欧洲西部的南北向拉张构造

THE N-S TRENDING EXTENSION STRUCTURES IN WEST EUROPE

在法国东部的大范围内,有很多走向南北的拉张构造。包括被渐新统充填的同沉积地堑,它们至今内外高程对比仍很强烈;南北走向的正断层,切割了更新统;南北向分布的新生代基性到酸性的各种火山岩,喷发最盛期在上新世,最新喷发距今仅数千年,最新的火山锥和低平火山口保存完好,排列成规整的南北方向。区内还有一些北东和北西向断裂,由一些迹象看,它们是南北向拉张构造的两组剪切构造。从地质环境分析,它们都只能是在东西向拉张情况下产生的。新生代以来在大西洋东岸这样大范围的、强烈的东西向拉张,显然和南北向延长的大西洋起源的海底扩张假设不相容,看来,大西洋起源的拉张说更符合于已有的各种资料。

In West Europe,there are a number of intense N-S trending extension structural features, distributed mainly in East France,They are composed of grabens,normal faults and volcanic rock zone.The latest volcanic cones and maars are regularly arranged in N-S direction.The widest one measuring about 300 kin,lies north of the central plateau,with a length of nearly 500 kin.The Rhine graben northeast of this area is not counted. The N-S trending grabens include the Rhine graben,the Bresse graben,the Limagne graben and other small ones.They are all filled with Oligocene sediments.From the lithofacies distribution of the Oligocene,the boundary faults of these grabens mainly are intermittently active synsedimen- tary normal faults.Sometimes trailing NE-and NW-faults.The contrasting height of the graben and the neighbouring land indicaks its current activity. N-S normal faults are well developed north of the Central Massif,often concentrated in to zones.Sometimes they cut the Pleistocene rocks.In the Central Massif,there are a few N-S faults,but NE and NW faults are well developed instead.Although the geometric features of near- ly all the faults in the Central Massif are unknown on the surface,they are thought to bo continua- tions of the normal faults on the northern side.From their location trailing features of the bound- nary faults.The NE-and NW-trending faults are two sets of conjugate shear features.On the southern side of the Central Massif,the N-S normal faults are poorly developed. Cenozoic volcanic rocks range from acidic to basic.They are well developed in the Central Massif,and extend discontinuously south-ward to the coast of the Mcditeranean.They arc dis- tributed is N-S direction.The latest volcanic cones and maars are well preserved,and arranged in a N-S direction.In some places,basic volcanic rock were intruded in to the Cretaceou and Oligocene to form NW-trending dyks.Volcanism began in early Tertiary and continued to Holocene,with a culmination pliocene.The latest eruption took several thousand years ago. All these features are found in the eastern coast of the Atlantic suggesting an E-W tensile stress field since early Tertiary.