硬件系统集成——海底大地电磁测量的关键技术

海底大地电磁探测是一项多学科交叉和多技术渗透的前缘课题 ,课题的目标之一是研制用于海底数据采集的大地电磁测量系统。入海的难度给该系统提出了特殊要求 ,即必须解决海下仪器安全及海面与海底间的设备运载问题。由于涉及多项技术内容 ,每项技术由相应的硬件完成 ,因而整个系统包括了多个集成部件 ,各部件分别实现密封承压、重载下沉、水下布极、释放上浮等各项功能。在系统集成过程中 ,除了要考虑各部件的协调装配外 ,系统整体指标的完善性是研究的重点。根据海上作业的特点和船只设备的具体情况 ,系统集成方案解决了结构、强度、平衡、保护等设计难题 ,提出了若干个既实用又可靠的工程技术方法。集成后的系统经过了从甲板投放、海底数据采集到设备回收全过程的试验。     

海洋大地电磁二维正演及结果分析

研究了海洋大地电磁法的二维正演并编制了相应程序 ,程序采用有限单元法求出海底各节点处的电磁场值 ,进一步计算得到视电阻率。为了验证程序的正确性与有效性 ,根据卡尼亚理论推导出计算一维海洋模型的阻抗公式 ,并得到视电阻率的解析解 ,将其与有限元法得出的数值解进行了对比 ,表明了此方法的正确性。通过对正演结果的分析 ,表明海洋大地电磁测深能够成功地反映海底的电性结构     

Propagating rift tectonics of a Caledonian marginal basin: Multi-stage seafloor spreading history of the Solund-Stavfjord ophiolite in western Norway

The Late Ordovician Solund-Stavfjord ophiolite in western Norway represents a remnant of the Iapetus oceanic lithosphere that developed in a Caledonian marginal basin. The ophiolite contains three structural domains that display distinctively different crustal architecture that reflects the mode and nature of magmatic and tectonic processes operated during the multi-stage seafloor spreading evolution of this marginal basin. Domain I includes, from top to bottom, an extensive extrusive sequence, a transition zone consisting of dike swarms with screens of pillow breccias, a sheeted dike complex, and plutonic rocks composed mainly of isotropic gabbro and microgabbro. Extrusive rocks include pillow lavas, pillow breccias, and massive sheet flows and are locally sheared and mineralized, containing epidosites, sulfide-sulfate deposits, Fe-oxides, and anhydrite veins, reminiscent of hydrothermal alteration zones on the seafloor along modern mid-ocean ridges. A fossil lava lake in the northern part of the ophiolite consists of a >65-m-thick volcanic sequence composed of a number of separate massive lava units interlayered with pillow lavas and pillow breccia horizons. The NE-trending sheeted dike complex contains multiple intrusions of metabasaltic dikes with one- and two-sided chilled margins and displays a network of both dike-parallel normal and dike-perpendicular oblique-slip faults of oceanic origin. The dike-gabbro boundary is mutually intrusive and represents the root zone of the sheeted dike complex. The internal architecture and rock types of Domain I are analogous to those of intermediate-spreading oceanic crust at modern mid-ocean ridge environments. The ophiolitic units in Domain II include mainly sheeted dikes and plutonic rocks with a general NW structural grain and are commonly faulted against each other, although primary intrusive relations between the sheeted dikes and the gabbros are locally well preserved. The exposures of this domain occur only in the northern and southern parts of the ophiolite complex and are separated by the ENE-trending Domain III, in which isotropic to pegmatitic gabbros and dike swarms are plastically deformed along ENE-striking sinistral shear zones. These shear zones, which locally include fault slivers of serpentinite intrusions, are crosscut by N20°E-striking undeformed basaltic dike swarms that contain xenoliths of gabbroic material. The NW-trending sheeted dike complex in the northern part of Domain II curves into an ENE orientation approaching Domain III in the south. The anomalous nature of deformed crust in Domain III is interpreted to have developed within an oceanic fracture zone or transform fault boundary.REE chemistry of representative extrusive and dike rocks from all three domains indicates N- to E-MORB affinities of their magmas with high Th/Ta ratios that are characteristic of subduction zone environments. The magmatic evolution of Domain I encompasses closed-system fractional crystallization of high-Mg basaltic magmas in small ephemeral chambers, which gradually interconnected to form large chambers in which mixing of primary magmas with more evolved and fractionated magma caused resetting of magma compositions through time. The compositional range from high-Mg basalts to ferrobasalts within Domain I is reminiscent of modern propagating rift basalts. We interpret the NE-trending Domain I as a remnant of an intermediate-spread rift system that propagated northeastwards (in present coordinate system) into a pre-existing oceanic crust, which was developed along the NW-trending doomed rift (Domain II) in the marginal basin. The N20°E dikes laterally intruding into the anomalous oceanic crust in Domain III represent the tip of the rift propagator. The inferred propagating rift tectonics of the Solund-Stavfjord ophiolite is similar to the evolutionary history of the modern Lau back-arc basin in the SW Pacific and suggests a complex magmatic evolution of the Caledonian marginal basin via multi-stage seafloor spreading tectonics.     

湘西北镍钼多金属矿床的元素组合及微量元素地球化学

湘西北镍钼多金属矿床富集了多种元素，形成一个以Ｎｉ、Ｍｏ、Ｃｕ、Ｚｎ、Ｐｄ、Ｐｔ、Ａｓ、Ｓｅ、Ｂａ、Ｖ、Ｐ为主的特殊元素组合；微量元素Ａｓ、Ｓｅ、Ｂａ等成１０＾１￣１０＾３倍富集，它们的地球化学特征表明，这类矿床属海底喷气沉积矿床，这组特殊元素来源和富集，与海底喷流作用有关。     

On the construction of geomagnetic timescales from non-prejudicial treatment of magnetic anomaly data from multiple ridges

When marine magnetic-anomaly data are used to construct geomagnetic polarity timescales, the usual assumption of a smooth spreading-rate function at one seafloor spreading ridge forces much more erratic rate functions at other ridges. To eliminate this problem, we propose a formalism for the timescale problem that penalizes non-smooth spreading behaviour equally for all ridges. Specifically, we establish a non-linear Lagrange multiplier optimization problem for finding the timescale that (1) agrees with known chron ages and with anomaly-interval distance data from multiple ridges and (2) allows the rate functions for each ridge to be as nearly constant as possible, according to a cumulative penalty function. The method is applied to a synthetic data set reconstructed from the timescale and rate functions for seven ridges, derived by Cande & Kent (1992) under the assumption of smooth spreading in the South Atlantic. We find that only modest changes in the timescale (less than 5 per cent for each reversal) are needed if no one ridge is singled out for the preferential assumption of smoothness. Future implementation of this non-prejudicial treatment of spreading-rate data from multiple ridges to large anomaly-distance data sets should lead to the next incremental improvement to the pre-Quaternary geomagnetic polarity timescale, as well as allow a more accurate assessment of global and local changes in seafloor spreading rates over time.     

现代海底热液成矿作用研究现状及发展方向

现代海底热水成矿作用研究的重大进展表现在两个方面：（１）大批活动的和窒息的热液活动区和硫化物矿床在洋脊、岛弧、弧后盆地及板内火山活动中心等海底环境相继发现。在沉积物饥饿洋脊，矿床规模较小，Ｃｕ－Ｚｎ为主，沉积物覆盖洋脊，矿床规模巨大，Ｐｂ－Ｚｎ为主。弧后扩张或弧间裂陷盆地，形成Ｐｂ－Ｚｎ→Ｚｎ－Ｐｂ－Ｃｕ→Ｃｕ－Ｚｎ矿床谱系。岛弧环境硫化物矿床不具规模，板内火山活动中心以氧化物－硫化物矿化为特色。（２）现代海底热水成矿作用观察和研究为古代ＶＭＳ矿床成因研究提供了重要信息，对现有成矿理论产生重要影响。现代成矿观念强调：①海底成矿作用虽可产生于不同环境，但均与张裂断陷事件密切相关。矿床规模和分布特点受张裂速率制约；②成矿物质主体来源于热水循环的火山－沉积岩和下伏基底物质；③硫化物堆积发生于丘堤－烟囱联合构成的机构和结壳下部，通过开放空间的硫化物充填和先成矿石淋滤迁移来实现。④热液流体呈双扩散对流循环。现代海底热水成矿作用的未来研究方向可概括为强度方向和广度方向。广度研究将加大力度去发现新的矿床，强度研究将采用地球物理方法并配以必要的钻探，深入揭示矿床的三维结构和热液体系及成矿机制。     

Discrimination of Seafloor Sediment Properties by VWA

Analytical results of sound velocity and spectrum for seafloor sediment ore obtained by VWA (velocity-wave-amplitude) discrimination technique. Based on velocity-wave-amplitude, an understanding is gained of the physical condition and structural characteristics of seafloor sediment, which is combined with other geological information of the sedimentary layer to synthetically discriminate the properties of seafloor sediment. Experimental results show that, by using the relationship between sound velocity, wave form envelope, amplitude shape and size, and such parameters as sedimentary structure, microstructure, bedding, grain composition, mineral composition, and physical-mechanics, etc., the basic properties of the shallow surface seafloor sediment in the experimental sea area can be discriminated and the burial depth of traces of ancient marine transgression and regression events in the borehole cores of seafloor sediment can be divided, thus making an attempt of and contribution to the practice of acoustically remote-sensing and telemetering seafloor sediment.     

Small-scale variability of seafloor features in the northern Peru Basin: Results from acoustic survey methods

During RV SONNE cruise SO-79 to the eastern Pacific Ocean, two areas of about 65×80 km in the northern Peru Basin were surveyed with the acoustic mapping systems HYDROSWEEP (bathymetry), PARASOUND (3.5 kHz high-resolution seismic system), and a deep-towed side-scan sonar system. In addition, we sampled sediments using piston and box corers. The data show an unexpected variability of seafloor features: The bathymetry is characterized by an abyssal hill topography with predominately N-S ridges up to 300 m high, and scattered volcanic hills. Moreover, one 2000-m-high seamount was mapped. PARASOUND shows several distinct reflectors within the sediment cover, all of which are attributed to carbonate-rich strata. In the northern area, the uppermost prominent reflector is related to the Mid-Brunhes Event (0.45 Ma) in the sediment cores, while the lowermost represents acoustic basement. In the southern area, the seismic pattern reveals an upper opaque zone and a lower transparent zone. The base of the opaque zone is marked by a distinct reflector which corresponds to a huge carbonate peak (6–7 Ma) in the sediment cores. However, despite this general pattern, the PARASOUND records show a highly variable situation, with the distribution of sediment echo types strongly influenced by the seafloor topography. The side-scan sonar revealed the existence of numerous small volcanic cones up to 25 m high and nearly free of sediment. Additionally, the sonar records show a patchy (up to 800 m across) seafloor reflectiviti. We interpret this patchiness as a local lack of manganese nodule coverage. Volcanic cones and the most distinct nodule-free patches are usually on ridges. We interpret this variability as caused by winnowing and erosion, an interpretation that is supported by the occurrence of outcrops of Tertiary strata. This regional small-scale variability argues for a highly dynamic depositional history of the Peru Basin.     

Sulfur isotopic composition of seafloor hydrothermal sediment from the Jade hydrothermal field in the central Okinawa Trough and its geological significance

Eighteen samples of hydrothermal sediments from the Jade hydrothermal field in the central Okinawa Trough have been analyzed. Sulfur isotopic values for 10 sulfide samples vary from 5.2 × 10~(-3) to 7.2× 10(-3), δ~(34)S values for 7 sulfate samples vary from 16.3 × 10~(-3) to 22.3 × 10~(-3), and 1 native sulphur sample has a δ~(34)S value of 8.2× 10~(-3). The major sources of sulfur for hydrothermal sediment are intermediate to acid volcanic rocks and sea water sulfate, and it is possible that the partial sulfur of hydrothermal sediment is from the pelagic sediment by the interaction between hydrothermal fluid and sediment. The reasons of causing the distinct differences in sulfur isotopic values for sulfide samples from hydrothermal sediment ( compared with other hydrothermal fields), are the differences in the sources of sulfur, the magmatic activity and the tectonic evolution in different hydrothermal fields. The sulfur evolution is a long and complex process in the seafloor hydrothermal system