Diverse magmas were generated from various sources under an extensional tectonic setting in the Korean Peninsula during the Early Cretaceous. To investigate this process, we conducted petrological and geochemical analyses of the Seolhwa Igneous Complex (SIC), located along the mid-western margin of the Korean Peninsula. The SIC comprises a granodioritic northern suite (zircon U-Pb ages: 110-120 Ma) and a dioritic southern suite (110.70 +/- 0.49 Ma). The two suites are spatially and temporally associated displaying coherent major and trace element trends, as well as enriched isotopic signatures, which suggests a comagmatic origin. The high concentrations of compatible elements (Mg# = 59.1-64.9; Ni = 66-210 ppm; Cr = 235-510 ppm) in the southern suite high-Mg diorites indicate derivation from a mantle source. However, their silica contents (SiO2 = 56.4-61.1 wt %) are higher than those of primitive basalts at comparable Mg# values and are more akin to primitive andesites. The enriched isotopic signatures [(87Sr/86Sr)i = 0.7136-0.7138; epsilon Nd(t) =-15.1 to-14.1], together with arc-like geochemical features, suggest a metasomatized mantle source. The presence of inherited zircon cores in the adakitic northern granodioritic suite, along with correlations between SiO2 contents and Sr-Nd isotopes [(87Sr/86Sr)i = 0.7129-0.7168; epsilon Nd(t) =-13.8 to-17.3], indicates significant crustal assimilation. Geochemical modeling suggests that the adakitic signature developed through assimilation-fractional crystallization processes from a parental melt similar to that of the southern suite. Primitive andesitic geochemical signatures comparable to the southern dioritic suite are observed in several other Early Cretaceous suites. We therefore propose that, although volumetrically minor, primitive andesitic melts were more widespread than previously recognized. Slab steepening and rollback-induced extension along the continental margin during the Early Cretaceous promoted partial melting of enriched subcontinental lithospheric mantle through decompression and thermal perturbation. Under such conditions, a spectrum of primitive mantle-derived melts, ranging from andesitic to basaltic, could be produced.

Two deep-mantle reservoirs branching from African LLSVP, the Réunion plume and Mascarene Basin Asthenospheric Reservoir (MBAR), have been proposed to influence magmatism along the Central Indian Ridge (CIR), yet distinct geochemical expression, spatial extents and relative contributions remain poorly constrained. In this study, we present major and trace element, volatile and in-situ Pb isotope data for olivine-hosted melt inclusions from a ridge-transform intersection at the CIR 16.5°S where low magma supply preserves primary mantle heterogeneity. The melt inclusions exhibit a broad range of trace element enrichment, collectively encompassing nearly the full compositional variability of the CIR MORB over a distance of ~1000 km. The melt inclusions are categorized into three types: E-MORB, N-MORB and anomalous melt inclusions. Although some anomalous inclusions show geochemical evidence of interaction with the lower crust and upper mantle, most preserve their primary mantle source signatures. E-MORB melt inclusions exhibit Pb isotopic, halogen, major and trace element compositions suggesting mantle source metasomatized by low-degree melts derived from the Réunion plume. In contrast, N-MORB melt inclusions show restricted La/Sm but wide variability in Pb isotope ratios defining FOZO-DMM array, independent of the Réunion plume signatures. These geochemical characteristics suggests MBAR contribution extends southward to ~16.5°S as previously inferred from geophysical data. The coexistence of the Réunion plume and MBAR signatures within individual melt inclusions suggests that melt inclusions provide critical role in resolving deep-mantle heterogeneity beneath the Indian Ocean while otherwise remaining cryptic in MORB whole-rocks or glasses, even in low-magma supply regions.

Abstract The conductive boundary layer (CBL) at the magmatic–hydrothermal interface of mid-ocean ridges (MORs) regulates the fundamental exchange of heat and chemical species between cooling magmas and circulating seawater. While this interface is well-documented at shallow, fast-spreading ridges and in ophiolites, its nature in deep-seated magmatic environments—particularly along slow-spreading ridge segments hosting oceanic core complexes (OCCs)—remains poorly constrained. Here, we investigate the physicochemical properties of this interface through a detailed microstructural, geochemical, and fluid inclusion analysis of hornfelsic diabase, the primary constituent of the CBL, recovered from the Onnuri OCC on the Central Indian Ridge. Our results characterize two distinct lithologies: hornblende hornfelsic and pyroxene hornfelsic diabase. Clinopyroxene geothermometry yields peak metamorphic temperatures of 815–987°C, with evidence of localized hydrous partial melting and the formation of amphibole-rich diorite. Despite these intense thermal conditions, the Onnuri hornfels exhibits remarkably low chlorine (Cl) signatures in both amphiboles (<663 ppm) and fluid inclusions (2.0–5.0 wt % NaCl eq.), reflecting interaction with fluids of seawater-like salinity. This geochemical signature contrasts sharply with the high-Cl brines and Cl-rich amphiboles typical of shallow fast-spreading systems. We demonstrate that this divergence is fundamentally rooted in the pressure-regulated phase behavior of seawater. Seawater P–T phase analysis identifies a critical hydrostatic pressure threshold of 80–100 MPa; beyond this limit, phase separation is effectively suppressed, whereas at lower pressures, it becomes increasingly pronounced as pressure declines. Consequently, the high-pressure regime prevents the formation of a basal brine layer—promoting interaction with low-salinity, seawater-like fluids—while the low-pressure regime facilitates brine accumulation. To evaluate whether this mechanism can be applied on a global scale, we performed a meta-analysis of mid-ocean ridge basalt (MORB) chemistry and hydrothermal vent datasets. Our analysis of global MORB datasets demonstrates that magma storage depth exerts the ultimate control over crustal Cl assimilation, with long-term, segment-scale magmatic flux operating as the underlying driver of this vertical architecture. Furthermore, hydrothermal vent fluid data exhibit a corresponding depth-dependent variability, with Cl concentrations stabilizing near seawater values as heat source depth increases. By synthesizing these multi-disciplinary constraints, we propose a unified, depth-dependent model for Cl cycling at the magmatic–hydrothermal interface. We conclude that the emplacement depth of the magmatic heat source, governed by segment-wide magmatic flux, serves as the primary determinant of the hydrostatic pressure of the hydrothermal cell, thereby controlling subseafloor brine formation, the extent of crustal Cl assimilation, and the chemical stability of hydrothermal vent fluids in the global MOR oceanic crust.

Deciphering Paleoproterozoic tectono-magmatic events is fundamental to reconstructing crust-mantle interactions and the tectonic assembly of East Asian continental blocks. However, the Orosirian tectono-magmatic records on the Korean Peninsula remain incompletely constrained, particularly in the southwestern Yeongnam Massif. Here, we investigate the Orosirian mafic xenoliths and metagranitoids from the Gangjin-Wando-Jangheung area to refine the timing of magmatism and evaluate magma sources and tectonic settings. Zircon U-Pb analysis indicates that the mafic xenoliths and metagranitoids formed early (ca. 1.98–1.94 Ga) and middle (ca. 1.89–1.87 Ga) Orosirian, respectively, documenting temporally distinct magmatic episodes.The mafic xenoliths represent mantle-derived magmas characterized by high Mg# (60–64) and elevated Ni and Cr contents. Their enrichment in light rare earth elements and large lithophile elements, coupled with pronounced negative Nb-Ta and moderate zircon εHf(t) values (−6.1 to +2.9) are consistent with derivation from enriched arc-related lithospheric mantle. The metagranitoids are calc-alkaline I-type granitoids interpreted to have formed by partial melting (5–15%) of a mafic igneous protolith compositionally similar to the mafic xenoliths, as supported by thermodynamic phase-equilibrium and numerical modeling. Their arc-like trace element patterns and low zircon εHf(t) values (−12.46 to +0.50) indicate magma generation in an arc-related setting involving old crustal components.These results demonstrate that two-stage Orosirian arc-related magmatism occurred in the southwestern Yeongnam Massif contrasting with contemporaneous tectono-magmatic histories of other major tectonic domains in the Korean Peninsula and the eastern North China Craton. This distinction suggests that the Yeongnam Massif evolved as a discrete tectonic domain during the Orosirian.

Understanding the basement architecture of oceanic core complexes (OCCs) is fundamental to deciphering the evolution of ultramafic-hosted hydrothermal systems. This study provides new constraints on the tectonic and structural framework of the Onnuri OCC (11 degrees 25 ' S, Central Indian Ridge) by leveraging an exceptional geological setting: two similar to 1-km-high vertical slopes that serve as deep structural windows into the massif's interior. By analyzing a comprehensive suite of rocks acquired from both the detachment surface and these extensive slopes, we reveal a profound spatial disparity in lithology and deformation intensity. While the detachment interface consists of high-strain ultramafic and mafic tectonites, the underlying similar to 1-km vertical sections are dominated by massive, evolved gabbros that retain primary, isotropic magmatic textures. This disparity suggests extreme tectonic strain partitioning, where a thin, mechanically weak ultramafic carapace effectively shielded a coherent magmatic interior from tectonic overprinting during exhumation. Moreover, the striking petrological consistency identified across the two slopes, coupled with the mechanical prerequisites for developing major brittle faults along rigid gabbroic units, bolsters the core-carapace model relative to a heterogeneous alternative. This core-carapace architecture implies the presence of a voluminous, integrated gabbroic core rather than isolated magmatic bodies embedded within a peridotite-dominant matrix. Integration of geomorphological and compiled seismic data confirms a tectonic transition from an active detachment phase to a secondary collapse stage. During this current stage, hydrothermal fluids are channeled through active high-angle normal faults and fissures rather than the detachment fault. We propose a mechanism in which this constrained basement architecture facilitates a stratified hydrothermal evolution: the evolved gabbroic core acts as a primary silica source for high-Si vent fluids, while ultramafic signatures (CH4) are acquired from deeper, olivine-rich reaction zones and the thin, uppermost carapace. Consequently, these results provide critical constraints on the deep architecture of the Onnuri OCC and its potential role in seafloor hydrothermal processes.

Copper-rich hydrothermal chimneys from the TA25 East vent field (TA25 EVF) in the Tonga Arc contain exceptionally high Te concentrations, reaching up to 1650 ppm in bulk samples. Here, we integrate mineralogical and geochemical data to constrain the occurrence and partitioning of Te and to clarify the processes responsible for its enrichment in an arc-related submarine hydrothermal system. Tellurium is hosted both as lattice-bound Te in sulfide minerals and as discrete polymetallic tellurides and native Te. Its distribution is governed by fluid evolution during chimney growth: under relatively reduced conditions, Te is preferentially incorporated into sulfide lattices, whereas fluid-seawater mixing decreases Te solubility and promotes the precipitation of tellurides and native Te, mainly through an increase in pH and, to a lesser extent, cooling. Sulfide recrystallization further redistributes Te and promotes its local reprecipitation as discrete Te-bearing phases along the grain boundaries of earlier sulfides. Mineralogical, geochemical, and sulfur isotope evidence collectively indicates a strong magmatic volatile contribution to hydrothermal mineralization at the TA25 EVF. Key evidence includes the occurrence of enargite-tennantite, specular hematite, and telluride-kaolinite clusters; enrichment in epithermal-suite elements (Au, Ag, As, Sb, Te, Bi, and Hg); elevated pyrite Te/As (up to 0.3) and Te/Sb (up to 6.58) ratios; sulfide delta S-34 values (+0.85 parts per thousand to + 5.12 parts per thousand) that may record seawater modification of a magmatic volatile-derived sulfur contribution; and CO2-rich (600-2500 ppm) hydrothermal plumes. Strong whole-rock associations among Au, Bi, and Te, together with polymetallic telluride assemblages and locally melt-like textures, suggest that aqueous transport may not fully account for their enrichment and that Bi-(Te)-rich melts could have played an additional role in Au scavenging. Additionally, fluid-controlled decoupling of Au from Te and Bi indicates pronounced small-scale chemical heterogeneity in hydrothermal fluids within a single vent field (similar to 371 m), reflecting spatially variable mixing among magmatic volatiles, hydrothermal fluids, and seawater along caldera-controlled fluid pathways. Consequently, our results underscore the importance of coupled magmatic-hydrothermal processes in driving Te enrichment in arc-related seafloor hydrothermal systems.

The Sagaing Fault is a prominent, right-lateral strike-slip fault that extends approximately 1,400 kilometers through central Myanmar. The Fault is one of the most seismically active fault systems in world, with a history of producing large and devastating earthquakes including recent 7.7 earthquake that struck near Mandalay. Although the primary cause of the earthquake is regarded as being the result of a rupture that occurred along the Sagaing Fault due to the Myanmar plate and Sunda plate sliding horizontally past each other, we here discuss the other geodynamic factors on the deadly nature of the Earthquake. Preparedness in advance is key to staying safe and reducing the damage caused by natural hazards. Ongoing scientific research and regular monitoring are also crucial for spotting early warning signs of natural hazards like earthquakes, landslides, and volcanic eruptions. Given the easy accessibility along the Sagaing Fault and volcanoe area such as the Mt. Popa region, further integrated research combining seismic, volcanological, petrological and tectonic studies is strongly encouraged and highly warranted.

The behavior of platinum-group elements (PGE) in sulfide-undersaturated primitive magmas may be controlled by crystallization of either Cr-spinel, platinum-group minerals (PGM) or olivine. Evaluation of the PGM-hosted PGE portion is challenging because PGM in volcanic rocks are small and rare. We report on the sizes and compositions of PGM associated with Cr-spinel, the PGE content of Cr-spinel and olivine, and the bulk rock PGE content from sulfide undersaturated arc volcanics of the Tumrok range (Eastern Kamchatka). Platinum-iron and Ir-Os alloys (< 30 to > 3000 nm in size) form inclusions in Cr-spinel. Their presence and composition are mostly independent of Cr-spinel chemistry. Bulk rock PGE contents are erratic and PGE concentrations in Cr-spinel are exceptionally variable (up to 2 orders of magnitude). Whereas PGM inclusions in Cr-spinel and PGE in solid solution in Cr-spinel significantly contribute to the bulk rock PGE budget, a considerable portion of the PGE must be present associated with minerals other than Cr-spinel. The variable PGE content of the rocks is attributed to a combination of: (a) disequilibrium kinetic effects at the Cr-spinel-melt boundary layer, strongly affecting PGE partitioning into Cr-spinel and crystallization of PGM in the layer; (b) the presence of some sufficiently large PGM to cause nugget effects; and (c) melt degassing.

Various crustal processes shape both the lower oceanic crust and mid-ocean ridge basalts (MORBs). To better understand how these crustal processes influence MORB compositions, we conducted comprehensive petrographic and geochemical investigations on gabbroic rocks and erupted lavas dredged from a segment of the Central Indian Ridge (CIR) spanning from 7 degrees 50 ' S to 8 degrees 30 ' S. The petrographic and geochemical analyses of the gabbroic rocks revealed evidence of melt-rock reaction through reactive porous flow in olivine gabbro and gabbro. This process resulted in distinctive features in clinopyroxene, including disequilibrium textures with a troctolite/anorthosite matrix, complex variations in Mg#-Cr-Ti [Mg# = molar Mg/(Mg + Fe2+)] relationships, and considerable enrichment and fractionation of incompatible trace elements. A significant finding of our study is the close resemblance of trace element ratios in MORB and olivine-hosted melt inclusions to those of melts in equilibrium with clinopyroxene from olivine gabbro and gabbro with Sr anomaly (Sr/Sr* = Sr-N/sqrt[Pr-N*Nd-N]; N refers to chondrite-normalized values) greater than similar to 0.7. This observation strongly indicates that the composition of MORB is influenced by the melt-rock reaction taking place in the lower oceanic crust. Furthermore, our findings suggest that evolved melts in equilibrium with clinopyroxene having Sr/Sr* values lower than similar to 0.7 are less likely to erupt onto the seafloor and are instead trapped within the lower oceanic crust. Oxide gabbronorite is characterized by coarse-granular, pegmatitic textures and exhibits mineralogically and chemically more evolved characteristics compared to olivine gabbro and gabbro. It is inferred that the oxide gabbronorite formed through the in situ freezing of highly evolved melts within a melt-rich layer. Finally, we present a comprehensive model for melt evolution in the lower oceanic crust at the 7 degrees 50 ' S-8 degrees 30 ' S CIR by integrating all petrological and geochemical data obtained from gabbroic rocks, MORB, and olivine-hosted melt inclusions. This holistic model contributes to a better understanding of the intricate processes governing MORB composition in the context of the lower oceanic crust dynamics at slow-spreading ridges.

Copper and gold-rich seafloor massive sulfide deposits formed in intra-oceanic subduction settings are typically associated with hydrous and oxidized magmas, but processes leading to their formation remain controversial. Sulfide-bubble interaction has been suggested to play an important role in metal transfer from magmas to seawater-derived hydrothermal fluids. Here we use textural observations of magmatic sulfides, geochemical numerical models of chalcophile element concentrations, and numerical models of magmatic sulfide growth within a mafic to felsic submarine magmatic suite (Fatu Kapa, SW Pacific) associated with copper-gold-rich seafloor massive sulfide deposits. We demonstrate that concomitant sulfide and aqueous fluid formation at the andesitic stage results in floating sulfide-bubble compound drops in magmas, which play a crucial role in the transfer of copper and gold toward the surface. We emphasize that late sulfide saturation in copper-gold-rich intra-oceanic subduction-derived felsic magmas favors upward sulfide transfer via flotation. The flotation of sulfide-bubble compounds in magmas plays an important role in forming Cu-Au hydrothermal seafloor ore deposits, according to petrographic observations, geochemical and physical modeling.

Along the Central Indian Ridge (CIR), the geochemical and isotopic signature of mid-ocean ridge basalts (MORB) from three segments between 8 degrees and 12 degrees S show a FOZO-like enrichment with elevated He-3/He-4 (R/R-A) (> 10 R-A), suggesting small-scale upwelling with a deep primordial mantle component. Based on complementary major and trace elements analysis as well as Sr, Nd and Pb radiogenic isotope compositions of MORB samples from the same location, we confirm the presence of a FOZO/C-like enriched signature characterized by high Pb isotope ratios (Pb-206/Pb-204 = 18.1134-19.1481; Pb-207/Pb-204 = 15.4710-15.6146 and Pb-208/Pb-204 = 37.8625-39.0332), relatively low Sr-87/Sr-86 (0.702767-0.702974) and high Nd-143/Nd-144 (0.512989-0.513118). In agreement with recent seismological studies highlighting an asthenospheric anomaly centered under the Mascarene Basin and flowing beneath the CIR, we propose that this plume-like anomaly named Mascarene Basin Asthenosphere Reservoir (MBAR) is the source of the enriched FOZO/C-like signature observed along this portion of the CIR. Furthermore, our analyses reveal that the source of the MBAR anomaly may have a unique geochemical signature in the Indian Ocean, distinct from other Indo-African plumes such as the R & eacute;union plume. Moreover, the primordial characteristics, and the location of the MBAR (next to the margin of the African LLSVP) suggest that this plume-like anomaly may be a disconnected blob/proto-plume of a broad mantle structure formed by different Indo-African plumes/upwelling (e.g., Afar and Bouvet plumes) and anchored in the lower mantle.

Porphyry Cu, and porphyry Cu-Au deposits, are associated with arc magmatism and their ore-forming systems generally follow the magmatic evolution of typical arcs. However, most arc magmas are barren and giant economic porphyry Cu +/- Au deposits are rare. In this study, we model variations in rare earth element concentrations in evolving arc magmas and giant porphyry Cu +/- Au systems to quantify the percentage of the fractionating minerals required to produce the observed changes. We find that, during the andesitic stage of fractionation, ore-forming systems in thick crusts fractionate similar to 35% more amphibole than an average of thick arc magma systems (the thick-crust reference suite) and that ore-forming systems in thin crusts fractionate twice as much amphibole as their equivalent thin-arc magma reference suite. Thick-crust ore-forming suites also fractionate similar to 50% less plagioclase, and thin-crust ore systems similar to 40% less plagioclase, than their associated reference suites during the same andesitic stage of fractionation. Taken together, these observations imply that ore-producing magmas are appreciably wetter than their associated barren reference suites. Our modeling also shows that similar to 80% more amphibole is required to reproduce the andesite stage of fractionation in the thick-crust reference suite than in its thin-crust equivalent, suggesting that magmas produced under thick crusts are wetter than those produced under thin crusts. On the other hand, the chalcophile element contents of the thick- and thin-crust ore-forming systems are similar to and higher than those of the thick- and thin-crust reference suites, respectively. Therefore, we suggest that the high water content plays a critical role in the formation of giant porphyry Cu ore in thick crusts, whereas both high chalcophile contents and high water contents are required to form giant porphyry Cu-Au deposits in thin crusts. The high fraction of amphibole fractionation in giant economic porphyry suites, compared with their relevant reference suites, results in lower Y in the ore-associated suites and this difference increases with fractionation. As a consequence, plots of Y against MgO can be used to identify porphyries that have economic potential and are preferred to Sr/Y plots because they are less affected by the intense alteration associated with giant porphyry Cu +/- Au deposits.

Post-collisional porphyry Cu deposits are genetically related to the magmas generated by partial melting of sulfide-bearing lithosphere fertilized by subduction components. The ore-forming magmas are suggested to be enriched in chalcophile elements compared to the barren magmas. However, the chalcophile element contents in the post-collisional magmas and its role in controlling the porphyry ore formation remain unclear. Platinum-group element (PGE) geochemistry has been used as a proxy for Cu and Au. In this study, we report PGE concentrations of representative post-collisional ore-associated and barren suites in the eastern Tethyan metallogenic domain. The ore-associated suites have moderate Pd and Pt contents ranging from 0.05 to 0.5 ppb, which are comparable to those associated with giant porphyry systems in continental arc settings. In contrast, most of the barren suites have systematically lower Pd and Pt concentrations below 0.1 and 0.05 ppb, respectively. Numerical models show that the ore-forming magmas, derived from partial melting of subduction-modified lithospheric mantle, have precipitated a small amount of sulfide phases during magma differentiation, leading to the moderate depletion of Pd and Pt in the ore-associated suites. Although the sulfide segregation has depleted highly chalcophile element contents, the ore-forming magmas contain sufficient Cu to form porphyry Cu deposits. This contrasts with the barren suites, which mainly originated from partial melting of the lower crust and contain about five times lower Cu contents, unfavorable for porphyry Cu mineralization. We suggest that moderate chalcophile element contents in the ore-associated magmas have increased the porphyry ore-forming potential in the eastern Tethyan domain.

Post-depositional alteration of water-soluble alkali elements, including K, Rb, and Cs, in archaeological ceramics has been detected in various studies. In particular, some studies reveal that firing temperature of ceramics differentially affects the degree of alterations. In this study, using INAA and pXRF, we analyze a total of 318 ceramic samples from 12 archaeological sites of the early historical periods of central Korea (2-5C CE) to explore whether firing temperature influences the degree of alteration of alkali elements during burial. INAA and pXRF data show significantly higher concentrations of K, Rb and Cs in high-fired ceramics compared to low-fired ceramics, although both high and low-fired ceramics were produced at the same loci, and clay and temper do not differ. It is suggested that higher porosity and permeability of low-fired ceramics enable alkali elements to leach out of ceramics during burial. The results show that firing temperature affects post-depositional alteration processes of alkali elements but are incompatible with previous studies that observe lower concentrations of those elements in high-fired ceramics. These disparities can be explained by differences in amount of CaO between ceramic samples used in our analysis and previous works, which may lead to different pore formation processes during firing, while other post-depositional environmental factors may also be involved in the differential alteration of water-soluble alkali elements.