Deep structure and origin of active volcanoes in China

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.

Three-dimensional crustal movement and the activities of earthquakes,volcanoes and faults in Hainan Island,China

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.

Baossi–Warack monogenetic volcanoes, Adamawa Plateau,Cameroon: petrography, mineralogy and geochemistry

Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line(CVL) are documented in this study. Basaltic lavas(<1 km^3) scattered around these vents and restricted volcaniclastic deposits were emplaced by Hawaiian and mild strombolian style eruptions. The lavas are porphyritic, mainly composed of olivine(chrysolite) and clinopyroxene(diopside and augite) phenocrysts and plagioclase(andesine) microphenocrysts. Accessory minerals include titano-magnetite and titano-hematite, nepheline,apatite and amphibole xenocrysts. Sanidine occurs in some samples and sodi-potassic albite in others. Some olivines and clinopyroxenes exhibit resorbed margins and thin reaction rims while plagioclase displays oscillatory zoning, and sieved textures as a result of magma mixing. Whole-rock geochemistry data indicates that the lavas are silica-undersaturated, composed of basanites and basalts, showing little compositional variations(SiO_2: 39.20 wt.%–48.01 wt.%,MgO: 5.29 wt.%–9.70 wt.%). Trace elements patterns of these lavas suggest they are enriched in LILE including Pb,probably due to crustal contamination. REE patterns suggest cogenetic magmas below Baossi 1 and Baossi 2 volcanoes,and distinct sources below Warack volcano and nearby lavas.The lavas studied show affinity to high-μ(HIMU), enriched type Ⅰ(EM1) and Oceanic Island Basalt(OIB)-like mantle signatures and thus indicate a heterogeneous mantle source underneath the vents as noted at other monogenetic and polygenetic volcanoes along the CVL. Primary melts derived from low degrees of partial melting(0.5%–2%) and encountered low rates of fractionation, and crustal contamination coupled with magma mixing. These melts evolved independently through structural weaknesses in the basement.

Deep geodynamics of far field interconti- nental back-arc extension: Formation of Cenozoic volcanoes in northeastern China

There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench ad- vancing, and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate subducts at low angle beneath the Eurasia plate, tomographic results indicate that the subducted Pacific slab does not penetrate the 670 km discontinuity, instead, it is lying flat above the interface. The flattening occurred about 28 Ma ago. Geo- dynamic computation suggests: when the frontier of the subducted slab reaches the phase boundary of lower and upper mantle, it may be hindered and turn flat lying above the boundary, facilitates the retreat of trench and back-arc extension. Volcanism in northeastern China is likely a product of such retreat of subduction, far field back-arc extension, and melting due to reduce of pressure while mantle upwelling.

FEASIBLE STUDY ON THE INTEGRATION SYSTEM FOR THE SPACE MONITORING OF MAJOR EARTHQUAKES AND VOLCANOES IN TERRESTRIAL LAND

With the rapid development of space technology,earth observation tech nology and sky observatory technolo-gy,they have played a more and more im portant part in monitoring and predi cting of earthquakes and volcanoes i n the terres-trial land.In recent years,the rela ted agencies have done the experimen ts and researches on monitoring and p redicting of earthquakes and volcanoes in the forewarning period by means of many appr oaches,such as satellite thermal in frared re-mote sensing(TIRS),Global Positioning System(GPS),differential interferometric syn thesis aperture radar(D-INSAR),astronomical time-latitude residual anomaly,and Geographic Information Systems (GIS),etc.A quite large number of re-search foundation has been built in t he fundamental theories and applica tion methods.The experiments and re searches have shown that these technology is e fficient methods for high frequency crust movement.If the existed separate scientific forces and results are possibly asse mbled together to form a more complete integration monitoring system wit h the combina-tion of space,sky observation,grou nd,deep geology and macro anomaly,i t will come into a new stage of monitoring and predicting of earthquakes and volca nic eruptions.

Mud volcanoes in the South Caspian basin: Nature and estimated depth of its products

In paper based on the results of previous studies and latest investigations of mud volcanoes in the South Caspian basin the depth occurrence of fluid, mud and rocks are calculated and modeled. Major factors causing formation of diapirism/mud volcanism in the South Caspian basin are Pliocene-Quaternary high sedimentation rates (up to 3 km/my), super thick sedimentary cover (up to 25-30 km), predominance of clayey rocks (reaching 80%) in the section, low temperatures (with 15℃-18℃/km gradient), overpressures reaching lithostatic, the onset of petroleum generation lowered to considerable depths. The majority of the mud volcanoes are associated with the petroleum bearing structures. Depths where the liquid, gaseous and solid products of mud volcanoes are sourced appear to be different. The gases have the deepest roots (7-15 km) which are the main force in formation and activity of MVs. Source of the fluidized clayey mass does not lie below 3-4 km. Oils emitted by mud volcanoes are the product of destruction of petroleum accumulations occurring beneath them.

Geochemistry and Tectonic Setting of Kohe Siahvolcanoes, North Qorveh, Sanandaj, Iran

The KoheSiah Volcanoes are located in the North of Qorveh city in the west of Iran. The KoheSiah volcanoes include several craters bearing domes located in the Kordestan Province, between latitudes 35&#176;23'13.54” to 35&#176;21'26.63”N and longitudes 47&#176;54'38.26”E to 47&#176;56'01.42”E. Based on the petrographic and geochemical analysis, the volcanic rocks in the KoheSiah area are classified as basalt, Alkali basalt, trachy-andesites and mugearite. The studied samples are alkaline with sodic to potasic feature based on Na2O/K2O ratios and belonging to Shoshonite series. Most of the alkaline volcanic rocks in the study area fall in the field of within in plate basalts (WPB) and represent of a mantle metasomatism trend associated with variable degrees in the partial melting of an enriched mantle source.

Yanshan, Gaoshan-Two Active Volcanoes of the Volcanic Cluster in Arshan, Inner Mongolia

The volcanic cluster in Arshan, inner Mongolia, is located in the west of the middle section of the Da Hinggan Mountains. There are more than forty Cenozoic volcanoes among which the Yanshan Volcano and Gaoshan Volcano are the active ones in broad sense and basaltic central vents. Arshan is a newly found volcanic active region in the Chinese continent. The volcanoes are perfectly preserved and composed of cinder cones, pyroclastic sheets and lava flows. Their cones are grand and the Gaoshan cone is about 362m high, and the depth of the Yanshan crater is about 140m. The pyroclastic sheet is mainly made up of scoria, and the distribution area of scoria with thickness more than i m is about 27km^2 . There are two Carbonized-wood sites in the pyroclastic sheet and the ^14C datings indicate ages of 1990±100a B. P and 1900 ±70a B. P, which are rectified by dendrodating. Basaltic lava flows are uncovered, and they change from pahoehoe in the early stage to aa in the later stage. There are lots of perfect fumarolic cones, fumarolic dishes and lava tumulus in the front zones. The spread of lava flow is controlled by the local topography and its main body flowed northwestwards covering the Holocene rivers and swamp deposits and blocked up the Halahahe river and its branches to create six lava-dam lakes. For these distinguishing features, Arshan volcanic cluster could be called another natural “Volcano Museum”.

Combustion Metamorphic Rocks as a Sign of Ancient Mud Volcanoes

Zones of combustion metamorphism(CM)are frequently associated with oil fields and adjacent bituminous marine sediments.A typical example is the Mottled Zone(MZ)complexes located within carbonate strata at the western margin of the Arabian petroleum province(Israel,Jordan).Being localized upon the eroded surface of Upper Cretaceous stratum, the MZ complexes are composed of brecciated sediments of the underlying Cretaceous sequence uplifted from depths of at least 1.5 km.They

Seismic Signature Analysis for Clarification of Mud Volcanoes from the New Mud Diapirs Discovered at the NE-SW Moroccan Atlantic Margin

Our aim is to clarify mud volcanoes from the new mud diapirs resulting from the seismic attributes analysis applied to the low resolution Burmah oil “1973-1974” seismic data. The latter was carried out on the Larache and Tanger-Larache offshores from the NE-SW Atlantic margin. The high resolution seismic data was essential for this evaluation. In this case, we applied seismic signature analysis to four seismic profiles from the map of the seismic data set, which includes all new mud diapirs. This helped us to classify different types of mud diapirs within the seismic profiles. And as a result, six deep mud diapirs from the Prerifaine Nappe of Morocco, a shallow mud diapir, and four seafloor-piercing mud diapirs have been observed. Furthermore, the seafloor-piercing mud diapirs show a mushroom-shaped and conical-shaped cone. As they break through the seafloor, these kinds of cones characterize mud volcanoes. In this case, we may conclude that the resultant seafloor-piercing mud diapirs are likely to be mud volcanoes. However, more geological sampling and seafloor observation are still required.

Towards a Volumetric Variation of Lake Kivu Gases by the Nyamulagira and Nyiragongo Volcanoes

After the volcanic eruption of January 17th, 2002, Goma Volcano Observatory (OVG) initiated carbon dioxide (CO2) monitoring in the fractures south of the Nyiragongo volcano and at the northern edge of Lake Kivu. During the period from March 17th, 2017 to June 10th, 2020, twice a week, a GA 5000 gasometer was used for CO2 in the fractures as well as in the mazukus, respectively, as part of a project funded by the Kingdom of the Netherlands through the Lake Kivu Monitoring Program (LKMP) in Rwanda. The level of volcanic activity was determined by the volume of gas emitted by the volcano and measured by a DOAS and the seismicity measured by a network of 15 seismometers managed by the OVG. The results show that the concentration of CO2 in the active fractures from recent Nyiragongo eruptions varies with volcanic activity and the occurrence of a large earthquake in the East African Rift;but in the mazukus there is almost no relationship between CO2 content and volcanic activity. The study also shows that the influence of carbon dioxide in mazukus on the carbon dioxide into the Lake Kivu waters remains a major research question. The purpose of this study is to establish the relationship between the existing Carbon Dioxide (mazukus) in the Northern watershed and that of the deep waters of Lake Kivu.

Volcanoes

In the past thousand years,volcanoes have claimed more than 300,000 lives. Volcanology is ayoung and dangerous science that helps us against the power of the Earth itself.We live on a fiery planet. Nearly 2000 miles beneath our feet, the Earth's inner core reachestemperatures of 12,000 degrees Fahrenheit. Molten rock or magma, rises to the earth's surface. Acold, rigid crust fractured into some twenty plates. When magma breaks through crust it

The Applicability and Productiveness of a Systematic Literature Review Methodology in Volcanology Research: Case of the Magma Pathway at the Mount Cameroon Volcano

The presented research illustrates the applicability and productiveness of the systematic literature review methodology, a non-empirical methodology in the geological sciences, particularly volcanology. The systematic literature review methodology is a replicable, rigorous, and transparent methodology for synthesizing existing literature to answer questions on a specific topic. The synthesis allows for knowledge consolidation, such as identifying knowledge gaps. In our illustration of this methodology, we focused on the expanding knowledge about the magma pathway at Mount Cameroon, one of Africa’s active volcanoes. Our synthesis of the relevant international geoscience research literature is based on the framework of knowledge about the magma pathway beneath a typical basaltic volcano. The framework has three primary components: magma supply, storage, and transport to erupting vents. Across these components is a total of twelve secondary components. The result is a previously non-existent and fragmented overall understanding of the magma pathway at Mount Cameroon. The gaps in the understanding (such as in the magma supply rates, timescales of chamber processes, and magma ascent rates) may be addressed in future research. Another key implication of the presented research lies in the proof of concept of the systematic literature review methodology as an applicable qualitative research methodology in the study of volcanoes.

Detection of a mud volcano in the Weitan Banks area of the northern South China Sea

Situated between the petroliferous Cenozoic Zhujiang(Pearl)River Mouth Basin and the mud volcano-rich Mesozoic Dongsha Basin in the middle sector of the northern South China Sea,the Weitan Banks area has been previously mapped as a basement high that is composed of Mesozoic magmatic rocks.In this study,we present several favorable indicators for petroleum geology that were detected from geophysical profiling and benthic sampling in the area.A conspicuous hill was discovered,named“Zhongwei Hill”,~80 m high above the~340 m deep seafloor and~1 km broad,in a depression with more than 7 km thick sedimentary strata.The Zhongwei Hill was seismically imaged with a mushroom-shaped structure and containing a cake-like crown,fluid flow pipes,and an~10 km broad anticline at depth.Thus,the hill represents a source-plumbing-eruption system.Shallow gas zones linked to deep fracture were found at or near the hill.Stratigraphic correlation indicates that the deep strata comprise the Jurassic and Paleogene strata,the major hosts of hydrocarbon source rocks.In addition to the hill,there are number of mounds from which three bottom water samples were collected and the samples are rich in dissolved methane with concentrations high up to~900 nmol/L,much higher than the background level(0.5–2 nmol/L).The benthic samples are rich in coarse sediment clastics,authigenic carbonate nodules,and deep-water habitats likely feeding on methanotrophic community.Given these observations and the context,we propose that the Zhongwei Hill represents a mud volcano,likely thermally driven,that seeps methane from Jurassic and Paleogene source layers,thus poses a favorable clue for significant hydrocarbon generation capacity in transitional zone of the Zhujiang River Mouth Basin and the Dongsha Basin.

Studies on the Extraction Methods of Metagenomic DNA from Mud Volcano in Xinjiang

[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.

S-wave velocity structure beneath Changbaishan volcano inferred from receiver function

The S wave velocity structure in Changbaishan volcanic region was obtained from teleseismic receiver function modeling. The results show that there exist distinct low velocity layers in crust in volcano area. Beneath WQD station near to the Tianchi caldera the low velocity layer at 8 km depth is 20 km thick with the lowest S-wave velocity about 2.2 km/s At EDO station located 50 km north of Tianchi caldera, no obvious crustal low velocity layer is detected. In the volcanic region, the thickness of crustal low velocity layer is greater and the lowest velocity is more obvious with the distance shorter to the caldera. It indicates the existence of the high temperature material or magma reservoir in crust near the Tianchi caldera. The receiver functions and inversion result from different back azimuths at CBS permanent seismic station show that the thickness of near surface low velocity layer and Moho depth change with directions. The near surface low velocity layer is obviously thicker in south direction. The Moho depth shows slight uplifting in the direction of the caldera located. We con- sider that the special near surface velocity structure is the main cause of relatively lower prominent frequency of volcanic earthquake waveforms recorded by CBS station. The slight uplifting of Moho beneath Tianchi caldera indicates there is a material exchanging channel between upper mantle and magma reservoir in crust.

Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China

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.

Study of Distal Pyroclastic-flow Stratum from Tianchi Volcano in 1215(±15) Eruption:Pyroclastic-flow Over Water

In this paper, we describe three strata at the distal part of the pyroclastic-flow from the Tianchi volcano in 1215 （±15） eruption. One of the strata with crosslayers that are different from typical pyroclastic-flow strata may come from a ground-surge. The grain-size and scanning electron microscopy （SEM） analysis was performed to study the origin of the pyroclastic-flow. Characteristics of grain-size distribution show that it is similar with the ash cloud. Through the SEM analyses, we found some quench structures with less damage on the surfaces of the vitric pumices. These phenomena indicate that there has been hydration in the transportation processes at the distal of pyroclastic-flow. It has partly changed the transportation mechanism of pyroclastic-flow, which transitions form dense flow to diluted flow. This paper develops a new distal pyroclastic-flow model in the Tianchi volcano that can be divided into three stages, i.e. the quench stage, expanding stage and depositing stage.

Magmatic Processes of Ashi Volcano, Western Kunlun Mountains, China

The Ashikule volcanic cluster （AVC） in western Kunlun Mountains is located in a graben region at the convergence of the Altun and Kangxiwa fault zones,and consists of more than 10 main volcanoes and dozens of volcanelloes.The Ashi volcano lies in the central part of the volcanic cluster.The lithology,chemical composition and texture of Ashi volcanic rocks were studied in detail,and their implication in magmatic processes was discussed.The phenocrysts in Ashi volcanic rocks consist mainly of plagioclase and pyroxene,and the statistical results of phenocryst contents show that the rocks can be subdivided into two groups.In group A,the content of pyroxene phenocrysts is generally higher than that of plagioclase phenocrysts,but an inverse relation occurs in group B.In TAS diagram,the compositions of both groups fall into the trachyandensite field,but they are obviously concentrated into two clusters.The two clusters exist also in the oxide diagrams.The pyroxene phenocrysts comprise augite,bronzite and hypersthene,and their Mg# histogram shows two peaks.Plagioclase phenocrysts with reaction rim are observed in rocks of both groups.The An values of the core are generally 30-40,and those of the rim are 44-48,which are closer to those of euhedral plagioclases.The bronzites are in equilibrium with the melt,and two sets of magma depths,i.e.,18-25 km and 13-18 km,can be estimated by using thermobarometer proposed by Putirka.The hypersthenes are not in equilibrium with the melt,and can be assigned to xenocrysts.The crystal size distribution （CSD） curves of plagioclase appear as kinked lines indicative of magma mixing.The above analyses show that two magma pockets might exist beneath the Ashi volcano.It is likely that they are connected with each other.The one has more evolved and contains more acidic magma,and the other is a trachyandensite magma pocket characterized by layering.The magma from the upper part of the trachyandensite magma pocket might mix with more acidic magma,resulting in a magma that is more acidic than the magma from the lower part.

The effect of Saccharomyces cerevisiae on digestion and mortality in the volcano rabbit(Romerolagus diazi)

An experiment was conducted to evaluate whether supplementation with a probiotic could enhance digestion and reduce mortality in the volcano rabbit in captivity. Two enclosures at Chapultepec Zoo, Mexico（114 individuals） were used in a crossover design（two periods of 60 days） with the following treatments： control group and supplementation with Saccharomyces cerevisiae（2×108 CFU/exhibit/day）. Supplementation with the probiotic negatively affected（P〈0.01） the digestibility of dry matter, organic matter, neutral detergent fiber（NDF） and energy. Mortality increased（P〈0.04） following supplementation with the probiotic（4.26% vs. 8.89%）, primarily in the juvenile rabbits. The results indicate that yeast supplementation in the volcano rabbit negatively affects digestion and mortality in captivity.