Deformation Patterns of an Accretionary Wedge in the Transition Zone from Subduction to Collision Offshore Southwestern Taiwan

Swath bathymetry data and seismic reflection profiles have been used to investigate details of the deformation pattern in the area offshore southwestern Taiwan where the Luzon subduction complex encroaches on the passive Chinese continental margin. Distinctive fold-and-thrust structures of the convergent zone and horst-and-graben structures of the passive margin are separated by a deformation front that extends NNW-ward from the eastern edge of the Manila Trench to the foot of the continental slope. This deformation front gradually turns into a NNE–SSW trending direction across the continental slope and the Kaoping Shelf, and connects to the frontal thrusts of the mountain belt on land Taiwan. However, the complex Penghu submarine canyon system blurs the exact location of the deformation front and nature of many morphotectonic features offshore SW Taiwan. We suggest that the deformation front offshore SW Taiwan does not appear as a simple structural line, but is characterized by a series of N–S trending folds and thrusts that terminate sequentially in an en-echelon pattern across the passive Chinese continental slope. A number of NE–SW trending lineaments cut across the fold-and-thrust structures of the frontal accretionary wedge and exhibit prominent dextral displacement indicative of the lateral expulsion of SW Taiwan. One of the prominent lineaments, named the Yung-An lineament, forms the southeastern boundary of the upper part of the Penghu submarine canyon, and has conspicuous influence over the drainage pattern of the canyon     

The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

The Agulhas Ridge is a prominent topographic feature that parallels the Agulhas-Falkland Fracture Zone (AFFZ). Seismic reflection and wide angle/refraction data have led to the classification of this feature as a transverse ridge. Changes in spreading rate and direction associated with ridge jumps, combined with asymmetric spreading within the Agulhas Basin, modified the stress field across the fracture zone. Moreover, passing the Agulhas Ridge’s location between 80 and 69 Ma, the Bouvet and Shona Hotspots may have supplied excess material to this part of the AFFZ thus altering the ridge’s structure. The low crustal velocities and overthickened crust of the northern Agulhas Ridge segment indicate a possible continental affinity that suggests it may be formed by a small continental sliver, which was severed off the Maurice Ewing Bank during the opening of the South Atlantic. In early Oligocene times the Agulhas Ridge was tectono-magmatically reactivated, as documented by the presence of basement highs disturbing and disrupting the sedimentary column in the Cape Basin. We consider the Discovery Hotspot, which distributes plume material southwards across the AAFZ, as a source for the magmatic material.     

Seismic Response Control of Offshore Platform Structures with Shape Memory Alloy Dampers

In this study, the seismic response control of offshore platform structures with Shape Memory Alloy (SMA) dampers is investigated. A new SMA damper and its restoring force medel are introduced for the calculation of seismic response reduction. Based on an actual platform structure and its mechanical medel, the parameters which may affect the rate of shock absorption are analyzed, such as the number, position and characteristics of the SMA dampers and the condition of the site where the platform is located. The results show that the SMA damper is an effective control device for offshore platforms and satisfactory control can be achieved by proper selection of the parameters.     

Geophysical Evidence of a Relict Oceanic Crust in the Southwestern Scotia Sea

The southwestern part of the Scotia Sea, at the corner of the Shackleton Fracture Zone with the South Scotia Ridge has been investigated, combining marine magnetic profiles, multichannel seismic reflection data, and satellite-derived gravity anomaly data. From the integrated analysis of data, we identified the presence of the oldest part of the crust in this sector, which tentative age is older than anomaly C10 (28.7 Ma). The area is surrounded by structural features clearly imaged by seismic data, which correspond to gravity lows in the satellite-derived map, and presents a rhomboid-shaped geometry. Along its southern boundary, structural features related to convergence and possible incipient subduction beneath the continental South Scotia Ridge have been evidenced from the seismic profile. We interpret this area, now located at the edge of the south-western Scotia Sea, as a relict of ocean-like crust formed during an earlier, possibly diffuse and disorganized episode of spreading at the first onset of the Drake Passage opening. The successive episode of organized seafloor spreading responsible for the opening of the Drake Passage that definitively separated southern South America from the Antarctic Peninsula, instigated ridge-push forces that can account for the subduction-related structures found along the western part of the South Scotia Ridge. This seafloor accretion phase occurred from 27 to about 10 Ma, when spreading stopped in the western Scotia Sea Ridge, as resulted from the identification of the marine magnetic anomalies.     

A seismic refraction study of cretaceous oceanic lithosphere in the Northwest Pacific Basin

A seismic refraction study on old (110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s^-1 to 8.35 km s^-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho.     

海水中磷酸盐在固体粒子上阴离子交换作用 海水中磷酸盐-固体粒子相互作用的台阶型等温线

通过研究氯化钠溶液中磷酸盐在4种固体粒子（针铁矿、δ－氧化锰、伊利石和高岭石）上的交换等温线及钙对上述交换等温线的影响，发现磷酸盐液－固界面作用的台阶型等温线（2个台阶），可用分级离子／配位子交换等温式定量描述。钙能够促进磷酸盐在针铁矿和δ－氧化锰上的交换作用，其机理是交换在固体粒子上的钙再结合溶液中的磷酸盐，形成表面无机三元络合物。     

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.     

二(甲基环戊二烯)钐氯化物合成和晶体结构研究

作者以 Sm Cl3 与 (CH3 Cp) Na反应分离得到了三价稀土有机配合物 [(CH3 Cp) 2 Sm Cl·THF]2 的单晶 ,X-射线四圆衍射测定 ,该配合物属正交晶系 ,Pbna空间群 ,晶胞参数 a=9.6 6 2 (2 ) ,b=16 .4 76 (9) ,c=2 0 .582 (9) ;α=β=γ=90°,Z=4。并分析比较 [(CH3 Cp) 2 Sm Cl· THF]2 与其他三价稀土一氯化物的结构特点     

珊瑚礁岩心声速垂向跃变及其指相意义

本文在南沙群岛永署礁南永1井珊瑚礁岩心声速测量的基础上，研究了珊瑚礁岩心声速的垂向跃变特征和相应地层沉积相变及地层侵蚀间断面的关系，分析了珊瑚礁岩心相变造成其声速跃变的原因，阐明了海平面升降形式珊瑚礁地层侵蚀间断面和产生相变的具体过程, 明了珊瑚礁岩心声速垂向跃变与相应地层古气候和海平面变化的关系，该项研究在岛礁工程建设和礁灰岩区石油勘探声学测井以及西太平洋边缘海古海洋学研究学方面具有重要的实用价值和理论意义。     

Analysis of Dynamic Characteristics of Submarine Free Spanning Pipelines by Complex Damping Method

Considering the effect of the internal flowing fluid and the external marine environmental condition, the differential equation for the vortex-induced vibration (V1V) of the free spanning pipeline is derived and is discretized by the Hermit interpolation function. The free vibration equation with the damping term is solved by the complex damping method for the natural frequency, and then the effect of fluid damping on the natural frequency of the free spanning pipeline is analyzed.The results show that fluid damping has a significant influence on the damped natural frequency of the free spanning pipeline in the lock-in state, while it has little influence when the pipeline is out of the lock-in state. In the meantime,the change of the free span length has the same effect on the damped natural frequency and the undamped natural frequency.