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   

大数据驱动下的数字古地理重建：现状与展望     

张蕾  钟瀚霆  陈安清  赵应权  黄可可  李凤杰  黄虎  刘宇  曹海洋  祝圣贤  穆财能  侯明才  JAMES G. Ogg 《高校地质学报》2020,26(1):73

古地理学是一门强数据依赖性学科,古地理重建作为古地理学的核心任务之一,着眼于研究地质历史时期地球表面的地理、生物、气候面貌及其演化规律。随着大数据时代的来临,海量古地理数据的不断积累和计算机技术的高速发展使得标准化、智能化的数字古地理重建成为可能。文章通过介绍国内外与古地理相关的代表数据库及团队,总结其优缺点,提出大数据驱动下的数字古地理重建核心思路:(1)建立标准化的古地理学知识体系;(2)建立开放互动、动态更新的古地理数据库,并利用机器阅读技术等拓展数据来源;(3)建立标准化的古地理学数据质量控制体系;(4)利用机器学习技术建立各类型古地理重建模型,深度挖掘数据;(5)以可实时更新的智能数字地图集或多维动画形式输出成果。  相似文献   

Morphometry and Morphostructural Studies of the Parts of Gola River and Kalsa River Basins,Chanphi-Okhalkanda Region,Kumaun Lesser Himalaya,India     

Lal. Kumar  Joshi  G.  Agarwal  K. K. 《Geotectonics》2020,54(3):410-427

Geotectonics - Study of morphometric parameters such as stream length (Lu) and stream length ratios (Rl), bifurcation ratio (Rb), drainage density (D), form factor (Rf), circularity ratio (Rc),...  相似文献   

Structure of Prominences with Normal and Inverse Polarities     

Korolkova  O. A.  Solov’ev  A. A. 《Geomagnetism and Aeronomy》2019,59(7):858-863

Geomagnetism and Aeronomy - Based on the measurements of their magnetic fields, solar prominences can be divided into two types: filaments with normal (N) or inverse (I) polarity. In an N-type...  相似文献   

Temporal and spatial variation of soil erosion in wooded rangelands of southwest Spain     

Judit Rubio-Delgado  Susanne Schnabel  Álvaro Gómez-Gutiérrez  Joaquín Francisco Lavado-Contador 《地球表面变化过程与地形》2019,44(11):2141-2155

Changes in land use are common in Mediterranean areas and are reported as having produced changes in the intensity of soil erosion. Dehesas are rangelands with a disperse tree cover, widespread in the south-western part of the Iberian Peninsula and similar ecosystems are also common in other areas with a Mediterranean climate. The aim of the present study is to analyse temporal and spatial variations of soil erosion rates estimated along three hillsides, located in two farms (Buitrera and Parapuños) in southwest Spain. To understand the temporal variation, soil erosion rates were studied in light of land use-management changes that took place during the last few centuries. Results indicate very low erosion rates prior to the 18^th century in both farms. In Buitrera, a first increase of soil loss rates was identified during the period 1831-1897, amounting to 7.4 t ha^-1 y^-1. A further increase took place during the 20^th century, reaching a mean erosion rate of 29.1 t ha^-1 y^-1. In Parapuños, data points to a significant increase from 1881 onwards, with an estimated mean erosion rate of 18.5 t ha^-1 y^-1. Those increases were presumably connected with an intensification of land use, such as cultivation and excessive livestock populations. Regarding spatial variation, the bare surface and the erosive power of run-off along the hillsides accounts for 76% of the soil erosion rates dispersion. At a local scale, the variability of erosion rates could not be explained, because of (i) uncertainty related to the micromorphology of the past soil surface and (ii) the role of tillage erosion in the past. However, the results obtained offer valuable data on the temporal and spatial variation of erosion rates in dehesas at the hillslope scale and a similar approach could be used for other rangelands with a disperse tree cover. © 2019 John Wiley & Sons, Ltd.  相似文献   

Zooplankton Size Structure in the Kolsay Mountain Lakes (Kungei Alatau,Southeastern Kazakhstan) and Its Relationships with Environmental Factors     

Krupa  E. G.  Barinova  S. S.  Romanova  S. M. 《Water Resources》2019,46(3):403-414

Water Resources - The size structure of zooplankton in Kolsay Lakes was characterized with the use of the values of Clarke W-statistic, ?-Shannon–Weaver, and the average individual mass...  相似文献   

Hydrochemical Features of Lake Itcul Ecosystem and the State of Phytoplankton     

Likhachev  S. F.  Sibirkina  A. R.  Dvinin  D. Yu.  Voitovich  G. A. 《Water Resources》2019,46(3):415-421

Water Resources - The results of hydrochemical analysis of water in Lake Itkul, which is a natural monument of Chelyabinsk oblast and an important recreation and tourist object for the population...  相似文献   

Zoning of Groundwater Quality for Plain Garmsar in Iran     

Abouzar Nasiri  Shirocova  Vera A.  Zareie  Sajad 《Water Resources》2019,46(4):624-629

Water Resources - Groundwater performs an important role in the territory of the plains Garmsar. In this study, on the basis of water samples, which were obtained from the wells of the region,...  相似文献   

The Natural Resource Management Planning Portal: Perspectives for NRM Planning and Reporting     

Birgita D. Hansen  Peter G. Dahlhaus  Robert G. Milne  Andrew D. MacLeod  Chris Pitfield 《社会与自然资源》2019,32(6):709-719

Natural Resource Management (NRM) is often conducted as a partnership between government and citizens. In Australia, government agencies formulate policy and fund implementation that may be delivered on-ground by community groups (such as Landcare). Since the late 1980s, over AUS$8b of Commonwealth investment has been made in NRM. However, quantitative evidence of environmental improvements is lacking. The NRM Planning Portal has been developed to (1) provide an online spatial information system for sharing Landcare and agency data; and (2) to facilitate NRM priority setting at local and regional planning scales. While the project successfully federates Landcare NRM activity data, challenges included (1) unstructured, non-standardized data, meaning that quantitative reporting against strategic objectives is not currently possible, and (2) a lack of common understanding about the value proposition for adopting the portal approach. Demonstrating the benefit of technology adoption is a key lesson for digital NRM planning.  相似文献   

Maximum Entropy and Random Forest Modeling of Mineral Potential: Analysis of Gold Prospectivity in the Hezuo–Meiwu District,West Qinling Orogen,China     

Zhang  Shuai  Xiao  Keyan  Carranza  Emmanuel John M.  Yang  Fan 《Natural Resources Research》2019,28(3):645-664

Natural Resources Research - This study tested and compared the mineral potential mapping capabilities of the random forest (RF) and maximum entropy (MaxEnt) algorithms using gold deposit...  相似文献