Rb-Sr and Sm-Nd mineral isochron ages of a pegmatitic gneiss from Oku-iwa Rock, Lutzow-Holm Complex, East Antarctica

Oku-iwa Rock is located in the transitional zone between granulite- and amphibolite-facies metamorphic zones in the Lutzow-Holm Complex (LHC), East Antarctica. Hornblende biotite (HB) gneiss widely outcrops in the northern part of this area. Sm-Nd and Rb-Sr mineral isochron ages obtained from pegmatitic HB gneiss are 578±36Ma and 431±14Ma with initial isotopic ratios of 0.511892±0.000040 and 0.70718±0.00038, respectively. The former mineral isochron age is consistent with the Rb-Sr whole rock isochron age of the HB gneiss (583Ma). The latter age is close to the previously published Rb-Sr mineral isochron age of granitic rocks (418Ma) in Oku-iwa Rock, implying that these ages represent the time when the rocks cooled down to the closure temperature of biotite. The granodioritic precursor formed at 674Ma was gradually cooled down and its temperature reached 700°C at 583Ma based on a previous report. Temperature of the HB gneiss rose at 578Ma by injection of source material for the pegmatitic HB gneiss and rose again at 529Ma (SHRIMP U-Pb zircon age) by regional metamorphism. At 485Ma, the temperature of the gneisses rose for the third time by intrusion of granitic rocks. After the intrusion, the constituent rocks of Oku-iwa Rock gradually cooled by uplifting and the temperature reached 310°C at 431Ma

Geochronological study of post-metamorphic granite from Kasumi Rock, Lutzow-Holm Complex, East Antarctica

Kasumi Rock is situated in the amphibolite-facies metamorphic zone in the Lutzow-Holm Complex, East Antarctica. In this area, granitic rocks occur as steeply dipping linear dykes with sharp intrusive contacts, and cross-cut the foliation of layered metamorphic rocks. A geochronological study of this post-metamorphic granite (PMG) has been performed. An Rb-Sr whole rock isochron for five granitic rocks defines an age of 492.1+-23.4 Ma with an initial ^87Sr/^86Sr ratio of 0.70535+-0.00027 (MSWD=0.08). In the Sm-Nd isochron diagram, four rock samples yield an age of 498.4+-90.6 Ma with an initial ^143Nd/^144Nd ratio of 0.511782+-0.000101 (MSWD=0.05). The whole rock isochron ages and mode of occurrence suggest that the Kasumi PMGs were intruded after regional cooling of the area, and probably affected local reequilibrium for isotopic systems of surrounding metamorphic rocks. The PMGs might have been slowly cooled and crystallized after the intrusion. The Kasumi PMGs have no genetic relation to the Oku-iwa PMGs as regards Rb-Sr and Sm-Nd isotopic systems, because the initial ratios of both PMGs are quite different from each other. This is interpreted to mean that the PMGs in the Lutzow-Holm Complex were originated from different source materials or had different chemical reaction processes with crustal materials

Geochemistry of the pre/syn-metamorphic granite in the Ongul Islands, East Antarctica

Latest Proterozoic to Early Paleozoic pre/syn- and post-metamorphic granites occur in the Lutzow-Holm Complex (LHC), East Antarctica. The pre/syn-metamorphic granites in the Ongul Islands consist of biotite hornblende (BH) granite and garnet biotite hornblende (GBH) granite. The Rb-Sr whole rock isochron age of 580±23Ma with an initial ^(87)Sr/^(86)Sr ratio of 0.70784±0.00059 is obtained from the BH granite. This age is slightly older than SHRIMP U-Pb zircon and CHIME monazite metamorphic ages (520-550Ma) from the complex. The BH granite has lower aluminum saturation index than the GBH granite. The pre/syn-metamorphic granites have a wide variation of εSr and εNd values at 580m.y. before the present, and the BH granite has lower εSr_(580Ma) and higher εNd_(580Ma) values than the GBH granite. One end of the variations in the ε diagram is close to the values of the mafic to intermediate metamorphic rocks in the island; the other is close to those of the old continental crust. These geochemical and isotopic features suggest that the PSMGs were originated by mixing between magma derived from mafic to intermediate metamorphic rocks and old continental crust

Preparation of Monodispersed Hydrophilic Polymer Microspheres in Gel Permeation Chromatography

Monodispersed porous polymer microspheres having diameter of ca. 50 μm were successfully prepared by suspension polymerization of styrene, polyoxyethylene methacrylate and ethylenegycol dimethacrylate. Monodispersed O/W emulsion was firstly made by SPG membrane emulsification technique, following droplets-swelling method of monodispersed seed emulsion by the addition of secondary emulsion. The effect of solvent used in suspension polymerization on porous structure of prepared polymer microspheres was investigated in this paper by identification with scanning electron microscopy, porosimeter and the performance in gel permeation chromatography. It was found that benzene, 1-butanol and butyl acetate worked as poor solvent for polymer prepared in this study and that polymer microspheres prepared with these solvents had larger pores. Gel permeation chromatography measurements indicates that polystyrene having molecular weight smaller than 50,000-100,000 can be clearly separated by using gel columns packed with polymer microspheres prepared with poor solvents

Region-Specific Responses of Adductor Longus Muscle to Gravitational Load-Dependent Activity in Wistar Hannover Rats

Response of adductor longus (AL) muscle to gravitational unloading and reloading was studied. Male Wistar Hannover rats (5-wk old) were hindlimb-unloaded for 16 days with or without 16-day ambulation recovery. The electromyogram (EMG) activity in AL decreased after acute unloading, but that in the rostral region was even elevated during continuous unloading. The EMG levels in the caudal region gradually increased up to 6th day, but decreased again. Approximately 97% of fibers in the caudal region were pure type I at the beginning of experiment. Mean percentage of type I fibers in the rostral region was 61% and that of type I+II and II fiber was 14 and 25%, respectively. The percent type I fibers decreased and de novo appearance of type I+II was noted after unloading. But the fiber phenotype in caudal, not rostral and middle, region was normalized after 16-day ambulation. Pronounced atrophy after unloading and re-growth following ambulation was noted in type I fibers of the caudal region. Sarcomere length in the caudal region was passively shortened during unloading, but that in the rostral region was unchanged or even stretched slightly. Growth-associated increase of myonuclear number seen in the caudal region of control rats was inhibited by unloading. Number of mitotic active satellite cells decreased after unloading only in the caudal region. It was indicated that the responses of fiber properties in AL to unloading and reloading were closely related to the region-specific neural and mechanical activities, being the caudal region more responsive