Arc Region Research Articles

Integrating the Holocene tephrostratigraphy for East Asia using a high-resolution cryptotephra study from Lake Suigetsu (SG14 core), central Japan

Tephra (volcanic ash) layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales. Highly productive arc regions, like those in East Asia, offer a considerable number of widespread isochrons, but before records can be confidently correlated using these layers, a refined and integrated framework of these eruptive events is required. Here we present the first high-resolution Holocene cryptotephra study in East Asia, using the Lake Suigetsu sedimentary archive in central Japan. The Holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques, which integrates the deposits from explosive eruptions from North Korea/China, South Korea and along the Japanese arc. This Lake Suigetsu tephrostratigraphy is now the most comprehensive record of East Asian volcanism, and the linchpin site for correlating sequences across this region. Major element glass geochemical compositions are presented for the tephra layers in the sequence, which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions. This study has significantly extended the ash dispersal of many key Holocene marker layers, and has identified the first distal occurrence of isochrons from Ulleungdo and Changbaishan volcanoes. Utilising the high-precision Lake Suigetsu chronology, we are able to provide constrained eruption ages for the tephra layers, which can be transferred into other site-specific age models containing these markers. This new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in Japan, and could be used to precisely assess the regional and hemispheric synchronicity of these events.

Updating active fault maps and sliprates along the Sumatran Fault Zone, Indonesia

The accuracy of active fault map, slip rate and its seismic parameters is crucial for seismic hazard analysis. Fault maps, segmentations and slip rates of the Sumatran Fault Zone (SFZ) have been revised in relation with ongoing activities for updating Indonesian seismic hazard map. In the northern part, several secondary fault strands in the eastern side of the main SFZ are added, including the Pidie, Biruen, Lhok-Sumawe, Peusangan, and Oreng faults. The Batee fault is now considered active. In the southern part, from Suoh pull-apart graben, SFZ branches into two major strands: the west and east Semangko fault segments. Toward south, the west and east Semangko faults are connected with series of marine grabens in the Sunda Strait, forming a 70-km-wide pull-apart structure that is bounded by SFZ and the Ujung Kulon fault, which carries SFZ dextral movement further south into southwest of Java island. Previously, slip rates along SFZ are considered increasing northward from about 5 mm/yr in Sunda Strait to 30 mm/yr in Toba Area. Consequently, fore arc region was thought to be stretched. Nowadays, according to the latest geological and GPS studies, slip rates appear to be more constant at ∼15 mm/yr. The total amount of parallel-SFZ extension on the Sunda-strait marine grabens is estimated to be about 18.7 km, almost identical with the largest geomorphic offset along SFZ. In assumption, the SFZ onset since 2 Ma indicates a slip rate of about 9 mm/yr in Sunda Strait. New slip rate measurement near Lake Ranau yields 8-12 mm/yr. Revised slip-rate measurements in both Lake Maninjau and Lake Toba yield about similar rates, ∼14-15 mm/yr. Thus, Sumatran fore-arc acts move northward along SFZ, which is more like a rigid block instead of much stretched.

M0.20–0.033: An Expanding Molecular Shell in the Galactic Center Radio Arc

Abstract We present high-frequency Karl G. Jansky Very Large Array (VLA) continuum and spectral line (NH3, H64α, and H63α) observations of the Galactic Center Radio Arc region, covering the Sickle H ii region, the Quintuplet cluster, and molecular clouds M0.20−0.033 and M0.10−0.08. These observations show that the two velocity components of M0.20−0.033 (∼25 and 80 km s−1), previously thought to be separate clouds along the same line-of-sight, are physically connected in position–velocity space via a third southern component around 50 km s−1. Further position–velocity analysis of the surrounding region, using lower-resolution survey observations taken with the Mopra and ATCA telescopes, indicates that both molecular components in M0.20−0.033 are physically connected to the M0.10−0.08 molecular cloud, which is suggested to be located on stream 1 in the Kruijssen et al. orbital model. The morphology and kinematics of the molecular gas in M0.20−0.033 indicate that the two velocity components in M0.20−0.033 constitute an expanding shell. Our observations suggest that the M0.20−0.033 expanding shell has an expansion velocity of 40 km s−1, with a systemic velocity of 53 km s−1, comparable to velocities detected in M0.10−0.08. The origin of the expanding shell is located near the Quintuplet cluster, suggesting that the energy and momentum output from this massive stellar cluster may have contributed to the expansion.

Three-Dimensional Electrical Resistivity Image of the Volcanic Arc in Northern Chile—An Appraisal of Early Magnetotelluric Data

Magnetotelluric investigations were carried out in the late 1980s across all morphological units of the South American subduction zone with the aim to observe lithosphere structures and subduction-induced processes in northern Chile, southwestern Bolivia, and northwestern Argentina at ~ 22°S. Earlier two-dimensional forward modeling yielded a complex picture of the lower crust and upper mantle, with strong variations between the individual morphological units as well as between forearc and backarc. The principal result was a highly conductive zone beneath the volcanic arc of the Western Cordillera starting at ~ 25 km depth. Goal of this work is to extend the existing 2-D results using three-dimensional modeling techniques at least for the volcanic arc and forearc region between 22°S and 23°S in Northern Chile. Dimensionality analysis indicates strong 3-D effects along the volcanic arc at the transition zone to the Altiplano, in the Preandean Depression and around the Precordillera Fault System at ~ 22°S. In general, the new 3-D models corroborate previous findings, but also enable a clearer image of lateral resistivity variations. The magmatic arc conductor emerges now as a trench-parallel, N–S elongated structure slightly shifted to the east of the volcanic front. The forearc appears highly resistive except of some conductive structures associated with younger sedimentary infill or young magmatic record beneath the Precordillera and Preandean Depression. The most prominent conductor in the whole Central Andes beneath the Altiplano and Puna is also modeled here; it is, however, outside the station array and thus poorly resolved in this study.

Altered CREB Binding to Activity-Dependent Genes in Serine Racemase Deficient Mice, a Mouse Model of Schizophrenia.

cAMP-response-element-binding protein (CREB) is a transcription factor ubiquitously expressed in the brain that regulates neuroplasticity by modulating gene expression. The influx of calcium through N-methyl-d-aspartate receptors (NMDARs) is a well-defined mechanism that leads to the increased expression of CREB-dependent genes, including brain derived neurotrophic factor (BDNF), microRNA-132, and activity-regulated cytoskeleton-associated protein (Arc). These molecules are implicated in the pathophysiology of schizophrenia. We previously demonstrated that serine racemase knockout (SR-/-) mice, which exhibit NMDAR hypofunction due to a lack of the forebrain NMDAR co-agonist d-serine, also have reduced expression of CREB-dependent genes in the hippocampus. Using chromatin immunoprecipitation, we show here that, in SR-/- mice, there is less CREB bound to the promoter regions of BDNF, microRNA-132, and Arc. These data suggest that NMDAR hypofunction in SR-/- mice leads to reduced CREB binding on known activity-dependent genes, in turn contributing to their reduced expression.

Cenozoic Shift From Compression to Strike‐Slip Stress Regime in the High Andes at 30°S, During the Shallowing of the Slab: Implications for the El Indio/Tambo Mineral District

AbstractIn the High Andes of central Chile, above the flat‐slab segment, analysis of more than 1,000 fault slip data from Miocene outcrops provides evidence for a change of the regional tectonic regime from compressional to strike slip. This shift in tectonic regime occurred during the waning stages of arc volcanism between 14 and 11 Ma, as a result of the shallowing of the Nazca plate, in conjunction with the migration of deformation to the Precordillera. During the early to middle Miocene, a compressive regime with horizontal σ1 axis (N86°E) was responsible for reverse slip along NNE to N‐striking faults. During the late Miocene, a shift to strike‐slip tectonics took place due to an increase in the absolute magnitude of the vertical stress component as the crust thickened and the gravitational potential energy increase. We argue that instead of the previously accepted highly compressional setting in the arc region during the slab flattening, the change to a strike‐slip regime was the main control on mineralization. Mineralization was controlled by the promotion of fluid expulsion from the magma chambers along active, subvertical strike‐slip fault systems with a high slip tendency, and focusing of fluids in localized areas undergoing extension. Under this strike‐slip regime, the El Indio, Tambo, and La Despensa fault systems formed as dextral strike‐slip systems. The tips and jogsites along these faults experienced local extensional stress fields, forming the El Indio and Tambo mineral districts.

Permian arc evolution associated with Panthalassa subduction along the eastern margin of the South China block, based on sandstone provenance and U–Pb detrital zircon ages of the Kurosegawa belt, Southwest Japan

We have studied the petrography, geochemistry, and detrital zircon U–Pb ages of sandstones from shallow-marine forearc sediments, accretionary complexes (ACs), and metamorphosed accretionary complexes (Meta-ACs) within the Kurosegawa belt of Southwest Japan. Those rocks formed in a forearc region of a Permian island arc associated with subduction of the Panthalassa oceanic crust along the eastern margin of the South China block (Yangtze block). The provenance of the shallow-marine sediments was dominated by basaltic to andesitic volcanic rocks and minor granitic rocks during the late Middle to Late Permian. The ACs were derived from felsic to andesitic volcanic rocks during the Late Permian. The provenance of Meta-ACs was dominated by andesitic volcanic rocks in the Middle Permian. The provenance, source rock compositions, and zircon age distribution for the forearc sediments, ACs and Meta-ACs have allowed us to reconstruct the geological history of the Permian arc system of the Kurosegawa belt. During the Middle Permian, the ACs were accreted along the eastern margin of the South China block. The Middle Permian arc was an immature oceanic island arc consisting of andesitic volcanic rocks. During the Late Permian, the ACs formed in a mature arc, producing voluminous felsic to andesitic volcanic rocks. A forearc basin developed during the late Middle to Late Permian. Subsequently, the Middle Permian ACs and part of the Late Permian AC underwent low-grade metamorphism in the Late to Early Jurassic, presenting the Meta-ACs.

沖縄トラフおよび石垣島南方で採取されたIMAGESコアに基づく過去約25万年間の表層・中層水の変動( 西太平洋におけるIMAGESコアを用いた高時間解像度の環境復元)

沖縄トラフおよび石垣島南方で採取されたIMAGESコアに基づく過去約25万年間の表層・中層水の変動( 西太平洋におけるIMAGESコアを用いた高時間解像度の環境復元)

Petrografia e geoquímica de gnaisses da região de Indiara, porção central do arco magmático de Goiás

Na região de Indiara, Goiás, ocorre uma extensa faixa de gnaisses relacionados ao Arco Magmático de Goiás, próximo ao contato com as rochas supracrustais da Sequência Metavulcanossedimentar Anicuns-Itaberaí. Dados geoquímicos e isotópicos (Sm/Nd) mostram que os gnaisses da região de Indiara não são semelhantes às rochas de regiões tipo do Arco Magmático de Goiás (regiões de Arenópolis, Firminópolis, Iporá e Mara Rosa). São rochas cálcio-alcalinas e peraluminosas, com composição predominantemente granítica, em contraste com o caráter prevalentemente cálcico e metaluminoso das regiões tipo, que também apresentam composição dominantemente tonalítica a granodiorítica. Os altos teores de SiO2, o caráter fortemente peraluminoso e os altos teores de coríndon normativo sugerem que os gnaisses da região de Indiara são derivados de granitos tipo-Sin-colisionais e/ou correspondem à mistura de protólitos ígneos e sedimentares. As idades modelo TDM (1,88 e 1,90 Ga) sugerem que os gnaisses da região evoluíram de crosta siálica mais antiga do que as rochas que compõem o Arco Magmático de Goiás.

Neogene-quaternary evolution from transpressional to transtensional tectonics in Northern Central America controlled by cocos: Caribbean subduction coupling change

The structural evolution of the western boundary of the Chortis Block, particularly in the Central America Volcanic Arc crossing El Salvador is poorly known. We have done a kinematic analysis from seismic and fault slip data and combined our results with a review of previous regional studies. This approach allowed us to constrain the tectonic evolution and the processes that control the deformation in northern Central America. Along the active volcanic arc we identified active transtensional deformation. On the other hand, we have identified two deformation phases in the back arc region: A first one of transpressional wrenching close to simple shearing (Miocene); and a second one characterized by almost E–W extension coincident with the extensional direction of the Honduras grabens opening. Our results reveal a change from transpressional to transtensional shearing coeval with a migration of the volcanism towards the trench in Late Miocene times. The strain change could be related to a transition from coupled to decoupled interface on the Cocos—Caribbean subduction, which could be caused by a slab roll-back of the Cocos Plate beneath the Chortis Block. The combination of different degrees of coupling on the subduction interface, together with a constant relative eastward drift of the Caribbean Plate, control the deformation style along the western boundary of the Chortis Block.

High-Current Vacuum Arc Mode Transition of a Horseshoe-Type Axial Magnetic Field Contact With Long Contact Gap

The objective of this paper is to determine the high-current vacuum arc mode transition diagram of a horseshoe-type axial magnetic field (AMF) contact with long contact gap. Drawn arc experiments were carried out in an $L$ – $C$ discharging circuit. Horseshoe-type contacts with contact material of CuCr50 and contact diameter of 120 mm were arranged in a demountable vacuum chamber. Full contact gap was 60 mm. The experiment current level ranged from 4 to 40 kA, stepped by 4 kA. Prospective arcing time was set as 2, 5, and 9 ms, respectively. The evolution of vacuum arc behavior was observed using a high-speed camera. Nonsynchronous evolution phenomenon of twin parallel arc columns was observed. With current level ranged from 24 to 40 kA, the maximum nonsynchronous duration transiting from small-gap constricted column mode to diffuse column mode, from diffuse column mode to diffuse arc mode, and from diffuse arc mode to multicathode-spot arc mode were 0.98, 1.09, and 1.55 ms, respectively. The nonsynchronous duration in various vacuum arc modes was determined as well. Summarizing all arc mode transition points in the experiment, a vacuum arc mode transition diagram of the horseshoe-type AMF contact was proposed. Boundary of uncontrollable arc region was determined, which could provide criteria of maximum arcing contact gap design. Besides, an effective arcing region was defined according to distribution of AMF and arc behaviors, in which AMF on the contact surface plane was higher than 75%Baxial–max.

Stimulus-evoked ERK-dependent phosphorylation of activity-regulated cytoskeleton-associated protein (Arc) regulates its neuronal subcellular localization

Activity-regulated cytoskeletal-associated protein (Arc) is implicated as a master regulator of long-term synaptic plasticity and memory formation in mammalian brain. Arc acts at synapses and within the nucleus, but the mechanisms controlling Arc localization and function are little known. As Arc transcription and translation are regulated by extracellularsignal-regulated kinase (ERK) signaling, we asked whether Arc protein itself is phosphorylated by ERK. GST-fused Arc of rat origin was able to pull down endogenous ERK2 from rat hippocampal lysates. Using a peptide array, we show that ERK binds a non-canonical docking (D) motif in the C-terminal domain of Arc, and this interaction is abolished by phosphorylation of Tyr309. Activated ERK2 phosphorylated bacterially expressed Arc in vitro at all five predicted sites, as confirmed by phospho-specific protein staining and LC–MS/MS analysis. In neuroblastoma cells expressing epitope tagged-Arc, we demonstrate ERK-dependent phosphorylation of Arc in response to activation of muscarinic cholinergic receptors with carbachol. Using phosphosite-specific antibodies, this stimulus-evoked phosphorylation was shown to occur on Ser206 located within the central hinge region of Arc. In cultured hippocampal neurons expressing phosphomutant Arc under control of the activity-dependent promoter, we show that Ser206 phosphorylation regulates the nuclear:cytosolic localization of Arc. Thus, the neuronal activity-induced phosphomimic exhibits enhanced cytosolic localization relative to phosphodeficient and wild-type Arc. Furthermore, enhanced Ser206 phosphorylation of endogenous Arc was detected in the dentate gyrus cytoskeletal fraction after induction of long-term potentiation (LTP) in live rats. Taken together, this work demonstrates stimulus-evoked ERK-dependent phosphorylation and regulation of Arc protein.

Geochemistry of coastal sands of Eastern Mediterranean: The case of Nisyros volcanic materials

Coastal sand samples collected from the northern part of Nisyros volcanic island (Dodecanese, Greece) were investigated for first time for their potential in strategic metals and compared with parental rocks of the island which are Quaternary volcanics with alternating lava flows, pyroclastic layers and lava domes and relevant materials located near granitoids of Northern Greece. The PXRD and SEM-EDS study of the sands revealed enhanced content of feldspars, Fe-Mn oxides, magnetite, tourmaline, pyroxenes, ilmenites, along with zircons, apatite and sulfide inclusions. The fresh hydrothermally deposited clayely material collected from the Nisyros caldera crater had a rather different mineralogical composition from the coastal one (alunite, anhydrite, opal-CT, quartz, kaolinite). UCC-normalized spidergrams indicated that the weathering processes contributed to accumulation of heavy minerals (mainly ilmenite), and strategic metals including V (1920mg/kg) and Nb (245mg/kg), in the coastal sand. The low REE concentration (ΣREE+Y=240mg/kg) could be attributed to the absence of REE-rich minerals. Moreover, the sands exhibit different geochemical patterns compared to the volcanic source rocks of the island, which are especially enriched in Large-Ion Lithophile Elements (LILE) and depleted in High Field Strength Elements (HFSE), such as Nb and Ta. On the other hand, the caldera material is enriched in volatile components, sulfur, chalcophile elements (Se, Bi, Hg, As, Pb) and Ba. Micro-XRF analyses of representative crystals showed that the high Nb content of the sands was associated with the Ti/Fe-rich phases (e.g. ilmenites). The geochemical composition of N Greece sands showed, because of their origin, enrichment not only in HFSE but also in REE.The study of the coastal heavy mineral sands originating from different geological environments of Greece provides information about the association of their mineral components with REE, other elements of economic interest (e.g. Co, Nb, Ta) and natural actinides. In addition, the study of the black sands of Nisyros island could be considered as a characteristic example of those from other parts of Hellenic Volcanic Arc (HVA) and other relevant Mediterranean regions.

Contrasting provenance and timing of metamorphism from paragneisses of the Araçuaí-Ribeira orogenic system, Brazil: Hints for Western Gondwana assembly

The Araçuaí orogen and the Ribeira belt make up a complex Neoproterozoic-Cambrian orogenic system, the Araçuaí-Ribeira orogenic system (AROS) located from the eastern to southeastern Brazil. Along the AROS, the Ediacaran Rio Doce magmatic arc represents a geotectonic connection between the Araçuaí and the Ribeira orogenic domains. Although the nature and evolution of the Rio Doce plutonic rocks is regionally well established, it lacks detailed studies on the paragneisses found along the western and central regions of this magmatic arc. Besides information on the nature and provenance of their sedimentary protoliths, the paragneisses provide data to unravel the palaeogeographic scenario from the precursor to arc-related basins. Six samples of Al-rich gneisses covering a large AROS region were selected for electron microprobe (EMP) mineral analyses in order to obtain geothermobarometric data and monazite ages, as well as for Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) isotopic analyses on zircon (U-Pb, Lu-Hf) and monazite (U-Pb). The different age spectra from detrital zircon grains and contrasting Hf isotopic signatures suggest a complex sedimentary history. Located in the western sector of the study region, the samples RC-02 and RC-34, with an 80% age peak of detrital zircon grains from 2158Ma to 1830Ma, εHf(t) from −2.2 to −22.7, and Hf TDM model ages from 3530Ma to 2440Ma, suggest sediment sources located in the São Francisco craton basement. The samples RC-03, also from the western sector, and RC-46 from the southern sector, have a more complex assemblage of detrital zircon grains with an 87% age peak from 987Ma to 592Ma, εHf(t) from +14.9 to −2.9, and Hf TDM model ages from 2220Ma to 720Ma, indicating provenance from mainly juvenile sources of distinct ages. Candidates to be juvenile sources for RC-03 and RC-46 sedimentary protoliths are the Rhyacian Juiz de Fora and Pocrane complexes in the basement of the Rio Doce arc, the Neoproterozoic Rio Negro arc system of the Ribeira belt, and AROS ophiolite complexes. Samples RC-30 and RC-38 from the eastern sector of the study region, with most detrital zircon ages between 650Ma and 552Ma and very negative εHf(t) (−25.3 to −16.5), suggest main sediment sources in the Rio Doce arc. By extending U-Pb analyses on metamorphic zircon and monazite, we have identified a complex timing of metamorphism, represented by metamorphic ages ranging from 621Ma to 480Ma, with the main collisional activity between 580Ma and 540Ma. Geothermobarometric studies on garnet porphyroblasts, syn-kinematic to the D2 regional foliation, show a retrograde metamorphic path typical of continental collision belts, starting with P-T conditions of Tmax=733°C and Pmax=6.43kbar. Our data also suggest: i) the studied paragneisses represent distinct Neoproterozoic basin stages, shifting from passive to active margin settings; ii) if the Rio Negro arc system really provided sediments for the basin stage represented by the RC-03 and RC-46 paragneisses, it would have amalgamated with the AROS before 614Ma; iii) the final amalgamation of Western Gondwana took place around 540Ma in the focused region; iv) an important re-heating period (520–480Ma) can be related to the AROS gravitational collapse, after Western Gondwana assembly.

Noble gas data from Goldfield and Tonopah epithermal Au-Ag deposits, ancestral Cascades Arc, USA: Evidence for a primitive mantle volatile source

The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected 3He/4He ratios (with atmospheric He removed) range widely from 0.05 to 35.8 times the air 3He/4He ratio (RA), with a median of 1.43 RA. Forty-one percent of measured 3He/4He ratios are ≥4 RA, corresponding to ≥50% mantle He assuming a mantle ratio of 8 RA. These results suggest that mafic magmas were part of the magmatic-hydrothermal system underlying Goldfield and Tonopah, and that associated mantle-sourced volatiles may have played a role in ore formation. The three highest corrected 3He/4He ratios of 17.0, 23.7, and 35.8 RA indicate a primitive mantle He source and are the highest yet reported for any epithermal-porphyry system and for the Cascades arc region. Compiled 3He/4He measurements from epithermal-porphyry systems in subduction-related magmatic arcs around the world (n=209) display a statistically significant correlation between 3He/4He and Au-Ag grade. The correlation suggests that conditions which promote higher fluid inclusion 3He/4He ratios (abundance of mantle volatiles and focused upward volatile transport) have some relation to conditions that promote higher Au-Ag grades (focused flow of metal-bearing fluids and efficient chemical traps). Results of this and previous investigations of He isotopes in epithermal-porphyry systems are consistent with the hypothesis posed in recent studies that mafic magmas serve an important function in the formation of these deposits.

Experimental Study on Deflection Behavior of Vacuum Arcs Under the Influence of External Transverse Magnetic Field

In real power system, when the three-phase short-circuit fault occurs, the vacuum arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum arc’s behavior. The experiments were conducted in a demountable vacuum chamber with pressure about $10^{-4}$ Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of arc column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on arc column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends.

MHD-RLC discharge model and the efficiency characteristics of plasma synthetic jet actuator

Major factors affecting efficiency of plasma synthetic jet actuator (PSJA) are analyzed based on a new discharge model in the present paper. The model couples the magnetohydrodynamics (MHD) equations with the resistor–inductor–capacitor (RLC) equations, and is able to resolve the time-dependent voltage fall on the sheath region and arc region, which is critical in analyzing energy loss in the heating process. This model is integrated into the commercial CFD software by a two-equation method. Results show that in a typical capacitive discharge at microsecond scale, the maximum energy loss is the sheath energy loss, which accounts for nearly half of the discharge energy, while the radiation loss is less than 5%. The discharge time is an important parameter for the PSJA efficiency. A short discharge time less than 1μs will effectively reduce the sheath energy loss, while a longer discharge time will decrease the thermodynamic efficiency.

Chemical interactions in the subduction factory: New insights from an in situ trace element and hydrogen study of the Ichinomegata and Oki-Dogo mantle xenoliths (Japan)

The uppermost mantle in back arc regions is the site of complex interactions between partial melting, melt percolation, and fluid migration. To constrain these interactions and evaluate their consequences on geochemical cycles, we carried out an in situ trace element and water study of a suite of spinel peridotite xenoliths from two regions of the Japan back arc system, Ichinomegata (NE Japan) and Oki-Dogo (SW Japan), using LA-ICPMS and FTIR spectrometry, respectively. This study provides the first full dataset of trace element and hydrogen compositions in peridotites including analyses of all their main constitutive silicate minerals: olivine, orthopyroxene and clinopyroxene. The Ichinomegata peridotites sample a LREE-depleted refractory mantle (Mg# olivine=0.90; Cr# spinel=0.07–0.23; Yb clinopyroxene=7.8–13.3×C1-chondrite, and La/Yb clinopyroxene=0.003–0.086×C1-chondrite), characterized by Th-U positive anomalies and constant values of Nb/Ta. The composition of the studied Ichinomegata samples is consistent with that of an oceanic mantle lithosphere affected by cryptic metasomatic interactions with hydrous/aqueous fluids (crypto-hydrous metasomatism). In contrast, the Oki-Dogo peridotites have low Mg# olivine (0.86–0.93) and a broad range of compositions with clinopyroxene showing “spoon-shaped” to flat, and LREE-enriched patterns. They are also characterized by their homogeneous compositions in the most incompatible LILE (e.g., Rb clinopyroxene=0.01–0.05×primitive mantle) and HFSE (e.g., Nb clinopyroxene=0.01–2.16×primitive mantle). This characteristic is interpreted as resulting from various degrees of melting and extensive melt-rock interactions. FTIR spectroscopy shows that olivine in both Ichinomegata and Oki-Dogo samples has low water contents ranging from 2 to 7ppm wt. H2O. In contrast, the water contents of pyroxenes from Ichinomegata peridotites (113–271ppm wt. H2O for orthopyroxene, and 292–347ppm wt. H2O for clinopyroxene) are significantly higher than in Oki-Dogo peridotites (9–35ppm wt. H2O for orthopyroxene, and 15–98ppm wt. H2O for clinopyroxene). This indicates a relationship between melt-rock interaction and water concentrations in pyroxenes. Our study suggests that the water content of the Japan mantle wedge is controlled by the late melt/fluid/rock interactions evidenced by trace element geochemistry: a mechanism triggered by magma-rock interactions may have acted as an efficient dehydrating process in the Oki-Dogo region while the Ichinomegata mantle water content is controlled by slab-derived crypto-hydrous metasomatism.

Formation of the Sun‐aligned arc region and the void (polar slot) under the null‐separator structure

AbstractFrom the global magnetosphere‐ionosphere coupling simulation, we examined the formation of the Sun‐aligned arc region and the void (polar slot) under the northward interplanetary magnetic field (IMF) with negative By condition. In the magnetospheric null‐separator structure, the separatrices generated from two null points and two separators divide the entire space into four types of magnetic region, i.e., the IMF, the northern open magnetic field, the southern open magnetic field, and the closed magnetic field. In the ionosphere, the Sun‐aligned arc region and the void are reproduced in the distributions of simulated plasma pressure and field‐aligned current. The outermost closed magnetic field lines on the boundary (separatrix) between the northern open magnetic field and the closed magnetic field are projected to the northern ionosphere at the boundary between the Sun‐aligned arc region and the void, both on the morning and evening sides. The magnetic field lines at the plasma sheet inner edge are projected to the equatorward boundary of the oval. Therefore, the Sun‐aligned arc region is on the closed magnetic field lines of the plasma sheet. In the plasma sheet, an inflated structure (bulge) is generated at the junction of the tilted plasma sheet in the far‐to‐middle tail and nontilted plasma sheet in the ring current region. In the Northern Hemisphere, the bulge is on the evening side wrapped by the outermost closed magnetic field lines that are connected to the northern evening ionosphere. This inflated structure (bulge) is associated with shear flows that cause the Sun‐aligned arc.

Nonequilibrium modeling study on plasma flow features in a low-power nitrogen/hydrogen arcjet thruster

Gasdynamic flow features in an electrothermal arcjet thruster with a mixture of 1:2 nitrogen/hydrogen as the working gas have been studied by a two-temperature numerical simulation. Seven species and 17 kinetic processes are included in the chemical kinetic model used to represent dissociation, ionization, and the corresponding recombination reactions in this nitrogen/hydrogen mixture system. Based on the gas flow characteristics inside the arcjet nozzle, a new method is introduced to define the edge of the cold boundary layer, which is more convenient to analyze the evolution and development of plasma flow in an arcjet thruster. The results show that the arcjet thruster performance is determined largely by the exchange of energy and momentum between the low-density, high-temperature arc region and the high-density, cool-flow region near the nozzle wall. A significant thermal nonequilibrium is found in the cold boundary layer in the expansion portion of the nozzle. The important chemical kinetic processes determining the distribution of hydrogen and nitrogen species in different flow regions are presented. It has been shown that the reaction rate of hydrogen species ionization impacted by electrons is much higher than that of nitrogen species ionization in the center of the constrictor of the arcjet thruster. This indicates that hydrogen species is very important in the conversion of applied electric energy into thermal energy in the constrictor region of the arcjet thruster.