东太平洋中国开辟区沉积物中热水活动的矿物学及地球化学证据  

Mineralogical and geochemical evidences for hydrothermal activity found in surface sediments in the Chinese Pioneer Area in the East Pacific

作　　者：周怀阳[1] 叶瑛[2] 沈忠悦[2] 倪建宇[1] 潘建明[1] 

机构地区：[1]国家海洋局海底科学重点实验室 [2]浙江大学地球科学系,浙江杭州310027

出　　处：《地球化学》2001年第4期299-304,共6页Geochimica

基　　金：中国大洋协会"九五"环境项目DY950603;国家"十五"973项目G2000078500

摘　　要：通过对东太平洋多金属结核中国开辟区表层沉积物和短柱状沉积物的系统观察和分析,首次根据矿物学和地球化学两方面的证据,发现中国开辟区沉积物中热水活动及其产物的存在。X射线衍射分析表明,沉积物样品中普遍含有重晶石,部分样品中含量高达10%以上。扫描电镜观察发现,重晶石均为完整自形晶,并与同为自形的石英及钠长石共生。根据本区重晶石的地质背景及结晶形态,可以认为它的形成环境与加利福尼亚湾瓜伊马斯盆地Guaymas相似,属热水成因。伴生的石英和钠长石亦为常见的热水矿物。这一共生组合的形成温度不低于70℃。地球化学研究发现,在柱状沉积物剖面上,Ba的垂向分布有两种类型,一种为平稳型,在一定深度范围内无明显变化;另一种为跃升型,并伴有其他活泼组分的同步变化。跃升型可视为热水活动在沉积历史上的记录。迄今为止,热水矿物组合主要见于东区的表层沉积物,而在西区,Ba在沉积物中的富集主要见于10cm以下层位。根据沉积速率推算,在中国开辟区西区的热水化活动记录比东区至少早0.1Ma。X-diffraction analysis indicates t hat barite is rather common in surface sediment sampled from the Chinese Pioneer Area in the East Pacific,some of them with a content over 10%of sediment.Under scanning electron microscope,barite in these samples occurs as euhedral crystal,co-existing with authigenic quartz and albite with the same idiomorph.Considering the geological setting and c rystal form,it is believed that barite occurred in the study area is compara ble with that found in the Guaymas Basin,Gulf of California,i.e.,with hydrothermal origin.The associate d quartz and albite are also commonly identified as thermal-water minera ls.Formation temperature of this parag enetic assemblage should be above 70℃.Geochemical research shows that distribution of Ba in the surface sed iments is rather uneven.In the verti cal profile of the columnar sediment s,there are two types of Ba distribution pattern.One is smooth,without apparent change in the sampling range;another is ascending,i.e.,increased sharply with depth,which is accompanied by c orresponding changes of some other components.The later can be regarded as thermal-water record in the sedi ments.Up to this moment,thermal-wa ter mineral assemblage is only found in t he surface sediment from the east dis trict,while in the west,Ba is highly concentrated in the horizon 10cm below surface.Calculated from the sedi mentary rate,hydrothermal record i n the west region of the Chinese Pioneer Ar ea is at least 0.1Ma older than that in the east.

关 键 词：沉积物 自生重晶石 自生钠长石 热水矿物组合 多金属结核 热水活动 

分 类 号：P736.2[天文地球—海洋地质] P736.4[天文地球—海洋科学]