Pb Isotope Data Research Articles

Metasomatized eclogite xenoliths from the central Kaapvaal craton as probes of a seismic mid-lithospheric discontinuity

The central region of the Kaapvaal craton is relatively understudied in terms of its lithospheric mantle architecture, but is commonly believed to be significantly impacted by post-Archean magmatism such as the ca. 2056 Ma Bushveld large igneous event. We investigate a collection of 17 eclogite xenoliths from the Cretaceous Palmietfontein kimberlite at the Western Limb of the Bushveld Complex for their mineralogical compositions (major and trace elements, plus Fe3+ contents), as well as stable oxygen and radiogenic Pb isotopic compositions to gain further insights into the nature and evolution of the central Kaapvaal cratonic mantle lithosphere. New U/Pb age determinations on mantle-derived zircon yield a magma emplacement age of ca. 75 Ma for the Palmietfontein Group-1 kimberlite, which means that the entrained eclogite xenoliths may record a protracted metasomatic history from the Proterozoic through to most of the Phanerozoic eon.Garnet δ18O values of up to 6.9‰ and positive Eu anomalies for the bulk rocks suggest seawater-altered oceanic crustal protoliths for the Palmietfontein eclogite xenolith suite, which is typical for the eclogitic components of the Kaapvaal root and other cratonic mantle sections worldwide. However, several features of the Palmietfontein eclogites are commonly not observed in other mantle-derived eclogite xenolith suites. Firstly, the samples studied yield relatively low equilibration pressures and temperatures between 2.7 and 4.5 GPa and 740–1064 °C, indicating a relatively shallow residence between 90 and 150 km depths. Secondly, euhedral coarse amphibole is present in several eclogite nodules where it is in equilibrium with ‘touching’ garnet, supporting eclogite residence within the amphibole stability field at uppermost lithospheric mantle conditions. Thirdly, primary omphacitic clinopyroxene is often overgrown by diopside, and is significantly enriched in incompatible trace elements. The clinopyroxene is also characterized by elevated 206Pb/204Pb of 17.28–19.20 and 207Pb/204 Pb of 15.51–16.27, and these Pb isotopic compositions overlap with those of Mesozoic Group-2 kimberlites from the Kaapvaal craton.Our results show that eclogites reside at ~85 km depth beneath the central Kaapvaal craton as part of a layer that corresponds to an approximately 50 km thick seismically-detected mid-lithospheric discontinuity. Mid-lithospheric discontinuities have been interpreted as metasomatic fronts formed by focussed crystallization of hydrous mineral phases from enriched volatile-bearing melts, and as such the strongly overprinted amphibole-bearing eclogite xenoliths from Palmietfontein may represent a physical expression of such seismically anomalous metasomatic layer at mid-lithospheric depth. Our Pb isotope data suggest that the focussed metasomatism can be attributed to volatile-rich melts reminiscent of potassic Group-2 kimberlites, which have been invoked in MARID-style metasomatic overprinting of the lower lithospheric mantle beneath the western Kaapvaal craton. However, the relatively low fO2 recorded by the Palmietfontein eclogites (minimum FMQ-4.5) suggests that the metasomatism at mid-lithospheric depth was less protracted compared to the more intensive and oxidizing metasomatism typically observed near the base of cratonic mantle roots. While it is possible that Proterozoic magmatic events were responsible for the focussed mid-lithospheric metasomatism of the Kaapvaal mantle, on the basis of the Pb isotope constraints the Palmietfontein eclogites were most likely overprinted during ca. 120 Ma Group-2 kimberlite magmatism.

Copper, Zinc and Lead Isotopic Delta Values and Isotope Ratios of Various Geological and Biological Reference Materials

Copper, Zn and Pb isotope ratios are important tracers for understanding geological and biological processes. We present optimised column separation methods using an anion exchange resin for Cu and Zn, and a Pb‐specific resin for Pb, and provide Cu, Zn and Pb isotope data for thirty‐three commercially available geological and biological reference materials (RMs) using MC‐ICP‐MS. Our measurement procedures can be applied to various environmental samples. The Cu, Zn and Pb yields were higher than 99.2%, and isotopic fractionation did not occur during column separation. Copper and Zn delta values of AGV‐2, BCR‐2, BIR‐1a, BHVO‐2, GSP‐2, NOD‐A‐1, NOD‐P‐1, DOLT‐4, BCR‐414, BCR‐279 and NIST SRM 1573a were in good agreement with previously reported values. The intermediate measurement precision for Cu and Zn delta values was better than ± 0.02‰ (2s). The δ65CuNIST976, δ66ZnJMCand206Pb/207Pb values determined in this study ranged from −0.19 to +0.73‰, −0.96 to +1.00‰ and 1.1172 to 1.2263, respectively. The δ66ZnJMCvariability (Δ66Znmax–min) in this study was relatively larger than that of δ65CuNIST976variability (Δ65Cumax–min). A combination of Cu, Zn and Pb isotopes can be used as potential environmental tracers to track the origins of these elements in the environment as well as to understand their influence on organisms.

B–Sr–Nd–Pb isotopic constraints on the origin of the Maoniuping alkaline syenite–carbonatite complex, SW China

The Maoniuping giant rare earth element deposit is genetically related to a Cenozoic alkaline syenite–carbonatite complex. However, the origin of the alkaline complex and the genesis of the Maoniuping deposit are still unclear. In this study, the origin of the Maoniuping complex was constrained through B–Sr–Nd–Pb isotopic data for fresh/unaltered alkaline syenites. Our results indicate that the Maoniuping alkaline syenite has arc-like trace element patterns with elevated initial 87Sr/86Sr (0.706040–0.706541), 206Pb/204Pb (18.00–18.32), 207Pb/204Pb (15.53–15.60), and 208Pb/204Pb (38.25–38.78) ratios, and relatively low εNd(t) values (–4.92 to –2.66), suggesting derivation by partial melting of fertile mantle source. It also has higher B contents (1.06–7.65 ppm) and heavier δ11B values (−5.38‰ to − 2.46‰) than the upper mantle, indicating modification of the mantle source by interaction with carbonatitic melts/fluids derived from marine sediments and altered oceanic crust within the subducting Indian slab. Our results, together with recently acquired seismic tomographic data, indicate that hybridisation in the mantle source was likely induced by subduction input of marine sediments to the mantle transition zone. Boron isotopes provide a novel indicator of the deep recycling of subducted crustal materials in the sources of alkaline magmas.

Magmatic-hydrothermal evolution of an unusual Mo-rich carbonatite: a case study using LA-ICP-MS fluid inclusion microanalysis and He–Ar isotopes from the Huangshui’an deposit, Qinling, China

The Huangshui’an deposit located in East Qinling (China) is an unusual case of a Si-rich carbonatite hosting economic Mo and minor Pb and REE mineralization. The role of mantle-sourced carbonatite melts and fluids in the formation of the Mo mineralization remains poorly understood. Our integrated study based on field geology, petrography, microthermometry, and LA-ICP-MS analysis of single fluid inclusions, and noble gas isotopes of pyrite permits to reconstruct the source characteristics, the magmatic-hydrothermal evolution of the carbonatitic fluids, and their controls on Mo mineralization. Fluid inclusions hosted in calcite in the carbonatite dikes have the highest concentrations of Mo (9.9–62 ppm), Ce (820–9700 ppm), Pb (1800–19500 ppm), and Zn (570–5800 ppm) and represent the least modified hydrothermal fluid derived from the carbonatite melt. Fluid inclusions hosted in calcite (Cal) and quartz (Qz2 and Qz3) of the stage I carbonatite dikes have different metal concentrations, suggesting that they formed from two distinct end member fluids. The FIA in calcite represent fluid A evolved from carbonatite melt with relatively high-ore metal concentrations, and those in quartz characterize fluid B having a crustal signature due to metasomatic reactions with the wall rocks. The FIA in quartz (Qz1) within the altered wall rock have overlapping elemental concentrations with those of massive quartz (Qz2) and vuggy quartz (Qz3) in carbonatite. This suggests that the volumetrically significant quartz in the Huangshui’an carbonatite has been formed by the introduction of Si by fluid B. The positive correlations between Rb, B, Al, Cl, and Sr in stage II fluid inclusions in late fluorite + quartz + calcite veins indicate that this late mineralization formed from the mixing of primary hydrothermal fluid B with meteoric water. The He–Ar isotope data, in combination with available C–O–Sr–Nd–Pb isotope data, constrain the carbonatite source as an enriched mantle source modified by contributions from crustal material which was probably the fertile lower crust in the region. This distinct source facilitated the enrichment in Mo, REE, and Pb in the primary carbonatite magma. The carbonatite magmatism and Mo mineralization at 209.5–207 Ma occurred in the regional-scale extensional setting at the postcollision stage of the Qinling Orogenic Belt.

Origin of sediment-hosted Pb-Zn mineralization in the Paleoproterozoic Mârmorilik and Qaarsukassak formations, Karrat Group, West Greenland

• We compare Pb-Zn mineralization at Black Angel and Qaarsukassak, West Greenland. • S-isotopes and Pb-isotopes address S and Pb sources to mineralizing systems. • A Re-Os isotopes demonstrate Paleoproterozoic-aged sulfide mineralization. • Black Angel, Qaarsukassak represent MVT and SEDEX mineralization, respectively. Sediment-hosted Pb-Zn mineralization occurs in the Mârmorilik and Qaarsukassak formations of the Paleoproterozoic Karrat Group in arctic West Greenland. The timing and model of mineralization of the historical Pb-Zn Black Angel Mine in the Mârmorilik Formation and how it might be related to Pb-Zn mineralization in the nearby Qaarsukassak Formation is enigmatic. This study aims to understand the origin of the Pb-Zn mineralization in both formations by petrographic analysis, pyrite- and ore-sulfide sulfur isotope analysis, Pb-Pb isotope analysis, and Re-Os isotope analysis of pyrite associated with the mineralization. Sulfur isotope results from secondary ion mass spectrometry show a range of δ 34 S values between 0‰ and +6.9‰ on sulfide minerals (pyrite, sphalerite, galena, pyrrhotite); isotopic fractionations and geothermometry suggest contributions from both bacterial sulfate reduction and abiotic thermochemical sulfate reduction processes. Isotopic analysis (Pb-Pb) of galena from ore zones hosted by the Mârmorilik Formation shows a relatively homogenous Pb isotope signature that is consistent with local basement as a likely source for the metals. Results from Re-Os analysis of pyrite indicate that the Mârmorilik and Qaarsukassak mineralizing events are Paleoproterozoic. Ore textures and mineralogy, as well as S and Pb isotope data, associated with the carbonate-hosted Mârmorilik Formation are most consistent with a Mississippi Valley-type (MVT) deposit model, whereas characteristics of the dominantly siliciclastic-hosted Qaarsukassak mineralization textures are most consistent with a sedimentary exhalative (SEDEX) mineralization model. The Mârmorilik (Black Angel) mineralization represents the oldest documented MVT deposit outside of the Neoarchean–Paleoproterozoic Transvaal basin in South Africa.

Origin of ore-forming fluids of Tokuzbay gold deposit in the South Altai, northwest China: Constraints from Sr–Nd–Pb isotopes

• A low I Sr (t) fluid system is required for formation of Tokuzbay gold deposit. • Pb isotopes of sulfides are similar with the ore hosting Altai Formation. • The gold mineralization may have originated from the metamorphic dehydration of sediments of Altai Formation. Orogenic gold deposits are the most important gold resource in the world. It is controversial whether their ore-forming fluids were sourced from metamorphic dehydration of the crust or the mantle. The Tokuzbay gold deposit is a typical orogenic-type gold deposit in the Central Asian Orogenic Belt , providing a case for discussing the source of ore-forming fluids. The auriferous quartz veins are fault-controlled and occur mainly in metamorphic sediments of Devonian Altai Formation and minor in diorite dikes, forming three ore types, i.e., quartz vein, altered metamorphic sediments and altered diorite dikes. We studied the Sr–Nd–Pb isotope characteristics of the ore sulfides, and magmatic and metamorphic rocks from the Tokuzbay gold deposit, and thereby discuss the source of the ore-forming fluids. The 87 Sr/ 86 Sr ratios of meta -sediment hosted ores scatter between 0.709474 and 0.715238, and I Sr (292 Ma) values range from 0.706570 to 0.714045. The diorite dikes hosted ores show more restricted 87 Sr/ 86 Sr ratios ranging from 0.706963 to 0.711519, and I Sr (292 Ma) values ranging from 0.706777 to 0.710612. The wall rocks of the Altai Formation have I Sr (292 Ma) values of 0.711778 and 0.714409, which are higher than ore sulfides. This indicates that the I Sr (292 Ma) values of initial ore-forming fluids that interacted with the Altai Formation are no higher than 0.706777, which is the lowest I Sr (292 Ma) value for disseminated ores. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for meta -sediment hosted ores range from 0.511882 to 0.512464, and −7.4 to 4.0, respectively. The calculated ( 143 Nd/ 144 Nd) i ratios and ε Nd (292 Ma) values for diorite dike hosted ores vary from 0.512293 to 0.512562, and from 0.6 to 5.9, respectively. The meta -sediments of Altai Formation show ε Nd (292 Ma) values ranging from −6.8 to −4.4 with an average of −5.8, which are lower than those of ore sulfides. This indicates that the ε Nd (292 Ma) values for the fluids that interacted with the wall rocks cannot be lower than 4.5, which is the average value for disseminated ores. The calculated ( 208 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i , and ( 206 Pb/ 204 Pb) i values of ore sulfides are 37.796–38.989, 15.512–15.707, 17.988–18.100, respectively. The wall rocks of the Altai Formation show relatively higher ( 206 Pb/ 204 Pb) i ratios, indicating that the ore-forming fluid that interacted with the Altai Formation are not higher than 17.988, which is the lowest values of sulfides from disseminated ores. Based on the Sr–Nd–Pb isotope data, we suggest the possible ore-forming fluids should have lower I Sr (292 Ma) values, higher ε Nd (292 Ma) values, and lower ( 206 Pb/ 204 Pb) i values compared to the those of ore sulfides and were possibly sourced from a source compositionally similar to the diorite dikes in addition to wall rocks of Altai Formation. Combining with the regional metamorphism and tectonic evolution , we suggest that the ore fluids have originated from the metamorphic dehydration of sediments of Altai Formation in the South Altai during the collision between Altai Orogen and Junggar Plate.

Tracing local sources and long-range transport of PM10 in central Taiwan by using chemical characteristics and Pb isotope ratios

Central Taiwan is among the most heavily polluted regions in Taiwan because of a complex mixing of local emissions from intense anthropogenic activities with natural dust. Long-range transport (LRT) of pollutants from outside Taiwan also contributes critically to the deterioration of air quality, especially during the northeast monsoon season. To identify the sources of particulate matter < 10 μm (PM10) in central Taiwan, this study performed several sampling campaigns, including three local events, one LRT event, and one dust storm event, during the northeast monsoon season of 2018/2019. The PM10 samples were analyzed for water-soluble ion and trace metal concentrations as well as Pb isotope ratios. Local sediments were also collected and analyzed to constrain chemical/isotopic signatures of natural sources. The Pb isotope data were interpreted together with the enrichment factors and elemental ratios of trace metals in PM10, and reanalysis data sets were used to delineate the sources of PM10 in central Taiwan. Our results suggested that Pb in PM10 was predominantly contributed by oil combustion and oil refineries during the local events (48–88%), whereas the lowest contributions were from coal combustion (< 21%). During periods of high wind speed, the contribution from natural sources increased significantly from 13 to 31%. Despite Pb represented only a small portion of PM10, a strong correlation (r = 0.89, p < 0.001, multiple regression analysis) between PM10 mass and the concentrations of Pb, V, and Al was observed in the study area, suggesting that the sources of PM10 in central Taiwan can be possibly tracked by using chemical characteristics and Pb isotopes in PM10. Moreover, the Pb isotopic signals of PM10 collected during the LRT event confirmed the impact of LRT from Mainland China, and the chemical characteristics of the PM10 significantly differed from those of the PM10 collected during local events. This study demonstrates the robustness of using a combination of Pb isotopic compositions and chemical characteristics in PM10 for source tracing in complex and heavily polluted areas.

Genesis of sediment‐hosted stratiform Cu–Co deposits of the Zambia Copperbelt: Geochemistry and S–Pb isotopes constraints from the Chambishi deposit

In this study, we present new field geology, whole‐rock geochemical and S–Pb isotope data for the Chambishi deposit in the Zambia Copperbelt (ZCB), in order to constrain the mineralization process and ore sulphur and metal source. The Lower Roan Subgroup clastic rocks are compositionally similar to the Post‐Archean Australian Shale and have low Chemical Index of Alteration, indicating a felsic and slightly weathered source, which we proposed to be the felsic Lufubu Metamorphic Complex (LMC). The Th, Ti, and Zr elemental features suggest that the Lower Roan Subgroup was deposited in a rift basin of passive margin. The 34S values of early‐stage diagenetic Cu‐Co sulphide (−6.2 to +6.6‰, Vienna Canyon Diablo Troilite [V‐CDT]) from the nodular and layered ores are lower than those of the late‐stage vein‐type hydrothermal Cu–Co sulphides and disseminated molybdenites (3.9–11.9‰, V‐CDT), indicating different sulphur precipitation mechanism in the two mineralization stages. Integrated with previous fluid inclusion studies, we suggest that the sulphur for the diagenetic sulphides was from bacterial reduction of sedimentary anhydrite and seawater sulphates, whereas that for the orogenic‐stage sulphides was from both diagenetic sulphide remobilization and from thermochemical sulphate reduction. The mean 238U/204Pb ratios of the diagenetic‐ and orogenic‐stage sulphides are 10.21 and 10.44, respectively, overlapping with those of the average Lufubu schist (10.38) and the Mufulira granodiorite (10.21), and suggest the LMC as the main ore metal source.

Late Paleozoic Age of Intrusive Rocks from the “Trondhjemite” Massif of the Tyrnyauz W–Mo Deposit (North Caucasus, Russia): The First Results of U–Pb Isotope Dating of Zircon (LA–ICP–MS Method)

Late Paleozoic Age of Intrusive Rocks from the “Trondhjemite” Massif of the Tyrnyauz W–Mo Deposit (North Caucasus, Russia): The First Results of U–Pb Isotope Dating of Zircon (LA–ICP–MS Method)

Lahroud, a Paleo-Tethys Remnant in Northwestern Iran: Implications for Geochemistry, Radioisotope Geochronology, and Tectonic Setting

Abstract —The Lahroud Ophiolite in northwestern Iran contains extensive zones of Paleozoic ophiolite as remnants of the Paleo-Tethys oceanic crust. The principal rock units are gabbro overlain by pillow basalt, which is intruded by granites and interbedded with pelagic sedimentary units including radiolarian cherts. Geochemistry and radioisotope studies, supported by Nd, Sm, Sr, and Pb isotope data, indicate that the Lahroud Ophiolite originates from a within-plate basaltic mantle source. The isotope studies show that the basalts are derived from Indian-type oceanic mantle sources. The radiogenic data indicate the involvement of subduction-related terrigenous materials in the source magma. All the rocks are geochemically cogenetic and were generated by fractionation of a melt with a composition of average E-MORB with a calc-alkaline signature. Two 40Ar/39Ar ages, 343 ± 3 Ma for muscovite minerals and 187.7 ± 7.7 Ma for glasses, suggest that metamorphic and basaltic rocks formed during the Late Paleozoic to Early Jurassic, respectively. Microfossil studies show the presence of Paleozoic biostratigraphy. The crystallization process and rifting into the oceanic crust in the Lahroud Ophiolite probably began in the Carboniferous, with volcanic activity continuing during the Late Triassic.

A perspective on potassic and ultrapotassic rocks: Constraints on the Paleoproterozoic late to post-collisional event in the São Francisco paleocontinent

The late- to post-collisional stage in orogenic systems is characterized by the coeval existence of bimodal potassic to ultrapotassic magmatic activity related to partial melting of an enriched lithospheric mantle together with crustal derived melts. In this paper, we present new whole rock geochemical analyses combined with zircon and titanite U–Pb and zircon Hf isotopic data from potassic to ultrapotassic rocks from six plutons that occur within the Archean Itacambira-Monte Azul block (BIMA), to discuss their petrogenesis and the tectonic implications for the São Francisco paleocontinent. The new U–Pb ages range from ca. 2.06 Ga to 1.98 Ga and reveal long-lasting potassic magmatism within the BIMA, which is within the late- to- post-collisional stage of the São Francisco paleocontinent evolution. The ultrapotassic rocks are compatible with a fluid-related metasomatized mantle source enriched by previous subduction events, whereas the potassic rocks are bimodal and have a transitional shoshonitic to A-type affinity. These rocks have a hybrid nature, possible related to the mixing between the mafic potassic/ultrapotassic rocks and high temperature crustal melts of the Archean continental crust. Our results also show an increase of within-plate signature towards the younger potassic magmas. The participation of an important Archean crustal component in the genesis of these rocks is highlighted by the common and occasionally abundant occurrence of Archean inherited zircons. The Hf isotopic record shows that most of the zircon inheritance has dominantly subchondritic εHf(t) values, which fits a crustal reworking derivation from a similar Eo- to Paleoarchean precursor crust. However, the presence of juvenile 2.36 Ga zircon inheritance in an ultrapotassic sample reveal the existence of a hidden reservoir that is somewhat similar to the described for the Mineiro Belt in southern São Francisco paleocontinent.

Geochemistry and mantle source characteristics of the Itasy volcanic field: Implications for the petrogenesis of basaltic magmas in intra-continental-rifts

We present new major and trace element and Sr, Nd, Pb, Hf, and Os isotope data for Quaternary basaltic lavas and tephra from the Itasy volcanic field, in order to assess the origin and sources of recent volcanism in the central highlands of Madagascar. Our age determinations provide further evidence for Pleistocene volcanism on the island, with ages between ∼31 and 104 ka. Mafic magmas from Itasy exhibit significant geochemical heterogeneity, and they are chemically distinct from those of the neighboring Ankaratra volcanic complex. Trace element signatures of the Itasy volcanic field are very similar to those of ocean island basalts (OIB), with significant enrichment in high field strength elements (e.g. Nb and Ta) and depletion in large ion lithophile elements (e.g. Rb, Cs, and K), and relatively high Nb/U (>45) and Ce/Pb (>25) ratios. Significant intra-volcanic field isotopic heterogeneity is observed, with well-defined negative correlations of 87Sr/86Sr with 206Pb/204Pb and 143Nd/144Nd. These correlations, along with highly radiogenic Os isotopic signatures in many Itasy samples, could be attributed to assimilation of the Precambrian basement. However, with the exception of Os, the elemental and isotopic characteristics of the Itasy magmas are inconsistent with significant crustal assimilation, and instead are interpreted to represent features of their mantle sources. The Itasy ΔεHf and Δ7/4 values fall within the range of MORB and OIB, and indicate derivation primarily from an asthenospheric mantle source. The absence of significantly negative ΔεHf in the Itasy magmas argues against the involvement of ancient recycled oceanic crust or stranded lower crust in their sources, but the presence of a low µ (LOMU) component in some Itasy magmas can be attributed to pollution of the asthenosphere by delaminated subcontinental lithospheric mantle. A simple two-stage, three-component mixing model indicates that a mixture of mantle containing 90% depleted asthenosphere (DMM) and 10% foundered SCLM, which is further mixed with 30 to 50% of a plume-type mantle component, can reproduce the isotopic compositions of the Itasy magmas. Based on our model, it is possible that easily fusible superplume materials might be widely distributed in the upper mantle underneath the EARS, from the Indian Ocean to the Red Sea-Gulf of Aden, and mixed with shallow asthenosphere that has itself incorporated eroded SCLM. These components are heterogeneously distributed at a small spatial scale, similar to that observed recently in other mafic monogenetic volcanic fields in both intraplate and subduction settings.

Imports or imitations?: Scientific and typological analysis of the bronze artefacts at the Moutuo Archaeological Site, Sichuan, China*

The typological and scientific analysis of bronze artefacts has been widely applied to the issue of local production versus important, which can be further linked to the long‐distance trade exchange and movement of raw materials, technology and people. Bronze artefacts bearing stylistic features of different regional origins have been discovered at the site of Moutuo in Sichuan, south‐west China. This study investigates the metal provenance of these artefacts by using the impurity patterns of the Oxford system. By combining the Pb isotopic data, it is feasible to distinguish the locally produced objects from those importations. This study contributes a detailed case study to the wider question of the movement of metal in south‐west China between the Late Bronze Age and Early Iron Age.

Petrogenesis and tectonic implications of the late Paleoproterozoic (ca. 1.7 Ga) post-collisional magmatism in the southwestern Gyeonggi Massif at Garorim Bay, South Korea

The Precambrian basement of the Gyeonggi Massif in the central Korean Peninsula consists mainly of Paleoproterozoic (2.0–1.8 Ga) gneisses. In this study, we present petrological, zircon U–Pb age and Hf isotope, and whole-rock geochemical and Sr–Nd–Pb isotope data for late Paleoproterozoic (ca. 1.7 Ga) granitic gneisses and anatectic granites from the southwestern Gyeonggi Massif. Zircon U–Pb dating of two granitic gneisses and three anatectic granites yielded ages of 1685 ± 14, 1693 ± 8, 1683 ± 18, 1690 ± 6, and 1706 ± 17 Ma, respectively. The samples exhibit LILE enrichment, negative Nb–Ta anomalies, high Ga/Al ratios and HFSE contents, similar to A-type granites. Compared with typical anorogenic intra-continental rift-related granites (A1-type), Y/Nb and Ce/Nb ratios of the samples are much higher, and similar to those of post-collisional granites (A2-type). The εHf(t) values of late Paleoproterozoic zircons from the granitic gneisses and anatectic granites range from –17.8 to –7.0 and –15.3 to –9.7, respectively, indicating derivation from ancient crustal sources. The zircon U–Pb ages of the anatectic granites show that some of the late Paleoproterozoic intrusions underwent re-melting (i.e., anatexis) in the Late Triassic (ca. 230 Ma). Whole-rock initial εNd (230 Ma) values of the anatectic granites (–29.4 to –28.1) and granitic gneisses (–26.3 to –24.3) are similar, indicating that the anatectic granites were sourced from the granitic gneisses. Late Paleoproterozoic igneous activity in the southwestern Gyeonggi Massif can be correlated with post-collisional activity in North China Craton, and was distinct from the coeval rift-related magmatism in South China Craton.

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.

Zircon U-Pb ages and Hf isotope analysis of Neoproterozoic Yaolinghe Group sedimentary rocks in the Chengkou area, South Qinling: Provenance and paleogeographic implications

The Yaolinghe Group sedimentary rocks exposed along the Dabashan fault zone are rich in pyroclastics and are thousands of meters thick. They provide key information for studying the tectonic location relationship between the Yangtze and Qinling blocks and the tectonic-sedimentary environment of the late Neoproterozoic continental margin. This study reports U–Pb and Lu-Hf isotope data of 438 and 408 detrital zircons from five samples of Yaolinghe Group sedimentary rock, collected in the Chengkou area, China. Combining the youngest detrital zircon U–Pb age for gravelly sandstone with data from previous studies, we constrained the maximum depositional time of the Yaolinghe Group sedimentary rocks in this area to ca. 650–635 Ma (i.e., Neoproterozoic Cryogenian). In the Chengkou area, the predominantly Neoproterozoic (1000–635 Ma) detrital zircons, with wide εHf(t) values ranging from −31.03 to 13.07 and an average of 2.00, were primarily derived from the adjacent regions of exhumed igneous rock in the South Qinling and Northern Yangtze blocks. Several minor age peaks at more than 1000 Ma indicate that this formation contains a small amount of recycled zircon. Further study indicates that the Yaolinghe Group sedimentary rocks were formed by near-source accumulation in a rift setting, located at the north margin of the Yangtze Block, during the breakup of Rodinia. As in previous studies, the retreat of the subducted slab may have led to continental rifting and extension of the Northern Yangtze Block, and the Yaolinghe Group sedimentary rocks in the Chengkou area recording the history of the last stage of Rodinia breakup.

Petrogenesis of the Loch B\xe0 ring-dyke and Centre 3 granites, Isle of Mull, Scotland

The Loch Bà ring-dyke and the associated Centre 3 granites represent the main events of the final phase of activity at the Palaeogene Mull igneous complex. The Loch Bà ring-dyke is one of the best exposed ring-intrusions in the world and records intense interaction between rhyolitic and basaltic magma. To reconstruct the evolutionary history of the Centre 3 magmas, we present new major- and trace-element, and new Sr isotope data as well as the first Nd and Pb isotope data for the felsic and mafic components of the Loch Bà intrusion and associated Centre 3 granites. We also report new Sr, Nd and Pb isotope data for the various crustal compositions from the region, including Moine and Dalradian metasedimentary rocks, Lewisian gneiss, and Iona Group metasediments. Isotope data for the Loch Bà rhyolite (87Sr/86Sri = 0.716) imply a considerable contribution of local Moine-type metasedimentary crust (87Sr/86Sr = 0.717–0.736), whereas Loch Bà mafic inclusions (87Sr/86Sri = 0.704–0.707) are closer to established mantle values, implying that felsic melts of dominantly crustal origin mixed with newly arriving basalt. The Centre 3 microgranites (87Sr/86Sri = 0.709–0.716), are less intensely affected by crustal assimilation relative to the Loch Bá rhyolite. Pb-isotope data confirm incorporation of Moine metasediments within the Centre 3 granites. Remarkably, the combined Sr–Nd–Pb data indicate that Centre 3 magmas record no detectable interaction with underlying deep Lewisian gneiss basement, in contrast to Centre 1 and 2 lithologies. This implies that Centre 3 magmas ascended through previously depleted or insulated feeding channels into upper-crustal reservoirs where they resided within and interacted with fertile Moine-type upper crust prior to eruption or final emplacement.

Geological characteristics and metallogenic age of Tengshan'ao Sn deposit in Dayishan of South Hunan and its prospecting significance

The Tengshan'ao Sn deposit, located at the Dayishan ore field, Nanling Range, is one of the recently explored deposits in this region. In this study, LA-MC-ICP-MS cassiterite U–Pb and muscovite 40Ar-39Ar isotopic dating analyses for altered granite-type Sn ores yielded ages of 156.7 ± 4.3 Ma and 151.1 ± 1.5 Ma, respectively. These ages are consistent to the LA-MC-ICP-MS zircon U–Pb age of the fine-grained two-mica monzogranite (158.2 ± 1.6 Ma), indicating a coeval magmatism and mineralization for the Late Jurassic Tengshan'ao Sn deposit. It is further demonstrated that the formation of this deposit is related to the Early Yanshanian (160-150 Ma) large-scale diagenesis and mineralization in Nanling Range. It is suggested that the late-stage fine-grained two-mica (muscovite) granite has an indicative significance for searching the altered granite type Sn polymetallic mineralization.

Age and Genesis of the Laodaizhanggou Pb-Zn-Ag Deposit in the Fudian Ore Field, Southern North China Craton: Implications for Regional Mineral Prospecting

The Fudian ore field in the southern North China Craton hosts the giant Donggou porphyry Mo deposit and several Pb-Zn-Ag vein deposits. Ore genesis of the Pb-Zn-Ag deposits and their relationships with the Donggou porphyry-related system are still controversial, which further restricts the regional prospecting and exploration. The Laodaizhanggou Pb-Zn-Ag deposit in the northwest of the ore field was focused in this study, to investigate its ore-forming age and genesis, and further to explore the implications for regional prospecting of Pb-Zn-Ag and Mo. The Pb-Zn-Ag veins at Laodaizhanggou are structurally controlled by the east-striking fault zones transecting the host volcanic rocks of Proterozoic Xiong’er Group. Field observations and textural relationships indicate that there are four paragenetic stages during ore-forming process, including the quartz-pyrite veins (stage I), siderite-polymetallic sulfide veins (stage II), ankerite-polymetallic sulfide veins (stage III), and quartz-calcite veins (stage IV). Ore-related sericite 40Ar/39Ar dating shows that the Pb-Zn-Ag mineralization at Laodaizhanggou was formed at 124.7±1.2 Ma. Carbonate minerals (siderite, ankerite, and calcite) have δ13CPDB values of −9.1‰ to −3.9‰ and δ18OSMOW of 12.1‰ to 15.6‰, corresponding to calculated values for the ore fluids of −8.0‰ to −2.8‰ and 4.9‰ to 10.1‰, respectively. These isotope values are in accordance with those of magmatic fluids. Sulfide minerals at Laodaizhanggou have δ34S values of 5.3‰ to 10.1‰, and galena separates have 206Pb/204Pb ratios of 17.380 to 17.458, 207Pb/204Pb ratios of 15.459 to 15.485, and 208Pb/204Pb ratios of 38.274 to 38.370. Both S and Pb isotope data of Laodaizhanggou are consistent with those of the Donggou porphyry Mo deposit and distal Sanyuangou and Wangpingxigou Pb-Zn-Ag deposits, suggesting they share a similar magmatic origin. However, the Laodaizhanggou deposit was not the distal product of the giant Donggou porphyry-related magmatic-hydrothermal system, as the former is about 7 Ma older than the latter. The ore-forming age of Laodaizhanggou is consistent with that of the phase 1 magmatism of Taishanmiao batholith, indicating the Laodaizhanggou deposit is genetically related to ca. 125 Ma magmatism in the area. Combined the geochronological and geochemical data on Laodaizhanggou and the regional geological setting, we propose that the fracture systems in the northeast of the Taishanmiao batholith are potential sites for prospecting Pb-Zn-Ag deposit and the deep part among Laodaizhanggou, Xizaogou, and Liezishan is a target for prospecting porphyry Mo deposit.

Simultaneous development of arc-like and OIB-like mafic dikes in eastern Guangdong, SE China: Implications for late Jurassic – early Cretaceous tectonic setting and deep geodynamic processes of South China

The Mesozoic South China is characterized by extensive magmatism, transition from Jurassic intraplate magmatism to Cretaceous active continental margin magmatism. However, the time and deep geodynamic processes accounting for the Mesozoic magmatism remains controversial. In this study, we presented new SIMS zircon UPb ages, in-situ Sr isotope of plagioclase, whole-rock geochemical and Sr–Nd–Pb isotopic data on three suites of mafic dikes in eastern Guangdong, namely Anliu (AL) and Sanjiaowo (SJW) and Jishuimen (JSM) mafic dikes. The AL (154.3 ± 3.4 Ma) and SJW (141.3 ± 4.0 Ma and 143.2 ± 2.3 Ma) dikes show arc-like geochemistry and “crust-like” isotopic signatures, likely derived from partial melting of a subduction metasomatized lithospheric mantle. Meanwhile, the JSM dikes (141.7 ± 3.2 Ma) exhibit OIB-type geochemical and isotopic features, and were likely derived from partial melting of an enriched asthenospheric mantle. The development of late Jurassic AL lamprophyre may represent the oldest Paleo-Pacific subduction-related arc-type mafic rocks so far recorded in South China. Development of dikes (SJW vs JSM) with different geochemical signatures (Arc vs OIB) at the same time within a limited space indicates that asthenosphere-related process overprint and co-operate with subduction-related magmatism and imply the initiation of Paleo-Pacific subduction roll-back was potentially at least ca.141 Ma.