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931.
D. A. Henry 《Australian Journal of Earth Sciences》2013,60(2):251-260
The rare calc‐silicate minerals cuspidine, bultfonteinite, foshagite and xonotlite occur in a calcsilicate skarn zone near Chesney Vale, in northern Victoria. They are associated with andradite-grossular garnet, vesuvianite, diopside, wollastonite, prehnite, epidote, fluorite, calcite, perovskite,sphene and possibly tobermorite. The calc‐silicate skarn zone has formed in thermally meta‐morphosed, Ordovician, deep‐marine sediments adjacent to an Early Devonian aplitic granite pluton. The assemblages are estimated to have formed at low pressure (<100 MPa) at temperaturesnot exceeding 600°C in the presence of a low‐Xco2 fluorine‐bearing fluid. The occurrence is the firstrecord of bultfonteinite and foshagite in Australia and the first record of cuspidine and xonotlite inVictoria. 相似文献
932.
Sediment shear Q from airgun OBS data 总被引:2,自引:0,他引:2
P. D. Bromirski L. N. Frazer F. K. Duennebier 《Geophysical Journal International》1992,110(3):465-485
933.
Nitin D. Rai Tor A. Benjaminsen Siddhartha Krishnan C. Madegowda 《Singapore journal of tropical geography》2019,40(1):124-139
Protected areas have had significant impacts on local communities primarily through the physical removal of people. In some instances, people continue to live within protected areas due to the inability of the state to evict them. The restrictions on livelihoods placed on people living inside protected areas lead to in situ displacement. We show how conservation enclosures in the Biligiri Rangaswamy Temple Tiger Reserve have produced a class of people that the state ‘lets die’ by banning customary practices such as fire use, hunting and harvesting of forest produce. Using longitudinal ethnographic, socio‐economic and ecological data, we demonstrate that conservation policy has alienated indigenous forest dwellers from their agricultural and forest‐land. The outcomes of conservation policy include dispossession through increased crop losses, reduced income from agriculture and forest produce, as well as a forest that is dominated by weeds due to fire suppression. The ban on hunting in particular has increased wildlife densities, which has enabled the state to accumulate revenues through the establishment of wildlife tourism facilities. All in all, centralized protected area governance has changed the relationships among people, forest and the state in a way that has produced adverse effects for both livelihoods and the ecosystem. 相似文献
934.
Based on laboratory and theoretical modeling results, we present the thermal and hydrodynamical structure of the plume conduit during plume ascent and eruption on the Earth’s surface. The modeling results show that a mushroom-shaped plume head forms after melt eruption on the surface for 1.9 < Ka < 10. Such plumes can be responsible for the formation of large intrusive bodies, including batholiths. The results of laboratory modeling of plumes with mushroom-shaped heads are presented for Ka = 8.7 for a constant viscosity and uniform melt composition. Images of flow patterns are obtained, as well as flow velocity profiles in the melt of the conduit and the head of the model plume. Based on the laboratory modeling data, we present a scheme of a thermochemical plume with a mushroom-shaped head responsible for the formation of a large intrusive body (batholith). After plume eruption to the surface, melting occurs along the base of the massif above the plume head, resulting in a mushroom-shaped plume head. A possible mechanism for the formation of localized surface manifestations of batholiths is presented. The parameters of some plumes with mushroom-shaped heads (plumes of the Altay-Sayan and Barguzin-Vitim large-igneous provinces, and Khangai and Khentei plumes) are estimated using geological data, including age intervals and volumes of magma melts. 相似文献
935.
Nazarova L. B. Razjigaeva N. G. Diekmann B. Grebennikova T. A. Ganzey L. A. Belyanina N. I. Arslanov K. A. Kaistrenko V. M. Gorbunov A. O. Kharlamov A. A. Golovatyuk L. V. Syrykh L. S. Subetto D. A. Lisitsyn A. P. 《Doklady Earth Sciences》2019,486(1):494-497
Doklady Earth Sciences - Results of a paleolimnological investigation of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP a warm... 相似文献
936.
The evolution of east coast of India sis discussed within the ambit of clearly identifiable four major tectonic stages which
had a profound effect in shaping the tectonic grain of the east coast basins. The evolutionary process began with rift related
crustal extension between India and Sri Lanka as a consequence of Africa-Antarctica rifting and development of Natal Basin.
An arm of this rift led to initial extension in the Cauvery Basin and failed. Later, the India-West Australia rift propagated
further in southwesterly direction initiating Mahanadi and Krishna-Godavari Basins. This extension was an oblique one with
Nayudupeta high acting as pivot. The oblique extension followed by asymmetric seafloor spreading developed transpression along
India-Sri Lanka and Antarctica junction, resulting in a NNW-SSE trending transcurrent fault along which Antarctica moved southward.
Subsequently, entire east coast evolved through a more or less uniform post rift stage. 相似文献
937.
J. Zverko I. Iliev I. Romanyuk I. Barzova D. Kudryavtsev I. Stateva E. Semenko 《Astrophysical Bulletin》2012,67(1):57-66
Axial rotation of a star plays an important role in its evolution, physical condition in its atmosphere and appearance of its spectrum. Methods of determinations of υ sin i are based on comparison of the observed profiles of spectral lines with theoretical ones. Their accuracy depends on the kind and quality of spectrograms as well as on the algorithms used. A frequently used method is the simple comparing of one line, e.g. the Ca II at 3933 Å or Mg ii at 4481 Å. This however, may result in a false value of υ sin i if low dispersion spectra are used. In this work we studied contemporary CCD as well as older photographic spectra of the multiple star HD90569. We determined the projected rotational velocity value to be υ sin i = 11 km/s. Besides formerly reported enhancing of lines of Cr, Fe, Mn and Sr, we found also large overabundances of rare earths, gallium and platinum. Helium, carbon, nitrogen, oxygen, aluminium, calcium, scandium and nickel are in deficit. The spectrum of the occultation double was not identified to be of the SB2-type, however, there are some observable evidences that the pair creates a binary with a long orbital period. Despite this there are also observations that leave such interpretation uncertain. 相似文献
938.
Investigating the propagation mechanism of unmodelled systematic errors on coordinate time series estimated using least squares 总被引:6,自引:8,他引:6
The propagation of unmodelled systematic errors into coordinate time series computed using least squares is investigated,
to improve the understanding of unexplained signals and apparent noise in geodetic (especially GPS) coordinate time series.
Such coordinate time series are invariably based on a functional model linearised using only zero and first-order terms of
a (Taylor) series expansion about the approximate coordinates of the unknown point. The effect of such truncation errors is
investigated through the derivation of a generalised systematic error model for the simple case of range observations from
a single known reference point to a point which is assumed to be at rest by the least squares model but is in fact in motion.
The systematic error function for a one pseudo-satellite two-dimensional case, designed to be as simple but as analogous to
GPS positioning as possible, is quantified. It is shown that the combination of a moving reference point and unmodelled periodic
displacement at the unknown point of interest, due to ocean tide loading, for example, results in an output coordinate time
series containing many periodic terms when only zero and first-order expansion terms are used in the linearisation of the
functional model. The amplitude, phase and period of these terms is dependent on the input amplitude, the locations of the
unknown point and reference point, and the period of the reference point's motion. The dominant output signals that arise
due to truncation errors match those found in coordinate time series obtained from both simulated data and real three-dimensional
GPS data. 相似文献
939.
Pimentel D 《社会与自然资源》1991,4(4):347-363
Destruction of forests and the considerable burning of fossil fuels is directly causing the level of carbon dioxide and other greenhouse gases including methane, carbon monoxide, and nitrous oxide in the atmosphere to rise. Population growth in the US and the world indirectly contributes to this global warming. This has led the majority of scientists interested in weather and climate to predict that the planet's temperature will increase from 1.5 to 4.5 degrees Celsius by 2050. These forecasted climactic changes will most likely strongly affect crop production. Specifically these scientists expect the potential changes in temperature, moisture, carbon dioxide, and pests to decrease food production in North America. The degree of changes hinges on each crop and its environmental needs. If farmers begin using improved agricultural technology, the fall in crop yields can be somewhat counterbalanced. Even without global warming, however, agriculture in North America must embrace sensible ecological resource management practices such as conserving soil, water, energy, and biological resources. These sustainable agricultural practices would serve agriculture, farmers, the environment, and society. Agriculturalists, farmers, and society are already interested in sustainable agriculture. Still scientists must conduct more research on the multiple effects of potential global climate change on many different crops under various environmental conditions and on new technologies that farmers might use in agricultural production. We must cut down our consumption of fossil fuel, reduce deforestation, erase poverty, and protect our soil, water, and biological resources. The most important action we need to take, however, is to check population growth. 相似文献
940.
Analysis of New Zealand geology using a fore-arc model (Crook, 1980a) leads to the recognition of four arc terrains. The west facing Tuhua volcanic arc was active from the Late Proterozoic until the Middle or Late Cambrian. Post-subduction sediments, neritic in the east and flysch in the west, accumulated on the Tuhua accretionary prism from the Late Cambrian until the Early Devonian. Thermal equilibration, metamorphism, granitoid plutonism and penetrative deformation occurred in the Middle to Late Devonian. A small area of Permian platform cover has escaped later erosion. The east-facing Rangitata Terrain records subduction from Early Permian to late Early Cretaceous. Much of its accretionary prism consists of a submarine fan complex derived from Western Antarctica and carried sideways into the trench. The accretionary prism is thick and completely kratonized in southern New Zealand, but the thickness is more variable northwards. There the overlying Upper Cretaceous to Upper Oligocene post-subduction sequence comprises shelf sediments (implying an intermediate-thickness prism) or flysch followed by shelf sediments (implying a thin prism). During the accumulation of this sequence the Rangitata Terrain was a passive continental margin. The south-facing Jurassic-late Oligocene Northland Terrain collided with this passive margin in northern New Zealand at the end of the Oligocene, forming the Northland Allochthon. Subduction then flipped and the oldest part of the Kaikoura Terrain volcanic arc formed on the outer part of the Northland Terrain. Originally this terrain faced northeast and consumed the southwestern part of the South Fiji Basin crust, but during the Miocene the arc migrated clockwise to assume its present northeastern orientation. The fore-arc model employed here satisfactorily explains most first-order and many second-order features of New Zealand geology without requiring modification, thus attesting to the model's versatility and robustness. New Zealand provides a basis for elaborating some aspects of the model, particularly the transition from the syn- to post-subduction phases of fore-arc evolution. Combination of this study with a similar study of the southeastern Australian Paleozoic yields insights into the Phanerozoic evolution of the Australian: Pacific Plates' active margin. 相似文献