Gakkel洋中脊基底隆起的非对称地壳结构          下载免费PDF全文

凌子龙  高金耀  赵俐红  杨春国  管清胜  张涛 《地球物理学报》2019,62(5):1755-1771

超慢速扩张的北冰洋Gakkel洋中脊具有六个沿扩张方向的线性基底隆起(本文编号为A—F).这些线性基底隆起在中轴两侧的地球物理场和地壳结构呈现不同程度的非对称性.本文利用Gakkel洋中脊的地形、空间重力异常(FAA)和航空磁力数据,计算了它的扩张速率、剩余地幔布格重力异常(RMBA)、地壳厚度和非均衡地形.根据中轴两侧地形和地壳厚度的对称关系,我们将六个基底隆起分为对称型和非对称型两种类型.整体上,B、D和F区基底隆起在中轴两侧的地形和地壳厚度的非对称幅值(两侧差值的绝对值)较小,其中地形的非对称幅值分别为～157m、～125m、～208m,地壳厚度的非对称幅值分别为～1km、～0.06km、～0.3km;而A、C和E区的非对称幅值较大,其中地形的非对称幅值分别为～510m、～410m、～673m,地壳厚度的非对称幅值分别为～2km、～2.5km、～1.1km.我们因此推断B、D和F区具有相对对称的地壳结构,而A、C和E区具有非对称的地壳结构.根据A、C和E区中轴两侧非均衡地形的对称关系和非对称地形的补偿状态,推测A区的非对称性可能是由岩浆分配不均所导致;而C区和E区的非对称性可能是由构造断层作用使断层下盘向上抬升变薄所导致.我们进一步推测洋中脊走向的改变可能使得构造作用更易集中于基底隆起的一侧.  相似文献   

Groundwater mixing between different aquifer types in a complex structural setting discerned by elemental and stable isotope geochemistry          下载免费PDF全文

Dorina Murgulet  Marlon Cook  Valeriu Murgulet 《水文研究》2016,30(3):410-423

Karst aquifers are well known for their intricate stratigraphy and geologic structures, which make groundwater characterization challenging because flowpaths and recharge sources are complex and difficult to evaluate. Geochemical data, collected from ten closely spaced production wells constructed in two karst aquifers (Bangor Limestone (Mb) and Tuscumbia Limestone/Fort Payne Chert (Mftp)) in Trussville, north‐central Alabama, illustrate two distinctive groundwater end‐members: (1) higher major ion, dissolved inorganic carbon, conductivity, alkalinity concentrations, heavier δ¹³C ratios (max: −10.2 ± 0.2‰ Vienna Pee Dee Belemnite (PDB)) and lower residence times (mean: 19.5 ± 2 years, n = 2) of groundwater in the Mb aquifer and (2) lower constituent concentrations, lighter δ¹³C ratios (min: −13.4 ± 0.2‰ PDB) and longer residence times of groundwater (mean: 23.6 ± 2 years, n = 4) in the Mftp aquifer. Summer and fall data and the binary mixing model show aquifer inter‐flow mixing along solution fractures and confirms the distinctive groundwater geochemistry of the two aquifers. Lowering of static water levels over the summer (drawdown from 2 to 5.2 m) leads to more reducing groundwater conditions (lower Eh values) and slightly enriched δ¹⁸O and δD ratios during the fall [δ¹⁸O: −4.8 ± 0.1 to −5.4 ± 0.1‰ Vienna Standard Mean Oceanic Water (VSMOW), n = 9; δD: −25.4 ± 1 to −27.4 ± 1‰ VSMOW, n = 9] when compared with summer season samples (δ¹⁸O: −5.1 ± 0.1 to −5.7 ± 0.1‰ VSMOW, n = 11; δD: −25.0 ± 1 to −30.6 ± 1‰ VSMOW, n = 11). GIS analyses confirm the localized origin of recharge to the investigated aquifers. The combination of GIS, field parameters and geochemistry analyses can be successfully used to identify recharge sources, evaluate groundwater flow and transport pathways and to improve understanding of how groundwater withdrawals impact the sustainability and susceptibility to contamination of karst aquifers. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

中印度洋脊Edmond热液区黄铁矿的标型特征及其对海底成矿作用环境的指示   总被引：1，自引：0，他引：1  

王叶剑  韩喜球  金翔龙  邱中炎  朱继浩 《矿物学报》2011,31(2):173-179

对中印度洋脊Edmond热液区的丘顶和丘坡进行电视抓斗取样,获得了大量的金属硫化物等热液作用产物样品。在进行细致的矿相学分析基础上,对硫化物中黄铁矿的标型特征及其演化进行了详细研究。结果表明,Edmond热液区的黄铁矿可分3种类型,其形态标型和成分标型分别具有以下特征:Ⅰ型:呈自形立方体状,S/Fe原子数比接近于2.00,微量元素具有高Cu,低Zn、As、Pb、Ni和Ag的特点,Cu/Zn值高,平均可达4.26;Ⅱ型:呈半自形立方体状,S/Fe原子数比平均2.03,具有高Zn、Co、低Cu的特点,Cu/Zn值(平均0.04)低;Ⅲ型:主要呈胶状、莓球状,S/Fe原子数比平均2.04,具有Ag、Pb、Zn、As元素富集的特点,Cu/Zn值介于前两者之间(平均1.09)。根据硫化物中矿物共生组合关系,认为这3类黄铁矿分别对应高温、中高温和低温成矿作用,黄铁矿的形态和成分能很好地指示热液区的成矿环境和成矿条件的演变。  相似文献   

The Statherian itabirite-bearing sequence from the Morro Escuro Ridge,Santa Maria de Itabira,Minas Gerais,Brazil     

《Journal of South American Earth Sciences》2015

The itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Brasiliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared granites of the anorogenic Borrachudos Suite (∼1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron formation (itabirite) correlatable with the sequences of the Serro Group, which underlies the metasedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge. A maximum Statherian deposition age (1668 Ma) was established using SHRIMP U–Pb isotopic constraints on zircon grains from conglomerate and quartzite units overlying the itabirite. The itabirite is predominantly hematitic and its geochemical characteristics are typical of a Lake Superior-type BIF deposited in a platformal, suboxic to anoxic environment distant from Fe-bearing hydrothermal vents. Close to the contact zone with amphibolites of the Early Neoproterozoic Pedro Lessa mafic suite, an increase of the magnetite content and crystallization of metasomatic Mg-hornblende and Ce-allanite can be observed. These mineralogical changes developed preferentially along the igneous contact zone but are probably co-genetic with the formation of alteration haloes in zircon grains during the Neoproterozoic Brasiliano orogeny (506 ± 6 Ma).  相似文献   

Migrating magmatism in a continental arc: Geodynamics of the Eastern Mediterranean revisited   总被引：1，自引：0，他引：1  

Yener Eyuboglu  M. Santosh  Francis O. Dudas  Sun-Lin Chung  Enver Akaryal&#x; 《Journal of Geodynamics》2011,52(1):2-15

  相似文献   

西南印度洋中脊50°E基性超基性岩石地球化学特征及其成因初探     

韩宗珠  张贺  范德江  丁蒙蒙  刘明  徐翠玲 《中国海洋大学学报(自然科学版)》2012,(9):69-76

西南印度洋中脊是典型的慢速扩张洋中脊之一。对采自西南印度洋中脊50°E附近的7件玄武岩和蛇纹石化橄榄岩样品所作的分析表明,基性玄武岩类SiO2含量为43.72%～48.40%,TiO2含量较少,为1.14%～1.52%;MgO含量为5.96%～10.98%;TFe2O3含量为4.55%～5.2%;Mg#值为0.53～0.64,里特曼指数σ为2.34～20.10。微量元素Zr/Nb和Y/Nb比值为显示N-MORB的性质,但是其他微量元素的比值(Ba/Nb,Ba/Th,La/Nb,Nb/U,Nb/Pb)均不显示正常洋中脊玄武岩的特征,微量元素原始地幔标准化蛛网图显示强烈富集K和Pb,亏损Nb,稀土元素显示较为平缓的分配模式。超基性蛇纹石化橄榄岩的主量元素特征为SiO2为38.91～45.49;TiO2含量为0.02～0.28;MgO含量很高,为36.87～40.61,TFe2O3含量为2.82～3.91,Mg#值为0.92～0.94。微量元素中Ni,Cr的含量很高,原始地幔标准化蛛网图显示橄榄岩强烈富集K和Pb,Ba,Th,La,Ce,Ti中等程度富集,而亏损Nb,Sr。稀土元素总量较低,标准化曲线显示轻稀土元素富集模式。结合地球化学特征及前人研究资料分析认为,西南印度洋中脊的基性岩和超基性岩属同源性质,其原始地幔物质可能为部分正常洋中脊亏损地幔混染了陆壳或远洋沉积物的结果。  相似文献   

Catastrophic middle Pleistocene jökulhlaups in the upper Susquehanna River: Distinctive landforms from breakout floods in the central Appalachians     

R. Craig Kochel  Richard P. Nickelsen  L. Scott Eaton 《Geomorphology》2009,110(3-4):80-95

Widespread till and moraines record excursions of middle-Pleistocene ice that flowed up-slope into several watersheds of the Valley and Ridge Province along the West Branch of the Susquehanna River. A unique landform assemblage was created by ice-damming and jökulhlaups emanating from high gradient mountain watersheds. This combination of topography formed by multiple eastward-plunging anticlinal ridges, and the upvalley advance of glaciers resulted in an ideal geomorphic condition for the formation of temporary ice-dammed lakes. Extensive low gradient (1°–2° slope) gravel surfaces dominate the mountain front geomorphology in this region and defy simple explanation. The geomorphic circumstances that occurred in tributaries to the West Branch Susquehanna River during middle Pleistocene glaciation are extremely rare and may be unique in the world. Failure of ice dams released sediment-rich water from lakes, entraining cobbles and boulders, and depositing them in elongated debris fans extending up to 9 km downstream from their mountain-front breakout points. Poorly developed imbrication is rare, but occasionally present in matrix-supported sediments resembling debris flow deposits. Clast weathering and soils are consistent with a middle Pleistocene age for the most recent flows, circa the 880-ka paleomagnetic date for glacial lake sediments north of the region on the West Branch Susquehanna River. Post-glacial stream incision has focused along the margins of fan surfaces, resulting in topographic inversion, leaving bouldery jökulhlaup surfaces up to 15 m above Holocene channels. Because of their coarse nature and high water tables, jökulhlaup surfaces are generally forested in contrast to agricultural land use in the valleys and, thus, are readily apparent from orbital imagery.  相似文献   

山脊线与坡度和峰值速度放大系数的相关性研究   总被引：1，自引：1，他引：0       下载免费PDF全文

蒋涵  周红  高孟潭 《地球物理学报》2015,58(1):229-237

地形效应是地震工程和地震学的重要研究内容.数值方法是研究地形效应的重要工具.然而以往关于地形特征对地形效应的影响的研究大多是基于二维简单模型.对三维真实地形特征和地震动放大的关系缺乏详细的研究.为了更好地描述三维地形特征,本文将地形用不同的地形特征因子来描述,并用算法将它们从地形数据中提取出来.从而使地形和放大系数的相关性的研究转换为不同地形特征因子和放大系数的相关性的研究上.本文中,我们选择芦山地区作为研究对象,用算法提取出特征因子山脊线和坡度.它们分别表征了山脊形态和山体的陡峭程度.我们又用谱元法分别模拟三种不同主频Ricker子波的地震波在起伏地表和水平地表模型中的传播,并得到了它们各自的峰值速度(PGV)放大系数.通过分析三个主频的PGV放大系数在山脊线上分布,我们发现放大系数幅值在山脊线上分布不均匀.放大系数较高的地方位于山脊线弯曲或宽度发生变化的附近.我们又统计了三个放大系数在滑动平均坡度上分布,并得到了放大系数均值和坡度的正相关曲线.结果表明坡度和放大系数两者在幅值分布上具有正相关性.  相似文献   

Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S,southern Mid-Atlantic Ridge   总被引：1，自引：0，他引：1  

王淑杰  李怀明  翟世奎  于增慧  邵宗泽  蔡宗伟 《海洋学报(英文版)》2017,36(2):22-34

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge(SMAR) was newly found during the 22 nd cruise carried out by the China Ocean Mineral Resources Research Development Association(COMRA). Sulfide samples were collected at three stations from the hydrothermal field during the26 th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types:(1) the Ferich sulfide, which contains mainly pyrite and chalcopyrite;(2) the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and(3) the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite(isocubanite and possible coarse pyrite), fine pyrite,sphalerite(marmatite), galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations(Py-I and Py-II) of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals(Py-I). Sphalerite in the Fe-Zn-rich sulfide is characterized by a"chalcopyrite disease" phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.  相似文献   

西南印度洋中脊三维地震探测中炮点与海底地震仪的位置校正   总被引：9，自引：3，他引：6       下载免费PDF全文

敖威  赵明辉  丘学林  李家彪  陈永顺  阮爱国  李守军  张佳政  吴振利  牛雄伟 《地球物理学报》2010,53(12):2982-2991

在海上实施三维地震探测过程中,人工震源枪阵中心与船上GPS的距离及地震探测作业中的船行方向造成炮点实际位置与预设位置有一定偏差;自由落体投放的OBS由于海流的影响会偏离原定设计位置(投放点),因此,炮点与海底地震仪(OBS)的位置校正是三维地震结构研究中的基本环节.本文利用艏向信息校正了炮点位置;采用蒙特卡洛和最小二乘法方法对海底地震仪的位置进行了校正,并探讨了直达水波曲线特征.结果表明 OBS位置一般偏离设计点1 km左右,其误差范围在20 m以内,校正后的OBS记录剖面展示了真实的记录情况.该研究结果为下一步西南印度洋的三维层析成像研究提供了坚实数据基础,同时为今后南海的三维深部地壳结构探测提供经验与借鉴.  相似文献