Negative Eu Anomalies Research Articles

Mineralogy and Petrology of Carbonatites and Fenites from Khlibodarivka Occurrence

The data of mineralogical studies of carbonatite veins and exocontact fenites in the open pit near the Khlibodarivka occurrence (Donetsk region, Volnovaha district) are presented. The thickness of carbonatite veins is neglegible, rarely exceeding 30 cm, and are mainly composed of calcite, alkaline amphibole and albite are the most common silicate minerals. Accessory minerals are more often represented by monazite, apatite, columbite, minerals of pyrochlore group, zircon, and opaque (ilmenite, rutile, magnetite, sulfides). In addition to the above-mentioned minerals, except for the minerals of pyrochlore group, chlorannite, aegyrine, REE-carbonates, baryte, allanite-(Ce), REE-apatite were found in the fenite haloes and veinlets. The reactionary interaction of the carbonatite melt enriched in alkalis and volatiles with the hosted enderbites caused the appearance of fenite halos both around the veins of carbonatites and the thin "net" of veinlets without a visible connection with carbonatites. The significant thickness of the fenite halos (usually twice as much in comparison to the thickness of the carbonatite veins), albitization of the surrounding rocks and saturation of the alkaline femic minerals of the carbonatite veins and fenites indicate that the initial carbonatite melt contained a significant amount of Na and volatile components (H2O, F, CO2, possibly Cl), and also had a more ferruginous composition of carbonates due to the presence of siderite or ankerite components (in the melt). As a result of the dissociation of primary carbonates, iron, as well as alkalis, was concentrated in the fluid phase and subsequently included in aegirine and alkaline amphiboles. The fenitization of host rocks took place in several stages. At the initial stage, the alkali-enriched fluids, mainly Na, F, and possibly Cl, were separated, while the later ones fluids were Fe-enriched and existing in more oxidized conditions. The fluids genetically related to carbonatites were penetrating into the host rocks caused the redistribution of trace elements. Barium, Th, and partly LREE were carried out from carbonatites most intensively, while Sr, Nb and a significant part of REE remained immobile due to the early crystallization of their host minerals and lack of subsequent autometasomatic alteration. Geochemistry of carbonatite veins (high content of incompatible elements such as Sr (11 7777 ppm), increased REE (1624 ppm), elevated Nb, chondrite-normalized pattern of REE, high (La/Yb)cn = 24.7 and absence of negative Eu anomaly (Eu* = 1.03) and endogenous ratios of isotopes of Sr (0.703), C and, partially, O) testify to their magmatic origin. It is possible that the insignificant thickness of the carbonatite veins and the intensive interaction of juvenile fluids with the host granitoids and meteoric fluids caused the enrichment of carbonatites with 18O (δ18O 8.4÷20), but with the preservation of primary δ13C (–8 ÷ –6.5). Currently, the increased concentrations of rare metals were not found in carbonatites of the Khlibodarivka village. However, the presence of carbonatite veins in association with fenite halo, spatial connection to the Oktyabrsky massif of alkaline rocks, as well as numerous fenite occurrences in this area, increase the prospects of this area for such mineralization.

Petrogenesis of Sn–W mineralized granites in the Dawei and Mawchi, regions of Myanmar

The Palaeocene granites of Dawei and the Eocene granites of Mawchi both host large‐ to medium‐scale Sn–W deposits and represent two metallogenically prominent segments of the SE Asian tin belt in Myanmar. Combined with previous geochemical data, new whole‐rock elemental and isotope analyses of tin‐mineralized granites were obtained to provide insights into sources involved in the formation of these granites. Tin granites in both regions are highly siliceous (76–80 wt%), peraluminous (A/CNK = 1.02–1.32), depleted in Sr, Ba, Zr and Ti but elevated in Li, Sn, Rb, Pb and U. The highly evolved nature of these granites is emphasized by their high Y/Ho (33–49) ratios as well as low Nb/Ta (1–11) and Zr/Hf (8–24) ratios. The chondrite‐normalized REE patterns, with M‐type tetrad effects (TE1,3 = 1.04–1.16) and strongly negative Eu anomalies (0.01–0.34), point to fractional crystallization of feldspars and other accessories during the evolution of the parental magma and are also indicative of the magmatic to hydrothermal transition that resulted in the pervasive mineralization of these bodies. The Pb isotopic compositions are variably enriched, with age‐corrected 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values ranging from 18.620 to 18.898, 15.728 to 15.770, and 38.288 to 39.402, respectively, all of which point to derivation from evolved crustal material. This is consistent with their low ɛNd(t) and ɛHf(t) values of −10.11 to −11.29, and −5.86 to −8.93, respectively. Collectively, these data suggest that crustal melting, fractional crystallization and late‐stage magma–fluid interactions all played important roles in the generation of the tin‐mineralized granites of Myanmar.

Geochemical and Isotopic Compositions of Fluorites from the Yama Fluorite Deposit in the Qilian Orogen in Northwest China, and Their Metallogenic Implications

The Yama area is characterized by numerous large-scale fluorite–quartz veins that are located along faults within the widespread Late Devonian–Late Silurian syenogranites in the Tataleng granitic batholith, Qilian Orogen, Northwest China. These fluorite–quartz veins contribute to an important fluorite reserve, but their ore genesis remains unresolved so far. In this study, trace elements, rare earth elements (REEs), and hydrogen, oxygen, and strontium isotopic compositions of fluorites are analyzed. The studied fluorite samples have similar chondrite-normalized REEs, including Y patterns, with relatively strong enrichment in heavy REEs, negative Eu anomalies, strongly positive Y anomalies, and comparably invariable Y/Ho ratios of 41.43–73.79, suggesting a unique hydrothermal genesis. The relatively variable values of δD and δ18O are −77.4‰ to −102.4‰ and −12.7‰ to −4.3‰, respectively, close to the meteoric water line. These fluorites yield relatively invariable analytical 87Sr/86Sr ratios of 0.749089−0.756628 (except for an anomalously high ratio), and their calculated initial 87Sr/86Sr ratios, based on the ore-forming ages provided, are apparently higher than the calculated initial 87Sr/86Sr ratios of syenogranite wall rocks. Collectively, the geochemistry of trace elements, REEs, and stable isotopes (H, O, and Sr) suggests that the ore-forming fluids were of meteoric origin and that the Sr sources were directly derived from the ore-forming fluids themselves rather than syenogranite wall rocks. Finally, it was considered that the Yama fluorite deposit is a fault-controlled hydrothermal vein-type deposit which was possibly related to the evolution of the Paleo-Tethys Ocean in the Permian–Triassic.

Mineralogy and Geochemical Characteristics of Scheelite Deposit at Xuebaoding in Pingwu, Sichuan Province, China

Featuring subtle lithological alterations in the host rocks and containing colossal gemstone crystals, the scheelite deposit at Xuebaoding in the Pingwu region of Sichuan Province exhibits characteristics typical of a vein-like hydrothermal-type deposit. The scheelite from the Xuebaoding region is renowned for its high saturation of color, perfect crystal shape, and pure color. In this study, its crystal structure and mineralogical, geochemical, and in situ Sr-Nd isotope characteristics are all systematically characterized. Our objective is to determine the source of ore-forming materials, the timing of the mineralization, and the chemical composition of scheelite, including major elements, trace elements, and rare earths elements (REE). The scheelite samples were analyzed with a variety of methods such as polarizing microscopy, X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), electron probing, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In addition, conventional gemological tests were performed using instruments including gemstone microscopes, GI-UVB ultraviolet fluorescent lamps, grating spectroscopy, etc. The results demonstrate that scheelite exhibits a high refractive index, excellent crystallinity, and a granular structure. Clear color bands and ring structures are observed within the minerals, accompanied by interference colors of light blue, blue, and yellow. Additionally, the mineral components are relatively concentrated, with muscovite and illite serving as accessory minerals. Furthermore, the chemical composition of scheelite reveals a WO3/CaO mass ratio that approaches or exceeds the ideal value. Moreover, it exhibits a wide range of variations in total rare earth element (∑REE) content, which is characterized by an enrichment of light rare earths (LREE), significant negative Eu anomalies, and insignificant Ce anomalies. In addition, the metallogenic formation of scheelite can be estimated to have occurred during the Toarcian stage in the Lower Jurassic Epoch period, approximately 183 Ma. The study further revealed that A-type granite serves as the genesis type of scheelite, with most of the ore-forming materials originating from the upper crust and a few derived from younger crustal sources.

Petrogenesis and metallogenic significance of late Mesozoic granites in the Akjilga mining area, Tajikistan: constraints from geochronology and geochemistry

The Akjilga (Акджилга) mining area in Tajikistan sits in the central part of the Pamir syntaxis in the western part of the Indo–Eurasia collisional orogenic belt. Recently, the mineralization phenomena of skarn-type tin polymetallic ore bodies and dolomite-type rare-earth metals in the copper polymetallic mining area have been reported. However, the limited knowledge on the genesis of granite and its relationship with mineralization in this area hinders further research. Here, the Late Mesozoic granite rocks in the mining area were studied by petrology, geochemistry, and zircon U–Pb dating. The results showed that the rocks comprise majorly porphyric biotite syenogranite and minorly porphyric biotite monzogranite. The zircon U–Pb age of the porphyric biotite syenogranite was 108.3 ± 2.0 Ma, highlighting the Early Cretaceous period. The porphyric biotite syenogranite features high silicon and potassium contents and low iron, magnesium, calcium, sodium, titanium, and phosphorus contents. Furthermore, their aluminum saturation indexes were 1.11–1.21. Therefore, they were classified as high-potassium calc-alkaline strong peraluminous rocks. Trace-element analysis showed the enrichment of large ionic lithophile elements and light rare-earth elements (REEs); the deficiency of high-field-strength elements and heavy REEs; and the negative anomalies of Nb, P, and Ti. Compared with ordinary granites, the porphyric biotite syenogranite exhibits a higher differentiation index (91.20–93.96) and strong negative Eu anomaly (0.05–0.26), as well as a low Zr content and abnormally low Nb/Ta, Zr/Hf, Y/Ho, ∑LREE/∑HREE ratios. Therefore, the rocks are considered highly differentiated I-type granites with good Sn polymetallic and rare-metal prospecting potentials, and it resulted in the subduction-collision of the Rushan-Pshart ocean between the Middle Pamir block and the South Pamir block during the northward subduction process of the Late Mesozoic New Tethys ocean (Shyok ocean).

Geochronology and Geochemistry of Volcanic and Intrusive Rocks from the Beizhan Iron Deposit, Western Xinjiang, NW China: Petrogenesis and Tectonic Implications

The Awulale Iron Metallogenic Belt (AIMB) located in Central Tianshan is a significant iron ore belt in China. The Beizhan area exhibits extensive volcanic and intrusive rocks that formed during or close to the iron mineralization period. The iron ores in Beizhan are found in Early Carboniferous rhyolite and dacite tuff. The rhyolite is enriched in LILEs and LREEs, depleted in HFSEs, and shows high positive εNd(t) values (+3.0–+4.0). Late Carboniferous intrusive rocks include a granite stock and diabase and diorite dykes. The zircon grains from the granite yield a weighted mean 206Pb/238U age of 311.8 ± 2.6 Ma. The geochemical features of the granite are similar to those of rhyolite, but with pronounced negative anomalies of Eu, Sr, P, and Ti and higher positive εNd(t) values (+4.9–+5.1). The zircons in the diorite dyke yield a weighted mean 206Pb/238U age of 299.2 ± 1.4 Ma. Both the diabase and diorite dykes show an enrichment of LREEs and depletion of HFSEs with high positive εNd(t) values (+3.3–+7.3 and +2.3–+2.6, respectively), although the Eu, Th, and Sr anomalies are more negative in the diorite compared to the diabase. The rhyolite displays high positive εNd(t) values and young Nd model ages (TDM2 = 760–838 Ma) and has Nb/Ta ratios (11.3–12.8) close to that of the continental crust, indicating that it originated from the partial melting of the juvenile lower crust. The granite has similar geochemical characteristics (TDM2 = 656–673 Ma and Nb/Ta ratio = 8.7–10.9) and is also believed to have originated mainly from the partial melting of the juvenile lower crust. The diabase and diorite dykes have low (Tb/Yb)N ratios (<2) and high Ba/Th (31.8–353.2 and 185.3–251.3, respectively) and Sr/Th (113.8–312.9 and 144.7–163.1) ratios, and exhibit a pronounced depletion of HREEs and Y and negative Th anomalies, suggesting that they originated from a spinel-garnet lherzolite mantle source. The Early Carboniferous rhyolite erupted in a continental arc setting, whereas the Late Carboniferous granites, diabase dykes, and diorite dykes formed in an extensional setting associated with the upwelling of the asthenosphere. Therefore, the magmatism and Fe mineralization in the AIMB are correlated with an extensional setting associated with oceanic slab breakoff.

Ordovician−Early Devonian granitic magmatism as the consequence of intracontinental orogenic activity along the Qinhang belt in South China

The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.

Petrogenesis of the Weideshan Pluton in Jiaodong and Its Implications for Gold Polymetallic Mineralization: Constraints from Zircon U-Pb-Hf Isotopes, Petrogeochemistry, and Whole-Rock Sr-Nd Isotopes

The Early Cretaceous Weideshan granites are associated with large-scale Au and polymetallic Cu-Mo-Pb-Zn mineralization. To investigate the petrogenesis of the Weideshan granite and constrain its tectonic setting during the Early Cretaceous, we conducted a zircon U-Pb-Hf isotope and whole-rock geochemical and Sr-Nd isotopic study of the granite. In situ zircon U-Pb dating of three granite samples yielded Early Cretaceous ages of 112.83 ± 0.80, 112.64 ± 0.91, and 111.82 ± 0.78 Ma. The samples had high-K calc-alkaline compositions and were enriched in the light rare earth and large-ion lithophile elements (e.g., K, Rb, Ba, Th, and U) and depleted in high-field-strength elements (e.g., Nb, Ti, and P). The samples had small negative Eu anomalies and initial 87Sr/86Sr and εNd(t) values of 0.70853–0.71029 and –18 to –14, respectively. The zircon εHf(t) values varied between −16 and −12, with corresponding two-stage model ages (tDM2) of 2180–2000 Ma. These characteristics indicated that the Weideshan pluton was formed in a back-arc extensional environment caused by subduction of the Paleo-Pacific Plate toward the Asian continent during the early Cretaceous. The magma was generated by crust–mantle interaction during lithospheric thinning. The diagenetic age of the Weideshan granites was the same as the formation age of gold and polymetallic ores in the Jiaodong area. The extensive fluid circulation induced by the magma emplacement may be the main source of ore-forming materials for the gold and polymetallic Cu-Mo-Pb-Zn deposits.

Geochemical characteristic of rocks and isotope dating of zircon from the andesite dyke of the rudyanskaya sequence (D2 rd) of the Middle Urals Eastern zone

Relevance. In the basin of the r. Pishma subvolcanic formations, localized in the fields of spreading of the Middle Devonian Rudyanskaya sequence, are presented by different on composition small bodies, sills and dykes, forming with volcanogenic rocks of the Rudyanskaya sequence a basalt-andesite-rhyolite complex, the formation of which is associated with volcanic activity, that took place in Middle Devonian in the environments close to the modern island arcs. Their isotope dating and geochemical characteristic are rather relevant for specification of the composition, volume and paleogeodynamic environment of the vulcanite formation. In the paper new data are presented on geochemistry of andesites of the dyke from the Diviy Kamen rock, considered as part of the Rudyanskaya sequence, as well as the age of zircon from them. Methods. Chemical analyses of vulcanites have been performed in the Centre of collective usage “Geoanalyst” of the Institute of Geology and Geochemistry of the UB of RAS (Ekaterinburg) by X-ray fluorescent method and ICP–MS method. Zircons were studied with scanning electron microscope JSM-6390L of the Jeol firm and with electrone-probe microanalyser Cameca SX100. The data on the U and Pb isotopes, as well as on elements-impurities in zircon grains were obtained by mass-spectrometry method with inductively coupled plasma with laser ablation (LA–ICP–MS) at the quadrupole ISP–MS NexION 300S with the attachment for laser ablation LA NWR 213. Purpose of researches. Getting new data on geochemical composition and age of the andesites of dyke in the section along the r. Pishma. Results. The andesite dyke intersects medium clastic unstratified tuffs and dipply occurring fragment of the lava flow of porphyry dacite. Andesites present themselves porphyry rocks with 20–30% of plagioclase phenocrysts. At the normalized many-component diagram the Ta–Nb minimum is displayed. For zircon grains are characteristic differentiated spectra, demonstrating the growth of compositions from light to heavy REE, positive Ce and negative Eu anomalies, typical of the zircon of magmatic genesis. For the first time geochronological study of zircons from andesites has been maded by method of LA–ICP–MS. 4 age groups of zircons, Ma: 390–387, 369–362, 337–345, 327–329 were revealed. Conclusions. The data obtained testify that andesites were formed under suprasubduction environments, and magmatic stage of rock formation corresponds to the upper Devonian varieties of zircons. Early Carboniferous datings can be associated with the thermal impact caused by the intrusion of a later dolerite dyke.

Bidirectional subduction of the Proto-Tethys Ocean: constraints from geochronology and geochemistry of S-type granites from Baoshan Block in western Yunnan (SW China)

Understanding the tectonic evolution of the Proto-Tethys Ocean is important for exploring the initial assembly of the Gondwana supercontinent. The closure of the Proto-Tethys Ocean represents the end of convergence along the northern edge of Eastern Gondwana. However, the timing and processes of the closing of the ocean have different interpretations. This work focuses on the Early Paleozoic granitic rocks in the Baoshan Block, SW China to constrain the tectonic evolution of the Proto-Tethys Ocean. Zircons from the Pinghe and Zhen'an granitic plutons yield concordant U–Pb ages from 489.8 to 467.7 Ma. The bulk-rock geochemical features suggest that these samples are high-K calc-alkaline, S-type granites enriched in light rare earth elements and depleted in heavy rare earth elements. With obvious negative Eu anomalies and high K 2 O/Na 2 O ratios (1.01–2.57), they are enriched in large ion lithophile elements and depleted in high field strength elements. These rocks were therefore derived from partial crustal melting associated with subduction of the converging plate. Previous studies on the Changning–Menglian suture zone have suggested that the Early Paleozoic magmatic activity in the Baoshan Block was related to the westward subduction of the Proto-Tethys Ocean. Combined with the Early Paleozoic subduction-related magmatic activity to the east, it is therefore suggested that the Changning–Menglian Ocean experienced bidirectional subduction.

Tonian rifting coeval with the last stages of amalgamation of Rodinia: Evidence from southern Borborema province, northeastern Brazil

During the last stages of assembly of the Rodinia supercontinent at 1000-900 Ma, rifting processes were occurring in places that would be part of Gondwana in the late Neoproterozoic. In the Borborema Province, northeastern Brazil, this event is known as Cariris Velhos. It is represented in the Alto-Pajeú Domain from the Central subprovince by a 700 km-long, 70 km-wide NE-SW belt comprising bimodal metavolcanic rocks and granitic orthogneisses. Orthogneisses with similar ages were found in previous works in the western Pernambuco-Alagoas Domain from the Southern subprovince immediately to the south of the ESE-trending dextral West Pernambuco shear zone. The Airi Complex comprises several elongate bodies that extend for at least 80 km. It consists of a bimodal sequence of metafelsic (granitic orthogneisses) associated with layers and enclaves of metamafic (amphibolites) rocks. Seven orthogneiss samples dated by LA-ICPMS yielded zircon U–Pb crystallization ages of 950–1011 Ma. Zircon Hf analyses from two samples yielded εHf(t) values ranging from −1.4 to 2.1 and TDM model ages of 1.7–1.9 Ga. Geochemical analyses allow to distinct different source rocks for the protoliths of the orthogneisses. Orthogneisses derived from metasedimentary sources have modal muscovite ± garnet, are ferroan, alkali-calcic and predominantly peraluminous, exhibiting strong negative Eu anomalies in chondrite-normalized rare earth elements diagrams. Orthogneisses derived from high-K mafic rocks are calc-alkalic, slightly peraluminous, with small or absent negative Eu anomalies. Orthogneisses from tonalitic sources are magnesian, calc-alkalic to alkali-calcic, and slightly peraluminous, without Eu anomalies. There is no correlation between crystallization ages and source rock types. The results indicate that the Airi Complex originated through partial melting of ancient heterogenous crustal sources. Therefore, its geochemistry reflects the nature of these sources, not the tectonic setting of intrusion. Emplacement of the complex was broadly coeval with well-documented extensional processes in the São Francisco/Congo Craton and represents a failed attempt to break-up a larger paleocontinent encompassing this craton and the basement of the Borborema Province.

Geochemistry and geochronology of Beiya giant Au polymetallic deposit: Implications for multistage ore-fluid pulses in a skarn system

Garnet is one of the most typical minerals in skarn deposits, and its texture and composition is a proxy for the changing physicochemical conditions. Thus, mineralogical and geochemical characterization of different garnet types can provide important information on the nature and evolution of ore-forming fluids. The Beiya gold-polymetallic deposit is China’s largest skarn-type Au deposit with Au reserves of >380 t. Although several studies have addressed the skarn formation mechanism and nature of fluid evolution, a systematic study on the changes in the composition and texture of garnet from wall rocks to ore-related intrusion has not yet been attempted. In this work, we carry out a systematic investigation along a horizonal profile in the open pit of the Beiya deposit. Our results show that the garnet in the profile belongs to grossular-andradite solid solution series with all grains showing well-developed fine oscillatory zoning. The garnets are of two types: the first type (Grt I) formed within the endoskarn, is reddish to red with euhedral-subhedral megacryst structure (>10 mm) and has altered surfaces. The second type (Grt II) occur in the proximal exoskarn, is red to brown–red, euhedral-subhedral, with medium- to fine- grained structure (0.3–4 mm) and displaying oscillatory zoning. Unlike Grt I, hydrous minerals occur in the pores among Grt II garnets, such as calcite, quartz, epidote and chlorite. Also, calcite-chlorite vein, quartz vein and quartz-chalcopyrite-pyrite vein cuts the Grt II garnets. Grt I is dominantly grossular (Adr14.88-43.58Grs55.25-82.87), depleted in the large ion lithophile elements (LILE), relatively enriched in high field strength elements (HFSEs) and enriched in heavy rare earth elements (HREEs) with negative Eu anomalies. Grt II is mostly andradite (Adr62.18-98.91Grs0-36.22), depleted in the LILE and HFSE, enriched in light rare earth elements (LREEs) with slightly positive Eu anomalies. Here we selected Grt II for in-situ LA-ICP-MS U-Pb dating, since Grt I contains negligible uranium. The results yielded a lower intercept 206Pb/238U age of 35.3 ± 1.8 Ma (MSWD = 0.68, n = 23). The calculated oxygen isotopic compositions of hydrothermal fluids in equilibrium with two types of garnets range from 6.46 ‰ to 8.56 ‰ (average 7.89 ‰), which are within the range of values for magmatic fluids. We infer that the physicochemical conditions of the hydrothermal fluid changed from relatively reduced, nearly neutral, and low water/rock ratios to slightly oxidized, slightly acidic, and high water/rock ratios. The chlorine content in the fluid increased during garnet growth. The fluctuating compositions of garnets in the skarn suggest multistage ore-fluid activities and the fluid evolution provide insights into the ore-forming process.

Late Magmatic Activity in the Tarim Large Igneous Province: Evidence from the Puchang Granites.

The magmatic evolution sequence and tectonic activity background of the Permian Tarim large igneous province were discussed based on the research of petrogeochemistry, chronology, and zircon Lu-Hf isotope of two types of granite distributed in the Puchang V-Ti-magnetite deposit in the northwestern margin of Tarim. The results show that the two types are characterized by high silica, alkali, and potassium content. Both types of granites are enriched with light rare earth elements, including porphyritic granites with a negative anomaly of Eu and biotite monzogranites with a weak positive anomaly of Eu. The trace elements generally show that the large-ion lithophile elements are enriched relative to the high-field-strength elements, P and Ti are obviously depleted, and Rb, U, and K are relatively enriched. The zircon U-Pb age of porphyritic granites is 275.7 ± 1.0 Ma, the εHf(t) value ranges from -6.6 to -3.3, and the tDM2 ranges from 1469 to 1684 Ma. The zircon U-Pb age of biotite monzogranites is 268.9 ± 1.4 Ma. The εHf(t) value ranges from -1.2 to 0.5, and the tDM2 ranges from 1232 to 1340 Ma. The two types of granite were formed in a postcollisional extensional environment at the end of the early Permian, which is related to the Permian Tarim mantle activity and asthenosphere upwelling. The porphyritic granite was derived from an enriched lithospheric mantle; the biotite monzogranite was formed by the melting of mantle with crust contamination; and basalt and intrusive complexes in the research area were formed in an extensional intraplate rift environment.

Inherited zircons in Early Cretaceous dyke: Implication of growth and reworking of continental crust in the Jiaodong Peninsula

Inherited zircons from Early Cretaceous dykes across the Jiaodong Peninsula provide a means of exploring magmatic episodes. Negative Eu anomalies, high Th and U contents, and high U/Yb ratios confirmed a zircon source of ancient continental crust. Differences in mineralogy, chronology, geochemistry, and Hf isotopes showed that these inherited zircons were not brought in by the Triassic Yangtze Craton collision. Zircons within 2938–2800 Ma confirmed that the ancient crust in the Jiaobei Terrane originated from the Mesoarchean crustal growth. This crustal growth continued until the Early Paleoproterozoic and was accompanied by crustal transformation activities in the later period. After the collision of the Jiao–Liao–Ji Belt, the Jiaodong Peninsula entered a typical craton period until it was reactivated at the end of the Neoproterozoic, which was characterised by the Archean crustal transformation. During the Palaeozoic, smooth crustal thickness change with limited addition of oceanic crust material indicated the Qinling–Dabie–Sulu Orogenic Belt as a distal island arc system that slowed the impact of Paleo-Tethys subduction. There was no record of positive-εHf(t) zircons in the Jiaodong Peninsula during the Mesozoic, but the crust thickened rapidly. This confirmed that the Paleo-Pacific Plate may have directly subducted beneath the lithospheric mantle and had little contact with the lower crust. This subduction pattern released little hydrous fluid but much heat, which prompted the remodelling of the lower crust in the Mesozoic. Furthermore, the large-scale lithospheric thinning event around 120 Ma was identified as a result of the delamination of the lithospheric mantle together with lower crust.

Petrogenesis of the early Permian Hongliujing granite complex in the Chinese Eastern Tianshan orogen: Evidence for crustal growth in the Central Tianshan microcontinent

The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt.

Petrogenesis of the Wushi carbonatites in the northwestern Tarim Basin: Implications to deep carbon recycling

Carbonatites are rarely exposed on the Earth's surface, and most of them are supposed to have been mantle-derived. However, in the most recent years, carbonatites with pronounced crustal signatures had also been recognized. Although carbonatites have attracted the attention of many researchers, their genesis remains controversial. In this study, we present a systematic C–O–Sr–Nd–Mg isotopic investigation on the carbonatites exposed in Wushi County located at the northwestern margin of the Tarim Basin to determine their petrogenesis. The Wushi carbonatites, containing the xenoliths of wall rocks, intruded into Precambrian sandstones as dykes. Carbonatites predominantly comprise calcite and accessory minerals, such as dolomite, apatite, mica and quartz, and thus are classified as calciocarbonatites. Trace element geochemistry indicates that the total rare earth element (REE) concentrations in Wushi carbonatites range from 13.6 to 57.3 ppm, with an average of 30.9 ppm. The chondrite-normalized REE patterns of the test samples indicate that light rare earth elements (LREE) in the samples have been enriched relative to their heavy rare earth elements (HREE) and that the LREE/HREE ratios vary from 6.0 to 9.1. The patterns also show negative Eu anomalies (δEu = 0.65–0.75) and weak negative Ce anomalies (δCe = 0.75–0.99). The primitive mantle-normalized trace element spider diagrams display the enrichment of large ion lithophile elements (LILE), such as Pb, Sr and Ba, and the strong depletion of high field strength elements (HFSE), such as Nb, Ta, Zr, Hf and Ti. The δ18OV-SMOW (15.9‰–18.2‰) and δ13CV-PDB (−2.97‰–3.36‰) values are more consistent with those of crust-derived carbonatites than with mantle-derived carbonatites. The values of δ18OV-SMOW and δ13CV-PDB are consistent with the high values of 87Sr/86Sr (0.7096–0.7110) and low values of 143Nd/144Nd (0.5118–0.5120). Typically, δ26Mg of the carbonatites (−1.76‰ to −1.27‰) is much lighter than the δ26Mg of the mantle (−0.25‰ ± 0.04‰) but heavier than the δ26Mg of sedimentary carbonates (−2.72‰ to −2.15‰) obtained from the neighbouring Western Tianshan orogenic belt. The light Mg isotope anomalies cannot be explained using secondary alteration, continental crustal contamination, kinetic isotope fractionation and fractional crystallization. Thus, these anomalies could be due to the isotope exchange reactions occurring between the oceanic crust and sedimentary carbonates during subduction. In this study, we propose a two-stage model to explain Wushi carbonatite formation based on its isotope characteristics. During the early stage of carbonatite formation, sedimentary carbonate rocks located along the northern margin of the Tarim Craton and oceanic crust were subducted into the deep mantle. Isotope exchange and carbonation occurred during subduction to form carbonated eclogite. In the second stage of carbonatite formation, the heat produced by the Permian mantle plume in the Tarim Basin melted the carbonated eclogite to produce carbonatite melt. Thus, the petrogenesis of the Wushi carbonatites revealed by the presence of multiple isotopes indicates that the carbonatite produced by carbonated eclogite in the deep mantle would exhibit typical crustal isotopic characteristics and provide new insights into deep carbon recycling.

Unraveling the early Paleozoic tectonic history of the South Qinling Belt: Evidence from geochronology, geochemistry, and Sm-Nd isotopes of meta-sedimentary rocks

The determination of the petrogenesis and age of meta-sedimentary rocks plays a crucial role in enhancing our understanding of regional tectonic evolution. In this study, we conducted comprehensive geochemical, zircon U-Pb, and Sm-Nd isotope dating analyses of the biotite gneiss of the Changjiaoba group to investigate the tectonic evolution of the South Qinling belt. The age range of detrital zircons from the biotite gneiss was estimated to be 446–2798 Ma, with prominent peaks observed at approximately 454, 660, 790, 1998, and 2770 Ma. The earliest data indicate that the final sedimentary age of the Changjiaoba group corresponds to the late Ordovician. The protoliths of the biotite gneiss were argillaceous rocks, classified as parametamorphic rock. The chondrite-normalized rare earth element (REE) diagram exhibited right-inclined patterns with negative Eu anomalies. The upper continental crust (UCC)-normalized trace element patterns exhibited insignificant enrichment of Ba, Sr, and K; negative anomalies of Hf, Th, U, and Ti; and depletion of Cr and Ni. Geochemical indicators suggest that the precursor sediments are felsic rocks that have undergone moderate weathering. The εNd (t) values of the biotite gneiss (−10.2 to −3.4) suggest a mixture of a few juvenile crust components and abundant ancient material, indicating an arc-realted setting. Collectively, our findings suggest that the primary material sources of the Changjiaoba group were predominantly the North Qinling belt during the Paleozoic and the Yangtze block during the Neoproterozoic. The tectonic setting discrimination diagrams imply that the biotite gneiss were formed in an active continental margin environment, supporting the notion of the northward oceanic subduction during the early Paleozoic. In conclusion, our study provides valuable insights into the composition and deposition history of the Changjiaoba group in the South Qinling belt, contributing to our understanding of the regional geology.

Geochronology, provenance, and tectonic setting of the meta-sedimentary rocks from the North Shahrekord metamorphic Complex, Iran

ABSTRACT The meta-sedimentary rocks from the North Shahrekord metamorphic Complex (NSMC) comprise micaschists, paragneisses, quartz-feldspathic schists, and marbles. Detrital zircons from the paragneisses yield ages of ca. 2811–507 Ma with most of the dated grains belonging to the Late Neoproterozoic to Cambrian, suggesting a maximum depositional age of the sedimentary protolith during the Late Ediacaran to the Early Cambrian times (543 ± 12 Ma). In contrast, detrital zircons from the quartz-feldspathic schists are mostly dominantly 692–577 Ma and a few at ca. 2369–703 Ma, suggesting that the maximum depositional age of 577 ± 9 Ma, Late Neoproterozoic. The age distribution of detrital zircons suggests that their main provenance was located within the Arabian-Nubian Shield and adjacent terranes. Rutiles from a paragneiss give a U-Pb lower-intercept age of 181 ± 3 Ma, indicating the occurrence of a high-pressure metamorphic event during the Early Jurassic. The trace element contents of the two rock units show enrichment in LREE relative to HREE and negative Eu anomalies, indicating upper continental crustal sources. The geochemical evidence (e.g. low to moderate Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration, high Index of Compositional Variability (PIA), and low Th/U) suggests that the quartz-feldspathic schists and paragneisses originated from an immature, and immature to less mature, respectively, intermediate-felsic igneous source and their protolith experienced a simple sedimentary recycling history with relatively weak to moderate chemical weathering. Geochemical and petrographic data also suggest that the precursor to the quartz-feldspathic schists and paragneisses were deposited in a continental island arc and a back-arc basin setting, respectively. Our new data, including depositional age, provenance, and geochemical evidence, provide perspectives on palaeogeographic affinities (provenance of sediments with different weathering and recycling materials), and paleotectonic reconstructions (from arc to back-arc) of the Iranian basement, exposed in the Sanandaj-Sirjan Zone, during Ediacaran.

Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.

A late Neoarchean continental arc system in the northeastern North China Craton: constrain from the Guanghua mélange in the Tonghua area, southern Jilin Province

ABSTRACT The late Neoarchean tonalite – trondhjemite – granodiorite (TTG) and mafic rocks record essential information regarding the early tectonic evolution of the North China Craton, which is crucial for understanding the onset and development of the plate tectonic regime. In this study, we present a comprehensive analysis of petrography, geochronology, and geochemistry of the Guanghua Mélange from the Tonghua area in NE China. The mélange comprises basalt, gabbro, pyroxene diorite, and trondhjemite, and is classified into three groups: basaltic – gabbroic rocks (Group #1), dioritic rocks (Group #2), and trondhjemites (Group #3). Zircon U-Pb analyses indicate that they formed at 2596–2550 Ma, 2531–2515 Ma, and 2502 Ma, respectively, with metamorphism occurring during ~ 2500–2450 Ma. Meanwhile, geochemical data indicate that the calc – alkaline basaltic rocks (Group #1) exhibit slight depletion of Nb or Ta with weakly negative Eu anomalies, suggesting derivation from the lithospheric mantle and formation within a continental arc environment. The pyroxene diorites (Group #2) display similar geochemical characteristics to Group #1, likely formed by partial melting of depleted mantle that underwent sgignificant metasomatism due to variable amounts of slab-derived fluids or melts. The tholeiitic granitoids (Group #3) exhibit strongly fractionated chondrite-normalized REE patterns with high (La/Yb)N and Sr contents, low Y contents, and depletion of Nb, Ta or Ti, resembling adakites generated in arc setting, indicating likely formation through partial melting of subducted oceanic crust. This process was controlled by the initial plate tectonics under a higher geothermal gradient. Consequently, when combined with previous findings, we conclude that an initial subduction of oceanic plate operated in the northeastern North China Craton during the late Neoarchean (>2.55 Ga). Subsequently, it transformed into modern-type plate tectonics during ~ 2.55–2.53 Ga, eventually followed by the continent-continent collision at ~ 2.50–2.45 Ga, resulting in the formation of the Ji – Liao – Ji (Jilin – Liaoning – Hebei) Collision Orogenic Belt.