TDMC Ages Research Articles

Crustal architecture and metallogeny associated with the Paleo-Tethys evolution in the Eastern Kunlun Orogenic Belt, Northern Tibetan Plateau

The Eastern Kunlun Orogenic Belt (EKOB) in the Northern Tibet Plateau hosts a wide variety of metal deposits related to the Late Paleozoic to Mesozoic magmatism. In this study, we investigate the spatio-temporal distribution of the Late Paleozoic to Mesozoic granitic rocks and associated metal deposits in the EKOB and provide a comprehensive compilation of the geochronological, geochemical and isotopic data on these rocks. We compute regional zircon Hf isotope and crustal thickness maps from the data, based on which a comprehensive model is proposed involving subduction (ca. 270–240 Ma), continental collision (ca. 240–224 Ma), and post-collisional extension (ca. 224–200 Ma) for the Late Paleozoic to Mesozoic Paleo-Tethys evolution in the EKOB.Zircon Hf isotopic and crustal thickness mapping of Late Paleozoic to Mesozoic magmatic rocks was carried out to evaluate their spatio-temporal and genetic links with the regional metallogeny. The polymetallic Fe-skarn and porphyry Cu (Mo) deposits in the EKOB are located above the Moho uplift region, featuring a comparatively thin crust. Granites associated with porphyry Cu (Mo) and polymetallic Fe skarn mineralization are commonly characterized by high εHf(t) and younger TDMc values, whereas granite related to Cu-Mo-Sn skarn deposits exhibit more variable εHf(t) values, TDMc ages, and the crust thickness, which suggest that more crustal materials contributed to the formation of Cu-Mo-Sn skarn deposits than those for porphyry Cu (Mo) and polymetallic Fe skarn mineralization. In contrast, vein-type Au deposits are located primarily where the Moho surface displays a depression, i.e., where the continental crust is relatively thick. The magmatic rocks associated with Au mineralization are characterized by low εHf(t) and high TDMc values, representing reworked ancient crustal components, similar to those associated with porphyry Mo and epithermal Ag-Pb-Zn-(Au) deposits. Our study indicates that the emplacement of magmatic-hydrothermal deposits was controlled by the crustal structure and magma sources.

Geochronology, petrogenesis and metallogenic implications of granitoids in the Xiaotuergen Cu deposit, Northern Chinese Altai Orogen, NW China: Constraints from zircon, apatite and whole-rock geochemistry

The Xiaotuergen Cu deposit is the first Cu deposit described in the Northern Chinese Altai Orogen, Xinjiang, NW China. The multiple phases of granitic intrusions occur in the Xiaotuergen region, including the intrusions of granodiorite porphyry, granite porphyry, and biotite monzogranite. Among these types of intrusions, Cu mineralization is considered to be closely related to the early Hercynian granodiorite porphyry. However, the precise emplacement ages, petrogenesis, redox states, and tectonic setting of the three Xiaotuergen granitoids and the relationship between these granitoids and mineralization was unclear. To resolve these issues, zircon U–Pb dates, zircon in situ trace element concentrations, Hf isotopic compositions, apatite in situ major element concentrations, and whole-rock geochemistry were determined in this study. Three different intrusive phases are recognized within the district; in order of deceasing age, these phases are biotite monzogranite, granodiorite porphyry, and granite porphyry, which have the ages of 400.2 ± 1.6 Ma to 399.6 ± 2.4 Ma, 390.3 ± 1.6 Ma to 377.1 ± 1.6 Ma, 381.0 ± 2.0 Ma to 378.7 ± 1.2 Ma, respectively, suggesting that they were emplaced during the Early-Middle Devonian. Geochemical data show that these intrusions are metaluminous to weakly peraluminous (A/CNK = 0.91–1.28), calc-alkalic to shoshonitic I-type granitoids. The two Harker plot trends reveal derivation from two magma sources (biotite monzogranite vs granodiorite porphyry and granite porphyry) that experienced different evolutionary processes. Multiple indicators, including the zircon Ce4+/Ce3+ ratio and oxygen fugacity (logfO2) values, apatite Mn oxybarometer, and whole-rock Fe2O3/FeO ratio, consistently indicate that the parental magma of the fertile granodiorite porphyry was more oxidized than that of the two barren intrusions (biotite monzogranite and granite porphyry). Furthermore, apatite grains from the fertile granodiorite porphyry have higher Cl contents and Cl/F ratios than those of the ore-barren biotite monzogranite and granite porphyry, which may have resulted from the higher water content of the parental magma and increased lithospheric mantle-derived fluid involvement in their generation. Thus, higher Cl/F ratios of apatite can be used to discriminate fertile granitoid intrusions that host Cu mineralization in the Northern Altai orogen. Zircon Hf isotopic compositions show widely ranging and mostly positive εHf (t) values (−4.2 to +11.4, mainly concentrated between +2 and +8). These isotope characteristics in combination with young zircon TDMC (Hf) ages (655–1,659 Ma; mainly concentrated between 850 Ma and 1250 Ma) indicate that the Xiaotuergen granitoids were most likely derived from the partial melting of juvenile lower crust, with some interaction of mantle materials from the underlying mantle wedge. The three Xiaotuergen granitoids were enriched in light rare earth elements and large ion lithophile elements, depleted in heavy rare earth elements, and showed negative Nb, Ta, Sr, P, and Ti anomalies, displaying typical arc geochemical affinities. Combined with the regional tectonic evolution, we propose that the Xiaotuergen granitoids were generated in a continental arc setting associated with subduction processes, which were the products of syn-accretion orogenic processes.

Geochronology, Whole-Rock Geochemistry, and Sr–Nd–Hf Isotopes of Granitoids in the Tongshanling Ore Field, South China: Insights into Cu and W Metallogenic Specificity

The Qin-Hang Metallogenic Belt (QHMB), an important metallogenic belt in South China, hosts Cu and W–Sn polymetallic deposits. The Tongshanling ore field in the QHMB is characterized by the coexistence of Cu- and W-bearing polymetallic deposits, which are related to granodiorite and granite porphyry. This study examined whole-rock geochemistry, geochronology, and Sr–Nd–Hf isotopes to determine the genetic relationship between diverse ore-related granitoids (i.e., granodiorite and granite porphyry) and Cu–W metallogeny in the Tongshanling ore field. Zircon LA-ICP-MS U–Pb dating shows that the granodiorite and granite porphyry in the Tongshanling ore field were emplaced at 163.7 ± 0.4 Ma to 154.7 ± 0.6 Ma and 161.1 ± 0.3 Ma, respectively. Geochemically, the granodiorites are classified as oxidized I-type, while the highly evolved granite porphyry is reduced A-type. The Lu–Hf isotopic composition of the granodiorites is characterized by εHf(t) values ranging from –10.49 to –4.99 (average = –7.17), with corresponding TDMC ages ranging from 1524 to 1877 Ma (average = 1682 Ma). In contrast, the granite porphyry has higher εHf(t) values (–3.60 to –1.58, average = –2.78) and younger TDMC (1310–1438 Ma, average = 1387 Ma). The εNd(t) values of granodiorite are −8.06 to −7.37 and the two-stage model ages (TDM2) are 1543–1598 Ma, while the granite porphyry has higher εNd(t) values (−3.0 to −3.4) and younger TDM2 ages (1195–1223 Ma). The results show that the granodiorite and granite porphyry were formed from partial melting of different Mesoproterozoic basement rocks under varying degrees of crust–mantle interaction. Granite porphyry underwent well-recorded fractional crystallization. Compared to the Cu-forming granodiorite, the W-forming granite porphyry has a higher differentiation index, higher crystallization temperatures of zircon (average = 708 °C versus 631 °C), and lower oxygen fugacity (median ΔFMQ = –2.21 versus –1.77).

The genesis of the granitic rocks associated with the Mo-mineralization at the Hongling deposit, eastern Tianshan, NW China: Constraints from geology, geochronology, geochemistry, and Sr-Nd-Hf isotopes

The eastern Tianshan is an important molybdenum metallogenic belt in the southern margin of the Central Asian Orogenic Belt (CAOB). The newly discovered Hongling Mo deposit is located in the north–east margin of the Kanggur–Huangshan shear zone in eastern Tianshan, NW China. However, the genesis of the granitic rocks associated with the Mo-mineralization is unclear. The monzogranite, monzogranite porphyry and porphyritic granite from the Hongling deposit are high-K calc-alkaline series and characterized by high SiO2 and Al2O3 and low MgO, TiO2, and P2O5 concentrations. They are enriched in K, Rb, U and Pb, and depleted in Nb, Ba, P, and Ti, with negative Eu anomalies. Zircon LA–ICP–MS U–Pb dating yielded mean ages for the monzogranite of 238 ± 5 Ma and 234 ± 3 Ma, monzogranite porphyry of 234 ± 2 Ma, and porphyritic granite of 232 ± 3 Ma, respectively, which coincide with molybdenite Re–Os model ages ranging from 227 ± 4 to 228 ± 4 Ma. The zircons from the monzogranite, monzogranite porphyry and porphyritic granite yield εHf (t) of 8.3–15.4, 8.4–16.1, and 7.8–14.7, respectively, and TDMc (Hf) ages of 0.23–0.76 Ga. The Hongling granites show a centralized distribution toward lower (87Sr/86Sr)i values of 0.70387–0.70450, higher εNd(t) values of 2.6 to 3.7, and TDM2(Nd) ages of 0.71–0.80 Ga. The geochemical characteristics of granitoids from the Hongling deposit are practically the same as the fertile granitoids from the Donggebi and Baishan deposits. The geochemical and isotopic data indicate that the Hongling granitoids were likely derived from the partial melting of the juvenile lower crustal materials generated during Precambrian to Paleozoic, with involving minor mantle components and related to intraplate extensional setting.

Crustal modelling from Pan-African granites of the Colomine Gold District, SE Cameroon: Insights from zircon U-Pb dating and Lu-Hf isotope systematics

The Neoproterozoic Pan-African Orogeny in the Adamawa-Yadé domain (AYD) of Cameroon is characterized by intense magmatism of metaluminous to weakly peraluminous I-type granites spatially associated with transcurrent shear zones. This domain provides a critical geological record that is important for unravelling the regional tectonic evolution and geodynamic setting. We present new zircon U-Pb ages and Lu-Hf isotope data from pre-collisional biotite granite and porphyritic K-feldspar granite of the gold-producing Colomine district. Zircon U-Pb ages of biotite granite samples suggest emplacement at 727 ± 8 Ma and at 671 ± 6 for the porphyritic K-feldspar granite. Metamorphic-hydrothermal events between 600 and 550 Ma resulted in Pb-loss of most dated zircons. Lu-Hf isotope data of zircon grains form the porphyritic K-feldspar granite with ϵHf(t) values of −28.7 to −22.6 and TDMc ages of 2.4–2.1 Ga overlap with those of the biotite granite (ϵHf(t) values of −29.4 to −19.6; TDMc ages of 2.5–1.9 Ga). Depleted mantle model ages and ϵHf(t) values suggest that the granites were derived from crustal reworking of older Archean to Paleoproterozoic crust with minor mixing from a juvenile component during the Pan-African. The formation of these pre-collisional granites is interpreted as related to accretion tectonics that started around 750 Ma and incorporating tectonic domains of the Central African Fold belt, namely, the NW Cameroon domain, Mayo-Kebbi domain and the Adamawa-Yade domain.

Late Mesozoic post-orogenic granitoids and its metallogenic implications: Constraints from Nantai porphyry Mo deposit, Northern Qinling, China

Late Mesozoic Nantai porphyry Mo deposit is located in the Northern Qinling terrane, eastern China. The intrusions at Nantai include lamprophyre, quartz porphyry, and granite porphyry. Among them, molybdenum mineralization is associated with quartz porphyry and granite porphyry. The ore-bearing porphyries and ore-barren lamprophyres emplaced at ca. 155–146 Ma and ca. 156–146 Ma, respectively. The calculated zircon ΔFMQ values for Nantai felsic and mafic intrusions are –5.0 to +9.1 (an average of + 2.2) and –6.7 to +5.0 (an average of +1.2), which are similar to those of contemporaneous giant Mo deposits in the south margin of the North China Block. The quartz porphyry and granite porphyry are characterized by relatively high SiO2 (73.39–75.49%), K2O (4.24–9.61%), and Rb (291–552 ppm) contents, but low total Fe2O3 (0.13–0.83 wt%), MgO (0.1–0.3 wt%), P2O5 (0.01–0.04 wt%), Sr (22.4–141.0 ppm) and Ba (79.8–1757 ppm) concentrations. These granitic samples have TDMC ages of 2204–1592 Ma, corresponding to negative εHf(t) values of –15.8 to –6.2. Geochemical and zircon Lu-Hf signatures as well as lead isotopic analyses for Nantai granitoids suggest that they belong to the high-fractionated I-type granites and were derived from partial melting of lower continental crust with coeval mantle-derived magma contribution. The lamprophyres show low SiO2 (47.59–49.08%) and Rb (96–120 ppm) contents, whereas they have high Ba (1598–2236 ppm), and Sr (771–990 ppm) concentrations, as well as a lack of negative Eu anomalies. The concentrated εHf(t) values (–0.6 to + 3.3), high (Hf/Sm)PMN and La/Sm ratios, as well as Pb isotopic features, indicate that they were derived from an enriched lithospheric mantle that had been metasomatized by subducted components with some crustal material contribution. Combined with our datasets and previous studies, we suggest that the Nantai porphyry Mo deposit formed in a post-orogenic setting.

Thermo-mechanical destruction of Archean cratonic roots: Insights from the Mesozoic Laiyuan granitoid complex, North China Craton

Igneous complexes with diverse magmatic suites provide essential targets for investigating magma differentiation processes and crust-mantle interaction. The North China Craton (NCC) is a crucial window to gain insights into craton destruction through voluminous magmatism during the Mesozoic involving extensive crust-mantle interaction. Here we investigate the granitoid suite from the Laiyuan complex in the central NCC to constrain the magmatic evolution and petrogenetic linkages and to gain insights into the process of crust-mantle interaction related to craton destruction. The Laiyuan granitoid complex comprises syenogranite, monzogranite, quartz monzonite and monzonite with mafic magmatic enclaves (MMEs). The granitoids were formed during the Early Cretaceous (137–128 Ma) with εHf(t) values and TDMC ages ranging from −21.8 to −16.8 and 2564 to 2255 Ma, respectively. The compositional variations of the different rock types suggest distinct magmatic evolution and petrogenesis. Geochemical and isotopic data indicate that the enriched lithospheric mantle-derived mafic magmas underwent early-stage plagioclase-dominated and late-stage hornblende-dominated fractional crystallization to form the monzonites and quartz monzonites. Geochemical modeling results suggest that the magma of the MMEs originated through mixing between lithospheric mantle-derived mafic magma and crust-derived felsic magma with post-injection hybridization to generate MMEs with variable compositions. The monzogranites are classified as high-K calc-alkaline I-type granites with higher SiO2 contents (69–71 wt%) and lower Mg# (41–44) than intermediate rocks. They were generated by partial melting of the basaltic lower crust, with the addition of mafic magma from an enriched mantle. The highly fractionated syenogranites with lower Mg# (18–27) were evolved from the monzogranitic magma through plagioclase-dominated crystal removal. The adakitic affinities of the monzonites and monzogranites were generated by crystallization of mantle-derived magmas and partial melting of continental crust of normal thickness (~40 km), respectively. The bottom-up crust-mantle interaction accounts for the compositional diversity of the Laiyuan granitoids, and suggests that thermo-mechanical destruction played a dominant role in the destruction of the central NCC as compared with the continental delamination process in the eastern NCC.

The multiple mineralizations and geodynamic settings of the Laozuoshan Cu–Au deposit in the Jiamusi Massif, NE China: Zircon U–Pb geochronological, elemental and Hf isotopic geochemical evidence

Situated in the centre of the Jiamusi Block, the Laozuoshan deposit is a large-sized deposit with composite of vein and lenticular Au orebodies and veinlet-disseminated Cu-Au orebodies. It is characterized by two types of mineralization, skarn Au mineralization and porphyry Cu-Au mineralization. The former occurs along the contact zone between granodiorite and Proterozoic metamorphic rocks in the eastern and central ore zones, while the latter is hosted in granodiorite porphyry and diorite in the western ore zone. In this study, we present the results of geochronological and geochemical analyses of these rocks which show the following features. (1) Zircon U–Pb dating results show that the ages of granodiorite, diorite and granodiorite porphyry are 264.6±2.6 Ma, 103.2±1 Ma and 104.6±1.8 Ma, respectively. (2) Whole-rock elemental compositions indicate that the granodiorite shows potassium-rich adakitic rock properties, and the diorite has typical island arc calc-alkaline magmatic properties. They are all characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). (3) The in-situ Hf isotope analysis results show that the granodiorite and diorite have εHf(t) values of −3.7 to −8.7 and −0.4 to 10.7, respectively, corresponding to TDMC ages of 2040–2500 Ma and 630–1650 Ma, respectively. These results indicate two periods of mineralization in the Laozuoshan deposit. Skarn mineralization occurred in the late Permian and was a result of metasomatism between partial melting magma that originated from thickened Paleoproterozoic lower crust and Proterozoic marble. Porphyry mineralization took place in the Early Cretaceous and was a result of the shallow emplacement of mid-Neoproterozoic mantle-derived magma with the addition of crustal materials. In terms of geodynamic settings, skarn Au and porphyry Cu-Au mineralization occurred in a compressional setting formed during the gradual closure of the Paleo-Asian Ocean, and a crustal-thinning setting formed from Eurasian Plate-ward subduction, retreating, and rollback of the Paleo-Pacific Plate, respectively.

Geochemistry and U-Pb-Lu-Hf zircon isotopes of Cu (±Au ± Mo) hosted granitoids of Malanjkhand pluton, Central India: Implications on petrogenesis, source, and crustal evolution

The early Paleoproterozoic granitoids (2.45–2.5 Ga) at Malanjkhand and surrounding regions, referred herein to as Malanjkhand granitoids (MG), host Cu (±Mo ± Au) deposit. The MG lie in the south of Central Indian Tectonic Zone (CITZ), forming an integral part of the Bastar Craton. Whole-rock geochemistry, zircon U-Pb-Lu-Hf isotopes of MG are presented with an aim to insight into petrogenesis of MG and its implication on crustal evolution of the Bastar Craton. U-Pb zircon geochronology suggests the formation of MG pluton at least by three felsic magmatic pulses generated at 2.50, 2.47, and 2.45 Ga. Geochemically both the mineralized and unmineralized MG are broadly identical. They bear moderately high Sr/Y and (La/Yb)N similar to as adakite-like melt. However, its typical non-slab-melt (young or old) origin can be predicted. The observed geochemical signatures may result from interactions of mantle-derived mafic melt with a felsic melt derived from pre-existing continental crust. It has been argued that mafic melt is essentially formed by partial melting of slab-melt metasomatised mantle/enriched mantle. Subsequently the mafic melt fractionated to form cumulates. On the other hand, the felsic melt was formed by the melting of Archean continental crust. The observed sub- to ultra-chondritic ɛHf(2.47Ga) zircons (−4.69 to +2.87) and TDMc ages (2.79–3.25 Ga) propound the origin of MG from ancient and juvenile crustal sources. The magmatic pulses (2.45–2.50 Ga) forming the MG and together with synchronous volcano-plutonic complexes from nearby Dongargarh region might have played significant role in rapid crustal growth of Bastar Craton at ~2.5 Ga.

Hf isotopic mapping of the Paleozoic-Mesozoic granitoids from the Jiamusi and Songnen blocks, NE China: Implications for their tectonic division and juvenile continental crustal growth

The long-standing controversies in tectonic boundary, the nature of basement rocks, and the Phanerozoic continental crustal growth in the eastern Central Asian Orogenic Belt (CAOB) in NE China have been the key barriers in the understanding of the regional tectonic evolution. In this paper, we integrated published and new zircon U–Pb and Hf isotopic data of the Phanerozoic granitoids from the Jiamusi Block and the Lesser Xing'an-Zhangguangcai Range (LXZR) for a zircon Hf isotopic mapping of the region. The mapping results outlined three Hf isotopic provinces on the basis of TDMC ages: Province I (TDMC = 2.0–1.6 Ga, εHf(t) = −7.0 to −5.2) and Province II (TDMC = 1.6–1.1 Ga, εHf(t) = −4.6 to +3.9) represent the ancient basements in the Jiamusi Block; Province III (TDMC = 1.1–0.4 Ga with εHf(t) = +2.1 to +13.1) represents the juvenile crustal components in the LXZR. Province I (total area ~ 6000 km2) is sporadically exposed within Province II (~121,000 km2); the latter is bounded to Province III (~144,000 km2) along a sharp SE-NW boundary ~130 km west of the Mudanjiang Fault. This suggests that at least the part of the Songnen Block to the east of this boundary was in the same tectonic unit with the Jiamusi Block in the Paleozoic. Province III spatially accounts for about 53% of the study area, indicating a significant Mesozoic growth of continental crustal in the easternmost CAOB.

Permian to Triassic tectonic evolution of the Alxa Tectonic Belt, NW China: Constraints from petrogenesis and geochronology of felsic intrusions

The Alxa Tectonic Belt (ATB) is located in the southern Central Asian Orogenic Belt (CAOB), and its tectonic affinity and evolutionary history related to the closure of the Paleo-Asian Ocean are not fully understood. To refine our understanding of these issues, an investigation that includes petrographic observations, whole-rock geochemistry, zircon UPb dating and Hf isotopic analyses was carried out on four felsic intrusions in the Zongnaishan–Shalazha Zone (ZSZ) and the Nuoergong–Honggueryulin Zone (NHZ) within this region. Despite their lithological differences, the four intrusions are identified as metaluminous, calc-alkaline to high-K calc-alkaline I-type granitoids that were derived from partial melting of heterogeneous crustal basement without significant fractional crystallization and crustal contamination. Zircon LA-ICP-MS UPb dating results suggest that they were emplaced from the late Permian to the early Triassic (i.e., 247.7 ± 0.7 Ma for the Shalazha granite, 253.2 ± 0.9 Ma for the Shalazha granodiorite, 253.3 ± 0.6 Ma for the Nuoergong granite, and 251.6 ± 0.9 Ma for the Nuoergong tonalite). Geochemically, these granitoids show typical signatures of arc magma, such as enrichments in Rb, Th, K, and Pb, depletions in Zr, Nb, and Ta, and low Sr/Y and (La/Yb)N values. On tectonic discriminant diagrams, they plot in volcanic arc to post-collisional fields, indicating a tectonic transition from oceanic subduction to closure in the late Permian to early Triassic. Interestingly, granitoids from the ZSZ have positive εHf(t) values ranging from +1 to +7.9 with young two-stage crustal ages (TDMC) of 781–1209 Ma, in sharp contrast to the extremely negative εHf(t) values (−15.8 to −8.7) and old TDMC ages (1831–2272 Ma) of the granitoids in the NHZ. In addition, the zircon Hf isotopes of the ZSZ and NHZ granitoids show similarities to those of the magmatic rocks in the southern CAOB and western North China Craton, respectively, implying that the northern and southern ATB have different tectonic affinities. Thus, we propose that the Paleo-Asian Ocean lasted subduction in the late Permian and may close in the early Triassic, with subsequent accretion of the northern juvenile exotic microcontinent (ZSZ) to the southern old crustal basement (NHZ).

Petrogenesis of ca. 113 Ma volcanic rocks in the central Lhasa subterrane, southern Tibet: Implications for the tectonic setting and continental crustal reworking

Voluminous Early Cretaceous volcanic rocks in the central Lhasa subterrane provide an ideal opportunity for understanding the mantle–crust interaction and tectonic‐magmatic evolution of the Lhasa Terrane. Here, we report zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Early Cretaceous volcanic rocks, including high‐silica rhyolites (117.2 ± 1.1 Ma) and contemporaneous andesites (114.1 ± 0.8 Ma) in the Sailipu area, central Lhasa subterrane. All these rocks show enriched light rare earth elements (LREE), and radioactive heat‐generating elements (e.g., Th, U, K, and Pb) but depleted high‐field‐strength elements (HFSEs, e.g., Nb, Ta, P, and Ti). The different bulk‐rock Sr–Nd–Pb and zircon Hf isotopic compositions of the rhyolites and andesites suggest that these rocks have distinct magma sources and petrogenetic history rather than an identical source involving assimilation‐fractional crystallization process. The Sailipu high‐silica rhyolites exhibit the characteristics of fractional crystallization and have varying zircon εHf(t) values (−12.2 to +5.2), negative εNd(t) values (−9.5 to −1.6), high and variable initial Sr isotopic compositions ([87Sr/86Sr]i = 0.7047–0.7116) and radiogenic Pb isotopic signatures (206Pb/204Pb = 18.784–18.802, 207Pb/204Pb = 15.722–15.737, and 208Pb/204Pb = 39.382–39.492). A combined process of magma mixing (involving crustal‐derived felsic melts and mantle‐derived mafic melts) and subsequent fractional crystallization were mainly responsible for the formation of these high‐silica rhyolites. The Sailipu andesites show more enriched Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7088–0.7154, εNd(t) = −9.9 to −6.7] relative to rhyolites, and less radiogenic Pb isotopic compositions (206Pb/204Pb = 18.632–18.669, 207Pb/204Pb = 15.686–15.689, 208Pb/204Pb = 39.140–39.201). They were likely derived from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments. We interprete these Early Cretaceous volcanic rocks as the product of slab break‐off during the southward subduction of the Bangong‐Nujiang Tethyan oceanic seafloor. The dominantly positive εHf(t) and ancient TDMC ages (0.85–1.90 Ga) of Sailipu high‐silica rhyolites further imply that, under the stress relaxation regime, the mantle‐derived melts locally reworked the ancient basement of the central Lhasa subterrane.

Syn-collisional magmatism at the Longgen Pb–Zn deposit, western Nyainqentanglha belt, Tibet: Petrogenesis and implications for regional polymetallic metallogeny

Syn-collisional orogeny generally lacks adequate fluids and has a low potential to form magmatic hydrothermal ore deposits. However, some syn-collisional Pb–Zn deposits have been recognized in the Nyainqentanglha polymetallic belt (NPB), central Lhasa subterrane and ore-related magma petrogenesis and the metallogenic geodynamic setting is limited. In this study, detailed petrology, geochemical and geochronological data of ore-related syn-collisional granite porphyries are evaluated to constrain the timing of mineralization and discuss the genesis and evolution of ore-related magma using the Longgen skarn Pb–Zn deposit as a case study. Zircon U–Pb dating of ore-related porphyries provides a weighted mean age of 61.2 ± 0.8 Ma, which is slightly earlier than the sphalerite Rb–Sr age of 59.1 ± 3.0 Ma, indicating that a Paleocene Pb–Zn mineralization event occurred during syn-collisional orogeny. The porphyries have high SiO2, K2O + Na2O, and are enriched in Rb, Th, U, Pb, LREEs, and A/CNK (0.94–1.15), but have low P2O5 and are depleted in Nb, Ta, and Ti. This suggests that the Longgen granite porphyries are metaluminous to weakly peraluminous high-K calc-alkaline “arc-like” granites. These porphyries have highly radiogenic isotopic compositions with (87Sr/86Sr)i 0.709513–0.713587, (207Pb/204Pb)i 15.657–15.713, and (208Pb/204Pb)i 38.964–39.163, but low εNd(t) values from − 6.7 to − 6.0, as well as negative zircon εHf(t) values from − 5.1 to − 3.2, corresponding to TDM2(Nd) ages of 1.37 to 1.42 Ga and zircon Hf TDMc ages of 1.30 to 1.42 Ga. This demonstrates that the Longgen granite porphyries may have been generated by the partial melting of Mesoproterozoic basement continental crust materials with significant amounts (30–50%) of mantle-derived melt input. Paleocene-Eocene (65–45 Ma) magmatic rocks associated with Pb–Zn and Fe–Cu deposits are compiled in the NPB. The Pb–Zn ore-related granitoids have relatively lower whole-rock εNd(t) and zircon εHf(t) values, higher (87Sr/86Sr)i values, and older TDMC ages than the coeval granitoids associated with Fe–Cu mineralization. This indicates that mantle material is more critical for the development of Fe–Cu ore-related granitoids than granitoids associated with Pb–Zn mineralization. The final results show that different sources of Paleocene–Eocene syn-collisional magma in the NPB are beneficial for different mineralization events during the syn-collisional orogeny of the Indian and Asian plates.

Petrogenesis of Archean TTGs and potassic granites in the southern Yangtze Block: Constraints on the early formation of the Yangtze Block

The southern Yangtze is underlain by Mesoarchean igneous rocks that were emplaced in two pulses, including trondhjemites at ca. 3092–3071 Ma followed by potassic granites at 2920 Ma. These represent the oldest TTG suites identified in the southern Yangtze and the oldest potassic granites in the entire Yangtze Block. Hf isotopic analysis reveals εHf(t) values of −2.49–7.49 and Hf crustal model ages (TDMC) of 3601–3000 Ma for zircons from the trondhjemites, whereas those from the potassic granites show εHf(t) values of −1.79–4.18 and TDMC ages of 3453–3043 Ma. The trondhjemites have high SiO2, Mg# and low Al2O3 and K2O/Na2O, and are highly evolved with low Ni, Cr and Co. The trondhjemites are characterized by low Sr/Y, Eu/Gd and (La/Yb)N, and high Y and HREE, typical of high-HREE and low-pressure TTGs. Their geochemical and isotopic compositions indicate that they are derived from melting of juvenile mafic crust with little contribution from older crustal materials, consistent with a plagioclase-bearing basaltic source. The multielement patterns of potassic granites are similar to that of the trondhjemites, albeit with lower HREE and Y contents. Their high K2O values, strongly fractionated REE patterns and low Y contents indicate the presence of garnet and/or amphibole as residual phases in the source region, which indicates they formed at higher pressure than the trondhjemites. The isotopic and geochemical data imply that the formation of the potassic granites could be related to reworking of older TTGs. The increasing K2O/Na2O of the 3092–3071 Ma trondhjemites to potassic 2920 Ma granites corresponds with stabilization, maturation and thickening of the Archean continental crust in the southern Yangtze. The geochemical data of the TTGs in the Kunming region show important differences from that of contemporaneous TTGs from the Kongling Complex, suggesting that southern Yangtze is composed by an independent old nucleus, which is exotic to the northern Yangtze. A synthesis of petrogenesis, geochronology, geochemistry and isotope data of Archean granites of the Yangtze Block provides important insights into the architecture of its Archean crust. We propose that the Yangtze Block can be subdivided into discrete northwestern, northeastern and southern domains, but which are all affected by late Paleoproterozoic tectonothermal events, suggesting that they had been assembled together by then to form the united Yangtze Block.

Geochemical factors revealing the differences between the Xitian and Dengfuxian composite plutons, middle Qin-Hang Belt: Implications to the W–Sn mineralization

The Xitian and Dengfuxian ore fields, located in the middle Qin-Hang Belt, are known for hosting large-scale W–Sn polymetallic deposits. The Xitian ore field hosts a series of small to large scale Sn–W deposits, including skarn-, quartz vein- and structurally altered rock-type, whereas the Dengfuxian ore field mainly contains a medium-scale quartz vein-type W deposit. These granitic rocks are composed of ore-barren Triassic and ore-related Jurassic granites. In this study, LA–ICP–MS zircon U–Pb dating of three representative samples from Dengfuxian Triassic granites (DTG), Xitian Jurassic granites (XJG) and Dengfuxian Jurassic granites (DJG) yields weighted mean 206Pb/238U ages of 231.2 ± 2.5 Ma, 152.5 ± 1.2 Ma and 155.9 ± 1.6 Ma, respectively. Chemical compositions of the Xitian Triassic granites (XTG) and DTG indicate that they belong to relatively lower fractionated granites, whereas the XJG and DJG are highly fractionated granites. The XTG and DTG have similar Lu–Hf isotopic compositions, which have peak εHf(t) values of ca. −5.9 and TDMC ages of ca. 1.57 Ga, and peak εHf(t) values of ca. −5.7 and TDMC ages of ca. 1.57 Ga, respectively. However, the XJG have higher peak εHf(t) values of ca. −5.4 and younger TDMC ages of ca. 1.52 Ga than those of the DJG with peak εHf(t) values of ca. −7.6 and TDMC ages of ca. 1.70 Ga, respectively. Furthermore, the XTG have εNd(t) values of −10.5 to −9.40 and Nd model ages (TDM2) of 1.86 to 1.76 Ga, which are similar to those of the DTG with εNd(t) values of −11.7 to −9.67 and Nd model ages (TDM2) of 1.95 to 1.79 Ga (Wu et al., 2016; Cai et al., 2015). The XJG have εNd(t) values of −11.0 to −9.1 and younger TDM2 ages of 1.69–1.84 Ga, which are fairly distinct to the reported Nd isotopes of the DJG (Cai, 2013). It is proposed that the XTG and DTG were originated from the similar magma chamber and formed from partial melting of the Proterozoic basement rocks of the South China Block (SCB) at low temperatures (ca. 690 °C) and oxygen fugacity (log(fO2) values of ca. −17), involved with a certain amount of mantle derived magma; Magmas of the XJG and DJG might be mainly originated from the partial melting of Proterozoic basement rocks of the SCB. In contrast, the formation of XJG and DJG are involved with a considerable and little mantle-derived magma, respectively. In addition, the magma temperatures and log(fO2) values of XJG are of ca. 856 °C and ca. −15, respectively, which are higher than those of the DJG (ca. 716 °C and ca. −17). That the Xitian and Dengfuxian Triassic granites did not induce W–Sn mineralization is likely attributed to their low fractionated signatures. The key factors leading to the Sn–W mineralization in the Xitian ore field and W mineralization in the Dengfuxian ore field might be magma source and temperature, since additional Sn could be provided by the mantle and/or released by melting of those Sn-bearing minerals at high temperatures (over than 780 °C).

Zircon U–Pb and Sm–Nd geochronology and geochemistry of the Sn–W deposits in the northern Guposhan ore field, Nanling Range, southern China

The Guposhan ore field, located in the central part of the Nanling Range and close to the giant Central South Peninsula tin ore belt, is well-known for its large-scale Sn (W) mineralization and hosts a series of middle to large scale Sn (W) deposits. In this study, medium to fine grained biotite granite, outcropped in the mining area, have zircon U–Pb ages of 162.8 ± 1.3 Ma (MSWD = 0.54) and 162.7 ± 1.2 Ma (MSWD = 0.66), respectively. These zircon ages are consistent to the Sm–Nd isotopic age of minerals (garnet, hornblende, clinopyroxene and orthopyroxene) from the skarn-type ores, which is 160.4 ± 4.8 Ma (MSWD = 1.3). These granites are characterized by high content of SiO2, K2O, Na2O and REEs, and high Ga/Al ratios, indicating that they belong to highly fractionated A-type granites with high-K calc-alkaline and aluminous-peraluminous signatures. The zircon Lu–Hf isotopes of these granites have εHf(t) values and TDMC ages of −2.66 to −1.71 and 1.32–1.38 Ga, respectively. Combined with the previous studies, it was proposed that the magma was formed by the mixing of crust-mantle components (ca. 50 and ca. 50%, respectively). In addition, magmas are characterized by low temperatures of ca. 710 °C and oxygen fugacity (log(fO2) values of −18.5 to −16.4. Formation of these granites were likely related to an intraplate extensional tectonic setting, triggered by roll-back of the subducted Paleo-Pacific plate beneath the South China Block (SCB). These granites are in favor of the Sn (W) mineralization, making the Guposhan ore district a large-scale Sn (W) mineralization ore field in the Nanling Range.

Petrogenesis and tectonic implications of the 2.1–2.0 Ga granitoids in Fuping Complex, North China Craton: Constraints from petrology, geochemistry and zircon U-Pb-Hf isotopes

Mid-Paleoproterozoic (2.2–2.0 Ga) magmatism in the Trans-North China Orogen (TNCO) is of great significance for the Paleoproterozoic geological evolution of the entire North China Craton (NCC). In this paper, we present geochemical, SHRIMP zircon U-Pb and Hf isotopic data on the 2.1–2.0 Ga granitoids in the Fuping Complex of the TNCO. These include the Nanying granitic gneiss, which yielded ages of 2075 ± 13 Ma, 2079 ± 9 Ma and 2073 ± 10 Ma, the Gangnan granitic gneiss, dated at 2081 ± 8 Ma, 2082 ± 14 Ma and 2063 ± 7 Ma, the Baiyangling granite with ages of 2077 ± 6 Ma, 2070 ± 19 Ma and 2069 ± 12 Ma, and the Shangzhuang granite, which yielded ages of 2072 ± 12 Ma and 2070 ± 12 Ma. The 2.1–2.0 Ga granitic rocks in Fuping Complex are enriched in SiO2, K2O + Na2O, rare earth elements (REEs) (except Eu), high field strength elements like Zr, Nb, Ga and Y, and depleted in CaO, Al2O3 and Sr. Their Ga/Al ratios and absolute Zr + Nb + Y + Ce contents are high and their average Zr saturation temperatures are as high as 890 °C, all of which are consistent with the features of A-type granite. The εHf(t) values of zircon in all samples are much lower than that of the depleted mantle at the same stage, while Hf model TDM1, TDMC ages have ranges of 2.3–2.7 Ga and 2.4–2.9 Ga, respectively, which are much older than the age of the granitoids. These zircon Hf model ages are similar to those of the Neoarchean TTG (Tonalite-Trondhjemite-Granodiorite) gneisses in the Fuping Complex. Therefore, based on a combination of petrology, geochemistry and isotopic characteristics, we infer that these four 2.1–2.0 Ga granitic plutons in the Fuping Complex are partial melts of the Neoarchean TTG gneiss generated in an extensional environment. Based on extensive data, the 2.1–2.0 Ga A-type granites and the mafic dikes in the Fuping Complex represent a bimodal magma association. Considering the sedimentary rocks of the Gantaohe Group, deposited in the same period, we deduce that the 2.1–2.0 Ga A-type granite in the TNCO Fuping Complex was emplaced in an intra-continental rift setting in the NCC. This evidence indicates that the North China Craton was initially stabilized at the end of the Neoarchean.

Zircon U–Pb ages and Hf isotopes of the Huai’an gneisses from the Tianzhen-Xinpingbu area: Implications for the tectonic evolution of the Trans-North China Orogen

One of the major advancements in understanding the formation and evolution of the North China Craton was the recognition of a Himalayan-type collisional belt in the central part of the craton, called the Trans-North China Orogen (TNCO), along which two micro-continental blocks, named the Eastern Block and Western Block, joined together to form a coherent craton. However, controversy still remains about the pre-collisional tectonic setting and architectures of the TNCO. In this contribution, field-based zircon U–Pb and Lu-Hf isotopic investigations were carried out on the Huai’an gneisses from the Tianzhen-Xinpingbu area in the northern part of the TNCO. The Huai’an gneisses consist predominantly of tonalitic-trondhjemitic-granodioritic (TTG) gneisses with minor gabbroic, dioritic and granitic gneisses. Our zircon U-Pb results show that the plutonic protoliths of the Huai’an gneisses were emplaced at 2.51–2.40 Ga and experienced a granulite-facies metamorphic event at 1.86–1.80 Ga. The magmatic zircons of these samples yield εHf(t) values from +1.9 to +7.0 and TDMC ages of 2862–2619 Ma. These positive εHf(t) values, associated with the lack of old inherited zircons, suggest the derivation of their precursor magmas from a juvenile crust without contamination of old continental crust. The TDMC model ages indicate that 2.8–2.6 Ga is the best estimation of the mantle extraction time for the source rocks in the Huai’an gneisses, revealing a major period of juvenile crustal growth. Thus it can be inferred that the partial melting of subducted oceanic crust slab produced the magmas of the Huai’an gneisses, which subsequently interacted with overlying mantle wedge during the ascent, suggesting an intra-oceanic arc environment for the Huai’an gneiss complex. Taken together, the development of the Huai’an gneiss complex was involved in a subduction-related magmatic event in an intra-oceanic arc at ~2.5 Ga, followed by collision between the Eastern and Western blocks at ~1.85 Ga.

Geochemistry and geochronology of zircons from granite-hosted gold mineralization in the Jiaodong Peninsula, North China: Implications for ore genesis

Large-scale quart-vein and structurally-controlled gold mineralization is intensely developed in the Jiaodong Peninsula, North China Craton and is typified by the Linglong and Jiaojia deposits, respectively. In this work, zircons from typical gold-bearing ores of the Sanshandao Northern Sea (SNS), Jiuqu (JQ) and Canzhuang (CZ) gold deposits were compared in terms of texture, U–Pb age, trace element content and Hf isotopic signatures in order to discern whether zircon from ore samples can be used as an indicator of ore genesis and grade. Most studied zircons are magmatic in origin with a hydrothermal overprint (i.e., zircons with core-rim assemblages, fractured-dissolution textures and hydrothermal activity-related fluid/mineral inclusions). Three zircon age clusters were differentiated: ~120 Ma, ~150 Ma and >2000 Ma. The ~120 Ma zircons show evidence of hydrothermal alteration (dark in cathodoluminescent images with hydrothermal rim textures) and are characterized by high LREE, P, Ti and εHf(t) (−21 to −15) and young TDMC (2100–2500 Ma). This suggests an interaction between the mantle and crust at the magma source, and that a P/Ti-rich, Al-poor, high temperature, high fO2, wet late-stage residual granitic melt and intense hydrothermal alteration played an important role in the formation of gold mineralization. The ~150 Ma zircons have high Y, Nb, Ta and U contents, low εHf(t) (−26 to −20) and old TDMC (2300–3000 Ma) ages, and HREE-enriched patterns with pronounced Ce and Eu anomalies. These features indicate a reduced, cool and Al-rich magma which did not favor gold mineralization, even though it was highly evolved. This also implies that the degree of magma differentiation is not the key factor that led to gold mineralization in the Jiaodong gold province. The >2000 Ma zircons are primarily limited to gold ores with high Pb contents, HREE-enriched patterns and variable Ce and Eu anomalies, indicating that they were inherited from the Paleoproterozoic (2000–2200 Ma) basement. In addition, the SNS high-grade ores yielded zircon with the greatest U-Pb age range (mainly 110–180 Ma) and the most pronounced hydrothermal overprinting, indicating that large-scale mineralization resulted from multi-stage granitic intrusion, with intense fluid dissolution and metasomatism. This research highlights that correlations between zircon age populations, Hf isotope signatures, internal structures and trace element patterns can provide insights into ore genesis and fluid evolution in gold mineralization systems.

Evidence for Archean crust in Iran provided by ca 2.7 Ga zircon xenocrysts within amphibolites from the Sanandaj–Sirjan zone, Zagros orogen

High-precision secondary-ion mass spectrometry (SIMS) U–Pb and Hf–O isotopic microanalyses of zircons from the central Sanandaj–Sirjan metamorphic zone (SSMZ) of the Zagros orogen, Iran, provide evidence of the presence of 2.7 Ga xenocrystic zircons, suggesting that the SSMZ records Neoarchean crustal components that have not previously been reported in Iran. The two amphibolite samples analyzed from the Muteh–Golpaygan metamorphic complex during this study include one sample (GQ-10) that yielded xenocrystic zircons with ages clustered around ca 2.7 Ga. The second sample (GC-15) contains zircons that show two distinct xenocrystic zircon domains with ages of (i) ca 2.7 and 2.5 Ga, and (ii) ca 52 Ma. The ca 2.7 Ga zircons and zircon domains have homogeneous, mantle-like δ18O values with a mean of 6.10 ± 0.69‰. They have εHf(t) values that vary between +0.2 to +6.8 with TDMC ages of 3.1–2.7 Ga, suggesting they crystallized from granitoid melts derived from juvenile components. However, the younger ca 2.5 Ga zircons yield an average δ18O value of 6.17 ± 0.24‰ and have evolved Hf isotopic compositions (εHf(t) −0.8 to −3.4; TDMC = 3.2–3.1 Ga), indicating that the older crust in this region underwent more intense later reworking than is the case for crustal material formed at ca 2.7 Ga. These data provide evidence of Neoarchean basement rocks in this region, indicating that the SSMZ records ancient crustal growth events. The youngest ca 52 Ma xenocrystic zircons within these samples most likely reflect the late Paleocene–Eocene magmatic ‘flare-up’ within Iran. These zircons have slightly elevated δ18O values (7.69 ± 0.21‰) and negative Hf isotopic compositions (εHf(t) −8.3 to −12.1; TDMC = 1.9–1.6 Ga), suggesting intensive crustal reworking at ca 50 Ma.