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91.
92.
93.
The partitioning of iron between Mg-rich perovskite (Pv) and ferropericlase (Fp) was investigated for a pyrolitic bulk composition over a wide range of simulated lower-mantle pressures and temperatures from 28 to 114 GPa and from 1,900 to 2,300 K, in a laser-heated diamond anvil cell (DAC). The recovered DAC samples are chemically homogeneous, indicating a relatively small temperature gradient during laser heating. The chemical compositions of coexisting Pv, Fp, and Ca-rich perovskite (CaPv) were determined by energy-dispersive X-ray spectroscopy (EDS) using an EDS instrument attached to a transmission electron microscope. Our results demonstrate that at pressures above 90 GPa, Pv becomes more Fe-rich with increasing pressure, which is likely due to the effects of high-spin to low-spin crossover of Fe3+ in Pv. We highlight that such a change in Fe–Mg partitioning between Pv and Fp should have a strong influence on the physical properties of the deep lower mantle. 相似文献
94.
Our blue planet Earth has long been regarded to carry full of nutrients for hosting life since the birth of the planet.Here we speculate the processes that led to the birth of early life on Earth and its aftermath, finally leading to the evolution of metazoans.We evaluate:(1) the source of nutrients,(2) the chemistry of primordial ocean,(3) the initial mass of ocean,and(4) the size of planet.Among the life-building nutrients,phosphorus and potassium play a key role.Only three types of rocks can serve as an adequate source of nutrients:(a) continent-forming TTG(granite),enabling the evolution of primitive life to metazoans;(b) primordial continents carrying anorthosite with KREEP(Potassium,Rare Earth Elements, and Phosphorus) basalts,which is a key to bear life;(c) carbonatite magma,enriched in radiogenic elements such as U and Th,which can cause mutation to speed up evolution and promote the birth of new species in continental rift settings.The second important factor is ocean chemistry.The primordial ocean was extremely acidic(pH = 1-2) and enriched in halogens(CI,F and others),S,N and metallic elements(Cd,Cu,Zn,and others),inhibiting the birth of life.Plate tectonics cleaned up these elements which interfered with RNA.Blue ocean finally appeared in the Phanerozoic with pH = 7 through extensive interaction with surface continental crust by weathering,erosion and transportation into ocean.The initial ocean mass was also important.The birth of life and aftermath of evolution was possible in the habitable zone with 3-5 km deep ocean which was able to supply sufficient nutrients. Without a huge landmass,nutrients cannot be supplied into the ocean only by ridge-hydrothermal circulation in the Hadean.Finally,the size of the planet plays a crucial role.Cooling of massive planets is less efficient than smaller ones,so that return-flow of seawater into mantle does not occur until central stars finish their main sequence.Due to the suitable size of Earth,the dawn of Phanerozoic witnessed the initiation of return-flow of seawater into the mantle,leading to the emergence of huge landmass above sea-level,and the distribution of nutrients on a global scale.Oxygen pump also played a critical role to keep high-PO2 in atmosphere since then,leading to the emergence of ozone layer and enabling animals and plants to invade the land. To satisfy the tight conditions to make the Earth habitable,the formation mechanism of primordial Earth is an important factor.At first,a ’dry Earth’ must be made through giant impact,followed by magma ocean to float nutrient-enriched primordial continents(anorthosite + KREEP).Late bombardment from asteroid belt supplied water to make 3-5 km thick ocean,and not from icy meteorites from Kuiper belt beyond cool Jupiter.It was essential to meet the above conditions that enabled the Earth as a habitable planet with evolved life forms.The tight constraints that we evaluate for birth and evolution of life on Earth would provide important guidelines for planetary scientists hunting for life in the exosolar planets. 相似文献
95.
Tetsuya?KomabayashiEmail author Kei?Hirose Yasuo?Ohishi 《Physics and Chemistry of Minerals》2012,39(4):329-338
The phase transition boundary between the face-centered cubic (fcc) structure and hexagonal close-packed (hcp) structure in an Fe–Ni alloy was determined at pressures from 25 to 107 GPa by using an internally resistive-heated diamond
anvil cell (DAC), combined with in situ synchrotron X-ray diffraction measurements. The fcc–hcp phase transition boundary in Fe–9.7 wt% Ni is located at slightly lower temperatures than that in pure Fe, confirming the
previous understanding that the addition of Ni expands the stability field of the fcc phase. The dP/dT slope of the boundary was determined to be 0.0426 GPa/K, which is slightly larger than that of pure Fe. The pressure interval
of the two-phase region is about 6 GPa at a constant temperature, implying that the previous estimates by laser-heated DAC
experiments of 10–20 GPa were overestimated. The two-phase region of fcc + hcp would be limited to a pressure of about 120 GPa even in Fe–15 wt%Ni, excluding the possibility of the existence of the fcc phase in the inner core if the simple linear extrapolation of the two-phase region is applied. The pressure and temperature
dependences of the c/a axial ratio of the hcp phase in Fe–9.7 wt% Ni are generally consistent with those in pure Fe, suggesting that Ni has minor effects on the c/a ratio. 相似文献
96.
97.
High-T torsion experiments on lizardite + chrysotile serpentinites produced mineralogical and micro/nanostructural changes,
with important implications in rheological properties. High-resolution TEM showed that specimens underwent ductile [by microkinking
and (001) interlayer glide] and brittle deformation (by microfracturing), together with dehydration and break-down reactions.
Lizardite is affected by polytypic disorder and microkinking [kink axial planes at high angle with respect to (001) planes],
that were not present in the initial ordered 1T-lizardite. Chrysotile fibres are deformed, resulting in elliptical cross-sections,
with strong loss of interlayer cohesion. Both lizardite and chrysotile break down to a fine intergrowth of olivine (up to
200 nm), talc (up to 30 nm) and poorly-crystalline material. Lizardite-out reaction preferentially occurs at kink axial planes,
representing sites of preferential strain and enhanced reactivity; conversely, chrysotile break-down is a bulk process, resulting
in large healed olivine aggregates, up to micrometric in size. Overall observations suggest that dehydration and break-down
reactions are more advanced in chrysotile than in lizardite. 相似文献
98.
You-Ichiro Sasajima Satoshi Nakada Naoki Hirose Jong-Hwan Yoon 《Journal of Oceanography》2007,63(6):913-926
The subsurface counter current beneath the Tsushima Warm Current is simulated using a three-dimensional circulation model.
The model well reproduces the counter current beneath the Tsushima Warm Current on the shelf break. The counter current appears
as nearshore parts of the subsurface clockwise circulations from spring to early winter. The clockwise circulations are separated
by developed shelves such as the Oki Spur and the Noto Peninsula, thus the counter current is not a continuous flow along
the Japanese coast in this model. The vertical structure of the counter current can be explained by a density structure with
the thermal wind relationship. The permanent and seasonal pycnoclines form mutually opposite horizontal density gradients
near the Japanese coast in summer. Such a density structure results in a speed maximum of the counter current away from the
bottom. It is remarkable that the second baroclinic mode is dominant in nearshore parts of the subsurface clockwise circulations
in summer, which are attributed to the density structure. Similar density structures are also found in some coastal regions
of the world oceans where subsurface counter currents are expected. 相似文献
99.
We investigated the sea level response of the Japan Sea to changes in atmospheric pressure using barotropic shallow water
models driven by idealized synoptic pressure forcing. The regional response lags behind the synoptic pressure forcing because
the adjustment is slowly established by water exchange through narrow, shallow straits. The sea level response of the realistic
Japan Sea to the idealized forcing varies with geographical location and shows zonally asymmetric variations in amplitude
and phase. The simulated response is in good agreement with the observed response of sea level recorded at Japanese coastal
tide gauges. The results of a simple one-dimensional model indicate that the zonally asymmetric pattern, with an eastward-propagating
pressure system, is essentially caused by bottom friction in shallow straits. This asymmetry arises if the typical wavelength
of the synoptic pressure system is slightly larger than the spatial scale of the Japan Sea. 相似文献
100.
A magnetodynamic model to deal with the acceleration and collimation of jets as a part of the global process of gravitational
contraction of the magnetized gas to the central gravitator is discussed. We first review its application to the star forming
jet case with several observational supporting evidence. Then, a justification will be given for the extension of this to
the AGN jet case, despite of the difference in orders of magnitudes in the scales as well as in the physical parameters. The
results of actual application of this magnetodynamic mechanism to the AGN case will be presented together with the discussions
for the origin of the radio lobes and hotspots, and we show that this mechanism can explain the enhancement of accretion and
the formation of the jet + lobe system consistently with the genetic consideration of the system.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献