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1.
An active source electromagnetic sounding system for marine use   总被引：2，自引：0，他引：2  
Instrumentation has been developed for carrying out active source electromagnetic sounding experiments in the deep oceans. Experiments of this type are directly and uniquely sensitive to the presence of molten or partially molten material, to temperature structure and to the porosity of upper crustal rocks such as those that accommodate hydrothermal circulation systems. Electromagnetic sounding experiments therefore represent an extremely desirable addition to the existing range of geophysical techniques for studying geological processes in thermally, hydrothermally or magmatically active regions—for example, at oceanic spreading centres.The instruments can be operated in regions of rugged, unsedimented sea bottom terrain, and are designed for investigating the distribution of electrical conductivity within the oceanic crust and uppermost mantle. The instrumentation consists of a deep towed, horizontal electric dipole transmitter and a set of free-fall, sea bottom, horizontal electric field recording devices.The transmitter is a deep-towed instrument, which is provided with power from the towing ship through a conducting cable. The transmitter package is fitted with an integral echo sounder, which allows it to be towed safely a short distance above the seabed. Electromagnetic signals are transmitted from a neutrally-buoyant antenna array, which is streamed behind the deep tow.The sea bottom receiving instruments each consist of a recoverable package which contains the instrumentation and digital recording system, an acoustic release unit, four low-noise, porous electrodes arranged in two orthogonal, horizontal dipoles, and a disposable bottom weight.The instruments have been used at sea on three occasions. On their most recent use, active source signals were successfully recorded during an experiment to investigate crustal magmatism and hydrothermal circulation beneath the axis of the East Pacific Rise.  相似文献   

2.
The outer rise on the distal periphery of a subduction system is caused by emplacement of an accreted load onto the flexed oceanic lithosphere. By examining the bathymetry and free-air gravity anomaly data collected by satellite observations and marine reflection seismic data collected during the TAIGER project, we demonstrate the characteristics of the flexural outer rise seaward of the Manila Trench. The region of the outer rise on the westernmost periphery of the Manila subduction system is characterized by the positive free-air gravity anomaly seaward parallel to the Manila Trench and the morphological rise at the south of the Manila subduction system. A flexure simulation is performed based on the flexural profiles along the southern Manila Trench-outer system and the resulting effective elastic thickness values may provide an alternative aspect for the spreading rates of the South China Sea basin. Since both the western periphery of the Taiwan collision belt and Manila subduction belt are dominated by the strain regime of extension of flexural origin, it appears that the strain regime of flexural extension associated with the flexural forebulge of the Western Taiwan Foreland Basin to the north, and the strain regime of flexural extension associated with the outer rise seaward of the Manila Trench to the south are meridionally interconnected. This revised understanding of the strain regime of flexural extension origin west of the Taiwan–Luzon convergent belt provides an alternative point of view on the strain regime offshore SW Taiwan.  相似文献   

3.
China''s 7000 m manned submersible JIAOLONG carried out an exploration cruise at the Mariana Trench from June to July 2016. The submersible completed nine manned dives on the north and south area of the Mariana Trench from the depth of 5500 to 6700 m, to investigate the geological, biological and chemical characteristics in the hadal area. During the cruise, JIAOLONG deployed a gas-tight serial sampler to collect the water near the sea bottom regularly. Five days later, the sub located the sampler in another dive and retrieved it successfully from the same location, which is the first time that scientists and engineers finished the high accuracy in-situ deployment and retrieval using a manned submersible with Ultra-Short Base Line (USBL) positioning system at the depth more than 6600 m. In this task, we used not only the USBL system of the manned submersible but also a compound strategy, including five position marks, the sea floor terrain, the depth contour, and the heading of the sub. This paper introduces the compound strategy of the target deployment and retrieval with the practical diving experience of JIAOLONG, and provides a promising technique for other underwater vehicles such as manned submersible or Remote Operated Vehicle (ROV) under similar conditions.  相似文献   

4.
We have obtained precise estimates of the position of Ocean Bottom Seismometers (OBS) on the sea bottom. Such estimates are usually uncertain due to their free falling deployment. This uncertainty is small enough, or is correctable, with OBS spacing of more than 10 km usually employed in crustal studies. But, for example, if the spacing is only 200 m for OBS reflection studies, estimates of the position with an accuracy of the order of 10 m or more is required.The determination was carried out with the slant range data, ship position data and a 1D acoustic velocity structure calculated from Conductivity–Temperature–Depth (CTD) data, if they are available. The slant range data were obtained by an acoustic transponder system designed for the sinker releasing of the OBS or travel time data of direct water wave arrivals by airgun shooting. The ship position data was obtained by a single GPS or DGPS. The method of calculation was similar to those used for earthquake hypocenter determination.The results indicate that the accuracy of determined OBS positions is enough for present OBS experiments, which becomes order of 1 m by using the DGPS and of less than 10 m by using the single GPS, if we measure the distance from several positions at the sea surface by using a transponder system which is not designed for the precise ranging. The geometry of calling positions is most important to determine the OBS position, even if we use the data with larger error, such as the direct water wave arrival data. The 1D acoustic velocity structure should be required for the correct depth of the OBS. Although it is rare that we use a CTD, even an empirical velocity structure works well.  相似文献   

5.
As an interoceanic arc, the Kyushu-Palau Ridge（KPR） is an exceptional place to study the subduction process and related magmatism through its interior velocity structure. However, the crustal structure and its nature of the KPR,especially the southern part with limited seismic data, are still in mystery. In order to unveil the crustal structure of the southern part of the KPR, this study uses deep reflection/refraction seismic data recorded by 24 ocean bottom seismometers to reconstruct a detail...  相似文献   

6.
We present major and trace element data of lava recovered from the northern Yap Trench in the western Pacific and discuss their petrogenesis and tectonic implications within the framework of interactions between the Caroline Ridge and Yap Trench. Rocks were collected from both landward and seaward trench slopes and exhibited geochemical characteristics similar to backarc basin basalt (BABB) and mid-ocean ridge basalt (MORB), including high Fe content, tholeiitic affinity, high TiO2 value at a given FeOT/MgO ratio, Ti/V ratio between 20 and 50, low Ba/Nb ratio and Th/Nb ratio, and trace element patterns commonly displayed by BABB and MORB, which are distinct from arc lava. These rocks seem to have been generated during mantle upwelling and decompression melting at a spreading center. However, compared with typical forearc lava produced by seafloor spreading in the Mariana forearc region, such as the early Eocene forearc basalts and late Neogene forearc lava in the southernmost Mariana Trench, the Yap Trench lava is derived from a more fertile mantle and feature a more minor subduction component; thus, they cannot be the products of forearc mantle decompression melting. We suggest that the landward slope lava represents backarc basin crust that was overthrust onto the forearc lithosphere during the collision of the Caroline Ridge with the Yap Trench (20–25 Ma), which played a key role in the evolution of the Yap subduction system. Moreover, the seaward slope lava represents the subduction plate crust that accreted onto the deep trench during the collision. This collision event resulted in the cessation of Yap Arc magmatism; thus, the Yap Trench volcanic rocks (<25 Ma) previously suggested to be arc magma products may actually represent the nascent island arc lava with a lower subduction component than in the mature Mariana Arc lava.  相似文献   

7.
A Seabeam reconnaissance of 1200 km of the deep sediment-starved axis of Tonga Trench delineated the fine-scale relief at the outcrop of a subduction zone generally characterized by tectonic erosion rather than accretion. The commonest axial cross-section has a steep (12°) irregular inner slope intersecting the thinly sedimented surface of Mesozoic ocean crust, which dips under it at 5–6°. There is little or no intervening turbidite fill, but small lenses interpreted as debris deposits occur at the foot of parts of the inner slope that lack basins or benches which elsewhere obstruct downslope sediment transport. The oceanic slope is severely broken by parallel but slightly sinuous fractures induced by bending of the plate, and entry of outer-slope grabens into the subduction zone is confirmed to be a morphologically and tectonically important process. Arrival of oceanic seamounts and volcanic ridges at the trench outer slope and axis affects the fracture pattern of the oceanic plate, the depth of the temporarily plugged axis, and the relief of the lower inner slope. Subduction of the Louisville guyot chain, or of the extensive hotspot swell and thick sediment apron that surrounds it, has important regional effects as well, shoaling 400 km of trench axis and causing development of a small accretionary prism with trench-slope basins. Because the intersection point of the hot-spot chain has moved rapidly south along the trench, structural changes that occur in the wake of guyot-chain subduction can also be inferred: accretion at the inner slope is followed by rapid tectonic erosion, which unroofs a wider strip of downgoing lithosphere and thereby deepens the trench axis. The longitudinal profile of axial depths, made locally irregular by the collision of medium-scale volcanic and tectonic relief on the oceanic plate, also has a step near 18.5° S, where there is a regional depth difference in the oceanic crust entering the trench.  相似文献   

8.
The structure of the oceanic crust adjacent to the Côte d’Ivoire–Ghana transform margin is deduced from multichannel seismic reflection and seismic wide-angle data, showing crustal heterogeneities within oceanic basement; the oceanic crust adjacent to the transform margin is half as thick as standard Atlantic oceanic crust. Refraction data indicate a gradual velocity transition towards typical mantle velocities. Such an abnormal oceanic crustal structure appears quite similar to crustal structures known along transform faults. This crustal thinning may be related to thermal effects of the nearby continental crust, on the oceanic accretion processes. We did not find geophysical evidence for oceanic crust contamination by continental lithosphere.  相似文献   

9.
We investigated the deformation in the accretionary wedge associated with subducted seamounts in the northern Manila Trench by combining observations from seismic profiles and results from laboratory sandbox experiments. From three seismic reflection profiles oriented approximately perpendicular to the trench, we observed apparent variations in structural deformation along the trench. A number of back-thrust faults were formed in the accretionary wedge where subducted seamounts were identified. In contrast, observable back-thrusts were quite rare along the profile without seamounts, indicating that seamount subduction played an important role in deformation of the accretionary wedge. We then conducted laboratory sandbox experiments to investigate the effects of subducted seamounts on the structural deformation of the accretionary wedge. From the analog modeling results we found that seamount subduction could cause well-developed back-thrusts, gravitational collapse, and micro-fractures in the wedge. We also found that a seamount may induce normal faults in the wedge and that normal faults may be eroded by subsequent seamount subduction. In addition, we constrained the crustal structure of the South China Sea plate from modeling free-air gravity data. The dip angle of the subducting plate, which was constrained by hypocenters of available earthquakes, increased from south to north in the northern Manila Trench. We found a laterally heterogeneous density distribution of the oceanic crust according to the gravity data. The density of subducted crust is ~2.92 g/cm3, larger than that of the South China Sea crust (2.88 g/cm3).  相似文献   

10.
Swath bathymetric, sonar imagery and seismic reflection data collected during the SOPACMAPS cruise Leg 3 over segments of the Vitiaz Trench Lineament and adjacent areas provide new insights on the geometry and the stuctural evolution of this seismically inactive lineament. The Vitiaz Trench Lineament, although largely unknown, is one of the most important tectonic feature in the SW Pacific because it separates the Cretaceous crust of the Pacific Plate to the north from the Cenozoic lithosphere of the North Fiji and Lau Basins to the south. The lineament is considered to be the convergent plate boundary between the Pacific and Australian Plates during midde to late Tertiary time when the Vitiaz Arc was a continuous east-facing are from the Tonga to the Solomon Islands before the development of the North Fiji and Lau Basins. Progressive reversal and cessation of subduction from west to east in the Late Miocene-Lower Plioene have been also proposed. However, precise structures and age of initiation and cessation of deformation along the Vitiaz Trench Lineament are unknown.The lineament consists of the Vitiaz Trench and three discontinuous and elongated troughs (Alexa, Rotuma and Horne Troughs) which connect the Vitiaz Trench to the northern end of the Tonga Trench. Our survey of the Alexa and Rotuma Troughs reveals that the lineament is composed of a series of WNW-ESE and ENE-WSW trending segments in front of large volcanic massifs belonging to the Melanesian Border Plateau, a WNW trending volcanic belt of seamounts and ridges on Pacific crust. The Plateau and Pacific plate lying immediately north of the lineament have been affected by intense normal faulting, collapse, and volcanism as evidenced by a series of tilted blocks, grabens, horsts and ridges trending N 120° to N100° and N60°–70°. This tectonism includes several normal faulting episodes, the latest being very recent and possibly still active. The trend of the fault scarps and volcanic ridges parallels the different segments of the Vitiaz Trench Lineament, suggesting that tectonics and volcanism are related to crustal motion along the lineament.Although the superficial observed features are mainly extensional, they are interpreted as the result of shortening along the Vitiaz Trench Lineament. The fabric north of the lineament would result from subduction-induced normal faulting on the outer wall of the trench and the zig-zag geometry of the Vitiaz Trench Lineament might be due to collision of large volcanic edifices of the Melanesian Border Plateau with the trench, provoking trench segmentation along left-lateral ENE-WSW trending transform zones. The newly acquired bathymetric and seismic data suggest that crustal motion (tectonism associated with volcanism) continued up to recent times along the Vitiaz Trench Lineament and was active during the development of the North Fiji Basin.  相似文献   

11.
活动大陆边缘的板片窗构造   总被引：7，自引：0，他引：7  
正俯冲的洋中脊的持续扩张作用将会使该洋中脊两侧的洋壳板片之间形成一个持续加宽的间隙,这个间隙称为板片窗。板片窗往往形成于小于10Ma左右具浮力的大洋岩石圈俯冲时期。板片窗形态依赖于3个主要因素：板块的相对运动、俯冲前的洋脊一转换断层组合样式、俯冲角度。影响板片窗形态的次要因素还有热侵蚀、相变等因素。在板片窗出现的活动大陆边缘,软流圈、岩石圈、大气圈、水圈发生独特的多圈层相互作用,是地球系统最为活跃的地带。由于该地带的洋底消减往往与生长轴呈一定角度相交,不仅引起盆地的不对称消减,而且使得板片窗之上的活动大陆边缘的构造、岩浆、成矿和热效应明显不同于洋中脊平行于俯冲带的消减作用产生的构造、岩浆、成矿和热效应。  相似文献   

12.
Rheology and strength of the lithosphere   总被引：2，自引：0，他引：2  
Mechanical properties of lithosphere are of primary importance for interpretation of deformation at all spatial and time scales, from local scale to large-scale geodynamics and from seismic time scale to billions of years. Depending on loading conditions and time scale, lithosphere exhibits elastic, brittle (plastic) or viscous (ductile) properties. As can be inferred from rock mechanics data, a large part of the long-term lithospheric strength is supported in the ductile or ductile-elastic regime, while it also maintains important brittle strength. Yet, at short seismic time scale (s), the entire lithosphere responds in elastic/brittle-elastic regime. Even though rock mechanics experiments provide important insights into the rheological properties of the lithosphere, their conditions (e.g., time scales, strain rates, temperature and loading conditions) are too far from those of real Earth. Therefore, these data cannot be reliably extended to geological time- and spatial scales (strain rates ∼10−17 to 10−13 s−1) without additional parameterization or validation based on geological time scale observations of large-scale deformation. For the oceanic lithosphere, the Goetze and Evan’s brittle-elastic-ductile yield strength envelopes (YSEs) were validated by geodynamic scale observations such as the observations of plate flexure. However, oceanic lithosphere behavior in subduction zones and passive continental margins is strongly conditioned by the properties of the continental counterpart, whose rheology is less well understood. For continents and continental margins, the uncertainties of available data sources are greater due to the complex structure and history of continental plates. For example, in a common continental rheology model, dubbed “jelly sandwich”, the strength mainly resides in crust and mantle, while in some alternative models the mantle is weak and the strength is limited to the upper crust. We address the problems related to lithosphere rheology and mechanics by first reviewing the rock mechanics data, Te (flexure) and Ts (earthquake) data and long-term observations such as folding and subsidence data, and then by examining the physical plausibility of various rheological models. For the latter, we review the results of thermo-mechanical numerical experiments aimed at testing the possible tectonic implications of different rheology models. In particular, it appears that irrespective of the actual crustal strength, the models implying weak mantle are unable to explain either the persistence of mountain ranges for long periods of time or the integrity of the subducting slabs. Although there is certainly no single rheology model for continents, the “jelly sandwich” is a useful first-order model with which to parameterize the long-term strength of the lithosphere. It is concluded that dry olivine rheology laws seem to represent well the long-term behavior of mantle lithosphere in oceans, margins and continents. As to the continent and margin crust rheology, analysis of the results of thermo-mechanical models and of Te data based on the most robust variants of flexural models, suggests that continental plates with Te 30-50% smaller than their theoretical mechanical thickness hm (i.e. Te = 20-60 km) should be characterized by a weak lower or intermediate crustal rheology enabling mechanical decoupling between crust and mantle. Older plates such as cratons are strong due to crust-mantle coupling and specific properties of the cratonic mantle lithosphere.  相似文献   

13.
We show the magnetic model of the Selli-Vavilov region. The Selli Line is known as the northwestern edge of the southern Tyrrhenian Basin. The tectonic evolution of the Tyrrhenian Basin is dominated by a Tortonian-Quaternary extension through the eastward movement of the Apennine subduction system. This migration has generated a diffuse stretching of the continental crust with the emplacement of new oceanic material. This latter occurred in several localized zones where the eastward retreating of the Ionian subduction system produced a strong depletion of the crust with formation of basins and correlated spreading. Nowadays the presence of oceanic crust is confirmed through direct drilling investigation but a complete mapping of the oceanic crustal distribution is still lacking. The Selli-Vavilov region shows a differentiated crustal setting where seamount structures, the oceanic basement portions and continental crust blocks are superimposed. To this aim, a 2D inversion of the magnetic data of this region was conducted to define buried structures. The magnetic susceptibility pattern was computed by solving the least squares problem of the misfit between the predicted and real data for separated wavebands. This method produced two 2D models of the high and low frequency fields of the Selli-Vavilov region. The two apparent susceptibility maps provide different information for distinct ranges of depth. The results of the inversions were also combined with seismic data of the Selli region highlighting the position of the highly magnetized buried bodies. The results confirm a role for the Selli Line as a deep crustal boundary dividing the Sardinian passive domain from the easternmost active region where different oceanic structures are located. The Selli Line has worked as a detachment fault system which has moved eastward. Finally, the Selli-Vavilov region may be interpreted as a tectonic result due to a passive asymmetrical rift occurred between the Tortonian and Pliocene.  相似文献   

14.
声学与海洋沉积学交叉领域研究可分为“沉积层声学特性的研究”、“海底高频声散射或低频声反射与底质类型之间关系的研究”、“回声参数反演海底类型技术”和“海底回声图象识别海底沉积类型技术”4个方面的研究,较详细论述了4个方面的国内外研究现状,最后提出了该领域进一步研究的战略思路。  相似文献   

15.
针对海底声学探测仪器采集数据量大而存储容量有限、数据传输带宽不足的实际问题,基于Lempel-Ziv-Welch(LZW)无损压缩算法,研究海底声学探测数据的实时压缩方法,提高数据压缩效果、节省传输带宽。并在LZW无损压缩算法的基础上结合数据存储的特点对压缩结果进行内存重新分配,极大提高压缩比(压缩数据大小/原始数据大小)。利用海底地震仪(OBS)采集的原始声学探测数据进行测试验证,结果表明该方法对于OBS声学探测数据有很好的压缩比,可用于对OBS采集的声学探测数据进行压缩处理,对于海底探测仪器的研发有很好的指导意义。  相似文献   

16.
Analysis of geophysical data obtained during a study of the insular slope in the central Kuril?Kamchatka Trench during projects Kuriles-2005 and Kuriles-2006 promoted by the Presidium of the Russian Academy of Sciences revealed a large submarine landslide in this area. The landslide, located at the bottom of the transverse valley confined to the Bussol l Graben, resulted from the failure of the northeastern wall of a graben composed of sedimentary material. It exceeds 35 km3 in size, representing one of the large submarine landslides discovered to date on the slope of the Kuril?Kamchatka Trench in submarine canyonfan environments.  相似文献   

17.
基于SRTM15_Plus水深数据,利用地形表面流水分析与等高线几何分析相结合的方法对亚洲大陆边缘海底峡谷进行识别,分析峡谷的形态、分布及演化进程。共识别出海底峡谷531条,按照平面形态分为直线型、蛇曲型和树枝型三种,数量分别为239条、75条和217条。直线型峡谷主要分布在白令海盆地、千岛盆地、南海等海域;蛇曲型峡谷主要分布在孟加拉湾东部俯冲带海域;树枝型峡谷主要分布在日本海沟、伊豆小笠原海沟和南海海槽交界处,南海以及苏门答腊俯冲带海域。根据峡谷的形态与分布,结合研究区内构造背景,讨论了峡谷“直线型-蛇曲型”的形态演化进程,并依据树枝型峡谷主干谷的形态信息,推测存在“蛇曲型-树枝型”、“直线性-树枝型”的形态演化进程。  相似文献   

18.
MODIS (Aqua and Terra) space images of the northwest part of the Pacific Ocean at instants of considerable tsunamis in 2009–2011 have been analyzed. Periodic cloud structures typical for internal gravity waves (IGWs) in the atmosphere have been revealed in the region of the Kuril Islands in five cases. It has been shown that the meteorological conditions observed during those events favored the appearance of such phenomena. The continuous oceanic upwelling in the region of the Kuril–Kamchatka Trench is a favorable factor for IGW generation due to the creation of temperature contrasts observed both in warm and cold seasons between the ground layer of the atmosphere and ocean surface. The estimate of the structure of cloud manifestations of atmospheric waves by satellite images testifies also to the influence of the Kuril Ridge orography on their appearance and propagation over the water area under study. The increase in amplitudes and duration of oscillations caused by the tsunami in the shelf zone can be an auxiliary factor for the IGW generation over coastal territories.  相似文献   

19.
针对深渊生物资源研究的需求，自主研发了用于全海深深度的深渊沉积物、水体和宏生物的保压取样装置，深渊沉积物保压转移装置，深渊微生物原位过滤及保存装置和高压培养高压酶学测定装置。在深海模拟环境验证了取样装置在万米深度下的工作性能。相关装置在“探索一号”科考船的TS15、TS21-1和TS21-2大洋科考航次中，搭载“奋斗者”号载人潜器、“2号”深渊着陆器、“原位实验”号着陆器于西菲律宾盆区和马里亚纳海沟进行了海上试验，成功获取了万米深度沉积物、水体和宏生物保压样品以及微生物原位过滤滤膜；成功进行了沉积物保压样品的保压转移试验。初步形成了深渊海域生物资源取样的装备技术体系，为深渊海底生物和基因资源开发，深渊生命过程等科学研究提供技术手段。  相似文献   

20.
 Crustal structure of the Co^te d’Ivoire–Ghana marginal ridge and its transition with oceanic lithosphere are deduced from multichannel seismic reflection, wide-angle seismic, and gravity data. The CIGMR is cut into rotated blocks and displays a crustal structure quite similar to that of the nearby northern Ivorian extensional basin. These results strongly support that the CIGMR represents an uplifted fragment of continental crust. Transition with the oceanic crust appears sharp; continental crustal thinning occurs over less than 5 km. We did not find evidence for underplating and/or contamination as anticipated from such a sharp contact between continental and oceanic crust. Received: 12 March 1995/Revision received: 2 July 1996  相似文献   

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