排序方式: 共有47条查询结果,搜索用时 15 毫秒
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本文介绍了断裂引起的应变量计算方法。断裂作用可导致连续应变和非连续应变。连续应变与断裂位移,断裂长度比值及断裂面上有效应力成正相关关系。影响非连续应变的因素有:断裂几何形态、断裂的旋转性、断裂规模。已经提出三种断裂旋转机制:刚性旋转,垂直剪切和斜向剪切。对于这三种机制,我们分别建立了断裂非连续应变的计算公式。这些公式与断裂的旋转角度和位移大小相关。刚性旋转时,断块内部没有任何塑性变形,因此地层的长度没有变化。它引起的非连续应变最小。垂直剪切作用使断块内地层变形,但水平方向的地层长度不变。推算的公式表明,对于相同的原始数据,它引起的非连续应变比刚性旋转机制引起的非连续应变大。斜向剪切也使断块内地层变形,但水平方向的长度也不变。在同等条件下,它引起的非连续应变比垂直剪切机制引起的非连续应变大。 相似文献
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Brown trout (Salmo trutta) are known to have effects on multiple trophic levels in New Zealand streams, but their impacts on lower trophic levels are less well understood within lentic systems. We examined the effects of brown trout removal using rotenone on zooplankton and phytoplankton community composition in the Upper Karori Reservoir, New Zealand. Significant shifts were observed in zooplankton and phytoplankton composition following removal of brown trout from the reservoir. Shifts in zooplankton community composition did not occur immediately following trout removal (February), but instead followed the likely timing of galaxiid spawning (July). The removal of brown trout likely resulted in reduced predation pressure on galaxiids. A major change occurred in the zooplankton community with the dominance shifting from larger crustaceans to smaller rotifers, indicating an increased predation pressure from the larval native galaxiid. A delayed response in zooplankton community composition change indicates rotenone was not the direct cause of this. A major shift in phytoplankton community composition occurred immediately following trout removal. This was not consistent with the trophic cascade hypothesis of reduced grazing pressure from larger zooplankton due to increased galaxiid predation as a result of brown trout removal. 相似文献
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雷州半岛第四纪火山岩激光40Ar/39Ar等时线定年研究 总被引:2,自引:1,他引:1
雷州半岛是我国新生代火山岩最重要的分布地区之一,火山活动主要集中在中晚更新世。前人对雷州火山岩的年代学研究以K-Ar法为主。研究表明,雷州火山岩测年结果大致分布在0.38~3.04Ma范围内。根据地层和火山岩层的叠置关系,雷州第四纪火山岩由于覆盖在被确定是1.87Ma和0.76Ma沉积的地层之上,故火山岩年龄应小于该地层年龄。K-Ar法定年结果与雷州地区地层叠置关系存在矛盾。本文通过对雷州半岛第四纪火山岩进行野外考察及采样,利用激光40Ar/39Ar年代学方法进行了精细定年。结果表明,雷州火山岩的喷发主要集中18万年前后。定年结果还表明,对于年轻样品,基于尼尔值计算的K-Ar年龄及40Ar/39Ar表观年龄偏老,等时线年龄相对较为可靠。对同一样品的斑晶、基质作斑晶-基质等时线计算,只有在斑晶基质满足同源条件时才有意义。本文首次提出,通过对比未照射样品的初始36Ar/38Ar值的均一性,以检验样品是否同源,确认斑晶-基质等时线年龄的可信度。据此,等时线的处理方法可以推广应用于特定区域内全部同源同时样品。 相似文献
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实验研究了原煤、型煤单轴压缩电磁辐射记忆效应特征、记忆内容及变化规律,探讨并分析了煤岩电磁辐射记忆效应机理.结果表明,煤岩变形破坏电磁辐射具有记忆先期最大应力、纵向应变、横向应变和体应变的能力,最直接的记忆内容是先期受到的应力、纵向应变和横向应变;当先期施加的应力水平大于70%~80%时,电磁辐射记忆能力迅速减弱,甚至根本失去记忆能力;煤岩损伤破坏过程的不可逆决定了电磁辐射过程的不可逆,电磁辐射过程的不可逆是煤岩变形破坏电磁辐射记忆效应的直接原因.煤岩电磁辐射记忆效应理论在地应力测试、巷道围岩不同应力区范围的确定及煤岩动力灾害预测等方面具有广阔的应用前景. 相似文献
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琼北火山岩激光40Ar/39Ar定年研究 总被引:1,自引:1,他引:0
新生代以来,雷琼地区多次、大量地喷发了一系列火山岩。前人主要基于K-Ar法对此划分了期次。本文采用激光40Ar/39Ar年代学方法,对琼北火山岩区进行了精细定年研究。低本底激光40Ar/39Ar法能够对低钾含量,极少量样品(毫克级)进行精细测定,非常适合极年轻火山岩的定年工作。结果显示的火山岩激光40Ar/39Ar法高质量数据表明琼北火山喷发活动时限跨越1.3~0.052Ma。在比较了表观年龄与等时线年龄差异之后,本文给出了年龄推荐值。正如测试数据所显示,本地区新生代火山岩普遍存在40Ar和36Ar过剩的问题,此时只有等时线年龄才代表喷发的真实年龄。 相似文献
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Masoud EDRAKI Sayyed Ahang KOWSAR 《山地科学学报》2007,4(2):136-145
Water is the most important limiting factor in the development of arid environments; therefore, optimization of water use is a necessity in desert reclamation projects. Evapotranspiration of a 6-year-old river red gum (Eucalyptus camaldulensis Dehnh.) plantation, located in a sedimentation basin of an artificial recharge of the Gareh Bygone Plain groundwater system in Iran’s southern Zagros Mountains, was studied during a 7-month period. A neutron moisture probe was used to monitor soil water changes in the root zone. Soil water depletion following rapid drainage for blocks receiving relatively high, medium and low volumes of floodwater were 809.6, 312.4, and 203.1 mm, respectively, for a 150-day period. Soil water potential during most of the study period was below -1.5 MPa. This study proves that river red gum in not a suitable species for desertification control where water conservation is of vital importance. Flood irrigation of trees on 8 Aug. 1991 provided the opportunity to throw doubt upon the claim of summer dormancy of river red gum. 相似文献
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丹凤地区光石沟铀矿床大毛沟岩株锆石U-Pb同位素定年及其地质意义 总被引:3,自引:0,他引:3
丹凤地区是我国伟晶岩型铀矿床的重要产区,光石沟铀矿床是该区最大的铀矿床之一,大毛沟岩株与光石沟铀矿床有密切的空间关系与成因联系。本文采用锆石LA-ICP-MS定年方法测定了大毛沟岩株的U-Pb同位素年龄,获得了代表大毛沟岩株形成年龄的锆石谐和曲线加权平均值年龄为418.3±8.8 Ma,与光石沟铀矿床的成矿年龄相当,说明光石沟铀矿床的成矿作用在时间上与该岩株的形成时间相当。同时,残留锆石中1980.5±19.47 Ma年龄的发现,说明大毛沟岩株白岗质花岗岩的物源可能与中下地壳秦岭群有关;E颗粒内核465Ma的年龄则可能代表灰池子岩体片麻状二长花岗岩的形成年龄,表明大毛沟岩株与灰池子岩体的形成年龄之间存在约30 Ma的时差。 相似文献