Landform‐oriented flow‐routing algorithm for the dual‐structure loess terrain based on digital elevation models

The loess landform in the Loess Plateau of China is with typical dual structure, namely, the upper smooth positive terrain and the lower cliffy negative terrain (P–N terrain for short). Obvious differences in their morphological feature, geomorphological mechanism, and hydrological process could be found in the both areas. Based on the differences, a flow‐routing algorithm that separately addresses the dual‐structure terrain would be necessary to encompass this spatial variation in their hydrological behaviour. This paper proposes a mixed flow‐routing algorithm to address aforementioned problems. First, the loess landform surface is divided into P–N terrains based on digital elevation models. Then, specific catchment area is calculated with the new algorithm to simulate the water flows in both positive and negative terrain areas. The mixed algorithm consists of the multiple flow‐routing algorithm (multiple‐flow direction) for positive areas and the D8 algorithm for negative areas, respectively. The approach is validated in two typical geomorphologic areas with low hills and dense gullies in the northern Shaanxi Loess Plateau. Four indices are used to examine the results, which show that the new algorithm is more suitable for loess terrain in simulating the spatial distribution of water accumulation, as well as in modeling the flow characteristics of the true surface by considering the morphological structures of the terrain. Copyright © 2013 John Wiley & Sons, Ltd.     

Frequency analysis of nonstationary annual maximum flood series using the time‐varying two‐component mixture distributions

The most popular practice for analysing nonstationarity of flood series is to use a fixed single‐type probability distribution incorporated with the time‐varying moments. However, the type of probability distribution could be both complex because of distinct flood populations and time‐varying under changing environments. To allow the investigation of this complex nature, the time‐varying two‐component mixture distributions (TTMD) method is proposed in this study by considering the time variations of not only the moments of its component distributions but also the weighting coefficients. Having identified the existence of mixed flood populations based on circular statistics, the proposed TTMD was applied to model the annual maximum flood series of two stations in the Weihe River basin, with the model parameters calibrated by the meta‐heuristic maximum likelihood method. The performance of TTMD was evaluated by different diagnostic plots and indexes and compared with stationary single‐type distributions, stationary mixture distributions and time‐varying single‐type distributions. The results highlighted the advantages of TTMD with physically‐based covariates for both stations. Besides, the optimal TTMD models were considered to be capable of settling the issue of nonstationarity and capturing the mixed flood populations satisfactorily. Copyright © 2016 John Wiley & Sons, Ltd.     

高光谱影像概率分类向量机分类方法研究

从分析基于支持向量机和相关向量机的高光谱影像分类方法的优势和不足出发,将基于概率分类向量机的方法用于高光谱影像分类试验。在贝叶斯理论框架下,概率分类向量机为基函数权值引入截断Gauss先验概率分布,使得不同类别的基函数权值具有不同符号的先验分布,并利用EM算法进行参数推断,得到足够稀疏的概率模型,弥补了相关向量机选取错误类别的样本作为相关向量的不足,从而有效地提高了模型的分类精度和稳定性。OMIS和PHI影像分类试验表明,概率分类向量机能够很好地应用在高光谱影像分类。     

新元古代扬子—华夏陆块拼合带：来自华南重磁异常的启示

扬子和华夏两大陆块是构成华南大陆的最基本单元, 但它们的拼合带位置（尤其是西延位置）是人们长期争论的焦点。本文以国家专项“深部探测技术与实验研究”探测得到的深反射地震剖面以及华南大陆的地质资料为约束, 对重、 磁异常作地壳构造融合解译, 追踪扬子—华夏陆块拼合带。由于华南大陆广泛发育具有剩磁多期、 多类的火山—侵入岩, 本文将磁异常换算为受剩磁影响小的解析信号作构造解译, 减小剩磁造成的地质解释偏差。研究认为, 扬子与华夏两陆块的拼合带东界为鹰潭—萍乡—衡阳—贺州—北海一线, 而西界为宜昌—张家界—铜仁—都匀—百色一线, 鹰潭以东和以北的拼合带位置因为受大规模岩浆岩的干扰而不清。     

Fluid Inclusion and Stable Isotope Geochemistry of the Shangxu Gold Deposit, Northern Tibet

正Objective The Shangxu gold deposit is located in the south of the middle Bangong-Nujiang suture zone in northern Tibet.The origin of this deposit as an orogenic gold deposit is debatable.The study of the Shangxu deposit has a profound implication on gold exploration in the BangongNujiang metallogenic belt and can also improve our understanding of gold mineralization in northern Tibet.     

黑河新生地区中侏罗世花岗质岩石锆石U-Pb年龄、地球化学特征及岩石成因

黑河新生地区西古兰河以北二长花岗岩的LA-ICP-MS锆石U-Pb同位素测试结果表明,其形成时代为中侏罗世((163.8±1)Ma)。这些中侏罗世二长花岗岩属于弱过铝质高钾钙碱性系列的Ⅰ型花岗岩,明显富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Zr、Hf、Nb、Ta),元素Sr具有明显的负异常,表明其原始岩浆起源于地壳火成岩的部分熔融。结合区域资料同时代火成岩的组合特征和古太平洋板块的构造演化,认为该二长花岗岩形成于活动大陆边缘,而其形成的地球动力学背景可能为古太平洋板块向欧亚板块俯冲造山后的伸展环境。     

湘南—桂东北地区寒武—奥陶纪沉积岩碎屑锆石U-Pb年代学特征及其地质意义

本文利用LA-ICP-MS分析技术,对湘南—桂东北地区寒武纪和奥陶纪沉积岩进行了碎屑锆石U-Pb年代学研究。获得有效年龄数据239组,年龄值变化范围较大(3146~474 Ma),主要集中分布于2633~2473 Ma(峰值2500Ma),1880~1521 Ma(峰值1650 Ma),1146~911 Ma(峰值970 Ma),896~720 Ma(峰值800 Ma)和682~474 Ma(峰值520 Ma)5个时间段。4件样品均记录了古太古代—中太古代年龄信息,同时以1146~911 Ma和896~720 Ma两个时间段年龄最集中,反映全球Grenville造山事件和全球Rodinia超大陆裂解事件对研究区影响显著。此外,本次还获得大量泛非期(520 Ma左右)锆石年龄,认为全球泛非事件对华夏地块及其邻区影响显著,反映华夏地块与冈瓦纳大陆可能有一定亲缘性。结合前人资料,认为研究区位于华夏地块和扬子地块西南段碰撞拼合带,研究区地层同时接受两地块物质沉积,物源主要来自华夏地块。     

对湖北大洪山地区一套紫红色砂-砾岩系沉积年代的再认识——碎屑锆石U-Pb年龄及其地质意义

湖北大洪山地区花山群六房咀组之上不整合覆盖了一套紫红色砂-砾岩。这套岩石的沉积时代存在争议,一种观点认为是南华纪早期;另一种观点认为是晚侏罗世。利用LA-ICP-MS分析技术,对这套碎屑沉积岩进行了碎屑锆石U-Pb测年,获得有效年龄数据125组,年龄值变化范围较大(3223~771Ma),主要集中于新太古代末—古元古代早期(约2500Ma)、古元古代(约2000Ma)和新元古代(约800Ma)3个时间段。对比鄂东南地区和三峡地区莲沱组岩石学特征和碎屑锆石年龄分布特征,认为其具有相似的物源,这套岩系沉积时代应该为南华纪早期而非晚侏罗世。综合分析扬子地块的前寒武纪年龄,认为扬子地块可能存在大量未岀露的新太古代末—古元古代早期(约2500Ma)基底,约2500Ma的岩石应该是扬子地块深部基底的重要组成部分。扬子地块存在广泛的古元古代(约2000Ma)岩浆活动,这期岩浆活动可能是Columbia超大陆聚合在扬子地块的响应。新元古代(约800Ma)扬子地块北缘存在Rodinia超大陆裂解同期裂谷,裂谷内基性岩可能为大洪山地区南华纪地层中基性岩砾石的物源。     

Dynamics and responses of vegetation to climatic variations in Ziya-Daqing basins,China

Examining the direct and indirect effects of climatic factors on vegetation growth is critical to understand the complex linkage between climate change and vegetation dynamics. Based on the Moderate Resolution Imaging Spectroradiometer(MODIS) Normalized Difference Vegetation Index(NDVI) data and meteorological data(temperature and precipitation) from 2001 to 2012, the trend of vegetation dynamics were examined in the Ziya-Daqing basins, China. The path analysis was used to obtain the information on the relationships among climatic factors and their effects on vegetation growth. It was found that the trends of growing season NDVI were insignificant in most plain dry land, while the upward trends were significant in forest, grass and dry land in Taihang Mountains. According to the path analysis, in 23% of the basins the inter-annual NDVI variation was dominated by the direct effect of precipitation, in 5% by the direct effects of precipitation and temperature, and in less than 1% by the direct effect of temperature or indirect effects of these two climatic factors. It indicated that precipitation significantly affected the vegetation growth in the whole basins, and this effect was not regulated by temperature. Precipitation increase(especially in July, August and September) was favorable to greenness enhancement. Summer temperature rising showed negative effect on plant productivity enhancement, but temperature rise in April was beneficial for the vegetation growth. When April temperature increases by 1℃, the onset date of greenness for natural vegetation will be 2 days in advance. There was a lag-time effect of precipitation or temperature on monthly NDVI for all land use types except grass.