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The northern parts of the Prathap and Laccadive Ridge system, eastern Arabian Sea, consist of three parallel basement ridge peaks at varied depths. The topographic highs are associated with either well-developed or subdued magnetic signatures. Model studies, constrained by seismic results, determine the varied nature and depth to the top of the causative basement bodies. Similarities of the geophysical signatures of the ridges and their structural resemblance perhaps point to their common origin. Hence we propose that the Prathap Ridge complex may be a part of the Chagos-Laccadive Ridge system and formed because of the Reunion hotspot activity. 相似文献
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Laser microprobe for the study of noble gases and nitrogen in single grains: A case study of individual chondrules from the Dhajala meteorite 总被引:1,自引:0,他引:1
A laser microprobe capable of analysing nitrogen and noble gases in individual grains with masses less than a milligram is
described. It can be used in both continuous wave (CW) mode, useful for stepwise heating of an individual grain, as well as
in pulsed mode, useful for ablating material from a small selected area of a sample, for gas extraction. We could achieve
low blanks (in ccSTP units) for 4He(4.8 x 10{-12}),22Ne(1.0 x 10{-12}),36Ar(1.0 x10
-13),84Kr(2.9 x 10{-14}),132 Xe(2.6 x 10{-14}), and N (87 pg), using this system. Preliminary data for individual chondrules from the Dhajala meteorite show that noble
gases and nitrogen from grains as small as 170 microgram can be analysed using the present laser microprobe setup. The amount
of trapped neon in Dhajala chondrules is very small, and nitrogen in the chondrules is isotopically heavier as compared to
the bulk meteorite. 相似文献
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Tsunamis have occurred in Canada due to earthquakes, landslides, and a large chemical explosion. The Pacific coast is at greatest risk from tsunamis because of the high incidence of earthquakes and landslides in that region. The most destructive historical tsunamis, however, have been in Atlantic Canada – one in 1917 in Halifax Harbour, which was triggered by a catastrophic explosion on a munitions ship, and another in 1929 in Newfoundland, caused by an earthquake-triggered landslide at the edge of the Grand Banks. The tsunami risk along Canada's Arctic coast and along the shores of the Great Lakes is low in comparison to that of the Pacific and Atlantic coasts. Public awareness of tsunami hazard and risk in Canada is low because destructive tsunamis are rare events. 相似文献
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Microtextural study of a single troilite‐metal nodule (TMN) from the Katol L6‐7 chondrite, a recent fall (May, 2012) in India suggests that the TMN is primarily an aggregate of submicron‐scale intergrowth of troilite and kamacite (mean Ni: 6.18 wt%) juxtaposed with intensely fractured silicates, mainly olivine (Fa: 25 mole%), low‐Ca pyroxene (Fs: 21.2 mole%), and a large volume of maskelynite. Evidence of shock textures in the TMN indicates a high degree of shock metamorphism that involves plagioclase‐maskelynite and olivine‐wadsleyite/ringwoodite transformations and formation of quenched metal‐sulfide melt textures due to localized shear‐induced frictional melting. It is inferred that the TMN formation is an independent, localized event by a high energy impact and its subsequent incorporation in the ejected chondritic fragment of the parent body. Katol chondrite has been calibrated with a peak shock pressure of S5 (~45 GPa) after Stöffler et al. (1991), whereas peak shock pressure within the TMN exceeds the shock facies S6 (>45 GPa) following Bennett and McSween (1996) and Stöffler et al. (1991). Overall, the shock‐thermal history of the Katol TMN is dissimilar as compared to the host chondrite. 相似文献
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The data of Reed (1983) are analysed to produce the following empirical equations for the amplitude p 0 (overall fluctuation) in Pascals of the air pressure wave associated with a volcanic eruption of volume V km3 or a nuclear explosion of strength M Mt: Here s is the distance from the source in km. $$\begin{gathered} \log _{10} p_0 = 4.44 + \log _{10} V - 0.84\log _{10} s \hfill \\ {\text{ }} = 3.44 + \log _{10} M - 0.84\log _{10} s. \hfill \\ \end{gathered} $$ Garrett's (1970) theory is examined on the generation of water level fluctuations by an air pressure wave crossing a water depth discontinuity such as a continental shelf. The total amplitude of the ocean wave is determined to be where c 2 1 = gh 1, c 2 2 = gh 2, g is acceleration of gravity, h 1 and h 2 are the water depths on the ocean and shore side of the depth discontinuity, c is the speed of propagation of the air pressure wave, and ? is the water density. $$B = \left[ {\frac{{c_2^2 }}{{c^2 - c_2^2 }} + \frac{{c^2 (c_1 - c_2 )}}{{(c - c_1 )(c^2 - c_2^2 )}}} \right]\frac{{p_0 }}{{g\varrho }}$$ It is calculated that a 10 km3 eruption at Mount St. Augustine would cause a 460 Pa air pressure wave and a discernible water level fluctuation at Vancouver Island of several cm amplitude. 相似文献