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Mantle xenoliths provide effective records of the metasomatic processes that affect continental lithosphere evolution, such as interaction with subducted components or modification via small-degree melts. Correlations between major/trace element geochemistry with stable and radiogenic isotope compositions can help constrain the source and timing of this metasomatism. We report new δ18O, δ44/40Ca, and δD values for twelve kimberlite-hosted mantle xenoliths from the Slave Craton (NWT, Canada), which show varying degrees of metasomatism. The δ18O values of olivine (δ18O ol = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ18O values (δ18O cpx = +5.31 ± 0.10‰; δ18O grt = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ44/40Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ44/40Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ18O and high δ44/40Ca values. In general, Δ18O cpx-ol and Δ18O grt-ol (ranging from −0.19‰ to +0.19‰ and from −0.56‰ to +0.35‰, respectively) are lower than expected equilibrium values at mantle temperatures. Strong negative correlations are found between δ18O grt and Δ18O grt-ol and garnet major and trace element composition (Na 2 O, H 2 O, La/Yb N). Furthermore, phlogopite-bearing kelyphitic rims have δD values (avg. = −126 ± 13‰; 1σ) lower than typical mantle values. Whole rock Sm-Nd model ages and oxygen isotope diffusion modeling suggest that metasomatism occurred during the Mesozoic, shortly before kimberlite entrainment, consistent with indications from diamond-forming fluids from the Slave craton. The combined low δ18O, δD, and high δ44/40Ca signature of the mantle peridotite xenoliths, along with the age constraints, suggest the metasomatic fluid/melt is sourced from a recycled oceanic crust component related to Mesozoic subduction in western North America. [ABSTRACT FROM AUTHOR]

Seafloor fabric indicators are the main features used for dating global-scale plate reorganizations. However, the lack of oceanic crusts older than 200 Ma limits their application only to the Mesozoic and Cenozoic eras. Furthermore, in cases such as the mid-Cretaceous time when reversals in Earth's magnetic field did not occur, the plate reorganization ages obtained from seafloor fabric indicators are imprecise. I propose the record of continental deformation as an alternative approach for dating these events. A compilation of cooling/deformation, migmatization, and unconformity ages recorded around the globe collectively indicates that continental deformation associated with the mid-Cretaceous plate reorganization culminated at 107 Ma. This age strongly correlates with ages obtained from other data such as palaeomagnetic poles. Considering that the deformational features similar to which are compiled in this study appear to be temporally correlated with other reorganization events, the record of globally distributed continental deformation might be used for other reorganization events whose timing is poorly constrained. [ABSTRACT FROM AUTHOR]

The aqueous alteration of the oceanic lithosphere provides significant energy that impacts the synthesis and diversity of organic compounds, which are crucial for the deep carbon cycle and may have provided the first building blocks for life. Although abiotic organic synthesis has been documented in mantle-derived rocks, the formation mechanisms and complexity of organic compounds in crustal rocks remain largely unknown. Here, we show the specific association of aliphatic carbonaceous matter with Fe oxyhydroxides in mafic crustal rocks of the Southwest Indian Ridge (SWIR). We determine potential Fe-based pathways for abiotic organic synthesis from CO2 and H2 using multimodal and molecular nano-geochemical tools. Quantum mechanical modeling is further employed to constrain the catalytical activity of Fe oxyhydroxides, revealing that the catalytic cycle of hydrogen may play a key role in carbon–carbon bond formation. This approach offers the possibility of interpreting physicochemical organic formation and condensation mechanisms at an atomic scale. The findings expand our knowledge of the existence of abiotic organic carbon in the oceanic crustal rocks and emphasize the mafic oceanic crust of the SWIR as a potential site for low-temperature abiotic organic synthesis. [ABSTRACT FROM AUTHOR]

We have developed a 3-D forward modeling method for the magnetometric resistivity (MMR) technique, specially focusing on the marine MMR method, which utilizes a vertical bipole source and seafloor receivers to measure magnetic field variations. The bipole source generates an artificial electric current between two electrodes: one on the sea surface and another on the seafloor. When computing the electric potential using the relaxation method, while conserving electric current, singularities arise at the electrode locations. To address this issue, we introduce two electrical resistivity structures to mitigate the effects of these singularities and to obtain magnetic field anomalies caused by arbitrary 3-D electrical resistivity anomalies beneath the seafloor. By determining the sign of the magnetic field anomaly, we can infer whether the electrical resistivity of the anomalous body is more conductive or more resistive compared to the surrounding oceanic crust. Furthermore, we demonstrate that increasing the number of bipole sources is more effective in exploring anomalous bodies than increasing the number of receivers. [ABSTRACT FROM AUTHOR]

We apply the stable potassium isotope system (41K/39K) to well-studied Mariana arc lavas, in which inter-island geochemical variability has been interpreted to reflect near constant addition of an aqueous fluid flux, that dominantly samples the subducting mafic oceanic crust and variable amounts of sediment melt addition to the sub-arc mantle wedge. The nature of the sediment component in the Mariana arc lavas remains enigmatic, with a mixture of melts from all subducted sediment lithologies and the altered-mafic oceanic crust seeming likely, but some interpretations point towards a component from melting of the volcaniclastic sediment alone. We present K isotopic data on a set of well-characterised Mariana arc lavas and sediment samples (from Ocean Drilling Program site 801). Our data show that the majority of Mariana arc lavas are isotopically heavy (ẟ 41K), by up to ∼0.2 ‰, relative to mid-ocean ridge basalt (MORB), but most of the subducting sediment samples are slightly isotopically lighter than, or indistinguishable from MORB. The volumetrically important volcaniclastic sedimentary unit however is significantly isotopically lighter than MORB, by ∼0.8 ‰, which reflects marine diagenetic processes. Thus, volcaniclastic material significantly influences the bulk sediment K isotope composition. We show that ẟ 41K compositions of the Mariana arc lavas can be reproduced by the addition of an aqueous fluid with isotopically heavy K (relative to MORB) and an additional fraction of an incompatible-element-enriched isotopically light melt component. Modelling of K isotopes together with K/La and radiogenic Nd indicate that the melt component is best explained by a mix of melts from bulk sediment and altered-mafic oceanic crust. Our results show that distinctive K isotopic variations in subduction zone inputs and K isotopic fractionation during dehydration reactions makes K a useful tracer of subduction zone processes. [ABSTRACT FROM AUTHOR]

In the Alpine Corsica, the Schistes Lustrés Complex consists of a stack of high-pressure metamorphic oceanic and continental units originated during the Late Cretaceous-Middle Eocene closure of the Western Tethys oceanic basin. This complex also includes the Bagliacone-Riventosa Fm. i.e. a thick succession of metaturbidites, whose interpretation is still matter of debate. In this paper, we provide the stratigraphic, metamorphic, and structural evidence that the Bagliacone-Riventosa Fm. belongs to the sedimentary cover of the Middle to Late Jurassic metaophiolites of the Inzecca Unit. The reconstructed succession of the Inzecca Unit thus comprises metaophiolites topped by metacherts and by the Erbajolo, Pietraggiolo and Bagliacone-Riventosa Fms. The former two formations derived from hemipelagic deposits whereas the latter two include both siliciclastic and carbonate turbidites. This succession is affected by a polyphase deformation history that is recognized as the same in all the metasedimentary formations, as testified by their structural field relationships. In addition, these formations experienced the same pressure-temperature metamorphic path, indicating their involvement in a subduction zone. This picture provides new evidence for the mechanism of underplating and exhumation of the oceanic slices within the frame of the subduction zone that developed since Late Cretaceous in the Western Tethys oceanic basin. [ABSTRACT FROM AUTHOR]

In slow spreading environments, oceanic crust is formed by a combination of magmatic and tectonic processes. Using full waveform inversion applied to active‐source ocean bottom seismometer data, we reveal the presence of a strong lateral variability in the 40–48 Ma old oceanic crust formed at the slow‐spreading Mid‐Atlantic Ridge in the equatorial Atlantic Ocean. Over a 120 km‐long section between the St Paul fracture zone (FZ) and the Romanche transform fault (TF), we observe four distinct 20–30 km long crustal segments. The segment affected by the St Paul FZ consists of three layers, an ∼2 km thick layer with a P‐wave velocity <6 km/s, a 1.5 km thick middle crust with a velocity of 6–6.5 km/s, and an underlying layer where velocity is ∼7 km/s, representing the lower crust. The segment associated with an abyssal hill morphology contains a high velocity of ∼7 km/s at 2–2.5 km below the basement, indicating the presence of primitive gabbro or serpenized peridotite. The segment associated with a low basement morphology seems to have 5.5–6.5 km/s velocity starting near the basement extending down to ∼4 km depth, indicating chemically distinct crust. The segment close to the Romanche TF, a velocity 4.5–5 km/s near the seafloor increasing to 7 km/s at 4 km depth indicates a magmatic origin. The four distinct crustal segments have a good correlation with the overlying seafloor morphology. These observed strong crustal heterogeneities could result from alternate tectonic and magmatic processes along the ridge axis, possibly modulated by thermal and/or chemical variations in the mantle during their formation along the ridge segment. Plain Language Summary: Generally magmatically accreted oceanic crust has a nearly uniform crustal structure. The speed of seismic waves, which is widely used as a proxy for the physical properties of the Earth, is relatively low in the upper crust but increases rapidly with depth, while in the lower crust the velocity is high but increases more slowly. Nevertheless, oceanic crust formed at slow‐spreading mid‐ocean ridges can be very heterogeneous. However, it is challenging to quantify the nature of this heterogeneity using conventional travel time based analyses. Here we apply a cutting‐edge full waveform inversion technique to an active‐source ocean bottom seismometer data set from the equatorial Atlantic Ocean. The aim is to create seismic velocity models of oceanic crust with enhanced details. The waveform inversion reveals four distinct zones within a 120 km long crustal section, with boundaries consistent with the seafloor morphology. The section contains two segments of normal oceanic crust, a segment with high velocities at shallow depth, possibly containing primitive gabbro, and another chemically distinct segment with nearly constant velocity in the whole crust. The observed strong crustal heterogeneities seem to result from a combination of magmatic and tectonic accretion processes possibly induced by thermally or chemically heterogeneous mantle. Key Points: We apply full waveform inversion to the crustal turning waves recorded by ocean bottom seismometers in the equatorial Atlantic OceanThe velocity model exhibits strong crustal velocity heterogeneity, containing four distinct segments correlating well with seafloor morphologyThe strong crustal heterogeneity seems to be caused by a combination of magmatic and tectonic processes [ABSTRACT FROM AUTHOR]

Epidote is a potential water carrier in subducting oceanic crust, and it is involved in temperature records from blueschist and eclogite exhumed from subduction zones. Thermal conductivity (κ) and thermal diffusivity (D) of epidote were measured at 303–1,473 K and 0.5–3.0 GPa using the transient plane‐source method. κ and D values decreased with temperature before dehydration, but increase anomalously with temperature after dehydration, and finally decreased with crystallization of the decomposition products. Thermal conductivity and thermal diffusivity of epidote exhibited a positive pressure dependence. The obtained κ and D values of epidote were significantly smaller than those of nominally anhydrous minerals and other hydrous minerals. X‐ray computed tomography analysis revealed that the pores inside the recovered samples were partially connected. κ and D values were dominated by conductive heat transport before dehydration, while the anomalous increase in the thermal parameters after dehydration may have been caused by the fluid inside the connected pores. Using variable thermal conductivity obtained in this study, the thermal structures of warm subducting slabs associated with epidote‐blueschist and epidote‐eclogite facies were modeled. Our estimations revealed that the temperatures of warm slabs below the forearc with the epidote‐blueschist and epidote‐eclogite facies may be lower 7–10 and ∼40–50 K compared to those determined using a constant thermal conductivity value. This implies that the presence of epidote‐blueschist and epidote‐eclogite could reduce the temperature of the slab, which may alter the dehydration depth of the slab. Plain Language Summary: Thermal structures of subducting oceanic crust control the arc volcanism, seismicity, and water cycle processes to some extent. The temperature of the slab is a key factor affecting the ability of hydrous minerals to carry water into the deep mantle. However, there are large discrepancies in the thermal structures of subducting slabs from thermal models and the rock record. In this study, thermal conductivity and thermal diffusivity of epidote, an important hydrous mineral in exhumed metamorphic rocks, were measured at high temperatures and pressures. Using the variable thermal conductivity with temperature and pressure, we constructed a model of the thermal structure of a warm subduction zone containing epidote‐blueschist and epidote‐eclogite facies. The simulations conducted in this study indicated that the temperatures of the subducting slab are lower than those reported in previous studies. Epidote could be an important water carrier for depths of up to 100 km. Key Points: Thermal conductivity (κ) and thermal diffusivity (D) of epidote were measured at 303–1,473 K and 0.5–3.0 GPaκ and D values of epidote exhibited three stages with temperatureThe presence of epidote‐blueschist and epidote‐eclogite may reduce the temperature of the slab [ABSTRACT FROM AUTHOR]

The Abu Farayed Granite (AFG), located in the southeastern desert of Egypt, was intruded during the early to late stages of Pan-African orogeny that prevailed within the Arabian–Nubian Shield. The AFG intrudes an association of gneisses, island arc volcano–sedimentary rocks, and serpentinite masses. Field observations, supported by remote sensing and geochemical data, reveal a composite granitic intrusion that is differentiated into two magmatic phases. The early granitic phase comprises weakly deformed subduction-related calc–alkaline rocks ranging from diorite to tonalite, while the later encloses undeformed granodiorite and granite. Landsat-8 (OLI) remote sensing data have shown to be highly effective in discriminating among the different varieties of granites present in the area. Furthermore, the data have provided important insights into the structural characteristics of the AFG region. Specifically, the data indicate the presence of major tectonic trends with ENE–WSW and NW–SE directions transecting the AFG area. Geochemically, the AFG generally has a calc–alkaline metaluminous affinity with relatively high values of Cs, Rb, K, Sr, Nd, and Hf but low contents of Nb, Ta, P, and Y. The early magmatic phase has lower alkalis and REEs, while the later phases have higher alkalis and REEs with distinctly negative Eu anomalies. The AFG is structurally controlled, forming a N–S arch, which may be due to the influence of the wadi Hodein major shear zone. The diorite and tonalite are believed to have been originally derived from subduction-related magmatism during regional compression. This began with the dehydration of the descending oceanic crust with differential melting of the metasomatized mantle wedge. Magma ascent was long enough to react with the thickened crust and therefore suffered fractional crystallization and assimilation (AFC) to produce the calc–alkaline diorite–tonalite association. The granodiorite and granites were produced due to partial melting, assimilation, and fractionation of lower crustal rocks (mainly diorite–tonalite of the early stage) after subduction and arc volcanism during a late orogenic relaxation–rebound event associated with uplift transitioning to extension. [ABSTRACT FROM AUTHOR]

Due to its unique geographical location and complex geological evolution processes, the South China Sea has been a focus of extensive research. Previous studies on the density structure of the South China Sea mostly focused on 2D density structures, with relatively limited research on 3D density structures. A comprehensive study is still needed to refine the expansion mechanism and tectonic evolution of the South China Sea. In this study, we utilized wavelet multi-scale analysis of gravity data to obtain a 3D density model of the South China Sea and discussed its tectonic evolution from the pattern of density anomalies. The inversion results show that (1) the expansion of the South China Sea caused the typical thin oceanic crust and parts of the continent–ocean transition zone may fracture due to the expansion; (2) the low-density anomaly in the upper mantle of Luzon Island may indicate partial melting or the upwelling of asthenosphere materials; and (3) the expansion of the South China Sea is influenced by multiple plate forces and uneven forces affect the distribution of high-density anomalies in the upper mantle. [ABSTRACT FROM AUTHOR]

Ten rock samples consisting of one pyroclastic density current (PDC1) deposit, seven lava flows (LF1–7), and two summit lava domes (LD1, 2) were studied to understand the petrogenesis and magma dynamics at Mt. Sumbing. The stratigraphy is arranged as LF1, PDC1, LF2, LF3, LF4, LF5, LF6, LF7, LD1, and LD2; furthermore, these rocks were divided into two types. Type I, observed in the oldest (LF1) sample, has poor MgO and high Ba/Nb, Th/Yb and Sr. The remaining samples (PDC1–LD2) represent type II, characterized by high MgO and low Ba/Nb, Th/Yb and Sr values. We suggest that type I is derived from AOC (altered oceanic crust)-rich melts that underwent significant crustal assimilation, while type II originates from mantle-rich melts with less significant crustal assimilation. The early stage of type II magma (PDC1–LF3) was considered a closed system, evolving basaltic andesite into andesite (55.0–60.2 wt% SiO2) with a progressively increasing phenocryst (0.30–0.48 ϕ PC ) and decreasing crystal size distribution (CSD) slope (from − 3.9 to − 2.9). The evidence of fluctuating silica and phenocryst contents (between 55.9–59.7 wt% and 0.25–0.41 ϕ PC , respectively), coupled with the kinked and steep (from − 5.0 to − 3.3) CSD curves imply the interchanging condition between open (i.e., magma mixing) and closed magmatic systems during the middle stage (LF4–LF6). Finally, it underwent to closed system again during the final stage (LF7–LD2) because the magma reached dacitic composition (at most 68.9 wt% SiO2) with abundant phenocryst (0.38–0.45 ϕ PC ) and gentle CSD slope (from − 4.1 to − 1.2). [ABSTRACT FROM AUTHOR]

The alteration of ocean crust through hydrothermal seawater circulation facilitates chemical exchange between Earth's surface and interior. Hydrothermal alteration leads to uranium (U) removal from seawater and net U uptake by the ocean crust, particularly during low temperature alteration that occurs on the vast ocean ridge flanks away from the spreading axes. Determining the timescales of U uptake and its associated 238U/235U signature has important implications for understanding U exchange processes during subduction and recycling into the mantle. Here we study the U systematics of ∼15 million year-old ocean crust drilled at Site 1256 on the eastern flank of the East Pacific Rise. Analysis of cores from the upper ∼1300 m of intact ocean crust at this site, reveal large variability in U concentrations and 238U/235U ratios. Many of the samples from the upper ∼600 m of extrusive lavas have elevated U concentrations and 238U/235U ratios lower than seawater, consistent with mechanisms of U uptake under relatively oxidised conditions. Samples from the underlying sheeted dikes and gabbros show evidence for hydrothermal U mobilisation, but negligible net U uptake. In contrast, in the transition zone between the extrusive lavas and the sheeted dikes, samples revealed large U enrichments and high 238U/235U ratios above seawater. This is consistent with uptake of the reduced U+4 species under relatively reducing conditions from seawater-derived hydrothermal fluids. In addition, large secular disequilibrium in 234U/238U ratios from samples in the lava-dike transition and upper sheeted dikes give evidence for U mobility within the last ∼1.5 million years, likely driven by deep channelled flow of seawater-derived hydrothermal fluids combined with preferential leaching of 234U from the rock matrix. Both the total estimated U uptake and mean 238U/235U at Site 1256 is lower than similar estimates from significantly older (>100 million years) altered ocean crusts at drill Sites 801 and 417/418. This shows the variable total U uptake and 238U/235U ratio in altered ocean crust over time, which needs to be taken into consideration when estimating global U budgets. [ABSTRACT FROM AUTHOR]

Mantle heterogeneity in lithology and geochemistry is often attributed to recycled subducted materials. While distinct mantle end‐members are identified by radiogenic isotopes, the specific recycled materials contributing to this heterogeneity remain debated. This study presents Mo‐Sr‐Nd‐Pb isotopic data for OIB‐like alkali basalts from the Maguan area in the southeastern Tibetan Plateau, focusing on slab inputs' role in mantle heterogeneity. The Miocene (ca. 13 Ma) Maguan alkali basalts are divided into two types based on petrographic and geochemical characteristics, showing similar Sr‐Nd‐Pb isotopic signatures but different Mo isotopic compositions. Type I basalts exhibit a wide δ98/95Mo range (−0.31‰ to −1.03‰, average −0.47‰ ± 0.06‰, 2SD = 0.40‰, n = 13), while type II basalts have heavy and constant δ98/95Mo values (−0.11‰ to −0.17‰, average −0.14‰ ± 0.01‰, 2SD = 0.05‰, n = 6). The unique low δ98/95Mo value (−1.03‰) in type I basalts is among the lowest reported in OIB‐like continental basalts. Type I basalts likely originate from an enriched asthenospheric mantle metasomatized by melts from recycled dehydrated oceanic crust and sediments, whereas type II basalts are derived from partial melting of an enriched asthenospheric mantle metasomatized by melts from recycled serpentinized peridotites. The residual Tethys oceanic slabs in the deep mantle significantly contribute to the mantle source of the Maguan basalts. The formation of Maguan Miocene magmas may be linked to mantle upwelling induced by the subduction of the West Burma plate. This study highlights the Mo isotopic system's utility in tracing complex slab fluxes generating mantle geochemical heterogeneity. Plain Language Summary: Recycling of subducted material can exert a profound influence on the deep mantle. Tracing superficial substances in the mantle is crucial for understanding Earth's evolution. However, radiogenic isotopic compositions for different enriched mantle end‐members overlap, hindering our understanding of which specific recycled materials contribute to enriched mantle end‐members. In this paper, we solve this problem by studying the molybdenum (Mo) isotope system in Cenozoic mantle‐derived basalts from the southeastern margin of the Tibetan Plateau. Our findings show that although the studied basalts have similar ratios of radiogenic isotopes, they can be divided into two types based on petrographic and geochemical characteristics, especially Mo isotopes. We attribute recycled dehydrated oceanic crust with sediments to isotopically lighter Mo and serpentinized peridotites to isotopically heavier Mo in their mantle sources. This study shows the mantle heterogeneity for Mo isotopes, and in turn demonstrates that the Mo isotope system for mantle‐derived magmas is an effective tool to track substances in the Earth's interior. Key Points: Miocene Maguan basalts have similar Sr‐Nd‐Pb isotopic compositions but a large range of Mo isotopic compositionsRecycled serpentinized peridotites yield high δ98/95Mo values, while recycled oceanic crust and sediments yield low δ98/95Mo valuesMo isotopes are effective tools to trace complex slab fluxes generating mantle geochemical heterogeneity [ABSTRACT FROM AUTHOR]

Iddingsitization is an aqueous alteration that is known to take place in meteorites and continental basalts providing a potential habitat for microbial life. However, little is known about the exact mode by which this reaction occurs in the hadal seafloor and its implication for the deep subsurface biosphere. A comprehensive investigation of hadal basalts from the southern Mariana Trench (SMT) conducted with microscopic examinations shows that iddingsite occurs as augite‐ hosted veins, rims, and mineral grains formed completely in place of augite within the SMT basalts. Carbon geochemistry indicates that organic matter with homogenous δ13C values between ‐27.8‰ and ‐27.2‰ might be biogenically accumulated in the SMT basalts. Furthermore, the close spatial relationships between carbonaceous matter (CM) and goethite in iddingsite point to microbial attachment to iddingsite minerals. Thus, iddingsitization might have fueled H2‐ utilizing microorganisms inhabiting the hadal oceanic crust, thereby leading to the formation of CM, as implied by oxygen isotopic compositions revealing low alteration temperatures (32‐83°C) favorable for microbial growth. In all, microbial biosignatures associated with iddingsite in the SMT basalts are highlighted, and these results could pave the way for deciphering the deep subsurface biosphere at hadal zones. [ABSTRACT FROM AUTHOR]

ABSTRACT Carbonate cementation in the Upper Permian sandstones informs the timing and temperature of hydrothermal activity in the south‐western Ordos Basin. This study presents a detailed examination of these hydrothermally influenced carbonate cements, constraining their age, carbonate diagenesis and relationship with regional geodynamic evolution. Sedimentological analyses demonstrate the development of deltaic plain and front sand bodies in the study area, which resulted in interbeds of volcanic matrix‐rich sandstones with matrix‐free sandstones. Petrography and electron microprobe analysis reveal four carbonate mineral growth phases of matrix‐free sandstones in the following sequence; scarce pure siderite, scarce Mg‐rich siderite, abundant blocky calcite and moderately abundant grain‐replacing calcite. The fluid inclusion data show anomalies of homogenization temperature of blocky carbonate cements during early diagenesis, over a wide range of ca 148 to 228°C. In addition, blocky carbonate cements show low δ13C (−5.9 to −13.1‰ Vienna PeeDee Belemnite) and δ18O (clustered tightly from −12.4 to −14.6‰ Vienna PeeDee Belemnite) values, interpreted to result from elevated temperatures during cementation, associated with activation of basement faults and concomitant hydrothermal fluid intrusion triggered by oceanic crust subduction in the south‐west margin of the Ordos Basin. Using in situ calcite U–Pb geochronology, the timing of hydrothermal activity was constrained to ca 247.0 ± 11 to 248.2 ± 4.7 Ma. This work provides a case study for applying intergranular calcite U–Pb dating to determine the absolute timing of fluid flow in sedimentary basins, offering tremendous potential to capture snapshots of various diagenetic evolution stages in sediments. The proposed diagenetic model can also provide new insights and understanding regarding hydrothermally influenced sediments. More importantly, hydrothermal activity may have commenced earlier than previously thought. The North Qinling Orogen uplift and associated Mianlue oceanic crust subduction may have begun at the Permian–Triassic transition with a protracted hydrothermal event in the south‐western Ordos Basin. [ABSTRACT FROM AUTHOR]

Earth owes much of its dynamic surface to its bimodal hypsometry, manifested by high-riding continents and low-riding ocean basins. The thickness of the crust in the lithosphere exerts the dominant control on the long-wavelength elevations of continents. However, there is a limit to how high elevations can rise by crustal thickening. With continuous crustal thickening, the mafic lower crust eventually undergoes a densifying phase transition, arresting further elevation gain--an effect clearly observed in modern orogenic belts. On early Earth, lower crust densification should also limit how high a thickening crust can rise, regardless of the thickening mechanisms. We suggest that lower crust densification combined with a thicker oceanic crust in the Archean may have limited the whole-Earth topographic relief to 3 to 5 kilometers at most--half that of the present day. Unless the oceans were far less voluminous, limited relief would inevitably lead to a water world on early Earth. [ABSTRACT FROM AUTHOR]

Changes in lithospheric composition and strength associated with rifting of the Rodinian supercontinent (ca. 780–485 Ma) served to localize Mesozoic tectonic activity in the McCall region of west-central Idaho, USA. Although discrimination diagrams support slab failure melting, ca. 150–121 Ma calcic magmatism in the Hazard Creek complex and chemically similar intrusive rocks of northeastern Oregon, USA (e.g., Cornucopia stock), is best explained by progressive loading of oceanic crust. Westward-directed thrusting across the Laurentian continental margin and adjacent island-arc terranes (Olds Ferry/Wallowa; Blue Mountains province) led to partial melting of metabasaltic source rocks at pressures and depths sufficient for garnet stability (>10 kbar, ∼35 km). Early pluton emplacement during right-oblique arc–continent collision overlapped in time with subduction zone reorganization, which involved a change in dip direction (westward to eastward) under the accreting Blue Mountains block. Ensuing magmatic activity predated and was concurrent with ca. 116 Ma thrust reactivation of the Wallowa/Olds Ferry boundary, which temporally overlapped with contractional deformation along the terrane–continent accretionary boundary. Later synorogenic magmatism was focused along the accretionary boundary, where rising anatectic melts were caught between the eastwar-dimpinging/northward-migrating (obliquely colliding) terrane block and continental margin backstop (Rodinian rift architecture). Middle Cretaceous dextral transpression viewed in this manner precludes the need for an outboard “hit-and-run” collider (Insular superterrane) and thus, a post-accretion shear zone in western Idaho. [ABSTRACT FROM AUTHOR]

The Sub-Antarctic South Atlantic Ocean has been inferred to have undergone a complex tectonic history involving dismemberment and plume-ridge interaction. Here we report new in situ major (electron probe microanalysis, EPMA), trace element (laser ablation–inductively coupled plasma–mass spectrometry, LA-ICP-MS), and Sr isotopic (laser ablation–multicollector–inductively coupled plasma–mass spectrometry, LA-MC-ICP-MS) compositions for minerals (olivine, clinopyroxene, and plagioclase) from the Northeast Georgia Rise (NGR; Sites 698 and 699), Islas Orcadas Rise (IOR; Site 701), and Meteor Rise (MR; Site 703) volcanic samples in the Sub-Antarctic South Atlantic Ocean. Plagioclases and clinopyroxenes from Sites 698, 699, and 703 are characterized by similar incompatible element patterns and Sr isotopic characteristics, suggesting that they are likely to have originated from a cogenetic mantle source. The plagioclases and clinopyroxenes exhibit an oscillatory, reverse, and normal zoning texture, and display clear evidence of Sr isotopic disequilibrium, suggesting dynamic and open fractional-crystallization processes as well as extensive mixing of compositionally distinct magmas. Rims and groundmass of plagioclase exhibit much more highly radiogenic Sr isotopes than their cores, likely indicating the involvement of both continental lithospheric and recycled oceanic crust. The in situ geochemical and isotopic compositions of these minerals exhibit the features of both the oceanic-island basalt–type TristanGough mantle plume track and the normal mid-oceanic-ridge basalt–type Mid-Atlantic spreading ridge (MAR) and Agulhas spreading ridge (AR) track. We speculate that the NGR, IOR, and MR were formed from the same mantle source with volcanic flow of the Tristan-Gough mantle plume. Subsequently, tectonic movement along the MAR and AR separated the originally combined MR-IORNGR, resulting in the incursion of depleted asthenospheric mantle and the contamination contributions of continental and recycled oceanic crust components. [ABSTRACT FROM AUTHOR]

The premise put forth by Wu et al. (2022) that the late Proterozoic and early Paleozoic development of the Appalachian Orogen was controlled by transform faults finds no support in the geology of the region. Such faults have been well studied on and offshore over the past century and a quarter by many federal and private agencies because of the seismic hazard they pose to nuclear power plants and dams and their significance in offshore exploration. The northwest-trending transform faults developed in the Middle Jurassic across early oceanic crust as the Atlantic Basin began to open, to offset the initial northeast-trending Late Triassic–Early Jurassic rifts and extended landward. These young transform faults, which were accompanied by north-trending rifts, could have played no part in the development of the Appalachian Orogen, Laurentia, Iapetus, or the Rheic Ocean. Furthermore, the presented plate reconstructions cannot be reconciled with the well-controlled geologic history revealed in southern New England (USA), where the Appalachian Collision Zone is exposed. Relations there demonstrate that northwest Africa and Laurentia had first collided during the late Proterozoic Pan African Orogeny, long before the times shown on the reconstructions by Wu et al. (2022). [ABSTRACT FROM AUTHOR]

The East Kunlun Orogenic Belt (E-KOB) in the northern Tibet Plateau has undergone a long multi-stage history of drifting, accretion, and collision of the Proto- and Palaeo-Tethyan oceans. It has been addressed a trench-arc-back-arc basin system of the Proto-Tethys in the E-KOB, and the tectonic history of this major ocean has been well constrained by previous studies. However, the evolution of the back-arc basin still remains unclear. In this study, the Yugusayi monzodiorite, quartz-bearing syenite, and gradually contacted skarn rocks characterized by garnet megacrysts, in the North Qimantagh Belt were investigated. To reveal the tectonic setting and skarnization mechanism, geochemical and geochronological studies were conducted on the intrusions and garnet skarn, and the elemental compositions of the garnet megacrysts were also analysed. These monzodioritic rocks have high MgO (6.87–8.31 wt.%), Sr and La contents, low Y and Yb contents, and relatively high La/Yb (31–55) and Sr/Y (41–51) ratios, resembling to high-Mg adakites. They display right-sloping chondrite-normalized REE patterns, enriched in LILEs, and depleted in Ti with significant Nb-Ta troughs, which are similar to those of continental arc rocks. Zircons from monzodiorite and skarn samples have contemporaneous U-Pb ages of 459 ± 3 Ma and 454 ± 4 Ma with εHf(t) values of − 8.53 to − 4.64 and − 7.7 to + 12.8, respectively. In addition, the chemical zoning garnet megacrysts are composed mainly of grossular and andraditic grossular, and are characterized by spoon-shaped REE patterns. Based on our new data and the regional geology, it can be concluded that the Yugusayi intrusive rocks formed in a subduction-related tectonic setting and resulted in the skarnization. These data not only provide key constraints on the initial subduction of the Qimantagh back-arc basin's oceanic crust, but also offer a unique opportunity to explore the Caledonian skarnization in the Qimantagh Belt. [ABSTRACT FROM AUTHOR]

Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust. [ABSTRACT FROM AUTHOR]

Continental intraplate volcano is an ideal probe to unravel the composition and structure of the deep Earth. The intraplate Changbaishan‐Tianchi volcano was one of the most hazardous eruptions on the Earth's planet. The long‐term activity of this volcano from the Pleistocene to 946 CE has erupted materials with a broad compositional range from basalt to rhyolite, which are expected to be associated with the continuous northeastward subduction of the Pacific plate, but the magma source remains controversial. In this paper, we present a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for selected eruptions of the Changbaishan‐Tianchi volcano, aiming to provide new insights into their magma source and the associated geodynamics. Radiogenic isotopic ratios and incompatible trace element compositions indicate that the erupted volcanic rocks at different stages, although with a varied differentiation degree, were derived from a common magma source characterized by a mixture of DM and EM1 end‐members. Zircon Hf and O isotopes are both relatively homogeneous for different lithologies and eruption stages, with the εHf(t) values varying between −5 and +5, and δ18O values between 3.58‰ and 5.97‰. Modeling of source mixing indicates that high‐temperature altered oceanic crust materials are an important component in the source of Changbaishan‐Tianchi volcano, likely derived from an ancient stagnant slab that has been reactivated by the subduction of the Pacific plate. This study demonstrates that the recycling of deeply subducted oceanic crust is potentially an important source and trigger for continental intraplate volcanism. Plain Language Summary: The Millennium Eruption (ME) of the Changbaishan‐Tianchi intraplate volcano at 946 common era (CE) was one of two largest explosive eruptions in the past 2,000 years, but its source is poorly constrained. This paper represents a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for providing a full picture of magma evolution and new insights into the magma source and the associated geodynamics. Our data indicate that high‐temperature altered oceanic crust, likely a former part of the subduction of the Pacific plate, has been an important component in the source of the Changbaishan‐Tianchi volcano. Therefore, the Changbaishan‐Tianchi volcano demonstrates that continental intraplate volcanism can also be impacted by long‐distance subduction of oceanic crusts. Key Points: The long‐term eruptions of the intraplate Changbaishan‐Tianchi volcano from the Pleistocene to 946 CE were derived from a common magma sourceZircon Hf and O isotopes indicate important contributions from subducted oceanic crust [ABSTRACT FROM AUTHOR]

Abstract Anisotropic structures within the crust are frequently perceived to originate from stress-induced cracks, which have been mainly estimated on land through different wave speeds of orthogonally polarized S waves propagating in the anisotropic media. However, such estimations of crustal anisotropic structures in ocean areas, particularly for subduction zones around trenches, have not been investigated in detail due to the lack of long-term ocean bottom observations. In this study, we used ocean bottom seismometers of a permanent network deployed across the Japan Trench and the southern part of the Kuril Trench and applied the shear-wave splitting analysis to P-to-s converted waves extracted by receiver function analyses using teleseismic events. We estimated the anisotropic structures in marine sediments and oceanic crust for the incoming Pacific Plate and marine sediments for the overriding North American Plate. The obtained fast polarization directions for the incoming plate are mainly oriented to be parallel to the trench axis for the marine sediment and oceanic crust, which are formed by normal faults and cracks due to the upward plate bending in the outer-rise region, whereas results for marine sediments at the northern part of the Japan Trench are obliquely aligned to the trench axis. The oblique direction is consistent with the magnetic lineations of the incoming plate, indicating that ancient faults within the plate, which were formed in the shallow part of the crust during the creation of the oceanic plate at the ridge, are reactivated by the plate flexure. For the overriding plate, the fast polarization directions in the northern and southern parts of the study area are nearly normal to the trench axis. The central part shows two distinct features: the fast polarization directions parallel to the trench axis and small degrees of anisotropy. These patterns may reflect crack alignments associated with the lateral variation in postseismic crustal deformation after the 2011 Tohoku-Oki earthquake. Our results suggest substantial lateral variations in the stress field at the tip of the overriding plate along the strike direction. Graphical Abstract

Anisotropic structures within the crust are frequently perceived to originate from stress-induced cracks, which have been mainly estimated on land through different wave speeds of orthogonally polarized S waves propagating in the anisotropic media. However, such estimations of crustal anisotropic structures in ocean areas, particularly for subduction zones around trenches, have not been investigated in detail due to the lack of long-term ocean bottom observations. In this study, we used ocean bottom seismometers of a permanent network deployed across the Japan Trench and the southern part of the Kuril Trench and applied the shear-wave splitting analysis to P-to-s converted waves extracted by receiver function analyses using teleseismic events. We estimated the anisotropic structures in marine sediments and oceanic crust for the incoming Pacific Plate and marine sediments for the overriding North American Plate. The obtained fast polarization directions for the incoming plate are mainly oriented to be parallel to the trench axis for the marine sediment and oceanic crust, which are formed by normal faults and cracks due to the upward plate bending in the outer-rise region, whereas results for marine sediments at the northern part of the Japan Trench are obliquely aligned to the trench axis. The oblique direction is consistent with the magnetic lineations of the incoming plate, indicating that ancient faults within the plate, which were formed in the shallow part of the crust during the creation of the oceanic plate at the ridge, are reactivated by the plate flexure. For the overriding plate, the fast polarization directions in the northern and southern parts of the study area are nearly normal to the trench axis. The central part shows two distinct features: the fast polarization directions parallel to the trench axis and small degrees of anisotropy. These patterns may reflect crack alignments associated with the lateral variation in postseismic crustal deformation after the 2011 Tohoku-Oki earthquake. Our results suggest substantial lateral variations in the stress field at the tip of the overriding plate along the strike direction. [ABSTRACT FROM AUTHOR]

Relicts of subducted oceanic lithosphere provide key information for the tectonic reconstructions of convergent margins. In the Central Alps, such relicts occur as isolated mafic–ultramafic lenses within the migmatites of the southern Adula nappe and Cima-Lunga unit. Analysis of the major-, minor-, and accessory minerals of these ophiolitic relicts, combined with zircon and rutile U–Pb ages and zircon oxygen isotopes, allows the reconstruction of different stages of their complex evolution. The mafic–ultramafic suite in Valle di Moleno consists of chlorite-harzburgites associated with metarodingites and retrogressed eclogites. Relic omphacite and kyanite in retrogressed eclogites provide evidence for subduction-related metamorphism. Increasing XPrp in the garnet mantle towards the rim documents heating during high-pressure metamorphism up to 800–850 °C. Polyphase inclusions and chemical zoning in garnet suggest fluid-assisted melting during high-pressure metamorphism dated at 31.0 ± 0.9 Ma. In Val Cama, chlorite-harzburgites, metarodingites and calcsilicate-metasediments occur. Detrital zircon ages in the metasediment suggest a Mesozoic deposition. The metarodingite-metaperidotite-metasediment association and the low δ18O signatures of zircon (δ18O 3.0–3.7‰), inherited from seafloor metasomatism of the protoliths, show that the rocks are derived from former altered oceanic crust. Amphibolite facies metamorphism related to the Central Alps Barrovian evolution in Val Cama occurred at 28.8 ± 1.5 Ma. The combined data from Moleno and Cama indicate a rapid transition (~ 2 Ma) from subduction to collisional metamorphism with corresponding exhumation rates of 3–6 cm/year. Fast exhumation tectonics may have been favored by slab break-off or slab extraction. U–Pb dating of rutile from both localities yields ages of ~ 20 Ma, suggesting that these rocks remained at amphibolite-facies conditions for about 10 Ma and underwent a second fast exhumation of 3 cm/year associated with vertical movements along the Insubric line. [ABSTRACT FROM AUTHOR]

The Alborz Mountains in north Iran underwent several tectono-metamorphic events during opening and closure of the Palaeotethys and Neotethys Oceans. These events are recorded by rare and discontinuously exposed metamorphic rocks, such as the HP-LT Asalem-Shanderman Complex and the Gasht Metamorphic Complex (GMC), that are considered to have been metamorphosed during the closure of the Palaeotethys Ocean. The GMC comprises poorly exposed metasediments and amphibolites metamorphosed under greenschist- to amphibolite-facies conditions, along with smaller volumes of granites. Different dating methods were applied to selected samples of the GMC basement to constrain the geological evolution of this part of the Alborz Mountains. A metagranite yielded two LA-ICP-MS U–Pb zircon ages of 638.4 ± 4.1 Ma and 590.3 ± 4.8 Ma that possibly date protolith crystallisation and later deformation and metamorphism, respectively, and a granite yielded a late Ediacaran 551 ± 2.5 Ma U–Pb zircon crystallisation age. A northern provenance from the basement to the South Caspian Basin can neither be established nor ruled out because no age data are available for this unit. Derivation of the GMC from Turan Block basement is unlikely, as this has a different crustal makeup and is probably composed of Paleoproterozoic and early Neoproterozoic material. The zircon ages are similar to published ages from the Arabian-Nubian Shield, indicating that this part of the Alborz basement may have belonged to the northern margin of Gondwana in the Neoproterozoic before rifting and drifting away along with other Iranian blocks (the Cimmerian terranes) during opening of the Neotethys Ocean. Chemical Th-U-total Pb ages for metamorphic monazites from two metapelite samples yielded a very large range of spot ages, of which c. 80% falls between 200 and 250 Ma, that do not allow to distinguish between Eo-Cimmerian and Main Cimmerian events in the GMC. However, they may indicate that the amphibolite-facies peak metamorphism of the GMC occurred sometime in the Triassic, in any case much later than the Carboniferous metamorphism in the neighbouring Asalem-Shanderman Metamorphic Complex to the north. Peak-metamorphic amphibole from amphibolite, retrograde white mica and foliation-defining biotite from metapelites and magmatic white mica from granite yielded much younger 175.1 ± 0.5 to 177.0 ± 0.4 Ma 40Ar/39Ar plateau ages. The Toarcian 40Ar/39Ar ages for minerals with different nominal closure temperatures reflect very rapid cooling of GMC basement below the Shemshak Group due to extension-triggered uplift. This late Toarcian to Aalenian extension event can be correlated with the regional Mid-Cimmerian unconformity of mid-Bajocian age (c. 170 Ma) that resulted from the tectonic movements causing rapid uplift and erosion. Extension probably started in the western Alborz Mountains in the Toarcian, migrated eastward, and culminated in the Aalenian in the eastern Alborz with the formation of a deep-marine basin. It was probably triggered by the onset of the subduction of Neotethys oceanic crust beneath the Central Iranian Microcontinent. [ABSTRACT FROM AUTHOR]

A new, Earth System Model of Intermediate Complexity, DCESS II, is presented that builds upon, improves and extends the Danish Center for Earth System Science (DCESS) Earth System model (DCESS I). DCESS II has considerably greater spatial resolution than DCESS I while retaining the fine, 100 m vertical resolution in the ocean. It contains modules for the atmosphere, ocean, ocean sediment, land biosphere and lithosphere and is designed to deal with global change simulations on scales of years to millions of years while using limited computational resources. Tracers of the atmospheric module are temperature, nitrous oxide, methane (12,13C isotopes), carbon dioxide (12,13,14C isotopes) and atmospheric oxygen. For the ocean module, tracers are conservative temperature, absolute salinity, water 18O, phosphate, dissolved inorganic carbon (12,13,14C isotopes), alkalinity and dissolved oxygen. Furthermore, the ocean module considers simplified dynamical schemes for large-scale meridional circulation and sea-ice dynamics, stratification-dependent vertical diffusion, a gravity current approach to the formation of Antarctic Bottom Water and improvements in ocean biogeochemistry. DCESS II has two hemispheres with six zonal-averaged atmospheric boxes and twelve ocean boxes distributed across the Indian-Pacific, the Atlantic, the Arctic and the Southern Oceans. A new, extended land biosphere scheme is implemented that considers three different vegetation types whereby net primary production depends on sunlight and atmospheric carbon dioxide. The ocean sediment and lithosphere model formulations are adopted from DCESS I but now applied to the multiple ocean and land regions of the new model. A model calibration was carried out for the pre-industrial climate and model steady-state solutions were compared against available modern-day observations. For the most part, calibration results agree well with observed data, included excellent agreement with ocean carbon species. This serves to demonstrate model utility for dealing with the global carbon cycle. Finally, two idealized experiments were carried out in order to explore model performance. First, we forced the model by varying Ekman transport out of the model Southern Ocean, mimicking the effect of Southern Hemisphere westerly wind variations and second, we imposed freshwater melting pulses from the Antarctic ice sheet on to the model Southern Ocean shelf. Changes in ocean circulation and in the global carbon cycle found in these experiments are reasonable and agree with results for much more complex models. Thus, we find DCESS II to be a useful and computational-friendly tool for simulations of past climates as well as for future Earth System projections. [ABSTRACT FROM AUTHOR]

Natural carbonatite is associated with various types of deposits, including rare earth elements (REEs) and high-field strength elements (e.g., Nb). Although the spatial relationship between fluorine enrichment and the formation of carbonatite-type deposits is well-established, the underlying mechanism remains unclear. In this study, we investigate the influence of fluorine on the partitioning of trace elements in carbonatite melts (CM) from the mantle to the crust. Elemental partitioning experiments were conducted at 3 GPa and 1100–1400 °C, both with and without fluorine. We determined trace element partition coefficients for the mineral-carbonatitic melt pairs involving the following minerals: clinopyroxene, olivine, spinel, perovskite, magnetite, calcite solid solution, magnesio wüstite. The addition of fluorine influences the types and stability of Ti-rich oxides. Fluorine-bearing systems crystallize magnetite, while fluorine-free systems crystallize perovskite. Compared to fluorine-free compositions, systems with 1.55–2.40 wt% fluorine in the melt exhibited significantly lower (clinopyroxene, spinel, olivine)-melt partition coefficients for REEs and HFSEs by half to one order of magnitude. The decreased uptake of these elements by clinopyroxene, spinel, and olivine may be attributed to changes in their speciation within the melt phase, consistent with the formation of REE-F complexes. Using our partition coefficients, we simulated the differences in trace element characteristics between carbonatite melts derived from the mantle under fluorine-bearing and fluorine-free conditions. The fluorine-bearing carbonatitic melt extracted from mantle peridotite displayed significantly higher trace element compositions compared to fluorine-free carbonatitic melt, with trace element concentrations being 5–10 times higher. We simulated the trace element characteristics of carbonatitic melts released from subducted sediments and ocean crusts and found that these ocean crusts or sediments can release fluorine-rich carbonatite melts that are naturally enriched in REE due to their high fluorine and REE contents. Therefore, the subduction of sediments or the recycling of ocean crusts is highly favorable for the formation of carbonatite-hosted REE deposits. This can explain why the majority of carbonatite-hosted REE deposits are typically found in continental margins with subducted materials signals in source region. Furthermore, we modeled the impact of different mineral crystallization and fractionation in the shallow crust on the trace element compositions of carbonatitic melts. Late-stage magma crystallization and differentiation of silicate and carbonate minerals are favorable for the further enrichment of ore-forming materials (e.g., REEs). [ABSTRACT FROM AUTHOR]

The Cadomian basement of SW Iberian Massif appears in the so-called Ossa-Morena Complex, which contains several allochthonous terranes that are key for deciphering the evolution of the Gondwana margin during the Neoproterozoic. In this context, the Calzadilla Ophiolite represents the remnants of an oceanic Ediacaran lithosphere formed by a boninitic mafic crust that overlies a serpentinized ultramafic section, the latter being the biggest outcrop of Cadomian serpentinites in Europe. In this work, the petrological and geochemical nature of the mantle section is analysed, as well as the tectonothermal evolution of both, the mafic crust and the ultramafic section. The algebraic analysis of whole rock geochemistry of the serpentinites indicates that the protolith corresponds to harzburgite. The geochemical fingerprint of the serpentinites, as well as the primary spinel crystals composition, shows that peridotites underwent high degrees of partial melting (up to 16%) in a forearc setting. Thermodynamic modelling and average PT methods were applied to serpentinites and mafic dykes from the ultramafic section as well as to amphibolites from the mafic section, both of which experienced progradation up to 4–5 kbar and 525–575°C. According to the data, the protoliths of the Calzadilla Ophiolite were formed in a peri-Gondwanan arc system developed during the subduction of oceanic crust below Gondwana. The roll-back of the subducting slab would induce the opening of the forearc basin at c. 602 Ma, protolith age of amphibolites from crustal section, with an extensive partial melting of the mantle wedge and the formation of boninitic-affinity magmas that constitute the mafic section of the Calzadilla Ophiolite. Metasomatism and serpentinization of the mantle wedge would occur via melt- and fluid–rock interactions. A compression-dominated stage at c. 540 led to the emplacement of the Calzadilla Ophiolite onto the Cadomian magmatic arc, with the development of the amphibolite-facies metamorphic imprint. [ABSTRACT FROM AUTHOR]

The West Kunlun orogenic belt located in the northwestern margin of the Qinghai-Tibet Plateau is an important record of the formation and northward extension of the plateau, but the current research mainly focuses on the tectonic activities of the Cenozoic era, and there is still considerable controversy regarding the formation and evolutionary history of pre-Cenozoic orogenic belts. This study focuses on Cretaceous sandstone samples from the Kedong region in the piedmont belt of the West Kunlun orogenic belt. U-Pb geochronological analysis was performed on 200 detrital zircon grains from the core samples. Combined with stratigraphic data and previous research, the main provenance direction was investigated to constrain the tectonic evolutionary history of the orogenic belt's peripheral regions. The results show that the detrital zircons are aged from 290 to 208 Ma, 520-310 Ma, 810-580 Ma, 1,400-880 Ma and 2,548-1,730 Ma, reflecting the complexity of provenance in this area. Based on a comprehensive analysis of the characteristics of igneous rocks, zircon age composition and stratigraphic conditions in potential source areas, it is concluded that the primary source regions include the East Kunlun orogenic belt and the North and South Kunlun terranes, with a low likelihood of contributions from within the Tarim Basin. The evolution of the West Kunlun orogenic belt can generally be divided into two opening and two closing phases. The detrital zircon ages predominantly exhibit two peak values at 259 Ma and 459 Ma, respectively representing the ages of transition from oceanic crust subduction to continentcontinent collision for the Paleo-Tethys Ocean and the Proto-Tethys Ocean. Additionally, there is a temporal gap between the evolution of the Proto-Tethys Ocean and the Paleo-Tethys Ocean. The Triassic period marks a transitional phase in tectonic evolution, shifting into an intracontinental evolutionary stage. This study provides new geochronological evidence for the early developmental history of the West Kunlun orogenic belt. [ABSTRACT FROM AUTHOR]

The study of the composition of sedimentary formations raises the problem of identifying extraterrestrial matter, in particular, distinguishing cosmic spherules from technogenic and volcanogenic ones. Based on a study of a collection of 482 bulk spherules separated from ferromanganese crusts of the Pacific Ocean floor, it is proposed to use relief forms on spherule surfaces as an additional feature of their origin. The paper describes in detail such relief forms arising as cosmic particles pass through the upper layers of Earth's atmosphere, and isolation and separation of the Fe–Ni cores from the spherules. The presence of a round hemispherical cavity on the flattened side of the spherule, a depression with concentric circles, or a "button" structure, as the presence of a Fe–Ni core, is sufficient but not necessary evidence for the cosmic origin of a spherule. [ABSTRACT FROM AUTHOR]

Seafloor abyssal peridotites are products after partial melting and melt-rock interaction, providing constraints on upper mantle processes and heterogeneity. Despite extensive studies of ophiolitic peridotites and a burgeoning dataset for dredged abyssal peridotites, limited studies have been undertaken on abyssal peridotite drill core samples. This omission means a lack of comparison between modern ocean mantle lithosphere and that of ophiolites, where field context is possible in the latter, but not the former. Ocean Drilling Program (ODP) Leg 153 near the Kane fracture zone, and ODP Leg 209, near the Fifteen-Twenty fracture zone, both on the mid-Atlantic Ridge but ∼1000 km distant from one another, recovered serpentinized mantle peridotites. We report whole-rock major-, trace- and highly siderophile-element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundances and 187Os/188Os ratios of peridotites from three cores (maximum depth of 200.8 m) from the two Legs to explore mantle heterogeneity within the Atlantic Ocean basin. Peridotites from ODP Leg 153 are relatively fertile, with Al 2 O 3 contents ranging from 1.1 to 2.7 wt%. They are characterized by relatively radiogenic 187Os/188Os (0.1259 ± 0.0017; 2 S.D.) and uniform HSE abundances. The ODP Leg 209 peridotites are highly refractory, with Al 2 O 3 contents ranging from 0.1 to 0.8 wt%, and imply that they record an extensively depleted mantle. They have 187Os/188Os of 0.1207 ± 0.0023 (2 S.D.) and fractionated HSE abundances, indicative of depletion occurring > 1 billion years ago. Marked heterogeneity both in the extent and timing of depletion are therefore evident along a large segment of the mid-Atlantic ridge that produces zero-age basalts. Measurement of Os isotopes in spatially associated mid-ocean ridge basalts (MORB) is challenging due to their sub ng/g Os contents. Instead, Nd isotopes of MORB are used to show that they are unlikely to have formed directly from abyssal peridotite-like sources. Abyssal peridotites therefore represent long-lived refractory residues during mantle upwelling with the sources of MORB being more enriched. Comparison between drilled abyssal peridotites and ophiolitic mantle reveals larger compositional variations in the latter. The overall higher melting extent in ophiolite mantle is likely reflective of a more complex life cycle than the modern oceanic lithosphere. [ABSTRACT FROM AUTHOR]

We investigate the crustal structure of the Northeastern (NE) South China Sea (SCS) rifted margin to constrain its crustal thickness and basement nature with implications for the Mesozoic and Cenozoic evolution of the SCS. First‐order interfaces interpreted from seismic reflection data were integrated into a 3D gravity inversion scheme to determine Moho depth and crustal thickness variations. A joint inversion of seismic and gravity data allowed us to determine crustal density variations along 2D profiles. The distal margin of the NE SCS is divided into two distinct crustal domains: the Southern Rift System (SRS), and the Southern High (SH). The SRS shows an extremely thinned crust on top of which thick Cenozoic sequences are observed. It is separated from the oceanic crust (∼6–8 km thick) by the SH, a comparatively thicker crustal domain (∼10–15 km thick) with significant magmatic additions. The distal NE SCS margin formed during the Cenozoic rifting of the SCS. The SH likely corresponds to a polygenic piece of crust, recording polyphase magmatic activity since the Mesozoic, with potentially significant activity during Cenozoic post‐rift time. The NE SCS margin is conjugate to Palawan whose basement is considered to be part of the exotic Luconia microcontinent that collided with Eurasia during the Late Cretaceous. Basement similarities between Palawan and the SH are highlighted, suggesting that the latter might also be part of Luconia. Our results suggest that the docking/suture zone between Eurasia and Luconia might have acted as a preferred zone for the Cenozoic rift development. Key Points: The Northeastern South China Sea rifted margin shows a contrasted crustal structure constrained by seismic and gravity dataPart of the distal margin corresponds to a dense polygenic continental crust that underwent polyphase magmatic activityThe former Mesozoic suture zone between Eurasia and Luconia acted as a weakness zone for the Cenozoic rifting [ABSTRACT FROM AUTHOR]

The two Large Low Velocity Provinces (LLVPs) in the lowermost Earth mantle are thought to affect large‐scale heat and material transport, governing mantle evolution. LLVPs have been interpreted as thermochemical piles of recycled oceanic crust (ROC) and/or other dense rock types. However, the role of ROC intrinsic viscosity in pile formation and related effects on mantle evolution remain poorly understood. Using mantle convection models, we show that, while ROC intrinsic density controls pile formation, intrinsic viscosity determines whether piles are internally convecting or stratified. Only high‐viscosity, stratified piles can preserve material over several billions of years. Pile stratification is therefore required to reconcile geochemical evidence for the survival of ancient reservoirs. Compositionally layered piles are also consistent with geophysical observations that point to vertical gradients in LLVP properties. As mineral physics constraints point to low‐viscosity ROC, our results suggest that LLVPs may be partly formed by early basal‐magma‐ocean cumulates. Plain Language Summary: Earthquake‐produced vibrations travel long distances inside the Earth, but slow down when they cross two large blobs that lie thousands of kilometers below Africa and the Pacific Ocean. The nature of these anomalies is controversial, but it is thought that the crust, the outermost rocky peel that is continuously formed on the Earth's surface, may penetrate the planet's interior, sink and accumulate to form large piles. We employ a specialized code that is widely used to simulate movements of masses inside rocky planets over billions of years, including the process of crust formation and accumulation. We experiment with how dense and soft/strong (i.e., easy/hard to deform) this sunken crust is, relative to the surroundings. We investigate how these largely unknown properties affect pile formation and find that crustal strength has a marginal role compared to its density. However, only high strength makes piles layered and able to store ancient material, consistent with current observations. As recent laboratory experiments point to a soft crust, our results suggest that the piles observed today mainly contain "primitive" material that settled in the deep Earth during the very early stages of our planet's formation, instead of crust. Key Points: Intrinsic viscosity of deep‐sunken oceanic crust does not affect its segregation and accumulation into pilesHigh‐viscosity piles are stratified and able to store Archean‐age materialsLarge low velocity provinces may not be mainly formed of low‐viscosity oceanic crust [ABSTRACT FROM AUTHOR]

Subduction infancy corresponds to the first few million years of the start of subduction following heat transfer from the incipient mantle wedge towards the slab‐top, as witnessed by metamorphic soles which represent slivers of oceanic crust metamorphosed up to granulite facies conditions welded beneath obducted ophiolites. In this study, integrated petrological, geochemical, mineralogical, geochronological, and thermodynamic studies were carried out on samples from the Yushugou high‐temperature metamorphic ophiolitic complex (YHTM) in the South Tianshan Accretionary Complex (STAC), where a massive exposure of coherent granulite accompanied by a thick peridotite body is preserved. Bulk‐rock compositions and Sr–Nd–Hf isotopes demonstrate the petrogenesis of meta‐basalts with oceanic island basalt (OIB)‐like and mid‐ocean ridge basalt (MORB)‐like affinities, with little infiltration by subduction‐derived melts and/or fluids (e.g., no negative Nb–Ta anomalies). Thermodynamic modelling and U–Pb chronology reveal that the YHTM meta‐basalts experienced granulite facies metamorphism of ~840–940°C and ~0.92–1.02 GPa at c. 392 Ma and then possibly reheating and zircon alteration in the Carboniferous. In addition, detrital zircons in sedimentary host rocks of the YHTM show limited Precambrian records and offer maximum depositional ages of c. 410–400 Ma together with the oldest Palaeozoic cluster around c. 470–450 Ma. It is suggested that the YHTM granulites could be of Ordovician–Silurian protolith and such an age pattern significantly deviates from those of adjacent terranes (the Central Tianshan, STAC, and North Tarim Craton). Combined with the compilation of pressure–temperature–time estimates of the YHTM and ages of regional ophiolites, arc intermediate‐mafic rocks, A‐type granites, and deformation, a model of induced, temporarily northward, intra‐oceanic subduction initiation is proposed, which probably occurred along the previously existing weak zone close to a seamount or oceanic plateau in the earliest middle Devonian during the northward subduction of the South Tianshan Ocean (STO). Anomalously high geothermal gradients could be triggered by asthenosphere upwellings, further facilitating the formation of OIB‐type metamorphic soles. The YHTM, which represents the remnant of metamorphic soles and associated ophiolites, was finally emplaced to the north margin of the STAC during the relatively long‐term (c. 160 million years) accretion and continuous subduction of the STO before its closure. This finding also presents a new natural example of OIB‐type metamorphic soles as a snapshot of fossil intra‐oceanic subduction infancy during the complex evolutionary history of the STO. [ABSTRACT FROM AUTHOR]

Mapping ocean‐continent transitions (OCTs) separating equivocal continental and oceanic crusts is fundamental to investigate breakup processes and define the age and location of initial seafloor spreading. However, proposed limits of OCTs are rarely consistent, do not use uniform criteria, and result in conflicting interpretations as shown for the case of the northern South China Sea (SCS). We review original datasets including reflection and refraction seismic sections, drilling and potential field data with the aim to develop a 'drilling‐constrained integrated geological‐geophysical' approach to define the OCT along the northern SCS, understand the breakup process, and to compare the OCT in the SCS with those at Atlantic type rifted margins. The result shows a narrow, 5–15 km wide OCT. It separates a segmented margin that rifted a former arc in the west and a forearc in the east, both facing a Penrose oceanic crust that thins from the west towards the east. Seafloor spreading may have first nucleated at two centres during magnetic anomaly C11 in the NE and central subbasins, which then locally propagated both W and E to break through salients and produce full breakup at 29 Ma (anomaly C10r). Breakup at the SCS shows many differences to Atlantic type margins, in part due to inheritance but also due to rift/spreading‐related parameters such as strain/spreading rates. [ABSTRACT FROM AUTHOR]

How eclogite/pyroxenite‐derived melts evolve through the refractory lithosphere above a plume remains poorly understood. Here we conducted layered experiments of reaction between tholeiitic melts and harzburgite at 2–3 GPa, 1,400–1,500°C, with a run duration ranging from 2 to 24 hr. The resulting residual melts exhibit lower SiO2, TiO2, Al2O3, FeO, CaO, and total alkali contents, higher Ni, MgO, and Mg#, and almost constant CaO/Al2O3 compared to the initial tholeiitic melts. The compositions of the residual melts are influenced by factors such as the melt/harzburgite mass ratio, temperature, and run duration. Decreasing the melt/rock ratio or increasing temperature and run duration leads to a greater extent of assimilation. Under disequilibrated conditions (2 hr), the residual melts have higher SiO2, FeO, and MgO, and lower CaO, Al2O3, and total alkali contents compared to those under equilibrated conditions. The results suggest that interface reactions involving olivine dissolution and orthopyroxene precipitation, and chemical diffusion occur simultaneously during the interaction process. The compositions of the residual melts are largely controlled by interface reactions within 2 hr, followed by dominant chemical diffusion between the melts and refertilized harzburgite from 2 to 24 hr. Based on the experimental results, we propose a two‐stage model for the origin of Hawaiian shield stage parental magmas. Eclogite/pyroxenite‐derived tholeiitic melts first react with harzburgite, with varying melt/rock ratios, to produce residual melts in the deep lithosphere. These residual melts subsequently mix with plume peridotite‐derived melts at shallow depths, contributing to the geochemical diversity observed in Hawaiian shield stage lavas. Plain Language Summary: We conducted experiments to understand how melts derived from subducted oceanic crust interact with surrounding rocks during their journey through the Earth's lithosphere. By simulating melt‐rock reaction along wall‐rock boundary under high‐pressure and high‐temperature conditions, we found that the interaction mechanism involves olivine dissolution and orthopyroxene precipitation. The extent of interaction between the melts and rocks depends on factors such as the amount of melt present and the duration of the interaction. We also observed that certain chemical reactions took place at the interface between the melts and rocks, which affect the composition of the resulting melts. Our findings suggest that the formation of magmas with specific chemical compositions, similar to those observed in Hawaiian shield stage lavas, can be elucidated by the reaction between tholeiitic melts derived from eclogite/pyroxenite and harzburgite. The harzburgite was generated through prior high‐degree melting of peridotite influenced by the high temperatures in the plume setting. We propose a two‐stage model involving initial reactions in the deep lithosphere followed by mixing of the melts in shallower depths. This model provides insights into the processes that contribute to the diversity of magmas observed in Hawaiian volcanic islands. Key Points: Eclogite melts reacting with harzburgite produce high SiO2, MgO, and Ni tholeiitic meltsResidual melt composition is influenced by melt size and reaction time, involving interface reactions and diffusionEclogite melt interaction with harzburgite, followed by mixing with peridotite melts, accounts for Hawaiian shield stage lava generation [ABSTRACT FROM AUTHOR]

Upper Cretaceous–Miocene alkaline SiO2-undersaturated volcanic rocks in the southern Central European Volcanic Province (CEVP) comprise two distinct rock series: (i) Upper Cretaceous–Eocene (~73–47 Ma) olivine nephelinites, basanitic nephelinites, and nepheline basanites have moderate to high MgO (8–16 wt. %), CaO, Ni, Co, Cr, Nb, and Ba, coupled with low F and SiO2 concentrations. These rocks contain abundant clinopyroxene and variable amounts of olivine macrocrysts as well as nepheline, K-dominated F-poor mica, and hydroxyapatite. Evolved and less common apatite-rich (phonolitic) haüynites/noseanites and haüyne nephelinites (~68–62 Ma) represent differentiated counterparts within this older group, showing higher alkali, Al2O3, P2O5, Nb, Zn, REE, and SO3 concentrations at low MgO (4–6 wt. %), CaO, Ni, Co, and Cr contents. (ii) Oligocene–Miocene (~27–9 Ma) olivine melilitites and melilite-bearing olivine nephelinites are characterized by even higher MgO (10–22 wt. %), CaO, Ni, Co, Cr, Nb, Ba, and high F contents at lower SiO2 concentrations, as reflected by the presence of abundant olivine macrocrysts, melilite, perovskite, Cr-rich spinel, F- and Ba-rich mica, and fluorapatite in addition to clinopyroxene and nepheline. Distinct mineral assemblages, crystallization trends, and various xenocrysts indicate different melt sources, a varying extent of enrichment, retention, and loss of volatiles (including timing of H2O and CO2 saturation), and limited wall rock interaction for the two rock groups. Partly resorbed, Fo-depleted olivine cores in the younger rocks and green-core pyroxenes in the older ones suggest early magma mixing. The nephelinitic–basanitic magmas derived from up to 6% partial melting of amphibole-bearing garnet/spinel lherzolite at or just above the lithosphere–asthenosphere boundary. This source was metasomatized involving hydrous melts or fluids. On the other hand, the melilite-bearing rocks probably originated in the upper asthenosphere by less than 3.5% partial melting of amphibole ± phlogopite-bearing garnet wehrlite, previously generated by subduction-related metasomatism with high CaO/MgO and CO2/(CO2 + H2O) ratios. Infiltration and storage of the metasomatic agents occurred in the former lower lithosphere, following continuous recycling of oceanic crust, comprising the release of Ca, CO2, H2O, further volatiles, and incompatible elements. Both volcanic episodes coincide with topographic uplift, erosion, rifting, and reactivation of lithosphere-scale faults, probably related to phases of strong mechanical coupling between Alpine orogen and European foreland. The first period overlapped with an era of prolonged N-directed intraplate compressional stress due to the Adriatic-Eurasian collision, provoking large-scale deformation, isostatic compensation, erosion, and consequent lithosphere thinning in the future CEVP. The second period is associated with the Oligocene–Miocene main stage of the European Cenozoic Rift System. Onset of volcanism was accompanied by a change in deformation in the Upper Rhine Graben from (W)NW extension to (E)NE extension and transtension by a complex interplay of evasive movements responding to shortening in Alps and Jura. Magma compositions, barely magmatic graben structures, volcanic activity outside rifts, and extensive exhumation suggest that in response to rifting, passive asthenospheric doming also contributed to magmatism by causing strong lithosphere–asthenosphere interaction and providing heat. [ABSTRACT FROM AUTHOR]

The subducting Pacific slab stagnates in the mantle transition zone and creates a big mantle wedge (BMW) system in East Asia. A similar BMW structure may have already existed since the Early Cretaceous (>120 Ma), but how such a structure evolved from Early Cretaceous to the present day remains unclear. We address this issue by comparing compositions and source heterogeneity of the 106–58 Ma basalts from Liaodong Peninsula and its adjacent areas (LPAA) in eastern China, with those formed in the modern BMW setting. The LPAA basalts display oceanic island basalts–like trace element patterns. Elemental and isotopic compositions of these basalts and their olivine phenocrysts point to peridotite and two recycled components in their source. One recycled component is altered lower oceanic crust given the low δ18Oolivine (2.8–5.2‰) of the ~99 Ma Liaoyuan alkali basalts. The second component consists of altered upper oceanic crust and pelagic sediments indicated by high δ18Oolivine (>6.0‰), represented by the ~58 Ma Luanshishanzi alkali basalts. The depleted mantle-like isotopes of these two components suggest derivation from a young HIMU source with characteristics of the Izanagi plate (e.g. Indian Ocean-type Sr-Nd-Pb-Hf isotopes), which may have resided in the mantle transition zone at that time. Our results reveal strong similarities between chemical and source characteristics of the mantle sampled by the 106–58 Ma LPAA basalts and those derived from the modern BMW. This implies that the BMW structure has been present since the Early Cretaceous, probably having lasted more than 120 Myr, and modulating the chemical properties of the upper mantle and influencing a variety of geological processes. [ABSTRACT FROM AUTHOR]

The petrogenesis and geodynamic setting of the Mesozoic magmatic rocks in the Erguna Block, NE China remains controversial, especially the relationship between magmatism and the subduction history of the Mongol–Okhotsk oceanic plate. Here we present data for the Early Jurassic–Early Cretaceous adakite-like magmatic rocks from Chaoman Farm in the northeastern part of the Erguna Block. Zircon U-Pb dating reveals that the syenogranites crystallized at around 190–180 Ma, while the monzonites, quartz diorite porphyries, and quartz monzonite porphyries were emplaced at around 147–143 Ma. The syenogranites, monzonites, quartz diorite porphyries, and quartz monzonite porphyries are adakite-like rocks. The syenogranites and quartz monzonite porphyries were produced by the partial melting of a thickened ancient mafic lower continental crust and a thickened juvenile lower crust, respectively. Meanwhile, the monzonites and quartz diorite porphyries were formed as a result of partial melting of the oceanic crust. In conclusion, the occurrence of these Early Jurassic magmatic rocks was closely linked to the process of southward subduction of the Mongol–Okhotsk oceanic plate. On the contrary, the Late Jurassic to early Early Cretaceous magmatism (147–143 Ma) occurred in an extensional environment, and was probably triggered by upwelling of the asthenosphere. [ABSTRACT FROM AUTHOR]

A-type granites have been the subject of considerable interest due to their distinct anorogenic geological background. The A-type and arc-related granites are crucial in deciphering the evolution of the ocean closure and continental collision in the Tibet Plateau. The demise of the Bangong–Nujiang suture zone (BNSZ) and the Yarlung–Tsangpo suture zone was accompanied by the emplacement of volumes of syn-collisional and post-collisional granites. Controversy has persisted regarding the contribution of the collisional granites within the Lhasa Block to the growth of the Tibetan Plateau. This study provides key evidence about the evolution of the Lhasa Block and Bangong–Nujiang Ocean (BNO) by the newly documented 1200 km long, Early Cretaceous A-type acidic magmatic belt. The resolution was achieved through the utilization of petrology, whole-rock geochemistry, zircon U-Pb geochronology, and in situ zircon Hf isotope analysis of the Burshulaling Granites in the eastern segment and previous existing data in the central and western segment of the Lhasa Block. The Burshulaling Granites are characterized as peraluminous, high-K calc-alkaline series, indicating a post-collision setting with high temperature and low pressure. The zircon grains from two granite samples yield 206Pb/238U ages of 115–113 Ma. In situ zircon Hf analyses with 206Pb/238U ages give εHf(t) of −6.2–0.6, showing prominent characteristics of crust-mantle interaction. Granites from east to west exhibit whole-rock geochemical and geochronological similarities that fall within the well-constrained Early Cretaceous time frame (117–103 Ma) and track post-collisional A-type acidic magmatic belt along BNSZ. We argue that this magmatism resulted from slab break-off or orogenic root detachment, leading to melting and mixing of the lower crust. Meanwhile, this study indicates the existence of the Bangong–Nujiang Ocean southward subduction or a collapse following an Andean-type orogen. [ABSTRACT FROM AUTHOR]

The Dalaku'an mafic–ultramafic intrusion, located in the western segment of the East Kunlun, presents conducive conditions for the magmatic Cu-Ni sulfide deposits. According to the detailed petrographic observation, the amphiboles within distinct rock types were analyzed by EPMA analysis. The crystallization conditions, such as temperature, pressure, oxygen fugacity, and water content of the magma, were calculated to explore the genesis of the intrusion. The amphiboles were divided into three types: Amp-I, characterized by low silicon content but enrichment of aluminum, titanium, and alkali, predominantly comprising Tschermakitic hornblende and Magnesio-hornblende with mantle-derived traits; Amp-II, exhibiting elevated silicon content but diminished levels of aluminum, titanium, and alkali, primarily constituted of Magnesio-hornblende; whereas Amp-III manifests as Actinolitic hornblende, indicative of crustal origins. The calculated temperatures of amphiboles ranged between Amp-I (955–880) °C, Amp-II (852–774) °C, and Amp-III (761–760) °C; the pressures ranged between Amp-I (454–274) MPa, Amp-II (194–93) MPa, and Amp-III (101–84) MPa; the oxygen fugacities (△NNO) ranged between Amp-I (0.93–2.17), Amp-II (1.55–2.52), and Amp-III (1.89); and the water contents (H2Omelt) ranged from (6.69–8.67) to (5.90–7.32). The magma experienced multiple stages of crystallization and underwent complex magma evolution at different depths. The high oxygen fugacity and water content could be attributed to the subduction of the oceanic crust. The magma source of the Dalaku'an intrusion was metasomatized by fluids from subducting plates, thereby originating within a post-collision extension. [ABSTRACT FROM AUTHOR]

We present new insight into the tectonic evolution of the Carmen basin (CB) in the southern Gulf of California (GC) from high-resolution bathymetry and two-dimensional seismic reflection data. Our goal is to document the seafloor morphology and sub-surface acoustic characteristics to understand the structure and crustal lithology across the CB. We identify three sub-basins with distinct geometries and evolutionary histories, with basement structures displaying a strong affinity with highly reflective, sigmoidal-shaped layers and the emplacement of high-amplitude tabular material underlying sediments with varying stratigraphic thicknesses. From the extent of new oceanic crust accreted along the CB, we estimate the age of the basin using a seafloor spreading rate of 52 mm/year, which is the average velocity of the relative plate motion between the Baja California microplate and the North American plate, as documented by previous authors. The southern and central sub-basins of the CB are mainly abandoned, while the northern one is currently the locus of seafloor spreading. This is evidenced by the juxtaposition of oceanic crust younger than ~ 1.9 Ma against older oceanic crust correlating in age with the adjacent Guaymas and Farallon basins to the northeast and southwest, respectively. We propose that mantle upwelling beneath the CB is a northward continuation of the East Pacific Rise, resulting in a fast-evolving system with sharp variations in strain localization within the seafloor spreading centers of the CB. [ABSTRACT FROM AUTHOR]

• We study the chemistry of the core and ocean of Enceladus based on different core compositions. • We study the hydrothermal products from the ocean-core interaction in the context of the chemistry of the plume of Enceladus. • We evaluate the chemistry of the ocean based on its possible pH values and the saturation indices of mineral products. • We find that the actual composition of the core poses a somewhat wide range of possible compositional scenarios. Measurements made by the Cassini spacecraft instruments were able to reveal the composition of the geysers of the Saturn moon, Enceladus, among which salts (sodium chloride, sodium bicarbonate and/ or sodium carbonate) and traces of silica could be the result of hydrothermal processes from the interaction of an inner liquid ocean with the core of Enceladus. The chemistry of the ocean should be closely connected to the chemistry of the core. Even though. the actual composition of the core is unknown, Enceladus has been characterised as a moon with a silicate core and different authors have estimated the properties of the ocean. A core with a silicate composition alone, does not necessarily justify most of the observed species of the plume. Given the many uncertainties, in the current work, we study the possible chemistry of the core and the ocean in the context of a four-layered Enceladus (dry core, hydrated core, ocean and crust) with three different compositional scenarios for the core: primordial (represented by an ordinary chondrite), composite (represented by a carbonaceous chondrite with an igneous inclusion) and non primordial (epresented by a given peridotite). The scenarios comprise a set of minerals that interact with a primordial ocean (either pure or enriched water) at a given temperature and pressure, producing a series of secondary minerals and compounds, some of them, coincident with the chemical species observed in the geysers. Specifically, we make a chemical speciation for each proposed compositional scenario with the software PhreeqC, however our analysis is limited to the study of interactions that reach a given equilibrium. In particular, output values like the potential of hydrogen of the ocean or the saturation indices of mineral products may give us hints about the chemistry of the ocean and the core. We find that, based on the species observed in the plume, the actual composition of the core (and the ocean as well) poses a somewhat wide range of possible compositional scenarios and each of our proposed scenarios and their products justify, to some extent, the observations of the plume. [ABSTRACT FROM AUTHOR]

A summary of the Jurassic‐Cretaceous rift to breakup tectonostratigraphy of the onshore Sverdrup Basin is correlated to the offshore Amerasia Basin in order to reconstruct a tectonic setting for the High Arctic Large Igneous Province (HALIP). The rift climax from the Canadian rifted margin is correlated with hyper‐extension of the continent‐ocean‐transition zone. Hyper‐extension of the continental lithosphere can accommodate plate motions of Arctic Alaska‐Chukotka away from the Canadian Arctic Islands and Lomonosov Ridge between ∼155 Ma and 135–133 Ma. After lithospheric breakup at ∼135–133 Ma, correlation of the post‐rift stage to the seafloor spreading anomalies M10n to M4n that are associated with oceanic crustal domains can accommodate plate motions from 135–133 Ma to 128 Ma. The uncertainties associated with the earliest magmas of HALIP overlap with the uncertainties on the timing of the latest seafloor spreading. The first main pulse of HALIP in the Aptian at 124–120 Ma post‐dates seafloor spreading and so HALIP was emplaced in a tectonic setting that closely resembles the present state of the south and eastern Amerasia Basin. At the paleogeographic center of the HALIP, the Alpha Ridge complex is consistent with the magmatic character and history of similar Cretaceous oceanic plateau in terms of volume and duration. Plain Language Summary: Prior to recently reported geochronological data from the High Arctic Large Igneous Province (HALIP), the temporal relations were highly uncertain between the tectonic stages of the onshore rift basin (Sverdrup Basin), the HALIP magmatism, and the elusive spreading history of the oceanic portion of the Amerasia Basin (Canada Basin). In the past decade, each of these components has been illuminated by new data to an extent that they can now be correlated. In the summary presented here: (a) it is proposed that the rift climax and the hyper‐extension in the continent‐ocean‐transition zone were coeval and linked processes; (b) that the breakup unconformity identified from the onshore rift basins is consistent with the earliest generation of oceanic crust; and (c) after rifting and seafloor spreading, magmatism of HALIP was a result of a mantle plume that rose to shallow levels below the thin lithosphere of the northern Amerasia Basin. Key Points: Correlation of the geochronology of the High Arctic Large Igneous Province (HALIP) to rift basin tectonostratigraphy indicates that it was emplaced well after the start of the post‐rift stageNon‐correlation of the geochronology of the HALIP to oceanic magnetic anomalies in the Canada Basin indicates it post‐dates seafloor spreadingThese correlations support the oceanic plateau model for the HALIP, centered above the thin lithosphere of the northern Amerasia Basin [ABSTRACT FROM AUTHOR]

New whole‐rock major and trace element geochemistry from the Leka Ophiolite Complex in Norway is presented and compared to the geochemical evolution and proposed tectonomagmatic processes recorded in the Izu‐Bonin‐Mariana system. These data demonstrate that the Leka Ophiolite Complex formed as forearc lithosphere during subduction initiation. A new high‐precision zircon U‐Pb date on forearc basalt constrains the timing of subduction initiation in the "Leka sector" of the Iapetus Ocean to 491.36 ± 0.17 Ma. The tectonomagmatic record of the Leka Ophiolite Complex captures only the earliest stages of subduction initiation and is thereby distinct from some other Appalachian–Caledonian ophiolites of similar age. The diversity of Appalachian–Caledonian ophiolite records may represent differing preservation and exposure of a variable forearc lithosphere. Plain Language Summary: The Leka Ophiolite Complex (LOC) represents a preserved fragment of oceanic crust that formed during subduction in the Iapetus Ocean. Geochemical information recorded in the LOC rocks shows that it formed during the initial phase of subduction. The age of subduction initiation in the Iapetus Ocean is estimated at 491.36 million years ago based on isotopic dating of minerals within the LOC rocks. Other fragments of preserved oceanic crust with similar ages are found in the Appalachian–Caledonian mountains; however, their geochemical information suggests that they may have formed during different stages of the subduction zone development. We consider the variations in the oceanic crustal record to reflect selective preservation of different parts of the variable oceanic crust formed during the development of a subduction zone in the Iapetus Ocean. Key Points: The Leka Ophiolite Complex (LOC) preserves a record of geochemical variation from forearc basaltic to boninitic magmatism, reflecting formation during initiation and early evolution of a subduction zoneA 491.36 ± 0.17 Ma U–Pb zircon date for an LOC forearc basalt is considered to date subduction initiation in the "Leka sector" of the Iapetus OceanDifferences between the LOC pseudostratigraphy and the model Izu‐Bonin‐Mariana forearc may result from selective preservation of the spatially variable forearc lithosphere in addition to the specific history of formation, obduction, deformation, and uplift/erosion records [ABSTRACT FROM AUTHOR]

An animated 100,000‐year‐interval tectonic reconstruction of the Woodlark Basin in the southwest Pacific illustrates how, at intermediate initial spreading rates, orogenic continents break up (dyke model), spreading segments nucleate, transform faults initiate and ocean basins evolve. We refine the location/timing of initial seafloor spreading and Euler poles of rotation back to 6.2 Ma. In the easternmost basin, where spreading younger than 2.6 Ma is not co‐polar with that to the west, we recognize the formation of a Ghizo microplate and Ranongga Transform Fault at ∼2.6 Ma and a 3‐degree rotational opening of the Itina Trough from 2.6 to 1.0 Ma. Allowing for that motion, we show that the 5.2–2.6 Ma seafloor in the easternmost basin formed co‐polar with that to the west. We also identify a ridge jump reorientation at ∼1.0 Ma that formed the NE‐trending Simbo Spreading Segment, whose neovolcanic zone includes Simbo Island and a submarine edifice to its south. Proposed deterministic models of ridge propagation (due to topographic gradients, mantle flow away from hotspots and/or changing plate motion) are not consistent with those observed; mantle chemical heterogeneities and melting anomalies are a potential cause that remains to be tested. We reconstruct the northern conjugate of the oldest extant oceanic crust and estimate the initiation of its subduction at ∼2.6 Ma, concomitant with observed changes in plate motion and segmentation. Where subducted, the young oceanic lithosphere between the conjugate rifted margins appears to be resorbed into the mantle, leaving a slab window where the Pacific subducted slab remains attached. Key Points: An animated tectonic reconstruction of the Woodlark Basin illustrates continental breakup and ocean basin formation and evolutionMost deterministic models of ridge propagation are not consistent with observations; mantle heterogeneities and melting anomalies may beThe Ghizo microplate and Ranongga Transform Fault formed ∼2.6 Ma; the Itina Trough rift graben rotated open by 3‐degrees from 2.6 to 1.0 Ma [ABSTRACT FROM AUTHOR]