Arc magma underplating is a fundamental process in building the continental crust, with zircon Hf–O isotopes widely used to trace its timing and material contributions. A key challenge to this approach is determining whether—and to what extent—high-δ18O zircon can archive crustal growth. By integrating bulk-rock trace element proxies and Nd isotopes, zircon Hf–O isotopes and xenocryst ages, and thermodynamic modeling, this study demonstrates that postcollision Eocene lavas in central Tibet were derived from partially molten mid–lower continental crust column composed of Early Cretaceous mafic arc underplates across depths between 35 km and 65 km. These lavas host zircon with supra-mantle δ18O values (>6.5‰) overlapping with those of olivine and zircon from nearby Early Cretaceous mafic–ultramafic arc roots, indicating that the mid–lower crust consists of high-δ18O materials of a mantle-derived origin. Combining our results with regional Early Cretaceous magmatic records and estimates of crustal shortening from the Early Cretaceous to the Eocene, we infer that this high-δ18O crust initially exceeded 15 km in thickness and formed through magmatic underplating during a brief phase of high-flux arc magmatism. Our findings suggest that the current zircon Hf–O isotope paradigm may oversimplify the timing and material contributions of continental crustal growth on both regional and global scales.

The ophiolite assemblages of the Yarlung-Zangbo Suture Zone (YZSZ) in southern Tibet represent fragments of the Neo-Tethyan lithosphere that once separated the Indian and Asian continents and are unique among global ophiolites in their characteristic thick-mantle and thin-crust architecture. However, the petrogenetic and tectonic processes responsible for this distinctive feature remain elusive. Here, we investigate the Xiugugabu ophiolite in the western YZSZ using integrated field observations, zircon U-Pb geochronology, bulk-rock geochemistry, and zircon Hf isotopes. Mafic rocks from the Xiugugabu ophiolite yield Early Cretaceous formation ages of ca. 124-120 Ma and define two coeval but geographically and geochemically distinct groups. Group A rocks were derived from a typical N-MORB-like depleted mantle, whereas Group B rocks record contributions from an ultradepleted mantle that experienced ancient melt extraction followed by subsequent melt refertilization, as indicated by their negative Zr-Hf anomalies, sub-MORB Zr/Hf and Nb/Ta ratios, and highly radiogenic zircon epsilon Hf(t) values (up to +21.1). Immobile trace-element discriminants (e.g., Th/Yb-Nb/Yb and Ti-V systematics) indicate that the Xiugugabu mafic rocks formed in a subduction-unrelated environment, most consistent with a slowspreading mid-ocean ridge, which can account for the thick-mantle and thin-crust ophiolite pseudostratigraphy. In contrast, coeval mafic rocks from the Xigaze ophiolite in central YZSZ display subduction-related signatures and have distinct paleomagnetic positions and sedimentary covers. Taken together, these observations indicate that the YZSZ ophiolites represent a tectonic collage assembled from compositionally and spatially distinct fragments of the Neo-Tethyan oceanic lithosphere.

The petrogenesis and tectonic setting of the widespread Mesozoic magmatic rocks in the Lhasa Block, China, are essential for understanding the evolution of the Neo-Tethys Ocean. Thus, in this study, for the first time, systematic geochronological, whole-rock geochemical, and Sr–Nd–Hf isotopic analyses were conducted on volcanic rocks of the Jiega Formation in the western region of the Central Lhasa Block. Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating identified six age groups: 107 ± 2 Ma, 108 ± 3 Ma, 109 ± 2 Ma, 109 ± 2 Ma, 113 ± 2 Ma, and 115 ± 2 Ma, indicating that the volcanic rocks formed during the late Early Cretaceous. The rocks were mainly composed of basalt, andesite, and dacite, exhibiting a compositional range from intermediate-basic to intermediate-acidic. The intermediate–mafic volcanic rocks were predominantly medium-K calc-alkaline, characterised by enrichment in Th, U, and Sr and relative depletion in Rb, Nb, and Ta. The intermediate–mafic volcanic rocks exhibited (87Sr/86Sr)i ratios and εNd(t) values ranging from 0.706886 to 0.709154 and − 6.23 to − 0.19, respectively, while their 176Hf/177Hf ratios ranged from 0.282424 to 0.282649, with corresponding zircon εHf(t) values of − 9.80 to − 2.26. In contrast, the intermediate–acidic volcanic rocks were predominantly high-K calc-alkaline, characterised by enrichment in Th, U, Hf, and Zr and depletion in Ba, Nb, Ta, and Ti. Their (87Sr/86Sr)i ratios and εNd(t) values ranged from 0.706116 to 0.709234 and − 7.05 to − 1.28, respectively, while their 176Hf/177Hf ratios ranged from 0.282486 to 0.282746, with corresponding zircon εHf(t) values of − 5.99 to + 0.93. The intermediate–basic and intermediate–acidic rocks exhibited similar variation patterns in chondrite- and primitive-mantle-normalised trace-element diagrams. The rocks also exhibited similar Sr–Nd–Hf isotopic compositions and typical active continental-margin arc-volcanic characteristics, possibly owing to partial melting of a mantle wedge enriched by subducted materials. However, the magmatic systems underwent fractional crystallisation accompanied by crustal assimilation during magma ascent. According to these findings, the volcanic rocks of the Jiega Formation might be products of southward subduction of the ancient oceanic basin represented by the Shiquan River–Lagkor Tso–Yunzhug–Nam Tso–Jiali ophiolitic mélange zone during the late Early Cretaceous.

The mass-independent Mo isotope composition of the Bulk Silicate Earth (BSE) bears great potential to investigate the origin of the Earth's latest 10-20% planetary building blocks. However, currently different estimates for the Mo isotope composition of the BSE render constraints on the composition of late-stage accretionary materials difficult. To address this issue and to revisit the Mo isotope composition of the BSE, we report highprecision molybdenum isotope data for a comprehensive set of terrestrial molybdenites from different locations around the globe covering mineralization ages that extend from the Archean to the Phanerozoic. The molybdenite results are used to constrain the Mo isotope composition of the BSE as follows: c92Mo = 0.04 + 0.06, c94Mo = 0.03 + 0.03, c95Mo = 0.01 + 0.01, c97Mo = 0.02 + 0.02, c100Mo = 0.05 + 0.06 (n = 16, 95% confidence interval, relative to the NIST SRM 3134 Mo standard). In contrast to previous studies, no resolvable c94Mo and c95Mo anomalies were observed, suggesting a BSE composition with predominantly non-carbonaceous chondrite provenance. Considering the analytical uncertainties of our new BSE estimate and literature data for carbonaceous and non-carbonaceous meteorites, it remains a viable option that 12+10% of the present-day Mo budget in the BSE derives from carbonaceous meteorite material delivered during late-stage accretion. This amount of Mo is consistent with the fraction of Mo that was delivered to Earth during its final 0.5% of accretion by the late veneer.

The Rhenium-Osmium (Re-Os) isotope system is a key technique for the direct dating and genetic tracing of metallic orel 190 deposits, sedimentary strata, and other geological materials, while Isotope Dilution-Negative-Thermal Ionization Mass Spectrometry (ID-N-TIMS) is currently the most widely used analytical method. Herein, the compositional accuracy of the Os-190 spike is critical for maintain the relinbitty-of-thaning results however, theunion of the labormory malibomotor spike tends drifrdms to amm physical factors such as temperature fluctuations and solvent evaporation. Therefore, this study established a rapid and efficient spike content correction method, a traceability correction method centered on the recommended age of the Huanglongpu molybdenite reference material (GBW04435; HLP), which was reverse verified using the reverse dilution method with Os-190 standard solution. The experimental results show that when correcting the Os-190 spike content based on the recommended age and original model age, the weighted average correction factors are 1.057 +/- 0.010 (95% confidence level) and 1.054 +/- 0.012 (95% confidence level), respectively. Correspondingly, the weighted average Os-190 spike contents are (112.46 plus/minus 1.06) * 10(-9) and (112. 14 +/- 1.28) x 10(-9), respectively. The reverse dilution correction results of the Os-190 standard solution indicate that the Os-190 spike content is (111.28 +/- 1.28) x10", which is essentially consistent with the recommended age correction results within the 20 error range. This combined main-auxiliary correction method not only provides a simple and efficient solution for verifying spike composition but also significantly reduces random errors via the auxiliary calibration mechanism. Compared with traditional methods, it greatly shortens the time and cost of secondary calibration of the Os-190 spike and significantly improves the accuracy and reproducibility of Re-Os isotope dating of molybdenite. It is important to note that this method is premised on the traditional calibration of the spike. Currently, it is primarily employed for the systematic, simplified correction of post-calibration Os-190 spike content. However, to achieve higher dating precision and accuracy, integration with the traditional precise calibration protocol for the Os-190 spike remains necessary.

Despite extensive research on the Comei large igneous province (LIP) in the Tethyan Himalaya, that has significantly enhanced our understanding of early Cretaceous tectonic evolution on Gondwana's northern margin, comprehensive studies on the complete magma-tectonic evolution of the Tethyan Himalaya during this period remain limited. Situated on East Gondwana's passive margin at mid-to-high southern paleolatitudes (39.6°–54.7°S), the Early Cretaceous Comei LIP (147–117 Ma) exhibits three main magmatic pulses (~140, 132, 119 Ma). The magmatic activity shows spatial and temporal variations, with the oldest ages in the central-east and the youngest in the central regions, indicating a complex distribution pattern beyond simple east-to-west progression. Its minimum erupted volume of 144,000 km3 and area of 180,000 km2 satisfy the defining criteria of a LIP. Peak emplacement (~132 Ma) reached ~50,400 km3/Myr assuming 70% volume emplaced within ≤2 Myr. The province comprises gabbroic intrusions, basaltic lavas, mafic sills/dikes, subordinate ultramafic intrusions, and felsic rocks. ΔNb values reveal two distinct mantle sources for the Comei LIP: an enriched plume source with recycled oceanic components (positive ΔNb) and a hydrated mantle source containing recycled continental crust (negative ΔNb). The Comei LIP also includes intermediate (diorite/tonalite) and silicic (A-type granite) rocks, which formed via amphibole separation during mafic magma fractionation and lower crustal melting, respectively. The Kerguelen mantle plume (~147–145 Ma initiation) influenced the Tethyan Himalaya via vertical and lateral spread of its plume head, centered in the Cuona-Kada-Tage-Longzi region. Its influence waned after ~120 Ma due to Indian Plate northward drift, ceasing plume magmatism and initiating rifting. The emplacement of the entire Comei LIP was controlled by E–W faults and facilitated by lithospheric thinning (60–80 km) and plate drift. This localization of plume activity exclusively in the Tethyan Himalaya contrasts with the plume-absent magmatism in coeval SW Australia, which is attributed to its thick lithosphere, compressional setting, and interior position within the LLSVP. Our revised geodynamic model for Eastern Gondwanas breakup integrates plume dynamics and plate kinematics, emphasizing the Indian Plate's rapid northward drift in driving plume-lithosphere interactions through three phases: pre-breakup plume coupling, conduit migration/rift nucleation, and oceanic breakup with the Southern Kerguelen Plateau formation. Future studies require resolving plume-lithosphere interactions via high-P experiments and diffusion chronometry, quantifying pyroxenite contributions, tracking deep carbon cycles (Ca-Mg isotopes), and integrated geodynamic modeling using ΔNb/FCKANTMS frameworks to decipher how plumes exploit lithospheric heterogeneity to drive supercontinental breakup.

The late accretion of exotic materials is significant in the study of the formation and evolution of the Earth and the Moon. The importance of platinum-group elements (PGEs) in tracking the late accretion stages of planetary formation has long been recognized. In previous studies, estimates of the flux of exotic materials added to the Moon have primarily been based on measurements of siderophile element concentrations in lunar regolith samples returned by the Apollo or Lunar missions. However, due to the analytical limitations at that time, only a few individual siderophile elements, such as Ni, Ir, Ge, Re, and Au, could be quantified. Among these elements, Ni is moderately siderophile, while Ge is moderately volatile, which means neither is the most ideal tracer for identifying the exotic materials in the moon. Advances in analytical techniques have significantly enhanced both the precision and accuracy of measurements for PGEs and Os isotopes. High-precision analytical techniques have established characteristic of PGEs patterns and Os isotope ratios in different meteorite types by ICPMS and TIMS. However, to date, no detailed study has been conducted on PGEs and Os isotopes in mature lunar soil.The CE-5 lunar soil (CE-5LS) collection site is located in an area far from the Apollo and Luna mission regions, and previous studies have confirmed that the surface basalts in the CE-5 sampling area are more than 1 billion years younger than those in the Apollo and Lunar mission regions[1, 2]. This implies that the exotic material flux and composition within the CE-5LS may differ significantly from those in the Apollo lunar soil.In this study, 1100 mg of CE-5LS samples were magnetically separated. And PGEs and Os isotopes were analyzed on the magnetic and non-magnetic fractions, respectively. The results indicate that the influx of exotic material at the CE-5 landing site amounted to approximately 0.8%, markedly lower than estimates based on the accumulation of exotic material in Apollo soil samples (1%–5%)[3-7]. Given that the accumulation of extraterrestrial material on the Moon correlates positively with the Moon's age, this conclusion is reasonable. The PGE patterns and Os isotope ratios in CE-5LS are consistent with those analysed in chondrites. Consequently, the exotic material accrated onto the Moon is predominantly chondrites. AcknowledgmentThe authors had the great honour of applying for and receiving approval to carry out studies on the CE-5 lunar samples allocated by the CNSA. This work was financially supported by the National Key Research and Development Project of China (2020YFA0714804). Reference[1] Che X. C., et al. (2021). Science 374:887.[2] Li Q. L., et al. (2021). Nature 600:54.[3] Ganapathy R., et al. (1970). Geochimica et Cosmochimica Acta Supplement 1:1117.[4] Baedecker P. A., et al. (1974). Lunar and Planetary Science Conference Proceedings 2:1625-1643.[5] Laul J. C., et al. (1974). Lunar and Planetary Science Conference Proceedings 2:1047-1066.[6] Boynton W. V., et al. (1975). Lunar and Planetary Science Conference Proceedings 2:2241-2259.[7] Higuchi H. and Morgan J. W. (1975). Lunar and Planetary Science Conference Proceedings 2:1625-1651.

The Pt-Os, Hf-W and Re-Os isotopes represent the three pivotal radiogenic isotopic systems as the refractory elements, which are indispensable and effective approaches for investigating deep Earth core-mantle material cycling, precisely constraining the timing of metallic ore deposits, and determining the ages and sources of organic-rich sediments (and oil and gas reservoirs). The existing analysis techniques still have shortcomings and are difficult to meet the requirements of high-precision analysis, i.e., it is an urgent need to develop new technologies to enhance the accuracy of measurement and the efficiency of analysis. This paper summarizes recent advances of our team on establishing and refining analytical techniques for isotopic systems of the refractory elements: (1) Establishment of a new high-precision Pt-Os analytical approach, i.e., the Sb-fire-assay Pt-Os isotope analysis that fundamentally differ from the traditional multi-Carius tube method; (2) Innovated two high-precision analysis techniques for W isotopes; (3) Optimization of Re-Os isotopic analysis in sulfides from metallic ore deposits, significantly enhancing the precision of metallogenic age determinations; (4) Refinement of accurate dating and genetic tracing techniques for organic-rich sediments (and oil and gas reservoirs) and achieving age precision at the current international forefront. The paper further outlines prospects for future advancements in Pt-Os, Hf-W and Re-Os isotope analytical techniques.

High-Mg andesites (HMAs) formed at convergent plate margins are of special importance in deciphering subduction processes and dynamics. Although abundant, diverse Middle-Late Jurassic (ca. 170-148 Ma) HMAs have been documented in Central Tibet (SW China), and their detailed spatiotemporal evolution and exact genetic and dynamic connections with the subduction of the Bangong-Nujiang Tethyan Ocean (BNTO) are not well constrained. Here, we report newly discovered 157-155 Ma sanukitic HMA dykes in the Qieli Tso ophiolite, central Tibet. Geochemical characteristics and simulation suggest they were generated by low-degree melting (3-6%) of sediment melt-fluxed mantle wedge at 1.8-2.2 GPa, 1230-1260 degrees C, resembling those of sanukite from SW Japan. Comprehensive geochemical analysis of the HMAs in central Tibet divides them into three types with distinctive magmatic processes: (1) boninitic HMAs, generated by melting of fluxed depleted mantle; (2) sanukitic HMAs, generated by melting of sediment melt-fluxed mantle; and (3) adakitic HMAs, generated by melting of subducted slab and lower crust. Moreover, significant spatiotemporal variation is displayed among these HMAs according to their current geography and inferred tectonic settings, i.e. ca. 170-160 Ma FAB-boninitic magmatism in the southern forearc region, ca. 169-155 Ma dominant sanukitic magmatism in the northern continental arc region, and ca. 155-148 Ma dominant adakitic magmatism in between them. These variations attest to a northward and then southward migration of the magmatism front. This migration, together with other geological evidence, is consistent with successive transitions of subduction dynamics of BNTO, likely from subduction initiation through ridge-trench collision to ridge subduction. The prolonged high heat flux during the whole transitioning process results in a burst of high-Mg magmatism.

Molybdenite, as an important metal sulfide, is widely found in hydrothermal deposits and is the main host mineral for the rare metal molybdenum and rhenium. The Re-Os isotope dating of molybdenite is a classic method for dating metal deposits. The molybdenite Re-Os dating method can directly determine the age of metal deposits and is the most effective means of directly obtaining the age of metal sulfide deposits. Isotope dilution molybdenite Re-Os dating (ID-TIMS or ID-ICP-MS) has been very mature after more than three decades of development. However, the overall analysis requires a large number of samples and involves a lengthy chemical separation and purification process, which also masks fine spatial variation information. In recent years, laser microprobe Re-Os dating of molybdenite has developed rapidly. Laser microprobe Re-Os dating of molybdenite can not only avoid the shortcomings of overall analysis but also achieve in-situ dating of molybdenite in thin sections, with a broad application prospect. This paper reviews the latest progress in laser microprobe Re-Os dating of molybdenite, summarizes the two main stages of its development, points out the current difficulties and coping strategies in laser microprobe Re-Os dating of molybdenite, and looks forward to the broad prospects of laser microprobe Re-Os dating of molybdenite and pyrite, and the following conclusions are obtained: (1) Plasma tandem mass spectrometry greatly reduces the interference of Re-187 on Os-187, and laser microprobe Re-187-Os-187 dating can be performed on sulfides such as molybdenite and pyrite with high Re content (> 10x10(-6) Re). Elemental imaging technology can not only reveal the relationship between trace elements in molybdenite but also quickly lock the high Re/Os areas of minerals, improving the success rate of Re-187-Os-187 dating of sulfides; (2) Selective reactive gases, nitrous oxide has a lower reaction efficiency with Re than methane, and its interference elimination ability is better than methane. Methane can improve the reaction efficiency of Os products, but its reaction efficiency with Re is also higher than that of nitrous oxide. Therefore, nitrous oxide is more suitable for laser microprobe Re-187-Os-187 dating of young molybdenite, and combined with high-sensitivity multi-collector magnetic tandem mass spectrometry (MC-ICP-MS/MS), it is expected to achieve high-precision laser microprobe Re-187-Os-187 dating of sulfides; (3) The interference of Re-187 and Os-187 has not been completely eliminated, and interference correction is still needed. Exploring suitable reactive gases, minimizing or even eliminating Re reaction products, and at the same time improving the sensitivity and reaction efficiency of Os, is the current difficulty in laser microprobe Re-Os dating of molybdenite and also the frontier field and development direction for future laser microprobe Re-Os dating of sulfides; (4) Experimental methods and the development of standard materials complement and promote each other. The serious lack of standard materials for laser microprobe Re-Os dating of sulfides is still the key problem that needs to be solved urgently. It can be believed that with the continuous progress of technology, laser microprobe Re-Os dating of sulfides may become as simple, fast and efficient as laser microprobe U-Pb dating of accessory minerals such as zircon, opening a new window for the study of metal deposit genesis and providing a new means.

The Central Asian Orogenic Belt represents the most important site of crustal growth in the Phanerozoic. However, the intricate evolution of multi-ocean regimes has given rise to uncertainties surrounding the processes of Mesozoic tectonic evolution and the dynamics of crustal growth. In this study, we conducted detailed geochronological and geochemical analyses of andesites collected from the eastern Central Asian Orogenic Belt. Zircon U-Pb dating results show that these andesites formed during the Late Triassic (ca. 235 Ma), and the Ti-in-zircon thermometer reveals high magma temperatures (>1100 degrees C) during their genesis. The elevated Mg# values at moderate SiO2 content of these Late Triassic andesites indicate an affinity with high-Mg andesites (HMAs). Notably, the andesites exhibit relatively low K2O/ Na2O ratios, high Sr/Y ratios, significant depletion of Nb and Ta, and trace element patterns resembling typical HMAs from the western Aleutian Islands. These characteristics suggest that they likely originated from the partial melting of subducted eclogite. Furthermore, the HMAs display relatively high zircon epsilon(Hf)(t) values and depleted whole- rock Sr-Nd isotopic compositions, which is indicative of a depleted mantle source. Therefore, we propose that these andesites were generated through the interaction of the subducting slab-derived melts and overlying mantle wedge. Considering that the final closure of the Paleo-Asian Ocean took place before the Late Triassic, these andesites probably erupted in a post-collisional setting. The formation of these HMAs could be best explained by the upwelling asthenosphere triggered by the break-off of the oceanic slab, which also contributed to continental crustal growth in Northeast China.

The formation of intermediate to silicic magmas in subduction zones is fundamental to understanding the genesis of Earth's continental crust. A prominent hypothesis posits that fractionation of amphibole-rich package from basaltic magmas in the mid-to-lower crust plays a central role in this process. This model assumes the widespread presence of amphibole-rich cumulates-such as hornblendites-within the mid- to lower crust beneath volcanic arcs; however, this assumption remains largely untested. Here, we integrate geochemical analyses and thermodynamic modelling to evaluate the equilibrium melt compositions and geophysical properties of olivine hornblendites from central Tibet and analogous rocks worldwide. Petrological, mineralogical, and isotopic analyses of spatially associated and coevally formed olivine hornblendite, gabbro, and andesite from an Early Cretaceous arc in central Tibet reveal that amphibole fractionation plays a cryptic role in generating some arc andesites, despite amphibole is not present as a phenocryst phase. Melts in equilibrium with amphibole in Tibetan and global hornblendites are predominantly andesitic (mean SiO2 = 62 wt%). Additionally, these olivine and pyroxene hornblendites exhibit relatively high seismic velocities (Vp > 7 km/s) and are primarily rooted in the mid-crust. However, large volumes of such high-velocity cumulates have not detected by geophysical studies beneath the middle crust of central Tibet or other volcanic arcs globally. Our findings indicate that amphibole formed via peritectic reactions produces melts with SiO2 contents rarely exceeding 65 wt%, implying that more silicic magmas likely require additional processes, such as magma mixing and/or partial melting of pre-existing crust.

The central Tibetan Plateau is widely recognized to have undergone significant surface uplift during the Late Cretaceous; however, the deep-seated geodynamic processes driving this uplift remain debated. Magmatic rocks, as direct records of lithospheric processes, provide critical constraints on the nature and evolution of the deep crust and mantle. This study presents a comprehensive petrographic, zircon U-Pb geochronological, geochemical, and Sr-Nd-Hf isotopic investigation of Late Cretaceous andesitic porphyrites from the Zhongcang area in the northern Lhasa Terrane, central Tibetan Plateau. Geochronological results indicate that the Zhongcang andesitic porphyrites crystallized at similar to 90 Ma. These rocks are characterized by relatively high SiO2 (62.00-62.96 wt%) and moderate K2O (0.96-1.14 wt%) contents, elevated Mg# values (51.6-53.7), high Sr (369-399 ppm) and low Y (10.2-10.9 ppm) concentrations, and high Sr/Y ratios (34.49-38.25), geochemically resembling high-Mg# adakitic rocks. They exhibit enrichment in large-ion lithophile elements and depletion in high-field-strength elements, with Th/U (3.82-4.42) and Nb/Ta (12.5-14.9) ratios comparable to those of continental crust. The heterogeneous zircon Hf isotopic compositions (epsilon(Hf)(t) = -7.7 to +10.7) indicates involvement of both juvenile and ancient crustal components, whereas whole-rock Sr-Nd isotopic compositions (Sr-87/Sr-86(i) = 0.704716-0.705051, epsilon(Nd)(t) = +0.23 to +0.59) suggest a mainly juvenial crustal source. Pressure estimates from whole-rock and zircon trace element barometry indicate that the crustal thickness of the northern Lhasa Terrane reached similar to 70 km during the early Late Cretaceous. Given that this period corresponds to the post-collisional setting of the Qiangtang-Lhasa terrane convergence, we propose that the Zhongcang andesitic porphyrites were derived from magmas generated by the delamination of the thickened juvenile lower crust with locally ancient components, which subsequently interacted with mantle materials during ascent. This lower crustal delamination not only contributed to surface uplift in the central Tibetan Plateau but may have also facilitated lithospheric thinning following crustal thickening.

The application of 182Hf - 182W system for accurate dating and tracing of planetary events relies on highly accurate and precise tungsten isotope measurements. However, high-precision measurement of W isotopes usually requires large samples, which greatly hampers the study of low-content and/or small-size samples. In this study, a two-column W purification procedure was developed for small-size samples with the whole procedure blank of less than 40 pg and the recovery greater than 97 %. Meanwhile, a high-precision W isotopes measurement method was developed for amounts of W larger than 30 ng using static Faraday cups with 1013, 1012, and 1011 Ω amplifiers by negative thermal ionization mass spectrometry (NTIMS). In particular, we designed a high-precision O isotopic composition measurement method in the form of ReO4, which greatly improved the precision and accuracy of W isotopes. By analyzing the SRM 3163 calibration solution, the long-term repeatability of the 182W/184W ratio was 0.864868 ± 6 ppm (2 RSD, n = 29, t = 12 months) when the W amount was greater than 30 ng. Measurements on actual samples have shown that these methods are applicable to terrestrial rocks, stony and iron meteorites with sample sizes of 20-400 mg. This new protocol significantly reduces the background of the W separation process and improves precision of W isotope measurement for small-size samples, as well as solves the critical problem of uncertainty in W isotope ratios due to the inability to accurately determine O isotope compositions in previous studies.

Post-collisional ultrapotassic volcanic rocks (UPVRs) in the Tethyan domain archive crucial information about the composition and evolution of the lithospheric mantle, offering valuable insights into deep geodynamic processes. The Tibetan Plateau, particularly the Lhasa Terrane in its southern part, remains a subject of debate regarding the genesis and geodynamic mechanisms of the UPVRs. This study investigates geochronology, mineralogy, and whole-rock geochemistry of the UPVRs in the Majiang area of Lhasa Terrane, southern Tibet. Zircon UPb dating reveals that these rocks formed at ca. 21 Ma. Petrologically, the Majiang volcanic rocks are classified as trachyandesites, while geochemically they qualify as ultrapotassic rocks (characterized by K2O > 3 wt%, MgO > 3 wt% and K2O/Na2O > 2). They exhibit a broad range of SiO2 contents (45.85-57.94 wt%) and high Mg# values (57.7-72.3). Elevated trace element concentrations, marked by enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs), suggest a mantle source influenced by fluid/melt interactions. The presence of phlogopite phenocrysts in the Majiang UPVRs suggests high magma temperatures (1116 +/- 15 degrees C) and low crystallization pressures (1.3 +/- 0.3 GPa). Trace element geochemical modeling indicates that the Majiang UPVRs likely originate from a garnet stable mantle domain and experience rapid magma ascent after their formation. The Majiang UPVRs exhibit high Th/U (8.97-19.08) and Th/La (2.27-2.45) ratios, low Hf/Sm (0.52-0.64) ratios, and enriched SrNd isotopes (Sr-87/Sr-86(i) = 0.717286-0.721658, epsilon(Nd)(t) = -9.55 - -9.28). These geochemical signatures suggest derivation from an enriched lithospheric mantle metasomatized by oceanic sediments. Integration of published data reveals that the UPVRs in both the eastern and western Lhasa Terrane share close geochemical affinities, suggesting a common mantle source. However, limited UPVR exposures in the eastern Lhasa Terrane and slightly more depleted SrNd isotopes in the Majiang UPVRs compared to those in the western Lhasa Terrane imply distinct Miocene geodynamic processes. Lithospheric convective thinning caused by post-collisional extension and mantle upwelling likely occurred more extensively in the eastern Lhasa Terrane. This process may have led to the gradual replacement of ancient lithospheric mantle by juvenile material in the east, contrasting with the more localized effects in the western Lhasa Terrane.

While heavy molybdenum (Mo) isotope compositions in arc-related rocks have been linked to slab-derived fluids, the origins of arc lavas with light isotopic Mo compositions remain enigmatic. The two potential sources for the origin of light Mo isotopes in arc rocks are (1) dehydrated oceanic crust 1, 2 and (2) subducting sediments 3, 4. Although the former has been extensively recognized, the latter still poses an enigma. We present the Mo-Sr-Nd-Hf isotope compositions and elemental data of a suite of Jiang Tso andesites to elucidate the chemical compositions of sediment-derived melts in the central Tibetan Plateau. The andesites from the Jiang Tso area show elevated Mg# values, along with trace element characteristics reminiscent of melts derived from sediments. Their Sr-Nd-Hf isotope compositions (87Sr/86Sri = 0.710260–0.710671, εNd(t) = –10.63 to –8.97, and εHf(t) = –9.38 to –8.02) closely resemble those of contemporaneous sediments in the central Tibetan Plateau. In addition, these andesites exhibit higher Ce/Mo ratios (396–587) and extremely lighter δ98/95Mo values (−1.62‰ to −0.69‰) compared to the depleted mantle (δ98/95Mo = –0.21‰ ± 0.02‰) 5, 6 and the majority of arc lavas (δ98/95Mo = –0.07‰ ± 0.04‰) 3, suggesting a more plausible explanation lies in the involvement of subducting sediments rather than dehydrated oceanic crust in the source. Our latest findings, integrated with previous studies, indicate that the arc-related rocks exhibiting light Mo isotopes may not solely originate from the rutile-breakdown oceanic crust source but could also result from sediment melting at various sub-arc depths. Consequently, sediment-derived melts play a crucial role in Mo isotope cycling and the formation of arc magmas in subduction zones. 1 Chen, S., et al., Nat. Comm. 10, 4773 (2019). 2 Freymuth, H., et al., EPSL 432, 176-186 (2015). 3 Huang, F., et al., GCA 341, 75-89 (2023). 4 König, S., et al., EPSL 447, 95-102 (2016). 5 McCoy-West, A.J., et al., Nat. Geos.12, 946-951 (2019). 6 Willbold, M. & Elliott T., CG 449, 253-268 (2017).