Quantitative elemental mapping of granulite-facies monazite: Textural insights and implications for petrochronology     

Owen M. Weller  Simon Jackson  William G. R. Miller  Marc R. St-Onge  Nicole Rayner 《Journal of Metamorphic Geology》2020,38(8):853-880

Texturally complex monazite grains contained in two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry (using spot sizes ≤5 µm) to quantitatively determine the spatial variation in trace element chemistry (with up to 1,883 analyses per grain). The maps highlight the chemical complexity of monazite grains that have experienced multiple episodes of growth, resorption and chemical modification by dissolution–precipitation during high-grade metamorphism. Following detailed chemical characterization of monazite compositional zones, a related U–Pb data set is re-interpreted, allowing petrologically significant ages to be extracted from a continuum of concordant data. Synthesis of these data with pseudosection modelling of prograde and peak conditions allows for the temporal evolution of monazite trace element chemistry to be placed in the context of the evolving P–T conditions and major phase assemblage. This approach enables a critical evaluation of three commonly used petrochronological indicators: linking Y to garnet abundance, the Eu anomaly to feldspar content and Th/U to anatectic processes. Europium anomalies and Th/U behave in a relatively systematic fashion, suggesting that they are reliable petrochronological witnesses. However, Y systematics are variable, both within domains interpreted to have grown in a single event, between grains interpreted to be part of the same age population, and between samples that experienced similar metamorphic conditions and mineral assemblages. These observations caution against generalized petrological interpretations on the basis of Y content, as it suggests Y concentrations in monazite are controlled by domainal equilibria. The results reveal a c. 45 Myr interval between prograde metamorphism and retrograde melt crystallization in the study area, emphasizing the long-lived nature of heat flow in high-grade metamorphic terranes. Such long timescales of metamorphism would be assisted by the growth, retention and dominance of high-Th suprasolidus monazite, as observed in this study, contributing to the radiogenic heating budget of mid- to lower-crustal environments. Careful characterization of monazite grains suggests that continuum-style U–Pb data sets can be decoded to provide insights into the duration of metamorphic processes.  相似文献   

Cryospheric Changes and Their Impacts on Water Resources in the Belt and Road Regions     

Shichang Kang  Wanqin Guo  Tonghua Wu  Xinyue Zhong  Rensheng Chen  Min Xu  Jinlei Chen  Ruimin Yang 《地球科学进展》2020,35(1):1-17

“Belt and Road” regions include Asia, Europe and eastern and northern Africa, with a wide spatial distribution. The cryosphere is undergoing rapid changes in the Belt and Road regions with global warming, and has an important impact on water resources, ecosystems and Arctic waterways in these regions. This article reviewed recent cryospheric changes and associated impacts on water resources in the Belt and Road regions during the last decades. The main cognitions are as follows: \mathrm{①} Most glaciers are shrinking and glacier mass balances are most negative, but there are regional differences in the changes of glaciers. \mathrm{②} Global temperature rise has resulted in permafrost degradation, including a rise in permafrost temperature and decreasing permafrost thickness as well as an increase in active layer thickness. \mathrm{③} There is a significant decrease in snow cover extent and an increase in snow depth. Snow cover duration has shortened, the onset of snow cover has delayed, and the end of snow cover has advanced. However, there are still obvious regional differences in the changes of snow cover. \mathrm{④} Arctic sea ice has declined precipitously in both extent and thickness in summer, and multi-year sea ice has decreased，indicating the precipitous retreat of sea ice. The freeze-up date of some lakes has been delayed, the break-up date has advanced, and the ice cover duration of river/lake ice has significantly shortened. \mathrm{⑤} Glacial runoff has increased significantly in China. Snowmelt and permafrost degradation have also increased the basin runoff, which indicates the important impact of cryospheric changes on runoff. This study will provide a baseline and important scientific support for addressing climate change and regional sustainable development.  相似文献   

西昆仑玛尔坎苏石炭纪大型锰矿带构造背景与成矿条件     

张连昌  张帮禄  董志国  谢月桥  李文君  彭自栋  朱明田  王长乐 《吉林大学学报(地球科学版)》2020,50(5):1340-1357

西昆仑北段玛尔坎苏地区探明的大型碳酸锰成矿带，是我国近年最重要的找矿成果之一。该锰矿带构造上属北昆仑晚古生代弧后伸展盆地，其构造动力学背景为古特提斯洋向北俯冲于塔里木地块之下形成的弧盆体系。锰矿体主要发育于晚石炭世喀拉阿特河组含炭泥质灰岩夹薄层灰岩中。矿石中主要金属矿物为菱锰矿（75%~95%），次为软锰矿、硫锰矿及少量黄铁矿等。含锰岩系岩性和岩相学研究表明，玛尔坎苏锰矿带属典型的海相沉积锰矿床，其矿床成因可能与晚古生代半局限盆地沉积和海底热液活动有关。海底热液活动可能为成矿提供了丰富的物质来源。含锰岩系元素和同位素地球化学特征表明，玛尔坎苏锰矿沉淀时的水体环境为常氧条件，而矿层下盘（部分）岩系的岩性及地球化学特征反映其沉积时的水体环境为低氧—贫氧条件。玛尔坎苏锰矿带锰矿石具有负的δ¹³C值（-23.3‰~-10.0‰），推测有机质导致的还原作用是该锰矿由原生氧化锰在成岩期转化为菱锰矿和形成富锰矿的重要机制。  相似文献   

Lidar-aided analysis of boreal forest backscatter at Ku band     

《International Journal of Applied Earth Observation and Geoinformation》2020

This paper analyzes the backscatter of the microwave signal in a boreal forest environment based on a Ku -band airborne Frequency-Modulated Continuous Waveform (FMCW) profiling radar—Tomoradar. We selected a half-managed boreal forest in the southern part of Finland for a field test. By decomposing the waveform collected by the Tomoradar, the vertical canopy structure was achieved. Based on the amplitude of the waveform, the Backscattered Energy Ratio of Canopy-to-Total (BERCT) was calculated. Meanwhile, the canopy fraction was derived from the corresponding point cloud recorded by a Velodyne VLP-16 LiDAR mounted on the same platform. Lidar-derived canopy fraction was obtained by counting the number of the first/ the strongest returns versus the total amount of returns. Qualitative and quantitative analysis of radar-derived BERCT on lidar-derived canopy fraction and canopy height are investigated. A fitted model is derived to describe the Ku-band microwave backscatter in the boreal forest to numerically analyze the proportion contributed by four factors: lidar-derived canopy fraction, radar-derived canopy height, the radar-derived distance between trees and radar sensor and other factors, from co-polarization Tomoradar measurements. The Root Mean Squared Error (RMSE) of the proposed model was 0.0958, and the coefficient of determination R2 was 0.912. The fitted model reveals that the correlation coefficient between radar-derived BERCT and lidar-derived canopy fraction is 0.84, which illustrates that lidar surface reflection explains the majority of the profiling /waveform radar response. Thus, vertical canopy structure derived from lidar can be used for the benefit of radar analysis.  相似文献   

Tree species identification within an extensive forest area with diverse management regimes using airborne hyperspectral data     

《International Journal of Applied Earth Observation and Geoinformation》2020

Information on tree species composition is crucial in forest management and can be obtained using remote sensing. While the topic has been addressed frequently over the last years, the remote sensing-based identification of tree species across wide and complex forest areas is still sparse in the literature. Our study presents a tree species classification of a large fraction of the Białowieża Forest in Poland covering 62 000 ha and being subject to diverse management regimes. Key objectives were to obtain an accurate tree species map and to examine if the prevalent management strategy influences the classification results. Tree species classification was conducted based on airborne hyperspectral HySpex data. We applied an iterative Support Vector Machine classification and obtained a thematic map of 7 individual tree species (birch, oak, hornbeam, lime, alder, pine, spruce) and an additional class containing other broadleaves. Generally, the more heterogeneous the area was, the more errors we observed in the classification results. Managed forests were classified more accurately than reserves. Our findings indicate that mapping dominant tree species with airborne hyperspectral data can be accomplished also over large areas and that forest management and its effects on forest structure has an influence on classification accuracies and should be actively considered when progressing towards operational mapping of tree species composition.  相似文献   

贵州省沿河县耕地土壤酸化现状及改良对策   总被引：1，自引：0，他引：1       下载免费PDF全文

夏瑞  谢东明  张与伦 《贵州地质》2020,37(3):409-415

土壤酸化是耕地退化的一种表现形式，在酸性、强酸性土壤中，多数农作物的生长会受到影响，会明显降低作物的生产能力。本文通过对比沿河县1980—1981年第二次土壤普查和2017—2019年耕地质量地球化学调查评价成果数据，分析全县土壤酸化现状和规律。结果表明，全县耕地土壤pH值分布于399880之间，平均为610。与1980—1981年第二次土壤普查时期相比，全县主要耕地土壤类型pH平均值均有下降，其中黄壤pH值降幅为591%；石灰土降幅为759%，从中性下降为酸性；紫色土降幅为2209%，从碱性降为酸性；全县主要土地利用类型土壤酸化范围变大，主要从中性转化为酸性，酸性转化为强酸性，耕地土壤酸化程度加深，水田酸化程度高于旱地。建议通过推进测土配方施肥工作合理调整化肥施用比例，大力提高耕地土壤有机质含量，积极推广使用石灰、白云石、粉煤灰、碱渣、生物质碳等生物改良剂，因地制宜建立土壤改良示范点等多项对策来缓解和治理耕地土壤酸化。  相似文献   

西昆仑穆呼锰矿床地质特征、控矿因素及成矿模式     

董志国  张连昌  董飞羽  张帮禄  谢月桥  查斌  彭自栋  王长乐 《吉林大学学报(地球科学版)》2020,50(5):1358-1372

穆呼锰矿床位于西昆仑造山带玛尔坎苏锰矿带东段，研究程度相对薄弱。穆呼锰矿床的含矿地层为上石炭统喀拉阿特河组，自下而上可分为角砾灰岩、钙质杂砂岩和含炭质泥灰岩3个岩性段，具有完整的海侵层序特征，反映了由逐步断陷到稳定沉积的盆地演化过程。锰矿层赋存于第三岩性段炭质泥灰岩中，矿石矿物主要为化学组分纯净的泥晶菱锰矿。根据详细的矿相学观察并综合前人研究成果，笔者认为菱锰矿是初始沉淀的锰（氢）氧化物与有机质通过成岩反应形成的。这种成矿机制需要3个基本条件：丰富的锰质来源、氧化还原分层的海水和有机质的大量埋藏。在穆呼一带，有利于满足以上条件的主要控矿因素包括：伸展拉张的构造背景、强烈的海底热液活动、海侵事件和温暖潮湿的古气候。笔者根据w（Ba）-w（P₂O₅）图解并结合区域对比分析，初步认为穆呼锰矿床的成矿模式可能属于最小含氧量带扩张型。  相似文献   

Metamorphism and geochronology of garnet amphibolite from the Beishan Orogen,southern Central Asian Orogenic Belt:Constraints from P-T path and zircon U-Pb dating     

《地学前缘(英文版)》2020,11(4):1189-1201

Numerous lenses of garnet amphibolite occur in the garnet-bearing biotite-plagioclase gneiss belt in the Baishan area of the Beishan Orogen,which connects the Tianshan Orogen to the west and the Mongolia-Xing'anling Orogen to the east.The study of metamorphism in Beishan area is of great significance to explain the tectonic evolution of Beishan orogen.According to the microstructures,mineral relationships,and geothermobarometry,we identified four stages of mineral assemblages from the garnet amphibolite sample:(1) a pre-peak stage,which is recorded by the cores of garnet together with core-inclusions of plagioclase(Pl_1);(2) a peak stage,which is recorded by the mantles of garnet together with mantle-inclusions of plagioclase(Pl_2)+amphibole(Amp_1)+Ilmenite(Ilm_1)+biotite(Bt_1),developed at temperature-pressure(P-T) conditions of 818.9-836.5℃ and7.3-9.2 kbar;(3) a retrograde stage,which is recorded by garnet rims + plagioclase(Pl_3)+amphibole(Amp_2)+orthopyroxene(Opx_1)+biotite(Bt_2)+Ilmenite(Ilm_2),developed at P-T conditions of 796.1-836.9℃ and5.6-7.5 kbar;(4) a symplectitic stage,which is recorded by plagioclase(Pl_4)+orthopyroxene(Opx_2)+amphibole(Amp_3)+biotite(Bt_3) symplectites,developed at P-T conditions of 732 ±59.6℃ and 6.1 ±0.6 kbar.Moreover,the U-Pb dating of the Beishan garnet amphibolite indicates an age of 301.9 ±4.7 Ma for the protolith and 281.4±8.5 Ma for the peak metamorphic age.Therefore,the mineral assemblage,P-T conditions,and zircon U-Pb ages of the Beishan garnet amphibolite define a near-isothermal decompression of a clockwise P-T-t(Pressure-Temperature-time) path,indicating the presence of over thickened continental crust in the Huaniushan arc until the Early Permian,then the southern Beishan area underwent a process of thinning of the continental crust.  相似文献   

“一带一路”建设背景下重庆与东盟国家贸易格局演变和影响因素分析     

杜瑜  宗会明 《世界地理研究》2020,29(4):697-707

“贸易畅通”是“一带一路”建设的重要内容，重庆作为中国西部地区内陆开放高地，贸易发展优势明显。运用贸易强度指数和HM指数，分析2001—2017年重庆与东盟国家贸易格局和贸易依赖程度，并分析影响重庆与东盟国家贸易格局的影响因素。结果表明：①重庆与东盟国家贸易联系紧密，增长速度快，贸易总额在“一带一路”沿线六大区域中始终保持领先地位；②马来西亚和泰国成为重庆与东盟国家中最重要的贸易伙伴，越南、新加坡、菲律宾和印度尼西亚紧随其后，而与缅甸、柬埔寨、老挝和文莱的贸易总额较少；③在进口方面，形成以马来西亚、泰国和越南为首的多元进口格局，泰国和越南进口伙伴地位上升。在出口方面，形成以马来西亚为首的多元出口新格局，越南出口地位下降；④在市场相互依赖程度方面，重庆出口对东盟国家特别是马来西亚和新加坡贸易市场的重要性程度上升，而对东盟国家市场依赖程度较小；⑤产业结构、贸易通道、文化交流和政策等是影响重庆与东盟国家贸易格局的重要影响因素。  相似文献   

中国海洋生态环境特征分析          下载免费PDF全文

林天维  孙子钧  柴清志  严志宇  孙冰 《海洋开发与管理》2020,37(5):36-40

随着社会不断地发展，资源需求不断增加，海洋生态环境污染日益严重的问题开始逐渐显现出来。文章对近18年的相关数据进行计算研究，从水体质量、富营养化、赤潮情况等方面对我国海洋水体环境进行了分析，指出虽然我国四大海区水质问题逐年改善，但南海的近岸污染问题、东海和渤海的赤潮问题等仍需加以重视。文章的大量数据分析为我国建立更符合国情的海洋生态环境治理决策提供了参考。  相似文献