eHf Values Research Articles

Genesis of the Yangyugou syenite-carbonatite complex-related REE deposit in the Qinling Orogenic Belt, Central China: Constraints from zircon U-Pb geochronology, Hf isotopes, and mineral geochemistry

The Qinling Orogenic Belt (Central China) is a world-class rare earth element (REE) metallogenic belt in which REE deposits are mainly hosted by alkaline rocks and/or carbonatites. The newly discovered Yangyugou REE deposit, hosted by alkaline complexes in this belt, is unusual because the REE mineralization mainly takes the form of Ba- and REE-bearing minerals, such as barytocalcite. In this study, we present whole-rock major and trace elements, zircon geochronology, Hf isotopes, and mineral geochemistry to investigate the enrichment of REE and Ba and origin of this deposit. The REE-bearing alkaline complex at the Yangyugou deposit consists of syenite and carbonatite. Carbonatite exhibits higher concentrations of REE and Ba compared to syenite. The concentrations of REE and BaO in the carbonatite can be up to 6214 ppm and 22.4 wt%, respectively, and exhibit a positive correlation. The carbonatite contains numerous Ba-rich minerals, primarily comprising barytocalcite and a smaller amount of bazirite. The REE concentrations of barytocalcite range from 3059 to 10032 ppm, and the Ba concentration can be as high as 37.4 wt%. The barytocalcite is the primary carrier of REE and Ba in the Yangyugou carbonatite. Zircons from the syenite have a 206Pb/238U weighted mean age of 438.9 ± 3.3 Ma (MSWD = 1.08). The εHf(t) values of these zircons range from −8.28 to −3.17, with two-stage Hf model ages of 1.61–1.93 Ga. Apatite from the syenite has initial 87Sr/86Sr ratios of 0.70906 to 0.70984. Our study indicates that syenite-carbonatite complex was probably derived from the enriched mantle that has been metasomatized by a Ba-rich fluid, and that the early Silurian alkaline magmatism may be related to the opening of the Erlangping back-arc basin.

Geochemical Composition Variations and Tectonic Implications of the Baoligaomiao Formation Volcanic Rocks from the Uliastai Continental Margin, Southeast Central Asian Orogenic Belt

Abstract The Permo-Carboniferous tectonic evolution in the Uliastai continental margin (UCM), north of the southeast central Asian Orogenic Belt, remains controversial. This work examined the geochemical composition of the felsic volcanic rocks from the lower and upper part of the Baoligaomiao Formation in the UCM. Zircon U-Pb ages reveal that the Baoligaomiao Formation has a long-lived eruption duration, from ca. 285 to 328 Ma. The lower part (ca. 328–310 Ma) of the Baoligaomiao Formation is dominated by clastic and pyroclastic rocks with subordinate intermediate-felsic volcanic rocks, whereas the upper part (ca. 307–285 Ma) mainly consists of felsic volcanic rocks and pyroclastic rocks. Calculations reveal that the felsic volcanic rocks from the lower part have low zircon saturation temperatures (TZr = 747℃–795℃), whereas those from the upper part exhibit high TZr (ca. 793℃–930℃). Zircons from the lower part exhibit high εHf(t) values and 176Lu/177Hf ratios, in contrast to the low εHf(t) values and 176Lu/177Hf ratios of zircons from the upper part. Those petrogeological and geochemical shifts might support the tectonic switch model in the UCM at the end of the Carboniferous, providing new constraints on the Late Carboniferous closure of the Hegenshan Ocean.

Geochemistry and zircon U–Pb dating of amphibolite in the Menderes Massif (western Türkiye): first record of Late Devonian extension

ABSTRACT The timing of extensional events in northern Gondwana remains elusive. In relations to this event, a new zircon U-Pb age and Hf isotopic compositions, and whole-rock geochemistry provided here for the amphibolites in the basement unit of the Menderes Massif (MM) within the Anatolide-Tauride Block (ATB). LA-ICP-MS U-Pb zircon dating of one sample yielded a crystallization age of 367.0 ± 2.5 Ma, providing the first record of Late Devonian (Famennian) mafic magmatism in the Menderes Massif. This sample contains inherited zircon grains with ages spanning from 588 Ma to 541 Ma, likely sourced from late Neoproterozoic country rocks. Chondrite-normalized rare earth element patterns exhibit enrichment in light rare earth elements and flat patterns for heavy rare earth elements, suggesting affinities with tholeiitic EMORB and ocean island basalt. The geochemical data, coupled with the positive εHf(t) values ranging from 0.5 to 7.8, indicate that the amphibolite likely originated from juvenile melts generated by partial melting of the asthenospheric mantle. This melt was subsequently modified by crustal contamination and fractional crystallization. Contemporaneous EMORB- and OIB-like mafic rocks are identified in the eastern Taurides and Iran, respectively. Both regional geological and geochemical evidence proposes that Late Devonian magmatism in the Anatolide-Tauride Block occurred in a within-plate tectonic setting. This magmatic activity might have been triggered by the northward subduction of the Paleotethys beneath the Pontides during the Devonian, a process that would produce a slab-pull force, creating an extensional tectonic regime along the northern margin of Gondwana.

Mesozoic crustal reworking at different depths in the North China Craton: Insight from the coexisting Early Cretaceous high and low Sr/Y granitoids

Crustal reworking, an important part of continental evolution, can occur in cratons even though they are generally rigid and stable. However, the reworking mechanisms are still debated. Here, we present detailed zircon UPb ages, mineral compositions, major and trace elements, and Sr–Nd–Pb–Hf isotopic data for the coexisting high and low Sr/Y granitoids in the Liaodong Peninsula to decipher the reworking mechanism in the eastern North China Craton (NCC). Mafic microgranular enclaves (MMEs) are common in the studied granitoids, and both the granitoids and their MMEs have consistent emplacement ages of 128–126 Ma. The low and high Sr/Y granitoids are characterized by high-K calc-alkaline I-type granites. They are enriched in light rare earth elements (REEs) and large ion lithophile elements (e.g., Rb, K, and Pb), with depletions in high field strength elements (e.g., Nb, Ta, P, and Ti). The low Sr/Y granitoids have homogeneous Sr–Nd–Pb-Hf isotopic compositions, indistinguishable from those of their MMEs, indicating that they are of cognate origin. Their high (87Sr/86Sr)i (0.713759–0.715341), low εNd(t) and εHf(t) values (−19.2 to −18.1 and − 20.9 to −15.0, respectively), and old two-stage Nd and Hf model ages (ca. 2.50 Ga) suggest that they are derived from partial melting of the ancient lower crust at a normal crustal depth. In contrast, the high Sr/Y granitoids show more depleted heavy REEs and higher Sr/Y (21.1–80.2) and (La/Yb)N (19.2–50.2) ratios, with very low Y (≤ 12.5 ppm) and Yb (≤ 1.11 ppm) contents and negligible Eu anomalies. Their enriched and variable Sr–Nd–Pb-Hf isotopes (e.g., εNd(t) = −20.8 to −14.9, εHf(t) = −24.3 to −9.2) are distinctly different from those of their MMEs (e.g., εNd(t) = −17.6 to −13.2, εHf(t) = −20.8 to −0.3), implying a magma mixing process. These features suggest that the high Sr/Y granitoids and their MMEs are formed by mixing of the thickened ancient lower crustal and lithospheric mantle-derived magmas, with minor contributions of the asthenospheric mantle. Combined with the coeval (129–114 Ma) high-Mg adakitic and A-type granitoids, the coexisting high and low Sr/Y granitoids may indicate intensive crustal reworking at variable depths in the NCC. The reworking is attributed to the asthenosphere upwelling and lithospheric delamination induced by the rollback of the subducting Paleo-Pacific plate.

Tracking carbonatitic melt infiltration in the Miaoya carbonatite–syenite complex (central China) from zircon textures and geochemistry

The Miaoya carbonatite-syenite complex, located at the Qinling Orogenic Belt (central China), which hosts both Nb and REE mineralization. We studied the relationship of zircon grains within the carbonatitic and syenitic matrix by scanning electron microscope and optical microscopy combined with cathodoluminescence (SEM– and OM–CL) to identify primary versus secondary features. The primary zircon grain zones with magmatic oscillatory zoning and dull CL luminance crystallized at a relatively early stage of magma differentiation. In contrast, the secondary zones of zircon grains showing bright CL luminance were formed by recrystallization and contained numerous fractures with micro-inclusions of calcite and apatite, etc. The complicated texture of zircons strongly implies that zircons in both syenite and carbonatite had experienced solid-state recrystallization and dissolution-reprecipitation processes, respectively. Temperatures calculated using the Ti-in-zircon thermometer are ∼ 600 ℃ for the secondary zircons both in syenite and carbonatite. Hence, recrystallization processes were probably caused by varying degrees of metasomatic reactions involving late-stage residual carbonatitic melts, which were initially generated by silicate–carbonate liquid immiscibility at an earlier stage of magma evolution. The metasomatic reactions led to distinct geochemical and isotopic compositions of the secondary zircon. For instance, the secondary zircon is characterized by relatively lower concentrations of trace elements (e.g., REE, Th, U and Pb), LREE/HREE ratios, disturbances of the U–Pb ages and heterogeneous εHf(t) values (0.41 to 10.2). Our results imply that metasomatism due to infiltration of late-stage residual carbonatitic melts could play an important role in the evolution and of carbonatite-syenite system and related mineralization.

Geochemistry, Chronology and Tectonic Implications of the Hadayang Schists in the Northern Great Xing’an Range, Northeast China

The Late Paleozoic tectonic evolution of the Xing’an block in the eastern Central Asian orogenic belt has long been the subject of debate. In this paper, a comprehensive study of U-Pb zircon ages, Lu-Hf isotopes and whole-rock elemental analyses was carried out on Hadayang schists. Representative samples of the epidote-biotite-albite schist and biotite-albite schist yielded the weighted mean 206Pb/238U ages of 360 ± 2 Ma and 355 ± 3 Ma, respectively. This indicated the presence of Late Devonian–Early Carboniferous intermediate-basic rocks in the eastern Xing’an block. The Hadayang schists exhibited a Na-rich, tholeiitic and calc-alkaline affinity in composition with low Mg# (35.2–53.0), Cr (23.7–86.5 ppm), Ni (21.1–40.0 ppm) and Co (12.1–30.6 ppm). They were characterized by enrichment of LILEs, depletion of HFSEs and highly positive zircon εHf(t) values (the average values were +8.93 and +9.29, respectively). The magma source of the Hadayang schists was a mantle that consisted of both spinel and garnet lherzolite, with a partial melting degree of 1%–5%, and it had undergone fractional crystallization of olivine, orthopyroxene and plagioclase. The Hadayang schists, together with other Late Devonian–Early Carboniferous intermediate-basic magmatic rocks in the eastern Xing’an block, were formed in an intracontinental extension tectonic setting similar to that of the North American Basin and Range basalt. Moreover, Late Devonian–Early Carboniferous ophiolite under a similar tectonic background in the western Xing’an block has been reported. We believe that the Xing’an block would - have been in the stage of intracontinental extension during the Late Devonian–Early Carboniferous.

A brief introduction to the detrital zircon U–Pb and Hf isotopic datasets for mainland China and adjacent regions

AbstractImprovements in analytical technique and data processing lead to a large deposit of detrital zircon U–Pb and Hf isotopic data in published journal articles, thesis and reports. With the support of Deep‐time Digital Earth Big Science Program, OneSediment Project conducted a team‐working effort to assemble the detrital zircon U–Pb and Hf isotopic data for mainland China and adjacent regions. Entity‐relationship diagram was constructed for detrital zircon data to determine what information need to be collected. Researchers and students from 13 institutions were organized together to fulfil this task and generated 13 detrital zircon datasets. The assembled datasets totally include 6635 samples and 560,596 analyses. The samples were checked in terms of lithology and stratigraphy according to the latest stratigraphic framework. Collected detrital zircon U–Pb and Hf isotopic data were recalculated for the best U–Pb age and εHf(t) values. They can be used to track crustal growth, tectonic evolution, provenance analysis and palaeogeographical change in regional and, when combined with other dataset, global scales.

Identifying crustal contributions in the Patagonian Chon Aike Silicic Large Igneous Province

The volcanic rocks of the Chon Aike Silicic Large Igneous Province (CASP) are recognized as magmas dominantly produced by crustal anatexis. Investigating the zircon of the CASP provides an opportunity to gain further insight into geochemical and isotopic differences of the potential magmatic sources (i.e., crust versus mantle), to identify crustal reservoirs that contributed to the felsic magmas during anatexis, and to quantify the contributions of the respective sources. We present a combined zircon oxygen and hafnium isotope and trace element dataset for 16 volcanic units of the two youngest volcanic phases in Patagonia, dated here with LA-ICP-MS U–Pb geochronology at ca. 148–153 Ma (El Quemado Complex, EQC) and ca. 159 Ma (western Chon Aike Formation, WCA). The EQC zircon have 18O-enriched values (δ18O from 7 to 9.5‰) with correspondingly negative initial εHf values (− 2.0 to − 8.0). The WCA zircon have δ18O values between 6 and 7‰ and εHf values ranging between − 4.0 and + 1.5. Binary δ18O-εHf mixing models require an average of 70 and 60% melt derived from partial melting of isotopically distinct metasedimentary basements for the EQC and WCA, respectively. Zircon trace element compositions are consistent with anatexis of sedimentary protoliths derived from LIL-depleted upper continental crustal sources. The overlap between a high heat flux environment (i.e., widespread extension and lithospheric thinning) during supercontinental breakup and a fertile metasedimentary crust was key in producing voluminous felsic volcanism via anatexis following the injection and emplacement of basaltic magmas into the lower crust.

Geodynamic evolution in the post-collisional stage of the East Kunlun Orogenic Belt: constraints from the Late Triassic intermediate–felsic igneous rocks

The Late Triassic igneous rocks associated with post-collision are widely distributed in the East Kunlun Orogenic Belt (EKOB), but their specific dynamic mechanism and evolutional process are still controversial. To address these key issues, we investigated the geochronology and geochemistry of intermediate–felsic igneous rocks from the EKOB, including trachyandesite, rhyolite, porphyritic monzogranite, syenogranite, granite porphyry and crystalline tuff. Zircon U–Pb isotopes of these rocks indicate that they were formed between 231.1 and 215.8 Ma (i.e. Late Triassic). These igneous rocks have moderate to high SiO2 (60.29–79.56 wt%) and low mantle compatible element contents (e.g. Co: 0.37–12.62 ppm; Ni: 1.55–15.59 ppm), suggesting that continental crustal-derived material played an important role in their formation. Porphyritic monzogranite (231.1 Ma), syenogranite (228.1 Ma), trachyandesite (227.4 Ma) and rhyolite (215.8 Ma) have Nb/U (1.41–4.71) and Ce/Pb (1.48–6.19) ratios like that of the crust, with εHf(t) values (–1.31 to 2.26) and old two-stage model (TDM2) ages of 1340–1119 Ma, suggesting that they originated from the partial melting of a Mesoproterozoic crust with minor mantle material involved in their source. Crystalline tuff (224.6 Ma) and granite porphyry (222.3 Ma) have Nb/U (1.93–3.81) and Ce/Pb (0.30–3.18) ratios, negative εHf(t) values (–7.04 to −5.12) and old TDM2 ages (1703–1581 Ma) closer to those of crust, suggesting that they were derived from the partial melting of a Paleo–Mesoproterozoic continental crust without addition of mantle material. Based on our new data and published data, the Late Triassic igneous rocks from the EKOB can be divided into three stages, 236–227, 226–218 and 216–208 Ma, corresponding to slab break-off, lithospheric mantle delamination and thickened lower crust delamination, respectively.

Geodynamic regime of the southeastern North China Craton before the Tectono-Magmatic Lull: evidence from ca. 2510 Ma and 2430 Ma igneous rocks in the Xuhuai micro-block

ABSTRACT The Tectono-Magmatic Lull (TML) refers to the period between 2.37 and 2.24 Ga when magmatic activity declined globally, the cause of which remains debated. The North China Craton (NCC), which was formed by assembling several micro-blocks in Neoarchean to Paleoproterozoic, preserves the most records of magmatism across the TML. In this contribution, we report petrological, geochemical, and zircon U-Pb-Hf isotopic data of Paleoproterozoic basement rocks from the Xuhuai (XH) micro-block in the southeastern part of the NCC, and use them to constrain the geodynamic regime at the onset of the TML. Our data reveal that the central part of the XH micro-block is mainly composed of biotite granodioritic gneiss and plagioclase amphibolite, which is divided into a ca. 2510 Ma suite of low- and medium-pressure TTGs and a ca. 2430 Ma bimodal igneous suite including high-pressure TTG and plagioclase amphibolite. Variable magmatic zircon εHf(t) values (1.9 to 7.2), Nb, Ta and Ti anomalies for the 2510 Ma TTGs indicate that the parental magma, which was involved with mantle materials, was generated in an active subduction environment in this pre-TML era. The felsic component of bimodal igneous rocks with high Na/Ta ratios (27 to 30) and stable Mg# (41 to 44) suggests their magma source region was as deep as the rutile stability field, and the delamination-derived asthenosphere mantle ascending. The influx of hot mantle induces thermal weakening and mechanical stretching of the overlying crust, leading to back-arc extension. The results of this study support the hypotheses that the NCC formed from micro-block amalgamation and the trigger of the TML could be the large-scale delamination of the lower crust into the mantle.

A synthesis of available detrital zircon data from the Qilian‐Qaidam‐Kunlun collage, northern Tibet

AbstractIn this article, we present a brief introduction to the procedure, methods and results of the collection and summarization of an updated detrital zircon U–Pb geochronology database for the Qilian‐Qaidam‐Kunlun collage in northern Tibet. A total of 620 samples with 59,830 raw data were compiled from 121 published papers, including 70 samples with in‐situ detrital zircon Lu–Hf isotopes. Samples from seven different geologic subunits are categorized. For sediments with different ages of deposition, we highlight the characteristics of age spans, probability density distributions, major peaks and εHf(t) values. Further syntheses of this metadata collection, the detailed raw data of which will be periodically accessible in the Deep‐Time Digital Earth repository, would be effectively applied to a variety of scientific attempts concerning the geologic history of the Qilian‐Qaidam‐Kunlun collage, in particular, provenance analyses, crustal evolution studies and supercontinent reconstructions.

Petrogenesis of Paleocene−Eocene gabbros in the Gangdese belt: Geochemical tracking of transitioning from oceanic subduction to continental collision related magmatism in southern Tibet

The composition of the sub-arc mantle and the mode and nature of geodynamic processes during the India-Asia collision that controlled the melt evolution beneath the Gangdese belt (southern Tibet) are still unclear. Here, we present new U-Pb ages and Hf isotopes of zircon, and whole-rock geochemical and Sr-Nd-Pb isotopic data of the Paleocene−Eocene Najinla gabbros from the East Gangdese magmatic belt, aiming to track the transitioning magmatism formed from oceanic subduction to continental collision in the region. Zircon U-Pb analyses of these mafic rocks yield emplacement ages of 54 ± 1 Ma and 63 ± 1 Ma. The gabbros are characterized by variable SiO2 (45.87−55.44 wt%), MgO (1.03−8.18 wt%), FeOT (3.74−12.33 wt%), and Al2O3 (13.45−25.45 wt%) contents. Most samples exhibit high Al2O3 (17.15−25.45 wt%) and relatively low MgO (1.03−6.11 wt%), similar to typical high-alumina basalts and high-alumina basaltic andesites. The Najinla gabbros show characteristic subduction-related signatures with enriched large-ion lithophile elements and depleted high field strength elements. They have depleted Sr-Nd isotopic compositions with low and relatively homogeneous initial 87Sr/86Sr isotopic ratios of 0.7045−0.7049 and positive εNd(t) ratios of +2.2 to +3.2. The Najinla gabbroic rocks also have positive zircon εHf(t) values, ranging from +5.6 to +10.9. These results collectively suggest that magmas of the gabbros formed by partial melting of the asthenosphere with negligible crustal contamination during their emplacement. We propose that the mantle source of the Najinla gabbros was strongly influenced and metasomatized by subducted Neotethyan oceanic crust-derived fluids in the mantle wedge. Rollback of the subducted Neotethyan slab in the early Eocene led to partial melting of the subduction-modified mantle and the formation of these gabbros.

Geochronology and geochemistry of early Paleozoic magmatism in the Qilian orogen: Constraints on closure of the Proto-Tethys Ocean

The Proto-Tethys Ocean was a Neoproterozoic to early Paleozoic ocean that opened upon the breakup of Rodinia and closed by Paleozoic oceanic and continental subduction. The Qilian orogenic belt is the northernmost orogen of the Proto-Tethys domain and consists of the North Qilian belt, the Central Qilian block and the South Qilian belt. The processes responsible for extensive early Paleozoic magmatism in the Qilian orogen are crucial to understanding the closure of the ocean. This paper presents a systematic investigation of early Paleozoic mafic and felsic rocks in the Qilian orogen. Gabbroic dikes from the Central Qilian block have LA-ICP-MS zircon U-Pb ages of 499–497 Ma with a wide range of εHf(t) values of −9.94 to + 4.28 and TDM1 model ages of 1557–929 Ma, and dioritic dikes have a LA-ICP-MS zircon U-Pb age of 489 ± 3 Ma, positive εHf(t) values of +7.61 to +10.53, TDM1 model ages of 684–790 Ma, and an amphibole 40Ar/39Ar age of 486.3 ± 4.3 Ma. Both sets of dikes were derived from partial melting of a heterogeneous spinel-facies lherzolite lithospheric mantle that was modified by fluids and melts from a subducted slab. The protolith of amphibolites from the Hualong block in the South Qilian belt was a mafic intrusion of 454 ± 2 Ma with negative εHf(t) values of −9.69 to −7.79 and TDM1 model ages of 1390–1478 Ma. Its trace element signature indicates that sediment-derived melts were involved in the magma formation. An amphibole 40Ar/39Ar age of 418.7 ± 3.8 Ma from an amphibolite records the timing of amphibolite facies metamorphism. Felsic volcanic tuffs and granitic intrusions from the Central Qilian block have zircon U-Pb ages of 507–440 Ma with a broad range of zircon εHf(t) values of −9.60 to + 11.87 and TDM2 model ages of 2037–584 Ma. They have geochemical characteristics similar to I-type and S-type granites that were sourced from partial melting of juvenile and ancient continental crust with minor input of mantle materials. The formation of the felsic rocks indicates the transition from an arc-related setting to a post-collisional setting. Combining our results with existing data, we suggest that the Central Qilian block was affected by both southward subduction of the North Qilian ocean and the northward subduction of the South Qilian ocean, resulting in the formation of an Andean-type continental arc along the northern margin of the Central Qilian block and a subduction-accretion system along the southern margin of the Hualong block at ca. 530–440 Ma. Collision of the Central Qilian, Hualong, Quanji and Qaidam blocks at ca. 440–418 Ma marks the final closure of the Proto-Tethys Ocean.

Middle Permian granitoids in the western section of the northern Qaidam Block, NW China: Petrogenesis and tectonic implications

Origin and tectonic setting of late Late Paleozoic to Early Mesozoic igneous rocks in the northern Qaidam Block (NQ) have long been a matter of debate. In this paper, we report new zircon U-Pb ages and Hf isotopic compositions and bulk rock major and trace elemental compositions for granitoids of the Yanchangbeishan area in the NQ. The granodiorite, tonalite, granodiorite, and syenogranite yielded zircon U-Pb ages of 271.9 Ma, 262.0 Ma, 272.4 Ma and 261.3 Ma, respectively, corresponding to εHf(t) values are 13.04–14.32, 8.14–10.77, 8.66–11.88, and 8.22–10.43, respectively. These granitoids are compositionally I-type granites and exhibit varying degrees of enrichment in Rb, Th, U, and K, and depletion in Nb, Ta, and Ti. According to field relationships, petrology, geochronology, and geochemistry, the granitoid types can be divided into three groups: (1) ca. 272 Ma granodiorites, which are formed through partial melting of metagreywackes and amphibolites derived from depleted mantle; (2) ca. 262 Ma tonalite, which represents a typical high-silica adakite derived from partial melting of subducted oceanic crust during the evolution of depleted mantle; and (3) ca. 261 Ma syenogranite, which is formed by the partial melting and high-degree fractional crystallization of mixed crustal materials. Considering our findings and the regional geological background, we propose a five-stage tectonic evolution model of subduction slab roll-back and subduction zone retreat for the late Late Paleozoic to Early Mesozoic of NQ.

Geology, geochronology, geochemistry and Hf-Sr-Nd isotopes of the ‘green-bean rocks’ (felsic tuffs) in the western Yangtze Block, China: Implications for genesis and enrichment mechanism of Li

The widespread ‘green-bean rocks’ (GBRs) in the western Yangtze Block (YZB) are traditionally considered to be originally felsic volcanic tuff. These greenish or yellowish green GBRs are characterized by the presence of bean-like grains. Although the GBRs are enriched in Li in addition to K, the enrichment mechanism of Li during the formation process of GBRs remains controversial. Detailed petrography, scanning electron microscopy, X-ray diffraction, whole-rock geochemistry, U-Pb dating and Hf-Sr-Nd isotopes have been conducted on the GBRs from the Longmendong section in the western YZB to shed light on the genesis of GBRs, Li enrichment mechanism, and further exploration.The zircon and apatite from Longmendong GBRs yielded U-Pb ages of 247.2 ± 0.6 Ma and 247.0 ± 11.0 Ma, respectively. Longmendong GBRs show bull-rock (87Sr/86Sr)i ratios ranging from 0.72602 to 0.72948 and εNd(t) values between −9.8 and −10.4. Zircons have low εHf(t) values and old two-stage Hf model ages (TDM2) ranging from −16.1 to −7.4 and 1741 to 2285 Ma, respectively. Apatite grains display high (87Sr/86Sr)i ratios and low εNd(t) values in the range of 0.72225–0.72461 and −9.93–−11.18, respectively. The combined evidence from textures, mineral compositions, whole-rock geochemistry and Sr-Nd-Hf isotopic compositions indicates that the GBRs originated from felsic volcanic ashes that erupted along the Sanjiang Orogen. The magma of volcanic ashes was sourced from the remelting of ancient crust in response to the initial collision of Indochina-Yangtze Blocks during the closure of the eastern Paleo-Tethys Ocean. The apatite grains separated from GBRs show significantly low Sr and Eu contents (136–223 ppm and 4.23–6.53 ppm, respectively) and low (La/Sm)N (0.97–1.11) and (Sm/Yb)N (3.49–4.56) ratios, indicating that apatite crystallized earlier than the plagioclase and the original magma are highly evolved. The magma of GBRs originated from ancient crust with significant differentiation, facilitating the initial enrichment of Li during the magma evolution. On the other hand, the GBRs have elevated levels of K2O, MgO and clay minerals (e.g., illite and illite/smectite mixed layer minerals), which are proportional to the Li concentrations. This suggests that Li in the GBRs is adsorbed by clay minerals in ionic form and experience additional enrichment during the transformation from volcanic ashes into clay minerals. Furthermore, the GBRs in the northeastern Sichuan basin under a limited sedimentary environment have relatively higher Li concentrations, suggesting that continuous evaporation also positively contributed to Li enrichment in GBRs. Geographically, GBRs in the Sichuan basin are closely related to underground Li-rich brines hosted within the adjacent strata. Therefore, the widespread Li-rich GBRs in the western YZB not only hold promise as a potential Li resource, but also serve as a marker layer for the prospecting Li brines in the Sichuan basin.

Zircon U–Pb–Hf isotope and geochemical constraints on the petrogenesis and tectonic setting of Mesoarchean granitoids from the Carajás province, Amazonian craton, Brazil

Based on U–Pb–Hf isotope and whole-rock geochemical data, this paper investigates the origin and tectonic setting of Mesoarchean granitoids from the Ourilândia do Norte area, Carajás province (northern Brazil) and compares them with other Archean units. The following units were selected: (i) tonalite-trondhjemite-granodiorite (TTG) from the Mogno and Rio Verde suites, represented by a 2.92 Ga tonalitic xenolith [εHf(2.92 Ga) = +2.0 to –0.2] and a 2.92 Ga porphyritic trondhjemite [εHf(2.92 Ga) = +2.3 to –3.5], respectively; (ii) the Ourilândia sanukitoid suite, composed of the 2.92 Ga Arraias granodiorite [εHf(2.92 Ga) = +1.9 to –4.4] and 2.88 Ga Ourilândia tonalite-granodiorite complex [εHf(2.88 Ga) = +3.2 to –1.0]; and (iii) the Boa Sorte granite (Canaã dos Carajás granitic suite), which provides four zircon populations dated at 3.04 Ga, 2.98 Ga, 2.93 Ga and 2.88 Ga. The 2.88 Ga population represents the granitic crystallization age, with εHf(2.88 Ga) values ranging from –0.8 to –4.1. The Paleoarchean geological record from the Carajás province is scarce and restricted to detrital zircons (<3.7 Ga), rare xenocrystals (<3.7 Ga) and crustal model ages (Hf-TDMC = 3.6–3.1 Ga), which indicate Paleoarchean crust extraction from the mantle. The zircon U–Pb–Hf isotope and whole-rock geochemistry data from the Mesoarchean granitoids support the hypothesis that the Carajás province experienced mantle enrichment and progressive crustal reworking during 3.1–2.8 Ga, similar to the Mesoarchean record from the Pilbara and Kaapvaal cratons. A proposed three-stage tectonic model explains the petrogenesis and Hf isotope signatures of the studied granitoids. Regardless of the extent of the Paleoarchean geological record, the available data allow us to postulate that the formation of Paleoarchean crust in the Carajás province involved a long-lived dome-and-keel setting (3.6–3.1 Ga), and that this crust was later recycled, allowing mantle enrichment during Mesoarchean low-angle subduction (3.07–2.92 Ga). Then, a short-lived collision defined by peak regional metamorphism (2.89–2.84 Ga) and associated with crustal thickening and slab breakoff gave rise to mantle- and crust-derived magmas at 2.88 Ga.

Late Paleoproterozoic collision-related granitic magmatism in the Cuoke Complex, SW China: New evidence for the early evolution of the Yangtze Block

The Paleoproterozoic tectonic evolution of the southwestern Yangtze Block has been ambiguous due to the scarce preservation of geological records, confusing the history of the entire Yangtze Block in the Nuna supercontinent. We here report an integrated study involving petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf-Nd isotopes of the recently identified late Paleoproterozoic granitoids from the Cuoke Complex in the southwestern Yangtze Block. LA-ICP-MS zircon U-Pb dating reveals three episodes of granitic magmatism at ca. 1.94 Ga, 1.89 Ga, and 1.85 Ga. Geochemically, the ca. 1.94 Ga albite granites (AGs) and ca. 1.89 Ga and 1.85 Ga monzogranites (MGs) exhibit features of I-type granite, while the ca. 1.85 Ga AGs display characteristics of A-type granite. The zircon εHf(t) values range from −13.0 to −8.1 for the 1.94–1.89 Ga granitoids and from −8.9 to −7.2 for the ca. 1.85 Ga granitoids, with two-stage model ages of 3.3–3.1 Ga and ca. 3.0 Ga, respectively, indicative of their derivation from remelting of Mesoarchean crustal materials. The relatively low heavy rare earth elements (HREEs) (e.g., Yb < 1.9 ppm) and Y (<18 ppm) contents, and moderately negative Eu anomalies of the ca. 1.94–1.89 Ga granitiods suggest they may have been produced in a late collisional or earliest post-collisional setting. The ca. 1.85 Ga AGs and MGs were probably formed in a post-collisional setting indicated by their high HREE (e.g., Yb > 1.9 ppm) and Y (>18 ppm) contents and strongly negative Eu anomalies. Combined with available data, we provisionally divided the tectonic evolution of the southwestern Yangtze Block into four stages: 1) ca. 2.01 Ga subduction, 2) ca. 1.97–1.95 Ga metamorphism associated with collision events, 3) ca. 1.94–1.89 Ga late collisional or earliest post-collisional stage, and 4) ca. 1.85 Ga post-collisional extensional stage. The subduction and collision of the southwestern Yangtze Block initiated slightly later than the northern part, but their near-synchronous tectonic process since ca. 1.97 Ga suggest they may have collaged together at that time. The ca. 1.94–1.89 Ga and ca. 1.85 Ga late collisional to post-collisional granitic magmatism likely recorded the convergence of discrete Archean rock provinces of the Yangtze Block during the Nuna supercontinent assembly.

Early Paleozoic granitic magmatism and mineralization in the Debao Sn-Cu deposit, South China: Constraints from zircon and cassiterite U-Pb geochronology and whole-rock geochemistry

Numerous W-Sn deposits are developed in South China. While the majority of these deposits are related to the Yanshanian granites, a few of them are associated with the Early Paleozoic granites, and their geological significance is poorly understood. The Debao deposit is a typical skarn Sn-Cu polymetallic deposit that is spatially related to the Early Paleozoic Qinjia granites. Zircon U-Pb dating of three lithofacies (coarse-grained biotite granite, medium-grained porphyritic biotite granite and fine-grained porphyritic biotite granite) of the Qinjia granites yielded emplacement ages of 437.8 ± 3.0 Ma, 440.2 ± 2.0 Ma and 441.0 ± 3.0 Ma, respectively, consistent with cassiterite U-Pb ages of skarn ore (439.6 ± 2.7 Ma), indicating a close genetic relationship between the granitic magmatism and Sn mineralization. Biotite from the Qinjia granites belong to the ferro-biotite series with relatively high F contents (up to 0.70 wt. %). The Biotite compositions plot near the Ni-NiO (NNO) buffer on a Fe3+-Fe2+-Mg2+ diagram, suggesting formation under relatively low oxygen fugacity. The Qinjia granites are characterized by highly silicious (70.37–72.88 wt. %), high alkali (Na2O + K2O = 6.98–8.88 wt. %) and metaluminous to strongly peraluminous with the A/CNK ratios of 0.92–1.21, belonging to the I-S transform-type granites. They are enriched in U, Th, Zr, Nd and Hf, and depleted in Ba, Sr, Nb, Ta and Ti. They display right-declining chondrite-normalized REE patterns with significant negative Eu anomalies (EuN/Eu* = 0.33–0.66), and have low Nb/Ta and K/Rb ratios, indicating that the Qinjia granites experienced a high degree of fractional crystallization. The zircon εHf(t) values (−2.7 to +1.4), together with TDMC of 1.59 to 1.33 Ga, indicate that the granites formed via partial melting of Mesoproterozoic crustal with minor addition of mantle materials. The reduced (fO2 near NNO and Ce4+/Ce3+ ratios of zircon < 100), fractionated and volatile-rich magma facilitated the enrichment of Sn in the residual melt and hydrothermal fluids. Combined with previous studies on the Early Paleozoic magmatic rocks and tectonic activities in South China, we suggest that the Qinjia granites and associated Sn-Cu mineralization were likely formed in the post-collisional extensional environment during the Wuyi-Yunkai orogeny.

Mid-Cretaceous to early Eocene Neo-Tethyan subduction records in West Sulawesi, Indonesia

Situated in the heart of the Indonesian archipelago, Sulawesi records well-developed Cenozoic magmatism, yet its Cretaceous magmatic evolution remains enigmatic. Here, we report new U-Pb-Hf isotopic data of detrital zircons from West Sulawesi, Indonesia to constrain its Cretaceous to Eocene magmatic tempo. Detrital zircons aged at ca. 105−80 Ma and ca. 70−45 Ma occur as the most dominant age populations and show high positive εHf(t) values, indicating derivation from juvenile sources with limited continental crustal contamination. Our new data, combined with available results, support the existence of an Andean-type continental margin in West Sulawesi during mid-Cretaceous to early Eocene times. Importantly, the magmatic tempo of West Sulawesi is also consistent with those of southern Lhasa (Tibet) and Sumatra (Indonesia), but contrasts with those of Paleo-Pacific subduction-related arcs in SE China, SE Vietnam, East Malaysia, and NW Borneo. Therefore, we put forward that West Sulawesi may be the southeasternmost component of the Neo-Tethyan arc system that spreads over 7500 km, from southern Tibet to SE Sundaland. Such a huge arc system with concurrent magmatic flare-ups and lulls in South Asia may have played a significant role in global-scale plate reorganization.

Atypical chromitite deposit in the Gaositai mafic-ultramafic complex, North China Craton: Geochemical, geochronological, and isotopic systematics

The Gaositai mafic-ultramafic complex in the North China Craton hosts a significant chromitite deposit featuring morphological and geochemical characteristics that deviate from the usual characteristics of typical high-Cr and low-Al podiform chromitites. Field observations and microscopic studies reveal notable variations in textural layering, mineralogy, and geochemical composition, challenging conventional features of stratiform chromitite deposits. Zircon UPb ages indicate that chromitite is most likely Carboniferous-Permian in age (330–275 Ma), but also contains numerous inherited zircons with concordant ages as old as 2544 Ma, reflecting a complex geological evolution. Post-formation metasomatic or metamorphic imprints can be evident by concordant zircon ∼247 Ma. Variable zircon εHf(t) values (−15 to +9.6) and depleted mantle model ages (432 to 2819 Ma) attest the presence of heterogeneous or reworked source materials.The PGE and trace element characteristics of the Gaositai chromitite are comparable to the geochemical features of Bushveld and Great Dyke deposits. Pyrite, millerite, norsethite, galena, and PGM (mainly OsIr alloys) inclusions are ubiquitous in chromite. Galena inclusions with homogenous Pb-isotopic ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) suggest a mixed sources of lead. In contrast, pyrite inclusions display significant variations in δ34SV-CDT values (−0.11 ‰ to 18.31‰) indicative of a crustal origin of sulfur. Bulk-rock ReOs isotope data of 0.1264–0.1294 shows 187Os/188Os ratios similar to abyssal peridotites, implying a potential connection between chromitite and the host ultramafic rocks. Highly disparate mantle model ages (55 to 2141 Ma) and re-depletion ages (28 to 692 Ma) suggest disturbance of the ReOs isotopic system during post-formational metasomatic or metamorphic events. These variations may, alternatively, reflect heterogeneity by subduction components. The obtained results do not support the Alaskan-type genesis of the host complex, but point towards an atypical stratiform type.