Boundary layer fractionation constrained by differential information from the Kutsugata lava flow, Rishiri volcano, Japan

Kuritani, Takeshi

doi:10.1029/1999jb900266

Cited by 15 publications

(5 citation statements)

References 45 publications

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“…We suggest that the basaltic magma fractionated plagioclase, olivine and clinopyroxene and formed a crystal-rich layer along the chamber walls as a boundary layer (e.g., Kuritani 1998Kuritani , 1999. Plagioclase phenocrysts can float in basaltic to basaltic andesite magmas (Nakano and Yamamoto 1991;Togashi et al 1991;Yasuda et al 2002).…”

Section: The Summit Eruptionmentioning

confidence: 94%

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

2005

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During the 2000 eruption at Miyakejima Volcano, two magmas with different compositions erupted successively from different craters. Magma erupted as spatter from the submarine craters on 27 June is aphyric basaltic andesite (<5 vol% phenocrysts, 51.4-52.2 wt% SiO 2 ), whereas magma issued as volcanic bombs from the summit caldera on 18 August is plagioclase-phyric basalt (20 vol% phenocrysts, 50.8-51.3 wt% SiO 2 ). The submarine spatter contains two types of crystal-clots, A-type and A 0 -type (andesitic type). The phenocryst assemblages (plagioclase, pyroxenes and magnetite) and compositions of clinopyroxene in these clots are nearly the same, but only A 0 -type clots contain Ca-poor plagioclase (An < 70). We consider that the A 0 -type clots could have crystallized from a more differentiated andesitic magma than the Atype clots, because FeO*/MgO is not strongly influenced during shallow andesitic differentiation. The summit bombs contain only B-type (basaltic type) crystal-clots of Ca-rich plagioclase, olivine and clinopyroxene. The Atype and B-type clots have often coexisted in Miyakejima lavas of the period 1469-1983, suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas. According to the temporal variations of mineral compositions in crystal-clots, the andesitic magma became less evolved, and the basaltic magma more evolved, over the past 500 years. We conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period, causing the andesitic magma to become less evolved with time. The mineral chemistries in crystal-clots of the submarine spatter and 18 August summit bombs of the 2000 eruption fall on the evolution trends of the A-type and B-type clots respectively, suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters. The 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber; as the collapse occurred, it may have caused disruption of crustal cumulates which then contaminated the ascending, deeper basalt. Thus, porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera. The historical magma plumbing system of Miyakejima was probably destroyed during the 2000 eruption, and a new one may now form.

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Section: The Summit Eruptionmentioning

confidence: 94%

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

2005

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“…The host quartz-bearing syenite underwent much weaker deformation. This indicates that the blocks underwent deformation before they were entrapped in the solidifying inner ring 1 and that the deformation was related to near-surface processes before complete (Langmuir, 1989;O'Hara and Fry, 1996;Nielsen and DeLong, 1992;Tait andJaupart, 1989, 1992;Bédard et al, 1992;Tait, 1988;Brophy et al, 1996;Kuritani, 1998Kuritani, , 1999aKuritani, , 1999bKuritani, , 2004Landi et al, 1999;Simura and Ozawa, 2011). However, several problems of this mechanism have been pointed out (Marsh, 1996;Huppert and Sparks, 1984), such as the difficulty of separating crystals suspended in the boundary layer in the natural system from fractionated melt and that the layer of mush containing fractionated melt are too thin to modify the chemical composition of the main magma body.…”

Section: A C C E P T E D I N J M P S P R E -P R O O Fmentioning

confidence: 99%

Magma fractionation and emplacement mechanism in a subvolcanic plumbing system in a continental region: constraints from the late Neoproterozoic Wadi Dib ring complex in the Eastern Desert, Egypt

SAAD,

OZAWA,

KURITANI

et al. 2023

Journal of Mineralogical and Petrological Sciences

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We examined an alkaline ring complex in the Eastern Desert of Egypt, Wadi Dib ring complex (WDRC), to understand formation mechanisms of the intimately related ring structure and chemical diversity. The WDRC consists of multiple circular rings of the oldest volcanic units, the middle-stage plutonic unit, and the youngest dike unit, and these units show overlapping whole-rock major element compositions. The compositional variation of the volcanic and plutonic units can be accounted for by a stepwise fractional crystallization starting with trachyte, without significant magma replenishment or crustal contamination. From the margin to the center and oldest to youngest, the plutonic unit consists of an outer ring (syenite), inner rings 1 (quartzbearing syenite) and 2 (quartz syenite), and a granitic core (syenogranite). The wholerock chemical composition of the plutonic unit is progressively more fractionated inwards from the outer ring to the granitic core through the inner rings. Syenites from the innermost outer ring show high degree of deformation, which gradually decreases outwards in the outer ring and abruptly decreases inwards in the outermost inner ring 1.The deformed syenites show microstructures suggesting reactive melt transportation.The country rocks neighboring the ring complex and equivalent blocks present in the periphery of the outer ring, the overlying volcanic unit and equivalent blocks present in the inner rings all show microstructures indicative of pyrometamorphism. Spatial variations in the microstructures in the plutonic unit indicate an increase in cooling rate from the outer ring to the granitic core and thus with time. These geological, chemical, and microstructural features of the WDRC suggest that the ring complex represents an evolving roof zone of a subvolcanic magma body located at a depth of a few km.Intimate coupling of growing roof and sidewall mushy boundary layers and later collapse of the roof boundary layer with occasional involvement of the overlying volcanic piles induced segregation of interstitial fractionated melt from the wall boundary layer to the collapse space driven by a pressure gradient induced by the collapse. The ascended fractionated melt started to crystallize to form a roof boundary layer of the next generation by increasing cooling efficiency, which thickened until the next collapse on a smaller horizontal scale inducing melt segregation from the wall boundary layer towards the roof zone. Repetition of the sequence with shallowing and decreasing the horizontal scale produced the ring structure and chemical diversity of the WDRC.

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“…Thus, the application of this model is limited to aphyric magmas (i.e., magmas with a small fraction of suspended crystals). Due to preferential crystallization along the wall of the magma chamber, limited crystallization occurs in the chamber center (Kuritani, 1999), which our model could be applied to. Furthermore, the low crystal fraction can result from efficient gravitational separation of crystals (Martin & Nokes, 1988, 1989).…”

Section: Model Limitations and Validationsmentioning

confidence: 99%

Settling of Immiscible Droplets: A Theoretical Model for the Missing Link Between Microscopic and Outcrop Observations

Zhang

Wang

et al. 2020

JGR Solid Earth

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Liquid immiscibility is a critical mechanism to diversify magma compositions. The physical separation of exsolved melt droplets is an essential process in generating new magmas. However, little attention has been paid to this physical process. In this study, we present a new model for segregation of immiscible melt droplets in which exsolution, settling, and coalescence are all considered. The separation of immiscible droplets is similar to that of crystals in magma when the discrete melt exsolves as large (millimeter-size) droplets and/or when the magma cools slowly. However, when immiscible melt droplets are small (micrometer-size) and/or magma cools rapidly, coalescence can significantly enhance their separation. The low interfacial tension between coexisting silicate melts leads to the exsolution of extremely small melt droplets. Furthermore, the high viscosity of silica-rich melt suppresses the coalescence of droplets. Consequently, the separation of highly viscous silica-rich melt droplets is slow but could have occurred in a slowly cooling magma such as the Skaergaard intrusion. By contrast, the coalescence rate of melt droplets with low viscosity is high. Iron-rich melt droplets, which have low viscosities, could have been separated from hydrous andesitic melts to form magnetite-apatite ore deposits at El Laco and Marcona. Furthermore, the viscosities of sulfide and carbonatitic melts are low. Therefore, immiscibility between sulfide and silicate melts may lead to the formation of magmatic sulfide deposits, and immiscibility between carbonatitic and silicate melts can support periodical eruptions of carbonatitic lava.

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Boundary layer fractionation constrained by differential information from the Kutsugata lava flow, Rishiri volcano, Japan

Cited by 15 publications

References 45 publications

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan

Magma fractionation and emplacement mechanism in a subvolcanic plumbing system in a continental region: constraints from the late Neoproterozoic Wadi Dib ring complex in the Eastern Desert, Egypt

Settling of Immiscible Droplets: A Theoretical Model for the Missing Link Between Microscopic and Outcrop Observations

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