Paleomagnetic constraints on the paleogeography and oroclinal bending of the Devonian volcanic arc in Kazakhstan   总被引：1，自引：0，他引：1  

Alexandra Abrajevitch  Rob Van der Voo  Natalia M. Levashova  Mikhail L. Bazhenov   《Tectonophysics》2007,441(1-4):67-84

Numerical modelling, incorporating coupling between surface processes and induced flow in the lower continental crust, is used to address the Quaternary evolution of the Gulf of Corinth region in central Greece. The post-Early Pleistocene marine depocentre beneath this Gulf overlies the northern margin of an older (Early Pleistocene and earlier) lacustrine basin, the Proto Gulf of Corinth Basin or PGCB. In the late Early Pleistocene, relief in this region was minimal but, subsequently, dramatic relief has developed, involving the creation of  900 m of bathymetry within the Gulf and the uplift by many hundreds of metres of the part of the PGCB, south of the modern Gulf, which forms the Gulf's main sediment supply. It is assumed that, as a result of climate change around 0.9 Ma, erosion of this sediment source region and re-deposition of this material within the Gulf began, both processes occurring at spatial average rates of  0.2 mm a^− 1. Modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is  4 × 10¹⁹ Pa s, indicating a Moho temperature of  560 °C. It predicts that the  10 mm a^− 1 of extension across this  70 km wide model region, at an extensional strain rate of  0.15 Ma^− 1, is partitioned with  3 mm a^− 1 across the sediment source,  2 mm a^− 1 across the depocentre, and  5 mm a^− 1 across the ‘hinge zone’ in between, the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the Gulf. This modelling confirms the view, suggested previously, that coupling between this depocentre and sediment source by lower-crustal flow can explain the dramatic development in local relief since the late Early Pleistocene. The effective viscosity of the lower crust in this region is not particularly low; the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity. In detail, the effective viscosity of the lower crust is expected to decrease northward across this model region, due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere; in the south the two are separated by the subducting Hellenic slab. The isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why, since  0.9 Ma, the modern Gulf has developed asymmetrically over the northern part of the PGCB, leaving the rest of the PGCB to act as its sediment source.  相似文献   

利用磷灰石裂变径迹资料反演合肥盆地古地温和估计沉降率与剥蚀率   总被引：5，自引：0，他引：5       下载免费PDF全文

薛爱民  杨小毛 《地球物理学报》1994,37(6):787-794

利用合肥盆地内６个磷灰石裂变径迹样品资料，反演模拟了该盆地自侏罗纪晚期以来各时代地层古地温变化，估算了沉降率与剥蚀率．模拟结果与其他地质资料推论一致，它揭示出该盆地南北两地存在不同的构造变化和受热史，反映了大别山构造发展对盆地南北两地区影响的差异．盆地南部靠近大别山地区的晚侏罗世地层在白垩纪早期埋藏温度曾大于１２０℃；早白垩世后期的构造抬升（剥蚀率约１３０ｍ／Ｍａ）使温度降至３０-４０℃；自白垩纪后期始，该地区一直处于动荡的但总体为持续抬升的构造环境中．盆地北部地区晚侏罗世与早白垩世早期地层在白垩纪期间埋藏温度曾达到和超过１００℃，但随后的大幅度构造抬升（剥蚀率约１９０ｍ／Ｍａ）使其温度降至３０-６０℃；第三纪早期，局部区域的裂陷（沉降率约６０ｍ／Ｍａ）使温度又升至８０℃左右．指出合肥盆地构造演化大体可分形成、隆升、局部裂陷和再隆升４个阶段．  相似文献   

黄土震陷研究及相关问题探讨     

王强  孙军杰  王兰民  陈秀清 《中国地震研究》2013,27(4):479-489

The research and achievements made on seismic subsidence of loess, obtained over the past 30 years, were reviewed. Seismic Subsidence of Loess （SSL） has been verified by microstructure characteristics, dynamic triaxial experiments, and in-situ explosion tests, and has become an important subject in the field of seismic loess engineering research. While, the research is still in the stage of theoretical study of saturated soil, and there are no representative cases of seismic subsidence of loess in historical earthquakes. It is difficult to express structure characteristics using microstructure morphology. While, soil mechanics are available methods for this. Seismic subsidence judgment is absolute in some certain value ranges for several parameters. Therefore, probabilistic judgment should be developed. The seismic subsidence ratio is estimated mostly by empirical formulas or semi- empirical and semi-theoretical formulas, which are based on laboratory data. These formulas are not established on the basis of physical process and mechanics of seismic subsidence, and this leads to more variables, complicated computation, and poor practicability. To solve these problems, we need to distinguish the main factors and corresponding variables, to establish a mechanics model for seismic subsidence estimation, and to characterize its physio-mechanical process. The key of anti-seismic subsidence treatment is to reduce the seismic subsidence property of soils, and to lower the interaction between the soil body and underground structures.  相似文献   

Classic swiss clastics (flysch and molasse) The alpine connection     

Peter Homewood  Olivier Lateltin 《Geodinamica Acta》2013,26(1):1-11

Abstract

Flysch and molasse are discussed in the light of alpine geodynamics. They are pre-collision and post-collision orogenic clastics which accumulated in basins under different geodynamic controls. We propose that in the case of the Alps, their succession records the change in geodynamics from pre-collision inversion of shallower extensio-nal structures, to post-collision inversion of one or more deep-seated features.

The classical flysch of the Prealps, lying within a pile of nappes at the front of the Western Alps, are invariably turbidite deposits. Flysch has therefore acquired a sedimentological connotation over the years, and this has been emphasized over the last few decades. Turbidite facies were also laid down in marginal and foreland locations during and a little after the collision between the South and North Tethyan Alpine margins, and this has obscured the possible deeper signification of flysch and molasse.

Geodynamic regimes dictate the subsidence behaviour of basins, so by use of geohistory analysis, the time and place of the onset of Molasse basin development may be located. This was at the southern margin of the Helvetic belt, from the start of the Oligocene. Along the Alpine traverse of Western Switzerland, the change in regime from flysch to molasse (i.e. from trench and forearc or retro-arc, to foreland basin deposits) suggests that a major deep-seated inversion structure was situated near the Helvetic-Ultrahelvetic boundary.  相似文献   

中国潜质页岩形成和分布   总被引：2，自引：0，他引：2  

张金川  杨超  陈前  赵倩茹 《地学前缘》2016,23(1):74-86

我国页岩盆地发育的大地构造背景复杂,板块规模偏小且地质活动性较强,彼此之间相互影响且在中、新生代以来受外缘板块环境影响较大,表现为南海北陆、南早北晚、南升北降等重大差异,在东西方向上,也由于塔里木与华北板块之间的演变差异而出现较大区别。中国页岩的分布主要受控于板块特点及构造、沉积之间的相互匹配,板块及其相互之间的相对运动造成了不同时代沉降沉积中心的迁移变化。塔里木、华北、华南三个板块均发生了四次沉降沉积中心的转移,但总体上表现为早古生代海相时期的由东向西转移、晚古生代海陆交互相时期的背离板块汇聚中心式转移、中生代陆相和海陆交互相时期的由东向西转移、新生代陆相时期的由西向东转移。潜质页岩及页岩气主要发育在中部地区,具有时代交替、南海北陆、东西分异、时空变迁等特点。南方下古生界海相页岩气原始地质条件优越,但有机质热演化程度高且后期改造强,页岩气的有利区分布既受控于构造与沉积条件,也更决定于构造与沉积两者的相互匹配;晚古生代为主的海陆交互相页岩分布范围广、累积厚度大,常与砂岩、煤系及灰岩频繁互层,有机质热演化程度较为适中,是我国页岩气进一步勘探开发的重要目标层系。北方以中新生代陆相为代表的页岩分布受控于盆地结构,是我国页岩油发育的主体区域。针对各套潜质页岩特点,页岩气勘探宜分别考虑。  相似文献   

Hydrogeomorphic control on tree growth responses in the Elton area of the Cheshire Saltfield, UK     

Jonathan G.A. Lageard  Ian B. Drew   《Geomorphology》2008,95(3-4):158-171

Increment cores were sampled from oak (Quercus robur) and ash (Fraxinus excelsior) growing at Elton, an area of the Cheshire Saltfield that has experienced significant subsidence and damage to the natural and built environments in the latter part of the twentieth century. Ring-width measurements for Elton trees permitted the construction of one main site chronology (Elton) and four sub chronologies (Elton A, Elton B, Elton C, Elton ASH). Ring-width difference between these and a control chronology identified periods of sustained growth reduction in oak trees commencing in AD 1859/1861, 1886 and 1934. Growth reductions after 1934 are related to watertable draw down caused by brine pumping from a concentration of nine boreholes at Elton, up to 2 km from tree sampling locations. Growth reductions in 1859/1861 and 1886 are likely to be the result of earlier phases of brine pumping in the Wheelock Valley, up to 5 km to the east of Elton, and these reductions correlate well with historic records of subsidence and pumping activity. Cessation of pumping in 1977 led to a lagged growth recovery in oak trees between 1981 and 1986, indicating that an artificial drought had been imposed on the Elton area for a period in excess off 100-y. This research demonstrates a hydrological separation of surface water and groundwater in an area where salt beds are overlain by till and that ring-width records of Q. robur can be used to reconstruct watertable variability and also the spatial impact of solution mining.  相似文献   

Evaluating and comparing methods of sinkhole susceptibility mapping in the Ebro Valley evaporite karst (NE Spain)     

J.P. Galve  F. Gutirrez  J. Remondo  J. Bonachea  P. Lucha  A. Cendrero 《Geomorphology》2009,111(3-4):160-172

Multiple sinkhole susceptibility models have been generated in three study areas of the Ebro Valley evaporite karst (NE Spain) applying different methods (nearest neighbour distance, sinkhole density, heuristic scoring system and probabilistic analysis) for each sinkhole type separately (cover collapse sinkholes, cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes). The quantitative and independent evaluation of the predictive capability of the models reveals that: (1) The most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density. These models can be generated in a simple and rapid way from detailed geomorphological maps. (2) The reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes. Consequently, the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences. (3) The predictive capability of the best models obtained in this research is significantly higher (12.5–82.5%) than that of the heuristic sinkhole susceptibility model incorporated into the General Urban Plan for the municipality of Zaragoza. Although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density, it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios.  相似文献   

张裂大陆边缘形成演化的数值模拟   总被引：6，自引：5，他引：1       下载免费PDF全文

陈林  宋海斌  许鹤华  刘洪 《地球物理学报》2009,52(11):2781-2787

本文在等黏态角落流模型的基础上,建立了上升离散地幔流场,将该流场作用于大陆岩石圈底部,能解释岩石圈减薄、裂解并最终形成海底扩张和张裂大陆边缘等一系列过程.数值模拟的结果表明,岩石圈在上升离散地幔流的作用下发生依赖于深度的伸展减薄,表现为不同深度的拉张因子不同,地表热流显著升高,热扰动引起的均衡调整造成地表沉降,同时热扰动造成岩石圈流变强度尤其是在变形中心处显著减小,脆性变形临界深度变浅,而韧性变形范围扩大.在上升离散地幔流的持续作用下最终导致大陆裂解,岩石圈地幔出露,形成海底扩张和张裂大陆边缘.  相似文献   

Basement tectonics and flexural subsidence along western continental margin of India     

D.K. Pandey  Nisha Nair  Anju Pandey  G. Sriram 《地学前缘(英文版)》2017,8(5):1009-1024

The Paleocene-recent post-rift subsidence history recorded in the Mumbai Offshore Basin off western continental margin of India is examined. Results obtained through 2-D flexural backstripping modelling of new seismic data reveal considerable thermo-tectonic subsidence over last ca. 56 Myr. Reverse postrift subsidence modelling with variable β stretching factor predicts residual topography of ca. 2000 m to the west of Shelf Margin Basin and fails to restore late Paleocene horizon and the underlying igneous basement to the sea level. This potentially implies that:(1) either the igneous basement formed during the late Cretaceous was emplaced under open marine environs; or(2) a laterally varying cumulative subsidence occurred within Mumbai Offshore Basin(MOB) during ca. 68 to ca. 56 Ma. Pre-depositional topographic variations at ca. 56 Ma across the basin could be attributed to the extensional processes such as varied lower crustal underplating along Western Continental Margin of India(WCMI). Investigations about basement tectonics after unroofing of sediments since late Paleocene from this region support a transitional and heavily stretched nature of crust with high to very high β factors. Computations of past sediment accumulation rates show that the basin sedimentation peaked during late Miocene concurrently with uplift of Himalayan-Tibetan Plateau and intensification of Indian monsoon system. Results from basin subsidence modelling presented here may have significant implications for further studies attempting to explore tectono-climatic interactions in Asia.  相似文献   

静压注浆法在既有构筑物地基加固中的应用     

陈松  张树胜 《山东国土资源》2010,26(4):25-27,30

通过对中石油天津分公司塘沽油库4#储油罐工程沉降超限原因的分析,找出了引起桩基础沉降的主要原因,从而采用静压注浆的地基处理方法,有效地改善桩间土的水理性质,提高了桩间土摩擦阻力,地基的加固缓解和消除了既有构筑物的沉降问题。  相似文献