日本西南部四国增生复合体中的锰矿分布     

Masaharu NAKAGAWA 《地球学报》2012,33(S1):50-54

Bedded manganese ore deposits occur in many localities within the accretionary belts of the Shikoku region, SW Japan. The deposits occur mostly in bedded chert or its metamorphosed equivalent. These chert-hosted manganese deposits are considered to have been manganese nodule/crust-bearing siliceous sediments on deep-sea floor and have been converted to manganese ores by low-grade metamorphism through subduction-accretion process. The mineral assemblages of the ores reflect the metamorphic grade of the accretionary complexes. On the other hand, iron-manganese deposits and some manganese deposits occurring directly over basalt are considered to have been the hydrothermal precipitates associated with submarine volcanism.  相似文献   

Jilin-Heilongjiang High-Pressure Metamorphic Belt: Evidence and Tectonic Implications     

ZHOU Jianbo  Simon A WILDE  HAN Jie 《《地质学报》英文版》2013,87(Z1):534-534

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Divergent and convergent margins in the North-Western alps confrontation to actualistic models     

Gérard M. Stampfli  Michel Marthaler 《Geodinamica Acta》2013,26(3):159-184

Abstract

Divergent and convergent margins actualistic models arc reviewed and applied to the history of the western Alps. Tethyan rifting history and geometry are analyzed : (he northern European margin is considered as an upper plate whereas the southern Apulian margin is a lower plate; the Bréche basin is regarded as the former break-away trough; the internal Bríançonnais domain represents the northern rift shoulder whilst the more external domains are regarded as the infill of a complex rim basin locally affected by important extension (Valaisan and Vocontian trough).

The Schistes lustres and ophioliles of the Tsaté nappe are compared to an accretionary prism : the imbrication of this nappe elements is regarded as a direct consequence of the accretionary phenomena already active in early Cretaceous; the Gels/Simme complex could originate from a more internal part of the accretionary prism. Some eclogitic basements represent the former Apulian margin substratum (Sesia) others (Mont-Rose) are interpreted as the former edge of the European margin. The history of the closing Tethyan domain is analyzed and the remaining problems concerning the cinematics, the presence/absence of a volcanic arc and the eoalpine melamorphism are discussed.  相似文献   

伶仃洋河口水域纳潮特性分析     

方神光  陈文龙  崔丽琴 《海洋科学》2012,36(6):105-112

为阐明伶仃洋河口水域纳潮现状和特性,分别采用经验公式和建立贴体曲线坐标系下的珠江河口二维数学模型的方法,对河口伶仃洋水域的纳潮特性进行了分析和探讨.数学模型的离散和求解采用纯隐格式的混合有限分析法,根据实测资料对其进行了验证.比较显示,采用实测资料和经验公式计算到的伶仃洋水域纳潮量与数学模型的计算结果相差在5%以内,从而证实了数学模型的可靠性.结果表明,伶仃洋海域的主要纳潮口门为伶仃洋口门,约占总纳潮量的87.7%,通过香港暗士顿水道进出的潮量仅占12.3%左右,显示伶仃洋口门为该海域的主要径潮通道,对该河口的防洪和生态具有重要的作用  相似文献   

全站仪无棱镜模式在岛礁地形测量中的应用     

李建军  刘晟  代大炉 《海洋测绘》2012,(3):59-61

针对岛礁地形测量的特点,提出了用全站仪无棱镜模式进行碎部点数据采集的方法,从理论上对其精度进行了论证分析,通过公式推导、数据图表分析,得出了全站仪无棱镜模式测定待定点位平面位置精度和点位高程精度与所测距离和天顶距之间的关系。同时通过全站仪的无棱镜模式和有棱镜模式对所选碎部点进行检核,实验数据结果表明都能完全符合规范的要求。  相似文献   

Flow of ultra-hot orogens: A view from the Precambrian, clues for the Phanerozoic   总被引：1，自引：0，他引：1  

Dominique Chardon  Denis Gapais  Florence Cagnard   《Tectonophysics》2009,477(3-4):105

This contribution emphasizes first-order structural and metamorphic characters of Precambrian accretionary orogens to understand the kinematics and thermomechanical state of the continental lithosphere in convergent settings involving massive juvenile magmatism. We define a new class of orogens, called ultra-hot orogens (UHO), in which the weakest type of lithosphere on Earth is deformed. UHO are characterized by (1) distributed shortening and orogen-scale flow combining vertical and horizontal longitudinal advection, under long-lasting convergence, (2) homogeneous thickening by combined downward movements of supracrustal units and three-dimensional mass redistribution in the viscous lower crust, and (3) steady-state, negligible topography and relief leveled by syn-shortening erosion and near-field sedimentation. The flow analysis of UHO provides clues to understanding crustal kinematics beneath high plateaus and suggests that the seismic reflectivity pattern of hot orogens is an image of the layering produced by lateral flow of the lower crust and associated syn-kinematic plutonism.In between the UHO and the modern cold orogens (CO), developed by shortening of lithosphere bearing a stiff upper mantle, two classes of orogens are defined. Hot orogens (HO, representative of Cordilleran and wide mature collisional belts) share flow pattern characteristics with UHO, but involve a less intense magmatic activity and develop high topographies driving their collapse. Mixed-hot orogens (MHO, representative of magmatic arcs and Proterozoic collisional belts) are orogens made of UHO-type juvenile crust and display CO-like structure and kinematics. This classification points to the fundamental link between the presence of a stiff lithospheric mantle and strain localization along major thrusts in convergent settings. A high Moho temperature (> 900 °C), implying thinning of the lithospheric mantle, enhances three-dimensional flow of the lithosphere in response to convergence. Overall, this classification of orogens emphasizes the space and time variability of uppermost mantle temperature in controlling plate interactions and continental growth.  相似文献   

全站仪棱镜常数未改正引起的测量误差分析   总被引：2，自引：0，他引：2  

詹长根  鲍家伟  黄德霖 《北京测绘》2005,(3):30-33

基于棱镜常数的概念,通过一典型测量模型分析在棱镜常数未改正的情况下所引起的测量误差,并结合案例阐述了误差对地籍测量工作的影响。由于棱镜常数未改正而引起的系统误差在界址点测量中是不可容忍的,必须改正。  相似文献   

全站仪垂距测量代替二、三、四等水准测量的研究   总被引：4，自引：0，他引：4  

陶元洲  王凤艳  庞贺民  王明常 《吉林大学学报(地球科学版)》2004,34(2):314-317

全站仪垂距测量进行高程测量,是基于三角高程测量和水准测量原理,在测点中间安置全站仪,不量仪器高和棱镜高,通过观测垂距以进行高差测量.经过理论分析和实验验证,精度可以达到二等水准,在丘陵低山地区,可以代替二、三、四等级水准测量.  相似文献   

南羌塘增生过程的中-晚三叠世岩浆记录:藏北玛依岗日-角木日地区基性岩墙   总被引：1，自引：1，他引：0  

高曦  李静超  袁国礼  王根厚  梁晓  郑艺龙  王泉 《岩石学报》2019,35(3):760-774

古特提斯洋向北俯冲形成增生杂岩,它们向南增生构成了南羌塘增生地体,且增生期内发育的岩浆岩可以用来研究南羌塘的增生过程。在南羌塘增生杂岩带内,由北向南,发育有玛依岗日(MG)辉长岩墙、角木日(JM)辉长辉绿岩墙。锆石U-Pb测年结果显示,两者分别形成于237. 1±2. 3Ma和230. 7±1. 8Ma,为南羌塘增生期内岩浆岩。它们的岩石地球化学特征均介于OIB与E-MORB之间,富集Ti、Nb,以及LREE和LILE。Nd-Pb同位素结果显示两者均起源于富集地幔源区。Sm/YbLa/Yb图解显示,两者均起源于尖晶石-石榴石二辉橄榄岩源区,相对于JM辉长辉绿岩MG辉长岩部分熔融程度较高。两者Mg#和Ni、Cr特征表明,MG辉长岩分异程度高于JM辉长辉绿岩。Th/Nb-La/Nb图解显示,相对于JM辉长辉绿岩MG辉长岩经历了一定程度的地壳混染。综合研究认为,MG辉长岩和JM辉长辉绿岩为古特提斯洋壳俯冲过程中软流圈上涌的两次岩浆活动的产物,并受俯冲洋壳和地幔楔影响。MG辉长岩和JM辉长辉绿岩记录了南羌塘的增生过程,它们为相关研究提供了岩浆岩证据。  相似文献   

Structure and tectonic evolution of the Late Jurassic–Early Cretaceous Wandashan accretionary complex,NE China     

Han Zheng  Kuo Wan  Pujun Wang  Song He  Xuqing Zhang 《International Geology Review》2019,61(1):17-38

The Late Jurassic–Early Cretaceous Wandashan accretionary complex (AC) in NE China is a key region for constraining the subduction and accretion of the Palaeo-Pacific Ocean; however, the protoliths and structure of the region remain poorly understood, resulting in debates regarding crustal growth mechanisms and subduction-related accretionary processes in Northeast China. In this contribution, we integrate detailed field observations, ocean plate stratigraphy (OPS) reconstruction, and associated geological data to determine the structure and tectonic evolution of the Wandashan AC. The Wandashan AC formed through the progressive incorporation of OPS units along an oceanic trench. The observed OPS comprises, in ascending order, Permian basalt and limestone, Middle Triassic–Early Jurassic chert, Middle Jurassic siliceous shale and mudstone, and Late Jurassic–Early Cretaceous turbidite. Numerous NNE–SSW-striking thrust faults have segmented the OPS into a series of bedding-parallel tectonic slices that were successively thrust over the Jiamusi massif along a basal thrust (the Yuejinshan Fault), producing a large-scale imbricate thrust system. The Wandashan AC underwent oceanward accretion via multiple deformational processes. The OPS units were detached and rearranged along or within a decollement through offscraping, underplating, thrusting, and duplexing. The units were then emplaced over the Jiamusi massif along the basal thrust. The timing of accretion and thrusting is constrained to the latest Middle Jurassic to earliest Early Cretaceous (ca. 167–131 Ma). Reconstructed accretion-related structural lines within the Wandashan AC trend dominantly NE–SW, close to the direction of Jurassic extension at the eastern Asian continental margin. Large-scale left-lateral strike-slip movement on the Dunmi Fault during the late Early Cretaceous resulted in the folding of structural lines within the Wandashan AC, producing their present-day westward-convex orientation.  相似文献