The origin of oriented lakes in the Andean foreland, Parque Nacional Torres del Paine (Chilean Patagonia)

The Parque Nacional Torres Del Paine and surrounding area in the Magallanes foreland basin in Chilean Patagonia is the site for numerous lakes fed by glaciers and rivers in the Andean highlands to the west. The lakes are elongate and have conspicuously systematic orientations. We hypothesize that the origin of the oriented lakes lies in the fault system, composed of a right-lateral strike-slip fault set oriented 58° from north, a left-lateral strike-slip set oriented 87°, and a thrust fault set oriented 167°, that exists within the underlying rocks. To test this hypothesis quantitatively, we determined the shape and orientation of the lakes by fitting each lake with an ellipse of appropriate aspect ratio, and later with multiple ellipses consistent with the composite geometry of some lakes. We then examined the faults in the area in terms of their kinematics, orientation and distribution. The distribution of lake orientations showed three distinct groups which appear to correspond to the three main fault groups. For lakes fitted with multiple ellipses, the difference in means between the right-lateral, left-lateral, and thrust faults and their corresponding groups of lakes are 3.05°, 1.57°, and 5.17°. Using a Kolmogorov–Smirnov (K–S) statistical test to compare the orientations of faults with respect to the lakes suggests that there is not a strongly significant difference between the fault orientations and the corresponding lake groups. These results indicate that the faults have a profound control on the orientation, shape, and distribution of the lakes. We attribute this to faults and their damage zones being weaker and therefore prone to a faster rate of erosion, and to stress perturbations associated with discontinuous faults resulting in localized high density fracturing and surface subsidence. These results have implications for lake and drainage system morphologies in other foreland basins along the Andes and other similar settings.     

DRASTIC-Fm: a modified vulnerability mapping method for structurally controlled aquifers in the southern Gulf Islands,British Columbia,Canada

DRASTIC, the methodology for mapping the intrinsic vulnerability of aquifers, is modified to incorporate the structural characteristics of fractured bedrock aquifers. In these aquifers, groundwater flow is predominantly through fractures, with large-scale fracture zones and faults acting as primary conduits for flow at the regional scale. The methodology is applied to the southern Gulf Islands region of southwestern British Columbia, Canada. Bedrock geology maps, soil maps, structural measurements, mapped lineaments, water-well information and topographic data, assembled within a comprehensive GIS database, form the basis for assigning traditional DRASTIC indices, while adding the structural indices necessary for capturing the importance of regional structural elements in recharge and well capture zone determinations.     

Velocity dependence of strength and healing behaviour in simulated phyllosilicate-bearing fault gouge

Despite the fact that phyllosilicates are widespread in fault zones, little is known about the strength of phyllosilicate-bearing fault rocks under brittle–ductile transitional conditions. In this study, we explored the steady state strength and healing behaviour of a simulated phyllosilicate-bearing fault rock, i.e. muscovite plus halite and brine, at room temperature, normal stresses of 1–9 MPa, atmospheric fluid pressure and sliding velocities of 0.001–13 μm/s, using a rotary shear apparatus. While 100% halite and 100% muscovite samples exhibit rate-independent frictional/brittle behaviour, the strength of mixtures containing 10–50% muscovite is both normal stress and sliding velocity dependent. At low velocities (< 1 μm/s), strength increases with increasing velocity and normal stress, and a mylonitic foliation develops. This behaviour results from pressure solution in the halite grains, which accommodates frictional sliding on the phyllosilicate foliation. The pervasive muscovite foliation, which coats all halite grains, prevents significant healing. At high velocities (> 1 μm/s), velocity-weakening frictional behaviour occurs, along with the development of a structureless, intermixed, cataclastic microstructure. The steady state porosity of samples deformed in this regime increases with increasing sliding velocity. We propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution. Towards higher sliding velocities, dilatation increasingly dominates over pressure solution compaction, so that porosity increases and frictional strength decreases. During periods of zero slip, pressure solution compaction occurs, causing a significant strength increase on reshearing. Our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions, but can simply result from oscillating fault motion rates. Our healing data suggest that foliated, aseismically creeping fault segments will remain weak and aseismic, whereas segments that have slipped seismically will rapidly re-strengthen and remain in the unstable, velocity-weakening regime.     

区域自动气象站故障预测方法的研究与应用

区域自动气象站是现代气象业务中重要的数据采集设备,区域站故障的维修维护尤为重要,本文总结日常区域站的维护,介绍了区域站的常见故障,分析了各种故障发生的时间及频率,为了更好的提前判断可能性故障,本文利用GIS强大的空间分析功能和可视化的特点,根据天气实况及预报情况对其进行空间分析,提前分析出因天气等外部环境引起的可能出现故障的站点,解决了常规区域站故障维修的滞后性,提前消除故障隐患,变被动为主动,最大限度地减少了自动站观测数据的缺测、异常情况,提高了资料的传输及时率和完整性。     

甘孜—理塘结合带锰结核的发现及其地质意义

在甘孜—理塘结合带内理塘县中木拉乡附近发现锰结核。通过地质填图和综合研究,该锰结核产于结合带内瓦能蛇绿混杂岩组中的黑色粉砂质板岩中。其沉积层序为玄武岩→硅质岩→含锰结核粉砂质板岩。锰结核主量元素具有高Mn、低Fe、Si、Ca的特点,其中Mn含量为42.19%,高出大洋锰结核平均值1.83倍,Mn/Fe值较高,达8.1。锰结核中除Cr高于大洋锰结核平均值2～7倍外,多数微量元素低于大洋锰结核平均值。稀土元素具有较明显的Ce正异常,稀土总量、轻重稀土分异程度、Eu异常特征与混杂岩中的砂岩、硅质岩近似,而与玄武岩差别较大。该锰结核产出于大陆边缘构造环境,火山活动微弱,代表甘孜—理塘洋扩张到最大程度时的沉积。其时甘孜—理塘洋规模仍是有限的。     

甘孜-理塘构造带泥盆系的深水沉积

甘孜－理塘构造带由大面积为三叠系地层覆盖而难以对其下覆的地层进行研究,导致了了们对甘孜－理塘构造带的构造演化认识产生很大分歧。通过对劳改皮沉积混杂岩体的地层学、生物学,沉积学和岩石化学等方面的研究,认为甘孜－理塘构造带三叠系盖层之下可能存在大面积的泥盆系、甚至上古生界的深水沉积。进而得出甘孜－理塘洋的演化历史应该向前推移到早泥盆世,而不是通常所说的晚二叠世,同时指出,沉积混杂岩是研究隐伏基底的重要