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The Daliangshan tectonic zone is a rhombic area to the east of the Anninghe and Zemuhe fault zones in the middle segment of the Xianshuihe-Xiaojiang fault system along the southeast margin of the Qinghai-Xizang (Tibet) Plateau. Since the Cenozoic era, the neotectonic deformation in the Daliangshan tectonic zone has presented not only sinistral slip and reverse faulting along the Daliangshan fault zone, but also proximate SN-trending crust shortening. It is estimated that the average crust shortening in the Daliangshan tectonic zone is 10.9±1.6 km, with a shortening rate of 17.8±2.2% using the method of balanced cross-sections. The crust shortening from folding occurred mainly in the Miocene and the Pliocene periods, lasting no more than 8.6 Ma. Based on this, a crust shortening velocity of 1.3±0.2 mm/a can be estimated. Compared with the left offset along the Daliangshan fault zone, it is recognized that crust shortening by folding plays an important part in transferring crustal deformation southeastward along the Xianshuihe-Xiaojiang fault system. 相似文献
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本文基于EGM2008重力场模型研究了青藏高原东南缘均衡重力异常和多尺度的布格重力异常特征,以鲁甸和景谷地震为例,认识其深部构造环境和动力学过程,为该区域的构造运动和地震孕育环境研究提供依据。结果表明,研究区布格重力异常和均衡重力异常与地质构造格局相关性较好,川滇地块剧烈的区域布格重力异常和非均衡状态与其强烈的地壳变形、断裂及地震活动密切相关。强震多分布在断裂带两侧重力异常的过渡地带和高梯度带,断裂带两侧横向和垂向的显著介质密度差异是强震孕育的深部构造背景。布格重力异常和均衡重力异常揭示的鲁甸、景谷震源区深浅差异性的重力异常特征,暗示鲁甸和景谷地震孕震环境的不同。 相似文献
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Aiming Lin 《Pure and Applied Geophysics》2008,165(2):215-233
Pseudotachylytes generated in granulite facies rocks are found in the Woodroffe thrust, central Australia. Petrologic evidence
and structural and textural features show that these pseudotachylytes contain typical melting-origin features including injection
occurrence, rounded and embayed clasts, and microlites within the fine-grained matrix, which formed contemporaneously with
the wall granulite facies rocks under conditions of ~8 kbar and ~650–700°C. These granulite-related pseudotachylyte (G-Pt)
veins are overprinted in subsequent deformation stages by three other types of pseudotachylytes including mylonite-related
(M-Pt) and ultramylonite-related (Um-Pt) pseudotachylytes that are then transcut by cataclasite-related pseudotachylytes (C-Pt).
The overprinting occurred following uplift of the lower crust where the G-Pt veins formed through the brittle-plastic transition
zone where the M-Pt and Um-Pt veins occurred within the brittle-dominated regime of the C-Pt generation zone in the upper
crust. The coexistence of multiple generations of large voluminous C-Pt, M-Pt, Um-Pt, and G-Pt veins indicates that numerous
large earthquakes accompanying distinct seismic slip which produced the pseudotachylytes occurred over an extended period
of seismicity and various depths of the crust within the Woodroffe thrust zone. The spatial distribution and structural features
of the multiple-stage pseudotachylytes suggest that coseismic slipping caused by large earthquakes which nucleated in the
brittle-dominated seismogenic zone propagated downward through the brittle-plastic transition zone into the plastic-dominated
granulite facies depth from the upper to lower crust. 相似文献
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T. Weiss S. Siegesmund W. Rabbel T. Bohlen M. Pohl 《Pure and Applied Geophysics》1999,156(1-2):97-122
—Seismic anisotropy is often neglected in seismic studies of the earth’s crust. Since anisotropy is a common property of many typically deep crustal rocks, its potential contribution to solving questions of the deep crust is evaluated. The anisotropic seismic velocities obtained from laboratory measurements can be verified by computations based on the elastic constants and on numerical data pertaining to the texture of rock-forming minerals. For typical lower crustal rocks the influence of layering is significantly less important than the influence of rock texture. Surprisingly, most natural lower crustal rocks show a hexagonal type of anisotropy. Maximum anisotropy is observed for rocks with a high content of aligned mica. It seems possible to distinguish between layered intrusives and metasediments on the basis of in situ measurements of anisotropy, which can thus be used to validate different scenarios of crustal evolution. 相似文献
6.
伽师-阿图什震区地壳深部结构特征的探测与研究 总被引:6,自引:0,他引:6
通过对两条测深剖面资料的处理计算和综合研究后发现,研究区壳幔结构具有明显的分层性。不同的地质构造块体在速度结构,构造特征上显示出较大差异。上,下地壳的分界C界面和M界面是具有较大起伏变化的界面,由伽师下方最浅的30.0km(C界面),45.5km(M界面)向西昆仑山区急剧加深至44.0km和70.0km;塔里木块体较高的速度结构意味着地壳结构和对“稳定”的特性;根据伽师地区震源深度大多分布在20-40km这一现象,可以认为,C,M界面的局部隆起,低速异常体和深大断裂的存在对于伽师强震群的孕育和发生具有一定的控制作用。 相似文献
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Xiaozhi Yang 《Surveys in Geophysics》2011,32(6):875-903
Electromagnetic measurements have demonstrated that the lower continental crust has remarkable electrical anomalies of high
conductivity and electrical anisotropy on a global scale (probably with some local exceptions), but their origin is a long-standing
and controversial problem. Typical electrical properties of the lower continental crust include: (1) the electrical conductivity
is usually 10−4 to 10−1 S/m; (2) the overlying shallow crust and underlying upper mantle are in most cases less conductive; (3) the electrical conductivity
is statistically much higher in Phanerozoic than in Precambrian areas; (4) horizontal anisotropy has been resolved in many
areas; and (5) in some regions there appear to be correlations between high electrical conductivity and other physical properties
such as seismic reflections. The explanation based on conduction by interconnected, highly conductive phases such as fluids,
melts, or graphite films in grain boundary zones has various problems in accounting for geophysically resolved electrical
conductivity and other chemical and physical properties of the lower crust. The lower continental crust is dominated by mafic
granulites (in particular beneath stable regions), with nominally anhydrous clinopyroxene, orthopyroxene, and plagioclase
as the main assemblages, and the prevailing temperatures are mostly 700–1,000°C as estimated from xenolith data, surface heat
flow, and seismic imaging. Pyroxenes have significantly higher Fe content in the lower crust than in the upper mantle (peridotites),
and plagioclase has higher Na content in the lower crust than in the shallow crust (granites). Minerals in the lower continental
crust generally contain trace amounts of water as H-related point defects, from less than 100 to more than 1,000 ppm H2O (by weight), with concentrations usually higher than those in the upper mantle. Observations of xenolith granulites captured
by volcano-related eruptions indicate that the lower continental crust is characterized by alternating pyroxene-rich and plagioclase-rich
layers. Experimental studies on typical lower crustal minerals have shown that their electrical conductivity can be significantly
enhanced by the higher contents of Fe (for pyroxenes), Na (for plagioclase), and water (for all minerals) at thermodynamic
conditions corresponding to the lower continental crust, e.g., to levels comparable to those measured by geophysical field
surveys. Preferred orientation of hydrous plagioclase, e.g., due to ductile flow in the deep crust, and alternating mineral
fabrics of pyroxene-rich and plagioclase-rich layers can lead to substantial anisotropy of electrical conductivity. Electrical
conductivity properties in many regions of the lower continental crust, especially beneath stable areas, can mostly be accounted
for by solid-state conduction due to the major constituents; other special, additional conduction mechanisms due to grain
boundary phases are not strictly necessary. 相似文献
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This paper approaches the neotectonic stress field based on the data of foeal mechanismsolution,ground stress measurement,tectonic mechanical analysis and geodetic surveying,and finds out that the orientations of the maximum principal comproessive sterss patterns arequite discordant with different methods and the stress patterns are widely differnt betweenthose in the shallow and deep part of the crust in North China.Based on the analysis ofabove-mentioned data,we established a duplex model by considering the diversities of theStress patterns in 3-dimentional spaces,the boundary conditions and the lithospheric media,and made an inverse calculation by using the finite element method.The calculated results fitwell with the reality in North China,i.e.the stress patterns in lower crust which is below thedetachment interface at the deptp of 10 km from ground surface are relatively consistent withnearly horizontal state and NE-ENE trending of the maximum principal compressive stressaxes,whereas the stress patt 相似文献
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Abstract In Japan and Korea, some Lower Cretaceous terrigenous clastic rocks yield detrital chromian spinels. These chromian spinels are divided into two groups: low-Ti and high-Ti. The Sanchu Group and the Yuno Formation in Japan have both groups, whereas the Nagashiba Formation in Japan and the Jinju Formation in Korea have only the low-Ti spinels. High-Ti spinels are thought to have originated in intraplate-type basalt. Low-Ti spinels (higher than 0.6 Cr#) were probably derived from peridotites, which are highly correlated with an arc setting derivation and possibly with a forearc setting derivation. Low-Ti spinels are seen in the Sanchu Group, the Nagashiba Formation and the Jinju Formation. Low-Ti spinels from the Yuno Formation are characterized by low Cr# (less than 0.6) and these chromian spinels appear to have been derived from oceanic mantle-type peridotite, including backarc. According to maps reconstructing the pre-Sea of Japan configuration of the Japanese Islands and the Korean Peninsula, the Korean Cretaceous basin was comparatively close to the Southwest Japan depositional basins. It is possible that these Lower Cretaceous systems were sediments mainly in the forearc and partly in the backarc regions. The peridotite might have infiltrated along major tectonic zones such as the Kurosegawa Tectonic Zone (= serpentinite melange zone) in which left lateral movement prevailed during the Early Cretaceous. 相似文献
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N. SRINIVASA RAO 《水文科学杂志》2013,58(6):877-892
Abstract Reports on the occurrence of fluoride in natural water resources and the associated health hazards due to human consumption have been made from many parts of India during the last decade. With the objective of organizing a systematic scientific programme to understand the behaviour of fluoride in natural water resources in relation to the local hydrogeological and climatic conditions and agricultural use, a typical area constituting the lower Vamsadhara River basin was chosen for a detailed study. High fluoride concentrations in the groundwater reaching a maximum of 3.4 mg 1?1 were observed to be associated with weathered formations of pyroxene amphibolites and pegmatites. The groundwater in the clayey soils contained much less fluoride as compared to the sandy soils. The complex depositional pattern of these sandy and clayey soils plays an important role in the uneven spatial distribution of fluoride in the groundwater. The contribution of fluoride from geological formations is far greater than that from agriculture: the maximum yield of fluoride by superphosphate fertilizer to irrigation water is observed to be 0.34 mg 1?1. The fluoride concentration is expected to be increased in the future as the groundwater is subsaturated with respect to fluorite. An inverse relationship between F and Ca and positive relationships of F with Na, HCO3, PO4 and electrical conductivity were observed. Best relationships were obtained in the fluoride range of 1.0–3.4 mg 1?1. 相似文献
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墨脱断裂展布于南迦巴瓦构造结的东侧,晚第四纪以来活动强烈,断裂水平运动表现为左旋走滑。为了进一步研究墨脱断裂倾向滑动特征及断裂活动性差异,文章基于DEM数据提取了4对横跨断裂矩形区域内的高程数据,计算获得沿断裂发育的31个流域盆地的面积高程积分值。研究表明,墨脱断裂两侧在同一高度出现对称的4组台地面,且从低到相邻的两级台面的高度差没有出现逐步增大的趋势,表明断裂没有表现出明显的倾向滑动;沿断裂分布的汇水盆地具有较大的面积高程积分值(0.42~0.60之间),反映出墨脱断裂所在区域目前总体表现为强烈的构造隆升;根据汇水盆地面积高程积分值的空间分布特征,区域地壳隆升强度沿墨脱断裂由南至北具有逐渐减弱的趋势,结合断裂地貌形态,认为在强隆升区面积高程积分值对断裂活动性具有一定的指示意义。 相似文献
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Abstract The Kokchetav Massif of Kazakhstan includes high to ultrahigh-pressure (HP–UHP) metamorphic rocks (some of which were recrystallized at depths in excess of 150 km), juxtaposed against much lower pressure metamorphic components. We investigated the relationship between the HP–UHP metamorphic unit and the low pressure (LP) unit (Daulet Suite) in the Sulu–Tjube area, where the metamorphic rocks have previously been interpreted as constituting a megamelange with subvertical structural attitudes. Analyses of fold structures suggest that the HP–UHP metamorphic unit overlies the LP unit across a west-dipping subhorizontal boundary. In addition, kinematic indicators display top-to-the-north senses of shear along the tectonic contact between the two units, indicating that the HP–UHP unit has been extruded northward onto the LP unit. Following the juxtaposition of the two units, upright folds developed in both units, and these are associated with the previously reported steeply dipping metamorphic foliations. These data have important implications for the mode of exhumation of the UHP rocks from upper mantle to shallow crustal depths. 相似文献
15.
Hiroshi Yamamoto Natsumi Nakamori Masaru Terabayashi Hafiz Ur Rehman Masahiro Ishikawa Yoshiyuki Kaneko Takashi Matsui 《Island Arc》2010,19(3):458-469
Geological observations in the Horoman area, south‐central Hokkaido, show that the Horoman peridotite complex of the Hidaka metamorphic belt is a tectonic slice about 1200 m thick. The peridotite slab is intercalated into a gently east‐dipping structure. The underlying unit is a Cretaceous–Paleogene accretionary complex. Riedel shear planes in the sedimentary layers of the accretionary complex near the structural bottom of the peridotite slab indicate top‐to‐the‐west (thrust) displacement. The overlying unit is composed of felsic–pelitic gneisses and mafic–felsic intrusive rocks (the Hidaka metamorphic rocks). The boundary surface between the peridotite complex and metamorphic rocks forms a domal structure. Microstructures of sheared metamorphic rocks near the structural top of the peridotite slab indicate top‐to‐the‐east (normal) displacement. The results combined with previous studies suggest that the Horoman peridotite complex was emplaced onto the Asian margin (Northeast Japan) during the collision between the Asian margin and the Hidaka crustal block. 相似文献
16.
龙门山中北段位于青藏高原东缘,该区作为高原向东扩展的前缘部位,其地形与河流水系的演化记录了高原隆升与挤压扩展及其气候环境效应的各种信息。龙门山中北段构造活动有明显差异,从中段逆冲为主转化为北段的走滑为主,本文采用定量化地貌参数从构造地貌的角度揭示了区域构造活动的差异。龙门山中北段地貌因子(坡度、地形起伏度和条带状剖面)的阶梯状分布特点,显示了高原扩展的逆冲推覆特征,在中央断裂处构造抬升作用最强,同时显示出了南北向构造活动减弱的趋势,由中段的逆冲转换为北段逆冲兼走滑的形式。北川-映秀断裂两侧流域的HI值也显示了断裂上盘高、下盘低、沿走向减弱的趋势。综合分析认为,本区构造活动是地貌演化的主控因素,龙门山中北段地形存在差异,北川-映秀断裂两侧的小流域地貌指数分析显示,构造抬升活动自南向北减弱,中段以逆冲为主,北段为逆冲兼走滑。 相似文献
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T. Bohlen W. Rabbel T. Weiss S. Siegesmund M. Pohl 《Pure and Applied Geophysics》1999,156(1-2):123-138
—Studies of seismic anisotropy in situ can help to discriminate between different rock types for the lower crust. In this context we investigate the sensitivity of an iterative linearized 3-D travel-time inversion scheme for transversely isotropic media with respect to two types of systematic errors wrong velocities and interface topography of the hanging wall of the lower crust. The computations simulate realistic field conditions such as found for the Variscan crust at the Urach geothermal anomaly. The study focusses on the possible information content of split S M ?S arrivals observed along two orthogonal expanding spread profiles. It ensues that an imperfect knowledge of the layer geometry is of minor importance compared to errors in the velocities of the hanging wall. In particular, upper crust anisotropy has to be considered carefully. Generally, the anisotropy of transversely polarized shear waves (SH waves) was recovered with higher accuracy than the anisotropy of vertically polarized shear waves (SV waves). 相似文献
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AbstractData unavailability is the main reason for limited applications of hydrodynamic models for predicting inundation in the developing world. This paper aims to generate moderately high-resolution hybrid terrain data by merging height information from low-cost Indian Remote Sensing satellite (IRS) Cartosat-1 stereo satellite images, freely-available Shuttle Radar Topograph Mission (SRTM) digital elevation model (DEM) data, and limited surveyed channel cross-sections. The study reach is characterized by anabranching channels that are associated with channel bifurcation, loops and river islands. We compared the performance of a simple 1D–2D coupled LISFLOOD-FP model and a complex fully 2D finite element TELEMAC-2D model with the hybrid terrain data. The results show that TELEMAC-2D produced significantly improved simulated inundation with the hybrid terrain data, as compared to the SRTM DEM. LISFLOOD-FP was found unsuitable to work with the hybrid DEM in a complicated fluvial environment, as it failed to efficiently divert water in the branches from the main channel.
Editor D. Koutsoyiannis; Associate editor A. Viglione 相似文献
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This paper presents a probable isostatic model of the East Anatolian Region, which lies in a belt of significant plate movements.
Probable locations of the horizontal and vertical discontinuities in the crust structure were determined using the normalized
full gradient (NFG) method. For the purpose of explaining the mechanism that supports topography corresponding to the crust
thickness in the region, calculations of effective elastic thickness (T
e) were carried out initially by utilizing admittance and misfit functions. According to these results, the effective elastic
thickness value obtained was less than the crust thickness, even though the isostatic model does not conform with the Airy
model. Consequently, it was assumed that there could be problems beneath the crust. Hence, the NFG method was applied on
the Bouguer gravity data of the region in order to investigate probable discontinuities in the crust structure. According
to the NFG results, vertical structural transitions were observed at a depth ranging between 10 and 30 km, which begin immediately
north of the Bitlis Zagros Suture Zone (BZSZ) and continue in a northerly direction. The relationship between the effective
elastic thickness (T
e; 13 km in average as determined in the last stage), and the seismogenic zone in the region was investigated. If the T
e value happens to be less then the crustal thickness, then one can say that there are problems in the crustal structure of
the region similar to Eastern Anatolia. Indeed, when NFG results of the study area are examined, numerous vertical and horizontal
discontinuities in the crust can be observed. These discontinuities, which correspond to low Bouguer gravity anomalies and
shallow focal depth-earthquakes, are probably the source of the factors which rule the tectonic mechanism of the region. 相似文献