面波偏振与中国大陆岩石层横向不均匀性   总被引：5，自引：2，他引：5       下载免费PDF全文

黄忠贤  陈虹  王贵华  吴依农 《地球物理学报》1994,37(4):456-468

本文利用７个ＣＤＳＮ台站的长周期数字地震记录和奇异值分解方法，分析了在中国大陆内传播的基阶勒夫波的偏振方向，从而确定波到达台站时的入射方向对于大圆方向的偏离．５°-１０°的偏角是常见的，最大偏角可达２０°左右．尤其是４０ｓ以下的勒夫波，在大多数路径上都显著偏离．这些观测到的现象可以用勒夫波穿过不同大地构造单元界线发生的折射作出定性解释．青藏块体的边界和天山褶皱带可引起２０-６０ｓ（或更长）周期的勒夫波发生折射；华北与华南地块间及华北平原和鄂尔多斯地块间的速度差异一般影响２０-４０ｓ之间的勒夫波；扬子地台与东南沿海褶皱的差异主要影响２０ｓ以下的波；２０ｓ以下的短周期勒夫波往往表现出复杂的多重路径现象．  相似文献   

卫星磁异常研究   总被引：1，自引：0，他引：1  

安振昌 《地球科学进展》1994,9(4):23-29

对卫星磁异常研究进行了评述，包括：卫星磁异常研究的主要内容，卫星资料处理，卫星磁异常图、理论计算、地质解释及我国的卫星磁异常研究。  相似文献   

球层岩石层模型对表面荷载的响应          下载免费PDF全文

傅容珊 《地球物理学报》1987,30(5):494-503

本文给出了在球层模型下,地球岩石层对表面荷载响应的解析解。计算了地球岩石层对圆盘形荷载和正弦型荷载的响应,及由此产生的重力异常。结果表明:1.岩石层弯曲不仅与其厚度有密切关系,而且与荷载尺度有关。当岩石层厚度与荷载尺度相比很小时,其弯曲与厚度关系不大,并呈现薄板效应。2.弹性模型岩石层在外加荷载下能承受数千巴的弯曲应力。3.弯曲应力在岩石层中的分布较为规则。由于大尺度荷载下岩石层出现薄板效应,传统的由弯曲刚度估算等效岩石层厚度的部分结果需要重新估价。  相似文献   

Three-dimensional numerical thermal and rheological modelling in the central Fennoscandian Shield     

K. Moisio  P. Kaikkonen   《Journal of Geodynamics》2006,42(4-5):95-114

A three-dimensional model for the central Fennoscandian Shield was constructed for analysing the thermal, the rheological and the structural conditions in the lithosphere. The mesh covers a rectangular area in the southern Finland with horizontal dimensions of 500 km × 400 km and a depth extent of 100 km. Structural boundaries are derived from the several deep seismic soundings carried out in the area. Constructed model is first used in the calculation of the thermal and the rheological models and secondly in analysing the stress and the deformational conditions with the obtained rheology. Thermal and structural models are solved with the finite element method. The calculated surface HFD is between 40 and 48 mW m⁻² in the Proterozoic southern part and below 40 mW m⁻² in the older and northern Archaean part of the model. The calculated rheological strength shows a layered structure with two individual rheologically weak layers in the crust and strong layer in the upper part of the lower crust. The minimum brittle–ductile transition (BDT) depth is around 10 km in the southern part of the model while in the north and north-eastern parts the BDT depth is around 45–50 km. Comparison with the focal depth data shows that as most of the earthquakes occur no deeper than the depth of 10 km are they located in the brittle regime. Resulting stress conditions and possible regions of deformation after the model is subjected to pressure of 50 MPa reveals that the stress field is quite uniformly distributed in different crustal layers and that the elastic parameters control more the state of the stress than the applied rheological structure. In the upper crust, the stress intensity has values between 42 and 45 MPa whereas in the middle crust the values are around 50 MPa. Comparison of the 3-D model with earlier 2-D models shows that some differences in the results are to be expected.  相似文献   

东北和华北地区上地幔成分和热状态对比及对中国东部岩石圈减薄的启示   总被引：3，自引：1，他引：3  

于宋月徐义刚  黄小龙葛文春 程锦 《岩石学报》2007,23(6):1252-1268

地幔成分与其上覆地壳年龄存在相关关系,年龄越老,地幔越亏损玄武质组分。本文对产于东北和华北地区的尖晶石相橄榄岩包体的成分进行了统计分析,结果显示东北地区橄榄岩包体比华北地区包体更亏损玄武质组分。这说明东北岩石圈地幔比华北上地幔更难熔,但其上覆地壳年龄却远小于华北地区地壳的年龄。这种地壳年龄和地幔组分之间的解耦暗示东北和华北地区的岩石圈地幔形成之后发生了大规模的改造。华北地区的壳幔解耦与中生代岩石圈减薄和增生有关,而东北地区的壳幔解耦则是该区地壳的多期改造和中生代岩石圈减薄和增生等过程综合作用的结果。两地区地幔成分的差异显然与部分熔融程度的不同有关,但影响部分熔融程度的因素很多,目前尚不能确定。包体的平衡温度统计和地温线对比显示东北岩石圈的地温梯度低于华北的地温梯度,可能是东北地区岩石圈减薄的时间要早于华北地区,或者华北岩石圈减薄程度可能大于东北地区的结果,因此中国东部岩石圈减薄存在时空不均一性。  相似文献   

Mixing of asthenospheric and lithospheric mantle-derived basalt magmas as shown by along-arc variation in Sr and Nd isotopic compositions of Early Miocene basalts from back-arc margin of the NE Japan arc     

Makoto Sato  Kenji Shuto  Masahiko Yagi 《Lithos》2007,96(3-4):453-474

We report trace element and Sr–Nd isotopic compositions of Early Miocene (22–18 Ma) basaltic rocks distributed along the back-arc margin of the NE Japan arc over 500 km. These rocks are divided into higher TiO₂ (> 1.5 wt.%; referred to as HT) and lower TiO₂ (< 1.5 wt.%; LT) basalts. HT basalt has higher Na₂O + K₂O, HFSE and LREE, Zr/Y, and La/Yb compared to LT basalt. Both suite rocks show a wide range in Sr and Nd isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr (SrI) = 0.70389 to 0.70631, initial ¹⁴³Nd/¹⁴⁴Nd(NdI) = 0.51248 to 0.51285). There is no any systematic variation amongst the studied Early Miocene basaltic rocks in terms of Sr–Nd isotope or Na₂O + K₂O and K₂O abundances, across three volcanic zones from the eastern through transitional to western volcanic zone, but we can identify gradual increases in SrI and decreases in NdI from north to south along the back-arc margin of the NE Japan arc. Based on high field strength element, REE, and Sr–Nd isotope data, Early Miocene basaltic rocks of the NE Japan back-arc margin represent mixing of the asthenospheric mantle-derived basalt magma with two types of basaltic magmas, HT and LT basaltic magmas, derived by different degrees of partial melting of the subcontinental lithospheric mantle composed of garnet-absent lherzolite, with a gradual decrease in the proportion of asthenospheric mantle-derived magma from north to south. These mantle events might have occurred in association with rifting of the Eurasian continental arc during the pre-opening stage of the Japan Sea.  相似文献   

Shear Wave Velocity Structure of the Sinai Peninsula from Rayleigh Wave Analysis     

V. Corchete  M. Chourak  H. M. Hussein 《Surveys in Geophysics》2007,28(4):299-324

The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999 in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a broadband station located in Egypt (KEG station). The dispersion curves were obtained for periods between 3 and 40 s, by digital filtering with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain a dispersion curve for each source-station path. These dispersion curves were inverted according to generalized inversion theory, to obtain shear wave velocity models for each source-station path, which is the main goal of this study. The shear velocity structure obtained for the Sinai Peninsula is shown through the shear velocity distributions with depth. These results agree well with the geology and other geophysical results, previously obtained from seismic and gravity data. The obtained velocity models suggest the existence of lateral and vertical heterogeneity. The shear velocity increases generally with depth for all paths analyzed in the study area. Nevertheless, in some paths a small low velocity channel in the upper or lower crust occurs. Along these profiles, it is found that the crustal structure of the Sinai Peninsula consists of three principal layers: upper crust with a sedimentary layer and lower crust. The upper crust has a sedimentary cover of 2 km thick with an average S-velocity of 2.53 km/s. This upper crust has a variable thickness ranging from 12 to 18 km, with S-wave velocity ranging from 3.24 to 3.69 km/s. The Moho discontinuity is located at a depth of 30 km, which is reflected by a sharp increase in the S-velocity values that jump from 3.70–4.12 to 4.33–4.61 km/s.  相似文献   

How is the European Lithosphere Imaged by Magnetotellurics?     

Toivo Korja 《Surveys in Geophysics》2007,28(2-3):239-272

I review recent investigations on the electrical conductivity of the lithosphere and asthenosphere in Europe. The principal method in the reviewed studies is the magnetotelluric method, but in many cases other electromagnetic methods (e.g., magnetovariational profilings and geomagnetic depth soundings) have provided additional information on subsurface conductivity or have been the primary method. The review shows that the magnetotelluric method has been used, and is being used, in all kinds of environments and for many different processes shaping the crust and lithosphere. The crust is very heterogeneous, both with respect to the scale of conductive/resistive features and interpretations: research targets vary from Archaean palaeostructures to ongoing processes. The European database of the depth to the lithosphere-asthenosphere boundary (LAB) in Europe is updated, and a new map showing lateral variations of the depth of LAB is provided. The compilation shows that (1) the Phanerozoic European lithosphere, with considerable variations (45–150 km), is much thinner than the Precambrian European lithosphere, (2) the Trans-European Suture Zone is a major electrical border in Europe separating electrically (as well as geophysically and geologically in general) two quite different settings, (3) the thinnest lithosphere is found under the extensional Pannonian Basin (45–90 km), (4) in most of the East European Craton there are no indications of a high conductivity zone in upper mantle. In many regions there is no information at all on upper mantle conductivity, which calls for pan-European projects to operate arrays of simultaneously recording instruments with long recording periods (2–8 months) and dense spatial sampling (20–50 km).  相似文献   

Speculations on evolution of the terrestrial lithosphere–asthenosphere system—Plumes and plates     

W.G. Ernst   《Gondwana Research》2007,11(1-2):38

In the early Earth, accretionary impact heating, including collision with a large, Mars-sized object, decay of short-lived radioisotopes, and (after an initial thermal run-up) continuous segregation of the liquid Fe–Ni core resulted in extensive the melting of the silicate mantle and in the formation of a near-surface magma mush ocean. Progressive, continuous degassing and chemical–gravitational differentiation of the crust–mantle system accompanied this Hadean stage, and has gradually lessened during the subsequent cooling of the planet. Mantle and core overturn was vigorous in the Hadean Earth, reflecting deep-seated chemical heterogeneities and concentrations of primordial heat. Hot, bottom-up mantle convection, including voluminous plume ascent, efficiently rid the planet of much thermal energy, but gradually decreased in importance with the passage of time. Formation of lithospheric scum began when planetary surface temperatures fell below those of basalt and peridotite solidi. Thickening and broadening of lithospheric plates are inferred from the post-Hadean rock record. Developmental stages of mantle circulation included: (a) 4.5–4.4 Ga, early, chaotic magma ocean circulation involving an incipient or pre-plate regime; (b) 4.4–2.7 Ga, growth of small micro-oceanic and microcontinental platelets, all returned to the mantle prior to 4.0 Ga, but increasing in size and progressively suturing sialic crust-capped lithospheric amalgams at and near the surface over time; (c) 2.7–1.0 Ga, assembly of cratons surmounting larger, supercontinental plates; and (d) 1.0 Ga–present, modern, laminar-flowing asthenospheric cells capped by gigantic, Wilson-cycle lithospheric plates. Restriction of komatiitic lavas to the Archean, and of ophiolite complexes ± alkaline igneous rocks, high-pressure and ultrahigh-pressure metamorphic terranes to progressively younger Proterozoic–Phanerozoic orogenic belts supports the idea that planetary thermal relaxation promoted the increasingly negative buoyancy of cooler oceanic lithosphere. The Thickening of oceanic plates enhanced the gravitational instability and the consequent overturn of the outer Earth as cold, top-down oceanic mantle convection. The scales and dynamics of deep-seated asthenospheric circulation, and of lithospheric foundering + shallow asthenospheric return flow evidently have evolved gradually over geologic time in response to the progressive cooling of the Earth.  相似文献   

豫西崤山白石崖岩株的深部过程——锆石年龄谱和稀土元素证据     

梁涛  卢仁 《地质论评》2023,69(3):2023030003-2023030003

崤山北部早白垩世侵入岩的简单年龄结果中包含了复杂地质信息,六个岩株的侵位年龄集中于~130 Ma和~145 Ma两期,复杂的单颗粒锆石年龄谱为反演区域构造背景提供了新途径。白石崖岩株锆石的U- Pb年龄和微量元素特征不仅对探讨其岩石成因和深部过程具有重要作用,而且为建立崤山北部燕山期侵入岩的精细的年代学框架和整合的成因模型提供新限定。白石崖岩株定年样品BSY03为斑状黑云母二长花岗岩,三次LA- ICP- MS锆石U- Pb测试中分析了77个测点,其中73个有效测点的年龄值分成~132 Ma（15个）、~145 Ma（49个）和~158 Ma（9个）三个年龄组,形成了锆石年龄谱,最晚一组加权平均年龄132. 1±1. 0 Ma为白石崖岩株的形成时代。3组年龄锆石均显示了轻稀土亏损和重稀土富集的特征,整体为Ce正异常及Pr、Nd负异常,~145 Ma和~158 Ma两组锆石的稀土总量分别为694×10-6 ~ 2213×10-6（平均值1309×10-6）和950×10-6~ 1849×10-6（平均值1360×10-6）,~132Ma组锆石的稀土总量变化范围介于429×10-6 ~ 2210×10-6,平均值为1495×10-6。3组锆石总体的形成温度为539 ~ 748 ℃;~158 Ma组锆石的温度较高,为601 ~ 748℃（平均值662℃）; ~145 Ma组和~132 Ma组锆石的温度分别介于539 ~ 717℃（平均值629℃）和553 ~ 701℃（平均值633℃）。锆石测点的Er、Yb、Lu和Y含量随年龄由早及晚的整体变化趋势均为升高,~132 Ma和~145 Ma组锆石的Ce4+/Ce3+值分别介于13. 2 ~ 121（平均值69. 7）和27. 6 ~ 107（平均值70. 3）,~158 Ma组锆石的Ce4+/Ce3+值介于3. 53 ~ 81. 4,其由早及晚的整体趋势均为先升高后降低。白石崖岩株的形成受控于崤山北部岩石圈拆沉作用,深部岩浆/流体因此得以释放,促成上部处于未完全固结晶粥状态的岩浆/流体库发生混合再活化作用,重获上侵能力的岩浆/流体卷携多期锆石（如~158 Ma和~145 Ma的锆石）在浅部构造有利部位固结成岩,并晶出~132 Ma锆石。  相似文献