临潼地震台氢气异常与地震对应关系研究

研究了1993年8月以来,临潼台氢气异常与远场MS≥5.0、近场ML≥4.0地震的对应关系.结果表明,临潼台氢气异常的映震范围涵盖了从青藏高原北部到鄂尔多斯块体周边的大部分地区,主要与青藏高原北部地区MS≥5.0地震有较好的相关性,特别是在氢气背景值低于仪器检测限的情况下效果更好.应用这种相关性,对判定整个青藏高原北部地区的短临地震活动情况,具有一定的指导意义.     

青藏高原北部地震活动形势及其与中国大陆地区地震活动的关系研究

简要回顾了中国学对地震大形势的主要研究结果。指出地震活动时空强分布的不均匀性是地震活跃期和平静期的外在表现，系统地分析了青藏高原北部地区的地震活动形势，指出20世纪以来，该区Ms≥6.0地震经历了6个活跃期和6个平静期，与中国大陆地区的地震活动不同步。2000年6月甘肃景泰5．9级地震和同年9月静海兴海6．6级地震的发生意味着该区进入了一个新的地震活跃期。     

雹云识别的物元可拓模型在低纬高原的构造及其效果检验

雹云识别是一个多参数的模式识别问题,应用物元可拓思想将单参数雹云识别的不相容性转化为相容性问题。在与成都地区雹云识别的物元可拓模型进行对比后,根据低纬高原地形及气候特点,通过适当增加参数,构造完成低纬高原雹云识别的物元可拓模型,以此进行雹云识别,准确率达86％以上。     

从青藏高原航磁资料分析尼泊尔8.1级地震构造背景

利用小波分析处理青藏高原航磁资料,得到多尺度的航磁异常分布图。一阶小波结果反映地壳浅部的构造特征,在第Ⅰ和第Ⅱ缝合带位置,存在多条明显的北西西向弧形构造,由正负相间的磁异常带组成;在格尔木附近第Ⅳ缝合带位置存在近东西向的负磁异常条带。三阶小波结果反映地壳深部的构造特征,在约84°～91°E存在明显的近南北向的负磁异常条带,是研究区主要的深部构造特征。尼泊尔8.1级地震和3次7级强余震发生在近南北向的负磁异常条带的南端。该位置是近东西向的喜马拉雅构造带和近南北向的深部负磁异常条带的交汇部位。总体来说,青藏高原航磁资料揭示的浅部构造为多条近东西走向的带状构造,而深部构造是以近南北走向为主要特征,复杂的立交构造交汇部位是发生尼泊尔8.1级大地震的深部构造背景。     

适用于青藏高原地区中大比例尺重力勘查的大地测量方法技术研究

中大比例尺重力勘查工作是各种物探方法中对大地测量精度(尤其是高程精度)要求最高的一种。近年来,在青藏高原地区开展的矿产地质调查项目中越来越多地应用了重力勘查手段,但由于青藏高原地区特殊的自然地理及人文环境,基础测绘程度低,因此,一些在人口稠密、经济发达的内地开展工作时常用的成熟大地测量方法在青藏高原地区已不方便或出现了新的问题。本文通过对青藏高原地区近年来开展中大比例尺重力勘查时测量工作遇到的实际问题进行梳理研究,结合具有针对性地方法技术试验成果,总结了一套解决问题的方法,可作为今后青藏高原及类似困难地区开展中大比例尺重力勘测时的参考。     

川西高原6-7月最低气温场重建研究

 经过单相关普查,选择川西高原甘孜、阿坝两州的14个树木年轮宽度年表和14个气象站的1961—2005年6—7月最低气温资料分别建立树轮宽度场和最低气温场。计算树轮宽度场和最低气温场的典型相关系数,发现两个场的第一特征向量和第三特征向量有较好的相关性。利用多元线性回归模型分别重建14个地点的1787—2005年6—7月最低气温序列和川西地区平均气温序列,重建6—7月最低气温场。分析最低气温重建场发现,第一特征向量能较好地反映川西地区的冷暖变化。在近两个世纪里,川西地区最低气温场第一特征向量的方差贡献率在增加,而最低气温场的收敛速度在减慢。     

Petrogenetic character and provenance of metabasalts in the aspiring and Torlesse Terranes, South Island, New Zealand: Implications for the gold endowment of the Otago Schist?

We report quantitative X-ray diffraction, whole-rock geochemical and Sm–Nd isotope data for metabasalts from the Aspiring and Torlesse Terranes in the South Island of New Zealand. These rocks underlie the Mesozoic metasedimentary Otago Schist which is anomalously enriched in gold and host to at least one world-class orogenic gold deposit at Macraes (> 125 t Au). Geochemical and Nd isotopic similarities between the samples point to a common history of the two terranes rather than the amalgamation of one or two allochthonous plate fragments. Furthermore, geochemical and Nd data suggest the metabasalts within both terranes formed in an oceanic but essentially non-subduction-related setting. The origin of the Aspiring and Torlesse basalts can be linked to the formation of an oceanic plateau that had resulted from a (?Permian) mantle plume initiation event proximal to a mid-oceanic rise or triple junction. Given the intrinsically gold-enriched nature of certain oceanic-character mafic rocks, the anomalous gold endowment of the Otago Schist may have been enhanced via the accretion and subduction of a gold-enriched oceanic plateau fragment. The metabasalts are generally enriched in gold (up to 13 ppb) compared to their enclosing metasedimentary rocks (typically ca. 1 ppb), with sulphide-rich metabasaltic rocks having up to 550 ppb Au. However, the relatively small volume of metabasalts in the Otago Schist precludes these rocks as the principal source for Otago Schist orogenic gold, with a primarily metasedimentary source of the gold potentially having a limiting effect on the overall endowment of the Otago Schist. This approach, that employs petrogenetic fingerprinting of potentially fertile source rocks for the assessment of gold endowment, might prove useful in the conceptual exploration targeting of relatively immature and poorly exposed terrains.     

青海杂多地区新生代构造特征与两种类型矿床的关系

青海南部存在着巨大的成矿潜力,研究该区的构造变形与成矿作用的关系,对于认识区内众多矿床(化)的构造背景和控矿要素具有重要意义.新生代的走滑断裂和逆冲推覆构造是大陆碰撞造山带成矿理论中晚碰撞阶段在青藏高原东、北缘的重要构造形式.走滑断裂呈北西向,控制着藏东一系列走滑拉分盆地和斑岩的产出;逆冲推覆构造走向北西,整体自南向北呈现很好的分带特征,可分为根带、中带和前锋带.研究区存在两种类型矿床,分别为走滑断裂控制的斑岩型矿床和逆冲推覆构造控制的热液型矿床.其中,切过地壳尺度的走滑断裂因减压作用导致含水地幔的部分熔融,进而导致富含挥发分的含矿斑岩上涌、侵位,形成纳日贡玛斑岩型钼(铜)矿;逆冲推覆作用是流体长距离迁移的动力来源,逆冲推覆构造前锋带的逆冲断层上(下)盘破碎带或次级断层附近是成矿流体迁移的疏导系统和金属汇聚、淀积的重要场所.     

Karst morphology and groundwater vulnerability of high alpine karst plateaus

High alpine karst plateaus are recharge areas for major drinking water resources in the Alps and many other regions. Well-established methods for the vulnerability mapping of groundwater to contamination have not been applied to such areas yet. The paper characterises this karst type and shows that two common vulnerability assessment methods (COP and PI) classify most of the areas with high vulnerability classes. In the test site on the Hochschwab plateau (Northern Calcareous Alps, Austria), overlying layers are mostly absent, not protective or even enhance point recharge, where they have aquiclude character. The COP method classifies 82% of the area as highly or extremely vulnerable. The resulting maps are reasonable, but do not differentiate vulnerabilities to the extent that the results can be used for protective measures. An extension for the upper end of the vulnerability scale is presented that allows identifying ultra vulnerable areas. The proposed enhancement of the conventional approach points out that infiltration conditions are of key importance for vulnerability. The method accounts for karst genetical and hydrologic processes using qualitative and quantitative properties of karst depressions and sinking streams including parameters calculated from digital elevations models. The method is tested on the Hochschwab plateau where 1.7% of the area is delineated as ultra vulnerable. This differentiation could not be reached by the COP and PI methods. The resulting vulnerability map highlights spots of maximum vulnerability and the combination with a hazard map enables protective measures for a manageable area and number of sites.     

Moho Depth of Qinghai-Tibet Plateau Revealed by Seismic Probing

The Qinghai (青海)-Tibet plateau is the newest and biggest orogenic belt in the world and a natural laboratory for researching continental geodynamics, such as continent-continent collision, convergence, subduction, and plateau uplift. From the 1950s to the present, there have been many active-source (deep seismic sounding and deep seismic reflection profiling) and passive-source seismic probing (broadband seismic observations) implemented to reveal the crust-mantle structure. In this article, the authors mainly summarize the three seismic probings to discuss the Moho depth of the Qinghai-Tibet plateau based on the previous summaries. The result shows that the Moho of the Qinghai-Tibet plateau is very complex and its depth is very different; the whole outline of it is that the Moho depth is deeper beneath the south than the north and deeper in the west than in the east. In the Qiangtang (羌塘) terrane, the hinterland of the Qinghai-Tibet plateau, the Moho is shallower than both the southern and the northern sides. The deepest Moho is 40 km deeper than the shallowest Moho. This trend records the crustal thickening and thinning caused by the mutual response between the India plate and the Eurasia plate, and the eastward mass flow in the Qinghai-Tibet plateau.