Dehydration of clastic sediments in subduction zones: Theoretical study using thermodynamic data of minerals     

Ying Li  Hans‐Joachim Massonne  Arne Willner  Hong‐Feng Tang  Cong‐Qiang Liu 《Island Arc》2008,17(4):577-590

Pseudosections for two sediments and one basalt calculated in the system K₂O–Na₂O–CaO–MgO–FeO–Fe₂O₃–Al₂O₃–TiO₂–SiO₂–H₂O for the P–T range 10 to 35 kbar, 300 to 900°C give useful insights into the amount of H₂O released from oceanic crust in subduction zones. In cold subduction zones (20 kbar–300°C to 35 kbar–500°C) hydrous minerals storing 3 to 4 wt% H₂O are still present in metasediments at depths of 120 km. In the same environment, metabasite releases 1 wt% H₂O in the depth range 100 to 120 km, but 4.5 wt% H₂O is transported to greater depths. In hot subduction zones (300°C hotter than the cold subduction zone at 100 km depth), dehydration events of metasediments in the depth range 50 to 80 km correspond to the breakdown of chlorite and paragonite. In the calculations no further water is released at greater depths because the modal content of phengite, the only hydrous mineral phase at these depths, remains almost constant. For the same P–T path, metabasite shows continuous dehydration between 40 and 80 km releasing almost 3 wt% H₂O. At 120 km depth less than 0.4 wt% of H₂O remains. In an average modern subduction zone (～6°C/km) most dehydration of sediments occurs at depths of 70 to 100 km and that of basalts at depths of 80 to 120 km. Only 1.3 wt% H₂O in metasediments and 1.6 wt% H₂O in metabasalt has the potential to be subducted to depths greater than 120 km. The dehydration behavior of sediments concurs with the generally held idea that subduction zone fluids are most effectively transported to great depths by cold subduction. In hot subduction zones, such as those characteristic of early Earth, most H₂O carried by oceanic crust is liberated at depths less than 120 km and, thus, would not contribute to island‐arc magmatism.  相似文献   

GIS技术在矿山场地平整中的应用   总被引：1，自引：1，他引：0  

邓辉  何政伟  赵银兵  倪忠云  刘敏红  张船红  杨晏立 《地理空间信息》2010,8(6):89-91

以方格网法计算土方量,利用ArcGIS空间分析模块对数字高程模型的空间分析功能和属性数据的计算,从而实现土地平整中土方量的快速计算。  相似文献   

Consistency of the activity–composition models of Holland,Green, and Powell (2018) with experiments on natural and synthetic compositions: A comparative study     

Marcos García-Arias 《Journal of Metamorphic Geology》2020,38(9):993-1010

The recent publication of new activity–composition models by Holland, Green and Powell (2018; Journal of Petrology 59 : 881–900), with a melt model calibrated for source compositions ranging from peridotitic to granitic, opens the door to the modelling of multiple petrogenetic processes at supersolidus conditions in which the composition of the melt phase changes considerably, without having to change the melt model. This melt model is also the first one using the internally consistent thermodynamic databases published by T. Holland and R. Powell that contains TiO₂ and Fe₂O₃, further expanding the application of this model to more realistic geological scenarios. The accompanying mineral models are also the first in containing some minor elements, like TiO₂ in garnet and K₂O in clinopyroxene. Consequently, it is relevant to test the applicability of these new models to a large P–T–X range of conditions before they can be used in full. Thermodynamic calculations made with the software Perple_X using these models were compared to experimental results, namely the modal proportions and the composition of the melt and several mineral solution phases. The experiments chosen for the comparative study covered a wide range of source compositions (from mafic to felsic), pressure (from 0.3 to 2.1 GPa), temperature (from 700 to 1,150°C) and total and added water content (structural water: 0.15–1.48 wt%; added water: 0–8 wt%; total water: 0.15%–8.15%). The results indicate that the extended melt model reproduces well the composition of the experimental melts, with an inverse correlation between component amount and fit: the best match is found for SiO₂ (−0.8% on average) and the worst match is found for those elements with the lowest amounts, TiO₂ and MgO (+241% and +235% on average, respectively; values indicate calculated minus experimental, times 100 and divided by experimental). The TiO₂ content in the melt model increases dramatically with increasing pressure, from +90% for P < 1.5 GPa to +593% for P > 1.5 GPa. No comparison was made on the Fe₂O₃ content, as the published iron contents of the experimental melts were always reported as FeO_t. In some cases, there is a substantial mismatch in the modal proportions between experiments and calculations, with the reactant phases less abundant and product phases more abundant in the calculations, an effect that is attributed to kinetic effects in the experiments and to the selected clinoamphibole model. Finally, the extended melt model was compared to the tonalitic melt model of Green et al. (2016; Journal of Metamorphic Geology, 34 : 845–869). Both melt models produce very similar results for SiO₂, Al₂O₃, Na₂O and K₂O, with slightly better results for the tonalitic melt model in FeO_t and MgO and for the extended melt model in CaO. No comparison is made on TiO₂ because the tonalitic melt model does not include this component. In summary, the new activity–composition models represent a significant contribution to thermodynamic calculations on the evolution of siliceous magmas where their composition, temperature and pressure changes substantially.  相似文献   

地质灾区光学立体影像植被与3维地形定量变化检测     

李畅  熊昊  陶顺勇  韩振坤 《遥感学报》2014,18(6):1258-1267

当前,经典的2维遥感变化检测方法不再适用于地质灾害引起的地表3维变化。此外,一般植被提取依赖近红外波段,而近红外影像未必能获取。因此,针对2010年和2011年汶川映秀地区的可见光航空立体像对,提出了一种检测植被和3维地形变化的方法。首先,生成研究区两个不同时期的DEM和DOM并完成配准,再利用CIE Lab色彩空间和Otsu分割算法对可见光DOM进行植被变化检测。然后,基于概率统计理论对新旧时期差分DEM提出了3维变化检测的自适应阈值确定方法,在高概率置信域条件下提取出地质灾害的高危区域。最后,对高危区域运用离散化积分方法估算出土方量的3维变化量。实验结果表明了所提出方法的可行性,有效性和实用性。本文不仅将常规遥感的2维变化检测升华至3维空间,而且对变化的3维地形进行了定量估计,可应用于地质灾害的遥感动态监测和评估。  相似文献   

基于近景摄影测量的基坑土方量计算及精度评价     

李天子  刘志奇  杨振明  王晓华 《测绘工程》2017,26(9)

土方量的计算是工程建设中的重要环节,计算精度将对合理选择施工方案有很大影响。针对传统土方量测量方法外业任务繁重、作业复杂、不能快速计算等问题,提出一种以非量测数码相机、多基线数字近景摄影测量为基础,通过获取DTM数据来计算土方量的方法。研究表明,与传统测量方法相比,计算结果误差小于5%,满足土方量计算的精度要求。也验证了近景摄影测量用于土方量计算的实用性和可行性,为快速、精准计算土方量提供了可靠途径。  相似文献   

Calculating on a round planet     

Nicholas R. Chrisman 《International journal of geographical information science》2017,31(4):637-657

Despite incontrovertible scientific evidence to support a round Earth, GIS software implementation typically models the Earth with flat map projections. This choice has consequences that vary from mild to severe. This paper explores solutions that range from moderate measures to correct for map projection errors to radical revisions of standard practice that place all calculations on the ellipsoid. On examination, the best practice requires a distinct projection choice for each geometric operation. Multiple reasons, from the technical to ethical, justify revised practices and increased vigilance for the errors induced by inappropriate projections.  相似文献   

Impact of anthropogenic geochemical change and aquifer geology on groundwater phosphorus concentrations     

《Applied Geochemistry》2016

Geologic and geochemical variations across a 4200 km² area of south-central Wisconsin (USA) were used to examine their relationship to phosphorus concentrations in groundwater from more than four hundred private water supply wells. Surficial geology in the study area ranged from Cambrian sandstones to Ordovician dolomites. Groundwater phosphorus concentrations were higher in aquifers of older Cambrian age compared to the concentrations in aquifers of younger Cambrian and Ordovician age. Because iron concentrations were relatively low in these waters and agricultural land use was similar in all geologic regions, we propose that the differences in bedrock phosphorus and anthropogenic geochemical impacts explain the differences in phosphorus concentrations between aquifers. Within the older Cambrian aquifers, groundwater phosphorus concentrations were elevated in groundwater with higher nitrate-nitrogen concentrations. This finding is consistent with the presence of phosphorus within sediment in these strata and geologic conditions that weakly buffered pH reduction from anthropogenic acidification. In contrast, groundwater phosphorus concentrations in younger Cambrian and Ordovician aquifers were not elevated in samples with higher nitrate. Anthropogenic acidification in these carbonate-rich aquifers was neutralized through increased carbonate weathering, which led to higher groundwater calcium and alkalinity and would limit the dissolution of phosphate-rich minerals, such as apatite, where present. Low iron concentrations observed in most samples suggest that the phosphorus release in the Cambrian strata occurs beyond the zone of secondary mineral retention in the soil. These results have important implications for the eutrophication of inland surface waters in areas with bedrock phosphorus and anthropogenic acidity that is not neutralized before it contacts phosphatic rock.  相似文献   

同位素双稀释剂计算软件(DS_CAL)的开发及其地球化学应用     

赵严  温汉捷  周正兵  万建军 《地质学报》2021,95(5):1644-1653

二十一世纪以来,随着多接收电感耦合等离子体质谱仪(MC-ICP-MS)和热电离质谱仪(TIMS)的发展和广泛应用,多种非传统稳定同位素体系(Li、B、Mg、Ca、Mo、Cd、Fe和Zn等)的分析方法得到了快速发展,而仪器的质量分馏校正是进行准确同位素分析的关键因素之一.双稀释剂法被认为是最理想的仪器质量分馏校正方案,能够获得高精度的同位素比值.然而,复杂的计算推导和数据处理在一定程度上限制了双稀释剂法的使用和推广.在前人双稀释剂理论研究的基础上,本研究自主开发了双稀释剂数据处理平台(DS_CAL,基于Microsoft Excel VBA).该平台集合了测试数据的批量导入、目标元素参数的添加与修改、数据批量计算等操作,能够同时处理稳定同位素和放射性成因同位素体系的双稀释剂法数据计算,且不同实验室也能够根据所使用稀释剂的组成自主修改计算参数.本文还通过Mo同位素测试和计算实例,不仅显示出双稀释剂法具有高的测试精度,还展示了DS_CAL在双稀释剂法数据处理计算中的便捷性与高效性.DS_CAL能够应用于所有适用双稀释剂法计算的同位素体系,该平台的开发将有助于同位素双稀释剂技术的推广和发展.  相似文献   

Modeling the near-field effects of the worst-case tsunami in the Makran subduction zone   总被引：1，自引：0，他引：1  

Mohammad Heidarzadeh  Moharram D. Pirooz 《Ocean Engineering》2009,36(5):368-28

As a first step towards the development of inundation maps for the northwestern Indian Ocean, we simulated the near-field inundation of two large tsunami in the Makran subduction zone (MSZ). The tsunami scenarios were based on large historical earthquakes in the region. The first scenario included the rupture of about 500 km of the plate boundary in the eastern MSZ, featuring a moment magnitude of M_w 8.6. The second scenario involved the full rupture of the plate boundary resulting from a M_w 9 earthquake. For each scenario, the distribution of tsunami wave height along the coastlines of the region is presented. Also, detailed runup modeling was performed at four main coastal cities in the region for the second scenario. To investigate the possible effect of splay fault branching on tsunami wave height, a hypothetical splay fault was modeled which showed that it can locally increase the maximum wave height by a factor of 2. Our results showed that the two tsunami scenarios produce a runup height of 12-18 m and 24-30 m, respectively. For the second scenario, the modeled inundation distance was between 1 and 5 km.  相似文献   

测量工作在土地整理类项目中的应用体会     

任志刚 《现代测绘》2012,35(2):57-58

本文介绍了测量工作在土地整理类项目中的应用并简述了点滴作业体会.  相似文献