滇西孟连曼信一带火山岩微枕状构造特征及其地质意义——兼论曼信—老厂一带火山岩时代     

肖龙  汪劲草 《矿产与地质》1996,(5)

首次发现报道了曼信一带海相火山岩微枕状构造的地质特征。主要根据野外第一手资料，分析探讨了曼信—老厂一带火山岩的时代，主要认识是：“依柳组”火山岩的主要形成于晚二叠世；老厂地区泥盆纪—中晚石炭世有少量基性—中性火山活动及三叠纪火山活动。  相似文献   

泰和盆地构造和演化初探     

王迪文  龙天 《江西地质科技》1997,24(4):165-169

我国大部分地区的小新生代盆地的成生、演化受断裂构造的控制,泰和盆地即是严格受断裂构造控制的走滑拉张型盆地。本文着重从盆地的基底构造、盆缘断裂构造及盆地同生、后期构造阐述了它们与盆地形成和演化的关系。  相似文献   

A new form of the cokriging equations     

Andrew E. Long  Donald E. Myers 《Mathematical Geology》1997,29(5):685-703

Myers developed a matrix form of the cokriging equations, but one that entails the solution of a large system of linear equations. Large systems are troublesome because of memory requirements and a general increase in the matrix condition number. We transform Myers’s system into a set of smaller systems, whose solution gives the classical kriging results, and provides simultaneously a nested set of lower dimensional cokriging results. In the course of developing the new formulation we make an interesting link to the Cauchy-Schwarz condition for the invertibility of a system, and another to a simple situation of coregionalization. In addition, we proceed from these new equations to a linear approximation to the cokriging results in the event that the crossvariograms are small, allowing one to take advantage of a recent results of Xie and others which proceeds by diagonalizing the variogram matrix function over the lag classes.  相似文献   

2001年四川雅江6.0级地震序列的破裂特征及发震构造   总被引：1，自引：0，他引：1  

龙思胜 《中国地震》2004,20(1):1-11

2001年雅江地震序列(主要地震是2月14日的Ms5．1和2月23日的Ms6．0地震)是四川地区近13年来的重要地震。选择2001年1月1日～6月30日期间，四川地震台网至少5个清晰的初动到时所记录的雅江地震序列中88次地震，并对其作了重新定位，对其中较大的13次地震用四川地区地震台网P波初动资料作了震源机制解。88次地震震源深度分布在2～16km，优势深度为9～llkm。前震、5．1级地震及其余震、6．0级地震及余震都紧邻孜河断裂分布，且按时段划分的震中优势分布方位与孜河断裂走向都是北西向。根据雅江地区近期大地形变场物质运移方向，选定了震源机制解的破裂面。13次较大地震震源机制解的主压应力P轴具有较大的垂向分量，水平投影方向为南东；地震类型都是左旋、走滑一正断型或正断一走滑型；大部分地震破裂面走向为北西一南东，倾向南西。根据前震、5．1级地震及其余震、6．0级地震及其余震震中优势分布方位，以及大多数较大地震破裂面走向和倾向，认为穿过震区的走向北西、倾向南西的孜河断裂是这次雅江地震序列的发震断裂。  相似文献   

综合物探方法在汤上屯地热勘探中的应用研究     

龙凡  韩天成 《地下水》2004,26(1):43-47

本文通过联剖、电测深、磁法和测温法等综合工作成果,分析、推断出汤上屯热水构造的产状、性质和热水出露条件,圈定出了热水分布范围.  相似文献   

Zircon U-Pb and oxygen isotope evidence for a large-scale O depletion event in igneous rocks during the Neoproterozoic     

Yong-Fei Zheng  Yuan-Bao Wu  Fu-Kun Chen  Long Li 《Geochimica et cosmochimica acta》2004,68(20):4145-4165

Oxygen isotope analysis and U-Pb dating were carried out on zircons from granite, granitic gneiss and eclogite in the Dabie-Sulu orogenic belt of east-central China. The results show a wide variation in zircon δ¹⁸O values from −10.9 to 8.5‰. Most of the values are lower than normal mantle zircon and almost half have prominently negative values. The low δ¹⁸O zircons have protolith ages of 700 to 800 Ma and metamorphic ages of 205 to 250 Ma, respectively. Fluid availability within the metaigneous rocks dictates the extent of metamorphic recrystallization and overgrowth. The igneous zircons have preserved their magmatic zoning and middle Neoproterozoic U-Pb age during the Triassic metamorphism, indicating low fluid availability. Widespread low δ¹⁸O values are identified in the magmatic zircons of middle Neoproterozoic age, within an outcrop area of over 20,000 km² along the northern edge of the South China Block. The low δ¹⁸O zircons record the presence of large volumes of low δ¹⁸O igneous rocks that were derived from remelting of meteoric-hydrothermally altered rocks at some time between 700 and 800 Ma.The U-Pb ages for metaigneous protoliths and granites are correlated not only with the timing of rifting accompanying the breakup of Rodinia, but also with contemporary glacial deposits in the South China Block at paleolatitudes of 30 to 40°N. Melting of glacial ice and snow is suggested, instead of the direct involvement of meteoric water, to produce the low δ¹⁸O fluid with oxygen isotopic signatures like the cold-climate meteoric water. The rifting created conditions favorable to anatexis of meteoric-hydrothermally altered rocks. Glaciated regions supplied copious water for the water-rock interaction during magma emplacement along rifting zones. Both rifting and glaciation favored the generation of the low δ¹⁸O magmas in the region. The low δ¹⁸O zircons are thus interpreted to have crystallized from the low δ¹⁸O magmas of middle Neoproterozoic age, and onset of the generation of low δ¹⁸O magmas in the northern margin of the South China Block is estimated to occur at about 758 ± 15 Ma. The large-scale remelting of hydrothermally altered crust not only results from repetitive emplacement of mafic magmas along the rifting zones with protracted episodes of water-rock interaction, but also involves rift systems that rapidly introduce large volumes of fluid through confined pathways and traps in a short space of time in response to tectonic triggers. Occurrence of the large-scale ¹⁸O depletion during the middle Neoproterozoic may be a manifestation of the cold paleoclimate related to the snowball Earth event.  相似文献   

川滇地区单断裂强震区与多断裂强震区     

龙思胜 《中国地震》2005,21(1):70-83

以《全国小震目录》(1965年1月1日～2002年lO月31日)和《四川地震台网快报目录》(2002年11月1日～2003年9月30日)为基础资料，研究了川滇地区地震活动性发展变化的主要特征，并提出“单断裂强震区”和“多断裂强震区”概念。发现川滇地区主要单断裂强震区在发生一些强震之后，已经陆续进入地震平静时段，近期发生强震的能力明显减弱。与此同时，“滇西南”、“龙陵-腾冲”、“丽江-武定”地区分别在较短时段内发生多次强震，表明这几个多断裂强震区陆续进入活跃时段，成为1984年以来川滇地区的地震主体活动区域。多断裂强震区具有区内中小断裂汇集、地质构造复杂、地震活跃时段多次出现、在同一活跃时段内又具有活跃小段与小段间距的小段组合形式等特征。对已有的和可能新生的多断裂强震区进行早期判定，以及对活跃时段、小段组合进行动态跟踪，对于川滇地区地震预报具有重要意义。  相似文献   

Element mobility during pyrite weathering: implications for acid and heavy metal pollution at mining-impacted sites   总被引：1，自引：0，他引：1  

Long Lu  Rucheng Wang  Fanrong Chen  Jiyue Xue  Peihua Zhang  Jianjun Lu 《Environmental Geology》2005,49(1):82-89

Based on back scattered electron images and electron micro-probe analysis results, four alteration layers, including a transition layer, a reticulated ferric oxide layer, a nubby ferric oxide layer and a cellular ferric oxide layer, were identified in the naturally weathering products of pyrite. These layers represent a progressive alteration sequence of pyrite under weathering conditions. The cellular ferric oxide layer correlates with the strongest weathering phase and results from the dissolution of nubby ferric oxide by acidic porewater. Leaching coefficient was introduced to better express the response of element mobility to the degree of pyrite weathering. Its variation shows that the mobility of S, Co and Bi is stronger than As, Cu and Zn. Sulfur in pyrite is oxidized to sulfuric acid and sulfate that are basically released into to porewater, and heavy metals Co and Bi are evidently released by acid dissolution. As, Cu and Zn are enriched in ferric oxide by adsorption and by co-precipitation, but they would re-release to the environment via desorption or dissolution when porewater pH becomes low enough. Consequently, Co, Bi, As, Cu and Zn may pose a substantial impact on water quality. Considering that metal mobility and its concentration in mine waste are two important factors influencing heavy metal pollution at mining-impacted sites, Bi and Co are more important pollutants in this case.  相似文献   

Variation of stream temperature among mesoscale habitats within stream reaches: southern Appalachians          下载免费PDF全文

S. Lynsey Long  C. Rhett Jackson 《水文研究》2014,28(7):3041-3052

Stream mesoscale habitats have systematic topographic relationships to hyporheic flow patterns, which may create predictable temperature variation between mesoscale habitat types. We investigated whether systematic differences in temperature metrics occurred between mesoscale habitats within reaches of small streams tributary to the upper Little Tennessee River, southern Appalachians. Surface water temperature was recorded over three or four mid‐summer days in four mesoscale habitat types: riffle, main riffle, pool and alcove in 44 stream segments (sites). Temperature metrics were calculated for each mesoscale habitat relative to the mean value of the metric over the stream: Δ maximum temperature, Δ average maximum temperature and Δ maximum daily variation and also for each site: standard deviation of the maximum temperature and average diurnal variation (ADV). Sites were categorized as fully or partially forested. Pool tailouts had statistically significantly lower Δ maximum temperature and Δ average maximum temperature than riffle tailouts in partially forested sites, although differences were small. This was the opposite of what was expected in the presence of hyporheic exchange, indicating hyporheic exchange is not a dominant driver of mesoscale habitat temperatures at these sites. Temperature differences between mesoscale habitat units were small and unlikely to have ecological significance. We also evaluated relationships between stream temperature and riparian condition, watershed % impervious surfaces, watershed % non‐forested and elevation. ADV and standard deviation of the maximum temperature were significantly higher in partially forested sites, indicating that partially forested sites have greater temperature ranges and spatial variation of maximum temperatures. ADV decreased with elevation and increased with % impervious surfaces. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Late Quaternary sea‐level change and evolution of Belfast Lough,Northern Ireland: new offshore evidence and implications for sea‐level reconstruction     

Ruth M. K. Plets  S. Louise Callard  J. Andrew G. Cooper  Joseph T. Kelley  Daniel F. Belknap  Robin J. Edwards  Antony J. Long  Rory J. Quinn  Derek W. T. Jackson 《第四纪科学杂志》2019,34(4-5):285-298

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions.  相似文献