Nitrogen (N) enrichment during alteration of the upper oceanic crust is a key regulator of N fluxes across the hydrosphere and lithosphere. However, the mechanisms that govern N uptake in altered oceanic crust (AOC) and its contribution to subduction budgets remain inadequately constrained, especially in marginal seas. Here, we present N concentration and isotopic data of altered basalts recovered from IODP Holes U1500B, U1503A, U1431E, U1433B, and U1434A in the South China Sea (SCS), a representative marginal sea. Our data show that the SCS altered basalts exhibit significantly higher N enrichment (7.0 to 72.6 ppm) than altered basalts from open ocean floors (1.3 to 48.4 ppm), while their delta N-15 values are broadly comparable (-6.6 parts per thousand to + 5.8 parts per thousand for the SCS basalts versus - 20.1 parts per thousand to + 8.3 parts per thousand for open ocean basalts). Two-component mixing modeling indicates that the enriched N in SCS altered basalts was mostly derived from sediments/seawater with a minor contribution from abiotic N-2 reduction. The pronounced N enrichment in the upper AOC of the SCS verifies that high N availability from the overlying clay-rich sediments (N = 227.0 to 453.8 ppm) is a main controlling factor. Meanwhile, our results also reveal that the alteration degree of basalt emerges as an important modulator of the magnitude of N uptake under high N-availability conditions. Integrating our new findings, we refine the global N input flux of the upper AOC section into subduction zones to 6.8 +/- 0.7 x 10(9) molyr(-1), nearly doubled previous estimates. Although marginal seas constitute only similar to 15 % of global trench lengths, they contribute 25 % of global N input flux from the upper AOC, owing to their elevated unit N input flux (25.9 +/- 8.1 x 10(4) mol yr(-1)center dot km(-1)) relative to open ocean floors (15.6 +/- 1.6 x 10(4) mol center dot yr(-1)center dot km(-1)). Together, these results highlight the pivotal role of marginal seas AOC in the deep N cycle and motivate a refined understanding of global N recycling that accounts for tectonic setting and alteration history.

Subduction zone is a unique channel on Earth regulating the long-term exchange of nitrogen (N) between Earth's surface and its interior. Increasing evidence has implied that the serpentinized forearc mantle wedge could be an overlooked sink for slab-derived N that potentially regulates the subduction-zone N cycle but has been poorly studied so far. Here we report the N concentrations and isotope compositions of a suite of lizardite serpentinites, lizardite-antigorite serpentinites, and antigorite serpentinites from the Mianlue tectonic melange in the Qinling Orogen. These samples cover the serpentine phase variations in serpentinized forearc mantle wedge overlain the subducting slab down to a depth of similar to 30 km, and thus provide a unique opportunity to unravel the role of the forearc mantle wedge serpentinization in subduction-zone N cycle. The results show that these serpentinites have significantly higher N concentrations (19.7 to 37.4 ppm) than seafloor serpentinites (3 to 19 ppm), indicating more efficient N uptake during fluid-rock interactions inside the subduction zone. The combined N concentrations and delta N-15 values suggest that the N added into these serpentinites was mainly mobilized directly from subducted sediments (with a delta N-15 range of -1 parts per thousand to +10 parts per thousand) with a small portion possibly derived from abiotic N-2 reduction (with delta N-15 value down to -13 %o). Despite the prograde phase change from lizardite to antigorite, these serpentinites display comparable N concentrations and no sign of metamorphic N devolatilization. The Mianlue serpentinites also show comparable N concentrations with the forearc serpentinized peridotites (dominated by lizardite/chrysotile) from the Mariana mud volcanoes and forearc antigorite serpentinites from the Tso Morari ultrahigh pressure unit exhumed from >100 km depth. These observations suggest strong N retention in the mantle wedge serpentinites during prograde metamorphism. If such N enrichment is typical in the serpentinized forearc mantle wedge, it means that up to 1.4(+/- 0.6) x 10(9) mol center dot yr(-1) slab N can be incorporated into global forearc mantle wedge. Although this amount only accounts for similar to 4 % of the sedimentary N input flux, it may account for a significant portion of the small amount of slab N released during early subduction. This implies that forearc serpentinites may play an unprecedentedly recognized role in subduction-zone N cycle. This role may be even more important in hot subduction zones. If N loss from Catalina Schist (i.e., similar to 70 % N loss in the forearc) is employed to represent hot subduction zones, our estimation shows that up to similar to 25 % of the lost sedimentary N could be re-fixed in forearc serpentinites. The strong N retention in forearc serpentinites as well as in the minerals after antigorite breakdown (e.g., chlorite, amphibole, clinopyroxene and garnet) facilitates deep recycling of slab N (even in the early Earth) if the serpentinized mantle wedge are dragged down by mantle flow. Alternatively, if the serpentinized mantle wedge is imbricated as a portion of the lithospheric mantle, it will enhance the fertilization (and thus heterogeneity) of the lithospheric mantle.

Subduction zones play a critical role in carbon exchange between Earth's surface and interior. While devolatilization of forearc serpentinites has been proposed as a contributor to arc magma genesis, its role in subductionzone carbon (C) and magnesium (Mg) cycling, as well as its influence on the Mg isotopic variability in global arc lavas, remains poorly constrained. This study investigates Mg isotope fractionation during interactions between forearc peridotites and CO2-rich fluids in the Mianlue tectonic melange, focusing on carbonate-bearing serpentinites from the Jianchaling and Liangyazi regions. Five Jianchaling lizardite-only serpentinites exhibit a narrow range of S26Mg values (-0.28 f 0.02 %o to -0.13 f 0.02 %o), similar to those of four Jianchaling antigoritelizardite serpentinites (-0.27 f 0.03 %o to -0.17 f 0.01 %o). In contrast, seven Liangyazi antigorite-only serpentinites display a broader S26Mg range (-0.27 f 0.03 %o to -0.01 f 0.02 %o). Magnesium isotope compositions of mineral separates reveal temperature-dependent inter-mineral Mg isotope fractionations between carbonate and co-precipitated serpentine minerals. Thermodynamic modeling and mass balance calculations indicate minimal Mg loss from peridotites to fluids during their interaction with CO2-rich fluids. Instead, subsequent fluid infiltration and carbonate dissolution are responsible for the observed Mg isotopic variations. The concurrent precipitation of isotopically heavy silicate minerals and light carbonates in the forearc provides a plausible explanation for the elevated S26Mg values observed in some arc lavas. In subduction zones where the forearc slab-top temperatures can exceed the stability limit of antigorite (600 - 700 degrees C), significant forearc decarbonation produces CO2-rich fluids that interact with forearc peridotites at the bottom of the mantle wedge, forming abundant isotopically heavy silicate minerals. The subsequent breakdown of these silicates and limited release of slab-derived carbonates at subarc depths may be responsible for the high S26Mg values and low CO2 outfluxes characteristic of these subduction zones. In contrast, subduction zones with cooler forearc slab-top temperatures, where subarc slab-top temperatures approach the stability limit of antigorite, experience less significant forearc decarbonation. In such settings, limited formation of isotopically heavy silicate phases and enhanced release of slab carbonates at subarc depths due to infiltrations of slab-derived fluids can potentially result in arc magmas with S26Mg values close to or slightly below the normal mantle. These findings underscore the critical role of fluid-rock interactions in the forearc region in regulating deep carbon cycling and shaping the Mg isotopic signatures of arc magmas.

East Kunlun Orogen (EKO) hosts numerous economically important deposits in western China, including the Baiganhu W-Sn deposit in the west and the Lalangmai W-only deposit in the east, which share similar geological characteristics. However, significant differences exist between the two deposits, which include the decoupling of W and Sn mineralisation and the smaller size of the mineralisation at Lalangmai compared to Baiganhu. These differences reflect contrasting magmatic and fluid evolution histories and offer a valuable opportunity to refine models for the W-Sn metallogenesis in the EKO. In this contribution, we present a comprehensive study of the geochemistry and mineralogy of garnet, diopside and scheelite from the Lalangmai W deposit, supplemented by published data on petrology and isotopic geochemistry of monzogranite. The data are further compared with those of Baiganhu to better illustrate nature of the geological bodies. The results suggest that the differences between the two areas can be largely attributed to variations in the nature of the granitic rocks. The Lalangmai granites are characterised by lower temperature of emplacement, the absence of biotite and are relatively enriched Sr-Nd isotopic signature compared to the Baiganhu granites. In addition, the prevalence of Al-rich garnets in the peraluminous, felsic, ilmenite-bearing intrusions at Lalangmai contrasts with the Fe-rich garnets related to alteration in the Baiganhu area. This mineralogical distinction possibly suppresses the deposition of Sn and W mineralisation at Lalangmai, given that Sn substitutes for Fe, which represents the principal mechanism of deposition. Furthermore, a lack of oscillatory zoning in garnet and scheelite, a more uniform REE pattern of scheelite, and the prevalence of Mo-elevated only scheelite indicate a relatively stable redox environment and felsic environment. The single-stage mineralisation during prograde phase, as opposed to fluid circulation and multi-phase interactions, further restrict the scale of the deposit. These findings highlight a spatial and genetic decoupling of W and Sn mineralisation and distinct styles of mineralisation across the orogen and share similar pattern to that of the Nanling region in China. The proposed model contributes to a deeper understanding of the diversified W-Sn mineralisation in the orogen and provides valuable insights for guiding future prospecting endeavours in both W-only and W-Sn systems.

NH3 or NH4+ is an essential component of the abiotic synthesis of organic compounds for the origin of life and an efficient greenhouse gas to address the faint young Sun paradox on the early Earth. Sustainable NH3 or NH4+ on the N2-dominated prebiotic Earth's surface requires potent abiotic N2 reduction (ANR) in hydrothermal systems, which has not been detected in the geological record despite numerous laboratory demonstrations. Here we report high concentrations and extreme 15N depletions of NH4+ in hydrothermal veins in oceanic crusts drilled from the South China Sea basin. Our data indicate that abundant 15N-depleted NH4+ was produced by ANR in deep fluid but progressively overprinted by 15N-enriched biogenic NH4+ toward the surface. Modeling suggests that ANR could supply up to 9.0 - 10.8×1010 mol⋅year-1 NH4+ to global oceans, which is minor to the large nitrogen inventory in modern oceans, but could quickly fertilize the oceans and supply NH3 to the atmosphere in the prebiotic Earth.

Regional metamorphism is characterized by complicated mineral-mineral reactions and fluid-mineral interactions, which may promote elemental migration and ore genesis. A robust tracer of metamorphic reactions and fluid activities is a key for identifying material sources and quantifying mass flow along metamorphic pathways. Here, through examinations of not only bulk-rock nitrogen (N) isotopic variation along six prograde metamorphic zones but more importantly inter-mineral comparison of isotopic equilibration/disequilibration in the classic Barrovian metamorphic sequence in the Mica Creek area in the Canadian Cordillera, we show that N isotopes are a sensitive tracer for probing metamorphic devolatilization, mineral reaction and external fluid infiltration at various spatial scales from prograde to retrograde stages. In detail, our results show that, despite a relatively large variation in bulk-rock N/Al molar ratio, low-grade rocks (slates and phyllites) display a narrow δ15N range, which suggests relatively homogeneous N isotope compositions in their protoliths. Biotite-zone schists show reduced N/Al ratios with elevated δ15N values, which is consistent with devolatilization of 15N-depleted NH3 from rocks during prograde metamorphism at T < 500 °C. In contrast, samples from high-grade rocks (kyanite zone and sillimanite–K-feldspar zone) do not follow the metamorphic devolatilization trend but decrease in both N/Al ratios and δ15N values, indicating overprinting by a relatively large-scale flow (over at least tens of kilometers) of a 15N-depleted external fluid during the high-grade stage. The fluid was likely derived from the granitic magmas that intruded into these rocks during or slightly post peak metamorphism. The δ15N values of minerals in kyanite and sillimanite–K-feldspar zones displays negative correlations between biotite and both muscovite and plagioclase, with high δ15Nbiotite values close to isotope equilibrium but low δ15Nbiotite values at isotope disequilibrium. These negative correlations can be best explained by a kinetic isotopic effect associated with metamorphic reactions that consume muscovite and plagioclase to produce biotite. This suggests that plagioclase may be more involved in the metamorphic reactions in pelitic rocks than previously assumed. This kinetic isotopic effect can result in a Δ15Nplagioclase-biotite > 5 ‰, much larger than the theoretically predicted equilibrium N isotope fractionation factor (Δ15Nplagioclase-biotite < 0.5 ‰ at T > 350 °C) but close to the large N isotope fractionation (Δ15Nplagioclase-biotite ≈ 8 ‰) recently observed in field samples. Our data also imply that plagioclase is susceptible to retrograde alteration. Overall, combined N signatures of bulk rocks and coexisting minerals can provide multiple lines of constraints on mineral reactions and fluid activities from prograde to retrograde metamorphism.

Lithium has become an important strategic critical metal in the world, and the granitic pegmatite type lithium deposit is one of the important types of lithium resources, which is also a popular interest in the current international ore deposit research. The granitic pegmatites are classified into LCT（Li–Cs–Ta）, NYF（Nb–Y–F）and mixed LCT+NYF type. The LCT type pegmatites are characterized by enrichment of rare elements Li, Rb,Cs, Be, Ga, Sn, Ta＞Nb and fluxing components B, P, F, usually related to late orogenic and post–orogenic peraluminous S–type granites in extensional background. In this paper, we review the temporal and spatial distribution characteristics of pegmatite type lithium deposits in the world. It is noted that the lithium mineralization events mainly occurred in the middle and late period of convergent orogeny associated with the supercontinent assembly. The study shows that the spatial distribution of granitic pegmatite lithium deposits in China is relatively concentrated, mainly distributed in nine lithium metallogenic belts, of which the main mineralization period is Triassic. Fractional crystallization of granitic magma and partial melting of lower crust material are the two significant formation modes of pegmatites. The four metallogenic mechanism of rare metal pegmatite mainly include fractional crystallization, magmatic immiscibility, supercritical fluids and constitutional zone refining（CZR）. We summarize the metallogenic characteristics, distribution characteristics, research progress and exploration prospect of the three typical pegmatite type lithium metallogenic belts, West Kunlun, Songpan–Ganze and Altay, in western China. The coupling relationship of structure–magmatism–metamorphism–mineralization is the key scientific problem that restricts the mineralization process and enrichment regularity of lithium.

Detailed sample descriptions (S1), description of high-temperature and low-temperature serpentinization (S2), analytical methods (S3), two-component mixing model (S4), estimation of nitrogen input flux of the serpentinized slab mantle (S5), Figure S1 (compilation of nitrogen concentration data of altered oceanic crust), Figure S2 (two-component mixing model), and Figure S3 (temperature and pressure conditions of meta-basalts, meta-gabbros and meta-serpentinites).

Uptake of nitrogen (N) during hydrothermal alteration of oceanic crust makes the altered oceanic crust (AOC) a significant N reservoir in parallel to seafloor sediments. While N enrichment in the upper (basaltic) oceanic crust during low-temperature alteration has been widely observed, the N characteristics of moderate- to hightemperature altered gabbroic oceanic crust, which accounts for similar to 70 vol% of the crustal material in subducting slabs, have been rarely studied. The lack of these data resulted in large uncertainties in calculating the N input flux of global subducting slabs and modeling the N quantities released through the arc and subducted into the deep mantle. To fill this gap, we examined the N concentrations and isotope compositions of 38 altered gabbroic rocks recovered by ODP/IODP drillings from three oceans, i.e., Hole 735B at the Atlantis Bank in the Southwest Indian Ridge, Hole 1309D at the Atlantis massif in the Mid-Atlantic Ridge, and Hole 1415P at the Hess Deep in the East Pacific Rise. All the gabbroic samples show significant N enrichment with mostly positive delta N-15 values (in average: 7.4 +/- 3.8 ppm and +0.6 (+/- 2.0)% for Hole 735B, 5.3(+/- 2.1) ppm and +1.4(+/- 1.3)% for Hole 1309D and 7.9(+/- 1.9) ppm and +2.0(+/- 1.8)% for Hole 1415P), which are comparable to those of altered basalts from global oceanic crust. The N concentrations and delta N-15 values of these gabbroic rocks can be readily explained by mixing between minor inherited mantle N and mainly secondary N derived from seawater. The secondary N-hosting minerals in altered gabbroic rocks are likely plagioclase, amphibole and chlorite formed during moderate- to high-temperature alteration stages. Using these new data, we obtained a global nitrogen input flux of 20.6(+0.9) (1.3) x 109 mol center dot yr (1) to 29.9(+/- 2.2) x 10(9) mol center dot yr (1) for subducting AOC, in which 50% - 64% is contributed by the altered gabbroic oceanic crust. Integrating with previous estimate of N input flux from seafloor sediments, a total N input flux of 74.9(+0.9) (1.3) - 84.2(+/- 2.2) mol center dot yr (-1) was estimated for global subducting slabs. Mass balance between this input N flux and various estimates of N output flux in global arcs gave a large range (from 47% - 53% to 10% - 20%) for the fraction of slab N to be subducted beyond the sub-arc depth to the deeper mantle. The upper end (47% 53%) of this range is more consistent with the results from other constraints, such as thermal structural control and comparison between altered gabbros and meta-gabbros.

The Baiganhu area in the Eastern Kunlun Terrane on the northern margin of the Tibetan Plateau contains world-class Sn-W deposits in close association with monzogranite. However, the origin of granite and the tectonic setting for the Sn-W mineralization have not been well constrained. Here we present the petrological and geochemical data of the granite (431 Ma) associated with the Sn-W mineralization to evaluate the geological-tectonic setting for the mineralization. The monzogranite has high SiO2 contents, ranging from 65.8 to 73.5 wt%, and shows a geochemical affinity with A2-type granites. Relatively high zircon saturation temperatures, ranging between 750 degrees C and 921 degrees C, suggest that the parental magmas were hot. The whole-rock epsilon(Nd) (t = 431 Ma) values range from -2.7 to -3.1 with T-DM ages between 1810 and 1040 Ma, and zircon epsilon(Hf) (t = 431 Ma) values range from + 0.7 to + 4.1 with T-DM ages between 1040 and 900 Ma. The data suggest that the magmas had significant contributions of old rocks. The granitic rocks intruded into quartz-muscovite schist of the Proterozoic Xiaomiao Complex, which underlies the vast area. Zircon grains in the schist are magmatic in origin based on sharp oscillatory zoning and high Th/U ratios (>0.2). The Pb-207-Pb-206 zircon ages (n = 25) of the schist range from 1898 +/- 2 to 1700 +/- 6 Ma, suggesting that the zircon grains originate from a Paleoproterozoic magmatic belt. Such ancient rocks, either as lower crustal component or subcontinental lithospheric mantle, contributed similar to 30 % to the parental magmas. We conclude that post-collisional extension within the Eastern Kunlun Terrane was accompanied by upwelling and adiabatic melting of the asthenospheric mantle which induced partial melting of subcontinental lithospheric mantle and lower crustal rocks and formed granitic magmas. Aqueous fluids separated from the granitic magma which preferentially incorporate W and Sn contributed to the mineralization in and around the granites.

Serpentinized oceanic peridotites might be an important reservoir delivering volatile elements including nitrogen (N) into the mantle via subduction. To determine N sources and estimate the budget of alteration-added secondary N in the oceanic mantle peridotite reservoir, we examined oceanic serpentinites from four Ocean Drilling Program (ODP) sites in the Pacific and Atlantic Oceans. Our results showed that, despite large variation in serpentinization condition (high temperatures up to >350 degrees C at Holes 895D, 1271B, and 920D; low temperatures <150 degrees C at Hole 1274A), serpentinites from all sites displayed ubiquitous and similar magnitude of N enrichment (3.2-18.6 ppm) from sediments/seawater sources (615N = -3.3%0 to +4.4%0), and these values were significantly elevated relative to the low N concentration (0.04-2.0 ppm) and 615N value (-5%0 +/- 2%0) of the depleted mantle. Based on these data, the serpentinized oceanic mantle is estimated to contribute 0.4 +/- 0.2-14.7 +/- 6.9 x 109 mol N annually to global subduction zones. Although this flux is smaller than that of subducting sediments (57 x 109 molyr(-1)), comparison between oceanic serpentinites and meta-serpentinites from subduction zones suggests that N can be effectively retained in serpentinites during prograde metamorphism. This implies that the serpentinized slab mantle could be a critical reservoir to deliver N enriched in 15N to the mantle (at least 70 km depth) and potentially to the deepest portions of the mantle sampled by deep-rooted mantle plumes.

The Middle to Late Devonian was characterized by the widespread deposition of organic-rich mudstone units and successive biotic crises and anoxic events in the marine realm, the cause of which remains debated and requires constraints from associated marine conditions. This study provides an example of the marine nitrogen cycle throughout the late Eifelian to middle Frasnian anoxic pulses. We present new and previously published organic whole-rock N (δ15Nbulk) and carbon (δ13Corg) isotopic datasets from organic-rich mudstone units of the Horn River Group (Canol and Hare Indian Formations) and overlying Imperial Formation in the Central Mackenzie Valley, Northwest Territories, Canada. In the ConocoPhillips Mirror Lake N-20 core, δ13Corg ranges from −31.0 ‰ to −24.3 ‰ with δ15Nbulk from −3.8 ‰ to +1.9 ‰, whereas the Husky Little Bear N-09 core is characterized by δ13Corg from −31.0 ‰ to −27.2 ‰ and δ15Nbulk from −2.0 ‰ to +5.9 ‰. The N isotopic signatures near 0 ‰ and a lack of δ15Nbulk – δ13Corg relationship are characteristic of N2 fixation by primary producers. Regular oscillations in δ15Nbulk are interpreted as the product of episodic, mild oxygenation events. Together, our δ13Corg and δ15Nbulk results suggest that locally, N2 fixation was the dominant source of N for primary producers in the late Eifelian to middle Frasnian, despite fluctuations in δ13Corg and global marine paleoredox. These findings contribute to our understanding of the nitrogen speciation and bioavailability associated with anoxic events, biotic crises, and widespread organic carbon burial in the Eifelian to Frasnian oceans.

West Kunlun is an important pegmatite-type Li-Be metallogenic belt in China. In recent years, a great breakthrough in prospecting has been made in Dahongliutan area, and a large mineral resource base has been formed. In this paper, detailed researches on petrography, geochronology and geochemistry of the spodumene granite pegmatites in Dahongliutandong, West Kunlun, can provide a new basis for the study of pegmatite-type lithium mineralization in this area. By using LA-ICP-MS zircon U-Pb dating, the ages of spodumene-bearing albite pegmatite and spodumene-bearing tourmaline granite pegmatite in the Dahongliutandong are 205.2±1.4Ma and 205.0±2.6Ma, respectively, in the Late Triassic. Geochemical study shows that spodumene-bearing granite pegmatites in the Dahongliutandong is characterized by high Si, rich Al, Na, calc-alkali, high differentiation and low K, Fe, Mg, Ca and Ti, and belongs to strongly peraluminous granite pegmatite.The pegmatites are obviously rich in elements such as Rb, U, Nb, Ta, Pb, P, Hf, but depleting in elements such as Ba, Th, La, Ce, Pr, Sr, Nd, Sm and Ti. The total amount of rare earth is low, with ∑REE of 0.56×10 -6 ～3.34×10 -6 , weak-medium negative Eu anomaly and δEu of 0.30～0.89. The pegmatites in the Dahongliutandong have low and negative εHf（t） values（ –4.6～0） and the old two-stage Hf model age T DM2 （1 497～1 208 Ma）, which indicates that their source rocks are from partial melting of ancient crustal materials. Based on the chronological data and the evolution characteristics of regional geological structure in West Kunlun, it is considered that pegmatite deposits in Dahongliutan area were formed in the background of postcollision between South Kunlun terrane and Tianshuihai terrane.

Late Triassic calc-alkaline I-type granites with abundant mafic microgranular enclaves (MMEs) are widespread in the West Kunlun Orogenic Belt, meanwhile, large quantities of Mesozoic granitic pegmatites also develop in this area, which makes an important pegmatite-type Li-Be metallogenic belt in China. In recent years, a great breakthrough in mineral resource prospecting has been made in Dahongliutan area, especially in the Qitaidaban pluton which is closely related in space with the pegmatite-type lithium deposits in this area. In this paper, we present a systematic research result from petrological, petrogeochemical, zircon U-Pb chronological and Sr-Nd-Hf isotopic studies on the biotite monzogranite and the MMEs in Qitaidaban, West Kunlun, to accurately determine their formation age, petrogenesis characteristics and tectonic settings, and thus to disclose their genetic relationship with rare metal pegmatite mineralization. The LA-ICP-MS U-Pb ages of zircons indicate that the mafic microgranular enclaves and the host biotite monzogranite are crystallized at 212.9 +/- 1.6Ma and 213.7 +/- 2.0Ma, respectively, i.e., in the Late Triassic, which provides strong evidence for the existence of magma mixing in this area. Whole-rock geochemical data indicate that the biotite monzogranite and the MMEs belong to weak peraluminous high-K calc-alkaline I-type granites, and the content of SiO2 in MMEs is lower than that of the host monzogranite. Furthermore, they are enriched in LILE (Rb, Th, U, K), relatively depleting in HFSE (such as Nb, P, Ti), and have similar Sr-Nd-Hf isotopic compositions. The biotite monzogranite has (Sr-87/Sr-86)i values of 0.70789 similar to 0.70839, epsilon(Nd)(t) values of -5.42 similar to-4.02, epsilon(Hf)(t) values of -4.8 similar to 4.8, and Hf isotope two-stage model age (t(DM2)) of 909 similar to 1516Ma; while the enclaves have (87Sr/86Sr)i values of 0.70833 similar to 0.71011, epsilon(Nd)(t) values of -6.36 similar to-5.05, epsilon(Hf)(t) values of -4.7 similar to 1.8, and Hf isotope two-stage model age (t(DM2)) of 1097 similar to 1509Ma, respectively. It is considered that they are the products of the mixing of a basic magma formed by partial melting of enriched lithospheric mantle and a felsic magma formed by melting of amphibolite in ancient lower crust. Based on a combined study of geochronology and evolutionary characteristics of regional structures in the West Kunlun, we consider that the biotite monzogranite and the MMEs in Qitaidaban were formed in the post-collisional extension stage of the Paleo-Tethys Ocean, which suggests that the West Kunlun Orogenic Belt had begun its post-collisional extension in the Late Triassic (213Ma), and thus it provides new chronological evidence for the tectonic and magmatic evolution of the Paleo-Tethys in West Kunlun. The rare metal pegmatites in Dahongliutan area are the products of crystallization and differentiation of the granitic magma which has the characteristics of a continuous differentiation and evolution, while the Qitaidaban granite pluton was formed in the middle of the whole magmatic evolution process, and as a result, it has indicative significance to the formation of rare metal pegmatites in Dahongliutan area.

Studies of alteration enrichment of nitrogen (N) in seafloor basalts clearly indicate that the upper oceanic crust is an important reservoir to transfer crustal N into Earth's interior. However, since previous studies have focused on relatively few DSDP/ODP/IODP drill cores, the factors controlling N enrichment in the altered upper oceanic crust at a global scale have not been revealed. Here we report N concentrations and isotope compositions of altered basalts from four additional DSDP/ODP Holes (556, 1224F, 417A and 543A). These new data, together with the published data from Holes 801C, 1149D, 1256D and 504B, enable systematic assessment of the potential affecting factors such as alteration degree, crustal age, spreading rate and sediment type, on N enrichment in the upper oceanic crust. The new data demonstrate ubiquitous N enrichment (1.3 – 48.4 ppm) in global seafloor basalts. The results indicate that, (i) the secondary N (in the form of ammonium) in altered basalts was sourced from sediment/seawater with δ15N values of 0‰ to +8‰, with a minor source from abiotic N2 reduction with δ15N values of -12‰ to -21‰; (ii) N enrichments in the upper oceanic crust do not correlate with crustal age, suggesting that the N uptake should mainly occur over early ages (likely within ∼20 Myr of crustal formation); (iii) the magnitude of N enrichment in the upper oceanic crust is primarily controlled by the N availability in the surrounding environment, which is ultimately related to the N abundance of basal sediments and/or seawater. The highest degree of N enrichment occurs in the upper oceanic crust overlain by N-rich basal sediments (claystone), i.e., at Hole 543A (N = 24.9±8.3 ppm; 1σ). In contrast, the lowest degree of N enrichment occurs in the upper oceanic crust overlain by N-poor basal sediments (chert), i.e., at Hole 1149D (N = 2.0±0.5 ppm; 1σ). With the consideration of this primary controlling factor, a global N input flux of 3.7±0.3 ×109 mol⋅yr−1 for the 300 – 600 m upper oceanic crust is calculated. These new data also demonstrate that N concentrations are relatively low in global altered basalts (average: 10.1±7.8 pm; 1σ). In comparison to their metamorphic equivalents, blueschists have much higher N concentrations (up to ∼122 ppm) whereas eclogites have N concentrations comparable to altered basalts. This implies further N enrichment in basaltic oceanic crust during early subduction and N devolatilization during deep subduction (by eclogite facies).

Lattice fixed nitrogen component in arc lavas from Kick'em Jenny (KEJ) was investigated for improving our understanding of two long-standing controversies in the recycling of subducting slab material. One is whether the crustal signatures in the Lesser Antilles arc rocks originated from slab recycling or crustal assimilation. The other is the budget of fixed nitrogen in arc crust, which is still a missing piece in the modeling of geodynamic nitrogen cycle. Our results show that the KEJ basaltic lavas contain variable amounts of labile nitrogen (removable by 400 °C heating) and 2.6–5.3 ppm refractory nitrogen with δ15N values of +0.8‰ to +6.6‰. The labile nitrogen was likely introduced on seafloor although the KEJ lavas appear to be strikingly fresh, whereas the refractory nitrogen was likely inherited from their magmatic source. Nitrogen isotopic signature of the refractory nitrogen cannot be explained by magmatic degassing, fractional crystallization and/or crustal assimilation. Instead, the data can be best explained by a mixing between the mantle and two δ15N-distinct endmembers, which are consistent with the two types of subducting sediments (i.e., marl/ooze and shale) recovered from the reference site (DSDP Site 144). This supports sediment recycling into the mantle source of the Lesser Antilles arc. Our modeling also yielded a nitrogen fixation flux of 2.3–4.7 × 103 moles N⋅yr⋅−1km−1 (or 1.8–3.8 × 106 moles N⋅yr−1 for the 800 km arc) in the Lesser Antilles arc crust. This is 2–3 orders of magnitude smaller than the nitrogen input flux into the Lesser Antilles trench solely from subducting sediments (1.3 × 106 moles N⋅yr⋅−1km−1 or 1.0 × 109 moles N⋅yr−1 for the entire 800 km trench). This suggests that arc crust is not a major repository of subducted nitrogen, at least in the Lesser Antilles. Instead, most of the crustal nitrogen subducted to the sub-arc depths is either retained in the subducting slab, stored in the metasomatized lithospheric mantle, and/or released back to the surface by volcanic emission.

西昆仑西北缘柯牙吾齐超镁铁岩的发现对于西昆仑西段构造演化研究和相关矿产资源的探寻具有重要意义.本文对该超镁铁岩7件样品进行了镜下鉴定、主量和微量元素分析,结果显示:超镁铁岩呈断续脉状产出,岩性主要为蛇纹石化辉橄岩;具有相对低SiO2(42.14％ ～47.43％)、低TiO2(0.03％ ～0.24％)、高MgO(24.69％ ～31.22％)、高FeOT(7.05％ ～11.65％)、贫碱(K2 O+Na2 O=0.55％ ～0.88％)的特征;Mg#值为79.98～86.70;样品的m/f比值介于3.96～7.82;样品中稀土总量(∑REE)不高(11.41×10-6～17.84×10-6),轻重稀土比值LREE/HREE为2.81～5.69;δEu显示弱的Eu正异常;相容元素Ni、Cr和Co含量高.在微量元素原始地幔标准化蛛网图上,表现为富集大离子亲石元素(LILE)Rb、Ba、U、Sr和Pb,相对亏损高场强元素(HFSE)Nb、P、Zr、Hf、Ti等,显示轻稀土富集的特征.结合区域构造背景分析认为,晚三叠世,古特提斯洋的闭合引起碰撞后伸展,来自亏损地幔岩浆受前期俯冲流体或者熔体改造,沿着深断裂上侵,过程中经历了一定程度的地壳混染,最终形成柯牙吾齐超镁铁岩.

The fate of subducted crustal nitrogen (N) in modern-style subduction zones remains hotly debated from nearly complete return to the surface via arc volcanoes to net ingassing into the deep mantle beyond the sub-arc depth. One of the major obstacles for this controversy is the lack of constraint on the input N flux from altered oceanic crust (AOC). While notable N enrichment by low-temperature hydrothermal alteration has been widely reported in the upper volcanic section of AOC, N behavior during high-temperature alteration of the underlying intrusive oceanic crust (i.e., sheeted dikes and gabbros) remains poorly understood. Here we examined the bulk-rock N concentrations and isotopic compositions of the AOC (with a main focus on sheeted dikes and gabbros, yet including basalts from sections that have not been examined before) from ODP/IODP Hole 1256D and DSDP/ODP Hole 504B, which are two reference sites for subducting material into the warm Central America (CA) subduction zone. The results show that the intrusive sections have comparable N concentrations and isotopic compositions to their overlying upper volcanic rocks at 1256D (sheeted dikes: 16.4(+/- 7.2)ppm and -1.3(+/- 1.5)parts per thousand; gabbros: 11.3(+/- 5.6) ppm and +1.3(+/- 1.0)parts per thousand; basalts: 11.8(+/- 3.8) ppm and +0.9(+/- 1.7)parts per thousand) and 504B (sheeted dikes: 7.6(+/- 2.1) ppm and +2.1(+/- 1.7)parts per thousand; basalts: 8.0(+/- 3.8) ppm and +2.4(+/- 2.9)parts per thousand). These data can be readily explained by mixing between inherited mantle N and secondary N mostly derived from seawater/sediments with a minor contribution from abiotic N-2 reduction. The secondary N in sheeted dikes and gabbros was mainly incorporated at moderate- to high-temperature (> 250 & DEG;C) alteration stages and likely resides in chlorite, secondary plagioclase and amphibole. These new data clearly indicate that the intrusive section of AOC is a non-negligible N reservoir. Using these data, together with previously published N concentration data of basalts from Holes 1256D and 504B and of subducting sediments from Hole 1039B offboard the CA trench, we obtained a total N input flux of 3.1(+/- 0.6) x 10(9) mol yr(-1) to 4.0(+/- 0.8) x 10(9) mol yr(-1) into the CA trench. Integrating recently published N output flux of 0.58 x 10(9) to 1.4(+/- 0.6) x 10(9) mol yr(-1) at the CA arc, an N recycling efficiency of 15(+/- 3)-45(+/- 5)% was yielded for the CA margin, indicating that up to 55(+/- 5)-85(+/- 3)% of subducted slab N is possibly transported beyond the sub-arc depth in this warm subduction zone. Based on the new finding of comparable N enrichment between basalts and intrusive oceanic crust, our modeling also gave a revised N recycling efficiency of 12(+/- 10)-17(+/- 12)% for the cold Izu-Bonin-Mariana (IBM) subduction zone, which is consistent with previous estimate of 4-17%. While these new estimates do not provide a conclusive constraint on the effect of subduction-zone thermal structure on N recycling, they consistently suggest that a large fraction of slab N (> 50%) can survive the sub-arc filter and be delivered to the deeper mantle in global subduction zones. (c) 2022 Elsevier Ltd. All rights reserved.