Contact Metamorphic Effect on Basaltic Rocks by the Koyama Gabbro Complex, Susa Area, Southwest Japan

Tertiary basaltic rocks around the Koyama gabbro complex mass, which occurs in the northeastern part of Yamaguchi Prefecture, have undergone intense contact metamorphism by the mass. Radiometric age determinations indicate that the metamorphism is of Miocene age. The contact aureole is rather narrow (a maximum of about 700 m), the metamorphic grade rapidly increasing toward the mass. In the comparatively lower temperature part of the contact aureole, the metamorphic paragenesis is actinolitic hornblende ± hornblende + epidote+ biotite+ oligoclase + quartz. Meanwhile, the highest-grade rocks are represented by the stable association of orthopyroxene+ clinopyroxene ± hornblende + biotite+ labradorite + quartz. The metamorphic temperature close to the contact with the mass is estimated to be 800 to 860°C. In the most-intensely metamorphosed basalts, most of such phenocrystic minerals as clinopyroxene and plagioclase can still preserve the essential chemical characteristics in the original rocks, whereas phenocrystic orthopyroxene appears to have been chemically changed its composition during the metamorphism

Control of vent geometry on the fluid dynamics of volcanic plumes: insights from numerical simulations

AbstractWe present three‐dimensional numerical simulations of eruption clouds from circular to linear fissure vents to investigate the control of vent shape on the height and stability of volcanic plumes during large explosive eruptions. Our results show that clouds ejected from circular or low‐aspect‐ratio (nearly square‐like) fissure vents can be associated with radially suspended flow (RSF) at the top of the jet region, whereas those emitted from narrow‐fissure vents are not. Non‐RSF plumes are more stable than those associated with RSF because the highly concentrated parts of the ejected mixture are easily dissipated and mixed with air near the vent. Plume height in the RSF regime decreases while that in the non‐RSF regime increases with increasing aspect ratio, even for a fixed magma flow rate. These observations suggest that the efficiency of air entrainment is influenced by the vent shape, which in turn controls the dynamics of eruption plumes

Effects of glycosylation on swimming ability and flagellar polymorphic transformation in Pseudomonas syringae pv. tabaci 6605

The role of flagellin glycosylation on motility was investigated in Pseudomonas syringae pv. tabaci. The swimming activity of glycosylation-defective mutants was prominently decreased in a highly viscous medium. The mutants showed differences in polymorphic transitions and in the bundle formation of flagella, indicating that glycosylation stabilizes the filament structure and lubricates the rotation of the bundle.</p