Understanding Magmatic System of Unzen Volcano (Nagasaki, Southwest Japan) Inferred from Broad-band Magnetotelluric Observation

2021 ◽  
Author(s):  
Agnis Triahadini ◽  
Koki Aizawa ◽  
Tasuku Hashimoto ◽  
Kazunari Uchida ◽  
Yuto Yamamoto ◽  
...  
Keyword(s):  
Magma Chamber ◽  
Broad Band ◽  
Magmatic Fluid ◽  
Volcanic Area ◽  
Resistivity Structure ◽  
Magmatic System ◽  
Magma Chambers ◽  
Unzen Volcano ◽  
Low Resistivity ◽  
Magnetotelluric Method

<p>Unzen Volcano is located in Shimabara Peninsula, Nagasaki, Japan. After 198 years of dormancy, the volcano erupted throughout 1990-1995 and resulted the emergence of new lava dome called Heisei-Shinzan. Following the eruption, numerous studies have been intensively conducted in Unzen volcano to assess the eruption mechanism and the magma plumbing system. Regarding to the magmatic system, the most preferred model is that the primary supply of magma is stored beneath Chijiwa bay. This magma chamber is located about 15 km west of the active dome at vertical depth approximately 15 km, and followed by subordinate shallower magma chambers beneath the volcano (e.g. Nakamura 1995; Kohno et al 2008). Upon the eruption, the magma ascended obliquely towards the summit in east direction (e.g. Umakoshi et al 2001). However, how main magma chamber  and shallower chambers are connected to the summit via oblique pathway is poorly imaged in terms of structure.<br>As widely known, Magnetotelluric method is highly sensitive to low resistivity zone caused by interconnected fluids. Low resistivity zone detected in the volcanic area usually can be interpreted as hydrothermal/magmatic fluid and or magma chamber containing partial melt (e.g. Aizawa et al 2014; Hill et al 2015). Thus, by using broadband Magnetotelluric method, we aim to investigate resistivity structure of Unzen volcano associated with magmatic system and its controlling structure (e.g. pathway and faults).<br>Although the shallow structures around Unzen volcano are estimated by the 2017-2019 campaigns (Triahadini et al 2019; Hashimoto et al 2020), we are unable to image deeper structure around the proposed location of magma chambers and magma pathway. To achieve our goals, during November-December 2020, we installed 35 new sites to cover whole area in Shimabara Peninsula. In total, deployed 99 Magnetotelluric stations covering Unzen volcano and Shimabara Peninsula. On this meeting, we would like to present our resistivity structure derived from all dataset.</p>

Magma recharging beneath the Weishan volcano of the intraplate Wudalianchi volcanic field, northeast China, implied from 3-D magnetotelluric imaging

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 913-918 ◽  
Author(s):  
Ji Gao ◽  
Haijiang Zhang ◽  
Senqi Zhang ◽  
Hailiang Xin ◽  
Zhiwei Li ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Magma Chamber ◽  
Northeast China ◽  
Volcanic Eruptions ◽  
Volcanic Field ◽  
Magmatic System ◽  
Low Velocity ◽  
Active Monitoring ◽  
Low Resistivity ◽  
Magma Reservoirs

Abstract The last volcanic eruptions at the intraplate Wudalianchi volcanic field in northeast China were ∼300 yr ago. Recent ambient noise tomography (ANT) imaged a potential magma chamber beneath one of its volcanoes, the Weishan volcano, which last erupted at ca. 50 ka. To image the spatial distribution of the magmatic system and estimate the melt fractions beneath the Weishan volcano, we use a dense magnetotelluric (MT) network (average site spacing of ∼1 km) around the Weishan cone to image a three-dimensional (3-D) resistivity structure beneath the volcano. For the first time, 3-D MT inversion illuminates the high-resolution spatial distribution of a very low-resistivity body of ∼0.3–3 Ω·m at depth of ∼2–15 km beneath the Weishan volcano. From the 3-D resistivity model, it can be deduced there exists a magma chamber in the upper and middle crust. From both low-velocity anomalies from ANT and low-resistivity anomalies from MT imaging, melt fractions of magma reservoirs are reliably estimated to be >∼15%. From the morphology of magma reservoirs and the shallow magma chamber, the Weishan volcano can be best described by the model of transcrustal magmatic system. Considering the significant melt fractions and active earthquakes and tremors occurring around magma reservoirs, the Weishan volcano is likely in an active stage with magma recharging. Therefore, it needs more active monitoring for better forecasting of its potential future eruptions.

Magmatic fluid pathways in the upper crust: insights from dense magnetotelluric observations around the Kuju Volcanoes, Japan

2021 ◽  
Vol 228 (2) ◽  
pp. 755-772
Author(s):  
Koki Aizawa ◽  
Mitsuru Utsugi ◽  
Keigo Kitamura ◽  
Takao Koyama ◽  
Makoto Uyeshima ◽  
...  
Keyword(s):  
Fluid Transport ◽  
Complex Structure ◽  
Broad Band ◽  
Active Faults ◽  
Low Frequency ◽  
High Strength ◽  
Volcanic Eruptions ◽  
Magmatic Fluid ◽  
Resistivity Structure ◽  
The North

SUMMARY Magnetotelluric (MT) observations have revealed subvertical electrical conductors that extend from shallow depths into the mid-crust at various geothermal zones, active volcanoes and active faults worldwide. These deeply rooted subvertical conductors have typically been interpreted to represent entire zones of dedicated fluid transport through the crust. We estimate the high-resolution 3-D crustal resistivity structure below the Kuju Volcanoes, Japan, using dense observations from 153 broad-band MT measurement sites and 40 telluric measurement sites. The resistivity structure highlights subvertical conductors that merge into a deep conductor to the north of the volcanoes, with deep low-frequency earthquakes occurring near the southeastern edge of this subvertical conductor at 10–30 km depth. This deep conductor branches into several subvertical conductors at 2–10 km depth, coinciding with a shallow zone where tectonic earthquakes rarely occur. The surface expressions of active geothermal areas and past volcanic eruptions are all located above the edges of the conductors at 2–6 km depth. Widespread conductive layers exist around the volcanoes above 2 km depth, and their distribution approximately corresponds to a low-gravity-anomaly zone. We discuss the nature of these subvertical conductors, the potential causes of their complex structure and their relationship to local magmatic fluid transport. These subvertical conductors, a shallow clay-rich layer, developed fracture systems and high-strength solidified magma may all contribute to magmatic fluid transport to the surface at the Kuju Volcanoes. In this study, we add the possibility that the edges of these subvertical conductors act as important magmatic fluid pathways.

A Modeling of the Magma Chamber Beneath the Changbai Mountains Volcanic Area Constrained by Insar and GPS Derived Deformation

2008 ◽  
Vol 51 (4) ◽  
pp. 765-773 ◽  
Author(s):  
Guo-Hu CHEN ◽  
Xin-Jian SHAN ◽  
Wooil M. Moon ◽  
Kyung-Ryul Kim
Keyword(s):  
Magma Chamber ◽  
Changbai Mountains ◽  
Volcanic Area

Genesis of porphyry and plutonic mineralisation systems in metaluminous granitoids of the Grampian Terrane, Scotland

1994 ◽  
Vol 85 (3) ◽  
pp. 221-237 ◽  
Author(s):  
David Lowry ◽  
Adrian J. Boyce ◽  
Anthony E. Fallick ◽  
W. Edryd Stephens
Keyword(s):  
Source Region ◽  
Crustal Contamination ◽  
Magma Ascent ◽  
Magmatic Fluid ◽  
Magmatic System ◽  
Low Salinity ◽  
Deep Faults ◽  
Supergene Enrichment ◽  
Propylitic Alteration ◽  
O 10

AbstractMineralisation associated with Late Caledonian metaluminous granitoids in the Grampian Terrane has been investigated using stable isotope, fluid inclusion and mineralogical techniques.A porphyry-stock-related style of mineralisation in the Grampian Terrane is characterised by a stockwork of veinlets and disseminations in dacite prophyries, consisting of quartz, dolomite, sulphides and late calcite, and well-developed wallrock alteration dominated by zones of phyllic, sericitic and propylitic alteration. On the basis of δ34S (+0·4±l·0‰), δ13C (−5·7‰ to + l·4‰) and δ18O (+10·8‰ to +19·9‰) it is likely that initial mineralising components were orthomagmatic with an input of external fluids during the later parageneses. Fluids were saline, boiling (up to 560°C), deficient in CO2, and ore deposition took place at depths of less than 3 km.Plutonic-hosted mineralisation in appinites, diorites, tonalites and monzogranites is commonly represented by sporadic disseminations and occasional veins consisting of quartz, calcite and sulphides. Wallrock alteration is generally propylitic with phyllic vein selvages. Deposition from a cooling magma sourced fluid is indicated by δ34S (+2·6±l·5‰), δ13C (−7·2‰ to −4·5‰) and δ18O (+9·5‰ to + ll·8‰) data. Fluids were CO2-rich and of low salinity; inclusions were trapped below ≈460°C, and formed at estimated depths of 3–5 km.Differences between these styles of mineralisation may due to multiple factors, the most important being the nature of the fluid: porphyry systems are dominated by greater volumes and much higher temperatures of hydrothermal fluids. Other controlling factors are likely to be the compositional characteristics of the melt source region, the mechanism of magma ascent, the level of emplacement, and the nature of the host metasediments. Variations in δ34S between the two groups are related, for the most part, to redox processes during magma and fluid genesis and not by crustal contamination.Nolarge porphyry-related mineral deposits have been found in the Grampian Terrane, unlike those in Mesozoic and Tertiary continental margin environments. This is largely due to a combination of detrimental factors which massively reducesthe probability of economic mineralisation. These include the already metamorphosed nature of the host Dalradian, the absence of seawater (which entered many subduction-related magmatic systems), a poorly-developed system of deep faults (most deposits too deep to be influenced by surface-derived fluids), and the absence of supergene enrichment. The main processes which aid the concentration of mineralisation involve encroachment of external fluids (formation, meteoric and seawaters) into the magmatic system, but these fluids were largely absent from the Grampian host block at the time of granitoid intrusion.The results of this study can be used in characterising the sources of fluids in sedimentary-hosted ore veins known (or considered) to be underlain by metaluminous granitoid batholiths, particularly in estimating the degree of magmatic fluid inputs into the vein systems: an example where this interaction has occurred (the Tyndrum Fault Zone) is discussed.

Crustal structure in the Tengchong volcanic area and position of the magma chambers

2013 ◽  
Vol 73 ◽  
pp. 48-56 ◽  
Author(s):  
Haiyan Yang ◽  
Jiafu Hu ◽  
Yili Hu ◽  
Yuanze Duan ◽  
Guangquan Li
Keyword(s):  
Crustal Structure ◽  
Volcanic Area ◽  
Magma Chambers

Influence of the Bell-Jar Magma Chamber Geometry on a Caldera Formation

2016 ◽  
Vol 825 ◽  
pp. 165-169
Author(s):  
Michael Somr ◽  
Petr Kabele
Keyword(s):  
Numerical Modeling ◽  
Magma Chamber ◽  
Magmatic System ◽  
Caldera Formation

The formation of a caldera poses a serious risk for the society and the environment. There are several established processes (mostly dealing with the conditions inside the reservoir), which must take place in order to reach a collapse leading to the caldera. The role of magma chamber geometry is investigated in this paper, exploiting the numerical modeling. The results indicates that the knowledge of the magmatic system dimensions can provide a helpful factor for an assessment of the caldera formation scenario.

Magma chamber formation by magma intrusion into the Earth's crust

2020 ◽  
Author(s):  
Ivan Utkin ◽  
Oleg Melnik
Keyword(s):  
Magma Chamber ◽  
Flow Rate ◽  
Structural Features ◽  
Numerical Dissipation ◽  
Magma Chambers ◽  
Magma Intrusion ◽  
Magma Flow ◽  
Formation Of Cracks ◽  
Heating Up ◽  
Magma Flow Rate

<p>The main mechanism of transport of magma in the Earth’s crust is the formation of cracks, or dikes, through which the melt moves towards the surface under the action of buoyancy forces and tectonic stresses. Due to the structural features of the crust or external stress fields, dikes often do not reach the surface, but penetrate the localized region in which the rocks melt, leading to the formation of magmatic chambers, whose volume can exceed thousands of cubic kilometers. We present a model of the formation of a magma chamber during the intrusion of dikes at a given flow rate. The model is based on the solution of heat equation and considers the actual melting diagrams of magma and rocks. It Is shown that, in case of magmatic fluxes typical of island arc volcanoes, magma chambers are formed over hundreds of years from the beginning of magma intrusion. The influence of the magma flow rate, the size of the dikes and their orientation on the volume of the formed magma chamber and its shape was investigated. The size of the chamber significantly exceeds the area of dike intrusion due to the displacement of magma and rocks of the crust, their heating up and melting. To calculate displacement of rock and magma in a numerical simulation, a hybrid method based on PIC/FLIP interpolation is developed, making it possible to avoid unphysical mixing due to numerical dissipation, thus preserving the fine details of the formed magma chamber.</p><p>This work was supported by RFBR, project number 18-01-00352</p>

The geochemistry of mafic and ultramafic from the Archaean greenstone belts of Sierra Leone

1983 ◽  
Vol 47 (344) ◽  
pp. 267-280 ◽  
Author(s):  
H. R. Rollinson
Keyword(s):  
Sierra Leone ◽  
Magma Chamber ◽  
Source Region ◽  
Double Diffusion ◽  
Ultramafic Rocks ◽  
Magma Chambers ◽  
Basaltic Rocks ◽  
Ocean Ridges ◽  
Different Depths ◽  
Greenstone Belts

AbstractThe Archaean (c. 2800 Ma) ultramafic rocks in eastern Sierra Leone cut basalt lavas and are mostly olivine-rich cumulates either iron-rich (Fo85–86) and derived from a basaltic or picritic parent, or more magnesian (Fo92–93) derived from an ultramafic melt with c. 18–25 wt. % MgO. In central Sierra Leone the ultramafic rocks are lavas predating tholeiitic basalts.The basalts show a wide variation in Zr/Y, suggesting that garnet was present in the source region of some of these rocks but not others. This implies that melting took place at different depths in the mantle. The REE evidence for basaltic rocks in the upper part of the Nimini belt succession suggests that they were derived from a mantle source region which had already suffered melt extraction. Ti/Zr ratios in the basaltic rocks are also variable and individual belts define different trends on a Ti vs. Zr plot implying that the basaltic rocks evolved in geographically distinct magma chambers. It is likely that the basaltic rocks evolved from a parental liquid with Ti/Zr = 90 via shallow level crystal fractionation. The source region for these rocks therefore had a lower than chondritic Ti/Zr.There are two possible models for the basaltic and ultramafic magmas in the Sierra Leone greenstone belts. First that the ultramafic and basaltic liquids were derived from mantle diapirs of differing size, but originating in the same region of the mantle. Ultramafic liquids were produced in small diapirs, which store large melt fractions, and basaltic liquids in larger diapirs which segregate larger melt fractions. A second model is based upon the double diffusion process suggested for magma chambers at mid-ocean ridges and involves a transient magma chamber from which basalts, derived from parental ultramafic liquids, are erupted, with ultramafic liquids rising directly to the surface when the magma chamber is frozen. The available data does not discriminate between these two models.

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