Petrogenesis of synorogenic high-temperature leucogranites (Damara orogen,Namibia): Constraints from U–Pb monazite ages and Nd,Sr and Pb isotopes

Two suites of leucogranites were emplaced at 508 ± 5.9 Ma in the Okombahe District of the Damara belt (Namibia) synchronous with the peak of regional high-temperature metamorphism. The Sr (⁸⁷Sr/⁸⁶Sr_init: 0.707 to 0.711), Nd (εNd_init: − 4.5 to − 6.6), and Pb isotopic (²⁰⁶Pb/²⁰⁴Pb: 18.51–19.13; ²⁰⁷Pb/²⁰⁴Pb: 15.63–15.69; ²⁰⁸Pb/²⁰⁴Pb: 38.08–38.66) compositions indicate that these peraluminous S-type granites were derived from mid- to lower-crustal rocks, which are slightly different to the metapelitic rocks into which they intruded. Since the leucogranites are unfractionated and show no evidence for assimilation or contamination, they constrain the temperature and pressure conditions of their formation. Calculated Zr and LREE saturation temperatures of ca. 850 °C indicate high-temperature crustal melts. High Rb/Sr and low Sr/Ba ratios are consistent with biotite dehydration melting of pelitic source rocks. Qz–Ab–Or systematics reveal that melting and segregation for the least fractionated samples occurred at ca. 7 kbar corresponding to a mid-crustal level of ca. 26 km. However, there is no evidence for a mantle component that could have served as a local heat source for crustal melting. Therefore, the hot felsic magmas that formed close to the time of peak metamorphism are the result of long-lasting high temperature regional metamorphic conditions and intra-crustal collision.     

Provenance of the Vazante Group: New U–Pb,Sm–Nd,Lu–Hf isotopic data and implications for the tectonic evolution of the Neoproterozoic Brasília Belt

The Vazante Group show varied U–Pb provenance patterns along the basin. Zircon ages range from 936 to 3409 Ma, but Paleo- and Mesoproterozoic terrains constitute the main sources of the original sediments. The youngest population (~ 930 Ma) establishes the maximum depositional age of the group. Sm–Nd T_DM data show the predominance of Paleoproterozoic ages (1.90–2.08 Ga) and also indicate some input from younger sources in rocks of the Lapa Formation (1.67 to 2.0 Ga) in the upper part of the group, whereas rocks of the Serra do Garrote Formation present the oldest model ages (2.03 to 2.76 Ga). Hf isotopic compositions of the detrital zircons indicate that they were derived mainly from recycled Paleoproterozoic crust with a minor Mesoproteroic juvenile component. Terranes within the São Francisco Craton represent the main sources of detrital sediments of this group and reinforce the interpretation that it may be a passive margin sequence developed along the western margin of the original continent. However, the origin of Mesoproterozoic grains remains uncertain. Slightly younger Sm–Nd model ages in the Lapa Formation, however, are not entirely consistent with derivation solely from the craton and may indicate contribution from younger sources, such as the Neoproterozoic Goiás Magmatic Arc.     

Constraints from zircon U–Pb ages, O and Hf isotopic compositions on the origin of Neoproterozoic peraluminous granitoids from the Jiangnan Fold Belt, South China

Zircon textures and micro-chemical compositions precisely record the origin and petrogenesis of granitoids, which are crucial for evaluating crustal growth and reworking, thermal and geodynamic evolution. Zircons in peraluminous granitoids from the three largest 820 Ma complexes (Guibei, Yueyang and Jiuling) in the Jiangnan Fold Belt in South China are used to constrain their sources and petrogenetic processes. Zircons in the Guibei granitoids have complex internal structures. Nearly all magmatic and inherited zircons have similar εHf (?6.8 to +5.6) and δ¹⁸O values (8.8–11.6 ‰) and dominantly lie between εHf evolution vectors for a crust created between 1.7 and 2.1 Ga, suggesting that the Guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material. However, the Yueyang granitoids contain zircons with high εHf (?0.5 to +9.7) and relatively low δ¹⁸O values (5.9–8.4 ‰) and two-stage model ages of 1.1–1.8 Ga, and thus may have been formed by melting of mafic rocks from the lower crust. The Jiuling granitoids and their enclaves contain more complex zircons with more variable εHf (?7.2 to +9.7) and δ¹⁸O values (7.0–10.6 ‰), and lie along the mixing trend between the above-proposed infracrustal and supracrustal granitoids. Therefore, the Neoproterozoic peraluminous granitoids in the Jiangnan Fold Belt were produced by melting and mixing of continental crust. Compared with extremely low (≤4 ‰) and negative δ¹⁸O values of Neoproterozoic igneous zircons formed in its northern active continental margin, the high δ¹⁸O peraluminous granitoids in the southeastern Yangtze Block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the Nanhua back-arc basin.     

Collision-related genesis of the Sharang porphyry molybdenum deposit,Tibet: Evidence from zircon U–Pb ages,Re–Os ages and Lu–Hf isotopes

Sharang is a low-fluorine, calc-alkaline porphyry Mo deposit hosted mainly in a granite porphyry of a multi-stage plutonic complex in the northern Gangdese metallogenic belt, largely with stockwork and ribbon-textured mineralization. The observed age estimates suggest that the formation of the magmatic host complex (52.9–51.6 Ma) and the ore deposit itself (52.3 Ma) occurred during the main stage of the India–Asia collision. The host rocks are characterized by lower zircon ε_Hf(t) values than those of the pre-ore and post-ore rocks. This suggests that the Lhasa terrane basement might play an important role in the formation of Sharang ore-forming intrusions. In view of the framework of magmatic–metallogenic events we suggest that slab roll-back may have induced melting of juvenile crust and ancient continental complexes during the India–Asia collision. This proposal focuses exploration for additional molybdenum deposits on the collision zone.     

Metapegmatites in the western Bohemian massif: ages of crystallisation and metamorphic overprint, as constrained by U–Pb zircon, monazite, garnet, columbite and Rb–Sr muscovite data

Granitic metapegmatites of two crystalline units of the western Bohemian massif, the Zone of Erbendorf-Vohenstrauss in Germany (ZEV), and the Zone of Teplá-Doma?lice in the Czech Republic (ZTD) have been dated by means of U–Pb and Rb–Sr methods. Ages interpreted to reflect emplacement and crystallisation of the pegmatites were found consistently to be approximately 480?Ma, as constrained by U–Pb analyses of primary magmatic zircon, monazite, garnet and columbite, and by Rb–Sr analyses of large pegmatitic muscovites. Later Devonian amphibolite-facies metamorphism caused ductile shearing of the pegmatites, leading to partial recrystallisation of pegmatitic material. A metamorphic, fine-grained generation of muscovite yielded consistent Rb–Sr ages of 371–376?Ma for both the ZEV and the ZTD, interpreted as dating the end of deformational activity. The Rb–Sr system of the large pegmatitic muscovites turned out to remain closed up to metamorphic temperatures of >600?°C. Deformation at elevated temperatures is identified as the dominant mechanism for opening of the Rb–Sr system of primary muscovites: apparent ages grade towards Devonian ages as the muscovites become more deformed and fragmented. The data derived from the metapegmatites point to a similar or common tectonometamorphic evolution for the ZEV and the ZTD since the Ordovician. Furthermore, the magmatic formation of granitic pegmatites implies an upper crustal position of the intruded rocks in Lower Ordovician times, clearly documenting the existence of two distinct metamorphic cycles. In contrast to this, in the neighbouring part of the Moldanubian, only unmetamorphosed granitic pegmatites with intrusion ages around 320?Ma are observed.     

Evolution of the Solonker suture zone: Constraints from zircon U–Pb ages,Hf isotopic ratios and whole-rock Nd–Sr isotope compositions of subduction- and collision-related magmas and forearc sediments

The Solonker zone in northern Inner Mongolia (China) is considered as the suture between the North China Craton and the South Mongolian microcontinent. Two magmatic belts are recognized along the suture zone: a subduction-related magmatic belt (represented by the Baolidao arc rocks), and a younger, collision-related granite belt (represented by the Halatu granites). We use zircon U–Pb ages, zircon in-situ Hf isotopic analyses and whole-rock Nd–Sr isotopic data of the two magmatic belts and related forearc sediments (the Xilinhot metamorphic complex) to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks. A gabbroic diorite (BLD-1) of the Baolidao arc was dated at 310 ± 5 Ma (by SHRIMP). This sample shows an ε_Nd(t) value of +2.5 and I_Sr of 0.7052. Hf isotopic analyses on 25 zircons from the same sample show ε_Hf(t) = +5.4 to +11.5. Another diorite sample (XH-2) of the same arc from south of Xilinhot displays even more “depleted” isotopic compositions, with ε_Nd(t) = +5.6 and I_Sr = 0.7037. The main population of zircons from this sample have highly variable and depleted Hf isotopic compositions (ε_Hf(t) = 0–18.3). The large variation in Hf isotopic composition of zircons (with largely the same crystallization age) from a single pluton is explained by a mixing process between depleted mantle-derived magma and continental crust in an active continental arc setting. The Halatu granite (HLT-2) was dated at 234 ± 7 Ma (by SHRIMP). Zircons from the granite also show a large variation of ε_Hf(t) values (+9.1 to ?26), despite most samples having whole-rock ε_Hf(t) > +2. The large variation in ε_Hf(t) values suggests that the granite formed probably by partial melting of two source regions – a dominant juvenile crust and a subordinate old continental crust. Most zircons from the Xilinhot metamorphic complex show ages comparable with those of the Baolidao arc rocks, suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism. Some zircons, however, show Precambrian ages that fall into two groups: one with ages of 780–900 Ma, resembling those from the South Mongolian microcontinent, and the other with ages of 1524–2900 Ma, similar to those of the North China Craton. Thus, the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents, and metamorphosed subsequently during collision in the late Paleozoic. Our zircon age data thus constrain timing of collision between the South Mongolian microcontinent and the North China Craton to have been between 296 and 234 Ma.     

U–Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian Pyrite Belt

A geochronology and Hf isotope study, using laser ablation-ICP-MS analysis of zircon grains, has been conducted to date felsic volcanic rocks from the Portuguese sector of the Iberian Pyrite Belt and to establish possible sources for these rocks. The ages obtained range from the Famennian to the Tournaisian, with the oldest ages reported in the Belt so far being identified in its southwestern part (Cercal area). Results also indicate that within each area, volcanism may have extended for significant periods of time. This suggests that caution is needed in interpreting possible migration trends for the volcanism, as the exact stratigraphic position of the sampled rocks is not always clear. Despite of this, the new data, coupled with previously reported information, suggests that volcanism migrated within the basin from the southwest to the northeast (present day coordinates). Projection from initial zircon ?Hf values towards the depleted mantle evolution curve, via an intermediate reservoir, allows the calculation of Hf protolith model ages that are predominantly Meso-Proterozoic. This is compatible with acid magmas resulting from the fusion of Phyllite–Quartzite (PQ) Formation metasedimentary rocks, which are beneath the volcanic rocks. This is because zircon grains from one PQ Formation sample provided Late Neo-Proterozoic ages and Paleo-Proterozoic to Late Archean U–Pb ages, and the Hf isotope signatures of these zircons can be expected to mix during fusion and result in protolith model ages that would be intermediate between the two U–Pb age populations, as recorded. Further supporting this source for the magmas, the distribution of U–Pb ages of (pre-Variscan) inherited zircon grains in the volcanic rocks is very similar to that shown by the detrital zircon grains from a PQ sample.     

Zircon U–Pb geochronology and Hf isotope geochemistry of magmatic and metamorphic rocks from the Hida Belt,southwest Japan

Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks from the Hida Belt,southwest Japan,lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia.Ion microprobe data for magmatic zircon domains from eight mafic to intermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean ~(206)Pb/~(238)U ages spanning the entire Permian period(302–254 Ma).Under cathodoluminescence,primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating,irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios( 0.2).These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids.Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton,together with the Yeongnam Massif in southern Korea.The arc magmatism along this system was commenced in the Carboniferous and culminated in the Permian–Triassic transition period.Highly positive εHf(t) values( +12) of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism.On the other hand,near-chondritic εHf(t) values(+5 to-2) of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin.Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints.Resumed highly positive zircon εHf(t) values(+9) shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.     

Retention of Sm–Nd isotopic ages in garnets subjected to high-grade thermal reworking: implications for diffusion rates of major and rare earth elements and the Sm–Nd closure temperature in garnet

Garnet is a vital mineral for determining constrained P–T–t paths as it can give both the P–T and t information directly. However, estimates of the closure temperature of the Sm–Nd system in garnet vary considerably leading to significant uncertainties in the timing of peak conditions. In this study, five igneous garnets from an early Proterozoic 2414 ± 6 Ma garnet—cordierite bearing s-type granite—which was subjected to high-T reworking have been dated to examine their diffusional behaviour in the Sm–Nd system. Garnets 8, 7, 6 and 2.5 mm in diameter were compositionally profiled and then dated, producing two-point Sm–Nd isochron ages of 2412 ± 10, 2377 ± 5, 2370 ± 5 and 2365 ± 8 and 2313 ± 11 Ma, respectively. A direct correlation exists between grain size and amount of resetting highlighting the effect of grain size on closure temperature. Major element EMPA and LA-ICPMS REE traverses reveal homogenous major element profiles and relict igneous REE profiles. The retention of REE zoning and homogenisation of major element zoning suggest that diffusion rates of REEs are considerably slower than that of the major cations. The retention of REE zoning and the lack of resetting in the largest grains suggest that Sm–Nd closure temperature in garnet is a function of grain size, thermal history and REE zoning in garnet.     

U–Pb baddeleyite ages and Hf,Nd isotope chemistry constraining repeated mafic magmatism in the Fennoscandian Shield from 1.6 to 0.9 Ga

The Palaeoproterozoic (1.90–1.60 Ga) crust of central Fennoscandia was intruded repeatedly by dolerite dikes and sills during the Neo- and Mesoproterozoic eons. We report 17 new baddeleyite U–Pb dates comprising six generations of dolerites (in Ma):

Blekinge-Dalarna dolerites	946–978
Protogine Zone dolerites	1,215–1,221
Central Scandinavian Dolerite Group	1,264–1,271
Tuna dikes and age equivalents in Dalarna	1,461–1,462
Värmland dolerites	～1,568
Breven-Hällefors dolerites	～1,595

The favoured tectonic model implies that the majority of these suites were related to active margin processes somewhere west (and possibly south) of the Fennoscandian Shield. Dolerite intrusions are interpreted to reflect discrete events of back-arc extension as the arc retreated oceanward. Initial Hf and Nd isotope compositions of the dolerite swarms fall between CHUR and normal-depleted mantle, and suggest a variably depleted and re-enriched mantle as the source for the here investigated 1.6 to 0.95 Ga old mafic rocks. Repeated recycling of older crustal components, mainly sediments (dominated by material with short residence ages) in earlier subduction systems may have been very efficient at producing geochemically and isotopically variably enriched lithospheric mantle sections beneath the Fennoscandian Shield.

     

Nature of magmatism and sedimentation at a Columbia active margin: Insights from combined U–Pb and Lu–Hf isotope data of detrital zircons from NW India

Detrital zircons from a Palaeoproterozoic quartzite, deposited between 1.85 and 1.82 Ga in the northern Aravalli orogen of NW India, show a distinctive age peak of ca. 1.85 Ga and variable, but largely subchondritic εHf_{1.85 Ga} between ? 1.3 and ? 21.0 corresponding to hafnium model ages of 2.5 to 3.6 Ga. These data indicate an important period of reworking of ancient (Eo- to Neoarchaean), strongly heterogeneous continental crust at this time. Prevalence of ca. 1.85 Ga subduction-related granitoids, almost identical U–Pb age spectra and εHf_t of detrital zircons in ca. 1.85 Ga metasedimentary rocks in the Aravalli orogen and the inner Lesser Himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late Palaeoproterozoic. All together, the data constrain a rapid succession of sedimentation, metamorphism and subduction-related magmatic activity and support the interpretation of an active geodynamic realm along the entire north Indian margin at ca. 1.85 Ga. Comparison of detrital zircon data in conjunction with published paleomagnetic data from north India and other crustal blocks of the Columbia supercontinent, additionally, suggest a close affinity of north India with Madagascar, the Cathaysia block of South China and South Korea during Columbia times.     

Petrogenesis of the Bao'anzhai granite and associated Mo mineralization,western Dabie orogen,east-central China: Constraints from zircon U–Pb and molybdenite Re–Os dating,whole-rock geochemistry,and Sr–Nd–Pb–Hf isotopes

Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon ²³⁸U–²⁰⁶Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial ⁸⁷Sr/⁸⁶Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(²⁰⁶Pb/²⁰⁴Pb)_i, 16.423–16.699; (²⁰⁷Pb/²⁰⁴Pb)_i, 15.285–15.345; (²⁰⁸Pb/²⁰⁴Pb)_i, 37.335–37.633], and is characterized by low ?_Nd(t) and ?_Hf(t) values (?14.92 to??14.22 and??21.67 to??19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionated I-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (²⁰⁶Pb/²⁰⁴Pb, 16.592–17.674; ²⁰⁷Pb/²⁰⁴Pb, 15.300–15.476; ²⁰⁸Pb/²⁰⁴Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit.     

U–Pb ages and Lu–Hf isotopes of detrital zircons from the southern Qinling Orogen: Implications for Precambrian to Phanerozoic tectonics in central China

The Qinling Orogen, central China, was constructed during the Mesozoic collision between the North China and Yangtze continental plates. The orogen includes four tectonic units, from north to south, the Huaxiong Block (reactivated southern margin of the North China Craton), North Qinling Accretion Belt, South Qinling Fold Belt (or block) and Songpan Fold Belt, evolved from the northernmost Paleo-Tethys Ocean separating the Gondwana and Laurentia supercontinents. Here we employ detrital zircons from the Early Cretaceous alluvial sediments within the Qinling Orogen to trace the tectonic evolution of the orogen. The U–Pb ages of the detrital zircon grains from the Early Cretaceous Donghe Group sediments in the South Qinling Fold Belt cluster around 2600–2300 Ma, 2050–1800 Ma, 1200–700 Ma, 650–400 Ma and 350–200 Ma, corresponding to the global Kenorland, Columbia, Rodinia, Gondwana and Pangaea supercontinent events, respectively. The distributions of ages and εHf(t) values of zircon grains show that the Donghe Group sediments have a complex source comprising components mainly recycled from the North Qinling Accretion Belt and the North China Craton, suggesting that the South Qinling Fold Belt was a part of the united Qinling–North China continental plate, rather than an isolated microcontinent, during the Devonian–Triassic. The youngest age peak of 350–200 Ma reflects the magmatic event related to subduction and termination of the Mian-Lue oceanic plate, followed by the collision between the Yangtze Craton and the united Qinling–North China continent that came into existence at the Triassic–Jurassic transition. The interval of 208–145 Ma between the sedimentation of the Early Cretaceous Donghe Group and the youngest age of detrital zircons was coeval with the post-subduction collision between the Yangtze and the North China continental plates in Jurassic.     

Tectonic regime switchover of Triassic Western Qinling Orogen: Constraints from LA-ICP-MS zircon U–Pb geochronology and Lu–Hf isotope of Dangchuan intrusive complex in Gansu,China

The Qinling Orogenic Belt, linking the Kunlun and Qilian Mountains to the west and continuing farther east to the Dabie Mountain, was assembled by the convergence and collision between the Greater South China and the North China blocks. The precise timing of the subduction and collision processes between these continental blocks and tectonic regime switchover is very equivocal. Zircon in-situ LA-ICP-MS U–Pb dating in this contribution indicates that the biotite monzogranite and monzogranite phases of the Dangchuan complex were crystallized at ca. 239.8 ± 2.3 Ma and 227.8 ± 1.2 Ma, respectively. The ca. 240 Ma biotite monzogranite displays ε_Hf(t) values ranging from −2.4 to +2.9, and corresponding T_DM2 of 1.72–1.94 Ga and T_DM1 of 0.77–0.88 Ga. The ca. 228 Ma monzogranite exhibits ε_Hf(t) values ranging from −4.3 to +1.9, and corresponding T_DM2 of 1.73–2.08 Ga and T_DM1 of 0.81–0.88 Ga. Lutetium–Hf isotopic composition indicates that the biotite monzogranite and monzogranite probably have the same parental magmas which were originated from hybrid sources of both reworking of Paleoproterozoic ancient crust and partial melting of the Neoproterozoic juvenile crust. The more negative ε_Hf(t) values of the monzogranite suggest more contribution of the ancient crust during the source contamination, or more possible crustal assimilation during their crystallization at ca. 228 Ma than precursor biotite monzogranite. Integrated with previous research and our detailed petrography, we propose that the Dangchuan complex underwent an episodic growth documenting the tectonic regime switchover from early Paleozoic to Triassic. The ca. 439 Ma inherited zircon recorded the persistent subduction of the oceanic crust, the ca. 240 Ma biotite monzogranite emplaced during the northward subduction of the Mianlue oceanic crust beneath the South Qinling block, and the ca. 228 Ma monzogranite emplaced during the syn-collisional process in a compressional setting.     

Magmatism and metallogeny associated with mantle upwelling: Zircon U–Pb and Lu–Hf constraints from the gold-mineralized Jinchang granite,NE China

The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin–Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones.In this study, we present U–Pb and Lu–Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb–Sr ages from the Jinchang gold deposit. The results show ²⁰⁶Pb/²³⁸U ages of 201 ± 3 Ma (MSWD = 1.1), 203 ± 4 Ma (MSWD = 1.4), 201 ± 5 Ma (MSWD = 2.1), and 110 ± 3 Ma (MSWD = 1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb–Sr isochron ages of 110 ± 4 Ma (MSWD = 1.04) and 107 ± 5 Ma (MSWD = 0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110 Ma and was temporally related to intrusion of the granite porphyry. Zircon ε Hf (200 Ma) values of the ca. 200 Ma granites vary from − 4.8 to + 8.1, with T^C_DM model ages of 727–1535 Ma, reflecting their derivation mainly by partial melting of juvenile Proterozoic crust. The gold-bearing 110 Ma granite porphyry returns ε Hf (110 Ma) values in the range of − 1.6 to + 9.8, with T^C_DM model ages of 542–1069 Ma, suggesting partial melts of juvenile Proterozoic crust with notable input of mantle components as compared to the ca. 200 Ma granites. Compiled oxygen (δ¹⁸O_SMOW = − 0.7–10.1) and hydrogen (δD_SMOW = − 99 to − 70) stable isotopic values of quartz from ores indicate that the ore-forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz-sulfide veins at the late stage. The Hf isotope data from the granite porphyry, integrated with the results from previous data on S and Pb isotopic composition of ores, constrain the source of ore-forming components as lower crust with discernible mantle inputs and wall rock assimilation. Our results have implications bearing on the widespread magmatism and metallogenic event during the Early Cretaceous time in East China, and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas.     

Mesoarchean convergent margin processes and crustal evolution: Petrologic,geochemical and zircon U–Pb and Lu–Hf data from the Mercara Suture Zone,southern India

The Mercara Shear Zone is sandwiched between the Western Dharwar Craton and the Coorg Block in the Southern Granulite Terrain of India, and is marked by steep gravity gradients interpreted to suggest the presence of underplated high-density material in the lower crust. Here we present geological, petrological and geochemical data, together with zircon U–Pb ages and Lu–Hf isotopes from a suite of metaigneous (TTG-related gneisses, charnockite, metagabbro, mafic granulite) and metasedimentary (quartz mica schist, khondalite, garnet biotite gneiss, kyanite–sillimanite bearing metapelite) rocks from this zone. Geochemical data on the magmatic suite suggests formation through subduction-related arc magmatism, whereas the metasediments represent volcano-sedimentary trench sequences. Phase equilibrium modeling of mafic granulites from the Mercara Shear Zone suggests P–T range of 10–12 kbar at 700 °C to 900 °C. The zircon data yield weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 3229 ± 80 Ma for metagabbro, 3168 ± 25 Ma for the charnockite, and 3181 ± 20 Ma for the mafic granulite. Ages ranging from 3248 ± 28 Ma to 3506 ± 26 Ma were obtained from zircons in the kyanite/sillimanite bearing metapelite, 3335 ± 44 Ma from khondalite, 3135 ± 14 Ma from garnet biotite gneiss, 3145 ± 17 Ma to 3292 ± 57 Ma from quartz mica schist and 3153 ± 15 Ma to 3252 ± 36 from TTG gneiss. The tightly defined ages of 3.1 to 3.2 Ga from igneous zircons in the magmatic suite suggest prominent Mesoarchean convergent margin magmatism. The timing of high grade metamorphism as constrained from metamorphic overgrowths in zircons is ca. 3.0 Ga which might mark the collisional event between the Western Dharwar Craton and the Coorg Block. Hf isotope features suggest magma derivation mostly from juvenile sources and the Lu–Hf model ages indicate that the crust building might have also involved partial recycling of basement rocks as old as ca. 3.8 Ga. Our study defines the Mercara Shear Zone as a terrane boundary, and possible Mesoarchean suture along which the Coorg Block was accreted to the Western Dharwar Craton. The accretion of these continental fragments might have coincided with the birth of the oldest supercontinent “Ur”.     

Re–Os and U–Pb Geochronology of the Erlihe Pb–Zn Deposit, Qinling Orogenic Belt, Central China, and Constraints on Its Deposit Genesis

The Erlihe Pb–Zn deposit is an important mine of the Pb–Zn metallogenic zone in the South Qinling Orogen. It has been considered a sedimentary exhalative deposit in previous investigations because the ore body occurs concordantly at the transitional location of an upright fold. Re and Os isotopic analyses for paragenetic pyrites with sphalerite and galena from the ore body have been used to determine the timing of mineralization and to trace the source of metallogenic materials. The Re–Os isotopic data of four pyrite samples construct an isochron, yielding a weighted average age of 226±17 Ma (mean square weighted deviation=1.7), which is considered the main mineralization age. A dioritic porphyrite vein sample, showing weaker mineralization, was also dated using the SHRIMP zircon U–Pb isotopic method to constrain the youngest metallogenic age of the ore deposit, because it distributes along a group of tensional joints cutting not only the upright fold in the deposit field, but also the main ore bodies. The dioritic porphyrite sample yields a weighted mean 206Pb/238U age of 221±3 Ma, which is slightly younger than the Re–Os isotopic isochron age of the pyrites, considered as the upper age limit of the mineralization, namely the ending age of the mineralization. The Os isotopic compositions of sulfide minerals distribute within a range between Os isotopic compositions of the crust and the mantle, indicating that the ore deposit can be derived from magma-related fluid, and the metallogenic materials are most likely derived from the mixing source of the crust and the mantle. The Erlihe Pb–Zn deposit and associated dioritic porphyrite vein, important records of Qinling tectonic–magmatism–mineralization activities, were formed during the Triassic collisional orogeny processes.     

Timing of closure of the eastern Mongol–Okhotsk Ocean: Constraints from U–Pb and Hf isotopic data of detrital zircons from metasediments along the Dzhagdy Transect

The Mongol–Okhotsk Belt, a major structural element of East Asia, is probably the youngest orogenic segment within the Central Asian Orogenic Belt. However, the timing of final closure of the Mongol–Okhotsk Ocean remains unresolved. Here, we present detrital zircon U–Pb–Hf isotopic data and whole-rock geochemical data (major and trace elements and Sm-Nd isotopes) for the metasedimentary rocks from the Un'ya–Bom Terrane, Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane. Our new zircon U-Pb ages suggest that all sedimentary formations along the Dzhagdy Transect are early Mesozoic in age, rather than Paleozoic as previously thought. The detrital zircons from the metasedimentary rocks in the Un'ya–Bom Terrane, the Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane yielded the youngest concordant ages of 194 ± 4, 193 ± 2, and 171 ± 2 Ma, respectively. Moreover, we note that the so-called sedimentary formations of these terranes are not single sedimentary sequences as previously suggested, but a set of an olistostrome or tectonic mélanges composed of rocks of different ages and origins. These sedimentary formations are probably relics of the Mongol–Okhotsk remnant basin that formed in the “gaps” between the southern margin of the North Asian Craton and the Amur Block during their collision. The absence of detrital zircons younger than 171 Ma in the sedimentary rocks of the Mongol–Okhotsk basin implies that the final closure of this basin could have taken place at the boundary of the Early and Middle Jurassic as a result of the collision or the development of the Mongol–Okhotsk orogenic belt in this region. After that, the Mongol–Okhotsk Belt underwent intense deformation related to within-plate strike-slip faulting, which could be attributed to the late Mesozoic rotation of the North Asian Craton relative to the continental massifs of East Asia.     

Constraints of molybdenite Re–Os and scheelite Sm–Nd ages on mineralization time of the Kukaazi Pb–Zn–Cu–W deposit,Western Kunlun,NW China

The Kukaazi Pb–Zn–Cu–W polymetallic deposit, located in the Western Kunlun orogenic belt, is a newly discovered skarn-type deposit. Ore bodies mainly occur in the forms of lenses and veins along beddings of the Mesoproterozoic metamorphic rocks. Three ore blocks, KI, KII, and KIII, have been outlined in different parts of the Kukaazi deposit in terms of mineral assemblages. The KI ore block is mainly composed of chalcopyrite, scheelite, pyrrhotite, sphalerite, galena and minor pyrite, arsenopyrite, and molybdenite, whereas the other two ore blocks are made up of galena, sphalerite, magnetite and minor arsenopyrite and pyrite. In this study, we obtained a molybdenite isochron Re–Os age of 450.5 ± 6.4 Ma (2σ, MSWD = 0.057) and a scheelite Sm–Nd isochron age of 426 ± 59 Ma (2σ, MSWD = 0.49) for the KI ore block. They are broadly comparable to the ages of granitoid in the region. Scheelite grains from the KI ore block contain high abundances of rare earth elements (REE, 42.0–95.7 ppm) and are enriched in light REE compared to heavy REE, with negative Eu anomalies (δEu = 0.13–0.55). They display similar REE patterns and Sm/Nd ratios to those of the coeval granitoids in the region. Moreover, they also have similar Sr and Nd isotopes [⁸⁷Sr/⁸⁶Sr = 0.7107–0.7118; ε_Nd(t) = ?4.1 to ?4.0] to those of such granitoids, implying that the tungsten-bearing fluids in the Kukaazi deposit probably originate from the granitic magmas. Our results first defined that the Early Paleozoic granitoids could lead to economic Mo–W–(Cu) mineralization at some favorable districts in the Western Kunlun orogenic belt and could be prospecting exploration targets.     

Carboniferous magmatism and mineralization in the area of the Fuxing Cu deposit,Eastern Tianshan,China: Evidence from zircon U–Pb ages,petrogeochemistry, and Sr–Nd–Hf–O isotopic compositions

The newly discovered Fuxing porphyry Cu deposit is located in the Dananhu–Tousuquan arc, adjacent to the Tuwu–Yandong Cu deposits of Eastern Tianshan, in the southern Central Asian Orogenic Belt. The Fuxing deposit is hosted by volcanic rocks (basalt and dacite) in the Early Carboniferous Qi'eshan Group and Carboniferous felsic intrusions (plagiogranite porphyry, monzogranite, and quartz diorite). New SIMS zircon U–Pb dating indicates that the plagiogranite porphyry and monzogranite emplaced at 332.1 ± 2.2 Ma and 328.4 ± 3.4 Ma, respectively. The basalts are characterized by low SiO₂ contents (47.47–54.90 wt.%), a lack of Eu anomalies, strong depletion of Na, Ta, and Ti elements but positive Sr, U, and Pb anomalies, high Y (20.8–28.2 ppm) and HREE concentrations (Yb = 2.23–3.06 ppm), and relatively low (La/Yb)_N (2.20–3.92) values; the dacite samples have high SiO₂ contents (66.13–76.93 wt.%), clearly negative Eu anomalies, high Mg^# values (36–51), and high Y (41.8–54.9 ppm) and Yb (5.76–8.98 ppm) concentrations. The basalts and dacites exhibit similar signatures as normal arc rocks, and were considered to be derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. In contrast, the plagiogranite porphyry, monzogranite, and quartz diorite show the same geochemical affinity with modern adakites, which are characterized by high SiO₂ contents (67.55–79.00 wt.%), minor negative to positive Eu anomalies, strong depletion of heavy rare earth elements (Yb = 0.17–1.19 ppm) and Y (1.86–10.1 ppm), positive K, Rb, Sr, and Ba but negative Nb, Ta, Th, and Ti anomalies, and high (La/Yb)_N ratios and Mg^# values. Moreover, these adakitic felsic intrusions display relatively high positive zircon ε_Hf(t) values (+ 11.4 to + 18.3), low ⁸⁷Sr/⁸⁶Sr (0.706080–0.711239), high ¹⁴³Nd/¹⁴⁴Nd (0.512692–0.512922) ratios, and consistent zircon δ¹⁸O values (4.41‰–5.48‰), suggesting that their parental magma were most likely derived from partial melting of the subducted oceanic crust followed by mantle peridotite interaction. Based on the whole-rock geochemical and Sr–Nd–Hf–O isotopic data, as well as detailed petrographic analyses, we further suggest that the Fuxing igneous rocks and associated porphyry Cu mineralization were generated by the northward subduction of the paleo-Tianshan oceanic plate beneath the Dananhu–Tousuquan island arc during the Early Carboniferous.