Reconstructing P–T paths during continental collision using multi-stage garnet (Gran Paradiso nappe, Western Alps)

Garnet–chloritoid-bearing micaschists from the Gran Paradiso massif (Western Alps) contain evidence of a polymetamorphic evolution. Detailed textural observations reveal that two stages of garnet growth are present in the micaschists, interpreted as: (i) relics of an early metamorphism of pre-Alpine age and (ii) newly grown Alpine garnet, respectively. Both generations of garnet preserve growth zoning. From thermocalc -based numerical modelling of mineral assemblages in pressure–temperature ( P – T ) pseudosections, we infer that garnet 1 grew at increasing temperature and slightly increasing pressure, whereas garnet 2 grew at decreasing pressure and slightly increasing temperature. Estimated P – T conditions are ∼620 °C, 6 kbar for the peak of the pre-Alpine event, and of 490 °C, 18–20 kbar for the pressure peak of the Alpine event. Modelling of the modal proportion and chemical composition of garnet (i) shows that the subsequent decompression (to 14–15 kbar at 550 °C) must have been accompanied by moderate heating and (ii) does not support a stage of final temperature increase following decompressional cooling. This argues against a late thermal pulse associated with mantle delamination. Preservation of growth zoning in both generations of garnet and the limited amount of diffusive re-equilibration at the boundary between the two garnets suggests that the rocks were subjected to fast burial and exhumation rates, consistent with data obtained from other internal Alpine units.     

侧限条件下充填散体压缩承载和传力特性

充填散体的压缩承载和传力特性对防控充填开采矿山的地表变形具有重要意义。通过河卵石、碎石、尾矿、河砂、尾砂5种散体材料和7组不同粒径河卵石的侧限压缩试验,以及河卵石数值模拟压缩试验,分析了其压实过程和粒径对其变形、承载的影响,揭示了散体压缩过程中的传力特性。结果表明：散体压缩过程可分为空隙压密、颗粒破碎压密和压实固结3个阶段,且散体类型和粒径对其非线性压实过程基本没有影响,但对其内部结构重组过程有较大影响;压缩过程中,存在一个临界密实度使不同粒径河卵石的承载能力次序发生反转,且河卵石散体平均变形模量与颗粒特征因子呈负指数关系;基于河卵石数值模拟压缩试验得到的散体内部力链强度分布和“压力拱”,很好地证实了室内压缩试验中散体垂直应力沿加载方向呈递减的趋势,以及侧向应力在整个散体高度上先增后减这一试验结果。     

Morphological Evolution and Its Response to the Navigational Improvements in the North Passage,Yangtze Estuary

By use of bathymetric chart,recent change of the riverbed in the North Passage of the Yangtze Estuary has been studied in this paper.The main channel of the upper,middle and lower(section)in the North Passage has been successively eroded and its groin field significantly deposited.At the same time,sediment has been deposited on the entrance region.Erosion and deposition had responded rapidly to the construction of the regulation engineering.There was about one year duration of lagging between erosion in the deep channel and the construction of the regulation engineering.The siltation lag of time in the groin field varied with the initial depth,but the average deposited thickness was about 0.5 m per year.Volumetric analysis demonstrates that there is a increasing trend of siltation in the North Passage after 2002,because of the difference in duration and quantity between erosion in the deep channel and deposition in the groin field.The water volume of the North Passage was reduced by ≈9%(280 million m3)between 2002 and 2006.Sediment budget reveals that the main sediment deposited in the North Passage takes its source from the river and the ocean.The decreasing water volume was attributable to shoaling in the groin field.Its triggering factors for increased sedimentation are the navigational improvements(jetties and groins)after 1998,which altered the passage boundary and destroyed the equilibrium state on the average ebb and flood sediment fluxes.The establishment of a stable estuary is attributed to a reduction in depth of the groin field.The forecast on the sediment deposition quantity and continuous infilling time in the groin system is about 325×106m3 and 6～7 years,respectively.     

水电项目对越南硒圣河地区社会经济发展及环境保护的影响

硒圣河是湄公河的主要分支之一,其集水区地形条件和水资源量均对水电开发十分有利。此外,无论从物种多样性还是生物量来看,硒圣河水生生物资源非常丰富。鱼类是当地人们的重要食物来源,粗略估计鱼类物种数量可能在200-300种之间,目前具有详细记录的鱼类大约为120种。截至目前,从越南境内硒圣河上游至越-柬边界总共开发了6个水电项目,兴建了一座4A级硒圣调蓄水库。流经柬埔寨的硒圣河部分,依据发展规划将兴建3座水电站,即硒圣5号电站（硒圣1号电站以下）、硒圣3号电站、硒圣2号电站。硒圣河水电项目对区域（越南和柬埔寨）社会经济的影响体现在：为地处偏远和困难的集水区创造了新的能源资源,改善了交通系统和农村地区的生活条件。与此同时,这些水电项目也对该区域自然环境产生了重大影响。例如,改变了下游流动机理变化,导致下游河道淤积,对沿河生态系统也产生了一定影响。     

A Statistical Analysis of X1- and X2- or Higher-Class Flares during Solar Cycles 21∼23

The X1- and X2- or higher class ?ares in solar cycles 21, 22, and 23 from 1986 to 2008 have been analyzed statistically in this paper. It is found in the statistical study that the number of the X1-class ?ares accounted for 52.71% of total X- and higher class ?ares, while, the number of the X2- and higher class ?ares accounted for 47.29% of total X- and higher class ?ares. No matter whether the X1- and X2- or higher class ?ares, most of them occured in the descending phases of the solar cycles. Moreover, the weaker the intensity of the solar cycle, the higher the ratio of the ?ares occurred in the descending phase of the solar cycle, and the stronger the intensity of solar ?ares, the higher the ratio of the ?ares occurred in the descending phases of the solar cycles. In addition, the phase difference between the peak of the smoothed monthly mean number of sunspots and that of the X-class ?ares has been calculated, which shows that the smoothed monthly mean number of the X1-class ?ares had a very noticeable time advance of 1 month with respect to that of sunspots in the cycles 21 and 22, but there was a time lag of 13 months in the cycle 23, while, for the X2- and higher class ?ares, there was a time lag of 9 months in the cycle 21, but a one-month time advance existed in the cycle 22, and again a time lag of 32 months appeared in the cycle 23.     

超强台风“威马逊”作用下红河三角洲海域水动力环境变化的数值研究

201409号超强台风"威马逊"于2014年7月从北部湾北部过境,对红河三角洲近岸海域的水动力环境产生重要影响。本文基于Delft3D建立三维潮、流、浪耦合数值模型,对红河三角洲水位、海流及波浪对台风的响应变化进行模拟。结果表明:威马逊台风期间,红河三角洲海域风速增大约6倍,风向由偏南风转为偏北风,表底层流速均受影响,其中表层变化较大,表现为北分量流速明显增大,流向变为偏南向,与风向主分量变化有关;波高增大为正常海况的9倍,时间变化与风速一致。本研究获得了从北部湾北部海域过境的台风影响下红河三角洲海域水动力环境的响应变化特征,对该海域的物质输运研究及海洋工程建设有重要意义。