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排序方式: 共有62条查询结果,搜索用时 31 毫秒
21.
Michael Zolensky Takashi Mikouchi Marc Fries Robert Bodnar Peter Jenniskens Qing‐zhu Yin Kenji Hagiya Kazumasa Ohsumi Mutsumi Komatsu Matthew Colbert Romy Hanna Jessie Maisano Richard Ketcham Yoko Kebukawa Tomoki Nakamura Moe Matsuoka Sho Sasaki Akira Tsuchiyama Matthieu Gounelle Loan Le James Martinez Kent Ross Zia Rahman 《Meteoritics & planetary science》2014,49(11):1997-2016
Based upon our characterization of three separate stones by electron and X‐ray beam analyses, computed X‐ray microtomography, Raman microspectrometry, and visible‐IR spectrometry, Sutter's Mill is a unique regolith breccia consisting mainly of various CM lithologies. Most samples resemble existing available CM2 chondrites, consisting of chondrules and calcium‐aluminum‐rich inclusion (CAI) set within phyllosilicate‐dominated matrix (mainly serpentine), pyrrhotite, pentlandite, tochilinite, and variable amounts of Ca‐Mg‐Fe carbonates. Some lithologies have witnessed sufficient thermal metamorphism to transform phyllosilicates into fine‐grained olivine, tochilinite into troilite, and destroy carbonates. One finely comminuted lithology contains xenolithic materials (enstatite, Fe‐Cr phosphides) suggesting impact of a reduced asteroid (E or M class) onto the main Sutter's Mill parent asteroid, which was probably a C class asteroid. One can use Sutter's Mill to help predict what will be found on the surfaces of C class asteroids such as Ceres and the target asteroids of the OSIRIS‐REx and Hayabusa 2 sample return missions (which will visit predominantly primitive asteroids). C class asteroid regolith may well contain a mixture of hydrated and thermally dehydrated indigenous materials as well as a significant admixture of exogenous material would be essential to the successful interpretation of mineralogical and bulk compositional data. 相似文献
22.
Xuelei Chen Asantha Cooray Naoki Yoshida Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2003,346(3):L31-L35
The first-year Wilkinson Microwave Anisotropy Probe data suggest a high optical depth for Thomson scattering of 0.17 ± 0.04 , implying that the Universe was reionized at an earlier epoch than previously expected. Such early reionization is likely to be caused by ultraviolet (UV) photons from first stars, but it appears that the observed high optical depth can be reconciled within the standard structure formation model only if star formation in the early Universe was extremely efficient. With normal star formation efficiencies, cosmological models with non-Gaussian density fluctuations may circumvent this conflict as high density peaks collapse at an earlier epoch than in models with Gaussian fluctuations. We study cosmic reionization in non-Gaussian models and explore to what extent, within available constraints, non-Gaussianities affect the reionization history. For mild non-Gaussian fluctuations at redshifts of 30 to 50, the increase in optical depth remains at a level of a few per cent and appears unlikely to aid significantly in explaining the measured high optical depth. On the other hand, within available observational constraints, increasing the non-Gaussian nature of density fluctuations can easily reproduce the optical depth and may remain viable in underlying models of non-Gaussianity with a scale-dependence. 相似文献
23.
Compositional zoning patterns of the major elements and REEs in prograde-zoned garnets whose Mg/(Mg + Fe) atomic ratios increase rimward have been widely used to understand the metamorphic P–T–t trajectories, and the diffusion-limited REE-uptake model is a promising way to interpret their growth rates and the REE diffusion kinetics in the low-temperature eclogite. In order to elucidate their growth kinetics with Skora et al.'s (2006) diffusion-limited REE uptake model for prograde-zoned garnets, we examine the trace-element zoning patterns of two prograde-zoned porphyroblastic garnets (~6 mm in size) in low-temperature eclogites from two different localities. Core-to-rim trace-element profiles in a garnet (prp5–9alm61–67sps1–3grs24–30) of a glaucophane-bearing epidote eclogite of Syros (Cyclades, Greece) are characterized by the presence of Y + HREE peaks in the mantle, which might be attributed to a continuous breakdown of the titanite to form rutile during the garnet growth. In contrast, those in a garnet (prp4–7alm61–68sps3–10grs23–24) extracted from a lawsonite-eclogite of the South Motagua Mélange (SMM) (Guatemala) have prominent central peaks of Y + HREEs. Although the REE profiles of both the garnets can be explained by the diffusion-limited uptake, their Mn profiles suggest that their growth-rate laws are different: i.e., diffusion-controlled (Syros) and interface-controlled (SMM). Prior to the model application, we optimize the number of the parameters as the garnet grows with the interface-controlled processes based on the growth Péclet number. In particular, we propose the ratio of the REE diffusivity in the eclogitic matrix to the garnet growth rate as the new parameter. Visualizing the values of the new parameters allows to readily understand the relationship between the REE profiles and the REE-diffusion/garnet-growth kinetics in low-T eclogite. Our model refinement leads to the simple quantitative characterization of core-to-rim REE profiles in garnet in low-temperature eclogites. 相似文献
24.
Tsuyoshi Komiya Shinji Yamamoto Shogo Aoki Keiko Koshida Masanori Shimojo Yusuke Sawaki Kazumasa Aoki Shuhei Sakata Takaomi D. Yokoyama Kenshi Maki Akira Ishikawa Takafumi Hirata Kenneth D. Collerson 《地学前缘(英文版)》2017,8(2):355-385
The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts. 相似文献
25.
Kazumasa Iwai Masumi Shimojo Shinichiro Asayama Tetsuhiro Minamidani Stephen White Timothy Bastian Masao Saito 《Solar physics》2017,292(1):22
The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations. 相似文献
26.
Samples from metamorphosed pillowed basalts and related Besshi-type deposits occurring in the Sanbagawa belt of the Shikoku
Island, southwest Japan, have been analyzed for 87Sr/86Sr, 143Nd/144Nd and 40 K/40Ar. This is to investigate the tectonic settings in which the original submarine volcanism and associated Besshi-type mineralization
occurred, as well as the age of metamorphism. Eight whole-rock samples of the pillow lavas metamorphosed in pumpellyite-actinolite
facies conditions yield a Rb-Sr isochron age of 107 ± 15 Ma with an initial ratio of 0.70401 ± 0.00006, while they do not
define a Sm-Nd isochron. We interpret the results as the metamorphic age, an interpretation consistent with the previously
reported Rb-Sr whole-rock age for the Sanbagawa pelitic schists. The overall ranges of the initial epsilon values at T = 107 Ma are: ɛNd (T ) = +7.8 to +4.3; ɛSr(T ) = +2.2 to −7.0, suggesting that the most likely source for the pillowed basalts is depleted oceanic mantle, a conclusion
supported by the previous Pb isotope studies. The K-Ar ages determined for twelve mineral separates from the Besshi-type deposits
range from about 60 to 112 Ma, with a mean age of about 80 Ma, in agreement with the previous K-Ar and Ar-Ar data for the
Sanbagawa pelitic and basic schists. The youngest age, 60 Ma, was obtained for sericite from the Hinooku deposit metamorphosed
in pumpellyite- actinolite facies conditions, while the oldest one for hornblende from the spotted amphibolite in the immediate
vicinity of the Shiragayama deposit metamorphosed in albite-biotite grade. The oldest age, 112 Ma, is interpreted to date
the peak metamorphism, consistent with the Rb-Sr data, though a possibility of excess Ar cannot always be ruled out. In view
of the closure temperatures of muscovite (350 °C) in the biotite zone, it is suggested that our K-Ar age data (<about 80 Ma)
represent the age of the retrograde metamorphism or subsequent uplift. Datable microfossils found in the Sanbagawa belt of
Shikoku suggest that the submarine basaltic volcanism and related Besshi-type mineralization occurred in an oceanic basin
away from the trench region in Late Triassic (conodont) to Late Jurassic (radiolarian) times.
Received: 5 March 1997 / Accepted: 14 May 1998 相似文献
27.
28.
During the long-term stability assessment of underground disposal repositories buried in sedimentary formations, one of crucial
scientific problems is to determine parameters of site formations. The analysis of response of the pore pressure due to atmospheric
loading provides a possible way of accurate estimation of formation parameters. In this paper, an analytical solution of response
of the pore pressure to atmospheric loading was derived starting from the Biot’s poroelasticity, and its corresponding numerical
solutions were developed by finite element methods for 1D and 2D situations. With comparison to the analytical solution, the
experimental results show that the numerical schemes sound reasonable to implement the assessment of response of the pore
pressure in horizontal multilayer sedimentary formations. In particular, it is effective for a 2D model over large area with
consideration of background horizontal groundwater flow. A highlight of this work is to construct a reasonable approach to
capture responses of the pore pressure to atmospheric loading, and at the same time to provide the feasibility of integrated
analysis of well monitoring data of pore pressure variance in Horonobe Underground Research Laboratory (URL), Hokkaido, Japan. 相似文献
29.
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