海山铁锰结壳基岩岩石学特征及其生长关系

SUBSTRATE LITHOLOGIC FEATURES OF FERROMANGANESE CRUSTS ON THE SEAMOUNTS AND THE GROWTH RELATIONSHIP

为了研究海山铁锰结壳基岩类型与结壳壳层生长的关系 ,对麦哲伦海山及中太平洋海山区取得的铁锰结壳及其基岩样品在电子显微镜下进行了观察和研究。结果表明 ,上述 2个区域基岩岩石类型主要有玄武岩、火山熔岩、火山碎屑岩、硅质岩和碳酸盐岩。其中麦哲伦海山玄武岩为块状构造 ,中太平洋海山玄武岩则主要为气孔—杏仁状构造 ,多发生蚀变或完全蚀变。硅质岩颗粒物质主要是硅藻 ,碳酸盐岩则以晶质灰岩为主。结壳壳层厚度在各类基岩类型上都有变化 。

In order to better understand ferromanganese crust growth in relation to seamount geology and substrate lithology, the substrates of ferromanganese crust, dredged from Magellan and central Pacific seamount areas by R/V“dayang 1”, have been observed and studied under optical microscope. The thickness of ferromanganese crusts collected from study areas varied from 0 1 cm to 14 5 cm. Based on the crust appearance characters, the crusts could be divided into three types as follows: ① the most of the crusts grew and spread continuously on outcrops of seamounts whose substrates were freshly broken from outcrops of seamount flanks and had crusts only on the side exposed to seawater; ② the crusts were similar in appearance to abyssal nodules whose core material was mostly the fragments of rock, old crust as well as some clay material, which was mainly distributed in the areas near top and foot of mountains; ③ the crusts had large rock cores and thin oxide coats found in the adjunct to outcrops. The hard substrates underlying crusts were predominantly basalt, volcanic clastic rock and volcanic lava, and secondly siliceous and carbonate rock. Basalt samples in the Magellan seamounts were in massive structure and porphyritic texture. The matrix of microlite cryptocrytalline and glassy texture had been found. Phenocrystal minerals were mainly plagioclase and olivine. The basalt samples in the central Pacific seamounts had porphyritic texture. But they were obviously different from the samples in Magellan seamounts, which mainly had feature of vesicular or amygdaloidal structure. The material filled with vesicles was mostly clay minerals and calcite at some places. As for Magellan seamounts, matrix was in microlite cryptocrytalline and glassy texture. And so were phenocrystal minerals. Volcanic lava and volcanic clastic rock mainly included basalt brecciated and glassy lava, volcanic breccias and tuff. Siliceous rock samples were mainly diatomite or rock with diatoms, which had granular fragmental texture. The granular fragments were mostly diatoms whose contents varied in the range between 70% and 80% in diatomite, and reached about 20% in rock with diatoms. Carbonate rock samples were dominantly micritic limestone and coarse sand sparite. In Magellan seamounts, the thickness of crusts on basalt changed from 0 1 to 0 3 cm. But in the central Pacific mountains, the crusts on basalts were much thicker than those on other kinds of substrates. The crusts on volcanic clastic rocks were thick in the range of 1 1 ～6 5 cm. And crust thickness on carbonate rocks changed from 0 8 to 2 5 cm in Magellan seamounts, but the maximum thickness reached 7 0 cm in the Mid Pacific seamounts. In this paper, the variations of crust thickness on the different kinds substrates were all rather large. And more data are needed to study the relation between crust growth and seamount geology and substrate characteristics.