Altered Lavas from the Floor of the Eastern North Atlantic
Altered Lavas from the Floor of the Eastern North Atlantic
复制标题
北大西洋东部海底的改造熔岩
作者：
D. Matthews
里特曼和其他人长期以来一直认为，在深海海底喷发的基性熔岩可能会立即发生蚀变，并固化为蛇纹细碧岩组合的岩石，克拉克和费弗最近的实验工作已经引起了人们对这种可能性的关注。蚀变玄武岩的物理性质和整体化学性质在以前的通信2中概述，几乎可以肯定是在深水下挤出的，并可能提供在这些条件下温和蚀变的例子。这些标本是从一个名叫燕子滩的深海小山上挖来的，海拔4-5公里。Mohorovičić不连续面以上4，960 m以下。北纬41° 21′处的水，西经十四度二十八分这些标本以及从附近一座小海山（西海山，山顶深度2 600米）采集的第二批标本，都经过了岩石学检验在薄片中，蚀变熔岩有50%是不透明的;没有一个保留了未蚀变的基质物质，400个标本中只有3个保存了未蚀变的斑晶或玻璃。本来文概述了据信影响到他们的蚀变过程的矿物学。
RITTMANN and others have long argued that basic lavas erupted on the ocean floor under great depths of water may suffer immediate alteration and solidify as rocks of the serpentine–spilite association, and recent experimental work by Clark and Fyfe1 has directed attention to this possibility. The altered basalts, the physical properties and bulk chemistry of which were outlined in a previous communication2, were almost certainly extruded under deep water and may provide an example of mild alteration under these conditions. The specimens were dredged from a small abyssal hill, named Swallow Bank, standing 4–5 km. above the Mohorovičić discontinuity under 4,960 m. of water at 41° 21′ N., 14° 28′ W. These specimens, and a second collection from a nearby small seamount (the Western Seamount, summit depth 2,600 m.), have been examined petrographically. In thin section the altered lavas are 50 per cent opaque; none retains unaltered groundmass material, and only three specimens out of four hundred preserve unaltered phenocrysts or glass. The present communication outlines the mineralogy of the alteration process which is believed to have affected them.