Large Rare Earth Research Articles

Crust–mantle interaction beneath the Pamir orogenic belt: Insights from the Miocene Dunkeldik carbonatite–syenite complex in Tajikistan

Only some carbonatite–syenite complexes in the world could form carbonatite-related rare earth element (REE) deposits, which is regarded as the main REE origin. The Miocene Dunkeldik carbonatite–syenite complex is located in the Dunkeldik magmatic field in Tajikistan between the Pamir and Tibetan plateaus. So far, the origin, tectonic setting, and REE mineralization potential of the Dunkeldik carbonatite–syenite complex remain unclear due to the limited isotopic values, which inhibit the further understanding the genesis of such carbonatite complex. This study presents zircon U–Pb age, whole-rock geochemical, and Sr–Nd–Pb isotope, and zircon Hf–O isotope data for the Dunkeldik carbonatite–syenite complex on the Pamir Plateau. Zircon U–Pb dating of syenite yielded two concordant ages of 10.27 ± 0.16 and 10.48 ± 0.21 Ma, indicative of formation in a post-collisional extensional setting related to India–Asia collision. Both the carbonatite and syenite exhibit similar enrichments in large-ion lithophile elements (e.g., Sr and Ba) and light REEs, depletions in high-field-strength elements (e.g., Nb and Ta) and heavy REEs, and small Eu anomalies. Whole-rock Sr–Nd–Pb isotopic compositions are highly enriched, with high (87Sr/86Sr)i (0.70971 to 0.70979), low εNd(t) (–8.9 to –9.2), and radiogenic Pb isotope composition (206Pb/204Pb (18.322–18.358), 207Pb/204Pb (15.689–15.695), and 208Pb/204Pb (39.091–39.149)). Zircons Hf-O isotope analyses yield low εHf(t) values (–9.5 to –19.0) and high δ18O value (7.4 ‰–9.5 ‰), respectively. These geochemical and isotopic features indicate that the complex was formed by partial melting of enriched lithospheric mantle during the Miocene India–Asia collision and was assimilated by upper crustal material during magma ascent. The carbonatite and syenite in the complex formed by melt immiscibility. The involvement of crustal material in the magma and less development of fenitization may responsible for the limited REE mineralization potential as compared with other large REE deposits that formed during coeval India–Asia collision.

Petrogenesis and Geochronology of A1-Type Rhyolites in the Late Late Triassic of the East Kunlun Orogenic Belt: Constraints on the End of the Paleo-Tethys Orogenic Event

The rhyolites which are widely exposed to the northern margin of the East Kunlun orogenic belt were chosen as a research object to discern the post-orogenic tectonic evolution of the East Kunlun orogenic belt and reconstruct the post-collision orogenic processes of the Buqingshan- A’nyemaqen Ocean. We researched zircon U-Pb ages and geochemistry characteristics of the Late Triassic rhyolites in the eastern segment of the East Kunlun Orogenic Belt in the northern Tibetan Plateau. Zircon U-Pb dating yields coeval ages of 200.4 ± 1.4 Ma and 202.8 ± 1.2 Ma for the Keri rhyolites of the East Kunlun Orogenic Belt, indicating that the volcanic rocks were formed in the Late Triassic Rhaetian–Early Jurassic Hettangian. The Keri rhyolite is a product of the late magmatism of the Elashan Formation volcanic rocks. The rhyolites include rhyolitic brecciated tuff lavas and rhyolitic tuff lavas. The rhyolites are peraluminous and are high-K calc-alkaline, with high contents of SiO2, K2O, TFe2O3, and low P2O5 contents. The A/CNK ratios range from 0.97 to 1.09, indicating that the rhyolites are metaluminous to weakly peraluminous. The chondrite-normalized rare earth element (REE) distribution shows a significant negative Eu anomaly and low total REE concentrations. All samples are depleted in high field strength elements (HFSEs, e.g., Eu, Sr, Ti, and P), heavy rare earth elements (HREEs), and enriched in large ion lithophile elements (LILEs, e.g., Rb, Zr, Nd, Th, and U) and light rare earth elements (LREEs). The Keri rhyolite has the characteristics of A1-type magmatic rock, formed in an anorogenic environment after the closure of the Paleo-Tethys Ocean, and was the product of late magmatism in the Elashan Formation volcanic rocks.

Geochronology and geochemistry of early Palaeozoic ultramafic rocks along Jiangshan‐Shaoxing Fault and their tectonic significance

AbstractThe origins of early Paleozoic orogen in South China have two different models: subduction model and intra‐continental model. Here we report two new identification of ~440 Ma arc‐related ultramafic intrusions in Tingzifan (TZF) and Fomuting (FMT) along Jiangshan‐Shaoxing fault (JSF) in South China, respectively. The Silurian ultramafic intrusions are composed of olivine pyroxenite, the SiO2, MgO and TiO2 contents of olivine pyroxenites are 39.67–41.25 wt%, 28.98–31.38 wt% and 0.23–0.51 wt%, respectively. The geochemical compositions of the olivines, clinopyroxenes and hornblendes suggest an arc‐related environment for these intrusions. As for the whole‐rock trace elements, the ultramafic intrusions contain low total rare earth element (REE) contents (27.59–34.26 μg/g) and high field strength elements (HFSEs), such as Nb, Zr, Hf, Ti, and are systematically enriched in large ion lithophile elements and light rare earth elements (LREEs). Trace element compositions share most features of Alaskan‐type ultramafic‐mafic intrusions. Isotopically, the TZF and FMT ultramafic intrusions are characterized by negative Zircons εHf(t) values (0.38–7.54). Combined with their whole‐rock and mineral chemistry as well as zircon Hf isotope, we suggest that the Alaskan‐type TZF and FMT pyroxenite were formed at the root of the continental arc by underplating and fractional crystallization of mafic magma which derived from subduction metasomatized mantle source. Thus, we proposed that the early Paleozoic ultramafic–mafic along Jiangshan‐Shaoxing fault were most likely related to early Paleozoic subduction of the Paleo‐South China Ocean between Cathaysia and Yangtze blocks, arguing that the origins of early Paleozoic orogen in the South China Block is a typical subduction‐accretionary collisional‐type orogenic belt rather than an intraplate belt.

Recycling of NdFeB magnets employing oxidation, selective leaching, and iron precipitation in an autoclave.

The increasing production of neodymium-iron-boron (NdFeB) magnets for technological applications results in disposal problems. NdFeB magnets contain a significant quantity of rare earth elements (REEs). China is the largest REEs producer, but it applies quotas and increases the export prices of REEs. To address this issue, this study aims at investigating the recovery process of REEs from scrap NdFeB magnets. After oxidation of NdFeB magnet powders, selective leaching with nitric acid was carried out to achieve high-purity REE-rich leaching liquor. First, the oxidation kinetics of NdFeB powders was studied in detail to determine the oxidation temperature and duration. Afterwards, the effects of selective leaching parameters, including acid concentration, leaching temperature, stirring speed and solid/liquid ratio, were examined by analysis of variance (ANOVA) analysis based on Taguchi method. The most substantial parameters were assigned to be the temperature and solid/liquid ratio. Eventually, the dissolution kinetics were studied to propose a model for REEs. Several universal equations for dissolution kinetics were tested, and (1 - (1 - x) = k × tn) gives the best results for REEs. The findings show that the leaching process follows the shrinking core model. Activation energy was calculated to be 40.375 kJ mol-1 for REEs. As the last step, the iron dissolved during leaching was precipitated as hematite in the autoclave. The hematite precipitation experiments were performed based on the Box-Behnken design. The effect of precipitation parameters was investigated by ANOVA analysis, and the precipitation process was optimized using response surface methodology (RSM), which resulted in the minimum iron and maximum REEs content in the leach liquor.

Petrogenesis and geochronology of the bronze fox porphyry Cu-Au deposit: Implications for the geodynamic evolution of the Gurvansaykhan Island arc, southern Mongolia

ABSTRACT A diversity of Devonian-Carboniferous volcanic arcs and granitoid intrusions are exposed in the Gurvansaykhan arc terrane of southern Mongolia. Several giant porphyry Cu-Au-Mo deposits are associated with intrusions within these arcs. The Bronze Fox deposit located in the central part of the Gurvansaykhan arc terrane is an example of a potentially economic deposit with affinity of adakite-like granitoid porphyry (i.e. 428 Mt grading 0.26% to 0.30% Cu for up to 2,437 Mlb of copper and 0.84 Moz gold). The genesis and magmatic evolution of the causative rocks of the Bronze Fox porphyry Cu-Au hosting rocks are poorly understood, and different models are still under debate. In the current study, we present new field observations and petrographic, geochemical, and geochronological data to describe the magmatic evolution and geodynamic settings. In addition, the mineral chemical data are reported from some selected rock-forming minerals to identify crystallization conditions of the studied rock suites by employing geothermobarometric methods. Zircon chronological data reveal the emplaced age at 331 ± 3.4 Ma for the volcanic lava, followed by mineralized granodiorite and monzodiorite with intruded ages of 326.5 ± 3.4 Ma and 326.5 ± 2.7 Ma, respectively. The studied intrusive and extrusive rocks are high-K-alkaline and metaluminous, characterized by high Mg#. They are enriched in large ion lithophile elements (Sr and Ba) and light rare earth elements (LREEs) and depleted in high field strength elements (Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The highly mineralized granodiorite intrusion yields zircon crystallization temperatures ranging from 631.8 to 779.4°C, and the monzodiorite intrusion, which contains relatively low-grade mineralization, has a wider range (599.0 to 803.4°C). The formation pressures of the former range from 0.5 to 0.2 kbar, which is equivalent to a depth of 1.38 km based on amphibole geochemical calculations. The results of mineral chemistry indicate that the unmineralized diorite unit was formed under medium pressure (~50 MPa) and high temperature (~750°C) at depths of 6.8 to 7.5 km. Similarities in geochemistry and petrographic features suggest that the igneous rocks probably originated from a similar magma source (i.e. from the melting of ancient oceanic crust and sediments) but experienced different degrees of partial melting or mixing with lower juvenile crust melts. The estimated fO2 values obtained by amphibole chemistry in the granodiorite and quartz diorite of the Bronze Fox copper-gold mineralization range from −13.0 to −11.8 and −13.2 to −10.8, respectively, confirming that these igneous rocks probably crystallized under relatively oxidized conditions above the nickel-nickel oxide (NNO) buffer. Such results yield an overall range between NNO +2.6 and NNO +1.4, which are characterized by high oxygen fugacities and high Ce4+/Ce3+ ratios that reflect oxidizing magma, thus indicating quite promising potential for porphyry Cu-Au mineralization in the region. Based on the findings of this work, we suggest a new tectonic model of arc magmatism that is a response to the subduction of the Paleo-Asian Ocean in the early Carboniferous period.

Petrogenesis of Alkaline Complex of the Longbaoshan Rare Earth Element Deposit in the Luxi Block, North China Craton, China

The alkaline complex in the southwest region of Luxi Terrane of the North China Craton is spatially correlated with the newly discovered Longbaoshan REE deposit. Its petrogenesis, however, remains ambiguous. In this study, we present an integrated petrology, whole-rock geochemistry, sphene U-Pb and rare earth element data from the Longbaoshan alkaline complex to investigate the petrogenesis, magma source and tectonic evolution. The Longbaoshan alkaline complex consists of mafic to intermediate rocks of hornblende diorite and alkaline hornblende syenite porphyry, biotite monzonite porphyry and aegirine diorite porphyrite. The hornblende diorites show a composition of low SiO2, high MgO, Fe2O3 and moderate Na2O, CaO and are metaluminous and medium-to-high-K calc-alkaline. The hornblende syenite porphyries, biotite monzonites and argirine diorite porphyrites display a relatively higher content of SiO2, Na2O, K2O and Al2O3 and lower contents of MgO, Fe2O3 and CaO and are metaluminous, peralkaline, high-K calcic-alkaline and shoshonite. The sphene U-Pb data shows that the parent magma of the hornblende diorite was emplaced at ca. 120 Ma. All these samples show a common depletion in Th, Nb-Ta and Zr-Hf and enrichment in large ion lithophile elements (e.g., Pb, Ba, Sr) and Light Rare Earth Elements. The magma may have experienced fractionation of pyroxene, amphibole, sphene, apatite and zircon during its evolution. The variable La content, La/Sm, Rb/Sr and (Ta/Th) N ratios indicate that the parent magma may produce by partial melting of a mantle source that was interacted with sediment-derived melts in a subduction setting. Therefore, we propose that the parent magma of the Longbaoshan alkaline complex was derived from a lithospheric mantle which was metasomatized by sediment-derived melt in a prior subduction process. The enriched magma was emplaced through an extension process and experienced subsequent fractionation and assimilation with the continental crust during the rollback of the Paleo Pacific Ocean plate.

Geochronology and petrogenesis of volcanic rocks in the Laurani epithermal Au–Ag–Cu deposit, northern Bolivian Altiplano

The Laurani Au–Ag–Cu deposit is a typical high-sulfidation (HS) epithermal deposit genetically related to volcanic rocks in the Bolivian Altiplano polymetallic belt (BAPB), yet few studies have been carried out on these volcanic rocks. Detailed petrographic observations show that the Laurani volcanic rocks comprise monzogranite porphyries, dacites, dacitic porphyries and tuffs. Zircon U–Pb dating demonstrates that they formed at 7.44 ± 0.15 Ma ∼7.65 ± 0.09 Ma in the late Miocene during the rapid uplift of the Altiplano. Geochemical features indicate these volcanic rocks belong to high-K calc-alkaline to shoshonite series, enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) and depleted in high field strength elements (HFSE) and heavy rare earth elements (HREE), with no Eu anomalies (Eu/Eu* = 0.80–1.11, mean = 0.95). We suggest that the magma sources of the Laurani volcanic rocks are primarily generated from the partial melting of the thickened lower crust, for: (1) No Eu anomalies indicate that plagioclase is absent in the residue, and the extensively depleted HREE and positively correlated high (Gd/Yb)N, (Dy/Yb)N, and (La/Yb)N ratios indicate that garnet is a dominant residual mineral in their source, which are consistent with the thickened lower crust; (2) 176Hf/177Hf ratios (0.282409–0.282544) and negative εHf(t) values (−13.15 to −8.37) confirm that the magmas are mainly evolved from the partial melting of the old lower crust; (3) Inherited zircons ages of 1.87–1.62 Ga are consistent with the basement ages of the Arequipa Massif between 1.9 Ga and 1.8 Ga, indicating that the magma sources are mainly generated from the partial melting of the Paleoproterozoic crust. These observations coincide with the thickened (60–80 km) felsic to intermediate lower crust beneath the Altiplano. Combined with the geodynamic process of rapid uplift of the Altiplano, we propose that the removal of the lower crust and/or mantle lithosphere and/or its interaction with the asthenosphere provide heat to contribute to the partial melting of the thickened lower crust to generate parental magma, then parental magma emplaces along the strike-slip Eucaliptus fault to form the Laurani volcanic rocks. Furthermore, numerous inherited zircon ages with a weighted mean of 1189 ± 30 Ma reflect the intense Grenvillian metamorphism in the Mesoproterozoic and the two ages 259.9 ± 5.11 and 231.7 ± 2.2 Ma indicate the Permian magmatic events in northern Bolivia. From this study, we infer that partial melting of the thickened lower crust during the rapid uplift of the orogenic belt may be an important magma formation mechanism.

Probabilistic assessment of dietary rare earth elements intake among people living near a rare earth ore

Rare earth elements (REEs) can cause neoplasms, reduce bone density, affect children's intelligence, etc., and diet is an important way for the human body to absorb REEs. With the increasing use of REEs, the impact on human health is becoming more and more important. So, we used a probabilistic assessment method with Monte Carlo simulation to evaluate the dietary intake of REEs by residents of a large light rare earth mining area in Shandong Province. 16 REEs in 447 samples (including wheat, maize, dry beans, vegetables, fruits and eggs) were detected. The mean value of total REEs for all samples was 286.96 μg/kg, and of light rare earth elements (LREEs) was 270.18 μg/kg. Among of LREEs, Ce, La, Nd and Pr were dominant. The REEs content of different food categories showed that wheat, leafy vegetables and allium vegetables had higher content of REEs, melons vegetables, root vegetables, fruits and eggs had the lowest content. The mean dietary intake of rare earth oxides for the whole population was 4.20 μg/kg bw/d, wheat and vegetables (leafy vegetables, allium vegetables and root vegetables) were the main sources of REEs. Dietary intake estimates of REEs by age and gender did not exceed the acceptable daily intake which means implying no impact on human health.

Identification of the early cretaceous granitic pluton and tectonic implications in the middle gangdese belt, southern tibet

The Gangdese magmatic belt of southern Tibet is an ideal place to study Neo-Tethyan subduction, continental crustal growth and reworking. However, there are still controversies with regard to the evolution of the Neo-Tethys Ocean, the magma source and the detailed diagenetic processes of igneous rocks in the Gangdese belt. The Early Cretaceous magmatic exposures are sporadic in the Gangdese magmatic belt. Thus the finding of the new exposure is key to understanding the scenarios of the Neo-Tethys Ocean and geological background of southern Tibet during the Early Cretaceous. In this contribution, we undertook systematic geochronology, whole-rock geochemistry and zircon Lu-Hf isotopic studies on a newly identified granitic pluton in the middle Gangdese belt (Quesang area), southern Tibet. The results show that zircon U-Pb dating of three representative samples yielded a weighted age of 120 ± 1.4 Ma, 117.3 ± 2.5 Ma and 114.0 ± 1.3 Ma, respectively, which indicate the emplacement and crystallization age belonging to the Aptian stage of the Early Cretaceous in response to the northward subduction of the Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane. In situ zircon Lu-Hf isotopic analyses indicate that ƐHf(t) values of the studied granitic pluton are predominantly positive ranging from 7.2 to 11.4, and one zircon shows negative ƐHf(t) value (−6.26), implying that a small amount of ancient continental crustal materials might have participated in the magma evolution. Geochemically, the granite samples are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in heavy rare earth elements (HREE), indicating arc-type geochemical characteristics or subduction-related tectonic setting. In addition, combined with mineral assemblages, zircon Lu-Hf isotopic features and low molar Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of 0.91–1.10, the studied samples show a close affinity with I-type granites. Moreover, zircon oxygen fugacity results show that Ce4+/Ce3+ values range from 185 to 12, with a mean value of 78, indicating a low oxygen fugacity setting similar to the Chile ore-barren granitic plutons. In combination with published data, we argue that the Gangdese magmatic belt may have developed continuous magmatism (145–105 Ma), and the notion of magmatic lull might deserve more consideration during the Early Cretaceous. In this study, the Early Cretaceous granitic pluton might be the result of the northward subduction of Neo-Tethys oceanic lithosphere beneath the Lhasa terrane at a normal angle.

The high-K calc-alkaline to shoshonitic volcanism of Limnos, Greece: implications for the geodynamic evolution of the northern Aegean

Genetic models for the formation of K-rich magmas in subduction-related settings range from partial melting of subduction-affected mantle sources to melting of crustal rocks depending on the local tectonic framework. The Miocene high-K calc-alkaline to shoshonitic rocks of Limnos Island reflect the magmatic activity in the northern Aegean, which migrated southwards in response to trench retreat and the collision of continental terranes in the Hellenic subduction system. New whole rock and mineral data of basaltic andesites, dacites and monzonites from Limnos indicate that the magmas underwent fractional crystallization of olivine, clinopyroxene, amphibole, apatite, and Fe-Ti oxides at 1100 to 700 °C and 0.5 to 0.1 GPa without significant assimilation of crustal rocks during the magma evolution. The strong enrichment of large ion lithophile elements and light rare-earth elements relative to depleted heavy rare earth and high-field strength elements points towards a mantle source that has been extensively hybridized by subducted sedimentary material. New Sr–Nd-Pb isotope data reveal a distinct isotopic composition of the Limnos rocks with high 207Pb/204Pb at low 206Pb/204Pb and 143Nd/144Nd ratios that is likely related to the subduction of the continental crustal succession of the Apulian block which was subducted prior to the onset of magmatism on Limnos. Partial melting models assuming a hybridized mantle source suggest that the primary melts of Limnos formed by melting of a phlogopite pyroxenite at melting degrees of 5 to 10%. Compositional differences between high-K calc-alkaline and shoshonitic magmas are explained by variable melting degrees and varying amounts of sediment supply to the mantle. The magmatic and tectonic evolution of Limnos island is typical for the Oligocene and Miocene volcanic centres of the migrating western Aegean arc front.

Analysis of the Rare Earth Mineral Resources Reserve System and Model Construction Based on Regional Development.

China is a large rare earth country that has pushed for related rare earth research, development, and application in the global development and progress of rare earths. The rare earth resource reserve strategy must be implemented by China due to the situation of rare earth resources at home and abroad, national security, and the need to strengthen the right to speak in the international market. This article builds the rare earth mineral resources reserve system and model from the perspective of regional development and uses the improved SURF algorithm to solve the problems of inaccurate mine location, mine location deviation, dislocation, overlap, and other issues, resulting in more accurate mineral resources reserve management data. The results show that the maximum relative error between the parallel profile method and the traditional method is 2.6%, which meets the requirement for mineral reserve calculation accuracy and can be used to calculate reserves. China's peak ionic rare earth output will be 46,797.06 tonnes in 2024, and then, it will decline at a 4% annual rate thereafter. This demonstrates how a graded reserve and orderly promotion can improve the workflow and efficiency of the rare earth mineral resources reserve.

Petrogenesis of the Early-Middle Triassic high-Mg andesitic rocks in the southern margin of the South China Block: Implications for the convergence between the South China and Indochina Blocks

Questions remain about whether the volcanic rocks and spatially associated mafic to intermediate intrusions in the Funing area, Southwestern China, are part of Emeishan large igneous province (ELIP) and formed in a plume-related extensional setting. Zircon U-Pb ages, geochemical and Sr-Nd-Hf isotopic data are reported for these volcanic rocks, in order to investigate their source, petrogenesis and tectonic setting. Zircon U-Pb dating yields an eruption age of 246 ± 2 Ma for the volcanic rocks, younger than that of the ELIP. They are calc-alkaline rocks, and are characterized by high MgO (>5 wt%) and Al2O3 contents at intermediate SiO2 contents (52.12–59.20 wt%), similar to those of high-Mg andesites, indicating a mantle source. They are enriched in large ion lithophile elements and light rare earth elements and are depleted in high field strength elements, with evidently negative Nb, Ta and Ti anomalies. They have relatively high Th/Nb and Th/La ratios and low Sr/Y and La/Yb ratios, with radiogenic initial Sr isotopic ratios (87Sr/86Sr i = 0.7080–0.7110) and negative εNd(t) (−8.8 to −6.5) and εHf(t) (−5.3 to −2.4) values. All of these geochemical features suggest that the Funing high-Mg andesitic rocks were derived from partial melting of an ancient, refractory lithospheric mantle that had been metasomatized by subducted sediment-derived fluids/melts before magma generation. In the context of other Early-Middle Triassic magmatism in the adjacent areas, we suggest that the Early-Middle Triassic volcanic rocks in the Funing area were generated in an arc setting, rather than by mantle plume-related melting. The spatial and temporal distribution of volcanic arc and the ophiolitic mélange in the China-Vietnam border region indicate Early to Middle Triassic northward subduction of the Babu (SW China)-Cao Bang (NE Vietnam) ocean basin beneath the southern margin of the South China Block.

Geochronology, geochemistry and Sr–Nd–Pb–Hf isotopes of the alkaline–carbonatite complex in the Weishan REE deposit, Luxi Block: Constraints on the genesis and tectonic setting of the REE mineralization

The Weishan rare earth element (REE) deposit at the southeastern margin of the North China Craton (NCC) is one of the three largest carbonatite-associated REE deposits (CARDs) in China. The REE-bearing carbonatite veins formed within quartz syenite and were controlled by NW- and NE-trending faults. The laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb ages of zircons from the quartz syenite and postmineralization granite porphyry dyke samples of the Weishan REE deposit yield weighted mean 206Pb/238U ages of 124.6 ± 1.5 Ma (n = 10, mean squared weighted deviation (MSWD) = 1.7) and 123.3 ± 1 Ma (n = 13, MSWD = 1.7), respectively. The quartz syenite and REE-bearing carbonatite in the Weishan REE deposit have similar Sr–Nd–Pb isotope compositions, and their diagenetic and metallogenetic ages are the same within error, indicating that they have a very close genetic relationship and originate from identical material sources. The Sr–Nd–Pb–Hf isotope compositions of both the quartz syenite and REE-bearing carbonatite are within the range of those of the Mesozoic isotopically enriched subcontinental lithospheric mantle (SCLM) beneath the southeastern margin of the NCC. The Weishan REE-bearing carbonatite is extremely enriched in REEs, Sr, and Ba and has a high Ba/Th ratio. A positive correlation between the REE and Ba contents and a negative correlation between the REE content and Sr/Ba ratio are observed in the Weishan carbonatite, indicating that the excessive enrichment of Sr, Ba, and REEs in the Weishan REE deposit might be related to the involvement of CO2-rich fluids from recycled marine sediments. Taking previous results on the Mesozoic tectonic evolution of the NCC into consideration, we infer that the parent metallogenic magma of the Weishan REE deposit formed by the partial melting of the REE-refertilized and isotopically enriched SCLM, which had been previously metasomatized by melts derived from the subducted South China Block (SCB) during continental collision and by high-flux REE- and CO2-rich fluids derived from subducted marine sediments and oceanic crust during the subduction of the Paleo-Pacific Plate.

Age and petrology of Eocene-Oligocene calc-alkaline volcanism in Biga Peninsula (NW Turkey): Implications for magma origin and geodynamic evolution

In NW Anatolia, Eocene-Oligocene post-collisional volcanism is represented by K-rich volcanic rocks, including high K calc-alkaline products. Magmatic rocks in the Dededağ area (Biga Peninsula, NW Turkey) can be classified into 6 different groups with lithostratigraphic and chronostratigraphic data using 40Ar/39Ar methods (Eocene-early Oligocene, 42.08 ± 0.09 to 29.02 ± 0.29 Ma). From the Eocene period, there are calc-alkaline Laledağ granodiorite, Beyçayır volcanics with andesite and dacite composition, and also Kızıldam volcanics with alkaline and basic character (basaltic trachyandesite, trachybasalt). Furthermore, in the Oligocene period, calc-alkaline volcanism started with Dededağ volcanics with dacite and rhyolite intermediate-acidic composition, continued with Kırcalar volcanics consisting of basalt and basaltic andesite, and Harmancık volcanics ranging from basalt to rhyolite. The calc-alkaline Çamyayla pluton with quartz monzonite composition intruded into Oligocene Dededağ and Harmancık volcanics in the region. Alkaline lavas in the region are classified as high-K and shoshonitic, and calc-alkaline lavas are medium-high-K. On N-type mid-ocean ridge basalt and chondrite-normalized trace element diagrams, enrichment was observed for all volcanic units with regard to large ion lithophile elements and light rare earth elements. High field strength elements and heavy rare earth elements were depleted in all volcanic units. These compositions reveal the participation of a mantle source that was enriched by subduction components. Using geochemical data, all the volcanic rocks differentiated as a result of magma mixing/replenishment and contamination/assimilation processes. Consequently, the source of volcanism is thought to derive from the compressional regime associated with collision during the Eocene-Oligocene, and from a previously-enriched lithospheric mantle source with subsequent effects of the extensional regime.

Highly differentiated felsic granites linked to Mo mineralization in the East Kunlun Orogenic Belt, NW China: Constrains from geochemistry, and Sr-Nd-Hf isotopes of the Duolongqiarou porphyry Mo deposit

The Mo deposits in the Kunlun-Qinling-Dabie orogen are mainly associated with porphyry or porphyry-skarn mineralisation in a collision or post-collision setting. However, collision-type Mo deposits that are related to granite and mineralization produced in magmatic systems remain poorly constrained. To better define the genetic relationship between the intrusions and Mo mineralization in collision setting, the geochronology, geochemistry, and Sr-Nd-Hf isotopes of the granodiorite and monzogranite in Duolongqiarou Mo deposit, East Kunlun Orogenic Belt (EKOB), NW China, are presented. Zircon U-Pb dating shows granodiorite and monzogranite ages of 237.6 ± 1.5 Ma and 236.8 ± 1.8 Ma, respectively, which is consistent with the molybdenite Re-Os weighted mean model age of 235.9 ± 1.4 Ma. This suggests that the granitic magma related to Mo mineralization at the Duolongqiarou formed during the Triassic (ca. 236 Ma). The ore-bearing monzogranites with high SiO2 contents (76.84–77.92 wt%) are peraluminous high-K calc-alkalic rocks, while the ore-barren granodiorites with low SiO2 contents (66.89–69.90 wt%) are metaluminous Na-rich calc-alkalic rocks. Both are enriched in large ion lithophile elements and light rare earth elements but depleted in high-field strength elements, which is characteristic of I-type granites. Ore-bearing and barren granites have similar εNd(t), εHf(t), and TDM2 age, indicating a similar magma source derived from partial melting of ancient Mesoproterozoic lower crustal components with involvement of mantle materials. The amphiboles of monzogranite show higher values of calculated pressures (average 122 MPa) and melt H2O content (average 5.7 wt%) than granodiorites, suggesting that monzogranites and granodiorites crystallized at different depths of the same magma chamber. Ore-bearing monzogranites show much lower contents of transition metals (e.g., Sc, V, and Cr), negative Eu anomalies (δEu = 0.32–0.46), and higher differentiation index values (94.52–96.92) compared to barren granodiorites. This suggests that high differentiation and fractionation promote Mo metal enrichment during magmatic evolution and subsequent formation of the magmatic-hydrothermal Duolongqiarou Mo deposit. The Duolongqiarou Mo deposit was formed in a collisional setting in response to the slab break-off of the EKOB Paleo-Tethys ocean. The results of this study combined with published data suggest that at least two generations of Mo polymetallic metallogenic events were observed in the Paleo-Tethys of the EKOB. This is very helpful to target porphyry Mo mineralization and guide regional exploration.

Magmatic and metamorphic evolution of the Latimojong Metamorphic Complex, Indonesia

In the Latimojong Metamorphic Complex of Sulawesi, Indonesia, magmatic minerals are occasionally preserved in metabasites and have been overprinted by a metamorphic assemblage of chlorite-actinolite-pumpellyite. The relict of magmatic minerals preserved within metamorphic rocks are used as a potential discriminant for magma chemistry and tectonic processes. The analysis of the stable isotopes of carbon and oxygen as well as Raman spectroscopy in carbonates are used to reconstruct the origin of carbon. Within the same metabasite sample heterogeneous chromian spinel comprising (i) high-Al chromite (#Cr = 100xCr/(Cr + Al) = 40–60); (ii) high- Cr chromite (#Cr > 70) implies spinel formation from a single batch magma but at different stages of fractional crystallization. Growing clinopyroxene phenocrysts in island-arc basalt (IAB)-type melt trapped floating chromian spinel crystals that developed through time to progressively more-Al depleted compositions. Whole-rock data provide evidence of a collision between the Indo-Australian and Eurasian Plates. The rare earth element (REE) patterns of metasedimentary rocks exhibit enrichment of large ion lithophile elements, light REE, and high REE relative to the primitive mantle and might be interpreted as slab dehydration during high-pressure metamorphism at mantle depths. Metamorphic conditions documented in the mineral compositions and structures (graphite) point to high pressure (up to 12 kb) and low temperature (300–415 °C) metamorphism typically observed in subduction zones. Mineral and whole rock geochemistry indicates that the Latimojong Metamorphic Complex underwent a tectonic evolution and accretion history similar to other metamorphic complexes in the southern parts of Sulawesi (i.e. Barru and Bantimala), although protoliths and metamorphic P-T conditions may have varied.

Petrogenesis of Postcollisional High-K Calc-Alkaline and Alkaline Magmatism in Southern Sinai, Egypt: The Role of Crustal Anatexis Combined with Convective Diffusion

Postcollisional magmatism is widely distributed in southern Sinai, the extreme northern part of the Neoproterozoic Arabian-Nubian Shield. This article deals with mineral and whole-rock chemistry of postcollisional syenogranites and associated volcanic rocks from three localities in southern Sinai: Iqna Sharay’a, Rusis-Rutig, and Um Shuki–Abu Khusheib. The studied volcanic rocks have compositions between rhyolites and dacites with minor andesite. The whole-rock chemical compositions of the investigated rock types together with the biotite chemistry are consistent with high-K calc-alkaline and alkaline/peralkaline magma. The studied syenogranites and most volcanic rocks are more akin to anorogenic alkaline within-plate environments. Only a few samples of Um Shuki–Abu Khusheib volcanic rocks display some characteristics of orogenic arc-type environments. The high-K calc-alkaline to alkaline affinity and the relative enrichments in large ion lithophile elements (especially K, Rb, and Ba) and light rare earth elements together with a significant negative Eu anomaly imply that the studied granites and volcanic rocks were generated by partial melting of lower to middle crustal materials accompanied by the underplated mafic magma produced in the lithospheric mantle (convective diffusion). This convective diffusion describes a specific scenario of active chemical interaction between mafic and silicic magmas in order to explain formation of voluminous high-K calc-alkaline and alkaline/peralkaline magmatism in postcollisional tectonic environments. The enhanced temperatures of A-type silicic magmas of more than 1000°C suggest that magma generation could occur even at the depth of the uppermost lithospheric mantle.

Mixed-valent metallic pyrochlore iridate: A possible route to non-Fermi liquids

Non-Fermi liquid behavior in some fermionic systems has attracted significant interest in last few decades. Certain pyrochlore iridates with stronger spin-orbit coupling strength have recently been added to the list. Here, we provide evidence of such a non-Fermi liquid ground state in another mixed-valent metallic pyrochlore iridate ${\mathrm{Pb}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, through the combined investigation of electronic, magnetic, and thermodynamic properties as a function of temperature ($T$) and applied magnetic field ($H$). Resistivity measurement showed a linear temperature dependence down to 15 K below which it shows $\ensuremath{\rho}\ensuremath{\sim}{T}^{3/2}$ dependence while magnetic susceptibility diverges as $\ensuremath{\chi}(T$) $\ensuremath{\sim}{T}^{\ensuremath{-}\ensuremath{\alpha}}$ ($\ensuremath{\alpha}<1$) below 10 K. While a strong negative ${\mathrm{\ensuremath{\Theta}}}_{\text{CW}}$ has been observed from Curie-Weiss fitting, the absence of any long-range order down to 80 mK only indicates the presence of strong inherent geometric frustration in the system. Heat capacity data showed ${C}_{p}\ensuremath{\sim}Tln({T}_{0}/T)+\ensuremath{\beta}{T}^{3}$ dependence below 15 K down to 1.8 K. More importantly spin-orbit coupling strength by x-ray absorption spectroscopy was found to be weaker in ${\mathrm{Pb}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ compared to other pyrochlore iridates. In the absence of any large moment rare earth magnetic ion, ${\mathrm{Pb}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ presents a rare example of an iridate system showing non-Fermi liquid behavior due to disordered distribution of ${\mathrm{Ir}}^{4+}$ and ${\mathrm{Ir}}^{5+}$ having markedly different strengths of spin-orbit coupling which might offer a prescription for achieving new non-Fermi liquid systems.

Tectonic timeline in the Mongol-Okhotsk oceanic regime: Insights from early Jurassic and early cretaceous mafic-intermediate dyke swarms in central Inner Mongolia, North China

Chronicling sequential mafic dyke swarms along convergent plate margins presents a key to outlining the tectonic timeline of complete Wilson orogenic cycles for any regional paleotectonic and global supercontinental reconstructions. This study documents two episodes of Mesozoic mafic dyke swarms from central Inner Mongolia in the combined northern China-southern Mongolia (NCSM) plate: The Gadabuqi (GDBQ) suite with an age of ca. 181 Ma from East Ujimqin and the Houtoumiao (HTM) suite with an age of ca. 131 Ma from West Ujimqin. The GDBQ suite consists of hornblende-rich appinitic rocks and ranges in SiO2 from 49.6 to 52.6%. They are calc-alkaline to high calc-alkaline and show enrichment in large ion lithophile element (LILE) and light rare earth element (LREE) but depletion in high field strength elements (HFSE), with whole-rock initial 87Sr/86Sr of 0.704608 to 0.706048, positive ƐNd(t) of +1.2 to +2.4 as well as zircon ƐHf(t) of +2.5 to +5.6 and δ18O of 5.4 to 6.5‰. These features attributed the GDBQ suite to a juvenile fluid-metasomatized lithospheric mantle source. By contrast, the HTM suite mainly comprises gabbronorites with SiO2 from 55.1 to 56.4% and shows a transitional character from high calc-alkaline to shoshonitic. They are variably enriched in LREE and LILE but depleted in HFSE, with whole-rock initial 87Sr/86Sr of 0.705656 to 0.706543, ƐNd(t) of −1.1 to +3.4 and zircon ƐHf(t) of +2.9 to +9.1 and δ18O of 6.1 to 7.8‰. These elemental and isotopic traits argued for a parental magma derivation from partial melting of a fertile asthenospheric mantle and syn-magmatic crustal assimilation and fractional crystallization. Besides representing the first recognition of two distinct basaltic underplating events in central Inner Mongolia, these two contrasting mafic dyke swarms are disposed to monitor a tectonic shift from Early Jurassic linear slab breakoff to Early Cretaceous pervasive lithospheric delamination in the Great Xing'an Range. In conjunction with polyphase magmatic records and multifarious manifestations of structural, metamorphic and sedimentological dimensions, the refined Mesozoic tectono-thermal sequence in the NCSM tract tends to encapsulate insightful testimonies for chronicling the tectonic timeline from pre-Jurassic ongoing subduction and slab roll back to prolonged post-collisional aftermath of the Jurassic to early Cretaceous times in the Mongolia-Okhotsk oceanic plate domain.

Final‐stage Southward Subduction of the Eastern Paleo‐Asian Ocean: Evidence from the Middle Permian Mafic Intrusions in the Northern Margin of the North China Craton

AbstractThe northern margin of the North China Craton (NCC) contains widespread Permian magmatic rocks, but the origin of these rocks remains controversial. This uncertainty hampers us from better understanding of tectonic framework and evolution of the eastern Paleo‐Asian Ocean, particularly with respect to its final‐stage subduction and closure time. To address these questions, this study presents petrological, zircon U‐Pb geochronological, whole‐rock geochemical and in situ zircon Hf isotopic data for these Permian mafic intrusions in the northern margin of the NCC. Precise zircon U‐Pb dating results indicate that these mafic intrusions were emplaced in the Middle Permian (ca. 260 Ma). Geochemically, the studied mafic intrusions have high MgO and transition metals element contents, with high Mg# values, indicating a mantle origin. These mafic intrusions are characterized by enrichments in large ion lithophile elements (LILEs; e.g., Rb, Ba, and K) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs), indicating that they were formed in a subduction‐related setting. These geochemical features, together with zircon ∊Hf(t) values (–1.1 to +11.2), indicate that their parental magmas were derived from partial melting of heterogeneous mantle wedge metasomatized by subduction‐related fluids, with the contributions of slab sediments. The studied mafic intrusions also show wide range of major and trace elements contents, and variable Mg# values, Eu and Sr anomalies, suggesting that their parental magmas had undergone variable degrees of fractional crystallization. Together with the E–W trending Permian continental arc along the northern margin of the NCC, we confirm that the generation of the Middle Permian mafic intrusions was related to southward subduction of the Paleo‐Asian oceanic lithosphere beneath the NCC and the Paleo‐Asian Ocean had not closed prior to the Middle Permian.