The thermodynamic regime of metamorphism in the ancient subduction zones

Based on mineralogical themometry and baroraetry and computation of mineral reactions modelling metamorphic sequence, a geotherm for metamorphic belts of the subduction zones has been deduced. Relatively low PT-values (3 kbar/200° C) correspond to zeolite and prehnite-pumpellyite metasediments and at higher pressures and temperatures (10 kbar/400 °C) lawsonite-glaucophane assemblages become unstable. The PT-curve achieves maximum at 11 kbar and 470° C to drop down to normal geotherm (Perchuk 1977). High concentration of H₂O in the metamorphic fluid has been revealed, the difference between P_f1 and being less than 2 kbar. Consideration has also been given to specific thermodynamic regime of zeolite and prehnite-pumpellyite zones of the younger island arcs, where lawsoniteglaucophane zones are absent. Here the geotherm has been found to rise from 0.2kbar/120° C up to 4 kbar/350° C and -regime similar to that of glaucophane schists formations.     

The variation of silver content in native gold particles as revealed by ESCA

Depth profiling analysis of native gold samples using X-ray photoelectron spectroscopy (XPS) shows the surface layers of lode gold to be significantly enriched with silver to a depth of 0.02–0.04 microns and the surface layers of placer gold to be depleted of silver up to a depth of several microns. The change in the surface composition of gold samples taken from oxidation zones is of more complicated character. Model experiments suggest the surface segregation of silver in lode gold samples to be due to outward diffusion and oxidation of silver at the surface. In placer gold the depletion of silver is caused by leaching of the latter from the surface layers.     

The history and the dynamics of the development of the west siberian platform

The area of the West Siberian platform is about 3.3 million km², the average thickness of the Mesozoic—Cenozoic platform mantle of sediments is 3 km, and the volume of sedimentary infilling is 10 million km³. The formation of the platform took place during a major tectonic cycle which in turn is divided into tectonic-sedimentary cycles as follows: Triassic, early-Middle Jurassic, late Jurassic, Neocomian, Aptian—Cenomanian, Turonian—Maastrichtian, Paleocene—early Oligocene and Middle Oligocene—Middle Pliocene. During the Triassic period in the arctic part of the platform large depressions were formed and continued to subside to the end of the Cretaceous. During early—Middle Jurassic part of the Triassic postorogenic shield began to subside. The late Jurassic epoch is characterized by maximum transgression and low rate of uncompensated subsidence of the basin floor. In Neocomian and Aptian—Cenomanian time, differential subsidence is sharply intensified, its rate increasing from south to north in the direction of Triassic downwarp. Turonian—Maastrichtian time is distinguished by wide transgression and reduction of subsidence rate. In Paleocene—early Oligocene the extent of the sea decreased and took the form of a submeridional gulf, the axial line of which approached the Urals. In the middle of the Oligocene epoch the sea became freshened and divided into separate basins. Eastern and northern parts of the platform were subsequently involved in the uplift. In the Neogene the region of subsidence took the form of a sublatitudinal depression extending along the southern mountain-folded margin of the platform.     

分汊河道主支汊交替主导因子的转换模拟

进口水流条件及河道周界特征的改变是促使分汊河道主支汊交替的两大主要因素,不同类型的汊道对两者敏感性存在差异,辨析不同汊道主支汊交替的主导因素是预测汊道演变的前提。以长江中游分汊河道为参考,通过调整进口水流动力轴线走向及两汊的长度比设置了30种概化方案,采用平面二维水沙数学模型探讨上述两种因素对主支汊交替的影响。结论表明:两汊长度比存在一个临界值,当汊长比低于此临界值时,进口主流动力轴线的偏移是影响主、支汊交替的主要动力因素;超过此临界值后,进口水流条件变化对汊道分流格局的影响将会明显减弱,影响主支汊交替的主导因子将转换为汊道间的阻力对比关系;通过概化计算得到此临界值约为1.5。     

The interaction of matter and radiation in the hot model of the Universe,II

Heating of the primaeval plasma prior to the epoch of recombination results in distortions in the Rayleigh-Jeans region of the microwave relic radiation spectrum (1–60 cm, or more exactly =2.5_–7/8 cm). The present observational data allow limits to be set to such energy injection from which follow upper limits to (a) the amount of antimatter in the universe; (b) the parameters of primaeval turbulence; and (c) the adiabatic fluctuation spectrum for small masses (M<10¹¹ M ).If the heating takes place prior to the epocht=10_1012/5 sec (and in particular at the annihilation of electron-positron pairs atT10⁸–10¹⁰ K,t<300 sec), no observable distortions are expected in the relic radiation spectrum. Here =/_crit is the dimensionless average density of matter in the universe.Translated from the Russian by D. F. Smith.     

黑河流域下游额济纳绿洲与水资源的关系

简要介绍了黑河流域下游额济纳绿洲自然概况,分析了黑河下游地表水、地下水近20年的变化趋势,进而对额济纳绿洲植被生长、植物种群演替、植被覆盖度以及绿洲的存亡与当地地下水埋深的关系作了剖析,并对规划年绿洲变化作了预测.指出了水资源是黑河下游额济纳经济社会可持续发展和生态环境建设的依托,如何稳定绿洲和使绿洲有适度规模发展,是生态保护的核心问题,具有重要的战略意义.     

阿尔金断裂带东南缘含油气盆地群的形成演化

沿阿尔金断裂带东南侧发育六个中、新生代的含油气盆地，盆地的边缘或盆地内部发育一系列的近东西走向、与阿尔金断裂锐角相交的断裂，该组断裂对盆地的隆坳格局和地层分布具有控制作用，盆地具有箕状结构或不对称结构特点。沿阿尔金断裂带方向，保罗系、白垩系、古近系、新近系的厚度和沉积特征在时空上呈有规律性变化，显示了阿尔金断裂带时、空活动的差异性。根据侏罗纪盆地在阿尔金断裂带两侧的展布特征和柴达木盆地西部发育的鼻状构造及其沉积演化特征，推断阿尔金断裂带中、新生代经历了多期不同方向的走滑运动。     

Lower Devonian Redeposited Serpentinite-Clastic Weathering Crust,Southern Urals

The structure and problems of origin of Lower Devonian breccia-conglomerates of the Sakmara–Voznesensk zone, southern Urals are considered. It was revealed that the breccia-conglomerates are composed of carbonatized serpentinite clasts and formed in a marine basin at the foothill of a relatively steep slope of a rather intensely dissected land. Clastic material of the breccia-conglomerates was mainly derived from carbonate weathering crusts of serpentinized ultramafic rocks.