New interpretation of the Franciscan mélange at San Simeon coast,California: tectonic intrusion into an accretionary prism     

Yujiro Ogawa  Ryota Mori  Toshiaki Tsunogae  Yildirim Dilek  Ron Harris 《International Geology Review》2015,57(5-8):824-842

Many concepts and interpretations on the formation of the Franciscan mélange have been proposed on the basis of exposures at San Simeon, California. In this paper, we show the distribution of chaotic rocks, their internal structures and textures, and the interrelationship between the chaotic rocks and the surrounding sandstones (turbidites). Mélange components, particularly blueschists, oceanic rocks, including greenstone, pillow lava, bedded chert, limestone, sandstone, and conglomerate, have all been brecciated by retrograde deformation. The Cambria Slab, long interpreted as a trench slope basin, is also strongly deformed by fluidization, brecciation, isoclinal folding, and thrusting, leading us to a new interpretation that turbiditic rocks (including the Cambria Slab) represent trench deposits rather than slope basin sediments. These rocks form an accretionary prism above mélanges that were diapirically emplaced into these rocks first along sinistral-thrust faults, and then along dextral-normal faults. Riedel shear systems are observed in several orders of scale in both stages. Although the exhumation of the blueschist blocks is still controversial, the common extensional fractures and brecciation in most of the blocks in the mélanges and further mixture of various lithologies into one block with mélange muddy matrix indicate that once deeply buried blocks were exhumed from considerable depths to the accretionary prism body, before being diapirically intruded with their host mélange along thrust and normal faults, during which retrograde deformation occurred together with retrograde metamorphism. Recent similar examples of high-pressure rock exhumation have been documented along the Sofugan Tectonic Line in the Izu forearc areas, in the Mineoka belt in the Boso Peninsula, and as part of accretionary prism development in the Nankai and Sagami troughs of Japan. These modern analogues provide actively forming examples of the lithological and deformational features that characterize the Franciscan mélange processes.  相似文献   

Middle to late Triassic mélange exhumation along a pre-Andean transpressional fault system: coastal Chile (26°–42° S)     

Terence T. Kato  Estanislao Godoy 《International Geology Review》2015,57(5-8):606-628

Mélanges occur as discontinuous, mappable, units along an extensive N–S-trending, steeply dipping zone of distributed shear in metamorphic complexes along the coast of central Chile. Large mélange zones, from north to south, near Chañaral, Los Vilos, Pichilemu, and Chiloé Island, contain variations in lithologic and structural detail, but are consistent in exhibiting cross-cutting fabric features indicating a progressive transition from earlier ductile to more brittle deformation. In the Infiernillo mélange near Pichilemu, Permian to Early Triassic, sub-horizontal schistosity planes of the Western Series schist are disrupted, incorporated into, and uplifted along high-angle, N–S- to NNE–SSW-trending brittle–ductile shears. Mylonitic and cataclastic zones within the mélange matrix indicate active lateral shear during cumulative exhumation from depths exceeding 12 km in some areas. Exotic lithologies, such as Carboniferous mafic amphibolite and blueschist, formed during earlier Gondwanide subduction, match well with similar rocks in the Bahia Mansa to Los Pabilos region 750 km to the south, suggesting possible dextral offset. The development of the Middle to Late Triassic, N–S=trending, near-vertical shear zones formed weaknesses in the crust facilitating later fault localization, gravitational collapse, and subduction erosion along the continental margin. The length and linearity of this zone of lateral movement, coincident with a general hiatus of regional arc magmatism during the Middle to Late Triassic, is consistent with large-scale dextral transpression, or possible transform movement, during highly oblique NNE–SSW convergence along the pre-Andean (Gondwana) margin. The resultant margin parallel N–S-trending shear planes may be exploited by seismically active faults along the present coastal area of Chile. The palaeo-tectonic setting during the transitional period between earlier Gondwanide (Devonian to Permian) and later Andean (Late Jurassic to present) subduction may have had some similarity to the presently active San Andreas transform system of California.  相似文献   

Integration of ASTER and landsat TM remote sensing data for chromite prospecting and lithological mapping in Neyriz ophiolite zone,south Iran          下载免费PDF全文

Alireza Eslami  Majid Ghaderi  Sankaran Rajendran  Amin Beiranvand Pour  Mazlan Hashim 《Resource Geology》2015,65(4):375-388

Chromite deposits in Iran are located in the ophiolite complexes, which have mostly podiform types and irregular in their settings. Exploration for podiform chromite deposits associated with ophiolite complexes has been a challenge for the prospectors due to tectonic disturbance and their distribution patterns. Most of Iranian ophiolitic zones are located in mountainous and inaccessible regions. Remote sensing approach could be applicable tool for choromite prospecting in Iranian ophiolitic zones with intensely rugged topography, where systematic sampling and conventional geological mapping are limited. In this study, Landsat Thematic Mapper (TM) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data were used for chromite prospecting and lithological mapping in the Neyriz ophiolitic zone in the south of Iran. Image transformation techniques, namely decorrelation stretch, band ratio and principal component analysis (PCA) were applied to Landsat TM and ASTER data sets for lithological mapping at regional scale. The RGB decorrelated image of Landsat TM spectral bands 7, 5, and 4, and the principal components PC1, PC2 and PC3 image of ASTER SWIR spectral bands efficiently showed the occurrence of major lithological units in the study area at regional scale. The band ratios of 5/3, 5/1, 7/5 applied on ASTER VNIR‐SWIR bands were very useful for discriminating most of rock units in the study area and delineation of the transition zone and mantle harzburgite in the Neyriz ophiolitic complex. Spectral Angle Mapper (SAM) technique was implemented to ASTER VNIR‐SWIR spectral bands for detecting minerals of rock units and especially delineation of the transition zone and mantle harzburgite as potential zones with high chromite mineralization in the Neyriz ophiolitic complex. The integration of information extracted from the image processing algorithms used in this study mapped most of lithological units of the Neyriz ophiolitic complex and identified potential areas of high chromite mineralization (transition zone and mantle harzburgite) for chromite prospecting targets in the future. Furthermore, image processing results were verified by comprehensive fieldwork and laboratory analysis in the study area. Accordingly, result of this investigation indicate that the integration of information extracted from the image processing algorithms using Landsat TM and ASTER data sets could be broadly applicable tool for chromite prospecting and lithological mapping in mountainous and inaccessible regions such Iranian ophiolitic zones.  相似文献   

40m天线面板调试与精度分析     

金旺  汪敏  张巨勇  赵辉  张萍  宋俊峰  许春 《天文研究与技术》2006,3(4):401-407

总结了40m天线面板安装调试及检测的过程，分析了反映望远镜面板指标的吨性能检测结果。结果表明天线面板精度优于原设计要求。  相似文献   

南秦岭勉略蛇绿构造混杂带辉长辉绿岩类微量-稀土元素地球化学   总被引：2，自引：0，他引：2  

赖绍聪 《地球科学与环境学报》2005,27(3):5-9

应用元素地球化学方法．研究了勉略带中辉长辉绿岩的相关特征．结果表明．勉略蛇绿构造混杂带内的辉长岩属高铝强碱质辉长岩类，是地幔橄榄岩部分熔融的产物。辉绿岩墙群属强碱铝质基性岩类，过渡族元素蛛网图与辉长岩类几乎完全相同，其不相容元素与辉长岩类总体趋势相一致．反映了一种递进岩浆演化趋势。因此，本区辉长岩与辉绿岩墙群具同源岩浆分异演化的地球化学特征．其均为勉略蛇绿岩的重要组成端元。  相似文献   

Science, Technology and Detectors for Extremely Large Telescopes     

Roberto Gilmozzi 《Experimental Astronomy》2005,19(1-3):5-13

The second decade of the third millennium will hopefully see a new generation of extremely large telescopes. These will have diameters from 30 to 100 meters and use advanced adaptive optics to operate at the diffraction limit in order to detect astronomical objects that are impossible to observe today, such as earth-like planets around nearby stars and the earliest objects in the Universe. Even for small fields of view, the requirements for detectors are daunting, with sizes of several gigapixels, very fast readout times and extremely low readout noise. In this paper I briefly review the science case for ELTs and the requirements they set on telescopes and instruments, and report on the status of the OWL 100 m telescope project and the challenges it poses.  相似文献   

云南天文台1m望远镜暗天体分光仪和照相机     

岑学奋  钱铜铃 《天文研究与技术》2003,(4):34-42

云南天文台1m望远镜终端之一的暗天体分光仪和照相机具有4种运行模式:缩焦照相机、无缝多目标光谱仪、有缝光谱仪和星冕仪。这4种运行模式能在几分钟的时间内相互转换,高效快速和灵活方便。该仪器的光学质量优秀,光学系统消像差,特别是消色差。由于光学系统消色差,所成像的低色散光谱在404.6～766.5nm全波段尖锐平直。在多色测光时,各测光波段的像面位置不变,同时兼有大视场的优点,可提高测光精度和测光效率。  相似文献   

Composition and assemblage characteristics of magnetic minerals in layer S<Subscript>5-1</Subscript> of Xifeng and Duanjiapo sections     

Jia?RongfenEmail author  Peng?Xianzhi  Zhou?Zheng  Liu?Dehan  Wang?Guanxin  Wang?Deqiang 《中国地球化学学报》2004,23(3):197-206

Relatively strongly magnetic fine components (< 30μm, XS-4J and DS-4J) which are most environmentally sensitive were separated from layer S_5-1 in the Xifeng and Duanjiapo loess sections and analyzed by MPV-3 for their morphometric characteristics and reflectance, SEM-ESD for their element contents and XRD for their mineral phases, respectively. The results showed that minerals in both samples are dominated by detrial Fe-Ti oxides of aeolian origin. In sample XS-4J the reflectance and iron contents of magnetic minerals are usually high. In addition to magnetite (Fe₃O₄), maghemite (γFe₂O₃) and hematite (Fe₂O₃), some Fe-high oxide (72.25 wt%–86.67 wt%), ilmenite (FeTiO₃), and magnetite-ulvöspinel [Fe(FeCr)O₄, Fe (FeNi)O₄] were also detected. In sample DS-4J obvious negative linear correlations were found between Ti and Fe, and the contents of Mn, Si, Al and Ca are usually high and the minerals are dominated by magnetite (maghemite), goethite (FeOOH) and limonite (containing Si and OH). In addition, the signs of corrosion of magnetic minerals and newly crystallized magnetite (maghemite) were recognized. Differences in the composition and assemblage characteristics of magnetite minerals between XS and DS reflect significant differences in source rocks and preserving conditions.  相似文献   

近4万年渤海西岸海侵时古海面的现代标高对比研究^*   总被引：2，自引：1，他引：1       下载免费PDF全文

魏灵  贾玉连  易朝路  王洪波  郭盛乔 《第四纪研究》2006,26(3):361-369

近4万年以来,相应于两次高太阳辐射暖湿期渤海西岸曾经两次海水泛陆事件,即40~28kaB.P.与10~4kaB.P.海侵事件。文章基于众多钻孔海相层中有孔虫、介形类等海相微体生物化石的组合特征恢复海水深度,重建了海侵最大时的古海面的现代标高。结果显示: 40~28kaB.P.海侵,海面的现代标高最高可达-11~-5m;10~4kaB.P.海侵则为2~3m。后者同众多研究所认为的中全新世存在高海面,海面高度为2~3m的结论大致吻合,前者则与全球气候尚处在间冰阶,冰川部分消融,世界洋面处在-50m的大背景不协调。而辽东与山东半岛沿海众多钻孔揭示,40~28kaB.P.渤海地区并没有高于-50~-20m海面存在的证据。通过区域环境的综合分析,认为40~28kaB.P.渤海西岸的海侵,是早玉木冰期持续4~5万年之久的冰期低海面环境,这种特殊的环境使现代渤海西岸的大部分区域远离沉积环境,成为冲刷侵蚀区,这种效应叠加在冰期边缘海式构造下沉与弧后盆地性质的构造下沉背景之上造成区域性异常地面低洼;渤海西岸异常地面低洼在间冰阶全球趋暖,冰川型海侵的过程中形成的区域性强烈"视"海侵(指示当时海侵时海水深度很大,而不是海水的陆泛范围大)。  相似文献   

几种再分析地表气温资料在中国区域的适用性评估   总被引：19，自引：3，他引：16       下载免费PDF全文

赵天保  符淙斌 《高原气象》2009,28(3):594-606

应用台站观测资料对ERA-40、NCEP/NCAR、NCEP/DOE和JRA-25等几种再分析地表(2m)气温资料在中国不同区域、不同年代和季节的气候均值、年际变化和变率特征及其气候趋势等所反映出来的适用性问题进行了系统评估.结果表明,几种再分析产品在全国大多数地区的气候变化研究中都具有一定的合理性,特别是1979年以后的资料可靠性更高一些.但相比而言,它们在冬季的可信度一般要高于夏季,东部地区的可信度一般要高于西部地区;ERA-40和JRA-25再分析产品的适用性要高于NCEP/NCAR和NCEP/DOE再分析产品;其中,JRA-25在均值、年际变化和变率特征的描述上具有更高的可靠性,而ERA-40在长期气候变化趋势(44年)的描述上则要明显优于NCEP/NCAR再分析产品.  相似文献