Connectivity of post-fire runoff and sediment from nested hillslopes and watersheds     

Codie Wilson  Stephanie K. Kampf  Sandra Ryan  Tim Covino  Lee H. MacDonald  Hunter Gleason 《水文研究》2021,35(1):e13975

Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to greater bare soil, runoff and erosion as compared to pre-fire conditions. This research examines the connectivity of post-fire runoff and sediment from hillslopes (< 1.5 ha; n = 31) and catchments (< 1000 ha; n = 10) within two watersheds (< 1500 ha) burned by the 2012 High Park Fire in northcentral Colorado, USA. Our objectives were to: (1) identify sources and quantify magnitudes of post-fire runoff and erosion at nested hillslopes and watersheds for two rain storms with varied duration, intensity and antecedent precipitation; and (2) assess the factors affecting the magnitude and connectivity of runoff and sediment across spatial scales for these two rain storms. The two summer storms that are the focus of this research occurred during the third summer after burning. The first storm had low intensity rainfall over 11 hours (return interval <1–2 years), whereas the second event had high intensity rainfall over 1 hour (return interval <1–10 years). The lower intensity storm was preceded by high antecedent rainfall and led to low hillslope sediment yields and channel incision at most locations, whereas the high intensity storm led to infiltration-excess overland flow, high sediment yields, in-stream sediment deposition and channel substrate fining. For both storms, hillslope-to-stream sediment delivery ratios and area-normalised cross-sectional channel change increased with the percent of catchment that burned at high severity. For the high intensity storm, hillslope-to-stream sediment delivery ratios decreased with unconfined channel length (%). The findings quantify post-fire connectivity and sediment delivery from hillslopes and streams, and highlight how different types of storms can cause varying magnitues and spatial patterns of sediment transport and deposition from hillslopes through stream channel networks.  相似文献   

内蒙古碾子沟钼矿床成矿流体来源、演化及成矿机理     

孙丰月  王睿  王一存  李顺达  王可勇  石开拓  孙清飞  王文元 《吉林大学学报(地球科学版)》2020,50(3):768-780

内蒙古自治区碾子沟钼矿床地处华北地台北缘西拉木伦钼成矿带西段，为一典型的中型石英脉型钼矿床。该钼矿床矿脉（体）主要产于燕山早期二长花岗岩-钾长花岗岩内NNW、NW向断裂构造体系之中，成矿作用过程经历了黄铁矿±辉钼矿＋石英（Ⅰ）、辉钼矿＋黄铁矿±黄铜矿＋石英（Ⅱ）、黄铜矿＋黄铁矿±闪锌矿＋石英（Ⅲ）及石英±方解石（Ⅳ）4个阶段。系统的流体包裹体岩相学、包裹体组分析、包裹体显微测温研究表明，矿床初始成矿流体为高温、中低盐度（490~550℃，盐度（w（NaC1））2%~10%，50~62 MPa）均匀的NaCl-H₂O体系热液，δ¹⁸O_H2O-SMOW（2.21‰）及δD_H2O-SMOW（-68.9‰）表明其主要来源于岩浆热液；成矿流体上升并不断汇聚于容矿断裂空间，伴随温度、压力降低（380~460℃，26~40 MPa→360~420℃，25~30 MPa）而进入两相不混溶区，流体开始发生沸腾→强烈沸腾作用，导致成矿元素Mo大量沉淀富集成矿，成矿晚期残余流体与大气降水混合（δ¹⁸O_H2O-SMOW为-2.41‰~2.51‰，δD_H2O-SMOW为-110.1‰~-105.5‰），矿床属燕山早期中高温岩浆热液型钼矿床。  相似文献   

内蒙古二连盆地中部古河道型铀矿床中烃类流体特征与铀成矿关系     

赵兴齐  秦明宽  范洪海  刘武生  康世虎  张字龙  周飞  蔡亚  史清平 《地球学报》2019,40(3):405-416

通过对二连盆地中部下白垩统赛汉组上段古河道型铀矿床砂岩中的酸解烃特征进行分析,探讨了酸解烃中烃类气体组成特征、成因及来源,并结合该区铀矿分布富集的地质特征初步探讨了该区油气与砂岩型铀成矿关系。结果表明,赛汉组上段古河道砂体中CH_4及C_2~+含量与铀含量呈正比,且在氧化带、氧化还原过渡带和还原带内烃类含量具明显的分带性。酸解烃气体组成特征参数C_1/ΣC、C_1/C_2+、C_2/iC_4、C_2/C_3、iC_4/nC_4、iC_5/nC_5、ln(C_1/C_2)、ln(C_2/C_3)表明,研究区赛汉组上段古河道砂体中的烃类气为有机成因的油型气,烃类气主要处于成熟-高成熟阶段,主要为原油伴生气和原油裂解气。根据研究区烃源岩地球化学特征及生排烃史分析认为,该区下白垩统赛汉组上段古河道型铀矿床中烃类气主要来源于下白垩统阿尔善组(K_1ba)湖相腐泥型或偏腐泥型烃源岩,其次为腾一段(K_1bt~1)低熟-成熟阶段的湖相烃源岩。研究区深大断裂、不整合面、主砂体或裂隙是该区深部油气向上逸散的主要通道,深大断裂及不整合面附近应是该区砂岩型铀矿找矿的重点方向;油气在该区古河道砂岩型铀成矿作用过程中具有吸附作用、还原作用和保矿作用,区内砂岩型铀成矿期次、油气聚散史明显受控于晚白垩世末—古新世期的反转构造作用。  相似文献   

基于空间插值的浙江省城市流时空演变特征研究          下载免费PDF全文

魏国恩  贺清云  朱翔  欧阳晓 《干旱区地理》2019,42(1):215--222

为了探寻发达省份内城市间相互作用的时空特征，该文以浙江省为样本单元，选取2005、2010年和2015年3个时间截面，采用反距离权重法和空间插值手段，从城市流强度视角展开了实证分析。结果表明：（1） 城市间的联系在不断加强，期间城市流强度值随时间的推移而整体得到提升，空间上由初始的“中心点”通过发展扩散向“中心域”转变，中心城市的辐射带动作用开始发挥成效。（2）结构上呈现出相对稳定的北高南低的分布格局，以杭州市为龙头，宁波为副核心，温州、绍兴、舟山为重要节点的多中心城市网络结构雏形初步形成。（3） 城市流强度的空间分异特征分析明显，但分异程度有了些许的改善，侧面说明空间上由初始的“中心点”通过发展扩散向“中心域”转变的基本观点。最后就浙江省如何加强省内城市间“流”的规模性、区域协调性和可持续性展开了讨论。  相似文献   

绿帘石记录俯冲带变质流体活动   总被引：1，自引：0，他引：1  

唐盼  郭顺 《岩石学报》2019,35(7):2045-2060

俯冲带是连接地球表生圈层和深部圈层的关键纽带,深刻影响着地球内部的运行方式和人类宜居环境。俯冲板片脱水释放的高压-超高压变质流体控制着俯冲带诸多重要地质过程,如地幔楔交代和部分熔融、岛弧岩浆活动、中/深源地震以及地球内部的元素迁移和分异等等。深入了解这些流体的源区、运移、成分和物理化学条件是理解这些流体性质和行为的前提和关键。绿帘石是俯冲带变质岩中一个常见的含水造岩矿物,具有较宽广的稳定温压范围(绿片岩相-榴辉岩相)、较高的微量元素含量和缓慢的体扩散行为(如Sr、Pb、Th、U、Cr、V和LREE),能够指示俯冲带(多期)变质流体活动和地球化学效应。本文总结了近年来俯冲带变质绿帘石研究的主要进展及其在揭示俯冲带流体活动方面的重要应用,包括探究俯冲带流体的起源、成分特征、运移方式、氧逸度条件、交代效应和多期次结晶行为。这些研究表明绿帘石是一个极好的变质流体活动记录器,能够为理解俯冲带流体活动和深部元素迁移提供关键信息。  相似文献   

四川米易海塔地区混合岩型铀矿流体包裹体特征     

郭锐  陈友良  刘凯鹏  郑玉文  胡漾 《矿物学报》2020,40(2):137-148

混合岩型铀矿是康滇地轴上最有希望取得找矿突破的铀矿类型,海塔地区的铀矿化即是该类型铀矿的典型代表。本文针对区内的长英质脉矿石、富晶质铀矿石英脉矿石和含矿热液石英脉中的石英流体包裹体进行了研究。结果表明,海塔地区混合岩型铀矿的成矿作用可分为2个阶段:早期混合岩化热液成矿阶段为高温、中低盐度流体,流体包裹体均一温度集中在380~540℃,盐度变化范围为16.15%~23.18%NaCl eqv,是区内铀成矿的主要阶段;晚期热液叠加改造成矿阶段为中低温、低盐度流体,流体包裹体均一温度集中在140~220℃,盐度变化范围为5.56%~23.18%NaCleqv,是区内富铀矿的形成阶段。流体包裹体的气相成分测试表明,长英质脉矿石石英包裹体中以CH4、CO2为主,其次为H2O和N2;而富晶质铀矿石英脉及含矿热液石英脉石英包裹体中以H2为主,部分含有CO2、CH4、H2O。氢、氧同位素研究表明,早期混合岩化成矿阶段的成矿流体可能为岩浆水与变质水的混合,而晚期热液叠加改造成矿阶段成矿流体中可能有大气降水的加入。  相似文献   

滇东南南秧田钨矿床白钨矿原位Sr同位素对成矿的指示     

王忠强  李超  张定才  江小均  周利敏  严清高 《岩矿测试》2020,39(2):285-299

南秧田钨矿床位于滇东南老君山W-Sn矿集区,地处扬子地块和印支地块的结合部位,地质背景复杂并遭受了多期岩浆活动和区域变质事件,其成矿时代和成因一直存在争议。本文对矽卡岩型和长石-石英脉型白钨矿开展了年代学、原位微量元素、Sr同位素研究,分析了两类白钨矿年龄、成因以及物质来源的差异。结果表明,长石-石英脉内与白钨矿共生辉钼矿的Re-Os同位素等时线年龄为151.0±1.3Ma,明显晚于矽卡岩矿体年龄,属于后期成矿事件。矽卡岩型白钨矿的轻稀土富集、重稀土强烈亏损,Eu呈明显负异常(δEu=0.46),∑REE平均含量为65.60μg/g,Mo平均含量为240.16μg/g,Sr平均含量为883.43μg/g;长石-石英脉型白钨矿稀土呈Eu正异常(δEu=2.8)的平坦型,∑REE平均含量为194.40μg/g,Mo平均含量为16.01μg/g,Sr平均含量为129.26μg/g。以上两者微量、稀土元素含量的差别显示它们具有性质明显不同的流体来源,Eu异常指示矽卡岩型白钨矿形成于氧逸度较高的环境,长石-石英脉型白钨矿形成于还原性环境。矽卡岩白钨矿~(87)Sr/~(86)Sr值相对较低,并且比较均一,介于0.71319～0.71491之间,表明成矿流体主要来自岩浆热液;长石-石英脉型白钨矿~(87)Sr/~(86)Sr值较高且变化范围大,介于0.71537～0.72803之间,平均0.72079,呈现出变质流体特征。两种不同类型白钨矿Sr同位素都具有二元混合的特征,显示长石-石英脉型白钨矿对矽卡岩型白钨矿有叠加改造作用,成矿流体与围岩的强烈交代作用是白钨矿形成的关键。  相似文献   

Quantifying flow resistance in mountain streams using computational fluid dynamics modeling over structure-from-motion photogrammetry-derived microtopography     

Yunxiang Chen  Roman A. DiBiase  Nicholas McCarroll  Xiaofeng Liu 《地球表面变化过程与地形》2019,44(10):1973-1987

Flow resistance in mountain streams is important for assessing flooding hazard and quantifying sediment transport and bedrock incision in upland landscapes. In such settings, flow resistance is sensitive to grain-scale roughness, which has traditionally been characterized by particle size distributions derived from laborious point counts of streambed sediment. Developing a general framework for rapid quantification of resistance in mountain streams is still a challenge. Here we present a semi-automated workflow that combines millimeter- to centimeter-scale structure-from-motion (SfM) photogrammetry surveys of bed topography and computational fluid dynamics (CFD) simulations to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. The workflow was applied to three field sites of gravel, cobble, and boulder-bedded channels with a wide range of grain size, sorting, and shape. Large-eddy simulations with body-fitted meshes generated from SfM photogrammetry-derived surfaces were performed to quantify flow resistance. The analysis of bed microtopography using a second-order structure function identified three scaling regimes that corresponded to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation σ_z of detrended streambed elevation normalized by water depth, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance and is furthermore tied to the characteristic length scale of rough surface-generated vortices. Horizontal length scales and surface complexity are secondary controls on flow resistance. A new resistance predictor linking water depth and vertical roughness scale, i.e.  H/σ_z, is proposed based on the comparison between σ_z and the characteristic length scale of vortex shedding. In addition, representing streambeds using digital elevation models (DEM) is appropriate for well-sorted streambeds, but not for poorly sorted ones under shallow and medium flow depth conditions due to the missing local overhanging features captured by fully 3D meshes which modulate local pressure gradient and thus bulk flow separation and pressure distribution. An appraisal of the mesh resolution effect on flow resistance shows that the SfM photogrammetry data resolution and the optimal CFD mesh size should be about 1/7 to 1/14 of the standard deviation of bed elevation. © 2019 John Wiley & Sons, Ltd.  相似文献   

Ore Genesis and Tectonic Significance of the Xiaojiashan Tungsten Deposit,Eastern Tianshan,Xinjiang, China: Evidence from Geology,Fluid Inclusions,and Stable Isotope Geochemistry     

Yunfei Zhou  Jiuhua Xu  Lihua Shan  Xihui Cheng  Yueping Deng  Wenhuan Feng  Lingxiao Qiao 《Resource Geology》2019,69(1):43-64

The Xiaojiashan tungsten deposit is located about 200 km northwest of Hami City, the Eastern Tianshan orogenic belt, Xinjiang, northwestern China, and is a quartz vein‐type tungsten deposit. Combined fluid inclusion microthermometry, host rock geochemistry, and H–O isotopic compositions are used to constrain the ore genesis and tectonic setting of the Xiaojiashan tungsten deposit. The orebodies occur in granite intrusions adjacent to the metamorphic crystal tuff, which consists of the second lithological section of the first Sub‐Formation of the Dananhu Formation (D₂d ₁²). Biotite granite is the most widely distributed intrusive bodies in the Xiaojiashan tungsten deposit. Altered diorite and metamorphic crystal tuff are the main surrounding rocks. The granite belongs to peraluminous A‐type granite with high potassic calc‐alkaline series, and all rocks show light Rare Earth Element (REE)‐enriched patterns. The trace element characters suggest that crystallization differentiation might even occur in the diagenetic process. The granite belongs to postcollisional extension granite, and the rocks formed in an extensional tectonic environment, which might result from magma activity in such an extensional tectonic environment. Tungsten‐bearing quartz veins are divided into gray quartz vein and white quartz veins. Based on petrography observation, fluid inclusions in both kinds of vein quartz are mainly aqueous inclusions. Microthermometry shows that gray quartz veins have 143–354°C of T_h, and white quartz veins have 154–312°C of T_h. The laser‐Raman test shows that CO₂ is found in fluid inclusions of the tungsten‐bearing quartz veins. Quadrupole mass spectrometry reveals that fluid inclusions contain major vapor‐phase contents of CO₂, H₂O. Meanwhile, fluid inclusions contain major liquid‐phase contents of Cl^?, Na⁺. It can be speculated that the ore‐forming fluid of the Xiaojiashan tungsten deposit is characterized by an H₂O–CO₂, low salinity, and H₂O–CO₂–NaCl system. The range of hydrogen and oxygen isotope compositions indicated that the ore‐forming fluids of the tungsten deposit were mainly magmatic water. The ore‐forming age of the Xiaojiashan deposit should to be ~227 Ma. During the ore‐forming process, the magmatic water had separated from magmatic intrusions, and the ore‐bearing complex was taken to a portion where tungsten‐bearing ores could be mineralized. The magmatic fluid was mixed by meteoric water in the late stage.  相似文献   

STUDY FOR ABNORMAL VARIATIONS OF UNDERGROUND FLUID IN LIJIANG AREA,YUNNAN PROVINCE BEFORE LUDIAN M_S6.5 EARTHQUAKE IN 2014     

YANG Zhu-zhuan  DENG Zhi-hui  YANG Yue-wen  DENG Sheng-chang  LI Qing 《地震地质》2018,40(2):480-498

The study is based on the underground fluid observation data in Lijiang area, northwest Yunnan Province. The data include the water level and temperature in Dangxiao well and Jinjia well, and the ion measurements in Ganze spring. Combining with the data of regional hydrogeology, rainfall, well structures, and the geothermal gradient, we analyzed the variations of each measurement item before the Ludian M_S6.5 earthquake on August 3, 2014 and discussed the possible mechanism for the abnormal variations. The water levels of both Dangxiao well and Jinjia well are influenced by local rainfall, but the former shows hysteresis according to rainy seasons and is the long trend influence; while the latter shows synchronization between high water level and rainy season, indicating good connection between well water and shallow aquifer. The recharge water for Dangxiao well is in relatively low temperature, and the temperature sensor is located at the major connecting section between the well water and the aquifer; the water temperature variation is mainly affected by the discharge status and variation of water level. The Jinjia well is always in static level, and the temperature sensor is below the major connecting section between the well water and aquifer, so the water temperature is affected little by water level variations and in smooth fluctuation. The recharge source for Ganze spring can generally increase the contents of calcium and magnesium ions, so does the conductivity. The water level data of Dangxiao well since 2012 are decomposed with wavelet technique. The results, excluding such high-frequency components as the noise and the semidiurnal and daily wave components influenced by earth tide, are further processed with difference method in order to eliminate the trend effect. The results show that the relative change of water level is enhanced and in relatively rapid increase before the Ludian M_S6.5 earthquake; the corresponding water temperature values are high. The tendency of water level in Jinjia well displays descending, while the corresponding water temperature shows ascending. The content of calcium ion, magnesium ion, bicarbonate ion, and conductivity of Ganze spring are descending, while the content of fluoride ion is ascending. The abnormal variations of underground fluid in Lijiang area appeared in turns and were accompanied with minor earthquakes before Ludian M_S6.5 earthquake, which indicates enhancing of regional stress and increasing of fluid activity.  相似文献