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1.
扎拉格阿木铜矿床位于锡林浩特地块北部边缘,矿体赋存于二叠纪砂质板岩和角砾岩中,受NE向断裂控制,为中温热液脉型铜矿床。本文通过流体包裹体和C?H?O?S?Pb同位素地球化学研究手段,来探讨扎拉格阿木铜矿成矿机制。成矿热液期存在5个成矿阶段:钾长石阶段、石英?绢云母阶段、石英?黄铁矿阶段、石英?多金属硫化物阶段、石英?方解石阶段。其中石英?多金属硫化物阶段为主成矿阶段,本阶段主要发育富液相、富气相、含子矿物包裹体;富液相包裹体均一温度与盐度分别为:138~289℃和2.06%~16.11% NaCl eqv;含子矿物包裹体均一温度与盐度分别为:320~374℃和32.68%~39.81% NaCl eqv,包裹体气体成分除少量CO2以外,均为H2O。H?O同位素分析表现为,石英中的〖δO〗^18值变化范围-8.5‰~7.5‰,流体的δD值变化范围为-116‰~-98‰,暗示早阶段成矿流体主要为岩浆热液,晚期伴有大气降水混入。C?O同位素分析表明,δ13C值为-6.9‰~ -10.1‰,δ18OSMOW介于2.5‰~11.7‰,在δ18O?δ13C 图上数据点落在岩浆水与大气水的中间区域。矿石硫化物的δ34S值介于-4.5‰~1.5‰,指示具有幔源岩浆硫的特征。矿石硫化物Pb同位素的208Pb/204Pb、207Pb/204Pb和206Pb/204Pb比值分别为38.034~38.609、15.497~15.655和18.141~18.446,推测Pb具有地幔来源的特点并伴有地壳或造山带Pb混入。成矿过程中伴随着流体沸腾作用,成矿物质沉淀受早期形成的岩浆热液与后加入大气降水混合的影响。  相似文献   
2.
燕山期甘坊复式岩体是宜丰锂铌钽稀有金属矿田重要的赋矿岩体,细晶岩作为甘坊岩体晚阶段岩浆演化的产物,与区内细晶岩型稀有金属成矿作用关系密切,但前人对该类岩石及其成矿作用特征研究较薄弱。本文以甘坊岩体南侧同安矿区内的花岗细晶岩为研究对象,对其展开系统的岩相学、锡石U-Pb年代学和全岩地球化学分析。锡石U-Pb定年结果表明,同安花岗细晶岩形成时代为138.3 Ma。全岩地球化学分析结果显示,该类岩石具高磷铝、富碱钙、贫镁铁钛的特征,且A/CNK值(1.71~1.88)较高,σ值(1.40~1.72)较低,属于典型的强过铝质、高钾钙碱性岩石。全岩微量及稀土元素成分显示,同安花岗细晶岩具有稀土元素强烈亏损,相对富集Rb、U、Nb、Ta、Pb、P、Hf和明显亏损Ba、Th、Sr、Ti等元素的特征。综上所述,同安花岗细晶岩属高分异的S型花岗岩,来源于地壳浅部变沉积岩物质的部分熔融。在演化过程中,经历过早期高度结晶分异过程和晚期的岩浆-热液相互作用,其中早期的高度结晶分异过程对Li成矿起到了初始富集的作用,而演化晚期的岩浆-热液相互作用才是Li元素高度富集并成矿的关键。  相似文献   
3.
胶东型金矿具有独特的成矿特征和成因机制,不同于国际已知金矿类型。为了深化认识控制矿床形成、变化和保存的地质要素及成矿过程,本文综合分析了胶东半岛晚中生代岩浆作用、构造活动和成矿特征及其构造背景,提出该区深部岩浆活动与地壳快速隆升及浅部变质核杂岩、张性断层、断陷盆地等伸展构造,共同控制了以Au为主的矿床成矿系列及成矿演化过程,谓之热隆-伸展成矿系统。阐明了晚中生代岩浆演化过程中的元素变化规律,发现了金矿化蚀变带中的低Ba、Sr含量异常及早白垩世胶东地壳中金丰度的显著变化,揭示了壳幔物质混合和伟德山型花岗岩岩浆活动对金成矿的贡献。认为这一成矿系统形成于古太平洋板块俯冲后撤的后俯冲伸展环境,由于软流圈上涌导致岩石圈地幔性质由富集向亏损转化,从而引起岩浆岩地球化学特征变化,地球化学元素重新调整,幔源含金流体与由重熔下地壳析出的壳源含金流体混合形成富金流体库,并产生贫金花岗岩。大规模岩浆活动为成矿元素的活化、迁移提供了热动力条件,上地壳伸展产生的断裂构造则为成矿元素聚集提供了良好空间。热隆-伸展成矿系统是中国东部晚中生代重要的成矿系统。  相似文献   
4.
宋雪龙  段士刚  蒋宗胜 《地质学报》2023,97(7):2241-2260
塔尔塔格铁矿是新疆西天山阿吾拉勒海相火山岩型铁成矿带内的一处中型铁矿床,其铁矿体呈透镜状产于粗安玢岩内顶部,在揭示海相火山岩中铁矿床与侵入岩关系方面具有重要意义。该铁矿床发育典型的磁铁矿 磷灰石组合,基本不含硫化物,矿石以似斑状、浸染状、球粒状和晶洞等构造类型为特色,磁铁矿内发育由条带状或叶片状钛铁矿和钛氧化物构成的出溶结构,并有少量的榍石、钍石、萤石等副矿物与之共生,矿床地质特征表明该矿床为典型的与富碱、中性侵入岩有关的IOA(iron oxide apatite)型铁矿床。该矿床围岩英安岩、赋矿粗安玢岩与成矿后正长花岗岩的锆石SHRIMP U Pb同位素加权平均年龄分别为311. 3±1. 4 Ma、304. 7±2. 9 Ma和301. 1±2. 8 Ma,铁矿石样品中与磁铁矿共生的榍石的LA ICP MS U Pb同位素加权平均年龄为302. 3±4. 0 Ma和303. 7±4. 2 Ma,成岩成矿年龄高度吻合,进一步确定其在晚石炭世晚期成矿。本文根据地质特征认为该矿床矿石是由粗安玢岩顶部富铁挥发分聚集而形成的,并初步提出“超浅成侵入岩顶部富挥发分囊体”成矿模型,即富碱、中性岩体超浅成侵位导致挥发分在岩体顶部迅速聚集形成多处富铁和挥发分的囊体,岩体冷凝固结的同时磁铁矿快速结晶成矿。塔尔塔格“IOA型”型铁矿的成因厘定,不仅表明海相火山岩型铁矿与IOA型铁矿可能存在成因联系,还暗示了海相火山岩型铁成矿带内具有寻找IOA型铁矿的潜力。  相似文献   
5.
Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (FV), stemflow funnelling ratio (FR), and stemflow ratio (F%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the FV, FR and F% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on FV and F% was more obvious under low intensity rainfall types. At the inter-event scale, FV had a strong positive linear correlation with rainfall amount (GP) and event duration (DE) for both tree species, whereas FR and F% had a positive logarithmic correlation with GP and DE only under high-intensity, short-duration rainfall type. FR and F% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   
6.
研究汛期短时强降水特征,对于南方低山丘陵地区山洪灾害的预报具有重要指导意义。以怀化市为研究区域,基于该区域11个国家站和403个区域自动气象站的2012-2017年4-9月期间逐小时降水量以及相对应的NCEP资料,分析了怀化市短时强降水的时空分布特征,得出了产生短时强降水天气系统模型,结果显示:①汛期短时强降水发生频率较高,时间集中,分布不均。主要出现在5~7月,占4~9月的72.9%,其次在8~9月;北部频数多,中南部少,西部最少,辰溪、麻阳和怀化三县交界处及沅陵县的大合坪附近是频发区域。②短时强降水日变化呈单峰型,4~10时最容易发生,峰值在8时,谷值在23时。③强度越强出现的频次越少;北部的强度和次数大于其它区域;50~79.9 mm/h,占总站数的68.4%;各月国家站的极值乘以2约等于区域站极值。④低涡型短时强降水出现概率最高,低涡位置和移动路径是短时强降水预报的关键点。  相似文献   
7.
Base flows are important for tropical regions with pronounced dry seasons, which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May–December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December–April dry season. Understanding this unusual base flow jump (BFJ) behaviour is critical to improve water provisioning in the seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area, and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven subcatchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross-correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall-related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross-correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in the tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment.  相似文献   
8.
Up-to-date forest inventory information relating the characteristics of managed and natural forests is fundamental to sustainable forest management and required to inform conservation of biodiversity and assess climate change impacts and mitigation opportunities. Strategic forest inventories are difficult to compile over large areas and are often quickly outdated or spatially incomplete as a function of their long production cycle. As a consequence, automated approaches supported by remotely sensed data are increasingly sought to provide exhaustive spatial coverage for a set of core attributes in a timely fashion. The objective of this study was to demonstrate the integration of current remotely-sensed data products and pre-existing jurisdictional inventory data to map four forest attributes of interest (stand age, dominant species, site index, and stem density) for a 55 Mha study region in British Columbia, Canada. First, via image segmentation, spectrally homogenous objects were derived from Landsat surface-reflectance pixel composites. Second, a suite of Landsat-based predictors (e.g., spectral indices, disturbance history, and forest structure) and ancillary variables (e.g., geographic, topographic, and climatic) were derived for these units and used to develop predictive models of target attributes. For the often difficult classification of dominant species, two modelling approaches were compared: (a) a global Random Forests model calibrated with training samples collected over the entire study area, and (b) an ensemble of local models, each calibrated with spatially constrained local samples. Accuracy assessment based upon independent validation samples revealed that the ensemble of local models was more accurate and efficient for species classification, achieving an overall accuracy of 72% for the species which dominate 80% of the forested areas in the province. Results indicated that site index had the highest agreement between predicted and reference (R2 = 0.74, %RMSE = 23.1%), followed by stand age (R2 = 0.62, %RMSE = 35.6%), and stem density (R2 = 0.33, %RMSE = 65.2%). Inventory attributes mapped at the image-derived unit level captured much finer details than traditional polygon-based inventory, yet can be readily reassembled into these larger units for strategic forest planning purposes. Based upon this work, we conclude that in a multi-source forest monitoring program, spatially localized and detailed characterizations enabled by time series of Landsat observations in conjunction with ancillary data can be used to support strategic inventory activities over large areas.  相似文献   
9.
辽北法库变质杂岩的形成时代、大地构造属性及其与长春-延吉缝合带的形成过程一直以来都是众多地质学者关注的重要科学问题。本文试图通过U-Pb年代学以及物质组成分析、变形变质作用特点分析和区域对比的方法来建立法库变质杂岩的时空格架,大地构造归属及区域构造演化。通过详细的野外工作和镜下分析得到法库变质杂岩存在至少两期变形作用特点及角闪岩相-高绿片岩相至低绿片岩相的变质作用特点。通过对杂岩体中不同类型变质岩的锆石SHRIMP U-Pb年代学研究得到中志留世糜棱岩化黑云母花岗闪长岩原岩年龄为433±3Ma;晚志留世绢云长英质糜棱岩原岩年龄为423±5Ma;早二叠世绢云绿泥方解斜长糜棱岩原岩年龄为292±2Ma;早三叠世长英质糜棱岩原岩年龄为250±3Ma。通过区域对比,笔者认为法库变质杂岩为索伦-西拉木伦缝合带东延的一部分是长春-延吉缝合带的重要组成,其形成演化具有复合型造山的特点,具有复杂的构造演化史。  相似文献   
10.
陈炳翰  范建福  刘建楠 《地质学报》2023,97(4):1329-1341
富金斑岩-矽卡岩矿床产出了大部分碲资源,其他类型碲矿资源时空分布规律暂未明确。在全国矿产资源潜力动态评价项目开展过程中,本文对中国碲矿资源特征、碲矿类型、时空分布进行分析与归纳,初步总结了中国碲矿成矿规律。本文对中国碲矿的资源特征进行了介绍;收集了全国45个含碲矿床的资料,将中国碲矿分为碱性-偏碱性侵入岩型、卡林-类卡林型、浅成低温热液型、斑岩-矽卡岩型、造山型、铜镍硫化物型6大预测类型;将碲矿形成时代分为元古宙、古生代、中生代、新生代4个成矿期,划分了9个碲成矿带,即吉黑、华北陆块西缘、华北陆块北缘、辽东、秦岭、苏鲁、长江中下游、三江、南岭成矿带;厘定出34个与碲矿有关的成矿系列,建立了中国碲矿成矿谱系。综合研究所得,中国碲矿以晚古生代和中生代华北和东北地区的浅成低温热液型、斑岩-矽卡岩型、铜镍硫化物型矿床,小秦岭-熊耳山地区的造山型矿床,长江中下游和滇川黔地区的斑岩-矽卡岩型、铜镍硫化物型矿床为主。  相似文献   
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