Zircon Hf Isotopic Data Research Articles

The genesis of the ores and intrusions at the Yuhai Cu–Mo deposit in eastern Tianshan, NW China: Constraints from geology, geochronology, geochemistry, and Hf isotope systematics

The Yuhai porphyry Cu–Mo deposit is located in the eastern Tianshan orogenic belt of the southern Central Asian Orogen Belt, being an economically important porphyry Cu deposit in NW China. The deposit comprises sixteen buried orebodies that are predominantly associated with dioritic and granodioritic intrusions and are structurally controlled by roughly NE-trending faults. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 441.6±2.5Ma (MSWD=0.03, n=24) for diorite and 430.4±2.9Ma (MSWD=0.04, n=19) and 430.3±2.6Ma (MSWD=0.09, n=24) for granodiorite. In situ zircon Hf isotope data on a diorite sample show εHf(t) values from +8.7 to +18.6, and two granodiorite samples exhibit similar εHf(t) values from +12.6 to +19.6 and +12.6 to +18.9, respectively. The dioritic and granodioritic intrusions belong to a low-K tholeiite series and are relatively enriched in large ion lithophile elements (K, Ba, Pb, and Sr) and are depleted in high field strength elements (Th, Nb, Ta, and Ti). Moreover, these intrusions have high SiO2, Al2O3 and MgO contents, low Na2O, P2O5 and TiO2 contents, low Nb/Ta ratios, and slightly positive Eu anomalies. Re–Os dating of molybdenite intergrowth with chalcopyrite yielded a well-constrained 187Re–187Os isochron age of 351.7±2.9Ma (MSWD=1.5) with a weighted average age of 355.7±2.4Ma (MSWD=0.69) Ma, indicating that the Yuhai Cu–Mo deposit is younger than the intrusion of the diorite and granodiorite. Combined with the regional geological history and above-mentioned data, we suggest that the Yuhai intrusions were most likely derived from the partial melting of mantle components that were previously metasomatized by slab melts formed by the northward subduction of the ancient Tianshan ocean plate beneath the Dananhu–Tousuquan island arc during the Silurian to Carboniferous. Under the subduction-related tectonic setting, the metasomatized mantle magma was emplaced into the shallow crust and induced the formation of the Early Carboniferous Yuhai Cu–Mo deposit, and the hydrothermal fluids of enriched sulfides probably played an important role in the Cu–Mo mineralization.

Petrogenesis of early Silurian intrusions in the Sanchakou area of Eastern Tianshan, Northwest China, and tectonic implications: geochronological, geochemical, and Hf isotopic evidence

ABSTRACTPalaeozoic intrusions in Eastern Tianshan are important for understanding the evolution of the Central Asian Orogenic Belt (CAOB). The Sanchakou intrusions situated in Eastern Tianshan (southern CAOB), are mainly quartz diorite and granodiorite. A comprehensive study of zircon U–Pb ages, zircon trace elements, whole-rock geochemistry, and Lu–Hf isotopes were carried out for the Sanchakou intrusive rocks. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 439.7 ± 2.5 Ma (MSWD = 0.63, n = 21) for the quartz diorite, and 430.9 ± 2.5 Ma (MSWD = 0.21, n = 21) and 425.5 ± 2.7 Ma (MSWD = 0.04; n = 20) for the granodiorites. These data, in combination with other Silurian ages reported for the intrusive suites from Eastern Tianshan, indicate an early Palaeozoic magmatic event in the orogen. In situ zircon Hf isotope data for the Sanchakou quartz diorite shows εHf(t) values of +11.2 to +19.6, and the two granodioritic samples exhibit similar εHf(t) values from +13.0 to +19.5. The Sanchakou plutons show metaluminous to weakly peraluminous, arc-type geochemical and low-K tholeiite affinities, and display trace element patterns characterized by enrichment in K, Ba, Sr, and Sm, and depletion in Nb, Ta, Pb, and Ti. The geochemical and isotopic signatures indicate that the Sanchakou dioritic and granodioritic magmas were sourced from a subducted oceanic slab, and subsequently underwent some interaction with peridotite in the mantle wedge. Combined with the regional geological history, we suggest the Sanchakou intrusions formed due to the northward subduction of the Palaeo-Tianshan Ocean beneath the Dananhu–Tousuquan arc during early Silurian time.

Tectonic evolution of the eastern Central Asian Orogenic Belt: Evidence from zircon U–Pb–Hf isotopes and geochemistry of early Paleozoic rocks in Yanbian region, NE China

We present the first evidence of an early Paleozoic terrane in the southern Yanbian region, NE China. We used LA-ICP-MS zircon U–Pb and Hf isotope techniques to analyze one plagioclase gneiss and two garnet-bearing two-mica quartz schists from the early Paleozoic Jiangyu Group, as well as two tonalites that intruded the Jiangyu Group. The tonalites yield weighted mean 206Pb/238U zircon crystallization ages of 423 and 422Ma. Zircons from the Jiangyu Group gneiss and two schist samples yield maximum depositional ages of 439±4, 443±2, and 443±5Ma, respectively. These constraints, together with the age of the tonalite intrusion, indicate that the Jiangyu Group was deposited between 443 and 423Ma (i.e., Silurian). In addition, detrital zircon age spectra of the three Jiangyu Group samples exhibit prominent age peaks at 442, 473, 513, 565, 600, 635, 671, 740, 1000, and 1162Ma, as well as secondary peaks between 1344 and 3329Ma. The occurrence of the prominent Meso- and Neoproterozoic detrital zircon age populations for the Jiangyu Group, combined with the corresponding zircon Hf isotopic data, reveals that the Jiangyu Terrane has a tectonic affinity with northeastern Gondwana. The early Paleozoic magmatism, as suggested by the medium-K calc-alkaline I-type tonalite intrusion and Jiangyu Group detrital zircon age spectra, corresponds to coeval subduction–accretion events along the southern margin of the eastern Central Asian Orogenic Belt (CAOB). Accordingly, we propose that the Jiangyu Group is part of an exotic terrane that rifted from northeastern Gondwana, drifted northward, and ultimately became involved in the early Paleozoic tectonic evolution of the southern margin of the eastern CAOB after the Early Cambrian.

The anatectic effect on the zircon Hf isotope composition of migmatites and associated granites

Zircon Hf isotope composition is widely used to trace the growth and evolution of continental crust. However, it is controversial whether the Hf isotope composition of magmatic zircons can faithfully reflect that of their sources, especially for S-type granites. In order to provide an insight into this issue, we have revisited the published Lu–Hf isotope data of zircons from well-studied migmatites and associated granites in the Sulu orogen and the Cathaysian terrane, respectively. The results show greatly elevated 176Hf/177Hf ratios (by more than 10ε units) for newly grown zircon domains compared to the relict zircon domains. This indicates considerable contributions from non-zircon Hf to anatectic melts during crustal anatexis and subsequent magmatism. Furthermore, this more radiogenic Hf isotope signature was not erased during magmatic processes such as crystal fractionation during melt ascent and emplacement. The budget of Hf isotopes in source rocks with respect to mineral Lu/Hf ratios suggests the involvement of Hf-bearing major minerals in anatectic reactions by dissolving Hf-bearing major minerals into the anatectic melts. The significant Hf isotope variations in some anatectic and magmatic zircon domains from the migmatites and granites suggest not only the source heterogeneity but also the variable non-zircon Hf contributions. As such, the Hf isotope compositions of anatectic and magmatic zircons are substantially dictated by the mass balance between the non-zircon Hf from anatectic reactions and the zircon-Hf from the dissolution of protolith zircons into the anatectic melts. They are primarily controlled by P-T conditions and mechanism of crustal anatexis, and the magmatic processes during melt evolution. The present study highlights the important contribution of non-zircon Hf to the anatectic and magmatic zircon domains. In this regard, the greatly elevated 176Hf/177Hf ratios for newly grown zircon domains in the migmatites and granites cannot reflect the Hf isotope compositions of their source rocks. Such a deviation must be kept in mind when linking relatively depleted Hf isotope compositions to the nature of source rocks in petrogenetic interpretation and to the growth of continental crust. The contribution of non-zircon Hf can also better account for the variable Hf isotope compositions often shown by zircons from S-type granites.

Underplating of basaltic magmas and crustal growth in a continental arc: Evidence from Late Mesozoic intermediate–felsic intrusive rocks in southern Qiangtang, central Tibet

Phanerozoic growth of continental crust has widely been considered as an important geological phenomenon and mainly occurs in an arc setting. However, the crustal growth models (mantle-derived basalt underplating or accretion of island or intra-oceanic arc complexes or oceanic plateau) have been disputed. Here we present new zircon LA–ICPMS U–Pb age, whole-rock major and trace element, Sr–Nd and zircon Hf isotopic data for Late Mesozoic intermediate–felsic intrusive rocks in the Rena Co area in southern Qiangtang, central Tibet. LA–ICP–MS zircon U–Pb dating for two granodiorite and three diorite samples and one granodiorite porphyry sample gives ages of ca. 150Ma, ca. 112Ma, respectively, indicating they were generated in the Late Jurassic–Early Cretaceous. All rocks are sub-alkaline in composition and belong to the high-Kcal-alkaline series. The ~150Ma diorites (SiO2=57.9–61.2wt.%) exhibit relatively high MgO (3.13–3.88wt.%) and Cr (52.4–282ppm) contents and Mg# (47–51) values, similar to magnesian diorites. They are geochemically characterized by uniformly low εNd(t) (−5.5 to −5.2), high (87Sr/86Sr)i (0.7071 to 0.7078) and Th/La (0.22–0.32), and variable zircon εHf(t) (−8.7 to +4.8) values. They were probably generated by melting of oceanic sediment diapirs, followed by interaction with the surrounding mantle during the northward subduction of Bangong–Nujiang Oceanic lithosphere. The ~150Ma granodiorites and ~112Ma granodiorite porphyries are characterized by low MgO (<3wt.%) contents and Mg# (<45) values, high Al2O3 (>15%wt.%) and Sr (>400ppm) and low Y (<18ppm) and Yb (<1.9ppm) contents, and high Sr/Y and La/Yb ratios, which are similar to those of typical adakites. The granodiorites have low εNd(t) (−7.6 to −3.7) and zircon εHf(t) (−9.8 to +0.2) and high (87Sr/86Sr)i (0.7069 to 0.7086) values, and were likely produced by partial melting of a thickened and heterogeneous ancient lower continental crust. The relatively depleted isotope compositions [(87Sr/86Sr)i=0.7054–0.7065; εNd(t)=−0.61 to +0.25; zircon εHf(t)=+4.7 to +9.7] of the granodiorite porphyries indicate that they were most probably generated by partial melting of newly underplated and thickened basaltic lower crust. Taking into account ophiolites in the Bangong–Nujiang Suture and Late Mesozoic magmatic rocks in the southern Qiangtang sub-block, we suggest that this area was located in a continental arc setting. Moreover, from the Late Jurassic to Early Cretaceous, the ancient lower crust in the southern Qiangtang sub-block was gradually replaced by mantle-derived juvenile materials. The crustal evolution indicates that, in a continental arc, basaltic magma underplating plays a key role in vertical crustal growth.

Tracking sediment dispersal during orogenesis: A zircon age and Hf isotope study from the western Amadeus Basin, Australia

The c. 570–530Ma intraplate Petermann Orogeny of central Australia involved high temperature and pressure metamorphism, deformation, and uplift of the Mesoproterozoic Musgrave region and associated components of the Neoproterozoic Centralian Superbasin. Orogenesis was accompanied by deposition of a syn-tectonic siliciclastic sedimentary package (Supersequence 4) in adjacent depocentres such as the Amadeus Basin. Here we investigate the provenance of Supersequence 4 within the western Amadeus Basin using U–Pb age and Hf isotope data for detrital zircons. The data from eight samples are dominated by Mesoproterozoic zircons (peak at c. 1.18Ga) matched by age and Hf isotopes to the Musgrave region. Smaller Palaeoproterozoic components match best with the Arunta region north of the Amadeus Basin. The latter zircons are likely reworked from older Amadeus Basin sediments uplifted and eroded during the Petermann Orogeny. The combined detrital zircon age signature from Supersequence 4 in the western Amadeus Basin is strongly similar to previously published data from successions of similar age in the eastern Amadeus Basin and from two metasedimentary units in the Charters Towers Province of Queensland; a K–S test indicates that these datasets are statistically identical at >95% confidence. This suggests a sediment pathway from the Petermann Orogen to the palaeo-Pacific margin of East Gondwana via the Amadeus Basin. From existing data, a similar pathway can be inferred from the Officer Basin to the Adelaide Rift Complex on the southern side of the Petermann Orogen, although these zircon age spectra show differences in pre- and post-Mesoproterozoic components compared to the Amadeus Basin. Differences in detrital zircon age spectra and lithology between confirmed Supersequence 4 and previously inferred components of Supersequence 4 at Uluṟu (Mutitjulu Arkose) and Kata Tjuṯa (Mount Currie Conglomerate) on the southern Amadeus Basin margin raise questions about the stratigraphic position of these latter units.

Geology of El Domo deposit in central Ecuador: a VMS formed on top of an accreted margin

El Domo is a Cu-Au-Zn-Ag volcanogenic massive sulfide deposit (VMS) within the Paleocene–Eocene submarine arc rocks of the Macuchi Formation in central Ecuador. The mineralization includes massive and semi-massive sulfides located at the interface between a submarine rhyodacite dome complex and overlying mafic volcanic and volcaniclastic rocks, including chaotic and unsorted debris flow deposits. Whole rock geochemical analyses show that the felsic rocks belong to a calc–alkaline sequence, whereas the mafic assemblages have a tholeiitic affinity, reflecting a magmatic association typically found in many VMS districts. This geochemical change temporally coincides with the formation of the massive sulfides. New zircon Hf isotopic data collected from a hanging wall rhyodacite suggest that the presence of an over-thickened crust of oceanic plateau affinity may have influenced the composition of the magmatic rocks. The timing of massive sulfide formation is constrained by an 40Ar/39Ar age of 41.49 ± 0.37 Ma (2σ) from the volcaniclastic sequence which hosts the massive sulfides and a U/Pb zircon age date of 42.13 ± 0.54 Ma (2σ) from the footwall rhyodacite; both ages are interpreted to provide minimum and maximum ages for mineralization. The massive sulfides are zoned and contain variable proportions of pyrite, sphalerite, and chalcopyrite. Minor accumulations of galena, bornite, tennantite, stromeyerite, and proustite are also present; the latter two minerals are the major carriers of silver whereas gold typically occurs as minute-free grains or in solid solution with silver. Ore minerals are intergrown with variable proportions of chlorite, barite, quartz, anhydrite, and smectite. The footwall rhyodacite hosts an irregular stringer zone which is rich in pyrite and gypsum and is characterized by intense quartz-sericite-pyrite alteration. The hanging wall volcaniclastic lithologies exhibit pervasive but vertically limited (8–10 m) silicification, chloritization, and argillization. Both felsic and mafic glass-rich rocks located near the contact between rhyodacites and mafic volcaniclastic rocks are replaced by massive to disseminated mineralization, likely controlled by their originally reactive and porous nature. Replacement appears to have taken place at very shallow depths, 10–20 m below the seafloor, as shown by: (1) the presence of massive sulfide clasts within the uppermost volcaniclastic horizons and (2) the absence of mineralization and alteration in the overlying debris flows. No evidence of exhalation on the seafloor has been found, and replacement below the sea floor was probably an efficient mechanism for preserving the VMS within such a highly dynamic volcanic system. Regionally, mineralization occurred within an extensional submarine arc setting whereby massive sulfides were preferentially controlled by the reactivation of NNE-SSW crustal-scale strike slip faults created during an earlier plate collision. Local stress regimes resulted in the formation of pull-apart basins within a regional transpressive setting and provided conduits for magmatic and hydrothermal discharge. The onset of volcanism and local extension coincided with an increase in the oblique convergence of the Farallon and the South American Plate.

Zircon U–Pb geochronology, Hf isotopes and geochemistry of intrusive rocks in the Gazu copper deposit, Iran: Petrogenesis and geological implications

The Gazu Cu deposit is located at the boundary between the Lut and Tabas Blocks in Central Iranian Microcontinent. The intrusions in the Gazu area are characterized by SiO2 contents ranging from 52.6 to 66.4wt.%, K2O from 1.98 to 3.64wt.%, and Na2O from 2.5 to 5.2wt.%. The intrusions have features typical of high-K calc-alkaline rocks, are metaluminous to weakly peraluminous, and formed in a volcanic arc setting. Zircon U–Pb age data for hornblende monzonite porphyry, hornblende monzodiorite porphyry, pyroxene monzonite, hornblende granite, hornblende quartz monzonite porphyry, and hornblende diorite porphyry are 68.1±1.7Ma, 67.74±0.72Ma, 67.41±0.94Ma, 65.9±3.7Ma, 65.1±1.2Ma, and 60.2±1.2Ma, respectively. Copper mineralization is related to the hornblende granite and hornblende quartz monzonite porphyry. Field observations and the U–Pb dating indicated three stages for intrusive rock emplacement: pre-mineralization intrusions (hornblende monzonite porphyry, hornblende monzodiorite porphyry, and pyroxene monzonite), syn-mineralization intrusions (hornblende granite and hornblende quartz monzonite porphyry), and post-mineralization intrusions (hornblende diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Ba, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, Zr, Y, and heavy rare earth elements, with light rare earth element enrichment ((La/Yb)N=6.4–13.4) and a weak negative Eu anomaly (Eu/Eu*=0.87–1.01). Zircon Hf isotope data indicate that the Gazu intrusive rocks are characterized by low positive εHf(t) values, with an average of 4.23, and show young Hf model ages (789–188Ma), indicating derivation from juvenile crust. Relatively low positive εHf(t) values, the wide range for εHf(t), and the presence of zircon xenocrysts can be explained by involvement of a mantle component that mixed with older continental crust (Cadomian).

Emplacement ages, geochemical and Sr–Nd–Hf isotopic characterization of Mesozoic to early Cenozoic granitoids of the Sikhote-Alin Orogenic Belt, Russian Far East: Crustal growth and regional tectonic evolution

The Sikhote-Alin Range of the Russian Far East is an important accretionary orogen of the Western Pacific Orogenic Belt. In order to study the formation and tectonic evolution of the orogen, we performed zircon U–Pb dating, as well as geochemical and Sr–Nd–Hf isotopic analyses on 24 granitoid samples from various massifs in the Primorye and Khabarovsk regions. The zircon dating revealed that the granitoids were emplaced from 131 to 56Ma (Cretaceous to Paleogene). In the Primorye Region, granitoids in the coastal Sikhote-Alin intruded the Cretaceous Taukha Accretionary Terrane from ca. 90 to 56Ma, whereas those along the Central Sikhote-Alin Fault zone intruded the Jurassic Samarka Accretionary Terrane during ca. 110–75Ma. The “oldest” monzogranite (131Ma) was emplaced in the Lermontovka area of the NW Primorye Region. Granitoid massifs along the Central Sikhote-Alin Fault zone in the Khabarovsk Region formed from 109 to 58Ma. Thus, the most important tectonothermal events in the Sikhote-Alin orogen took place in the Cretaceous.Geochemical analysis indicates that most samples are I-type granitoids. They have initial 87Sr/86Sr ratios ranging from 0.7040 to 0.7083, and initial Nd isotopic ratios, expressed as εNd(t) values, from +3.0 to −5.0 (mostly 0 to −5). The data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies, including the subducted accretionary complex±hidden Paleozoic-Proterozoic basement rocks. Based on whole-rock Nd isotopic data, we estimated variable proportions (36–77%) of juvenile component (=mantle-derived basaltic rocks) in the generation of the granitic magmas. Furthermore, zircon Hf isotopic data (εHf(t)=0 to +15) indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation.The quasi-continuous magmatism in the Sikhote-Alin orogen suggests that the Paleo-Pacific plate subduction was very active in the Late Cretaceous. The apparently regular progression of granitic intrusion ages from 80 to 56Ma in the Taukha Terrane may reflect oblique underflow of the Paleo-Pacific plate beneath the Eurasian continental margin. Subduction was not only manifested by granitic intrusion, but also by abundant silicic volcanism. The Late Cretaceous Paleo-Pacific plate motion probably changed from parallel or sub-parallel to oblique relative to the continental margin of the Sikhote-Alin, leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks. Late Cretaceous rapid sea-floor spreading at ca. 100Ma induced highly active subduction and led to voluminous magmatism in the entire Circum-Pacific realm. Finally, the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between Sikhote-Alin and SW Japan.

Lithospheric Architecture of the Lhasa Terrane and Its Control on Ore Deposits in the Himalayan-Tibetan Orogen

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.

Geology, geochronology and geochemistry of the Saishitang Cu deposit, East Kunlun Mountains, NW China: Constraints on ore genesis and tectonic setting

The Saishitang Cu deposit, located on the eastern area of the Eastern Kunlun Orogenic Belt (EKOB), and on the northern margin of the Tibetan Plateau, is one of the most important copper deposits in Qinghai Province, China. Skarn and Cu orebodies mainly occur as stratoids or lenses along the contact zone between the quartz diorite and Lower to Middle Triassic metamorphosed tuff and marble. In this study, we use new zircon U–Pb ages, molybdenite Re–Os ages, granitoid geochemical compositions, and zircon Hf isotope data to constrain the ore genesis and the tectonic setting of the Saishitang Cu deposit. The quartz diorite is composed of inner medium- to fine-grained quartz diorite phase and an outer porphyritic quartz diorite phase. U–Pb dating of zircons by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) yield ages of 222.7±2.3Ma and 222.6±2.4Ma for the inner and outer phase of quartz diorite, respectively. Molybdenite separated from ore-bearing quartz veins yields a Re–Os isochron age of 223.4±1.5Ma, indicating a close temporal link between magmatism and mineralization. Geochemically, the quartz diorite shows high contents of SiO2 (59.63–68.21wt.%), Al2O3 (15.57–18.13wt.%) and Na2O (3.07–3.56wt.%), with A/CNK values between 0.90 and 1.01 and Mg# between 46 and 52, classified as the calc-alkaline I-type granite. The trace element patterns are characterized by high LREE (LREE/HREE=7.36–13.03), weak negative Eu anomalies (δEu=0.69–0.86), relative enrichment of Rb, Th, K, and Pb, and depletion of Nb, Ta, P, and Ti. The quartz diorite has variable εHf(t) values (−2.5 to 4.87) and Mesoproterozoic two-stage model ages (997 to 1387Ma). Based on petrological and geochemical features, we infer that the quartz diorite is derived from the partial melting of thickened lower crust with an additional input of mantle components. According to the geological, geochemical, and mineralogical features, we propose that the Saishitang Cu deposit is a skarn deposit with minor porphyry-type mineralization and the porphyry–skarn mineral system is related to the crust–mantle interaction. Based on the tectonic evolution of the Paleo-Tethys Ocean during the Late Triassic, we infer that the intrusions and associated Cu mineralization were related to regional extension of the EKOB in a post-collision environment. The results also show that most porphyry–skarn Cu deposits in the EKOB have similar mineralization ages (240–220Ma) and the Late Triassic granitoids in the EKOB present significant potential for the prospecting of porphyry–skarn Cu deposits.

Convergent margin magmatism and crustal evolution during Archean-Proterozoic transition in the Jiaobei terrane: Zircon U–Pb ages, geochemistry, and Nd isotopes of amphibolites and associated grey gneisses in the Jiaodong complex, North China Craton

Mafic metavolcanic rocks and grey gneisses are the dominant components of many Archean terranes and preserve significant imprints and information of the crustal evolution. Here we present in situ zircon U–Pb geochronology, whole-rock geochemistry and Nd isotopes of the amphibolites and associated grey gneisses in the drill holes from the Jiaobei terrane, North China Craton. The LA-ICP-MS zircon U–Pb data show that the magmatic protoliths of two amphibolites and two grey gneisses crystallized at 2457–2503Ma followed by the metamorphism at ∼1.8–1.9Ga. These rocks exhibit heterogeneous whole-rock Nd isotopic compositions, with the most radiogenic analyses (ɛNd(t)=+3.8 to +6.9) plotting on or close to the depleted mantle evolution array and the most unradiogenic ɛNd(t) extending down to −2.4. The data suggest that both ∼2.5Ga depleted mantle and ancient continental crust at least as old as 3.05 Ga contributed to the magma source. In combination with previous zircon Hf isotopic data, it is suggested that the ∼2.5–2.6Ga magmatic events in the entire Jiaobei terrane were mostly derived from the reworking of the pre-existing ∼2.7–2.8Ga crustal material. However, large variations in Hf–Nd isotopic compositions of abundant rocks at ∼2.5Ga and ∼2.7–2.8Ga in the Jiaobei terrane were likely to have resulted from interaction of mantle-derived juvenile magma with ancient crustal materials in the source region. Thus, the peaks of zircon Hf crustal model ages from these rocks do not represent the actual time of crustal growth, but could be artifacts of interaction of magmas from different sources. Geochemical features show that the protoliths of the amphibolites are tholeiitic basalts and can be subdivided into two groups: high-Mg tholeiite basalts (Group I) and high-Fe tholeiite basalts (Group II). Trace element systematics indicate that the Group I amphibolites show good affinity to subduction-related tholeiitic arc basalts, whereas the Group II amphibolites represent back-arc lavas modified by subduction components. The two groups of amphibolites and associated grey gneisses collectively define an arc-back-arc tectonic setting in the study area at ∼2.5Ga. Integrated with the previous data from other areas in Jiaobei, it can be inferred that Archean-Proterozoic transition in the whole Jiaobei terrane witnessed subduction-related magmatism in a convergent margin.

Zircon U‐Pb Geochronology and Hf Isotopic Constraints on Petrogenesis of Plagiogranite from the Cuomuqu Ophiolite, Bangong Lake Area, North Tibet

AbstractField observation, geochemical signatures and zircon Hf isotope data indicate that Cuomuqu ophiolite in the Bangonghu area was formed in a back‐arc basin (BAB) above a supra‐subduction zone (SSZ). Zircon U‐Pb dating of the diabase from the Cuomuqu massif yielded an age of 164.3±1.9 Ma, thus indicating that the ophiolite complex was formed in the Middle Jurassic during back‐arc extension of the mature Bangonghu‐Nujiang Ocean. The zircon εHf(t) and TDMC values of the plagiogranite are similar to the εHf(t) and TDM of the diabase, respectively. The mode of occurrence of plagiogranites and their bulk‐rock and Hf isotope characteristics indicate that they were derived from the mantle, associated with the surrounding gabbro and diabase, and were formed by partial melting of altered and hydrated mafic rocks under shear conditions during lateral drifting of the oceanic crust. The zircon U‐Pb age of the plagiogranite is 156.4±1.4 Ma, and it is 7.9 Ma younger than the hosting diabase. In this study, zircon chronological and Hf isotopic data were tentatively analyzed to determine the genesis of plagiogranites in the Cuomuqu ophiolite complex.

The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: New insights from zircon U–Pb and Hf isotope data

Two of the major granite belts of Southeast Asia are the Main Range and Eastern Province. Together, these are interpreted to represent the magmatic expression of the closure of Palaeo-Tethys during Late Palaeozoic to Early Mesozoic times. Recent geochronological and geochemical work has better delineated these belts within Peninsular Malaysia, thereby providing important constraints on the timing of Palaeo-Tethys suturing. However, the northern extension of this Palaeo-Tethyan suture is less well understood. Here we present new ion microprobe U–Pb zircon age data from northern Thailand and eastern Myanmar. Measured ages of 219 and 220Ma from the Kyaing Tong granite imply northern extension of the Main Range Province into eastern Myanmar. The Tachileik granite in far eastern Myanmar yields an age of 266Ma, consistent with published Eastern Province ages, and this therefore constrains the northern extension of the Palaeo-Tethys suture in eastern Myanmar. We further discuss how this suture may extend northwards into Yunnan. A Late Cretaceous age (70Ma) measured in Thailand represents later magmatic activity, and is similar to published magmatic ages from central Myanmar. This younger magmatism is interpreted to be related to the subduction of Neo-Tethys prior to India–Asia collision. Further, we present new laser ablation zircon Hf isotope data from eastern Myanmar which suggest that Palaeoproterozoic crust underlies both the Main Range and Eastern Province granites. Our εHf model age of ca. 1750Ma from Sibumasu, the basement underlying eastern Myanmar, lies within the range of other model ages reported thus far for the Baoshan Block north in Yunnan, interpreted by some to be the northern extension of Sibumasu.

Late Triassic intrusive complex in the Jidong region, Jiamusi–Khanka Block, NE China: Geochemistry, zircon U–Pb ages, Lu–Hf isotopes, and implications for magma mingling and mixing

Whole-rock major and trace element geochemistry together with zircon U–Pb ages and Lu–Hf isotope compositions are reported for a Late Triassic intrusive complex in the Jidong region, Jiamusi–Khanka Block, NE China. Zircon U–Pb dating yields ages between 211 and 208Ma for enclaves of microgranular diorite and quartz diorite, and between 211 and 209Ma for the host granitoids. These ages correlate with a previously established intensive Late Triassic magmatic event along the eastern Asian margin. Field observations, together with petrographic features, geochemistry, and zircon Hf isotope data, preclude simple crystal fractionation or restite unmixing as a genetic link for the various rock types within the intrusive complex. The syenogranite suite has high SiO2 (75.5–76.3wt.%) and low MgO (0.15–0.19wt.%), and yields enriched LILE and LREE patterns. Most of the zircons in the syenogranites have two-stage model ages of 766 and 1461Ma, together with positive εHf(t) values of +0.6 to +9.1. These results indicate that the granitoid magmas were generated by partial melting of Meso- to Neoproterozoic lower crust. The gabbro suite has a restricted range of SiO2 (46.1–51.9wt.%) together with high Mg# values (49–70) and high concentrations of Ni, Co, and Cr. Zircons from two diorite samples have single-stage Hf model ages of 557–787Ma and εHf(t) values of +1.9 to +8.3 that are consistent with the coeval gabbros previously studied in the Jidong region. These features, together with the observation that all the gabbros are enriched in LREE and LILE, suggest that the mafic magmas were derived from melting of depleted Neoproterozoic lithospheric mantle that had been metasomatized by slab-derived fluids. It is concluded that the dominant igneous suites within the Late Triassic intrusive complex formed by mingling/mixing of felsic and mafic magmas. The geochemical data, combined with regional geological investigations, indicate that the Late Triassic intrusive complex formed during lithospheric extension caused by slab break-off of the Yuejinshan oceanic plate that was subducting westward beneath the Jiamusi–Khanka Block.

Age Constraints on Late Mesozoic Lithospheric Extension and Origin of Felsic Volcanism in the Songliao Basin, NE China

Late Mesozoic lithospheric extension in NE Asia resulted in the development of a large extensional province and widespread formation of volcanosedimentary basins. Songliao basin is the biggest in that region, situated between the Siberian and Sino-Korean (North China) cratons. The Songliao basin contains voluminous volcanic rocks as a major part of the basin fill. Volcanic successions form a significant but unexposed part of the late Mesozoic magmatic province in NE China. Here we report zircon U-Pb ages and geochemical data for felsic volcanic rocks from the Songliao basin. Zircon populations of two types of rhyolites with distinct I- and A-type affinities, analyzed by laser ablation inductively coupled plasma mass spectrometry, yielded similar U-Pb ages of 114 ± 2 and 113 ± 2 Ma, respectively. Whole-rock Nd and zircon Hf isotope data of the felsic rocks indicate an origin from newly formed crustal protoliths. The I-type dacites and rhyolites show geochemical signatures with subduction-related affinity, indicating generation by partial melting of juvenile crust that originated from melting of subduction-modified mantle sources, whereas the A-type rhyolites have higher heavy rare earth element and high field strength element concentrations and lower Ba/Nd ratios that are interpreted as evidence for melting of I-type felsic lower crustal sources in an intraplate tectonic environment. Typical geochemical compositions of A-type rhyolites indicate anorthite-rich plagioclase as a residual magmatic phase and imply melting at shallow crustal levels. The A-type felsic rocks were generated during a period of maximum lithospheric extension below eastern China around 110 Ma, and this thinning process was probably related to the retreat of the Paleo-Pacific trench.

Zircon U–Pb geochronology, geochemistry and Hf isotopes of the Late Cretaceous Hongshan intrusion, western Yunnan, SW China

The Hongshan quartz monzonite porphyry is one of the Yanshanian intrusions in the southern part of the Yudun Arc. Detailed zircon U–Pb data of four samples yielded ages of 78.8–80.7 Ma, indicating that the Hongshan intrusion was emplaced during the late stage of Late Cretaceous. The Hongshan intrusion shows shoshonitic and high‐K calc‐alkaline, with A/CNK = 0.64–1.14. The rocks show an obvious fractionation between light and heavy rare‐earth elements (average [La/Yb]N = 38.85), with negative Eu anomalies (Eu/Eu* = 0.60–0.87), enrichment in large‐ion lithophile elements (Rb, Th, U and K) and depletion in high field‐strength elements (Nb, Ta and P). Rocks have high Sr and low Y content which are characteristics of adakitic rocks, suggesting magma derivation from thickened lower crust. In order to evaluate the nature of the source region, Hf isotope data of zircons were acquired through LA‐MC‐ICPMS. The negative and variable εHf(t) values demonstrate that the Hongshan intrusion was derived from ancient crust, without mantle‐derived components and is significantly different from the Triassic intrusions in the southern part of the Yudun Arc. The three Yanshanian intrusions in Hongshan, Relin and Tongchangou are remarkably similar in terms of geochronology, geochemistry and Hf isotopes. We therefore infer that these intrusions had the same magmatic source and we correlate the tectonics with northward subduction of Tethys underneath the Asian continent. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Petrogenesis of Cretaceous igneous rocks from the Duolong porphyry Cu–Au deposit, central Tibet: evidence from zircon U–Pb geochronology, petrochemistry and Sr–Nd–Pb–Hf isotope characteristics

The Duolong porphyry Cu–Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole‐rock elemental and Sr–Nd–Pb isotope and zircon Hf isotopic data of syn‐ and post‐ore volcanic rocks and barren and ore‐bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu–Au mineralization. LA–ICP–MS zircon U–Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore‐bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post‐ore basaltic andesite. All the samples show high‐K calc‐alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc‐type magmas. Syn‐ and post‐ore volcanic rocks show initial Sr ratios of 0.7045–0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408–18.642, (207Pb/204Pb)t of 15.584–15.672 and positive zircon εHf(t) values of 1.3–10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore‐bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054–0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5–9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong–Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Early Permian East-Ujimqin mafic–ultramafic and granitic rocks from the Xing’an–Mongolian Orogenic Belt, North China: Origin, chronology, and tectonic implications

The East-Ujimqin complex, located north of the Erenhot–Hegenshan fault, North China, is composed of mafic–ultramafic and granitic rocks including peridotite, gabbro, alkali granite, and syenite. We investigated the tectonic setting, age, and anorogenic characteristics of the Xing’an–Mongolian Orogenic Belt (XMOB) through field investigation and microscopic and geochemical analyses of samples from the East-Ujimqin complex and LA-MC-ICP-MS zircon U–Pb dating of gabbro and alkali granite. Petrographic and geochemical studies of the complex indicate that this multiphase plutonic suite developed through a combination of fractional crystallization, assimilation processes, and magma mixing. The mafic–ultramafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from a mantle source. The mafic–ultramafic magmas triggered partial melting of the crust and generated the granitic rocks. The granitic rocks are alkali and metaluminous and have high Fe/(Fe+Mg) characteristics, all of which are common features of within-plate plutons. Zircon U–Pb geochronological dating of two samples of gabbro and alkali granite yielded ages of 280.8±1.5 and 276.4±0.7Ma, placing them within the Early Permian. The zircon Hf isotopic data give inhomogeneous εHf(t) values of 8.2–14.7 for gabbroic zircons and extraordinary high εHf(t) values (8.9–12.5) for the alkali granite in magmatic zircons. Thus, we consider the East-Ujimqin mafic–ultramafic and granitic rocks to have been formed in an extensional tectonic setting caused by asthenospheric upwelling and lithospheric thinning. The sources of mafic–ultramafic and granitic rocks could be depleted garnet lherzolite mantle and juvenile continental lower crust, respectively. All the above indicate that an anorogenic magma event may have occurred in part of the XMOB during 280–276Ma.

Petrogenesis and tectonic implications of early Paleozoic granitic magmatism in the Jiamusi Massif, NE China: Geochronological, geochemical and Hf isotopic evidence

This paper reports geochronological, whole-rock geochemical and zircon Hf-isotopic data for the early Paleozoic granitic rocks in the Jiamusi Massif in the eastern segment of the Central Asian Orogenic Belt (CAOB), in order to investigate their precise geochronological framework, petrogenesis, sources and tectonic setting. LA-ICP-MS zircon U–Pb age data indicate that the syenogranite, monzogranite and granodiorite were emplaced during the period of 530–484Ma. Geochemically, these granitoids have high SiO2 (64.66–79.17%) and K2O (3.08–7.33%), low MgO (0.14–2.63%) and CaO (0.37–3.87%), with A/CNK and δEu values of 0.89–1.10 and 0.16–1.77, respectively. These rocks are characterized by enrichment in Rb and Nd, and depletion in Nb, Ta, P and Ti. In addition, in-situ Hf isotopic analyses of zircons from the granitic rocks reveal that they have εHf (t)=−5.8 to +2.3, with two-stage Hf model ages (TDM2) varying from 1.3Ga to 2.4Ga, indicating that they probably originated from the partial melting of a dominantly “old” Paleo-Mesoproterozoic crustal source. Additionally, these granites have variable major and trace element concentrations. Magmatic zircons from these rocks record consistent homogeneous U–Pb ages but have heterogeneous εHf (t) values, reflecting that they resulted from fractional crystallization and crustal assimilation. Based on these geochemical data combined with regional geological investigations, we propose that the early Paleozoic granitic magmatism in the study area occurred in a post-collisional extensional setting, which was probably related to the collapse of a thickened crust.