High-pressure sound velocity of perovskite-enstatite and the possible composition of the Earth’s lower mantle

The compressional sound velocity V_p for enstatite of polycrystalline specimens were measured at pressures from 40 to 140 GPa using the optical analytical techniques under shock loading. The dependence of V_P, (in km/s) on Hugoniot pressure (P, in GPa) can be described by InV_p= 3.079-0.691 In(P) + 0.094(lnP)². V_p satisfies Birch’s law:V _p = 4.068 + 1.677_ρ, where ρ is corresponding density, which indicated that enstatite is stable throughout the conditions of the lower mantle. The wave velocityP is 0.5% lower and the wave velocity S is 2% higher than that of PREM respectively. We concluded that the lower mantle is mainly composed of perovskite-(Mg_1-x, Fe_x) SiO₃ and only a small amount of (Mg_1-x, Fe_x) O is allowed in it.     

Evidence for tritium production in the Earth's interior

We have made a new investigation on the vertical profiles of tritium and helium isotopes in Lakes Van and Nemrut(Eastern Turkey),using experimental data from the reference by Kipfer et al.for study of long-term vertical mixing and deep water renewal in Lake Van.Lakes Van and Nemrut are crater lakes.Lake Nemrut is at the western border of Lake Van.The 3He and 4He are injected at the bottom of Lakes Van and Nemrut,and the both helium isotopes are confirmed from the mantle source.From 3H(tritium) data in Lakes Van and Nemrut,we have observed "3H anomaly" at the vertical profile of 3H concentrations in Lake Nemrut.The 3H concentration at the lake bottom is 10% higher than at the surface.The difference of 3H concentrations between surface and bottom is about 3.7±1.2 TU.This excess 3H should be injected from the lake bottom.An investigation on the origin of the injected tritium has been made.The results show the conventional origins are excluded,such as residence of precipitation tritium from nuclear testing in the early 1950s-1960s and tritium from known nuclear reactions.Based on the correlation of excess 3H with 3He and heat flow in Lake Nemrut,we infer that the 3He and 3H might be all from the mantle source,and produced by the supposed natural-nuclear-fusion,which might occur in an environment rich in water(H) and(U Th) at high temperature and high pressure in the deep Earth.Detection of tritium in the Earth's interior is a key evidence for exploration of natural nuclear fusion in the deep Earth.Based on the published data,we have found that the excess 3He and 3H injected at the bottom of Lake Laacher(Germany) were also released from the mantle source.The present work will be helpful to the further study of mechanism of natural nuclear fusion in the Earth's interior.     

Oxygen isotopic heterogeneity in the mantle: Evidence from clinopyroxene megacrysts of Nüshan, eastern China

Major element, REE and oxygen isotopic compositions of fourteen clinopyroxene megacrysts from Nushan, eastern China have been obtained. They are believed to represent crystallization products of one mantle-derived alkali basaltic magma. Oxygen isotopic ratios are homogeneous within the same sample, but heterogeneous among different samples, 18O values of these megacrysts are from 4.86‰ to 6.48‰. We suggest that the oxygen isotopic variation of clinopyroxene megacrysts should be inherited from their source magma, and the heterogeneity of source magma results from contamination of subducted oceanic materials.     

Evaluation of crustal stability in the lower Yellow River region

The evaluation of crustal stability in the lower Yellow River region （LYR） is vital to the engineering project of the Yellow River embankment and construction of the Huang-Huai-Hai plain. From three aspects of tectonic stability, surface stability and medium stability, this paper analyzes in detail the factors such as tectonic activity, tectonic stress, exogenic geologic disasters and ground material composition which affect crustal stability in the study area and the spatial distributions of subordinate degree of the evaluation factors. It then constructs the crustal stability evaluation model of fuzzy mathematics based on GIS by using AHP to among the various factors find out the interrelations comprehensive evaluation of fuzzy mathematics and the functions of spatial overlay and spatial database of ArcGIS. Based upon this the crustal stability evaluation is carried out, the results show that the areas of stable and instable regions are basically the same, being 48.72% and 51.28% respectively. The area of moderate stable region takes a dominant position, being about 70.58%. The crust instable region presents zonal distribution and under the control of tectonic faulted belt. But the region where the LYR runs across is mostly instable with a total length of the river being 568.345 km, or 78.93% of all. The river reach where the crustal stability is relatively poor along the LYR is concentrated in the Lankao-Dongping section.     

Progress in researching into the transition of the Mesozoic tectonic systems in southeast China

This paper presents the latest progress made on the research of Mesozoic tectonic system transition from the E-W paleo-Tethyan tectonic domain into NE-NNE western Pacific domain in southeast China. Tectonism of the west Pacific domain began at middle Jurassic (J₂) and formed a set of NE-trending structures, non-coaxially overprinting on E-trending tectonic belts which may be early and coevally produced by the paleo-Tethyan domain. Thus began the tectonic domain transition from the E-trending paleo-Tethyan to the NE-trending Pacific and fully finished at the early Cretaceous. The eastern Nanling area was a junction zone of the transition at middle Jurassic (J₂), and ever since the junction zone might obliquely migrate to the coastal region, where is the east part of this study area. To the north of the Nanling area, the Ganjiang Fault Zone was the boundary between two tectonic domains. Corresponding to the transition of tectonic system, the geodynamics of SE China changed from a compressional system to an extensional system, which continued until the end of Mesozoic-Tertiary.     

Spatial pattern of the flood disaster risk in the protected zone of the lower Yellow River embankment

Flood disaster risk is analyzed by using hydraulics simulating method in the protected zone of the embankment along the Huayuankou-Lankao section of the lower Yellow River. According to the results of hydraulics simulation and spatially distributed conditions of social-economic property, the index system for identifying flood disaster risk is established. Flood disaster risk is identified, and spatial pattern of that is analyzed by means of map algebra functions of geographic information system （GIS） and synthetical cluster of fuzzy mathematics. The results show that the first grade flood disaster risk zone is mainly located in the northeast of the study area, with an average floodwater depth of 1.36 m, average flood velocity of 0.33 m/s, average GDP density of 4.35 million yuan/km^2, and average population density of 841.43 person/km^2; the second grade flood disaster risk zone is mainly distributed in the northwest of the study area; the third grade mainly in the southeast; the fourth grade mainly in the southwest; and it is relatively safe in the rest of the zones. This attempt on the methods and technique for identifying flood disaster risk can serve as a reference to the researches in other similar regions.     

Velocity structure of the crust and uppermost mantle in the boundary area of the Tianshan Mountains and the Tarim Basin

A portable 3-component broadband digital seismic array was deployed across the Tianshan orogenic belt (TOB) to investigate the lithospheric structure. Based on receiver function analysis of the teleseismic P-wave data, a 2-D S-wave velocity profile of the boundary area of the TOB and the Tarim Basin was obtained at the depths of 0--80 km.Our results reveal a vertical and lateral inhomogeneity in the crust and uppermost mantle. Four velocity interfaces divide the crystalline crust into the upper, middle and lower crust. A low velocity zone is widely observed in the upper-middle crust. The depth of Moho varies between 42 and 52 km. At the north end of the profile the Moho dips northward with a vertical offset of 4--6 km, which implies a subduction front of the Tarim Basin into the TOB. The Moho generally appears as a velocity transitional zone except beneath two stations in the northern Tarim Basin, where the Moho is characterized by a typical velocity discontinuity. The fine velocity structure and the deep contact deformation of the crust and upper most mantle delineate the north-south lithospheric shortening and thickening in the boundary area of the TOB and the Tarim Basin, which would be helpful to constructing the geodynamical model of the intracontinental mountain-basin-coupling system.     

Thermodynamic evolution of lithosphere of the North China craton： Records from lower crust and upper mantle xenoliths from Hannuoba

Lithospheric thinning in East China attracts much attention of geologists. In many cases where a lithospheric thinning is inferred, the trigger for instability is a preced-ing episode of crustal thickening by the continental colli-sion[1]. Lithospheric processes (e.g. lithospheric thinning) could be recorded by the thermal history of the lower crustal and upper mantle xenoliths. Xu et al.[2] suggested that the cooling (from >1200 to 850℃) recorded by spinel harzburgite from Northeast China …     

Daily variation of carbon flux in soils of Populus euphratica forests in the middle and lower reaches of the Tarim River

In order to lucubrate the daily variation of respiration in soils of Populus euphratica forests and analyze its relationship with environmental factors in the middle and lower reaches of the Tarim River, the LI-8100 instrument of soil CO2 flux system was used to measure the parameters of soil carbon flux and air temperature 10 cm above ground surface along the profiles of Usyman, Archy River, Yengisu and Karday, and the relationships between the soil carbon flux and the soil moisture content were analyzed. The nonlinear regression analysis was carried out with the software SPSS13.0. We observed that: (1) soil respiration began to be restrained when the air temperature was up to 30℃ 10 cm above the ground surface; (2) the rates of soil respiration under the forests of Populus euphratica were significantly different at various moisture contents, the soil carbon flux was high along the Usyman profile,which has a high soil moisture content, and it was low along the profiles of Archy River, Yengisu and Karday, which has a low soil moisture content; (3) the exponential model can be used to explain the relationship between soil respiration and air temperature 10 cm above the ground surface. The average Q10 values along the profiles of Usyman, Archy River, Yengisu and Karday are 0.61, 0.16, 0.22 and 0.35 respectively, much lower than the average of the world; (4) there is a positive correlation between the soil carbon flux and the soil moisture content     

Daily variation of carbon flux in soils of Populus euphratica forests in the middle and lower reaches of the Tarim River

In order to lucubrate the daily variation of respiration in soils of Populus euphratica forests and analyze its relationship with environmental factors in the middle and lower reaches of the Tarim River, the LI-8100 instrument of soil CO2 flux system was used to measure the parameters of soil carbon flux and air temperature 10 cm above ground surface along the profiles of Usyman, Archy River, Yengisu and Karday, and the relationships between the soil carbon flux and the soil moisture content were analyzed. The nonlinear regression analysis was carried out with the software SPSS13.0. We observed that: (1) soil respiration began to be restrained when the air temperature was up to 30℃10 cm above the ground surface; (2) the rates of soil respiration under the forests of Populus euphratica were significantly different at various moisture contents, the soil carbon flux was high along the Usyman profile, which has a high soil moisture content, and it was low along the profiles of Archy River, Yengisu and Karday, which has a low soil moisture content; (3) the exponential model can be used to explain the relationship between soil respiration and air temperature 10 cm above the ground surface. The average Q10 values along the profiles of Usyman, Archy River, Yengisu and Karday are 0. 61, 0.16, 0. 22 and 0. 35 respectively, much lower than the average of the world; (4) there is a positive correlation between the soil carbon flux and the soil moisture content.     

Water in granulites: implications for the nature and evolution of the lower continental crust

The tower continental crust is one of the most important sphere-layers in the deep earth, and is the direct place where the crust-mantle interactions occur. Granulttes are the dominated rocks in the lower crust, and have critical implications for the knowledge of the composition, nature and evolution of the deep crust; fluids are important mediums influencing many geochemical, geophysical and geodynamical characteristics of the lower crust, and may also play a fundamental role in the petrogenesis of granulites and the formation of the lower crusts. In this paper, we review recent advances involved with the deep continental crust, granulites and fluids, and some longstanding debates. Combined with the Fourier-transform infrared spectroscopy (FTIR) analysis performed on the mineral assemblages (cpx, opx, plag and grt) in lower crustal granulite xenoliths and terrains (exposed section) from east China, it is suggested that structural water, dominated by OH, in these nominally anhydrous phases may constitute the most important water reservoir in the deep crust. This structual water may help to understand many lower crustal geological processes and phenomena (e.g. seismic activities and electrical conductive anomalies), and influences from these water must be taken into consideration.     

Simple scaling relations in geodynamics： the role of pressure in mantle convection and plume formation

Scaling relations are important in extrapolating laboratory experiments to the Earth‘s mantle. In planetary interiors, compression becomes an important parameter and it is useful to explore scalings that involve volume. I use simple volume scaling relations that allow one to extrapolate laboratory experiments and upper mantle behavior, in a thermodynamically self-consistent way, to predict lower mantle behavior. The relations are similar to the quasi-har-monic approximation. Slabs and plates have characteristic dimensions of hundreds of kilometers and time constants of 100 million years, but the volume scalings predict order of magnitude higher values in the deep mantle. The scaling relations imply that the deep mantle is a sluggish system with ancient features. They imply irreversible chemical stratification and do not favor the plume hypothesis.     

Water in granulites: implications for the nature and evolution of the lower continental crust

The lower continental crust is one of the most important sphere-layers in the deep earth, and is the direct place where the crust-mantle interactions occur. Granulites are the dominated rocks in the lower crust, and have critical implications for the knowledge of the composition, nature and evolution of the deep crust; fluids are important mediums influencing many geochemical, geophysical and geodynamical characteristics of the lower crust, and may also play a fundamental role in the petrogenesis of granulites and the formation of the lower crusts. In this paper, we review recent advances involved with the deep continental crust, granulites and fluids, and some long-standing debates. Combined with the Fourier-transform infrared spectroscopy (FTIR) analysis performed on the mineral assemblages (cpx, opx, plag and grt) in lower crustal granulite xenoliths and terrains (exposed section) from east China, it is suggested that structural water, dominated by OH, in these nominally anhydrous phases may constitute the most important water reservoir in the deep crust. This structual water may help to understand many lower crustal geological processes and phenomena (e.g. seismic activities and electrical conductive anomalies), and influences from these water must be taken into consideration.     

Effect of the Interface Anisotropy on Optical Interface Spin Waves in an A-B-A System

计入外磁场、体和界面单轴各向异性后，研究了铁磁和反铁磁层间耦合的Ａ－Ｂ－Ａ三链系统中的光学界面自旋波及其存在的充要条件．结果发现，在三链系统中，有两种不同类型的光学界面自旋波，它们在不同界面各向异性条件下，均可存在０～２个自旋波解     

Physiological response of natural plants to the change of groundwater level in the lower reaches of Tarim River, Xinjiang

Based on the analysis of the three-year (2000-2002) monitoring data of the four times intermittent stream water conveyance to the lower reaches of Tarim River where the stream flow was dried up for more than 30 years and the measurement of PRO, SOD and POD in plants collected from 24 vegetation plots, it is concluded that the stream water conveyance plays an important role in lifting groundwater level. The groundwater nearby the watercourse was raised from 5～8 m in depth before the stream water conveyance to 2.5～5 m after stream water conveyance. The physiological response of Phragmites communis, Tamarix spp. And Populus euphratica to the change of groundwater is sensitive and represents a grads change obviously. The growth of the plants in the lower reaches of Tarim River is stressed by drought to various degrees. Lengthways, the drought stress exposed to the plants increases with groundwater depth from the upper sections to the lower sections; and breadthwise, the drought stress exposed to the plants is increased with the increase of distance away from the river channel of stream intermittent water releases and of the groundwater depth. Combining the field investigation and the analysis of the plots, it is considered that the stress groundwater depths for the Phragmites communis, Tamarix spp. And Populus euphratica are 3.5 m, 5 m and 4.5 m respectively.     

Assessment of waterrecharging based on ecological features of riparian forest in the lower reaches of Tarim River

The occurrence and development of riparian forests which are mainly dominated by mesophytes species relate closely with surface water. Since there is no water discharge to the lower reaches of Tarim River in past 5 decade years, the riparian forests degrade severely. Based on the analyses of the monitored data of Yingsu, Argan and Luobuzhuang in 2002 and 2003, the effect of water-recharging is discussed. The water-recharging project neglects the fact that that it is flooding that controls the process of Populus euphratica colonizing on the bare surface, but focuses on groundwater influence on vegetation. The flooding control deviates Inherent laws of riparian forests development, so the natural regeneration of riparian forests is checked. The response scope of riparian plants on groundwater uplift is extremely narrow, and most riparian communities have not been optimized. No seedlings of dominant species are found in flooding areas because their physio-ecological characteristics are ignored. The vegetation changes in vicinities of stream only reflect the demand of mesophytes species on the shallow groundwater, however, the water-recharging fails to provide suitable habitats for the seedlings establishment of riparian plants. The present water-recharging scheme is difficult to realize vegetation restoration.     

Assessment of water-recharging based on ecological features of riparian forest in the lower reaches of Tarim River

The occurrence and development of riparian forests which are mainly dominated by mesophytes species relate closely with surface water. Since there is no water discharge to the lower reaches of Tarim River in past 5 decade years, the riparian forests degrade severely. Based on the analyses of the monitored data of Yingsu, Argan and Luobuzhuang in 2002 and 2003, the effect of water-recharging is discussed. The water-recharging project neglects the fact that that it is flooding that controls the process of Populus euphratica colonizing on the bare surface, but focuses on groundwater influence on vegetation. The flooding control deviates Inherent laws of riparian forests development, so the natural regeneration of riparian forests is checked. The response scope of riparian plants on groundwater uplift is extremely narrow, and most riparian communities have not been optimized. No seedlings of dominant species are found in flooding areas because their physio-ecological characteristics are ignored. The vegetation changes in vicinities of stream only reflect the demand of mesophytes species on the shallow groundwater, however, the water-recharging fails to provide suitable habitats for the seedlings establishment of riparian plants. The present water-recharging scheme is difficult to realize vegetation restoration.     

The effects of transition metal in Sn-based pyrochlores on the methane catalytic combustion

Lanthanum stannate pyrochlores, La₂Sn₂O₇ and La₂SnMO₇ (M=Mn, Fe, Co, Ni, Cu), were successfully prepared by citric acid method and confirmed by XRD. TG and TPR characterizations showed that the introduction of transitional metals resulted in significant impacts on the structures and redox performances of prochlores. All the selected transitional metals could significantly improve their methane catalytic combustion performance. Among the doped pyrochlores, La₂SnCoO₇ pyrochlore possessed optimum activities at low temperatures, and Fe?doped pyrochlore showed highest reactivity for high temperature combustion and was proved to be promising materials for high temperature catalytic combustion. The reactivity differences of La₂SnMO₇ were reasonably attributed to the strong interactions between Sn and transitional metal.