Analytical accuracy and precision of major and trace elements for bulk rocks using a 1:5 dilution glass bead by XRF.

Yajima, Kazuhito; Ono, Masaru; Fujimaki, Haruyuki

doi:10.2465/gkk.30.28

Cited by 14 publications

(5 citation statements)

References 4 publications

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“…Major-element compositions for 12 samples (Table 1) were measured on fused glass beads, using X-ray fl uorescence (XRF) spectrometry at Hirosaki University and Tohoku University. The analytical procedure used has been described in detail by Fujimaki and Aoki (1987) and Yajima et al (2001). An additional eight samples (Table 1) were analyzed for major elements by electron microprobe at Tohoku University; these samples were not analyzed for trace elements.…”

Section: Geochemistry Analytical Methodsmentioning

confidence: 99%

Geochemistry and geochronology of the Troodos ophiolite: An SSZ ophiolite generated by subduction initiation and an extended episode of ridge subduction?

Osozawa

Shinjo

et al. 2012

Lithosphere

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New trace-element, radiogenic isotopic, and geochronologic data from the Troodos ophiolite, considered in concert with the large body of previously published data, give new insight into the tectonic history of this storied ophiolite, as well as demonstrating the variability of suprasubduction-zone ophiolites, and differences between them and commonly used modern analogs. Similar to earlier studies, we fi nd that island-arc tholeiite of the lower pillow lava sequence erupted fi rst, followed by boninite. We further divide boninitic rocks into boninite making up the upper pillow lava sequence, and depleted boninites that we consider late infi ll lavas. We obtained an Ar-Ar age from arc tholeiite of 90.6 ± 1.2 Ma, comparable to U-Pb ages from ophiolite plagiogranites. New biostratigraphic data indicate that most of the basal pelagic sedimentary rocks that conformably overlie the boninitic rocks are ca. 75 Ma. This suggests that voluminous eruption of boninitic rocks persisted until ca. 75 Ma. Limited eruption of boninitic lavas may have continued until 55.5 ± 0.9 Ma, based on the Ar-Ar age we obtained. The duration of arc magmatism at Troodos (at least 16 m.y., with some activity perhaps extending 35 m.y.) without the development of a mature arc edifi ce greatly exceeds that of other well-studied suprasubduction-zone ophiolites. We propose that Troodos was formed over a newly formed subduction zone, similar to many proposed models, but that the extended period of magmatism (boninitic) resulted from a prolonged period of ridge subduction.

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Section: Geochemistry Analytical Methodsmentioning

confidence: 99%

Geochemistry and geochronology of the Troodos ophiolite: An SSZ ophiolite generated by subduction initiation and an extended episode of ridge subduction?

Osozawa

Shinjo

et al. 2012

Lithosphere

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“…3. All iron calculated in FeO for groundmass glass composition Analytical procedures: Major element compositions were determined by X-ray fluorescence analysis (XRF) as described in Yajima et al (2001). Ferric/Ferrous and ignition loss were determined following the method of Tiba (1970).…”

Section: Physical Properties Of Lavamentioning

confidence: 99%

Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan

Maeno

Taniguchi

2006

Bull Volcanol

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The 1934The -1935 Showa Iwo-jima eruption started with a silicic lava extrusion onto the floor of the submarine Kikai caldera and ceased with the emergence of a lava dome. The central part of the emergent dome consists of lower microcrystalline rhyolite, grading upward into finely vesicular lava, overlain by coarsely vesicular lava with pumice breccia at the top. The lava surface is folded, and folds become tighter toward the marginal part of the dome. The dome margin is characterized by two zones: a fracture zone and a breccia zone. The fracture zone is composed of alternating layers of massive lava and welded oxidized breccia. The breccia zone is the outermost part of the dome, and consists of glassy breccia interpreted to be hyaloclastite. The lava dome contains lava with two slightly different chemical compositions; the marginal part being more dacitic and the central part more rhyolitic. The fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature, lower viscosity, and lower yield stress than the central rhyolite. The high-temperature dacite lava began to effuse in the earlier stage from the central crater. The front of the dome came in contact with seawater and formed hyaloclastite. During the later stage, low-temperature rhyolite lava effused subaerially. As lava was injected into the growing dome, the fracture zone was produced by successive fracturing, ramping, and brecciation of the moving dome front. In the marginal part, hyaloclastite was ramped above the sea surface by progressive increments of the new lava. The central part was folded, forming pumice breccia and wrinkles.

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“…The instrumental settings of XRF are similar to those described by Yajima et al (2001). The whole -rock compositions of the mingled pumice clasts and dacitic fragments in the dacitic -fragment -bearing gray pumice clasts (see next section) have not been determined because of textural heterogeneities in the mingled pumice and the small size of the dacitic fragments.…”

Section: Methodsmentioning

confidence: 72%

Two types of dacitic pumices from the caldera-forming eruption of Numazawa Volcano, NE Japan

Ishizaki

Masubuchi

Aono

2009

Journal of Mineralogical and Petrological Sciences

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The 3400 BC caldera -forming eruption of Numazawa Volcano in NE Japan started with a cataclysmic pyroclastic flow eruption (~ 2 km 3 dense rock equivalent), which accounted for more than 90% of the total volume of the eruption products. This was followed by a Plinian eruption, phreatomagmatic eruptions, and a second Plinian eruption. The juvenile pyroclasts produced during the first two eruption phases are mostly dacitic, whereas those in the two subsequent phases are essentially andesitic. We recognized two distinct types of dacitic pumices: white and gray pumices. The two pumices are virtually identical in terms of both whole -rock composition (~ 64.8 -66.1 wt% SiO 2 ) and crystal content (~ 40 -46 vol%), but are very different in terms of texture. The white pumice, which typically contains abundant euhedral phenocrysts, is the dominant variety and occurs throughout the pyroclastic flow deposits and in the overlying Plinian fall deposit. The gray pumice, which typically has bread -crusted surfaces and contains ubiquitous crystal fragments and xenoliths, occurs in the upper flow units of the pyroclastic flow deposits. We suggest that the textural differences between the two types of pumices reflect the difference in local stress conditions within the volcanic conduit below the magma fragmentation level. The abundance of euhedral phenocrysts in the white pumice suggests that it is the vesicular equivalent of the dacite that chamber ascended through the central part of the conduit that suffered low shear stress. In contrast, the magma that generated the gray pumice is thought to have originated from similar dacitic magma; the gray pumice magma was probably produced by the mechanical breakage of phenocrysts during magma ascent along the region of high shear stress near the conduit walls. The limited accumulation of the gray pumice in the upper units of the pyroclastic flow deposits suggests that crystal size reduction mainly occurred during the late stage of the pyroclastic flow eruption prior to the first Plinian eruption. It is likely that an abrupt conduit blockage caused by the waning of the eruption activity and the resulting temporal high shear stress at the conduit walls promoted crystal fragmentation, thus forming the gray -pumice magma and resulting in the subsequent eruption being a Plinian eruption.

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Analytical accuracy and precision of major and trace elements for bulk rocks using a 1:5 dilution glass bead by XRF.

Cited by 14 publications

References 4 publications

Geochemistry and geochronology of the Troodos ophiolite: An SSZ ophiolite generated by subduction initiation and an extended episode of ridge subduction?

Geochemistry and geochronology of the Troodos ophiolite: An SSZ ophiolite generated by subduction initiation and an extended episode of ridge subduction?

Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan

Two types of dacitic pumices from the caldera-forming eruption of Numazawa Volcano, NE Japan

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