微晶丘成因新认识

A NEW CONSIDERATION ON THE GENESIS OF MUD MOUND

微晶丘主要由灰泥组成,仅见少量生物碎屑,其成因尚无圆满解释。借鉴现代海底勘查成果,依据北京西山微晶丘、白云鄂博赋矿微晶丘、腮林忽洞微晶丘的特征,认为微晶丘是海底热水(伴CO2)的化学作用产物:现代海底勘查发现的微晶丘是形成于洋中脊、热点或弧后盆地;北京西山等地的纯灰岩微晶丘是形成于大陆内部;而白云鄂博赋矿白云岩是一个大型微晶丘,形成于被动大陆边缘。微晶丘中的生物作用仅是深海热水活动的伴生作用,并不是微晶丘形成的主导作用。

The genesis of mud mound (also called as micrite mound), which is mainly composed of lime mud, only a few bioclast, has still not been resolved. In explorations on the sea bottom, it is found that a lot of mordern mud mounds are being formed in mid-ocean ridges, hot-spots or back-arc basins by hydrothermal with CO_2 and bio-activeity. Based on the characteristics of the mud mounds in Bayan Obo (i.e. the ore-hosted dolostone), Heilaobao (southeastern 25 km to Bayan Obo) and the Western Hills, Beijing, and considering the discovery of mordern explorations on the sea bottom, writers consider that the mud mounds are formed by hydrothermal (with CO_2), too, while the bio-process is only a companied process; the mud mound in Bayan Obo is formed in passive continental margin, the mud mounds in the Western Hills, Beijing, are formed within continental. This consideration is helpful to study the geneis of the famous Bayan Obo Fe-Nb-REE deposit and the flux limestone and chemical limestone in the Western Hills, Beijing, and its neighbuorhood. Further study is needed.