Crustal Structure of the Chuan-Dian Block Revealed by Deep Seismic Sounding and its Implications for the Outward Expansion of the East Tibetan Plateau

The Chuan-Dian Block (CDB) is located in the southeastern margin of the Tibetan Plateau, with a complex geological structure and active regional faults. The present tectonic condition with strong crustal deformation is closely related to the ongoing collision of the India and Eurasia plates since 65 Ma. The study of the crustal structure of this area is key to revealing the evolution and deep geodynamics of the lateral collision zone of the Tibetan Plateau. Deep seismic sounding is the most efficient method with which to unravel the velocity structure of the whole crust. Since the 1980s, 19 deep seismic sounding profiles have been captured within the CDB area. In this study, we systematically integrate the research results of the 19 profiles in this area, then image the 3D crustal velocity, by sampling with a 5 km spacing and 2D/3D Kriging interpolation. The results show the following. (1) The Moho depth in the study area deepens from 30 km in the south to 66 km in the north, whereas there is no apparent variation from west to east. The Pn wave velocity is higher in stable tectonic units, such as 7.95 km/s in the Lanping-Simao block and 7.94 km/s in the western margin of the Yangtze block, than in active or mobile tectonic units, such as 7.81 km/s in the Baoshan block, 7.72 km/s in the Tengchong block and 7.82 km/s in the Zhongdian block. (2) The crustal nature of the Tengchong block, the northern Lanping-Simao block and the Zhongdian block reflects a type of orogenic belt, having relatively strong tectonic activities, whereas the crustal nature of the central Lanping-Simao block and the western margin of the Yangtze block represents a type of platform. The different features of the upper-middle crust velocity, Moho depth and Pn wave velocity to both sides of the Red River fault zone and the Xianshuihe fault zone, reflect that they are clearly ultra-crustal. (3) Based on the distribution of the low velocity zones in the crust, the crustal material of the Tibetan Plateau is flowing in a NW–SE direction to the north of 26°N and to the west of 101°E, then diverting to flowing eastwards to the east of 101°E.     

山区农户耕地利用集约度及其影响因素——以重庆市12个典型村为例

耕地利用集约度对粮食安全、生态环境和耕地保护有深刻影响。利用重庆市酉阳县、武隆县、巫山县3个县12个典型村972份有效农户调查样本,基于货币额衡量生产成本,对比分析不同类型农户的耕地利用集约度差异,同时综合价值形态指标与实物形态指标对其内部结构进行分析比较,然后运用多元线性回归模型定量分析不同类型农户内部耕地利用集约度的影响因素,以期为政府制定山区农业发展政策与措施提供科学依据。研究表明:1不同类型农户的耕地利用集约度及其内部结构存在较大差异,劳动集约度、资本集约度与耕地利用集约度基本呈现自然资产型人力资产型基本型缺失型的关系;2研究区正经历着农村劳动力快速转移过程,农户生计多样化显著,但生计多样化并不一定意味着耕地集约度的降低;3农业生产补贴和经济作物播种面积比重对自然资产型农户有显著的正向影响,故农业发展政策应集中在提高农业生产补贴和调整农业产业结构方面,前提是继续采取有效措施改善农村交通水利等基础设施,建立农业发展的平台。     

桂东南藤县印支期基性侵入岩锆石U-Pb年龄、岩石地球化学及其区域构造意义

桂东南灵山-藤县断裂带内基性侵入岩的演化背景,是认识钦杭结合带西南段构造演化的关键。本文采用LAICP-MS技术测得三门滩岩体角闪苏长岩和东胜岩体石英角闪苏长岩的锆石U-Pb年龄分别为230.0Ma±0.9Ma和236.5Ma±1.3Ma。岩石地球化学特征显示出低镁、富钛铁的特征;稀土含量低且变化大,∑REE(43~189)×10-6,δEu值0.79~1.63,以具Eu正异常为特征;大离子亲石元素(LILE)Rb、Ba、Th强烈富集,伴有Ce、P和Sm弱富集的"三隆起"特征,高场强元素(HFSE)Ta、Nb和Zr、Hf在弱富集的背景上显示为"谷"形,总体显示为大陆性火山弧钙碱性玄武岩的地球化学特征。研究认为,藤县基性侵入岩形成于中三叠世,属大陆性火山弧钙碱性玄武岩,形成于活动大陆边缘弧环境,为桂东南地区印支期大陆边缘造山带的地质记录。     

渝东北地区五峰组-龙马溪组黑色页岩储层特征

以渝东北地区浅海陆棚相沉积的五峰组-龙马溪组泥页岩为研究对象,通过岩石薄片鉴定、矿物含量分析、扫描电镜、物性分析、有机地球化学分析等手段,剖析了泥页岩的岩相学、矿物学特征、储集空间类型。结果表明,五峰组-龙马溪组主要有炭质页岩、泥岩、泥质粉砂岩、硅质岩、泥灰岩和斑脱岩6种岩相类型。黑色页岩的有机质类型为Ⅰ型干酪根,有机碳含量较高,TOC普遍大于2%,最大达7.56%,平均为3.09%;有机质成熟度比较高,Ro值为1.65%~2.33%,基本上处于高成熟-过成熟阶段。矿物成分以石英矿物和黏土矿物为主,黏土矿物主要为伊利石和伊蒙间层。扫描电镜下观察,微孔隙主要包括矿物晶间孔、晶内孔、微裂缝以及有机质内微孔等。平均孔隙度为2.90%,平均渗透率为0.005×10-3μm2。     

长寿地区Se元素地球化学特征

文章阐述了重庆市长寿区渡舟镇—江南镇一带表层土壤中Se元素的含量水平、空间分布以及Se元素与Pb,Zn,Hg等8个重金属元素、pH值之间的关系。研究区表层土壤中Se元素经迭代剔除后背景均值为0.14×10-6,处于低含量水平;Se含量在城镇区域明显高于农田区域,局部富Se水平;土壤中Se元素分布主要受地层、岩性及土壤对Se元素富集特性的控制,在侏罗系中下统自流井组—新田沟组中,Se元素含量随地层年代由老到新逐渐减少;在侏罗系中上统沙溪庙组—蓬莱镇组中,随地层时代由老到新呈逐渐增加的趋势;随着Se元素含量的升高,As,Cd,Cr,Cu,Pb,Zn元素含量逐渐升高,呈显著正相关关系(P0.01),Hg,Ni元素含量略具升高趋势,而pH值则无明显升降,相关性不明显。     

重庆老鼓楼衙署遗址鸿雁(Anser cygnoides)骨骼及其表面痕迹研究

中国考古中发现有弋射活动图像、弋射专用平头箭镞,但一直未发现弋射所获飞禽遗骸.近期,重庆老鼓楼衙署遗址(29°33′13″N,106°34′46″E)考古发掘中,首次出土了一批宋代时期的鸿雁骨骼和早期人类弋射痕迹.骨骼材料包括有胸骨、锁骨、肋骨、肱骨、尺骨、胫骨等,较多骨骼保存比较完整.骨骼测量数据包括:胸骨完整长度为145.2～ 148.8mm,肱骨完整长度为161.0mm,胫骨完整长度为144.0～ 147.0mm等.弋射,是中国先秦至宋元时期针对捕获飞禽而长期延续的专业射猎活动.通过对鸿雁骨骼表面进行显微观测分析,发现有些骨骼上保存有弋射用平头箭镞所造成的破损性孔洞.其破损特征为:箭镞入口处孔洞痕较小,痕迹边缘平滑,痕迹周缘局部呈现向内压入式破裂;箭镞出口处孔洞因受到撞击力放射性扩散,出口面积明显大于入口面积.从箭镞出口处观察,孔洞壁面因平头箭镞撞击,造成局部骨骼呈现碎屑性剥落,使洞壁形态为坡面状;部分碎屑因有骨质纤维与洞壁相连接,所以现在在洞壁坡面上,仍然可以观察到有部分保留的骨质碎屑.弋射用平头箭镞在鸿雁胸骨上留下的孔洞,其整体形态为人口小、出口大的“喇叭口状”.历史时期,鸿雁冬季广泛分布于长江流域避寒、觅食,夏季北迁至蒙古、俄罗斯西伯利亚南部地区栖息、繁殖,其规律性迁徙及集群性活动,成为中国古代先民生产活动中的重要环境参照,并也成为中国思想文化中的重要载体.鸿雁在很早就被人工驯化为中国鹅,成为中国重要的肉蛋家禽品种.重庆老鼓楼衙署遗址鸿雁骨骼的批量出现,是我国考古工作中第一次发现鸿雁骨骼.该批实物资料为分析和认识中国历史时期鸿雁分布范围、活动规律等提供了重要线索.     

Tectonic Relationship between the Late Ordovician and Late Silurian palaeogeographies of southeastern Australia

The Ordovician palaeogeography of southeastern Australia was an east‐facing mafic volcanic island arc separated from the Gondwanan continent by a marginal sea, probably floored by oceanic crust. By mid‐Silurian the palaeogeography had changed to an almost wholly ensialic configuration, with meridional horsts and grabens east of the Wagga Metamorphic Belt and widespread silicic magmatism. By extending a previously postulated match between the modern Andaman Basin and parts of southeastern Australia in the Late Ordovician, the transition from the Late Ordovician to Late Silurian palaeogeography can be explained. The entire Ordovician and Silurian interval can be understood in terms of a relatively simple and constant plate geometry involving southeastern Australia in regional dextral shear.     

HYDROGEOLOGY & ENGINEERING GEOLOGY 1.HYDROGEOLOGY

正20141153Cai Xiaoju(Gansu Institute of Engineering Geology,Lanzhou 730000,China)Survey and Development of Underground Water in Rocky Mountainous Area of Longxi Loess Plateau(Gansu Geology,ISSN1004-4116,CN 62-1191/P,22(2),2013,p.62-66,2     

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Spatial variation of the vegetative roughness in Mediterranean torrential streams affected by check dams

This study focuses on the spatial variations in vegetative roughness associated with morphological channel adjustments due to the presence of check dams in Mediterranean torrential streams. Manning’s n values were estimated using methods established by previous studies of submerged and non-submerged vegetation in laboratory flume experiments and field work. The results showed a linear decrease in shrub density and rate of variation of the roughness coefficient versus degree of submergence with increasing distance upstream from the check dam, while downstream, the filling of the check dam and the bed incision had the most influence. A regression analysis was applied by fitting the data to different models: relationships between Manning’s n and the flow velocity were found to be of the power type for shrubs in all upstream sections, while relationships of flow velocity versus hydraulic radius in the sections closest to check dams showed a good fit to second-order polynomial equations.