Drinking water supplies in Ulaanbaatar, the capital of Mongolia, are completely dependent on groundwater sourced from pumping
wells located in an alluvial plain of the Tuul River which flows through Ulaanbaatar. The interaction between groundwater in the
alluvial plain and river surface water was investigated using a hydrological and multi-tracers approach. The observed groundwater
contour map clearly shows that the Tuul River recharges the floodplain groundwater and groundwater flows from east to west.
The similarity of chemical and stable isotopic compositions suggests that groundwater is mainly recharged by Tuul River water in
the vicinity of the river. In addition, considering groundwater contours and chemical composition, groundwater in the northern and
southern mountain sides contribute to floodplain groundwater. Stable isotopic information suggests that winter season precipitation
also contributes to the groundwater, because groundwater in a specific region has a considerably lower isotopic ratio. Using
the End Member Mixing Analysis applying oxygen-18, SiO2 and HCO3- as tracers, the contribution ratios of the Tuul River,
groundwater in the northern and southern mountain regions, and winter season precipitation to floodplain groundwater are estimated
to be 58% to 85%, 1% to 54%, 0% to 16%, and 0% to 12%, respectively. 相似文献
Two semi-asymmetric flow patterns of typhoons are chosen to qualitatively determine the effect of exchange of horizontal momentum between inflow and outflow layers and the environment on the motion of typhoons. The results show that only the asymmetric flow component (residual after azimuthal mean flow has been removed) could cause a net momentum input into or output from a typhoon and therefore contribute to the changes in speed and direction of the typhoon movement. A typhoon with major inflow and/or outflow channels on its right (left) side would tend to accelerate and turn left (decelerate and turn right); On the other hand, a typhoon with major inflow and/or outflow channels in the rear (front) semicircle would tend to accelerate and turn right (decelerate and turn left). 相似文献
40Ar---39Ar age determinations on samples selected on deformational criteria form the basis of a proposal of a new detailed tectonometamorphic history of the Montagne Noire (the southern part of the Massif Central, France).
This range is classically divided into a cover and an axial gneissic and migmatitic core which was metamorphosed under high T/medium P conditions. The basement is structurally overlain by epimetamorphic Paleozoic sediments in the north. In the south, equivalent rocks form a well-known pile of recumbent nappes. The Variscan history of this area comprises early shortening and thickening of the continental crust. The climax of this event took place around 320 Ma ago, as is shown by previous Rb---Sr data and by 40Ar---39Ar measurements. New developments in structural analyses have led to a better understanding of the late evolution of the area in terms of diapiric uplift of the core. South-southwestwards verging recumbent nappes have been emplaced and were weakly metamorphosed in their lower parts. This movement was accompanied and followed by dextral extensional wrenching of the Paleozoic cover along the northern and southern margins of the axial zone. Attendantly, ductile shear zones were formed.
In order to decipher the complex history, three structural levels have been dated with the 40Ar---39Ar method. These levels are: (1) The migmatitic and gneissic series in the axial core, where micas yield ages of c. 315 Ma; (2) Mylonites from the northern and southern shear zones where biotites and muscovites yield ages of c. 310 Ma; (3) Muscovites and biotites from the epimetamorphic nappe structures yielding ages of c. 297 Ma. The later ages may represent a younger thermal pulse. These data are compared and discussed in the light of previous radiometric studies of the area and precise biostratigraphic constraints. A detailed geodynamic evolution of the studied segment is proposed. 相似文献