山西吕梁山北段中生代构造特征及对成矿的制约

为进一步研究山西吕梁山北段中生代构造特征及对成矿的制约,利用数字化填图方法,在偏关县一带开展1:25万区域地质调查。发现几条中生代大型构造带,查明了这些大型构造带的空间展布、性质、断裂组合及运动学特征; 证实了中生代为该区重要的多金属成矿期,成矿作用尽管与中生代岩浆活动关系密切,但在空间上分布受NE向隐伏构造的制约; 大型挠褶构造是地壳强烈隆升的标志,区内大型构造带多数是在挠褶构造的基础上叠加断层而形成的。该研究对于探讨山西中—新生代构造的演化发展具有重要意义。     

关于L—Fuzzy子群

本文利用模型子群概念，引入了Ｌ－Ｆｕｚｚｙ子群概念。基于模糊集合的层次结构特征，得到Ｌ－Ｆｕｚｚｙ了群若干重要性质；给出并证明Ｌ－Ｆｕｚｚｙ子群的一系列等价刻划；文章最后讨论Ｌ－Ｆｕｚｚｙ子群同态性质 。     

A multi‐geochronological study of the Hakusan volcano,central Japan

The Hakusan volcano, central Japan, is located in a region where two subducting plates (the Pacific Plate and the Philippine Sea Plate) overlap near the junction of four plates adjacent to the Japanese Islands (the Pacific Plate, the Philippine Sea Plate, the Eurasia Plate, and the North American Plate). The Hakusan volcano consists of products from four major volcanic episodes: Kagamuro, Ko‐hakusan, and Shin‐Hakusan I and II. To date the eruption events of the Hakusan volcano we applied thermoluminescence and fission track methods. ²³⁸U(²³⁴U)–²³⁰Th disequilibrium and ²⁰⁶Pb/²³⁸U methods were applied to date the zircon crystallization ages for estimating the magma residence time before the eruptions. The eruption ages we obtained are ca 250 ka for Kagamuro, ca 100 ka and ca 60 ka for Ko‐Hakusan, ca 50 ka for Shin‐Hakusan I, and <10 ka for Shin‐Hakusan II. They are concordant with previous reports based on K–Ar dating. Some of the pyroclastic rocks, possibly originating from Shin‐Hakusan II activities, are dated to be ca 36 ka or 50 ka, and belong to the Shin‐Hakusan I activity. The zircon crystallization ages show several clusters prior to eruption. The magma residence time was estimated for each volcanic activity by comparing the major crystallization events and eruption ages, and we found a gradual decrease from ca. 500 ky for the Kagamuro activity to ca. 5 ky for the Shin‐Hakusan II activity. This decrease in residence time may be responsible for the decrease in volume of erupted material estimated from the current topography of the region. The scale of volcanic activity, which was deduced from the number of crystallized zircons, is more or less constant throughout the Hakusan volcanic activity. Therefore, the decrease in magma residence time is most likely the result of stress field change.     

Active tectonics around the junction of Southwest Japan and Ryukyu arcs: Control by subducting plate geometry and pre‐Quaternary geologic structure

The origin of active faults in the Inner zone of the western part of Southwest Japan was explained by a decrease of the minimum principal stress and reactivation of ancient geologic structures. Although the E–W maximum principal stress in Southwest Japan due to the collision of the Southwest and Northeast Japan arcs along the Itoigawa–Shizuoka Tectonic Line is assumed to decrease westward, the density of active strike‐slip faults increases in the western margin of the Southwest Japan Arc (western Chugoku and northern Kyushu) where the subducting Philippine Sea Plate dips steeply. The E–W maximum compressional stress is predominant throughout Southwest Japan, while the N–S minimum principal stress that is presumably caused by coupling between Southwest Japan arc and Philippine Sea Plate decreases due to the weak plate coupling as the plate inclination increases under the western margin of Southwest Japan. The increase of the fault density in the western margin of the arc is attributed to a decrease of the minimum principal stress and consequent increase of shear stress. Low slip rates of the active faults in this region support the view that the westward increase of fault density is not a response to increasing maximum stress. These faults of onshore and offshore lie in three distinct domains defined on the basis of fault strike. They are defined domains I, II, and III which are composed of active faults striking ENE–WSW, NW–SE, and NE–SW, respectively. Faulting in domains I, II, and III is related to Miocene rift basins, Eocene normal faults, and Mesozoic strike‐slip faults, respectively. Although these active faults are strike‐slip faults due to E–W maximum stress, it is unclear whether their fault planes are the same as those of pre‐Quaternary dip‐slip faults.     

Rapid societal change as a proxy for regional environmental forcing: Evidence and explanations for Pacific island societies in the 14–15th centuries

Given the unquestioned impacts of recent/future environmental changes on human societies, it is reasonable to posit that past societal responses could be used as proxies of contemporaneous environmental forcing and might help identify the drivers of these, particularly where independent evidence of the effects of these events is inadequate. Such areas include Pacific oceanic islands for most of which there is evidence of a societal perturbation in the 14th and 15th centuries that saw the outbreak of region‐wide conflict, abandonment of coastal settlements and the abrupt end of long‐distance cross‐ocean voyaging networks. The contemporaneity of these effects across a vast region requires a driver that is external to particular island groups with the only possibility that of oceanic origin, most likely large waves (tsunamis or storm surges) or rapid sea‐level change. The explanation is less important than the principle that societal changes can be used as proxies for environmental activity.     

无限群p拟Frattini子群

群G中所有极大子群之交称之为G的Frattini子群。给出一种新的广义的Frattini子群——p拟Fratti—ni子群的定义,并研究基本性质,例如p拟既约性质、p拟可消性质和p拟补充性质等。同时对正规子群,同态像和直积的p拟Frattini子群也进行了研究。     

埃迪卡拉纪—寒武纪之交微生物岩特征对比及古海洋学意义: 以汉南—米仓山地区为例*

寒武纪初期不仅发生了宏体生物大爆发,而且也出现了地质历史时期少见的蓝细菌鞘体大规模钙化事件。埃迪卡拉纪—寒武纪之交海水化学性质的转变对真核生物的演化起到了重要作用,但是这种转变对微生物岩发育特征以及蓝细菌钙化事件的产生有无影响,目前尚不明确。鉴于此,对华南上扬子北缘汉南—米仓山地区上埃迪卡拉统—寒武系第二统多个典型微生物岩发育剖面进行了系统野外调查和室内岩石学分析,结果表明:上埃迪卡拉统灯影组叠层石广泛发育,以平铺状、缓波状特征为主,而凝块石既可以呈补丁状分布于叠层石纹层间,又可以呈细小的凝絮状、粘结状特征构成厚层岩层;寒武系第二统仙女洞组叠层石丰度显著降低,以高大、坚硬的丘状隆起为特点,包括单独的凝块石丘,以及微生物与古杯的联合建丘。虽然寒武系第二统微生物岩的层状结构和凝块结构与埃迪卡拉系相比并无太大差异,但是寒武系微生物岩内部保存有大量的钙化微生物化石,已识别出附枝菌(Epiphyton)、肾形菌(Renalcis)和葛万菌(Girvanella)等多种类型。在收集、整理前人有关微生物岩特征和发育资料的基础上,本次研究初步整理出华南寒武系第二统微生物岩的时空分布特点,发现寒武纪第二世第三期是钙化微生物大量发育的一个时期,在随后的第四期达到一个小的高峰。对于此次蓝细菌钙化作用幕的启动机制,除前人提出的海水高钙离子浓度和蓝细菌体内二氧化碳浓缩机制等认识外,寒武纪早期海水性质的转变(方解石质原生矿物受成岩改造程度较低)、适度的陆源碎屑输入(黏土组分保护作用)也有利于钙化微生物结构的保存,应引起重视。     

中国东西部两县域气象要素对呼吸系统疾病影响的分层对比研究

利用安徽省阜南县以及贵州省锦屏县2015—2016年医保住院数据，细化两县呼吸系统疾病住院人群年龄分层，并从月份、节气、候不同时间尺度逐步递进的角度，采用描述性研究方法与相关性分析方法，探析两地各年龄段人群住院人数分布及其地域差异。结果表明：（1）两县9岁以下儿童呼吸系统疾病高发，20~39岁人群住院率较低。（2）两县各人群呼吸系统疾病入院高峰基本出现在2—3月（立春—清明、第10-20候）和11—12月（大雪—冬至）。除个别人群外，两县均是夏、秋两季呼吸系统疾病入院人数较少。（3）阜南县50~59岁人群呼吸系统疾病秋季入院风险的增加与当地气温日较差增大和相对湿度降低有关，滞后5 d左右影响明显。（4）总体来看，干冷环境可能会造成两县居民呼吸系统疾病入院人数的增多。此外，锦屏县居民还需格外防范春季相对低温高湿天气及暖季较低气温日较差所带来的呼吸系统疾病风险。