岩石蠕变声发射特性研究现状与展望

蠕变是岩石一种重要的力学特性,与工程的长期安全稳定和安全密切相关。声发射技术作为一种无损检测手段,被广泛应用于岩石变形破坏研究领域。本文阐述了近年来基于声发射技术开展岩石蠕变特性方面的研究进展,主要包括不同岩性、加载方式、应力水平下岩石蠕变声发射特性,岩石蠕变破坏声发射前兆特征。在此基础上,提出了几点今后需要进一步深入研究的问题。     

关键元素与生命健康:中国耕地缺硒吗?

地球上的生命和非生命都是由自然界已发现的92种化学元素组成的,通过全国土壤地球化学基准值与人体血液元素含量对比研究,发现血液中40~50种化学元素平均值与土壤地球化学基准值的分布高度一致,表明这些关键元素与生命息息相关。近年大家持续关注的硒(Se)元素是人体必需的微量元素,缺乏会产生健康风险,但摄入过量也会导致中毒,因此被称为健康窗口元素。过去研究认为,中国耕地缺硒是造成健康危害的原因之一。本文通过对全国3 382个网格化点位土壤采样,获得Se的地球化学基准值和空间分布数据,发现中国贫硒国土面积,按照世界卫生组织推荐值(0.1 mg/kg)和中国规范(0.125 mg/kg)计算,分别占21.1%和31.6%;适宜区(0.125~0.40 mg/kg)面积大约555万km²,占国土面积约57.1%;富硒区(>0.40 mg/kg)面积达110万km²,占国土面积约11.2%。贫硒国土主要分布在青藏高原和内蒙古局部地区,而中国9大平原的粮食主产区耕地总体上不缺硒,其中珠江三角洲平原、广西平原、成都平原、长江中下游平原是富硒区(>0.40 mg/kg),华北平原、东北平原、三江平原、关中平原是硒边缘区-适量区(0.125~0.40 mg/kg),只有河套平原是缺硒区(<0.125 mg/kg)。根据覆盖全国的网格化土壤采样分析结果,发现低硒带呈不连续的片状分布于内蒙古东部至青藏高原一带,与传统认为“低硒带分布于东北三省至西南云贵高原”不完全一致。硒的空间分布模式主要受地质背景、岩石类型、土壤类型和自然地理景观控制。     

浅钻岩石地球化学测量在皖东江山金矿的应用及找矿预测

江山金矿是皖东浅覆盖区内的典型隐伏矿床,常规化探采集的表层土壤样品异常不明显.利用浅钻在江山金矿区内采集了运积物覆盖层之下的岩石样品.江山金矿岩石地球化学异常明显,根据江山金矿的地球化学特征总结了异常模式.在研究区内共圈定了5处异常区.其中III号组合异常为江山金矿的矿致异常.江山金矿外围的组合异常具有寻找Au、Pb多金属矿的良好前景.可在II号组合异常内开展进一步的矿产勘查工作,争取找矿突破.     

巴音戈壁盆地塔木素铀矿床含矿砂岩成岩作用类型、演化序列及其对铀成矿的约束

勘查和研究发现部分砂岩型铀矿床中不仅有表生氧化流体作用还存在深部流体的参与,这类砂岩型铀矿床蚀变类型多样且成因复杂.塔木素砂岩型铀矿表生流体和深部流体活动都很明显,砂岩普遍固结且后生蚀变类型独特,因此,恢复成岩成矿事件及其演化过程,对揭示铀沉淀富集机理至关重要.本文通过镜下鉴定、电子探针、扫描电镜分析等,系统研究了塔木素矿床含矿砂岩成岩作用特征与后生蚀变矿物生成序列,重塑了成岩成矿事件的演化过程.研究结果显示,塔木素矿床砂岩中压实作用较弱而胶结作用很强,重结晶作用普遍,是造成目的层致密的主要原因,赤铁矿、褐铁矿化、碳酸盐化、石膏化是该地区主要的胶结类型.将该地区的成岩演化划分为沉积-早成岩阶段、早期氧化流体作用阶段、热流体改造阶段和晚期氧化流体弱改造阶段.成岩环境由弱碱性向酸性环境转变的过程中的氧化还原过渡部位是造成铀沉淀的关键,大规模的氧化作用是矿床形成的基础,后期热流体活动对早期形成的低品位铀矿石进行叠加改造,是成矿的关键环节.     

谈新形势下地勘单位改革发展的现状及未来发展方向

新中国成立以来,地勘单位先后在计划经济和市场经济下为国家的发展做出了重要贡献,也先后经历了初步探索、属地化管理、事企分体运行等不同阶段。十九大以来,随着事业单位改革的逐步深入,地勘单位改革迫在眉睫。为了更好的适应时代发展,又快又好地进行地勘单位转型,通过研究不同历史时期地勘单位发展的问题和困难,指出现阶段面临的主要问题是改革意愿不强烈、转型工勘领域受阻、资本占有率低和人才匮乏。以此为基础,提出转变思想、学习集团化企业路线、投身地方产业结构、全面提升自然资源意识、加强自身建设和长期持续稳定转型的发展建议,供转型发展的地勘单位参考。     

Late Neoarchean crustal growth under paired continental arc-back arc system in the North China Craton

The late Archean (~3.0–2.5 Ga) was a key period of continental growth globally, which is widely considered to reflect the onset of vigorous plate tectonic activity, although related continental growth modes remain contentious. Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton. The rocks in this suite include amphibolites, clinopyroxene amphibolites, and hornblende plagioclase gneisses. We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during ~2549–2511 Ma.The (clinopyroxene) amphibolites correspond to meta-basaltic rocks, with some containing high modal content of titanite. These rocks show moderate to high FeO_T (8.96–13.62 wt.%) and TiO₂ (0.59–1.59 wt.%), flat to less fractionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addition, they display positive zircon ?_Hf(t) values (+2.6 to +8.7), and are devoid of crustal contamination or fractional crystallization. Combined with the low Nb/Yb (mostly < 1.60) and (Hf/Sm)_N (mostly < 0.95), low to moderate Th/Yb (0.08–0.54), and low V/Sc (5.53–9.19) ratios, these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids. The hornblende plagioclase gneisses are meta-andesitic rocks, and occur interlayered with the basaltic rocks. They are transitional between tholeiitic and calc-alkaline rock series, and show fractionated REE patterns with evidently negative Th, Nb, and Ta anomalies. The depleted zircon ?_Hf(t) values (+2.4 to +8.4) and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.In general, the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts. Combined with regional geological data, it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting. On a regional context, we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton (particularly the Eastern Block), i.e., (1) arc-continent accretion along northwestern part of the Eastern Block; and (2) paired continental arc-back arc system surrounding the ~3.8–2.7 Ga continental nuclei to the southeast.     

A novel index to evaluate discretization methods:A case study of flood susceptibility assessment based on random forest

The selection of a suitable discretization method(DM)to discretize spatially continuous variables(SCVs)is critical in ML-based natural hazard susceptibility assessment.However,few studies start to consider the influence due to the selected DMs and how to efficiently select a suitable DM for each SCV.These issues were well addressed in this study.The information loss rate(ILR),an index based on the informa-tion entropy,seems can be used to select optimal DM for each SCV.However,the ILR fails to show the actual influence of discretization because such index only considers the total amount of information of the discretized variables departing from the original SCV.Facing this issue,we propose an index,infor-mation change rate(ICR),that focuses on the changed amount of information due to the discretization based on each cell,enabling the identification of the optimal DM.We develop a case study with Random Forest(training/testing ratio of 7:3)to assess flood susceptibility in Wanan County,China.The area under the curve-based and susceptibility maps-based approaches were presented to compare the ILR and ICR.The results show the ICR-based optimal DMs are more rational than the ILR-based ones in both cases.Moreover,we observed the ILR values are unnaturally small(＜1％),whereas the ICR values are obviously more in line with general recognition(usually 10％-30％).The above results all demonstrate the superiority of the ICR.We consider this study fills up the existing research gaps,improving the ML-based natural hazard susceptibility assessments.     

Effect of freeze–thaw cycles on strength and ductility and microstructure of cement-treated silt with polypropylene fiber

Acta Geotechnica - In this paper, the strength, ductility and microstructure behavior of cement-treated silt with polypropylene fiber was studied by a host of experimental studies. The influence of...     

Machine learning reveals the influences of grain morphology on grain crushing strength

Acta Geotechnica - Grain morphology has significant impacts on the mechanical behaviors of granular materials. However, its influences on grain breakage are still poorly understood due to the...     

世界气象中心(北京)全球预报服务共享平台设计与实现

世界气象中心(北京)建设是中国气象局承担世界气象组织(WMO)的全球数据处理和预报系统(GDPFS)要求的任务,为全球实时气象预报预测业务提供高效丰富的无缝隙天气气候监测、预报、预测分析指导产品及数据产品服务共享,提高区域性国际天气业务会商交流效率,国家气象中心设计并实现了世界气象中心(北京)全球预报服务共享平台,通过分析全球监测、预报预测等业务数据海量、异构、实时性强等特征,采用浏览器/服务器(B/S结构)多层架构和分布式实时处理、任务调度等关键技术实现了全球实况监测、天气模式、气候模式、模式检验数据的高效加工预处理、产品分析制作、产品自动流转、网络服务共享和业务指导等全流程业务功能,并提供了国际天气预报会商等专业化功能。平台自2018年6月6日业务运行以来,已有13个国家和地区注册会商用户,超过15万次全球访问量,为全球专业用户高效提供了全球实时天气监测、预报服务产品业务指导,未来将成为中国气象局对外气象业务指导和气象服务的重要窗口和纽带。