海底热液活动与海洋科学研究

本文简要介绍了海底热液活动的研究历史 ,以及目前研究的几个主要问题。指出海底热液活动是海洋中永远存在的自然现象。热液区主要分布在大洋中脊、弧后盆地和热点区。在这些区域由于地质构造的不稳定性 ,造成冷海水通过隙缝下渗 ,并在岩浆房作用下形成高温热水。热水在上升通道中与围岩作用 ,并发生复杂的岩 -水反应 ,从而改变了海水的化学成分。流出的热液可以形成多种矿物沉积 ,其中最有价值的是 Zn,Cu,Fe,Pb的硫化物。岩 -水反应可以产生可观的元素通量 ,因此 ,对海水元素恒定性的解释需要重新审视。利用 3 He/热比值可以计算海洋的热通量。热液活动为耐温生物的研究提出了新的课题     

现代海底热液沉积物的硫同位素组成及其地质意义

共收集到现代海底热液沉积物的1264个硫同位素数据,结合我们对冲绳海槽Jade热液区和大西洋中脊TAG热液区中表层热液沉积物的硫同位素研究成果,对比分析了不同地质-构造环境中海底热液沉积物的硫同位素组成特征及其硫源问题.结果表明:(1)现代海底热液沉积物中硫化物的硫同位素组成集中分布在1‰～9‰之间,均值为4.5‰(n=1042),而硫酸盐矿物的硫同位素组成主要分布在19‰～24‰之间,均值为21.3‰(n=217);(2)无论在洋中脊还是在弧后盆地扩张中心,无沉积物覆盖热液活动区中热液沉积物与有沉积物覆盖热液活动区相比,其硫同位素组成的分布范围相对狭窄;(3)各热液活动区中硫化物硫同位素组成的不同,反映出各自硫源的差异性.无沉积物覆盖洋中脊中热液成因硫化物的硫主要来自玄武岩,部分来自海水,是玄武岩和海水硫酸盐中硫不同比例混合的结果,而在弧后盆地和有沉积物覆盖的洋中脊,除了火山岩以外,沉积物和有机质均可能为热液硫化物的形成提供硫;(4)现代海底热液沉积物硫同位素组成的变化和硫源的不同可能归因于海底热液体系中流体物理化学性质的变化、岩浆演化和构造-地质背景的不同.     

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.     

Geologic setting of the Snake Pit hydrothermal site: An active vent field on the Mid-Atlantic Ridge

TheSnake Pit Hydrothermal Site lies on the axis of the Mid-Atlantic Ridge at 23°22′ N latitude, about 30 km south of the Kane Transform Intersection. Active ‘black smoker’ vents and a surrounding field of hydrothermal sediment occur at the crest of a laterally extensive neovolcanic ridge. It is one of the first active hydrothermal vent fields to be found on a slow-spreading ridge axis and despite significant differences in its geologic setting from those of the East Pacific Rise, has many similarities to its fast-spreading counterparts. Although preliminary reports have documented many interesting aspects of these vents and their surroundings, new data collected from the manned submersible ALVIN and the deep-towed ANGUS camera system define the regional tectonic setting as well as the local geologic environment of this fascinating area. The Snake Pit vents are located on a local peak of a volcanic constructional ridge at a depth of 3450 m, 700–800 m deeper than vents known from the East Pacific Rise, Galapagos, or Juan de Fuca spreading centers. The vent field is at least 600 m long and up to 200 m wide and is covered by a thick blanket of greenish to yellow-orange hydrothermal sediment. Both active and extinct vents are perched along the crests of steep-sided sulfide mounds that reach heights of over 40 m. High-temperature (350° C) fluids are vented from black smoker chimneys and low-temperature (226° C) fluids seep from sulphide domes and subordinate anhydrite constructions. Water temperatures, flow rates, fluid chemistries, and mineralization are strikingly similar to vents of faster spreading ridge crests; however, a somewhat distinct fauna inhabit the area.     

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     

大西洋中脊TAG热液活动区中热液沉积物的稀土元素地球化学特征

用ＩＣＰ－ＭＳ对ＴＡＧ热液活动区表层热液沉积物中６个块状硫化物样品进行了稀土元素分析。所有样品均表现出正Ｅｕ异常（ＥｕＮ／Ｅｕ＊Ｎ＝１．２７～２．６８）和ＬＲＥＥ相对富集（ＬａＮ／ＹｂＮ＝１５．７９～４７．６２）的球粒陨石标准化配分模式,热液沉积物样品中稀土元素组成的变化是由于海底热液循环体系中热液流体和海水不同程度混合作用的结果,并且,海水与热液流体的混合作用是在热液沉积物形成以前发生的,与黑烟囱流体的稀土元素配分模式对比,表明热液沉积物的ＲＥＥ部分来自下伏的玄武岩基底,在热液沉积物的形成过程中,ＬＲＥＥ得到了较高程度的富集,同时,海底热液沉积物的稀土元素中Ｅｕ的变化可以一定程度的反映出热液流体的演化特征。     

基于矩匹配算法的山区影像地形辐射校正方法研究

针对山区遥感影像地形辐射校正问题,应用现有模型(如C校正)进行地形辐射校正很难达到理想效果。引入矩匹配算法,利用DEM数据计算坡度、坡向等地形信息,以特定坡度和坡向数据为参考依据,对影像进行地形辐射校正。通过北京房山区SPOT5影像进行试验,表明该方法能在很大程度上消除地形阴影,更好地反映阴影区域的细节信息,同时光谱特性保真程度较好,原模糊的影像区域通过处理基本上达到有效识别地物的要求。     

在轴向应力-应变下海底沉积物声速及其变化

对南海南部海域海底浅表层沉积物短柱状样进行轴向应力-应变/声学测量,结果表明沉积物纵波声速有三种不同的变化结果:(1)声速从应变过程开始随应力-应变曲线变化,在最大应力时声速同时也是最大值,结束时可能高于或低于开始时的声速;(2)声速从应变过程开始逐渐减小,结束时是最小值;(3)声速从应变过程开始逐渐增大,最大值出现在结束时.这些结果与海底浅表层沉积物的物理力学性质、颗粒接触状态、颗粒的微结构等特征有关.研究结果可为深入认识南海南部各种海底沉积物作为承载界面的可靠性、声遥测遥感海底沉积物的工程力学性质等科学目的提供理论依据.     

原位测量技术在黄海沉积声学调查中的应用

介绍了最新研制的基于液压驱动贯入的自容式海底沉积声学原位测量系统及其在南黄海中部海底沉积声学调查中的应用。该系统可以实现对海底沉积物声速和声衰减系数进行原位测量,通过液压驱动装置将四根声学探杆匀速贯入到海底沉积物中,减少了对沉积物的扰动,可按照预设的工作参数在海底全自动工作,无需甲板上人员实时控制,采集的声波信号自容式存储于存储单元。系统工作水深为500 m,测量深度为1 m,测量频率为30 kHz,采样频率为10 MHz。使用该系统在南黄海中部获得了40个站位不同类型沉积物的声学特性原位测量数据,并使用CTD剖面仪对该系统声速测量进行了标定,相对误差均小于0.5%,表明该系统测量数据准确、可靠。