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1.
High-density transient electromagnetic (TEM) profiles have been obtained along a 170 km long transect in central Victoria north of Bendigo. The transect lies within two of the fault-bounded subdivisions of the western Lachlan Fold Belt (the Bendigo and Melbourne Zones) and coincides with part of a 2006 seismic-reflection traverse and a 2007 magnetotelluric (MT) survey commissioned by Geoscience Victoria as part of the Victorian Government's Gold Undercover initiative. In addition to providing near-surface information that will assist with geological mapping, the TEM survey also presents a viable method for the removal of static offsets present in the MT data. The new dataset also provides an immediate comparison and verification of data acquired along the same line by the helicopter-borne Versatile Transient Electromagnetic (VTEM) system. Ground-based data have been obtained for a total of 55 sites, and high-quality decay curves have revealed a variety of conductivity characteristics with typical penetration to depths of 100 m. Major geological structures can clearly be identified in both the ground and airborne sections, with very good lateral correlation present between the two. The fault zones are easily distinguished as regions characterised by bands of high conductivity along with significant variability in the near-surface structure. 相似文献
2.
R. A. Cayley R. J. Korsch D. H. Moore R. D. Costelloe A. Nakamura C. E. Willman 《Australian Journal of Earth Sciences》2013,60(2):113-156
A ～400 km long deep crustal reflection seismic survey was acquired in central Victoria, Australia, in 2006. It has provided information on crustal architecture across the western Lachlan Orogen and has greatly added to the understanding of the tectonic evolution. The east-dipping Moyston Fault is confirmed as the suture between the Delamerian and western Lachlan Orogens, and is shown to extend down to the Moho. The Avoca Fault, the boundary between the Stawell and Bendigo Zones, is a west-dipping listric reverse fault that intersects the Moyston Fault at a depth of about 22 km, forming a V-shaped geometry. Both the Stawell and Bendigo Zones can be divided broadly into a lower crustal region of interlayered and imbricated metavolcanic and metasedimentary rocks and an upper crustal region of tightly folded metasedimentary rocks. The Stawell Zone was probably part of a Cambrian accretionary system along the eastern Gondwanaland margin, and mafic rocks may have been partly consumed by Cambrian subduction. Much of the Early Cambrian oceanic crust beneath the Bendigo Zone was not subducted, and is preserved as a crustal-scale imbricate thrust stack. The seismic data have shown that a thin-skinned structural model appears to be valid for much of the Melbourne Zone, whereas the Stawell and Bendigo Zones have a thick-skinned structural style. Internal faults in the Stawell and Bendigo Zones are mostly west-dipping listric faults, which extend from the surface to near the base of the crust. The Heathcote Fault Zone, the boundary between the Bendigo and Melbourne Zones, extends to at least 20 km, and possibly to the Moho. A striking feature in the seismic data is the markedly different seismic character of the mid to lower crust of the Melbourne Zone. The deep seismic reflection data for the Melbourne Zone have revealed a multilayered crustal structure that supports the Selwyn Block model. 相似文献
3.
With the super-wide band magnetotelluric sounding data of the Jilong (吉隆)-Cuoqin (措勤) profile (named line 800) which was completed in 2001 and the Dingri (定日)-Cuomai (措迈) profile (named line 900) which was completed in 2004,we obtained the strike direction of each MT station by strike analysis,then traced profiles that were perpendicular to the main strike direction,and finally obtained the resistivity model of each profile by nonlinear conjugate gradients (NLCG) inversion. With these two models,we described the resistivity structure features of the crust and the upper mantle of the center-southern Tibetan plateau and its relationship with Yalung Tsangpo suture: the upper crust of the research area is a resistive layer with resistivity value range of 200-3 000 ?·m. The depth of its bottom surface is about 15-20 km generally,but the bottom surface of resistive layer is deeper in the middle of these two profiles. At line 900,it is about 30 km deep,and even at line 800,it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km,and a conductive layer is beneath it with resistivity even less than 5 ?·m. This conductive layer is composed of individual conductive bodies,and at the south of the Yalung Tsangpo suture,the conductive bodies are smaller with thickness about 10 km and lean to the north slightly. However,at the north of the Yalung Tsangpo suture,the conductive bodies are larger with thickness about 30 km and also lean to the north slightly. Relatively,the conductive bodies of line 900 are thinner than those of line 800,and the depth of the bottom surface of line 900 is also shallower. At last,after analyzing the effect factors to the resistivity of rocks,it was concluded that the very conductive layer was caused by partial melt or connective water in rocks. It suggests that the middle and lower crust of the center-southern Tibetan plateau is very thick,hot,flabby,and waxy. 相似文献
4.
The arcuate nappe structure on the north edge of the Wuliang Mountains in westernYunnan Province is a complex nappe structural system with multiple superimposed structures.The autochthonous system is a WNW-trending arcuate fold belt consisting of the Jurassic andCretaceous and the allochthonous system is mainly composed of Upper Triassic rocks. Generally,the nappe structure moved from south to north, with the hanging wall thrusting in a WNW direc-tion for a distance of over 10km. The deep nappe structural system was formed at depths ofabout 5-10km in an environment not exceeding the greenschist facies. It occurred in theOligocene (about 40-20 Ma). 相似文献
5.
祁连造山带处在特提斯构造域的北缘,经历了早古生代原特提斯洋发育以来的构造演化,是青藏高原东北缘高原隆升与扩展的关键构造带。本文依据区域地质调查与构造地质填图,结合前人地球物理场资料,阐述了中国西北和祁连造山带断裂构造体系特征。通过超宽频大地电磁测深(MT)剖面数据采集处理,以及浅、中—深层电性剖面反演与构造解释,分析了祁连造山带全地壳深部结构特征与盆山耦合关系,揭示了原特提斯洋构造域北祁连洋板块向南和向北进行双向俯冲的化石俯冲带深部结构特征;俯冲消减的北祁连洋板块的宽度约在600 km以上。其中,北祁连洋向南在柴达木—祁连地块之下的俯冲作用角度较缓,俯冲带向南延伸的距离较远,其俯冲断离的板片可以达到现今柴达木盆地的北缘;北祁连洋向北的俯冲作用产状较陡,其俯冲断离的板片具有向南陡倾的产状倒转特征,可能与中生代以来、特别是印度—亚洲大陆碰撞的远程效应引起的挤压构造变形有关。大地电磁测深剖面的浅层反演与构造解释,验证了祁连山北缘断裂以北发育的榆木山逆冲推覆构造,榆木山构成飞来峰构造,将早白垩世酒泉盆地的一个分支掩盖在外来的逆冲推覆体之下;飞来峰之下具有油气勘查前景。根据早白垩世晚期普遍发育的伸展作用,限定榆木山逆冲推覆构造发育的时间在早白垩世早期,从而提供了青藏高原北缘早白垩世早期高原隆升与扩展的证据。综合前人资料和本研究成果,建立了祁连造山带自新元古代以来的构造演化概念模型。 相似文献
6.
嫩江-八里罕断裂是松辽盆地西缘的一条重要断裂,对区域中-新生代盆地的形成演化至关重要。由于该断裂中段地表覆盖厚层第四系,其深部构造特征研究程度较弱。本文通过对横跨嫩江-八里罕断裂的1条大地电磁测深测线和1条地震测线进行处理和解译,结合区域钻井结果解译了该断裂深部、浅部构造特征。结果表明,深部电性结构横向上以"八"字型低阻条带为界与地质单元具有较好的对应关系;结合已有地质认识推断东倾的L3低阻条带是嫩江-八里罕断裂的电性响应。该断裂是1条东倾的超壳断裂,浅部产状较陡、向深部逐渐趋缓,整体上由2条东倾的反"Y"字型断裂和1条西倾的断裂组成,呈花状构造样式,指示断裂曾历经强烈的挤压应力环境。 相似文献
7.
Total field magnetic data were collected over the Krishna-Godavari basin covering 20, 000 sq.km with an average spacing of 8.5 km. This was mainly to study the long wavelength features related with the deep structures. Aeromagnetic map of the region compared well with the ground maps. The anomaly maps show a combination of NE-SW, NS/NNE-SSW and NW-SE trends. The anomalies of ground data are transformed to isolate the sources at different depths. The second vertical derivative and downward continuation maps bring out clearly the NE-SW and NS/NNE-SSW trends related to the coastal basin and Eastern Ghats implying that they are shallow. These are probably superposed on much deeper NW-SE trending structural features of Pre-Gondwana breakup as evidenced in the Horizontal Gradient of Pseudogravity and upward continuation maps. From the offshore magnetic data it appears that these trends extend up to the Ocean Continent Boundary. It is inferred that the deeper features are associated with rifting of Dharwar and Bastar cratons within the Indian plate, prior to the rifting of India from Gondwanaland. The superposed horst and graben structures are related to the formation of the pull-apart Krishna-Godavari basin as a result of rifting and drifting of India from Gondwanaland. These two structural features are associated with two different tectonic events. 相似文献
8.
Tan Handong Jin Sheng Wei Wenbo Chen Leshou Deng Ming Department of Applied Geophysics China University of Geosciences Beijing China John Booker Nong Wu Martyn Unsworth University of Washington WA USA Alan Jones Geological S 《中国地质大学学报(英文版)》2000,11(3)
INTRODUCTIONThe Qinghai- Xizang(Tibetan) plateau is the typical re-gion of the continent- continentcollision,convergence and con-solidation,which is still active now.Its uplifting has a closerelationship to the collision and consolidation of the India andEurasia plates.The Yarlung Zangbo suture is the final left-over after the collision and consolidation of the India andEurasia plates.Further research on the suture is of signifi-cance in studying the subduction,collision and last amalg… 相似文献
9.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(9):837-840
This paper describes a magnetotelluric (MT) survey carried out on the western edge of the Amiata geothermal region (Tuscany, Italy). In order to enhance the resolution of subsurface conductivity along the survey line and to define the deep features related to geothermal system heat recharge a continuous profiling method was used The standard wide-band MT data were collected at 28 sites, and 130 high frequency telluric-magnetotelluric (TMT) soundings were carried out at sites adjacent to the main wide-band sites. To tackle the problem of high electrical noise in the area the wide-band data were recorded simultaneously at two sites of the profile (local remote) and at a third far remote and electrically quiet site.Two-dimensional (2D) inversion of both TM and TM-TE data was performed, taking into account topographic and coast effects. The inversion results were able to define both shallow and deep resistivity anomalies whose structural significance is in good agreement with information derived from other geophysical data.Of particular geothermal interest is the evidence of a large conductive anomaly at a depth ranging between 2 and 4 km within the deep metamorphic basement. This anomaly could indicate the presence of a hitherto unidentified deep reservoir that is in communication with the reservoir exploited at present in the Amiata area. 相似文献
10.
The present study is an attempt to determine the sedimentary cover, and structural trends in the central part of Sinai Peninsula, Egypt. This study has been implemented by the integration of gravity and magnetic methods. Gravity data has been used for 2D modelling along some profiles perpendicular to the main structural trends of the study area. Magnetic data will be analyzed to determine the depth to the basement surface. The depths obtained from magnetic data will be used as a control points in the gravity modelling in order to minimize the error and facilitate the iteration of the suggested models. The basement relief map from magnetic and gravity output has been produced. This map indicates that, the basement depths, generally, increases from south to north and from east to west direction of the study area. The sedimentary cover is about 1.5-2 km in the southern part and increases to more than 4 km in the northeastern and western parts and changes gradually in the other parts of the study area. Results of structural trend analysis indicate that, the study area is greatly affected by several structural trends; N-S, E-W, NW-SE, and NNE-SSW directions. These trends are associated with the Baltim fault trend, Tethyan trend, Gulf of Suez, and Aqaba trend, respectively. 相似文献
11.
华南大陆历经长期复杂的构造演化,其浅部复杂而多样的构造形态与深部壳幔结构及其动力学机制有着密切联系,但当前的深部探测资料有限,深部构造并不明确。为了研究华南的深部岩石圈结构状态,布设了多条宽频长周期大地电磁联合探测剖面。通过对景德镇-温州剖面的数据处理,获得了该剖面的岩石圈电性结构模型。分析表明:华夏地块与扬子地块东部的江南造山带以江绍断裂为界;华夏地块整体呈现高阻特征,可能具有深部岩石圈背景的上虞-政和-大浦断裂将其分为华夏褶皱带与东南沿海岩浆岩带;扬子地块东部的江南造山带整体电阻率较低,结构更破碎,受到深部改造明显,岩石圈底界约为110 km;剖面发现3处低阻带通道,可能与软流圈上涌相关;江绍断裂呈喇叭状向深部张开,华夏地块与扬子地块的裂解拼合可能与断裂深部的高导体活动有关。华夏地块与扬子地块的接触状态呈现为双向汇聚,华夏地块在上地幔挤入扬子地块,深部接触边界可能越过江绍断裂带。 相似文献
12.
Clive E. Willman 《Mineralium Deposita》2007,42(5):449-463
The Bendigo and Castlemaine goldfields are classic examples of structurally controlled orogenic gold deposits in the Bendigo
Zone of central Victoria, SE Australia. Detailed mapping and biostratigraphic interpretation has led to a better understanding
of the regional structural controls of this type of gold-quartz mineralisation. Mineralised quartz veins are hosted by the
Castlemaine Group, an Early-to-Middle Ordovician turbidite succession at least 3,000 m thick. Gold deposits are controlled
by low-displacement faults that are clustered into several belts (the goldfields) indicating a regional structural control.
The timing of mineralisation overlapped with that of the major period of deformation including folding, cleavage development
and regional faulting. The Bendigo and Castlemaine goldfields are located in an area termed the Whitelaw thrust sheet bounded
by two unmineralised, high-displacement, regional-scale faults. Mapping has revealed an interrelationship between the regional-scale
faults, regional structural style and goldfield location. The goldfields lie immediately west of the boundary between the
upper and lower portions of the thrust sheet and are characterised by symmetric folds with sub-horizontal to synclinal enveloping
surfaces, relatively low co-axial strains and moderate cleavage development. The non-gold-bearing areas immediately east of
each goldfield correspond with the lower part of the Whitelaw thrust sheet and are characterised by higher non-coaxial strains,
stronger cleavage and folds with wide west-dipping limbs giving rise to easterly vergent sections and steeply west-dipping
enveloping surfaces. That mineralisation was an integral part of the thin-skinned style of deformation in the central Bendigo
Zone is indicated by timing relationships and the interrelationship between local-scale mineralised structures and regional-scale
features such as large-displacement unmineralised faults, regional variations in fold style and overall thrust sheet geometry.
The work supports previous models that suggest mineralised fluids were focussed along a linked system of deep-seated faults.
The primary conduits may have been major regional-scale ‘intrazone’ faults, which are inferred to sole into detachments near
the base of the Castlemaine Group. It is proposed that these structures linked with minor intrazone faults and then with networks
of low-displacement mineralised faults that were strongly controlled by folds. The location of minor intrazone faults was
probably controlled by internal thrust sheet geometry. The distribution of gold deposits and of gold production suggests that
maximum fluid flow was concentrated along the eastern margins of networks of low-displacement faults. 相似文献
13.
苏北盆地高邮凹陷热史恢复与成藏期判识 总被引：3，自引：0，他引：3
在镜质体反射率、磷灰石裂变径迹和包裹体均一温度系统测试分析的基础上,对高邮凹陷主要构造带进行古地温梯度计算和热史恢复。确定了高邮凹陷主要构造单元古地温梯度:镜质体反射率计算出深凹带古地温梯度为35.6℃/km,北斜坡西为43.9℃/km,北斜坡东为33.2℃/km;磷灰石裂变径迹计算出深凹带古地温梯度为31.4℃/km,北斜坡西为39.3℃/km,北斜坡东为50℃/km;包裹体均一温度计算出深凹带古地温梯度为29℃/km,北斜坡西为42.5℃/km,北斜坡东为32.3℃/km。对比分析现今地温梯度得出:深凹带古地温梯度高于现今0～7℃/km;北斜坡西古地温梯度高于现今10～15℃/km;北斜坡东古地温梯度高于现今4～21℃/km,今古地温梯度变化规律为深凹带变化小,斜坡带变化大。将典型单井埋藏史-热史与包裹体均一温度综合分析,判识高邮凹陷深凹带成藏期介于46～37Ma,北斜坡成藏期介于40.9～37.5Ma,具有深凹带早于北斜坡的规律,判定出三垛期为苏北盆地高邮凹陷主要成藏时期。 相似文献
14.
《International Geology Review》2012,54(12):1129-1144
Groups of grabens in west Anatolia have contrasting E-W and NE-SW orientations and are the subject of debate as to their relative ages and relationships. We investigated the E-W-trending Gediz graben and its neighboring NE-SW-trending Gördes, Demirci, and Selendi grabens, which form an important graben system representative of the region. We studied gravity data from one profile and magnetotelluric (MT) data from two profiles, 73 km and 93 km long. The data supports the hypothesis that the Gediz graben was superimposed onto the (older) NE-SW grabens. 2D gravity and MT modelling revealed an undulating graben floor, varying in depth between 500 and 3000-4000 m (gravity-MT); within the graben two apparent basins 3–4 and 1.5-2.5 km deep (gravity-MT) are separated by a subsurface horst. The residual gravity map appears to indicate the continuation of NE-SW grabens from north of Gediz graben to beyond its southern border. The MT model revealed three main zones of varying thickness within the crust. The britde upper crust comprises two zones: sedimentary fill (apparent resistivity 15-50 ohm.m) and Menderes massif basement (200 ohm.m). The third zone is highly conductive lower crust (10 ohm.m), identified by our MT modeling at an average depth of 10 km. This conductive layer was considered in conjunction with two other regional features, high heat flow values and shallow earthquake focal depths. A heat flow map shows a very high average value of 108 mWm?2 for west Anatolia and 120-300 mWm?2 for the Gediz graben area specifically, compared with the world average of 80 mWm?2. Seismological records showing shallow earthquake focal depths together with the high conductivity zone were taken to indicate a partially melted, viscoelastic lower crust. 相似文献
15.
Prasanta K. Patro Khasi Raju S. V. S. Sarma 《Journal of the Geological Society of India》2018,92(5):529-532
Magnetotelluric (MT) studies along a few traverses, some cutting across the Western Ghats, during the last few years have provided basic insights into the shallow as well as the deeper electrical structure in the regions near and east of the Western Ghat belt. The MT models broadly show a two layered lithospheric electrical structure with an upper high resistive layer (several thousands of Ωm) and a lower moderately conductive layer (a few tens to a few hundred Ωm). The depth of the interface between the two layers is found to vary from about 120–160 km in the south in the SGT to around 80 km in the north in the northern DVP. Another impressive feature that could be noticed in these electrical models is the presence of well-defined major near vertical crustal conductive feature associated with the region of Western Ghat belt, presumably associated with the tectonic evolution of the Western Ghats. Further, these models also brought out several other well-defined conductors that might be linked to structural features like faults, shear zones, etc., in the region. These conductors pierce through the crustal column and some of these, particularly those oriented in NW-SE direction, i.e., oriented transversely with respect to the ambient compressive stress direction of the Indian shield, assume significance in understanding the seismicity of the region. 相似文献
16.
Magnetotelluric (MT) geophysical profiling has been applied to the determination of the deep structure of the Longling–Ruili fault (LRF), part of a convergent strike-slip fault system, underneath thick Caenozoic cover in Ruili basin in southwestern Yunnan, China. The recorded MT data have been inverted using a two-dimensional (2-D) nonlinear conjugate gradients scheme with a variety of smooth starting models, and the resulting models show common subsurface conductivity structures that are deemed geological significant. The models show the presence of a conductive (5–60 Ω m) cover sequence that is thickest (1–1.5 km) in the centre of the basin and rapidly pinches out towards the margins. A half-graben structure is interpreted for the Ruili basin. This is underlain by about 7–10 km thick upper crustal layer of high resistivity (>200–4000 Ω m) that is dissected by steep faults, which we interpret to flatten at depth and root into an underlying mid-crustal conductive layer at about 10 km depth. The mid-crustal layer does not appear to have been severely affected by faulting; we interpret it as a zone of partial melt or intracrustal detachment. The MT models suggest SE directed thrusting of basement rocks in the area. The Longling–Ruili fault is interpreted as a NW-dipping feature bounding one of the identified upper crustal fragments underneath Ruili city. We suggest that MT imaging is a potent tool for deep subsurface mapping in this terrain. 相似文献
17.
重力场多尺度刻痕分析与满加尔坳陷深层构造 总被引：5，自引：0，他引：5
区域高精度重力场测量可以获得关于沉积盆地深部构造的丰富信息。本文在分析满加尔坳陷内部深层构造探测存在问题的基础上,开展了重力测量,并采用重力异常的小波多尺度分析和刻痕分析等新方法,研究了满加尔坳陷内部深层构造,揭示了坳陷内早古生代地层的密度分带。应用小波多尺度分析方法可以把只与深层构造有关的地质信息提取出来。运用新的人工智能原理把隐含在区域重力场中有关刻痕的所有特征参数提取出来,可以客观地为沉积盆地内部构造单元划分提供可靠依据。结合区域重力场多尺度分析及刻痕分析的信息提取新方法,称为多尺度刻痕分析。比较研究区深层(7~8km)密度扰动与电阻率异常可见,满加尔坳陷内沿纬度40°线北侧和经度85°线同时都有低密度扰动和低电阻率异常分布,说明坳陷内深层沉积岩低密度扰动与流体活动通道有一定关系。综合脊形化系数图和边界刻痕系数图,圈定了深层满中高密度扰动带和满南和满北低密度扰动带,为深层油气勘探提供重要基础资料。 相似文献
18.
苏鲁造山带深部构造的接收函数图象 总被引：3，自引：0，他引：3
宽频地震探测获得横切苏鲁造山带的滨州-日照剖面和蓬莱-青岛剖面的接收函数图象。在图中识别出一系列密度界面和断裂面。新Moho面深度35~41km,形态清晰连续完整,表明苏鲁造山带形成以来的壳幔相互作用已经相当彻底。苏鲁造山带和胶辽朝地块的岩石圈底面深度105km,靠近郯庐断裂逐渐抬升到90km。在苏鲁造山带内部识别出了造山过程中形成的构造界面。它们所勾画出的深部构造图案支持扬子板块拖带北中国板块边缘深俯冲剥蚀模型,并且指示苏鲁超高压变质带的北界位于莱西一线的胶莱盆地之下。 相似文献
19.
K. Vozoff D. Kerr R. F. Moore D. L. B. Jupp R. J. G. Lewis 《Australian Journal of Earth Sciences》2013,60(3):361-375
The Murray Basin is geologically featureless, has been sparsely covered by geophysics, and is penetrated by a few scattered wells. Only drilling and reflection seismic work have provided consistently reliable depth information. They have indicated the presence of narrow troughs, which contain more than 3 km of Palaeozoic sediment, covered by basement highs with less than 300 m of Mesozoic and Cainozoic cover. Six widely spaced magnetotelluric (MT) sites were occupied in the north central Murray Basin. Results showed a 5 km thick horizontal section at Pooncarie, with a probably average porosity of 10%. Higher porosities, and probably a thicker section, were indicated near Little Topar, but the structural complexity there requires that additional data be acquired for positive interpretation. A persistent conductivity increase near 100 km suggests that the method may respond well to the base of the tectonic plate. The MT method appears well suited to the onshore exploration problems currently faced in Australia. 相似文献
20.
CRUSTAL STRUCTURE IN EASTERN REGION OF QINGHAI—TIBET PLATEAU 相似文献