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Balsaminaceae are world-famous ornamental flowers because of their high species diversity, rich variation, peculiar flower patterns, and long ornamental cycles. To study the species diversity, distribution patterns, and distribution hotspots of Balsaminaceae in China, we updated the list of Balsaminaceae by systematically searching the related literature. The distribution pattern and hotspots of Impatiens spp. were analyzed using the ArcGIS 10.8.2 software. Combining 19 meteorological factors and one elevation factor, the Maxent model was applied to analyze the dominant environmental factors that govern the distribution of Impatiens spp. As of February 2023, Balsaminaceae in China included 360 taxa in two genera, including one taxon in the genus of Hydrocera, 359 taxa in the genus Impatiens, 271 national endemic species, and 157 provincial endemic species. Impatiens spp. showed a diffusion pattern from the tropical and subtropical regions to the high-latitude and high-elevation regions concentrated in Southwest China, especially in the Hengduan Mountains in the broad sense, Southern Tibet, the Yunnan–Guizhou–Guangxi karst region, the Qinling–Daba Mountains, and the southeastern hills. The highest species richness was found in the 1200~1500 m elevation range, with 164 species of Impatiens spp. This high species richness was maintained at between 900 and 2700 m, the elevation range where Impatiens spp. are concentrated. When 100% of the species were screened out, 110 hotspots were found, including Southeast Yunnan, Northwest Yunnan, Southern Tibet, and Western Sichuan, where most of the hotspots were concentrated and overlapped with global biodiversity centers, but other hotspots were more scattered. Annual precipitation, the minimal temperature of the coldest month, the altitude and temperature annual range, and four environmental variables with a cumulative contribution of 93.7% were the dominant environmental factors affecting the distribution of Impatiens spp. in China. This study lays the foundation for subsequent studies of Balsaminaceae diversity and is conducive to the development and use of Impatiens spp. resources. [ABSTRACT FROM AUTHOR]

There has been intense debate on the mechanism of crustal recycling in subduction zones, and Fe–Mg isotopes may provide new constraints on this issue. This study reports Fe–Mg isotope data for mafic plutonic rocks from the eastern and central Gangdese arc, along with their associated trench sediments in southern Tibet. The δ26Mg values of the eastern Gangdese arc rocks show negative correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but positive correlations with εNd(t) and εHf(t) values. Conversely, the δ56Fe values of the eastern Gangdese arc rocks show positive correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but negative correlations with εNd(t) and εHf(t) values. The Mg and Fe isotopic compositions of the central Gangdese arc rocks are comparable with those of the eastern ones, but they do not correlate with Sr–Pb–Nd–Hf isotopic compositions. Notably, the Fe–Mg isotopic compositions of most arc rocks fall between those of local trench sediments and the mantle wedge. Combined qualitative analyses and quantitative simulations suggest that: (a) the Fe–Mg isotope variations observed in the eastern Gangdese arc rocks highlight the important role of source mixing between sediment‐derived melts and peridotite, whereas (b) the Fe–Mg isotope variations observed in the central Gangdese arc rocks reflect the superposition of carbonated serpentinite‐derived Mg‐rich fluids‐peridotite source mixing and source melting. The strong correlations between Fe–Mg isotope ratios and traditional geochemical tracers provide further evidence for the recycling of crustal materials in subduction zones via various types of slab‐derived fluids and melts. Plain Language Summary: Currently, there is an ongoing debate surrounding the mechanism of transporting subducting slab‐derived materials to fuel magmatism in subduction zones. The stable isotopes of iron and magnesium—major constituents in arc rocks—are considered potential tools to resolve this dispute. However, establishing a direct link between the Fe–Mg isotopic compositions of arc rocks and specific transporting mechanisms has proven challenging. Thus far, no significant correlations have been observed between Fe–Mg isotope ratios and traditional tracers for slab materials in arc rocks, such as radiogenic Sr–Pb–Nd–Hf isotope ratios. Further complicating matters, obtaining Fe–Mg isotopic data for subducting sediments in certain subduction zones is often difficult. In this study, we simultaneously analyzed the Fe–Mg isotope compositions of the Gangdese arc rocks and their associated valuable trench sediments. For the first time, our findings unveil strong correlations between Fe–Mg and Sr–Pb–Nd–Hf isotopic compositions in arc rocks. This finding, from the viewpoint of the isotopic composition of major elements, provides new evidence for the transport of crustal materials from the subducting slab to the mantle wedge sources via various types of fluids and melts rather than by mechanically mixed solids. Key Points: The Fe–Mg isotopic compositions of the Gangdese arc mafic plutonic rocks are closely connected to their associated trench sedimentsGood correlations between Fe–Mg isotope ratios and radiogenic Sr–Pb–Nd–Hf isotope ratios are found in mafic arc rocks for the first timeFe–Mg isotopes provide further evidence for crustal recycling in subduction zones via various types of slab‐derived fluids and melts [ABSTRACT FROM AUTHOR]

Serpentinite plays a crucial role in element mobility during seawater hydrothermal alteration of mid-ocean ridge peridotite on the seafloor and fluid metasomatism of peridotite in the subduction zone. However, element mobility and Mg isotope fractionation during serpentinization of peridotites are still uncertain. In order to address this issue, we present a geochemical study of serpentinites and their associated peridotites in the Xigaze ophiolite from southern Tibet. The serpentinites have lower MgO contents and Mg/Si ratios than the peridotites. The low Mg/Si ratios in serpentinites, along with the Isocon calculation results, indicate the Mg loss during serpentinization. In terms of trace elements, the serpentinites have higher contents of Ba, U, Sr and Pb than the peridotites, though both types of ultramafic rocks exhibit similar REE distribution patterns and HFSE contents. The serpentine-magnetite O isotope thermometry yields a relatively low serpentinization temperatures of 200–300 °C. The trace element composition of the serpentinites is distinct from that of forearc serpentinites but consistent with that of mid-ocean ridge ones. The peridotites show mantle-like δ26Mg values of –0.27 to –0.23‰ with an average of –0.25 ± 0.03‰ (2SD, n = 6). In contrast, the serpentinites have systematically higher δ26Mg values of –0.21 to –0.09‰ with an average of –0.16 ± 0.09‰ (2SD, n = 8). The Mg isotope composition of serpentinites shows no correlations with either the chemical weathering proxy or the talc modal content, indicating that the Mg isotope fractionation between serpentinite and peridotite is not caused by chemical weathering of the serpentinites. Instead, it probably resulted from the serpentinization of peridotite on the seafloor. Thus, there is the loss of not only element Mg but also isotopically light Mg during the serpentinization of peridotites. The isotopically heavy Mg serpentinites can be carried to oceanic subduction zones, giving rise to higher δ26Mg mantle sources for various basalts. The isotopically light Mg can be released into the seawater, regulating the Mg isotope composition of seawater in geological history. Taking into account the sources and sinks of Mg in subduction zone fluids, the formation of isotopically heavy Mg serpentinites during seafloor serpentinization can be probably an important process in changing the Mg isotope composition of mantle sources. [ABSTRACT FROM AUTHOR]

Environment context: One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. Rationale: Ozone (O3) behaviour over the Tibetan Plateau has attracted attention in recent decades. However, few long-term measurements have been performed in the region. Methodology: Field observations were conducted at a mountain site on the southeastern Tibetan Plateau from June 2014 to July 2015 in order to understand the behaviour of surface O3 and its influencing factors. Backward trajectory cluster analysis was applied to understand long-range transport sources and their relative contributions. Results: The monthly average O3 ranged from 22.1 to 48.6 ppb with a common high spring ozone concentration phenomenon. The O3 diurnal variation exhibited a similar pattern to those in polluted areas but the cause was different. The O3 mixing ratio was significantly positively correlated with mixed-layer depth and wind speed, and negatively with temperature and relative humidity, indicating strong vertical air exchange. Approximately 50% of air mass trajectories originated from the northeastern Bengal Bay region, with fairly low O3 (CO) mixing ratios and high humidity. Others originated from the north Indian subcontinent (28%) and the Middle East (18%), with fairly high O3 (and CO) and low humidity. Discussion: The average relative contributions of different air masses to surface O3 and CO were small and scattered but large for trajectories arriving at 14:00 hours when vertical air exchange was close to its strongest for the day. The tropospheric O3 sink may be common in the highlands, indicating a negative greenhouse effect there. The O3 sink at Linzhi was estimated in the range of 4.5–5.5 ppb h−1 at maximum. Summary. One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. [ABSTRACT FROM AUTHOR]

Alkalic basalts from continental regions have been widely used to fingerprint chemically and lithologically distinct components in the mantle. However, superimposed on mantle source effects are the effects of intra-crustal magma differentiation, which may be underestimated when exclusively considering fractional crystallization (FC) in melt-rich magma chambers. Here we present extensive mineralogical and geochemical data for mafic cumulates and dolerite dikes from central Tibet to demonstrate that tholeiitic magma differentiation occurred in crystal-rich mushes and melt-filled fractures. The mafic cumulates provide a snapshot of the percolation of water-poor (<0.9 wt% H2O), oxide-undersaturated, tholeiitic melts through slightly hotter mushes (50–60% crystals) with a framework of primitive olivine ± plagioclase crystals. The highly corroded olivines indicate that thermo-chemical disequilibrium between the later percolating melts and pre-existing crystal framework triggered melt–mush reactions in an open system. High-temperature (>1060°C) reactions were accompanied by a decreasing melt mass, causing the initial tholeiitic melts to evolve into alkalic mafic melts during slow cooling. This process involved the dissolution and reprecipitation of olivine, plagioclase, and clinopyroxene as well as the late crystallization of high-TiO2 (up to 3.4 wt%) clinopyroxene and kaersutite. In contrast, the same tholeiitic magmas (i.e. dolerite dikes) that intruded the cold country rocks along fractures produced silica-rich residual melts saturated in Fe–Ti oxides and sodic plagioclase by FC during rapid cooling. The residual melt was always in equilibrium with the instantaneous crystal during closed-system FC, so there was no reaction between the interstitial melt and adjacent crystal even after a high degree of crystallization. Alkalic mafic melts that can be formed by melt–mush reactions exhibit strong enrichment of incompatible element contents (e.g. Ti and alkali and rare earth elements) and ratios (e.g. Ce/Y), but little Si enrichment and Mg depletion, compared with the parental tholeiitic magma, which cannot be reproduced by simple FC. We argue that tholeiitic melt–mush reactions at mid- to lower-crustal pressures (≥0.5 GPa) are a new mechanism for the generation of interstitial alkalic mafic melts in continental mush reservoirs. Continental alkalic basalts could be produced by this mechanism if such interstitial melts were concentrated into melt lenses by compaction and then transported rapidly upward to the surface by focused flow. [ABSTRACT FROM AUTHOR]

Rodingite is produced by Ca-rich fluid metasomatism of mafic igneous rocks in oceanic lithosphere. Despite its importance for the composition of subduction zone magmas, its formation mechanism still remains obscure. To address this issue, we investigated the major-trace element and Mg–O–Sr–Nd isotope compositions of rodingites in serpentinites from the Xigaze ophiolite, southern Tibet. Coexisting gabbros and rodingites show consistently depleted Sr Nd isotope compositions, suggesting their formation in a mid-ocean ridge setting. The rodingites exhibit variable δ26Mg values from −0.61‰ to −0.14‰, with an average of −0.37‰ ± 0.28‰ (n = 19; 2 SD), mostly lower than those of −0.26‰ to −0.13‰ for the protolith gabbros. Compared to the relatively homogeneous δ18O values of 6.1‰–6.7‰ for the gabbros, the rodingites show highly variable δ18O values from 3.8‰ to 9.4‰. The rodingites can be subdivided into two groups based on mineral assemblages and formation conditions. Group I rodingite is prehnite-dominated and hydrogarnet-free, formed at temperatures of 200–300 °C, and has higher δ18O values of 8.1‰ ± 1.4‰ (n = 15) and δ26Mg values of −0.32‰ ± 0.19‰ (n = 12). Group II rodingite consists mainly of hydrogarnet and clinopyroxene, formed at temperatures of 300–400 °C, and has lower δ18O values of 5.4‰ ± 2.5‰ (n = 7) and δ26Mg values of −0.44‰ ± 0.35‰ (n = 7). Modeling of the fluid–rock interactions between the protolith gabbro and fluid was undertaken using the Mg O isotope compositions of the serpentinizing fluid inferred from the associated serpentinites. Based on the modeling results, we propose that the metasomatism of gabbros by Ca-rich, low-δ26Mg fluids produced during serpentinization would result in the Mg O isotope compositions of the rodingites. Such rodingites with low δ26Mg values would generate the geochemical heterogeneity in the mantle wedge overlying the subducting oceanic lithosphere and eventually give rise to Ca-rich, low-δ26Mg basaltic magmas. The results indicate that low δ26Mg values of basaltic rocks cannot be unambiguously ascribed to carbonated mantle sources. • The Xigaze rodingites show low δ26Mg and variable δ18O values. • The rodingites were formed through metasomatism of gabbros by serpentinizing fluids under seafloor. • The subduction of rodingites in subduction zones can greatly affect mantle Mg isotopic composition. [ABSTRACT FROM AUTHOR]

The initial Hf isotope composition of zircon in high-grade metamorphic rocks is an important tracer for protolith origin as well as for the growth and evolution of continental crust. However, less attention has been paid to the behavior of Lu-Hf isotopes in peritectic reactions during partial melting of the continental crust. In this paper, we present a combined study of zircon U-Pb ages, Lu-Hf isotopes and trace elements as well as petrology and whole-rock geochemistry for migmatites close to the eastern Himalayan syntaxis in southeastern Tibet. The results show that peritectic zircons in the migmatites have significantly higher 176Hf/177Hf ratios than their protolith zircons. More interestingly, the 176Lu/177Hf ratios and the contents of high field strength elements (such as Nb, Ta, and Hf) and heavy rare earth elements are significantly elevated in the peritectic zircons compared to the protolith zircons. This suggests that garnets with high Lu/Hf ratios and other minerals (such as titanite, ilmenite, amphibole, and biotite) with moderate Lu/Hf ratios were decomposed during crustal anatexis, contributing to the Hf isotope composition of peritectic zircons. This is confirmed by petrographic observations that garnet and biotite occur as residues or remnants in mesosomes (biotite gneiss) and some leucosomes (felsic veins), but are absent in the melanosomes of the target migmatites. Therefore, the peritectic zircons were produced together with anatectic melts through peritectic reactions and acquired the elevated 176Lu/177Hf ratios compared to the inherited zircons from the protoliths if no peritectic garnet was coevally produced during the crustal anatexis. In this regard, the greatly elevated Hf isotope compositions of peritectic zircons in anatectic granites cannot faithfully reflect the Hf isotope composition of parental rocks. As such, great care must be taken when using Hf isotope ratios to trace the nature of parental rocks with respect to magmatic processes and crustal evolution. • Peritectic zircon have higher Lu/Hf and Hf isotopic ratios than protolith zircons. • Peritectic zircon also have higher HFSE contents than protolith zircons. • Minerals with high Lu/Hf ratios than zircon were decomposed during crustal anatexis. [ABSTRACT FROM AUTHOR]