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How Small-volume Basaltic Magmatic Systems Develop: a Case Study from the Jeju Island Volcanic Field, Korea
Abstract
Jeju is a volcanic field that has erupted from around 1·8 Myr to c. 1 kyr ago. Activity began with dispersed, basaltic, monogenetic, phreatomagmatic eruptions. Continuing monogenetic volcanism was later joined by more voluminous lava effusion events building a central composite shield. Samples from older (>0·7 Ma) and younger (<0·2 Ma) monogenetic centres were analysed for their whole-rock major element, trace element and Sr-Nd-Pb isotopic compositions. Pyroclastic products from the monogenetic centres are dominantly alkali basalt to trachybasalt, whereas the more voluminous lava flows and domes of the central edifice consist of subalkali basalt and alkali basalt to trachyte. Lavas from the Early Pleistocene monogenetic centres are depleted in MgO, Cr and Ni, reflecting considerable olivine fractionation. By contrast, Late Pleistocene-Holocene monogenetic centre magmas fractionated clinopyroxene + olivine at deeper levels. Isotopic compositions show little variation across the suite; however, the Late Pleistocene-Holocene monogenetic centres have generally lower 87Sr/ 86Sr and 208Pb/ 204Pb and higher 143Nd/ 144Nd than the older centres and subalkali lavas. Major and trace element and isotope data suggest a common, shallower source for the high-Al alkali and subalkali lavas, in contrast to a deeper source for the low-Al alkali magmas. We propose that mantle melting was initiated under partially hydrous conditions at a pressure of near 2·5 GPa, followed by drier conditions and extension of the melting zone to 3-3·5 GPa, with a concomitant increase in the volume of melt derived from the shallower part of the system to produce subalkaline magmas. Increasing melt production at shallow depths may be related to accelerated heat transfer resulting from deepening of the melting zone, or increased mantle upwelling. Mantle lenses were uplifted, probably lubricated by shear zones created during the opening of the Sea of Japan c. 15 Myr ago, and reactivated during rotation of the Philippine Sea plate direction of subduction at around 2 Ma. This is the first hypothesized link between subduction processes and intraplate volcanism at Jeju. © The Author 2012. Published by Oxford University Press. All rights reserved.
... Ho et al., 2003;Kuritani et al., 2011;Li et al., 2017b), and their isotopic compositions reveal prominent regional-scale variations in the source region. (Zou et al., 2000;Chen et al., 2009;Brenna et al., 2012aBrenna et al., , 2012b. Basalts from the Korean Peninsula near the southern end of the Japan Sea show a transitional feature between EM1-and EM2type OIB (Choi et al., 2006). ...
... Among the lavas from Fuding, the basanites have high MgO (>10 wt%) and Ni (>280 ppm) abundances, which are close to those of the primitive magmas derived from the mantle (Brenna et al., 2012a). From basanites toward weakly alkaline basalts, olivine is a dominant phase as suggested by an increase of CaO and decreases of Fe 2 O T 3 and Ni with decreasing MgO (Fig. 5a, d and g). ...
... The low-MgO suites (Zhangzhou and Zhanjiang) display high SiO 2 and Al 2 O 3 , and low Fe 2 O T 3 and Ni abundances, suggesting early fractionation from a more primitive parent melt (Brenna et al., 2012a). The most primitive sample 17ZJ16-2 with the highest MgO (8Á5 wt%) and Ni abundance (226 ppm) was chosen as the starting material to model crystal fractionation using PETROLOG 3. The variations of Cr, CaO and CaO/ Al 2 O 3 against MgO in the Zhanjiang lavas roughly form two trends. ...
Subduction processes introduce crustal materials into the mantle, and mantle plumes return them to the surface. However, when and how the subducted materials were recorded in the plume-related basalts remains unclear. Here we investigate geochronology, bulk-rock composition, and Sr–Nd–Pb isotopes of Cenozoic basalts from Southeast China, occurring near the west Pacific subduction zone and the seismically detected Hainan plume. Volcanism beginning in the late Oligocene in the continental margin of SE China consistently becomes younger landward. Together with a compilation of published results on the synchronous basalts from the South China Sea seamounts and the Indochina peninsula, the volcanoes close to the Pacific subduction zone exhibit more radiogenic Pb and Sr isotopes associated with less radiogenic Nd isotopes compared with those of the inland volcanoes. Such spatiotemporal variations in radiogenic isotopes imply oceanic crusts of different ages in the source, each corresponding to a different geographical volcanic belt. Major-element features such as low CaO, high TiO2 and high Fe/Mn ratios imply that pyroxenite/eclogite could serve as a source lithology of the SE China basalts. Specific trace-element signatures reveal the important roles of recycled oceanic crust along with surface sediment, which was inconsistently dehydrated during subduction. A geologically, geochemically, and geophysically plausible scenario is proposed to illustrate the time–space–source correlation of the late Cenozoic basaltic lavas in SE Asia. The Hainan plume delivered the ancient subducted crust (1·5 Ga) from the core–mantle boundary and, subsequently, the subducted Pacific plate crustal materials from the mantle transition zone to the shallow mantle as a result of mantle convection induced by continuous subduction of the Pacific plate. Such recycled materials of different ages contributed to the geographical compositional heterogeneities of the late Cenozoic basaltic lavas in SE Asia.
... Jeju Island, South Korea, is an elongate volcanic island that formed in an intraplate tectonic setting (Brenna et al., 2010(Brenna et al., , 2012a(Brenna et al., , 2015Choi et al., 2006;Kwon, 1993a, 1993b;Tatsumi et al., 2005) (Fig. 1). Volcanic activity at Jeju Island commenced at~1.9 ...
... Halla is the highest peak (1950 m a.s.l.) on the island (Fig. 1b). Hundreds of small-volume, dispersed, monogenetic volcanoes are superimposed on the large-volume deposits from the central Halla eruptions to form the present Jeju volcanic edifice (Brenna et al., 2012a(Brenna et al., , 2012b (Fig. 1b-c). ...
... The volcanic rocks of Jeju Island are composed mainly of alkalineseries basalts to trachytes, with lesser tholeiitic basalts/basaltic andesites intercalated with the alkaline rocks (Baek et al., 2014;Brenna et al., 2012aBrenna et al., , 2012bChoi et al., 2006;Lee, 1982;Kwon, 1993a, 1993b;Tatsumi et al., 2005). Trachytic lavas form domes and extensive flows in the central Mt. ...
Volcanic rocks on Jeju Island, South Korea, are dominantly alkaline suites (basalt to trachyte) with small amounts of intercalated tholeiitic (TH) basaltic rocks. The alkaline suites can be subdivided into high-Al alkaline (HAA) and low-Al alkaline (LAA) sub-suites. We determined the major- and trace-element abundances, and Sr–Nd–Pb–Mg isotopic compositions for 60 samples from four boreholes and nine outcrops on Jeju Island to better understand their petrogenesis and mantle source characteristics. The samples yield whole-rock⁴⁰Ar/³⁹Ar ages of ~968–24 ka. The HAA suite formed slightly earlier than the other suites. On a primitive-mantle-normalized trace-element diagram, Jeju basaltic rocks exhibit typical oceanic island basalt (OIB)-like large-ion lithophile element (LILE) enrichments without significant Nb or Ta depletions. No meaningful correlation was observed between SiO2 and Sr–Nd–Pb–Mg isotope compositions. However, some samples, especially the TH and HAA suites, exhibit positive Eu and Sr anomalies, coupled with elevated ⁸⁷Sr/⁸⁶Sr, Δ7/4Pb, and Pb/Ce ratios, indicating an important role of ancient anorthosite assimilation during its evolution. Furthermore, they show negative K and Rb anomalies. The basaltic rocks have fractionated Nb/Ta and Zr/Hf ratios with negative Ti anomalies. They have elevated Dy/Yb ratios within the range of melts derived from garnet lherzolite, but have Yb contents much higher than those of garnet lherzolite melts, instead plotting close to those of eclogite-derived melts. They also have high Fe/Mn ratios (>~60) and FeO/CaO–3MgO/SiO2 values (>0.45), similar to melts from pyroxenite/eclogite sources. The Sr–Nd–Pb isotopic compositions display a good linear array between depleted mid-ocean-ridge basalt (MORB) mantle and enriched mantle type 2 (EM2). There are no discernible ¹⁴³Nd/¹⁴⁴Nd, Δ8/4Pb, and δ²⁶Mg isotopic differences among the three suites, implying their derivation from a compositionally homogeneous source by variable degrees of melting. The Mg isotopic compositions yield δ²⁶Mg values of −0.53‰ to −0.20‰ extending to a much lower value than normal mantle (δ²⁶Mg = −0.25‰ ± 0.04‰). These observations suggest the presence of recycled rutile-bearing eclogite, carbonate, and sedimentary components in the mantle source of the Jeju volcanic rocks together with a peridotite component. No significant spatiotemporal changes in the mantle sources and melting conditions were observed.
... The Northeast China Cenozoic basalts have an EM1 (enriched mantle 1)-type Ocean Island Basalt (OIB) isotopic affinity ( Figure 1A), likely attributed to the incorporation of ancient sediments from the stagnant subducted paleo-Pacific plate in the mantle transition zone (Huang and Zhao, 2006;Li and Van der Hilst, 2010;Li et al., 2015;Xu et al., 2018) and the lithospheric thinning of the North China Craton (Xu, 2001;Gao et al., 2002;Ma et al., 2014). The Southeast China and Jeju Island Cenozoic basalts have an EM2 (enriched mantle 2)-type OIB isotopic affinity ( Figure 1A), likely due to the presence of the Hainan plume extending to 660 km depth (Zou et al., 2000;Lebedev and Nolet, 2003;Chen et al., 2009;Brenna et al., 2012a;2012b), even to 1,300 km depth (Huang and Zhao, 2006) and 1,900 km depth (Montelli et al., 2006) beneath the Leiqiong Peninsula. The excess mantle temperature (Wei and Chen, 2016), the Holocene volcanic extrusion rate Li et al., 2020), the geochemical features Yu et al., 2018;, and the low-velocity seismic structure (Huang and Zhao, 2006;Montelli et al., 2006;Brenna et al., 2012a;2012b) collectively testify the crucial role of Hainan plume in the extensive volcanic activities beneath the SE Asia. ...
... The Southeast China and Jeju Island Cenozoic basalts have an EM2 (enriched mantle 2)-type OIB isotopic affinity ( Figure 1A), likely due to the presence of the Hainan plume extending to 660 km depth (Zou et al., 2000;Lebedev and Nolet, 2003;Chen et al., 2009;Brenna et al., 2012a;2012b), even to 1,300 km depth (Huang and Zhao, 2006) and 1,900 km depth (Montelli et al., 2006) beneath the Leiqiong Peninsula. The excess mantle temperature (Wei and Chen, 2016), the Holocene volcanic extrusion rate Li et al., 2020), the geochemical features Yu et al., 2018;, and the low-velocity seismic structure (Huang and Zhao, 2006;Montelli et al., 2006;Brenna et al., 2012a;2012b) collectively testify the crucial role of Hainan plume in the extensive volcanic activities beneath the SE Asia. However, apart from the above-mentioned Hainan plume, there is still controversy about the origin of the EM2-type reservoir beneath the SE Asia, such as the proposed asthenosphere mantle origin (Choi et al., 2006), the delaminated lithospheric mantle (Zou and Fan, 2010), the presence of a sialic crustal component or a slab-derived component (Tu et al., 1991;Qiu et al., 2019), the subducted pelagic sediments (Wang and Zhang, 2022), and the thermally metasomatized continental lithospheric mantle (Zhou and Mukasa, 1997;Ho et al., 2003;Hoàng et al., 2013;Qiu et al., 2019). ...
The origin of the EM2 (enriched mantle 2)-type reservoir beneath the Southeast Asia is controversial. In this study, we present new in-situ major and trace element (olivine, clinopyroxene, and plagioclase), and Sr isotopic compositions (plagioclase) for Leiqiong basaltic rocks to explain the potential source of Leiqiong EM2-like reservoir. Leiqiong olivines show the normal zoning textures with in-situ trace element heterogeneity, Leiqiong plagioclases exhibit the complex zoning textures with in-situ ⁸⁷Sr/⁸⁶Sr isotopic disequilibria. It likely suggests the contribution to an individual crystal by the incorporation of heterogeneous components. The olivine and plagioclase phenocrysts, and the calculated Leiqiong clinopyroxene-equilibrium melts show the features of OIB-type enriched compositions associated with the plume, likely indicating the presence of Hainan mantle plume. The clear disequilibrium of ⁸⁷Sr/⁸⁶Sr isotopic ratios among bulk-rock, plagioclase phenocryst, and groundmass likely indicates the isotopically heterogeneous mantle source and the influence of the recycled subduction-related H2O-enriched oceanic fluid/melts carried by the deep Hainan plume. Leiqiong olivines are crystallized by the incorporation of pyroxenitic mantle source, but different from those from olivine-rich peridotitic mantle lithology, likely due to the reaction between eclogite-derived silicate melts (recycled oceanic crust) and peridotite.
... The apparent depletion in HFSE is due to the enrichment of their neighboring incompatible elements (Ba to U & La to Sr), implying the possibility of highly metasomatized SCLM involvement rather than a subduction event. A high Nb/Ta ratio (14.09-22.52) in the BQMVR confirms the involvement of metasomatic agents in SCLM (Brenna et al., 2012;Foley et al., 2002). ...
... The enrichment of highly incompatible elements and depletion in Zr, Hf, Rb, and K (Fig. 10) and superchondritic Zr/Hf ratios (38.78-48.14) raise the possibility that the mantle source for the Bijar-Qorveh HA suite rocks has been overprinted by hydrous phases, amphibole and/or phlogopite (Brenna et al., 2012;LaTourrette et al., 1995;Pilet et al., 2008). Negative Rb and positive Ba anomalies (Fig. 10) as well as elevated Sr/Y (60-135) in the HA suite support the involvement of amphiboles rather than phlogopites in the mantle source region (Adam and Green, 2006). ...
The Quaternary Bijar-Qorveh mafic volcanic rocks (BQMVR) occur in the Sanandaj-Sirjan Zone (SSZ) of Iran, a segment of the Alpine-Himalayan Orogeny with a Gondwana-affinity basement. Phases 1 and 2 of BQMVR are silica-undersaturated (basanite, tephrite, and phonotephrite) and form a highly alkaline or HA suite. The last phase, phase 3, of BQMVR is silica-saturated (alkali olivine basalt and hawaiite) and is called the mildly alkaline or MA suite. BQMVR share well-known subduction-related negative Nb-Ta anomalies, and their Nb abundances are high enough to be classified as ‘high-Nb like basalts’. However, they do not show geochemical characteristics of typical high-Nb basalts. Trace element abundances and patterns of the MA suite mimic garnet-bearing spinel peridotite partial melts, whereas the HA suite is too rich in incompatible trace elements to match normal mantle partial melts. Enriched trace element patterns of the HA suite are akin to hornblendite experimental partial melts, and are likely derived from a garnet-amphibole peridotite source. Sr-Nd-Pb isotopic characteristics of the BQMVR indicate a subcontinental lithospheric mantle affinity. The HA suite tends toward the EM1 array, whereas the MA suite follows the EM2 array. The highly radiogenic Sr-Nd isotopes of the MA suite indicate significant crustal contamination. Lithospheric delamination beneath the SSZ that followed Arabia-Eurasia collision, triggered garnet-amphibole peridotite partial melting that interacted with 10-30% of the asthenospheric component to have formed the HA suite. Mantle melting at shallower lithosphere depths followed and produced the MA suite. MELTS modeling shows the BQMVR underwent fractional crystallization of clinopyroxene ± olivine. Whole-rock thermobarometric calculations suggest derivation of the primary melts at a depth of ~97 km, however the Cpx-thermobarometer indicates that such melts equilibrated at lower crust depths at a depth of 45 km close to the Moho. The present Quaternary volcanostratigraphic study provides substantial clues for major post-collisional alkaline high-Nb mafic volcanism bearing signatures of two distinct magmatic stages; an early phase (phases 1 and 2) rooted in a deeper garnet amphibole peridotite followed by phase 3 rooted in a garnet-poor spinel peridotite.
... Previous studies on Jeju volcanic rocks have focused on the history of volcanism, the magma sources, and the tectonic settings [14,16,18,21,[26][27][28]. Our study, additionally, aimed at investigating the underlying mechanism in the generation of the evolved volcanic rocks (trachybasalt to trachyte) on the island. ...
... The basement rocks of Jeju Island include granites and silicic volcanic rocks of Jurassic to Cretaceous age, as well as gneisses of unknown age that were observed in drill cores as xenoliths in the basalts and tuffs [9,16,17,20,21]. Mantle xenoliths are observed within volcanic rocks distributed extensively on Jeju Island and include spinel peridotites and pyroxenites [21,27,34], as well as gabbroic and anorthite xenoliths [11][12][13]20,21,34,35]. ...
The major and trace elements of Quaternary alkaline volcanic rocks on Jeju Island were analyzed to determine their origin and formation mechanism. The samples included tephrite, trachybasalts, basaltic trachyandesites, tephriphonolites, trachytes, and mantle xenoliths in the host basalt. Although the samples exhibited diversity in SiO2 contents, the relations of Zr vs. Nb and La vs. Nb indicated that the rocks were formed from the fractional crystallization of a single parent magma with slight continental crustal contamination (r: 0–0.3 by AFC modeling), rather than by the mixing of different magma sources. The volcanic rocks had an enriched-mantle-2-like ocean island basalt signature and the basalt was formed by partial melting of the upper mantle, represented by the xenolith samples of our study. The upper mantle of Jeju was affected by arc magmatism, associated with the subduction of the Pacific Plate beneath the Eurasian Plate. Therefore, we inferred that two separate magmatic events occurred on Jeju Island: one associated with the subduction of the Pacific Plate beneath the Eurasian Plate (represented by xenoliths), and another associated with a divergent setting when intraplate magmatism occurred (represented by the host rocks). With AFC modeling, it can be proposed that the Jeju volcanic rocks were formed by the fractional crystallization of the upper mantle combined with assimilation of the continental crust. The xenoliths in this study had different geochemical patterns from previously reported xenoliths, warranting further investigations.
... Because of the spatially and temporally dispersed nature of eruptions and their relatively short duration (weeks to a few years), such systems do not generally construct large volcanic edifices. The lack of burial of early eruptions means that field-scale eruptive histories can be investigated comprehensively from the onset of activity (Condit & Connor, 1996;Leonard et al., 2017), revealing changes occurring within the magma source area over the lifetime of the volcanic field (Brenna et al., 2012a;Valentine & Perry, 2006). Individual small volcanoes often form single scoria or phreatomagmatic cones or maars with small lava fields (Valentine and Gregg, 2008) and erupted volumes <<1 km 3 (Kereszturi et al., 2013), implying low magmatic flux from the mantle (Valentine & Hirano, 2010;Valentine & Perry, 2007). ...
... These were interpreted to represent crystal growth in storage areas within both the upper lithospheric mantle and the lower crust with subsequent magma mixing and crystal recycling (Figure 4.4a). Clinopyroxene crystals similarly display diverse zoning and distinct compositions (Figure 4.4b) in the Pannonian Basin volcanoes (Jankovics et al., 2016), as well as Eastern Austria (Dobosi et al., 1991), Jeju Island (Brenna et al., 2012a), the Hopi Buttes Volcanic Field (United States) (Re et al., 2017), and the Eifel Volcanic Field (Duda & Schmincke, 1985), for example. The occurrence of crystals derived from several levels within the plumbing systems and that have interacted with diverse magma batches implies that the plumbing system of even small-volume basaltic volcanoes is not as simple as the rock petrography may superficially suggest. ...
Intraplate basaltic systems, often occurring as fields of small monogenetic volcanoes, are dominated by eruption of alkaline basaltic rocks, ranging from nephelinite/basanite to transitional/subalkaline. Their generally primitive erupted compositions imply limited crustal modification, and hence they provide an important probe into deep, lithospheric mantle and partial melting processes. Partial melting and magmatic ascent processes can be investigated using the composition of crystals, glass, and whole rock, although a combination of these is preferable. The whole‐rock chemical variability within single eruptions or over the temporal and spatial extent of a volcanic field is controlled by the characteristics of the primary melting source, as well as near‐source percolative/reaction processes. Coupled crystal‐ and ‐whole‐rock detailed investigations are most promising to constrain the processes that modify primary melts into the primitive magmas that accumulate before ascent. Complex crystal textures and chemistry have so far demonstrated that basaltic magmas are principally processed and modified within the lithospheric mantle with minor modification en route through the crust. Fractional crystallization and magma mixing modify melts throughout ascent, and can imprint secondary chemical intra‐eruptive variability. Quantifiable temperature and pressure parameters based on crystal‐melt compositions constrain the depth of formation, and hence provide information about the role of different mineral phases in deep versus shallow chemical evolution. Volatile components in the melt (e.g., H2O and CO2) can be quantified on glass and melt inclusions. These analyses, coupled with solubility models, may help to reconstruct initial dissolved volatile content to further constrain the source characteristics and magmatic ascent dynamics. Integrated studies of crystals and melt paint a picture of extended lithospheric mantle to minor crustal processing resulting from the complex deep plumbing of monogenetic basaltic systems. This highlights the need for improved resolution to characterize true primary signatures and hence elucidate the formation of intraplate alkaline basalts.
... In order to test the prevailing hypotheses, we report a study of Jeju Island, a large Cenozoic intraplate volcanic center in the Korean Strait (Brenna et al., 2012a;Koh et al., 2013). According to previous studies (Choi et al., 2006;Kim et al., 2019;Tatsumi et al., 2005), trace element patterns are similar to the OIB trend, and radiogenic isotope compositions (Sr, Nd, Hf, and Pb) show the DMM-EM2 mixing relationship, like basalts reported in southeast Asia. ...
... Compared to the alkaline basalts, the tholeiitic basalts are less enriched in incompatible elements (Fig. 3) and have higher 87 Sr/ 86 Sr ratios, lower 144 Nd/ 143 Nd ratios, and higher Δ7/4 Pb values (Kim et al., 2019;Tatsumi et al., 2005). These differences in the radiogenic isotopes between the tholeiitic and alkaline basalts have been discussed in terms of the different depths of magma formation (Brenna et al., 2012a;Brenna et al., 2012b;Tatsumi et al., 2005) or anorthosite assimilation (Kim et al., 2019). Nevertheless, the tholeiitic and alkaline basalts have similar trends in the source lithologies based on the olivine compositions ( Figs. 7 and 8) and whole-rock compositions (Kim et al., 2019). ...
Jeju Island, South Korea, is a Cenozoic intraplate volcano located in East Asia. The Jeju basalts display ocean island basalt (OIB)-like trace element patterns and enriched mantle type 2 (EM2) radiogenic isotope compositions, but the source that enriched the mantle remains unclear. Here we report new geochemical compositions of basalts and xenoliths, including the first helium isotope and element analysis of olivine phenocrysts to constrain the source of basalt. Olivines in the Jeju basalts have 3He/4He ratios of 3.5 to 7.3 Ra while olivines in the mantle xenoliths are 2.9 to 6.3 Ra. They provide no evidence of a lower mantle plume but overlap the range of the regional subcontinental lithospheric mantle (SCLM) and OIBs with low 3He/4He values. Olivine phenocrysts included in the basalts show variations in Mn, Ni, and Ca concentrations with forsterite (Fo) contents, similar to the trend for olivines crystallized from the pyroxenite-derived melts. Elemental ratios of Ca-Fe-Ni-Mg-Mn for the olivines also indicate the pyroxenite contribution. Considering our results, it is suggested that the main source of the Jeju basalts is the SCLM containing pyroxenite. In addition, the tomography image shows the low-velocity zone extending to the asthenosphere mantle beneath the central Jeju Island. This implies that the localized asthenospheric upwelling is caused by edge-driven convection, and the high-velocity zones exist around Jeju island indicating a thick cratonic lithosphere. Therefore, we propose that the interaction between the SCLM component containing pyroxenite and the rising asthenosphere is the main mechanism to generate enriched basaltic magmas for the Cenozoic intraplate volcanism in East Asia, including Jeju Island.
... The basement contains Jurassic to Cretaceous granitoids and unconsolidated sediments, volcaniclastics and pre-Cambrian gneisses, which appear as xenoliths in tuffs and in drill cores (Baek et al., 2014;Choi et al. 2006;Lee 1982;Tatsumi et al. 2005). Spinel peridotite and pyroxenite xenoliths are common in alkali basalt lavas and tuffs and represent mantle-derived components (Yun et al. 1998;Choi et al. 2005;Kil et al. 2008;Brenna et al. 2012). ...
Jeju Volcanic Island is the largest island in South Korea and is considered a continental shelf intraplate volcanic island. In this study, MELTS, a powerful program for modeling magmatic evolution processes, was applied to simulate the fractional crystallization process of the low-alumina alkaline volcanic rock suite on Jeju Island. MELTS modeling was conducted at many isobaric pressures ranging from 2.0 GPa to 0.1 GPa, different oxygen fugacities (fO 2 ) from FMQ-3 to FMQ + 3, and different H 2 O contents. The results demonstrate that the most suitable fractionation model for the Jeju low-alumina alkaline magma involves a pressure of 0.2 GPa to 0.1 GPa and an oxygen fugacity close to the FMQ buffer. Additionally, an H 2 O content of 0.5 wt.% is the most consistent with the evolution trend and mineral composition of the natural rock suite on Jeju Island. Although MELTS possesses several limitations in terms of the stability of calibration, such as spinel overestimation and a lack of experiments on hydrous minerals (which should be improved), MELTS performs well in terms of temperature and pressure prediction and in terms of the assessment of other factors of the fractional crystallization process on Jeju Island. Consequently, to evaluate a magmatic process in a particular region, MELTS should be combined with other analyses and not relied upon independently.
... Through dating the sedimentary formation beneath the tuff ring, known as the Gosan Formation, it is estimated that Suwolbong formed around 17,000 years ago, when sea levels were 130 meters lower than today. OSL dating of the accidental quartz grains within the tuff ring, furthermore, estimates a formation date of around 18,000 years ago (Sohn, 1996;Cheong et al., 2007;Ahn et al., 2018;Brenna et al., 2012). Therefore, the tuff ring formed in a subaerial environment through phreatomagmatic explosions as magma violently interacted with groundwater at the height of the last ice age. ...
... Songaksan, Jeju Island, Korea, is a basaltic tuff ring produced by phreatomagmatic eruptions 3.7 ka BP in a coastal setting. A number of studies have been done on Songaksan regarding both syn-eruptive and post-eruptive depositional processes (Chough and Sohn, 1990;Sohn et al., 2002;Sohn and Sohn, 2019;Go and Sohn, 2021), magmatic processes (Sohn et al., 2002;Brenna et al., 2011;Brenna et al., 2012), diatreme processes (Go et al., 2017), and eruptive setting and ages (Sohn et al., 2002;Cheong et al., 2007;Ahn et al., 2015;Sohn et al., 2015;Yoon et al., 2017). Due to these previous studies, systematic and stratigraphically controlled sampling and high-resolution interpretations of ash aggregation processes in relation to diatreme conditions and depositional processes are possible. ...
Aggregation of ash generated by explosive volcanic eruptions controls the dispersal and residence time of ash in the atmosphere and, therefore, the hazard to aviation. Ash aggregation is particularly common in hydromagmatic volcanoes produced by explosive magma-water interactions. Nevertheless, few studies have been done on this process because of the lower risk of volcanic hazards posed by these volcanoes in comparison to classical stratovolcanoes. Observations of the microscopic textures of the tuff samples from a Holocene tuff ring in Jeju Island, Korea, show that the ash particles occur mainly in the form of coated particles and ash lumps, which are either rich or poor in clay minerals derived from the substrate. The clay-rich aggregates formed in the diatreme by cohesive and capillary bonding of clay-rich and water-undersaturated debris. When the diatreme was filled with clay-poor and water-saturated debris, particles were ejected mainly without ash coats and aggregation. Once emitted from the diatreme, the aggregates and uncoated/solitary particles could be further aggregated together or accreted on larger particles by liquid bonding, producing clay-poor aggregates, multiple-coated particles, and composite ash lumps. The ash aggregation occurred mainly in co-surge ash clouds and ash plumes but not in pyroclastic surges, in which the time available for ash aggregation was too short (a few tens of seconds or less). This study demonstrates that the substrate characteristics and environmental factors that can influence the material properties of the diatreme fill, such as the clay mineral and water contents, are the prime controls of ash aggregation in hydromagmatic volcanoes.
... Beginning with hydrovolcanic activities in the Quaternary Period of the Cenozoic era, Jeju Island was formed following volcanic activity around 1.8 million years ago (Park et al., 2000;Brenna et al., 2012a;Koh et al., 2013;Brenna et al., 2015). Located at the center of the island is Mt. ...
... Two endmember models propose that it may result either from deep-seated mantle plumes rooted in the core-mantle boundary (the "plume" theory; Morgan, 1971), or from lithospheric deformation related to plate tectonics without any input of lower mantle material (the "plate" theory; Anderson, 2000Anderson, , 2005Foulger, 2010). In the latter case, magmatism would stem from shallow thermal instabilities in the upper mantle (King and Ritsema, 2000) or from the collection of already existing partial melts in a heterogeneous upper mantle (Valentine and Perry, 2007;Valentine and Hirano, 2010;Brenna et al., 2012;Smith et al., 2021). In the context of lithospheric extension, asthenospheric decompression is an additional process for mantle partial melting and magma production (Ruppel, 1995). ...
... Two endmember models propose that it may result either from deep-seated mantle plumes rooted in the core-mantle boundary (the "plume" theory; Morgan, 1971), or from lithospheric deformation related to plate tectonics without any input of lower mantle material (the "plate" theory; Anderson, 2000Anderson, , 2005Foulger, 2010). In the latter case, magmatism would stem from shallow thermal instabilities in the upper mantle (King and Ritsema, 2000) or from the collection of already existing partial melts in a heterogeneous upper mantle (Valentine and Perry, 2007;Valentine and Hirano, 2010;Brenna et al., 2012;Smith et al., 2021). In the context of lithospheric extension, asthenospheric decompression is an additional process for mantle partial melting and magma production (Ruppel, 1995). ...
Many continental rifts are subjected to volcanism in tandem with rifting, which has raised a long-standing debate about whether magmatism is the cause or the consequence of plate fragmentation. To re-evaluate this chicken-and-egg question, we took advantage of five decades of research on the East African Rift System (EARS), the largest active continental rift on Earth, to explore the spatial and temporal relationship between rifting and magmatism. By comparing the co-occurrence of tectonics and volcanism since the Eocene with the present-day seismicity, we delimit the EARS as a ~ 5000 km-wide zone of volcano-tectonics made of four branches affecting not only East Africa but also the Mozambique channel and Madagascar. We then developed a quality filtering procedure of published radiometric ages in order to build two independent, robust, and comprehensive age compilations for magmatism and rifting over this extended EARS. Our thorough quality-checked selection of ages reveals that the EARS presents two distinct regimes of volcanism. Since the Upper Eocene, the rift system was affected by (1) pulses of volcanism in 500–1000 km-wide areas, and (2) a discontinuous but remarkably simultaneous volcanic activity, scattered along the four branches of the EARS since 25–27 Ma. Combining this spatio-temporal evolution of volcanism with a critical review of the timing of rifting, we show that the tectonics of the EARS evolves through time from trap-scale to plate-scale rifting. Until the Middle Miocene, extension structures first developed following flood basalt events and plateau uplifts. Then, volcanism resumed synchronously all over the EARS at ca. 12–12.5 Ma, followed by a general extensional deformation. This evolution, which cannot be explained by the sole action of a plume or of tectonics, is therefore interpreted in an intermediate way in which the EARS results from (1) extensive stresses acting on the African lithosphere in the long-lived context of the Gondwana breakup and (2) an overall complex mantle upwelling dynamics arising from the African Large Low Shear Velocity Province (LLSVP). We propose that extension stresses affecting the African lithosphere also modulate the melting of mantle anomalies and/or the collection of magma through the Pan-African belts. This influence explains the synchronous occurrence of many magmatic and tectonic events in the EARS and at the boundaries of the Nubia and Somali plates. Finally, our results suggest that the source of extension stresses affecting the African plate probably evolved from a dominant far-field origin to prevailing variations of gravitational potential energy (GPE) and a diverging basal shear of the Nubia and Somali lithosphere. This change would stem from an increase of the mantle flux in the Middle Miocene, yielding a change in the EARS’ dynamics from trap-scale to plate scale rifting.
... It is worth noting that there are conflicting theories about the origin of volcanism on Jeju Island. One theory interprets the entire island as a shield volcano [33], while another suggests that it is a composite volcano [34][35][36]. Also, according to a study conducted by [37], Jeju Island was formed based on the accumulation of outpoured lava flows and pyroclastic According to the extensive fieldwork and interpretation of stratigraphy, the alkalibasalts lava effusion on land started about 1 Ma years ago and continued until the Holocene [37,[39][40][41]. ...
Lava tubes, a major geomorphic element over volcanic terrain, have recently been highlighted as testbeds of the habitable environments and natural threats to unpredictable collapse. In our case study, we detected and monitored the risk of lava tube collapse on Jeju, an island off the Korean peninsula’s southern tip with more than 200 lava tubes, by conducting Interferometric Synthetic Aperture Radar (InSAR) time series analysis and a synthesized analysis of its outputs fused with spatial clues. We identified deformations up to 10 mm/year over InSAR Persistent Scatterers (PSs) obtained with Sentinel-1 time series processing in 3-year periods along with a specific geological unit. Using machine learning algorithms trained on time series deformations of samples along with clues from the spatial background, we classified candidates of potential lava tube networks primarily over coastal lava flows. What we detected in our analyses was validated via comparison with geophysical and ground surveys. Given that cavities in the lava tubes could pose serious risks, a detailed physical exploration and threat assessment of potential cave groups are required before the planned intensive construction of infrastructure on Jeju Island. We also recommend using the approach established in our study to detect undiscovered potential risks of collapse in the cavities, especially over lava tube networks, and to explore lava tubes on planetary surfaces using proposed terrestrial and planetary InSAR sensors.
... Beaucoup de travaux de recherche ont été menés sur les volcans monogéniques, mettant l'accent sur leur nature depuis la source jusqu'à la surface (Smith et al., 2008;Brenna et al., 2010;Valentine et Hirano, 2010). L'ascension rapide du magma et la courte histoire éruptive des volcans permettent d'étudier différents aspects de ce volcanisme, par exemple ils peuvent renseigner sut l'évolution magmatique des systèmes qui ont alimenté plusieurs petits volcans pendant de longues durées (millions d'années) (Németh et al., 2001;Kereszturi et al., 2011;Németh, 2011;Brenna et al., 2012). ...
This thesis aims to characterize the Aguelmane Sidi Ali monogenetic volcano (2.27 Ma) through a multidisciplinary study, in order to constrain its eruptive dynamics and the genesis of its magmas. The volcanological study allowed us to present an eruptive schema for this strombolian cone and to understand its volcanic setting. We suggest that the Aguelmane Sidi Ali scoria cone was formed by a short lived eruption that started with an initial explosive activity that produced pyroclastic deposits of Strombolian type. Following this initial phase and as the cone grew, the eruption changed to a Hawaiian lava-fountain style. Subsequently, the eruption became more stable, and changed to a
second regular Strombolian activity, rebuilding a new cone and leading to a volcano of 0.02 km3. Based on new petrographic and mineralogical data, this study made it possible to highlight the presence of Ba- and Ti-rich oxyphlogopite (up to 14.0 % pds BaO and 13.1 % pds TiO2). This exceptional mineral occurs mostly as euhedral to subhedral crystals lining the walls of zeolitic veinlets and cavities in the nephelinites. The Ba-coupled, Ti-Tschermak and Ti-oxy substitutions are major mechanisms of Ba and Ti incorporation in these micas. We propose that the latter may have crystallized under the influence of Ba-rich fluids derived from nephelinitic melts during late magmatic stages. In this study, we also performed major element spot analyses along profiles on Mg and Fe chemically zoned olivines from alkali basalts with the aim of investigating their time residence before
the eruption. The most probable diffusion times estimated through our modeling of diffusion, range from 1 to 2 months, from root zones located in the asthenospheric mantle and the Moho at 60 km and 35 km depth, respectively. Based on their geochemical compositions in major and trace elements, the lavas of the ASA volcano are classified as: alkaline basalts with normative nepheline and nephelinites, showing no genetic liaison. The two magmas are extracted from an enriched sub�continental mantle with a spinel peridotite composition, subject to differential melting rates: around 1% for nephelinites and 4 to 5% for alkaline basalts.
Keywords: Middle Atlas, Volcanism, Monogenetic, Transfer, Oxyphlogopite
... Jeju Island is a cumulative volcanic field located 90 km south of the Korean Peninsula (Brenna et al. 2012b). The island is predominately composed of Quaternary high-Al and low-Al alkali basaltic to trachytic lava (Tatsumi et al. 2005, Brenna et al. 2012a. The sampled outcrop is at least 15 m high and exposed for more than 30 m ( Figure 2c). ...
U‐Th disequilibrium dating uses the ratio of the intermediate 230Th daughter isotope to the 238U parent isotope to date zircon crystallisation for volcanic and plutonic rocks in Pleistocene–Holocene deposits. It is frequently used to constrain the duration and rate of magma recharge in volcanic systems. While ≤ 350 ka zircon is not in secular equilibrium in the 230Th system, the current U‐Th disequilibrium methodology uses reference materials that are > 350 ka. No reference material ≤ 350 ka has been available to validate the accuracy of the approach and ensure methods are repeatable across laboratories. This study presents zircon SS14‐28 from Jeju Island (South Korea) as a suitable reference material for U‐Th disequilibrium dating. Zircon SS14‐28 was analysed using two analytical approaches (SIMS and LA‐ICP‐MS) and four instruments: CAMECA IMS 1280, ASI SHRIMP II, sector field high resolution LA‐ICP‐MS and multi‐collector LA‐ICP‐MS, in four laboratories. These methods each individually result in isochrons gradients within uncertainty (2s) of each other (CAMECA: 0.532 ± 0.051 (MSWD = 0.64); SF‐HR‐LA‐ICP‐MS: 0.536 ± 0.054 (MSWD = 1.3); MC‐LA‐ICP‐MS: 0.533 ± 0.041 (MSWD = 0.67); SHRIMP II: 0.68 ± 0.22 (MSWD = 0.3)). The age proposed in this study is 82 ± 6 ka calculated from a combined isochron gradient of 0.529 ± 0.025 (MSWD = 0.87, n = 132).
... Individual eruption sequences may involve one or more distinct batches of primitive magma with mixing and/or sequential extraction of individual batches reflecting a range of melt parameters and depths of melt sourcing (e.g. Brenna et al., 2012;McGee et al., 2013;Brenna et al., 2021). Despite broad ranges of chemical composition, consistent temporal patterns of compositional evolution in fields as a whole are not normally observed. ...
The Auckland intraplate volcanic province consists of four small fields of basaltic monogenetic volcanoes. Each of these was active for a period of ~1 Myr and during the last 3 Myr the locus of magmatic activity migrated northward in discrete ~50 km steps. The most recent of these volcano fields is the Auckland Volcanic Field (AVF) in which individual eruptions have produced discrete magma batches within the composition range nephelinite to sub-alkaline basalt. This range of compositions is explained by partial melting involving variable melt/solid ratios together with modal heterogeneity in their mantle source. Eruptions in the field have been irregularly spaced during its 200 kyr life with repose periods varying between ≤0.1 and 13 kyr. Although most of Auckland's volcanoes represent a single period of eruption, paired eruption sequences in which smaller more alkaline magma batches have been followed by more voluminous less alkalic magmas have also occurred. A significant flare-up in activity at about 30 kyr produced compositionally discrete eruptions from at least five spatially separate locations all within a temporal interval of as little as 100 years. An interpretation of these data is that each event (volcano) in the AVF represents a discrete batch of magma extracted from an source with the capacity of producing a compositional variety of magma. Such a source forms when upwelling mantle undergoes adiabatic rise and exists as a metastable entity at the asthenosphere-lithosphere boundary for prolonged periods (10⁵–10⁶ years) during which time it is tapped to create individual magma batches. The shorter term magma extraction events that produced individual volcanoes in the AVF are suggested to be the result of crustal scale tectonic events. The behaviour of these four spatially separate monogenetic volcanic systems at temporal intervals of <10⁶ years is likely linked to the long term tectonic evolution of the Pacific-Australian Plate boundary beneath the New Zealand region.
... Delivery of enriched crustal trace element and isotope signatures, characteristic of OIBs globally, to the source of East Asian Cenozoic continental intraplate basalts has also been linked to the Mesozoic rollback of the Paleo-Pacific slab, which induced rutile dehydration at post-arc depths (Xu and Zheng, 2017;Zheng et al., 2020). Bivariate plots of Nb/Th vs. Zr/Nb and Zr/Y vs. Nb/Y (Fig. 10E-F) (Brenna et al., 2012a;Kimura et al., 2018;Kuritani et al., 2011;Wang et al., 2017;Zou et al., 2003), indicate that crustal contamination has not affected the geochemical composition of most East Asian Holocene intraplate basalts. Therefore, the geochemical evidence suggests that recent slab metasomatism has not significantly contributed to the composition and formation of the East Asian Holocene intraplate volcanoes. ...
A number of Holocene volcanoes in East Asia — Jeju, Ulleungdo, Tianchi, Longgang, Jingbohu, Erkeshan and Wudalianchi — are located far (600–1500 km) from the nearest subduction zone. The origin of these intraplate volcanoes remains unclear, and mechanisms proposed to explain their origin include plume activity and subduction processes with or without slab fluid involvement. Here we evaluate the feasibility of these mechanisms. We present an analysis of available geophysical data, including slab geometry models and the full-waveform FWEA18 tomography model, as well as statistical tests on a compilation of geochemical data. High-resolution tomography data provide no evidence for a deep-seated mantle plume. Instead, the tomography shows that Tianchi, Longgang, Jingbohu, Erkeshan and Wudalianchi are located above edges of the Pacific slab, which is stagnant near the 660 km discontinuity under East Asia. The tomography also shows that Jeju is situated above a section of the Philippine Sea slab that has subducted to the 410 km discontinuity. While the intraplate volcanoes are underlain by subducted slabs, their geochemical signatures do not support melting via slab metasomatism typical of subduction zones. Instead, the Holocene intraplate volcanoes are alkaline and have trace element compositions comparable to those of ocean island basalts. Given the absence of geophysical or geochemical evidence for plume activity or slab metasomatism, we propose that volcanism has been generated by decompression melting associated with convective upwellings at the edges of the Pacific and Philippine Sea slabs. Tectonic reconstructions suggest that the Pacific slab may have been stagnant in the mantle transition zone for millions of years, so we speculate that localised convection at Pacific slab edges was triggered by changes in Western Pacific subduction dynamics during late Neogene–Quaternary time. The geophysical and geochemical data also suggest that Quaternary rollback of the Philippine slab might be responsible for volcanism at Jeju, which is located at the leading edge of the Philippine Sea slab.
... A notable feature of MVFs is the occasional compositional variation of magma during eruption (Nemeth et al., 2003;Smith et al., 2008;Brenna et al., 2010, Brenna et al., 2012a, 2012bMcGee et al., 2012). Geochemical variations have been commonly attributed to mantle source heterogeneities, fractional crystallization, melting, crustal contamination, and ascent dynamics (Timm et al., 2011;Kereszturi and Nemeth, 2012;McGee et al., 2013;Smith and Nemeth, 2017). ...
The Kamo Volcanic Field (KVF), a partly preserved Quaternary volcanic sequence of three small-volume basaltic
volcanoes located about 10 km northwest of the Aira caldera in the Kagoshima graben in southwestern Kyushu,
Japan. It forms part of the volcanic arc of Japan and consists of the Late Pleistocene Aojiki volcano and two Holo�cene maars: Sumiyoshiike and Yonemaru. Here, we report the first results of a combined lithostratigraphic and
petrogenetic study of these three volcanoes. Eruptive products of Aojiki volcano comprise an initial scoriaceous
tephra, a lava flow and scoria fall from the cone. Sumiyoshiike and Yonemaru maar products are mainly scoria
fall and pyroclastic surge deposits, which are closely related in time and were principally emplaced by
phreatomagmatic explosive eruptions. Major and trace element data of the eruptive products suggest four groups
of magmas. Aojiki scoria (G1: SiO2= 50.3-51.4) are the most evolved, followed by Aojiki tephra/lava (G2: SiO2 =
48.1-50.7), while Sumiyoshiike (G3: SiO2 = 47.0-48.5) and Yonemaru (G4: SiO2= 46.3-48.5) are relatively less
evolved. These magmas are derived from the same spinel bearing (lithospheric) mantle source previously
metasomatized by subducting fluids and might have evolved in independent magma chambers mainly by frac�tional crystallization and crustal contamination except for G1 magma which may have suffered some associated
... However, comprehensive studies of monogenetic eruptions based on whole-rock major, trace element, and isotope geochemistry have increasingly revealed systematic changes in the composition of the magma with the eruption progress, which often correlate with changes in the volcano-stratigraphy (e.g. Brenna et al., 2010Brenna et al., , 2011Brenna et al., , 2012McGee et al., 2012). These chemical variations have been attributed to a range of processes, including complex heterogeneous mantle melting and subsequent mixing of multiple magma batches, and/or variable degrees of fractionation and crustal assimilation (e.g. ...
Paricutin volcano is the youngest monogenetic cone from the Michoacán-Guanajuato volcanic field (Mexico), with an excellent historical eruption record from February 1943 to March 1952. The magma emitted during the nine years of activity was compositionally zoned from basaltic andesite to andesite. This eruption has been considered a classic example of magma differentiation controlled by crustal assimilation combined with fractional crystallization. However, a recent geochemical study of the eruption products points to mantle source heterogeneity and fractional crystallization as the key processes involved in the compositional variability of the magmas. Here we present a detailed petrological characterization of the minerals (olivine, plagioclase, pyroxene, Cr-spinel, and (Ti-) magnetite) to shed light into the processes that led to the chemical evolution of the eruptive products. Our sample set includes the early tephra from the first weeks/months and the whole sequence of lava flows that followed. The mineral assemblage, texture, and chemical composition show a systematic evolution between the products from the opening of the explosive vent to the effusive stage. The early tephra are basaltic andesites with oscillatory-zoned olivine and plagioclase, zoned Cr-spinel, and rare pyroxene xenocrysts. In contrast, later erupted tephra and post-January 1944 lavas are basaltic andesites and andesites with normally-zoned olivine, Cr-spinel inclusions in equilibrium with the host olivine, and frequent orthopyroxene (after December 1947) with minor chemical zoning. The mineral chemistry data and the olivine diffusion timescales, together with whole rock geochemistry, suggest a convective magma regime with large temperature and oxygen fugacity gradients characterized by short timescales (few days) during the opening stage, followed by a steadier magma regime with longer timescales (few months) and including periodic magma recharge, mixing, and fractional crystallization. In addition, the mineralogical evidence we have gathered does not support considerable crustal assimilation at Paricutin. This study shows that monogenetic eruptions are far from being geochemically simple, and instead involve multiple magma batches with complex storage and mixing stages.
... However, comprehensive studies of monogenetic eruptions based on whole-rock major, trace element, and isotope geochemistry have increasingly revealed systematic changes in the composition of the magma with the eruption progress, which often correlate with changes in the volcano-stratigraphy (e.g. Brenna et al., 2010Brenna et al., , 2011Brenna et al., , 2012McGee et al., 2012). These chemical variations have been attributed to a range of processes, including complex heterogeneous mantle melting and subsequent mixing of multiple magma batches, and/or variable degrees of fractionation and crustal assimilation (e.g. ...
Paricutin volcano is the youngest monogenetic cone from the Michoacán-Guanajuato volcanic field (Mexico), with an excellent historical eruption record from February 1943 to March 1952. The magma emitted during the nine years of activity was compositionally zoned from basaltic andesite to andesite. This eruption has been considered a classic example of magma differentiation controlled by crustal assimilation combined with fractional crystallization. However, a recent geochemical study of the eruption products points to mantle source heterogeneity and fractional crystallization as the key processes involved in the compositional variability of the magmas. Here we present a detailed petrological characterization of the minerals (olivine, plagioclase, pyroxene, Cr-spinel, and (Ti-) magnetite) to shed light into the processes that led to the chemical evolution of the eruptive products. Our sample set includes the early tephra from the first weeks/months and the whole sequence of lava flows that followed. The mineral assemblage, texture, and chemical composition show a systematic evolution between the products from the opening of the explosive vent to the effusive stage. The early tephra are basaltic andesites with oscillatory-zoned olivine and plagioclase, zoned Cr-spinel, and rare pyroxene xenocrysts. In contrast, later erupted tephra and post-January 1944 lavas are basaltic andesites and andesites with normally-zoned olivine, Cr-spinel inclusions in equilibrium with the host olivine, and frequent orthopyroxene (after December 1947) with minor chemical zoning. The mineral chemistry data and the olivine diffusion timescales, together with whole rock geochemistry, suggest a convective magma regime with large temperature and oxygen fugacity gradients characterized by short timescales (few days) during the opening stage, followed by a steadier magma regime with longer timescales (few months) and including periodic magma recharge, mixing, and fractional crystallization. In addition, the mineralogical evidence we have gathered does not support considerable crustal assimilation at Paricutin. This study shows that monogenetic eruptions are far from being geochemically simple, and instead involve multiple magma batches with complex storage and mixing stages.
... Jeju Island is a 31 km by 73 km elliptical cumulative volcanic field of Quaternary age, situated 90 km south of the Korean peninsula ( Figure 1, Supplementary Material II Figure 1, 2) (Brenna et al., 2012;Woo et al., 2013a). Jeju Island is formed predominantly by lavas ranging from high-Al and low-Al alkali basalts to trachytes (Tatsumi et al., 2005;Brenna et al., 2012aBrenna et al., , 2012b. The island comprises Jurassic to Cretaceous basement, covered by continental shelf deposits of quartzite and mudstone, overlain by approximately 100 m of volcaniclastic deposits (Seoguipo formation). ...
Models of volcanic eruption periodicity are vital for hazard prediction, but require an understanding of the past pattern of melt evolution and transport. Zircon double-dating combines (U-Th)/He methods with U-Pb and U-Th disequilibrium geochronology to determine the timing of volcanic eruptions for rocks with a particular emphasis on those younger than ca. 1 Ma. This paper focuses on the Jeju Island intraplate volcano in South Korea, and compares a previously proposed model for trachyte eruption with new zircon double-dating results.
The results document four episodes of trachyte eruption on Jeju. The oldest trachytes were erupted at ca. 750–477 ka, followed by an episode at ca. 97–53 ka. Two further eruptive episodes occurred at ca. 31–23 ka and ca. 2 ka. This ca. 2 ka eruption age is the first geochronological documentation of such young eruptive activity from the island. In addition to the new eruption ages, there is evidence for three separate stages of zircon crystallisation, which are correlated with the three oldest eruption stages. The strong temporal correlation of zircon crystallisation and eruption on Jeju points to a simple magmatic plumbing system. These observations have important implications for hazard monitoring and mitigation on Jeju Island by highlighting the historical trachyte eruptions and the magmatic tempo for this system.
... A notable feature of MVFs is the occasional compositional variation of magma during eruption (Nemeth et al., 2003;Smith et al., 2008;Brenna et al., 2010, Brenna et al., 2012a, 2012bMcGee et al., 2012). Geochemical variations have been commonly attributed to mantle source heterogeneities, fractional crystallization, melting, crustal contamination, and ascent dynamics (Timm et al., 2011;Kereszturi and Nemeth, 2012;McGee et al., 2013;Smith and Nemeth, 2017). ...
Abstract
The Kamo Volcanic Field (KVF), a partly preserved Quaternary volcanic sequence of three small-volume basaltic volcanoes located about 10 km northwest of the Aira caldera in the Kagoshima graben in southwestern Kyushu, Japan. It forms part of the volcanic arc of Japan and consists of the Late Pleistocene Aojiki volcano and two Holocene maars: Sumiyoshiike and Yonemaru. Here, we report the first results of a combined lithostratigraphic and petrogenetic study of these three volcanoes. Eruptive products of Aojiki volcano comprise an initial scoriaceous tephra, a lava flow and scoria fall from the cone. Sumiyoshiike and Yonemaru maar products are mainly scoria fall and pyroclastic surge deposits, which are closely related in time and were principally emplaced by phreatomagmatic explosive eruptions. Major and trace element data of the eruptive products suggest four groups of magmas. Aojiki scoria (G1: SiO2=50.3-51.4) are the most evolved, followed by Aojiki tephra/lava (G2: SiO2 =48.1-50.7), while Sumiyoshiike (G3: SiO2 =47.0-48. 5) and Yonemaru (G4: SiO2=46.3-48.5) are relatively less evolved. These magmas are derived from the same spinel bearing (lithospheric) mantle source previously metasomatized by subducting fluids and might have evolved in independent magma chambers mainly by fractional crystallization and crustal contamination except for G1 magma which may have suffered some associated mixing.
... Individual eruption sequences may involve one or more distinct batches of primitive magma with mixing and/or sequential extraction of individual batches reflecting a range of melt parameters and depths of melt sourcing (e.g. Brenna et al., 2012;McGee et al., 2013;Brenna et al., 2021). Despite broad ranges of chemical composition, consistent temporal patterns of compositional evolution in fields as a whole are not normally observed. ...
... In this case, the poloidal-like mantle flow affected areas located at 800 km away from the trench. Brenna et al. (2012Brenna et al. ( , 2015 also invoked a mantle upwelling triggered by a distal subduction to explain the magmatic activity in Jeju Island volcanic field (Korea). Here, small volumes of recent (1.8 Ma-1Ka) OIB type magmas erupted~650 km away from the southwestern Japan subduction zone, where the subduction of the Philippine Sea Plate induced the upwelling of mantle flow (however, for constrating interpretations of the Korean magmatism see Tang et al., 2014;Kimura et al., 2018). ...
The complex European–Adria geodynamic framework, which led to the formation of the Alpine belt, is considered responsible for the orogenic magmatism that occurred in the Central Alps along the Periadriatic/Insubric Line (late Eocene–early Oligocene) and the anorogenic magmatism that occurred in the Southeastern Alps (late Paleocene–early Miocene). While the subduction-related magmatic activities are, as expected, near convergent margins, the occurrence of the intraplate-related magmatism is still puzzling. Therefore, in this work new geochemical and geochronological data of magmatic products from the Veneto Volcanic Province (VVP, north–east Italy) are provided to constrain the Cenozoic intraplate magmatism of the Southeastern Alps. The VVP is formed by dominant basic–ultrabasic (from nephelinites to tholeiites) magmatic products and by localized acid (latitic, trachytic, and rhyolitic) volcanic and subvolcanic bodies. Trace element patterns and ratios suggest that the mantle source of the alkaline magma types was a garnet lherzolite possibly metasomatised by carbonatitic melts and with residual phlogopite.
According to the biostratigraphic records and our new ⁴⁰Ar/³⁹Ar ages, VVP eruptions occurred in several pulses, reflecting the extensional phases experienced by the Eastern Alpine domain. The volcanism started in the late Paleocene in the western sector of the VVP where activity was widespread also during the Eocene (45.21 ± 0.11 Ma – 38.73 ± 0.44 Ma). In the eastern sector eruptions took place in the early Oligocene (32.35 ± 0.09 Ma – 32.09 ± 0.29 Ma) and in the early Miocene (~23–22 Ma).
From the studies so far undertaken, the anorogenic magmatic activity of the VVP was interpreted as resulting from mantle upwellings through slab window(s) following the European slab break-off, which occurred at ~ 35 Ma. However, considering (i) new tomographic images evidencing a continuous subvertical (~ 500 km in depth) slab beneath the Central Alps, and (ii) the onset of magmatic activity in the VVP in the late Paleocene (i.e., before the slab break-off) and its continuation until the Miocene, a better suited geodynamic scenario is required to explain the anorogenic magmatism. The westward rollback of the European slab caused the retreat and steepening of the subducting plate. As a consequence, sub-slab mantle material escaped and upwelled from the front of the slab and created a poloidal mantle flow. The latter induced the breakdown of carbonates in calcareous metasediments and carbonated metabasics within the subducting oceanic slab, providing carbonatitic melts, which could be responsible for the metasomatism of the VVP mantle sources. After that, the poloidal mantle flow also induced (i) the extensional deformation in the overriding Adria microplate, (ii) the decompressional melting of VVP mantle sources, and (iii) the intraplate affinity of the VVP magmatism. During these processes, the Adria microplate also rotated counterclockwise, forming sedimentary basins, and allowing the poloidal mantle flow to affect different portions of the overlying lithosphere, generating syn-estensional magmatism within the VVP.
... All lavas of this island belong to alkali rock series. Geology and petrology of this island were first summarized by Lee [1982 a, b] and later, Brenna et al. [2012] discussed basaltic magmatic systems in the Jeju Island volcanic area mainly from a geochemical standpoint. Hasenaka et al. [1998 a, b] discussed geomorphological characteristics of the monogenetic volcanoes on this island, and completed a catalogue of these cones. ...
Monogenetic volcanoes are a frequent type of volcanisms on Earth. They are frequently paired with polygenetic ones. We can distin- guish them by their place of origin. If a new vent opens on or near an existing volcano, it will join with a main crater of the volcano, or form a parasite on a flank of the volcano. If the vent opens at a certain distance from an existing volcano, its activities are independent of that volcano and its magma sources are also separate. At present we have difficulty in distinguishing between monogenetic and poly- genetic volcanoes, when we do not know the formers’ history of eruptions. We are sure that Jorullo and Paricutin, both born before our eyes, are important and indispensable examples for discussion on monogenetic volcanism. The present discussion starts fundamentally from the knowledge of these two volcanoes. Among examples of monogenetic cones, we find clusters of monogenetic cones much smaller than Jorullo and Paricutin in volume, and densely distributed in a certain area of the world. The present paper discusses the three areas in the Far East. Morphological characteristics of the three areas show a strong volume contrast between component cones of the cluster areas and the twins of Jorullo and Paricutin. Averaged component volume of the former is approximately equal to 1 / 102 times as large as that of the latter. The present author tentatively presents qualitative interpretation of the above quantitative characteristics, mainly from a geophysical standpoint.
... Such studies have revealed that even small individual eruptions can be petrogenically complex, fed by mixed magmas or single magma batches that have undergone variable fractional crystallization and/or assimilation (e.g. Strong and Wolff, 2003;Cervantes and Wallace, 2003;Johnson et al., 2008;Erlund et al., 2009;Brenna et al., 2010Brenna et al., , 2012McGee and Smith, 2016;Hughes et al., 2018). The ability to characterize compositional changes in single eruptions can provide detailed insight into the relative roles and rates of processes that affect individual batches of basaltic magma, which may be subtle or homogenized and undetectable in studies of longer-term, multi-eruption time scales and processes. ...
The Blue Dragon lava flow in southern Idaho is one of the largest Holocene basaltic flows in the contiguous U.S.
Multispectral remote sensing and field mapping of the flow have revealed its 280 km2 surface is divided into five large
sub-areas with different spectral reflectance and morphology that correspond with distinct periods of the eruption. The
flow grew outward from its source fissures primarily via a complex system of lava tubes, and stratigraphic relations at
the boundaries of the mapped sub-areas provide temporal information about their order of emplacement. This offers a
unique opportunity to reconstruct chemical and mineralogical changes in the source magmas as the eruption
progressed. In this first comprehensive study of the compositional diversity of the Blue Dragon flow, geochemical data
from 28 rock samples show that over the course of the eruption the lavas became progressively more primitive and
depleted in incompatible trace elements, and Pb isotopes show subtle increases. These observations are best
explained by eruption from a zoned magma source due to variable assimilation-fractional crystallization (AFC), with the
initial eruption of more evolved and enriched magmas that may have been residual from the previous eruption,
followed by progressively higher proportions of a more primitive and depleted component from deeper in the system.
Differences in lava surface color and morphology among the five mapped eruptive phases may indicate changes in
eruptive temperature, flow rate, or both as the Blue Dragon eruption progressed. The results support a growing body
of evidence that systematic studies of geochemical variations in monogenetic and short-duration lava flows can reveal
the relative influence of processes that affect single batches of magma.
... Jeju Island is an intraplate alkali basaltic volcano built on the southeastern Yellow Sea continental shelf 9,10 (Fig. 1A). Songaksan is a young phreatomagmatic volcano, which erupted ~3.7 ka BP at the southwestern coast of the island 11,12 (Fig. 1B), providing a complete cross-section of a tuff ring (Fig. 1C). ...
The distinction between primary and secondary volcaniclastic deposits, which are currently defined as the “direct” products of volcanic eruptions and the “reworked” products of the former, respectively, is the first step to interpreting volcaniclastic deposits, particularly the genetic connection with active volcanism. The distinction appears straightforward, but is not always applicable to natural deposits. During the 3.7 ka BP eruption of the Songaksan tuff ring, Jeju Island, Korea, there was an invasion of typhoon. The tuff ring was partly submerged underwater and affected by wave activity for over a day, resulting in a peculiar volcaniclastic deposit composed of both vent-derived (primary) and substrate-derived (reworked or secondary) volcaniclastic particles. We propose a new term “reprocessed” for a category of volcaniclastic deposits or particles, which originated directly from volcanic eruption but was deposited finally by nonvolcanic processes. Here we show that both reprocessed and reworked particles can coexist in the same volcaniclastic deposit, making it impossible to differentiate it into either a primary or a secondary deposit according to the current definition of volcaniclastic deposits. We thus define the secondary volcaniclastic deposits as comprising either or both of reprocessed and reworked volcaniclastic particles.
... Monogenetic systems typically erupt basaltic magmas within a wide compositional range from strongly silica undersaturated to saturated and oversaturated (Smith and Németh, 2017). Strikingly, many mono- genetic volcanoes are characterized by a systematic change in the chemical composition of the magma as the eruption progresses, often clearly correlated with the volcano-stratigraphy ( Brenna et al., 2010Brenna et al., , 2011Brenna et al., , 2012McGee et al., 2012;Németh et al., 2003;Rasoazanampanary et al., 2016;Smith et al., 2008). These variations have been variously attributed to variable degrees of fractionation/ crystallization ( Luhr and Carmichael, 1985), different degrees of crustal assimilation (e.g., McBirney et al., 1987;Cebriá et al., 2011), high pressure crystal-melt interactions (e.g., Smith et al., 2008), successive partial melting of distinct source components (e.g., Cook et al., 2005;Haase and Renno, 2008), and/or variations in melting and ascent dy- namics (e.g., McGee et al., 2011;Reiners, 1998). ...
Paricutin volcano is the youngest and most studied monogenetic cinder cone in the Michoacán-Guanajuato volcanic field (Mexico), with an excellent historical record of its nine years (February 1943 to March 1952) of eruptive activity. The eruption produced lavas and tephras that range in composition from basalt to andesite. We have conducted new major and trace element and isotopic studies (whole rock Sr-Nd-Pb-Os) of the Paricutin lavas and tephras spanning the entire duration of the eruption, together with xenoliths found in early erupted lavas and bombs, and crustal samples representative of the Paricutin basement. This work contributes to our understanding of the potential roles of mantle source heterogeneity, subduction-related metasomatism, and crustal assimilation in the petrogenesis of arc magmas; moreover this study underscores the complexity of magma generation and evolution in monogenetic volcanoes. Although Paricutin has been traditionally considered as the classical example of magma evolution by fractional crystallization and crustal contamination, our multi-isotopic study has revealed that Paricutin compositional variations are inconsistent with significant crustal assimilation. Alternatively, we suggest that Paricutin's geochemical evolution can be explained by a combination of variable degrees of fractional crystallization of magmas produced by melting heterogeneous mantle beneath the TMVB that has been metasomatized by subduction components including sediment- and oceanic crust-derived fluids.
Jeju Volcanic Island is the largest island in South Korea which is known as the continental shelf intraplate volcanic island. MELTS, one of the powerful programs utilizing for modeling magmatic evolution processes, is applied to simulate fractional crystallization process of low-alumina alkaline volcanic rock suite in Jeju Island. At many isobaric pressure conditions from 2.0 GPa to 0.1 GPa as well as different oxygen fugacities (fO 2 ) from FMQ-3 to FMQ + 3 and H 2 O content, MELTS modeling were conducted as various calculations. The results demonstrate that the most suitable fractionation model for Jeju low-alumina alkaline magma would occur from 0.2 GPa to 0.1 GPa with oxygen fugacity FMQ buffer. These contain 0.5 wt.% H 2 O in the system leading to more consistent with evolution trending of as well as mineral composition in natural rock suite on Jeju Island. Although MELTS still possesses several limitations in the stability of calibration such as spinel overestimation as well as a lack of experiments for hydrous minerals which have been renovated, MELTS exhibits its affection on temperature and pressure prediction as well as assess other factor of fractional crystallization process on Jeju Island. Consequently, to evaluate a magmatic process in a particular region, it would be better to combine MELTS with other analyses rather than operating independently.
The origin of the late Cenozoic intraplate volcanoes in the NE Asia has sparked debate, with explanations ranging from deep mantle plume to lithospheric extension and decompression melting of mantle upwelling by distal subduction tectonics. The Jeju volcanic field (JVF), being the closest late Cenozoic intraplate volcano to the subduction zone, sheds light on whether the intraplate volcanism is primarily plume-related or linked to plate tectonics. This study determined the primary magma composition for JVF basalts, using the most primitive bulk-rock samples (MgO > 8.5 wt%), by incrementally adding olivine to melt until reaching equilibrium with olivine (Mg# = 90) in the residual mantle. The estimated temperature and pressure of mantle melting are 1,466–1,587 °C and 2.1–4.1 GPa for anhydrous primary magma and 1,347–1,512 °C and 2.0–3.6 GPa for hydrous primary magma within the acceptable range of water contents (H2O = 2–4 wt%) reported from the Chinese intraplate basalts. The pressure estimates suggest that the minimal depth of the lithosphere-asthenosphere boundary is approximately ∼50–55 km. The mantle potential temperature for anhydrous primary magma is estimated to be 1,460–1,580 °C, higher than 1,300–1,400 °C of the ambient upper mantle, indicating a hot thermal regime below the JVF. Despite the absence of geophysical evidence for a mantle plume beneath the JVF, this study proposes that the hot mantle wedge is likely caused by the lateral influx or edge-driven convective upwelling of thermal plume near the leading edge of the stagnant Pacific Plate slab, contributing to the big mantle wedge. Intraplate volcanism in the JVF is proposed to be driven by lithospheric extension and decompression melting of the convective upwelling of hot sub-lithospheric mantle, influenced by distal subduction tectonics in the hot subduction zone. This model is supported by the present-day tectonics observed in the hot Ryukyu subduction zone, SW Japan.
To constrain the timing of magma emplacement and eruption of volcanic rocks at Mt. Halla, Jeju Island, South Korea, a range of dating techniques (U-Pb, U-Th disequilibrium, and (U-Th)/He dating of zircon, and 40Ar/39Ar dating of groundmass) were applied to one trachyandesite sample and one trachyte sample. Trachyandesite sample CS92-7 from north of Mt. Halla yielded a homogeneous population of zircon U-Pb crystallization ages averaging 97 ± 3 ka and U-Th disequilibrium ages averaging 96.2 + 6.2/−10.6 ka. Both groundmass 40Ar/39Ar ages and zircon (U-Th)/He ages corrected for disequilibrium record the time of sample cooling, yielding ages of 105 ± 5 ka and 105.4 ± 4.0 ka, respectively. The nearly concordant crystallization and cooling ages are interpreted to document eruption of the sample shortly after its relatively rapid crystallization in the magma reservoir. The eruption age of this sample, based on the available geo- and thermochronological results, is estimated at 100.4 ± 7.6 ka. Trachyte sample SS35-23 from south of Mt. Halla yielded an overdispersed spectrum of zircon crystallization ages, suggesting protracted crystallization in the magma reservoir over a period of at least 140 ka. Weighted mean ages of 40.0 ± 5.9 ka and 39.4 ± 3.8 ka (determined from U-Pb and U-Th disequilibrium dating of the youngest coherent subpopulation, respectively), provide a maximum limit for the eruption age. The eruption age is directly constrained in this work at 32.4 ± 8.4 ka by (U-Th)/He data. The 40Ar/39Ar age of 54 ± 7 ka is distinctly different from the zircon crystallization and eruption ages, and is considered to be inaccurate due to a possible issue with sample contamination or excess argon. The combined geochronological methods applied in this study constrain the timing of zircon crystallization, magma residence, and eruption of volcanic rocks on Jeju Island, and provide essential information further improving our understanding of the chronological history of volcanic rocks on Jeju Island.
Using a multidisciplinary approach to understand the subsurface processes behind the formation of maar‐diatreme volcanoes is of growing interest. While geophysical characterization can visualize the diatreme and the feeding dike system beneath the volcano at a reasonable scale, such data are rare and generally unavailable. Stratigraphic‐controlled sampling and geochemical analysis of pyroclasts within the ejecta ring can, however, provide substantial information on dike evolution and the influence of the magmatic plumbing system on the growth of these volcanoes. Such investigation is presented here for the Barombi Mbo Maar (BMM), a complex maar of the Cameroon Volcanic Line (CVL) composed of a pile of tephra units linked to multiple explosive phases that were grouped into three eruptive episodes. Major and trace element compositions of lavas collected from the different eruptive units indicate that the erupted magmas at BMM consist mainly of basalt, trachybasalt and basanite, with Oceanic Island Basalts (OIB) and high μ ( μ = ²³⁸ U/ ²⁰⁴ Pb) (HIMU) signatures. Compositional modelling suggests that partial melting occurred at different degrees in the garnet‐to‐spinel transition zone from one episode to another. The repetition of eruptions with big gaps between them, the presence of another large adjacent old maar crater next to the 2.5 km crater of the BMM, and the overall similarity in geochemical compositions from one eruption to another suggest a deep high‐productive zone in the mantle beneath the BMM. The latter productive zone was capable of generating magma batches episodically to fuel several individual monogenetic eruptions at the same location.
This article carried out an integrated study of the mineral composition, whole-rock elemental geochemistry, and zircon U-Pb dating for the rift-related alkaline volcanoes at Wadi Natash, South Eastern Desert (SED), Egypt, to investigate their magmatic evolution and origin. The Natash volcanoes (NV) are characterized by explosive and extrusive polyphases trending in NW-SE with a diverse compositional range of basalts, trachyandesites, trachytes, and rhyolites/comendites categorized by distinct high concentration of HFSEs and REEs. Zircon U-Pb dating offers ages of 96 ± 2.5 to 86 ± 2 Ma, constraining Late Cretaceous eruption of the NV. The basalts have high HFSE, REE, and Nb/U ratios similar to Nb-rich basalts derived from OIB source. The trachyandesites/trachytes and rhyolites have high ratios of Ga/Al (8–12), HFSF (Nb = 79–283 ppm, Zr = 433–1807 ppm), and REE (671–728 ppm) and low concentrations of Sr, P, Ti, and Eu which are analogous to typical A1-type granites. The Nb enrichment in all rock types (81–283 ppm) is controlled by both magmatic and hydrothermal processes. The NV were originated from an enriched lithospheric mantle source metasomatized by asthenosphere-derived fluids and then experienced fractional crystallization (FC) with no significant input of crustal contamination. Petrographical and geochemical criteria elucidate olivine + clinopyroxene as the main fractionated phases, followed by hornblende + plagioclase + Fe-Ti oxides + apatite during the more evolved stage. In addition to FC, the phenocryst textures conform a variety of magmatic processes, such as multi-crustal storage, crystallization, volatile fluxing, and degassing and magmatic evolution in open systems with a fluctuating temperature, pressure, and water. The geothermobarometic data point to a polybaric-polythermal system with numerous magma residence regions fluctuating from lower-middle (1.4–1.25 GPa and 1154–1136 °C) to shallow crustal levels as demonstrated by plagioclase crystallization (0.75–0.26 GPa and 1048–980 °C) and Fe-Ti oxides (937–904 °C) when magmas ascend to the surface. The evolution of the NV can be linked to mantle plume magmatism and extensive Mesozoic alkaline ring complexes recorded along the Egypt/Sudan border, Northeast Africa, and Northern Arabia in an extensional setting, highlighting that the assembly of the Rodinia supercontinent might have been finalized prior to ca. 86 Ma.
Zinc isotope data for late Cenozoic intraplate basalts from Mt. Baekdu (North Korea) and Jeju Island (South Korea) were determined to characterize their mantle source lithologies. The average δ⁶⁶Zn values (relative to JMC-Lyon) are 0.34‰ ± 0.08‰ (2SD; N = 13) for the Mt. Baekdu basalts and 0.37‰ ± 0.08‰ (2SD; N = 12) for the Jeju basalts, which are higher than values for refractory peridotites (0.18‰ ± 0.06‰) from the lithospheric mantle beneath the North China Craton. Given that Zn isotopic fractionation is limited during lithospheric processes, such as crustal contamination, magmatic differentiation, degassing, or thermal/chemical diffusion, the elevated δ⁶⁶Zn values indicate the incorporation of recycled carbonates into the sub-lithospheric mantle source. Plots of Zn/Fe versus δ⁶⁶Zn or δ²⁶Mg for the Korean basalts can be explained by mixing of at least three source lithologies: (1) carbonated peridotite; (2) recycled siliciclastic sediments; and (3) eclogite. Strontium–Nd–Pb isotopic systematics show that the mantle source follows the DMM-EM1 array for the Mt. Baekdu basalts and a DMM-EM2 array for the Jeju basalts. Both the enriched components have isotopically light Zn and heavy Mg, which are typical of recycled siliciclastic sediments. Combined with the Pb isotope and trace element data, the Zn isotopic compositions suggest that the EM1 component could be ancient K-hollandite-bearing siliciclastic sediments and the EM2 component could be recently recycled clay-rich pelagic sediments.
The spatial distribution of vents is ultimately controlled by the geometry of the magma source at depth, stress orientation and pre‐existing crustal structures. In this work, the spatial patterns of vent distribution in Jeju Island, South Korea, are examined through several methods. Comparison of the obtained distribution patterns with previous knowledge about the volcanic evolution of the island, and recent results of seismic tomographic images provides a comprehensive interpretation of vent distribution in terms of the underlying structure of the sub‐volcanic system. Thus, it is proposed that under certain conditions the probability density functions of some groups of vents can be used to obtain rough estimates of the depths of magma storage. Also, it is shown that the overall spatial pattern of vents provides an integrated image of the sub‐volcanic system both in space and time. The results reported in this work can therefore help us to avoid unjustified speculations concerning the nature of activity present in zones of distributed volcanism elsewhere.
The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence, which are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectively. The tuff ring is overlain by another marine volcaniclastic formation, suggesting erosion and reworking by marine processes because of post-eruption changes of the sea level. Dramatic changes of the chemistry, accidental componentry, and ash-accretion texture of the pyroclasts are also observed between the tuff beds deposited before and after the storm invasion. The ascent of a new magma batch, related to the chemical change, could not be linked with either the Earth and ocean tides or the meteorological event. However, the changes of the pyroclasts texture suggest a sudden change of the diatreme fill from water-undersaturated to supersaturated because of an increased supply of external water into the diatreme. Heavy rainfall associated with the storm is inferred to have changed the water saturation in the diatreme. Songaksan demonstrates that there was intimate interaction between the volcano and the environment.
Jeju Island is an intraplate volcanic island with enigmatic origins, located on the continental shelf south of the Korean Peninsula. A dense temporary seismic array, operated on Jeju Island from 2013 to 2015, revealed several important constraints on the magma plumbing system of Jeju Island. In this study, we determined the deep crustal seismic structure beneath Jeju Island from the teleseismic P-to-S converted phases (receiver functions) recorded from 20 temporary and three permanent stations. We removed the contribution of near-surface reverberations in the resulting receiver functions by applying a resonance removal filter. We estimated crustal P-to-S velocity ratio (VP/VS) and discontinuity depth to provide teleseismic constraints on the composition and structure. We observed two major seismic discontinuities, which are the upper boundaries of a mid-to-lower crustal low-velocity zone (LVZ) and the Moho transition zone. The depth to the upper boundary of the LVZ is deep in the west and southeast (24–30 km) and shallow in the northeast (8–11 km). The LVZ can be interpreted as an extensively distributed residual magma plumbing system, with magma batches stalled at various levels and at various degrees of crystallization, consistent with the chemical diversity of Jeju magmas. The seismic characteristics of the Moho transition zone vary greatly among regions. The top interface of the Moho transition zone is at a wide range of depth (26–40 km), and is shallow at 26–29 km depths beneath central Jeju, suggesting a complex Moho topography. The presence of mafic cumulates and partially molten mushes may contribute to the observed shallow seismic discontinuity at a depth of 26–29 km. The lack of obvious crustal thickening below the shield volcano, Mt Halla, may be associated with mantle upwelling or presence of mafic underplating and cumulates below Jeju. Spatial variations of crustal VP/VS represent highly heterogeneous crustal composition, resulting from magma differentiation during the evolution of the island.
Jeju Island offshore of the southern Korean Peninsula is an isolated intraplate volcano formed by multiple basaltic eruptions from the Pleistocene (∼1.8 Ma) to the Holocene (∼3.7 ka). Due to the lack of available seismic data, magma structures at upper crustal depths of the island have not been clearly revealed. In this study, we imaged upper crustal isotropic and radial anisotropic structures beneath the island using ambient noise data from a temporary seismic network. A series of transdimensional hierarchical Bayesian inversions were performed to construct upper crustal (1–10 km) isotropic and anisotropic structures. Surface wave (Rayleigh and Love wave) group and phase velocity dispersion data were jointly inverted for 2–15 s. The results show that layers of negative anisotropy (VSH < VSV) are predominant at shallower (<2 km) and deeper (>5 km) depths, which was interpreted as reflecting dyke swarms responsible for the more than 400 cinder cones at the surface and the vertical plumbing systems supplying magma from deeper sources, respectively. Additionally, a layer with significantly positive radial anisotropy (VSH > VSV, up to 5 per cent) was found at middle depths (2–5 km), and was interpreted as horizontally aligned magma plumbing systems (e.g. sills) through comparisons with several other volcanoes worldwide. In comparison with the isotropic structure, the positive anisotropic layer was separated into upper and lower layers with locally neutral to slightly fast and slower shear wave velocities, respectively, beneath the largest central crater (Mt. Halla). Such a structure indicates that the cooled upper part of the magma plumbing systems formed within the horizontally developed sill complex, and is underlain by still-warm sill structures, potentially with a small fraction of melting. With dykes predominant above and below, the island-wide sill layer and locally high-temperature body at the center explain the evolution of the Jeju Island volcanoes by island-forming surface lava flows and central volcanic eruptions before and after the eruptions of cinder cones.
Stable isotope signatures of geologic, atmospheric, and hydrologic sources are transferred to the ecosystem through the food chain. The present study used Sr isotope data of soil and plant samples collected from Jeju Island to explore the roles of these sources in the local bioavailable Sr pool. X-ray diffraction and Sr isotope data revealed that the soil materials came from diverse sources such as weathered volcanic bedrock, marine carbonate sediments, and allochthonous aeolian dust. Dilute (1 M) ammonium nitrate- and acetic acid-leachates of the soil samples yielded 87Sr/86Sr ratios between 0.7047 and 0.7092, which were slightly but discernably higher than ratios for Jeju volcanic rocks reported in the literature (0.7045 ± 0.0004). This indicates that relatively more radiogenic Sr, probably in carbonate and aeolian dust, was preferentially released to the leachates. Geopedological control over the bioavailable Sr pool was demonstrated by the positive 87Sr/86Sr correlation between leachable soil fractions and the corresponding plant samples. The enhanced 87Sr/86Sr ratios of plants (0.7062–0.7092, average = 0.7077 ± 0.0012) reflect the influence of seawater. These Sr isotope data provide a scientific basis for addressing archaeological and historical questions related to Jeju Island.
Southwest Japan is an island arc formed by subduction of the Philippine Sea (PHS) plate. The Quaternary magmatism in this region is characterized by eruptions of high‐Sr andesites and dacites, considered to have been derived by melting of the PHS plate. The loci of these volcanoes spatially coincide with seismic discontinuities of the subducted PHS plate. Thus, the magmatism is interpreted as the result of slab melting at the plate tears. However, the processes that promote slab tearing remain unclear. In this study, we applied geochronological and geochemical analyses to late Cenozoic volcanic rocks in southwest Japan as tracers of slab morphology. Two different magma types, ocean‐island basalt (OIB) and island‐arc basalt (IAB), have occurred over 12 million years (Myr). These two magmas are attributed to different integrations of melts extracted from an originally fertile mantle; the OIBs from high temperature melt (1,300–1,400°C) were extracted at a depth of 40–80 km, whereas the IABs were extracted from a shallower, lower temperature region (30–60 km, 1,200–1,350°C). Secular change in Sr enrichment of IAB likely arose due to a transition of slab‐derived fluids, incorporated into magmas as they formed, from water‐ to melt‐dominant one. Progressive shallowing of the subducted PHS plate is responsible for secular change in the properties of slab‐derived fluids as well as rollback of OIB volcanoes. Production of chemically variable magmas in the Chugoku district is the surface expression of distorting slab morphology by interaction between mantle and the subducting plate.
Jabal Al Abyad (2093 m) represents a case study of cone-type monogenetic volcano in Harrat Khaybar, Saudi Arabia., formed in subaerial intracontinental setting. Its formation involved multiple eruption styles including phreatomagmatic eruption of tuff cone truncated by spatter cone of glassy rhyolitic lava flow. The main construction of Jabal Al Abyad is a thick felsic tuff sequence interbedded in part with obsidian rocks. The felsic tuffs range from coarse to fine ash comprising mainly crystal fragments, lithic fragments and vitric shards. The sequence also exhibits changing from massive to stratified lithofacies. The geochemical signatures indicate that Jabal Al Abyad volcanics are rhyolitic peralkaline within plate volcanic rocks related to continental rifting system. Al Abyad volcanics are classified into two groups: A and B of which the former (A) is characterized by relatively higher Ti, Zr, Y, Hf, Th, La, and Ce concentrations. The peralkaline within plate signature, low La/Nb and elevated Nb/Ta ratios (11–17, OIB-like signature) as well as high concentrations of HFSEs (Zr, Y, La, Ce, Rb, Nb, Hf) support the genetic relationship and a heterogeneous mantle origin for the Al Abyad volcanics. The REE and trace element modeling interpretations indicate that a progressive closed-system fractional crystallization of an assemblage dominated by plagioclase and clinopyroxene from the alkaline mafic magma similar to that of St. Helena-SH-35 could produce range of composition from intermediate to acidic ones.
Spectacular reactions textures developed during the non-isochemical breakdown of orthopyroxene and spinel in peridotite mantle xenoliths in intraplate alkaline basalts from the Auckland Volcanic Field and the Dunedin Volcano in New Zealand, and Jeju Island in South Korea. Mantle orthopyroxene is replaced by symplectitic intergrowths of silica-rich glass and olivine (± clinopyroxene ± orthopyroxene) with individual minerals showing large diffusion gradients at their margins proximal to the host melt. The glasses are basaltic to trachytic and formed by incongruent melting of orthopyroxene and subsequent re-equilibration by diffusion and mixing during changing boundary conditions with the host magma. Although the glass composition is strongly dependent on the alkalinity of the host magma, the distance to the reacting contact and the respective phase assemblage that develops in the reaction zone (melt + ol ± clinopyroxene ± orthopyroxene), the most evolved melts converge at trachytic composition. Diffusion-driven Fe enrichment for mantle olivine indicates residence timescales within the host magma on the order of weeks to several months.
Monogenetic volcanoes can yield eruptive suites displaying substantial complexity in compositional characteristics. The Bahariya monogenetic volcanoes (BMV) in the Western Desert, Egypt are a good example. They comprise complex stratigraphic deposits involving scoria cone, lava flows, and subvolcanic sills and dikes related to diverse eruptive styles. Whole-rock and mineral chemistry and 40Ar–39Ar geochronology are used here to document the petrogenesis, source characteristics, and evolution of the Bahariya volcanoes. The architecture of the BMV is the product of two alkali magma batches: pyroclastics and lava flows forming explosive scoria cone (batch 1) and subvolcanic sills (batch 2). The two batches show contrast in the concentrations of incompatible trace elements and REE as well as element ratios such as Nb/Yb, Gd/Yb, Nb/U, and Ce/Pb (36, 5.0, 44, 30 vs. 17, 4.0, 39, 24 for batch 1 and 2, respectively). New whole-rock 40Ar/39Ar dating displays consistent age of 23.71 ± 0.06 and 23.73 ± 0.01 Ma for magma emplacement of batch 2. Batches 1 and 2 share common LILE and LREE enrichments and HFSE depletions, analogous to a HIMU-like, mantle-derived OIB source described from other Paleogene–Oligocene intraplate magmatic provinces in North Africa and worldwide. Trace element modeling proposes a derivation of the Bahariya volcanoes from parental melts generated by 8–12% partial melting of garnet lherzolite and amphibole-bearing garnet lherzolite at 2.18 ± 0.33 and 1.77 ± 0.33 GPa for batch 1 and batch 2, respectively, across the lithosphere–asthenosphere boundary at c. 70–90 km depth (2.14–2.76 GPa). These sources had been earlier metasomatized by volatile-, LILE- and HFSE-rich fluid(s) originating from Neoproterozoic subduction or a Phanerozoic plume. Fractional crystallization involved olivine + clinopyroxene in both batches followed by Fe–Ti oxides + apatite in batch 2. Furthermore, crust contamination/assimilation was an irrelevant process at crustal level during magma ascend to the surface. Data results of the geo-barometric computations disclose two magma storage levels involving intermediate to lower crustal levels at c. 35 km (1.05 GPa) for batch 1 and mid-crustal level at c. 25 km depth (0.75 GPa) for batch 2. This study delivers proof that magmas emitted at Bahariya depression can undergo complex polymagmatic processes during their storage and passage in the crust, mainly due to the existence of a multilevel plumbing system. The origin of the BMV, as with other within-plate volcanoes in North Egypt, appears to be allied to extension-induced asthenosphere upwelling activated by limited exclusion of thickened lithospheric root under a passive rift tectonic regime coupled with the development of lithospheric thinning and continental breakup in North Africa.
This chapter deals with some of the basic concepts of geochemistry. We commence our journey on the road from geochemistry to geochemometrics. The analytical methods can be classified into eight major groups. The lower limits of detection (LODs) of most instruments are not random numbers but obey the odd–even effect of nuclear stability. From an extensive database of Pliocene to Holocene fresh igneous rocks, we illustrate the way statistics and computation can be applied to the geochemistry of earth materials. Both central tendency and dispersion parameters are presented as a novel approach for the subject of geochemistry. This would be a major step towards geochemometrics. The major and most common trace element concentrations of all volcanic rock types are presented and evaluated from the Student t and ANOVA tests, documenting thus the similarities and differences between or among different magma and rock types. These statistical inferences are presented for the first time in the literature. More importantly, the geochemometric methodology for the composition of earth materials is established.
Jeju Island, which lies on the continental shelf in the southern Korean Peninsula, is the emergent portion of a basaltic volcanic field that has erupted since the Early Pleistocene (ca. 1.8 Ma). Volcanic activity that continued into historic times (ca. 1 ka) formed an elongated shield with a central edifice (Mt. Halla) and more than 300 monogenetic cones and rings. The establishment of a temporal framework for Jeju volcanism, particularly during the Late Pleistocene and Holocene activities, requires geochronological tools other than radiometric dating techniques, which are based on parent-daughter isotope pairs with geologically long half-lives, such as ⁴⁰Ar/³⁹Ar dating. In this study, we conducted quartz optically stimulated luminescence (OSL) dating of palaeosols intercalated with basaltic lava flows and scoria deposits, presumably ejected from three monogenetic volcanoes (Cheoreum, Darangsh and Dunjibong volcanoes) in the northeastern part of the island. Quartz extracts from the palaeosols had moderate to dim sensitivity to optical stimulation, but several prerequisite tests of the measurement protocols for equivalent dose estimation were successful. The coarse (63–250 μm) and fine (4–11 μm) quartz fractions yielded continuous wave (CW)-OSL ages of 19.9–7.0 and 18.6–6.7 ka, respectively, both of which were broadly consistent with the radiocarbon dates (10245–7440 Cal yr BP). These ages indicate that lava flows and scoria deposits covering the palaeosols are younger than ~7 ka. The pulsed OSL signals in coarse quartz extracts from the palaeosols suffered from poor counting statistics, thus it is recommended that they not be applied solely (i.e., without any other absolute ages to compare) to dating dim samples. From one of the sites investigated here, the averaged sedimentation rate of the palaeosol is estimated to be ~0.05 mm/yr, based on stratigraphically consistent CW-OSL ages. The OSL ages presented in this paper, together with previous OSL and radiocarbon ages, confirm that Jeju volcanic island was regionally active during the Holocene.
Jeju Island (JI) is an intraplate volcanic field located at the continental margin of Northeast Asia. This volcanic island has been formed by multiple eruptions from the Pleistocene to the Holocene (~3.7 ka), which have yielded hundreds of monogenetic volcanic cones and a central basaltic shield. To understand the volcanic structures and mechanism beneath JI, we deployed 20 broadband temporary seismometers across the island for over two years (October 2013 to November 2015). We investigated the crustal and upper mantle structures in JI for the first time using the gathered data. Through teleseismic travel time tomography, we obtained images of the lithospheric structure related to the volcanic system. A major finding was the identification of a prominent low‐velocity anomaly (<‐0.3 km/s in P wave velocity relative to the surrounding high‐velocity region) beneath the summit of the central shield volcano at greater depths (50–60 km), which separates into low‐velocity zones at shallower depths (10–45 km). Based on previous geological observations, the anomalies were interpreted as a magmatic system, potentially with partial melting. Moreover, relatively high‐velocity zones were consistently imaged to the north, east, and west of the island, indicating relatively thick lithospheric structures at the southern margin of the continental lithosphere beneath the Korean Peninsula. Based on the geometries of the imaged structures, we suggest that a focused decompressional melting at sublithospheric depths and complex magma interactions within the lithosphere resulted in the characteristics of JI volcanism as intraplate magmatic activities that are isolated in space and confined in time.
SUMMARY: Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs.
In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (≤1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (≤2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type (eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by
This study presents petrochemistry and absolute ages of subsurface volcanic rock cores from twenty(20) boreholes in the eastern lowland (altitude loom below) of Jeju Island, Handeong-Jongdal-Udo-Susan-Samdal-Hacheon areas, and discusses topography and volcanism in the area. The subsurface volcanic rock cores are mainly basalts in composition with minor tholeiitic andesites and basaltic trachyandesites. Sequences of intercalated tholeiitic, transitional and alkalic lavas suggest that tholeiitic and transitional to alkalic lavas must have erupted contemporaneously. Especially, occurrences of trachybasalts and basaltic trachyandesites at the bases in the area imply that the volcanism in the area was initiated with slightly differentiated alkaline magma activity. The absolute ages of the subsurface volcanic rock cores range from . The lava-forming Hawaiian volcanic activities of the eastern lowland can be divided into five sequences on the basis of sediment distribution, whole rock geochemistry and absolute ages of the subsurface volcanic rock cores; stage I-U, stage II and stage III during syn-depositional stage of Seoguipo Formation, and stage IV and stage V(younger than 100Ka) during post-depositional stage. In the eastern lowland of Jeju Island, compositional variations and local occurrences of the subsurface volcanic rocks as well as existences of various intercalated sediment layers (including hydrovolcanogenic clasts) suggest that the volcanism must have continued for long time intermittently and that the land has been progressively glowed from inland to coast by volcanic activities and sedimentation. It reveals that the subsurface volcanic rocks in the eastern lowland of Jeju Island must have erupted during relatively younger than 200Ka of stages IV and V. The results of this study are partly in contrast with those of previous studies. This study stresses the need that previous reported volcanic activities in Jeju Island based on K-Ar ages of volcanic rocks should be carefully reviewed, and that stratigraphic correlation from boreholes should be conducted by quantitative criteria combined with petrography and petrochemstry as well as radiometric studies of volcanic rock cores.
Three-dimensional shear wave speed structure of the upper mantle beneath
the Japanese Islands and the surrounding regions is constructed from the
measurements of inter-station phase speeds of surface waves. We employ
the dense broad-band seismic network (F-net), deployed throughout Japan,
as well as permanent stations of global seismic network in East Asia. A
temporary broad-band seismic network in Far-East Russia, which has been
constructed as a part of the Stagnant Slab Project since 2004, is also
used in combination with the permanent stations. Using seismic events
from 2005 to 2007 with moment magnitude greater than 6.0 and depth
shallower than 100 km, we measure the phase speeds of the
fundamental-mode Rayleigh and Love waves, working with the conventional
two-station technique. Phase speed maps of the Japanese Islands and the
Sea of Japan are obtained from the inversions of inter-station phase
speeds that are measured for a large number of station-pairs. We have
collected over 5300 paths for Rayleigh waves and 3800 paths for Love
waves. The phase speed maps of Rayleigh waves, in the period range from
25 to 140 s, are inverted to obtain an isotropic 3D shear wave speed
model in the depth range from 40 to 200 km. The isotropic S wave model
represents prominent fast wave speed anomalies in northeastern Japan,
associated with the subducting Pacific Plate. Fast anomalies of the
lithosphere beneath the Sea of Japan are also imaged, implying that the
average thickness of lithosphere beneath the Yamato Rise and Japan Basin
is about 60±10 km. Immediately below this oceanic lithosphere,
slow anomalies are found in the asthenosphere beneath the entire region
of the Sea of Japan in the depth down to about 200 km. In southwestern
Japan, the low-angle subduction of the Philippine Sea Plate is mapped
clearly, indicating that the northern end of the plate extends beyond
the northern coast of the Chugoku region, reaching beneath the Oki
Islands in the Sea of Japan. A strong low velocity anomaly off the west
coast of Kyushu is found in the depth down to about 130 km, which
supports the existence of an upwelling flow beneath this area. We also
invert the phase speed maps of Rayleigh and Love waves in the period
range from 30 to 80 s simultaneously, to construct the radially
anisotropic shear wave speed model. A remarkable anisotropy with SH >
SV is found in the mantle wedge beneath northeastern Japan, while only
weak anisotropy is seen beneath the Sea of Japan. Such anisotropic
properties, which cannot readily be obtained from body wave studies
only, will be an important key to understanding the dynamic processes in
this tectonically actively region.
The technique of joint inversion of surface-wave dispersion and teleseismic P-wave receiver functions is used as a tool to derive a three-dimensional image of crustal velocities in the southern part of the Korean peninsula. The station-specific surface-wave dispersion consists of two components a long-period (10 150 sec) Rayleigh-wave phase velocity dispersion for the peninsula and short period (0.5 20 sec) tomographic Rayleigh- and Love-wave group velocity dispersion based on an analysis of > 2100 empirical Green's functions derived from the cross-correlation of ground noise recorded with broadband velocity and acceleration sensors. When combined with teleseismic P-wave receiver functions from broadband, short-period and acceleration sensors at 58 sites, a three-dimensional picture of the south Korean crust results. Spatial variations are seen in the depth to the Moho (28 32 km) and the degree of an upper crustal shear-wave velocity gradient from 3.0 to 3.5 km/s. Shear-wave velocities in the upper kilometer are typically greater than 3.0 km/s except in the southeast in the volcanoclastic Gyeongsang basin where the velocities are 5-10% lower. An average velocity structure is used for moment tensor inversion. The unique aspect of this effort is the use of the many accelerometers which permits fine spatial resolution of the structure.
The Songaksan tuff ring (STR) is one of several recent hydrovolcanic centers on Jeju Island, Korea, which provides an excellent example of proximal-to-distal facies changes in wet pyroclastic surge deposits. A multidisciplinary study has been carried out on the STR and adjacent lithostratigraphic units to constrain absolute age, geochemical characteristics, and Quaternary depositional history. A number of rock units were identified inside the crater of the STR, including Scoria deposit I, trachybasalt lava, Scoria deposit II, and a late-stage basaltic tuff, indicative of a rather complex sequence of magmatic and phreatomagmatic eruptions after the construction of the tuff ring. Petrochemical analysis shows that the STR was generated from different magma batches that fractionated from a homogenous magma chamber, and the early erupted magma was more evolved and volatile-rich. Reworking of the STR commenced shortly after the hydromagmatic eruption in a high-energy nearshore environment, resulting in deposition of the Hamori Formation. The formation is composed of planar-stratified and low- to high-angle cross-stratified tuffaceous (pebbly) sandstones and occurs up to an altitude of about 4 m above present sea level. 14C dating of molluscan shells beneath the formation indicates that it began to be deposited after about 4000 yr BP. Detailed sedimentary logging reveals that the formation consists of several stratal packages bounded by laterally persistent and distinct lithologic boundaries, probably formed by millennial-scale sea-level fluctuations. Occurrence of another hydrovolcanic sequence (the Sinyangri Formation) on the opposite side of Jeju Island, having similar sedimentary characteristics and ages, suggests that the sea-level fluctuations as seen in the Hamori Formation have affected a wide area of Jeju Island, probably related to the high-frequency sea-level oscillations during the post-6 ka BP regression period in the East Asian region. It can be concluded that the formation of the STR was possible because of the Holocene transgression, which made the present coastal areas water-saturated and adequate for hydrovolcanic eruptions. The STR in turn contributed to record high-frequency sea-level fluctuations during the Holocene via acting as a local and short-lived but affluent source of loose sediment.
We have determined the pressure and temperature of the spinel–garnet transition close to the solidus of fertile and depleted peridotite from a combination of synthesis, sandwich and garnet-seeded experiments. Garnet is unstable in MORB-Pyrolite below 2.8 GPa (depths 1450°C) are required to generate the 3–5% melting in the garnet field implied by recent trace element and isotope studies. It appears likely, therefore, that the `garnet signature' arises from some mechanism other than anhydrous melting of garnet peridotite.
Ultramafic xenoliths found in alkali basalts from Jeju Island, Korea are mostly spinel lherzolites accompanied by subordinate amount of spinel harzburgites and pyroxenites. The combination of results from a two-pyroxene geothermometer and Ca-in-olivine geobarometer yields temperature-pressure (T-P) estimates for spinel peridotites that fall in experimentally determined spinel lherzolite field in CaO-Fe-MgO-Al2O3-SiO2-Cr2O3 (CFMASCr) system. These T-P data sets have been used to construct the Quaternary Jeju Island geotherm, which defines a locus from about 13 kbar at 880 degreesC to 26 kbar at 1040 degreesC. The geothermal gradient of Jeju Island is greater than that of the conventional conductive models, and may be as a result of a thermal perturbation by the heat input into the lithospheric mantle via the passage and emplacement of magma. Spinel-lherzolite is the main constituent rock-type of the lithospheric mantle beneath Jeju Island. Pyroxenites may be intercalated in peridotites at similar depth and temperature as re-equilibrated veins or lenses.
Geophysicists disagree whether Earth's mantle is a single convective cell or whether it is divided into convective layers. In his Perspective, Anderson reviews the evidence and concludes that the case for layered convection is strong. He also argues that plate tectonics may be driving upper mantle convection, rather than the other way around as traditionally believed. Sophisticated convection simulations will be needed to test this hypothesis.
High-P phase equilibria studies on a high-MgO basalt from the Tortuga ophiolite complex indicate that olivine + orthopyroxene + clinopyroxene + garnet are its liquidus phases at 25 kbar. The data are combined with results obtained on other tholeiitic basalt compositions, and are used to construct pseudoliquidus phase diagrams for evaluating and predicting the nature of primary magmas and melting of the mantle at high P. -J.A.Z.
The Tertiary to Recent basalts of Victoria and Tasmania have mineralogical and major element characteristics of magmas encompassing the range from quartz tholeiites to olivine melilitites. Abundances of trace elements such as incompatible elements, including the rare earth elements (REE), and the compatible elements Ni, Co and Sc, vary systematically through this compositional spectrum. On the basis of included mantle xenoliths, appropriate 100 Mg/Mg + Fe+2 (68-72) and high Ni contents many of these basalts represent primary magmas (i.e., unmodified partial melts of mantle peridotite). For fractionated basalts we have derived model primary magma compositions by estimating the compositional changes caused by fractional crystallization of olivine and pyroxene at low or moderate pressure. A pyrolite model mantle composition has been used to establish and evaluate partial melting models for these primary magmas. By definition and experimental testing the specific pyrolite composition yields parental olivine tholeiite magma similar to that of KilaeauIki, Hawaii (1959-60) and residual harzburgite by 33 per cent melting. It is shown that a source pyrolite composition differing only in having 0.3-0.4 per cent TiO2 rather than 0.7 per cent TiO2, is able to yield the spectrum of primary basalts for the Victorian-Tasmanian province by ∼4 per cent to ∼25 per cent partial melting. The mineralogies of residual peridotites are consistent with known liquidus phase relationships of the primary magmas at high pressures and the chemical compositions of residual peridotite are similar to natural depleted or refractory lherzolites and harzburgites. For low degrees of melting the nature of the liquid and of the residual peridotite are sensitively dependent on the content of H2O, CO2 and the CO2/H2O in the source pyrolite.The melting models have been tested for their ability to account for the minor and trace element, particularly the distinctively fractionated REE, contents of the primary magmas. A single source pyrolite composition can yield the observed minor and trace element abundances (within at most a factor of 2 and commonly much closer) for olivine melilitite (4-6 per cent melt), olivine nephelinite, basanite (5-7 per cent melt), alkali olivine basalt (11-15 per cent melt), olivine basalt and olivine tholeiite (20-25 per cent melt) provided that the source pyrolite was already enriched in strongly incompatible elements (Ba, Sr, Th, U, LREE) at 6-9 x chondritic abundances and less enriched (2.5-3 x chondrites) in moderately incompatible (Ti, Zr, Hf, Y, HREE) prior to the partial melting event. The sources regions for S.E. Australian basalts are similar to those for oceanic island basalts (Hawaii, Comores, Iceland, Azores) or for continental and rift-valley basaltic provinces and very different in trace element abundances from the model source regions for most mid-ocean ridge basalts. We infer that this mantle heterogeneity has resulted from migration within the upper mantle (LVZ or below the LVZ) of a melt or fluid (H2O, CO2-enriched) with incompatible element concentrations similar to those of olivine melilitite, kimberlite or carbonatite. As a result of this migration, some mantle regions are enriched in incompatible elements and other areas are depleted.Although it is possible, within the general framework of a lherzolite source composition, to derive the basanites, olivine nephelinites and olivine melilitites from a source rock with chondritic relative REE abundances at 2-5 x chondritic levels, these models require extremely small degrees of melting (0.4 per cent for olivine melilitite to 1 per cent for basanite). Furthermore, it is not possible to derive the olivine tholeiite magmas from source regions with chondritic relative REE abundances without conflicting with major element and experimental petrology arguments requiring high degrees (≧15 per cent) of melting and the absence of residual garnet. If these arguments are disregarded, and partial melting models are constrained to source regions with chondritic relative REE abundances, then magmas from olivine melilitites to olivine tholeiites can be modelled if degrees of melting are sufficiently small, e.g., 7 per cent melting for olivine tholeiite. However, the source regions must be heterogenous from ∼1 to ∼5 x chondritic in absolute REE abundances and heterogerieous in other trace elements as well. This model is rejected in favor of the model requiring variation in degree of melting from ∼4 per cent to ∼25 per cent and mantle source regions ranging from LREE-enriched to LREE-depleted relative to chondritic REE abundances.
The crystallization sequences in olivine-rich nephelinitic and basanitic compositions have been experimentally studied under dry conditions at pressures up to 36 kb. Electron microprobe analyses of olivines, clinopyroxenes, garnets, and orthopyroxenes enable calculation of possible crystal fractionation trends for these magmas at various pressures. Low-pressure fractionation is dominated by olivine and yields derivative liquids of higher silica content and showing rapid iron enrichment. At pressures of 18-27 kb, fractionation is controlled by aluminous clinopyroxene with minor olivine or garnet. Derivative liquids show marked depletion in calcium accompanying silica depletion and increasing degree of undersaturation. .At pressures greater than 27 kb, crystal fractionation is controlled by garnet+clinopyroxene separation. Chemical analyses of these phases allow quantitative calculations of possible fractionation which show that large degrees of crystallization are required to produce quite small changes in silica content and in degree of undersaturation. In addition, fractionation by garnet and clinopyroxene separation is accompanied by depletion in calcium content in the more undersaturated rocks and high degrees of crystallization are necessarily accompanied by enrichment in iron relative to magnesium. These effects are inconsistent with the characteristics of natural magmas of mantle derivation in the range from alkali olivine basalts to olivine melilitites. It is concluded that separation of garnet and clinopyroxene under upper mantle conditions does not produce the natural magma series from olivine-rich tholeiite to olivine nephelinite and olivine melilitite. The transient role of orthopyroxene over a very small P, T range in the melting interval of two of the experimental compositions suggests that an olivine-rich basanite may be developed by small degrees of partial melting of a source pyrolite under dry conditions at 60-80 km depth. This liquid, which would form in equilibrium with residual olivine, aluminous orthopyroxene, and aluminous clinopyroxene, would contain approximately 5 per cent normative orthoclase, 5 per cent albite, 12 per cent nepheline, 20 per cent anorthite, 22 per cent diopside, and 31 per cent olivine.
Abundant spinel lherzolite xenoliths showing distinctively different textural types such as protogranular, porphyroclastic, and mylonitic texture are trapped in the basaltic rocks from southeastern part of Jeju Island. These xenoliths show the textural spectrum from coarse-grained protogranular through porphyroclastic with bimodal grain size to fine-grained and foliated mylonitic texture. They tend to decrease in grain sizes and show more linear grain boundaries and more frequent triple junctions from protogranular through porphyroclastic to mylonitic. Spinel has different occurrence mode according the textural type. Spinel is always associated with orthopyroxene in protogranular texture, whereas it is scattered and independent of orthopyroxene in mylonitic texture. Additionally, porphyroblast from porphyroclastic and mylonitic textures has internal deformation features such as kink band, undulatory extinction and curved lamella, whereas neoblast is strain-free. These textural features indicate increasing degree of static/dynamic recrystallization from protogranular through porphyroclastic to mylonitic texture. The mg#[] of olivine, orthopyroxene and clinopyroxene is relatively constant (ol: 88-91; opx: 89-92; cpx: 89-92) regardless of textural differences. The mg# of constituent minerals, NiO content (0.3~0.4 wt%) and MnO content (0.1~0.2 wt%) of olivine are similar to those of mantle xenoliths worldwide, also indicating that studied spinel lherzolite xenoliths were mantle residues having experienced 20~25% partial melting. The geochemical and textural characteristics have close relations showing that LREE and incompatible trace elements content of orthopyroxene and clinopyroxene increases from protogranular through porphyroclastic to mylonitic. These observations suggest that the studied mantle xenoliths experienced metasomatism by LREE enriched melt or fluid after partial melting, indicating a close relation between deformation and metasomatism. The metasomatism was possibly confined to narrow shear zones from where porphyroclastic and mylonitic textured xenoliths originated. These shear zones might favorably drive the percolation of LREE-enriched melts/fluids responsible for the metasomatism in the lithospheric mantle below the Jeju Island.
In order to understand the melting processes in the Hawaiian plume,
which may involve a mixture of peridotite and entrained former oceanic
crust (eclogite), we carried out basalt/peridotite sandwich melting
experiments with NMORB-like CRB72-31, Archaean Fe-rich basalt CLG46 and
a fertile peridotite KLB-1. Melts similar to a relatively unfractionated
Koolau tholeiite (SiO2 = 53, MgO = 7 wt%) can be produced
directly by partial melting of CLG46 at 2.5-3.0 GPa and 1350-1400°C.
The conditions are slightly below the dry solidus of mantle peridotite.
At or above the peridotite solidus, melts become saturated with olivine
and are similar to picritic magma in Kilauea (SiO2 = 48, MgO
= 16). In the basalt/peridotite sandwich melting experiments, melt
proportion within the basalt domain decreases as temperature increases
near the peridotite solidus. Due to this effect, the degree of partial
melting in the basalt layer is low at a temperature just above the
peridotite solidus. Accordingly, the picritic melts produced at
temperatures slightly above the peridotite solidus are more enriched in
incompatible elements (K, Ti) than those produced at somewhat lower
temperatures in the basalt layer. Two fundamental melting modes were
found in the basalt/peridotite hybrid magma source: partial melting of
eclogite domains, and reactive melting of both eclogite and peridotite
domains. These results help to explain the origin of the two magma types
in Hawaiian volcanoes (Koolau-type tholeiite and Kilauea-type picrite).
Based on the melting experiments and the growth history of Koolau
volcano, a model of melting process in the Hawaiian plume is proposed
which advocates lower plume temperatures and larger block size of
entrained eclogite than previous studies.
Partial melting of a relatively fertile garnet-lherzolite from Thaba
Putsoa kimberlite (PHN 1611) has been studied at pressures between 5 and
30 kbar in the temperature range between 1200° and 1500°C.
Compositions of partial melts were determined with the method using
aggregates of diamond, by which melts were separated from coexisting
cystalline phases and analysed without effect of quenching. The degree
of melting of peridotite was estimated by K2O contents in
melts on the assumption that K in peridotite is completely partitioned
into partial melts. The temperature-melt fraction curves show sharp
changes in the slope at melt fractions of about 20% at 10 kbar and about
17% at 15 kbar, where Ca-rich clinopyroxene disappears. Above this
melting range, olivine and orthopyroxene with or without subcalcic
clinopyroxene are the crystalline phases. Melt fractions up to about 20%
are formed with a small increase in temperature at 10 and 15 kbar,
whereas above this melting range, melt fraction does not increase
significantly with increasing temperature. The compositional changes of
melts are well demonstrated as a function of degree of melting; MgO, FeO
and Cr2O3 increase almost linearly with increasing
degree of melting, whereas Al2O3, Na2O
and TiO2 also decrease monotonically with increasing degree
of melting from 5 to 35%. The variations of SiO2 and CaO have
a maximum and a minimum, respectively at about 20% melt fraction which
is associated with the disappearance of Ca-rich clinopyroxene. With
increasing pressure, SiO2 and Al2O3
decrease, whereas MgO and FeO increase when melts formed by the same
degree of melting are compared.
The compositions of partial melts are olivine tholeiitic for melt
fractions between 10 and 25% at pressures between 10 and 20 kbar, alkali
basaltic for melt fractions less than 10% at pressures higher than 15
kbar,and picritic (MgO >15%) for melt fractions greater than 25% at
pressures lower than 20 kbar and for melt fractions greater than 14% at
pressures higher than 25 kbar. Melts formed at 10 kbar in the
temperature range between 1225° and 1275°C and for melt
fractions between 10 and 20% are close to, but a few to 10% more
olivine-rich than the primitive MORB compositions.
A variety of atypical plume-like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed, and seismological imaging has shown ubiquitous small-scale convection in the uppermost mantle in regions such as the Mediterranean region, the western US, and around the western Pacific. We argue that the three-dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics. The testable surface expressions of this process are the outside-arc alkaline volcanism, topographic swell, and low-velocity seismic anomalies associated with partial melt. Using three-dimensional, simplified numerical subduction models, we show that focused upwellings can be generated both ahead of the slab in the back-arc region (though ~ five times further inward from the trench than arc-volcanism) and around the lateral edges of the slab (in the order of 100 km away from slab edges). Vertical mass transport, and by inference the associated decompression melting, in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities. The upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation. We discuss representative case histories from the Pacific and the Mediterranean where we find possible evidence for such slab-related volcanism.
A new method for the measurement of calcium isotope ratios and total calcium, using a double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) instrument equipped with a shielded torch, is presented. The method was applied for the measurement of the 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca ratios and total calcium by isotope dilution in urine samples from two different nutritional experiments set up to determine the calcium absorption from various foods. The isotope ratios were measured with a precision of 0.25%, 0.23% and 0.05% RSD for 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca, respectively. The precision of the 44Ca/42Ca ratio is only limited by counting statistics, whereas the precision is limited by uncertainty from the needed background and interference
corrections when the minor 43Ca isotope is used for analysis. Uncertainty calculations on the determination of calcium absorption in the nutritional experiments are presented. These calculations show that, for a double stable isotope procedure (administration of enriched stable 44Ca and 42Ca), the overall uncertainty is controlled by the precision of the ICP-MS measurement of the isotope ratios (44Ca/43Ca, 42Ca/43Ca), whereas, for a mixed radioisotope–stable isotope procedure (administration of enriched stable 44Ca and the 47Ca radioisotope), the overall uncertainty is mainly controlled by the uncertainty in the measurement of total calcium by isotope dilution ICP-MS. From these results, it was concluded that, when optimizing the performance of nutritional experiments, the emphasis should be placed on different parameters depending on the exact analysis
involved. The results also show that uncertainty calculations are very useful in pinpointing the critical parameters of an experiment.
Major and trace element have been analyzed from alkaline basalts from southwestern, Japan, Korea, and northeastern China. No significant differences were found in the immobile incompatible element ratios, such as Zr, Y, Hf, Th, and Ti. These ratios, as well as normalized incompatible element patterns, resemble those of continental and oceanic island alkaline basalts. However, southwestern Japanese alkaline basalts show evidence of K, Ba, and Rb enrichment and a slight depletion in Ta relative to La, implying a weak island arc signature. Korean and Chinese alkaline basalts do not have such a signature. Rare earth elements (REE) show near-constant La/Sm ratios and a crossover at the high REE end of patterns for each area studied. The parallelism in light REE can be derived if the magmas are mixtures formed by (1) relatively large degrees of partial melting of an enriched mantle plume from deeper in the mantle and (2) a small degree of partial melting of a depleted mid-ocean ridge basalt (MORB)-type source. These observations when combined with seismic results suggest that the upper mantle beneath southwestern Japan has been weakly affected by metasomatism caused by dehydration and/or partial melting of subducted Pacific plate (not Philippine Sea plate). The mantle plume may have reacted with weakly metasomatized MORB-type depleted mantle to produce alkaline basalt magmas retaining mild island arc characteristics in southwestern Japan. However, the metasomatism by the subduction of the Pacific plate has not affected the mantle beneath Korea and northeastern China. Here the interaction between plume and MORB-type mantle produced alkaline basalt magma similar to normal continental and oceanic alkaline basalts.
We describe a newly calibrated model for the thermodynamic properties of magmatic silicate liquid. The new model, pMELTS, is based on MELTS [Ghiorso and Sack, 1995] but has a number of improvements aimed at increasing the accuracy of calculations of partial melting of spinel peridotite. The pMELTS algorithm uses models of the thermodynamic properties of minerals and the phase equilibrium algorithms of MELTS, but the model for silicate liquid differs from MELTS in the following ways: (1) The new algorithm is calibrated from an expanded set of mineral-liquid equilibrium constraints from 2439 experiments, 54% more than MELTS. (2) The new calibration includes mineral components not considered during calibration of MELTS and results in 11,394 individual mineral-liquid calibration constraints (110% more than MELTS). Of these, 4924 statements of equilibrium are from experiments conducted at elevated pressure (200% more than MELTS). (3) The pMELTS model employs an improved liquid equation of state based on a third-order Birch-Murnaghan equation, calibrated from high-pressure sink-float and shockwave experiments to 10 GPa. (4) The new model employs a revised set of end-member liquid components. The revised components were chosen to better span liquid composition-space. Thermodynamic properties of these components are optimized as part of the mineral-liquid calibration. Comparison of pMELTS to partial melting relations of spinel peridotite from experiments near 1 GPa indicates significant improvements relative to MELTS, but important outstanding problems remain. The pMELTS model accurately predicts oxide concentrations, including SiO2, for liquids from partial melting of MM3 peridotite at 1 GPa from near the solidus up to ~25% melting. Compared to experiments, the greatest discrepancy is for MgO, for which the calculations are between 1 and 4% high. Temperatures required to achieve a given melt fraction match those of the experiments near the solidus but are ~60°C high over much of the spinel lherzolite melting interval at this pressure. Much of this discrepancy can probably be attributed to overstabilization of clinopyroxene in pMELTS under these conditions. Comparison of pMELTS calculations to the crystallization and partial melting experiments of Falloon et al. [1999] shows excellent agreement but also suffers from exaggerated calculated stability of clinopyroxene. Finally, comparison of pMELTS calculations to the garnet peridotite experiments of Walter [1998] at 3-7 GPa reveals disparities between calculations and experiments that increase with pressure. The most prominent of these disparities is manifest as overprediction of the stability of garnet and underprediction of that of olivine. Part of this problem may be attributed to inadequacies in the Birch-Murnaghan equation of state in reproducing the behavior of highly compressible liquids at high pressures and temperatures.
Ilchulbong (Sunrise Peak) tuff cone is a UNESCO World Heritage site that owes its scientific importance to the outstanding coastal exposures that surround it. It is also one of the classic sites that provided the sedimentary evidence for the primary pyroclastic processes that occur during phreatomagmatic basaltic eruptions. It has been long considered, based on the cone morphology, that this classic cone was produced via eruption from a single vent site. Reanalysis of the detailed sedimentary sequence has now revealed that two subtle paraconformities occur in this deposition sequence, one representing a significant time break of perhaps days to weeks or months, during which erosion and compaction of the lower cone occurred, the conduit cooled and solidified and a subsequent resumption of eruption took place in a new vent location. Detailed geochemical study of the juvenile clasts through this cone reveals that three separate alkali basaltic magma batches were erupted, the first and third erupted may be genetically related, with the latter showing evidence for longer periods of shallow-level fractionation. The second magma batch erupted was generated in a different mantle source area. Reconstructing the eruption sequence, the lower Ilchulbong cone was formed by eruption of magma 1. Cessation of eruption was accompanied by erosion to generate a volcano-wide unconformity, associated with reworked deposits in the lower cone flanks. The eruption resumed with magma 2 that, due to the cooled earlier conduit, was forced to erupt in a new site to the west of the initial vent. This formed the middle cone sequence over the initially formed structure. The third magma batch erupted with little or no interval after magma 2 from the same vent location, associated with cone instability and slumping, and making up the deposits of the upper cone. These results demonstrate how critical the examination for sedimentary evidence for time breaks in such eruption sequences is for detecting potential shifts in eruption chemistry and vent location. It appears that if eruption breaks are short, successive magma batches follow the same path, whereas if pauses are greater than a critical period, conduit solidification will force vent migration for subsequent magma batches. This has important implications for examining the controls of vent migration at other monogenetic volcanoes and for emergency management planning during future similar types of eruptions.
Analysis of multi-channel seismic data from the northern East China Sea Shelf Basin (ECSSB) reveals three sub-basins (Socotra, Domi, and Jeju basins), separated by structural highs (Hupijiao Rise) and faulted basement blocks. These sub-basins show a typical rift-basin development: faulted basement and syn-rift and post-rift sedimentation separated by unconformities. Four regional unconformities, including the top of acoustic basement, have been identified and mapped from multi-channel seismic data. Faults in the acoustic basement are generally trending NE, parallel to the regional structural trend of the area. The depths of the acoustic basement range from less than 1000 m in the northwestern part of the Domi Basin to more than 4500 m in the Socotra Basin and 5500 m in the Jeju Basin. The total sediment thicknesses range from less than 500 m to about 1500 m in the northwest where the acoustic basement is shallow and reach about more than 5500 m in the south.
The spatial extent of an outstanding mantle upwelling in the west of Kyushu island, Japan, has been estimated by a genetic algorithm inversion. Here we show how the mantle upwelling manifests in modeling of observed anomalies of temporal geomagnetic variations, i.e., magnetovariational anomalies around southwest Japan. Observed ratios of the vertical to horizontal geomagnetic components at short periods are known as indicators of subsurface electrical contrasts. However, they are also sensitive to the presence of oceans and continents because of much more conductive seawater than land rocks. To circumvent the difficulty, we used three-dimensional nonuniform thin sheet approximation to subtract out the conductive as well as inductive effects of the ocean on the magnetovariational anomalies. The observed anomalies were then inverted by a genetic algorithm inversion for conductance (the product of electrical conductivity and thickness) with the known bathymetry as a priori information. The derived conductance model has particular sensitivity to the northeastern portion of spatial extent of the mantle upwelling probably centered at the East China Sea. The upwelling may result in horizontal flows of the uppermost mantle, which induce the horizontal stress field that can trigger hazardous shallow intraplate earthquakes of large magnitude, such as the earthquake off the west coast of Fukuoka Prefecture that occurred on 20 March 2005. The northeastern rim of the mantle upwelling thus revealed can also be related to an unidentified boundary between the Amurian plate and the Eurasia plate.