Geochemical Characteristics of Wuyang Siliceous Rocks in the Southern Margin of North China Craton and its Constraint on the Formation Environment of BIF of Tieshanmiao Formation

Precambrian banded iron formation(BIF) is one of the most important mineral resources in China, mostly abundant in the North China Craton(NCC) with relatively less common in South China. Since the BIF and siliceous rocks both originated from chemical deposition, the syngenetic BIF and Siliceous rocks can help evaluate their environment of formation. We examine here the mineralogy and geochemistry of siliceous rocks associated with the Tieshanmiao Formation BIF, aiming to decipher the conditions of formation of both BIF and Siliceous rocks in the Wuyang area in the NCC. Analysis of the geochemical characteristics of whole rock shows that the Si O2 content of the siliceous rock ranges from 90.11% to 94.85% and is relatively high overall. Trace element contents of Ba and U are also high, the Ba/Sr ratio ranges from 3.89 to 25.28 and the U/Th ratio ranges from 0.09 to 0.20. Finally, the ΣREE value of rare earth elements ranges from 57.03 ppm to 152.59 ppm, and these indexes all indicate that siliceous rock resulted from hydrothermal deposition. Plots of Al2 O3-Si O2, Si O2/(K2 O+Na2 O)-Mn O2/Ti O2 and Mn-10×(Cu+Co+Ni)-Fe in discrimination diagrams also verify this interpretation. However, both the Mg O content, ranging from 0.16 to 0.32, and the Fe/Ti ratio, ranging from 2.50 to 9.72, suggest that terrigenous material was added during the depositional process. Major and trace element parameters of siliceous rock, such as the Al/(A1+Fe+Mn) ratio(from 0.81 to 0.93), Mn O/Ti O2(from 0.00 to 0.17), Al/(Al+Fe)(from 0.82 to 0.93), Sc/Th ratio(from 0.21 to 0.50), U/Th(from 0.09 to 0.20),(La/Yb)N(from 0.83 to 3.04), and the(La/Ce)N(from 0.01 to 0.02) all imply that the siliceous rock formed in a continental margin. In addition, the Sr/Ba ratio from 0.08 to 0.26, the δCe value from 0.31 to 0.90, and the δEu value from 0.14 to 0.58, all indicate that the siliceous rock was formed at a relatively deeper water depth and under weak hydrodynamic conditions. Siliceous rock and BIF formed in the same geological setting, with the Si O2/(K2 O+Na2 O) ratio of siliceous rock ranging from 28.61 to 47.43, the Si O2/Al2 O3 ratio from 16.53 to 32.37, and the Si O2/Mg O ratio from 287.28 to 592.81, which are all in agreement with chemical deposition associated with volcanic eruptions. The Al2 O3/Ti O2 ratio from 37.82 to 50.30 indicates that the magma source of siliceous rock was of slightly intermediate composition. During the Late Archean in the Wuyang area, the high concentration and high purity Si O2 quickly precipitated from hydrothermal fluids to finally result in the accumulation of siliceous rock in a marginal sea, while the input corresponding to iron formation components was deposited to form iron formation layers, and limestone was only the product formed during the deposition intervals of siliceous rock and iron formations. In this study, the synsedimentary siliceous rocks of BIF act as a new way to provide direct evidence to understand the formation environment of BIF due to its high geochemical stability.     

Final Closure Time of the Paleo‐Asian Ocean: Implication from the Provenance Transformation from the Yangjiagou Formation to Lujiatun Formation in the Jiutai Area,NE China

The Jiutai area is tectonically situated at the eastern segment of the Central Asian Orogenic Belt(CAOB) and is close to the North China Craton(NCC) to the south, serving as an ideal place to investigations of the closure of the PaleoAsian Ocean(PAO). Sandstone samples collected from the Yangjiagou Formation and the Lujiatun Formation in this area have been studied in detail in terms of petrology, geochronology and geochemistry. The maximum depositional time of the Yangjiagou and Lujiatun formations has been constrained to early Middle Triassic(ca. 245 Ma) and middle Late Triassic(ca. 219 Ma), respectively. The Yangjiagou Formation, with a major provenance of dissected island arcs, is dominantly composed of Phanerozoic sediments from Northeastern China(NE China) massifs. The Lujiatun Formation, with major sediments from active continental margins, has a relatively larger proportion of Precambrian sediments, in which the ～1.85 Ga and ～2.5 Ga sediments are typical of the crystalline basements of the NCC and NE China massifs, which were uplifted and eroded during the closure of the PAO. Besides, both formations show the enrichment in LREEs and the depletion in HREEs, the common Eu negative anomalies, and trace element contents similar to that of the upper continental crust. Based on the provenance analysis of these two formations, the final closure time of the PAO in this area is constrained as from the early Middle Triassic(ca. 245 Ma) to the middle Late Triassic(ca. 219 Ma).     

板块运动的机制与动力来源学术争鸣

目前人类对地球的认识仍很肤浅,无论国外还是国内对于地球动力学问题仍在探索过程中,Science杂志2005年公布的125个重大科学问题中的第10个问题是“地球内部是如何运行的”,提出地球动力来源还尚未解决。 2017年出版的《中国学科发展战略--板块构造与大陆动力学》认为板块构造理论虽然取得了巨大成功,但该学说依然存在其形成以来就存在的难题,即板块动力、板块起源及板块上陆三大问题,驱动板块运动的动力机制是最为重要的问题,也是亟待解决的问题。 研讨会分两个环节,一是主要观点报告环节,二是讨论争鸣环节。 在报告环节,涉及动力机制的主要有5位报告人,分别阐述了他们的主要观点。梁光河提出了新大陆漂移说,通过大量证据分析认为传统的海底扩张驱动大陆漂移的模式存在很多问题,很多地质和地球物理观测事实说明持续推动大陆漂移的动力不是海底的持续扩张,而是大陆板块后下方持续的岩浆上涌推动大陆板块向前漂移,那是一个自发的连锁反应。万天丰认为传统的海底扩张传送带模式很难解释大陆板块漂移速度远远大于地幔对流速度这个问题,提出了陨击说。陨石撞击诱发地幔底劈推动大陆板块运动这个新的驱动模式。唐春安提出了地球龟裂说,认为地球内部热能的积累与释放,使得地质历史上岩石圈地幔具有冷热交替的周期。毛小平分析认为,目前所提出的地球动力中,只有周向应力具有足够数量级的应力,可以推动板块运动;周向应力在岩石圈薄弱处释放从而产生地壳相对运动;长期以来解释不了的“地壳异常压力”其实就是周向应力,而可独立于重力的构造力、碰撞力并不存在。 在讨论争鸣环节,大家针对地壳运动的动力来源自由发言。梁光河指出万天丰提出的陨石撞击可以较好地解释超大陆裂解的初始动力,但不同意陨石撞击可以提供持续的大陆漂移的动力,以印度板块的北漂为例,因为地幔的巨大黏滞阻力,需要无数个陨石定点撞击印度板块后面才可能持续推动印度板块漂移。唐春安提出地球的锅盖效应,因此上地幔具有冷热周期,在热周期地壳才会大规模漂移,按照力学机制,大洋中脊和转换断层不可能是海底扩张产生的,应该是大陆漂移拉开产生的断裂系统。最后杨巍然总结发言,认为陨石撞击是一个重要因素,地球上的构造运动都可以归结为开合运动,海底扩张和大陆漂移都是存在的,地体构造也是科学的。研讨会取得的共识是：大陆的确存在大规模水平运动,传统的地幔对流传送带驱动模式存在很多与观测事实不符的问题,需要重新认识驱动机制和驱动力的问题,对板块俯冲问题多数持怀疑甚至反对的观点。其驱动力应该来自重力和地球内部热力,但它们之间是如何相互作用的,仍需要进行更深入的研究。     

湖南常德南斗姆湖地区早更新世砾石层砾组分析与沉积特征研究

为了查明洞庭盆地西缘早更新世砾石层沉积特征及沉积环境,在1:5万地质调查基础上,对常德南斗姆湖地区几处第四系砾石层剖面进行了较系统的测量与统计。结果表明: 砾石成分主要来源于寒武纪或前寒武纪地层。砾石分选系数S_a 为1.16~1.64,部分测点S_a>1.40,反映砾石形成时水动力很强,部分砾石层为快速堆积。砾石扁度F为2.06~2.32,大于2.0,砾石以扁平状为主。砾石普遍弱—中等风化,部分砾石强风化,反映砾石在沉积搬运过程中存在风化暴露。砾向分析显示古水流主要来源于SWW—NW向,表明砾石层形成时期古地貌与现有地貌有较大差异。剖面对比得出,区内砾石层是在冲洪积扇基础上发育的以辫状河相为主的沉积体。对研究区砾石层沉积相及古地貌的新认识,为区内金刚石原生矿床的找矿工作提供支撑。     

高速公路、市场潜力与人力资本空间分布研究

基于我国2000年、2010年250个城市数据,通过高速公路网测算城市间时间距离以刻画城市的国内和国外市场潜力,控制城市教育水平、内部市场规模、产业结构、行政级别等。考虑空间自相关,采用空间计量模型研究不同空间尺度市场潜力对人力资本空间分布的差异化影响。结果发现:高速公路网的基本建成使得市场潜力显著影响城市的人力资本积累,城市越靠近国内市场中心则人力资本水平越低,越靠近国外市场则人力资本水平越高。考虑规模效应和竞争效应布局城市交通网络,加强教育投入,能够有效提高城市人力资本水平。     

合浦珠母贝丝氨酸蛋白酶抑制因子基因pfser1克隆与表达

【目的】克隆合浦珠母贝(Pinctada fucata)丝氨酸蛋白酶抑制因子pfser1基因,探讨该基因的组织表达及其在天然免疫过程中的作用,以及与生物矿化过程的关系。【方法】通过RACE技术获得pfser1基因的全长,通过生物信息学分析其序列结构特征,利用实时荧光定量PCR方法检测pfser1基因在不同组织中的表达,检测健康合浦珠母贝在被大肠杆菌(Escherichia coli)MG1655刺激后和在贝壳损伤修复实验中pfser1基因表达量的变化。【结果】合浦珠母贝pfser1基因cDNA全长为1240 bp,包含1035 bp的开放阅读框(ORF),编码344个氨基酸,氨基酸序列的功能结构域含有丝氨酸蛋白酶抑制因子Serpin家族保守结构域。pfser1基因在合浦珠母贝各个组织中均有表达,在外套膜边缘膜中表达量最高;大肠杆菌MG1655刺激后,该基因表达量显著升高;在贝壳损伤修复过程中,pfser1基因表达先升高后受到抑制。【结论】pfser1基因所表达的蛋白参与了合浦珠母贝的天然免疫应答过程,并与生物矿化过程有一定关系。     

Preface to the Special Issue on the 14th International Conference on Mesoscale Convective Systems and High-Impact Weather

<正>A mesoscale convective system (MCS) is an organized cluster of thunderstorms known to be the most important convective mode in causing disastrous high-impact weather, such as heavy rainfall, hail, damaging winds, and tornadoes. The small spatial scale and fast temporal evolution of MCSs make their observation and prediction very challenging. East Asia is home to the world’s most prominent monsoon, setting the stage for various severe convective weather events. MCSs and their associated ...     

多测绘技术手段与遗址保护

采用全站仪离散点测量、三维激光扫描、无人机航拍对大型古遗址进行数据采集,分析了各种测绘手段的作业方法及流程,得到一系列测绘成果,并利用三维浏览软件实现遗址的三维展示,为遗址修缮与保护提供了数据支持。     

GIS支持下的油气多因素综合预测方法——以苏里格气田苏120区为例

苏里格气田为一致密沙岩气田,油气富集区的预测优选为气藏开发奠定基础。常规的油气富集区预测方法存在着多学科成果综合分析困难、预测过程复杂、效率低下等弊端,本文针对苏里格120区块开展了基于GIS的油气富集区多因素综合预测方法的研究。首先借助GIS的空间数据库,实现多学科成果图件的集成管理;然后基于空间定位,从多学科成果图件中提取预测多因子,构建油气多因素综合预测模型;再次,运用GIS强大的叠加分析方法进行多因素综合预测,自动生成油气富集区预测平面图。本文的研究,为油气富集区的预测提供了新的技术方法,有效地提高了预测效率。     

点云信息提取研究进展和展望

点云是目前摄影测量、遥感、计算机视觉等多个领域广泛应用的数据源之一,而信息提取是点云处理、分析和应用的必经环节。为此,学术界已经提出了大量点云信息提取方法。本文从基元类型、提取特征、特征选择与分类器等3个视角概括了点云信息提取的相关研究现状,总结出点云信息提取存在的5个主要问题,点明了点云信息提取的6个主要发展趋势,并着重介绍了"融合多基元的点云信息提取范式"。