The crustal nature of the northern Mozambique Ridge,Southwest Indian Ocean     

Nelta David Matsinhe  Yong Tang  Chun-Feng Li  Jiabiao Li  Estev?o Stefane Mahanjane  He Li  Yinxia Fang 《海洋学报(英文版)》2021,40(7):170-182

The Mozambique Ridge (MOZR) is one of the basement high structures located in the Southwest Indian Ocean, parallel to the Southeast African continental margin. It was formed as a result of the tectono-magmatic evolution of the Gondwana breakup. The origin of the MOZR has been highly debated, with models suggesting either continental or oceanic origin. With new free-air gravity anomaly and multichannel seismic (MCS) reflection data, we present results of 2D density modeling along two seismic profiles acquired by R/V Xiangyanghong 10 at the northern Mozambique Ridge (N-MOZR) between 26°S and 28°S. We observed high free-air gravity anomaly and strong positive magnetic anomaly related to the emplaced seaward dipping reflectors (SDR) and high density lower crustal body (HDLCB), and high Bouguer gravity anomaly associated with the thinning of the continental crust underneath the N-MOZR over a distance of ~82 km. This suggests a thinned and intruded continental crust bound by the Mozambique Fracture Zone (MFZ) that is characterized by gravity low and negative magnetic anomaly. This fracture zone marks the continent-ocean boundary (COB) while the N-MOZR is the transform margin high, i.e., marks the continent-ocean transition (COT) of the Southern Mozambique margin, following the definition of transform margins. We suggest that the N-MOZR was formed by continental extension and subsequent breakup of the MFZ, accompanied by massive volcanism during the southward movement of the Antarctica block. The presence of SDR, HDLCB, and relatively thick oceanic crust indicates the volcanic nature of this transform margin.  相似文献   

被动型氢原子钟原子跃迁谱线特性分析     

谢勇辉  林传富 《中国科学院上海天文台年刊》2011,(0)

被动型氢原子钟原子跃迁谱线特性直接决定了整机的性能指标。本文理论分析了影响原子跃迁谱线特性的各项因素,并对3个主要影响因素进行了实验研究。  相似文献   

灰色马尔可夫理论在地震预测方面的研究     

王党席  董平江  韩晓飞 《地震地磁观测与研究》2013,34(3)

以陕南地区汶川地震余震资料数据为实例,提出灰色马尔可夫模型对地震进行预测.利用传统的GM(1,1)模型对数据进行拟合和初步预测,运用马尔可夫模型的状态区间和状态转移矩阵对初步预测值进行修正,并对下一组地震数据进行预测.结果表明,模型预测精度高,预测值与实际值接近,可以作为今后地震预报的辅助手段.  相似文献   

断层带流体对断层强度和强震孕育的影响     

宋娟  周永胜 《国际地震动态》2013,(12):5-16

大量研究表明,流体在断层弱化中起着非常重要的作用.在地壳浅部脆性域,自由水通过流体孔隙压力减小断层有效正压力,从而降低断层摩擦强度;在地壳深部,矿物中的微量结构水弱化岩石流变强度.另外,流体-岩石相互作用等化学过程,如长石水解反应,对断层强度的影响也非常显著.断层深部流体通过物理作用与化学作用影响着岩石的变形机制,从而影响断层力学性质与地震孕育和发生.断层内部流体孔隙压力周期性变化是断层带脆-塑性转化、裂缝张开与愈合等的直接体现,这种变化控制着断层强度与强震周期性发生现象.  相似文献   

青藏高原及邻区大地构造单元初步划分   总被引：146，自引：59，他引：146  

潘桂棠  李兴振等 《地质通报》2002,21(11):701-707

青藏高原及邻区大地构造单元的划分是当前该地区板块构造精细结构研究的关键,也是板内构造研究的基础理论问题。本文在前人工作的基础上,结合青藏高原及邻区新一轮1∶25万区域地质调查成果,基于多岛弧盆系的形成是大洋向大陆岩石圈构造体制演化转换的标志这一认识,将弧-弧、弧-陆及陆-陆碰撞结合带和夹持于其间的陆块、岩浆弧划分为一级单元,构成青藏高原及邻区构造单元的基本骨架;以南昆仑俯冲碰撞结合带和班公湖-丁青-碧土-昌宁-孟连结合带为界,划分出:泛华夏大陆早古生带秦祁昆构造区、泛华夏大陆晚古生代—三叠纪羌塘-三江构造区及冈瓦纳北缘晚古生代—中生代冈瓦纳-喜马拉雅构造区。这样的厘定不仅对青藏高原及邻区的地质科学研究具有重要的理论意义,而且对青藏高原空白区区域地质调查和成矿地质条件分析等也有重要的实际意义。  相似文献   

“Forever Hmong”: Ethnic Minority Livelihoods and Agrarian Transition in Upland Northern Vietnam   总被引：1，自引：0，他引：1  

Sarah Turner 《The Professional geographer》2013,65(4):540-553

This article examines how ethnic minority Hmong farmers have adapted to, circumnavigated, or resisted state-sponsored agrarian change and other interventions in the northern Vietnam uplands over the past twenty years. Based on longitudinal research with Hmong informants, I examine to what extent their livelihood strategies have led to wealth creation or differentiation. The article highlights the most important transformations, as farmers conceive and voice them, to Hmong agrarian livelihoods over this period, the importance of longitudinal fieldwork to help unravel endogenous wealth definitions, and the complex impacts of state interventions on ethnic minority ways of making a living.  相似文献   

Spatiotemporal index for analyzing controls on snow climatology: application in the Colorado Front Range     

Eric E. Richer  Stephanie K. Kampf  Steven R. Fassnacht  Cara C. Moore 《自然地理学》2013,34(2):85-107

Mountain snowpacks are important water supplies that are susceptible to climate change, yet snow measurements are sparse relative to snowpack heterogeneity. We used remote sensing to derive a spatiotemporal index of snow climatology that reveals patterns in snow accumulation, persistence, and ablation. Then we examined how this index relates to climate, terrain, and vegetation. Analyses were based on Moderate Resolution Imaging Spectroradiometer eight-day snow cover from 2000 to 2010 for a mountain watershed in the Colorado Front Range, USA. The Snow Cover Index (SCI) was calculated as the fraction of years that were snow covered for each pixel. The proportion of SCI variability explained by independent variables was evaluated using regression analysis. Independent variables included elevation, northing, easting, slope, aspect, northness, solar radiation, precipitation, temperature, and vegetation cover. Elevation was the dominant control on SCI patterns, due to its influence on both temperature and precipitation. Grouping SCI values by elevation, we identified three distinct snow zones in the basin: persistent, transitional, and intermittent. The transitional snow zone represents an area that is sensitive to losing winter snowpack. The SCI can be applied to other basins or regions to identify dominant controls on snow cover patterns and areas sensitive to snow loss.  相似文献   

转型期社区医疗服务多元供给模式——以广州市天河区为例     

齐兰兰  周素红  闫小培 《热带地理》2013,(2):187-194

以广州市统计局提供的第六次人口普查数据作为人口统计数据源,以天河区卫生局提供的社区医疗机构数据作为社区医疗服务研究数据源,以广州市天河区作为研究案例,总结出社区医疗服务存在政府供给、单位制供给、集体经济供给、社会力量供给4种模式。各供给模式均具有受卫生局领导、政府部门监管和作为城市医疗体系的基础等一系列共性,同时在供给主体、服务对象、筹资与财务管理和人事管理等方面存在差异性,形成相互补充的多元模式共存体系,社区医疗服务的准公共物品属性、社会经济体制转型与城乡二元体制、居民的多元化需求和不同供给主体的利益诉求综合作用是多元模式共存的机制。只有充分利用多元模式供给主体、全方位协调机制要素、进行合理的制度设计,才能更好地促进社区医疗服务均等化,同时为其他城市公共服务供给提供参考借鉴。  相似文献   

三江特提斯复合造山与成矿作用   总被引：72，自引：4，他引：68  

邓军  侯增谦  莫宣学  杨立强  王庆飞  王长明 《矿床地质》2010,29(1):37-42

三江特提斯构造带作为全球特提斯构造在中国大陆最典型的发育地区,经历了复杂而完整的演化历史:从晚前寒武纪—早古生代泛大陆解体与原特提斯洋形成,经古特提斯多岛弧盆系发育与古生代—中生代增生造山/盆山转换,到新生代印度-亚洲大陆碰撞与叠加改造,完好地记录了超级大陆裂解→增生→碰撞的完整演化历史和大陆动力学过程,可谓是中国大陆构造演化的典型缩影。复合造山和叠加转换导致了三江特提斯域复杂的成矿演化,主要表现为:①在构造转换阶段,于元古代刚性基底基础上发育大量叠加改造型矿床,具有独特的金属组合(Sn-Cu,Sn-Pb-Zn,Fe-Cu等);②火山成因块状硫化物(VMS)矿床伴随特提斯岩石圈演化,连续发育于陆缘裂谷(Cu)→初始洋盆(Cu-Zn)→大洋岛弧(Cu-Zn-Pb)→弧间裂谷或弧后盆地(Pb-Zn-Ag)→弧-陆碰撞裂陷盆地(Cu-Pb-Zn)等阶段及诸环境;③特提斯阶段的岛弧型斑岩Cu矿被碰撞造山阶段的大陆型斑岩Cu矿所取代;④世界级规模的金属成矿带和巨型矿床,在新生代碰撞造山期爆发式产生。尽管已有的研究从整体上勾画出了三江特提斯域的基本构造特征和成矿面貌,但仍有许多重要问题尚未解决:①三江复合造山带构造叠加、...  相似文献   

长江中下游及其邻区中生代构造体制转换   总被引：16，自引：13，他引：3  

宋传中  周涛发  闫峻  任升莲  李加好  涂文传  张妍 《岩石学报》2010,26(9):2835-2849

长江中下游及其邻区中生代以来经历了特提斯、古亚洲、太平洋三大构造体制复杂的转换过程,地壳活动频繁,不同期次、不同方向、不同性质的构造叠加强烈,并控制了区内的岩浆活动和热液成矿。(1)印支晚期特提斯构造体制作用,具有俯冲带性质的襄樊-广济断裂带和先后具有左旋平移转换断层性质的郯庐断裂带产生。(2)燕山早期特提斯构造体制向古亚洲构造体制和太平洋构造体制转换,其一,晚侏罗世古亚洲构造体制近南北向挤压,桐柏-大别造山带形成共轭剪切带。其二,晚侏罗世与早白垩世之交古太平洋板块活动,NE向展布的华南板内构造形成。(3)燕山晚期脉动式伸展构造产生大规模火山喷发和岩浆活动;晚白垩世-始新世长江中下游地区盆-岭构造形成。(4)喜马拉雅早期太平洋构造体制下近E-W向挤压作用,近S-N向展布的红色盆地发生反转,呈NE-SW向线状展布。  相似文献