Trace element composition and degree of partial melting of pelitic migmatites from the Aoyama area, Ryoke metamorphic belt, SW Japan: Implications for the source region of tourmaline leucogranites   总被引：1，自引：1，他引：0  

Tetsuo Kawakami  Tomoyuki Kobayashi 《Gondwana Research》2006,9(1-2):176

Degree of partial melting of pelitic migmatites from the Aoyama area, Ryoke metamorphic belt, SW Japan is determined utilizing whole-rock trace element compositions. The key samples used in this study were taken from the migmatite front of this area and have interboudin partitions filled with tourmaline-bearing leucosome. These samples are almost perfectly separated into leucosome (melt) and surrounding matrix (solid). This textural feature enables an estimate of the melting degree by a simple mass-balance calculation, giving the result of 5–11 wt.% of partial melting. Similar calculations applied to the migmatite samples, which assume average migmatite compositions to be the residue solid fraction, give degree of melt extraction of 12–14 wt.% from the migmatite zone. The similarity of the estimated melting degree of 5–11 wt.% with that in other tourmaline–leucogranites, such as Harney Peak leucogranite and Himalayan leucogranites, in spite of differences in formation process implies that the production of tourmaline leucogranites is limited to low degrees of partial melting around 10 wt.%, probably controlled by the breakdown of sink minerals for boron such as muscovite and tourmaline at a relatively early stage of partial melting. Because the amount of boron originally available in the pelitic source rock is limited (on average 100 ppm), 10 wt.% of melting locally requires almost complete breakdown of boron sink mineral(s) in the source rock, in order to provide sufficient boron into the melt to saturate it in tourmaline. This, in turn, means that boron-depleted metapelite regions are important candidates for the source regions of tourmaline leucogranites.  相似文献   

Age gap between the intrusion of gneissose granitoids and regional high‐temperature metamorphism in the Ryoke belt (Mikawa area), central Japan          下载免费PDF全文

Kota Takatsuka  Tetsuo Kawakami  Etienne Skrzypek  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata 《Island Arc》2018,27(1)

The relationships between the intrusion of gneissose granitoids and the attainment of regional high‐T conditions recorded in metamorphic rocks from the Ryoke belt of the Mikawa area, central Japan, are explored. Seven gneissose granitoid samples (tonalite, granodiorite, granite) were collected from three distinct plutonic bodies that are mapped as the so‐called “Older Ryoke granitoids.” Based on bulk‐rock compositions and U–Pb zircon ages obtained by laser ablation inductively coupled plasma mass spectrometry, the analyzed granitoids can be separated into two groups. Gneissose granitoids from the northern part of the area give weighted mean ²⁰⁶Pb/²³⁸U ages of 99 ±1 Ma (two samples) and 95 ±1 Ma (one sample), whereas those from the southern part yield 81 ±1 Ma (two samples) and 78–77 ±1 Ma (two samples). Regional comparisons allow correlation of the northern granitoids (99–95 Ma) with the Kiyosaki granodiorite, and mostly with the Kamihara tonalite found to the east. The southern granitoids are tentatively renamed as “78–75 Ma (Hbl)?Bt granite” and “81–75 Ma Hbl?Bt tonalite” (Hbl, hornblende; Bt, biotite). and seem to be broadly coeval members of the same magmatic suite. With respect to available age data, no gneissose granitoid from the Mikawa area shows a U–Pb zircon age which matches that of high‐T metamorphism (ca 87 Ma). The southern gneissose granitoids (81–75 Ma), although they occur in the highest‐grade metamorphic zone, do not seem to represent the heat source which produced the metamorphic field gradient with a low dP/dT slope.  相似文献   

Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data   总被引：2，自引：0，他引：2  

Hiroshi Uchida  Shiro Imawaki  Jian-Hwa Hu 《Journal of Oceanography》1998,54(1):115-122

Sea-surface geostrophic velocities for the Kuroshio region calculated from TOPEX/POSEIDON altimetry data together within situ oceanographic data are compared with surface velocities derived from drifting buoy trajectories. The geostrophic velocities agree well with the observed velocities, suggesting that the Kuroshio surface layer is essentially in geostrophic balance, within measurement error. The comparison is improved a little when the centrifugal acceleration is taken into account. The observed velocities are divided into the temporal mean and fluctuation components, and the partitioning of velocities between these two components is examined. For the Kuroshio region, most of the fluctuation components of the velocities derived from drifting buoys are found to be positive. This result suggests that Eulerian mean velocities for the Kuroshio region estimated from drifting buoy data tend to be larger than actual means, due to the buoy’s tendency to sample preferentially in the high-velocity Kuroshio.  相似文献   

Sea level response to wind field fluctuation around the tip of the Izu Peninsula   总被引：1，自引：0，他引：1  

Hirofumi Hinata  Tetsuo Yanagi  Chizuru Satoh 《Journal of Oceanography》2008,64(4):605-620

The mechanism of a characteristic sea level response (barotropic coastal ocean response) to wind field fluctuation around the tip of the Izu Peninsula observed during the middle of December 2000 to the middle of January 2001 was investigated based on three types of numerical experiments using the Princeton Ocean Model with various parameters. The response was characterized by the relaxation of sea level falling (rising) during eastward upwelling (westward downwelling) favorable wind regime. Analyses of quasi-realistic numerical model results in terms of the vertically integrated momentum balances and vorticity balance for the barotropic mode revealed that: 1) development/abatement of two anomalous circulations generated around the tip of the Izu Peninsula controls the sea level response through the acceleration/deceleration of a quasi-geostrophic barotropic coastal current between the circulations; 2) nonlinear vorticity advection by the Kuroshio Current and by the coastal current, coupled with vorticity diffusion, decelerates the quasi-geostrophic coastal current in the latter half of the wind regimes, which induces the relaxation of sea level rise/fall. The results of the quasi-realistic numerical experiment suggest that an analysis of the vorticity balance for the barotropic mode contributes to a better understanding of sea level responses to wind in coastal regions with strong currents and complex topography. In addition, a numerical experiment with idealized spatially uniform density stratification and a quasi-realistic wind field shows that if the Kuroshio Current had been shifted far offshore from the Izu Peninsula during the observation period, westward propagating continental shelf waves would have controlled the coastal sea level response.  相似文献