Aso volcano has the largest caldera (18
×
25 km) in the southwestern Japan Island Arc, which was formed as a result of four gigantic pyroclastic-eruption cycles. The latest eruption cycle (Aso-4 ...cycle, 90 ka) produced the most voluminous deposits (>
600 km
3) among the four eruption cycles. We investigated pre-eruptive magma chamber configurations and processes in compositionally stratified Aso-4 pyroclastic eruptions based on whole-rock chemical, phenocryst mineralogical, and Sr isotope analyses of juvenile clasts. Previous stratigraphical studies have suggested that the Aso-4 cycle is divided into two subcycles, in both of which eruption of voluminous silicic is followed by eruption of mafic magma. Geochemical and mineralogical results indicate that the pre-eruptive magma chamber was composed of three layers: silicic, hybrid, and mafic magma layers from the top to the bottom. The silicic magma layer was relatively homogenous, whereas the mafic magma layer was compositionally zoned where magma became more silicic with height. The hybrid magma was generated by mixing the silicic magma and the silicic end of the zoned mafic magma layer (i.e. the uppermost part of the mafic magma layer). The first subcycle began with evacuation of the upper silicic magma and successively proceeded to tap the lower hybrid and mafic magmas. The eruption of the first subcycle stopped before the whole magma chamber evacuated. During this subcycle, the hybrid magma and the upper part of the mafic magmas layer were selectively withdrawn and mixed with the overlying silicic magma. The second subcycle eruption started with the new hybrid magma, and followed by eruption of the mafic magma.
This report describes the laparoscopic resection of a rectal GIST after treatment with imatinib mesylate. A 56-year-old male presented with a submucosal tumor (longest diameter, 8 cm) arising in the ...lower rectum. A core needle biopsy revealed that the tumor contained bundles of spindle-like cells. Immunostaining revealed that the tumor was positive for c-kit and CD34. Analysis of the c-kit gene revealed a substitution of ACA (threonine) by GCA (alanine) at codon 574 of exon 11. Imatinib mesylate (400 mg/day) was given as preoperative adjuvant therapy for 3 months, and the tumor shrank to 5 cm in diameter. Proctectomy with transanal anastomosis could be performed laparoscopically, while preserving the anus. There was no evidence of recurrence 2 years 6 months after surgery. Preoperative adjuvant chemotherapy with imatinib mesylate may permit the use of less invasive treatment procedures, allowing anal preservation.
Abstract Prostaglandin E2 (PGE2 ) and prostaglandin E (EP) receptor signaling pathways have been implicated in the promotion of tumor growth and angiogenesis. However, little is known about their ...roles in lymphangiogenesis during tumor development. The present study evaluates whether endogenous PGE2 exhibits a critical role in tumor-associated lymphangiogenesis. Treatment of male C57BL/6 mice with a cyclooxygenase-2 inhibitor, celecoxib, for seven days resulted in a 52.4% reduction in tumor size induced by subcutaneous injection of murine Lewis lung cells. Celecoxib treatment down-regulated the expression of vascular endothelial growth factor receptor (VEGFR)-3 in stromal tissues by 73.9%, and attenuated expression of podoplanin, a marker for lymphatic endothelial cells. To examine the role of host PGE receptor signaling, we tested four kinds of EP receptor knockout mice. At Day 7 after tumor cell implantation, EP3 receptor knockout mice, but not EP receptor knockout mice lacking EP1, EP2, or EP4, exhibited a 53.3% reduction in tumor weight, which was associated with a 74.5% reduction in VEGFR-3 mRNA expression in tumor stromal tissues. At Day 14, VEGFR-3 expression in EP3–/– mice remained significantly lower than that of their wild-type (WT) counterparts. The expression of VEGF-C in the tumor stromal tissues in EP3–/– mice were also reduced by 22.1% (Day 7) and 44.1% (Day 14), respectively. In addition, the level of immunoreactive podoplanin in the tumor tissues from EP3–/– mice was less than that of WT. These results suggest that host EP3 receptor signaling regulates tumor-associated lymphangiogenesis by up-regulating expression of VEGF-C and its receptor, VEGFR-3, in tumor stromal tissues. Host EP3 blockade together with COX-2 inhibition may be a novel therapeutic strategy to suppress tumor-associated lymphangiogenesis.
To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated ...with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous titanomagnetite and titanohematite, indicating a low oxidation state and high titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation.
A total of 28 historically erupted lava samples were collected from three active volcanoes (Hualalai, Mauna Loa and Kīlauea) on the island of Hawaiʽi, and their argon isotopic compositions were ...determined in order to clarify whether mass-dependent fractionation occurs in hotspot volcanoes and to find out how the effect of extraneous
40Ar can be avoided in K-Ar or
40Ar/
39Ar dating. Comparison between groundmass and whole rock samples revealed that the latter has higher
40Ar/
3
6Ar ratios than the former, indicating extraneous
40Ar contamination. The amount of extraneous
40Ar contained in whole rock samples corresponds to an apparent age increase of up to 0.5 my. Groundmass samples of Mauna Loa and Kīlauea agreed well with the mass fractionation line through the atmospheric composition. Many of the Hualalai groundmass samples, however, showed evidence of extraneous
40Ar contamination. Comparison between a 180–250 μm and 250–500 μm groundmass fraction revealed that the argon isotopic composition of a 180–250 μm fraction agreed with the mass fractionation line, while the 250–500 μm fraction still contained extraneous
40Ar, suggesting that the 180–250 μm fraction is more suitable for the accurate dating of young and/or low-K volcanics.
Abstract Microsomal prostaglandin (PG) E synthase 1 (mPGES-1) is a major PGE synthase and has recently been reported to be expressed at high levels in several cancer types. We previously reported ...that the PGE receptor EP3 is expressed in bone marrow (BM) derived cells, enriched in stromal tissue, and enhances the potential for tumor angiogenesis. In the present study, we examined the role of mPGES-1-expressing BM cells on tumor angiogenesis using BM chimeric mice. After lethal radiation, wild-type (WT) BMs were excised and replaced with BM cells isolated from mPGES-1 knockout mice (mPGES-1−/− ). Lewis lung carcinoma cell were implanted subcutaneously and the levels of neoangiogenesis were measured tumor growth in mPGES-1−/− BM chimeric mice was significantly reduced compared to that observed in WT BM chimeric mice. Tumor-associated angiogenesis as measured by histological analysis was localized to tumor stroma, and was significantly lower in mPGES-1−/− BM chimeric mice compared to that in WT BM chimeric mice. Tumor sections probed by immunohistochemistry revealed that vascular endothelial growth factor (VEGF) that was present in the stromal tissue was markedly reduced in mPGES-1−/− BM chimeric mice compared to WT BM chimeras. These results suggest that the recruitment of mPGES-1-expressing BM cells to tumor-associated stromal tissue is crucial for tumor growth and angiogenesis, and correlates with gene expression of host VEGF in stroma. Taken together, these data suggest that regulation of mPGES-1-expressing BM cell recruitment to the site of primary tumors may be a novel strategy for the treatment of solid tumors.
The Ikeshiro pyroclastic-flow deposit at Yufu volcano, Kyushu in Japan, consists of typical block-and-ash flows generated by collapse of the Ikeshiro lava dome erupted ca. 2000 years ago. Lava clasts ...in the Ikeshiro pyroclastic-flow deposit were previously found to consist to two types of rock sample with different magnetic mineral assemblages established by rock magnetic experiments Saito et al., 2003, J. Volcanol. Geotherm. Res. 126, 127–142. We examined iron–titanium oxides in samples from the Ikeshiro pyroclastic-flow deposit with an optical microscope and with an electron microprobe analyzer. As a result, samples were classified into two types with different iron–titanium oxide mineral assemblages. Type A oxides are characterized by homogeneous titanomagnetite and titanohematite. Type B oxides are exsolved and composed of two or three phases: Ti-poor titanomagnetite, titanohematite, pseudobrookite and rutile. The reconstituted compositions of type B oxides show the same Fe/Ti ratio as type A oxides. This indicates that type B oxides are produced by oxidation of type A oxides. Type A oxides yield an equilibrium temperature of about 800–850 °C at an oxygen fugacity of NNO+2 using a two-oxide geothermobarometer. This indicates that deuteric oxidation in the lava dome separated samples of each type. Type A rocks originated in oxygen-poor parts of the lava dome with temperatures of about 800–850 °C, while type B rocks originated in oxygen-rich parts of the lava dome. Type A oxides remained unoxidized, while type B oxides oxidized and were transformed into complex grains by intense deuteric oxidation. The collapse of the lava dome generated the Ikeshiro pyroclastic flow. All oxides were quenched from about 800–850 °C and preserved their compositions by rapid cooling.
Remarkable changes in volcanism and tectonism have occurred in a synchronous manner since 1.5–2 Ma at the junction of the Southwest Japan Arc and the Ryukyu Arc. Although extensive volcanism occurred ...in Kyushu before 2 Ma, the subduction‐related volcanism started at ca 1.5 Ma, forming a NE–SW trend volcanic front, preceded by significant changes in whole‐rock chemistry and mode of eruptions at ca 2 Ma. The Median Tectonic Line has intensified dextral motion since 2 Ma, with a northward shift of its active trace of as much as 10 km, accompanied by the formation of rhomboidal basins in Central Kyushu. Crustal rotation and incipient rifting has also occurred in South Kyushu and the northern Okinawa Trough over the past 2 million years. We emphasize that the commencement age of these events coincides with that of the transition to the westward convergence of the Philippine Sea plate, which we interpret as a primary cause of these synchronous episodes. We assume that the shift in subduction direction led to an increase of fluid component contamination from subducted oceanic slab, which then produced island‐arc type volcanism along the volcanic front. Accelerated trench retreat along the Ryukyu Trench may have caused rifting and crustal rotation in the northern Ryukyu Arc.
We dated two rhyolitic lava plateaus, the Yamakogawa rhyolite and the Haneyama rhyolite, that are assumed to have erupted within a short time interval, in the middle of the Hohi Volcanic Zone, ...central Kyushu, Japan. The groundmass with phenocrysts removed was dated by the conventional K–Ar method using peak-height comparisons without an
38Ar spike.
Our results show that the Yamakogawa rhyolite erupted more than once over a short time interval, from 1.17 to 1.22
Ma. The Haneyama rhyolite is distinctly younger, ranging from 0.67 to 0.71
Ma. The Yamakogawa rhyolite is slightly older than, and therefore probably unrelated to the Yabakei pyroclastic-flow deposit and other known widespread tephra.
The Yamakogawa Rhyolite, which erupted in the early Quaternary period in central Kyushu, Japan, comprises seven units, three contain of which spatter and stretched pumice. Our fieldwork shows that ...these are the deposits of strombolian fire-fountains and rheomorphic tuff. Such deposits derived from silicic magma have been previously described and still are controversial. Some of the reasons given for their formation were exclusively peralkaline composition and high-magmatic temperature. The chemical analyses of the Yamakogawa Rhyolite show nonperalkaline composition and low-magmatic temperature. Moreover, the mineral assemblage of the Yamakogawa Rhyolite suggests that its water content was indistinguishable from other rhyolitic deposits. This is the first report that demonstrates that eruption of silicic magma as fire-fountain and pyroclastic flow with rheomorphism is not, necessarily, restricted to peralkaline composition, high-magmatic temperature and low-water content rhyolite.
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