马尼拉俯冲带北段增生楔形态结构及演化过程     

王红丽  赵强  黄金莲  范建柯 《海洋科学》2019,43(8):1-16

为揭示马尼拉增生楔的形态结构并加深对其演化过程的理解,本文对横穿马尼拉俯冲带北段的几条典型地震剖面进行了深度偏移处理,得到叠前深度偏移剖面和深度-速度模型,并对马尼拉增生楔的形态结构及内部特征进行了精细解释,将马尼拉增生楔分为原始沉积段、褶皱变形段、逆冲推覆段和背逆冲段四个部分,分别代表增生楔演化的不同阶段。推断马尼拉增生楔下部存在由早期仰冲的菲律宾海板块的残留块体构成的弧前基盘,弧前基盘是控制马尼拉增生楔形成演化的关键构造。弧前基盘前端是拆离滑脱面突然降阶并在地震剖面上"隐没"的部位;弧前基盘向增生楔底部的不断挤入导致了逆冲脱序断层的渐次发育以及增生楔向弧前基盘之上的不断爬升,导致了增生楔上、下陆坡地貌的分化,并为褶皱变形段和逆冲推覆段的地层形变提供了主要的应力。  相似文献   

华南及邻区中新生代大地构造单元     

郭福祥 《南方国土资源》2000,13(1):1-6,40

华南大陆部分中新生代大地构造单元属南华造山带,可分为NW-NWW向的滨特提斯褶皱系和NE向的滨太平洋褶皱系.滨太平洋褶皱系包含东南大陆边缘弧褶皱带和东南大陆边缘弧后褶皱带,是晚三叠世以来多期次继承性造山运动累积叠加形成的.主要褶皱时代,在陆缘弧褶皱带是晚侏罗-中始新世;在陆缘弧后褶皱带是中晚始新世之交.讨论了华南及邻区中新生代大地构造格局及其成因和羽状对称特点,以及陆壳减薄板段、主动大地构造单元和被动大地构造单元几个概念.  相似文献   

云开地块北缘构造带中变质基性火山岩的地球化学特征及其大地构造意义   总被引：7，自引：0，他引：7  

覃小锋  潘元明  夏斌  李容森  周府生  胡贵昂  陆国斌 《地球化学》2007,36(3):311-322

对云开地块北缘构造带中变质基性火山岩的地质、地球化学综合研究结果证明,该区存在洋中脊型 (MORB)和岛弧型 (IAT)两类玄武岩.MORB型具有大体类似的地球化学性质,它们均含较低的 TiO2(0.80%～ 1.62%,平均值 1.50% )和 P2O5(0.05%～ 0.15%,平均值 0.13% ),轻稀土元素呈亏损-平坦型,具洋中脊玄武岩特征;而 IAT型含更低的 TiO2(0.47%～ 1.26%,平均值 0.80% )和 P2O5(0.04%～ 0.07%,平均值 0.06% ),轻稀土元素呈富集型,具岛弧型玄武岩特征.MORB和 IAT组合的出现说明位于华南板块西南端的广西云开地区在 Grenville期 (四堡期 )可能存在过洋盆,它们很可能代表了 Grenville期 (四堡期 )造山作用形成统一的 Rodinia超级大陆以前的一个"多岛洋盆"系统,华夏古陆和扬子板块可能在该古洋盆于新元古代早期发生的全球性 Grenville期 (四堡期 )造山运动而发生消减消失后才开始碰撞和造山,形成统一的 Rodinia超级大陆.  相似文献   

面向三极科学的三维可视化系统应用研究     

吴阿丹  车涛 《冰川冻土》2021,43(1):274-284

南极、北极和青藏高原作为地球的"三极"是全球变化的敏感区和研究热点.随着天空地一体化对地观测技术的快速发展,三极时空信息呈现出海量、高时效、多维度的大数据特征.但由于缺乏有效的可视化手段,这些数据很难被非科研人员理解和认知.如何面向不同人群,快速直观地展示三极最新科学发现所产生的时空数据,已成为数据可视化研究迫切需要解...  相似文献   

大地问题中截面椭圆弧长的一种解法     

严伯铎  田洪祯  常宏伟 《海洋测绘》2007,27(6):1-3

介绍了利用子午线弧长的直接算法来解算大地问题中截面椭圆弧长的一种直接解法。该法具有计算方便且简单的特点。通过实例计算证明效果良好。  相似文献   

Iranshahr blueschist: subduction of the inner Makran oceanic crust          下载免费PDF全文

H. Omrani  M. Moazzen  R. Oberhänsli  M. E. Moslempour 《Journal of Metamorphic Geology》2017,35(4):373-392

The Makran accretionary prism in SE Iran and SW Pakistan is one of the most extensive subduction accretions on Earth. It is characterized by intense folding, thrust faulting and dislocation of the Cenozoic units that consist of sedimentary, igneous and metamorphic rocks. Rock units forming the northern Makran ophiolites are amalgamated as a mélange. Metamorphic rocks, including greenschist, amphibolite and blueschist, resulted from metamorphism of mafic rocks and serpentinites. In spite of the geodynamic significance of blueschist in this area, it has been rarely studied. Peak metamorphic phases of the northern Makran mafic blueschist in the Iranshahr area are glaucophane, phengite, quartz±omphacite+epidote. Post peak minerals are chlorite, albite and calcic amphibole. Blueschist facies metasedimentary rocks contain garnet, phengite, albite and epidote in the matrix and as inclusions in glaucophane. The calculated P–T pseudosection for a representative metabasic glaucophane schist yields peak pressure and temperature of 11.5–15 kbar at 400–510 °C. These rocks experienced retrograde metamorphism from blueschist to greenschist facies (350–450 °C and 7–8 kbar) during exhumation. A back arc basin was formed due to northward subduction of Neotethys under Eurasia (Lut block). Exhumation of the high‐pressure metamorphic rocks in northern Makran occurred contemporarily with subduction. Several reverse faults played an important role in exhumation of the ophiolitic and HP‐LT rocks. The presence of serpentinite shows the possible role of a serpentinite diapir for exhumation of the blueschist. A tectonic model is proposed here for metamorphism and exhumation of oceanic crust and accretionary sedimentary rocks of the Makran area. Vast accretion of subducted materials caused southward migration of the shore.  相似文献   

Delaunay三角网生长法的一种改进方法   总被引：2，自引：0，他引：2  

吴佳奇  徐爱功 《测绘科学》2012,37(2):103-104,187

为了提高Delaunay三角网的构建速度,本文对三角网生长法进行了改进,提出了一种基于生长法的"弧带搜索排除"方法,通过一系列的圆弧将离散点区域划分成几个弧带,构网时,规定只可在当前弧带搜索第三点,该弧带离散点搜索完毕后进入下一弧带,如此循环。采用VC++6.0加以实现。测试表明,该方法能够加快构网速度,生成的三角形形状良好,具有一定的实际效用。  相似文献   

天津市新建的具有独特风格的桥梁     

黄大健 《中国勘察设计》2009,(10):64-70

天津市近几年来新建了多座具有独特风格和景观效果的新型桥梁,本文主要介绍其中的三座斜拉桥、三座拱桥、一座自锚式悬索桥和一座集交通、观光、游览为一体的巨型摩天轮桥梁,以及三座经装修改建、使旧桥换新颜的实例。  相似文献   

The Xiong'er volcanic belt at the southern margin of the North China Craton: Petrographic and geochemical evidence for its outboard position in the Paleo-Mesoproterozoic Columbia Supercontinent   总被引：12，自引：0，他引：12  

Guochun  Yanhong  Min 《Gondwana Research》2009,16(2):170

The Xiong'er volcanic belt, covering an area of more than 60,000 km² along the southern margin of the North China Craton, has long been considered an intra-continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the Paleo-Mesoproterozoic supercontinent Columbia. However, such interpretations cannot be accommodated by lithology, mineralogy, geochemistry and geochronology of the volcanic rocks in the belt. Lithologically, the Xiong'er volcanic belt is dominated by basaltic andesite and andesite, with minor dacite and rhyolite, different from rock associations related to continental rifts or mantle plumes, which are generally bimodal and dominated by mafic components. However, they are remarkably similar to those rock associations in modern continental margin arcs. In some of the basaltic andesites and andesites, amphibole is a common phenocryst phase, suggesting the involvement of H₂O-rich fluids in the petrogenesis of the Xiong'er volcanic rocks. Geochemically, the Xiong'er volcanic rocks fall in the calc-alkaline series, and in most tectono-magmatic discrimination diagrams, the majority of the Xiong'er volcanic rocks show affinities to magmatic arcs. In the primitive mantle normalized trace-element diagrams, the Xiong'er volcanic rocks show enrichments in the LILE and LREE, and negative Nb–Ta–Ti anomalies, similar to arc-related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge. Nd-isotope compositions of the Xiong'er volcanic rocks suggest that 5–15% older crust has been transferred into the upper lithospheric mantle by subduction-related recycling during Archean to Paleoproterozoic time. Available SHRIMP and LA-ICP-MS U–Pb zircon age data indicate that the Xiong'er volcanic rocks erupted intermittently over a protracted interval from 1.78 Ga, through 1.76–1.75 Ga and 1.65 Ga, to 1.45 Ga, though the major phase of the volcanism occurred at 1.78–1.75 Ga. Such multiple and intermittent volcanism is inconsistent with a mantle plume-driven rifting event, but is not uncommon in ancient and existing continental margin arcs. Taken together, the Xiong'er volcanic belt was most likely a Paleo-Mesoproterozoic continental magmatic arc that formed at the southern margin of the North China Craton. Similar Paleo-Mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of Laurentia, the southern margin of Baltica, the northwestern margin of Amonzonia, and the southern and eastern margins of the North Australia Craton, which are considered to represent subduction-related episodic outbuilding on the continental margins of the Paleo-Mesoproterozoic supercontinent Columbia. Therefore, in any configuration of the supercontinent Columbia, the southern margin of the North China Craton could not have been connected to any other continental block as proposed in a recent configuration, but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the North China Craton.  相似文献   

New insights into the origin of O–Hf–Os isotope signatures in arc lavas from Tonga–Kermadec     

Simon Turner  Monica Handler  Ilya Bindeman  Katsuhiko Suzuki   《Chemical Geology》2009,266(3-4):196-202

O, Hf and Os isotope data are presented for lavas from the highly depleted Tonga–Kermadec arc. O isotope values overlap with those of MORB limiting the amount of interaction with the arc crust. δ¹⁸O does not increase northwards as would be expected from the ~ 4 fold increase in subduction rate if slab-derived fluids had high ¹⁸O/¹⁶O ratios. Thus, the overall northward decrease in HFSE concentrations likely reflects depletion due to prior melt extraction, not increasing extents of melting. Hf isotopes are strongly negatively correlated with Be isotopes consistent with mixing of subducted pelagic sediment into the mantle wedge and do not require Hf to be fluid mobile. With the exception of a boninite from the north Tongan trench, the northern Tonga lavas do not overlap the Hf isotope composition of either the Samoan plume or the subducting Louisville volcaniclastic sediments. Thus, the Pb isotope signatures in these lavas must have been added by fluids and sediment melts derived from the Louisville volcaniclastics with minimal mobilisation of Hf. This suggests conservative behaviour for this element due to the formation of residual zircon during partial melting of the subducted sediments. ¹⁸⁷Os/¹⁸⁸Os ranges from 0.1275 to 0.4731 and the higher Os isotope ratios reflect the sensitivity of this system to even minor interaction with altered arc crust. Conversely, the lowest Os ratios are subchondritic and indicate that transfer of radiogenic Os from the slab is not all pervasive and provide an important constraint on the composition of the mantle wedge. Remarkably, the least radiogenic sample is a dacite demonstrating that evolved magmas can develop by fractionation from mantle-derived magmas with minimal interaction with the arc crust.  相似文献