Variation of Slab Component in Ancient and Modern Merapi Products: A Detailed Look into Slab Derived Fluid Fluctuation over the Living Span of One of the Most Active Volcanoes in Sunda Arc

Holocene eruptions of Merapi have produced both medium-K and high-K calc alkaline series which correspond to products older and younger than 1900 years respectively. The change has been attributed to increasing sediment input as the volcano matures. This study presents two Merapi samples which represent Ancient and Modern Merapi. The two samples are analyzed for subduction components including B, Ba, Sr, and Pb using X-ray fluorescence (XRF) spectrometer and prompt gamma ray analysis (PGA). Our finding shows that Ancient Merapi sample from Plawangan Hill lava is close in affinities with younger than 1900 years high-K magma series. On the other hand, Modern Merapi sample from 2006 eruption juvenile is plotted within medium-K magma series which are observed in eruption products older than 1900 years. Ratios of fluid mobile elements to high field strength element (HFSE) (i.e. B/Nb, Ba/Y, Pb/Nb) consistently show that Ancient Merapi sample has higher input of slab derived fluid than Modern Merapi sample. A model using B/Nb and Ba/Nb suggests that Plawangan magma requires 1.5 % of sediment derived fluid, higher than estimated in 2006 eruption magma (1.2 %) and medium-K series magma, and within the range of high-K series magma, to explain its slab component enrichment. This evidence suggests that slab derived component addition to the sub-arc mantle wedge highly fluctuates over short period of evolution of a volcano. One possible explanation is the presence of veined hydrous metasomatized sub-arc mantle as Merapi magma source which allows melting of different mantle area to produce fluctuation of slab components in the course of evolution of Merapi magmas

シベリアの新生代火山活動

論文Articl

Geochemistry of shield stage basalts from Baluran volcano, East Java, Sunda arc

We report petrography and geochemistry of basaltic lava flows from the shield stage of Baluran, a Quaternary volcanic center in the rear of East Java, Sunda Arc, Indonesia. These basalts contain abundant plagioclase, clinopyroxene, olivine, and minor magnetite. Geochemically, they resemble other medium-K calc alkaline basalts from eastern Java’s volcanoes, but they are less enriched in light ion lithophile elements (LILE) and Pb. The predicted primary basalt of Baluran lavas can be sourced to a more primitive primary melt composition which may also generate medium-K calc-alkaline magmas in the region. The fractionation trajectory of these primary magmas shows the importance of plagioclase, clinopyroxene, olivine, and magnetite phase removal from the melt. Regardless of the diverse composition of the derivatives, the calculated primary basalts from the eastern Java are all in the field of nepheline-normative. This finding suggests variably small degree of melting of clinopyroxene-rich mantle source is at play in the generation of these magmas. Our result further suggests that the clinopyroxene source rock is possibly present as veins in peridotite mantle which have experienced metasomatism by addition of slab-derived fluids at differing proportion

Effects of the 2016 Kumamoto earthquakes on the Aso volcanic edifice

Abstract Large earthquakes occurred in the central part of Kumamoto Prefecture on April 14–16, 2016, causing severe damage to the northern segment of the Hinagu faults and the eastern segment of the Futagawa faults. Earthquake surface ruptures appeared along these faults and on the Aso volcanic edifice, which in turn generated landslides. We conducted landform change analysis of the central cones of Aso volcano by using satellite and aerial photographs. First, we categorized the topographical changes as surface scarps, arc-shaped cracks, and linear cracks. Field survey indicated that landslides caused the scarps and arc-shaped cracks, whereas faulting caused the linear cracks. We discovered a surface rupture concentration zone (RCZ) formed three ruptures bands with many surface ruptures and landslides extending from the west foot to the center of the Aso volcanic edifice. The magmatic volcanic vents that formed during the past 10,000 years are located along the north margin of the RCZ. Moreover, the distribution and dip of the core of rupture concentration zone correspond with the Nakadake craters. We conclude that a strong relationship exists between the volcanic vents and fault structures in the central cones of Aso volcano. Graphical abstract

Contrasting volcanism in the Michoacán-Guanajuato Volcanic Field, central Mexico: Shield volcanoes vs. cinder cones

El Campo Volcánico de Michoacán-Guanajuato (40,000 km2), de la Faja Volcánica Trans-Mexicana (FVTM), contiene volcanes de tamaño pequeño y mediano, y carece de grandes volcanes compuestos. Los volcanes de tamaño pequeño incluyen a 900 conos cineríticos y 100 volcanes de otros tipos tales como conos, domos y gruesos derrames de lava no asociados con conos y maares. En contraste, los volcanes de tamaño medio incluyen más de 300 volcanes y algunos domos de lava. Ambos grupos de volcanes coexisten en tiempo y espacio. Las lavas asociadas a conos cineríticos poseen un amplio rango composicional de 47 a 67 % en contenido de Si02, con abundantes basaltos de olivino calcialcalinos y andesitas basálticas. Existen también unas cuantas rocas alcalinas. Las lavas de volcanes escudo son todas andesitas calcialcalinas que muestran un rango limitado de Si02 (comúnmente 55%-61% ), con ocurrencia común de fenocristales de ortopiroxeno. Se han encontrado composiciones similares para flujos de lava que no están asociados a conos. Estas lavas y las de los escudos, representan erupciones efusivas, menos explosivas. Los volcanes escudo tienen derrames de lava más largos y volúmenes mayores que los derrames que no están asociados con conos, indicando con esto una tasa efusiva y un aporte de magma mayores que estos últimos. Debido a que sus lavas están más fraccionadas que las lavas calcialcalinas de conos cineríticos, pero que se grafican en el mismo tren composicional que éstas, po- ~ siblemente aquéllas sean producto de cristalización fraccionada de basaltos primitivos calcialcalinos, los cuales se encuentran en algunos conos cineríticos. doi: https://doi.org/10.22201/igeof.00167169p.1994.33.1.54

Tectonic stress field and fractal distribution of volcanoes in the Michoacan-Guanajuato region of the Mexican Volcanic Belt

El campo de esfuerzos tectónicos del Campo Volcánico de Michoacán-Guanajuato es estimado a partir de la orientación de fallas normales y del alineamiento de los volcanes: σ1 (el esfuerzo principal compresional máximo) es vertical en toda la región y σ2 se orienta E-W en el área norte y NE-SW en el área sur. El origen del campo de esfuerzos es atribuido al deslizamiento en dirección a la trinchera de la porción de arco sobre la superficie del límite quebradizo/dúctil inducido por el enrollamiento del eje de la Trinchera Mesoamericana. Esto se atribuye a la tasa de subducción de la Placa de Cocos que es más lenta que la tasa crítica de 7.2 cm/año. La distribución espacial de los centros volcánicos y el volumen de los cuerpos volcánicos son fractales; las dimensiones fractales son 1.63 y 1.44 respectivamente. El origen de la fractalidad y los valores elevados de la dimensión fractal son explicados mediante una analogía con la interdigitación viscosa o invasión percolante en medio poroso que es un efecto del perfil del esfuerzo cortical del campo de esfuerzos tensional

(Table T1) Mineralogy and geochemistry of ODP Hole 192-1183A and Hole 192-1186A sediments, Ontong Java Plateau

Boron, Ca, Na, and Gd concentrations and H intensity in sediments obtained during Ocean Drilling Program Leg 192 were determined by prompt gamma neutron activation analysis. The results show strong positive correlation between B content and H intensity in carbonate samples; chalk samples have higher B contents than limestone samples. Average B content is 9.1 ppm for the chalk and 5.2 ppm for the limestone. When chert blocks or clay minerals are present in the carbonate samples, B content increases (up to 91 ppm)