中国蛇绿岩带形成时代研究中的两个误区

TWO MISTAKES IN THE STUDY OF THE FORMATION AGE OF THE OPHIOLITE BELTS, CHINA

对中国蛇绿岩带形成时代的研究曾出现两个误区 ,第一个误区发生在 70年代以前 ,大多数地质学家主要依据混杂堆积中灰岩块体中生物化石来确定蛇绿岩带的形成时代 ,由于这些大化石所形成的时代一般都要比蛇绿岩带的形成时间早 ,它不能代表板块碰撞的真正时间 ;第二个误区发生在 70年代之后 ,广大地质工作者普遍利用放射虫来确定蛇绿岩带的形成时代 ,但是 ,在蛇绿岩带中有时出现两套放射虫硅质岩 ,一套属于外来移置体 ,与洋壳无关 ;另一套位于枕状玄武岩上 ,真正代表洋壳的残余。在以往发表的地质文献中 ,大多数作者都没有把放射虫硅质岩在蛇绿岩中的位置阐述清楚 ,因此 。

There are two mistakes in researching the formation age of the ophiolite belts, China. The first mistake took place before 1970's when many geologists determined the formation age of the Ophiolite belts mainly based on the macrofossils of the limestone block in the melanges. Because the age shown by these macrofossils is generally earlier than the formation age of the Ophiolite belts, it can not represent the true time of plate collisions. The second one took place after the 1970's when numerous geological workers determined the formation age of the Ophiolite belts commonly based on the radiolites and radiolarian faunas. But, in the Ophiolite belts sometimes there are two sets of radiolites. The first radiolite belongs to allochthonous removal with the characters of deep water and without any relation with the oceanic crust; the second radiolite represents relics of true oceanic crust overlying the pillow basalt. In all published geological references, most geologists did not describe the positions of the radiolites in the ophiolite belts, therefore, the conclusions drawn by them for the formation age of the ophiolite belts are always doubtful.