Structural evolution of the Ongul Islands, Lutzow-Holm Complex, East Antarctica

We describe outcrop-scale folds at ten localities in the Ongul Islands, including five localities where interference patterns of more than two stages of folding are observed, along with structural data summarized in stereogram. F_(m-1) are recognized as isoclinal to rootless folds with fold axes trending NNW-SSE. S_(m-1) is defined by orthopyroxene, hornblende and biotite aligned parallel to the compositional layering and as axial planar foliation in F_(m-1) folds, and is folded by tight F_m. F_m have axial traces that trend NNW-SSE and subvertical axial planes dipping ENE and striking NNW-SSE. Axial planar foliation S_m is defined by biotite and hornblende in the hinges of F_m. F_(m-1) axes typically trend parallel to F_m axes and can be discriminated only in areas showing interference patterns. F_(m+1) are gentle to open with axes trending approximately N-S. Boudinage formed before Dm and interboudin partitions are filled with orthopyroxene-bearing leucosome. Judging from minerals constituting D_(m-1) and D_m structures, D_(m-1) occurred under granulite-facies conditions and at least part of D_m probably under amphibolite-facies conditions

Detailed observation of subgrained/aggregated sillimanite enclosed in garnet by cathodoluminescence imaging and Raman spectroscopy

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / 3F Seminar room, National Institute of Polar Researc

Timing of ductile deformation and peak metamorphism in Skallevikshalsen, Lutzow-Holm Complex, East Antarctica

The geological structures of Skallevikshalsen, Lutzow-Holm Complex, East Antarctica are mainly controlled by two stages of ductile deformation, D_(m-1) and D_m. The D_(m-1) stage is characterized by the development of isoclinal F_(m-1) folds with fold axes gently plunging ENE or SWS, and axial planes parallel to the compositional layering (S_(m-1)) of the metamorphic rocks. The D_m stage is characterized by the development of tight folds with axes parallel to F_(m-1) and almost vertical axial planes. An axial planar foliation, S_m, defined by the alignment of biotite and hornblende, is formed in the hinges of F_m folds. No change in direction of elongation took place between D_(m-1) and D_m. Microstructural study and field observations show that a stretching lineation on S_(m-1) defined by the alignment of sillimanite was formed during D_(m-1). The alignment of sillimanite inclusions in garnet rims probably corresponds to an older schistosity formed during D_(m-2), which had a different orientation of principal strain axes than those of D_(m-1) and D_m. Peak metamorphic mineral assemblages are preserved in garnet cores, and their formation is considered to predate D_(m-2). Absence of the alignment of inclusions in garnet cores suggests that peak metamorphism was attained under conditions without strong deformation

Structural analysis of the Lutzow-Holm Complex in Akarui Point, East Antarctica, and overview of the complex

Two phases of major deformation are responsible for the dominant structures at Akarui Point, Prince Olav Coast, East Antarctica. The first phase, referred to as D_(m-1), is associated with the formation of foliation defined by biotite and hornblende aligned sub-parallel to compositional layering. The foliation is locally parallel to the axial planes of isoclinal and intrafolial folds of gneissic layers. Boudins are present with long axes subparallel to the axes of F_(m-1) folds. A second phase of deformation, denoted as D_m, produced a crenulation lineation and axial planar foliation that trends NW-SE throughout the area. This foliation is parallel to the axial plane of the large-scale Akarui Point Synform, which has a fold axis plunging gently SE, suggesting that the Akarui Point Synform formed during D_m. A locally-developed third phase of deformation (D_(m+1)) produced gentle folding of S_(m-1) and S_m. Chemical compositions of biotite grains that define S_(m-1) and S_m are similar. Migmatite shows close associations with D_(m-1) and D_m structures. This suggests that both phases of deformation were contemporaneous with high-grade metamorphism. Compilation of structural data in other areas reveals that D_(m-1) and D_m controlled dominant structures of the Lutzow-Holm Complex. Several folding events after D_m may be responsible for differing orientations of D_m structures between localities

Syn-metamorphic B-bearing fluid infiltrations deduced from tourmaline in the Main Central Thrust zone, Eastern Nepal Himalayas

Mode of occurrence and chemical composition of tourmaline in pelitic schists from the Main Central Thrust (MCT) zone of the Lesser Himalayan Sequences (LHS) are described in detail with the aim of deducing the chemical characteristics of tourmaline formed through B-bearing fluid infiltration and of estimating the composition of the syn-metamorphic fluids. Metasomatic tourmalines from the tourmalinized wall rocks show significant increases in XCa [=Ca/(Ca + Na)] at almost constant XMg [=Mg/(Mg + Fe²⁺)] from the cores or mantles to the rims. Tourmaline in tourmaline-rich (> 1.0 vol%) pelitic schists from the biotite zone to the kyanite zone also show marked increase in XCa at almost constant XMg, and are interpreted as a product of B-bearing fluid infiltration. Abundant margarite and anorthite formed in the pelitic schists intercalated with the metadolostone layers suggesting that the B-rich fluid became Ca enriched as it interacted with metadolostone layers, and metasomatically introduced Ca into the pelitic schists. Infiltration of such B- and Ca-rich fluids into pelitic schists likely resulted in production of abundant tourmaline with the compositional trend of increasing XCa at almost constant XMg. Most of the tourmaline in tourmaline-rich pelitic schists are in equilibrium with plagioclase, suggesting that the fluid composition was buffered by the pelitic schists. Composition of tourmaline in the pelitic schists with <1 vol% tourmaline mostly show increase in XCa and wider range of XMg values, reflecting its growth during prograde metamorphism. The composition of fluids that coexisted with tourmaline is estimated by applying experimentally-determined fluid/tourmaline chemical relationships to the composition of tourmaline from veins associated with tourmalinization, pelitic schists with <1 vol% tourmaline and tourmaline-rich pelitic schists. Assuming coexisting anion to be Cl, the salinity estimated for these rock types was ~0.44–0.59 mol/l NaCl + CaCl₂ that is similar to or slightly lower than the present-day seawater. Veins associated with tourmalinization and tourmaline-rich pelitic schists are sporadically distributed in the MCT zone of the LHS, suggesting that the syn-metamorphic, B-bearing saline fluid infiltrations took place widely in the MCT zone, and the fluid pathways were localized and channeled. Our observation supports the scenario whereby infiltration of fluid into the High Himalayan Crystallines (HHC) caused vapor-saturated partial melting of the HHC to give tourmaline leucogranite melts contemporaneous with inverted metamorphism in the MCT zone

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

Disequilibrium REE compositions of garnet and zircon in migmatites reflecting different growth timings during single metamorphism (Aoyama area, Ryoke belt, Japan)

Chemical disequilibrium of coexisting garnet and zircon in pelitic migmatites (Aoyama area, Ryoke belt, SW Japan) is shown by microtextural evidence and their heavy rare earth element (HREE) patterns. In zircon, two stages of metamorphic rim growth is observed under cathodoluminescence image, although their SHRIMP UPb zircon ages are similar at ca. 92 Ma. Inner and outer rims of zircon tend to show steep HREE patterns irrespective of the UPb age. The inner rims tend to give higher U content than the outer rims; some rim analyses give various Th/U ratios of 0.02–0.07 compared to the very low (<0.02) values seen in the rest of rim analyses. The higher-Th/U values are ascribed to the mixed analyses between thin prograde domains and thick retrograde overgrowths. Zircon grains with inclusions similar to previously-reported melt inclusions are further enclosed in garnet, supporting the growth of thin zircon domains coexisting with garnet during the prograde metamorphism. Garnet rims are commonly replaced by biotite-plagioclase intergrowths, indicating a back reaction with partial melts. Garnet exhibits decrease in HREE and Y concentrations towards the rim, pointing to its prograde growth. The garnet cores have prograde xenotime inclusions, show steep HREE patterns, and yield growth temperature of ~530–570 °C by a YAG-xenotime thermometer. On the other hand, the garnet rims have no xenotime inclusion and show flat HREE patterns. Rare garnet domains including sillimanite needles also show flat HREE patterns and low Y concentrations, which is interpreted as a product of dehydration melting consuming biotite and sillimanite at near-peak P-T conditions (~800 °C and ~0.5 GPa). One such garnet domain gives nearly-equilibrium REE distribution pattern when paired with the matrix zircon rims. Retrograde xenotime is present in the cracks in garnet and in the biotite-plagioclase intergrowths, suggesting that retrograde breakdown of garnet released HREE and Y to form it. Considering the availability of HREE and Zr and presence of melt inclusions in zircon rims, most part of the zircon rims with positive HREE patterns likely grew during the melt crystallization stage, meaning that the zircon rims and presently-preserved garnet domains did not grow in equilibrium. The above scenario was tested by the array plot analysis and it gave a result consistent with microtextural and traditional REE distribution constraints. Combination of microtextural and the array plot analyses may become a powerful tool to reliably correlate the zircon ages to the P-T evolution of the high-grade metamorphic rocks

CHANGES IN SPRINT PERFORMANCE AND KINETICS DURING THE ACCELERATION PHASE OF RUNNING OF A WORLD RECORD HOLDER

INTRODUCTION: Previously, it was reported that faster athletes tend to produce vertical ground reaction force (GRF) impulse during the acceleration phase of sprint (Hunter et al. 2005). The purpose of this study was to investigate changes in sprint performance and kinetics during the acceleration phase of running for a world record holder

EFFECTS OF JOINT MOVEMENT ON THE ACCURACY OF 3-POINT SHOOTING IN BASKETBALL

INTRODUCTION: The 3-point shot is particularly important, since a player is required to shoot from a distance that requires both momentum of a ball and movement accuracy. However, there have been only few studies on a 3-point shot. The purpose of this study is to clarify characteristics of players who possess high accuracy of a 3-point shot with respect to joint movements and the ball trajectory

Denudation Process of Crystalline Nappes in a Continental Collision Zone Constrained by Inversion of Fission‐Track Data and Thermokinematic Forward Modeling: An Example From Eastern Nepalese Himalaya

Thermochronological methods were applied to the Higher Himalayan Crystalline (HHC) nappe and the underlying Lesser Himalayan Sequences (LHS) to elucidate the denudation process for the middle- and upper-crust of eastern Nepal over millions of years. Thermochronological inverse modeling was undertaken for new results of fission-track (FT) age and FT length data of zircon and apatite in order to reconstruct the time-temperature (t-T) paths in the temperature range of 60–350°C. Eight t-T paths calculated along the across-strike section show that the cooling process of the HHC nappe in this study area is characterized by the following three aspects: (a) gradual cooling followed by rapid cooling and subsequent gradual cooling, (b) northward-younging of the timing of the rapid cooling, and (c) gradual cooling followed by <2 Myr rapid cooling in the frontmost part of the HHC nappe. The observed FT ages and t-T paths were then compared with those predicted by forwarding thermokinematic modeling. The results of the thermokinematic modeling for the “Flat-Ramp-Flat MHT model”, in which the HHC and the underlying LHS are denudated in direct proportion to the uplift of rocks transported along the Main Himalayan Thrust (MHT), reproduced the observed t-T paths and FT ages in eastern Nepal. This indicates that the observed FT ages and t-T paths reflect a denudation process driven by the movement of the MHT with a flat-ramp-flat geometry and that the denudation rate and its spatial distribution have roughly been constant in eastern Nepal since ca. 9 Ma