排序方式： 共有5条查询结果，搜索用时 15 毫秒
1
1.
2.
High‐grade mylonites occur in the Takahama metamorphic rocks, a member of the high‐pressure low‐temperature type Nagasaki Metamorphic Rocks, western Kyushu, Japan. Mafic layers within the mylonites retain reaction microstructures consisting of margarite aggregates armoring both corundum and kyanite. The following retrograde reaction well accounts for the microstructures in the CaO–Al2O3–SiO2–H2O system: 3Al2O3 + 2Al2SiO5 + 2Ca2Al3Si3O12(OH) + 3H2O = 2Ca2Al8Si4O20(OH)4 (corundum + kyanite + clinozoisite + fluid = margarite). Mass balance analyses and chemical potential modeling reveal that the chemical potential gradients present between kyanite and corundum have likely driven the transport of the CaO and SiO2 components. The mylonitization is considered to take place chronologically after peak metamorphism and before the above reaction, based on the following features: approximately constant thickness of the margarite aggregates, random orientation of margarite, and local modification of garnet composition at a boudin neck that formed during mylonitization. The estimated peak temperature of 640°C and the pressure–temperature conditions of the above reaction indicate that the mylonitization took place at temperature between 530 and 640°C at pressures higher than 1.2 GPa, approximately equivalent to the depth of the lower crust of island arcs. 相似文献
3.
ABSTRACT Groundwater temperature at an arbitrary depth and at an arbitrary point is determined not only by heat transported by conduction but also by advection caused either by infiltration of rain, snowmelt or irrigated water, or by seepage from surface water bodies. Therefore, characteristic changes of groundwater temperature are observed in recharging and discharging areas within a groundwater flow system. The changes may be one-, two-, or three-dimensional, depending on individual situations. Since heat is a conservative quantity in the subsurface environment, groundwater temperature can be used as a tracer to reveal the regional structure of a groundwater flow system. A case study showing the importance of groundwater temperature in a regional groundwater survey is presented taking Nagaoka plain, Japan, as an example. The groundwater temperatures were measured in observation wells with diameters of 65 to 250 mm and depths of 20 m or more. Marked seasonal changes in temperature depth profiles showing advective effects in the horizontal direction from the Shinano River, and in the vertical direction from upper and lower aquifers, were observed. The temperature depth profiles were classified into six types. The distribution of these types does not contradict the regional structure of the groundwater flow system revealed by the potential distribution. As groundwater temperature is an easily measureable element in a hydrological survey, the method described in the present paper is appropriate for a field study in an uninstrumented groundwater basin. 相似文献
4.
Chemical Th–U–total Pb isochron method (CHIME) monazite dating was carried out for pelitic–psammitic migmatites and the Ao granite (one of the Younger Ryoke granites) from the Aoyama area, Ryoke metamorphic belt, Southwest Japan. The Ao granite gives an unequivocal age of 79.8 ± 3.9 Ma. The monazite grains in migmatites yield an age of 96.5 ± 1.9 Ma with rims and patchy domains of 83.5 ± 2.4 Ma. The 83.5 ± 2.4‐Ma overprinting on migmatites over the garnet–cordierite zone suggests a wide and combined effect of thermal input and fluid activity on the monazite grains caused by the contact metamorphism by the Younger Ryoke granites including the Ao granite. This contact metamorphism has not been detected from the major metamorphic mineral assemblage previously, possibly because the migmatites already possessed the high‐temperature mineral assemblage before the granite intrusions and were immune from contact metamorphism in terms of major metamorphic minerals. However, monazite records contact metamorphism clearly. Therefore, the field mapping of the CHIME monazite age is a powerful tool for recognition of polymetamorphism in high‐temperature metamorphic terrains where later thermal effects can not be easily detected by the growth of new major metamorphic minerals. 相似文献
5.
1