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1.
富碱侵入岩具有深源浅成的属性,是示踪地幔组成的窗口。位于东天山与塔里木克拉通北缘交界处的阔克塔格以西出露一处以正长岩为主体、包含少量中—基性岩石单元的富碱侵入岩。LA- ICP- MS锆石U- Pb测年显示其侵位于227~224 Ma之间,为印支期岩浆作用产物。该岩体具有富碱(Na2O+K2O=7. 93%~ 12. 28%)、富铝(Al2O3=15. 62%~18. 67%)、贫镁(MgO=0. 12%~4. 01%)、贫钛(TiO2=0. 14%~1. 63%)的特征,属于准铝质的(A/CNK=0. 78~1. 00)高钾钙碱性—钾玄岩系列。微量元素表现出高场强元素Nb、Ta、Th、U、Zr、Hf的富集,不相容元素Sr、P、Ti的亏损特征;轻重稀土分馏明显((La/Yb)N=15. 09~34. 90),表现为轻稀土强烈富集的右倾型曲线,Eu异常变化较大(δEu=0. 12~1. 72)。在同位素组成上,富碱侵入岩呈现相对宽泛但总体富集的全岩Sr- Nd和锆石Hf同位素特征,(87Sr/86Sr)i=0. 70489~0. 70581,εNd(t)=14. 56~6. 74,εHf(t)=11. 48~+3. 06,锆石δ18O值(5. 49‰~6. 87‰)略高于地幔值(5. 3‰±0. 6‰)。阔克塔格西富碱侵入岩具A1型花岗岩特征,形成于板内伸展构造环境中。基于主、微量元素及Sr- Nd- Hf- O同位素特征,笔者认为该杂岩体为同源岩浆演化产物,源于富集岩石圈地幔的原始岩浆上升并经历AFC(同化混染- 分离结晶)过程。晚三叠世塔里木克拉通北缘—东天山—北山地区处于板内构造体制,A1型花岗岩和正长岩差异化的时空分布特征很可能记录了古亚洲洋自西到东 “剪刀式”的闭合过程。  相似文献   
2.
吉尔吉斯斯坦北天山构造带的矿床学数据缺乏,制约了天山造山带境内外成矿对比。布丘克金矿床位于吉尔吉斯斯坦北天山构造带中部。金矿体为石英复脉,呈带状发育于NWW向韧性剪切带中。矿体倾向SSW,倾角60°~70°,赋矿围岩主要为侵入于早古生代变质碎屑杂岩中的正长斑岩。布丘克金矿床成矿期石英流体包裹体观察、石英H-O同位素、硫化物S同位素测试结果显示,布丘克金矿床石英脉中包裹体大小集中在2~10μm之间,类型以H2O-CO2型、富CO2型、水溶液型包裹体为主,成分以富CO2、含CH4为特征。成矿流体具有中温(200~320℃)、低盐度(3%~7%NaCleqv)特征;石英δDV-SMOW值介于-108.1‰~-90.2‰之间,δ18O流体值介于4.86‰~9.26‰之间;黄铁矿δ34S分布在0‰左右(-0.9‰~1.6‰)。综合本文数据、矿床地质特征、区域地质资料,本文认为布丘...  相似文献   
3.
利用多源项目获得的补充加密GNSS观测资料计算研究区高空间分辨率的GNSS水平运动速度场和应变率场,采用地震波形资料,通过CAP方法求解震源机制解,在此基础上使用阻尼区域应力反演方法分析川滇地块区域构造应力场的空间分布特征。结合主要断裂的活动特性,综合分析川滇地区的地壳形变特征。结果表明:1)块体浅部的最大主压应力与地表的最大主压应变率由SSE向转变为近SN向,呈现出较好的一致性,GNSS观测至少可反映20 km以内的地壳形变;2)川滇块体南部的东向滑移和顺时针旋转,可能受青藏高原推挤、华南块体阻挡及印度板块与欧亚板块之间北向运动速率自西向东递减而形成的右旋剪切拖拽作用的顺时针力偶的综合影响;3)川滇块体在综合力偶作用下SE向挤出和顺时针旋转的同时,受到走滑逆冲断裂带的吸收转换,使得青藏高原物质SE向挤出有限。  相似文献   
4.
区域中长期地震危险性数值分析研究,需要对其初始构造应力场有所了解,但目前以及未来一段时期内仍无法直接观测到深部孕震层区域的应力场状况.本文首先基于岩石库仑-摩尔破裂准则,利用青藏高原及邻区百年历史范围内的强震信息,来反演估算该区域的初始应力场.然后,考虑区域构造应力加载及强震造成的应力扰动共同作用,重现了历史强震的发展过程.然而对于初始应力场的反演估算,本文仅能给出区域其上下限的极限值,并不能唯一确定.因此,采用Monte Carlo随机法,进行大量独立的随机试验计算,生成数千种有差异的区域初始应力场模型,且保证每种模型都能令历史强震有序发生,但未来应力场演化过程不尽相同.最后,将数千种模型在未来时间段内的危险性预测结果集成为数理统计结果,据此给出了区域未来的地震危险性概率分布图.初步结果显示未来强震危险性概率较高地区集中在巴颜喀拉块体边界及鲜水河断裂带地区.  相似文献   
5.
This paper presents the shake table test results of a novel system for the design of precast reinforced concrete bridges. The specimen comprises a slab and four precast columns. The connections are dry and the columns are connected to the slab by an ungrouted tendon. One of the tendon ends is anchored above the slab, in series with a stack of washer springs, while the other end is anchored at the bottom of the column. The addition of such a flexible restraining system increases the stability of the system, while keeping it relatively flexible allowing it to experience negative post-uplift stiffness. It is a form of seismic isolation. Anchoring the tendon within the column, caps the design moment of the foundation, and reduces its size. One hundred and eighty-one shake table tests were performed. The first 180 caused negligible damage to the specimen, mainly abrasion at the perimeter of the column top ends. Hence, the system proved resilient. The 181st excitation caused collapse, because the tendons unexpectedly failed at a load less than 50% of their capacity (provided by the manufacturer), due to the failure of their end socket. This highlights the importance of properly designing the tendons. The tests were used to statistically validate a rigid body model. The model performed reasonably well never underestimating the median displacement response of the center of mass of the slab by more than 30%. However, the model cannot predict the torsion rotation of the slab that was observed in the tests and is due to imperfections.  相似文献   
6.
徐楠  吴才来  刘畅 《地质学报》2023,97(12):4067-4084
南阿尔金造山带位于塔里木盆地和柴达木盆地之间,是中国西北地区重要的俯冲-碰撞杂岩带,其早古生代构造演化过程是近年来的研究热点之一,然而,洋壳俯冲的时限一直存在争议。本文对茫崖石英二长岩开展岩石学、地球化学、锆石U-Pb年代学和锆石Lu-Hf同位素地球化学研究,探讨其岩石成因及成岩时的构造环境。样品显示高碱、富钾、低钛、贫铁及Nd-Ta-Ti异常等与钾玄岩相似的地球化学特征,成岩年龄为511~495 Ma, εHf(t)主要为-3.51~-0.08,少量介于0.04~1.69之间。我们认为俯冲洋壳到达角闪岩相边界时释放大量水并上升进入地幔楔,导致地幔楔橄榄岩发生角闪石化交代作用,由于地幔楔沿俯冲带向下拖曳而温度升高,角闪石化橄榄岩熔融形成的熔体在上升过程诱发上地壳物质部分熔融,壳源岩浆混合少量幔源岩浆形成了石英二长岩,该期花岗岩是对造山带从大洋岛弧环境向活动大陆边缘过渡的岩石学响应。因此,南阿尔金洋壳可能在约517 Ma前已经开始俯冲。  相似文献   
7.
Cropland fallows are the next best-bet for intensification and extensification, leading to increased food production and adding to the nutritional basket. The agronomical suitability of these lands can decide the extent of usage of these lands. Myanmar’s agricultural land (over 13.8 Mha) has the potential to expand by another 50% into additional fallow areas. These areas may be used to grow short-duration pulses, which are economically important and nutritionally rich, and constitute the diets of millions of people as well as provide an important source of livestock feed throughout Asia. Intensifying rice fallows will not only improve the productivity of the land but also increase the income of the smallholder farmers. The enhanced cultivation of pulses will help improve nutritional security in Myanmar and also help conserve natural resources and reduce environmental degradation. The objectives of this study was to use remote sensing methods to identify croplands in Myanmar and cropland fallow areas in two important agro-ecological regions, delta and coastal region and the dry zone. The study used moderate-resolution imaging spectroradiometer (MODIS) 250-m, 16-day normalized difference vegetation index (NDVI) maximum value composite (MVC), and land surface water index (LSWI) for one 1 year (1 June 2012–31 May 2013) along with seasonal field-plot level information and spectral matching techniques to derive croplands versus cropland fallows for each of the three seasons: the monsoon period between June and October; winter period between November and February; and summer period between March and May. The study showed that Myanmar had total net cropland area (TNCA) of 13.8 Mha. Cropland fallows during the monsoon season account for a meagre 2.4% of TNCA. However, in the winter season, 56.5% of TNCA (or 7.8 Mha) were classified as cropland fallows and during the summer season, 82.7% of TNCA (11.4 Mha) were cropland fallows. The producer’s accuracy of the cropland fallow class varied between 92 and 98% (errors of omission of 2 to 8%) and user’s accuracy varied between 82 and 92% (errors of commission of 8 to 18%) for winter and summer, respectively. Overall, the study estimated 19.2 Mha cropland fallows from the two major seasons (winter and summer). Out of this, 10.08 Mha has sufficient moisture (either from rainfall or stored soil water content) to grow short-season pulse crops. This potential with an estimated income of US$ 300 per hectare, if exploited sustainably, is estimated to bring an additional net income of about US$ 1.5 billion to Myanmar per year if at least half (5.04 Mha) of the total cropland fallows (10.08 Mha) is covered with short season pulses.  相似文献   
8.
This paper presents an approach to stream length-gradient index analysis to identify tectonic signatures. The graded profile of the Dez River in Zagros Mountains, Iran, indicates that the area has been tectonically disturbed, and it triggers landslide hazards. The high-gradient index shows that a steeper gradient could be potentially a signature for landslides identification. The digital surface models acquired by airborne LiDAR were used in this study to generate the HRDEM. Our result shows a great potential for improving landslide investigations by implementing stream length-gradient index derived from the HRDEM in conjunction with the landslide inventories data-set in the GIS environment. We also identified a correlation between the stream length-gradient index and the graded topographic profile with slopes and landslides. This empirical approach was verified by geodata analytics and landslide inventories data-set in conjunction with field observations. This study has identified the locations of high-gradient indices with susceptible to landslides.  相似文献   
9.
湖南鲁塘矿区为我国著名的煤系石墨矿区,煤系石墨的形成受岩浆热作用和构造作用的双重控制,其成矿和赋存都与构造格局密切相关。为深入研究构造作用对煤系石墨成矿的影响,通过野外地质调查和光学显微镜下观察、X射线衍射和拉曼光谱等测试分析方法,分析研究区构造特征和煤系石墨特征。研究结果表明,受区域构造活动的影响,鲁塘矿区构造格局呈现出分区分带性特征,东西方向可划分为东部、中部和西部3个条带;南北方向可划分为北部、中部和南部3个分区。自西向东,随着与岩体距离逐渐减小,煤层受岩浆热作用的影响逐渐增大,煤的石墨化程度也逐渐增高。由南向北,构造变形强度逐渐增强,导致北部分区形成以封闭式高温-高压的成矿环境为主,同时,应力作用促进了煤的石墨化,导致煤的石墨化程度较高;中部分区内构造情况复杂,形成不同温度压力条件的成矿环境,煤的石墨化程度差异性明显;南部分区构造情况简单,主要构成开放式环境,煤的石墨化程度较低,仅在近岩体附近可形成煤系半石墨。研究成果为煤系石墨资源勘探提供了有力依据。   相似文献   
10.
Undernutrition, obesity, climate change, and freshwater depletion share food and agricultural systems as an underlying driver. Efforts to more closely align dietary patterns with sustainability and health goals could be better informed with data covering the spectrum of countries characterized by over- and undernutrition. Here, we model the greenhouse gas (GHG) and water footprints of nine increasingly plant-forward diets, aligned with criteria for a healthy diet, specific to 140 countries. Results varied widely by country due to differences in: nutritional adjustments, baseline consumption patterns from which modeled diets were derived, import patterns, and the GHG- and water-intensities of foods by country of origin. Relative to exclusively plant-based (vegan) diets, diets comprised of plant foods with modest amounts of low-food chain animals (i.e., forage fish, bivalve mollusks, insects) had comparably small GHG and water footprints. In 95 percent of countries, diets that only included animal products for one meal per day were less GHG-intensive than lacto-ovo vegetarian diets (in which terrestrial and aquatic meats were eliminated entirely) in part due to the GHG-intensity of dairy foods. The relatively optimal choices among modeled diets otherwise varied across countries, in part due to contributions from deforestation (e.g., for feed production and grazing lands) and highly freshwater-intensive forms of aquaculture. Globally, modest plant-forward shifts (e.g., to low red meat diets) were offset by modeled increases in protein and caloric intake among undernourished populations, resulting in net increases in GHG and water footprints. These and other findings highlight the importance of trade, culture, and nutrition in diet footprint analyses. The country-specific results presented here could provide nutritionally-viable pathways for high-meat consuming countries as well as transitioning countries that might otherwise adopt the Western dietary pattern.  相似文献   
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