Amorphization of Serpentine at High Pressure and High Temperature

Pressure-induced amorphization of serpentine was observed at temperatures of 200° to 300°C and pressures of 14 to 27 gigapascals with a combination of a multianvil apparatus and synchrotron radiation. High-pressure phases then crystallized rapidly when the temperature was increased to 400°C. These results suggest that amorphization of serpentine is an unlikely mechanism for generating deep-focus earthquakes, as the temperatures of subducting slabs are significantly higher than those of the rapid crystallization regime.     

Transcrystalline melt migration and Earth's mantle

Plate tectonics and volcanism involve the formation, migration, and interaction of magma and gas. Experiments show that melt inclusions subjected to a thermal gradient migrate through olivine crystals, under the kinetic control of crystal-melt interface mechanisms. Exsolved gas bubbles remain fixed and eventually separate from the melt. Scaled to thermal gradients in Earth's mantle and geological times, our results account for the grain-scale segregation of primitive melts, reinterpret CO2-rich fluid inclusions as escaped from melt, and question the existence of a free, deeply percolating fluid phase. Melt migration experiments also allow us to quantify crystal growth kinetics at very low undercoolings in conditions appropriate to many natural systems.     

Structure and dynamics of Earth's lower mantle

Processes within the lowest several hundred kilometers of Earth's rocky mantle play a critical role in the evolution of the planet. Understanding Earth's lower mantle requires putting recent seismic and mineral physics discoveries into a self-consistent, geodynamically feasible context. Two nearly antipodal large low-shear-velocity provinces in the deep mantle likely represent chemically distinct and denser material. High-resolution seismological studies have revealed laterally varying seismic velocity discontinuities in the deepest few hundred kilometers, consistent with a phase transition from perovskite to post-perovskite. In the deepest tens of kilometers of the mantle, isolated pockets of ultralow seismic velocities may denote Earth's deepest magma chamber.     

Asymmetric phase effects and mantle convection patterns

Recent high-pressure experiments and thermodynamic calculations have shown that the Clapeyron slope of the spinel-perovskite phase transition at a depth of 660 kilometers in the Earth's mantle changes from negative to positive at temperatures above 1700 degrees to 2000 degrees C. In numerical experiments that account for this phase behavior, cold downwelling flows were impeded at the phase boundary, but hot plumes ascended to the upper mantle with ease. The resultant mantle convection was partially layered and strongly time-dependent. Mantle layering was weaker when the mantle was hotter and when the Rayleigh number was larger.     

蛇形双流道平板式太阳能空气集热器的设计与试验

平板式太阳能空气集热器是太阳能利用的一种重要方式。通过对传统平板式太阳能空气集热器的流道进行改进,从而设计出一种新型平板式太阳能空气集热器,其流道形式为蛇形上、下双流道式。针对大庆市的地理位置与气候条件,制作出两个模型,对其进行性能测试。通过Fluent软件进行模拟,将模拟所得结果与实验结果进行对比,对比结果基本吻合。结果表明,蛇形双流道平板式太阳能空气集热器的集热效率比传统集热器集热效率高21.74%。     

Coeval large-scale magmatism in the Kalahari and Laurentian cratons during Rodinia assembly

We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle.     

Development of diapiric structures in the upper mantle due to phase transitions

Solid-state phase transitions in time-dependent mantle convection can induce diapiric flows in the upper mantle. When a deep mantle plume rises toward phase boundaries in the upper mantle, the changes in the local thermal buoyancy, local heat capacity, and latent heat associated with the phase change at a depth of 670 kilometers tend to pinch off the plume head from the feeding stem and form a diapir. This mechanism may explain episodic hot spot volcanism. The nature of the multiple phase boundaries at the boundary between the upper and lower mantle may control the fate of deep mantle plumes, allowing hot plumes to go through and retarding the tepid ones.     

Seismic determination of elastic anisotropy and mantle flow

When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.     

Eclogites, pyroxene geotherm, and layered mantle convection

Temperatures of equilibration for the majority (81 percent) of the eclogite xenoliths of the Roberts Victor kimberlite pipe in South Africa range between 1000 degrees and 1250 degrees C, falling essentially on the gap of the lower limb of the subcontinental inflected geotherm derived from garnet peridotite xenoliths. In view of the Archean age (>2.6 x 10(9) years) of these eclogites and their stratigraphic position on the geotherm, it is proposed that the inflected part of the geotherm represents the convective boundary layer beneath the conductive lid of the lithospheric plate. The gradient of 8 Celsius degrees per kilometer for the inflection is characteristic of a double thermal boundary layer and suggests layered convection rather than whole mantle convection for the earth.     

Eastern Indian 3800-million-year-old crust and early mantle differentiation

Samarium-neodymium data for nine granitic and tonalite gneisses occurring as remnants within the Singhbhum granite batholith in eastern India define an isochron of age 3775 +/- 89 x 10(6) years with an initial (143)Nd/(144)Nd ratio of 0.50798 +/- 0.00007. This age contrasts with the rubidium-strontium age of 3200 x 10(6) years for the same suite of rocks. On the basis of the new samarium-neodynium data, field data, and petrologic data, a scheme of evolution is proposed for the Archean crust in eastern India. The isotopic data provide evidence that parts of the earth's mantle were already differentiated with respect to the chondritic samarium-neodymium ratio 3800 x l0(6) years ago.     

The superswell and mantle dynamics beneath the South pacific

The region of sea floor beneath French Polynesia (the "Superswell") is anomalous in that its depth is too shallow, flexural strength too weak, seismic velocity too slow, and geoid anomaly too negative for its lithospheric age as determined from magnetic isochrons. These features evidently are the effect of excess heat and extremely low viscosity in the upper mantle that maintain a thin lithospheric plate so easily penetrated by volcanism that 30 percent of the heat flux from all hot spots is liberated in this region, which constitutes only 3 percent of the earth's surface. The low-viscosity zone may facilitate rapid plate motion and the development of small-scale convection. A possible heat supply for the Superswell is a mantle reservoir enriched in radioactive isotopes as suggested by the geochemical signature of lavas from Superswell volcanoes.     

Upper mantle discontinuity topography from thermal and chemical heterogeneity

Using high-resolution stacks of precursors to the seismic phase SS, we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers (km) deep within Earth beneath South America and the surrounding oceans. Detailed maps of phase boundary topography revealed deep 410- and 660-km discontinuities in the down-dip direction of subduction, inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures. Mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature. In some regions, multiple reflections from the discontinuities were detected, consistent with partial melt near 410-km depth and/or additional phase changes near 660-km depth. Thus, the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes.     

Small-scale convective instability and upper mantle viscosity under california

Thermal calculations and convection analysis, constrained by seismic tomography results, suggest that a small-scale convective instability developed in the upper 200 kilometers of the mantle under California after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the San Andreas transform boundary. The upper bound for the upper mantle viscosity in the slab window, 5 x 10(19) pascal seconds, is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions. These model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time-dependent small-scale convection that can generate localized areas of uplift and subsidence.     

不同畦沟深度对辣椒反季节栽培时土壤温度、水分和辣椒生长的影响

为了明确大棚辣椒反季节栽培时畦沟深浅对辣椒生长和产量的影响,在大棚内以畦沟深5 cm、20 cm、35 cm不同处理进行整地做畦,研究了不同畦沟深度对辣椒反季节栽培时土壤温度、水分及辣椒生长、光合参数和产量的影响。结果表明,畦沟深35 cm的处理同畦沟深20 cm、5 cm的处理相比,土壤温度最高,土壤含水量最小;畦沟深35 cm处理的辣椒株高显著高于其他两个处理;各处理辣椒植株的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、胞间CO2浓度(Ci)和叶绿素含量等光合指标均以畦沟深35 cm处理的最高,畦沟深5 cm处理的最低,其中气孔导度(Gs)和蒸腾速率(Tr)等指标3个处理间存在显著差异,净光合速率(Pn)、胞间CO2浓度(Ci)和叶绿素含量等指标,畦沟深35 cm处理与畦沟深5 cm处理相比,存在显著差异;畦沟深35 cm的处理产量比畦沟深20 cm、5 cm的处理分别增加4.32%和19.57%。说明大棚辣椒反季节栽培时采用深沟高畦进行整地做畦,可以提高土温,降低土壤湿度,促进植株生长,提高植物的光合作用,增加产量。     

Accumulation of suspended barite at mesopelagic depths and export production in the southern ocean

The relation between the accumulation of barite (BaSO(4)) microcrystals in suspended matter from the mesopelagic depth region (100 to 600 meters) and the type of production in the euphotic layer (new versus recycled) was studied for different Southern Ocean environments. Considerable subsurface barite accumulated in waters characterized by maintained new production and limited grazing pressure during the growth season. On the other hand, little if any barite accumulated in areas where relatively large amounts of photosynthetically fixed carbon were transferred to the microheterotrophic community and where recycled production became predominant.     

Hotspots, basalts, and the evolution of the mantle

The trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. The relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment-depletion patterns. Their combined volume occupies most of the mantle above the 670 kilometer discontinuity. The source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that lost its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are consistent with the evolution of a terrestrial magma ocean.     

Optical properties of the South pole ice at depths between 0.8 and 1 kilometer

The optical properties of the ice at the geographical South Pole have been investigated at depths between 0.8 and 1 kilometer. The absorption and scattering lengths of visible light ( approximately 515 nanometers) have been measured in situ with the use of the laser calibration setup of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino detector. The ice is intrinsically extremely transparent. The measured absorption length is 59 +/- 3 meters, comparable with the quality of the ultrapure water used in the Irvine-Michigan-Brookhaven and Kamiokande proton-decay and neutrino experiments and more than twice as long as the best value reported for laboratory ice. Because of a residual density of air bubbles at these depths, the trajectories of photons in the medium are randomized. If the bubbles are assumed to be smooth and spherical, the average distance between collisions at a depth of 1 kilometer is about 25 centimeters. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated.