斜长岩事件年龄及其地质意义

THE AGE OF ANORTHOSITE EVENT AND ITS GEOLOGICAL IMPLICATIONS

斜长岩岩体主要由斜长岩、苏长岩、辉长岩、纹长二长岩、石英二长岩、石英正长岩等组成。它仅出现在前寒武变质地层中，在地球演化历史中的意义引起了人们的关注，值得探讨。本文不拟研究斜长岩岩石学方面的一些问题，只着重它的产出时代和构造意义作一粗浅讨论。

It is proposed by the authors in the light of isotopic age data now available thatanorthosite event is better to be assigned to two periods, i.e., the Karelian period(1700--2000 m.y.) and the Grenville period (1000-1300 m.y.), rather than simply1300 ± 200 m.y. as suggested by Herz, N. in 1969. This division is in agreementwith earth history. It is noticed that anorthosite always occurs in the active zonesbetween plates, indicating a close relationship with deep faults. Anorthosite of theKarelian period is found principally in tectonic zones that strike approximately NWWor NEE in Eurasian (possibly North American) plate. Grenville anorthosite, consti-tuting two (possibly three) belts running roughly in NNE or NNW direction, occursin orogenic zones marginal to the present continents resulted from the breaking upof Pangaea. This suggests that the breaking up of the ancient continent of Pangaeastarted to operate as early as late Precambrian and was probably responsible for thecontinental drift along these tectonic belts during the late Paleozoic.