A Kinematic Thermal Model for Descending Slabs with Velocity Boundary Layers: A Case Study for the Tonga Subducting Slab   总被引：3，自引：0，他引：3  

ZHANG Keliang an  WEI Dongping 《《地质学报》英文版》2011,85(1):211-222

For the purpose of investigating the influence of metastable olivine (MO) phase transformations on both deep seismicity and stagnation of slabs, we constructed a 2-dimensional finite element thermal model for a 120 Ma-old 50o dipping oceanic lithosphere descending at 10 cm/yr with velocity boundary layers, which would mitigate the interference of constant velocity field for the slab. The resulting temperatures show that most of intermediate and deep earthquakes occurring within the Tonga slab are occurring inside the 800oC and 1200oC isotherm, respectively. The elevation of olivine transformation near ~410 km and respective persistence of metastable olivine and spinel within the transition zone and beneath 660 km would thus result in bimodal positive, zonal, negative density anomalies, respectively. These results together with the resulting pressure anomalies may reflect the stress pattern of the Tonga slab: (i) slab pull force exerts above a depth of ~230 km; (ii) MO existence changes the buoyancy force within the transition zone and facilitates slab stagnation at a depth of 660 km; (iii) as the subducting materials accumulated over 660 km, deepest earthquakes occur due to MO transformation; (iv) a flattened ‘slab’ may penetrate into the lower mantle due to the density increment of Sp transformation.  相似文献   

Geological comparative studies of Japan Arc System and Kyushu-Palau Arc   总被引：5，自引：3，他引：2  

YAN Quanshu  SHI Xuefa 《海洋学报(英文版)》2011,30(4):107-121

Based on the published data of structure geology,geochronology,petrology and isotope geochemistry,the authors of this paper have conducted studies on the tectonic evolution history of Japan arc system and Kyushu-Palau ridge(KPR) . The studies show that the initial Japan arc system was resulted from the subduction of ancient Pacific plate beneath Eurasian Plate in Permian. It was part of an Andean-type continental volcanic arc which occurred in the offshore in the east of Asian during late Mesozoic era. The formation of tertiary back-arc basin(Japan Sea) resulted in the fundamental tectonic framework of the present arc system. Since Quaternary the system has been lying at E-W compression tectonic setting due to the eastward subduction of Amur Plate. It is expected that Japan arc system will be juxtaposed with Asian continent,which is similar to the present Taiwan arc system. The origin of Philippine Sea Plate(PSP) is still in debate. Some studies argued that it is a trapped oceanic crust segment,while the others insisted that it is a back-arc basin accompanied with ancient IBM arc. However,it is all agreed that the tectonic evolution of PSP started since 50 Ma,i.e.,PSP has drifted from the site around equator at 50 Ma to the present site,and the subduction of PSP along Nankai trough-Ryukyu Trench beneath the Japan arc system during 6-2 Ma led to the formation of the present Ryukyu arc system. Of the PSP,the KPR has been found with the oldest rocks formed at 38 Ma. Combining with its geochemical characteristics of oceanic arc tholeiite,it is suggested that KPR is an intraoceanic volcanic arc,more specifically,a relic arc(i.e.,rear arc of the ancient IBM) after rifting of ancient IBM. In addition,Amami-Daito province is of arc tectonic affinity,but has been affected by mantle plume. Therefore,based on their respective tectonic evolution history and geochemical characteristics of rock samples,it is inferred that there is no genetic relationship between Japan arc system and KPR. It is noted that rocks reflecting continental crust basement feature have been collected on the northern tip of KPR,which may be related to the process of KPR accreting on Japan arc,but the arc-continent accretion process are still at initial stage of modern continental crust accretion model. However,due to the scarcity of data of the northern tip of KPR,crustal structure of this location and its adjacent Nankai trough need to be further constrained by geophysical studies in the future.  相似文献   

马里亚纳南部弧内坡橄榄岩中的角闪石成分对于弧下地幔交代流体的指示     

董彦辉  初凤友  朱继浩  张平萍 《海洋学报》2011,33(5):91-96

马里亚纳弧前的橄榄岩被认为是SSZ型蛇绿岩的现代等同物,记录了弧下地幔与俯冲流体的交代反应,其中的角闪石被认为是俯冲流体交代的产物.电子探针的数据表明角闪石主要包括透闪石和镁闪石两种,其中前者具有低的钠含量,后者则具有明显高的钠、铝含量,但Mg#较低.角闪石的组成反映了俯冲流体具有高硅、钙、铝、钠等元素的特征.形成成分...  相似文献   

Neogene-Quaternary tectonic evolution of the Leeward Antilles islands (Aruba, Bonaire, Curaçao) from fault kinematic analysis     

Jean-Claude Hippolyte  Paul Mann 《Marine and Petroleum Geology》2011,28(1):259-277

Aruba, Bonaire, and Curaçao are islands aligned along the crest of a 200-km-long segment of the east-west-trending Leeward Antilles ridge within the broad Caribbean-South America plate boundary zone presently characterized by east-west, right-lateral strike-slip motion. The crust of the Leeward Antilles ridge represents the western segment of the Cretaceous-early Cenozoic Great Arc of the Caribbean, which obliquely collided, with the continental margin of northern South America in early Cenozoic time. Following the collision, the ridge was affected by folding and was segmented by oblique, northwest-striking normal faults that have produced steep-sided, northwest-trending, elongate islands and narrow shelves separated by deepwater, sediment-filled and fault-controlled basins. In this paper, we present the first fault slip observations on the Neogene carbonate rocks that cover large areas of all three islands. Our main objective is to quantify the timing and nature of Neogene to Quaternary phases of faulting and folding that have affected the structure and topography of this area including offshore sedimentary basins that are being explored for their petroleum potential. These data constrain three fault phases that have affected Aruba, Bonaire, and Curaçao and likely the adjacent offshore areas: 1) NW-SE-directed late Paleogene compression; 2) middle Miocene syndepositional NNW-SSE to NNE-SSW extension that produced deep rift basins transverse to the east-west-trending Leeward Antilles ridge; and 3) Pliocene-Quaternary NNE-trending compression that produced NW-SE-trending anticlines present on Aruba, Curaçao and Bonaire islands. Our new observations - that include detailed relationships between striated fault planes, paleostress tensors, and bedding planes - show that prominent bedding dips of Neogene limestone on Aruba, Bonaire and Curaçao were produced by regional tectonic shortening across the entire Leeward Antilles ridge rather than by localized, syndepositional effects as proposed by previous workers. We interpret Pliocene-Quaternary NNE-directed shortening effects on the Leeward Antilles ridge as the result of northeastward extrusion or “tectonic escape” of continental areas of western Venezuela combined with southeastward shallow subduction of the Caribbean plate beneath the ridge.  相似文献   

Measurement and modeling of bed shear stress under solitary waves   总被引：1，自引：0，他引：1  

Jaya Kumar Seelam  Paul A. Guard  Tom E. Baldock 《Coastal Engineering》2011

Direct measurements of bed shear stresses (using a shear cell apparatus) generated by non-breaking solitary waves are presented. The measurements were carried out over a smooth bed in laminar and transitional flow regimes (~ 10⁴ < R_e < ~ 10⁵). Measurements were carried out where the wave height to water depth (h/d) ratio varied between 0.12 and 0.68; maximum near bed velocity varied between 0.16 m/s and 0.51 m/s and the maximum total shear stress (sum of skin shear stress and Froude–Krylov force) varied between 0.386 Pa and 2.06 Pa. The total stress is important in determining the stability of submarine sediment and in sheet flow regimes. Analytical modeling was carried out to predict total and skin shear stresses using convolution integration methods forced with the free stream velocity and incorporating a range of eddy viscosity models. Wave friction factors were estimated from skin shear stress at different instances over the wave (viz., time of maximum positive total shear stress, maximum skin shear stress and at the time of maximum velocity) using both the maximum velocity and the instantaneous velocity at that phase of the wave cycle. Similarly, force coefficients obtained from total stress were estimated at time of maximum positive and negative total stress and at maximum velocity. Maximum positive total shear stress was approximately 1.5 times larger than minimum negative total stress. Modeled and measured positive bed shear stresses are well correlated using the best convolution model, but the model underestimates the data by about 4%. Friction factors are dependent on the choice of normalizing using the maximum velocity, as is conventional, or the instantaneous velocity. These differ because the stress is not in phase with the velocity in general. Friction factors are consistent with previous data for monochromatic waves, and vary inversely with the square-root of the Reynolds number. The total shear stress leads the free stream fluid velocity by approximately 50°, whereas the skin friction shear stress leads by about 30°, which is similar to that reported by earlier researchers.  相似文献   

Study on scattering wave force of horizontal and vertical plate type breakwaters   总被引：1，自引：0，他引：1  

王科  张犀  高鑫 《中国海洋工程》2011,25(4):699-708

The interaction between wave and horizontal and vertical plates is investigated by the boundary element method,and the relations of wave exciting force with plate thickness,submergence and length are obtained.It is found that:1) The efficient wave exciting force exists while plate submergence is less than 0.5 m,and the plate is very thin with order O(0.005 m).2) The maximum heave wave exciting force exists,and it is the main factor for surface and submerged horizontal plate while the roll force can be ignored.3) The maximum sway wave exciting force exists,it is the main factor for surface or submerged vertical plate,and the roll force is about 20 times of horizontal plate.  相似文献   

平板对下游方柱流体动力性能影响分析     

闫岱峻  苏玉民  于宪钊 《海洋工程》2011,29(4):8-13

基于有限体积法求解二维粘性不可压缩Navier-Stokes方程,分别采用层流模型和Realizable k-ε模型研究Re=250和Re=104前置平板与下游方柱间的流动干扰现象,分析不同尺度的平板布置在不同位置时对下游方柱的绕流场及流体动力性能的影响。计算发现在方柱上游布置平板可以有效的控制方柱的绕流场,减小方柱的阻力系数和升力系数;随着平板尺度的增加,方柱的阻力系数、升力系数呈下降趋势;并且存在较好的平板布置区间,可以最大程度的降低方柱和平板的阻力系数及方柱的升力系数,从而达到良好的减振、降噪的效果。  相似文献   

佳木斯地块东部二叠纪方山花岗岩体的锆石U—Pb年代学、地球化学特征及其地质意义   总被引：1，自引：0，他引：1  

蒲建彬  张兴洲  郭冶  曾振  付秋林  张宏涛  刘洋 《世界地质》2015,34(4):903-913

本文报道了佳木斯地块东部方山花岗岩体的锆石LA--ICP--MS U--Pb定年结果、全岩地球化学特征,确定了花岗质岩石的形成时代以及大地构造背景。花岗岩的锆石主要呈自形-半自形晶,振荡环带发育,Th/U在0.26~1.16之间,显示其典型的岩浆成因;测年结果表明这些花岗岩形成于早二叠世(278 Ma,277 Ma)。方山花岗岩呈现出弱过铝质高钾钙碱性的地球化学特征,这些岩石轻稀土富集,重稀土亏损,具有Eu负异常,富集大离子亲石元素(Rb、K等),相对亏损高场强元素(Nb、Ta、P、Zr和Ti)。该区花岗岩地球化学特征与佳木斯东缘二叠纪的美作、青山、楚山、柴河、石场、锦山等岩体相似,体现出火山弧型花岗岩的特征。结合区域研究资料,我们认为佳木斯地块东缘在早二叠世期间为活动大陆边缘。  相似文献   

钦-杭结合带在中生代构造转折事件以前的板块构造机制   总被引：5，自引：0，他引：5  

曾长育  周永章  郑义  虞鹏鹏  牛佳  梁锦 《地学前缘》2015,22(2):54-63

钦州湾—杭州湾结合带是位于扬子与华夏两大古陆块中间的巨型构造结合带,在演化成西太平洋活动大陆边缘之前,经历了多期次的构造-岩浆事件。扬子和华夏板块于新元古代通过四堡造山运动(1 000~880 Ma)沿江山—绍兴断裂,经赣东北、湘中至钦州湾地区发生碰撞-拼合事件,拼合界线大致位于钦州湾—杭州湾结合带内,形成"两陆夹一盆"的主要格局。后碰撞过程经历了造山后岩浆活动和大陆拉张裂解两个过程,在结合带形成广阔的拉张盆地,加里东期(460~410 Ma)以及印支期(250~200 Ma)发生的碰撞-拼合事件导致扬子和华夏地块多次再造,引发强烈的构造-岩浆活动,并形成了华南统一的沉积环境。受西太平洋板块俯冲影响,华南地区中生代构造转折事件(125~140 Ma)使华南地区主要构造背景由碰撞挤压调整为岩石圈减薄,成为华南最重要的岩浆活动和成矿期。根据内部结构的不均一性和演化历史差异,钦州湾—杭州湾结合带可分为北段、中段和南段3段。其中,中段与传统南岭大体一致;北段为南岭以北地区,即绍兴—江山—萍乡一带;南段为南岭以南地区,大致与云开隆起—十万大山盆地相当。年代学和地球化学研究显示,在云开地块西缘的一系列变质基性岩、超基性岩和变质基性火山岩形成于新元古代洋中脊(MORB)或者岛弧(ITA)特征的构造环境,最近在岑溪一带发现形成于加里东期(441 Ma)的变质火山岩同样具有MORB型地球化学特征。在十万大山两侧发现早中生代的酸性火山岩和流纹岩具有典型岛弧型火山岩地球化学特征。可见结合带南段曾经存在古老洋壳,先后经历了新元古代、加里东期和印支期的碰撞造山事件,与北段演化历史具有一致性。  相似文献   

“大洋板块地层”的重建与意义——以藏南仲巴地区为例     

魏玉帅  李亚林  陈曦  王成善  李祥辉  李鑫  钟瀚涏 《地质通报》2015,34(10):1789-1801

混杂岩是古增生楔存在的标志之一,一般由枕状玄武岩、灰岩、放射虫硅质岩、硅质页岩、砂岩等混乱无序组成。目前"大洋板块地层"(OPS)运用放射虫地层学方法对混乱的增生楔断片进行重建取得了良好效果,并清晰地展示了大洋板块俯冲和洋底物质连续增生的历史。在西藏仲巴地区填图过程中,结合放射虫年代学分析鉴定结果,以OPS重建的思路和理论作为指导,重建了仲巴地区混杂岩的大洋板块地层,并恢复了该区域特提斯洋在洋中脊大洋板块增生至消亡的岩石序列,自下而上分别为侏罗纪海山玄武岩、海山覆盖物侏罗系—白垩系碳酸盐岩、海山周围沉积的侏罗系—白垩系放射虫硅质岩和硅质页岩,以及海沟附近的白垩系陆源碎屑岩等,为特提斯洋大洋板块俯冲的方向、持续时间和古大地构造环境提供了信息。  相似文献