On the origin of the galactic ridge recombination lines     

K. R. Anantharamaiah 《Journal of Astrophysics and Astronomy》1986,7(3):131-139

Radio recombination lines are known to be observable at positions along the galactic ridge which are free of discrete continuum sources. Based on the results of a recent survey of H272α lines it is shown that most of the observed galactic ridge recombination lines can be explained as emission from outer low-density envelopes of normal Hn regions. The distribution of low-density ionized gas and discrete HII regions as a function of the distance from the galactic centre is also derived.  相似文献   

Unpairing metamorphic belts: P–T paths and a tectonic model for the Ryoke Belt, southwest Japan     

MICHAEL BROWN 《Journal of Metamorphic Geology》1998,16(1):3-22

Southwest Japan is divided into Outer and Inner Zones by the Median Tectonic Line (MTL), a major transcurrent fault. The Outer Zone is composed of the Sambagawa (high-pressure intermediate or high P/T type metamorphism), Chichibu and Shimanto Belts. In the Inner Zone, the Ryoke Belt (andalusite– sillimanite or low P/T type metamorphism) was developed mainly within a Jurassic accretionary complex. This spatial relationship between high P/T type and low P/T type metamorphic belts led Miyashiro to the idea that metamorphic belts were developed as ‘paired’ systems. Textural relationships and petrogenetically significant mineral assemblages in pelites from the Ryoke Belt imply peak P–T conditions of ≈5 kbar and up to 850 °C in migmatitic garnet–cordierite rocks from the highest-grade metamorphic zone. It is likely that the thermal anomaly responsible for metamorphism of the Ryoke Belt was related to a segment of the Farallon–Izanagi Ridge as it subducted under the eastern margin of the Asian continent during the Cretaceous. The sequence of mineral assemblages developed in pelites implies a metamorphic field gradient with shallow dP/dT slope, inferred to have been generated by a nested set of hairpin-like ‘clockwise’P–T paths. These P–T paths are characterized by limited prograde thickening, minor decompression at peak-T , and near-isobaric cooling, features that may be typical of P–T paths in low P/T type metamorphic belts caused by ridge subduction. A ridge subduction model for the Ryoke Belt implies that juxtaposition of the high-P/T metamorphic rocks of the Sambagawa Belt against it was a result of terrane amalgamation. Belt-parallel ductile stretching, recorded as syn-metamorphic, predominantly constrictional strain in both Ryoke and Sambagawa Belt rocks, and substantial sinistral displacement on the MTL are consistent with left-lateral oblique convergence. Diachroneity in fast cooling of the Ryoke Belt is implied by extant thermochronological data, and is inferred to relate to progressive SW to NE docking of the Sambagawa Belt. Thus, an alternative interpretation of ‘paired’ metamorphic belts in Japan is that they represent laterally contemporaneous terranes, rather than outboard and inboard components of a trench/arc ‘paired’ system. Amalgamation of laterally contemporaneous terranes during large translations of forearcs along continental margins may explain other examples of ‘paired’ metamorphic belts in the geological record.  相似文献   

一种多因子加权平均温度模型的构建方法     

李得宴  杨维芳  高志钰  蒋玉祥  李蓉蓉 《测绘科学》2021,46(3):73-79

针对在地基GNSS水汽反演的过程中,天顶湿延迟转换为大气可降水量时如何建立精确的大气加权平均温度(Tm)模型的问题,该文在建立Tm模型前全面考虑了对Tm有显著影响的变量并选择最优回归子集。但分析发现,最优回归子集中各变量之间存在较强的相关性,这将会导致变量之间存在多重共线性,从而影响模型的稳定性和可靠性。选择2013—2015年相关气象数据作为变量并应用岭回归的方法削弱变量之间的多重共线性,建立稳定的多因子Tm回归模型。并利用该模型分别预测2016年1—12月、2019年1—7月的Tm,均方根误差分别为2.3 K和2.0 K,预测精度较高,这将为高精度的水汽反演奠定较好的数据基础。  相似文献   

Geological Evolution of Longhushan World Geopark in Relation to Global Tectonics     

Timothy M Kusky  叶明和  王军鹏  王璐 《中国地质大学学报(英文版)》2010,(1)

The South China fold belt has experienced a complex series of tectonic events that span 1.0 billion years of earth history. Longhushan (龙虎山) World Geopark is located on the Proterozoic suture between the Yangtze craton and Cathyasia block and highlights the long history of this belt. Collision of the Cathyasia and Yangtze cratons 1.0 billion years ago was associated with the formation of the Rodinian supercontinent where most of the planet's landmasses were amalgamated into one block. Jurassic through Early...  相似文献   

无震脊或海山链俯冲对超俯冲带处的地质效应   总被引：3，自引：1，他引：2  

鄢全树  石学法 《海洋学报》2014,36(5):107-123

全球海底分布着众多的无震脊或海山链,且在太平洋、印度洋及大西洋均存在靠近俯冲带的海岭。除小安德列斯弧外的巴拉克达脊和蒂勃朗脊起源自转换断层外,一般认为它们由与板块构造动力学迥异的地幔柱动力学所形成的。在板块汇聚边缘处,与扩张脊处所形成的正常洋壳一起,无震脊或海山链俯冲于陆缘弧或洋内弧之下,其对弧及弧后地区的地质效应(构造、地貌、地震以及岩浆作用等)有别于正常洋壳俯冲。无震脊或海山链的俯冲通常造成俯冲带地区的上驮板块的局部异常抬升、俯冲剥蚀作用效应的加强、海沟的向陆迁移以及地震强度的增加。同时,无震脊或海山链俯冲时,其携带的具富集地球化学特征的物质不仅影响着地幔地球化学,也对弧及弧后火山熔岩化学产生明显影响,并对超俯冲地区的热液矿床的形成产生重要影响。最后,本文指出了我国有关无震脊或海山链俯冲的可能的研究方向包括黄岩海山链俯冲对吕宋岛弧的可能影响、印度洋无震脊俯冲对青藏高原局部地区的影响,有我国学者参与的IODP344航次的研究对象——科科斯脊俯冲对哥斯达黎加地震成因的效应以及位于西太平洋地区靠近俯冲带的一些无震脊等。  相似文献   

Seismic geomorphology,architecture and genesis of Miocene shelf sand ridges in the Pearl River Mouth Basin,northern South China Sea     

《Marine and Petroleum Geology》2014

Multiple stages of large-scale shelf sand ridges, including the shoreface-attached and the offshore types, have developed in the Miocene successions on the mid-shelf region of the Pear River Mouth Basin, northern South China Sea. Utilizing a high-quality 3D seismic data set, accompanying 2D seismic profiles and well logs, the morphology, architecture and genesis of these shelf sand ridges have been systematically investigated in this study. The ridges are of very large scale, with the largest one having a maximum height of 64 m, a width of more than 20 km and a length of 37 km within the 3D survey area. Being mound-shaped, they also display obvious asymmetry character, with the ridge crest preferentially located on the SE side. Three main internal components, including the ridge front, central ridge and the ridge tail, have been recognized through careful anatomy analysis of the two most well-imaged ridges, each displaying distinct expressions on seismic amplitudes and geometries. In the plan view, most of the shelf sand ridges are generally NE–SW oriented and widening to the SW direction. Scouring features can also be clearly observed along the SW direction, including scour depressions and linear sandy remnants. On well logs, the shelf sand ridges are represented by an overall coarsening-upward pattern. Intervals with blocky sandstones are preferentially present on higher locations due to a differential winnowing process controlled by shelf topography.Plenty of evidence indicates that these ridges were primarily formed by the reworking of forced regressive or lowstand deltaic deposits under a persistent southwesterly flowing current during the subsequent transgression. This very current is a composite one, which is speculated to consist of winter oceanic current, SCSBK (South China Sea Branch of Kuroshio) intrusion onto the shelf and internal waves propagating from the Luzon Strait. Tidal currents might have contributed to the SE growth of the ridge. In response to the reglaciation of Antarctic ice-sheet and the closure of Pacific-Indian ocean seaway in the middle Miocene, the intensification of the North Pacific western boundary current was considered to have potential links to the initiation of the shelf sand ridges at ∼12 Ma. The development of shelf ridges was terminated and replaced by rapid deltaic progradation at ∼5.5 Ma.  相似文献   

Hydrogeochemistry and sustainability of freshwater lenses in the Samborombón Bay wetland,Argentina     

《Journal of South American Earth Sciences》2015

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西南印度洋中脊热液区烃类有机质组成及其成因意义     

雷吉江  初凤友  于晓果  李小虎  陶春辉  葛倩 《地学前缘》2015,22(1):281-290

利用气相色谱(GC)、气相色谱-质谱联用仪(GC-MS)测定了西南印度洋中脊49.6°E热液区热液产物中的可溶有机质,结合生物标志物和单体同位素分析,对烃类有机质的组成、来源及成因意义进行了探讨。硫化物烟囱体以正构烷烃(3.437~3.962μg/g)为主要烃类,L/H1,C22以上烷烃具有轻微奇碳数优势(CPI=1.140~1.209),NAR接近0;生物标志物类型丰富(Sq、IS40、烷基环己烷),C31藿烷22S/(R+S)高达0.77,且缺少17β(H),21β(H)构型藿烷;低碳数饱和脂肪酸为主要脂肪酸类型,异构/反异构脂肪酸含量显著,缺少单不饱和脂肪酸。热液蚀变岩以异构烷烃(2.094μg/g)为主要烃类,正构烷烃以低碳数(L/H=1.33)、偶碳优势(CPI=0.377)为特征;脂肪酸以单不饱和脂肪酸为主。结果表明,海洋原生生物体是49.6°E热液区主要的烃类有机质输入源,热液流体温度及化学条件是控制热液喷口区原生生物群落分布及热液产物中烃类有机质组成的主要因素。生物标志物类型显示硫化物烟囱体中具有产甲烷古菌与硫酸盐还原菌共存的现象,反映出热液流体中富含H2,表明49.6°E热液区具有非生物合成烃类的可能。  相似文献   

东南极普里兹湾陆隆区脊状沉积体的结构和形成过程     

沈中延  杨春国  高金耀  纪飞 《地球学报》2015,36(6):709-717

东南极普里兹湾陆隆区发育数个近垂直陆缘的脊状沉积体,这些沉积体记录了区域冰川活动和底流变化的历史。本文主要利用多道地震资料和水深资料对这些脊状沉积体的平面展布、走向上的结构差异进行了研究,在此基础上讨论了不同脊状沉积体的形成过程。结果表明研究区内脊状沉积体有两种不同结构类型:西部Wild峡谷两侧不对称发育的浊流堤岸沉积形成两个平行峡谷的脊状沉积体;东部数个脊状沉积体的形成与其下长期存在的浊流活动引起的穿时沉积间断面有关。不同峡谷的浊流活动起始时代不一,西部的Wild峡谷起始时代和陆隆区冰海沉积起始时代(P1)一致;东部Wilkins峡谷以及Murray峡谷从后期的P3(约26.1 Ma)开始,代表普里兹湾地区的一次冰川极盛事件。研究区所有峡谷及其浊流活动均随时间向海扩展,造成相应的脊状沉积体向海扩展。在脊状沉积体外缘区域,浊流输送而来的细粒沉积物在向西的底流作用下形成大型深海沉积物波。  相似文献   

西藏雅鲁藏布江缝合带西段东波蛇绿岩的构造背景特征   总被引：2，自引：0，他引：2  

熊发挥  杨经绥  李源  刘钊  郭国林  周文达  陈松永  李毅兵  徐向珍  牛晓露 《地球学报》2015,36(1):31-40

西藏东波蛇绿岩位于雅鲁藏布江缝合带西段,由地幔橄榄岩、辉石岩和辉长岩等组成。地幔橄榄岩主要为方辉橄榄岩、纯橄岩和少量二辉橄榄岩。岩体的边界出露玄武岩和硅质岩等。地幔橄榄岩中有少量辉石岩和辉长岩的脉岩,宽约1 m,走向北西,与岩体的构造线方向基本一致。各岩相岩石地球化学研究结果表明,东波蛇绿岩的岩相存在较大的差异,玄武岩具有与洋岛玄武岩(OIB)相似的地球化学特征,而地幔橄榄岩中辉石岩、辉长岩脉与洋中脊玄武岩(MORB)相似,形成于洋中脊环境,并受后期俯冲流体作用的改造。东波岩体中二辉橄榄岩具有与深海地幔橄榄岩较一致的轻稀土亏损特征,而方辉橄榄岩和纯橄岩的地球化学特征显示出岩体形成于MOR环境,后受到SSZ环境的改造。东波蛇绿岩的岩石地球化学特征显示其洋中脊叠加洋岛的构造背景。  相似文献