The Oceanic Anoxic Event 1a (OAE 1a) represents one of the most significant environmental perturbations during the Cretaceous. During OAE 1a, changes in climate and ocean redox conditions exhibit noteworthy spatiotemporal heterogeneity. However, environmental changes in the Eastern Tethys during OAE 1a remain poorly constrained. In this study, high-resolution geochemical data of organic carbon isotope (δ13Corg), redox-sensitive trace elements (RSTEs), and total sulfur (TS) were used to correlate the OAE 1a interval of two sections in the Eastern Tethys: the Gucuo II section in Southern Tibet and the Ocean Drilling Program (ODP) Site 765C in the Argo Abyssal Plain. Paleoredox and paleoclimate proxies of these sections exhibit similar trends across OAE 1a, indicating synchronized environmental changes. RSTEs and TS contents increase before OAE 1a, remain elevated during OAE 1a, and decrease to near background values after OAE 1a, indicating preceding deoxygenation and prolonged reoxygenation in the Eastern Tethys. Weathering proxies, including the chemical index of alteration (CIA), chemical index of weathering (CIW), and Ti/Na ratios, exhibit a decreasing trend beginning before the onset of OAE 1a and continuing into early OAE 1a, followed by an increasing trend during late OAE 1a, indicating a delayed enhancement in weathering in the Eastern Tethys. Regionally, the delayed weathering enhancement might have resulted from dry climate and/or transient cooling episodes during early OAE 1a. This study elucidated the regional environmental response of the Eastern Tethys to OAE 1a, contributing to a more comprehensive understanding of the initiation and cessation mechanisms of OAE 1a.

The Tonian Period captures critical co-evolutionary transitions between marine redox conditions and early life, but the sediments that have undergone low-grade metamorphism complicate investigations into contemporaneous marine redox conditions. In this study, comprehensive analysis of whole rock and pyrite chemistry in slates of the Tongtawan Formation (similar to 800 Ma) is conducted to reconstruct oceanic redox conditions and evaluate diagenetic/metamorphic impacts on these sediments. The size of framboidal pyrites mostly ranges from 3.33 to 7.67 mu m, indicating a predominantly ferruginous deep ocean, with minor occurrences of euxinic or dysoxic conditions. However, depressed ratios of highly reactive iron to total iron (i.e., Fe-HR/Fe-T mostly <0.38) in whole rock seem to indicate oxic conditions. This is attributed to the consumption of highly reactive iron due to chloritization during diagenesis/metamorphism. Pyrite morphology and diagnostic trace element ratios confirm its syngenetic to early-diagenetic origins, validating pyrite chemistry as a robust proxy for contemporaneous seawater composition. In situ LA-ICP-MS analyses document pronounced enrichments of elements (e.g., Co, Ni, Mo, and Mn) in pyrites, exceeding typical Tonian and Mesoproterozoic records. These enrichments reflect enhanced inventory in the ocean due to atmospheric and oceanic oxygenation-with Mo exhibiting the most diagnostic response-and additional fluxes from the erosion of mafic/ultramafic rocks and from hydrothermal inputs linked to the mantle plume and Rodinia breakup (e.g., Co, Ni, and Mn). This indicates Tonian oceans possessed a significantly expanded element reservoir during the Tonian, displaying enhanced oxidation levels despite largely ferruginous deep waters against a backdrop of increasing atmospheric oxygen.

A large hydrothermal field at depths >4300 meters was found on the east Caroline plate in the western Pacific Ocean. Here, we show that large hydrothermal pipes with steep walls and breccia-dominated bottoms suggest explosions of billion metric tons of TNT (trinitrotoluene) equivalent. More than 800 short-duration seismic events were detected within 28 days along a 150-kilometer profile, indicating widespread ongoing explosive gas release. We suggest that billions of tons of hydrogen gas were produced through serpentinization associated with fluid infiltration via fractures formed by bending of the oceanic plate. Hydrogen was retained in fractures sealed by mud and carbonate. However, hydrogen alone cannot produce the explosive capacity responsible for the formation of pipes. Oxygen released from circulating seawater can be concentrated at crustal depths and then mixed with mantle-derived hydrogen. Explosion of the gas mixture releases large amounts of heat that triggers further explosions of compressed hydrogen gas and results in the formation of hydrothermal pipes.

Mid-ocean ridge basalts (MORBs) from the Indian Ocean have been demonstrated to have more enriched radiogenic isotopic compositions than MORBs from the Pacific and Atlantic Oceans. However, the origin of such anomaly is still under debate. To better constrain the genesis of the isotopic anomaly observed in Indian MORBs, we present a systematic Ca-Sr-Nd isotopic study of a suite of MORBs from the Central Indian Ridge (CIR) between 19 and 20 degrees S and the adjacent Gasitao Ridge. The delta 44/40 Ca values of these MORBs vary from 0.70 to 0.89 parts per thousand, most of which are similar to those of reported Pacific and Atlantic MORBs. However, some samples from the northern part of the studied CIR region showed slightly lower delta 44/40 Ca values than the average of the reported Pacific and Atlantic MORBs. Notably, these delta 44/40 Ca values are correlated with Sr-Nd isotopic ratios, which extend from the depleted MORB mantle to a component with lower delta 44/40 Ca and more enriched Sr-Nd isotopic compositions, suggesting the presence of an enriched component in the source of these Indian MORBs. Recent studies have proposed that lower continental crust has similar delta 44/40 Ca values to the estimated Bulk Silicate Earth, indicating that the low delta 44/40 Ca signatures of some Indian MORBs are unlikely to be produced by delaminated lower continental crust. Garnet in the residue and recycled carbonate-rich marine sediments with oceanic crust can cause lower delta 44/40 Ca signatures in mantle-derived rocks. However, trace element ratios and our model calculations suggest that these two factors can hardly induce the correlated Ca-Sr-Nd trends in these Indian MORBs. Instead, recently reported subcontinental lithospheric mantle xenoliths that experienced silicate and/or carbonatite metasomatism, which also show low delta 44/40 Ca and enriched Sr-Nd isotopic compositions, correspond with the correlated Ca-Sr-Nd trends in the studied Indian MORBs. Moreover, ancient metasomatized subcontinental lithospheric mantle materials have been observed in abyssal peridotites from the Southwest Indian Ridge. Therefore, delaminated subcontinental lithospheric mantle maybe the most likely cause of the Ca-Sr-Nd isotopic anomaly in Indian MORBs. Our study suggests that combined Ca-Sr-Nd isotopes can be treated as potential tracers to the genesis of mantle heterogeneity.

The Kunlun hydrothermal system near the Mussau Trench in the western Pacific consists of 20 large round/oval craters of hundreds of meters in diameter. The total area is 11.1 square kilometers, i.e., over a hundred times larger than the Lost City. Four of the larger craters were prospected using the human occupied vehicle Fendouzhe and have steep walls similar to those of kimberlite pipes, with depths of up to 130 meters. Ecosystems have been observed in smaller pits on the bottom of these pipes. Hydrogen concentrations of ~5.9 to 6.8 millimoles per kilogram in hydrothermal fluids have been obtained using in situ Raman spectra. The estimated total hydrogen flux of Kunlun is 4.8 × 1011 moles per year, which is >5% of the estimated global submarine abiotic hydrogen flux. Hydrogen-rich, alkaline fluids generated by serpentinization have formed large-scale carbonate rocks within the pipes below the carbonate compensation depth, and both dolomite and calcite have been identified.

Abyssal peridotites and mid-ocean ridge basalts (MORB) offer only a partial glimpse into the mantle's composition and the magmatic process beneath the mid-ocean ridges. Recently, lower crustal cumulates have emerged as potential candidates for capturing a broader range of mantle heterogeneity and depicting a detailed process in MORB generating system. However, it remains uncertain to what extent the lower crustal cumulates can represent mantle source variability. In this study, we present detailed in-situ geochemical and isotopic data, including major and trace element compositions of minerals and in-situ Sr isotopic analysis on plagioclase from lower crustal cumulates collected at 14°45′N on the Mid-Atlantic Ridge (MAR). Trace element compositions of melt in equilibrium with clinopyroxenes from the lower crustal cumulates exhibit strong similarities to nearby MORBs. Exception is that the equilibrium melt of the core of a clinopyroxene oikocryst records a transitional MORB composition, different from the more enriched MORB composition at rims. This phenomenon, together with element changing in minerals from cores to rims, suggests a history of melt-rock interactions, during which more enriched melts transport through minerals that had previously crystallized from relatively more depleted melts. The in-situ 87Sr/86Sr ratios, which vary from 0.70249 to 0.70306, span the range of the global MORB Sr isotope values. Thus, both the trace element compositions and 87Sr/86Sr ratios of cumulate minerals confirm the coexistence of depleted and enriched melts. Our findings furtherly suggest that the melts from heterogenous mantle components underwent incomplete mixing in the lower oceanic crust, even in the crystal mush, thus preserving variable heterogeneities not seen in MORB. Through integrated analyses of geochemistry, isotopic data, and geophysical information from existing literature, we identify the most likely mantle components in the study area as depleted peridotites veined with recycled oceanic crust (pyroxenites).

Oxygen fugacity is a key factor in controlling the formation of porphyry molybdenum deposits. We present new data on Lengjia monzogranite and compile the Mesozoic magmatism data of the Jiaodong Peninsula to elucidate the correlation between magma oxygen fugacity and porphyry Mo mineralization. Zircon U -Pb geochronology indicates that the formation of the Lengjia monzogranite occurred at 113.7 Ma, while molybdenite Re -Os geochronology shows that the Lengjia Mo deposit was formed at 113.5 +/- 3.0 Ma. The Lengjia monzogranite, characterized by low Sr/Y ratios (12.28 - 20.16), low Sr, and high Yb and Y concentrations, can be classified as a non-adakite I -type granite. It had low zircon epsilon Hf (t) values (-23.8 - -13.8) and ancient TDM2 (Hf) (2047-2680 Ma) with variable zircon O isotopic compositions (5.82 %o - 7.38 %o). The Lengjia monzogranite was formed by partial melting of the Paleoproterozoic crustal source and mantle components metasomatized by slab-derived melt. The zircon trace element calculation revealed that the Weideshan suite had higher Delta FMQ values (0.32 - 4.47, average is 2.27) compared to the Guojialing suite (-0.91 - 2.88, average is 0.82) and Linglong suite (-1.81 - 2.76, average is 0.37). The oxidized Weideshan suite resulted from the increased involvement of mantle metasomatized by slab-derived melt. The elevated oxygen fugacity promoted the porphyry Mo-metallogenic potential of the Weidshanian suite. We propose that the Linglong suite was related to the northwestward flatslab (subhorizontal) subduction of the Izanagi plate (Paleo-Pacific plate), the Guojialing suite was formed by low-angle northwestward subduction of the Izanagi plate, and the Weideshan suite was related to the northwestward subduction and major slab rollback of the Pacific plate.

Determining the evolutionary history of mantle oxygen fugacity (fo2) is crucial, as it controls the fo2 of mantle-derived melts and regulates atmospheric composition through volcanic outgassing. However, the evolution of mantle fo2 remains controversial. Here, we present a comprehensive dataset of plume-derived komatiites, picrites, and ambient mantle-derived (meta)basalts, spanning from ~3.8 Ga to the present, to investigate mantle thermal and redox states evolution. Our results indicate that fo2 of both mantle plume-derived and ambient mantle-derived melts was lower during the Archean compared to the post-Archean period. This increase in the fo2 of mantle-derived melts over time correlates with decreases in mantle potential temperature and melting depth. By normalizing fo2 to a constant reference pressure (potential oxygen fugacity), we show that the fo2 of both the mantle plume and ambient upper mantle has remained constant since the Hadean. These findings suggest that secular mantle cooling reduced melting depth, increasing the fo2 of mantle-derived melts and contributing to atmospheric oxygenation.

Tephra layers in the western Philippine Sea, characterized by abundant volcanic glass shards, may provide crucial evidence on the eruption history of volcanoes and tectonic evolution of the western Pacific. A 220-ka sediment core from the Benham Rise in the western Philippine Sea offers new insights into the provenance of four intercalated tephra layers (T1–T4, in chronological order) containing either colorless or brown glass shards. Relative to primitive mantle, all glass shards are enriched in large-ion lithophile elements, such as Rb, Cs, and Pb, and depleted in high field-strength elements, such as Th, Nb, and Ta, indicating a subduction-related origin. The colorless glass shards are characterized by high SiO2 (>78

Porphyry deposits supply most of the world's Cu and Mo resources. Most porphyry deposits are developed in magmatic arcs above subduction zones. However, abundant Miocene porphyry Cu-Mo deposits have been found in the post-collision stage in Tibet, more than similar to 30 Myr after the Indian-Eurasian continental collision. The magma source and the enrichment process of ore-forming elements for these post-collision porphyry deposits remain controversial. Here, we present Sr-Nd-Mo isotope compositions of a suite of mineralized and barren igneous rocks from the Rongmucuola pluton in the Miocene post-collisional Qulong porphyry Cu-Mo deposit in Tibet to reveal their magma sources and ore-forming processes. Our results indicate that the mineralized and barren igneous rocks in the Qulong deposit were derived from a cogenetic source with similar Sr-Nd isotope compositions (Sr-87/Sr-86((i)) = 0.7049-0.7050 and epsilon(Nd)(t) = -0.24 to 0.20). However, the mineralized igneous rocks have large variations in delta Mo-98/95 values (-0.30 parts per thousand to 0.74 parts per thousand; relative to NIST SRM 3134) and Mo/Ce ratios (0.01 to 4.84) compared to those of the barren igenous rocks (delta Mo-98/95 = -0.74 parts per thousand to -0.02 parts per thousand; Mo/Ce = 0.01 to 0.04). In combination with the higher LOI values, Mo/Ce and Cs/Ta ratios and Cu concentrations and lower Ce/Pb ratios of the mineralized igneous rocks relative to the barren igneous rocks, we propose the mineralized igneous rocks were affected by ore-forming hydrothermal fluids originated from the exsolution of later co-genetic magmas, which significantly changed the isotopic and elemental compositions of intrusions and resulted in Mo mineralization. The fluid-rock interaction modeling supports this interpretation and successfully reproduce the observed delta Mo-98/95 and Mo/Ce compositions of mineralized igneous rocks. Our study indicates that the exsolved magmatic-hydrothermal fluids have heavy Mo isotopes, and the fluids with a slightly heavier Mo isotope composition have the greatest potential for mineralization. As the water-rock reaction progresses, leading to the precipitation of Mo-rich minerals, ore-forming fluids with a heavier Mo isotope composition may not have significant mineralization potential. This highlights that Mo isotope system is an effective tool to study the ore-forming processes of porphyry deposits.

The formation of most jadeitites and other jadeite‐rich rocks (jadeitoids) during subduction is thought to occur by precipitation (P‐type) or metasomatism (R‐type) by infiltration of Na‐Al‐Si‐rich aqueous fluids because of the compositional similarity of the rocks to inferred subduction fluids. Whether these rocks can form by isochemical metamorphism (I‐type) during subduction is still hotly debated. A characteristic of I‐type jadeitoid is that it exhibits a similar prograde metamorphic record as associated eclogite, in contrast to P‐ and R‐type jadeitite and jadeitoids that are typically enclosed in serpentinite derived from the mantle wedge and either lack a prograde metamorphic history (R‐type and P‐type) or probably experience a prograde history (R‐type) that is difficult to discern owing to the high variance of the jadeite‐dominated assemblages and alteration by subduction fluids. The recently discovered Baqing (eastern‐central Tibet) jadeitoid is enclosed by quartzo‐feldspathic schist and has a peak metamorphic assemblage of almandine + jadeite/omphacite + phengite/paragonite + rutile + quartz, similar to eclogite. Abundant mineral inclusions in almandine, especially rutile inclusions with increasing Zr contents from the core to rim of almandine, provide an opportunity to further decode the jadeitoid‐forming processes. In this study, pseudosections and Zr‐in‐rutile thermometry, together with conventional geothermobarometers, were employed to decipher the metamorphic history of Baqing jadeitoids. Two analysed Baqing jadeitoids exhibit a similar clockwise P–T path, starting from early metamorphic conditions of 5–7 kbar, 350–440°C, to different peak conditions (27–29 kbar, 730–760°C, or 20–23 kbar, 670–710°C), followed by relatively consistent retrograde metamorphic conditions of 6–7 kbar, 530–600°C. This result indicates a similar subduction history to the Baqing eclogite. In addition, the Baqing jadeitoids show similar geochemical characteristics to some Na‐rich, K‐depleted and Ca‐depleted sedimentary rocks or plagiogranite. Therefore, we propose an isochemical genesis for the Baqing jadeitoid, rather than a metasomatic origin.

The Hawaiian-Emperor seamount chain has shown two subparallel geographical and geochemical volcanic trends, Loa and Kea, since ∼5 Ma, for which numerous models have been proposed that usually involve a single mantle plume sampling different compositional sources of the deep or shallow mantle. However, both the dramatically increased eruption rate of the Hawaiian hotspot since ∼5 Ma and the nearly simultaneous southward bending of the Hawaiian chain remain unexplained. Here, we propose a plume-plume interaction model where the compositionally depleted Kea trend represents the original Hawaiian plume tail and the relatively enriched Loa trend represents an emerging plume head southeast of the Hawaiian plume tail. Geodynamic modeling further suggests that the interaction between the existing Hawaiian plume tail and the emerging Loa plume head is responsible for the southward bending of the Hawaiian chain. We show that the arrival of the new plume head also dramatically increases the eruption rate along the hotspot track. We suggest that this double-plume scenario may also represent an important mechanism for the formation of other hotspot tracks in the Pacific plate, likely reflecting a dynamic reorganization of the lowermost mantle.

Multiple lines of evidence revealed that enormous CO2 was input into the ocean-atmosphere system during Oceanic Anoxic Event 1a (OAE 1a), which led to a series of environmental perturbations (e.g. temperature rising, enhanced weathering, promoted primary productivity and marine anoxia). Among them, increased carbon isotope fractionation (Δ13Ccarb-org) between the carbonate (δ13Ccarb) and organic carbon (δ13Corg) in the sediments is one of the most important indicators to the enhanced atmospheric pCO2. However, only a few research reported high-resolution paired carbon isotopes during OAE 1a, which were almost limited around the western Tethys. Here, we report new paired carbon isotopes of the Early Cretaceous sediments from the ODP site 866A in the western Pacific and the Lingshan Island section in the Sulu orogenic belt. The δ13Ccarb curves from both sections correlate well with OAE 1a, in which a positive δ13Ccarb excursion is identified between the C3–C6 segments. The Δ13Ccarb-org displays a ∼7–11‰ positive shift coinciding with the δ13Ccarb excursion, indicating a remarkable increase and a gradual decrease in CO2 in water and atmosphere, which further support significant atmospheric pCO2 changes during OAE 1a on a global scale. The sediments also show a few variations in carbon isotope records during OAE 1a between different locations, which may reflect different influences from local environments, and the deviations of stratigraphic correlation and diagenesis cannot be ruled out either.

Whether or not oceanic crust basalts are affected by plate subduction is a hot topic of debate. The South China Sea is one of the largest marginal basins in the western Pacific Ocean and has been surrounded by subduction of the Pacific plate and Indian plate, yet, to date, no study has clearly shown evidence of subduction in the geochemistry of volcanism in the basin due to a lack of sampling of igneous crust basalts on the seafloor. The International Ocean Discovery Program Expedition 349 cored seafloor basalts near the fossil spreading ridges of the eastern (Site U1431) and southwestern (Site U1433 and U1434) subbasins in the South China Sea. The recovered basalt samples indicated a pyroxenite-bearing peridotite mantle source. Here, we report Mg isotopic data from 14 of these oceanic crust basalt samples. The δ26Mg values of most basalts from the three drill holes were higher (up to −0.10‰) than that of the average mantle (−0.25‰). The lack of correlations of δ26Mg with geochemical indices of magmatic processes (e.g., MgO, CaO/Al2O3, La/Sm, Nb/Zr) suggests that crystal fractionation and partial melting had insignificant effects on the Mg isotopic compositions of the South China Sea basalts. Thus, the variations in Mg isotopes were inherited from their mantle sources. Considering the highly varied Ce/Pb ratios and elevated 87Sr/86Sr values but mantle-like 143Nd/144Nd values, we propose that the varied δ26Mg values were likely caused by metasomatism of subduction-released fluids. The coupling of Mg and Sr-Fe isotopes provides robust evidence that the high-δ26Mg values of the South China Sea basalts resulted from mixing among pyroxenite-bearing peridotite mantle, the nearby Hainan plume materials, and subducting serpentinite-released fluids. Therefore, these Mg isotopes suggest that the mantle source of the South China Sea basalts was influenced by subducted materials, providing further evidence of the initial expansion, formation, and evolution of the South China Sea during plate subduction.

The three-phase coexistence line of the CO2 hydrate was determined using molecular dynamics (MD) simulations. By using the classical and modified Lorentz-Berthelot (LB) parameters, the simulations were carried out at 10 different pressures from 3 to 500 MPa. For the OPC water model, simulations with the classic and the modified LB parameters both showed negative deviations from the experimental values. For the TIP4P/Ice water model, good agreement with experimental equilibrium data can be achieved when the LB parameter is adjusted based on the solubility of CO2 in water. Our results also show that the influence of the water model on the equilibrium prediction is much larger than the CO2 model. Current simulations indicated that the H2O-H2O and H2O-CO2 cross-interactions' parameters might contribute equally to the accurate prediction of T3. According to our simulations, the prediction of T3 values showed relatively higher accuracy while using the combination of TIP4P/Ice water and EPM2 CO2 with modified LB parameter. Furthermore, varied χ values are recommended for accurate T3 estimation over a wide pressure range. The knowledge obtained in this study will be helpful for further accurate MD simulation of the process of CO2/CH4 replacement.

Early Cretaceous A-type granites are widespread in the Shandong Peninsula, which can be used to elucidate the tectonic evolution of the eastern China and the destruction of the North China Craton. However, their genesis is still controversial. Several competing models, ranging from slab break-off, postorogenic extension, foundering of the lower crust and ridge subduction, were proposed. Here, we report zircon U–Pb ages, whole-rock and apatite geochemical compositions of the Laoshan granite and discuss its tectonic implications. The Laoshan granite has typical characteristics of A-type granite with high FeO T /(FeO T + MgO) ratios (0.90–0.97) and 10000*Ga/Al ratios (2.70–3.36) and high total alkali (Na 2 O + K 2 O: 7.95–8.70 wt%) contents and Zr+Nb+Ce+Y (most >350 ppm) concentrations. The Laoshan granite is further classified as A 1 -type based on the Yb/Ta-Y/Nb and Ce/Nb-Y/Nb diagrams and the Nb-Y-3Ga and Nb-Y-Ce triangular discriminant diagrams. Zircon U–Pb dating of two Laoshan granite samples yielded emplacement ages of 117.8 ± 1.0 Ma and 120.1 ± 1.3 Ma, respectively. The oxygen fugacity of the Laoshan granite magma is low, as indicated by zircon Ce 4+ /Ce 3+ ratios (most <300). The crystallization temperature of zircon varies significantly, ranging from 652 to 830°C. The apatite compositions show that the Laoshan granite has high F (2.09–2.72 wt%) and low Cl (0.01–0.09 wt%) contents, consistent with influence by fluid released from the decomposition of phengite. Apatite rare earth elements show that mantle sources are also involved in Laoshan A-type granite. Combined previous studies of A-type granitic plutons in the Shandong Province and the Lower Yangtze River belt with the drifting history of the Pacific plate, we propose that the flat subduction of the spreading ridge between the Pacific and the Izanagi plates was responsible for the formation of Laoshan A-type granite.

Iron isotope heterogeneity of subduction-related primitive magmas was traditionally thought to be predominantly attributed to the addition of slab-derived components. However, the specific subducted material responsible for inducing Fe isotope heterogeneity in the subarc-backarc mantle remains poorly constrained. Here we report Fe isotopic compositions of a series of backarc basin basalts (BABBs) from the Woodlark Basin (an intra-arc rift basin), Vate Trough (a nascent rear-rift basin), and Lau Basin (a relatively mature basin) in the southwestern Pacific. Even though these BABBs have various geochemical compositions ranging from mid-ocean ridge basalts (MORB)-like to arc-like, which should be affected by various amounts of the slab-derived fluids and/or sediment melts, their δ56Fe values (0.05–0.18‰) are within the range of global MORB (0.05–0.17‰). After correction for crystal fractionation, the primitive δ56Fe values (δ56Fe-prim) displayed no co-variation with indicators of subduction contributions (e.g., Ce/Pb, Nb/U, Ba/La, and Th/Yb) or source redox conditions caused by slab inputs (e.g., V/Yb, V/Ti), suggesting that the δ56Fe-prim values of these BABBs are rarely affected by subduction metasomatism and the change in oxygen fugacity caused by subducted input. Therefore, we proposed that the MORB-like δ56Fe values of the studied BABBs were primarily caused by mantle melting processes. Furthermore, we presented a compilation of available Fe isotopic data for BABBs and island arc basalts (IABs) and used these data to evaluate Fe isotope heterogeneity in subduction settings. In particular, compared with δ56Fe-prim of MORB, the δ56Fe-prim of BABBs from the Central Lau Spreading Centre in the Lau Basin and the IABs have lower values, whereas BABBs from the Rochambeau Ridges in the Lau Basin have higher δ56Fe-prim values. By comprehensively considering the factors affecting the variation in Fe isotopic compositions in magmatic rocks in subduction zones (e.g., crystal fractionation, partial melting of the mantle, redox conditions, and subduction-related metasomatism), we proposed that the varied Fe isotopic compositions in subduction settings could reflect their heterogeneous sources, which may be related to plate subduction. Specifically, during plate subduction, a melt-depleted refractory forearc mantle peridotite (with low δ56Fe values) could be dragged by subducted slab into subarc or backarc depths, resulting in light Fe isotopic enrichment in island arc magmas or BABBs; additionally, serpentinites (both in the slab and mantle wedge) can generate light Fe isotopic enrichment in island arc magmas. High δ56Fe values in the BABB (e.g., from the Rochambeau Ridges in the Lau Basin) may result from the toroidal influx of nearby upwelling plume components or the assimilation of hydrothermally altered oceanic crust.

Carbon dioxide has been increasing in the atmosphere since the industrialization, resulting in global warming, which in turn enhanced methane emissions from permafrost regions. However, methane emitted into the atmosphere is quickly oxidized, such that the intensity and threat of methane emission in the past are severely underestimated. Here we show that the ratio between annual changes in atmospheric oxygen and carbon dioxide concentrations (ΔO2/ΔCO2 index) dropped dramatically between 1945 and 1958. There are no such abrupt changes in the fossil fuel combustion curve. Considering that atmospheric methane has the residence time less than ∼9 years through biological and chemical processes, this crisis is attributed to the World War II, which had disturbed gas hydrates underneath ocean floors and permafrost regions. Consistently, the land-ocean temperature index fluctuated more severely in permafrost regions than the global average during the WWII, indicating stronger greenhouse effects induced by methane emission. This is supported by the changes in the ΔO2/ΔCO2 index, coupled with higher atmospheric methane concentrations and lower δ13CO2 in permafrost regions in the last three decades, suggesting accelerated methane emission. The anthropogenic carbon dioxide emission has been pushing the accelerated thawing of permafrost, which promotes methane emission that further intensifies permafrost thawing and global warming. Such a positive feedback at an inflection point of Earth climate may break the glacial-interglacial cycle and initiate a long-lasting greenhouse period.