This study statistically examines the relationship between nodule occurrences and seafloor slope gradients in the Eastern Pacific to infer topographic preferences favorable for ferromanganese nodule distribution. At the local scale, analysis of high-resolution multibeam bathymetry and near-bottom photographs from the Clarion-Clipperton Zone indicates that nodules preferentially occur on low-angle slopes (1-5 degrees), rather than on flat terrains (0-1 degrees) or steep slopes (>5 degrees). At the regional scale, 1,286 grid cells (2 degrees & times;2 degrees) across the Eastern Pacific were classified as nodule occurrence-present or occurrence-absent based on compiled survey records. Using global bathymetric data, the proportions of flat, low-angle, and steep slopes within each grid cell were quantified. Statistical analysis reveals that nodule occurrence probability increases with increasing low-angle slope proportion, whereas it decreases with increasing flat-terrain proportion. Together, these dual-scale statistical results suggest that nodules may preferentially occur on low-angle slopes of the seafloor. This relationship may provide a topographic basis for delineating prospective areas for deep-sea ferromanganese nodules using seafloor bathymetric data.

Biogeochemical mineralization is increasingly recognized as a significant factor in the formation of submarine hydrothermal sulfide deposits. While several mechanisms by which hydrothermal organisms may facilitate metal deposition have been documented in many seafloor hydrothermal deposits, the potential involvement of biogenic processes in the mineralization of hydrothermal deposits in the southern Mid-Atlantic Ridge (SMAR) has been largely overlooked until now. In this study, we investigate sulfide chimney sample from the volcanic-hosted Tongguan hydrothermal field on the SMAR and present several lines of evidence for biogeochemical mineralization. Mineralogical analysis infers four types of biogenic pyrite and chalcopyrite structures: macrobiotic-related tube structures, microbial-related quasi-stromatolite, quasi-oncolite and globular structures. These biogenic structures exhibit selective enrichment of elements such as Mn, Pb, and Cu in biogenic pyrite compared to abiotic pyrite. In-situ sulfur isotope studies indicate that biogenic minerals possess lower δ34S values than abiotic minerals. We identified three biomineralization mechanisms: an “active” mineralization process mediated by macro-organism, a “passive” mineralization process associated with microbial mats, and a microbial assimilatory sulfate reduction process. Our research suggests that the role of biogenic processes in SMAR hydrothermal mineralization should be given further consideration.

The hydrothermal signatures of mid-ocean ridge sediments are crucial geochemical data providing insights into investigating hydrothermal anomalies and locating seafloor massive sulfide deposits. This paper outlines the geochemical features of 24 surface sediments and one sediment core (26V-GC01, 294 cm) along the South Mid-Atlantic Ridge (SMAR) from 18°S to 22°S, an area where hydrothermal active fields have yet to be discovered. The surface sediments mainly consist of biogenic carbonates, aluminosilicates, and hydrothermal Fe-Mn (oxy) oxides. The core sediments primarily comprise organic matter, detrital materials, hydrothermal components, and substances scavenged from seawater. The rare Earth element (REE) patterns suggest the presence of hydrothermal contributions within the surface and core sediments. The enrichment factors for Fe, Mn, Cu, and Zn in surface sediments suggest these metals are concentrated at the 19°S, 21°S, and 21.5°S segments, further indicating their potential as hydrothermal active fields. Downcore variations of Fe, Mn, P, Cu, Pb, V, and Co suggest at least six episodes of hydrothermal activity. The impact of hydrothermal processes on the sediments from SMAR 18°S to 22°S indicates that the study area has the potential to host a significant number of hydrothermal active fields.

The increasing demand for mineral resources has spurred the exploration of deep-sea hydrothermal sulfide deposits rich in polymetallic elements. The complex terrains of hydrothermal fields pose challenges to geological mapping. This paper introduces a novel framework that combines semantic segmentation models with an image enhancement algorithm for intelligent mapping of mineralized zones in seabed. When tested in hydrothermal fields, the method achieved exceptional accuracy and efficiency. The performance of four segmentation models—Fast-SCNN, DeepLab V3 + , K-Net, and SegFormer—was evaluated utilizing high-resolution images. K-Net outperformed the other methods, with mean intersection-over-union of 76.86

AbstractDeciphering the Earth's deep carbon cycle, from mantle plumes to mid‐ocean ridges, remains incompletely understood. In this study, we analyze the magnesium isotope composition of basalts collected from the South Mid‐Atlantic Ridge (SMAR), which have been influenced by the off‐axis Saint Helena plume originating from the core‐mantle boundary. The magnesium isotope composition of SMAR basalts falls within a similar range (−0.22 to −0.32‰; average −0.25‰ ± 0.03‰) to that of known global oceanic basalts. However, isotope mixing calculations suggest that the lighter magnesium isotope composition in the SMAR basalts is due to the incorporation of approximately 5%–10% recycled carbonate material carried by the Saint Helena plume into the SMAR asthenosphere. This finding not only highlights the interaction between ridges and off‐axis plumes but also proposes a comprehensive model for the Earth's deep carbon cycle, spanning from the subduction zone through the core‐mantle boundary to the mid‐ocean ridge system.

The South Mid-Atlantic Ridge simultaneously develops magmatic-controlled hydrothermal fields and tectonic-controlled hydrothermal fields. The magmatic-controlled hydrothermal fields are located on the new volcanic ridges within rift valleys, while the tectonic-controlled hydrothermal fields are primarily situated on the off-axis detachment faults. Due to the differences in the basements, it is still unclear whether there are significant differences in the spatial morphology and physicochemical properties of hydrothermal plume formed by the mixing of hydrothermal fluids with seawater under these two different settings. To explore this question, we conducted a comparative study of the Chihu (23.5 degrees S) and Xunmei (26 degrees S) hydrothermal fields to investigate the differences in hydrothermal plumes characteristics. The Chihu hydrothermal field is tectonic-controlled hydrothermal field associated with detachment faults, and the Xunmei hydrothermal field is magmatic-controlled hydrothermal field. The study found that the Xunmei plume is a high-temperature, high-salinity non-reversed plume, while the Chihu plume includes both non-reversed and low-temperature, low-salinity reversed plumes. In addition, this study extracted sensitive indicators for prospecting and found that turbidity is a more sensitive indicator for hydrothermal activity compared to the temperature and salinity.

Hydrothermal activity on the modern seafloor varies depending on the tectonic setting. In particular, the neovolcanic zones (NVZs) along mid-ocean ridges, where magmatism is intense, generally host high-temperature hydrothermal activities. These high-temperature hydrothermal activities on the NVZs can promote the development of many polymetallic sulfide deposits. Currently, many high-temperature hydrothermal activities and sulfide accumulations have been discovered on the NVZs of major mid-ocean ridges worldwide, but relatively few have been found in the Southern Mid-Atlantic Ridge (SMAR), which limits our understanding of the hydrothermal mineralization characteristics on the NVZs of SMAR. Fortunately, in 2015, a new hydrothermal field—Tongguan—developed on the NVZ of the SMAR was discovered. In this study, we conducted mineralogical and sulfur isotope studies on hydrothermal chimney and massive sulfide samples collected from the Tongguan field. We revealed the mineral composition and growth sequence in the chimney structures and sulfides and discovered two different chimney growth patterns featuring rhythmic banding and opal-filled structures. Additionally, sulfur isotopes suggest the presence of mixing between seawater within the oceanic crust and the upwelling hydrothermal fluid in this hydrothermal field. Our investigation revealed small-scale fluid heterogeneities during the submarine hydrothermal mineralization process, which is due to fluctuations in fluid temperatures and mineral deposition within individual vent frameworks. This work provides a reference for further understanding and comprehension of hydrothermal mineralization on the NVZs of SMAR.

In modern seafloor hydrothermal mineralization systems, subseafloor deposits are crucial alongside seafloor massive sulfides, consisting mainly of stockwork at the periphery and semi-massive sulfides at the central of subseafloor ore bodies. These two ore types exhibit contrasting mineralogical and elemental compositions, and the difference between their formation processes are unclear due to sampling challenges. The mafic-hosted Taiji-2 hydrothermal field, located on the Southern Mid-Atlantic Ridge, presents pyrite-enriched subseafloor sulfides on the seafloor, providing a good research opportunity. Our study included comprehensive analyses of mineralogy, pyrite chemistry, and in-situ sulfur isotopes through LA-MC-ICP-MS method on Taiji-2 subseafloor samples. Our findings suggest: (1) a hybrid source of ore-forming materials, (2) increased seawater involvement and decreased temperature and sulfur fugacity from the periphery to the central of subseafloor deposits, and (3) multistage of subseafloor ore-forming activities. Additionally, we characterized the seafloor alteration of Taiji-2 subseafloor sulfides. These results enhance our understanding of subseafloor mineralization in seafloor hydrothermal field.

The compositions of metalliferous sediments associated with hydrothermal vents can provide key geochemical data for locating seafloor sulfides. In this study, we present the geochemistry of seabed sediments from the Xunmei hydrothermal field (HF) in the South Mid-Atlantic Ridge (SMAR). The results indicate that the sediments are mainly composed of pelagic material (biogenic calcium components), basaltic debris, iron-manganese oxides, and hydrothermal components. The sediments are significantly enriched in Cu, Zn, Fe, and Co deriving from hydrothermal fluids, as well as Mn, V, Mo, U, and P, which are primarily scavenged from seawater. The northeastern Xunmei has the highest concentrations of Cu and Zn, while the northeastern, northern, and southern regions are characterized by great inputs of Fe. Manganese and Mo are mainly enriched in the western and southern parts and show a strong positive correlation, indicating that Mo is mainly scavenged by Mn oxides. Uranium, P, and Fe exhibit strong positive correlations, suggesting that they coprecipitate with Fe from hydrothermal plumes. Vanadium and Co are introduced into sediments in different ways: V is scavenged and coprecipitated by hydrothermal plumes, and Co is derived from sulfide debris. Based on the contents of Cu and Zn and Cu/Fe (0.159), Zn/Fe (0.158), and Fe/Mn (1440) ratios, it can be inferred that a high-temperature hydrothermal vent existed in northeastern Xunmei. In combination with the distribution patterns of the above elements, the hydrothermal vents in the southern part ceased erupting after a short period of activity. In addition, the high Mn anomaly and the high U/Fe ratios at the boundaries of the investigated area indicate the presence of a relatively oxidized environment in southwestern Xunmei.

Six hydrothermal sediment samples were collected from the Xunmei and Tongguan hydrothermal fields along the southern Mid-Atlantic Ridge during the China Ocean Cruise DY46 in 2017. Sulfides and oxides in the samples were separated, and Cu and Zn isotope compositions were analyzed. Results show that the ranges of δ65Cu values of the bulk sediments, sulfides, and oxides were 0.36‰–2.46‰, -0.21‰–1.10‰, and 0.68‰–1.52‰, respectively. The δ65Cu values of sulfides in four samples (46II-14, 46II-30, 46III-06, and 46II-09) were relatively low (-0.21‰–0.50‰), corresponding to the δ65Cu values of sulfides from inactive old hydrothermal chimneys in northern Mid-Atlantic Ridge (nMAR), suggesting that the sulfides in the sediments were originated from collapsed dead chimney mainly. While the δ65Cu values of the other two samples (46III-02 and 46III-08) were relatively high (1.10‰–0.96‰), corresponding to the δ65Cu values for active hydrothermal chimneys sulfides in nMAR, which indicated that the sulfides in these two samples might mainly come from sulfide particles settled from active hydrothermal plume. Because of the high density of sulfide particles, they tended to settle near the hydrothermal vents first. Therefore, high δ65Cu values of sulfides in 46III-02 and 46III-08 implied that undiscovered active hydrothermal vents near the sampling positions of 46III-02 in the Xunmei hydrothermal field and 46III-08 in the Tongguan hydrothermal field. The δ66Zn values of hydrothermal sediments and sulfides ranged 0.11‰–0.43‰ and 0.29‰–0.67‰, respectively. In the four samples from the Xunmei hydrothermal field, a positive correlation was found between the distance of the sampling position from sulfide mineralized spot and the Zn isotopic ratio, showing that the greater the distance from the mineralized spot, the heavier the Zn isotope composition as seen in two samples (46II-30 and 46II-14) of the Xunmei-3 spot. This result aligned with the findings of Wilkinson et al. (2005) and Baumgartner et al. (2023), suggesting that the lower the Zn isotope composition, the closer it is to the hydrothermal vent. However, in the Xunmei hydrothermal field, the Zn isotope composition in the other two samples (46III-02 and 46III-06) showed the opposite trend. This indicated that there might be an active hydrothermal vent near the sampling location of sample 46III-02. This observation aligned with the Cu isotope analysis results. This study showed that Cu-Zn isotopes are good indicators for understanding the formation mechanisms of hydrothermal sediments and for locating active hydrothermal vents.

Numerous investigations into the northern Mid-Atlantic Ridge (the NMAR), a typical slow-spreading mid-ocean ridge, have revealed that NMAR is favorable for the development of long-lived detachment faults and the formation of oceanic core complexes (OCCs). OCCs are often conducive to the development of ultramafic-hosted hydrothermal deposits with significant resource potential. However, as a counterpart of the NMAR on the Southern Hemisphere, the southern Mid-Atlantic Ridge (SMAR), also belonging to the class of slow-spreading ridges, has only received very limited investigation. This prompts the inquiry as to whether the SMAR, like the NMAR, can foster the development of OCC and associated hydrothermal deposit. To address this issue, we present the identification of an OCC (named as Kaifeng OCC) at the intersection of the SMAR and the Martin Vaz transform fault (similar to 23 degrees S). This discovery is accompanied by evidence detailing a new detachment fault breakaway on an old detachment footwall. Collected samples reveal indications of hydrothermal activity, encompassing (1) residual sulfide containing chalcopyrite within honeycomb-like structures, (2) reddish-brown Fe oxides and atacamite, partially concretized by dolomite, and (3) a dark gray Mn-oxide crust. These mineralogical features indicate the presence of gossans, commonly iron oxide-dominated cover layers that envelope the outer surface of weathered seafloor sulfide deposits, which subsequently undergo modifications due to subsequent hydrothermal activities. Our work proves the existence of OCC and associated hydrothermal deposits at a ridge-transform intersection of the SMAR.

Pelagic sediment enriched in critical metals (e.g. rare earth elements and yttrium, REY) has attracted much attention in recent years. Extensive research has focused on identifying the specific host mineral of REY in bulk pelagic sediment, however, research on clay-sized fraction of REY-rich sediment has not been fully understood yet. In this study, we aimed to investigate the host phase and migration mechanism of REY in clay-sized fractions from two cores, GC23 and GC17, located on the western and eastern sides of the East Pacific Rise (EPR), respectively. To the best of our knowledge, this is the first comprehensive investigation of the clay-sized fraction of REY-rich sediment associated with hydrothermal activity. Results show that GC23 contains negligible clay minerals but well-crystallized Fe oxyhydroxides, while GC17 is rich in smectite and poor-crystallized Fe oxyhydroxides. REY are predominantly hosted in poorly crystallized Fe-Mn oxyhydroxides, with some phosphorus selectively scavenged by Fe oxyhydroxides from seawater. In addition, fluorapatite nanocrystals were first observed within the matrix of Fe oxyhydroxides using transmission electron microscopy (TEM), indicating the formation of fluorapatite. The post-Archean average shale (PAAS)-normalized REY patterns show similar seawater-like patterns in both the clay-sized and silt-sized fraction. The clay-sized fractions primarily derived from hydrothermal plumes plays an important role in scavenging REY from ambient seawater. This study represents a significant step towards understanding the formation of REY-rich sediment related to hydrothermal activity. A two-stage mineralization process is proposed for the formation of REY-rich sediment near the EPR fields. Firstly, REY are initially scavenged by hydrothermal Fe-Mn oxyhydroxide particles from seawater during their lateral dispersion with hydrothermal plumes under low sedimentation rate until they are buried by newly formed precipitates. With the process of early diagenesis, poor crystallized Fe oxyhydroxides will be experienced recrystallization. Subsequently, REY would be released into porewater with the process of recrystallization due to their tendency to remain in a poorly crystallized phase. Ultimately, they are captured by biogenic apatite and/or fluorapatite. The case study indicates that REY-rich sediments may primarily formed within the dispersion area of hydrothermal plumes. Simultaneously, the necessity of slow sedimentation rates, greater water depth, and deep currents all accountable for the formation of REY-rich layers.

The Xunmei hydrothermal field, located at 26°S along the South Mid-Atlantic Ridge, is an active submarine hydrothermal system underlain by a basaltic substrate. This field comprises two distinct types of basalts: massive basalts, characterized by aphyric to moderately porphyritic textures without large vesicles, and vesicular basalts, known for their highly vesicular nature. Olivine-hosted melt inclusions within the massive basalts exhibit a diverse range of chemical compositions. Type-A melt inclusions are distinguished by lower levels of K2O, Rb, Ba and U, but higher concentrations of S, Co, Ni, and Cu. Conversely, Type-B melt inclusions exhibit higher levels of K2O, Rb, Ba and U, but lower concentrations of S, Co, Ni, and Cu. Although both types of melt inclusions show similar ranges of La/Sm, La/Yb, Sr/Yb, and Zr/Nb, the significant differences in K2O/TiO2 and Nb/U indicate that the massive basalts likely originate from the mixing of two distinct melts derived from different source regions. Data from melt inclusions and quenched basaltic glasses, combined with theoretical calculations, indicate that Type-I melts, represented by the Type-A melt inclusions, were sulfide-saturated during the crystallization of olivine at depth, evolving into sulfide-unsaturated melts as they ascended towards the seafloor. Approximately 50

A newly discovered hydrothermal field, named Yunzang and predominantly hosted by mafic rocks, was recently identified at 25.3 degrees S on the South Mid-Atlantic Ridge (SMAR). This is the first report on the sulfide mineralogy and sulfur isotopic composition of sulfide chimney and massive sulfide ores collected from Yunzang field, SMAR. Based on mineralogical morphology, texture, crystallinity, assemblage and zonation, five specific stages of mineralization can be divided for the sulfide chimney at Yunzang. These stages range from low- to hightemperature hydrothermal conditions, along with an additional stage of seafloor weathering. The observed variations in morphology and crystallinity from low- and medium-temperature stages to high- and high- to medium-temperature stages suggest an evolution in the ore-forming conditions. Initially, the environment was characterized by instability and low-temperature conditions, with significant seawater influx. Subsequently, there was a shift towards a more stable regime dominated by high-temperature ore-forming fluid condition. The positive delta 34S values of all the sulfides from Yunzang hydrothermal field suggest 79-92 % and 69-79 % of sulfur were generated from the leaching of basalt for sulfide chimney and massive sulfide, respectively, the rest sulfur were from reduced seawater sulfate. The delta 34S values of massive sulfide (3.5-6.8 %o, average = 5.1 +/- 0.9 %o) are mostly higher than that of sulfide chimney (1.1-4.5 %o, average = 2.8 +/- 0.8 %o) are mainly caused by sub-surface reactions between preexisting sulfate and re-circulating fluid. An incremental increase of delta 34S values from the external edge to the interior orifice indicating the Yunzang chimney maturation is relatively lower and the duration of hydrothermal activity was short. These results enrich our comprehension of mineralization in the seafloor hydrothermal system.

Numerous hydrothermal activities were observed along the southern Mid-Atlantic Ridge (SMAR) in recent years. In this study, six clay-sized surface sediments collected from three hydrothermal fields (Caifan, Xunmei and Taiji) and one sample from Kaifeng seamount were analyzed for mineralogical and geochemical compositions. X-ray diffraction (XRD) results reveal that samples are mainly composed of fine-grained goethite, chlorite, and occasionally with jarosite and smectite. Interestingly, smectite not observed under XRD patterns are determined with the application of transmission electron microscope (TEM). Smectite is probably formed by interaction between Fe-oxyhydroxides (goethite) and detrital/hydrothermal silicates. Major and minor elements geochemical data indicate samples from Caifan and Xunmei are highly influenced by hydrothermal activities, and alteration of sulfides was prominent. However, it is not true for the sample from Kaifeng seamount and Taiji hydrothermal field, where are dominant by Mg-rich chlorite of volcanic rocks origin rather than aeolian. Rare earth element (REE) concentrations of both clay-sized and bulk sediment were compared to illustrate the REE characteristics and the degree of hydrothermal contribution. In the Taiji hydrothermal field and Kaifeng seamount, REE were mainly present in clay-sized fraction and chlorite may act as an efficient carrier of REE in these samples. On the other hand, in the Caifan and Xunmei hydrothermal fields, only goethite (or Fe-oxyhydroxides) plays an important role on carry of REE rather than smectite due to low abundance and poor crystallinity.

We present new major and trace element and Sr-Nd-Pb isotope data for basalts from the 25.3–27.7°S segments of the South Mid-Atlantic Ridge (SMAR). A fractional crystallization model shows that olivine, plagioclase, and clinopyroxene crystals crystallized in the magmatic chamber underlying the SMAR 27.1°S and 27.7°S segments, while the SMAR 25.3°S segment basaltic lavas are dominated by fractional crystallization of olivine and plagioclase. Their Ce/Yb, (Tb/Yb)N, and Fe/Mn ratios suggest a mantle source lithology dominated by spinel-lherzolite. The linear correlations between Mg# and TiO2, Ba, and Zr/Nb indicate that SMAR basalts in this study have primary mantle melts with similar chemical compositions and partial melting extents. The along-ridge variations in the fractionation-corrected incompatible element (Ba, Zr/Nb, (La/Sm)N) and Sr-Nd-Pb isotope compositions of the SMAR 20–40°S basalts show that Tristan mantle plume materials exist in the SMAR asthenosphere and gradually decrease from the southern SMAR 35°S segment in the vicinity of Tristan Island to the northern SMAR 25.3–27.7°S segments. The mixing models of the fractionation-corrected Ba contents, (La/Sm)N ratios and radiogenic Sr-Nd-Pb isotope ratios show that variable degrees of contamination by the Tristan mantle plume contribute to the heterogeneous SMAR 20–40°S mantle source. The proportion of Tristan plume-related materials retained in the SMAR 20–40°S asthenosphere is <10%, which gradually decreases from south to north. By integrating the evolution of the South Atlantic and the historical interaction between the SMAR system and the Tristan mantle plume, we demonstrate that the systematic variations in the geochemical compositions of the SMAR 25.3–27.7°S basalts are induced by the presence of the Tristan mantle plume materials in the southern SMAR asthenosphere.

Seafloor hydrothermal sulfides at slow-spreading mid-ocean ridges (MORs) are of economic and scientific significance. The formation of newly discovered submarine hydrothermal sulfides on the South Mid-Atlantic Ridge (SMAR), particularly with respect to the fluid evolution, remains poorly understood. The Xunmei hydrothermal field is a typical volcanic dome-type hydrothermal field at 26(degrees)S on the SMAR. Based on the mineralogical zonation and assemblages, six distinct ore-forming stages were identified from low- to high-temperature stages with a seafloor weathering stage. The crystallinity of pyrite/marcasite and grain size of chalcopyrite increase gradually from the outer rim to the inner conduit of a sulfide chimney. The positive delta(SV)-S-34-CDT values of pyrite/ marcasite (2.1%o-8.2%o), chalcopyrite (2.5%o-5.6%o), and sphalerite (2.9%o-7.0%o) suggest 62%-91% of S was derived from the leaching of basement basalts, 9%-38% from reduction of seawater sulfate. In situ trace element data for sulfides show enrichments in Mn, Ag, Tl, and Pb in outer zones A and B, while enrichments in Se, In, and Sn in inner zones C and D, indicating an increase in precipitation temperature during chimney growth. Low pyrite Co contents, low Tl/Pb, low Sb/Pb, low Bi/Pb, high As, Ag, Cu, and Pb concentrations, suggesting that the pyrites precipitated from fluids that may have undergone supercritical phase separation during their ascent. High-temperature, Cl-depleted, vapor-rich hydrothermal fluids discharged into ambient cold seawater over multiple stages and probably evolved from low (<240 C-degrees) to medium (- 263 C-degrees) and high (- 317 C-degrees) temperatures, reached a highest temperature of -335 C-degrees, and then evolved to medium to low temperatures (270 C-degrees to <240 C-degrees) during the wanning of hydrothermal venting. The sulfur fugacity (fS(2)) likely evolved from a relatively low to high condition within the scope of intermediate sulfidation, and then decreased to low condition. The redox states (fO(2)) probably were strongly affected by seawater influx and evolved from relatively oxidized to original reduced conditions. The salinity decreased during chimney growth. Sulfide precipitation in the Xunmei hydrothermal field probably was the result of a combination of fluid-seawater mixing and phase separation. We propose a chimney growth and hydrothermal evolution models for the Xunmei hydrothermal field.

为揭示晚更新世以来西太平洋暖池黏土矿物输入变化的控制因素,对采自西菲律宾海本哈姆隆起上的Ph05-5 孔沉积物中的黏土矿物组成、来源和堆积速率进行了分析.结果表明,220 ka以来,该孔沉积物中的黏土矿物主要以伊利石(13%)和蒙皂石(8%)为主,其次为绿泥石(6%)和高岭石(2%).伊利石和绿泥石主要来源于亚洲大陆,蒙皂石主要源于菲律宾海周围岛屿的火山物质在海底遭受海水侵蚀后形成的自生Fe-蒙皂石和西菲律宾海周围岛屿上的物质风化后形成的他生Al-蒙皂石.220 ka以来,伊利石和绿泥石的堆积速率表现出明显的冰期高-间冰期低的旋回变化,与该孔总的风尘堆积速率、亚洲风尘和北太平洋风尘堆积速率一致.冰期/间冰期太阳辐射降低/增强、亚洲内陆干旱程度加强/减弱,是导致伊利石等源于亚洲内陆的黏土矿物向菲律宾海输入增加/减少的主控因素.Ph05-5 孔蒙皂石的堆积速率同样表现出明显的冰期高-间冰期低的特征,与该孔总的火山物质堆积速率一致.蒙皂石在轨道尺度的变化,主要受到海平面变化和热带类ENSO过程影响的降雨过程控制.冰期低海平面,菲律宾岛和海水的混合作用加强,使得蒙皂石的输入增加.此外,冰期在热带太平洋类拉尼娜较强,降雨量增加,导致向菲律宾海输入的火山物质(蒙皂石)增加,间冰期则相反,由于类厄尔尼诺增强,菲律宾岛区域干旱,火山物质(蒙皂石)向菲律宾海的输入减少.

Mantle convection plays a key role in magmatism and volcanism on Earth. The final distribution of deep mantle material upwelled into the asthenosphere cannot be clearly tracked using seismic imaging techniques. Where mid-ocean ridges and plumes interact, the along-ridge variations in plume-affected basalts constrain the spatial extent of the plume-related flow in the asthenosphere. These variations are helpful for revealing convection throughout the mantle from the core-mantle boundary (CMB) to the bottom of the lithosphere. In this study, regional geophysical data, as well as the results of geochemical independent component analysis of radiogenic Sr–Nd-Pb isotopes of South Mid-Atlantic Ridge (SMAR) basalts, were used to analyze the distribution characteristics of the plume-affected asthenosphere beneath the South Atlantic Ocean. We determined that the ridge scope of the Ascension plume-influenced SMAR segments is bounded by the Ascension transform fracture (~ 7.5°S) to the north and the Bode Verde transform fracture (~ 11.1°S) to the south, while the Saint Helena plume-contaminated SMAR segments are bounded by the Cardno transform fracture (~ 14.2°S) to the north and the Trinidade transform fracture (~ 20.8°S) to the south. Furthermore, we determined that the melt extraction process taking place between the mantle plume and ridge system may weaken the plume-related geochemical signals of these plume-affected MORBs. Our results suggest that the distribution of plume-related asthenosphere under the South Atlantic is influenced by large transform faults that block the propagation of the plumes along the bottom of the lithosphere, as well as the propagation of plume-affected materials along the ridge system.

Ion-adsorption deposits (IADs) are important types of REE deposits. Previous studies have found that, in IAD, REE3+ adsorb on the surface of clay minerals in the form of multi-coordinated hydrated complexes, [REE(H2O)8/9]3+, forming exchangeable outer-sphere adsorption complex. Actually, there are two types of basal surfaces in clay minerals, the (001) surface and the (00−1) surface, and it is not clear whether there are differences in the adsorptions on these two types. Additionally, the electron transfer mechanism in the adsorption structures cannot be revealed. To address these issues, we employ first-principles calculations based on density functional study to simulate the outer-sphere adsorption structures of representative Y3+ ion on the two types of basal surface of kaolinite. The study reveals that both the (001) surface and the (00–1) surface can serve as adsorption surfaces, but the (00–1) surface forms more stable adsorption structures with adsorbate-[Y(H2O)8]3+ due to the absence of hydroxyl group repulsion effects. The adsorption process involves electron transfer from the kaolinite basal surface to the adsorbate, forming hydrogen bonds. The primary orbital interaction in this process is between the O-2p orbitals of the adsorbate and the surface O-2p orbitals. This work contributes to a quantum-level understanding of the nature of ion adsorption in ion-adsorption deposit.