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31.
Porphyroblast rotation during crenulation cleavage development: an example from the aureole of the Mooselookmeguntic pluton, Maine, USA 总被引:1,自引:0,他引:1
In the low‐pressure, high‐temperature metamorphic rocks of western Maine, USA, staurolite porphyroblasts grew at c. 400 Ma, very late during the regional orogenesis. These porphyroblasts, which preserve straight inclusion trails with small thin‐section‐scale variation in pitch, were subsequently involved in the strain and metamorphic aureole of the c. 370 Ma Mooselookmeguntic pluton. The aureole shows a progressive fabric intensity gradient from effectively zero emplacement‐related deformation at the outer edge of the aureole ~2900 m (map distance) from the pluton margin to the development of a pervasive emplacement‐related foliation adjacent to the pluton. The development of this pervasive foliation spanned all stages of crenulation cleavage development, which are preserved at different distances from the pluton. The spread of inclusion‐trail pitches in the staurolite porphyroblasts, as measured in two‐dimensional (2‐D) thin sections, increases nonlinearly from ~16° to 75° with increasing strain in the aureole. These data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage. The data spread is qualitatively modelled for both pure and simple shear, and both solutions match the data reasonably well. The spread of inclusion‐trail orientations (40–75°) in the moderately to highly strained rocks is similar to the spread reported in several previous studies. We consider it likely that the sample‐scale spread in these previous studies is also the result of porphyroblast rotation relative to one another. However, the average inclusion‐trail orientation for a single sample may, in at least some instances, reflect the original orientation of the overgrown foliation. 相似文献
32.
Shubhra Goel Shalini Nihar Ranjan Patra 《Geotechnical and Geological Engineering》2006,24(6):1511-1525
Inclined anchors are widely used in a variety of civil engineering problems to resist oblique loads, most relevant being in
transmission towers and in rocks and dams for structural strengthening. In the present study, the breakout resistance of the
inclined anchors in sand has been worked out using limit equilibrium approach. The breakout resistance has been calculated
for different soil friction angles with varying relative depth ratio and anchor inclination. The break out factor increases
continuously with the inclination of the anchor. A comparison of predicted values of break out resistance of anchors by the
proposed analysis with the experimental values as reported by the other researchers showed reasonably good agreement. 相似文献
33.
用直线和曲线滑面两种模型,模拟预应力锚索加固含有水平软弱层的高陡边坡的潜在滑动面,通过对锚索加固的力学机理分析来阐述预应力在滑动面主滑方向上产生分力的原因。从锚索受力角度上对锚索倾角的取值范围进行探讨,结合实际造孔过程有不同程度的孔斜或弯曲以及获取较好的锚固灌浆效果,就仰角锚固和俯角锚固两种锚固条件分别得出锚索倾角的取值范围,并以此来判定锚索的预应力是否会在滑动面走向方向上产生不利于坡体稳定的下滑力。 相似文献
34.
大气CO2浓度升高对土壤中不同粒级碳的影响 总被引:4,自引:0,他引:4
不同粒级土壤中的碳有着不同的周转规律,在高CO2浓度条件下,它们含量的变化将在一定程度上反映土壤碳是累积还是减少,对明确土壤碳的变化趋势有重要意义.采用田间培养试验初步模拟研究在高CO2浓度条件下土壤不同粒级碳的分布.结果表明,加入秸秆培养1年,由于CO2浓度升高的原因导致在低氮(LN)、常规氮(NN)和高氮(HN)水平下土壤中碳分别增加0.01、1.10、1.22g/kg,表现为粒级〈53μm土壤颗粒中碳分别增加1.53、2.19、2.70g/kg.粒级〈53μmm土壤颗粒碳量的增加,主要是由于其重量分配百分数显著增加36.2%,碳浓度增加5.4%;粒级〉250μm和250~53μm土壤颗粒部分虽然其碳浓度分别增加20.8%和17.3%(P〈0.05),怛由于重量分配百分数分别显著降低22.8%和36.1%,结果碳量降低.试验表明高CO2浓度导致不同粒级土壤的分配及碳浓度的变化;高氮施肥水平下有增加土壤碳量特别是小粒级土壤碳量的趋势. 相似文献
35.
36.
Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible
spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the
spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to
retrieve vertical profiles of ozone (O3) and nitrogen dioxide (NO2) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured
and recalculated slant column densities (SCDs) and they are found to be well matching. O3 and NO2 vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡
SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and
they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities
(TCDs) of O3 and NO2 along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003.
The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer
and minimum in the winter season. Increasing trend is found in column density of NO2 in stratospheric, tropospheric and surface layers, but no trend is observed in O3 columns for above layers during the period 2000–2003 相似文献
37.
38.
从深基坑安全监测实例出发,介绍了一种简便、易行、稳定、可靠的射线形水平位移基准网,同时适用用小角法高精度位移监测.另外就温度的变化对水平位移值的影响,降水施工对地面沉降,深层土体位移的影响及测斜管埋设的重要性提出了自己的观点、认识与体会,希望对类似工程有一定参考价值. 相似文献
39.
40.
Uncertainties in polar motion and length-of-day measurements are evaluated empirically using several data series from the space-geodetic techniques of the global positioning system (GPS), satellite laser ranging (SLR), and very long baseline interferometry (VLBI) during 1997–2002. In the evaluation procedure employed here, known as the three-corner hat (TCH) technique, the signal common to each series is eliminated by forming pair-wise differences between the series, thus requiring no assumed values for the “truth” signal. From the variances of the differenced series, the uncertainty of each series can be recovered when reasonable assumptions are made about the correlations between the series. In order to form the pair-wise differences, the series data must be given at the same epoch. All measurement data sets studied here were sampled at noon (UTC); except for the VLBI series, whose data are interpolated to noon and whose UT1 values are also numerically differentiated to obtain LOD. The numerical error introduced to the VLBI values by the interpolation and differentiation is shown to be comparable in magnitude to the values determined by the TCH method for the uncertainties of the VLBI series. The TCH estimates for the VLBI series are corrupted by such numerical errors mostly as a result of the relatively large data intervals. Of the remaining data sets studied here, it is found that the IGS Final combined series has the smallest polar motion and length-of-day uncertainties. 相似文献