Two Types of Archaean Grey Gneiss in North China and Their Geological Significance1,2 |
| |
| Authors: | Wang Renmin |
| |
| Abstract: | Abstract Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Hengshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep - level migmatization with a high degree (30% ±) of fusion. As the sub - stratum in the root of the early - stage high - grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large - amplitude upward emplacement, rather simple mineral composition, only slight changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high - grade greenstone belt and then fusion and emplacement with a low degree (15% ±) of fusion. In this paper an attempt is made to furnish important information about palaeoplate tectonics and early crustal evolution by means of a study of grey gneisses. |
| |
| Keywords: | Archaean grey gneiss plate tectonics |
|
| 点击此处可从《Acta Geologica Sinica》浏览原始摘要信息 |
| 点击此处可从《Acta Geologica Sinica》下载免费的PDF全文 |
|
