REE Patterns Research Articles

Post-collisional magmatism and local lithospheric thinning in the Neoproterozoic Alto Pajeú Domain, northeastern Brazil: Geochemical and isotopic evidence

The 595–560 Ma post-collisional magmatism in the Alto Pajeú Domain, Borborema Province, northeastern Brazil, is characterized by the intrusion of voluminous high-K calc-alkaline, shoshonitic and ultrapotassic magmas. The nature of the source rocks and the geodynamic context associated with the generation and emplacement of this post-collisional magmatism is still enigmatic. In this study, we report new UPb ages, elemental geochemistry, mineral chemistry and SrNd isotope data for rocks from the Pajeú batholith. LA-ICP-MS zircon UPb dating revealed that this batholith was formed by at least two distinct magma pulses. The oldest pulse (ca. 592 Ma) consists mainly of porphyritic quartz monzonites to monzogranites with abundant mafic microgranular enclaves (MMEs), while the younger pulse (ca. 568 Ma) is composed of equigranular biotite granites. The porphyritic monzogranites are magnesian, have intermediate to acidic compositions (SiO2 = 62.2–67.6 wt%) and high Mg# (44–55) values. In contrast, biotite granites are ferroan, have high SiO2 (69.3–73.1 wt%) and low Mg# (16–36) values. Both rock types are characterized by enrichment in LREE and LILE and depletion in HREE and HFSE, but with more fractionated REE patterns for biotite granites ([La/Yb]N = 67.4–101.5) than for porphyritic rocks ([La/Yb]N = 35.8–54.8). The SrNd isotopic values for the different rock types are roughly similar. However, biotite granites show slightly higher initial 87Sr/86Sr (0.71265–0.71412) ratios and more negative εNd (t) (−18.45 to −18.67) values than porphyritic monzogranites (initial 87Sr/86Sr ratios from 0.71077 to 0.71155 and εNd (t) from −16.04 to −16.96). These geochemical and isotopic signatures, together with mineral chemistry data, suggest different sources for the two rock types. The biotite granites are of purely crustal origin, derived by partial melting of a Paleoproterozoic amphibolitic lower continental crust, while a mixture of melts derived from the Paleoproterozoic continental crust and magmas derived from an enriched lithospheric mantle could explain the origin of porphyritic monzogranites. Based on the spatial and temporal distribution of magmatic rocks from the Alto Pajeú Domain, we suggest that a local lithospheric thinning model could explain the evolution of post-collisional magmatism in this region of the Borborema Province.

Alkaline Silicate Metasomatism Recorded through Fe-Ti-Rich Mantle Xenoliths from the Calatrava Volcanic Field (Spain)

Much of the lithospheric subcontinental mantle (SCLM) sampled in the Calatrava Volcanic Field (CVF) shows refertilization by alkaline metasomatic agents. The Cerro Pelado and El Palo ultramafic xenolith suites record the best evidence of this type of metasomatism in this volcanic field. Several groups of peridotite (lherzolite, wehrlite, and dunite) and pyroxenite (clinopyroxenite and websterite) xenoliths have been distinguished. Despite having scarce phlogopites and amphiboles as modal metasomatic phases, all studied xenoliths present a variable cryptic metasomatism, highlighted by the strong Fe-Ti enrichment and fractionated REE patterns in the most evolved wehrlite and pyroxenite varieties. They show a common trend of an Fe-Ti-Ca increase, whereas the pyroxenites are more depleted in Fe compared to the lherzolites and wehrlites. Trace-element (REE and multi-trace) patterns are roughly similar among them, suggesting different interactions and refertilization degrees by alkaline silicate melts. The same Sr–Nd isotopic EAR composition, combined with trace-element chemistry of metasomatic xenolith phases and phenocrysts from the Calatrava volcanics, highlights the main role of this magmatism in percolation processes beneath Central Iberia. These mantle xenoliths also show variable amounts of interstitial glass that originated by in situ partial melting, favored by the enriched chemical nature of cryptically metasomatized clinopyroxene during their volcanic transport. This alkaline-refertilized mantle type represents the main domain within the SCLM beneath Central Iberia, as was also recorded in other Western European Cenozoic volcanic fields.

Geogas prospecting for igneous ore deposits covered by regolith: the Zijinshan high-sulfidation epithermal Cu–Au deposit in the Cathaysia Block

The mining industry faces a challenge due to the scarcity of outcrop or near-surface mineral deposits, necessitating the development of low-cost and efficient prospecting methods to explore through cover. Inductively coupled plasma mass spectrometry has been applied to geological sample analysis, and scientists have gradually improved the method of geogas prospecting. As a result, geogas prospecting has shown promising results in detecting underlying concealed Au, U and Cu–Ni deposits covered by Gobi sand and Quaternary sediments. To verify the effectiveness of this method for exploring underlying concealed mineral deposits developed in igneous covered areas, the Zijinshan high-sulfidation epithermal Cu–Au deposit, a concealed mineral deposit in southeastern China, was selected as the experimental field. Our experiments revealed nanoscale particles composed of Au, Cu–Fe and Cu–other elements in the geogas captured above the ore bodies of the deposit. Furthermore, Cu–nanoscale particles retain the isotopic composition of copper found in both the oxidation zone and deep copper ores. The geogas samples exhibited similar C1-chondrite normalized REE distributions, with REE patterns indicating significant enrichment of LREE relative to HREE and similar (La)N/(Sm)N and (Gd)N/(Yb)N ratios. These characteristics are similar to those of the gold ores, copper ores, altered rock and bedrock near the ore bodies. These findings suggest that deep-penetration geochemical methods using geogas can be a valuable tool for uncovering underlying concealed mineral deposits in igneous covered areas.

Provenance of volcano-sedimentary features using tourmaline and REE compositional analysis, in the Paraná Basin, southern Brazil

The present research focuses on sediments' compositional analysis, in the Paraná Basin, to demonstrate provenance contributions for the volcano-sedimentary features distributed along three regions of the Basin's border. In this context, the analyzed sediments, which are generally attributed to the Botucatu Formation, interact with volcanic lava flows from the Serra Geral Formation, establishing a volcano-sedimentary interaction. Nonetheless, the classic description for the Botucatu Formation comprehends almost ubiquitous fine to medium sandstones, while the herein sedimentary rocks vary from fine-grained to very coarse sediments. The granulometry difference raises questions about unexplained events during the Cretaceous volcanism (Serra Geral Formation) over the Botucatu desert. Accordingly, the studied area is distributed into regions A, B, and C from the center to the eastern of the state respectively, covering the Paraná basin's border where the volcano-sedimentary rocks can be outcropped. The methodologies employed involve the analysis of tourmaline compositions and REE patterns. These analytical tools help identify provenance variations and the development of local processes. As a result, the data indicate the predominance of meta-pelites and metapsammites in region A, while in region C there is a prevalence of granitoids contribution, while region B is a transition area showing contributions of both meta-pelites, metapsammites, and granitoids that are attributed to some units of the Sul-Rio-Grandense Shield.

Tungsten mineralization in the Huangjindong gold deposit, southern China: Insights from scheelite texture, in-situ trace elements and Sr isotope compositions

Scheelite and wolframite are two primary tungsten minerals in nature. The occurrence of tungsten minerals varies in different types of deposits, with scheelite rather than wolframite typically forming in orogenic gold deposits. However, the explanation for this phenomenon remains unclear. Huangjindong deposit, located in the center of the Jiangnan Orogenic Belt in southern China, is a typical orogenic gold deposit with scheelite mineralization. Texture, in-situ trace elements and Sr isotope compositions of scheelite from this deposit were investigated to explore the formation process of scheelite and the source of tungsten of similar orogenic gold deposits.Three hydrothermal stages have been identified at this deposit: milky scheelite + quartz (pre-gold Stage I); gold + sericite + sulfide + quartz (syn-gold Stage II); and dolomite + quartz (post-gold Stage III). Scheelite primarily occurs during the initial pre-gold stage. Local color differences in CL image have developed along rims and in domains adjacent to fractures of scheelite due to slight late-stage hydrothermal alteration of scheelite along their fractures. The intense development of sericite and chlorite alteration in the host rocks indicates that the water–rock reaction consumed a large amount of H+. Within the scheelite-quartz veins, the presence of brecciated slate enclaves and localized quartz geodes, indicating that the fluid experienced significant pressure drop. This indicates that the water–rock reaction and the decrease in pressure resulted in the precipitation of scheelite. The dominance of tungsten mineral precipitation due to pressure reduction serves as the main factor driving the development of scheelite over wolframite within the deposit, which also elucidates the reason that tungsten mineralization associated with orogenic gold deposits predominantly features scheelite. The characteristics of scheelite without oscillatory zoning, high Sr (1180–8600 ppm) and low Mo (bdl-0.18 ppm) concentrations, and flat REE pattern are similar to those of scheelite in orogenic gold deposits worldwide. The high 87Sr/86Sr ratio (0.7539–0.7663) indicates that the tungsten-bearing ore-forming fluids derived from deep-seated metamorphic fluids.

Subduction-related mafic-silicic magmatism in the Nubian Shield: Tectono-magmatic implications of ensialic island arc association at Central Eastern Desert, Egypt.

For the Wadi El Mayet, the metagabbro-granodiorite-tonalite intrusive complex (MIC) occupies the eastern sector of famous wadi Mubarak–Dabr complex which considered as the largest intrusion in the Egyptian Eastern Desert. The basement associations in the area include volcano-sedimentary rocks, metavolcanics, and ultramafics. The whole successions were intruded by MIC, and granites. The (MIC) comprises multifarious gabbroic varieties namely: olivine, pyroxene, hornblende, uralitized gabbros and rare amphibolites, while silicic portion includes tonalite and granodiorite. Microprobe analytical chemistry of gabbros and granites refers that: the amphiboles are calcic magnesio hornblende formed at low pressure conditions. Chlorites have corundophillite composition. Plagioclase range between labradorite, andesine and oligoclase. Biotite is mainly siderophylite. Muscovite minerals are mainly cheladonite. Geothermo-barometers calculations reveal crystallization temperatures of 550 °C and 860 °C for granites and metagabbros respectively. The (MIC) cover a wide silica range (44.5–74.5 wt %). It has transitional tholeiitic to calc-alkaline magmas. The gabbroic rocks show distinct fecundity with LILE (e.g. Rb, Ba, U and Th), but show observed shortage in most HFSE (e.g. Zr, Nb, Ta). The REE patterns show enrichment in light REE and posse variably positive Eu. It is suggested that, the gabbroic units were likely generated by fractional crystallization of mafic magmas produced through partial melting of metasomatized mantle within island-arc environments. Tonalite - granodiorite (TG) suite show calc-alkaline magmas of I-type settings. They also exhibit enrichment in Ba, Zr, Hf, Rb, U and Th, while P, Nb, Ta and Sr are depleted. Such reductions are harmonious with fractionation of K-feldspar phases. The (TG) show enrichment of (LREE) compare to (HREE) this proposes either the existence of persistent garnet or LREE fertile magma sources. The (TG) is believed to be formed through dehydration melting processes at lower crust settings. Based on the field, geochemistry and structure elements, the investigated mafic and silicic suites are not linked to a single magma origin. The (MIC) can be comparable with intrusions formed in ensialic island-arcs settings. At subduction zone integration between mantle (basaltic suites) and silicic magmas from lower crust forming the early stages of (MIC) crystallization. The whole association was suffered by insignificant fractionation processes and addition of crustal materials during the final stages of (MIC) emplacement.

Late Cryogenian and early Ediacaran rare-metal rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb-isotopic compositions

Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian–Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U–Pb ages and O-isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628–633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7–678.9 Ma with δ 18 O V-SMOW c . 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material : Details of analytical details and supplementary tables and figures are available at https://doi.org/10.6084/m9.figshare.c.6949402

The December 2018 eruption at Etna volcano: a geochemical study on melt and fluid inclusions

This study focus on the Mt Etna December 2018 eruption with the aim of investigating the geochemical characteristics of the feeding magma. New data on major and trace element geochemistry of olivine-hosted melt inclusions (MI) in volcanic products are presented together with the noble gas geochemistry of fluid inclusions (FI) in olivines. The noble gas geochemistry of fluid inclusions (FIs) in olivines was also investigated. The major element composition of MIs is variable from tephrite/trachybasalt to phonotephrite/basaltic trachyandesite, with SiO2 = 45.51–52.72 wt%, MgO = 4.01–6.02 wt%, and CaO/Al2O3 = 0.34–0.72. Trace element patterns of MIs present a typical enrichment in LILE and LREE, depletion in HFSE, and relatively fractionated REE patterns: (La/Lu) N= 18.8–41.08, with Eu/Eu* = (0.5–1.8). Positive anomalies in Sr (Sr/Sr* = 0.8–2.3) and Ba can be ascribed to the assimilation of plagioclase-rich cumulates in the magmatic reservoir. The variable Ba/La (9.8–15.8), K/Nb (260–1037), Ce/Nb (1.9–3.4), Rb/La (0.4–1.6), and Ba/Nb (10.8–25.8) ratios reveal mixing between two types of end-member magmas comparable to those emitted from 1) the 2001 Upper Vents and 2002–03 Northern Fissures (Type-1) and 2) the 2001 Lower Vents and 2002–03 Southern Fissures (Type-2), respectively. Type-2 represents a magma that was under the influence of a crustal component, whereas Type-1 is compatible with a HIMU–MORB-type heterogeneous mantle source. It appears that the 2018 MIs have captured the two different types of magmas, and the lack of homogenization may imply a very fast ascent (a few months). Compatible with the contemporary presence of primordial HIMU–MORB and crust-contaminated end-members are the data on noble gases from FI that highlighted an 3He/4He value of 6.5–6.6Ra. The hypothesis of two different types of magmas, identified by the trace element geochemistry in MIs, is, thus, reinforced by helium isotopic data on FI of the 2018 eruption together with data from other Etnean eruptions and allows the inference of a bicomponent magma mixing.

Depositional age and formation conditions of Archean banded iron formations, Bundelkhand Craton, Central India: Geochemistry, neodymium isotopes and U-Pb zircon geochronology

In this study, we present major and trace element concentrations, U-Pb zircon geochronology as well as neodymium isotopic compositions of the banded iron formations (BIFs) from the Bundelkhand Craton, India. The study aims to constrain the source characteristics, depositional age and evaluate the paleoenvironmental implications of the Meso-Neoarchean seawater from which the BIF precipitated. The presence of a 2898 ± 26 Ma rounded zircon grain in the Girar BIFs indicates their maximum depositional age, which is consistent with the reported age of the metabasalts (2989 ± 190 Ma). Bearing in mind the errors, we consider the age of the studied BIFs to be ca. 2850 Ma. The BIFs from Mauranipur are associated with 2810 Ma dacite and formed at the same time. They have zircon with ages of 2718 ± 22, 2573 ± 66, 2070 ± 29 and 1934 ± 39 Ma. The BIFs from Babina are associated with 2540 Ma felsic volcanics and can be considered of the same age. Our study shows that the sedimentation of BIF in the Girar and Mauranipur greenstone belts took place in the Mesoarchean between ca. 2850 and 2810 Ma, respectively, and in the Babina greenstone belt in the Neoarchean at ca. 2540 Ma.A positive correlation between TiO2 and Zr, Al2O3 and Zr, Zr and Th/U, Y and Zr, Ni and Cr, as well as Hf and Zr, may suggest a detrital component to the BIF derived from terrigenous mafic and felsic sources. The PAAS-normalized REE patterns of the Bundelkhand BIFs are characterized by depleted LREEs, positive La, Eu, Y anomalies and Y/Ho ratios mostly ranging between 18 and 47. The studied BIFs are broadly similar to worldwide BIF occurrences at the time with the exception of the Mauranipur BIFs, which show elevated MnO concentrations (0.92 to 4.82 wt%). The studied BIF samples from the Bundelkhand Craton display a wide range of εNd(t) ranging from −6.57 to + 4.12. The broad range of isotopic values along with the above-noted geochemical signatures suggest that the BIF from the Bundelkhand Craton had significant inputs from submarine hydrothermal sources as well as pre-existing continental crust. The elevated manganese concentrations in BIFs from Mauranipur may imply the availability of free oxygen in seawater on the Bundelkhand Craton during the Mesoarchean.

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.

REE and trace element mobility during the transformation of basalt to laterite and bauxite, Payas Province, Türkiye

The bauxites of the Payas area in the eastern Mediterranean region of Turkey occur as a stratigraphically continuous layer between Early and Late Cretaceous shallow marine carbonates. The laterites represent an in situ formation and mark a key stratigraphic layer in the region. Bauxite pockets are also present in the laterites, formed from the reworking of the laterites and accumulated in depressions in the karst terrain. Therefore, bauxite occurrences are found locally in this stratigraphic layer. The parental rock was a Ti-rich basalt that is compositionally similar to Hawaiian basalts, as indicated by petrographic features and distinctive trace element composition (Zr/TiO2 and Nb/Y). The behavior of elements during the lateritization and bauxitization processes was interpreted using the composition of the Hawaiian basalts with the iron laterite and Ti-rich bauxites of the Payas Region. During lateritization, Fe, Al, Ti, Cr, Nb, and Ta, were largely immobilie while REE and other trace elements, except for Rb, Ni, Co, and Pb were significantly removed. Approximately 75 % of the REE were removed at the end of the bauxitization and/or transportation of the lateritic soil into the karstic depressions. REE were not equally mobile with La to Ce and Lu to Yb having a relatively lower mobility than highly mobile middle REE. During the transformation of laterite to bauxite, low mobility elements such as Ti, Nb, Th, Cr, Hf, and Sn were enriched in the bauxite phase. In comparison to other elements, Rb, As, Pb, Mo, and Ni were strongly removed from the lateritic material during the bauxitization processes. The transfer of MREE during lateritization and bauxitization would have resulted in the enrichment of both light and heavy REE (concave pattern) in contemporaneous seawater. In other words, silicate weathering periods on land should be marked by a concave REE pattern with positive Eu anomaly in marine sediments throughout the geological period.

Indosinian anatexis of Paleoproterozoic granites in the east Cathaysia Block, South China

AbstractGranulite facies metamorphism and crustal anatexis exist in the East Cathaysia Block, the exact timing of granulite facies partial melting and its link with orogenesis have not been well constrained. In this study, we carried out petrography, whole rock geochemistry, and zircon U–Pb dating, trace elements and Hf isotopes analyses on Dazhe gneissic granite and banded migmatite from the Badu Group in southwest Zhejiang province in the East Cathaysia Block. The melts were produced through the dehydration of biotite, such as biotite + quartz + plagioclase = orthopyroxene + K‐feldspar + melt and biotite + quartz + plagioclase + sillimanite = garnet + K‐feldspar + melt. Zircons from these rocks show clear core‐rim structure and yield rim and core concordant ages at 233 Ma and 1.83 Ga, respectively. The zircon rims suggesting the melts and the cores are suggesting the protolith of Dazhe gneissic granite and banded migmatite were crystallized from an evolving magma. The zircon cores and rims have negative εHf(t) = −2.2 ~ −6.3 and εHf(t) = −22.8 ~ −32.4, and they give suggestion of the presence of Neoarchean components. Although the major‐element compositions of the gneissic granite and banded migmatite are slightly different, the trace‐element spider diagram and REE pattern show they are similar, and then we find that the protoliths are A‐type granodiorite/diorite. Combined with the published data, we suggested that the Dazhe gneissic granite and banded migmatite were formed through granulite facies partial melting at 233 Ma, which was promoted by crustal shortening and thickening of the collision orogeny between East Cathaysia Block and an unknown terrane with a NNE trend structure line. The protoliths (granite or granodiorite) of Dazhe gneissic granite and banded migmatite crystallized at 1.83 Ga by reworking of the Neoarchean components of East Cathaysia Block. The Paleoproterozoic (1912–1819 Ma) collisional orogeny and the later intraplate rifting stage are corresponding to the aggregation and breakup of the Columbia supercontinent.

Genesis of Sulfide Mineralization in the Gallala Area Kurdistan Region, Iraq: Constraints from Major and Trace Elements of Sulfide Ore Mineralization and their Host Rocks

This article presents and interprets new geochemical data from the Gallala sulfide mineralization, situated in the Choman District of the Kurdistan Region of Iraq close to the Iraq and Iranian border. The host rocks belong to the Walash-Naopurdan Group, which developed in the Paleocene-Eocene age in the Zagros Suture Zone. The ore mineral assemblage of the Gallala area consists of pyrite, chalcopyrite, sphalerite, and magnetite. The mineral chemistry and geochemical analysis indicate that there is a significant variation in concentrations of pyrite, chalcopyrite, sphalerite, and magnetite from the Gallala mineralization. The trace element characteristics of the sulfide mineralization and their host rocks indicate that the ore-forming materials were derived from hydrothermal fluids being interacted with the igneous rocks. The trace element signatures and REE distributions of the studied samples, tectonically lead to suggest island-arc and back-arc environments in the Gallala area. Additionally, the REE patterns of the Gallala sulfides indicate the ore-forming fluids are related to arc-related hydrothermal systems. The integration of geochemical features along with the chemistry of ore mineralization such as the Selenium/Sulfur ratio of pyrite, Co/Ni ratios from both pyrite and chalcopyrite, the Zn/Cd values from the sphalerite, and the petrogenetic discriminate diagrams of magnetite reveal that the genesis of the sulfide mineralization can be attributed to volcanogenic to hydrothermal ore-formations with high to medium temperatures origin.

Genesis and tectonic setting of an Early Palaeozoic skarn in the East Kunlun Orogenic Belt, China: constraints from adakitic rocks and garnet megacrysts

ABSTRACT The East Kunlun Orogenic Belt (E-KOB) in the northern Tibet Plateau has undergone a long multi-stage history of drifting, accretion, and collision of the Proto- and Palaeo-Tethyan oceans. It has been addressed a trench-arc-back-arc basin system of the Proto-Tethys in the E-KOB, and the tectonic history of this major ocean has been well constrained by previous studies. However, the evolution of the back-arc basin still remains unclear. In this study, the Yugusayi monzodiorite, quartz-bearing syenite, and gradually contacted skarn rocks characterized by garnet megacrysts, in the North Qimantagh Belt were investigated. To reveal the tectonic setting and skarnization mechanism, geochemical and geochronological studies were conducted on the intrusions and garnet skarn, and the elemental compositions of the garnet megacrysts were also analysed. These monzodioritic rocks have high MgO (6.87–8.31 wt.%), Sr and La contents, low Y and Yb contents, and relatively high La/Yb (31–55) and Sr/Y (41–51) ratios, resembling to high-Mg adakites. They display right-sloping chondrite-normalized REE patterns, enriched in LILEs, and depleted in Ti with significant Nb-Ta troughs, which are similar to those of continental arc rocks. Zircons from monzodiorite and skarn samples have contemporaneous U-Pb ages of 459 ± 3 Ma and 454 ± 4 Ma with εHf(t) values of − 8.53 to − 4.64 and − 7.7 to + 12.8, respectively. In addition, the chemical zoning garnet megacrysts are composed mainly of grossular and andraditic grossular, and are characterized by spoon-shaped REE patterns. Based on our new data and the regional geology, it can be concluded that the Yugusayi intrusive rocks formed in a subduction-related tectonic setting and resulted in the skarnization. These data not only provide key constraints on the initial subduction of the Qimantagh back-arc basin’s oceanic crust, but also offer a unique opportunity to explore the Caledonian skarnization in the Qimantagh Belt.

Early Paleozoic back-arc basin in the East Kunlun Orogen, northern Tibetan Plateau: Insight from the Wutumeiren ophiolitic mélange

The Early Paleozoic tectonic architecture of East Kunlun Orogen in the northern Tibetan Plateau is crucial to deciphering the tectonic evolution of the Proto-Tethys ocean. The Wutumeiren ophiolitic mélange located in the Qimantagh-Xiangride suture between the North Qimantagh and Central Kunlun belts represents essential records of the Proto-Tethyan tectonic domain. It comprises serpentinite, dolerite, basalt and black chert with minor siltstone. The serpentinites possess high MgO, low SiO2 and ΣREE contents, and are characterized by slight depletion of mid-REE, showing ophiolitic ultramafic affinities. Both dolerites and basalts exhibit tholeiitic compositions with high Mg# numbers, low (Na2O + K2O)/SiO2 ratios and ΣREE contents. In comparison, the dolerites show flat patterns of REE, while the basalts display slight enrichment of LREE. All these features suggest they were generated from an E-MORB-type mantle source by different degrees of partial melting. The cherts exhibit distinctive high SiO2 and low ΣREE contents, and show depletion of LREE with negative Ce anomalies and high Y/Ho rations, indicating they are typical abyssal cherts. Together with the comparable basements on both sides of the suture, a back-arc basin setting is suggested for these ophiolitic components. The SHRIMP zircon U–Pb age of 416 ± 34 Ma for the basalt, and the youngest age of 490.6 ± 6.6 Ma for the black siltstones interbedded with cherts signal the back-arc basin from ca. 490–416 Ma. We thus infer a west-Pacific-type active continental margin in the East Kunlun Orogen associated with the northward subduction of the Proto-Tethys oceanic crust in the Early Paleozoic.

Apatite geochemical composition of Mesozoic granitoids in the eastern Jiangnan Orogen, S. China: insights into petrogenesis and intrinsic magmatic variables

ABSTRACT The geochemical compositions of apatite are commonly used to provide reliable constraints on the intrinsic magmatic variables of the parental magma. There is a widespread distribution of Mesozoic granitic rocks in the eastern Jiangnan Orogen (EJNO), which include I-type and A-type granitoids. This study aims to investigate the geochemical composition of apatite in 11 representative I-type and A-type granitic intrusions from the EJNO to understand their petrogenesis, intrinsic magmatic variables, and polymetallic mineralization potential. The results show that apatites in these granitoids were characterized by oscillatory zonation and homogeneous texture, and exhibited high F, and low Cl contents, as well as high REE, Y, and Th contents, indicating magmatic origin. These apatites were divided into two groups depending on their geochemical characteristics and original rock types. In Group I apatites (in the I-type granitoids), the absence of an abrupt change in major and trace element concentrations from the core to the rim of the apatite crystals, combined with their low levels of MgO, Sr, and HREY (HREE+Y), serves as evidence to classify the I-type granitoids as low Sr-Y adakitic granitoids with a low Mg#, which can be attributed to the partial melting of the thickened lower crust. In Group A apatites (in the A-type granites), the normal increase in incompatible elements from the core to the rim, as well as the presence of a flat REE pattern with pronounced Eu anomalies, can be attributed to crystal fractionation of plagioclase, allanite, and zircon. Furthermore, Group I apatites have higher SO3, Cl, and molar OH/F and Cl/F ratios compared to Group A apatites. Quantitative calculation by apatite-melt partitioning and modelling suggests that the I-type granitic magmas were more volatile-rich and more oxidized than A-type granitic magmas. Taken together, based on the relationship between the intrinsic magmatic variables and the behaviour of ore-forming elements, our study demonstrates that early I-type granitoids of the EJNO have a strong W-Mo-Cu polymetallic mineralization potential, while late A-type granites may possess rare metal mineralization potential.

Deciphering the ore-forming process of Sb-W deposits through scheelite and stibnite trace element geochemistry

Antimony (Sb) and tungsten (W) and deposits typically form in distinct and unrelated ore-forming environments. However, in rare cases, ore deposits may present combined Sb-W mineralization within a single deposit. These contrasting occurrences introduce uncertainty within the Sb-W ore deposit model, which ultimately guides mineral exploration strategies. Scheelite and stibnite are prevalent ore minerals in Sb-W deposits, making their trace element compositions valuable for enhancing our understanding of the genesis of Sb-W ore systems. In this study, we conducted a systematic investigation of trace element compositions in scheelite and stibnite samples from the Chashan and Zhazixi Sb-W deposits in South China to decipher the primary ore-forming processes. Scheelite from the Sb-W deposits is characterized by low Na, Nb, Ta and Mo contents, and variable Nb/Ta ratios. These results present a remarkably different geochemical signature when compared with granite-related W deposits, indicating that W mineralization in Sb-W deposits was derived from a non-magmatic origin. Moreover, when combining the trace element signature with reported fluid inclusion and isotopic data, it can be concluded that ore-forming fluids of the Chashan and Zhazixi Sb-W deposits were primarily composed of deep-circulating meteoric groundwater. Scheelite from the Chashan deposit presents relatively flat REE patterns with large positive Eu anomalies, whereas the Zhazixi deposit is characterized by bell-shaped REE patterns with weak Eu anomalies. This suggests that the two Sb-W deposits may differ slightly in their source rock composition, which is also supported by the different trace element compositions of stibnite. Stibnite from the Zhazixi deposit is relatively enriched in As, Se and Pb, whereas stibnite from the Chashan deposit contains higher Sn, Zn, Mo, Ag, In and Sr, further indicating that the initial fluids of the two deposits may have undergone different degrees of fluid-rock interaction with their distinctive source rocks. This study demonstrates that the genesis of the Zhazixi and Chashan Sb-W deposits significantly differ when compared to the ore-forming processes that control granite-related W or metamorphic W deposits. Moreover, the formation of these Sb-W deposits appears to share a similar genetic model consistent with low-temperature Sb deposits in South China. In this model, deep-circulating meteoric groundwater infiltrates and leaches Sb and W from fertile source rocks through fluid-rock interaction. Concealed granites may have solely served as a thermal source for the convection and upward migration of ore-forming fluids, while the fertility of source rocks and the intensity of fluid-rock interaction are expected to have played a crucial role in the formation of Sb-W deposits.

Geochemistry of the Triassic metacarbonate rocks from the Sakar Unit, Sakar-Strandzha zone, SE Bulgaria

The geochemistry of Triassic metacarbonate rocks from the Sakar unit, Sakar-Strandzha zone recorded condition on deposition environments and primary (protoliths) composition. The metacarbonate yielded trace element distribution that conform seawater condition on shallow shelves under oxic conditions and coincide interpretation of Chatalov (1990). The REE pattern determines low to moderate contamination of terrigenous material. The significant variation of Sr can be efficient for distinguish the metacarbonates in SE Bulgaria.

Geochemical dichotomy of Tethyan oceanic mantle and the supercontinent connection: Insights from Os isotopic signatures of mantle peridotites from Naga Hills ophiolite

Naga Hills Ophiolite (NHO) represents a thrusted section of relict Neo-Tethyan oceanic lithosphere comprising distinct crustal and upper mantle lithologies that preserve imprints of different stages of evolution of ancient ocean basins and subsequent accretion onto continental margins during late Cretaceous-Eocene collision involving Indian and Eurasian Plates. This study presents bulk geochemistry and Re-Os isotopic compositions for the mantle peridotites of NHO to address their petrogenetic aspects, implications for Neo-Tethyan upper mantle heterogeneity and thermo-tectonic evolution of Neo-Tethyan oceanic lithosphere through subduction-accretion-collision processes. Geochemical characteristics of the mantle peridotites, as reflected from their chondrite normalized REE patterns, binary relationship between fractionation depletion indices, low Re/Os, suggest that these are mantle residues resulting from ∼ 5–20 % of melt extraction from a spinel peridotite source that experienced decompression melting in a fore-arc extensional setting in response to subduction initiation. Isotopically, these mantle peridotites are subchondritic with 187Os/188Os (0.1218–0.1266) and γOs values of −3.73 to −0.09 comparable with the depleted MORB source. LILE-LREE enrichment, HFSE depletion, and U-shaped chondrite-normalized REE patterns demonstrated by the studied samples with Re addition collectively corroborate multistage petrogenetic processes in compliance with geodynamic transition from extensional to compressional regime in a suprasubduction zone environment and partial melting of a chemically heterogeneous source mantle. This compositional heterogeneity can be equated with mantle depletion by melt extraction and refertilization by influx of slab-dehydrated fluids and percolation of boninitic melts. The non-radiogenic Os isotope signatures, negative γOs values and wide spectrum of melt extraction ages for these mantle peridotites correspond to (i) multiple melt production and melt extraction events prior to the opening of Neo-Tethyan seaway (ii) detachment and incorporation of ancient, depleted SCLM fragments into oceanic mantle concurrent with subduction driven ocean basin closure-congregation of Gondwana Supercontinent and emergence of Neo-Tethyan embryonic ocean in response to disintegration of Gondwana Supercontinent.

Assembling the Proto-Yangtze Block in the late Paleoproterozoic: Constraints from a refined Magmatic-Metamorphic framework of the Cuoke Complex, SW China

The Archean-Paleoproterozoic records of the southwestern and northern Yangtze are key components in establishing the early history of the Yangtze Block as a whole. To date, knowledge of the late Paleoproterozoic evolutionary history of the Yangtze Block has been largely derived from its northern margin. This study documents the presence of ca. 1.93 Ga metamorphic zircons and 1.89–1.86 Ga metamorphic-hydrothermal reset zircons from igneous rocks in the Cuoke Complex of southwestern Yangtze, as well as ca. 1.93 Ga and 1.86 Ga xenotime growths in a meta-volcaniclastic rock (tuff). In addition, the origin of 2.0–1.85 Ga zircons from magmatic rocks in both the Cuoke and Phan Si Pan complexes of the southwestern Yangtze Block are reassessed. Based on new and published CL images, U contents and REE patterns, we argue that the 2.0–1.85 Ga ages are reset from primary 2.3 Ga magmatic zircons during a widespread metamorphic-hydrothermal overprinting event. Integrated U-Pb data reveal two metamorphic peaks at 2.0–1.95 Ga and ca. 1.85 Ga in both northern and southwestern Yangtze, indicating the two domains came together at 2.0–1.95 Ga to form the proto-Yangtze Block. The geological records of northern and southwestern Yangtze match well with those of northern Laurentia and Siberia, respectively, suggesting an internal location for the proto-Yangtze Block within Nuna. This contrasts with its inferred external location within the Rodinia supercontinent, suggesting the transition between the two Proterozoic supercontinents involved significant reconfiguration of at least some of the constituent core continental blocks.