–8.4) formed by the partial melting of juvenile material ultimately derived from depleted mantle which had been modified by melts derived from sediment on the downgoing slab. The biotite granite and granite with mantle-like δ18O (4.6‰–6.5‰, one value of 2.7‰), positive εNd(t) (1.4–1.8) and high εHf(t) (3.6–9.4) formed from partial melting of juvenile material derived from depleted mantle. The one low δ18O value from the biotite granite is probably the result of post magmatic alteration. The geochemical data suggest that the granitic rocks of the Haobugao area were not contaminated by older crust and formed in an extensional environment related to Paleo-Pacific oceanic slab rollback.

Geographical drivers of geochemical and mineralogical evolution of Motianling peatland (Northeast China) exposed to different sources of rare earth elements and Pb, Nd, and Sr isotopes

Geochemical shifts triggered by surface runoff and atmospheric fallout in a Chinese peatland were investigated by using Pb, Sr, and Nd, REE and by SEM mineralogical analysis. Motianling peatland (Northeast China) is located at 1670 m a.s.l., near the China–Mongolia border. Based on division of profile into two phases of different trophy, the total ∑REE value determined for the minerotrophic part of the profile (from 62 to 46 cm) varied from 67 to 31 mg·kg−1 and mineralogical analysis revealed the occurrence of weathered volcanic rocks, supported by a high εNd value (−3.26). After the transition from minerotrophic to more ombrotrophic conditions, the peatland became independent of the local bedrock weathering, which was manifested by a much lower concentration of REE (7–20 mg·kg−1) and lower εNd values (−7.37; −8.11). Moreover, PAAS-normalized pattern of REE distribution in the bottom part revealed the highest Eu/Eu* value (1.24), as well as a slight enrichment in Eu. The anthropogenic effect was visible from 1964, during which period the spheroidal aluminosilicate particles (SAP), produced by coal-fired power-plant activity, appeared for the first time, followed by an abrupt decrease in 206Pb/207Pb isotopic signature to 1.167. The dimensions of SAP (~1.5 μm), as well as the time of first appearance, indicated long-range transport. The REE ratios obtained in this study are characteristic of the eolian deposition signature, which is like the Gobi and northern Chinese deserts. The anthropogenic activity was manifested by a slight enrichment in Gd during reduced delivery of natural dust. Both, North Chinese and Asian part of the Russian industry supply anthropogenic dust. Topography, wind direction, and patterns of precipitation, as well as the initial phases of Asian industrial development, are the most important drivers promoting the deposition of chemical elements.

Late Paleozoic subduction-related magmatism in NE China and its implication: Insights from intrusions in the Handagai Fe[sbnd]Cu deposit

North East (NE) China forms the easternmost part of the Central Asian Orogenic Belt. However, its Paleozoic geological evolution process remains controversial, especially the complex subduction-accretion-orogeny processes of the Paleo-Asian Ocean plate, as well as the linking magmatism-metallogenic with tectonic evolution during that time. This paper reports the results of geochemical, geochronological, and isotopic analyses of igneous rocks at the Handagai skarn Fe–Cu deposit to elucidate the late Paleozoic tectonic framework and evolution of NE China and the setting of ore formation. New zircon LA–ICP–MS U–Pb data for monzogranite, quartz diorite, and quartz monzodiorite record Carboniferous ages of 350 ± 2 Ma, 321 ± 3 Ma, and 319 ± 2 Ma, respectively. The monzogranites have high SiO2 (69.57–71.97 wt%) and total-alkali (6.68–7.56 wt%) contents and relatively low MgO contents (0.60–1.03 wt%) and Mg numbers (33–41). They have arc-type trace-element signatures, with enrichment in large-ion lithophile elements and light rare earth elements, together with depletion in Nb, Ta, P, and Ti. Their whole-rock Sr–Nd–Pb and zircon in-situ LuHf isotopic compositions ((87Sr/86Sr)i = 0.7008–0.7062; εNd(t) = −1.9 to +1.9; (206Pb/204Pb)t = 17.900–19.006; εHf(t) = 5.04–15.28) and young two–stage Nd–Hf model ages (TDM2 = 1105–749 Ma and 899–574 Ma, respectively) indicate that their precursor magma was derived from partial melting of Mesoproterozoic to Neoproterozoic juvenile lower crust that had been metasomatized by fluids/melts from an enriched mantle wedge. The quartz diorites and quartz monzodiorites are characterized by intermediate SiO2 (58.21–61.47 wt%), high MgO (3.62–5.42 wt%), and low CaO (3.15–4.96 wt%) contents, and high Cr (151–222 ppm) and Ni (97–131 ppm) contents, as well as elevated Sr and Ba. They have strong Nb and Ta depletion and highly fractionated rare earth elements, indicating a geochemical affinity to typical high-Mg andesites. These rocks exhibit mid-ocean ridge basalt (MORB)-like whole-rock Nd–Sr–Pb–Hf isotopic characteristics, with high εNd (t) and εHf (t) values of +1.60 to +3.20 and + 10.21 to +13.61, respectively, and relatively low (87Sr/86Sr)i and (206Pb/204Pb)i ratios of 0.7028–0.7045 and 16.768–17.856, respectively. They also have low Sr/Y (30–59), Ba/Th (75–213), and Ba/La (26.05–38.24), but elevated Th/Yb (4.51–7.36), Th/Nb (0.78–1.17), and Rb/Y (2.79–6.29) ratios. We conclude that they were generated by partial melting of depleted lithospheric mantle previously metasomatized by subduction-related fluids and sediment melts. These results, integrated with regional geological, geochronological, and geochemical data, constrain the tectonic evolution of NE China during the late Paleozoic. This involved normal subduction at 400–335 Ma, ridge subduction at 333–319 Ma, and slab break–off at 315–272 Ma. The high-Mg andesitic/dioritic magmas had high oxygen fugacities and high water and volatile (e.g., Cl, S) contents, and sufficient ore resources (e.g., Cu, Au, Fe) from the mantle wedge to be favorable for Cu (–Au–Fe) mineralization.

Constraints of Late Triassic mafic-felsic volcanic rocks in northwestern Laos on the Eastern Paleotethyan post-collisional setting

Early Mesozoic volcanic rocks in northwestern Laos are rarely reported and important for investigating the Paleotethyan tectonic evolution and regional correlation in SE Asia. In this study, New zircon ages and whole-rock geochemical data are presented for the newly identified volcanic rocks in northwestern Laos. Twelve volcanic rocks yield zircon U–Pb ages of 228–234 Ma. The volcanic rocks in northwestern Laos contain basalt, basaltic andesite, andesite, and rhyolite and can be geochemically subdivided into three groups. Both Group 1 and 2 samples belong to the calc-alkaline mafic-intermediate volcanic rocks. Group 1 has εNd (t) values of −0.52 to +1.20, εHf (t) values of +0.9 to +3.6 and δ18O values of 6.3–7.0‰. In contrast, Group 2 has lower εNd (t) values of −2.82 to −5.89 and εHf (t) values of −4.0 to +1.4 and higher δ18O values of 6.6–8.1‰ than Group 1. Group 3 samples are high-K calc-alkaline rhyolites with high εNd (t) (−0.08 to +0.74) and positive εHf (t) (+4.6 to +13.2) values. Geochemical characteristics suggest that the Group 1 and 2 samples were derived from a metasomatized lithospheric mantle modified by sediment-derived components, and Group 3 rhyolites were derived from partial melting of juvenile mafic rocks with a crustal component. Our results, along with the geological observations and reported ages suggest that the Late Triassic volcanic rocks in northwestern Laos were formed in a post-collisional setting, and provide the key studies for the connection between the Lancangjiang and Chiang Khong-Lampang-Tak zones.

Phonotephrite and phonolite in the Tarim Large Igneous Province, northwestern China: Petrological, geochemical and isotopic evidence for contrasting mantle sources and deep carbon recycling

The igneous units of Permian Tarim Large Igneous Province (TLIP) is typically characterized by alkaline affinity. Here we report for the first time the petrological, geochemical and isotopic characteristics of phonotephrite and phonolite dykes from the Wajilitag complex in the northwestern margin of the TLIP. Our data, especially Sr-Nd-Mg isotopes, suggest that the dykes have different mantle sources. Phonotephrite with mantle-like Mg isotope values (−0.295 to −0.382 ‰), relatively enriched Sr isotopes (0.70487 to 0.70574) and slightly lower εNd(t) values (−0.23 to +2.06), were possibly derived from a lithospheric mantle source that was metasomatized by calcitic carbonate melt. The phonotephrites are highly evolved rocks formed through fractional crystallization from a parental magma which is similar to that of the mafic–ultramafic intrusions. Phonolites show relatively depleted Sr isotopes (0.70362 to 0.70409), higher εNd(t) values (+1.27 to +3.45), markedly lighter Mg isotopes (−0.851 to −0.906‰) than the normal mantle indicating a mantle plume source with the involvement of carbonated eclogite. The parental magma of phonolites may be related to the liquid immiscibility with calciocarbonatites present in the Wajilitag complex due to their similar extremely light Mg isotopic compositions. The distinct geochemical features between two series of dykes in the Wajilitag complex reflect the diversity of mantle source of the TLIP, and their Sr-Nd-Mg isotopic characteristics indicate the role of subducted recycled sedimentary carbonates at different depths in the mantle.

Geochronology and petrogenesis of Triassiclow‐Timafic intrusions in Funing: Implications for the tectonic evolution of Nanpanjiang Basin,SWChina

The Nanpanjiang Basin, one of the largest Triassic turbidite basins in the South China Block, has long been disputed with respect to its tectonic affinity. To better understand the tectonic processes of the basin, we conducted geological mapping, geochronological, and geochemical studies on the mafic intrusions (the Anding group) in Funing emplaced within the southern Nanpanjiang Basin. The Anding group mafic intrusions in Funing consist of gabbronorite and gabbroic diorite, and they are characterized by low TiO2(0.54–1.18 wt%) and Ti/Y ratios (162–222), low (La/Yb)CNratios (3.28–4.19), flat REE patterns, pronounced negative Nb, Ta and Ti anomalies. These mafic intrusions can be further divided into two subgroups: the Group 1 at 244 ± 3 Ma and the Group 2 at 224 ± 2 Ma. The Group 1 exhibits negative Eu anomalies, high Th/Hf ratios (1.61–1.91), high (87Sr/86Sr)iratios (0.708710–0.711843), and lowεNd(t) values (−6.70 to −7.82), while the Group 2 exhibits positive Eu anomalies, lower Th/Hf ratios (1.05–1.07), lower (87Sr/86Sr)iratios (0.708397–0.708425) and higher εNd(t) values (−3.28 to −3.21). Both the Group 1 and Group 2 are derived from partial melting of spinel‐bearing lithospheric mantle and formed at an intracontinental back‐arc setting. These results, combined with regional considerations, support a new model that the Triassic Nanpanjiang Basin is an intracontinental back‐arc extensional basin triggered by the westward subduction of the Palaeo‐Pacific Plate, and the Triassic magmatism in Funing was a response to the extension.

Opening of the Proto-Tethys Ocean: Implications from the late Neoproterozoic mafic dike swarms in the South Qinling Belt, South China

Magmatism in the passive margin records continuum rift of continental lithosphere and onset of seafloor spreading. The ca. 650 Ma ultramafic-mafic dike swarms are the latest magmatic episode in the South Qinling Belt during the Neoproterozoic, and therefore provide a window to address their mantle sources, and the continental rift to drift transition. These mafic dikes have distinct geochemical signatures, and can be grouped as N-MORB-, E-MORB-, and Arc-affinities. The Shiziyan amphibole gabbros have low Rb/Y (<0.75), Nb/Y (<0.15), Nb/Zr (<0.05), Th/Zr (<0.01) ratios, positive εNd (+4.3 to +5.4), low Sri (0.70650–0.70759) and moderate 207Pb/204Pb (15.48) and 206Pb/204Pb (17.57), similar to N-MORB, suggesting that they were derived from an asthenosphere mantle. The Yindongshan pyroxenites display enrichment of LILEs and HFSEs, similar to the E-MORB characters. They also have low Sri (0.70384–0.70410), high εNd (+4.2 to +5.4), and 207Pb/204Pb (15.53–15.54) and 206Pb/204Pb (18.18–18.37). They have high zircon εHf (+13.1 to +15.0), but low δ18O values (+4.43 to +5.17‰). These chemical features indicate an enriched mantle source with involvement of recycled component. The Duchongshan olivine gabbros show arc-like geochemical features, with high Nb/Zr (0.07–0.16), Nb/Yb (3.52–20.1) ratios, and high Sri (0.70545–0.70586), negative εNd (−6.1 to −5.2), large variable zircon εHf (−0.5 to +4.2) and high δ18O (+5.41 to +6.41‰). These features favor that they were derived from a subduction-modified lithosphere mantle followed by significant crustal contamination. The northern Yangtze Block experienced secular crustal extension and developed into a volcanic rift margin during the middle to late Neoproterozoic. Mafic dike swarms emplaced into the volcanic successions and unconformably overlayed by late Ediacaran neritic to abysmal deposition. The magmatic termination and sedimentary facies transition indicate that the northern Yangtze Block broke up during the late Neoproterozoic and the Proto-Tethys Ocean opened at ca. 650 Ma.

Arc-related peridotite blocks exhumed to the Eastern Block of the North China Craton prior to 2.47 Ga

AbstractThe Songling and Majiayu peridotite blocks occur in the Eastern Block, North China Craton (NCC). Geothermobarometry data show that the Songling peridotites began exhumation from a depth of c. 70 km (c. 23 kbar). During exhumation, the Songling peridotites were intruded by an upper-crust-derived, high-δ18O (up to +7.28‰ in zircon) trondhjemitic dyke at 2.47 Ga and experienced granulite-facies metamorphism. The Songling peridotites have hybrid mantle wedge (HMW) -like high SiO2 (&gt; 45 wt%), high FeOt (c. 10 wt%) content, high modal orthopyroxene abundance (&gt; 35%) and high ϵNd(t) (+18.4 to +21.4), which were generated by the reaction between peridotite and eclogite-derived melts. The clinopyroxenes from the Songling peridotites were in equilibrium with a Nb-, Zr- and Ti-depleted arc-like magma. The Majiayu peridotites are characterized by depletion of Nb, Zr and Hf and are highly enriched in FeOt, Th and light rare earth elements (LREEs), which can be interpreted as an open system reaction between hydrous melts and fore-arc mantle peridotites. These two peridotite blocks are considered to be arc-related mantle peridotites that experienced melt extraction and metasomatism in different styles. They were exhumed to the north margin of the North China Craton during the c. 2.47 Ga arc–continent collision along the Zunhua structural belt.

Petrogenesis of the Jurassic Guiping Complex in the Southwestern South China Block: Insights into the Subduction Processes of the Paleo-Pacific Slab

Late Jurassic NE-trending A-type granitoids are widespread in the Shihang belt, South China, though their petrogenesis and geodynamic settings remain controversial. The Guiping complex is located on the southwest margin of the Shihang belt. In this study, the petrography, major and trace element geochemistry, whole-rock Sr-Nd isotopes, and zircon U-Pb geochronology of the Guiping complex were investigated. The Guiping complex is composed of the Fenghuangling and Xishan plutons; both plutons yielded zircon U-Pb ages of ca. 160 Ma. The Fenghuangling pluton has low SiO2 content of 54.26% to 60.31%, whereas the Xishan pluton exhibits high SiO2 content of 65.19% to 71.18%. Both of them are metaluminous and belong to the high-K calc-alkaline series and are enriched in large-ion lithophile elements (LILEs) such as Rb, Th, U, and Pb. The Fenghuangling and Xishan plutons showed enrichment in light rare earth elements (LREEs) and high-field strength elements (Nb, Ta, Zr, and Hf) and depletion in heavy rare earth elements (HREEs). Marked Nb and Ta negative anomalies were not observed. Due to the high contents of Zr + Ce + Nb + Y and high Ga/Al ratios, all the samples belonged to the group of A-type granites. The Fenghuangling and Xishan plutons had low ISr (mainly in the range of 0.7046–0.7058) and high εNd(t) (−0.60 to 1.94) values, though obviously different from those of the Precambrian basement in South China. Furthermore, they lie between the ocean island basalt (OIB) of the asthenosphere and the arc basaltic rocks of the enriched lithospheric mantle. Therefore, we proposed that the basaltic parental magma of the Guiping complex originated from partial melting of the enriched lithospheric mantle, which was metasomatized by asthenosphere-related OIB-type basaltic magma. Mafic microgranular enclaves in the Xishan pluton displayed positive Nb and Ta anomalies, which is consistent with OIB-type basalts. The enclaves also had similar Sr-Nd isotopic compositions to the Xishan pluton. That indicated that the enclaves were probably formed by mixing of the OIB-type basaltic magma and the Xishan pluton. In conclusion, the formation of the Late Jurassic NE-trending A-type granite belt was attributed to back-arc extension as a result of the rollback of the Paleo-Pacific Plate.

Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky complex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

Recycling of continental crust in the southern North China Craton: Constraints from the Sr–Nd–Pb–Hf–O isotopic compositions of Early Cretaceous Funiushan granites

This paper reports new zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb–Hf–O isotopic compositions for the Funiushan (FNS) pluton of the southern North China Craton (NCC). These data and statistical analyses of previously reported compositions of late Mesozoic granites from the southern NCC are used to constrain late Mesozoic continental recycling and geodynamic processes. The FNS pluton includes coexisting early Early Cretaceous (140 Ma), late Early Cretaceous (130–116 Ma) and highly evolved granites (HEGs; 126–125 Ma). The early Early Cretaceous granites have high Sr contents (332–566 ppm), high Sr/Y (53–138) and (La/Yb)N (29–52) ratios, and low MgO contents (0.15–0.48 wt%). They have relatively low (87Sr/86Sr)i values (0.7051–0.7054), relatively high εNd(t) values (−4.11 to −3.96) and variable εHf(t) values (−22.9 to −0.53). They are also characterized by high initial 206Pb/204Pb values (17.893–17.975) and relatively low δ18O values (5.34‰–7.48‰) as well as Neoproterozoic (851–734 Ma) inherited zircons, suggesting that they have an adakitic affinity formed by recycling of subducted continental crust of the Yangtze Craton (YC) with input from a mantle component. In contrast, the late Early Cretaceous granites have relatively high (87Sr/86Sr)i values (0.7077–0.7085), low εNd(t) values (−14.2 to −12.0), relatively high initial 206Pb/204Pb values (17.398–17.497), εHf(t) values of −23.7 to −10.7, and δ18O values of 5.76‰–6.55‰. These data, and the Neoproterozoic zircon ages (716–702 Ma), indicate that the primary magmas formed from recycled YC crust with a minor contribution from the NCC basement. The late Early Cretaceous HEGs have relatively high εNd(t) values (−9.33 to −8.70), high initial 206Pb/204Pb values (17.656–17.885), intermediate εHf(t) values (−12.3 to −6.18), and relatively low δ18O values (5.22‰–6.72‰), indicating that they formed from subducted YC and mantle material. Previous work on granites of the southern NCC has established two phases of granite formation. Late Jurassic to early Early Cretaceous I-type granites (160–130 Ma) occur throughout the southern NCC. These are adakitic and formed from thickened lower continental crust (LCC). Late Early Cretaceous A-type granites (130–110 Ma) formed from thinned LCC. The differences between Late Jurassic to early Early Cretaceous granites and late Early Cretaceous granites reflect a transformation in tectonic regime from thickening to thinning, which is attributed to rollback of the subducting Paleo-Pacific Plate.

Two-stage rollbacks of the paleo-Pacific plate beneath the Cathaysia block during Cretaceous: Insights from A-type granites and volcanic rocks

Petrogenesis and tectonic implications of the Cretaceous A-type rocks in the Cathaysia block remain controversial. We address this issue by the inland early Cretaceous (137–136 Ma) A-type Tiantangshan volcanic-intrusive complex and late Cretaceous A-type (96 Ma) Shihu-Huilong syenogranites, and integrating them with Cretaceous A-type rocks in the Cathaysia block. The Tiantangshan volcanics (trachyte-trachydacite-rhyolite) have εNd(t) (−3.5 to −2.6) and zircon εHf(t) (−3.0 to −1.3), suggesting their forming by partial melting of crust with significant addition of asthenosphere mantle-derived magma. The Tiantangshan granite, genetically connected with the volcanics, having higher εNd(t) (-1.2 to −0.8) and zircon εHf(t) (avg. 0.6) with more evolved composition, was likely formed by extensive fractional crystallization of the parental magma of the volcanics, recharged by asthenosphere-derived magma. The Shihu-Huilong syenogranites have initial 87Sr/86Sr (0.707987 to 0.708939), εNd(t) (−3.7 to −4.0) and zircon εHf(t) (avg. −1.6 to −0.6), suggesting a hybrid crustal and asthenospheric magma source. The early Cretaceous A-type rocks, distributed in the inland region with northeastward younging trend, mostly have A2 chemical features and inhomogeneous isotopic composition. However, the Tiantangshan and Baijuhuajian A-type rocks are distinct by A1 chemical subgroup and more depleted isotopic composition, likely reflective of intensified extensional back-arc environment due to slab rollback with high dipping angle. We propose an asynchronous and asymmetric rollback model during early Cretaceous that southern subducted paleo-Pacific plate started to retreat earlier than its northern part, and the rollback gradually developed northeastward. The late Cretaceous A-type granites in the coastal region, and Shihu-Huilong granites, are all characterized by A1 subgroup with relatively homogeneous isotopic composition, suggesting more involvement of asthenospheric materials in magma sources, and that the coastal region was entirely under an intensified extensional back-arc environment due to slab rollback with high dipping angle. The rollback of the subducted paleo-Pacific plate during Cretaceous likely occurred as two discrete stages.

Petrogenesis of the Late Jurassic Cu-Mo mineralization-related Xianyang granite porphyry in the Dehua district, Southeast China: Response to the subduction of paleo-Pacific slab and implication for regional exploration

The Dehua Au-polymetallic ore cluster, as one of the most important area in the Wuyi Au-Cu-Mo metallogenic belt, consists of many large to middle sized epithermal Au deposits and recently discovered porphyry Cu-Mo deposits. We first study the geochronology and geochemistry characteristics of the Cu-Mo mineralization-related Xianyang granite porphyry to constrain its petrogenesis, tectonic setting and metal endowment. LA-ICP-MS zircon U-Pb dating yield a precise age of 157.2 ± 0.8 Ma for the Xianyang granite porphyry, indicating that the granite porphyry was emplaced during the Late Jurassic. The Xianyang granite porphyry was suggested to be generated under continental arc setting, associated with subduction of the paleo-Pacific slab beneath the South China Block. The Xianyang granite porphyry belongs to the high-K calc-alkaline series, with SiO2 of 71.16–72.02 wt% and K2O of 4.28–4.69 wt%. It shows light rare earth element-enriched distribution patterns with (La/Yb)N of = 9.74–13.93, enrichment in large ion lithophile elements, but depletion of high field strength elements, with negative Nb, Ta and Ti anomalies, suggesting an arc magma geochemical affinity. It has lower initial 87Sr/86Sr ratios of 0.7079–0.7086 and relatively higher εNd(t) and εHf(t) values of −8.03 to −7.69 and − 8.86 to −5.48, respectively, than those of basement rocks of the Cathaysia block, suggesting that it was most likely generated by partial melting of the regional ancient crustal materials, with the involvement of asthenosphere mantle-derived materials. The Xianyang granite porphyry has remarkably high zircon Ce4+/Ce3+ values of 119–404 (mean = 245) and EuN/EuN* values of 0.37–0.60 (mean = 0.51), indicating a high oxygen fugacity, which is favor of the formation of the Xianyang porphyry Cu-Mo mineralization. Combining with published research results for regional subvolcanic rocks-related epithermal Au deposits, the porphyry Cu-Mo deposits and epithermal Au deposits in the Dehua ore cluster share similar petrogenetic-metallogenic ages and magma sources in the continental arc setting during the Late Jurassic period. The identification of the coeval porphyry-epithermal Cu-Mo-Au metallogenic system in the Dehua ore cluster highlights the possibility of finding the hidden porphyry Cu-Mo orebodies beneath the discovered epithermal Au deposits.

Cu-Ni mineralization in Early Permian mafic complexes in the Kalatage area of eastern Tianshan (NW China): Petrogenetic constraints from geochronology, geochemistry, and Hf-Sr-Nd-Os isotopes

The Early Permian was a critical period in the long history of accretion and collision of the southern Altaid orogen. Early Permian mafic-(ultramafic) intrusions and mafic–ultramafic-related sulfide Cu-Ni deposits are common in the eastern Tianshan, but the sulfide Cu-Ni deposits related to the mafic intrusions are still poorly studied, and yet provide key information on the ambient tectonic evolution. In order to help understand their petrogenesis, we report new data on the Early Permian mafic intrusions and related sulfide Cu-Ni deposits in the Dananhu arc of the eastern Tianshan in NW China. The ore-bearing Yueyawan complex is a well-differentiated, zoned mafic intrusion consisting of troctolite, olivine gabbro, layered gabbro, gabbro, and leucogabbro from the bottom upwards. The ore bodies are primarily strata-bound within olivine gabbros and troctolites at the bottom of the complex. The ores are more enriched in Cu than Ni than the more enriched, disseminated, veined and massive equivalents. Gabbros from the mafic complex yield zircon crystallization ages that range from 265 Ma to 273 Ma. The gabbros are tholeiitic and characterized by typical subduction-related geochemical signatures with low TiO2 contents, enrichments in Rb, Ba, U, K, Pb, and Sr, depletion in Nb and Ta, positive Eu and Ti anomalies, high εNd(t) values of +7.44 to +8.06, zircon εHf(t) values of +11.68 to +20.58, and low (87Sr/86Sr)i (0.703322–0.703416). The gabbroic rocks have positive correlations between SiO2 and TiO2, Al2O3, CaO, Nb, and Y, and negative correlations between SiO2 and MgO, Ni, and Co. The (187Os/188Os)i and γOs values of sulfides from the Yueyawan complex that contains Cu-Ni deposits range from 0.266 to 0.372 and 112 to 197, respectively. These geological, petrological, and geochemical characters indicate that the gabbros were mantle-derived, and that fractionation and crustal contamination were essential for the genesis of the magmatic Cu-Ni sulfide deposits. After integrating our data with those of previous investigations, we conclude that the protoliths of the sulfide deposits were probably derived from an asthenospheric garnet-free mantle in a subduction setting in the Early Permian. Oblique ocean-ridge subduction and a resultant slab window plausibly induced asthenospheric upwelling that gave rise to the generation of the mantle-derived melts, which likely moved into strike-slip faults through a slab window in the supra-subduction zone. Strong fractionation, crustal contamination, and multi-stage eruptions led to formation of the Cu-Ni sulfide deposits.

The Silurian to devonian magmatic evolution of the Eastern Tianshan Terrane: New insights from geochemistry, geochronology, and Sr–Nd–Hf isotopes of new-discovered Sidingheishan porphyry Cu–Mo deposit, NW China

The Sidingheishan porphyry Cu–Mo deposit is located in the northeastern margin of the Kanggur–Huangshan Shear Zone of the Eastern Tianshan Terrane (ETT) in the Xinjiang Province of northwestern China. Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA–ICP–MS) zircon U–Pb dating of rocks in the area yielded an emplacement age of 427 ± 3 Ma for the ore-bearing granodiorite, which is intruded by 406 ± 3 to 397 ± 4 Ma gabbro, and a 382 ± 4 Ma monzogranite. These rocks have a tholeiitic to calc–alkaline and metaluminous geochemical affinities, with A/CNK values ranging from 0.65 to 1.14. The Silurian granodiorite and Carboniferous monzogranite are enriched in LREEs and LILEs (i.e. K, Ba, Pb and Sr), depleted in HREEs and HFSEs (i.e. Nb, Ta and Ti), and slightly positive Eu anomalies (Eu/Eu* = 0.94–1.39) indicative of crystal fractionation. The granodiorite and monzogranite have elevated MgO assays (0.36–1.85 wt%) and Mg# values (34–52), low (87Sr/86Sr)i ratios of 0.70320–0.70435, high εNd(t) values (5.9–6.9), TDM2 Nd model ages between 687 and 568 Ma, and εHf(t) values between + 8.37 and + 17.44. The geochemistry of the Early Devonian gabbro is characterised by its low SiO2 assays of 47.69–51.34 wt% and high Al2O3 assays of 18.07–22.91 wt% and MgO assays of 2.29–7.09 wt% (with Mg# values of 38–64), εNd(t) values of 4.7–6.9, εHf(t) of 8.04–17.97, and (87Sr/86Sr)i values of 0.70371–0.70420. The gabbro samples are enriched in LILEs, depleted in HFSEs, and have positive Eu anomalies. Combined with the regional geological history and above mentioned data, we suggest that the Sidingheishan granodiorite and monzogranite were formed during partial melting of subducted oceanic crust interacting with the lithospheric mantle. We also proposed that the Devonian gabbro developed during an extensional tectonic setting involving subduction–related magmatism in a continental arc margin rather than during mantle plume activity in the post–collisional extensional tectonic setting. The Sidingheishan granodiorite and associated porphyry Cu–Mo mineralisation were generated in an arc setting, associated with the N-dipping subduction of the Palaeo–Tianshan oceanic plate beneath the Dananhu–Tousuquan island arc.

Superimposed mineralization in the deformed Yulekenhalasu porphyry Cu-Mo deposit (Northwest China): Rb-Sr geochronology, S isotope, and trace element analysis of chalcopyrite

The Yulekenhalasu porphyry Cu–Mo deposit is located ca. 40 km southwest of Qinghe, in the Chinese Altay-East Junggar section of the Central Asian Orogenic Belt, NW China. The belt preserves multistage tectonic-hydrothermal and porphyry Cu-Mo mineralization events associated with arc to syn- and post-collision environments over 87 m.y. The 359 Ma deformed granitic porphyries are characterized by positive εNd(t) (+0.62 to + 3.77) and (87Sr/86Sr)initial values (0.704304–0.705960), and old crustal model ages of 747 to 1216 Ma, whereas a 272 Ma sample from late chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins yielded (87Sr/86Sr)initial values of 0.704415 to 0.705764, high εNd(t) values (+5.81 to + 5.88) and young crustal model ages (715 to 614 Ma) suggesting an increasingly juvenile mantle source over time. Seven fragments of a single deformed chalcopyrite grain yielded an Rb-Sr isochron age of 358.6 ± 4.8 Ma (2σ, MSWD = 1.8), which is consistent with the 360 Ma recrystallized zircon grains in the deformed host granitic porphyries. Eight fragments of chalcopyrite from the chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins formed along cleavage planes yielded a younger Rb-Sr isochron age of 272.2 ± 2.6 Ma (2σ, MSWD = 1.8). The younger age is interpreted as the lower age limit for the Mo and Cu mineralization in the post-collisional stage. The heterogeneous initial Sr isotopic compositions of chalcopyrite in the Yulekenhalasu deposit are likely the result of phyllosilicate inclusions. Disseminated chalcopyrite crystals in the granitic porphyry have different trace elemental contents than chalcopyrite in the deformed granitic porphyry and late chalcopyrite veins. Our Rb-Sr and trace element data for chalcopyrite grains constrain the age and geochemistry of multistage mineralization in porphyry Cu-Mo deposits. In-situ S isotope data of chalcopyrite from the deformed granite porphyries and chalcopyrite-feldspar-quartz-muscovite veins display a similar mantle origin. The 272 Ma mineralization event at Yulekenhalasu is coeval with the formation age of the Cu-Ni-(PGE) sulfide deposit in the Chinese Altay, indicating that hydrothermal mineralization like that in porphyry deposits can form proximal to ultramafic–mafic rocks and potentially may have a genetic relationship with mantle-derived Cu-Ni-(PGE) sulfide deposits.