海洋地球物理学和海洋地质学的发展

MARINE GEOPHYSICS AND ITS IMPACT ON DEVELOPMENT OF MARINE GEOLOGY

  • 摘要: 回顾了20世纪60年代板块学说的诞生,以及海洋地球物理学及海洋地球物理学家对这场地球科学革命所做出的巨大贡献。二次世界大战中,海洋技术飞速进步;战后,西方国家的海洋地球物理学家利用这些技术在海上开展了广泛的地球物理调查,积累了大量资料,有了许多重要发现。大洋地震带原来是一条裂谷带;大洋地磁场存在以中脊为中心,向两边正负相间的对称异常条带;大洋底沉积很薄,且从中脊向两边逐步加厚;大洋地壳仅厚数千米,而大陆地壳厚达30千米以上;大洋中脊处热流值很高,向两边逐步减小;地球的地震波速度从地表到约深80 km逐步增大,从80 km深度处速度开始减小,说明地球表层存在岩石圈,其下部存在软流圈;在海沟处,地震震中分布从海沟开始,向下沿约45°倾角到700 km深处,这可能是大洋岩石圈俯冲之处。由此地球科学家提出了板块构造假说,认为地幔深处的岩浆沿大洋中脊处向上运移,在海底处不断产生新洋壳;新洋壳(岩石圈)不断向两边运动,在海沟处向大陆岩石圈之下俯冲、消亡;当大洋岩石圈俯冲消亡之后,两边的大陆就发生碰撞,形成造山带,因此,地球上最老的大陆年龄达38亿年,而大洋岩石圈最老年龄只有1.8亿年。板块构造学说坚持活动论,是大陆漂移假说的发展之结果,更是地球科学深刻革命的开始。当它上陆之后,地球科学就掀起了革命的风暴。

     

    Abstract: The establishment of Palate Tectonics marked the revolution of earth sciences in 1960s. Marine geophysics and marine geophysicists made great contribution to the revolution. During the Second World War, the development of marine technology was prioritized by both sides of the war. After it up to 1960s, extensive geophysical surveys had been carried out at seas, and a great amount of data acquired with many new discoveries. For examples, it was found that the earthquake zone in the mid-ocean is in fact a rifting valley; the marine magnetic anomalies are symmetry on both sides of the oceanic mid-ridges; the sediments on the ocean floor are thin, and gradually thicken on both sides of the ridge; the oceanic crust is only several kilometers thick, but the continental crusts could reach a thickness over 30km; the heat flow at the mid-ridges is higher than expected, and decreases on both sides as the distance from the ridge increases; the seismic velocities increase from surface to 80km, and reduce from 80km to 150km of depth. The upper part is thus called lithosphere, and the lower part called asthenosphere; the earthquake epicenters are distributed along a zone dipping at 45 from the trench down to over 700km below the land, it is the subduction zone of the oceanic lithosphere. The discoveries mentioned above brought about a big change of scientific philosophy and paved the way for the theory of plate tectonics.

     

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