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[Display omitted] • High precision dating of near-seafloor deep-tow magnetic and IODP constraints on SW Sub-Basin. • Magnetic anomalies of the SW sub-basin are shown to be symmetric, with variable spreading rates. • Spreading rate and roughness of SW Sub-basin influenced by mantle temperature. Marine magnetic lineations play important role in interpreting the age and spreading processes of the oceanic crust. However, it is difficult to identify magnetic lineations from sea surface observations in a deep and narrow low-latitude slow-spreading inactive ocean basin for many reasons, such as the highly filtered low-amplitude magnetic anomalies, highly oblique magnetization, contamination from narrow stripes, etc., which may hamper accurate lineation discrimination and identification. The spreading history of the Southwestern Sub-basin of the South China Sea (SW-SCS), which is located in such a low-latitude tectonic setting, has been debated for a long time. Near-seafloor deep-tow magnetic measurements provide high-resolution reversal records, making accurate lineation discrimination feasible. Corrections, including diurnal variation correction, regional field correction, and de-skewing, are explored. The results, calibrated with drill sites from the International Ocean Discovery Program (IODP) Expedition 349, show that the spreading ages of the SW-SCS range from ∼ 21 to 15 Ma (from C6A to C5B) and the full spreading rate ranges from 26 to 46 mm/yr, with an average rate of 37 mm/yr. Spreading was initially symmetric but later became asymmetric, with a rate differential reaching 10%. Combined with two seismic profiles, it is found that the roughness of the oceanic basement to the south of the extinct ridge is mainly influenced by faulted blocks, whereas to the north it is mainly influenced by magmatism. The RMS seafloor roughness is estimated to be 211 m in the south and 191 m in the north respectively. This indicates that SW-SCS seafloor spreading tends to be a transition type between axial high and axial low at the intermediate-slow spreading rate. There is a large valley in the spreading center, but the roughness far away from the center is low. the RMS basement roughness is obviously lower than that of the typical slow spreading oceanic basin. we conjecture that the larger than normal syn-spreading magma may be the reason for the low roughness. A long history of being subducted might be the deep-seated reason for all these behaviors where, and the mantle is rich in water and carbon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eclogitization kinetics of oceanic crust layers controlled Precambrian subduction. • Discrete eclogitization induced flat subduction in Precambrian. • Flat subduction builds short-lived overthickened layered mantle. Flat (shallow) subduction is mainly proposed as an Archean-Paleoproterozoic process, contributing to the growth of continental lithosphere. However, numerical models of Precambrian subduction commonly show steep subduction. Here we investigate the effects of lithology-dependent eclogitization (minor for gabbroic lower crust, strong for basaltic upper crust) of oceanic crust during subduction. We performed 2D petrological-thermomechanical modeling of subduction at potential mantle temperatures up to 250 °C warmer than present, using a numerical approach that accounts for buoyancy effects from both mantle depletion and eclogitization. The modeling reveals that increases in mantle potential temperature and the related thickness of oceanic crust and depleted mantle may induce transition to the flat subduction regime at ΔT ≥ 150 °C but only when a delayed eclogitization of gabbroic compared to basaltic crust is taken into account. Otherwise, subduction operates in the steep slab regime. Flat Precambrian subduction models show episodic bimodal magmatism within arcs located > 400 km from the trench, caused by short-lived (1–4 Myr) subduction transients consisting of three consecutive stages: (1) twisting downward of the eclogitized slab portion, (2) subvertical descent and break-off of this twisted portion, (3) rising of the remnant non-eclogitised slab tip and continuation of flat subduction. Limited formation of TTG-series granitoids is caused by partial melting of the subducting basaltic layer but becomes less pronounced at ΔT = 250 °C. Flat subduction produces an overthickened, layered keel-like continental mantle root, with an intermediate layer of subducted oceanic crust. However, construction of long-lived mantle keels by this mechanism might be limited by peeling off of the gradually eclogitizing oceanic crust and the underlaying mantle when plate convergence ends. At elevated mantle temperatures flat subduction produces voluminous hydration of the mantle wedge, forming a subcrustal serpentinite mélange layer that becomes a potential source of fluids in the subsequent evolution of the overlying continental crust. [ABSTRACT FROM AUTHOR]

In this paper, we address two key features of the behaviour of Fe-rich amphibole at high temperatures: (1) the Fe2+ → Fe3+ + e − exchange within the crystal bulk, and (2) the consequent rise in electrical conductivity. Cycling heating-cooling experiments were done in situ up to 542 °C (815 K) at beamline B11 of the Diamond Synchrotron Laboratory (UK). X-ray absorption spectra at the Fe K-edge and electrical resistivity were measured simultaneously on a single crystal of riebeckite with a composition very close to the ideal formula A□BNa 2 C(Fe2+ 3 Fe3+ 2)TSi 8 O 22 W(OH) 2. The Fe3+/Fe tot ratio was monitored via analysis of the pre-edge feature in the XANES spectra. Our data show slight oscillations of the oxidation state of Fe with temperature cycling up to around 400 °C (673 K), followed by a substantial gradual increase in Fe2+ → Fe3+ oxidation that starts at ~450 °C (~723 K) and is completed at ~525 °C (~798 K). The conductivity (σ) measured along the crystallographic c-axis oscillates strongly with cycling temperature allowing us to conclude that it is intrinsically related to the electron hopping induced by thermal treatment. The activation-energy derived from the σ(T) trend is E a = 74.4 ± 0.6 kJ/mol (0.77 ± 0.01 eV), in agreement with small-polaron conduction. This study provides direct and robust support of the conduction mechanisms in Fe-amphibole previously inferred from indirect methods. Given that riebeckite is a significant component in the glaucophanitic amphiboles common in blueschists associated with subducted oceanic crust, our data provide a link between atomic-scale processes and Earth-scale anomalous conductivity observed via geophysical measurements. [Display omitted] [ABSTRACT FROM AUTHOR]

Drilling rigs for deep seabed shallow strata are commonly used to explore ocean cobalt-rich crust resources and other fields. This paper mainly presents the structure and mechanism of a mobile drilling rig for use in acquiring seafloor cores that are up to 1.5 m in length. The software Sim center Amesim is used to establish the mobile drilling rig’s hydraulic propulsion system model, which is the basis and a core part of the rig. Moreover, closed-loop and PID (proportion-integral-differential) control methods are separately used to control the hydraulic propulsion system for simulation analysis. Comparison of the simulation results shows that the PID control method is more convincing in verifying the design rationality of the hydraulic propulsion system. In the simulation of the PID-controlled hydraulic propulsion system, the co-simulation technology of Sim center Amesim and MATLAB/Simulink not only establishes the hydraulic and control models but also determines the relevant simulation parameters, thereby helping improve system simulation efficiency. In its verification deployment in the South China Sea, the mobile drilling rig has been operated many times at different depths, and some cores have been successfully obtained. It was also used during the 55th Voyage of China Oceanic Scientific Expedition, which was supported by the China Ocean Mineral Resources R&D Association. Several sites were explored, and a large number of cobalt-rich crust cores were obtained. Theory and sea trials are explained to support further research on the survey of abyssal resources. [ABSTRACT FROM AUTHOR]

The introduction of electric vehicles (EVs) into the automotive market has boosted the advancement of energy storage technology. Although lithium-ion batteries (LIBs) could provide a solution to the emerging EV market, it needs to overcome the issue of high material cost and limited resources. This leads the research direction to sodium-ion batteries (SIBs), the most potential alternative batteries with infinite sodium resource from the ocean and earth crust. In the current work, Prussian blue (PB) with a crystal structure of face-centered cubic is used as cathode material for rechargeable SIBs with PB size ranging from 0.5 μm to 1 μm. Low interstitial water and low vacancies PB (Na0.58Fe[Fe(CN)6]0.93γ0.07·1.67H2O) with high purity has been successfully synthesized at room temperature via a simple single iron source precipitation method. An excellent electrochemical performance has been shown with specific discharge capacity of 133 mAh g−1 and with 90% capacity retention over 200 cycles. [ABSTRACT FROM AUTHOR]

Homogenized melt inclusions in olivine were studied in Archean komatiites from the Barberton Greenstone Belt, Weltevreden Formation in South Africa (3.3 Ga), Abitibi Greenstone Belt in Canada (2.72 Ga), and the Belingwe Greenstone Belt in Zimbabwe (2.69 Ga). Contamination of the komatiite melts with crustal material enriched in Rb, Cl, and H2O during the crystallization of olivine is demonstrated. Uncontaminated melts have mantle Rb/Nb ratios but are significantly enriched in Cl and H2O relative to K and Ce, respectively, exhibiting similar incompatibility during crystallization and partial mantle melting. These observations suggest the presence of a chlorine- and water-enriched mantle source before 3.3 Ga. The excess Cl and H2O contents in the komatiites are assumed to result from the interaction of partially molten mantle plumes with the mantle transition zone. The most likely source of Cl and H2O enriching the deep mantle is the oceanic lithosphere that endured a seafloor alteration. We conclude that the recycling of the altered oceanic lithosphere into the mantle, probably via subduction, began in the first billion years of the Earth's history. Delamination of the Archean crust could not cause transport of chlorine and water into the deep mantle. [ABSTRACT FROM AUTHOR]

The Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau is considered as the main suture of the Paleozoic Paleo-Tethys that separates Gondwana-derived continental fragments from Eurasia-derived ones. Understanding the evolutionary history of this orogenic belt is of critical importance in the reconstruction of the tectonic history of Paleo-Tethys. The CMOB preserves well-exposed blueschist facies rocks, albeit their tectonometamorphic history and protolith signatures remain poorly constrained. Here we present, for the first time, results from a detailed investigation of lawsonite-bearing blueschist rocks, including epidote-magnesioriebeckite schist and garnet-ferroglaucophane schist from the CMOB and involving petrological, mineralogical, thermodynamic modeling, whole-rock geochemical, and geochronological studies. The epidote-magnesioriebeckite schist samples and garnet-ferroglaucophane schist samples display OIB- and E-MORB-like geochemical affinities, respectively, and have whole-rock ε Nd (t) values in the range of −5.4–+4.4, suggesting that their protoliths were mainly oceanic crust with limited degree of crustal assimilation. Magmatic zircon grains from the garnet-ferroglaucophane schist samples yield protolith ages of 253–250 Ma. Combined with previous data, our data represent the youngest ages of rock formation in the Paleo-Tethyan Ocean reported to date. The epidote-magnesioriebeckite schist samples show a peak assemblage of magnesioriebeckite + lawsonite + augite-aegirine + phengite + titanite + allanite, with peak P–T conditions of 12.4–16.8 kbar and 350–406 °C. In contrast, the garnet-ferroglaucophane schist samples preserve a peak assemblage of garnet + ferroglaucophane + omphacite + lawsonite + phengite + titanite/ilmenite/rutile ± allanite and yield peak P–T conditions of 19.5–22.6 kbar and 490–510 °C. The epidote-magnesioriebeckite schists and garnet-ferroglaucophane schists record a nearly complete clockwise P–T loop characterized by a steep prograde P–T path with a low thermal gradient of ~5–8 °C/km followed by cooling or overprinting by isothermal decompression. Reconstruction of the metamorphic P–T evolution, together an evaluation of previous age data, allows us to propose rapid subduction of cold oceanic lithosphere to depths of 50–75 km at a rate of ~6.3–9.3 km/Myr during Early-Middle Triassic (248–240 Ma), followed by exhumation in the Late Triassic (231–214 Ma). The short time lag (<10 Ma) between the protolith generation and the high-pressure metamorphic peak further supports a rapid subduction process. Our results suggest that the young oceanic slab was dragged down by the thicker, long-lived, and cold downgoing Paleo-Tethyan Ocean plate, where it experienced blueschist-facies metamorphism. The co-occurrence of lawsonite-bearing epidote-magnesioriebeckite schists and garnet-ferroglaucophane schists and eclogites further points to a cold thermal structure at the convergent plate interface, leading to the interpretation that the CMOB represents a typical oceanic subduction-accretion belt. The results presented in this study provide important insights into the geodynamic evolution of the Paleo-Tethys. Unlabelled Image • Discovery of lawsonite-bearing blueschists with metamorphic P–T conditions of up to 510 °C, and 22.6 kbar • Protoliths derived from oceanic crust with some degree of crustal contamination • Magmatic zircon U-Pb ages of 253–250 Ma represent the youngest ages in the Paleo-Tethyan Ocean. • Metamorphism during cold and rapid slab subduction to depths of 58–75 km at a rate of ~6.3–9.3 km/Myr [ABSTRACT FROM AUTHOR]

We present results of a study of the morphology, internal structure, and chemical composition of oceanic zircon, which show that zircon is a sensitive indicator of tectonic and physicochemical processes occurring in the lower oceanic crust. Crystallization of magmatic zircon in gabbroids is not an instantaneous process; it proceeds in the course of differentiation of parental melts in the tectonically active mid-ocean ridge (MOR) setting. The main geochemical indicator of crystallization differentiation during magma cooling is an increase in Hf content toward the zircon grain edge. Zoning is also observed in magmatic zircons from oceanic plagiogranites (OPG), but it is weaker, apparently because of the narrower temperature range of zircon crystallization in these rocks. The OPG zircons are depleted in REE as compared with the least altered magmatic zircons of gabbro, which is probably due to the formation of OPG during the partial melting of gabbro with the participation of concentrated water-salt fluid, a derivate of seawater, and due to the co-crystallization of zircon and apatite. High-temperature hydrothermal processes within slow-spreading MORs lead to a partial or complete recrystallization of zircon as a result of dissolution/redeposition. A significantly reduced cerium anomaly and the presence of microinclusions of xenotime, uranium and thorium oxides or silicates, and, sometimes, baddeleyite in zircon alteration zones indicate a reducing type and high alkalinity of the hydrothermal fluid. The fluid, a derivate of seawater, acquires these features during circulation near the axial zone of ridges as a result of phase separation in the system H2O-NaCl and interaction of the fluid with abyssal peridotites of oceanic core complexes. The estimated solubility of zircon in basic melts indicates that even near-solidus crystallization of zircon is highly unlikely in anhydrous basaltic melts but is possible in differentiates of deep-seated hydrous basic magmas. The Ti-in-Zrn geothermometer must be used with caution, because variations in the Ti content in zircon might be controlled not only by temperature but also by other factors, especially when mineral inclusions in zircon testify to a drastic change in its growth (dissolution) conditions. A geothermometer based on the distribution of Zr and Hf between zircon and the host rock has several advantages over indicators of the crystallization temperature of magmatic zircon that are based on the zircon saturation index and the content of Ti in zircon. It does not depend on the composition of melt and on the correct estimates of the SiO2 and TiO2 activity. In addition, reconstruction of the Zr and Hf fractionation trends during crystallization of zircon from granitoid melts makes it possible to evaluate the temperature of separation of more differentiated melt fractions. [ABSTRACT FROM AUTHOR]

The Labrador Sea is part of the Atlantic rift system which opens during Early Cretaceous times in the intracontinental domain. The rifting stage continues and generates an expansion center, with the establishments of an oceanic ridge during Late Cretaceous-Paleocene times. The rifting was asymmetric with a gradual propagation northward. The Cretaceous stretching and thinning of the continental crust led to the development of the transitional domain, with a controversial origin either thinned continental or oceanic. With this study, we bring new evidences for the presence of exhumed upper mantle in the transition domain based on geometry of the detachment faults, typical “S” shape, and we emphasize the role of the detachments in the rifting of continental crust and its ultimate break-up. We observed the lateral change, from South to North, of the continental to oceanic crust transition, from a step-up to a step-down. Based on, we suggest that it might reflect the changes in the upper versus lower plate position of the Labrador Sea, a change accommodated across the Snorri Fracture Zone. [ABSTRACT FROM AUTHOR]

The research sheds light on the age, origin, and tectonic environment of two significant alkaline plutons, Sullya and Angadimogar, located in the Mercara Shear Zone in the Southern Granulite Terrain of southern India. The zircon U-Pb dating indicates that the plutons crystallized at 829 ± 3.7 Ma and 831 ± 4.7 Ma, respectively. The zircon geochemistry suggests that Sullya and Angadimogar plutons underwent distinct crystallization processes, with zircons from Angadimogar samples crystallizing at varying temperatures over a prolonged period with limited f O 2 levels and zircons from Sullya samples crystallizing at stable temperatures and variable redox conditions. Most of the zircons from both plutons have trace element characteristics indicating formation in the continental crust. In contrast, some zircons from Sullya have trace elements similar to those found in the oceanic crust. The presence of two distinct types of zircons in Sullya samples indicates that the parental melt of the Sullya pluton consisted of magma from multiple sources. The average estimated temperature for zircon crystallization in Sullya was 691 °C, while the mean temperature in Angadimogar was 802 °C. The research implies that the plutons were emplaced parallel to the shear plane during an extensional regime, reactivating the paleo shears during the late Proterozoic era. The study highlights the importance of using multiple geochemical and geochronological techniques to gain a better understanding of the complex geological evolution of the Precambrian terrains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Geothermal gradients show power-law trends for tectonic variables in oceanic and continental settings. • Crustal age may best predict geothermal gradients in oceans, and lithosphere thickness in continents. • Tectonic basin types characterized by unique ranges of geothermal gradients. • The approach guides geothermal energy exploration in frontier environments. The heat budget of sedimentary basins is determined by heat transfer across the lithosphere-asthenosphere boundary and lithospheric heat sources, such that the tectonic evolution of their host continental and oceanic lithosphere ultimately impact the present-day heat flow and average geothermal gradients. Recent increase in availability of publicly-accessible geothermal gradient measurements across the world provides an opportunity to globally assess the dominant controls on the thermal regime of sedimentary basins. Thus, we compile a global dataset of ∼ 152,000 unique data points with constrained bottomhole temperature measurements and assess the relationships between geothermal gradient and selected independent tectonic variables, including crustal and lithospheric thicknesses, crustal age, sediment thickness, and basin type. The results show that in both oceanic and continental settings, geothermal gradients exhibit a non-linear, systematic variation with the tectonic variables. We find that oceanic geothermal gradients decrease with increasing crustal age and lithospheric thickness. Geothermal gradients in the continents show no clear relationships with thermotectonic crustal age, but decrease with increasing crustal and lithospheric thicknesses. Gradients drop significantly at 1.5 km sediment-cover thickness, likely reflecting the effect of high sedimentation rates, but show a striking rise at > 12 km thicknesses, potentially influenced by thinned lithosphere and thermal blanketing effects. The commonly-assumed 'normal' gradient of 25 °C/km for continents is only valid for a narrow range (1.5–12.5 km) of sedimentary cover-thickness, and oceanic 'normal' gradient may be as high as 50–75 °C/km for > 20 Ma crustal age and > 50 km-thick lithosphere. We show that, conditionally, crustal age may best predict average geothermal gradients in oceanic settings, and lithosphere thickness in continents. Further, we observe that tectonic basin types exhibit distinct ranges of gradients that reflect their prevalent tectonic and geodynamic origins. Despite the complexities of determining shallow-crustal thermal conductivities, the results provide insights that fingerprint distinct tectonic settings based on the broad distribution of their geothermal gradients. [ABSTRACT FROM AUTHOR]

For nearly three decades, various phases of the scien tific Ocean Drilling Programs have deployed sealed-hole observa to riesin deep-ocean boreholes for long term subseafloor monitoring to address a range of hydrologic and geodynamic objectives. We summarize the scientific motivation for these observatories and review some important early results from those installed in young oceanic crust and subduction zones. We also summarize the evolution of the borehole observatory designs and associated instrumentation, from simple single-interval installations with autonomous low-rate temperature and pressure monitoring to recent multiple-zone installations with sophisticated downhole instrument packages connected to seafloor cabled networks that provide power and high-rate, real-time data access. We emphasize recent advances, illustrated with example data drawnmainly from transects of borehole observatories offshore Japan and Cascadia. These examples illustrate the value of borehole observatory data in resolving a wide range of crustal geodynamic responses from long periods of gradual geodetic change and a ccumulation of stress to episodes of rapid deformation associated with both seafloor spreading and subduction processes. [ABSTRACT FROM AUTHOR]

Cooling of the Earth's mantle since the Meso-Archean is predicted by thermal and petrological models to have induced a secular change in the composition of primary mantle-derived magmas – and thus bulk oceanic crust; in particular, suggesting a decrease in maficity over time. This hypothesis underpins several recent studies that have addressed key geological questions concerning evolving plate tectonic styles, the rates and timing of continental crust formation, comparative planetology, and the emergence of complex life on Earth. Major, minor, and trace element geochemical analyses of (meta)mafic rocks preserved in the geological record allows exploration of this theory, although no consensus currently exists about the magnitude of this change and what compositions – if anything – constitute representative examples of Paleo-, Meso-, or Neo-Archean primitive oceanic crust. In this work, we review the current state of understanding of this issue, and use phase equilibria to examine the different mineral assemblages and rock types that would form during metamorphism of basalt of varying maficity in subduction zone environments. The presence (or absence) of such metamorphic products in the geological record is often used as evidence for (or against) the operation of modern-day subduction-driven plate tectonics on Earth at particular time periods; however, the control that secular changes in composition have on the stability of mineral assemblages diagnostic of subduction-zone metamorphism weakens such uniformitarianistic approaches. Geodynamic interpretations of the Archean metamorphic rock record must therefore employ a different set of petrological criteria for determining tectonothermal histories than those applied to Proterozoic or Phanerozoic equivalents. [ABSTRACT FROM AUTHOR]

A major part of the biologic activity on Earth is hidden underneath our feet in an environment coined the deep biosphere which stretches several kilometers down into the bedrock. The knowledge about life in this vast energy-poor deep system is, however, extremely scarce, particularly for micro-eukaryotes such as fungi, as most studies have focused on prokaryotes. Recent findings suggest that anaerobic fungi indeed thrive at great depth in fractures and cavities of igneous rocks in both the oceanic and the continental crust. Here we discuss the potential importance of fungi in the deep biosphere, in particular their involvement in fundamental biogeochemical processes such as symbiotic relationships with prokaryotes that may have significant importance for the overall energy cycling within this vast subsurface realm. Due to severe oligotrophy, the prokaryotic metabolism at great depth in the crust is very slow and dominantly autotrophic and thus dependent on e.g. hydrogen gas, but the abiotic production of this gas is thought to be insufficient to fuel the deep autotrophic biosphere. Anaerobic fungi are heterotrophs that produce hydrogen gas in their metabolism and have therefore been put forward as a hypothetical provider of this substrate to the prokaryotes. Recent in situ findings of fungi and isotopic signatures within co-genetic sulfide minerals formed from bacterial sulfate reduction in the deep continental biosphere indeed seem to confirm the fungi-prokaryote hypothesis. This suggests that fungi play a fundamental biogeochemical role in the deep biosphere. [ABSTRACT FROM AUTHOR]

Although lawsonite eclogite is predicted to be common at depth of ~ 45–300 km in subduction zones, it is rarely exposed at Earth's surface. In this study, we identified a lawsonite (pseudomorph)-bearing eclogite in Yuka terrane, North Qaidam UHPM belt. It is mainly composed of garnet, amphibole, clinozoisite, quartz and rutile with minor omphacite relics and talc. Petrographic investigation identified abundant rectangular- or rhombic- shaped mineral aggregates composed of polycrystalline clinozoisite or polyphase clinozoisite + paragonite ± phengite ± quartz and clinozoisite + amphibole ± quartz ± Na-rich plagioclase occurring in garnet porphyroblasts. The peculiar shape, mineral assemblages and reconstructed compositions of these aggregates show that they are pseudomorphs after lawsonite. Phase equilibrium modeling predicts that the lawsonite (pseudomorph)-bearing eclogite experienced a clockwise P–T evolution with a peak stage at 570 °C, 27 kbar, near the quartz–coesite transition boundary. Geochemical data show that the lawsonite (pseudomorph)-bearing eclogite has a MORB-like affinity with flat Chondrite–normalized rare earth element (REE) distribution patterns. Zircons from this sample have similar δ 18 O values (5.38 ± 0.10‰) with the normal mantle (5.3 ± 0.3‰), indicating that the protolith of the lawsonite (pseudomorph)-bearing eclogite is derived directly from mantle rock without continental crust contamination. The MORB-like character and zircon O isotopic composition of the lawsonite (pseudomorph)-bearing eclogite indicate that its protolith is likely to be an oceanic crustal slice. SIMS and LA–ICP–MS zircon U–Pb dating yielded a 436–438 Ma eclogite-facies metamorphic age for the lawsonite (pseudomorph)-bearing eclogite, similar to the continental subduction age of the North Qaidam UHPM belt, but did not obtain its protolith age. These data indicate that the protolith of the lawsonite (pseudomorph)-bearing eclogite may be either a piece of Proterozoic ocean that was emplaced in the active continental margin of the Qaidam block during the amalgamation of the Rodinia supercontinent, or the early Paleozoic oceanic crust in the transition zone between the Qilian Ocean and the Qaidam block. [ABSTRACT FROM AUTHOR]

• Extreme rainfall driven rainwater DOC evolution was investigated in megacity. • Content, deposition flux and impacting factors of rainwater DOC were assessed. • DOC was mainly form the emission of municipal waste, agriculture and traffic. • The high level of DOC deposition flux was found due to the extreme rainfall. Air pollution and related wet deposition process (rainfall) caused environmental hazards under the climate change, particularly in urban regions, attracting global concern and challenges. Atmospheric dissolved organic carbon (DOC) deposition is not only the major removal pathway of OC from atmosphere, but also a significant influence factor of urban haze pollution and local climate. Although the significance of DOC deposition to carbon budgets is confirmed, the extreme rainfall influenced OC transfers from the atmosphere to land is poorly understood. This study systematically investigated the rainwater DOC in Beijing during the extreme rainfall period of 2021 to explore its status, source, and flux. The results showed that the rainwater DOC concentration level is close to the Asian and global mean level, while the DOC deposition flux was relatively high due to high rainfall amount and rainfall scouring, and the overall declined trend of DOC concentrations was identified. Source identification revealed that human OC emissions (municipal wastes, agricultural and traffic emission) are the primary sources of DOC, whereas ocean and crust source contributed negligibly. This research clarified the extreme rainfall-driven rainwater DOC dynamics in a megacity and supported the evaluation of global carbon budgets. [ABSTRACT FROM AUTHOR]

The laterite profiles investigated in the present study developed after the emplacement of a slab of oceanic crust and upper mantle sequence (the Semail ophiolite) onto the East Arabian margin during the late Cretaceous. The laterites formed as a result of prolonged weathering of the ophiolite assemblage under tropical to subtropical conditions. Nine laterite profiles have been examined for their Ni potential along a NW-SE segment of the Oman Mountains. The preserved laterite profile shows variations in thickness, mineralogy, and chemical composition. The profiles show a vertical succession from bedrock protolith through saprolite, oxide laterite, to clay laterite. The laterite profiles are unconformably capped either by clastics rocks of the Late Cretaceous Qahlah Formation or by Palaeogene carbonates of the Jafnayn or Abat Formations. The protolith corresponds either to a fine-grained, blackish to greenish serpentinized peridotite or to a coarse-grained dark green altered layered gabbro. The bulk geochemistry of the studied profiles indicates a typical low Ni-laterite pattern in which magnesium (Mg) and silica (Si) become depleted towards the top of the profile, whereas iron (Fe) and aluminum (Al) increase. A significant enrichment in Ni and Co occurred as a result of the laterization process. Ni concentrations average 0.63% (Ibra), 0.72% (East Ibra), 0.67% (Al-Russayl), and 0.33% (Tiwi). Other elements such as Cr, V, Pb, TiO 2 , Zr, Ba, and Zn were also remobilized across the profiles during the laterization processes. [ABSTRACT FROM AUTHOR]

We present a comprehensive description of the blastomylonites of the Ikat thrust localized within the Ikat terrane in the East Transbaikalian branch of the Central Asian Orogenic Belt. The metamorphic rocks of the Garga block are thrust over the almost unmetamorphosed Cambrian deposits of the Ikat Formation. The geologic position of the thrust and the structure and mineral and petrochemical compositions of the blastomylonites in the suture zone are considered, and U-Pb dating of detrital zircon is carried out. The blastomylonites develop after the gneisses of the Garga block; the block protolith, admixed with felsic volcanic material, was no older than the Neoproterozoic (750–800 Ma). The 40 Ar/ 39 Ar age of the thrust is estimated at 282 ± 0.4 Ma based on metamorphic biotite from the blastomylonites. The thrust marks the transpression period during the Late Paleozoic processes of tectonometamorphic activity related to the subduction of the Mongol-Okhotsk oceanic crust beneath the Siberian continent. [ABSTRACT FROM AUTHOR]

Post-collisional potassium-rich rocks are a critical petrogenetic and geodynamic marker across the European Variscan Belt. We present a detailed characterization of the only potassium-rich mafic intrusions identified so far in the Ossa-Morena Zone (Iberian Massif). Using new major, trace and Sm Nd isotopic whole-rock analyses, as well as mineral chemistry analyses, we discussed the petrogenesis of the early Carboniferous potassium-rich Veiros and Vale de Maceira (Portugal) stocks in the geotectonic framework of the southern Iberia, marked by the collision of the Ossa-Morena Zone, a Gondwanan terrane, with the South Portuguese Zone, a Laurussian terrane. The Veiros and Vale de Maceira shoshonites (s.l.) range from gabbros to syenites, with a predominance of monzonites and monzogabbros, characterized by different proportions of olivine, clinopyroxene, orthopyroxene, plagioclase, alkali feldspar, phlogopite and brown hornblende. The Veiros stock is mainly composed of fine-grained ultrapotassic rocks, and the Vale de Maceira stock is composed chiefly of medium-grained shoshonite rocks. A small group of hornblende-bearing medium-grained calk-alkaline rocks was also identified. The stocks have high contents of K 2 O, MgO, total alkalis, Th and other LILE, high ratios of LREE/HREE and LREE /HFSE, and show a Nb-Ta-Ti negative anomaly, typical of orogenic settings. Sr and Nd isotopes yielded moderate radiogenic Sr and unradiogenic Nd, that might suggest the involvement of a crustal component. However, the combined use of isotopic and elemental compositions rules out significant contamination by crustal materials upon ascent and emplacement. Instead, a source metasomatised by subduction-related fluids and hydrous melts from the slab is proposed. This diversely metasomatised source was a phlogopite-amphibole-bearing and (phlogopite-free) amphibole-bearing lherzolite at the upper part of the garnet stability field in the sub-continental lithospheric mantle. The Devonian mafic volcanic rocks point to a northward dipping (present coordinates) subduction of the Rheic oceanic plate underneath the Ossa-Morena Zone during the Variscan Orogeny. However, the Veiros and Vale de Maceira magmas originated during the post-collisional stage from the partial melting of the supra-subduction metasomatized lithosphere. The melting occurred during a period of enhanced heat due to asthenospheric upwelling related to the slab break-off of the Rheic's slab. The stocks are concomitant with the profusion of granitoid intrusions, which is compatible with a post-collisional tectonic setting. They are also coeval with the opening of the Beja-Acebuches back-arc, likely related to slab roll-back of a segment of the Rheic oceanic crust, implying polyphasic subduction and a complex geodynamic setting for the late stages of oceanic closure in southern Iberia. [ABSTRACT FROM AUTHOR]

The Southeast Anatolian Orogenic Belt (SAOB), the most extensive segment of the Alpine-Himalayan Orogenic Belt, resulted from the northward subduction of the southern branch of the Neotethys oceanic crust beneath the Anatolian micro-plate. We present new whole-rock geochemistry, zircon U–Pb ages, and Lu–Hf isotope data from the stocks and dykes with a length of up to tens of meters belonging to the Keban magmatic rocks, eastern Turkey. These rocks are represented by syenite and quartz monzonite intruded into the Keban metamorphic complex. The geochemistry data indicates that the samples bear mostly metaluminous, variably high alkalines (K 2 O + Na 2 O), Ga/Al ratios and zircon saturation temperature, and typically the A-type granite characters. According to the Y/Nb vs Yb/Ta diagram, the Keban magmatic rocks show A 1 -type geochemical signatures modified by crustal melts. Syenite and quartz monzonite samples from Keban magmatic rocks give zircon U–Pb ages of 77.4 ± 0.34 Ma, 76.3 ± 0.3 Ma and 76.36 ± 0.34 Ma, respectively. On the primitive mantle-normalised trace element patterns, the Keban magmatic rocks show enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs). They are coupled with slightly negative Nb–Ta anomalies. Chondrite-normalised rare earth-element patterns show strong enrichment in LREEs relative to HREEs, a typical A-type granites feature. The zircons have negative εHf (t) values that vary from −2.68 to −0.41, and Hf model ages (T DM2) range from 1171.54 to 1329.26 Ma, indicating the enriched lithospheric mantle sources and crustal contribution. The sources and evolution of the alkaline magmas might be related to the post-collisional tectonic setting. • We present the presence of A 1 -type intrusions, eastern Turkey. • U–Pb LA–ICP–MS zircons yielded ages between 76.3 and 77.4 Ma. • Negative Lu–Hf isotopes indicate an enriched mantle source. • Intrusions could be related to the post-collisional tectonic setting. [ABSTRACT FROM AUTHOR]

A data analysis of 171 broadband vertical-component records of 62 shallow crustal distant events in the northern Indian Ocean region was undertaken to investigate the far-source geometric attenuation rate, high-frequency cutoff filter parameter (kappa), and apparent source characteristics. Event magnitude varied from 4.0 to 5.9 in the short-period body-wave magnitude (mb) scale, and hypocentral distance ranged between 2.3° (260 km) and 14.1° (1578 km) for the dataset. The far-source geometric attenuation rate was estimated by fitting data to a predefined attenuation equation at a frequency range of 0.5-8.5 Hz, using the multiple linear regression method. A secondary regression in the frequency domain on constants resulting from the main (first) regression was performed to find kappa and the second hinge point of the trilinear geometric attenuation function. Source characteristics (stress drop, comer frequency, and moment magnitude) of selected events were determined using the Brune (1970, 1971) model. The average far-source geometric attenuation rate was determined to be R-05 (R is hypocentral distance) for the selected frequency range, but at low frequencies (below about 2 Hz) slightly lower rates than the average were observed. Kappa was found to be 0.041 ± 0.009 s. The second hinge point of the geometric attenuation function was estimated to be 120 ± 30 km, and the complete form of the function, after considering compliancy G=1/551.3√120/R, R>120 km with actual records, was collated as Average static stress drops were found to be 9.5 and 16.0 MPa for the mb 4-5 and 5-6 magnitude bands, respectively. Corner frequencies approximately fell within 1.0-7.0 Hz for the dataset. Derived attenuation parameters were also validated using a ground-motion comparison between recorded and stochastically simulated events. [ABSTRACT FROM AUTHOR]

Marine ferromanganese nodules and crusts containing Mn, Cu, Ni and Co in the most promising resource-grade concentrations and quantities, together with Fe and Zn (all elements of biogeochemical importance) are found far from land on the deep seafloor of the Pacific Ocean. The biogeochemical, chemical and physical mechanisms contributing to their formation, distribution, abundance and – for these six elements – variability in their concentrations in these deposits, are the main focus of the present review. The mechanisms addressed include biological productivity, sedimentation types and rates, bottom water characteristics, the Calcium Carbonate Compensation Depth, the depth and intensity of the oxygen minimum zone, and biogeochemical characteristics of the six focal elements. Particular attention is given to comparisons between the deposits found in the north and the south Pacific, in order to present an overarching view of our current understanding of the mechanisms that apply to both nodules and crusts in both oceanic hemispheres, including examination of the possible existence of a marine ferromanganese oxide continuum. The renewed interest in the commercial exploitation of these deposits has stimulated a welcome increase in scientific research that is essential to informing the public discourse on seabed mining. We briefly reflect on the work addressed in this review in that context. [ABSTRACT FROM AUTHOR]

We sought to map the depth and density contrast of the Mohorovicic discontinuity (Moho) across the Red Sea area and to model sedimentary thickness from gravity data. The gravity data that are used are a combination of satellite and terrestrial gravity data processed into a Bouguer anomaly grid. A 200-km low-pass filter was used to separate this grid into regional and residual gravity grids. We inverted the regional gravity grid to a Moho depth map based on a density contrast map that is constrained by published seismic results. The interpreted Moho is shallowest (<10 km) along the axis of the central Red Sea, ~13 km along the axis to the south, and ~20 km in the northern Red Sea. The depth increased to ~20-25 km at the coast and 35-40 km in the adjacent continents. The residual gravity data provided insights into the tectonic fabric along the whole rift and provided a good correlation with magnetic lineaments where these are available. We used the complete Bouguer anomaly to model sedimentary thicknesses constrained by wells and the interpreted Moho. The modeling results are consistent with the presence of largescale, ridge parallel tilted fault blocks forming subbasins with a maximum depth of about 6-7 km. Our models suggest that the northern Red Sea has an asymmetric basement surface with the western side deeper than the eastern side. The results indicate the presence of oceanic crust in the central and southern parts of the Red Sea, but not in the north. The very thin crust and interpreted oceanic crustal density in the central Red Sea suggest that this area is fully oceanic although possibly quite young. [ABSTRACT FROM AUTHOR]

We present two regional, lithospheric cross sections that illustrate eastward- and southeastward-dipping, subducted slabs to depths of 315 km beneath the surface of Colombia in northwestern South America. These cross-sectional interpretations are based on relocated earthquake hypocentral solutions, models supported on gravity and magnetic regional data, and coda-Q (Qc) tomography. The method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system. Mapping of earthquake-defined Benioff zones combined with tomographic imaging reveals the presence of an ~240 km long east-west-striking slab tear, named here the Caldas tear. The proposed Caldas tear separates a zone of shallow, 20°-30°-dipping, southeastward subduction in the area of Colombia adjacent to Panama and the Caribbean Sea, which is not associated with subduction-related volcanism, from an area of steeper, 30°-40°-dipping, slab adjacent to the eastern Pacific Ocean that is associated with an active north-south chain of active arc volcanoes. We propose that the Caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the Panama indenter, an extinct island arc that began subducting beneath northwestern South America about 12 Ma. The area south of the Panama indenter is Miocene oceanic crust of the Nazca plate, which subducts eastward beneath northwestern South America at normal angles and melts to form a north-south-trending active volcanic arc. In addition to the formation of the Caldas tear, we propose that impedance of the thicker crustal area of the Panama arc-indenter over the past 12 Ma may have led to down-dip break-off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate-depth earthquakes beneath east-central Colombia. [ABSTRACT FROM AUTHOR]

Abstract: The paradox of the Earth''s continental crust is that although this reservoir is generally regarded as having differentiated from the mantle, it has an andesitic bulk composition that contrasts with the intrinsic basaltic composition of mantle-derived melts. Classical models for new crust generation from the mantle in two-stage processes fail to account for two fundamental facts: the absence of ultramafic residues in the lower crust and the hot temperature of batholith magma generation. Other models based on the arrival of already-fractionated silicic magmas to the crust have not received the necessary attention. Addition of new crust by relamination from below of subducted materials has been formulated as a process complementary to delamination of mafic residues. Here we show important support to relamination from below the lithosphere as an important mechanism for new crust generation in magmatic arcs of active continental margins and mature intraoceanic arcs. The new support is based on three independent lines: (1) thermo-mechanical modeling of subduction zones, (2) experimental phase relations and melt compositions of subducted materials and (3) geochemical relations between mafic granulites (lower crust) and batholiths (upper crust). The mineral assemblage and bulk geochemistry of lower crust rocks are compared with solid residues left after granite melt segregation. The implication is that an andesite magma precursor is responsible for the generation of new continental crust at active continental margins and mature oceanic arcs. According to our numerical and laboratory experiments, melting and eventual reaction with the mantle of subducted oceanic crust and sediments produce the andesite magmas. These ascend in the form of mantle wedge diapirs and are finally attached (relaminated) to the continental crust, where they crystallize partially and produce the separation of the solid fraction to form mafic granulites (lower crust) and granitic (sl) liquids to form the batholiths (upper crust). [Copyright &y& Elsevier]

Abstract: The Tartoq Group, located in SW Greenland, consists of supracrustal rocks of mainly tholeiitic basaltic composition, including pillow lavas, sills/dykes and gabbros, as well as ultramafic rocks. Metamorphic grade ranges from greenschist facies to granulite facies. The Tartoq Group crops out as a series of blocks and slivers that are imbricated with originally intrusive Mesoarchaean TTG orthogneisses. The supracrustal rocks form part of a SE vergent fold and thrust belt consistent with the imbrication of TTG gneisses and supracrustal rocks along a convergent margin. LA-ICP-MS U–Pb zircon dating of an intrusive TTG sheet yields a minimum age of 2986±4Ma for the Tartoq Group. This age is consistent with MC-ICP-MS Lu–Hf and Sm–Nd isotopic whole-rock data for mafic samples from different blocks of the Tartoq Group, which yield errorchron ages of 3189±65Ma and 3068±220Ma, respectively. The mafic supracrustal rocks of the Tartoq Group have chondrite-normalized REE patterns with LaCN/SmCN of 0.67–1.96 and rather flat primitive mantle-normalized multi-element patterns, except for scattered LILE contents, and generally negative Nb-anomalies with Nb/Nb* of 0.26–1.31. Th/Yb varies between 0.06 and 0.47 and Nb/Yb between 0.45 and 4.4 indicative of an arc affinity when compared to rocks from modern settings. The similar geochemistry of the different lithological units, together with their coeval formation, as evident from trace element geochemical trends, supports a co-magmatic origin for the rock assemblage and their formation as imbricated relics of oceanic crust. Accordingly, we propose that the Tartoq Group represents remnants of Mesoarchaean oceanic crust, which formed in a suprasubduction zone geodynamic environment. [Copyright &y& Elsevier]

Abstract: High-Mg metabasalts and metapicrites discovered within the Urtagol Formation in the central zone of the Tunka bald mountains (East Sayan) are studied. In geochemistry the high-Mg metavolcanics are similar to subductional rocks. We have established that the Nb-rich recycled material of oceanic crust (RSC) was a source of elements for high-Ti metabasalts, and subductional fluid rich in LREE and Th relative to Nb was the source of these elements for high-Ti metapicrites. The enrichment of low-Ti metavolcanics, formed, probably, at the early stages of the basin opening, was due to the contamination of melt with continental-crust material. A comparison of the metavolcanics with nonmetamorphosed analogs is made, and some genesis aspects are considered. The results obtained led to the conclusion that the metavolcanics mark the paleospreading of the back-arc basin. [Copyright &y& Elsevier]

Abstract: The Alvand Intrusive Complex is located near Hamedan (Iran) and crops out over an area 400km2 intruding the Sanandaj-Sirjan plutono-metamorphic belt. The emplacement age of the AIC is constrained to Upper to Middle Jurassic, based on U–Pb zircon geochronogic data. This complex consists of granites (monzogranite and syenogranite), leucocratic granitoids (leucocratic tonalite, leucocratic granodiorite, and leucocratic quartz monzodiorite), mesocratic granitoids (tonalite, granodiorite, and quartz diorites), and abundant aplitic and pegmatitic dikes. The sequence of intrusion is as follows gabbro-diorites→mesocratic granitoids→granites and aplites and pegmatites associated with granites →leucocratic granitoids, based on emplacement relationships. Geochemically, this complex is metaluminous (ACNK=0.87) to peraluminous (ACNK=1.15). The mineralogical, lithological, and geochemical studies along with field observations indicate that the Alvand granites have S-type characteristics, leucocratic granitoids are arc-related I-type intrusions, mesocratic granitoids (tonalite and quartz diorites) possess transitional H-type features and granodiorites have S-type attributes. This complex has petrochemical characteristics that span the high K calc-alkaline and calc-alkaline series and displays the geochemical characteristics typical of magmatic arc intrusions related to an active continental margin. Depletion in Ti, Nb, Ta, Zr, Hf, Y, and HREE and enrichment in K, Rb, Cs, Th, and LREE are consistent with an arc setting associated with the subduction of Neo-Tethyan oceanic crust beneath the Sanandaj-Sirjan zone. [Copyright &y& Elsevier]

Abstract: Polished sections of ferromanganese crusts on underwater rises in the Sea of Japan were studied with a JXA8100 microprobe analyser. Mineral phases of REE have been detected. They have Ln2O3 chemical composition, where Ln is La–Ce–Pr–Nd, La–Ce–Nd, or, much more rarely, La–Ce and La–Ce–Pr. With regard to the same chemical composition of REE grains in the ore crusts and basalts from Medvedev Volcano, it has been concluded that these REE were supplied during postvolcanic gas–hydrothermal processes. [Copyright &y& Elsevier]

Abstract: According to geological, petrological, geochemical, and geochronological studies, the Haraa Gol terrane in the western Hentiyn Mts. is dominated by two rock assemblages of different ages, associated with the initiation and development of the island arcs and marginal spreading seas of the Mongol–Okhotsk Ocean. The Late Cambrian, Early Ordovician, and Middle Ordovician were marked by the effusion of basalt and basaltic andesite and the formation of gabbro and gabbro-dolerite in back-arc spreading basins. In the Late Silurian–Devonian, after a short pause, tectonomagmatic processes were activated, with the formation of differentiated island-arc volcanics, gabbro, and granitoids. Their absolute 40Ar–39Ar age is given in the paper. The model age of the T Nd(DM) protolith of the Haraa Gol igneous rocks corresponds to the composition of the Mesoproterozoic juvenile crust. [Copyright &y& Elsevier]

Abstract: We present results of geochemical studies and isotope dating of eclogites and associated rocks from the Kuru-Vaara quarry, Belomorian Belt, Northeastern Baltic Shield. The southern and northern eclogites are similar in geochemical features. Their protoliths were primitive, mainly high-Mg basalts of oceanic affinity derived from a primitive mantle source rather than from a depleted mantle source characteristic of modern MORB. The post-eclogitic intrusive rocks show obvious evidence for crustal contamination. The eclogite-hosting tonalitetrondhjemite-granodiorite (TTG) gneisses form a coherent series including high-Al and low-Al varieties. The trace element data show that the TTG series formed through the hydrous partial melting of the southern eclogites in the presence of garnet and amphibole in the field of the rutile stability (>15 kbar). Zircons from the southern eclogites exhibit features of their strong re-equilibration by coupled dissolution–repre-cipitation processes but have locally preserved patches with a primary magmatic zoning. The geochemistry of the patches points to the oceanic provenance of protolithic zircons; their isotope dating (SHRIMP-II) yielded a concordant age of 2821 ± 21 Ma. Zircons from the trondhjemite gneiss with geochemical features of Archean adakite were dated at 2805 ± 11 Ma, which suggests the syneclogitic facies origin of the TTG melts. The concordant age of high-pressure zircons from the northern eclogites is 2722 ± 21 Ma, close to the age of the earlier described Gridino eclogites. The overview of the isotopically dated eclogite bodies show the presence of at least three temporally distinct groups of eclogites in the Belomorian Belt, ∼2.86–2.87, ∼2.82–2.80, and ∼2.72 Ga, which is in a good accordance with the known isotopic ages for major crust-forming events in the belt. This, in turn, implies a close genetic relationship between the eclogites and the TTG origin, which might be consistent with the model of the short intermitted events of subduction of the thickened Archean oceanic crust. The presence of HP/UHP eclogites of different ages and the structural style of the Belomorian Belt permit it to be assigned to megamélange belts. [Copyright &y& Elsevier]

Abstract: Processing of the oceanic lithosphere in subduction zones gives rise to arc magmatism, and strong compositional links exist between trench input and arc output. Here we address the question whether these compositional links are sufficiently strong to allow for ‘tracing’ the composition of the sedimentary and igneous oceanic crust through the chemistry of arcs. The tracing approach hinges critically on whether key characteristics of the subducted slab are transmitted to arcs. Results from forward and inverse modeling, verified by observations from modern arc settings, demonstrate that elements Sr, Pb, Nd and Hf that are associated with radiogenic isotopes may preserve chemical characteristics of the subducted slab in arc magmas. The data indicate that the much thicker igneous subducted crust dominates the recycled flux to arcs. The flux from the highly enriched, but thin sediment layer is buffered, and may be even concealed, by the concomitant contributions from igneous crust, and/or subarc mantle, despite the much better visibility of sediment components in trace element and isotope space. Arc Pb and Pb isotopes are the most promising tracers that may capture the isotopic diversity of subducted MORB-type and OIB-type crust with sufficient temporal and spatial resolution. While arc Sr is also strongly controlled by the flux from the subducted crust, arc data may allow for distinguishing among radiogenic Sr recycled from altered oceanic crust or from subducted sediment in moderately radiogenic arcs (87Sr/86Sr<~0.7045). Co-mingling of Nd and Hf from igneous subducted crust with mantle contributions mostly hinders the isotopic identification of subducted crust through arc chemistry. However, Nd and Hf may provide complementary information about the efficiency of recycling, and recycling via subduction erosion. The tracing approach appears feasible in Cenozoic arcs where much of the original subduction context is preserved. First results from the Izu Bonin and Central American arcs show that plate tectonic events like oceanic plate formation and destruction, subduction of hotspot tracks and the closure of oceanic gateways are recorded in the chemistry of arcs. A comparative evaluation of Cenozoic global arcs may hence significantly complement the information from the modern oceanic basins, help to obtain a more complete image of the oceanic crustal composition and implicate the geochemical processes by which it formed. Possibly, the tracing approach may also be useful in ancient, inactive arcs to obtain information on the composition of oceanic crust subducted in the geological past. [Copyright &y& Elsevier]

Abstract: Mt. Ishimaki is the Jurassic accretionary complex of the Chichibu Belt in Toyohashi City, near Nagoya in central Japan. The Ishimaki limestone is thought to be seamount-type limestone. The P1 elements of the conodonts Norigondolella navicula and Ancyrogondolella quadrata found in the limestone indicate it is of Norian age. The Sr isotopic compositions of 45 Ishimaki limestone samples ranged from 0.7055 to 0.7077. Eighteen of these samples had lower Sr isotopic compositions than the lowest Sr isotopic composition (0.7068) of seawater throughout the Phanerozoic. The Sr isotopic compositions in the limestone block are generally lower at the base of the block and higher at the top. The present Sr isotopic compositions of the Ishimaki limestone are unlikely to have been reduced by post-depositional alteration because most of the limestone samples had a low amount of Mn (<300ppm) or high Sr/Mn ratios (>2) and the conodont elements had low (1–2) CAI (conodont alteration index) values. Additionally, there was little acid-insoluble residue. Thus, the low Sr isotopic compositions are thought to represent the strontium of the past ambient seawater. The low Sr isotopic compositions are in complete disagreement with the generally recognised range of seawater Sr isotopic compositions in the Norian stage of the Late Triassic (0.7075–0.7078) because the depositional environment of the Ishimaki limestone was closed or semi-closed from the Panthalassic Ocean. Therefore, the Sr isotopic composition of the limestone differs from that of the Panthalassic seawater. The low Sr isotopic compositions were probably affected by Sr inflows from mafic oceanic crust by hydrothermal fluid circulation or from hinterlands surrounded by mafic rocks by river water circulation. [Copyright &y& Elsevier]

Abstract: We estimate detailed three-dimensional seismic velocity structures in the subducting Pacific slab beneath Hokkaido, Japan, using a large number of arrival-time data from 6902 local earthquakes. A remarkable low-velocity layer with a thickness of ~10 km is imaged at the uppermost part of the slab and is interpreted as hydrated oceanic crust. The layer gradually disappears at depths of 70–80 km, suggesting the breakdown of hydrous minerals there. We find prominent low-velocity anomalies along the lower plane of the double seismic zone and above the aftershock area of the 1993 Kushiro-oki earthquake (M7.8). Since seismic velocities of unmetamorphosed peridotite are much higher than the observations, hydrous minerals are expected to exist in the lower plane as well as the hypocentral area of the 1993 earthquake. On the other hand, regions between the upper and lower planes, where seismic activity is not so high compared to the both planes, show relatively high velocities comparable to those of unmetamorphosed peridotite. Our observations suggest that intermediate-depth earthquakes occur mainly in regions with hydrous minerals, which support dehydration embrittlement hypothesis as a cause of earthquake in the subducting slab. [Copyright &y& Elsevier]

Abstract: We propose a model of the geodynamic evolution of the Dzhida island-arc system of the Paleoasian Ocean margin which records transformation of an oceanic basin into an accretion-collision orogenic belt. The system includes several Vendian-Paleozoic complexes that represent a mature oceanic island arc with an accretionary prism, oceanic islands, marginal and remnant seas, and Early Ordovician collisional granitoids. We have revealed a number of subunits (sedimentary sequences and igneous complexes) in the complexes and reconstructed their geodynamic settings. The tectonic evolution of the Dzhida island-arc system comprises five stages: (1) ocean opening (Late Riphean); (2) subduction and initiation of an island arc (Vendian-Early Cambrian); (3) subduction and development of a mature island arc (Middle-Late Cambrian); (4) accretion and formation of local collision zones and remnant basins (Early Ordovician-Devonian); and (5) postcollisional strike-slip faulting (Carboniferous-Permian). [Copyright &y& Elsevier]

In the Boğazkale region (Çorum, Central Anatolia), pieces of Neotethyan oceanic lithosphere are found in an ophiolitic mélange. Within the mélange, there are occurrences of isolated diabase dykes that intrude serpentinized and carbonatized ultramafics. The diabases are phaneritic, holocrystalline and equigranular, and consist of plagioclase and hornblende as the main primary mineral phases. They have all undergone low-grade alteration, to varying extents, as reflected by the presence of secondary minerals, including chlorite, epidote, prehnite and actinolite. Immobile trace element systematics suggest that all diabases are of subalkaline basalt composition and display negative Nb anomalies in the N-MORB-normalized plots. They also display flat to slightly LREE-depleted patterns in chondrite-normalized diagrams. The relative Th (and La) enrichment coupled with N-MORB-like HFSE composition of the diabases suggests their derivation from a depleted mantle source metasomatized by slab-derived fluids/melts. Overall trace element characteristics are consistent with an oceanic back-arc origin. 40Ar-39Ar radiometric dating on the hornblende grains extracted from the two diabase dykes yield ages of 176.30 ± 0.52 Ma and 178.82 ± 0.80 Ma (Toarcian, Early Jurassic). This suggests the existence of an intra-oceanic subduction zone within the Izmir-Ankara-Erzincan (IAE) Ocean during the Early Jurassic, which can also be traced along the western (Vardar Zone) and the eastern (Sevan/Akera ophiolites) extensions of the Northern Neotethys. This result requires the presence of a Northern Neotethyan oceanic crust of pre-Early Jurassic age, which in turn may suggest that oceanization of the IAE Ocean have occurred during the Late Triassic or earlier. [ABSTRACT FROM AUTHOR]

The Central Pontides (northern Turkey) is one of the key localities to understand the geodynamic evolution of the Palaeo- and Neotethyan oceans. It consists of the pre-Jurassic basement units, the Early Jurassic and the Early Cretaceous accretionary complexes, the widespread Middle Jurassic continental arc magmatics and the Late Jurassic to Tertiary cover units. The Early Cretaceous accretionary complex is represented by the Central Pontide Structural Complex and includes the Middle Jurassic oceanic units, which were metamorphosed during the Early Cretaceous. Apart from these oceanic units, a few metaophiolite and serpentinite fragments have been recognized within the basement units, which may represent the remnants of an older ocean. The pre-Middle Jurassic Devrekani Metaophiolite is the largest oceanic fragment and tectonically intercalated within/between the Devrekani Metamorphics and the Çangaldağ Metamorphic Complex. It is mainly composed of harzburgites, dunites with chromite veins and metagabbros, and cut by metabasaltic andesites and metadacites. Petrographically, the gabbro consists mainly of plagioclase and clinopyroxene, and displays phaneritic/porphyritic texture. In contrast, the metabasaltic andesite includes plagioclase and mica phenocrysts within a fine-grained groundmass. Also, the metadacite is composed predominantly of quartz, plagioclase, and mica minerals. Two different magmatic groups belonging to completely different tectono-magmatic settings have been geochemically determined based on the immobile trace element systematics. The metadacites and metabasaltic andesites are akin to continental arc magmatics and characterized by negative Nb and Ta anomalies and depleted HFSE relative to Th and La contents. However, the metagabbro samples display the geochemical signatures of boninitic rocks and characterized by highly depletion in HFSEs and REEs relative to N-MORB. The Devrekani Metaophiolite in the Central Pontides may represent another remnant of pre-Middle Jurassic oceanic crust generation and can be north-eastward continuation of the Permian-aged Almacık complex and the Boğazköy Metaophiolite fragment in the western Sakarya Composite Terrane. It may have been cut by intrusions of the extensive Middle Jurassic continental arc magmatism after its imbrication within the basement unit. The presence of pre-Middle Jurassic oceanic units may indicate that the Paleozoic ocean may have survived as the Jurassic Intra-Pontide Ocean between the Scythian Platform and Sakarya Composite Terrane during the Mesozoic time. Thus, the Intra-Pontide Suture may normally include the Palaeozoic and Mesozoic remnants of the long-lived northward subducting Tethyan ocean. [ABSTRACT FROM AUTHOR]

Two Marinobacter sp. NP-4 and NP-6 were isolated from a deep oceanic basaltic crust at North Pond, located at the western flank of the Mid-Atlantic Ridge. These two strains are capable of using multiple carbon sources such as acetate, succinate, glucose and sucrose while take oxygen as a primary electron acceptor. The strain NP-4 is also able to grow anaerobically under 20 MPa, with nitrate as the electron acceptor, thus represents a piezotolerant. To explore the metabolic potentials of Marinobacter sp. NP-4 and NP-6, the complete genome of NP-4 and close-to-complete genome of NP-6 were sequenced. The genome of NP-4 contains one chromosome and two plasmids with the size of 4.6 Mb in total, and with average GC content of 57.0%. The genome of NP-6 is 4.5 Mb and consists of 6 scaffolds, with an average GC content of 57.1%. Complete glycolysis, citrate cycle and aromatics compounds degradation pathways are identified in genomes of these two strains, suggesting that they possess a heterotrophic life style. Additionally, one plasmid of NP-4 contains genes for alkane degradation, phosphonate ABC transporter and cation efflux system, enabling NP-4 extra surviving abilities. In total, genomic information of these two strains provide insights into the physiological features and adaptation strategies of Marinobacter spp. in the deep oceanic crust biosphere. [ABSTRACT FROM AUTHOR]

Trace metal concentrations (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd, As, Hg) were determined in water, sediment and biota samples collected from the San Benito Islands off the Pacific Coast of Baja California, Mexico for a geochemical forensic study. Due to the proximity to the continental – oceanic crust interface and high biological endemism, the islands demanded a profound geochemical survey for evaluating the presence and provenance of trace metals. Results suggested that the metals in the region are mainly originated from the geogenic sources (Fe, Mn, Ni, Cr, Cu, Co), deep water circulation (Cd), atmospheric deposition (Pb) and hydrothermal processes (As). Dissolved phase is the major metal carrier of Pb with an average value of 0.182 mg L−1, while Fe (1.60%), Mn (335.42 mg kg−1), Ni (61.77 mg kg−1), Zn (32.36 mg kg−1) and Cr (28.7 mg kg−1) are mainly present in the particulate phase. High values of Pb, As, Cd and Hg in biota with no biological functions are highly toxic and are especially critical to those predators (Sea lions) in the region due to the process of biomagnification. For a qualitative exposure assessment of trace metals, several indices namely Heavy metal Evaluation Index (HEI), Nemerow Pollution Index (NPI), Bioconcentration Factor (BCF) and Biota Sediment Accumulation Factor (BSAF) were calculated. The indices revealed that the overall pollution status of the region is "moderate". This study advocates a preliminary environmental surveillance in trace metal concentrations for implementing better conservation strategies in maintaining and promoting the ecological richness and endemism of the islands. Image 1 • Geochemical assessment of trace metals in San Benito Islands was carried out. • Local geogenic sources are considered to be the main source of metals. • Calculated geochemical indices indicate moderate pollution in the region. [ABSTRACT FROM AUTHOR]