The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and ...The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and where are the danger zones.Three largest eruptions since 1900,the Hunga Tonga-Hunga Ha’apai,the Mt.Pinatubo,and the Novarupta were found to be associated with subductions of volatile-rich sediments and located close to slab windows.Among them,the Hunga Tonga-Hunga Ha’apai is close to subducting seamount chains;the Mt.Pinatubo is right next to subducting fossil ridges.Both seamount chains and fossil ridges have water depths much shallower than the carbonate compensation depths(CCD)in the Pacific Ocean.Seismic image shows that a seamount is subducting towards the Novarupta volcano.Subduction of volatile-rich sediments and a slab window nearby are the two most important favorable conditions for catastrophic eruptions.Slab windows expose the mantle wedge to the hot asthenosphere,which increases the temperature and dramatically promotes the partial melting of the carbonate-fluxed domains,forming volatile-rich magmas that powered explosive eruptions.展开更多
This study presents the first systematic investigation of the rock geochemistry,hydrogeochemistry,geochronology,and formation mechanisms of the calcareous travertine-type cold volcano at Muji,Xinjiang.The Muji cold vo...This study presents the first systematic investigation of the rock geochemistry,hydrogeochemistry,geochronology,and formation mechanisms of the calcareous travertine-type cold volcano at Muji,Xinjiang.The Muji cold volcano is composed predominantly of travertine,which exhibited light rare earth element enrichment relative to heavy rare earth elements.The δ^(13)C values range from 7.1‰ to 11.1‰,while δ^(18)O values span from -12.3‰ to -7.8‰,classifying it as hypogean travertine.CO_(2) primarily originates from carbonate rock decarbonation,with a portion derived from the mantle.Water samples collected from the crater show HCO 3-Ca and HCO 3-Ca·Mg hydrochemistry types.U-Th dating of calcite indicates the Muji cold volcano formed between approximately 6.3 and 2.7 ka BP.The morphology and distribution pattern of the cold volcanoes are primarily controlled by hydrostatic pressure and the southwest boundary fault of the Muji Basin.Hydrostatic pressure of groundwater determines the growth height of the cones.The bead-like distribution orientation of the volcanic cones and the major axis direction of the elliptical contour lines of the cones align with the strike of the southwest boundary fault of the Muji Basin,indicating significant control by this fault.展开更多
The 7 ka old Qixiangzhan lava flow(QXZ,Tianchi volcano)represents the last eruptive event before the 946 CE,caldera-forming‘Millennium’eruption(ME).Petrographic,whole rock,mineral composition,Sr-Nd isotopic data on ...The 7 ka old Qixiangzhan lava flow(QXZ,Tianchi volcano)represents the last eruptive event before the 946 CE,caldera-forming‘Millennium’eruption(ME).Petrographic,whole rock,mineral composition,Sr-Nd isotopic data on QXZ show that:(a)the lava consists of two components,constituted by comenditic obsidian fragments immersed in a continuous,aphanitic component;(b)both components have the same geochemical and isotopic variations of the ME magma.The QXZ and ME comendites result from fractional crystallization and crustal assimilation processes.The temperature of the QXZ magma was about 790℃ and the depth of the magma reservoir around 7 km,the same values as estimated for ME.QXZ had a viscosity of 10^(5.5)-10^(9) Pa s and a velocity of 3-10 km/yr.The emplacement time was 0.5-1.6yr and the flow rate 0.48-1.50 m^(3)/s.These values lie within the range estimated for other rhyolitic flows worldwide.The QXZ lava originated through a mixed explosive-effusive activity with the obsidian resulting from the ascent of undercooling,degassing and the fragmentation of magma along the conduit walls,whereas the aphanitic component testifies to the less undercooled and segregated flow at the center of the conduit.The QXZ lava demonstrates the extensive history of the ME magma chamber.展开更多
The phenomenon of mud volcanism has a connection with the processes of hydrocarbon generation.However,the genesis of sediments is not often taken into consideration.The study of mud volcanoes in the West Kuban margina...The phenomenon of mud volcanism has a connection with the processes of hydrocarbon generation.However,the genesis of sediments is not often taken into consideration.The study of mud volcanoes in the West Kuban marginal marine basin and the Junggar freshwater basin revealed significant isotope-geochemical differences due to various types of sedimentation.The waters from both basins exhibit three principal geochemical facies:Na-HCO_(3),Na-Cl-HCO_(3),and Na-Cl,of which the latter type of water is the dominant.The analysis of genetic coefficients(Cl/Br,Na/Br,and B/Cl)allowed us to distinguish different pathways of mud volcanic water evolution:evaporite dissolution,formation(sedimentation)waters,and waters formed by active water-rock interaction.Through statistical research,we were able to determine that noticeable variations in the behavior of chemical elements in waters from different areas can reflect discrepancies in the geological environment and the evolutionary stage of the diagenetic water transformation.Using thermodynamic modeling,the main directions of mass transfer were shown.It was established that the waters of the Junggar Basin were at a relatively early stage of evolution and had reached equilibrium only with carbonates,while in the formation waters of the West Kuban Basin,element concentrations were also controlled by silicate minerals.The correlations betweenδ^(18)O andδ~2H values and saturation indices of halides,aluminosilicates,sulfates,and borates confirm the enrichment of water with heavy isotopes during interactions with rocks without evaporation or thermal water partition.These reactions are characterized by clay dehydration and water enrichment with^(18)O and B.The data obtained made it possible to clarify the depths of formation of mud-volcanic fluids and their possible stratigraphic sources.展开更多
The thought of living near an active volcano probably sounds like an unimaginable experience-and rightly so.An active volcano can turn a forested hillside into a lifeless wasteland in seconds.From molten avalanches of...The thought of living near an active volcano probably sounds like an unimaginable experience-and rightly so.An active volcano can turn a forested hillside into a lifeless wasteland in seconds.From molten avalanches of rock to razor-sharp lung-shredding ash,volcanoes threaten people's lives and property.展开更多
The release of accumulated stress through earthquakes is known to devote to the mud volcanism occurrence,which may in turn affect subsequent regional seismicity.Mud volcanoes have been observed on the northeast contin...The release of accumulated stress through earthquakes is known to devote to the mud volcanism occurrence,which may in turn affect subsequent regional seismicity.Mud volcanoes have been observed on the northeast continental margin of the South China Sea as well.Based on the mud volcanoes and earthquakes catalogue,we measured the spatial and temporal distribution of z and b values,to explore the geodynamic process of the repeated eruptions of mud volcanoes influence on the regional seismicity.The results suggest a close correlation between the b-z values and mud volcanism occurrence in the SW Taiwan.Generally,the z-value anomalies in where the mud volcanoes eruptions show unchanged negative values and indicate seismic quiescence before a big earthquake,whereas the b-values often show periodicity fluctuations around the value of 0.5.This may indicate a mutual triggering relationship between the mud volcanoes and earthquakes.We infer that mud volcano eruptions help to partition and release part of the regional stress accumulation from the seismogenic structures,thus balancing the local stress and mitigating large-magnitude seismicity occurring probability.展开更多
Multifarious regions around the world are exposed to natural hazards and disasters,each with unique characteristics.A higher frequency of extreme hydro-meteorological events,most probably related to climate change,and...Multifarious regions around the world are exposed to natural hazards and disasters,each with unique characteristics.A higher frequency of extreme hydro-meteorological events,most probably related to climate change,and an increase in vulnerable population have been addressed as potential causes of such disasters.To mitigate the consequences of these disasters,Disaster Risk Management,including hazard assessment,elements-at-risk mapping,vulnerability and risk assessment of spatial components as well as Earth Observation(EO)products and Geographic Information Systems(GIS),should be considered.Multihazard assessment entails the evaluation of relationships between various hazards,including interconnected or cascading events,as well as focusing on various levels from global to local community levels,as each level manifests particular objectives and spatial data.This paper presents an overview of the diverse types of spatial data and explores the methods applied in hazard and risk assessments,with volcanic eruptions serving as a specific example.The rapid development of scientific research and the advancement of Earth Observation satellites in recent years have revolutionized the concepts of geologists and researchers.These satellites now play an indispensable role in supporting first responders during major disasters.The coordination of satellite deployment ensures a swift response along with allowing for the timely delivery of critical images.In tandem,remote sensing technologies and geographic information systems(GIS)have emerged as essential tools for geospatial analysis.The application of remote sensing and GIS for the detection of natural disasters was examined through a review of academic papers,offering an analysis of how remote sensing is utilized to assess natural hazards and their link to climate change.展开更多
Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly...Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly known.Here,we present new geochronological,geochemical and isotopic data on two trachytic suites outcropping on the northern and southern upper slopes of TV.Detailed zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry(LA-MC-ICP-MS)U-Pb dating,Rb-Sr isochron dating of plagioclase and hornblende,^(40)Ar/^(39)Ar chronology with mineral chemistry,whole-rock element and Sr-Nd-Pb isotope data are used to explore their origins and evolutionary mechanisms during the late Middle Pleistocene.Our data indicate that the trachytes mainly consist of sanidine,orthoclase and plagioclase,with minor albite,quartz and hornblende.They formed at 0.353-0.346 Ma(lava flow from the northern slope)and 0.383-0.311 Ma(lava flow from the southern slope),respectively.The TV trachytes are characterized by high K_(2)O/Na_(2)O and AR values,with low A/CNK and Mg~#values.They are enriched in rare earth elements(REEs;except Eu),depleted in Sr and Ba,crystallizing at 742-858℃.The TV trachytes have high(^(87)Sr/^(86)Sr)_i values(0.70776-0.71195),positiveε_(Nd)(t)values(0.61-2.93)and radiogenic^(206)Pb/^(204)Pb values(17.515-17.806).These values are similar to those of the Pleistocene and Holocene TV trachytes.Geochemical data indicate that they were formed by fractional crystallization from a basaltic melt and assimilated upper crust material.The trace element pattern of the studied trachytes is consistent with an evolution from basaltic melts representative of an enriched mantle source.The vent from which the trachytic magma was erupted probably collapsed inside the caldera during the TV'Millennium'eruption(ME)in 946 AD.The contemporaneous emission of basaltic and trachytic magma during the Middle-Late Pleistocene suggests the coexistence of fissural basaltic volcanism and central-type trachytic volcanism,the latter of which was associated with a magma chamber in the upper crust during the TV cone-construction stage.展开更多
Subduction zones are critical interfaces for lithospheric volatile fluxes,where complex tectonic and geochemical interactions facilitate the release of gases and fluids from deep-seated reservoirs within the Earth’s ...Subduction zones are critical interfaces for lithospheric volatile fluxes,where complex tectonic and geochemical interactions facilitate the release of gases and fluids from deep-seated reservoirs within the Earth’s crust.Mud volcanism,as a dynamic manifestation of these processes,contributes CH_(4)emissions that influence the global methane budget and impact marine ecosystems.Although∼2000 CH_(4)-rich mud extrusions have been documented in subduction zones globally,the geological origins and subduction-related geochemical and tectonic mechanisms driving these emissions remain poorly understood.This research examines the Makran subduction zone which hosts one of the world’s largest accretionary wedge and extensive CH_(4)-rich mud extrusions,as a model system.Integrated geochemical,geophysical,and geological observations reveal that thermogenic CH_(4)and clay-rich fluidized muds originate from deeply buried Himalayan turbidites(underthrusted sediments),driven by organic-rich sediment maturation and high fluid overpressure.Key tectonic features,including thrust faults,overburden pressure of wedge-top sediments,normal faults,brittle fractures,and seismicity,facilitate CH_(4)-rich mud extrusions into the hydrosphere and atmosphere.The extruded gases are predominantly CH_(4),with minor C_(2)H_(6),C_(3)H_(8),i-C_(4)H_(10),and n-C_(4)H_(10)while the mud breccia exhibits a chemical composition dominated by SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3),enriched with trace elements(Rb,Zr,and V)and clay minerals,quartz,and carbonates.Geochemical indicators suggest intense chemical weathering and mature sediments classifying the mud breccia as litharenite and sub-litharenite,indicative of deep burial and compaction.These findings model the evolution of CH_(4)-rich mud extrusions through three geological stages:(i)Eocene to Early Miocene pre-thermogenic formation of the CH_(4)-rich source,(ii)Middle Miocene to Pliocene syn-thermogenic CH_(4)and fluidized mud generation,and(iii)Pleistocene to Recent post-thermogenic CH_(4)-rich fluidized mud migration.These findings underscore the critical yet often overlooked role of subduction-related geochemical and tectonic processes in CH_(4)generation and emission,with significant implications for the global CH_(4)budget and marine ecosystems.展开更多
[Objective]To seek one effective extraction method of metagenomic DNA from mud volcano.[Method]The metagenomic DNA from mud volcano was extracted by CTAB extraction method,SDS-enzyme method,improved method,reagent kit...[Objective]To seek one effective extraction method of metagenomic DNA from mud volcano.[Method]The metagenomic DNA from mud volcano was extracted by CTAB extraction method,SDS-enzyme method,improved method,reagent kit method.The extraction of four kinds of methods were compared.[Result]The extracted rate in reagent sets method was the highest,next was improved method,the extracted quantity in SDS-enzyme method was maximum.DNA extracted by the improved method was diluted ten times for PCR.[Conclusion]Considering economy and purity,the improved method can be used as one effective extraction method of metagenomic DNA from mud volcano.展开更多
Geohazards,such as earthquakes,landslides, tsunamis,volcanic eruptions,floods,melting permafrost, and metastable soils impact people’s lives worldwide.Population growth is forcing people to live in areas that have cl...Geohazards,such as earthquakes,landslides, tsunamis,volcanic eruptions,floods,melting permafrost, and metastable soils impact people’s lives worldwide.Population growth is forcing people to live in areas that have classically supported low population densities including steep slopes,low-lying coasts,and along floodplains and currently climate change is exacerbating risk in these regions.展开更多
Kueishan Tao (24°51′N, 121°55′E) is located at a tectonic junction of the fault system extension of Taiwan and the southern rifting end of the Okinawa Trough. A cluster of over 30 vents, at a water depth o...Kueishan Tao (24°51′N, 121°55′E) is located at a tectonic junction of the fault system extension of Taiwan and the southern rifting end of the Okinawa Trough. A cluster of over 30 vents, at a water depth of about 10-20 m off the eastern tip of the tao emits hy-drothermal fluids and volcanic gases such as H2S. A sulfur chimney or mound, formed by condensation of the sulfur contained in the hydrothermal fluid, can usually be seen around the vents. The tallest chimney reaches 6 m. Vents discharging a yellowish fluid have temperatures between 92 and 116 ℃ and flow rates as high as 158 t/h; vents discharging a whitish fluid have lower temperatures of between 48 and 62 ℃ and lower flow rates of about 7.0 t/h. These world-record, breaking low pH (as low as 1.52) fluids are totally different from those found in the black and white-chimneys of the mid-ocean ridges. Magnesium and SiO2 data indicate that these hydrothermal fluids probably originate from a depth of 915-1 350 m below the surface.While the ratios of major ions relative to the sodium of these hydrothermal fluids are quite similar to open ocean water, the ratios of SO4 and chloride to sodium seem to be higher for some of the vents. It is suggested that the volcanic gases contribute SO4 and chlorine to the fluids, hence increasing their ratios relative to sodium. Some hydrothermal fluids, however, are found to be depleted of the major elements which can have been caused by phase separation. The concentrations of iron and manganese in the fluids are much lower than those found in the mid-ocean ridges, while the aluminium content is higher. Four species of benthos (Xenograpsus testudi-natus, a snail, a sea anemone, and a Sipuncala), 1 species of algae (Corallinaceae), and 1 species of fish (Siganus fusescens) were recorded near the hydrothermal vents. A mitochondria DNA sequence comparison of Xenograpsus testudinatus with 6 other decapod species shows the greatest number of nitrogen base differences in the DNA fragments from 225 to 270. The gene diversity in this DNA region possibly results from the unusual habitat. A sediment core was collected at a pond near the eastern side of the tao. No volcanic ash could be detected in the core sample spanning 3 620 a.展开更多
Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during ...Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding downstream.展开更多
Three identical model boxes were made from transparent plexiglass and angle iron. Using the method of sinking water and according to the sedimentary rhythm of saturated calcium carbonate （lime-mud） intercalated with...Three identical model boxes were made from transparent plexiglass and angle iron. Using the method of sinking water and according to the sedimentary rhythm of saturated calcium carbonate （lime-mud） intercalated with cohesive soil, calcites with particle sizes diameters of ≤ 5 μm, 10–15 μm and 23–30 μm as well as cohesive soil were sunk alternatively in water of three boxes to build three test models, each of which has a specific size of calcite. Pore water pressure gauges were buried in lime-mud layers at different depths in each model, and connected with a computer system to collect pore water pressures. By means of soil tests, physical property parameters and plasticity indices （Ip） were obtained for various grain-sized saturated lime-muds. The lime-muds with Ip ranging from 6.3 to 8.5 （lower than 10） are similar to liquid saturated silt in the physical nature, indicating that saturated silt can be liquefied once induced by a strong earthquake. One model cart was pushed quickly along the length direction of the model so that its rigid wheels collided violently with the stone stair, thus generating an artificial earthquake with seismic wave magnitude greater than VI degree. When unidirectional cyclic seismic load of horizontal compression-tension-shear was imposed on the soil layers in the model, enough great pore water pressure has been accumulated within pores of lime-mud, resulting in liquefaction of lime-mud layers. Meanwhile, micro-fractures formed in each soil layer provided channels for liquefaction dewatering, resulting in formation of macroscopic liquefaction deformation, such as liquefied lime-mud volcanoes, liquefied diapir structures, vein-like liquefied structures and liquefied curls, etc. Splendid liquefied lime-mud eruption lasted for two to three hours, which is similar to the sand volcano eruption induced by strong earthquake. However, under the same artificial seismic conditions, development of macroscopic liquefied structures in three experimental models varied in shape, depth and quantity, indicating that excess pore water pressure ratios at initial liquefaction stage and complete liquefaction varied with depth. With size increasing of calcite particle in lime-mud, liquefied depth and deformation extent increase accordingly. The simulation test verifies for the first time that strong earthquakes may cause violent liquefaction of saturated lime-mud composed of micron-size calcite particles, uncovering the puzzled issue whether seafloor lime-mud can be liquefied under strong earthquake. This study not only provides the latest simulation data for explaining the earthquake-induced liquefied deformations of saturated lime-mud and seismic sedimentary events, but also is of great significance for analysis of foundation stability in marine engineering built on the soft calcium carbonate layers in neritic environment.展开更多
We synthesize significant recent results on the deep structure and origin of the active volcanoes in China's Mainland. Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subduc...We synthesize significant recent results on the deep structure and origin of the active volcanoes in China's Mainland. Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge, whereas the intraplate magmatism in China has different origins. The active volcanoes in Northeast China （such as the Changbai and Wudalianchi） are caused by hot upwelling in the big mantle wedge （BMW） above the stagnant slab in the mantle transition zone and deep slab dehydration as well. The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate （or Indian plate）. The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs＇ deep subduction in the east and the Indian slab＇s deep subduction in the west down to the lower mantle. The stagnant slab finally collapses down to the bottom of the mantle, which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab-plume interactions.展开更多
The origins of gases in springs, pools and wells from the Wudalianchi (WDLC) volcanic area are discussed based upon molecular and isotope compositions of the gases. Nine gas and water samples were collected from bubbl...The origins of gases in springs, pools and wells from the Wudalianchi (WDLC) volcanic area are discussed based upon molecular and isotope compositions of the gases. Nine gas and water samples were collected from bubbles and water of the springs and pools in the WDLC volcanic area, Northeastern China, in August 1997. The molecular components were measured with a MAT-271 mass spectrometer (MS), helium isotope ratios with a VG-5400 MS, and δ13C with a MAT-251 MS in the Lanzhou Institute of Geology. The gases are enriched in CO2, and most of the CO2 concentrations are over 80% (V). The helium and methane concentrations have relatively wide ranges of 0.7 to 380×10?6 and 4 to 180×10?6, respectively. The 3He/4He ratios are between 1.05 Ra and 3.1 Ra (Ra = 1.4×10?6); the 4He/20Ne values are between 0.45 and 1011, larger than the atmospheric value (0.32). The δ13C (PDB) values of carbon dioxide range from ?9.6 to ?4.2%%. These geochemical data demonstrate that the spring water is from aquifers at different depths, and that helium and carbon dioxide are derived from the mantle, and are contaminated by crust gases during deep fluid migration. Also, there are larger fluxes of deep-earth matter and energy in the WDLC volcanic area.展开更多
Hainan Island is a seismic active region, where Qiongshan M7.5 earthquake occurred in 1605 and several seismic belts appeared in recent years, especially the NS trending seismic belt （NSB） located in the northeast p...Hainan Island is a seismic active region, where Qiongshan M7.5 earthquake occurred in 1605 and several seismic belts appeared in recent years, especially the NS trending seismic belt （NSB） located in the northeast part of the island. Here is also a magmatic active region. The lava from about 100 volcanoes covered more than 4000 km^2. The latest eruptions occurred on Ma＇anling-Lei Huling volcanoes within 10,000 years. The neotectonic movement has been determined by geological method in the island and its adjacent areas. In the paper, the present-day 3D crustal movement is obtained by using Global Positioning System （GPS） data observed from 2009 to 2014 and leveling observations measured in 1970s and 1990s respectively. The results show the horizontal movement is mainly along SEE direction relative to the Eurasian Plate. The velocities are between 4.01 and 6.70 mm/a. The tension rate near the NSB is less than I mm/a. The vertical movement shows the island uplifts as a whole with respect to the reference benchmark Xiuyinggang. The average uplifting rate is 2.4 mm/a. The rates are 2-3 mm/a in the northwest and 3-5mm/a in the northwest. It shows the deformation pattern of the southwest island is upward relative to the northeast, which is different from the result inferred from the coastal change and GPS. Haikou and its adjacent region present a subsidence in a long time. The southern part of the middle segment of the Wangwu-Wenjiao fault uplifts relative to the northern. Meanwhile, the western part uplifts relative to the eastern NSB. The vertical crustal motion and the two normal faults nearly correspond to the terrain. The NSB is located along the Puqiangang-Dazhibo fault, which is assessed as a segmented fault with a dip of 80°-90° and party exposed. The 3D deformations and other studies reveal the present activities of earthquakes, volcanoes and the faults. The small earthquakes will still occur in the NS belt and the volcanoes are not active now.展开更多
Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in thr...Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.展开更多
The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyr...The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyroxene thermometer of Brey and Kohler （1990）, and using the oxybarometry of Nell and Wood （1991）, the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 （n = 8）, which is comparable to that of abyssal peridotites and the asthenospheric mantle. ThefO2 values of peridotites, together with their bulk rock compositions （e.g., Mg#, Al2O3, CaO, Ni, Co, Cr） and mineral compositions （e.g., Mg# of olivine and pyroxene, Cr# [=Cr/ [Cr＋Al]] and Mg# [=Mg/[Mg＋Fe2~] of spinel）, suggest that the present-day subcontinental lithospheric mantle （SCLM） beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements （PGE）, which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field （LVF） in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton （NCC） in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospberic mantle.展开更多
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA22050103)the Taishan Scholar Program of Shandong(No.ts201712075)。
文摘The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and where are the danger zones.Three largest eruptions since 1900,the Hunga Tonga-Hunga Ha’apai,the Mt.Pinatubo,and the Novarupta were found to be associated with subductions of volatile-rich sediments and located close to slab windows.Among them,the Hunga Tonga-Hunga Ha’apai is close to subducting seamount chains;the Mt.Pinatubo is right next to subducting fossil ridges.Both seamount chains and fossil ridges have water depths much shallower than the carbonate compensation depths(CCD)in the Pacific Ocean.Seismic image shows that a seamount is subducting towards the Novarupta volcano.Subduction of volatile-rich sediments and a slab window nearby are the two most important favorable conditions for catastrophic eruptions.Slab windows expose the mantle wedge to the hot asthenosphere,which increases the temperature and dramatically promotes the partial melting of the carbonate-fluxed domains,forming volatile-rich magmas that powered explosive eruptions.
基金supported by the National Natural Science Foundation of China(Grant No.42272349).
文摘This study presents the first systematic investigation of the rock geochemistry,hydrogeochemistry,geochronology,and formation mechanisms of the calcareous travertine-type cold volcano at Muji,Xinjiang.The Muji cold volcano is composed predominantly of travertine,which exhibited light rare earth element enrichment relative to heavy rare earth elements.The δ^(13)C values range from 7.1‰ to 11.1‰,while δ^(18)O values span from -12.3‰ to -7.8‰,classifying it as hypogean travertine.CO_(2) primarily originates from carbonate rock decarbonation,with a portion derived from the mantle.Water samples collected from the crater show HCO 3-Ca and HCO 3-Ca·Mg hydrochemistry types.U-Th dating of calcite indicates the Muji cold volcano formed between approximately 6.3 and 2.7 ka BP.The morphology and distribution pattern of the cold volcanoes are primarily controlled by hydrostatic pressure and the southwest boundary fault of the Muji Basin.Hydrostatic pressure of groundwater determines the growth height of the cones.The bead-like distribution orientation of the volcanic cones and the major axis direction of the elliptical contour lines of the cones align with the strike of the southwest boundary fault of the Muji Basin,indicating significant control by this fault.
基金funded by the National Natural Science Foundation of China(Grant Nos.41972313 and 41790453)the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University。
文摘The 7 ka old Qixiangzhan lava flow(QXZ,Tianchi volcano)represents the last eruptive event before the 946 CE,caldera-forming‘Millennium’eruption(ME).Petrographic,whole rock,mineral composition,Sr-Nd isotopic data on QXZ show that:(a)the lava consists of two components,constituted by comenditic obsidian fragments immersed in a continuous,aphanitic component;(b)both components have the same geochemical and isotopic variations of the ME magma.The QXZ and ME comendites result from fractional crystallization and crustal assimilation processes.The temperature of the QXZ magma was about 790℃ and the depth of the magma reservoir around 7 km,the same values as estimated for ME.QXZ had a viscosity of 10^(5.5)-10^(9) Pa s and a velocity of 3-10 km/yr.The emplacement time was 0.5-1.6yr and the flow rate 0.48-1.50 m^(3)/s.These values lie within the range estimated for other rhyolitic flows worldwide.The QXZ lava originated through a mixed explosive-effusive activity with the obsidian resulting from the ascent of undercooling,degassing and the fragmentation of magma along the conduit walls,whereas the aphanitic component testifies to the less undercooled and segregated flow at the center of the conduit.The QXZ lava demonstrates the extensive history of the ME magma chamber.
基金partly supported by the NSFC-RSF Joint Research project(Nos.42261134534,23-47-00035)funded by the Chinese Academy of Sciences President’s International Fellowship Initiative(Nos.2024VCA0006,2024VCB0013)the National Natural Science Foundation of China(No.42442006)。
文摘The phenomenon of mud volcanism has a connection with the processes of hydrocarbon generation.However,the genesis of sediments is not often taken into consideration.The study of mud volcanoes in the West Kuban marginal marine basin and the Junggar freshwater basin revealed significant isotope-geochemical differences due to various types of sedimentation.The waters from both basins exhibit three principal geochemical facies:Na-HCO_(3),Na-Cl-HCO_(3),and Na-Cl,of which the latter type of water is the dominant.The analysis of genetic coefficients(Cl/Br,Na/Br,and B/Cl)allowed us to distinguish different pathways of mud volcanic water evolution:evaporite dissolution,formation(sedimentation)waters,and waters formed by active water-rock interaction.Through statistical research,we were able to determine that noticeable variations in the behavior of chemical elements in waters from different areas can reflect discrepancies in the geological environment and the evolutionary stage of the diagenetic water transformation.Using thermodynamic modeling,the main directions of mass transfer were shown.It was established that the waters of the Junggar Basin were at a relatively early stage of evolution and had reached equilibrium only with carbonates,while in the formation waters of the West Kuban Basin,element concentrations were also controlled by silicate minerals.The correlations betweenδ^(18)O andδ~2H values and saturation indices of halides,aluminosilicates,sulfates,and borates confirm the enrichment of water with heavy isotopes during interactions with rocks without evaporation or thermal water partition.These reactions are characterized by clay dehydration and water enrichment with^(18)O and B.The data obtained made it possible to clarify the depths of formation of mud-volcanic fluids and their possible stratigraphic sources.
文摘The thought of living near an active volcano probably sounds like an unimaginable experience-and rightly so.An active volcano can turn a forested hillside into a lifeless wasteland in seconds.From molten avalanches of rock to razor-sharp lung-shredding ash,volcanoes threaten people's lives and property.
基金supported by the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(No.SML2021SP318)the National Postdoctoral Program for Innovative Talents(No.BX20190391)+1 种基金the Guangdong Province Introduced Innovative R&D Team of Geological Processes and Natural Disasters around the South China Sea founded by the Science and Technology Department of Guangdong Province(No.2016ZT06N331)the Guangdong Basic and Applied Basic Research Foundation(Nos.2019A1515110305,2021A1515011130,2021A1515110288)。
文摘The release of accumulated stress through earthquakes is known to devote to the mud volcanism occurrence,which may in turn affect subsequent regional seismicity.Mud volcanoes have been observed on the northeast continental margin of the South China Sea as well.Based on the mud volcanoes and earthquakes catalogue,we measured the spatial and temporal distribution of z and b values,to explore the geodynamic process of the repeated eruptions of mud volcanoes influence on the regional seismicity.The results suggest a close correlation between the b-z values and mud volcanism occurrence in the SW Taiwan.Generally,the z-value anomalies in where the mud volcanoes eruptions show unchanged negative values and indicate seismic quiescence before a big earthquake,whereas the b-values often show periodicity fluctuations around the value of 0.5.This may indicate a mutual triggering relationship between the mud volcanoes and earthquakes.We infer that mud volcano eruptions help to partition and release part of the regional stress accumulation from the seismogenic structures,thus balancing the local stress and mitigating large-magnitude seismicity occurring probability.
文摘Multifarious regions around the world are exposed to natural hazards and disasters,each with unique characteristics.A higher frequency of extreme hydro-meteorological events,most probably related to climate change,and an increase in vulnerable population have been addressed as potential causes of such disasters.To mitigate the consequences of these disasters,Disaster Risk Management,including hazard assessment,elements-at-risk mapping,vulnerability and risk assessment of spatial components as well as Earth Observation(EO)products and Geographic Information Systems(GIS),should be considered.Multihazard assessment entails the evaluation of relationships between various hazards,including interconnected or cascading events,as well as focusing on various levels from global to local community levels,as each level manifests particular objectives and spatial data.This paper presents an overview of the diverse types of spatial data and explores the methods applied in hazard and risk assessments,with volcanic eruptions serving as a specific example.The rapid development of scientific research and the advancement of Earth Observation satellites in recent years have revolutionized the concepts of geologists and researchers.These satellites now play an indispensable role in supporting first responders during major disasters.The coordination of satellite deployment ensures a swift response along with allowing for the timely delivery of critical images.In tandem,remote sensing technologies and geographic information systems(GIS)have emerged as essential tools for geospatial analysis.The application of remote sensing and GIS for the detection of natural disasters was examined through a review of academic papers,offering an analysis of how remote sensing is utilized to assess natural hazards and their link to climate change.
基金financially supported by the project of the National Observation and Research Station of the Institute of Geology,China Earthquake Administration(Grant No.NORSCBS22-06)the Youth Science and Technology Development Project of the Jilin Earthquake Agency(Grant No.JZQ-202402)+1 种基金the Earthquake Science and Technology Spark Project(Grant No.XH23013B)the China Scholarship Council(Grant No.202104190014)。
文摘Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly known.Here,we present new geochronological,geochemical and isotopic data on two trachytic suites outcropping on the northern and southern upper slopes of TV.Detailed zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry(LA-MC-ICP-MS)U-Pb dating,Rb-Sr isochron dating of plagioclase and hornblende,^(40)Ar/^(39)Ar chronology with mineral chemistry,whole-rock element and Sr-Nd-Pb isotope data are used to explore their origins and evolutionary mechanisms during the late Middle Pleistocene.Our data indicate that the trachytes mainly consist of sanidine,orthoclase and plagioclase,with minor albite,quartz and hornblende.They formed at 0.353-0.346 Ma(lava flow from the northern slope)and 0.383-0.311 Ma(lava flow from the southern slope),respectively.The TV trachytes are characterized by high K_(2)O/Na_(2)O and AR values,with low A/CNK and Mg~#values.They are enriched in rare earth elements(REEs;except Eu),depleted in Sr and Ba,crystallizing at 742-858℃.The TV trachytes have high(^(87)Sr/^(86)Sr)_i values(0.70776-0.71195),positiveε_(Nd)(t)values(0.61-2.93)and radiogenic^(206)Pb/^(204)Pb values(17.515-17.806).These values are similar to those of the Pleistocene and Holocene TV trachytes.Geochemical data indicate that they were formed by fractional crystallization from a basaltic melt and assimilated upper crust material.The trace element pattern of the studied trachytes is consistent with an evolution from basaltic melts representative of an enriched mantle source.The vent from which the trachytic magma was erupted probably collapsed inside the caldera during the TV'Millennium'eruption(ME)in 946 AD.The contemporaneous emission of basaltic and trachytic magma during the Middle-Late Pleistocene suggests the coexistence of fissural basaltic volcanism and central-type trachytic volcanism,the latter of which was associated with a magma chamber in the upper crust during the TV cone-construction stage.
基金funded by the National Natural Science Foundation of China(Grants No.92058213 and No.U22A20581)the Specific Research Fund of the Innovation Platform for Academicians of Hainan Province(Grant No.YSPTZX202204)key R&D projects of Hainan Province(ZDYF2024GXJS022).
文摘Subduction zones are critical interfaces for lithospheric volatile fluxes,where complex tectonic and geochemical interactions facilitate the release of gases and fluids from deep-seated reservoirs within the Earth’s crust.Mud volcanism,as a dynamic manifestation of these processes,contributes CH_(4)emissions that influence the global methane budget and impact marine ecosystems.Although∼2000 CH_(4)-rich mud extrusions have been documented in subduction zones globally,the geological origins and subduction-related geochemical and tectonic mechanisms driving these emissions remain poorly understood.This research examines the Makran subduction zone which hosts one of the world’s largest accretionary wedge and extensive CH_(4)-rich mud extrusions,as a model system.Integrated geochemical,geophysical,and geological observations reveal that thermogenic CH_(4)and clay-rich fluidized muds originate from deeply buried Himalayan turbidites(underthrusted sediments),driven by organic-rich sediment maturation and high fluid overpressure.Key tectonic features,including thrust faults,overburden pressure of wedge-top sediments,normal faults,brittle fractures,and seismicity,facilitate CH_(4)-rich mud extrusions into the hydrosphere and atmosphere.The extruded gases are predominantly CH_(4),with minor C_(2)H_(6),C_(3)H_(8),i-C_(4)H_(10),and n-C_(4)H_(10)while the mud breccia exhibits a chemical composition dominated by SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3),enriched with trace elements(Rb,Zr,and V)and clay minerals,quartz,and carbonates.Geochemical indicators suggest intense chemical weathering and mature sediments classifying the mud breccia as litharenite and sub-litharenite,indicative of deep burial and compaction.These findings model the evolution of CH_(4)-rich mud extrusions through three geological stages:(i)Eocene to Early Miocene pre-thermogenic formation of the CH_(4)-rich source,(ii)Middle Miocene to Pliocene syn-thermogenic CH_(4)and fluidized mud generation,and(iii)Pleistocene to Recent post-thermogenic CH_(4)-rich fluidized mud migration.These findings underscore the critical yet often overlooked role of subduction-related geochemical and tectonic processes in CH_(4)generation and emission,with significant implications for the global CH_(4)budget and marine ecosystems.
基金Supported by National Natural Science Foundation of China~~
文摘[Objective]To seek one effective extraction method of metagenomic DNA from mud volcano.[Method]The metagenomic DNA from mud volcano was extracted by CTAB extraction method,SDS-enzyme method,improved method,reagent kit method.The extraction of four kinds of methods were compared.[Result]The extracted rate in reagent sets method was the highest,next was improved method,the extracted quantity in SDS-enzyme method was maximum.DNA extracted by the improved method was diluted ten times for PCR.[Conclusion]Considering economy and purity,the improved method can be used as one effective extraction method of metagenomic DNA from mud volcano.
文摘Geohazards,such as earthquakes,landslides, tsunamis,volcanic eruptions,floods,melting permafrost, and metastable soils impact people’s lives worldwide.Population growth is forcing people to live in areas that have classically supported low population densities including steep slopes,low-lying coasts,and along floodplains and currently climate change is exacerbating risk in these regions.
文摘Kueishan Tao (24°51′N, 121°55′E) is located at a tectonic junction of the fault system extension of Taiwan and the southern rifting end of the Okinawa Trough. A cluster of over 30 vents, at a water depth of about 10-20 m off the eastern tip of the tao emits hy-drothermal fluids and volcanic gases such as H2S. A sulfur chimney or mound, formed by condensation of the sulfur contained in the hydrothermal fluid, can usually be seen around the vents. The tallest chimney reaches 6 m. Vents discharging a yellowish fluid have temperatures between 92 and 116 ℃ and flow rates as high as 158 t/h; vents discharging a whitish fluid have lower temperatures of between 48 and 62 ℃ and lower flow rates of about 7.0 t/h. These world-record, breaking low pH (as low as 1.52) fluids are totally different from those found in the black and white-chimneys of the mid-ocean ridges. Magnesium and SiO2 data indicate that these hydrothermal fluids probably originate from a depth of 915-1 350 m below the surface.While the ratios of major ions relative to the sodium of these hydrothermal fluids are quite similar to open ocean water, the ratios of SO4 and chloride to sodium seem to be higher for some of the vents. It is suggested that the volcanic gases contribute SO4 and chlorine to the fluids, hence increasing their ratios relative to sodium. Some hydrothermal fluids, however, are found to be depleted of the major elements which can have been caused by phase separation. The concentrations of iron and manganese in the fluids are much lower than those found in the mid-ocean ridges, while the aluminium content is higher. Four species of benthos (Xenograpsus testudi-natus, a snail, a sea anemone, and a Sipuncala), 1 species of algae (Corallinaceae), and 1 species of fish (Siganus fusescens) were recorded near the hydrothermal vents. A mitochondria DNA sequence comparison of Xenograpsus testudinatus with 6 other decapod species shows the greatest number of nitrogen base differences in the DNA fragments from 225 to 270. The gene diversity in this DNA region possibly results from the unusual habitat. A sediment core was collected at a pond near the eastern side of the tao. No volcanic ash could be detected in the core sample spanning 3 620 a.
基金The research was funded by the Natural Science Foundation of China(40172033)and the state volcano program of the tenth Five-Year Plan period(2001BA601B06-01-4).
文摘Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding downstream.
基金supported by the National Natural Science Foundation of China(NSFC-41272066)the Program for Changjiang Scholars & Innovative Research Team of the University of China(IRT-13075)
文摘Three identical model boxes were made from transparent plexiglass and angle iron. Using the method of sinking water and according to the sedimentary rhythm of saturated calcium carbonate （lime-mud） intercalated with cohesive soil, calcites with particle sizes diameters of ≤ 5 μm, 10–15 μm and 23–30 μm as well as cohesive soil were sunk alternatively in water of three boxes to build three test models, each of which has a specific size of calcite. Pore water pressure gauges were buried in lime-mud layers at different depths in each model, and connected with a computer system to collect pore water pressures. By means of soil tests, physical property parameters and plasticity indices （Ip） were obtained for various grain-sized saturated lime-muds. The lime-muds with Ip ranging from 6.3 to 8.5 （lower than 10） are similar to liquid saturated silt in the physical nature, indicating that saturated silt can be liquefied once induced by a strong earthquake. One model cart was pushed quickly along the length direction of the model so that its rigid wheels collided violently with the stone stair, thus generating an artificial earthquake with seismic wave magnitude greater than VI degree. When unidirectional cyclic seismic load of horizontal compression-tension-shear was imposed on the soil layers in the model, enough great pore water pressure has been accumulated within pores of lime-mud, resulting in liquefaction of lime-mud layers. Meanwhile, micro-fractures formed in each soil layer provided channels for liquefaction dewatering, resulting in formation of macroscopic liquefaction deformation, such as liquefied lime-mud volcanoes, liquefied diapir structures, vein-like liquefied structures and liquefied curls, etc. Splendid liquefied lime-mud eruption lasted for two to three hours, which is similar to the sand volcano eruption induced by strong earthquake. However, under the same artificial seismic conditions, development of macroscopic liquefied structures in three experimental models varied in shape, depth and quantity, indicating that excess pore water pressure ratios at initial liquefaction stage and complete liquefaction varied with depth. With size increasing of calcite particle in lime-mud, liquefied depth and deformation extent increase accordingly. The simulation test verifies for the first time that strong earthquakes may cause violent liquefaction of saturated lime-mud composed of micron-size calcite particles, uncovering the puzzled issue whether seafloor lime-mud can be liquefied under strong earthquake. This study not only provides the latest simulation data for explaining the earthquake-induced liquefied deformations of saturated lime-mud and seismic sedimentary events, but also is of great significance for analysis of foundation stability in marine engineering built on the soft calcium carbonate layers in neritic environment.
基金partially supported by Grant-in-aid for Scientific Research(Kiban-B.11440134,Kiban-A 17204037) from Japan Society for the Promotion of Science and by some financial support from the Global Center of Excellence(G-COE) program of Tohoku University
文摘We synthesize significant recent results on the deep structure and origin of the active volcanoes in China's Mainland. Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge, whereas the intraplate magmatism in China has different origins. The active volcanoes in Northeast China （such as the Changbai and Wudalianchi） are caused by hot upwelling in the big mantle wedge （BMW） above the stagnant slab in the mantle transition zone and deep slab dehydration as well. The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate （or Indian plate）. The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs＇ deep subduction in the east and the Indian slab＇s deep subduction in the west down to the lower mantle. The stagnant slab finally collapses down to the bottom of the mantle, which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab-plume interactions.
文摘The origins of gases in springs, pools and wells from the Wudalianchi (WDLC) volcanic area are discussed based upon molecular and isotope compositions of the gases. Nine gas and water samples were collected from bubbles and water of the springs and pools in the WDLC volcanic area, Northeastern China, in August 1997. The molecular components were measured with a MAT-271 mass spectrometer (MS), helium isotope ratios with a VG-5400 MS, and δ13C with a MAT-251 MS in the Lanzhou Institute of Geology. The gases are enriched in CO2, and most of the CO2 concentrations are over 80% (V). The helium and methane concentrations have relatively wide ranges of 0.7 to 380×10?6 and 4 to 180×10?6, respectively. The 3He/4He ratios are between 1.05 Ra and 3.1 Ra (Ra = 1.4×10?6); the 4He/20Ne values are between 0.45 and 1011, larger than the atmospheric value (0.32). The δ13C (PDB) values of carbon dioxide range from ?9.6 to ?4.2%%. These geochemical data demonstrate that the spring water is from aquifers at different depths, and that helium and carbon dioxide are derived from the mantle, and are contaminated by crust gases during deep fluid migration. Also, there are larger fluxes of deep-earth matter and energy in the WDLC volcanic area.
基金supported by the National Natural Science Foundation of China(41372345)
文摘Hainan Island is a seismic active region, where Qiongshan M7.5 earthquake occurred in 1605 and several seismic belts appeared in recent years, especially the NS trending seismic belt （NSB） located in the northeast part of the island. Here is also a magmatic active region. The lava from about 100 volcanoes covered more than 4000 km^2. The latest eruptions occurred on Ma＇anling-Lei Huling volcanoes within 10,000 years. The neotectonic movement has been determined by geological method in the island and its adjacent areas. In the paper, the present-day 3D crustal movement is obtained by using Global Positioning System （GPS） data observed from 2009 to 2014 and leveling observations measured in 1970s and 1990s respectively. The results show the horizontal movement is mainly along SEE direction relative to the Eurasian Plate. The velocities are between 4.01 and 6.70 mm/a. The tension rate near the NSB is less than I mm/a. The vertical movement shows the island uplifts as a whole with respect to the reference benchmark Xiuyinggang. The average uplifting rate is 2.4 mm/a. The rates are 2-3 mm/a in the northwest and 3-5mm/a in the northwest. It shows the deformation pattern of the southwest island is upward relative to the northeast, which is different from the result inferred from the coastal change and GPS. Haikou and its adjacent region present a subsidence in a long time. The southern part of the middle segment of the Wangwu-Wenjiao fault uplifts relative to the northern. Meanwhile, the western part uplifts relative to the eastern NSB. The vertical crustal motion and the two normal faults nearly correspond to the terrain. The NSB is located along the Puqiangang-Dazhibo fault, which is assessed as a segmented fault with a dip of 80°-90° and party exposed. The 3D deformations and other studies reveal the present activities of earthquakes, volcanoes and the faults. The small earthquakes will still occur in the NS belt and the volcanoes are not active now.
基金funded by the National Natural Science Foundation of China under Grant Nos.41972313 and 41790453by the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University,China.
文摘Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.
基金supported by grants from National Natural Science Foundation of China (Nos.40873016,41173034,90814003)supportedby a grant from China Geological Survey (No.1212011121088)
文摘The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyroxene thermometer of Brey and Kohler （1990）, and using the oxybarometry of Nell and Wood （1991）, the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 （n = 8）, which is comparable to that of abyssal peridotites and the asthenospheric mantle. ThefO2 values of peridotites, together with their bulk rock compositions （e.g., Mg#, Al2O3, CaO, Ni, Co, Cr） and mineral compositions （e.g., Mg# of olivine and pyroxene, Cr# [=Cr/ [Cr＋Al]] and Mg# [=Mg/[Mg＋Fe2~] of spinel）, suggest that the present-day subcontinental lithospheric mantle （SCLM） beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements （PGE）, which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field （LVF） in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton （NCC） in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospberic mantle.
