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The tectonic transition from subduction to collision is a fundamental process during orogenesis, yet the magmatic expression of this transition and related deep geodynamic processes remain unclear. This study focuses on a newly identified volcanic belt within the Moyun–Zaduo–Sulu area of the North Qiangtang Block and presents new zircon U-Pb data that indicate that this belt formed during the Middle Triassic (247–241 Ma), a time characterized by a regional transition from subduction to collisional tectonism. The volcanic belt is located to the south of a Permian to Early Triassic arc and is dominated by high-K calc-alkaline and peraluminous rhyolites. These rhyolites have low Mg#, Nb/Ta, and δEu values, contain low contents of Sr, have high Rb/Sr and whole-rock eNd(t) values, and show positive zircon eHf(t) values, all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material. The migration of Middle Triassic volcanism in this region was most likely caused by rollback of the subducting Longmucuo–Shuanghu Tethyan oceanic slab. Combining our new data with previously published results of numerical modeling of subduction–collisional processes and regional data from north-central Tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision. This combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction, the transition from subduction to collision, and collisional tectonism.

Many intrusions with adakite-like affinities in collisional zones have obviously higher K2O contents and K2O/Na2O ratios compared with counterparts in subduction zones. A suite of Eocene post-collisional high-K2O adakite-like intrusions, mafic microgranular enclaves, and potassic–ultrapotassic lamprophyres in the Machangqing complex are associated with the Indian–Asian collision within the western Yangtze Craton, southeastern Tibet. The potassic–ultrapotassic lamprophyres, with a zircon U–Pb age of 34·1 ± 0·2 Ma, have high K2O and MgO contents, are enriched in light rare earth elements and large ion lithophile elements, and display high Rb/Sr, and low Ba/Rb and Nb/U ratios. They show enriched isotopic compositions [i.e. (87Sr/86Sr)i = 0·7070–0·7082, εNd(t) = −3·2 to −2·8], and zircon εHf(t) values (−1·6 to +2·6). Their parental magmas are inferred to have been derived from partial melting of an enriched lithospheric mantle, metasomatized by subduction-related fluids. The adakite-like intrusions, with zircon U–Pb ages of 35·4 ± 0·4 and 35·2 ± 0·3 Ma, are characterized by high SiO2 (68·8–71·1 wt%) and Al2O3 (14·0–15·3 wt%) contents, high Sr/Y (41–118) ratios, and low Y (5·3–14·7 ppm) contents. They show low contents of compatible elements (e.g. Ni = 9·5–36·2 ppm) and total REE, and lower Mg# values than the lamprophyres and mafic microgranular enclaves. The adakite-like intrusions have positive large ion lithophile element anomalies, especially potassium, negative high field strength element anomalies, negative εNd(t) (−5·5 to −3·3), and high (87Sr/86Sr)i (0·7064–0·7070) and zircon εHf(t) values (0·0 to +2·7), indicating that they were formed by partial melting of the juvenile lower crust. Mafic microgranular enclaves hosted in the adakite-like intrusions, with U–Pb ages similar to the lamprophyre of c. 34 Ma, exhibit disequilibrium textures, and some of them contain phlogopite. They exhibit potassic–ultrapotassic affinity, and relatively high compatible element contents. They are also characterized by enriched isotopic compositions with (87Sr/86Sr)i = 0·7063–0·7074, εNd(t) = −6·6 to −4·1, and variable zircon εHf(t) values (−0·6 to +3·2). Petrological and geochemical evidence suggests that the mafic microgranular enclaves were formed by magma mixing between potassic–ultrapotassic and pristine adakite-like melts. We propose a magma mixing model for the origin of the high-K2O adakite-like intrusions from the Machangqing complex. In this model, the formation of high-K2O adakite-like intrusions occurred in three stages: (1) partial melting of metasomatized lithospheric mantle generated potassic–ultrapotassic mafic melts; (2) underplating of these mafic melts beneath thickened juvenile lower crust resulted in partial melting of juvenile mafic lower crust and the generation of adakite-like melts; (3) magma mixing involved 80 % pristine adakite-like melts and 20 % potassic–ultrapotassic melts. This leads to the enrichment of K2O in these adakite-like intrusions, and magma differentiation further promotes K2O enrichment. These results are applicable to compositionally similar adakite-like rocks produced in other collisional zones, such as the Tibet, Sulu–Dabie and Zagros orogenic belts. From which we conclude that in continental collision zones, the post-collisional mantle-derived magmas characterized by potassic–ultrapotassic affinities are spatially associated with coeval collision-related adakite-like intrusions that originated from lower crustal melting. The emplacement of adakite-like and potassic–ultrapotassic rocks is controlled by the same fault systems, which increases the possibility of interaction between these two magma suites.

The Mengshan district is located in the eastern segment of the Jiangnan Orogen in South China. Multi-phase intrusions were emplaced in this district, with the medium-grained porphyritic biotite granite and its marginal phase (fine-grained porphyritic biotite granite) genetically related to metal and non-metal mineralization. In this study, zircon U–Pb ages and trace elements, whole-rock geochemistry, and Nd isotopes were systematically analyzed for medium- and fine-grained porphyritic biotite granite in the Mengshan district, with the aim of elucidating the origin, evolutionary process, redox state, and mineralization competency of the studied granites. The Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA–ICP–MS) zircon U–Pb dating provided a weighted mean age of 226.6 ± 0.5 to 225.9 ± 0.5 Ma for the studied Mengshan granites, synchronous with the late-episode Triassic magmatism-mineralization in South China. The studied Mengshan granites are high-Si and -K, low-P, and weakly peraluminous, exhibiting features of highly evolved I-type granites. The detailed whole-rock geochemistry and Nd isotopes, and zircon trace elements and Hf isotopes demonstrated that the studied Mengshan granites were likely derived from disequilibrium melting of Proterozoic metamorphic basements that were composed of meta-igneous and metasediments and underwent fractional crystallization of plagioclase, K-feldspar, biotite, Fe-Ti oxide, zircon, and apatite. Low whole-rock K/Rb (2O3/FeO ratios (mostly < 0.5), zircon Ce4+/Ce3+ ratios (mostly lower than 90), and oxygen fugacity (below ΔFMQ + 1.4). The data in this study indicate that the Mengshan granites, especially the more evolved fine-grained porphyritic biotite granite, are favorable for W, Sn, Mo (

Cenozoic high–Sr/Y shoshonites in western Yunnan, China, are spatially and temporally associated with porphyry deposits and mafic volcanic rocks that formed at a post–collisional setting. However, the petrogenesis of these rocks and the origins of the associated mineralization remain unclear. Here we present new geochemical data for the high–Sr/Y shoshonites and associated mafic microgranular enclaves (MMEs) in the Jinshajiang–Ailaoshan mineralization belt, which formed as a result of India–Asia collision during the Cenozoic. Both fertile and barren shoshonitic porphyries were emplaced during the Eocene–Oligocene (32–37 Ma) and are characterized by enrichment in large–ion lithophile elements (LILE), depletion in high field strength elements (HFSE), high K2O (4–6 wt%), Sr contents (674–1370 ppm), and low Y contents (7–18 ppm). The barren Zhanhe, Yongsheng, Songgui, and Jianchuan, and fertile Machangqing (Cu–Au–Mo mineralization) porphyry intrusions have variable zircon eHf(t) values of −6 to +9 and old TDM2 ages of 1433 to 900 Ma. However, the barren Shigu porphyry intrusion yields relatively positive zircon eHf(t) values (−4 to +8) and younger TDM2 ages (903–631 Ma). These features indicate that the Shigu intrusion was derived from late Permian juvenile lower crust, and the other high Sr/Y shoshonites were derived mainly from Neoproterozoic juvenile lower crust. Fertile and barren porphyries have variable whole–rock eNd(t) values (−5 to −0.7) and (87Sr/86Sr) i ratios (0.70595–0.70788) that are within the range of coeval mafic magmas in western Yunnan. The MMEs comprise mafic enclaves and andesitic enclaves that formed during the Eocene (34–35 Ma) and have spheroidal shapes, igneous textures and contain acicular apatites. This indicates that the MMEs are globules of coeval mafic magma that was injected into and mixed with the host shoshonitic magma. The enclaves show low TiO2 contents (0.7–0.8 wt%), high MgO (6–9 wt%), Cr (184–450 ppm) and Ni contents (98–157 ppm), positive LILE anomalies, marked negative HFSE anomalies, a narrow range of eNd(t) values (−1.2 to −0.6), and (87Sr/86Sr) i values of 0.70556–0.70635. The andesitic enclaves show adakitic geochemical affinities and have similar zircon eHf(t) values (−2.7 to +2.5) to the host porphyries, whereas, the mafic enclaves have relatively negative zircon eHf(t) values (−8.7 to +1.5), similar to enriched mantle. These evidences suggest the high−Sr/Y shoshonites were produced by partial melting of juvenile lower crust mixed with ultrapotassic or potassic mafic magmas as represented by the andesitic enclaves. The mafic enclave melts were derived from enriched mantle metasomatized by slab–derived fluids, which elevated the Mg#, Cr, Ni contents of the host porphyries at Machangqing, Zhanhe and Yongsheng. Zircon saturation temperatures (TZr) of the high–Sr/Y shoshonitic rocks range from 735 to 777 °C and indicate the shoshonites were derived mainly from water–fluxed melting of lower crust. The Manchangqing fertile intrusion had a high oxidation state (zircon Ce4+/Ce3+ = 38–180, average = 91) and was derived by mixing between juvenile lower–crustal melts and voluminous coeval lamprophyres. In contrast, the barren Jianchuan, Songgui, Shigu, Yongsheng and Zhanhe high–Sr/Y shoshonites formed by partial melting of juvenile lower crust and some mixing with mafic lavas, and are characterized by low oxygen fugacity (zircon Ce4+/Ce3+ = 0.5–77, average = 20). As such, we suggest the mafic magmas triggered water–fluxed, moderate–degree partial melting of the lower crust and caused amphibole breakdown during melting. This process could not provide enough water for the formation of porphyry Cu-Au deposits in western Yunnan, and therefore formed low–fO2, relatively low–H2O, and barren high–Sr/Y magmas. However, ultrapotassic magmas (e.g., lamprophyres) with high H2O are able to trigger intense water–fluxed, partial melting of metal–fertilized lower crust, which generated high–fO2, relatively high–H2O, fertile, high–Sr/Y shoshonitic magmas in this intracontinental setting.

Phanerozoic adakites typically represent modern analogues of Middle–Late Archean (3.5–2.5 Ga) tonalite–trondhjemite–granodiorite rocks (TTGs) due to their similarities in geochemical compositions. However, no Phanerozoic analogues have been reported for the Early Archean TTGs (>3.5 Ga), which are characterized by low Sr, Y and HREEs contents with low MgO and compatible elements contents, until recent years. The newfound Phanerozoic analogues have been defined as a new adakite subgroup named as “Jamaican–type adakites” (JTAs), and been regarded as the results of partial melting of subducted oceanic plateau crust. JTA–like magmas also occur in the Nuri complex, southern Tibet. We report whole–rock geochemical, Sr Nd isotopic data, zircon U Pb ages and in-situ Hf isotopic data for adakitic quartz diorites, quartz monzonites and JTA–like quartz porphyries in the Nuri complex. Zircon U Pb dating indicates that these rocks were emplaced in the Late Cretaceous at 93.5–92.1 Ma. Combined with the continuous variation trends of major and trace elements, the similarities in terms of whole–rock Sr Nd and zircon Hf isotopic compositions indicate that the three types of rocks are genetically related, while the quartz diorites should represent the relatively primitive melts. High MgO (5.00–5.41 wt%), Cr (138–159 ppm), Ni (65.9–96.8 ppm) contents and Mg# values (66–69), high e Hf (t) values (10.5–11.9), e Nd (t) values (3.7), and low ( 87 Sr/ 86 Sr) i values (0.7046–0.7050) indicate that the quartz diorites were derived from partial melting of subducted Neo–Tethyan oceanic slab, and subsequently underwent metasomatic reaction with the mantle wedge during their ascent. Quartz monzonites and JTA–like quartz porphyries were originated from quartz diorites by two stages of fractional crystallization. Low MgO and compatible elements contents of the quartz porphyries were caused by fractionation of hornblende, biotite, with minor magnetite and allanite, while low Sr contents and Sr/Y ratios were mainly controlled by plagioclase fractionation. This means that the JTA–like geochemical features of the quartz porphyries were generated by fractional crystallization from the adakites derived from partial melting of subducted slab, rather than directly derived from partial melting of subducted oceanic plateau. Therefore, various petrogenetic possibilities of the JTA–like magmas should be considered when using them as modern analogues.

The 1600 km-long Gangdese magmatic belt features extensive Paleocene–Eocene I-type intrusive rocks and coeval volcanic successions, which can be divided into Group I (~69–53 Ma), Group II (~53–49 Ma), and Group III (~49–43 Ma), corresponding to Neo-Tethyan slab rollback, Neo-Tethyan slab breakoff, and ongoing Indian-Asian collision, respectively. The magmas from these three groups show significant variations in geochemical and isotopic compositions, which provide the information of the growth of continental crust in southern Tibet. The most voluminous magmatism in the Gangdese belt occurred during ~53–49 Ma. High zircon saturation temperature (up to 800 °C) and Ti in zircon temperature (up to 980 °C) estimations suggest there is a period of thermal anomaly during ~53–49 Ma. Starting from ~53 Ma, magmas have increased K2O contents, and their zircons have decreased Th/U ratios, and Y and Yb contents. Zircons from Group II have the most heterogeneous Hf isotopic compositions (eHf(t) = −5.3 to 15.1). These are evident of ingress of asthenosphere mantle in the arc, extensive crustal melting, and magma mixing. Magma underplating during this time is the main mechanism for the growth of continental crust. With the Indian-Asian collision going on, the magmas in Group III show high Th/Y and La/Yb ratios and K2O contents, but significantly low Tzr and T(ti-zr) values (mostly below 750 °C). These features suggest the water-fluxed melting of early arc residues occurred in the late stage of growth of continental crust. The crust has been thickened and nearly mature at this stage. This study has great implication on understanding of growth of continental crust in orogenic belts.

The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debated in comparing with its western counterparts. One major issue concerns the timing and nature of the Sanandaj-Sirjan magmatic-metamorphic belt (SSMB), which is made predominantly of metamorphic rocks and Jurassic to Early Cretaceous large plutonic complexes. The Alvand and Qory are two largest plutonic complexes locating in north-central and southern segments, respectively, of the SSMB. Careful LA-ICP-MS U/Pb analyses of the magmatic zircons from the Alvand plutonic complex reveal a smooth spectra, along which the concordant age increase gradually from 120 to 190 Ma; while that of Qory is step-like consisting of two stages, a Jurassic and a late Early Cretaceous ones, respectively. New geochemical data, combined with zircon Lu/Hf results suggest that (1) the Alvand granitoids mostly resulted from a long-lived, successive injection of juvenile-crust-sourced magma batches without obvious fractionation crystallization (FC); but (2) the two stages granitoids of the Qory complex both generated by FC of juvenile-crust-sourced magmas; and (3) the gabbros of the Alvand complex are geochemically of E-MORB-affinity while those of the Qory complex are typical continental arc mafic rocks. Previously published petrological and 40Ar/39Ar data have identified a broken, Jurassic to Early Cretaceous high-pressure metamorphic belt to the southwest of the SSMB, which likely represents the closed, southeastern equivalent of the northern Neotethyan Ocean, north of the Taurides-Anatolia-Armenia block. Thus, the SSMB in Iran, the Kapan belt in Caucasus, and the Serbo-Macedonian belt in northern Turkey form a huge Jurassic to Early Cretaceous continental margin arc system recording northeastwards subduction of the older Northern Neotethyan Ocean beneath Eurasia. The Albian-Cenomanian ophiolites such as Koy, Kermanshah, and Neyriz in Iran represent the eastern counterpart of the younger Southern Neotethyan Ocean, south of the Taurides-Anatolia-Armenia block. During the subduction of the Old Neotethys, an intraplate transform fault likely opened and generated a slab-window beneath the Alvand region, which provided a constant energy source to steadily heat the low crust. This model satisfactorily interprets the unusual geochronological framework and geochemistry of the Alvand complex.

Voluminous Jurassic granitoids within the Sanandaj–Sirjan Zone (SSZ) provide insight into the magmatic arc formed in the active margin of Eurasia. Here, we present new in situ zircon U–Pb, whole-rock major and trace element, and Sr–Nd isotopic data for the Gorveh Plutonic Complex (GPC) of the northwestern SSZ in Iran. Six samples from the plutons within the GPC yielded zircon U–Pb ages that range from 151 to 146 Ma. These plutons can be subdivided into two groups based on their geochemistry. Group 1 rocks (the Mobarak Abad diorites and the Gorveh gabbros and diorites) contain relatively high concentrations of the high field strength elements (HFSE; Nb, Ta, Zr, and Ti) and have low Th/Nb (0.20–0.56) and moderate Sm/Yb ratios (1.51–2.32), low (87Sr/86Sr)i values (0.70354–0.70622), and high eNd(t) values (2.3–5.4). These features indicate that the Group 1 rocks formed from magmas derived from a subduction-modified region of the subcontinental lithospheric mantle. The Group 2 plutons (the Bolban Abad granites and the Gorveh quartz monzonites) have A-type granites affinities, including high K2O + Na2O and Zr + Nb + Ce + Y concentrations, and high FeOtot/MgO and 10,000 × Ga/Al ratios. These A-type rocks are enriched in Rb, Th, and K, and depleted in Ba, U, Nb, Ta, Sr, P, and Ti. The Group 2 plutons have different Sr–Nd isotopic compositions to each other, indicating they were derived from different sources and record different igneous processes. The Gorveh quartz monzonites have high (87Sr/86Sr)i ratios (0.70552–0.70617), negative eNd(t) values (−1.1 to −5.4), and extremely low concentrations of MgO (0.32–0.35 wt%), suggesting they were derived from an igneous quartzo-feldspathic crustal source. In comparison, the Bolban Abad granites have positive eNd(t) values and contain high concentrations of SiO2 and low concentrations of MgO, suggesting that they formed from Group 1 magmas that subsequently underwent assimilation and fractional crystallization processes. Combining these new data with the results of previous research, we conclude that this Jurassic magmatism was the result of the formation of a slab window within the subducting Neo-Tethys slab, a process that caused the partial melting of overlying continental lithospheric material.

The giant Zhuxi tungsten deposit is located in the Taqian-Fuchun Ore Belt in northeastern Jiangxi province, and genetically associated with the Zhuxi granitic stocks and dykes. Three mineralization-related granites including granite porphyry dykes (GP), biotite granitic stocks (BG), and white granitic dykes (WG), were identified in the Zhuxi deposit. SHRIMP zircon U–Pb analysis for the three granitic rocks present ages ranging from 153.5 ± 1.0 Ma to 150.4 ± 1.0 Ma. The BG mainly contains quartz, microcline, albite, biotite and muscovite with minor accessory minerals including zircon, apatite, monazite, Ti/Fe oxides, and dolerite. However, the WG is mainly composed of quartz, microcline and albite with minor muscovite and accessory minerals. The GP is a medium-grained porphyritic granite and its phenocrysts include quartz, alkali feldspar, muscovite and plagioclase. All the Zhuxi granites have high SiO2 content (71.97 wt%–81.19 wt%) and total alkali (3.25 wt%–9.42 wt%), and their valid aluminum saturation index (ASI) values show a wide range of 1.03 to 2.49. High Rb/Sr ratios, low Sr content (

Late Mesozoic magmatism is extensively developed in the eastern Jiangnan Orogen and is closely related to W, Mo, Cu, Au, and Sn mineralization. Late Mesozoic granitoids show various petrological and mineralizing features that vary spatially (northern Jiangxi Province and southern Anhui Province) and temporally (early stage: 154 to 136 Ma, late stage: 136 to 126 Ma). In this study, we analyzed zircon trace element data from four Late Mesozoic granitoids. Together with published zircon trace element data and biotite compositions from granitoids in the eastern Jiangnan Orogen and W–Sn, Mo and Cu deposits, we use these data to determine the magmatic redox state of the Late Mesozoic granitoids, which is useful in determining mineralization competency and is instructive during exploration. The results show that early stage granitoids of southern Anhui Province are oxidized, characterized by high zircon Ce4+/Ce3+ (median = 278), Ce/Nd (median = 17.1), and EuN/EuN* (median = 0.42) ratios, and high biotite Fe3+/Fe2+ ratios (median = 0.23) and XMg values (median = 0.48). The late stage granitoids of southern Anhui Province are relatively reduced, showing lower zircon Ce4+/Ce3+ (median = 49.7), Ce/Nd (median = 12.7), and EuN/EuN* (median = 0.16) ratios, and lower biotite Fe3+/Fe2+ ratios (median = 0.11) and XMg values (median = 0.38). The early stage granitoids of northern Jiangxi Province show a somewhat reduced redox state. They have comparatively low zircon Ce4+/Ce3+ (median = 17.28), Ce/Nd (median = 4.50), and EuN/EuN* (median = 0.17) ratios, and comparatively low biotite Fe3+/Fe2+ ratios (median = 0.07, N = 160) and XMg values (median = 0.35). The late stage granitoids of northern Jiangxi Province are strongly reduced, characterized by low zircon Ce4+/Ce3+ (median = 17.03), Ce/Nd (median = 0.72), and EuN/EuN* (median = 0.02) ratios, and low biotite Fe3+/Fe2+ ratios (median = 0.06) and XMg values (median = 0.25). Geochemical and isotopic data reveal that early stage granitoids in northern Jiangxi Province were sourced from Neoproterozoic metasedimentary rocks, whereas those in southern Anhui Province originated from Neoproterozoic volcanic–sedimentary sequences. The late stage granitoids in the eastern Jiangnan Orogen formed under an extensional regime and were generated by anatexis with various mantle inputs. The results suggest that early stage granitoids of southern Anhui Province have the potential for Cu (>1 Mt) and Mo (>0.3 Mt) mineralization, whereas late stage granitoids are related to W, Cu (

Dating of bitumen can potentially constrain both the timing of mineralization and hydrocarbon deposition in hydrocarbon-bearing hydrothermal deposits. Here we report for the first time direct Sm-Nd dating on bitumen from the Erdaokan Ag-Pb-Zn deposit, a newly discovered, large, hydrocarbon-bearing hydrothermal deposit with 2964 kt of ore and 1535 t Ag with an average grade of 517 g/t Ag, 0.6 wt% Pb and 0.41 wt% Zn in the Back-Arc basin of NE Great Xing’an Range, NE China. Dating results show that Sm-Nd isochron age of four bitumen samples is 234.6 ± 1.2 Ma and an isochron age that includes three galena and four bitumen samples is 234.9 ± 1.4 Ma. In order to verify these ages, we performed Rb-Sr dating on pyrite and galena from the same deposit and U-Pb dating of zircon from the adjacent diorite porphyrite dike, which yielded ages of 232.9 ± 2.3 Ma and 234.2 ± 2.8 Ma, respectively. The highly concordant ages from multiple techniques confirms that bitumen Sm-Nd isotopic dating is reliable, and that the ages obtained in our study represent the hydrocarbon deposition as well as mineralization timing in the deposit. We conclude that, in the Duobaoshan metallogenic belt, the Erdaokan Ag-Pb-Zn deposit is the first identified large, Middle Triassic, hydrocarbon-bearing silver-lead–zinc deposit and is of great significance to the regional metallogenesis research and prospecting work in the Great Xing’an Range.

The Miocene Sungun porphyry Cu–Mo systems, located in Azerbaijan belt, NW Iran, is associated with the high-Sr/Y magmas, which were engendered in a post-collisional setting. However, the petrogenesis of these fertile magmas and their mineralisation are still unknown. In this study, we present whole-rock major-trace elements, zircon U–Pb dating and the Lu–Hf isotopes in the ore-forming porphyries of the Sungun porphyry systems. The corresponding results showed that the samples were rich in large-ion lithophile elements and poor in high-field-strength elements; moreover, they presented both high K2O (2.4–3.5 wt%) and Sr (727–770 ppm) and low Y (11–14 ppm) contents. The zircon U–Pb age of the Sungun porphyry was ~19 Ma, with positive eHf(t) ratios (5.5–11.8) and young TDM2 ages between 322 and 705 Ma. Additionally, the Sungun high-Sr/Y porphyries contained anhydrites (CaSO4); and had high zircon Ce4+/Ce3+ ratios (33–728), relatively low zircon saturation temperatures (620–804 °C), and plagioclases with excess Al content. Overall, these evidences suggest that a water-fluxed melting of the subduction-modified juvenile lower crust might have generated a high oxygen fugacity, leading to the formation of the hydrous and S-rich Sungun fertile magmas in the NW Urumieh–Dokhtar magmatic Arc.

The Paleo-Tethyan tectonic evolution of north-central Tibet remains controversial, particularly regarding the nature and extension of associated sutures. The Yushu melange, located in the junction part of the western Jinshajiang, the southern Jinshajiang and the Ganzi–Litang sutures, is a key area to reveal the Paleo-Tethyan tectonics of this area. This study presents new geochronological and geochemical data for the Zhimenda volcanic suite of the Yushu Melange. These rocks preserve a record of back-arc magmatism along the northern margin of the North Qiangtang Block. The Zhimenda volcanics are composed of ignimbrite, basalt, and porphyritic tuff intercalated with terrigenous clastic rocks. Zircon 206 Pb/ 238 U ages of the ignimbrites indicate they formed at ~ 254 Ma. The basalts are relatively enriched in large-ion lithophile elements and depleted in high field strength elements. Their high MgO, Ni, and Cr contents, relatively high Sm/Yb and Rb/Nb values, and positive zircon e Hf (t) and bulk e Nd (t) values suggest they were derived from the partial melting of a depleted subcontinental lithospheric mantle source metasomatized by hydrous fluids. The Zhimenda basalts are geochemically similar to back-arc basin basalts in the Okinawa Trough. They were erupted related to subduction of the Longmuco–Shuanghu Paleo-Tethyan oceanic plate beneath the North Qiangtang Block. We propose that the Yushu Melange converges with the Ganzi–Litang Suture Zone to the east, rather than with the Jinshajiang Suture Zone to the southeast, and that a huge Permian trench–arc–back-arc system developed in north-central Tibet.

The recently discovered Zhuxi W–Cu ore deposit is located within the Taqian–Fuchun Ore Belt in the southeastern edge of the Yangtze Block, South China. Its inferred tungsten resources, based on new exploration data, are more than 280 Mt by 2016. At least three paragenetic stages of skarn formation and ore deposition have been recognized: prograde skarn stage; retrograde stage; and hydrothermal sulfide stage. Secondly, greisenization, marmorization and hornfels formation are also observed. Scheelite and chalcopyrite are the dominant metal minerals in the Zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding Carboniferous carbonate sediments (Huanglong and Chuanshan formations) and the Neoproterozoic slate and phyllites. The scheelite was mostly precipitated during the retrograde stage, whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage. A muscovite 40Ar/39Ar plateau age of about 150 Ma is interpreted as the time of tungsten mineralization and molybdenite Re–Os model ages ranging from 145.9 ± 2.0 Ma to 148.7 ± 2.2 Ma (for the subsequent hydrothermal sulfide stage of activity) as the time of the copper mineralization. Our new molybdenite Re–Os and muscovite 40Ar/39Ar dating results, along with previous zircon U–Pb age data, indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 Myr, from 150.6 ± 1.5 to 145.9 ± 1 Ma, and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite. The new ages reported here confirm that the Zhuxi tungsten deposit represents one of the Mesozoic magmatic–hydrothermal mineralization events that took place in South China in a setting of lithospheric extension during the Late Jurassic (160–150 Ma). It is suggested that mantle material played a role in producing the Zhuxi W–Cu mineralization and associated magmatism.

Understanding the geological history of the Lhasa Terrane prior to the India–Asia collision (~ 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene (~ 18–10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183–174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr–Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I–S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

The deep crustal continental components and architecture of the western Central Asian Orogenic Belt (CAOB) have long been a matter of debate. This article presents an integrated study of published geochronological and Hf-in-zircon isotopic data for inherited zircons from the Palaeozoic granitoid rocks and associated felsic volcanic rocks of the Chinese Altai, East Junggar, and nearby regions. The aim is to trace the age spatial distribution of deep old crustal components. Our data set comprises 463 published age data obtained by SHRIMP and LA-ICP-MS from felsic igneous rocks in these areas. Among these samples, zircon xenocrysts were observed in 69 granitic rocks and 15 felsic volcanic rocks from the Chinese Altai and 30 granitoid rocks and five felsic volcanic rocks in the East Junggar, respectively.Three major zircon xenocrysts provinces are defined based on the distribution of these inherited zircon ages, combined with Hf-in-zircon isotopes. Province I, mainly situated in the eastern part of th...

The Cenozoic Mianning–Dechang (MD) rare earth element (REE) belt in eastern Tibet is an important source of light REE in southwest China. The belt is 270 km long and 15 km wide. The total REE resources are >3 Mt of light rare earth oxides (REO), including 3.17 Mt of REO at Maoniuping (average grade = 2.95 wt.%), 81,556 t at Dalucao (average grade = 5.21 wt.%), 0.1 Mt at Muluozhai (average grade = 3.97 wt.%), and 5764 t of REO at Lizhuang (average grade = 2.38 wt.%). Recent results from detailed geological surveys, and studies of petrographic features, ore-forming ages, ore forming conditions, and wallrock alteration are synthesized in this paper. REE mineralization within this belt is associated with carbonatite–syenite complexes, with syenites occurring as stocks intruded by carbonatitic sills or dikes. The mineralization is present as complex vein systems that contain veinlet, stringer, stockwork, and brecciated pipe type mineralization. Carbonatites in these carbonatite-related REE deposits (CARDs) are extremely rich in light REEs, Sr (>5000 ppm), and Ba (>1000 ppm), and have low Sr/Ba and high Ba/Th ratios, and radiogenic Sr–Nd isotopic compositions. These fertile magmas, which may lead to the formation of REE deposits, were generated by the partial melting of sub-continental lithospheric mantle (SCLM) that was metasomatized by REE- and CO2-rich fluids derived from subducted marine sediments. We suggest that this refertilization occurred along cratonic margins and, in particular, at a convergent margin where small-volume carbonatitic melts ascended along trans-lithospheric faults and transported REEs into the overlying crust, leading to the formation of the CARDs. The formation of fertile carbonatites requires a thick lithosphere and/or high pressures (>25 kbar), a metasomatized and enriched mantle source, and favorable pathways for magma to ascend into the overlying crust where REE-rich fluids exsolve from cooling magma. The optimal combination of these three factors only occurs along the margins of a craton with a continental root, rather than in modern subduction zones where the lithosphere is relatively thin. U–Pb zircon dating indicates that the Maoniuping, Lizhuang, and Muluozhai alkali igneous complexes in the northern part of the belt formed at 27–22 Ma, whereas the Dalucao complex in the southern part of the belt formed at 12–11 Ma. Biotite and arfvedsonite in Lizhuang and Maoniuping REE deposit have 40Ar/39Ar ages of 30.8 ± 0.4 Ma (MSWD = 0.98) and 27.6 ± 2.0 Ma (MSWD = 0.06), respectively. Biotitaion alteration in syenite and fenitization caused by the relatively amount of carbonatite on syenite and host rocks is the main alteration along the whole belt. Initial Sr (0.7059–0.7079), 143Nd/144Nd (0.5123–0.5127), and 207Pb/204Pb (15.601–15.628) and 208Pb/204Pb (38.422–38.604) isotopic compositions of fluorite, barite, celestite, and calcite in the MD belt are similar to those of the associated syenite and carbonatite. Given the relatively high contents of Cl, F, SO42−, and CO2 in the rocks of the complexes, it is likely that the REEs were transported by these ligands within hydrothermal fluids, and the presence of bastnasite indicates that the REEs were precipitated as fluorocarbonates. Petrographic, fluid inclusion, and field studies of the ores indicate that bastnasite and other REE minerals formed during the final stages ( The mineralization formed from magmatic and meteoric fluids containing CO2 derived from the decarbonation of carbonatite, as indicated by C–O isotopic values of hydrothermal calcite and bastnasite (δ13C = −4.8 to −8.7 and δ18O = 5.8 to 12.5‰) and O–H isotopic values of quartz (330 °C) and arfvedsonite (260 °C), which correspond to fluid isotope compositions of δ18O = 0.3–9.8‰ and δD = −70.0 to −152.8‰ in the belt. This study indicates that formation the largest REE deposits are related to voluminous carbonatite–syenite complexes, compositionally similar ore-forming fluids, extensive alteration, multiple stages of REE mineralization, and tectonic setting.

Recent studies argue that subduction-modified, Cu-fertilized lithosphere controls the formation of porphyry Cu deposits in orogenic belts. However, it is unclear if and how this fertilization process operates at cratonic edges, where numerous large non-arc Au-rich deposits form. Here we report data from lower crustal amphibolite and garnet amphibolite xenoliths hosted by Cenozoic stocks that are genetically related to the Beiya Au-rich porphyry deposits along the western margin of the Yangtze craton, China. These xenoliths are thought to represent cumulates or residuals of Neoproterozoic arc magmas ponding at the base of arc at the edge of the craton that subsequently underwent high-pressure metamorphism ca. 738 Ma. The amphibolite xenoliths are enriched in Cu (383–445 ppm) and Au (7–12 ppb), and a few garnet amphibolite xenoliths contain higher Au (6–16 ppb) with higher Au/Cu ratios (2 × 10 −4 to 8 × 10 −4 ) than normal continental crust. These data suggest that metal fertilization of the base of an old arc at the edge of the craton occurred in the Neoproterozoic via subduction modification, and has since been preserved. The whole-rock geochemical and zircon Hf isotopic data indicate that melting of the Neoproterozoic Cu-Au–fertilized low-crustal cumulates at 40–30 Ma provided the metal endowment for the Au-rich porphyry system at the cratonic edge. We therefore suggest that the reactivated cratonic edges, triggered by upwelling of asthenosphere, have the potential to host significant Au ore-forming systems, especially non-arc Au-rich porphyry deposits.

New major and trace elemental, Sr–Nd–Pb isotope, and zircon U–Pb geochronological and Hf–O isotope data of post-collisional potassic and ultrapotassic volcanic rocks (PVRs and UPVs, respectively) along with geochemical data of PVRs, UPVs, and Mg-rich potassic rocks (MPRs) in the literature are used to constrain their mantle source and genesis. The PVRs, UPVs, and MPRs share similar geochemical features but with some discrepancies, suggesting that they were derived from subcontinental lithospheric mantle (SCLM) with isotopic heterogeneity resulting from the varying contributions of subducted Indian lower crust into the mantle source (ca. 6–20%, ca. 8–30%, and ca. 9–30%, respectively). The zircon Hf–O isotopic compositions of these rocks can be classified into two groups, including Group I rocks with high δ18O (6.7–11.3‰), low eHf(t) (− 17.0 to − 12.0), and old Hf crustal model ages (1.87–2.19 Ga) that indicate an ancient SCLM source, and Group II rocks with δ18O values of 6.8–10.7‰, eHf(t) values of − 11.8 to − 6.3, and younger Hf crustal model ages (1.50–1.86 Ga). The negative correlation defined by δ18O and eHf(t) of Group II samples suggests a two-component mixing between mantle- and crust-derived melts, in which the latter would be the subducted Indian lower crust as indicated by the similar negative eHf(t) values between Group II samples (− 11.8 to − 6.3) and the High Himalayan gneiss (− 14.2 to + 0.3). Thus we propose two enrichment events to account for the Hf–O isotopic compositions of the PVRs and UPVs/MPRs: the first involves the enrichment of the overlying SCLM that was metasomatized by fluids derived from dehydration of the subducted Indian lower crust, and the second invokes the enrichment of the overlying SCLM metasomatized by melts of the already dehydrated different proportions of the Indian lower crust. We argue that break-off of the northwards subducted Indian Plate in the early Miocene caused the asthenospheric upwelling under the Indian plate through slab window, resulting in varying degrees of partial melting of the overlying metasomatized heterogeneous SCLM to produce the primitive magmas of the PVRs, UPVs, and MPRs in an extensional setting. These observations and interpretations imply that the Indian lower crust was subducted beneath the Lhasa terrane in the Early–Middle Miocene.

Ore systems are located in zones of enhanced and focused heat and fluids flux within the lithosphere. In order to target deep ore deposits under cover, a better understanding of lithospheric architecture is essential, especially in relation to magmatism and fluids. Here we attempt an integrated approach using zircon Lu Hf isotopic mapping (455 samples with 5049 zircon analyses, including 1021 new data), combined with whole-rock geochemistry and isotopes of mantle-derived mafic rocks, high-resolution seismic tomography from 325 seismic stations and new thermochemical modelling, to establish the lithosphere architecture in southeastern Tibet. The integrated data suggest lithospheric refertilisation accompanied by heat flux from the asthenosphere, and also reveal the evolutionary pathway of the volatile components. The approach adopted in our study can be used in exploration for porphyry Cu Au, orogenic-Au and rare earth element deposits in Southeastern Tibet, and illustrate the usefulness of lithosphere-architecture mapping as a useful tool for mineral exploration.

The Bilihe gold deposit, along the northern margin of the North China Craton (NCC), is hosted in Permian intrusions that were emplaced into Bainaimiao Group greenschist- to amphibolite-facies Mesoproterozoic basement rocks, the early Paleozoic Bainaimiao Arc, and late Paleozoic sedimentary and volcanic cover rock sequences. The Middle Ordovician to Early Silurian calc-alkaline arc comprises volcanic sequences of basalt, andesite, and felsic lavas, and an intrusive complex ranging from gabbro through granite. The deposit is genetically related to ilmenite-series and highly fractionated quartz diorite porphyry host rocks. The most fractionated variety of the quartz diorite porphyry is granitic, which contains dendritic quartz phenocrysts and occurs at the top part of the intrusions. Gold mostly occurs as Au grains (> 990 fineness) in trails in dendritic quartz, and the gold trails typically occur along certain crystallographic elements of dendritic quartz. The gold is believed to have crystallized directly from magma at temperatures of at least 750–800 °C. The Fe2O3/(Fe2O3 + FeO) ratio of the quartz diorite ranges from 0.21 to 0.29, and there is significantly more ilmenite than magnetite, suggesting that the magma was moderately reduced. There are also post-ore syenogranite porphyries in the deposit area. Zircon U-Pb LA-ICP-MS dating in this study shows that two samples of the volcanic wallrock have ages of 274 ± 3 Ma and 270 ± 4 Ma, two samples of gold-forming quartz diorite porphyries have ages of 261 ± 2 Ma and 259 ± 3 Ma, with 440–400 Ma and 1344–1316 Ma cores, and one syenogranite porphyry sample is dated at 253 ± 3 Ma. The mineralized quartz diorite porphyries exhibit a high-K calc-alkaline composition, high Mg# (46–51), and a high content of compatible elements (V: 114–164 ppm; Cr: 80–93 ppm; Ni: 37–42 ppm) and Rb, Th, and U, as well as depletions in Ba, Sr, and HFSE (e.g., Ti, Nb, and Ta), suggesting melt from a slab fluid-metasomatized enriched mantle. The LREE enrichment, the intermediate oxidation state, and the presence of the Silurian and Mesoproterozoic zircon cores indicate that crustal materials also played a significant role in porphyry formation. In addition, the rocks have slightly negative eNd(t) (− 2.5–0.1), but variable (87Sr/86Sr)i (0.70328–0.70573). Based on the above features, we propose that quartz diorite porphyries were produced by partial melting of the metasomatized mantle coupled with the assimilation of crustal materials of the Bainaimiao Group, Late Ordovician-Silurian subduction-related plutons, and Late Carboniferous-Early Permian marine sedimentary rocks. The assimilation of rocks of the Bainaimiao Group, which have an elevated gold content of 26.3 ppb, is speculated to have played important roles in the formation of a rarely documented magmatic gold deposit. In contrast, syenogranite porphyries are characterized by high contents of K2O + Na2O (10.3–10.6 wt%), Al2O3 (16.3–16.5 wt%), K, Hf, and Zr; low CaO (0.6–1.2 wt%), Mg# values (17–21), compatible elements (V: 16–21 ppm; Cr: 4.9–7.9 ppm; Ni: 2.8–4.5 ppm), and Eu, Sr, and HFSE; and positive eNd(t) (1.4–1.5) with low (87Sr/86Sr)i (< 0.70431), indicating that the porphyries were formed by partial melting of the subduction-modified lower crust with a minor input of asthenospheric materials. It is concluded that the quartz diorite porphyries formed during the southward subduction of the Paleo-Asian ocean underneath the northern margin of the NCC. This confirms that the northern margin was not a passive continental margin, but an active margin with subduction and development of a continental arc. In addition to Bilihe, there are at least four more gold deposits (Hadamiao, Changshanhao, Saiyinwusu, and Chaihulanzi) that formed at the northern margin of the NCC from Middle Permian to Early Triassic. Such a timing indicates that they may also be ultimately related to the tectonic regime imposed by southward subduction of the Paleo-Asian ocean. Based on the new understanding of the tectonic setting, with significant known mineral occurrences along the length of the margin, it is inferred that the > 1000-km-long northern margin of NCC may have a large potential for subduction-related mineralization.

Jiru is a poorly studied Cu deposit located in the west segment of the Gangdese porphyry Cu belt (GPCB), 200 km west of Lhasa. The deposit consists of both collisional- and postcollisional-stage porphyry-type Cu systems, which are genetically associated with the early Eocene granitoid batholith and the Miocene Jiru porphyry stock, respectively. In this study, we present zircon U–Pb LA-ICP-MS dates and Hf isotopes, whole rock geochemical and Pb isotope geochemical data for the main intrusions in the Jiru deposit. The early Eocene granitoid samples (~ 49 Ma) are characterized by magmatic arc geochemical features, slightly concave REE patterns and well-developed negative Eu anomalies. These geochemical characteristics suggest that the granitoid melts were generated by partial melting of a metasomatized mantle, and that the melt had undergone fractional crystallization of amphibole and plagioclase. In contrast, the Miocene porphyry intrusions (16.4–15.5 Ma) at Jiru are characterized by high K contents, adakitic affinities (e.g., high Sr/Y and La/Yb ratios), subduction signatures (e.g., enriched Cs, Rb, Ba and depleted Nb, Ta, Ti), positive zircon eHf(t) values (1–6) and variable 208Pb/204Pb ratios (38.5–39.0), similar to other post-collisional porphyry intrusions in the Gangdese belt. Based on the above features, we propose that the Miocene porphyry intrusions at Jiru were generated by partial melting of subduction-modified lower crust. Well-developed negative Eu anomalies and low Sr/Y ratios (generally

The 1600 km-long Gangdese magmatic belt features extensive Paleocene–Eocene I-type intrusive rocks and coeval volcanic successions, abundant but more localized Oligo-Miocene calc-alkaline to alkaline plutons, and Miocene potassic to ultrapotassic volcanic rocks. These Cenozoic igneous rocks record geodynamic changes related to the India–Asia collision which began at ~ 55–50 Ma. New and published lithogeochemical and multiple isotopic (Os–Sr–Nd–O–Hf) analyses of these Cenozoic igneous rocks reveal that the Paleocene–Eocene magmas have similar compositions to continental arc rocks throughout the belt, but later Miocene magmas show sharp longitudinal contrasts in geochemical and isotopic compositions, which are also correlated with the occurrence of porphyry-type mineralization. Sparse Miocene high-K calc-alkaline to shoshonitic volcanic rocks in the eastern Gangdese belt have low to moderate (87Sr/86Sr)i ratios (0.7057–0.7121), moderately negative eNdi values (− 9.4 to − 3.4), low (187Os/188Os)i ratios (0.154–0.210), highly variable eHfi values (− 5.9 to + 10.1), and low zircon δ18O values (+ 5.0–+ 6.7‰), which are interpreted to reflect derivation by partial melting of subduction-modified Tibetan sub-continental lithospheric mantle (SCLM). In contrast, Miocene high-K calc-alkaline to shoshonitic volcanic rocks in the western Gangdese belt have higher (87Sr/86Sr)i ratios (0.7069–0.7263), more negative eNdi values (− 17.5 to − 6.0) and eHfi values (− 15.2 to + 0.7), and crust-like zircon δ18O values (+ 6.2–+ 8.8‰), but mantle-like (187Os/188Os)i values (0.156–0.182), and high Ni and Cr contents. These features suggest that potassic to ultrapotassic magmas in the western Gangdese belt were also derived from partial melting of Tibetan SCLM but with ~ 3–25% input of melts ± fluids from the underthrust Indian plate (87Sr/86Sr = 0.74–0.76, eNd = − 18 to − 10, δ18O = + 10 − + 14‰). In contrast, Miocene alkaline magmas to the east were unaffected by this source. Oligo-Miocene calc-alkaline to high-K calc-alkaline granitoids related to large porphyry Cu–Mo deposits in the eastern Gangdese belt (east of ∼ 89° E) are geochemically broadly similar to the early Paleocene–Eocene rocks. They are thought to be derived from partial melting of subduction-modified lower crust with mixing of alkaline melts from partial melting of SCLM, and have relatively low (87Sr/86Sr)i ratios (0.7047–0.7076), high eNdi values (− 6.1 to + 5.5) and eHfi values (1.4–8.7), moderate (187Os/188Os)i ratios (0.224–0.835), and low zircon δ18OVSMOW values (+ 5.5–+ 6.6‰). These magmas also had high water contents (weak Dy/Yb enrichment, characterized with amphibole fractionation) and oxidation states (ΔFMQ 0.8–2.9), which explain their unique association with porphyry Cu–Mo mineralization. In contrast, Miocene high-K calc-alkaline to shoshonitic granitoids in the western Gangdese belt (west of ∼ 89° E) show differences in geochemical and isotopic compositions to the earlier Paleocene–Eocene magmatism, and are characterized by crust-like zircon δ18O values (+ 6.2–+ 8.8‰), high (87Sr/86Sr)i ratios (0.7147–0.7165), negative eNdi values (− 11.3 to − 7.9), crust-like (187Os/188Os)i values (0.550–1.035), and low eHfi values (− 13.0 to 3.9). These magmas are interpreted to reflect involvement of melts ± fluids from the underthrust Indian plate and high degrees of crustal contamination upon emplacement. Only one small porphyry Cu–Mo deposit is known to be associated with these western granitoids. We suggest that this difference reflects the variable extent of underthrusting of the Indian plate continental lithosphere beneath Tibet in the Oligo-Miocene, and diachronous breakoff of the Greater India slab. In the absence of underthrust Indian lithosphere to the east of ~ 89° E in the Oligo-Miocene, slab breakoff triggered asthenospheric upwelling and partial melting of previously subduction-modified Tibetan lithosphere, generating hydrous, oxidized calc-alkaline magmas with the potential to generate porphyry Cu–Mo deposits. In contrast, underthrusting of the Indian plate to the west at this time limited the involvement of asthenospheric melts and the extent of partial melting of subduction-modified lithosphere, with the result that melts ± fluids derived from the underthrust lithosphere were infertile.

Porphyry copper deposits (PCDs) in Iran are dominantly distributed in Arasbaran (NW Iran), the middle segment of the Urumieh–Dokhtar Magmatic Arc (UDMA), and Kerman (central SE Iran), with minor occurrences in eastern Iran and the Makran arc. This paper provides a temporal–spatial and geodynamic framework of the Iranian porphyry Cu (Mo–Au) systems, based on geochronologic data obtained from zircon U–Pb and molybdenite Re–Os dating of host porphyritic rocks and molybdenites in 15 major PCDs. The dating results define a long metallogenic duration (39–6 Ma), and suggest a long history of tectonic evolution from the accretionary orogeny related to early Cenozoic closure of the Neo-Tethys Ocean to subsequent collisional orogeny for the Iranian porphyry copper systems. The oldest porphyry mineralization occurred in the eastern part of Iran after the closure of a branch of the Neo-Tethyan (Sistan) Ocean between the Lut and Afghan blocks in the late Eocene (39–37 Ma). This was followed by mineralization in the Kerman porphyry copper belt over a time interval of about 20 m.y., where two metallogenic epochs have been recognized, including late Oligocene (29–27 Ma) and Miocene (18–6 Ma). The Bondar-e-Hanza deposit formed in the late Oligocene, while and the remaining dated deposits belong to Miocene epoch. According to the deposits' characteristics and their ages, the Miocene epoch can be divided into early, middle, and late stages. The Darreh Zar, Bakh Khoshk, Chah Firouzeh and Sar Kuh deposits formed during the early–middle Miocene. The largest porphyry deposits occur in the middle stage during the middle Miocene (14–11 Ma) and include the Sar Cheshmeh, Meiduk, Dar Alu and Now Chun deposits. These deposits were formed during crustal thickening, uplift, and rapid exhumation of the belt. The final stage of porphyry mineralization occurred during the late Miocene (9–6 Ma), and formed the Iju, Kerver, Kuh Panj and Abdar deposits. There were two porphyry mineralization stages in the Arasbaran porphyry copper belt in NW Iran, including an older late Oligocene (29–27 Ma) and a younger early Miocene (22–20 Ma) events. The Haft Cheshmeh deposit belongs to the older stage, and the world-class Sungun and Masjed Daghi deposits formed during the early Miocene. In the middle segment of the UDMA (Saveh–Yazd porphyry copper belt), PCDs formed during middle Miocene time (17–15 Ma). The geochronological results reveal that the porphyry mineralization moved from the northwest to southeast of UDMA over the time. Our dating results, combined with the possible late Eocene–Oligocene timing for collision between the Arabian and Iranian plates, support a model for Iranian PCD formation by partial melting of previously subduction-modified lithosphere in a post-subduction and post-collisional tectonic setting.

The northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt (NGPB), characterized by skarn and porphyry deposits, is one of the most important metallogenic belts in the Himalaya–Tibetan continental orogenic system. This belt extends for nearly four hundred kilometers along the Luobadui–Milashan Fault in the central Lhasa subterrane, and contains more than 10 large ore deposits with high potential for development. Three major types of mineralization system have been identified: skarn Fe systems, skarn/breccia Pb–Zn–Ag systems, and porphyry/skarn Mo–Cu–W systems. In this study, we conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf isotopic study of ore-forming rocks in the NGPB, specifically the Jiangga, Jiaduopule, and Rema skarn Fe deposits, and the Yaguila Pb–Zn–Ag deposit. Although some of these deposits (porphyry Mo systems) formed during the post-collisional stage (21–14 Ma), the majority (these three systems) developed during the main (‘soft collision’) stage of the India–Asia continental collision (65–50 Ma). The skarn Fe deposits are commonly associated with granodiorites, monzogranites, and granites, and formed between 65 and 50 Ma. The ore-forming intrusions of the Pb–Zn–Ag deposits are characterized by granite, quartz porphyry, and granite porphyry, which developed in the interval of 65–55 Ma. The ore-forming porphyries in the Sharang Mo deposit, formed at 53 Ma. The rocks from Fe deposits are metaluminous, and have relatively lower SiO2, and higher CaO, MgO, FeO contents than the intrusions associated with Mo and Pb–Zn–Ag mineralization, while the Pb–Zn–Ag deposits are peraluminous, and have high SiO2 and high total alkali concentrations. They all exhibit moderately fractionated REE patterns characterized by lower contents of heavy REE relative to light REE, and they are enriched in large-ion lithophile elements and relatively depleted in high-field-strength elements. Ore-forming granites from Fe deposits display 87Sr/86Sr(i) = 0.7054–0.7074 and eNd(t) = − 4.7 to + 1.3, whereas rocks from the Yaguila Pb–Zn–Ag deposit have 87Sr/86Sr(i) = 0.7266–0.7281 and eNd(t) = − 13.5 to − 13.3. In situ Lu–Hf isotopic analyses of zircons from Fe deposits show that eHf(t) values range from − 7.3 to + 6.6, with TDM(Hf)C model ages of 712 to 1589 Ma, and Yaguila Pb–Zn–Ag deposit has eHf(t) values from − 13.9 to − 1.3 with TDM(Hf)C model ages of 1216 to 2016 Ma. Combined with existing data from the Sharang Mo deposit, we conclude that the ore-forming intrusions associated with the skarn Fe and porphyry Mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central Lhasa subterrane, respectively. Melting of the ancient continental material was critical for the development of the Pb–Zn–Ag system. Therefore, it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the India–Asia continental collision.

The Beiya ore deposit is located in the northwestern Yangtze Block, to the southeast of the Tibetan Plateau, SW China. The deposit is hosted by a porphyritic monzogranitic stock that is cross-cut by a porphyritic granite and later lamprophyre dikes. The whole-rock geochemistry of the porphyritic monzogranite and granite intrusions is both potassic and adakite-like, as evidenced by high K2O/Na2O (2.2 to 24.8), Sr/Y (53.2 to 143.2), and (La/Yb)N (4.9 to 28.9) ratios. Both intrusions have comparable zircon U–Pb ages of ca. 36 Ma and eHf(t) values of − 6.8 to + 2.7. Zircons within these intrusions have Hf isotope crustal model ages with a prominent peak at ca. 840 Ma, and both of the intrusions have similar Sr–Nd–Pb isotopic compositions that are comparable to the compositions of amphibolite xenoliths hosted by potassic felsic intrusions in western Yunnan. The contemporaneous lamprophyre dikes show Nb–Ta depletion, enriched (87Sr/86Sr)i and eNd(t), and extremely low Nb/U ratios (1.6–3.6), suggesting that these dikes were formed from magmas generated by partial melting of a metasomatized subcontinental lithospheric mantle (SCLM). The geochemistry of the porphyritic intrusions and the lamprophyre dikes suggests that the Beiya porphyries formed as a result of partial melting of a thickened and K-rich region of the lower crust, triggered by melting of metasomatized SCLM. The ca. 840 Ma U–Pb ages and eHf(t) values (− 6.8 to + 2.7) of xenocrystic zircons within the porphyritic intrusions suggest that these zircons were produced in a continental arc setting at ca. 840 Ma. The peak Hf model age of the zircons crystallized from the intrusions and the U–Pb ages of the xenocrystic zircons within the intrusions suggest that these porphyritic intrusions formed from magmas sourced from a juvenile crust that formed at ca. 840 Ma. This juvenile crust is most likely the source for the metals within the porphyry–skarn deposits in the study area, as the SCLM-derived lamprophyre dikes in this area are barren. Massive Fe–Au orebodies (~ 99 million metric tons at an average grade of 2.61 g/t Au) within the study area are generally located within the skarn-altered boundary of the porphyritic monzogranite stock and along the faults in the surrounding Triassic carbonates. The Fe–Au orebodies are spatially and genetically associated with skarn comprising garnet and diopside. Petrographic observations show that the massive Fe–Au orebodies mainly consist of hematite and magnetite with disseminated pyrite that hosts native gold and electrum. The porphyritic granite contains porphyry-style mineralization in the form of disseminated and veinlet-hosted pyrite and chalcopyrite. Pyrite-hosted lattice-bound gold is present within both the massive Fe–Au and the porphyry-type mineralization in the study area, and is present at concentrations up to 10 ppm Au (as determined by in situ LA-ICP-MS analysis). Subsequent weathering altered the primary magnetite–hematite–sulfide assemblage in the Fe–Au orebody into a magnetite–limonite assemblage, and generated laterite-type mineralization in which gold is hosted by limonite.

The Jiagang W-Mo deposit is the first greisen-type tungsten deposit recognized in the Lhasa terrane, and thus it has important genetic implications for understanding the regional tungsten mineralization potential. Greisen-type orebodies dominate in the deposit. Ores characterized by veinlets and dissemination are located in intensively altered monzogranite and contact zones between the monzogranites and sedimentary rocks. The minor quartz vein-type orebodies occuring as large quartz veins mainly precipitated in the sedimentary rocks. Intrusions associated with the Jiagang deposit are monzogranites, which can be subdivided into medium-grained monzogranite (MMG), porphyritic monzogranite (PMG), and fine-grained monzogranite (FMG). The zircon U-Pb ages of the PMG and MMG are 18.2 ± 0.2 Ma and 18.6 ± 0.1 Ma, respectively. These ages are consistent with the muscovite 40Ar-39Ar plateau ages (18.7 ± 0.2 Ma, 18.5 ± 0.2 Ma) and the molybdenite Re-Os isochron age (19.0 ± 0.3 Ma) within errors, indicating that the Jiagang W-Mo mineralization took place during the post-collisional stage of the Indo-Asian continental collision. The mineralization is temporally, spatially and genetically associated with the monzogranitic intrusions. The FMGs have the lowest SiO2 contents (70.8–71.5 wt%), lowest differentiation index (DI = 85.7–86.3) and least obviously negative Eu anomalies (Eu/Eu* = 0.22–0.42). The PMGs and MMGs have higher SiO2 contents (72.6–76.3 wt%), higher differentiation index (DI = 89.3–92.7) and more negative Eu anomalies (Eu/Eu* = 0.11–0.24). Almost all of the rocks are strongly peraluminous (A/CNK = 1.02–1.29), enriched in LILEs and depleted in HFSEs. Concentrations of K2O, CaO, FeOT and TiO2 of the three types of monzogranites show negative correlations with SiO2, while P2O5 exhibits the opposite trend. Values of Nb/Ta decrease with SiO2 contents, and those of (La/Yb)N increase with La contents. Whole rock eNd(t) of the FMGs range from −11.3 to −11.1 with two-stage Nd isotopic model ages (TDM2) of 1741–1797 Ma, which are similar to those of the PMGs and MMGs (eNd(t) = −10.9– −10.6; TDM2 = 1709–1816 Ma). Zircon eHf(t) values of the PMG and MMG range from −13.8 to −5.3 with two-stage Hf isotopic model ages of 1439–1979 Ma. These data suggest that the ore-forming monzogranites are strongly peraluminous S-type granites, which should be derived from anatexis of the Proterozoic metagreywackes underneath the central Lhasa subterrane. The PMG and MMG are highly fractionated through various degrees of fractional crystallization of plagioclase, K-feldspar, biotite, monazite and allanite from the parental melts represented by the FMG. Zircon trace elements suggest that oxygen fugacity of the ore-forming magmas is relatively low and decreased as the magmas evolved, which is favorable to remove substantial tungsten from melts into the tungsten-mineralizing hydrothermal fluids. A high degree of fractional crystallization of the crustally-derived magmas with relatively low magmatic oxidation state are the critical factors determining the generation of the tungsten mineralization in the Jiagang deposit. Combined with the existing breakthroughs in prospecting exploration, we propose that the central Lhasa subterrane has great metallogenic potential in W-(Mo) mineralization associated with the Indo-Asian continental collision.

Numerous Au-rich deposits in the western South China Block, SW China, provide insights into the gold enrichment process at a lithospheric scale. Zhenyuan is a giant gold deposit in the western South China Block, but its genesis remains controversial with competing hypotheses of magmatic–hydrothermal and metamorphic–hydrothermal development. Here, we present new petrographic, major and trace element, and zircon U–Pb age data for quartz porphyry from the Zhenyuan deposit to evaluate the specific gold enrichment process. Zircon SHRIMP and LA–ICP–MS results demonstrate that the Zhenyuan quartz porphyries crystallized at ca. 255–247 Ma. This age is broadly consistent with the Re–Os age of gold-bearing pyrite measured in previous studies. The porphyries are characterized by high-K calc-alkaline compositions and exhibit significant enrichment in LILEs and LREEs, and strong depletion in HFSEs. They share the same source (Au-rich lower crust) with Cenozoic Au-bearing intrusions. The initial melts had a weak oxidation state (ΔFMQ = –0.15–0.55), which favored Au accumulation and migration. However, the gold was precipitated with the crystallization of Ti–Fe oxides in the middle crust, resulting in the emplacement of Au-poor magma in the upper crust. The gold orebodies in the Zhenyuan deposit formed due to Cenozoic hydrothermal processes, as evidenced by our observations of ore-bearing pyrite and Ar–Ar ages of phlogopite measured in previous studies. Combined with regional mineralization data, we propose lithosphere-scale processes for gold accumulation, migration, and precipitation from the Neoproterozoic to Cenozoic. Specifically, we predict an Au-rich middle crust beneath the western South China Block.

The Hegenshan ophiolite-arc-accretionary belt adjacent to the Solonker suture in central Inner Mongolia marks the closure of a back-arc ocean basin and an Early Permian extensional setting is a critical region to understand the final closure of the Paleo-Asian Ocean in relation to the construction of the Central Asian Orogenic Belt (CAOB). Since the Paleo-Asian Ocean still existed in Solonker during Permian, the Early Permian extensional regime as indicated by the widely distributed Permian A-type granites in this accretionary belt remains enigmatic. In order to address this issue, we investigate the large-scale Early Permian EW-trending dyke swarm in the Hegenshan belt through an integrated study on petrology, zircon U-Pb isotopic ages, whole rock major-trace elements, and Sr-Nd-Pb isotopes. These dykes were emplaced in the volcanic-plutonic complex of the Carboniferous continental arc. Our zircon U-Pb results show an age range of 289.9 ± 3.6 Ma to 274.6 ± 4.6 Ma for the dyke emplacement, which is slightly younger than the post-subduction bimodal volcanic-plutonic suite (305–299 Ma) which is closely associated with the dyke swarm. Based on field characteristics and geochemical data on the dykes, we recognize two magma types: calc-alkaline dykes and A-type granitic dykes. The calc-alkaline dykes include diorite and granodiorite, whereas the A-type granitic dykes are composed of granite porphyry and rhyolite, corresponding to a major phase of Early Permian bimodal magmatism in the Hegenshan belt. The diorite-granodiorite dykes exhibit a continuous evolutionary trend of calc-alkaline magma from gabbro through diorite to granodiorite. They also display enrichment in LILEs and LREEs, and depletion of HFSEs. These characteristics are consistent with the Late Carboniferous calc-alkaline plutons which are spatially and temporally associated with the diorite-granodiorite dykes. We therefore infer a common magma system, with the parent magma sourced from enriched lithosphere mantle. The granite porphyry-rhyolite dykes show marked consistency in geochemical and Sr-Nd-Pb isotopic compositions with the Late Carboniferous A-type granite and rhyolite in this area. Compared with the calc-alkaline diorite-granodiorite dykes, the granite porphyry-rhyolite dykes have significantly higher Rb, Th, HFSEs (Nb, Ta), HREEs (Yb) and Y, and lower Sr and Ba. These rocks exhibit the features of A2-type granites, possibly inherited from pre-existing subduction-related juvenile lower crust. The large-scale dyke swarm with bimodal signature suggests an extensional setting in the Carboniferous continental arc. Combined with the age data (305–299 Ma) of the Late Carboniferous bimodal magmatic rocks in the study area which denote the maximum age of the slab break-off, the emplacement time of the dyke swarm (289–274 Ma) provides robust constraints on the Early Permian extensional tectonic regime (305–274 Ma) in the Hegenshan accretionary belt. The Early Permian extension in this belt occurred prior to the closure of the Paleo-Asian Ocean and formation of the Central Asian Orogenic Belt, and the Hegenshan belt likely represents a back-arc formed through the northward subduction of the Paleo-Asian Ocean during Permian.

Northward Neo-Tethyan oceanic lithosphere subduction beneath southern Tibet in the Mesozoic–Early Cenozoic produced continental arc magmas in the ~ 1600 km-long Gangdese belt. The most voluminous magmatism occurred in the Paleocene–Eocene, and is characterized by extensive I-type calc-alkaline to high-K calc-alkaline Linzizong volcanic rocks, and coeval plutons. These rocks have been extensively studied in the eastern Gangdese belt (east of ∼ 89°E), but few data exist from the western Gangdese belt. New data for eleven samples of these rocks, combined with existing data from the literature, show that they are similar to the eastern Gangdese belt rocks, with relative depletions in Nb, Ta, P, and Ti, and enrichments in Rb, Ba, Th, U, K, Pb, Zr, and Hf on a primitive mantle-normalized trace element diagrams, typical of continental arc-related igneous rocks. However, compared to the east, western Gangdese igneous rocks range to higher K2O contents (up to 6.1 wt.%), higher (87Sr/86Sr)i ratios (up to 0.7151), and lower eNdi values (down to − 8.1), suggesting that an evolved crustal source was involved in arc magmatism. The Gangdese arc magmatism lasted to ~ 80 Ma, and has a gap or quiescent period afterwards. Starting at ~ 69 Ma, the arc magmatism initiated and shifted southward from ~ 30.5°N to ~ 29.5°N in southern Tibet with an abrupt change of India-Asia convergence rate. The magmas through the whole Gangdese belt at ~ 69–53 Ma are characterized by intermediate eNdi values (− 0.6 to + 4.0), positive eHfi values (+ 3.8 to + 7.1), intermediate δ18O values (+ 5.0‰ to + 6.5‰), and low Th/Y and La/Yb ratios (

The genesis of continental collision-related porphyry Cu deposits (PCDs) remains controversial. The most common hypothesis links their genesis with magmas derived from subduction-modified arc lithosphere. However, it is unclear whether a genetic linkage exists between collision- and subduction-related PCDs. Here, we studied Jurassic subduction-related Cu-Au and Miocene collision-related Cu-Mo porphyry deposits in south Tibet. The Jurassic PCDs occur only in the western segment of the Jurassic arc, which has depleted mantle-like isotopic compositions [e.g., ( 87 Sr/ 86 Sr) i = 0.7041–0.7048; e Nd(t) as high as 7.5, and e Hf(t) as high as 18]. By contrast, no Jurassic PCDs have been found in the eastern arc segment, which is isotopically less juvenile [e.g., ( 87 Sr/ 86 Sr) i = 0.7041–0.7063, e Nd(t) < 4.5, and e Hf(t) ≤ 12]. These results imply that incorporation of crustal components during underplating of Jurassic magma induced copper accumulation as sulfides at the base of the eastern Jurassic arc, inhibiting PCD formation at this time. Miocene PCDs are spatially confined to the Jurassic arc, and the giant Miocene PCDs cluster in its eastern segment where no Jurassic PCDs occur. This suggests that the arc segment barren for subduction-related PCDs could be fertile for collision-related PCDs. Miocene ore-forming porphyries have young Hf model ages and Sr-Nd-Hf isotopic compositions overlapping with those of the Jurassic rocks in the eastern segment, whereas contemporaneous barren porphyries outside the Jurassic arc have abundant zircon inheritance and crustlike Sr-Nd-Hf isotopic compositions. These data suggest that remelting of the lower crustal sulfide-bearing Cu-rich Jurassic cumulates, triggered by Cenozoic crustal thickening and/or subsequent slab break-off, led to the formation of giant Miocene PCDs. The spatial overlap and complementary metal endowment between subduction- and collision-related magmas may be used to evaluate the mineral potential for such deposits in other orogenic belts.

We have investigated a suite of Miocene high-Mg diorite porphyries from Qulong in southern Tibet, the largest porphyry Cu–Mo deposit in China. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating shows that the high-Mg diorite porphyry was emplaced at 15.7±0.2 Ma, which is slightly younger than the Qulong adakite-like Rongmucuola pluton (c. 19.5–16.4 Ma). The Qulong high-Mg diorites have phenocrysts showing disequilibrium textures and include high-Mg# clinopyroxene (0.91–0.97). These porphyry rocks exhibit both ultrapotassic and adakite-like features, and are characterized by high contents of MgO (4.2–5.1 wt %), K2O (3.2–3.6 wt %), and compatible trace elements (e.g. Ni: 115–142 ppm; Cr: 214–291 ppm), as well as by high Sr/Y and La/Yb ratios. The rocks have highly radiogenic isotopic compositions with (87Sr/86Sr)i = 0.707004–0.707198, eNd(t)=-5.1 to -5.5, 207Pb/204Pb = 15.697–15.704, and 208Pb/204Pb = 39.082 – 39.116, as well as variable zircon eHf values of -3.0 to +5.9. Petrographic, elemental, and isotopic evidence suggests that the Qulong high-Mg diorites were formed by mixing between ultrapotassic and adakite-like melts, derived from metasomatized Tibetan lithospheric mantle and juvenile lower crust, respectively. In contrast, the Qulong pre-ore Rongmucuola pluton is characterized by high SiO2 (66.3–68.9 wt %) and Al2O3 (16.4–17.0 wt %) contents, high Sr/Y ratios (121–151), low compatible element contents (e.g. Ni = 16.0 – 17.4 ppm; Cr=14.5–20.2 ppm), low Mg# values (0.44–0.52), positive large-ion lithophile element (LILE) anomalies, marked negative high field strength element (HFSE) anomalies, positive eNd(t) values (+0.4 to +2.5), and low (87Sr/86Sr)i values (0.704847–0.705237). These features indicate that the Rongmucuola pluton was formed by partial melting of subduction-modified juvenile lower crust within the garnet stability field. The newly identified Qulong high-Mg diorite allows us to propose a mixing model for the origin of the Gangdese high-K, adakite-like rocks. In this model, the formation of these rocks occurred in two stages: (1) partial melting of highly metasomatized lithospheric mantle that generated ultrapotassic mafic melts; (2) underplating of such melts beneath thickened juvenile lower crust, which resulted in melting of the lower crust and the generation of adakite-like magmas. Mixing of the adakite-like melt with ultrapotassic magmas elevated the K2O, MgO, and other LILE (e.g. Rb and Ba) contents of the adakite-like melt. Exogenous water necessary for formation of the Gangdese porphyry Cu systems was mainly added during mixing of ultrapotassic magma with adakite-like melt at lower and/ or upper-crustal depths, reflecting the large decrease in the H2O solubility of the ultrapotassic mafic melt upon ascent and decompression. Upper-crustal fractionation of the Rongmucuola magma could also possibly increase the water content of mineralization-related, adakite-like porphyry intrusions at Qulong. Fluid exsolution from the ultrapotassic magma is likely to have been a key process in the generation of the Gangdese porphyry Cu deposits, as well as other porphyry Cu deposits in the Tibetan collisional orogens.

The Himalayan Mianning–Dechang (MD) rare earth element (REE) belt in western Sichuan Province, southwestern China, is approximately 270 km long and 15 km wide, and contains total reserves of more than 3 Mt of light REEs (LREEs), comprising one giant (Maoniuping), one large (Dalucao), two small–medium-sized (Muluozhai and Lizhuang), and numerous smaller REE deposits. The belt occurs within the eastern Indo-Asian collision zone (EIACZ), where its location is controlled by large-scale strike-slip faults and tensional fissure zones. Himalayan carbonatite–syenite complexes consist predominantly of alkaline syenite stocks and carbonatite sills or dikes that host REE mineralization. Previous studies have reported inconsistent ages for alkaline magmatism syenite formation and REE mineralization. Here, we present new results of sensitive high-resolution ion micro-probe U–Pb dating of zircons from syenites from the Dalucao, Maoniuping, Lizhuang and Diaoloushan areas, the first systematic and precise age determinations for these rocks in the MD belt. The new data give concordant ages of 12.13 ± 0.19 and 11.32 ± 0.23 Ma for the Dalucao deposit, 22.81 ± 0.31 and 21.3 ± 0.4 Ma for Maoniuping, 26.77 ± 0.32 Ma for Muluozhai, and 27.41 ± 0.35 Ma for Lizhuang. These ages, which should be regarded as maximum ages for the REE mineralization in the study area, can be split into two groups, i.e. 11–12 Ma in the southern part of the MD belt and 12–27 Ma in the northern part, suggesting a progression of magmatism from north to south. These data suggest that the majority of carbonatite–syenite magmatism within the EIACZ occurred during the main stage of Himalayan metallogenesis. The ages presented in this study suggest that strike-slip shear along the MD belt was initiated at ca. 27 Ma and ended ca. 12 Ma. This timing is consistent with movements along the adjacent Ailaoshan–Red River strike-slip fault in southeastern Tibet (to the south of the MD belt) and one of the three Cenozoic strike-slip faults in eastern Tibet. Ascent of an asthenospheric mantle diapir beneath the EIACZ in the Cenozoic may have provided a thermal mechanism for the generation of magmas that formed the carbonatite–syenite complexes in the study area. Alternatitvely, the magmas may have been generated by decompression melting associated with the transition from a transpressional to a transtensional regime at 38–40 Ma. The precise age results for syenite magmatism in the study area indicate that this transition occurred prior to carbonatite–syenite magmatism and the formation of the MD REE belt, which is consistent with the regional tectonic model.

Uplift of the Tibetan Plateau and related crustal shortening are key issues in understanding collisional geodynamics, and magmatic rocks that formed in this compressional setting provide clues to the processes involved. Numerous granitic porphyry dikes have been identified in the Angsai area of the northern Qiangtang block in north-central Tibet. These dikes were emplaced along NW–SE-striking reverse faults that run parallel or sub-parallel to the thrust belt, suggesting that they are syn-collisional. New LA-ICP-MS zircon 206Pb/238U and magmatic biotite 40Ar/39Ar results demonstrate that the dikes crystallized at ca. 64 Ma, and the bulk geochemistry of the dikes shows that they are adakitic, with high Sr/Y and La/Yb ratios, and low Y and Yb contents. Their low MgO, Ni, and Cr contents, along with positive zircon eHf(t) and bulk eNd(t) values, suggest that the adakitic rocks were the result of partial melting of a juvenile thickened lower crust. Our new data indicate the uplift of north-central Tibet which started as early as 64 Ma. Synthesizing available geochronological, geochemical, and structural data, it seems that the crustal shortening and uplift of the plateau is a long-lived process consisting of a rapid early stage, and a slow and more constant later stage. Collision-related magmatic activity peaked at the time of transition between those two stages.

In the Gangdese belt of southern Tibet, Paleocene-Eocene magmas record the final stage of Neo-Tethyan subduction and are associated with few economic porphyry deposits. In contrast, magmas formed during later stages of the India-Asia collision in the Oligo-Miocene are associated with several large porphyry Cu-Mo ± Au deposits, especially in the eastern part of the belt (~89°E–93°E). In a previous study, we showed that these Oligocene-Miocene magmas were more hydrous than the earlier Paleocene-Eocene magmas. In this study, we show that the later magmas were also more oxidized. Paleocene-Eocene rocks from the eastern Gangdese belt are characterized by low zircon Ce4+/Ce3+ ratios (mostly 50; 32.3–141.9, average = 74.3 ± 30.1, n = 33) and higher f O2 values (ΔFMQ 0.8–2.9, average = 1.8 ± 0.8, n = 6; estimated from magnetite-ilmenite pairs). Estimates of magmatic oxidation state from amphibole compositions also show an increase from ΔFMQ 1.2 to 2.1 (average = 1.6 ± 0.2, n = 40) in the Paleocene-Eocene to 2.0 to 2.8 (average = 2.5 ± 0.2, n = 58) in the Miocene. Sparse whole-rock Fe3+/Fe2+ ratios show the same general trend. The amphibole results are systematically shifted to higher ΔFMQ compared to data from magnetite-ilmenite pairs, but their trend is internally consistent. The higher oxidation states (and water contents) of Miocene igneous rocks from the eastern Gangdese belt may explain their unique association with large porphyry deposits in Tibet, because it has been shown from other studies that the potential for hydrous calc-alkaline magmas to transport Au is maximized near ΔFMQ 1.0, and Cu at higher f O2 (ΔFMQ > 1.0). In comparison, the somewhat less oxidized and less hydrous Paleocene- Eocene magmas would have been less fertile for the formation of such deposits. We suggest that these differences reflect the tectonomagmatic evolution of the Cenozoic Gangdese collisional orogen, from early collision-related magmatism in the Paleocene-Eocene to late collisional magmatism in the Miocene. Asthenospheric upwelling following slab breakoff in the Miocene caused interaction between mantle-derived magmas and previously subduction modified Tibetan lithosphere. The resultant evolved magmas had high oxidation states and water contents, which are favorable properties for the subsequent formation of magmatic-hydrothermal porphyry Cu-Mo ± Au deposits.

article i nfo We have conducted a whole-rock geochemical, U-Pb zircon geochronological, and in situ zircon Hf- Oi sotopic compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz-diorite). U- Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two- mica granite were emplaced at ca. 96 Ma and 80-76 Ma, respectively, and that the Nuri quartz-diorite was emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and mafic enclaves in the Langxian area, felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite- like rocks. The high Mg-numbers, high abundance of compatible elements, high eNd(t) (2.7 and 2.8) and δ 18 O (8.9 and 9.2‰) values, elevated zircon eHf(t) (11.0-17.0) values, and low 87 Sr/ 86 Sr(i) ratios (0.7040), collectively indicatethattheNuriadakite-likequartz-dioritewasderivedfrompartialmeltingofthelowtemperaturealtered Neo-Tethyan oceanic crust, and that these dioritic magmas subsequently interacted with peridotite as they rose upwards through the overlying mantle wedge. The observation of identical differentiation trends, similar whole- rock Sr-Nd and zircon Hf isotopic compositions, and consistently low (Dy/Yb)N ratios among the Langxian igneous suite rocks, indicates that the adakite-like granodiorite was produced by low-pressure fractional crystal- lization of precursor magmas now represented by the (relict) mafic enclaves. However, relatively high Al2O3 contents, low MgO, Cr and Ni contents, and low (La/Yb)N and (Dy/Yb)N values indicate that the two-mica granite was derived from partial melting of the southern Tibetan mafic lower crust in the absence of garnet, while isotopic data suggest that at least 70% of the magma source region was juvenile materials. Combined with the presence of HT (high temperature) charnockitic magmatism, HT granulite facies metamorphism, and large volumes of Late Cretaceous batholiths, the oceanic-slab-derived Nuri adakitic rocks indicate a substantial high heat flux in the Gangdese batholith belt during the Late Cretaceous, which may have been related to subduction ofaNeo-Tethyanmid-oceanridgesystem.According to thismodel,hot asthenosphere wouldrise upthroughthe correspondingslabwindow,andcomeintodirectcontactwithboththeoceanicslabandthebaseoftheoverlying

The Yao’an porphyry Au system, Machangqing porphyry Cu-Mo system, and Beiya porphyry-skarn Au system, are spatially and temporally associated with potassic felsic intrusions emplaced during the Eocene to Oligocene epochs at 37 to 33 Ma in a postcollisional intracontinental setting in western Yunnan, western Yangtze craton, China. The Yao’an monzonite and quartz monzonite porphyry intrusions are alkaline and potassic with high K 2 O/Na 2 O ratios (1.1–1.5). They have Sr-Nd-Pb isotopes similar to coeval lamprophyres and are characterized by uniform zircon ɛ Hf (−6.4 to −8.7) and δ 18 O values (6.6–7.0‰). They are interpreted as products of fractional crystallization of lamprophyre-like potassic mafic magma derived from ancient metasomatized lithospheric mantle, a scenario similar to the mid-Cretaceous postcollisonal Scheelite Dome gold system in Yukon, Canada. The Machangqing granitic intrusions are high K calc-alkaline and show high Sr, Sr/Y, and La/Yb, but low Y and Yb geochemical signatures. They have Sr-Nd-Pb isotope compositions similar to amphibolite xenoliths hosted by potassic felsic intrusions in western Yunnan. The zircon ɛ Hf values of the Machangqing granitic intrusions are positive (0.3–4.7), and the zircon-depleted Hf mantle model ages are 1.1 to 0.8 Ga. They also have mantle-like zircon δ 18 O values (5.5–6.4‰). The Machangqing granites were most likely derived from partial melting of Neoproterozoic lower crust. The Beiya granitic intrusions are alkaline, with high K 2 O/Na 2 O (1.9–2.7), Sr/Y and La/Yb ratios, high Sr contents, and low Y and Yb contents. They contain abundant zircon inheritance and have variable magmatic zircon ɛ Hf (−4 to +4) and the highest magmatic zircon δ 18 O values (6.6–7.8‰). The Beiya felsic intrusions are interpreted to be derived from partial melting of a K-rich mafic source mixed with a metasedimentary component. The Eocene-Oligocene intracontinental potassic intrusions and associated mineralization in western Yunnan are located proximal to the Mesozoic Jinsha suture, suggesting that this Mesozoic lithospheric boundary may have provided a first-order control on localization of Cenozoic mineral systems. These potassic felsic intrusions are coeval with regional potassic mafic magmatism in western Yunnan and were emplaced between 37 to 33 Ma, after the collision between India and Asia at ca. 60 to 55 Ma. It is therefore postulated that continental collision may have preferentially thickened the continental lithospheric mantle (CLM) adjacent to the Jinsha suture, in which overthickened lower continental lithospheric mantle was subsequently removed during 37 to 33 Ma, inducing melting of residual metasomatized lithospheric mantle as well as lower crust. The gold-rich Yao’an and Beiya intrusions are alkaline and potassic, characterized by high zircon δ 18 O values (>6.5‰), which is consistent with supracrustal contributions. In contrast, the Cu-Mo-rich Machangqing intrusions are high K calc-alkaline with mantle-like zircon δ 18 O values ( ɛ Hf signatures, indicating negligible supracrustal recycling. Empirically, source compositions played an important role in determing the metal endowment among intrusions formed under the same tectonic setting with similar ages in western Yunnan. In western Yunnan, gold tends to be associated with alkaline and potassic melts with a supracrustal contribution, whereas Cu-Mo mineralization seems to be more related with juvenile crustal sources with little supracrustal influence.

The Oligocene to the Miocene was a critical period for the growth of the Tibetan Plateau. This growth is commonly considered to have been controlled by deep geodynamic processes. The ultrapotassic and adakite-like igneous rocks that developed during this period offer constraints on these deep-seated processes in southern Tibet. Whole-rock geochemistry, U-Pb zircon geochronology, and in situ zircon Hf isotopes have been determined for the mafic enclaves and host adakite-like granitoids in the Oligocene Chongmuda-Mingze intrusive complex of southern Tibet. The host rocks, including granodiorite and monzogranite, are mainly high-K and calc-alkaline in composition. Their whole-rock geochemistry (low MgO, Ni, and Cr contents; negative eNd(t) values [−2.5 to −3.4]; and low 87Sr/86Sr(i) values [0.7061–0.7066]) and in situ zircon eHf(t) values (0.6–6.1) indicate that they were derived by partial melting of a juvenile lower crust, implying that the southern Tibetan crust was already thickened to up to 50 k...

The relationship between potassic felsic intrusions, cospatial and cotemporal with potassic mafic magmatism, and strike–slip displacement along the Ailao Shan-Red River shear zone in western Yunnan, SW China has been highly controversial. We report 22 new SHRIMP zircon U–Pb ages from 19 potassic felsic intrusions located as far as 150 km east and 50 km west of the shear zone to constrain temporal relationships. The results show that the felsic intrusions in western Yunnan were emplaced between 36.9 ± 0.3 Ma and 32.5 ± 0.3 Ma. This age range is significantly shorter than previous dating of 38 Ma to 23 Ma using K–Ar and Ar–Ar methods from 15 intrusions, indicating that the latter are reset or cooling ages. Potassic felsic intrusions are coeval with potassic mafic volcanic rocks (36.6 Ma to 33.4 Ma) in the same area, supporting a possible genetic link between the two end members. The dated intrusions occur over a 200 km wide zone across the Ailao Shan-Red River shear zone; therefore they are unlikely genetically related to shearing. Rather, potassic mafic magmatism in western Yunnan may be related to delamination and melting of previously subduction-modified mantle lithosphere along the Mesozoic Jinsha suture reactivated in the Eocene–Early Oligocene, following the India-Asia continental collision; potassic felsic magmas were crustal melts hybridized with mafic liquids. Delamination in turn facilitated and localized initiation of the Ailao Shan-Red River shear zone at ca. 32 Ma during continental extrusion.

We describe the whole-rock geochemistry, biotite Ar–Ar and zircon U–Pb geochronology, and in situ Hf–O isotopic compositions of the Linzhi two-mica granitoid in the southeastern Lhasa terrane. The granitoids are calc-alkaline to high-K calc-alkaline in composition, and they have geochemical affinities with adakites. The whole-rock geochemistry, with high SiO2 and Al2O3 contents, low MgO, Cr, and Ni contents, low Mg# values, negative eNd(t) (− 6.2 to − 2.9), and low 87Sr/86Sr(i) (0.7059–0.7074), together with the in situ zircon Hf–O isotopic data (eHf(t) = − 2.7 to 2.7; δ18O = 7.2‰–8.8‰), indicates that the granitoid was derived mainly from the partial melting of a rejuvenated lower crust underneath the Lhasa terrane. This lower crust was dominated by ancient crustal material with the minor involvement of juvenile mantle inputs (

Among the Phanerozoic magmatic pulses that substantially modified the structure and composition of the subcontinental lithosphere of the North China Craton (NCC), the Mesozoic suite includes a wide variety of high Sr/Y and La/Yb rocks. The spatio-temporal distribution and characterization of these rocks are fundamental to evaluating the various models of decratonization of the NCC. Here we report petrologic, geochemical, Sr–Nd–Pb and U–Pb zircon isotopic data on the Mesozoic volcanic rocks from northern Taihang orogen in the eastern NCC. The magmatic zircons in these rocks display high Th/U values (0.4–1.7) and yield a 206Pb/238U age range of 152 Ma to 138 Ma, with a weighted mean of 145.6 Ma. The cores of inherited zircon xenocrysts yield discordant ages of 1840 Ma and 2013 Ma suggesting derivation from ancient crustal sources. Most of the volcanic rocks of our study posses moderately high initial 87Sr/86Sr ratios ranging from 0.7060 to 0.7062, and relatively low initial 143Nd/144Nd values from 0.5116 to 0.5117, defining a tight cluster in 87Sr/86Sr versus 143Nd/144Nd plots. They show low initial 206Pb/204Pb (16.590–16.807), 207Pb/204Pb (15.247–15.269) and 208Pb/204Pb (36.656–36.820) values. The associated hornblendites have isotopic compositions identical to those of the volcanic rocks and define continuous variation trends reflecting common parent magma. Geochemical modeling shows that the high Sr/Y and La/Yb signatures of the Mesozoic volcanic rocks from the northern Taihang orogen are primarily the result of fractional crystallization of mantle-derived melts. We evaluate the magma tectonics through the MASH (melting, assimilation, storage, homogenization) model with subsequent evolution of the hybrid magmas and their emplacement controlled by structural conduits. Our interpretation is in deviation from previous models involving partial melting in a thickened lower crust, and crustal delamination, but provides a more robust mechanism to account for the field relations including the occurrence of a wide compositional variety of lithologies in the same region, distinct petrological features such as reverse zoning of some phenocryst phases, geochemical characteristics including smooth fractionation trends, as well as the presence of multiple age populations of inherited zircons.

article i nfo The Lhasa Terrane in southern Tibet has long been accepted as the last geological block accreted to Eurasia before its collision with the northward drifting Indian continent in the Cenozoic, but its lithospheric architecture, drift and growth histories and the nature of its northern suture with Eurasia via the Qiangtang Terrane remain enigmatic. Using zircon in situ U-Pb and Lu-Hf isotopic and bulk-rock geochemical data of Mesozoic-Early Tertiary magmatic rocks sampled along four north-south traverses across the Lhasa Terrane, we show that the Lhasa Terrane has ancient basement rocks of Proterozoic and Archean ages (up to 2870 Ma) in its centre with younger and juvenile crust (Phanerozoic) accreted towards its both northern and southern edges. This finding proves that the central Lhasa subterrane was once a microcontinent. This continent has survived from its long journey across the Paleo-Tethyan Ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the Qiangtang Terrane to the north and with the Indian continent to the south. Zircon Hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks (e.g., ~50-90%, 0-70%, and 30-100% to the Mesozoic magmatism in the southern, central, and northern Lhasa subterranes, respectively). We suggest that much of the Mesozoic magmatism in the Lhasa Terrane may be associated with the southward Bangong-Nujiang Tethyan seafloor subduction beneath the Lhasa Terrane, which likely began in the Middle Permian (or earlier) and ceased in the late Early Cretaceous, and that the significant changes of zircon eHf(t) at ~113 and ~52 Ma record tectonomagmatic activities as a result of slab break-off and related mantle melting events following the Qiangtang-Lhasa amalgamation and India-Lhasa amalgamation, respectively. These results manifest the efficacy of zircons as a chronometer (U-Pb dating) and a geochemical tracer (Hf isotopes) in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics.

We present new Re–Os molybdenite age data on three porphyry Cu–Mo–Au deposits (Yulong, Machangqing, and Xifanping). These deposits are associated with the Himalayan adakitic magmatism that occurred in a continental collision environment, controlled by large-scale Cenozoic strike-slip faults in the eastern Indo–Asian collision zone. Three distinct episodes of Cu–Mo–Au mineralization are recognized. At Yulong, Re–Os isotopic data of four molybdenite samples from sulfide-quartz veins in the quartz–sericite alteration zone yield an isochron with an age of 40.1±1.8 Ma (2σ), coincident to a zircon sensitive high-mass resolution ion microprobe (SHRIMP) age of 40.9±0.1 Ma for the host monzogranite. The molybdenite Re–Os dates, together with K–Ar, Rb–Sr, U–Pb, and 40Ar/39Ar dates on the pre- and intra-ore porphyries, suggest that Cu–Mo–Au mineralization formed during the late stage (∼40 Ma) of regional porphyry magmatism, but hydrothermal activity probably lasted to at least ∼36 Ma. At Machangqing, molybdenite Re–Os data from the K–silicate and quartz–sericite alteration zones yield an isochron with an age of 35.8±1.6 Ma (2σ), which is identical to the zircon SHRIMP and bulk-rock Rb–Sr ages (35∼36 Ma) of the host granite, but older than bulk-rock K–Ar dates (31∼32 Ma) for associated Au-bearing quartz syenite with advanced argillic alteration. At Xifanping, five molybdenite samples from the K–silicate alteration zone yield the youngest Re–Os isochron age in the area, at 32.1±1.6 Ma (2σ). The Re–Os molybdenite dates here are younger than K–Ar ages (33.5∼34.6) for hydrothermal biotite and actinolite. There is a positive correlation between the absolute age of the deposits and their Cu and Au reserves in the eastern Indo–Asian collisional zone. Episodic stress relaxation probably caused multiple magmatic intrusions, which most likely resulted in three episodes of Cu–Mo–Au mineralization in the eastern Indo–Asian collision zone.

The latest zircon U-Pb SHRIMP dating of two ore-bearing porphyry samples from the Chongjiang and Nanmu Co-Mo deposits in the Gangdese porphyry copper belt yields ages of 14.0 Ma and 15.36 Ma. These ages are consistent with molybdenite Re-Os ore-forming ages of 13.99 Ma and 14.67 Ma. These geochronological results also reveal that ore-forming process of the Gangdese copper belt occurred simultaneously with rapid crustal uplifting of the Gangdese orogen inferred by previous researchers. Studies have demonstrated that these ore-bearing porphyries have geochemical characteristics of adakite. Nd, Sr, and Pb isotopic data in this study further indicate that these porphyries formed from partial melting of subducted ocean-crust slabs under eclogite-facies metamorphic conditions and contain minor amount of subducted sediments mixed in the magma source. The temporal overlapping of ore-forming process and rapid crustal uplifting in the Gangdese orogen was not accidental and instead reflects a geodynamically linked relationship. Generation and extraction of the ore-bearing adakitic magma caused further increase in density of the residual eclogitic slabs, which, in turn, forced them to delaminate and asthenospheric upwelling at higher velocities. Conversely, extentional tectonic environment brought about by asthenospheric upwelling provided necessary conditions for up-intrusion of the ore-bearing magma and concentration of ore-forming metals.

Magmatic-hydrothermal ore deposits in collisional orogens are new targets for modern mineral exploration, yet it is unclear why they preferentially occur in some specific tectonic environments within these orogenic belts. We integrate geologic and geochemical data (especially zircon U-Pb dating and Lu-Hf isotope data) for Mesozoic-Cenozoic magmatic rocks and associated ore deposits in the Lhasa terrane, a highly endowed tectonic unit within the Himalayan-Tibetan orogen, and provide the first example in a continental collision terrane of the application of zircon Hf isotope data to image the lithospheric architecture and its relationship with ore deposits. Three crustal blocks are identified within the Lhasa terrane by the Hf isotope mapping method. They include a central long-lived Precambrian microcontinent with local reworking and two surrounding juvenile Phanerozoic crustal blocks with significant mantle contributions to constituent magmatic rocks. The three crustal blocks are bounded by two E-W–trending terrane-boundary faults, and each block is cut by two N-S–striking concealed faults. Isotopic signatures of zircons from the juvenile crustal blocks indicate that the Phanerozoic continental crust grew from several Mesozoic volcanic-plutonic arcs and by underplating of mantle-derived magmas generated during Mesozoic accretion and Cenozoic collision. Mesozoic subduction-related porphyry Cu-Au deposits and Cenozoic collision-related Cu-Mo deposits are exclusively located in regions with high e Hf(>5) juvenile crust. Cu enrichment during differentiation of high f o2 arc magmas is the key for the formation of Mesozoic subduction-related porphyry Cu-Au. By contrast, remelting of the lower crustal Cu sulfide-rich magmatic cumulates within the juvenile crust is interpreted to have played a key role in the formation of Cenozoic collision-related Cu-Mo deposits. Granite-related Pb-Zn deposits cluster in the oldest crustal regions or developed along the margin of the old crustal block bounded by lithospheric faults. The porphyry Mo deposits are localized along the reworked margins of the old crustal block. It is suggested that crustal reworking released Mo from the old crust to form porphyry Mo deposits, whereas leaching of Pb and Zn from the Paleozoic carbonate cover strata by felsic intrusion-driven fluids is critical to the formation of Pb-Zn ore deposits. Skarn Fe-Cu ore deposits are typically localized along a terrane boundary fault, i.e., lithospheric discontinuity, through which crust-derived felsic melt mixed with Cu-rich mantle-derived mafic magmas ascending upward. Associated granitoid rocks usually bear microgranular mafic enclaves and show a zircon Hf isotope array from negative to positive e Hf values (−7.3 to +6.7), supporting mixing of juvenile mantle and evolved crustal sources. The Hf isotope maps show temporal-spatial relationships between crustal structure and the location of ore deposits, demonstrating that the structure, nature, and composition of the crust controlled the localization of ore deposits and the migration of ore-forming metals in the terrane. This study shows that the lithospheric architecture of an orogenic terrane can be imaged by Hf isotope mapping to provide mappable units which can be used to explore for ore deposits at the terrane scale.