北冰洋地质构造及其演化

THE STRUCTURE AND TECTONIC REVOLUTION OF ARCTIC OCEAN

北冰洋及其周围的陆架海资源十分丰富,尤其是油气和煤炭。但受自然条件的限制,调查程度很低,许多地质与构造问题尚未解决。区域构造的认识主要依赖航磁测量结果。本文试图综合各国对北冰洋地区的研究现状,形成对该区地质构造及其演化的认识:(1)欧亚海盆磁条带清晰,对海盆构造和演化历史认识争议最小,识别的最老磁条带为25,因此海盆大致于58Ma开始张开。磁条带13之后,Yermak高地与莫里斯·杰塞普隆起分离,欧亚海盆与北大西洋连通。(2)从地壳结构与地壳厚度,以及其他资料来看,阿尔法海岭-门捷列夫海岭与罗蒙诺索夫海岭一样,应为陆壳,可能是先后从巴伦支陆架裂离形成的。(3)马卡罗夫海盆为典型的洋壳,其形成方式和时代还很少约束,其中观点之一是在晚赛诺曼期-早始新世,随阿尔法海岭-门捷列夫海岭裂离巴伦支陆架,海底扩张形成,并随Gakkel扩张中心在晚古新世的形成而逐步衰退。(4)加拿大海盆可能是北冰洋最早形成的海盆,其形成时间与机制至今仍所知甚少,但可能是从140—135Ma至95—80Ma,随新西伯利亚-楚科奇-阿拉斯加微板块旋转裂离加拿大北部陆缘形成。(5)北冰洋的演化大致可以分为3个主要阶段:晚侏罗世-早白垩世、晚白垩世-新生代早期、新生代。第一阶段,加拿大海盆地的扩张中心形成、演化与消亡,第二阶段是拉布拉多-巴芬-马卡罗夫扩张中心的形成与演化,在始新世停止活动,第三阶段,极慢速的Mohna、Knipovich和Gakkel洋中脊的扩张,致使欧亚海盆形成。

There are very abundant natural resources,especially the oil,gas and coal in the Arctic Ocean and surrounding shelf seas.But a very few geological and geophysical survey has been finished in the area,due to the rigorous natural conditions.Many issues are still controversial.The main knowledge for the tectonics in the area is based on the aeromagnetic survey.The tectonic features of Arctic Ocean are reviewed in this paper.First,the tectonic features of Eurasian Basin and its evolution is most uncontroverted due to the typical linear magnetic anomalies.The Basin opened from the period of linear magnetic anomaly 25,about 58Ma,and after linear magnetic anomaly 13,about 35 Ma,Yermak Plateau broke from Morris Jesup Rise and it makes the Arctic Ocean linking to the North Atlantic.Secondly,the crust beneath Alpha Ridge and Mendeleev Ridge should be continental,similar with the Lomonosov Ridge,according to their crustal structure and thickness.It is possible that both of the Ridges broke from the Eurasian shelf.Thirdly,the crust beneath Makarov Basin is typical oceanic,but its revolution is fewer constrained.One of the main opinions about it is that it was formed by spread from Cenomanian to early Eocene,and declined by development of Gakkel spread center.Fourthly,as oldest basin in Arctic Ocean,the forming of Canadian Basin is poorly understood.But it is presumed that the basin was forming in a period between 140—135Ma to 95—80Ma,as New Siberian-Chukchi-Alaska microplate rifting from Canadian Margin in ＂wind screen wiper＂ fashion.Fifthly,the tectonic revolution of Arctic and adjacent area includes 3phases：Late Jurassic-Early Cretaceous,Late Cretaceous-Early Cenozoic and Cenozoic.PhaseⅠis determined by the formation,evolution,and extinction of the spreading center in the Canada Basin,while PhaseⅡis connected to the development of the Labrador-Baffin-Makarov centers branch and PhaseⅢ pertains to the formation of the spreading system of ultraslow Mohna,Knipovich,and Gakkel mid-ocean ridges that has functioned until now in the Norwegian-Greenland and Eurasia basins.