Changbaishan Tianchi Volcano Research Articles

Magnetotelluric evidence for the deep causes of different eruptive styles of Changbaishan Tianchi and Longgang volcanoes

Longgang Volcano (LGV) and Changbaishan Tianchi Volcano (CTV) share a common magmatic source at mantle depths. However, the two volcanoes have produced completely different types of eruptions. By performing 3D inversion of an MT dataset that completely covers the LGV and CTV, we have obtained high-resolution electrical resistivity images. The results reveal that the two volcanoes have distinct magmatic plumbing systems, and this is likely the reason for their different eruptive styles. Results from 3D modeling do not show a magma chamber in the shallow crust beneath LGV, interpreted as the rapid rise of the magma from the mantle is responsible for producing a series of densely distributed volcanic cones in the LGV field. In contrast, there is a magma chamber in the upper crust beneath the CTV, where the fractional crystallization and mixing of magma has occurred. This magma chamber has facilitated multiple centralized eruptions, and thereby has led to the formation of the large CTV volcanic cone. These results indicate that differences in their crustal structures may have controlled the different eruptive activities of the LGV and CTV in CVS, Northeast China.

Geochemistry of apatites from preshield and postshield basalts and their petrogenetic implications: A case study of the Naitoushan basalt and Heishigou dike in the Changbaishan Tianchi volcano, NE China

Geochemistry of apatites from preshield and postshield basalts and their petrogenetic implications: A case study of the Naitoushan basalt and Heishigou dike in the Changbaishan Tianchi volcano, NE China

Genesis of giant plagioclase phenocrysts in Cenozoic basalts from Songhuajiang River, Northeast China: Implications for the magma plumbing system of the shield-forming stage beneath Changbaishan-Tianchi Volcano

Genesis of giant plagioclase phenocrysts in Cenozoic basalts from Songhuajiang River, Northeast China: Implications for the magma plumbing system of the shield-forming stage beneath Changbaishan-Tianchi Volcano

Modelling the post-caldera plumbing system of Changbaishan volcano (China) from integrated geochemical, isotopic, geobarometric, and geophysical data

The Changbaishan Tianchi volcano is the largest active volcano of China and the 946 CE VEI 6 “Millennium eruption” (ME) is responsible for the formation of its summit caldera. After the ME, the volcanic activity is characterized by smaller eruptions most of which are recorded only in historical documents. Here we analyze the deposits of the ME and 1403 CE eruption outcropping in the Heishigou section, which is located east of the Chagbaishan Tianchi caldera. We present whole-rock, glass, mineral, isotopic, and geobarometric data to obtain information on the vertical extent of the caldera and post-caldera plumbing system of the volcano. Results show that the plumbing system of the 1403 CE eruption is located between 1.9 and 5.4 km depth, which is also the depth range of the shallower reservoir of the ME. Therefore, the magma reservoir of the ME was active also after the caldera collapse. The 1403 CE magma stored in the ME reservoir evolved by fractional crystallization of the residual ME trachytic magma and underwent the contamination of upper crust material. The 1403 CE event was triggered by the injection of less evolved, mafic magma from depth. The inferred depth of the shallower ME reservoir and that of the 1403 CE eruption is the same of the present-day main geophysical anomalies (low seismic velocity and low resistivity) recorded below the Changbaishan Tianchi caldera. In addition, the source of the deformations related to the uplift during unrest episodes between 2002 and 2020 suggests a refilling of the 1403 CE plumbing system. We conclude that the plumbing system of the 1403 CE, post-caldera activity at Changbaishan Tianchi volcano is the same of the ME eruption and it is still active. This system may be recharged from the arrival of less evolved magma from depth. The proposed conceptual model of the post-caldera volcanism at Changbaishan Tianchi represents a reference framework to interpret the signals of unrest and decipher the dynamics of the present-day plumbing system.

U–Pb geochronology and geochemistry of dikes in the Changbaishan Tianchi volcanic field (NE China) and their relations with the coeval Jingbohu and Longgang monogenetic volcanic fields

ABSTRACT The plain around the intraplate Changbaishan Tianchi volcano in NE China includes monogenetic cones whose shallowest plumbing system consists of dikes, and three main phases of activity are recognized since 2.8 Ma. The monogenetic volcanism mainly developed in the shield-forming phase (2.8–0.3 Ma), but the age and geochemical features of many of these vents remain poorly known. Here, we present geochemical, Sr‒Nd‒Pb isotopic and zircon trace element data from two dikes feeding monogenetic vents located north and northwest of the Changbaishan Tianchi volcano. Our aim is to constrain the emplacement age, the magma evolution processes, and the mantle source. We compare our results with those from the Jingbohu and Longgang monogenetic vents located north and west of the Changbaishan Tianchi volcano to investigate possible mantle heterogeneities in the recent NE China volcanism. The two Changbaishan dikes have 230Th disequilibrium-corrected ages of 1.27 and 1.00 Ma and show a basaltic composition with a potassic affinity. The Mg# values are 35.48–34.27 and 66.09–65.79. The whole-rock compositions, trace element compositions, and Sr‒Nd variations are consistent with fractional crystallization and minor contamination with lower crustal material, indicating an OIB-like mantle source with an EMI component possibly related to fluids released from the underlying Pacific flat slab. The melting depth determined from Na/Ti and Sm/Yb is between 140 and 180 km, i.e. the asthenospheric mantle. The dikes are characterized by (K2O+Na2O)/δEu, La/Ba, Ba/Nb, La/Sm, and La/Nb values similar to those of the Jingbohu and Longgang basaltic rocks. We conclude that the NE China volcanism at approximately 1 Ma was related to a single, relatively homogeneous OIB-like mantle source modified by ascending slab-derived fluids. According to the available geophysical data, the ascending magmas stopped at the mantle/lower crust interface and experienced limited crustal contamination.

The Qixiangzhan eruption, Changbaishan-Tianchi volcano, China/DPRK: new age constraints and their implications

Zircon double dating (ZDD) of comendite lava reveals an eruption age of 7.0 ± 0.9 ka for the Qixiangzhan eruption (QXZ), Changbaishan-Tianchi volcano, China/DPRK. This age is supported by new 40Ar/39Ar sanidine experiments and a previous age control from charcoal at the base of the QXZ. The revised age supports correlations with distal ash in Eastern China and Central Japan and establishes a significant (estimated at Volcanic Explosivity Index 5+) eruption that may provide a useful Holocene stratigraphic marker in East Asia. The new age indicates that the QXZ lava does not record a ca. 17 ka Hilina Pali/Tianchi geomagnetic field excursion but rather a heretofore unrecognized younger Holocene excursion at ca. 7–8 ka. Comparison between U–Th zircon crystallization and ZDD as well as 40Ar/39Ar sanidine ages indicates a protracted period of accumulation of the QXZ magma that extends from ca. 18 ka to the eruption age. This connotes an eruption that mixed remobilized early formed crystals (antecrysts) from prior stages of magma accumulation with crystals formed near the time of eruption. Based on these results, a recurrence rate of ca. 7–8 ka for the Changbaishan-Tianchi magma system is found over the last two major eruption cycles.

Petrochemical characteristics and geological significance of the tephra buried under peat deposits: Constrains on the Changbaishan Millennium eruption

Changbaishan Tianchi volcano is one of the most famous active volcanoes in Northeast Asia. Its Millennium eruption (ME, 946–947 CE) is considered to be one of the largest explosive eruptions over the past 2000 years, which had produced widely distributed tephra layer across Northeast Asia. However, little attention has been paid to the tephra buried in peatlands around this volcano. Here we present petrographic, geochemical and AMS14C data of the volcanic glasses within a new discovered macro-tephra layer buried in the Yueliangwan peatland, northeast China. The results suggest that buried tephra was the product of Changbaishan Millennium eruption. The eruptive sequence of the ME included comendite eruption and trachyte eruption from bottom to top. Tectonic background analyses reveal that Changbaishan Tianchi volcano regions belong to the anorogenic within plate back-arc extensional tectonic environments. Eruptive and sedimentary processes of the buried tephra were postulated as follows: a large amount of volcanic glasses formed through the eruption of trachyte magma that had high contents of rare earth elements (REE) and trace elements (TE). Then, fine grained volcanic glasses were sprayed into the atmosphere and transported to the Yueliangwan areas. The volcanic glasses deposited and formed airborne pumice layer. This buried tephra layer would act as a key isochronous marker horizon for the chronological framework in a range of sedimentary contexts across Northeast Asia. And it provides accurate eruptive sequence of Changbaishan Millennium eruption. This study would attract more attentions on the buried tephra in peatlands around active volcanoes, which would be of significance for the reconstructions of volcanic eruption history.

The magma system beneath Changbaishan-Tianchi Volcano, China/North Korea: Constraints from three-dimensional magnetotelluric imaging

Changbaishan-Tianchi volcano is a potentially hazardous intraplate volcano, and has gained increasing concern because of its volcanic unrest between 2002 and 2006. However, the magma system beneath this volcano is not well understood yet. Electrical resistivity is highly sensitive to the presence of interconnected partial melt and/or saline fluid. A total of 41 magnetotelluric (MT) sites were occupied along a ~120 km profile crossing the Tianchi volcano. Both broadband and long period MT data were collected for each site. A crustal and uppermost mantle resistivity model was constructed by three-dimensional (3D) inversion of the quality off-diagonal impedance of MT data. Beneath the volcano, the model shows three spatial consistent high conductive zones at a depth of 3–5, 10–16 and 40–60 km, separately. Melt fraction of 6–8% is required to interpret the uppermost mantle high conductive anomaly, which might be caused by the decompression melting of upwelling asthenosphere. The middle crust high conductive zone is interpreted as a magma chamber with 7–30% melt, which could be supplied by the partial melting in the uppermost mantle. The porous saline zone with porosity of about 2% is preferred for the upper crust high conductive anomaly.

Development and status of active volcano monitoring in China

Abstract Following decades of geological surveys and studies, 14 active volcanic fields have been identified in China. Evidence for Holocene volcanism in several of these areas highlights the need to understand and monitor volcanic hazards in those regions. Six volcano observatories have thus been established in the past 40 years. This work reviews China's national capability and history of volcano monitoring, with emphasis on the Changbaishan–Tianchi Volcano Observatory and the Tengchong Volcano Observatory. The Changbaishan–Tianchi Volcano Observatory (CTVO) was constructed in 1996 and began monitoring in 1999, with limited recorded observations dating back to 1973. Currently, CTVO is the largest and most advanced observatories in China. The monitoring network of the CTVO incorporates 11 seismic and 15 GPS stations, two levelling routes and three gas geochemistry sampling points. The Changbaishan–Tianchi Volcano experienced unrest during 2002–05, evidenced in elevated levels of seismicity and ground deformation, as well as shifts in gas geochemistry. After 2006, the volcano returned to quiescence, with activities at background levels as recorded in 1973–2001. The monitoring network of Tengchong Volcano Observatory incorporates eight seismic stations, 20 GPS points, 95 levelling points and three gas geochemistry sampling points. The observations made since 1965 indicate significant seismicity, with more than 3000 events recorded in 2011, mostly related to regional tectonics. Tengchong is known for its widespread hot springs, with temperatures up to 105°C recorded at Dagunguo spring. The four other observatories are Longgang Volcano Observatory, Jingbohu Volcano Observatory, Wudalianchi Volcano Observatory and Qiongbei Volcano Observatory. They are equipped with seismic, geodetic and geochemical monitoring equipment. These areas saw only low levels of activity over the past several decades, but related fault systems are relatively active. In a relatively short time, China has gained considerable experience in observatory design and volcano monitoring and has trained up a sizeable task force, laying the foundation for sustained volcano monitoring at the national level. Future efforts must focus on maintaining and expanding observational capacity, as well as gaining better dynamic understanding to inform volcano hazard assessment.

Late Pleistocene to present day eruptive history of the Changbaishan-Tianchi Volcano, China/DPRK: New field, geochronological and chemical constraints

Volcanic unrest during 2002–2006 renewed attention on Changbaishan-Tianchi volcano as the source of the powerful explosive eruption (VEI 6 to 7) Millennium Eruption of 946 CE (Common Era). However, progress in understanding the potential risk is complicated by discordant accounts of the most recent, explosive eruptive history. Several eruptions since the Late Pleistocene, such as the Tianwenfeng (TWF), Qixiangzhan (QXZ), Millennium (ME), Baguamiao (BGM), Liuhaojie (LHJ), 1403 CE event (1403), and even a 1903 CE event have been proposed, but the stratigraphic order, ages, distributions, and even the very existence of some of these, are still not fully ratified. Based on recent detailed stratigraphic logs of over 100 surface exposures and three deep trenches, coupled with new geochronologic and petrochemical data (including trace elements on glass and pyroxene), we can now clarify these relationships.Herein we propose that the 946 CE Millennium eruption, be formally re-named the Generalized Millennium Eruption (GME) to avoid entrenched confusion and to formally acknowledge the composite comendite-trachyte nature of the eruption. Thus three eruptions, the TWF, QXZ and the GME are confirmed. The TWF eruption is the first powerful explosive eruption at Changbaishan-Tianchi and we find evidence that this eruption may have initiated the Tianchi caldera. It produced an extensive fallout pumice deposit, that on the basis of new Optically Stimulated Luminescence (OSL) and radiocarbon (14C ages) of overlying sedimentary strata indicates an eruption age >42 ka. This new age constraint coupled with geochemical fingerprints confirms a correlation to the ~50.6 kyr B-J ash in Japan Sea. The next eruption was the predominately effusive QXZ that produced a clastogenic lava flow down the north slope of the edifice. An age of ~4–8 ka is proposed based on new radiocarbon (14C) ages of charcoal at the base and from overlying sediment. Although the age of the GME is well established as late 946 CE, there are some intriguing details in historical records of ash falls in Japan that indicate two separate events on Nov 3, 946 CE and Feb 7, 947 CE. We speculate that these correspond to the comendite and trachyte stages of the GME respectively. Subsequent to the GME, no evidence of any post-GME eruptions have been found. These findings clarify and refine the history of the explosive stage of the Changbaishan-Tianchi volcano that began ~51 kyr. This improved understanding should serve as a basis for further studies at Changbaishan-Tianchi and inform a better-constrained assessment of volcano hazard.

Characteristics and source-sink response of the Lahar deposits in Changbaishan-Tianchi volcano and adjacent area following the Millennium Eruption

Characteristics and source-sink response of the Lahar deposits in Changbaishan-Tianchi volcano and adjacent area following the Millennium Eruption

Formation mechanism of yellow pumice in the deposition of Tianwenfeng eruption at Changbaishan-Tianchi volcano

Formation mechanism of yellow pumice in the deposition of Tianwenfeng eruption at Changbaishan-Tianchi volcano

Facies variations in the pyroclastic density currents (PDCs) produced by the Millennium Eruption of the Changbaishan Tianchi volcano, NE China

Facies variations in the pyroclastic density currents (PDCs) produced by the Millennium Eruption of the Changbaishan Tianchi volcano, NE China

Geomorphology of the underwater caldera of the Changbaishan Tianchi volcano using 3D virtual visualization

Based on high‐precision multibeam underwater terrain data, 3D virtual visualization technology is adopted to reconstruct the Changbaishan Tianchi Volcano Crater, China, because this technology can intuitively show the shape of underwater calderas. Results indicate that the current terrain of the lakebed at the Tianchi Caldera mainly formed by a combination of one volcanic explosion, eruption and collapse in the periods of the Tianwen Peak and the Millennium Eruption, and it is also associated with the orographic uplift caused by the subsequent and frequent activities of the magma chamber. Two boccas at different periods are observed at the lakebed of the Tianchi Caldera: the large bocca located in the centre of the caldera that probably formed 5,000–4,000 years ago during the eruption period and the small bocca located in the west of the large bocca that probably formed in the Millennium Eruption period. The eruption resulted in the collapse of the magma cave, thus forming a semi‐annular dike and two lava domes along the topographic slope, which extends along the lakebed with the direction of 30°–45°NE. The southern and northeastern feet of the collapsed crater slid downward and accumulated, with the southern foot of the crater touching the southern end of the ridged dike.

Lahar deposits generated after the Millennium eruption of the Changbaishan Tianchi volcano in the Erdaobaihe River system, China

After the Plinian Millennium Eruption (including the ME-I and ME-II eruptive stages) of Changbaishan Tianchi volcano in 969 ± 20 CE, two large-volume lahars were deposited mainly on the northern flank of the Erdaobaihe River, which flows through the only outlet from Tianchi Lake: (1) a lahar deposit containing gray and black pumice (Lahar (G&B) P) and (2) a lahar deposit containing lithic particles (Lahar L). Based on the sedimentary characteristics of lahar outcrops and grain-size and compositional analyses performed using standard dry sieving techniques, examination of thin sections and geochemical analyses, the origins, transport and deposit processes and fluid phase variations of the two lahar deposits are studied. These two lahar deposits are fan-like in the flat medial area (23–60 km from the crater) and fill channels in the distal mountainous area (>60 km from the crater). Lahar L in the medial area represents a complete composite lahar flow deposit with a frontal debris head (very coarse gravel texture, extremely poor sorting, massive and matrix-supported structure) and a hyperconcentrated fluid phase body and tail (coarse sandy texture, very poor sorting, faint horizontal stratification with thin lenses of gravel, clast-supported structure). Lahar L in the distal area represents the material that passed the debris flow head, and the fluid phase changes from debris flow to hyperconcentrated (poor sorting, clear thin horizontal stratification) downcurrent. The fluid phase of Lahar (G&B) P changes from debris flow in the medial area (medium gravel to fine sand, very poor sorting, thick horizontal stratification with floating pumice on each unit surface) to hyperconcentrated flow (poor sorting, thin horizontal stratification, clear normal graded bedding) and to stream flow (moderate sorting, cross-bedding) in the distal area. Lahar (G&B) P was likely formed by the mixing of water from Tianchi Lake and pyroclastic flows of ME-II. Lahar L was likely triggered by a sudden release (dam break) from Tianchi Lake. An assessment of the risk posed to the stability of Tianchi Lake is as important as an assessment of the eruption risk.

Effect of redox conditions on the evolution of magmas of Changbaishan Tianchi volcano, China–North Korea

In this paper we use data on composition of melt, fluid, and crystal inclusions in minerals to reconstruct the compositions and formation conditions of the parental melts for the trachybasalts, trachybasaltic andesites, comendites, and pantellerites of Changbaishan Tianchi (Paektusan) volcano on the border of China and North Korea. The melts crystallized within broad temperature and pressure ranges of 1200–700 °C and 3100–1000 bar. The redox conditions expressed as ΔNNO are +0.9 to +1.4 log units for the basalt melts, −1.6 to −2.1 log units for the trachybasaltic andesite melts, −2.6 to −1.9 log units for the comendite melts, and −1.6 to −3.2 log units for the pantellerite melts. All melts are rich in alkalis and FeO. The sulfur contents of the mafic melts vary from 0.06 to 0.13 wt%. The pantellerite melts are sulfur-free, but the groundmass of the pantellerites contain pyrite crystals. Mafic melts have a range in water contents from 0.1–1.0 wt%. The H2O contents of the comendite melts vary from 3.7 to 4.8 wt%, and the pantellerite melts contain 0.2–0.6 wt% H2O. It has been revealed that the magma crystallization was accompanied by changes in oxygen fugacity caused by the decompression of the magma chamber beneath Changbaishan Tianchi volcano. Such decompression resulted in open-system crystal fractionation during magma degassing. We propose that the degassing is responsible for variations in water and sulfur contents in the melts. As the pressure decreases, the gas phases become progressively enriched in H2O and S, and the S oxidation state is changed from S2− to S4+. Sulfur degassing in the form of SO2 at decompression and spinel precipitation during open-system magmatic differentiation resulted in melt reduction.

Magmatic Evolution of Changbaishan Tianchi Volcano, China–North Korea: Evidence from Mineral-Hosted Melt and Fluid Inclusions

Data on mineral-hosted melt, fluid, and crystalline inclusions were used to study the composition and evolution of melts that produced rocks of Changbaishan Tianchi volcano, China–North Korea, and estimate their crystallization parameters. The melts crystallized within broad ranges of temperature (1220–700°C) and pressure (3100–1000 bar), at a drastic change in the redox potential: Δ log $$f_{O_2}$$ from NNO + 0.92 to +1.42 for the basalt melts, NNO –1.61 to –2.09 for the trachybasaltic andesite melts, NNO –2.63 to –1.89 for the comendite melts, and NNO –1.55 to –3.15 for the pantellerite melts. The paper reports estimates of the compositions of melts that produced the continuous rock series from trachybasalt to comendite and pantellerite. In terms of trace-element concentrations, all of the mafic melts are comparable with OIB magmas. The silicic melts are strongly enriched in trace elements and REE. The most strongly enriched melts contain concentrations of certain elements almost as high as in ores of these elements. The paper reports data on H2O concentrations in melts of different composition. It is demonstrated that the variations in the H2O concentrations were controlled by magma degassing. Data are reported on the Sr and Nd composition of the rocks. The deviations in the Sr isotopic composition are proportional to the 87Sr/86Sr ratio and could be produced in a melt with a high enough 87Sr/86Sr ratio during a geologically fairly brief time period. The evolution of melts that produced rocks of the volcano was controlled by crystallization differentiation of the parental basalt magmas at insignificant involvement of melt mixing and liquid immiscibility of silicate and sulfide melts. The alkaline salic rocks were generated in shallow-sitting (13–3.5 km) magmatic chambers in which the melts underwent profound differentiation that gave rise to pantellerites and comendites strongly enriched in trace elements (Th, Nb, Ta, Zr, and REE). Data on the composition of the magmas and parameters of their derivation are used to develop a generalized petrologic–geodynamic model for the origin of Changbaishan Tianchi volcano.

The VEI-7 Millennium eruption, Changbaishan-Tianchi volcano, China/DPRK: New field, petrological, and chemical constraints on stratigraphy, volcanology, and magma dynamics

Field relations, petrography, bulk and micro-scale chemistry reveal that the most recent history of hazardous Changbaishan-Tianchi volcano should be revised with important implications for volcanic hazard in NE Asia. Currently, the two most recent large eruptions are identified separately as a VEI 5 trachytic Baguamiao eruption (BGM) and the much heralded VEI 7, late 946CE (Common Era) “Millennium” eruption (ME) of comendite. However, we find that the former is part of the latter based on the following evidence: (1) trachytic fallout of the BGM lies directly on the comendite tephra of the ME without any indication of depositional hiatus; (2) abundant mingled trachyte-comendite pumice in the tephra deposits; (3) similar chemistry of mingled pumice and its components to those in the BGM and ME products; (4) correlation of bimodal glass shard compositions in the distal ‘B-Tm’ ash from the Japan Sea with comendite and trachyte glass from the BGM and ME products. Based on the above evidence, we suggest that the great Millennium eruption of 946CE should be revised finally to include the BGM trachyte as its final stage. Furthermore, deposits attributed to two other trachytic eruptions in 1668 and/or 1702CE (also called Baguamiao by some authors), and 1903CE referred to in historic accounts were also examined. Our field observations, petrography, bulk and micro-scale chemistry combined with previously published Ra/Th ages indicate that all these trachytes are either primary deposits of the ME or its reworked deposits. Thus our findings do not support two separate post-ME eruptions and require that volcanic hazard assessment at Changbaishan volcano include this new interpretation.Recently published geochronological data integrated with our new petrochemical and volcanological framework informs the magma dynamics leading to the ME. The ME comendite, derived from a parental trachyte similar to the BGM started accumulating at shallow levels around 12ka to 8ka. Around 4 to 1.6ka the BGM trachyte sensu strictu separated from its basaltic parent and started accumulating and crystallizing separately from the ME comendite. Just prior to the ME eruption, mingling of trace amounts of a third more mafic hybrid is implicated by the composition of mafic glass selvedges. The strong evidence for mixing of all these endmembers in the eruption products suggests that recharge mixing and overturn of this predominantly comendite-trachyte system occurred during the ~1ka ME. The common occurrence of comendite and trachyte in the last 100ka (also maybe 1Ma) at Changbaishan-Tianchi suggests that conditions for trachyte-comendite magma interactions are prevalent in the magma system of Changbaishan and maybe crucial in catastrophic eruptions there.

Crust structure beneath Jilin Province and Liaoning Province in China based on seismic ambient noise tomography

We imaged the crust structure beneath Jilin Province and Liaoning Province in China with fundamental mode Rayleigh waves recorded by 60 broadband stations deployed in the region. Surface-wave empirical Green's functions were retrieved from cross-correlations of inter-station data and phase velocity dispersions were measured using a frequency–time analysis method. Dispersion measurements were then utilized to construct 2D phase velocity maps for periods between 5 and 35s. Subsequently, the phase-dispersion curves extracted from each cell of the 2D phase velocity maps were inverted to determine the 3D shear wave velocity structures of the crust. The phase velocity maps at different periods reflected the average velocity structures corresponding to different depth ranges. The maps in short periods, in particular, were in excellent agreement with known geological features of the surface. In addition to imaging shear wave velocity structures of the volcanoes, we show that obvious low-velocity anomalies imaged in the Changbaishan-Tianchi Volcano, the Longgang-Jinlongdingzi Volcano, and the system of the Dunmi Fault crossing the Jingbohu Volcano, all of which may be due to geothermal anomalies.

Evolution of melts of the Changbaishan Tianchi volcano (China–North Korea) as a model of ore–magmatic system formation: Data from melt inclusions studies

The composition and evolution of the melts of trachytes from the volcano were studied based on examining the inclusions of mineral-forming media by means of X-ray and ion microanalysis. A correlation was shown between the degree of enrichment of these melts in rare elements and the processes of magmatic differentiation. It was found that trachytes of the volcano were generated in highly differentiated alkaline melts enriched in Hf, Nb, Zr, Ta, U, Th, Rb, Y, and REEs under 1020–1060°C. The evolution of melts was determined by the processes of crystal fractionation. The main volatile components in the melts are water, fluorine, and chlorine with the concentrations of 0.1–0.5, 0.2–0.5, and 0.2–0.3 wt %, respectively. The melt crystallization was accompanied by degassing caused by the decrease in the outer pressure. The low concentrations of water and fluorine represent the melt composition by these components exclusively at the time of the melt movement towards the Earth’s surface just before the eruption.