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1.
The Late Cretaceous–Cenozoic evolution of the North German Basin has been investigated by 3-D thermomechanical finite element modelling. The model solves the equations of motion of an elasto-visco-plastic continuum representing the continental lithosphere. It includes the variations of stress in time and space, the thermal evolution, surface processes and variations in global sea level.The North German Basin became inverted in the Late Cretaceous–Early Cenozoic. The inversion was most intense in the southern part of the basin, i.e. in the Lower Saxony Basin, the Flechtingen High and the Harz. The lower crustal properties vary across the North German Basin. North of the Elbe Line, the lower crust is dense and has high seismic velocity compared to the lower crust south of the Elbe Line. The lower crust with high density and high velocity is assumed to be strong. Lateral variations in lithospheric strength also arise from lateral variations in Moho depth. In areas where the Moho is deep, the upper mantle is warm and the lithosphere is thereby relatively weak.Compression of the lithosphere causes shortening, thickening and surface uplift of relatively weak areas. Tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression. Contemporaneously, the margins of the weak zone subside. Cenozoic subsidence of the northern part of the North German Basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north.The modelled deformation patterns and resulting sediment isopachs correlate with observations from the area. This verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation. 相似文献
2.
横跨银川盆地北西西向的深地震反射剖面,清晰揭示了银川盆地边界断裂以及整个地壳的结构构造特征,这对研究具活动大陆裂谷性质的银川盆地浅-深构造关系具有重大的意义。贺兰山东麓山前断裂、黄河断裂作为银川盆地的西、东边界断裂,前者为一条缓倾斜、延伸至上、下地壳边界的犁式断裂,而后者则为一条切穿地壳并延伸进入上地幔的深大断裂。根据深地震反射剖面揭示的地壳结构特征,银川盆地浅部结构并非前人认为的"堑中堑"结构,而是表现为由一系列东倾犁式正断层控制的新生代断陷。略微下凹的Moho面几何形态以及厚2~3.2 km的层状强反射带为下地壳最显著的反射特征。Moho面深度与强反射带厚度变化趋势与银川盆地沉积厚度变化趋势几乎一致。本文认为,强反射带的成因可能是由源自地幔的基性岩浆以岩席状的形式底侵进入地壳底部造成的,而这部分形成强反射带的物质可能补偿了因银川盆地断陷而造成的地壳减薄,最终导致银川盆地之下Moho面并未像之前所认为的那样隆起。 相似文献
3.
长江中下游宁芜火山岩盆地深部结构特征——来自反射地震的认识 总被引：5，自引：2，他引：3
宁芜火山岩盆地是长江中下游成矿带的重要组成部分,盆地内广泛产出玢岩型铁矿床。为探讨宁芜火山岩盆地深部结构,作者完成了三条穿越宁芜火山岩盆地的深反射地震剖面。三条剖面的长度不一,NW01剖面长度42km,NW02长56.3km,NW03长27.1km。三条剖面的排列长度都为720道,采样间隔2ms,记录长度16s。因为本文的主要研究对象是宁芜火山岩盆地上地壳的结构特征,因此只用了总记录长度的前4s数据。通过本次研究揭示了宁芜矿集区的上地壳精细结构、岩浆和断裂系统的空间展布形态。不仅验证了以往对盆地的部分认识,而且给出了新的认识。(1)发现了直接控制盆地火山-岩浆活动的南东和北西边界断裂并非人们经常认为的两大基底深断裂:方山-南陵断裂和长江断裂带,而是北西向F1和南东向F2断裂;(2)宁芜火山岩盆地以马鞍山-薛津断裂为界向北北东方向滑脱,造成了盆地南西高北东低的隆凹构造格局;(3)阐明了就位于盆地下方的为火山-岩浆活动提供补给和热源的岩浆房的空间展布特征;(4)清晰地厘定了盆地内的断裂系统,其中最主要的断裂是隐伏于宁芜火山岩盆地深部的控制深部岩浆活动的盆中基底断裂(BCF),控制着深部岩浆岩的空间展布格局并对宁芜火山岩盆地的地层和断裂系统有强烈地改造作用。本文的发现为宁芜火山岩盆地深部结构认识、成矿预测及成矿动力学分析提供了可借鉴的证据。 相似文献
4.
青藏高原东北缘岩石圈密度与磁化强度及动力学含义 总被引：4，自引：0，他引：4
利用横贯柴达木盆地南北的格尔木—花海子剖面岩石圈二维P波速度结构以及地震波速度与介质密度之间的关系,建立了该剖面岩石圈二维密度结构与二维磁化强度的初始模型。依据重磁同源原理,在柴达木盆地重、磁异常的二重约束下完成了重磁联合反演,获得了该剖面岩石圈二维密度结构与二维磁化强度分布。结果表明:柴达木盆地地壳厚度沿测线变化较大,平均厚度约60km。在柴达木盆地南缘地壳厚约50km,达布逊湖附近地壳最厚为63km左右,大柴旦附近地壳较薄,为50km左右。柴达木盆地的地壳纵向上可分为三层,即上地壳、中地壳与下地壳。位于盆地中部的中、下地壳分别发育大范围的壳内低密度体,并处于上地幔隆起的背景之上;横向上可将盆地分成南北两个部分,分界在达布逊湖附近。整个剖面结晶基底埋深变化也很大,在达布逊湖附近为12km,在昆仑山北缘基底几乎出露地表。结晶基底的展布形态与地壳底界,即莫霍面呈近似镜像对称。综合研究认为,柴达木盆地的岩石圈结构存在着明显的南北差异,其分界在达布逊湖的北面。在盆地南部,岩石圈介质横向变化较小,各层介质分布正常;在盆地的北侧,岩石圈结构特别在中、下地壳和上地幔顶部横向上发生了变化。壳内低密度体的存在意味着柴达木盆地具有较热的岩石圈和上地幔,加之基底界面与莫霍面的镜像对称分布,形成与准噶尔盆地和塔里木盆地的构造差异。多种地球物理参数所揭示的地壳上地幔结构及其横向变化特点为柴达木盆地构造演化及青藏高原北部边界的地球动力学研究提供了岩石圈尺度的地球物理证据。 相似文献
5.
M. Friberg C. Juhlin A.G. Green H. Horstmeyer J. Roth A. Rybalka & M. Bliznetsov 《地学学报》2000,12(6):252-257
New deep seismic reflection data provide images of the crust and uppermost mantle underlying the eastern Middle Urals and adjacent West Siberian Basin. Distinct truncations of reflections delineate the late-orogenic strike-slip Sisert Fault extending vertically to ∼28 km depth, and two gently E-dipping reflection zones, traceable to 15–18 km depth, probably represent normal faults associated with the opening of the West Siberian Basin. A possible remnant Palaeozoic subduction zone in the lower crust under the West Siberian Basin is visible as a gently SW-dipping zone of pronounced reflectivity truncated by the Moho. Continuity of shallow to intermediate-depth reflections suggest that Palaeozoic accreted island-arc terranes and overlying molasse sequences exposed in the hinterland of the Urals form the basement for Triassic and younger deposits in the West Siberian Basin. A highly reflective lower crust overlies a transparent mantle at about 43 km depth along the entire 100 km long seismic reflection section, suggesting that the lower crust and Moho below the eastern Middle Urals and West Siberian Basin have the same origin. 相似文献
6.
深地震反射大炮数据能够准确地获得下地壳和Moho的精细结构及其横向变化信息,揭露岩石圈尺度的构造样式与深部过程。中亚造山带东段位于古亚洲洋、蒙古—鄂霍茨克洋和古太平洋三大构造域的叠合区域,其岩石圈结构记录了大洋,特别是古亚洲洋消亡方式和大陆增生的深部过程。本文选用横过中亚造山带东段（奈曼旗—东乌珠穆沁旗,长约400 km）深地震反射剖面中的24个大炮数据和2个中炮数据,通过数据处理获得了近垂直反射的大炮单次剖面,揭露出中亚造山带东段下地壳及Moho的精细结构,刻画出古亚洲洋消亡极性与中亚造山带增生造山的深部过程：西拉木伦缝合带与贺根山缝合带构成古亚洲洋消亡的双缝合带,西拉木伦缝合带下方古亚洲洋板块以向南消亡为主,贺根山缝合带下方古亚洲洋板块以向北消亡为主,后者规模大于前者。在两个缝合带之间下地壳呈现出几个大规模的块状弧状反射体,推测是大洋中的残余微地块,在古亚洲洋消亡过程中拼接在一起,成为中亚造山带增生造山的一部分,并遭受了碰撞挤压和后造山伸展作用。Moho位于双程走时12 s附近（厚度约36 km）,近于水平展布,沿整条剖面起伏不大。平缓的Moho成因与造山后的地壳伸展作用相关。 相似文献
7.
We present high-resolution receiver function images along a 700-km long dense seismic array extending from northern Tibetan Plateau to the Alxa block, crossing the entire Qilian thrust belt (QTB). The dense stations, with less than ~2 km station intervals, allow the receiver functions to unveil unprecedented details of crustal structures across the northern frontier of the growing Tibetan Plateau. The migration image shows a thickened and strongly deformed QTB crust, with an uneven Moho and complex internal structures that are indicative of pure-shear shortening. The Alxa block, in contrast, has a thinner crust, a flat Moho, and little internal crustal deformation. These results suggest that the lateral growth of NE Tibetan Plateau is restricted by the strong Asian lithosphere, which shows no visible subduction beneath the Tibetan Plateau as previously suggested. 相似文献
8.
In 1991, a deep seismic reflection line, MPNI-9101, was acquired in the southern North Sea from the Mesozoic Broad Fourteens Basin, across the West Netherlands Basin onto the London-Brabant Massif (LBM). The resultant section shows a strongly reflective lower crust beneath the area of Mesozoic basin development. This lower crustal reflectivity continues to be strong beneath the LBM. The travel time to the base of the reflective zone increases from approximately 11.0 s beneath the Mesozoic basins to 12.5 s beneath the LBM, suggesting a southward thickening of the crust (Rijkers et al., 1993). Based on these travel times and information from deep wells and refraction surveys. Moho depth is estimated to increase from about 31 km beneath the Mesozoic basins to about 38 km beneath the LBM. This difference in depth to the Moho can partly be explained by coaxial stretching of the crust beneath the Mesozoic basins. In comparison with the Mesozoic basins, the crust beneath the LBM was thickened during the Caledonian and Variscan orogenies. 相似文献
9.
Spectral analysis of the digital data of the Bouguer anomaly of North India including Ganga basin suggest a four layer model with approximate depths of 140, 38, 16 and 7 km. They apparently represent lithosphere–asthenosphere boundary (LAB), Moho, lower crust, and maximum depth to the basement in foredeeps, respectively. The Airy’s root model of Moho from the topographic data and modeling of Bouguer anomaly constrained from the available seismic information suggest changes in the lithospheric and crustal thicknesses from ∼126–134 and ∼32–35 km under the Central Ganga basin to ∼132 and ∼38 km towards the south and 163 and ∼40 km towards the north, respectively. It has clearly brought out the lithospheric flexure and related crustal bulge under the Ganga basin due to the Himalaya. Airy’s root model and modeling along a profile (SE–NW) across the Indus basin and the Western Fold Belt (WFB), (Sibi Syntaxis, Pakistan) also suggest similar crustal bulge related to lithospheric flexure due to the WFB with crustal thickness of 33 km in the central part and 38 and 56 km towards the SE and the NW, respectively. It has also shown the high density lower crust and Bela ophiolite along the Chamman fault. The two flexures interact along the Western Syntaxis and Hazara seismic zone where several large/great earthquakes including 2005 Kashmir earthquake was reported.The residual Bouguer anomaly maps of the Indus and the Ganga basins have delineated several basement ridges whose interaction with the Himalaya and the WFB, respectively have caused seismic activity including some large/great earthquakes. Some significant ridges across the Indus basin are (i) Delhi–Lahore–Sargodha, (ii) Jaisalmer–Sibi Syntaxis which is highly seismogenic. and (iii) Kachchh–Karachi arc–Kirthar thrust leading to Sibi Syntaxis. Most of the basement ridges of the Ganga basin are oriented NE–SW that are as follows (i) Jaisalmer–Ganganagar and Jodhpur–Chandigarh ridges across the Ganga basin intersect Himalaya in the Kangra reentrant where the great Kangra earthquake of 1905 was located. (ii) The Aravalli Delhi Mobile Belt (ADMB) and its margin faults extend to the Western Himalayan front via Delhi where it interacts with the Delhi–Lahore ridge and further north with the Himalayan front causing seismic activity. (iii) The Shahjahanpur and Faizabad ridges strike the Himalayan front in Central Nepal that do not show any enhanced seismicity which may be due to their being parts of the Bundelkhand craton as simple basement highs. (iv) The west and the east Patna faults are parts of transcontinental lineaments, such as Narmada–Son lineament. (v) The Munghyr–Saharsa ridge is fault controlled and interacts with the Himalayan front in the Eastern Nepal where Bihar–Nepal earthquakes of 1934 has been reported. Some of these faults/lineaments of the Indian continent find reflection in seismogenic lineaments of Himalaya like Everest, Arun, Kanchenjunga lineaments. A set of NW–SE oriented gravity highs along the Himalayan front and the Ganga and the Indus basins represents the folding of the basement due to compression as anticlines caused by collision of the Indian and the Asian plates. This study has also delineated several depressions like Saharanpur, Patna, and Purnia depressions. 相似文献
10.
11.
Mi-Kyung Yoon Mikhail Baykulov Stefan Dümmong Heinz-Jürgen Brink Dirk Gajewski 《International Journal of Earth Sciences》2008,97(5):887-898
The influence of deep crustal processes on basin formation and evolution and its relation to current morphology is not well
understood yet. A key feature to unravel these issues is a detailed seismic image of the crust. A part of the data recorded
by the hydrocarbon industry in the late 1970s and 1980s in the North German Basin were released to the public recently. The
seismic reflection data were recorded down to 15 s two-way travel time. The mean Common Midpoint fold of about 20 is relatively
low compared to contemporary seismic acquisitions. The processing of the 1980s focussed on the sedimentary structures to explore
the hydrocarbon potential of this area. We applied the Common Reflection Surface stack technique to the data sets, which is
well suited for low-fold data. The reprocessing was focussed on the imaging of the subsedimentary crustal range. The reprocessed
images show enhanced reflections, especially in the mid and lower crustal part. Also, the image of the salt structures in
the graben area was improved. Furthermore, the reprocessed images indicate an almost flat Moho topography in the area of the
Glückstadt Graben and an additional lower crustal structure, which can be correlated with a high-density body found in recent
gravity modeling studies. 相似文献
12.
Wolfgang Horst Michael Börngen Ernst R. flueh 《International Journal of Earth Sciences》1994,83(1):161-169
Out of a dense network of seismic reflection lines for hydrocarbon exploration in the North-east German Basin, several lines were recorded to 12 s TWT to obtain information about the structure of the crust and the crust-mantle transition. One of these profiles is presented here. This stretches for 110 km in a NNE direction between Neustrelitz and the island of Usedom. It reaches from the External Variscides in the south across the North German Massif into the Rügen-Pomorze Terrane in the Baltic Sea. Below Cenozoic-Mesozoic-Paleozoic cover with clear reflections down to base Zechstein, the reflectivity varies considerably with depth and also laterally. The Paleozoic and Precambrian sediments and basement are generally void of reflections, but the lower crust and the Moho show strong reflections. To the north the reflectivity decreases, and the Moho depth increases to beyond the bottom of the record section at 12 s. There are no direct indications for deep-reaching faults such as the Trans-European Fault in the north. The North German Massif acted as a ramp towards the Variscan Orogeny, similar to the London-Brabant Massif further west. 相似文献
13.
YANG Wencai 《Continental Dynamics》1997,(1)
1.IntroductionSincethediscoveryofcoesiteandndcrodiamond,theDabie-Suluultra-highPressure(UHP)meta-morphicbelthasbeenattractingworldwideattentionsofgeoscientists.Studyingthisoutstandinggeologicalregionmaygreatlyenhanceourunderstandingofmetamorphism,deepeffectsofcontinentalcollisionandgeodynandcsinconvergentplateboundaries.Thestudymayalsobeveryhelpfultoprovideevidencetorevealinteractionbetweenthecrustandthemantle,andtheformationofnewtypesofdiamonddeposits.EncouragedbytheinternationalContinenta… 相似文献
14.
The superdeep North Caspian, South Caspian, and Barents basins have their sedimentary fill much thicker and the Moho, correspondingly, much deeper than it is required for crustal subsidence by lithospheric stretching. In the absence of large gravity anomalies, this crustal structure indicates the presence under the Moho of a thick layer of eclogite which is denser than mantle peridotite. Crustal subsidence in the basins can be explained by high-grade metamorphism of mafic lower crust. The basins produced by lithospheric stretching normally subside for the first ～100 myr of their history, while at least half of the subsidence in the three basins occurred after that period, which is another evidence against the stretching formation mechanism. According to the seismic reflection profiling data, stretching can be responsible for only a minor part of the subsidence in the Caspian and Barents basins. As for the South Caspian basin, there has been a large recent subsidence event in a setting of compression. Therefore, eclogitization appears to be a realistic mechanism of crustal subsidence in superdeep basins. 相似文献
15.
庐-枞金属矿集区深地震反射剖面解释结果——揭露地壳精细结构,追踪成矿深部过程 总被引：18，自引：4，他引：14
深地震反射剖面揭示了庐枞矿集区全地壳的精细结构,在研究火山岩盆地的深部构造、探讨成矿深部过程等方面取得了新认识。从长江至大别山下,Moho由30km左右加深至33km左右,罗河矿下方Moho错断大约3km。庐枞火山岩盆地是一个沿着罗河断裂向东发育的"耳状"非对称盆地,并不存在另外一半隐伏在红层之下的盆地。罗河铁矿对应Moho错断处,处在构造的转换带上。罗河断裂之下存在近于透明的弱反射区域,可能是地幔流体和岩浆上涌、喷发的通道。郯庐断裂、罗河-缺口断裂、长江断裂是庐枞地区的三个重要断裂。郯庐断裂带为不对称花束状构造,近于直立,切穿地壳。小岭矿与龙桥矿可能产出在一个隆起的火成岩体的两翼。 相似文献
16.
I. Panea R. Stephenson C. Knapp V. Mocanu G. Drijkoningen L. Matenco J. Knapp K. Prodehl 《Tectonophysics》2005,410(1-4):293-309
The DACIA PLAN (Danube and Carpathian Integrated Action on Process in the Lithosphere and Neotectonics) deep seismic sounding survey was performed in August–September 2001 in south-eastern Romania, at the same time as the regional deep refraction seismic survey VRANCEA 2001. The main goal of the experiment was to obtain new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basins developed within and adjacent to the seismically-active Vrancea zone, including the Focsani Basin. The seismic reflection line had a WNW–ESE orientation, running from internal East Carpathians units, across the mountainous south-eastern Carpathians, and the foreland Focsani Basin towards the Danube Delta. There were 131 shot points along the profile, with about 1 km spacing, and data were recorded with stand-alone RefTek-125s (also known as “Texans”), supplied by the University Texas at El Paso and the PASSCAL Institute. The entire line was recorded in three deployments, using about 340 receivers in the first deployment and 640 receivers in each of the other two deployments. The resulting deep seismic reflection stacks, processed to 20 s along the entire profile and to 10 s in the eastern Focsani Basin, are presented here. The regional architecture of the latter, interpreted in the context of abundant independent constraint from exploration seismic and subsurface data, is well imaged. Image quality within and beneath the thrust belt is of much poorer quality. Nevertheless, there is good evidence to suggest that a thick (10 km) sedimentary basin having the structure of a graben and of indeterminate age underlies the westernmost part of the Focsani Basin, in the depth range 10–25 km. Most of the crustal depth seismicity observed in the Vrancea zone (as opposed to the more intense upper mantle seismicity) appears to be associated with this sedimentary basin. The sedimentary successions within this basin and other horizons visible further to the west, beneath the Carpathian nappes, suggest that the geometry of the Neogene and recent uplift observed in the Vrancea zone, likely coupled with contemporaneous rapid subsidence in the foreland, is detached from deeper levels of the crust at about 10 km depth. The Moho lies at a depth of about 40 km along the profile, its poor expression in the reflection stack being strengthened by independent estimates from the refraction data. Given the apparent thickness of the (meta)sedimentary supracrustal units, the crystalline crust beneath this area is quite thin (< 20 km) supporting the hypothesis that there may have been delamination of (lower) continental crust in this area involved in the evolution of the seismic Vrancea zone. 相似文献
17.
《Gondwana Research》2014,25(3-4):902-917
The South China continent has a Mesozoic intraplate orogeny in its interior and an oceanward younging in postorogenic magmatic activity. In order to determine the constraints afforded by deep structure on the formation of these characteristics, we reevaluate the distribution of crustal velocities and wide-angle seismic reflections in a 400 km-long wide-angle seismic profile between Lianxian, near Hunan Province, and Gangkou Island, near Guangzhou City, South China. The results demonstrate that to the east of the Chenzhou-Linwu Fault (CLF) (the southern segment of the Jiangshan–Shaoxing Fault), the thickness and average P-wave velocity both of the sedimentary layer and the crystalline basement display abrupt lateral variations, in contrast to layering to the west of the fault. This suggests that the deformation is well developed in the whole of the crust beneath the Cathaysia block, in agreement with seismic evidence on the eastwards migration of the orogeny and the development of a vast magmatic province. Further evidence of this phenomenon is provided in the systematic increases in seismic reflection strength from the Moho eastwards away from the boundary of the CLF, as revealed by multi-filtered (with band-pass frequency range of 1–4, 1–8, 1–12 and 1–16 Hz) wide-angle seismic images through pre-stack migration in the depth domain, and in the P-wave velocity model obtained by travel time fitting. The CLF itself penetrates with a dip angle of about 22° to the bottom of the middle part of the crust, and then penetrates with a dip angle of less than 17° in the lower crust. The systematic variation in seismic velocity, reflection strength and discrepancy of extensional factors between the crust and the lithosphere, are interpreted to be the seismic signature of the magmatic activity in the interest area, most likely caused by the intrusion of magma into the deep crust by lithospheric extension or mantle extrusion. 相似文献
18.
We examine the formation of the Michigan Basin in terms of elastic flexure of the lithosphere. The shape of the flexure accurately determines the flexural rigidity of the lithosphere and the lateral extent of the load responsible for the flexure. The amplitude of differential subsidence then gives the magnitude of the load. Gravity anomalies in the southern peninsula of Michigan further restrain the dimensions of the load. We propose a model for the formation of the Michigan Basin involving mantle diapirs. We suggest that the first stage in its evolution was diapiric penetration of the lithosphere by hot asthenospheric mantle rock to the vicinity of the Moho. The heating of the lower crust by these hot rocks caused the transformation of lower crust, meta-stable gabbroic rocks to eclogite. Initially the lighter mantle rocks nearly balanced the heavier eclogite. As the mantle rocks cooled by conduction, the basin subsided under the load of the eclogite. The thermal contraction mechanism is supported by evidence that the flexural rigidity of the lithosphere increases with time. This is the effect of thickening of the elastic lithosphere as cooling progresses. 相似文献
19.
The crustal structure of the central Eromanga Basin in the northern part of the Australian Tasman Geosyncline, revealed by coincident seismic reflection and refraction shooting, contrasts with some neighbouring regions of the continent. The depth to the crust-mantle boundary (Moho) of 36–41 km is much less than that under the North Australian Craton to the northwest (50–55 km) and the Lachlan Fold Belt to the southeast (43–51 km) but is similar to that under the Drummond and Bowen Basins to the east.The seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the North Australian and Lachlan provinces. In particular, there is a sharp velocity increase at mid-crustal depths (21–24 km) which has not been observed with such clarity elsewhere in Australia (the Conrad discontinuity?).In the lower crust, the many discontinuous sub-horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust, further emphasising the differences between the upper and lower crust. The crust-mantle boundary (Moho) is characterised by an increase in velocity from 7.1–7.7 km/s to a value of 8.15 + 0.04 km/s. The depth to the Moho under the Canaway Ridge, a prominent basement high, is shallower by about 5 km than the regional Moho depth; there is also no mid-crustal horizon under the Canaway Ridge but there is a very sharp velocity increase at the Moho depth of 34 km. The Ridge could be interpreted as a horst structure extending to at least Moho depths but it could also have a different intra-crustal structure from the surrounding area.The sub-crustal lithosphere has features which have been interpreted, from limited data, as being caused by a velocity gradient at 56–57 km depth with a low velocity zone above it.Because of the contrasting crustal thicknesses and velocity gradients, the lithosphere of the central Eromanga Basin cannot be considered as an extension of the exposed Lachlan Fold Belt or the North Australian Craton. The lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m, consistent with an upper crustal basement of tightly folded meta-sedimentary and meta-volcanic rocks. The crustal structure is consistent with a pericratonic or arc/back-arc basin being cratonised in an episode of convergent tectonics in the Early Palaeozoic. The seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment. 相似文献
20.
Recent 24 s deep seismic reflection records revealed five flat reflectors in the lithospheric mantle in Eastern China. With increasing depth, they are named M1 to M5 and can be seen on both field single-shot and stacked records. Reflector M1 corresponds to the Moho discontinuity, whereas M5 may be the reflection from the bottom of the current lithosphere, which is about 78 km deep according to geothermal measurements. The other three reflectors seem peculiar and might result from interactions between the lithosphere and deeper mantle. Based on lithological and geochemical data, it is suggested that the lithosphere has been thinned from about 150 km to about 60 km in the Late Mesozoic, and then has been thickened to about 78 km during the Cenozoic. The thinning process produced a granulite layer in the old lower crust caused by magmatic underplating, whereas an eclogite layer formed beneath owing to the subduction of the Paleo-Tethys and Yangtze Craton during the Permian and Early Mesozoic. Reflector M2 at about 12 s two-way traveltime (TWT) might result from the Paleozoic Moho, which represents the boundary between the previous granulite and eclogite facies. Reflector M3 at about 14 s might correspond to the bottom of the eclogite layer, beneath which the old lithospheric mantle remained. The old and the newly developed mantle may have different compositions, resulting in reflector M4. The multi-layered mantle reflectors demonstrate a mantle structure that possibly correlates with the lithospheric thinning process that occurred in Eastern China during the Late Mesozoic. The discovery of multi-layered mantle reflectors in the studied areas indicates a high heterogeneity of the upper mantle. Reflection seismology with improved technology, together with velocity and resistivity imaging and rock-physics measurements, can provide more details of the heterogeneity and related dynamic processes that occurred in the lithospheric mantle. 相似文献